Laser-Induced Dry Etching of GaAs with High Aspect Ratio
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LASER-INDUCED DRY ETCHING OF GaAs WITH HIGH ASPECT RATIO Cheon Lee, Hirokazu Sayama, Susumu Namba, and Mikio Takai Faculty of Engineering Science and Research Center for Extreme Materials, Osaka University, Toyonaka, Osaka 560, Japan.
ABSTRACT Laser-induced thermochemical reactions have been investigated for GaAs in a CCl 2F2 gas ambient using an argon-ion laser. The chemical compositions of the reaction products deposited on the etched groove were measured by Auger electron spectroscopy (AES). The conditions of laser power, scan speed, and CC12F 2 gas pressure under which the etching reaction occurs without deposition of the residue were clarified. High etching rates up to 267 am/s and an aspect ratio of 4.5 have been achieved by a single scan of a laser beam. Microprobe photoluminescence and Raman scattering measurement were carried out on the etched surface to characterize damage induced by this processing.
INTRODUCTION Laser-induced chemical processing which can be used to directly and controllably etch fine structures in semiconductors has been widely investigated [1-3]. In laser-induced etching of materials, laser beams directly excite species in the vicinity of substrate surfaces, resulting in photochemical reaction, or locally heat substrate surfaces, resulting in thermochemical reaction. Features of high aspect ratio obtained by laser processing are an important requirement in the fabrication of advanced electronic devices. To obtain such features in GaAs substrate, our previous studies on laser-induced processing have provided a method with high process rate, high precision and low damage, in which laser-induced etching of GaAs in a CC14 gas atmosphere [4] or in a KOH aqueous solution [5] was performed. However, wet processing is incompatible for connection with the other processes and dry processing in a CC14 could not provide high etching rate and high aspect ratio. In this study, a new approach to etch GaAs by laser irradiation in a CCI 2 F2 gas atmosphere has been performed to obtain trenches with high aspect ratio and high etching rate. CCl 2F 2 has a high vapor pressure of up to several atmospheres at room temperature, which may enhance etching reaction, whereas CC14, used in our previous studies, has a vapor pressure of below 100 Torr. Furthermore, CC12 F2 is considered to be more suitable for application of semiconductor industry, because it is chemically stable at room temperature, much safer to human body than CC14 and does not stain the metal parts in the vacuum system. Microprobe PL and Raman scattering measurements were performed to optically characterize etched surfaces.
EXPERIMENTAL PROCEDURES Samples of n-type GaAs(100) with a carrier density of 10' 8cm- 3 were mounted on a vacuum chamber. The chamber was fixed on an electronically controlled X-Y-Z stage and evacuated by a turbomolecular pump down to 10' Torr. The ambient CCl 2F 2 gas was introduced into the chamber through a needle valve at a pressure ranging from 15 to Mat. Res. Soc. Symp. Proc. Vol. 236. ©1992 Materials Research Soci
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