JPS6122453B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention is applicable to impurity diffusion, impurity intrusion, etc.
The present invention provides a heat treatment method that is effective in preventing thermal deterioration of materials during the material heat treatment process.

As typified by the semiconductor industry, heat treatment processes are extremely important and constitute many manufacturing processes. In other words, typical examples of heat treatment processes in the semiconductor industry include thermal diffusion of impurity elements into the base material crystal, heat treatment after ion implantation, thermal intrusion of impurities, and electrode metal formation on the semiconductor surface. It can be said that there is no limit to the number of methods such as heat treatment.

However, the heat treatment process is always accompanied by the danger of thermally deteriorating the semiconductor base material crystal. for example
When compound semiconductor materials such as GaAs, GaP, and InP are heated to high temperatures in an atmosphere where the partial pressure of the base material constituent elements is lower than the thermal equilibrium value, the base material constituent elements bring the atmosphere closer to the thermal equilibrium value. A large amount of so-called stoichiometric defects, ie, atomic vacancies, etc., are generated in the base material crystal through the surface. However, in many cases, these stoichiometric defects significantly reduce the basic properties of semiconductor crystals, such as mobility and carrier life, and the performance of devices manufactured with these stoichiometric defects deteriorates. will be low.

For example, it is now considered a self-evident fact that in GaP crystals, this stoichiometric defect is an important factor governing the characteristics of luminescence from GaP crystals, and it also affects the performance of various compound semiconductors. It is also considered as an important controlling factor. In addition, many people are beginning to pay attention to this stoichiometric defect as a critical factor that governs the reliability of devices made from compound semiconductors. As mentioned above, stoichiometric defects are an important factor that determines the properties of materials; in compound semiconductors, they have long been called alkali halides, although they have only recently begun to attract attention.
Research is progressing on compounds such as NaCI, KCl, and NaI.

Due to its basic properties, GaAs is a material that has produced many practical devices (e.g., infrared light emitting diodes, P-n junction injection lasers, oak diodes, field effect transistor light receiving devices, etc.), and it is also a material that has been used as a compound. Since GaAs is a semiconductor, it is very easy to introduce stoichiometric defects through careless heat treatment processes, so GaAs will be explained below as an example of a material.

This is a very common heat treatment process for GaAs, and an important example is thermal diffusion along the p-type impurity.

Since thermal diffusion along the axis is indispensable in the production of GaAs light-emitting diodes and striped double heterojunction laser diodes called planar type, the following explanation is further explained below.
Let's explain this using an example of thermal diffusion into GaAs.

When diffusing GaAs along its surface, it must be done in a thermally balanced vapor consisting of Ga, As, and Zn around the GaAs base material. As scatters and stoichiometric defects occur on the surface.

It is well known that when Zn is diffused into GaAs in a system that deviates significantly from the thermal equilibrium described above, the surface condition of GaAs may be significantly disturbed and the diffusion front may even become rough.

HC
Casey Jr) and MB Punishyu (MB
Trans-actions of Metallurgical Society of A.I.M.E.
Society of AIME), Vol. 242, pp. 406-412 (March 1968), examined the phase diagram of a ternary system consisting of Ga, As, and Zn to determine the thermal equilibrium state when Zn is diffused. It is stated that thermal diffusion of Zn that minimizes the introduction of stoichiometric defects into the diffusion substrate requires the use of an alloy consisting of, for example, 5% Ca, 45% Zn, and 50% As as a Zn diffusion source, and it is necessary to improve reproducibility. A good Zn diffusion source was proposed.

However, this ternary Zn diffusion source consisting of Ga, As, and Zn is synthesized in a sealed tube at high temperatures (approximately 1100°C) and high pressure, resulting in dangerous inspections, and materials for the sealed tube and crucible. It is difficult to be a good diffusion source from a purity standpoint as it is heavily contaminated. Also, this
Zn diffusion under thermal equilibrium vapor pressure using the above-mentioned Zn diffusion source proposed by Cathay and Punish, which consists of Ga, As, and Zn, is diffusion in a place where the vapor pressure of As is higher than that of Ga, and the vapor pressure of Zn is also higher than that of Ga. Because of the high
The concentration of Zn in the diffusion layer is high, and the Zn concentration on the surface of the GaAs substrate exceeds 10 ²⁰ cm ^-3 even during thermal diffusion at 700°C. Therefore, in order to perform diffusion with a surface concentration of Zn of 10 ¹⁹ cm ^-3 or less, a system consisting of Zn and Ga is used as a diffusion source. Moreover, the system consisting of Zn and Ga
Closed-tube diffusion using a Zn diffusion source requires extremely accurate microweighing of Ga and Zn;
The melting point of the alloy consisting of Ga and Zn is low at approximately 30°C or less, and the diffusion source is easily contaminated with oxygen in the air, making it inconvenient to handle.Also, the quartz material normally used for sealing tube materials is high temperature due to the Ga metal. easy to get wet,
Due to its easy reaction, it is difficult to achieve Zn diffusion with good reproducibility.

In addition, low-concentration diffusion of Zn can be achieved by using a Zn-doped SiO ₂ film.
H. Kawano and Kei Mori reported in the Japanese Journal of _Applied Phys.
Applied Physics), Vol. 15, No. 4, p. 727 (1976), this diffusion temperature is favorable because it requires a high temperature of 900°C or higher, and reactions occur at the interface between the SiO ₂ film and the GaAs substrate. It is not a significant Zn diffusion source.

Furthermore, Zn diffusion in an open tube requires precise control of Zn vapor pressure on the GaAs substrate surface and control of Ga and As vapor pressure on the GaAs substrate to prevent thermal deterioration of the GaAs substrate. , As, and
Reproducible Zn diffusion is difficult because Zn vapor must be flowed into the reaction tube and controlled. Also, in this method, a larger amount of
Ga, As, and Zn vapors are emitted, making it extremely dangerous for humans.

Therefore, the purpose of the present invention is to diffuse Zn at low concentrations of, for example, 10 ¹⁹ cm ^-3 or less using an extremely simple device, without the need for vacuum processes associated with sealed quartz tubes, the frequency of quartz burner processing, or the need for open tubes. The object of the present invention is to provide a heat treatment method that eliminates the generation of harmful gases and the difficulty of controlling vapor pressure, etc., and achieves heat treatment with good reproducibility without impurity diffusion or thermal deterioration.

According to this invention, a heat treatment method characterized by using a container sealed with molten metal is obtained.

The gist of the heat treatment method of this invention is to add or add some or all of the constituent elements of the material to be heat treated to the material to be heat treated and a container placed at a separate location to remove impurities from the base material. When adding, a substance consisting of the specified element is put in, and the opening or gap to the outside of the container is sealed with metal molten at least at the heat treatment temperature, at least when the material to be heat treated is heat treated. It is extremely effective in preventing thermal deterioration of heat-treated materials.

Hereinafter, as an example of the present invention, an application example of the present invention used for thermal diffusion of Zn into GaAs will be described in detail with reference to the drawings.

FIG. 1 is a cross-sectional view showing the concept of an apparatus for thermally diffusing Zn into GaAs to which the heat treatment method of the present invention is applied. FIG. 1a shows the stage before heat diffusion, and FIG. 1b shows the state of the device at the stage of heat diffusion. A method for thermally diffusing Zn into GaAs using the heat treatment method of the present invention will be described in detail.

First, as shown in Fig. 1a, a material 3 consisting of 0.5 g of Ga and 20 mg of GaAs is placed in a container 1 made of carbon or the like, and at the same time, Ga5 is placed in a cylindrical groove 5 at the top of the container 1. ’ is inserted. Also, the lid 2 of container 1
Holes 6 and 7 were drilled through the hole, hole 6 was filled with Zn6' and hole 7 was filled with As or GaAs as required.
7' is installed. A substrate installation hole is made in the upper part of the lid 2, and a GaAs film 4' for Zn thermal diffusion is installed therein. The cylindrical tapered part 8 of the lid 2 is pushed into the Ga 5' during thermal diffusion as shown in FIG. This allows the lid to move.

Further, a high frequency coil 11 serving as a heat source for heat diffusion is arranged around the container 1 via a reaction tube 10.

To perform diffusion in this state, first place the container 1 and the lid 2 separately in the reaction tube ₁₀ as shown in FIG. In order to replace the atmosphere with ₂ gases and maintain an H ₂ atmosphere, H ₂ is supplied and discharged at a rate of 100 ml/mm. After that, a current is passed through the high frequency coil 11, and the container 1 is heated.
Heated to 800℃. At this time, the lid 2 is the substrate 4',
GaAs or As (DaAs if performed) 7′Zn
6' is kept far enough away from container 1 to keep the temperature below 100°C. By heating container 1 to 800°C and keeping it for 30 minutes, enough GaAs is melted in Ga solution 3, and the oxygen contamination that Ga solution 3 and Ga 5' received during the installation stage is removed in the reducing atmosphere _H2. . Thereafter, the current flowing through the high frequency coil 11 was reduced to set the temperature of the container 1 to the Zn diffusion set temperature of 700°C. In this case, 5 mg of Zn6' was prepared. After the container 1 reaches a sufficient temperature of 700° C., the quartz piece sealing tube 9 is moved from the outside and the lid 2 is immediately placed over the container 1.
This situation is shown in FIG. 1b. In the state shown in FIG. 1b, the tapered portion 8 of the lid 2 is inserted into the Ga 5' and the inside of the container is sealed. At this time, the liquid level of the Ga solution 3 is pushed up by the carbon forming the lid 2, and becomes higher than the hole in which the Zn 6' is inserted. The space inside the sealed container 1 is designed to be as small as possible as shown in the figure, and the entire container including the container 1 and the lid 2 is approximately 10
After a few minutes, the diffusion temperature of 700℃ is reached, and the cavity inside the container is filled with Ga.
An equilibrium state is created between the steam, As vapor, and Zn vapor due to Zn dissolved in the Ga solution 3. In this state, Zn and As vapors dissolve into Ga 5', but only in small amounts, and from the sources of Ga and As vapors, Ga solution 3 and GaAs 7' (GaAs 7' is dissolved in order to quickly increase the As pressure in the space inside the container). Vapors of Ga and As are always supplied so that the inside of the cavity is in a thermal equilibrium system, and the GaAs substrate 4' allows the thermal diffusion of Zn without causing any thermal deterioration that would cause the stoichiometric ratio to change. will be carried out. In the example shown in this example, the Ga solution 3 is GaAs when the container is sealed.
I made sure that the solution did not rise to 7. Above Zn
In diffusion, when the diffusion time is t, the diffusion depth increases in proportion to √, but when √=1, the diffusion depth was 0.6 μm. It was also confirmed that the surface condition of GaAs after diffusion is almost the same as before diffusion, and that the flatness of the diffusion front surface is also very good. The surface concentration of Zn in the diffusion layer was 7×10 ¹⁸ cm ^-3 .

As described above, the heat treatment method according to the present invention was applied.
We have described the thermal diffusion method of Zn into GaAs, but Ga5'
Similar Zn diffusion results were obtained by using In metal instead of Zn. Also, when As was used instead of GaAs7', the Zn diffusion results were good and similar to the above results. Note that it is possible to perform heat treatment except for GaAs 7'.

In the above embodiment, an example was described in which the heat treatment method of the present invention was applied to the thermal diffusion method of Zn to GaAs, but the method of the present invention does not need to limit the base materials to GaAs, and It is not limited to the process. In other words, it goes without saying that it can be applied to a wide variety of heat treatment processes for compound semiconductor materials, including various compounds and compound semiconductors. Further, although Ga was used in the embodiment as the molten metal that is the gist of the present invention, various metals that melt at the heat treatment temperature may be used depending on the type of material to be heat treated. For example, when heat-treating AlGaAs at a temperature higher than the melting point of Al, 660.2°C, Al can be used as the molten metal, and when heat-treating the HgTe or HgCdTe compounds, Hg can be used as the molten metal. Furthermore, the molten metal is not limited to the elements constituting the material to be heat treated; Al may be used when heat treating GaAs, and Hg may be used when heat treating compounds other than HgTe and HgCdTe.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example in which the heat treatment method of the present invention is applied to a method for thermally diffusing Zn into GaAs. Figure b is a cross-sectional view during thermal diffusion. In Figure 1, reference numeral 1 is a carbon container, 2 is a carbon lid, 3 is Ga0.5g,
A material consisting of 20 mg of GaAs, 4 is a thermally diffused material insertion part 4' is a GaAs substrate of a thermally diffused material, 5 is a cylindrical groove formed in the container 1, and 4 is a GaAs substrate for sealing the container of the present invention.
5' is included. 6 is a hole for inserting the diffusion material Zn 6', 7 is a hole for inserting powdered GaAs 7' prepared to quickly increase the As pressure inside the container 1 during heat treatment, and 8 is a cylindrical tapered part attached to the lid 2. 9 is a sealed quartz tube for supporting and moving the lid 2, 10 is a quartz reaction tube, and 11 is a high frequency coil serving as a heat source.

Claims (1)

[Claims] 1. A first container containing a compound semiconductor and a second container containing a material containing at least a part of the constituent elements of the compound semiconductor are sealed with molten metal, A heat treatment method characterized by heat treating a compound semiconductor. 2. The heat treatment method according to claim 1, wherein a compound semiconductor is used as the material to be heat treated, and impurities are thermally diffused into the semiconductor. 3. The heat treatment method according to claim 2, wherein the molten metal contains at least a part of the constituent elements of the material to be heat treated.