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The etching of anisotropic blind vias in silicon with diameters of 5–10  µm and an aspect ratio ~2–4 with controlled sidewall inclination is reported. The motivation for this work is the creation of a vertical, or three dimensional interconnect. Via formation by reactive ion etch (RIE) processing is the focus of this project. Arrays of vias have been etched in 125 mm diam silicon (100) wafers using a photoresist mask. A parallel plate RIE system with a SF₆/O₂ gas mixture is used. The effects of O₂/(SF₆+O₂) gas flow ratio, electrode bias, and chamber pressure on etch rate and feature profile have been studied. Visualization of the via profiles using scanning electron microscopy is used to identify the key parameters that control the sidewall slope. This slope is important for the subsequent deposition of via lining materials before filling with Cu. Our results indicate that the O₂/(SF₆+O₂) ratio is a key parameter in determining the sidewall slope, however the electrode bias and chamber pressure are critical in determining the physical and chemical process balance that determine the anisotropy of the etch process. ©2005 American Vacuum Society