Abstract: A wafer transfer mechanism used for transferring wafers between cassettes and a boat uses sensors to detect and to measure any offset of the actual center of each wafer being transferred with respect to the expected or precalibrated center of that wafer. An appropriate adjustment is made to effectively eliminate such offset so that each wafer can be transferred throughout the system without any edge contact between a wafer and the boat or the cassette. The system also includes a boat exchange unit having a rotatable turntable which is used in association with two boats. The boat exchange unit permits a continuous mode operation in which one boat can be undergoing a loading or unloading of wafers at one station on the turntable while another boat is at or is moving to or from a heating chamber loading or unloading station on the turntable.