Metrics to Assess Fracture Quality for Variable Shaped Beam Lithography

CD control requirements for advanced node masks are in the low single digit nanometer range. CD control for Variable Shaped Beam (VSB) lithography that is used to manufacture these masks is dependent on the post-fracture figure layout. Shot linearity, shot size repeatability, and shot placement repeatability can affect CD control differently based on the figure layout. The potential CD error contribution from poorly optimized fracture strategies thus can be a significant contributor to the total CD error. In this paper we present a set of fracture quality metrics based on the impact on mask CD control and methods using EDA software to grade fracture strategies based on these fracture quality metrics. We also discuss applications of this metric for fracture tool design and the implementation of different fracture strategies into mask manufacturing including examinations of the predictability of fracturing results. Finally, we will discuss the usage of existing information about the design (such as design intent) in conjunction with the proposed quality metrics to judge different fracture strategies.