Impact of Fe and Cu Contamination on the Minority Carrier Lifetime of Silicon Substrates

Abstract

The effects of trace amounts of Fe and Cu in p-and n-type silicon were investigated with microwave photoconductance decay and surface photovoltage. The wafers received controlled amounts of surface contamination of Fe and Cu that are relevant for ultralarge scale integrated technologies. The substrate doping type has a strong impact on the effect of the metallic impurities. Fe, as expected, strongly degrades the minority carrier lifetime of p-type substrates. On the other hand, the impact of Fe on n-type silicon is at least one order of magnitude lower than on p-type. In contrast, Cu is highly detrimental to n-type material, but has no significant impact on the minority carrier properties of p-type silicon for the contamination levels studied.

Surface photovoltage phenomena: theory, experiment, and applications

“…For high (low) values of S b , L is highly underestimated (overestimated) by L app . Unrealistically large and small apparent diffusion lengths correlated with low and high S b , respectively, have indeed been observed by several groups [429,513,547,548]. The demarcation line between the two phenomena lies at S b DaL, for which L app L, regardless of sample thickness.…”

“…63, changes in S can change the SPV magnitude as well as the slope of the linear curve used to extract L n , but not the intercept (and hence extracted L n ) value. The second advantage of the SPV technique is that it may be used in a contactless manner and that it is cheaper and more simple in both operation and interpretation than other contactless methods, e.g., microwave PCD ("PCD) [428,429]. The SPV technique is also easy to use due to the availability of an ASTM protocol.…”

“…In light of the clear advantages of SPV-based Fe-monitoring tools, it is no wonder that recent literature suggests that such tools are actively used or evaluated for in-line monitoring at many leading Si-technology centers, including, e.g., Hewlett-Packard [506], Hitachi [493], IMEC [429] SGSThomson [498], Advanced Micro Devices [507±511], Nortel [499], Philips Semiconductors [500], and more. SPV-based diffusion length monitoring and mapping in Si wafers has been used not only to assess Fe and Cr contamination, but also to assess the impact of a host of other technological steps, e.g., rapid thermal processing [512,513] and other annealing steps [514,515], gettering procedures [513,515,516], and plasma processes [496,506].…”

“…It is therefore clear that even if there is no direct excitation of the back part of the sample (i.e., condition (5.7c), 1a ( l, is maintained), the sample cannot be treated as semi-in®nite and the effects of the back surface must be taken into account. While Goodman plots made when condition (5.7c) is not valid frequently remain highly linear, it is clear that use of the simple equations (2.61) or (5.3) should yield an erroneous value of L. Indeed, comparisons between SPV and PCD [445,547], mPCD [429,430], or electrolytic metal tracing (ELYMAT) [430,548] measurements on Si indicated a very good agreement for large sample thicknesses and a poor one for sample thicknesses approaching the diffusion length. In recent years, this has become a more and more pressing problem, especially in industrially-oriented monitoring of Si wafers, due to the improvement in Si wafer quality.…”

Novel Characterization Technique for Oxidation Processes

“…About 75 % of iron is known to remain in the oxide layer even after hightemperature annealing at 1150 o C (5). Cu atoms have a tendency to diffuse almost totally into the p-type silicon bulk (3,5), while expected to pile up at the n-type Si/SiO 2 interface during annealing (6).…”