Optimization of primary beam conditions for secondary ion mass spectrometry depth profiling of shallow junctions in silicon using the Perkin–Elmer 6300

Abstract

Submicron ULSI designs require the measurement of ultra-shallow junction implants with peak concentrations within 10 nm below the surface of a wafer. Secondary ion mass spectrometry (SIMS) can provide the necessary depth resolution and sensitivity when optimized. The Perkin–Elmer Physical Electronics Model 6300 secondary ion mass spectrometer was used to analyze As and B junctions produced with preamorphization and low-energy ion implantation. Cs+ and O+2 primary ion beams were used for As and B depth profiling, respectively. The primary beam energy and angle of incidence can be independently varied in this instrument. Lower primary energy and shallower angle of incidence reduced the beam broadening effect caused by atomic mixing. Conditions were optimized using a 3 keV primary beam at a 60° angle of incidence for both As and B implanted samples. Lower beam energies resulted in crater edge effects due to poor primary beam focus quality. Other instrumental factors, including electronic ion gating, secondary ion energy, and primary beam current were also evaluated. With a 30° incidence O+2 ion beam, B+ profile distortion was observed and was attributed to SIMS sputter-induced segregation.