Inventors:
Chin-Chin Chen - Scotch Plains NJ
Martin Feldman - Baton Rouge LA
Herbert A. Waggener - Pottersville NJ
Assignee:
AT&T Bell Laboratories - Murray Hill NJ
International Classification:
H01J 3720
Abstract:
Conventional alignment procedures in electron beam (e-beam) direct write systems typically use an e-beam exposure tool as a scanning electron microscope (SEM) to imagine wafer alignment marks. However, electrical charging of the wafer surface by the electron beam can typically result in image distortions which generally can lead to alignment inaccuracies. The inventive method and apparatus advantageously overcome the alignment inaccuracies associated with the charging effects, by optically aligning the wafer to a reference axis of the electron beam. In a preferred embodiment of this invention, light is focused on a diffraction grating on the wafer, used as an alignment mark, and the diffracted light is spatially filtered and detected. Spatially filtering the diffracted light, eliminating the 0th order of the diffracted light, provides increased depth of focus. Also in this particular embodiment, travel of the wafer stage for optical alignment remains below the electron lens column by mounting an optical head (used for directing light onto the wafer, for spatially filtering the diffracted light, and for directing the spatially filtered light to the detection means) to the pole tip of the electron lens column.