JP2633403B2 - Method for producing silicon carbide single crystal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a silicon carbide single crystal. More specifically, the present invention relates to a method for manufacturing a silicon carbide single crystal capable of growing a silicon carbide single crystal having no antiphase boundary on a silicon single crystal substrate and having few stacking faults and excellent surface flatness.

[0002]

2. Description of the Related Art Silicon carbide has a wide band gap (2.2-3.
3 eV). It is also extremely stable thermally, chemically, and mechanically, and has excellent characteristics of being resistant to radiation damage. On the other hand, an element using a conventional semiconductor material such as silicon is difficult to use particularly under severe conditions such as high temperature, high output driving, and radiation irradiation. Therefore, a semiconductor element using silicon carbide is expected to be applied in a wide range of fields as a semiconductor element that can be used even under such severe conditions.

[0003] However, a crystal growth technique capable of stably supplying a high-quality silicon carbide single crystal having a large area on an industrial scale in consideration of productivity has not yet been established. Therefore, despite being a semiconductor material with many advantages and possibilities as described above,
Its practical use has been hindered.

Conventionally, on a laboratory scale, a silicon carbide single crystal is grown by, for example, a sublimation recrystallization method (Rayleigh method), or a silicon carbide single crystal obtained by this method is used as a substrate and a chemical vapor phase is formed thereon. The silicon carbide single crystal layer is epitaxially grown by a growth method (CVD method) or a liquid phase epitaxial growth method (LPE method), thereby obtaining a silicon carbide single crystal having a size that allows a trial manufacture of a semiconductor device.

However, in these methods, the area of the obtained single crystal is small, and it is difficult to control the size and shape with high precision. Further, it is not easy to control the polymorphism and impurity concentration of silicon carbide.

In order to solve these problems, the present inventors have proposed a method for vapor-phase growing a silicon carbide single crystal on a substrate made of a silicon single crystal which is inexpensive and easily available (Japanese Patent Application No. Sho. 58-76842). Also, a vapor phase growth method has been developed in which a surface of a silicon single crystal substrate is heated and carbonized in a hydrocarbon gas atmosphere to form a silicon carbide thin film, and then a silicon carbide single crystal layer is grown thereon. ing.
These methods are called heteroepitaxial growth methods because different types of single crystal layers are grown on a single crystal substrate.

In general, in the heteroepitaxial growth method, there are differences in lattice constant, coefficient of thermal expansion, chemical bonding, and the like between the growth layer and the substrate single crystal, so that crystal defects (in particular, stacking faults) are generated in the growth layer. Likely to happen.

For example, since there is a difference in lattice constant of about 20% between a silicon single crystal and a silicon carbide single crystal, a silicon carbide single crystal layer grown on a silicon single crystal substrate , {111}, a large number of stacking faults are distributed.
Such stacking faults extend along an octahedral plane having one point as an apex on the interface between the silicon single crystal substrate and the silicon carbide single crystal layer. Therefore, a defect pattern having a shape corresponding to the octahedral cut appears on the surface of the silicon carbide single crystal growth layer. For example, when a Si (100) substrate is used, the shape of the defect pattern is a square whose sides are parallel to the <011> direction. These stacking faults adversely affect the electrical characteristics of the obtained silicon carbide single crystal, and thus pose a serious problem in applying the silicon carbide single crystal as various electric materials.

When a silicon carbide charcoal crystal is grown on a Si (100) substrate, a defect called an antiphase boundary exists in the obtained silicon carbide single crystal. When such defects exist, it is difficult to form an element at a desired position on the substrate.

[0010]

However, even if any of the above methods is used, a silicon carbide single crystal in which these defects are reduced cannot be obtained with good reproducibility.

Recently, the growth plane orientation has changed from the [100] direction to <
011> direction (for example, [011] direction or [011] direction).
It has been reported that an antiphase boundary can be removed by growing a silicon carbide single crystal on a silicon single crystal substrate tilted in one of the [-1] directions (K. Sh).
ibahara et al., Appl. Phys. Lett. ,
50 (1987) 1888; S. Kong et al.
Mater. Res. 3 (3), May / Jun 19
88).

However, when a silicon single crystal substrate whose growth plane orientation is inclined from the [100] direction to the <011> direction is used, the antiphase boundary can be removed, but stacking faults cannot be reduced. Can not. Therefore, at present,
There is a need for a manufacturing method capable of stably supplying a silicon carbide single crystal having not only an antiphase boundary but also reduced stacking faults on an industrial scale.

An object of the present invention is to solve the above-mentioned conventional problems. It is an object of the present invention to provide a silicon carbide single crystal having no surface phase boundary and having few stacking faults and excellent surface flatness. An object of the present invention is to provide a method which can be manufactured well.

[0014]

In the method of manufacturing a silicon carbide single crystal according to the present invention, when growing a silicon carbide single crystal on a silicon single crystal substrate, the growth plane orientation is inclined at a predetermined angle in a predetermined direction ( A silicon single crystal substrate (having a so-called off-angle) is used, thereby achieving the above object. The orientation of the growth plane of the silicon single crystal substrate (that is, the direction perpendicular to the substrate surface) is inclined from the [100] direction of the silicon single crystal to the off direction, and is shifted from the [011] direction to the [01-1] direction. Is 5 to 40 degrees and the inclination angle φ measured from the [100] direction to the off direction.
Is 1 to 7 degrees. FIG. 1 is a schematic perspective view in which the growth surface of such a substrate is partially enlarged. As shown in this figure, an atomic level surface step exists along the off direction B on the growth surface of a silicon single crystal substrate whose growth plane direction A is inclined from the [100] direction to the off direction B. The growth plane direction A is uniquely expressed using the deflection angle θ measured from the [011] direction to the [01-1] direction and the inclination angle φ measured from the [100] direction to the off direction B. You.

In the present invention, the deflection angle θ of the growth plane direction A of the silicon single crystal substrate is set to 5 to 40 degrees, and the inclination angle φ is set to 1 to 7 degrees. By using such a substrate, a silicon carbide single crystal having no stacking faults and having excellent surface flatness can be obtained without the problem of the antiphase boundary. Further, by using such a silicon carbide single crystal having excellent crystallinity, deterioration of electrical characteristics due to antiphase boundaries and stacking faults is suppressed, and a silicon carbide semiconductor device having improved device characteristics can be obtained.

However, when a silicon single crystal substrate having a tilted growth plane orientation is used, as described above, surface steps at the atomic level appear on the growth plane. Irregularities corresponding to surface steps may occur. The occurrence of such irregularities lowers characteristics such as a pn junction or a Schottky junction formed for forming the element when the element is formed on the grown silicon carbide single crystal, and reduces the size of the element. Make it difficult. Therefore, when a silicon single crystal substrate having an inclined growth plane orientation is used, it is possible to form a silicon carbide single crystal on a silicon carbide single crystal despite the fact that the occurrence of antiphase boundaries and stacking faults is reduced. In some cases, the characteristics of the device are not sufficiently improved.

Generally, a single crystal of silicon carbide is Si → C →
Bonds are formed in the order of Si. When a Si—Si bond or a C—C bond is formed, the Si dimer or C dimer at this site behaves as an impurity and decreases the growth rate at this site. This is considered to be a cause of the generation of irregularities on the growth surface of the silicon carbide single crystal. Such impurities are particularly likely to occur at the edges of the surface steps at the atomic level that appear on the growth surface of the substrate.

In order to solve such a problem, in the manufacturing method of the present invention, when growing a silicon carbide single crystal by, for example, a CVD method, a hydrogen chloride gas is added to a source gas. This chlorine hydrogen gas reduces the formation of the above-mentioned Si dimer and C dimer, and as a result, prevents the occurrence of irregularities on the surface of the grown silicon carbide single crystal.

In the case where a silicon single crystal substrate whose growth plane orientation is not inclined is used, in order to improve the crystallinity of the silicon carbide single crystal grown at a low temperature and to selectively grow the material, It has been proposed to add hydrogen chloride gas to the gas (Y. Ohshita et al., J. App.
l. Phys. , 66 (9), 1 November 1
989). However, it has not been suggested that the above-described problems that occur when a silicon carbide single crystal is grown on a silicon single crystal substrate having a tilted growth plane orientation can be solved.

Examples of the silicon source gas used in the production method of the present invention include silane (SiH ₄ ), dichlorosilane (SiH ₂ Cl ₂ ), and trichlorosilane (SiHC).
l _3), silicon tetrachloride (SiCl _4), trimethylchlorosilane _{((CH 3) 3 SiCl)} , dimethyldichlorosilane _{((CH 3) 2 SiCl 2} ), and the like disilane (Si ₂ H _6). Examples of the carbon source gas include methane (CH ₄ ), ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ),
Acetylene (C ₂ H ₂ ); These source gases are introduced into a reaction tube of a vapor phase growth apparatus together with a carrier gas such as hydrogen or argon. The flow ratio of the source gas to the carrier gas is about 0.005 to 0.05%. When hydrogen chloride gas is added, the flow ratio of the hydrogen chloride gas to the carrier gas is about 0.03% to 0.2%. is there.

[0021]

Embodiments of the present invention will be described below.

(Embodiment 1) In this embodiment, first, as shown in FIG. 1, a silicon single crystal substrate in which the growth plane direction A is inclined from the [100] direction to the off direction B (ie, has an off angle). Was prepared. The deflection angle θ of the growth plane orientation A was set to 10, 20, 30, and 40 degrees (for comparison, 0 and 45 degrees). Further, the inclination angle φ was set to 1, 2, 3, 5, and 7 degrees (for comparison, 0 and 9 degrees). That is, 42 types of substrates in which these deflection angles θ and inclination angles φ are combined are used.

FIG. 2 shows an example of a vapor phase growth apparatus used in the manufacturing method of the present invention. Here, this vapor phase growth apparatus will be briefly described. Inside a water-cooled quartz reaction tube 1, a graphite sample table 2 covered with silicon carbide is installed by a graphite support rod 3. The sample stage 2 may be installed horizontally or may be appropriately inclined. A work coil 4 is wound around the outer periphery of the reaction tube 1, and the sample stage 2 can be heated to a desired temperature by flowing a high-frequency current. A branch pipe 5 serving as a gas inlet is provided on one side of the reaction tube 1, and cooling water is supplied into the quartz tube outside the quartz reaction tube 1 via branch pipes 6 and 7. The other end of the reaction tube 1 is closed by a stainless steel flange 8 and is sealed by a stopper plate 9, a bolt 10, a nut 11, and an O-ring 12 arranged on the periphery of the flange 8. A branch pipe 13 serving as a gas outlet is provided at the center of the flange 8.

Using such a vapor phase growth apparatus, a silicon carbide single crystal was grown on the various silicon single crystal substrates as described below.

First, a silicon single crystal substrate 1 is placed on a sample stage 2.
5 was placed. Then, while flowing acetylene (C ₂ H ₂ ) as a carbon source gas at a flow rate of 0.9 SCCM and hydrogen (H ₂ ) as a carrier gas at a flow rate of 3 SLM from the branch pipe 5 to the inside of the reaction tube 1, the work is performed. A high-frequency current is applied to the coil 4 to heat the sample stage 2 and the silicon single crystal substrate 15
Was heated to 1,350 ° C. By holding at this temperature for 2 minutes, the surface of the silicon single crystal substrate 15 is carbonized,
An extremely thin silicon carbide single crystal film was formed.

Next, by supplying the silicon source gas together with the carbon source gas and the carrier gas into the reaction tube 1, the silicon carbide single crystal is grown on the silicon single crystal substrate 15 on which the silicon carbide single crystal thin film is formed. Was. Disilane (Si ₂ H ₆ ) was used as a silicon source gas, and acetylene (C ₂ H ₂ ) was used as a carbon source gas. Each flow rate was 0.9 SCCM. Hydrogen (H ₂ ) was used as a carrier gas, and its flow rate was 3 SLM. In addition,
The heating temperature of the substrate was 1,350 ° C. By growing for 2 hours under such conditions, a silicon carbide single crystal having a thickness of 15 μm was obtained.

By observing the silicon carbide single crystal thus obtained with an electron microscope, the existence of antiphase boundaries and stacking faults was examined. The results obtained when various silicon single crystal substrates having a deflection angle θ of the growth plane orientation A of 0, 10, 20, 30, or 40 degrees and an inclination angle φ of 2 or 7 degrees are used. As shown in FIG. In this figure, open circles (○) and open triangles (△) represent evaluation values regarding the stacking fault density when the inclination angle φ is 2 degrees and 7 degrees, respectively. , Represents an evaluation value relating to the length of all stacking faults per unit area when the inclination angle φ is 2 degrees and 7 degrees, respectively.

As can be seen from FIG. 3, the density of stacking faults significantly decreased as the deflection angle θ of the growth plane direction A increased, regardless of whether the inclination angle φ was 2 degrees or 7 degrees. Similarly, the length of all stacking faults per unit area also decreased significantly as the deflection angle θ of the growth plane orientation A increased. Such a tendency was also obtained for other inclination angles φ.

As a general tendency, when the inclination angle φ of the growth plane azimuth A is 1 to 7 degrees and the deflection angle θ is 5 to 40 degrees, an antiphase boundary does not occur, and the stacking faults do not occur. Was greatly reduced, and good results as shown in FIG. 3 were obtained.

On the other hand, the deflection angle θ used for comparison
Is 0 °, the density of stacking faults was large and many long stacking faults were present. When the deflection angle θ is 45
In the case of the degree, the density was very specific and many antiphase boundaries occurred, so that the density of stacking faults could not be evaluated.

On the other hand, when the inclination angle φ of the growth plane orientation A exceeds 7 degrees, the surface flatness of the grown silicon carbide single crystal is reduced. Conversely, if the inclination angle φ is less than 1 degree, for example, 0 degree (ie, in the case of a Si (100) substrate),
Many antiphase boundaries occurred, and the electrical characteristics of the obtained silicon carbide single crystal deteriorated.

As described above, the deflection angle θ of the growth plane azimuth A is 5
When a silicon single crystal substrate having an inclination angle φ of 1 to 7 degrees is used, a silicon carbide single crystal having good surface flatness without an antiphase boundary and with few stacking faults is used. Is obtained.

Embodiment 2 In this embodiment, by adding hydrogen chloride gas to the source gas, antiphase boundaries and stacking faults are reduced, and a silicon carbide single crystal having more excellent surface flatness is grown. I let it.

First, as shown in FIG. 1, the growth plane direction A is inclined from the [100] direction to the off direction B (ie,
A silicon single crystal substrate (having an off angle) was prepared. The deflection angle θ of the growth plane orientation A was set to 26.5 degrees. The inclination angle φ was set to 4.5 degrees. These angles are from the [100] direction to the [011] direction and [0-1].
This corresponds to the case of being inclined by 2 degrees and 4 degrees in both directions of the [1] direction.

Next, a silicon carbide single crystal was grown on the silicon single crystal substrate as follows using the vapor phase growth apparatus shown in FIG.

First, a silicon single crystal substrate 1 was placed on a sample stage 2.
5 was placed. While flowing propane (C ₃ H ₈ ) as a carbon source gas at a flow rate of 0.2 SCCM and hydrogen (H ₂ ) as a carrier gas at a flow rate of ₃ SLM from the branch pipe 5 into the inside of the reaction tube 1, the work was performed. A high-frequency current is applied to the coil 4 to heat the sample stage 2, and the silicon single crystal substrate 15 is heated.
Was heated to 1,350 ° C. By holding at this temperature for 2 minutes, the surface of the silicon single crystal substrate 15 is carbonized,
An extremely thin silicon carbide single crystal film was formed.

Next, the silicon source gas is supplied into the reaction tube 1 along with the carbon source gas, the carrier gas, and the hydrogen chloride gas, so that the silicon single crystal substrate 15 on which the silicon carbide single crystal thin film is formed is carbonized. A silicon single crystal was grown. Silane (SiH ₄ ) as silicon source gas
And propane (C ₃ H ₈ ) as a carbon source gas. Each flow rate was 0.2 SCCM. The flow rate of the hydrogen chloride gas was 3 SCCM. Hydrogen (H ₂ ) was used as a carrier gas, and its flow rate was 3 SLM. The heating temperature of the substrate was 1,350 ° C.
By growing for 2 hours under these conditions, a silicon carbide single crystal having a thickness of 5 μm was obtained.

The surface of the silicon carbide single crystal thus obtained was flat, and the surface roughness was about 5 nm.
On the other hand, the surface of the silicon carbide single crystal prepared in the same manner as in the above example except that hydrogen chloride gas was not added had a surface roughness of about 100 nm. In addition, defect evaluation by an electron microscope showed that a silicon carbide single crystal having no antiphase boundary and no stacking fault was obtained.

The effect of adding hydrogen chloride gas is considered as follows. When a silicon carbide single crystal is grown on a silicon single crystal substrate having atomic level surface steps as shown in FIG. 4, on each step having a (100) plane,
<011> direction (for example, [011] direction and [011] direction
-1] direction), stacking faults X and Y occur. The stacking faults X and Y are separated at the edge portion of each step and become short defects. Since the stacking faults X and Y are short, the energy of these faults increases and becomes unstable, and the stacking faults eventually disappear as the growth proceeds.
In this manner, a silicon carbide single crystal free of not only an antiphase boundary but also a stacking fault is obtained.

Further, when hydrogen chloride gas is not added, the probability of adhesion between Si and C on the silicon single crystal substrate is different, and more Si is adhered. The irregularities corresponding to are generated.
However, by adding the hydrogen chloride gas to the source gas, generation of a Si-Si dimer formed by the adhesion of Si is prevented, and unevenness on the surface of the growth layer is reduced. Thus, a silicon carbide single crystal having excellent surface flatness can be obtained.

Next, a Schottky diode was manufactured using the silicon carbide single crystal obtained above. The electrical characteristics of the Schottky junction are shown by solid lines in FIG. The dotted line in the figure shows the characteristics of a Schottky diode using a silicon carbide single crystal obtained without adding hydrogen chloride gas to the source gas. As is clear from this figure, by adding hydrogen chloride gas to the source gas, a Schottky diode in which the reverse leakage current is significantly reduced can be obtained. This indicates that the addition of hydrogen chloride gas contributes not only to the reduction of antiphase boundaries and stacking faults but also to the improvement of surface flatness.

Further, in order to examine the flow rate dependence of the effect of adding hydrogen chloride gas, a silicon carbide single crystal was grown using various hydrogen chloride gas flow rates, and the stacking fault density generated on the surface thereof was measured. As a substrate, a silicon single crystal substrate having a growth plane orientation A of a deflection angle θ of 30 degrees and an inclination angle φ of 3 degrees was used. The flow rates of the carbon source gas and the silicon source gas were 0.9 SCCM, respectively, and the flow rate of the carrier gas was 3 SLM. FIG. 6 shows the result. As is apparent from this figure, the stacking fault density is significantly reduced by adding a hydrogen chloride gas at a flow rate within a predetermined range to the source gas. Typically, the flow rate of the hydrogen chloride gas is in the range of 1 to 7 SCCM when the flow rate of the carrier gas is 3 SLM in consideration of the improvement of the surface flatness. This flow rate is the ratio to the flow rate of the carrier gas.
It corresponds to about 0.03% to 0.2%.

Further, in order to investigate the effect of the addition of hydrogen chloride gas on the surface roughness, the surface roughness of the silicon carbide single crystal obtained as described above was measured with a probe. FIG. 7A shows the results when the flow rate of the hydrogen chloride gas was 5 SCCM. For comparison, FIG. 7B shows the result when hydrogen chloride gas was not added. The standard of the surface roughness is arbitrary. As is clear from these figures, grooves of about 0.1 μm in depth were formed on the surface of the silicon carbide single crystal obtained without adding hydrogen chloride gas, whereas hydrogen chloride gas was added. The surface of the silicon carbide single crystal obtained as described above is very flat, and the surface roughness is significantly improved.

[0044]

According to the manufacturing method of the present invention, it is possible to grow a silicon carbide single crystal excellent in surface flatness with few antiphase boundaries and stacking faults on a silicon single crystal substrate. In addition, since such a silicon carbide single crystal can be obtained with good reproducibility, a silicon carbide single crystal having excellent crystallinity can be supplied stably. Since the obtained silicon carbide single crystal has few antiphase boundaries and stacking faults, when a pn junction or a Schottky junction is formed, its electrical characteristics do not deteriorate. Also,
Since the surface flatness is excellent, a fine element can be easily formed using photolithography or the like. Therefore, a semiconductor device using a silicon carbide single crystal having excellent electrical characteristics (for example, a field effect transistor (FET), a complementary MOS integrated circuit (C-MOS), and various power devices) can be produced on an industrial scale. It will be possible to produce well.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing surface steps at an atomic level appearing on a growth surface of a silicon single crystal substrate used in a manufacturing method of the present invention, and a direction angle θ and a tilt angle φ defining a growth plane orientation A.

FIG. 2 is a sectional view showing an example of a vapor phase growth apparatus used in the manufacturing method of the present invention.

FIG. 3 is a graph showing the deflection angle dependence of stacking faults in various silicon carbide single crystals prepared in one example of the present invention.

FIG. 4 is a perspective view showing surface steps at the atomic level appearing on the surface of a silicon single crystal substrate whose growth plane orientation is inclined, and stacking faults X and Y generated in the [011] and [01-1] directions, respectively. It is a schematic diagram.

FIG. 5 shows characteristics of a Schottky diode using a silicon carbide single crystal prepared in another embodiment of the present invention to which hydrogen chloride gas is added, and characteristics of a silicon carbide single crystal prepared by a conventional manufacturing method. FIG. 4 is a graph showing characteristics of a Schottky diode.

FIG. 6 is a graph showing the dependence of the stacking fault density on the silicon carbide single crystal surface on the flow rate of hydrogen chloride gas in another embodiment of the present invention in which hydrogen chloride gas is added.

7A is a graph showing the surface roughness of a silicon carbide single crystal obtained by adding hydrogen chloride gas, and FIG. 7B is a graph showing silicon carbide obtained without adding hydrogen chloride gas. It is a graph which shows the surface roughness of a single crystal.

[Explanation of symbols]

 1 Reaction tube 2 Graphite sample table 15 Silicon single crystal substrate

Claims (2)

(57) [Claims] 1. A method for producing a silicon carbide single crystal, comprising the step of growing a silicon carbide single crystal on a silicon single crystal substrate, wherein the growth plane orientation of the substrate is off from the [100] direction of the silicon single crystal. In the direction of the growth plane [01]
The deflection angle θ measured from the [1] direction to the [01-1] direction is 5 to 5.
A method for manufacturing a silicon carbide single crystal, wherein the inclination angle φ measured from the [100] direction to the off direction is 1 to 7 degrees. 2. When the silicon carbide single crystal is grown by a chemical vapor deposition method using a silicon source gas and a carbon source gas, a hydrogen chloride gas is added to the source gas.
The method according to claim 1.