INFLUENCE OF OXYGEN CONCENTRATION AND ANNEALING ON MORPHOLOGY AND ELECTRICAL-PROPERTIES OF SEMIINSULATING POLYCRYSTALLINE SILICON

Semi-insulating polycrystalline silicon films, deposited by low-pressure chemical vapor deposition on oxidized Si substrates at O concentrations from 2 up to 35 at. % O, have been annealed at 920-degrees-C for 30 min. Transmission electron microscopy revealed the presence of crystalline Si grains. The average Si grain radius decreases with O content going from almost-equal-to 15 up to almost-equal-to 2 nm, while electrical resistance increases with O concentration of almost four orders of magnitude. We attribute the resistance increase at large O contents to the presence of SiO2 shells, two monolayers thick, covering the Si grains. At these large O contents a noticeable increase in Si grain size and electrical conductance is observed in samples annealed at 1200-degrees-C for 30 min. These results can be interpreted on the basis of thermal instability of the oxide shells. This assumption is supported by observations of native oxide breaking against high-temperature annealings.