JPH0129370B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for forming a polyimide layer with good adhesion on the surface of a substrate made of a silicon-containing material. In recent years, polyimide has attracted attention as a heat-resistant polymer. In other words, this polyimide has excellent heat resistance, and has many excellent advantages such as excellent electrical insulation, low stress distortion, and mechanical strength.
It is an organic material that is attracting attention because it does not cause cracks even when formed into a thick film and has minimal pinholes. However, the above polyimide is a silicon wafer,
The drawback is that it has poor adhesion to the surface of a substrate made of a silicon-containing material such as glass, making it difficult to bond. For this reason, various proposals have been made to improve the adhesion of the polyimide, one of which is that when synthesizing a polyimide precursor by a polymerization reaction between an aromatic tetracarboxylic dianhydride and a diamino compound, There is a method of using diaminosiloxane as the diamino compound. This method introduces Si-O-Si bonds derived from diaminosiloxane into the molecular skeleton, and these bonding parts form chemical bonds with silicon atoms in silicon-containing materials such as silicon wafers and glass. The purpose is to improve adhesion by using these as active sites for adhesion to silicon-containing materials. However, in the above proposed method, diaminosiloxane is used in a considerable proportion of the diamino compound or as all of the diamino compound, so even if the adhesion can be improved, the moisture resistance properties of the polyimide layer will be significantly impaired. There's a problem. Moreover, excessive use of diaminosiloxane is not necessarily preferable in terms of heat resistance, electrical insulation, mechanical strength, etc. inherent to polyimide. Furthermore, in the proposed method, a polyimide precursor synthesized using an excess of diaminosiloxane and a polyimide precursor synthesized without using diaminosiloxane at all, that is, using a diamine that does not contain a silicon atom in the molecule, are mixed. There is also a method to do this, but even in this case, the same problem as mentioned above occurs because the silicon content in the mixture is large, and because it is a mixture, it has poor adhesion, moisture resistance, and other general properties. It was not possible to obtain stable performance because the performance varied easily between the two. On the other hand, this type of siloxane-modified polyimide precursor is desired to be a high molecular weight material with high intrinsic viscosity in view of heat resistance and other general properties, but in this case, the However, there is a problem in that the viscosity of the solution becomes high and a practical solids concentration cannot be obtained. For example, the feed concentration during the synthesis of polyimide precursors is generally set to be at least 5 to 15% by weight for economical reasons, but even with such a low feed concentration, spin In order to obtain a solution viscosity suitable for coating, dipping or brushing, considerable further dilution is required after the polymerization reaction. Such a dilution operation causes variations in solution viscosity between manufacturing lots and complicates the coating process, and also causes repellency and uneven thickness in the formed coating film due to a significant decrease in solid content concentration. This results in an adverse effect on the performance of the polyimide layer. In view of the above, the present invention makes it possible to form a polyimide layer that exhibits a viscosity that allows coating in a highly concentrated state, has excellent adhesion to the surface of a substrate made of a silicon-containing material, and has good moisture resistance. This discovery was made as a result of extensive research in order to obtain a siloxane-modified polyimide precursor that has the inherent heat resistance, electrical insulation, and mechanical strength. That is, this invention provides the following general formula in an inert solvent; (R ₁ is a divalent organic group, R′ is a monovalent organic group,
n is an integer from 1 to 1000) A diamino compound consisting of a diamino siloxane represented by the formula (n is an integer from 1 to 1000) and a diamine that does not contain a silicon atom in the molecule is combined with an aromatic tetracarboxylic dianhydride, and the diamino siloxane is the total amount of the diamino compound. 1 to 4
By conducting a polymerization reaction at a ratio of mol%,
A solution of a siloxane-modified polyimide precursor with a silicon content of 0.5% by weight or less was obtained, and this solution was heated at 40 to 80°C.
made of a silicon-containing material, characterized in that the precursor is heated and aged to lower the intrinsic viscosity of the precursor, and then this solution is applied to the surface of the substrate made of the silicon-containing material, and then heat-treated at a high temperature to form a polyimide layer. The present invention relates to a method for forming a polyimide layer with good adhesion on the surface of a substrate. As described above, in this invention, the diaminosiloxane used to improve the adhesion of the polyimide layer is necessary and sufficient within the above specified range, and when used in such a proportion, the amount of moist heat occupied in the polyimide precursor increases. Since the siloxane bonds, which are easily broken by decomposition or acid or alkali, are extremely small, the moisture resistance of the polyimide layer is not reduced, and the inherent heat resistance, electrical insulation, and mechanical strength of polyimide are maintained. I found out that there is no need to worry about damaging it. On the other hand, the siloxane-modified polyimide precursor synthesized using diaminosiloxane in the above-mentioned proportion has the same drawback as conventional precursors in that it has a high solution viscosity. However, according to the present invention, when the polyimide precursor solution after the polymerization reaction is further heated and aged at a specific temperature, its intrinsic viscosity decreases due to molecular cleavage or rearrangement of the precursor, and the polyimide precursor solution is not diluted with a solvent after that. When a solution with a high concentration and low viscosity is obtained by this method, it not only has excellent adhesion and moisture resistance properties as a polyimide layer achieved by the above method. In addition, it has been found that it has almost no adverse effect on heat resistance, mechanical strength, electrical insulation, etc. In the diaminosiloxane represented by the general formula (1) in this invention, two R ₁ and each R' in the formula may be the same or different,
A wide variety of conventionally known methods are included. Typical examples are as follows. The diamine that does not contain a silicon atom in its molecule (hereinafter simply referred to as silicon-free diamine) used in this invention has the following general formula (2); H ₂ N−R ₂ −NH ₂ …(2) (R ₂ is a divalent organic group that does not contain _a silicon atom. It may be the same as or different from ₁ . Particularly suitable are aromatic diamines, representative examples of which include metaphenylenediamine, paraphenylenediamine, 4.
4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 2,2'-bis(4-aminophenyl)propane, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone , 4,4'-diaminodiphenyl sulfide,
Benzidine, benzidine-3,3'-dicarboxylic acid, benzidine-3,3'-didisulfonic acid, benzidine-3-monocarboxylic acid, benzidine-3-
Examples include monosulfonic acid, 3,3'-dimethoxy-benzidine, para-bis(4-aminophenoxy)benzene, meta-bis(4-aminophenoxy)benzene, metaxylylenediamine, paraxylylenediamine, and the like. In this invention, the aromatic tetracarboxylic dianhydride to be polymerized and reacted with the diamino compound consisting of the above diaminosiloxane and silicon-free diamine has the following general formula (3); (Ar is a tetravalent organic group) Typical examples include pyromellitic dianhydride, 3.
3', 4, 4'-benzophenonetetracarboxylic dianhydride, 3, 3', 4, 4'-biphenyltetracarboxylic dianhydride, 2, 3, 3', 4'-biphenyl tetra Carboxylic dianhydride, 2, 3, 6, 7-naphthalenetetracarboxylic dianhydride, 1, 2, 5,
6-naphthalenetetracarboxylic dianhydride, 1.
4,5,8-naphthalenetetracarboxylic dianhydride, 2,2'-bis(3,4-dicarboxyphenyl)propane dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride , 3・4・9・
10-perylenetetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, 2,2'-bis(2,3-dicarboxyphenyl)propane dianhydride, 1,1 '-Bis (2・3
-dicarboxyphenyl)ethane dianhydride, benzene-1,2,3,4-tetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 1,2,7, Examples include 8-phenanthrenetetracarboxylic dianhydride. A particularly suitable aromatic tetracarboxylic dianhydride for this invention is 3,3',4,4'-biphenyltetracarboxylic dianhydride. When this dianhydride is used, under a high temperature and high humidity atmosphere, for example, 121℃,
A polyimide layer with excellent electrical properties as measured by the 2-atm pressure pressure test (hereinafter simply referred to as PCT), that is, extremely good moisture resistance properties, can be obtained. Of course, the moisture resistance can be improved even when other dianhydrides are used. In this invention, it is necessary to simultaneously polymerize the diaminosiloxane and the silicon-free diamine with the aromatic tetracarboxylic dianhydride. For example, in a method in which both diamino compounds are polymerized separately and then mixed, This causes variations in adhesion and moisture resistance, making it impossible to stabilize quality. As mentioned above, the diaminosiloxane used in this polymerization reaction is 1 to 4 mol%, preferably 3 to 3.5 mol% of the total amount of the diamino compound,
Further, the amount used must be determined so that the silicon content contained in the obtained siloxane-modified polyimide precursor is 0.5% by weight or less. Unless these quantitative relationships are satisfied, it becomes difficult to achieve both adhesion and moisture resistance. The ratio of the diamino compound consisting of diaminosiloxane and silicon-free diamine to the aromatic tetracarboxylic dianhydride is usually equimolar, but one may be slightly increased if necessary. The polymerization reaction may be carried out according to conventionally known methods, generally in the presence of an inert solvent and in a stream of nitrogen gas, while taking into consideration the polymerization heat generation and generally limiting the temperature to below 40°C, particularly preferably below 30°C. The reaction may be carried out until a predetermined degree of polymerization is obtained. In addition, in applications such as forming a polyimide layer of a semiconductor element, the polyimide forming material must be prevented from being contaminated with ionic impurities. Care must be taken to avoid contamination from cationic impurities such as Na ⁺ , K ⁺ , Ca ²⁺ and anionic impurities such as Cl ^- .
In particular, Na ⁺ ions have a negative effect on the electrical properties of semiconductors. Therefore, during polymerization, both the raw material monomer and the solvent should be sufficiently purified by well-known methods before use. For example, it is desirable that the concentration of Na ⁺ ions is 5 PPM or less, preferably 1 PPM or less. Examples of inert solvents used in such polymerization reactions include N-methyl-2-pyrrolidone,
Highly polar basic solvents such as N.N'-dimethylacetamide, N.N'-dimethylformamide, N.N'-dimethylsulfoxide, and hexamethylphosphoramide are used. All of these types of solvents are highly hygroscopic, and absorbed water causes a decrease in molecular weight during polymerization and storage stability, so it is recommended to thoroughly dehydrate with a dehydrating agent before use. . Moreover, general-purpose solvents such as toluene, xylene, benzonitrile, benzene, and phenol can also be used together with these solvents. However, the amount used should be within a range that does not reduce the solubility of the polyimide precursor produced. The degree of polymerization of the siloxane-modified polyimide precursor synthesized by the above method can be easily detected by examining the intrinsic viscosity [η] of the reactant. It is desirable that the polymerization degree is high. This is because if it is lower than this, good results will not be obtained in terms of heat resistance and other general properties. The intrinsic viscosity [η] described in this specification is
It means the value calculated according to the following formula using N-methyl-2-pyrrolidone as a solvent at a measurement temperature of 30±0.01°C (static bath). [η] = ln (t/to)/C t; Falling time to of the polymer solution measured with an Ubbelohde viscometer; Falling time C of the solvent measured in the same manner as above; Polymer concentration (assumed to be 0.5% by weight) In the invention, subsequent to the above polymerization reaction step, heat aging is carried out in the same reaction vessel in a nitrogen stream by raising the temperature to 40 to 80°C, preferably 50 to 60°C. By this heat aging, the siloxane-modified polyimide precursor having a high degree of polymerization obtained in the above-mentioned polymerization reaction undergoes appropriate molecular cleavage or rearrangement, thereby reducing the molecular weight. The degree of molecular weight reduction is determined by the relationship between solution viscosity and polyimide properties, and it is generally preferable to set the intrinsic viscosity to 0.3 to 0.7. As a guide, the solution viscosity is about 1,000 to 20,000 centipoise at a solution concentration of 25% by weight. If the above-mentioned intrinsic viscosity becomes too low, the layer forming ability in the final stage will be poor, and the insulation properties, heat resistance and other properties will be impaired when applied to semiconductors. The reason why the heat aging temperature was set at 40 to 80℃ is that at temperatures exceeding 80℃, especially at temperatures above 100℃, crosslinking reactions proceed and there is a risk of gelation. This is because sufficient effects cannot be obtained and the aging time becomes long, impairing workability. Even if the siloxane-modified polyimide precursor as the final product obtained in this way has a lower degree of polymerization, it is still a silicon-free diamine as shown in the following general formula (4). The bonding unit of and diaminosiloxane added to aromatic tetracarboxylic dianhydride via an amide bond is
It has a random polymer structure, and is characterized by having a structure in which very few siloxane bonds are incorporated into the molecular chain of this polyimide precursor. (R ₁ , R ₂ , R', n and Ar are as described above, l
and m are both positive integers, m/l+m=0.01
~0.04) (R ₁ , R ₂ , R', Ar, n, l, and m are as described above.) Such a siloxane-modified polyimide precursor has a low solution viscosity, and for example, when the charging concentration in the polymerization reaction step is 20 to 25 Even when the weight is % or higher, even if it is not diluted after the heat aging process,
It has a viscosity suitable for spin coating, dipping or brushing. In this invention, the above precursor solution is applied to the surface of a silicon-containing material such as a silicon wafer by the above coating method, and then subjected to high temperature heat treatment, dehydrated and cyclized. It is possible to form a layer made of polyimide as represented by the above-mentioned general formula (5), which exhibits excellent adhesion to the like. This polyimide layer has excellent moisture resistance, as well as inherently good heat resistance, chemical resistance, mechanical strength, and excellent electrical insulation properties, making it suitable for various applications that require these properties. It has the advantage of being widely applicable. EXAMPLES Below, examples of the present invention will be described in more detail. Example 1 A 500 ml flask equipped with a stirrer, condenser, thermometer and nitrogen purging device was fixed on a water bath.
N・N'-dimethylformamide 148.71, which was dried over calcium hydride for a day and night, and then distilled after purging with nitrogen.
g was added into the above flask, nitrogen was poured into the flask, and a polymerization reaction was carried out in the following manner. First, use a 1 ml microsyringe to
-aminopropyl)tetramethyldisiloxane (diaminosiloxane of formula A above) 0.87g
(0.0035 mol) and then 19.3 g (0.0965 mol) of 4,4'-diaminophenyl ether were charged and stirred until dissolved. Thereafter, 29.4 g (0.1 mol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride was gradually added. The reaction system was stirred while maintaining the temperature below 30°C until a clear viscous solution was obtained. The 25% by weight solution of the siloxane-modified polyimide precursor obtained in this way has a viscosity (hereinafter the same) measured with a BH type viscometer at 25°C that is at least the measurement upper limit (2,000,000 centipoise), and the intrinsic viscosity of the precursor was 1.67, and the silicon content was 0.397% by weight. Next, as a heating and aging step, the water bath was removed and replaced with a hot water bath, and the same reaction vessel was heated and stirred at 55±5°C, heated and aged in a nitrogen stream for 6 hours, and then continued for another 28 hours, for a total of 34 hours. By heating and aging, the molecular weight was reduced to an intrinsic viscosity of 0.42 and a solution viscosity of 4400 centipoise. This precursor solution was spin-coated onto a silicon wafer, heated to 150°C for 1 hour in a hot air dryer, and then heated to 200°C for 1 hour.
Heat treatment was performed at 250° C. for 6 hours to form a strong polyimide layer with good adhesion. The infrared absorption spectrum of this polyimide layer is 1780 cm ^-1 and
Absorption of >C=O due to imide group formation was observed at 1720 cm ^-1 . In addition, the above spin coat is
This was carried out by dropping 2 to 3 g of the precursor solution at a rotational speed of 3500 rpm. Example 2 Same as Example 1 except that the amount of purified N/N'-dimethylformamide used was 125.91 g and 21.8 g (0.1 mol) of pyromellitic dianhydride was used as the aromatic tetracarboxylic dianhydride. A polymerization reaction is performed to produce a high molecular weight siloxane-modified polyimide precursor with a silicon content of 0.469% by weight, an intrinsic viscosity of 1.65, and a solution viscosity of 2,000,000 centipoise or more.
A 25% by weight solution was obtained. Next, as a heating aging step, the above precursor solution was heated and aged for 24 hours at 55 ± 5°C in the same manner as in Example 1 to lower the molecular weight until the intrinsic viscosity was 0.38 and the solution viscosity was 2200 centipoise. did. Example 1 This precursor solution was applied onto a silicon wafer.
Spin coat in the same manner as above and dry in a hot air dryer at 150℃.
A strong polyimide layer with good adhesion was formed by heat treatment at 200°C for 1 hour, 200°C for 1 hour, and 300°C for 1 hour. Example 3 The amount of purified N/N'-dimethylformamide used was 156.53 g, and 32.2 g of 3,3',4,4'-benzophenonetetracarboxylic dianhydride was used as aromatic tetracarboxylic dianhydride ( The polymerization reaction was carried out in the same manner as in Example 1, except that 19.107 g (0.0965 mol) of 4,4'-diaminodiphenylmethane was used as the silicon-free diamine, and the silicon content was 0.377 wt. A 25% by weight solution of a high molecular weight siloxane modified polyimide precursor with a % intrinsic viscosity of 1.38 and a solution viscosity of 1700000 centipoise was obtained. Next, as a heat aging step, the above precursor solution was heated at 55±5°C in the same manner as in Example 1.
By heating and aging for 15 hours, the intrinsic viscosity is 0.45.
The molecular weight was lowered to a solution viscosity of 2300 centipoise. Example 1 This precursor solution was applied onto a silicon wafer.
After spin coating in the same manner as above, heat treatment was performed to form a polyimide layer with good adhesion. This layer is 6
After several months, the tensile strength decreased to 40% of the initial value, but it was still strong enough to be used. Comparative Example 1 The amount of purified N・N′-dimethylformamide used was 148.27 g, the amount of 4・4′-diaminodiphenyl ether used was 19.9 g (0.0995 mol), and the amount of bis(3-
The polymerization reaction was carried out in the same manner as in Example 1, except that the amount of tetramethyldisiloxane (aminopropyl) used was 0.1243 g (0.0005 mol). A 25% by weight solution of a high molecular weight siloxane-modified polyimide precursor having a viscosity of 2,000,000 centipoise was obtained. Next, as a heating aging step, the above precursor solution was heated and aged in the same manner as in Example 1 to lower the molecular weight until the intrinsic viscosity was 0.41 and the solution viscosity was 2700 centipoise. This precursor solution was spin-coated onto a silicon wafer in the same manner as in Example 1, and then heat-treated to form a polyimide layer. Comparative Example 2 The amount of purified N/N'-dimethylformamide used was 149.22 g, the amount of 4,4'-diaminophenyl ether used was 18.6 g (0.093 mol), and the amount of bis(3-aminopropyl)tetramethyldisiloxane used was 149.22 g. A polymerization reaction was carried out in the same manner as in Example 1, except that the amount used was 1.7395 g (0.007 mol), and the silicon content was reduced.
0.791% by weight, intrinsic viscosity 0.80, solution viscosity
A 25% by weight solution of 50000 centipoise siloxane modified polyimide precursor was obtained. Next, as a heat aging step, the above precursor solution was heated and aged in the same manner as in Example 1 to reduce the molecular weight until the intrinsic viscosity was 0.45 and the solution viscosity was 5100 centipoise. This precursor solution was spin-coated onto a silicon wafer in the same manner as in Example 1, and then heat-treated to form a polyimide layer. Comparative Example 3 Bis(3-aminopropyl)tetramethyldisiloxane and 4,4'-diaminodiphenyl ether were polymerized separately with pyromellitic dianhydride in the same proportions as in Example 2, and then both were mixed. A 25% by weight solution of the polyimide precursor mixture was obtained.
The intrinsic viscosity of the polyimide precursor obtained from diaminosiloxane was 0.63, and the intrinsic viscosity of the polyimide precursor obtained from silicon-free diamine was 2.00. The silicon content in the polyimide precursor mixture was 0.469% by weight, and the solution viscosity was above the upper limit of measurement (2,000,000 centipoise). Next, the above solution was further heated and aged in the same manner as in Example 1, so that the intrinsic viscosity was reduced.
The molecular weight was lowered to 0.53, and the solution viscosity was 4100 centipoise. This precursor solution was spin-coated in the same manner as in Example 2, and then heat-treated in the same manner to form a polyimide layer. Comparative Example 4 The amount of purified N/N'-dimethylformamide used was 99.27 g, and the amount of pyromellitic dianhydride used was 21.8 g (0.1 g) as the aromatic tetracarboxylic dianhydride.
Example 1 except that 10.42 g (0.0965 mol) of para-phenylenediamine was used as the silicon-free diamine and 0.87 g (0.0035 mol) of bis(3-aminopropyl)tetramethyldisiloxane was used as the diaminosiloxane. A polymerization reaction was carried out in the same manner as above, and the silicon content was 0.594% by weight and the intrinsic viscosity was
1.58, a 25% by weight solution of the siloxane modified polyimide precursor was obtained with a solution viscosity of 1800000 centipoise. Next, as a heating aging step, the above precursor solution was heated and aged in the same manner as in Example 1 to reduce the molecular weight until the intrinsic viscosity was 0.39 and the solution viscosity was 1900 centipoise. This precursor solution was spin-coated onto a silicon wafer in the same manner as in Example 1, and then heat-treated to form a polyimide layer. Next, the above Examples 1 to 3 and Comparative Examples 1 to 4
The polyimide layer obtained was tested for adhesion and electrical insulation under the same environmental conditions. Furthermore, the coatability (state of the coating film) by spin coating when forming the polyimide layer was visually observed. These results were as shown in the following table. In addition, "B" in Examples 1 to 3 is the result of each example, and "A" is the high molecular weight obtained in the polymerization reaction step by omitting the heat aging step in each example for reference. , are the test results when a polyimide layer was formed by diluting a highly viscous siloxane-modified polyimide precursor solution with a solvent to the extent that it could be coated.

[Table] As is clear from the above table, according to the present invention, it has excellent applicability to the surface of substrates made of silicon-containing materials such as silicon wafers and glass, and can prevent cracks and
It is possible to form a polyimide layer that overcomes defects caused by paint film defects such as pinholes, has excellent adhesion, heat resistance, low stress properties, mechanical strength, and moisture resistance, thereby increasing the stable supply and reliability of semiconductor devices. It can be seen that it contributes to improving sexual performance. It is also clear that in Example 1, in which 3,3',4,4'-biphenyltetracarboxylic dianhydride is used as the aromatic tetracarboxylic dianhydride, the effect is particularly remarkable. It is. On the other hand, unlike this invention, in the case where heat treatment is not performed after the polymerization reaction ("A" in each example), the coating properties are poor, and the amount of diaminosiloxane used is small (Comparative Example 1) On the other hand, when the amount used is large (Comparative Examples 2 and 4), the adhesion is impaired or the moisture resistance is deteriorated, and even if the amount of diaminosiloxane used is within the range of this invention, diaminosiloxane and silicon-free diamine It can also be seen that when a method of separately reacting these with an aromatic tetracarboxylic dianhydride (Comparative Example 3), good results were not obtained in terms of adhesion, moisture resistance, etc. As another experiment, a siloxane-modified polyimide precursor having an intrinsic viscosity of 0.75 and a solution viscosity of 30,000 centipoise was prepared by changing the heat treatment time in the heating aging step in Example 1 to 6 hours, and using this, a polyimide layer was formed in the same manner as above. When formed, the properties of the coating film upon spin coating were improved to some extent, but some uneven thickness was observed and the coating properties were inferior to that of Example 1. Conversely, a siloxane-modified polyimide precursor with an intrinsic viscosity of 0.28 and a solution viscosity of 600 centipoise was created by setting the heat treatment time to 60 hours.
When a polyimide layer was formed using this, microcracks were generated in the polyimide layer because the molecular weight was too low, and the dielectric breakdown voltage decreased.

Claims (1)

[Claims] 1. In an inert solvent, the following general formula; (R ₁ is a divalent organic group, R′ is a monovalent organic group,
n is an integer from 1 to 1000) A diamino compound consisting of a diamino siloxane represented by the formula (n is an integer from 1 to 1000) and a diamine that does not contain a silicon atom in the molecule is combined with an aromatic tetracarboxylic dianhydride, and the diamino siloxane is the total amount of the diamino compound. 1 to 4
By conducting a polymerization reaction at a ratio of mol%,
A solution of a siloxane-modified polyimide precursor with a silicon content of 0.5% by weight or less was obtained, and this solution was heated at 40 to 80°C.
made of a silicon-containing material, characterized in that the precursor is heated and aged to lower the intrinsic viscosity of the precursor, and then this solution is applied to the surface of the substrate made of the silicon-containing material, and then heat-treated at a high temperature to form a polyimide layer. A method of forming a polyimide layer with good adhesion on the surface of a substrate.