Amorphous silicon carbide thin film and its preparation method and application

Abstract

The application belongs to the technical field of solar cells, and relates to an amorphous silicon carbide film and a preparation method and application thereof. The preparation method comprises the following steps: providing a substrate; and depositing the amorphous silicon carbide film on the substrate by using a plasma enhanced chemical vapor deposition method. In the plasma enhanced chemical vapor deposition method, parameters include: a reaction gas comprising a silicon source and a carbon source, and an inert gas as a protective gas; the carbon source is propylene; and the flow rate ratio of the silicon source and the propylene is (1-5):(1-3). In the application, propylene is used as the carbon source, and the amorphous silicon carbide film is prepared in cooperation with the silicon source under the limitation of a specific flow rate ratio. On one hand, propylene can provide controllable carbon active groups, and it is easy to obtain a near-stoichiometric thin film. On the other hand, propylene has a decomposition tendency to generate unsaturated hydrocarbons, which can inhibit the hydrogen content to form a SiC network, reduce stress, and can reduce gas phase nucleation, reduce roughness, and be beneficial to obtaining a dense and uniform thin film.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology, specifically relating to an amorphous silicon carbide thin film, its preparation method, and its application. Background Technology

[0002] Back-contact solar cells, due to their absence of electrodes obstructing the front surface, exhibit high photoelectric conversion efficiency and are widely used in the photovoltaic field. An anti-reflection layer, a crucial component of back-contact solar cells, is placed on the light-receiving surface to reduce incident light reflection loss and passivate surface defects. Therefore, the material selection and structural design of the anti-reflection layer significantly impact the cell's performance.

[0003] Amorphous silicon-based thin films, such as amorphous silicon carbide (a-SiC), amorphous silicon nitride (a-SiNx), and their stacked structures, have been widely studied and applied to antireflection layers due to their excellent passivation effect and tunable optical properties.

[0004] For example, patent CN120456664A discloses a combined passivated back contact battery, including an N-type silicon wafer, a second intrinsic amorphous silicon layer, a microcrystalline silicon layer, and an antireflection layer sequentially disposed on the front side of the silicon wafer, and a second semiconductor opening region, a first semiconductor opening region, and a transition region disposed on the back side of the silicon wafer. The antireflection layer is a single-layer amorphous silicon carbonitride layer or a stacked structure composed of amorphous silicon carbide layer and amorphous silicon carbonitride layer. The second semiconductor opening region is composed of a first intrinsic amorphous silicon layer, a P-type amorphous silicon layer, a transparent conductive film, and a metal electrode sequentially disposed on the back side of the silicon wafer. The first semiconductor opening region is composed of a tunneling oxide layer, an N-type polycrystalline silicon layer, a transparent conductive film, and a metal electrode sequentially disposed on the back side of the silicon wafer. An opening is etched on the transparent conductive film surface of the transition region to form an insulating trench. Although this approach reduces reflection loss and improves battery reliability to some extent by introducing amorphous silicon carbide-based thin films as antireflection layers, it still has the following technical drawbacks in practical applications: 1) High film stress limits deposition thickness; the thickness of the amorphous silicon carbide layer is only 10-50 nm. Due to the large residual stress inside the film, when attempting to increase the thickness to improve passivation or optical matching, the film is prone to cracking or peeling; 2) Narrow refractive index adjustment range limits optical matching capability; the refractive index of the amorphous silicon carbide layer is only 2.01-2.2; 3) High surface roughness of the film not only increases light scattering loss but may also affect the interface contact of subsequent functional layers.

[0005] Therefore, how to effectively reduce the stress of amorphous silicon carbide thin films to achieve thick film deposition, while widening its adjustable refractive index range and reducing surface roughness, is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide an amorphous silicon carbide thin film, its preparation method, and its applications. This invention uses propylene as a carbon source in conjunction with a silicon source to prepare amorphous silicon carbide thin films via plasma-enhanced chemical vapor deposition (PECVD). Compared to conventional carbon sources, propylene exhibits superior reactivity in a plasma environment: Firstly, propylene can provide carbon-active groups in a more controllable manner, making it easier to match with a silicon source to achieve a near 1:1 stoichiometric ratio for silicon carbide thin film preparation, thereby broadening the adjustable range of refractive index; secondly, the decomposition pathway of propylene tends to generate unsaturated hydrocarbons rather than atomic hydrogen, effectively suppressing the hydrogen content in the film, promoting the formation of a more robust SiC network, significantly reducing the stress of the film, and facilitating the deposition of thick films; thirdly, the reactivity of propylene can effectively reduce the pre-formation tendency of powdery carbon particles in the gas phase, reducing the surface roughness of the film and contributing to obtaining high-quality silicon carbide thin films with uniform surface and excellent density. In summary, by introducing propylene as a carbon source, this invention achieves an optimal balance between deposition rate, carbon activity control, and film quality, providing a wider and more stable process window and effectively solving the technical problems of high film stress, narrow refractive index adjustment range, and high roughness in the prior art.

[0007] To achieve this objective, the present invention employs the following technical solution: In a first aspect, the present invention provides a method for preparing an amorphous silicon carbide thin film, the method comprising the following steps: Provide substrate; An amorphous silicon carbide thin film was deposited on the substrate using plasma-enhanced chemical vapor deposition. In the plasma-enhanced chemical vapor deposition method, the parameters include: the reaction gas includes a silicon source and a carbon source, and the protective gas is an inert gas; the carbon source is propylene; and the flow rate ratio of the silicon source to propylene is (1-5):(1-3).

[0008] It should be noted that methane is the most stable hydrocarbon with a high CH bond energy, making it difficult to decompose in plasma. This results in low carbon utilization efficiency and a slow deposition rate. Therefore, to obtain sufficient carbon incorporation into the film, high flow rates or power are often required, leading to a narrow process window. Acetylene is highly reactive, readily decomposing to provide a carbon source and achieving a fast deposition rate. However, precisely because of its high reactivity, it easily forms a large number of C2 groups and carbon clusters in plasma, resulting in excessive amorphous carbon (sp). 2 The carbon-rich film, embedded in the SiC network, has high hardness but also huge internal stress, making it easy to peel off and affecting its electrical and optical properties.

[0009] This invention uses propylene as a carbon source in conjunction with a silicon source to prepare amorphous silicon carbide thin films via plasma-enhanced chemical vapor deposition. Compared with conventional carbon sources, propylene exhibits superior reactivity in a plasma environment: First, propylene's reactivity lies between that of methane and acetylene. It decomposes more easily than methane, providing higher carbon utilization and deposition rate, while not being as reactive as acetylene to produce a large number of carbon clusters. Therefore, it can provide carbon-active groups in a more controllable manner, making it easier to match with a silicon source to achieve silicon carbide thin films with a stoichiometric ratio close to 1:1, thereby broadening the adjustable range of refractive index. Second, the decomposition pathway of propylene tends to generate unsaturated hydrocarbons rather than atomic hydrogen, effectively suppressing the hydrogen content in the film and promoting the formation of a more robust SiC network. This significantly reduces the stress of the film, which is beneficial for achieving thick film deposition. Third, the reactivity of propylene can effectively reduce the pre-formation tendency of powdery carbon particles (referred to as "dust") in the gas phase, reducing the surface roughness of the film and contributing to obtaining high-quality silicon carbide thin films with uniform surface and excellent density. In summary, by introducing propylene as a carbon source, this invention achieves an optimal balance between deposition rate, carbon activity control, and film quality, providing a wider and more stable process window and effectively solving the technical problems of high film stress, narrow refractive index adjustment range, and high roughness in the prior art.

[0010] In this invention, the flow ratio of silicon source to propylene is (1-5):(1-3), where the range of silicon source selection "1-5" can be, for example, 1, 2, 3, 4, or 5, and the range of propane selection "1-3" can be, for example, 1, 2, or 3. The flow ratio of silicon source to propylene has a significant impact on the refractive index of amorphous silicon carbide thin films. When the flow ratio of silicon source to propylene is too large, the film composition is silicon-rich amorphous silicon carbide (a-SiC:H), and even amorphous silicon (a-Si:H) clusters are embedded in the SiC network. Since the refractive index of amorphous silicon (a-Si) is very high (typically 3.5-4@633nm), and the refractive index of stoichiometric SiC is about 2.6-2.7, this is equivalent to "doping" a high-refractive-index a-Si phase into SiC, thereby increasing the overall average refractive index. When the flow ratio of silicon source to propylene is too small, the film composition is deposited as carbon-rich amorphous silicon carbide (a-SiC:C), and the film begins to contain more and more sp. 2 and sp 3 The bonded amorphous carbon (aC) phase exhibits a complex trend in refractive index variation: initially carbon-rich: when a small amount of excess sp begins to appear... 3 When carbon (similar to diamond, with a refractive index of approximately 2.4) is present, the refractive index may decrease slightly. Highly carbon-rich: when a large amount of sp... 2When carbon (graphite phase, with complex refractive index and high real extinction coefficient) forms, the optical properties of the thin film become complex. The refractive index increases again, but at the same time, the extinction coefficient increases sharply, and the film becomes opaque. In this case, refractive index measurements are not very meaningful and the values ​​are unstable. Therefore, with a suitable silicon source to propylene flow ratio, the film composition is well-bonded amorphous silicon carbide (a-SiC), where Si-C bonds form the main network, the hydrogen content is low, and the refractive index reaches its characteristic peak range. At this point, the film is most dense and has the highest optical density.

[0011] Furthermore, the flow ratio of silicon source to propylene can precisely control the chemical composition and microstructure of the thin film. When the flow ratio is too high, the silicon content in the film is high, which tends to form an amorphous silicon network structure and may even contain excess silicon clusters, leading to stress imbalance. Conversely, when the flow ratio is too low, the carbon content in the film is high, making it easier to form sp(s). 2 or sp 3 Hybridized carbon clusters (such as graphitic carbon) will experience biased compressive stress.

[0012] Preferably, the silicon source includes silane.

[0013] Preferably, the inert gas includes argon and helium.

[0014] This invention uses a combination of argon and helium as the inert gas. The main functions of argon are: 1) generating and maintaining plasma: Ar atoms have a large atomic mass and are easily ionized under an electric field, forming a stable, high-density plasma, which is the "engine" of the PECVD process; 2) physical bombardment sputtering: Due to the large mass of Ar plasma ions, they have high kinetic energy after being accelerated by an electric field. This bombardment can effectively bombard the surface of the growing film, sputtering away poorly bonded, weak atoms (such as excessive H or sp atoms). 2Helium promotes densification and disrupts columnar crystal growth, resulting in a very smooth, pore-free, glass-like uniform amorphous silicon carbide film. The main functions of helium are: 1) Highly efficient heat carrier: Helium atoms have low mass and high velocity, possessing the highest thermal conductivity of all gases. This effectively transfers heat from the plasma region to the substrate surface, helping to control the substrate temperature, making its distribution more uniform, and avoiding localized overheating; 2) Promotes uniform dissociation: High thermal conductivity helps stabilize the plasma and transfer energy more evenly to the reactant gases, promoting their uniform dissociation, thereby improving the uniformity of film thickness and composition; 3) Diluent: It dilutes the reactant gases together with Ar, preventing excessively high concentrations that lead to excessively fast deposition rates and powder formation; 4) Helium can improve plasma distribution, possessing an extremely long mean free path and extremely high diffusion rate within the vacuum chamber, compensating for the slow diffusion of argon; 5) Helium's thermal conductivity is approximately 10 times that of argon, meaning it is an extremely efficient heat transfer medium that can effectively improve the temperature distribution of the substrate.

[0015] Compared to the traditional Ar+H2 combination, it has the following advantages: 1) Safety: He is an inert gas, completely non-flammable and non-explosive, while H2 is a highly flammable and explosive gas. When mixed with air, its explosive limits are extremely wide, and leaks pose a serious risk. Therefore, using He eliminates significant safety hazards and the associated costs of safety facilities. 2) Good process stability and repeatability: The reducing properties of H2 react with byproducts deposited on the chamber walls and electrodes (such as SiO2, SiN). x 1) Reactions occur, constantly changing the "historical" state of the chamber walls, leading to process drift and poor repeatability. He, on the other hand, is inert and does not participate in any chemical reactions, maintaining long-term process stability. 2) Good uniformity: He has a small atomic mass and extremely strong diffusion ability, which can effectively promote the uniform distribution of reactant gases and improve heat conduction within the chamber, making the temperature and plasma distribution more uniform, thus obtaining excellent film thickness uniformity. H2 also has a small mass, but its chemical reactivity can interfere with the uniform plasma field. 3) Good temperature control: He has the highest thermal conductivity of all gases (second only to H2), but its specific heat capacity is much lower than that of H2. This means that He can efficiently and quickly conduct heat away from the substrate, preventing local overheating and achieving precise temperature control. Although H2 also has high thermal conductivity, its high specific heat capacity makes its temperature change more "lagging". 4) Thin film stress is easy to adjust and tends to decrease: H2 generates a large amount of H in the plasma. + H2 +Plasma, with its light mass ions, can acquire high energy under high bias voltage, intensely bombarding thin films and easily introducing excessive stress. He bombardment, on the other hand, is gentler, making it easier to find a balance between densification and low stress by adjusting the Ar / He ratio. 6) No effect on stoichiometry: He is inert and does not affect the stoichiometric ratio of the silicon source and propylene, while H2 participates in surface reactions; for example, it may inhibit carbon incorporation (by etching away weak CH bonds, or with CH...). x (The CH4 generated by the group reaction is removed), resulting in a more silicon-rich film, changing the stoichiometry and properties of the film. 7) Avoiding hydrogen etching and silicon etching: H2 generates a large amount of active atomic hydrogen in plasma, etching the silicon network. When silane is used as the silicon source, atomic hydrogen reacts with Si, hindering the formation of SiC and reducing the silicon incorporation efficiency, thus affecting the control of the stoichiometry. The combination of argon and helium completely avoids this problem. 8) Lower hydrogen content: There is no need to use H2 as a carrier gas, fundamentally eliminating the hydrogen source, which is beneficial for obtaining amorphous silicon carbide films with low hydrogen content, high thermal stability, and high mechanical strength.

[0016] For example, the type of substrate is not limited; it may be a silicon wafer, a glass sheet, or sapphire.

[0017] Preferably, the flow rate of the silicon source is 50-300 sccm, for example, it can be 50 sccm, 100 sccm, 150 sccm, 200 sccm, 250 sccm or 300 sccm, etc.

[0018] Preferably, the flow rate of propylene is 50-500 sccm, for example, it can be 50 sccm, 100 sccm, 200 sccm, 300 sccm, 400 sccm or 500 sccm, etc.

[0019] Preferably, the flow rate ratio of argon to helium is (0.5-5):(0.5-3), wherein the range of argon selection "0.5-5" can be, for example, 0.5, 1, 2, 3, 4 or 5, and the range of helium selection "0.5-3" can be, for example, 0.5, 1, 2 or 3.

[0020] This invention allows for precise control of the average mass and energy of ion bombardment by adjusting the flow ratio of argon and helium within a suitable range. For example, when high density is required, the proportion of Ar can be increased to introduce compressive stress; conversely, when it is necessary to reduce compressive stress or promote surface migration, the proportion of He can be increased to utilize its mild heating effect to relax the thin film structure.

[0021] Preferably, in the plasma-enhanced chemical vapor deposition method, the parameters further include: radio frequency power of 100-1200W, for example, 100W, 300W, 500W, 700W, 900W, 1000W or 1200W, etc.

[0022] In this invention, radio frequency (RF) power is the master switch affecting plasma state and ion bombardment effect. If the RF power is too low, the plasma density is low, the ion energy is low, and the deposition process is closer to thermochemical vapor deposition, resulting in insufficient surface mobility and the formation of loose, porous films with tensile stress. Increasing the RF power can increase the plasma density, which means more reactive groups and more bombarding ions, accelerating the deposition rate and increasing ion energy. Ions gain greater kinetic energy after being accelerated by the electric field. However, if the RF power is too high, excessive ion bombardment can "kick" atoms into metastable positions, causing lattice distortion and defects. At the same time, due to the excessively strong sputtering effect, it may cause compressive stress overload on the film, or even cause Ar gas to be trapped in the film, generating additional stress, leading to film warping or peeling. Therefore, appropriate RF power allows moderate ion bombardment to begin to exert a densification effect, effectively eliminating tensile stress and gradually transforming it into compressive stress. This is an important factor in obtaining high-quality, dense films.

[0023] Preferably, the flow rate of the argon gas is 500-5000 sccm, for example, it can be 500 sccm, 1000 sccm, 2000 sccm, 3000 sccm, 4000 sccm or 5000 sccm, etc.

[0024] Preferably, the flow rate of the helium gas is 500-3000 sccm, for example, it can be 500 sccm, 1000 sccm, 1500 sccm, 2000 sccm, 2500 sccm or 3000 sccm, etc.

[0025] Preferably, in the plasma-enhanced chemical vapor deposition method, the parameters further include: a deposition temperature of 200-450℃, for example, 200℃, 250℃, 300℃, 350℃, 400℃ or 450℃, etc.

[0026] In this invention, the surface roughness of the thin film can be optimized by adjusting the deposition temperature. Temperature works through the following mechanisms: 1) Enhancing surface mobility: At lower temperatures, precursor fragments (such as SiH) deposited from plasma onto the substrate surface... x CH xThe adsorbed atoms and groups have low kinetic energy and are "stuck" at their initial landing sites, unable to move sufficiently to find stable locations with the lowest energy (i.e., lattice sites or step edges). This restricted diffusion leads to island growth, where each island grows independently. When they eventually meet and merge, they form obvious grain boundaries and trenches, resulting in surface roughness. Increasing the temperature provides additional thermal kinetic energy to the adsorbed atoms and groups, enabling them to diffuse over longer distances on the surface. This promotes layer-by-layer growth, where atoms can move to defects or steps, thus "smoothing" the surface and obtaining a smoother film. 2) Promoting chemical reactions and bond recombination: Increased temperature provides the energy needed to overcome reaction barriers, causing Si-H, CH, and other chemical bonds to break further, forming more stable Si-C bonds. This helps to form a denser and stronger network structure, reducing local inhomogeneities caused by weak bonds or incompletely reacted dangling bonds, thereby reducing roughness. 3) Reduced hydrogen content: Increasing the temperature effectively promotes H2 precipitation, significantly reducing the hydrogen content in the film. Lower H content means a more complete and uniform Si-C covalent network, which directly leads to a smoother and denser surface. 4) Impact on nucleation density: Higher initial nucleation density is beneficial for forming more continuous and smoother films. Temperature affects the nucleation process by influencing the adsorption / desorption balance and diffusion rate of the precursor on the substrate surface. A suitable temperature window can optimize the nucleation density, laying the foundation for subsequent smooth growth.

[0027] Preferably, the preparation method includes the following steps: (1) Provide plasma-enhanced chemical vapor deposition equipment and perform vacuuming.

[0028] (2) The substrate is placed in the chamber of the plasma-enhanced chemical vapor deposition equipment and the substrate is preheated; wherein the distance between the substrate and the spray plate is 300-500 mil (for example, it can be 300 mil, 400 mil or 500 mil, etc.).

[0029] A silicon source with a flow rate of 50-300 sccm, a propylene source with a flow rate of 50-500 sccm, an argon source with a flow rate of 500-5000 sccm, and a helium source with a flow rate of 500-3000 sccm are introduced into the chamber. The chamber pressure is 4-10 torr (e.g., 4 torr, 6 torr, 8 torr, or 10 torr, etc.) and stabilized for 20-40 seconds (e.g., 20 seconds, 30 seconds, or 40 seconds, etc.). The flow rate ratio of the silicon source to the propylene source is (1-5):(1-3), and the flow rate ratio of the argon source to the helium source is (0.5-5):(0.5-3).

[0030] (3) Set the radio frequency power of the plasma-enhanced chemical vapor deposition equipment to 100-1200W and the chamber pressure to 4-10 torr (e.g., 4 torr, 6 torr, 8 torr or 10 torr, etc.) for a deposition process of 40-80s (e.g., 40s, 50s, 60s, 70s or 80s, etc.). After the deposition process is completed, purge and vacuum are performed to obtain an amorphous silicon carbide thin film on the substrate.

[0031] It should be noted that "mil" is an imperial unit of length, 1 mil = 0.001 inches = 25.4 μm.

[0032] In a second aspect, the present invention provides an amorphous silicon carbide thin film, which is prepared by the preparation method described in the first aspect.

[0033] Preferably, the refractive index of the amorphous silicon carbide thin film is 1.9-2.9, for example, it can be 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8 or 2.9.

[0034] Preferably, the thickness of the amorphous silicon carbide film is 200-500 nm, for example, it can be 200 nm, 300 nm, 400 nm or 500 nm.

[0035] It should be noted that the thickness can be measured using an ellipsometer. The measurement method is as follows: select 49 points evenly distributed on the sample surface as the test objects, and deduct the edge area of ​​5mm to eliminate the edge effect. Take the average value as the final thickness of the film.

[0036] Preferably, the roughness Ra of the amorphous silicon carbide thin film is less than 1.5 nm, for example, it can be 1.4 nm, 1.3 nm, 1.2 nm or 1.1 nm.

[0037] Preferably, the thickness uniformity of the amorphous silicon carbide film is ≤1.5%, for example, it can be 1.5%, 1.4%, 1.3%, 1.1%, 1% or 0.9%, etc.

[0038] Thirdly, the present invention provides a back contact battery, wherein the antireflection layer in the back contact battery comprises an amorphous silicon carbide thin film as described in the second aspect.

[0039] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0040] Compared with the prior art, the present invention has the following beneficial effects: This invention employs propylene as a carbon source in conjunction with a silicon source to prepare amorphous silicon carbide thin films via plasma-enhanced chemical vapor deposition. Compared to conventional carbon sources, propylene exhibits superior reactivity in a plasma environment: Firstly, propylene can provide carbon-active groups in a more controllable manner, facilitating the preparation of silicon carbide thin films with a near stoichiometric ratio of 1:1 when matched with a silicon source, thereby broadening the adjustable range of refractive index. Secondly, the decomposition pathway of propylene tends to generate unsaturated hydrocarbons rather than atomic hydrogen, effectively suppressing the hydrogen content in the film, promoting the formation of a more robust SiC network, significantly reducing film stress, and facilitating the deposition of thick films. Thirdly, the reactivity of propylene effectively reduces the pre-formation tendency of powdery carbon particles in the gas phase, reducing film surface roughness and contributing to the acquisition of high-quality silicon carbide thin films with uniform surface and excellent density. In summary, this invention, by introducing propylene as a carbon source, achieves an optimal balance between deposition rate, carbon activity control, and film quality, providing a wider and more stable process window, and effectively solving the technical problems of high film stress, narrow adjustable refractive index range, and high roughness in existing technologies. Detailed Implementation

[0041] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0042] The scope of this invention can be defined by lower and upper limits. The selected lower and upper limits define the boundaries of a specific range. The range defined in this way can be defined by the inclusion or exclusion of endpoints. Any endpoint can be independently selected for inclusion or exclusion, and all lower and upper limits can be arbitrarily combined to form new ranges. That is, any lower limit can be combined with any upper limit to form an effective range. For example, if the ranges of 60~120 and 80~110 are listed for specific parameters, it should be understood that the ranges of 60~110 and 80~120 also fall within the scope of this invention. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are also listed, then all ranges of 1~3, 1~4, 1~5, 2~3, 2~4 and 2~5 fall within the scope of this invention. In this invention, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between 0 and 5 have been fully listed in this document, and "0~5" is only a shortened representation of this set of numerical combinations. When a parameter is expressed as an integer ≥2, it is equivalent to listing positive integers that meet the requirements, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. When a parameter is expressed as an integer selected from "2~10", it is equivalent to listing any integer among 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0043] In this invention, "a combination of at least two" refers to a quantity greater than or equal to 2 unless otherwise specified. For example, "any one or a combination of at least two" means that any one of the listed items can be selected, or a combination of at least two of the listed items formed in a manner that does not conflict and enables the implementation of this invention. In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" cover any one of two or more related listed items, as well as any and all combinations of the related listed items. The arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" means a set consisting of A, B, and combinations of A and B, where "containing A and / or B" can be understood, depending on the context of the statement, as containing A, containing B, or simultaneously containing both A and B. In this invention, "optional" means that the corresponding feature, component, step or solution is not necessary, that is, it is selected from either "with" or "without". If there are multiple "optional" limitations in a technical solution, unless otherwise specified and there is no technical conflict or mutual constraint, each "optional" limitation is independent and does not affect the others.

[0044] In this invention, technical features or solutions described using open-ended terms such as "comprising" or "including" do not exclude additional non-conflicting elements beyond the listed elements unless otherwise specified. They are considered to disclose both closed-ended features or solutions consisting solely of the listed elements and open-ended features or solutions that may include additional non-conflicting elements beyond the listed elements. For example, if A includes a1, a2, and a3, unless otherwise specified, this means that A can consist only of a1, a2, and a3, or it can include other non-conflicting elements based on a1, a2, and a3. This corresponds to the disclosure of technical solutions such as "A consists of a1, a2, and a3," "A is selected from a1, a2, and a3," and "A not only includes a1, a2, and a3, but may also include other non-conflicting elements." All embodiments and optional embodiments of this invention, unless otherwise specified and without technical conflict, can be combined to form new technical solutions, and such combinations fall within the scope of this invention. The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various locations throughout the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this invention can be combined with other embodiments that do not conflict with the technology. The ordinal numbers "first," "second," "third," and "fourth," etc., used in the expressions "first aspect," "second aspect," "third aspect," and "fourth aspect" in this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly specifying the importance or quantity of the indicated technical features. They serve only as a non-exhaustive enumeration and do not constitute a closed limitation on quantity.

[0045] In this invention, the order in which the steps are written in the methods described in each embodiment does not imply a strict execution order. The actual execution order of each step should be determined based on its function and possible internal logic. Unless otherwise specified, all steps of this invention can be executed in the order they are written, or in any order without technical conflict. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) executed sequentially, or it may include steps (b) and (a) executed sequentially. If the method also includes step (c), then step (c) can be added to the method in any order without conflict, including but not limited to the execution order of steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0046] Example 1 This embodiment provides a method for preparing amorphous silicon carbide thin films, the method comprising the following steps: (1) Provide a single-cavity monolithic PECVD device with an RF system of AENI and a frequency of 13.56MHz.

[0047] The cavity is evacuated.

[0048] (2) Transfer the silicon wafer into the chamber of the single-cavity single-wafer PECVD equipment and place it on the ejector pin of the hot plate (the temperature of the hot plate is 250°C).

[0049] The hot plate and the ejector pin move relative to each other, and the silicon wafer falls onto the hot plate. The hot plate continues to move to the set position, so that the distance between the silicon wafer and the spray plate is 400 mil, and the silicon wafer is preheated, purged and vacuumed.

[0050] The chamber is supplied with silane at a flow rate of 230 sccm, propylene at a flow rate of 50 sccm, argon at a flow rate of 3000 sccm, and helium at a flow rate of 2000 sccm. The chamber pressure is 7 torr, and the chamber is stabilized for 30 seconds. The flow rate ratio of silane to propylene is 4.6:1, and the flow rate ratio of argon to helium is 3:2.

[0051] (3) Set the RF power of the single-cavity single-wafer PECVD equipment to 500W and the chamber pressure to 7torr. Perform a deposition process for 60s. After the deposition is completed, turn off the RF power supply, stop the introduction of silane and propylene, and keep argon and helium continuously introduced for 10s to purge the remaining reaction gases.

[0052] The chamber of a single-cavity, single-wafer PECVD device is evacuated, and then the silicon wafer is transferred out to obtain an amorphous silicon carbide thin film with a thickness of 298.9 nm.

[0053] Example 2 This embodiment provides a method for preparing amorphous silicon carbide thin films, the method comprising the following steps: (1) Provide a single-cavity monolithic PECVD device with an RF system of AENI and a frequency of 13.56MHz.

[0054] The cavity is evacuated.

[0055] (2) Transfer the silicon wafer into the chamber of the single-cavity single-wafer PECVD equipment and place it on the ejector pin of the hot plate (the temperature of the hot plate is 350°C).

[0056] The hot plate and the ejector pin move relative to each other, and the silicon wafer falls onto the hot plate. The hot plate continues to move to the set position, so that the distance between the silicon wafer and the spray plate is 400 mil, and the silicon wafer is preheated.

[0057] The chamber is supplied with silane at a flow rate of 100 sccm, propylene at a flow rate of 300 sccm, argon at a flow rate of 500 sccm, and helium at a flow rate of 3000 sccm. The chamber pressure is 7 torr, and the chamber is stabilized for 20 seconds. The flow rate ratio of silane to propylene is 1:3, and the flow rate ratio of argon to helium is 0.5:3.

[0058] (3) Set the RF power of the single-cavity single-wafer PECVD equipment to 100W and the chamber pressure to 7torr. Perform a deposition process for 80s. After the deposition is completed, turn off the RF power supply, stop the introduction of silane and propylene, and keep argon and helium continuously introduced for 10s to purge the remaining reaction gases.

[0059] The chamber of a single-cavity, single-wafer PECVD device is evacuated, and then the silicon wafer is transferred out to obtain an amorphous silicon carbide thin film with a thickness of 400 nm.

[0060] Example 3 This embodiment provides a method for preparing amorphous silicon carbide thin films, the method comprising the following steps: (1) Provide a single-cavity monolithic PECVD device with an RF system of AENI and a frequency of 13.56MHz.

[0061] The cavity is evacuated.

[0062] (2) Transfer the silicon wafer into the chamber of the single-cavity single-wafer PECVD equipment and place it on the ejector pin of the hot plate (the temperature of the hot plate is 450°C).

[0063] The hot plate and the ejector pin move relative to each other, and the silicon wafer falls onto the hot plate. The hot plate continues to move to the set position, so that the distance between the silicon wafer and the spray plate is 400 mil, and the silicon wafer is preheated.

[0064] The chamber is supplied with silane at a flow rate of 300 sccm, propylene at a flow rate of 60 sccm, argon at a flow rate of 5000 sccm, and helium at a flow rate of 500 sccm. The chamber pressure is 7 torr, and the pressure is maintained for 40 seconds. The flow rate ratio of silane to propylene is 5:1, and the flow rate ratio of argon to helium is 5:0.5.

[0065] (3) Set the RF power of the single-cavity single-wafer PECVD equipment to 1200W and the chamber pressure to 7torr. Perform a deposition process for 40s. After the deposition is completed, turn off the RF power supply, stop the introduction of silane and propylene, and keep argon and helium continuously introduced for 10s to purge the remaining reaction gases.

[0066] The chamber of a single-cavity, single-wafer PECVD device is evacuated, and then the silicon wafer is transferred out to obtain an amorphous silicon carbide thin film with a thickness of 200 nm.

[0067] Example 4 The difference between this embodiment and Embodiment 1 is that the temperature of the hot plate is 400°C.

[0068] The remaining preparation methods and parameters are consistent with those in Example 1.

[0069] Example 5 The difference between this embodiment and Embodiment 4 is that the silane flow rate is 200 sccm.

[0070] The remaining preparation methods and parameters are consistent with those in Example 4.

[0071] Example 6 The difference between this embodiment and Embodiment 1 is that the flow rate of silane is 150 sccm and the flow rate of propylene is 100 sccm.

[0072] The remaining preparation methods and parameters are consistent with those in Example 1.

[0073] Example 7 The difference between this embodiment and Embodiment 1 is that the flow rate of the helium is adjusted so that the flow rate ratio of the argon to the helium is 0.5:5.

[0074] The remaining preparation methods and parameters are consistent with those in Example 1.

[0075] Example 8 The difference between this embodiment and Embodiment 1 is that the flow rate of the helium gas is adjusted so that the flow rate ratio of the argon gas to the helium gas is 6:0.5.

[0076] The remaining preparation methods and parameters are consistent with those in Example 1.

[0077] Example 9 The difference between this embodiment and Embodiment 1 is that the temperature of the hot plate is 150°C.

[0078] The remaining preparation methods and parameters are consistent with those in Example 1.

[0079] Example 10 The difference between this embodiment and Embodiment 1 is that the temperature of the hot plate is 500°C.

[0080] The remaining preparation methods and parameters are consistent with those in Example 1.

[0081] Example 11 The difference between this embodiment and Embodiment 1 is that the radio frequency power is 50W.

[0082] The remaining preparation methods and parameters are consistent with those in Example 1.

[0083] Example 12 The difference between this embodiment and Embodiment 1 is that the radio frequency power is 1500W.

[0084] The remaining preparation methods and parameters are consistent with those in Example 1.

[0085] Comparative Example 1 The difference between this comparative example and Example 1 is that the helium gas with a flow rate of 2000 sccm is replaced with H2 with a flow rate of 1000 sccm.

[0086] The remaining preparation methods and parameters are consistent with those in Example 1.

[0087] Comparative Example 2 The difference between this comparative example and Example 1 is that propylene is replaced with methane at the same flow rate.

[0088] The remaining preparation methods and parameters are consistent with those in Example 1.

[0089] Comparative Example 3 The difference between this comparative example and Example 1 is that propylene is replaced with an equal flow rate of acetylene.

[0090] The remaining preparation methods and parameters are consistent with those in Example 1.

[0091] Comparative Example 4 The difference between this comparative example and Example 1 is that the flow rate of propylene is adjusted so that the flow rate ratio of silane to propylene is 1:5.

[0092] The remaining preparation methods and parameters are consistent with those in Example 1.

[0093] Comparative Example 5 The difference between this comparative example and Example 1 is that the flow rate of propylene is adjusted so that the flow rate ratio of silane to propylene is 6:1.

[0094] The remaining preparation methods and parameters are consistent with those in Example 1.

[0095] Performance testing The amorphous silicon carbide thin films prepared in the above embodiments and comparative examples were characterized, including refractive index, roughness, thickness uniformity and stress.

[0096] The refractive index can be measured using an ellipsometer. The measurement method involves selecting 49 points uniformly distributed on the sample surface as the test objects, and subtracting a 5mm edge region to eliminate edge effects. The average value is taken as the final refractive index of the film. Roughness Ra can be measured using an atomic force microscope (AFM). The measurement method involves setting the scanning range to 5μm × 5μm and the number of sampling points to 256 points × 256 lines. The arithmetic mean roughness within the test area is taken as the final Ra value of the film. Thickness uniformity can be measured using an ellipsometer. The measurement method involves selecting 49 points uniformly distributed on the sample surface as the test objects, and subtracting a 5mm edge region to eliminate edge effects. Thickness uniformity (Sigma U%) is calculated using the following formula: Sigma U% = (Standard deviation of thickness at 49 points / Average thickness at 49 points) × 100%. Stress characterization is performed using a stress meter. The test method involves selecting a scanning line along the diameter of the silicon wafer, uniformly measuring 20 points, and setting the edge removal distance to 10mm to eliminate edge effects.

[0097] The test results are shown in Table 1.

[0098] Table 1

[0099] analyze: As shown in Table 1, in the process of preparing amorphous silicon carbide thin films by PECVD, the present invention employs silicon source and propylene with appropriate flow ratios, and argon and helium with appropriate flow ratios. With the assistance of appropriate RF power and deposition temperature, the optimal balance is achieved between deposition rate, carbon activity control and film quality, providing a wider and more stable process window. This effectively solves the technical problems of high film stress, narrow refractive index adjustment range and high roughness in the prior art.

[0100] A comparison of Examples 1 and 7-8 shows that if the flow ratio of argon to helium is too small, the amount of helium will be too large. Due to the light mass of helium ions, the ion bombardment energy is insufficient, leading to a decrease in the density of the thin film. Furthermore, the ionization energy of helium is much higher than that of argon, increasing the difficulty of ignition and worsening the stability of gaseous ionization. If the flow ratio of argon to helium is too large, the amount of argon will be too large. Due to the high energy and strong momentum of argon ions, excessive bombardment will cause damage and defects to the thin film. Moreover, the thermal conductivity of argon is much worse than that of helium, resulting in a wider ion energy distribution near the plasma sheath, which makes it easier for homogeneous nucleation to occur in the gas phase of the reaction chamber, forming silicon or carbon dust particles.

[0101] A comparison of Examples 1 and 9-10 shows that if the hot plate temperature is too low, the deposition temperature will be too low, resulting in precursor fragments (such as SiH) deposited from the plasma onto the substrate surface. x CH xThe kinetic energy of these nuclei is low, and they "stick" to their initial landing position, unable to move sufficiently to find the lowest energy stable position (i.e., lattice sites or step edges). This restricted diffusion leads to island growth, where each island nucleus grows independently. When they eventually meet and merge, they form obvious grain boundaries and trenches, resulting in a rough surface. If the hot plate temperature is too high, the deposition temperature will be too high, increasing stress and causing the film to crack, and also causing thermal damage to the underlying film.

[0102] As can be seen from the comparison between Example 1 and Examples 11-12, if the radio frequency power is too low, the plasma density is low, the ion energy is low, the deposition process is closer to thermochemical vapor deposition, the surface mobility is insufficient, and it is easy to form a loose, porous film with tensile stress. If the radio frequency power is too high, the strong ion bombardment will "kick" the atoms into metastable positions, causing lattice distortion and defects. At the same time, due to the excessive sputtering effect, it may cause compressive stress overload on the film, and even cause Ar gas to be trapped in the film, generating additional stress, resulting in film warping or peeling.

[0103] A comparison of Example 1 and Comparative Example 1 reveals the following drawbacks of using a combination of argon and hydrogen: H2 is a highly flammable and explosive gas, posing a serious risk of leakage; H2 has an extremely wide explosion limit range when mixed with air, resulting in a serious risk of leakage; the chemical reactivity of H2 can interfere with a uniform plasma field; H2's high specific heat capacity makes its temperature changes more "lag-dependent"; H2 can participate in surface reactions, for example, it may inhibit carbon incorporation (by eroding weak CH bonds, or by reacting with CH bonds). x (The group reaction generates CH4 which is removed), resulting in a more silicon-rich film, which changes the stoichiometry and properties of the film; H2 in plasma generates a large number of active hydrogen atoms, which etch the silicon network.

[0104] A comparison of Example 1 and Comparative Examples 2-3 shows that if propylene is replaced with an equal flow rate of methane, methane, being the most stable hydrocarbon with a high CH bond energy, is difficult to decompose in plasma, resulting in low carbon utilization efficiency, slow deposition rate, and insufficient production capacity. If propylene is replaced with an equal flow rate of acetylene, acetylene is highly reactive, readily decomposes, and provides a carbon source, leading to a fast deposition rate. However, precisely because of its high reactivity, it easily forms a large number of C2 groups and carbon clusters in plasma, resulting in the generation of excessive amorphous carbon (sp). 2 The carbon-rich film, embedded in the SiC network, has high hardness but also huge internal stress, making it easy to peel off and affecting its electrical and optical properties.

[0105] As can be seen from the comparison between Example 1 and Comparative Examples 4-5, if the flow ratio of silane to propylene is too small, the film composition is deposited as carbon-rich amorphous silicon carbide (a-SiC:C), and the film begins to contain more and more sp. 2 and sp 3 The bonded amorphous carbon (aC) phase exhibits a complex trend in refractive index variation: initially carbon-rich: when a small amount of excess sp begins to appear... 3 When carbon (similar to diamond, with a refractive index of approximately 2.4) is present, the refractive index may decrease slightly. Highly carbon-rich: when a large amount of sp... 2 When carbon (graphite phase, with complex refractive index and high real extinction coefficient) is formed, the optical properties of the thin film become complex. The refractive index increases again, but at the same time, the extinction coefficient increases sharply, and the film becomes opaque. At this time, the refractive index measurement is not very meaningful and the value is unstable, and the stress will be biased towards compressive stress. If the flow ratio of silane and propylene is too large, the composition of the thin film is silicon-rich amorphous silicon carbide (a-SiC:H), and even amorphous silicon (a-Si:H) clusters are embedded in the SiC network. The refractive index of amorphous silicon (a-Si) is very high (usually 3.5-4@633nm). The refractive index of stoichiometric SiC is about 2.6-2.7. Therefore, in this case, it is equivalent to "doping" a high-refractive-index a-Si phase into SiC, thereby increasing the overall average refractive index, and the stress will be biased towards tensile stress.

[0106] It should be noted that the present invention is illustrated through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing an amorphous silicon carbide thin film, characterized in that, The preparation method includes the following steps: (1) Provide plasma-enhanced chemical vapor deposition equipment and perform vacuuming; (2) The substrate is placed in the chamber of the plasma-enhanced chemical vapor deposition equipment and the substrate is preheated; wherein the distance between the substrate and the spray plate is 300-500 mil; A silicon source with a flow rate of 50-300 sccm, a propylene source with a flow rate of 50-500 sccm, an argon source with a flow rate of 500-5000 sccm, and a helium source with a flow rate of 500-3000 sccm are introduced, and the chamber pressure is controlled at 4-10 torr and stabilized for 20-40 seconds; wherein, the flow rate ratio of the silicon source to the propylene source is (1-5):(1-3), and the flow rate ratio of the argon source to the helium source is (0.5-5):(0.5-3); (3) Set the radio frequency power of the plasma-enhanced chemical vapor deposition equipment to 100-1200W, the chamber pressure to 4-10 torr, and the deposition temperature to 200-450℃. Perform a deposition process of 40-80s. After the process is completed, perform purging and vacuuming to obtain an amorphous silicon carbide thin film on the substrate.

2. The method for preparing amorphous silicon carbide thin films according to claim 1, characterized in that, The silicon source includes silane.

3. An amorphous silicon carbide thin film, characterized in that, The amorphous silicon carbide thin film is prepared by the preparation method described in claim 1 or 2.

4. The amorphous silicon carbide thin film according to claim 3, characterized in that, The refractive index of the amorphous silicon carbide thin film is 1.9-2.9; And / or, the thickness of the amorphous silicon carbide film is 200-500 nm; And / or, the roughness Ra of the amorphous silicon carbide film is <1.5 nm.

5. A back-contact battery, characterized in that, The antireflective layer in the back contact battery includes the amorphous silicon carbide thin film as described in claim 3 or 4.

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