Patent ID: 7239376

Claim:
A projection system for creating images in a photoresist layer on a semiconductor wafer positioned beneath the projection system from a mask supported in the system on a mask support comprising: first and second opposing and separated stages defining an open central region there between for supporting first and second opposing edge regions of a glass mask; each of said stages carrying a respective rigid chucking bar having a bottom surface, an inner side surface, an outer side surface and an upper surface; the first one of said bars supporting and holding on its upper surface the first edge region of a glass mask; the second one of said bars supporting and holding on its upper surface the opposing second edge region of said mask, said second edge region being opposite to and separated. from said first edge region by a central region of said mask; said central portion of the mask spanning the open central region between said stages and being subject to the force of gravity, each of said bars having an inner side closest to the center of the mask and an outer side closest to the edge of the mask, said inner side being higher than said outer side to create a slanted upper surface on each of said bars so that the direction of the slant on the upper surface of one bar is opposition to the slant on upper surface of the other bar; and the upper surface of each of said bars carrying means for holding a respective edge of said mask placed thereon, for applying a force for bending the respective edge held thereon away from the center of the mask sufficient to substantially reduce or eliminate any gravitational induced sag in the unsupported center of the mask.