JPH03112127A - Method of forming silicon carbide - Google Patents

Abstract

PURPOSE:To obtain SiC wherein the purity is high even at a growth temperature lower by 200 deg.C or more than usual growth temperature by using organic metallic gas, which has the coupling between a group III or V atom and a halogen atom within a molecule, as carbonic material in the chemical vapor growth method for silicon carbide. CONSTITUTION:As the metallic gas which has a small amount of couplings between group III or V atoms and halogen atoms within molecules, for example, diethyl potassium chloride DEGaCl is used. When growing it, DEGaCl is used. When growing it, DEGaCl 1 is kept at 60 deg.C in a cryostat 2, and is supplied, shield being bubbled, to a reaction pipe 4 using Ar gas 3. The middle pipe 4 is set to 80 deg.C by a heater to prevent the precipitation of DEGaCl, and the flow rate of gas 3 and the flow rate of SiH4 gas 6 are controlled by a flow controller 7. An Si substrate 8 is set onto a carbonic susceptor 9, and the temperature is raised to a growth temperature by high frequency heating, and the pressure within the reaction pipe 4 is kept at 2Torr by pressure controllers 10 and 11 and a pump 12. Hereupon, the substrate 8 is put to 830 deg.C in advance so as to remote a natural oxide film in advance, and the growth is done at 800 deg.C.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for growing silicon carbide.

[Prior Art] Silicon carbide (S i C) has a large band gap and is therefore attracting attention as a material for blue light emitting elements and highly heat-resistant transistors. There are several crystal structures of SiC, among which β-5iC has a band gap of 2.3 eV.
It is expected to be used as an emitter material for silicon hetero bipolar transistors because it has a large size and has fewer mismatches with silicon than other crystal structures.

Crystal growth of SiC can be done by liquid phase growth method or vapor phase growth method (CVD).
) etc. have been carried out. Among these, CVD is advantageous in terms of mass production because it can grow a large number of substrates on large area substrates. Conventionally, CVD of SiC is
There have been many reports of growth using silane and diglorsilane as silicon raw materials, and acetylene (C, H,) and butane (C, H,) as carbon raw materials (Haka Daio, 36th Applied Physics Association Conference) Proceedings.

1a-ZL-8, page 249).

[Problem to be solved by the invention]

When fabricating a heterobipolar transistor, the emitter layer is formed last. Therefore, SiC is grown after the collector-base pn junction is formed on the silicon substrate. C.H.

In CVD using C, H, as carbon raw materials, a growth temperature of 1000° C. or higher is required because the decomposition temperature of the gas is high.

At such high temperatures, the diffusion of impurities in silicon becomes considerably large, resulting in a disadvantage that the impurity profile formed in the substrate becomes sloppy. This is a major problem especially when forming thin bases to reduce base running time.

An object of the present invention is to provide a method for forming silicon carbide that solves the above problems.

[Means to solve the problem]

In order to achieve the above object, the method for forming silicon carbide according to the present invention includes the steps of chemical vapor deposition of silicon carbide.
As the carbon raw material, an organometallic gas having at least a bond of an M group or V broad atom and a halogen atom in the molecule is used.

[Function] Hereinafter, diethylgallium chloride ((C,H,), GaCR: DEGaC is used as an organometallic gas having at least a bond between an m group or V broad atom and a halogen atom in the molecule.
Let me explain using Q) as an example.

It has been reported that DEGaCQ decomposes into GaCQ and ethyl radicals at temperatures above 380°C due to thermal decomposition (C).

5asaoka et al., Japanese Journal of Applied Physics 6
urnal of Applied Physics),
Volume 7, 1988, page L490).

The ethyl radicals generated by the decomposition react with the silicon substrate to form β-8iC. On the other hand, GaCQ desorbs from the silicon surface at a certain high substrate temperature.

Here, in order to confirm that SiC is actually formed and that the SiC growth layer is not contaminated with Ga, DEGa
The adsorption state of CQ on the Si surface was determined by X-ray photoelectron spectroscopy (XP
S), observed by reflection high energy electron diffraction (RHEED). When DEGaC4 was adsorbed onto a silicon substrate at 260°C, the Si peak energy was 99 eV, the same as that of bulk silicon, and no chemical shift was observed. Since a Ga peak was observed,
It was found that Ga was present on the substrate surface. On the other hand 520
When adsorbed at °C, the St peak was chemically shifted to 101 eV, and no Ga signal was observed. When reflection high energy electron diffraction (RHEED) observation was performed, a diffraction spot corresponding to β-5iC was obtained. From this, it has become clear that by using DEGaCR as a carbon raw material, SiC without Ga contamination can be formed at a low temperature of 520°C.

〔Example〕

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

In this example, diethyl gallium chloride DEGa (j2) is used as an organometallic gas having at least a bond between a group m or V atom and a halogen atom in its molecule.

FIG. 1 is a schematic diagram of a SiC vapor phase growth apparatus based on the present invention. In the figure, DEGaCQ (diethyl gallium chloride) ■ was kept at 60° C. in a constant temperature bath 2. D.E.
GaCQ is bubbled with argon gas 3, and then passed through the reaction tube 4.
is supplied to The temperature of the intermediate piping was raised to 80° C. by a heater 5 to prevent precipitation of DEGaC:12. The flow rate of argon gas 3 and the flow rate of SiH4 gas 6 were controlled by a flow rate controller 7. The substrate 8 is set on a carbon susceptor 9 and heated to a growth temperature by high frequency heating. The pressure inside the reaction tube 4 was maintained at 2 Torr by a pressure controller 10,11 and a pump 12. The DEGaCQ carrier gas flow rate was 400 sec, the S i H4 gas flow rate was 5,
10105e, growth was performed with total argon at 2sQm. Before starting growth, the silicon substrate was heated to 830° C. to remove the natural oxide film, and then growth was performed at a substrate temperature of 800° C.

A SiC grown film was obtained under the above growth conditions. At this time, the growth rate was 150 people/m f n. Growth film X
When line diffraction measurement was performed, a peak corresponding to β-5iC was obtained from the grown layer. Furthermore, as a result of 50MS measurement,
It was found that the grown film was a highly pure film with a Ga concentration of 1O''cm-'' or less, confirming the effect of the present invention.

In this example, diethyl gallium chloride was used as an organometallic gas having at least a bond between an m-group or V broad atom and a halogen atom in the molecule, but the present invention is not limited thereto. A similar effect can be obtained by using an organometallic gas in which the V-broad atom is either arsenic or phosphorus. Similar effects can also be obtained by using an organometallic gas in which the halogen atom in the molecule is one of fluorine, chlorine, bromine, and iodine.

The organic group in the raw material organometallic molecule is not limited to ethyl group,
It is clear that similar effects can be obtained with methyl groups, butyl groups, etc.

rEffects of the invention] The present invention allows the growth temperature to be lowered by 20°C than the conventional growth temperature.
It has become possible to grow SiC with high purity at a growth temperature lower than 0°C.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a SiC growth apparatus according to the present invention. l...diethyl gallium chloride

Claims (1)

[Claims] (1) A method for forming silicon carbide, which is characterized in that, in the chemical vapor deposition method of silicon carbide, an organometallic gas having at least a bond of a group III or V group atom and a halogen atom in its molecule is used as a carbon raw material.