Channel Strain Analysis in Damascene-gate pMOSFETs on Si (100) and (110) Substrate by Conventional and Cross-sectional Raman Spectroscopy

Channel strain in damascene gate pMOSFETs with compressive stress liner (c-SL) and embedded SiGe (eSiGe) were studied by micro-Raman spectroscopy with a quasi-line-shape UV excitation (λ=363.8nm). The channel strain profiles were obtained by the conventional mea-surement from the surface after dummy gate removal. The compressive strains at the channel edges were larger than that at the channel center for the relatively long gate length (Lgate). As the Lgate became smaller, although it became hard to recognize the strain profile, the compres-sive strain at the channel center increased by the superposition of the strain at the channel edges. However, channel strain disappeared in the measurement data for the channel length less than 160 nm. Thus, we extended the laser exposure time from 10 to 40 minutes to extract the channel strain component from obtained Raman spectra. The Raman peaks consisted of two or three peaks for the Lgate less than 160 nm. By multi peak fitting, we have succeeded in measuring the extremely large stress of - 2.4 GPa in the channel of Lgate = 30 nm pMOSFET. We also per-formed the cross-sectional measurements for the samples before and after metal-gate/high-k gate stack formation. Channel strain profiles were obtained similar to those by the conventional mea-surement. Extremely high device performance can be clearly explained by the compressive stress derived from the Raman measurements both in the Lgate dependence and eSiGe effect. We also demonstrated that Raman spectroscopy using cross-sectional measurement can evaluate the channel strain even in the MOSFETs after gate stack formation.