Ion implantation beam monitor

An ion implantation apparatus comprising a holder for a substrate to be implanted, a source of ions to be implanted in the substrate, a flight tube through which ions from the source travel towards the holder, an ion accelerator arranged to supply an acceleration bias between the source and the flight tube such that the ions are accelerated to an acceleration energy, a low resistance, electrically conductive return current path connected to conduct the entirety of a return current to the flight tube which is required to maintain the flight tube at substantially the same potential as the substrate holder, and a return current monitor arranged to provide a signal representative of the return current flowing through the return current path.

An ion implantation apparatus comprising a holder for a substrate to be implanted, a source of ions to be implanted in the substrate, a flight tube through which ions from the source travel towards the holder, an ion accelerator arranged to supply an acceleration bias between the source and the flight tube such that the ions are accelerated to an acceleration energy, a beam stop arranged to absorb a portion of the ion beam not absorbed by the substrate or substrate holder, and to generate a beam stop current therefrom, an electrically conductive controlled return current path connected to conduct the entirety of a return current to the flight tube which is required to maintain a desired potential difference between the substrate holder and the flight tube, and a comparator arranged to provide a signal representative of the difference between the controlled current through the return current path and the beam stop current.

A method of implanting ions in a substrate at a desired implant energy, comprising accelerating ions to a transport energy by supplying an acceleration bias between an ion source and a flight tube through which the ions travel, transporting the ions through the flight tube to the substrate, generating a return current signal representative of the entirety of the current returned to the flight tube, the return current being controlled such that a desired potential difference is maintained between the substrate holder and flight tube, and monitoring the ions transported through the flight tube to the substrate based upon the signal representative of the return current.

A method of monitoring the quality of an ion beam in an ion implantation apparatus, comprising accelerating ions to a transport energy by supplying an acceleration bias between an ion source and a flight tube through which the ions travel, transporting the ions as in an ion beam through the flight tube to a substrate, generating a return current signal representative of the entirety of the current returned to the flight tube, the return current being controlled such that a desired potential difference is maintained between the substrate holder and flight tube, and monitoring the quality of the ion beam based upon the signal representative of the return current.