Energy distribution measurements with a BiGa liquid metal alloy ion source

The liquid metal ion source, is now the basis of focused ion beams systems that use a variety of heavy metal ions (with currents of 1pA – 30nA) which can be focused into diameters smaller than 10nm with current densities of several A/cm2. The predominate use of these systems has been in various aspects of IC fabrication. Implantation is an essential process for the fabrication of electronic devices and integrated circuits. One of the most important parameters in the operation of focused ion beam (FIB) columns is the energy spread of the ion beam, normally expressed as the full width at half the maximum height of the energy distribution (FWHM). When it was demonstrated that failure analysis and integrated circuit modification could be done with focused ion beams utilizing liquid metal ion sources, the resulting technological “push” for high performance caused the rapid development of new ion beam instrumentation. Among other applications, FIBs are now used for research lithography, direct implantation (using alloy metal ion sources with ion species including As, B, Bi, Ga, Ge, Au and Be), lithographic mask repair and a wide variety of micromachining uses.
An interesting element for materials investigation and modification is bismuth, which offers a broad spectrum of applications. Silicon doped with bismuth is an interesting choice because the ionization energy of Bi in Si is much larger than that of other group-V elements. Turning now to the present work we investigated a BiGa LMIS. We present the energy spread (ΔΕ) of the main ions of the beam drawn from the BiGa source as a function of source current (i). In conclusion, even though the deviation from the 2/3 power law of the low – current portion of the ΔΕ versus I curves has been explained in terms of instabilities at the emitter that set in at a particular level of current.