Patent ID: 7772571

Claim:
A method of determining a selected scan distance to be used in scanning a wafer with an implant beam, the method comprising: a) calculating a dose distribution along a first direction across the wafer based on size or intensity of the implant beam and a scan distance, wherein the scan distance is the distance measured in the first direction between a first path and a final path of the implant beam scanning the wafer along a second direction across the wafer in multiple paths, wherein the scan distance is less than the sum of the height of the implant beam and the diameter of the wafer, and wherein the first and second directions are about perpendicular; b) determining a relative velocity profile between the implant beam and the wafer along the second direction based on the dose distribution determined in step a), wherein the relative velocity profile is to be used in scanning the wafer with the implant beam along the second direction in multiple paths, wherein the relative velocity profile is not constant along the second direction across the wafer; c) calculating a dose uniformity on the wafer based on the wafer being scanned using the relative velocity profile and the dose distribution calculated in step a); d) repeating steps a)-c) until the calculated dose uniformity meets one or more uniformity criteria, wherein the scan distance is adjusted in repeating steps a)-c); and e) when the calculated dose uniformity does meet one or more uniformity criteria, storing the scan distance used in step a) as the selected scan distance.