Chemical Treatment Effect of Si(111) Surfaces in NH4F Solution Studied by Spectroscopic Ellipsometry

Abstract

Chemically treated Si(111) surfaces in NH4F (40%) solution at 20° C have been studied using spectroscopic ellipsometry (SE) and exsitu atomic force microscopy (AFM). The SE data clearly indicate that the solution causes the removal of the native oxide with an etch rate of ∼ 15 Å/min. Just after the native oxide is etched away completely (t∼ 70 s), the SE data yield the spectrum of a slightly roughened surface. With further etching, the Si surface becomes gradually rougher. The roughened surface thickness immersed for t∼ 600 s, for example, is ∼ 16.5 Å with a void fraction of ∼ 42%, obtained using an effective medium approximation (EMA); the resulting AFM image of this sample indicates a roughened surface of ∼ 14 Å rms with the emergence of pillars and hollows. It can thus be concluded that SE can be used to assess important chemical treatment parameters of crystalline Si.