JPH0691078B2 - Vapor phase oxide film formation method - Google Patents

Description

The present invention relates to an oxide film forming technique among thin film forming techniques.

[Prior Art] One of the most competitive fields in the current semiconductor industry
The following description will be made in relation to the oxide film technology.

In the case of oxide film formation technology, the cause of contamination is that mobile ions supplied into the gas from the quartz tube tube wall surface, boat, gas pipe, etc. during oxidation and impurities remaining during surface treatment of the substrate are oxidized. May enter the membrane. Further, particles may enter the oxide film and form pinholes. Further, it is fully conceivable that due to the miniaturization of the device, the junction portion tends to be thinner, and the redistribution of impurities due to OH doping will have an adverse effect.

Against the background of the above situation, the present methods for oxidizing silicon include not only O ₂ and N ₂ O, but also halogen oxidation such as HCl,
A mixed gas of O ₂ , such as Cl ₂ , Br ₂ , trichlorethylene, etc. is used. As a result, alkali ions existing in the oxide film or at the interface are fixed, impurities that enter from the outside are blocked, and oxidation-induced stacking faults are suppressed. Thus, it is considered that the halogen-added oxidation has an influence on the production of a stable device having a low interfacial charge density and the improvement of the yield.

Further, one of the applications of the halogen oxidation method is a method called tube cleaning. When the quartz tube is heated in an oxidation furnace and treated with HCl gas, etc., inside,
In the subsequent oxidation step, a SiO ₂ film with excellent interfacial properties is formed, which is an effective cleaning method especially when using a new furnace or quartz tube.

When manufacturing semiconductor products, the oxide film is a selective diffusion mask,
It is used as surface passivation, gate insulating film for MOS devices, insulating film for capacitors, ultra-thin oxide film for non-volatile memory, and also for controlling impurity concentration in silicon substrate. These applications are based on the fact that the oxide film is an insulating film having a high degree of purity, but due to the variety of applications, many times (usually 4 to 6 times) are required when manufacturing one semiconductor product or intermediate product. ) The oxide film formation process must be performed. Moreover, since the properties of the oxide film have a great influence on the performance of the product, further thinning of the oxide film, high purity, and high quality are required. Therefore, since the oxide film forming step is more susceptible to impurities than other steps, it is necessary to prevent the invasion of impurities, especially the intrusion of water, into the gas used for forming the oxide film.

However, with respect to the gases used in these oxide film forming techniques, a refiner for removing water was hardly installed except for a part thereof immediately before the oxidation or between the cylinder and the oxidation.

At present, an adsorption method using a molecular sieve is partially used for drying gas in the manufacturing process of these semiconductor wafers and semiconductor devices. Molecular sieve is relatively easy to dry general gas, and is widely used as a physical desiccant which does not cause troubles such as deliquescent and swelling. (However, it is difficult to dry at a water content of 1 ppm at a low temperature, which is difficult at room temperature.) However, in general heating regeneration, a high temperature of 200 to 400 ° C is required for a long time, and repeated heating regeneration is used. As a result, there is a drawback that suspended dust is generated. Further, the acidic gas such as hydrogen chloride gas causes the molecular sieve to be crushed, which causes suspended dust.

Although not related to the dehumidification of these semiconductor-related gases at all, a method of using a polymer film as a dehumidification method for gases is generally known from JP-A-53-97246 and JP-A-54-152679. However, there is no description that these methods are used for dehumidification of semiconductor manufacturing gas.

Also, the films disclosed therein cannot dehumidify to a highly dry state, which is necessary for gases used for semiconductors.

[Problems to be Solved by the Invention] Various impurities may adhere to the quartz tube wall surface, boat, susceptor, diffusion furnace, piping, etc. of the CVD device, and these impurities may enter during single crystal growth. It is well known that when an oxide film is formed, it is also known that there are obstacles due to the invasion of impurities. No matter how precisely the device is manufactured, this kind of trouble cannot be avoided, and the product yield is always reduced due to alkali ions and deposits. Especially in gas-phase oxidation such as O ₂ dry oxidation and halogen oxidation such as hydrochloric acid oxidation, whether or not the drying of gases is strictly controlled affects the yield of the product. For example, HCl gas may contain several tens of ppm of water even if it is a commercially available high-purity gas, and there are few suitable devices that can remove water during use.
Further, as the gas in the cylinder is consumed, the water content in the cylinder rapidly increases, is mixed with the gas, and is supplied to the reactor. Moisture contained in this gas has considerably affected the yield of the oxide film.

Therefore, the removal of water contained in all gases used in the gas phase oxidation method, especially water in corrosive gases such as HCl gas, is widely needed in the semiconductor market. It was a strong technique.

[Means and Actions for Solving Problems] According to the present invention, when a semiconductor wafer, a semiconductor device, or an intermediate product thereof is manufactured, one side of a film of a fluorinated copolymer having a cation exchange group is formed. A general gas and / or a corrosive gas is contacted with a dry purge gas on the other side, or a general gas dehumidified by depressurizing the other side and / or a corrosive gas is used. There is provided a method for forming a vapor phase oxide film, which comprises forming an oxide film by using the above method.

The vapor phase oxide film forming method of the present invention is preferably used for forming a dry oxide film such as dry O ₂ oxidation, oxygen partial pressure oxidation, halogen oxidation, and plasma oxidation.

The general gas that is the gas to be dried of the present invention, O ₂ , N ₂ O,
Gases such as H ₂ , N ₂ and Ar are referred to as corrosive gases.
Refers to HCl, Cl ₂ , Br _2, etc. However, trichlorethylene is not corrosive, but shall fall into this category.

The gas to be dried in the method of the present invention is usually a gas that is filled in a cylinder that is generally obtained on the market or a gas that is supplied by a pipeline from an on-site manufacturing apparatus in a factory or adjacent land, and the water vapor concentration is The gas is not that expensive.

Regarding the gas filled in the cylinder, it is usually more than 10 ppm
It is about several tens of ppm, but in some cases it is 100 ppm or more.

It is possible to obtain the target dehumidification level by changing the membrane area of the water separator or making it in multiple stages according to the concentration of the target gas.

The fluorinated copolymer having a cation exchange group used in the present invention is preferably one having a cation exchange group such as a sulfonic acid group, a carboxylic acid group or a phosphoric acid group. The use of a fluorinated copolymer having a sulfonic acid group is the best in terms of easiness of production, high water content of the membrane, and thermal stability.

The fluorinated copolymer having a sulfonic acid group has various structures, and among them, particularly, the general formula (I) A fluorine-based copolymer containing a repeating unit represented by is preferred.

Tetrafluoroethylene as the fluorine-based copolymer,
Fluorinated olefins such as trifluoroethylene, perfluorovinyl ether, vinylidene fluoride, vinyl fluoride and the general formula (II) Those obtained by copolymerizing the perfluorovinyl ether monomer represented by the above are preferable.

The sulfonic acid group of the fluorine-based copolymer is preferably introduced as an ion exchange capacity in an amount of 0.5 to 2.5 meq / g H-type dry resin in the copolymer.
By setting the ion exchange capacity of the fluorine-based copolymer within the range of 0.5 to 2.5 meq / g H-type dry resin, the permeation rate of water vapor is not significantly reduced, and the melting point of the copolymer is high. The polymer thin film can be easily manufactured, and the physical strength of the polymer thin film can be maintained without lowering the physical strength. More preferably, the ion exchange capacity is 0.8 to 1.8 meq / g H-type dry resin.

Metal salts as salt of a sulfonic acid group of the fluorine-based copolymer used in the present invention, it is possible to use the ammonia salt form, SO ₃ H type most permeation rate of the water content is high water vapor is large, It has sufficient thermal stability and is preferable.

The shape of the fluorine-based copolymer may be any of a flat membrane, a tubular shape and a hollow fiber membrane, but a hollow fiber membrane having a large membrane area per unit volume and a high treatment capacity is particularly preferable.

For example, in order to achieve a high degree of dryness with a water content of 10 ppm or less, particularly a water content of 5 ppm or less, the airtightness of the device is important, and the hollow fiber membrane is also preferred from that point.

The film of the fluorinated copolymer having a cation exchange group used in the present invention is preferably a film of the fluorinated copolymer containing the repeating unit represented by the general formula (I), which has been pretreated by heating. . The heating pretreatment of this film means that after forming a thin film of a fluorine-based copolymer obtained by copolymerizing a monomer represented by the general formula (II) and a fluorinated olefin,
This is to convert the terminal group SO ₂ F into SO ₃ H by hydrolyzing with an alkali and treating with a strong acid, and then heat-treating the polymer.

The heat treatment can be carried out, if necessary, while purging a dry gas, for example, nitrogen gas having a water content of 5 ppm or less, or under reduced pressure.

A heat treatment temperature of 60 to 250 ° C is suitable. If the temperature is too high, the ion-exchange group may be eliminated and the performance may be deteriorated. The heat treatment temperature is particularly preferably 70 to 200 ° C.

The copolymer causes tens of percent shrinkage by the heat treatment, and by using the heat treatment film, the gas can have a high moisture content of 5 ppm or less, and further, the moisture content at room temperature can be highly dehumidified of 1 ppm or less. . Therefore, it can be said that the film obtained by heat-treating the above-mentioned copolymer has a performance of dehumidifying to a limit value which cannot be considered by the conventional common sense of the film.

The heat treatment causes the copolymer to shrink by several tens of percent, and the water absorption rate is also reduced.

A film obtained by heat-treating a film of a fluorocopolymer containing a repeating unit represented by the above general formula (I) has a relationship between the water absorption W and the ion exchange capacity Q of formula (III) 1.20Q-1.964 < logW <1.20Q-1.742 (III) It has excellent properties, and particularly exhibits excellent performance in highly drying gas.

The heat-treated film having the relationship of the formula (III) enables a high degree of dehumidification with a water content of 1 ppm or less at room temperature. Therefore, it is naturally possible to dehumidify the moisture content to any value such as 10 ppm or less and 5 ppm or less by setting the conditions as necessary. In actual use, it may be 10 ppm or less in some cases, 5 ppm or less, and even 3 ppm or less or 1 ppm or less, but the present invention is applicable to any of these cases.

In the case of a flat membrane among the above-mentioned heat-treated membranes, it can be easily determined by measuring the water absorption whether or not it is produced by the heat treatment.

However, if the membrane is a thin hollow fiber, the water absorption rate is difficult to measure, so that the determination can be made by measuring the heat shrinkage start temperature described below.

Attach a light weight (sufficient to straighten the thread but not enough to stretch it) to the hollow fiber membrane and hang it in the air tank. In that state, the temperature of the air tank is gradually raised, and the change in the yarn length is read and measured with a telescope. Fig. 5 shows an example of the measurement results in a graph with temperature on the horizontal axis and length on the vertical axis. L ₂₅ is a length of 25 ° C. and L _t is a length at a temperature of t ° C. In FIG. 5, the temperature indicated by the arrow, that is, the maximum temperature at which there is no dimensional change due to temperature rise is defined as the "maximum temperature at which there is no heat shrinkage." Several hollow fibers having different heat treatment temperatures (t) were prepared, the "maximum temperature (T) without heat shrinkage" was measured, and the results were plotted on a graph, as shown in FIG. That is, T = t (1), and the heat treatment temperature (t) of the hollow fiber membrane can be known by measuring the maximum temperature (T) without heat shrinkage.

The gas to be dried may be supplied to either side of the thin film of the fluorocopolymer. A dry purge gas having a low water content is passed through the membrane to the water permeation side, or a partial pressure difference, which is a driving force for membrane permeation, is generated by reducing the pressure with a vacuum pump or the like to achieve the purpose of dehumidification.

The film used in the present invention is preferably a thin film having a thickness of several μ to several hundred μ. Regarding the film thickness, the thinner the film, the greater the water vapor permeability and the better the performance, which is preferable.
Limited by pressure resistance. For hollow fiber membranes, depending on the diameter of the hollow fiber, wall thickness of 40 to 60 for inner diameters of 400 to 500μ
μ is preferred.

A dry purge gas with a low water content is a gas that is supplied to remove the water contained in the gas to be dried by removing the film, and is a gas that is inert and difficult to react even if the temperature rises. preferable. The reduced pressure means a pressure lower than the atmospheric pressure, although it depends on the pressure of the supplied source gas.

In the present invention, an oxide film is formed by using the dehumidified gas by using the above-mentioned film having an excellent dehumidifying ability. The oxide film is formed by introducing the highly dehumidified general gas and / or the corrosive gas in the oxidizing device.

[Effects of the Invention] The effects of the present invention can be summarized as follows.

(1) If moisture enters in the oxide film formation process in the production of semiconductor wafers, semiconductor devices or intermediate products thereof, it will cause stacking faults, while this defective portion will become a deposition site of oxygen molecules and impurities will also adhere to this portion. However, by removing the water, one of the causes of the stacking fault can be removed. Therefore, a high-quality oxide film can be stably formed, and the product yield can be improved.

(2) When gases such as HCl, Cl ₂ , Br ₂ , N ₂ O, and H ₂ are supplied from the cylinder, the gas in the cylinder affects the quality of the supplied gas as it is used. Moisture contained in the gas in a small amount also rapidly increases and adversely affects oxide film formation. However, in the present invention, the moisture content of all gases including the above-mentioned gases is made extremely small and always constant, and the oxide film is formed by a gas of stable quality, so that high purity and high quality are achieved. It is possible to form an oxide film of, and thus improve the product yield.

(3) O _2, as same as the above (2) H _2, N _2, Ar gas or the like, is supplied by pipeline from factory-site manufacturing apparatus or adjacent land, the further piping in the factory to the location of the reactor During transportation, a valve or the like is attached to the joint or branching portion of the pipe during this period, but water or the like may also enter from such a portion. Therefore, finally, also with respect to these gases, dehumidification is performed immediately before the reactor according to the present invention to reduce the water content of the gas to be used, and an oxide film is always formed with a stable gas having a constant quality. It is possible to form a high-purity, high-quality oxide film without being adversely affected by poor connection of a valve or the like.

(4) If the halogen gas contains water, impurities may be mixed in this water, or water may remain in the gaps of the equipment in the reactor, causing unexpected reactions when unexpected with other gases. Although this may occur, since the oxide film is formed by the gas excluding water according to the present invention, an unexpected reaction that adversely affects is suppressed and a high quality oxide film can be formed.

(5) The membrane used in the present invention has a higher dehumidifying ability than the molecular sieve and does not generate dust. Therefore, it is possible to dehumidify at room temperature, and the cooling means and dust removing means required when using the molecular sieve are used. It becomes unnecessary, and the entire apparatus used in the oxide film forming step can be simplified.

(6) By removing the water content of the corrosive gas, the corrosion of the pipe through which the corrosive gas passes is prevented, so that the generation of fine heavy metals and dust is prevented. At the same time, preventing corrosion of the pipes and gas flow rate regulators extends the life of these accessory devices and contributes to a significant cost reduction.

[Examples] The present invention will be described in more detail with reference to production examples, reference examples and examples, but the present invention is not limited to the examples.

In addition, the measurement of the water content of gas in the production examples, reference examples, examples and comparative examples was performed by a dew point meter or a moisture meter, and depending on the gas, the Karl Fischer method.

Production example With tetrafluoroethylene And ion-exchange capacity of 0.94 meq / g H
A mold dry resin was obtained. The resin obtained is molded at a molding temperature of 250 ° C.
A film having a thickness of μm was prepared, and after hydrolyzing this film with an alkaline alcohol solution, ion exchange was performed with a hydrochloric acid aqueous solution to make the end of the side chain a sulfonic acid type (H type) and air-dried. The obtained film was subjected to dry temperature treatment in vacuum, and the equilibrium water absorption was determined at 25 ° C (Fig. 1).

As shown in Fig. 1, the water absorption rate decreased significantly when the dry heat treatment temperature was about 70 ° C or higher. The water absorption was almost constant even at higher temperatures.

Similarly, the monomer species were changed as shown in Table-A to prepare a polymer film having an ion exchange capacity of 0.8 to 1.1 meq / g, and a polymer film having the water absorption rate shown in Table-A was prepared. Table-A
From the results, the relation between the ion exchange capacity and the water absorption rate of the membrane of the present invention is shown by the shaded area in FIG.

Reference example with tetrafluoroethylene Was copolymerized to obtain an H type dry resin having an ion exchange capacity of 0.9 meq / g. The obtained resin is melt-spun with a molding machine equipped with a die for hollow fiber production, inner diameter 500 μm, film thickness 60 μ
m hollow fiber membrane was obtained.

After the hollow fiber was hydrolyzed with an alkaline alcohol solution, ion exchange was performed with a hydrochloric acid aqueous solution to make the end of the side chain a sulfonic acid type (H type) and air dried. 40 cm length of the obtained thread
400 pieces of the dried product were bundled and fixed to a separator made of SUS with epoxy resin at both ends to make a moisture separator as shown in FIG.
N ₂ gas adjusted to a water content of 1 ppm (dew point −76 ° C.) or less was pressurized to 5 kg / cm ² G in the water separator, and was hollow at a flow rate of 0.5 / min (flow rate converted to atmospheric pressure. I shed it inside the thread.

Similarly, N ₂ gas adjusted to have a water content rate of 1 ppm (dew point −76 ° C.) or less was flowed at 0.75 / min. This was placed in a constant temperature bath at 70 ° C. and heat-treated for 3 hours, then the water separator was returned to room temperature, and the water content was 31 ppm (dew point −52 ° C.) and the pressure was adjusted to 5 kg / cm ² G N ₂ gas (sample gas ) Is flowed inside the hollow fiber at a rate of 0.5 ppm and a water content of 1 ppm (dew point −
N ₂ gas adjusted to 76 ° C.) or less was flowed at 0.75 / min. When the dew point of the sample gas at the outlet of the water separator was measured, the water content was 1 ppm (dew point −76 ° C.) or less. Continuous operation as it is, and after 24 hours, the water content of the sample outlet is 1 ppm (dew point −
It remained below 76 ° C).

On the other hand, with respect to the purge gas on the outside of the hollow fiber, the moisture content at the outlet dew point of the water separator was measured after 24 hours, and the water content was 4.6 ppm.
It was (dew point -66 ° C). After that, after about 1000 hours of continuous operation under the same conditions, the outlet water content of the sample gas remains below 1 ppm (dew point -76 ° C), and the amount of water reduced by the water separator of the sampling gas and the water separation of the purge gas The ratio of the amount of water increased by the vessel was 1.2: 1, which was in good agreement within the measurement error.

As for the other films of the present invention, the same results as in the reference example were obtained as shown in Table-A.

Comparative Reference Example When the sample gas and the purge gas were measured under the same conditions as in Example 2 without the heating pretreatment in the same apparatus as in the Reference Example, the water content of the sample gas after 44 hours was 10.6 ppm.
It did not reach the (dew point -60 ° C).

Example 1 (i) Nitrogen gas pressurized to a moisture content of 1 ppm or less (measured with a moisture meter) and a pressure of 5 kg / cm ² G was applied to the same moisture separator as in the reference example.
Flowed inside the hollow fiber at 0.5 / min. Moisture content 1 on the outside
Dry nitrogen gas (purge gas) below ppm at atmospheric pressure 0.7
5 / divided. Put this in a constant temperature bath at 70 ° C, preheat for 3 hours, return to room temperature, and then set the moisture content inside the hollow fiber.
The water content at the outlet of the moisture separator of the sample gas was measured and was 3 ppm when adjusted to 31 ppm and switched to 0.5 / min of hydrogen chloride gas (sample gas) pressurized to 5 kg / cm ² G. The water content at the outlet of the sample gas remained 3 ppm even after 24 hours of continuous operation.

On the other hand, with respect to the purge gas on the outside of the hollow fiber, the water content at the outlet of the water separator was measured after 24 hours, and it was 5 ppm.

Then, under the same conditions, the outlet water content of the sample gas after about 1200 hours remained at 3 ppm.

Next, hydrogen chloride gas with a moisture content of 3 ppm after treatment with a moisture separator was used to form an oxide film using the oxidizer shown in Fig. 4 to produce an intermediate product for semiconductor devices. A yield improvement of 4% was realized as compared with the case of using.

(Ii) again Almost the same results were obtained for the hollow fiber membrane of the polytetrafluoroethylene copolymer having the repeating unit of (ion exchange capacity 0.94 meq / H type dry resin).

Example 2 (i) The same moisture separator as in Example 1 was used, the pressure of the sample gas was set to the same condition, and the moisture content after treatment was measured in the moisture separator as in Example 1 using the depressurization method. Then, the results shown in Table 1 below were obtained.

Next, hydrogen chloride gas with a water content of 3 ppm after treatment with a water separator was used to form an oxide film using an oxidizing device as shown in Fig. 4 to produce an intermediate product for semiconductor devices. A yield improvement of 4% was realized as compared with the case of using it.

(Ii) again Almost the same results were obtained for the hollow fiber membrane of the polytetrafluoroethylene copolymer having the repeating unit of (ion exchange capacity 0.94 meq / H type dry resin).

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the dry heat treatment temperature and the equilibrium water absorption of the polymer semipermeable membrane obtained in the production example, and FIG. 2 is the production example.
Ion exchange capacity 0.8 ~ produced by dry heat treatment at 70 ℃ or higher
A graph showing the relationship between the polymer water absorption rate (W) and the ion exchange capacity (Q) of the polymer semipermeable membrane of 1.1, Fig. 3 is a conceptual diagram of a water separator used for carrying out the method of the present invention, Fig. 4 is a conceptual diagram showing the position where the water separator is used in the oxidizer, and Fig. 5 is a graph for obtaining the maximum temperature without heat shrinkage of the hollow fiber membrane, where the horizontal axis is temperature and the vertical axis is t ° C
It is the ratio of the length (L _t ) of the hollow fiber membrane at 25 ° C. to the length (L ₂₅ ) at a temperature of 25 ° C. FIG. 6 is a graph showing the relationship between the heat treatment degree (t) of the hollow fiber membrane and the maximum temperature at which heat shrinkage does not occur. The heat treatment temperature can be determined from this graph. 1 ... Hollow fiber membrane, 2 ... Sample gas inlet, 3 ... Sample gas outlet, 4 ... Purge gas inlet (closed when decompressing), 5 ... Purge gas outlet (decompressing when decompressing), 6 ... ... cell, 7 ... diaphragm, 8 ... moisture separator, 9 ... oxidizer, 10 ... various cylinders, 11 ... cock (valve).

Claims (1)

[Claims] 1. When manufacturing a semiconductor wafer, a semiconductor device or an intermediate product thereof, a general gas and / or a corrosive gas is contacted with one side of a film of a fluorinated copolymer having a cation exchange group. , A vapor phase characterized by forming an oxide film using a general gas and / or a corrosive gas dehumidified by bringing a dry purge gas into contact with the other side or depressurizing the other side Method for forming oxide film.