Characterization of Si1-xGex Epilayer Thickness, Ge and Doped Boron Concentration with UV-Vis-IR Spectroscopic Ellipsometer

Lattice mismatch in SiGe/Si heterostructure provides a way to improve silicon based device performance through modification of the band gap and band alignment. The ability to precisely determine epilayer thickness and Ge concentration is essential for calibrating growth processes and thus control film quality. Spectroscopic ellipsometry is a non-destructive optical technique and has advantages for in-line process monitoring over SIMS, TEM and other destructive techniques. With UV-Vis-IR spectroscopic ellipsometer, not only epilayer thickness and Ge concentration can be obtained with the UV-Vis channel, but also p-type dopant concentration with the IR channel. In this presentation, an alloy model will be introduced first to obtain Ge concentration. The principle to determine dopant concentration and electric properties of the film will be given secondly. With the advanced SOPRA ellipsometer tool, four types of samples were characterized, which are (a) single SiGe layer (Box), (b) SiGe layer with Si cap, (c) SiGe layer with graded Ge concentration and (d) Boron doped SiGe layer. Uniformity for these samples was also examined, which is an essential measure for improving process performance and device yield. Finally, results from spectroscopic ellipsometry were compared with that from other technique such as SIMS for dopant concentration and Xrd for thickness and %Ge.