Ultrathin SiO2 film growth on Si by highly concentrated ozone

The growth mechanism of SiO2 thin film on Si(100) and Si(111) by ozone was investigated using various surface/interface analytical techniques such as X-ray photoelectron spectroscopy (XPS), second harmonic generation (SHG) an d medium energy ion scattering spectroscopy (MEIS). Two different ozone gen erators were fabricated and used for the investigation. The first ozone gen erator, which was used for the study of initial oxidation, supplies low pre ssure (< 10(-2) Pa) and high purity (> 80%) ozone gas by vaporization of pu re liquid ozone at low temperature (< 100 K). The second ozone generator, u sed mainly for ultrathin SiO2 film growth, supplies high pressure (1 atm) o zone gas with concentration < 30% by desorbing ozone adsorbed on silica-gel . Through the comparison of ozone oxidation to the oxidation with molecular oxygen, followings features of the ozone oxidation were made clear. (i) At omic oxygen dissociated from ozone molecules at Si surface directly attacks the back bond of Si, hence it can oxidize hydrogen-terminated Si which oxy gen molecules cannot. (ii) The oxide thin film growth proceeds in layer-by- layer manner, especially at the initial stage of oxidation. (iii) Formation of suboxids at and/or near the SiO2/Si interface was suppressed, leading t o a stable Si-O-Si network formation even at low pressure and low temperatu re condition. In addition to these features, the existence of no (or very t hin) structural transition layer was suggested for ozone oxide film from ME IS experiments and etching experiment with dilute HF solution, while those experiments for thermally grown oxide showed the existence of the transitio n layers with thickness of approximately 1 nm. (C) 2000 Elsevier Science B. V. All rights reserved.