Improvements in and relating to methods of manufacturing semi-conductor bodies of silicon carbide

摘要

1,031,835. Semi-conductor devices. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. June 4, 1963 [June 6, 1962], No. 22157/63. Heading H1K. In a method of producing a silicon carbide body with a PN junction, extrinsic material of one conductivity type is deposited on a substratum of silicon carbide material of the opposite conductivity type and the combined total of the concentrations of donor impurities in both deposited and substratum regions is equal to, or greater than (if the substratum is N-type) or less than (if it is P-type) the combined total of the concentrations of acceptor impurities. This ensures that any movement due to diffusion effect, of the PN junction which exists initially at the interface between substratum and deposited regions is such that the junction moves into the deposited region and not into the substratum region where it might reach the outer edge and so be eliminated. Fig. 17 shows a section of a silicon carbide crystal in which 96 shows the boundary between the P-type substratum 93 and the newly deposited material and the PN junction 95 which has been shifted into the deposited region due to diffusion during the deposition process. A thin intrinsic region may exist between the P and N regions. Fig. 13 shows an apparatus for producing such crystals. Lumps of silicon carbide 62 are placed in a graphite vessel 61 to leave a central chamber 83 in which silicon carbide crystals are deposited when the material is heated to 2000‹ C. Aluminium and nitrogen are used as acceptor and donor impurities. Aluminium carbide may be placed around support 64, and a flow of argon supplied via pipe 82; heating is effected by means of copper electrodes 78 with cooling ducts 79, connected to carbon oven 77. The process results in the deposition of P-type silicon carbide crystals containing 7 x 1018 atoms per c.c. of aluminium. After 4 hours heating, nitrogen is added to the argon so that the silicon carbide material then deposited contains 14 x 1018 atoms per c.c. of nitrogen in addition to the aluminium. The combined total of donor concentrations thus equals the combined total of acceptor concentrations and under these conditions the PN junction tends to remain stationary at the original boundary (i.e. where the nitrogen was introduced) in spite of subsequent diffusion effects. In a further example, aluminium chloride added to the argon was used to provide the aluminium impurity. Deposition may alternatively be effected from a melt or by evaporation, sublimation, thermal decomposition or reaction.