<title>Subhalf-micron mask defect detectability and printability at 1X reticle magnification</title>

Abstract

There have been several studies on the printability of subhalf-micron defects using reduction steppers. These studies typically involved 1X reticles with defect sizes greater than 0.3 micrometers . Because submicron 1X projection systems are being incorporated into numerous fabrication lines, there is a clear need to determine the impact of subhalf-micron defects using these systems. This paper examines defect detection and measurement capability on 1X reticles and the printability of those defects on production submicron 1X steppers. This analysis will enhance the understanding of the relationship between defect size and 1X projection optics and allows for determination of optimal defect specifications. A test reticle representative of a 64 Mb DRAM metal layer was manufactured with a programmed series of attached and isolated defects ranging from 0.15 to 0.5 micrometers . Both clear and opaque polarity defects were designed. The defects were identified and measured on two different reticle autoinspection systems. The performance of the two systems was compared to the reticle database to evaluate capture rates and efficiency. Actual reticle defect sizes were measured using low voltage SEM metrology. Defect printability was determined using a 1X i-line projection stepper with focus and exposure optimized for nominal critical dimensions (CD). The defects that printed on the wafer were measured and compared to the defects measured on the reticle. The effects of varying wafer exposure dose and focus within a 10 percent CD process window on defect printability were also evaluated. The results of the mask inspection comparison and the reticle versus wafer defect maps are compared.