JPH0897142A - Semiconductor substrate and its manufacture - Google Patents

Abstract

PURPOSE: To provide a semiconductor substrate where an SiC film excellent in crystallinity and surface smoothness is made on an Si substrate. CONSTITUTION: Concerning a semiconductor substrate 10, where an SiC film 12 is made by heteroepitaxially growing an SiC single crystal on an Si substrate 11, a middle layer 13 made of SiC including one or more kinds dopant selected from a group of N, B, and Al is provided between the Si substrate 11 and the SiC film 12, and this middle layer 13 is not less than 20Å and not more than 500Å in thickness, and the concentration of the dopant is in the range not less than 1×10<20> /CM<3> and not ore than 1×10<22> /cm<3> .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to Si epitaxial growth by growing a SiC single crystal on a Si substrate.
The present invention relates to a semiconductor substrate on which a C film is formed and a manufacturing method thereof.

[0002]

2. Description of the Related Art A semiconductor made of SiC is silicon (S
i) or because it has a larger forbidden band width than semiconductors such as GaAs, it is expected to be applied to blue and green light emitting devices with short wavelengths, and also has high mechanical strength and excellent heat resistance and radiation resistance. It is expected to be applied to transistors that operate in high temperature environments and environment-resistant transistors that operate in space environments. This SiC has polymorphs such as cubic crystal (hereinafter referred to as 3C), hexagonal crystal (hereinafter referred to as 6H and 4H), and rhombohedral crystal (hereinafter referred to as 15R). Among them, 3C-SiC cannot be grown by the current technology because it is impossible to grow a single crystal, so that 3C-SiC must be produced by heteroepitaxial growth. As a substrate material for this 3C-SiC, 6H
-SiC, Si, etc. have been used, but since the 6H-SiC substrate has the drawback that it is expensive and a large-diameter one cannot be obtained, a technique for producing 3C-SiC on the Si substrate has been sought. (For example, Sadafumi Yoshida et al. “Study of SiC environment-resistant optical devices”, IEICE Vocabulary Report, p404-p419, Vol.48,
1984). In this conventional technique, a vertical vapor deposition apparatus is used, acetylene gas (C ₂ H ₂ ) is used as a C source, and silane (S
iH ₄ ) is used as a Si source to grow a SiC film on a Si substrate.

[0003]

However, since the lattice constant of Si is about 20% larger than that of 3C-SiC, the above-mentioned conventional technique allows the 3C-layer to be directly deposited on the Si substrate.
When a SiC single crystal is epitaxially grown, SiC /
A mismatch of crystal lattices at the atomic level occurs at the Si interface, resulting in mismatched dislocations and crystal defects such as stacking faults. Due to this crystal defect, the SiC film is likely to grow three-dimensionally in the initial stage of SiC growth, the flatness of the film surface is significantly deteriorated, and the crystallinity of the formed SiC film is deteriorated. . These problems have been great obstacles in manufacturing a semiconductor device from the semiconductor substrate. An object of the present invention is to provide a semiconductor substrate in which a SiC film having excellent crystallinity and surface smoothness is formed on a Si substrate, and a manufacturing method thereof.

[0004]

As shown in FIG. 1, the present invention is an improvement of a semiconductor substrate 10 having a SiC film 12 formed by heteroepitaxially growing a SiC single crystal on a Si substrate 11. Its characteristic structure is Si
S containing one or more dopants selected from the group consisting of N, B and Al between the substrate 11 and the SiC film 12.
An intermediate layer 13 made of iC is provided, and the intermediate layer 13 has a thickness of 20 angstroms or more and 500 angstroms or less, and the dopant concentration is 1 × 10 ²⁰ /
It is in the range of not less than cm ^{3 and not} more than 1 × 10 ²² / cm ³ . Here, when the thickness of the intermediate layer is less than 20 Å and the concentration of the dopant is less than 1 × 10 ²⁰ / cm ³ ,
Deterioration of crystallinity of the formed SiC film was observed, and the effect of providing the intermediate layer was poor. When the thickness of the intermediate layer exceeds 500 angstroms, the surface smoothness of the formed SiC film is poor and the buffer function as the intermediate layer is lost. Further, if the dopant concentration exceeds 1 × 10 ²² / cm ³ , for example, if the N concentration is too high, the Si ₃ N ₄ phase will be generated,
Polycrystallization occurs and the crystallinity of the SiC film is deteriorated. The preferable thickness of the intermediate layer is 50 angstroms or more and 200 angstroms or less, and the preferable concentration of the dopant is 5 × 10 ²⁰ / cm ³ or more and 1 × 10 ²¹ / cm ³ or less. The thickness of the SiC film on the intermediate layer is 1 depending on the application.
It is formed to have a thickness of at least 5 μm.

In the method of manufacturing a semiconductor substrate of the present invention, as shown in FIG. 2, a methane gas (while heating the Si substrate 11 to 850 ° C. or more and 1200 ° C. or less) using a molecular beam deposition apparatus at the initial growth of a SiC single crystal. CH ₄ ) and at the same time one or more molecular beams selected from the group consisting of N, B and Al as a dopant are supplied to the Si substrate 11 to carbonize the Si substrate 11 and form an intermediate layer on the Si substrate 11. A layer 13 is formed, and the molecular beam deposition apparatus 20 is formed on the intermediate layer 13.
Alternatively, it is characterized in that a SiC single crystal is heteroepitaxially grown using a vapor phase growth apparatus. Here, if the substrate temperature at the time of forming the intermediate layer exceeds 1200 ° C., it becomes difficult to dope each of the dopants at a high concentration. When the substrate temperature is lower than 850 ° C, the crystallinity of the SiC film deteriorates. Ammonia (NH ₃ ) can be used as the N source as the dopant, diborane (B ₂ H ₆ ) can be used as the B source, and metallic Al or the like can be used as the Al source. Further, boron nitride (BN) may be used as a common dopant material for the N source and the B source.

The SiC layer on the intermediate layer is formed by a molecular beam film forming apparatus or a vapor phase film forming apparatus. According to the molecular beam deposition apparatus, since the intermediate layer and the SiC layer can be deposited by the same apparatus, the work of loading and unloading the substrate can be omitted, which is efficient. When formed by a vapor phase film forming apparatus, there are advantages that the film forming rate is excellent and mass productivity is high. In these film forming apparatuses, Si powder, silicon wafer, SiH _4, etc. are used as the Si source, and C
CH ₄ , C ₂ H ₂ , C ₃ H ₈ or the like is used as the source.

[0007]

When the SiC film is directly formed on the Si substrate, a crystal lattice mismatch at the atomic level occurs at the SiC / Si interface due to the difference in the respective lattice constants.
Although crystal defects such as stacking faults have occurred, in the present invention, a dopant such as N, B, or Al is added between the Si substrate 11 and the SiC film 12 at 1 × 10 ²⁰ / cm ³ or more and 1 × 10 ²² / cm. ³
By providing an intermediate layer of SiC containing at the following concentrations,
The above-mentioned dopant atoms generate dislocations, and these dislocations are SiC.
It inhibits the propagation to the film and improves the crystallinity of the single crystal grown thereafter. If CH ₄ is used as the C source,
Unlike the case of using conventional C ₂ H ₂ , C ₃ H _8, etc., the dopant can be doped at a high concentration. Also the use of C ₂ H ₂ to C source, easily SiC crystals grow in three dimensions, those surface smoothness of the formed SiC film is poor, CH ₄ as C source
When used, the SiC crystal grows two-dimensionally and the surface smoothness of the SiC film is improved. The reason for this is not yet fully understood at this stage, but when C ₂ H ₂ is used as the C source,
While C ₂ H ₂ is bonded to _two Si atoms on the lattice edge of the Si substrate surface, when CH ₄ is used as the C source, CH ₄ is a CH ₃ group for each Si atom on the lattice edge of the Si substrate surface. It is presumed that it is due to coupling to the lattice edge in the form of.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings. <Example 1> By the molecular beam film forming apparatus 20 shown in FIG. 2, the intermediate layer 13 and the SiC on the Si substrate 11 as shown in FIG.
Each of the films 12 was formed. First, the diameter is 2 inches and the thickness is 5
A 00 μm Si substrate is mounted on the substrate holder 21 of the apparatus 20, CH ₄ is supplied to the molecular beam source cell 22 as the C source, NH ₃ is supplied to the molecular beam source cell 23 as the N source, and the molecular beam source cell 24 Si powder was supplied as a Si source. Vacuum container 2
5 was made into an ultrahigh vacuum, and the Si substrate 11 was heated to 980 degreeC. After that, at the same substrate temperature, the cell shutter 22a is opened to remove the cracking temperature 1100 from the molecular beam source cell 22.
The molecular beam 22b of CH ₄ is irradiated on the Si substrate 11 at a temperature of 5.0 ° C. and a molecular beam intensity of 5.0 × 10 ⁻⁵ Torr. 5.0 × 10 ^-7 Torr, N
The Si substrate 11 was irradiated with a molecular beam of H ₃ . CH ₄ and NH ₃
The irradiation time was 30 minutes. This gives a thickness of 200
Angstrom SiC intermediate layer 13 is Si substrate 11
Formed on top (FIG. 1). Then, the temperature of the Si substrate 11 is set to 950 ° C., and the cell shutter 22a is opened.
The cell shutter 23a was closed and, instead, the cell shutter 24a of the closed molecular beam source cell 24 was opened. As a result, the CH ₄ molecular beam 22b and the Si molecular beam 24b were simultaneously irradiated onto the intermediate layer 13 to obtain the semiconductor substrate 10 on which the SiC film 12 having a thickness of 1 μm was formed (FIG. 1). The irradiation time was 4 hours. The heating temperatures of the molecular beam source cells 22 and 24 were 1100 ° C. and 1600 ° C., respectively, and the molecular beam intensities were 1 × 10 ⁻⁵ Torr and 1 × 10 ⁻⁷ Torr, respectively. In FIG. 2, 26 is a quadrupole mass spectrometer, 2
Reference numeral 7 is a molecular beam monitor ion gauge, 28 is a substrate position adjusting rotary manipulator, 29 is a reflection electron beam diffractometer (hereinafter referred to as RHEED), 30 is a RHEED fluorescent screen, 31 is a gate valve, and 32 is a liquid nitrogen shroud.

<Embodiment 2> As in Embodiment 1, the molecular beam deposition apparatus 20 is used to form SiC having a thickness of 200 angstroms.
After forming the intermediate layer 13 of Si on the Si substrate 11, the device 20
The Si substrate is taken out of the vacuum container 25, and is loaded into a vertical vapor deposition apparatus (not shown), and SiH ₄ is used as the Si source.
Using C ₂ H ₂ as a C source, a SiC film was formed on the intermediate layer at 1470 ° C. for 2 hours to obtain a semiconductor substrate.

<Comparative Example 1> When the intermediate layer is formed, C
A semiconductor substrate in which an intermediate layer and a SiC film were formed on a Si substrate was obtained in the same manner as in Example 2 except that C ₂ H ₂ was used as the source.

Comparative Example 2 A semiconductor substrate having an intermediate layer and a SiC film formed on a Si substrate was prepared in the same manner as in Example 2 except that NH ₃ was not used as a dopant when forming the intermediate layer. Obtained.

<Evaluation> The surfaces of the semiconductor substrates of Example 2 and Comparative Example 1 were observed with a differential interference microscope to examine the surface smoothness of each. FIG. 3 for the second embodiment.
3 (a) and FIG. 3 (b) show Comparative Example 1, respectively. As shown in FIG. 3 (b), the SiC film of Comparative Example 1 is inferior in surface smoothness because the black spots, which are projections, are dense, whereas as shown in FIG. 3 (a). Example 2
It was found that the SiC film of No. 2 had a reduced density of black dots as protrusions and was excellent in surface smoothness. In addition, in Example 1 and Comparative Example 1, each surface was observed by RHEED when the intermediate layer was formed. Example 1 is shown in FIG. 4A, and Comparative Example 1 is shown in FIG. 4B. As is apparent from FIG. 4B, since the diffraction pattern of Comparative Example 1 appeared in a spot-like shape over a wide field, SiC intermediate crystals grew in the SiC intermediate layer and the crystal plane was not smooth. I heard that,
As is clear from FIG. 4A, the diffraction pattern of Example 1 appeared in a narrow field in a streaky manner, and thus Si
It was found that the crystal plane of the intermediate layer of C was smooth.

[0013]

As described above, when a SiC film is directly formed on a Si substrate, a crystal lattice mismatch at the atomic level occurs at the SiC / Si interface due to the difference in the respective lattice constants. According to the present invention, the Si substrate and the S
Since an SiC intermediate layer containing a dopant such as N, B, or Al at a predetermined concentration is provided between the iC films, the dopant atoms inhibit the generation of dislocations and the propagation of these dislocations into the SiC film. Can be obtained, and the crystallinity of the single crystal grown thereafter is improved. Further, unlike the case of using conventional C ₂ H ₂ , C ₃ H _8, etc., when CH ₄ is used as the C source by the method of the present invention, the dopant can be doped at a high concentration, and
The SiC crystal grows two-dimensionally, the conventional three-dimensional growth is eliminated, and the surface smoothness of the SiC film is improved. As a result, according to the method of the present invention, a high-quality SiC film having excellent crystallinity and surface smoothness can be formed on a Si substrate with good control.

[Brief description of drawings]

FIG. 1 is a partial sectional view of a semiconductor substrate according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a molecular beam deposition apparatus according to an embodiment of the present invention.

FIG. 3 (a) is a differential interference microscope photograph showing the crystal structure of the surface of the SiC substrate of the example. (B) A differential interference microscope photograph showing the crystal structure of the SiC substrate surface of the comparative example.

FIG. 4 (a) is a reflection electron diffraction photograph showing the crystal structure of the SiC intermediate layer of the example. (B) A reflection electron diffraction photograph showing the crystal structure of the SiC intermediate layer of the comparative example.

[Explanation of symbols]

 10 semiconductor substrate 11 Si substrate 12 SiC film 13 intermediate layer 20 molecular beam deposition apparatus

[Procedure amendment]

[Submission date] September 27, 1994

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 3

[Correction method] Change

[Correction content]

[Figure 3]

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Fig. 4

[Correction method] Change

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[Figure 4]

Claims (5)

[Claims] 1. A semiconductor substrate having a SiC film (12) formed by heteroepitaxially growing a SiC single crystal on a Si substrate (11), wherein the SiC film (12) is provided between the Si substrate (11) and the SiC film (12). An intermediate layer (13) made of SiC containing one or more dopants selected from the group consisting of N, B and Al is provided, and the intermediate layer (13) has a thickness of 20 angstroms or more.
A semiconductor substrate having a thickness of 0 Å or less and a concentration of the dopant of 1 × 10 ²⁰ / cm ³ or more and 1 × 10 ²² / cm ³ or less. 2. A method of manufacturing a semiconductor substrate, wherein a SiC film (12) is formed by heteroepitaxially growing a SiC single crystal on a Si substrate (11), comprising a molecular beam deposition apparatus (at the time of initial growth of the SiC single crystal). 20) is used to heat the Si substrate (11) to 850 ° C. or higher and 1200 ° C. or lower while simultaneously CH _{4 and} N and B as dopants.
And Si by supplying one or more kinds of molecular beams selected from the group consisting of Al and Al to the Si substrate (11).
The substrate (11) is carbonized to form an intermediate layer (13) on the Si substrate (11), and a SiC single crystal is formed on the intermediate layer (13) by using the molecular beam deposition apparatus (20). A method for manufacturing a semiconductor substrate, which comprises heteroepitaxial growth. 3. The method for producing a semiconductor substrate according to claim 2, wherein a single crystal of SiC is heteroepitaxially grown on the intermediate layer (13) by using CH ₄ as a C source and Si powder or SiH ₄ as a Si source. 4. A method for manufacturing a semiconductor substrate, wherein a SiC film (12) is formed by heteroepitaxially growing a SiC single crystal on a Si substrate (11), comprising: a molecular beam deposition apparatus (at the time of initial growth of the SiC single crystal; 20) is used to heat the Si substrate (11) to 850 ° C. or higher and 1200 ° C. or lower while simultaneously CH _{4 and} N and B as dopants.
And Si by supplying one or more kinds of molecular beams selected from the group consisting of Al and Al to the Si substrate (11).
Carbonizing the substrate (11) to form an intermediate layer (13) on the Si substrate (11), and heteroepitaxially growing a SiC single crystal on the intermediate layer (13) using a vapor phase growth apparatus. A method for manufacturing a characteristic semiconductor substrate. 5. The method for producing a semiconductor substrate according to claim 4, wherein a SiC single crystal is heteroepitaxially grown on the intermediate layer (13) using C ₂ H ₂ as a C source and SiH ₄ as a Si source.