Effect of thermal etching on silicon epitaxial growth by vacuum sublimation

Abstract

Silicon epitaxial growth by vacuum sublimation was studied with emphasis on the effect of thermal etch of the substrate on the surface concentration of carbon. A calculation of surface concentration of carbon on a Si substrate during thermal etch in the vacuum system shows that prolonged thermal etch at a higher temperature progressively enhances a pile-up of involatile impurity on the substrate surface and formation of precipitates above solid solubility limits, which would cause generation of interfacial defects. This effect was experimentally confirmed with various temperatures and periods of thermal etch and with the use of LOPEX material. Experimentally optimized temperature and period of thermal etch with the use of LOPEX Si yielded a good quality epitaxial P/ N junction; low defect density 0–100 over the area of 10 −4 cm −2, low reverse saturation current of less than 1 × 10 −4 A/ cm 2 at half of breakdown voltage of 90 V. Uniformity of multiplication factor M over the reverse biased P/ N junction was measured with a laser probe. The variation around the average value over the area of a mesa junction structure 600 μm diam. was less than 10 per cent. Static I– V characteristics of PN junction, Schottky barrier NN + diodes and P + NN + diodes fabricated from grown layers by vacuum sublimation were also demonstrated.