Detailed Investigation of Surface Passivation Methods for Lifetime Measurements on P-Type Silicon Wafers

Abstract

The effect of five different common surface passivation techniques on the measured bulk lifetime values of multiand monocrystalline p-type silicon wafers was investigated. Mono-[Czochralski (Cz) and floatzone (FZ)] and multicrystalline [mc and edge-defined film-fed growth (EFG)] silicon wafers were either deposited with a dielectric passivating layer of SiN x , Al 2 O 3 , or amorphous silicon (a-Si) or were passivated chemically with 0.08 M iodine-ethanol (IE) or 0.07 M quinhydrone-methanol (QM) solutions. The temporal stability of annealed and nonannealed Cz wafers that were passivated with QM and IE was tested. The lifetime values of EFG, mc, and FZ wafers that were subjected to repeated QM passivation and mc wafers that were subjected to IE passivation without a surface etching between passivations were found to decrease with each passivation. Lifetime values of a set of 11 mc wafers that were passivated with Al 2 O 3 were found to decrease about 30% after a period of four weeks in darkness. The decrease was reversible by annealing the samples. The lifetime values of annealed Cz samples that were passivated with Al 2 O 3 and a-Si were found to decrease by >20% within 5 h of annealing. Subsequent tests on 200-Ω·cm FZ material did (for a-Si) and did not (for Al 2 O 3 ) show surface passivation degradation over this time period. Neighboring mc wafers were passivated dielectrically or wet chemically with IE or QM and characterized with photoluminescence imaging. All mc wafers that were subjected to dielectric passivation methods that include annealing at 400 • C displayed a greater area of high lifetime values but fewer areas of very high lifetime values, providing visible evidence of internal gettering and/or defect redistribution.

Temporary Surface Passivation for Characterisation of Bulk Defects in Silicon: A Review

“…Takato et al provided an early report on the quinhydrone‐ethanol/methanol based passivation scheme, achieving a very low S of ≈4 cm s −1 on high resistivity p‐type silicon, one of the lowest reported for this passivation scheme . Only Pollock et al have demonstrated a lower S of 1.3 cm s −1 , however this measurement was also performed on high resistivity p‐type silicon . Chhabra et al demonstrated that a moderate level of surface passivation is retained when the silicon samples are taken out of the quinhydrone‐methanol solution .…”

“…Benzyl‐alcohol based passivation schemes are regarded as a viable alternative method to I‐E and I‐M methods and generally offer better stability . In general, three benzyl species have been examined, hydroquinone (HQ), ­p‐benzoquinone (BQ), and quinhydrone (QHY), where the latter is the combination of HQ and BQ.…”

“…In the surveyed literature for benzyl‐alcohol passivation, the favored wet chemical pre‐treatment is the piranha etch followed by a dilute HF dip . In contrast to halogen‐alcohol passivation, an S below 1 cm s −1 has not been reported for benzyl‐alcohol passivation, which could be a consequence of the relatively unexplored wet chemical pre‐treatment processes.…”

Investigation of Lifetime-Limiting Defects After High-Temperature Phosphorus Diffusion in High-Iron-Content Multicrystalline Silicon

“…1 with all images scaled to the same limits. The sample surfaces were passivated with quinhydrone methanol [22] for the measurement.…”

Impact of surface preparation prior to Al<inf>2</inf>O<inf>3</inf> deposition for i-PERC cells

“…The mechanism of the Al 2 O 3 passivation degradation is still not clear yet. Some previous works report such degradation and attribute it either to the formation of BO complexes in the Al 2 O 3 samples [23] either to the presence of moisture in air [24]. However, the mechanisms occurring at the interface between Si and this interfacial oxide/ Al 2 O 3 is still not fully understood yet and complementary works have to be led to determine the rootcause and prevent this degradation.…”