Decaborane, an alternative approach to ultra low energy ion implantation

Ion beams of decaborane (B₁₀H₁₄) 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 (B₁₀H_x⁺) 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 B₁₀H_x⁺ 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