Ionization and mass spectrometry of decaborane for shallow implantation of boron into silicon

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 (B10H14), 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 350 degreesC 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 B10Hx+ 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. (C) 2000 The Electrochemical Society. S0013-4651(00)03-071-8. All rights reserved.