Design, modeling and control of a modular contactless wafer handling system

In the photovoltaic solar cell industry as in the semiconductor industry, efforts to reduce the thickness of silicon wafers are in progress. Wafer damage and breakage during handling can lead to unacceptable yields and alternative solutions have to be proposed. This paper presents a modular contact-free wafer handling system that responds to the industrial requirements in terms of throughput and flexibility. The system is based on simple unidirectional modules that can be assembled together to form the desired trajectory. A complete and accurate physical model of the modular system describing the motion of the wafer transported by directed air-jets is proposed. A decentralized control at the block level is realized to damp the object motion. The experimental results show a great reduction of the response time compared to free motion and a standard deviation of the servo error below the millimeter. In addition, simulations show that a 150 mm wafer could reach a speed up to 2.9 m/s on large conveyors.