Back contact solar cell and preparation method thereof

Abstract

The invention provides a back contact solar cell and a preparation method thereof. The back contact solar cell comprises a silicon substrate, a first doped region, a second doped region and an isolation region, wherein the first doped region, the second doped region and the isolation region are alternately arranged on the first surface of the silicon substrate; the doping polarities of the first doped region and the second doped region are opposite; the first film layer structure, the second film layer structure and the third film layer structure are respectively arranged on the surfaces, far away from the silicon substrate, of the first doped region, the second doped region and the isolation region; the first film layer structure and the second film layer structure are separated by the third film layer structure; wherein the first film layer structure comprises a first back film hollow structure, the second film layer structure comprises a second back film hollow structure, the diameters of cavities in the first back film hollow structure and the second back film hollow structure are smaller than 10m, the structure effectively improves the passivation effect of the refractive index of the back film layer of the back contact solar cell, and meanwhile, the laser film opening effect is enhanced; ohmic contact of metal electrodes is facilitated, and the cell conversion efficiency and the assembly power are improved.

Description

Technical Field

[0001] This disclosure relates to the field of back-contact solar cell technology, and particularly to back-contact solar cells and their fabrication methods. Background Technology

[0002] Currently, the back-contact solar cell coating route is a very promising crystalline silicon cell technology route, favored by domestic and international markets for its high conversion efficiency, low manufacturing cost, and aesthetically pleasing module appearance.

[0003] In related technologies, the back-contact solar cells with coating routes use PECVD (Plasma-Enhanced Chemical Vapor Deposition) coating on the back side. The film structure types usually include alumina + single-layer silicon nitride film, alumina + stacked silicon nitride film, alumina + silicon nitride + silicon oxide film, etc. The film is opened by laser drilling, and then the electrode is fabricated by metallization coating.

[0004] However, in order to match the laser-cutting effect, the refractive index of the back film layer of the back contact solar cell is generally made relatively low. However, the low refractive index film layer has poor passivation and a large loss of cell efficiency. At the same time, the dense silicon nitride film layer is prone to leaving film-cutting residue when laser-cutting, which leads to poor ohmic contact of the metal electrode during metallization coating, resulting in lower module power. Summary of the Invention

[0005] This disclosure provides a back-contact solar cell and a method for its fabrication.

[0006] In a first aspect, this disclosure provides a back-contact solar cell, comprising: a silicon substrate, the silicon substrate including a first surface, wherein a first doped region, a second doped region, and an isolation region are alternately disposed on the first surface; the doping polarities of the first doped region and the second doped region are opposite; a first film structure disposed on the surface of the first doped region away from the silicon substrate; a second film structure disposed on the surface of the second doped region away from the silicon substrate; and a third film structure disposed on the surface of the isolation region away from the silicon substrate, wherein the first film structure and the second film structure are separated by the third film structure; wherein the first film structure includes a first backsheet hollow structure, the second film structure includes a second backsheet hollow structure, and the cavity diameter in the first backsheet hollow structure and the second backsheet hollow structure is less than 10 µm.

[0007] Secondly, this disclosure provides a method for fabricating a back-contact solar cell, including:

[0008] Preparation of silicon substrate;

[0009] A first doped region, a second doped region, and an isolation region are alternately deposited on a first surface of the silicon substrate, wherein the doping polarities of the first doped region and the second doped region are opposite. The process includes: depositing a first film structure on the surface of the first doped region away from the silicon substrate; depositing a second film structure on the surface of the second doped region away from the silicon substrate; and depositing a third film structure on the surface of the isolation region away from the silicon substrate. The first film structure and the second film structure are separated by the third film structure. The first film structure includes a first backsheet hollow structure, and the second film structure includes a second backsheet hollow structure. The cavity diameter in the first and second backsheet hollow structures is less than 10 µm.

[0010] The back-contact solar cell and its preparation method provided in this disclosure effectively improve the passivation effect of the refractive index of the back film layer of the back-contact solar cell, while enhancing the laser-induced film opening effect, which is beneficial for ohmic contact of the metal electrodes, thereby improving the cell conversion efficiency and module power.

[0011] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this disclosure, nor is it intended to limit the scope of this disclosure. Other features of this disclosure will become readily apparent from the following description. Attached Figure Description

[0012] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the embodiments of the present disclosure to explain the disclosure and do not constitute a limitation thereof. The above and other features and advantages will become more apparent to those skilled in the art from the detailed description of exemplary embodiments with reference to the accompanying drawings, in which:

[0013] Figure 1 This is a structural diagram of a back-contact solar cell provided in an embodiment of the present disclosure;

[0014] Figure 2 This is a structural diagram of an N-type BC cell in a back-contact solar cell provided in an embodiment of the present disclosure;

[0015] Figure 3 This is a schematic diagram of a partial film structure of an N-type BC cell in a back-contact solar cell provided in an embodiment of the present disclosure;

[0016] Figure 4 A flowchart illustrating a method for fabricating a back-contact solar cell according to an embodiment of this disclosure;

[0017] Figure 5 This is a flowchart illustrating a method for fabricating a back-contact solar cell for an N-type BC battery, as provided in an embodiment of this disclosure.

[0018] Figure 6 A 3D magnified microscopic schematic diagram of the first backsheet hollow structure and the second backsheet hollow structure in a back-contact solar cell provided in this embodiment of the present disclosure;

[0019] Figure 7 for Figure 6 A magnified view of a portion of the image;

[0020] Figure 8 for Figure 7 A magnified view of a portion of the image;

[0021] Figure 9 A magnified 3D microscope diagram of the molded light spot of the film layer in the back contact solar cell provided in the embodiment of this disclosure;

[0022] Figure 10 This is a 3D microscope magnified schematic diagram of the molded light spot of the film layer in a back-contact solar cell in a related technology. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solutions of this disclosure, exemplary embodiments of this disclosure are described below with reference to the accompanying drawings, including various details of the embodiments of this disclosure to aid understanding. These should be considered merely exemplary. Therefore, those skilled in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this disclosure. Similarly, for clarity and conciseness, descriptions of well-known functions and structures are omitted in the following description.

[0024] Where there is no conflict, the various embodiments of this disclosure and the features thereof in the embodiments may be combined with each other.

[0025] As used herein, the term “and / or” includes any and all combinations of one or more related enumerated entries.

[0026] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. As used herein, the singular forms “a” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that when the terms “comprising” and / or “made of” are used in this specification, they specify the presence of features, integrals, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups thereof. Words such as “connected” or “linked” are not limited to physical or mechanical connections but can include electrical connections, whether direct or indirect.

[0027] Unless otherwise specified, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art. It will also be understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and this disclosure, and will not be interpreted as having an idealized or overly formal meaning, unless expressly so defined herein.

[0028] According to the back-contact solar cell and its fabrication method in this disclosure, the crystalline silicon back-contact solar cell with a suitable coating route can be an N-type BC cell. The back side of the N-type BC cell consists of a tunneling oxide / P-type polycrystalline silicon layer, a tunneling oxide / N-type polycrystalline silicon layer, trenches isolating the P-region and N-region, and a back passivation film. The front passivation film is composed of conventional ultrathin silicon oxide / alumina / silicon nitride / silicon oxynitride / silicon oxide. One surface of the back-contact solar cell includes a silicon wafer substrate. From the inside out, the back surface of the substrate is sequentially composed of ultrathin silicon oxide, alumina, two layers of high-refractive-index silicon nitride, two layers of silicon oxynitride with gradually decreasing refractive index, one layer of silicon oxide, and a hollow backsheet structure. This structure can improve the passivation effect of the backsheet refractive index of the back-contact solar cell, while increasing the hollow backsheet structure enhances the laser-induced film opening effect, facilitates ohmic contact of the metal electrodes, and thus improves the cell conversion efficiency and module power.

[0029] Figure 1 A structural diagram of a back-contact solar cell provided in an embodiment of this disclosure is shown, as follows: Figure 1 As shown, the back-contact solar cell includes: a silicon substrate 1, which includes a first surface 2, with alternating first doped regions 3, second doped regions 4, and isolation regions 5 disposed on the first surface 2; the doping polarities of the first doped regions 3 and the second doped regions 4 are opposite; a first film structure 6, disposed on the surface of the first doped regions 3 away from the silicon substrate 1; a second film structure 7, disposed on the surface of the second doped regions 4 away from the silicon substrate 1; and a third film structure (not shown), disposed on the surface of the isolation region 5 away from the silicon substrate 1. The first film structure 6 and the second film structure 7 are separated by the third film structure. The first film structure 6 includes a first backsheet hollow structure 8, and the second film structure 7 includes a second backsheet hollow structure 9. The cavity diameter in the first backsheet hollow structure 8 and the second backsheet hollow structure 9 is less than 10 µm. The silicon substrate 1 can be a silicon wafer substrate.

[0030] It should be understood that in the embodiments disclosed in this invention, the cavity shape is similar to the bubble shape.

[0031] It should be understood that in the embodiments disclosed in this invention, the maximum cavity diameter of the first back membrane hollow structure 8 is less than 10µm, and the maximum cavity diameter of the second back membrane hollow structure 9 is less than 10µm.

[0032] It should be understood that, in the embodiments disclosed in this invention, the cavity diameter measurement process can be as follows: first, determine the projection of the cavity on the surface of the silicon wafer or film layer; second, measure the distance between any two points on the projection edge; and finally, take the longest distance between the two projection points as the diameter of the cavity.

[0033] In some alternative embodiments, the hollow diameter can be measured using a scanning electron microscope, an optical metallurgical microscope, or a 3D microscope.

[0034] Specifically, measuring the cavity diameter in the hollow structures of the first and second back membranes using scanning electron microscopy (SEM) requires following the core process of sample preparation, SEM setup, image acquisition, dimensional measurement, and data statistics. The key is to ensure a flat sample cross-section and clear imaging. The specific steps are as follows:

[0035] I. Sample preparation: Obtain clear cross-sections of the first and second back membrane hollow structures.

[0036] Solar cell backsheets are mostly made of polymer or composite film materials, which are relatively soft. Direct cutting can easily lead to cavity deformation, so appropriate sample preparation methods are required.

[0037] For sampling, cut a 5mm × 5mm sample from the back membrane, ensuring that the sampling area includes the hollow structure to be measured. If the back membrane is a multi-layer composite structure, ensure that the sampling direction is perpendicular to the extension direction of the cavity to facilitate subsequent observation of the cross-section.

[0038] When preparing the cross-section, it is important to avoid cavity collapse and deformation. Specifically, the cryogenic fracture method or the ultrathin sectioning method can be used.

[0039] The cryogenic fracture method involves immersing the sample in liquid nitrogen for 5-10 minutes until it becomes completely brittle. Then, the sample is quickly broken off with tweezers or a blade to obtain a stress-free natural cross-section. This method can preserve the original morphology of the cavity to the greatest extent and is suitable for polymer materials.

[0040] For cross-section preparation processes requiring high precision, the ultrathin slicing method can be used. If it is necessary to observe nanoscale cavities, an ultrathin slicer can be used to slice the sample into thin slices with a thickness of 50-100 nm, which is suitable for measuring cavities with extremely small dimensions.

[0041] Charge accumulation is eliminated through conductivity treatment. The backing film is a non-conductive polymer, and the sample cross-section needs to be treated with gold or carbon spraying.

[0042] The gold sputtering process uses an ion sputtering instrument with a gold sputtering thickness of 5-10nm, resulting in high imaging brightness, which is suitable for morphological observation.

[0043] During carbon spraying, the carbon spraying thickness is 2-5nm, which is suitable for subsequent EDS elemental analysis and avoids interference from gold.

[0044] It should be understood that if a field emission SEM is used and equipped with a low vacuum mode, observation can be performed directly under low vacuum without the need for spraying, thus reducing damage to the sample.

[0045] To fix the sample, place the prepared sample with the cross-section facing upwards and attach it to the SEM sample stage with conductive adhesive, ensuring that the sample and the sample stage are electrically connected to prevent charge effects.

[0046] II. SEM Debugging and Image Acquisition: Obtaining clear images of the cavity morphology.

[0047] Vacuum the sample chamber. The specific vacuum mode can be selected based on the sample's conductivity: high vacuum mode for coated samples and low vacuum mode for uncoated samples. Wait for the vacuum level to reach the instrument's requirements; typically, high vacuum needs to be lower than [insert value here]. To avoid electron beam scattering affecting image quality.

[0048] Set the electron beam parameters, selecting an accelerating voltage of 5-15kV. Excessive voltage can damage the sample surface, while insufficient voltage will result in inadequate resolution; 5-10kV is recommended for polymer materials. Set the working distance to 5-10mm; a smaller working distance provides higher resolution, suitable for observing small cavities. Use a secondary electron (SE) detector as the preferred method to acquire high-resolution morphological images of the cavity cross-section. If it is necessary to distinguish the cavity from the surrounding medium, a backscattered electron (BSE) detector can be used.

[0049] The image acquisition process begins by scanning the sample at a low magnification (e.g., 500×) to locate the target area containing the hollow structure. The magnification is then gradually increased, such as from 2000× to 10000×, and adjusted according to the cavity size. Once the image is focused, at least 5-10 images from different fields of view are captured to ensure the reliability of the statistical results. When saving the images, a lossless format, such as TIFF, is selected for ease of subsequent measurements.

[0050] III. Cavity diameter measurement: Quantitative analysis is performed using image analysis software. Specialized software such as ImageJ, NanoMeasurer, or the image analysis module built into the SEM image is selected for scale calibration, length measurement, and data statistics. Scale calibration ensures measurement accuracy. In the SEM image, the instrument automatically labels a scale bar, such as "1μm" corresponding to the actual length in the image. In the analysis software, the "scale calibration" function associates the scale bar in the image with the actual length, ensuring accurate measurement units, such as how many nanometers or micrometers one pixel corresponds to.

[0051] In the diameter measurement process, for circular or near-circular cavities, the diameter of the maximum inscribed circle or equivalent circle of the cavity is measured to avoid measurement errors caused by cross-sectional inclination. For elliptical or irregular cavities, the major axis and minor axis diameters are measured separately, and the two values ​​are recorded or the average value is taken as the characteristic diameter. At least 20-30 cavities are measured in each image to cover different fields of view and reduce random errors.

[0052] IV. Data Statistics and Error Analysis to Output Reliable Results: First, the data is organized by entering all measured diameter data into a table, removing obvious outliers, such as data from deformed cavities caused by sample preparation defects. Then, statistical analysis is performed to calculate the average, standard deviation, maximum, and minimum diameter values, reflecting the dimensional distribution characteristics of the hollow structure. For a more intuitive presentation, a dimensional distribution histogram can be drawn. Error sources analysis includes sample preparation errors, instrument errors, and human errors. Sample preparation errors include cavity deformation and cross-sectional tilt; instrument errors include electron beam drift and scale calibration deviation; and human errors include measurement point selection deviations. These errors can be reduced by repeated measurements by multiple people.

[0053] Fifth, it should be noted that sample preparation is crucial in the process of hollow diameter measurement. The freeze-fracture method requires rapid operation to avoid plastic deformation after the sample is heated. The coating thickness should not be too thick, otherwise it will cover the fine structure of the cavity. When measuring, a complete cavity cross section should be selected to avoid damaged or blocked cavities.

[0054] In some alternative embodiments, the hollow structure of the first back membrane contains cavities with a diameter between 0.3 μm and 5 μm.

[0055] In some alternative embodiments, the hollow structure of the second back membrane contains cavities with a diameter between 0.3 μm and 5 μm.

[0056] In some alternative embodiments, the average diameter of the hollow cavity in the first back membrane hollow structure is greater than the average diameter of the hollow cavity in the second back membrane hollow structure.

[0057] In some optional embodiments, the number of cavities in the first back membrane hollow structure is greater than or equal to the number of cavities in the second back membrane hollow structure and is greater than or equal to 0 and less than 300 cavities / mm².

[0058] It should be understood that the number of cavities in the hollow structure of the first back membrane can be the average number of cavities contained in its unit volume, and the number of cavities in the hollow structure of the second back membrane can be the average number of cavities contained in its unit volume.

[0059] Regarding the measurement of the number of hollow structures in the first and second back membrane hollow structures, firstly, multiple unit volumes are randomly selected from the first and second back membrane hollow structures, such as three or five unit volumes, and the number of hollow structures contained in each unit volume is measured. Based on the measurement results, the average number of hollow structures contained in each unit volume of the first back membrane hollow structure is calculated, and the average number of hollow structures contained in each unit volume of the second back membrane hollow structure is also calculated.

[0060] In some alternative embodiments, the number of cavities in the first back membrane hollow structure is less than 50 per mm², and / or the number of cavities in the second back membrane hollow structure is less than 400 per mm².

[0061] In some alternative embodiments, the cavity occurrence rate at the junction of tower bases is greater than the cavity occurrence rate on the surface of the tower base.

[0062] In some optional embodiments, the average absorbance of the cavity in the hollow structure of the first back film is less than the average absorbance of the cavity in the hollow structure of the second back film. Absorbance is a physical quantity that measures the degree to which a material absorbs light of a specific wavelength. In the embodiments of the present invention, the absorbance of the cavity refers to the influence of the cavity on the absorbance of the film layer through light scattering, light reflection and changes in optical path. The greater the influence, the greater the absorbance of the cavity and the darker the color of the cavity. The smaller the influence, the smaller the absorbance of the cavity and the lighter the color of the cavity.

[0063] In some alternative embodiments, the cavity in the hollow structure of the first back membrane appears in the color of at least one of the following colors under a 3D microscope: white, yellow, and green.

[0064] In some alternative embodiments, the cavity in the hollow structure of the second back membrane appears in the color of at least one of the following colors under a 3D microscope: white, yellow, green, and magenta.

[0065] In some alternative embodiments, the light spot of the film structure on the silicon substrate has one or more of the following characteristics, but is not limited to:

[0066] Feature 1: The light spot appears uniformly white under a 3D microscope, and the edge of the light spot is smooth with no film residue.

[0067] Feature 2: The size of the light spot ranges from 16µm to 25µm.

[0068] Feature 3: The residual film coverage at the edge of the light spot is less than 1%, while the control group light spot appears as an uneven white under a 3D microscope, with a spot size of 15µm to 23µm and residual film at the edge of the spot.

[0069] It should be understood that the light spot in the embodiments of the present invention includes the laser-opening light spot and other light spots. The light spot film coverage rate is the ratio of the area of ​​the residual film after laser film opening to the surface area of ​​the cavity.

[0070] Taking an N-type BC battery as an example, the silicon substrate is an N-type silicon substrate, the first surface is the back side of the N-type silicon substrate, the first doped region is a P-type region, the second doped region is an N-type region, the first film structure is a P-type back film structure, the second film structure is an N-type back film structure, and the third film structure is an isolation region film structure.

[0071] Figure 2 A structural diagram of an N-type BC cell in a back-contact solar cell is shown. As shown in the figure, the N-type BC cell includes: an N-type silicon substrate 10, a back surface of the N-type silicon substrate 11, a P-type region 12, an N-type region 13, an isolation region 14 of the N-type BC cell, a P-type back film structure 15 and an N-type back film structure 16, a first back film hollow structure 17 of the N-type BC cell, and a second back film hollow structure 18 of the N-type BC cell.

[0072] Figure 3 This illustration shows a partial film structure of an N-type BC cell in a back-contact solar cell according to an embodiment of the present disclosure. Taking the P-type region of the N-type BC cell as an example, as shown... Figure 3 As shown, the P-type region 12 structure includes: a first tunneling oxide layer 121, a P-type polysilicon layer 122, and a P-type back film structure 123.

[0073] Similar to the P-region structure, the N-type region 13 structure includes: a second tunneling oxide layer, an N-type polysilicon layer, and an N-type back film layer structure.

[0074] A P-type back-side film structure 123 is deposited on the surface of the P-type region 12 away from the N-type silicon substrate 10. See Figure 3 The P-type back film structure 123 may include: a first ultrathin silicon oxide layer 1231, a first aluminum oxide layer 1232, a first double-layer silicon nitride 1233, a first double-layer silicon oxynitride, a first silicon oxide layer 1236, a first back film hollow structure 1237 of the N-type BC battery, and a P-region electrode 1238. The refractive index of each silicon nitride layer in the first double-layer silicon nitride is greater than a first preset threshold. The first double-layer silicon oxynitride includes a first silicon oxynitride layer 1234 and a second silicon oxynitride layer 1235. The refractive index of the first silicon oxynitride layer 1234 is greater than the refractive index of the second silicon oxynitride layer 1235.

[0075] In an N-type BC cell, an N-type back film structure is deposited on the surface of the N-type region 13 away from the N-type silicon substrate. The N-type back film structure may include: a second ultrathin silicon oxide layer, a second aluminum oxide layer, a second double-layer silicon nitride, a second double-layer silicon oxynitride, a second silicon oxide layer, a second back film hollow structure of the N-type BC cell, and an N-region electrode. The refractive index of each silicon nitride layer in the second double-layer silicon nitride is greater than a second preset threshold. The second double-layer silicon oxynitride includes a third silicon oxynitride layer and a fourth silicon oxynitride layer. The refractive index of the third silicon oxynitride layer is greater than the refractive index of the fourth silicon oxynitride layer.

[0076] The back-contact solar cell provided in this embodiment, taking an N-type BC cell as an example, includes a first film layer structure, namely a P-type back film layer structure, comprising a first tunneling oxide layer, a P-type polycrystalline silicon layer, a first ultrathin silicon oxide layer, a first aluminum oxide layer, a first double-layer silicon nitride, a first double-layer silicon oxynitride, a first silicon oxide layer, a first back film hollow structure, and a P-region electrode. The refractive index of each silicon nitride layer in the first double-layer silicon nitride is greater than a first preset threshold. The first double-layer silicon oxynitride includes a first silicon oxynitride layer and a second silicon oxynitride layer. The refractive index of the first silicon oxynitride layer is... The refractive index of the second silicon oxynitride layer is greater than that of the second silicon oxynitride layer. The second film structure, namely the N-type back film structure, includes a second tunneling oxide layer, an N-type polycrystalline silicon layer, a second ultrathin silicon oxide layer, a second aluminum oxide layer, a second double-layer silicon nitride, a second double-layer silicon oxynitride, a second silicon oxide layer, a second back film hollow structure, and an N-region electrode. The refractive index of each silicon nitride layer in the second double-layer silicon nitride is greater than a second preset threshold. The second double-layer silicon oxynitride includes a third silicon oxynitride layer and a fourth silicon oxynitride layer, with the refractive index of the third silicon oxynitride layer being greater than that of the fourth silicon oxynitride layer. Back-contact solar cells using this structure effectively improve the passivation effect of the back film refractive index, while also increasing the back film hollow structure and enhancing the laser-driven film-opening effect, which is beneficial for ohmic contact of the metal electrodes, thereby improving cell conversion efficiency and module power.

[0077] In some optional embodiments, the first preset threshold value ranges from 2.05 to 2.25.

[0078] In some optional embodiments, the second preset threshold value ranges from 2.05 to 2.25.

[0079] In some alternative embodiments, the refractive index of the first silicon oxynitride layer ranges from 1.80 to 1.95.

[0080] In some alternative embodiments, the refractive index of the second silicon oxynitride layer ranges from 1.65 to 1.85.

[0081] In some alternative embodiments, the refractive index of the third silicon oxynitride layer ranges from 1.80 to 1.95.

[0082] In some alternative embodiments, the refractive index of the fourth silicon oxynitride layer ranges from 1.65 to 1.85.

[0083] In some alternative embodiments, the thickness of the first ultrathin silicon oxide layer ranges from 0.05 nm to 1 nm.

[0084] In some alternative embodiments, the thickness of the second ultrathin silicon oxide layer ranges from 0.05 nm to 1 nm.

[0085] In some alternative embodiments, the thickness of the first alumina layer ranges from 3 nm to 10 nm.

[0086] In some alternative embodiments, the thickness of the second alumina layer ranges from 3 nm to 10 nm.

[0087] In some alternative embodiments, the thickness of the first silicon oxynitride layer ranges from 2 nm to 15 nm.

[0088] In some alternative embodiments, the thickness of the second silicon oxynitride layer ranges from 2 to 15 nm.

[0089] In some alternative embodiments, the thickness of the third silicon oxynitride layer ranges from 2 nm to 15 nm.

[0090] In some alternative embodiments, the thickness of the fourth silicon oxynitride layer ranges from 2 nm to 15 nm.

[0091] In some alternative embodiments, the thickness of the first silicon oxide layer ranges from 5 nm to 80 nm.

[0092] In some alternative embodiments, the thickness of the second silicon oxide layer ranges from 5 nm to 80 nm.

[0093] In some alternative embodiments, the number of cavities in the P region on the back side is greater than or equal to the number of cavities in the N region on the back side, and is greater than or equal to 0.

[0094] Figure 4 A flowchart illustrating a back-contact solar cell deposition method provided in this disclosure. (Refer to...) Figure 4 The method includes:

[0095] S41, Deposited silicon substrate.

[0096] S42. Alternatingly depositing a first doped region, a second doped region, and an isolation region on a first surface of a silicon substrate, wherein the doping polarities of the first doped region and the second doped region are opposite, including: depositing a first film structure on the surface of the first doped region away from the silicon substrate; depositing a second film structure on the surface of the second doped region away from the silicon substrate; and depositing a third film structure on the surface of the isolation region away from the silicon substrate; wherein the first film structure and the second film structure are separated by the third film structure; the first film structure includes a first back film hollow structure, the second film structure includes a second back film hollow structure, and the cavity diameter in the first back film hollow structure and the second back film hollow structure is less than 10µm.

[0097] Taking an N-type BC cell as an example, the silicon substrate is an N-type silicon substrate, the first surface is the back side of the N-type silicon substrate, the first doped region is a P-type back film structure, the second doped region is an N-type back film structure, and the third film structure is an isolation region film structure. The first film structure is deposited on the side of the first doped region away from the silicon substrate by depositing a P-type back film structure on the side of the P-type back film structure away from the N-type silicon substrate. The second film structure is deposited on the side of the second doped region away from the silicon substrate by depositing an N-type back film structure on the side of the N-type back film structure away from the N-type silicon substrate.

[0098] The aforementioned first doped region and the first film structure disposed thereon, which is far from the silicon substrate, are P-type back-side film structures. The P-type back-side film structure may include: a first tunneling oxide layer, a P-type polycrystalline silicon layer, a first ultrathin silicon oxide layer, a first aluminum oxide layer, a first double-layer silicon nitride, a first double-layer silicon oxynitride, a first silicon oxide layer, a first back-film hollow structure, and a P-region electrode. The refractive index of each silicon nitride layer in the first double-layer silicon nitride is greater than a first preset threshold. The first double-layer silicon oxynitride includes a first silicon oxynitride layer and a second silicon oxynitride layer. The refractive index of the first silicon oxynitride layer is greater than the refractive index of the second silicon oxynitride layer.

[0099] The aforementioned second doped region and the second film structure disposed thereon, which is far from the silicon substrate, are N-type back-side film structures. The N-type back-side film structure may include: a second tunneling oxide layer, an N-type polycrystalline silicon layer, a second ultrathin silicon oxide layer, a second aluminum oxide layer, a second double-layer silicon nitride, a second double-layer silicon oxynitride, a second silicon oxide layer, a second back-film hollow structure, and an N-region electrode. The refractive index of each silicon nitride layer in the second double-layer silicon nitride is greater than a second preset threshold. The second double-layer silicon oxynitride includes a third silicon oxynitride layer and a fourth silicon oxynitride layer. The refractive index of the third silicon oxynitride layer is greater than the refractive index of the fourth silicon oxynitride layer.

[0100] See Figure 5 The above method for depositing N-type BC solar cells includes the following process:

[0101] S51, depositing an N-type silicon substrate.

[0102] S52. Alternately deposit a P-type back film structure, an N-type back film structure, and an isolation region film structure on the back side of an N-type silicon substrate. Deposit a P-type back film structure on the surface of the P-type back film structure away from the N-type silicon substrate, deposit an N-type back film structure on the surface of the N-type back film structure away from the N-type silicon substrate, and deposit a third film structure on the surface of the isolation region away from the silicon substrate. The P-type back film structure and the N-type back film structure are separated by the isolation region film structure. The P-type film structure includes a first back film hollow structure, and the N-type film structure includes a second back film hollow structure. The cavity diameter in the P-type back film hollow structure and the N-type back film hollow structure is less than 10µm.

[0103] Specifically, S52 deposits a P-type back-side film structure on the surface of the P-type back-side film structure away from the N-type silicon substrate, which includes (not shown in the figure): depositing a first tunneling oxide layer on the side of the P-type back-side film structure away from the N-type silicon substrate, depositing a P-type polycrystalline silicon layer, depositing a first ultrathin silicon oxide layer, depositing a first aluminum oxide layer, depositing a first double-layer silicon nitride, depositing a first double-layer silicon oxynitride, depositing a first silicon oxide layer, depositing a first back-film hollow structure and a P-region electrode. The refractive index of each silicon nitride layer in the first double-layer silicon nitride is greater than a first preset threshold. The first double-layer silicon oxynitride includes a first silicon oxynitride layer and a second silicon oxynitride layer. The refractive index of the first silicon oxynitride layer is greater than the refractive index of the second silicon oxynitride layer. The cavity diameter in the first back-film hollow structure is between 0.1µm and 10µm.

[0104] Specifically, S52 deposits an N-type back-side film structure on the surface of the N-type back-side film structure away from the N-type silicon substrate, which includes (not shown in the figure): depositing a second tunneling oxide layer on the side of the N-type back-side film structure away from the N-type silicon substrate, depositing an N-type polycrystalline silicon layer, depositing a second ultrathin silicon oxide layer, depositing a second aluminum oxide layer, depositing a second double-layer silicon nitride, depositing a second double-layer silicon oxynitride, depositing a second silicon oxide layer, depositing a second back-side hollow structure and an N-region electrode. The refractive index of each silicon nitride layer in the second double-layer silicon nitride is greater than a second preset threshold. The second double-layer silicon oxynitride includes a third silicon oxynitride layer and a fourth silicon oxynitride layer. The refractive index of the third silicon oxynitride layer is greater than the refractive index of the fourth silicon oxynitride layer. The cavity diameter in the second back-side hollow structure is between 0.1µm and 10µm.

[0105] It should be understood that after wet polishing, N-type silicon wafers are deposited with tunneling oxide and polycrystalline silicon layers using LPCVD thermal oxidation technology. Then, boron diffusion and phosphorus diffusion are performed in a high-temperature diffusion furnace to obtain tunneling oxide, P-type polycrystalline silicon, tunneling oxide, and N-type polycrystalline silicon passivation contact structure. Finally, laser and wet methods are used to isolate the P-region and N-region.

[0106] In some alternative embodiments, in S52, depositing the first ultrathin silicon oxide layer includes a first deposition process, and / or, in S52, depositing the second ultrathin silicon oxide layer includes a first deposition process.

[0107] The first deposition process includes: inserting the silicon wafer into the aluminum boat and placing it in the ALD cavity, evacuating, preheating, and when the internal pressure reaches the set value, turning on the ozone generator at 10%-95% power, and introducing ozone gas for 1s-200s at a temperature range of 150℃-300℃ and a pressure of 0.1mbar-0.8mbar. Then, purging the cavity with high-purity nitrogen for 1s-100s. The thickness of the first ultrathin silicon oxide layer and the second ultrathin silicon oxide layer is approximately 0.05-1nm.

[0108] In some alternative embodiments, in S52, depositing the first alumina layer includes a second deposition process, and / or, in S52, depositing the second alumina layer includes a second deposition process.

[0109] The second deposition process includes: alternating introduction of trimethylaluminum (TMA) and H2O vapor into the process chamber at a temperature range of 150℃-300℃ and a pressure of 0.1mbar-0.8mbar. First, TMA is introduced for 1s-20s, followed by N2 purging for 1s-10s, then H2O vapor is introduced for 1s-30s, and finally N2 purging for 1s-10s, thus completing the deposition of alumina thin films. The thickness of the first and second alumina films is 3-10nm.

[0110] In some optional embodiments, the first double-layer silicon nitride includes a first primary silicon nitride layer and a first layer of silicon nitride. In S52, depositing the first double-layer silicon nitride on the first alumina layer using PECVD includes a third deposition process. And / or, the second double-layer silicon nitride includes a second primary silicon nitride layer and a second layer of silicon nitride. In S52, depositing the second double-layer silicon nitride on the second alumina layer using PECVD includes a fourth deposition process. The third deposition process includes depositing the first primary silicon nitride layer and the first layer of silicon nitride, and the fourth deposition process includes depositing the second primary silicon nitride layer and the second layer of silicon nitride. The first and second primary silicon nitride layers closer to the silicon substrate have lower deposition power to reduce plasma bombardment damage to the alumina, while the first and second silicon nitride layers farther from the silicon substrate have higher deposition power to ensure the deposition rate.

[0111] The deposition of the first and second silicon nitride layers includes the following parameters: temperature range of 450℃-550℃, ammonia flow rate to silane flow rate ratio of 5:11, silane flow rate range of 1500sccm-2000sccm, ammonia flow rate range of 7500sccm-16000sccm, pressure range of 1000Torr-2000mTorr, duty cycle range of m:n, RF power range of 6000W-25000W, and duration range of 90s-300s. Specifically, m ranges from 2 to 5, n ranges from 50 to 90, and the refractive index of the first and second silicon nitride layers is 2.05-2.25.

[0112] The deposition of the first and second silicon nitride layers includes the following parameters: temperature range of 450℃-550℃, ammonia flow rate to silane flow rate ratio of 5:11, silane flow rate range of 1500sccm-2000sccm, ammonia flow rate range of 7500sccm-20000sccm, pressure range of 1000Torr-2000mTorr, duty cycle range of m:n, RF power range of 15000W-25000W, duration range of 500s-900s, and RF power of 15000W-25000W for both the first and second silicon nitride layers.

[0113] In some optional embodiments, the first double-layer silicon oxynitride includes a first silicon oxynitride layer and a second silicon oxynitride layer. In S52, the deposition of the first double-layer silicon oxynitride by PECVD includes a fifth deposition process, and / or, the second double-layer silicon oxynitride includes a third silicon oxynitride layer and a fourth silicon oxynitride layer. In S92, the deposition of the second double-layer silicon oxynitride by PECVD includes a sixth deposition process. The fifth deposition process includes depositing the first silicon oxynitride layer and depositing the second silicon oxynitride layer, and the sixth deposition process includes depositing the third silicon oxynitride layer and depositing the fourth silicon oxynitride layer.

[0114] The deposition of the first and third silicon oxynitride layers includes the following parameters: temperature range of 450℃-550℃, nitrous oxide flow rate: ammonia flow rate: silane flow rate ratio of 8:3:1, silane flow rate range of 700sccm-1000sccm, ammonia flow rate range of 6300sccm-9000sccm, nitrous oxide flow rate range of 700sccm-1000sccm, pressure range of 1000mTorr-2000mTorr, duty cycle range of a:b, radio frequency power range of 15000W-25000W, duration range of 10s-100s, where a ranges from 2 to 5 and b ranges from 100 to 130, the refractive index of the first and third silicon oxynitride layers is 1.80-1.95, and the thickness is 2nm-15nm.

[0115] The deposition of the second and fourth silicon oxynitride layers includes the following parameters: temperature range of 450℃-550℃, nitrous oxide flow rate: ammonia flow rate: silane flow rate ratio of 16:3:1, silane flow rate range of 400sccm-600sccm, ammonia flow rate range of 1200sccm-1800sccm, nitrous oxide flow rate range of 6400sccm-9600sccm, pressure range of 1000mTorr-2000mTorr, duty cycle range of a:b, radio frequency power range of 15000W-25000W, duration range of 10s-100s, refractive index of the second and fourth silicon oxynitride layers of 1.65-1.85, and thickness of 2nm-15nm.

[0116] In some alternative embodiments, in S52, the deposition of the first silicon oxide layer by PECVD includes a seventh deposition process, and / or, in S52, the deposition of the second silicon oxide layer by PECVD includes a seventh deposition process.

[0117] The seventh deposition process includes: a temperature range of 450℃-550℃, a nitrous oxide to silane flow rate ratio of 10-20, a silane flow rate range of 500sccm-700sccm, a nitrous oxide flow rate range of 5000sccm-12000sccm, a pressure range of 900mTorr-2000mTorr, a duty cycle range of c:d, a ​​radio frequency power range of 10000W-25000W, a duration range of 50s-500s, where c ranges from 2 to 5, d ranges from 100 to 160, the refractive index of the first and second silicon oxide layers is 1.45-1.75, and the thickness is 5nm-80nm.

[0118] In some alternative embodiments, the first deposition process is cycled 1 to 100 times; further, the first deposition process can be cycled 1 to 10 times.

[0119] In some alternative embodiments, the second deposition process is cycled 10 to 150 times, and further, the second deposition process can be cycled 25 to 45 times.

[0120] For ease of understanding, this invention describes in detail a back-contact solar cell fabrication method through a specific embodiment, specifically using an N-type BC cell fabrication method, including:

[0121] 1. After wet polishing, N-type silicon wafers are deposited with tunneling oxide and polycrystalline silicon layers using LPCVD thermal oxidation technology. Then, boron diffusion and phosphorus diffusion are performed in a high-temperature diffusion furnace to obtain tunneling oxide / P-type polycrystalline silicon and tunneling oxide / N-type polycrystalline silicon passivation contact structures. Finally, laser and wet methods are used to isolate the P-region and N-region.

[0122] 2. First, deposit an ultrathin layer of silicon oxide (0.6 nm) and aluminum oxide (6 nm).

[0123] Specifically, after inserting the silicon wafer into the aluminum boat, it is placed in the ALD chamber, evacuated, preheated, and the internal pressure reaches the set value. The ozone generator is then turned on at 40% power. Under a temperature range of 295℃ and a pressure of 0.7 mbar, ozone gas is introduced for 90 seconds, followed by purging the chamber with high-purity nitrogen for 10 seconds. This process is repeated 5 times to complete the ultrathin silicon oxide deposition with a thickness of approximately 0.6 nm. Then, under the same temperature and internal pressure, trimethylaluminum (TMA) and H2O vapor are alternately introduced into the process chamber. TMA is introduced first for 8 seconds, followed by purging with N2 for 10 seconds, then H2O vapor for 8 seconds, and then purging with N2 for 10 seconds. This process is repeated 42 times to complete the alumina film deposition with a thickness of 6 nm.

[0124] 3. Two layers of high-refractive-index silicon nitride are deposited on alumina using PECVD. The silicon nitride film layer closer to the silicon substrate has a lower deposition power to reduce plasma bombardment damage to the alumina, while the silicon nitride layer farther from the silicon substrate has a higher deposition power to ensure the deposition rate.

[0125] The first layer of high-refractive-index silicon nitride was deposited with a refractive index of 2.15 and a thickness of 25 nm. The process conditions were as follows: temperature 530℃, ammonia flow rate to silane flow rate ratio of 5.3, silane flow rate of 1900 sccm, ammonia flow rate of 10070 sccm, pressure of 1200 mTorr, duty cycle of 5:90, RF power of 10000 W, and duration of 290 s.

[0126] A high-refractive-index silicon nitride sublayer with a refractive index of 2.08 and a thickness of 110 nm was deposited. The process conditions were as follows: temperature 530℃, ammonia flow rate to silane flow rate ratio of 10.8, silane flow rate of 1600 sccm, ammonia flow rate of 17300 sccm, pressure of 1600 mTorr, duty cycle of 4:50, RF power of 24000 W, and duration of 760 s.

[0127] 4. PECVD deposition of two layers of silicon oxynitride with different refractive indices.

[0128] High-refractive-index silicon oxynitride was deposited with a refractive index of 1.88 and a thickness of 8 nm. The process conditions were as follows: temperature 530℃, nitrous oxide flow rate: ammonia flow rate: silane flow rate of 8:3:1, silane flow rate of 800 sccm, ammonia flow rate of 2400 sccm, nitrous oxide flow rate of 6400 sccm, pressure of 1100 mTorr, duty cycle of 5:150, RF power of 22000 W, and duration of 80 s.

[0129] Low-refractive-index silicon oxynitride was deposited with a refractive index of 1.69 and a thickness of 7 nm. The process conditions were as follows: temperature 530℃, nitrous oxide flow rate: ammonia flow rate: silane flow rate of 16:3:1, silane flow rate 450 sccm, ammonia flow rate 1350 sccm, nitrous oxide flow rate 7200 sccm, pressure 1200 mTorr, duty cycle 5:120, RF power 24000 W, and duration 50 s.

[0130] 5. PECVD deposition of silicon oxide with a refractive index of 1.59 and a thickness of 80nm. The process conditions are as follows: temperature 530℃, nitrous oxide to silane flow rate ratio of 12, silane flow rate of 550sccm, nitrous oxide flow rate of 6600sccm, pressure of 950mTorr, duty cycle of 4:200, RF power of 24000W, and duration of 400s.

[0131] 6. Deposit the front-side film using conventional methods: ultrathin silicon oxide / alumina / silicon nitride / silicon oxynitride / silicon oxide, then sinter and test.

[0132] Figure 6 , Figure 7 , Figure 8 This is a 3D magnified microscopic schematic diagram of the first and second hollow backsheet structures in a back-contact solar cell, provided in an embodiment of this disclosure. Figure 6 , Figure 7 The P-type cavity 19 and the N-type cavity 20 are significantly different in number, color, size and distribution.

[0133] Figure 9 , Figure 10This is a 3D microscope magnified schematic diagram of the light spot of the film layer in the back contact solar cell provided in the embodiment of the present disclosure, which shows that there is no mold opening residue in the light spot of the film layer in the back contact solar cell in the embodiment of the present disclosure.

[0134] The stacked film structure of ultra-thin silicon oxide + aluminum oxide + high-refractive silicon nitride + silicon oxynitride + silicon oxide provided by this invention, with the addition of a unique hollow back film structure, not only solves the problem of poor passivation of the back film layer, but also improves the ohmic contact effect of the coated battery metal electrode, increasing the battery conversion efficiency by 0.06% and the module power by 0.93W. Table 1 shows the comparison results of the cell conversion efficiency of the experimental group and the control group, and Table 2 shows the comparison results of the module power of the experimental group and the control group.

[0135] Table 1

[0136]

[0137] Table 2

[0138]

[0139] In some embodiments, the ultrathin silicon oxide is made to 0.3 nm, the aluminum oxide to 5 nm, the bottom layer high-refractive-index silicon nitride to 2.08 and 23 nm thick, the second layer silicon nitride to 2.02 and 90 nm thick, the bottom layer silicon oxynitride to 5 nm thick, the top layer silicon oxynitride to 5 nm thick, the top layer silicon oxide to 1.49 and 50 nm thick, without stacking a hollow back film structure, the battery efficiency is improved by 0.03 to 0.05%.

[0140] It is understood that the various method embodiments mentioned above in this disclosure can be combined with each other to form combined embodiments without violating the principle and logic. Due to space limitations, this disclosure will not elaborate further. Those skilled in the art will understand that in the above methods of specific implementation, the specific execution order of each step should be determined by its function and possible internal logic.

[0141] Example embodiments have been disclosed herein, and while specific terminology has been used, it is for illustrative purposes only and should be construed as such, and is not intended to be limiting. In some instances, it will be apparent to those skilled in the art that features, characteristics, and / or elements described in connection with particular embodiments may be used alone, or in combination with features, characteristics, and / or elements described in connection with other embodiments, unless otherwise expressly indicated. Therefore, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of this disclosure as set forth by the appended claims.

Claims

1. A back-contact solar cell, characterized in that, include: A silicon substrate includes a first surface, on which a first doped region, a second doped region, and an isolation region are alternately disposed; the first doped region and the second doped region have opposite doping polarities; a first film structure is disposed on the surface of the first doped region away from the silicon substrate; a second film structure is disposed on the surface of the second doped region away from the silicon substrate; and a third film structure is disposed on the surface of the isolation region away from the silicon substrate. The first film structure and the second film structure are separated by the third film structure. The first film structure includes a first backsheet hollow structure, and the second film structure includes a second backsheet hollow structure. The cavity diameter in the first backsheet hollow structure and the second backsheet hollow structure is less than 10 µm.

2. The back-contact solar cell according to claim 1, characterized in that, The cavity diameter in at least one of the first back membrane hollow structures and / or at least one of the second back membrane hollow structures is between 0.3µm and 5µm.

3. The back-contact solar cell according to claim 1, characterized in that, The average diameter of the hollow cavity in the first back membrane hollow structure is greater than the average diameter of the hollow cavity in the second back membrane hollow structure.

4. The back-contact solar cell according to claim 1, characterized in that, The number of cavities in the first back membrane hollow structure is greater than or equal to the number of cavities in the second back membrane hollow structure and is greater than or equal to 0 cavities / mm². The difference between the number of cavities in the second back membrane hollow structure and the number of cavities in the first back membrane hollow structure is less than 300 cavities / mm².

5. The back-contact solar cell according to claim 1, characterized in that, The number of cavities in the first back membrane hollow structure is less than 50 per mm², and / or the number of cavities in the second back membrane hollow structure is less than 400 per mm².

6. The back-contact solar cell according to claim 1, characterized in that, The average absorbance of the cavity in the first backsheet hollow structure is less than the average absorbance of the cavity in the second backsheet hollow structure.

7. The back-contact solar cell according to claim 6, characterized in that, The cavity in the hollow structure of the first back membrane appears in at least one of the following colors under a 3D microscope: white, yellow, and green.

8. The back-contact solar cell according to claim 6, characterized in that, The cavities in the hollow structure of the second back membrane appear in at least one of the following colors under a 3D microscope: white, yellow, green, and magenta.

9. The back-contact solar cell according to claim 1, characterized in that, The light spot of the film structure on the silicon substrate appears uniformly white under a 3D microscope.

10. The back-contact solar cell according to claim 9, characterized in that, The diameter of the light spot ranges from 16µm to 25µm.

11. The back-contact solar cell according to claim 10, characterized in that, The residual film coverage at the edge of the light spot is less than 1%.

12. A method for fabricating a back-contact solar cell, characterized in that, include: Preparation of silicon substrate; A first doped region, a second doped region, and an isolation region are alternately deposited on a first surface of the silicon substrate, wherein the doping polarities of the first doped region and the second doped region are opposite. The process includes: depositing a first film structure on the surface of the first doped region away from the silicon substrate; depositing a second film structure on the surface of the second doped region away from the silicon substrate; and depositing a third film structure on the surface of the isolation region away from the silicon substrate. The first film structure and the second film structure are separated by the third film structure. The first film structure includes a first backsheet hollow structure, and the second film structure includes a second backsheet hollow structure. The cavity diameter in the first backsheet hollow structure and the second backsheet hollow structure is less than 10 µm.

13. The method according to claim 12, characterized in that, The back-contact solar cell is an N-type BC cell, the silicon substrate is an N-type silicon substrate, the first surface is the back side of the N-type silicon substrate, the first doped region is a P-type region, the second doped region is an N-type region, the first film structure is a P-type back-side film structure, the second film structure is an N-type back-side film structure, and the third film structure is an isolation region film structure. Depositing the first film structure on the surface of the first doped region away from the silicon substrate involves depositing the P-type back-side film structure on the surface of the P-type region away from the N-type silicon substrate. Depositing the second film structure on the surface of the second doped region away from the silicon substrate involves depositing the N-type back-side film structure on the surface of the N-type region away from the N-type silicon substrate. Depositing the P-type backplane film structure on the surface of the P-type region away from the N-type silicon substrate sequentially includes: depositing a first tunneling oxide layer on the side of the P-type backplane film structure away from the N-type silicon substrate, depositing a P-type polycrystalline silicon layer, depositing a first ultrathin silicon oxide layer, depositing a first aluminum oxide layer, depositing a first double-layer silicon nitride, depositing a first double-layer silicon oxynitride, depositing a first silicon oxide layer, depositing the first backplane hollow structure and the P-region electrode, wherein the refractive index of each silicon nitride layer in the first double-layer silicon nitride is greater than a first preset threshold, the first double-layer silicon oxynitride includes a first silicon oxynitride layer and a second silicon oxynitride layer, and the refractive index of the first silicon oxynitride layer is greater than the refractive index of the second silicon oxynitride layer; and / or The deposition of the N-type back film structure on the surface of the N-type region away from the N-type silicon substrate includes, in sequence: depositing a second tunneling oxide layer on the side of the N-type back film structure away from the N-type silicon substrate, depositing an N-type polycrystalline silicon layer, depositing a second ultrathin silicon oxide layer, depositing a second aluminum oxide layer, depositing a second double-layer silicon nitride, depositing a second double-layer silicon oxynitride, depositing a second silicon oxide layer, depositing a second back film hollow structure and an N-region electrode, wherein the refractive index of each silicon nitride layer in the second double-layer silicon nitride is greater than a second preset threshold, and the second double-layer silicon oxynitride includes a third silicon oxynitride layer and a fourth silicon oxynitride layer, wherein the refractive index of the third silicon oxynitride layer is greater than the refractive index of the fourth silicon oxynitride layer.

14. The method according to claim 13, characterized in that, Depositing a first ultrathin silicon oxide layer includes a first deposition process, and / or, depositing a second ultrathin silicon oxide layer includes the first deposition process; The first deposition process includes: inserting the silicon wafer into the aluminum boat and placing it in the ALD cavity, evacuating, preheating, and when the internal pressure reaches the set value, turning on the ozone generator at 10%-95% power, and introducing ozone gas for 1s-200s at a temperature range of 150℃-300℃ and a pressure of 0.1mbar-0.8mbar, and then purging the cavity with high-purity nitrogen for 1s-100s.

15. The method according to claim 14, characterized in that, Depositing a first alumina layer includes a second deposition process, and / or, depositing a second alumina layer includes the second deposition process; The second deposition process includes: alternatingly introducing trimethylaluminum (TMA) and H2O vapor into the process chamber at a temperature range of 150℃-300℃ and a pressure of 0.1mbar-0.8mbar. First, TMA is introduced for 1s-20s, then N2 is introduced for 1s-10s, then H2O vapor is introduced for 1s-30s, and then N2 is introduced for 1s-10s.

16. The method according to claim 13, characterized in that, The first double-layer silicon nitride includes a first primary silicon nitride layer and a first layer of silicon nitride. Depositing the first double-layer silicon nitride on the first alumina layer using PECVD includes a third deposition process. And / or, the second double-layer silicon nitride includes a second primary silicon nitride layer and a second layer of silicon nitride. Depositing the second double-layer silicon nitride on the second alumina layer using PECVD includes a fourth deposition process. The third deposition process includes depositing the first primary silicon nitride layer and depositing the first layer of silicon nitride, and the fourth deposition process includes depositing the second primary silicon nitride layer and depositing the second layer of silicon nitride. Wherein... The deposition of the first silicon nitride layer and the deposition of the second silicon nitride layer include: a temperature range of 450℃-550℃, an ammonia flow rate to silane flow rate ratio of 5:11, a silane flow rate range of 1500sccm-2000sccm, an ammonia flow rate range of 7500sccm-16000sccm, a pressure range of 1000Torr-2000mTorr, a duty cycle range of m:n, a radio frequency power range of 6000W-25000W, and a duration range of 90s-300s, wherein m ranges from 2 to 5 and n ranges from 50 to 90; The deposition of the first silicon nitride layer and the deposition of the second silicon nitride layer include: a temperature range of 450℃-550℃, an ammonia flow rate to silane flow rate ratio of 5:11, a silane flow rate range of 1500sccm-2000sccm, an ammonia flow rate range of 7500sccm-20000sccm, a pressure range of 1000Torr-2000mTorr, a duty cycle range of m:n, a radio frequency power range of 15000W-25000W, and a duration range of 500s-900s.

17. The method according to claim 13, characterized in that, The first double-layer silicon oxynitride includes a first silicon oxynitride layer and a second silicon oxynitride layer. Depositing the first double-layer silicon oxynitride using PECVD includes a fifth deposition process. And / or, the second double-layer silicon oxynitride includes a third silicon oxynitride layer and a fourth silicon oxynitride layer. Depositing the second double-layer silicon oxynitride using PECVD includes a sixth deposition process. The fifth deposition process includes depositing the first silicon oxynitride layer and depositing the second silicon oxynitride layer, and the sixth deposition process includes depositing the third silicon oxynitride layer and depositing the fourth silicon oxynitride layer; wherein... The deposition of the first silicon oxynitride layer and the deposition of the third silicon oxynitride layer include: a temperature range of 450℃-550℃, a nitrous oxide flow rate: ammonia flow rate: silane flow rate ratio of 8:3:1, a silane flow rate range of 700sccm-1000sccm, an ammonia flow rate range of 6300sccm-9000sccm, a nitrous oxide flow rate range of 700sccm-1000sccm, a pressure range of 1000mTorr-2000mTorr, a duty cycle range of a:b, a radio frequency power range of 15000W-25000W, and a duration range of 10s-100s, wherein a ranges from 2 to 5 and b ranges from 100 to 130; The deposition of the second silicon oxynitride layer and the deposition of the fourth silicon oxynitride layer include: a temperature range of 450℃-550℃, a nitrous oxide flow rate: ammonia flow rate: silane flow rate ratio of 16:3:1, a silane flow rate range of 400sccm-600sccm, an ammonia flow rate range of 1200sccm-1800sccm, a nitrous oxide flow rate range of 6400sccm-9600sccm, a pressure range of 1000 mTorr-2000 mTorr, a duty cycle range of a:b, a radio frequency power range of 15000W-25000W, and a duration range of 10s-100s.

18. The method according to claim 13, characterized in that, The deposition of the first silicon oxide layer by PECVD includes a seventh deposition process, and / or the deposition of the second silicon oxide layer by PECVD includes the seventh deposition process; The seventh deposition process includes: a temperature range of 450℃-550℃, a nitrous oxide to silane flow rate ratio of 10-20, a silane flow rate range of 500sccm-700sccm, a nitrous oxide flow rate range of 5000sccm-12000sccm, a pressure range of 900mTorr-2000mTorr, a duty cycle range of c:d, a ​​radio frequency power range of 10000W-25000W, and a duration range of 50s-500s, where c ranges from 2 to 5 and d ranges from 100 to 160.

19. The method according to claim 15, characterized in that, The first deposition process is repeated 1 to 10 times, and / or the second deposition process is repeated 25 to 45 times.

Images