Analysis of selectively grown epitaxial Si1-xGex by spectroscopic ellipsometry and comparison with other established techniques

The increased interest in epitaxial Si1-xGex/Si heterostructures for device applications requires very good control of layer thickness and composition . Unfortunately, most of the well-developed characterization methods, such as Rutherford backscattering spectroscopy (RBS), secondary ion mass spectro scopy, and photoluminescence measurements are unsuitable as production meas urement tools. On the other hand, spectroscopic ellipsometry (SE) allows a fast, in-line, and nondestructive analysis, including wafer mapping capabil ities. This paper demonstrates the suitability of SE for the determination of both Ge content and layer thickness of epitaxial Si1-xGex for Ge content s between 1 and 35%. By describing the optical dispersion by means of the h armonic oscillator model, we obtained a clear correlation between the Ge co ntent and E-n(1), the resonant energy of the first oscillator, and n(max), the peak value of the real part of the refractive index. The small spot (30 x 30 mu m) size allows one to characterize Si1-xGex layers selectively gro wn in an isolation structure. The small window size prevents RES measuremen ts. SE allowed the fine tuning of a selective epitaxial growth process with regard to growth rate, Ge incorporation, and wafer uniformity. (C) 2000 Th e Electrochemical Society. S0013-4651(99)05-063-6. All rights reserved.