In this paper, we present the Luminescent's ILT approach that can rapidly solve for the optimal photomask design. We
will discuss the latest development of ILT at Luminescent in the areas of sub-resolution assist feature (SRAF) generation
and optimization to improve process window, and mask rule compliance (MRC). Results collected internally and from
customers demonstrate that ILT is not only an R&D tool, but also a tool quickly maturing for production qualification at
advanced technology nodes. By enforcing the proper constraints while optimizing the masks, ILT can improve process
windows while maintaining mask costs at a reasonable level.
In this paper, we present the Luminescent's ILT approach that can rapidly solve for the optimal photomask design. We
will discuss the latest development of ILT at Luminescent in the areas of sub-resolution assist feature (SRAF)
generation, process-window-based ILT and mask rule compliance (MRC). Results collected internally and from
customers demonstrate that ILT is not only an R&D tool, but also a tool quickly maturing for production qualification at
advanced technology nodes. By enforcing the proper constraints while optimizing the masks, ILT can improve process
windows while maintaining mask costs at a reasonable level.
An implementation of inverse lithography technology is studied with special attention to
illustrating and analyzing the placement, accuracy, and efficacy of subresolution assist elements.
One-dimensional placement through pitch is characterized, and 2D capability is demonstrated for
repeated patterns. Differences between the methods of mask preparation afforded by this system
as compared to current practices are described.
Inverse Lithography Technology (ILT) is a rigorous approach to determine the mask shapes that produce the desired on-wafer
results. In this paper, we briefly describe an image (or pixel))-based implementation of ILT in comparison to OPC
technologies, which are usually edge-based. Such implementation is more computationally scalable and avoids laborious
segmentation script-writing, which becomes more complex for newer generations because of complicated proximity
effects. In this paper, we will give an overview of ILT, present some simulation and wafer examples to demonstrate the
benefit of ILT, clarify common myths about ILT, discuss and show examples to illustrate the impact in every step of the
mask making process. Specifically, studies done with several leading mask shops around the world on mask
manufacturability (including data fracturing, writing strategy and writing time, mask inspection), will be shown.
Many RET technologies, such as rule and model based OPC, the use of sub-resolution assist features, and various PSM methodologies, can be thought of as heuristics employed in an attempt to design improved photomasks. Unfortunately, these traditional approaches are running into severe difficulties at advanced technology nodes (90nm and beyond). We discuss how one can find the optimal photomask by rigorously solving the lithography inverse problem. The design of the optimal mask takes into consideration not only pattern fidelity under nominal conditions, but also the size of the process window and the constraints and costs of mask manufacturing. By formulating the problem in a rigorous mathematical framework, we find highly optimal solutions which do not arise from traditional ad hoc approaches. The resulting masks often provide substantially improved depth-of-focus and exposure latitude, enabling geometries that may be otherwise unattainable.
In this paper we present unintuitive patterns generated by inverse lithography technology. We show examples of contact hole masks designed with ILT that enjoy larger process windows than OPC. We also show variations in ILT-generated masks as the pitch of the contact hole array changes. In another example, we show poly masks designed for better process window to be substantially different from poly masks designed for better fidelity at nominal exposure-defocus (ED) condition. The mask with better fidelity has broken lines in comparison to the original layout. In a third example, we show deep trench mask patterns designed with ILT that, at first glance, bear no resemblance to the original layout, yet provide high fidelity in optical images. These patterns, although complex at first sight, can be generated in substantially simpler form with proper constraints without losing the spirit of ILT masks.
This paper presents ILT masks written by a DUV laser writer and a VSB e-beam writer, and their corresponding wafer print results. ILT mathematically determine the mask features that produce the desired on-wafer results. ILT-generated masks sometimes are non-intuitive, and different than those produced by past approaches; therefore, their manufacturability must be understood. In this study ILT was applied to create binary chrome-on-glass (CoG) masks with feature sizes ranging from 130 nm to 45 nm (at the wafer scale). The masks were written with both DUV laser (AMAT Alta 4300) and electron beam (JEOL JBX-9000) pattern generators. Wafers were then printed on a 193 nm scanner (ASML 1400, NA = 0.75). Mask image quality and wafer image quality (SEM micrographs and focus-exposure CD performance) were collected. In addition, it was also demonstrated that ILT has the capability to tune the mask complexity by constraining fracture figure size and the minimum mask feature/space.
We show how to beat the `fundamental' noise limits in optical lithography using entangled quantum states. In this talk we will give the theoretical background to optical lithography and its quantum formulation. A proof-in-principle experimental demonstration is described.
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