Ion implanter and beam stop therefor

摘要

A beam stop (23) has a charge collecting member (40) which extends in the direction of scanning of a scanned beam by less than the total distance scanned, so that variation in the charge signal derived from the collecting member can provide a timing signal for use in monitoring alignment of the scanned beam. In a preferred embodiment, the beam stop plate (42) has slits (65-69) leading to apertures (60-64) containing charge collecting rods (73-75) located within the thickness of the beam stop plate (42).