Direct Bonding of Multiple Curved, Wedged and Structured Silicon Wafers as X-Ray Mirrors

Abstract

In this paper we present the technological basis for assembling multiple structured silicon plates using direct wafer bonding. Each individual plate is prebend and bonded on the growing stack, up to 35 plates, that forms a stiff self supporting structure. Throughout the production of the structured plates and the assembly of the curved monolithic silicon structures our focus lies on maintaining pristinely clean and ultra flat surfaces as this is a prerequisite for direct wafer bonding. The application relies on void free bonds imposing stringent requirements for cleanliness that we address with a carefull cleaning process and an automated stacking process in a particle free environment. Several metrology tools have been developed that operate in line to ensure plate to plate alignment, cleanliness and figure accuracy. The process is adaptable to work with plates of various dimensions, have metal coatings, with an intregral wedge and bend radii.