Method and apparatus for exposing multi-level registered patterns

Abstract

An electron-beam array lithography (EBAL) system and method of operation is described. The method comprises deriving fiducial marking signals from a lenslet stitching grid of fiducial elements formed on a standard stitching target for calibrating the boundaries of the fields of view of the respective lens elements of an array of lenslets. The fiducial marking signals are used to stitch together the individual fields of view of the lens elements in the array of lenslets in order to cover a desired area of a workpiece surface to be subsequently exposed to the electron beam, for example, the surface of a semiconductor wafer upon which a plurality of integrated circuit chips are to be formed. In order to register the levels of multi-level patterns written on the same chip, each chip is provided with a registration fiducial grid comprised of fiducial marks at the corners and only at the corners of the chips. Computer mapping of the stitching calibration grid and the chip registration grid to a computer ideal mathematical grid standard is provided. This is achieved by measuring the x-y coordinate position of the fiducial marking elements after precisely locating the positions of their centers using an electron beam or light probe. From these measurements, deviations between the actual position of each marking element and its corresponding location on the computer ideal mathematical grid are determined, and such deviations are used to modify the deflection signals of the electron beam column to correct for deviations from the ideal mathematical grid.