Routine depth profiling of ultra shallow junctions by secondary ion mass spectrometry

Low energy ion implantation is used to form sub-100 nm shallow junctions in ULSI fabrication. In order to completely characterize these junctions, instrumental depth resolution must be optimized and the transient ion yield changes in the near surface region must be minimized. Depth profiling of shallow junctions has previously been demonstrated in a research environment, but the analysis protocols are quite complicated. We have developed a method to routinely profile ultra-shallow junctions by combining oxygen flooding and high depth resolution profiling. The surface secondary ion mass spectrometry technique which normally requires a magnetic sector instrument gets rid of the surface transient whereas the best depth resolution is more readily achieved using a quadrupole instrument. Two analyses no performed and the data are combined to accurately determine the depth distribution of ultra shallow dopants in silicon. Using optimized analytical conditions, the depth resolution is shown to be better than 0.7 nm. The analytical procedures described in this paper are being employed for the routine and commercial characterization of shallow dopants in silicon. (C) 1998 Elsevier Science S.A.