Modeling of particle removal using non-contact brush scrubbing in post-CMP cleaning processes

Particle removal using non-contact brush scrubbing for post-CMP (Chemical Mechanical Planarization) cleaning is investigated analytically. The removal of SiO2 and Al2O3 particles adhered onto SiO2 film coated on the wafer surface are considered. The cleaning fluid (H2O/NH4OH = 1:25 and 1:200) flowing between the brush and wafer urface is treated as a thin-film fluid flow. The flow field details and its effect on the drag force acting on the adhered particles are discussed. In addition to the drag force, the electrical double layer (EDL) and thermophoretic force effects on particle removal are also considered. It was found that the dominant force in achieving particle removal using a rolling mechanism is the drag force. The EDL and thermophoretic forces have an insignificant effect on particle removal. Based on the results from this study, particles of submicron size can be removed from a wafer surface using higher brush rotation speed and pure deionized (DI) water as the cleaning fluid.