Reticle defect printability for Sub-0.3k1 Chromeless Phase Lithography (CPL) technology

Chromeless Phase Lithography (CPL) with a high NA exposure tool is shown to be an attractive technology solution for the 65nm node [1]. Under strong image enhancement conditions, the traditional definition of minimum defect printability specifications is no longer adequate. This paper investigates defect printability issues for CPL technology. Based on optimized scattering bar OPC treatments through pitch, a set of defect printability quantification (DPQ) patterns was designed. In the DPQ design, a number of defect types have been programmed with progressively increasing defect size from 0.05(lambda/NA) to 0.3(lambda/NA). Each defect type and size on the actual CPL reticle were then fully characterized using an advanced CD SEM metrology system, the KLA8450R(TM) with both wafer and reticle capabilities. This is a very critical step for quantifying defect printability, since in order to accurately assess the printability, the defect dimension must be well correlated to the original DPQ design on the reticle. The DPQ reticle was then printed using a high numerical aperture (NA) scanner (ASML/850(TM)) so that it is possible to characterize the defect printability for each of the programmed defects and the impact on CD through pitch. Minimum printable defect (MPD), maximum non-printable defect (MNPD), and critical dimension (CD) variation percentage were used as metrics to characterize the critical defect size and the sensitivity of each defect type. The purpose of this study is to understand the tolerance of the CLM technology to printable defects and establish a realistic and sensible defect specification.