Micron-Scale Friction and Sliding Wear of Polycrystalline Silicon Thin Structural Films in Ambient Air

Micron-scale static friction and wear coefficients, surface roughness, and resulting wear debris have been studied for sliding wear in polycrystalline silicon in ambient air at micro-Newton normal loads using on-chip sidewall test specimens, fabricated with the Sandia SUMMiT V™ process. With increasing number of wear cycles friction coefficients increased by a factor of two up to a steady-state regime, concomitant with a decay (after an initial sharp increase) in the wear coefficients and roughness. Wear coefficients were orders of magnitude smaller than reported macroscale values, suggesting that the wear resistance is higher at micrometer dimensions. Based on our observations, a sequence of micron-scale wear mechanisms is proposed involving: 1) a short adhesive wear regime (< 10⁴ cycles), where the oxide is worn away and the first silicon debris particles form and 2) a regime dominated by abrasive wear, where silicon particles (50-100 nm) are created by fracture through the grains (~500 nm). These particles subsequently oxidize and agglomerate into larger debris clusters, while "ploughing" by this debris leads to abrasive grooves associated with local cracking events rather than plastic deformation.