JPH10294448A - Manufacture of high breakdown voltage semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a punch through breakdown from occurring at a transistor part with a pnp structure, by applying an inorganic polymer precursor substance onto a pn-junction surface by the sol/gel method, and forming a silicone rubber finally. SOLUTION: Polyimide resin 7 that is a second insulation film is formed on a silicon dioxide film 6, and further a third insulation film a silicone rubber 8, is formed on it. A positive electric charge 10 exists in the silicon dioxide film 6. Even if a slight negative electric charge occurs in the second insulation film 7 and the third insulation film 8, it can be regarded that a positive electric charge exists in first, second, and third insulation films effectively due to the positive electric charge 10. An accumulation layer where the number of electrons is larger inside is formed on an n-type semiconductor region, thus extending the distance between an edge part 91b of a depletion layer being spread into the n-type semiconductor region and a p-type semiconductor region 3 as compared with the inside, and preventing a punch through breakdown from occurring at a transistor part with a pnp structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a surface stabilizing protective film of a high breakdown voltage semiconductor device.

[0002]

2. Description of the Related Art As a prior art relating to a high breakdown voltage semiconductor device, for example, IEEE PROC. Vol.129, Pt.I
No. 5, p. 376 (1982) is known. In this prior art, a pnp structure exposed on a side surface of a thyristor is processed into a double positive bevel shape. When a reverse bias is applied to a pn junction, a depletion layer on the surface is mainly an n-layer due to the positive bevel structure. It is described that a high withstand voltage can be achieved because it spreads to the side, and a depletion layer is unlikely to spread at a concave portion of the end face, so that punch-through breakdown at a pnp portion of the end face can be prevented.

As a conventional technique for manufacturing a semiconductor device having a high breakdown voltage, a technique disclosed in Japanese Patent Application Laid-Open No. 3-245536 is known. In this conventional technique, one main surface of a semiconductor substrate having a pn junction exposed on a side surface is fixed to an upper surface of a metal plate,
After etching the side surface, remove the oxide film generated on the side surface,
By the manufacturing method of covering the side surfaces with the protective film, the exposed surface of the pn junction can be prevented from being covered with the oxide film containing the heavy metal as in the related art, so that the leakage current through the heavy metal in the oxide film can be prevented. It is said that a high breakdown voltage semiconductor device having excellent reliability can be obtained.

[0004]

The former prior art described above has the advantage of increasing the blocking voltage of the so-called main thyristor, while the latter prior art has the advantage that the so-called contaminated oxidation containing heavy metals in the so-called pnp transistor section at the end face. Although it has the effect of removing the film and obtaining a clean semiconductor surface, the leakage current increases due to fluctuations in the polarity and magnitude of the charge in the surface protective film, such as in life tests where the film is exposed to high temperatures with a specified voltage applied. And the problem of reduced withstand voltage has not been considered.

An object of the present invention is to provide a highly reliable semiconductor device manufacturing method which solves the problems of the conventional semiconductor device manufacturing method.

[0006]

A feature of a method of manufacturing a semiconductor device according to the present invention to achieve the above object is that a semiconductor substrate has a pair of main surfaces and at least one pn junction is exposed on a side surface. And a method of manufacturing a semiconductor device in which an insulating protective film is formed on a surface of a pn junction exposed on a side surface of the semiconductor substrate, wherein an inorganic polymer precursor is spin-coated or immersed on the pn-junction surface by a sol-gel method. A step of coating the silicon dioxide film by heating and drying afterwards, and a step of forming by heating and drying and curing after spin coating or dip coating the polyimide resin,
This is a method for manufacturing a high withstand voltage semiconductor device including a step of forming a silicone rubber.

Further, the silicon dioxide film formed by the sol-gel method is a method of producing an inorganic polymer precursor by mixing tetraethoxysilane, pure water, nitric acid and ethanol.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing a first embodiment of a high breakdown voltage semiconductor device according to the present invention. In the embodiment of FIG. 1, a sectional view of a thyristor is shown as a semiconductor device. 1 is an n-type semiconductor region serving as an n-base layer, 2 is a p-type semiconductor region serving as a p-base layer, and 3 is p-type semiconductor region serving as a p-emitter layer.
A + type semiconductor region, 4 an n + type semiconductor region serving as an n emitter layer, 40 a cathode electrode of a main thyristor, 41 a cathode electrode of a thyristor for receiving a light trigger signal, 42 a cathode electrode of an auxiliary thyristor, and a p + type An anode electrode 30 is connected to the semiconductor region 3. Reference numeral 6 denotes a silicon dioxide film formed by using the sol-gel method according to the present invention. A polyimide resin 7 as a second insulating film is formed on the silicon dioxide film 6, and a third insulating film is formed on the polyimide resin 7. A certain silicone rubber 8 is formed.

FIG. 2 is a view for explaining an operation in which the silicon dioxide film 6 formed by using the sol-gel method according to the present invention is effective for improving the reliability. 2, the description of the same reference numerals as those in FIG. 1 is omitted. In FIG. 2, reference numeral 9 denotes an n-type semiconductor region 1 serving as an n-base layer and a p-type semiconductor region serving as a p-base layer when a forward blocking voltage in which the anode electrode 30 is positive and the cathode electrode 40 is negative is applied. 2, a depletion layer 91a and 91b extending from the pn junction composed of Pn.
Is a depletion layer end extending to the n-type semiconductor region 1. 10 is a positive charge in the silicon dioxide film according to the present invention.

When a forward blocking voltage is applied, the end portion 91b of the depletion layer extending to the n-type semiconductor region 1 becomes
Since the end face of the pn junction composed of the p-type semiconductor region 2 and the p-type semiconductor region 2 has a positive bevel structure, when the applied voltage is relatively low, the width of the depletion layer at the end face becomes wider than the inside, and has a function of lowering the electric field strength. . Further, when the forward blocking voltage is further increased, the depletion layer end 92b further expands, but since the end face of the pn junction formed by the n-type semiconductor region 1 and the p-type semiconductor region 3 has a negative bevel structure, the n-type semiconductor The surface of the region 1 is hardly spread from the inside, and the surface has a structure in which punch-through breakdown of a pnp structure is unlikely to occur.

However, when a so-called high-temperature bias test or the like is performed in which the semiconductor device is exposed to a high temperature while a forward blocking voltage is applied, no positive charge 10 is present in the silicon dioxide film according to the present invention, and the second insulating film 7 is directly connected to the n-type semiconductor. When formed in contact with the region 1, a slight negative charge of about 1 to 6 × 10 ¹⁰ / cm ² is generated in the second insulating film 7 and the third insulating film 8, and the n-type semiconductor region 1 is formed. Since a depletion layer or an inversion layer is formed on the surface of the transistor, punch-through breakdown occurs in the transistor portion having a pnp structure including the p-type semiconductor region 2, the n-type semiconductor region 1, and the p + -type semiconductor region 3, and the breakdown voltage is reduced. However, there is a problem that the leak current increases. Therefore, the silicon dioxide film 6 formed by using the sol-gel method according to the present invention has about 1 to
Since a positive charge 10 of about 2 × 10 ¹¹ / cm ² is present, even a slight negative charge of about 1 to 6 × 10 ¹⁰ / cm ² exists in the second insulating film 7 and the third insulating film 8. Occurs, the silicon dioxide film 6 formed using the sol-gel method according to the present invention.
Because of the positive charge 10 of about 1-2 × 10 ¹¹ / cm ² ,
Effectively, it can be considered that a positive charge of 0.4 to 1.9 × 10 ¹¹ / cm ² exists in the first insulating film, the second insulating film, and the third insulating film, and the n-type semiconductor region 2, a distance between the end 91b of the depletion layer spreading over the n-type semiconductor region and the p-type semiconductor region 3 is larger than that of the inside, as shown in FIG. Can be longer. Therefore, punch-through breakdown does not occur in the transistor portion having the pnp structure including the p-type semiconductor region 2, the n-type semiconductor region 1, and the p + -type semiconductor region 3 on the end face, and the breakdown voltage does not decrease in various life tests. A highly reliable semiconductor device can be obtained.

Next, a method of manufacturing the high breakdown voltage semiconductor device shown in FIG. 1 according to the present invention will be described. First, the resistivity is 50
Aluminum serving as a p-type impurity is diffused from both main surfaces of the n-type semiconductor substrate 1 having a high resistance of 0 ± 50 Ω · cm. In this case, the surface impurity concentration is about 1 × 10 ¹⁶ / cm ³ and the diffusion depth is about 150 μm. At this time, when the n + type semiconductor region 4 serving as the final n emitter layer is formed, the sheet resistance of the p type semiconductor region 2 serving as the p base layer immediately below the n + type semiconductor region 4 is about 800 to 900 Ω / □. Then, the thickness is adjusted by etching.

Subsequently, the surface impurity concentration is about 1 × 10 ¹⁹ to
An n + type semiconductor region 4 serving as an n emitter layer having a high impurity concentration of 1 × 10 ²⁰ / cm ³ is formed to a depth of about 8 μm by diffusion of P (phosphorus) using phosphorous hypochlorite. (A).

Subsequently, the n + type semiconductor region 4 on the cathode side is divided by known photoetching, aluminum is vapor-deposited on both main surfaces, and the aluminum on the cathode side is processed by known photoetching to form a p-type semiconductor region 2. The cathode electrode 40 of the main thyristor partially short-circuited with
Cathode electrode 4 of thyristor that receives light trigger signal
1. The cathode electrode 42 of the auxiliary thyristor is formed, and aluminum on the anode side is processed by known photoetching to form the anode electrode 30 (b). Next, the end face of the wafer was processed into a Σ shape by a known sand blasting method or a beveling technique using a grinding machine, the end face processed into the Σ shape was etched to remove processing distortion, washed with pure water, and dried. Thereafter, a silicon dioxide film 6 serving as a first insulating film formed using the sol-gel method according to the present invention is deposited (c).

The silicon dioxide film 6 is formed by mixing tetraethoxysilane, pure water, nitric acid and ethanol at a molar ratio of 1: 1.
The raw materials mixed at a ratio of 3: 0.25: 45 are spin-coated, and dried by heating at a temperature range of 200 to 500 ° C. in the air.
Cured. The anode electrode 30 and the cathode electrode 40 may be covered with a cover having good airtightness, dipped and then dried and cured by heating. Further, a second insulating film such as a polyimide resin is spin-coated on the first insulating film, and dried on a hot plate at 80 ° C. for 5 minutes.
It was cured by heating at 00 ° C. for 1 hour, 150 ° C. for 1 hour, and 250 ° C. for 4 hours (d).

Thereafter, the semiconductor substrate is placed in a container having a predetermined mold, and silicone rubber to be a third insulating film is filled on the second insulating film. It was cured by heating at 200 ° C. for 2 hours for 1 hour (e).

Finally, the semiconductor device base is placed in a ceramic package, the atmosphere inside the package is made of dry nitrogen, and the package is sealed to complete a high withstand voltage semiconductor device. The breakdown voltage of the semiconductor device manufactured through the above-described steps was 9000 V, and the variation was ± 300 V.

(Embodiment 2) FIG. 4 shows an example in which a method for manufacturing a high breakdown voltage semiconductor device according to the present invention is applied to a gate turn-off thyristor. In FIG. 4, the description of the same reference numerals as in FIG. 1 is omitted. Reference numeral 5 denotes an n + type semiconductor region for anode short circuit, and reference numeral 20 denotes a gate electrode connected to a p-type semiconductor region serving as a p-base layer. In FIG. 1, the end face of the semiconductor substrate is beveled in the shape of a triangle. However, the gate turn-off thyristor shown in FIG. 4 has a blocking function only in the forward direction, and thus has a p-type semiconductor region 2 and an n-type semiconductor region 1.
The end surface of the n-junction is processed into a regular bevel shape. The method of forming an insulating film according to the present invention is substantially the same as that described in detail with reference to FIG.
After depositing the electrode, the end surface of the wafer is processed into a regular bevel shape by a known sand blasting method or a beveling technique using a grinding machine so that the end surface becomes a positive bevel, and the processed end surface is etched to remove processing distortion, After cleaning with pure water and drying, a first insulating film 6, a second insulating film 7, and a third insulating film 8 are formed by using the sol-gel method according to the present invention. The package was housed in a ceramic package, the atmosphere inside the package was made of dry nitrogen, and the package was sealed to complete a high withstand voltage semiconductor device. The withstand voltage of the manufactured semiconductor device is 8000 V, and its variation is ± 200 V. Particularly, since a positive charge exists in the first insulating film 6 formed by using the sol-gel method according to the present invention, Even if a so-called high-temperature bias test or the like is performed while exposing the substrate to a high temperature while applying a forward blocking voltage, a storage layer having more electrons than the inside is formed on the surface of the n-type semiconductor region 1,
The surface of the n-type semiconductor region 1 is inverted to the p-type, and it is possible to prevent a decrease in breakdown voltage due to electric field concentration on the surface of the n-type semiconductor region 1 near the n + -type semiconductor region 5.

(Embodiment 3) FIG. 5 shows an example in which a method of manufacturing a high breakdown voltage semiconductor device according to the present invention is applied to a diode.
5, the description of the same reference numerals as in FIG. 1 is omitted.
Reference numeral 11 denotes an n-type semiconductor region, 13 denotes a p + -type semiconductor region serving as an anode layer, and 14 denotes an n + -type semiconductor region serving as a cathode layer. Similarly to the gate turn-off thyristor shown in FIG. 4, the end face of the pn junction composed of the p + type semiconductor region 13 and the n type semiconductor region 11 is processed into a regular bevel shape.
The method of forming an insulating film according to the present invention is substantially the same as that described in detail with reference to FIG. 3. After a predetermined semiconductor region is formed by diffusion, an electrode is vapor-deposited, and a wafer is formed so that an end face becomes a positive bevel. The end face is processed into a regular bevel shape by a known sand blasting method or beveling technique using a grinding machine, and the processed end face is etched to remove processing distortion,
After cleaning with pure water and drying, a first insulating film 6, a second insulating film 7, and a third insulating film 8 are formed by using the sol-gel method according to the present invention. The package was housed in a ceramic package, the atmosphere inside the package was made of dry nitrogen, and the package was sealed to complete a high withstand voltage semiconductor device. The withstand voltage of the manufactured semiconductor device was 6000 V, and its variation was ± 200 V.

As described with reference to FIG. 4, even in the embodiment shown in FIG. 5, even when a so-called high-temperature bias test or the like, in which the device is exposed to a high temperature while applying a forward blocking voltage, is performed, the n + type It is possible to prevent a decrease in withstand voltage due to electric field concentration on the surface of the n-type semiconductor region 11 near the semiconductor region 14.

In the method of manufacturing a high breakdown voltage semiconductor device according to the present invention described in detail above, the p-type semiconductor region 2 is formed using p-type impurity aluminum.
Similarly, the formation of the type semiconductor regions 3 and 13 is not limited to aluminum as the p-type impurity in the present invention, and boron (B) or gallium (Ga) may be used. Also,
Although the n + type semiconductor region 4 is formed using phosphorus (P) as an n type impurity, the n + type semiconductor regions 5 and 14 have been described.
Similarly, the present invention is not limited to phosphorus as an n-type impurity, and antimony (Sb) or arsenic (As) may be used.

Further, according to the method of manufacturing a high breakdown voltage semiconductor device of the present invention described in detail above, a high temperature bias test (applied voltage is 80% of rated voltage, junction temperature is 125 or
The test was performed at 150 ° C. and a test time of 1000 h). However, there was no change in the breakdown voltage, and the leakage current increased only 40% of the initial value.
High reliability was confirmed. A high-temperature storage test (junction temperature: 200 ° C., test time: 1000 h) was performed, but there was no change in withstand voltage and the leak current was 10% of the initial value.
It was confirmed that it showed high reliability.

[0024]

According to the method of manufacturing a high-breakdown-voltage semiconductor device according to the present invention, a high-breakdown-voltage and high-reliability semiconductor device can be obtained even if there is some variation in the charge in the passivation film made of an organic substance.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of a high breakdown voltage semiconductor device according to the present invention.

FIG. 2 is a cross-sectional view illustrating the operation of the high breakdown voltage semiconductor device according to the present invention.

FIG. 3 is an explanatory view showing a manufacturing process of the first embodiment of the high breakdown voltage semiconductor device according to the present invention.

FIG. 4 is a cross-sectional view in which the method of manufacturing a high breakdown voltage semiconductor device according to the present invention is applied to another semiconductor device.

FIG. 5 is a cross-sectional view in which the method of manufacturing a high withstand voltage semiconductor device according to the present invention is applied to still another semiconductor device.

[Explanation of symbols]

1,11 ... n-type semiconductor region, 2 ... p-type semiconductor region, 3,
13 ... p + type semiconductor region, 4,5,14 ... n + type semiconductor region, 6 ... first insulating film, 7 ... second insulating film, 8 ... third insulating film, 9 ... depletion layer, 10 ... positive charge, 20 ... Gate electrode, 3
0: anode electrode, 40, 41, 42: cathode electrode,
91a, 91b, 92a, 92b ... depletion layer ends.

Continuing from the front page (72) Inventor Muneo Tsuruoka 3-1-1, Sachimachi, Hitachi-shi, Ibaraki Pref. Hitachi, Ltd. Hitachi Plant

Claims (3)

[Claims] 1. A semiconductor device having a pair of main surfaces and at least one p
In a method of manufacturing a semiconductor device in which an n-junction is exposed on a side surface of a semiconductor substrate and an insulating protective film is formed on a surface of the pn junction exposed on a side surface of the semiconductor substrate, a silicon dioxide film is formed on the pn junction surface by a sol-gel method. , A step of forming a polyimide resin, and a step of forming a silicone rubber. 2. A silicon dioxide film formed by a sol-gel method is spin-coated with an inorganic polymer precursor or heat-dried and cured after dip coating, and a polyimide resin is spin-coated or heat-dried after dip coating.・ Curing the silicone rubber, put the semiconductor substrate in a predetermined container,
The method for manufacturing a high-voltage semiconductor device according to claim 1, wherein the semiconductor device is cured after being filled in a container. 3. The method according to claim 1, wherein the silicon dioxide film formed by the sol-gel method is a mixture of tetraethoxysilane, pure water, nitric acid, and ethanol to form an inorganic polymer precursor.