Electron spectroscopic analysis of the SiO2/Si system and correlation with metal-oxide-semiconductor device characteristics

ESCA (electron spectroscopy for chemical analysis) measurement results on thin SiO2/Si samples are examined comprehensively, critically, and in detail to show that it is possible to correlate these results with MOS (metal-oxide-semiconductor) device characteristics such as flatband (threshold) voltage, oxide breakdown field, mobile-ion density, hole and electron trap density, and hot-carrier lifetime. Up to now, much effort has been made to detect SiO2 phases at SiO2/Si interfaces since they are thought to have a significant effect on MOS device characteristics. However, correlating the SiO2 phases with device characteristics is difficult and involves overcoming two problems. First, the chemical state is difficult to determine exactly due to x-ray-irradiation effects. Second, the amount of defects and impurities which influence device characteristics is usually below the ESCA detection limit (10(12)-10(13) cm(-2)) in device-quality SiO2/Si samples. Investigation of the first problem led to the conclusion that it is possible to correct for these effects from the x-ray intensity or oxide thickness dependence of the chemical shift. However, accurate (better than +/-0.2 eV) chemical state determination is not easy. It is therefore necessary to approach this detection problem from a different viewpoint. Our first attempt involves measuring the ESCA thickness, which decreases when oxide defects like unoxidized Si or uneven thickness (or pinholes) are present, resulting in breakdown field degradation. Our second attempt started while we were studying how to interpret the measured chemical shift. The photoelectron peaks of the SiO2 and the Si can be observed to shift due to small amounts of charged defects and impurities; although they cannot be detected as peaks. This method is considered to be especially useful for characterizing ultrathin (a few mn thick) SiO2/Si samples which are difficult to characterize using conventional C-V (capacitance-voltage) measurements because of tunneling currents. Accordingly, we discuss the data obtained in steady-state and transient peak position measurements of SiO2/Si samples containing 10(10)-10(12) cm(-2) of Na (sodium) ions, 10(12)-10(13) cm(-2) of hole and electron traps, and 10(14)-10(21) cm(-3) of impurities such as P (phosphorus) (in the Si). It is shown that a correlation with MOS characteristics is possible. A close scrutiny of various results concerning x-ray irradiation time, intensity, and oxide thickness dependence of the above peak positions indicates that electric charging during ESCA measurements is correlated to the trap-capturing process. As MOS characteristics are also related to this process, more studies in this direction are needed and will certainly yield more information on the defects influencing the MOS characteristics and the trap-capturing mechanism. (C) 1996 American Institute of Physics.