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

In this paper, we present the technological basis for the production of structured silicon X-ray mirrors using direct wafer bonding. We dice 12" silicon wafers into rectangular plates, which are then structured to have a thin membrane and several ribs. As a next step we wedge the plates on both sides. Using in-house developed stacking robots, we then elastically deform the plates into conical shapes and bond the plates into a stack, which finally consists of several tens of such plates in a stiff self-supporting structure. Throughout the production of the structured plates and their assembly into stacks, we focus on maintaining pristinely clean surfaces as this is a prerequisite for direct wafer bonding. Several metrology tools have been developed, operating in-line, to ensure precise plate to plate alignment, high cleanliness and an accurate figure. The process is adaptable to work with plates of various dimensions, with metal coatings and with different bend radii.