STEM‐EDX Dopant Profiling of S‐D Implants in Submicron FETs

Abstract

N‐channel, submicron gate length MOSFET device structures have been examined in cross section, using STEM coupled with x‐ray analysis. The technique was calibrated by first analyzing a full wafer implant where the doping profile was known from RBS and SIMS. In cases where the probed region melted under the beam, the As signal was enhanced up to a factor of four due to solid/liquid segregation. Arsenic dopant profiles of the source and drain implants were measured both as a function of depth and as a function of lateral position across the gate edge. The experimental doping profiles were compared to electrical measurements of the channel length as well as the predictions of two process simulators, CUSTOM and SUPRA. The physical gate length, measured with cross‐sectional TEM, was 0.515 μm. The channel length, defined by the As concentration of 1018/cm3, was . Extrapolation of the measured As S/D profiles to , the channel doping level, indicated that the metallurgical channel length, i.e., the separation of the two compensation points, was . This value is greater than the electrically measured channel length value of 0.28 μm but is in good agreement with the CUSTOM and SUPRA values of 0.44 μm. Possible reasons for the discrepancy are discussed.