The development of a 12-inch wafer prealigner with optical character recognition

A prealigner is a device that orients a wafer or a substrate so that its center is set at a predefined place and its flat or notch is set at a predefined angle. Different from 8-inch wafers managed collectively in one magazine, each 12-inch wafer has to be managed individually because each 12-inch wafer is very expensive. Thus, prealigners for 12-inch wafers needs to be able to recognize optical characters of each wafer as well as to extract information about the orientation and center of a wafer. In this paper, a 12-inch wafer prealigner with optical character recognition is proposed. Existing prealigners using step motors have used commercial motor drivers and a simple velocity profile, so it brings about high cost and low performance. In the proposed prealigner, the low-cost micro-step motor drivers are developed and a high-performance smooth velocity profile is generated, which results in a precise and quick movement. Some experiments on the proposed prealigner are performed and their results are discussed.