JPS63199236A - Low-stress and heat-resistant resin - Google Patents

Abstract

PURPOSE:To obtain a low-stress and heat-resistant resin, having a specific chemical structure, excellent heat resistance and mechanical strength as well as low thermal expansion coefficient and suitable as electrical and electronic materials. CONSTITUTION:A polyimide resin, obtained by synthesizing a polyamic acid (derivative) from a tetracarboxylic acid (derivative) and a diamine (derivative) and carrying out processing, such as coating, molding, film forming, etc., using the above-mentioned polyamic acid (derivative) and thermosetting the processed material to carry out imidation and containing 60-90mol.% unit structure expressed by formula I (n is 0 or 2) and 10-40mol.% unit structure expressed by formula II (m is 0 or 2).

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a polyimide resin having a specific chemical structure, which has high heat resistance, good mechanical strength, and low coefficient of thermal expansion suitable for electrical and electronic materials. This provides a useful new material that has the following properties.

[Conventional technology]

The thermal expansion coefficient (linear expansion coefficient) of most organic polymers is 4, even in the temperature range below the glass transition temperature.
X10' or more, and has a much larger value than metals and inorganic materials. Many problems arise due to the large linear expansion coefficient of organic materials. In other words, this is the reason why the development of applications for organic polymers is not progressing as expected. For example, even in the case of polyimide resin, which has extremely high heat resistance and has recently begun to be used as a protective film for LSIs and ICs, if it is applied to a metal plate or arbor material whose coefficient of thermal expansion is smaller than that of polyimide, the coefficient of expansion will decrease. Thermal stress caused by the difference in the On the other hand, there are problems such as not being able to perform photolithography for patterning, or extremely poor resolution, and problems such as peeling off the passivation film or causing cracking of the silicon wafer itself if the thermal stress is too large. There's a problem.

In addition, for flexible printed circuit boards (FPC) consisting of a film and a conductor, it is desirable to have a metal foil coated with a flexible film material or bonded by heat and pressure. Since thermocompression bonding is required, there is a problem in that the material curls due to thermal stress caused by a difference in thermal expansion coefficients after cooling to room temperature.

As described above, there are many problems due to the large coefficient of linear expansion of organic polymers, and there has been a strong desire for a long time to develop a polyimide resin having a low coefficient of expansion that improves these problems.

Under these circumstances, several polyimides having low expansion coefficients have recently been announced.

For example, according to Numata et al.
@, Japanese Patent Publication No. 60-250031.

JP-A-61-60725, etc., or by Matsuura et al., JP-A-60-210629, JP-A-6
0-210894@, JP-A-60-221426, JP-A-60-221427, JP-A-61-69833@
There are examples of polyimides with low coefficients of thermal expansion made using specific raw material components, such as those shown in .

Further, as an example of producing a polyimide film having a low coefficient of thermal expansion, Ota et al. have disclosed in JP-A-61-18133 that an imidization method using chemical ring closure is used.

[Problem that the invention seeks to solve]

However, the polyimide proposed by Numata et al. and Matsuura et al. requires some kind of orientation treatment in order to improve its performance as a low expansion material.

This point is described in detail in JP-A No. 61-60725, and the orientation treatment is described, for example, in Section 5, line 13 of the upper left blade ram, and Section 6, line 12 of the lower left blade ram to lower right blade ram 19. The effects are stated in rows and are quantitatively described in the experimental results of Examples 2 to 8 in Section 11, Table 1.

It is effective to carry out this orientation treatment mainly by stretching during the drying or effecting process. Specifically, after forming into a film, it is fixed on an iron frame and heated to harden. Preferably, the conditions are such that stretching is caused by thermal expansion. In the above specification, this method reduces the coefficient of linear thermal expansion to 60 to 2.5% of that in the case of free curing. However, due to this property, when these polyimides are used as a coating material, they exhibit certain physical properties when a coating film is formed and cured on a material with a relatively large coefficient of thermal expansion, such as copper, but they are not suitable for ceramics, On materials with a small coefficient of thermal expansion such as silicon wafers, there is almost no stretching or orientation due to thermal expansion of the base material, so the coefficient of thermal expansion does not decrease sufficiently.
There is a problem that residual stress is large.

This problem is particularly noticeable when thick films are applied all at once, and although it is somewhat improved by stacking multiple thin films, it is still insufficient. Therefore, ceramics,
There was a desire for a polyimide material with a low coefficient of thermal expansion that could be used in professional wrestling by coating it on a material with a low coefficient of thermal expansion, such as a silicon wafer, and curing it by heating.

In addition, these polyimides generally have poor mechanical strength,
It is a brittle polymer with particularly low elongation compared to other currently known polyimides.

This is particularly true for polyimides derived from pyromellitic anhydride and paraphenylene diamine, which is also described in Example 1 of the above specification. The mechanical strength of the coating film is greatly related to the reliability of the device, and a low expansion polyimide with greater elongation has been desired.

In addition, as described in the above-mentioned specifications, these polyimides first undergo processing such as coating, molding, and film formation as a polyimide precursor, and then heat-cure and imidize. However, the solubility in organic solvents at the polyimide precursor stage is poor, and the polymer tends to precipitate from the solution.
It also had the problem of poor processability compared to other currently known polyimides. Therefore, improvements in this respect have also been desired.

(Means to Solve the Problem) Even if the Ministry of Invention and others perform the coating and curing process on a material that does not have the above problems, that is, a material with a low coefficient of thermal expansion, the polyimide white will have a low coefficient of thermal expansion and will not be affected by heat. The following research was conducted with the aim of developing a new polyimide resin that has no residual stress, high mechanical strength, and excellent processability as a precursor.

First, we made polyimide from various tetracarboxylic acids and diamines and evaluated them. As a result, we found that polyimide synthesized from pyromellitic acid and paraphenylenediamine or its methyl group-substituted product has no residual stress even when coated and cured on a silicon wafer. Unfortunately, this polymer had low mechanical strength and insufficient solubility of the precursor, making it unsuitable for practical use.

When we attempted to copolymerize this polymer with other diamines, we found that 60 to 90 mol% of the diamine was substituted with phenylenediamine or its methyl group. If 10 to 40 mol% of the diamine is metaphenylene diamine or its methyl group-substituted derivative, it can be coated and cured on a low thermal expansion material such as a silicon wafer, and there is almost no residual stress. The present invention has been completed based on the discovery that the adhesive strength is comparable to that of ordinary commercially available coated polyimide, the precursor has sufficient solubility, and the processability is good, giving satisfactory results.

In other words, the present invention contains 60 to 90 mol% of a unit structure represented by the following formula (1) (in the formula, m is an integer from O to 2); ) is an integer of 10
It is a polyimide resin characterized by containing from 40 mol% to 40 mol%.

The present invention will now be described in detail.

First, the method for producing polyimide of the present invention is to synthesize a polyamic acid or a derivative thereof from a tetracarboxylic acid or a derivative thereof and a diamine or a derivative thereof, and then use this to coat, mold, form a film, etc. It is manufactured through a process of processing, followed by heat curing and imidization.

As the heracarboxylic acid or its derivative, pyromellitic anhydride, pyromellitic diester, diacid chloride of pyromellitic diester, pyromellitic acid diamide, etc. are used. In addition, when biphenyltetracarboxylic anhydride, 3.3', 4.4'-bensif 1nontetracarboxylic acid anhydride, or derivatives thereof are used, coating on a substrate with a low coefficient of thermal expansion is possible. , the residual stress during the curing process is large, which is undesirable.

Examples of diamines or derivatives thereof include paraphenylene diamine, 2,5-tolylene diamine, and paraxylylene diamine.
2,5-diamine, metaxylylene-2,5-diamine, isocyanate derivatives, silylated derivatives, etc. of these diamines in an amount of 60 to 90 mol% of the diamine analogs.
Contains metaphenylene diamine, 2,4-toluylene diamine, 2゜6-tolylene diamine, metaxylylene-2゜4-diamine, metaxylylene-4,6-diamine, varaxylylene-2,6-diamine, or isocyanates thereof. Derivatives, silylated derivatives, etc. are used in an amount of 10 to 40 mol% of the total diamines. Among these diamines, when a combination of phenylene diamine and meta-phenylene diamine is used, a product excellent in heat resistance and solubility of the polyimide precursor can be obtained. Furthermore, the more methyl substituents there are, the greater the elongation of the polyimide. Para-phenylenediamine is also not preferable if the mole % of the methyl base-substituted diamine exceeds 90, since the elongation of the polyimide decreases and the solubility of the polyimide precursor deteriorates. Further, metaphenylenediamine is not preferable if the mole % of its methyl group-substituted product in diamines exceeds 40, since the residual stress will not be sufficiently reduced when coated and cured on a low thermal expansion material such as a silicon wafer.

Within the allowable composition range of diamines, the larger the mole percentage of para-phenylene diamine or its methyl group-substituted derivative in diamines, the greater the relative residual stress when coated and cured on a low thermal expansion material such as a silicon wafer. Since the elongation of polyimide and the solubility of the polyimide precursor tend to be relatively low, it is necessary to select the optimum ratio depending on the purpose of use.

In the present invention, various methods can be used to synthesize polyamic acid or its derivative from tetracarboxylic acid or its derivative and diamine or its derivative. For example, the method disclosed in the aforementioned patent publication of Numata et al., in which a tetracarboxylic dianhydride and a diamine are reacted in a polar solvent to produce a polyamic acid, can be used. In addition, the present inventors et al.
22@.

A method of producing a polyamic acid ester by reacting a tetracarboxylic acid diester and a diamine in the presence of a dehydration condensing agent, as shown in JP-A-61-127731, can also be used. In addition, Lubner et al.
A method for producing a polyamic acid ester by reacting a tetracarboxylic acid diester diacid chloride and a diamine in the presence of a base, as used in Publication No. 1422, was reported by Imafuru et al. in Proceedings of the 53rd Autumn Annual Meeting of the Chemical Society of Japan, 4. The method shown in No. ^-05, in which a tetracarboxylic acid anhydride is reacted with a silylated diamine, can also be used. It is also possible to use a reaction between a tetracarboxylic acid and a diisocyanate.

Among these synthesis methods, the method of Numata et al. is preferable because it is a simple synthesis method, and the method of Lubner et al. and the method of the present inventors are preferable because the produced polyamic acid ester has good solubility and storage stability. preferable. However, our method is the most preferred because it has a lower content of impurity ions.

Synthesized polyamic acid or its derivatives are mainly made into a solution and then processed by coating, molding, film formation, etc. The solvent used in this process is N-methylpyrrolidone, dimethylacetamide, dimethylsulfate, etc. Polar solvents such as fluoride, T-butyrolactone, cyclohexinone, cyclopentanone, tetrahydrofuran, and dioxane are preferred, and other solvents may be mixed as necessary to improve coating properties. As this solvent, the synthesis reaction solution can be used as it is as a solvent during synthesis.

Furthermore, a photoactive substance can be added to this solution to impart photosensitivity as described in JP-A No. 61-293204.

An adhesion aid such as a silane coupling agent, an aluminum chelating agent, a titanium chelating agent, etc. can also be added to this solution.

Next, the above-mentioned solution is applied to the base material, which has been subjected to treatments to increase adhesive strength such as application of an adhesion aid, etching, and plasma treatment as necessary, followed by drying, and the necessary molding.
After processing such as buttering, it is cured by heating to obtain polyimide coatings, films, molded products, etc.

Heat curing is performed using an oven, hot plate, electromagnetic heating device, etc. in a stream of an inert gas such as nitrogen or in air.

[Effect]

Polyimide synthesized from para-phenylene diamine and pyromellitic acid is a polyimide with the most rigid structure in the world, and has various characteristic properties such as a low coefficient of thermal expansion, high modulus of elasticity, and high heat resistance. However, it also had drawbacks such as almost no elongation and was brittle, so it was not put into practical use.

This property is thought to be due to the strong self-orientation of the structure described above.

In the present invention, by copolymerizing this structure with other specific leaps, we were able to achieve improved elongation and processability while retaining strong self-orientation, resulting in low expansion. It seems that we have been able to develop a material that becomes a polyimide with a low coefficient of thermal expansion through self-orientation even on a base material with a low coefficient of thermal expansion.

〔Effect of the invention〕

The polyimide of the present invention can form a heat-resistant film with almost no residual stress even on substrates with low thermal expansion coefficients such as silicon wafers through a simple process of coating and curing, and is widely used in electronic materials and semiconductors. It is a useful material that can be applied to various fields.

Furthermore, the polyimide of the present invention has high elongation and is excellent in reliability when applied to the above fields.

In general, the polyimide precursor of the present invention has good solubility;
This improves workability during processing.

(Example 1) Examples of the present invention are shown below, but the present invention is not limited thereto.

Synthesis Example 1 Pyromellit M was added to a 500 d separable flask.
pIA hydrate 21.8 g, 2-hydroxyethyl methacrylate 27.0 g, γ-butyrolactone 100 rn
17.0 g of pyridine was added while stirring under water cooling. After stirring at room temperature for 16 hours, a solution of 41.29 dicyclohexyl carbodiimide in 40 Inl of γ-butyrolactone was added over 10 minutes under water cooling, followed by addition of paraphenylenediamine (hereinafter abbreviated as P-PD) 8
．． 1 g of metaphenylene diamine (hereinafter abbreviated as M-PD>2.09) suspended in 20 WIl of γ-butyrolactone was added over 15 minutes.

Furthermore, dimethylacetamide 707 was added and 3
After stirring for an hour, 5In1 of ethanol was added and further stirred for 1 hour. After filtering the precipitate, the resulting solution was added to 101% of ethanol, the resulting precipitate was washed with ethanol, and then dried under vacuum to give a pale yellow color. powder was obtained. (The quantified powder in N-methylpyrrolidone, 30°C, 0.59/d
Viscosity number at I (hereinafter v, n).

) was 32.8 dl/g.

The obtained powder was dissolved in N-methylpyrrolidone at 23°C at 36°C.
Solution It! determined using an E-type viscometer at % solution! i degree(
(hereinafter abbreviated as η) was 133.9 voices.

This solution was left at room temperature for 10 days, but no polymer was deposited. This polymer is designated as A-0020.

Synthesis Examples 2-3. Comparative Synthesis Examples 1 to 3 Synthesis was carried out in the same manner as Synthesis Example 1 except that the amounts of P-PD and M-PD were changed. The results are shown in Table 1.

Synthesis Examples 4-15. Comparative Synthesis Examples 4 to 11 Synthesis was carried out in the same manner as in Example 1 except that the diamines were changed to those shown in Table 2. The results are shown in Table 2.

(Leaving space below) Synthesis Example 16 The same amount of diamine as used in Synthesis Example 1 was placed in a flask equipped with a thermometer and a stirring device, and N-methylpyrrolidone (
Dissolved with >181 g of NMP. Next, the flask was placed in a water bath at 20°C, and the same amount of pyromellitic anhydride as used in Example 1 was added little by little in powder form over 15 minutes. After the reaction system became homogeneous, it was stirred at room temperature for 5 hours, and further heated and stirred at 85°C until the viscosity at 23°C became approximately 50 poise. This polymer is designated 8-0020.

A solution of this polymer was allowed to stand at room temperature for 3 days, but no turbidity, polymer precipitation, or assimilation of the solution occurred.

Synthesis Examples 17-25. Comparative Synthesis Examples 12 to 16 diamines,
A polymer solution was obtained in the same manner as in Synthesis Example 16, except that the same amount of polymer as used in the above-mentioned Synthesis Example or Comparative Synthesis Example was used. Table 3 shows the numbers and results of the corresponding synthesis examples or comparative synthesis examples.

(Margin below) Comparative synthesis example 17 3.3' instead of pyromellitic anhydride.

4.4'-Biphenyltetracarboxylic anhydride 29.6
g, using 10.0 g of para-phenylenediamine,
Synthesis Example 1 except that 3,3'dimethylbenzidine is not used
Synthesis was carried out in the same manner. 1 v, n of crushed powder
, was 27.2. η was 63.2.

The solution used for the measurement of η was allowed to stand at room temperature for 10 days, but no polymer was precipitated. This polymer is called C-oooo.

Comparative Synthesis Example 18 Except for using 3.3', 4.4'-benzophenonetetracarboxylic anhydride 32.29 instead of 3.3', 4.4'-biphenyltetracarboxylic anhydride.
Synthesis was carried out in the same manner as Comparative Synthesis Example 17. The v, n, of the 1q powder was 25.3. η was 55.3.

The solution used for the measurement of η was allowed to stand at room temperature for 10 days, but no polymer was precipitated. This polymer is designated C-1000.

Comparative Synthesis Example 19 As diamines, dianodiphenyl ether 18.7
Synthesis was carried out in the same manner as in Synthesis Example 1 except that g was used.

The obtained powder had v and n of 25.8.

η was 53.0. The solution used for the measurement of η was allowed to stand at room temperature for 10 days, but no polymer was precipitated.

This polymer is designated C-2000.

Reference Example 1 Measurement of Residual Stress A 0.2% methanol solution of γ-aminopropyldimethoxymethylsilane was spin coated on a 370 μm thick 3-inch silicon wafer at sooorpm for 30 seconds.
It was heated for 10 minutes in a hot plate at .degree. After cooling, the solution of polyamic acid or polyamic acid ester obtained in the synthesis example or comparative synthesis example was spin-coated so that the film thickness after curing was 15 to 30μ, and dried at 90 ° C. for 30 minutes to 3 hours. The mixture was further heated at 140°C for 2 hours and at 350°C for 2 hours to obtain a polyimide coating. After cooling, the central part 3cIIt of the back of the wafer was measured with a contact type surface roughness meter (manufactured by SLOAN, O
Curvature was measured using E, TA, and IIA). If the distance from the center of the string to the bow of the obtained figure that can be approximated to a hollow bow shape is measured and this is referred to as A, then the residual stress δ is expressed by the following equation (3).

E: Young's modulus of the silicon wafer ■ = Poisson's ratio of the silicon wafer D: Measurement length TS: Thickness of the silicon wafer T: Coating film thickness (after curing) Here, the wavy lined part of the equation is the value specific to the silicon wafer. Therefore, it becomes a constant in this measurement. Therefore, the residual stress, δ, is expressed by the following equation (4).

Calculating the value of K here, we get K=3.91 [Kl/wi].

Next, the coating film was scratched and the coating film thickness T was measured using the same contact type surface roughness meter, and the value of the residual stress δ was obtained according to formula (4) using ◯ and Δ.

Reference Example 2 Measurement of Mechanical Strength-1 Synthesis Examples 1 to 15 and Comparative Synthesis Examples 1 to 11. To the solutions prepared in 17 to 19, 1.0% of 4,4゛-bis(dimethylamino)benzophenone and 1- Phenyl-1,2-propanedione-2-(0-ethoxycarbonyl)oxime1.
5%, triethylene glycol diacrylate 3.0%
was added and stirred for 8 hours to form a homogeneous solution. After leaving this photosensitive composition for 16 hours to defoam,
m, thickness 30~ on an aluminum disk with a diameter of 7.50R
The coating was applied by spinning to a thickness of 60 μm. After drying at 70°C for 1 hour and cooling, using an ultra-high pressure mercury lamp (8 mw/rvt) and a photomask, a dumbbell-shaped pattern with a straight part of width 3M and length 2011IIr1 and a slightly wider part for sandwiching was made into 120 pieces. Exposure for seconds. Next, using a spray set generator, the unexposed areas were dissolved with a 3:1 mixture of N-methylpyrrolidone and isopropyl alcohol.
Rinse with isopropyl alcohol. This pattern was then heated at 140°C for 2 hours and at 350°C for 2 hours to obtain an aluminum disk with a polyimide pattern. Soak this in 3N hydrochloric acid to dissolve the aluminum, wash with water,
A test piece was obtained by drying at 70°C for 8 hours. From this test piece, tensile test ta manufactured by Toyo Baldwin Co., Ltd.
(TENSILON, UTH-II-20 type) was used to measure tensile strength, elongation, and tensile modulus.

Measurement of Mechanical Strength-2 The solutions obtained in Synthesis Examples 16 to 25 and Comparative Synthesis Examples 12 to 16 were uniformly applied to a glass plate using an applicator.
It was dried at 100° C. for 30 to 60 minutes to form a film, peeled off from the glass plate, fixed to an iron frame, and held at 140° C. and 350° C. for 2 hours, respectively, to obtain a polyimide film with a thickness of 15 to 30 μm. This was cut into a size of 3 m x 80 m to obtain a test piece. Using this, measurements were performed in the same manner as in Mechanical Strength Measurement-1.

Examples 1-23. Comparative Examples 1 to 16 For each of the synthesized polymers, the residual stress and mechanical strength when imidized by the methods of Reference Examples 1 and 2 were measured. The results are shown in Table 4. If the elongation is marked as "brittle", it is brittle and cannot be measured.

Reference example 3 Examples 2 and 3. The same photosensitive composition as that used in the measurement of mechanical strength in Example 1 was coated on a silicon wafer substrate coated with polyimide prepared in Comparative Examples 14, 15, and 16 to a thickness of 5 μm. It was spin-coated t5 and dried at 70°C for 30 minutes. After cooling, use a super high liquid mercury lamp (8 mw/
cri ) and a photomask, from 1 μm in width to 50
A pattern of rectangular holes with different sizes down to μm was exposed for 20 seconds. Next, using a spray developing machine,
Dissolve the unexposed holes with a 3:1 mixture of N-methylpyrrolidone and isopropyl alcohol, rinse with isopropyl alcohol, and check to see how many holes have been developed in the center of the wafer. , this was taken as the resolution. The results are shown in Table 5.

(Margin below) Table 5

Claims (1)

[Claims] Primary formula (1) ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(1) 60 to 90 moles of the unit structure represented by (in the formula, n is an integer from 0 to 2) Contains 10 to 40 mol% of the unit structure represented by the following formula (2) ▲Mathematical formula, chemical formula, table, etc.▼...(2) (In the formula, m is an integer from 0 to 2) Characteristic polyimide resin.