JPS6357400B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a single crystal of silicon carbide, SiC, and in particular to the 6H modification of this crystal by sublimation and partial decomposition of an industrial silicon carbide crystal and onto the seeds in a reaction vessel under a protective gas. Relating to a method of manufacturing by growth.

For mass production of blue-light LEDs (light emitting diodes) made of silicon carbide SiC and to take advantage of their wide bandgap, high melting point and high thermal conductivity, as large a substrate as possible with certain properties is required. Such substrates are prepared from crystalline plates processed from the crystal slag that happens to occur during the so-called Acheson process. However, it often appears unsuitable for the individual substrates, since during epitaxy regions are created with luminescent phenomena of other colors.

As is well known, single crystals of silicon carbide can be produced by the so-called Lely process by sublimation of partially decomposed compounds into carbon- and silicon-rich vapors and growth in a reaction chamber. In the case of this method, industrial silicon carbide is decomposed and a single crystal consisting of α-SiC is placed in a reaction chamber at a relatively high temperature of about 2500°C and a relatively high pressure.
It can grow on the inner walls of hollow cylinders made from chunks of SiC. A temperature gradient is then maintained from the center of the hollow cylinder both towards the ceiling and towards the bottom of the reaction chamber.
The spread of this single crystal plate is small [Inst.Phys.Conf.
No. 53 (1980) pages 21-35].

Furthermore, it is known that single crystals of silicon carbide can be grown on seed crystals of silicon carbide at temperatures of 1800 to 2600°C. The growth rate is influenced by temperature, axial temperature gradient and protective gas pressure. Single crystal has a temperature of 1800℃ and 10 ^-3
This is caused by a temperature gradient of approximately 30° C./cm at a pressure of ~10 ⁻⁴ mbar. In this method, it is difficult to produce single crystals with desired crystal transformations, especially 6H transformation [Inorganic Materials, Vol. 14 (1978
), pp. 830-838].

The object of the present invention is to produce a 6H-transformed single crystal of silicon carbide having a sufficient size and a small amount of impurities so that it can be used as a substrate for a light emitting diode. In a known method for producing such single crystals using single crystal seeds,
This is based on the recognition that the temperature gradient has been selected too high and the protective gas pressure has been selected too low.

Furthermore, diagrams are known in which the equilibrium vapor pressure on SiC systems is plotted as a function of temperature. From this diagram, the adjustment of the total vapor pressure can be estimated (Knippenberg
Author) “Growth Phenomena in Silicon Garbide”
Philips Research Reports No. 18 (June 1963)
Pages 164-166 of 161-274).

The above object, according to the invention, is such that the temperature gradient in the growth direction in the reaction vessel is at most 25°C/cm;
This is achieved by maintaining the seeds at a temperature of 2100-2300° C. and adjusting the pressure of the protective gas to be at least as great as the sum of the gas pressures of the components of the deposit. In this case, the temperature gradient should be at most 20℃/
cm and the pressure of the protective gas is adjusted to compensate for the internal pressure caused by the highly heated SiC system. For this purpose, the pressure of the protective gas is adjusted to a range of approximately 1 to 5 mbar, preferably approximately 1.5 mbar.
Select a range of ~2.5mbar. In that case, a single crystal several centimeters long grows on the seed.

In a particularly advantageous apparatus for carrying out the process according to the invention, the gaseous precipitate components are conducted into the precipitation zone substantially against the temperature gradient. This introduction
For example, only porous graphite is placed outside the reaction chamber on both sides of the precipitation zone, and silicon carbide prepared for sublimation is placed above the precipitation zone, alongside the reaction chamber and behind the separation wall of the porous chamber. This can be done easily.

The required temperature gradient provides additional cooling to the seeds,
This is achieved by providing additional thermal insulation to the lid of the reaction chamber. A particularly advantageous alternative configuration of the device is obtained by providing an additional heating device in or on the lid.

The invention will now be further explained with reference to the drawing, which shows an example of a device for carrying out the method according to the invention.

In the illustrated embodiment of the precipitation apparatus, the reaction chamber 2 comprises a precipitation region 4 and an introduction region 6, for example about
It has a cylindrical side wall 8 made of solid porous graphite with an inner diameter of 25 mm and a length L of, for example, about 100 mm, with relatively large holes. For example, a diameter d of about 15 mm
A disk-shaped seed 10 made of single-crystal silicon carbide and having a height h of, for example, about 0.5 mm is arranged on a platform 12 made of, for example, electrolytic graphite and forming the bottom of the reaction chamber 2. The upper part of the reaction chamber is closed by a lid 14, which is provided with a thickened section, not labeled in detail in the figure, which is used for centering the side wall 8.
For heating the reaction chamber 2 and the precipitate components, a hollow cylindrical heating wall 16 and an upper heating plate 17 and a lower heating plate 18 are provided, which may be made of electrolytic graphite, for example, and are preferably water-cooled. It is inductively coupled to the coil 20. The space between the side wall 8 and the heating wall 16 is provided with a filling 22 of solid porous graphite located around the deposition region 4 in its lower part. Above the filling 22, concentrically to the introduction region, the intermediate space is made of highly pure granular industrial silicon carbide 24, preferably having a particle size of, for example, about 200 to 300 μm, and consisting to a large extent of 6H transformation, but for example 4H. It is filled with green silicon carbide which may also contain crystals of modified as well as cubic structure.

The reaction vessel equipped with heating means is surrounded by a vessel 26, which preferably consists of a thermal insulator and serves as a heat shield. Graphite foil (Sigraflex), which is wound or stacked as a hollow cylinder, is suitable as a thermal insulator. It is arranged in a vacuum vessel 28, made of quartz, for example, and only schematically shown in outline by dashed lines in the figure. The vacuum container 28 is equipped in a known manner with the necessary means for operation, such as connections to a vacuum pump and gas lines.

To start the precipitation process, the vacuum vessel 28 and with it the reaction chamber 2 are filled with a protective gas, for example argon, and then the reaction chamber 2 is heated to the desired operating temperature of about 2200.degree. Subsequently, the resulting gaseous SiC system components, namely Si, Si ₂ C and SiC ₂
evacuate to a pressure approximately equivalent to the gas pressure of The sum of the gas pressures of these components is approximately 2 Torr. The number above species 10 as the pressure in reaction chamber 2 decreases
A single crystal 30 with a height H of cm, for example 3 cm, is grown. This size is sufficient for direct use as a substrate for a semiconductor device made of silicon carbide.

In another embodiment of the device, a special cooling system can be provided for the seeds 10, which may consist, for example, of a cooling finger 30 terminating in the platform 12 and passing through the vacuum vessel 28.

Furthermore, above the upper heating plate 17 there is preferably a special thermal insulation, by means of which the heating gradient from the deposition zone 4 to the introduction zone 6 can be controlled.
In a further embodiment of the device, this thermally insulating layer can be designed at the same time as an additional heating means 19 made of graphite, for example, and which can be inductively coupled to the induction coil 20.

[Brief explanation of drawings]

The figure is a sectional view of an apparatus for carrying out the method of the invention. 2...Reaction chamber, 4...Precipitation region, 10...Seed,
14... Lid, 16... Heating wall, 17... Upper heating plate, 18... Lower heating plate, 20... Induction coil,
28...Vacuum container, 30...Single crystal.

Claims (1)

Claims: 1. A method for producing 6H-transformed single crystals of silicon carbide by sublimation and partial decomposition of industrial silicon carbide crystals and growth on the seeds in a reaction vessel under protective gas, comprising: The temperature gradient in the growth direction in the reaction vessel is at most 25℃/cm, and the seeds are
A method for producing a silicon carbide single crystal, the method comprising: maintaining the temperature at a temperature of °C, and adjusting the pressure of a protective gas so that it is at least as large as the sum of the gas pressures of the components of the precipitate. 2. The manufacturing method according to claim 1, wherein the temperature gradient is at most 20°C/cm. 3. The manufacturing method according to claim 1, wherein the temperature is about 2200°C. 4. The manufacturing method according to any one of claims 1 to 3, characterized in that the pressure of the protective gas is maintained in the range of 1 to 5 mbar. 5. The manufacturing method according to any one of claims 1 to 4, characterized by cooling the seeds. 6. The manufacturing method according to any one of claims 1 to 5, characterized in that heat dissipation from the lid of the reaction chamber is prevented. 7. The manufacturing method according to any one of claims 1 to 5, characterized in that the lid of the reaction chamber is additionally heated.