Ensemble average laser light scattering (EALLS)-an effective alternative to particle counting for monitoring turbidity in ultrapure water [for semiconductor rinsing]

A high sensitivity laser light scattering (LLS) instrument capable of measuring nephelometric turbidity in ultrapure water (UPW) is described. Readings from various stages of the purification process are compared to those from a sophisticated particle counter. Simplicity, ease of use, and relatively low cost, provide EALLS with very significant advantages over particle counters and open the possibility of utilizing several instruments in each UPW loop. Data from such a bank of instruments has the potential for identifying and isolating sources of particulate contamination, thereby enabling significant savings in filter replacement costs as well as down time.