JP3210161B2 - Semiconductor substrate and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor substrate and a method of manufacturing a semiconductor substrate, and more particularly to a method of using a silicon carbide layer as an operation layer of a semiconductor device.

[0002]

2. Description of the Related Art SiC (silicon carbide) is a semiconductor.
There are more than 120 types of crystalline silicon carbide. For example, the crystal structure of silicon carbide is 4H, 6H, 3C
There are things. Note that H indicates a hexagonal system and C indicates a cubic system. Silicon carbide has a band gap of 2.2 to 3.3 eV. That is, silicon carbide has a wider energy gap than silicon. Also, compared to silicon, silicon carbide is extremely stable thermally, chemically, and mechanically. For this reason, a semiconductor element using silicon carbide as an operation layer can withstand use in an environment at a temperature higher than the upper limit temperature when using a silicon element, and can withstand large power control.

The bandgap of β-type silicon carbide (silicon carbide having a 3C structure) is 2.2 eV, which is about twice the bandgap of silicon. The electron mobility of silicon carbide having a 3C structure reaches 900 cm ² / V · S. For these reasons, silicon carbide having a 3C structure has attracted attention as an operating layer of a high-speed semiconductor device. Further, α-type silicon carbide, for example, silicon carbide having a 6H structure has a band gap of 3.3 eV, which is larger than that of silicon carbide having a 3C structure. As a result, silicon carbide having a 6H structure is expected as an operating layer of a photoelectric conversion semiconductor device between visible light and near ultraviolet light. Further, both p-type silicon carbide and n-type silicon carbide are materials that exist more stably than p-type silicon and n-type silicon. This is unusual as a semiconductor having a wide energy gap.

Conventionally, a semiconductor device using silicon carbide as an active layer has been formed on an epitaxial substrate. This epitaxial substrate is obtained by epitaxially growing a silicon carbide layer on a predetermined substrate portion. As this semiconductor device, a “silicon carbide semiconductor device” disclosed in Japanese Patent Application Laid-Open No. 1-268121 is known. As shown in FIG. 11, this silicon carbide semiconductor device has an n-type silicon carbide substrate 111, an n-type silicon carbide layer 112, a p-type silicon carbide layer 113, a Ti layer 114, and an Al—Si alloy electrode layer 115. And a Ni electrode layer 116.

[0005] The method of manufacturing the silicon carbide semiconductor device is as follows.
First, n-type silicon carbide layer 112 is epitaxially grown on n-type silicon carbide substrate 111. Next, p-type silicon carbide layer 113 is epitaxially grown on n-type silicon carbide layer 112. At this time, the p-type silicon carbide layer 11
3, a silicon carbide natural oxide film is grown. Next, a Ti layer 114 that reacts with oxygen more strongly than silicon carbide is laminated on the silicon carbide natural oxide film. As a result, Ti layer 114 reacts with oxygen in the silicon carbide natural oxide film growing on p-type silicon carbide layer 113 to reduce the silicon carbide natural oxide film. Further, an Al—Si alloy electrode layer 115 is formed on the Ti layer 114 by patterning. Note that a Ni electrode layer 116 is formed below the n-type silicon carbide substrate 111. And after this, 80
Heat treatment at 0-1000 ° C. As a result, the Al—Si alloy component of the Al—Si alloy electrode layer 115
Spreads evenly throughout. Then, the Al-Si alloy electrode layer 1
15 is electrically connected to the p-type silicon carbide layer 113 without being hindered by the silicon carbide natural oxide film.

In this silicon carbide semiconductor device, current-voltage characteristics between adjacent electrode layers 115 are examined.
As a result, the line indicating the current-voltage characteristic becomes linear between the electrode layers 115 and 115, and the above-mentioned publication discloses that the electrode layer 115 has perfect ohmic properties.

[0007]

However, in such a conventional silicon carbide semiconductor device, the electrode layer 1
Fifteen ohmic properties were not perfect. Specifically, when the current-voltage characteristics between the electrode layers 115 of the conventional silicon carbide semiconductor device were strictly measured, the line showing the current-voltage characteristics was the curve (b) shown in FIG. This curve (b) approximates a straight line to some extent but is not a straight line. That is, I and V are not in a proportional relationship. Therefore, even if an ohmic electrode is formed on a conventional semiconductor substrate, the ohmic property is incomplete.

[0008]

Therefore, the inventor of the present application has proposed that the silicon carbide layer 113 of the conventional silicon carbide semiconductor device before the Ti layer 114 is laminated is HFS (HYDROG).
EN FORWARD SCATTERING: hydrogen forward scattering analysis). As a result, silicon carbide layer 1
Above 13, 1.5% (% by weight based on silicon carbide layer 113) hydrogen atoms were detected in addition to Si and C. This 1.5% or more of hydrogen atoms is considered to cause deterioration of the upper portion of silicon carbide layer 113 and cause ohmic failure of electrode layer 115.

Therefore, as in the prior art, the Ti layer 114
Depending on only the removal of silicon carbide natural oxide film using
Complete ohmic properties cannot be obtained, and the influence of alteration on the upper portion of the silicon carbide layer 113 cannot be excluded.

It is considered that the reason why 1.5% or more of hydrogen atoms are contained in the upper portion of silicon carbide layer 113 is due to the H ₂ carrier gas used for epitaxial growth. This silicon carbide layer 113 after the epitaxial growth, when lowering the silicon carbide substrate 111 from the temperature of the epitaxial growth to room temperature, but to stop the supply of gas and the silicon source gas of the carbon source, supplies of H ₂ carrier gas Because it will continue.

Therefore, the inventor of the present application removed the altered portion of the p-type silicon carbide layer 113 and exposed the inside of the silicon carbide layer 113 (the portion below the altered portion). The exposed portion of the silicon carbide layer 113 was analyzed by the HFS method. As a result, 1% or less of hydrogen atoms were detected. Further, a predetermined electrode was formed on the exposed portion of the silicon carbide layer 113, and its current-voltage characteristics were examined. As a result, as shown in FIG. 12, the current-voltage characteristics became a complete straight line (a). Therefore, the electrode layer 115 has perfect ohmic properties.
As a result, one hydrogen atom is added to the surface of silicon carbide layer 113.
If it is contained in excess of%, ohmic properties will be incomplete,
It has been found that when the content of hydrogen atoms is 1% or less, the ohmic property becomes perfect.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of such knowledge, and an object of the present invention is to provide a semiconductor substrate capable of forming an electrode having complete ohmic properties and a method of manufacturing the semiconductor substrate. It is.

[0013]

According to a first aspect of the present invention, there is provided a semiconductor substrate having a silicon carbide layer, wherein the single crystal silicon carbide layer contains hydrogen atoms, and the single crystal silicon carbide contains 99% by weight or more. And a semiconductor substrate whose hydrogen atoms are 1% by weight or less.

According to a second aspect of the present invention, after a single crystal silicon carbide layer is epitaxially grown on a single crystal semiconductor substrate, hydrogen gas is used as a carrier gas.
This is a method for manufacturing a semiconductor substrate, comprising: an altered layer forming step of forming an altered layer containing more than 1% by weight of hydrogen atoms on the single crystal silicon carbide layer; and a removing step of removing the altered layer.

According to a third aspect of the present invention, in the removing step, a thermally oxidized layer is formed by thermally oxidizing the altered layer, and the thermally oxidized layer is removed with a solution. It is a manufacturing method.

Further, the invention according to claim 4 is a method of manufacturing a semiconductor substrate in which, in the removing step, the affected layer is removed by polishing.

According to a fifth aspect of the present invention, in the removing step, a thermally oxidized layer is formed by thermally oxidizing a polished strained layer generated by polishing the altered layer. This is a method for manufacturing a semiconductor substrate in which an oxide layer is removed with a solution.

[0018]

In the semiconductor substrate according to the first aspect of the present invention, the surface portion of the single crystal silicon carbide layer contains 99% or more of single crystal silicon carbide and 1% or less of hydrogen atoms. . For this reason, even if an ohmic electrode is formed on the single crystal silicon carbide layer, the ohmic properties will be perfect.

As the ohmic electrode, Al, Al
-Si, Au, Cr, Mo, Ni, Ta, TaSi 2,
_{Ti, W, Au-Ta,} WSi 2, TiSi 2 , etc. are suitable. The ohmic electrode is formed by a vacuum evaporation method, sputtering, or the like.

In the method of manufacturing a semiconductor substrate according to the present invention, a single-crystal silicon carbide layer is epitaxially grown on the single-crystal semiconductor substrate. At this time, a hydrogen gas is used as a carrier gas. As a result, the upper part of the single-crystal silicon carbide layer is altered and becomes an altered layer. This alteration means that when an ohmic electrode is formed on the single crystal silicon carbide layer, the ohmic property becomes incomplete. Further, the altered layer is removed. As a result, the surface portion of the single crystal silicon carbide layer is formed normally. That is, even if an ohmic electrode is formed on this single-crystal silicon carbide layer, the ohmic properties will be perfect.

As the single crystal semiconductor substrate portion, a material such as single crystal silicon or single crystal silicon carbide is suitable. The single-crystal silicon carbide layer is 4H, 6H, or 3H.
It has a crystal structure such as C. The epitaxial growth is
Depending on the type of material of the single crystal semiconductor substrate portion, its crystal structure and the crystal structure of the single crystal silicon carbide layer, homoepitaxial growth or heteroepitaxial growth is performed. For such epitaxial growth, VPE (vapor phase epitaxial method), LPE (liquid phase epitaxial method), and MBE (molecular beam epitaxial method) are used. The VPE includes CVD (chemical vapor deposition) and PVD (physical vapor deposition). Also, LP
E includes a dipping method and a rotating dipping method.

For example, silicon source gases used in CVD include SiH ₄ , SiCl ₄ , SiHCl ₃ ,
SiHCl ₂ , (CH ₃ ) ₃ SiCl, (CH ₃ ) ₂ S
iCl _{2 and the} like are suitable. Further, as the gas of the carbon source, CCl ₄ , hydrocarbon or the like is suitable. This hydrocarbon includes CH ₄ , C ₂ H ₂ , C ₂ H ₄ , C
₂ H ₆ , C ₃ H _{8 and the} like are suitable. H ₂ is suitable as a carrier gas.

For example, a CV using a silicon source gas, a carbon source gas, and a carrier gas as described above.
In D, it is possible to epitaxially grow a single crystal silicon carbide layer having a 3C structure on a single crystal silicon substrate at a temperature of 800 to 1400 ° C. Also, if the temperature is 8
It is possible to epitaxially grow a single crystal silicon carbide layer having a 3C structure on a single crystal silicon carbide substrate having a 6H structure at 00 to 1400 ° C. Further, by using the carbon source gas and the carrier gas, the substrate temperature is set to 8
A thin carbonized layer is formed on a single crystal silicon substrate at a temperature of 00 to 1400 ° C., and thereafter, a gas of the above silicon source is added to epitaxially grow a single crystal silicon carbide layer having a 3C structure on the carbonized layer. It is. Further, it is possible to epitaxially grow a single crystal silicon carbide layer having a 6H structure on a single crystal silicon carbide substrate having a 6H structure at a temperature of 1200 to 1500 ° C.

In the method of manufacturing a semiconductor substrate according to the third aspect of the present invention, the altered layer of the silicon carbide layer is thermally oxidized. As a result, the altered layer becomes a thermal oxidation layer. This thermal oxide layer comprises a silicon dioxide layer. This thermal oxide layer is removed with a solution. For example, it is immersed in an HF-based liquid and chemically removed. As a result, the surface portion of the single crystal silicon carbide layer is formed normally.

In the method for manufacturing a semiconductor substrate according to the present invention, the altered layer of the single-crystal silicon carbide layer is polished and removed. As a result, the surface portion of the single crystal silicon carbide layer is formed normally. For example, mechanical polishing using diamond slurry is suitable as the polishing.

In the method of manufacturing a semiconductor substrate according to the present invention, the altered layer of the single crystal silicon carbide layer is polished. As a result, a part of the altered layer is removed, and the remaining altered layer becomes a polished strained layer containing strain during polishing. This polishing strain layer is thermally oxidized. As a result, the polishing strain layer becomes a thermal oxide layer. This thermal oxide layer is removed with a solution. As a result,
The surface portion of the single crystal silicon carbide layer is formed normally. Further, even when the altered layer of the single crystal silicon carbide layer is thick, it can be removed in a short time by polishing.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings.

First, a single crystal silicon substrate 1 is prepared (FIG. 1). This single crystal silicon substrate 1 is
Heat to 0 ° C. and supply C ₃ H ₈ gas, SiH ₄ gas, and H ₂ gas. As a result, 3
A single-crystal silicon carbide layer 2 having a C structure is heteroepitaxially grown. At this time, the single-crystal silicon carbide layer 2 has an n-type,
The carrier concentration is 10 ¹⁷ / cm ³ and the film thickness is 2 to 20 μm. At this time, the altered layer 3 having a thickness of 50 to 80 nm is formed on the single crystal silicon carbide layer 2 (FIG. 2).

Thereafter, in an atmosphere of O ₂ and H ₂ O,
Heat treatment is performed at a temperature of 1000 to 1200 ° C. for 2 to 100 hours. As a result, the altered layer 3 is thermally oxidized to become a thermally oxidized layer 4 (FIG. 3). Next, the thermal oxide layer 4 is removed by etching with an HF solution (FIG. 4). Immediately thereafter, the Ti layer 5 and the Ni electrode layer 6 are formed with a diameter of 0.5 mm and an interval of 5 mm by a vacuum deposition method (FIG. 5).

The Ti layer 5 is formed after the HF treatment.
Is used to reduce the silicon oxide natural oxide film grown on the single-crystal silicon carbide layer 2 before the formation of the silicon carbide layer. The Ti layer 5 is not limited to Ti and may be any metal that reacts more strongly with oxygen than silicon carbide. For example,
Cd, Cr, Ni, Mg and the like are suitable. When the current-voltage characteristics between the electrode layers 6 and 6 are examined, FIG.
Is the same straight line as the straight line (a). Therefore, the electrode layer 6
Is perfectly ohmic.

Next, a second embodiment of the present invention will be described.

First, a single crystal silicon carbide layer 7 having a 3C structure is heteroepitaxially grown on a single crystal silicon substrate 1 in the same manner as in the first embodiment. As a result, a thickness of 100 nm
(See FIG. 6).

The altered layer 8 having a thickness of 100 nm is polished with a polishing solution containing a diamond slurry to remove a thickness of about 50 to 80 nm. The remaining altered layer 8 contains a strain during polishing and becomes a polished strained layer 9 (FIG. 7). Thereafter, heat treatment is performed in an atmosphere of O ₂ and H ₂ O at a temperature of 1000 to 1200 ° C. for 0.5 to 40 hours. As a result, the polishing strain layer 9 having a thickness of 20 to 50 nm is thermally oxidized and the thermally oxidized layer 1 is formed.
It becomes 0 (FIG. 8). Next, as in the first embodiment, the thermal oxide layer 10 is removed by etching with an HF solution (FIG. 9). Immediately after this, T
An i layer 5 and a Ni electrode layer 6 are formed (FIG. 10). When the current-voltage characteristics between the electrode layers 6 and 6 are examined, FIG.
The straight line is the same as the straight line (a) of No. 2 and the ohmic property of the electrode layer 6 is perfect.

In the second embodiment, the deteriorated layer 8 is thicker than the first embodiment, as compared with the first embodiment. When the thickness is large, using the method of the first embodiment requires a long time for thermal oxidation. As a result, the time for forming the surface portion of single-crystal silicon carbide layer 5 normally becomes longer. However, in the case of the second embodiment, the polishing strain layer 9 thinner than the altered layer 8 is thermally oxidized. For this reason, the thermal oxidation time is short. As a result, the time for forming the surface portion of single crystal silicon carbide layer 5 normally is also shortened.

[0035]

According to the present invention, a silicon carbide substrate on which an electrode having perfect ohmic properties can be formed can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing one step of a method for manufacturing a semiconductor substrate according to a first embodiment.

FIG. 2 is a cross-sectional view showing one step of a method for manufacturing a semiconductor substrate according to the first example.

FIG. 3 is a sectional view showing one step of a method for manufacturing a semiconductor substrate according to the first example.

FIG. 4 is a sectional view showing one step of a method for manufacturing a semiconductor substrate according to the first example.

FIG. 5 is a sectional view showing one step of a method for manufacturing a semiconductor substrate according to the first example.

FIG. 6 is a cross-sectional view showing a step of the method for manufacturing a semiconductor substrate according to the second embodiment.

FIG. 7 is a cross-sectional view showing one step of a method for manufacturing a semiconductor substrate according to the second embodiment.

FIG. 8 is a cross-sectional view showing one step of a method for manufacturing a semiconductor substrate according to the second embodiment.

FIG. 9 is a cross-sectional view showing one step of a method for manufacturing a semiconductor substrate according to the second embodiment.

FIG. 10 is a cross-sectional view showing a step of the method for manufacturing a semiconductor substrate according to the second embodiment.

FIG. 11 is a sectional view showing a conventional semiconductor substrate.

FIG. 12 is a graph showing current-voltage characteristics between metal electrodes of the conventional example and the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Single crystal silicon substrate 2 Single crystal silicon carbide layer 3 Altered layer 4 Thermal oxidation layer

──────────────────────────────────────────────────続 き Continued from the front page (72) Eiji Kamiyama, Inventor Central Research Laboratory, 1-297 Kitabukuro-cho, Omiya City, Saitama Prefecture (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21 / 28-21/288 H01L 21/44-21/445 H01L 29/40-29/43 H01L 29/47 H01L 29/872 H01L 21/20

Claims (5)

(57) [Claims] In a semiconductor substrate having a single-crystal silicon carbide layer, the single-crystal silicon carbide layer contains hydrogen atoms, the single-crystal silicon carbide is 99% by weight or more, and the hydrogen atoms are 1% by weight. A semiconductor substrate characterized by the following. 2. The method according to claim 1, wherein a single-crystal carbon carbide is formed on the single-crystal semiconductor substrate.
After epitaxially growing the iodine layer, carrier gas and
And the top of this single crystal silicon carbide layer using hydrogen gas
A method for manufacturing a semiconductor substrate, comprising: a step of forming a deteriorated layer containing hydrogen atoms exceeding 1% by weight ; and a step of removing the deteriorated layer. 3. The method according to claim 2, wherein in the removing step, a thermally oxidized layer is formed by thermally oxidizing the altered layer, and the thermally oxidized layer is removed with a solution. 4. The method according to claim 2, wherein, in the removing step, the altered layer is removed by polishing. 5. In the removing step, a polished strained layer is formed by polishing the altered layer, a thermally oxidized layer is formed by thermally oxidizing the polished strained layer, and the thermally oxidized layer is The method for manufacturing a semiconductor substrate according to claim 2, wherein the semiconductor substrate is removed by a solution.