In molecular layer deposition (MLD), the growth per cycle (GPC) depends on process conditions with no well-defined temperature window. During MLD of polyurea using toluene diisocyanate (TDIC) and ethylendiamine (ED) as MLD precursors, the GPC decreased with deposition temperature from 0.22 nm at 0 degrees C to 0.022 nm at 45 degrees C. While we observed the reaction of toluene diisocyanate with the underlying SiO2 at 45 degrees C, at 22 degrees C, in situ infrared spectroscopy indicates that the MLD film is not anchored to the substrate via covalent bonds. TDIC and ED displayed different temperature-dependent interactions with the growing polyurea film during MLD. Specifically, at lower temperatures, ED was more likely to be added to the film via physisorption, and as a consequence, TDIC was more likely to double react with both its functional groups to -NH2 sites within the film. While the lower GPC at higher temperature is driven predominantly by a decrease in ED physisorption, the rate of TDIC double reaction must also decrease due to the lower density of available reactive sites. As a result, at higher temperatures, both ED physisorption and TDIC double reactions are suppressed, and the ratio of polyurea linkages formed in each half-cycle was closer to unity. While the GPC was the highest at 0 degrees C, we also show that the films deposited at a lower temperature were unstable in both vacuum and the ambient and showed up to similar to 15% decrease in thickness, most likely due to the desorption of physisorbed precursor molecules.

We investigate antimony (Sb)-doped Czochralski-grown silicon as an alternative n-type substrate for photovoltaic applications, and characterize their axial resistivity distribution, donor properties, and mechanical strength. We find that Sb-doped ingots can achieve a more uniform resistivity distribution along the axial direction compared to P-doped counterparts. Dopant concentration profiles in P-doped ingots can be accurately modelled using the standard Scheil's equation, accounting only for dopant segregation during solidification. In contrast, modelling Sb-doped ingots requires consideration of both dopant segregation and evaporation effects to fit the dopant distribution accurately. Using electron paramagnetic resonance spectroscopy at 9 K, we observe two hyperfine lines in P-doped samples, and six hyperfine lines for Sb121 and eight for Sb123 isotopes, with the number of hyperfine lines governed by the nuclear spins. We further identify two-atom Sb clustering in the Sbdoped wafers, confirmed through simulations of the additional weak electron paramagnetic resonance peaks. Finally, we find that 140 mu m as-cut planar Sb-doped wafers exhibit slightly higher mechanical strength compared to P-doped wafers.

Monocrystalline Si (c-Si)-based photovoltaic devices created with passivating contacts basedon nonconductive dielectric layers, such as thick (>1.7 nm) silicon oxide, silicon oxynitride, or transition metal oxides, require some method to create conductive pathways for charge-carrier transport. These methods can range from the thermal breakup of oxides to wet chemistries that etch nanopores in the dielectric. In this work, we demonstrate a laser-based method to create conductive pinholes via selective localized melting of the tips of pyramids on randomly textured c-Si surfaces. This method of creating pinholes results in a minimal loss of surface passivation (<3 fA/cm(2) increase in J(0)) while enabling contact resistivities of <15 m Omega & centerdot;cm(2).

We report on the area-selective, O3 and O2-plasma-assisted atomic layer deposition (ALD) of SiO2 on plasma-deposited SiO2 with Cu as the nongrowth surface. Di-sec-butyl-aminosilane (DSBAS) was used as the Si precursor for SiO2 ALD. We studied the surface functionalization of Cu and the ALD process on bare and functionalized Cu surfaces using in situ reflection-absorption infrared spectroscopy (RAIRS). The Cu surface was functionalized at 100 °C using heptanethiol (HT) supplied from the gas phase. The native oxide on Cu promoted the uptake of HT and led to the formation of a multilayer hydrocarbon passivation layer. Since O3 and O2 plasma degraded the organic layer, the inhibitor was redosed during every cycle in a three-step A-B-C-type ALD process (A: HT; B: DSBAS; C: O3 or O2 plasma) performed at a substrate temperature of 100 °C. In situ RAIRS and X-ray photoelectron spectroscopy (XPS) show that combustion of the hydrocarbon passivation layer by O3 and O2 plasma leads to the formation of surface carbonates, and these were more readily formed during the O3-based process compared to the O2 plasma ALD process. Within the sensitivity of the RAIRS setup, for both the ALD processes, surface -SiH3 groups were not detected after the DSBAS partial cycle. High-resolution XPS indicated some SiO2 growth and partial oxidation of the Cu surface after theA-B-C ALD processes. Approximately 5 nm of SiO2 was deposited on the SiO2 growth surface for both O3 and O2 plasma-assisted ALD with high selectivity. However, perfect growth selectivity could not be obtained due to the formation of surface carbonates.

During atomic layer etching, the selective surface prefunctionalization of plasma-deposited SiNx over SiO2 with benzaldehyde has been shown to effectively retard the etching of SiNx by accelerating the formation of an etch-stop layer: this, in turn, enhances the etch selectivity for SiO2 over SiNx. The uptake of benzaldehyde is lower if the SiNx surface has been pre-exposed to the atmosphere or an etching plasma. We demonstrate a H-2/Ar plasma pretreatment strategy to improve the uptake of benzaldehyde on a pre-etched SiNx surface. Using in situ attenuated total reflection Fourier transform infrared spectroscopy, we first show that surface treatment of as-deposited SiNx with Ar or H-2 plasmas reduces the surface reactivity to benzaldehyde most likely due to a loss of surface -NHx (x = 1, 2) groups. In contrast, surface pretreatment of the as-deposited SiNx surface with an Ar-diluted H-2 plasma largely retains the surface reactivity to benzaldehyde under optimal conditions. We then translate this H-2/Ar plasma pretreatment step to practical applications. We first remove a thin surface layer of SiNx with one ALE cycle, which consists of a C4F6/Ar plasma modification step followed by an Ar plasma activation step: this step mimics a SiNx surface that has been exposed to an etching plasma, which leaves a surface CFx residue. Using in situ infrared spectroscopy, we show that surface pretreatment with a H-2/Ar plasma under these optimal conditions can partially remove the CFx residue on the SiNx surface. We further show that H-2/Ar plasma treatment can restore benzaldehyde uptake to similar to 80% of that on an as-deposited surface. Finally, we show that after treating the pre-etched SiO2 surface with an H-2/Ar plasma, the SiO2 surface reactivity with benzaldehyde remains low, leading to an increase in the aldehyde attachment selectivity to pre-etched SiNx over SiO2 surfaces by similar to 50%, and a recovery of similar to 80% of that on as-deposited surfaces.

We assessed light- and elevated-temperature induced degradation (LeTID) in n-type Czochralski (Cz) Si wafers, and industrial tunnel oxide passivating contact (TOPCon) Si solar cells processed with and without the laser-enhanced contact optimization (LECO). A recovery pre-treatment at 20 °C under 2 sun improved wafer and TOPCon cell performance, after which the samples were subjected to LeTID at 120–130 °C under 1 sun. P- and Sb-doped Cz Si wafers showed similar recovery and LeTID behavior, whereas As-doped wafers exhibited higher recovery and degradation, likely due to the differences in grown-in intrinsic defect concentrations. Liquid surface passivation confirmed that changes in the lifetimes during recovery pre-treatment and LeTID are due to the changes in defects in the bulk. Lifetime analysis suggests defects responsible for recovery are either shallow-level defects, or deep-level defects with higher capture cross-section for electrons than holes. The defect responsible for LeTID in n-type Cz Si appears similar in properties to that known in p-type Cz Si. In TOPCon cells that were fired with a higher cooling rate of ∼100 °C/s, LeTID reduced photoconversion efficiency by up to 0.7% absolute. These cells, if processed with LECO, showed smaller changes in device performance parameters during recovery and LeTID. When these TOPCon cells were fired with a slower cooling rate of ∼30 °C/s, performance shifts were minimal. For another fully metallized cell with LECO obtained from an industrial production line, performance shifts were minimal and remained within typical warranty tolerances after LeTID, indicating incorporation of mitigation strategies in current manufacturing.

During SiN x etching with HF plasma, ammonium fluorosilicate (AFS) forms as a transient byproduct significantly influencing the etch behavior. While AFS formation during SiN x etching has been known for several decades, the underlying mechanism for its formation and removal remains unclear. In this study, we have used in situ attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy to study the changes in the chemical boning on the SiN x surface during reactive ion etching, along with the AFS formation and removal dynamics. We have also identified the reaction products generated in the plasma using in situ quadrupole mass spectrometry. For applications such as etching of alternating stacks of SiO 2 and SiN x for the fabrication of 3-D NAND memory devices, it is desirable to etch SiN x and SiO 2 at approximately the same rate. Our initial hypothesis is that AFS formation accelerates the etching of SiN x compared to SiO 2 . Therefore, to promote the etching of SiO 2 we nitrided the surface with an NH₃ plasma to create surface Si-NH x ( x = 1, 2) species (see Fig. 2a). Subsequent HF plasma exposure revealed AFS formation on the SiO 2 surface (Fig. 2b), but it lowered the SiO 2 etch rate compared to the untreated surface. Therefore, to accelerate the etch rate of SiO 2 in a HF plasma, we will report on other process parameters including the average ion energy during etching and surface nitridation, effect of diluents in the gas phase, and the substrate temperature.

During reactive ion etching of SiNx in fluorine-based plasmas where HF is produced through a combination of gas-phase and surface reactions, ammonium fluorosilicate (AFS) has been reported to form on the SiNx surface. However, the underlying mechanism for AFS formation and its role in SiNx etching is still unclear, particularly during etching under energetic ion bombardment. In this work, using in situ attenuated total reflection Fourier-transform infrared spectroscopy, we show that during SiNx etching with a CH2F2/Ar plasma, when the substrate was at room temperature at a bias voltage of −240 V, an etch stop occurred with the simultaneous accumulation of graphitic hydrofluorocarbon and AFS on the SiNx surface. Under nominally similar conditions in a CH2F2/Ar plasma, but with the substrate at 70 or 120 °C, no etch stop was observed along with the absence of hydrofluorocarbon and AFS. By eliminating the formation of a graphitic hydrofluorocarbon layer in a SF6/H2 plasma, also at a bias voltage of −240 V, we reveal that AFS accumulation does not necessarily lead to an etch stop, and a steady-state thickness of AFS appears on surface as a result of a balance between AFS formation due to SiNx etching and AFS decomposition due to the impingement of energetic ions and H radicals. The effect of the substrate bias voltage on the etch behavior and surface composition was also studied in CH2F2/Ar and SF6/H2 plasmas. Our results show that the AFS is likely mixed with the underlying SiNx film under energetic ion bombardment instead of being present as a well-defined uniform layer. As a result, the presence of AFS does not necessarily lead to an etch stop. AFS formed on the SiNx surface decomposed when exposed to H radicals generated in H2 plasma under self-bias. Therefore, we conclude that the H radicals can play a dual role where they facilitate AFS formation by scavenging F radicals to form HF, but can also directly remove AFS formed on the surface. Finally, the slow removal of AFS by increasing the temperature to 70 °C suggests that AFS accumulation can be controlled with the substrate temperature.

The next-generation silicon photovoltaics will be based on passivating electron- and hole-selective contacts with both very low interface recombination and contact resistivities. While the emerging mainstream TOPCon technology has developed excellent electron-selective poly-Si/tunneling SiOx contacts, hole-selective contacts, especially on textured surfaces, have remained a significant challenge. This contribution introduces novel high-performance hole selective poly-Si contacts on pyramid-textured Si, enabled by electrochemically produced hole transport nanopinholes in a 10 nm oxynitride passivating dielectric stack capped by p + poly-Si. The highly passivating oxynitride layer is produced via atomic intermixing of O and N atoms in the initial SiOx/SiNy layer stack upon thermal annealing. Carrier transport is governed by nanopinhole density and size are tuned by Ag nanoparticle electrodeposition and surface attachment chemistries. This results in passivating hole contact resistivities in the m Omega-cm2 range, while preserving interface recombination current prefactor around 5 fA/cm2.

The next‐generation silicon photovoltaics will be based on passivating electron‐ and hole‐selective contacts with both very low interface recombination and contact resistivities. While the emerging mainstream TOPCon technology has developed excellent electron‐selective poly‐ Si/tunneling SiO x contacts, hole‐selective contacts, especially on textured surfaces, have remained a significant challenge. This contribution introduces novel high‐performance hole selective poly‐ Si contacts on pyramid‐textured Si, enabled by electrochemically produced hole transport nanopinholes in a 10 nm oxynitride passivating dielectric stack capped by p + poly‐ Si. The highly passivating oxynitride layer is produced via atomic intermixing of O and N atoms in the initial SiO x /SiN y layer stack upon thermal annealing. Carrier transport is governed by nanopinhole density and size are tuned by Ag nanoparticle electrodeposition and surface attachment chemistries. This results in passivating hole contact resistivities in the mΩ‐cm 2 range, while preserving interface recombination current prefactor around 5 fA/cm 2 .

We report on the degradation and recovery of surface passivation of fired poly-Si/SiOx passivating contacts with hydrogen containing Al2O3 during annealing in the dark and under illumination. Upon firing to a peak temperature of 670 degrees C, the iVoc for symmetric test structures with n+, p+, and intrinsic poly-Si/SiOx contacts decreases due to a loss of surface passivation. Upon further annealing over the temperature range of 200-350 degrees C in the dark, depending on the type of doping, the surface passivation either shows further degradation followed by recovery, or direct recovery to the initial iVoc. Annealing at higher temperatures and/or higher illumination intensities accelerates the kinetics for both degradation and recovery processes. We show that the degradation and recovery processes are thermally activated and proceed identically in subsequent firing and annealing steps showing their cyclic nature. We present a series reaction model to explain the kinetics of degradation and recovery processes for n+ and intrinsic poly-Si/SiOx contacts. By fitting the model's rate expressions to the data, the determined effective activation energy barriers for degradation and recovery for n+ poly-Si/SiOx contacts in the dark are 1.24 and 1.51 eV, which are lowered under 7.5 Suns illumination to 0.76 and 1.15 eV, respectively.

Molecular layer deposition (MLD) is of interest as a technique for growing ultrathin polymeric films for various applications. However, the basic surface adsorption and reaction process are still not well understood, leading to challenges in achieving high growth rates and good reproducibility. This study uses in situ Fourier-transform infrared spectroscopy in combination with in situ ellipsometry to better understand the initial stages of MLD of polyurea. 1,4 diisocyanatobutane (DICB) and diethylene triamine (DETA) were used as MLD precursors, and polyurea was grown through the reaction between an isocyanate group supplied by DICB and an amine group supplied by DETA. The growth per cycle was fit from ellipsometry measurements to be 0.022 nm/cycle. Film growth was also confirmed by infrared spectroscopy, which showed isocyanate groups being alternately added and consumed during the DICB and DETA half-cycles. Amide I/II modes increased in absorbance with every half-cycle as polyurea linkages were formed between incoming molecules and the growing film. We show that although some surface reactive sites are terminated during film deposition, new sites are introduced by precursor physisorption. Furthermore, we show that different precursors have different rates of double reaction and physisorption, highlighting the complex interactions between the molecular precursors and the growing film. DICB has a high rate of double reactions and a low rate of physisorption, as evidenced by the loss of isocyanate sites throughout initial stages of growth. To maintain linear film growth, DETA physisorbs into the film, thereby adding new amine sites for incoming molecules to react with. These results provide useful insight into mechanisms that control the MLD of thin films.

The reactive ion etching (RIE) of SiNx is commonly realized with fluorocarbon plasmas. During RIE, a carbon-rich CFx film typically accumulates on the surface, which controls the etch rate. Using in situ attenuated total reflection Fourier transform infrared spectroscopy, we show that O-2 dilution of a C4F6/Ar plasma prevents the continuous built-up of a CFx film during RIE, resulting in linear etching of SiNx. Using in situ ellipsometry and ex situ x-ray photoelectron spectroscopy, we established a relationship between the surface bonding on SiNx and the steady-state etch rate in C4F6/O-2/Ar plasmas with varying O-2 to C4F6 flow rate ratios at substrate temperatures of 70 and 120 degrees C. Two distinct regimes for O-2 dilution were identified: at low O-2 to C4F6 ratios, the etch rate is governed by the thickness of the surface CFx layer, while the mixing layer composition dominates etching at higher O-2 to C4F6 ratios. At both substrate temperatures, the SiNx etch rate increases dramatically with increasing O-2 to C4F6 flow rate ratios, but beyond a ratio of 0.75, there is a much more gradual increase in the SiNx etch rate with increasing O-2 dilution as the CFx layer becomes much thinner. We also observed different temperature dependence for the etch rate of SiNx in the low and high O-2 dilution regimes: the etch rate was lower at 70 degrees C than at 120 degrees C for low O-2 dilutions, but the trend reversed for higher O-2 dilutions. A possible explanation for this phenomenon is that a higher sticking coefficient for CxFy radicals at 70 degrees C leads to the formation of a thicker CFx film on the SiNx surface at lower O-2 dilutions, resulting in a slower etching in the CFx layer-dominated regime. In the high O-2 dilution regime where the etch behavior is governed by the supply of etchants, a higher sticking coefficient for the CxFy radicals at 70 degrees C leads to a higher etch rate than at 120 degrees C for the same O-2 to C4F6 flow rate ratio.

Monocrystalline silicon solar cells can achieve photoconversion efficiencies exceeding 26%; however, performance-limiting defects that trap carriers continue to be a challenge. In this work, we have characterized Si solar cells with tunneling SiOx/polycrystalline-Si (poly-Si) passivating contacts (TOPCon) on As-doped Czochralski Si wafers with electrically detected magnetic resonance (EDMR) spectroscopy. We fabricated 2 × 20 mm2 TOPCon-like mini solar cells with edge passivation alongside larger 4 cm2 sister cells and obtained similar device characteristics. We performed EDMR spectroscopy at 300 K on two minicells with different degrees of surface passivation based on the recombination parameter, Jo, values of 40 and 310 fA/cm2. We optimized the resolution and the signal-to-noise ratio of the EDMR response of the minicells by varying the forward bias voltage and the magnetic field modulation amplitude. We detect two distinct signals with EDMR spectroscopy, an axial-like signal at g = 2.009, 2.0087, and 2.0015, and an isotropic signal at g = 2.0024, which we attribute to Si dangling bonds (Pb0 and Pb centers) and boron–oxygen related defects, respectively, at or near the c-Si/SiOx interface. The EDMR signals were lower for the cell with a lower value of Jo, while the ratio of the two defect populations was very similar. The EDMR signal increases with forward bias but drops to zero at bias voltages >0.5 V, consistent with interface defects within or near the boron-doped emitter depletion region. Our study demonstrates a method to fabricate minicells that can be characterized with EDMR spectroscopy to detect industrially relevant defects in TOPCon cells.

While different methods exist to determine the contact resistivity in semiconductor devices, these methods are limited to measurement of the majority carrier contacts. The measurement of p‐ or n‐type contacts on n‐ or p‐type crystalline silicon, respectively, is challenging due to the blocking diode formed by the p–n junction. In this article, we address this problem for tunneling oxide passivating contacts used in high‐efficiency Si solar cells. We propose a universal method to extract contact resistivity on symmetric test structures with polycrystalline silicon on SiO x (poly‐Si/SiO x ) passivating contacts under illumination, both for p–n and high–low‐junction passivated contacts. In this method, we demonstrate that the total contact resistance of each cell grid finger to the base wafer is governed by its effective contact area, defined by the transfer length extending from both sides of the finger. Therefore, the grid contact resistance of a poly‐Si contact depends on the ratio of the doped poly‐Si sheet resistance to the tunneling contact resistivity.

We report on the influence of the areal density of reactive surface sites and the growth temperature on the growth per cycle (GPC) during O2-plasma-assisted atomic layer deposition (ALD) of SiO2 using di-sec-butylaminosilane (DSBAS) and dimethylamino trimethylsilane (DMATMS) as precursors. The surface reactions during ALD were monitored using in situ attenuated total reflection Fourier transform infrared spectroscopy. ALD was performed on plasma-deposited SiO2 films, and as the deposition temperature was increased from 100 to 500 °C, the areal density of isolated surface Si-OH groups decreased by a factor of ∼ 8. At 100 °C, ∼ 30% more surface Si-OH groups reacted with DMATMS than DSBAS. This shows that in the first ALD half-cycle, the initial aminosilane coverage is determined by the size of the aminosilane ligand, which reacts with surface Si-OH groups to form an alkylamine as the reaction product. However, in situ ellipsometry shows that the steady-state GPCs for DMATMS and DSBAS at 100 °C were ∼ 1.3 and ∼ 1.8 Å, respectively, which shows that the initial surface coverage of these precursors does not influence the GPC. As the plasma deposition and ALD temperatures were increased from 100 to 500 °C, the GPC for ALD of SiO2 with DSBAS decreased from ∼ 1.8 to ∼ 1.0 Å due to a lower steady-state surface Si-OH density during ALD at higher temperatures. We further show that for DSBAS and DMATMS, a 500 °C preheat step did not influence the GPC. Finally, we attribute the higher GPC for ALD of SiO2 with DSBAS versus DMATMS to a higher efficiency for the formation of surface Si-OH from surface -SiH3 groups versus surface -Si(CH3)3 groups during O2 plasma exposure.

In monocrystalline Si (c-Si) solar cells, identification and mitigation of bulk defects are crucial to achieving a high photoconversion efficiency. To spectroscopically detect defects in the c-Si bulk, it is desirable to passivate the surface defects. Passivation of the c-Si surface with dielectrics such as Al2O3 and SiNx requires deposition at elevated temperatures, which can influence defects in the bulk. Herein, we report on the passivation of different Czochralski (Cz) Si wafer surfaces by an organic copolymer, Nafion. We test the efficacy of the surface passivation at temperatures ranging from 6 to 473 K to detect bulk defects using electron paramagnetic resonance (EPR) spectroscopy. By comparing with state-of-the-art passivation layers, including Al2O3 and liquid HF/HCl, we found that at room temperature, Nafion can provide comparable passivation of n-type Cz Si with an implied open-circuit voltage (iVoc) of 713 mV and a recombination current prefactor J0 of 5 fA/cm2. For p-type Cz Si, we obtained an iVoc of 682 mV with a J0 of 22.4 fA/cm2. Scanning electron microscopy and photoluminescence reveal that Nafion can also be used to passivate the surface of c-Si solar cell fragments scribed from a solar cell module by using a laser. Consistent with previous studies, analysis of the EPR spectroscopy data confirms that the H-terminated surface is necessary, and fixed negative charge in Nafion is responsible for the field-effect passivation. While the surface passivation quality was maintained for almost 24 h, which is sufficient for spectroscopic measurements, the passivation degraded over longer durations, which can be attributed to surface SiOx growth. These results show that Nafion is a promising room-temperature surface passivation technique to study bulk defects in c-Si.

Poly-Si/SiOx passivating contact silicon solar cells have reached very high efficiencies. The PV industry is rapidly moving from the conventional passivated emitter and rear contact cell (PERC) to the Tunnel oxide passivating contact cells (TOPCon). With the remarkable efficiencies and market share shift, the imperative now moves towards determining the long-term stability of passivating contacts cells including both polarities of the poly-Si/SiOx contacts. Several studies have identified a low temperature degradation/regeneration mode in n+ poly-Si contacts post firing. In this work we investigate the underlying factors contributing to the degradation of both n+ and p+ poly-Si/SiOx passivating contacts for n-type Cz silicon solar cell, by exploring the hypothesis that the degradation is caused by the formation of pinholes in the tunneling oxide layer.