Additive, low-hydrofluoric-acid etching solution and etching method cooperating with ultrasound

Abstract

The invention discloses an additive, a low hydrofluoric acid etching solution and an etching method cooperating with ultrasound. The multi-component additive comprises the following components in percentage by mass: 0.01%-0.5% of a penetration enhancer, 2%-10% of a PSG activating component, 0.1%-0.5% of organic protonic acid, 0.1%-0.5% of an interface cleaning component and 0.1%-0.5% of a reaction stabilizing component. The multi-component additive is used for preparing a low-concentration hydrofluoric acid etching solution, and the low-concentration hydrofluoric acid etching solution is used for etching PSG (Phosphosilicate Glass) of a silicon wafer under the synergistic effect of ultrasonic waves, so that the defects in the prior art can be effectively overcome. According to the method, the chemical efficiency of the low-concentration HF is fully exerted through precise coupling of a series of collaborative mechanisms under the drive of ultrasonic-assisted specific energy, the PSG can be quickly and uniformly etched, the dosage of the HF is reduced to 50% or above of that of a traditional process, the production cost is reduced, and the method is safe and environmentally friendly.

Description

Technical Field

[0001] This invention relates to the fields of photovoltaic and semiconductor technology, and in particular to a multi-component additive, a low-concentration hydrofluoric acid etching solution containing the additive, and a process method for etching the PSG layer of a silicon wafer using the etching solution in conjunction with ultrasound. Background Technology

[0002] The photovoltaic industry is accelerating its iteration towards high-efficiency and low-cost technologies. Wet processes, a crucial step in solar cell fabrication (such as texturing, alkaline polishing, RCA, BSG removal, and PSG removal), are essential for reducing non-silicon costs. In TOPCon cell structures, the poly layer plays a vital role. As a passivation layer, it provides excellent ohmic contact between the silicon substrate and metal electrodes, reducing carrier recombination probability, and as a dielectric layer, it facilitates smooth carrier output. Polyfinger technology is a back-side poly patterning and thinning technique that finely adjusts the poly layer thickness. It can thin non-electrode areas while maintaining the poly layer thickness beneath the electrodes, thereby improving cell performance. The Polyfinger fabrication process requires etching to remove the deposited phosphosilicate glass (PSG) layer, thus eliminating parallel resistance and potential electrode short circuits in the solar cell.

[0003] Currently, the removal of PSG in this field requires etching with 10%-20% hydrofluoric acid. Although this method has a fast etching rate, it has many drawbacks: it brings high chemical costs, serious safety hazards and huge environmental pressure. Specifically, (1) poor safety: high concentrations of HF are extremely corrosive and toxic, which is extremely harmful to the human body and requires very high operating standards. (2) environmental pollution: high concentrations of fluorine-containing waste liquid are costly to treat and are not environmentally friendly. (3) poor etching uniformity: the reaction is violent at high concentrations, which can easily lead to uneven etching and may damage the silicon substrate or the front structure of the device. (4) equipment corrosion: high concentrations of HF severely corrode production equipment such as etching tanks and pipelines, increasing maintenance costs.

[0004] While the industry widely recognizes the urgency of reducing HF concentration, simply lowering the concentration leads to a significant decrease in etching rate and a sharp deterioration in uniformity. The root cause lies in four core bottlenecks associated with using low-concentration HF: 1. Mass transfer limitation: Insufficient diffusion rate of HF molecules to the PSG surface, unable to maintain a rapid reaction. 2. Insufficient reaction kinetics: The Si-OP bond network in PSG has high chemical stability, and low-concentration HF is insufficient to effectively disrupt its structure. 3. Byproduct coverage: Insoluble or poorly soluble byproducts such as fluorosilicates and fluoroborates generated during the reaction will cover the active surface, physically hindering the continued reaction. 4. Impurity ion poisoning: Metal ions (such as Fe³⁺, Al³⁺) introduced from silicon wafers, equipment, or the environment can catalyze harmful side reactions or form fluoride precipitates, poisoning the reaction interface.

[0005] Therefore, overcoming the shortcomings of existing methods that reduce HF concentration when etching PSG layers leads to a significant decrease in etching rate and a sharp deterioration in uniformity is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the technical problem of significant attenuation of etching rate and drastic deterioration of uniformity caused by reducing HF concentration when etching PSG layers, this invention provides a multi-component additive, a low-concentration hydrofluoric acid etching solution containing the additive, and an etching method synergistic with ultrasound. Using this etching solution, the PSG layer on a silicon wafer can still be removed efficiently, uniformly, and stably even in a low-concentration hydrofluoric acid solution.

[0007] The present invention provides a multi-component additive comprising the following components by mass percentage: Penetration enhancer 0.01%-0.5%, PSG activating component 2%-10%, organic protic acid 0.1%-0.5%, Interface cleaning component 0.1%-0.5%, reaction stabilizing component 0.1%-0.5%.

[0008] Preferably, the penetration enhancer is one of n-propanol, 1,4-dioxane, 1,2-hexanediol, isobutanol or isopropanol and N-methylpyrrolidone or 1,4-dioxane, compounded in a mass ratio of 2:1 to 1:1.

[0009] Preferably, the PSG activating component is at least one of potassium fluoride, sodium fluoride, or ammonium bifluoride.

[0010] Preferably, the organic protic acid is at least one of acetic acid, propionic acid, formic acid, or oxalic acid.

[0011] Preferably, the interface cleaning component is at least one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, oleamide propyl hydroxysulfonate betaine, sodium lauroyl glutamate, or sodium cocoyl glutamate.

[0012] Preferably, the reaction stabilizing component is at least one of citric acid, triacetic acid, malonic acid, or ethylenediaminetetraacetic acid.

[0013] The low-concentration hydrofluoric acid etching solution provided by this invention comprises the following components by mass percentage: Hydrofluoric acid 0.5% - 2%, the multi-component additive 1% - 5%, and the balance being deionized water.

[0014] This invention also provides a method for ultrasonic-assisted hydrofluoric acid etching of PSG, comprising the following steps: Step 1: Prepare the low-concentration hydrofluoric acid etching solution according to the specified ratio; Step 2: Place the low-concentration hydrofluoric acid etching solution in an ultrasonic device, set the frequency and power density of the ultrasonic waves, and start the ultrasonic waves; Step 3: Immerse the photovoltaic silicon wafer with the PSG layer into the low-concentration hydrofluoric acid etching solution and process it at a set temperature for a set time. Step 4: After etching is complete, remove the silicon wafer for cleaning, rinse with ultrapure water overflow, slowly lift it, and dry it.

[0015] Preferably, in step 2, the set frequency is 20~80 kHz and the u power density is 300~800 W / m².

[0016] Preferably, in step 3, the set temperature is 25-35℃ and the set time is 0.5-2 minutes.

[0017] This invention constructs a precise directional etching and timely cleaning system, in which each component of the multi-component additive interacts positively with the ultrasonic field through deep coupling: 1. Superior Synergistic Effect: The additives of this invention do not simply add up the functions of each component, but rather create a synergistic effect of "1+1>2" with the ultrasonic field. The penetration enhancer penetrates powerfully with the help of ultrasonic cavitation; the interface cleaning component cleans the surface efficiently under ultrasonic disturbance; and the reaction stabilizing component rapidly complexes impurity ions under ultrasonic-enhanced mass transfer. These three components work together to efficiently convert the physical energy of ultrasound into chemical etching power.

[0018] 2. Significantly reduced HF usage: The concentration of existing hydrofluoric acid is 10%-20%, which is 10-20 times higher than that of this application. While achieving the same or even better etching effect, the concentration of HF in this application is reduced to 0.5%-2%, which greatly reduces chemical consumption, waste liquid treatment costs, and environmental safety risks.

[0019] 3. High efficiency and uniformity: Even at low HF concentrations, the etching rate is significantly improved, shortening the process time. Simultaneously, this system achieves excellent intra-wafer and inter-wafer uniformity, effectively avoiding over-etching or incomplete etching, thus improving product yield.

[0020] 4. Protecting the silicon substrate: Low concentrations of HF have a weak corrosive effect on the silicon substrate. Combined with gentle ultrasonic treatment, it helps to obtain a smoother silicon surface with fewer defects, which is beneficial to improving the minority carrier lifetime and final conversion efficiency of the battery.

[0021] 5. Strong process compatibility: The method of this invention is easy to integrate into existing photovoltaic cell production lines. It only requires adding the additive of this invention to the existing HF cell and turning on the ultrasonication. The modification cost is low and the economic benefits are significant.

[0022] 6. Final Results: Through this series of interconnected and mutually amplifying precise collaborations, this invention successfully reduced the working concentration of HF from the traditional >10% to below 3%, a reduction of more than 70%, and even more than 80%. At the same time, the etching rate and uniformity are superior to the traditional high-concentration HF process, and a silicon substrate with better surface quality and less damage is obtained, achieving a comprehensive breakthrough in safety, environmental protection, cost and performance.

[0023] The multi-component additive, etching solution, and etching method synergistically combined with ultrasound provided by this invention effectively overcome the shortcomings of existing technologies. The etching system provided by this invention, driven by specific energy with ultrasound assistance, constructs a highly efficient and directional microscopic reaction environment through the precise coupling of a synergistic mechanism of "synergistic penetration-interface activation-dynamic cleaning-steady-state maintenance." This maximizes the chemical efficacy of low-concentration HF, achieving rapid and uniform etching of PSG while reducing HF usage to less than 50% of that in traditional processes, thus lowering production costs and ensuring safety and environmental friendliness. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the etching process of a silicon wafer using an ultrasonic synergistic etching solution. Figure 2 This is a microscope image of the back side after PSG etching removal in Example 1; Figure 3 This is a microscope image of the back side after PSG etching removal in Example 2; Figure 4 This is a microscope image of the back side after PSG etching removal, which is Comparative Example 1. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the following specific embodiments are only used to explain the invention and do not constitute a limitation thereof.

[0026] The multi-component additive provided by this invention comprises the following components by mass percentage: Penetration enhancer 0.01%-0.5%, PSG activating component 2%-10%, organic protic acid 0.1%-0.5%, Interface cleaning component 0.1%-0.5%, reaction stabilizing component 0.1%-0.5%.

[0027] The penetration enhancer can be selected from a low-boiling-point polar solvent, such as one of n-propanol, 1,4-dioxane, 1,2-hexanediol, isobutanol or isopropanol, and a high-boiling-point coordination solvent, such as N-methylpyrrolidone or 1,4-dioxane, in a mass ratio of 2:1 to 1:1.

[0028] This penetration enhancer possesses low surface tension and a low boiling point, making it extremely sensitive to ultrasonic cavitation and readily vaporizing to form microbubbles. Under the localized, instantaneous high-temperature and high-pressure (hot spot) environment generated by the collapse of cavitation bubbles, isopropanol molecules readily vaporize, intensifying the intensity and density of the microjets. These high-frequency microjets, like "microscopic water jets," powerfully scour and penetrate the static boundary layer and micropores of the PSG surface, creating microscopic channels for HF molecules and opening and widening transport channels for subsequent reactants. Its core function is to solve the mass transfer bottleneck problem where HF molecules "cannot reach" the reaction interface at low concentrations.

[0029] The highly polar carbonyl functional group in N-methylpyrrolidone (a molecular carrier and directional anchoring agent) can form a transient "HF-NMP" complex with HF molecules through hydrogen bonding. Under the intense macroscopic and microscopic convection of ultrasound, this complex is transported to the PSG surface more efficiently than free HF molecules. More importantly, NMP preferentially adsorbs on the Si-OH and P-OH sites on the PSG surface, locally reducing the interfacial energy. This is equivalent to establishing a "bridgehead" or "forward base" for HF at the reaction front, significantly increasing the local effective concentration and residence time of HF molecules reaching the reaction sites. Therefore, this penetration enhancer has the function of reducing the amount of HF required.

[0030] The PSG activating component is at least one of potassium fluoride, sodium fluoride, or ammonium bifluoride. As a pre-corrosion and pore-forming agent, the PSG activating component provides F⁻ ions that preferentially react with tricoordinated boron (B³⁺) in the PSG network to generate soluble BF⁻ ions. This process "chiseles" numerous nanoscale pores and structural defects in the dense PSG layer, significantly increasing the attackable specific surface area of ​​HF molecules. This means that an HF molecule can now attack chemical bonds from multiple directions, multiplying its destruction efficiency. This allows one HF molecule to exert the destructive effect equivalent to several molecules on a high-concentration, flat surface, "softening" and "destroying" the PSG structure with the energy assistance of ultrasound, providing optimal attack sites for HF. The organic protic acid is at least one of acetic acid, propionic acid, formic acid, or oxalic acid. The H⁺ provided by the organic protic acid protonates the bridging oxygen bonds (Si-O-Si and Si-OP) in the PSG, causing these strong covalent bonds to polarize and elongate, significantly reducing bond energy. This is equivalent to significantly lowering the activation energy barrier required for HF molecules to break these chemical bonds. Under the continuous acoustic energy input provided by ultrasound, this protonation-weakening process is accelerated and homogenized, resulting in a significant improvement in the etching efficiency of low-concentration HF.

[0031] The interface cleaning component is at least one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, oleamidopropyl hydroxysulfonate, sodium lauroyl glutamate, or sodium cocoyl glutamate.

[0032] Under ultrasonic waves, the interface cleaning component can be more uniformly adsorbed onto the silicon wafer surface, reducing the liquid-solid interface energy and preventing the adhesion of reaction products. Simultaneously, through its emulsifying effect, it helps to peel off and remove insoluble substances such as fluorosilicates generated during the reaction, exposing a fresh PSG reaction interface. Under the powerful physical shear force of ultrasound, the stripping agent promptly removes reaction byproducts, ensuring the reaction continues at a high speed. Simultaneously, it can form a dense adsorption layer on the hydrophobic silicon substrate, thermodynamically preventing byproduct adhesion by reducing the interface energy. The excellent permeability of the interface cleaning component allows it to effectively penetrate the interface between byproducts and PSG, acting as a "molecular crowbar" to weaken their binding force. Through the steric hindrance effect of its long-chain molecules, it physically prevents the loosened byproducts from redepositing onto the clean surface. The powerful shear force and shock waves generated by the ultrasonic cavitation effect can instantly and continuously peel off, pulverize, and emulsify the reaction byproducts "loosened" and "encapsulated" by the aforementioned surfactants from the interface, dispersing them into the bulk solution. This ensures that each HF molecule can precisely attack the highly reactive PSG surface, avoiding its consumption or waste on ineffective, inert byproduct coatings, thereby greatly improving the utilization efficiency of HF and the continuity of the etching process.

[0033] The reaction stabilizing component is at least one of citric acid, triacetic acid, malonic acid, and ethylenediaminetetraacetic acid. This stabilizing component strongly complexes with metallic impurities such as Fe³⁺ and Al³⁺ that may be present or generated during the etching process of the silicon wafer. These ions are "highly effective poisons" for HF, catalyzing side reactions that consume HF or forming insoluble fluoride precipitates (such as FeF₃) that firmly cover the active sites, leading to the ineffective consumption of a large amount of HF. This stabilizing component preemptively complexes with these metal ions, deactivating them and ensuring that all limited HF molecules are effectively used in the main PSG etching reaction. The polybasic acid properties stabilize the pH of the etching system within the optimal range of 2.5-3.5. Under this pH environment, the HF / HF₂⁻ equilibrium shifts towards the active species HF₂⁻, and each additive component (especially component B) maintains optimal chemical activity. Ultrasound enhances mass transfer, ensuring that citric acid can quickly reach any area with pH fluctuations or impurities, creating a globally stable and efficient working environment for low-concentration HF systems, and playing a role in pH buffering and homeostasis maintenance.

[0034] Through the above series of precise combinations, the energy of physical ultrasound and chemical additives is focused on the reaction interface, which gives a very small number of HF molecules extremely high "reaction efficiency" and "targeting". This allows the etching rate and uniformity to be achieved or even surpassed by traditional high-concentration HF processes when the HF concentration is reduced by 70%-90%, while obtaining a cleaner silicon surface with less damage.

[0035] The low-concentration hydrofluoric acid etching solution provided by this invention comprises the following components by mass percentage: Hydrofluoric acid 0.5% - 2%, multi-component additives provided by this invention 1% - 5%, balance deionized water.

[0036] This invention also provides a method for ultrasonic-assisted hydrofluoric acid etching of PSG, comprising the following steps: Step 1: Prepare the low-concentration hydrofluoric acid etching solution according to the specified ratio.

[0037] Step 2: Place the low-concentration hydrofluoric acid etching solution in an ultrasonic device, set the frequency to 20~80 kHz and the power density to 300~800 W / m², and start the ultrasonic treatment.

[0038] Step 3: Immerse the photovoltaic silicon wafer with the PSG layer into the low-concentration hydrofluoric acid etching solution and etch for 0.5-2 minutes at a temperature of 25-35℃.

[0039] Step 4: After etching is complete, remove the silicon wafer for cleaning, rinse with ultrapure water overflow, slowly lift it, and dry it.

[0040] The drying method is not limited; it can be heating drying, hot air drying, or other drying methods.

[0041] The present invention will be further described below with reference to the accompanying drawings, embodiments, and comparative examples.

[0042] Example 1: 1. Formulation of multi-component additives: Weigh the following ingredients by mass percentage: 0.5% isopropanol, 0.1% N-methylpyrrolidone, 10% ammonium fluoride, 1% acetic acid, 0.2% sodium dodecyl sulfate, 0.3% cocamidopropyl hydroxysulfonate betaine, 0.4% ethylenediaminetetraacetic acid, and 87.5% deionized water. Mix the ingredients at room temperature and stir until a homogeneous and transparent solution is formed to obtain the multi-component additive.

[0043] 2. Preparation of low-concentration hydrofluoric acid etching solution: Add an appropriate amount of deionized water to the etching tank, and while stirring, add the aforementioned multi-component additives until the final concentration reaches 4% (w / w). Finally, slowly add 40% concentrated hydrofluoric acid to adjust the final concentration to 1% (based on 40% HF) hydrofluoric acid solution. Continue stirring and mixing until homogeneous to obtain the low-concentration hydrofluoric acid etching solution. In industrial production, the 1% concentration hydrofluoric acid obtained in the etching tank is prepared in units of "40% hydrofluoric acid". The 10%-20% concentration hydrofluoric acid used in conventional tanks in existing technologies is also prepared in units of "40% hydrofluoric acid".

[0044] 3. Ultrasonic-assisted hydrofluoric acid etching method for PSG Please refer to Figure 1 The temperature of the low-concentration hydrofluoric acid etching solution in the etching tank was controlled at 40℃, the frequency was set to 40kHz, the power density to 400 W / m², and the ultrasonic generator was turned on. A batch of N-type single-crystal silicon wafers with phosphosilicate glass (PSG thickness approximately 120 nm) deposited on the back were transferred into the etching tank, and the etching process lasted for 2 minutes. After processing, the wafers were rinsed with ultrapure water overflow, ultrasonically cleaned (1 MHz), and then slowly pulled out in the cleaning tank and placed in a drying tank to dry the surface moisture.

[0045] Example 2 1. Formulation of multi-component additives: Weigh the following ingredients by mass percentage: 1,4-dioxane 1%, isopropanol 2%, potassium fluoride 5%, acetic acid 1 part, sodium lauroyl glutamate 0.2%, cocamidopropyl hydroxysulfonate betaine 0.1%, citric acid 0.5%, and 90.2% deionized water. Mix and stir the above ingredients at room temperature until a homogeneous and transparent solution is formed to prepare a multi-component additive.

[0046] 2. Preparation of low-concentration hydrofluoric acid etching solution: Add an appropriate amount of ultrapure water to the etching tank, and add the above-mentioned additives to a final concentration of 3% (w / w) while stirring. Finally, slowly add 49% concentrated hydrofluoric acid to adjust the final concentration of the hydrofluoric acid solution to 1.5% (based on a concentration of 40% HF). Continue stirring and mixing to obtain a low-concentration hydrofluoric acid etching solution.

[0047] 3. Ultrasonic-assisted hydrofluoric acid etching method for PSG Please refer to Figure 1 The temperature of the low-concentration hydrofluoric acid etching solution in the etching tank was controlled at 28°C. The ultrasonic generator was turned on, and the frequency was set to 40 kHz with a power density of 300 W / m². A batch of N-type single-crystal silicon wafers with phosphosilicate glass (PSG thickness of approximately 120 nm) deposited on the back were transferred into the etching tank, and the processing time was 2 minutes. After processing, the wafers were rinsed with ultrapure water overflow, ultrasonically cleaned (1 MHz), and then slowly pulled out in the cleaning tank and placed in a drying tank to dry the surface moisture.

[0048] Comparative Example 1: A traditional etching process was used with a 10% HF aqueous solution as the etching solution. No additives were used, and no ultrasound was performed. The etching process was carried out by immersion in the solution for 2 minutes at the same temperature, followed by post-treatment.

[0049] Comparative Example 2: A low-concentration 1% HF solution was used as the etching solution without any additives. The etching was performed under the same ultrasonic conditions as in Example 1 for 2 minutes, followed by post-treatment.

[0050] In Comparative Examples 1 and 2 above, the concentration of HF was prepared in units of "40% hydrofluoric acid".

[0051] Performance test results and comparisons of silicon wafer samples etched in Example 1 and Comparative Examples 1 and 2: The uniformity of PSG removal was confirmed by observing the surface dehydration rate and uniformity. The etching rate of the hydrofluoric acid etching of the phosphosilicate glass layer was calculated by testing the PSG removal thickness per unit time using a multi-wafer gravimetric method: 1. Accurately weigh the silicon wafer before etching (W1). 2. Thoroughly clean and dry after etching, and weigh the wafer after etching (W2). 3. Calculate the average etching thickness and rate by weight reduction, PSG density, and area. Repeat the calculation of the average etching rate using multiple wafers. The surface roughness of the silicon wafer after PSG etching was detected using a white light interferometer. The sheet resistance of the back side of the etched silicon wafer was non-destructively measured using a four-probe sheet resistance tester. The insulating PSG layer was selectively removed, exposing the conductive phosphorus diffusion layer silicon surface underneath. The probes of the four-probe tester could directly contact the conductive layer, thereby obtaining a stable and reasonable sheet resistance value, thus confirming that the PSG had been completely removed. The silicon wafer sample etched in Example 1 was tested with the silicon wafer samples etched in Comparative Examples 1 and 2. The following four performance indicators were compared, as shown in Table 1: Table 1 Performance indicators of silicon wafers after PSG etching using different etching methods

[0052] Conclusion: Embodiment 1 of the present invention demonstrates superior overall performance: PSG is completely removed, and the etching rate is relatively fast, such as... Figure 2 , Figure 3 As shown.

[0053] Comparative Example 1 demonstrates that using the additive of this invention can reduce the degree of silicon wafer damage caused by traditional high-concentration HF etching of PSG, while the etching rate is still lower than that of this invention. Figure 4 As shown.

[0054] Comparative Example 2 demonstrates that without the additives of this invention, using only 1% HF as the etching solution, PSG cannot be completely etched under ultrasonic assistance.

[0055] From the appendix Figure 2 , Figure 3 and Figure 4 As can be seen from the results, after using high-concentration HF and low-concentration HF + additives + ultrasonic etching PSG, the poly silicon layer was not etched, and the tower base size was approximately the same, indicating that the method of the present invention can achieve the expected results.

[0056] The experimental data fully demonstrate that the present invention achieves high-speed, high-quality, and uniform etching of PSG at a low hydrofluoric acid concentration (1%) through the deep synergy of multi-component additives and ultrasonic fields. The overall performance is superior to that of the traditional high-concentration HF process, and it proves that the technical effect of the present invention cannot be achieved by relying solely on ultrasound or solely on low-concentration HF. It has extremely high industrial application value.

[0057] The above description is merely a specific embodiment of the present invention. It should be noted that any modifications, equivalent substitutions, and variations made within the spirit and framework of the present invention should be included within the protection scope of the present invention.

Claims

1. A multi-component additive comprising the following components in weight percentages: Penetration enhancer 0.01%-0.5%, PSG activating component 2%-10%, organic protic acid 0.1%-0.5%, Interface cleaning component 0.1%-0.5%, reaction stabilizing component 0.1%-0.5%.

2. The multi-component additive as described in claim 1, characterized in that, The penetration enhancer is a compound of one of n-propanol, 1,4-dioxane, 1,2-hexanediol, isobutanol or isopropanol and N-methylpyrrolidone or 1,4-dioxane in a mass ratio of 2:1 to 1:

1.

3. The multi-component additive as described in claim 1, characterized in that, The PSG activating component is at least one of potassium fluoride, sodium fluoride, or ammonium bifluoride.

4. The multi-component additive as described in claim 1, characterized in that, The organic protic acid is at least one of acetic acid, propionic acid, formic acid, or oxalic acid.

5. The multi-component additive as described in claim 1, characterized in that, The interface cleaning component is at least one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, oleamide propyl hydroxysulfonate betaine, sodium lauroyl glutamate, or sodium cocoyl glutamate.

6. The multi-component additive as described in claim 1, characterized in that, The reaction stabilizing component is at least one of citric acid, triacetic acid, malonic acid, or ethylenediaminetetraacetic acid.

7. A low-concentration hydrofluoric acid etching solution comprising the multi-component additive as described in any one of claims 1 to 6, comprising the following components by mass percentage: Hydrofluoric acid 0.5% - 2%, the multi-component additive 1% - 5%, and the balance being deionized water.

8. A method for ultrasonic-assisted etching of PSG with low concentration hydrofluoric acid as described in claim 7, comprising the following steps: Step 1: Prepare the low-concentration hydrofluoric acid etching solution according to the specified ratio; Step 2: Place the low-concentration hydrofluoric acid etching solution in an ultrasonic device, set the frequency and power density of the ultrasonic waves, and start the ultrasonic waves; Step 3: Immerse the photovoltaic silicon wafer with the PSG layer into the low-concentration hydrofluoric acid etching solution and process it at a set temperature for a set time. Step 4: After etching is complete, remove the silicon wafer for cleaning, rinse with ultrapure water overflow, slowly lift it, and dry it.

9. The method for etching PSG as described in claim 8, characterized in that, In step 2, the frequency of the ultrasonic wave is set to 20~80 kHz, and the power density is 300~800 W / m².

10. The method for etching PSG as described in claim 8, characterized in that, In step 3, the set temperature is 25-35℃ and the set time is 0.5-2 minutes.

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