In this paper we discuss a laser focus drilling technique which has recently been developed for advanced
immersion lithography scanners to increase the depth of focus and therefore reduce process variability of contact-hole
patterns. Focus drilling is enabled by operating the lithography light-source at an increased spectral bandwidth, and has
been made possible by new actuators, metrology and control in advanced dual-chamber light-sources. We report wafer
experimental and simulation results, which demonstrate a process window enhancement for targeted device patterns.
The depth of focus can be increased by 50% or more in certain cases with only a modest reduction in exposure latitude,
or contrast, at best focus. Given this tradeoff, the optimum laser focus drilling setting needs to be carefully selected to
achieve the target depth of focus gain at an acceptable contrast, mask error factor and optical proximity behavior over
the range of critical patterning geometries. In this paper, we also discuss metrology and control requirements for the
light-source spectrum in focus drilling mode required for stable imaging and report initial trend monitoring results over
several weeks on a production exposure tool. We additionally simulate the effects of higher-order chromatic aberration
and show that cross-field and pattern-dependent image placement and critical dimension variation are minimally
impacted for a range of focus drilling laser spectra. Finally, we demonstrate the practical process window benefits and
tradeoffs required to select the target focus drilling laser bandwidth set-point and increase effectiveness of the sourcemask
solution for contact patterning.