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It is known that the contact etch rate decreases with decreasing diameter. Etch depth measurements for deep submicron contacts will be shown to depend linearly on (1/contact diameter). This experimental dependence will then be compared to that predicted for various theoretical etching models. One way in which these models differ is the assumed rate limiting species: ions or neutrals. Another difference is the interaction of neutrals with the sidewalls of the contact. The nature of this interaction differs for the various models. The models also differ in the effect of the contact sidewalls on the ion trajectory. All of the models predict a decreasing etch depth as a function of contact diameter. However, some of the models more accurately predict the observed (1/contact diameter) dependence of the measured etch depth. It will be suggested that elements of the various theoretical models be combined. In particular, contact etching probably depends on both the ions and neutrals. Accurate models would therefore take into account the different aspect ratio dependences of these charged and uncharged species. It is also urged that modeling should address not only the etch depth at a given etch time, but also as a function of the etch time. The models and experiments should also look at a range of contact diameters (0.1–1.0 μm). Both models and experiments should also determine the side wall angle and the curvature of the etching front in the oxide. © 1998 American Vacuum Society.