JP5428964B2 - Semiconductor device and method for manufacturing semiconductor device - Google Patents

Description

  The present invention relates to a semiconductor element that reduces the residual stress of a substrate and hardly warps, and a method for manufacturing the semiconductor element.

  In order to protect the surface of the semiconductor element and prevent deterioration due to the influence of the external environment, the surface of the semiconductor element is covered with an insulating film. For such an insulating film, polyimide having good thermal, electrical and mechanical properties is mainly used.

  However, the coefficient of thermal expansion of polyimide is higher than that of silicon, SiC, GaN or the like used as a substrate material for semiconductor elements. For this reason, a crack was generated in the polyimide film coated on the surface of the semiconductor element due to heating or heat generation during the manufacturing process or use of the semiconductor element, or the substrate was easily warped due to a difference in thermal expansion between the polyimide film and the substrate. . In recent years, a reduction in the thickness of the substrate has been studied for the purpose of improving the electrical characteristics of the semiconductor element. However, as the thickness of the substrate decreases, the strength of the substrate rapidly decreases and warpage tends to occur. For this reason, such troubles are particularly likely to occur during the manufacture and use of a semiconductor element having a thinner substrate or a power semiconductor element in which the maximum use temperature of the semiconductor element is exposed to a higher temperature.

  As described above, in the case of a thinned silicon power semiconductor element having a maximum temperature use temperature of 175 ° C. or higher and a high breakdown voltage next-generation power semiconductor element (SiC, GaN), the yield is improved during the manufacturing process and the device is used for a long time. There were many risk factors due to thermal residual stress to ensure reliability.

  As a solution to such a problem, the surface of the semiconductor element is covered with a polyimide film having a low coefficient of thermal expansion, and the thermal stress generated at the interface between the substrate and the insulating film is relieved so that the semiconductor element is used or manufactured. Attempts have been made to suppress cracks in the insulating film and warping of the substrate. For example, Patent Document 1 has a repeating unit formed from a polycondensation product of tetracarboxylic acid or its acid anhydride and diamine in a main chain on a circuit formed on a silicon wafer. It is disclosed to form a photosensitive polyimide precursor having an actinic functional group at the terminal. It is described that the thermal expansion coefficient of the polyimide film thus formed is preferably 20 ppm / ° C. or less.

JP 2004-285129 A

  However, a polyimide film having a low coefficient of thermal expansion generally has a high film elastic modulus and is hard and brittle, and the surface becomes rough when the film surface is polished by a cutting flattening method. Moreover, the polyimide precursor composition capable of forming a polyimide film having a low coefficient of thermal expansion has poor varnish stability and poor handling properties. Furthermore, since the varnish stability is poor, it is difficult to form an insulating film having a low heat dissipating property due to low miscibility with heat dissipating fillers.

  Moreover, since the photosensitive polyimide material is generally expensive, there is a problem that the material cost increases. Furthermore, there is a risk of film adhesion after film formation and long-term reliability degradation due to the influence of the functional group and additives used for imparting photosensitivity.

  Accordingly, an object of the present invention is to provide a semiconductor element protected by an insulating film having excellent heat resistance and mechanical properties, and a method for manufacturing the same, even if the substrate is thinned.

Upon achieving the above object, a semiconductor device of the present invention, one in the substrate, the first surface electrode, and an insulating film covering at least a portion of the first surface electrode is formed, the back surface on the other of said substrate A semiconductor element in which an electrode is formed , wherein the substrate has a thickness of 150 μm or less, and the insulating film is made of at least one acyl compound selected from aromatic tetracarboxylic acid and aromatic tetracarboxylic dianhydride. A polyimide film having a thermal expansion coefficient of 2 to 24 ppm / ° C. obtained by imidizing a polyimide precursor composition containing a polyamic acid obtained by reacting at least 1 mol% more than the aromatic diamine. And

  In the semiconductor element of the present invention, the insulating film preferably has a thickness of 1 to 50 μm.

  In the semiconductor element according to the present invention, the aromatic diamine may be 2,2′-di (p-aminophenyl) -5,5′-bisbenzoxazole, p-phenylenediamine, 4,4′-diaminobiphenyl, and 4, It is preferable to contain 70-100 mol% of one or more selected from 4'-diaminobenzanilide.

  In the semiconductor element of the present invention, the acyl compound is composed of pyromellitic acid, pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 3,3 ′, 4,4′-biphenyltetra. 70 to 100 mol% of at least one selected from carboxylic dianhydride, 3,3 ', 4,4'-benzophenone tetracarboxylic acid and 3,3', 4,4'-benzophenone tetracarboxylic dianhydride It is preferable to contain.

  In the semiconductor element of the present invention, the polyimide precursor composition preferably contains an insulating heat dissipating filler.

  In the semiconductor element of the present invention, the polyamic acid has a polystyrene-equivalent weight average molecular weight of 50,000 to 200,000 and the ratio of polyamic acid is 70 to 100% by mass, and the polystyrene-equivalent weight average molecular weight is 10,000 or more. It is preferable that the ratio of the polyamic acid which is less than 50,000 is 0-30 mass%.

  In the semiconductor element of the present invention, an inorganic thin film insulating layer is preferably formed between the insulating film and the first surface electrode. The inorganic thin film insulating layer is preferably composed of silicon oxide and / or silicon nitride.

  In the semiconductor element of the present invention, a second surface electrode is formed on the surface of the insulating film, and the first surface electrode and the second surface electrode are electrically connected via a contact electrode formed by communicating the insulating film. It is preferable that it is comprised.

  In the semiconductor element of the present invention, it is preferable that the substrate is made of one or more selected from silicon, SiC, and GaN.

In addition, the method for manufacturing a semiconductor element of the present invention includes a first surface electrode forming step of forming a first surface electrode on one surface of a substrate, and an aromatic tetracarboxylic acid on the surface of the substrate on which the first surface electrode is formed. Applying a polyimide precursor composition containing a polyamic acid obtained by reacting at least 1 mol% of an acyl compound selected from an acid and an aromatic tetracarboxylic dianhydride by 1 mol% or more than the aromatic diamine, imidized, thermal expansion coefficient and the insulating film forming step of forming an insulating film made of a polyimide film of 2~24ppm / ℃, the substrate on which the first surface electrode and the insulating film is formed at least, said first surface electrode and formed side by polishing the opposite surface to adjust the thickness to 150μm or less, after forming the back electrode on the surface of the polished side die for separating the element units by dicing from the first surface electrode side Characterized in that it comprises a ring step.

  In a method for manufacturing a semiconductor device, a resist composition is applied to a substrate on which the first surface electrode is formed, pre-baked to form a resist film, and a contact hole is formed on the first surface electrode through the resist film. The contact electrode is formed in the contact hole, the resist film is peeled off, the insulating film forming step is performed, and then the second surface electrode is formed on the insulating film through the contact electrode It is preferable to do.

  According to a method for manufacturing a semiconductor device, a via portion is opened in an insulating film formed in an insulating film forming step, a contact electrode is formed in the opened via portion, and then a second surface electrode is formed on the insulating film via the contact electrode. Is preferably formed.

  In the method of manufacturing a semiconductor device, after forming the second surface electrode on the insulating film, the other surface of the substrate is polished to adjust the thickness to 150 μm or less, and the back electrode is formed on the polished surface. Alternatively, after finishing the insulating film forming step, the other surface of the substrate is polished to adjust the thickness to 150 μm or less, and a back electrode is formed on the polished surface, and then on the insulating film. It is preferable to form a second surface electrode.

According to the present invention, on the surface of the substrate on which the first surface electrode is formed, one or more acyl compounds selected from aromatic tetracarboxylic acid and aromatic tetracarboxylic dianhydride are added to the surface of the aromatic diamine. A polyimide precursor composition containing a polyamic acid obtained by reacting more than 1 mol% or more is applied and imidized to form an insulating film.
Since this polyimide precursor composition has good varnish stability and excellent handleability, it is easy to manage the manufacturing process of the semiconductor element. Moreover, the polyimide film obtained by forming this polyimide precursor composition is excellent in heat resistance and has appropriate flexibility and strength. Furthermore, since the thermal expansion coefficient is 2 to 24 ppm / ° C., which is close to that of the semiconductor element substrate, the residual stress at the substrate interface is reduced, and the warpage of the substrate, cracks in the insulating film, etc. Can be suppressed. Therefore, according to the present invention, a highly reliable semiconductor element can be manufactured with high productivity over a long period of time.

It is the schematic of the semiconductor element of this invention. It is the schematic which shows 1st Embodiment of the manufacturing process of the semiconductor element of this invention. It is the schematic which shows 2nd Embodiment of the manufacturing process of the semiconductor element of this invention.

The insulating film used for the semiconductor element of the present invention will be described.
The insulating film used in the semiconductor element of the present invention includes a polyamic acid obtained by reacting an aromatic diamine with one or more acyl compounds selected from aromatic tetracarboxylic acid and aromatic tetracarboxylic dianhydride. It is a polyimide film formed by imidizing a polyimide precursor composition.

(Aromatic diamine)
Aromatic diamines include 2,2′-di (p-aminophenyl) -5,5′-bisbenzoxazole, p-phenylenediamine, 4,4′-diaminobiphenyl and 4,4′-diaminobenzanilide. What contains 70-100 mol% of 1 or more types chosen is used preferably. These aromatic diamines have a relatively rigid structure, and can form a polyimide film having excellent heat resistance while reducing the coefficient of thermal expansion. When the ratio of the aromatic diamine (hereinafter also referred to as rigid structure diamine) to the whole aromatic diamine is less than 70 mol%, the heat resistance tends to be lowered.

  When 2,2'-di (p-aminophenyl) -5,5'-bisbenzoxazole is used as the rigid structure diamine, a very highly heat-resistant and flexible polyimide film can be obtained. Moreover, this polyimide film has a relatively small elastic modulus, is excellent in surface flatness during cutting, and is further excellent in filler dispersibility.

  In addition, when 4,4'-diaminobenzanilide is used as the rigid structure diamine, a polyimide film having excellent filler dispersibility can be obtained.

  In addition, when p-phenylenediamine, 4,4'-diaminobiphenyl, or 4,4'-diaminobenzanilide is used as the rigid structure diamine, the manufacturing cost can be reduced because the chemical cost is low. Furthermore, since the reactivity with the acyl compound is high, the cycle time during the reaction can be shortened.

  In addition to the above-mentioned rigid structure diamine, a flexible structure diamine (hereinafter also referred to as a flexible structure diamine) may be used in combination with the aromatic diamine. By using the flexible structure diamine in combination, the flexibility of the polyimide film and the adhesion to a metal or a substrate can be enhanced.

  When using a flexible structure diamine, 30 mol% or less is preferable, as for the ratio of the flexible structure diamine with respect to the whole aromatic diamine, 3-20 mol% is more preferable, and 3-10 mol% is especially preferable. When the ratio of the flexible structure diamine exceeds 30 mol%, the heat resistance of the polyimide film may be insufficient. Moreover, the addition effect may be hardly acquired as it is less than 3 mol%.

  Examples of the flexible structure diamine include a diamine containing an ether structure in the main chain, a diamine containing a heterocycle in the main chain, and a diamine having a siloxane structure in the main chain.

  Examples of the diamine containing an ether structure in the main chain include oxydianiline.

  As the diamine containing a hetero ring in the main chain, a diamine having a thiophene ring is preferable. Specifically, 2,5-bis (4-aminobenzoyl) thiophene is a preferred example. By using 2,5-bis (4-aminobenzoyl) thiophene, it is possible to form a polyimide film having excellent adhesion to metal. The reason can be estimated as follows. That is, 2,5-bis (4-aminobenzoyl) thiophene is flexible, and at the same time as the anchor effect due to the flexibility of the resin, the S element of the thiophene ring is coordinated to the metal so that it adheres to the metal. It is thought that it contributes effectively.

  The diamine having a siloxane structure in the main chain is preferably a diamine represented by the following formula (1). More preferably, it is a diamine of the following formula (2). By using the diamine of the following formula (1), the adhesion to the substrate and the metal can be improved.

(In Formula (1), R ¹ and R ² are divalent hydrocarbon groups which may be the same or different. R ^{3 to} R ⁶ may be the same or different. A monovalent hydrocarbon group that may be present, and n is an integer of 1 or more.)

(Acyl compound)
Examples of acyl compounds include pyromellitic acid, pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 3 , 3 ′, 4,4′-benzophenonetetracarboxylic acid and those containing 70 to 100 mol% of one or more selected from 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride are preferably used. It is done. Since these acyl compounds have a relatively rigid structure and can form a rod-like rigid straight chain, it is possible to form a polyimide film excellent in heat resistance while lowering the coefficient of thermal expansion. If the ratio of the acyl compound (hereinafter also referred to as rigid structure acyl compound) to the whole acyl compound is less than 70 mol%, the heat resistance tends to be lowered.

  When 3,3 ′, 4,4′-biphenyltetracarboxylic acid or 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride is used as the rigid structure acyl compound, the reason is unknown, The varnish stability of the polyimide precursor can be improved. Furthermore, the resulting polyimide film has a low elastic modulus, excellent elongation at break, tends to favor surface resistance during cutting, and works favorably, such as flatness.

  When pyromellitic acid or pyromellitic dianhydride is used as the rigid structure acyl compound, the thermal expansion coefficient of the polyimide film can be further reduced.

  The acyl compound includes an aromatic tetracarboxylic acid having a structure in which two or more aromatic rings are bonded by an ester bond, an ether bond, and a ketone bond in addition to the rigid structure acyl compound described above and acid anhydrides thereof ( Hereinafter, it may also contain a flexible structure acyl compound). These flexible structure acyl compounds are flexible, have a flexible structure, and can increase the flexibility of the polyimide film.

  When the flexible structure acyl compound is used, the ratio of the flexible structure acyl compound to the whole acyl compound is preferably 30 mol% or less, more preferably 3 to 20 mol%, and particularly preferably 3 to 15 mol%. If the proportion of the flexible structure acyl compound exceeds 30 mol%, the heat resistance of the polyimide film may be insufficient. Moreover, the addition effect may be hardly acquired as it is less than 3 mol%.

  Examples of the flexible structure acyl compound include 3,3 ′, 4,4′-benzophenone tetracarboxylic acid, 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, and the like.

(Polyimide precursor composition)
The polyimide precursor composition contains at least a polyamic acid obtained by reacting the aromatic diamine and the acyl compound. In the present invention, as the polyamic acid, a polyamic acid obtained by reacting the acyl compound by 1 mol% or more more than the aromatic diamine is used. Preferably, 1.01 to 1.15 mol, more preferably 1.02 to 1.08 mol, particularly preferably 1.02 to 1.05 mol of the acyl compound is reacted with 1 mol of the aromatic diamine. Is a polyamic acid obtained.

The polyimide film obtained by imidizing the polyimide precursor composition containing this polyamic acid has a high thermal decomposition temperature. Furthermore, the decomposition gas generated at the initial stage of the thermal decomposition includes a carboxyl group and an acid anhydride group at the molecular end. The main component is carbon dioxide gas (CO ₂ ) generated by thermal decomposition, which can suppress decomposition of the main chain polymer of the polyimide film and is excellent in heat resistance.

  On the other hand, it is easy to obtain a polyamic acid having an amino group at the molecular end by reacting an acyl compound at a ratio of 1 mol or less with respect to 1 mol of the aromatic diamine, but a polyamide having an amino group at the molecular end. The acid easily forms a salt by reacting the carboxyl group of the polyamic acid with the amino group at the molecular end. When such a salt is formed, the molecular weight of the polyamic acid tends to decrease due to the catalytic effect, and the viscosity of the polyimide precursor composition tends to change over time. Furthermore, hydrolysis of the polyamic acid is easily promoted by water or the like generated during thermal imidation of the polyimide precursor composition, and the molecular weight of the resulting polyimide film is likely to decrease. Furthermore, since the terminal amino group is unstable to heat, it is more thermally decomposed than a polyimide film formed by imidizing a polyamic acid having a structure in which the molecular end is end-capped with a carboxyl group or an acid anhydride group. The starting temperature tends to be low, and the heat resistance tends to be impaired.

  In the present invention, the ratio of the polyamic acid having a polystyrene-equivalent weight average molecular weight of 50,000 to 200,000 is 70 to 100% by mass, and the polystyrene-equivalent weight average molecular weight is 10,000 to less than 50,000. It is preferable that the ratio of the polyamic acid which is is 0-30 mass%.

Polyamic acid having a weight average molecular weight in terms of polystyrene of 50,000 or more and 200,000 or less (hereinafter also referred to as high molecular weight polyamic acid) has good varnish viscosity, good handling properties, and good filler dispersibility. . Furthermore, a polyimide film having excellent heat resistance and mechanical strength (breaking strength, breaking elongation, etc.) can be obtained.
Polyamide acid having a polystyrene-equivalent weight average molecular weight of 10,000 or more and less than 50,000 (hereinafter also referred to as low molecular weight polyamide acid) tends to decrease the mechanical strength of the polyimide film after film formation. Since the proportions of carboxyl groups and acid anhydride groups at the molecular terminals are increased, varnish stability, filler dispersibility, and substrate adhesion are improved.
And if the ratio of high molecular weight polyamic acid is 70-100 mass% and the ratio of low molecular weight polyamic acid is 0-30 mass%, it is excellent in varnish stability, filler dispersibility is good, A polyimide film having excellent mechanical strength and excellent heat resistance is easily obtained. When a high molecular weight polyamic acid and a low molecular weight polyamic acid are mixed and used, a polyimide film having the functions of both resins can be obtained.

  In addition, when mixing and using high molecular weight polyamic acid and low molecular weight polyamic acid, it is preferable to select and use the combination of high molecular weight polyamic acid and low molecular weight polyamic acid which is excellent in compatibility. Particularly preferably, polyamic acids having the same main chain structure are used. If the compatibility between the high molecular weight polyamic acid and the low molecular weight polyamic acid is good, the polyimide film after imidization is completely integrated and excellent in long-term reliability.

  Polyamide acid having a low polystyrene equivalent weight average molecular weight can be obtained by reacting the polyamic acid with a polystyrene equivalent weight average molecular weight by increasing the ratio of the acyl compound to the aromatic diamine.

  In the present invention, the polystyrene-reduced weight average molecular weight is a value determined by the weight average molecular weight measurement described in Examples described later.

  In the present invention, the polyimide precursor composition contains a solvent such as NMP (N-methylpyrrolidone), DMAc (dimethylacetamide), DMF (dimethylformamide), DMSO (dimethylsulfoxide) to adjust the viscosity. You may go. These solvents are preferably contained in the polyimide precursor composition in an amount of 75 to 95% by weight, more preferably 80 to 92% by weight, and the viscosity of the polyimide precursor composition is adjusted to 5 to 300 Pa · S.

  In the present invention, the polyimide precursor composition may contain an insulating heat dissipating filler. By including the insulating heat dissipating filler, the cooling property of the obtained polyimide film can be improved. Moreover, since this polyimide precursor composition is excellent in filler dispersibility, even if it contains an insulating heat dissipating filler, handling properties are not easily impaired.

  There is no limitation in particular as an insulating thermal radiation filler, A conventionally well-known thing can be used. Preferred is boron nitride. Boron nitride is excellent in cooling characteristics and further in affinity with the amide structure, so that it is easily dispersed uniformly in the polyimide precursor composition and is difficult to separate from the polyimide film after film formation.

  The insulating heat dissipating filler is preferably contained in the polyimide precursor composition in an amount of 1 to 30% by weight, more preferably 3 to 30% by weight, based on the weight of the polyimide resin. If the content of the insulating heat dissipating filler is less than 3% by weight, the effect of addition is hardly obtained. When it exceeds 30% by weight, it becomes difficult to uniformly disperse in the polyimide precursor composition, and furthermore, the varnish stability tends to be lowered.

(Insulating film)
The insulating film used for the semiconductor element of the present invention is made of a polyimide film obtained by forming the polyimide precursor composition.

  The method for forming the polyimide precursor composition is not particularly limited, and can be formed by a conventionally known method. For example, a polyimide precursor composition is applied to the surface of an object to be coated such as a substrate, a process such as heat drying is performed to form a coating film of the polyimide precursor composition, and this is performed by thermal imidization. Can be mentioned. Moreover, the adhesiveness with a to-be-coated object can be improved by processing the surface of a to-be-coated object beforehand with a coupling agent. As the coupling agent, a silane coupling agent, an aluminum coupling agent, a titanium coupling agent, or the like can be used. A treatment method using a coupling agent can be performed by a conventionally known method. For example, a wet treatment method in which a coupling agent is dissolved in a solvent and applied to the surface of the object to be coated, a dry method in which the object to be coated is exposed to the vapor of the coupling agent, and the like.

  The insulating film used for the semiconductor element of the present invention has a coefficient of thermal expansion of 2 to 24 ppm / ° C, preferably 2 to 18 ppm / ° C, more preferably 2 to 11 ppm / ° C, and particularly preferably 2 to 7 ppm / ° C. In order to increase the coefficient of thermal expansion, the ratio of the flexible diamine or the flexible acid anhydride may be increased. In order to lower the coefficient of thermal expansion, the ratio of rigid structure diamine or rigid structure acid anhydride may be increased.

  The insulating film used for the semiconductor element of the present invention has an elastic modulus of preferably 2 to 8 Gpa, and more preferably 4 to 7 Gpa. If the elastic modulus is less than 8 Gpa, the elongation at break is excellent, the surface resistance during cutting tends to be favorable, and the flatness and the like work advantageously. When the elastic modulus exceeds 8 Gpa, the film becomes hard and brittle, and the cutting flatness deteriorates. In order to increase the elastic modulus of the insulating film, the ratio of the rigid structure diamine or the rigid structure acyl compound may be increased within the above range. In order to lower the elastic modulus, the ratio of the flexible structure diamine or the flexible structure acyl compound may be increased within the above range.

  The insulating film used in the semiconductor element of the present invention preferably has an elongation at room temperature of 10% or more, more preferably 30% or more, as measured by the method of measuring film breaking strength and breaking elongation described in Examples below. . If the elongation is 30% or more, the stress on the contact electrode can be sufficiently relaxed by the elongation of the film.

(Semiconductor element)
Next, the semiconductor element of the present invention will be described.

  1A and 1B are schematic views of a semiconductor device of the present invention, in which FIG. 1A is a plan view and FIG. 1B is a cross-sectional view taken along line YY of FIG. 1A. .

  In this semiconductor element, a first surface electrode 2 is formed on the surface side of a substrate 1 so as to connect unillustrated semiconductor cells by a circuit. An insulating film 3 is formed on the entire surface of the substrate 1 so as to cover the first surface electrode. A plurality of contact electrodes 4 are formed on the first surface electrode 2, and are joined to the second surface electrode 5 formed on the insulating film 3 via the contact electrode 4. A back electrode 6 is formed on the back side of the substrate 1.

  The substrate 1 is not particularly limited. Any substrate used as a substrate for a semiconductor element can be preferably used. Especially, what is comprised by 1 or more types chosen from silicon | silicone, SiC, and GaN is used preferably.

  The thickness of the substrate 1 is preferably 150 μm or less, and more preferably 100 μm or less. By reducing the thickness of the substrate, the semiconductor element can be miniaturized. When the thickness of the substrate exceeds 150 μm, the function improvement due to the thin plate may not be sufficiently obtained.

  Examples of the first surface electrode 2 include a nickel alloy, an aluminum alloy, and the like. The first surface electrode 2 can be formed by a conventionally known method such as sputtering, vapor deposition, or plating process.

  Examples of the contact electrode 4 include those made of copper, aluminum or the like. The total surface area of the contact electrode 4 is preferably 10 to 50% of the surface area of the first surface electrode 2, and more preferably 25 to 30%. If the total value of the surface area of the contact electrode 4 is within the above range, heat generated by the first surface electrode 2 can be easily transmitted to the upper portion, and heat dissipation is improved. The contact electrode 4 can be formed by a conventionally known method such as sputtering, vapor deposition, or plating process.

  Examples of the second surface electrode 5 include a structure in which a nickel / chromium / gold layer is laminated on copper and aluminum, and is composed of wiring for solder bonding. The second surface electrode 5 can be formed by a conventionally known method such as sputtering, vapor deposition, or plating process.

  Examples of the back electrode 6 include a four-layer structure of Al layer / Ti layer / Ni layer / Au layer. The back electrode 6 may be formed on the entire back surface of the substrate, or may be formed on a part thereof. The back electrode 6 can be formed by a conventionally known method such as a plating process.

  The insulating film 3 is as described above. The thickness of the insulating film is preferably 1 to 50 μm, and more preferably 3 to 25 μm. If the thickness of the insulating film is less than 1 μm, the effect as a protective film may be hardly obtained. On the other hand, if it exceeds 50 μm, it is difficult to reduce the size of the semiconductor element. Furthermore, the residual stress derived from the polyimide film may become unnecessarily large and cause warping.

  In the present invention, an inorganic insulating thin film may be interposed between the surface side of the substrate 1 including the first surface electrode 2 and the insulating film 3. By interposing the inorganic insulating film, the leakage resistance performance on the surface of the semiconductor element is improved. Examples of the inorganic insulating film include silicon nitride and silicon oxide. The silicon nitride thin film suppresses excessive charging under the thin film and contributes to the stability of the device. The inorganic insulating film may be arbitrarily formed at a required site by using a vapor deposition process after forming the first surface electrode 2.

  When an inorganic insulating film is interposed, the thickness of the inorganic insulating film is preferably 0.1 to 5 μm, and more preferably 0.3 to 2.5 μm. When the thickness is less than 0.1 μm, the effect of the inorganic insulating film is hardly obtained. Moreover, when it exceeds 5 micrometers, it will become easy to enter a crack.

  Although the semiconductor element shown in FIG. 1 includes the back electrode 6, the back electrode 6 is not always necessary and the back electrode 6 may not be provided.

(Semiconductor element manufacturing method)
[First Embodiment]
Next, a first embodiment of a method for manufacturing a semiconductor device of the present invention will be described with reference to FIG.

  First, a first surface electrode 2 is formed on a substrate 1 (substrate before polishing) so as to connect semiconductor cells (not shown) with a circuit (FIG. 2A).

  Next, a resist is applied to the surface of the substrate 1 on which the first surface electrode 2 is formed (FIG. 2B), and this is prebaked to form a resist film 10. Then, a contact hole is formed on the first surface electrode 2 through the resist film 10, and the contact electrode 4 is produced in the contact hole by using an electrolytic plating method (FIG. 2C). By peeling off the resist film 10, a substrate having the contact electrode 4 formed on the first surface electrode 2 is obtained (FIG. 2D).

  Next, a polyimide precursor composition is applied to the entire surface of the substrate 1 in a form in which the first surface electrode 2 and the contact electrode 4 are embedded, and is heated and dried to form a coating film of the polyimide precursor composition. The insulating film 3 is formed by thermal imidization (FIG. 2E). In the case of interposing an inorganic insulating film, it is optionally formed through a method such as a vapor deposition process on the surface side of the substrate 1 and the required portion of the first surface electrode 2 before applying the polyimide precursor composition. The method for applying the polyimide precursor composition is not particularly limited, and examples thereof include a spin coat method, a bar coater method, and a spray application method. The imidation of the coating film of the polyimide precursor composition is preferably performed so that the final curing temperature is 300 to 400 ° C. This high temperature treatment effectively works to improve the strength of the contact electrode 4 because it also anneals the plating layer of the contact electrode 4.

  Next, the surface of the insulating film 3 is cut by polishing or cutting, and the upper part of the contact electrode 4 is cut out on the insulating film 3 to be exposed (FIG. 2F).

  Next, a second surface electrode 5 (emitter electrode, gate electrode) is formed on the insulating film 3 via the contact electrode 4 exposed on the insulating film 3 (FIG. 2G).

  Next, the surface electrode side is fixed to a jig or the like, and the back surface side of the substrate 1 is polished to adjust the substrate 1 to a predetermined thickness (preferably 150 μm or less). Examples of the polishing method include known CMP (chemical mechanical polishing method).

  Next, the back surface electrode 6 is formed on the back surface side of the substrate 1 adjusted to a predetermined thickness (FIG. 2 (f)). The back electrode 6 may be formed on the entire back surface of the substrate, or may be partially formed.

  Then, the back surface electrode side is fixed to a jig or the like, the front surface electrode side is diced from the insulating film 3 by a method such as die size using a diamond rotary blade, and each element is cut out to manufacture the semiconductor device of the present invention. it can.

  In the case of manufacturing a semiconductor element that does not have the back electrode 6, the back surface side of the substrate 1 is polished and adjusted to a predetermined thickness, and then the back electrode side is fixed to a jig or the like, and the front electrode side is fixed. Each element can be cut out by dicing the insulating film 3. For chipping and crack suppression during dicing, methods such as half cut / back surface polishing dicing can be employed.

[Modification of First Embodiment]
Next, a modification of the first embodiment will be described.
In the first embodiment described above, after the second surface electrode 5 is formed, the back surface side of the substrate 1 is polished. However, in this embodiment, the insulating film 3 is polished or cut to obtain the contact electrode 4. After the upper surface of the substrate 1 is cut out on the insulating film 3, the surface electrode side is adjusted to a predetermined thickness by polishing the back surface side of the substrate 1, and after forming the back electrode, the second surface electrode 5 is formed on the insulating film 3. Form.
By polishing the back surface side of the substrate 1 in this way, the in-plane uniformity of the substrate thickness and the insulating film thickness after the substrate polishing is increased, and the substrate 1 can be made thinner.

[Second Embodiment]
Next, a second embodiment of the semiconductor device manufacturing method of the present invention will be described with reference to FIG.

  First, the first surface electrode 2 is formed on the substrate 1 (substrate before polishing) so as to connect semiconductor cells (not shown) with a circuit (FIG. 3A).

  Next, a polyimide precursor composition is applied to the entire surface side of the substrate 1 in the form of embedding the first surface electrode 2, and is heated and dried to form a coating film of the polyimide precursor composition. An insulating film 3 is formed (FIG. 3B).

  Next, a via hole 11 is formed on the first surface electrode 2 through the insulating film 3 (FIG. 3C). A method for forming the via hole 11 is not particularly limited, and a conventionally known method such as a laser via forming method or a dry etching method can be used.

  Next, the contact electrode 4 is produced in the via hole 11 using an electrolytic plating method (FIG. 3D).

  Next, the second surface electrode 5 (emitter electrode, gate electrode) is formed on the insulating film 3 via the contact electrode 4 exposed on the insulating film 3 (FIG. 3E).

  Next, the front surface electrode side is fixed to a jig or the like, and the back surface side of the substrate 1 is polished to adjust the substrate 1 to a predetermined thickness (FIG. 3F).

  Next, the back surface electrode 6 is formed on the back surface side of the substrate 1 adjusted to a predetermined thickness (FIG. 3G).

  And the semiconductor element of this invention can be manufactured by fixing a back surface electrode side to a jig | tool etc., and dicing the surface electrode side from the insulating film 3, and cutting out each element.

[Measuring method]
-Weight average molecular weight measurement Measuring device: LC-10AD manufactured by Shimadzu (analysis software: CLASS-VP, GPC for CLASS-VP)
UV detection: measurement wavelength 270 nm
Column: Plgel 5 μm MIXED-C 300 × 7.5 mm made by PL
Plgel 5 μm Guard 50 × 7.5 m, 2 columns, temperature: 36 ° C.
Eluent: N, N-dimethylformamide (DMF) 500 ml / L, tetrahydrofuran (THF) 500 ml / L, phosphoric acid 5.8 g / L mixed liquid Flow rate: 1 ml / min (pump flow rate error ± 2%)
Standard polystyrene: Tosoh standard kid resin concentration 0.1Wt%

-Varnish stability Adjusted by adding a mixed solvent in which N-methylpyrrolidone (NMP) and dimethylacetamide (DMAc) are mixed at a weight ratio of 1: 1 so that the viscosity of the polyimide precursor composition is 30 Ps. Then, the viscosity after standing for 48 hours at 25 ° C. was measured under the conditions of 25 ° C., 20 rpm or 100 rpm using an E-type rotational viscometer manufactured by Toki Sangyo Co., Ltd. and an M type for medium viscosity. In the case of a viscosity change within ± 10%, it was marked with ◯, in the case of a viscosity change of ± 10-12%, it was marked with △, and the others were marked with ×.

-Filler dispersibility After adding 25 mass% of boron nitride with an average particle diameter of 5 micrometers to a polyimide precursor composition with respect to the resin weight, it stirred and disperse | distributed. The dispersibility after standing at 25 ° C. for 3 hours was visually observed. In the case of uniform dispersion, “◯” was given, in the case of slight sedimentation separation, “Δ”, and in the case of sedimentation separation, “X”.

-Thermal expansion coefficient measurement Measuring device: EXSTAR TMA / SS6000 manufactured by Seiko Instruments
Measurement sample: 4 mm × 20 mm × 10 μm
Measurement conditions: The change in the coefficient of thermal expansion during the second cooling of 25 ° C. → 300 ° C. → 25 ° C. → 300 ° C. → 25 ° C. cycle was recorded.
Temperature increase rate: 5 ° C / min Load: 2g (air atmosphere)

1% weight decay start temperature measuring device: EXSTAR 6000 manufactured by Seiko Instruments
Measurement sample: 2 to 500 mg
Measurement conditions: While supplying N 2 gas at a flow rate of 200 ml / min, the temperature was raised from room temperature to 600 ° C. at a rate of temperature rise of 10 ° C./° C., and the 1% weight decay start temperature was recorded.

-Elastic modulus measurement Measuring device: EXSTAR TMA / SS6000 manufactured by Seiko Instruments
Measurement sample: 9 mm × 20 mm × 10 μm
Measurement conditions: minimum tension / compression force = 50 mN, tension / pressure gain = 1.2, initial force amplitude = 50 mN, frequency = 1 Hz, temperature change program = room temperature to 300 ° C., heating rate = 5 ° C./min

・ Breaking strength, breaking elongation Measuring device: Precision universal testing machine Autograph made by Shimadzu Floor type AG-10kNX
Measurement sample: 0.01 mm × 10 mm × 35 mm
Measurement conditions: Tensile speed 10 mm / min (25 ° C.)

Thermal decomposition start temperature and cracked gas measurement Measuring device: FT / IR-470 Plus-Irtron IRT-30 (Nikolay)
Heating temperature: Start temperature 100 ° C. to 700 ° C. (30 min)
Temperature increase rate: 20 ° C / min
(GC department)
Column: Ultra ALLOY-DTM 2.5m x 0.15mm
Temperature: 300 ° C
Inlet: 300 ° C
Interface: 280 ° C
Carrier gas: 50 Kpa Total flow rate 60 mL / min

-Thermal conductivity measurement The polyimide precursor composition was applied and prebaked on a silicon substrate so that the film thickness after film formation was 30 to 40 µm. The polyimide precursor composition was further applied thereon. After repeating this operation to adjust the film thickness, thermal imidization was performed to prepare a sample, and the thermal conductivity was measured using a rapid thermal conductivity meter (QTM-50) manufactured by Kyoto Electronics Industry Co., Ltd.

[Manufacture of insulating films]
(Production Example 1)
In a 500 mL separable flask equipped with a high-viscosity stirrer and a nitrogen gas line, 12.54 g (0.03 mol) of 2,2′-di (p-aminophenyl) -6,6′-bibenzoxazole was weighed. . Next, 90 g of a mixed solvent (hereinafter referred to as a mixed solvent) in which N-methylpyrrolidone (NMP) and dimethylacetamide (DMAc) were mixed at a weight ratio of 1: 1 was added, and the mixture was stirred at room temperature for 30 minutes.
To this mixed reaction liquid, 9.18 g (0.0312 mol) of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride was added in a powder form while stirring on ice. Furthermore, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride adhering to the reaction vessel using 20 g of the mixed solvent was added while washing. After stirring for 2 hours with ice cooling, the temperature was raised to 25 ° C. and then stirring for 24 hours to obtain a polyamic acid. Table 1 shows the weight average molecular weight, varnish stability, and filler dispersibility of this polyamic acid.
An appropriate amount of the above mixed solvent was added to the obtained polyamic acid to adjust the viscosity to 30 to 50 Ps to obtain a polyimide precursor composition. This polyimide precursor composition was applied to a silicon substrate that had been treated with a coupling agent using a spinner, and prebaked using a hot plate at 90 ° C. for 6 minutes. (The coating thickness was adjusted so that the post-curing thickness was 8 μm). Next, using an inert oven, thermal imidization is performed by a temperature process of 50 ° C. × 60 minutes → 150 ° C. × 30 minutes → 250 ° C. × 60 minutes × final cure temperature (350 or 400 ° C.) × 60 minutes → cooling (room temperature). A film was formed.
Then, using 50% hydrofluoric acid, the film formed from the silicon substrate was peeled off, sufficiently washed with water and dried by heating at 130 ° C. for 3 hours to obtain a film for evaluation, and the breaking strength (MPa) and elongation at break ( %), Coefficient of thermal expansion (ppm / ° C.), elastic modulus (GPa), 1% weight decay start temperature (° C.), degassing detection temperature (° C.), and type of cracked gas. The results are summarized in Table 1.

(Production Example 2)
In Production Example 1, instead of 12.54 g (0.03 mol) of 2,2′-di (p-aminophenyl) -6,6′-bibenzoxazole, 3.25 g (0.03 mol) of p-phenylenediamine was used. A polyimide precursor composition was prepared by obtaining a polyamic acid in the same manner as in Production Example 1 except that (mol) was used. Using this polyimide precursor composition, a film was formed in the same manner as in Production Example 1.

(Production Example 3)
Instead of 12.54 g (0.03 mol) of 2,2′-di (p-aminophenyl) -6,6′-bibenzoxazole in Production Example 1, 6.82 g of 4,4′-diaminobenzanilide ( A polyimide precursor composition was prepared by obtaining a polyamic acid in the same manner as in Production Example 1 except that 0.03 mol) was used. Using this polyimide precursor composition, a film was formed in the same manner as in Production Example 1.

(Production Example 4)
In Production Example 1, instead of 12.54 g (0.03 mol) of 2,2′-di (p-aminophenyl) -6,6′-bibenzoxazole, 2,2′-di (p-aminophenyl) ) -6,6′-bibenzoxazole 12.18 g (0.0291 mol) and Si diamine 0.224 g (0.0009 mol) represented by the following formula (2) were used in the same manner as in Production Example 1. Thus, a polyamic acid was obtained to prepare a polyimide precursor composition. Using this polyimide precursor composition, a film was formed in the same manner as in Production Example 1.

(Production Example 5)
In Production Example 1, instead of 12.54 g (0.03 mol) of 2,2′-di (p-aminophenyl) -6,6′-bibenzoxazole, 2,2′-di (p-aminophenyl) ) -6,6′-bibenzoxazole 9.16 g (0.0219 mol) and 2,5-bis (4-aminobenzoyl) thiophene 2.61 g (0.0081 mol) In the same manner as in Example 1, a polyamic acid was obtained to prepare a polyimide precursor composition. Using this polyimide precursor composition, a film was formed in the same manner as in Production Example 1.

(Production Example 6)
In Production Example 1, 6.8 g (0.0312 mol) of pyromellitic dianhydride was used instead of 9.18 g (0.0312 mol) of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride. A polyimide precursor composition was prepared by obtaining a polyamic acid in the same manner as in Production Example 1 except that was used. Using this polyimide precursor composition, a film was formed in the same manner as in Production Example 1.

(Production Example 7)
In Production Example 3, 6.8 g (0.0312 mol) of pyromellitic dianhydride was used instead of 9.18 g (0.0312 mol) of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride. A polyimide precursor composition was prepared by obtaining a polyamic acid in the same manner as in Production Example 3 except that was used. Using this polyimide precursor composition, a film was formed in the same manner as in Production Example 1.

(Production Example 8)
In Production Example 5, 6.8 g (0.0312 mol) of pyromellitic dianhydride was used instead of 9.18 g (0.0312 mol) of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride. A polyimide precursor composition was prepared by obtaining a polyamic acid in the same manner as in Production Example 5 except that was used. Using this polyimide precursor composition, a film was formed in the same manner as in Production Example 1.

(Production Example 9)
In Production Example 1, instead of 9.18 g (0.0312 mol) of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic acid A polyimide precursor composition was prepared in the same manner as in Production Example 1 except that 10.06 g (0.0312 mol) of anhydride was used. Using this polyimide precursor composition, a film was formed in the same manner as in Production Example 1.

(Production Example 10)
A polyamic acid was obtained in the same manner as in Production Example 1 except that the amount of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride used in Production Example 1 was changed to 12.55 g (0.03 mol). Thus, a polyimide precursor composition was prepared. Using this polyimide precursor composition, a film was formed in the same manner as in Production Example 1.
The viscosity of this polyimide precursor composition exceeded 100 Ps, and varnish handling was greatly deteriorated. Moreover, when the mixed solvent of Example 1 was added and the viscosity was reduced to 30 Ps, the resin concentration was reduced to 5.0%, and thick film coating was difficult. Moreover, varnish stability deteriorated. The initial cracked gas component was also detected as a gas derived from a benzene ring (C6-based gas).

(Production Example 11)
In Production Example 1, the amount of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride used was 12.55 g (0.03 mol), and 2,2′-di (p-aminophenyl)- A polyimide precursor composition was prepared by obtaining a polyamic acid in the same manner as in Example 1 except that the amount of 6,6′-bibenzoxazole used was 13.06 g (0.0312 mol). Using this polyimide precursor composition, a film was formed in the same manner as in Production Example 1.
This polyimide precursor composition had extremely poor varnish stability. In addition, the elongation at break of the film is low, and there is a concern about insufficient strength. Furthermore, the degassing start temperature was low, and the gas from the benzene ring was detected as the initial cracking gas component.

(Production Example 12)
In Production Example 2, the amount of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride used was 12.55 g (0.03 mol), and the amount of p-phenylenediamine used was 3.25 g (0 (0.03 mol), a polyamic acid was obtained in the same manner as in Production Example 2 to prepare a polyimide precursor composition. Using this polyimide precursor composition, a film was formed in the same manner as in Production Example 1.
The viscosity of this polyimide precursor composition exceeded 100 Ps, and varnish handling was greatly deteriorated. Moreover, when the mixed solvent of Example 1 was added and the viscosity was reduced to 30 Ps, the resin concentration was reduced to 5.1%, and thick film coating was difficult. Moreover, filler dispersibility was also bad. The initial cracked gas component was a gas derived from a benzene ring.

(Production Example 13)
In Production Example 2, the amount of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride used was 12.55 g (0.03 mol), and the amount of p-phenylenediamine used was 3.38 g (0 0.032 mol) was obtained in the same manner as in Production Example 2 to obtain a polyamic acid to prepare a polyimide precursor composition. Using this polyimide precursor composition, a film was formed in the same manner as in Production Example 1.
This polyimide precursor composition had extremely poor varnish stability. In addition, the elongation at break of the film is low, and there is a concern about insufficient strength. Furthermore, the degassing start temperature was low, and the gas from the benzene ring was detected as the initial cracking gas component.

(Production Example 14)
A commercially available low thermal expansion self-adhesive resin varnish (trade name: “SP-042” manufactured by Toray Industries, Inc.) was used to evaluate varnish stability and filler dispersibility. Further, a film was formed using this resin varnish in the same manner as in Production Example 1, and the breaking strength (MPa), elongation at break (%), coefficient of thermal expansion (ppm / ° C.), elastic modulus (GPa), 1% weight The decay start temperature (° C.), degassing detection temperature (° C.), and the type of decomposition gas were evaluated.
This resin varnish had poor varnish stability and had a problem in handling properties. Further, the degassing start temperature was as extremely low as 300 ° C.

[Production and evaluation of composite films]
The same as in Production Example 1, except that the amount used of 9.18 g (0.0312 mol) of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride was changed to 9.53 g (0.0324 mol). In the same manner as in Example 1, polyamic acid was obtained. The weight average molecular weight of this polyamic acid was 38000.
Next, 30 g of the polyamic acid obtained was mixed with 70 g of the polyamic acid of Production Example 1. Since the two types of polyamic acids have the same main chain structure, they were completely dissolved to form a uniform varnish. To this varnish, 4.8 g of boron nitride (trade name “HP-40”, manufactured by JFES, average particle diameter of 5 μm, equivalent to 30% by mass with respect to the total mass of polyamic acid) was added and stirred to obtain a polyimide precursor. A composition was prepared. Boron nitride was uniformly dispersed in the varnish. The thermal conductivity of the film formed from this polyimide precursor composition was 1.4 (W / m / K).
On the other hand, the thermal conductivity of the film formed using the polyimide precursor composition prepared in the same manner except that boron nitride was not added was 0.2 (w / m / k). Thus, the heat dissipation characteristics were remarkably improved by adding boron nitride.

[Manufacture of semiconductor elements]
A semiconductor element was manufactured according to the procedure shown in FIG.
On a silicon substrate (substrate thickness 500 μm) having a first surface electrode 2 (nickel electrode) formed by connecting semiconductor cells in a circuit, a plating resist (trade name “ZPN103”, negative-type sensitized rubber resist, manufactured by Nippon Zeon) After coating, exposure and development processes were performed to form a 20 μm-thick resist film in which the contact hole 11 was formed on the first surface electrode 2.
The contact electrode 4 was created in the contact hole using the electrolytic plating method (FIG. 2- (c)). Using a special stripping solution, the resist film 10 was stripped to expose the contact electrode 4 (FIG. 2- (d)).
On this board | substrate, the polyimide precursor composition synthesize | combined by the manufacture example 1 is apply | coated so that a film thickness after curing may be set to 20 micrometers or more, and it heat-imidizes on the cure conditions of manufacture example 1, and a polyimide film (insulating film 3) ) Was produced (FIG. 2- (e)).
The polyimide film on the silicon substrate 1 is cut (cutting apparatus DAS8920, manufactured by DISCO Corporation) to scrape the contact electrode 4, and the contact electrode 4 is exposed on the upper surface of the insulating film 3 (FIG. 2- (F)).
Next, after forming the second surface electrode 5 on the polyimide film surface from the contact electrode 4 by sputtering, the polyimide surface was fixed, the back surface of the silicon substrate was polished, and the silicon substrate 2 was thinned to 100 μm. The thinned silicon substrate did not warp and was flat, and no chipping of the silicon substrate was observed. We were able to proceed to the next process stably.
After sequentially laminating the back electrode 6 by sputtering, the chip was divided from the polyimide surface using a dicer, and a semiconductor element free from warpage and chipping could be obtained.

1: Substrate 2: First surface electrode 3: Insulating film 4: Contact electrode 5: Second surface electrode 6: Back electrode 10: Resist film 11: Via hole

Claims (16)

While the substrate, a first surface electrode, and an insulating film covering at least a portion of the first surface electrode is formed, a semiconductor element back electrode formed on the other of said substrate,
The thickness of the substrate is 150 μm or less;
The insulating film includes a polyamic acid obtained by reacting at least 1 mol% of an acyl compound selected from aromatic tetracarboxylic acid and aromatic tetracarboxylic dianhydride with respect to the aromatic diamine. A semiconductor element, which is a polyimide film obtained by imidizing a polyimide precursor composition and having a thermal expansion coefficient of 2 to 24 ppm / ° C.   The semiconductor element according to claim 1, wherein the insulating film has a thickness of 1 to 50 μm.   The aromatic diamine is from 2,2′-di (p-aminophenyl) -5,5′-bisbenzoxazole, p-phenylenediamine, 4,4′-diaminobiphenyl and 4,4′-diaminobenzanilide. The semiconductor element of Claim 1 or 2 containing 70-100 mol% of 1 or more types chosen.   The acyl compound is pyromellitic acid, pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 3 , 3 ′, 4,4′-benzophenone tetracarboxylic acid and 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride are contained in an amount of 70 to 100 mol%. 4. The semiconductor element according to any one of 3.   The semiconductor element according to claim 1, wherein the polyimide precursor composition contains an insulating heat dissipating filler.   The semiconductor element according to claim 5, wherein the insulating heat dissipating filler is boron nitride.   Polyamide having a ratio of polyamic acid having a polystyrene-equivalent weight average molecular weight of 50,000 to 200,000 in a range of 70 to 100% by mass and a polystyrene-equivalent weight average molecular weight of 10,000 to less than 50,000. The semiconductor element in any one of Claim 1 to 6 whose ratio of an acid is 0-30 mass%.   The semiconductor element according to claim 1, wherein an inorganic thin film insulating layer is formed between the insulating film and the first surface electrode.   The semiconductor element according to claim 8, wherein the inorganic thin film insulating layer is made of silicon oxide and / or silicon nitride.   A second surface electrode is formed on the surface of the insulating film, and the first surface electrode and the second surface electrode are electrically connected via a contact electrode formed by communicating the insulating film; The semiconductor device according to claim 1. Said substrate is of silicon, SiC, is composed of one or more selected from GaN, a semiconductor device according to any of claims claims 1 to 10. A first surface electrode forming step of forming a first surface electrode on one surface of the substrate;
One or more kinds of acyl compounds selected from aromatic tetracarboxylic acid and aromatic tetracarboxylic dianhydride are reacted on the surface of the substrate on which the first surface electrode is formed in an amount of 1 mol% or more than the aromatic diamine. An insulating film forming step of applying an imidized polyimide precursor composition containing a polyamic acid obtained in this manner to form an insulating film made of a polyimide film having a thermal expansion coefficient of 2 to 24 ppm / ° C ;
The surface of the substrate on which at least the first surface electrode and the insulating film are formed is polished on the surface opposite to the side on which the first surface electrode is formed to adjust the thickness to 150 μm or less. And a dicing process of separating the element unit by dicing from the first surface electrode side. A resist composition is applied to the substrate on which the first surface electrode is formed, pre-baked to form a resist film, and a contact hole is formed on the first surface electrode through the resist film. a contact electrode within, after peeling off the resist film, performs the insulating film forming step, and then, forming the second surface electrode on the insulating film through the contact electrode, according to claim 12 A method for manufacturing a semiconductor device. Is opened via part in the insulating film formed in the insulating film forming step, after forming the contact electrode in the opened via portion, a second surface electrode on the insulating film through the contact electrode, claim 12 The manufacturing method of the semiconductor element of description. 15. The method of manufacturing a semiconductor element according to claim 13 , wherein after forming the second surface electrode on the insulating film, the other surface of the substrate is polished , and a back electrode is formed on the polished surface. After completion of the insulating film forming step, polishing the other surface of the substrate, after forming the back electrode on the surface of the polished side to form a second surface electrode on the insulating film, according to claim 13 or 14. A method for producing a semiconductor element according to 14 .