A target chamber for a mechanically scanned ion implanter in which semiconductor wafers are maintained in contact with a rotating target disk entirely by body forces, thus eliminating the need for clamping members contacting the wafer surface. The axis of the disk is inclined, and the disk is in the form of a shallow dish having an inclined rim with cooled wafer-receiving stations formed on the inner surface of the rim. Centrifugal force is relied on to force the wafers against the cooled disk. Each wafer-receiving station includes fence structures which are engaged by the wafer during loading and when the disk is spinning. The fence structures are resilient so that wafer damage and thus particulate contamination is minimized. In accordance with another aspect of the invention the ion beam is projected against the wafers obliquely to the radius of the disk as to minimize striping effects and overscan.