JP5475269B2 - Method for forming thin film conductive film - Google Patents

Description

  The present invention relates to a method for forming a thin film conductive film, for example, a method for forming a thin film conductive film functioning as an electrode or a resistor such as a ferroelectric or a solar cell.

Conventionally, a thick film conductive paste is often used as a material constituting an electrode or wiring of an electronic component, and glass powder may be added to such a thick film conductive paste. By adding glass powder to the thick film conductive paste,
(1) Softening and flowing during firing of the conductive film to promote sintering of the conductive powder (2) Effects such as improving the adhesion strength of the thick film conductive film can be obtained. In addition, lead-based glass is used as the glass powder added to the thick film conductive paste. However, in recent years, lead-free glass has been required in consideration of the environment.

  On the other hand, as an example of a conductive metal component, an example using ruthenium as described in Patent Document 1 is known. However, a rare metal such as ruthenium (rare metal) has a large price fluctuation in product cost. Affect. For this reason, it is common to refrain from using rare metals such as ruthenium in the conductive paste as much as possible. On the other hand, even if the amount of ruthenium used is suppressed, stabilization of the conductive film characteristics is indispensable, and it is necessary to stabilize the conductive film shape.

JP 2004-88019 A

  The conventional thick film conductive paste described above, for example, in Patent Document 1, is a mixture of a ruthenium oxide compound and glass powder in a weight ratio of (70 to 90) :( 5 to 30), and therefore requires a large amount of ruthenium. And Moreover, since it contains glass powder, for example, baking at about 800 ° C. is necessary, and there is a problem that manufacturing costs including material costs cannot be reduced. Furthermore, as a film forming method, for example, screen printing or a dry process such as sputtering is employed. For this reason, it becomes difficult to reduce the amount of rare metal such as ruthenium used, resulting in a problem that an increase in manufacturing cost cannot be avoided.

  Furthermore, in manufacturing various electronic devices, heat treatment may be performed for crystallization of an oxide material. At that time, when a normal metal material is used for the conductive film formed in the electronic device, the surface thereof is oxidized, and the characteristics are remarkably changed. For this reason, an oxide conductive film is sometimes used instead of a metal material, and formation of a conductive film using a stable oxide metal is desired.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a method for forming a stable thin film conductive film having a smooth and uniform surface state and little fluctuation in characteristics. It is.

The following configuration is provided as means for achieving the above object and solving the above-described problems. That is, the method of forming the resistance-body thin conductive film according to the present invention, after heating the pre substrates 300 ° C. to 450 ° C., a precursor solution containing a preparative squirrel (acetylacetonato) ruthenium and toluene to the substrate A ruthenium oxide conductive film having a thickness of 20 nm or more is formed on the surface of the substrate by spraying a plurality of times toward the substrate.
Furthermore, the present invention provides a method of resistance-body thin conductive film forming the ruthenium oxide conductive film of the thin film on the substrate surface, a predetermined concentration containing preparative squirrel (acetylacetonato) ruthenium and toluene precursor solution A step of heating, a step of heating the substrate to 300 ° C. to 450 ° C., and a step of spraying the precursor solution toward the heated substrate, and the film thickness of the ruthenium oxide conductive film is 20 nm or more. The precursor solution is sprayed a plurality of times so that

  According to the present invention, a smooth, uniform, and low resistance ruthenium oxide conductive film can be formed, and the amount of ruthenium used for forming the thin film conductive film can be greatly reduced. It becomes possible to make it less.

  In order to obtain a method for forming a thin-film conductive film using an oxide metal, the inventors of the present application have developed an efficient method for forming a thin-film conductive film that minimizes the amount of ruthenium oxide that exhibits particularly excellent properties among oxide metals. I came to the idea. Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings and tables.

  FIG. 1 is a flow chart showing a metal film deposition (deposition) process in time series according to an embodiment of the present invention. In the film forming process shown in FIG. 1, in the first step S1, a solution having a predetermined concentration in which metal powder is dissolved in a solvent (a spray precursor solution sprayed in a process described later) is prepared. Specifically, tris (acetylacetonato) ruthenium (III) was prepared as a metal powder (organometallic compound). As a solvent, toluene was used as a preferable solvent in consideration of solubility of ruthenium and adhesion to a substrate. In addition, although a solvent is not limited to this, Preferably a low boiling point solvent about 80 degrees C or less is used.

  In this embodiment, 0.4 g of tris (acetylacetonato) ruthenium (III) as a metal powder and 10.125 g of toluene as a solvent were stirred and mixed for 5 minutes to prepare a precursor solution. In addition, you may use an ultrasonic wave in order to mix more uniformly. In addition to the above examples, the concentration of the precursor solution may be selected in consideration of the solubility of ruthenium.

  In step S3, as a stage before entering a spraying process to be described later, a substrate (substrate) that is a film formation target is heated in advance to a predetermined temperature. In step S5, the above-described precursor solution is sprayed toward a substrate having a predetermined substrate temperature. FIG. 2 shows a schematic configuration of a spray device used in the metal film deposition process according to the present embodiment. In FIG. 2, the precursor solution described above is stored in the container 2, and the precursor solution is introduced into the injector 1 through the pipe 3.

  The precursor solution is atomized together with, for example, air by the injector 1 and sprayed toward the substrate 5 from the nozzle 7. The table 4 includes a heater 9 that can be heated to about 500 ° C., for example. Note that the nozzle 7 is positioned vertically above the center of the substrate 5, and the interval between the nozzle 7 and the substrate 5 can be appropriately changed according to the film forming conditions, the film forming environment, and the like. Step S <b> 7 is a film forming process, and the precursor solution sprayed in step S <b> 5 reaches the surface of the substrate 5 and covers the upper surface of the substrate, whereby a conductive film having a predetermined thickness is formed on the substrate 5.

  Hereinafter, as an example of a method for forming a thin film conductive film according to the present invention, results of forming a film on a substrate while changing various film forming conditions such as temperature, and effects thereof will be described in detail.

<First embodiment>
In the first embodiment of the present invention, an insulating substrate such as a quartz substrate or an alumina ceramic substrate is placed on the table 4 shown in FIG. Further, the precursor solution described above is placed in the container 2. The substrate 5 is heated in advance to a predetermined temperature, and the precursor solution is sprayed on the substrate 5. By heating the substrate 5 in advance, the solvent contained in the sprayed precursor solution is evaporated, the organometallic compound is thermally decomposed, and a ruthenium oxide film is formed on the substrate 5. In the first embodiment, spraying is performed at predetermined time intervals.

  Table 1 shows measured values of film thickness (changes in film thickness with the number of sprays) in the first example. Here, the concentration of the precursor solution was 0.086 mol / L, a quartz substrate was used as the substrate 5, the heating temperature of the substrate 5 was 450 ° C., the spraying interval was 3 seconds, and the number of sprays was changed. .

  From Table 1, it can be seen that the film thickness increases as the number of sprays of the precursor solution increases. This means that the layers are stacked each time you spray. It has also been found that if the substrate 5 is not heated at least to such an extent that the solvent evaporates, it is difficult to overlap the film beyond the thickness obtained by the surface tension of the solvent.

When the film formation state was evaluated by an X-ray diffractometer (XRD), it was confirmed that a ruthenium dioxide (RuO ₂ ) film was formed on the substrate 5. Further, when the transparency of the obtained RuO ₂ film was observed, it was found that the film was substantially transparent up to about 8 sprays, and thereafter the transparency decreased as the film thickness increased. Furthermore, when the surface state of the obtained RuO ₂ film was imaged with an atomic force microscope (AFM), it was found that a film having a substantially uniform thickness was formed. For example, a film having a substrate temperature of 350 ° C. and a film thickness of about 70 nm has a mean surface roughness of about 2 nm.

  FIG. 3 shows the change in resistance (conductance) with increasing film thickness for each metal film sample in Table 1. FIG. 3 shows that the resistance value basically decreases as the film thickness increases. On the other hand, a resistance value was not obtained in a thin film such as a sample sprayed twice. This is assumed to be because a stable film cannot be obtained when the number of sprays is small. For this reason, when the film thickness is thinner than 20 nm, the resistance value cannot be obtained or the variation in the resistance value is large, and the control is difficult. Therefore, in order to ensure good electrical performance as a conductive film, it is desirable that the film thickness is 20 nm or more, and the number of sprays is also the number of times that film thickness can be obtained.

<Second embodiment>
In the second embodiment of the present invention, the number of sprays of the precursor solution was 30, and the heating temperature of the substrate 5 was changed as described below. Other than that, it formed into a film on the same conditions as the 1st Example mentioned above. FIG. 4 shows the result of confirming the change in the characteristics of the sample manufactured in the second embodiment, and specifically shows the characteristics of the RuO ₂ film accompanying the change in the substrate temperature. In FIG. 4, the horizontal axis represents the heating temperature of the substrate, and the vertical axis represents the conductance (represented by the symbol ■ in the figure), the resistivity (represented by the mark ● in the figure), and the characteristics of the RuO ₂ film. The film thickness (indicated by ▼ in the figure) is shown.

  As shown in FIG. 4, when the temperature of the substrate 5 was 450 ° C., the resistance value was the lowest and the film thickness was the thickest. On the other hand, the resistance value was highest at a substrate temperature of 200 ° C., and the film thickness was small. When the substrate temperature is low, it is assumed that the organometallic compound is not sufficiently thermally decomposed and the organic substance remains to increase the resistance value. Further, it is considered that the film thickness was not formed due to the loss of the solution.

According to the second example, it was confirmed that the resistance value of the RuO ₂ film can be controlled by controlling the heating temperature of the substrate 5 as shown in FIG. Note that thermal decomposition does not occur when the substrate temperature is about 150 ° C., and the RuO ₂ film volatilizes at 600 ° C. or higher. Therefore, it is preferable that the heating temperature of the board | substrate 5 shall be 190 degreeC-500 degreeC, for example. In practice, the substrate 5 may be heated by reflow or the like after the RuO ₂ film is formed. In that case, it is more preferable to set the heating temperature of the substrate 5 to, for example, about 300 to 450 ° C. in order to stabilize the film such as suppression of the characteristic change of the RuO ₂ film.

<Third embodiment>
In the third embodiment of the present invention, the substrate temperature was changed to 300 ° C., 350 ° C., and 400 ° C., and the number of sprays of the precursor solution was changed from 10 times to 50 times at each temperature. Then, a film thickness different RuO ₂ film, it was confirmed that the resistance value characteristics. FIG. 5 shows a change in resistance value with an increase in film thickness when the substrate temperature is changed for the sample manufactured in the third example.

From FIG. 5, it can be confirmed that the film thickness increases in proportion to the increase in the number of sprays of the precursor solution. Further, it was confirmed that when the substrate temperature was lowered, the resistance value of the RuO ₂ film was higher than when the substrate temperature was high. The reason is that the thermal decomposition of the organometallic compound is not promoted when the substrate temperature is low.

<Fourth embodiment>
In the fourth embodiment of the present invention, the quartz substrate and the alumina substrate were set to 300 ° C. and 350 ° C., respectively, and a RuO ₂ film was formed on the substrates. In the fourth example, the thickness of the RuO ₂ film was adjusted by changing the number of sprays of the precursor solution in the range of 10 to 50 times.

FIG. 6 shows a comparison of the characteristics of the quartz substrate and the alumina substrate for the sample produced in the fourth example, and the vertical axis represents the resistance value of the RuO ₂ film. According to the fourth example, the RuO ₂ film formed on the quartz substrate had a resistance value lower than that of the RuO ₂ film formed on the alumina substrate with substantially the same film thickness. This is because the quartz substrate has a smoother surface than the alumina substrate, and it was confirmed that a RuO ₂ film having a lower resistance value is formed when the smoothness of the substrate surface is higher.

<Fifth embodiment>
In the fifth embodiment of the present invention, the precursor solution was sprayed 30 times and the substrate temperature was 450 ° C. Further, a quartz substrate was used as the substrate 5 and the film was formed by changing the concentration of the precursor solution. In the fifth example, the resistance value of the RuO ₂ film formed with the precursor solution of each concentration was measured. FIG. 7 shows the result of measuring the change in resistance value accompanying the change in the concentration of the precursor solution in the fifth example.

7 that according to the fifth example, the higher the concentration of the precursor solution, the more the RuO ₂ film having a lower resistance value is formed. On the other hand, in the fifth example, no resistance value was obtained for a solution having a low concentration, specifically, a solution having a concentration of 0.0215 mol / L or less. For a solution in such a concentration range, a conductive film can be obtained by increasing the number of sprays, but in order to form a stable conductive film, it is efficient to have a concentration of 0.029 mol / L or more. it is conceivable that. In the fifth example, the maximum concentration was 0.086 mol / L. This is because when the concentration is higher than this, there arises a problem that ruthenium is not sufficiently dissolved.

<Sixth embodiment>
In the sixth embodiment of the present invention, a precursor solution was prepared by adding titanium (Ti) in addition to ruthenium as a metal material. As the solvent, toluene and IPA were used. The metal molar concentration was 0.086 mol / L. By spraying this precursor solution onto a quartz substrate heated to 450 ° C., a metal oxide film made of RuO ₂ —TiO ₂ was formed. The number of sprays was 30.

  FIG. 8 shows the results of measuring the change in resistance characteristic when the Ti content is changed in the sixth example. FIG. 8 shows that the resistance value increases as the Ti content increases. When the precursor solution contains Ti having a conductivity lower than that of ruthenium, the resistance value of the metal oxide film can be increased. For example, when a high resistance value is required, for example, as a resistor. Is preferred. Further, the temperature characteristics of the metal oxide film can be changed.

<Seventh embodiment>
The seventh example is an example in which silicon (Si) is contained instead of titanium contained in the precursor solution in the sixth example. Toluene was used as the solvent. The metal molar concentration was 0.086 mol / L. By spraying this precursor solution onto a quartz substrate heated to 450 ° C., a metal oxide film made of RuO ₂ —SiO ₂ was formed. The number of sprays was 10 times. FIG. 9 is a result of measuring a change in resistance value characteristics when the Si content is changed in the seventh embodiment. FIG. 9 shows that the resistance increases as the Si content increases. When the precursor solution contains Si having a lower conductivity than ruthenium, the resistance value of the metal oxide film can be increased. For example, when a high resistance value is required, such as a use as a resistor. Is preferred.

  In the sixth and seventh examples, Ti and Si are included in the precursor solution. However, the present invention is not limited to this, and both Ti and Si are included in the precursor solution. Also good.

  As described above, according to the embodiment of the present invention, by using ruthenium oxide exhibiting excellent characteristics as an oxide metal for the conductive film, the surface is not oxidized and the characteristics are not fluctuated stably. A conductive film can be provided. That is, by forming a thin ruthenium oxide conductive film by spraying a precursor solution containing ruthenium onto the substrate by a spray method, a smooth and uniform conductive film can be formed on the upper surface of the substrate. As a result, it is possible to significantly reduce the amount of ruthenium used for reducing the height of various devices and forming a conductive film. At the same time, manufacturing costs can be reduced compared to dry processes such as sputtering.

  Moreover, by using a precursor solution that does not require lead glass, it is possible to eliminate lead that adversely affects the environment and is harmful to the human body. Accordingly, the conventional conductive paste containing glass required a baking temperature of about 800 ° C. However, in the present invention, the substrate can be formed by heating at a temperature of about 400 ° C. Manufacturing costs can be kept low. Furthermore, it is possible to form a transparent thin film conductive film, and it can be used for various applications in which a transparent electrode is used, such as a display or a solar cell.

It is the flowchart which showed the film-forming (film-forming) process of the metal film in the embodiment which concerns on this invention in time series. It is a figure which shows schematic structure of the spraying apparatus used at the film-forming process of the metal film in the Example which concerns on this invention. It is a figure which shows resistance value change accompanying the increase in the film thickness about each metal film sample in 1st Example which concerns on this invention. It is a figure which shows the film | membrane characteristic by the board | substrate temperature change in 2nd Example based on this invention. It is a figure which shows the change of the resistance value accompanying the film thickness increase by the substrate temperature change in 3rd Example based on this invention. It is a figure which compares and shows the resistance value change by the difference in the board | substrate in the 4th Example which concerns on this invention. It is a figure which shows the result of having measured the change of the resistance value accompanying the density | concentration change of a precursor solution in the 5th Example which concerns on this invention. It is a figure which shows the change of the resistance value characteristic accompanying Ti content change in the 6th Example which concerns on this invention. It is a figure which shows the change of the resistance value characteristic accompanying Si content change in the 7th Example which concerns on this invention.

Explanation of symbols

1 Injector 2 Container 3 Piping 4 Table 5 Substrate 7 Nozzle 9 Heater

Claims (2)

Pre After heating the substrate to 300 ° C. to 450 ° C., preparative squirrel (acetylacetonato) ruthenium and toluene the thickness is more than 20nm on the substrate surface by spraying a plurality of times toward the base precursor solution containing A method for forming a thin film conductive film for a resistor, comprising forming a ruthenium oxide conductive film. A method of forming a thin film ruthenium oxide conductive film on a surface of a substrate, comprising :
A step of preparing a predetermined concentration of the precursor solution containing preparative squirrel (acetylacetonato) ruthenium and toluene,
Heating the substrate to 300 ° C. to 450 ° C .;
Spraying the precursor solution toward the heated substrate,
A method of forming a thin film conductive film for a resistor, comprising spraying the precursor solution a plurality of times so that the film thickness of the ruthenium oxide conductive film is 20 nm or more.

Images