Ultra-Fast Anisotropic Silicon Etching with Resulting Mirror Surfaces in Ammonia Solutions

The effect of an arsenic (III) salt addition on the anisotropic etching performance of aqueous ammonia solutions is presented. Here we demonstrate that the intake of small amounts of this salt considerably alters the etching behavior of ‹100›-oriented silicon. During the etching process, an elementary As-film precipitates at the dissolving Si-surface and floats on it as etching proceeds. The real surfactant like behavior of the arsenic compound results in etch rates as high as 95 µm/h at 70 °C. In addition, the etched surface appears mirror like to the naked eye and shows a rms-roughness below 5 nm as confirmed by AFM measurements.