Implant Angle Control on Optima MD

Implant angle control is increasingly important with each new device node. Some devices have demonstrated a sensitivity of threshold voltage of about 100 mV/deg for implant angle and require implant angles to be held within +/- 0.2 deg for process control. There are many sources of angle variation in single wafer implanters. Mechanical orientation can usually be controlled to high precision, but an accurate control of the implant angle requires knowledge of the actual beam angle relative to the surface or crystal planes of the wafer. In-situ methods to measure beam angles in both the horizontal and vertical planes are required and it is necessary that these methods be calibrated to the surface or crystal planes of the wafer to achieve the required angle control. Optima MD has incorporated methods to automatically measure beam angles prior to implant in both planes, and correct for any deviation from the desired implant angle. The symmetric parallelizing lens that corrects angles without bending the beam enables a method of calibrating the horizontal angle mask to crystal planes with one or two wafers. This paper discusses the methods of measurement, calibration, and accuracy of the Optima MD angle control system.