JPH11162850A - Silicon carbide substrate and its production, and semiconductor element using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain excellent reproducibility of a smoothed surface even in a substrate kept at a low temperature by controlling the existence ratio of carbon to silicon on the growth surface of silicon carbide crystal so that silicon atoms may exceed carbon atoms. SOLUTION: The surface of a silicon carbide substrate 1 before the start of growth of silicon carbide crystal is made to have an off-cut surface tilting 0.05 deg. or more and 10 deg. or less from either of the (0001) plane of a hexagonal system silicon carbide and (111) plane of a cubic system silicon carbide crystal. The silicon carbide substrate 1 and silicon atom 2 are combined with an Si-Si bond 3 on such a growth surface 1a of silicon carbide crystal, and the quantity of supply of silicon atom 2 and carbon atom is controlled so that the silicon atom 2 exceeds the carbon atom in quantity. Thus, a silicon carbide thin film having an excellent crystal structure can be grown epitaxially at a low temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon carbide substrate having a hexagonal or cubic crystal structure, a silicon carbide substrate in which crystal layers having different crystal systems are laminated, and silicon carbide thereof. A production method by homoepitaxial growth or heteroepitaxial growth of a substrate,
And a semiconductor device using these silicon carbide substrates.

[0002]

2. Description of the Related Art Silicon carbide crystals have attracted attention in recent years because of their favorable characteristics as semiconductor materials, such as a wide band gap, a high saturation electron velocity, and a high thermal conductivity. Single crystal substrates of 6H or 4H hexagonal silicon carbide are commercially available and used. In addition, cubic silicon carbide, which is expected to be used particularly for high-speed, high-power semiconductor devices, is difficult to grow a large single crystal usable as a substrate. A thin film or the like is used.

[0003] The above-mentioned silicon carbide crystal is prepared by using a mixed gas such as silane or propane as a raw material and using hydrogen as a carrier gas at a temperature exceeding 1300 ° C, usually 1500 ° C.
It is formed by a normal pressure CVD method at a high temperature of about ℃.

[0004]

However, the detailed growth mechanism of the silicon carbide crystal has not been clarified, and the relationship between the supply amount of the source gas and the substrate temperature is grasped and controlled.
A technique for epitaxially growing a silicon carbide thin film with good reproducibility has not been sufficiently completed industrially. Therefore, the conventional technology for manufacturing a silicon carbide substrate has various problems as follows.

First, the above-described crystal growth of silicon carbide is performed as described above.
Due to the high temperature required, selective areas by masking
Crystal growth or high-concentration nitrogen doping
Or it is difficult. That is, the high
Because there is no mask material that can withstand temperature,
It is difficult to grow the crystal only in a predetermined area
Is silicon carbide particularly difficult to selectively etch?
It is difficult to form a desired semiconductor element or semiconductor circuit.
It has become difficult. Also, under high temperature as above
When nitrogen doping is performed, the crystal growth film is likely to be rough.
For example, 5 × 10 ¹⁸Pieces / cm^ThreeHigh concentration of
Is difficult to group. In addition, the odor of crystal growth at high temperatures
Of feed gas, adhesion on substrate surface, re-evaporation
Mechanism is complicated, for example,
Grasping and controlling the relationship with the substrate temperature, etc., and carbonizing with good reproducibility
More difficult to grow silicon thin film epitaxially
It has become difficult. J.App by T.Kimoto et al.
lied Physics Vol. 73, No.2 1993 (pp.726-732)
Is the off-cut surface of the {0001} surface in the (Formula 4) direction
Flow formation using a carbonized crystal substrate with
6H hexagonal carbonization at relatively low temperature by lengthening
A technique for forming a silicon crystal has been proposed.
However, it is necessary to heat to about 1200 ° C.

Next, it is difficult to epitaxially grow a single crystal thin film of hexagonal silicon carbide or cubic silicon carbide having good crystallinity. In particular, when a cubic silicon carbide crystal is formed on a silicon substrate, lattice mismatch is large, and it is difficult to obtain good crystallinity. Also, for example, even when formed on a 6H hexagonal silicon carbide crystal, a cubic silicon carbide crystal including a double positioning boundary due to the occurrence of twin tends to grow. The inventors of the present application disclosed in Japanese Patent Application Laid-Open No. 7-172997 that a silicon atom on a growth surface of a silicon carbide crystal was made to be excessive with respect to a carbon atom so that a cubic crystal having a (001) plane was obtained. The method of forming the silicon carbide thin film, and the method in which carbon atoms are made excessive with respect to silicon
1) a cubic silicon carbide thin film having a plane, or (000)
1) A method for forming a hexagonal silicon carbide thin film having a plane has been proposed. However, even in this case, although relatively good crystallinity can be obtained, it has been difficult to surely or largely suppress the occurrence of twins and the like.

Furthermore, a silicon carbide crystal having a crystal system different from that of the silicon carbide substrate cannot be heteroepitaxially grown on the silicon carbide substrate through a favorable interface. That is, for example, when a silicon carbide crystal is grown in a step flow on a hexagonal silicon carbide substrate, the formed silicon carbide crystal is restricted by the crystal structure of the substrate,
Since it is likely to be hexagonal silicon carbide, it is difficult to heteroepitaxially grow cubic silicon carbide or the like.

In view of the above, the present invention can epitaxially grow silicon carbide having good crystallinity at a relatively low temperature, and can selectively grow a crystal in a selective region by masking or a high concentration silicon carbide. A method of manufacturing a silicon carbide substrate that can easily perform nitrogen doping and that can be heteroepitaxially grown so that silicon carbides of different crystal systems are stacked through a good interface, and formed by the manufacturing method. It is an object of the present invention to provide a silicon carbide substrate that has been made, and a semiconductor element that can operate at high speed using such a silicon carbide substrate.

[0009]

Means for Solving the Problems The present inventors control the abundance ratio of carbon and silicon on the growth surface of a silicon carbide crystal so that silicon atoms become excessive with respect to carbon atoms.
The present inventors have discovered that a smooth surface can be obtained with good reproducibility even on a substrate kept at a relatively low temperature, and that a high-performance epitaxial thin film having good crystallinity can be obtained. Based on this discovery, the present invention has been completed.

That is, as shown in FIG. 1, a Si—Si bond 3 is formed on a silicon carbide crystal growth surface 1 a of a substrate 1.
Excessive silicon atoms 2 bonded to substrate 1 tend to diffuse actively on silicon carbide crystal growth surface 1a. This is S
i-Si bond 3 is a carbon atom of C-Si or C-C
This is because the bond is weaker than the bond. therefore,
When carbon atoms are supplied in a state where silicon atoms are excessive as described above, silicon atoms are easily bonded to the substrate 1 and carbon atoms at appropriate lattice positions, and therefore, even at a relatively low temperature, uniformity, Good crystallinity with excellent flatness can be easily obtained. Note that the present inventors have disclosed in Japanese Patent Application Laid-Open
According to 172997, in a cubic silicon carbide having a (001) plane, an excessive supply of silicon atoms
1) A technique for supplying an excessive amount of carbon atoms in hexagonal silicon carbide or the like having a plane is proposed. It has been newly found that better crystallinity can be obtained by such a mechanism, and the present invention has been completed.

As described above, if the crystal growth surface is off-cut so that the predetermined crystal plane is shifted from the crystal orientation by 0.05 ° or more and 10 ° or less, a crystal having better crystallinity grows. . This is done by off-cut
This is because a terrace 4 and a step edge 5 are formed on the crystal growth surface as shown in FIG. 2, and a step flow growth 6 in which the step edge 5 grows on the terrace 4 occurs. The easy diffusion of the silicon atoms promotes step flow growth 6,
It enables epitaxial growth even at low temperatures. Here, when the above-mentioned off-cut is set to less than 0.05 ° from the crystal orientation, the terrace width becomes too wide, and a long-distance surface diffusion is required for step flow growth. It will be necessary. On the other hand, if the off-cut exceeds 10 ° from the crystal orientation, the density of the step edge becomes too high, and secondary nuclei of growth are generated from the step edge, and the film is likely to be roughened.

Regarding the off-cut direction, when the growing silicon carbide crystal is a hexagonal crystal, the off-cut surface is inclined in the (Formula 1) direction or the following (Formula 5) direction. An optimum terrace and step edge can be obtained for a proper step flow growth. That is, in the case of the following (Equation 5), as shown in FIG. 3A, the step edge 5 before crystal growth is in the (Equation 1) direction, but the step edge of the step flow growth 6 is 12 with respect to the (Equation 5) direction of the off-cut inclination direction
There are two (Equation 5) directions forming an angle of 0 °, and step flow growth is performed while forming a jagged saw-toothed step edge. Here, since the growth portions 6a and 6b of the step flow growth 6 are the same crystal in the case of hexagonal crystal, good crystallinity can be obtained. However, in this case, as the crystal growth progresses, step bunching in which a plurality of growth steps overlap becomes remarkable, and the unevenness of the growth film surface may become large. The present inventors have found that it is effective to use an off-cut surface inclined in the (Equation 1) direction in order to reduce such irregularities on the surface of the grown film. In this case, good crystallinity can be obtained, and the above-described step bunching hardly occurs, so that a silicon carbide substrate having high growth surface flatness can be formed. Such a silicon carbide substrate is effective, for example, when fine processing is required.

[0013]

(Equation 5)

On the other hand, when a cubic crystal is grown, if an off-cut surface inclined in the (Equation 5) direction is used, the growth portion 6
The crystals a and 6b are mirror images of each other, and a double positioning boundary is formed. The double positioning boundary does not decrease even if the crystal growth is continued. Therefore, as a result of various studies, the present inventors have found that, as shown in FIG. 3 (b), by using an off-cut surface inclined in the (Equation 1) direction, even when a cubic crystal grows, It has been found that crystals can be grown without generating twin boundaries. In this case,
A linear step edge 5 in the above (Formula 5) direction is formed before and after the crystal growth, and the growth portions 6d to 6f of the step flow growth 6 become the same crystal, and a good single-phase crystallinity is obtained. Specifically, for example, cubic silicon carbide including a substantially defect-free crystal surface portion of 1 mm square or more can be obtained. The effect in the off-cut direction is effective if the magnitude of the component in the (Equation 1) direction in the off-cut direction is greater than the magnitude of the component in the (Equation 5) direction. It was effective even if it deviated slightly from the direction.

In order to keep the silicon atoms in an appropriate excess state, it is preferable to use the surface rearrangement structure of the crystal growth surface as an index. Specifically, for example, a hexagonal (0
When crystallizing a hexagonal crystal on the (001) plane (Si plane),
Good crystal growth by controlling the supply of silicon and carbon atoms so that the surface structure is between approximately 1 × 1 surface structure and approximately √3 × √3 surface rearrangement structure Can be. Similarly, when a cubic crystal is grown on a hexagonal (0001) plane (Si plane) or a cubic (111) plane (Si plane), the hexagonal (Formula 2) plane (C plane) ) When a hexagonal crystal is crystallized thereon, and when the (Formula 2) plane (C plane) of the hexagonal crystal or the (Formula 3)
When crystallizing a cubic crystal on the plane (C plane), almost 1
It is preferable to control so as to be between × 1 and approximately 3 × 3.

That is, when the surface is rearranged as described above, it is possible to supply silicon atoms that actively diffuse on the silicon carbide crystal growth surface, and to suppress the precipitation of silicon crystal grains. can do. It should be noted that it is not always necessary to control so as to change over the above range, but it is only necessary to be between them. For example, when growing a cubic crystal on a hexagonal (0001) plane (Si plane), {3 ×}
Control may be performed so as to be between 3 and 3 × 3, or control may be performed such that a substantially constant surface rearrangement structure between them is obtained. Furthermore, without necessarily controlling the supply amount while detecting the surface rearrangement structure, the surface rearrangement structure is detected in advance, and the supply amounts and supply patterns of silicon atoms and carbon atoms are determined. The crystal may be grown without performing the above detection.

In addition, it is preferable that the number of silicon atoms excessively present on the silicon carbide crystal growth surface is reduced to 5 atomic layers or less, because the crystallinity of the grown thin film by precipitation of silicon crystal grains on the silicon carbide crystal growth surface is reduced. -It is preferable because deterioration of flatness can be easily prevented.

Further, by supplying one or both of the silicon atoms and the carbon atoms intermittently, it becomes easy to keep the silicon atoms in an excessive state. In particular, when silicon atoms and carbon atoms are alternately supplied to the silicon carbide crystal growth surface, the surface state can be dynamically changed, and the control of the silicon excess state becomes easier. In addition, while silicon atoms are supplied continuously, carbon atoms may be supplied intermittently. In this case, it is easy to maintain the silicon excess state for a long time, so that a silicon carbide thin film having better crystallinity can be obtained. Further, supply of only silicon atoms is performed until a surface rearrangement structure of approximately √3 × √3 or 3 × 3 is obtained, and supply of carbon atoms is performed until a surface structure of approximately 1 × 1 is obtained. Also, it is easy to keep the excess number of silicon atoms optimal.

The temperature of the silicon carbide crystal growth surface is 6
It is preferable that the temperature is not lower than 00 ° C and not higher than 1300 ° C. When the temperature is lower than 600 ° C., diffusion of silicon atoms is not sufficient, and it is difficult to obtain the above-described effects. On the other hand, if the temperature of the growth surface exceeds 1300 ° C., it is not suitable for selective growth of a silicon carbide thin film and high-concentration doping of nitrogen, which will be described later, as in the conventional high-temperature DVD method. Note that 13
Even at a temperature exceeding 00 ° C., the effect of forming a silicon carbide crystal having good crystallinity as described above is obtained similarly.

In the doping with nitrogen, a silicon carbide thin film can be doped with nitrogen by supplying a reactive nitrogen-containing gas such as ammonia as a nitrogen source to the silicon carbide crystal growth surface. In other words, since silicon carbide can be grown at a relatively low temperature as described above, a silicon carbide thin film having good crystallinity containing a high concentration of nitrogen at the substitution position can be easily obtained. Has 5x
It is also possible to obtain a silicon carbide thin film containing nitrogen atoms of 10 ¹⁸ atoms / cm ³ or more, and more preferably 10 ^{19 to} 5 × 10 ¹⁹ atoms / cm ³ or more.

In the crystal growth in the above temperature range, since a film is formed in a low temperature region, a region masked by, for example, a silicon oxide thin film is set on a part of the growth surface, and a region other than this region is set. A silicon carbide thin film can be grown in the portion. In the conventional high-temperature film formation, there was no material that could be used as a masking material and selective growth could not be performed. However, according to this preferred example, patterning for element formation is performed on silicon carbide that is difficult to selectively etch. It becomes possible.

Further, prior to the growth of the silicon carbide crystal, the crystal growth surface is cleaned so that the crystal growth surface has a √3 × 表面 3 surface rearrangement structure, thereby forming a silicon carbide thin film having excellent crystallinity. Can grow. The above cleaning is
Specifically, for example, in a hydrogen atmosphere or vacuum
The heating is preferably performed by heating to a temperature of from 00 ° C to 1300 ° C. If the cleaning temperature is lower than 800 ° C., surface impurities such as an oxide film remain and the cleaning becomes insufficient. On the other hand, if the cleaning temperature is higher than 1300 ° C., silicon atoms evaporate from the vicinity of the growth surface and the surface becomes less clean. This is because carbonization may proceed.

Next, the lamination of silicon carbide crystals having different crystal systems will be described. This lamination is performed by step flow growth using a method of growing a silicon carbide crystal having a different crystal system from the substrate by setting the substrate temperature, and using an off-cut substrate having regions where silicon carbide crystals of different crystal systems are formed. The method can be performed by the following method.

The method of setting the substrate temperature is based on the finding that the crystal system of silicon carbide to be grown can be controlled by changing the substrate temperature.
In other words, when growing a crystal using an off-cut substrate, if the temperature of the substrate surface is set to just below the minimum temperature at which complete step flow growth occurs, a stable crystal system at that substrate temperature will become a step on the substrate surface. It takes advantage of growing while being weakly affected. In other words, the silicon or carbon atoms supplied on the terrace are
Before the surface diffuses on the terrace and reaches the step, it aggregates on the terrace to form microcrystals. The microcrystal becomes the most stable crystal system determined by the substrate surface temperature without being affected by the step. The microcrystal grows, but encounters a step before becoming a stable large crystal and further grows with some influence of the step to become a stable large crystal.
Therefore, unlike the complete step flow growth, the growth does not completely reflect the crystal system of the substrate.

Therefore, for example, 6H hexagonal silicon carbide ｛0
900 ° C on 4 ° off-cut substrate with 001 ° plane
When the growth as described above is maintained at the substrate surface temperature of
A 3C cubic silicon carbide thin film grows. In this case, as described above, if the off-cut direction is inclined in the above-mentioned (Equation 1) direction of a substantially hexagonal crystal, the 3C
A cubic silicon carbide thin film was obtained. This direction provides an optimal terrace and step edge for the step flow growth. Further, for example, 4H hexagonal silicon carbide $ 000
When the substrate is grown at a substrate surface temperature of 1500 ° C. on a 1 ° off cut substrate of 1 ° plane, a 6H hexagonal silicon carbide thin film grows. When crystal growth of hexagonal silicon carbide is performed in this way, the inclination direction of the off-cut may be the (Equation 5) direction. Here, if the substrate temperature rises, the surface diffusion occurs more. Therefore, in order to grow silicon carbide of a different crystal system, it is necessary to increase the step width (decrease the off-cut angle). In the case where crystal growth is performed in an excessive state of silicon atoms as described above, the temperature of the silicon carbide crystal growth surface is set to 600 ° C. or higher and 18 ° C. or higher.
When the temperature was not higher than 00 ° C., a thin film having good crystallinity was obtained. 60
If the temperature is 0 ° C. or lower, even if silicon atoms are bonded to the substrate by Si—Si bonds, surface diffusion becomes insufficient, and good crystal growth is not performed. At a temperature of 1800 ° C. or higher, sublimation of silicon carbide from the growth surface becomes remarkable, and it is difficult to control the growth conditions. For the first time, growth at a low temperature within the range of the present invention enables growth of a silicon carbide having a different crystal system from a substrate having a good crystallinity.

On the other hand, the method of using an off-cut substrate (pre-treatment substrate) having a region in which silicon carbide crystals of different crystal systems are formed is characterized in that the carbon carbide crystal grows from the step located on the upstream side in the step flow growth direction. This utilizes the fact that a silicon crystal grows while proceeding on a terrace on the downstream side. In other words, different silicon carbide crystals of different crystal systems are formed on the substrate in advance, and complete step flow growth is performed using the silicon carbide crystals. Then, the crystal proceeds and grows on the crystalline silicon carbide crystal formed in the region, and is stacked. In this case, the growth proceeds while the interface between silicon carbide crystals of different crystal systems is maintained very well.

In the formation of the pre-processed substrate as described above, the silicon atoms are made to be in an excessive state, and a silicon oxide thin film or the like is used as a mask at a low temperature to selectively form a crystal system different from the substrate in a part of the substrate surface. It can be easily performed by growing silicon carbide crystal. Even without using the selective growth as described above, a silicon carbide crystal having a crystal system different from the crystal system of the substrate is grown on the silicon carbide substrate whose crystal plane is inclined with respect to the surface. A similar pre-processed substrate can also be formed by removing the grown silicon carbide by etching while partially leaving the substrate surface exposed.

According to the above method, a silicon carbide thin film in contact with a good interface can be grown and laminated, and various combinations of a laminated structure, a sandwich structure, and a multi-layer laminated structure can be obtained. Can be easily formed.

Specifically, for example, first, 3C cubic silicon carbide is selectively grown on at least a part of the substrate surface where the {0001} plane of hexagonal silicon carbide such as 6H and 4H is inclined with respect to the surface. A pre-processed substrate is formed. When the pre-processed substrate is subjected to step flow growth by ordinary CVD growth, a {111} plane of 3C cubic silicon carbide is stacked on a {0001} plane of hexagonal silicon carbide such as 6H or 4H, Alternatively, a stacked structure in which {0001} planes of hexagonal silicon carbide such as 6H and 4H are stacked on {111} planes of 3C cubic silicon carbide can be formed.

Further, for example, by slightly increasing the substrate temperature at the time of forming the pre-processed substrate, it is possible to reduce the {0}
6H hexagonal silicon carbide is selectively grown on at least a part of the substrate surface where the 001 ° plane is inclined with respect to the surface.
A laminated structure in which the {0001} plane of 4H hexagonal silicon carbide is laminated on the {0001} plane of H hexagonal silicon carbide, or
It is possible to form a stacked structure in which the {0001} plane of 6H hexagonal silicon carbide is stacked on the {0001} plane of H hexagonal silicon carbide.

Further, according to the pattern of the region of the different crystal system in the pre-processed substrate, for example, the cubic silicon carbide crystal of 3C sandwiched between the crystals of hexagonal silicon carbide such as 4H and 6H is included. Alternatively, it may include a 6H hexagonal silicon carbide crystal sandwiched between 4H hexagonal silicon carbide crystals. More specifically, for example, when a step of 3C cubic silicon carbide having a different crystal system from that of the substrate is formed in a central portion of a 6H hexagonal substrate by pretreatment, for example, 3C cubic /
A 6H hexagonal lamination interface and a 6H hexagonal / 3C cubic lamination interface are formed, and a good interface is formed with no defects or the like during growth. In this case, the growth of silicon carbide proceeds at the step edge, and the crystal system at the step edge determines the crystal system of silicon carbide to grow. That is, since the atomic arrangement on the terrace surface does not affect the crystal of the growth layer that grows only on the surface layer, it does not substantially affect the difference in the crystal system such as hexagonal or cubic. Therefore, as the step flow growth of the pre-processed substrate is continued, the interface between different crystalline silicon carbides and the crystallinity of the silicon carbide itself are improved.

Also, without using the selective growth, silicon carbide whose crystal plane is inclined with respect to the surface, for example, 3C cubic silicon carbide having a crystal system different from the crystal system of the substrate over the entire surface of a 6H hexagonal substrate Is removed in the same manner as described above, and thereafter, the grown 3C cubic silicon carbide is partially removed and etched away to leave a portion where the 6H hexagonal crystal is exposed again and a portion where the 3C cubic crystal remains. Even if a processing substrate is formed and the pre-processing substrate is grown in a step flow,
A silicon carbide substrate including a stacked structure of silicon carbide having different crystal systems was formed.

The silicon carbide substrate of the present invention is a silicon carbide substrate of good crystallinity manufactured by the above-described manufacturing method, and can have the following features. That is, in the silicon carbide substrate of the present invention, for example, the edge of the growth step existing on the growth surface of silicon carbide is selected from the step edge (Formula 4) of hexagonal silicon carbide and the [110] step edge of cubic silicon carbide. Can be provided. Also,
For example, 5 × 10 ¹⁸ pieces / cm ³ or more, and further, 10 ¹⁹ to
It may have a feature that 5 × 10 ¹⁹ / cm ³ or more nitrogen atoms are included in the substitution position. Also, for example, a silicon carbide substrate formed on the surface of a hexagonal silicon carbide substrate,
It can be characterized by being made of a cubic silicon carbide single crystal including a defect-free crystal surface portion of mm square or more. In addition, for example, the substrate may be characterized by being a substrate selectively epitaxially grown on a part of a silicon carbide substrate. The silicon carbide substrate of the present invention has such features,
It becomes highly useful as a substrate for a semiconductor element utilizing the excellent thermal conductivity, dielectric breakdown voltage, large band gap, and the like of silicon carbide.

Further, as described above, if a semiconductor element is formed by a silicon carbide substrate in which single-layer silicon carbide crystals having different crystal systems and good crystallinity are stacked via a steep interface of the crystal structure, A semiconductor element which can operate at high speed can be obtained. That is, when different types of silicon carbide crystals having different crystal structures are in contact with each other at a clean hetero interface, a two-dimensional electron gas is formed by injecting an electron into the lower conduction band energy at the hetero interface. ,
Utilizing the high carrier mobility of this two-dimensional electron gas,
High-speed electronic devices such as HFETs can be formed.

More specifically, for example, when an HFET is formed using a laminated structure of 6H hexagonal silicon carbide having a wide band gap of 2.86 eV and 3C cubic silicon carbide having a narrow band gap of 2.3 eV, Carriers are injected into the channel layer of 3C cubic silicon carbide having a low doping concentration from 6H hexagonal silicon carbide having a high doping concentration, and a two-dimensional electron gas is formed at the 6H / 3C interface. Since the two-dimensional electron gas exhibits high carrier mobility, high-speed operation can be performed.

The two-dimensional electron gas as described above can be used at an interface between silicon carbide having different crystal structures and band gaps.
It is formed not only at the H / 3C interface but also at the 4H / 3C interface, 4H / 6H interface, and the like. At the heterointerface between these different crystalline silicon carbides, only the way of stacking the silicon carbide bilayer is different, and the structure and composition of the silicon carbide bilayer are not changed. Very small. Therefore, other gallium arsenide (GaAs)
And the like, it is possible to form a hetero-interface which is better than that of a mixed crystal based interface, and thus a semiconductor element having better characteristics can be formed.

[0037]

(Embodiment 1) As Embodiment 1 of the present invention, an example in which hexagonal silicon carbide is grown on a silicon surface (Si surface) of hexagonal silicon carbide will be described.

First, a 6H hexagonal silicon carbide single crystal substrate having a 3.5 ° off-cut plane in the (Equation 5) direction of the (0001) plane (Si plane) was prepared by molecular beam epitaxy (MB).
E) Introduce into the device and set the background pressure to 10
The substrate was heated to 1100 ° C. at ^-9 Torr or less. Thereby, the substrate is cleaned, and according to high energy reflected electron diffraction (RHEED), √ as shown in FIG.
It was confirmed that the surface had a 3 × √3 surface rearrangement structure.

Next, while keeping the temperature of the substrate at 1100 ° C., silicon atoms were supplied from k-cell heated to 1380 ° C., and 8 k
V, carbon atoms were supplied at a power of 100 mA. More specifically, first, by supplying silicon atoms for one-third atomic layer, the surface rearrangement structure of 原子 3 × √3 was more clearly observed. That is, as shown in FIG.
An excessive number of silicon atoms for the atomic layer is deposited on the terrace. In this state, when about the same number of carbon atoms as the silicon atoms are supplied to the surface of the substrate, the above-mentioned √3 × √3
The RHEED diffraction streak indicating the surface rearrangement structure is weakened and approaches a 1 × 1 pattern. That is, the silicon atoms deposited on the terrace and the newly supplied carbon atoms gather near the step edge 5 and crystallize as shown in FIG. 2, and a step flow growth 6 of hexagonal silicon carbide occurs, and The surface of the terrace 4 has a surface rearrangement structure close to a 1 × 1 pattern. In this case, the length of the step flow growth is a length corresponding to the number of atoms of the ３ atomic layer. Specifically, for example, assuming that the step height is equivalent to two atomic layers (a silicon layer and a carbon layer), step flow growth occurs by １ ／ of the terrace length.

Thereafter, the supply of silicon atoms and the supply of carbon atoms are repeated, so that the surface rearrangement structure becomes $ 3.
While changing between × √3 and 1 × 1, a highly crystalline hexagonal silicon carbide epitaxial thin film having a smooth surface is formed.

When the growth surface of the silicon carbide thin film formed as described above was observed by an SEM photograph, FIG.
As shown schematically, it was confirmed that the crystal was grown such that the step edges 5 in the (Formula 4) direction crossing each other at an angle of 120 ° proceeded.

As described above, by supplying silicon atoms and carbon atoms so that silicon atoms become slightly excessive, a silicon carbide thin film having a favorable crystal structure can be formed at a relatively low temperature.

As described above, when an off-cut surface inclined in the (Equation 5) direction is used as the original silicon carbide substrate, step bunching in which a plurality of growth steps overlap as crystal growth progresses is remarkable. As a result, irregularities on the surface of the grown film may be increased. Therefore, when such an unevenness is likely to be a problem in microfabrication or the like, it is preferable to use an off-cut surface inclined in the (Equation 1) direction. In this case, as in the above case, good crystallinity can be obtained at a relatively low temperature, step bunching is less likely to occur, and the flatness of the growth surface is improved.

Similar crystal growth was performed even when a 4H hexagonal silicon carbide substrate was used as the original silicon carbide substrate. Here, when a 4H hexagonal silicon carbide substrate is used, if the temperature of the substrate is maintained at a relatively high temperature (for example, 1600 ° C. when the off-cut angle is 1 °), the same 4H as the original silicon carbide substrate is obtained. While the crystal structure of (Homoepitaxial growth) is formed, if the temperature is kept lower (for example, 1500 ° C. when the off-cut angle is 1 °), the crystal structure of 6H is obtained regardless of the crystal structure of the original silicon carbide substrate. Is formed (heteroepitaxial growth).

The heating temperature of the substrate is as described above.
What is necessary is just to set according to the crystal structure to be formed.
When the temperature is higher than or equal to ° C., the degree of diffusion of silicon atoms is relatively large, so that crystal growth with good crystallinity can be easily performed. On the other hand, when the temperature is 1300 ° C. or lower, selective region crystal growth by high-density nitrogen doping or masking as described in Embodiments 4 and 5 described later can be easily performed. Even when the temperature exceeds 1300 ° C., the effect of forming a silicon carbide crystal having good crystallinity as described above is obtained similarly. That is, when heating to the same temperature as the conventional one, a silicon carbide crystal having better crystallinity can be formed, and in order to obtain the same crystallinity as the conventional one, the temperature is set lower than the conventional one. be able to.

In the control of the supply of silicon atoms and carbon atoms, after the surface rearrangement structure becomes √3 × √3, supply of a larger amount of silicon atoms is continued, and the number of excess carbon atoms is reduced to hexagonal carbonization. If the number of silicon atoms exceeds approximately 5 atomic layers in the silicon crystal, crystal grains (droplets) of silicon are likely to be generated. On the other hand, if supply of a larger amount of carbon atoms is continued after 1 × 1, the carbon atoms having low diffusivity tend to deposit on the terrace. In any of these cases, appropriate step flow growth is hindered, but the responsiveness of supply control of silicon atoms or the like does not necessarily have to be so high, and √3 × √3 or 1 × 1 Even in the state, for example, if the above-described supply control is performed within several minutes, an appropriate step flow growth can be performed. Further, even if the surface rearrangement structure is not necessarily controlled to change from √3 × √3 to 1 × 1, the surface rearrangement structure may be constant or within a certain range as long as it is between these. Should be controlled.

Further, the supply of the silicon atoms and the carbon atoms is not limited to the above-mentioned alternate supply, and either one may be supplied continuously and the other may be supplied intermittently. In this case, the intermittent supply of carbon atoms is relatively easy to control. Further, even if both are supplied continuously, it is sufficient to control the silicon atoms so that a slight excess state is maintained.

In addition, high energy reflection electron beam diffraction (RHE)
Although the supply of silicon and carbon atoms is controlled by detecting the surface rearrangement structure by ED), the composition ratio of the substrate surface is directly measured by Auger analysis or ESCA analysis, etc. The abundance ratio may be controlled. Further, the surface rearrangement structure may be detected in advance, the supply amounts and supply patterns of silicon atoms and carbon atoms may be determined, and the crystal may be grown at the manufacturing stage without performing the above detection.

Further, the off-cut angle (tilt angle) of the original silicon carbide substrate is not limited to 3.5 ° as described above, but may be 0.5 °.
When it is about 05 ° or more and about 10 ° or less, favorable crystallization by step flow growth can be easily performed.

Although an example of crystal growth using a molecular beam epitaxy (MBE) apparatus has been described, the invention is not limited to this.
A VD device or the like may be used.

The supply sources of silicon atoms and carbon atoms are not limited to those described above, and other supply sources such as a gas such as silane, propane, and acetylene may be used.

(Embodiment 2) As Embodiment 2 of the present invention, an example in which hexagonal silicon carbide is grown on a carbon plane (C plane) of hexagonal silicon carbide will be described.

In the second embodiment, a single crystal of 6H or 4H hexagonal silicon carbide having a 3.5 ° off-cut surface in the (Equation 5) direction of the (Equation 2) plane (C plane) A substrate is used. This substrate was introduced into a molecular beam epitaxy apparatus and cleaned as in the first embodiment. In this case, a certain surface rearrangement structure was not confirmed. This is presumably because the (Equation 2) plane (C plane) does not have a particularly stable and clean surface rearrangement structure.

Next, when silicon and carbon are sequentially supplied in the same manner as in the first embodiment, first, when silicon atoms for a 17/9 atomic layer are supplied to the surface of the substrate, as shown in FIG. A 3 × 3 surface rearrangement structure results. Also, when about the same number of carbon atoms as the above silicon atoms are supplied, the RHEED diffraction streak showing the 3 × 3 surface rearrangement structure is weakened and approaches a 1 × 1 pattern, which corresponds to the number of atoms of about 4 atomic layers. Flow growth of hexagonal silicon carbide occurs.

Hereinafter, by repeating the supply of silicon and the supply of carbon, the surface rearrangement structure changes between 3.times.3 and 1.times.1, and a highly crystalline hexagonal crystal having a smooth surface is obtained. A silicon carbide homoepitaxial thin film was obtained.

As described above, when crystal growth of hexagonal silicon carbide is performed on the C-plane of hexagonal silicon carbide, supply control of silicon atoms and carbon atoms is different from that of the first embodiment.
By supplying silicon atoms and carbon atoms so that silicon atoms become slightly excessive, a silicon carbide thin film having a favorable crystal structure can be formed at a relatively low temperature.

In the second embodiment as well, various modifications as described in the first embodiment are possible.

(Embodiment 3) As Embodiment 3 of the present invention, an example in which cubic silicon carbide is grown on a silicon surface (Si surface) of hexagonal silicon carbide will be described.

In the third embodiment, (000
1) A single-crystal substrate of 6H or 4H silicon carbide having a 3.5 ° off-cut plane in the (Formula 1) direction of the plane (Si plane) is used. This substrate was introduced into a molecular beam epitaxy apparatus and heated to 1100 ° C. for cleaning in the same manner as in the first embodiment. In this case, high energy reflected electron diffraction (RHE)
ED), it was confirmed that the surface had a surface rearrangement structure of √3 × √3 (FIG. 4) as in the first embodiment.

Next, crystal growth is performed in the same manner as in the first embodiment except that the substrate temperature and the supply amounts of silicon and carbon are different. That is, by lowering the temperature of the substrate, 9
After maintaining the temperature at 00 ° C., when silicon is supplied first, silicon atoms of １ ／ atomic layer are supplied as in the first embodiment, whereby the surface rearrangement structure of √3 × 構造 3 is more improved. Although it is clearly observed, when the supply of silicon is further continued, as shown in FIG. 7, a 3 × 3 surface rearrangement structure in which an excessive number of silicon atoms corresponding to a 16/9 atomic layer is deposited on the terraces. State. When about the same number of carbon atoms as the silicon atoms are supplied, the RHEED diffraction streak showing the 3 × 3 surface rearrangement structure is weakened, and the 1 × 3
Step pattern growth of cubic silicon carbide (111), which is close to one pattern and corresponds to the number of atoms of about 4 atomic layers, occurs.

Here, the cubic crystal grows instead of the hexagonal crystal as in the first and second embodiments because the substrate temperature is kept at 900 ° C. At such a relatively low temperature, the degree of surface diffusion of silicon atoms deposited on the surface of the terrace 4 is low, and when carbon atoms are supplied, the cubic crystal which is relatively stable at the above temperature on the terrace 4 when the carbon atoms are supplied. Cubic silicon carbide can be heteroepitaxially grown on hexagonal silicon carbide as described above because complete step flow growth in which crystallization occurs near the step edge 5 is not performed.

Thereafter, by repeating the supply of silicon and the supply of carbon, the surface rearrangement structure is changed from 3 × 3 to √3
A good crystallinity cubic silicon carbide heteroepitaxial thin film having a smooth surface was obtained while changing between × 、 １3 and 1 × 1.

As described above, silicon carbide is supplied at a relatively low temperature by supplying silicon atoms and carbon atoms so that silicon atoms become slightly excessive, thereby forming a cubic silicon carbide thin film. Can be easily done. In particular, as described above, cubic silicon carbide is grown on a hexagonal silicon carbide substrate having the (0001) plane off-cut surface in the (Equation 1) direction by step flow to obtain a single-phase cubic crystal without twins. Silicon carbide can be crystal-grown.
More specifically, when cubic silicon carbide was grown to a thickness of, for example, 20 μm, a heteroepitaxial thin film having a defect-free single crystal surface over a range of 1 mm square or more was obtained.

Note that, regardless of whether a hexagonal silicon carbide substrate of 6H or 4H is used as the original silicon carbide substrate,
Similar crystal growth was performed. The (Equation 2) plane (C
A hexagonal silicon carbide substrate having an off-cut surface of 3.5 ° or the like in the (Formula 1) direction of the (surface) may be used. Further, a cubic silicon carbide substrate may be used as the original silicon carbide substrate. In this case, (00) in the above hexagonal silicon carbide
The (111) plane (Si plane) or the (112) plane (C plane) in the <112> direction, which corresponds to the off-cut plane in the (numerical 1) direction of the (01) plane or the (numerical 2) plane. If a cubic silicon carbide substrate having a cut surface is used, a cubic silicon carbide thin film having a similarly favorable crystal structure can be formed.
Here, as described above, the (Formula 2) plane (C plane) of the hexagonal crystal is used.
Also, when cubic silicon carbide is crystallized using the cubic (111) plane (Si plane) or the (Equation 3) plane (C plane), as an index for controlling the supply of silicon atoms and carbon atoms, A 1 × 1 × 3 × 3 surface rearrangement structure can be applied. Further, even when a hexagonal or cubic silicon carbide substrate having an off-cut surface in the (Equation 5) direction or the <110> direction is used, twins are likely to occur in the formed cubic silicon carbide crystal. By supplying an excessive amount of silicon atoms, the effect of easily crystallizing at a relatively low temperature can be obtained.

In the third embodiment, in addition to the above, various modifications as described in the first embodiment are possible.

(Embodiment 4) When crystal growth of hexagonal or cubic silicon carbide is performed in the same manner as in Embodiments 1 to 3, ammonia gas is supplied at a pressure of about 2 × 10 ⁻⁸ Torr. . As a result, at least 5 × 10 ¹⁸ / cm ⁻³ , and depending on conditions such as the substrate temperature, 10 ¹⁹
/ Cm ^-3 or more, or 5 × 10 ¹⁹ / cm ^-3 or more in the lattice substitution position, and a carbonized crystal thin film having good crystallinity without film roughness or the like could be formed. .
That is, by supplying silicon atoms and carbon atoms so that silicon atoms become slightly excessive, crystallization can be performed while keeping the substrate temperature low as described above.
High-density doping can be easily performed by efficiently introducing nitrogen atoms into the lattice substitution positions of the silicon carbide crystal.

(Embodiment 5) Prior to silicon carbide crystal growth, as shown in FIG. 8, a mask pattern made of a silicon oxide film 12 having an opening 12a formed in the surface of hexagonal silicon carbide substrate 11, as shown in FIG. Was formed. More specifically, a silicon oxide film 12 having a thickness of, for example, 500 nm is sputter-deposited on, for example, the surface of a hexagonal silicon carbide substrate 11 and patterned by photolithography using buffered hydrofluoric acid etching to form an opening 12a. did.

The above-mentioned hexagonal silicon carbide substrate 11 is introduced into a CVD growth chamber, and as in the case of using the molecular beam epitaxy apparatus in the above-described first to third embodiments, silicon atoms are added so that silicon atoms become slightly excessive. And the supply of carbon atoms were controlled to epitaxially grow a silicon carbide crystal. This allows
A flat silicon carbide thin film with good crystallinity could be selectively formed only in the region of the opening 12a. That is,
Since the temperature of the substrate can be kept low as described above, the silicon oxide film 12 is not damaged.
Silicon carbide can be easily grown only in a desired region of the substrate.

The material of the mask pattern is not limited to the silicon oxide film as described above. That is, since the substrate temperature can be kept low, various known mask materials can be used.

Further, the present invention is not limited to the case where a CVD apparatus is used.
Masking as described above may be performed when using a molecular beam epitaxy apparatus as in the first to third embodiments.

(Embodiment 6) An example of forming a silicon carbide substrate in which hexagonal silicon carbide crystals and cubic silicon carbide crystals are stacked will be described. In this example, a stacked structure in which a cubic silicon carbide crystal layer is interposed between hexagonal silicon carbide crystal layers is formed.

First, as shown in FIG. 9A, similar to the fifth embodiment, the silicon oxide film
2 in the (Equation 1) direction of the {0001} plane
Cubic silicon carbide crystal 3 on 6H or 4H hexagonal silicon carbide crystal 31 having off-cut surface 31b of
Form 2 Next, as shown in FIG. 9B, the silicon oxide film 12 is removed by a buffer hydrofluoric acid treatment to form a pre-processed substrate 33.

The pre-processed substrate 33 is introduced into a CVD growth chamber, and normal step flow growth is performed. More specifically, for example, the atmospheric pressure is atmospheric pressure, the substrate temperature is 1600 ° C., hydrogen as a carrier gas is 2 slm, and silane is 1 scc.
m and propane are grown under a CVD condition of 1 sccm.

As a result, as shown in FIG. 9C, the hexagonal silicon carbide crystal 3 having a thickness of about 3 μm in one hour, for example, is obtained.
4 and cubic silicon carbide crystal 35 are grown in a step flow. In this case, since the substrate temperature is relatively high, step flow growth of the same crystal structure as the original crystal structure is performed at each of the step edges 31a and 32a. In other words, hexagonal silicon carbide crystal 34 grows from hexagonal step edge 31a, and cubic step edge 32a.
A cubic silicon carbide crystal 35 grows from a, and crystallization proceeds in the direction of the respective oblique interfaces. Therefore, cubic silicon carbide crystal 3 between hexagonal silicon carbide crystals 34, 34
5 is formed. It was confirmed that the interface between hexagonal silicon carbide crystal 34 and cubic silicon carbide crystal 35 formed in this manner was a steep interface having no defects and complete crystallinity.

As described above, cubic silicon carbide is grown by step flow growth using an off-cut substrate having a region in which cubic silicon carbide crystals are formed in advance and a region in which hexagonal silicon carbide crystals are formed. It is easy to form a hexagonal silicon carbide crystal on a crystal, to form a cubic silicon carbide crystal on a hexagonal silicon carbide crystal, and to alternately form both.

It should be noted that even when a hexagonal silicon carbide substrate of 6H or 4H is used as the original hexagonal silicon carbide substrate for forming the pre-processed substrate, a laminated structure can be similarly formed. .

The off-cut angle (tilt angle) of the original silicon carbide substrate is not limited to 4 ° as described above, but may be 0.05 °.
If the angle is not less than about 10 ° and not more than about 10 °, the above-described laminated structure can be easily formed by step flow growth.

The formation of the pre-processed substrate and the step flow growth of the pre-processed substrate are performed by a molecular beam epitaxy apparatus and a CV
Not only the method using the D apparatus but also various known crystal growth methods can be applied.

Further, the pre-processed substrate is the same as that of the fifth embodiment.
By forming in the same manner as described above, it is easy to form a pre-processed substrate on which a single-phase cubic silicon carbide crystal without twins is formed as described above. However, the present invention is not limited to this. What is necessary is that a good crystallinity region having a different crystal system is formed.
By using a pre-processed substrate in which a region having a different crystal system from another region is formed at a substrate temperature of about 1800 ° C. or less, a laminated structure with good crystallinity at an interface can be easily formed.

(Embodiment 7) Another example of forming a silicon carbide substrate in which a hexagonal silicon carbide crystal and a cubic silicon carbide crystal are stacked in the same manner as in the sixth embodiment will be described. In this example, a stacked structure in which a hexagonal silicon carbide crystal layer is interposed between cubic silicon carbide crystal layers is formed.

First, a cubic silicon carbide crystal 42 having a thickness of, for example, 30 nm is grown over the entire surface of hexagonal silicon carbide crystal 41 as shown in FIG. Let it.

Next, the mask pattern 43 of the metal mask
As shown in FIG. 10 (b), oxygen ions are implanted into only a predetermined region 42a of the cubic silicon carbide crystal 42 at an acceleration voltage of 30 keV and a dose of about 10 ¹⁶ cm ^−2. Further, wet oxidation is performed for 1 hour in an oxygen atmosphere at 1100 ° C. Thereby, the area 4
The cubic silicon carbide crystal 42 in the portion 2a becomes a complete oxide film.

Thereafter, when a buffered hydrofluoric acid etching process is performed, the portion of the region 42a that has become the oxide film is removed, and as shown in FIG.
Pretreatment substrate 44 having hexagonal silicon carbide crystal 41 exposed in part of 2 is formed.

Therefore, as in the sixth embodiment, when the pre-processed substrate 44 is introduced into a CVD growth chamber to grow a crystal, as shown in FIG.
A stacked structure in which hexagonal silicon carbide crystal 45 is interposed between 6, 46 is formed.

(Embodiment 8) An example in which a silicon carbide substrate having a 6H hexagonal silicon carbide crystal layer interposed between 4H hexagonal silicon carbide crystal layers will be described.

First, a single crystal substrate of 4H hexagonal silicon carbide having a 1 ° off-cut surface in the (Formula 1) direction of the (0001) plane (Si plane) is masked with a graphite plate or graphite sheet having a predetermined mask pattern. Then, it is introduced into a CVD growth chamber, and step flow growth is performed only in a partial region corresponding to the mask pattern. More specifically, for example, the pressure is set to atmospheric pressure, the substrate temperature is set to 1500 ° C., hydrogen is used as a carrier gas at 2 slm, silane is set at 1 sccm, and propane is grown at a CVD condition of 1 sccm for 10 minutes.
In a predetermined region on the surface of the H hexagonal silicon carbide substrate,
A 6H hexagonal silicon carbide thin film having a thickness of about 0.5 μm is formed to be a pre-processed substrate. In this case, the substrate is 4H silicon carbide as described above, but the substrate temperature is 15
The 6H silicon carbide crystal grows when the temperature is kept at 00 ° C. and the terrace width is relatively wide (off-cut angle is 1 °). That is, in the case of the substrate temperature or the like as described above, the degree of surface diffusion of silicon atoms and carbon atoms on the terrace surface becomes insufficient, and complete step flow growth for crystallization near the step edge is not performed. Crystallization of 6H silicon carbide, which is relatively stable at the above-mentioned temperature, is likely to occur, resulting in heteroepitaxial growth.

Next, the pre-processed substrate is introduced into a CVD growth chamber, and normal step flow growth is performed. More specifically, for example, the atmospheric pressure is atmospheric pressure, the substrate temperature is 1600 ° C.,
2 slm of hydrogen as carrier gas and 1 sc of silane
cm and propane are grown under CVD conditions of 1 sccm.

Thus, for example, 4H and 6H hexagonal silicon carbide crystals having a thickness of about 3 μm are grown in a step flow in one hour, for example. In this case, since the substrate temperature is high, step flow growth of the same crystal structure as the original crystal structure is performed at each step edge. That is, 4
From the H or 6H step edge, 4H or 6H hexagonal silicon carbide crystals grow, respectively, and crystallization proceeds in the direction of the oblique interface. Therefore, a laminated structure in which 6H hexagonal silicon carbide crystals are interposed between 4H hexagonal silicon carbide crystals is formed.

The stacking of the silicon carbide crystal layers of different crystal systems is not limited to that described in the sixth to eighth embodiments, and silicon carbide crystal regions of different crystal systems are partially formed in advance. By performing step flow growth using an off-cut substrate, a plurality of silicon carbide crystal layers of various crystal systems can be easily stacked.

(Embodiment 9) Under the CVD conditions shown in Embodiment 8, the substrate temperature is 1600 ° C., and the substrate is
From the {0001} plane of the hexagonal silicon carbide crystal,
When a crystal was grown to a thickness of 5 μm as an off-cut surface inclined by 3.5 ° in the direction, step bunching hardly occurred, and a surface roughness of 10 nm or less was obtained. On the other hand, when the off-cut direction was set to the above (Equation 5) under the same conditions, the surface roughness showed a roughness of several tens nm or more after the growth of a film thickness of 5 μm by step bunching. Note that the formed silicon carbide crystals had good crystallinity.

That is, when the increase in surface roughness due to step bunching poses a problem, for example, in the case of using for fine processing, the problem is solved by using the off-cut direction in the above (Formula 1) direction. can do.

The same effect can be obtained not only in the case of silicon carbide of 6H but also in the case of silicon carbide of another crystal system.

(Embodiment 10) Embodiments 6 to 8
An example of a semiconductor device using a silicon carbide substrate as shown in FIG.

As shown in FIG.
A cubic silicon carbide layer 52 is stacked on a semi-insulating hexagonal silicon carbide substrate 51 via a steep hetero interface, and the surface of the cubic silicon carbide layer 52 is doped with nitrogen (N). Hexagonal silicon carbide layer 53 is laminated.
The layered structure as described above is formed by the method described in the sixth to eighth embodiments.

A source electrode 54, a drain electrode 55, and a gate electrode 56 are provided in the information of the doped hexagonal silicon carbide layer 53. The source electrode 54 and the drain electrode 55 are formed by vapor deposition of nickel (Ni) and photolithography, and are alloyed by heat treatment with argon (Ar) at 1000 ° C. for 3 minutes. These source electrode 54 and drain electrode 55
Is ohmic-joined to the doped hexagonal silicon carbide layer 53. On the other hand, the gate electrode is formed by vapor deposition of gold (Au) and photolithography, and is Schottky-bonded to the doped hexagonal silicon carbide layer 53.

The two-dimensional electron layer 57 formed of carriers at the interface between the cubic silicon carbide layer 52 and the doped hexagonal silicon carbide layer 53 is composed of a source electrode 54 and a drain electrode 5.
5 affects the electrical conduction. That is, the two-dimensional electron layer 57 is controlled in accordance with the bias potential applied to the gate electrode 56, and the source electrode 54, the drain electrode 5
The conduction state between 5 changes, and it operates as a high-speed FET. Specifically, in a device having a gate interval of 1 μm,
A gain was observed at a frequency of 10 MHz or more.

[0097]

The present invention is embodied in the form described above and has the following effects.

That is, when a silicon carbide crystal is grown in a step flow, silicon atoms and carbon atoms are supplied so that silicon atoms become slightly excessive, so that a silicon carbide thin film having a favorable crystal structure at a relatively low temperature. Can be epitaxially grown, and crystal growth in a selective region by masking and high-concentration nitrogen doping can be easily performed. In addition, by performing step flow growth using an off-cut substrate having regions in which mutually different silicon carbide crystals are formed in advance, a silicon carbide substrate in which silicon carbide crystals of different crystal systems are stacked is formed. Can be easily done. Further, by forming a semiconductor element using a silicon carbide substrate in which silicon carbide crystals of different crystal systems are stacked, a semiconductor element capable of high-speed operation can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view conceptually showing an example of a manufacturing method of the present invention.

FIG. 2 is an explanatory view conceptually showing growth of a silicon carbide crystal on an off-cut surface in an example of the manufacturing method of the present invention.

FIG. 3 is an explanatory diagram conceptually showing growth of a silicon carbide crystal on an off-cut surface in an example of the manufacturing method of the present invention.

FIG. 4 is an explanatory view showing a √3 × √3 surface rearrangement state of a hexagonal silicon carbide (0001) plane (Si plane).

FIG. 5 shows an example of the surface of the silicon carbide thin film of the present invention.
It is explanatory drawing which represented the EM photograph typically.

FIG. 6 is an explanatory view showing a 3 × 3 surface rearrangement state of the (Formula 2) plane (C plane) of hexagonal silicon carbide.

FIG. 7 is an explanatory diagram showing a 3 × 3 surface rearrangement state of a hexagonal silicon carbide (0001) plane (Si plane).

FIG. 8 is a perspective view showing selective growth of a silicon carbide thin film in an example of the manufacturing method of the present invention.

FIG. 9 is an explanatory diagram showing a manufacturing process of the silicon carbide substrate according to the sixth embodiment.

FIG. 10 is an explanatory diagram showing a manufacturing process of the silicon carbide substrate of the seventh embodiment.

FIG. 11 is a cross-sectional view showing a configuration of a semiconductor device of a tenth embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 1a Silicon carbide crystal growth surface 2 Silicon atom 3 Bond 4 Terrace 5 Step edge 6 Step flow growth 6a, 6b Growth part 6d-6f Growth part 11 Hexagonal silicon carbide substrate 12 Silicon oxide film 12a Opening 31 Hexagonal silicon carbide Crystal 31a Step edge 31b Off-cut surface 32 Cubic silicon carbide crystal 32a Step edge 33 Pretreatment substrate 34 Hexagonal silicon carbide crystal 35 Cubic silicon carbide crystal 41 Hexagonal silicon carbide crystal 42 Cubic silicon carbide crystal 42a Area 43 Mask pattern 44 Pretreatment substrate 45 Hexagonal silicon carbide crystal 46 Cubic silicon carbide crystal 51 Hexagonal silicon carbide substrate 52 Cubic silicon carbide layer 53 Doped hexagonal silicon carbide layer 54 Source electrode 55 Drain electrode 56 Gate electrode 57 Two-dimensional electron layer

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C30B 25/18 C30B 25/18 25/20 25/20 29/36 29/36 H01L 21/205 H01L 21/205 29/16 29 / 16 29/778 29/80 H 21/338 29/812

Claims (40)

[Claims] 1. A method of manufacturing a silicon carbide substrate, comprising: supplying silicon atoms and carbon atoms to a surface of a silicon carbide substrate to grow a silicon carbide crystal; Is an off-cut surface inclined at least 0.05 ° and at most 10 ° from any one of the {0001} plane of the hexagonal silicon carbide crystal and the {111} plane of the cubic silicon carbide crystal. In addition, on the surface of the silicon carbide substrate, the supply amounts of the silicon atoms and the carbon atoms are controlled so that the silicon atoms are excessive with respect to the carbon atoms. Method. 2. The method for manufacturing a silicon carbide substrate according to claim 1, wherein said silicon carbide crystal to be grown is a hexagonal silicon carbide crystal, and said silicon carbide substrate is grown before said silicon carbide crystal starts growing. A method for manufacturing a silicon carbide substrate, characterized in that the surface is an off-cut surface inclined substantially in the following (formula 1) direction from the {0001} plane of the hexagonal silicon carbide crystal. (Equation 1) 3. The method for manufacturing a silicon carbide substrate according to claim 1, wherein said silicon carbide crystal to be grown is a cubic silicon carbide crystal, and said silicon carbide substrate is grown before said silicon carbide crystal starts growing. An off-cut surface whose surface is inclined from the {0001} plane of the hexagonal silicon carbide crystal substantially in the (Equation 1) direction, and an off-cut surface whose surface is inclined substantially in the <112> direction from the {111} plane of the cubic silicon carbide crystal A method for manufacturing a silicon carbide substrate, characterized in that the surface is any one selected from surfaces. 4. The method for manufacturing a silicon carbide substrate according to claim 1, wherein the surface of the silicon carbide substrate before the start of the growth of the silicon carbide crystal is a (0001) plane of a hexagonal silicon carbide crystal, The silicon carbide crystal to be grown is a hexagonal silicon carbide crystal, and the supply of the silicon atoms and the carbon atoms is controlled by controlling the surface structure of the silicon carbide substrate to be approximately 1 × 1 surface structure and approximately {3 ×} A method for manufacturing a silicon carbide substrate, wherein the method is performed so as to be between three surface rearranged structures. 5. The method for manufacturing a silicon carbide substrate according to claim 1, wherein a surface of said silicon carbide substrate before starting growth of said silicon carbide crystal has a (0001) plane of hexagonal silicon carbide crystal and a cubic crystal Any one of the (111) planes of the silicon carbide crystal, wherein the silicon carbide crystal to be grown is a cubic silicon carbide crystal, and the supply of the silicon atoms and the carbon atoms is controlled by A method for manufacturing a silicon carbide substrate, wherein the method is performed such that the surface structure of the silicon carbide substrate is between a substantially 1 × 1 surface structure and a substantially 3 × 3 surface rearrangement structure. 6. The method of manufacturing a silicon carbide substrate according to claim 1, wherein the surface of the silicon carbide substrate before the start of the growth of the silicon carbide crystal is the following (formula 2) plane of the hexagonal silicon carbide crystal. The silicon carbide crystal to be grown is a hexagonal silicon carbide crystal, and the control of the supply amounts of the silicon atoms and the carbon atoms is such that the surface structure of the silicon carbide substrate is approximately 1 × 1 and approximately 3 ×. A method for manufacturing a silicon carbide substrate, wherein the method is performed so as to be between three surface rearranged structures. (Equation 2) 7. The method of manufacturing a silicon carbide substrate according to claim 1, wherein a surface of said silicon carbide substrate before the start of growth of said silicon carbide crystal is formed of said hexagonal silicon carbide crystal, and Any one of the following (formula 3) planes of the cubic silicon carbide, wherein the silicon carbide crystal to be grown is a cubic silicon carbide crystal, and the supply amounts of the silicon atoms and the carbon atoms are controlled. Is performed such that the surface structure of the silicon carbide substrate is between a substantially 1 × 1 surface structure and a substantially 3 × 3 surface rearrangement structure. (Equation 3) 8. The method for manufacturing a silicon carbide substrate according to claim 1, wherein the supply of the silicon atoms and the carbon atoms is controlled on a surface of the silicon carbide substrate, and a silicon-silicon bond is provided on the surface. The number of excess silicon atoms bonded by the method is less than or equal to 5 atomic layers in the silicon carbide crystal. 9. The method of manufacturing a silicon carbide substrate according to claim 1, wherein at least one of the silicon atoms and the carbon atoms supplied to the surface of the silicon carbide substrate is intermittently supplied. A method for manufacturing a silicon carbide substrate. 10. The method of manufacturing a silicon carbide substrate according to claim 9, wherein said silicon atoms are supplied continuously while said carbon atoms are supplied intermittently. Production method. 11. The method of manufacturing a silicon carbide substrate according to claim 9, wherein said silicon atoms and said carbon atoms are intermittently supplied at mutually different timings, and only said silicon atoms are supplied. The surface rearrangement structure of the silicon carbide substrate is substantially √3 × √3 surface rearrangement structure;
The carbon atoms are supplied until the surface rearrangement structure of the silicon carbide substrate becomes substantially a 1 × 1 surface structure, while the carbon atoms are supplied until any surface rearrangement structure selected from the × 3 surface rearrangement structure is obtained. A method for manufacturing a silicon carbide substrate, wherein the method is performed. 12. The method for manufacturing a silicon carbide substrate according to claim 1, wherein said silicon carbide crystal is formed while maintaining a surface temperature of said silicon carbide substrate at 600 ° C. or more and 1300 ° C. or less. A method for manufacturing a silicon carbide substrate, comprising: growing a silicon carbide substrate. 13. The method for manufacturing a silicon carbide substrate according to claim 12, wherein the silicon carbide crystal is doped with nitrogen by supplying a reactive nitrogen-containing gas to the surface of the silicon carbide substrate. A method for manufacturing a silicon carbide substrate. 14. The method of manufacturing a silicon carbide substrate according to claim 12, wherein said silicon carbide substrate is covered with a masking member having a predetermined masking pattern, and said silicon carbide crystal is only covered in a predetermined region of said silicon carbide substrate. A method for manufacturing a silicon carbide substrate, comprising: growing a silicon carbide substrate. 15. The method for manufacturing a silicon carbide substrate according to claim 14, wherein said masking member is a silicon oxide thin film. 16. The method of manufacturing a silicon carbide substrate according to claim 1, wherein the surface of said silicon carbide substrate at the start of growth of said silicon carbide crystal has a (0001) plane of hexagonal silicon carbide crystal and a cubic crystal Any one of the {111} planes of the silicon carbide crystal, and prior to growing the silicon carbide crystal, the surface rearrangement structure of the silicon carbide substrate is substantially {3 × {3 surface rearrangement} A method for manufacturing a silicon carbide substrate, comprising cleaning a surface of the silicon carbide substrate so as to have a structure. 17. The method for manufacturing a silicon carbide substrate according to claim 16, wherein the silicon carbide substrate is selected from a group consisting of a hydrogen atmosphere and a vacuum.
The temperature of the surface of the silicon carbide substrate is 800 ° C. or higher, and
A method for manufacturing a silicon carbide substrate, wherein the cleaning is performed by heating the silicon carbide substrate to 1300 ° C. or lower. 18. A method for manufacturing a silicon carbide substrate in which silicon carbide crystals of different crystal systems are stacked, wherein a region where the first silicon carbide crystal is formed and a crystal different from the first silicon carbide crystal A pre-processed substrate having a region in which a second silicon carbide crystal is formed, wherein the crystal planes of the first silicon carbide crystal and the second silicon carbide crystal are aligned with respect to the surface of the pre-processed substrate. Forming the inclined pretreatment substrate; and performing step flow growth of the first silicon carbide crystal and the second silicon carbide crystal on the pretreatment substrate, thereby forming the first silicon carbide crystal, Forming a stacked structure of silicon carbide crystals having different crystal systems grown from the second silicon carbide crystal. 19. The method for manufacturing a silicon carbide substrate according to claim 18, wherein the step of forming the pre-processed substrate is performed in a predetermined region on the original silicon carbide substrate having the first silicon carbide crystal. A method of manufacturing a silicon carbide substrate, comprising a step of growing a second silicon carbide crystal in a step flow. 20. The method for manufacturing a silicon carbide substrate according to claim 18, wherein the step of forming the pre-processed substrate comprises: forming a silicon carbide substrate on the original silicon carbide substrate having the first silicon carbide crystal;
A step of growing the second silicon carbide crystal in a step flow; and a step of removing a part of a predetermined region in the second silicon carbide crystal to partially expose the first silicon carbide crystal. A method for manufacturing a silicon carbide substrate, comprising: 21. The method for manufacturing a silicon carbide substrate according to claim 18, wherein said first silicon carbide crystal has a {0001} plane inclined with respect to said surface of said pretreatment substrate. Silicon carbide, wherein the second silicon carbide crystal is a cubic silicon carbide crystal formed by performing step flow growth on a predetermined region of the first silicon carbide crystal. Substrate manufacturing method. 22. The method of manufacturing a silicon carbide substrate according to claim 18, wherein said first silicon carbide crystal has a 4H hexagonal carbide having a {0001} plane inclined with respect to said surface of said pretreatment substrate. In addition to being a silicon crystal, the second silicon carbide crystal is a 6H hexagonal silicon carbide crystal formed by performing step flow growth on a predetermined region of the first silicon carbide crystal. A method for manufacturing a silicon carbide substrate. 23. The method of manufacturing a silicon carbide substrate according to claim 18, wherein a surface of said first silicon carbide crystal is at least 0.05 ° and at least 10 ° from a {0001} plane of a hexagonal silicon carbide crystal. The second silicon carbide crystal has a tilted off-cut surface, and the second silicon carbide crystal has a shape such that silicon atoms are excessive with respect to carbon atoms in a predetermined region on the surface of the first silicon carbide crystal. A method for manufacturing a silicon carbide substrate, comprising a silicon carbide crystal formed by controlling the supply of atoms and the carbon atoms. 24. The method for manufacturing a silicon carbide substrate according to claim 23, wherein a surface of said first silicon carbide crystal is inclined substantially in said (Equation 1) direction from a {0001} plane of said hexagonal silicon carbide crystal. A method of manufacturing a silicon carbide substrate, wherein the silicon carbide substrate has an off-cut surface. 25. The method for manufacturing a silicon carbide substrate according to claim 23, wherein the temperature of the surface of said first silicon carbide crystal is maintained at 600 ° C. or higher and 1800 ° C. or lower. 2
A method for manufacturing a silicon carbide substrate, comprising: growing a silicon carbide crystal. 26. A silicon carbide substrate having a silicon carbide crystal grown by supplying silicon atoms and carbon atoms to the surface of the silicon carbide substrate, wherein the surface of the silicon carbide substrate before the start of the growth of the silicon carbide crystal Is an off-cut surface tilted by 0.05 ° or more and 10 ° or less from any one of the {0001} plane of the hexagonal silicon carbide crystal and the {111} plane of the cubic silicon carbide crystal. The silicon carbide crystal is a silicon carbide crystal grown by controlling the supply amounts of the silicon atoms and the carbon atoms such that silicon atoms are excessive with respect to carbon atoms on the surface of the silicon carbide substrate. A silicon carbide substrate, characterized in that: 27. The silicon carbide substrate according to claim 26, wherein the grown silicon carbide crystal is a cubic silicon carbide crystal, and the surface of the silicon carbide substrate before the start of the growth of the silicon carbide crystal has a hexagonal shape. An off-cut surface inclined substantially in the (Formula 1) direction from the {0001} plane of the crystalline silicon carbide crystal, and the silicon carbide crystal has a defect-free single crystal surface over a range of 1 mm square or more. Silicon carbide substrate. 28. The silicon carbide substrate according to claim 26, wherein a reactive nitrogen-containing gas is supplied to a surface of said silicon carbide substrate during the growth of said silicon carbide crystal, whereby a lattice substitution position in said silicon carbide crystal is provided. 5 × 10 ¹⁸ pieces / cm ³
A silicon carbide substrate comprising the above nitrogen. 29. A silicon carbide substrate having a silicon carbide crystal grown by supplying silicon atoms and carbon atoms to a surface of the silicon carbide substrate, wherein the silicon carbide crystal is formed before the growth of the silicon carbide crystal. A silicon carbide substrate having a crystal system different from the crystal system of the silicon carbide substrate, wherein the crystal is grown in a predetermined selective region on the silicon carbide substrate. 30. A silicon carbide substrate having a silicon carbide crystal in which silicon atoms and carbon atoms are supplied to the surface of a silicon carbide substrate and grown in a step flow, wherein the silicon carbide crystal is a hexagonal silicon carbide crystal, and In addition to being selected from cubic silicon carbide crystals, the surface of the silicon carbide crystal has a step edge in the following (Formula 4) direction in the hexagonal silicon carbide crystal, and a [110] direction in the cubic silicon carbide crystal. A silicon carbide substrate having any one of step edges selected from step edges. (Equation 4) 31. A silicon carbide substrate having a silicon carbide crystal in which silicon atoms and carbon atoms are supplied to the surface of a silicon carbide substrate and grown in a step flow, wherein the silicon carbide crystal is a hexagonal silicon carbide crystal; Any one of cubic silicon carbide crystals, wherein the surface of the silicon carbide crystal before the start of the growth of the silicon carbide crystal is inclined from the {0001} plane of the hexagonal silicon carbide crystal in the (Formula 1) direction. Any one of an off-cut surface and an off-cut surface inclined in the <112> direction from the {111} plane of the cubic silicon carbide crystal, and the silicon carbide crystal has a surface roughness of 10 nm or less. A silicon carbide substrate, characterized in that: 32. A single-phase first silicon carbide crystal and a second phase silicon carbide crystal each having a different crystal system and a single phase, wherein the first silicon carbide crystal and the second silicon carbide crystal Are stacked via a steep interface of the crystal structure. 33. The silicon carbide substrate according to claim 32, wherein said first silicon carbide crystal and said second silicon carbide crystal are:
A silicon carbide substrate, wherein silicon carbide crystals in each of the above regions in a pretreatment substrate having regions in which silicon carbide crystals having different crystal systems are formed are formed by step flow growth. 34. The silicon carbide substrate according to claim 33, wherein said pre-processed substrate is a {0001} of hexagonal silicon carbide crystal.
An original silicon carbide substrate having an off-cut surface inclined at an angle of 0.05 ° or more and 10 ° or less from a surface, and the silicon substrate described above such that silicon atoms are excessive with respect to carbon atoms on the surface of the original silicon carbide substrate. A silicon carbide substrate, wherein regions of silicon carbide crystals having different crystal systems are formed by atoms and silicon carbide crystals formed by controlling the supply amount of carbon atoms. 35. The silicon carbide substrate according to claim 34, wherein a surface of said original silicon carbide substrate is an off-cut surface inclined substantially in said (Equation 1) direction from a {0001} plane of a hexagonal silicon carbide crystal. A silicon carbide substrate, comprising: 36. The silicon carbide substrate according to claim 32, wherein said first silicon carbide crystal and said second silicon carbide crystal are a hexagonal silicon carbide crystal having a {0001} plane, and {111}. One of the cubic silicon carbide crystals having a surface and the other, and the first silicon carbide crystal,
And a silicon carbide substrate, wherein one of the second silicon carbide crystals is laminated on the other surface. 37. The silicon carbide substrate according to claim 32, wherein said first silicon carbide crystal and said second silicon carbide crystal are a 6H hexagonal silicon carbide crystal having a {0001} plane, and a {0001} One of the 4H hexagonal silicon carbide crystal having the｝ plane and the other, and the other is stacked on the surface of one of the first silicon carbide crystal and the second silicon carbide crystal. A silicon carbide substrate. 38. The silicon carbide substrate according to claim 32, wherein said first silicon carbide crystal includes two layers of said first silicon carbide crystal and one layer of said second silicon carbide crystal. A hexagonal silicon carbide crystal having a {0001} plane, while the second silicon carbide crystal is a cubic silicon carbide crystal having a {111} plane, and the two-layer first silicon carbide crystal; The second of the above one layer
And a silicon carbide crystal are stacked such that the one layer of the second silicon carbide crystal is located between the two layers of the first silicon carbide crystal. 39. The silicon carbide substrate according to claim 32, comprising two layers of said first silicon carbide crystal and one layer of said second silicon carbide crystal, wherein said first silicon carbide crystal is 4H with {0001} face
The second silicon carbide crystal is a 6H hexagonal silicon carbide crystal having a {0001} plane, while the second silicon carbide crystal is a hexagonal silicon carbide crystal. A silicon carbide substrate, wherein two silicon carbide crystals are stacked such that the one layer of second silicon carbide crystal is located between the two layers of first silicon carbide crystal. 40. The first silicon carbide crystal and the second silicon carbide crystal having different crystal systems from each other and each including a single-phase first silicon carbide crystal and a second silicon carbide crystal. Has a silicon carbide substrate stacked via a steep interface of a crystal structure.