JP3322740B2 - 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 for manufacturing a semiconductor substrate, and more particularly to a single crystal carbon as a device forming layer.
Semiconductor substrate having silicon nitride layer and method for producing the same
I do .

[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 forbidden band width 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. 10, the 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, an n-type silicon carbide substrate 111 is prepared. On this n-type silicon carbide substrate 111, an n-type silicon carbide layer 112 is epitaxially grown. This n-type silicon carbide layer 112
A p-type silicon carbide layer 113 is epitaxially grown thereon. At this time, a silicon carbide natural oxide film is growing on p-type silicon carbide layer 113. On this silicon carbide natural oxide film, a Ti layer 114 that reacts more strongly with oxygen than silicon carbide is laminated. 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 n
An Ni electrode layer 116 is formed under the silicon carbide substrate 111. Thereafter, heat treatment is performed at 800 to 1000 ° C. As a result, the Al—Si alloy component of the Al—Si alloy electrode layer 115 diffuses uniformly in the Ti layer 114. And Al-
Si alloy electrode layer 115 is electrically connected to 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 are examined between adjacent electrode layers 115 (A) and 115 (B). As a result, the electrode layers 115 (A), 115
It is disclosed in the above-mentioned publication that the line showing the current-voltage characteristic becomes a straight line between (B) and that the electrode layer 115 can obtain perfect ohmic properties.

[0007]

However, in such a conventional silicon carbide semiconductor device, the electrode layer 1
Fifteen ohmic properties were not perfect. Specifically, electrode layer 115 of a conventional silicon carbide semiconductor device
When the current-voltage characteristics between (A) and 115 (B) 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
At the surface of Sample No. 13, hydrogen atoms other than Si and C were detected in an amount of 1.5% or more (% by weight based on silicon carbide layer 113). It is considered that 1.5% or more of the hydrogen atoms alter the surface 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
You cannot get perfect ohmic properties. The influence of the alteration of the surface of silicon carbide layer 113 cannot be excluded.

[0010] Then, causes including 1.5% or more of hydrogen atoms in the surface portion of the silicon carbide layer 113 is believed to be due to H ₂ carrier gas used in the epitaxial growth.
This is because when the temperature of the silicon carbide substrate 111 is reduced from the temperature of the epitaxial growth to room temperature after the epitaxial growth of the silicon carbide layer 113, the supply of the carbon source gas and the silicon source gas is stopped.
_{This is because two} carrier gases are continuously supplied.

Therefore, during the temperature drop process, the supply of the silicon source gas was stopped, and the supply of the H ₂ carrier gas and the carbon source gas was continued. As a result, a carbon layer was formed on silicon carbide layer 113. After removing the carbon layer, the surface of silicon carbide layer 113 was analyzed by the HFS method. As a result, no hydrogen atom was detected. That is, the detection of hydrogen atoms is 0%. Further, an electrode layer 115 was formed on the silicon carbide layer 113, and its current-voltage characteristics were examined. As a result of this characteristic, as shown in FIG. 11, the current-voltage characteristic becomes a perfect straight line (a). Therefore, the electrode layer 115 has perfect ohmic properties. Therefore, when the surface portion of silicon carbide layer 113 contains 1.5% of hydrogen atoms, ohmic properties become incomplete, and when the surface portions do not contain hydrogen atoms, ohmic properties become complete. The carbon layer can be easily removed by thermal oxidation and HF solution.

[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 the first aspect of the present invention, there is provided a single crystal silicon carbide layer serving as an operation layer of a semiconductor device.
In the semiconductor substrate having, on the single crystal silicon carbide layer
This single crystal silicon carbide layer in the epitaxial process
Graphite layer is formed to prevent deterioration of surface
It is a semiconductor substrate .

[0014] According to a second aspect of the invention, the single binding
The silicon carbide layer has a thickness of about 2.4 to 2.6 μm.
A semiconductor substrate according to claim 1 .

[0015] The invention of claim 3, the graph
The semiconductor substrate according to claim 1 or 2, wherein the thickness of the fight layer is 50 nm or more.

Further, the invention according to claim 4 provides a single crystal half-crystal.
Epitaxial formation of single-crystal silicon carbide layer on conductive substrate
Elongating epitaxial process and this single crystal silicon carbide
Having a carbon layer forming step of forming a carbon layer on the layer
A method of manufacturing a body substrate, comprising:
While maintaining the single crystal semiconductor substrate portion at a predetermined temperature ,
Supply silicon source gas and carbon source gas
In the carbon layer forming step, the silicon layer is formed at the predetermined temperature.
Stop supply of con source gas and release carbon source gas.
This is a method for manufacturing a semiconductor substrate to be supplied .

Further, the invention according to claim 5 is characterized in that
In the taxi process, the single crystal semiconductor substrate is heated to a predetermined temperature.
While keeping the silicon source gas and carbon source
Source gas, and in the carbon layer forming step,
When the temperature of the semiconductor substrate is lowered from the predetermined temperature,
Stop supply of con source gas and release carbon source gas.
A method for manufacturing a semiconductor substrate according to claim 4, wherein the supply is performed.

The invention according to claim 6 is characterized in that the carbon
After the layer forming step, the carbon layer is thermally oxidized to
Forming a thermal oxide layer to form an oxide layer;
The method according to claim 4 or 5, further comprising a removing step of removing.
It is a manufacturing method of the described semiconductor substrate .

[0019]

In the semiconductor substrate according to the present invention, the graphite layer , which is a protective layer, prevents the surface of the single crystal silicon carbide layer from being altered. This alteration means that the surface of the single crystal silicon carbide layer is oxidized and contaminated, or that the surface of the single crystal silicon carbide layer contains more than 1% of hydrogen atoms. Because of the graphite layer , handling of the semiconductor substrate can be facilitated. For example, if there is this graphite layer , the semiconductor substrate may be left in the air for two to three days. At this time, the surface of the silicon carbide layer is not oxidized and is not contaminated. Furthermore, even if the graphite layer is removed and an ohmic electrode is formed on the single-crystal silicon carbide layer, the surface portion of the silicon carbide layer does not deteriorate, so that the ohmic properties are perfect.

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

The graphite layer, which is a protective layer, is compared with a single crystal silicon carbide layer in which the surface portion is exposed as it is.
It is hard to be polluted. Further, the graphite layer is not oxidized at room temperature and is chemically stable.

If the thickness of the graphite layer is less than 50 nm, it is not possible to prevent the surface of the single crystal silicon carbide layer from being altered. For example, hydrogen atoms penetrate the graphite layer and are present at more than 1% on the surface of the single crystal silicon carbide layer. Further, before forming the semiconductor element, graphite
The graphite layer is removed by thermal oxidation, and the thickness of the graphite layer is preferably 100 nm or less.

In the method of manufacturing a semiconductor substrate according to the present invention, a single crystal silicon carbide layer is epitaxially grown on a single crystal semiconductor substrate. A carbon layer is formed on the single crystal silicon carbide layer. As a result, deterioration of the surface of the single crystal silicon carbide layer can be prevented.

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 has a crystal structure such as 4H, 6H, or 3C. In the epitaxial growth of the single crystal silicon carbide layer, homoepitaxial growth or heteroepitaxial growth is performed 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. For such epitaxial growth,
VPE (gas phase epitaxy), LPE (liquid phase epitaxy), and MBE (molecular beam epitaxy) are used. The VPE includes CVD (chemical vapor deposition) and PVD (physical vapor deposition). Also, L
PE includes a dipping method and a rotating dipping method.

For example, as a silicon source gas used in CVD, 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. As a carrier gas, H ₂ , Ar, or the like is suitable.

For example, 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, using the carbon source gas and the carrier gas, the temperature is 800
Forming a thin carbonized layer on a single crystal silicon substrate at 1400 ° C., and then adding the silicon source gas,
A single crystal silicon carbide layer having a 3C structure can be epitaxially grown on the carbonized layer. 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 whose substrate temperature is 1200 to 1500 ° C.

In the formation of the carbon layer, for example, the supply of the silicon source gas is stopped and the supply of the carbon source gas is continued while the single crystal semiconductor substrate is maintained at the temperature for epitaxial growth. Furthermore, continuous processing is possible from the epitaxial growth of the single crystal silicon carbide layer to the formation of the carbon layer. Further, since the operation of the manufacturing apparatus is not stopped, the processing time is short. Alternatively, as the formation of the carbon layer, the supply of the silicon source gas may be stopped and the supply of the carbon source gas may be continued when the temperature of the single crystal semiconductor substrate is lowered from the temperature of the epitaxial growth. In this case, since the carbon layer is formed during the cooling process, the processing time can be further reduced.

Further, the carbon layer is thermally oxidized. As a result,
The carbon in the carbon layer diffuses out of the single crystal silicon carbide as carbon dioxide or carbon monoxide, and a thermal oxidation layer is formed on the single crystal silicon carbide layer. This thermal oxide layer is a silicon dioxide layer. This thermal oxide layer is removed. As this removing method, for example, a method of immersing in an HF-based liquid or the like to chemically remove it is suitable. The thermal oxide layer may be removed by polishing or the like. 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 are perfect.

[0029]

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). A single crystal silicon carbide layer 2 having a 3C structure is formed on the single crystal silicon substrate 1, and a carbon layer 3 is formed on the single crystal silicon carbide 2 (FIGS. 2 and 3).

More specifically, the single crystal silicon carbide layer 2 and the carbon layer 3 are formed using a vapor phase growth apparatus shown in FIG. This vapor phase growth apparatus is a vertical substrate horizontal mounting type. Reference numeral 11 denotes a reaction chamber made of quartz glass. The quartz glass itself forming the reaction chamber 11 is cooled by water. Inside the reaction chamber 11, a substrate mounting table 17 made of graphite is provided. The single crystal silicon substrate 1 can be mounted horizontally on the substrate mounting table 17. Reference numeral 12 denotes a gas inflow pipe provided at an upper portion of the reaction chamber 11. The gas inflow pipe 12 is further branched into a first inflow pipe 13, a second inflow pipe 14, and a third inflow pipe 15. Reference numeral 16 denotes a gas outlet pipe provided at the bottom of the reaction chamber 11. A high-frequency coil 19 is provided outside the reaction chamber 11.
Are wound around. This high-frequency coil 19 heats the substrate mounting table 17 by induction. As a result, the single crystal silicon substrate 1 is kept at a constant temperature.

Then, under the conditions shown in FIG. 8 and the following steps (I) to (V), a reaction gas is injected from the gas inflow pipe 12 so that a desired single crystal silicon carbide is deposited on the single crystal silicon substrate 1. Layer 2 is heteroepitaxially grown.

The step (I) is a vapor phase etching,
This is a step of raising the temperature of the single crystal silicon substrate 1 from room temperature to 1000 ° C. Specifically, the temperature of the single-crystal silicon substrate 1 is maintained at 1000 ° C. for 5 to 20 minutes, and H ₂ gas is injected into the reaction chamber 11 from the third inlet pipe 15 at a rate of 2.0 l / min. As a result of this vapor phase etching, contaminants on the surface of the single crystal silicon substrate 1 are removed. At this time, HCl gas may be supplied simultaneously with H ₂ gas. Thereafter, the temperature of single crystal silicon substrate 1 is lowered from 1000 ° C. to room temperature.

In the step (II), the temperature of the single-crystal silicon substrate 1 is raised from room temperature to 1400 ° C., and the C ₃ H _{8 is} supplied from the first inlet pipe 13 into the reaction chamber 11 during the temperature rise.
9.0 ml / min of gas and H from the third inflow pipe 15
_Two gases are fed at 2.0 l / min. As a result, a thin carbide layer is formed on single crystal silicon substrate 1.

In the step (III), the single-crystal silicon substrate 1 on which the thin carbonized layer is formed is kept at 1400 ° C. for 2 hours while the C
₃ H ₈ gas was supplied at 1.5 ml / min.
1.0 ml / min of H ₄ gas and 4.0 l / min of H ₂ gas are supplied from the third inlet pipe 15. As a result, a 3C-structure single-crystal silicon carbide layer 2 having a layer thickness of about 2.4 μm is heteroepitaxially grown on the thin carbide layer (see FIG. 2).

The (IV) step is a step of growing a single crystal silicon substrate 1 after growing a single crystal silicon carbide layer 2 having a 3C structure.
Is maintained at 1400 ° C. for about 10 minutes, and C ₃ H ₈ gas is introduced into the reaction chamber 11 through the first inflow pipe 13.
5 ml / min, and continues to send 4.0 l / min _{H 2} gas from the third inlet pipe 15. The supply of the SiH ₄ gas from the second inflow pipe 14 is stopped. As a result, a carbon layer 3 having a layer thickness of about 100 nm is formed on single crystal silicon carbide layer 2 having a 3C structure (see FIG. 3).

Thereafter, in the step (V), the temperature of the single crystal silicon substrate 1 is decreased from 1400 ° C. to room temperature.

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 carbon layer 3 is thermally oxidized to form a thermally oxidized layer 4 (FIG. 4). Next, the thermal oxide layer 4 is removed by processing with an HF solution (FIG. 5). Immediately thereafter, the Ni electrode layer 5 is formed with a diameter of 0.5 mm and an interval of 5 mm by a vacuum evaporation method (FIG. 6). The current-voltage characteristics between the Ni electrode layers 5 and 5 are the same as the straight line (a) in FIG. Therefore, the ohmic property of the electrode layer 5 is perfect.

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

The second embodiment is a modification of the first embodiment (II).
The configuration is the same up to the step. (III ') shown in FIG.
In the step, the single crystal silicon substrate 1 on which the thin carbonized layer is formed is kept at 1400 ° C. for 2 hours and 10 minutes, and 1.5 ml of C ₃ H ₈ gas is supplied from the first inflow pipe 13 into the reaction chamber 11. / Min, 1.0 ml / min of the SiH ₄ gas from the second inlet pipe 14 and 4.0 l / min of the H ₂ gas from the third inlet pipe 15. As a result, a 3C-structure single crystal silicon carbide layer 2 having a layer thickness of about 2.6 μm is heteroepitaxially grown on the thin carbide layer. That is, in the step (III ′), the supply of the SiH ₄ gas is not stopped in the step (IV) of the first embodiment, as compared with the first embodiment.

The step (IV ′) is a single crystal silicon substrate 1 after a single crystal silicon carbide layer 2 having a 3C structure is grown.
Is cooled from 1400 ° C., and during this time, C ₃ H ₈ gas is introduced into the reaction chamber 11 from the first inlet pipe 13.
5 ml / min, and continues to send 4.0 l / min _{H 2} gas from the third inlet pipe 15. In this (IV ′) step, the supply of the SiH ₄ gas from the second inflow pipe 14 is stopped. As a result, single-crystal silicon carbide layer 2 having a 3C structure
A carbon layer 3 having a layer thickness of 50 to 100 nm is formed thereon at a temperature lowering rate. The subsequent method is the same as in the first embodiment.

[0041]

According to the silicon carbide substrate of the present invention, an electrode having perfect ohmic properties can be formed.

[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 one step of a method for manufacturing a semiconductor substrate according to the first example.

FIG. 7 is a longitudinal sectional view showing a vapor phase growth apparatus used in the method for manufacturing a semiconductor substrate according to the first embodiment.

FIG. 8 is a graph showing temperature versus time when forming a silicon carbide layer and a carbon layer in the method for manufacturing a semiconductor substrate according to the first embodiment.

FIG. 9 is a graph showing temperature with respect to time when forming a silicon carbide layer and a carbon layer in the method for manufacturing a semiconductor substrate according to the second embodiment.

FIG. 10 is a cross-sectional view showing a conventional semiconductor substrate.

FIG. 11 is a graph showing current-voltage characteristics between metal electrodes according to a conventional example and the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Single crystal silicon substrate 2 Single crystal silicon carbide layer 3 Carbon layer (protective layer) 4 Thermal oxidation layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-224225 (JP, A) JP-A-2-125877 (JP, A) JP-A-59-219929 (JP, A) JP-A-4- 114995 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 21/205 C01B 31/36 601 H01L 21/28 301

Claims (6)

(57) [Claims] 1. A single-crystal carbon as an operation layer of a semiconductor device
In a semiconductor substrate having a silicon layer, on the single crystal silicon carbide layer,
Of the single crystal silicon carbide layer
A semiconductor substrate on which a graphite layer is formed . 2. The single-crystal silicon carbide layer has a thickness of about 2.
The semiconductor substrate according to claim 1, wherein the thickness is 4 to 2.6 μm. 3. The semiconductor substrate according to claim 1, wherein the thickness of the graphite layer is 50 nm or more. 4. A single crystal silicon carbide is formed on a single crystal semiconductor substrate portion.
Epitaxial process for epitaxial growth of elementary layers
And a carbon layer form in which a carbon layer is formed on the single crystal silicon carbide layer
A method of manufacturing a semiconductor substrate, comprising the steps of:
While maintaining the temperature at a predetermined temperature, silicon source gas and gas
A carbon source gas, and in the carbon layer forming step, silicon
Stop supply of source gas and supply carbon source gas
Of manufacturing a semiconductor substrate. 5. The method according to claim 1, wherein in the epitaxial step, the single bonding is performed.
While maintaining the crystal semiconductor substrate at a predetermined temperature,
And supplying a source gas and a carbon source gas. In the carbon layer forming step, the single crystal semiconductor substrate portion is lifted up.
When the temperature drops from the specified temperature, supply of silicon source gas
Claim 4 wherein the supply is stopped and the carbon source gas is supplied.
The manufacturing method of the semiconductor substrate as described in the above. 6. After the step of forming a carbon layer, the carbon layer is removed.
Thermal oxide layer formation to form thermal oxide layer by thermal oxidation
And a removing step of removing the thermal oxide layer.
A method for manufacturing a semiconductor substrate according to claim 5.