Future generations of Si electronic devices will need very shallow p-n junctions, in the tens of nanometer range. Implantation of B to form p-type junctions of such low depth requires very low energies, below 1 keV, where the ion beam formation and transport are hindered by space-charge effects. Shallow implantation also can be achieved using higher energy beams of ionized large molecules, such as decaborane (B 10 H 14 ), since the atoms are implanted with only a fraction of the beam energy. Measurements of electron impact ionization and breakup of decaborane in the electron energy range, 25-260 eV, and temperatures up to 350ЊC are reported here. Ions containing 10 B atoms were found to be the dominant component in all measured mass spectra. In another set of experiments, the beams of the B 10 H x ϩ cluster ions were generated in an electron impact ionization source, mass analyzed, transported through a 2.5 m long ion beam line, and implanted into Si. No significant breakup of the ions and no neutral beam component were found. Beams of ions with ten B atoms were formed more easily and are more robust than initially thought. The results confirm the potential of decaborane cluster ions for low energy implantation of boron.
Ion beams of decaborane (B1,,HI4) are used to form ultra shallow p-type junctions in Si. Because the ion energy is partitioned between the atoms of the molecule, B atoms are implanted with only approximately one tenth of the energy of the beam. Thus severe problems created by the space charge of ultra low energy (ULE) ion beams are minimized. Moreover, standard ion implanters equipped with a decaborane ion source may be capable of ultra shallow (tens of nm) implantation of boron. Ionization and ion beam properties of decaborane were studied in the energy range of 2 -10 kV. Under proper conditions in the ion source, most of the extracted ions consist of 10 B atoms (B1&+) and they can be transported through the implanter without significant break-up or neutralization. Boron depth profiles measured by SIMS in Si wafers implanted with BloH,' and B' ions of equivalent energy are the same but it appears that the retained dose achieved with the molecular ions is higher than with the monomer ions for the same B fluence. The effect may be due to a different Si sputtering yield per impinging B atom with the two types of ions. Si wafers with test MOS devices were implanted with decaborane ions and ULE BF2' ions of equivalent energy. Measured device characteristics are very similar. The results confirm the potential of decaborane ion beams as an alternative technology for manufacturing of ultra-shallow p-type junctions in Si.
Formation of p-type shallow junctions for future generations of Si devices will require ion implantation of B at very low energies (< 1 keV). An alternative to implantation of monomer ions at very low energy is implantation of large molecular ions at a higher energy. In an ion beam of decaborane (B10H14) each of the B atoms carries only 9% of the ion kinetic energy. We have examined ionization properties of decaborane and built an experimental ion source and an implantation apparatus with magnetic mass analysis. Analyzed decaborane ion beams with energies from 2 to 10 keV and beam currents of several microamperes were obtained. Si samples were implanted with decaborane ions and the implanted dose measured by current integration was compared with B content obtained by nuclear reaction analysis. Experiments with electrostatic beam deflection show that the large ions survive the transport in the implanter environment and that neutralization is negligible. During implantation, the retained B dose is reduced in comparison with the nominal implanted dose due to sputtering. Dose loss is greater at 200 eV compared to 500 eV. The properties of decaborane ion beams and the prospects of using them for shallow implantation of B into Si are discussed.
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