Anisotropic ArF Laser-Assisted Cl 2 Etching of GaAs
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ANISOTROPIC ArF LASER-ASSISTED Ch2 ETCHING OF GaAs PALOMA TEJEDOR AND FERNANDO BRIONES Centro Nacional de Microelectr6nica, Serrano 144, 28006 Madrid, Spain. ABSTRACT ArF laser etching of n-GaAs (100) in Cl 2 gas ambient has been investigated as a function of laser fluency and the main thermodynamical parameters of the process (pressure, temperature and gas phase composition). Experimental results indicate that GaAs laser etching in the presence of C12 occurs by a combination of thermally and photochemically initiated reaction steps. The etch rate was found to be kinetically controlled by the surface reaction between photogenerated Cl adatoms and GaAs, with an activation energy of 6.3 Kcal/mol. Vertical etch profiles with smooth bottom surfaces were obtained at substrate temperatures above 150'C, low Cl2 partial pressures (< 1.5 m Torr), and low laser fluences (< 25 mJ/cm2 ) for etch masks parallel to the
0"11' 1 direction. INTRODUCTION The development of dry etching techniques that can provide good control of etch rate and profile, damage free etched surfaces with smooth morphology, and short processing times is essential to the fabrication of Ill-V semiconductor optoelectronic and high-speed devices. Laser-assisted dry etching of GaAs in various halogenated gas environments has been demonstrated to be a promising alternative technique by several authors [1-6]. In particular, ArF excimer laser etching of GaAs at 193 nm in the presence of bromine-based parent gases has been successfully applied by Brewer et al [3-5] to large area processing and fabrication of submicrometer resolution features. The etching process was photochemical in origin and resulted in high crystallographic anisotropy under masking conditions with the low-order crystal planes etching rates following the sequence (11 )B > (100) > (110) > (11 1)A. KrF laser etching of GaAs at 248 nm in Cl 2 gas ambient has also been shown to be an efficient dry etching process by Koren et al. [6]. However, the etching mechanism and the chemical processes involved have not been fully elucidated to date. The aim of this paper is to study the physical-chemical mechanisms involved in the ArF laser-assisted etching of GaAs in the presence of Cl 2 gas and to examine its possible application to substrate patterning. In the following we show that anisotropic etching of GaAs in C12 gas ambient occurs when the ArF laser-assisted reaction is kinetically controlled by the surface reaction between photogenerated Cl atoms and GaAs. In addition, the effect of laser light fluence and relevant thermodynamical parameters on etch reaction rate, surface morphology and etch profile is discussed. EXPERIMENTAL Samples were masked n-type GaAs (100) substrates (1.8x10' 5 Si atoms/cm2 ). The
Mat. Res. Soc. Symp. Proc. Vol. 201. c 1991 Materials Research Society
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2000 A-thick PECVD SiO 2 patterned test mask was oriented along the [0T1] and the [01 1] directions. Experiments were carried out using an ArF laser that emitted 300 mJ pulses of 17 ns duration at 193 nm and repetition rat
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