CMP C hemical M echanical P lanarization Carried out by Eran Cantrell, Bobby O’Ryan, And Maximus (CMP)

OBJECTIVES -I ncrease removal rate - I nvent a way to roughen pad surface - M easure effect of roughening on removal rate and uniformity - M easure effect of slurry flow rate on removal rate and uniformity - R each conclusion of how to better maintain machine efficiency

Background -T he CMP (Chemical Mechanical Planarization) process polishes silicon wafers, using slurry (liquid sandpaper) and a platen (polishing pad) to prepare the wafers for lithography. This requires the wafers to be as smooth and uniform as possible. This process is affected by the slurry flow rate, the pad roughness, pressure on the wafer, the platen spin rate, and the length of time the wafer is polished.

Equipment Description Load  Polish  Unload  Clean  Load Uses Air, N 2, DIW, Slurry, Water, Electricity Control Box Carrier Primary Polish Platen Slurry Delivery Arm Cleaning Station Control Me Wafer Boat Load Station Final Slurry Pump Primary Slurry Pump Final Polish Platen Wafer Boat Polishing Arm Unload Station

Experimental Conditions F ive conditions were set up. This was to test the impact of two variables, while keeping all else constant: the slurry flow rate, and the pad roughening. C onditions were set up from low SFR (75 ml/min) and low PR (30 sec), increasing to high SFR (225 ml/min) and high PR (2 min). The standard was 150 ml/min of flow rate, and 1 min of roughening. T he CRPM (carrier rotations per min) rate stayed 50 rpm constant. T he platen stayed at 30 rpm when polishing, 60 rpm when roughening. P olishing time was 30 sec constant. T he mass and thickness of the wafers were measured before and after to determine which method was removing the most material.

Data

E ach colored line represents the average of the closest three data points surrounding it. While you can see an up-down variation between averages, if you look at the individual data it is impossible to tell the groups apart.

Data

Recommendations for Future Work R oughening technique should be more mechanical, and methodical. D evelop a technique to measure pad roughness.

Conclusion P ad roughening appears to increase the removal rate of the silicon dioxide film, and improves wafer uniformity. D ue to confidence interval overlap, an optimal roughening time cannot be selected. S imilar conclusions can be made about slurry flow rate.

Acknowledgements W e would like to thank Jason Hower, for his tutoring throughout this process; D r. Milo Koretsky, for his helpful advice; M aximus, who endured our unorthodox methods; A ll the companies who have donated materials (Intel and Sumco); A nd the rest of the SESEY staff, for all the support and funding (and effort) they have provided for the students.