Nano-scale Tribological Behavior of Polycrystalline Silicon Structural Films in Ambient Air

Dynamic friction, wear volumes and wear morphology have been studied for sliding wear in polysilicon in ambient air at μN normal loads using on-chip micron-scale test specimens. With increasing number of wear cycles, the friction coefficients show two distinct types of behavior: (i) an increase by a factor of two and a half to a steady-state regime after peaking at three times the initial value of about 0.10 ± 0.04, with no failure after millions of cycles; (ii) an increase by a factor larger than three followed by failure after ~10⁵ cycles. Additionally, the average nanoscale wear coefficient sharply increased in the first ~10⁵ cycles up to about 10^-4 and then decayed by an order of magnitude over the course of several million cycles. For both modes of behavior, abrasive wear is the governing mechanism, the difference being attributed to variations in the local surface morphology (and wear debris) between the sliding surfaces. The oxidalion of worn polysilicon surfaces only affects the friction coefficient after periods of inactivity (>30 mm).