JP2001230245A - Method for manufacturing semiconductor device - Google Patents

Abstract

(57) Abstract: In a semiconductor device having a surface protective film, an exposed bonding surface is stabilized to improve reliability. After etching a side surface of a mesa diode chip, a surface protection film for generating reaction water is applied to the side surface of the mesa diode chip.
Heat treatment at 00 to 450 ° C. to form a modified oxide film 5 on the bonding surface.
Grow. The planar type semiconductor device also has the effect of reducing leakage current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device having a protective film for stabilizing characteristics.

[0002]

2. Description of the Related Art Semiconductor devices are roughly classified into two types. One is a pn exposed on the main surface of the semiconductor substrate.
It is a planar semiconductor element in which the junction is covered with an extremely stable oxide film, and is widely used as a semiconductor device in various fields because of its high reliability and excellent fine processing. The other is related to the present invention, and is a so-called mesa semiconductor device in which a pn junction is exposed on a side surface of a semiconductor substrate and the surface is covered with a protective film.

[0003] The mesa-type semiconductor element has a simple structure and a simple manufacturing method, and can easily have a high withstand voltage. Therefore, the mesa-type semiconductor element is mainly used in the field of individual elements such as a high withstand voltage diode, a mass production diode, and a power thyristor. Many are used. FIG.
(A) is a cross-sectional view of the most common resin-sealed mesa diode. The side surface of the diode chip 4 in which the lead wires 2 are joined by the solder layer 3 is etched with a hydrofluoric acid, nitric acid-based silicon etching solution, or an alkali-based etching solution, and has a surface having surface protection and stress buffering effects. A protective resin layer 6 is applied. Further, a sealing resin 1 is formed by transfer molding of an epoxy resin, thereby obtaining a resin-sealed semiconductor device.

In the mesa type semiconductor device, since the end of the junction is exposed on the side surface of the semiconductor substrate, it is difficult to form a high quality oxide film such as a thermal oxide film thereon. Particularly, in a semiconductor device in which semiconductor chips are stacked, the process temperature is limited to a low temperature due to a brazing material for bonding between the semiconductor chips, and silicone rubber, silicone varnish, glass, or the like is used as a surface protective film. .

On the other hand, in a planar type semiconductor device in which an end of a pn junction is exposed on a main surface of a semiconductor substrate and an upper portion thereof is covered with an oxide film, a high-quality oxide film formed by thermal oxidation serves as a surface protection film. Reliability is maintained.

[0006]

However, the mesa semiconductor device and the planar semiconductor device have the following problems. In the conventional formation of a surface protection film for a mesa-type semiconductor device, processing steps such as etching with a mixed acid or an alkali solution, washing with pure water, and hot-air drying are performed. (Referred to as oxide film)
Is generated. When a protective film as described above is formed on the natural oxide film, a surface level corresponding to the quality of the natural oxide film generated in the pretreatment step is formed, and one of the important characteristics particularly in a long-term reliability test. One problem is that the leakage current at the time of applying a reverse bias increases.

The mechanism will be described with reference to a schematic sectional view of the SiO ₂ / Si interface in FIG. 6B and an energy state diagram in FIG. In FIG. 6B, after the etching with the etching solution, there is a natural oxide film 8 on the exposed semiconductor surface, and a dangling bond 21 with a broken bond at the SiO ₂ / Si interface 7. The dangling bond 21 is very active. Even if the surface is covered with a protective film, the protective film itself or an ionic substance dissolved in moisture penetrating through the protective film gradually bonds to the dangling bond 21. As a result, as shown in FIG. 6C, a new interface level 22 is generated in the forbidden band. In Figure, E _c is the conduction band minimum, E _v is the valence band upper end, E _F is the Fermi energy, E
_i is the intrinsic Fermi energy. The interface level 22 promotes the recombination of carriers and causes an increase in leakage current.

[0008] On the other hand, in the planar type semiconductor device, although the exposed surface of the junction is protected by a stable oxide film (hereinafter referred to as SiO ₂ film) and stabilized, the leakage current still remains in the long-term reliability test. There is a problem that increases.
The mechanism is considered as follows. For example, when an aluminum (hereinafter abbreviated as Al) thin film or the like is formed as an electrode, an electron beam or a plasma particle generated from a deposition apparatus causes an oxide film (hereinafter abbreviated as SiO ₂ film) or Si
At the O ₂ / Si interface, although the number is small, the bond may be broken and a dangling bond may be generated. An ionic substance binds to the dangling bond to form a trap level.

In a planar type semiconductor device,
As an electrode material such as an electrode, a wiring, and an external take-out pad, an Al thin film is usually formed by vacuum deposition, sputtering, chemical vapor reaction, or the like. However, since Al is an amphoteric element, a pressure cooker test ( PC below
T)), there is a problem of deterioration due to corrosion.

In view of these problems, an object of the present invention is to stabilize dangling bonds by modifying the surface of a semiconductor, enhance resistance to charged particles, prevent corrosion of Al electrodes, etc. An object of the present invention is to provide a method for manufacturing a highly reliable semiconductor element that does not deteriorate.

[0011]

In order to solve these problems, the present invention is to apply a protective film material which generates reaction water by a polymerization reaction as a protective film of a semiconductor device, and heat-treat it. As such a surface protective film, for example, there is a polyimide resin. For example, when a polyimide film used is heated to form a film, reaction water is generated at the same time, and at the Si interface in contact with SiO ₂ in the exposed silicon surface, the reaction of Si + 2H ₂ O → SiO ₂ + 2H ₂ results in a mesa type. In the device, a defective portion of the natural oxide film on the surface is supplemented, and the oxide film is densified to form a modified oxide film, and the occurrence of interface order is suppressed to reduce leakage current. The planar element, in the SiO ₂ film, SiO ₂ / Si
Dangling bonds) of the interface stabilizing and SiO ₂
The film is further densified and modified to eliminate leakage current. The Al surface of the electrode, the _{2Al + 3H 2 O → Al 2} O 3 + 3H 2 becomes reactive, or a natural oxide film further dense of Al electrode surface compensates for defect site, to form a modified layer on the surface, the Al electrode Increase the corrosion resistance of

The heat treatment temperature is preferably 200 to 450 ° C. At a temperature of 200 ° C. or more, the thickness of the modified oxide film or the modified layer becomes 2 nm or more, and the effect of reducing the leakage current becomes remarkable. If the temperature is 450 ° C. or higher, there is a possibility that the brazing material for bonding between chips, the electrode material and the like may be adversely affected as described above, which is not desirable. Incidentally, the reaction of the conventional surface protective film will be described. In each case, the silicon surface is made hydrophobic so that water is not interposed between the silicon surface and the protective film.

For example, in the case of a silicone resin-based resin, a dealcoholization reaction occurs by heat treatment, and the resin bond is formed while bonding to another intramolecular group to form a small molecule. In addition, in the case of polyester as well, although it is obtained by polycondensation of dimethyl terephthalate and polyhydric alcohol (ethylene glycol), polyester and methyl alcohol are produced.

In forming a glass film, fine particles of lead or zinc-based glass powder are deposited on the exposed silicon surface by an electrophoresis method or a deposition method, and heated and fired at 500 to 600 ° C. to form a glass film at a predetermined portion. No water intervenes.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on examples. [Embodiment 1] FIG. 1A is a sectional view of a mesa diode which is one embodiment of the present invention.

The side surface of the diode chip 4 to which the lead wire 2 is soldered is etched using a hydrofluoric acid, nitric acid-based silicon etching solution or an alkali-based etching solution, and a surface protection film 6 of polyimide resin is formed on the surface thereof. FIG. 6 shows that the sealing resin 1 is further formed by transfer molding of epoxy resin.
As in (a), but the modified oxide film 5
Is different.

The method of manufacturing this mesa diode is as follows.
Through such a process. First, the surface energy unique to mesa-type semiconductors
Pitching process (HF-HNO_Three-H_ThreePO _Four, KOH)
Remove the outer periphery of diode chip 4 with clean silicon
Finish on exposed surface. It dicers the diode wafer
Scratches and strained layers when cutting with lead wires, etc.
This is for removing dirt. Then, in order to get pressure resistance
The surface protection film 6 is applied to the most important clean bonding surface by a coating method.
After the formation, heat treatment is performed at 200 ° C. or higher for 1 hour. This and
Reaction water is generated, and the natural oxide film is converted to a dense oxide film.
To form the modified oxide film 5 and remove the exposed bonding surface.
Stabilize. And the whole is resin-sealed with mold resin 1
I do.

A high-temperature application test was performed on a mesa diode sealed as shown in FIG. 1 and a conventional mesa diode using a silicone resin as a surface protective film as a comparative example. The temperature is 130 ° C. and the applied voltage is 1 kV. The result is shown in FIG. The vertical axis represents the leakage current, and the horizontal axis represents the application time. In the comparative example, the leakage current is large from the beginning, and the leakage current gradually increases from about 1 hour, whereas the diode of Example 1 shows a small leakage current even for 100 hours and is stable. . That is, the leakage current could be suppressed.

The mechanism will be described with reference to a schematic cross-sectional view of the SiO ₂ / Si interface in FIG. 1B and an energy state diagram in FIG. In FIG. 1 (b), by performing a heat treatment in the presence of the reaction product water, SiO ₂ /
The Si atoms of the dangling bonds at the Si interface 7 and the O atoms of the reaction water are combined to form a defect-free SiO ₂ layer. That is, the modified oxide film 5 covering the bonding surface is formed. Therefore, since there is no dangling bond, a new interface level due to the ionic substance or the like dissolved in the moisture penetrating through the protective film 6 does not occur. This state is represented by an energy phase diagram of a semiconductor as shown in FIG. 1C in which there is no interface level in the forbidden band.

Therefore, by forming the modified oxide film 5 as in this embodiment, the surface has a very small interface level which promotes the recombination of carriers, and as a result, the leakage current due to the interface level does not increase. is there. [Embodiment 2] The second embodiment of the present invention is applied to a planar type semiconductor device, and FIGS. 3 (a) to 3 (c) are cross-sectional views for explaining the state of application.

After a thermal oxide film 13 is formed on an n-type silicon wafer 11 and a mask pattern is formed, boron is diffused to form a p-type diffusion region 12, and a p-type diffusion region 12 is formed.
An anode electrode 14 is provided in contact with the silicon wafer 11 and a cathode electrode 16 is provided in contact with the back surface of the silicon wafer 11 [FIG.
(A)]. As a surface protective film 15, a polyimide resin was applied by a spin coating method, and then heat-treated at 250 ° C. for 1 hour [FIG. At this time, the surface protection film 15 is cured and the reaction water 17 is generated.

During the heat treatment, the reaction water 17 forms the oxide film 13
Is transmitted to reach the SiO ₂ / Si interface, and a modified layer 18 similar to that of Example 1 is considered to be formed [FIG. A high-temperature, high-humidity, and medium-voltage application test was performed on the planar diode of Example 2 and a conventional planar diode using a silicone resin as a surface protective film as a comparative example. FIG. 4 shows the results.

As an evaluation method, a high temperature (Ta = 85 ± 3)
℃), high humidity (85% RH) atmosphere and voltage (VR) 12
00V was applied, and the fluctuation of the leakage current (IR, unit μA) during the application was followed. t = 100, 240, 500, 1000
h is the application time. The measurement was performed at room temperature (Ta = 2).
(5 ± 5 ° C.) and a voltage (VR) of 1500 V.

The first column is the initial properties. Application time 1
At 00 hours, there is no difference between the two. However, in the comparative example, the leakage current gradually increased after 240 hours or more, whereas the planar type diode of Example 2 did not increase the leakage current even after 1000 hours, and was stable. . [Embodiment 3] The third embodiment of the present invention is applied to a planar type semiconductor device, and FIG. 5 is a sectional view for explaining the application.

As shown in FIG. 3B, an Al electrode is provided.
Apply a polyimide film to the planar semiconductor element
When heat-treated, the reaction product water 17 is naturally
This also affects the electrode 14. That is, the Al electrode 1
4 Surface is modified by reaction water 17 and the surface of Al electrode
Then, a modified layer 19 is formed. Normally about 5 nm on Al electrode surface
Oxide film is formed, but by the method of the present invention, 10 nm
More dense Al _TwoO_ThreeResulting in the formation of a modified film
As a result, corrosion resistance increases. This application is a practical application of this embodiment.
In the diode type, the PCT (steam pressurization test)
Corrosion of the Al electrode is reduced to about 1/3 compared to the conventional type.
Was.

[0026]

As described above, according to the present invention, as a protective film of a semiconductor device, a protective film material which produces reaction water by a polymerization reaction is applied and heat-treated, so that a semiconductor element utilizing the reaction water is used. An object of the present invention is to provide a semiconductor element whose surface has been stabilized and reformed, and which has significantly improved reliability.

The present invention is effective regardless of whether the semiconductor element is a mesa type semiconductor element or a planar type semiconductor element. In a semiconductor element having an Al electrode, the surface of the electrode is stabilized. Is quite extensive.

[Brief description of the drawings]

1A is a sectional view of a mesa diode according to a first embodiment of the present invention, FIG. 1B is a schematic sectional view of an SiO ₂ / Si interface, and FIG. 1C is an energy band diagram of a Si surface.

FIG. 2 illustrates a mesa diode 13 according to the first embodiment of the present invention.
Leakage current characteristic diagram in 0 ° C B / T test

FIGS. 3A to 3C are cross-sectional views illustrating the application of the second embodiment of the present invention to a planar diode.

FIG. 4 is a graph showing leakage current characteristics of a planar diode according to a second embodiment of the present invention in a high-temperature, high-humidity, and medium-voltage application test;

FIG. 5 is a sectional view of a planar diode according to a third embodiment of the present invention.

FIG. 6A is a cross-sectional view of a conventional mesa diode,
(B) is a schematic cross-sectional view of the SiO ₂ / Si interface, (c)
Is the energy band diagram of the Si surface

[Explanation of symbols]

1 molding resin 2 leads 3 solder layer 4 semiconductor chip 5 modifying oxide film 6 surface protection film 7 SiO ₂ / Si interface 8 natural oxide film 11 n-type silicon wafer 12 p diffusion region 13 SiO ₂ film 14 anode electrode 15 surface protection Film 16 cathode electrode 17 reaction water 18 reformed layer 19 reformed layer 21 dangling bond 22 interface level

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takahiro Kuboyama 1-1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki, Kanagawa Prefecture Inside Fuji Electric Co., Ltd. (72) Inventor Katsuyuki Nozaki 1, Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa No. 1 Inside Fuji Electric Co., Ltd. (72) Inventor Hideaki Ito 1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture F-term (reference) 5F005 AH03 BA01 BB02 GA01 5F058 AA10 AC04 AF04 AG01 AH03

Claims (6)

[Claims] 1. A method for manufacturing a semiconductor device, comprising applying a protective film material which generates reaction water by a polymerization reaction as a protective film of the semiconductor device, followed by heat treatment. 2. The method according to claim 1, wherein the heat treatment is performed at 200 to 450 ° C. 3. A mesa-type semiconductor device wherein a semiconductor device is formed substantially parallel to a main surface of a semiconductor substrate and has a junction exposed on a side surface of the semiconductor substrate. The method of manufacturing a semiconductor device according to claim 1, wherein: 4. A semiconductor device having a junction exposed at a main surface of a semiconductor substrate, wherein the exposed portion is covered with an oxide film. 3. The method for manufacturing a semiconductor device according to claim 1, wherein the method is modified. 5. A planar type semiconductor device having a junction exposed at a main surface of a semiconductor substrate, an exposed portion thereof covered with an oxide film, and having an aluminum film as an electrode. 5. The method according to claim 1, wherein a modified layer is formed on the film. 6. The method for manufacturing a semiconductor device according to claim 1, wherein the surface protection film is a polyimide resin.