JP2680617B2 - Method for growing silicon carbide single crystal - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for growing a silicon carbide single crystal used in an electronic device.

(B) Conventional technology Since silicon carbide (SiC) is a semiconductor material that is physically and chemically stable and has a wide band gap, it has attracted attention as a material for environment-resistant semiconductor elements and short wavelength light emitting diodes. There is.

SiC has various crystal forms such as 3C type, 4H type, 6H type and 15R type with the same composition. Of these, 3C-type SiC is expected to be used as an active device that operates under high temperature or radiation irradiation. In addition, 6H type SiC has a band gap of approximately 3.0 eV.
And is used as a blue light emitting element. 4H type Si
Since C has a bandgap of about 3.2 eV and is wider than that of the 6H type, it is considered to be used for a blue to violet light emitting diode and a hedello junction device with other crystalline SiC.

As a method for growing a single crystal for a SiC substrate, a sublimation method utilizing a decomposition sublimation process of a SiC raw material and an Acheson method for synthesizing a SiC compound and a C compound at a high temperature are used. But,
In the Acheson method, it is difficult to control the impurities and the crystal size, and thus the sublimation method is often used. According to this sublimation method, as disclosed in JP-A-62-66000, a high quality single crystal is obtained under specific growth conditions.

(C) Problems to be solved by the invention Fig. 3 shows Philips Research Reports, Volume 18 (1963),
P161 describes the generation rate of each crystal form of SiC crystals generated in the crucible when the SiC raw material housed in the crucible is heated under normal pressure, with the heating temperature as a parameter. However, in this growth method, a seed crystal was not used, but it was grown from SiC powder, and thus the generated crystal is due to spontaneous nucleation. As can be seen from the figure, the 4H type has a large number of other crystals such as those that open from approximately 1800 ° C to approximately 2600 ° C, 6H type and 15R type. As described above, it is generally difficult to control the crystal form of SiC to be grown, and it is difficult to independently grow the 4H form even in the growth method disclosed in JP-A-62-66000. .

Therefore, the present invention provides a growth method capable of independently growing a 4H-type SiC single crystal.

(D) Means for Solving the Problem The present invention is to grow a 4H-type SiC single crystal on a seed crystal made of a silicon carbide single crystal kept at a temperature lower than that of the raw material by heating and sublimating a raw material made of silicon carbide. In the method, the temperature of the seed crystal is 2350 to 2450 ° C, and the temperature gradient between the seed crystal and the raw material is 5 to 20 ° C / cm,
It is characterized in that the gas pressure in the reaction system is 5 to 10 mbar.

(E) Action Under the above growth conditions, only 4H-type SiC single crystal grows stably.

(F) Example FIG. 1 shows an example of a crystal growth apparatus used in the method of the present invention. In the figure, (1) is a crucible made of graphite having a circular cross section, (2) is a SiC raw material, and (3) is sublimated S.
A guide made of graphite that guides iC to a SiC seed crystal (5) described later, and has an inner diameter reduced along the traveling direction of sublimated SiC. (4) is a growth container made of graphite, and (5) is a SiC seed crystal, which is placed and fixed on the inner upper surface of the growth container (4) so as to face the SiC raw material. (6) is a SiC ingot grown on the seed crystal (5). Such a crystal growth apparatus is placed in a reaction tube (not shown) and is heated by a high frequency induction heating coil wound around the reaction tube.

In such a crystal growth apparatus, a hexagonal type (Hexagonal) SiC substrate was used as the seed crystal (5), and crystal growth was carried out by variously changing the seed crystal temperature, the raw material temperature and the pressure in the reaction system. Here, the raw material temperature was set so that the temperature gradient between the raw material and the seed crystal was 10 ° C / cm. The pressure in the reaction system was adjusted by using an inert gas such as Ar gas. Table 1 shows the relationship between the crystal form of the crystals obtained by the above experiment and the growth conditions.

As is clear from Table 1, the growing SiC has independently obtained 6H type on the low temperature side and 4H type on the high temperature side with the seed crystal temperature around 2250 ° C as the boundary. However, the crystal form of SiC grown at a seed crystal temperature of 2250 ℃ was poor in reproducibility, and both 6H and 4H forms were obtained. Although not shown in the table, when the seed crystal temperature exceeds 2450 ° C., thermal etching occurs, which makes crystal growth difficult. Therefore, in the seed crystal temperature range of 2350 to 2450 ° C, 4H-type SiC grows independently. At this time, the pressure in the reaction system is appropriately 5 to 10 mbar. That is, if the pressure is 5 mbar or less, the growth rate is too fast,
Crystals with good crystallinity cannot be obtained, and if it exceeds 10 mbar, the growth rate becomes slow and it becomes impractical.

In addition, in this experiment, the temperature gradient between the raw material and the seed crystal was
Although the temperature was set to 10 ° C./cm, the same results as in Table 1 were obtained within the range of 5 to 20 ° C./cm, and crystals having good crystallinity were obtained within the above-mentioned temperature range and pressure range.

Next, using a hexagonal SiC substrate as a seed crystal, a SiC single crystal was grown under the growth conditions of a seed crystal temperature of 2350 ° C, a raw material temperature of 2450 ° C, a temperature gradient of 10 ° C / cm, and a pressure of 7 mbar in the reaction system. The measurement result of the Raman scattering spectrum is shown in FIG. The peak wave numbers 611, 781, and 967 shown in the figure are all unique to the 4H-type SiC single crystal, and are unique to the 6H-type.
No peaks at 68 and 789 are visible. That is, it is understood that the crystal form of such a SiC single crystal is the 4H type and does not include the 6H type crystal form.

(G) Effect of the Invention According to the method of the present invention, the seed crystal temperature is 2350 to 2450 ° C.,
A 4H-type SiC single crystal with good crystallinity can be independently grown by setting the temperature gradient between the seed crystal and the raw material to 5 to 20 ° C / cm and the gas pressure in the reaction system to 5 to 10 mbar. .

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a crystal growth apparatus used in the method of the present invention, FIG. 2 is a characteristic view showing a Raman scattering spectrum of a SiC single crystal produced by the method of the present invention, and FIG. 3 is Philip.
Si described in s Research Reports, Volume 18 (1963), P161.
FIG. 7 is a characteristic diagram showing the generation ratio of each crystal form of C. (1) …… crucible, (2) …… SiC raw material, (5) …… S
iC seed crystal.

Claims (1)

(57) [Claims] 1. A method of growing a 4H-type silicon carbide single crystal on a seed crystal made of a silicon carbide single crystal kept at a temperature lower than that of the raw material, by sublimating a raw material made of silicon carbide by heating. Growth of a silicon carbide single crystal characterized in that the temperature is 2350 to 2450 ° C, the temperature gradient between the seed crystal and the raw material is 5 to 20 ° C / cm, and the gas pressure in the reaction system is 5 to 10 mbar. Method.