Influence of hydrogen on interstitial iron concentration in multicrystalline silicon during annealing steps

Abstract

The influence of in-diffusing atomic H into an annealed multicrystalline silicon (mc-Si) wafer on the concentration of interstitial iron [Fe i ] was investigated. Neighboring wafers with similar initial [Fe i ] were annealed with and without in-diffusing H. In-diffusion was realized by exposing the samples to a microwave induced remote hydrogen plasma at 400 C. [Fe i ] was detected based on lifetime measurements before and after dissociating the FeB complex. Surface passivation was achieved by a quinhydrone-methanol solution at room temperature to avoid further temperature steps or in-diffusion of H during surface passivation. From [Fe i ] measurements before and after the annealing steps with and without H, the influence of H alone on [Fe i ] could be accessed. The results were compared to previous experiments where the same SiN x :H layers were used as surface passivation for multiple [Fe i ] measurements of mc-Si samples before and after several anneals at 400 C. It could be shown that a H plasma atmosphere has a strong additional effect on the reduction of [Fe i ] compared to temperature effects alone. A formation of H-Fe i complexes associated with the passivation of the electrical activity of Fe i could be shown to be improbable because no depassivation of Fe i could be observed in subsequent annealing steps at 400 C.

Hydrogénation effect on low temperature internal gettering in multicrystalline silicon

“…They suggest that hydrogenation enhances the diffusivity of the bulk iron [17]. A similar finding is reported by Karzel et al [16]. However, a study was not performed on samples from different height positions in an ingot, which is important as the microstructures (particularly dislocation densities) vary significantly [15].…”

“…Recent studies by Liu et al [17], Karzel et al [16] and Leonard et al [30] provide evidence for hydrogen interacting with bulk iron. Our working assumption is that the hydrogen in Set I samples stabilizes bulk lifetime upon annealing at 400 °C.…”

“…They did not however report the effect on bulk lifetime in detail. Furthermore, it is possible that Krain et al's results were influenced by the hydrogenation effect due to silicon nitride passivation as reported in recent studies by Karzel et al and Liu et al [16,17]. In order to minimize a possible hydrogenation effect, we have recently performed a comprehensive study into low temperature internal gettering using a room temperature iodine-ethanol passivation scheme for samples from different height position of a commercially grown mc-Si ingot [14,15].…”

Gettering of interstitial iron in silicon by plasma-enhanced chemical vapour deposited silicon nitride films

“…Others have suggested that the reduction was due to the accelerated precipitation of iron driven by hydrogenenhanced iron diffusivity. 18 However, this hypothesis cannot explain the observed iron loss at higher annealing temperatures, at which the iron solubility limits were well above the dissolved iron concentrations in silicon, meaning that such an iron relaxation precipitation process should not proceed.…”

“…[13][14][15][16][17] The mechanism for this iron reduction has remained unresolved, and it has been hypothesised that it might be caused by the hydrogenation of iron in silicon. [13][14][15][16][17] This hypothesis was based on the reports that showed that the recombination activity and the concentration of interstitial iron in silicon were reduced after hydrogen incorporation, via exposure to hydrogen plasma, [18][19][20] hydrogen ion implantation, 21 wet chemical etching, 22 or deposition of PECVD silicon nitride films. 23 While there have been reports of the detection of new defect levels assigned to possible Fe-H complexes, [21][22][23] from theoretical calculations the binding energy of Fe-H pairs was found to be weak, 24 indicating the unlikelihood of the Fe-H pairs withstanding the relatively high temperatures used for firing.…”