Metal contamination reduction in the evolution of ion implantation technology

In this paper we discuss the results of various approaches to the problem of metal contamination in ion implantation processes. Lifetime techniques (photocurrent and surface photovoltage measurements) are used for the evaluation of metal contamination in implanted wafers. Energy reduction is found to be uneffective in metal contamination reduction. A schematic model was developed to calculate the iron penetration in the silicon matrix for different implantation energies. The results of these calculations confirm that no contamination reduction can be expected by reducing implantation energy only. Metal contamination in ion implantation processes is mostly an iron contamination due to sputtering from parts close to the wafer during the implantation, so modifications of the wafer support effectively reduce such contamination. However a residual iron contamination due to sputtering is still present, unless silicon-coated supports are used. Under such conditions contamination by sputtering is suppressed, and some contamination from the backside contact is detected.