Effects of laser bandwidth on tool to tool CD matching

According to the ITRS roadmap, low k1 imaging requires extremely tight control of Critical Dimension (CD). Maintaining the same performance from one exposure to another for new imaging requirements has become increasingly important, particularly for matching dry and wet systems. Tool to tool CD matching depends on many factors, for example, lens aberrations, partial coherence, laser spectral bandwidth and short range flare. We have performed a detailed study of laser bandwidth effects on tool CD matching for typical 65nm node structures exposed on immersion ArF scanners. A high accuracy on-board spectrometer was used to characterize the lithography Laser bandwidth, allowing measurements of both the FWHM and E95 parameters of the laser spectrum. Spectral bandwidth was adjusted over a larger range than normally experienced during wafer exposures using Cymer's Tunable Advanced Bandwidth Stabilization device (T-ABS) to provide controlled changes in bandwidth while maintaining all other laser performance parameters within specification. Measurements of both Lines and Contact Holes on 65nm node structures through all pitches were made and correlated with bandwidth to determine the sensitivity of IDB and C/H to bandwidth variation. We demonstrated that bandwidth can be adjusted for CD matching on different tool using the T-ABS function.