Investigation of the effects of low energy high dose ion bombardment in metals and compound semiconductors

Abstract

The effect of low energy nitrogen molecular ion beam bombardment on metals and compound semiconductors has been studied, with the aim to investigate at the effects of ion and target properties. For this purpose, nitrogen ion implantation in aluminium, iron, copper, gold, GaAs and AIGaAs is studied using XPS and Angle Resolve XPS. A series of experimental studies on N⁺₂ bombardment induced compositional changes, especially the amount of
nitrogen retained in the target, were accomplished. Both monoenergetic implantation and non-monoenergetic ion implantation were investigated, using the VG Scientific ESCALAB 200D system and a d. c. plasma cell, respectively.
When the samples, with the exception of gold, are exposed to air, native oxide layers are formed on the surfaces. In the case of monoenergetic implantation, the surfaces were cleaned using Ar⁺ beam bombardment prior to implantation. The materials were then bombarded with N₂+ beam and eight sets of successful experiments were performed on each sample, using a rastered N₂+ ion beam of energy of 2, 3, 4 and 5 keV with current densities of 1 μA/cm² and 5 μA/cm²2 for each energy. The bombarded samples were examined by ARXPS. After each
complete implantation, XPS depth profiles were created using Ar⁺ beam at energy 2 ke V and current density 2 μA/cm² . As the current density was chosen as one of the parameters, accurate determination of current density was very important. In the case of glow discharge, two sets of successful experiments were performed in each case, by exposing the samples to nitrogen plasma for the two conditions: at low pressure and high voltage and high pressure and low voltage. These samples were then examined by ARXPS.
On the theoretical side, the major problem was prediction of the number of ions of an element that can be implanted in a given matrix. Although the programme is essentially on experimental study, but an attempt is being made to understand the current theoretical models, such as SATVAL, SUSPRE and TRIM. The experimental results were compared with theoretical predictions, in order to gain a better understanding of the mechanisms responsible.
From the experimental results, considering possible experimental uncertainties, there is no evidence of significant variation in nitrogen saturation concentration with ion energy or ion current density in the range of 2-5 ke V, however, the retention characteristics of implantant seem to strongly depend on the chemical reactivity between ion species and target material. The experimental data suggests the presence of at least one thermal process. The discrepancy
between the theoretical and experimental results could be the inability of the codes to account for molecular ion impact and thermal processes.