Sidewall surface chemistry in directional etching processes

A prerequisite of successful microstructure fabrication in electronic mater ials using plasma-based etching methods is the ability to maximize the rati o of ion-enhanced etching reactions relative to spontaneous etching reactio ns. To produce vertical etching profiles, the rate of the etching reaction in line-of-sight of the plasma has to be large, whereas the lateral etching rate should vanish. We present a review of the approaches that have been u sed for silicon, aluminum, SiO2 and polymeric materials to suppress etching reactions at microstructure sidewalls. These approaches include the judici ous choice of the primary etching gas, adding certain gases to the main etc hing gas, lowering the substrate temperature, mask material redeposition, o r alternate etch and deposition cycles. Our knowledge of the sidewall chemi stry resulting from these approaches, e.g. the production of sidewall passi vation layers, and experimental methods that have been employed to study th ese, are reviewed. The impact of sidewall chemistry on the etching profiles of the final microstructure is also discussed. (C) 1998 Elsevier Science S .A. All rights reserved.