Measurements of normal and friction forces during brush scrubbing

In order to gain some insights for post CMP cleaning, we measured the forces during brush scrubbing. In this experiment, both the normal force Fn and shear (friction) force Fs generated by a single sponge sliding on the plate were measured. The Fn of PVA increased quickly and attained its maximum value. After that, Fn gradually decreased to a constant value even in the same compression distance. Fs followed the same trend as well. This result indicates that the initial contact of PVA brush generate high friction force. The Fn of polyurethane also increased quickly and attained its maximum value, however the Fs do not followed. On the contrary, the both forces of melamine show the almost constant value. In addition, we observed the impact behavior of PVA brush by high-speed photograph. When the impact speed is slow, water inside the brush remains around the brush, however water is spattered to the surrounding air as increasing the impact speed.