Etching of self-sharpening (338) tips in (100) silicon

Numerous papers have appeared in recent years describing various methods of achieving nonoscale tips for vacuum microelectronics. In single-crystalline (100) Si, wet anisotropic etching (KOH in this case) has been affected by the truncation, or blunting, of the tip when the masking oxide or nitride is completely underetched, which exposes the quickly etching (100) surface plane. The paper reports for the first time the activation of {338} type sidewalls, which under our conditions results in an etching effect along the [100] direction that exceeds the ordinary etching rate of the (100) plane, thus resulting in a self-sharpening tip. Secondary planes reported in the literature have traditionally been of low index, such as {122}, {112}, {113}, or {133}, although {114} and even {225} have also been reported. Comparison of the relevant angles of each of these planes reveals similarities that may lead to ambiguities found in the literature. A statistical analysis of the data presented in this paper lends confidence to the assertion that the {338} family defines the sidewalls of the tips. Also, a novel and highly promising double tip (tip on a tip) is herein reported preliminarily, in (110) oriented Si; this is currently under analysis.