JPH07116406B2 - Passive method for semiconductor device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a passivation method for a semiconductor device using a polyimide resin.

[Prior Art] High breakdown voltage large current semiconductor devices such as power diodes, glass as a passivation film for thyristors,
Silicone resins and polyimide resins are known.

Glass is the most stable passivation film because it does not allow gas and moisture to pass through. However, when the thickness is 50-100 μm or more, the expansion coefficient of the semiconductor element and the glass are different, and cracks tend to occur. Discharge is likely to occur at the part.

Further, a silicone resin, for example, a type obtained by heating a polysiloxane having a silanol group has a hard coating and has the same problem as glass. On the other hand, a polyimide resin has heat resistance and flexibility and is promising as a passivation film. However, there are some problems, for example, when left in a moist heat atmosphere, there is a problem of reduced reliability such as an increase in leak current.

[Problems to be Solved by the Invention] An object of the present invention is to solve the above problems and provide a method for obtaining a highly reliable passivation film for a semiconductor device.

[Means for Solving the Problems] The present invention provides (1) a passivation method in which a polyimide-based varnish is applied to an exposed surface of a PN junction portion of a semiconductor element, and heat treatment is performed. General formula (However, in the formula, R ₁ is a trivalent or tetravalent organic group, R ₂ is a divalent organic group, and m is 1 or 2.), and a polyamic acid having a structural unit [I], b) General formula (However, R ₃ , R ₄ , and R ₅ are hydrocarbon groups having 1 to 30 carbon atoms, and R ₃
Each of R ₅ to R ₅ can have a substituent or a bonding group at its carbon. n is 1 to 3. ) A tertiary amine compound represented by the formula (4) and a compound of (c) colloidal silica are used.

The semiconductor element according to the present invention refers to an element having a PN junction and having an exposed PN junction.

Examples include a diode as shown in JP-B-52-5586, JP-B-55-12737 and JP-B-57-16500, a thyristor element and a transistor element as shown in JP-B-60-58582. Not limited to.

The exposed surface of the PN junction may or may not be covered with an inorganic film such as SiO ₂ . Usually Si
Those covered with O ₂ are preferably used.

The polyamic acid having the structural unit [I] in the present invention means a polymer having a structure represented by the above general formula and having an imide ring or other cyclic structure by heating or a suitable catalyst (hereinafter referred to as a polyimide-based polymer). Can be called).

In the structural unit [I], R ₁ is a trivalent or tetravalent organic group having at least 2 carbon atoms. From the viewpoint of heat resistance of the polyimide-based polymer, R ₁ preferably has a structure in which the bond with the carbonyl group of the polymer main chain is directly formed from an aromatic ring or an aromatic heterocycle. Therefore, R ₁
Is preferably a trivalent or tetravalent group containing an aromatic ring or an aromatic heterocycle and having 6 to 30 carbon atoms.

As a more preferable specific example of R ₁ , (In the formula, the bond represents a bond with the carbonyl group of the polymer main chain, and the carboxyl group is located at the ortho position with respect to the bond, but this bond is not described in the above structural formula).

However, the present invention is not limited to these.

In the polymer having the structural unit [I], R ₁ may be composed of only one of these or may be a copolymer composed of two or more.

Particularly desirable as R ₁ is (However, in the formula, the definition of the bond is the same as above).

In the above structural unit [I], R ₂ is a divalent organic group having at least two carbon atoms, but from the viewpoint of heat resistance when a polyimide-based polymer is used, R ₂ is an amide group of the polymer main chain. Those having a structure in which the bond is directly formed from an aromatic ring or an aromatic heterocycle are preferable. Therefore, R ₂ contains an aromatic ring or an aromatic heterocycle and has 6 to 30 carbon atoms.
The divalent group of is preferable.

Specific preferred examples of R ₂ include: (In the formula, the bond represents a bond with the amide group of the main chain) and the like. Further, these may have respective substituents such as an amino group, an amide group, a carboxyl group, a sulfonamide group, etc. within a range that does not adversely affect the heat resistance of the polyimide polymer. Among the compounds having each of these substituents, particularly preferred examples Is mentioned.

In the polymer having the structural unit [I], R ₂ may be composed of only one of these, or may be a copolymer composed of two or more.

Further, in order to improve the adhesiveness of the polyimide-based polymer, it is possible to copolymerize an aliphatic group having a siloxane structure as R ₂ within a range that does not lower the heat resistance. As a preferred specific example And so on.

Specific examples of the polymer having the structural unit [I] as a main component include pyromellitic dianhydride and 4,4′-diaminodiphenyl ether, pyromellitic dianhydride and 3,3 ′, 4,4′- Benzophenone tetracarboxylic acid and 4,4'-diaminodiphenyl ether, 3,3 ', 4,4'-benzophenone tetracarboxylic dianhydride and 4,4'-diaminodiphenyl ether, 3,3', 4,4'-biphenyl With tetracarboxylic dianhydride
4,4'-diaminodiphenyl ether, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride and 3,3', 4,4'-benzophenone tetracarboxylic dianhydride and 4,4'-diamino Diphenyl ether, pyromellitic dianhydride and 3,3′-diaminodiphenyl sulfone, pyromellitic dianhydride and 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride and 3,3 ′-(or 4,4 ′
-) Diaminodiphenyl sulfone, 3,3 ', 4,4'-benzophenone tetracarboxylic dianhydride and 3,3'-(or 4,4 '-) diaminodiphenyl sulfone, 3,3', 4,4 ' -Biphenyltetracarboxylic dianhydride and
3,3 '-(or 4,4'-) diaminodiphenyl sulfone, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride and 3,3', 4,4'-benzophenonetetracarboxylic acid Dianhydride and 3,3 '-(or 4,4'-) diaminodiphenyl sulfone, pyromellitic dianhydride and 4,4'-diaminodiphenyl ether and bis (3-aminopropyl) tetramethyldisiloxane, pyromellitic Acid dianhydride and 3,3 ′, 4,4′-benzophenone tetracarboxylic acid dianhydride and 4,4′-diaminodiphenyl ether and bis (3-aminopropyl) tetramethyldisiloxane, 3,3 ′, 4, 4'-benzophenone tetracarboxylic dianhydride, 4,4'-diaminodiphenyl ether and bis (3-aminopropyl) tetramethyldisiloxane, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride And objects
4,4'-diaminodiphenyl ether and bis (3-
Aminopropyl) tetramethyldisiloxane, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride and 3,3', 4,4'-benzophenone tetracarboxylic dianhydride and 4,4'-diamino Diphenyl ether and bis (3-aminopropyl) tetramethyldisiloxane, pyromellitic dianhydride and 3,3 ′-(or 4,4 ′-) diaminodiphenylsulfone and bis (3-aminopropyl) tetramethyldisiloxane, Pyromellitic dianhydride and 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride and 3,3 ′-(or 4,4 ′
-) Diaminodiphenyl sulfone and bis (3-aminopropyl) tetramethyldisiloxane, 3,3 ', 4,4'-benzophenone tetracarboxylic dianhydride and 3,3'-(or 4,4 '-) diamino Diphenylsulfone and bis (3-aminopropyl) tetramethyldisiloxane, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride
3,3 '-(or 4,4'-) diaminodiphenyl sulfone and bis (3-aminopropyl) tetramethyldisiloxane, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride and 3,3' Polyamic acid synthesized from ′, 4,4′-benzophenone tetracarboxylic dianhydride and 3,3 ′-(or 4,4 ′-) diaminodiphenyl sulfone and bis (3-aminopropyl) tetramethyldisiloxane Is preferably used.

The polymer containing the structural unit [I] as a main component may be composed of the structural unit [I] alone or may be a copolymer with another structural unit. It is desirable to select the type and amount of the structural unit used in the copolymer within a range that does not significantly impair the heat resistance of the polyimide-based polymer obtained by the final heat treatment. Structural units of polyamide amic acid and polyester amic acid are typical examples,
It is not limited to these.

The tertiary amine compound in the present invention has the following general formula (However, R ₃ , R ₄ , and R ₅ are hydrocarbon groups having 1 to 30 carbon atoms, and R ₃
Each of R ₅ to R ₅ can have a substituent or a bonding group at its carbon. n is 1 to 3. ) Is represented by. As a substituent or a bonding group, -OC
H _3, -OH, -O-, And so on.

Preferred specific examples include trimethylamine, triethylamine, tri-n-propylamine, tri-n-butylamine, methyldiethylamine, dimethyl-n-propylamine, N, N-dibutyl-2-ethylhexylamine, N-methyldiallylamine, 3 -Dimethylaminopropanol, N-isobutyldiethanolamine, dimethyl-3-dimethoxypropylamine, N, N, N ', N'-tetramethyl-1,2-diaminoethane, N, N, N', N'-tetramethyl Diaminopropane, N, N, N ', N'-tetraallyl-1,4-diaminobutane, N, N, N', N'-pentamethyldiethylenetriamine, N, N-dimethylbenzylamine, dimethylaminoacetaldehyde diethyl acetal, 2-dimethylaminoethyl acetate, dimethylaminoethyl methacrylate, dimethy Aminoethyl acrylate, diethylaminoethyl methacrylate, although diethylaminoethyl acrylate, but are not limited to.

In particular, an aliphatic tertiary amine having a strong basicity is preferable because it has a large effect of promoting imide ring closure. Particularly preferred specific examples include, but are not limited to, triethylamine, tripropylamine, triallylamine, 2-dimethylaminoethyl acetate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, and the like. Not done.

These compounds may be used alone or 2
You may use it as a mixture of 2 or more types.

In addition, organic basic compounds such as primary amines, secondary amines, quaternary amines and pyridine derivatives, piperidine derivatives, etc. within a range that does not adversely affect the coating properties, the stability of solutions and the transparency of coating films. May be added.

The tertiary amine is preferably added in an amount of 0.2 to 3.0 equivalents, more preferably 0.25 to 2.0 equivalents, based on the carboxyl groups of the polyamic acid. When the amount is less than the lower limit, the effect of promoting imide ring closure is not sufficiently observed, and when the amount is more than the upper limit, the viscosity stability during storage is deteriorated.

The colloidal silica used in the present invention is a colloidal solution of high molecular weight silicic acid anhydride. This is commercially available as silica sol, and the dispersion medium is usually water, but those dispersed in an organic solvent (organo silica sol) are also commercially available (for example, OSCAL manufactured by Catalysts & Chemicals Industry Co., Ltd.).

The silica sol dispersed in the organic solvent is prepared by substituting water, which is a dispersion medium of the aqueous silica sol, with the organic solvent.
The dispersion medium can be replaced by a method of adding an organic solvent to the aqueous silica sol and distilling off water by means such as distillation. Depending on the type of solvent, add lower alcohol,
The surface of the silica particles may be partially esterified.

From the viewpoint of compatibility with polyamic acid, organosilica sol dispersed in an organic solvent is desirable. Particularly preferred is an organosilica sol dispersed in an aprotic polar solvent such as dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, which is a solvent for polyamic acid.

Addition amount S (wt%) of colloidal silica is 5 to 70 (wt%)
Is preferable, and more preferably 10 to 50 (wt%).
The addition amount S (wt%) of colloidal silica is given by the following equation.

When the amount is less than the lower limit, the effect of improving the properties is not remarkable, and when the amount is more than the upper limit, the film-forming ability is deteriorated.

Next, an example of the method for producing the varnish used in the present invention will be described.

The polyamic acid having the structural unit [I] in the present invention is preferably carried out by reacting a diamine and a tetracarboxylic dianhydride in an organic solvent at a temperature of about 15 ° C to 50 ° C for several hours. A tertiary amine compound and colloidal silica are added to and mixed with the produced polymer solution,
After adjusting the viscosity and the concentration with a diluent, an excess is carried out to obtain the varnish of the present invention.

Examples of organic solvents and diluents used in this reaction include:
Aprotic polar solvents such as N-methyl-2-pyrrolidone and N, N-dimethylacetamide can be mentioned.

Next, a semiconductor device passivation method of the present invention will be described.

First, the varnish is applied to the exposed surface of the P-N junction of the semiconductor element with a brush or the like.

After coating, the coating film is heat-treated to be a heat-resistant polymer having an imide ring or other cyclic structure. Heat treatment temperature is 200-350 ℃
Done in. The heat treatment time may be 10 minutes to 180 minutes. The heat treatment may be performed at a single temperature, or may be performed stepwise or continuously while raising the temperature.

Moreover, you may pre-process at the temperature of 200 degreeC or less. In this way, the exposed surface of the P-N junction of the semiconductor element is passivated with the above-mentioned heat resistant polymer.

Next, embodiments of the present invention will be described based on examples.

[Examples] Examples 1 to 4 564.5 g of diaminodiphenyl ether and 44.7 g of bis (3-aminopropyl) tetramethyldisiloxane were dissolved in 5680 g of N-methyl-2-pyrrolidone to prepare an amine solution. 327 g of pyromellitic dianhydride in this amine solution,
483 g of benzophenone tetracarboxylic acid dianhydride was added and reacted at 50 ° C. for 3 hours to obtain a polymer solution (A) of 120 poise at 25 ° C.

Colloidal silica (manufactured by Catalysts & Chemicals Industry Co., Ltd.) in which an amine compound as shown in Table 1 was added to this polymer solution (A) in an equivalent amount to the carboxyl group of polyamic acid and further dispersed in N-methyl-2-pyrrolidone , Product name OSCAL)
Was added, blended and passed through to obtain a varnish.

Next, this varnish was applied by brush coating to the exposed surface of the P-N junction of the power diode. After coating, pretreatment was performed at 100 ° C. for 1 hour, then at 135 ° C. for 1 hour, and heat treatment was performed at 250 ° C. for 1 hour in nitrogen. After cooling this device to room temperature, the reverse leak current at 1.2 KV was measured with a curve tracer, Model 5802, manufactured by Kikusui Electronics Co., Ltd. This value is the initial value. Next, after exposing this element to saturated steam at 120 ° C. and 2 atm for 3 hours, the leak current was similarly measured. This measured value is the value after the reliability test.

These data are shown in Table 1.

Comparative Example 1 (Conventional Method) The same procedure as in Example 1 was performed using a varnish (polymer solution (A)) containing no amine compound and colloidal silica. The data are shown in Table 1.

As is apparent from Table 1, the element obtained by the method of the present invention has a smaller leak current than the conventional element even after the initial value and after the wet heat treatment, and is excellent in reliability.

EFFECTS OF THE INVENTION Since the present invention is configured as described above, a highly reliable polyimide resin passivation film can be obtained.

Claims (1)

[Claims] 1. A passivation method in which a polyimide-based varnish is applied to an exposed surface of a P-N junction portion of a semiconductor element and heat treatment is performed, the varnish is represented by the general formula (a): (However, in the formula, R ₁ is a trivalent or tetravalent organic group, R ₂ is a divalent organic group, and m is 1 or 2.) and a polyamic acid having a structural unit [I], (B) General formula (However, R ₃ , R ₄ , and R ₅ are hydrocarbon groups having 1 to 30 carbon atoms, and R ₃
Each of R ₅ to R ₅ can have a substituent or a bonding group at its carbon. n is 1 to 3. ) A tertiary amine compound represented by the formula (4) and a mixture of (c) colloidal silica are used for the passivation of a semiconductor device.