GB911360A - Process for growing crystals - Google Patents

Abstract

A dendritic crystal of a semi-conductor material crystallizing in a cubic lattice structure, e.g. silicon, is pulled from a super-cooled central portion of a melt heated by electron bombardment and contained in a crucible of the same material using a seed crystal having at least one interior twin plane and orientated as shown in Fig. 3. An annular or arcuate electron gun may be employed. The central portion may be melted before super-cooling by increasing the power of the electron gun or by employing auxiliary heating, e.g. a further electron gun or an induction coil. A graphite shield, optional having heating means, may be situated above the electron gun to reduce the temperature gradient. Electron bombardment may be effected at a vacuum of 5 X 10-4 mm. The seed crystal may have an odd (preferably 3) or an even number of interior twin planes. The pulled crystal may be intrinsic or may contain a doping agent which may be present in the material before melting or may be added <PICT:0911360/III/1> <PICT:0911360/III/2> <PICT:0911360/III/3> to the melt. The tip of the seed may be melted before contact with the melt. The seed may be plunged 0,2 inch into the melt before pulling. The pulling speed may be 0,5-12 inches/min. The central portion of the melt may be super-cooled 5 DEG -40 DEG C. As shown in Fig. 1, a block of silicon 18 and a graphite support 16 are contained in a vessel having glass walls 30, an evacuation conduit 31, and an orifice 36 to enable withdrawal of the dendritic crystal. A molten pool is formed by means of an electron gun 20 (see Group XL(a)) optionally together with auxiliary heating means (not shown). After formation of the molten pool, heating is reduced so as to supercool the central portion 54 of the melt (Fig. 2) and pulling is commenced. The electron gun may be rotated during pulling. Specifications 889,058 and 911,359 are referred to.