Morphological Aspects of Silicon Oxidation in Aqueous Solutions

Abstract

Aqueous etching of silicon is important to many processes in the microelectronics industry, including the cleaning of silicon wafers, the detection of dislocations and defects, and the fabrication of micromachined structures. In most of these processes, the anisotropy of the etchant is very important, because it controls the morphology of the etched surfaces. In some cases, the microscopic anisotropy or site-specificity of the etchant is of primary importance. For example, Ohmi et al.[1]have shown that atomic-scale roughness generated by RCA cleaning solutions, which are commonly used to clean silicon wafers, can degrade the performance of metal-oxide-semiconductor fieldeffect transistors (MOSFETs) subsequently fabricated on the cleaned wafer. To prevent this, highly anisotropic silicon cleaning solutions that produce atomically smooth Si(100) faces are highly sought after. Microscopic anisotropy also controls the performance of defect etchants, which are commonly used to quantify dislocation densities. These etchants apparently attack the strained bonds around each atomicscale dislocation and produce macroscopic etch pits that can be detected optically. For other purposes, atomicscale etchant anisotropy is less important than the macroscopic anisotropy — the face-specificity. For example, basic solutions etch Si(111) faces exceedingly slowly, so these etchants can be used to easily fabricate smooth, precisely oriented (111) facets for vee-grooves 2 , inkjet nozzles 3, or other micromachining applications 4.