Particle removal from silicon wafer surface in wet cleaning process

Particle removal from silicon wafer surfaces was studied using acid and alkaline solutions employed in wet cleaning processes found in semiconductor manufacturing. It was demonstrated that alkaline solutions are superior to acid solutions in terms of particle removal efficiency. The following particle removal mechanism in the alkaline solutions was confirmed: the solutions etch the wafer surfaces to lift off particles, and the particles are then electrically repelled by the wafer surfaces. It was determined experimentally that an etch rate of 0.25 nm/min or more is required to lift off the particles adsorbed on the wafer surfaces. It was also confirmed that when the pH value of NH₄OH-H₂O₂-H₂O solution becomes higher, polystyrene latex spheres and natural organic particles are oxidized, with their surface turning into a gel and their shape changing. The particle removal efficiency was demonstrated to be degraded by the oxidation of organic particles. The results suggest that the mixing ratio of the NH₄OH-H₂O₂-H ₂O solution should be set at 0.05:1:5