JPH0259620B2 - - 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, heat-resistant polymers such as polyimide, polyamideimide, and polyhydantoin, which have many excellent advantages such as heat resistance, electrical insulation, and mechanical strength, have been used as protective films such as organic passivation films for semiconductor devices and junction protective films for diodes. The use of has been considered. However, these heat-resistant polymer films have a problem in that they have poor adhesion to the surface of a device such as a silicon wafer, and not only cannot stabilize the surface of the device, but also reduce the reliability of the semiconductor device. For this reason, various proposals have been made to improve the adhesion of the heat-resistant polymer membrane, one of which is to create a polyimide precursor using a polymerization reaction between an aromatic tetracarboxylic dianhydride and a diamino compound. There is a method of using diaminosiloxane as the diamino compound mentioned above when synthesizing the body. 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, it will not be possible to form a polyimide adhesive film or juncture. There was a drawback that the moisture resistance as a protective film was significantly impaired. Furthermore, excessive use of diaminosiloxane is not necessarily preferable in terms of heat resistance, electrical insulation, mechanical strength, etc. inherent to polyimide. Similarly, in the proposed method, there are polyimide precursors synthesized using an excessive amount of diaminosiloxane and polyimide precursors synthesized without using diaminosiloxane at all, that is, using diamines that do not contain silicon atoms in the molecule. There is also a method of making a mixture with the body, but even in this case, the same problem as mentioned above occurs because the silicon content is large in the mixture, and since it is a mixture, it has poor adhesion, moisture resistance, and other general problems. Characteristics tended to vary between lots, making it difficult to obtain stable performance. From the above points of view, the present invention provides a polyimide protective film that has excellent adhesion to the element surface and has good moisture resistance, and that this polyimide protective film has inherent heat resistance, electrical insulation, mechanical strength, etc. This discovery was made as a result of extensive research in order to obtain a siloxane-modified polyimide precursor that can be used as a siloxane-modified polyimide precursor. That is, the present invention provides the following general formula on the semiconductor element surface: (R ₁ is a divalent organic group, R′ is a monovalent organic group,
n is an integer from 1 to 1000) and a diamine that does not contain a silicon atom in the molecule are polymerized simultaneously with an aromatic tetracarboxylic dianhydride,
The use ratio of the above diamino siloxane is in the range of 1 to 4 mol% of the total amount of the diamino compound, and the silicon content contained in the final reaction product is 0.5% by weight.
The present invention relates to a method for forming a protective film for a semiconductor device, characterized in that a siloxane-modified polyimide precursor obtained as follows is coated and then subjected to high-temperature heat treatment to form a polyimide protective film. 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 discovered that there is no need to worry about damaging the 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 preferred 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'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfide, benzidine, benzidine-3,3'-dicarboxylic acid, benzidine- 3,3'-disulfonic 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 are as follows. Namely, pyromellitic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3・
3′・4′-biphenyltetracarboxylic dianhydride,
2.3.6.7-naphthalenetetracarboxylic dianhydride, 1.2.5.6-naphthalenetetracarboxylic dianhydride, 1.4.5.8-naphthalenetetracarboxylic dianhydride, 2. 2′-screw (3・4
-dicarboxyphenyl)propane dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)propane dianhydride, carboxyphenyl) 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,
Examples include 7,8-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 passivation film or a juncture protective film was greatly improved. be able to. Of course, the moisture resistance can be improved by using other dianhydrides, but when used as a passivation film, it is desirable to increase the thickness of the film. In this invention, it is necessary to simultaneously polymerize the diaminosiloxane and the silicon-free diamine with the aromatic tetracarboxylic dianhydride. For example, it is not possible to polymerize both diamino compounds separately and then mix them together. , resulting in variations in adhesion and moisture resistance, making it impossible to stabilize quality. Further, as mentioned above, the diaminosiloxane used at this time is 1 to 4 mol%, preferably 3 to 3.5 mol%, of the total amount of the diamino compound, and is contained in the polyimide precursor that is the final reactant. The silicon content must be 0.5% by weight or less. If none of 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 a conventionally known method, and is generally carried out in the presence of an organic solvent in a nitrogen gas stream while limiting the temperature to usually 60°C or less, preferably 30°C or less, taking into account the polymerization heat generated. The reaction may be carried out until a high degree of polymerization is obtained. This degree of polymerization can be easily detected by examining the intrinsic viscosity [η] of the reactant. Examples of organic solvents include N-methyl-2-
Pyrrolidone, N・N'-dimethylacetamide,
Highly polar basic solvents such as 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. As shown in the following general formula (4), the polyimide precursor obtained by the present invention has a silicon-free diamine and a diaminosiloxane bonded to each other via an amide bond. The bonding units added to the anhydride have a random polymer structure, and are characterized by having a structure in which very few siloxane bonds are incorporated into the molecular chain of the 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.) In the present invention, the polyimide precursor is coated on the surface of the semiconductor element, and then subjected to high-temperature heat treatment to dehydrate and ring the polyimide precursor. The above general formula (5) shows excellent adhesion to silicon wafers etc. by
A protective film made of polyimide as shown in 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. Demonstrates excellent performance as a juncture protective film. Note that the polyimide used as the organic passivation film must be protected from being contaminated by ionic impurities. Care must be taken to ^avoid contamination from cationic impurities such as Na ⁺ , K ⁺ , Ca ²⁺ , and anionic impurities such as Cl ^- ; adversely affects the electrical properties of Therefore, during polymerization, both the raw material monomer and the solvent should be sufficiently purified by well-known methods before use. For example, 5PPM or less, preferably 1PPM for Na ⁺ ions
The following is desirable. Examples of this invention will be described below. In the following, the intrinsic viscosity [η] will be used as a parameter indicating the degree of polymerization (molecular weight) of the polyimide precursor.
This intrinsic viscosity was measured using N-methyl-2-pyrrolidone as a solvent at a temperature of 30±0.01℃ (in a constant temperature bath).
It was calculated according to the following formula. [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; Polyimide precursor (polymer) concentration (0.5 wt. %) Example 1 A 500 ml flask equipped with a stirrer, condenser, thermometer and nitrogen purging device was fixed on a water bath.
280.90 g of purified N-methyl-2-pyrrolidone, which had been dried over phosphorus pentoxide for one day and then distilled under reduced pressure, was added to the flask, and nitrogen was flushed into the flask. Next, using a 1 ml microsyringe, 0.87 g (0.0035 mol) of bis(3-aminopropyl)tetramethyldisiloxane represented by the above formula A was added, followed by 19.3 g of 4,4'-diaminodiphenyl ether.
(0.0965 mol) and stirred until dissolved.
Next, 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 polyimide precursor obtained in this way is
Its intrinsic viscosity was 1.67 and silicon content was 0.397% by weight. A solution containing this precursor was spin-coated onto a silicon wafer and heated in a hot air dryer at 150°C for 1 hour, 200°C for 1 hour, and 250°C for 6 hours to form a polyimide protective film. In the infrared absorption spectrum of the polyimide protective film thus formed, >C=O absorption due to imide group formation was observed at 1780 cm ^-1 and 1720 cm ^-1 . The formed polyimide protective film was strong and had good adhesion to the silicon wafer under normal conditions. Also PCT
It was found that the adhesiveness was highly improved without peeling even after treatment. Example 2 Example except that 281.46 g of purified N-N'-dimethylacetamide was used as the solvent and 0.97 g (0.0035 mol) of bis(4-aminobutyl)tetramethyldisiloxane represented by the above formula B was used as the diaminosiloxane. A 15% by weight solution of the polyimide precursor was prepared in the same manner as in 1. The intrinsic viscosity of the polyimide precursor at this time is 1.81
and the silicon content was 0.396% by weight. Example 1 using the above polyimide precursor solution
When a polyimide protective film was formed on a silicon wafer under the same conditions as in Example 1, the toughness and adhesion of the protective film were the same as in Example 1. Example 3 The amount of purified N-methyl-2-pyrrolidone used
A 15% by weight solution of the polyimide precursor was prepared 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. The polyimide precursor thus obtained had an intrinsic viscosity of 1.65 and a silicon content of 0.469% by weight. A solution containing this precursor was spin coated in the same manner as in Example 1, and then dried in a hot air dryer at 150°C for 1 hour.
A polyimide protective film was formed by heating at 200°C for 1 hour and at 300°C for 1 hour. The formed polyimide protective film was strong, had good adhesion both under normal conditions and by PCT, and no peeling from the silicon wafer was observed. Example 4 The amount of purified N-methyl-2-pyrrolidone used
295.67 g, 32.2 g (0.1 mol) of 3,3',4,4'-benzophenonetetracarboxylic dianhydride as aromatic tetracarboxylic dianhydride, and 4,4' as silicon-free diamine. A 15% by weight solution of a polyimide precursor having an intrinsic viscosity of 1.38 and a silicon content of 0.377% by weight was prepared in the same manner as in Example 1, except that 19.107 g (0.0965 mol) of -diaminodiphenylmethane was used. Example 1 using the above polyimide precursor solution
When a polyimide protective film was formed on a silicon wafer under the same conditions as in Example 1, the adhesion of the protective film was the same as in Example 1, but the tensile strength decreased to 40% of the initial value after 6 months. It was recognized that he had done so. Although it was found that the toughness of the protective film deteriorated over time, it was strong enough to be used as a passivation film. Example 5 The amount of purified N-methyl-2-pyrrolidone used
259.36 g, 14.7 g (0.05 mol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 10.9 g (0.05 mol) of pyromellitic dianhydride as aromatic tetracarboxylic dianhydride. Polyimide precursor 15 was prepared in the same manner as in Example 1 except that
A wt% solution was made. The intrinsic viscosity of the obtained polyimide precursor is 1.52
And the silicon content was 0.430% by weight. Example 3 using the above polyimide precursor solution
When a polyimide protective film was formed on a silicon wafer in the same manner as in Example 1, the toughness and adhesion of the protective film were the same as in Example 1. Comparative Example 1 The amount of purified N-methyl-2-pyrrolidone used was
280.07 g, the amount of 4,4'-diaminodiphenyl ether used was 19.9 g (0.0995 mol), and the amount of bis(3-aminopropyl)tetramethyldisiloxane used was 0.1243 g (0.0005 mol). A 15% by weight solution of a polyimide precursor having an intrinsic viscosity of 2.37 and a silicon content of 0.057% by weight was prepared in the same manner as in Example 1. When a polyimide protective film was formed on a silicon wafer using this solution under the same conditions as in Example 1, it did not peel off from the silicon wafer under normal conditions, but it peeled off easily with PCT. Comparative example 2 The amount of purified N-methyl-2-pyrrolidone used
281.86 g, the amount of 4,4'-diaminodiphenyl ether used was 18.6 g (0.093 mol), and the amount of bis(3-aminopropyl)tetramethyldisiloxane used was 1.7395 g (0.007 mol). A 15% by weight solution of the polyimide precursor was prepared in the same manner as in Example 1. The polyimide precursor thus obtained had an intrinsic viscosity of 0.80, and had a lower molecular weight than the polyimide precursor obtained in Example 1. Further, the silicon content of this precursor was 0.791% by weight. When a polyimide protective film was formed on a silicon wafer using the polyimide precursor thus obtained under the same conditions as in Example 1, the toughness and adhesion of the protective film were the same as in Example 1. It was hot. 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 3, and then both were mixed. A 15% 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. When a polyimide protective film was formed on a silicon wafer using this solution under the same conditions as in Example 3, the adhesion to the silicon wafer was inferior to that in Example 3, and the properties tended to vary and could easily be used with PCT. There were cases where it peeled off. Comparative example 4 The amount of purified N-methyl-2-pyrrolidone used
187.52 g, 21.8 g (0.1 mol) of pyromellitic dianhydride as the aromatic tetracarboxylic dianhydride, 10.42 g (0.0965 mol) of para-phenylene diamine as the silicon-free diamine, and bis(3 A 15% by weight solution of the polyimide precursor was prepared in the same manner as in Example 1, except that 0.87 g (0.0035 mol) of (aminopropyl)tetramethyldisiloxane was used. The intrinsic viscosity of this polyimide precursor was 1.58, and its silicon content was 0.594% by weight. When a polyimide protective film was formed on a silicon wafer using the polyimide precursor solution thus obtained in the same manner as in Example 1, the adhesion of the protective film was the same as in Example 1. Next, the above Examples 1 to 5 and Comparative Examples 1 to 4
Each polyimide protective film obtained in the above was tested for adhesion and electrical insulation under the same environmental conditions. The results were as shown in the following table. The thickness of each polyimide protective film is
It was adjusted to 50±5μ.

[Table] As is clear from the above table, it can be seen that the polyimide protective films according to Examples 1 to 5 of the present invention have excellent electrical properties and adhesion at high temperature and high humidity. Further, in particular, Examples 1 and 2 using 3,3',4,4'-biphenyltetracarboxylic dianhydride as the aromatic tetracarboxylic dianhydride.
It can also be seen that, compared to Examples 3 to 5 in which other dianhydrides were used, both of the above properties, especially the electrical properties at high temperature and high humidity, were significantly superior. On the other hand, the polyimide protective film formed in Comparative Example 1 was not inferior in electrical properties, but was inferior in adhesiveness to the silicon wafer. In addition, Comparative Example 2,
Although the polyimide protective film formed from Example 4 does not have much problem in adhesion, it has inferior electrical properties under high temperature and high humidity. The measured resistivity was approximately 1/100. Comparative Example 3 is a polyimide protective film formed from a mixed solution of a silicon-free polyimide precursor and a silicon-containing polyimide precursor, but in this case, the total silicon content is within the range of the present invention. However, it can be seen that good results were not obtained in terms of adhesion and electrical properties under high temperature and high humidity conditions.

Claims (1)

[Claims] 1. On the semiconductor element surface, 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) and a diamine that does not contain a silicon atom in the molecule are polymerized simultaneously with an aromatic tetracarboxylic dianhydride,
The use ratio of the above diamino siloxane is in the range of 1 to 4 mol% of the total amount of the diamino compound, and the silicon content contained in the final reaction product is 0.5% by weight.
1. A method for forming a protective film for a semiconductor device, which comprises applying a siloxane-modified polyimide precursor obtained as follows, followed by high-temperature heat treatment to form a polyimide protective film.