Patent Number: 052182096
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The ion implanter shown in FIG. 1 has a wafer holding disk 1 of the centrifugal holding type, and is characterized in that each wafer rest lb of the disk 1 has a wafer holding surface 1c curved nearly in the same manner as the conically-curved inner surface of the disk 1. Since wafer rest 1b of the wafer holding disk 1 of the ion implanter provided in accordance with the present invention has the wafer holding surface 1c curved nearly in the same manner as the conically-curved inner surface of the disk 1, the wafer 2 is pushed onto the wafer holding surface 1c by a centrifugal force due to the rotation of the disk so that the top surface of the wafer is conically curved. For that reason, an ion beam 3 is irradiated upon the entire top surface of the wafer 2 always perpendicular to the surface, namely, the angle of the implantation of the ions into the surface does not deviate. A preferred embodiment of the present invention is hereafter described with reference to FIGS. 1 and 2. FIG. 1 corresponds to FIG. 6, and shows a section of the wafer holding disk 1 of the ion implanter in the circumferential direction of the disk along the line B--B shown in FIG. 5. The disk 1 has wafer rests 1b, in turn, having wafer holding bottoms 1c on which wafers 2 are held. Each wafer holding bottom 1c is a curved surface defined by a cone having the same axis and slope as the conically-curved inner surface of the peripheral portion 1a of the wafer holding disk 1. When the disk 1 is rotated, each wafer 2 is pushed onto the wafer holding bottom 1c of the wafer rest 1b by centrifugal force so that the surface of the wafer is curved to conform with the wafer holding bottom. For that reason, an ion beam 3 is irradiated upon the surface of the wafer 2 perpendicularly to the surface at any point thereon with regard to the circumferential direction of the disk 1, as shown in FIG. 2. In other words, the angle of implantation of ions to the wafer 2 by the implanter does not deviate from the perpendicular. If such a wafer 2 is held on a spherically curved rest (not shown) by an annular clamper at the time of the implantation of ions into the wafer, the wafer 2 is spherically curved so that the maximum deformation of the peripheral edge of the wafer relative to the center thereof is nearly as large as 1 mm. As for the ion implanter of the present embodiment, the wafer 2 is not spherically curved but conically curved so that the influence of the curving on the quality of the ion-implanted wafer 2 is much smaller than that of the spherical curving of the former wafer, as understood through the examination of the case that when pieces of paper are wound on a conically or cylindrically curved surface and a spherically curved surface, respectively, the piece of paper wound on the former surface does not wrinkle while the other piece of paper wound on the latter surface wrinkles. For example, even if the wafer 2 is 200 mm in diameter and is deformed by about several millimeters at its peripheral edge relative to its center at the time of the curving and holding of the wafer on the wafer holding bottom 1c of the wafer rest 1b, the quality of the ion-implanted wafer is not affected by the deformation. The wafer holding surface 1c of each wafer rest 1b of the wafer holding disk 1 of an ion implanter provided in accordance with the present invention is a conically curved surface on which a wafer 2 is pushed by centrifugal force due to the rotation of the disk so that the beam-irradiated surface of the wafer 2 is conically curved to correspond to the wafer holding surface 1c of the wafer rest 1b and the inner surface of the peripheral portion of the disk. For that reason, an ion beam 3 is irradiated upon the surface of the wafer 2 perpendicularly to the entire surface, namely, the angle of the implantation of ions into the surface does not deviate. This results in enhancing the accuracy of the implantation of the ions into the wafer to heighten the uniformity of the quality of the wafer. The foregoing description of the preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiment was chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.