Anisotropic Etching of Crystalline Silicon in Alkaline Solutions: I . Orientation Dependence and Behavior of Passivation Layers

作者：Helmut Seidel, Laszlo Csepregi, Anton Heuberger, Helmut Gustav Baumgärtel · 发表于：Journal of The Electrochemical Society · 年份：1990 · DOI：10.1149/1.2086277 · 被引用次数：1637 · 研究领域：Semiconductor materials and devices、Silicon Nanostructures and Photoluminescence、Electronic and Structural Properties of Oxides

The anisotropic etching behavior of single‐crystal silicon and the behavior of SiO 2 and Si 3 N 4 in an ethylenediaminebased solution as well as in aqueous KOH , NaOH , and LiOH were studied. The crystal planes bounding the etch front and their etch rates were determined as a function of temperature, crystal orientation, and etchant composition. A correlation was found between the etch rates and their activation energies, with slowly etching crystal surfaces exhibiting higher activation energies and vice versa. For highly concentrated KOH solutions, a decrease of the etch rate with the fourth power of the water concentration was observed. Based on these results, an electrochemical model is proposed, describing the anisotropic etching behavior of silicon in all alkaline solutions. In an oxidation step, four hydroxide ions react with one surface silicon atom, leading to the injection of four electrons into the conduction band. These electrons stay localized near the crystal surface due to the presence of a space charge layer. The reaction is accompanied by the breaking of the backbonds, which requires the thermal excitation of the respective surface state electrons into the conduction band. This step is considered to be rate limiting. In a reduction step, the injected electrons react with water molecules to form new hydroxide ions and hydrogen. It is assumed that these hydroxide ions generated at the silicon surface are consumed in the oxidation reaction rather than those from ...