JP2009274899A - Method for manufacturing substrate for epitaxy of silicon carbide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a silicon carbide substrate, which is suitable as a substrate for epitaxial growth, under such a condition in a reactive chamber that the supply of carbon is suppressed. <P>SOLUTION: The method for manufacturing a substrate 4 for the epitaxy of silicon carbide comprises raising the temperature of a silicon carbide substrate 4 to an epitaxial growth temperature in argon atmosphere to subject the surface of the substrate 4 to an argon treatment, under such a condition in a reaction chamber that the supply of carbon is suppressed, and stopping heating for raising the temperature and the supply of argon gas at the stage when the temperature of the substrate reaches the epitaxial growth temperature. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a substrate for silicon carbide epitaxial, and more specifically, heat treatment is performed on the surface of a silicon carbide substrate using a gas having a specific composition under conditions in a reaction chamber in which carbon supply is suppressed, thereby suppressing Si droplets. The present invention relates to a method for manufacturing a silicon carbide epitaxial substrate having a smooth surface.

In recent years, silicon carbide single crystal semiconductor elements that can be expected to significantly improve performance due to high electrical conversion efficiency and high thermal conductivity compared to conventional silicon semiconductor elements have been developed toward the realization of low loss and downsizing in the electronics field. Promising as a power semiconductor device material. The silicon carbide single crystal semiconductor element is obtained by forming an epitaxial thin film on a semiconductor substrate using a film forming apparatus such as a CVD (Chemical Vapor Deposition) apparatus.
According to this film forming apparatus, a Si raw material gas and a C raw material gas, which are raw material gases, are supplied together with a carrier gas to a reaction chamber equipped with a susceptor and a heat insulating material, and a silicon carbide single crystal thin film is epitaxially grown on a silicon carbide substrate. be able to.

However, when epitaxial growth is performed under the conditions in a reaction chamber equipped with a graphite susceptor, graphite insulation, etc. in a general film-forming device, there are generations of hydrocarbons and impurities originating from this film-forming device. Therefore, it is difficult to precisely control the epitaxial growth conditions of the silicon carbide single crystal.
For this reason, a technique for epitaxially growing a silicon carbide single crystal on a silicon carbide substrate under reaction chamber conditions in which the supply of carbon is suppressed, such as using silicon carbide as a susceptor or using silicon carbide coated graphite whose susceptor surface is coated with silicon carbide. Is being considered.

On the other hand, since a silicon carbide substrate slicing technique and polishing technique are still not sufficient as compared with a silicon substrate (silicon wafer) technique, a damage layer or scratches called scratches are generated on the entire surface of the silicon carbide substrate. Much of the final device performance depends on the quality of the epitaxial thin film grown on the silicon carbide substrate, and the epitaxial thin film is affected by the underlying layer. It is necessary to obtain a flat and clean surface by removing the damaged layer on the surface of the silicon carbide substrate.
For this reason, the etching process by the hydrogen atmosphere of a silicon carbide substrate was proposed as a pretreatment of the epitaxial growth to a silicon carbide substrate (patent documents 1-4).

Japanese Patent Laid-Open No. 2001-0707030 JP 2002-255692 A JP 2005-277229 A JP 2005-311348 A

  In Patent Document 1 described above, a silicon carbide substrate is placed in a reaction furnace, the silicon carbide substrate is heated to introduce hydrogen gas or a mixed gas of hydrogen and argon, and the atmospheric pressure is reduced to less than 760 Torr (1 atm). A method for manufacturing a silicon carbide semiconductor device including a step of etching the surface of a silicon carbide substrate is described.

  In the above Patent Document 2, a silicon carbide single crystal wafer is pretreated in a hydrogen gas or hydrogen chloride gas circulation atmosphere at a temperature of 1550 ° C. or higher, and then a silicon carbide epitaxial film is epitaxially grown on the wafer. A method for manufacturing a substrate is described. As a specific example, an example is shown in which a silicon carbide epitaxial substrate is obtained by epitaxial growth after pretreatment at a temperature and atmosphere using a graphite susceptor with only hydrogen gas or a mixed gas of hydrogen gas and hydrogen chloride gas. ing.

  Patent Document 3 described above describes a method for manufacturing a silicon carbide smoothed substrate in which a source gas is added during hydrogen etching in smoothing a silicon carbide substrate. And silane is described as source gas and there is no description about the kind of susceptor.

  Patent Document 4 described above describes a method for manufacturing a bipolar semiconductor device in which the surface of a silicon carbide substrate is processed by hydrogen etching, and then silicon carbide is epitaxially grown from the processed surface to form an epitaxial layer. There is no description of the type of susceptor.

As described above, the silicon carbide epitaxial substrate manufacturing methods described in the publicly known literature are reactions that are unknown in the reaction chamber under the premise of carbon supply such as using a graphite susceptor or the carbon supply is unknown. There is no known method for manufacturing a silicon carbide epitaxial substrate having a smooth surface by heat treatment under reaction chamber conditions with suppressed carbon supply, due to pretreatment of epitaxial growth by hydrogen etching under room conditions .
Accordingly, an object of the present invention is to provide a method for manufacturing a silicon carbide epitaxial substrate suitable as a substrate for epitaxial growth under reaction chamber conditions in which the supply of carbon is suppressed.

As a result of intensive studies aimed at achieving the above object, the present inventors have found that when the silicon carbide substrate is heated at a high temperature by supplying hydrogen gas under the reaction chamber conditions in which the supply of carbon is suppressed, the substrate surface becomes Si. As a result of further investigation, the present invention was completed.
According to the present invention, the temperature of the silicon carbide substrate is increased to the epitaxial growth temperature under an argon atmosphere under the conditions in the reaction chamber in which the supply of carbon is suppressed, and the substrate surface is treated with argon. The present invention relates to a method for manufacturing a silicon carbide epitaxial substrate in which heating and argon gas supply are stopped.

  According to the present invention, it is possible to obtain a silicon carbide epitaxial substrate having a smooth surface with suppressed Si droplets, which is suitable as a substrate for epitaxial growth under reaction chamber conditions in which carbon supply is suppressed.

A preferred embodiment of the present invention will be described below.
1) The manufacturing method described above, wherein after heating for raising temperature and supply of argon gas are stopped, hydrogen gas is further supplied to etch the substrate surface.
2) The said manufacturing method whose reaction chamber conditions which suppressed supply of carbon are comprising a susceptor with silicon carbide or silicon carbide coat graphite.
3) The said manufacturing method whose reaction chamber conditions which suppressed supply of carbon are comprising a heat insulating material with a silicon carbide or silicon carbide coat graphite.
4) The said manufacturing method which supplies a hydrogen gas for 5 to 60 minutes and etches the substrate surface.

The present invention will be described below with reference to the drawings. FIG. 1 is a schematic view of one embodiment of a film forming apparatus used in the production method of the present invention, and FIG. 2 is a graph showing the time variation of heating temperature and the time variation of supply gas in one embodiment of the present invention. FIG. 3 is a graph showing the time change of the heating temperature and the time change of the supply gas in another embodiment of the present invention.
In FIG. 1, a film forming apparatus includes a susceptor 2 made of, for example, silicon carbide or silicon carbide coated graphite and a heat insulating material 3 made of, for example, silicon carbide or silicon carbide coated graphite, in a reaction chamber 1, and carbonized on the susceptor 2. A chamber for forming a thin film on the silicon substrate 4, such as a quartz chamber, is provided outside the reaction chamber 1 with an in-apparatus heating device 5, for example, a high-frequency power source, and a thermocouple thermometer 6 for measuring the in-apparatus heating temperature. , An argon gas and other gases such as hydrogen carrier gas, source gas supply piping (not shown), an exhaust pipe (not shown), and a thin film extracting device (not shown) for taking out the formed thin film. . 1 is a cross-sectional view of the inside of the reaction chamber.

In the present invention, for example, a silicon carbide substrate is heated up to an epitaxial growth temperature in an argon atmosphere under a reaction chamber condition using a film forming apparatus shown in FIG. The present invention relates to a method for manufacturing a silicon carbide epitaxial substrate in which heating for raising temperature and stopping supply of argon gas are stopped when the epitaxial growth temperature is reached. First, a silicon carbide substrate is formed under reaction chamber conditions in which carbon supply is suppressed. It is necessary to raise the temperature to the epitaxial growth temperature in an argon atmosphere.
As the reaction chamber conditions in which the carbon supply is suppressed, preferably, the susceptor is made of silicon carbide or silicon carbide coated graphite, or the heat insulating material is made of silicon carbide or silicon carbide coated graphite. In particular, it is preferable to combine the susceptor with silicon carbide or silicon carbide coated graphite and the heat insulating material with silicon carbide or silicon carbide coated graphite.

  Then, in order to raise the temperature of the silicon carbide substrate to the epitaxial growth temperature in an argon atmosphere under the reaction chamber conditions in which the supply of carbon is suppressed, argon gas is supplied from the beginning of the temperature rise as shown in FIG. . Moreover, the said temperature rise shows the state which the temperature which a thermocouple thermometer rises within the temperature range until it reaches epitaxial growth temperature. There are no particular restrictions on the temperature raising conditions, and the temperature may be raised at a constant rate of temperature rise as shown in FIG. good.

In the method of the present invention, the argon gas is preferably supplied at a supply rate of 10 to 5000 sccm (abbreviation of standard cc / min, ccm normalized at 0 ° C.), particularly 50 to 2500 sccm. . The pressure is preferably 1 torr to 2 atm, particularly 2 torr to 1 atm, and preferably 2 to 100 torr.
Further, as a preferred aspect of the present invention, it is preferable to stop heating for heating and supply of argon gas, and further supply hydrogen gas to etch the surface of the silicon carbide epitaxial substrate.

In the present invention, it is necessary to supply argon gas during the temperature rise under the above-described reaction chamber conditions in which the carbon supply is suppressed. If hydrogen gas as an etching gas is supplied during the temperature rise, silicon carbide Silicon droplets are generated on the substrate surface. The generation of Si droplets by hydrogen gas is inevitable as long as hydrogen gas is present, whether hydrogen gas alone or a mixed gas of hydrogen gas and argon gas.
It is considered that the following reaction occurs on the surface of the silicon carbide substrate by heating the silicon carbide substrate in a hydrogen atmosphere as a factor for generating Si droplets by supplying hydrogen gas during the temperature rise.

Silicon carbide + 2H ₂ → Si (s) + CH ₄ (g) +0.72 eV (1)
It is considered that Si (s) generated on the surface of the silicon carbide substrate remains on the surface as droplets.
This Si (s) is considered to evaporate by heating according to the following formula.
Si (s) → Si (g) +4.4 eV (2)
The evaporation of Si due to this reaction is slow in the low temperature range and fast in the high temperature range due to the activation energy. Also, because of the saturation vapor pressure, the evaporation rate is proportional to 1 / square root of the pressure, so the amount of Si remaining on the silicon carbide substrate surface varies depending on the temperature and pressure, and eventually Si drops on the silicon carbide substrate surface in a hydrogen gas atmosphere. It is inevitable to remain as a lett.

On the other hand, in the present invention, argon gas is supplied during temperature rise and hydrogen gas is not supplied, so that it is possible to reach a high temperature while suppressing the generation of Si droplets. It is considered that Si thus evaporated immediately does not remain on the silicon carbide substrate surface, and a flat silicon carbide epitaxial substrate surface can be obtained without hydrocarbon. Moreover, according to this invention, the deterioration of the planarization which occurs under the supply of hydrocarbon can be suppressed.
Furthermore, since the only gas that is being heated is argon, there is almost no influence on the surface by the temperature rising conditions in the temperature rising process, particularly the temperature rising rate. For this reason, even if a film forming apparatus (growth furnace) having a different shape and type is used, reproducibility can be easily obtained as compared with the case where hydrogen gas is supplied during temperature rise.

In the present invention, the silicon carbide epitaxial substrate in the present invention can be obtained by stopping the heating for raising the temperature and supplying the argon gas when the epitaxial growth temperature is reached under the argon atmosphere.
In the present invention, as shown in FIG. 3, after the argon gas supply is stopped when the epitaxial growth temperature is reached, the surface of the silicon carbide epitaxial substrate may be etched by supplying hydrogen gas. In this case, the temperature is not particularly limited as long as the temperature is equal to or higher than the epitaxial growth temperature. The temperature is kept constant in the above range or the temperature is lowered in the above range and the substrate surface is etched with hydrogen gas to obtain a silicon carbide epitaxial substrate. May be.

The epitaxial growth temperature is preferably 1500 ° C. or higher and lower than 2000 ° C., particularly 1500 ° C. or higher and 1800 ° C., and particularly preferably 1500 to 1650 ° C.
The conditions for etching the substrate surface by continuously supplying hydrogen gas after stopping the supply of the argon gas are as follows: hydrogen gas supply amount of about 10 to 5000 sccm, especially about 50 to 2500 sccm, 1500 ° C. to less than 2000 ° C. In particular, a temperature of about 1500 to 1800 ° C., particularly a temperature of 1500 to 1650 ° C., a time of 5 minutes to 2 hours, particularly a time of 5 to 60 minutes is preferable.

In the silicon carbide epitaxial substrate obtained by the method of the present invention, generation of silicon carbide droplets is suppressed on the substrate surface, the surface polishing strain layer is removed, and SRq is preferably 1 nm or less, particularly 0.5 nm or less, Among them, it has a flat surface of 0.4 nm or less.
As shown in FIG. 4, a carrier gas (for example, hydrogen gas), a Si source gas, and a C source gas are subsequently supplied to the surface of the silicon carbide epitaxial substrate obtained by the above method to form a silicon carbide single crystal. It can be epitaxially grown.
According to the method of the present invention, a silicon carbide epitaxial substrate suitable for epitaxial growth can be produced under the reaction chamber conditions in which the supply of carbon is suppressed, and the substrate itself has good characteristics and the reaction as it is. By epitaxially growing a silicon carbide single crystal in a room, generation of hydrocarbons and impurities originating from a conventional film forming apparatus can be suppressed.

There is no restriction | limiting in particular as a method of making the said silicon carbide single crystal grow epitaxially, Arbitrary methods are employable.
For example, the thin film formed by epitaxial growth may be a single layer or two or more types of multilayers. In the case of a thin film made of only silicon carbide, p-type and n-type single crystals may be joined to each other, or thin films made of different types of crystals may be joined to each other.
Examples of the Si source gas for epitaxially growing the silicon carbide include SiH ₄ and dichlorosilane, and examples of the C source gas include methane, propane, and acetylene.

Further, the temperature in the reaction chamber during epitaxial growth (for example, the thermocouple temperature of the susceptor) is preferably 1000 ° C. or higher and lower than 2000 ° C., particularly 1500 to 1800 ° C., preferably 1 to 2 to 2 atm in pressure and thickness. However, in the case of 5 to 10 μm, it is preferable to perform epitaxial growth usually with a reaction time of 1 to 2 hours (growth time for each element).
It is preferable to change the ratio of the raw material Si raw material and the C raw material depending on which one of the susceptors and the heat insulating material is used in combination. For example, when a silicon carbide susceptor and a silicon carbide heat insulating material are used in combination, C / Si of an appropriate raw material supply ratio at the time of silicon epitaxial crystal growth is 6.

  A silicon carbide epitaxial thin film can be formed by silicon carbide epitaxial growth on the surface of a silicon carbide epitaxial substrate having a smooth surface without Si droplets obtained by the production method of the present invention.

Examples of the present invention are shown below, but the present invention is not limited to the following examples.
In each of the following examples, the surface roughness of the silicon carbide epitaxial substrate is measured by an atomic force microscope, and displayed by SRq (indicating the root mean square roughness of the roughness curved surface).

Example 1
Using the film forming apparatus (CVD apparatus) shown in FIG. 1, a silicon carbide epitaxial substrate was manufactured and evaluated in the following steps.
1) The cleaned silicon carbide substrate was placed in a reaction chamber of a CVD apparatus equipped with a silicon carbide susceptor and a silicon carbide heat insulating material.
2) Heating is started under a pressure of 5 torr while flowing 500 sccm of argon gas.
3) The substrate surface is heated at a constant temperature increase rate of 50 ° C./min, and the substrate surface is treated with argon. When the epitaxial growth temperature (1650 ° C.) is reached, heating for temperature increase is stopped, and the silicon carbide epitaxial substrate Got.

After stopping the heating, the temperature was lowered, the silicon carbide epitaxial substrate was taken out, and the surface shape of the substrate was evaluated using an AFM (Atomic Force Microscope). The experimental results are summarized in Table 1. A surface shape photograph of the silicon carbide epitaxial substrate obtained in Example 1 by AFM is shown in FIG.
Moreover, as a result of measuring the surface roughness of the obtained silicon carbide epitaxial substrate, it was a flat surface with SRq = 0.5 nm as a mirror surface.

Example 2
After stopping the heating, the same procedure as in Example 1 was performed except that a step of etching the surface of the silicon carbide epitaxial substrate by supplying hydrogen gas was added as shown in the following steps.
1) The cleaned silicon carbide substrate was placed in a reaction chamber of a CVD apparatus equipped with a silicon carbide susceptor and a silicon carbide heat insulating material.
2) Heating is started under a pressure of 5 torr while flowing 500 sccm of argon gas.
3) The substrate surface is heated at a constant temperature increase rate of 50 ° C./min to treat the substrate with argon. When the epitaxial temperature (1650 ° C.) is reached, heating for temperature increase is stopped and the supply gas is changed from argon. The substrate was switched to hydrogen and held for 30 minutes to obtain a silicon carbide epitaxial substrate.

After holding for 30 minutes, the temperature was lowered, the silicon carbide epitaxial substrate was taken out, and the surface shape of the substrate was evaluated using AFM. The experimental results are summarized in Table 1. FIG. 6 shows a photograph of the surface shape of the silicon carbide epitaxial substrate obtained in Example 2 by AFM.
Moreover, as a result of measuring the surface roughness of the obtained silicon carbide epitaxial substrate, it was a flat surface with SRq = 0.2 nm as a mirror surface.

Comparative Example 1
As shown in the following steps, the same procedure as in Example 1 was performed except that the supply gas during the temperature increase was changed from argon to hydrogen.
1) The cleaned silicon carbide substrate was placed in a reaction chamber of a film forming apparatus provided with a silicon carbide susceptor and a silicon carbide heat insulating material.
2) Heating is started under a pressure of 2 torr while flowing 500 sccm of hydrogen gas.
3) The temperature was increased at a constant temperature increase rate of 50 ° C./min, and when the epitaxial temperature (1650 ° C.) was reached, heating for temperature increase was stopped to obtain a silicon carbide epitaxial substrate.

After stopping the heating, the temperature was lowered, the silicon carbide epitaxial substrate was taken out, and the surface shape of the substrate was evaluated using AFM. The experimental results are summarized in Table 1. A surface shape photograph of the silicon carbide epitaxial substrate obtained in Comparative Example 1 by AFM is shown in FIG.
Generation | occurrence | production of Si droplet was confirmed on the substrate surface for silicon carbide epitaxial (the white part scattered on the whole surface of FIG. 7 is Si droplet).

Comparative Example 2
As shown in the following steps, the same procedure as in Example 2 was performed except that the supply gas during the temperature increase was changed from argon to hydrogen.
1) The cleaned silicon carbide substrate was placed in a reaction chamber of a film forming apparatus provided with a silicon carbide susceptor and a silicon carbide heat insulating material.
2) Heating is started under a pressure of 2 torr while flowing 500 sccm of hydrogen gas.
3) The temperature was raised at a constant heating rate of 50 ° C./min, and when the epitaxial temperature (1650 ° C.) was reached, heating for raising the temperature was stopped and held for 30 minutes to obtain a silicon carbide epitaxial substrate. .

After holding for 30 minutes, the temperature was lowered, the silicon carbide epitaxial substrate was taken out, and the surface shape of the substrate was evaluated using AFM. The experimental results are summarized in Table 1. FIG. 8 shows a surface shape photograph of the silicon carbide epitaxial substrate obtained in Comparative Example 2 by AFM.
Generation of Si droplets was confirmed only at the periphery of the substrate (the area where Si droplets appear white in the periphery of FIG. 8).

  From the comparison of FIG. 5 (Example 1) and FIG. 6 (Example 2) with FIG. 7 (Comparative Example 1) and FIG. 8 (Comparative Example 2) and Table 1, the reaction of suppressing the supply of carbon of the present invention Obtained by raising the temperature of the silicon carbide substrate to the epitaxial growth temperature in an argon atmosphere under indoor conditions, treating the substrate surface with argon, and stopping heating and argon gas supply when the temperature reaches the epitaxial growth temperature. It is understood that the silicon carbide epitaxial substrate thus obtained has a smooth surface with generation of Si droplets suppressed on the substrate surface and is suitable as a substrate for epitaxial growth of a silicon carbide single crystal.

FIG. 1 is a schematic view of one embodiment of a CVD apparatus used in the present invention. FIG. 2 is a graph showing the time change of the heating temperature and the time change of the gas supply in one embodiment of the present invention. FIG. 3 is a graph showing the time change of the heating temperature and the time change of the gas supply in another embodiment of the present invention. FIG. 4 is a graph showing a temperature change and a gas supply time change of an example in which epitaxial growth is performed subsequent to another embodiment of the present invention. FIG. 5 is a surface shape photograph of the silicon carbide epitaxial substrate obtained in Example 1 by AFM. FIG. 6 is a photograph of the surface shape of the silicon carbide epitaxial substrate obtained in Example 2 by AFM. FIG. 7 is a surface shape photograph of the silicon carbide epitaxial substrate obtained in Comparative Example 1 by AFM. FIG. 8 is a photograph of the surface shape of the silicon carbide epitaxial substrate obtained in Comparative Example 2 by AFM.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reaction chamber 2 Susceptor 3 Heat insulation material 4 Board | substrate 5 In-apparatus heating apparatus 6 Thermocouple thermometer 10 Film-forming apparatus

Claims (5)

  Under the reaction chamber conditions with suppressed carbon supply, the silicon carbide substrate is heated to the epitaxial growth temperature in an argon atmosphere to treat the substrate surface with argon, and when the epitaxial growth temperature is reached, heating for heating and argon gas are performed. A method for manufacturing a silicon carbide epitaxial substrate, the supply of which is stopped.   The manufacturing method according to claim 1, wherein after the heating for raising the temperature and the supply of argon gas are stopped, the substrate surface is further etched by supplying hydrogen gas.   The production method according to claim 1 or 2, wherein the reaction chamber condition in which carbon supply is suppressed is that the susceptor is composed of silicon carbide or silicon carbide-coated graphite.   The production method according to any one of claims 1 to 3, wherein the condition in the reaction chamber in which the supply of carbon is suppressed is that the heat insulating material is composed of silicon carbide or silicon carbide-coated graphite.   The manufacturing method according to claim 2, wherein the substrate surface is etched by supplying hydrogen gas for 5 to 60 minutes.