Plasma Immersion Ion Implantation with Lithium Ions

Summary form only given. A new method was developed with the aim of creating plasma lithium for plasma immersion ion implantation. First, an argon glow discharge with operation pressures ranging from 2.0x10^-2 mbar to 1.0 mbar is generated by negatively polarizing an electrode from -400 V to -1500 V. Small pieces of metallic lithium, 99.9 % pure, fill a conic crucible, 2.0 cm depth, in electric contact with electrode. Argon ions from the plasma are used to bombard this target, where heat is produced by the momentum transfer between the impacting ions and the crucible as well as by joule heating. By controlling the operation pressure and the electrode voltage polarization, it is possible to heat easily the crucible to temperatures above lithium melting point (180 degC), causing its evaporation. Lithium atoms are then ionized by the collisions with plasma particles. Double Langmuir probe measurements indicated variation on the density of the plasma from 4.0x10⁹ cm^-3 to 10¹⁰ cm^-3, after lithium evaporation. Parts of silicon wafer immersed into this mixed plasma were submitted to repetitive negative high voltage pulses (3 kV/4 mus/2.5 kHz), in order to attract plasma ions by using a high frequency compact pulser. High resolution X-ray diffraction performed in these samples revealed very high strain on the analyzed layers, indicating ion implantation in comparison with low strain in the samples submitted just to the argon discharge case.