Wafer cleaning method

Abstract

The application provides a wafer cleaning method, and relates to the technical field of semiconductor manufacturing, and is designed to solve the problem of low single wafer cleaning efficiency in the prior art by adding a back surface cleaning step in a single wafer cleaning process to reduce wafer back surface particles. The wafer cleaning method comprises the following steps: loading a wafer back surface to a Bernoulli chuck; in a first cleaning stage, the wafer rotates at a first preset speed, deionized water is sprayed to the front surface of the wafer, and nitrogen gas is sprayed to multiple positions on the wafer back surface and along the circumference of the wafer at a first preset gas flow rate; in a second cleaning stage, the rotation speed of the wafer is increased to a second preset speed, cleaning liquid is sprayed to the front surface of the wafer, and the nitrogen gas spraying flow rate to the wafer back surface is increased to a second preset gas flow rate; and in a drying stage, the spraying of the cleaning liquid to the front surface of the wafer is stopped, and the nitrogen gas sprayed to the wafer back surface is heated to a drying temperature. The wafer cleaning method has high cleaning efficiency.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and more specifically, to a wafer cleaning method. Background Technology

[0002] In the semiconductor integrated circuit manufacturing process, in order to prevent impurities such as particles, organic matter, and metal contaminants from damaging the circuits manufactured inside the wafer, it is usually necessary to clean the wafer after each process step.

[0003] Wafer cleaning methods include tank cleaning and single-wafer cleaning. In single-wafer cleaning, a fixture holds and fixes the wafer, rotating it while simultaneously removing contaminants from the front side through chemical spraying and rotational rinsing. While this method achieves cleaning of the wafer's front side, secondary particles often form in the clamping contact area due to fixture material wear, structural damage caused by clamping stress, and residual process media. Under the centrifugal force of rotation, these secondary particles diffuse across the entire back side of the wafer and may transfer to the front side in subsequent processes, causing defects such as short circuits in devices.

[0004] To address the aforementioned issues, related technologies employ a back-side cleaning step in the wafer cleaning process. However, this increases the time required for wafer cleaning, resulting in lower wafer cleaning efficiency. Summary of the Invention

[0005] The purpose of this invention is to provide a wafer cleaning method to solve the technical problem of low single-wafer cleaning efficiency caused by the related technology of adding a back-side cleaning step in the single-wafer cleaning process to reduce back-side particles.

[0006] The wafer cleaning method provided by this invention includes:

[0007] The back side of the wafer is mounted to a Bernoulli chuck.

[0008] In the first cleaning stage, the wafer rotates at a first preset speed, deionized water is sprayed onto the front side of the wafer, and nitrogen gas is sprayed onto the back side of the wafer and multiple positions along the circumference of the wafer at a first preset gas flow rate.

[0009] In the second cleaning stage, the wafer rotation speed is increased to a second preset speed, cleaning fluid is sprayed onto the front side of the wafer, and the nitrogen injection flow rate on the back side of the wafer is increased to a second preset gas flow rate; and

[0010] During the drying stage, the spraying of cleaning fluid onto the front side of the wafer is stopped, and nitrogen gas sprayed onto the back side of the wafer is heated to the drying temperature.

[0011] Furthermore, multiple nitrogen injection ports on the back side of the wafer form a circular injection area, the center of which coincides with the center of the wafer. The radius of the circular injection area is R1, and the radius of the wafer is R2, where R1 = (4 / 5)R2 ± 10 mm.

[0012] Furthermore, among the multiple nitrogen injection ports on the back side of the wafer, the distance between any two adjacent nitrogen injection ports is a, 5mm≤a≤10mm; and / or, the distance between the nitrogen injection port on the back side of the wafer and the back side of the wafer is b, 2mm≤b≤3mm.

[0013] Furthermore, in the first cleaning stage, the thickness of the center liquid film and the thickness of the edge liquid film on the front side of the wafer are detected and compared; when the result is greater than the set value, the deionized water flow rate is adjusted.

[0014] Furthermore, if the thickness of the central liquid film is greater than the thickness of the edge liquid film, the flow rate of deionized water is increased in stages; if the thickness of the central liquid film is less than the thickness of the edge liquid film, the flow rate of deionized water is decreased in stages.

[0015] Furthermore, in the first cleaning stage, the spray flow rate of the deionized water is 200-300 mL / min;

[0016] If the thickness of the central liquid film is greater than the thickness of the edge liquid film, then in the phased increase of the deionized water flow rate, the increase of the deionized water in each phase is 8 to 12 mL / min.

[0017] If the thickness of the central liquid film is less than the thickness of the edge liquid film, then in the phased reduction of the deionized water flow rate, the reduction of the deionized water in each phase is 8-12 mL / min.

[0018] Further, the thickness of the center liquid film and the thickness of the edge liquid film on the front side of the wafer are detected and compared; when the result is greater than a set value, the deionized water flow rate is adjusted. Specifically, the absolute value of the difference between the center liquid film thickness and the edge liquid film thickness is compared with the smaller of the two values, and the ratio is compared with a set value. When the ratio is greater than the set value, the deionized water flow rate is adjusted, wherein the set value is 10% to 20%.

[0019] Furthermore, in the second cleaning stage, the step of spraying cleaning fluid onto the front side of the wafer includes gradually increasing the flow rate of the cleaning fluid sprayed onto the front side of the wafer.

[0020] Furthermore, in the second cleaning stage, the rate of decrease in the concentration of the cleaning solution after the wafer front cleaning is completed is detected and compared with a preset rate of decrease; when the rate of decrease in the concentration of the cleaning solution is less than the preset rate of decrease, a high-flow cleaning solution spray for a first set duration is triggered.

[0021] Furthermore, the first preset speed is 150-250 rpm; the second preset speed is 500-800 rpm.

[0022] Furthermore, the first preset gas flow rate is 100-150 L / min, and the second preset gas flow rate is 150-200 L / min.

[0023] Furthermore, the drying stage includes: a transition and separation stage, in which the wafer rotation speed is increased to a third preset speed, the flow rate of the cleaning liquid sprayed onto the front side of the wafer is gradually reduced, and the nitrogen gas sprayed onto the back side of the wafer is heated to a transition temperature, so that the flow rate of the nitrogen gas sprayed onto the back side of the wafer is maintained at a second preset gas flow rate; the transition temperature is lower than the drying temperature.

[0024] Furthermore, during the transition and detachment stage, the thickness of the cleaning liquid film on the front side of the wafer is detected and compared with a preset liquid film thickness; when the cleaning liquid film thickness is greater than the preset liquid film thickness, the rotation speed of the wafer is increased, and when the cleaning liquid film thickness is less than the preset liquid film thickness, the rotation speed of the wafer is decreased.

[0025] Furthermore, the transition temperature is 40–45°C, and the drying temperature is 53–57°C.

[0026] Furthermore, the third preset speed is 1400-1600 rpm.

[0027] Furthermore, the drying stage also includes: a final drying stage, in which nitrogen gas sprayed onto the back side of the wafer is increased from the transition temperature to the drying temperature; and a purge gas is introduced onto the front side of the wafer.

[0028] Furthermore, in the final drying stage, the center temperature and edge temperature of the back side of the wafer are detected and compared; when the difference between the center temperature and the edge temperature is less than or equal to a set temperature value, the wafer is kept rotating at the second preset speed for a second preset time, nitrogen gas at the drying temperature is kept flowing through the back side of the wafer for a second preset time, and purge gas is kept flowing through the front side of the wafer for a second preset time.

[0029] The beneficial effects of the wafer cleaning method of this invention are:

[0030] In this wafer cleaning method, a Bernoulli chuck is used to load the wafer, achieving non-contact clamping and fixing of the wafer. This effectively blocks particulate contamination between the fixture and the wafer, reducing secondary particles generated on the wafer. By dividing the wafer cleaning into two stages, in the first cleaning stage, the wafer is rotated at a low, preset speed. This allows deionized water sprayed onto the front side of the wafer to slowly cover the front side, achieving pre-wetting of the front side, reducing surface tension, and increasing the hydrophilicity of the front side. Simultaneously, nitrogen gas is introduced at multiple locations on the back side of the wafer along the circumference, forming a gas barrier covering the back side of the wafer.

[0031] In the second cleaning stage, increasing the wafer rotation speed to a second preset speed increases the centrifugal force of the cleaning fluid. This ensures thorough cleaning of the front side of the wafer while confining the cleaning fluid to the edges, reducing radial splashing. Simultaneously, increasing the nitrogen injection flow rate increases the rigidity of the nitrogen curtain formed on the back side of the wafer, preventing the migration of cleaning fluid from the front to the back side after the increased centrifugal force. This synergistic effect of centrifugal force and nitrogen flow rate reduces process media residue on the back side of the wafer. After the first and second cleaning stages, increasing the nitrogen temperature accelerates the evaporation of the liquid film on the front side of the wafer through thermal convection, inhibiting crystallization and ensuring effective wafer cleaning.

[0032] Therefore, this wafer cleaning method utilizes a Bernoulli chuck to achieve non-contact wafer fixation, filling the space between the chuck and the wafer with flowing gas, thus preventing particulate contamination between the chuck and the wafer. By spraying nitrogen gas at multiple circumferential positions on the back of the wafer and simultaneously increasing the nitrogen flow rate as the wafer rotation speed increases, a rigid gas curtain can be formed on the back of the wafer, blocking the cleaning fluid at the edges. Furthermore, the nitrogen gas sprayed circumferentially on the back of the wafer can be superimposed with the airflow from the Bernoulli chuck, enhancing the gas protection effect on the back of the wafer and improving the stability of the Bernoulli chuck's wafer clamping. Simultaneously, because the nitrogen gas flows outwards under the obstruction of the back of the wafer after being sprayed, free particles on the back of the wafer can be discharged under the guidance of the nitrogen gas, reducing their adhesion to the wafer and thus enhancing the cleaning effect. The above cleaning process has good process compatibility and does not require an additional wafer backside cleaning step, effectively improving the problem of low single-wafer cleaning efficiency caused by the additional wafer backside cleaning step in related technologies. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0034] Figure 1 This is a schematic flowchart of a wafer cleaning method provided in an embodiment of the present invention;

[0035] Figure 2 This is a schematic diagram illustrating the principle of the wafer cleaning method provided in an embodiment of the present invention;

[0036] Figure 3 This is a schematic diagram showing the distribution of nitrogen injection ports in the wafer cleaning method provided in an embodiment of the present invention;

[0037] Figure 4 This is a schematic flowchart of another wafer cleaning method provided in an embodiment of the present invention.

[0038] Explanation of reference numerals in the attached figures:

[0039] 100 - Wafer; 110 - Wafer front; 120 - Wafer back;

[0040] 200 - Nitrogen injection nozzle; 300 - Circular injection area; 400 - Injection pipeline; 500 - Bernoulli suction cup. Detailed Implementation

[0041] In the single-wafer cleaning process, in order to reduce secondary particles on the back side of the wafer, related technologies often add a back-side cleaning step after the front side of the wafer is cleaned to rinse the particles present on the back side. However, this not only increases the time required for single-wafer cleaning, resulting in low single-wafer cleaning efficiency, but also requires additional back-side cleaning equipment, which occupies a large space.

[0042] Related technology two uses edge holders with polymer coatings or low-friction materials to reduce secondary particles generated on the back of the wafer by reducing mechanical contact with the back of the wafer. However, the clamping contact cannot completely avoid particle generation, and the edge holders need to be maintained and replaced frequently, which is costly.

[0043] Related technology three uses reduced rotation speed or spray flow rate to reduce the probability of fluid splashing to the back side, thereby reducing process media residue on the back side of the wafer. However, this weakens the rinsing effect on the front side of the wafer, which needs to be compensated by extending the cleaning time on the front side of the wafer, thus reducing production capacity.

[0044] Therefore, the purpose of this invention is to provide a wafer cleaning method to at least solve the technical problem of low single-wafer cleaning efficiency caused by the related technology of adding a back-side cleaning step in a single-wafer cleaning process to reduce back-side particles.

[0045] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0046] like Figure 1 As shown, this embodiment provides a wafer cleaning method, including:

[0047] Step S100: As Figure 2 As shown, the back side of the wafer 120 is mounted onto the Bernoulli chuck 500.

[0048] In this wafer cleaning method, the Bernoulli chuck 500 is used to load the wafer 100, which realizes non-contact clamping and fixing of the wafer 100, effectively blocking particulate contamination between the fixture and the wafer 100, and reducing secondary particles generated on the wafer 100.

[0049] Specifically, the Bernoulli chuck 500 can be positioned directly below the wafer 100, that is, the center of the Bernoulli chuck 500 is directly opposite the center of the wafer 100 along the thickness direction of the wafer 100.

[0050] Step S200: In the first cleaning stage, the wafer 100 rotates at a first preset speed, sprays deionized water onto the front side 110 of the wafer, and sprays nitrogen gas onto the back side 120 of the wafer and multiple positions along the circumference of the wafer 100 at a first preset gas flow rate.

[0051] Specifically, the first preset speed can be 150-250 rpm, preferably 200 rpm. In this step, the wafer 100 rotates at a lower first preset speed, which allows the deionized water sprayed onto the front side 110 of the wafer to slowly cover the front side 110 of the wafer, thereby pre-wetting the front side 110 of the wafer, reducing the tension of the front side 110 of the wafer, and increasing the hydrophilicity of the front side 110 of the wafer.

[0052] Please continue to refer to Figure 2 and combined Figure 3The back side 120 of the wafer is provided with multiple nitrogen injection ports 200, which are arranged at intervals along the circumference of the wafer 100. These ports allow for simultaneous injection of nitrogen gas at multiple locations along the circumference of the back side 120, forming a gas barrier covering the wafer back side 120. The nitrogen gas injected from the circumferentially arranged ports 200 can be superimposed on the nitrogen gas flowing from the Bernoulli chuck 500 at the center, enhancing the gas protection effect on the back side 120 and improving the stability of the Bernoulli chuck 500 in holding the wafer 100.

[0053] It should be noted that, Figure 2 This is only used to illustrate the principle of the airflow path in the wafer cleaning method. Based on this, a sufficient gap is reserved between the back side of the wafer 120 and the Bernoulli chuck 500 to indicate the airflow path with corresponding arrows. In reality, the distance between the back side of the wafer 120 and the Bernoulli chuck 500 is relatively small.

[0054] It should also be noted that in this embodiment, each nitrogen injection port 200 can be integrated on the Bernoulli chuck 500. At the same time, multiple flow channels can be provided on the Bernoulli chuck 500, which are respectively connected to each nitrogen injection port 200 for supplying nitrogen, thereby realizing nitrogen injection at multiple positions along the circumferential direction on the back side 120 of the wafer.

[0055] Specifically, the first preset gas flow rate is 100-150 L / min. In this step, nitrogen is introduced at a lower flow rate, which can reduce nitrogen consumption and lower the cleaning cost of wafer 100.

[0056] Step S300: Second cleaning stage, the rotation speed of wafer 100 is increased to the second preset speed, cleaning fluid is sprayed onto the front side 110 of the wafer, and the nitrogen injection flow rate of the back side 120 of the wafer is increased to the second preset gas flow rate.

[0057] Specifically, the second preset speed can be 500-800 rpm, preferably 600 rpm. In this step, increasing the rotation speed of the wafer 100 can increase the centrifugal force of the cleaning solution. While ensuring the thorough cleaning of the front side 110 of the wafer, it can also confine the cleaning solution to the edge of the front side 110 of the wafer, thereby reducing the radial splashing of the cleaning solution on the front side 110 of the wafer.

[0058] In the first and second cleaning stages described above, after the nitrogen gas is sprayed onto the back side 120 of the wafer, it will flow to all sides under the obstruction of the back side 120. Therefore, during this process, the free particles on the back side 120 of the wafer can be discharged under the guidance of the nitrogen gas, so as to reduce the adhesion of these particles on the wafer 100 and thus enhance the cleaning effect on the wafer 100.

[0059] Specifically, the second preset gas flow rate is 150-200 L / min. In the second cleaning stage, the flow rate of nitrogen gas introduced is greater than that in the first cleaning stage. This setting can increase the rigidity of the nitrogen gas curtain formed on the back side 120 of the wafer, so as to block the migration of cleaning liquid from the front side 110 of the wafer to the back side 120 of the wafer after the centrifugal force of the cleaning liquid increases. By utilizing the synergistic change of the centrifugal force of the cleaning liquid and the flow rate of nitrogen gas, the residual process media on the back side 120 of the wafer is reduced.

[0060] Step S400: Drying stage, stop spraying cleaning fluid onto the front side 110 of the wafer, and heat the nitrogen gas sprayed onto the back side 120 of the wafer to the drying temperature.

[0061] After the first and second cleaning stages are completed, by increasing the temperature of nitrogen gas, thermal convection can be used to accelerate the evaporation of the liquid film on the front side of the wafer 110 and inhibit crystallization, so as to ensure the cleaning effect of the wafer 100.

[0062] Therefore, this wafer cleaning method not only achieves non-contact fixation of the wafer 100 using the Bernoulli chuck 500 during the loading stage, allowing the space between the Bernoulli chuck 500 and the wafer 100 to be filled with flowing gas, thus preventing particulate contamination between the fixture and the wafer 100, but also has good process compatibility during the cleaning stage, eliminating the need for an additional wafer backside 120 cleaning step. This effectively improves the problem of low single-wafer cleaning efficiency caused by the additional wafer backside 120 cleaning step in related technologies.

[0063] In this embodiment, the spray pipe 400 can be used to spray deionized water and cleaning solution onto the front side 110 of the wafer.

[0064] Please continue to refer to Figure 3 In this embodiment, multiple nitrogen injection ports 200 on the back side 120 of the wafer form a circular injection area 300, wherein the center of the circular injection area 300 coincides with the center of the wafer 100, the radius of the central injection area is R1, and the radius of the wafer 100 is R2, where R1 = (4 / 5)R2 ± 10 mm. That is, the injection point of each nitrogen injection port 200 on the back side 120 of the wafer is approximately located at a position on the wafer 100 from its center to 5 / 6 of its radius, and the multiple nitrogen injection ports 200 form a circular jet array.

[0065] By positioning the nitrogen injection port 200 at the aforementioned location, on the one hand, it avoids the situation where the distance between the port and the edge of the wafer 100 is too far, which would prevent the formation of an effective gas curtain near the edge of the wafer 100 on the back side 120, thus weakening the blocking effect on the cleaning fluid on the front side 110 of the wafer. On the other hand, it also avoids the situation where the distance between the port and the edge of the wafer 100 is too close, which would limit the guiding effect of the back side 120 after the nitrogen gas impacts upwards, thus preventing the particles from being effectively discharged.

[0066] Furthermore, the above configuration allows nitrogen gas ejected from multiple nitrogen injection ports 200 to form a complete gas curtain on the back side 120 of the wafer, thereby effectively blocking the cleaning fluid on the front side 110 of the wafer and preventing the cleaning fluid on the front side 110 of the wafer from flowing down from the edge of the wafer 100 to the back side 120 of the wafer.

[0067] Preferably, please continue to refer to Figure 3 Multiple nitrogen injection nozzles 200 are arranged at equal intervals along the circumference of the wafer 100. This arrangement ensures that a complete gas curtain is formed on the back side 120 of the wafer while maintaining uniform stress on the back side 120.

[0068] In this embodiment, wafer 100 is 12 inches with a radius of 150 mm, and the nitrogen injection port 200 is 30 mm away from the edge of wafer 100.

[0069] Please continue to refer to Figure 3 In this embodiment, among the multiple nitrogen injection ports 200 on the back side 120 of the wafer, the distance between any two adjacent nitrogen injection ports 200 is a, where 5mm≤a≤10mm.

[0070] This configuration avoids two adjacent nitrogen injection ports 200 being too close together, resulting in an excessively high density of nitrogen injection ports 200 and thus increased cleaning costs. On the other hand, it also avoids two adjacent nitrogen injection ports 200 being too far apart, resulting in poor circumferential stiffness of the nitrogen gas curtain formed on the back side 120 of the wafer, which would cause the cleaning fluid on the front side 110 of the wafer to flow from the part of the nitrogen gas curtain with lower circumferential stiffness to the back side 120 of the wafer.

[0071] Please continue to refer to Figure 2 In this embodiment, the distance between the nitrogen injection port 200 on the back side 120 of the wafer and the back side 120 of the wafer is b, where 2mm≤b≤3mm.

[0072] This configuration avoids the situation where the nitrogen gas flow cannot form a complete nitrogen gas curtain on the back side of the wafer 120 due to the nitrogen gas nozzle 200 being too close to the wafer back side 120. On the other hand, it also avoids the situation where the nitrogen gas curtain formed has limited rigidity due to the nitrogen gas nozzle 200 being too far from the wafer back side 120.

[0073] In this embodiment, during the first cleaning stage, the thickness of the center liquid film and the thickness of the edge liquid film on the front side 110 of the wafer are detected and compared; when the result is greater than the set value, the deionized water flow rate is adjusted.

[0074] During the rotation of wafer 100, the centrifugal force and gravity cause differences in the liquid film thickness between the central and edge regions of the wafer's front side 110. Significant differences in this thickness can lead to substantial variations in the cleaning effectiveness between the central and edge regions. By monitoring the liquid film thickness at both the center and edges, the liquid film thickness in each region can be determined in real time. This allows for adjustments to the deionized water flow rate when a significant difference in liquid film thickness exists between the two regions, ensuring that both areas achieve approximately the same cleaning effect.

[0075] In this embodiment, the detection of the center liquid film thickness and edge liquid film thickness of the wafer front 110 can be achieved by an infrared sensor.

[0076] Specifically, when the thickness of the central liquid film is greater than that of the edge liquid film, the flow rate of deionized water is increased in stages; when the thickness of the central liquid film is less than that of the edge liquid film, the flow rate of deionized water is decreased in stages.

[0077] When the central liquid film thickness is relatively thick, the edge liquid film thickness is relatively thin. This allows for an increase in the flow rate of deionized water. With the swing-arm spraying method of the spray pipe 400, more deionized water can be sprayed onto the edge area of ​​the wafer front side 110, thereby compensating for the liquid film thickness in the edge area and reducing the difference in liquid film thickness between the edge area and the central area.

[0078] Similarly, when the central liquid film thickness is thinner, the edge liquid film thickness is thicker, which can reduce the flow rate of deionized water. Under the swing-arm spraying method of the spray pipe 400, the amount of deionized water sprayed to the edge area of ​​the wafer front 110 is reduced, thereby reducing the difference in deionized water flow rate between the edge area and the central area, thus ensuring the consistency of the liquid film thickness on the wafer front 110.

[0079] In this embodiment, during the first cleaning stage, the spray flow rate of deionized water is 200-300 mL / min.

[0080] By limiting the spray flow rate of deionized water within the above range, on the one hand, it can prevent the cleaning effect on the front side 110 of the wafer from being limited due to insufficient deionized water flow rate, and on the other hand, it can also avoid waste caused by excessive deionized water flow rate.

[0081] In this embodiment, when the thickness of the central liquid film is greater than that of the edge liquid film, the increase in deionized water flow rate in each stage can be 8 to 12 mL / min; when the thickness of the central liquid film is less than that of the edge liquid film, the decrease in deionized water flow rate in each stage can be 8 to 12 mL / min.

[0082] This setting enables fine-tuning of the deionized water flow rate. On the one hand, it avoids the need for repeated increases and decreases due to small changes in flow rate each time, resulting in low adjustment efficiency. On the other hand, it also avoids over-adjustment due to excessive increases and decreases in flow rate each time, which would cause an opposite difference between the thickness of the central liquid film and the thickness of the edge liquid film.

[0083] Preferably, when the deionized water flow rate is increased in stages by making the central liquid film thickness greater than the edge liquid film thickness, the increase in deionized water in each stage is 10 mL / min; when the deionized water flow rate is decreased in stages by making the central liquid film thickness less than the edge liquid film thickness, the decrease in deionized water in each stage is 10 mL / min.

[0084] In this embodiment, the thickness of the center liquid film and the thickness of the edge liquid film on the front side 110 of the wafer are detected and compared. When the result is greater than a set value, the deionized water flow rate is adjusted. Specifically, the absolute value of the difference between the center liquid film thickness and the edge liquid film thickness is compared with the smaller of the two values. The ratio is then compared with a set value. When the ratio is greater than the set value, the deionized water flow rate is adjusted. The set value is 10% to 20%.

[0085] With the above settings, on the one hand, it can avoid triggering deionized water flow rate adjustment when the difference between the thickness of the central liquid film and the thickness of the edge liquid film is too small due to detection errors or instantaneous fluctuations in the liquid film thickness. On the other hand, it can also avoid the inability to adjust in time when the difference between the thickness of the central liquid film and the thickness of the edge liquid film is too large, thus ensuring the timeliness of triggering deionized water flow rate adjustment.

[0086] Preferably, deionized water flow rate regulation is triggered when the thickness difference between the central liquid film thickness and the edge liquid film thickness is greater than 15%. That is, deionized water flow rate regulation is triggered when the central liquid film thickness is 15% thicker than the edge liquid film thickness or the edge liquid film thickness is 15% thicker than the central liquid film thickness.

[0087] In this embodiment, the step of spraying cleaning fluid onto the front side 110 of the wafer in the second cleaning stage includes gradually increasing the flow rate of the cleaning fluid sprayed onto the front side 110 of the wafer.

[0088] By gradually increasing the flow rate of the cleaning fluid sprayed onto the front side 110 of the wafer, the flow rate is gradually increased to the target flow rate. On the one hand, this avoids a large impact on the front side 110 of the wafer due to a sudden increase in the flow rate of the cleaning fluid to the target flow rate, thus providing a certain degree of protection for the wafer 100. On the other hand, it also makes the flow rate of the cleaning fluid increase synchronously with the increase in the rotation speed of the wafer 100, so that the cleaning fluid can still achieve full coverage of the front side 110 of the wafer after the rotation speed of the wafer 100 increases. By utilizing this synergistic effect of flow rate and rotation speed, the cleaning effect on the front side 110 of the wafer is improved.

[0089] In this embodiment, the cleaning fluid flow rate can be increased to 1200 mL / min in three stages. Specifically, in the initial stage, the cleaning fluid flow rate can be 400 mL / min, and then it is increased by 400 mL / min every 10 seconds. That is, the change process of the cleaning fluid flow rate is: 400 mL / min → 800 mL / min → 1200 mL / min.

[0090] In this embodiment, during the second cleaning stage, the rate of decrease in the concentration of the cleaning solution after cleaning the front side 110 of the wafer is detected and compared with a preset rate of decrease; when the rate of decrease in the concentration of the cleaning solution is less than the preset rate of decrease, a high-flow cleaning solution spray for a first set duration is triggered.

[0091] In the second cleaning stage, the front side 110 of the wafer is cleaned with a cleaning solution to remove contaminants adhering to it. At this stage, the contaminants are mixed in the cleaning solution. By detecting the rate of decrease in contaminant concentration in this portion of the cleaning solution, the cleaning effect on the front side 110 of the wafer can be determined in a timely manner. Specifically, when the rate of decrease in contaminant concentration is less than the preset rate, it indicates that the difference between the two measured rates is not significant. In this case, a considerable amount of contaminants still adhere to the front side 110 of the wafer. Therefore, the cleaning solution spray flow rate can be increased to ensure sufficient removal of contaminants and guarantee the cleaning effect on the front side 110 of the wafer.

[0092] Specifically, in this embodiment, a conductivity sensor can be used to detect the concentration of contaminants in the recovered cleaning fluid. The rate of decrease in the contaminant concentration can be determined using the detection results at two discrete time points. When the conductivity sensor detects a high conductivity in the recovered cleaning fluid, it indicates severe contamination. In this case, there are many contaminants in the cleaning fluid, and the cleaning fluid flow rate needs to be increased to ensure the cleaning effect.

[0093] In this embodiment, the preset descent rate can be 4% to 6%, preferably 5%; the first set duration can be 3 to 7 seconds, preferably 5 seconds; in the triggered high-flow cleaning fluid spray, the flow rate of the cleaning fluid is greater than 1200 mL / min, preferably 1500 mL / min.

[0094] like Figure 4 As shown, this embodiment also provides another wafer cleaning method, specifically, the drying stage includes:

[0095] Step S401: Transition and removal stage, the rotation speed of wafer 100 is increased to the third preset speed, the flow rate of cleaning liquid sprayed to the front side 110 of wafer is gradually reduced, and the nitrogen gas sprayed to the back side 120 of wafer is heated to the transition temperature, so that the flow rate of nitrogen gas sprayed to the back side 120 of wafer is maintained at the second preset gas flow rate, wherein the transition temperature is lower than the drying temperature.

[0096] During the transition and separation phase, increasing the rotational speed of wafer 100 increases its centrifugal force. Simultaneously, by gradually reducing the flow rate of the cleaning fluid sprayed onto the front side 110 of the wafer, rather than reducing it all at once, the wettability of the liquid film on the front side 110 is maintained to prevent film rupture and the formation of dry spots that could affect the cleaning effect. In this process, by first heating the nitrogen gas sprayed onto the back side 120 of the wafer to a transition temperature below the drying temperature, a gradually increasing temperature gradient is formed on wafer 100 during the drying process. This ensures stable heating of wafer 100, allowing it to gradually transition from room temperature to the final drying temperature, preventing damage to wafer 100 due to excessive temperature changes.

[0097] In addition, by maintaining the nitrogen flow rate sprayed onto the back side of the wafer 120 at the second preset gas flow rate, the back side of the wafer 120 can still form a nitrogen gas curtain with stable rigidity during the transition and removal stage, preventing the cleaning fluid on the front side of the wafer 110 from flowing to the back side of the wafer 120 during the transition and removal stage.

[0098] Specifically, the third preset speed is 1400-1600 rpm.

[0099] By limiting the third preset speed within the above range, on the one hand, it can avoid insufficient centrifugal force during the throwing process due to insufficient rotation speed of wafer 100, which would prevent the cleaning fluid from fully covering the front side 110 of the wafer after the flow rate is reduced. On the other hand, it can also avoid excessive centrifugal force due to excessive rotation speed of wafer 100, which would cause local rupture of the liquid film.

[0100] Preferably, the third preset speed is 1500 rpm.

[0101] Specifically, the transition temperature is 40–45°C, and the drying temperature is 53–57°C.

[0102] By limiting the transition temperature within the aforementioned range, it is possible to prevent poor heating of wafer 100 during the transition and peeling stage due to a low transition temperature, while also preventing large temperature variations on the back side 120 of the wafer due to a high transition temperature, which could damage wafer 100. This setting can reduce the viscosity of the cleaning solution film and promote its uniform peeling.

[0103] By limiting the drying temperature within the above range, it is possible to prevent the drying efficiency from decreasing due to poor heating effect on wafer 100 in the final drying stage caused by a low drying temperature, and at the same time, it is also possible to prevent the wafer 100 from being overheated due to a high drying temperature.

[0104] In this embodiment, during the transition and shedding stage, the thickness of the cleaning liquid film on the front side 110 of the wafer is detected and compared with a preset liquid film thickness; when the cleaning liquid film thickness is greater than the preset liquid film thickness, the rotation speed of the wafer 100 is increased, and when the cleaning liquid film thickness is less than the preset liquid film thickness, the rotation speed of the wafer 100 is decreased.

[0105] This setting can adjust the cleaning liquid film thickness on the front side 110 of the wafer in a timely manner when it deviates from the preset liquid film thickness, thus avoiding excessively thick cleaning liquid film that prolongs the cleaning time, and avoiding excessively thin cleaning liquid film that causes some areas to be uncovered by the cleaning liquid, thereby affecting the cleaning effect.

[0106] Specifically, when the cleaning liquid film is thick, the rotation speed of wafer 100 can be increased to accelerate the radial flow of the cleaning liquid by increasing centrifugal force, so that the cleaning liquid film gradually becomes thinner; when the cleaning liquid film is thin, the rotation speed of wafer 100 can be reduced to weaken the radial flow of the cleaning liquid by reducing centrifugal force, so that the cleaning liquid film gradually becomes thicker.

[0107] The thickness of the cleaning fluid film can be detected by laser detection or by infrared sensor detection.

[0108] Please continue to refer to Figure 4 In this embodiment, the drying stage further includes:

[0109] Step S402: Final drying stage, nitrogen gas sprayed onto the back side 120 of the wafer is heated from the transition temperature to the drying temperature; purge gas is introduced into the front side 110 of the wafer.

[0110] During the final drying stage, the temperature of the nitrogen gas sprayed onto the back side 120 of the wafer is further increased, which can improve the evaporation efficiency of the cleaning solution and the particle stripping rate, thereby improving the cleaning efficiency of wafer 100. Furthermore, by introducing purge gas into the front side 110 of the wafer, suspended particles after stripping can be removed, reducing the risk of particle deposition and removing trace residues on the wafer surface. Simultaneously, this further enhances the evaporation efficiency of the cleaning solution, preventing watermarks or process impurities from remaining.

[0111] Specifically, the purging gas can be nitrogen at room temperature, and its flow rate can be 10 L / min.

[0112] In this embodiment, during the final drying stage, the center temperature and edge temperature of the back side 120 of the wafer are detected and compared; when the difference between the center temperature and the edge temperature is less than or equal to a set temperature value, the wafer 100 is kept rotating at a second preset speed for a second preset time, nitrogen gas at the drying temperature is introduced into the back side 120 of the wafer for a second preset time, and purge gas is introduced into the front side 110 of the wafer for a second preset time.

[0113] During the final drying stage, when the temperature difference between the center and edge of the back side 120 of the wafer is less than or equal to the set temperature value, it indicates that the temperature uniformity of the back side 120 of the wafer is good. At this time, under the premise of this temperature uniformity, the wafer 100 continues to rotate at the second preset speed, nitrogen gas is introduced into the back side 120 of the wafer at the drying temperature, and purge gas is introduced into the front side 110 of the wafer. After the second preset time, the cleaning of the wafer 100 is completed, and the rotation speed of the wafer 100 can be reduced to prepare for unloading.

[0114] Specifically, the set temperature value can be 3℃; the second set duration can be 20 to 30 seconds, preferably 25 seconds.

[0115] Specifically, the temperature uniformity of the back side 120 of the wafer can be detected using an infrared thermal imager.

[0116] Specifically, after a second set time period, the rotational speed of wafer 100 can be reduced to 500 rpm in preparation for unloading.

[0117] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

[0118] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the term "comprising" or any other variations thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0119] In the above embodiments, descriptions of directions such as "up", "down", and "side" are based on the accompanying drawings.

[0120] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A wafer cleaning method, characterized in that, include: The back side of the wafer (120) is mounted to the Bernoulli chuck (500); In the first cleaning stage, the wafer (100) rotates at a first preset speed, and deionized water is sprayed onto the front side (110) of the wafer. Nitrogen gas is sprayed onto the back side (120) of the wafer and at multiple positions along the circumference of the wafer (100) at a first preset gas flow rate. The nitrogen gas sprayed along the circumference is used to superimpose with the nitrogen gas flowing out of the Bernoulli chuck (500) at the center position to enhance the gas protection effect on the back side (120) of the wafer and improve the stability of the Bernoulli chuck (500) in holding the wafer (100). In the second cleaning stage, the wafer (100) rotation speed is increased to a second preset speed, cleaning fluid is sprayed onto the front side (110) of the wafer, and the nitrogen injection flow rate on the back side (120) of the wafer is increased to a second preset gas flow rate; and During the drying stage, the spraying of cleaning fluid onto the front side (110) of the wafer is stopped, and the nitrogen gas sprayed onto the back side (120) of the wafer is heated to the drying temperature.

2. The wafer cleaning method according to claim 1, characterized in that, Multiple nitrogen injection ports (200) on the back side (120) of the wafer form a circular injection area (300), the center of the circular injection area (300) coincides with the center of the wafer (100), the radius of the circular injection area (300) is R1, and the radius of the wafer (100) is R2, wherein R1 = (4 / 5)R2 ± 10 mm.

3. The wafer cleaning method according to claim 1, characterized in that, Among the multiple nitrogen injection ports (200) on the back side (120) of the wafer, the distance between any two adjacent nitrogen injection ports (200) is a, 5mm≤a≤10mm; and / or, the distance between the nitrogen injection port (200) on the back side (120) of the wafer and the back side (120) is b, 2mm≤b≤3mm.

4. The wafer cleaning method according to claim 1, characterized in that, In the first cleaning stage, the thickness of the center liquid film and the thickness of the edge liquid film on the front side (110) of the wafer are detected and compared; when the result is greater than the set value, the deionized water flow rate is adjusted.

5. The wafer cleaning method according to claim 4, characterized in that, If the thickness of the central liquid film is greater than the thickness of the edge liquid film, the flow rate of deionized water is increased in stages; if the thickness of the central liquid film is less than the thickness of the edge liquid film, the flow rate of deionized water is decreased in stages.

6. The wafer cleaning method according to claim 5, characterized in that, In the first cleaning stage, the spray flow rate of the deionized water is 200-300 mL / min; If the thickness of the central liquid film is greater than the thickness of the edge liquid film, then in the phased increase of the deionized water flow rate, the increase of the deionized water in each phase is 8 to 12 mL / min. If the thickness of the central liquid film is less than the thickness of the edge liquid film, then in the phased reduction of the deionized water flow rate, the reduction of the deionized water in each phase is 8-12 mL / min.

7. The wafer cleaning method according to claim 4, characterized in that, The thickness of the center liquid film and the thickness of the edge liquid film on the front side (110) of the wafer are detected and compared. When the result is greater than a set value, the deionized water flow rate is adjusted. Specifically, the absolute value of the difference between the center liquid film thickness and the edge liquid film thickness is compared with the smaller of the two values. The ratio is then compared with a set value. When the ratio is greater than the set value, the deionized water flow rate is adjusted. The set value is 10% to 20%.

8. The wafer cleaning method according to claim 1, characterized in that, In the second cleaning stage, the step of spraying cleaning fluid onto the front side (110) of the wafer includes gradually increasing the flow rate of the cleaning fluid sprayed onto the front side (110) of the wafer.

9. The wafer cleaning method according to claim 1, characterized in that, In the second cleaning stage, the rate of decrease of the cleaning fluid contamination concentration after the wafer front (110) cleaning is detected and compared with a preset rate of decrease; when the rate of decrease of the cleaning fluid contamination concentration is less than the preset rate of decrease, a high flow rate of cleaning fluid is triggered for a first set duration.

10. The wafer cleaning method according to claim 1, characterized in that, The first preset speed is 150-250 rpm; the second preset speed is 500-800 rpm.

11. The wafer cleaning method according to claim 1, characterized in that, The first preset gas flow rate is 100-150 L / min, and the second preset gas flow rate is 150-200 L / min.

12. The wafer cleaning method according to any one of claims 1-11, characterized in that, The drying stage includes: a transition and separation stage, in which the rotation speed of the wafer (100) is increased to a third preset speed, the flow rate of the cleaning liquid sprayed onto the front side (110) of the wafer is gradually reduced, and the nitrogen gas sprayed onto the back side (120) of the wafer is heated to a transition temperature, so that the flow rate of the nitrogen gas sprayed onto the back side (120) of the wafer is maintained at a second preset gas flow rate; the transition temperature is lower than the drying temperature.

13. The wafer cleaning method according to claim 12, characterized in that, During the transition and detachment phase, the thickness of the cleaning liquid film on the front side (110) of the wafer is detected and compared with a preset liquid film thickness; when the cleaning liquid film thickness is greater than the preset liquid film thickness, the rotation speed of the wafer (100) is increased, and when the cleaning liquid film thickness is less than the preset liquid film thickness, the rotation speed of the wafer (100) is decreased.

14. The wafer cleaning method according to claim 12, characterized in that, The transition temperature is 40–45°C, and the drying temperature is 53–57°C.

15. The wafer cleaning method according to claim 12, characterized in that, The third preset speed is 1400-1600 rpm.

16. The wafer cleaning method according to claim 12, characterized in that, The drying stage further includes: a final drying stage, in which nitrogen gas sprayed onto the back side of the wafer (120) is raised from the transition temperature to the drying temperature; and a purge gas is introduced into the front side of the wafer (110).

17. The wafer cleaning method according to claim 16, characterized in that, During the final drying stage, the center temperature and edge temperature of the back side of the wafer (120) are detected and compared; when the difference between the center temperature and the edge temperature is less than or equal to a set temperature value, the wafer (100) is rotated at the second preset speed for a second preset time, nitrogen gas at the drying temperature is introduced into the back side of the wafer (120) for a second preset time, and purge gas is introduced into the front side of the wafer (110) for a second preset time.

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