Exposure of a halftone mask by conventional and off-axis illumination

摘要

Abstract: The halftone mask, also called the attenuated phase shifting mask, is assumed to be a preferred candidate among many types of masks since it can be applied to all feature types and it is relatively easy to fabricate. We studied the process latitude of the halftone mask with normal illumination and the combination of the halftone mask with off-axis illumination by computer simulation, the fabrication of the halftone mask, and exposure with an i-line stepper. The greatest improvement of process latitude can be achieved for contact hole pattern when the halftone mask is used. The isolated space and the isolated line pattern show minimal gain by the halftone mask or the off-axis illumination, but the line/space pattern can be made by the off-axis illumination. The process latitude can be enlarged by the proper mask bias and the aspect ratio. !2