Effect of mechanical properties of PVA brush rollers on frictional forces during post-CMP scrubbing

Tribological attributes of post-chemical mechanical planarization (CMP) brush scrubbing process were investigated as a function of type and velocity of the brush roller, applied pressure, and the pH of the cleaning solution, Coefficient of friction (COF) results were significantly different for the two types of brush rollers over a wide range of operating conditions. The two types of rollers were subjected to a battery of dynamic mechanical analyses and shown to be identical to one another in terms of flexural storage modulus and tan δ. By quantifying the extent of deformation of the entire brush roller during actual scrubbing using real-time pressure sensing technology, it became apparent that for a given applied load on the brush, the less compliant brush roller (by about 10%) resulted in proportionately higher COF, thus underscoring the importance of brush design and method of mechanical testing of the roller for imparting desired amounts of shear force on the surface of the wafer during scrubbing.