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We report an investigation of charge transfer in high-k dielectric stacks on Si by second harmonic generation (SHG). Ultrathin (2–6 nm) films of HfO2, ZrO2, and Al2O3 grown on Si surfaces by atomic layer deposition were investigated and compared to conventional SiO2-based gate dielectrics. From the SHG rotational anisotropy (SHG-RA) of Si-(high-k) and Si–SiO2 systems, optical roughness of the films was found to increase in the following order: SiO2, Al2O3, and (ZrO2 and HfO2). The optical roughness is regarded as a quantity describing the nonuniformity in the distribution of interfacial defects capable of charge trapping. Time dependent second harmonic generation (TD-SHG) measurements were carried out to understand charge trapping and detrapping dynamics and trapped charge densities. Relative comparison of the four dielectrics revealed that Al2O3 films have the highest densities of trapped and fixed charge while silicon oxides exhibited less charge trapping, consistent with electrical measurements performed on similar structures. In contrast to SiO2 films, detrapping was significantly suppressed in the high-k films due to significantly reduced leakage currents. We also observed ambient effects in charge trapping at the dielectric/air(vacuum) interface that could be significantly reduced by covering the dielectric film with a thin (semitransparent) metal (aluminum) overlayer. [ABSTRACT FROM AUTHOR]

The oxidation of H terminated silicon surfaces is a significant and controversial problem in silicon device fabrication. Second-harmonic generation rotational anisotropy (SHG–RA) provides a convenient means to monitor the chemical state of the Si surfaces, and to follow the conversion of H terminated surface to SiO2 by oxidation as a function of time in ambient. The change in SHG–RA of Si(111)–H was shown to correlate well with the ellipsometric thickness. SHG is sensitive to the initial stage of oxidation (induction period) as well as to the logarithmic oxide growth. SHG is sensitive to the electronic properties of the surface, therefore it is a sensitive probe of the quality of H terminated Si(111) surface. Under ambient conditions, (20% relative humidity, 23 °C) the initial oxidation rate is at most 2×10-6 ML/s. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The stability of any semiconductor surface passivating layer is key to applications. Second harmonic generation (SHG) can be used to probe the chemical state of semiconductor interfaces, as well as investigate the mechanisms of chemical transformation. While the SHG rotational anisotropy changes upon sulfidation or alkylation of Ge surfaces, SHG appears far less sensitive to H and Cl passivation of germanium surfaces than to silicon surfaces. Investigation of the stability of chemically modified germanium surfaces using a number of additional techniques, including atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), reveals that H- and Cl-terminated Ge(1 1 1) rapidly re-oxidize in ambient. S- and alkyl-terminations are more robust, showing little sign of oxide formation after a month in ambient. [Copyright &y& Elsevier]