Experimental In-Situ Observatory on Brownian Motion Behavior of 105 nm Sized Silica Particles During Chemical Mechanical Polishing of 4H-SiC by an Evanescent Field

The experimentally observing optical systems for on-machine measurement have been developed to study on nano-polishing phenomena during the chemical mechanical polishing process, which is a wet process in semiconductor manufacturing. The developed optical system employs an evanescent field to selectively enhance exclusively the observatory of phenomena occurring on the surface being polished, offering a lateral resolving power of approximately 400 nm, in the slurry concentration of up to 5 wt% based on the numerical aperture of the objective lens. In addition, there is also the observability of 105 nm and down to 55 nm-sized silica particles without requiring additive fluorescence agents in or around the nano-particles, even when these particles are moving on surfaces such as silica glass or hard materials (silicon carbide: 4H-SiC). Consequently, the motion behavior of nano-particles disjoining with polishing pad asperity was explored and discussed, in this paper. Experimental results revealed that the polishing pad spatially constrains the movement of particles between the pad and the substrate surface, guiding them toward the surface being polished. During pad sliding, fluidically dragged nano-particles exhibit slower movement than the polishing pad sliding speed while retaining the Brownian motion. Furthermore, 105 nm-sized silica particles did not continuously approach to attach onto the SiC surface; the nano-particles approached in steps with reduced Brownian motion in all directions before attaching. This behavior can be attributed to the effects of van der Waals attraction and electrostatic repulsion forces between the particle and the substrate surfaces.