Effects of laser bandwidth on tool to tool CD matching
2008
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.
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