JP3174415B2 - Method for manufacturing substrate for liquid jet recording head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate based on polycrystalline silicon used for a liquid jet recording head for performing recording by discharging a recording liquid from a discharge port by utilizing thermal energy, and the substrate. And a method for producing the same. The present invention further relates to a liquid jet recording head and a liquid jet recording apparatus using the substrate.

[0002]

2. Description of the Related Art A liquid for recording by discharging a recording liquid such as ink from a discharge port by using thermal energy and causing the recording liquid to adhere to a recording medium such as paper, plastic sheet or cloth. The ejection recording method is a non-impact recording method and has advantages such as low noise, no particular limitation on the recording medium, and easy recording of a color image. An apparatus for performing such a liquid ejection recording method, that is, a liquid ejection recording apparatus has a relatively simple structure, and liquid ejection nozzles can be arranged at a high density, so that the recording apparatus can be relatively easily operated at high speed. It has the advantage that it can be achieved. For these reasons, the above-described liquid jet recording method has attracted public attention, and many studies have been made on the recording method. Incidentally, some liquid jet recording apparatuses for performing the liquid jet recording method have been marketed and put to practical use.

FIG. 5A is a cutaway perspective view of a main part of a recording head used in such a liquid jet recording apparatus.
FIG. 5B is a sectional view of a principal part taken along a liquid path of the recording head shown in FIG. 5A and perpendicular to the substrate.

As shown in FIGS. 5A and 5B, a recording head generally has a plurality of discharge ports 7 for discharging a recording liquid such as ink, and a plurality of discharge ports 7 corresponding to each of the discharge ports 7. Liquid paths 6, a liquid chamber 10 for supplying a recording liquid to each liquid path 6, a heating resistor 2a for applying thermal energy to the recording liquid, and a wiring for supplying an electric signal to the heating resistor 2a. It has a liquid jet recording head substrate 8 on which 3a and 3b are arranged.

As shown in FIG. 5B, the substrate 8 for the liquid jet recording head is generally provided with a heating resistor layer 2 on a base 1, and a good electrical conductivity is provided on the heating resistor layer 2. A wiring layer 3 made of a material having the above-described structure is laminated, and a portion where the wiring layer 3 is not disposed becomes a heating resistor 2a.

In this configuration, the wirings 3a, 3a
b, when an electric signal is applied to the heating resistor 2a via
The heating resistor 2a generates heat. Further, the protective layer 4 can be provided on the liquid jet recording head substrate 8 for the purpose of covering the wirings 3a and 3b and the heating resistor 2a. The protective layer 4 is provided with a heating resistor 2a, wirings 3a and 3b due to contact with a recording liquid or penetration of the liquid.
Contributes to the prevention of electrolytic corrosion and electrical insulation breakdown.

As the substrate 1 constituting such a liquid jet recording head substrate 8, a plate-like member made of a material such as single crystal silicon, glass or ceramics can be used. However, a substrate made of single-crystal silicon is usually used exclusively. The reason is as follows. That is, when glass is used as the base 1, since the glass is inferior in heat conductivity, if the heat generation period (drive frequency) of the heating resistor 2a is increased, the heat generated by the heating resistor is excessively accumulated in the base 1. As a result, the ink in the liquid jet recording head is heated by the accumulated heat, bubbles are generated, and ink ejection failure is likely to occur. When ceramics are used as the base 1, there is an advantage that a base having a relatively large size can be manufactured and a material having a higher thermal conductivity than glass can be selected.

However, in the case of a ceramic substrate,
Generally, since raw material powder is fired, several μm to several tens μm
surface defects such as pinholes and small protrusions
Such surface defects tend to cause failures such as short-circuiting or disconnection of the wiring, which causes a reduction in yield. Also, the surface roughness is usually about Ra (center line average roughness) = 0.15 μm, and an optimum surface roughness for forming the heat-generating resistor layer 2 having excellent durability cannot be obtained. In many cases, for example, when a liquid jet recording head is manufactured by using an alumina ceramic substrate, the heating resistance layer 2 may be peeled off from the substrate 1 or the heating resistance layer disposed at a defective portion may be removed due to these causes. Cavitation occurs when the foamed foam disappears in the portion, which causes disconnection of the heat generating resistance layer and the like, and has a drawback that the durability life is shortened.

In order to solve these problems in the case of using a ceramic substrate, the surface of the ceramic substrate 1 is polished and smoothed to improve the adhesion of the heat-generating resistance layer 2 and the cavitation is reduced by one part. There is a proposal to prevent the premature disconnection of the heat-generating resistance layer caused by concentrating on a portion. However, in this proposal, since alumina generally has high hardness, there is a limit in adjustment of the surface roughness, and this is not practical.

There is also a proposal to improve the above-mentioned problems by providing a glaze layer (a glassy layer is welded) on the surface of a ceramic substrate to form an alumina glaze substrate. However, in the formation method that can adopt the glaze layer as a formation method, the thickness of the layer cannot be reduced to 40 to 50 μm or less, and a problem of heat storage occurs as in the case of the glass substrate. Is also not practical.

When single-crystal silicon is used for the substrate 1, there is no problem of excessive heat storage when the above-mentioned glass or ceramic is used for the substrate 1, and the surface is very good. There is almost no concern about problems such as these. From these facts, for example, JP
As can be seen in JP-A-1275741, a single-crystal silicon wafer is used as a substrate for a liquid jet recording head utilizing the above-described thermal energy.

In recent years, in the field of recording using the liquid jet recording method, early provision of a recording apparatus capable of obtaining higher quality recording at higher speed is desired. From the viewpoint of responding to the demand for high-speed recording, keen research on a large-sized recording head such as a so-called full-line head having a width corresponding to the recording width has been conducted in order to enable recording on a wide recording medium. Has been established.

As a result of such research, as described above, a single-crystal silicon wafer is optimal as a substrate for a recording head as long as the recording head is relatively small, but is not suitable for increasing the size of the recording head. It is pointed out that the use of a single-crystal silicon wafer as a base causes the following inconveniences, and that there is a problem that needs to be solved before a single-crystal silicon wafer can be used as a base for a large recording head. ing.

That is, when the recording head substrate is made of single-crystal silicon, the single-crystal silicon substrate, that is, the single-crystal silicon wafer is usually formed by cutting out a single-crystal ingot manufactured by a single-crystal pulling method. . At present, the size of a single crystal ingot that can be manufactured by this single crystal pulling method is limited to a rod-shaped one having a diameter of 8 inches and a length of about 1 m. Therefore, there is naturally a limit to the single crystal substrate that can be obtained by cutting out the obtained single crystal ingot. In addition, as much as possible to cut out a long base from such a single crystal ingot, the use efficiency of the ingot becomes very poor, and the obtained single crystal wafer becomes irreversibly expensive, This in turn adds cost to the end product. In addition, in the substrate for the liquid jet recording head, in order to transfer heat to the recording liquid better,
A heat storage layer (lower layer) is provided directly below the heating resistor to achieve a good balance between heat storage and heat dissipation. In this case, the substrate is thermally oxidized on the surface of the single-crystal silicon wafer cut from the above-described single-crystal ingot to form a heat storage layer of an SiO ₂ layer, and after forming the above-described heat-generating resistance layer, wiring, and the like, It is manufactured by separating each recording head.

However, when the present inventor studied to obtain a large-sized recording head, as shown in FIG. 9A, the liquid-jet recording head substrate manufactured using a single-crystal silicon substrate was cut from the end. It has been found that a problem arises in that the cut-out workpiece of the liquid jet recording head is deformed like a bow. And the deformation amount is up to 60 ~ 90μm
In many cases, if this deformation is forcibly corrected, the work-in-progress will often be destroyed, and even if the deformation is small, it will be uniform even in the polishing process following the process of cutting out the work-in-progress. It has been found that there is a problem that it is difficult to perform appropriate polishing, or it is difficult to electrically connect the wiring and the ICs and the like disposed on the in-process product with high precision. Even if a liquid jet recording head can be manufactured using a work-in-process that is still bent, the bending of the head causes a shift in the position at which the recording liquid adheres to the recording medium. It has been found that there is a problem that image quality is deteriorated such as missing dots or unevenness. In addition, it was found that when the portion causing the deformation, that is, the end of the silicon wafer was not used as the substrate for the recording head, the production cost of the recording head would be extremely high. When the cause of such deformation of the recording head work-piece is deformed, the substrate not provided with the above-described thermal oxide layer as the heat storage layer is bent. No deformation was observed, and it was found that the above-mentioned deformation was caused by the thermal oxidation process. The deformation occurs because the edge of the single crystal silicon wafer, particularly the four corners, is cooled most quickly when the single crystal silicon wafer is cooled after the heat treatment, as shown by the arrow in FIG. A tensile stress is generated at the outer edge of the base, and the stress is distributed in the base in a state as indicated by a sign (+) in FIG. 8B, and the stress is distributed from such a wafer as shown in FIG. 9A. It has been found that when a part is cut to form a substrate, a part of this stress is released to cause bending deformation.

Alternatively, when a heating resistor or a film for wiring is laminated on a single-crystal silicon substrate, the stress causes the substrate for a liquid jet recording head to be warped, so that the focus position shifts during patterning and the exposure is performed. It turned out to be bad. Therefore, when single crystal silicon is used as a substrate for a recording head, there is naturally a limit in achieving a longer length. For this reason, in order to produce a long head for achieving higher-speed printing, it is required to form a liquid ejecting recording head unit by integrating a shorter recording head. However, in this case, it is extremely difficult to adjust the seam portion of the head so as not to adversely affect the recorded image.

Accordingly, the shape of the substrate for the liquid jet recording head is not restricted by the manufacturing process, and there is no problem such as deformation of the substrate for the liquid jet recording head due to the increase in size, and high-speed high-quality recording can be easily performed. It has been desired to provide an inexpensive liquid jet recording substrate that can achieve the above.

[0018]

SUMMARY OF THE INVENTION It is a principal object of the present invention to solve the above-mentioned problems with the conventional liquid jet recording head substrate and to use a specific material which enables a large recording head to be obtained. To provide a long substrate for a liquid jet recording head using a base that has been used. Another object of the present invention is to provide a long substrate for a liquid jet recording head using a long substrate made of polycrystalline silicon.

Another object of the present invention is to achieve a large-sized recording head without integrally connecting a plurality of liquid jet recording heads as in the case of using the above-mentioned single crystal silicon wafer. It does not cause problems such as deformation of the work-in-progress of the liquid jet recording head and deterioration of the quality of the recorded image due to the deformation as in the case of using a single-crystal silicon wafer, and poor exposure due to warpage of the substrate for the liquid jet recording head. An object of the present invention is to provide the above-described liquid jet recording head.

Another object of the present invention is to provide a liquid jet recording apparatus using the above liquid jet recording head, which can achieve higher image quality and higher speed recording. Another object of the present invention is to provide a substrate for a liquid jet recording head which includes forming a thermally oxidized layer having good surface properties on the surface of a substrate made of polycrystalline silicon used for the substrate for a liquid jet recording head described above. It is to provide a manufacturing method of. The present inventor has studied through the experiments described below in order to solve the above-described problems in the conventional liquid jet recording head substrate and achieve the above object. As a result, the inventor
The following findings were obtained. That is, in the case where polycrystalline silicon is used as the base of the substrate for a liquid jet recording head, (i) in the case of using the above-described single crystal silicon wafer, problems relating to size restriction and deformation of the substrate can be eliminated, A recording head capable of recording a high-quality recorded image at a high speed can be provided at a low price; and
(Ii) forming a thermal oxide layer on the surface of the polycrystalline silicon substrate; forming a thermal oxide layer on the surface of the substrate by heat treatment; When the thermal softening treatment is performed up to, the thermal oxide layer has a smooth continuous surface without surface steps, thereby providing a thermal oxide layer with good surface properties.
I got the knowledge.

[0021]

The present invention has been completed based on the above findings obtained by the present inventors through experiments. The present invention includes a substrate for a liquid jet recording head having the configuration described below, a liquid jet recording head and a liquid jet recording apparatus using the substrate, and a method for manufacturing the substrate.

A substrate for a liquid jet recording head according to the present invention is a liquid in which an electrothermal transducer having a heating resistor for generating heat and a pair of wirings electrically connected to the heating resistor is provided. A substrate for an ejection recording head, wherein a substrate constituting the substrate is made of polycrystalline silicon.

The substrate for a liquid jet recording head according to the present invention can achieve even a very long substrate at a low price as compared with the case where the above-mentioned single crystal silicon wafer is used as a substrate. In addition, there are advantages such that no deformation occurs even in a long shape, and a highly accurate wiring pattern can be easily achieved.

A liquid jet recording head according to the present invention comprises a discharge port for discharging liquid, a heating resistor for generating thermal energy for discharging liquid from the discharge port, and a heating resistor electrically connected to the heating resistor. A substrate for a liquid jet recording head, on which an electrothermal converter having a pair of wirings for supplying an electric signal for generating thermal energy to the heating resistor is disposed; and the electrothermal converter of the substrate. And a flow path for supplying a liquid in the vicinity of the liquid jet recording head, wherein the base constituting the substrate is made of polycrystalline silicon.

The liquid jet recording head of the present invention has an advantage that a desired length can be easily achieved. That is, when the above-described single crystal silicon wafer is used, the lengthening of the liquid jet recording head can be achieved only by integrating a plurality of heads, but the present invention does not require such an integrating operation. .

Therefore, the long liquid jet recording head provided by the present invention is disturbed in the recorded image caused by the integration of a plurality of heads when the length is increased by using a single crystal silicon wafer. There is no problem of the occurrence.
In addition to these advantages, the liquid jet recording head provided by the present invention has further advantages. That is, since the flatness of the substrate is maintained and there is no deformation of the work-in-progress, the yield is good, and a high-quality image can be obtained because of the high accuracy of the position of the liquid ejected from the ejection port. Can be.

A liquid jet recording apparatus according to the present invention includes a discharge port for discharging liquid, a heating resistor for generating thermal energy for discharging liquid from the discharge port, and a heating resistor electrically connected to the heating resistor. A liquid jet recording head substrate on which an electrothermal converter having a pair of wirings for supplying an electric signal for generating thermal energy to the heating resistor is disposed; and the electrothermal converter of the substrate. A liquid jet recording head having a flow path for supplying a liquid in the vicinity of the substrate, wherein a substrate constituting the substrate is made of polycrystalline silicon; and an electric signal is supplied to the heating resistor of the recording head. And an electric signal supply means for performing the operation.

Since the liquid jet recording apparatus of the present invention uses the above-described liquid jet recording head, it has an advantage that high-quality recording can be performed at a high speed.

According to a method of manufacturing a substrate for a liquid jet recording head according to the present invention, an electrothermal transducer having a heating resistor for generating thermal energy and a pair of wirings electrically connected to the heating resistor is formed on a substrate. A method for manufacturing a liquid jet recording head substrate formed on an oxide layer as a heat storage layer formed thereon, wherein the manufacturing method has a smooth surface as a heat storage layer on the polycrystalline silicon substrate. Thermal oxidation layer (hereinafter, this may be referred to as thermal oxidation layer, SiO ₂ film, or SiO
_{(Referred to as two} layers). The step of forming the thermal oxide layer in the method of manufacturing a substrate for a liquid jet recording head of the present invention is performed as described in the following (i) or (ii). That is, (i) a predetermined polycrystalline silicon substrate is prepared, and a thermal oxidation process is performed on a surface portion of the polycrystalline silicon substrate to form a thermal oxide layer (ie, a SiO ₂ layer). Is subjected to a thermal softening treatment to form a thermal oxide layer (ie, a heat storage layer) having a smooth surface on the polycrystalline silicon substrate. (Ii) A predetermined polycrystalline silicon substrate is prepared, and a thermal oxidation treatment and a thermal softening treatment are substantially simultaneously performed on a surface portion of the polycrystalline silicon substrate to form a thermal oxide layer having a smooth surface (that is, a heat storage layer). ) Is formed on the polycrystalline silicon substrate.

According to the method of manufacturing a substrate for a liquid jet recording head of the present invention, a good thermal oxide layer is formed while maintaining the smoothness of the surface even though polycrystalline silicon having a rough surface is used as a base. Therefore, a desired heat storage layer equivalent to the above-described heat storage layer formed on the single crystal substrate can be formed on the polycrystalline silicon substrate. The heat storage layer has a good smooth surface and excellent durability, so that a wiring or the like can be formed in a desired state on the heat storage layer, and there is no fear that a problem such as disconnection occurs in the heat storage layer.

[0031]

[Action]

2. Description of the Related Art Conventionally, plate-shaped polycrystalline silicon members have been used in the field of solar cells. If the polycrystalline silicon member is to be used as a substrate for a liquid jet recording head, it is necessary to provide a precise wiring or the like on the polycrystalline silicon member. It is said. However, unlike a single-crystal member, a polycrystalline silicon member has crystals of various orientations. Therefore, even if polishing for obtaining a mirror surface is performed, the desired surface property of a substrate for a liquid jet recording head is obtained. It is general recognition in the art that it is difficult to achieve, and therefore no attempt has been made in the field of liquid jet recording heads to use polycrystalline silicon as a substrate.

The inventor of the present invention, ignoring such recognition, attempted to use polycrystalline silicon as a substrate of a liquid jet recording head substrate through an experiment described below. As a result, they have found that polycrystalline silicon can be effectively used as a substrate of a substrate for a liquid jet recording head.

Hereinafter, an experiment performed by the present inventors will be described.

[Experiment A] In the case of a conventional single crystal wafer, mechanochemical polishing has been used because it is necessary to minimize the surface processed and deteriorated layer as a semiconductor device. In the case of mechanochemical polishing, a polishing agent for polishing is obtained by adding various alkalis such as NaOH, KOH and organic amine to colloidal silica in the case of primary polishing, and a polishing agent obtained by adding ammonia to colloidal silica in the case of secondary polishing.

When the surface of a polycrystalline silicon substrate is processed by the above-mentioned polishing means, a step is generally generated. The following experiment was conducted on the assumption that the reason for this is that the amount of silicon etched by the alkali component in the polishing agent varies depending on the crystal orientation.

A single crystal substrate sample was prepared as follows. First, a boron dopant produced by crushing a high-purity polycrystalline rod having a residual impurity concentration of 1 ppb or less produced by a precipitation reaction by hydrogen reduction and thermal decomposition of SiHcl ₃ and pulling it up in the <111> direction by the CZ method. A P-type single crystal ingot (8 inch × 110 cm) was shaped into a prism using a grinder, and then cut into a plate using a multi-wire saw. Next, the surface layer was removed and flattened by about 30 μm by lapping.

On the other hand, as a sample of the polycrystalline silicon substrate, high-purity polycrystalline silicon produced by precipitation reaction by hydrogen reduction and thermal decomposition used for production of single crystal silicon, or a material obtained by crushing single crystal silicon is used. After heating and melting to 1420 ° C in a crucible, pour into a graphite mold,
It was cooled to form a 40 cm square ingot. Next, the ingot was cut into a plate shape using a multi-wire saw. Next, the surface portion was removed by about 30 μm by lapping to make it flat.

As described above, 300 (mm) × 150
(Mm) × 1.1 (mm) (300 × 1 for simplicity)
It is abbreviated as 50 × 1.1 (mm). ) Were prepared for each of single-crystal silicon and polycrystalline silicon as shown in Table 1.

[0039]

[Table 1] As a polishing apparatus, a single-side polishing machine manufactured by Speed Fam Co., Ltd. was used.

The polishing process was divided into primary polishing and secondary polishing under the conditions described below, and the presence or absence of the addition of alkali and the surface finishing performance were evaluated during the primary polishing.

The evaluation results are summarized in Table 1.

Primary polishing conditions: polishing cloth; polyurethane-impregnated polyester nonwoven fabric, abrasive: colloidal silica (particle diameter: 0.06 μm), polishing pressure: 250 g / cm ² ,
Polishing temperature: 42 ° C, processing speed: 0.7 μm / mi
n Secondary polishing conditions: polishing cloth; suede-type foamed polyurethane, abrasive: silica fine powder (0.01 μm), polishing pressure: 175 g / cm ² , polishing temperature: 32 ° C.
Processing speed: 0.2 μm / min From the results shown in Table 1, it can be seen that even if a polycrystalline silicon substrate is used, smoothness equivalent to that of a single crystal substrate can be obtained by eliminating alkali addition during polishing. It has been found that crystalline silicon can be used as a substrate for a liquid jet recording head.

Experiment B In this experiment, the difference in the amount of deformation between a single-crystal silicon substrate and a polycrystalline silicon substrate when a long substrate was formed was examined.

A substrate sample of single-crystal silicon was prepared as follows. That is, first, a crushed high-purity polycrystalline silicon rod having a residual impurity concentration of 1 ppb or less produced by a precipitation reaction by hydrogen reduction and thermal decomposition of SiHcl ₃ was melted, and pulled up in the <111> direction by the CZ method. From a boron dopant P-type single crystal ingot (8 inch × 110 cm), it was shaped into a prism using a grinder, and then cut into a plate using a multi-wire saw. Next, lapping 3
After removing the surface layer by about 0 μm and flattening, the end portion was chamfered by a beveling machine, and the final surface was finished by polishing to finish the mirror surface substrate with a surface roughness Rmax of 150 °.

Next, the substrate surface was thermally oxidized by a pyrogenic oxidation method (hydrogen combustion oxidation method) as schematically shown in FIG. The oxidation is performed, for example, as follows. That is, hydrogen and oxygen are separately guided into the thermally oxidized base quartz tube 73, and react in the quartz tube 73 to generate H ₂ O, and the remainder is burned. Quartz tube 73
A base 71 for performing a thermal oxidation treatment is disposed therein, and is heated by an electric furnace 74.

The thermal oxidation of the prepared substrate is performed by the above-described oxidizing apparatus and method, and the gas pressure; 1 atm;
By introducing oxygen at 1150 ° C. for a treatment time of 14 hours, a thermal oxide layer of 3 μm was obtained.

In this way, five single crystal silicon substrate samples having the dimensions shown in Table 2 were prepared.

[0048]

[Table 2] On the other hand, a polycrystalline silicon substrate sample is a high-purity polycrystal produced by a precipitation reaction by hydrogen reduction and thermal decomposition used for the production of a single crystal, or a crushed single crystal, and heated to 1420 ° C. in a quartz crucible. After melting, the mixture was poured into a graphite mold and cooled to form a 120 cm square ingot. The faster the cooling rate is, the smaller the crystal grain size is, so the grain size is smaller outside the ingot in contact with the mold,
It becomes larger near the center. A plate-like polycrystalline silicon was cut out of this ingot at a position where the average crystal grain size became 2 mm with a multi-wire saw.

Next, after lapping, the surface layer was removed and flattened by about 30 μm, the edge was chamfered with a beveling machine, and the final surface was finished by polishing to obtain a mirror surface with a surface roughness Rmax of 150 °. Finished on a substrate.

Next, a thermal oxidation layer was formed with a thickness of 3 μm by the above-mentioned pyrogenic method under the same conditions as those described above. Thus, six polycrystalline substrate samples having the dimensions shown in Table 2 were prepared.

Next, an aluminum layer (4500.degree.) As a wiring, a hafnium; Hf layer (1500.degree.) As a heating resistor, and protection of the upper layer on the respective surfaces of the single crystal silicon substrate sample and the polycrystalline silicon substrate sample. A Ti layer (50 °) as a layer for improving adhesion to the layer, and SiO ₂ (1.5 μm), Ta (5000 °), and polyimide (3 μm) as a protective layer were respectively laminated to form six substrates.

In the case of the liquid jet recording head manufacturing process, in the next step, a 20 μm-thick negative dry film is laminated to form a flow path, and the flow path is patterned by exposing the flow path. If the substrate is warped, the focus position shifts, resulting in exposure failure. Therefore, the degree of warpage was evaluated for each of the obtained substrates. The degree of warpage was measured by placing the sample on a surface plate and measuring the maximum displacement using a dial gauge having a minimum scale of 1 μm. Table 2 shows the results.

The results shown in Table 2 are 300 (mm) × 1
The maximum warpage amount of a polycrystalline silicon substrate sample having a sample size of 50 (mm) × 1.1 (mm) is set to 1, and the other samples are relative values of the maximum warpage amount.

As is clear from the results shown in Table 2,
In the case of the polycrystalline silicon substrate sample, only the same amount of warpage is exhibited in all sizes used in the experiment, whereas in the case of the single crystal silicon substrate sample, 500 (mm) x 150 (mm)
An increase in the amount of warpage was observed from the sample size of 1.1 (mm), and a sample size of 800 (mm) × 150 (mm) × 1.1 (mm) shows a warpage amount relative value of 3; a warpage amount relative value. In the case of No. 2, when actual exposure is carried out, an exposure defect due to a shift of the focus position considerably occurs, and the warpage amount relative value 3
Would all result in poor exposure; and for a single crystal silicon substrate sample, 500 (mm) x 150 (mm) x 1.
The sample size of 1 (mm) is the limit at which a liquid jet recording head can be manufactured.

Experiment C In this experiment, the relationship between the crystal grain size and the deformation due to the warpage of the substrate was examined for a single crystal silicon substrate and a polycrystalline silicon substrate. In the same manner as in Experiment B, the size was 300 (mm) × 150 (mm) × 1.1 (m
m), ten mirror single-crystal silicon substrates (sample No. 1) were prepared. Separately, in the same manner as in Experiment B, the size was 300 (mm) × 150 (mm) × 1.1.
A plurality of (mm) mirror-surface polycrystalline silicon substrates were prepared. At this time, since the crystal grain size of the substrate is selected from polycrystalline silicon ingots, since the crystal grain size increases from the surface in contact with the mold toward the center, an appropriate portion is selected when cutting out from the ingot. By,
In Table 3, the sample No. A plurality of substrates (sample Nos. 2 to 8) having an average crystal grain size shown in the sections 2 to 8 were obtained for each ten sheets.

[0056]

[Table 3] At this time, the average crystal grain size of the substrate was determined according to JIS G05.
No. 52 was measured by a crystal grain size measuring method according to the cutting method described in the section of the ferrite crystal grain size test method. The surface of each of the prepared single-crystal silicon substrate (sample No. 1) and polycrystalline silicon substrate was 3 μm by pyrogenic oxidation in the same manner as described in Experiment B.
Was formed.

An integrated long liquid jet recording head is manufactured by cutting a liquid jet recording head substrate into strips for each head-in-process product, but the problem with this is that the head-in-process cut out from both ends of the substrate is problematic. There is a problem that only the article bends like a bow. FIG. 9A shows a state in which bowing or bending occurs.

However, if the polished surface is warped in the polishing step, the distance between the heating element and the discharge port surface cannot be made uniform, which causes a problem in print quality.

Then, for the purpose of calculating the process yield in the polishing process, two samples for bending measurement were prepared for each substrate by cutting the substrate from both ends into strips each having a width of 10 mm with a slicer. 20 samples were prepared for each sample in Table 3.

The sample thus prepared was placed on a precision XY table with a linear scale, and the maximum amount of bending was measured.

FIGS. 9 (B), 9 (C) and 9 (D) are explanatory views of the bow / bend measurement method adopted in this case.

The points a and b in FIG. 9D are represented by X in the XY table.
The amount of bending in the Y direction was measured along the axis.

A sample exceeding the allowable bending amount in the polishing step was regarded as a reject, and the pass rate under each condition was counted. Third
In the table, sample No. Sample No. 8 has a pass rate of 1 for a sample having an average crystal grain size of 0.01 mm, and for other samples, Sample No. The relative value to the value of 8 was shown.

From the results shown in Table 3, it has been found that a polycrystalline silicon substrate is less deformed by warpage than a single crystal silicon substrate. And also in the polycrystalline silicon substrate, those having an average crystal grain size exceeding 8 mm have little advantage over single crystal silicon, and those having an average crystal grain size of more than 2 mm and an average crystal grain size of 8 mm or less are:
Although superior to single crystal silicon, it was found to be inferior to those having an average crystal grain size of 2 mm or less.
From this, it was found that the average crystal grain size of the polycrystalline silicon substrate was preferably 8 mm or less, more preferably 2 mm or less.

Experiment D The substrate constituting the liquid jet recording head substrate was as follows.
Since wiring is provided on the base, the surface of the base is required to be smooth to a desired state. Therefore, it is necessary to satisfy this requirement even when the substrate is made of polycrystalline silicon.

By the way, polycrystalline silicon is used in the field of solar cells. In this case, the surface condition of the substrate made of polycrystalline silicon is different from that of the substrate constituting the substrate for a liquid jet recording head. There is no severe requirement regarding surface smoothness as described above. Incidentally, a polycrystalline silicon substrate used for a solar cell usually contains inclusions. That is, a polycrystalline silicon ingot used for obtaining a polycrystalline silicon substrate for a solar cell is manufactured by melting silicon in a quartz crucible and cooling and solidifying the molten silicon. The silicon melt is chemically very active, and quartz as the constituent material of the crucible material is also Si
It reacts like O ₂ + Si → 2SiO. As a result, the silicon firmly adheres to the inner wall of the crucible during cooling and solidification. If strain due to the difference in the thermal expansion coefficient between quartz and silicon is added thereto, the crucible is easily cracked. Therefore, when the ingot is taken out of the crucible, a powdery release agent is applied to the inner wall surface of the crucible so that it can be easily taken out. Therefore, the release agent inevitably intervenes in the polycrystalline silicon ingot. Such inclusions do not pose any problem in solar cells. However, when wiring is applied on a substrate made of such polycrystalline silicon, if the surface of the substrate is first polished and mirror-finished, the inclusions become defects such as pits or projections of several tens of μm and remain on the surface of the substrate. . In the case where such defects are present, when wiring is patterned by photolithography technology, a portion where resist cannot be applied or a portion where the resist accumulates occurs, resulting in disconnection or short circuit of the wiring. There is. In addition, if such a defect is located at a position where the heating resistor is disposed, cavitation damage is concentrated when bubbles generated for discharging ink are eliminated, resulting in early disconnection.

In this experiment, the influence of the inclusions contained in the polycrystalline silicon when the substrate constituting the substrate for the liquid jet recording head was made of polycrystalline silicon was examined in the background described above. We examined from the quantitative viewpoint.

As a sample, first, in the same manner as in Experiment B, 330 (mm)
A single crystal substrate having dimensions of × 150 (mm) × 1.1 (mm) was cut out, subjected to lapping and polishing, and finished into a mirror-finished substrate having a surface roughness of Rmax 150 °. This substrate was used as Sample 1. At this stage, the surface condition of the substrate (sample 1) was observed by a substrate surface inspection apparatus (trade name: Scantech, manufactured by Nagase & Co., Ltd.) using a CCD reading method. As a result, since there was no inclusion of the release agent, the number of defects per area of the substrate was 1 / cm ² or less at all measurement points in the range of the detection capability diameter of 1 μm or more. The results are shown in Table 4.

[0069]

[Table 4] Separately from the above, silicon was melted in a quartz crucible in which a release agent was not applied to the inner surface, and then a 50 cm square polycrystalline silicon ingot was formed. From this ingot, a polycrystalline silicon substrate having the same dimensions as that of the single crystal silicon substrate was cut out, and the surface thereof was wrapped and polished to finish a mirror surface substrate having a maximum surface roughness of 150 °. This substrate was used as Sample 2. The surface condition of the single-crystal silicon substrate (sample 1) was observed in the same manner as in the case of the single-crystal silicon substrate (sample 1). As a result, since there is no inclusion of the release agent, the number of defects per area of the substrate is 1
1 piece / cm ² at all measurement points in the range of μm or more
It was below. The results are shown in Table 4.

Next, Sample 2 was used except that a release agent was used.
A plurality of substrates (samples 3 to 6) were prepared by performing the same operation as in the case of preparing. The amount of the release agent used was different for each sample. The surface condition of each of the obtained substrates (samples 3 to 6) was observed in the same manner as in the single-crystal silicon substrate (sample 1).

As a result, the number of defects in each of Samples 3 to 6 was 5 / cm ² or less, 10 / cm ² or less,
The number was 0 / cm ² or less and 100 / cm ² or less. next,
The surface of each of the substrates (samples 1 to 6) was subjected to a thermal oxidation treatment in the same manner as in the experiment B,
A 3 μm thermal oxide layer was obtained.

Next, as a test wiring pattern for detecting disconnection or short circuit due to inclusions, an Al film was formed on the thermal oxide layer of each sample to a thickness of 4500 ° by a magnetron sputtering method. , Wiring width 20 μm,
A folded wiring pattern having a wiring interval of 10 μm was formed. At this time, the number of folded wirings of each sample is assumed to be the wiring pattern of the liquid jet recording head, and the wiring length is 8 mm and the number of wirings is 4736.
A test pattern was used. 15 test patterns were formed for each sample.

A continuity test was performed by bringing the probe pins into contact with the ends of each wiring. The continuity test was evaluated on the basis of a test in which no disconnection or short circuit was found. The evaluation result is the number of patterns without any disconnection or short circuit for 15 test patterns, that is, the number of passed patterns / 1.
Five test patterns were expressed as yield. The results obtained are as shown in Table 4.

From the results shown in Table 4, the following was found. That is, (i) polycrystalline silicon having no release agent inclusions exhibits the same yield as single crystal silicon; (ii) even polycrystalline silicon having release agent inclusions has a defect number of 1 μm or more in diameter. Those having 5 / cm ² or less show the same yield as single crystal silicon; (iii) those having 10 / cm ² or less of defects having a diameter of 1 μm or more have higher yields than those having 5 / cm ² or less. (Iv) Those having 50 or less defects / cm ^{2 with a} diameter of 1 μm or more are not practical because the yield is greatly deteriorated.
Those having a number of defects of 100 m / cm ² or less are not practical. From the findings, the following findings were obtained. That is, a polycrystalline silicon member which can be effectively used as a substrate constituting a liquid jet recording head substrate preferably has a smooth surface (smooth state), and the number of defects having a diameter of 1 μm or more is 10 / cm ² or less. And
More preferably, the number of defects having a diameter of 1 μm or more is 5 / cm ²
It must be:

Experiment E In this experiment, a study was made from the viewpoint of eliminating the surface step caused by polycrystalline silicon when the base constituting the substrate for the liquid jet recording head was composed of polycrystalline silicon. As described in the Background Art section above, when single crystal silicon is used as a substrate constituting a substrate for a liquid jet recording head, the heat radiation property of the substrate is used in order to obtain better characteristics as a liquid jet recording head. And balance heat storage
Generally, a heat storage layer is formed on the surface of a single crystal silicon substrate. As the heat storage layer, an SiO ₂ layer formed by thermally oxidizing a surface portion of the single crystal silicon substrate is usually used. The present inventor uses a polycrystalline silicon substrate instead of the single crystal silicon substrate, and thermally oxidizes a surface portion of the polycrystalline silicon substrate to form a SiO ₂ layer as a heat storage layer, as in the case of forming the heat storage layer. Was formed, and the surface state of the SiO ₂ layer was observed. As a result, it was found that a maximum difference of about several thousand degrees was generated between crystal grains on the surface of the SiO ₂ layer.

If such a step is present on the base constituting the substrate for a liquid jet recording head, damage is concentrated on the step due to thermal shock of heating and cooling or cavitation generated during ejection of the recording liquid. If the heating resistor is formed on the stepped portion, there arises a problem that the reliability in terms of the durability life is reduced. That is, particularly when the ejection of the recording liquid is repeated at a high speed, the cavitation concentrates on the step portion, whereby the heating resistor is broken at an early stage.

As a measure to solve such a problem, the above S
After forming the iO ₂ layer, the surface of the SiO ₂ layer may be polished and flattened. However, this method does not provide a satisfactory solution to the problem. That is,
As described above, the surface step of the SiO ₂ layer is about several thousand degrees, and in addition, it is desirable that the SiO ₂ layer has a thickness of several microns. It is difficult to desirably solve the problem without disturbing the function of the _two layers. Another solution to the problem is to make the SiO ₂ layer quite thick,
It is conceivable to perform the above-mentioned polishing on the surface, but in this case, there is a problem that such an excessively thick SiO ₂ layer does not function as a desired heat storage layer, and it is not practical from an economic viewpoint. .

The inventor has proposed that the heat storage layer (ie, SiO ₂
Layer) is formed by a vacuum film forming method, that is, a sputtering method,
Attempts were made in each of the thermal CVD method, the plasma CVD method, and the ion beam evaporation method, but in any case, the film thickness became uneven, the film formation took a long time, or occurred during the film formation. Dust was mixed into the film and projections with a diameter of several microns were generated, which caused destruction by cavitation. It has also been found that the occurrence of such protrusions causes a current to leak therefrom, causing an electrical short circuit.
From these facts, the vacuum film formation method uses the heat storage layer (that is, S
(iO ₂ layer). The inventor of the present invention has attempted to form the heat storage layer (SiO ₂ layer) by employing each of the spin-on-glass method and the dip pulling method. In any case, the quality of the formed SiO ₂ layer is low. Bad, it is difficult to achieve good film quality, and sometimes impurity particles are mixed in the film,
It has been found that none of these film forming methods can be adopted.

In the field of semiconductor device manufacturing, a flattening process is employed as a technique for improving the problem of disconnection at a step portion of a multilayer wiring. For example, a planarization process widely used in MOS LSI is a reflow technique for a PSG film. This technique P ₂ having mole percent SiO ₂ film formed by the CVD method is O ₅
Is included to lower the softening point of the PSG film as an interlayer insulating film, and to perform a heat treatment (reflow treatment) to flatten the steps of the PSG film. The reflow temperature at this time is about 800 to 1000 ° C. in consideration of the influence of heat on the formed wiring and the like.

However, the substrate constituting the substrate for a liquid jet recording head is made of polycrystalline silicon, and the above-mentioned step in the thermal oxide layer formed on the polycrystalline silicon substrate is eliminated by the above-mentioned flattening process. Cannot be adopted.

That is, in the case of a liquid jet recording head which is completely different from the above-mentioned semiconductor device in terms of structure, function and behavior, and purpose of use, recording is performed on the recording head substrate using the recording head. In this case, the heat generating resistor generates heat at about 1100 ° C. in order to generate thermal oxide layer energy for discharging a recording liquid, and thus it is required that the heat generating resistor has a characteristic capable of sufficiently withstanding this temperature. Therefore, it is essential that the substrate constituting the substrate satisfies this requirement. By the way, when the substrate is made of polycrystalline silicon completely different from the PSG film in the semiconductor device, and a thermal oxide layer is formed on the polycrystalline silicon substrate,
As described above, a step occurs on the surface of the thermal oxide layer. The present inventor has attempted a step eliminating method in the semiconductor device described above to eliminate the step.
The goal could not be achieved. This point is clear from the experimental results described below. That is, even if a reflow processing temperature (about 1100 ° C.) which is much higher than the upper limit of the reflow processing temperature (about 1000 ° C.) used for eliminating the step in the semiconductor device described above, the surface step of the thermal oxide layer is eliminated. Could not.

As is apparent from the above description, the substrate constituting the substrate for the liquid jet recording head is made of polycrystalline silicon, and the step (ie, the step on the surface of the thermal oxide layer formed on the polycrystalline silicon substrate) There is no effective means to eliminate the surface step.

From the above, the present inventor tried through an experiment described below to solve the problem of the occurrence of steps on the surface of the thermal oxide layer through a thermal softening treatment. That is, in the following experiments, the present inventor outlines two methods: (i) performing a thermal oxidation treatment on the surface portion of the polycrystalline silicon substrate to form a thermal oxide layer; A method of performing a thermal softening treatment and a method of (ii) simultaneously performing a thermal oxidation treatment and a thermal softening treatment on the surface of a polycrystalline silicon substrate were attempted.

The following is a description of (a) a thermal oxidation layer (SiO 2) formed when the surface of a polycrystalline silicon substrate is subjected to a thermal oxidation treatment.
₍₂ ) the reason why the surface of the polycrystalline silicon substrate having the step subjected to the thermal oxidation treatment is subjected to the thermal softening treatment in the softening temperature range of the thermal oxidation layer on the surface of the polycrystalline silicon substrate having the step subjected to the thermal oxidation treatment. FIG. 4A to FIG. 4 show that the inventor of the present invention has found through an experiment why the SiO ₂ layer having no surface step is formed on the surface of the polycrystalline silicon substrate.
This will be described with reference to FIG.

When the polycrystalline silicon substrate 11 as shown in FIG. 4A is thermally oxidized as it is, the volume increases at the time of thermal oxidation, and the thermal oxidation rate is increased due to the difference in the crystal orientation of the crystal plane of each crystal grain 12. Is different, as shown in FIG.
Experiments have confirmed that the thickness of the thermal oxide film 13 generated for each crystal grain 12 is different, and a step is generated on the surface. In FIG. 4B, line a indicates the position of the surface of the polycrystalline silicon substrate 11 before thermal oxidation. For example, on the surface of the polycrystalline silicon substrate 11, a thermal oxide layer (S
When the iO ₂ layer 13 is formed, the formed thermal oxide layer has a step of about 1000 ° on the surface.

In the case of a recording head made using a polycrystalline silicon substrate having a thermal oxide layer having such a surface step, when bubbles disappear on a heating resistor formed on the substrate. The cavitation damage generated in the recording head is concentrated on the step portion of the substrate, and the heating resistor is destroyed very early after the driving of the recording head.

Here, the process of thermal oxidation of the surface of the polycrystalline silicon substrate will be discussed. In a very early stage of forming a thermal oxide layer formed by thermally oxidizing the surface portion of the polycrystalline silicon substrate, a linear rule is established between the thickness of the thermal oxide layer 13 and the oxidation rate. That is, the reaction of oxygen (O ₂ ) at the interface between polycrystalline silicon (Si) and silicon oxide (SiO ₂ ) constituting the thermal oxide layer is rate-limiting. In this case, the oxidation rate of oxygen varies depending on the orientation of the crystal plane.

On the other hand, after the thermal oxide layer 13 is formed to a certain thickness or more, the process of diffusing oxygen in the thermal oxide layer 13 becomes rate-determining. It is considered that the diffusion rate of oxygen in the thermal oxide layer 13 is not affected by the orientation of the crystal plane of the silicon crystal grains 12.

Therefore, the step on the surface of the thermal oxide layer (that is, thermal oxide film) 13 for each crystal grain 12 of the polycrystalline silicon substrate 11 occurs at the very beginning of the thermal oxidation step, and to a certain extent, After the formation of the layer 13 proceeds,
It can be considered that the step does not increase.

FIG. 4 shows the step thus generated.
As shown in (C), heating at a temperature (softening temperature) high enough not to melt the polycrystalline silicon material (that is, thermal softening treatment)
Then, the thermal oxide layer gradually shows fluidity, and a smooth surface can be obtained.

That is, the surface state of the thermal oxide layer is deformed by applying heat so that the surface steps of the thermal oxide layer are averaged, and the surface becomes smooth. Therefore, the thermal oxide layer is provided on the thermal oxide layer of the polycrystalline silicon substrate. Cavitation damage is not concentrated on the heating resistor, and durability is improved.

In the case of the present invention, unlike the case of flattening the interlayer insulating film on the wiring when forming the multilayer wiring in the LSI manufacturing process,
Since the surface step of the thermal oxide layer formed on the polycrystalline silicon is flattened, it is possible to achieve the smoothing with only a slight fluidity.

The above-mentioned thermal softening treatment is a thermal oxidation treatment (ie,
This may be performed after the formation of the thermal oxide film), or may be performed concurrently with the thermal oxidation treatment.

It is also possible to introduce a predetermined impurity into the polycrystalline silicon substrate to be used and to perform a thermal softening treatment. By introducing the impurities, the softening temperature of the thermal oxide layer is lowered, and the processing efficiency can be improved. That is, the temperature for softening may be relatively low, and the processing time can be shortened. When the softening treatment is performed at a relatively high temperature, the softening of the thermal oxide layer proceeds effectively, so that the steps can be more effectively smoothed. As described above, by promoting the softened state of the thermal oxide layer, the adhesion of the thermal oxide layer formed on the polycrystalline silicon substrate to the heating resistor formed thereon can be improved.

The present inventor conducted a verification experiment on the effect of performing the thermal softening treatment by preparing a substrate for a liquid jet recording head.

Experiment E-1 The present inventor examined the effects of a polycrystalline silicon substrate having a thermally oxidized layer formed by performing the above-described thermal softening treatment subsequent to the thermal oxidation treatment, and prepared a liquid jet recording head substrate. And studied.

That is, first, a polycrystalline silicon ingot having an average crystal grain size of about 4 mm was prepared by the casting method described above. Five square substrates were cut out from the obtained ingot. Wrap each substrate,
Polishing was performed to obtain a mirror substrate having a size of 300 mm × 150 mm × 1.1 mm and a surface roughness of Rmax150 °, which was used as a polycrystalline silicon substrate. Next, a thermal oxidation treatment was applied to the surface of the polycrystalline silicon substrate to form a thermal oxide layer in the same manner and under the same conditions as in Experiment B except that the tube (see 73 in FIG. 7) was made of SiC.

Each of the five polycrystalline silicon substrates having the thermal oxide layers thus obtained was introduced into a thermal oxidation furnace, and the furnace temperatures were set at 1380 ° C., 1330 ° C., and 1280, respectively.
The temperature was kept at 1230 ° C. and 1180 ° C. for 1 hour to perform a thermal softening treatment on the thermal oxide layer. Thus, the sample N
o. 1, 2, 3, 4 and 5 polycrystalline silicon substrates were prepared.

By treating the polycrystalline silicon substrate as described above, a polycrystalline silicon substrate having a heat storage layer formed of a thermal oxide film (SiO ₂ film) on the surface was obtained. The thickness of the formed heat storage layer (that is, the SiO ₂ layer) was 3.0 μm in each case. Next, the shape of the step on the surface of the heat storage layer was examined with a stylus roughness meter and evaluated.
The measurement method and evaluation criteria for the step shape at that time were as follows.

Stylus scanning distance: 10 mm Measurement location: 15 locations per substrate Measurement location: a line segment that divides the short side 150 mm of the substrate into four equal parts,
Total 15 intersection points of line segments that divide the long side 300mm into 6 equal parts
Section.

Evaluation criteria: The maximum height of the step in the 15 measurement points was 0 μm or more and less than 0.05 μm.
A value of 〇 or more and less than 0.1 μm was evaluated as Δ, and a value of 0.1 μm or more was evaluated as ×.

Sample No. The surface steps of 1 and 2 are ◎, sample N
o. The surface steps of Sample Nos. 3 and 4 are Δ. The surface step of No. 5 was x.

Next, for each of the polycrystalline silicon substrates (samples Nos. 1 to 5) thus obtained, a heating resistor made of HfB ₂ [size: 20 μm × 100 μm, thickness:
0.16 μm, wiring density: 16Pel (ie 16 lines / mm)]
Were formed and an electrode (width 20 μm, thickness 0.6 μm) made of Al connected to each heating resistor. Furthermore, SiO ₂
A protective layer made of / Ta is formed by sputtering on the portion where the heat generating resistor and the electrode are formed.
A substrate for a liquid jet recording head having the configuration shown in FIG. 1A and FIG. 1B was prepared.

Sample No. Substrate 1 was too hot softening temperature, so the substrate was deformed, and the substrate was cracked when applying a photoresist with a roll coater in the liquid jet recording head manufacturing process, producing a liquid jet recording head. I couldn't do it.

Sample No. For each of the substrates 2 to 5, a liquid path and a liquid chamber are formed on the heat storage layer by a dry film or the like, and a discharge port is formed by cutting a slicer, and the structure shown in FIGS. 5A and 5B is used. Each of the liquid jet recording heads was prepared.

With respect to each of the obtained four liquid jet recording heads, a driving pulse (print signal) having a pulse width of 1.1 Vth (Vth is a foaming voltage) and a pulse width of 10 μs was repeatedly applied to each heating resistor, and ink was discharged from each discharge port. Was discharged, and a discharge durability test was performed. The number of integrated drive pulses is 1 × 10 ⁷ , 1
The durability of the liquid jet recording head is determined by calculating the residual ratio of the heating resistors when the heating resistors reach × 10 ⁸ and 3 × 10 ⁸ , that is, the number of the heating resistors that are not disconnected with respect to the total number of the heating resistors. evaluated. The results are shown in Table 5-1. The results were as shown in columns 2 to 5.

[0107]

[Table 5] Sample No. Regarding 2 to 4, in each case, no cavitation breakage occurred and 3 × 1 of the driving pulse
0 ⁸ times also residual rate after the repetition of the De' 100%. However, the sample No. In the case of No. 5, cavitation fracture occurred from an early stage, and the residual ratio was lowered.

From the above results, it is possible to obtain a heat storage layer having a smooth surface step by performing a thermal softening treatment at a temperature in the range of about 1230 ° C. to 1330 ° C. after the polycrystalline silicon substrate is thermally oxidized. It was also confirmed that extremely good results were obtained in the discharge durability test.

Experiment E-2 In this experiment, the effect of forming a thermal oxide layer (heat storage layer) on a polycrystalline silicon substrate by simultaneously performing thermal oxidation and thermal softening was examined. Five mirror-finished substrates having a size of 300 (mm) × 150 (mm) × 1.1 (mm) and a surface roughness of Rmax150 ° were prepared in the same manner as in Experiment E-1. These were formed on a polycrystalline silicon substrate (sample N
o. 6 to 10). Next, a thermal storage layer (thermal oxide layer) was formed on each of these polycrystalline silicon substrates by simultaneously performing a thermal oxidation treatment and a thermal softening treatment using the same apparatus as that used in Experiment E-1.

That is, each polycrystalline silicon substrate was placed in a thermal oxidation furnace, oxygen was introduced therein by a pyrogenic method, and the interior of the thermal oxidation furnace was maintained at a predetermined temperature to apply heat to the surface of the polycrystalline silicon substrate. An oxidation treatment and a thermal softening treatment were simultaneously performed to form a heat storage layer (thermal oxidation layer, ie, SiO ₂ layer). The furnace temperature at that time differs in each case.
80 ° C, 1330 ° C, 1280 ° C, 1230 ° C and 11
80 ° C. In order to obtain a heat storage layer (thermally oxidized SiO ₂ layer) of 3 μm, the heating times were 5, 7, 8, 11 and 14, respectively.
Time. Thus, the sample No. Five to six polycrystalline silicon substrates were prepared.

By treating the polycrystalline silicon substrate as described above, a polycrystalline silicon substrate having a heat storage layer made of a thermal oxide film (SiO ₂ film) formed on the surface was obtained. The layer thickness of the formed heat storage layer (that is, the SiO ₂ layer) was 3.0 μm in each case.

Next, the shape of the step on the surface of the heat storage layer was examined and evaluated with a stylus type roughness meter. The measurement and evaluation at that time were performed in the same manner as in Experiment E-1.

The sample No. The surface steps of 6 and 7 are ◎, sample N
o. The surface steps of Sample Nos. 8 and 9 are Δ. The surface step of No. 10 was x.

Next, for each of the polycrystalline silicon substrates thus obtained, a heating resistor made of HfB ₂ [size: 20 μm × 100 μm, thickness: : 0.16 μm, wiring density: 1
6Pel (ie, 16 wires / mm)] and an electrode made of Al connected to each of the heating resistors (width 20 μm, thickness 0.6 μm)
m) was formed. Further, a protective layer made of SiO ₂ / Ta is formed by sputtering on the portion where the heating resistor and the electrode are formed, and the liquid jet recording head having the structure shown in FIGS. 1A and 1B is formed. A substrate was prepared.

Sample No. The substrate of No. 6 had a thermal softening temperature that was too high, so that the substrate was deformed, and the substrate was broken when a photoresist was applied by a roll coater in the liquid jet recording head manufacturing process, and the liquid jet recording head was manufactured. I couldn't do it.

Sample No. For each of the bases 7 to 10, a liquid path and a liquid chamber are formed on the formed heat storage layer by a dry film or the like, and a discharge port is formed by slicer cutting, and FIGS. 5A and 5B Each of the liquid jet recording heads having the configuration shown in FIG.

With respect to each of the four obtained liquid jet recording heads, a drive pulse (print signal) having a pulse width of 1.1 Vth (Vth is a foaming voltage) and a pulse width of 10 μs was repeatedly applied to the heating resistor, and ink was discharged from each discharge port. Was discharged, and a discharge durability test was performed. The number of integrated drive pulses is 1 × 10 ⁷ , 1
The durability of the liquid jet recording head is determined by calculating the residual ratio of the heating resistors when the heating resistors reach × 10 ⁸ and 3 × 10 ⁸ , that is, the number of the heating resistors that are not disconnected with respect to the total number of the heating resistors. evaluated. The results are shown in Table 5-2. The results were as shown in columns 7 to 10.

[0118]

[Table 6] Sample No. No cavitation breakage occurred in any of the cases 7 to 9, and 3 × 10
Even after ⁸ repetitions, the residual ratio was 100%. However, the sample No. In the case of 10, cavitation fracture occurred from an early stage, and the residual ratio was reduced.

From the above results, 1230 ° C. to 1330
Simultaneous thermal oxidation treatment and thermal softening treatment of the polycrystalline silicon substrate at a temperature in the range of about ℃ gives a heat storage layer with a smooth surface step shape, and extremely good results in the discharge durability test. It was confirmed that it could be obtained.

Experiment E-3 In this experiment, a thermal oxidation treatment was performed on the surface portion of the polycrystalline silicon substrate, which was performed in Experiment E-1, to form a thermal oxide layer (heat storage layer). In the method of softening treatment, the effect of doping impurities into the thermal oxide layer formed by the thermal oxidation treatment and performing the thermal softening treatment on the doped thermal oxide layer was examined.

First, in the same manner as in Experiment B, 300 (mm)
Fifteen mirror-like substrates having a size of × 150 (mm) × 1.1 (mm) and a surface roughness of Rmax150 ° were prepared.
These were made of a polycrystalline silicon substrate (samples No. 11 to No. 11).
25). Sample No. Each of 11 to 25 was first subjected to a thermal oxidation treatment in the same manner as in Experiment E-1 to form a thermal oxide layer. Then, the formed thermal oxide layer was doped with impurities as follows.

That is, doping of the surface of the thermal oxide layer (SiO ₂ layer) with impurities was performed by the normal pressure CVD method.
As a dopant, a liquid source of POCl ₃ was used,
It was introduced into the furnace with a carrier N ₂ gas and kept in a saturated state. At this time, the diffusion time was 30 minutes, and the diffusion temperature was
o. Samples 11 to 15 were set to 1050 ° C.
o. For samples 16 to 20, the temperature was set to 1000 ° C.
o. The temperature was set to 950 ° C. for 21 to 25. .

For each of the obtained samples, the surface phosphorus concentration was measured using a secondary ion mass spectrometer (model name: IMS-3F, CAME).
The measurement was performed using a CA (hereinafter abbreviated as SIMS).

Sample No. 1 having a diffusion temperature of 1050 ° C. Each of 11 to 15 has 5 × 10 ²¹ atoms / cm ³ and a diffusion temperature of 10
Sample No. of 00 ° C. Each of 16 to 20 is 1 × 10
Sample No. ^{21 having 21} atoms / cm ³ and a diffusion temperature of 950 ° C. Each of 21 to 25 was 1 × 10 ²⁰ atoms / cm ³ .

Subsequent to the impurity doping, a thermal softening treatment was performed in the same manner as in Experiment E-1. At that time, the heat softening treatment time was fixed at 1 hour, and the softening temperature was 12 hours.
80 ° C, 1230 ° C, 1180 ° C, 1130 ° C, 108
Five conditions of 0 ° C. were set. Table 5-3 shows the thermal softening temperature of each sample.

[0126]

[Table 7] Thus, the sample No. Fifteen polycrystalline silicon substrates of 11 to 25 were prepared.

By treating the polycrystalline silicon substrate as described above, a polycrystalline silicon substrate having a heat storage layer made of a thermal oxide film (SiO ₂ film) formed on the surface was obtained. The layer thickness of the formed heat storage layer (that is, the SiO ₂ layer) was 3.0 μm in each case.

With respect to each sample, the shape of the step on the surface of the formed heat storage layer was examined with a stylus type roughness meter and evaluated. The measurement and evaluation at that time were the same as in Experiment E-1.

The sample No. The surface steps of Sample Nos. 19 and 23 are Δ. The surface steps of 20, 24 and 25 were x.

The surface steps of all the other samples were ◎.

Next, using a photolithography technique, a heating resistor made of HfB ₂ [size: 20] was formed on the heat storage layer formed on each of the thus obtained polycrystalline silicon substrates.
μm × 100 μm, thickness: 0.16 μm, wiring density: 16 Pel (ie, 16 wires / mm)] and electrodes made of Al connected to each heating resistor (width 20 μm, thickness 0.6 μm) did. Further, a protective layer made of SiO ₂ / Ta is formed by sputtering on the portion where the heating resistor and the electrode are formed, and the liquid jet recording head having the structure shown in FIGS. 1A and 1B is formed. A substrate was prepared.

For each of the liquid jet recording head substrates thus obtained, a liquid path and a liquid chamber are formed on the substrate by a dry film or the like, and a discharge port is formed by cutting a slicer. One liquid jet recording head having the configuration shown in FIG. 5B was prepared.

For each of the obtained liquid jet recording heads, a drive pulse (print signal) having a pulse width of 1.1 Vth (Vth is a bubbling voltage) and a pulse width of 10 μs is repeatedly applied to the heating resistor to cause ink to be ejected from each ejection port. And a discharge durability test. When the integrated number of drive pulses is 1 × 10 ⁷ , 1 × 10 ⁸ ,
The durability of the liquid jet recording head was evaluated by obtaining the residual ratio of the heating resistors when the value reached 3 × 10 ⁸ , that is, the number of the heating resistors that were not disconnected with respect to the total number of the heating resistors. The results are shown in Table 5-3.
o. Nos. 11 to 25 were as shown in the respective columns.

The sample No. In each of the cases 11 to 15, a large number of disconnections of the heat-generating low antibody occurred from the stage where the cumulative driving pulse was small. Observation of the broken portion with a scanning electron microscope revealed that peeling occurred between the thermally oxidized SiO ₂ layer and the heating resistor. Sample No. In each of 11 to 15, since the impurity surface concentration is high, the softening temperature of the heat storage layer (thermally oxidized SiO ₂ layer) immediately below the heat generating resistor decreases, and the maximum temperature reaches about 1100 ° C., and the temperature of the heat generating low antibody changes. Is considered to have occurred.

Sample No. For samples 16 to 25, sample Nos. 20, sample no. 24, sample no. In the case of Sample No. 25, cavitation rupture occurred from an early stage and the residual ratio was lowered. 16 to 19, sample no.
In the cases of Nos. 21 to 23, no cavitation breakage occurred in any case, and the residual ratio was 100% even after the driving pulse was repeated 3 × 10 ⁸ times.

From the above results, the higher the impurity surface concentration, the smoother the step can be made at a lower thermal softening temperature. However, if the impurity is doped to such an extent that the impurity softens at 1080 ° C. or lower, the heat generating resistor is not heated. At the temperature of the thermal storage layer (thermal oxidation layer,
That is, it was found that the SiO ₂ layer) was deformed, and the durability of the antibody with low heat generation was reduced.

The thermal oxidation layer (SiO ₂ layer) has a softening temperature of 1
If impurities are doped at a temperature of 130 ° C. or higher and as low as possible, the step can be effectively eliminated at a temperature lower than 100 ° C. as compared with the case without doping, and the operating temperature of the processing furnace is relatively low. It has been found that the lowering of the furnace length is advantageous in terms of manufacturing cost because the life of the furnace is extended.

The upper limit of the softening temperature is lower than 1330 ° C. at which no adverse effect due to the deformation of the polycrystalline silicon substrate occurs as in the case of Experiments E-1 and E-2.

In addition, when the same temperature condition and time for thermal softening treatment as in the case where no doping is employed, the softened state of the thermal oxide layer is further advanced, and the surface state of the thermal oxide layer is preferably further reduced in level. It will be.

(Detailed Description of Preferred Embodiments) The feature of the present invention lies in the base constituting the substrate for a liquid jet recording head. The substrate is made of polycrystalline silicon, and is characterized by having a heat storage layer (thermal oxide layer) having smooth surface properties on the surface of the polycrystalline silicon. The heat storage layer is formed by subjecting a surface portion of the polycrystalline silicon to a thermal oxidation treatment and a thermal softening treatment.

When the substrate is made of polycrystalline silicon, the surface of the substrate is generally not flat because of its crystal grains. As described in the above experiment, the thermal oxide layer formed on the surface has a step. The surface has an accompanying surface.

The present invention is based on an experiment conducted by the present inventor to solve the problem of the level difference, in particular, a fact found in an experiment E. In the present invention, the polycrystalline silicon substrate having a heat storage layer having a smooth surface property is prepared by preparing a substrate made of polycrystalline silicon and subjecting a surface portion of the substrate to a thermal oxidation treatment and a thermal softening treatment. This is realized by forming a heat storage layer having a smooth surface without any steps on the surface of the base.

In the present invention, since the polycrystalline silicon substrate having such a heat storage layer is used as a component of a substrate for a liquid jet recording head, the substrate is not uniformly formed by heating or cooling. Even if an internal stress is generated due to the shrinkage, the deformation does not substantially occur as a problem.

The thermal softening treatment may be performed after a thermal oxidation treatment is performed on the polycrystalline silicon substrate to form a thermal oxidation layer (heat storage layer), or may be performed concurrently with the thermal oxidation treatment. Is also good. When the thermal oxidation treatment and the thermal softening treatment are performed simultaneously and concurrently, the time required for performing these treatments separately and forming a desired heat storage layer on a polycrystalline silicon substrate can be significantly shorter. .

When the heat softening treatment is performed independently, for example, lamp heating such as a halogen lamp or a xenon lamp, continuous oscillation heating or pulse oscillation heating using a laser such as CO ₂ , YAG, Ar, or electron beam. The thermal softening treatment may be performed only on a desired portion of the surface of the polycrystalline silicon substrate, for example, only on a portion where a heating resistor is formed, by continuous oscillation heating, pulse oscillation heating, high-frequency heating, or the like.

The thermal softening treatment needs to be performed at a temperature lower than the melting temperature of polycrystalline silicon as a base material. Specifically, it is desirable that the temperature at this time is selected in the range of 1230 ° C. to 1330 ° C. as clarified in Experiment E.

In the present invention, when the thermal oxidation treatment and the thermal softening treatment are performed separately, impurities are introduced into the thermal oxide layer formed by performing the thermal oxidation treatment, and then the impurity is doped into the thermal oxide layer. The object of the present invention can be achieved even by performing a heat softening treatment. The thermal softening treatment in this case can be performed at a temperature lower than the temperature in the thermal softening treatment when no impurities are used. In this case, as impurities to be introduced into the thermal oxide layer, impurities generally used in the semiconductor technical field, such as P, B, and As, can be selectively used.
As a method for introducing such impurities into the thermal oxide layer, an impurity introduction method employed in semiconductor technology can be employed. The concentration of impurities introduced into the thermal oxide layer varies depending on the type of impurities used. In general, the upper limit of the concentration is determined so that the heat storage layer is not softened by the temperature at which the heating resistor formed on the heat storage layer (thermal oxide layer) generates heat. It is appropriately determined in consideration of softening to a desired state by a softening treatment to provide a smooth surface.

The heat softening treatment performed in the present invention mainly includes
This step is performed for the purpose of eliminating the steps on the surface of the thermal oxidation layer and obtaining a smooth surface state. The heat-generating resistor formed on the desired smooth surface of the desired thermal oxide layer formed by performing the thermal softening treatment ensures the desired adhesion to the thermal oxide layer.

The substrate for a liquid jet recording head provided by the present invention includes an electrothermal converter having a heating resistor for generating heat and a pair of wirings electrically connected to the heating resistor. A substrate made of a polycrystalline material prepared as described above, wherein the surface of the substrate has an oxide layer formed by performing a thermal oxidation treatment and a thermal softening treatment.

The liquid jet recording head provided by the present invention comprises a discharge port for discharging liquid, a heating resistor for generating thermal energy for discharging liquid from the discharge port, and a heating resistor. A substrate for a liquid jet recording head, wherein the substrate is provided with an electrothermal transducer having a pair of wirings electrically connected to the heating element and supplying an electric signal for generating the thermal energy to the heating resistor. A liquid jet recording head having a flow path for supplying a recording liquid in the vicinity of the electrothermal transducer, wherein a surface of a polycrystalline material constituting the substrate is subjected to thermal oxidation treatment and thermal softening. And an oxide layer formed by performing the treatment.

Further, the liquid jet recording apparatus provided by the present invention comprises: (a) a discharge port for discharging liquid, a heating resistor for generating thermal energy for discharging liquid from the discharge port, A liquid ejecting recording head substrate, which is electrically connected to the heating resistor, and on which an electrothermal transducer having a pair of wires for supplying an electric signal for generating the thermal energy to the heating resistor is disposed; (B) a flow path for supplying a recording liquid in the vicinity of the electrothermal converter of the substrate, and the surface of the polycrystalline material constituting the substrate (a) is thermally oxidized. It has an oxide layer formed by performing a treatment and a thermal softening treatment.

A method of manufacturing a substrate for a liquid jet recording head provided by the present invention is directed to an electrothermal converter having a heating resistor for generating thermal energy and a pair of wirings electrically connected to the heating resistor. A method for manufacturing a substrate for a liquid jet recording head, wherein a substrate is formed on a substrate, wherein a substrate composed of polycrystalline silicon is used as a substrate constituting the substrate,
The surface of the polycrystalline substrate is subjected to a thermal oxidation treatment for forming an oxide layer and a thermal softening treatment for softening the surface to have a smooth surface shape, so that the surface has a smooth surface property. It is characterized in that a heat storage layer is formed.

In the present invention, a substrate composed of polycrystalline silicon (hereinafter simply referred to as a polycrystalline silicon substrate) used as a substrate constituting a substrate for a liquid jet recording head is a single crystal silicon substrate. Since deformation is less likely to occur, as described in the above experiment,
There is a remarkable effect that the length of the recording head, which is difficult to achieve when using a single crystal silicon substrate, can be easily achieved.

Since such a polycrystalline silicon substrate is used as a substrate constituting a substrate for a liquid jet recording head, the substrate can be easily made to have a desired length, and in this case, As described in Experiment B above, since the amount of warpage is smaller than that of the single crystal silicon substrate, a long recording head which is hardly affected by warpage can be easily achieved. In addition, the long recording head does not cause pixel disturbance that occurs when a plurality of small recording heads are integrally connected to form a long recording head.

Further, since a long recording head can be easily obtained, it is possible to obtain a recording apparatus capable of achieving higher-speed recording.

The amount of warpage is proportional to the average crystal grain size of the polycrystalline silicon substrate, as clarified in Experiment C described above. In view of the demand for improving the yield during the production of the recording head, the preferred average crystal grain size of the polycrystalline silicon as the base constituting the substrate for the liquid jet recording head is 8 m.
m, and a more preferred average crystal grain size is 2 mm or less. When a polycrystalline silicon substrate having an average crystal grain size in such a range is used, there is no problem of warpage of the substrate, and a long liquid jet recording capable of obtaining a higher quality recorded image at a high speed. A head substrate can be easily achieved.

Since it is necessary to form a heating resistance layer, wiring, and the like on the polycrystalline silicon substrate constituting the liquid jet recording head substrate, it is desirable that there be no defects such as pits and projections. When many of these defects are present on the surface of the base, the defects may cause disconnection or short circuit in the heat-generating resistance layer formed on the base. As clarified in Experiment D described above, in order to obtain a high production yield and good recording characteristics, a defect having a diameter of 1 μm or more existing on the surface of the polycrystalline silicon substrate used for the recording head substrate is required. Is preferably 10 / cm ² or less, more preferably 5 / cm ² or less.

Hereinafter, embodiments of the substrate for a liquid jet recording head according to the present invention will be described. FIG. 1A is a schematic plan view of a main part of an example of the substrate for a liquid jet recording head of the present invention. FIG.
FIG. 2B is a cross-sectional view taken along line XX ′ of FIG. FIG. 2 is a schematic sectional view of a base constituting the substrate for a liquid jet recording head.

The liquid jet recording head substrate 8 has a heating resistor 2a for generating thermal energy for ejecting a recording liquid on the polycrystalline silicon substrate 1, and the heating resistor 2a is electrically connected to the heating resistor 2a. It has an electrothermal converter composed of a pair of connected wires 3a and 3b.

The heating resistor 2a and the wirings 3a and 3b are
A heating resistance layer 2 made of a material having a certain level of volume resistivity and an electrode layer 3 made of a material having good electrical conductivity are laminated on the base 1 by, for example, sputtering, and then a photolithography process is performed. Is formed by patterning into a predetermined shape.

Then, when an electric signal is applied to the heating resistor via the wirings 3a and 3b, the heating resistor generates heat. Desirable materials for forming the heating resistance layer 2 include hafnium boride (HfB ₂ ), tantalum nitride (Ta ₂ N), rubidium oxide (RuO ₂ ), Ta-Al alloy, and Ta-Al-Ir alloy. Various metals, alloys, metal compounds, cermets and the like are used. Further, as a material forming the wiring layer 3, a metal having high conductivity, for example, aluminum or gold can be used.

The wiring 3 is provided on the substrate 8 for the liquid jet recording head.
The protective layer 4 is provided so as to cover the heating resistors a and 3b and the heating resistor 2a. The protective layer 4 includes a heating resistor 2a, wirings 3a and 3a due to contact with ink and permeation of ink.
It is provided for the purpose of preventing the electrolytic corrosion of b and electrical breakdown. Such a protective layer can be made of an electrically insulating material such as SiO ₂ , SiC, and Si ₃ N ₄ . The protective layer may have a multilayer structure. In that case, for example, a layer made of Ta or Ta ₂ O ₅ can be laminated on a layer made of the above-mentioned electric insulating material to form a protective layer.

In the above-described embodiment of the liquid jet recording head, the direction in which the liquid is discharged from the discharge port is substantially the same as the direction in which the liquid is supplied to the heating resistor. Perpendicular) are included in the liquid jet recording head of the present invention. Hereinafter, an embodiment of a liquid jet recording head using the above-described substrate will be described.

The main structure of the recording head has been described with reference to FIGS. 5A and 5B in the background of the invention, but will be briefly described again. A liquid path 6 for supplying ink as a recording liquid is formed in the vicinity of each of the heating resistors 2a by connecting the top plate 5 to a substrate. Then, the ink in the liquid path is heated by the respective heating resistors to generate air bubbles, and the ink is ejected from the ejection port 7 by the pressure of the air bubbles to perform printing.

FIGS. 5A and 5B show a liquid jet recording head having a one-to-one correspondence between the number of heating resistors and the number of ejection ports. The recording head of the present invention is not limited to this. That is, such a form that a plurality of heating resistors correspond to one discharge port,
Any embodiment to which the above-described substrate can be applied is an embodiment of the present invention. Further, FIGS. 5A and 5B show a recording head in which the substrate surface on which the heating resistor is disposed is substantially parallel to the direction in which ink is ejected, but the present invention is not limited to this. It goes without saying that the direction in which the ink is ejected and the substrate surface may intersect with each other without intersecting. Further, the liquid jet recording head of the present invention may be a recording head that is incorporated in the apparatus or is detachable from the recording apparatus and receives supply of ink from an ink tank via a tube or the like, Further, the recording head may be detachable from the recording device and detachably connected to the ink tank.

As the recording liquid applicable to the recording head of the present invention, various liquids can be used.
Dye 0.5 20 wt%, water-soluble organic solvent such as (polyhydric) alcohol, polyalkylene glycol 10-80 wt%, water 1
An ink composition having an ink composition of 0 to 90 wt% can be preferably used, and specific examples of the ink composition include CI food black 23 wt%, diethylene glycol 25 wt%, and N-methyl-2-pyrrolidone 20.
wt% and water of 52 wt%.

FIG. 6 is an external perspective view showing an example of an ink jet recording apparatus (IJRA) in which the recording head according to the present invention is mounted as an ink jet head cartridge (IJC).

In FIG. 6A, reference numeral 120 denotes the platen 1
24 is an ink jet head cartridge (IJC) including a nozzle group for discharging ink while facing the recording surface of the recording paper sent on the recording paper 24. Reference numeral 116 denotes a carriage HC that holds the IJC 120. The carriage HC is connected to a part of a drive belt 118 that transmits the driving force of the drive motor 117, and is slidable with two guide shafts 119A and 119B disposed in parallel with each other. By doing, IJC120
Reciprocating over the entire width of the recording paper.

Here, an ink jet head cartridge having a small recording head has been described as a recording head. However, the present invention is not limited to the full line type according to the present invention, such as a full line type capable of recording in accordance with the recordable width of recording paper. Needless to say, a long recording head can be used, and when such a long recording head is used, there is almost no warpage as described above, and a plurality of short recording heads are used. In this case, it is possible to obtain a recording apparatus capable of further utilizing a feature that there is no image disturbance and a feature that high-speed printing can be performed.
Reference numeral 126 denotes a head recovery device, which is disposed at one end of the movement path of the IJC 120, for example, at a position facing the home position. The head recovery device 126 is operated by the driving force of the motor 122 via the transmission mechanism 123, and the IJ
Capping of C120 is performed. This head recovery device 1
In connection with the capping of the IJC 120 by the cap portion 126A of the ink jet head 26, ink suction by an appropriate suction means provided in the head recovery device 126 or IJC 12
The ink is fed by an appropriate pressurizing means provided in the ink supply path to the ink supply path 0, and the ejection recovery processing such as removing the thickened ink in the nozzles by forcibly discharging the ink from the ejection port is performed. Also, by performing capping at the end of recording or the like, IJC is protected.

Reference numeral 130 denotes a blade disposed on the side surface of the head recovery device 126 and formed of silicon rubber as a wiping member. The blade 130 is held in a cantilever form by a blade holding member 130 </ b> A, and similarly to the head recovery device 126, a motor 122 and a transmission mechanism 123 are provided.
And the engagement with the ejection surface of the IJC 120 becomes possible. Accordingly, the blade 130 is moved to the IJC 12 at an appropriate timing in the recording operation of the IJC 120 or after the ejection recovery processing using the head recovery device 126.
In this case, the projection is made to protrude into the movement path of the IJC 120 to wipe off dew condensation, wetness, dust and the like on the discharge surface of the IJC 120 with the movement of the IJC 120.

The printing apparatus has an electric signal applying means for applying an electric signal for ejecting ink to the recording head. Further, the recording apparatus is not limited to the above-described embodiment in which recording is performed on recording paper, but also includes a textile printing apparatus which records a pattern on cloth or the like. In this printing apparatus, since it is necessary to perform high-speed recording on a very wide cloth, it is particularly desirable to apply a long and good recording head of the present invention.

(Other Embodiments) The present invention provides an excellent effect particularly in an ink jet recording head and an ink jet recording apparatus of a type in which ink is ejected by thermal energy among ink jet recording methods.

The typical configuration and principle are described in, for example, US Pat. Nos. 4,723,129 and 4,740.
It is preferable to use the basic principle disclosed in the specification of Japanese Patent No. 796. This method can be applied to both the so-called on-demand type and the continuous type. In particular, in the case of the on-demand type, liquid (ink)
By applying at least one drive signal corresponding to the recorded information and providing a rapid temperature rise exceeding nucleate boiling to an electrothermal transducer arranged corresponding to the sheet or liquid path in which , Heat energy is generated in the electrothermal transducer, and the film is boiled on the heat-acting surface of the recording head.
As a result, air bubbles in the liquid (ink) can be formed in one-to-one correspondence with the drive signal, which is effective.

The liquid (ink) is ejected through the ejection opening by the growth and contraction of the bubble to form at least one droplet. When the drive signal is formed into a pulse shape, the growth and shrinkage of the bubble are performed immediately and appropriately, so that the ejection of liquid (ink) having particularly excellent responsiveness can be achieved, which is more preferable. As the pulse-shaped drive signal, US Pat.
Those described in 463359 and 4345262 are suitable. In addition, US Pat. No. 4,431,131 of the invention relating to the rate of temperature rise of the heat acting surface.
If the conditions described in the specification of JP-A No. 24 are adopted, more excellent recording can be performed.

The configuration of the recording head may include a combination of a discharge port, a liquid path, and an electrothermal converter (a linear liquid flow path or a right-angled liquid flow path) as disclosed in the above-mentioned respective specifications. U.S. Pat. No. 4,558,333 and U.S. Pat.
A configuration using the specification of Japanese Patent No. 59600 is also effective for the present invention. In addition, Japanese Unexamined Patent Publication (Kokai) No. 123670/1984 discloses a configuration in which a common slit is used as a discharge portion of an electrothermal converter for a plurality of electrothermal converters, and an aperture for absorbing pressure waves of thermal energy. The present invention is also effective as a configuration based on Japanese Patent Application Laid-Open No. 59-138461, which discloses a configuration corresponding to a discharge unit.

Further, in a full-line type recording head having a length corresponding to the width of the maximum recording medium that can be recorded by the ink jet recording apparatus, the above-described effects can be more effectively exerted as described above.

In addition, the print head is replaceable with a print head of a replaceable chip type, which can be electrically connected to the main body of the apparatus or supplied with ink from the main body of the apparatus, or is integrated with the print head itself. The present invention can also be applied to a case where a cartridge type recording head provided in a specific manner is used.

The recording mode of the ink jet recording apparatus is not limited to the recording mode of only the mainstream color such as black, but may be a single recording head or a combination of plural recording heads. The present invention is also very effective for an apparatus provided with at least one of full colors by color mixture.

In the embodiments of the present invention described above, the ink is described as a liquid. However, the ink is solidified at room temperature or lower, and is softened or liquid at room temperature. Generally, the temperature is controlled within the range of 70 ° C. or more and 70 ° C. or less to control the temperature so that the viscosity of the ink is in the stable ejection range. Therefore, the ink is in a liquid state when the recording signal for ejection is applied. I just want it. In addition, the temperature rise due to thermal energy is positively prevented by using it as energy for changing the state of the ink from a solid state to a liquid state, or an ink that solidifies in a standing state for the purpose of preventing evaporation of the ink is used. In any case, heat energy is applied by heat energy, such as one in which ink is liquefied and ejected as an ink liquid by application of heat energy according to a recording signal, or one which already starts to solidify when reaching a recording medium. The use of an ink that liquefies for the first time is also applicable to the present invention. In such a case, the ink is disclosed in JP-A-54-5.
No. 6,847, or Japanese Patent Application Laid-Open No. 60-71260, in which the porous sheet is opposed to the electrothermal converter while being held as a liquid or solid substance in the concave portions or through holes of the porous sheet. It is good.

[0180]

EXAMPLES Example 1 Preparation of Polycrystalline Silicon Substrate Constituting Liquid Jet Recording Head Substrate A polycrystalline silicon ingot as a starting material was prepared as follows. That is, high-purity polycrystalline silicon produced by hydrogen reduction and deposition reaction by thermal decomposition used for production of single-crystal silicon is used, and introduced into a quartz crucible.
After heating to 0 ° C. and melting, the mixture was poured into a graphite mold and cooled to prepare an 80 cm square polycrystalline silicon ingot. At this time, no release agent was used. Next, at a position where the average crystal grain size becomes 2 mm from the ingot, the sample No. in Table 6 was used. No. 1 to No. Twelve sheets were cut out with a multi-wire saw into a plate having the dimensions shown in each column.

[0181]

[Table 8] The surface of each of the obtained 12 polycrystalline silicon plates was removed by about 30 μm by lapping, flattened, and chamfered with an end beveling machine.

Thereafter, the surface was polished with a single-side polishing machine manufactured by Speed Fam Co., Ltd., and the surface roughness was set to Rmax1.
It was finished to a mirror substrate of 50 °. At this time, polishing was performed without adding an alkali in order to prevent a surface step due to etching by an alkali component in the abrasive having crystal orientation dependence.

Here, the surface roughness of each polycrystalline silicon plate, ie, the surface of the polycrystalline silicon substrate was measured by a substrate surface inspection apparatus in the same manner as in Experiment D. Was 1 / cm ² or less at all measurement points.

Further, the surface smoothness of each polycrystalline silicon substrate was measured using a non-contact type surface roughness measuring device manufactured by Lasertec Co., Ltd., and it was confirmed that no step was generated.

Next, 4 of the above-mentioned polycrystalline silicon substrates were used.
The sheet was subjected to a thermal oxidation treatment by a pyrogenic method to form an SiO ₂ layer as a heat storage layer on the polycrystalline silicon substrate. The thermal oxidation conditions at this time were as follows.

Thermal oxidation temperature: 1150 ° C. Furnace pressure: 1 atm Thermal oxidation time: 14 hours Subsequently, a thermal softening treatment was performed on each of the four substrates on which the SiO ₂ layer was formed, and a step on the surface of the SiO ₂ layer was formed. Was smoothed. The conditions of the heat softening treatment were as follows.

Thermal softening temperature: 1330 ° C. Furnace pressure: 1 atm Thermal softening time: 1 hour Thus, a 3 μm thermal oxide layer (SiO ₂ layer) as a heat storage layer
Thus, four sheets (sample Nos. 1 to 4) of a polycrystalline silicon substrate for a liquid jet recording head having the following were obtained.

Further, another four of the above-mentioned polycrystalline silicon substrates were used, and each substrate was subjected to a thermal oxidation treatment by a pyrogenic method and a thermal softening treatment for preventing a step from being formed in the SiO ₂ layer. Were performed substantially simultaneously. Thus, a heat storage layer having no steps was formed on the polycrystalline silicon substrate. The heat treatment conditions at this time were as follows.

Heating temperature: 1330 ° C. Furnace pressure: 1 atm Heating time: 7 hours Thus, a 3 μm thermal oxide layer (SiO ₂ layer) as a heat storage layer
Thus, four polycrystalline silicon substrates (sample Nos. 5 to 8) for a liquid jet recording head having the above-mentioned structure were completed.

Further, each of the remaining four polycrystalline silicon substrates was subjected to a thermal oxidation treatment by a pyrogenic method to form an SiO ₂ layer as a heat storage layer on the polycrystalline silicon substrate. Then, the formed Si
Impurities were diffused in the O ₂ layer. The thermal oxidation conditions and impurity diffusion conditions at this time were as follows.

Thermal oxidation conditions Thermal oxidation temperature: 1150 ° C. Furnace pressure: 1 atm Thermal oxidation time: 14 hours Impurity diffusion conditions Diffusion source: POCl ₃ Diffusion method: Normal pressure thermal CVD method Diffusion temperature: 1000 ° C. The impurity concentration of P diffused into the surface of the crystalline silicon substrate was 1 × 10 ^{21 as} a result of SIMS measurement.
atom / cm ³ .

[0192] Subsequently, subjected to thermal softening treatment for the SiO ₂ layer each base four formed is, SiO ₂
The level difference on the layer surface was smoothed. The conditions of the heat softening treatment at this time were as follows.

Thermal softening temperature: 1130 ° C. Furnace pressure: 1 atm Thermal softening time: 1 hour Thus, a 3 μm thermal oxide layer (SiO ₂ layer) as a heat storage layer
Thus, four polycrystalline silicon substrates (samples No. 9 to No. 12) for a liquid jet recording head having the following were obtained.

With respect to each of the substrates No. 1 to No. 12, the shape of the step on the surface of the heat storage layer was examined with a stylus type roughness meter and evaluated. The measurement method and evaluation criteria of the step shape were as follows.

Stylus scanning distance: 10 mm Measurement location: 15 locations per base Measurement location: a line segment that divides the shorter side 150 mm of the base into four equal parts,
Long side 600mm, 500mm, 400mm, 300mm
A total of 15 points at the intersections of line segments that divide each into six equal parts.

Evaluation Criteria: The maximum height of the step in the 15 measurement points was 0 μm or more and less than 0.05 μm.
A value of 〇 or more and less than 0.1 μm was evaluated as Δ, and a value of 0.1 μm or more was evaluated as ×.

As a result, all of the samples No. 1 to No. 12 were ◎, and it was found that all the substrates had a smooth surface with a smoothed step.

Next, the sample No. No. 1 to No. A plurality of heating resistors made of HfB ₂ (size: 20 μm × 100 μm, thickness: 0.16 μm, heating resistance vs. pitch interval: 63.5 μm) using photolithography technology for each of the 12 substrates.
And an electrode made of Al connected to each heating resistor (width 20μ)
m, a film thickness of 0.6 μm), and SiO ₂ / Ta (SiO ₂
A protective layer having a thickness of 1.3 μm and a thickness of Ta: 0.5 μm) is formed by sputtering on the portion where the heating resistor and the electrode are formed.
The substrate for a liquid jet recording head having the configuration shown in FIG.
Created. (Samples No. 1 to No. 12) Next, each of the obtained twelve liquid jet recording head substrates was exposed at the time of exposure when forming a plurality of ink flow paths by photolithography using a photosensitive dry film. As described above, whether or not the ink flow path could be formed accurately was observed, and the exposure pass rate was calculated.

That is, the sample No. Sample Nos. 1, 5, and 9 were 8576 pieces per head. For Nos. 2, 6, and 10, 7244 pieces per head, sample Nos. 3, 7,
Sample No. 11 was 5504 per head.
With respect to 4, 8, and 12, pattern samples of a liquid jet recording head each having 4288 ink discharge channels per head were prepared in 15 samples per substrate. Sample No. No. 1 to No. For each of the 12 samples, out of the 15 pattern samples created, the focus position was shifted due to the warpage of the substrate, and even if at least one pattern was missing in the pattern of the discharge port, it was rejected. The exposure pass rate was calculated based on the criteria for accepting no occurrence at all.

The results obtained are shown in Table 6.

As is clear from the results shown in Table 6,
Sample No. No. 1 to No. It is understood that all 12 have a 100% exposure pass rate.

Furthermore, since the thermal oxide layer is softened and its surface is smoothed, it is understood that the adhesion of the heating resistor formed on the thermal oxide layer is extremely good.

Comparative Example 1 Preparation of Single Crystal Silicon Substrate Constituting Substrate for Liquid Jet Recording Head A single crystal silicon ingot was used as a starting material in the same manner as in Example 1 to obtain Comparative Sample No. 1
Through No. Four mirror single-crystal silicon substrates (comparative samples No. 1 to No. 4) having the dimensions shown in the respective columns and having a surface roughness of Rmax 150 ° were prepared. In addition,
In each case, an alkali was added during polishing. Next, in the same manner as in Example 1 except that the thermal softening treatment was not performed after the thermal oxidation, each single crystal was thermally oxidized by a pyrogenic method to form a 3.0 μm thermally oxidized heat storage layer. (Comparative Samples No. 1 to No. 4) were prepared.

[0204]

[Table 9] Next, the comparative sample No. 1 to No. Four single-crystal silicon substrates were used separately, and four liquid jet recording head substrates (Comparative Samples No. 1 to No. 4) were prepared in the same manner as in Example 1.

The obtained comparative sample No. 1 to No. For each of the liquid ejecting recording head substrates of No. 4, the pass rate of exposure was calculated in the same manner as in the example.

Table 8 shows the obtained results. As is clear from the results shown in Table 8, Comparative Sample No. A decrease in the exposure pass rate was observed in Sample No. 2, and the majority of Comparative Sample Nos. 1 failed. The comparative sample N having a short length
o. Nos. 3 and 4 showed a 100% exposure pass rate.

Example 2 Preparation of a Liquid Jet Recording Head Using a Polycrystalline Silicon Substrate In this example, the liquid jet recording head shown in Table 6 prepared in Example 1 was used.
Liquid jet recording head substrates (Sample Nos. 1 to N)
o. Using each of 12), 15 liquid jet recording heads each having the configuration shown in the sectional view of FIG. 3 were manufactured by the following method.

First, a plurality of ink flow paths were formed on a substrate for a liquid jet recording head by photolithography using a photosensitive dry film, and cut by a slicer to separate heads and form discharge ports. Next, the discharge port surface was polished to correct defects such as chipping generated during cutting.

In this manner, fifteen liquid jet recording head in-process products were prepared for each liquid jet recording head substrate. A heating resistor driving IC is connected to each of the fifteen in-process products by using a flip-chip connection method to form a discharge port pitch of 63.5.
A μm liquid jet recording head was prepared.

Thus, the sample No. No. 1 to No. Fifteen liquid jet recording heads were prepared for each of the twelve liquid jet recording head substrates. (Hereinafter, sample No. 1
Toshi No. A group consisting of 15 liquid jet recording heads obtained from each of Sample Nos. 1 ′ to sample No. 12 '. ) Sample No. 1 'to No. 1 Regarding the manufacturing process yield of the liquid jet recording head of 12 ′, for a predetermined ratio determined by the number of discharge ports, a sample having a rate better than the ratio was evaluated as 、, and a sample worse than the ratio was evaluated as ×. The results are shown in Table 7. Sample No. 1 'to No. 1 In each of the liquid jet recording heads 12 ', the state of occurrence of the defect rate was within a predetermined level.

[0211]

[Table 10] Next, the sample No. 1 'to No. 1 For each of the liquid jet recording heads selected at random for each of 12 ', a drive pulse (print signal) having a pulse width of 1.1 Vth (Vth is a foaming voltage) and a pulse width of 10 μs is repeatedly applied to each heating resistor, and each ejection port is formed. , And a discharge durability test was performed.

The evaluation in the durability test was performed as follows. That is, the integrated number of drive pulses is 1 × 10 ⁷ , 1
The durability of the liquid jet recording head is determined by calculating the residual ratio of the heating resistors when the heating resistors reach × 10 ⁸ and 3 × 10 ⁸ , that is, the number of the heating resistors that are not disconnected with respect to the total number of the heating resistors. evaluated. Table 7 shows the obtained results. As is clear from the results shown in Table 7, the residual ratio was 100% even after 3 × 10 ⁸ repetitions of the drive pulse in each case, which was a result having no problem in the discharge durability performance.

Next, the sample No. 1 'to No. 1 12 '
Using a different liquid jet recording head randomly selected for each of the above, the printing dot spacing accuracy and density unevenness were evaluated as printing performance. The ink composition used is as follows.

Dye: C.I. I. Direct Black 193 3 wt% Diethylene glycol 25 wt% N-methyl-2-pyrrolidone 20 wt% Ion-exchanged water 52 wt% In this evaluation, all the nozzles eject paper containing variation in the ink bleed rate within a predetermined range. Scanning was performed perpendicularly to the ejection direction of the liquid jet recording head in a state where the nozzles were arranged, and a print sample having four types of print widths in the nozzle arrangement direction and a paper feed direction of 200 mm was obtained. At this time, when the paper feed speed is an ejection frequency of 1 KHz, the print dot interval in the paper feed direction is 63.5.
It was adjusted to be μm. The head driving conditions were set as follows.

Heating resistor applied voltage: 1.1 Vth, (Vth is foaming voltage) Driving frequency: 1 KHz (heating resistor applied interval) Pulse width: 10 μs (one pulse application time of heating resistor) Indicates the print width at the recording head. The printing samples obtained here were evaluated for printing accuracy and printing density unevenness as described below.

Evaluation of Printing Accuracy Using a magnifying glass with a fine scale, the printing dot interval (dot center interval) of the printing sample was measured, and the range of the variation was determined. One measurement range was set to 2 cm square, and measurement was performed by selecting any 10 places on the print sample. X is the paper feed direction and the vertical direction, and Y is the paper feed direction.
Those having a dot interval in the Y direction within a range of 43.5 μm to 83.5 μm were regarded as acceptable.

The sample No. All of 1 ′ to 12 ′ passed the printing accuracy.

Evaluation of Print Density Unevenness The print sample was measured for density unevenness using a Macbeth densitometer. The entire surface of the print sample was read by a CCD scanner, and the optical density was measured for each 1 cm width in the direction perpendicular to the paper feed direction.

A sample having an optical density of 0.2 or less in an adjacent area over the entire surface of the print sample was judged to be acceptable.

The sample No. All of 1 'to 12' passed the print density unevenness.

Comparative Example 2 Preparation of a Liquid Ejection Recording Head Using a Single Crystal Silicon Substrate A substrate for a liquid ejection recording head shown in Table 8 prepared in Comparative Example 1 and Comparative Sample Nos. 1 to 4 , Liquid jet recording heads (Comparative Samples No. 1 'to No. 4') were manufactured in the same manner as in Example 2.

Comparative Sample No. 1 'to No. 1 For each of 4 ′, the yield was evaluated in the same manner as in Example 2. Table 9 shows the obtained results. In the manufacturing process total yield evaluation column of Table 9, evaluation results for the yield expected from the number of discharge ports of each sample are shown by the following evaluation criteria.

X: No good liquid jet recording head was finally found.

Δ: A non-defective liquid jet recording head is very small and not practical.

：: When the yield expected from the number of nozzles is not exceeded.

[0226]

[Table 11] The following is understood from the results shown in Table 9. That is, the comparative sample No. In the case of 1 ', a practically usable liquid jet recording head cannot be produced. Comparative sample No. In the case of 2 ', the production yield of a practically usable liquid jet recording head is extremely low. Comparative sample No. 3 ′ and No. 4 'has no problem in production yield.

Next, Comparative Sample No. 2 ′ to No. 4 '
For each of them, an ejection durability test and evaluation of printing accuracy and density unevenness were performed as printing performance in the same manner as in Example 2. As a result, a practically usable liquid jet recording head, that is, Comparative Sample No. 2 ′, No. 3 ′ and No.
Regarding 4 ′, the evaluation of printing accuracy and density unevenness as the discharge durability test and printing performance were all passed.

Comparative Example 3 Preparation of a Liquid Ejection Recording Head Using a Single Crystal Silicon Substrate
A liquid jet recording head unit having 8576 ejection ports (comparative sample No. 4 ″, see Table 10) using two liquid jet recording heads 4 ′ and connecting the two heads integrally. )created.

[0229]

[Table 12] First, the head unit was prepared as follows.
That is, an aluminum support member was used, and the first liquid jet recording head was fixed to one surface of the support member. Next, the second head was arranged and fixed on the other surface of the support member such that the arrangement interval of the ejection ports was as constant as possible over the entire length of the liquid jet recording head unit including the connection area.

The comparative sample No. 4 ″ of the liquid jet recording head unit thus obtained was subjected to an ejection durability test and evaluation of printing accuracy and density unevenness in the same manner as in Example 2. The ejection durability test was passed. However, the printing accuracy was rejected due to the assembling error of the connecting portion between the two heads.
(Fail) due to the difference in (foaming voltage).

The results of these evaluations are summarized in Table 10.

[0232]

As described above, the present invention solves the above-mentioned problems with respect to the conventional liquid jet recording head substrate, and a substrate made of a specific material capable of obtaining a large recording head. And a long substrate for a liquid jet recording head utilizing the above. Further, a long substrate for a liquid jet recording head using a long substrate made of polycrystalline silicon can be provided.

According to the present invention, it is possible to increase the size of the recording head without integrally connecting a plurality of liquid jet recording heads as in the case of using the above-mentioned single crystal silicon wafer. Liquid jet recording, which does not cause problems such as deformation of the work-in-progress of the liquid jet recording head and deterioration of the quality of the recorded image due to the deformation, or exposure failure due to warpage of the liquid jet recording head substrate as in the case of using A head can be provided.

Further, the present invention can provide a liquid jet recording apparatus using the above liquid jet recording head, which can achieve higher image quality and higher speed recording. In addition, the present invention includes forming a thermally oxidized layer having good surface properties on the surface of a substrate made of polycrystalline silicon used for the substrate for a liquid jet recording head described above. A manufacturing method can be provided.

[Brief description of the drawings]

FIG. 1A is a schematic plan view of a main part of a substrate for a liquid jet recording head according to a position embodiment of the present invention, and FIG.
3 is a cross-sectional view of a main part taken along line XX ′ of FIG.

FIG. 2 is a schematic cross-sectional view of a base constituting a substrate for a liquid jet recording head.

FIG. 3 is a schematic cross-sectional view illustrating a production example of a liquid jet recording head.

FIGS. 4A to 4C are diagrams illustrating formation of a thermal oxide film on the surface of a polycrystalline silicon substrate.

5A is a cutaway perspective view of a main part of the liquid jet recording head, and FIG. 5B is a vertical sectional view of the main part in the flow path direction of the liquid jet recording head.

FIG. 6 is a diagram illustrating an example of a recording apparatus including the liquid jet recording head according to the invention.

FIG. 7 is a diagram showing an example of a thermal oxidation device for thermally oxidizing the surface of a base constituting a substrate for a liquid jet recording head.

FIGS. 8A and 8B are diagrams illustrating a mechanism of bowing and bending occurring on a base.

9 (A) to 9 (C) are views for explaining a state of occurrence of bowing and bending occurring when the base is cut off, and FIG. 9 (D) is an explanatory view of a method for measuring the degree of bowing and bending of the base.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Base 2a Heating resistor 3a, 3b Wiring 6 Liquid path 7 Discharge port 8 Substrate for liquid jet recording head 10 Liquid chamber

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B41J 2/16 B41J 2/05

Claims (9)

(57) [Claims] 1. A method for manufacturing a substrate for a liquid jet recording head comprising an electrothermal transducer having a heating resistor for generating thermal energy and a pair of wirings electrically connected to the heating resistor, A step of forming an oxide layer by thermally oxidizing the surface of the polycrystalline substrate using a substrate made of a polycrystalline substance as a substrate constituting the substrate; A process of holding the oxide layer at a temperature in the range of 1 to 1330 ° C. and thermally softening the oxide layer to smooth the surface. 2. The method according to claim 1, wherein the polycrystalline substance is polycrystalline silicon. 3. The method according to claim 1, wherein the thermal oxidation step and the thermal softening step are sequentially performed. 4. The method according to claim 1, wherein the thermal oxidation step and the thermal softening step are performed substantially simultaneously. 5. A method for manufacturing a substrate for a liquid jet recording head, comprising: an electrothermal transducer having a heating resistor for generating thermal energy and a pair of wirings electrically connected to the heating resistor, A step of forming an oxide layer by thermally oxidizing the surface of the polycrystalline substrate, using a base made of a polycrystalline substance as a base constituting the substrate, and diffusing impurities into the oxide layer, A method of thermally softening the oxide layer to smooth the surface thereof. 6. An impurity diffused in the oxide layer is 1 ×
6. The method for manufacturing a substrate for a liquid jet recording head according to claim 5, wherein the temperature is set to 10 ²¹ atoms / cm ³ or less, and the thermal softening step is performed at a temperature in a range of 1130 ° C. to 1330 ° C. 7. The method according to claim 5, wherein the polycrystalline substance is polycrystalline silicon. 8. The method according to claim 5, wherein the thermal oxidation step and the thermal softening step are sequentially performed. 9. The method according to claim 5, wherein said thermal oxidation step and said thermal softening step are performed substantially simultaneously.