Detectability and printability of programmed defects in the contact layer for 256-Mb-DRAM grade reticle

As field size is increased and design rule goes down to O.l8pm, more tight control of defects on the reticle is required than before. T his requirement is m ore critical on contact patterns than line and space(L/S) patterns in the case of the same size of defect. In this paper, test reticles which have background normal contact patterns and background OPC(optical Proximity Correction) contact patterns, respectively, have been investigated for 256M DRAM level. We included a wide variety of programmed defects in background patterns. The geometry of the background contact patterns on the reticle has been designed for 0.3 1 pm m ore or less when printed on a wafer with a 4X reduction stepper. The programmed defects are used for the sensitivity evalution of a defect inspection system, i.e, detectability. Also printability of these defects on the wafer is performed by using a 4X reduction DUV(248nm) stepper to deterrn me not only the reticle defect specification but also the detectability required for the defect inspection system. Test results are as follows: First, the defect specifications required for 256M DRAM can be determined. Second, OPC contact patterns have better wafer results than normal contact patterns in view of depth of focus(DOF) and defect printability. Third, inspection technique for OPC patterns remains the task to be solved. Keywords : detectability, printability, programmed defect, OPC, DOF, serif, simulation