Effect of microfabrication processes on surface roughness parameters and micro/nanoscale friction behavior of silicon surfaces
Etching process can affect the surface roughness and hence the tribological properties of silicon surfaces. This study qualifies and compares surface roughness parameters of silicon surfaces etched with KOH (6M, 8M and 10M), TMAH and DRIE. IPA was added to 8M KOH and TMAH and their micro/nanoscale friction behavior was evaluated. Results showed that DRIE produces the smoothest etched surface compared to the anisotropic etchants and also exhibits a slightly lower number of contacts at a given load. Surfaces etched with 6M KOH have high roughness and also exhibits high kurtosis and positive skewness and 6M KOH appears to be the best anisotropic etchant to produce surfaces with low friction. Although TMAH and KOH produced comparable roughness up to 5 [mu]m scan size, at larger scan sizes TMAH produced rougher surfaces than KOH. The use of IPA additive resulted in enhancement of sub-micron roughness features but a reduction in the long-range roughness of the surfaces to yield smoother surfaces than the pure etchants at scan sizes above 20 [mu]m. All the etched surfaces exhibit pit like features at 20 [mu]m scan sizes. Surface roughness evolution spectroscopy (SRES) showed that TMAH produces slightly larger pits than KOH and using IPA resulted in an increase in the maximum pit size. The 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 elastic contact 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.