Theoretical and Experimental Study of Particle Distribution from Magnetron Sputtering with Masks for Accurate Thickness Profile Control

Differential deposition and profile coating are two common deterministic fabrication methods for figure correction of high-precision mirrors. The generation of the desired particle distribution on the substrate as the growing function is an important prerequisite, especially for two-dimensional correction. A model of particle distribution considering the etched ring shape, mask structure, and mask distance between the target and substrate is established. The model is verified by deposition experiments using a series of circular holes with different hole sizes and distances of the mask from the substrate. According to the model, a smallest deposition beam width of 2.79 mm can be obtained using a hole with a 3 mm diameter. The shape of the particle distribution gradually changes from convex to concave as the mask moves away from the substrate for different holes. A two-dimensional figure correction of a flat mirror was demonstrated using a hole with a 6 mm diameter. The peak-to-valley (PV) value is reduced from 74.23 nm to 10.09 nm, and the root mean square (RMS) value is reduced from 18.38 nm to 1.36 nm within a 130 mm × 20 mm area. The model could provide useful guidance for high-precision two-dimensional figure correction applications.