Effect of microfabrication processes on surface roughness parameters of silicon surfaces

Surface roughness parameters affect the real area of contact and hence the friction in micro/nanoscale systems. Few studies have addressed the interplay between surface roughness of processed surfaces using prevalent microfabrication processes and their anticipated tribological behavior. In this paper, the effects of different etchants on the surface roughness of a Si (100) surface were investigated using atomic force microscopy. The etchants studied were TMAH (25% aqueous at 90 degreesC) and KOH solution (6, 8 and 10 M at 80 degreesC). The surfaces generated by these wet-etching techniques were compared with the surface generated by deep reactive ion etching (DRIE). Quantitative surface roughness parameters (root mean square (RMS), peak-to-valley distance (PTV), skewness (Sk), kurtosis (K) and autocorrelation length (ACL)) of the various surfaces were obtained from atomic force microscope images at different scan sizes. Results showed that DRIE produced the smoothest etched surface while TMAH produced the roughest surface. KOH (8 M) produced smoother surfaces than 6 and 10 M solutions. A dry contact model based on using the Pearson system of curves to generate the probability density function from the measured roughness parameters was used to estimate real area of contact and number of contacts for the various surfaces. From the contact model, we find that DRIE and 6 M KOH surfaces show the least number of contacts and are therefore the preferred etching methods to realize surfaces with minimum adhesion/friction. (C) 2004 Elsevier B.V. All rights reserved.