The effect of anisotropic wet etching on the surface roughness parameters and micro/nanoscale friction behavior of Si(100) surfaces

Etching processes can affect the surface roughness and hence the tribological properties of silicon surfaces. In this paper, we evaluate the surface roughness parameters and micro/nanoscale friction behavior of Si(1 0 0) surfaces etched using 8 M KOH and tetramethyl ammonium hydroxide (TMAH) solution with and without isopropyl alcohol (IPA) additive. Amplitude and spatial parameters were evaluated using atomic force microscopy (AFM) and profilometry at scan sizes ranging from 1 to 500 mu m. Results showed that TMAH and KOH produced comparable roughness up to 5 mu m scan size and that at larger scan sizes, TMAH produced rougher surfaces than KOH. The use of IPA additive caused enhancement of sub-micron roughness features as well as a reduction in the long-range roughness of the surfaces resulting in smoother surfaces than the pure etchants. All etched surfaces exhibited pit like features with TMAH producing slightly larger pits than KOH. Surface roughness evolution spectroscopy (SRES) showed that using IPA resulted in an increase in the maximum pit size. Single asperity friction behavior correlated well with the adhesive forces for the various surfaces - KOH and TMAH showed comparable behavior and the use of IPA resulted in lower friction forces. However the use of IPA resulted in surfaces with higher real area of contact, which was responsible for higher friction forces in multiple asperity contacts on the microscale. This study demonstrates that the choice of etchants and additives affect the surface roughness and microscale friction behavior of the resulting surfaces. (c) 2004 Elsevier B.V. All rights reserved.