Manufacturing challenges for curvilinear masks

To achieve the ultimate resolution and process control from an optical (193i 1.35NA) scanner system, it is desirable to be able to exploit both source and mask degrees of freedom to create the imaging conditions for any given set of patterns that comprise a photomask. For the source it has been possible to create an illumination system that allows for almost no restrictions in the location and intensity of source points in the illumination plane [1]. For the mask, it has been harder to approach the ideal continuous phase and transmission mask that theoretically would have the best imaging performance. Mask blanks and processing requirements have limited us to binary (1 and 0 amplitude, or 1 and -0.25 amplitude (6% attenuated PSM)) or Alternating PSM (1, 0 and -1 amplitude) solutions. Furthermore, mask writing (and OPC algorithms) have limited us to Manhattan layouts for full chip logic solutions. Recent developments in the areas of mask design and newly developed Multi-Beam Mask Writers (MBMW) have removed the mask limitation to Manhattan geometries [2]. In this paper we consider some of the manufacturing challenges for these curvilinear masks.