Decaborane as ion source material for boron implantation

Formation of p-type shallow junctions for future generations of Si technology will require ion implantation of B at very low energies, i.e. below 1 keV, where the beam formation and transport at reasonably high currents are hindered by Coulomb repulsion of ions at high volume density. An alternative to implantation of monomer ions at a very low energy is implantation of large molecular ions at a higher energy. In the latter case, the implantation depth of the atoms corresponds to a fraction of the beam energy, partitioned between the atoms of the molecule. The decaborane molecule (B₁₀H₁₄) is of particular interest for implantation of p-type shallow junction in Si, because each of the B atoms carries only 9% of the molecule's kinetic energy. Experimental PMOS devices made using decaborane implantation have been demonstrated recently. It also has been shown that transient enhanced diffusion (TED) of B in Si implanted with B ions and with decaborane ions at the equivalent dose and energy are the same. The prospect for using decaborane in ion sources is examined, based on measurements of its ionization and dissociation properties. It is shown that decaborane molecules are effectively ionized by electron impact in the energy range near 100 eV.