Activation of the Si(100)/Cl 2 Etching Reaction at High Cl 2 Translational Energies
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ACTIVATION OF THE Si(100)/C12 ETCHING REACTION AT HIGH Cl2 TRANSLATIONAL ENERGIES FRANCIS X. CAMPOS, GABRIELA C. WEAVER, CURTIS J. WALTMAN AND STEPHEN R. LEONE* Joint Institute for Laboratory Astrophysics, University of Colorado and National Institute of Standards and Technology, and Department of Chemistry, University of Colorado, Boulder, Colorado, 80309-0440 "Staff member, Quantum Physics Division, National Institute of Standards and Technology. Abstract Exposing a Si(100) surface to a pulsed beam of neutral Cl2 with high translational energy results in etching at a rate faster than that seen with chlorine at thermal energies. The Cl2 beam used in these experiments is produced by laser vaporization of cryogenic films. It has a broad energy distribution which can be varied by changing laser energy and film thickness. Beams with mean energies as low as 0.4 eV result in etching >10 times faster than etching by thermal Cl 2 . When Cl2 beams are used which have considerable flux above 3 eV, the etching rate increases by a further factor of 3.6 ± 0.6. This rate increase, which occurs at energies just above the Si-Si bond energy, suggests that kinetic energy can be efficiently utilized to break surface bonds. INTRODUCTION We investigate the effect of high chlorine kinetic energy on the rate of the neutral Cl 2 -Si etching reaction. The reaction is of technological interest because it is suitable for the manufacture of submicron features in silicon-based semiconductor devices. This interest has led to a number of important studies [112]. The C12 -Si etching reaction is also a good candidate for fundamental studies of gas-surface reactions because variation of the reaction conditions within reasonable limits can produce very large changes in the reaction rate. At room temperature, chlorine etches silicon very little, if at all. If additional energy is provided to the reactants through laser irradiation [1-4], ion bombardment [5-91, a plasma discharge [10,11], or a molecular beam [1,121, rapid and anisotropic etching occurs. Careful control of the amount of energy available to the reactants will provide information about the energetic barriers to reaction. In the present experiments, laser ablation of cryogenic chlorine films provides energy directly to the Cl molecules, primarily in the form of kinetic energy. Measurements of the etching rate using a molecular beam scattering method reveal a strong dependence of the etching rate on the Cl 2 energy. Molecular beams with mean kinetic energies as low as 0.4 eV are found to etch room temperature silicon. The data also demonstrate the existence of an energetic barrier to reaction with a value in the range of 3-6 eV.
Mat. Res. Soc. Symp. Proc. Vol. 236. @1992 Materials Research Society
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EXPERIMENTAL
The experimental apparatus is shown in Fig. 1. The main chamber of our apparatus contains a four-axis manipulator which holds the silicon sample, two quadrupole mass spectrometers used for analysis of the direct Cl2 beam and the SiClx etching products, an ion sputter gun fo
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