Structural Effect of PVA Brush Nodule on Particle Removal Efficiency during Brush Scrubber Cleaning

Brush cleaning can trigger both mechanical and chemical reaction to efficiently remove the adsorbed particles on the wafer. However, the removal mechanism of nanosized particles by brush cleaning is far from clear because no direct experimental data, such as the friction and contact force of the interface between brush and wafer surface, are available to back up the theoretical models in the literature. In this paper, we set up a monitoring system to measure the friction force of the interface between brush and wafer surface during brush cleaning to investigate the effect of the brush nodule structure having different nodule heights and nodule gaps on particle removal efficiency. To confirm the mechanical effect of the brush nodule structure, an oxide wafer contaminated with Polystyrene latex (PSL) particles (mean diameter: 300 nm) was cleaned with each PVA brush having different brush nodule structures using de-ionized water (DIW). The silica particle (mean diameter: 22 nm) and chemical solution (NH4OH, 0.1 wt%) were also used to investigate the chemical-aided particle removal. The remaining particles were measured with a Surfscan 6420 (KLA Tencor) and the friction force monitoring was conducted by using a Cleaner812-L (G&P Technology). The results indicated that a higher brush nodule height produced lower friction force, resulting in lower particle removal efficiency. When the nodule gap became smaller, the contact area between brush nodule and wafer surface became larger, resulting in higher particle removal efficiency. However, the experimental results using silica particles and 0.1 wt% of NH4OH showed different trends under each condition. The particle removal mechanism with silica particle and NH4OH was also verified by measuring the zeta potential between the particle and wafer.