Particular contamination below about 0.3 microns in averagediameter on an IC wafer substrate is detected by forming a film ofa volatile liquid on the wafer's surface and observing interferencepatterns formed by particles during the evaporation process. Theseinterference patterns magnify the "effective" particle size manytimes, making detection through an optical microscope possible.
Process for detection of sub-micron particulate contamination on a bare (planar) substrate
Menon, V. (1991). IPC No. U.S. Process for detection of sub-micron particulate contamination on a bare (planar) substrate. (U.S. Patent No. 5061068).