Patent attributes
An improved reticle frame structure surrounds the perimeter of a reticle substrate and contacts it at the edge with precision guidance surfaces as the reticle is lowered onto the device. In an embodiment, the reticle contacts conical sections that correct its position and orientation along the plane of its mask surface, and spherical surfaces to position the reticle at its standardized datum reference areas. Near the intersection of the X and Y reference planes, a minimal area of the reticle face comes to rest on a spherical mounting surface as far away from the reticle mask as possible. This surface completes a tripod of vertical support in conjunction with the cones, which maintain contact with the reticle edges only. Secondary and tertiary spherical support surfaces can be provided for vertical support of the other two lateral corners of the reticle face to mitigate reticle tilt while it is being lowered onto the tripod contact points.
