Image Number 16 for United States Patent #5738574.
An apparatus for polishing semiconductor wafers and other workpieces that includes polishing pads mounted on respective platens at multiple polishing stations. Multiple wafer heads, at least one greater in number than the number of polishing stations, can be loaded with individual wafers. The wafer heads are suspended from a carousel, which provides circumferential positioning of the heads relative to the polishing pads, and the wafer heads oscillate radially as supported by the carousel to sweep linearly across the respective pads in radial directions with respect to the rotatable carousel. Each polishing station includes a pad conditioner to recondition the polishing pad so that it retains a high polishing rate. Washing stations may be disposed between polishing stations and between the polishing stations and a transfer and washing station to wash the wafer as the carousel moves. A transfer and washing station is disposed similarly to the polishing pads. The carousel simultaneously positions one of the heads over the transfer and washing station while the remaining heads are located over polishing stations for wafer polishing so that loading and unloading of wafers and washing of wafers and wafer heads can be performed concurrently with wafer polishing. A robot positioned to the side of the polishing apparatus automatically moves cassettes filled with wafers into a holding tub, and transfers individual wafers vertically held in the cassettes between the holding tub and the transfer and washing station. The multiple polishing pads can be used to sequentially polish a wafer held in a wafer head in a step of multiple steps. The steps may be equivalent, may provide polishes of different finish, or may be directed to polishing different levels.