An investigation of particle removal efficiency and feature damage has been conducted in NH 4 OH/NH 4 HCO 3 cleaning solutions irradiated with megasonic energy. By adjusting the pH of the solution in the range of 8.2 -8.5, high particle removal efficiency (PRE) was achieved while feature damage was reduced significantly. The sonoluminescence data collected from NH 4 OH and NH 4 OH/NH 4 HCO 3 solutions indicate significant suppression of transient cavitation in alkaline solutions containing aqueous CO 2 .Index Terms-Megasonic cleaning, particle removal efficiency (PRE), feature damage, CO 2 (aq.), sonoluminescence (SL)