Grade tie bar only (GTO) and graded grade tie bar only (GGTO) aperture masks

摘要

A mask useable to direct an electron beam having a cone side and a grade side. The cone side includes a plurality of troughs that extend partially into the mask but do not extend to the grade side. Apertures are formed in the bottoms of the troughs that extend through to the grade side. The apertures are separated by both actual and virtual tie bars. In a preferred embodiment, some of the virtual tie bars extend from the grade side, through the trough to the cone side. The occurrence of these cone side virtual tie bars varies in concentration across the extent of the mask such that the concentration is heavy in areas where clipping is desired, and light in areas where clipping is not desired. In another preferred embodiment, the size, shape and location of the cone side virtual tie bars vary across the extent of the mask to accommodate for the angle of the electron beam travel and the necessity for localized clipping.