JPS622530A - Impurity thermal diffusion into semiconductor substrate - Google Patents

Abstract

PURPOSE:To prevent a III-V Group compound semiconductor substrate from decompos ing even if the pressure of the V Group element is not applied to the semiconductor substrate at the time of thermal diffusion of an impurity and to enable stable thermal diffusion of the impurity by a method wherein a film; having a large diffusion coeffi cient and a small diffusion coefficient is provided on the substrate. CONSTITUTION:A wafer 1 is constituted of a III-V Group compound semiconductor substrate 2, diffusion masks 4 and a film 3. The film 3 has a large diffusion coefficient of diffusing substance 7 and small diffusion coefficient of the substrate-constituting element. An SiO2 film, for example, is used for the film 3. For the diffusion masks 4, an Si3N4 film, for example, is used. The wafer 1 is vacuum-sealed in a quartz ampul 6 along with a diffusing substance, such as the Zn 7, and when a heat treatment is performed, such as impurity as the Zn is diffused in the semiconductor substrate in the parts where the Si3N4 diffusion masks are not provided, because the diffusion coefficient of the Zn is large in the SiO2 film. However, the volatilization of the V Group element handly generate from the semiconductor substrate because the diffusion coefficient of the V Group element in the SiO2 film is small. As a result, the substrate can be prevented from being decomposed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for thermally diffusing impurities into a semiconductor substrate, and particularly relates to a method for thermally diffusing ZnD into a ■-v group compound semiconductor substrate, such as a GaAS substrate.

[Prior Art] Fig. 2 is a sectional view showing a conventional wafer in which impurities are partially thermally diffused, and Fig. 3 is a vacuum ampoule for thermally diffusing impurities into the wafer shown in Fig. 2. FIG.

In FIG. 2, a wafer 5 is composed of a ■-v group compound semiconductor substrate 2 and a diffusion mask 4. As shown in FIG. (2)-V group compound semiconductor substrate 2 is a material for a semiconductor element, and impurities are diffused into it. (2)-V group compound semiconductor substrate 2 is, for example, a GaAs substrate.

The diffusion mask 4 is a film provided on the surface of the substrate for the purpose of partially diffusing impurities into the substrate, and a material is used such that the diffusion coefficient of the diffusion substance to be diffused into the substrate is small for that film. .

In FIG. 3, in addition to the wafer 5 shown in FIG. 2, a diffusion material 7 and a substance 8 of group V elements are sealed in a vacuum ampoule 6. An example of the vacuum ampoule 6 is a quartz ampoule, for example, Zn is used as the diffusion substance serving as an impurity source, and AS is used as the V group element.

Next, a conventional diffusion method for partially thermally diffusing impurities into a wafer will be described with reference to FIGS. 2 and 3.

First, as a first step, a predetermined region on the GaAs I plate 2 is masked with a diffusion mask 4. As the diffusion mask 4, for example, St 3 N4 is used. Next, as a second step, the wafer 5 masked with the diffusion mask 4 is
is vacuum-sealed in a quartz ampoule 6 together with a diffusion material 7 and a group V element material 8, and heat-treated in a predetermined furnace.

This process causes the diffusion material 7 to diffuse into the semiconductor substrate from the unmasked areas of the wafer 5. In this process, the substance 8 of group V elements such as AS enclosed in the quartz ampoule 6 serves to prevent the volatilization of the group V elements from the semiconductor substrate 2 due to the high temperature heat treatment, thereby preventing decomposition of the I plate. Next, as a third step, the quartz ampoule 6, which has undergone thermal diffusion, is taken out of the furnace and rapidly cooled.

[Problems to be solved by the invention] As mentioned above, in the conventional thermal diffusion method, it is necessary to enclose a group V element in order to prevent the substrate from decomposing. There was a drawback that the substrate was contaminated by markings on the surface. Furthermore, since the diffusion state of the diffusing substance strongly depends on the pressure of the group V element, there is also a drawback that the controllability of diffusion is poor.

Therefore, the present invention was made to solve the problems of the conventional method as described above.
It is an object of the present invention to provide a method for thermally diffusing impurities into a semiconductor substrate of group (1)-v group without enclosing group elements.

[Means for Solving the Problems] The present invention has a structure in which the elements constituting the substrate have a small diffusion coefficient;
In addition, after a film having a large impurity diffusion coefficient is provided on the surface of the m-V group compound semiconductor substrate, the impurity is thermally diffused.

[Function] In the present invention, when performing thermal diffusion of impurities, the semiconductor substrate does not decompose even if the substance of group V element is not enclosed in a vacuum ampoule.

〔Example〕

FIG. 1 is a diagram showing a cross section of a wafer 1 to which a method of thermally diffusing impurities into a semiconductor substrate according to an embodiment of the present invention is applied.

The wafer 1 is composed of a ■-v group compound semiconductor substrate 2 and a diffusion mask 4 and 113.

Compared to the conventional wafer 5, the wafer 1 has a structure in which l113 is inserted between the semiconductor substrate 2 and the diffusion mask 4. Here, ll[3 is an index in which the diffusion coefficient of the diffusing substance 7 is large and the diffusion coefficient of the element constituting the substrate is small; for example, 810. A membrane is used. Further, for the diffusion mask 4, for example, 5lsN4111 is used.

Next, one embodiment of the present invention will be described.

First, a wafer 1 as shown in FIG.
It is vacuum sealed inside and heat treated.

In this case, there is no need to enclose the group V element substance in the quartz ampoule 6.

Since impurities such as zn have a large diffusion coefficient in StOz, they are diffused into the semiconductor substrate in areas where 5isN<diffusion mask is not provided. However, volatilization of group V elements from the semiconductor substrate is almost non-existent because the diffusion coefficient of group V elements in 5I02 is small, and decomposition of the substrate can be prevented.

In the above-mentioned embodiments, the sealed tube method was described, but the diffusion may be performed by an open tube method such as that used in the manufacture of silicon devices.

Also at this time, there is no need to flow a gas such as A s Hs to prevent the volatilization of the V group element.

Furthermore, in the above embodiment, the film 3 having a large diffusion coefficient of the diffusion substance and a small diffusion coefficient of the substrate constituent elements was inserted between the semiconductor substrate 2 and the diffusion mask 4. Exactly the same effect can be obtained by adding heat.

[Effects of the Invention] As described above, according to the present invention, when diffusing impurities, the diffusion coefficient of the pure substance on the semi-integrated root substrate of the -V group compound is large and the diffusion coefficient of the substrate constituent elements is large. Since the film is provided with a small value, the semiconductor substrate does not decompose even if the pressure of group V elements is not applied to the semiconductor substrate during thermal diffusion of impurities, and stable diffusion can be performed.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a cross section of a wafer to which a method of thermally diffusing impurities into a group IV compound semiconductor substrate according to an embodiment of the present invention is applied. FIG. 2 is a sectional view showing a conventional wafer. FIG. 3 is a conceptual diagram showing the conventional vacuum ampoule shown in FIG. 2 for thermally diffusing impurities into the wafer. In the figure, 1 is a wafer, 2 is a semiconductor substrate, 3 is a film, and 4
indicates a diffusion mask, 6 indicates a quartz ampoule, and 7 indicates a diffusion substance.

Claims (2)

[Claims] (1) A method for thermally diffusing impurities into a III-V compound semiconductor substrate, comprising: forming a film in which the diffusion coefficient of an element constituting the semiconductor substrate is small and the diffusion coefficient of an impurity to be diffused into the semiconductor substrate is large; A method for thermally diffusing impurities into a semiconductor substrate, the method comprising thermally diffusing impurities after being provided on the substrate. (2) Claim 1, wherein the film is a SiO_2 film.
The method for thermally diffusing impurities into a semiconductor substrate as described in Section 1.