JPH06310440A - Silicon carbide semiconductor and film formation method thereof - Google Patents

Abstract

PURPOSE:To provide a high-resistance semiconductor made of silicon carbide(SiC) with fewer crystal defects by carrying out epitaxial growth on a crystalline silicon carbide substrate using a mixture of hydrogen, silicon hydride, carbon hydride and germanium hydride. CONSTITUTION:A substrate 2 made of silicon carbide(SiC) is put on a susceptor 4, and the susceptor 4 is mounted on a reaction tube 3. The air in the reaction tube 3 is removed into a vacuum state, and HCl gas is supplied to remove an oxide film on an SiC substrate 2. After that, nonosilane, propane and hydrogen gases, and germanium hydride as a raw-material gas for adding a germanium element are supplied from a gas inlet 6, an epitaxial growth step is carried out by heating the SiC substrate 2. A flow rate of germanium hydride is so shifted that an SiC epitaxial layer 1 contains germanium with a concentration of 0.1 to 10atom%. Consequently, an empty hole of the crystal, which functions otherwise as a donnor, is filled with a germanium atom, and thereby high- resistance SiC semiconductor can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon carbide (hereinafter referred to as SiC) semiconductor, which is attracting attention for use in a semiconductor device, and a film forming method thereof.

[0002]

2. Description of the Related Art SiC having a wide band gap of 2.2 to 3.3 eV is not only wider in band gap than Si, which is a typical semiconductor material, but also has high thermal conductivity, dielectric breakdown field and It has a saturated drift velocity of electrons. This Si
By utilizing the excellent property of C, it is expected to be applied not only to blue light emitting elements but also to high temperature operating devices and high power devices. 6 was obtained by the Acheson method or Rayleigh method as a method for forming a SiC film as a semiconductor material.
Using a silane gas as a Si source gas and a methane or propane gas as a C source gas on a crystal plane obtained by polishing an H-SiC crystal substrate by tilting 5 ° in the [1120] direction with respect to the (0001) plane According to Matsunami et al., Ext. A, that epitaxial growth is performed by the atmospheric pressure CVD method at a growth temperature of 1500 ° C.
bstr.19thConf. Solid State Devices and Materials.
The method disclosed in Tokyo (1987) p.227 is general.

[0003]

The intentionally undoped SiC epitaxial growth film formed by the above method exhibits n-type. It has been clarified that there are three kinds of impurity levels from the study of photoluminescence of the SiC epitaxial film. The source of the donor of the impurity level of n-type SiC is considered to be nitrogen based on nitrogen gas mixed from the air or present as an impurity in the source gas. However, it is not easy to obtain SiC having high resistance only by preventing the mixture of nitrogen gas, and at most a SiC film having a carrier concentration of about 2 × 10 ¹⁵ / cm ³ can be obtained.

A possible source of donors other than nitrogen is crystal defects. For example, ZnSe, which is a typical IIVI compound semiconductor, has been clarified to have an n-type because the vacancies of Se in the crystal serve as donors when not intentionally doped, thus reducing crystal defects. By doing Zn
Higher resistance of Se is attempted. Furthermore, when trying to grow GaAs, which is a typical group IIIV compound semiconductor, at low temperature by molecular beam epitaxy, there is a drawback that Ga atoms cannot sufficiently diffuse on the growth surface and crystal defects increase. However, it has been clarified that crystal defects are reduced by adding In, which has a high diffusion rate on the surface even at a low temperature. Although crystal defects have been reduced in IIVI group compound semiconductors and IIIV group compound semiconductors in this way, high resistance semiconductor epitaxial growth films have been obtained, but such methods should be used in IVIV group compound semiconductors to reduce crystal defects. No attempt has been made to

An object of the present invention is to solve the above problems and provide a high resistance SiC semiconductor with reduced crystal defects and a film forming method thereof.

[0006]

In order to achieve the above object, the SiC semiconductor of the present invention contains germanium (Ge) of 0.
It is made of SiC containing 1 to 10 atomic%. And
In such a method for forming a SiC film, a mixed gas of hydrides of SiC and Ge and hydrogen is used as a source gas, and epitaxial growth is performed on a SiC crystal substrate. In that case, the hydride of C is methane (CH ₄ ) or propane (C ₃ H ₈ ), and the hydride of Ge is GeH.
₄ or Ge ₂ H ₆ is effective.

[0007]

[Function] Ge has a bond energy with Si or C smaller than that of Si-C and diffuses more easily than Si or C on the surface during film formation. Therefore, film formation of IIVI group compound or IIIV compound film is performed. By analogy with the method, it is considered that by adding Ge, lattice defects due to Si or C vacancies are reduced, and SiC with high resistance can be obtained. When the Ge concentration exceeds 10 atomic%, lattice mismatch with the SiC substrate becomes remarkable and the film quality deteriorates. When it is less than 0.1 atomic%, the effect of Ge addition is not obtained.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention is shown in FIGS. (0
An SiC epitaxial layer 1 containing Ge was deposited on a 6H—SiC crystal substrate 2 with the (001) plane off by 5 ° in the [1120] direction, as shown in FIG. This film was grown as shown in FIG. That is, the SiC substrate 2 is placed on the susceptor whose surface is coated with SiC, which has been baked in high-purity hydrogen in advance, the susceptor 4 is placed in the center of the quartz reaction tube 3, and then the reaction tube 3 is placed. After vacuuming the exhaust port 7 sufficiently to reduce the residual nitrogen gas in the tube, add 1 slm of HCl gas.
Flow for 5 minutes at 1200 ℃ using high frequency coil 5
The oxide film on the SiC substrate 2 was removed. After that, monosilane, propane and hydrogen gas were added at 0.3 sccm and 0.2, respectively.
At a flow rate of sccm and 3 slm, germanium hydride GeH ₄ was fed as a source gas at a flow rate of 0.01 sccm from the gas introduction port 6 to further add Ge, and the SiC substrate 2 was heated to 1500 ° C. for epitaxial growth. In addition, monosilane, propane, and germanium hydride were used as raw material gases preliminarily diluted with hydrogen. As a result of analysis, Ge in the epitaxial layer 1 thus grown was 5 atom%. When the hole measurement of this epitaxial film 1 was performed, it showed an n-type, but the residual carrier concentration was 9x.
At 10 ¹⁴ / cm ³ , a high resistance epitaxial film having a resistivity of 10 kΩcm could be obtained. Next, the same growth was performed using Ge ₂ H ₆ as germanium hydride. The residual carrier concentration was 8 × 10 ¹⁴ / cm ³ and the resistivity was 12 k.
We were able to obtain an epitaxial film with high resistance of Ωcm.
In this way, when various epitaxial layers 1 were grown by changing the flow rate of germanium hydride, the characteristics of the epitaxial layer 1 did not depend on the types of GeH ₄ and Ge ₂ H ₆ ,
It became clear that it depends only on the concentration of Ge in SiC. Then, when the Ge concentration is 10 atomic% or more, the lattice mismatch with the SiC substrate 2 becomes remarkable, and the deterioration of the film quality becomes remarkable. Further, when the Ge concentration is 0.1 atomic% or less, the effect of the addition of Ge has no effect, and the high-resistance SiC epitaxial layer 1 cannot be obtained.

[0009]

According to the present invention, by adding Ge to SiC, it is possible to fill the holes in the crystal acting as the donor with Ge atoms and obtain a high resistance SiC semiconductor. Such addition of Ge can be easily performed by mixing Ge hydride with a CVD source gas.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a SiC film formed according to an embodiment of the present invention.

FIG. 2 is a sectional view of a SiCVD film forming apparatus according to an embodiment of the present invention.

[Explanation of symbols]

 1 SiC epitaxial layer 2 SiC crystal substrate 3 reaction tube 5 high frequency coil 6 gas inlet 7 exhaust port

Claims (6)

[Claims] 1. A silicon carbide semiconductor comprising silicon carbide containing 0.1 to 10 atomic% of germanium. 2. The film formation of a silicon carbide semiconductor according to claim 1, wherein silicon, carbon and germanium are epitaxially grown on a silicon carbide crystal substrate by using a mixed gas of hydride and hydrogen of each as a source gas. Method. 3. The method for forming a silicon carbide semiconductor according to claim 2, wherein the hydride of carbon is methane. 4. The hydride of carbon is propane.
A method for forming a film of a silicon carbide semiconductor as described above. 5. The method for forming a silicon carbide semiconductor film according to claim 2, 3 or 4, wherein the hydride of germanium is GeH ₄ . 6. The method for forming a silicon carbide semiconductor according to claim 2, 3 or 4, wherein the hydride of germanium is Ge ₂ H ₆ .