초록 ▼

Dose uniformity of a scanning ion implanter is determined. A base beam current is measured at the beginning and/or the end of a complete scan over the whole substrate area. This base beam current is measured at a time when the measurement should be unaffected by outgassing from a substrate being imp

Dose uniformity of a scanning ion implanter is determined. A base beam current is measured at the beginning and/or the end of a complete scan over the whole substrate area. This base beam current is measured at a time when the measurement should be unaffected by outgassing from a substrate being implanted and a base dose distribution map is then calculated for the scan in question. During the scan itself beam instability events are detected and the magnitude and position in the scan of the detected instability events is measured. Corresponding deviations in the calculated base dose map are determined and subtracted from the previously calculated base dose distribution map to provide a corrected distribution map. By determining overall dose uniformity substractively in this way, good overall accuracy can be obtained with lesser accuracy in the measurement of the beam instability events.

대표청구항 ▼

1. A method of determining dose uniformity of a scanning ion implanter which performs at least one relative scan between an ion beam and a substrate to be implanted, the method comprising the steps ofmeasuring base beam current at at least one of before and after said scan so as to be unaffected by

1. A method of determining dose uniformity of a scanning ion implanter which performs at least one relative scan between an ion beam and a substrate to be implanted, the method comprising the steps ofmeasuring 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, over the substrate, of said detected beam instability events, determining from said measured magnitude and scan position corresponding deviations in the calculated base dose map, andsubtracting said deviations from the base dose distribution map to provide a corrected dose distribution map.2. A method as claimed in claim 1, wherein beam instability events are detected and said magnitude and position thereof are measured by taking multiple measurements during said scan of a current of beam ions bypassing the substrate.3. A method as claimed in claim 2, wherein the current of beam ions during said scan is measured by sampling the current at a selected frequency.4. A method as claimed in claim 3, wherein said selected frequency is not less than 1 kHz.5. A method as claimed in claim 1, wherein the implanter performs a plurality of said scans to complete an implant, said base beam current being measured for each said scan, and said beam instability events being detected, said magnitude and position thereof being measured and said dose map deviations being determined during each said scan.6. A method as claimed in claim 5, wherein a complete corrected dose distribution map for the full implant is derived at the end of the implant from said base beam current measurements and said dose map deviations for said plurality of said scans.7. A method as claimed in claim 5, wherein an accumulated corrected dose distribution map is derived after each one of said scans, from said base beam current measurements and said dose map deviations for said one of said scans and all preceding said scans of the implant, and an operator alert is signalled if the accumulated corrected dose distribution map after said one of said scans forecasts that a desired final dose uniformity for the complete implant will not be achieved.8. A method as claimed in claim 7, wherein the implant is halted after a scan for which the subsequent accumulated dose distribution map data forecasts that the desired final dose uniformity will not be achieved.9. A method as claimed in claim 7, wherein a forecast dose uniformity for the complete implant is calculated from the dose uniformity error indicated in the accumulated corrected dose distribution map after the latest of said scans, relative to the dose so far delivered to the substrate.10. A method as claimed in claim 2 when carried out in an ion implanter comprising a rotatable substrate holder in the form of a spoked wheel having a plurality of substrate supports on respective spokes thereof with openings between adjacent said substrate supports, the substrate holder being mounted for rotation about an axis of the wheel and the current of beam ions passing between substrate supports being sampled at discrete time intervals such that during a scanning operation, a plurality of samples is taken as beam ions pass between adjacent pairs of substrate supports on the holder.11. A method as claimed in claim 1, wherein said at least one relative scan is a two-dimensional relative scan.12. A method as claimed in claim 1, wherein the implanter comprises a source of ions at a source potential, a mass selector structure at a base potential, and a process chamber containing a substrate holder at a target potential, and beam instability events are detected and said magnitude and position thereof are measured by monitoring the total current returning to the mass selector structure which is required to maintain the substrate holder at the target potential.13. 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 ofmeasuring 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.14. An ion implanter comprisingan 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 whicha) 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, andd) is further arranged to subtract said deviations from the base dose distribution map to provide data defining a corrected dose distribution map.15. An ion implanter as claimed in claim 14, wherein the substrate holder is arranged such that the entire beam bypasses the substrate holder when missing any substrate thereon at the beginning or the end of said scan, and the faraday collector is located downstream of said substrate holder to receive beam ions bypassing the substrate holder.16. An ion implanter as claimed in claim 15, wherein said substrate holder is such that at least a portion of the beam ions bypass the substrate holder and any substrate thereon at least at regular intervals during the or each said pass and said beam instability monitor is responsive to signals from said detector during the or each said pass to detect beam instability events and to measure said magnitude and position thereof.17. An ion implanter as claimed in claim 16, wherein the controller comprises a digital processor arranged to sample the signals from the detector at a pre-selected frequency, and a memory for storing the sampled signals.18. An ion implanter as claimed in claim 17, wherein said processor is arranged to process the sampled signals to produce and store in said memory electronic signals representing said corrected dose distribution map.19. An ion implanter as claimed in claim 14, wherein the controller is arranged to operate the implanter, in response to said corrected dose distribution map, to implant ions into the substrate so as to compensate for dose uniformity errors.20. An ion implanter as claimed in claim 16 operative such that said relative scan is a two-dimensional raster scan, the or each said pass being relatively slow and containing a plurality of relatively fast sweeps whereby at least a portion of the beam ions bypass the substrate holder and any substrate thereon during at least one part of each sweep.21. An apparatus as claimed in claim 20, in which the substrate holder is a rotatable wheel having an axis of rotation and a plurality of radially spaced substrates supported upon spokes spaced radially around the wheel, said wheel axis being mounted for reciprocating motion transverse to said beam direction to provide said relatively slow passes as rotation of the wheel provides said relatively fast sweeps.22. An ion implanter as claimed in claim 14, wherein the implanter is operative to perform a plurality of said scans to complete an implant, and said controller is responsive to signals from the detector to measure said base beam current for each said scan, and said beam instability monitor is operative to detect and measure beam instability events for each said scan.23. An ion implanter as claimed in claim 22, wherein said controller is arranged to provide data defining an accumulated dose distribution map after each one of said scans, and is further arranged to monitor said accumulated dose distribution map data after each scan to forecast whether a desired final dose uniformity value for the complete implant will be achieved.24. An ion implanter as claimed in claim 23, wherein the controller is further arranged to generate an operator alert if said accumulated dose distribution map data forecasts that said desired final dose uniformity will not be achieved.25. An ion implanter as claimed in claim 24, wherein the controller is further arranged to halt the implant after a scan for which the subsequent accumulated dose distribution map data forecasts that the desired final dose uniformity will not be achieved.26. An ion implanter as claimed in claim 14, having a source of ions at a source potential, a mass selector structure at a base potential and a process chamber containing said substrate holder at a target potential, wherein said beam instability monitor is responsive to the total current returning to the mass selector structure which is required to maintain the substrate holder at the target potential.