Curvilinear masks overview: manufacturable mask shapes are more reliably manufacturable

BackgroundCurvilinear masks are coming. With multibeam mask writers in production, leading-edge mask shops now are able to write curvilinear masks in the same mask write times as any Manhattan masks. As Samsung and Luminescent showed long ago, curvilinear mask shapes produce the best wafer process windows.AimThe goal of our study is to provide an overview of the current state of the development of curvilinear masks.ApproachWe cover the technical background and motivation for curvilinear masks, and the practical application of curvilinear inverse lithography technology (ILT) masks written by both multibeam and variable-shaped beam mask writers. ILT is a form of optical proximity correction, wherein software computes target mask shapes to optimize wafer quality, both in the nominal lithographic projection conditions being as close to the target wafer shapes as possible, and to minimize the amount of variation in the shape or size due to mask and wafer manufacturing variation. We review the current state of readiness of the mask-making infrastructure for curvilinear masks, including mask rule checking, metrology, inspection, and repair. We also review studies that show that curvilinear masks bias more faithfully to the wafer, and that curvilinear masks are more reliably manufacturable.ResultsCurvilinear masks have been shown to be more manufacturable.ConclusionsManufacturable mask shapes are more reliably manufactured. Curvilinear masks improve both mask and wafer variability. We suggest that allowing certain curvilinear targets can make designs more manufacturable and more resilient to manufacturing variation on wafers, while decreasing power, increasing clock speeds, and making designs smaller.