Cost-driven mask strategies considering parametric yield, defectivity, and production volume

We provide new yield-aware mask strategies to mitigate emerging variability and defectivity challenges. To address variability, we analyze critical dimension variability with respect to reticle size and its impact on parametric yield. With a cost model that incorporates mask, wafer, and processing cost, considering throughput, yield, and manufacturing volume, we assess various reticle strategies (e.g., single-layer reticle, multiple-layer reticle, and small and large size) considering field-size– dependent parametric yield. To address defectivity, we compare para-metric yield due to extreme ultraviolet mask blank defects for various reticle strategies in conjunction with reticle floorplan optimizations such as shifting of the mask pattern within a mask blank to avoid defects being superposed by performance-critical patterns of a design. C 1 Introduction Photomask cost is a highly critical issue in manufacturing. Semiconductor manufacturers have long sought cost-effective photomask strategies. Multiple copies of a single layer of one project (IC) are patterned in a full-size mask blank to obtain a single-layer reticle (SLR), used in most high-volume products. In a multiproject reticle, the same layer of several different projects (ICs) is implemented on a single reticle; this allows sharing of mask costs between individual project owners. Beyond a " single-layer-per-reticle " strategy, multilayer (ML) and multiproduct strategies are also implemented on a single reticle, 1 and an algorithm to enable the layer placement and quality-check procedure according to a parametrized cost function is proposed. 2 In addition, ret-icle size and number of dies per reticle are other knobs that can be tweaked by manufacturers or designers. IC manufacturing traditionally uses the maximum possible reticle size. This is commonly believed to maximize lithography tool throughput and minimize manufacturing cost. However, as reticle size increases, the mask cost (write, inspection, defect disposition, repair, etc.) also increases. For high-volume products, mask cost can be disregarded, but for low-volume products—in light of shuttle-based prototyping, design revisions and respins, market competition, and other factors—mask cost has a significant impact on overall cost per die. Also, larger reticles can result in larger critical dimension (CD) variation in silicon, leading to parametric yield loss that potentially increases manufacturing cost. Hence, a new cost model is required to comprehend reticle size-dependent cost changes. Besides the issue of variability, defectivity [notably, mask blank defects in extreme ultraviolet lithography (EUVL)] looms as a critical issue for mask generation and product yield. EUVL uses reflective masks instead of the traditional optical transmission masks. EUVL mask blanks …