Advanced metrology tool for Si1-xGex characterization: Infrared Spectroscopic Ellipsometer (IRSE)

The ability to precisely determine epilayer thickness and Ge concentration in Si_1-xGe_x is essential for calibrating growth processes and thus control film quality. Spectroscopic ellipsometry is a nondestructive optical technique and has advantages for in-line process monitoring over SIMS, TEM and other destructive techniques. With integrated UV-Vis-IR spectroscopic ellipsometer, not only epilayer thickness and Ge concentration can be obtained with the UV-Vis channel, but also dopant concentration with the IR channel. Therefore, an advanced SOPRA IRSE 300 metrology tool will be used to characterize Si_1-xGe_x epilayers. The sub 50-nm Si_1-xGe_x films were processed with LPCVD in an AMAT 5200 Centura platform. The precursors for Si_1-xGe_x growth are SiH₄ and GeH₄. B₂H₆ was used as the p-type dopant source (B) for certain samples. CH₃SiH₃ was also utilized as a carbon source to minimize boron out diffusion. Five types of samples were prepared and characterized, which are (a) single Si_1-xGe_x layer (Box), (b) Si_1-xGe_x layer with Si cap, (c) Si_1-xGe_x layer with graded Ge concentration, (d) Boron doped Si_1-xGe_x layer and (e) carbon effect on both undoped and doped Si_1-xGe_x epilayers. 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 XRD for thickness and %Ge.