Removal of nano-sized surface particles by CO2 gas cluster collisions for dry cleaning

Gas cluster cleaning is a method of dry cleaning avoiding the loss or damage of materials by forming aerosol clusters of tens to thousands of molecules via cooling and a pressure drops of a gas. Particle removal for dry cleaning techniques mainly relies on momentum transfer of the aerosol. Therefore, the generated aerosol size and velocity are key parameters for the aerosol cleaning method. To optimize and investigate gas cluster cleaning equipment, prediction of the cluster sizes is performed through indirect measurements, accomplished by measuring dent sizes on a photoresist (PR) film. An experimental analysis of variables such as the nozzle temperature, CO2 flow rate, gap distance between the surface and nozzle exit, and impaction angle was performed. To measure the cleaning performance of the equipment, CeO2 and SiO2 particles in the 30-300 nm range, which can occur in the semiconductor manufacturing process, were deposited on a Si wafer and cleaned. This paper studies gas clusters derived from gas cluster cleaning equipment. As a result, the particle removal efficiency (PRE) measurement showed a cleaning efficiency of more than 97% for CeO2 contaminants and greater than 92% for SiO2-based particles.