In this paper, we report our recent investigations into the effect of resist processing on defect printability.
Simulations are conducted using both aerial image threshold and resist models in an attempt to determine the effect of
the resist process. There is good agreement between the resist model simulation and the printing data obtained using the
EUV micro exposure tool (MET) and a programmed defect mask. The CD error, or defect printability, introduced by
edge defects on 70nm semi-iso lines predicted by the aerial image threshold model is larger than that by both the resist
model and the actual printing results. However, this favorable difference vanishes for edge defects on 30nm lines. Mask
error enhancement factor (MEEF) is used to understand the discrepancy between the aerial image threshold model and
the resist model. Image quality measured by normalized image log slope (NILS) and resist process window characterized
by exposure latitude are closely related to image MEEF and resist MEEF respectively, and ultimately determine defect
printability for a given patterning and resist processing. Defect printability increases exponentially as the feature size
shrinks. This nonlinear behavior presents a challenge for defining defect specifications for EUV lithography based on
extrapolations from currently available printing data.
EUV lithography has the ability to support 22 nm logic manufacturing and beyond. Similar to the DUV lithographic
systems, partial coherence on EUV lithographic systems can have a big impact on process latitude for critical layers.
Thus, it is important to understand the effect of partial coherence on EUV imaging systems. In this paper, process
windows with various illumination settings are investigated. The experiments are conducted using the MET station at
the Advance Light Source (ALS). In addition to the annular and dipole illuminations which reported in our last
paper1, C-quad and Quad illuminations are used to explore the impact of the partial coherence on the process window.
Even though the MET system has resolutions below 30nm dense lines, the exposures are targeted for 60nm, 50nm, and
45nm dense features due to the resist limitation. The experimental results are compared with simulation results using
Intel's lithography modeling tool, I-Photo. Resist and aerial image threshold models are used for the comparison
study. The experimental results correlate well with the resist based simulation results, but some discrepancies are
observed for the aerial image threshold cases. We believe the discrepancies are due to the resist limitations. We found
that the dipole shows the largest Depth of Focus for dense lines and spaces.
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