JPH0786199A - Method for manufacturing silicon carbide semiconductor device - Google Patents

Abstract

(57) [Summary] [Purpose] p was obtained by introducing Al into a SiC semiconductor element at a desired concentration.
Forming a shaped region enables semiconductor device fabrication. [Composition] Outward diffusion of Al during annealing after ion implantation,
It is prevented by forming a silicon nitride film on the surface to obtain the desired Al concentration. The occurrence of trouble due to the difference in the coefficient of thermal expansion between silicon nitride and SiC is prevented by laminating silicon oxide films on both sides of the silicon nitride film.

Description

Detailed Description of the Invention

[0001]

The present invention relates to silicon carbide (hereinafter referred to as SiC).
Aluminum (A) for forming a p-type region in the element body.
l) of the present invention relates to a method for manufacturing a SiC semiconductor device.

[0002]

2. Description of the Related Art SiC having a wide band gap of 2.2 to 3.3 eV has a characteristic that the maximum electric field strength is higher than that of silicon and is expected as a material for a high breakdown voltage semiconductor element. Doping of impurities is indispensable for manufacturing semiconductor devices. If ion-implanted into SiC at high temperature, p with Al or Ga
Forming is the Journal of the Electrochemical Soci
ety, Vol 119 (1972) p. 1355 by Addamiano et al. and Sov. Phys. Semicond, Vol 9 (1976) p. 820 by Gusev et al.

[0003]

Generally, an ion-implanted semiconductor substrate is continuously subjected to an annealing process for electrically activating impurities. However, the Al ion-implanted into the SiC element diffuses outward in the annealing process, that is, the Al in SiC.
It was difficult to implant Al ions in that the desired impurity concentration could not be obtained due to the phenomenon that Al was released outside the substrate.

An object of the present invention is to solve this problem and provide a method of manufacturing a SiC semiconductor device in which Al is ion-implanted into a SiC element body to form a region having a desired impurity concentration.

[0005]

In order to achieve the above object, a method of manufacturing a SiC semiconductor device according to the present invention is performed by implanting Al ions into a predetermined region of a SiC element body, and at least performing the ion implantation.
It includes a step of coating the surface of the region where Al ions are implanted with a silicon nitride film and then annealing. The thickness of the silicon nitride film is preferably 0.1 μm or more and 0.5 μm or less. It is effective to interpose a silicon oxide film between the silicon nitride film and the SiC body. The thickness of the silicon oxide film is preferably 0.5 μm or less. Further, it is effective to deposit a silicon oxide film also on the anti-oxidation silicon film side of the silicon nitride film. In this case, it is a good method to make the thicknesses of both silicon oxide films substantially equal.

[0006]

[Function] Although the reason has not been sufficiently clarified, it has been experimentally found that the silicon nitride film forms a solid solution with Al and has an Al outward diffusion blocking effect. A thickness of 0.1 μm or more is required to prevent outward diffusion. If it is too thick, the amount of Al dissolved in it will be too large, so it is preferable to keep it to 0.5 μm or less. However, silicon nitride has a smaller coefficient of thermal expansion than SiC, and due to the difference in coefficient of thermal expansion, thermal stress may be generated between the SiC element body and the silicon nitride film, which may cause cracks in the nitride film. During annealing, Al diffuses out through these cracks and Si
There may be variations in Al concentration during C. The silicon oxide film acts as a buffer film for both. The oxide film thickness needs to be 0.5 μm or less so that the film deposition time is as short as possible and the amount of Al that diffuses outward into the oxide film is small. And, it is effective to make the thickness of the nitride film approximately equal to that in order to prevent the nitride film from cracking. However, when the annealing temperature is increased in order to form a deep diffusion layer, thermal stress is generated between the silicon oxide and silicon nitride due to the difference in thermal expansion coefficient between them, and a crack is generated in the nitride film. Therefore, by sandwiching the nitride film between the oxide films on both sides, generation of thermal stress is suppressed as much as possible.

[0007]

EXAMPLE FIGS. 1 (a) and 1 (b) show an Al ion implantation process according to an example of the present invention. First, Al ions 2 are ion-implanted into the SiC substrate 1 [FIG. 1 (a)]. At this time, the ion implantation conditions are an acceleration voltage of 100 keV, a dose amount of 3 × 10 ¹⁴ cm ⁻² , and an ion species of ²⁷ Al ⁺ . Next, a nitride film 3 is formed on the surface of the SiC substrate [FIG. 1 (b)]. The nitride film is formed by, for example, a sputtering method or a plasma CVD method. This nitride film makes Al
However, the solid solubility of Al in the nitride film is large, and the thicker the nitride film, the greater the amount of Al that forms a solid solution in the nitride film due to the outward diffusion during annealing. However, if the nitride film is too thin, Al may pass therethrough, and pinholes are likely to be formed, so that Al may diffuse outward in the pinhole portion. The appropriate thickness of the nitride film is about 0.1 to 0.5 μm. Further, if the nitride film thickness varies within the surface of the SiC substrate, a local difference occurs in the amount of Al diffused into the SiC substrate. Therefore, the in-plane distribution of Al concentration in the SiC substrate also varies. That is, the nitride film 3 needs to be formed to have the above-mentioned thickness and a uniform thickness within the surface of the SiC substrate. Then, annealing was performed at a temperature of 1200 ° C. in a nitrogen atmosphere for 10 hours.

Another embodiment shown in FIGS. 2 (a) to 2 (d) is shown.
First, on the SiC substrate, as in the method shown in FIG.
Are ion-implanted [Fig. 2 (a)]. Next, 0.
An oxide film 4 having a thickness of about 1 μm is formed [FIG. 2 (b)].
Next, the nitride film 3 is formed on the oxide film 4 by the same method as that shown in FIG. 1 [FIG. 2 (c)]. At this time, the nitride film needs to be a film having a uniform film thickness of about 0.1 to 0.5 μm for the same reason as in the case where only the nitride film is used as the outward diffusion preventing film for Al as shown in FIG. is there. Further, an oxide film 5 is formed again on the nitride film 3 [FIG. 2 (d)]. An oxide film 4 is formed as a buffer film between the SiC substrate 1 and the nitride film 3 to suppress the generation of thermal stress due to the difference in thermal expansion coefficient between SiC and silicon nitride, but to increase the annealing temperature. Therefore, the nitride film 3 is sandwiched between the oxide film 4 and the oxide film 5. In the structure in which the outward diffusion preventing film is composed of only the silicon nitride film 3 or the silicon oxide film 4 and the silicon nitride film 3 as shown in FIG. 1, a crack is generated in the nitride film 3 during annealing, and this crack causes the SiC In some cases, the in-plane concentration distribution of Al varied within the substrate. As shown in FIG. 2, when the outward diffusion preventing film has a structure composed of the oxide film 4, the nitride film 3 and the oxide film 5, no crack occurs after annealing at 1500 ° C. for 10 hours.
At this time, it was effective to make the thickness of the oxide film 5 equal to the thickness of the oxide film 3 in order to prevent the nitride film 3 from cracking.

FIG. 3 shows the Al concentration distribution in the p-type region of the semiconductor device manufactured according to the embodiment of the present invention.
The Al concentration on the surface of the element body is about 1 × 10 ¹⁹ cm ^-3 and the diffusion depth is 2μ.
A concentration distribution of about m was obtained uniformly.

[0010]

According to the present invention, by utilizing the Al outward diffusion blocking effect of silicon nitride, the surface of the SiC element body is covered with a silicon nitride film after Al ion implantation to obtain a desired concentration in SiC. At Al
The introduction area could be formed. Also silicon nitride and Si
The occurrence of troubles due to the difference in the coefficient of thermal expansion from C could be prevented by stacking the silicon oxide film.

[Brief description of drawings]

FIG. 1 shows an Al ion implantation process in one embodiment of the present invention.
Sectional views shown in order of (a) and (b)

FIG. 2 is a sectional view showing an Al ion implantation step in another embodiment of the present invention in the order of (a) to (d).

FIG. 3 is a concentration distribution diagram in a p-type region of a SiC semiconductor device manufactured according to an example of the present invention.

[Explanation of symbols]

 1 SiC substrate 2 Al ion 3 Silicon nitride film 4, 5 Silicon oxide film

Claims (6)

[Claims] 1. A method of implanting aluminum into a predetermined region of a silicon carbide body, at least covering the surface of the region where the aluminum ion implantation is performed with a silicon nitride film, and then annealing. A method for manufacturing a characteristic silicon carbide semiconductor device. 2. A silicon nitride film having a thickness of 0.1 μm or more and 0.5.
The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein the thickness is not more than μm. 3. A method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein a silicon oxide film is interposed between the silicon nitride film and the silicon carbide body. 4. A method for manufacturing a silicon carbide semiconductor device according to claim 3, wherein the thickness of the silicon oxide film is 0.5 μm or less. 5. The method for manufacturing a silicon carbide semiconductor device according to claim 3, wherein a silicon oxide film is deposited also on the anti-silicon oxide film side of the silicon nitride film. 6. The method for manufacturing a silicon carbide semiconductor device according to claim 5, wherein the thicknesses of both silicon oxide films are made substantially equal.