Next generation end hall ion source in the optical thin film production process

Abstract

Increased performance of optical coatings with ion assist during electron beam evaporator deposition (IAD) has been well established. Over the years, the gridless Mark II end-Hall ion source has been widely used to produce IAD optical coatings (antireflective coatings, dielectric filters and mirrors) on unheated substrates with low losses, high precision and high environmental stability. We report on the performance of a next generation end- Hall ion source (Mark II⁺) in an optical coating production environment in replacement of the earlier Mark II. The Mark II⁺ was thoroughly re-designed with two major effects: (1) ion generation was enhanced resulting in a significant increase in ion current density of about 20%, and (2) serviceability was greatly improved by incorporating a removable and replaceable anode sub-assembly. The question arises as to how the enhanced output of the Mark II⁺ might affect the properties of optical coatings when replacing a Mark II source in established IAD coating processes. To answer this question, the spatial distribution of optical films parameters of high and low index oxide materials were analyzed when using either ion source. The coating process and results produced with the Mark II⁺ are basically compatible those of the Mark II, with slight changes in the spatial distribution of refractive index and film thickness. Given the higher ion flux output of the improved Mark II⁺, the ion source parameters for minimum absorption can be adjusted to lower, more energy saving levels. Thus the Mark II⁺ is a tool to achieve comparable or marginally better results for optical coatings with higher efficiency.