A MWT battery etching method

Abstract

The present invention relates to a MWT battery etching method, belonging to the field of battery preparation technology. The method involves subjecting a silicon wafer after phosphorus diffusion to an etching process, wherein phosphorus-silicate glass is formed on the front side of the silicon wafer due to the phosphorus diffusion step. In the etching process, the present application uses a film spraying device to spray a nitric acid solution, so that the front side of the silicon wafer is covered with the nitric acid solution to form a nitric acid solution film; the silicon wafer is placed on a roller for movement, and the back and side of the silicon wafer react with the etching solution to remove the PN junction on the back and side of the silicon wafer. The film spraying device forms a nitric acid solution film on the surface of the silicon wafer, and since phosphorus-silicate glass is formed on the surface of the silicon wafer, the nitric acid solution will not corrode the surface of the silicon wafer. When the nitric acid solution passes through the perforations on the silicon wafer, and since the dripping is nitric acid solution, it will not dilute the etching solution, that is, it will not affect the etching effect, thereby solving the etching tailing phenomenon. The method of the present application only converts the water film in the conventional technology into a nitric acid solution film, without adding steps and new equipment, and is low in cost.

Description

Technical Field

[0001] The invention relates to a MWT battery etching method, belonging to the technical field of battery preparation. Background Art

[0002] Metal Wrap Through (MTW) solar cells have perforations in their silicon substrates, filled with metal electrodes that direct current from the front electrode to the back of the cell, creating a back-contact structure. MWT cells with a back-contact structure offer the advantages of high power and aesthetics when packaged into modules.

[0003] The MWT cell fabrication process includes an etching step after the phosphorus diffusion step. While phosphorus diffusion is intended to form a PN junction on the front of the silicon substrate, PN junctions also form on the back and sides of the silicon substrate and need to be removed. The etching step primarily removes these PN junctions.

[0004] In the existing etching process, a silicon substrate is typically placed on a roller, which floats the silicon substrate on the surface of the etching solution and transports it forward. A water film sprayer forms a water film on the side of the silicon substrate facing away from the etching solution. The etching solution only reacts with the back and sides of the silicon substrate, while the water film on the front side protects the front side from corrosion (both nitric acid and hydrofluoric acid are volatile). However, for the silicon substrate of an MWT cell, due to the perforations in the silicon substrate, water from the water film can enter the etching solution through the perforations, diluting the etching solution concentration near the perforations and affecting the etching effect. As the silicon substrate is transported forward, a trailing region forms in the opposite direction of the transport. This trailing region is darker due to poor etching performance, while the normal region is brighter due to better etching performance. The leading edge of the trailing region represents the perforations through which water leaks. The existing solution involves spraying or silk-screening wax on the front side of the perforations to block the perforations and prevent water from leaking out. Furthermore, the wax required for cleaning and removal after etching. Therefore, the existing technology is costly and has complicated steps. Summary of the Invention

[0005] The purpose of the present invention is to provide a low-cost MWT battery etching method to solve the etching tailing problem caused by perforation and water leakage of the MWT battery.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solutions: a MWT cell etching method, wherein a silicon wafer after phosphorus diffusion is subjected to an etching process, wherein phosphorus-silicate glass is provided on the front side of the silicon wafer. During the etching process, the silicon wafer is placed on a roller so that the silicon wafer and the roller move relative to each other. A film spraying device is provided above the silicon wafer, and the film spraying device sprays a nitric acid solution so that the front side of the silicon wafer is covered with the nitric acid solution to form a nitric acid solution film; the back and sides of the silicon wafer react with the etching solution to remove the PN junction on the back and sides of the silicon wafer.

[0007] Furthermore, the etching solution is a mixed solution A of nitric acid and hydrofluoric acid, the nitric acid is 68% nitric acid, the hydrofluoric acid is 49% hydrofluoric acid, and the mixed solution A is prepared according to a volume ratio of 68% nitric acid, 49% hydrofluoric acid and water of 4.3:1:1.75.

[0008] Furthermore, a self-repairing solution is added to the etching solution, and the self-repairing solution is a mixed solution B of nitric acid and hydrofluoric acid, and the mixed solution B is prepared in a volume ratio of 68% nitric acid to 49% hydrofluoric acid of 1:1.5.

[0009] Furthermore, the nitric acid solution sprayed by the film spraying device is 68% nitric acid.

[0010] Furthermore, the film spraying device includes a water pipe and a nozzle connected to the water pipe, and the nozzle is arranged toward the roller.

[0011] Furthermore, the water pipe and the nozzle are both made of acid-resistant materials.

[0012] The beneficial effects of the present invention are as follows: A MWT cell etching method of the present application involves subjecting a phosphorus-diffused silicon wafer to an etching process, wherein the front surface of the silicon wafer is coated with phosphosilicate glass due to the phosphorus diffusion step. During the etching process, a nitric acid solution is sprayed through a film spraying device, covering the front surface of the silicon wafer with the nitric acid solution to form a nitric acid solution film. The silicon wafer is placed on a roller and moved relative to the roller, allowing the back and sides of the silicon wafer to react with the etching solution, thereby removing the PN junction on the back and sides of the silicon wafer. The film spraying device forms a nitric acid solution film on the surface of the silicon wafer. Because the phosphosilicate glass is formed on the surface of the silicon wafer, the nitric acid solution does not corrode the silicon wafer surface. The etching method works by nitric acid oxidizing silicon to form silicon dioxide, and hydrofluoric acid reacting with the silicon dioxide to dissolve the formed silicon dioxide. The combination of nitric acid and hydrofluoric acid is required to complete the etching reaction. However, the nitric acid solution formed does not complete the etching reaction when it passes through the perforations in the silicon wafer. Furthermore, since the nitric acid solution drips, it does not dilute the etching solution, thus not affecting the etching effect, thereby resolving the etching tailing phenomenon. The method of the present application only converts the water film in conventional technology into a nitric acid solution film, without adding steps and new equipment, and is low in cost.

[0013] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a structural schematic diagram of the MWT battery etching process of Example 1 of the present application. DETAILED DESCRIPTION

[0015] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0016] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the scope of protection of the present application. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description created by the present application, unless otherwise specified, "multiple" means two or more.

[0017] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0018] Example 1

[0019] See Figure 1 This embodiment provides a MWT cell etching method, which performs an etching process on the silicon wafer 2 after phosphorus diffusion.

[0020] It should be noted that the purpose of phosphorus diffusion is to form a PN junction on the front side of the silicon wafer 2. However, in actual production, PN junctions will also form on the back and sides of the silicon wafer 2 and need to be removed. The main purpose of the etching process is to remove the PN junctions formed on the back and sides of the silicon wafer 2. A layer of phosphosilicate glass is formed on the front side of the phosphorus-diffused silicon wafer 2. The silicon wafer 2 of the MWT cell is provided with a through hole 3.

[0021] In this embodiment, the etching process places the silicon wafer 2 on the roller 4 so that the silicon wafer 2 and the roller 4 move relative to each other. A film spraying device is provided above the silicon wafer 2. The film spraying device sprays nitric acid solution so that the front of the silicon wafer 2 is covered with the nitric acid solution to form a nitric acid solution film 1; while the back and sides of the silicon wafer 2 react with the etching solution to remove the PN junction on the back and sides of the silicon wafer 2.

[0022] As described above, roller 4 allows silicon wafer 2 to float on the surface of the etching solution and move it forward. Before entering the etching solution, a film sprayer sprays the wafer 2 with a nitric acid solution film 1. A layer of phosphosilicate glass (phosphorus-doped silicon oxide, formed during phosphorus diffusion) is applied to the front surface of the silicon substrate, protecting it from corrosion.

[0023] Among them, the roller 4 is at least partially immersed in the etching solution, and the silicon wafer 2 is set above the liquid level of the etching solution. The roller 4 carries the etching solution to the back of the silicon wafer 2 by dipping it in the liquid for etching. The film spraying device includes a water pipe 6 and a nozzle 7 connected to the water pipe 6. The nozzle 7 is set toward the roller 4. In detail, the nozzle 7 is set toward the silicon wafer 2. In this embodiment, the nitric acid solution sprayed by the film spraying device is 68% nitric acid. Preferably, the film spraying device is made of acid-resistant material, that is, the material of the water pipe 6 and the nozzle 7 are both acid-resistant materials. Acid-resistant materials can better extend the service life and shorten the frequency of replacement of ordinary materials due to corrosion by 68% nitric acid.

[0024] The etching solution is a mixed solution A of nitric acid and hydrofluoric acid. In the present embodiment, the nitric acid is 68% nitric acid and the hydrofluoric acid is 49% hydrofluoric acid. The mixed solution A is proportioned according to the volume ratio of 68% nitric acid, 49% hydrofluoric acid and water of 4.3:1:1.75. It should be noted that in other embodiments, nitric acid and hydrofluoric acid solutions of other volume ratios can also be used. As production proceeds, the chemicals in the etching solution are continuously consumed, so chemicals are continuously replenished during production, and the etching solution is added with a self-replenishing solution, which is a mixed solution B of nitric acid and hydrofluoric acid. The mixed solution B is proportioned according to the volume ratio of 68% nitric acid to 49% hydrofluoric acid of 1:1.5. It should be noted that the nitric acid and hydrofluoric acid solutions used in the mixed solution B here are the same solution, but when the etching solution etches the silicon wafer 2, the nitric acid is responsible for oxidizing the silicon into silicon dioxide, and the hydrofluoric acid is responsible for dissolving the generated silicon dioxide. Nitric acid and hydrofluoric acid must work together to achieve etching, and the consumption ratio is inconsistent. Therefore, during self-replenishment, the volume ratio of 68% nitric acid to 49% hydrofluoric acid is 1:1.5.

[0025] The principle of this embodiment is as follows: the water film formed on the surface of silicon wafer 2 during the traditional etching process is replaced with a nitric acid solution film 1, which is allowed to drip through the perforations 3 of the MWT cell. When the etching solution etches silicon wafer 2, nitric acid is responsible for oxidizing silicon to silicon dioxide, while hydrofluoric acid is responsible for dissolving the generated silicon dioxide. Nitric acid and hydrofluoric acid work together to achieve etching. In the traditional process, water dripping from perforations 3 dilutes the concentration of the etching solution in the adjacent part. Dilution has a greater impact on the nitric acid oxidation reaction than on the hydrofluoric acid dissolution reaction, and the main reason for the poor etching effect is the dilution of the nitric acid. However, the concentration of nitric acid in the nitric acid solution film 1 in this embodiment is similar to that of the nitric acid solution in the etching solution, which will not have a significant impact on the etching reaction, thereby solving the problem of etching tailing.

[0026] In summary, the present invention relates to an MWT cell etching method that involves subjecting a phosphorus-diffused silicon wafer to an etching process, wherein the front surface of the silicon wafer is coated with phosphosilicate glass due to the phosphorus diffusion step. During the etching process, the present invention utilizes a film spraying device to spray nitric acid solution, covering the front surface of the silicon wafer with the nitric acid solution to form a nitric acid solution film. The silicon wafer is placed on a roller so that the silicon wafer and the roller move relative to each other, and the back and sides of the silicon wafer react with the etching solution to remove the PN junction on the back and sides of the silicon wafer. The film spraying device forms a nitric acid solution film on the surface of the silicon wafer. Because the phosphosilicate glass is formed on the surface of the silicon wafer, the nitric acid solution does not corrode the surface of the silicon wafer. The etching method works by oxidizing nitric acid with silicon to form silicon dioxide, and then reacting with hydrofluoric acid with silicon dioxide to dissolve the formed silicon dioxide. The combination of nitric acid and hydrofluoric acid is required to complete the etching reaction. However, the nitric acid solution formed does not complete the etching reaction when it passes through the perforations in the silicon wafer. Furthermore, since the nitric acid solution is dripping, it does not dilute the etching solution, which does not affect the etching effect, thereby resolving the etching tailing phenomenon. The method of the present application only converts the water film in conventional technology into a nitric acid solution film, without adding steps and new equipment, and is low in cost.

[0027] The various technical features and detection items of the above-mentioned embodiments can be arbitrarily combined. In order to make the description concise, not all possible combinations of the various technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0028] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A MWT battery etching method, characterized in that: The phosphorus-diffused silicon wafer is subjected to an etching process, wherein the front surface of the silicon wafer is provided with phosphorus-silicate glass. During the etching process, the silicon wafer is placed on a roller so that the silicon wafer and the roller move relative to each other. A film spraying device is provided above the silicon wafer, and the film spraying device sprays nitric acid solution so that the front surface of the silicon wafer is covered with the nitric acid solution to form a nitric acid solution film; the back and side surfaces of the silicon wafer react with the etching solution to remove the PN junction on the back and side surfaces of the silicon wafer; The etching solution is a mixed solution A of nitric acid and hydrofluoric acid, and the nitric acid is 68% nitric acid; The nitric acid solution sprayed by the film spraying device is 68% nitric acid.

2. The MWT cell etching method according to claim 1, wherein: The hydrofluoric acid is 49% hydrofluoric acid, and the mixed solution A is prepared according to a volume ratio of 68% nitric acid, 49% hydrofluoric acid, and water of 4.3:1:1.

75.

3. The MWT cell etching method according to claim 2, wherein: A self-repairing solution is added to the etching solution. The self-repairing solution is a mixed solution B of nitric acid and hydrofluoric acid. The mixed solution B is prepared in a volume ratio of 68% nitric acid to 49% hydrofluoric acid of 1:1.

5.

4. The MWT cell etching method according to claim 1, wherein: The film spraying device includes a water pipe and a spray head connected to the water pipe, and the spray head is arranged toward the roller.

5. The MWT cell etching method according to claim 4, wherein: The water pipe and the nozzle are both made of acid-resistant materials.

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