Impact of RET on physical layouts

In this paper, we briefly describe the lithography developments known as RET (Resolution Enhancement Technologies), which include off-axis illumination in litho tools, Optical and Process Correction (OPC), and phase shifting masks (PSM). All of these techniques are adopted to allow ever smaller features to be reliably manufactured, and are being generally adopted in all manufacturing below 0.25 microns. However, their adoption also places certain restrictions on layouts. We explore these restrictions, and then provide suggestions for layout practices that will facilitate the use of these technologies, especially the generation of a clean target layout for use as input layers for photomask preparation, and the use of verification tools that use process simulation.

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