(Dr. Steven Danyluk, advisor)
"Investigation and Modeling of Fluid Pressures in Chemical Mechanical Polishing"
Two-dimensional pressure mapping of the fluid pressure using membrane pressure
sensors reveals a large, asymmetrical sub-ambient pressure region. This sub-ambient
pressure is believed to be present during chemical mechanical polishing (CMP).
A theory of the sub-ambient pressure phenomenon observed during the wet sliding
of a disk on a polymeric pad will be presented. It is hypothesized that the
phenomenon is a result of the tilt of the disk as a result of shear forces acting
on it by the polymeric pad. Tilt measurements of the disk carried out by a capacitive
sensing technique indicate that the disk is tilted in a certain way when the
pad is rotating. The orientation of the disk changes with pad speed. A two-dimensional
mixed-lubrication model based on the Reynolds equation will be developed using
a finite differencing scheme. Preliminary theoretical results indicate that
when the tilt angles in the experiments are used, the experimental pressure
map can be re-created. In addition, some preliminary tilt experiments with actual
CMP wafer carrier show similar results.