JPS58186940A - Preparation of semiconductor apparatus - Google Patents

Abstract

PURPOSE:To prevent lowering of impurity concentration at the surface of boron diffusion region surface and also prevent deterioration of reverse current reduction effect and deterioration after life test. CONSTITUTION:A P type region is formed as a base 12 by diffusing P type impurity to the internal surface of an N type silicon substrate 11, and an N type region is formed as an emitter 13 by diffusing an N type impurity, for example, boron to a part of internal surface. An oxide film 14 is formed by executing thermal processing in the oxygen gas ambient and then annealing is carried out by changing the ambient condition to inactive gas, for example, to the nitrogen gas ambient. A power transistor is formed by forming a base electrode 16 and emitter electrode 17. A lowered concentration at the surface of boron diffused layer is recovered by additionally executing the thermal processing under the inactive gas ambient within the same furnace at the same or higher temperature immediately after the thermal processing under the acidic ambient.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method of manufacturing a semiconductor device, and particularly to a method of manufacturing a semiconductor device having a boron diffusion layer.

[Technical background of the invention and its problems]

The following properties are required for the surface protective film of a normal planar PN junction.

■ Good insulation and electrical stability, ■ Small polarization, ■ Few film defects, ■ Good blocking properties against diffusion of impurities, ■ Good moisture resistance, ■ Adhesion to base material. ■Low-stress membrane; ■Low impurity content in the membrane; ■Low interfacial charge density; Physically, chemically, and mechanically stable. It's a good thing. Various materials have been studied and implemented using various formation methods to meet these requirements, but in general, silicon oxide films are used, which mostly satisfy the above requirements and can be formed rationally and easily. ing. The method for forming this silicon oxide film includes: ■ Drying of high temperature oxidation, reaction with silicon in a wet oxygen atmosphere to 81-$-0,→810° ■ Reaction with silicon in a steam atmosphere to 8 + +2H
*0→810. +2H.

■H by reaction with silicon in a mixed gas of hydrogen and oxygen, -4-)0. → Horse 0.2H, O+81 → 840
t-1-2H.

■ Method of mixing HCl in this atmosphere ■ Reaction of monosilane and oxygen using low temperature oxidation CVD method 8iH4-
)0. →8i0. There is a method of forming a silicon oxide film using a +2Ht deposition method.

Among these methods, a commonly used method is a high temperature oxidation method in which an oxide film is formed in a steam atmosphere. On the other hand, an oxide film formed by a low-temperature oxidation CVD method has the advantage that a thick oxide film can be easily formed compared to an oxide film formed by a high-temperature oxidation method, but the film density is rough due to the low temperature. It has poor moisture resistance and weak chemical resistance of about 60, making it unsuitable as a stable surface protective film. but,
If it were to be used as a surface protective film, it would need to be treated at a high temperature of 1000° C. or higher to achieve a film thickness comparable to that of an oxide film produced by high-temperature oxidation. However, rather than adopting such a method of increasing the number of steps, oxide film formation in a steam atmosphere is often used, which is a simple and highly productive high-temperature oxidation method, even if the oxide film formation time is a little longer. I think that the.

FIG. 1 shows a semiconductor element (diode) having a boron impurity diffusion layer. That is, N-type silicon substrate 1
A P shadow region 2 in which boron impurities are diffused is formed on the inner surface of one side to form a P-N junction, and a V9 Con oxide film 3 is formed on this surface as a surface protective film in a steam atmosphere using the high temperature oxidation method. Then, a silicon oxide film 4 is formed as a second surface protection film on the surface. Such semiconductor devices have the following problems. That is, v9
When an oxide film is formed by the reaction with silicon, a phenomenon occurs in which the surface impurity concentration of the formed layer in which boron impurities are diffused decreases.

This phenomenon is that the boron concentration on the silicon substrate surface is sucked out into the oxide film and decreases, but the P shadow area 2
The impurity concentration distribution in the depth direction is the distribution shown by curve A in Figure 182. That is, the ratio of the surface concentration of the P shadow region 2 in the silicon substrate 1 to the boron concentration in the oxide film after the oxide film 4 is formed is 0.3 or less. In diodes and transistors with such impurity concentrations, the region of reduced boron concentration on the V recon surface may be reversed due to alkaline ions such as sodium (Na) trapped in the surface storage l['Ws, or external contamination may occur. Due to negative influences,
When the PN junction is reverse biased, there is a problem in that the reverse current increases as shown by curve C in FIG. Furthermore, there is a drawback that the rate of variation of the reverse current with respect to the initial value after the life test becomes large as shown by the X mark in FIG. 4, resulting in deterioration of reliability.

[Purpose of the invention]

This invention was made in view of the above circumstances, and its objectives are to minimize the decrease in the silicon surface impurity concentration after forming an oxide film on the boron diffusion region, to reduce the reverse current, and to reduce the lifetime test. It is an object of the present invention to provide a method for manufacturing a semiconductor device that can obtain stable characteristics with little deterioration even after the manufacturing process.

[Summary of the invention]

This invention forms a boron diffusion region on the inner surface of a semiconductor substrate, forms an oxide film on the surface, and then heats it in an inert gas atmosphere, such as nitrogen gas, to increase the impurity concentration on the surface of the boron diffusion region. This prevents a decrease in the reverse current and prevents deterioration of characteristics after a life test.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. Note that this example uses medium power NPN)
This is a case where it is applied to the manufacture of transistors. In FIG. 5, a − conductivity type semiconductor substrate, for example, an N type silicon substrate 11
A P-type impurity is diffused on the inner surface of the substrate to form a P shadow region, which is used as the base 12. An N-type impurity, such as boron, is diffused into a part of the inner surface of the region of the paste 12 to form an N shadow region, which is used as the emitter 13. Next, oxidized Il! on the surface! form 14.

That is, an oxide film is formed by performing heat treatment at 1000° C. for about 30 minutes in a steam-like oxygen gas atmosphere, and then additional heat treatment is performed. That is, the steam-like oxygen gas atmosphere is changed to an inert gas atmosphere, such as nitrogen gas atmosphere, and annealing is performed at 900° C. for 20 minutes. After this annealing process, the oxide film 14 is selectively etched in order to take out the electrodes of the paste 12 and emitter 13. Next, a metal layer, for example, an A1 layer, is formed on the front and back surfaces of the substrate for forming electrodes, and selectively etched to form a collector electrode 15, a space electrode 16, and an emitter electrode 11, respectively, thereby forming a power transistor.

The power transistor configured in this way has an initial characteristic of I
The variation in Cll0 becomes smaller and the I after the life test
A characteristic in which the fluctuation range of CBO is reduced can be obtained. In addition, as a method for forming the oxide film 14, after a steam oxidation process at 1000°C and an oxidation process at 1000°C in an atmosphere of HCl→-0, the atmosphere around the substrate shoulder area was changed to a nitrogen gas atmosphere, and the atmosphere was heated at 900°C for 20 minutes. By forming a power transistor using the annealing method, as shown in the impurity concentration profile of the boron diffusion layer shown in curve B in Figure 2, the surface concentration is raised compared to the profile obtained by the conventional manufacturing method. A value of -X100>0.5 is obtained. An actual value of 0.76 was obtained. As a result, as shown by the broken line in Figure 3, the initial characteristic reverse current (ICBO)
The value of becomes smaller and the variation becomes smaller, 168
The fluctuation width of the reverse current (Icmo) after the time life test also became small, with no large fluctuations (deterioration) as shown by the circles in FIG. 4. In actual mass production, defects have been reduced to the same level as before.

As explained above, immediately after heat treatment in an oxidizing atmosphere, heat treatment (annealing) in an inert gas atmosphere at the same temperature or higher is added in the same furnace to reduce the concentration on the surface of the boron diffusion layer. By performing one recovery, it is possible to obtain a stable method for manufacturing a semiconductor device in which the initial characteristics and the reverse current after the life test are small, and the deterioration is extremely small.

The reason why the method of this invention has the same effect of reducing the surface impurity concentration is that it is based on the basic principle of impurity diffusion, and the oxidizing atmosphere, which is a factor in reducing the rkI concentration, is traversed, and an inert gas such as nitrogen is used. By switching to the atmosphere and adding temperature-controlled heat treatment, the amount of boron impurities diffused into the silicon substrate is redistributed from areas with high concentration to areas with low concentration, and the peak value of the impurity concentration decreases slightly, resulting in a lower concentration of boron. It is thought that the surface concentration that had been present will rise (recover) in the form of -F filling.

In the above embodiments, a steam oxidation method was used as an oxide film forming means, but any method may be used as long as it is an oxide film forming means. Further, although an example has been described in which additional heat treatment is performed after forming an oxide film in a nitrogen gas atmosphere, any inert gas may be used.Furthermore, the additional heat treatment time may be determined using any inert gas.

The bonding position of a predetermined diffusion layer must be set within a range that does not affect the characteristics.

〔Effect of the invention〕

As explained above, according to the present invention, a method for manufacturing a semiconductor device is provided in which the V9 surface after forming an oxide film on a boron diffusion region is small and stable characteristics with little deterioration even after a life test are obtained. Can be provided.

[Brief explanation of drawings]

Figure 1 is a structural cross-sectional view for explaining a semiconductor element (diode) having a boron diffusion layer manufactured by a conventional manufacturing method.
The figure is a characteristic curve diagram showing the distribution state of impurity concentration on the surface of the boron diffusion layer according to the method of the present invention and the conventional method.
The figure is a characteristic curve diagram showing how the reverse current is simplified by the characteristic shown in FIG. 2 in comparison with the conventional method and the method of the present invention. Fig. 4 is a characteristic curve diagram showing how the reverse current characteristic shown in Fig. 3 changes after the life cycle is compared with the conventional method and the method of the present invention, and Fig. 5 shows the method of the present invention applied to the manufacturing method of a power transistor. It is a structural sectional view for explaining an example. 11...N type silicon substrate, 12...P shadow area, 1
3...N shadow area, 14...Oxide film, 15...Collector ゛4! 16...Base electrode, 17...Emitter electrode.

Claims (4)

[Claims] (1) A method for manufacturing a semiconductor device, which comprises forming an oxide film on the surface of a boron diffusion region by forming the oxide film by high-temperature heat treatment and then heat-treating it in an inert gas atmosphere. (2) The method for manufacturing a semiconductor device according to claim 1, wherein the inert gas atmosphere is a nitrogen gas atmosphere. (3) The method for manufacturing a semiconductor device according to claim 1, wherein the heat treatment in the inert gas atmosphere is performed in the same furnace as the oxide film forming furnace. (4) The method of manufacturing a semiconductor device according to claim 1, wherein the heat treatment in the inert gas atmosphere is performed immediately after the formation of the oxide film.