Ion implantation apparatus

An ion implantation apparatus comprising:

• an ion source comprising an arc chamber for generating ions and a drawing electrode separated from and movable relative to said arc chamber for drawing ions from said arc chamber;
• a mass separator for transporting into a beam only ions desired for implantation in a material;
• an ion implantation chamber for receiving the ion beam and for supporting the material on which the ion beam is incident over an area of the material for implantation of the ions in the ion beam in the material;
• and
• means for moving said drawing electrode relative to said arc chamber to control the separation between said drawing electrode and said arc chamber in response to a calculation of the area of the material considering the normalized perveance of said ion source at said drawing electrode, the ions for implantation, accelerating voltage, ion beam current, and ion beam current density distribution.