Mass Separation Issues for the Implantation of Doubly Charged Aluminum Ions

A phenomenon in aluminum implantation, where doubly charged Al ions may randomly and unnoticed be replaced by another ion species, is discussed. SIMS measurements were performed in order to reveal missing Al implants as well as to identify the ion species that gets implanted instead. In order to determine the contamination mechanism, simulations of mass interferences and mass spectra were carried out. It is shown that the correlation between doubly charged Al ions and the contaminating ion species strongly depends on the mass resolution of the implanter.