Correlation of screen oxide thickness and iron levels introduced during batch high-current implants

Iron is one of the most critical contaminants adversely affecting the performance of advanced microelectronic devices. The maximum tolerated Fe levels are becoming increasingly lower with subsequent device generations. In this paper, we present results on the dependence of Fe concentration on the thickness of the screen oxide used during high-dose implants. Implants were performed on two different batch high-current implanters using As⁺ ion beams at energies of 10 keV and 80 keV. Analysis was carried out after cleaning and stripping the oxide, using minority carrier lifetime measurements (Elymat) and secondary ion mass spectrometry (SIMS). Very good correlation between the two techniques is established. Results show reduction of the Fe levels in the wafer with increasing screen oxide thickness for all considered tools. In all cases, the Fe was a surface contaminant with no implanted energetic component. The dependence of Fe levels on sputtering yield is also investigated