Volume 2, Issue 5 (May 2005)
Understanding Polymeric Pads in Pre-CMP Conditioning
Experiments were conducted to understand the principles behind polymeric pads during pre-CMP conditioning. Nylon, polycarbonate, and polyurethane pads were tested against copper pins in a slurry containing 3 wt % alumina nanoparticles. The surface properties of pads were estimated after conditioning. The wear of pads along with friction coefficient was evaluated during friction experiments. Results show that contact angles of polycarbonate and polyurethane pads increase with their surface roughness, while those of nylon show the opposite tendency. Surface roughness of pads induced by conditioning could influence the wear performance of nylon and polycarbonate, more than that of the polyurethane pad. Our previous study has shown that the stimulation of friction induces materials transfer during CMP. In this work, we further investigated the effect of such transfer on wear mechanisms of pads during conditioning and polishing. Compared with nylon and polycarbonate, chemical and material properties of polyurethane and their tribological performance are more stable. This makes polyurethane a unique material for CMP.