JP2014218397A - Manufacturing method of silicon carbide single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a silicon carbide single crystal having low penetration dislocation density by a sublimation recrystallization method.SOLUTION: After a first ingot 21 made of silicon carbide is formed by liquid phase growth on a first seed crystal 11, a second seed crystal is formed from the first ingot 21 and a second ingot of silicon carbide is grown on the second seed crystal by a sublimation recrystallization method. The first ingot 21 of which the penetration dislocation density is reduced by using the liquid phase growth forms the second seed crystal. Because the thus formed second seed crystal is used for the second ingot, the second ingot having low penetration dislocation density is obtained by the sublimation recrystallization method.

Description

  The present invention relates to a method for manufacturing a silicon carbide single crystal, and more particularly to a method for manufacturing a silicon carbide single crystal using a sublimation recrystallization method.

  In recent years, the use of silicon carbide (SiC) as a semiconductor material has been actively studied. The large band gap of SiC can contribute to improving the performance of the semiconductor device. A mass production method of SiC single crystal requires not only the quality of the crystal but also a sufficient growth rate. In view of this point, the most common method at present is the sublimation recrystallization method. This method is disclosed, for example, in US Pat. No. 7,314,520 (Patent Document 1).

US Pat. No. 7,314,520

  When the sublimation recrystallization method is used, the threading dislocation density of the obtained single crystal is approximately the same as the threading dislocation density of the seed crystal. For this reason, even if the crystal growth process conditions are adjusted, it is difficult to significantly reduce the threading dislocation density of the single crystal obtained.

  The present invention has been made in view of the above problems, and an object thereof is to provide a method for producing a silicon carbide single crystal having a low threading dislocation density.

  The method for producing a silicon carbide single crystal of the present invention includes the following steps. A first ingot made of silicon carbide is formed by liquid phase growth on the first seed crystal. A second seed crystal is formed from the first ingot. A second ingot is grown on the second seed crystal by the sublimation recrystallization method.

  According to this manufacturing method, a smaller threading dislocation density can be obtained while using the sublimation recrystallization method.

It is sectional drawing which shows schematically the 1st process of the manufacturing method of the silicon carbide single crystal in Embodiment 1 of this invention. It is sectional drawing which shows schematically the 2nd process of the manufacturing method of the silicon carbide single crystal in Embodiment 1 of this invention. It is sectional drawing which shows schematically the 3rd process of the manufacturing method of the silicon carbide single crystal in Embodiment 1 of this invention. It is sectional drawing which shows schematically the 4th process of the manufacturing method of the silicon carbide single crystal in Embodiment 1 of this invention. It is sectional drawing which shows schematically the 5th process of the manufacturing method of the silicon carbide single crystal in Embodiment 1 of this invention. It is sectional drawing which shows schematically the 6th process of the manufacturing method of the silicon carbide single crystal in Embodiment 1 of this invention. It is sectional drawing which shows schematically the 7th process of the manufacturing method of the silicon carbide single crystal in Embodiment 2 of this invention. It is sectional drawing which shows schematically the 8th process of the manufacturing method of the silicon carbide single crystal in Embodiment 2 of this invention. It is sectional drawing which shows roughly the 9th process of the manufacturing method of the silicon carbide single crystal in Embodiment 2 of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, an outline will be described in the following (i) to (ix).

  (i) The method for producing a silicon carbide single crystal of the present invention includes the following steps. A first ingot made of silicon carbide is formed by liquid phase growth on the first seed crystal. A second seed crystal is formed from the first ingot. A second ingot is grown on the second seed crystal by the sublimation recrystallization method.

  According to this manufacturing method, the second ingot is grown by the sublimation recrystallization method on the second seed crystal made from the first ingot whose threading dislocation density is reduced by using liquid phase growth. . Thereby, the threading dislocation density of the second ingot obtained by the sublimation recrystallization method can be reduced.

  (ii) In the above (i), the first ingot may have an impurity excluding the dopant at a first concentration, and the second ingot has an impurity excluding the dopant at a second concentration. Also good. The first concentration may be greater than the second concentration.

  When the first concentration is higher than the second concentration, more impurities other than the dopant can be used as an additive added to the melt for promoting the liquid phase growth of the first ingot. Thereby, liquid phase growth can be promoted more. This can alleviate the problem of liquid phase growth where the growth rate is slow. Further, the fact that the first density is higher than the second density means that the second density is lower than the first density. Thereby, the density | concentration of the impurity except the dopant in a 2nd ingot is made small. In terms of semiconductor physical properties, it is usually preferable that the concentration of impurities excluding dopants is small. Therefore, the second ingot can have more preferable semiconductor physical properties.

  (iii) In the above (ii), the second ingot may contain at least one of nitrogen and aluminum as a dopant.

  In this case, the conductivity of the second ingot can be increased by nitrogen or aluminum.

(iv) In the above (ii) or (iii), the second concentration may be smaller than 4 × 10 ¹⁴ cm ⁻³ .

  In this case, the concentration of impurities excluding the dopant in the second ingot is smaller than the normal detection limit by glow discharge mass spectrometry, which is a method generally used in quantitative measurement of the impurity concentration in the semiconductor. In other words, the second concentration is substantially zero. As a result, the concentration of impurities excluding the dopant in the second ingot is substantially zero.

(v) In the above (ii) to (iv), the first concentration may be higher than 4 × 10 ¹⁴ cm ⁻³ .

  In this case, the concentration of the impurities excluding the dopant in the first ingot is larger than the normal detection limit by glow discharge mass spectrometry, which is a method generally used in quantitative measurement of the impurity concentration in the semiconductor. In other words, the first ingot substantially contains impurities excluding the dopant. By allowing such inclusion, a larger amount of impurities excluding the dopant as an additive can be used in the melt used for liquid phase growth.

  (vi) In the above (i) to (v), the first ingot may contain a transition element as an impurity excluding the dopant.

  Thereby, liquid phase growth can be promoted. Therefore, the first ingot can be formed efficiently.

  (vii) In the above (i) to (vi), the first ingot may contain chromium as an impurity excluding the dopant.

  Thereby, liquid phase growth can be promoted more. Therefore, the first ingot can be formed more efficiently.

  (viii) In the above (i) to (vii), the dopant concentration of the second ingot may be higher than the dopant concentration of the first ingot.

Accordingly, the second ingot can sufficiently have an n-type or p-type conductivity type.
(ix) The method for producing a silicon carbide single crystal of (i) to (viii) may further include the following steps. A third seed crystal is formed from the second ingot. A third ingot is grown on the third seed crystal by the sublimation recrystallization method.

  The third seed crystal has a threading dislocation density that is as low as the threading dislocation density of the second seed crystal. Therefore, the third ingot grown on the third seed crystal also has a low threading dislocation density. The third seed crystal for growing the third ingot can be efficiently formed by the sublimation recrystallization method. From the above, it is possible to efficiently manufacture the third ingot having a low threading dislocation density.

Next, details will be described in Embodiments 1 and 2 below.
(Embodiment 1)
A method for manufacturing a silicon carbide single crystal (second ingot) in the present embodiment will be described below.

  Referring to FIG. 1, seed crystal 11 (first seed crystal) made of SiC is prepared. The crystal structure of the seed crystal 11 is preferably a hexagonal system. In this case, the plane orientation of the seed crystal 11 (the orientation of the lower surface in the figure) preferably has an off angle smaller than 15 ° with respect to {0001}, and more preferably has an off angle smaller than 10 °. The crystal structure polytype is preferably 4H or 6H. The seed crystal 11 may be supported by the support portion 42. The support part 42 may be made of graphite.

  A crucible 41 is also prepared. The crucible 41 preferably contains C atoms, more preferably made from carbon, for example made from graphite. A material containing Si atoms is accommodated in the crucible 41. This material preferably contains solid Si. Solid Si is, for example, Si grains. The melt 31 is obtained in the crucible 41 by melting the material by heating with the heater 40. As the heater 40, for example, a resistance heating type such as a graphite heater or an induction heating type can be used. The temperature of the melt 31 is preferably 2500 ° C. or less, and more preferably 2300 ° C. or less. The melt 31 is preferably disposed in an inert gas.

  The melt 31 has liquid Si in which C atoms are dissolved as a main component. The C atoms in the melt 31 may be supplied by dissolving the C atoms from the crucible 41 into the melt 31. It is preferable that the melt 31 further contains an additive for promoting liquid phase growth described later. The additive may be a non-conducting impurity that does not function as a donor or acceptor for the SiC semiconductor. That is, the additive may be an impurity excluding the dopant. Here, the dopant is an impurity that can function as a donor or acceptor for the SiC semiconductor. For example, each of nitrogen and aluminum is a kind of dopant. As this impurity excluding the dopant, a transition element is preferable, and a 3d transition element is more preferable. As the 3d transition element, Cr, Ti or Fe is preferable, and Cr is particularly preferable.

The seed crystal 11 is immersed in the melt 31. By causing the temperature of the seed crystal 11 to be lower than the temperature of the liquidus line of the melt 31, SiC liquid phase growth occurs on the seed crystal 11. As a result, as shown in FIG. 2, an ingot 21 (first ingot) made of SiC is formed. The concentration (first concentration) of the impurity excluding the above-described dopant in the ingot 21 may be higher than 4 × 10 ¹⁴ cm ⁻³ . After the growth is completed, the seed crystal 11 and the ingot 21 are taken out from the crucible 41.

  Referring to FIG. 3, in the liquid phase growth, the progress of threading dislocation DS starting from threading dislocation of seed substrate 11 is likely to be interrupted during the growth. For this reason, the threading dislocation density of the ingot 21 tends to be smaller than the threading dislocation density of the seed crystal 11 as the growth proceeds. That is, the threading dislocation density of the later grown portion of the ingot 21 (the lower portion in FIG. 3) tends to be particularly small.

  Referring to FIG. 4, seed crystal 12 (second seed crystal) is formed from ingot 21. One seed crystal 12 or a plurality of seed crystals 12 can be cut out from the ingot 21 by the slice indicated by the broken line L. Seed crystal 12 has a pair of main surfaces (an upper surface and a lower surface in FIG. 4). Of these two main surfaces, the surface (the lower surface in FIG. 4) formed at a stage where the growth of the ingot 21 has progressed is the growth surface of the seed crystal 12 (the lower surface of the seed crystal 12 in FIG. 6, ie, the seed crystal 12). It is preferable to use it as the surface on which the ingot 22 is grown. Thereby, the threading dislocation density on the growth surface can be further reduced (see FIG. 3). In order to sufficiently reduce the dislocation density on the growth surface, the growth surface is preferably separated from the seed crystal 11 by a distance D or more.

  Note that the seed crystal 11 and the entire ingot 21 may be used as the seed crystal 12 without performing the above-described slicing. In this case, not the seed crystal 11 side but the ingot 21 side (the lower side of the structure shown in FIG. 4) is used as the growth surface.

  Referring to FIG. 5, a reaction chamber 50 having a container portion 51 and a lid portion 52 is prepared. The reaction chamber 50 is preferably made of graphite. The seed crystal 12 is bonded onto the lid 52 so that the growth surface of the seed crystal 12 is exposed. In addition, a solid raw material 32 for growing SiC by sublimation recrystallization is stored in the container 51. The solid material 32 preferably contains SiC, and is made of, for example, SiC powder. Next, the lid portion 52 is attached to the container portion 51 so that the growth surface (the lower surface in the drawing) of the seed crystal 12 faces the solid raw material 32.

  Referring to FIG. 6, ingot 22 (second ingot) is grown on the growth surface (lower surface in the figure) of seed crystal 12 by the sublimation recrystallization method. In other words, the ingot 22 is grown by sublimation of the solid raw material 32 and subsequent recrystallization on the seed crystal 12. The temperature for sublimating the solid raw material 32 is, for example, 2100 ° C. or higher and 2500 ° C. or lower. The pressure in the reaction chamber 50 during the growth of the ingot 22 is preferably 1.3 kPa or more and atmospheric pressure or less, and more preferably 13 kPa or less in order to increase the growth rate. During the growth of the ingot 22, atoms serving as dopants may be added to the atmosphere in the reaction chamber 50. Thereby, the density | concentration of the dopant of the ingot 22 obtained can be enlarged. Thereby, the concentration of the dopant of the ingot 22 can be easily made larger than the concentration of the dopant of the ingot 21. For example, nitrogen as a dopant can be included in the ingot 22 by including nitrogen in the atmosphere.

Thus, ingot 22 as a silicon carbide single crystal in the present embodiment is obtained. The ingot 22 has an impurity excluding the above-described dopant at a second concentration. The second concentration is preferably less than 4 × 10 ¹⁴ cm ⁻³ . Since the sublimation recrystallization method is used for the formation of the ingot 22, an additive for promoting the growth as desired as in the case of the liquid phase growth is not particularly required. Therefore, the second concentration can be reduced without any particular inconvenience. For example, a plurality of SiC wafers can be cut out from the ingot 22. The SiC wafer has a low threading dislocation density and an impurity concentration excluding a low dopant, and is suitable for manufacturing a semiconductor device.

  According to the present embodiment, on the seed crystal 12 (FIG. 4) made from the ingot 21 (FIG. 3) whose threading dislocation density is reduced by using liquid phase growth, the ingot 22 ( FIG. 6) is grown. Thereby, the threading dislocation density of the ingot 22 obtained by the sublimation recrystallization method can be reduced. In particular, the threading screw dislocation density can be reduced.

  The ingot 22 may contain at least one of nitrogen and aluminum as a dopant. In this case, the conductivity of the ingot 22 can be increased by nitrogen or aluminum. The addition of nitrogen into the ingot 22 can be easily performed by including nitrogen atoms in the process gas in the sublimation recrystallization method.

In the growth surface of the seed crystal 12 (the lower surface in FIG. 5), the threading dislocation density is preferably 3000 cm ⁻² or less. The threading screw dislocation density is preferably 100 cm ^-2 or less. If the threading screw dislocation density is 100 cm ⁻² or less, there is often no problem even if it is 10 cm ⁻² or more.

  The concentration of the impurities excluding the dopant of the ingot 21 may be higher than the concentration of the impurities excluding the dopant of the ingot 22. This is because the ingot 21 is a material of the seed crystal 12 used for forming the ingot 22 and is not assumed to be a material of the semiconductor device. Therefore, the concentration of impurities (first concentration) excluding the dopant of the ingot 21 may be higher than the second concentration. Thereby, in order to promote the liquid phase growth of the ingot 21, more impurities except the dopant can be used as an additive added to the melt 31 (FIG. 2). This can alleviate the problem of liquid phase growth where the growth rate is slow. On the other hand, the low concentration of impurities excluding the dopant of the ingot 22 can contribute to enhancing the characteristics of a semiconductor device manufactured using the ingot 22 as a material.

The concentration of impurities (second concentration) excluding the dopant of the ingot 22 (FIG. 6) is preferably smaller than 4 × 10 ¹⁴ cm ⁻³ . In this case, the second concentration is smaller than a normal detection limit by glow discharge mass spectrometry, which is a method generally used in quantitative measurement of impurity concentration in a semiconductor. In other words, the ingot 22 has substantially no impurities other than the dopant.

The concentration of impurities (first concentration) excluding the dopant of the ingot 21 (FIG. 2) is preferably greater than 4 × 10 ¹⁴ cm ⁻³ . In this case, the first concentration is larger than a normal detection limit by glow discharge mass spectrometry, which is a method generally used in quantitative measurement of impurity concentration in a semiconductor. In other words, the ingot 21 substantially contains impurities excluding the dopant. By allowing such inclusion, a larger amount of impurities excluding the dopant as an additive for promoting growth can be used in the melt 31 (FIG. 2) used for liquid phase growth.

  The impurities excluding the dopant may contain a transition element. Thereby, liquid phase growth can be promoted more. Therefore, the ingot 21 (FIG. 2) can be formed more efficiently. When the impurities excluding the dopant include chromium, liquid phase growth can be further promoted.

  The dopant concentration of the ingot 22 (FIG. 6) may be greater than the dopant concentration of the ingot 21 (FIG. 2). Thereby, the ingot 22 may have a sufficient conductivity type of n-type or p-type. The dopant may include nitrogen. Thereby, the ingot 22 may have nitrogen as a donor.

(Embodiment 2)
In the method for manufacturing a silicon carbide single crystal (third ingot) of the present embodiment, first, ingot 22 (FIG. 6) is formed by the same process as in the first embodiment. Next, as shown in FIG. 7, seed crystal 13 (third seed crystal) is formed from ingot 22. Specifically, the seed crystal 13 is cut out by slicing the ingot 22 as indicated by a broken line L. Next, as shown in FIGS. 8 and 9, an ingot 23 (third ingot) is grown on the seed crystal 13 by a sublimation recrystallization method. 8 and FIG. 9 are substantially the same as the steps in FIG. 5 and FIG. 6 (Embodiment 1).

  According to the present embodiment, the seed crystal 13 has a threading dislocation density that is as low as the threading dislocation density of the seed crystal 12. Therefore, the ingot 23 grown on the seed crystal 13 also has a low threading dislocation density. The seed crystal 13 for growing the ingot 23 can be efficiently formed by a sublimation recrystallization method. From the above, the ingot 23 having a low threading dislocation density can be efficiently produced.

(Example)
A seed crystal 11 (FIG. 1) was prepared using a general sublimation recrystallization method. The seed crystal 11 had a threading dislocation density of 8000 cm ⁻² and a threading screw dislocation density of 1500 cm ⁻² . A melt 31 (FIG. 1) was obtained by heating Si and Cr to 1600 ° C. or higher in a crucible 41 made of carbon. By bringing the seed crystal 11 into contact with the melt 31, an ingot 21 (FIG. 2) was grown on the seed crystal 11 by 500 μm. The Cr concentration in the ingot 21 was 8 × 10 ¹⁶ cm ⁻³ according to glow discharge mass spectrometry. This ingot 21 was used as the seed crystal 12. The growth surface of the seed crystal 12 had a threading dislocation density of 2400 cm ⁻² and a threading screw dislocation density of 80 cm ⁻² .

Ingot 22 was grown by sublimation recrystallization at 2000 ° C. or higher using seed crystal 12 (FIG. 6). The Cr concentration in the ingot 22 was less than the detection limit (4 × 10 ¹⁴ cm ⁻³ ) according to glow discharge mass spectrometry. Ingot 22 (silicon carbide single crystal) is, in the surface (lower surface in FIG. 6) which is located opposite to the seed crystal 12 had threading dislocation density 3200 cm ^-2 and the through screw dislocation density 90cm ^-2.

  The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as being restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

11-13 seed crystals (first to third seed crystals)
21-23 ingots (first to third ingots)
31 Melt 32 Solid material 40 Heater 41 Crucible 42 Support part 50 Reaction chamber 51 Container part 52 Lid part D Distance DS Threading dislocation

Claims (9)

Forming a first ingot made of silicon carbide by liquid phase growth on a first seed crystal;
Forming a second seed crystal from the first ingot;
And a step of growing a second ingot on the second seed crystal by a sublimation recrystallization method.   The first ingot has an impurity excluding the dopant at a first concentration, the second ingot has an impurity excluding the dopant at a second concentration, and the first concentration is the second concentration. The method for producing a silicon carbide single crystal according to claim 1, wherein the method is larger than the concentration.   The method for producing a silicon carbide single crystal according to claim 2, wherein the second ingot contains at least one of nitrogen and aluminum as a dopant. 4. The method for producing a silicon carbide single crystal according to claim 2, wherein the second concentration is lower than 4 × 10 ¹⁴ cm ⁻³ . 5. The method for producing a silicon carbide single crystal according to claim 2, wherein the first concentration is higher than 4 × 10 ¹⁴ cm ⁻³ .   The method for producing a silicon carbide single crystal according to claim 1, wherein the first ingot includes a transition element as the impurity excluding the dopant.   The method for producing a silicon carbide single crystal according to claim 1, wherein the first ingot includes chromium as the impurity excluding a dopant.   The method for producing a silicon carbide single crystal according to claim 1, wherein a concentration of the dopant of the second ingot is higher than a concentration of the dopant of the first ingot. Forming a third seed crystal from the second ingot;
A method for producing a silicon carbide single crystal according to claim 1, further comprising a step of growing a third ingot on the third seed crystal by a sublimation recrystallization method.

Images