Ion-air gun cleaning of substrates prior to thin film deposition

Abstract

It is a common practice to give cleaned mirror substrates, and other optical surfaces, a final "dusting" with high pressure N2, or air, just prior to deposition of thin reflective coatings. The object of this procedure is to remove any particles that may have settled on the substrate since chemical cleaning and washing. Some types of "guns" used for blowing dust off a surface work well. However, other types, such as those containing a radioactive polonium source, can charge the substrate so that it attracts even more dust. In this report, the connection between electrostatic charge on a substrate and its dust "gettering" (dust collecting) ability is established. Also, test results are presented for the charging and discharging capabilities of various types, and manufacturers, of dusting guns.