Production of silicon mirror plates

Abstract

Silicon pore optics are currently under development for missions such as the International X-ray Observatory (IXO) as an alternative to the glass or nickel shell mirrors that were used in previous generation X-ray telescopes. The unprecedented effective area requirement of the IXO requires a modular optics design suitable for mass production. In this paper we discuss the current state-of-the-art in plate manufacturing technology. We provide examples of process innovations that have directly impacted the cost per mirror plate and have reduced the manufacturing cost of a mirror module. We show how a switch from silicon to silica as the reflective surface results in a simplified process flow without a corresponding change in the optical performance. We demonstrate how standard photolithographic techniques, applied in the semiconductor industry, can be used to pattern a reflective layer. The 5 arc-second angular resolution requirement of the IXO has stimulated a theoretical analysis of engineering tolerances in relation to angular resolution. We prove that improved control of the wedge angle by means of etch rate monitoring results in improved angular resolution. The results of this investigation will be used as the basis for future development in design for mass production.