The role of surface cleanliness in contamination control

Abstract

Contamination control is required for products and processes that are sensitive to particulate contamination. A cleanroom will be used to create an environment with low particle concentration. In contamination control traditionally the focus is on air cleanliness. This works fine for particles smaller than 5 micrometer. However in many cases particles larger than 5 micrometer are the major threat for products like optical systems. Contamination control of macroparticles (< 5μm) especially visible particles (< 25μm) should focus more on surface cleanliness. Surface contamination can become airborne locally and subsequently deposit on critical surfaces or can be transferred during direct and indirect contact. Many years of collecting particle deposition rate data in various industries has demonstrated the presence of macroparticles and visible particles. Next to limiting the generation of particles and removing airborne particles by ventilation, frequent and effective removal of surface particles by cleaning will reduce the likelihood of contamination significantly. Therefore monitoring surface cleanliness of floors, work surfaces, equipment and tools surfaces in the entire cleanroom will demonstrate the quality of cleanroom use and operational procedure, especially the cleaning program. New instrumentation makes this possible. The role of surface contamination in clean controlled environments and monitoring methods is as important as air cleanliness.