Focus on Design for Manufacturing (DFM) in semiconductor device design has increased as semiconductor manufacturing technology has become more complex. Many of the techniques developed to improve wafer yield and manufacturability can also be applied to the photomask manufacturing process. For example, for the last several technology nodes, semiconductor manufacturers have known that pattern density and uniformity can have significant impact on wafer processes such as etching and chemical mechanical polishing. Photomask manufacturing can also be impacted by pattern density and its uniformity.
Some of these DFM practices can be beneficial if applied directly to photomask manufacturing while some of them can make photomask manufacturing significantly more difficult. Optical proximity correction (OPC), which involves convoluting the design shape to account for optical, physical and chemical processes, is increasingly required to support advanced lithography; some of the operational parameters of the OPC, such as the fragmentation run length, challenge mask resolution capability, image fidelity, defect inspection, mask repair, and dimensional metrology of photomasks. Sub-resolution assist features (SRAFs), which are utilized to create robust wafer lithography are often the most challenging mask features to create. The size and placement of SRAFs on photomasks are factors that impact photomask manufacturability in terms of image resolution, inspection, and dispositioning criteria. As OPC and other DFM processes become more widely deployed in an effort to make robust wafer manufacturing processes, the photomask maker needs to be involved to evaluate the implications to photomask manufacturing and assist in optimizing these DFM procedures to maximally benefit both the photomask and semiconductor manufacturing processes.