Detection of copper contamination in silicon by surface photovoltage diffusion length measurements

Abstract

Surface photovoltage minority carrier lifetime/diffusion length analysis of copper contaminated silicon was performed. It was observed that copper and copper associated defects degrade minority carrier lifetime more in n-type than in p-type silicon. This finding is explained by analysis of copper related defect levels identified by other deep level transient spectroscopy studies. In copper contaminated p-type silicon, an optical or thermal activation procedure significantly degrades the diffusion length. A process similar to that of Fe–B in p-type silicon is proposed. The activation process dissociates the Cu–Cu pairs, a weak recombination center in p-type silicon, and the copper forms extended substitutional defects in silicon, which have much greater recombination activity. No recovery of diffusion length was observed following such an activation procedure. The difference in copper and iron diffusion length recovery properties after activation can be used to differentiate iron contamination from copper contamination.

Recombination activity of light-activated copper defects in p-type silicon studied by injection- and temperature-dependent lifetime spectroscopy

“…Early contributions attributed Cu-LID to the dissociation of a recombination inactive pure copper complex, which was long presumed to be Cu s Cu i pair, and the subsequent formation of highly recombination active Cu s complexes. 14,30 However, this reaction does not explain the aforementioned decrease of Cu þ i concentration during light-soaking. Moreover, DLTS studies on intentionally Cu contaminated material revealed the existence of two acceptor energy states located at E v þ 0:41…0:45 eV [31][32][33][34] and E c À 0:16 eV 24 and a donor energy level at E v þ 0:22 eV, 24,35 which were later associated with the substitutional copper defect.…”

“…6,7 This phenomenon is referred to as copper-related light-induced degradation (Cu-LID), and it has been suggested to arise from increased bulk recombination [8][9][10] caused by copper precipitation 11,12 or substitutional copper complexes. [13][14][15] Nevertheless, the recombination mechanisms at Cu-LID defects still remain unclear, and the current literature information is lacking in an accurate parametrization of the recombination activity of such defects. Therefore, it is important to determine the recombination parameters of Cu-LID defects in order to quantify their effect on minority carrier lifetime and predict their impact on the overall solar-cell performance.…”

Accelerated light-induced degradation for detecting copper contamination in p-type silicon

“…The Cu-LID has been confirmed to originate from bulk recombination, 5 which is proposed to be caused by copper precipitation 7 or substitutional copper release through copper complex dissociation during illumination. 8,9 The formed defects have been found to be stable at 200 C in wafers with initial interstitial copper concentration of 10 14 cm À3 . 10 In addition to copper defects, the involvement of boron and oxygen in the formation of a metastable recombinationactive defect (BO-LID) has been extensively reported as the major cause of degradation in low-resistivity boron-doped Czochralski (Cz) silicon.…”

Quantitative copper measurement in oxidized p-type silicon wafers using microwave photoconductivity decay

“…4 The recombination lifetime method is, therefore, not suitable as such for the detection of trace Cu contamination. Nevertheless, Henley et al 5,6 observed recently using surface photovoltage method that in copper contaminated samples optical or thermal activation decreases the diffusion length. They proposed that extended substitutional defects are formed as a result of the activation process.…”