JPH0445973B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an epitaxial growth method that is frequently used in the manufacture of semiconductor devices.

Superlattice devices, which have recently been in the spotlight for application to semiconductor devices, particularly ultra-high frequency devices, semiconductor lasers, etc., can be obtained by periodically forming multiple crystal layers with a thickness of 100 Å or less. One of the methods for producing this superlattice element using compound semiconductor crystals is the thermal decomposition of organic metals such as trimethylgallium (TMG) and trimethylaluminum (TMA) and hydrides such as arsine (AsH ₃ ). Crystal growth by reaction (Motalorganic Chomioal)
Vapor Doposition (MOCVD). this
MOCVD is considered to be a mass-producible crystal growth method because the growth rate can be controlled by the flow rate and there is no need for a temperature gradient near the crystal substrate.

FIG. 1 is a schematic diagram of the main parts of an existing apparatus for growing GaAs or AsAlAs, for example on a GaAs crystal substrate. This FIG. 1 omits the raw material section and the exhaust system, and only shows the reaction system. In the figure, reference numeral 1 denotes a reaction chamber made of quartz, and a SiC-coated pedestal 3 heated by a high-frequency coil 2 is installed in the center of the reaction chamber 1. 4, 5, and 6 are on/off doggle valves that turn on and off the gas flowing into the reaction chamber 1, and 7, 8, and 9 are McFlow controllers that can adjust the flow rate, respectively (AsH ₃ + H ₂ ),
(TMG+H ₂ ) and (TMA+H ₂ ) gases are supplied. The piping is stainless steel, and the connections use swivel locks.

Then, the pedestal 3 is activated by the high frequency coil 2.
When growing GaAs, valves 4 and 5 are opened and AsH ₃ and TMG are introduced into the reaction chamber 1. For GaAlAs growth, valves 4, 5 and 6 are opened and AsH 3 is introduced into the reaction chamber 1. ₃ , TMG, and TMA are introduced into reaction chamber 1. Note that the composition ratio of GaAlAs is controlled depending on the flow rates of TMG and TMA.

In a growth apparatus with such a configuration, the film thickness of the growth layer is controlled by opening and closing valves 5 and 6 under the control of gas velocity and vapor pressure such as TMG, but the minimum film thickness that can be controlled is 100. It is about 200 Å. Controlling the film thickness below this was extremely difficult due to the influence of residual gas in the reaction chamber from the valve before and after opening and closing. Therefore, it is considered impossible to manufacture superlattice elements using such existing equipment.

The present invention was tried in view of such problems, and its characteristics are that a tank for storing a reaction gas is provided between the gas supply system and the reaction chamber, and a predetermined amount of gas sealed in the tank is provided. The point is that the reactant gas at a pressure lower than the predetermined pressure is to be led out to the reaction chamber.

FIG. 2 shows an epitaxial growth apparatus for carrying out the epitaxial growth method of the present invention.
10 is a reaction chamber, and 11 is a SiC coated pedestal installed in the reaction chamber 10, which has a rotation function and is heated by a high frequency coil 12. 13
14 is the first gas supply system used when growing GaAs, 15 is the second gas supply system used when growing GaAlAs, and 15 is the first gas supply system used when growing GaAs.
a third gas supply system that supplies valves 1 and 1, respectively.
6, 17, 18 and a flow meter 19 that can control the flow rate.
20 and 21 are provided. 22 is a first tank section disposed between the flow meter 19 of the first gas supply system 13 and the reaction chamber 10, and has valves on both input and output sides.
A first tank T ₁ with valves V ₁ and V ₂ and a valve V ₃ ,
a second tank T ₂ with V ₄ ;
Note that M ₁ and M ₂ are pressure gauges for the tanks T ₁ and T ₂ , respectively. The second gas supply system 14 also includes a valve V ₅ ,
The second tank section 23 is composed of a third tank T ₅ in which V ₆ is arranged, a fourth tank T ₄ in which valves V ₇ and V ₈ are arranged, and pressure gauges M ₃ and M ₄ . It is provided. Note that 24 is a pressure gauge for measuring the pressure inside the reaction chamber 10.

Then, from the third gas supply system 15 (AsH ₃ +
The reaction chamber 10 is brought into a reduced pressure state using the vacuum suction pump 25 provided in the exhaust system 25 while flowing H ₂ ). During this pressure reduction, the first and second gas supply systems 1
The valves V ₂ , V ₄ , V ₆ , and V ₈ of No. 3 and 14 are opened to bring each tank T ₁ , T ₂ , T ₃ , and T ₄ into a reduced pressure state equal to that of the reaction chamber 10 . Next, each valve V ₂ , V ₄ , V ₆ ,
V ₈ is closed, and then valves V ₁ , V ₃ , V ₅ , and V ₇ are opened to supply each tank T ₁ ,
Required to grow GaAs to T ₂ (TMG + AsH ₃
+H ₂ ) is sealed at a predetermined pressure, and in the second gas supply system 14, each tank T ₃ , T ₄ is filled with (TMG+TMA+AsH ₃ +
H ₂ ) is sealed at a predetermined pressure, and valves V ₁ , V ₃ , V ₅ , and V ₇ are closed after each gas is filled.

After energizing the high frequency coil 12 and bringing the growth substrate A such as GaAs placed on the SiC coated pedestal 11 to a predetermined room temperature, the valve V ₂ is opened.
GaAs is grown on the surface of substrate A using the (TMG + AsH ₃ + H ₂ ) gas in tank T ₁ , and then the valve V ₂ is grown on the surface of substrate A.
At the same time as closing the valve V4, open the valve _V4 and grow GaAs with the gas in the tank _T2 . At this time, valve V ₁ is opened again in tank T ₁ to fill it with gas.

At the same time as the valve V ₄ is closed, the SiC coated pedestal 11 is rotated 180° in a short period of time, so that the substrate A that was facing the first gas supply system 13 is brought to face the second gas supply system 14, and vice versa. The substrate B is made to face the first gas supply system 13. During this time tank T ₂
is filled with gas.

After rotation, open valve V ₆ for board A and (TMG + TMA + AsH ₃ + H ₂ ) in tank T ₃ .
GaAlAs is grown, and then GaAlAs is similarly grown using the gas in tank _T3 . During this time, board B
GaAs is grown on the surface using the same procedure as described above.

A pair of tanks T ₁ each containing GaAs and GaAlAs,
After being grown using the gases in T ₂ , T ₃ , and T ₄ , the SiC coated pedestal 11 is rotated 180° again to re-grow GaAs on substrate A and GaAlAs on substrate B, respectively.

Thereafter, the above-described growth process is repeated as many times as necessary to manufacture the superlattice.

According to the method of the present invention, it is possible to control extremely thin films, and of course it is also possible to control even thicker films.
The reason for this is that it is possible to control a small amount of gas. That is, the amount of gas filled into the tank can be controlled by a pressure gauge provided in each tank, and can also be controlled by changing the capacity of the tank. The flow rate of gas flowing out of the tank is also important as a growth condition, and this flow rate is controlled by the pressure difference between the reaction chamber and the tank. If it is necessary to further increase the thickness of the grown film, increase the number of times the tanks in each supply system are switched.
This can be achieved by supplying from tanks alternately.

Also, according to the above-mentioned growth process, GaAs and
The distribution of the heterojunction with GaAlAs suddenly becomes steep, but this is because the growth locations are different, and the main reason for this is probably that the growth gas is immediately switched.

Furthermore, as described above, by supplying the growth gas perpendicularly to the substrate surface, the grown film thickness and impurity distribution can be made extremely uniform.

Next, specific examples of the method of the present invention will be described.
The following example uses GaAs with a film thickness of 10 Å and
The case where a Ga0.75Al0.25As crystal layer is obtained is shown.

TMG container temperature, 0℃, 64mmHg, TMA container temperature, 20℃, 9.2mmHg, tank T ₁ , T ₂ capacity, 500 c.c., tank T ₃ , T ₄ capacity, 250 c.c. Bubbling GaAs-based TMG Amount of _H2 15c.c./min AsH ₃ 300c.c./min _H2 5/min Amount of H2 that bubbles GaAlAs TMG 15c.c./min Amount of _H2 that bubbles _TMA 40c.c./min AsH ₃ 300c.c./min H ₂ 5/min Each tank filling pressure 2 atm Reaction chamber pressure 76Torr Under the above conditions, each tank has one gas at 5Å
The growth of .

Although the above explanation has been made regarding the case of a heterojunction between GaAs and GaAlAs, the present invention is applicable to other
It goes without saying that it can also be applied to group and - group compounds. Furthermore, the present invention may be achieved by increasing the gas pressure without necessarily reducing the pressure in the reaction chamber.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of a conventional epitaxial growth apparatus, and FIG. 2 is a conceptual diagram of an epitaxial growth apparatus for implementing the method of the present invention, in which 10 is a reaction chamber, 1
1 is a SiC coated pedestal, 13, 14 and 15 are gas supply systems, 22 and 23 are tank parts, T is a tank, and V is a valve, respectively.

Claims (1)

[Claims] 1. When supplying growth gas from each of a plurality of gas supply systems to an epitaxial reaction system in which a growth target substrate is installed, a growth gas tank is placed between the desired gas supply system and the reaction system, and a growth gas tank is placed in the tank. By filling the required amount of growth gas for one epitaxial growth at a predetermined pressure from a desired gas supply system and setting the pressure in the reaction system lower than the predetermined pressure, growth can be carried out from the growth gas tank to the reaction system when necessary. An epitaxial growth method characterized by deriving a gas.