Hydrogen-plasma-enhanced oxygen precipitation in silicon

Abstract

Czochralski-grown silicon crystals with different carbon concentrations havebeen heat-treated in µ-wave hydrogen plasma in the temperature range500-700 °C. For comparison, control samples have been treated in afurnace in a nitrogen ambient. Infrared (IR) absorption measurements show thatthe loss of oxygen atoms from solution due to the formation of SiO2precipitates is strongly enhanced by the H-plasma treatment in bothcarbon-lean and carbon-rich Si crystals. The loss of oxygen is accompanied bythe loss of substitutional carbon atoms from solution in the C-rich samples.The frequencies and shapes of the IR absorption bands associated with theprecipitates are different in C-rich and C-lean crystals, indicating theformation of different types of precipitate particle. The former bands (Crich) are similar following heat treatments in a H-plasma or in N2 gas. Itis inferred that a fast diffusing species penetrates into Si crystals duringthe H-plasma treatment, leading to a catalytic enhancement of oxygen diffusionthat in turn leads to enhanced precipitation. Possible mechanisms for theenhanced oxygen diffusion and precipitation are discussed briefly.