Effect of annealing a silicon wafer in argon with a very low oxygen partial pressure

The surface roughening of a silicon wafer during annealing in argon at an extremely low oxygen partial pressure, which restricts the conditions for the suppression of oxidation-induced stacking faults, was investigated. It was found that surface roughening occurs when the oxygen partial pressure is lower than 3 x 10(-5) atm. The roughening is brought about by the generation of square pits and the anomalous growth of film. Fiber-like material is, sometimes, formed in the periphery of the wafer. It was found that grown film and the faber-like material are SiO2 and that the pits have the shape of an inverted pyramid. The mechanism of this roughening is discussed with considering a boundary layer. As a result, the formation of the inverted-pyramidal pits is attributed to the occurrence of SiO evaporation in the boundary layer, where the gas flow is stagnant and the oxygen partial pressure is extremely low. The four exposed surfaces at the bottom of a pit have a (111) surface orientation. The anomalous growth, of the oxide and the formation of the fiber-like material were interpreted to be due to the reoxidation of the evaporating SiO at the edge of the boundary layer and its redeposition in the form of SiO2 on the wafer. It was concluded that the inclusion of oxygen at a partial pressure higher than 4x10(-5) atm is important to prevent surface roughening during annealing even in an inert gas like argon. (C) 2000 American Institute of Physics. [S0021-8979(00)04424-8].