Investigation on the passivated Si/Al2O3 interface fabricated by non-vacuum spatial atomic layer deposition system

Abstract

. Investigation on the passivated Si/Al2O3 interface fabricated by non-vacuum spatial atomic layer deposition system, nano Online (2016). DOI: https://doi.org/10.1515/nano.11671_2015.154Originally published in: Shui-Yang Lien, Chih-Hsiang Yang, Kuei-Ching Wu, Chung-Yuan Kung. Investigation on the passivated Si/Al2O3 interface fabricated by nonvacuum spatial atomic layer deposition system, Nanoscale Research Letters. 10 (2015). DOI: https://doi.org/10.1186/s11671-015-0803-9Lien et al., 2015. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.Currently, aluminum oxide stacked with silicon nitride (Al2O3/SiNx:H) is a promising rear passivation material for high-efficiency P-type passivated emitter and rear cell (PERC). It has been indicated that atomic layer deposition system (ALD) is much more suitable to prepare high-quality Al2O3 films than plasma-enhanced chemical vapor deposition system and other process techniques. In this study, an ultrafast, non-vacuum spatial ALD with the deposition rate of around 10 nm/min, developed by our group, is hired to deposit Al2O3 films. Upon post-annealing for the Al2O3 films, the unwanted delamination, regarded as blisters, was found by an optical microscope. This may lead to a worse contact within the Si/Al2O3 interface, deteriorating the passivation quality. Thin stoichiometric silicon dioxide films prepared on the Si surface prior to Al2O3 fabrication effectively reduce a considerable amount of blisters. The residual blisters can be further out-gassed when the Al2O3 films are thinned to 8 nm and annealed above 650°C. Eventually, the entire PERC with the improved triple-layer SiO2/Al2O3/SiNx:H stacked passivation film has an obvious gain in open-circuit voltage (V oc) and short-circuit current (J sc) because of the increased minority carrier lifetime and internal rear-side reflectance, respectively. The electrical performance of the optimized PERC with the V oc of 0.647 V, J sc of 38.2 mA/cm2, fill factor of 0.776, and the efficiency of 19.18% can be achieved.Keywords: PERC; Non-vacuum spatial atomic layer deposition; Al2O3/SiNx:H stacked rear passivation; Blister; Triple-layer SiO2/Al2O3/SiNx ; H stacked passivation films BackgroundFor the past decade years, dielectric films have become promising materials applied in high-efficiency silicon solar cells due to their superior surface passivation effect.An attractive candidate for outstanding Si surface passivation is aluminum oxide (Al2O3), which can be deposited by physical vapor deposition (PVD) system [ 1], chemical vapor deposition (CVD) system [2-4], liquid-phase deposition (LPD) technique [5,6], and atomic layer deposition (ALD) system [7][8][9]. Generally, ALD system is the most suitable choice for the deposition of Al2O3 owing to some advantages: (i) capable of producing very thin conformal and unif...

Efficient silicon nitride SiNx:H antireflective and passivation layers deposited by atmospheric pressure PECVD for silicon solar cells

“…Afterwards, rear‐side emitter removal process was performed, and the surfaces were cleaned by hot HNO 3 solution followed by HF‐Dip and DI water rinsing. For iV oc samples and PERC solar cells, a 6‐nm‐thick Al 2 O 3 layer was then deposited on the rear‐side by using ultrafast spatial ALD process . This step was followed by the so‐called outgassing process, which is a 10‐minute low temperature annealing under N 2 at 550°C performed mainly to avoid blistering of the rear‐side stack layer .…”

“…However, a high positive Q f present in the SiN x layer is found to be detrimental for the passivation of boron highly doped p + emitters on n‐type solar cell architectures or back surface field (BSF) present in p‐PERC or p‐PERT solar cell architectures, as it induces a depletion layer near the surface which increases the charge carrier recombination rate . Thus, the surface passivation of such p + emitter/BSF is generally realized by applying either ultrathin (<10 nm) silicon oxide (SiO x ) or aluminum oxide (AlO x ) layers, which are usually capped by a thicker protective SiN x film (70‐150 nm) . Particularly, AlO x /SiN x stacks lead to very low SRV (≤10 cm.s −1 ) on moderately doped n‐type and p‐type Si wafers and correspondingly low j 0e (≤ 50 fA.cm −2 ) on p + emitter/BSF .…”

“…Thus, the surface passivation of such p + emitter/BSF is generally realized by applying either ultrathin (<10 nm) silicon oxide (SiO x ) or aluminum oxide (AlO x ) layers, which are usually capped by a thicker protective SiN x film (70‐150 nm) . Particularly, AlO x /SiN x stacks lead to very low SRV (≤10 cm.s −1 ) on moderately doped n‐type and p‐type Si wafers and correspondingly low j 0e (≤ 50 fA.cm −2 ) on p + emitter/BSF . While ultrathin AlO x layers may be deposited by atomic layer deposition (ALD) or LP‐PECVD, the SiN x capping layer is usually deposited by LP‐PECVD.…”

“…For instance, PERC solar cells currently require three vacuum‐based processes for the deposition of the passivation layers: SiN x ARC on the front side and AlO x /SiN x passivation stack layers on the rear side . AlO x thin film providing high quality rear passivation properties can already be deposited at atmospheric pressure by using high‐throughput spatial ALD technique . However, a technological bottleneck for increasing the solar cell production throughput is the deposition of SiN x thin layers at atmospheric pressure conditions.…”

H2O/O2 Vapor Annealing Effect on Spin Coating Alumina Thin Films for Passivation of Silicon Solar Cells

“…Since some carriers recombine in the bulk and some recombine near the surface, carrier lifetimes could be improved after AlO x passivation owing to the reduction of surface recombination velocity or, in other words, the reduction of recombination rate of carriers on the surface of the wafers. Therefore, lifetime improvements were mainly attributed to the effect of AlO x passivation and can be explained by the elimination of the recombination centers including defects and dangling bonds at or near the surface owing to the formation of interfacial SiO x [22,23]. The increase of SiO x at the interface increases the passivation quality and can reduce dangling bonds by bonding of the oxygen atoms of SiO x with negatively charged Al atoms [24].…”