Energy-loss mechanism of single-crystal silicon microcantilever due to surface defects generated during plasma processing

The mechanism behind the degradation of the mechanical properties of silicon (Si) microcantilevers caused by plasma-induced surface defects was investigated. The resonant frequency (f) and quality factor (Q factor) were deteriorated by defects generated after irradiating Ar plasma. We found that Young's modulus in the surface region was decreased after the plasma irradiation, but this does not explain the drastic change to the resonant frequency. The decrease could be explained by using a model in which a surface defect layer causes energy dissipation. Hydrogen annealing at 450 °C and rapid thermal annealing at 1000 °C could not repair the mechanical properties degraded by the plasma irradiation. After annealing, Young's modulus was not recovered while the dangling bonds were diminished, because the annealing could not restore the crystalline structure of the silicon. These results indicate that extensive defects such as dislocations or amorphous phases may be generated during plasma irradiation, causing energy dissipation. Since the degraded mechanical property in the plasma processes cannot be restored by annealing, it is important to prevent any damage from occurring at any stage of the processes.