ALBERT

Notes: Very simple vacuum conductance arguments indicate that in the reactive ion etching of high aspect ratio features, the conductance is adequate to allow etch products to flow out of the feature without building up a pressure which would allow gas phase collisions to become important. On the other hand, the conductance can be expected to limit the flow of the reactive species to the bottom of the feature where the etching is taking place, thus creating the possibility of an etch rate dependence on the aspect ratio of the etched feature.

Notes: The ion-assisted etching of Si with F atoms has been studied over the temperature range from 77 K to room temperature. Separately controllable beams of F atoms and 1 keV Ar+ ions are used in an ultrahigh-vacuum environment. Neutral etch products are measured with modulated beam mass spectrometry. The ion-assisted etch rate is seen to increase as the temperature is decreased whereas the spontaneous etch rate goes to zero at low temperatures. The nature of the etch products is essentially independent of temperature over this temperature range. Evidence is presented indicating that the spontaneous etching of Si by F atoms at 77 K is blocked by the formation and condensation of Si2F6. © 1994 American Institute of Physics.

Notes: A GaAs 〈001〉 crystal at room temperature has been exposed to a flux of hydrogen atoms with and without simultaneous 2-keV argon ion bombardment. A modulated molecular beam mass spectrometric detection system is used to monitor the volatile products evolved from the surface, and in situ Auger electron spectroscopy is used to monitor the surface conditions. With the H atom flux alone no volatile products were observed but an arsenic deficiency was seen with Auger electron spectroscopy. With simultaneous H atom exposure and Ar+ bombardment, arsenic hydrides were observed with the mass spectrometer and a larger arsenic deficiency was observed on the processed surface. No gallium hydrides were observed at any time.

Notes: Surface recombination coefficients of O and N radicals in pure O2 and N2 plasmas, respectively, have been estimated on the stainless steel walls of a low-pressure inductively coupled plasma reactor. The recombination coefficients are estimated using a steady state plasma model describing the balance between the volume generation of the radicals from electron-impact dissociation of the parent molecules, and the loss of the radicals due to surface recombination. The model uses radical and parent molecule number densities and the electron energy distribution function (EEDF) as input parameters. We have measured the radical number density using appearance potential mass spectrometry. The parent neutral number density is measured using mass spectrometry. The EEDF is measured using a Langmuir probe. The recombination coefficient of O radicals on stainless steel walls at approximately 330 K is estimated to be 0.17±0.02, and agrees well with previous measurements. The recombination coefficient of N radicals is estimated to be 0.07±0.02 on stainless steel at 330 K. © 2000 American Institute of Physics.

Notes: Surface reactions of atomic halogen atoms play important roles in various plasma etching processes, commonly used in microlectronics manufacturing. However, relatively little is known about the surface chemistry of these key reactive intermediates. Previous measurements of the recombination coefficients of Cl, Br, and F on various surfaces in a molecular beam apparatus indicated that the recombination reaction is pseudofirst order [G. P. Kota, J. W. Coburn, and D. B. Graves, J. Vac. Sci. Technol. A 16, 270 (1998); 16, 2215 (1998)]. One mechanism that would result in pseudofirst order kinetics is a two-step process in which the first halogen atom adsorbs into a relatively strongly bound chemisorbed state, and the second atom reacts with it either through a direct reaction, or after being physisorbed onto the halogenated surface. In this article, we report experiments in which surfaces are first exposed to a molecular beam of one type of halogen atom, then the surface is exposed to a second type of halogen. During the second exposure, the heteronuclear reaction product is monitored with a mass spectrometer. Finally, the surface is sputtered and the mass spectrometer is used to detect any remaining presence of the original halogen atom. Analogous experiments were also performed with isotopically enriched mixtures of chlorine. These experiments unambiguously demonstrate that halogen atom surface recombination involves a two step adsorption-abstraction mechanism. Under all conditions studied, the surface recombination reactions proceeded at rates on the order of surface collision frequencies. The relative magnitudes of the heteronuclear rates (as a function of surface composition and halogen atom type) scaled in the same way as the homonuclear recombination probabilities measured previously. In every case examined, after the second halogen exposure, the surface retained a significant coverage of the halogen that had been originally exposed to the surface. This leads to the conclusion that only a fraction of the strongly bound surface sites are available for abstraction by free radical attack. Absolute calibration of the incident and evolved species fluxes allowed an estimate to be made of the reactive site densities for several surfaces. These ranged from 1012 to 1015 cm−2 depending on the surface. © 1999 American Institute of Physics.

Notes: The plasma-assisted etching of magnetron-sputtered polycrystalline tungsten films in CF4-H2 and CF4-O2 glow discharges has been studied as a function of ion energy using quartz-crystal microbalance methods supplemented by vacuum-transfer Auger electron spectroscopy and actinometric emission spectroscopy.

Notes: The plasma potential of 13.56-MHz low-pressure argon glow discharges has been measured for various modes of applying the rf power in a geometrically asymmetric planar system. The plasma potential is determined from the energy distribution of positive ions incident on the grounded electrode. The voltages on the excitation electrode (target electrode) are carefully measured and the capacitive sheath approximation is used to relate these measured voltages to the measured plasma potential. This approximation is successful in most of the situations encountered in this low-pressure (20 mTorr) relatively low-power density regime. The effects of superimposing dc voltages on the excitation electrode are discussed.

Notes: A study of the etching and deposition of plasma perfluoropolymer thin films has been carried out by using quartz-crystal microbalance methods for a range of feed gas mixtures.