Imaging and nano-probing of doping in Si by site-specific scanning spreading resistance microscopy (SSRM)

Due to the continuous reduction of the critical dimensions of semiconductor devices, it becomes very important to know the two dimensional (2D) doping profile for improving device performance. Scanning spreading resistance microscopy (SSRM) performed in high vacuum is a powerful technique for quantitative 2D-doping profiling, with high spatial resolution and wide dynamic range of carrier concentration, as well as capability of site-specific analysis for accurate position. In this paper, we review SSRM applications to source/drain engineering in Si devices and their correlation with device characteristics by demonstrating several case studies. We also demonstrate direct observation of discrete dopant distribution and fluctuation of active boron (B) in scaled nFETs and in various B-doped epi-layers by site-specific SSRM. The B fluctuation is attributed to segregation of B dopant, which depends on thermal diffusion and occurs even under thermal equivalent conditions without structural stress. Site-specific SSRM is demonstrated to be capable of observing discrete dopants in silicon.