JPH0355438B2 - - Google Patents

Description

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

[Prior art and its problems]

Vapor phase epitaxially grown crystals of - group compound semiconductors such as GaAs and InP are used for optical devices such as light emitting diodes and laser diodes,
It is widely applied to microwave devices such as FETs. By the way, when epitaxial growth is performed on a substrate crystal by vapor phase growth, the substrate crystal is usually etched. This etching includes chemical etching using a solution, which is carried out before the substrate crystal is set in the reaction tube, and vapor phase etching, which is carried out after setting the substrate crystal in the reaction tube and immediately before growth. The purpose of the former is mainly to remove the destructive layer that remains on the surface of the substrate crystal during mirror polishing, and the purpose of the latter is mainly to remove the oxide film formed on the surface after chemical etching until it is set in the reaction tube. The purpose is to remove attached impurities such as dirt 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 be formed at the interface between the epitaxial layer and the substrate crystal. All of these are harmful to device fabrication. Therefore, this vapor phase etching is an essential process for crystal growth.

Incidentally, recently, selective growth has been carried out in which a part of a crystal is selectively etched and an epitaxial layer having different electrical and optical properties from the surrounding crystal is grown thereon. In this case, precise control of the etching depth is often required. For example, when growing a contact layer for forming source and drain electrodes in a GaAs FET, conventional selective etching methods involve chemical etching using a solution through a mask such as SiO ₂ . It has been mainly used. However, with this method, it is difficult to precisely control the etching depth required by the device, and furthermore, after chemical etching, the substrate crystal is taken out into the air and set in the reaction tube, so it is difficult to perform epitaxy as described above. At the interface between the carrier layer and the substrate crystal, a portion called a dip layer where the carrier concentration is extremely reduced may occur. This was also a very undesirable phenomenon for the contact layer.

Conventional vapor phase etching will be explained using the hydride vapor phase growth method shown in FIG. Taking the growth of GaAs as an example, a Ga source boat 9 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, GaCl is produced and transported downstream. In addition, AsH ₃ which is a hydride of As is supplied from the pipe 2 that bypasses the Ga source boat 9 together with the H ₂ carrier gas.
These two gases mix in the region of the substrate crystal 3 and growth occurs. Gas phase etching is performed by supplying HCl gas from bypass pipe 2, and Ga
The etching rate was controlled by adjusting the ratio with HCl gas for transport. However, in this conventional method, the etching rate is greatly affected by growth conditions such as substrate crystal temperature, HCl gas flow rate for Ga transport, or AsH ₃ flow rate, and it is difficult to control the etching depth with the accuracy required for device fabrication. That was impossible.

Furthermore, the etching depth was large in the upstream part and small in the downstream part, so there was great non-uniformity.

[Purpose of the invention]

The purpose of the present invention is to eliminate such conventional drawbacks in vapor phase etching of - group compound semiconductors,
The present invention aims to provide a vapor phase etching method that allows precise control of etching depth.

[Structure of the invention]

According to the present invention, in the vapor phase etching method of a - group compound semiconductor, the first step is to adsorb a halogen or hydrogen halide gas onto the crystal surface, and the step of adsorbing a halogen or hydrogen halide gas from the crystal surface as a halide of a group element of the - group compound semiconductor. A second step of volatilizing the elements removes one molecular layer from the crystal surface of the - group compound semiconductor as a whole, and etching is performed by repeating the first and second steps. A method for vapor phase etching of - group compound semiconductors is obtained.

[Operation] The present invention is divided into two steps. First, a halogen gas such as Cl ₂ or
This is the first step to adsorb hydrogen halide gas such as HCl. For example, in the case of GaAs and HCl gas,
If the substrate crystal temperature is relatively high, etching will occur immediately due to the supply of HCl gas, but as will be described in the examples below, when the substrate crystal temperature reaches about 400°C,
Even if HCl gas is supplied onto the substrate crystal, no etching occurs and only HCl adsorption occurs. After HCl is adsorbed in this way, the supply of HCl gas is stopped, and then the substrate crystal temperature is increased by some method to remove Ga from the crystal surface as GaCl.
This is the second step. It is thought that the As atoms that have broken the Ga bond will 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 method according to the present invention, the etching depth depends only on the number of repetitions of the first and second steps, and can be controlled on a monolayer basis. . Furthermore, HCl
Adsorption occurs uniformly over the entire surface of the substrate, regardless of temperature, below a certain substrate temperature, so the etching depth is, in principle, completely uniform.

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 schematically shows the vapor phase etching apparatus used in this example. In this apparatus, HCl is supplied with _H2 carrier gas from upstream of reaction tube 1.
Supply gas. In addition, AsH _3, which is a hydride of As, is transferred to H ₂ from the bypass pipe 2 inserted into the reaction tube.
Supplied with carrier gas. As the substrate crystal 3, GaAs with (100) plane orientation was used. The temperature of the reaction tube was controlled by resistance heating and maintained at 400°C in the upstream part and 600°C in the downstream part. The gas flow conditions are as follows.

HCl 5c.c./min AsH ₃ 5c.c./min H ₂ 2000c.c./min As for the etching procedure, first, the substrate crystal 3
was placed in the low temperature region 4 upstream of the reaction tube, and the temperature was raised to a predetermined temperature (400°C). When that temperature is reached, HCl is supplied, HCl is sufficiently adsorbed there for 10 seconds (first step), and the substrate crystal 3 is moved downstream to the high temperature region 5 (600 ° C.) (second step). After 10 seconds, the substrate crystal 3 was moved again to the low temperature region 4 upstream of the reaction tube. This is regarded as one cycle, and 300 cycles were performed here. After that, 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 Å. This indicates that one molecular layer is etched in one 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.
We investigated changes in etching depth by varying the HCl flow rate, but the result remained unchanged: approximately one molecular layer was etched in one cycle. These results clearly demonstrate the effect of the present invention, in which the etching depth depends only on the number of repetitions of the first and second steps and can be precisely controlled in units of a single molecular layer (approximately 3 Å). I'm watching. Further, the uniformity of etching in each case was excellent with a measurement error of ±1% or less. Furthermore, the etched surface is
A product with excellent specularity and no surface defects or special morphology was obtained.

Although this example only performs etching, it is possible to easily perform etching by combining this with conventional growth methods.
It should be clear that a continuous process of growth can be achieved.

Embodiment 2 In this embodiment, a case will be described in which the present invention is applied to a case where a part of a GaAs substrate crystal is vapor phase etched through a window of a SiO ₂ mask and regrown at that location. FIG. 2 shows an outline of the growth apparatus used in this example. In this growth apparatus, HCl gas can be supplied to the upper reaction chamber 6 from upstream thereof together with H ₂ carrier gas. Further, the substrate crystal 3 can be irradiated with the argon laser beam 7 from upstream. Lower reaction chamber 8
A Ga source boat 9 is placed upstream of the Ga source boat 9, from which HCl gas can be supplied along with _H2 carrier gas. In addition, from the pipe 2 that bypasses the Ga source boat 9, AsH ₃ , which is a hydride of As, is transferred to H ₂
Can be supplied with carrier gas. The substrate crystal 3 is semi-insulating GaAs (100) as shown in Figure 3.
A SiO ₂ mask is formed on top, and a 10 μm wide window 1 is formed there.
A wafer with No. 1 opened was used. The temperature of the reaction tube was controlled by resistance heating, and the temperature of the Ga source was kept at 800°C and the temperature of the substrate crystal was kept at 400°C. The gas flow conditions are as follows.

Upper reaction chamber HCl 5c.c./min H ₂ 2000c.c./min Lower reaction chamber HCl 5c.c./min AsH ₃ 5c.c./min H ₂ 2000c.c./min First, perform the etching procedure. show. The substrate crystal 3 was set in a reaction tube, and the temperature was raised to a predetermined temperature (400° C.) in the upper reaction chamber 6. When that temperature was reached, HCl was supplied, and HCl was sufficiently adsorbed for 10 seconds (first step). Next, the supply of HCl was stopped, and the substrate crystal 3 was irradiated with an argon laser beam (second step). This is considered one cycle, and here 700 cycles were performed. On the other hand, the lower reaction chamber 8
HCl was supplied to the Ga source, and AsH ₃ gas and dopant gas H ₂ S for doping about 1×10 ¹⁸ cm ⁻³ were supplied from the bypass pipe 2. When the process is completed in the upper reaction chamber 6, the substrate crystal 3 is moved to the lower reaction chamber 8, and GaAs is deposited to a thickness of approximately 2000 Å.
grown to a thickness of As a result of examining the grown crystal, it was found that the GaAs portion of window 11 was first etched;
It was found that a highly doped layer had regrown at that location. By the way, when we evaluated the etching depth, we found that GaAs was etched to a thickness of about 2000 Å. This indicates that approximately one molecular layer is etched in one cycle. The uniformity of the etching depth in the etched area was within a measurement error of less than ±1%. Furthermore, the epitaxial layer regrown on the etched area had very few surface defects such as hillocks and had excellent mirror finish.

〔Effect of the invention〕

As described above, by using the vapor phase etching method of - group compound semiconductors according to the present invention, it is possible to precisely control the etching depth in units of one molecular weight and to ensure extremely high uniformity. Therefore,
The vapor phase etching method of the present invention is applicable to manufacturing various devices.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining Embodiment 1 of the present invention, and is a schematic diagram of a vapor phase etching apparatus to which the present invention is applied when performing vapor phase etching over the front surface of a GaAs substrate crystal. FIG. 2 is a diagram for explaining Example 2 according to the present invention, and is a schematic diagram of a growth apparatus in which a part of a GaAs substrate crystal is vapor-phase etched through a window of an SiO ₂ mask and regrown at that location. FIG. 3 is a diagram showing the SiO ₂ pattern on the substrate crystal used in Example 2. FIG. 4 is a diagram for explaining a conventional vapor phase etching method. 1...Reaction tube, 2...Bypass pipe, 3...
Substrate crystal, 4...Low temperature region, 5...High temperature region, 6
...Upper reaction chamber, 7...Laser light, 8...Lower reaction chamber, 9...Ga source boat, 10...Mask,
11...window.

Claims (1)

[Claims] 1 In a vapor phase etching method for a group-1 compound semiconductor, the first step is to adsorb halogen or hydrogen halide gas onto the crystal surface, and the second step is to volatilize the group element from the crystal surface as a halide of the group element of the group-1 compound semiconductor. A - group compound semiconductor characterized in that by the second step, one molecular layer is removed from the crystal surface of the - group compound semiconductor as a whole, and etching is performed by repeating the first step and the second step. vapor phase etching method.