JP6152981B2 - Silicon carbide single crystal - Google Patents

Description

  The present invention relates to a silicon carbide (hereinafter referred to as SiC) single crystal that can be used as a material for a power MOSFET or the like.

  Conventionally, a sublimation recrystallization method has been widely used as a method for growing a SiC single crystal. This sublimation recrystallization method involves joining a seed crystal to a graphite pedestal placed in a graphite crucible, heating and sublimating the SiC raw material arranged at the bottom of the crucible, and supplying the sublimation gas to the seed crystal. A SiC single crystal is grown on top. As a method for producing a SiC single crystal using such a sublimation recrystallization method, for example, there is a method disclosed in Patent Document 1. Specifically, in the manufacturing method described in Patent Document 1, basal plane dislocation is suppressed by doping an SiC single crystal with an acceptor element (aluminum (Al)) together with a donor element (nitrogen (N)). .

JP 2009-167047 A

However, the technique disclosed in Patent Document 1 is a technique for suppressing basal plane dislocations and does not consider suppression of stacking faults. As the nitrogen concentration is increased, stacking faults increase and the crystallinity decreases. In particular, if the concentration of nitrogen is higher than 2 × 10 ¹⁹ cm ^−3, stacking faults are further increased, and crystallinity is significantly reduced.

  An object of this invention is to provide the SiC single crystal which can suppress a stacking fault in view of the said point.

In order to achieve the above object, in the invention described in claim 1, the donor element and the acceptor element are both doped, and the difference between the concentration of the donor element and the acceptor element is 6 × 10 cm ²⁰ cm ^{−. 3} is a more and 1 × 10 ²¹ cm ^-3 or less, and is characterized in that the stacking fault density is a 10 cm ^-1 or less.

Thus, when the SiC single crystal (5) is grown by the sublimation recrystallization method, the acceptor element such as aluminum is simultaneously doped in addition to the donor element such as nitrogen, and the concentration of the acceptor element is determined from the concentration of the donor element. The value obtained by subtracting is set to be 6 × 10 cm ²⁰ cm ⁻³ or more and 1 × 10 ²¹ cm ⁻³ or less. As a result, it is possible to obtain a SiC single crystal in which stacking faults are not substantially generated, and the stacking fault density can be 10 cm ⁻¹ or less.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows an example of a corresponding relationship with the specific means as described in embodiment mentioned later.

It is sectional drawing which showed a mode when the SiC single crystal 5 was grown using the SiC single crystal manufacturing apparatus concerning 1st Embodiment of this invention. It is a graph which shows the result of having investigated about the density | concentration of nitrogen, aluminum, specific resistance, and the presence or absence of the generation | occurrence | production of a stacking fault when growing the multiple types of SiC single crystal 5 using the SiC single crystal manufacturing apparatus shown in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other will be described with the same reference numerals.

(First embodiment)
A first embodiment of the present invention will be described. As shown in FIG. 1, the SiC single crystal manufacturing apparatus is provided with a first crucible 1 and a second crucible 2 made of graphite and made cylindrical.

  The first crucible 1 sublimates SiC raw material powder (SiC raw material) 3 provided at the bottom of the first crucible 1 by heat treatment to grow a SiC single crystal 5 on a SiC single crystal substrate 4 as a seed crystal. Is. That is, the first crucible 1 is used as a crystal growth container for the SiC single crystal 5.

  The first crucible 1 includes a bottomed cylindrical crucible body 1a having an open upper surface and a disk-shaped lid 1b that closes the opening of the crucible body 1a. Further, with the portion protruding at the center of the lid 1b constituting the first crucible 1 as a pedestal 1c, the SiC single crystal substrate 4 is bonded on the pedestal 1c via an adhesive or the like (not shown). Pedestal 1c has substantially the same dimensions as SiC single crystal substrate 4 to be joined. In the present embodiment, the SiC single crystal substrate 4 is circular, and the pedestal 1c is also circular. And the center of the base 1c is arrange | positioned on the central axis of the 1st crucible 1, and the SiC single crystal substrate 4 is also arrange | positioned on the central axis. The shapes of SiC single crystal substrate 4 and pedestal 1c are arbitrary, and are not limited to a circle, and may be other polygonal shapes such as a quadrangle, a hexagon, and an octagon.

  A graphite connecting pipe 6 is connected to the side wall of the crucible main body 1 a and is connected to the second crucible 2 through the connecting pipe 6. Although the connecting pipe 6 is connected to the side wall of the crucible body 1a in the first crucible 1 here, it may be connected to the lid material 1b, the bottom surface of the crucible body 1a, or the like.

  Moreover, although not shown in figure, the 1st crucible 1 is mounted in the rotation apparatus, and the 1st crucible 1 is comprised so that it can rotate centering on the center axis | shaft. When the first crucible 1 is rotated, the SiC single crystal substrate 4 bonded to the pedestal 1 c is also rotated about the central axis of the first crucible 1.

  Although not shown, a heating device such as a heater is provided outside the first crucible 1 so as to surround the outer periphery of the first crucible 1. The center of the heating device is a concentric shaft with the central axis of the first crucible 1 or the rotating device. By controlling the power of the heating device arranged in this way, the temperature in the first crucible 1 is appropriately adjusted. For example, when the SiC single crystal 5 is grown, the temperature of the SiC single crystal substrate 4 as a seed crystal is kept at a temperature about 100 ° C. lower than the temperature of the SiC raw material powder 3 by adjusting the power of the heating device. Can be drunk.

  Furthermore, although not shown in figure, the 1st crucible 1 is accommodated in the vacuum container which can introduce | transduce donor element gas, such as nitrogen for dope, argon gas, etc. FIG. In this vacuum vessel, the first crucible 1 can be heated, and donor element gas or argon gas is introduced into the first crucible 1 from the gap between the graphite that has become high temperature or the gap between the crucible body 1a and the lid 1b. It can be done.

On the other hand, the second crucible 2 sublimates an acceptor element-containing material (for example, Al ₄ C ₃ ) 7 provided at the bottom of the second crucible 2 by heat treatment, and passes the acceptor element-containing gas through the connecting pipe 6 to the first crucible 1. Supply to the side.

  The second crucible 2 includes a bottomed cylindrical crucible body 2a whose upper surface is open, and a disc-shaped lid member 2b that closes the opening of the crucible body 2a. The first crucible 1 It is arrange | positioned in a vacuum vessel like. A connecting pipe 6 is connected to the side wall of the crucible body 2 a and is connected to the first crucible 1 through the connecting pipe 6. Here, the connecting pipe 6 is connected to the side wall of the crucible body 2a in the second crucible 2, but it may be connected to other parts such as the lid 2b.

  Although not shown, a heating device such as a heater is provided outside the second crucible 2 so as to surround the outer periphery of the second crucible 2. The center of the heating device is a concentric axis with the central axis of the second crucible 2. By controlling the power of the heating device arranged in this way, the temperature in the second crucible 2 is appropriately adjusted.

  As described above, the SiC single crystal manufacturing apparatus according to the present embodiment is configured. Then, the manufacturing method of the SiC single crystal 5 using the SiC single crystal manufacturing apparatus comprised in this way is demonstrated.

First, after placing the SiC raw material powder 3 in the crucible main body 1a, the lid 1b in which the SiC single crystal substrate 4 is attached to the base 1c is installed in the crucible main body 1a, and this is installed in the vacuum vessel. Moreover, after arrange | positioning the acceptor element containing material 7 in the crucible main body 2a, it lid | covers with the lid | cover material 2b. Subsequently, the inside of the vacuum container including the insides of the first and second crucibles 1 and 2 is brought into a reduced pressure state by discharging gas using an exhaust mechanism (not shown) provided in the vacuum container. Then, the first and second crucibles 1 and 2 are heated to a predetermined temperature by heating the first and second crucibles 1 and 2 with a heating device. For example, the first and second crucibles 1 and 2 are heated to 2000 to 2400 ° C. at an atmospheric pressure of about 1 to 100 Torr (1.3 × 10 ^{2 to} 1.3 × 10 ⁴ Pa), and the second crucible 2 is 1500. Heated to ˜2000 ° C. Then, the SiC raw material contained in the sublimation gas of the SiC raw material powder 3 is obtained by sublimation recrystallization while introducing the donor element gas and the argon gas into the first crucible 1 by introducing them into the vacuum vessel. It is deposited on the SiC single crystal substrate 4. Thereby, SiC single crystal 5 grows, and nitrogen serving as a donor element and aluminum serving as an acceptor element are simultaneously doped into SiC single crystal 5. In this way, SiC single crystal 5 can be manufactured.

The stacking fault density (cm ⁻¹ ) when the SiC single crystal 5 was produced in this way was examined by experiment. Specifically, by using nitrogen as the donor element and aluminum as the acceptor element, the concentration of nitrogen and aluminum in the SiC single crystal 5 is adjusted by adjusting the amount of nitrogen gas introduced and the heating temperature of the second crucible 2. It was adjusted. Thereby, the result shown in FIG. 2 was obtained.

In the experiment, a plurality of types of SiC single crystals 5 were grown under different growth conditions. For each SiC single crystal 5, the concentration of nitrogen or aluminum was examined by SIMS analysis, or the specific resistance was measured by a hole measurement or eddy current type measurement device. The stacking fault density (cm ⁻¹ ) was examined by examination, observation after KOH etching, and X-ray topography observation. In FIG. 2, nine types (growth crystals No. 1 to 9) are shown. The hole measurement is performed by, for example, cutting the prepared SiC single crystal 5 into a 1 cm square, applying a voltage to two diagonals of the four corners, applying an electric field, and flowing the holes in the other two diagonals. Is used to measure the specific resistance.

As shown in this figure, n-type 4H—SiC could be grown as the SiC single crystal 5. In addition, each of the nine types of SiC single crystals 5 was examined. A relatively large number of stacking faults occurred only for No. 7 and the other growth crystal Nos. Regarding 1 to 6, 8, and 9, almost no stacking fault occurred. In more detail, the growth crystal no. 1 to 6, 8, and 9 had no crystal defects or had a stacking fault density of 10 cm ⁻¹ or less even if they existed. And when it confirmed about the stacking fault density (cm ^<-1 >), it turned out that the difference of the density | concentration of nitrogen and the density | concentration of aluminum is concerned with generation | occurrence | production of the stacking fault.

Specifically, the growth crystal No. The SiC single crystal 5 of No. 7 has a nitrogen concentration of 1.2 × 10 ²¹ cm ⁻³ and an aluminum concentration of 1.7 × 10 ²⁰ cm ^−3, and the aluminum concentration is subtracted from the nitrogen concentration. The value is 1.03 × 10 ²¹ cm ⁻³ . If the value obtained by subtracting the aluminum concentration from the nitrogen concentration is 1 × 10 ²¹ cm ⁻³ or less, it was found that stacking faults hardly occur. Therefore, if the value obtained by subtracting the aluminum concentration from the nitrogen concentration in SiC single crystal 5 is 1 × 10 ²¹ cm ⁻³ or less, stacking faults can be substantially prevented from occurring in SiC single crystal 5. I can say that.

In all cases, the experimental results shown in FIG. 2 show that the specific resistance is relatively low, 1.0 to 11.2 mΩcm, and the nitrogen concentration is higher than 7.7 × 10 ²⁰ cm ^−3. No. 5 to 9, the specific resistance was 1.0 to 2.5, and a low resistance could be realized as a specific resistance required for device characteristics. The value obtained by subtracting the aluminum concentration from the nitrogen concentration in these cases was 6.0 × 10 ²⁰ cm ⁻³ or more. For this reason, when the specific resistance is considered in addition to the stacking fault, the value obtained by subtracting the aluminum concentration from the nitrogen concentration is 6.0 × 10 ²⁰ cm ⁻³ or more and 1 × 10 ²¹ cm ⁻³ or less. It can be said that it is preferable.

As described above, when the SiC single crystal 5 is grown by the sublimation recrystallization method, aluminum is simultaneously doped in addition to nitrogen, and the value obtained by subtracting the aluminum concentration from the nitrogen concentration is 1 × 10 ²¹ cm. ^-3 or less. Thereby, it is possible to obtain the SiC single crystal 5 in which stacking faults hardly occur.

(Other embodiments)
The present invention is not limited to the embodiment described above, and can be appropriately changed within the scope described in the claims.

For example, in the above embodiment, the case where nitrogen is used as the donor element and aluminum is used as the acceptor element has been described. However, these are only examples. For example, as the donor element, other group V elements such as phosphorus and arsenic can be used. As the acceptor element, other group III elements such as boron and gallium can be used. As described above, even when the donor element or the acceptor element is changed, the value obtained by subtracting the acceptor element concentration from the donor element concentration is set to 1 × 10 ²¹ cm ⁻³ or less. The same effect as the embodiment can be obtained.

DESCRIPTION OF SYMBOLS 1 1st crucible 1a Crucible body 1b Lid 1c Pedestal 2 2nd crucible 2a Crucible body 2b Lid 3 SiC raw material powder 4 SiC single crystal substrate 5 SiC single crystal 6 Connection pipe

Claims (5)

A donor element and the acceptor element are both doped, and the value obtained by subtracting the concentration of the acceptor element from the concentration of the donor element is a 6 × 10cm ²⁰ cm ^-3 or more and 1 × 10 ²¹ cm ^-3 or less, and A silicon carbide single crystal having a stacking fault density of 10 cm ⁻¹ or less.   2. The silicon carbide single crystal according to claim 1, wherein the donor element is any one of a group V element such as nitrogen, phosphorus, or arsenic.   3. The silicon carbide single crystal according to claim 1, wherein the acceptor element is any one of a group III element such as aluminum, boron, or gallium. The silicon carbide single crystal according to any one of claims 1 to 3 , wherein a specific resistance is 11.2 mΩcm or less. The silicon carbide single crystal according to any one of claims 1 to 3 , wherein a specific resistance is 2.5 mΩcm or less.

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