Effect of diamond disc conditioner design and kinematics on process hydrodynamics during copper CMP

This study focused on determining the effect of diamond disc design (i.e. the particular arrangement of diamonds on the disc), conditioner kinematics, and conditioner pressure on slurry distribution under the wafer as measured by the apparent slurry film thickness (and hence the apparent distance) between the wafer and the pad during actual polishing. To achieve this goal, the study successfully used the Dual Emission UV Enhanced Fluorescence technique that required the slurry to be tagged with two different fluorescent dyes in order to take advantage of the dyes' fluorescence properties as seen by two CCD cameras through a transparent quartz 'wafer'. Results indicated that: • Slurry film thickness strongly depended on diamond disc design. Type - I design resulted in the thickest fluid film followed by Type - II and Type - III. Close examination of DEUVEF video tapes as well as a separate flow rate study, performed using the Type - I disc, suggested that the thicker fluid film caused by the disc was at least partially due to enhanced slurry flow due to the diamond disc. • The wafer was tilted towards the center of the pad during polishing and that the extent of wafer tilt was a strong function of diamond disc pressure. The tilt was believed to be due to uneven pad asperity rebound in the radial direction of the pad. Higher pressures were believed to cause less rebound and therefore less wafer tilt. • In most cases, increasing the oscillation frequency of the diamond disc decreased slurry film thickness. Simulation of furrows generated by all of the diamonds on the conditioner as a function of various oscillation frequencies showed a greater density of furrows associated with a sweep frequency of 15 per minute thus suggesting taller asperities and therefore thicker slurry films in the pad-wafer interface.