Apparatus and method for reducing implant angle variations across a large wafer for a batch disk

Abstract

A method to rotate individual pad of a batch disk to an implant angle and lock them in place, with the pad surface having conical or near conical surface to minimize the implant angle variation across a wafer on the pad for both tilt angle and twist angle, at large tilt angle implant. The implanter includes a disk with multiple attached pads that can hold substrates securely when the hub is at rest or rotates. The disk rotates around its spin axis, which moves laterally at a programmed speed profile so that all substrates on the hub can get evenly touched by the fixed ion beam. The pad rotation axis is at an angle with the disk spin axis, and the angle is preferable 90 degrees. The nominal of the pad surface is at an angle, i.e., a tilt angle, relative to the incident ion beam. A rotation mechanism is applied to each individual pad to rotate the pad to the desired tilt angle. A locking mechanism is applied to each individual pad assembly to lock the pad at the desired tilt angle with minimum angle variation under high centrifugal force during fast disk spin. The locking mechanism includes: a) add brake to the rotation mechanism in the pad assembly so that the pad cannot rotate due to mechanical friction force or lock-key. B) use motor to hold the pad assembly. The sum of the friction torque and the motor holding torque should be larger than the centrifugal torque. A torque balancing mechanism is applied to pad mechanical design to minimize the total pad rotation torque under centrifugal force during fast disk spin by adding mass to counter balance the original wafer pad mass.