Multi-axis Active Vibration Suppression for Wafer Transfer Systems

Vibration suppression is critical in precision mechatronic systems for nanofabrication. For automated wafer handling in semiconductor plants, Overhead Hoist Transport (OHT) vehicles transport wafers carried in Front Opening Unified Pods (FOUPs); while the wafers are transported in a FOUP, semiconductor chips are at risk of damage by excited small particles due to mechanical vibration. Active suppression of the FOUP vibrations has been proposed to improve the production yield. However, there are two main challenges that make it a non-trivial problem. First, moving FOUPs carried by the OHT vehicles have no external anchoring point as a momentum source for control efforts. Second, no sensor attachment is permitted on mass-production FOUPs, which makes feedback control more challenging without measurement. Since the goal is to suppress the large FOUP acceleration peaks instead of eliminating all vibration, an inertia-based counterbalancing system is designed to address these challenges. To validate this idea, a custom testbed is designed for multi-axis vibration generation and suppression. A Disturbance Observer-Based Controller (DOBC) is developed and implemented on the hardware. During the experiment, 38 percent of the OHT hand unit vibration (and 42 percent of FOUP vibration) suppression is achieved in the OHT travel direction. Moreover, multi-axis FOUP-level acceleration-peak reduction is achieved to verify the effectiveness of the proposed method.