Large-Scale Active Contactless Transportation System for Semiconductor Wafers

Abstract

The relentless advancement of semiconductor and photovoltaic technologies has been driven by the demand for smaller, lighter, and more efficient electronic devices. A key trend accompanying this evolution is the reduction in substrate thickness, which lowers material costs and improves performance, alongside the increase in wafer diameter to enhance throughput. As a result, modern manufacturing increasingly relies on silicon wafers that are both thin and large in area. This combination fundamentally alters the mechanical behavior of wafers, resulting in them being highly compliant, fragile, and sensitive to external disturbances. Currently, conventional wafer handling systems rely on mechanical contact through robotic grippers and end-effectors, which have long been acceptable for mechanically robust substrates. However, for ultra-thin wafers, even minimal contact forces can induce warpage, micro-cracks, or fracture. Moreover, repeated dry contact unavoidably generates nanoparticles through friction and micro-wear, contributing to contamination that degrades yield and device reliability. In the literature, although contactless wafer handling approaches have been proposed to eliminate mechanical contact, they fail to achieve contactless positioning and transportation functionalities while remaining manufacturable and scalable to large working areas.

Therefore, this thesis addresses this gap by developing a scalable contactless wafer transportation system based on active air-bearing principles, with a strong emphasis on manufacturability and practical upscaling. As a first step, a novel contactless force actuator is introduced, featuring a continuous deformable air-bearing surface composed of compliant-mechanism-based unit cells. This design enables effective generation of viscous traction forces while significantly simplifying mechanical construction for easier fabrication and component integration, compared to prior discrete-cell architectures. Experimental validation demonstrates stable levitation, a fly height of 42.5 µm, and high traction force up to 90 mN, confirming the feasibility of the proposed approach.

To enable automated and efficient actuation of the compliant air-bearing system, a tunable hybrid reluctance actuator is developed. By exploiting adjustable magnetic reluctance, the actuator achieves passive and tunable stiffness reduction with high force efficiency and low disturbance transmissibility. Experimental results demonstrate substantial stiffness reduction up to 88.5%, while also revealing the necessity of closed-loop control to mitigate dynamic instabilities at high reduction levels.
Building on these components, a modular contactless wafer transportation system is realized through redesigned airflow pathways and integrated vacuum resistances, ensuring stable levitation even when the wafer partially uncovers the bearing surface. Closed-loop experiments confirm reliable contactless transportation and ±2.5 µm positioning accuracy. Finally, the modular concept is extended to a large-scale system by integrating multiple modules into a unified flat surface. Experimental results validate the scalability of the design, improved manufacturability, and highlight surface quality as a critical factor governing fly height, vacuum consumption, and traction force.

Overall, this work establishes a viable foundation for scalable, manufacturable contactless wafer transportation. While further improvements in surface finishing, vacuum management, actuator capability, and control strategies are required, the presented concepts represent a significant step toward practical, high-performance contactless handling solutions for next-generation semiconductor manufacturing.