JPH0329292B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to a method for forming a polyimide insulating film on the surface of a semiconductor element, such as the exposed surface of a PN junction of a semiconductor element. [Background Art] Conventionally, polyimide silicon, that is, siloxane-modified polyimide, which has excellent moisture resistance and adhesion, has been used as a junction protection film for a PN junction of a semiconductor device or a passivation film on the surface of a semiconductor device. However, some high-voltage, large-current semiconductor devices, especially high-voltage diodes, include diodes made of square chip-shaped semiconductor devices, and as a junction protective film for this PN junction,
When conventional polyimide films obtained by heating and curing siloxane-modified polyamic acid solutions are used, the film thickness at the edges of square chips may become too thin and cause electrical discharge, resulting in lower product yields and lower initial good product rates. There was a problem with improvement. In other words, in a commonly used silicon diode made of a round cylindrical mesa semiconductor element, as shown in FIG.
The N-type region 3a and the P-type region 3b are connected to a P-N junction surface 5.
The semiconductor element 4 bonded with the lead wires 1a, 1
b with solder, and these are sealed with a molding material 2 such as epoxy resin. Semiconductor element 4
The surface of the wire including a part of the lead wire is covered with a polyimide film 6. However, when the semiconductor element 4 is a rectangular chip as shown in FIG. 2, the polyimide film 6 becomes very thin at the four corner edges, which causes discharge and causes a significant increase in leakage current in the reverse direction. This was caused by the low solid content concentration, which is the polyimide forming component concentration, of the siloxane-modified polyamic acid, which is a coating solution for forming a polyimide film. Generally, a coating solution used for forming a polyimide insulating film is composed of a polyamic acid or a derivative thereof dissolved in an inert solvent. However, because the above polymer has a high molecular weight, the concentration of polymer that can be dissolved in practical use is generally 5 to 30% by weight.
Furthermore, when applying to the above-mentioned diodes, etc., in order to improve the application workability such as brushing and dispensing methods, it is further diluted with a solvent to lower the solution viscosity to usually 50 to 130 centipoise (cps). There is. However, the polymer concentration at this viscosity is usually 2
As a result, the edge portion of the square chip becomes extremely thin. Therefore, in order to improve edge coverage, attempts have been made to apply multiple coats to thicken the edges.
This method increases the number of steps and reduces workability. At least in order to achieve sufficient edge coverage with one application, the coating solution needs to be a highly concentrated solution with a high solid content. Furthermore, there is a difference in level at the adhesive part of the semiconductor element to the lead wire.
It is also necessary to be able to form a transparent and tough film even if the thickness is 100 μm or more and the maximum film thickness is 100 μm or more. FIG. 4 is a cross-sectional view of one embodiment of a high voltage transistor, which is a discrete semiconductor. That is, a power transistor element 11 is fixed on a silver-plated copper frame 8 equipped with a heat sink, and bonded to a lead frame with aluminum wires 9. On the surface of this element, a power transistor element 11 made of conventional polyamic acid or its derivative is fixed. polyimide protective film 1
2 are provided, and these are sealed with a molding material 10 such as epoxy resin. This polyimide protective film 12 is mainly used for the purpose of improving the moisture resistance of semiconductors, and usually exhibits sufficient characteristics with a film thickness of about 5 to 20 μm. Due to the surface tension of the coating solution, the wall thickness is often over 100μm,
A phenomenon occurred in which the polyimide film did not become a transparent film but turned into powder in this thick part. This is due to the fact that conventional polyamic acid coating solutions lack the ability to form thick films. In the polyimide film powdered in this way,
The dielectric withstand voltage decreases significantly, resulting in an increase in leakage current.
This caused a drop in withstand pressure. Further, a similar problem has occurred on the side surfaces of semiconductor elements having a thickness of 300 μm or more. [Purpose of the Invention] The present invention was made in view of the above circumstances, and an object of the present invention is to provide a method for forming a film on the surface of a semiconductor element, in which a thick polyimide film can be formed without complicated coating work. purpose. [Disclosure of the Invention] In order to achieve the above object, the method of forming a film on the surface of a semiconductor element of the present invention includes a step of preparing a semiconductor element whose element surface is coated with a solution for forming a polyimide film, and a step of forming a polyimide film. A method for forming a film on the surface of a semiconductor element comprising the step of curing film-forming components in a solution by heating to form a polyimide film, the polyimide film-forming solution containing 99 to 80 mol% of the following A component and B component 1~
It uses an imide ring-containing low molecular weight polymer solution obtained by dissolving 20 mol% of a diamino compound and an aromatic tetracarboxylic acid ester in equimolar or approximately equimolar amounts in an inert solvent and heat-treating the solution. . A: (a) Aromatic tetranuclear diamine represented by the following general formula (1) [In formula (1), R ₁ and R ₂ are hydrogen, an alkyl group having 1 to 4 carbon atoms, or CF ₃ and may be the same or different from each other. R ₃ , R ₄ , R ₅ , R ₆ are hydrogen,
They are halogens or alkyl groups having 1 to 4 carbon atoms, and may be the same or different. (b) A diamine consisting of a diamine that does not contain a silicon atom in its molecule other than the components (a) and B above. However, the mutual molar ratio of (a) and (b) is 100:0 ~
It is 70:30. B: Diaminosiloxane represented by the following general formula (2) [In formula (2), R ₇ is a divalent organic group, R ₈ is a monovalent organic group, and n is an integer of 1 to 1000. ] That is, this invention uses in combination the aromatic tetranuclear diamine of the general formula (1) that has an affinity for organic solvents and the diaminosiloxane of the general formula (2) that has high adhesiveness to the surface of a semiconductor element. By dissolving these diamines and esters, which are slightly less reactive than aromatic tetracarboxylic dianhydrides, which are sensitive to diamines, in an inert solvent and subjecting them to heat treatment, polyamides can be produced. Polymers containing imide rings (polyimide in which all condensed parts are imidized, some By creating a polymer or oligomer with a polyimide-polyamic acid structure in which unclosed parts are left and the remainder is imidized, the solution for forming a polyimide film can be highly concentrated, making it possible to form a thick polyimide film on the surface of a semiconductor element. It is meant to be. The semiconductor element surface to be treated with the imide ring-containing low molecular weight polymer solution (polyimide film forming solution) usually means the exposed surface of the PN junction. However, it also includes a case where a glass pinning film or the like is formed on this exposed surface. This imide ring-containing low molecular weight polymer solution is an aromatic tetranuclear diamine (component A) represented by the above formula (1).
and diaminosiloxane (component B) represented by the above formula (2). A suitable aromatic tetranuclear diamine is 2,2-bis[4-(4-
Examples include aminophenoxy)phenyl]propane. Other preferred representative examples include 2,2
-bis[3-methyl-4-(4-aminophenoxy)phenyl]propane, 2,2-bis[3-chloro-4-(4-aminophenoxy)phenyl]
Propane, 1,1-bis[4-(4-aminophenoxy)phenyl]ethane, 1,1-bis[3-
Methyl-4-(4-aminophenoxy)phenyl]
Methane, 1,1-bis[3-chloro-4-(4-
aminophenoxy)phenyl]ethane, 1,1-
Bis[3,5-dimethyl-4-(4-aminophenoxy)phenyl]ethane, bis[4-(4-aminophenoxy)phenyl]methane, bis[3-
Methyl-4-(4-aminophenoxy)phenyl]
Methane, bis[3-chloro-4-(4-aminophenoxy)phenyl]ethane, bis[3,5-dimethyl-4-(4-aminophenoxy)phenyl]
Examples include methane. Note that up to 30 mol% of the aromatic tetranuclear diamine represented by the above general formula (1) can be a conventional diamine that does not contain a silicon atom in its molecule as part of the A component. Use beyond this point must be stopped because the ability of the resulting polyimide film-forming solution (hereinafter abbreviated as "film-forming solution") to form a thick film will be impaired. Examples of such conventional diamines include metaphenylenediamine,
Mononuclear diamines such as paraphenylene diamine,
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'-disulfonic acid, benzidine- 3-monosulfonic acid, benzidine-3-monocarboxylic acid, dinuclear diamines such as 3,3'-dimethoxybenzidine, 4,4''-diamino-p-terphenyl, 1,4-bis(m-aminophenoxy)benzene , 1,4-bis(p-aminophenoxy)benzene, 1,4-bis(m-
aminosulfonyl)benzene, 1,4-bis(p
-aminophenylsulfonyl)benzene, 1,4
-trinuclear diamines such as bis(m-aminophenylthioether)benzene, 1,4-bis(p-aminophenylthioether)benzene, 4,4'-
Diaminodiphenyl ether-3-carbonamide, 3,4'-diaminodiphenyl ether-4-
Diaminocarbonamide compounds such as carbonamide, 3,4'-diaminodiphenyl ether-3'-carbonamide, 3,3'-diaminodiphenyl ether-4-carbonamide, 4,4'-(4-aminophenoxy) Diphenylsulfone, 4,4'-
(3-aminophenoxy)diphenylsulfone,
Tetranuclear diamines not included in general formula (1) such as 4,4'-(4-aminophenoxy) diphenyl sulfide, 4,4'-(4-aminophenoxy) biphenyl, hexamethylene diamine, heptamethylene diamine and alicyclic diamines such as 1,4-diaminocyclohexane, isophorone diamine, and 4,4'diaminodicyclohexylmethane. The diaminosiloxane (component B) represented by the above general formula (2) is used as an adhesion improver in order to improve the adhesion of the produced polyimide film to the semiconductor element. However, if a large amount is used, the heat resistance etc. of the produced polyimide film will be impaired, so the amount used needs to be set at 1 to 20 mol% of the total diamino compound. The preferred amount is 1 to 4 mol%. In other words, if the amount of diaminosiloxane used exceeds 20 mol%, the heat resistance and moisture resistance of the resulting polyimide film will decrease,
On the other hand, if it is less than 1 mol %, the adhesion to the semiconductor element will be poor. Representative examples of such diaminosiloxanes are as follows. In this invention, an aromatic tetracarboxylic acid ester is used as the acid to be reacted with the diamino compound consisting of the A component and the B component. As such an aromatic tetracarboxylic acid ester, one having a molecular weight of about 200 to 700 is usually used. This type of ester is produced, for example, by reacting an aromatic tetracarboxylic dianhydride with a monohydric alcohol having 4 or less carbon atoms. Examples of such alcohols include methanol, ethanol, n-
Examples include propanol, sec-propanol, n-butanol, sec-butanol, and tert-butanol. Among these alcohols, methanol, ethanol, n-propanol, sec-
It is preferable to use butanol, and methanol and ethanol are most preferable. Representative examples of the aromatic tetracarboxylic dianhydride reacted with the monohydric alcohol include 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′-bis(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'-(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 things, 1, 2, 7, 8
-phenanthrenetetracarboxylic dianhydride. Esterification is carried out by adding an excess amount of alcohol to the aromatic tetracarboxylic dianhydride to a reaction vessel, heating to reflux at the boiling point of the alcohol, and converting the anhydride group into 1
This can be carried out by preparing a polyester of an aromatic tetracarboxylic acid diester or more having a structure in which at least one alcohol is reacted with each ester, and distilling off the excess alcohol after the reaction is completed. Among the above aromatic tetracarboxylic acid esters,
Particularly preferred are 3,3'-4,4'-biphenyltetracarboxylic acid dimethyl ester and 3-
3',4,4'-biphenyltetracarboxylic acid diethyl ester. These suitable esters usually do not have anhydride groups. When these aromatic tetracarboxylic acid esters are used, the thickest polyimide film can be formed, and the formed polyimide film is equivalent to a polyimide film with the same structure obtained via polyamic acid. It has characteristics. Of course, it is possible to form a thick film even when dianhydride esters other than the above-mentioned esters are used, but it is preferable to take measures such as relaxing the heating conditions. In this invention, first, a film-forming liquid is manufactured using the above raw materials, for example, in the following manner. That is, 99 to 80 mol% of A component mainly consisting of aromatic tetranuclear diamine represented by formula (1) and 1 to 20 mol% of B component consisting of diaminosiloxane represented by formula (2).
A diamino compound having a composition of
After making a homogeneous and transparent solution, heat it to 80-200℃,
Polycondensation proceeds by dealcoholization reaction. As a result, the desired film-forming liquid is obtained. The film forming solution obtained in this way has a low molecular weight imide ring-containing polymer, and furthermore, aromatic tetranuclear diamine with high solvent affinity is introduced into the polymer, so that polyimide formation is possible. The component polymer described above can be dissolved at a high concentration. The solid content concentration (the above polymer concentration), which is the concentration of the polyimide forming component in this film-forming solution, may vary depending on the application, but as a guide, the solution viscosity of the coating solution is
It is preferable that the solid content concentration is 20% by weight or more when adjusted to 100cps (at 25±0.1°C). Note that the heat treatment of the inert solvent solution is preferably performed at a temperature of 80 to 200°C as described above. By heating under the above temperature conditions, a low molecular weight polymer containing an imide ring having a molecular weight of 2,100 to 200,000 can be obtained. Here, the above molecular weight indicates the weight average molecular weight determined by gel permeation chromatography using polystyrene as a reference material and tetrahydrofuran as a developing solvent. In addition, depending on the type of ester group in the aromatic tetracarboxylic acid ester, the reaction rate of the dealcoholization reaction may become faster in rare cases, and the molecular weight of the polymer containing an imide ring may increase beyond 200,000. , insolubilization in inert solvents may also occur. Such cases can be dealt with by conducting the reaction at a low temperature, etc. In addition, the above-mentioned inert solvent that dissolves the aromatic tetracarboxylic acid ester and the diamino compound is
Does not react with the above esters and diamino compounds,
Furthermore, it refers to an organic solvent that can dissolve the produced low molecular weight polymer. An example of such an inert solvent is N-methyl-2-pyrrolidone, N,
N'-dimethylformamide, N,N'-dimethylacetamide, N,N'-dimethylsulfoxide,
Examples include highly polar basic solvents such as hexamethylphosphoramide. Of course, other solvents such as tetrahydrofuran, acetophenone, cyclohexanone, triethylene glycol dimethyl ether, and dioxane can also be used. Moreover, these solvents can also be used in combination with general-purpose solvents such as toluene, xylene, benzonitrile, benzene, and phenol. However, the amount used must be controlled within a range that does not reduce the solubility of the resulting polymer. Next, using the film forming liquid obtained as described above, a polyimide film is formed on the surface of the semiconductor element in the following manner. That is, the film forming liquid is applied to the surface of the semiconductor element. In this case, the film-forming liquid is usually applied not only to the element surface but also to the vicinity thereof. Since this film forming liquid is a highly concentrated liquid, a thick coating layer can be formed by one application. Then, heat this to 200-350°C. As a result, the low molecular weight polymer in the film forming solution is polymerized and converted into polyimide, forming a thick polyimide film. Note that the above film forming solution may occasionally contain unreacted monomers, but these unreacted monomers may have a negative effect on the above coating film.
Since it reacts with low molecular weight polymers (polymers and oligomers) when heated at 200-350°C, there is no need to remove it specifically. The polyimide film formed on the surface of the semiconductor element as described above has good heat resistance, chemical resistance, mechanical properties, and excellent electrical insulation properties inherent to polyimide. Therefore,
It can be applied to various conventionally known uses. The above film forming liquid is also useful as a binder for pastes in which various fillers are dispersed, since it is excellent in not only thick film forming properties but also moldability. That is, it can be used as a binder for a heat-resistant conductive paste in which conductive fillers such as silver powder, gold powder, palladium powder, etc. are dispersed, for chip bonding, electrodes of electronic parts, etc. It can also be used as a screen printing paste to prevent soft errors by dispersing an organic or inorganic filler with a uranium or thorium content of 5 ppb or less. [Effects of the Invention] As described above, the present invention uses the aromatic tetranuclear diamine of the general formula (1) and the diaminosiloxane of the general formula (2) together, and combines these diamines with an aromatic tetracarboxylic acid ester. A solution of a low molecular weight polymer containing a high concentration of imide rings, prepared by reacting with It becomes possible to form on the surface. Therefore, there is no need to apply the solution many times as in the past. In other words, even for conventional prismatic chip-shaped semiconductor devices, which required multiple coatings to form a thin film on the edges of the prismatic areas, it is now possible to reduce the film thickness at the edges to a sufficient thickness with a single coating. You will be able to finish it. Furthermore, it is now possible to easily form a polyimide film thicker than 100 μm, which has been impossible with conventional polyamic acid solutions due to the powdering phenomenon. In particular, in this invention, the diamine and aromatic tetracarboxylic acid ester are not dissolved as they are and used as a solution for forming a polyimide film, but are used after a considerable reaction. During the heat treatment, almost no alcohol is liberated from the aromatic tetracarboxylic acid ester. Therefore, an excellent effect can be obtained in that the polyimide film does not have micropores that occur when free alcohol escapes into the atmosphere. As described above, according to the present invention, it is possible to coat a semiconductor element with a single application.
A transparent polyimide insulating film with a thickness of 100 μm or more can be formed. Therefore, in addition to protective films for diodes and transistors, the present invention is useful for forming protective films for cyclers and integrated circuits such as ICs and LSIs that require thick films. In particular, the α-ray shielding film for VLSI memory cells usually requires a film thickness of 20 to 70 μm.
To achieve this thickness, conventionally a large amount of a coating solution made of polyamic acid or its derivatives was applied using a spinner method or potting method, but the amount of application was strictly controlled to prevent the polyimide film from turning into powder. This required sophisticated and complicated processes such as controlling coating accuracy. However, according to the present invention, it is possible to form a film with a predetermined thickness in a single application, which eliminates the need for the above-mentioned sophisticated and complicated processes, simplifying the overall process and making the work easier. It becomes possible to realize simplification. Further, the present invention can be applied to liquid crystal alignment films of liquid crystal cells made of glass substrates including transparent electrodes, laminates, and various insulating films. Next, examples will be described. In addition, in the following examples, solution viscosity and solid content concentration were measured as follows. (1) Solution viscosity Measured at 25±0.1°C using an E-type rotational viscometer. (2) Solid content concentration Solid content concentration (%) = W ₃ - _{W 1} / W ₂ - W ₁ × 100 Where, W ₁ : Weight of shear dish (g) W ₂ : Weight of sample and shear dish (g) W ₃ : Weight (g) of sample and shear after drying at 150°C for 60 minutes and further at 200°C for 60 minutes Example 1 In a flask equipped with a stirrer, cooling tube and thermometer, 3, 3', 4, 29.4 g (0.1 mol) of 4'-biphenyltetracarboxylic dianhydride and methanol
160 g (5 mol) was added, and the mixture was heated under reflux at 64 to 65° C. for 6 hours until the reaction system became transparent. Thereafter, excess methanol was distilled off, and the methanol residue was further completely distilled off under reduced pressure. The obtained esterified product has an acid value of 311, and the IR spectrum shows that it is 3.
It was confirmed to be 3'-4,4'-biphenyltetracarboxylic acid dimethyl ester. Next, 35.8 g of 3,3',4,4'-biphenyltetracarboxylic acid dimethyl ester obtained in this way
(0.1 mol) and 39.57 g of 2,2-bis[4-(4-aminophenoxy)phenyl]propane
(0.0965 mol) and 0.87 g (0.0035 mol) of bis(3-aminopropyl)tetramethyldisiloxane were added to 69.8 g of N-methyl-2-pyrrolidone,
Stir at 40°C for 2 hours to obtain a clear solution, followed by
Stirring was continued for 20 hours at 80°C to form a transparent viscous solution (film-forming liquid). The film-forming solution obtained in this way has a solid content concentration of 50.3% and a solution viscosity of
It was 4000cps. Next, the above film-forming solution was poured into water, and the resulting reprecipitated polymer was dried under reduced pressure, and then an infrared absorption spectrum was measured, as shown in Figure 6.
Based on imide groups at 1780 cm ^-1 and 1720 cm ^-1 >
A characteristic absorption band of C=O appeared. From this result, it was confirmed that the above polymer contained an imide ring. Example 2 In a reaction vessel similar to Example 1, 3, 3', 4,
4′-biphenyltetracarboxylic dianhydride 29.4g
(0.1 mol) and n-propanol 300g (5 mol)
was added and heated under reflux at 97°C for 4 hours until the reaction system became transparent. Thereafter, excess n-propanol was distilled off to synthesize 3,3',4,4'-biphenyltetracarboxylic acid di-n-propyl ester. Then, to 41.4 g of the obtained 3,3',4,4'-biphenyltetracarboxylic acid di-n-propyl ester,
38.95 g (0.095 mol) of 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1.24 g (0.005 mol) of bis(3-aminopropyl)tetramethyldisiloxane, and 81.6 g of N-methyl-2-pyrrolidone. After stirring at 60°C for 2 hours, stirring at 105°C for 2 hours and further at 150°C for 1 hour, the desired film-forming solution was prepared. The solid content concentration of the obtained film-forming solution was 50.5%, and the solution viscosity was
It was 4900cps. Next, the film-forming solution obtained as described above was poured into water, and the resulting reprecipitated polymer was dried under reduced pressure, and then ^an infrared absorption spectrum was measured _. A characteristic absorption band >C=O based on the imide group appeared at 1720 cm ^-1 . From this, it was confirmed that the above polymer was a polymer containing an imide ring. Example 3 In place of 3,3',4,4'-biphenyltetracarboxylic dianhydride, the same mole of 3,3',4,4'-benzophenonetetracarboxylic dianhydride was used. Other than that, the solid content concentration was determined in the same manner as in Example 1.
A film-forming solution with a concentration of 50.0% and a solution viscosity of 1800 cps was prepared. Next, the film-forming solution obtained as described above was poured into water, and the resulting reprecipitated polymer was dried under reduced pressure, and then ^an infrared absorption spectrum was measured. A characteristic absorption band of >C=O based on imide groups was observed at 1720 cm ^-1 , and it was confirmed that this was a polymer containing imide rings. Example 4 2,2-bis[4-(4-aminophenoxy)
Phenyl]In place of propane 41.0g (0.1mol),
33.62 g (0.082 mol) of 2,2-bis[4-(4-aminophenoxy)phenyl]propane and 4.47 g (0.018 mol) of bis(3-aminopropyl)tetramethyldisiloxane were used. A film forming solution having a solid content concentration of 50.0% and a solution viscosity of 1300 cps was obtained in the same manner as in Example 1 except for the above. Next, the film-forming solution obtained as described above was poured into water, and the resulting reprecipitated polymer was dried under reduced pressure, and then ^an infrared absorption spectrum was measured. A characteristic absorption band of >C=O based on imide groups was observed at 1720 cm ^-1 , and it was confirmed that this was a polymer containing imide rings. Comparative Example 1 Aromatic tetracarboxylic dianhydride was used as it was without being esterified. That is, in the same reaction vessel as in Example 1, 29.4 g (0.1 mol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2,
39.57 g (0.0965 mol) of 2-bis[4-(4-aminophenoxy)phenyl]propane and bis(3
-aminopropyl)tetramethyldisiloxane
0.87 g (0.0035 mol) and 279.4 g of N-methyl-2-pyrrolidone were added and stirred while maintaining the temperature at 30° C. or lower (particularly at or near room temperature). As a result, the polymerization reaction proceeded quickly and the viscosity of the reaction system increased, yielding a polyamic acid solution with a solid content concentration of 19.9% and a solution viscosity of 2,000,000 cps or more. Next, this was heated and aged at 60°C to reduce the solution viscosity to 3000 cps, and then N
- Diluted with methyl-2-pyrrolidone to a solution viscosity of 105 cps. The solid content concentration of this polyamic acid solution was 10.5%. Comparative Example 2 In a reaction vessel similar to Example 1, 35.8 g (0.1 mol) of 3,3',4,4'-biphenyltetracarboxylic acid dimethyl ester obtained in Example 1 and 4,4'-
19.3 g (0.0965 mol) of diaminodiphenyl ether and 0.87 g (0.0035 mol) of bis(3-aminopropyl)tetramethyldisiloxane were added to 49.6 g of N-methyl-2-pyrrolidone and stirred at 40°C for 2 hours. The mixture was completely dissolved and then stirred at 80°C for 20 hours to form a clear viscous solution. This polymer solution had a solid content concentration of 49.8% and a solution viscosity of 2000 cps. Next, the coating solutions obtained in Examples 1 to 4 and Comparative Examples 1 to 2 were brushed onto the P-N junction surface of a high-voltage silicon diode having a square chip shape, including a part of the lead frame. After coating, drying and curing, the semiconductor device was sealed with a resin molding material. Table 1 shows its drying and curing conditions, initial characteristics (forward voltage, good product rate, reverse withstand voltage good product rate...
…expressed as the number of non-defective products out of 100 samples) and 121℃,
The results of measuring the reverse leakage current yield after the 2 atm steam pressure cutter test (abbreviated as PCT) are shown.

[Table] When the polyimide forming coating solution prepared in Examples 1 to 4 is used, as shown in Figure 3, the edges of the rectangle can be covered thickly with a polyimide film, thereby preventing electrical discharge at the edges. This makes it possible to improve the initial non-defective product rate. Further, as shown in FIG. 5, similar effects were observed when the solution obtained in the above example was applied as an insulating film of a high voltage transistor. In addition, the above-mentioned Examples 1 to
4. The coating solutions obtained in Comparative Examples 1 and 2 were sequentially diluted with the solvents constituting the solutions, and the viscosity (measured at 25±1° C.) at a predetermined concentration was measured and graphed as shown in FIG. Straight line a shows that of Example 1, b shows that of Example 2, c shows that of Example 3, d shows that of Example 4, straight line e shows that of Comparative Example 1, and f shows that of Comparative Example 2. As is clear from FIG. 10, it can be seen that the solutions of Examples have significantly higher solid content concentrations than those of Comparative Examples. Although Comparative Example 2 has a high solid content concentration, the resulting polyimide film becomes opaque and cannot be put to practical use.

[Brief explanation of the drawing]

1A and 2A are longitudinal cross-sectional views of an example of a conventional semiconductor device, FIG. 1B and FIG. 2B are cross-sectional views thereof, and FIG. 4 is a cross-sectional view of another example of a conventional semiconductor device. FIG. 3A is an explanatory diagram of an example of a semiconductor device manufactured using the method of the present invention, FIG. 3B is a cross-sectional view thereof, and FIG. A vertical cross-sectional view of another example of a semiconductor device, FIGS. 6 to 9 are infrared absorption spectra of polyimide obtained in Examples, and FIG. 10 is a solid content concentration-solution viscosity diagram of a coating solution. .

Claims (1)

[Claims] 1. A method comprising: preparing a semiconductor element whose surface is coated with a solution for forming a polyimide film; and heating and curing film-forming components in the solution for forming a polyimide film to form a polyimide film. A method for forming a film on the surface of a semiconductor element, wherein the solution for forming a polyimide film contains a diamino compound and an aromatic tetracarboxylic acid ester comprising 99 to 80 mol% of component A and 1 to 20 mol% of component B. 1. A method for forming a film on the surface of a semiconductor device, comprising using a solution of an imide ring-containing low molecular weight polymer obtained by dissolving the imide ring-containing low molecular weight polymer in an inert solvent in equimolar or approximately equimolar amounts and heat-treating the solution. A: (a) Aromatic tetranuclear diamine represented by the following general formula (1) [In formula (1), R ₁ and R ₂ are hydrogen, an alkyl group having 1 to 4 carbon atoms, or CF ₃ and may be the same or different from each other. R ₃ , R ₄ , R ₅ , R ₆ are hydrogen,
They are halogens or alkyl groups having 1 to 4 carbon atoms, and may be the same or different. (b) A diamine consisting of a diamine that does not contain a silicon atom in its molecule other than the components (a) and B above. However, the mutual molar ratio of (a) and (b) is 100:0 ~
It is 70:30. B: Diaminosiloxane represented by the following general formula (2) [In formula (2), R ₇ is a divalent organic group, R ₈ is a monovalent organic group, and n is an integer of 1 to 1000. ] 2 Aromatic tetracarboxylic acid ester is 3,
The method for forming a film on the surface of a semiconductor device according to claim 1, wherein the 3',4,4'-biphenyltetracarboxylic acid ester is used. 3. Claim 1, wherein the imide ring-containing low molecular weight polymer solution is set so that the solid content concentration is 20% by weight or more when the solution viscosity is adjusted to 100 cps (25 ± 1 ° C.), or 2. The method for forming a film on the surface of a semiconductor element according to item 2.