Study on a condition for forming the high density of silicon needles with high aspect ratio

Abstract

We have developed a process to fabricate needle-shaped silicon crystals (silicon needles) by highly selective anisotropic dry etching. The etching masks are fine SiOx clusters in the silicon substrate. Under high density of these clusters, side etching easily occurs at the silicon needles in the process of dry etching. This mechanism is as follows. As the dry etching proceeds, the etching area becomes smaller and smaller due to existing high density of silicon needles. This leads to reduction in the deposition rate of sidewall passivation film, because gas for this film comes from the etched silicon substrate. Accordingly, for forming high density of the silicon needles, the deposition rate must be kept higher than the etching rate of the sidewall passivation film during the dry etching. By adjusting the deposition rate, we confirmed this mechanism and obtained high density 3×108 cm−2 of the silicon needles with an aspect ratio of 5 without side etching. Such silicon needles can be expected to lead to high emission current density and electric field enhancement when applying the silicon needles to a field emitter array.