AVS 49th International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP1
In-situ Observation of Chemical State of a Si Electrode Surface during a Galvanostatic Oscillation in Fluoride Electrolytes Using Infrared Absorption Spectroscopy

Tuesday, November 5, 2002, 5:30 pm, Room Exhibit Hall B2

Session: Surface Science Poster Session
Presenter: Y. Kimura, Tohoku University, Japan
Authors: Y. Kimura, Tohoku University, Japan
J. Nemoto, Tohoku University, Japan
M. Niwano, Tohoku University, Japan
Correspondent: Click to Email
Electrochemical etching of silicon (Si) is an important technique for the fabrication of micro- and nano-structures on Si, and therefore, it has been extensively investigated theoretically and experimentally. It is well known that when an anodic potential below about 1 V is applied to a Si electrode, porous silicon (PS) forms in the vicinity of the surface. Interestingly, when a higher anodic potential, several volts or more, is applied to a Si electrode, an oscillation in the anodic potential or the anodic current density takes place. Previously, the oscillation has been interpreted as being due to alternative formation and removal of silicon oxide on the Si electrode surface. However, the chemistry of a Si electrode surface during galvanostatic oscillation has not been fully understood. In this study, we have investigated a galvanostatic oscillation phenomenon during anodization of a silicon (Si) crystal electrode in fluoride electrolytes using infrared absorption spectroscopy in multiple internal reflection geometry (MIR-IRAS). We confirm that the electrode surface is covered with a thin oxide layer during the course of galvanostatic oscillation. We observe a weak oscillation of the oxide thickness that synchronizes with the oscillation of an anodic potential. We also find that when the anodic potential falls to its minimum, hydrogen-substituted oxide (suboxide, Si(O@sub 3@)-H) forms on the electrode surface. We propose a model of galvanostatic oscillation in which it is assumed that an decrease in the anodic potential is due to the formation of pits in the oxide over layer and low-quality oxides containing Si(O@sub 3@)-H species are preferentially formed at the pit sites. We suggest that formation of an inhomogeneous oxide layer plays a crucial role for the galvanostatic oscillation phenomenon.