JPH0259622B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of forming a protective film for a semiconductor element. Conventionally, the surface protection film (passivation film) of semiconductor elements has been developed using CVD (Chemical Vapor
Although the use of silicon dioxide has been considered using methods such as deposition (deposition) method, its application to semiconductors has been delayed because thin silicon dioxide films have drawbacks such as being prone to cracks and having many pinholes. There is. In recent years, heat-resistant polymers, particularly polyimide, have been attracting attention in this field as a new material to replace the above-mentioned silicon dioxide film. In other words, this heat-resistant polymer has sufficient heat resistance to withstand wire bonding, and also 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. On the other hand, the diode juncture protective film is
Conventionally, silicone rubber, silicone varnish, etc. have been used to protect the P-N junction surface (junction) of semiconductor devices, but silicone compounds are generally permeable to water and are not suitable for semiconductor devices. When comprehensively evaluated, a decrease in reliability was unavoidable in terms of moisture resistance. In recent years, heat-resistant polymers such as polyimide, which themselves have excellent moisture resistance, have been used for this junction protective film. As described above, heat-resistant polymers, mainly polyimide, are being considered as protective films for various semiconductor processing, but these types of heat-resistant polymers have a high adhesion to device surfaces such as silicon wafers. It has the disadvantage that it is inferior in quality and difficult to adhere to, and as a result, the reliability of semiconductor devices has not been satisfactory. For this reason, various proposals have been made to improve the adhesion of the above-mentioned heat-resistant polymers, and one of them is to create a polyimide precursor using a polymerization reaction between an aromatic tetracarboxylic dianhydride and a diamino compound. When synthesizing, there is a method of using diaminosiloxane as the above diamino compound. This method introduces Si-O-Si bonds derived from diaminosiloxane into the molecular skeleton, and this bond creates a chemical bond between the silicon atoms of the silicon-containing material that makes up silicon wafers, etc. 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 it is possible to improve the adhesion, the moisture resistance of the polyimide protective film will be greatly affected. There is a problem of damage. 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. There is also a method of using a mixture as a mixture, but even in this case, the silicon content in the mixture is large, causing the same problems as mentioned above, 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 protective film. In view of the above, the present invention provides a polyimide protective film that exhibits a viscosity that allows coating in a highly concentrated state, has excellent adhesion to the element surface, 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 properties such as 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.
A method for forming a protective film for a semiconductor device, which method comprises heating and aging the precursor to lower the intrinsic viscosity of the precursor, applying this solution to the surface of the semiconductor device, and then applying high-temperature heat treatment to form a polyimide protective film. This is related. As described above, in this invention, the diaminosiloxane used to improve the adhesion of the polyimide protective film is necessary and sufficient within the above specified range, and when used in such a proportion, the diaminosiloxane is used to improve the adhesion of the polyimide protective film. Since the number of siloxane bonds that are easily broken by wet thermal decomposition or acids or alkalis is extremely small, the moisture resistance properties of the polyimide protective film are not reduced, and polyimide's inherent heat resistance, electrical insulation, and mechanical strength are maintained. It has been found that there is no need to worry about damaging such things. 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. It is possible to obtain a solution viscosity that can be coated with a polyimide protective film, and when a solution of high concentration and low viscosity is obtained by this method, it not only has excellent adhesion and moisture resistance properties as a polyimide protective film achieved by the above method. about,
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 not containing a silicon _atom ) These include aromatic diamines, aliphatic diamines, and alicyclic diamines represented by It may be the same as or different from R ₁ of . 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'-disulfonic acid, benzidine-3-monocarboxylic acid, benzidine-3-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 with excellent electrical properties, in other words extremely good moisture resistance, was obtained through the 2-atm pressure pressure test (hereinafter simply referred to as PCT), and its performance as a surface protective film or junction protective film was greatly improved. can be done. Of course, it is possible to improve the moisture resistance properties by using other dianhydrides, but it is desirable to increase the thickness of the film when it is used as a passivation film. 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. Note that the polyimide used as a protective film on the surface of the semiconductor element 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 can affect the electrical properties of the polyimide protective film. Adversely affect. 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 film 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 element surface such as a silicon wafer by the above coating method, and then subjected to high temperature heat treatment, dehydrated and cyclized, thereby achieving excellent adhesion to the silicon wafer etc. It is possible to form a protective film made of polyimide as represented by the above-mentioned general formula (5) which exhibits properties.
This polyimide protective film has excellent moisture resistance, as well as excellent heat resistance, chemical resistance, mechanical properties, and excellent electrical insulation properties, and is used as a surface protective film for semiconductor devices and diodes. Demonstrates excellent performance as a juncture protective film. 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) tetramethylenedisiloxane (diaminosiloxane of formula A above) 0.87g
(0.0035 mol) and then 19.3 g (0.0965 mol) of 4,4'-diaminodiphenyl ether were charged and stirred until dissolved. Thereafter, 29.4 g (0.1
mol) was added gradually. 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 thus obtained has a viscosity (hereinafter the same) measured using a BH type viscometer at 25°C that is at least the upper measurement 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, in the heating and aging process, 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.
A tough polyimide surface protection film (passivation film) was formed by heat treatment at 250°C for 6 hours. In the infrared absorption spectrum of this polyimide protective film, >C=O absorption due to imide group formation was observed at 1780 cm ^-1 and 1720 cm ^-1 . The spin coating was performed by dropping 2 to 3 g of the precursor solution at a rotation 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 tough polyimide surface protective film 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. This precursor solution was applied to silicon wafer devices (P-N
A junction protective film made of polyimide was formed by brush coating and heat treatment on the joint surface (bonding surface). Although the tensile strength of this protective film decreased to 40% of the initial value after 6 months, it was still strong enough to be used as a junction protective film. 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 surface protective film. Comparative Example 2 The amount of purified N/N'-dimethylformamide used was 149.22 g, the amount of 4,4'-diaminophel ether used was 18.6 g (0.093 mol), and the amount of bis(3-aminopropyl)tetramethyldisiloxane was used. quantity
Example 1 except that it was 1.7395 g (0.007 mol)
Carry out a polymerization reaction in the same manner as above to reduce the silicon content.
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 surface protective film. 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 surface protective film. 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 heat-ripening step, the above precursor solution was heat-ripened in the same manner as in Example 1 to lower 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 surface protective film. Next, the above Examples 1 to 3 and Comparative Examples 1 to 4
The polyimide protective film obtained was tested for adhesion and electrical insulation under the same environmental conditions. Moreover, the applicability (state of the coating film) when forming the polyimide protective film 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 protective film 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, the present invention has excellent coating properties on device surfaces such as silicon wafers, can overcome defects caused by coating film defects such as cracks and pinholes, and has excellent adhesion and It can be seen that a polyimide protective film with excellent heat resistance, low stress properties, mechanical strength, and moisture resistance can be formed, contributing to the stable supply and reliability improvement of semiconductor devices. In addition, in this invention, the aromatic tetracarboxylic dianhydride is 3,3',4,4'-
It is also clear that the effect is particularly remarkable in Example 1 using biphenyltetracarboxylic dianhydride. 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 protective film was formed in the same manner as above. After forming the
Although the properties of the coating film during spin coating were improved to some extent, some uneven thickness was observed and the coating properties were inferior to those of Example 1. Conversely, the heat treatment time
When a siloxane-modified polyimide precursor with an intrinsic viscosity of 0.28 and a solution viscosity of 600 centipoise was made for 60 hours and a polyimide protective film was formed using this, microcracks occurred in the protective film because the molecular weight had been reduced too much, resulting in insulation failure. The breakdown voltage decreased, and the film could not exhibit its performance as a semiconductor surface protective film or junction protective film.

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.
A method for forming a protective film for a semiconductor element, comprising: reducing the intrinsic viscosity of the precursor by heating and aging the precursor, and then applying this solution to the surface of the semiconductor element, followed by high-temperature heat treatment to form a polyimide protective film.