Sheldon Wayman, INFICON, East Syracuse, NY
Traditionally, optical coaters require costly optical monitors to support high precision physical vapor deposition processes. However, optical coating tool manufacturers do not always provide optical monitors on all of their tools. In doing so, the tool users have to test a substrate from a large batch to verify film thickness. If there was an incorrect layer thickness, the entire batch would be scrapped or reworked, wasting time and money. Thin film deposition monitors with quartz crystal microbalance technology have been used for decades to monitor physical vapor deposition, but today’s precision optical coatings demand higher thickness accuracy. The Z-match equation used in most deposition monitors to calculate thickness only takes into account the Z-ratio for the film currently being deposited. In reality, there could be multiple materials on the same crystal with different Z-ratios. This results in a compounding error in the thickness reading as the multi-layer stack grows. For optical processes where there could be hundreds of layers on the same crystal, the thickness error can be significant. In order to satisfy this need, INFICON has patented a new revolutionary technique for determining multi-layer thin film deposition on a piezoelectric crystal and have integrated it into a new deposition controller, Zevision^® IMC300.