(Dr. Minami Yoda, advisor)
"Visualization of Particle Dynamics at Various Spatial Scales"
Chemical-mechanical polishing (CMP) is currently the leading surface
preparation process for planarizing silicon wafers to nanometer-scale
smoothness in the manufacture of integrated circuits. In CMP, an abrasive
particle-containing slurry (actually a dilute suspension) is sheared or
rotated between a rough compliant polymeric pad and a smooth rigid silicon
wafer. The process involves complex, poorly understood interactions
between the pad, the wafer and the abrasive colloidal particles that wear
or polish the wafer.
To model the CMP process, the particle dynamics of a sheared colloidal
suspension were experimentally visualized immediately next to a glass
"wafer". A novel diagnostic technique employing evanescent wave
illumination was developed to directly measure, in real time, the velocity
and concentration of fluorescent colloidal particles within 400 nm of the
glass surface, or the abrasive particles that interact with and polish
this surface. The effects of particle size, particle density and shear
rate were investigated. The effect of pad geometry was also investigated
by using a variety of silicon surfaces with periodic cylindrical
asperities to simulate the "pad" rotating above the glass "wafer". This
work is the first to investigate the interfacial dynamics of submicron
diameter particles in a representative CMP geometry.