METHOD FOR MAKING THERMALLY OXIDIZED BORON DOPED POLYCRYSTALLINE SILICON

摘要

A method for the in-situ boron doping of polycrystalline silicon is disclosed wherein the boron-to-silicon ratio is increased beyond the limit of solubility of boron in silicon. Using appropriate flow rates of SiH4, B2H6, and H2, and deposition temperature, boron rich silicon is deposited upon a substrate. The boron is in solution in the silicon to the limit of its solubility and is present in excess amounts in boron-rich phases believed to be boron silicides. The deposited boron-rich polycrystalline silicon is subjected to a thermal oxidation step during which the dissolved boron is depleted into the growing oxide while the boron-rich phases decompose allowing the freed boron to go into solution in the silicon to replace the boron which is lost to the thermal oxide. By proper selection of parameter values, based upon experimentally determined silicon resistivity-to-B2H6 flow rate-to-thermal oxidation relationships, the boron-rich phases are substantially eliminated from the polycrystalline silicon at the same time that the thermal oxidation step is completed thereby yielding minimum resistivity doped silicon in the final structure.