JP2007284298A - Epitaxial silicon carbide single crystal substrate and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an epitaxial silicon carbide single crystal substrate having a high quality silicon carbide single crystal thin film with few defects on a silicon carbide single crystal substrate, and to provide a method for producing the same. <P>SOLUTION: The epitaxial silicon carbide single crystal substrate is produced by growing a silicon carbide single crystal thin film 2 for suppressing development of epitaxial defects on a silicon carbide single crystal substrate 1, followed by growing a silicon carbide single crystal thin film 3 which is a layer in which a device is formed on the silicon carbide single crystal thin film 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an epitaxial silicon carbide (SiC) single crystal substrate and a method for manufacturing the same.

  Silicon carbide (SiC) has attracted attention as an environmentally resistant semiconductor material because it is excellent in heat resistance and mechanical strength and is physically and chemically stable. In recent years, the demand for SiC single crystal substrates has increased as a substrate for high-frequency, high-voltage electronic devices.

  When manufacturing a power device, a high-frequency device, etc. using a SiC single crystal substrate, a SiC thin film is epitaxially grown on the substrate by a method called thermal CVD (thermochemical vapor deposition) or ion implantation is usually performed. In general, the dopant is directly implanted by the method, but in the latter case, annealing at a high temperature is required after the implantation, so that thin film formation by epitaxial growth is frequently used.

Micrographs of typical defects (epitaxial defects) observed when epitaxial growth is performed on a SiC single crystal substrate are shown in FIGS. 1 (a) to (c). The SiC single crystal substrate has a (0001) plane (Si plane). Fig. 1 (a) shows the succession of micropipe defects existing in the substrate. Recent research progress has made it relatively easy to obtain a substrate with 10 micropipes / cm ² or less. Therefore, epitaxial defects caused by micropipes are not becoming a big problem. The defects shown in FIGS. 1 (b) and (c) are defects found only on the epitaxial layer, and in particular, FIG. 1 (b) is often called a carrot defect, and FIG. 1 (c) is often called a comet defect. When these exist under the electrodes of the device, it is known to cause characteristic deterioration such as a decrease in breakdown voltage (Non-patent Document 1). The density of these defects is usually about 50 to 100 pieces / cm ² , but the device electrode area is increased to 1 to 2 mm square or more with the recent increase in output of devices. Therefore, one or more defects are present under the electrodes, degrading the device characteristics and reducing the yield.

The defects shown in Fig. 1 (b) and (c) occur because normal epitaxial growth is hindered by defects such as polishing scratches and minute irregularities present on the SiC single crystal substrate. The frequency often depends on the growth method. In general, a lateral CVD apparatus is often used for epitaxial growth. The CVD method has a simple apparatus configuration and can control growth by gas on / off, and is therefore a growth method with excellent controllability and reproducibility of the epitaxial film. FIG. 2 shows a typical growth sequence for the growth, together with the gas introduction timing. First, a substrate is set in a growth furnace, the inside of the growth furnace is evacuated, and hydrogen gas is introduced to adjust the pressure to 1 × 10 ^{4 to} 3 × 10 ⁴ Pa. Thereafter, the temperature of the growth furnace is raised while keeping the pressure constant, and the substrate is etched in hydrogen chloride by introducing hydrogen or hydrogen chloride at about 1400 ° C. for 10 to 30 minutes. This is for removing the altered layer on the surface of the substrate due to polishing or the like, and providing a clean surface. Thereafter, the temperature is raised to a growth temperature of 1500 to 1600 ° C., and SiH ₄ and C ₃ H ₈ that are raw material gases are introduced to start growth. The SiH ₄ flow rate is 4-5 cm ³ per minute, the C ₃ H ₈ flow rate is 1-3 cm ³ per minute, and the growth rate is 5-6 μm per hour. This growth rate is determined in consideration of productivity because the film thickness of the normally used epitaxial layer is about 10 μm. When the film is grown for a certain period of time and a desired film thickness is obtained, the introduction of SiH ₄ and C ₃ H ₈ is stopped, and the temperature is lowered with only hydrogen gas flowing. After the temperature has dropped to room temperature, the introduction of hydrogen gas is stopped, the growth chamber is evacuated, an inert gas is introduced into the growth chamber, the growth chamber is returned to atmospheric pressure, and the substrate is taken out.

  However, when epitaxial growth is performed by the above method, after the substrate etching in hydrogen or hydrogen chloride, there are still minute irregularities and roughness on the substrate, so when the source gas is introduced, Growth starts with minute irregularities and roughness. As a result, normal epitaxial growth is not performed, epitaxial defects such as those shown in FIGS. 1 (b) and 1 (c) occur, and the characteristics and yield of devices using such epitaxial films are reduced. become.

Therefore, it is a SiC epitaxial growth substrate that is expected to be applied to devices in the future. However, with the current technology, it is difficult to reduce the number of epitaxial defects to such an extent that the device characteristics and yield are not deteriorated. On the other hand, in SiC, there is a (000-1) plane (C plane) that is in the reversed position in the c-axis direction with respect to the (0001) plane (Si plane). It is known that good surface morphology with few defects can be obtained. However, when the C plane is used, it is difficult to reduce the residual impurity density in the epitaxial growth layer compared to the Si plane. Therefore, when such an epitaxial growth substrate is used, the device leakage current is large. Another problem occurs, which becomes an adverse effect of practical use.
Patent Document 1 describes a method for reducing the number of epitaxial defects, but this is for a so-called on-axis substrate in which the off-angle of SiC is less than 1 °. In this case, the cause of the occurrence of epitaxial defects is nucleation on the surface terrace due to the small number of surface steps due to the on-axis substrate (Non-Patent Document 2). By making the adsorbed atoms or molecules easily reach the step, continuous step flow growth is performed to reduce the number of epitaxial defects.
However, the method of Patent Document 1 is applied to epitaxial defects on a substrate with a normal off angle due to minute irregularities and roughness, because the generation mechanism is different from the defect on the on-axis substrate. Have difficulty.
JP 2006-28016 A K. Kimoto, et al., IEEE Transactions on Electron Devices, Vol.46, No.3, (1999) pp.471-477 K. Kimoto, et al., Phys.stat.sol. (B), Vol.202, (1997) pp.247-262

  The present invention provides an epitaxial SiC single crystal substrate having a high-quality epitaxial film with few epitaxial defects in the epitaxial growth, and a method for manufacturing the same.

The present invention has been completed by finding that the above-described problems can be solved by paying attention to the relationship between the growth rate or growth temperature at the time of starting epitaxial growth and the epitaxial defect. That is, the present invention
(1) At least one suppression layer of a silicon carbide single crystal thin film formed on a silicon carbide single crystal substrate and suppressing generation of defects, and an active layer of a silicon carbide single crystal thin film formed on the suppression layer; An epitaxial silicon carbide single crystal substrate characterized by comprising:
(2) The epitaxial silicon carbide single crystal substrate according to (1), wherein an off angle of the silicon carbide single crystal substrate is larger than 1 °,
(3) The epitaxial silicon carbide single crystal substrate according to (1), wherein the thickness of the suppression layer of the silicon carbide thin film is 1 μm or less,
(4) The epitaxial silicon carbide single crystal substrate according to (1), wherein the thickness of the active layer of the silicon carbide thin film is 50 μm or less,
(5) After epitaxially growing at least one suppression layer of a silicon carbide single crystal thin film that suppresses the occurrence of defects on the silicon carbide single crystal substrate, the active layer of the silicon carbide single crystal thin film on the suppression layer is epitaxially grown A method for producing an epitaxial silicon carbide single crystal substrate, characterized in that
(6) The method for producing an epitaxial silicon carbide single crystal substrate according to (5), wherein the epitaxial growth of the suppression layer and the active layer is performed using a thermal chemical vapor deposition method (CVD method),
(7) The method for producing an epitaxial silicon carbide single crystal substrate according to (5) or (6), wherein an off angle of the silicon carbide single crystal substrate is larger than 1 °,
(8) The method for producing an epitaxial silicon carbide single crystal substrate according to (5) or (6), wherein the growth temperature when epitaxially growing the suppression layer is less than 1500 ° C.
(9) The method for producing an epitaxial silicon carbide single crystal substrate according to (5) or (6), wherein the growth rate when epitaxially growing the suppression layer is 1 μm or less per hour,
(10) The method for producing an epitaxial silicon carbide single crystal substrate according to (4) or (5), wherein the growth temperature when epitaxially growing the active layer is 1500 ° C. or higher,
(11) The method for producing an epitaxial silicon carbide single crystal substrate according to (4) or (5), wherein the growth rate when epitaxially growing the active layer is 3 μm or more per hour,
(12) A device using the epitaxial silicon carbide single crystal substrate according to any one of (1) to (4),
It is.

  According to the present invention, there is provided an epitaxial SiC single crystal substrate having a high-quality epitaxial film (a deterring layer and an active layer) with few epitaxial defects even if the SiC single crystal substrate is epitaxially grown on a Si surface. Is possible.

  In addition, since the manufacturing method of the present invention is a CVD method, an epitaxial film (a deterrence layer and an active layer) having an easy apparatus configuration, excellent controllability, and high uniformity and reproducibility can be obtained.

  Furthermore, since the device using the epitaxial SiC single crystal substrate of the present invention is formed on a high quality epitaxial film with few epitaxial defects, its characteristics and yield are improved.

The specific contents of the present invention will be described.
First, epitaxial growth on a SiC substrate is described. The apparatus preferably used for epitaxial growth in the present invention is a horizontal CVD apparatus. The CVD method has a simple apparatus configuration and can control growth by gas on / off, and is therefore a growth method with excellent controllability and reproducibility of the epitaxial film. The growth sequence is the same as in FIG. 2 until the SiC substrate is set and etching in hydrogen or hydrogen chloride is performed.

After that, the growth temperature is increased to 1500 to 1600 ° C., and the raw material gases SiH ₄ and C ₃ H ₈ are flown. At that time, the flow rate of SiH ₄ and C ₃ H ₈ is reduced, the growth rate is lowered, Start. The portion where defects such as minute irregularities and roughness of the substrate are present easily becomes traps of the introduced gas molecules or atoms, and the trap further proceeds as a nucleus, thereby preventing normal epitaxial growth. Epitaxial defects such as 1 are considered to occur. Therefore, as described above, by lowering the growth rate than usual and reducing the gas introduction rate, even if the introduced gas molecules or atoms are trapped, they are trapped before the next substance comes. Since molecules and atoms can move again to other locations on the substrate, they are less likely to be nuclei and are therefore expected to reduce epitaxial defects.

  Furthermore, the introduced source gas may reach the substrate in a state where it is not completely decomposed, and it may be trapped by the above defects and become a large nucleus, but it can be completely decomposed by reducing the gas introduction rate. The rate of nucleation is increased, and the effect of suppressing nucleation is also considered. From the description so far, the effect of reducing the growth rate is to avoid aggregation of source gas molecules or atoms in the substrate defect. The aforementioned growth rate decrease in Patent Document 1 is for continuous step flow growth when using an on-axis substrate, and has a more general off angle of 8 ° or 4 ° in the present invention. It can be understood that the effect is different from the case of using an off-axis substrate. In addition, due to the effect of the present invention, the above-mentioned defects that have not become traps are subjected to normal epitaxial growth thereon, so that the unevenness and roughness gradually become smaller, and the action as a trap is eventually lost. It is done.

Based on these considerations, regarding the flow rate of SiH ₄ and C ₃ H ₈ , which is a factor controlling the growth rate, the flow rate of SiH ₄ at the start of growth (at the start of inhibition layer formation) is 0.5-1 cm ^{3 /} min. The growth of the C ₃ H ₈ flow rate is 0.3-0.5 cm ³ per minute, the growth rate is 0.5-1 μm / hour, the normal value of 1 / 5-1 / 10, and the epitaxial defects are reduced. I was able to. Note that the initial growth rate is preferably 0.5 to 1 μm per hour because it is difficult to perform epitaxial growth when the re-evaporation of the substance adhering to the substrate is made small.

Next, the relationship between the growth temperature and the epitaxial defects is the same as in FIG. 2 until the etching in hydrogen or hydrogen chloride, and then the growth temperature is kept at the normal 1500 to 1600 ° C. with the raw material gas flow rate kept as before. We will describe the case where growth is started from the beginning. When the temperature is lowered, the source gas molecules or atoms trapped in the defects present on the SiC substrate cannot obtain energy for rearrangement, and the trapped gas source itself or the source gas itself is also lost. It is expected to become a larger nucleus because it is difficult to be completely decomposed. However, on the other hand, if the movement of the substrate surface is reduced, the probability of encountering the trap itself decreases, so that the trapped source gas molecules or atoms are decomposed over time without growing to the nucleus, and epitaxial It is also possible that this is not a defect.
From such consideration, the inventors considered that the epitaxial defects can be reduced by optimizing the initial growth temperature, and conducted experiments. As a result, it has been found that growing at an initial growth temperature (growth temperature when the deterrence layer is grown) is less than 1500 ° C, and more than 1400 ° C and less than 1500 ° C is optimal for reducing epitaxial defects. It was.

  According to the present invention, it has become possible to lower the growth rate or growth temperature at the initial stage of growth and reduce the occurrence of epitaxial defects than before, but the thickness of the layer (inhibition layer) formed at the initial stage of growth is therefore 1 μm or less is sufficient, and more preferably between 0.5 μm and 1 μm. If the thickness of the suppression layer exceeds 1 μm, if the growth rate is low, the suppression layer is too thick and the productivity is lowered, and if the growth temperature is low, the thickness of the suppression layer is increased. This is because the incorporation of impurities from the atmosphere increases and residual impurities increase, which affects the film quality. Further, it is desirable that the suppression layer has a thickness of 0.5 μm or more so as not to be affected by the trap of the substrate.

After growing this deterring layer, the growth temperature is 1500 ° C. or higher, preferably 1500-1600 ° C., and the growth rate is SiH ₄ flow rate 2-3 cm ^{3 /} min, C ₃ H ₈ flow rate 0.5-1.5 min / min. cm ³ sets per hour 3μm or more by the, preferably in the hour 5~6μm by setting the SiH ₄ min flow rate 4~5cm _^3, C ³ H ₈ flow rate per minute 1 to 3 cm ^3, device The layer to be formed (active layer) is grown. A schematic diagram of the grown epitaxial substrate is shown in FIG. In FIG. 3, 1 is a SiC single crystal substrate, 2 is a suppression layer, and 3 is an active layer. A device is formed on the active layer. The thickness of the active layer is preferably 10 μm or more and 50 μm or less in consideration of the breakdown voltage of the device, the productivity of the epitaxial film, and the like. In addition, when the substrate off-angle is 1 ° or less, the number of steps existing on the substrate surface is small, so normal epitaxial growth is difficult to be performed, and when it exceeds 10 °, when producing a substrate from an ingot, The yield is reduced because it is necessary to cut more diagonally. Therefore, it is desirable to be greater than 1 ° and not more than 10 °, but more preferably between 4 ° and 8 °.

(Example 1)
From a SiC single crystal ingot for 2 inch (50 mm) wafers, sliced at a thickness of about 400 μm, and then subjected to rough grinding and normal polishing with diamond abrasive grains, on the Si surface of the SiC single crystal substrate with 4H type polytype, Epitaxial growth was performed. The off angle of the substrate is 8 °. As a growth procedure, a substrate was set in a growth furnace, the inside of the growth furnace was evacuated, and then the pressure was adjusted to 1.6 × 10 ⁴ Pa while introducing 16 L of hydrogen gas per minute. Thereafter, the temperature of the growth furnace was raised while keeping the pressure constant, and after reaching 1400 ° C., 10 cm ^{3 of} hydrogen chloride was flowed per minute and the substrate was etched for 10 minutes. After etching, the temperature was raised to 1550 ° C., the SiH ₄ flow rate was 1 cm ^{3 /} min, the C ₃ H ₈ flow rate was 0.5 cm ^{3 /} min, and a deterrent layer was grown about 0.5 μm. The growth rate at this time was 1 μm per hour. After growing the suppression layer, the temperature was not changed, the SiH ₄ flow rate was 4 cm ^{3 /} min, the C ₃ H ₈ flow rate was 2 cm ^{3 /} min (growth rate was 5 μm / h), and the active layer was grown by about 10 μm.

An optical micrograph of the active layer surface after epitaxial growth is shown in FIG. The growth surface is a mirror surface, and the defect density is about 1/3 to 1/5, which is a triangle or carrot / comet defect density of 20 pieces / cm ² or less. FIG. 5 shows an AFM image of the surface after growth. FIG. 5 shows that the Ra value is 0.19 nm, which is a good surface with high flatness.

(Example 2)
Epitaxial growth was performed on the Si surface of a 2 inch (50 mm) SiC single crystal substrate having a 4H-type polytype, which was sliced, roughly ground, and normally polished in the same manner as in Example 1. The off angle of the substrate is 8 °. The growth procedure is the same as in Example 1 until the etching of hydrogen chloride. After etching, the temperature was raised to 1450 ° C., the SiH ₄ flow rate was 4 cm ^{3 /} min, the C ₃ H ₈ flow rate was 2 cm ^{3 /} min, and a deterrent layer was grown about 0.5 μm. The growth rate of the suppression layer at this time was 3 μm per hour. After growing the suppression layer, the flow rate of SiH ₄ and C ₃ H ₈ was not changed, the temperature was set to 1550 ° C., and the active layer was grown to 10 μm. The growth rate of the active layer at this time was 5 μm per hour. The growth surface was a mirror surface, the density of epitaxial defects was 30 / cm ² or less, and the surface Ra was 0.25 nm.

(Comparative example)
As a comparative example, epitaxial growth was performed on the Si surface of a 2 inch (50 mm) SiC single crystal substrate having a 4H type polytype, which was sliced, roughly ground, and normally polished as in Example 1. The off angle of the substrate is 8 °. The growth procedure is the same as in Example 1 until the etching of hydrogen chloride. After etching, the temperature was raised to 1550 ° C., the SiH ₄ flow rate was 4 cm ^{3 /} min, the C ₃ H ₈ flow rate was 2 cm ^{3 /} min, and the active layer was grown about 10 μm without growing the deterring layer. Epitaxial defects as shown in Fig. 1 (b) and (c) occur on the surface after growth, and the density is about 100 / cm ^2. I can't understand. The surface Ra was 0.37 nm at the portion where no epitaxial defect was present, and the surface roughness was too large at the portion where the defect was present, so measurement was impossible.

According to the present invention, it is possible to produce a SiC single crystal substrate having a high-quality epitaxial film with few defects in epitaxial growth on a SiC substrate. Therefore, if an electronic device is formed on such a substrate, it can be expected that the characteristics and yield of the device are improved. For example, in a Schottky barrier diode, unevenness caused by surface defects induces electrolytic concentration and degrades the breakdown voltage of the device, but it is considered that such defects are eliminated by increasing the flatness of the surface. In this embodiment, SiH ₄ and C ₃ H ₈ are used as the material gas, but the same applies to the case where trichlorosilane is used as the Si source, C ₂ H ₄ is used as the C source, and the like.

The optical microscope image which shows the state of the defect which exists on the SiC epitaxial film grown by the prior art. The figure which shows the growth sequence of the SiC epitaxial film by a prior art. The cross-sectional schematic diagram of the epitaxial SiC substrate grown by the example of this invention. The optical microscope image which shows the surface state of the SiC epitaxial film grown by the example of this invention. The AFM image which shows the surface state of the SiC epitaxial film grown by the example of this invention.

Explanation of symbols

1 SiC single crystal substrate
2 Deterrence layer
3 Active layer

Claims (12)

  A silicon carbide single-crystal thin film formed on the silicon carbide single-crystal substrate for suppressing generation of defects; and an active layer of the silicon carbide single-crystal thin film formed on the suppression layer. An epitaxial silicon carbide single crystal substrate characterized by the above.   2. The epitaxial silicon carbide single crystal substrate according to claim 1, wherein an off angle of the silicon carbide single crystal substrate is larger than 1 °.   2. The epitaxial silicon carbide single crystal substrate according to claim 1, wherein the thickness of the suppression layer of the silicon carbide thin film is 1 μm or less.   2. The epitaxial silicon carbide single crystal substrate according to claim 1, wherein the thickness of the active layer of the silicon carbide thin film is 50 μm or less.   The silicon carbide single crystal thin film for suppressing the generation of defects is epitaxially grown on the silicon carbide single crystal substrate, and then the active layer of the silicon carbide single crystal thin film on the suppression layer is epitaxially grown. A method for producing an epitaxial silicon carbide single crystal substrate.   6. The method for producing an epitaxial silicon carbide single crystal substrate according to claim 5, wherein the epitaxial growth of the suppression layer and the active layer is performed using a thermal chemical vapor deposition method (CVD method).   7. The method for producing an epitaxial silicon carbide single crystal substrate according to claim 5, wherein an off angle of the silicon carbide single crystal substrate is larger than 1 °.   7. The method for producing an epitaxial silicon carbide single crystal substrate according to claim 5, wherein a growth temperature when epitaxially growing the suppression layer is less than 1500 ° C.   7. The method for producing an epitaxial silicon carbide single crystal substrate according to claim 5, wherein a growth rate when epitaxially growing the inhibition layer is 1 μm or less per hour.   7. The method for producing an epitaxial silicon carbide single crystal substrate according to claim 5, wherein a growth temperature at the time of epitaxially growing the active layer is 1500 ° C. or higher.   7. The method for producing an epitaxial silicon carbide single crystal substrate according to claim 5, wherein a growth rate when epitaxially growing the active layer is 3 μm or more per hour.   A device comprising the epitaxial silicon carbide single crystal substrate according to claim 1.

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