Low Energy Ion Implantation

Amorphous carbon is a novel material with which to study defects and to understand the physics of disorder, which can be enhanced by ion irradiation [163], Ion implantation studies of different types of carbon at low energies (100 keV to 1 MeV) and high dosages (10 ions/cm ) attracted the attention of many scientists [164]. The role of the ion beam in low-energy ion implantation is to displace the carbon atoms and introduce disorder in the material. In diamond-like carbon films... 

N. Koshida, Y. Suzuki, and T. Aoyama, Low energy ion implantation studies of polyacetylene films, Nud. Inst. Meth. 837139 108 (1989). 

The passivation of dry-etching damage by low energy hydrogen implantation from a Kaufman ion source (0.4 keV) has also been reported (Singh et al., 1984b). The Si samples were either initially bombarded with a... 

Compositional and Structural Changes of Polymers under Low-to Medium-Energy Ion Implantation... 

Ion implantation has also been used to increase the barrier height of metal-semiconductor Schottky-barrier diodes (46). This is accomplished by implanting low energy ions of opposite conductivity type into the semiconductor surface. The implanted ions change the field and potential in the surface region and reduce the diode current. Figure 16 shows the variation of current density versus forward voltage for various values of ion implantation dose (58). 

It should be noted that during the implantation of low-energy ions (e.g., 100-keV B ) in polyethylene, polyamide, and some other polymers, the carbon enrichment turns out to be maximal at some depth below the surface of the irradiated target, which is evidenced by the depth profile of carbon excess in the implanted layer reconstructed from RBS spectra. In this case the oxygen depth profile is, generally, saddle shaped, because the additional maximum of oxygen concentration... 

It should be noted that even at a low energy of implanted species (100 keV) the size of nanopores that are formed in the implanted layer turns out to be enough to make the insertion of large molecules possible (for instance, the dicarbollyl complex of cobalt readily diffuses into polyethylene implanted with 150-keV ions [75]). In the case of energetic ions (with energies of several hundreds of MeV), the pore size increases and the implanted polymer can be doped with fullerenes [61]. Thus, the concentration of C o molecules that difhise into polyimide implanted with 500-MeV ions from toluene solution amounts to as much as 1.8 x 10 fullerene molecules per track (the fullerene concentration was evaluated by a neutron depth profiling technique using Li ions, known to form the insoluble adduct with Cfio as the tracer [61]). 

The vacancy is very mobile in many semiconductors. In Si, its activation energy for diffusion ranges from 0.18 to 0.45 eV depending on its charge state, that is, on the position of the Fenni level. Wlrile the equilibrium concentration of vacancies is rather low, many processing steps inject vacancies into the bulk ion implantation, electron irradiation, etching, the deposition of some thin films on the surface, such as Al contacts or nitride layers etc. Such non-equilibrium situations can greatly affect the mobility of impurities as vacancies flood the sample and trap interstitials. 

---