Energy distribution properties of focused ion beams from liquid metal ion sources

Summary form only given, as follows. The field-emitted electron and ion beams in a high-voltage diode are found to be sources of very high brightness. For example, liquid metal ion sources (LMIS) produce ion beams of 5 /spl mu/A current from a source size estimated to 10/sup -7/ cm. This is why the focused ion beams are often used in the direct doping of semiconductors, in lithography, in semiconductor mask repair, and in micromachining. The width of energy distribution in high-brightness beams is often several tens of electron volts, even if thermal agitation at the emitter is a fraction of an electron volt. Typical diode voltage of the field emission source is 10 kV, which is much larger than several tens of electron volts. The energy distribution may not look important. However, a 10-eV energy spread causes a tremendous problem if the ion beams mentioned above must be focused to a spot the size of a fraction of a micron (/spl mu/m) to be useful in semiconductor mask repair. A theoretical model for energy spread and shift of peak energy distribution in a charged particle beam is developed. The beam may expand radially and axially as it propagates downstream. Charged particles placed randomly in the beam possess different potentials, which are converted to different kinetic energies as the beam propagates and expands. This randomness introduces energy spread in the beam. It is also shown that the shift of peak energy distribution in beam particles is proportional to the one-third power of the beam current, which is the manifestation of random particle locations.