Patent Number: 048067695
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion implantation system used for manufacturing semiconductor devices. More particularly, it relates to a cooling of an ion target mechanism in the ion implantation system using a high ion dosage. 2. Description of the Related Art There is an urgent need for a high-speed throughput in an ion implantation (injection) process. The throughput speed is generally defined by the following times: an ion implantation time T.sub.I , a handling time T.sub.H for exchanging a target disk having semiconductor wafers thereon and mounted on a mechanism, and a time T.sub.P for pumping a vacuum chamber. An improvement of the throughput speed can be achieved by shortening these times. The ion implantation time T.sub.I can be reduced by increasing an ion beam current from approximately 10 mA to 30 mA, which will provide a high ion dosage, approximately 10.sup.15 cm.sup.-2 to 10.sup.16 cm.sup.-2. On the other hand, the reduction of the handling time T.sub.H and the pumping time T.sub.P can be realized by applying a method in which dual end stations are used; a method in which a system has two end stations and the wafer handling and the vacuum pumping for one end station are carried out during the ion implantation of the other end station. Another method for reducing the pumping time T.sub.P is a direct-exchange of the semiconductor wafers. The dual end station method, however, requires the use of a bulky facility, and the direct wafer exchange method in the vacuum chamber involves a difficult operation, and the quality of a semiconductor wafer may be reduced because dust may be generated from movable portion of the target disk in the vacuum chamber. Therefore, a target disk exchange method has been proposed ("A high-throughput mechanically scanned target chamber", G. Ryding and A. Armstrong, on pp. 319 to 325, "Nuclear Instruments and Methods", No. 189, by North Holland Publishing Company, 1981). The prior art ion implantation system using the disk exchangeable target mechanism has a low implantation reliability due to heat generated during subjecting the semiconductor wafers on the disk to high ion dosages. This will be described in more detail with reference to a specific example. SUMMARY OF THE INVENTION An object of the present invention is to provide an ion implantation system using a disk exchangeable target mechanism which can be effectively cooled even when semiconductor wafers on the disk are being subjected to a high ion dosage. Another object of the present invention is to improve the throughput speed of ion implantation by using the above ion implantation system. Still another object of the present invention is to improve the reliability of ion implantation when using a high ion dosage. According to the present invention, there is provided a disk exchangeable target mechanism of an ion implantation system including an exposure chamber for inserting the disk exchangeable target mechanism and introducing accelerated ion beams directed to a semiconductor wafer on the disk exchangeable target mechanism, having: a metal target disk on which a semiconductor wafer(s) to be ion-implanted can be mounted on a first face thereof, a support including a metal base having the target disk mounted thereon, and a shaft incorporated with the base. The support is rotatable in the exposure chamber by a force applied to the shaft during a ion-implantation process, and the target disk is detachable from the support when to be taken out of the exposure chamber. The target mechanism further includes a medium, provided between a second face of the target disk opposing the first face and the base, for providing a thermal contact therebetween. The thermal contact medium may have a high contactability with metal, and the thermal contact medium may also have a high thermal conductivity. The thermal contact medium further may be stable in a vacuum. The base of the support may be provided with a cavity, and the shaft may be provided with holes communicated with the cavity. A cooling medium is inserted into the cavity through a hole and the inserted cooling medium is drained from the cavity through another hole. The target disk may be provided with a thermal transportation unit transporting thermal energy at a portion(s) where the temperature is high by applying ion implantation energy to another portion(s) where the temperature is low. The thermal transportation unit may include a heat pipe(s), and the heat pipe(s) may include a cooling medium having a low boiling temperature. The heat pipes may be radially provided with respect to a rotation center of the target disk. Note, any combinations of the above may be used.