Breakthrough curvilinear ILT enabled by multi-beam mask writing

Abstract

Background: Multi-beam mask writers have been one of the most significant additions to the semiconductor manufacturing equipment arsenal in over a decade. The ability of multi-beam mask writers to write masks with a constant write time regardless of mask shapes or complexity has made them an eagerly anticipated advancement to help write curvilinear mask shapes for both today’s advanced 193i nodes and for extreme ultra-violet (EUV) lithography in the future. Perhaps the most obvious application for these new pixel-based mask writers is the production of curvilinear inverse lithography technology (ILT) masks. ILT has been seen as a promising solution to many of the challenges of advanced-node lithography, whether optical or EUV. However, the runtimes and mask writing times associated with this computational technique have limited its practical application. Until recently, it had been used for critical “hotspots” on chips, but had not been used for entire chips. Aim: The introduction of multi-beam mask writing, along with the advent of graphics processing unit (GPU)-accelerated computing for mask and wafer, have enabled the introduction of a new approach to full-chip ILT using these new technologies. The goal was to produce full-chip, curvilinear ILT within the traditional turnaround times of mask shops. Approach: The solution to the runtime problem for ILT has been particularly vexing, as the traditional approach to runtime improvement—partitioning and stitching—has failed to produce satisfactory results, either in terms of runtime or in terms of quality. In 2019, D2S introduced an entirely new, stitchless approach, systematically designed for ILT, multi-beam mask writers, and GPU acceleration, that makes full-chip ILT a practical reality in production for the first time. Results: We present this new ILT approach, first introduced using a multi-beam mask writer to create the complex curvilinear mask shapes. We also review findings that targeting curvilinear mask shapes creates masks that are more resilient to manufacturing variation. Finally, we review the results of this new, stitchless full-chip curvilinear ILT as applied to memory chip making. We show mask making and wafer print results, including pattern fidelity and process window, to demonstrate the actual benefit of such technologies—a doubling in the wafer process window—for semiconductor manufacturing.