DE1619986C3 - Process for the production of silicon carbide crystals with a p-n junction - Google Patents

Description

The invention relates to the production of silicon carbide crystals for semiconductor devices.

It is known that silicon carbide crystals with a pn junction can be produced by doping successively during the growth of the crystal by recrystallization and / or condensation in an inert gas atmosphere on the wall of a space delimited by silicon carbide at temperatures of about 2500 ^{0 C,} which bring about the various conductivity properties of silicon carbide, are fed into the gas atmosphere.

As a result of diffusion of the doping into the crystals at the very high temperatures, however, a sharp transition between the p and η zones not achieved.

Tests leading to the invention have shown that, among the usual dopings for silicon carbide, aluminum, which acts as an acceptor, promotes the growth of silicon carbide crystals by recrystallization and / or condensation to a significant extent. This makes it possible to carry out the growth of the p-conductive part of the crystal at a ^{temperature 200 to 300 °} C. lower than was required for the formation of the η-conductive part, which results in a greatly reduced diffusion in the boundary zone between these parts . In this way, a crystal with a considerably sharper transition between the p- and η-zones can be realized, which is particularly beneficial for the quality of semiconductor devices, such as diodes and transistors, manufactured with these crystals in the usual way.

The invention relates to a method for producing silicon carbide crystals in which a pn junction is obtained by successively doping the various conductivity properties in silicon carbide during the growth of the crystals by recrystallization and / or condensation in an inert gas atmosphere in a space delimited by silicon carbide bring about, are fed to the crystallization chamber, characterized in that ^{n-type silicon carbide crystals are formed at temperatures of 2300 to 2600 0} C in the presence of a donor, the temperature is ^{reduced to below 2000 0} C, then after the crystallization chamber is completely freed of donor aluminum has been supplied to this space as an acceptor and the growth of the silicon carbide crystals is continued at a temperature which is 200 to 300 ^° C. lower than that at which the n-type crystals have been formed.

The invention is illustrated in more detail below with reference to the drawing and a few examples.

example 1

As in Fig. 1 shown in section, a core 2 is inserted into a graphite tube 1 and the gap filled with silicon carbide 3 obtained by pyrolysis of methylchlorosilane SiHCbCHj in hydrogen has been.

The silicon carbide powder is pressed on and the core 2 is carefully removed, whereupon the whole is sintered will.

The resulting vessel consisting of the graphite cylinder 1 and the cylinder 4 made of sintered silicon carbide is, as shown in FIG. 2, closed on both sides by plates 5. Is heated with 0.1% of nitrogen at atmospheric pressure by means of the high frequency coil 7 to 2550 ⁰ C. Subsequently, in a quartz envelope 6 in argon. Plate-shaped silicon carbide crystals, which are n-conductive, arise almost perpendicular to the vessel wall through recrystallization and / or condensation.

After cooling, as in FIG. 3 illustrates, the vessels 1 to 4 are placed on a graphite vessel 9 which contains aluminum carbide 10, and the whole is closed by means of a plate 5. On heating of the crystals at 2250 ° C and the aluminum carbide 10 to 2100 ⁰ C in an argon atmosphere, then p-type silicon carbide, aluminum as acceptor contains 8, epitaxially deposited on the crystals.

In Fig. 4 such a crystal is shown schematically in section. The η-conductive part 11 of the crystal contains about 0.001% nitrogen and the p-type portion 12 contains about 0.1% aluminum.

This crystal is sawn into platelets, each 1 mm ² and 0.5 mm thick, which, as shown in FIG. 5 is shown on an enlarged scale, on the η-conductive part 11 and the p-conductive part 12 are provided with platinum contact wires 13 by melting a gold alloy 14 with 5% tantalum at 1300 ° C.

The resulting diode radiates when loaded with 10 V. 30 mA orange light off. At higher injection currents, such as. B. 300 mA, blue light is emitted.

Example 2

In a manner similar to that described in Example 1, plate-shaped η-conductive silicon carbide crystals are obtained 8 produced, on which silicon carbide is deposited epitaxially, which by the addition of aluminum and boron is p-type through the gas phase. For this purpose, a mixture of aluminum carbide and Given boron carbide. The deposition of the p-conducting silicon carbide is carried out at the same temperatures as indicated in example 1.

Due to the presence of the aluminum, the deposition could take place at a lower temperature

can be made than in the formation of the n-type Substrate crystals was necessary, and due to the fact that boron diffuses faster into silicon carbide As aluminum, the absorbed boron is the color of the light emitted by a diode (Fig. 5) will. With an injection current of 30 mA at 10 V, green light is emitted. At higher injection currents, such as B. 300 mA, has the light, as well

decisive for the p-n junction and therefore for the 5 as with the diode according to the example!, a blue color.

1 sheet of drawings

Claims (1)

Claim: Process for the production of silicon carbide crystals, in which a pn-junction is obtained by doping successively during the growth of the crystals by recrystallization and / or condensation in an inert gas atmosphere in a space delimited by silicon carbide, which induce different conduction properties in silicon carbide, the crystallization space are supplied, characterized in that ^{n-type silicon carbide crystals are formed at temperatures of 2300 to 2600 0} C in the presence of a donor, the temperature is reduced to below 2000 ° C, then after the crystallization space has been completely freed from the donor, this Space is supplied as an acceptor and the growth of silicon carbide crystals is continued at a temperature lower by 200 to 300 ° C than that at which the η-type crystals have been formed.