Room-temperature method for minimizing light-induced degradation in crystalline silicon

Abstract

Although light-induced degradation (LID) in crystalline silicon is attributed to the formation of boron-oxygen recombination centers, copper contamination of silicon has recently been observed to result in similar degradation. As positively charged interstitial copper stays mobile at room temperature in silicon, we show that the bulk copper concentration can be reduced by depositing a large negative charge onto the wafer surface. Consequently, light-induced degradation is reduced significantly in both low- and high-resistivity boron-doped Czochralski-grown silicon.

Formation kinetics of copper-related light-induced degradation in crystalline silicon

“…Another difference is that the lifetime does not recover during the final 210 C anneal, indicating that Cu-LID dominates the degradation in the intentionally contaminated Cz-Si samples. 10,12,13 From the saturated normalized defect density, the copper concentrations are estimated as 1.1Â10 14 cm À2 in the 0.5-ppm and 1.6 Â 10 14 cm À2 in the 1-ppm-contaminated low-res samples, respectively. 23 In the 1-ppm high-res samples, the copper concentrations is estimated as 1.2 Â 10 14 cm À2 , which is lower than the low-res sample density due to a thicker wafer.…”

“…12 However, the effect of Cu-LID has been shown to decrease after the deposition of a large negative surface, attracting Cu þ i from the bulk towards the sample surface. 13,14 During illumination of oxidized copper-contaminated Si, lifetime degradation has been measured together with a significant interface defect density increase, suggesting that surface passivation degradation is solely responsible for copper-related LID. 15 Cu-LID has since been proven to be a bulk effect, 16 but it is uncertain whether copper also affects surface passivation during illumination in corona-charged oxidized Si.…”

Preventing light-induced degradation in multicrystalline silicon

“…The negative corona charge is deposited at RT onto a high quality thermal oxide with low interface defect density, while the Al 2 O 3 charge is formed in the poorer Si/Al 2 O 3 interface during a yet unknown 25 process around 400 C. In addition, mitigating LID in Cz-Si requires a negative corona charge density $10 13 cm À2 on an oxidized wafer, 16 while typical Al 2 O 3 charge densities amount to $10 12 cm À2 . 25 In this article, we subject mc-Si wafers from different parts of the ingot to illumination in order to further understand the formation of LID in commercially available mc-Si.…”

“…16,17 The negative corona charge is assumed to move interstitial Cu þ i towards the wafer surface, 18,19 reducing the copper bulk concentration and preventing precipitation during illumination. Even though a large negative corona charge reduces LID in Cz-Si, the same effect may not occur in mcSi, since copper is thought to precipitate 20,21 easily in mc-Si already prior to illumination.…”

Light‐induced degradation in copper‐contaminated gallium‐doped silicon

“…The wafers were subsequently annealed for 20 min at 800 °C in a nitrogen atmosphere in order to diffuse the copper contamination into the wafer bulk. Finally, a positive corona charge was deposited on the wafers, in order to keep copper in the wafer bulk [12].…”