Counting efficiency comparison of liquid optical particle counters below 100 nm
Gary Van Schooneveld
CT Associates, Inc.
Sung In Moon
Semiconductor manufacturing requirements continuously challenge the particle measurement suppliers to provide instruments capable of detecting and sizing increasingly smaller particles. A number of manufacturers have introduced liquid optical particle counters (OPC) with specified detection limits of ? 30 nm. It is important that the users of these instruments understand the particle counting efficiency of these instruments relative to particle size as they apply these improved instruments to their process measurements.
SEMI C77-0912, TEST METHOD FOR DETERMINING THE COUNTING EFFICIENCY OF LIQUID-BORNE PARTICLE COUNTERS FOR WHICH THE MINIMUM DETECTABLE PARTICLE SIZE IS BETWEEN 30 nm AND 100 nm is an available method for comparing OPS’s. Prior work1 has noted the importance of understanding the particle size distribution of the PSL as these materials often do not have a normally distributed particle size distribution, particularly below 100 nm (Figure 1).
This paper will review the results of measuring the counting efficiency of multiple OPC’s using multiple sizes of PSL and the method described in SEMI C77. Poly-dispersed challenges were also prepared with varying particle concentration vs. size slopes for measuring instrument response to a simulated, “real-world” distribution. Finally, three particle challenges (Figure 2) prepared from colloidal silica were used to compare the counter responses to non-PSL particle challenges.
Ultrapure Water Micro 2015 October 27-28, 2015 Portland, OR