Effects of Chamber Pressure on the Performance of CO2 Beam Cleaning

As the size of functional patterns in the semiconductor chips shrinks down to below 100 nm, removing nanoscale contaminant particles is an important technological challenge that the current semiconductor manufacturing industry must overcome. Several cleaning methods proposed to date, such as megasonic cleaning [1], droplet impact [2], and cryogenic aerosol cleaning [3], have difficulties in cleaning of sub-100 nm contaminant particles, let alone their tendency to induce pattern damages. Kim et al. [4] has recently developed a new method, where CO2 solid particles nucleated from a supersonic nozzle physically attack contaminant nanoscale particles on the wafer, thus detaching them. A drawback of this novel scheme is that the cleaning must be executed in vacuum because CO2 gas needs to sublimate into solid and be accelerated supersonically as exiting the nozzle. This has adverse effects on the cost and rate of the semiconductor manufacturing process. Here we investigate the effects of vacuum chamber pressure on the performance of the CO2 dry cleaning system. We observe the cryogenic CO2 beams, dents induced by CO2 solid particles, and wafer surfaces initially contaminated with cerium oxide particles, which indicate the effects of the chamber pressure.