Inverse lithography is most commonly utilized to guide optimizing RET (Resolution Enhancement Technology) solution such as SRAF (Sub-resolution Assist Feature) placement and OPC (Optical Proximity Correction) edge dissection and fragmentation. Inverse lithography recipe often features an array of user-controlled parameters, which allow refined tuning of inverse solution maximizing for various common objectives such as common DOF, NILS, and pvband (process variability band). In practice, some test case shows that the inverse lithography engine can be perturbed to produce novel solution maximizing other unconventional objectives such as OPC solution’s mask-friendliness, OPC convergence at extreme dense-to-iso transition, and multi-structure common focus range. However, the parameter tuning process can be time-consuming and requires expert knowledge of the tool. Also, parameters correlation to those objectives is often highly non-linear. All these reasons make inverse lithography recipe parameter tuning for unconventional objective a non-trivial task. Genetic Algorithm (GA) has been demonstrated to be effective at solving non-trivial optimization tasks such as SRAF rule optimization , OPC recipe optimization [2,3] and source mask optimization [4-6], and. Here we propose to use modified GA based engine for inverse lithography recipe optimization. We will show experimental results and discuss the benefits and challenges. We will demonstrate with three real test cases that this flow has a reasonable TAT and improved inverse lithography solutions.
Inverse Lithography Technology (ILT) is gaining acceptance as part of a comprehensive OPC solution especially as a
repair technique to locally improve process window where conventional OPC does not have enough degrees of freedom
to produce acceptable results.  Since ILT is significantly more computationally intensive than conventional OPC, a
localized application of ILT does not significantly increase OPC cycle time. As ILT methods mature and become more
efficient, combined with the availability of huge compute clusters for post tape out data processing, the possibility of
full-field ILT OPC could soon become reality. Full-field ILT OPC may provide improved process window and greater
layout flexibility as long as multi-patterning methods with 193 nm exposure wavelength remain the primary lithography
strategy for advanced technology nodes.
Due to limitations of photomask lithography tools that prevent efficient exposure of non-Manhattan shapes, ILT OPC
output is typically post-processed to conform to mask MRC rules, rendering the raw all-angle features to a
Manhattanized equivalent. Previous comparisons of raw vs Manhattan ILT OPC at earlier nodes have shown that a
Manhattanized output can be made to print on wafer with equivalent process window while conforming to mask
manufacturing rules.[2,3,4] In this paper we use wafer-level lithography simulation to compare raw vs Manhattanized
ILT output based on current advanced nodes and MRC rules. We expand this study to include a mask model to ensure
that mask corner rounding effects are considered.