(General References [342, 343])

Surface preparation is an essential step in all vacuum coating processing and is critical to the nucleation and interface formation steps of the coating process. These "prepared" surfaces, in turn, determine the adhesion of the coating, the surface coverage, and in many cases the structure and the properties of the resulting deposit. Surface preparation includes not only cleaning but in some cases modification of the chemical, morphological, or mechanical properties of the surface or the near-surface region [344]. These changes can affect the nucleation of the depositing atoms on the surface and the growth of the coating. Cleaning comprises both that done external to the deposition chamber (external cleaning) and that done in the deposition chamber (in situ cleaning).

External cleaning for vacuum coating is generally similar to that used in other manufacturing processes of the type called "critical cleaning [342]" or "precision cleaning." Precision cleaning is sometimes defined as "cleaning a surface that already looks clean." A few external cleaning techniques have been developed specifically for vacuum coating or were initially used for vacuum coating. These include ultraviolet-ozone (UV/O ₃) oxidative cleaning and sputter (physical) cleaning.

UV/O ₃ cleaning was initially developed by Sowell, Cuthrell, Bland, and Mattox in 1974 to clean very fragile quartz-crystal structures that were contaminated with Carnauba wax during grinding and polishing [345]. The cleaning technique was found to be very effective for removing contaminants that formed volatile oxidation products, such as hydrocarbons, from oxidation-resistant surfaces, such as glass, or...