Development of an Adaptive System ID Method for Enabling Advanced E-Beam Sweep Pattern Design

Electron beam (E-beam) vacuum deposition is extensively used for the production of precision optical coatings due to its ability to economically deposit a wide range of source materials. To manufacture superior optical devices, high precision optical coatings are required. One measure of the process capabilities is the accuracy and repeatability of each layer’s optical thickness. A major limitation to controlling optical thickness, especially for large-scale and multi-layer optics, is the variability in the vapor plume geometry due to non-uniform evaporation of the source material. For sublimating materials, like silica, variations in the size and direction of the vapor plume has been attributed to topography on the melt surface, which forms due to uneven source depletion caused by non-uniform heating. In this paper, an experimentally based adaptive system identification method is used to develop custom sweep patterns to control a complicated nonlinear system with both process and equipment nonlinearities.