Atomic fluorine beam etching of silicon and related materials

A 1 eV neutral atomic fluorine beam has been shown to produce etch rates in silicon as high as 1 mu m/min. Using a CaF2 resist layer we fabricated 120 mu m deep by 1 mu m wide trenches (aspect ratio 120:1) in silicon with lit tle sidewall taper (slopes of about 1000:1) or aspect-ratio dependent etchi ng effects. Achieving such anisotropic etching suggests that the scattered species do not contribute significantly to sidewall etching under the condi tions of this experiment. We estimate that the ultimate depth attainable fo r a 1 mu m wide trench is about 250 mu m and that the critical parameter fo r attaining a trench of a certain depth is the aspect ratio. Our observatio ns and analysis suggest that this etching technique can be used to fabricat e trenches on a nanoscale level while maintaining high aspect ratios of 100 or greater. (C) 2000 American Vacuum Society. [S0734-211X(00)03501-0].