Method and apparatus for improved ion dose accuracy
Patent 4680474 Issued on July 14, 1987. Estimated Expiration Date: 
May 22, 2005. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.
May 22, 2005. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.Patent ReferencesWafer transfer system Patent #: 4449885 InventorsApplicationNo. 06/736888 filed on 05/22/1985US Classes:250/492.2, Irradiation of semiconductor devices250/441.11, With air lock or evacuation means414/217, APPARATUS FOR MOVING MATERIAL BETWEEN ZONES HAVING DIFFERENT PRESSURES AND INHIBITING CHANGE IN PRESSURE GRADIENT THEREBETWEEN414/939Including wafer charging or discharging means for vacuum chamberExaminersPrimary: Anderson, Bruce C.Assistant: Berman, Jack I. Attorney, Agent or FirmInternational ClassesH01J 37/18 (20060101)H01J 37/317 (20060101) H01J 37/02 (20060101) AbstractThe implant chamber pressure during ion implantation is controlled within a specified intermediate pressure range higher than the baseline pressure. Implanted dose errors resulting from neutralizing collisions of the beam with residual gas molecules are held constant and can be compensated. The pressure is maintained within the specified intermediate pressure range by a control system including a controllable vacuum valve associated with a vacuum pump, a chamber pressure sensor and a valve controller responsive to the pressure sensor. The valve controller opens and closes the valve to maintain the chamber pressure within the specified range after introduction of a wafer.Other References
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