A method for rapidly removing residual crystals from the surface of a wafer after acid etching

Abstract

This invention relates to the field of semiconductor wafer manufacturing technology, specifically a method for rapidly removing residual crystals from the surface of wafers after acid etching. The method includes sequentially performing pure water pre-rinsing, alkaline cleaning with circulating heated alkaline cleaning solution, multi-stage pure water rinsing, and rework inspection after acid etching to remove residual crystals. This invention introduces alkaline cleaning treatment after acid etching, utilizing the neutralization reaction of sodium hydroxide with acidic residues, combined with the wetting, penetration, and stripping effects of auxiliary cleaning agents, to rapidly remove residual crystals, white spots, crystal patches, and chemical residues from the wafer surface, significantly improving the appearance quality under spotlight or oblique light inspection conditions. The combined process of pure water pre-rinsing, heated circulating alkaline cleaning, multi-stage pure water overflow rinsing, and selective repeated cleaning after inspection improves residue removal efficiency and cleaning uniformity, reduces sodium ion and reaction product residues, and is suitable for high-cleanliness rework of semiconductor wafers after acid etching.

Description

Technical Field

[0001] This invention relates to the field of semiconductor wafer manufacturing technology, and in particular to a method for rapidly removing residual crystals from the surface of a wafer after acid etching. Background Technology

[0002] In semiconductor wafer manufacturing, wafers typically undergo acid etching to remove surface damage layers, adjust surface morphology, or perform customized cleaning processes. However, after acid etching, the wafer surface is prone to residues of acidic solutions, acid etching reaction byproducts, and residual crystals formed by the drying or localized enrichment of the acidic system. These residual crystals may not be noticeable under normal visual conditions, but under spotlight, oblique light, or high appearance standard inspection conditions, they easily manifest as white spots, crystal patches, stains, or color differences, thus affecting the wafer's appearance quality and customer acceptance.

[0003] In existing processing methods, residual crystals on the wafer surface after acid etching are typically reworked by re-etching or extending the acid etching time. While this method can remove some surface residues to a certain extent, re-etching introduces new acid residue risks and may lead to uneven wafer surface etching, localized over-etching, increased color differences, and longer rework processes. Especially when customers have higher requirements for wafer surface appearance, relying solely on acid etching for rework makes it difficult to simultaneously achieve efficient residue removal, surface consistency, and cost control.

[0004] Therefore, there is an urgent need to provide a method that can quickly remove residual crystals on the surface of wafers after acid etching, so that the acid residual crystals can be effectively removed through subsequent cleaning processes without repeating acid etching or reducing acid etching rework, while reducing chemical residue, appearance color difference and rework costs. Summary of the Invention

[0005] To address the technical problems existing in the prior art, embodiments of the present invention provide a method for rapidly removing residual crystals from the surface of a wafer after acid etching. The technical solution is as follows: A method for rapidly removing residual crystals from the surface of a wafer after acid etching includes the following steps: S1. Place the wafer that has been acid-etched and has residual crystals on its surface in a loading tank, and pre-rinse the wafer with pure water in an overflow manner to remove free acid from the wafer surface. S2. The pre-rinsed wafer is transferred to an alkaline cleaning tank so that the wafer comes into contact with an alkaline cleaning solution, which includes sodium hydroxide, an auxiliary cleaning agent and pure water. S3. The alkaline cleaning solution is circulated in the alkaline washing tank, and the wafer is subjected to alkaline washing under heating conditions, so that the acidic residual crystals on the wafer surface are removed from the wafer surface by the neutralization, dissolution and peeling action of the alkaline cleaning solution. S4. Transfer the alkaline-washed wafers sequentially to at least two pure water rinsing tanks and rinse them using pure water overflow to remove the alkaline cleaning solution and soluble residues generated by the reaction from the wafer surface. S5. Perform appearance inspection or residue inspection on the rinsed wafer. If the inspection result does not meet the preset benchmark, repeat steps S2 to S4 once or twice until the residual crystals on the wafer surface meet the preset benchmark.

[0006] As a further aspect of the present invention, the auxiliary cleaning agent is a surface-active auxiliary agent used to reduce the surface tension of the wafer and promote the stripping of residual crystals, preferably EC-1; in the alkaline cleaning solution, the mass concentration of sodium hydroxide is 0.05% to 5%, the mass concentration of the auxiliary cleaning agent is 0.01% to 2%, and the pH value of the alkaline cleaning solution is controlled at 10.5 to 13.5.

[0007] As a further embodiment of the present invention, in step S3, the temperature of the alkaline washing treatment is 50℃~70℃, the circulation flow rate is 15L / min~21L / min, and the treatment time is 5min~20min; preferably, the temperature of the alkaline washing treatment is 60±2℃, the circulation flow rate is 18±3L / min, and the treatment time is 10min.

[0008] As a further embodiment of the present invention, in step S1, the pre-rinsing time is 5 min to 15 min; in step S4, the at least two pure water rinsing tanks include a first pure water rinsing tank and a second pure water rinsing tank, the pure water overflow flow rate of the first pure water rinsing tank and the second pure water rinsing tank is 8 L / min to 12 L / min, and the rinsing time is 5 min to 15 min; the pre-rinsing, the first pure water rinsing and the second pure water rinsing are all 10 min.

[0009] As a further aspect of the present invention, during the alkaline washing process in S3, the pH value or conductivity of the alkaline cleaning solution is monitored, and sodium hydroxide, auxiliary cleaning agent or pure water is added according to the monitoring results to maintain the alkalinity of the alkaline cleaning solution within a preset range, so as to ensure the ability to remove residual crystals while inhibiting over-corrosion of the wafer surface and color difference in appearance.

[0010] As a further aspect of the present invention, in step S3, the alkaline cleaning solution forms a dynamic shearing effect relative to the wafer surface through circulating jets, turbulence within the tank, lifting and swinging of the wafer carrier, or intermittent rotation of the wafer carrier. The dynamic shearing effect and the neutralization reaction of the alkaline cleaning solution work together to remove residual crystals, thereby improving the uniformity of residual crystal removal in the wafer edge region, wafer recess region, and wafer gap region.

[0011] As a further embodiment of the present invention, in step S4, the first pure water rinsing tank is used to remove alkaline cleaning solution and neutralization reaction products carried on the wafer surface, and the second pure water rinsing tank is used to reduce ion residues on the wafer surface. When the pH value of the effluent from the second pure water rinsing tank is 6 to 8 and / or the conductivity of the effluent is lower than the preset conductivity threshold, it is determined that the rinsing has reached the rinsing endpoint.

[0012] As a further aspect of the present invention, the appearance inspection in S5 includes at least one of spotlight inspection, oblique light inspection, or image acquisition inspection; when white spots, crystal spots, acid corrosion stains, or chemical residues are still detected on the wafer surface, steps S2 to S4 are repeated without acid corrosion treatment, thereby replacing acid corrosion rework with alkaline washing rework.

[0013] The beneficial effects of the technical solutions provided in the embodiments of the present invention include at least the following: This invention introduces an alkaline cleaning process after acid etching, utilizing the neutralization reaction of sodium hydroxide with acidic residues, combined with the wetting, penetration, and stripping effects of auxiliary cleaning agents. This rapidly removes residual crystals, white spots, crystal patches, and chemical residues from the wafer surface, significantly improving the appearance quality under spotlight or oblique light inspection conditions. Compared to traditional re-acid etching rework methods, this invention avoids problems such as secondary acid residues, localized over-etching, and increased color differences. The combined process of pure water pre-rinsing, heated circulating alkaline washing, multi-stage pure water overflow rinsing, and selective repeated cleaning after inspection improves residue removal efficiency and cleaning uniformity, reduces sodium ion and reaction product residues, and further enhances process stability and rework yield by controlling pH, conductivity, temperature, flow rate, and cleaning endpoint. This reduces rework processes, chemical consumption, and production costs, making it suitable for high-cleanliness rework of semiconductor wafers after acid etching. Attached Figure Description

[0014] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0015] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0016] Please see Figure 1This invention provides a technical solution: a method for rapidly removing residual crystals from the surface of a wafer after acid etching, comprising the following steps: S1. Place the wafer that has been acid-etched and has residual crystals on its surface into the loading tank, and pre-rinse the wafer with pure water in an overflow manner to remove free acid from the wafer surface. S2. Transfer the pre-rinsed wafer to an alkaline cleaning tank so that the wafer comes into contact with an alkaline cleaning solution, which includes sodium hydroxide, auxiliary cleaning agent and pure water. S3. In the alkaline washing tank, the alkaline cleaning solution is kept in a circulating state, and the wafer is subjected to alkaline washing under heating conditions, so that the acidic residual crystals on the wafer surface are removed from the wafer surface by the neutralization, dissolution and peeling action of the alkaline cleaning solution. S4. Transfer the alkaline-washed wafers sequentially to at least two pure water rinsing tanks and rinse them using pure water overflow to remove the alkaline cleaning solution and soluble residues generated by the reaction from the wafer surface. S5. Perform appearance inspection or residue inspection on the rinsed wafer. If the inspection result does not meet the preset benchmark, repeat steps S2 to S4 once or twice until the residual crystals on the wafer surface meet the preset benchmark.

[0017] Specifically, this invention is applicable to the rework cleaning of semiconductor wafers after acid etching. Before being transferred to subsequent appearance inspection, acid-etched wafers may develop crystalline residues due to localized acid retention, precipitation of reaction byproducts, or insufficient cleaning. In practice, the concentration of free acid on the wafer surface can be reduced first by overflowing pure water to prevent localized severe reactions when the wafer directly enters the alkaline washing environment. Then, an alkaline system is used to neutralize and dissolve the residual crystals, and circulation increases the frequency of contact between the solution and the wafer surface. After alkaline washing, multi-stage pure water rinsing gradually removes the alkaline components and soluble reactants from the wafer surface. Finally, appearance standards are used to determine whether further alkaline washing and rework are necessary. This eliminates the need for re-acid etching to remove residual crystals, reducing the risk of color differences and surface damage caused by secondary acid etching.

[0018] As a further aspect of the present invention, the auxiliary cleaning agent is a surface-active auxiliary agent used to reduce the surface tension of the wafer and promote the stripping of residual crystals, preferably EC-1; in the alkaline cleaning solution, the mass concentration of sodium hydroxide is 0.05% to 5%, the mass concentration of the auxiliary cleaning agent is 0.01% to 2%, and the pH value of the alkaline cleaning solution is controlled at 10.5 to 13.5.

[0019] Furthermore, the alkaline cleaning solution can use sodium hydroxide as the main alkaline component to neutralize acidic residues. The auxiliary cleaning agent can be a cleaning aid with wetting, dispersing, or interfacial tension-reducing properties, allowing the cleaning solution to penetrate the tiny gaps between residual crystals and the wafer surface, making the crystals easier to peel off. EC-1 can be used as the auxiliary cleaning agent, or an equivalent non-ionic or weakly alkaline compatible cleaning aid can be selected based on the wafer material, type of acid etching solution, and properties of the residues. If the sodium hydroxide concentration is too low, the removal rate of residual crystals will be insufficient; if the concentration is too high, it may increase the risk of wafer surface roughening or color difference. Therefore, in actual production, the alkalinity can be adjusted within a suitable range according to the severity of the residues, and the mass production concentration can be determined through small-batch validation.

[0020] As a further embodiment of the present invention, in S3, the temperature of the alkaline washing treatment is 50℃~70℃, the circulation flow rate is 15L / min~21L / min, and the treatment time is 5min~20min; preferably, the temperature of the alkaline washing treatment is 60±2℃, the circulation flow rate is 18±3L / min, and the treatment time is 10min.

[0021] Furthermore, the temperature, circulation flow rate, and processing time of the alkaline washing process can be set as synergistic control parameters. Appropriate heating can increase the rate of dissolution and neutralization of residual crystals, but excessively high temperatures may lead to chemical evaporation, overly strong alkaline reactions, or changes in the wafer surface condition. Circulation flow rate can enhance the chemical renewal and rinsing capabilities, but excessive flow may cause wafer shaking or secondary particle adhesion. The processing time needs to balance removal efficiency and surface uniformity. In practice, a medium-temperature alkaline washing condition of around 60℃ can be prioritized, coupled with a stable circulation flow rate, to allow continuous exchange of the chemical solution between the wafers, thereby completing the removal of acidic residual crystals in a shorter time.

[0022] As a further embodiment of the present invention, in S1, the pre-rinsing time is 5 min to 15 min; in S4, at least two pure water rinsing tanks include a first pure water rinsing tank and a second pure water rinsing tank, the pure water overflow flow rate of the first pure water rinsing tank and the second pure water rinsing tank is 8 L / min to 12 L / min, and the rinsing time is 5 min to 15 min; the pre-rinsing, the first pure water rinsing and the second pure water rinsing time are all 10 min.

[0023] Furthermore, pre-rinsing and rinsing with pure water serve different purposes. Pre-rinsing primarily reduces the amount of free acid brought into the alkaline washing tank by the wafer, stabilizing the chemical solution in the tank. The first rinsing after alkaline washing rapidly dilutes and removes alkaline chemicals adhering to the wafer surface. Subsequent rinsing further reduces ion and reaction product residues. Compared to single-tank rinsing, multi-stage rinsing reduces cross-contamination and lowers the probability of chemicals brought from the chemical tank re-drying and crystallizing on the surface. In actual production, the number of rinsing stages and overflow intensity can be adjusted according to the number of tanks, wafer load, and pure water supply capacity.

[0024] As a further aspect of the present invention, during the alkaline washing process in S3, the pH value or conductivity of the alkaline cleaning solution is monitored, and sodium hydroxide, auxiliary cleaning agent or pure water is added according to the monitoring results to maintain the alkalinity of the alkaline cleaning solution within a preset range, so as to ensure the ability to remove residual crystals while inhibiting over-corrosion of the wafer surface and color difference in appearance.

[0025] Furthermore, to improve process stability, a chemical solution status monitoring system can be implemented during the alkaline washing process. By monitoring the pH value, conductivity, or batch number of the alkaline washing solution, it can be determined whether the alkalinity of the solution has decreased due to the introduction of acidic substances, or whether the cleaning ability has diminished due to prolonged use. When the monitoring results deviate from the set range, the cleaning ability can be restored by adding sodium hydroxide, supplementing auxiliary cleaning agents, or replacing part of the solution. This control method can avoid over- or under-processing caused by relying solely on fixed-time cleaning, ensuring that wafers of different batches and with different levels of residue can achieve relatively consistent cleaning results.

[0026] As a further aspect of the present invention, in S3, the alkaline cleaning solution forms a dynamic shearing action relative to the wafer surface by means of circulating jet, turbulence in the tank, lifting and swinging of the wafer carrier, or intermittent rotation of the wafer carrier. The dynamic shearing action and the neutralization reaction of the alkaline cleaning solution work together to remove residual crystals, thereby improving the uniformity of residual crystal removal in the wafer edge region, wafer recess region, and wafer gap region.

[0027] Furthermore, to improve the cleaning effect on wafer edges, inter-wafer gaps, and localized low-flow-rate areas, liquid flow disturbances or wafer carrier movement can be introduced into the alkaline cleaning tank. Circulating jets ensure a continuous flow of fresh cleaning solution onto the wafer surface, while turbulence within the tank reduces dead zones. The lifting or intermittent rotation of the carrier alters the relative position between the wafer and the liquid flow, subjecting firmly adhered crystal residues to the combined effects of chemical reaction and fluid shearing. This method is particularly suitable for batch wafer cleaning scenarios, reducing cleaning variations between wafers in different locations within the same batch and improving overall appearance consistency.

[0028] As a further embodiment of the present invention, in S4, the first pure water rinsing tank is used to remove the alkaline cleaning solution and neutralization reaction products carried on the wafer surface, and the second pure water rinsing tank is used to reduce the residual ions on the wafer surface. When the pH value of the effluent from the second pure water rinsing tank is 6 to 8 and / or the conductivity of the effluent is lower than the preset conductivity threshold, it is determined that the rinsing has reached the rinsing endpoint.

[0029] Furthermore, the endpoint of the rinsing process can be further determined by the state of the water effluent from the pure water tank. After alkaline washing, the wafer surface may carry a small amount of alkaline liquid film and neutralization reaction products. If rinsing is insufficient, watermarks, white spots, or ion residues may still form after drying. Therefore, the pH value, conductivity, or resistivity of the effluent from the final rinsing tank can be used as a basis for judgment. When the final rinsing water is close to neutral and reaches the preset cleanliness level, it can be considered that the soluble residues on the wafer surface have been sufficiently removed. This method transforms the rinsing process from experience-based control to quantifiable control, which helps reduce subsequent defects and rework.

[0030] As a further aspect of the present invention, the appearance inspection in S5 includes at least one of spotlight inspection, oblique light inspection, or image acquisition inspection; when white spots, crystal spots, acid corrosion stains, or chemical residues are still detected on the wafer surface, steps S2 to S4 are repeated without acid corrosion treatment, thereby replacing acid corrosion rework with alkaline washing rework.

[0031] Furthermore, after wafer rinsing, the wafer surface can be inspected using spotlights, oblique lights, or automatic image acquisition equipment. Wafers still exhibiting white spots, crystal patches, acid etching stains, or chemical residue can be re-entered into the alkaline washing and rinsing process, instead of being prioritized for rework using acid etching again. The number of repetitions can be limited within a reasonable range based on the wafer surface condition to avoid repeated processing causing new surface anomalies. This closed-loop rework method can meet customers' high appearance standards while reducing the process risks associated with acid etching rework and improving the rework yield for defects such as etching stains and chemical residues.

[0032] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for rapidly removing residual crystals from the surface of a wafer after acid etching, characterized in that, Includes the following steps: S1. Place the wafer that has been acid-etched and has residual crystals on its surface in a loading tank, and pre-rinse the wafer with pure water in an overflow manner to remove free acid from the wafer surface. S2. The pre-rinsed wafer is transferred to an alkaline cleaning tank so that the wafer comes into contact with an alkaline cleaning solution, which includes sodium hydroxide, an auxiliary cleaning agent and pure water. S3. The alkaline cleaning solution is circulated in the alkaline washing tank, and the wafer is subjected to alkaline washing under heating conditions, so that the acidic residual crystals on the wafer surface are removed from the wafer surface by the neutralization, dissolution and peeling action of the alkaline cleaning solution. S4. Transfer the alkaline-washed wafers sequentially to at least two pure water rinsing tanks and rinse them using pure water overflow to remove the alkaline cleaning solution and soluble residues generated by the reaction from the wafer surface. S5. Perform appearance inspection or residue inspection on the rinsed wafer. If the inspection result does not meet the preset benchmark, repeat steps S2 to S4 once or twice until the residual crystals on the wafer surface meet the preset benchmark.

2. The method for rapidly removing residual crystals from the surface of a wafer after acid etching according to claim 1, characterized in that: The auxiliary cleaning agent is a surface-active auxiliary agent used to reduce the surface tension of the wafer and promote the stripping of residual crystals, preferably EC-1; in the alkaline cleaning solution, the mass concentration of sodium hydroxide is 0.05% to 5%, the mass concentration of the auxiliary cleaning agent is 0.01% to 2%, and the pH value of the alkaline cleaning solution is controlled at 10.5 to 13.

5.

3. The method for rapidly removing residual crystals from the surface of a wafer after acid etching according to claim 1, characterized in that, In step S3, the alkaline washing treatment temperature is 50℃~70℃, the circulation flow rate is 15L / min~21L / min, and the treatment time is 5min~20min; preferably, the alkaline washing treatment temperature is 60±2℃, the circulation flow rate is 18±3L / min, and the treatment time is 10min.

4. The method for rapidly removing residual crystals from the surface of a wafer after acid etching according to claim 1, characterized in that, In step S1, the pre-rinsing time is 5 min to 15 min; in step S4, the at least two pure water rinsing tanks include a first pure water rinsing tank and a second pure water rinsing tank, the pure water overflow flow rate of the first pure water rinsing tank and the second pure water rinsing tank is 8 L / min to 12 L / min, and the rinsing time is 5 min to 15 min; the pre-rinsing, the first pure water rinsing and the second pure water rinsing time are all 10 min.

5. The method for rapidly removing residual crystals from the surface of a wafer after acid etching according to claim 1, characterized in that, During the alkaline washing process in S3, the pH value or conductivity of the alkaline cleaning solution is monitored, and sodium hydroxide, auxiliary cleaning agent or pure water is added according to the monitoring results to maintain the alkalinity of the alkaline cleaning solution within a preset range, so as to ensure the ability to remove residual crystals while inhibiting over-corrosion of the wafer surface and color difference in appearance.

6. The method for rapidly removing residual crystals from the surface of a wafer after acid etching according to claim 1, characterized in that, In step S3, the alkaline cleaning solution forms a dynamic shearing effect on the wafer surface through circulating jets, turbulence within the tank, lifting and swinging of the wafer carrier, or intermittent rotation of the wafer carrier. The dynamic shearing effect and the neutralization reaction of the alkaline cleaning solution work together to remove residual crystals, thereby improving the uniformity of residual crystal removal in the wafer edge region, wafer recess region, and wafer gap region.

7. The method for rapidly removing residual crystals from the surface of a wafer after acid etching according to claim 1, characterized in that, In step S4, the first pure water rinsing tank is used to remove alkaline cleaning solution and neutralization reaction products carried on the wafer surface, and the second pure water rinsing tank is used to reduce ion residue on the wafer surface. When the pH value of the effluent from the second pure water rinsing tank is 6 to 8 and / or the conductivity of the effluent is lower than the preset conductivity threshold, it is determined that the rinsing has reached the rinsing endpoint.

8. The method for rapidly removing residual crystals from the surface of a wafer after acid etching according to claim 1, characterized in that, The appearance inspection in S5 includes at least one of spotlight inspection, oblique light inspection, or image acquisition inspection; when white spots, crystal spots, acid corrosion stains, or chemical residues are still detected on the wafer surface, steps S2 to S4 are repeated without acid corrosion treatment, so that alkaline washing rework replaces acid corrosion rework.

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