Development of a four-electrode extraction system for a large area ion source with a wide range of operational conditions
We have developed a four-electrode extraction system for a large area ion source with a wide range of operational conditions, that is, a beam energy of 1-100 keV, a beam current density of 7 nA/cm 2-7 μA/cm 2, and ion source gases of BF 3 or PH 3. Uniformity of the beam profile was less than ± 10% in the 15 × 15 cm 2 area. Control of the beam optics was done by varying the electric field in the extraction region. The optimum field intensity was investigated experimentally and the result agreed quite well with that of the computer simulation. By designing the gap ratio (the distance of the extraction region/the distance of the acceleration region) with a small value, we could control the beam with energies of 1-100 keV by varying the extraction voltage from 0 to 2 kV.