Investigation of silicon wear against non-porous and micro-porous SiO2 spheres in water and in humid air

Abstract

Tribochemical wear, a method to achieve controlled material removal without residual damage on substrates, plays a very important role in super-smooth silicon surface manufacturing. By using non-porous SiO₂ spheres and micro-porous SiO₂ spheres, the wear of silicon substrates was comparatively investigated in DI water, humid air (50% RH) and dry air. The wear behaviors presented entirely different cases at the same load in DI water and humid air: (a) less material removal of silicon against non-porous SiO₂ spheres than micro-porous SiO₂ spheres in water and (b) more serious wear of silicon substrate against non-porous SiO₂ spheres in humid air. When the wear tests were operated in dry air, no obvious damage was incurred on the silicon surface against the non-porous SiO₂ spheres but slight wear was observed against micro-porous SiO₂ spheres under the given conditions. Raman results revealed that a hydrolysis reaction was involved in the tribochemical wear of the silicon substrate and the micro pores in SiO₂ spheres could accelerate this process. The corresponding analysis suggests an exponential dependence of wear rate on contact stress, which is consistent with the stress-assisted chemical kinetics model. Although with much lower elastic modulus, micro-porous SiO₂ spheres caused a larger wear rate of silicon substrate than non-porous SiO₂ spheres at the same contact pressure both in water and humid air. The results indicate that the micro-porous SiO₂ spheres can promote the tribochemical reaction due to the storage of water molecules in micro pores.