JPS59107523A - Method for formation of protective film on semiconductor element - Google Patents

Abstract

PURPOSE:To enable to form a polyimide protective film of excellent close-contacting and dampproof characteristics by a method wherein a specific ratio of diaminosiloxane and non-silicon containing diamine are simultaneously polymerization-reacted with aromatic titracarboxylic acid dianhydride. CONSTITUTION:The diamino compound, consisting of the diaminosiloxane indicated in general formula I and the diamine containing no silicon atom in a molecule, is polymerization-reacted with aromatic tetracarboxylic acid dianhydride. In ths case, a solution of siloxane denatured polyimide precursor, having silicon content of 0.5wt% or below, is obtained by performing a polymerization reaction using the ratio wherein diaminosiloxane will be brought to 1-4mol% the total diamino compound. The intrinsic viscosity of the precursor is reduced by ripening with heat at 40-80 deg.C, and after application of said solution on the surface of a semiconductor element, a polyimide protection film is formed by performing a high temperature heat treatment. As a result, a polyimide protection film of excellent close-contacting and dampproof properties can be formed.

Description

[Detailed description of the invention] The present invention relates to a method for forming a protective film for a semiconductor element.

Since then, surface protection film for semiconductor devices (panoscination film)
is CVD (Chemical Vapor De
The use of silicon dioxide has been considered using methods such as the position method, but thin silicon dioxide films have drawbacks such as being prone to cracking and having many pinholes, which has delayed its application to semiconductors. There is. In recent years, new materials have been introduced in this field as an alternative to the silicon dioxide film mentioned above.
Heat-resistant polymers, especially polyimides, are attracting attention. In other words, this heat-resistant polymer has sufficient heat resistance to withstand wire bonding, and also has many outstanding advantages such as excellent electrical insulation, low stress strain, and mechanical strength, and can be made into a thick film. It is an organic material that is attracting attention because it does not cause cranking even when it is in use, and it suppresses pinball.

On the other hand, silicon rubber, silicon wafer, etc. have traditionally been used as junction protective films for diodes, and they have the function of protecting the P-N junction surface (junction) of semiconductor elements, but silicon compounds are generally resistant to water. It is essentially transparent, and when evaluating semiconductors comprehensively,
In terms of moisture resistance, a decrease in reliability could not be avoided. In recent years, heat-resistant polymers such as polyimide, which themselves have excellent moisture resistance, have been used for this junction protective film.

In this way, 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 a 5i-0-3i bond derived from diaminosiloxane into the molecular skeleton, and this bond forms a chemical bond between it and the silicon atom of the silicon-containing material constituting the silicon wafer. The purpose is to improve adhesion by holding the hand and using this as an active site for adhesion to the silicon-containing material.

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. Further, excessive use of diaminosiloxane was 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, 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, the adhesion, moisture resistance, and other general properties are poor. It was not possible to obtain stable performance due to the easy variation between the two.

On the other hand, this kind of siloxane-modified polyimide precursor is desired to be a high molecular weight material with high intrinsic viscosity due to heat resistance and other general properties, but in this case, it is desirable to make it a high molecular weight material with high intrinsic viscosity. 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 cording, dipping or brushing, considerable further dilution is required after the polymerization reaction. Such a dilution operation causes variations in solution viscosity between manufacturing lofts and complicates the coating process, and also causes uneven thickness of the formed coating film due to a significant decrease in solid content concentration. This results in a negative 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 good adhesion to the wide surface of an element, 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 possesses the original heat resistance, electrical insulation, and mechanical strength.

That is, this invention provides the following general formula in an inert solvent: (R+ is a divalent organic group, R' is a monovalent organic group,
n is an integer from 1 to 1,000) and a diamine that does not contain a silicon atom in the molecule. By carrying out a polymerization reaction at a ratio of 1 to 4 mol% of the total amount, a solution of a siloxane-modified polyimide precursor with a silicon content of 0.5% by weight or less is obtained, and this solution is heated and aged at 40 to 80°C. A method for forming a protective film for a semiconductor element, which comprises: reducing the intrinsic viscosity of the precursor, applying this solution to two surfaces of the semiconductor element, and then subjecting it to high-temperature heat treatment to form a polyimide protective film. It is.

Thus, in this invention, the above-mentioned specific range of diaminosiloxane used to improve the adhesion of the polyimide protective film is necessary and sufficient. Since the siloxane bonding portion, which is easily broken by thermal decomposition or acid or alkali, is extremely small, the moisture resistance of the polyimide protective film is not deteriorated, and polyimide's inherent heat resistance, electrical insulation, and mechanical properties are maintained. It was discovered that there is no need to worry about loss of strength.

On the other hand, a siloxane-modified polyimide precursor synthesized using diaminosiloxane in the above-mentioned ratio is 1. If left as is, it has the disadvantage of high solution viscosity, similar to conventional precursors. 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 it is then possible to coat the polyimide precursor solution without diluting it with a solvent. not to mention the excellent adhesion and moisture-resistance properties of the polyimide overcoat achieved by the above means, when obtained in this manner as solutions of high concentration and low viscosity. 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, the two R1s and each R' in the formula may be the same or different, and a wide variety of conventionally known diaminosiloxanes are included. Typical examples are as follows.

Diamine that does not contain a silicon atom in the molecule used in the invention of (hereinafter simply referred to as silicon-free diamine)
is an aromatic diamine or an aliphatic diamine represented by the following general formula (2) Diamines and alicyclic diamines are included, and R2 in the formula may be the same as or different from R in the general formula (1). Particularly preferred are aromatic diamines, representative examples of which include meta-phenylene diamine, para-phenylene diamine, 4,4'-diaminodiphenylmethane,
4,4'-diaminodiphenyl ether, 2,2'-bis(4-aminophenyl)propane, 3,3'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenyl sulfite ,
henzidine, henzidine-3,3'-dicarboxylic acid, henzidine-3,3'-disulfonic acid, benzidine-3-
Monocarboxylic acid, benzidine-3-monosulfonic acid, 3
-3'-dimethoxyhenzidine, para-bis(4-aminophenoxy)benzene, meta-bis(4-aminophenoquine)benzene, metaxylylenediamine, paraquinlylenediamine, and the like.

In this invention, the aromatic tetracarboxylic dianhydride polymerized with the diamino compound consisting of the above diaminosiloxane and silicon-free diamine has the following general formula (3); % formula % (Ar is a tetravalent organic group Typical examples include pyromellitic dianhydride, 3, 3', 4, 4
'-henzuphenonetetracarboxylic dianhydride, 3.3
゛・4・4′-biphenyltetracarboxylic dianhydride,
2,3,3',4'-biphenyltetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, ■,2,5,6~naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,2゛-bis(3,4-dicarboxyphenyl)propananhydride, bis(3,4-dicarboxyphenyl)sulfonic dianhydride, 3・4,9,1O-perylenetetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, 2,2゛-bis(2,3-dical-1-diphenyl)propanide dianhydride , 1,1'-bis(2,3-dicarboxyphenyl)
Ethannianhydride, benzene-1,2,3,4-tetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride There are anhydrous substances.

Aromatic tetracarboxylic acid diss especially suitable for this invention
Water t+ is 3,3',4,4'-biphenyltetracarboxylic dianhydride. When this dianhydride is used, the electrical properties of the pressure tester test (hereinafter simply referred to as PCT) under a high-temperature atmosphere, for example, 121°C and 12 atmospheres, are very low. can be obtained, and the performance as a surface protection film or a junction/protection film can be greatly improved. 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 applied as a panosylon film.

In this invention, it is necessary to simultaneously polymerize the diaminosiloxane and the silicon-uncombined diamine with the aromatic tetracarboxylic dianhydride. This results in variations in moisture resistance and moisture resistance, making it impossible to stabilize quality.

As mentioned above, the diaminosiloxane used in this polymerization reaction is 1 to 4 mol% of the total amount of diamino compounds.
, preferably 3 to 3.5 mol%, and the amount used must be set so that the silicon content contained in the obtained siloxane-modified polyimide precursor is 0.5% by weight or less. Must be. Unless these quantitative relationships are satisfied, it becomes difficult to achieve both adhesion and moisture resistance. The ratio of the diamino compound consisting of the diaminosiloxane and the silicon-free diamine to the aromatic tetracarboxylic dianhydride is usually equimolar, but if necessary, one may be slightly increased.

The polymerization reaction may be carried out according to conventionally known methods, and is generally limited to 40°C or less, preferably 30°C or less, in the presence of an inert solvent, with nitrogen gas flowing out, and in consideration of polymerization heat generation. The reaction may be carried out until a predetermined degree of polymerization is obtained.

Note that polyimide as a protective film on the surface of a semiconductor element is
Contamination with ionic impurities must be avoided. Care must be taken to avoid contamination from cationic impurities such as Na'', K'', Ca'', and anionic impurities such as Cβ-, and in particular Na' ions affect the electrical properties of the polyimide protective film. Therefore, during polymerization, both the raw material monomer and the solvent should be sufficiently purified by well-known methods before use.

For example, pJa' ion is 5 PPM or less, preferably IPI
) M or less is desirable.

The inert solvent used in such a polymerization reaction is
For example, N-methyl-2-pyrrolidone, N-N'-dimethylacetamide, N-N'-dimethylpol broadamide,
Highly polar basic solvents such as N-N'-dimethylsulfoxide and hexamethylphosphoramide are used. All of these types of solvents are highly hygroscopic (absorbed water causes a decrease in molecular weight during polymerization and a decrease in storage stability, so be sure to thoroughly dehydrate with a dehydrating agent before use). Good.

In addition, general-purpose solvents such as toluene, 4-lune, hendinitrile, henzene, and phenol can also be used in combination 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 degree of polymerization is as high as 3 to 3.0. 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 measured using N-methyl-2-pyrrolidone as a solvent and at a measurement temperature of 30
It means the value calculated according to the following formula at ±0.01°C (constant temperature bath).

[η) = Iln (t/t o) /ct; 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 (0.5% by weight and In the present invention, following the above polymerization reaction step, heating .mu.m formation is carried out in the same reaction vessel in a nitrogen stream by raising the temperature to 40 to 80 DEG C., preferably 50 to 60 DEG 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, when the solution concentration is 25, the viscosity of the solution is i, o o
It is about 0 to 20,000 centivoise. 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 when used in semiconductors will be impaired.

The reason why the heat aging temperature was set at 40 to 80°C is that at temperatures exceeding 80°C, especially at temperatures above 100'C, the crosslinking reaction proceeds and there is a risk of gelation. This is because the effect of microorganism (μ) cannot be obtained sufficiently and the ripening time becomes long, impairing workability.

Even though 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 units of diaminosiloxane and aromatic tetracarboxylic dianhydride added to aromatic tetracarboxylic dianhydride via amide bonds have a polymer structure that is random, and the molecular chain of this polyimide precursor has very few It is characterized by having a slightly integrated structure.

(R+, , Rz, R', n and Ar are m as described above.
/j! +m=0.01 to 0.04) (R1, R
(2, R', Ar, n, R, and rn are as described above)) Such a siloxane-modified polyimide precursor has a low solution viscosity, and for example, when the concentration in the polymerization reaction step is 20
Even when the content is 25% by weight or more, it has a viscosity suitable for spin cording, dipping, brushing, etc., even if it is not diluted after the heat aging process.

In this invention, the above precursor solution is coated on the element surface such as a silicon wafer by the above coating method, and then subjected to high temperature heat treatment, dehydrated and cyclized, so that it does not splatter on the silicon wafer etc. The above general formula (
A protective film made of polyimide as shown in 5) can be formed.

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. Demonstrates excellent performance as a diode junction protective film.

EXAMPLES Below, examples of the present invention will be described in more detail.

Example 1 A 500 mm flask equipped with a stirrer, a condenser, a thermometer, and a nitrogen purging device was fixed on a water bath. The N-
1.48.71 g of N'-dimethylformamide was added into the flask, nitrogen was introduced into the flask, and a polymerization reaction was carried out in the following manner.

First of all, 1m7! 0.87 g (0°003
5 mol) and then 19.3 g (0,0965 mol) of 4,4'-diaminodipheniether were added and stirred until dissolved. Then, 29.4 g (0.1 mol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride
was added gradually. Clear viscosity while keeping the reaction system below 30°C? The 25% by weight solution of the siloxane-modified polyimide precursor thus obtained has a viscosity (the same applies hereinafter) measured with a 25° CBH type viscometer that is the upper limit of measurement. (2,000,
000 centipoise) or more, the intrinsic viscosity of the precursor was 1.67, and the silicon content was 0.397% by weight.

Next, as a heat aging step, the water bath was removed and replaced with a hot water bath, the same reaction vessel was heated and stirred at 55±5°C, heated and aged in a nitrogen stream for 6 hours, and then heated for an additional 28 hours, for a total of 34 hours. By aging, the intrinsic viscosity becomes 0.
42, the molecular weight was lowered until the solution viscosity reached 47,400 centivoids.

Spin code this precursor solution onto a silicon wafer,
1 hour at 150°C in a hot air dryer, 1 hour at 200°C,
Heat treated at 250°C for 6 hours to protect the tough polyimide surface If! (vansivation film) was formed. The infrared absorption spectrum of this polyimide protective film is 1,780
cm-' and 1,720 cm-', <>C=O absorption was observed due to imide group formation. The above spin code was performed by dropping 2 to 3 g of the precursor solution at a rotation speed of 3,500 rpm.

Example 2 The amount of purified N-N'-dimethylformamide used was 125
．． The polymerization reaction was carried out in the same manner as in Example 1, except that 21.8 g (0.1 mol) of pyromellitic dianhydride was used as the aromatic tetracarboxylic dianhydride, and the silicon content was 0.91 g. A 25% by weight solution of a siloxane-modified polyimide precursor having a high molecular weight of Tipoise or higher 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, so that the intrinsic viscosity was 0.38 and the solution viscosity was 2.2.
The molecular weight was reduced to 0.00 centivoids.

This precursor solution was spin-coded onto a silicon wafer in the same manner as in Example 1, and dried at 150°C for 1 hour in a hot air dryer.
A tough polyimide surface protective film was formed by heat treatment at 200°C for 1 hour and at 300°C for 1 hour.

Example 3 The amount of purified N-N'-dimethylformamide used was 156
．． 53 g, 32.2 g (0.1 mol) of 3,3',4,4'-henzuphenone tetracarboxylic dianhydride as aromatic tetracarboxylic dianhydride, and 4. 4'-Diaminodiphenylmethane 19.1
A polymerization reaction was carried out in the same manner as in Example 1, except that 0.07 g (0.0965 mol) was used, and the silicon content was 0.07 g (0.0965 mol).
377% by weight intrinsic viscosity is 1.38, solution viscosity is 1.7
A 25% by weight solution of a high molecular weight siloxane-modified polyimide precursor with 00,000 centivoids was obtained.

Next, as a heating aging step, the above precursor solution was heated and aged for 15 hours at 55±5'c in the same manner as in Example 1, so that the intrinsic viscosity was 0°45 and the solution viscosity was 2. The molecular weight was reduced to 300 centimeter voice.

This precursor solution was coated onto the silicon wafer element (1)--N junction surface) and then heated to form a junction retention gI film made of polyimide. This protective film is
Although the tensile strength after 6 months had decreased to 40% of the initial value, 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.
27g, the amount of 4,4'-diaminodiphenyl ether used was 19.9g (0,0995 mol), and the amount of )bis(3-aminopropyl)tetramethyldisiloxane used was 0.
．． The polymerization reaction was carried out in the same manner as in Example 1, except that the amount was 1243 g (0,0035 mol). ,000,000 centivoice high molecular weight siloxane modification; l? A 25% solution of IJ imide precursor was obtained.

Next, in the heating step, the above precursor solution was heated and aged in the same manner as in Example 1, and the intrinsic viscosity was 0.41. The s-liquid viscosity was reduced to a low molecular weight (2) until the viscosity reached 2,700 centivoids. This precursor solution was spin-coated on a silicon wafer in the same manner as in Example 1, and then heated to form a polyimide surface protective film.

Comparative Example 2 The amount of purified N'N'-dimethylbormamide used was 149.22 g, the amount of 4,4'-diaminopher ether used was 18.6 g (0,093 mol), and the amount of bis(3
- Use of (aminopropyl)tetramethyldisiloxane■
Except that it was set to 1.7395g (0,007 mol),
A polymerization reaction was carried out in the same manner as in Example 1 to prepare a 25% by weight solution of a siloxane-modified polyimide precursor having a silicon content of 0.791% by weight, an intrinsic viscosity of 0°80, and a solution viscosity of 50,000 centivoids. Obtained.

Next, in the heating W) formation step, the above precursor solution is heated and aged in the same manner as in Example 1 to lower the molecular weight until the intrinsic viscosity becomes 0.45 and the solution viscosity becomes 5,100 centivoise. did. This precursor solution was spin-coded 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 in Example 2
After carrying out a polymerization reaction with pyromellitic dianhydride separately in the same proportion as , the two were mixed to obtain a 25% by weight solution of a polyimide precursor mixture. 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 200. The silicon content in the Boliimi 1-precursor mixture was 0.469% by weight, and the solution viscosity was at the upper limit of measurement (2,00o
, o o o centiboise).

Next, the above solution was further heated in the same manner as in Example 1 to reduce the molecular weight until the intrinsic viscosity was 0.53 and the solution viscosity was 4,100 centiboise. 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'-dimethylpolamide used was 99.
27 g, 21.8 g (0.1 mol) of pyromellitic dianhydride as aromatic tetracarboxylic dianhydride,
Parafated nylene diamine is used as a silicon-free diamine.
Polymerization reaction was carried out in the same manner as in Example 1, except that 0.42 g (0,0965 mol) and 0.87 g (0,0035 mol) of bis(3-aminopropyl)tetra,methyldisiloxane were used as diaminosiloxane. The silicon content was 0.594% by weight, the intrinsic viscosity was 1.58,
A 25% by weight solution of a siloxane-modified polyimide precursor having a solution viscosity of 1.8 o o and o o o centiboise was obtained.

Next, as a heat-ripening step, the above precursor 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 1,900 centipoise. . This precursor 't8? (fr,
After spin-coding was performed on a La7 silicon wafer in the same manner as in Example 1, a polyimide surface protection film was formed by further heat treatment.

Next, the polyimide protective films obtained in Examples 1 to 3 and 1L Comparative Examples 1 to 4 were 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, rBJ in Examples 1 to 3 is the result of each example, and rAJ is the high molecular weight obtained in the polymerization reaction step by omitting the heat aging step in each example for reference.
These are 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.

As is clear from the above table, the present invention has excellent coating properties on device surfaces such as silicon wafers, and can overcome defects caused by coating film defects such as cracks and pinholes.
It can be seen that a polyimide protective film with excellent adhesion, heat resistance, low stress, mechanical strength, and moisture resistance can be formed, contributing to stable supply of semiconductor devices and improved reliability. It is also clear that the effect is particularly remarkable in Example 1 in which 3,3',4,4'-biphenyltetracarboxylic dianhydride is used as the aromatic tetracarboxylic dianhydride in this invention. be.

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, the amount used is large (Comparative Example 2.4)
However, the adhesion may be impaired or the moisture resistance properties may be deteriorated, and even if the amount of diaminosiloxane used is within the range of this invention, diaminosiloxane and silicon-free diamine must be reacted separately with aromatic tetracarboxylic dianhydride. It can also be seen that when the method (Comparative Example 3) is adopted, good results cannot be obtained in terms of adhesion, moisture resistance, etc.

Claims (1)

[Claims] (11 In an inert solvent, the following general formula; (R, is a divalent organic group, R' is a monovalent organic group, n
is an integer from 1 to 1,000) and a diamine that does not contain a silicon atom in the molecule. By carrying out a polymerization reaction at a ratio of 1 to 4 mol% of the amount,
A solution of a siloxane-modified polyimide precursor having a silicon content of 0.5% by weight or less is obtained, this solution is heated and aged at 40 to 80°C to lower the intrinsic viscosity of the precursor, and then this solution is applied to the surface of a semiconductor element. 1. A method for forming a protective film for a semiconductor device, which comprises applying a polyimide protective film to a polyimide film and then subjecting the film to high-temperature heat treatment to form a polyimide protective film.