Method for preparing aluminum oxide and aluminum nitride composite film by hot-wire assisted atomic layer deposition

Abstract

The application discloses a method for preparing an aluminum oxide and aluminum nitride composite film by hot-wire assisted atomic layer deposition, and steps of the method comprise the following: alternately introducing Al(CH3)3 and O3 or H2O / O3 according to a time sequence for depositing an aluminum oxide film to prepare a single-layer aluminum oxide film; adjusting a hot-wire surface temperature to 700-1200 DEG C, alternately introducing Al(CH3)3 and NH3 according to a time sequence for depositing an aluminum nitride film, cracking ammonia to generate a nitrogen active group by using a high-temperature hot wire, and preparing a single-layer aluminum nitride film. By changing the cycle number and sequence of deposition of the two kinds of films, the alternating deposition of the aluminum oxide and aluminum nitride films is realized, and thus a multilayer composite structure film is obtained. The atomic layer deposition technology and the high-temperature hot wire cracking technology are used, the AlN film with a high dielectric constant is introduced, the compactness of a passivation film can be effectively improved, and the interface and edge passivation effect of a photovoltaic cell and other devices is significantly improved.

Description

Technical Field

[0001] This application belongs to the field of thin film preparation technology, and in particular relates to a method for preparing alumina and aluminum nitride composite thin films by hot filament-assisted atomic layer deposition. Background Technology

[0002] With the widespread application of TOPCon (Tunnel Oxide Passivated Contact) solar cells in two-piece and four-piece processes, the laser cutting process can cause phenomena such as remelted silicon, microcracks, dislocation defects, and the collapse of the polycrystalline silicon layer and tunnel oxide layer at the edge of the cell, resulting in serious edge carrier recombination problems and reducing the photoelectric conversion efficiency of the cell.

[0003] To address the aforementioned edge recombination problem, the industry currently widely employs ALD (Atomic Layer Deposition) technology. This technology uses TMA (Trimethylaluminum, chemical formula Al(CH3)3) as the aluminum source and H2O (water) or ozone as the oxygen source to deposit aluminum oxide (AlO2) on the battery surface. x Water vapor films are used to improve passivation. However, conventional water-source alumina films have limited density, and water vapor molecules easily reside in the micropores and microcracks generated by laser cutting, causing edge leakage and oxidation of the metal electrodes. To further improve passivation and increase the density of the alumina film, although the passivation effect at the battery edges was improved to some extent after introducing ozone, the strong oxidizing properties of ozone led to accelerated oxidation of the metal electrodes on the battery surface. This unintended oxidation increased contact resistance, directly affecting the charge carrier collection capacity of the electrodes, and ultimately limiting further improvement in the overall battery performance.

[0004] Therefore, existing thin film deposition processes face a contradiction between "improving the passivation effect of the thin film" and "protecting the metal electrode". There is an urgent need to develop a new passivation thin film preparation method that can provide excellent and dense passivation effect without aggravating the oxidation of the metal electrode. Summary of the Invention

[0005] The purpose of this application is to provide a method for preparing alumina (AlO) by hot-wire assisted atomic layer deposition. x The method of combining aluminum nitride (AlN) with aluminum nitride (AlO) composite films, inheriting the AlO... x Building upon the advantages of thin-film passivation, this paper introduces AlN thin films with high dielectric constants, transforming the current single AlO₂... x The passivation film was adjusted to AlO x / AlN / AlO x AlO with sandwich structure and multilayer composite structure x / AlN / … / AlO x The passivation film significantly improves the passivation effect.

[0006] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows: This application provides a method for preparing alumina and aluminum nitride composite films by hot-wire assisted atomic layer deposition, including the following steps: (1) Substrate pretreatment: If the substrate is a single-crystal silicon wafer with a doped layer or an intrinsic poly-Si thin film deposited, the substrate is pretreated by cleaning and degassing. If the substrate is a TOPCon or BC cell that requires edge passivation, the substrate edges are aligned and anti-wrapping plating isolation protection is applied. Then, an intrinsic amorphous silicon thin film prefabricated layer of a certain thickness is deposited on the edge of the cell using hot wire vapor deposition technology or low pressure vapor deposition technology. (2) AlO x Thin film deposition: Using Al(CH3)3 as the aluminum source and O3 or H2O / O3 as the oxygen source, Al(CH3)3 and O3 or H2O / O3 are alternately introduced according to the atomic layer deposition sequence of alumina thin films to prepare a monolayer AlO on the substrate. x film; (3) AlN thin film deposition: Adjust the pulse duty cycle or power output of the hot wire heating power supply to make the surface temperature of the hot wire reach 700-1200℃. Use Al(CH3)3 as aluminum source and NH3 decomposed by the hot wire at high temperature as nitrogen source. Al(CH3)3 and NH3 are alternately introduced according to the atomic layer deposition sequence of aluminum nitride thin film. NH3 decomposes into nitrogen active groups through the hot wire at high temperature to prepare a single layer AlN thin film. (4) Multilayer composite film deposition: Repeat steps (2) and (3) above, by changing the deposition of AlO x The number of cycles for AlO and AlN thin films to achieve AlO x AlO was prepared by alternating deposition of Al and AlN, resulting in multilayer composite structures of varying thicknesses. x / AlN / AlO x or AlO x / AlN / … / AlO x The film is the composite film of aluminum oxide and aluminum nitride.

[0007] Optionally, in step (3), the surface temperature of the hot wire is changed by adjusting the pulse duty cycle or power output of the hot wire heating power supply to control the thermal decomposition efficiency of NH3.

[0008] Optionally, in step (4), a three-layer composite structure AlO is prepared. x / AlN / AlO xThe specific process for thin films includes reducing the vacuum level in the deposition chamber to 1×10⁻⁶. -3 Below Pa, the substrate temperature is heated to 150-350℃, and argon gas is introduced to maintain the vacuum degree of the deposition chamber at 0.1-10.0 Pa. Al(CH3)3 and O3 or H2O / O3 are alternately introduced according to the atomic layer deposition sequence of alumina thin film, and 2-8 nm AlO is prepared after 20-80 cycles. x Thin films: Adjust the duty cycle or power output of the hot filament heating power supply to achieve a hot filament surface temperature of 700-1200℃. Al(CH3)3 and NH3 are alternately introduced according to the atomic layer deposition sequence of aluminum nitride thin films. NH3 is decomposed by the high-temperature hot filament to release nitrogen-active groups. After 100-200 cycles, a 10-20 nm AlN thin film is prepared. Al(CH3)3 and O3 or H2O / O3 are alternately introduced according to the atomic layer deposition sequence of alumina thin films. After 20-80 cycles, a 2-8 nm AlO thin film is prepared. x Thin film, thereby obtaining a three-layer composite structure of AlO x / AlN / AlO x film.

[0009] Optionally, in step (4): by changing the deposited AlO x By varying the number of cycles and the alternation sequence of AlN, multilayer composite structures of AlO with different thicknesses were prepared. x / AlN / AlO x or AlO x / AlN / … / AlO x film.

[0010] Optional, substrate pretreatment, specifically including: After cleaning and drying, the substrate was placed on the sample holder in the deposition chamber. The vacuum dry pump and molecular pump were then turned on sequentially to achieve a vacuum level of 1.0 × 10⁻⁶ in the deposition chamber. -3 Below Pa, heat the substrate to 150°C and degas the substrate for half an hour.

[0011] Compared with the prior art, the beneficial effects of the embodiments of this application are: The method for preparing alumina and aluminum nitride composite films by hot-wire assisted atomic layer deposition provided in this application uses Al(CH3)3 as the aluminum source, O3 or H2O / O3 as the oxygen source, and NH3 from high-temperature hot-wire decomposition as the nitrogen source. This method modifies the atomic layer deposition of AlO2. x The number of cycles with AlN is used to alternately grow AlO composite structures on the substrate. x / AlN / AlO x or AlO x / AlN / … / AlO xMultilayer thin films significantly improve passivation performance, offering promising applications for photovoltaic cells and optoelectronic devices. Compared to single alumina films, this invention, by introducing AlN with a high dielectric constant, substantially enhances the passivation effect of the composite film. However, the high dielectric constant AlN film is prone to hydrolysis during growth, affecting the density of the composite film. Therefore, after atomic layer deposition of alumina, it is necessary to reduce the amount of residual H2O in the deposition chamber. O3 can be used to completely or partially replace H2O, resulting in composite films with different passivation effects. Furthermore, the multilayer composite structure significantly reduces the number of deposition cycles containing water vapor molecules, effectively solving the problem of water vapor retention and leakage. Simultaneously, the use of ammonia pyrolysis technology not only avoids pinhole defects caused by plasma deposition, endowing the composite film with high density and eliminating the need for annealing, but the hydrogen (H) produced by its pyrolysis can also effectively reduce the oxide layer on the surface of the metal electrode, further improving electrode contact performance. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a schematic diagram of the deposition chamber structure and the high-temperature hot wire ammonia cracking in this invention.

[0014] Figure 2 Atom layer deposition of AlO2 was shown. x Thin film timing diagram.

[0015] Figure 3 The timing diagram of atomic layer deposition of AlN thin films is shown.

[0016] Figure 4 This is a SEM image of the surface morphology of a laser-cut silicon-based solar cell in a related technology.

[0017] Figure 5 These are SEM images of the front and cross-section surfaces of a battery with a deposited polycrystalline silicon layer in related technologies. Detailed Implementation

[0018] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0019] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0020] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0021] Currently AlO x For thin films used on silicon wafer edges, AlO is often prepared using TMA and H2O. x The thin film, due to the use of water vapor as an oxygen source, suffers from leakage current in the laser-cut micropores caused by water vapor molecules remaining there, affecting edge passivation and thus impacting AlO₂. x The passivation effect, coupled with the oxidation of metal electrodes by the resident water vapor molecules, increases the contact resistance and directly affects the photoelectric conversion efficiency of solar cells.

[0022] The method for preparing alumina and aluminum nitride composite thin films by hot-wire assisted atomic layer deposition provided in this application has the following characteristics and effects: 1) Solving the problem of water vapor source molecule retention: This application uses O3 to completely or partially replace H2O, eliminating or reducing the retention of water vapor source molecules. Of course, O3 will oxidize the electrode, since AlO x The film layer only undergoes 20-80 cycles, which is a short time, so the oxide film layer is relatively thin. In addition, during the AlN preparation process, the hot wire decomposes NH3 to generate H, which can effectively reduce the oxide film layer and improve the contact performance of the metal electrode.

[0023] 2) Improved passivation effect: Introducing AlN films with high dielectric constants can effectively improve the passivation effect. Generally, AlN is used for passivation in single-layer applications. AlO₂, lacking a multilayer composite structure, offers a different approach. x / AlN / AlO x As reported in the passivation layer section, sandwich and AlO were therefore used. x / AlN / … / AlO x The novel composite structure has significant technical benefits for passivation.

[0024] 3) AlN preparation uses PECVD to dissociate NH3 or N2 to generate an N source. However, when Ar+ plasma bombards NH3 or N2, it generates many pinholes on the film surface, affecting the film density. After deposition, high-temperature annealing is required to eliminate these pinholes. This application, however, uses ammonia pyrolysis technology, which avoids pinhole generation on the film surface and eliminates the need for annealing, achieving the high density characteristic imparted by ALD technology. Therefore, the multilayer composite AlO2 structure... x / AlN / AlO x The passivation effect of the thin film can be significantly improved.

[0025] 4) Currently, most ALD devices are thermal ALD (T-ALD) and plasma ALD (PEALD), and there are no reports on hot wire ALD (HW-ALD) devices.

[0026] To illustrate the technical solution described in this application, specific embodiments are provided below.

[0027] Please see Figures 1 to 3 As shown in the embodiments of this application, a method for preparing an alumina / aluminum nitride composite thin film by hot-wire assisted atomic layer deposition is provided. This method employs hot-wire assisted ammonia pyrolysis and atomic layer deposition technology to deposit an AlOx / AlN / AlOx thin film on a pretreated substrate, including the following steps: (1) Substrate pretreatment: If the substrate is a single-crystal silicon wafer with a doped layer or an intrinsic poly-Si thin film deposited, the substrate is pretreated by cleaning and degassing.

[0028] For example, the pretreatment includes: placing the cleaned and dried single-crystal silicon substrate onto the sample holder in the deposition chamber, and sequentially turning on the vacuum dry pump and the molecular pump to achieve a vacuum level of 1.0 × 10⁻⁶ in the deposition chamber. -3 Below Pa, heat the monocrystalline silicon substrate to 150°C and degas the monocrystalline silicon substrate for half an hour.

[0029] If the substrate is a TOPCon or BC cell that requires edge passivation, the substrate edges should be aligned and protected against wrapping. Since laser cutting can cause remelted silicon, microcracks, dislocation defects, etc., at the edges of the silicon wafer, hot filament vapor deposition or low pressure vapor deposition technology should be used to deposit an intrinsic amorphous silicon thin film prefabricated layer of a certain thickness on the edge of the cell.

[0030] (2) AlO x Thin film deposition: Reduce the vacuum level in the deposition chamber to 1×10⁻⁶. -3Below Pa, the substrate temperature is heated to 150-350℃, and argon gas is introduced to create a vacuum of 0.1-10.0 Pa in the deposition chamber. Al(CH3)3 and O3 or H2O / O3 are alternately introduced according to the atomic layer deposition sequence (TMA pulse time = 0.5-1s, TMA purge time = 2-6s, O3 or H2O / O3 pulse time = 0.5-2s, O3 or H2O / O3 purge time = 5-10s). After 20-80 cycles, AlO3 with a thickness of 2-8 nm is prepared. x film.

[0031] (3) AlN thin film deposition: Adjust the duty cycle or power output of the hot wire heating power supply to make the surface temperature of the hot wire 700-1200℃. Al(CH3)3 and NH3 are alternately introduced according to the atomic layer deposition sequence of aluminum nitride thin film (TMA pulse time = 0.5-1s, TMA purging time = 2-6s, NH3 pulse time = 0.5-2s, NH3 purging time = 5-12s). NH3 is decomposed by the high temperature hot wire to release nitrogen active groups. After 100-200 cycles, an AlN thin film of 10-20nm is prepared.

[0032] (4) AlO x Thin film deposition: Al(CH3)3 and O3 or H2O / O3 are alternately introduced according to the atomic layer deposition sequence (TMA pulse time = 0.5-1s, TMA purge time = 2-6s, O3 or H2O / O3 pulse time = 0.5-2s, O3 or H2O / O3 purge time = 5-10s), and Al(CH3)3 and O3 or H2O / O3 are prepared after 20-80 cycles to obtain AlO3 films with a thickness of 2-8nm. x Thin film. This method produces a three-layer composite AlOx / AlN / AlOx thin film.

[0033] In this embodiment of the application, the deposition of AlO2 can be changed. x The number of cycles for AlN can achieve AlO x AlO was prepared by alternating deposition of Al and AlN, resulting in multilayer composite structures of varying thicknesses. x / AlN / AlO x or AlO x / AlN / … / AlO x Multilayer thin film.

[0034] To further clarify the technical effects achieved by this application, a comparative analysis of the technical solution of this patent and related technical solutions is now conducted.

[0035] Figure 4 The SEM surface morphology of a laser-cut silicon-based solar cell in related technologies shows that the surface at the laser-cut area is relatively rough, with microcracks and micropores.

[0036] Figure 5 The SEM images show the front and cross-sectional surface morphology of a battery with a deposited polycrystalline silicon layer in a related technology. It can be seen that the thin film surface has obvious grain boundaries and a large number of microcracks. Figure 5 The left side shows the surface morphology of the front SEM image. Figure 5 The right side shows the surface morphology of the cross-section using SEM.

[0037] With the widespread application of two-piece and four-piece dicing processes in TOPCon and TBC solar cells, silicon wafer edge passivation has become a research hotspot. Since the interface of the diced silicon wafer is positively charged, a negatively charged thin film (Al₂O₃) needs to be deposited. x It carries a negative charge, while Si x N y and SiO x N y (Positively charged), therefore, the battery edge passivation industry uses AIO (Alternating Induction) technology. x For thin films, mainstream manufacturers currently use TMA and H2O as source atomic layer deposition methods for AlO2. x Thin film. When water vapor is used as an oxygen source, water vapor molecules will reside in the laser-cut micropores and microcracks on the battery surface (see...). Figure 4 , Figure 5 This caused partial leakage, affecting AlO. x The passivation effect, coupled with the oxidation of metal electrodes by the resident water vapor molecules, increases the contact resistance and causes fluctuations in the photoelectric conversion efficiency of solar cells.

[0038] The rationale behind this application is that the amount and duration of water vapor molecule introduction affect AlO₂. x The key reasons for passivation and electrode contact.

[0039] Analysis and verification of the proposed solution and its effects: 1) To reduce the amount of water vapor molecules introduced in a single cycle, this application uses O3 to completely or partially replace H2O; 2) Reduce the number of ALD deposition cycles containing water vapor molecules: Use 20nm AlO₂ as the substrate material used by battery manufacturers. x The passivation film, in this application, has been optimized to a 2nm AlO film. x / 18nmAlN / 2nmAlO x By significantly reducing AlO x Thin film thickness (i.e., reducing the number of ALD deposition cycles containing water vapor molecules) significantly reduces the amount and time of water vapor molecule introduction. 3) AlN passivation effect: The passivation effect of AlN thin films prepared by PEALD is higher than that of AlO by thermal ALD. x Therefore, the introduction of AlN with its high dielectric constant can effectively improve the edge passivation effect of silicon-based solar cells.

[0040] For example, Kiho Kong of Samsung Corporation published a paper titled "1-nm-thick epitaxial AIN passivation for highly efficient flexible InGaN red micro-LEDs" in Nature Communications on July 1, 2025. This paper demonstrates that by introducing AlN (PEALD deposition using TMA and plasma-derived NH3) instead of thermally deposited Al2O3 or SiO2 films, the external quantum efficiency of the micro-LEDs reached 6.5% at a wavelength of 649 nm, indicating that AlN has a strong passivation effect. Since PEALD produces many pinholes on the film surface, after 1-25 deposition cycles, Kiho Kong used plasma to heat the AlN film (450W for 40s) to eliminate the pinholes left by the plasma, which also improved the crystallinity of AlN.

[0041] 4) The AlN (HW-ALD deposition using TMA and hot-wire pyrolysis NH3 as sources) of this application does not produce pinholes on the film surface and does not require annealing, thus achieving the high density characteristics imparted by ALD technology. Therefore, the multilayer composite structure of AlN... x / AlN / A1O x It can effectively reduce the amount and time of water vapor molecules entering the electrode. In the AlN preparation process, the hot wire decomposes NH3 to generate H, which can effectively reduce the oxide film layer of the metal electrode and improve the contact performance of the metal electrode.

[0042] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for preparing alumina and aluminum nitride composite thin films by hot-wire assisted atomic layer deposition, characterized in that, Includes the following steps: (1) Substrate pretreatment: If the substrate is a single-crystal silicon wafer with a doped layer or an intrinsic poly-Si thin film deposited, the substrate is pretreated by cleaning and degassing. If the substrate is a multi-slice TOPCon or BC cell that requires edge passivation, align the substrate edges and perform anti-wrapping plating isolation protection. Then, use hot wire vapor deposition technology or low pressure vapor deposition technology to deposit an intrinsic amorphous silicon thin film prefabricated layer of a certain thickness on the edge of the cell. (2) AlO x Thin film deposition: Reduce the vacuum level in the deposition chamber to 1×10 -3 Below Pa, the substrate temperature is heated to 150-350℃, and argon gas is introduced to maintain the vacuum degree of the deposition chamber at 0.1-10.0 Pa. Using Al(CH3)3 as the aluminum source and O3 or H2O / O3 as the oxygen source, Al(CH3)3 and O3 or H2O / O3 are alternately introduced according to the atomic layer deposition sequence of alumina thin films. Specifically, the TMA pulse time is 0.5-1 s, the TMA purge time is 2-6 s, the O3 or H2O / O3 pulse time is 0.5-2 s, and the O3 or H2O / O3 purge time is 5-10 s. After 20-80 cycles, a 2-8 nm monolayer AlO3 is prepared on the substrate. x film; (3) AlN thin film deposition: The surface temperature of the hot filament is changed by adjusting the pulse duty cycle or power output of the hot filament heating power supply to control the thermal decomposition efficiency of NH3, so that the surface temperature of the hot filament reaches 700-1200℃. Al(CH3)3 is used as the aluminum source and NH3 decomposed by the high-temperature hot filament is used as the nitrogen source. Al(CH3)3 and NH3 are alternately introduced according to the atomic layer deposition sequence of aluminum nitride thin film, wherein the TMA pulse time is 0.5-1s, the TMA purging time is 2-6s, the NH3 pulse time is 0.5-2s, and the NH3 purging time is 5-12s. NH3 decomposes into nitrogen active groups through the high-temperature hot filament, and a 10-20nm monolayer AlN thin film is prepared after 100-200 cycles. (4) Multilayer composite thin film deposition: Repeat steps (2) and (3) above, by changing the deposited AlO x The number of cycles for AlO and AlN thin films to achieve AlO x AlO was prepared by alternating deposition of Al and AlN, resulting in multilayer composite structures of varying thicknesses. x / AlN / … / AlO x The film is the composite film of aluminum oxide and aluminum nitride.

2. The method for preparing alumina and aluminum nitride composite thin films by hot-wire assisted atomic layer deposition according to claim 1, characterized in that, Substrate pretreatment specifically includes: After cleaning and drying, the substrate was placed on the sample holder in the deposition chamber. The vacuum dry pump and molecular pump were then turned on sequentially to achieve a vacuum level of 1.0 × 10⁻⁶ in the deposition chamber. -3 Below Pa, heat the substrate to 150°C and degas the substrate for half an hour.

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