Tilt and interfacial fluid pressure measurements of a disk sliding on a polymeric pad

Previous experimental work has shown that negative fluid pressure does develop at the disk/pad interface during chemical mechanical polishing. However these studies dealt with one-dimensional measurement and modeling. To better understand the problem, two-dimensional pressure mapping is carried out. In addition, the orientation of the disk is measured with a capacitive sensing technique. Results reveal a large negative pressure region at the disk/pad interface that is skewed toward the leading edge of the disk. The disk is also found to be leaning down toward the leading edge and toward the center of the pad. A mixed-lubrication model based on the Reynolds equation and taking into account the disk orientation angles has been developed. Modeling and experimental results show similar trends, indicating the tilting of the disk as a dominant factor in causing the negative pressure phenomenon.