DE1619987B2 - PROCESS FOR THE PRODUCTION OF CRYSTALS, IN PARTICULAR FOR SEMICONDUCTOR DEVICES - Google Patents

Description

The invention relates to a method as characterized in the preamble of the claim.

It is known that semiconductor crystals can be produced by having a seed crystal with brought into contact with a melt of the semiconductor material and a temperature gradient in the boundary layer is maintained so that the seed crystal grows.

Naturally, this process only applies to substances that melt at acceptable temperatures can be brought into question, such as silicon and germanium.

It is also known that silicon carbide at an acceptable temperature from a molten saturated solution in chromium can grow on a seed crystal. This substance is called a solvent can be used because the silicon carbide is readily soluble in it and this solvent is not in a disturbing degree the crystal is absorbed. This process is carried out in an inert gas at an atmospheric pressure the temperature slightly exceeding the melting point of the solution, namely at about 1800 ° C. The growth rate was due to the small temperature difference between the seed crystal and the solution of the crystal is disturbingly low.

This can be significantly improved if the crystallization takes place under a reduced gas pressure, in which the solvent evaporates, is carried out. In the surface layer with which the When the seed crystal is in contact, a state of supersaturation is caused, which is much faster Crystal growth induced.

It is also known that such a method is also of interest for semiconductor materials other than silicon carbide is. This does not only apply to semiconductor compounds, such as gallium phosphide, which are not or very difficult can be crystallized directly from a melt, but also for semiconducting elementary substances, such as silicon, which when dissolved in a low melting solvent, e.g. B. tin, with proportionate are crystallizable at low temperatures.

The solvent must then not only, as already mentioned above, an acceptable solubility of the Have semiconductor material and are not absorbed into the crystal to a disruptive extent, but also at the melting temperature have such a high vapor pressure that if necessary at reduced Pressure a sufficiently rapid evaporation of the solvent and rapid crystal growth takes place.

The latter requirements with regard to the solvent have the consequence that the choice of a solvent for crystallizing a particular semiconductor is very limited and sometimes even not a useful one Solvent will be present.

The invention aims to counter this disadvantage.

ίο The invention is based on the knowledge that the State of supersaturation instead of the physical removal of solvents through evaporation, optionally under reduced pressure, can be achieved in a simple manner by chemical means can.

According to the invention, the supersaturation and the crystallization are brought about that a gas is supplied to the atmosphere above the solution, which at the temperature of the melt reacts with the solvent and forms a volatile compound.

This way of evacuating solvent is less restrictive or less restrictive at least in a different sense restrictive influence on the choice of solvent than in the case that this if necessary, must take place under reduced pressure by evaporation. Most as a solvent suitable substances, such as gallium for gallimphosphide, silicon for silicon carbide and tin in the case of silicon, namely have a low vapor pressure at their melting point. Chrome, which as Solvent for silicon carbide is a favorable exception in this regard. Many of the However, at their melting temperature, possible solvents easily form with gaseous reagents, such as oxygen, sulfur and halogens, volatile compounds, causing solvents quickly can be withdrawn from the solution.

example 1

As shown in the drawing, a seed crystal 1 of gallium phosphide is placed on the surface of a saturated solution 2 of 4 mol.% gallium phosphide in gallium placed in a quartz tube 4 placed graphite vessel 3 in argon atmospheric pressure with the aid of the furnace 5 at a temperature is kept melted at 1050 ° C.

Chlorine is then passed through the quartz tube 4 at 50 ecm per minute. This will take Formation of volatile gallium chloride solvent (gallium) removed from the melt, so that in the Surface layer becomes supersaturated and the gallium phosphide seed crystal occurs at a rate by more than 30 μΐη per hour increases

Example2

Using a device of the type described in Example 1, a solution of 5 at.% Silicon in tin Melted in a quartz vessel at 900 ° C.

When passing hydrochloric acid gas at atmospheric pressure at a rate of 100 ecm per Minute, a silicon seed crystal placed on the solution grows at a rate of 25 μm per Hour on. This growth occurs because of the oversaturation in the surface view that it brings about is that solvent (tin) is removed from the solution in the form of volatile tin chloride.

When the solution is by evaporation in an argon atmosphere at a pressure of 10 mm

Solvent is withdrawn, one reaches only a crystal growth of 10 μm per at the same temperature Hour.

Finally, it should be noted that the method according to the invention can also be carried out in such a way that the seed crystal is fixed with respect to the graphite cup, the seed crystal being able to grow in that the solvent disappears and the liquid level in the cup decreases accordingly.

1 sheet of drawings

Claims (1)

Claim: Process for the production of crystals, in which a seed crystal with a saturated solution of the to brought into contact with crystallizing material in a molten solvent, the solution oversaturated and the material to be crystallized is crystallized therefrom in such a way that the seed crystal grows, characterized in that it brings about supersaturation and crystallization be that a gas is supplied to the atmosphere above the solution which is at the temperature of the Melt reacts with the solvent and forms a volatile compound.