DE1077187B - Process for the production of single crystals from semiconducting materials - Google Patents

Description

Process for the production of single crystals from semiconducting materials There are already various methods of producing single crystals from semiconductor materials be # known, whereby a single-crystalline seed in the melt of the semiconductor material immersed and then slowly withdrawn from the melt, so that part of the The surface of the enamel is raised and the orientation is uniform when it solidifies of the seed crystallizes.

In the known method, it is disadvantageous that often "envelopes" and high dislocation densities occur d. That is, when pulling the single crystal, disturbances in growth arise, with changes in orientation occurring. These phenomena occur in particular with semiconductors with a high melting point. Furthermore, there is the difficulty of pulling single crystals from melts of semiconducting compounds if, for. B. AlSb, a component at the melting temperature has a high vapor pressure and the vapor is reflected on the colder parts of the apparatus. This disrupts the stoichiometric ratio in the melt, because one component always - and again from the melt into the vapor state.

In order to allow the single crystal pulling operations to proceed without disturbance, i. H. In order to achieve a uniform and low-dislocation arrangement of the particles, it is necessary that three conditions are met: The melting of the semiconductor material must have a clean surface in the crucible that is free of recognizable impurities, such as skin or the like.

It must also be at the phase boundary, i.e. H. at the interface between crystal and melt, a large vertical temperature gradient must be present.

Furthermore, no radial, i. left be present along the phase boundary running temperature gradient.

Compliance with these conditions is exemplified below studied for silicon.

The silicon is mostly melted in quartz crucibles. It does occur, however from the quartz already below the softening point Si02 # blast out which is the cooler parts and thus precipitate on the silicon pieces and after Melting on the surface to form a thin membrane. Using others Crucible material fails to react with the silicon, so it forms z. B. when using graphite crucibles silicon carbide. The precipitation of the Si02 vapors on the melting material are prevented if the crucible is only in the lower Fills the part with pieces of silicon and holds the crucible in the inner furnace. When immersed of the cultivation germ in the melt is the necessary large temperature gradient not present perpendicular to the phase interface.

Urn a high temperature gradient perpendicular to the phase interface Getting between melt and single crystal has already been proposed in the Bracket of the breeding germ to pass through cooling water and to cool it. However, this is difficult and means a complicated outlay in terms of equipment because it takes place at the same time the movements of the breeding germ required for breeding must be observed. It it was found that the temperature gradient decreased as the crystal decreased grew because the heat conduction of the semiconductor material is low and the melt is also lowers down.

In another known method, for. B. blown hydrogen gas from ring-shaped nozzles for flushing onto the drawn material. Although in this case, a sufficiently large vertical temperature coefficient is achieved, at the same time creates j edoch a significant radial temperature coefficient, which is undesirable.

It is also known in the manufacture of single crystals from compounds to work with volatile components in a Z-wide temperature oven in order to reduce the The walls of the vessel and the parts outside of the melting vessel are at one temperature to be kept above the condensation or sublimation temperature. The heater is divided into a plurality, one of which keeps the melt at temperature, the other heating devices keep the parts of the melting device on one Temperature above the condensation or sublimation point, the come into contact with the volatile components. There will thus be the reduction one component avoided in the melt; however, it does not become a constant large one vertical temperature coefficient achieved.

For the production of single crystals from the melt, it is also known around the rod drawn from the melt, at least in the lower area in the axial direction to arrange a reflective screen that tapers conically at the top. A favorable radial temperature gradient is achieved here, but compliance a constant large vertical temperature coefficient is not guaranteed.

In all of these processes, it is disadvantageous that when melting the Semiconductor material, the contents of the crucible are not at the same temperature as the crucible is held so that vapors from the crucible material are deposited on the melt.

These shortcomings are avoided when producing a single crystal of a semiconducting material according to the invention before the dipping of the germ The crucible with the melt is slightly raised opposite the heater and the surface of the Melt at a constant distance from the heat source during the pulling process is held.

The inventive method ensures that the to melting goods during melting at a not significantly lower temperature is held as the crucible material, so that escaping vapors from the crucible material cannot condense on the melt material. For growing the single crystal the melt is lifted so far out of your area of the furnace that the immersed The germ of the oven is not significantly heated and so the desired temperature gradient is achieved.

A device is used to carry out the method according to the invention required, which allows the crucible to move relative to the heat source. Such Devices are known per se.

The subject matter of the invention is exemplified with reference to the figures explained.

Fig. 1 shows a single crystal growing device for carrying out the method according to the invention in a simplified representation in section. A quartz tube 1 serves as a container, which is provided with a water-cooled brass joint 2 and 3 each at the top and bottom. A projection 4 rises sideways from the tube, which has a ground joint 5 and is closed with a glass envelope which contains a viewing window 6 made of temperature-resistant glass. The upper brass joint 2 contains a bush 7 through which the pull rod 6 , which carries the germ holder 9 with the cultivated germ 10, is passed. In the quartz tube 1 bE there are several projections 11 on which the furnace 12 rests. The furnace 12 contains without resistances as a heat source. The connections for the Ileizspirale are carried out through the seals 13 .

To accommodate the melt, z. B. the silicon pieces, the crucible 14 is used. The crucible hangs on a type of crankshaft 15, which protrudes through a pipe socket 16 into the quartz tube 1 and is held by means of a stuffing box 17 in # äem water-cooled brass ground joint 18. The entire process must take place in an inert gas atmosphere. For this purpose, purified hydrogen gas is pressed into the quartz tube through the hose attachment 19 and discharged again through the hose attachment 20.

The workflow begins with the melting of the silicon pieces 21 in the quartz crucible 14, the crucible being lowered all the way into the furnace 12 by one Precipitation of Si 0 vapors on the. Avoid top of the silicon chunks 21.

After melting of the silicon, the crucible according to Fig. 2 is raised from the position 22 to the position 23 and the immersed Zuchtkeirn by the pulling rod in the melt, the exact Siliziumschinelze is maintained at least the melting temperature. The germ of breeding will. then drawn from the melt at a very low speed in order to initiate an orderly crystallization process. The still disruptive influences of a low temperature gradient radially to the phase interface between the single crystal and the melt are compensated for by a rotating and an oscillating movement el along the axis of the growth nucleus, as is known from other single crystal pulling devices. During the pulling process, the crucible is lifted intermittently by the lifting device acting as a crank so that the surface of the melt always remains at the same height above the furnace from the beginning to the end of the single crystal pulling process.

Claims (1)

Claim: A method for pulling a single crystal from the melt by means of a nucleus dipped into the melt and slowly extracted, characterized in that the crucible with the melt is raised slightly in relation to the heater before the nucleus is dipped in and that the surface of the melt is in at a constant distance from the heat source. Considered publications-German Patent No. 944 209; German Auslegeschriften No. 1 044 769, 1051806; British Patent No. 784,617.