JPS6034010A - Reaction tube - Google Patents

Abstract

PURPOSE:To maintain the sharpness of the switching of the composition by a method wherein a wall of a reaction tube is composed of double-wall and a large number of fine holes are drilled in an inner wall and a gas is spouted out of a space between the inner and outer walls toward the center of the reaction tube so that the material gas is prevented from flowing toward the wall of the reaction tube. CONSTITUTION:A substrate holder 3 on which a semiconductor substrate 4 is placed is contained in a reaction tube. The 2nd tube wall 2' in which a large number of fine piercing holes are drilled is provided to the inside of the 1st tube wall 2 of the reaction tube. One end of the 2nd tube wall 2' is joined with the 1st tube wall 2 and another end is kept open. H2, N2 or an inert gas is introduced into the space between the tube walls 2 and 2' to produce a protecting gas layer on the inner surface of the tube wall 2'. Under this condition, reactive gas is introduced through a reaction tube inlet 1 and forwarded toward the substrate 4 while being surroundedby the protecting gas layer. With this constitution, a sharp composition profile at a boundary of the substrate 4 and a growth layer can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thin film forming apparatus, particularly a vapor phase crystal growth apparatus, in which a steep change in composition or doping is increasingly required when forming a multilayer thin film crystal. ing. A thin film growth device with these characteristics is the molecular beam epitaxy (abbreviated as MBE).
) There is a device.

However, the MBE method requires ultra-high vacuum equipment with an IQ Torr level, is not easy to maintain, and is not necessarily suitable for mass production.

If crystals with equivalent properties can be obtained by vapor phase growth at or near normal pressure, a significant improvement in thin film productivity is expected. When growing a thin film by vapor phase growth, there are several factors that can affect the steepness of the composition change, and one of the most important is the adsorption/desorption process of the source gas on the reaction tube wall. There is. One composition (
When switching the growth layer from 5) to another composition (Bl), the gas constituting composition (5) is adsorbed on the reaction tube wall, and even after the composition is switched, the absorbed composition The gas associated with υ desorbs into the reaction tube, which changes the composition (
It mixes with the raw material gas of B) and disturbs the composition (hook).

As a result, composition switching of thin crystals using the vapor phase growth method generally results in slightly inferior results compared to the MBE method. The purpose of the present invention is to improve the above-mentioned drawbacks and provide a reaction tube that can ensure rapid composition switching. By ejecting gas from the space in the middle toward the center of the reaction tube and preventing the raw material gas from moving toward the reaction tube wall, a memory effect is achieved due to the adsorption and desorption of the raw material gas onto the reaction tube wall. is prevented.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 f2) shows an example of the repulsion tube portion of the conventional vapor phase growth method. This example shows a reaction tube portion of the organometallic pyrolysis method, in which raw material gas is introduced from the reaction tube 1 and directed toward the substrate 4 on the heated substrate holder 3. Reaction tube inlet 1
A part of the introduced gas is adsorbed on the reaction tube wall 2 before reaching the substrate 4. FIG. 1(b) is an enlarged view of the left half of FIG. 1(a), and shows the state after the composition has been switched from A to B. From the reaction tube population 1, raw material gas 0 corresponding to the composition σ3) has already flowed in, but on the tube wall 2, the raw material gas 0 corresponding to the composition (Δ) when grown
Gas (generally a plurality of gases) is adsorbed, and this slowly desorbs and mixes with the raw material gas [B] and heads toward the substrate 4.

Therefore, while desorption continues, the growth composition correspondingly becomes a third gradually changing composition that is neither composition [B] nor composition [A]. FIG. 2 shows an embodiment of the present invention, in which a second tube wall 2' having a large number of penetrating pores arranged densely inside the first tube wall 2 of the reaction tube is used as the first tube wall 2'. This is a reaction tube installed inside the tube wall.

In this example, the 20th tube wall is combined with the first reaction tube wall at the neck portion 1' of the reaction tube population 1, but adsorption/desorption at the reaction tube inlet 1 and its upstream portion becomes a further problem. Sometimes the second tube wall may extend inside these. 1st
Between the pipe wall of In this case, it is injected from the direction of C). Since the protective gas flows into the reaction tube through the pores formed in the second tube wall, a gas flow is generated in the vicinity of the reaction tube wall in a direction perpendicular to the reaction tube wall toward the center of the reaction tube. During the growth of this stale composition, the gas related to composition (5) has difficulty approaching the second reaction tube wall, causing lIr! to the tube wall. The probability of finishing first becomes significantly smaller. Therefore, as shown in Figure 2, the gas related to composition (5) does not mix into the anti-l1iS tube through the sharp part of the reaction tube wall after changing the gas to uniform growth. Crystals with compositional profiles with steep interfaces are obtained. Figure 3 Nike M. , 7Ga0.4As and Al0.1Ga
This figure shows the change in composition near the interface during two-layer growth of 0.9As, where 11 shows the results obtained using the conventional method (results obtained using the conventional method), and 12 shows the results obtained using the reaction tube of the present invention. This shows that.

1 by conventional method? This device is effective because the transition is 58 or less and the width is 1 width when the W transition I@rl is approximately 15A and f) is used. It shows. In the example shown in Figure 3, the growth method is based on organometallic pyrolysis, and the raw material is (CH3)3Al(
CH3)3Ga, AsH3, H2 as carrier gas,
H2 is also used as a protective gas. In Fig. 2, the plate holder 3 is exposed to high frequency heat (71)
It is rising to 0 '0. Therefore, 1M degree of growth is approximately 7
It's oo'U.

Although the above examples used a tub-shaped reaction tube, similar effects can be expected with a vertical anti-IJR tube, and other C
It is also applicable to the vapor phase growth method of ti b'i.

[Brief explanation of the drawing]

FIG. 1 ta+ is a diagram showing a reaction tube in conventional vapor phase growth, FIG. , Figure 3 shows AlGaA
FIG. 2 is a comparison diagram of composition profiles of a conventional method and an example of the present invention in growing S. For Figures 1 to 3, 1...Reaction tube population, 2...Reaction tube wall,
3...Substrate holder, 4...Substrate, 5...Reaction tube outlet, 1'...Neck part of reaction tube inlet, 2'...Second
is the reaction tube wall. In Figure 2g3, 11 (dimensions conventional method) shows the composition profile of AJGaAs at □, and 12 shows the profile according to the present invention. Figure 1 CG) (a) (b) Figure 2

Claims (1)

[Claims] A second tube wall having countless through holes is provided inside the first tube wall of the reaction tube in which the thin film is coated on the substrate, and between the first and second tube walls l:? A reaction tube characterized in that A is provided with a gas inlet.