A method for manufacturing a tbc solar cell

Abstract

The application discloses a preparation method of a TBC solar cell, which comprises the following steps: dipping a substrate into a specified solution at a predetermined temperature to perform texturing, and controlling the texturing time within a predetermined time; sequentially depositing a tunneling oxide layer and an intrinsic polysilicon layer on the back of the substrate; depositing a mask layer on the side of the intrinsic polysilicon layer away from the tunneling oxide layer; forming a first opening area on the mask layer, and performing boron diffusion on the first opening area to form a boron-doped polysilicon layer; forming a second opening area on the mask layer, and performing phosphorus diffusion on the second opening area to form a phosphorus-doped polysilicon layer; the mask layer remains between the first opening area and the second opening area; and depositing an anti-reflection layer on the back of the substrate. The application can shorten the production process and reduce the risk of laser damage to the cell.

Description

Technical Field

[0001] This invention relates to the field of solar cell manufacturing technology, and in particular to a method for preparing a TBC solar cell. Background Technology

[0002] Bifacial solar cells such as PERC (Passivated Emitter and Rear Cell), TOPCon (Tunnel Oxide Passivated Contact), and HJT (Heterojunction with Intrinsic Thin-layer) all have metal grid lines blocking the front side, preventing the absorption of some incident light and resulting in an unattractive front appearance. IBC (Interdigitated Back Contact Cell) places all electrode grid lines on the back of the cell, thus exhibiting a higher short-circuit current Jsc. Simultaneously, the back metal grid lines can be widened to reduce series resistance Rs, thereby increasing the fill factor FF. This makes the cell not only highly efficient but also aesthetically pleasing. Furthermore, TBC (Tunneling Barrier Cell) cells, which combine TOPCon and BC (Buried Contact Technology) technologies, have attracted widespread attention due to their significant potential for efficiency improvements.

[0003] However, TBC cells with a tunneling passivation structure on the back side still cannot achieve large-scale mass production due to their complex fabrication process and high production cost. Currently, the back side structure of TBC cells involves various combinations of masking, laser, and wet processing, and the isolation problem between the n-region and p-region remains significant. The manufacturing process is complex and lengthy, affecting the cell production efficiency.

[0004] Currently, most TBC fabrication technologies employ multi-step masking and paste printing methods. For example, one approach involves laser removal of the n-region BSG (borosilicate glass) followed by polycrystalline silicon (polycrystalline silicon) deposition for p-area expansion (i.e., boron expansion), and then a second laser scan to form the isolation region. Alternatively, existing technologies typically involve laser transfer of phosphorus paste and boron paste onto the substrate, followed by laser grooving to isolate the n- and p-regions. However, this method is costly in terms of pastes and complex in process. Another approach involves fabricating multiple mask layers separately and subsequently removing them to pattern the n- and p-regions. However, this multi-step mask removal process is not only cumbersome but also costly, making mass production impossible. Summary of the Invention

[0005] The purpose of this invention is to propose a method for preparing TBC solar cells that can shorten the production process and reduce the risk of laser damage to the cells.

[0006] To address the aforementioned technical problems, this invention provides a method for preparing a TBC solar cell, comprising the following:

[0007] The substrate is immersed in a predetermined temperature and a specified solution for texturing, and the texturing time is controlled within a predetermined time.

[0008] A tunneling oxide layer and an intrinsic polycrystalline silicon layer are sequentially deposited on the back side of the substrate;

[0009] A mask layer is deposited on the side of the intrinsic polysilicon layer away from the tunneling oxide layer;

[0010] A first opening region is formed on the mask layer, and a boron-doped polycrystalline silicon layer is formed on the first opening region by boron diffusion.

[0011] A second opening region is formed on the mask layer, and a phosphorus-doped polycrystalline silicon layer is formed on the second opening region by phosphorus diffusion; the mask layer remains between the first opening region and the second opening region; and

[0012] An antireflection layer is deposited on the back side of the substrate.

[0013] Furthermore, the predetermined temperature is between 60°C and 80°C.

[0014] Furthermore, the specified solution includes KOH solution or NaOH solution.

[0015] Furthermore, the mass fraction of the KOH solution or NaOH solution is 1% to 3%.

[0016] Furthermore, the predetermined time is in the range of 15-25 minutes.

[0017] Furthermore, the step of depositing a mask layer on the side of the intrinsic polysilicon layer away from the tunneling oxide layer specifically includes: preparing the mask layer on the intrinsic polysilicon layer using PECVD or LPCVD methods.

[0018] Furthermore, the thickness of the mask layer is in the range of 150nm to 450nm.

[0019] Furthermore, the mask layer is made of silicon nitride material that is resistant to laser damage.

[0020] Furthermore, forming the first opening region on the mask layer specifically includes: using a picosecond green laser to create a groove in the p-region of the mask layer to form the first opening region.

[0021] Furthermore, the step of forming a boron-doped polysilicon layer on the first opening region specifically includes: forming a BSG layer in the first opening region using a boron expansion process, and after passing through a first specified temperature, the intrinsic polysilicon layer located between the first opening region and the tunneling oxide layer becomes the boron-doped polysilicon layer.

[0022] Furthermore, forming the second opening region on the mask layer specifically includes: using a picosecond green laser to create a groove in the n region of the mask layer to form the first opening region.

[0023] Furthermore, the step of forming a phosphorus-doped polycrystalline silicon layer by phosphorus diffusion in the second opening region specifically includes: forming a PSG layer in the second opening region using a phosphorus diffusion process, and after passing through a second specified temperature, the intrinsic polycrystalline silicon layer located between the second opening region and the tunneling oxide layer becomes the phosphorus-doped polycrystalline silicon layer.

[0024] Furthermore, the deposition of the antireflection layer on the back side of the substrate specifically includes: removing the BSG layer and PSG layer by a chain cleaning method, and then depositing the antireflection layer on the back side of the substrate.

[0025] Furthermore, the thickness of the antireflective layer is in the range of 40nm to 90nm.

[0026] Furthermore, the antireflection layer is made of silicon nitride.

[0027] Furthermore, the length of the remaining mask layer is in the range of 40μm to 80μm.

[0028] Through the above technical solution, the present invention has the following beneficial effects:

[0029] The method involves texturing a substrate by immersing it in a predetermined temperature and a specified solution for a predetermined time; sequentially depositing a tunneling oxide layer and an intrinsic polycrystalline silicon layer on the back side of the substrate; depositing a mask layer on the side of the intrinsic polycrystalline silicon layer away from the tunneling oxide layer; forming a first opening region on the mask layer, and performing boron diffusion propagation on the first opening region to form a boron-doped polycrystalline silicon layer; forming a second opening region on the mask layer, and performing phosphorus diffusion propagation on the second opening region to form a phosphorus-doped polycrystalline silicon layer; leaving a mask layer between the first and second opening regions; and depositing an antireflection layer on the back side of the substrate. This method shortens the production process, reduces the risk of laser damage to the battery, and allows for interoperability of laser equipment, saving costs. Attached Figure Description

[0030] Figure 1 This is a flowchart of a method for preparing a TBC solar cell according to an embodiment of the present invention;

[0031] Figure 2This is a schematic diagram of the structure in which a tunneling oxide layer and an intrinsic polycrystalline silicon layer are sequentially formed on the back side of a substrate in a method for fabricating a TBC solar cell according to an embodiment of the present invention.

[0032] Figure 3 This is a schematic diagram of the structure for forming a mask layer in the fabrication method of a TBC solar cell according to an embodiment of the present invention;

[0033] Figure 4 This is a schematic diagram of the structure of forming a first opening region on the mask layer in the fabrication method of a TBC solar cell according to an embodiment of the present invention;

[0034] Figure 5 This is a schematic diagram of the structure in which a BSG layer is formed in the first opening region during the fabrication method of a TBC solar cell in one embodiment of the present invention.

[0035] Figure 6 This is a schematic diagram of the structure in which a second opening region is formed on the mask layer in the fabrication method of a TBC solar cell according to an embodiment of the present invention;

[0036] Figure 7 This is a schematic diagram of the structure in which a PSG layer is formed in the second opening region during the fabrication method of a TBC solar cell in one embodiment of the present invention.

[0037] Figure 8 This is a schematic diagram of the structure of an antireflection layer formed on the back side of a substrate in a method for preparing a TBC solar cell according to an embodiment of the present invention.

[0038] In the figure, 100 is the substrate; 1 is the tunneling oxide layer; 2 is the intrinsic polysilicon layer; 3 is the mask layer; 4 is the first opening region; 5 is the boron-doped polysilicon layer; 6 is the BSG layer; 7 is the second opening region; 8 is the phosphorus-doped polysilicon layer; 9 is the PSG layer; and 10 is the antireflection layer. Detailed Implementation

[0039] The following description, with reference to schematic diagrams, illustrates a method for preparing a TBC solar cell according to the present invention, which represents a preferred embodiment of the invention. It should be understood that those skilled in the art can modify the invention described herein while still achieving its advantageous effects. Therefore, the following description should be understood as being of general knowledge to those skilled in the art and is not intended to limit the invention.

[0040] The serial numbers assigned to components in this document, such as "first," "second," etc., are merely used to distinguish the described objects and have no sequential or technical meaning. The terms "connection" and "linkage" used in this application, unless otherwise specified, include both direct and indirect connections (linkages). In the description of this invention, it should be understood that the terms "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention.

[0041] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0042] The invention is described more specifically by way of example in the following paragraphs with reference to the accompanying drawings. The advantages and features of the invention will become clearer from the following description and claims. It should be noted that the drawings are in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the invention.

[0043] like Figure 1-8 As shown in the figure, an embodiment of the present invention proposes a method for preparing a TBC solar cell, comprising the following steps:

[0044] S1. Immerse the substrate 100 in a predetermined temperature and a specified solution to perform texturing, and control the texturing time within a predetermined time.

[0045] S2. A tunneling oxide layer 1 and an intrinsic polysilicon layer 2 are sequentially deposited on the back side of the substrate 100.

[0046] S3. Deposit a mask layer 3 on the side of the intrinsic polysilicon layer 2 away from the tunneling oxide layer 1;

[0047] S4. A first opening region 4 is formed on the mask layer 3, and a boron-doped polycrystalline silicon layer 5 is formed on the first opening region 4 by boron diffusion.

[0048] S5. A second opening region 7 is formed on the mask layer 3, and a phosphorus-doped polycrystalline silicon layer 8 is formed on the second opening region 7 by phosphorus diffusion; the mask layer 3 remains between the first opening region 4 and the second opening region 7; and

[0049] S6. Deposit an antireflection layer 10 on the back side of the substrate 100.

[0050] The predetermined temperature is between 60℃ and 80℃.

[0051] Preferably, the specified solution includes KOH solution or NaOH solution. Since KOH solution or NaOH solution can be recovered and reused in a closed-loop system, the chemical texturing process using KOH solution or NaOH solution is more environmentally friendly.

[0052] Furthermore, the mass fraction of the KOH solution or NaOH solution is 1% to 3%. Those skilled in the art will understand that the mass fraction of the KOH solution or NaOH solution can also be selected and set according to actual needs.

[0053] In this embodiment, the predetermined time is within the range of 15-25 minutes. Appropriate time control ensures that the silicon wafer surface achieves the ideal roughness, effectively reducing reflection while avoiding absorption losses caused by excessive roughness. Excessive texturing time may lead to excessive etching and wear of the silicon wafer (substrate 100); appropriate time control can reduce this wear and extend the lifespan of the silicon wafer (substrate 100). A texturing time range of 15-25 minutes is sufficient to complete the surface modification of the silicon wafer (substrate 100) while ensuring high production efficiency and avoiding unnecessary extended waiting times. Furthermore, within the predetermined texturing time range, process stability can be ensured, reducing process deviations caused by time fluctuations.

[0054] Furthermore, as those skilled in the art will know, the scheduled time can also be set according to actual needs.

[0055] In S1, such as Figure 2 As shown, the tunneling oxide layer 1 is formed using PEALD (Plasma Enhanced Atomic Layer Deposition), a process performed at a specific deposition temperature. The deposition temperature can be set according to actual requirements.

[0056] In S2, such as Figure 3As shown, the deposition of the mask layer 3 on the side of the intrinsic polysilicon layer 2 away from the tunneling oxide layer 1 specifically includes: preparing the mask layer 3 on the intrinsic polysilicon layer 2 using PECVD (Plasma Enhanced Chemical Vapor Deposition) or LPCVD (Low Pressure Chemical Vapor Deposition).

[0057] In this embodiment, the thickness of the mask layer 3 is in the range of 150nm to 450nm, for example, the thickness of the mask layer 3 is 150nm or 450nm, so that it can be adapted to different process requirements, enhance the selectivity of etching, and also improve the uniformity of the pattern.

[0058] Preferably, the mask layer 3 is made of laser-damage-resistant silicon nitride material, which improves processing accuracy and production efficiency.

[0059] In S3, such as Figure 4 As shown, forming the first opening region 4 on the mask layer 3 specifically includes: using a picosecond green laser to slot in the p region of the mask layer 3 to form the first opening region 4 (the area outside the p region is unaffected by boron due to the presence of the remaining mask layer 3). Using a picosecond green laser can provide high-precision and low-damage processing effects, and can also improve the performance and reliability of the finished product.

[0060] In S3, such as Figure 5 As shown, the step of forming a boron-doped polycrystalline silicon layer 5 by boron diffusion process on the first opening region 4 specifically includes: forming a BSG layer 6 (boron-doped silicon glass) in the first opening region 4 using a boron diffusion process, and after passing through a first specified temperature, the intrinsic polycrystalline silicon layer 2 located between the first opening region 4 and the tunneling oxide layer 1 becomes the boron-doped polycrystalline silicon layer 5.

[0061] The first specified temperature can be set according to actual needs.

[0062] In addition, the use of boron diffusion process to form BSG layer 6 in the first opening region 4 helps to improve the performance, stability and reliability of the finished product, and also helps to optimize production efficiency and cost control.

[0063] In S4, such as Figure 6As shown, forming the second opening region 7 on the mask layer 3 specifically includes: using a picosecond green laser to slot in the n region of the mask layer 3 to form the second opening region 7 (due to the presence of the remaining mask layer 3, the intrinsic polysilicon layer 2 between the remaining mask layer 3 and the tunneling oxide layer 1 is not affected by phosphorus). Using a picosecond green laser can provide high-precision and low-damage processing effects, and can also improve the performance and reliability of the finished product.

[0064] In S4, such as Figure 7 As shown, the process of forming a phosphorus-doped polycrystalline silicon layer 8 by phosphorus diffusion on the second opening region 7 specifically includes: forming a PSG layer 9 (phosphorus-doped silicon glass) in the second opening region 7 using a phosphorus diffusion process, and after passing through a second specified temperature, the intrinsic polycrystalline silicon layer 2 located between the second opening region 7 and the tunneling oxide layer 1 becomes the phosphorus-doped polycrystalline silicon layer 8.

[0065] The second specified temperature can be set according to actual needs.

[0066] In addition, the use of phosphorus diffusion process to form PSG layer 9 in the second opening zone 7 and the process of advancing it at a second specified temperature helps to improve the performance, stability and reliability of the finished product, while also helping to optimize production efficiency and cost control.

[0067] In this embodiment, the remaining mask layer 3 is located between the n region and the p region, thus isolating the n region and the p region.

[0068] By placing an isolation layer (i.e., the remaining mask layer 3) between the n-region and p-region, current can be prevented from flowing directly from the n-region to the p-region, avoiding short circuits. This also improves the switching characteristics of the TBC solar cell (i.e., the finished product), reduces leakage current, and thus enhances the overall performance of the TBC solar cell. Furthermore, the isolation layer between the n-region and p-region reduces performance degradation of the TBC solar cell due to impurity diffusion or defects, improving its long-term reliability.

[0069] Preferably, the remaining mask layer 3 has a length in the range of 40μm to 80μm, which can reduce the number of adjustments during the production process and improve production efficiency.

[0070] As will be known to those skilled in the art, the length of the remaining mask layer 3 can be set according to actual needs to achieve optimal performance and reliability.

[0071] In S5, such as Figure 8As shown, the antireflection layer 10 is deposited on the back side of the substrate 100. The antireflection layer 10 is an optical coating used to reduce or eliminate reflection loss caused by light reflection on the surface of the medium. Specifically, it includes: removing the BSG layer 6 and PSG layer 9 by chain cleaning (a multi-step cleaning process), and then depositing the antireflection layer 10 on the back side of the substrate 100.

[0072] In solar cells, the deposition of antireflection layer 10 can significantly improve the light absorption efficiency of TBC solar cells and reduce the reflection of light on the surface of TBC solar cells.

[0073] Preferably, the thickness of the antireflection layer 10 is in the range of 40 nm to 90 nm. Within this thickness range, the antireflection layer 10 can effectively reduce the reflection of incident light on the surface of the TBC solar cell because the antireflection layer 10 of a specific thickness can cause a phase shift in the reflected light, thereby interfering with and canceling out the light that continues to propagate. By reducing reflection, more light can enter the interior of the TBC solar cell and be absorbed by the active layer, thereby improving the overall light absorption rate and efficiency of the TBC solar cell. The thickness of the antireflection layer 10 can be optimized for specific wavelengths of light to achieve better spectral response, especially in solar cells, where it can improve the absorption of different wavelengths of sunlight. By increasing the light absorption rate, the conversion efficiency of the solar cell can be directly improved; for other photovoltaic TBC solar cells, this can improve their responsivity and sensitivity.

[0074] As will be known to those skilled in the art, the thickness of the antireflective layer 10 can be set according to actual needs.

[0075] In a preferred embodiment, the antireflection layer 10 is made of SiNx (silicon nitride). By using SiNx as the material of the antireflection layer 10, it is possible to maintain excellent optical performance while providing improvements in chemical stability, thermal stability, and electrical performance.

[0076] Furthermore, this embodiment also proposes a TBC solar cell, which is prepared using the TBC solar cell preparation method described above.

[0077] In this embodiment, firstly, a texturing process is used to immerse the original n-type silicon wafer (i.e., substrate 100) in a KOH or NaOH solution with a mass fraction of 1% to 3% at a temperature of 60°C to 80°C for texturing, with the texturing time controlled to be 15 to 25 minutes. Then, as... Figure 2 As shown, a tunneling oxide layer 1 and a first intrinsic polycrystalline silicon layer 2 are formed using LP (Low Pressure Chemical Vapor Deposition). Figure 3As shown, a mask layer 3 is fabricated on the intrinsic polycrystalline silicon layer 2 using PECVD or LPCVD methods. The thickness of the mask layer 3 is 150 nm to 450 nm, and the mask layer 3 can be made of a laser-damage-resistant material such as silicon nitride. Figure 4 As shown, a picosecond green laser is used to create a groove in the p-region of the mask layer 3 to form the first opening region 4; as Figure 5 As shown, using a conventional boron diffusion process, a BSG layer 6 is formed in the first opening region 4. After passing through a first specified temperature, the intrinsic polysilicon layer 2 located between the first opening region 4 and the tunneling oxide layer 1 becomes a boron-doped polysilicon layer 5. Figure 6 As shown, a picosecond green laser is used to create a second opening region 7 by slotting in region n of mask layer 3; as Figure 7 As shown, after forming a PSG layer 9 in the second opening region 7 using a conventional phosphorus diffusion process and advancing it to a second specified temperature, the intrinsic polysilicon layer 2 located between the second opening region 7 and the tunneling oxide layer 1 becomes a phosphorus-doped polysilicon layer 8. Figure 8 As shown, the BSG layer 6 and PSG layer 9 on the back side are removed by chain cleaning, and then an antireflection layer 10 is deposited on the back side of the substrate 100 with a film thickness of 40nm to 90nm.

[0078] In summary, the method for preparing a TBC solar cell proposed in this invention has the following advantages:

[0079] The method involves texturing a substrate by immersing it in a predetermined temperature and a specified solution for a predetermined time; sequentially depositing a tunneling oxide layer and an intrinsic polysilicon layer on the back side of the substrate; depositing a mask layer on the side of the intrinsic polysilicon layer away from the tunneling oxide layer; forming a first opening region on the mask layer and performing boron diffusion propagation on the first opening region to form a boron-doped polysilicon layer; forming a second opening region on the mask layer and performing phosphorus diffusion propagation on the second opening region to form a phosphorus-doped polysilicon layer; leaving a mask layer between the first and second opening regions; and depositing an antireflection layer on the back side of the substrate. This method can shorten the production process and reduce the risk of laser damage to the battery; moreover, the laser equipment is compatible with each other, saving costs.

[0080] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for producing a TBC solar cell, characterized by, The method comprises the following steps: immersing the substrate into a solution with a predetermined temperature for a predetermined time; depositing a tunneling oxide layer and an intrinsic polysilicon layer on the back of the substrate in sequence; depositing a mask layer on the side of the intrinsic polysilicon layer away from the tunneling oxide layer; forming a first opening area on the mask layer and forming a boron-doped polysilicon layer on the first opening area by boron diffusion and pushing, specifically comprising: forming a BSG layer on the first opening area by boron diffusion, and after pushing at a first specified temperature, the intrinsic polysilicon layer between the first opening area and the tunneling oxide layer becomes the boron-doped polysilicon layer; forming a second opening area on the mask layer and forming a phosphorus-doped polysilicon layer on the second opening area by phosphorus diffusion and pushing; the mask layer remains between the first opening area and the second opening area; and depositing an anti-reflection layer on the back of the substrate.

2. The method for producing a TBC solar cell according to claim 1, wherein The predetermined temperature is 60-80℃.

3. The method for producing a TBC solar cell according to claim 1, wherein The solution comprises KOH solution or NaOH solution.

4. The method for producing a TBC solar cell according to claim 3, wherein The mass fraction of the KOH solution or NaOH solution is 1%-3%.

5. The method for preparing a TBC solar cell according to claim 1, wherein The predetermined time is 15-25 min.

6. The method for preparing a TBC solar cell according to claim 1, wherein The method of depositing the mask layer on the side of the intrinsic polysilicon layer away from the tunneling oxide layer comprises: preparing the mask layer on the intrinsic polysilicon layer by PECVD or LPCVD method.

7. The method for producing a TBC solar cell according to claim 6, wherein The thickness of the mask layer is 150-450 nm.

8. The method for producing a TBC solar cell according to claim 6, wherein The mask layer is made of laser damage resistant silicon nitride.

9. The method for producing a TBC solar cell according to claim 1, wherein The method of forming the first opening area on the mask layer comprises: forming the first opening area by slotting the p region of the mask layer with a picosecond green laser.

10. The method for producing a TBC solar cell according to claim 1, wherein The method of forming the second opening area on the mask layer comprises: forming the first opening area by slotting the n region of the mask layer with a picosecond green laser.

11. The method for producing a TBC solar cell according to claim 10, wherein The method of forming the phosphorus-doped polysilicon layer on the second opening area by phosphorus diffusion and pushing comprises: forming a PSG layer on the second opening area by phosphorus diffusion, and after pushing at a second specified temperature, the intrinsic polysilicon layer between the second opening area and the tunneling oxide layer becomes the phosphorus-doped polysilicon layer.

12. The method for producing a TBC solar cell according to claim 11, wherein The method of depositing the anti-reflection layer on the back of the substrate comprises: removing the BSG layer and PSG layer by chain cleaning, and then depositing the anti-reflection layer on the back of the substrate.

13. The method of producing a TBC solar cell according to claim 1, wherein The thickness of the anti-reflection layer is 40-90 nm.

14. The method of producing a TBC solar cell according to claim 1, wherein The anti-reflection layer is made of silicon nitride.

15. The method of producing a TBC solar cell according to claim 1, wherein The length of the remaining mask layer is 40-80 μm.

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