Assessment of post-CMP cleaning mechanisms using statistically-designed experiments

Abstract

Post-CMP wafer cleaning commonly uses a combination of double-sided brush scrubbing, megasonic cleaning, and spin-rinse drying to remove polishing residues from wafer surfaces. This paper investigates double-sided brush scrubbing and spin-rinse drying by evaluating IPEC Planar’s Avanti 9000 post-CMP cleaner for the removal of diluted slurry solutions from previously polished and cleaned W sheet wafers. Diluted SC-1 (H2O/NH4OH/H2O2= 20:1:1) and DI water were used as the cleaning solutions in the brush and spin-rinse drying units, respectively. Results show that the number of brush cycles, the brush pressure, and the brush rotating speed are key parameters in the removal of particles with diameters greater than 0.21 μm from the wafer. Two factor interactions between: (1) the number of brush cycles and the brush pressure, and (2) the number of brush cycles and the brush rotating speed are also important to the process performance. In addition, operating the spin-rinse drying unit at the typical rotating speed (1000 rev./min) is not adequate for submicron particle removal from the wafer. A theoretical analysis of the hydrodynamics of the brush cleaning suggests that particles are removed from wafers due to direct particle-brush contact, but that particle redeposition onto the wafers may occur.