On Step-and-Scan Trajectories used in Wafer Scanners in Semiconductor Manufacturing

Adopting the ideal reliable machine model, the throughput of a lithography machine can be given as the reciprocal of the operation time. This time can be defined at the die level where the actual exposure process takes place as the time unit per die. A closer look at the motion profiles, namely step-and-scan trajectories, suggests that a multi-disciplinary design optimization should be involved when such profiles are selected or designed. Being the reference motion used, the step-and-scan trajectories not only affect the machine performance, but also affect its throughput and to an extent the die yield as well. Structural vibration, and thermal loading at the actuators due to friction and repetitive motion may build up because of following the reference motion. Moreover, since the exposure process and equipment are synchronized with the reference motion, deformation and thermal stress may affect the reticle, the wafer and the projection elements if the exposure high-energy duration and frequency are not taken into consideration while designing the reference motion. From dynamics point of view, reference motion with higher-order derivatives enhances the tracking performance of the machine, however, its operational cost is usually overlooked. In this paper, we present a case-study that outlines the aforementioned aspects using three step-and-scan profiles of the same order. We conclude by posing the following research question: what is the best combination of orders of the step and the scan trajectories that jointly meet the desired performance and operating conditions?