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.

Silicon pore optics development for ATHENA

“…The SPO development in the past focused on demonstrating in a holistic approach the entire production chain, from wafer up to optical bench level, at one focal length and radius, on which we reported extensively in [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. This included a complete set of environmental tests on mirror module level, resulting in a technology readiness level (TRL) of ~5 at the current stage.…”

X-Ray Pore Optics Technologies and Their Application in Space Telescopes

“…High-Z metallic coatings such as platinum, tungsten, gold, or iridium are typically used to increase the reflectivity [24]. Patterning of the coated surface by metallic masks [25] or lithographic processes [21] is necessary to ensure bondability of the silicon mirror plates during the stacking process.…”

“…New processes and associated tools are developed only where required. The silicon pore optics production can be grouped as follows: The production of silicon mirror plates [21] starts with dicing SEMI standard 100 300 mm silicon wafers, which are double sided polished and 0.775 mm thick, into square plates. The diced plates are then coated with a protective layer to prevent damage to the superpolished surface during the subsequent production steps (see Figure 6).…”

Performance of multilayer coated silicon pore optics

“…The samples used during the reflectometry campaign were ribbed, wedged Si plates 5 , as used to construct X-ray Optical Units (XOU) within the SPO development program 6 . Several samples were uncoated with the reflective surface being the wedged SiO 2 layer that results from the plate production process.…”