JPH05190454A - Vapor phase epitaxial growth device - Google Patents

Abstract

PURPOSE:To get a device by which epitaxial crystals uniform in thickness can easily and surely be obtained. CONSTITUTION:A device, which grows epitaxial crystals on a substrate 6 by mans of thermal decomposition of gas by installing a board susceptor loaded with a board 6 for epitaxial growth inside a reaction tube 1, and supplying gas for epitaxial growth into the reaction tube 1, is constituted by keeping the sectional area of the reaction tube 1 corresponding to the position in the vicinity of the end 6A on gas upstream side of the board 6 smaller than the sectional area of the reaction tube 1 corresponding to the position in the vicinity of the end 6B on gas downstream side of the board 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vapor phase epitaxial growth apparatus, and more particularly to a vapor phase epitaxial growth apparatus capable of obtaining an epitaxial crystal having a uniform thickness on the entire surface of a substrate.

Mercury, cadmium, tellurium (Hg), which has a narrow energy band gap, is used as a material for forming an infrared detection element.
_1-x Cd _x Te) compound semiconductor crystals are used, and MOCVD (Metal Organic Chemical Vapor Depo Depo) is used as a method for forming the crystals in a thin layer state on a large-area substrate.
sition: metalorganic vapor phase epitaxy method) has been conventionally used.

[0003]

2. Description of the Related Art A conventional vapor phase epitaxial growth apparatus used for MOCVD is shown in FIG. As shown in FIG.
A gas introduction pipe 2 for introducing a gas for epitaxial growth,
The reaction tube 1 has a cap 3 provided with a gas discharge tube 4 for exhausting unnecessary gas after epitaxial growth, and a reaction tube 1 made of a horizontal quartz horizontal tube has a carbon substrate heating table 5 inside.
Is placed, and a substrate 6 for epitaxial growth of gallium arsenide (GaAs) or the like is placed thereon.

A high frequency induction coil 7 for heating the substrate heating table 5 is installed around the reaction tube 1. Further, to the gas introduction pipe 2, a mercury evaporator 8 containing mercury, a dimethyl Cd evaporator 9 containing dimethyl cadmium, and a diisopropyl Te evaporator 11 containing diisopropyl tellurium are connected, and these evaporators 8 and 9 are connected. Introducing hydrogen gas into 11 and 11, mercury, dimethyl Cd, diisopropyl
Hydrogen gas carrying Te is introduced into the reaction tube 1.

A method for growing an epitaxial crystal on a substrate using such a vapor phase epitaxial growth apparatus will be described. First, the reaction tube 1 is evacuated to a predetermined vacuum degree.

Then, from the gas inlet tube 2, mercury, dimethyl Cd
Further, an epitaxial growth gas composed of hydrogen gas carrying diisopropyl Te is introduced into the reaction tube 1, and a high frequency induction coil 7 provided around the reaction tube 1 is energized to heat the substrate heating table 5, The upper substrate 6 for epitaxial growth is heated, and the epitaxial growth gas introduced into the reaction tube 1 is decomposed by heating on the substrate 6,
An epitaxial crystal of Hg _1-x Cd _x Te is grown on top.

[0007]

By the way, the above-mentioned substrate 6 for epitaxial growth is required to have a larger area in order to obtain a larger number of sensing elements than one substrate. look,
Gas upstream end 6A of substrate 6 and gas downstream end of substrate 6
The distance L between 6B (that is, the dimension corresponding to the diameter of the substrate 6) tends to increase.

Since the epitaxial growth gas supplied into the reaction tube 1 is thermally decomposed and consumed in the reaction tube 1 by the epitaxial growth, the epitaxial growth gas near the gas downstream side end portion (6B) of the substrate is consumed. The concentration of
The concentration of the epitaxial growth gas in the vicinity of the gas upstream end (6A) of the substrate tends to be lower than that of the epitaxial growth gas.

Therefore, the thickness of the epitaxial crystal formed on the surface of the substrate 6 tends to be thinner on the gas downstream side than on the gas upstream side, so that the entire surface of the substrate has a uniform thickness. There is a problem that an epitaxial crystal cannot be obtained.

This has a disadvantage that not only the thickness of the epitaxial crystal but also the composition of the epitaxial crystal is not uniform. On such a substrate for epitaxial growth, in order to solve the problem that the epitaxial crystal of uniform thickness is not formed, the angle of the inclined surface of the tapered substrate heating table in JP-A-64-54723, There is a method of changing the flow rate of the epitaxial growth gas passing over the substrate for epitaxial growth on the surface of the substrate by partially changing the position where the substrate is placed, but the shape of the substrate heating table is partially changed. However, the processing of the heating table is complicated. Further, this method is not preferable because the gas flow on the substrate surface is easily disturbed and stable epitaxial growth cannot be performed.

An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional apparatus and to provide a vapor phase epitaxial growth apparatus capable of obtaining a uniform epitaxial crystal on a substrate.

[0012]

The vapor phase epitaxial growth apparatus of the present invention, as set forth in claim 1, has a reaction tube,
In a device in which a substrate heating table on which a substrate for epitaxial growth is placed is installed, an epitaxial growth gas is supplied into the reaction tube, and an epitaxial crystal is grown on the substrate by thermal decomposition of the gas. The cross-sectional area of the reaction tube corresponding to the position near the side end is kept smaller than the cross-sectional area of the reaction tube corresponding to the position near the gas downstream end of the substrate.

Further, as described in claim 2, the dimension between the upper inner wall surface of the reaction tube and the surface of the substrate is gradually increased from the gas upstream end of the substrate toward the gas downstream end of the substrate. By increasing the cross-sectional area of the reaction tube to a predetermined cross-sectional area at the end of the reaction tube on the gas outflow side, the gas flow velocity in the vicinity of the gas upstream side end of the substrate is increased. It is characterized in that the flow velocity is kept higher than the gas flow velocity in the vicinity.

[0014]

The vapor phase epitaxial growth apparatus of the present invention is shown in FIG.
As shown in FIG. 3, the epitaxial growth gas flowing into the reaction tube 1 has a cross-sectional area of the reaction tube 1 corresponding to a position in the vicinity of the gas upstream side end portion 6A of the substrate 6 which starts to contact the substrate 6, Is smaller than the cross-sectional area of the reaction tube in the vicinity of the gas downstream end 6B of the substrate 6 at which the contact with the substrate 6 ends. Then, the end portion of the reaction tube 1 on the gas outflow side is kept to have a predetermined cross-sectional area.

In this way, the gas reaching the gas upstream side end portion 6A of the substrate 6 is consumed by flowing on the substrate 6 as shown by the arrow a, but the gas flow velocity near the gas upstream side end portion 6A. Therefore, thermal decomposition of the epitaxial growth gas does not easily occur in the vicinity of the gas upstream end 6A on the substrate 6. Since the gas flow velocity is extremely low near the gas downstream side end portion 6B of the substrate, the high-concentration epitaxial growth gas that has not been thermally decomposed reaches the vicinity of the gas downstream side end portion 6B of the substrate 6. Since the cross-sectional area of the reaction tube 1 is increased along the moving direction of the gas and the distance from the inner wall surface 1A at the upper part of the reaction tube 1 to the substrate 6 is increased, the gas flow velocity is decreased, Since the gas component is replenished by diffusion as shown by the arrow b, the gas whose concentration fluctuation is small is supplied to the entire surface of the substrate 6.

Therefore, most of the epitaxial growth gas is consumed near the gas upstream end 6A of the substrate 6,
The disadvantage of the conventional apparatus that the high concentration epitaxial growth gas does not reach in the vicinity of the gas downstream side end portion 6B can be solved, and the epitaxial crystal with a uniform thickness grows on the substrate.

[0017]

Embodiments of the present invention will be described in detail below with reference to the drawings. As shown in FIG. 1, in the vapor phase epitaxial growth apparatus of the present invention, the cross-sectional area of the reaction tube 1 is closer to the gas downstream end 6B of the substrate 6 than near the gas upstream end 6A of the substrate 6. The reaction tube 1 is maintained so as to gradually increase, and has a predetermined cross-sectional area in the vicinity of the end portion 1B on the gas outflow side of the reaction tube 1.

For example, a quartz reaction tube 1 having a horizontal dimension of 80 mm, a vertical dimension of 30 mm and a rectangular cross section is used, and the surface of the substrate 6 is near the gas upstream end 6A of the substrate 6. The dimension L ₁ between the inner wall of the reaction tube 1 and 5 mm,
In the vicinity of the gas downstream side end portion 6B of the substrate 6, this dimension L ₂ 15
Maintaining a size of ~ 20 mm, the end portion of the reaction tube 1 on the gas downstream side
The cross-sectional area near 1B should be kept constant.

With this arrangement, the gas upstream end of the substrate 6 where the substrate 6 and the epitaxial growth gas start contacting each other
The gas flow velocity in the vicinity of 6A becomes higher than the gas flow velocity in the vicinity of the gas downstream side end portion 6B where the substrate 6 and the epitaxial growth gas stop contacting each other, and the thermal decomposition of the epitaxial growth gas occurs at the gas upstream side end portion of the substrate 6. The high-concentration epitaxial growth gas, which is hard to occur in the vicinity of 6A and is not thermally decomposed, reaches the entire surface of the substrate 6.

In the vicinity of the gas downstream end 6B of the substrate 6, the distance from the inner wall surface 1A of the upper portion of the reaction tube 1 to the substrate 6 is increased, so that the gas flow velocity is extremely low,
The high-concentration gas components that have almost stayed and have not been consumed in the vicinity of the gas upstream side end portion 6A are replenished by diffusion, so that the gas with little concentration fluctuation is supplied to the entire surface of the substrate 6. Become. Therefore, as in the conventional apparatus, the epitaxial growth gas is consumed near the gas upstream end 6A of the substrate 6, and the gas downstream end of the substrate 6 is consumed.
The inconvenient phenomenon that the high concentration epitaxial growth gas does not reach the vicinity of 6B disappears, and the epitaxial crystal having a uniform thickness grows on the substrate 6.

Using the apparatus of the present invention, for example, hydrogen gas carrying diisopropyl Te and dimethyl Cd is introduced into the reaction tube 1 at a flow rate of 8 liter / min, and the diameter is 3 inches.
The GaAs substrate 6 is heated to a temperature of 450 ° C., and Cd is placed on the substrate 6.
When a Te epitaxial crystal was grown, the thickness distribution of the epitaxial crystal at the center of the substrate 6 and at the end of the substrate 6 was fluctuated between 15 and 20% in the conventional apparatus. With the device, the thickness variation is 5
It was experimentally confirmed that a high-quality epitaxial crystal was obtained within the range of ~ 6%.

[0022]

As described above, according to the present invention, the gas flow velocity near the gas upstream side end of the substrate is made higher than the gas flow rate near the gas downstream side end of the substrate. Since the high-concentration epitaxial growth gas that has not been consumed in the vicinity of the gas upstream side end portion of the substrate is supplied onto the substrate, there is an effect that an epitaxial crystal having a uniform thickness can be grown on the substrate.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a device of the present invention.

FIG. 2 is an explanatory diagram of the principle of the present invention.

FIG. 3 is an explanatory diagram of a conventional device.

[Explanation of symbols]

 1 Reaction tube 1A Inner wall surface 1B Terminal 2 Gas inlet tube 3 Cap 4 Gas exhaust tube 5 Substrate heating table 6 Substrate 6A Gas upstream end 6B Gas downstream end 7 High frequency induction coil

Claims (2)

[Claims] 1. A reaction vessel (1) is provided with a substrate heating table (5) on which a substrate (6) for epitaxial growth is placed, and an epitaxial growth gas is supplied into the reaction tube (1). In an apparatus for growing an epitaxial crystal on a substrate (6) by thermal decomposition of gas, a cross-sectional area of the reaction tube (1) corresponding to a position near the gas upstream end (6A) of the substrate (6). Is kept smaller than the cross-sectional area of the reaction tube (1) corresponding to the position in the vicinity of the gas downstream side end (6B) of the substrate (6). 2. The upper inner wall surface of the reaction tube (1) according to claim 1.
The dimension between (1A) and the surface of the substrate (6) gradually increases from the gas upstream end (6A) of the substrate (6) toward the gas downstream end (6B) of the substrate (6). The cross-sectional area of the reaction tube (1)
By maintaining a predetermined cross-sectional area at the end (1B) on the gas outflow side of (1), the gas flow velocity near the gas upstream end (6A) of the substrate can be adjusted near the gas downstream end (6B) of the substrate. The vapor phase epitaxial growth apparatus is characterized in that the gas flow rate is kept higher than the gas flow rate.