Abstract: An apparatus is provided which determines whether a member is placed correctly on a base. The apparatus comprises an arm mounted for movement toward and away from the base which normally holds the member in place on the base. The arm has a projection which extends a distance beyond the surface of the arm and toward the base. When the member is in a first or third position relative to the base, the projection makes contact with the member. When the member is in a second position relative to the base, the projection clears the member and is positioned in close proximity to the side of the base. The apparatus determines the position of the member by sensing with a photosensor a corresponding position of the arm displaced from the base. The displacement distance of the arm relative to the base is due to the distance that the projection extends beyond the surface of the arm.

Abstract: An apparatus is described which controls the movement and positioning of a platen on which wafers may be mounted. The apparatus comprises a stepper motor having a motor sprocket member operatively coupled to a platen by a drive mechanism. The drive mechanism comprises a chain which cooperates with the the stepper motor by engaging with the motor sprocket member. The drive mechanism also comprises a platen chain sprocket having a platen shaft member. The platen is movably connected to the platen shaft member. The chain cooperates with the platen by engaging with the platen chain sprocket. Operation of the stepper motor rotates the motor sprocket member and drives the drive mechanism, thereby rotating the platen chain sprocket and determining the movement and positioning of the platen. The apparatus is capable of controlled movement and positioning of the platen inside processing equipment, such as ion implantation equipment.