PRECIPITATION OF ARSENIC DIFFUSED INTO SILICON FROM A TISI2 SOURCE

The diffusion into a rho-type Si substrate of arsenic ions implanted into TiSi2 layers has been investigated for several thermal diffusion treatments in the 900-1100-degrees-C temperature range. The drive-in was performed using either a rapid thermal annealing system or a traditional furnace. Shallow (20-80-nm depth) junctions were obtained with a high (10(19)-10(20)/cm3) dopant concentration at the silcide-silicon interface. The amount of diffused arsenic atoms measured by Rutherford backscattering spectrometry increases linearly with the square root of the annealing time. A similar relation was found for the amount of electrically active arsenic, as measured by Van der Pauw structure in combination with anodic oxidation. The two quantities differ and the inactive dopants precipitate in the diffused layer as seen by transmission electron microscopy. This behavior might be associated to the high tensile stress induced by the silicide layer on the surface silicon region and to its influence on the solid solubility and clustering of arsenic atoms. Precipitates are easily dissolved after thermal annealing in the absence of the TiSi2 layer.