The spatiotemporal structure of the sheath and the ion energy distribution (IED) at the electrode of a collisionless electropositive glow discharge were studied with a model that is valid for arbitrary radio frequencies (rf). The model is based on the work of P. A. Miller and M. E. Riley [J. Appl. Phys. 82, 3689 (1997)] and uses an effective electric field to which the heavy ions respond. Given the plasma density and electron temperature at the sheath edge, and the waveform of either the potential or total current across the sheath, the spatial and/or temporal profiles of the following quantities were obtained: sheath thickness and capacitance, electron and ion densities, potential, and individual components of the current. An analytic expression for the energy split of the IED function was also obtained. The product ωτi of applied radian frequency ω and ion transit time τi is a critical parameter for describing the sheath dynamics.

A three-dimensional finite element fluid model and a corresponding simulation tool have been developed for studying azimuthal asymmetries and their effect on etch uniformity in inductively coupled plasma ͑ICP͒ reactors. For silicon etching with chlorine in an ICP reactor with a planar coil, four different cases were examined: ͑a͒ uniform power deposition without a focus ring, ͑b͒ uniform power deposition with a focus ring, ͑c͒ nonuniform power deposition without a focus ring, and ͑d͒ nonuniform power deposition with a focus ring. When etching is ion driven, the power deposition profile is most important for etch uniformity, because azimuthal nonuniformities in the ion production rate can persist even down to the wafer level. For uniform power deposition, the effect of asymmetric pumping becomes more important. A focus ring can play an important role in alleviating azimuthal nonuniformities, especially in the nonuniform power deposition cases. Gas inlets pointing parallel to the wafer plane introduce only local disturbances in the species profiles.

The radial distribution of the measured voltage drop across a sheath formed between a 300mm electrode and an argon plasma discharge is shown to depend on the excitation radio frequency, under constant power and pressure conditions. At a lower frequency of 13.56MHz, the voltage drop across the sheath is uniform across the 300mm electrode, while at higher frequencies of 60 and 162MHz the voltage drop becomes radially nonuniform. The magnitude and spatial extent of the nonuniformity become greater with increasing frequency.

The spatial structure and temporal evolution of the electric fields in a sheath formed in a dual frequency, 300 mm capacitive argon discharge are measured as functions of relative mixing between a low frequency current and a high frequency current. It is found that the overall structure of the sheath (potential across the sheath and the thickness of the sheath) are dominated by the lower frequency component while (smaller) oscillations in these quantities are dictated by the higher frequency component. Comparisons of the measured spatial and temporal profiles are made for Lieberman's and Robiche et al sheath model and with a particle in a cell calculation.

In this article, we give an overview about the chemical and physical processes that play a role in etching at lower wafer temperatures. Conventionally, plasma etching processes rely on the formation of radicals, which readily chemisorb at the surface. Molecules adsorb via physisorption at low temperatures, but they lack enough energy to overcome the energy barrier for a chemical reaction. The density of radicals in a typical plasma used in semiconductor manufacturing is one to two orders of magnitude lower than the concentration of the neutrals. Physisorption of neutrals at low temperatures, therefore, increases the neutral concentration on the surface meaningfully and contributes to etching if they are chemically activated. The transport of neutrals in high aspect ratio features is enhanced at low temperatures because physisorbed species are mobile. The temperature window of low temperature etching is bracketed at the low end by condensation including capillary effects and diminished physisorption at the high end. The useful temperature window is chemistry dependent. Besides illuminating the fundamental effects, which make low temperature processing unique, this article illustrates its utility for semiconductor etching applications.