Drying equipment and alkaline polishing process equipment and optimization methods for alkaline polishing process

Abstract

This invention relates to the field of semiconductor manufacturing technology, and discloses a drying apparatus, an alkaline polishing process equipment, and an optimized alkaline polishing process method. The drying apparatus includes: a base plate and sidewalls surrounding the base plate; a first hot air unit disposed within the drying tank and located on the base plate, extending along a second direction and adapted to blow air toward the surface of the base plate; a second hot air unit disposed within the drying tank and installed on a basket frame, extending along a first direction and adapted to blow air toward the basket end plate; and a third hot air unit disposed within the drying tank and installed on the basket frame, extending along a second direction and adapted to blow air toward the basket bottom rod. The drying apparatus provided by this invention increases airflow from multiple directions, improving the drying effect and solving the problem of stubborn areas such as the bottom end plate of the basket, the basket bottom rod, and the bottom of the tank being unable to be dried.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing process technology, specifically to a drying apparatus, alkaline polishing process equipment, and an alkaline polishing process optimization method. Background Technology

[0002] Currently, the fabrication process of TOPCon solar cells (TOPCon solar cells are tunneling oxide passivated contact solar cells with N-type silicon as the substrate) mainly includes: cleaning and texturing – boron diffusion – oxidation – BSG removal (the process of removing borosilicate glass (BSG) from the silicon wafer edge) – alkaline polishing – LPCVD (low-pressure chemical vapor deposition, which uses heating to react gaseous compounds on the silicon wafer surface under low pressure and deposit them into a solid thin film) – phosphorus diffusion – PSG removal (the process of removing phosphorus silicate glass (PSG) from the silicon wafer edge) – RCA (wet chemical cleaning method, used to remove the front and edge polycrystalline silicon layers and the front BSG) – ALD (atomic layer deposition) – front film – back film – screen printing – sorting. Among them, the alkaline polishing process is mainly used for silicon wafer processing. It uses a high-concentration alkaline solution to etch the silicon wafer, relying on the isotropic nature of the lattice atoms to flatten the textured pyramids, while removing the back and borosilicate glass (BSG) from the boron diffusion process.

[0003] After alkaline polishing, the silicon wafers need to be dried. A common drying method involves placing the wafers in a basket, then placing the basket in a drying tank. An external drying fan heats the tank, circulating hot air to dry the wafers. However, the basket, as the wafer carrier, has areas like the bottom rod, bottom end plate, and bottom of the tank that are often dry spots, resulting in water droplets remaining after drying. These water droplets affect the drying temperature, reduce drying capacity, and cause liquid residue on the wafers, leading to EL defects (EL defects refer to various defects or quality problems found during EL inspection of photovoltaic panels; EL inspection can detect various types of defects, including but not limited to oxidation, burning, and black edges). Figures 4(A) to 4(D) As shown.

[0004] Stubborn parts such as the bottom end plate of the drying basket, the bottom rod of the drying basket, and the bottom of the tank cannot be completely dried. This is due to two main reasons: firstly, the design of the drying tank is unreasonable, limiting its drying capacity; secondly, from the perspective of the alkaline polishing process, the following factors contribute: ① Mismatched acid tank concentration and slightly poor dehydration effect of slow cold water extraction, resulting in liquid residue in the alkaline polishing basket; ② Excessive water stains on the silicon wafers before entering the drying tank, causing the temperature of the basket to drop when it enters the drying tank, shortening the effective drying time and reducing the drying effect; ③ The bottom rod of the drying basket is not effectively dried due to its position within the drying tank. This, in turn, leads to water droplets remaining in the drying tank and at the bottom of the unloading basket end plate, affecting the stability of the alkaline polishing process and causing some EL yield problems. Summary of the Invention

[0005] In view of this, the present invention provides a drying device, an alkaline polishing process equipment, and an alkaline polishing process optimization method to solve the problem that water droplets remain in the drying tank and at the bottom of the unloading basket end plate after drying, which affects the stability of the alkaline polishing process and causes some EL yield.

[0006] In a first aspect, the present invention provides a drying apparatus, comprising:

[0007] A base plate and side wall panels surrounding the base plate; the base plate and side wall panels together form a drying trough;

[0008] Flower basket rack, set inside the drying tank; the flower basket rack is suitable for placing flower baskets, and the flower baskets contain silicon wafers, which are arranged parallel to the first direction, and multiple silicon wafers are placed inside the flower baskets and arranged parallel to and spaced apart along the second direction;

[0009] The first hot air unit is disposed in the drying tank and located on the bottom plate. The first hot air unit extends along the second direction and is adapted to blow air toward the surface of the bottom plate.

[0010] The second hot air unit is set in the drying trough and installed on the flower basket frame. The second hot air unit extends along the first direction and is adapted to blow air toward the flower basket end plate.

[0011] The third hot air unit is located in the drying trough and installed on the flower basket frame. The second hot air unit extends in the second direction and is adapted to blow air toward the bottom rod of the flower basket.

[0012] In one alternative implementation, a third hot air unit and / or a second hot air unit are disposed at the bottom of the flower basket frame along the height direction.

[0013] In one alternative implementation, the number of first hot air units is multiple;

[0014] At least one first hot air unit is located in the middle of the drying tank and has a first air inlet that blows air in a first direction toward both sides;

[0015] At least one first hot air unit is located near the side wall of the drying tank and has a first air inlet that blows air in a first direction toward the side away from the side wall.

[0016] In one alternative implementation, the number of second hot air units is multiple;

[0017] At least one second hot air unit is located in the middle of the drying tank and has a second air inlet that blows air in the second direction to both sides;

[0018] At least one second hot air unit is located near the side wall of the drying tank and has a second air inlet that blows air in a second direction toward the side away from the side wall.

[0019] In one alternative implementation, the number of third hot air units is one or more;

[0020] One or more third hot air units are located in the middle of the drying tank and have third air inlets that blow air in the first direction toward both sides.

[0021] In one alternative embodiment, the side wall panel is provided with an air outlet that blows air toward the side of the flower basket rack.

[0022] Beneficial effects: The drying device provided in the embodiments of the present invention improves the drying effect by adding air inlet diversion pipes on the side and bottom of the drying tank and increasing air blowing in multiple directions, which can solve the problem of stubborn parts such as the bottom end plate of the flower basket, the bottom rod of the flower basket, and the bottom of the tank that cannot be dried.

[0023] Secondly, the present invention also provides an alkaline polishing process apparatus, including: a drying device as described above.

[0024] Since the alkaline polishing process equipment includes a drying device, which has the same effect as a drying device, it will not be described in detail here.

[0025] Thirdly, the present invention also provides a method for optimizing an alkaline polishing process, applied to the alkaline polishing equipment described above; the alkaline polishing process optimization method includes:

[0026] Pre-cleaning was performed at a process temperature of 67℃-70℃ for 120 seconds. The initial NaOH concentration was 1.1%, the initial H2O2 concentration was 6%, the self-replenishing NaOH concentration was 0.01%, and the self-replenishing H2O2 concentration was 0.09%. A continuous circulation, basket bubbling mode was used.

[0027] The water tank is used to rinse off the desorbed impurities and residual chemicals on the silicon wafer surface with deionized water in one pass. The time is set to 120 seconds, and the overflow mode can be either overflow with a basket or continuous overflow.

[0028] Alkali polishing was performed at a set temperature of 67℃-69℃ and a set time of 280±20s. The initial NaOH concentration was 3.5%, the initial ADDI concentration was 0.4%, the self-replenishing NaOH concentration was 0.09%, and the self-replenishing ADDI concentration was 0.04%. The process was carried out in a continuous circulation, basketless bubbling mode.

[0029] The secondary water rinsing tank uses deionized water to rinse away the desorbed impurities and residual chemicals on the silicon wafer surface. The time is set to 120 seconds, and the overflow mode can be either basket overflow or continuous overflow.

[0030] For post-cleaning, the process temperature is set at 67℃-70℃, the cleaning time is 120 seconds, the initial NaOH concentration is selected as 0.9%, the initial H2O2 concentration is selected as 5%, the self-replenishing NaOH concentration is selected as 0.01%, and the self-replenishing H2O2 concentration is selected as 0.09%. The process is carried out in a continuous circulation mode with a basket bubbling.

[0031] Three rinses are performed in the water tank, using deionized water to rinse away the desorbed impurities and residual chemicals on the silicon wafer surface. The set time is 120 seconds, and the overflow mode can be either overflow with a basket or continuous overflow.

[0032] Mixed pickling was performed at room temperature for 130 seconds. The initial HF concentration was set at 1.1%, and the self-replenishing HF concentration was set at 0.11%.

[0033] The process involves four water rinsing cycles, using deionized water to remove desorbed impurities and residual chemicals on the silicon wafer surface. The set time is 120 seconds, and the overflow mode uses a basket overflow.

[0034] For lifting, set the process temperature to 48℃-50℃, add lifting additive, select an initial concentration of 2%, select a self-replenishing concentration of 0.06%-0.08%, control the lifting speed at 3mm / s-5mm / s, and adopt the overflow mode of basket overflow or continuous overflow.

[0035] Drying: Set the process temperature to 95±3℃ and the time to 600 seconds.

[0036] In one alternative embodiment, the lifting additive comprises a surfactant; wherein the surfactant comprises polyvinylpyrrolidone.

[0037] Lifting additives also include: sodium polystyrene sulfonate and deionized water.

[0038] In one optional embodiment, the concentration of polyvinylpyrrolidone is selected as 7%; the concentration of deionized water is selected as 85%; and the concentration of sodium polystyrene sulfonate is selected as 8%.

[0039] Beneficial Effects: This invention reduces the problem of water carryover to silicon wafers before they enter the drying tank by optimizing the alkaline polishing process. Through improvements to the acid mixing tank, slow lifting process, and the addition of an air inlet diversion pipeline to the drying tank, this invention solves the problem of liquid carryover at the bottom rod of the basket, the bottom end plate of the basket, and the bottom of the drying tank, resulting in significant improvement and eliminating liquid carryover during alkaline polishing. Furthermore, after effectively improving the liquid carryover problem in the alkaline polishing drying tank, the proportion of oxidation contamination caused by water carryover at the bottom rod of the basket, the bottom end plate of the basket, and the bottom of the drying tank decreases to 0.04%, the proportion of edge blackening decreases to 0.06%, and the proportion of scorching decreases to 0%. The significantly improved yield reduces the difficulty of process control and better reduces the points where the alkaline polishing process affects yield variation, achieving better matching with subsequent processes, further improving the process window of subsequent processes, and reducing yield fluctuations. Attached Figure Description

[0040] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0041] Figure 1 This is a schematic diagram of the drying apparatus of the present invention. Figure 1 ;

[0042] Figure 2 This is a schematic diagram of the drying apparatus of the present invention. Figure 2 ;

[0043] Figure 3 This is a schematic diagram of a flower basket containing a silicon wafer according to the present invention;

[0044] Figure 4(A) illustrates the EL defect caused by liquid inclusion in the battery cell. Figure 1 ;

[0045] Figure 4(B) illustrates the EL defect caused by liquid inclusion in the battery cell. Figure 2 ;

[0046] Figure 4(C) illustrates an EL defect caused by liquid inclusion in the battery cell. Figure 3 ;

[0047] Figure 4(D) is a schematic diagram of EL defects caused by liquid in the battery cell.

[0048] Explanation of reference numerals in the attached figures:

[0049] 11. Side wall panel; 111. Air outlet; 12. Base plate; 13. Flower basket rack;

[0050] 2. First hot air unit; 21. First air inlet;

[0051] 3. Second hot air unit; 31. Second air inlet;

[0052] 4. Third hot air unit; 41. Third air intake;

[0053] 5. Flower basket; 51. Flower basket base rod; 52. Flower basket end plate; 6. Silicon wafer. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," 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 this 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 this invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0056] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0057] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0058] In the alkaline polishing process, some stubborn parts such as the bottom end plate of the drying basket, the bottom rod of the drying basket, and the bottom of the tank may not be completely dried. This is due to two reasons: firstly, the drying capacity is limited by the unreasonable design of the drying tank; and secondly, the alkaline polishing process is unreasonable.

[0059] From a drying perspective, the common drying method involves placing silicon wafers in a basket, then placing the basket into a drying tank. An external drying fan heats the air, and a blower circulates the hot air into the tank, continuously heating and drying the wafers. However, the machine primarily relies on side-mounted air vents to deliver air to the center of the tank for continuous drying. During the drying process, areas such as the basket's bottom rod, bottom end plate, and the bottom of the tank are often in drying dead zones, resulting in water droplets remaining in these areas after drying. Furthermore, the drying tank is made of PP material, which has poor drying performance, causing water droplets to remain in the basket or tank, increasing the difficulty of process control and pre- and post-processing matching. In addition, water droplets affect the drying temperature; the tank temperature drops sharply by 20°C-30°C upon the basket entering, reducing drying capacity and significantly shortening the effective drying time. This leads to liquid residue on the wafers, resulting in poor electroluminescence (EL) performance and potentially causing wafer scorching, oxidation, and edge blackening. Figures 4(A) to 4(D) As shown.

[0060] Analysis of the alkaline polishing process reveals the following contributing factors: ① Mismatched acid bath concentration and slightly ineffective slow dehydration with cold water lead to liquid residue in the alkaline polishing basket; ② Excessive water residue on the silicon wafers before entering the drying tank causes temperature fluctuations and reduced drying efficiency when the basket enters; ③ The basket's bottom rod, due to its position within the drying tank, cannot achieve effective drying. This, in turn, results in water droplets remaining in the drying tank and at the bottom of the basket's end plate, affecting the stability of the alkaline polishing process and causing yield issues in some EL (electrode lamination) processes.

[0061] Therefore, it is evident that the current conventional alkaline polishing process and drying method cannot solve the problems of material feeding and liquid carryover in the drying tank during alkaline polishing.

[0062] This invention optimizes and improves the alkaline polishing process, while increasing the air inlet pipeline of the drying tank to improve the silicon wafer drying efficiency, reduce liquid carryover caused by insufficient drying, improve the liquid carryover problem in the drying tank, and thus solve some EL abnormalities.

[0063] The following is combined Figures 1 to 3 The following describes embodiments of the present invention.

[0064] According to an embodiment of the present invention, in one aspect, a drying apparatus is provided, comprising:

[0065] The base plate 12 and the side wall plates 11 surrounding the base plate 12; the base plate 12 and the side wall plates 11 together form a drying trough;

[0066] Flower basket rack 13 is set in the drying tank; flower basket 5 is suitable for placing in the flower basket rack 13, and silicon wafer 6 is placed in the flower basket 5. The silicon wafer 6 is arranged parallel to the first direction, and multiple silicon wafers 6 are placed in the flower basket 5 and arranged parallel to and spaced apart along the second direction.

[0067] The first hot air unit 2 is disposed in the drying tank and located on the bottom plate 12. The first hot air unit 2 extends along the second direction and is adapted to blow air toward the surface of the bottom plate 12.

[0068] The second hot air unit 3 is disposed in the drying trough and installed on the flower basket frame 13. The second hot air unit 3 extends along the first direction and is adapted to blow air toward the flower basket end plate 52 of the flower basket 5.

[0069] The third hot air unit 4 is located in the drying trough and installed on the flower basket frame 13. The second hot air unit 3 extends along the second direction and is adapted to blow air toward the bottom rod 51 of the flower basket 5.

[0070] In some embodiments, the third hot air unit 4 and / or the second hot air unit 3 are disposed at the bottom of the flower basket frame 13 along the height direction.

[0071] The drying device provided in the embodiments of the present invention improves the drying effect by adding air inlet diversion pipes on the side and bottom of the drying tank and increasing air blowing in multiple directions, which can solve the problem of stubborn parts such as the bottom end plate of the flower basket, the bottom rod of the flower basket, and the bottom of the tank that cannot be dried.

[0072] In some embodiments, the number of first hot air units 2 is multiple;

[0073] At least one first hot air unit 2 is disposed in the middle of the drying tank and has a first air inlet 21 that blows air in the first direction to both sides; thereby achieving the purpose of drying the surface of the bottom plate 12 and fully improving the drying efficiency.

[0074] At least one first hot air unit 2 is disposed in the drying tank near the side wall plate 11, and has a first air inlet 21 that blows air in the first direction toward the side away from the side wall plate 11.

[0075] In some embodiments, the number of second hot air units 3 is multiple;

[0076] At least one second hot air unit 3 is set in the middle of the drying tank and has a second air inlet 31 that blows air in the second direction to both sides; so as to dry the flower basket end plates 52 on both sides and in the middle, thereby fully improving the drying efficiency.

[0077] At least one second hot air unit 3 is disposed in the drying tank near the side wall plate 11, and has a second air inlet 31 that blows air in the second direction toward the side away from the side wall plate 11.

[0078] In some embodiments, the number of third hot air units 4 is one or more;

[0079] One or more third hot air units 4 are located in the middle of the drying tank and have third air inlets 41 that blow air in the first direction toward both sides.

[0080] The drying device of the present invention increases the air inlet diversion pipeline of the drying tank by adding multiple horizontal and vertical hot air units at the bottom of the drying tank, wherein the hot air unit can be a hot air pipe, thereby increasing the airflow distribution during drying and improving the drying efficiency.

[0081] In this embodiment, there are three first hot air units 2; one first hot air unit 2 is located in the middle of the drying tank and has a first air inlet 21 that blows air in a first direction towards both sides; two first hot air units 2 are respectively located in the drying tank near the side wall plate 11 and have a first air inlet 21 that blows air in a first direction towards the side away from the side wall plate 11. The three hot air pipes work together to fully cover the surface of the bottom plate 12, achieving the purpose of drying the surface of the bottom plate 12 and greatly improving the drying efficiency.

[0082] In this embodiment, there are three second hot air units 3; one second hot air unit 3 is located in the middle of the drying tank and has a second air inlet 31 that blows air in the second direction towards both sides; two second hot air units 3 are located near the side wall plate 11 of the drying tank and have a second air inlet 31 that blows air in the second direction towards the side away from the side wall plate 11. This achieves the purpose of drying the flower basket end plates 52 on both sides and in the middle, thus greatly improving the drying efficiency.

[0083] In this embodiment, there is one third hot air unit 4. The third hot air unit 4 is located in the middle of the drying tank and has a third air inlet 41 that blows air towards both sides in the first direction. This achieves the purpose of drying the bottom rod 51 of the flower basket and greatly improves the drying efficiency.

[0084] The first hot air unit 2 is mainly designed to improve the liquid accumulation at the bottom of the tank. Because the drying temperature alone cannot dry the water droplets after they condense, the addition of the first hot air unit 2 on both sides and in the middle allows the water droplets to be blown away by the bidirectional air intake pipe in the middle section when they fall to the bottom of the tank. Then, the water droplets are completely dried by the air intake pipes on both sides.

[0085] Secondly, the third hot air unit 4 dries the accumulated liquid on the bottom rod 51 of the flower basket. Because the flower basket is placed inside the tank, conventional drying processes for the bottom rod 51 are ineffective, and hot air drying alone cannot solve this problem. The bidirectional air intake and diversion pipeline of the third hot air unit 4 can solve the problem of water droplet residue in this location. Adding this bidirectional air intake and diversion device can effectively blow away and dry the water droplets carried by the bottom rods on both sides of the flower basket.

[0086] Secondly, the second hot air unit 3 mainly performs diversion drying on the flower basket end plate 52. Because the flower basket end plate 52 is close to the base, conventional drying methods cannot dry this part. Therefore, after adding three diversion devices on both sides and in the middle, diversion drying is performed on the flower basket end plate 52. The middle part is bidirectional air intake diversion, because the middle part is the common bearing area of ​​the flower basket, thus ensuring that the entire flower basket end plate 52 is dried.

[0087] In some embodiments, combined with Figure 1 As shown, the side wall panel 11 has an air outlet 111, which blows air towards the side of the flower basket rack 13.

[0088] According to an embodiment of the present invention, in another aspect, an alkaline polishing process apparatus is also provided, comprising: a drying device as described above.

[0089] In addition to improving silicon wafer drying efficiency by adding air inlet pipes to the drying tank, this invention also ensures that the silicon wafers have sufficient dehydration properties before entering the drying tank. This requires optimizing the acid concentration in the acid bath to determine if a specific concentration range provides optimal dehydration without negatively impacting efficiency. Secondly, since the silicon wafers are hydrophobic after acid treatment, increasing the slow-lift temperature effectively reduces the surface tension of water, minimizing water droplets carried when leaving the drying tank. Finally, the addition of a drying tank air inlet distribution pipe ensures more uniform airflow distribution, guaranteeing complete drying of water droplets at locations such as the bottom of the basket rod, the bottom of the basket end plate, and the bottom of the drying tank, reducing EL defects caused by water carried into the drying tank.

[0090] In related technologies, alkaline polishing processes mainly utilize low-concentration acid baths and slow cold water extraction. However, the acid bath concentration directly affects the dehydration of silicon wafers. Furthermore, because the surface tension of water at room temperature is greater than that of warm or hot water, slow cold water extraction offers no advantage in drying, resulting in severe water-carrying issues after extraction. Optimizing the alkaline polishing process can improve the dehydration of silicon wafers before they enter the drying bath.

[0091] According to an embodiment of the present invention, in another aspect, an alkali polishing process optimization method is also provided, applied to the alkali polishing process equipment as described above; the alkali polishing process optimization method includes:

[0092] Pre-cleaning was performed at a process temperature of 67℃-70℃ for 120 seconds. The initial NaOH concentration was 1.1%, the initial H2O2 concentration was 6%, the self-replenished NaOH concentration was 0.01%, and the self-replenished H2O2 concentration was 0.09%. The process was carried out using a continuous circulation and basket bubbling mode.

[0093] Hydrogen peroxide, with its strong oxidizing properties, is used to clean surface contaminants. Conventional pre-cleaning processes typically maintain a pre-cleaning temperature of around 60℃-65℃. Hydrogen peroxide reacts with NaOH; at 90℃-100℃, it can decompose by 90%; however, at 60℃, the decomposition rate is only about 50%. This slow decomposition results in poor cleaning effectiveness, leaving contaminants adsorbed on the silicon wafer surface, increasing the difficulty of dehydration.

[0094] Through repeated experiments, it was found that when the process temperature is below 67℃, the NaOH concentration is below 1.1%, the H2O2 concentration is below 6%, the self-replenished NaOH concentration is below 0.01%, and the self-replenished H2O2 concentration is below 0.09%, the hydrogen peroxide reaction rate is too slow, resulting in poor cleaning and leaving some adsorbed dirt on the surface unremoved. Conversely, when the process temperature is above 70℃, the NaOH concentration is above 1.1%, the H2O2 concentration is above 6%, the self-replenished NaOH concentration is above 0.01%, and the self-replenished H2O2 concentration is above 0.09%, the hydrogen peroxide reaction rate is too fast. This leads to hydrogen peroxide replenishment exceeding consumption, resulting in complete consumption of hydrogen peroxide, poor cleaning, and the possibility of direct reaction with the silicon wafer, damaging the surface structure, causing inefficiency, abnormal appearance, and failure to achieve the expected cleaning effect. Only when the process temperature is between 67℃ and 70℃, the cleaning time is 120 seconds, the initial NaOH concentration is 1.1%, the H2O2 concentration is 6%, the self-replenished NaOH concentration is 0.01%, and the self-replenished H2O2 concentration is 0.09%, can the best cleaning effect be achieved because the hydrogen peroxide reaction and cleaning effect are optimal, thus completely removing the dirt adsorbed on the silicon wafer surface.

[0095] The water tank is used to rinse off desorbed impurities and residual chemicals on the silicon wafer surface with deionized water in one pass. The time is set to 120 seconds, and the overflow mode can be either overflow with a basket or continuous overflow.

[0096] Alkali polishing was performed at a set temperature of 67℃-69℃ and a set time of 280±20s. The initial NaOH concentration was 3.5%, the initial ADDI concentration was 0.4%, the self-replenishing NaOH concentration was 0.09%, and the self-replenishing ADDI concentration was 0.04%. The process was carried out in a continuous circulation, basketless bubbling mode.

[0097] Alkali polishing improves back-side reflectivity and structure, enhances long-wavelength response, and reduces back-side recombination. The back-side is polished with an alkali, while additives protect the front side from corrosion. Different etching depths in the polishing tank result in variations in the flatness of the silicon wafer's back side. Higher etching depths lead to smoother back-side surfaces, reducing the likelihood of water droplets remaining on the wafer and thus improving its dehydration properties.

[0098] Through repeated experiments, it was found that when the process temperature is below 67℃, the time is below 260s, the initial NaOH concentration is below 3.5%, the ADDI concentration is below 0.4%, the self-replenished NaOH concentration is below 0.09%, and the self-replenished ADDI concentration is below 0.04%, the polishing effect will decrease, the etching amount on the polished surface will be low, and the flatness of the silicon wafer polished surface will decrease, which will be detrimental to the subsequent dehydration of the silicon wafer. However, when the process temperature is above 69℃, the time is above 300s, the initial NaOH concentration is above 3.5%, the ADDI concentration is above 0.4%, the self-replenished NaOH concentration is above 0.09%, and the self-replenished ADDI concentration is above 0.04%, the polishing etching amount will be too high, the silicon wafer will become thinner, increasing the risk of silicon wafer adsorption in the subsequent tank, and the high etching amount on the silicon wafer will result in a large load on the printed product, which is likely to lead to inefficiency. Only when the process temperature is between 67℃ and 69℃, the time is set at 280±20S, the initial NaOH concentration is 3.5%, the ADDI concentration is 0.4%, the self-replenished NaOH concentration is 0.09%, and the self-replenished ADDI concentration is 0.04%, can the back-side flatness be at its optimal level because the silicon wafer etching amount is at its best, thus improving the dehydration effect.

[0099] The secondary water rinsing tank uses deionized water to rinse away the desorbed impurities and residual chemicals on the silicon wafer surface. The time is set to 120 seconds, and the overflow mode can be either basket overflow or continuous overflow.

[0100] For post-cleaning, the process temperature was set at 67℃-70℃, the cleaning time was 120 seconds, the initial NaOH concentration was selected as 0.9%, the initial H2O2 concentration was selected as 5%, the self-replenished NaOH concentration was selected as 0.01%, and the self-replenished H2O2 concentration was selected as 0.09%. The process was carried out in a continuous circulation mode with a basket bubbling.

[0101] Hydrogen peroxide, with its strong oxidizing properties, is used to clean surface contaminants. Conventional pre-cleaning processes typically maintain a pre-cleaning temperature of around 60℃-65℃. Hydrogen peroxide reacts with NaOH; at 90℃-100℃, it can decompose by 90%; however, at 60℃, the decomposition rate is only about 50%. This slow decomposition results in poor cleaning effectiveness, leaving contaminants adsorbed on the silicon wafer surface, increasing the difficulty of dehydration.

[0102] Through repeated experiments, it was found that in the post-cleaning stage, when the process temperature is below 67℃, the initial NaOH concentration is below 0.9%, the initial H2O2 concentration is below 5%, the self-replenished NaOH concentration is below 0.01%, and the self-replenished H2O2 concentration is below 0.09%, the hydrogen peroxide reaction rate is too slow. Because of this, the cleaning effect is poor, and some adsorbed dirt on the surface cannot be completely cleaned. Conversely, when the process temperature is above 70℃, the initial NaOH concentration is above 0.9%, the initial H2O2 concentration is above 5%, the self-replenished NaOH concentration is above 0.01%, and the self-replenished H2O2 concentration is above 0.09%, the hydrogen peroxide reaction rate is too fast. This leads to hydrogen peroxide replenishment exceeding consumption, resulting in complete consumption of hydrogen peroxide. Consequently, the cleaning effect is poor, and the hydrogen peroxide may react directly with the silicon wafer, damaging the surface structure, causing inefficiency and abnormal appearance, thus failing to achieve the expected cleaning effect. Only when the process temperature is 67℃-69℃, the time is set to 120 seconds, the initial NaOH concentration is 0.9%, the H2O2 concentration is 5%, the self-replenished NaOH concentration is 0.01%, and the self-replenished H2O2 concentration is 0.09%, can the best cleaning effect be achieved because the hydrogen peroxide reaction and cleaning effect are optimal, thus completely removing the dirt adsorbed on the silicon wafer surface.

[0103] The wafer is rinsed three times with deionized water to remove desorbed impurities and residual chemicals on the silicon wafer surface. The time is set to 120 seconds, and the overflow mode can be either basket overflow or continuous overflow.

[0104] Mixed pickling was performed at room temperature for 130 seconds. The initial HF concentration was set at 1.1%, and the self-replenishing HF concentration was set at 0.11%.

[0105] Silicon wafers often have organic contaminants such as grease and lubricants on their surface. These organics adhere to the wafer surface and affect subsequent processing steps. Hydrofluoric acid, with its excellent corrosive and solubilizing properties, can effectively remove organic contaminants from the silicon wafer surface. Secondly, the silicon wafer surface may contain metallic impurities such as iron and copper. These impurities can degrade the electrical properties of the silicon wafer surface, thus affecting device performance. Hydrofluoric acid can react with these metallic impurities, dissolving them to remove them. Furthermore, the silicon wafer surface may have an oxide layer (such as silicon dioxide), which reduces the purity and smoothness of the silicon wafer surface. Hydrofluoric acid can chemically react with these oxides, dissolving the oxide layer and making the silicon wafer surface clean and smooth. Under certain conditions, hydrofluoric acid can rapidly dissolve a very thin layer of silicon on the wafer surface, thus achieving a surface purification effect. Therefore, increasing acid concentration is positively correlated with the dehydration properties of the silicon wafer; improving the initial and subsequent addition of HF can help achieve optimal dehydration of the silicon wafer.

[0106] Through repeated experiments, it was found that during the mixed acid washing stage, when the initial HF concentration was less than 1.1% and the self-replenished HF concentration was less than 0.11%, the low hydrofluoric acid concentration prevented the complete removal of surface metal impurities and oxide layers, resulting in poor dehydration of the silicon wafers after the acid bath. Conversely, when the initial HF concentration was higher than 1.1% and the self-replenished HF concentration was higher than 0.11%, the overall hydrofluoric acid concentration was too high. While this allowed for complete removal of metal impurities and oxide layers, the high concentration increased production costs, and there was a risk of HF vaporization during the robotic arm's basket lifting process, potentially introducing contamination into other silicon wafers. Only when the initial HF concentration was 1.1% and the self-replenished HF concentration was 0.11% did the hydrofluoric acid cleaning effect reach its optimal level, and no vaporization occurred during the robotic arm's basket lifting process, thus achieving the best removal effect and completely removing metal contaminants and oxide layers from the silicon wafer surface.

[0107] The process involves four water rinsing cycles, using deionized water to remove desorbed impurities and residual chemicals on the silicon wafer surface. The cycle time is set to 120 seconds, and the overflow mode uses a basket overflow.

[0108] For the lifting process, set the process temperature to 48℃-50℃, add lifting additives, select an initial concentration of 2%, select a self-replenishing concentration of 0.06%-0.08%, control the lifting speed at 3mm / s-5mm / s, and adopt either basket overflow or continuous overflow mode.

[0109] In related technologies, additives are not used in the lifting step. This invention adds a lifting additive to the lifting step. This additive acts in the slow lifting groove, primarily improving the wet basket weave pattern and enhancing the dehydration effect during slow lifting. This further addresses the dehydration problem after the silicon wafer leaves the slow lifting groove, thereby improving surface dehydration while further reducing water droplets entering the drying tank, reducing drying difficulty. Secondly, the better dehydration effect reduces drying difficulty, indirectly reducing the inconsistency in oxide layer thickness caused by liquid residue at the basket caliper location, and reducing the proportion of basket weave patterns.

[0110] In some embodiments, the lifting additive comprises a surfactant; wherein the surfactant comprises polyvinylpyrrolidone.

[0111] Lifting additives also include: sodium polystyrene sulfonate and deionized water.

[0112] In some embodiments, the concentration of polyvinylpyrrolidone is selected as 7%; the concentration of deionized water is selected as 85%; and the concentration of sodium polystyrene sulfonate is selected as 8%.

[0113] Because the surface tension of water decreases with higher temperatures, increasing the temperature significantly improves the water content of silicon wafers as they detach from the slow-lift basket. There are no large water droplets. When the wafers are lifted into the drying tank by a robotic arm, the increased water temperature reduces the surface tension of the water, thus reducing the amount of water droplets carried by the silicon wafers and baskets during the slow-lift process.

[0114] Through repeated experiments, it was found that during the slow-lifting process, when the temperature is below 48℃, the high surface tension of the water results in more water droplets being carried away upon removal from the water, affecting drying. While the surface tension of water is low when the slow-lifting temperature is above 50℃, the excessively high temperature causes water vapor to form, potentially creating new dirt or defects. Only when the temperature is between 48℃ and 50℃ is the surface tension of the water and water vapor evaporation optimal, resulting in the best dehydration performance.

[0115] Drying: Set the process temperature to 95±3℃ and the time to 600 seconds.

[0116] The drying step uses the drying device provided in the embodiment of the present invention. By adding an air inlet diversion pipeline, the bottom rod of the alkali throwing basket, the bottom end plate of the basket, and the bottom of the drying tank are free of water droplets, which is a significant improvement compared to before the addition. The bottom rod of the basket, the bottom end plate of the basket, and the bottom of the drying tank are continuously blew to achieve the best drying state.

[0117] This invention optimizes the alkaline polishing process to reduce water carryover issues before silicon wafers enter the drying tank. By improving the acid mixing tank, slow-lifting process, and adding an air inlet diversion pipe to the drying tank, this invention solves the problem of liquid carryover at the bottom rod of the basket, the bottom end plate of the basket, and the bottom of the drying tank, resulting in significant improvement and eliminating liquid carryover during alkaline polishing. Furthermore, after effectively improving the liquid carryover issue in the alkaline polishing drying tank, the proportion of oxidation and contamination caused by water carryover at the bottom rod of the basket, the bottom end plate of the basket, and the bottom of the drying tank decreased to 0.04%, the proportion of edge blackening decreased to 0.06%, and the proportion of scorching decreased to 0%. The significantly improved yield reduces the difficulty of process control and better minimizes process variation points in the alkaline polishing stage, achieving better compatibility with subsequent processes.

[0118] This invention relates to an alkaline polishing process for silicon wafers after BSG removal. Through process optimization, it reduces water droplets before the wafers enter the drying tank and improves drying efficiency by increasing the air inlet pipe of the drying tank. The alkaline polishing machines used in the tank-type alkaline polishing process all employ the alkaline polishing process optimization method of this invention, making corresponding optimizations and adjustments to the acid tank concentration, slow pull-out temperature, and air inlet pipe of the drying tank during the alkaline polishing process. By optimizing the alkaline polishing process, the silicon wafers have better dehydration properties before entering the drying tank, reducing drying difficulty; and it solves the problem of liquid carryover caused by insufficient drying during the alkaline polishing process.

[0119] The following examples and comparative examples verify the specific effects of the drying device, alkaline polishing process equipment, and alkaline polishing process optimization method provided by the present invention.

[0120] Comparative Example 1:

[0121] After removal from the PSG (Pressure Processing Unit), the silicon wafers are carried in baskets and fed into the alkaline polishing machine by a robotic arm for further processing.

[0122] Pre-cleaning: Process temperature: 60-65℃, time: 90s, initial NaOH concentration: 0.5%, H2O2 concentration: 2%, self-replenishing NaOH concentration: 0.005%, self-replenishing H2O2 concentration: 0.04%, circulation / bubbling mode: continuous circulation, with basket bubbling. Purpose of the step: To clean surface contaminants using the strong oxidizing properties of hydrogen peroxide.

[0123] Water tank: 90 seconds, overflow mode: overflow with basket or continuous overflow. Purpose of the step: To rinse away desorbed impurities and residual chemicals on the silicon wafer surface with deionized water.

[0124] Alkali polishing: Process temperature: 62-64℃, time: 220s, initial NaOH concentration: 1.8%, ADDI concentration: 0.15%, self-replenishing NaOH concentration: 0.04%, self-replenishing ADDI concentration: 0.02%, circulation / bubbling mode: continuous circulation, with basket bubbling, purpose of the step: alkaline polishing improves the reflectivity and structure of the back side, enhances long-wave response and reduces back side recombination, and uses alkali to polish the back side to protect the front side from corrosion;

[0125] Water tank: 90 seconds, with or without overflowing basket; purpose of the step: to rinse away residual chemicals on the silicon wafer surface with deionized water.

[0126] Post-cleaning: Process temperature: 60-65℃, time: 90s, initial NaOH concentration: 0.5%, H2O2 concentration: 2%, self-replenishing NaOH concentration: 0.008%, self-replenishing H2O2 concentration: 0.04%, circulation / bubbling mode: continuous circulation, with basket bubbling. Purpose of the step: To clean surface contaminants using the strong oxidizing properties of hydrogen peroxide.

[0127] Water bath: 90 seconds, with or without overflowing basket. Purpose of the step: To rinse away residual chemicals on the silicon wafer surface with deionized water.

[0128] Mixed pickling: Process temperature: room temperature, time: 90 seconds, initial HF concentration: 0.5%, self-replenished HF concentration: 0.04%.

[0129] Water tank: 90 seconds, with or without overflowing basket. Purpose of the step: to rinse away residual chemicals on the silicon wafer surface with deionized water.

[0130] Slow lifting: Process temperature: 20-35℃, lifting speed controlled at 3-5mm / s, with basket overflow or continuous overflow, step purpose: to rinse the silicon wafer surface with deionized water to remove residual chemicals, and then lift it into the drying tank by a robotic arm.

[0131] Drying: Process temperature: 90±5℃, time: 500S.

[0132] Example 1:

[0133] After removal from the PSG (Pressure Processing Unit), the silicon wafers are carried in baskets and fed into the alkaline polishing machine by a robotic arm for further processing.

[0134] Pre-cleaning: Process temperature: 66℃, time: 100s, initial NaOH concentration: 0.7%, H2O2 concentration: 3%, self-replenishing NaOH concentration: 0.01%, self-replenishing H2O2 concentration: 0.06%, circulation / bubbling mode: continuous circulation, with basket bubbling. Purpose of the step: The strong oxidizing property of hydrogen peroxide helps clean surface contaminants. Result: The cleaning effect is not significantly improved at this concentration.

[0135] Water tank: 100 seconds, overflow mode: overflow with basket or continuous overflow, purpose of the step: to rinse off the desorbed impurities and residual chemicals on the silicon wafer surface with deionized water.

[0136] Alkali polishing: Process temperature: 66℃, time: 240-250s, initial NaOH concentration: 2%, ADDI concentration: 0.2%, self-supplementing NaOH concentration: 0.06%, self-supplementing ADDI concentration: 0.025%, circulation / bubbling mode: continuous circulation, no basket bubbling. Purpose: Alkali polishing improves the back surface reflectivity and structure, enhances long-wave response, and reduces back surface recombination. The back surface is polished using alkali, while additives protect the front surface from corrosion. Results: At this concentration, the etching amount increases slightly, and the improvement in flatness is not significant.

[0137] Water tank: 100 seconds, overflow mode: overflow with basket or continuous overflow, purpose of the step: to rinse off the desorbed impurities and residual chemicals on the silicon wafer surface with deionized water.

[0138] Post-cleaning: Process temperature: 66℃, time: 100s, initial NaOH concentration: 0.7%, H2O2 concentration: 3%, self-replenishing NaOH concentration: 0.01%, self-replenishing H2O2 concentration: 0.06%, circulation / bubbling mode: continuous circulation, with basket bubbling. Purpose of the step: The strong oxidizing property of hydrogen peroxide helps clean surface contaminants. Result: The cleaning effect is not significantly improved at this concentration.

[0139] Water tank: 100 seconds, overflow mode: overflow with basket or continuous overflow, purpose of the step: to rinse off the desorbed impurities and residual chemicals on the silicon wafer surface with deionized water.

[0140] Mixed acid washing: Process temperature: room temperature, time: 90-100 seconds, initial HF concentration: 0.7%, self-replenished HF concentration: 0.06%. Purpose of the step: Increased acid concentration has a positive correlation with silicon wafer dehydration; improving the initial HF concentration and replenishment helps the silicon wafer reach its optimal dehydration state. Result: At this concentration, the dehydration effect of the acid bath is slightly improved.

[0141] Water tank: 100 seconds, overflow mode: overflow with basket or continuous overflow, purpose of the step: to rinse off the desorbed impurities and residual chemicals on the silicon wafer surface with deionized water.

[0142] Slow Pulling: Process temperature: 35-39℃, add 1% slow pulling additive initially, 0.02% self-replenishment, pulling speed controlled at 3-5mm / s, with basket overflow or continuous overflow. Purpose of the step: Rinse the silicon wafer surface with deionized water to remove residual chemicals, then pull it into the drying tank via a robotic arm. Increasing the water temperature reduces the surface tension of the water, reducing water droplets carried by the silicon wafer and basket when detaching from the slow pulling process. Effect: Increasing the temperature improves the water retention of the silicon wafer when detaching from the slow pulling basket; at this temperature, the water retention is slightly improved.

[0143] Drying: Process temperature: 95℃, time: 500s. Result: After adding the air inlet diversion pipeline, there were no water droplets on the bottom rod of the alkali-throwing basket, the bottom end plate of the basket, and the bottom of the drying tank, which is a significant improvement compared to before the addition. Continuous blowing was performed on the bottom rod of the basket, the bottom end plate of the basket, and the bottom of the drying tank. However, under the 500s drying condition, there was a slight liquid residue problem on the bottom rod of the basket, the bottom end plate of the basket, and the bottom of the drying tank.

[0144] Example 2:

[0145] After removal from the PSG (Pressure Processing Unit), the silicon wafers are carried in baskets and fed into the alkaline polishing machine by a robotic arm for further processing.

[0146] Pre-cleaning: Process temperature: 67℃, time: 110s, initial NaOH concentration: 0.7-0.9%, H2O2 concentration: 4-5%, self-replenishing NaOH concentration: 0.01%, self-replenishing H2O2 concentration: 0.07-0.09%, circulation / bubbling mode: continuous circulation, with basket bubbling. Purpose of the step: The strong oxidizing property of hydrogen peroxide effectively cleans surface contaminants. Result: The cleaning effect is slightly noticeable at this concentration.

[0147] Water tank: Time 110s, overflow mode: overflow with basket or continuous overflow, purpose of the step: to rinse off the desorbed impurities and residual chemicals on the silicon wafer surface with deionized water.

[0148] Alkali polishing: Process temperature: 67℃, time: 260-270s, initial NaOH concentration: 2.5%, ADDI concentration: 0.3%, self-replenishing NaOH concentration: 0.07-0.08%, self-replenishing ADDI concentration: 0.02-0.03%, circulation / bubbling mode: continuous circulation, no basket bubbling. Purpose: Alkali polishing improves the back surface reflectivity and structure, enhances long-wave response, and reduces back surface recombination. The back surface is polished using alkali, while additives protect the front surface from corrosion. Results: At this concentration, etching depth increases, and flatness is slightly improved.

[0149] Water tank: Time 110s, overflow mode: overflow with basket or continuous overflow, purpose of the step: to rinse off the desorbed impurities and residual chemicals on the silicon wafer surface with deionized water.

[0150] Post-cleaning: Process temperature: 67℃, time: 110s, initial NaOH concentration: 0.7-0.9%, H2O2 concentration: 4-5%, self-replenishing NaOH concentration: 0.01%, self-replenishing H2O2 concentration: 0.07-0.08%, circulation / bubbling mode: continuous circulation, with basket bubbling. Purpose of the step: The strong oxidizing property of hydrogen peroxide effectively cleans surface contaminants. Result: The cleaning effect is slightly noticeable at this concentration.

[0151] Water tank: Time 110s, overflow mode: overflow with basket or continuous overflow, purpose of the step: to rinse off the desorbed impurities and residual chemicals on the silicon wafer surface with deionized water.

[0152] Mixed acid washing: Process temperature: room temperature, time: 110-130 seconds, initial HF concentration: 0.8-0.9%, self-replenishing HF concentration: 0.7-0.9%. Purpose of this step: Increased acid concentration has a positive correlation with silicon wafer dehydration; improving the initial HF concentration and subsequent replenishment helps the silicon wafer reach its optimal dehydration state. Result: At this concentration, the dehydration effect of the acid bath is significantly improved.

[0153] Water tank: Time 110s, overflow mode: overflow with basket or continuous overflow, purpose of the step: to rinse off the desorbed impurities and residual chemicals on the silicon wafer surface with deionized water.

[0154] Slow Pulling: Process temperature: 40-45℃, add 1.5% slow pulling additive initially, 0.04% self-replenishment, pull speed controlled at 3-5mm / s, with basket overflow or continuous overflow. Purpose of the step: To rinse the silicon wafer surface with deionized water to remove residual chemicals, then pull it into the drying tank via a robotic arm. Increasing the water temperature reduces the surface tension of the water, reducing water droplets carried by the silicon wafer and basket when detaching from the slow pulling process. Result: Increasing the temperature improves the water retention of the silicon wafer when detaching from the slow pulling basket; the improvement is more significant at this temperature, resulting in fewer water droplets after slow pulling.

[0155] Drying: Process temperature: 95℃, time: 550s. Result: After adding the air inlet diversion pipeline, there were no water droplets on the bottom rod of the alkali-throwing basket, the bottom end plate of the basket, and the bottom of the drying tank, which is a significant improvement compared to before the addition. Continuous blowing was performed on the bottom rod of the basket, the bottom end plate of the basket, and the bottom of the drying tank. Under the 550s drying condition, there was only a slight amount of liquid on the bottom rod of the basket, the bottom end plate of the basket, and the bottom of the drying tank.

[0156] Example 3:

[0157] After removal from the PSG (Pressure Processing Unit), the silicon wafers are carried in baskets and fed into the alkaline polishing machine by a robotic arm for further processing.

[0158] Pre-cleaning: Process temperature: 67-70℃, time: 120s, initial NaOH concentration: 1.1%, H2O2 concentration: 6%, self-replenishing NaOH concentration: 0.01%, self-replenishing H2O2 concentration: 0.09%, circulation / bubbling mode: continuous circulation, with basket bubbling. Purpose of the step: The unique strong oxidizing property of hydrogen peroxide effectively cleans surface contaminants. Result: The cleaning effect is significantly improved at this concentration.

[0159] Water tank: Time 120 seconds, overflow mode: overflow with basket or continuous overflow, purpose of the step: to rinse off the desorbed impurities and residual chemicals on the silicon wafer surface with deionized water.

[0160] Alkali polishing: Process temperature: 67-69℃, time: 280±20s, initial NaOH concentration: 3.5%, ADDI concentration: 0.4%, self-replenishing NaOH concentration: 0.09%, self-replenishing ADDI concentration: 0.04%, circulation / bubbling mode: continuous circulation, no basket bubbling. Purpose: Alkali polishing improves the back surface reflectivity and structure, enhances long-wave response, and reduces back surface recombination. The back surface is polished using alkali, while additives protect the front surface from corrosion. Results: At this concentration, etching depth increases, and flatness is significantly improved.

[0161] Water tank: Time 120 seconds, overflow mode: overflow with basket or continuous overflow, purpose of the step: to rinse off the desorbed impurities and residual chemicals on the silicon wafer surface with deionized water.

[0162] Post-cleaning: Process temperature: 67-70℃, time: 120s, initial NaOH concentration: 0.9%, H2O2 concentration: 5%, self-replenishing NaOH concentration: 0.01%, self-replenishing H2O2 concentration: 0.09%, circulation / bubbling mode: continuous circulation, with basket bubbling. Purpose of the step: The unique strong oxidizing property of hydrogen peroxide effectively cleans surface contaminants. Result: The cleaning effect is significantly improved at this concentration.

[0163] Water tank: Time 120 seconds, overflow mode: overflow with basket or continuous overflow, purpose of the step: to rinse off the desorbed impurities and residual chemicals on the silicon wafer surface with deionized water.

[0164] Mixed acid pickling: Process temperature: room temperature, time: 130-140 seconds, initial HF concentration: 1.15%, self-replenished HF concentration: 0.12%. Purpose of this step: Increased acid concentration has a positive correlation with silicon wafer dehydration; improving the initial and subsequent addition of HF helps the silicon wafer reach its optimal dehydration state. Result: At this concentration, the silicon wafer dehydration effect is significantly improved.

[0165] Water tank: Time 120 seconds, overflow mode: overflow with basket or continuous overflow, purpose of the step: to rinse off the desorbed impurities and residual chemicals on the silicon wafer surface with deionized water.

[0166] Slow lifting: Process temperature: 48-50℃, add 2% slow lifting additive initially, self-replenish 0.06-0.08%, lifting speed controlled at 3-5mm / s, with basket overflow or continuous overflow. Purpose of the step: Rinse the silicon wafer surface with deionized water to remove residual chemicals, then lift it into the drying tank by a robotic arm. The surface tension of the water decreases after the water temperature is increased, reducing the water droplets carried by the silicon wafer and basket when they are removed from the slow lifting process. Effect: The water situation of the silicon wafer when it is removed from the slow lifting basket is improved at the increased temperature, with no obvious large water droplets. The water situation is significantly improved at this temperature, and the amount of water droplets carried after slow lifting is significantly reduced.

[0167] Drying: Process temperature: 95±3℃, time: 600s, effect: After adding the air inlet diversion pipeline, there are no water droplets on the bottom rod of the alkali-throwing basket, the bottom end plate of the basket, and the bottom of the drying tank. This is a significant improvement compared to before the addition. Continuous blowing is carried out on the bottom rod of the basket, the bottom end plate of the basket, and the bottom of the drying tank to achieve the best drying state. Under the 600s drying time, the liquid on the bottom rod of the basket, the bottom end plate of the basket, and the bottom of the drying tank has basically disappeared, achieving a complete drying effect.

[0168] Example 4:

[0169] After removal from the PSG (Pressure Processing Unit), the silicon wafers are carried in baskets and fed into the alkaline polishing machine by a robotic arm for further processing.

[0170] Pre-cleaning: Process temperature: 75-80℃, time: 150s, initial NaOH concentration: 2%, H2O2 concentration: 6%, self-replenishing NaOH concentration: 0.01%, self-replenishing H2O2 concentration: 0.1%, circulation / bubbling mode: continuous circulation, with basket bubbling. Purpose of the step: The unique strong oxidizing property of hydrogen peroxide cleans surface contaminants. Effect: Rapid decomposition of hydrogen peroxide, occasional abnormal appearance of discharged materials;

[0171] Water tank: Time 120 seconds, overflow mode: overflow with basket or continuous overflow, purpose of the step: to rinse off the desorbed impurities and residual chemicals on the silicon wafer surface with deionized water.

[0172] Alkaline polishing: Process temperature: 73-78℃, time: 280±20S, initial NaOH concentration: 4%, ADDI concentration: 0.6%, self-replenished NaOH concentration: 0.12%, self-replenished ADDI concentration: 0.06%, circulation / bubbling mode: continuous circulation, no basket bubbling, purpose: alkaline polishing improves back-side reflectivity and structure, enhances long-wavelength response and reduces back-side recombination, using alkali to polish the back-side, while additives protect the front-side from corrosion. Results: At this concentration, etching depth increases significantly, and flatness is significantly improved, but silicon wafers exhibit adsorption in subsequent baths.

[0173] Water tank: Time 120 seconds, overflow mode: overflow with basket or continuous overflow, purpose of the step: to rinse off the desorbed impurities and residual chemicals on the silicon wafer surface with deionized water.

[0174] Post-cleaning: Process temperature: 67-70℃, time: 120s, initial NaOH concentration: 0.9%, H2O2 concentration: 5%, self-replenishing NaOH concentration: 0.01%, self-replenishing H2O2 concentration: 0.09%, circulation / bubbling mode: continuous circulation, with basket bubbling. Purpose of the step: The unique strong oxidizing property of hydrogen peroxide cleans surface contaminants. Effect: Rapid decomposition of hydrogen peroxide, occasional abnormal appearance of discharged materials;

[0175] Water tank: Time 120 seconds, overflow mode: overflow with basket or continuous overflow, purpose of the step: to rinse off the desorbed impurities and residual chemicals on the silicon wafer surface with deionized water.

[0176] Mixed acid washing: Process temperature: room temperature, time: 160s, initial HF concentration: 1.25%, self-replenished HF concentration: 0.2%. Purpose of the step: Increased acid concentration has a positive correlation with silicon wafer dehydration; improving the initial HF concentration and subsequent replenishment helps the silicon wafer reach its optimal dehydration state. Result: At this concentration, the silicon wafer dehydration effect is significantly improved.

[0177] Water tank: Time 120 seconds, overflow mode: overflow with basket or continuous overflow, purpose of the step: to rinse off the desorbed impurities and residual chemicals on the silicon wafer surface with deionized water.

[0178] Slow Pulling: Process temperature: 55-60℃, add 4% slow pulling additive initially, self-replenish 0.1-0.2%, pull speed controlled at 3-5mm / s, with basket overflow or continuous overflow. Purpose of the step: Rinse the silicon wafer surface with deionized water to remove residual chemicals, then pull it into the drying tank via a robotic arm. Increasing the water temperature reduces the surface tension of the water, reducing water droplets carried by the silicon wafer and basket when detaching from the slow pulling process. Result: At higher temperatures, the water retention of the silicon wafer when detaching from the slow pulling basket is improved, with no obvious large water droplets. The improvement in water retention is significant at this temperature, and the amount of water droplets carried after slow pulling is significantly reduced.

[0179] Drying: Process temperature: 95±3℃, time: 800S. Result: After adding the air inlet diversion pipeline, there were no water droplets on the bottom rod of the alkali-throwing basket, the bottom end plate of the basket, and the bottom of the drying tank, which is a significant improvement compared to before the addition. Continuous blowing was performed on the bottom rod of the basket, the bottom end plate of the basket, and the bottom of the drying tank to achieve the best drying state. Under the 800S drying time, any liquid residue on the bottom rod of the basket, the bottom end plate of the basket, and the bottom of the drying tank basically disappeared, achieving a complete drying effect.

[0180] This set of experiments still achieved the desired drying purpose compared to Example 3. However, the overall process, including pre-cleaning, alkaline polishing, post-cleaning, excessively high concentration in the pickling tank, excessively high temperature during slow lifting, and prolonged drying, all failed to meet mass production conditions. Production capacity and energy consumption were both too high, and the slow lifting and excessively high acid tank concentration resulted in poorer performance in terms of EL (efficacy) compared to Example 3.

[0181] Comparison of data between the comparative example and the four embodiments:

[0182] Table 1. Statistical table of dehydration data for each implementation plan.

[0183]

[0184] In summary, the dehydration results of the comparative examples were generally average, with a drying effect of 70%. Example 1 showed a slight improvement in dehydration performance, with a drying effect of 75%. Example 2 showed a more significant improvement in dehydration performance, with a drying effect of 85%. Example 3 showed a significant improvement in dehydration performance, with a drying effect of 95%. Example 4 showed a significant improvement in dehydration performance, with a drying effect of 98%. Based on the tracking data, Example 3 is the optimal implementation scheme. Compared with the comparative examples, the examples showed improvements in dehydration / drying effects in the acid tank, slow lifting, drying tank, and bottom of the tank. Furthermore, the addition of an air inlet diversion pipe to the drying tank largely solved the problems of liquid carryover in the bottom rod, bottom end plate, and tank of the alkali-polished basket. All indicators related to yield improved.

[0185] The electrical performance data of the comparative example and the four embodiments are compared as follows:

[0186] Table 2 Electrical performance data for each implementation scheme

[0187]

[0188]

[0189] The comparative data and the data of the four examples are compared as follows:

[0190] Table 3 EL Proportion Statistics for Each Implementation Plan

[0191] Comparative Example 2.30％ 2.50％ 2.00％ 0.09％ Example 1 1.30％ 1.50％ 0.80％ 0.07％ Example 2 0.57％ 0.47％ 0.05％ 0.06％ Example 3 0.04％ 0.06％ 0.00％ 0.04％ Example 4 0.06％ 0.04％ 0.00％ 0.07％

[0192] Wherein, Uoc is the open-circuit voltage, Isc is the short-circuit current, Rs is the series resistance, Rsh is the parallel resistance, FF is the fill factor, and Ncell is the cell conversion efficiency. The conversion efficiency of the comparative example cell is 26.28%, the conversion efficiency of the example cell is 26.29%, the conversion efficiency of the example cell is 26.30%, the conversion efficiency of the example cell is 26.30%, and the conversion efficiency of the example cell is 26.30%. Compared with the comparative example, the conversion efficiency of the four examples is improved by 0.01-0.02%. In general, the higher conversion efficiency of the examples is mainly due to the improvement of Uoc and Isc. The fundamental reason is the optimization of the alkaline polishing process and the superposition of the air diversion device in the drying tank, which reduces EL contamination and improves the yield, making the alkaline polishing process more stable and the compatibility of the front and rear processes better, thereby improving the open-circuit voltage and short-circuit current, and thus improving the cell conversion efficiency. The EL defect rate in the comparative example was approximately 2-2.5%. The yield of all three examples showed some improvement, but Example 4 showed a slight increase in other contaminants, possibly due to the excessively high temperature during slow pulling, leading to partial water evaporation. In summary, Example 3 is the optimal solution. Example 3 not only optimized the alkaline polishing process but also solved the liquid carryover problem in the drying tank, improved process stability, reduced EL defects, decreased the number of process variation points in the alkaline polishing stage, and increased the cell conversion efficiency by 0.02%.

[0193] The production route used in this invention follows the production route of Topcon products. As a variation, this invention is not limited to the production process of Topcon products; it can also be used in the production processes of other types of solar cells. It is primarily applicable to cleaning processes such as texturing, alkaline polishing, RCA (Rich Carbon Fiber) treatment, and rework cell cleaning.

[0194] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Although embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present invention, and all such modifications and variations fall within the scope defined by the present invention.

Claims

1. An optimization method for an alkaline polishing process, characterized in that, The alkaline polishing process optimization method includes: Pre-cleaning was performed at a process temperature of 67℃-70℃ for 120 seconds. The initial NaOH concentration was 1.1%, the initial H2O2 concentration was 6%, the self-replenishing NaOH concentration was 0.01%, and the self-replenishing H2O2 concentration was 0.09%. A continuous circulation, basket bubbling mode was adopted. The water tank is used to rinse off the desorbed impurities and residual chemicals on the silicon wafer surface with deionized water in one pass. The time is set to 120 seconds, and the overflow mode can be either overflow with a basket or continuous overflow. Alkali polishing was performed at a set temperature of 67℃-69℃ and a set time of 280±20s. The initial NaOH concentration was 3.5%, the initial ADDI concentration was 0.4%, the self-replenishing NaOH concentration was 0.09%, and the self-replenishing ADDI concentration was 0.04%. The process was carried out in a continuous circulation, basketless bubbling mode. The secondary water rinsing tank uses deionized water to rinse away the desorbed impurities and residual chemicals on the silicon wafer surface. The time is set to 120 seconds, and the overflow mode can be either basket overflow or continuous overflow. For post-cleaning, the process temperature is set at 67℃-70℃, the cleaning time is 120 seconds, the initial NaOH concentration is selected as 0.9%, the initial H2O2 concentration is selected as 5%, the self-replenished NaOH concentration is selected as 0.01%, and the self-replenished H2O2 concentration is selected as 0.09%. The process is carried out in a continuous circulation mode with a basket bubbling. Three rinses are performed in the water tank, using deionized water to rinse away the desorbed impurities and residual chemicals on the silicon wafer surface. The set time is 120 seconds, and the overflow mode can be either overflow with a basket or continuous overflow. Mixed pickling was performed at room temperature for 130 seconds. The initial HF concentration was set at 1.1%, and the self-replenishing HF concentration was set at 0.11%. The process involves four water rinsing cycles, using deionized water to remove desorbed impurities and residual chemicals on the silicon wafer surface. The set time is 120 seconds, and the overflow mode uses a basket overflow. For lifting, set the process temperature to 48℃-50℃, add lifting additive, select an initial concentration of 2%, select a self-replenishing concentration of 0.06%-0.08%, control the lifting speed at 3mm / s-5mm / s, and adopt the overflow mode of basket overflow or continuous overflow. Drying: Set the process temperature to 95±3℃ and the time to 600 seconds. The lifting additive comprises a surfactant; wherein the surfactant includes polyvinylpyrrolidone. The lifting additive also includes sodium polystyrene sulfonate and deionized water.

2. The method for optimizing the alkali polishing process according to claim 1, characterized in that, The concentration of polyvinylpyrrolidone was selected as 7%; the concentration of deionized water was selected as 85%; and the concentration of sodium polystyrene sulfonate was selected as 8%.

3. The method for optimizing the alkaline polishing process according to claim 1, characterized in that, The optimized alkaline polishing process is implemented using a drying device, which includes: A base plate (12) and side wall panels (11) surrounding the base plate (12); the base plate (12) and the side wall panels (11) together form a drying trough; Flower basket rack (13) is set in the drying tank; the flower basket rack (13) is suitable for placing flower baskets (5), the flower baskets (5) contain silicon wafers (6), the silicon wafers (6) are arranged parallel to the first direction, and multiple silicon wafers (6) are placed in the flower baskets (5) and arranged parallel and spaced apart along the second direction; A first hot air unit (2) is disposed in the drying tank and located on the bottom plate (12). The first hot air unit (2) extends along the second direction and is adapted to blow air toward the surface of the bottom plate (12). The second hot air unit (3) is disposed in the drying trough and installed on the flower basket frame (13). The second hot air unit (3) extends along the first direction and is adapted to blow air toward the flower basket end plate (52) of the flower basket (5). The third hot air unit (4) is disposed in the drying trough and installed on the flower basket frame (13). The second hot air unit (3) extends in the second direction and is adapted to blow air toward the bottom rod (51) of the flower basket (5).

4. The method for optimizing the alkaline polishing process according to claim 3, characterized in that, The third hot air unit (4) and / or the second hot air unit (3) are disposed at the bottom of the flower basket frame (13) along the height direction.

5. The method for optimizing the alkaline polishing process according to claim 3, characterized in that, The number of the first hot air unit (2) is multiple; At least one of the first hot air units (2) is located in the middle of the drying tank and has a first air inlet (21) that blows air in the first direction to both sides. At least one first hot air unit (2) is disposed in the drying tank near the side wall plate (11) and has a first air inlet (21) that blows air in a first direction toward the side away from the side wall plate (11).

6. The method for optimizing the alkali polishing process according to claim 3, characterized in that, The second hot air unit (3) consists of multiple units; At least one second hot air unit (3) is located in the middle of the drying tank and has a second air inlet (31) that blows air in the second direction to both sides. At least one second hot air unit (3) is disposed in the drying tank near the side wall plate (11) and has a second air inlet (31) that blows air in the second direction toward the side away from the side wall plate (11).

7. The method for optimizing the alkaline polishing process according to claim 3, characterized in that, The number of the third hot air units (4) is one or more; One or more of the third hot air units (4) are located in the middle of the drying tank and have a third air inlet (41) that blows air in the first direction toward both sides.

8. The method for optimizing the alkali polishing process according to claim 3, characterized in that, The side wall panel (11) is provided with an air outlet (111), which blows air towards the side of the flower basket frame (13).

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