Using accelerator techniques to verify details in SIMS profiles

Recent use of ultra-low energy (ULE) ion implantation in the semiconductor industry has placed increasing pressure on SIMS depth profiling capabilities. We have used nuclear reaction analysis (NRA) to calibrate implantation doses of boron ULE implants as an essential check of the SIMS accuracy. Comparison of NRA done in two different laboratories has revealed differences of up to 15%, making it essential to calibrate the measurements against an accurate standard. It has become evident in the last few years that the accepted SIMS depth profiling method for ULE B implants, low-energy oxygen bombardment with an oxygen leak, causes significant segregation of boron during the SIMS profile. High-resolution ERD measurements appear to be one of the few techniques other than SIMS that can resolve the near-surface details of the boron distribution. Careful comparisons of the ERD and SIMS profiles allow us to refine our SIMS correction procedures to produce the most accurate measurement of the boron distribution. Similarly, ULE As implants show significant segregation of As toward the native oxide interface as a result of annealing. To ensure that we measure these distributions accurately, MEIS has been employed to examine the As distribution within 10 nm of the surface.