Toward CO2 Beam Cleaning of 20-nm Particles in Atmospheric Pressure

We propose an optimal strategy for cleaning 20-nm contaminants in atmospheric pressure by using CO2 solid particles injected from a supersonic nozzle. We found that an excessively small exit diameter of the nozzle results in the shock wave, which decreases the particle removal efficiency (PRE). Based on the incompressible flow theory, we developed a supersonic nozzle that can issue CO2 solid particles without shock wave. The shape of CO2 beam and PRE of the developed nozzle are compared with the results of a pre-existing nozzle for vacuum condition by analyzing scanning electron microscopy (SEM) image of substrates. The results show that when we use the newly developed nozzle in atmospheric pressure, PRE is above 95 % without pattern damage. This work can pave the way for cleaning nanoscale contaminants that occur during manufacture of semiconductor chips at little cost.