Wafer cleaning method

Abstract

The invention provides a wafer cleaning method, relates to the technical field of semiconductor manufacturing, and is designed to solve the problem of low single-chip cleaning efficiency in a manner of adding a back cleaning step in a single-chip cleaning process to reduce particles on the back of a wafer in the prior art. The wafer cleaning method comprises the steps that the back face of a wafer is loaded to a Bernoulli suction cup; in the first cleaning stage, the wafer rotates at a first preset speed, deionized water is sprayed to the front face of the wafer, and nitrogen is sprayed to the back face of the wafer and multiple positions in the circumferential direction of the wafer at a first preset gas flow; in the second cleaning stage, the rotating speed of the wafer is increased to a second preset speed, cleaning liquid is sprayed to the front face of the wafer, and the nitrogen spraying flow on the back face of the wafer is increased to a second preset gas flow; and a drying stage: stopping spraying the cleaning liquid to the front surface of the wafer, and heating the nitrogen sprayed to the back surface of the wafer to a drying temperature. The cleaning device is high in cleaning efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor manufacturing, in particular to a wafer cleaning method. BACKGROUND

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

[0003] The wafer cleaning method includes a tank cleaning process and a single wafer cleaning process. In the single wafer cleaning process, a clamp is used to fix and rotate the wafer, and at the same time, the contaminants are removed from the front surface of the wafer through chemical spraying and rotating flushing. Although this method can clean the front surface of the wafer, secondary particles are often generated in the clamping contact area due to the wear of the clamp material, the structural damage of the wafer caused by clamping stress, and the residue of process medium. Under the action of the rotating centrifugal force, these secondary particles will spread to the entire back surface of the wafer and may be transferred to the front surface of the wafer in the subsequent process, causing defects such as device short circuit.

[0004] To solve the above problems, the related art adds a back surface cleaning step in the single wafer cleaning process, but this increases the time required for single wafer cleaning, resulting in low single wafer cleaning efficiency. SUMMARY

[0005] The purpose of the present application is to provide a wafer cleaning method to solve the technical problem of low single wafer cleaning efficiency caused by the related art method of adding a back surface cleaning step in the single wafer cleaning process to reduce the particles on the back surface of the wafer.

[0006] The wafer cleaning method provided by the present application comprises:

[0007] loading the back surface of the wafer to a Bernoulli chuck;

[0008] In the 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 the back surface of the wafer at a first preset gas flow rate and along the circumference of the wafer;

[0009] In the 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 back surface of the wafer is increased to a second preset gas flow rate; and

[0010] In the drying stage, the spraying of cleaning liquid to the front surface of the wafer is stopped, and the nitrogen gas sprayed to the back surface of the wafer is heated to a drying temperature.

[0011] Further, the plurality of nitrogen injection ports on the back of the wafer enclose a circular injection area, the center of the circular injection area coincides with the center of the wafer, the radius of the circular injection area is R1, and the radius of the wafer is R2, wherein R1=(4 / 5)R2±10mm.

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

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

[0014] Further, if the center liquid film thickness is greater than the edge liquid film thickness, the deionized water flow is increased in stages; if the center liquid film thickness is less than the edge liquid film thickness, the deionized water flow is reduced in stages.

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

[0016] In the deionized water flow is increased in stages, the increase of the deionized water in each stage is 8-12mL / min;

[0017] In the deionized water flow is reduced in stages, the decrease of the deionized water in each stage is 8-12mL / min.

[0018] Further, the center liquid film thickness and the edge liquid film thickness on the front of the wafer are detected and compared; when the result is greater than a set value, the deionized water flow adjustment is triggered, and the specific method is that the ratio of the absolute value of the difference between the center liquid film thickness and the edge liquid film thickness to the smaller value of the two is compared with a set value, when the ratio is greater than the set value, the deionized water flow adjustment is triggered, wherein the set value is 10%-20%.

[0019] Further, in the second cleaning stage, the step of spraying cleaning liquid to the front of the wafer includes gradually increasing the flow of cleaning liquid sprayed to the front of the wafer.

[0020] Furthermore, in the second cleaning stage, the rate of decrease of the pollution concentration of the cleaning liquid after cleaning the front side of the wafer is detected and compared with the preset rate of decrease; when the rate of decrease of the pollution concentration of the cleaning liquid is less than the preset rate of decrease, the high-flow cleaning liquid injection for the first set time 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 separation stage, in which the wafer rotation speed is increased to a third preset speed, the flow rate of the cleaning liquid sprayed to the front side of the wafer is gradually reduced, and the nitrogen sprayed to the back side of the wafer is heated to a transition temperature so that the flow rate of the nitrogen sprayed to 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, in the transition separation 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 thickness of the cleaning liquid film is greater than the preset liquid film thickness, the rotation speed of the wafer is increased, and when the thickness of the cleaning liquid film is less than the preset liquid film thickness, the rotation speed of the wafer is reduced.

[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 the nitrogen gas sprayed onto the back side of the wafer is raised from the transition temperature to the drying temperature; and a purge gas is introduced into 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 the set temperature value, the wafer is kept rotating at the second preset speed for a second set time, nitrogen at the drying temperature is kept flowing to the back side of the wafer for a second set time, and purge gas is kept flowing to the front side of the wafer for a second set time.

[0029] The beneficial effects brought about by the wafer cleaning method of the present invention are:

[0030] In this wafer cleaning method, a Bernoulli chuck is used to load the wafer, achieving non-contact clamping and fixation of the wafer, effectively blocking particle contamination between the fixture and the wafer, and reducing secondary particles generated on the wafer. By dividing the wafer cleaning into two stages, in which, in the first cleaning stage, the wafer is rotated at a lower first preset speed, the deionized water sprayed onto the front of the wafer slowly covers the front of the wafer, achieving pre-wetting of the front of the wafer, reducing tension on the front of the wafer and increasing the hydrophilicity of the front of the wafer. At the same time, nitrogen gas is introduced at multiple locations along the back of the wafer and along the circumference of the wafer to form a gas barrier covering the back of the wafer.

[0031] In the second cleaning stage, by increasing the wafer rotation speed to a second preset speed, the centrifugal force of the cleaning liquid can be increased. While ensuring comprehensive cleaning of the front side of the wafer, the cleaning liquid can also be confined to the edge of the front side of the wafer to reduce radial splashing of the cleaning liquid on the front side of the wafer. At the same time, by increasing the nitrogen injection flow rate, the rigidity of the nitrogen gas curtain formed on the back side of the wafer can be increased, thereby blocking the migration of the cleaning liquid from the front side of the wafer to the back side after the centrifugal force of the cleaning liquid increases. The synergistic change of the cleaning liquid centrifugal force and the nitrogen flow rate can be used to reduce the residual process medium on the back side of the wafer. After the completion of the first and second cleaning stages, by increasing the temperature of the nitrogen gas, thermal convection can be used to accelerate the volatilization of the liquid film on the front side of the wafer and inhibit crystallization to ensure the cleaning effect of the wafer.

[0032] Thus, it can be seen that in this wafer cleaning method, the use of a Bernoulli chuck can achieve non-contact fixation of the wafer, so that the space between the Bernoulli chuck and the wafer as a fixture is filled with flowing gas, blocking particle contamination between the fixture and the wafer; by spraying nitrogen at multiple locations along the circumference of the back of the wafer and increasing the nitrogen flow rate as the wafer rotation speed increases, a rigid air curtain can be formed on the back of the wafer, achieving cleaning liquid blocking at the edge. Moreover, the nitrogen sprayed circumferentially to the back of the wafer can also be superimposed with the airflow of the Bernoulli chuck, on the one hand, enhancing the gas protection effect on the back of the wafer, and on the other hand, improving the stability of the Bernoulli chuck in clamping the wafer. At the same time, since the nitrogen gas will flow in all directions under the blocking effect of the back of the wafer after being sprayed onto the back of the wafer, in this process, free particles on the back of the wafer can be discharged under the guidance of the nitrogen gas, thereby reducing the adhesion of these particles to the wafer, thereby enhancing the cleaning effect of the wafer. The above cleaning process has good process compatibility and does not require an additional wafer backside cleaning step, which effectively improves the problem of low single-wafer cleaning efficiency caused by the additional wafer backside cleaning step in related technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the following briefly introduces the drawings required for use in the embodiments or related technical descriptions. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0034] Figure 1 A schematic flow chart of a wafer cleaning method provided in an embodiment of the present invention;

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

[0036] Figure 3 A schematic diagram of the distribution of nitrogen injection ports in the wafer cleaning method provided by an embodiment of the present invention;

[0037] Figure 4 A schematic flow chart of another wafer cleaning method provided in an embodiment of the present invention.

[0038] Description of reference numerals:

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

[0040] 200-nitrogen injection port; 300-circular injection area; 400-injection pipeline; 500-Bernoulli suction cup. DETAILED DESCRIPTION

[0041] In the single-wafer cleaning process, in order to reduce secondary particles on the back of the wafer, the relevant technology will add a back-side cleaning step after the front-side cleaning of the wafer is completed to flush the particles on the back. However, this will not only increase the time required for single-wafer cleaning, resulting in lower single-wafer cleaning efficiency, but also require additional back-side cleaning equipment, which takes up a lot of space.

[0042] Related technology 2 uses an edge clamp with a polymer coating or low-friction material to reduce secondary particles generated on the back of the wafer by reducing mechanical contact with the back of the wafer. However, clamping contact cannot completely prevent particle generation. Moreover, the edge clamp needs to be frequently maintained and replaced, which is costly.

[0043] Related technology three uses lowering the rotation speed or spray flow to reduce the probability of fluid splashing to the back side, thereby reducing the process medium residue on the back side of the wafer. However, this will weaken the flushing effect on the front side of the wafer, and it is necessary to extend the cleaning time on the front side of the wafer as compensation, which reduces production capacity.

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

[0045] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the following detailed description of the specific embodiments of the present invention is given in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

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

[0047] Step S100: Figure 2 As shown, the wafer backside 120 is loaded onto the Bernoulli chuck 500 .

[0048] In the wafer cleaning method, the Bernoulli suction cup 500 is used to load the wafer 100, thereby achieving non-contact clamping and fixing of the wafer 100, effectively blocking particle contamination between the clamp and the wafer 100, and reducing secondary particles generated in the wafer 100.

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

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

[0051] Specifically, the first preset speed may be 150-250 rpm, preferably 200 rpm. In this step, the wafer 100 rotates at the relatively low first preset speed, so that the deionized water sprayed onto the wafer front surface 110 slowly covers the wafer front surface 110, thereby pre-wetting the wafer front surface 110, reducing tension on the wafer front surface 110 and increasing the hydrophilicity of the wafer front surface 110.

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

[0053] It should be noted that Figure 2 It is only used to provide a principle explanation of the airflow path in the wafer cleaning method. Based on this, sufficient gap is reserved between the back side of the wafer 120 and the Bernoulli suction cup 500 to indicate the airflow path through corresponding arrows. In practice, the distance between the back side of the wafer 120 and the Bernoulli suction cup 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 suction cup 500. At the same time, a plurality of flow channels respectively connected to each nitrogen injection port 200 for supplying nitrogen can be provided on the Bernoulli suction cup 500, 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 the wafer 100.

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

[0057] Specifically, the second preset speed can be 500-800 rpm, preferably 600 rpm. In this step, the rotation speed of the wafer 100 is increased, which can increase the centrifugal force of the cleaning liquid. While ensuring comprehensive cleaning of the wafer front side 110, the cleaning liquid can also be confined to the edge of the wafer front side 110 to reduce radial splashing of the cleaning liquid on the wafer front side 110.

[0058] In the above-mentioned first cleaning stage and second cleaning stage, since the nitrogen gas will flow around under the blocking effect of the back side 120 of the wafer after being sprayed onto the back side 120 of the wafer, in this process, the free particles on the back side 120 of the wafer can be discharged under the guidance of the nitrogen gas to reduce the adhesion of these particles on the wafer 100, thereby enhancing the cleaning effect on the wafer 100.

[0059] Specifically, the second preset gas flow rate is 150-200 L / min. During the second cleaning phase, the nitrogen flow rate is higher than during the first cleaning phase. This configuration increases the rigidity of the nitrogen curtain formed on the wafer backside 120, thereby blocking the migration of cleaning liquid from the wafer front side 110 to the wafer backside 120 after the centrifugal force of the cleaning liquid increases. This synergistic change in the cleaning liquid centrifugal force and the nitrogen flow rate reduces process medium residue on the wafer backside 120.

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

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

[0062] It can be seen that the wafer cleaning method not only realizes non-contact fixation of the wafer 100 by using the Bernoulli suction cup 500 during the loading stage, so that the space between the Bernoulli suction cup 500 as a clamp and the wafer 100 is filled with flowing gas, thereby blocking particle contamination between the clamp and the wafer 100, but also has good process compatibility in the cleaning stage, without the need to add a cleaning step for the back side of the wafer 120, effectively improving the problem of low single-wafer cleaning efficiency caused by the additional cleaning step for the back side of the wafer 120 in the related technology.

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

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

[0065] By setting the nitrogen injection port 200 at the above-mentioned position, on the one hand, it can be avoided that the nitrogen injection port 200 is too far away from the edge of the wafer 100, resulting in the inability to form an effective air curtain on the back side 120 of the wafer near the edge of the wafer 100, thereby weakening the blocking effect on the cleaning liquid on the front side 110 of the wafer. On the other hand, it can also be avoided that the nitrogen is too close to the edge of the wafer 100, resulting in the limited guidance effect of the back side 120 of the wafer after colliding upward to the back side 120 of the wafer, thereby failing to effectively export the particles.

[0066] Moreover, the above arrangement enables the nitrogen gas ejected through the multiple nitrogen injection ports 200 to form a complete gas curtain on the back side 120 of the wafer, thereby effectively blocking the cleaning liquid on the front side 110 of the wafer, and preventing the cleaning liquid on the front side 110 of the wafer from flowing downward from the edge of the wafer 100 to the back side 120 of the wafer.

[0067] Preferably, please refer to Figure 3 The plurality of nitrogen injection ports 200 are arranged at equal intervals along the circumference of the wafer 100. This arrangement forms a complete gas curtain on the back side 120 of the wafer while ensuring uniform force on the back side 120 of the wafer.

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

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

[0070] Through this arrangement, on the one hand, it is possible to avoid the increase in cleaning costs caused by the two adjacent nitrogen injection ports 200 being too close to each other, resulting in an excessive density of the nitrogen injection ports 200. On the other hand, it is also possible to avoid the poor consistency of the circumferential stiffness of the nitrogen gas curtain formed on the back side 120 of the wafer due to the two adjacent nitrogen injection ports 200 being too far apart, thereby causing the cleaning liquid on the front side 110 of the wafer to flow from the part with lower circumferential stiffness of the nitrogen gas curtain 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 wafer back side 120 and the wafer back side 120 is b, where 2 mm ≤ b ≤ 3 mm.

[0072] This arrangement can, on the one hand, prevent the nitrogen gas flow from being unable to form a complete nitrogen gas curtain on the back side 120 of the wafer due to the nitrogen injection port 200 being too close to the wafer back side 120; and on the other hand, it can also prevent the nitrogen gas curtain from having limited stiffness due to the nitrogen injection port 200 being too far from the wafer back side 120.

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

[0074] During the rotation of the wafer 100, the liquid film thicknesses of the center region and the edge region of the wafer front surface 110 are different due to the rotation centrifugal force and gravity. When the difference is large, the cleaning effect of the center region and the edge region is different. By detecting the center liquid film thickness and the edge liquid film thickness, the center liquid film thickness and the edge liquid film thickness can be obtained in time. When the center liquid film thickness and the edge liquid film thickness are different, the flow of the deionized water is adjusted to ensure that the center region and the edge region have substantially the same cleaning effect.

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

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

[0077] When the center liquid film thickness is thick, the flow of the deionized water is increased, and more deionized water can be sprayed to the edge region of the wafer front surface 110 under the swing arm spraying mode of the spray pipeline 400, so as to compensate the liquid film thickness of the edge region and reduce the difference between the liquid film thicknesses of the edge region and the center region.

[0078] Similarly, when the center liquid film thickness is thin, the flow of the deionized water is reduced, and the deionized water sprayed to the edge region of the wafer front surface 110 is reduced under the swing arm spraying mode of the spray pipeline 400, so as to reduce the difference between the deionized water flow of the edge region and the center region, thereby ensuring the consistency of the liquid film thickness of the wafer front surface 110.

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

[0080] By limiting the spray flow of the deionized water within the above range, on the one hand, the cleaning effect of the wafer front surface 110 can be limited due to the insufficient deionized water flow, and on the other hand, the waste of the deionized water can be avoided due to the excessive deionized water flow.

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

[0082] This setting can achieve fine-tuning of the deionized water flow rate. On the one hand, it avoids the flow rate increasing or decreasing too little each time, which requires repeated increases or decreases, resulting in low adjustment efficiency. On the other hand, it also avoids the flow rate increasing or decreasing too much each time, which causes over-adjustment and results in an opposite difference in the thickness of the central liquid film and the edge liquid film.

[0083] Preferably, when the thickness of the central liquid film is greater than the thickness of the edge liquid film so as to increase the deionized water flow rate in stages, the increase in the amount of deionized water in each stage is 10 mL / min; when the thickness of the central liquid film is less than the thickness of the edge liquid film so as to reduce the deionized water flow rate in stages, the reduction in the amount of deionized water in each stage is 10 mL / min.

[0084] In this embodiment, the central liquid film thickness and the edge liquid film thickness of the wafer front side 110 are detected and compared; when the result is greater than the set value, the deionized water flow adjustment is triggered. The specific method is to compare the absolute value of the difference between the central liquid film thickness and the edge liquid film thickness and the ratio of the smaller value between the two, and compare the ratio with the set value. When the ratio is greater than the set value, the deionized water flow adjustment is triggered, wherein the set value is 10% to 20%.

[0085] Through the above-mentioned setting, on the one hand, it is possible to avoid triggering the deionized water flow adjustment when the difference between the center liquid film thickness and the edge liquid film thickness is too small due to detection error or instantaneous fluctuation of the liquid film thickness. On the other hand, it is also possible to avoid the inability to adjust in time when the difference between the center liquid film thickness and the edge liquid film thickness is too large, thereby ensuring the timeliness of triggering the deionized water flow adjustment.

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

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

[0088] By gradually increasing the flow rate of the cleaning liquid sprayed onto the front side 110 of the wafer, the flow rate of the cleaning liquid is gradually increased to the target flow rate. On the one hand, it can avoid a large impact on the front side 110 of the wafer due to the instantaneous increase of the flow rate of the cleaning liquid to the target flow rate, and play a certain protective role on the wafer 100. On the other hand, it also makes the flow rate of the cleaning liquid increase synchronously with the increase in the rotation speed of the wafer 100, so that after the rotation speed of the wafer 100 increases, the cleaning liquid can still achieve full coverage of the front side 110 of the wafer. 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 the embodiment, the cleaning liquid flow rate can be raised to 1200 mL / min in three stages. Specifically, in the initial stage, the cleaning liquid flow rate can be 400 mL / min, and then the flow rate is raised by 400 mL / min every 10 s, i.e., the change process of the cleaning liquid flow rate is: 400 mL / min→800 mL / min→1200 mL / min.

[0090] In the second cleaning stage, the cleaning liquid is used to clean the wafer front surface 110 to remove the attached pollution impurities, at this time, the pollution impurities will be mixed in the cleaning liquid. By detecting the pollution concentration reduction rate of the cleaning liquid, the cleaning effect of the wafer front surface 110 can be known in time. Specifically, when the pollution concentration reduction rate of the cleaning liquid is less than the preset reduction rate, it indicates that the pollution concentration reduction rates of the cleaning liquid measured at two different times are not much different, and at this time, the wafer front surface 110 still has a lot of pollution impurities attached. Therefore, the cleaning effect of the wafer front surface 110 can be ensured by increasing the injection flow rate of the cleaning liquid to ensure sufficient removal of the pollution impurities.

[0091] In the second cleaning stage, the cleaning liquid is used to clean the wafer front surface 110 to remove the attached pollution impurities, at this time, the pollution impurities will be mixed in the cleaning liquid. By detecting the pollution concentration reduction rate of the cleaning liquid, the cleaning effect of the wafer front surface 110 can be known in time. Specifically, when the pollution concentration reduction rate of the cleaning liquid is less than the preset reduction rate, it indicates that the pollution concentration reduction rates of the cleaning liquid measured at two different times are not much different, and at this time, the wafer front surface 110 still has a lot of pollution impurities attached. Therefore, the cleaning effect of the wafer front surface 110 can be ensured by increasing the injection flow rate of the cleaning liquid to ensure sufficient removal of the pollution impurities.

[0092] Specifically, in the embodiment, the pollution impurity concentration in the recovered cleaning liquid can be detected by using the conductivity detection sensor, and the pollution concentration reduction rate of the cleaning liquid can be obtained by using the detection results at two discrete time points. When the conductivity detection sensor detects that the conductivity of the recovered cleaning liquid is high, it indicates that the pollution is serious, and at this time, there are a lot of pollution impurities in the cleaning liquid, and the cleaning effect needs to be ensured by increasing the flow rate of the cleaning liquid.

[0093] In the embodiment, the preset reduction rate can be 4% to 6%, and preferably 5%; the first set time length can be 3 to 7 s, and preferably 5 s; and the triggered high-flow cleaning liquid injection has a flow rate greater than 1200 mL / min, and preferably 1500 mL / min.

[0094] As shown in FIG. 6, the embodiment also provides another wafer cleaning method, and specifically, the drying stage includes: Figure 4

[0095] Step S401: transition spin-off stage, the wafer 100 rotation speed is raised to a third preset speed, the cleaning liquid flow rate injected to the wafer front surface 110 is gradually reduced, the nitrogen gas injected to the wafer back surface 120 is heated to a transition temperature, and the nitrogen gas flow rate injected to the wafer back surface 120 is maintained at a second preset gas flow rate, wherein the transition temperature is lower than the drying temperature.​

[0096] During the transitional spin-off phase, by increasing the rotational speed of the wafer 100, the centrifugal force of the wafer 100 can be increased. At the same time, by gradually reducing the flow rate of the cleaning liquid sprayed onto the wafer front 110, rather than reducing the flow rate of the cleaning liquid sprayed onto the wafer front 110 all at once, the wettability of the liquid film on the wafer front 110 can be maintained to prevent the liquid film from rupturing and the formation of dry spots that affect the cleaning effect. In the above process, by first heating the nitrogen sprayed onto the wafer back 120 to a transition temperature lower than the drying temperature, a gradually increasing temperature gradient can be formed on the wafer 100 during the drying process, ensuring a stable temperature increase of the wafer 100, allowing the wafer 100 to gradually transition from room temperature to the final drying temperature, and avoiding damage to the wafer 100 due to excessive temperature changes.

[0097] In addition, by maintaining the nitrogen flow rate sprayed onto the back side 120 of the wafer at the second preset gas flow rate, a nitrogen gas curtain with stable rigidity can still be formed on the back side 120 of the wafer during the transition separation stage, thereby preventing the cleaning liquid on the front side 110 of the wafer from flowing to the back side 120 of the wafer during the transition separation 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 that the wafer 100 rotates at an insufficient speed, resulting in insufficient centrifugal force in the separation process, causing the cleaning liquid to be unable to fully cover the front side 110 of the wafer after the flow rate is reduced. On the other hand, it can also avoid that the wafer 100 rotates at an excessive speed, resulting in excessive centrifugal force, and then causing 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 to the above range, it is possible to prevent poor heating of the wafer 100 during the transitional separation phase due to a low transition temperature. It is also possible to prevent large temperature fluctuations on the wafer backside 120 due to a high transition temperature, which could damage the wafer 100. This setting can reduce the viscosity of the cleaning liquid film and promote uniform separation.

[0103] By limiting the drying temperature to the above range, it is possible to prevent the wafer 100 from being heated poorly in the final drying stage due to a low drying temperature, thereby reducing the drying efficiency. 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 separation stage, the thickness of the cleaning liquid film on the front side of the wafer 110 is detected and compared with the 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 reduced.

[0105] This setting can make timely adjustments when the cleaning liquid film thickness on the wafer front side 110 deviates from the preset liquid film thickness, avoiding the cleaning liquid film being too thick and prolonging the cleaning time, and avoiding the cleaning liquid film being too thin and causing local areas to not be covered by the cleaning liquid and affecting the cleaning effect.

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

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

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

[0109] Step S402 : in the final drying stage, the nitrogen gas sprayed onto the wafer back surface 120 is raised from the transition temperature to the drying temperature; and a purge gas is introduced into the wafer front surface 110 .

[0110] During the final drying stage, the temperature of the nitrogen gas sprayed onto the wafer backside 120 is further increased, which can improve the evaporation efficiency of the cleaning liquid and the particle stripping rate, thereby improving the cleaning efficiency of the wafer 100. In addition, by passing a purge gas to the wafer frontside 110, the suspended particles after stripping can be removed, reducing the risk of particle deposition and removing trace residues on the wafer surface. At the same time, the evaporation efficiency of the cleaning liquid can be further enhanced to avoid water marks or process impurities.

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

[0112] In this embodiment, in 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 the set temperature value, the wafer 100 is kept rotating at a second preset speed for a second set time, nitrogen at a drying temperature is kept introduced to the back side 120 of the wafer for a second set time, and purge gas is kept introduced to the front side 110 of the wafer for a second set time.

[0113] In the final drying stage, when the difference between the center temperature and the edge temperature of the back surface 120 is less than or equal to a set temperature value, it indicates that the temperature uniformity of the back surface 120 is good, at this time, under the premise of the temperature uniformity, the wafer 100 continues to rotate at the second preset speed, the nitrogen gas is supplied to the back surface 120 at the drying temperature, and the purge gas is supplied to the front surface 110, and after a second set 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℃, and the second set time can be 20-30s, preferably 25s.

[0115] Specifically, the temperature uniformity of the back surface 120 can be detected by an infrared thermal imager.

[0116] Specifically, after the second set time, the rotation speed of the wafer 100 can be reduced to 500rpm to prepare for unloading.

[0117] Although the present application is disclosed as above, the present application is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present application, and the protection scope of the present application should be subject to the scope defined by the claims.

[0118] Finally, it should be noted that in this document, relational terms such as first and second and the like can be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", "includes", "including" or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without limitation, an element preceded by "comprises a" does not, without more constraints, foreclose the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0119] In the above embodiments, the description of the orientation such as "upper", "lower", "side" and the like is based on the drawings.

[0120] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one 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 present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to 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 loaded onto the Bernoulli chuck (500); In a first cleaning stage, the wafer (100) is rotated at a first preset speed, deionized water is sprayed toward the front side (110) of the wafer, and nitrogen is sprayed toward the back side (120) of the wafer and at multiple locations along the circumference of the wafer (100) at a first preset gas flow rate; In the second cleaning stage, the rotation speed of the wafer (100) is increased to a second preset speed, the cleaning liquid 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 a second preset gas flow rate; as well as During the drying phase, the spraying of the cleaning liquid 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 a drying temperature.

2. The wafer cleaning method according to claim 1, wherein: A plurality of nitrogen injection ports (200) on the back side of the wafer (120) 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, wherein: Among the multiple nitrogen injection ports (200) on the back side of the wafer (120), 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 of the wafer (120) and the back side of the wafer (120) is b, 2mm≤b≤3mm.

4. The wafer cleaning method according to claim 1, wherein: In the first cleaning stage, the central liquid film thickness and the edge liquid film thickness of the wafer front side (110) are detected and compared; when the result is greater than a set value, the deionized water flow rate adjustment is triggered.

5. The wafer cleaning method according to claim 4, wherein: 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 reduced in stages.

6. The wafer cleaning method according to claim 5, wherein: In the first cleaning stage, the injection flow rate of the deionized water is 200 to 300 mL / min; 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, and the increase in the amount of deionized water in each stage is 8 to 12 mL / min; If the thickness of the central liquid film is less than the thickness of the edge liquid film, the flow rate of the deionized water is reduced in stages, and the reduction amount of the deionized water in each stage is 8 to 12 mL / min.

7. The wafer cleaning method according to claim 4, wherein: The central liquid film thickness and the edge liquid film thickness of the wafer front side (110) are detected and compared; when the result is greater than a set value, deionized water flow regulation is triggered, specifically by comparing the absolute value of the difference between the central liquid film thickness and the edge liquid film thickness with the ratio of the smaller value of the two, comparing the ratio with a set value, and triggering deionized water flow regulation when the ratio is greater than the set value, wherein the set value is 10% to 20%.

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

9. The wafer cleaning method according to claim 1, wherein: In the second cleaning stage, the rate of decrease of the pollution concentration of the cleaning liquid after cleaning the front side (110) of the wafer is detected and compared with the preset rate of decrease; when the rate of decrease of the pollution concentration of the cleaning liquid is less than the preset rate of decrease, the high-flow cleaning liquid injection for the first set time is triggered.

10. The wafer cleaning method according to claim 1, wherein: 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, wherein: 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 to 11, characterized in that: The drying stage includes: a transition 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 sprayed onto the back side (120) of the wafer is heated to a transition temperature so that the flow rate of the nitrogen 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, wherein: During the transition separation stage, the thickness of the cleaning liquid film on the front side of the wafer (110) 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 reduced.

14. The wafer cleaning method according to claim 12, wherein: The transition temperature is 40-45°C, and the drying temperature is 53-57°C.

15. The wafer cleaning method according to claim 12, wherein: The third preset speed is 1400-1600 rpm.

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

17. The wafer cleaning method according to claim 16, wherein: In the final drying stage, the center temperature and the 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 the set temperature value, the wafer (100) is kept rotating at the second preset speed for a second set time, nitrogen gas at a drying temperature is kept flowing to the back side (120) of the wafer for a second set time, and purge gas is kept flowing to the front side (110) of the wafer for a second set time.

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