Diffusion and precipitation of As from a CoSi 2 diffusion source

Abstract

Arsenic ions were implanted into CoSi 2 thin layers and subsequently diffused into the underlying silicon substrate. Junctions in the range between 30 and 400 nm depth were obtained with a high dopant concentration (10 19-10 20 cm -3) at the silicide-silicon interface. Coherent Si-As precipitates were found at the silicide-silicon interface near the CoSi 2 grain boundaries. The precipitate formation has been associated with the high tensile stress induced by the silicide layer on the surface silicon region and to its influence on the dopant solid solubility. The precipitate density decreases if the silicide thickness is reduced, i.e. if the tensile stress produced by a silicide layer gets lower. These precipitates are easily dissolved during high temperature annealing after the silicide layer removal. A new delineation technique based on TEM analysis of selectively etched samples has evidenced that the intersections of silicide grain boundaries with a silicon surface act as diffusion sources.