Projection lithography on curved substrates

Abstract

A microlithography system, capable of performing high resolution imaging on large-area curved surfaces, based on projection lithography. The system utilizes a high-resolution lens to image a curved mask directly onto a curved substrate. The system uses a curved mask which is identical in shape to the curved substrate, in order to achieve a constant track length for conjugate object and image points, thereby maintaining focus over the full area of curved substrates having height variations that greatly exceed the depth-of-focus of the imaging lens. Magnification errors are controlled by continuous adjustments of the z-position of the projection lens during scanning, with the adjustments depending upon the topography of the curved mask and substrate. By performing the lithography using a step-and-scan seamless-patterning microlithography system, it is possible to pattern over large areas, greater than the field size of the lens. When the mask and substrate are mounted on a common scanning platform, the system operates with an inverted mask. The system also has provisions for making the appropriate curved projection masks, using a planar contact printing technique to pattern high-resolution features on a flexible film which is stretched over a curved mask blank and secured by a frame, with the option of using the system itself to replicate the curved mask onto an indeterminate number of curved fused-silica mask blanks, by projection printing.