Low energy implantation of boron with decaborane ions
Committee for the Interdisciplinary Program in Materials Science and Engineering
Doctor of Philosophy
Materials Science and Engineering
Chin, Ken K.
Farmer, Kenneth Rudolph
Jacobson, Dale C.
Poate, J. M.
Low Energy Implantation
Si MOS Devices
The goal of this dissertation was to determine the feasibility of a novel approach to forming ultra shallow p-type junctions (tens of nm.) needed for future generations of Si MOS devices. In the new approach, B dopant atoms are implanted by cluster ions obtained by ionization of decaborane (B10H14)vapor. Each B atom carries only ~9% of the cluster kinetic energy and the B dose per unit charge is 10 times larger than in the case of monomer ion beams. Thus, the problems of spacecharge, limiting the extraction and transport of low energy (< = 1 keV) beams of B+ ions, can be overcome.
To test this concept, an experimental ion implanter with an electron impact ion source and magnetic mass separation was built at the Ion Beam and Thin Film Research Laboratory at NJIT. Beams of B10Hx+ ions with currents of a few microamperes and energies of 1 to 12 keV were obtained and used for implantation experiments. There was no measurable neutral beam component (< 1%), no breakup of the cluster ions (< 2%) and no vapor B transport in the system. Profiles of B and H atoms implanted in Si were measured by Secondary Ion Mass Spectroscopy (SIMS) before and after rapid thermal annealing (RTA). From the profiles, the junction depth of 57 nm (at 1018 cm-3 B concentration) was obtained with 12 keV decaborane ions followed by RTA. Outdiffusion during RTA resulted in reduction of the concentration of the implanted H by two orders of magnitude to the level of only twice the concentration in an unimplanted control sample. The dose of B atoms that can be implanted at low energy into Si is limited by sputtering as the ion beam sputters both the matrix and, the implanted atoms. As the number of sputtered B atoms increases with the implanted dose and approaches the number of the implanted atoms, equilibrium of B in Si is established. This effect was investigated by comparison of the B dose calculated from the ion beam integration with B content in the sample measured by Nuclear Reaction Analysi s fNRA). Maximum (equilibrium) doses of 1.35 x 1016 B cm-2 and 2.67 x 1016 B cm-2 were obtained at the beam energies of 5 and 12 keV, respectively. Sputtering yield of Si with B10Hx+ ions was determined by measurement of the amount of Si removed by a known ion dose. This is the first reported measurement of the sputtering yield with the decaborane cluster ions. The surface morphology measured by Atomic Force Microscopy (AFM) indicates that decaborane ions result in smoothing rather than roughening of the Si surface.
The problem of forming shallow p-type junctions in Si is related not only to implantation depth, but also to transient enhanced diffusion (TED). TED in Si implanted with B10Hx+ was measured on boron doping superlattice (B-DSL) marker layers. It was found that TED, following decaborane implantation, is the same as with monomer B+ ion implantation of equivalent energy and that it decreases with the decreasing ion energy. This confirms the earlier preliminary findings with unanalyzed decaborane beams and agrees with current TED theory (+1 model). This dissertation demonstrated the feasibility of implantation of B with decaborane ions for shallow junction fonnation in Si. The findings of the fundamental decaborane ion beam properties and its effect in Si have provided scientific foundation for the continuing efforts of industry in further advancement of semiconductor technology.
njit-etd2001-063 (194 pages ~ 16,368 KB pdf)
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Created June 03, 2002