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

Future generations of Si electronic devices will need very shallow p-n junc tions, in the tens of nanometer range. Implantation of B to form p-type jun ctions of such low depth requires very low energies, below 1 keV, where the ion beam formation and transport are hindered by space-charge effects. Sha llow implantation also can be achieved using higher energy beams of ionized large molecules, such as decaborane (B10H14), since the atoms are implante d with only a fraction of the beam energy. Measurements of electron impact ionization and breakup of decaborane in the electron energy range, 25-260 e V, and temperatures up to 350 degreesC are reported here. Ions containing 1 0 B atoms were found to be the dominant component in all measured mass spec tra. In another set of experiments, the beams of the B10Hx+ cluster ions we re generated in an electron impact ionization source, mass analyzed, transp orted through a 2.5 m long ion beam line, and implanted into Si. No signifi cant 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 ini tially thought. The results confirm the potential of decaborane cluster ion s for low energy implantation of boron. (C) 2000 The Electrochemical Societ y. S0013-4651(00)03-071-8. All rights reserved.