Image Number 2 for United States Patent #4816693.
A uniform ion implantation dose control apparatus controls the implantation of ion particles onto at least one wafer mounted on a rotating disk in the pathway of the ion particle beam. A grounded scanning wire is repeatedly moved across the beam to produce an emission of secondary electrons which is linearly proportional to the beam particle current. The secondary electrons emitted are collected and formed into a current I.sub.s by a collector electrode. Portions of the current I.sub.s on the collector electrode are sampled. While the vacuum conditions within the beamline are good, the beams electrical current I.sub.FC is measured and the collector current I.sub.s sample is calibrated therewith so that when the beamline vacuum becomes a high pressure vacuum, additional collector current I.sub.s samples may be utilized to determine a theoretical beam current I which is a function of the beam particle current I.sub.p =I/q. This theoretical beam current I is utilized to move the rotating disk along a radial pathway perpendicular to the beam pathway at a velocity V which is proportional to the theoretical beam current I.