Laser ion source for Ge ion implantation of silicon surfaces

A novel technique for ion implantation of electronics materials by means of a laser ion source emitting multi-energetic ion streams was investigated. A UV pulsed laser beam, at intensities of the order of 108 W/cm2, was employed to produce plasma in a vacuum from a Ge target. The apparatus utilized was very versatile and able to contain an expansion chamber in order to allow the plasma to be diluted before the application of an accelerating voltage. The mean ion energy increased with the laser pulse energy and the ion charge state, and ranged between about 100 eV and 1 keV. To increase the ion energy a post-acceleration up to 50 kV was employed, which resulted in ion energies from about 50 keV to about 150 keV, depending on the charge state. The multi-energetic ion beam, with current density of the order of 10 mA/cm2, was employed to irradiate silicon substrates and to obtain surface implantations up to a depth of about 150 nm. During the implantation process the ion beams were generated with a repetition rate of the laser pulse of 1 Hz. The depth profiles of the ion implants were investigated by Rutherford backscattering spectrometry and laser ablation – inductively coupled plasma – mass spectrometry.