Comparative Study of Experimental Techniques for Boron Profiling at Poly-Si/SiO₂ Interface

Abstract

Electrical characterization of MOS structures and device modeling require accurate information about dopant concentration, particularly at the poly-Si/SiO2 interface. We compare four experimental techniques (secondary ion mass spectrometry SIMS, resonant ion mass spectrometry RIMS, differential Hall effect profiling, and spreading resistance analysis) to measure boron and free carrier concentrations in poly-Si, SiO2 and crystalline Si. We find that no single technique completely characterizes the entire MOS structure, and that spreading resistance analysis in particular substantially underestimates the free carrier concentration at the poly-Si/SiO2 interface. We conclude that in most cases of technological interest the magnitude of the poly depletion effect scales with the average carrier concentration at some distance away from the interface and that the interfacial effects, such as dopant segregation, are of only secondary importance. These findings are supported by theoretical modeling of capacitance-voltage behavior of boron-doped MOS capacitors.