Implant layer patterning is becoming challenging with node shrink due to decreasing critical dimension (CD) and usage
of non-uniform reflective substrates without bottom anti-reflection coating (BARC).
Conventional OPC models are calibrated on a uniform silicon substrate and the model does not consider any wafer
topography proximity effects from sub-layers. So the existing planar OPC model cannot predict the sub-layer effects
such as reflection and scattering of light from substrate and non-uniform interfaces. This is insufficient for layers without
BARC, e.g., implant layer, as technology node shrinks.
For 45-nm and larger nodes, the wafer topography proximity effects in implant layer have been ignored or compensated
using rule based OPC. When the node reached 40 nm and below, the sub-layer effects cause undesired CD variation and
resist profile change. Hence, it is necessary to model the wafer topography proximity effects accurately and compensate
them by model based OPC. Rigorous models can calculate the wafer topography proximity effects quite accurately if
well calibrated. However, the run time for model calibration and OPC compensation are long by rigorous models and
they are not suitable for full chip applications. In this paper, we demonstrate an accurate and rapid method that considers
wafer topography proximity effects using a kernel based model. We also demonstrate application of this model for full
chip OPC on implant layers.
In situ spectroscopic ellipsometry, deep UV ellipsometry, and imaging ellipsometry were employed to study the
absorption of liquid by photoresist(PR) used for 193 nm immersion lithography. When 140 nm thick PR was soaked in
water over a period of >70 minutes, ~7% increase in thickness was observed. From the analysis of ellipsometric spectra
covering from near infrared to deep UV, we could estimates less than 2 vol. % uptake of water by PR after completion of
soaking. This resulted in very small decrease in refractive index of PR (~0.4%). When imaging ellipsometry was used,
the absorption of water by PR in much shorter periods could be detectible. In imaging ellipsometry, the microscopic
images of (Δ,Ψ ) in small area are obtained thanks to two dimensional multi-channel detection systems such as CCD.
Using imaging ellipsometry, we could observe the interaction of PR with water even upon 1 s of contact. Also, we found
that the water absorption or interaction was not uniform over surface. More studies are required for the implication of
this observation. Obviously, imaging ellipsometry is a good technique to inspect water mark in immersion lithography.
We also repeated similar experiments for high reflective index liquid (JSR HIL-001) but to find negligible change by
imaging ellipsometry.
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