Rectangular scale-similar etch pits in monocrystalline diamond

Etching of monocrystalline diamond in oxygen and water vapor at 1100 °C through small pores in a silicon nitride film produced smooth-walled rectangular cavities. The cavities were imaged by electron microscopy and measured by interferometric microscopy. The observed cavities ranged in width from approximately 1 μm up to 72 μm, in each case exhibiting smooth, vertical sidewalls, a flat bottom, and a depth equal to half its width. Cavity boundaries were determined to lie along slow-etching {100} crystallographic planes, suggesting the possibility of a powerful class of techniques for high-aspect-ratio bulk micromachining of diamond.