Damage to Si layer caused by various types of SiO2 etchers during overetching has been studied by thermal wave modulated reflectance (TW) and x-ray photoelectron spectroscopy (XPS) methods. It has been found that SiO2 etchers with 380 or 400 kHz RF form considerably damaged layers containing SiC and SiFx(x = 1-3) while those with 13.56 MHz RF cause little damage. This difference is attributed to the difference in ion energy which is dependent on bias frequency. Further, the influence of the damaged layer containing SiC and SiFx on Ti silicidation in salicide (self-aligned silicide) ss has been studied. It has been found that the sheet resistance of TiSi2 layer increases when Ti is deposited on a damaged layer Auger electron spectroscopy (AES) measurement has revealed that SiC in the damaged layer suppressed Ti silicidation process and that carbon atoms pile up around TiN/TiSi2 interface.