Microscopic uniformity in plasma etching

Abstract

As we enter the era of ultra-large-scale integrated circuit manufacture, plasma etching grows more important for fabricating structures with unprecedented dimensions. For feature sizes below 1 μm and aspect ratios (depth/width) much larger than one, etching rates have been observed to depend on aspect ratio and pattern density. Such dependencies tend to increase the cost of manufacturing because even small changes in device design rules, cell design, or wafer layout can result in time-consuming, new plasma process development. In addition, microscopically nonuniform etching affects the trade-off between chips lost from failure to clear and chips lost by damage from overetching. Although aspect ratio and pattern dependent etching have been observed for a large variety of material systems and processing conditions, the fundamental causes underlying these effects are poorly understood. Partly, this results from use of confusing and conflicting nomenclature and a lack of careful, quantitative comparisons between experiment and theory. In this article we review recent literature on microscopic uniformity in plasma etching and carefully define terminology to distinguish between aspect ratio dependent etching (ARDE) and the pattern dependent effect known as microloading. For ARDE, we use dimensional analysis to narrow the range of proposed mechanisms to four which involve ion transport, neutral transport, and surface charging. For microloading, we show that it is formally equivalent to the usual loading effect, where the reactant concentration is depeleted as a result of an excessive substrate load.

Parametric Study of Proton-Implanted Photonic Crystal Vertical-Cavity Surface-Emitting Lasers

“…For a given etching time, the smaller diameter holes etched to a shallower depth. This dependence is attributed to size-dependent etch effects [18]. The etch-depth data was empirically fit with a logarithmic function for the purpose of interpolating etch depths for all devices in the paper.…”

Gas-Surface Dynamics and Profile Evolution during Etching of Silicon

“…The pursuit of ever smaller dimensions of circuit patterns for ultralarge scale integration has placed unrelenting demands on plasma etching. Etch rate nonuniformities [1] and peculiar etching topographies [2] hinder the production of very fine structures. Trial-anderror development of process recipes for modern etchers has overcome these problems for current technologies, but new solutions are required as targeted device dimensions extend below 200 nm and aspect ratios exceed 10:1.…”

“…"Microtrenching" describes the appearance of a sharp groove near the foot of the etched feature [4,5] and has been attributed in models to reflection of ions from the sidewalls [4,5] and surface diffusion [8]. "Aspect ratio dependent etching" (ARDE) refers to the etch rate dependence on the relative spacing between features [1,6] and has been linked [6] to deposition of etch inhibitors, ion deflection, Knudsen transport of neutrals, ion and neutral shadowing effects, and surface diffusion. Finally, "undercutting," or loss of material beneath the mask that defines the circuit pattern, has been ascribed to reactant species which desorb from the bottom of the trench [7].…”

Design and Fabrication of a Planar Three-DOFs MEMS-Based Manipulator

“…This effect is known as loading and is caused by the difference in exposed Si [27]. Also, the difference in aspect-ratio (ARDE) has influence on the resulting etch depth [27], [28]. The effect, for some part, is caused by difference in diffusion of the etching agent toward the bottom of the trench and can be weakened by reducing the overall etch rate lessening the significance of transport, or by applying more fluor carbon.…”