Method of determining dose uniformity of a scanning ion implanter

A method of implanting ions into a substrate in a vacuum chamber of a scanning ion implanter which performs at least one relative scan between an ion beam and the substrate to be implanted, the method comprising the steps of

• measuring base beam current at at least one of before and after said scan so as to be unaffected by outgassing from a substrate being implanted,
• calculating from the measured base beam current a base dose distribution map over the substrate for the scan,
• detecting beam instability events and measuring the magnitude and position in the scan, during scanning of the substrate, of said detected beam instability events,
• determining from said measured magnitude and scan position corresponding deviations in the calculated base dose map,
• subtracting said deviations from the base dose distribution map to provide a corrected electronically recorded dose distribution map,
• and subsequently operating the implanter in response to the corrected map to compensate for dose uniformity errors.

An ion implanter comprising

• an ion beam source for generating in a beam direction a beam of ions to be implanted,
• a substrate holder for supporting a substrate to be implanted, the implanter being operative to perform at least one relative scan between said beam and a substrate on the substrate holder wherein said scan comprises at least one pass across the substrate to uniformly cover the whole substrate, the entire beam missing any substrate on the substrate holder at at least one of the beginning and the end of said scan,
• a faraday collector located to receive beam ions missing the substrate holder and any substrate thereon,
• a detector connected to the faraday to provide signals representing the current of beam ions received by the faraday collector,
• a beam instability monitor to detect beam instability events and to measure the magnitude and position in the scan over the substrate of said beam instability events,
• and a controller which
• a) is responsive to signals from the detector at at least one of the beginning and the end of the scan to measure a base beam current value which is unaffected by outgassing from a substrate being implanted,
• b) is arranged to calculate, from the measured base beam current value, data defining a base dose distribution map over the substrate for the scan,
• c) is further arranged to determine deviations in the base dose distribution map corresponding to the detected beam instability events, and
• d) is further arranged to subtract said deviations from the base dose distribution map to provide data defining a corrected dose distribution map.