Formation Mechanism and Properties of Electrochemically Etched Trenches in n‐Type Silicon

Three-dimensional structures in silicon are increasingly coming into use for the fabrication of mechanical nd electri-cal 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 ~m depth and 0.6 ~m diam) and for power component application (e.g., 60 ~tm depth and 10 ~m diam) have been produced by a standard masking technique. The trench formation is explained by a model which takes into account he conditions of the space charge region the minority carrier current and the crystal ori-entation. A passivating sidewall ayer 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. Since trench etching is becoming more and more impor-tant in silicon device fabrication, a large number of studies have been carried out to improve p lasma etching tech-niques. However, submicron trench processes still suffer f rom structural effects wh ich dominate the trench geome-