Proceedings Article | 12 November 2024
KEYWORDS: Photomasks, Critical dimension metrology, Semiconducting wafers, Scanning electron microscopy, Metrology, Optical proximity correction, Scanners, Line edge roughness, Contour extraction, Lithography
In the rapidly changing photomask industry, the shift from conventional Manhattan masks to curvilinear masks marks a pivotal development. This transformation is largely driven by advancements in multi-beam mask writer technologies, which bring notable improvements to both mask manufacturing and wafer production. The integration of GPU-accelerated full-chip, curvilinear inverse lithography technology (ILT), along with the move from edge-segmented optical process correction (OPC) to curvilinear OPC, and the adoption of the MULTIGON format, has accelerated the use of curvilinear masks in various layers of wafer fabrication. The advantages of curvilinear masks extend far beyond the surface. In this paper, we will explore the factors pushing the industry toward curvilinear mask designs, analyzing their benefits in terms of process windows, mask rules, mask error enhancement factor (MEEF), and mask variability. The mask production process—encompassing mask writing, CD SEM, inspection, aerial image review, and repair—operates within the pixel or image domain, making curvilinear masks a natural fit. However, challenges remain, particularly in mask metrology, where traditional mask critical dimension (CD) standards, a shared specification between mask and wafer fabrication, are not well-defined for curvilinear patterns. This paper proposes a new CD specification designed for curvilinear masks and demonstrates that curvilinear masks offer less mask variability compared to traditional Manhattan masks.
