In situ control and monitoring of doped and compositionally graded SiGe films using spectroscopic ellipsometry and second harmonic generation

We have implemented linear and nonlinear optical spectroscopies to monitor and control the growth of SixGe1-x films. Using spectroscopic ellipsometry and the virtual substrate approximation (VSA), controlled growth of composi tionally graded SiGe films deposited by chemical vapor deposition (CVD) is achieved by adjustment of disilane now based on feedback from ellipsometric inputs, Stepped and linear growth profiles are investigated. Using spectro scopic, surface second harmonic generation (SHG) by a tunable, unamplified Ti:sapphire 100 femtosecond (fs) laser, shifts of the SH spectral feature n ear the Si E-1 critical point with varying Ge composition are observed. A c omparison is made to linear spectroscopy and related qualitatively to surfa ce composition. Data acquisition time is then reduced to a few seconds by s ubstituting a 10 fs laser and spectrally dispersing generated SH radiation onto an array detector, thus enabling real-time spectroscopic SHG. The refl ected SH spectrum near the E-1 region is also highly sensitive to bull; bor on doping of SiGe. Definite trends in the peak positions and amplitudes as a function of boron incorporation are observed and interpreted qualitativel y in terms of dc-electric-field-induced SHG in the depletion region. The re sults demonstrate the feasibility of SE and spectroscopic SHG operating as complementary, in situ sensors of Sice CVD. (C) 2000 Elsevier Science B.V. All nights reserved.