18 September 1995 Investigation of metal contamination by photocurrent measurements: validation and application to ion implantation processes
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Abstract
In this work we present a systematic study about the metal contamination induced by ion implantation, with the aim to identify contamination mechanisms and possible solutions to the problem. Lifetime measurements have been used in order to evaluate the level of contamination in implented wafers. Lifetime values have been extracted from photocurrent measurments (Elymat technique). Implantations of iron and cromium have been used in order to validate the study of lifetime versus injection level as a technique for the identification of contaminants and for the quantitative evaluation of their concentration. The contamination level in ion implanted wafers has been characterized varying main implantation parameters (species of the implanted ion, dose, current, energy, angle) and surface condition (whether bare or oxidized silicon). Ion implantation is responsible for a a heavy lifetime degradation (i.e. metal contamination), which increases in proportion to implantation dose and comes from the side exposed to the ion beam. The distribution of lifetime over wafer surface provides relevant information. Details of the implanter endstation (e.g., the clamping system) usually show up in wafer maps of lifetime. Results coming from different equipments concur to indicate that contaminants come from material sputtered from the loading disk. This conclusion is confirmed by the dependence of lifetime on implantation energy and tilt angle. The chemical nature of the contaminant can in some cases be identified by injection level spectroscopy. Implantation of heavy ions is mainly responsible for iron contamination; some other impurity (maybe cromium) is detected in boron-implanted wafers. From the point of view of device processing, the problem can be circumvented by implantation through a screening exide. Vice versa gettering techniques remove only a limited fraction of the contaminants introduced during the implantation.
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Maria Luisa Polignano, Maria Luisa Polignano, C. Bresolin, C. Bresolin, F. Cazzaniga, F. Cazzaniga, Anna Sabbadini, Anna Sabbadini, G. Queirolo, G. Queirolo, } "Investigation of metal contamination by photocurrent measurements: validation and application to ion implantation processes", Proc. SPIE 2638, Optical Characterization Techniques for High-Performance Microelectronic Device Manufacturing II, (18 September 1995); doi: 10.1117/12.221187; https://doi.org/10.1117/12.221187
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