Particle measurements with liquid-borne particle counters: Effects of counting efficiency

摘要

Liquid extraction of semiconductor tool components followed by particle measurements with a liquid-borne particle counter (LPC) is an effective method to determine surface particle contamination on parts. As device geometries continue to shrink, nanoparticles (100 nm or smaller) have attracted more and more attention. Unfortunately, light-scattering based counters capable of measuring these nanoparticles operate at Less Than Perfect Counting Efficiency (<100%, LTPCE) due to design limitations. With limited understanding of this limitation, testing results from different labs with different counters can be drastically different and thus confusing. This work studies the effect of counting efficiency on measurement results through comparative measurements with counters of different counting efficiencies. This study showed counting efficiency affects measurement accuracy significantly but has limited or no effect on measurement precision on the same counter. The effect of counting efficiency on accuracy depends on the composition of the particle as well as particle size and/or distribution. It is difficult to find a universal and straightforward way to correct the adverse effect of LTPCE in order to achieve standardized particle measurements among those counters.