The surface transient in Si for SIMS with oblique low-energy O2+ beams

The surface transient in Si and SiGe for secondary ion mass spectrometry (SIMS) analysis with low-energy and obliquely incident O-2(+) beams was studied. In particular, the transition width (z(tr), the depth at which equilibrium secondary Si+ intensity was reached) was measured for various impact energies (0.56 keV less than or equal to E-p less than or equal to 2 keV) and incidence angle (45 degrees < theta < 77 degrees to the surface normal). For E-p < 700 eV and theta > 60 degrees, the transition widths for relatively fresh surfaces were 3-4 nm, offering good conditions for ultra-shallow SIMS analysis. At E-p = 1 keV and theta = 60 degrees, the differences in z(tr) between various secondary ions (Si+, SiO+, Ge+ and GeO+) were marginal and only O+ and Si-2(+) ions reached equilibrium significantly earlier. We found that z(tr) is about twice the mean penetration depth of the primary ions. In addition, the thickness of the native oxide of Si wafers was measured as a function of the storage time in air. It varied from 0.6 nm after 1 day to 1.5 nm after 2 Sears. Copyright (C) 1999 John Wiley & Sons, Ltd.