Zinc Oxidation and Redeposition Processes in Aqueous Alkali and Carbonate Solutions: I . pH and Carbonate Ion Effects in Film Formation and Dissolution

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Abstract
Three‐dimensional structures in silicon are increasingly coming into use for the fabrication of mechanical and electrical devices. The fabrication of deep trenches is one of the most important problems in VLSI (very large scale integration) technology. In this study the spontaneous trench formation in n‐type silicon immersed in hydrofluoric acid under anodic bias is demonstrated and the resulting microstructures are characterized. Trenches with arbitrary cross sections and high aspect ratios for microelectronic (e.g., 42 μm depth and 0.6 μm diam) and for power component application (e.g., 60 μm depth and 10 μm diam) have been produced by a standard masking technique. The trench formation is explained by a model which takes into account the conditions of the space charge region the minority carrier current and the crystal orientation. A passivating sidewall layer is not needed in this model. The dimensions and the shape of anodically etched trenches can be varied over a wide range by adjusting the critical parameters.