A wafer cleaning method

Abstract

The present application discloses a wafer cleaning method. The wafer cleaning method according to an embodiment includes: performing a first etching on the wafer; performing overflow water injection on the wafer using a first central port and a first auxiliary port, the water injection flow rate of the first central port being a first flow rate, and the water injection flow rate of the first auxiliary port being a second flow rate; performing a second etching on the wafer; performing overflow water injection using a second central port and a second auxiliary port, the water injection flow rate of the second central port being a third flow rate, and the water injection flow rate of the second auxiliary port being a fourth flow rate; in a rinsing chamber, injecting water from a water injection port at the bottom of the tank at a fifth flow rate for a third cleaning until the water resistivity meets the process requirements; and performing a drying process on the wafer. The first, second, third, and fourth flow rates are 5 L / min to 22 L / min, the fifth flow rate is 20 L / min to 30 L / min, and the third cleaning time is 150 s to 1000 s. This cleaning method can avoid water marks caused by poor water film replacement in trenches with a large aspect ratio, thereby improving the product yield.

Description

Technical Field

[0001] This application relates to the field of semiconductor technology. More specifically, it relates to a wafer cleaning method, and particularly to a drying and cleaning process method for wafers with grooves on their surfaces. Background Art

[0002] In the process of manufacturing semiconductor devices, almost every process involves a wafer cleaning step. For example, after the trenches of trench MOS are etched, the wafer needs to be cleaned to remove the natural oxide layer and deposited contaminants formed during the trench etching process. Then, a gate oxide layer (abbreviation: "gate oxide") is formed on the sidewalls of the trenches, and polysilicon is deposited in the trenches to form a polysilicon gate. In this process, the cleaning effect directly affects the quality of the gate oxide and polysilicon, and thus affects the performance of trench MOS products. Especially for trench MOS products with a large aspect ratio, once the cleaning effect fails to meet the process requirements, such as the appearance of "water marks", it often leads to voids during polysilicon filling, and even affects the subsequent polysilicon etching step. Seriously, it will cause abnormal circuit functions and a significant reduction in product yield.

[0003] Refer to Figure 1 As shown, the figure shows the actual morphology of the product after etching and degluing the polysilicon in the trench MOS product. It can be seen from the figure that the position circled by the dotted line near the active region boundary is the pattern abnormality caused by water marks during the cleaning process, and polycrystalline voids can be seen. Since the gate oxide layer needs to be grown and polysilicon needs to be deposited as soon as possible after wafer cleaning, and it is basically impossible to determine whether "water marks" have occurred through existing detection means after cleaning. It can only be determined through detection or testing the reasons for pattern or parameter abnormalities after polysilicon etching is completed or even after product processing is completed. At this time, it is impossible to rework the abnormal products, and only the entire wafer can be scrapped, resulting in serious waste.

[0004] Therefore, a wafer cleaning method is needed to solve the "water mark" problem on the wafer surface, especially in the wafer cleaning process during the production of trench MOS products. Summary of the Invention

[0005] To solve the above problems, this application adopts the following technical solutions:

[0006] The first aspect of this application provides a wafer cleaning method, including:

[0007] Performing a first etching on the oxide film on the wafer surface with a first hydrofluoric acid aqueous solution in a first etching chamber;

[0008] In the first overflow chamber, overflow water injection is carried out using the first central port and multiple first auxiliary ports to perform the first overflow cleaning on the first corroded wafer. The first central port is located at the center of the bottom of the first overflow chamber tank body, the water injection flow rate is the first flow rate, the multiple first auxiliary ports surround the first central port, and the water injection flow rate is the second flow rate;

[0009] In the second corrosion chamber, the wafer after the first overflow cleaning is subjected to a second corrosion using the second hydrofluoric acid aqueous solution to remove the oxide film on the wafer surface;

[0010] In the second overflow chamber, overflow water injection is carried out using the second central port and multiple second auxiliary ports to perform the second overflow cleaning on the second corroded wafer. The second central port is located at the center of the bottom of the second overflow chamber tank body, the water injection flow rate is the third flow rate, the multiple second auxiliary ports surround the second central port, and the water injection flow rate is the fourth flow rate;

[0011] In the rinsing chamber, water is injected from the water injection port at the bottom of the tank body at the fifth flow rate to perform the third cleaning until the water resistivity reaches the process requirements; and in the drying chamber, the wafer after the third cleaning is dried to complete the wafer cleaning. Among them, the first to fourth flow rates are 5 L / min to 22 L / min, the fifth flow rate is 20 L / min to 30 L / min, and the third cleaning time is 150 s to 1000 s.

[0012] In some alternative embodiments, the time for the first overflow cleaning and the second overflow cleaning is: 150 s to 1000 s;

[0013] The volume ratio of H2O to HF in the first hydrofluoric acid aqueous solution is (10 to 50):1, and the volume ratio of H2O to HF in the second hydrofluoric acid aqueous solution is (100 to 300):1.

[0014] In some alternative embodiments, during the third cleaning, the resistivity of the water reaching the process requirements is: greater than or equal to 16 MΩ·cm.

[0015] In some alternative embodiments, the drying process further includes:

[0016] Immerse the wafer after the third cleaning in the water at the bottom of the tank body in the drying chamber;

[0017] Perform overflow water injection on the tank body and introduce a carrier gas into the top of the drying chamber for pre-cleaning;

[0018] Control the wafer carrier to rise in stages and drain the water completely;

[0019] Inject carrier gas again through the first vent at the top of the trough and the second vent at the bottom to perform the drying preparation stage treatment; and introduce carrier gas carrying a desiccant through the first vent to complete the drying treatment. Among them, in the drying preparation stage, the drying preparation time is 5 s to 100 s, and the carrier gas flow rates of the first vent and the second vent are 40 L / min to 80 L / min.

[0020] In some alternative embodiments, the staged ascent further includes a first stage and a second stage.

[0021] In the first stage, control the wafer support to ascend at a first speed, and more than 1 / 3 of the wafer detaches from the water surface at the end of the first stage. The first speed is less than or equal to 2 mm / s. In the second stage, control the wafer support to ascend at a second speed and start draining water, and the wafer completely detaches from the water surface at the end of the second stage. The second speed is less than or equal to 1 mm / s.

[0022] In some alternative embodiments, the time for introducing carrier gas carrying a desiccant through the second vent is 100 s to 1000 s.

[0023] In some alternative embodiments, the drying chamber further includes at least one exhaust vent. The method further includes: during the drying treatment, exhaust air using the exhaust vent at an exhaust air pressure of 120 Pa to 170 Pa.

[0024] In some alternative embodiments, during pre - cleaning, the water injection methods include water injection at a sixth flow rate and a seventh flow rate from the bottom of the trough. Among them, the flow rate of the sixth - flow - rate water injection is 10 L / min to 50 L / min, and the flow rate of the seventh - flow - rate water injection is 1 L / min to 5 L / min.

[0025] In some alternative embodiments, after the first overflow cleaning and before the second etching, the method further includes:

[0026] Immerse the wafer after the first overflow cleaning in the first cleaning chamber with a first chemical solution to perform the first particle cleaning. The first chemical solution is a mixed solution of NH4OH, H2O2, and H2O, and the volume ratio of NH4OH, H2O2, and H2O is 1:2:(50 - 100);

[0027] In the first rapid - drainage rinsing chamber, perform the first rapid - drainage rinsing on the wafer after the first particle cleaning. Immerse the wafer after the first rapid - drainage rinsing in the second cleaning chamber with a second chemical solution to perform the second particle cleaning. The second chemical solution is a mixed solution of HCl, H2O2, and H2O, and the volume ratio of HCl, H2O2, and H2O is 1:2:(50 - 100); and in the second rapid - drainage rinsing chamber, perform the second rapid - drainage rinsing on the wafer after the second particle cleaning.

[0028] In some alternative embodiments, the desiccant is vaporized isopropyl alcohol and the carrier gas is nitrogen.

[0029] The beneficial effects of the present application are as follows:

[0030] The present application provides a wafer cleaning method. During the first overflow cleaning and the second overflow cleaning, multi-region water injection is performed through the central port at the bottom center of the tank body and the auxiliary ports surrounding the center, and the water injection flow rates of the central port and the auxiliary ports are strictly controlled during each overflow cleaning to completely remove the hydrofluoric acid solution remaining on the wafer surface during the oxide film corrosion process. More importantly, during the pre-drying rinse, under the condition of monitoring the water resistivity, the third cleaning is performed at a strictly controlled water injection flow rate and treatment time, thereby changing the hydrophobicity of the wafer surface to hydrophilicity, so as to form a complete and high-quality water film during the cleaning process, thus being able to completely solve the water mark problem in the trenches and improve the product yield. Description of the Drawings

[0031] Figure 1 It is the subsequent gate oxide layer morphology defect caused by water marks during the trench cleaning process in the prior art;

[0032] Figure 2 It is a schematic flow chart of the wafer cleaning method according to the embodiment of the present application;

[0033] Figure 3 It is the specific method flow chart of the wafer cleaning method according to an embodiment of the present application;

[0034] Figure 4 It is a schematic diagram of the overflow cleaning chamber included in the overflow cleaning device applying the embodiment of the present application;

[0035] Figure 5 It is a schematic diagram of the rinsing chamber included in the fast drainage rinsing device applying the embodiment of the present application;

[0036] Figure 6 It is a schematic diagram of the cleaning chamber included in the resistivity measuring cleaning device applying the embodiment of the present application;

[0037] Figure 7 It is a schematic diagram of the drying chamber included in the drying device applying the embodiment of the present application. Detailed Embodiments

[0038] To more clearly illustrate the present application, the present application will be further described below in conjunction with embodiments and the drawings. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the protection scope of the present application.

[0039] It should be understood that the ordinal numbers such as "first", "second", "third", etc. used in the specification are only for convenient description and distinction, and do not represent specific quantities or priorities.

[0040] As Figure 2 shown, an embodiment of the present application provides a wafer cleaning method, including:

[0041] Step S1: Perform a first etching on the wafer using a first hydrofluoric acid aqueous solution in a first etching chamber;

[0042] Step S2: Perform overflow water injection using a first central port and a plurality of first auxiliary ports in a first overflow chamber to perform a first overflow cleaning on the wafer after the first etching. The first central port is located at the center of the bottom of the first overflow chamber tank body, the water injection flow rate is a first flow rate, the plurality of first auxiliary ports surround the first central port, and the water injection flow rate is a second flow rate;

[0043] Step S3: Perform a second etching on the wafer after the first overflow cleaning using a second hydrofluoric acid aqueous solution in a second etching chamber to remove the oxide film on the wafer surface;

[0044] Step S4: Perform overflow water injection using a second central port and a plurality of second auxiliary ports in a second overflow chamber to perform a second overflow cleaning on the wafer after the second etching. The second central port is located at the center of the bottom of the second overflow chamber tank body, the water injection flow rate is a third flow rate, the plurality of second auxiliary ports surround the second central port, and the water injection flow rate is a fourth flow rate;

[0045] Step S5: In the rinsing chamber, inject water at a fifth flow rate from the water injection port at the bottom of the tank body to perform a third cleaning until the water resistivity reaches the process requirements;

[0046] Step S6: Perform a drying process on the wafer after the third cleaning in a drying chamber to complete the wafer cleaning.

[0047] In the above process, the first to fourth flow rates are 5 L / min to 22 L / min, the fifth flow rate is 20 L / min to 30 L / min, and the third cleaning time is 150 s to 1000 s.

[0048] The wafer cleaning method of this embodiment includes first etching, first overflow cleaning, second etching, second overflow cleaning, third cleaning, and drying. During the first overflow cleaning and the second overflow cleaning, multi-region water injection is carried out by using the central port at the bottom center of the tank body and the auxiliary ports surrounding the center, and the water injection flow rates of the central port and the auxiliary ports at the bottom of the tank body are strictly controlled during each overflow cleaning process to thoroughly remove the hydrofluoric acid solution remaining on the wafer surface during the oxide film etching process. In particular, the inventor found through experiments that when rinsing before drying, adjusting the water injection flow rate can improve the water mark problem. It is speculated that the water injection flow rate in this step affects the hydrophilicity and hydrophobicity of the wafer surface, and further affects the quality of the water film on the wafer surface. Based on this, the inventor optimized the water injection flow rate during the third cleaning process, thus thoroughly solving the "water mark" problem and improving the product yield.

[0049] To facilitate the understanding of the process flow of each step of this application embodiment, the following will be described in detail with reference to Figure 3 the specific example flow chart shown, Figures 4 to 7 in which the key equipment involved in each step is shown, and the specific process of each step will also be described in combination with these equipment schematic diagrams in the following method description.

[0050] In step S1, the oxide film on the wafer surface is first etched with the first hydrofluoric acid aqueous solution in the first etching chamber.

[0051] Referring to Figure 3 shown, step S1 corresponds to the DHF1 process in the specific flow, and the main equipment used is the etching chamber filled with the liquid medicine. The etching chamber generally includes a tank body and a top cover that closes the tank body, and the tank body and the top cover form a cavity for accommodating the liquid medicine. Since the structure of this equipment is relatively simple and easy to understand, the equipment structure is not specifically shown.

[0052] During the first etching process, since the liquid medicine used is DHF, that is, diluted hydrofluoric acid, this step is denoted as DHF1 in the industry. In this application, the etching chamber used in this step is called the first etching chamber, and the corresponding hydrofluoric acid aqueous solution is called the first hydrofluoric acid aqueous solution to distinguish it from DHF2 later.

[0053] In this step, the first etching chamber is filled with the first hydrofluoric acid aqueous solution for etching the previous oxide film, and the volume ratio of H2O to HF in the first hydrofluoric acid aqueous solution is (10 - 50):1. In the first etching step, usually, the wafer is clamped and placed in the first etching chamber by a manipulator for soaking, so that the first hydrofluoric acid aqueous solution fully contacts and reacts with the oxide film on the wafer surface to remove the oxide layer on the wafer surface.

[0054] Specifically, the temperature of the first hydrofluoric acid aqueous solution is usually at room temperature, and its service life is usually 2000 min to 3000 min. It can process 20 to 60 batches of wafers in total. When either the service life of the liquid medicine or the number of wafer processing batches reaches the upper limit, the liquid medicine in the first etching chamber needs to be replaced to ensure that the liquid medicine always maintains sufficient etching ability. In addition, to ensure that the hydrofluoric acid aqueous solution can fully etch the oxide film, the hydrofluoric acid aqueous solution in the tank body should have a certain circulation flow rate, and the circulation flow rate is preferably 10 L / min to 20 L / min.

[0055] In step S2, usually, a manipulator is used to transfer the wafer that has been first etched in the first etching chamber to the first overflow chamber for the first overflow cleaning (OF1).

[0056] Figure 4 The structural schematic diagram of the first overflow chamber 1 used for the first overflow cleaning is shown in. The first overflow chamber 1 includes a tank body 11. Multiple teeth 111 for fixing the wafer are arranged in the tank body 11. In step S2, when the wafer is placed in the tank body 11, the wafer can be kept in a vertical state by the clamping of two adjacent teeth 111, that is, the wafer surface is parallel to the depth direction of the tank body 11, and multiple wafers are arranged parallel to each other. The teeth 111 can either have a certain space from the bottom of the tank body 11 through a support frame as shown in Figure 4 or be directly arranged at the bottom of the tank body 11, which is not specifically limited in this article.

[0057] In addition, referring to Figure 4 shown, the tank body 11 also includes a plurality of water injection ports arranged at the bottom. The water injection ports include a central port located at the center of the bottom and a plurality of auxiliary ports surrounding the central port. The 2 auxiliary ports shown in the figure are only exemplary, and the specific number depends on the equipment model. In addition, the bottom of the tank body 11 also includes at least one water outlet, and an overflow water outlet is also provided at the top. The above central port, auxiliary ports, and water outlets can all be opened and closed, and the flow rates of water inlet and outlet can be controlled.

[0058] As Figure 4 shown, the water injected from the central port at the bottom of the tank body 11 enters the tank body 11 in the direction indicated by arrow A; the water injected from the auxiliary ports at the bottom of the tank body 11 enters the tank body 11 in the directions indicated by arrows B1 and B2; when overflowing, the excess water flows out along the outflow channels in the side walls of the tank body 11 in the directions indicated by arrows C1 and C2, and the overflow water outlet is located at the top of the outflow channels; arrow D shows the direction in which the water in the tank body 11 is discharged from the bottom drain port.

[0059] Specifically in step S2, the manipulator fixes the wafer that has undergone the first etching in the first etching chamber into the cogs, and ultrapure water is overflow-injected through the first central port and multiple first auxiliary ports of the first overflow cleaning chamber. The water injection flow rate of the first central port is the first flow rate, and the water injection flow rate of the first auxiliary port is the second flow rate. In the embodiments of the present application, both the first flow rate and the second flow rate are 5 L / min to 22 L / min, and the specific values of the first flow rate and the second flow rate may be the same or different. By simultaneously using the first central port located at the bottom of the tank body 11 and multiple auxiliary ports surrounding the first central port for water injection, and both injecting water at a flow rate of 5 L / min to 22 L / min, the water flows generated by the central and multiple water injection ports surrounding the center can interact with each other, so as to ensure that the entire surface of each wafer perpendicular to the tank body 11 can be in the surging water flow, thereby effectively removing the hydrofluoric acid remaining on the wafer surface, especially in the grooves on the wafer surface.

[0060] Preferably, it has been proven through experiments that the time for the first overflow cleaning should be 150 s to 1000 s. When processed for 150 s to 1000 s under the above-mentioned water injection flow rates of the first flow rate and the second flow rate, it can ensure that the cleaned wafer meets the process requirements of product cleaning.

[0061] Considering that wafers are very likely to be contaminated with various volatile substances during the processing to form impurity particles, metal ions, and organic substances, therefore, referring to Figure 3 as shown, after the first overflow cleaning (OF1), the cleaning method may further include: the first particle cleaning (SC1), the first quick drain rinse (QDR1), the second particle cleaning (SC2), and the second quick drain rinse (QDR2).

[0062] The first cleaning chamber used for the first particle cleaning and the second cleaning chamber used for the second particle cleaning are similar in equipment structure to that used for the first etching, that is, a cleaning chamber filled with a chemical solution. The cleaning chamber also includes a tank body and a top cover that closes the tank body, and the specific structure will not be described in detail.

[0063] Figure 5 The schematic diagram of the equipment main body structure of the first quick drain rinse chamber used for the first quick drain rinse and the second quick drain rinse chamber used for the second quick drain rinse is shown. Those skilled in the art can understand that although the equipment main body structures in the two steps are shown in the same view, the purpose is to illustrate that the equipment structures used in the two times are the same, but the two steps do not use the same equipment. The purpose of doing this is to avoid cross-contamination of the chemical solution during the cleaning process, which will not be described in detail here.

[0064] As Figure 5As shown, the fast-drainage rinsing chamber 2 includes a tank body 21, and a plurality of teeth 211 for fixing the wafer are also arranged in the tank body 21. When the wafer is placed in the tank body 21, the wafer can be kept in a vertical state by the clamping of two adjacent teeth 211, that is, the wafer surface is parallel to the depth direction of the tank body 21, and multiple wafers are arranged parallel to each other. The teeth 211 can either have a certain space from the bottom of the tank body 21 through a support frame as shown in Figure 5 or be directly arranged at the bottom of the tank body 21, which is not specifically limited in this article.

[0065] In addition, referring to Figure 5 As shown, the tank body 21 of the fast-drainage rinsing chamber 2 further includes a plurality of water injection ports and at least one water outlet arranged at the bottom, and a plurality of spray ports arranged at a position near the top of the side wall. The water injection ports are arranged around the bottom center, and the drain port is arranged at the bottom center. The 4 water injection ports shown in the figure are only exemplary, and the specific number depends on the equipment model. The number of spray ports is also only an example, and this application does not limit it. The above water injection ports, spray ports and water outlets can all be opened and closed, and the flow rates of water inlet and outlet can be controlled.

[0066] As shown in Figure 5 When injecting water, the water is injected along the bottom of the tank body 21 as indicated by the arrows B1, B2, B3 and B4; when spraying, the water is sprayed into the tank body 21 in the directions indicated by the arrows E1 and E2; the arrow D shows the direction of the water in the tank body 21 discharged from the bottom drain port.

[0067] Specifically, in the first particle cleaning step, the wafer after the first overflow cleaning can be transferred to the first cleaning chamber by a manipulator, and the wafer is soaked in the first cleaning solution for the first particle cleaning. Preferably, the first cleaning solution is a mixed solution of NH4OH, H2O2 and H2O, and the volume ratio of NH4OH, H2O2 and H2O is: 1:2:(50-100). Through this setting, the impurity particles and organic substances on the wafer surface can be removed.

[0068] More specifically, the liquid temperature of the first liquid medicine in the first cleaning chamber should be 30°C to 60°C, the service life of the liquid medicine should be 720 min to 2000 min, and the liquid medicine can cumulatively process 20 to 60 batches of wafers. When one of the service life of the liquid medicine and the cumulative number of wafer processing batches reaches the upper limit, the liquid medicine in the first cleaning chamber needs to be replaced to ensure that the liquid medicine always maintains sufficient impurity dissolution ability. In addition, to ensure that the first liquid medicine can effectively dissolve impurities, the first liquid medicine in the tank body should have a certain circulation flow rate, and the circulation flow rate is preferably less than or equal to 20 L / min. In addition, to further improve the impurity removal effect, ultrasonic waves can be provided while the wafer is being soaked. The power of the ultrasonic waves is 200 W to 1200 W. Through this setting, the first liquid medicine can be fully vibrated, so that the undissolved particles can be separated from the wafer surface while dissolving the particles, improving the impurity removal effect.

[0069] In the first fast drainage rinsing step, the wafer after the first particle cleaning is transferred to the first fast drainage rinsing chamber by a manipulator, and the wafer is subjected to the first fast drainage rinsing with ultrapure water. In order to effectively rinse off the residual first liquid medicine and reactants on the wafer surface, water is discharged quickly through the spray nozzle and the water injection port at the same time. The flow rate of the spray nozzle is 15 L / min to 25 L / min, and the flow rate of the water injection port is 25 L / min to 35 L / min.

[0070] The metal ions on the wafer surface often cannot be completely cleaned in one time, so a second particle cleaning step specifically for metal ions is required again.

[0071] Specifically, the wafer after the first fast drainage rinsing is soaked in the second cleaning chamber with the second liquid medicine. The second liquid medicine is a mixed solution of HCl, H2O2 and H2O, and the volume ratio of HCl, H2O2 and H2O is: 1:2:(50 - 100).

[0072] After that, in the second fast drainage rinsing chamber, the wafer after the second particle cleaning is subjected to the second fast drainage rinsing with ultrapure water to remove the residual second liquid medicine and reactants on the wafer surface.

[0073] More specifically, the liquid temperature of the second liquid medicine in the second cleaning chamber should be 30°C to 60°C. In addition, to ensure that the second liquid medicine can effectively dissolve metal ions, the second liquid medicine in the tank body should have a certain circulation flow rate, and the circulation flow rate is preferably 10 L / min to 20 L / min.

[0074] In the second fast-drain rinsing step, to effectively rinse away the remaining second chemical solution and reactants on the wafer surface, water is also discharged rapidly through the spray nozzles and the water injection ports simultaneously. The flow rate of the spray nozzles is 15 L / min to 25 L / min, and the flow rate of the water injection ports is 25 L / min to 35 L / min. The specific process is similar to that of the first fast-drain rinsing and will not be elaborated here.

[0075] In step S3, the wafer after the first overflow cleaning is secondarily etched in the second etching chamber using a second hydrofluoric acid aqueous solution.

[0076] Refer to Figure 3 As shown, this step corresponds to the DHF2 process in the specific process. The main equipment used is an etching chamber filled with a chemical solution, and its structure is the same as that in DHF1 and will not be elaborated here.

[0077] In this step, the second etching chamber is filled with a second hydrofluoric acid aqueous solution for etching the thinned oxide film. The volume ratio of H2O to HF in the second hydrofluoric acid aqueous solution is (100 - 300):1. This thinned oxide film is usually a natural oxide layer. Specifically, the temperature of the chemical solution of the second hydrofluoric acid aqueous solution is usually 23 ± 0.5 °C, the service life of the chemical solution is usually 2000 min to 3000 min, and the number of batches of the chemical solution passing through is 20 to 60 batches. When either the service life or the number of batches of the chemical solution passing through reaches the upper limit, the chemical solution in the second etching chamber needs to be replaced to ensure that the chemical solution always maintains sufficient etching ability. Additionally, to ensure that the hydrofluoric acid aqueous solution can fully etch the thinned oxide film, the hydrofluoric acid aqueous solution in the tank body should have a certain circulation flow rate, and the circulation flow rate is preferably 5 L / min to 22 L / min.

[0078] In step S4, the robot transfers the wafer secondarily etched in the second etching chamber to the second overflow chamber for the second overflow cleaning.

[0079] Refer to Figure 3 As shown in the specific flow chart, this step corresponds to the OF2 process, and the structure diagram of the equipment used is as shown in Figure 4 As shown. Similarly, although the main body structures of the equipment in both OF1 and OF2 steps are shown in Figure 4 to illustrate that the equipment structures used in the two times are the same, the two steps do not use the same piece of equipment. The purpose of doing this is to avoid cross-contamination of the chemical solutions during the cleaning process and will not be elaborated here.

[0080] Specifically, the manipulator fixes the wafer that has been etched by the second oxide film in the second etching chamber into the chuck teeth, and ultra-pure water is injected in an overflow manner through the second central port and multiple second auxiliary ports of the second overflow cleaning chamber. The water injection flow rate of the second central port is the third flow rate, and the water injection flow rate of the second auxiliary port is the fourth flow rate. In the embodiments of the present application, both the third flow rate and the fourth flow rate are 5 L / min to 22 L / min, and the specific values of the third flow rate and the fourth flow rate may be the same or different. By simultaneously using the second central port located at the bottom of the tank body 11 and multiple second auxiliary ports surrounding the second central port for water injection, and both injecting water at a flow rate of 5 L / min to 22 L / min, the water flows generated by the central and the multiple water injection ports surrounding the center can interact with each other, so that it can be ensured that the entire surface of each wafer in the tank body 11 perpendicular to it can be in the surging water flow, and thus the surface of the wafer, especially the hydrofluoric acid and reactants remaining in the grooves on the wafer surface, can be effectively removed.

[0081] Preferably, it has been proven through experiments that the time for the first overflow cleaning should be 150 s to 1000 s. When the wafer is treated with water at the above first flow rate and second flow rate for 150 s to 1000 s, it can be ensured that the cleaned wafer meets the process requirements of product cleaning.

[0082] In step S5, in the rinsing chamber, water is injected from the water injection port at the bottom of the tank body at the fifth flow rate for the third cleaning until the water resistivity reaches the process requirements.

[0083] As Figure 6 shown, the rinsing chamber 3 includes a tank body 31, and multiple chuck teeth 311 for fixing the wafers are arranged in the tank body 31. When the wafers are placed in the tank body 31, they can be kept in a vertical state by being clamped by two adjacent chuck teeth 311, that is, the wafer surface is parallel to the depth direction of the tank body 31, and multiple wafers are arranged parallel to each other. The chuck teeth 311 can either have a certain space from the bottom of the tank body 31 through a support frame as Figure 6 shown, or be directly arranged at the bottom of the tank body 31, which is not specifically limited herein. In addition, referring to Figure 6 shown, the tank body 31 further includes multiple water injection ports arranged at the bottom and an overflow water outlet arranged at the top of the tank body 31. In addition, at least one water outlet is further included at the bottom of the tank body 11. The water injection ports are arranged around the bottom center, and the water injection ports shown in the figure are only exemplary, and the specific number depends on the equipment model. The above water injection ports and water outlets can all be opened and closed, and the flow rates of water inlet and outlet can both be controlled.

[0084] As Figure 6 shown, when injecting water, the water is injected along the bottom of the tank body 31 as indicated by the arrows B1 and B2; when overflowing and discharging water, it overflows and discharges in the directions of the arrows C1 and C2; the arrow D shows the direction in which the water in the tank body 31 is discharged from the bottom drain port.

[0085] Specifically, for step S5, this step corresponds to Figure 3 the process FR in , and this step is also the most important step in the embodiments of the present application.

[0086] Specifically, in this step, by controlling the water injection flow rate and treatment time of the water injection port, a high-quality and complete water film can be formed on the surface of the wafer before the drying treatment, thereby ensuring that the desiccant can effectively displace the water film without leaving water marks during the drying process. In this step, the resistivity can be detected at any time or sampled, and the present application does not make a limitation. In the specific implementation process, when it is detected that the resistivity of water is stably maintained at 16 MΩ · cm or above, it can be considered that the process requirements are met.

[0087] Specifically, in step S5, water is injected from the water injection port at the bottom of the tank body 31 at the fifth flow rate for the third cleaning. The fifth flow rate is 20 L / min to 30 L / min, and the third cleaning time is 150 s to 1000 s. Through repeated experimental verification, it is found that by controlling the flow rate of the water injection port at the bottom of the rinsing chamber 3 to 20 L / min to 30 L / min and the cleaning time to 150 s to 1000 s, through this optimization adjustment, the water mark problem can be effectively solved. It is speculated that the above injection flow rate and cleaning time can change the surface of the wafer from hydrophobic to hydrophilic, thereby forming an effective, uniform, and moderately thick water film on the surface of the wafer, thus avoiding the contact between the surface of the wafer and air. After entering the drying chamber, the desiccant IPA can effectively displace the water film, thereby improving the drying effect and solving the "water mark" problem of polycrystals in trench MOS products.

[0088] In addition, it should be noted here that although a water film is not directly formed in the first overflow cleaning and the second overflow cleaning steps, through the effective removal of hydrofluoric acid during the cleaning process, the influence of hydrofluoric acid on the hydrophilicity and hydrophobicity of the wafer surface can be reduced, which is beneficial to the improvement of the hydrophobicity to hydrophilicity of the wafer surface in the third cleaning, and thus effectively improves the formation quality of the water film.

[0089] In some alternative embodiments, in the third cleaning, when it is monitored that the resistivity of water is greater than or equal to 16 MΩ · cm, stop water injection and end the cleaning. By monitoring the resistivity of water, the purpose is to confirm whether the surface of the wafer has been thoroughly cleaned. When the resistivity is greater than or equal to 16 MΩ · cm, it is considered that the water in the rinsing chamber is ultrapure water, that is, there is no chemical solution on the surface of the wafer.

[0090] In step S6, the wafer after the third cleaning is dried in the drying chamber to complete the wafer cleaning.

[0091] This step corresponds to Figure 3The DRY process therein is carried out inside a drying device.

[0092] Referring to Figure 7 As shown, the main structure in the drying device for completing the drying process is the drying chamber 4. The drying chamber 4 includes a tank body 41 for accommodating ultrapure water and an arc-shaped cover 42 for closing the top opening of the tank body 41. In other words, the bottom of the drying chamber 4 is the tank body 41, and the top of the drying chamber 4 is the space defined by the cavity of the arc-shaped cover 42 and the water surface in the tank body 41. Among them, a wafer carrier 411 for carrying the wafers to be dried is arranged in the tank body 41. The wafer carrier 411 is a liftable wafer carrier and can be lifted up to the cavity of the arc-shaped cover 42 at most under the control of the drying device to facilitate loading the wafers to be dried, and then lowered into the tank body 41 so that the wafers can be taken out of the chamber after drying. The arc-shaped cover 42 is openable and closable relative to the tank body 41 for loading the wafers to be dried.

[0093] Those skilled in the art should understand that Figure 7 the structure of the wafer carrier 411 therein is only schematic. This application does not aim to limit it to a pillar-type bracket structure. Any structure that can be raised and lowered based on the control of the drying device is allowed. This application does not limit the limit position of the lifting of the wafer carrier 411, and this limit position can be different for different drying devices. In addition, although not shown, the surface of the wafer carrier 411 should also include teeth for fixing the wafers so that multiple wafers placed on the wafer carrier can be placed vertically along the depth direction of the tank body 41.

[0094] Specifically, the drying chamber 4 further includes: a plurality of water injection ports and at least one drain port provided at the bottom of the tank body 41, and at least one overflow outlet provided at the top of the tank body 41. In addition, the drying chamber 4 may further include at least one water injection port provided at the bottom of the tank body 41. The flow rate of each water injection port is controllable, and the drain port can be opened and closed; the overflow outlet is used to ensure that the liquid level will not be higher than the interface between the tank body 41 and the arc-shaped cover 42 during water injection. Figure 7 In [the figure], when overflowing, the excess water flows out along the outflow channels in the side walls of the tank body 41 as indicated by arrows C1 and C2, and the overflow outlet is located at the top of the outflow channels; the water injected from the bottom of the tank body 41 enters the tank body 41 in the directions indicated by arrows F and G; arrow D shows the direction in which the water in the tank body 41 is discharged from the bottom drain port.

[0095] In addition, the drying chamber 4 further includes a plurality of gas pipes. These gas pipes include a top gas pipe M1 provided at the top of the drying chamber 4 and an M2 located at the bottom of the tank body 41 for introducing gas into the drying chamber. For example, carrier gas and carrier gas carrying a desiccant are introduced through the gas pipe M1, and carrier gas is introduced through the gas pipe M2. Figure 7 In [the figure], for the convenience of display, solid triangles located on the wall surface of the arc-shaped cover 42 and the bottom of the tank body 41 are used to represent the jet nozzles at the ends of the gas pipes.

[0096] Specifically for step S6, the drying process further includes: immersing the wafer after the third cleaning in the water in the bottom tank 41 of the drying chamber 4; overflowing and filling water into the tank 41, and introducing a carrier gas into the top 42 of the drying chamber for pre-cleaning; controlling the wafer carrier 411 carrying the wafer to rise in stages and drain the water completely; injecting the carrier gas again through the first vent M1 located at the top of the tank and the second vent M2 located at the bottom for the drying preparation stage treatment; and introducing the carrier gas carrying the desiccant through the first vent to complete the drying process. Wherein, in the drying preparation stage, the drying preparation time is 5 s to 100 s, and the carrier gas flow rates of the first vent and the second vent are 40 L / min to 80 L / min. The flow rates of the first vent and the second vent can be the same or different as long as they both meet the above range.

[0097] Wherein, the carrier gas can be nitrogen, and the desiccant can be vaporized isopropyl alcohol (IPA).

[0098] According to the above settings, by controlling the drying preparation time and the carrier gas flow rates of the first vent and the second vent that cooperate with it, it can ensure that the water film morphology on the wafer surface is not damaged during this process, ensure the effect of subsequent replacement of the water film by the desiccant, and thus avoid the formation of water marks on the wafer surface.

[0099] In some alternative embodiments, the rising in stages further includes: the first stage and the second stage.

[0100] In the first stage, control the wafer carrier 411 to rise at the first speed. At the end of the first stage, more than 1 / 3 of the wafer to be dried is out of the water surface. The first speed is less than or equal to 2 mm / s. In the second stage, control the wafer carrier to rise at the second speed and start draining water, and at the end of the second stage, the wafer to be dried is completely out of the water surface. The second speed is less than or equal to 1 mm / s.

[0101] By controlling the rising speed of the wafer carrier, especially the speed at which the wafer in the wafer carrier is lifted from the water to a position where more than one-third and less than one-half of the wafer is out of the water surface, it can effectively avoid the influence of the water outlet fluctuation on the water film on the wafer surface when the wafer is lifted out of the water surface. Maintaining a high-quality water film on the wafer surface is beneficial to the full replacement effect of the water film by the desiccant, and thus avoids the formation of water marks.

[0102] In some alternative embodiments, the time for introducing the carrier gas carrying the desiccant through the second vent is 100 s to 1000 s. Optimizing the drying time of the desiccant can effectively improve the effect of replacing the water film with IPA on the wafer surface and improve the drying effect, avoid the formation of water marks, and is beneficial to ensuring the quality of the subsequent gate oxide layer and polysilicon, etc.

[0103] In some alternative embodiments, during pre-cleaning, the water injection methods include water injection at a sixth flow rate and a seventh flow rate from the bottom of the tank body, where the flow rate of the sixth flow rate water injection is 10 L / min to 50 L / min, and the flow rate of the seventh flow rate water injection is 1 L / min to 5 L / min.

[0104] With this setting, during pre-cleaning, by controlling the flow rates and times of water injection at multiple different positions, the water in the tank body 41 surges as a whole, preventing the water in the grooves of the wafer to be dried from returning to a static state before the wafer is completely out of water in subsequent steps, thereby avoiding water vapor residue in the grooves and improving the drying effect.

[0105] In addition, considering that the air pressure in the drying chamber also affects the effect of IPA replacing the water film and the drying effect during the drying process, preferably, the drying chamber 4 further includes at least one exhaust port (not shown), and the drying process further includes: exhausting air at an exhaust pressure of 120 Pa to 170 Pa using the exhaust port during the drying process. With this setting, the chamber pressure can be balanced by controlling the ventilation and exhaust pressures, ensuring the replacement effect of IPA on the water film, avoiding water marks on the surface of the wafer after drying, and improving the product yield.

[0106] This application provides a wafer cleaning method. During the first overflow cleaning and the second overflow cleaning, multi-region water injection is performed using the central port at the center of the bottom of the tank body and the auxiliary ports surrounding the center, and the water injection flow rates of the central port and the auxiliary ports in each overflow cleaning are controlled to thoroughly remove the hydrofluoric acid solution remaining on the surface of the wafer during the oxide film corrosion process. More importantly, during the pre-rinse before drying, under the condition of monitoring the water resistivity, the third cleaning is performed at a controlled water injection flow rate, thereby changing the hydrophobicity of the wafer surface to hydrophilicity, forming a complete and high-quality water film during the cleaning process, and thus being able to completely solve the "water mark" problem and improve the product yield.

[0107] The wafer cleaning method provided by this application is particularly suitable for trench products with a large aspect ratio, especially deep trench products with an aspect ratio greater than 3:1. In a typical example, in the process of fabricating a trench-type VDMOS (Vertical Double-diffused Metal Oxide Semiconductor), after etching to form a trench (the trench depth is 1.3 micrometers and the width is 0.25 micrometers, i.e., the aspect ratio is 5.2:1), the above cleaning method is used for wafer cleaning. Subsequently, after forming a gate oxide layer on the sidewall of the trench, filling polysilicon in the trench and performing back-etching, when observing the wafer under a microscope, no "water marks" are seen at the active region boundary and the pattern is normal.

[0108] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, rather than limitations on the implementation manners of the present application. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is impossible to list all the implementation manners here. Any obvious changes or variations derived from the technical solutions of the present application still fall within the protection scope of the present application.

Claims

1. A wafer cleaning method, characterized in that, Including: Performing a first etching on the oxide film on the surface of the wafer in a first etching chamber using a first hydrofluoric acid aqueous solution; Performing overflow water injection in a first overflow chamber using a first central port and a plurality of first auxiliary ports to perform a first overflow cleaning on the wafer after the first etching. The first central port is located at the center of the bottom of the first overflow chamber tank body, the water injection flow rate is a first flow rate, the plurality of first auxiliary ports surround the first central port, and the water injection flow rate is a second flow rate; Performing a second etching on the wafer after the first overflow cleaning in a second etching chamber using a second hydrofluoric acid aqueous solution to remove the oxide film on the surface of the wafer; Performing overflow water injection in a second overflow chamber using a second central port and a plurality of second auxiliary ports to perform a second overflow cleaning on the wafer after the second etching. The second central port is located at the center of the bottom of the second overflow chamber tank body, the water injection flow rate is a third flow rate, the plurality of second auxiliary ports surround the second central port, and the water injection flow rate is a fourth flow rate; In a rinsing chamber, injecting water at a fifth flow rate from a water injection port at the bottom of the tank body to perform a third cleaning until the water resistivity meets the process requirements; and Performing a drying treatment on the wafer after the third cleaning in a drying chamber to complete the wafer cleaning, wherein, the first to fourth flow rates are 5 L / min to 22 L / min, the fifth flow rate is 20 L / min to 30 L / min, and the third cleaning time is 150 s to 1000 s.

2. The wafer cleaning method according to claim 1, wherein Wherein, the time of the first overflow cleaning and the second overflow cleaning is: 150 s to 1000 s; The volume ratio of H2O to HF in the first hydrofluoric acid aqueous solution is (10 to 50):1, and the volume ratio of H2O to HF in the second hydrofluoric acid aqueous solution is (100 to 300):

1.

3. The wafer cleaning method according to claim 1, wherein Wherein, During the third cleaning, the resistivity of the water meeting the process requirements is: greater than or equal to 16 MΩ · cm.

4. The wafer cleaning method according to claim 1, wherein the drying treatment further includes: Immersing the wafer after the third cleaning in the water at the bottom of the tank body of the drying chamber; Performing overflow water injection on the tank body and introducing a carrier gas into the top of the drying chamber for pre-cleaning; Controlling the wafer carrier to rise in stages and drain the water completely; Injecting the carrier gas again through a first vent port at the top of the tank body and a second vent port at the bottom for drying preparation stage treatment; and Introducing a carrier gas carrying a desiccant through the first vent port to complete the drying treatment, wherein, in the drying preparation stage, the drying preparation time is 5 s to 100 s, and the carrier gas flow rates of the first vent port and the second vent port are 40 L / min to 80 L / min.

5. The wafer cleaning method according to claim 4, wherein The rising in stages further includes a first stage and a second stage, In the first stage, controlling the wafer carrier to rise at a first speed, and when the first stage ends, more than 1 / 3 of the wafer is out of the water surface, and the first speed is less than or equal to 2 mm / s, In the second stage, controlling the wafer carrier to rise at a second speed and start draining water, and when the second stage ends, the wafer is completely out of the water surface, and the second speed is less than or equal to 1 mm / s.

6. The wafer cleaning method according to claim 4, wherein The time for introducing the carrier gas carrying the desiccant through the second vent port is 100 s to 1000 s.

7. The wafer cleaning method according to claim 4, wherein, The drying chamber further includes at least one air outlet, and the method further includes: during the drying process, exhausting air through the air outlet at an exhaust air pressure of 120 Pa to 170 Pa.

8. The wafer cleaning method according to claim 4, wherein, During the pre-cleaning, the water injection methods include water injection at a sixth flow rate and a seventh flow rate from the bottom of the tank body, where the flow rate of the water injection at the sixth flow rate is 10 L / min to 50 L / min, and the flow rate of the water injection at the seventh flow rate is 1 L / min to 5 L / min.

9. The wafer cleaning method according to claim 1, wherein after the first overflow cleaning and before the second etching, the method further includes: immersing the wafer after the first overflow cleaning in a first cleaning chamber with a first chemical solution to perform a first particle cleaning, the first chemical solution being a mixed solution of NH4OH, H2O2, and H2O, and the volume ratio of NH4OH, H2O2, and H2O being: 1:2:(50 - 100); performing a first quick drain rinse on the wafer after the first particle cleaning in a first quick drain rinse chamber, immersing the wafer after the first quick drain rinse in a second cleaning chamber with a second chemical solution to perform a second particle cleaning, the second chemical solution being a mixed solution of HCl, H2O2, and H2O, and the volume ratio of HCl, H2O2, and H2O being: 1:2:(50 - 100); and performing a second quick drain rinse on the wafer after the second particle cleaning in a second quick drain rinse chamber.

10. The wafer cleaning method according to any one of claims 4-8, characterized in that, The desiccant is vaporized isopropyl alcohol, and the carrier gas is nitrogen.

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