AVS 47th International Symposium
    Semiconductors Wednesday Sessions
       Session SC+EL+SS-WeM

Paper SC+EL+SS-WeM1
Infrared Study of the Initial Stages of Etching of Si Electrode Surfaces in HF Solution

Wednesday, October 4, 2000, 8:20 am, Room 306

Session: Passivation and Etching of Semiconductors
Presenter: M. Niwano, Tohoku University, Japan
Authors: Y. Kimura, Tohoku University, Japan
Y. Kondo, Tohoku University, Japan
J. Nemoto, Tohoku University, Japan
M. Niwano, Tohoku University, Japan
Correspondent: Click to Email
Porous Si has been a promising class of materials used for light-emitting devices and nano-scale electronic devices, and a number of theoretical and experimental investigations have been performed on the formation and optical properties of porous Si. A conventional method of synthesizing porous Si is to apply an anodic (positive) potential to a Si electrode in aqueous etching solutions such as dilute hydrofluoric acid (HF) solution. However, the mechanism of pore formation has not been fully understood. In order to control the structure of porous Si, we need an understanding of the microscopic etching process of Si electrode surfaces during immersion in etching solution. In this study, we have investigated in-situ and in real time the etching process on p-Si(100), (111), and (110) electrode surfaces in dilute HF solution, using infrared absorption spectroscopy (IRAS) in the multiple internal reflection (MIR) geometry, and analyzed infrared absorption spectra in the Si-H stretching vibration region of the electrode surface to examine how surface Si atoms are removed. At electrode potential below approximately 1 V, surface roughening occurs to produce hydride species in the vicinity of the electrode surface. At initial stages of etching of a Si(100) electrode, monohydride species is dominantly populated by the removal of dihydride species on the topmost layer of the electrode surface. We suggest that removal of monohydride species is favored over that of dihydride species, leading to the formation of pores on the etched surface. At electrode potential above 1 V, all the hydride species are etched away, leading to electropolishing of the surface. For electrochemical etching of Si(110), monohydride species are removed from the topmost layer to populate dihydride species on the second layer of the surface. For etching of the Si(111) surface, it appears that removal of surface Si atoms more favorably takes place at step sites than on terraces.