Regardless of the accuracy of the monitor, it can only control the film thickness at a single point in the vacuum chamber, which is generally the middle position of the workpiece holder. If the film thickness of the vacuum plating apparatus at this position is not absolutely uniform, the substrate away from the center position cannot obtain a uniform thickness. Although the shield can eliminate the long-term non-uniformity, some film thickness changes are caused by the instability of the evaporation source or the different expression of the film, so it is almost impossible to eliminate, but the structure of the vacuum chamber The proper choice of source and evaporation source can minimize these effects.
In the past few years, more and more users have asked coating system manufacturers to provide high-performance small-size, simple optical coating systems. At the same time, users' performance requirements have not been reduced, but have been improved, especially in the film. Density and minimization of spectral changes after water absorption.
Nowadays, the average size specification of the system has been reduced, and the production of optical coating using small-sized equipment has also become a purely technical problem. Therefore, the key to choosing a modern optical coating system depends on careful consideration of the expected properties of the coated product, the size and physical properties of the substrate, and all the technical factors necessary to ensure a highly consistent process.