JPS62153199A - Gaseous-phase etching device for iii-v compound semiconductor - Google Patents

Abstract

PURPOSE:The titled device capable of precisely controlling etching depth in a monomo lecular layer unit, wherein a halogen gas or a hydrogen halide gas is adsorbed on surface of substrate crystal in a low-temperature zone and an element of group III is vaporized as a halide of the element of group III of III-V compound semiconductor in a high-temperature zone. CONSTITUTION:In a gaseous-phase etching device for III-V compound semiconductor such as GaAs, etc., a substrate holder 2 capable of transporting a reaction tube 1 in the longer direction in the interior of a reaction chamber of the reaction tube and a resistant heating means 4 to heat the interior of the reaction tube is set at the outside. Firstly, the substrate holder 2 is transferred, substrate crystal 3 is placed at a low-temperature zone 6 at the upper stream of the reaction tube, the temperature of the crystal is raised to desired temperature (600 deg.C) and HCl is fed to the zone and sufficiently adsorbed on the surface of the substrate crystal (first process). Then, the substrate crystal is transferred to a high-temperature zone 7 (600 deg.C) at the down stream and Ga is removed as GaCl from the surface of crystal (second process). The substrate crystal 3 is retransferred to the low-temperature zone 6 at the upper stream of the reaction tube. The above-mentioned processes are repeated by using this device so that the titled extremely precisely controlled etching can be carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a highly precisely controlled vapor phase etching apparatus for ■-V group compound semiconductors.

[Prior art and its problems]

Vapor phase epitaxially grown crystals of m-v group compound semiconductors such as GaAs and InP are widely applied to optical devices such as light emitting diodes and laser diodes, and microwave devices such as FETs. By the way, when epitaxial growth is performed on a substrate crystal by optical growth, the substrate crystal is usually etched.

- This etching includes chemical etching using a solution, which is performed before setting the substrate crystal in the reaction tube, and vapor phase etching, which is performed after setting the substrate crystal in the reaction tube and immediately before growth. The purpose of the former is to remove the destructive layer that remains on the surface of the substrate crystal during mirror polishing, and the purpose of the latter is to remove the oxidized layer that is formed on the surface between the time of chemical etching and the time of setting it in the reaction tube. The purpose is to remove attached impurities such as films and dust, and to remove metamorphic layers formed during temperature rise. If this vapor phase etching is not sufficient, the oxide film, minute dust, etc. remaining on the surface become nuclei, resulting in a growth surface with many surface defects such as hillocks.

Further, a portion called a dip layer where the carrier concentration is extremely reduced may occur at the interface between the epitaxial layer and the substrate crystal. All of these are harmful to device fabrication. Therefore, this serious etching is an essential process for crystal growth.

By the way, a conventional vapor phase etching apparatus will be explained using a hydride eye growth apparatus shown in FIG. Ga
Taking the growth of As as an example, a Ga source port 10 is placed upstream of the reaction tube 1, and HCl gas is supplied together with H2 carrier gas from the upstream side.

As a result, GaCβ is generated and transported downstream.

Further, As H3, which is a hydride of As, is supplied from the pipe 5 bypassing the Ga source port 10 together with the H2 carrier gas. These two gases mix in the region of the substrate crystal 3 and growth occurs. Gas phase etching is carried out by supplying HCl gas from the bypass pipe 5,
The etching rate was controlled by adjusting the ratio to HCl gas for Ga transport. However, in this conventional apparatus, the etching rate is greatly affected by growth conditions such as substrate crystal temperature, HCl gas flow rate for Ga transport, or ΔsH3 flow, and it is difficult to control the etching depth with the precision required for device fabrication. That was impossible.

[Purpose of the invention]

An object of the present invention is to provide a vapor phase etching apparatus which eliminates the conventional drawbacks in vapor phase etching of group 1-V compound semiconductors and allows precise control of the etching depth.

[Structure of the invention]

According to the present invention, in a vapor phase etching apparatus for a group IV compound semiconductor, there is provided a reaction tube, a movable substrate holder provided inside the reaction tube and holding a substrate crystal, and a movable substrate holder provided inside the reaction tube to hold a substrate crystal; The device is equipped with a heating means for heating the inside of the reaction tube while maintaining a temperature gradient, and adsorbs halogen or hydrogen halide gas onto the substrate crystal surface in the low temperature region, and adsorbs the halogen or hydrogen halide gas on the substrate crystal surface in the high temperature region. A vapor phase etching apparatus for IV group compound semiconductors is obtained, which is characterized by volatilizing group (I) elements from the substrate crystal surface as elemental halides.

[Effect]

Two steps are carried out in the device of the invention. This is the first step in which halogen or hydrogen halide gas is first adsorbed onto the substrate crystal. For example, in the case of GaAs and HCj' gas, if the substrate crystal temperature is relatively high, etching will occur immediately upon supply of HCl gas, but as will be described in the examples below, when the temperature reaches about 400°C, etching will occur on the substrate crystal. Even if HCl gas is supplied, no etching occurs; only adsorption of HCl occurs. In this way HCl
After adsorption, the supply of HCl gas is stopped, and then this substrate crystal is moved to a high temperature region to remove Ga from the crystal surface as GaCβ. This is the second step. It is thought that the As atoms, whose bond with Ga is broken, fly out into the gas phase by themselves. Through these first and second steps, one molecular layer of the substrate crystal surface is etched. Therefore, when using the gas phase etching apparatus according to the invention, the etching depth depends only on the number of repetitions of the first and second steps, and moreover, in units of monolayers (
It can be controlled by approximately 3 people.

Next, the present invention will be specifically explained based on examples.

〔Example〕

Embodiment 1 In this embodiment, a case will be described in which the present invention is applied to vapor phase etching the entire front surface of a GaAs substrate crystal. FIG. 1 shows an outline of the vapor phase etching apparatus of this embodiment.

The reaction tube 1 has one reaction chamber, and is provided with a substrate holder 2 that moves one step in the longitudinal direction of the reaction tube. On the outside of the reaction tube 1, there is provided a resistance heating semi-immersion 4 for heating the inside of the reaction tube.

In this apparatus, a reaction tube 1 supplies HCl gas together with H2 chimal gas from upstream. In addition, ASH3, which is a hydride of AS, is released from the bypass pipe 5 inserted into the reaction tube.
is supplied together with H2 carrier gas. As the substrate crystal 3, Ga and As having (100) plane orientation were used. The temperature of the reaction tube is controlled by resistance heating means 4.
The temperature was kept at 0°C and the downstream part was kept at 600°C.

The gas flow conditions are as follows.

HCl1 5 cc/m1nASH35CC
/m1n 82 2.000 c c c/rn i In the etching procedure, first, the substrate holder 2 is moved, the substrate crystal 3 is placed in the low temperature region 6 upstream of the reaction tube, and the temperature is raised to a predetermined temperature (400° C.). did. When that temperature is reached, HC
I was supplied, and HCI was sufficiently adsorbed there for 10 seconds (
(first step), the substrate crystal 3 is placed in the downstream high temperature region 7 (600
℃), then move the substrate crystal 3 again after 10 seconds (second step).
was moved to the low temperature area 6 upstream of the reaction tube. This was defined as a -cycle, and 300 cycles were performed here. After this,
When the substrate crystal 3 was taken out and the etching depth was evaluated, it was found that the GaAs was etched to a thickness of approximately 850 mm. This indicates that a monolayer was etched in the − cycle.

Next, the temperature at the upstream part of the reaction tube was varied between 200 and 400°C, and the temperature at the downstream part of the reaction tube was varied between 600 and 750°C.
Changes in the etching depth were investigated by changing the CI flow rate, but the result remained unchanged: approximately one molecular layer was etched in each cycle. These results demonstrate that the depth of etching depends only on the number of repetitions of the first and second steps, and that the effect of the present invention is that it can be precisely controlled in units of one molecular layer (approximately 3 people). It shows itself well. Furthermore, the etched surface had no surface defects or special morphology, and had excellent specularity.

Example 2 In this example, a case will be described in which the present invention is applied to a continuous process of etching and growth using a GaAs substrate crystal. Figure 2 shows an outline of the apparatus used. The reaction tube 1 has two reaction chambers, an upper reaction chamber 8 and a lower reaction chamber 9, and inside the reaction tube 1 there is a space between these reaction chambers in the vertical direction.
and a substrate holder 2 which can be moved longitudinally within the reaction chamber 8.9. A resistance heating means 4 is provided outside the reaction tube 1 to heat the inside of the reaction tube.

In this apparatus, HCj2 gas and As hydride A s
Supply H3. A Ga source port 10 is placed upstream of the subordinate reaction chamber 9, and H2 carrier gas and H2 are supplied from the upstream of the Ga source port 10.
Supply Cl gas. In addition, from the pipe 5 bypassing the Ga source port 10, ASH, which is a hydride of As, is
3 with H2 carrier gas. As the substrate crystal 3, a GaAs (100) wafer was used. The temperature of the reaction tube 1 is controlled by resistance heating means 4, and the temperature of the reaction tube 1 is controlled by a resistance heating means 4.
The source part was kept at 800°C, the high temperature region 11 of the upper reaction chamber 8 and the growth region 12 of the lower reaction chamber 9 were kept at 600°C, and the low temperature region 13 of the upper reaction chamber 8 was kept at 400°C. The gas flow conditions are as follows.

Upper reaction chamber HCff 5 CC/m1n82
2.000 cc/m i lower reaction chamber HCI (Ga) 5 cc/m1n AS83
5 CC/m1n82 2.000
First, the etching procedure will be described.

The substrate crystal 3 was set in the substrate holder 2, and the temperature was raised to a predetermined temperature (400° C.) in the low temperature region 13 of the upper reaction chamber 8. When that temperature is reached, supply HCI and HC1 for 10 seconds.
The first step is to ensure sufficient adsorption of I). Next, the supply of HCI was stopped, and the substrate crystal 3 was moved to the high temperature region 11 (second step), and after 10 seconds, the substrate crystal 3 was again moved to the low temperature region 13 downstream of the reaction tube. This was defined as a -cycle, and 700 cycles were performed here. On the other hand, Ga in the lower reaction chamber 9
HCI was supplied to the source, and A s H3 gas and a dopant gas H2S for doping about 1×10 18 cm −3 were supplied from the bypass pipe 5 . When the process in the upper reaction chamber 8 is completed, the substrate crystal 3 is moved to the growth region 12 of the lower reaction chamber 9, and about 20% of GaAs is grown.
It grew to a thickness of 00 people. Examination of the grown crystal revealed that it had first been etched and a highly doped layer had regrown in its place. When we evaluated the etching depth at the exit point, it was found that GaAs was approximately 200
Etched to a thickness of 0A! J) It was found that

This indicates that approximately one monolayer was etched in the − cycle.

Further, the epitaxial layer had very few surface defects such as hillocks and had excellent specularity.

Furthermore, as a result of examining the carrier concentration profile in the growth direction, there was no dip layer with a reduced carrier concentration at the interface between the epitaxial layer and the substrate crystal.

〔Effect of the invention〕

As described above, by using the vapor phase etching apparatus for IV group compound semiconductors according to the present invention, it is possible to precisely control the etching depth in units of one monolayer, and the interface between the substrate crystal and the epitaxial layer can be controlled precisely. It can be made very steep.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining Embodiment 1 according to the present invention,
1 is a schematic diagram of a vapor phase etching apparatus to which the present invention is applied when performing vapor phase etching on the crystal surface of a GaAs substrate. FIG. 2 is a diagram for explaining Embodiment 2 according to the present invention,
1 is a schematic diagram of an apparatus for performing a continuous etching-growth process using a GaAS substrate crystal; FIG. FIG. 3 is a diagram for explaining a conventional vapor phase etching apparatus using the hydride method.

Claims (1)

[Claims] (1) In a vapor phase etching apparatus for III-V compound semiconductors, a reaction tube, a movable substrate holder provided inside the reaction tube and holding a substrate crystal, and provided outside the reaction tube, It is equipped with a heating means that heats the inside of the reaction tube while maintaining a temperature gradient, and adsorbs halogen or hydrogen halide gas to the substrate crystal surface in the low temperature region, and adsorbs I in the high temperature region.
A vapor phase etching apparatus for a III-V compound semiconductor, characterized in that a group III element is volatilized from a substrate crystal surface as a halide of a group III element of a group II-V compound semiconductor.