JPH06283478A - Method of etching semiconductor crystal - Google Patents

Abstract

PURPOSE:To make an etching surface a mirror surface without using corrosive gas, and have excellent controllability of an etching speed, and further use a prior art MOCVD, MBE device as it is, when etching a semiconductor crystal. CONSTITUTION:An organic metal gas is used as etching gas. Dimethyl zinc (DMZn) received within a bubbler 1a is bubbled with H2 and flows at 50mumol/ min within a reaction tube 11. All carrier flux is set at 5000sccm. A GaAs substrate 12 is etched at 0.11mum for 20min, and an etching speed is 5.6nm/min with excellent controllability. An etching surface is a mirror surface with no damages. It is presumed that this is because DMZn is resolved on the GaAs substrate to obtain methylradical CH3*, which reacts to Ga or As on the uppermost crystal surface to evaporate as Ga(CH3)n or As(CH3)n. Also, the organic metal gas is not corrosive.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a gas etching method for semiconductor crystals.

[0002]

2. Description of the Related Art Etching of semiconductor crystals is a process which is used in most cases in the manufacturing process of electronic devices and optical devices regardless of whether they are electronic devices or optical devices. The etching methods are roughly classified into wet etching using a solution and dry etching using a gas or an ionized gas or a radical gas. By the way, the manufacturing process of a semiconductor device in recent years is very complicated, and processing by etching and crystal growth are sequentially introduced. In particular, in recent ultrafine semiconductor devices, dry etching has become the mainstream from the viewpoints of uniformity, ultrafine processing accuracy, and controllability, and crystal growth methods such as vapor phase growth and molecular beam epitaxy are also used from the same viewpoint. Is often used.

Considering the step of performing crystal growth again after etching, it is important that the semiconductor surface is not contaminated at all immediately before the start of crystal growth. For example, when a semiconductor crystal is once exposed to the air, various impurities and organic substances floating in the air adhere to the crystal surface, and impurities are accumulated at the regrowth interface or crystal defects are introduced.

To avoid this, a method capable of performing etching and crystal growth in the growth apparatus is used, or a method in which the etching apparatus and the growth apparatus are coupled by a loading chamber that is not exposed to the atmosphere. Can be considered.

As a method capable of performing etching and crystal growth in a conventional growth apparatus, there is Applied Physics Letters (Appl. Phys. Lett.).
1991, 59, pp. 2021-201. In the conventional etching method, a semiconductor crystal such as InP or GaAs is installed in a metal organic chemical vapor deposition apparatus (MOCVD apparatus), and the substrate is heated by local heating by high frequency heating. After that, HCI was introduced into the device,
The crystals were etching.

[0006]

In the conventional etching method, a gas such as HCI having a very high reactivity and a high corrosiveness has been used. When such a gas is used, there is a big problem that the apparatus used is corroded. In particular, molecular beam epitaxy equipment (MB
In a device that requires an ultra-high vacuum, such as the E device), there is a problem of vacuum contamination due to etching of the inner surface of the chamber by HCI gas, and the vacuum exhaust device such as a turbo molecular pump or a cryopump fails. There was a problem such as doing. In addition, in an etching method using a corrosive gas such as HCI, especially an HC such as InP is used.
A material that is easily etched with respect to I has a drawback that it is very difficult to etch it while maintaining its specularity, and damage such as crystal defects is likely to be introduced near the crystal surface. Furthermore, there is a problem with such materials that the etching rate is not controllable.

On the other hand, in the method of connecting the etching apparatus and the growth apparatus by a loading chamber that is not exposed to the atmosphere, the combined apparatus itself is very large, and the floor for installing this apparatus has a large area. There was a big problem in terms of cost such as being necessary.

The object of the present invention is that it is possible to use the MOCVD equipment or MBE equipment which has been generally used in the past without modification, and since it is not corrosive, it does not corrode the equipment itself. An object of the present invention is to provide an etching method which has excellent mirror surface properties and extremely high controllability of etching rate.

[0009]

In order to achieve the above object, the present invention is characterized in that an organic metal gas is used as a semiconductor etching gas.

[0010]

FUNCTION The organometallic gas is used in MOCVD and MBE, and it is known that it is not corrosive. Therefore,
There is no problem of damaging the device. Further, the organometallic gas itself does not have strong reactivity with the semiconductor crystal.

The etching mechanism according to the method of the present invention is not clearly known. However, dimethylzinc (DMZn; Zn (CH ₃ ) ₂ ) is used as the organometallic gas, and GaAs is used as the semiconductor crystal. It is inferred from the experiments by the present inventors that DMZn is decomposed on the GaAs substrate and The generated methyl radical CH ₃ ^* reacts with Ga or As on the outermost surface of the crystal to produce (Ga (CH ₃ ) _n or A
It is considered that it becomes s (CH ₃ ) _n and evaporates. Although the obtained etched surface is a mirror surface, it is considered that the reaction of the methyl radical is due to the reaction with the atom on the outermost surface. For the same reason, no damage layer is introduced.

Further, even in a material having a high reactivity with HCI such as InP, etching by a completely similar etching mechanism occurs and the controllability of etching is high.

By the way, the organic chemical groups constituting the organometallic gas include methyl group (CH ₃ —) and ethyl group (C ₂ H).
₅ -), tertiary butyl group _{(t-C 3 H 7 -} ), n -butyl group _{(n-C 3 H 7 -} ), there are many others.
In order for the etching to proceed smoothly, it occurs during the etching process of the semiconductor crystal.
It is better that ₃ ) _n and As (CH ₃ ) _n do not redeposit on the crystal. From this viewpoint, the organic metal having a methyl group is
Since it is generally more thermally stable than those having other chemical groups, it can be said that the redeposition of etching products is less. Of course, the metal constituting the organic metal gas may be other elements such as sulfur and selenium in addition to zinc, and thus may be an ethyl group or another chemical group depending on the use conditions.

[0014]

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view of an MOCVD apparatus used for explaining this embodiment. The growth apparatus used is adapted to heat the GaAs substrate 12 installed in the reaction tube 11 by induction heating of the high frequency coil 13. Further, the reaction tube 11, AsH ₃ and PH ₃ and H ₂ as a carrier gas, and a plurality of organometallic are supplied by bubbling H _2. In this embodiment, a case where dimethylzinc (DMZn) is used as an organic metal and a semi-insulating undoped GaAs substrate is used as a semiconductor crystal will be described. Further, in order to measure the etching depth, SiO of 20 μm width and 300 μm pitch
A GaAs substrate on which _two selective masks were formed was also prepared at the same time. The etching procedure is as follows.

After the pressure inside the reaction tube is set to 76 Torr, AsH ₃ is supplied to the reaction tube 11 and the substrate 12 is heated to 5%.
The temperature was raised to 80 ° C., and the surface of the substrate was cleaned for 10 minutes. Dimethyl zinc contained in bubbler la (D
MZn) was bubbled with H ₂ and the substrate temperature was set to 450 ° C. After stopping the supply of AsH ₃ , DMZn was supplied to the reaction tube 11. The flow rate of DMZn at this time is 50μ.
mol / min, total carrier flow rate is 5000 sc
cm. An etching experiment was performed when the etching time was 5 minutes, 10 minutes, and 20 minutes, respectively. as a result,
It was confirmed that the etching surface was a mirror surface for all the samples and the etching depth was proportional to the time. The etching rate under this condition was 5.6 nm / min.

Since DMZn was used as the organic metal, Z
There is concern about contamination of the GaAs substrate by n. To investigate this, the substrate etched for 20 minutes (etching amount;
0.11 μm), electrical and optical measurements were performed. In the electrical measurement, a metal needle was set on the etched surface to measure the current-voltage. As a result, no current flows even when 500 V is applied (current detection lower limit 1
It was found that no p-type GaAs layer was formed by nA) and Zn. Further, from the result of the photoluminescence measurement at 4.2K, the photoluminescence intensity and the spectrum were completely in agreement even when compared with the substrate without etching. From the agreement of the spectra, it was confirmed that there was no Zn contamination, and from the agreement of the intensities, no damage was introduced.

(Example 2) DMZn as an organometallic gas
And a case of using a semi-insulating Fe-doped InP substrate as a semiconductor crystal will be described. The growth apparatus used is the same as in Example 1.

After the pressure inside the reaction tube is set to 76 Torr, the substrate 12 is heated to 50 while supplying PH ₃ to the reaction tube 11.
The temperature was raised to 0 ° C., and the surface of the substrate was cleaned for 10 minutes. Dimethyl zinc contained in bubbler 1a (DM
Zn) was bubbled with H ₂ and the substrate temperature was set to 380 ° C. After stopping the supply of PH ₃ , DMZn was supplied to the reaction tube 11. The flow rate of DMZn at this time is 100 μm
ol / min, total carrier flow rate is 5000 scc
m. After etching for 20 minutes, the supply of DMZn was stopped, PH ₃ was supplied again, and then the substrate temperature was adjusted to 6
It was set to 00 ° C. Trimethylindium (TMIn) contained in the bubbler 1b was bubbled with H ₂ and supplied to the reaction tube 11. The flow rates of TMIn and PH ₃ at this time are 20 μmol / min and 6 mmol, respectively.
It was / min. InP was grown for 1 hour. The etching amount in this sample can be estimated to be 40 nm from the etching rate under this condition.

The obtained sample was a mirror surface, and had HBr and H ₃
The etch pit density with the mixed solution of PO ₄ was also the same as that of the initial substrate, and dislocation growth was not observed. Further, as a result of secondary ion mass spectrometry measurement (SIMS measurement) in the depth direction, no impurities such as Zn, C, and O were detected at the regrowth interface, and it was confirmed that the interface was good. .

In the present embodiment, dimethylzinc was used as the organic metal gas, but the present invention is not limited to this and other organic metals such as diethylzinc and dimethylsulfur may be used.

In this embodiment, GaA is used as the semiconductor crystal.
Although s and InP are used, the present invention is not limited to this, and other III-V group compound semiconductors, II-VI group compound semiconductors, Si or the like may be used.

In this embodiment, an organometallic vapor phase epitaxy apparatus was used as the growth apparatus, but the present invention is not limited to this.
Obviously, it can be applied to a molecular beam epitaxy apparatus and the like.

[0023]

The MOCVD apparatus and MBE apparatus which have been generally used in the past can be used without modification, which is very economical. Since the raw material used is not corrosive, it does not corrode the device itself, and it is not necessary to consider failure or repair of the device. Since the reactivity of the raw material used is much lower than that of HCI and the like, the etching surface is excellent in specularity and the controllability of the etching rate is also very high. Since this method is very simple, it can be widely used industrially.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an example of a growth apparatus used in the method of the present invention.

[Explanation of symbols]

 1a-1c Bubbler 11 Reaction tube 12 Substrate 13 High frequency coil

Claims (2)

[Claims] 1. A method for etching a semiconductor crystal, wherein an organometallic gas is used as a semiconductor etching gas. 2. Among the chemical groups constituting the organometallic gas,
2. The method for etching a semiconductor crystal according to claim 1, wherein the etching method includes at least a methyl group.