JPS6347136B2 - - Google Patents

Abstract

PURPOSE:To prevent the generation of a low electron concentration region in the interface of a growth layer, and to improve quality by washing the inside of a reaction vessel, in which a post epitaxial layer is shaped to the GaAs epitaxial wafer, with an acidic liquid and treating the wafer at a high temperature in hydrogen or an inert gas. CONSTITUTION:An n<-> active layer 12 having 10<15>cm<-3> electron concentration is formed discontinuously through pre-epitaxial growth and an n<+> layer 13 through post epitaxial growth to the low resistance n type GaAs wafer 11 as a substrate preparing an appliance such as a gun diode, and the wafer is used. Extraneous matter in the reaction vessel 49 is dissolved with nitrohydrochloric acid prior to the post epitaxial growth, and washed with pure water, fluoric acid and pure water. The wafer is dried, the vessel 49 is set without mounting the wafer, a gas such as hydrogen refind at high purity is flowed, and the wafer is heated for fourty min at 850 deg.C. The wafer 412 is placed, and post epitaxial growth is conducted at a tmperature such as 600-720 deg.C while using organic gallium and arsine as reaction gases. Accordingly, the electronic concentration, the controllability of the thickness and the reproducibility of the epitaxial layer can be improved, and the scattering, etc. of the threshold value of the gun diode can be removed.

Description

Detailed Description of the Invention This invention provides organic gallium and arsine AsH ₃ on a gallium arsenide GaAs epitaxial wafer with a pre-stage epitaxial vapor growth layer formed on the substrate.
The present invention relates to a method of manufacturing a GaAs epitaxial wafer in which a subsequent epitaxial layer is formed discontinuously by a pyrolytic vapor deposition method.

In general, Gunn diodes, variable capacitance diodes, and the like are examples of semiconductor elements in which front and rear epitaxial layers are discontinuously formed on a substrate. All of these semiconductor devices require precision control of the electron concentration and thickness of the pre-stage epitaxial layer formed on the GaAs substrate.

Therefore, first, measure the electron concentration and thickness of the formed first-stage epitaxial layer, and after confirming that the desired electron concentration and thickness have been achieved, discontinuously form the second-stage epitaxial layer on the epitaxial layer. It is common practice to repeat the method of stacking layers.

For example, GaAs epitaxial wafers for Gunn diodes are n-type low resistivity wafers, as shown in Figure 1.
On the GaAs substrate 11 is an n ^- layer, for example, an electron concentration of 1×
The active layer 12 with a thickness of 10 ¹⁵ /cm ³ and a thickness of 10 μm is used as a pre-stage epitaxial layer, and an n ⁺⁺ layer with an electron concentration of 5×
A low resistivity 13 having a resistivity of 10 ¹⁷ /cm ² and a thickness of 3 μm is provided as a subsequent epitaxial layer. Since the main characteristics of Gunn diode are determined by the electron concentration and thickness of the active layer 12, the active layer 12 is usually
After forming ^{n +} Growing layers.

As a method for forming a wafer with this structure, in addition to the conventional vapor phase growth method called the arsenic trichloride AsCl ₃ method,
Liquid phase growth methods are well known, but in order to obtain epitaxial wafers with uniform electron concentration and thickness with good control using these growth methods, the wafer area that can be obtained in each growth process is at most 10 ^cm3 . However, the disadvantage is that it is not suitable for mass production. For this purpose, thermal decomposition of organic gallium and AsH ₃ is used, which is called the pyrolysis method.
In the GaAs vapor phase growth method, all of the raw materials can be introduced into the reaction vessel in a gaseous state, and the growth region within this vessel only needs to be at a single temperature range, so it is possible to control the electron concentration, thickness, etc. of the epitaxial layer. This method is attracting attention as a method that has good controllability and reproducibility, and is more suitable for mass production than the above two methods. For example, materials from the Semiconductor Transistor Study Group of the Institute of Electronics and Communication Engineers, published in March 1976.
SSD-75-83, pp. 27-36 describes an epitaxial layer for a Hall element formed using the thermal decomposition of trimethylgallium (CH ₃ ) ₃ Ga and AsH ₃ , which emits electrons over an area of 30 cm ^{2 .} It is stated that the concentration and thickness were uniform.

Therefore, if the latter stage n ⁺⁺ is formed using the thermal decomposition method, it should be possible to improve mass productivity compared to the above-mentioned AsCl ₃ method or liquid phase growth method. However, when n ⁺⁺ is formed using a thermal decomposition method and a Gunn diode is prototyped using this epitaxial wafer, the above-mentioned result is obtained.
Although the electron concentration and thickness of the n ^- layer and n ⁺⁺ layer each vary by less than 5%, the oscillation is thought to reflect the variation in the thickness of the n ^- layer the most among Gunn diode characteristics. As shown in the histogram of FIG. 2, the threshold voltage of . In this epitaxial wafer, as shown in the electron concentration profile curve in Figure 3, a low electron concentration region is formed at the boundary between the n ⁺⁺ layer and the n ^- layer, and the width of this region and the amount of decrease in electron concentration are It is clear that the values vary within the same wafer and each time the growth is repeated. In order to create such a low electron concentration region, the threshold voltage for oscillation of the Gunn diode is varied.

The present invention provides a manufacturing method that allows GaAs epitaxial wafers to be obtained without intervening undesired boundary regions except for these points. That is, this invention is a GaAs epitaxial wafer on which a pre-stage epitaxial vapor-phase grown layer is grown, and organic gallium and AsH ₃ are discontinuously grown on the surface of the pre-stage epitaxial vapor-phase grown layer by a pyrolytic vapor-phase growth method. When forming the subsequent epitaxial vapor phase growth layer, a cleaning step is performed in which the inside of the reaction container is cleaned with an acidic cleaning solution prior to placing the GaAs epitaxial wafer, and after cleaning, high-purity hydrogen or an inert gas is introduced into the container. The present invention relates to a method for manufacturing GaAs epitaxial wafers in which a heating process is performed at a temperature higher than the vapor phase growth temperature while flowing.

In this invention, the meaning of the discontinuous formation of the second-stage epitaxial vapor-phase grown layer is that the operation is temporarily stopped in order to make the second-stage epitaxial vapor-grown layer different in quality from the first-stage epitaxial vapor-phase grown layer, and while the operation is stopped, the second-stage epitaxial vapor-phase grown layer is formed in a discontinuous manner. This refers to the time required to measure the epitaxially grown layer.

An embodiment of the present invention will be described below with reference to the drawings. A schematic diagram of the epitaxial apparatus used in this example is shown in FIG. Hydrogen _H2 for dilution
The gas is used through a purification device 41, a part of which is introduced into a stainless steel container 42 filled with (CH ₃ ) ₃ Ga, and supplied to a reaction container 49 containing a certain amount of (CH ₃ ) ₃ Ga gas. . In addition, AsH ₃ is directly supplied from a high-pressure container 43 filled with H ₂ gas diluted to 10%. Similarly, the hydrogen sulfide gas H ₂ S used to add n-type impurities when forming the n-type impurity doped layer is also H ₂
It is diluted with gas to a predetermined concentration and supplied directly from the voltage container 44 filled with the gas. The above gases are controlled at predetermined flow rates by the flow meters 45, 46, 47, and 48, respectively, and guided to the reaction vessel 49. These gases are heated by a heating table 41 heated by a high frequency coil 410.
1, and deposited as a pre-stage GaAs epitaxial layer on a GaAs substrate 412 placed on a heating table 411.

The wafer is taken out of the container in order to form the n ⁺⁺ layer for the Gunn diode as a subsequent epitaxial layer. First, the reaction vessel 49 is removed from the epitaxial apparatus, and is immersed in aqua regia to dissolve deposits of arsenic compounds, GaAs, etc. adhering to the interior of the vessel. After this, the aqua regia was replaced with deionized water, and then
Immerse in ~10 vol.% hydrofluoric acid aqueous solution for 1 to 2 minutes. After sufficiently purging with deionized water again, the reaction vessel 49 is taken out and dried in clean air passed through a filter. Next, this reaction vessel 49 was placed in the epitaxial apparatus again, and heated on the heating table 4 at 850°C for 40 minutes while flowing high-purity H ₂ gas that had passed through the purification device 41 into the vessel.
Heat 11. After the heating table 411 has cooled down to near room temperature, the epitaxial wafer 412 on which the n ^- layer has been formed is placed on the heating table 411 . This wafer has an n ^- electron concentration and a thickness of 1×10 ¹⁵ /
Within-wafer variation is 10% for cm ³ and 10 μm, respectively.
within The area is 25 cm ² in total, including 5 5 cm ² wafers. The ⁿ -epitaxial temperature was set at 660°C. Total H ₂ gas flow rate 9.5 l/min, H ₂ gas flow rate 33 ml/min through the container 42 filled with (CH ₃ ) ₃ Ga and kept at 0° C., AsH ₃ diluted to 10% with H ₂ gas.
Flow rate 200ml/min, _H2 to add n-type impurities
A flow rate of 300 ml/min of H ₂ S diluted with gas to 150 ppm is introduced into the reaction vessel 49 to form an n ⁺⁺ layer with a thickness of 3 μm. The electron concentration of the n ⁺⁺ layer is 5×10 ¹⁷ /cm ³ . n ⁺⁺
The surface electron concentration and thickness of the layer are within 10% over 25 cm ² except at the very periphery of the wafer. FIG. 5 shows the electron concentration profile curve near the boundary between the n ⁺⁺ and n ^- layers obtained in this example. The low electron concentration layer at the interface between the n ⁺⁺ and n ^- layers that appeared in Figure 3 has disappeared. Moreover, after repeating the same growth 10 times, it is clear that such an effect can always be reproduced. The variation in characteristics of GaAs Gunn diodes prototyped using epitaxial wafers produced by the method described above has been significantly improved. For example, the variation in the oscillation threshold voltage of Gunn diodes is extremely small as shown in Figure 6, less than half that of Figure 2. It has been reduced to As described above, according to the present invention, while maintaining mass productivity, ^{which is a characteristic of the thermal decomposition method, the subsequent epitaxial n ++ layer} can be grown without changing the electron concentration near the interface of the previous epitaxial n - layer. It is possible to provide an epitaxial wafer that can be grown and has good Gunn diode characteristics.

In this example, a method for manufacturing an epitaxial wafer for Gunn diodes was explained.
The gist of the present invention is that a multilayer epitaxial layer with small variations in electron concentration and thickness of each epitaxial layer can be formed by discontinuous epitaxy by cleaning and heating the reaction vessel. Therefore, it may be applied not only to Gunn diodes but also to all GaAs device wafers formed by discontinuous epitaxy. Furthermore, in the above embodiment, H ₂ S is used as a material to add n-type impurities, but n-type impurity raw materials such as solid sulfur S, gaseous monosilane SiH ₄ , germane GeH ₄ , hydrogen selenide H ₂ Se, etc. may also be used. or,
(C ₂ H ₅ ) ₃ Ga may be used instead of (CH ₃ ) ₃ Ga, and a resistance heating method may be used in the heating portion of the epitaxial device. Growth temperature may range from 600 to 720°C. The acid solution for washing the reaction vessel may be only aqua regia. In addition to H ₂ gas, the gas flowed into the reaction vessel when performing the heating step of the reaction vessel may be an inert gas such as nitrogen N ₂ or argon Ar.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of an epitaxial wafer for Gunn diodes, Figure 2 is a histogram of the oscillation threshold voltage of a Gunn diode made using an epitaxial wafer having an electron concentration profile as shown in Figure 3; Figure 3 shows the electron concentration profile curve near the interface between the front and rear epitaxial layers when the latter epitaxial n ⁺⁺ layer is formed using the conventional thermal decomposition method. A schematic diagram of an epitaxial device, FIG. 5 shows a subsequent stage epitaxial n ⁺⁺
Electron concentration profile curve diagram near the interface of both the front and rear epitaxial layers when the layers are formed, No. 6
The figure is a histogram of the oscillation threshold voltage of a Gunn diode manufactured using the epitaxial wafer according to the present invention. Figure 1: 11...Low resistivity n-type GaAs substrate, 1
2... Active layer: front stage epitaxial n ^- layer, 13
...Low resistivity layer for forming ohmic electrode: latter-stage epitaxial n ⁺⁺ layer, Figure 4: 41...Hydrogen gas purification device, 42...
Stainless steel container containing trimethyl gallium, 43...
... High-pressure container containing arsine gas, 44 ... High-pressure container containing hydrogen sulfide gas, 45-48 ... Flowmeter, 49
...Reaction container, 410 ...High frequency coil, 411
...Heating table, 412...GaAs substrate.

Claims (1)

[Claims] 1. A post-epitaxial vapor growth layer is discontinuously formed on the surface of the pre-epitaxial vapor-phase growth layer of a gallium arsenide epitaxial wafer on which a pre-stage epitaxial vapor-phase growth layer is formed on the substrate by a pyrolytic vapor-phase growth method of organic gallium and arsine. When forming a phase growth layer, prior to placing the gallium arsenide epitaxial wafer, there is a cleaning process in which the inside of the reaction vessel is cleaned with an acidic cleaning solution, and after cleaning, air is washed while flowing high-purity hydrogen or an inert gas into the vessel. A method for manufacturing a gallium arsenide epitaxial wafer, characterized by performing a heating process at a temperature higher than the phase growth temperature.