Chapter 13 - Cleaning

Abstract

Cleaning is the reduction of surface contamination to an acceptable level so that desirable processing and film/coating properties can be obtained. It can be divided into external cleaning (ex situ cleaning), which is performed exterior to the deposition system and where the external processing environment is important, and in situ cleaning, which is performed in the deposition system, where system-related and process-related contamination are important. External cleaning includes gross cleaning to remove large amounts of contaminants, often by removing some of the substrate surface (etching). Specific cleaning is directed toward removing a specific contaminant such as particulates, or hydrocarbons. If possible, the substrates should be contained in holding fixtures that remove the necessity and potential variability of manual handling of critical surfaces. Fluids are often used in cleaning processes. Fluid baths should be continuously filtered and monitored so as to replace or replenish the active ingredients as they are used or become contaminated. The particle content of the fluid can be continually monitored. In cases of removing heavy contamination, the surface of the fluid can be “skimmed” as contaminants such as oils rise to the surface. It can be done by using “overflow” tanks or skimming the surface with absorbent toweling.