Cleaning method and system for improving metal level on surface of silicon wafer

Abstract

The embodiment of the invention relates to the technical field of silicon wafer cleaning, and discloses a cleaning method and system for improving the surface metal level of a silicon wafer. The method comprises the steps that a silicon wafer is ground, the treated ground silicon wafer is washed with deionized water, the treated silicon wafer is washed with a DHF, ammonia water, hydrogen peroxide and water mixed solution at the room temperature for 270-300 s, and then the silicon wafer is washed with high-purity water for 270-300 s; the washed silicon wafer is put into an ozone and hydrochloric acid mixed cleaning tank to be washed for 270-300 s, and then rapid high-purity water secondary washing is carried out for 270-300 s; the silicon wafer subjected to secondary flushing is cleaned for 270-300 s by adopting a nitric acid solution under the room temperature condition, and then rapid high-purity water third-time flushing is carried out for 270-300 s; and drying the silicon wafer which is washed for the third time, and packaging to obtain a final silicon wafer product. The technical problem that precious metal is difficult to remove in the silicon wafer cleaning process in the prior art can be at least solved.

Description

Technical Field

[0001] The present application relates to the technical field of silicon wafer cleaning, and in particular to a cleaning method and system for improving the metal level on the surface of a silicon wafer. Background Art

[0002] Semiconductor silicon wafers are essential semiconductor materials in the fields of automobiles, mobile phones, PCs, etc. As the semiconductor industry's requirements for silicon substrates become increasingly stringent, in order to ensure the high performance, high stability and high quality of the final components, the final silicon substrate surface needs to have extremely high cleanliness.

[0003] However, the inventors have found that there are at least the following technical problems in the related art: the traditional RCA cleaning method uses SC1 cleaning solution + SC2 cleaning solution or DHF combined with ultrasonic cleaning process, and HF cleaning removes the natural oxide film on the surface, so the metal attached to the natural oxide film is dissolved in the cleaning solution again, and DHF cleaning can inhibit the formation of the natural oxide film. Therefore, it is easy to remove metals such as Al, Fe, Zn, Ni on the surface, but as the natural oxide film dissolves into the cleaning solution, a part of precious metals such as Cu (with a higher redox potential than hydrogen) will adhere to the silicon surface, making it difficult to remove, so it is difficult to remove metals such as Cu by DHF cleaning. At the same time, since the oxide film on the surface of the silicon wafer is removed, the surface will become hydrophobic, and the hydrophobic silicon wafer surface is easy to adsorb metals again, resulting in a situation where the metal still has an increase in pollution after DHF, and it is necessary to improve this deterioration.

[0004] Therefore, there is an urgent need for a semiconductor silicon wafer cleaning method and corresponding device that can improve the levels of metals such as Cu and Ca and reduce subsequent adsorption contamination. Summary of the invention

[0005] One purpose of the present application is to provide a cleaning method and system for improving the metal level on the surface of silicon wafers, at least to solve the technical problem of the prior art that it is difficult to remove precious metals during the silicon wafer cleaning process.

[0006] To achieve the above objectives, some embodiments of the present application provide the following aspects:

[0007] In a first aspect, some embodiments of the present application provide a cleaning method for improving the metal level on the surface of a silicon wafer, comprising the following steps:

[0008] Grinding the silicon wafer, washing the ground silicon wafer with deionized water, washing the treated silicon wafer with a mixed solution of DHF, ammonia, hydrogen peroxide and water at room temperature for 270-300 seconds, and then washing with high-purity water for 270-300 seconds, wherein the pH value of the mixed solution is greater than 9;

[0009] The washed silicon wafer is placed in a mixed cleaning tank of ozone and hydrochloric acid for cleaning for 270-300 seconds, followed by a rapid secondary cleaning with high-purity water for 270-300 seconds, wherein the pH value of the mixed ozone and hydrochloric acid is less than 1;

[0010] The silicon wafer after the secondary washing is cleaned with nitric acid solution at room temperature for 270-300 seconds, and then quickly rinsed with high-purity water three times for 270-300 seconds;

[0011] The silicon wafers after three rinses are dried and packaged to obtain the final silicon wafer products.

[0012] In a second aspect, some embodiments of the present application further provide a cleaning system for improving the metal level on the surface of a silicon wafer, comprising: a first cleaning unit, a second cleaning unit, a third cleaning unit, and a packaging unit;

[0013] The first cleaning unit is used to grind the silicon wafer, wash the ground silicon wafer with deionized water, wash the processed silicon wafer with a mixed solution of DHF, ammonia, hydrogen peroxide and water at room temperature, and rinse with high-purity water;

[0014] The second cleaning unit is used to place the rinsed silicon wafer into a mixed cleaning tank of ozone and hydrochloric acid for cleaning, and perform a rapid secondary rinse with high-purity water;

[0015] The third cleaning unit is used to clean the silicon wafer after the second cleaning with a nitric acid solution at room temperature, and then perform three rapid cleanings with high-purity water;

[0016] The packaging unit is used to dry the silicon wafers after three rinses, and obtain the final silicon wafer products after packaging.

[0017] Compared with the related art, in the solution provided by the embodiment of the present application:

[0018] The present invention uses an SC-1+DHF cleaning process, adds a hydrophilic surfactant or a water-soluble metal chelating agent to DHF, and under the action of the surfactant or the hydrophilic chelating agent, increases the removal ability of metals such as Cu, and adds an HCL+O3 process to improve the hydrophilicity of the silicon wafer surface and reduce metal adsorption pollution. In the final rinsing, an HNO3 solution is used to reduce Ca surface pollution, thereby improving the metal level overall, and obtaining the best process conditions for removing metals by adjusting the concentration and the process steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] One or more embodiments are exemplarily described by pictures in the corresponding drawings, and these exemplified descriptions do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings represent similar elements, and unless otherwise stated, the figures in the drawings do not constitute proportional limitations.

[0020] Figure 1 A schematic flow chart of a cleaning method for improving the metal level on the surface of a silicon wafer according to the first embodiment of the present application;

[0021] Figure 2 This is a schematic diagram of the structure of a cleaning system for improving the metal level on the surface of a silicon wafer according to the third embodiment of the present application. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0023] First embodiment

[0024] The first embodiment of the present application relates to a cleaning method for improving the metal level on the surface of a silicon wafer. Figure 1 As shown, the method may include the following steps:

[0025] S101, grinding the silicon wafer, washing the ground silicon wafer with deionized water, washing the treated silicon wafer with a mixed solution of DHF (Diluted Hydrofluoric Acid, dilute hydrofluoric acid), ammonia water, hydrogen peroxide and water for 270-300 seconds at room temperature, and then washing with high-purity water for 270-300 seconds, wherein the pH value of the mixed solution is greater than 9;

[0026] S102, placing the rinsed silicon wafer in a mixed ozone and hydrochloric acid cleaning tank for cleaning for 270-300 seconds, followed by a rapid secondary high-purity water rinse for 270-300 seconds, wherein the pH value of the mixed ozone and hydrochloric acid is less than 1;

[0027] S103, washing the silicon wafer after the secondary washing with a nitric acid solution at room temperature for 270-300 seconds, and then rapidly washing it with high-purity water three times for 270-300 seconds;

[0028] S104, drying the silicon wafer after three rinses, and obtaining the final silicon wafer product after packaging.

[0029] In this embodiment, since room temperature is used and the solution is not heated during the cleaning process, the amount of hydrogen peroxide volatilized during the cleaning process can be reduced, so that after a cleaning operation on the silicon wafer, only a small amount of hydrogen peroxide needs to be supplemented to meet the cleaning requirements. That is to say, compared with the existing process, the amount of hydrogen peroxide supplemented can be reduced by about 60%, which greatly saves the amount of hydrogen peroxide used and saves costs.

[0030] It is not difficult to find that, compared with the related art, in the solution provided by the embodiment of the present application:

[0031] The silicon wafer cleaning process is an indispensable process in the silicon wafer production process. In the traditional mature RCA cleaning process technology, the cleaning device used is mostly a multi-tank immersion cleaning system, and the cleaning process is basically: SC1 cleaning liquid-DHF cleaning liquid-SC2 cleaning liquid. The composition of SC1 cleaning liquid is NH4OH, H2O2, H2O. The purpose of SC1 cleaning is mainly to remove particle pollution and organic impurities, and it can also remove some metal ions; although the silicon wafer can remove some metals after SC1 cleaning liquid, the adhesion of the natural oxide film on the surface of the silicon wafer, especially the Al oxide film problem has not been solved, so it is necessary to use DHF cleaning liquid for cleaning. DHF cleaning liquid is composed of HF (Hydrofluoric Acid, hydrofluoric acid) and H2O. DHF cleaning can corrode the natural oxide film generated on the surface when using SC1 cleaning, while the silicon wafer itself is almost not corroded. However, in the acidic solution, the surface of the silicon wafer is negatively charged, and the surface of the particles is positively charged. There is an attraction between the two, and the impurity metal particles are easy to adhere to the surface of the wafer, so SC2 cleaning liquid is needed for cleaning. SC2 cleaning solution is composed of HCl, H2O2, H2O. SC2 cleaning solution is an acidic solution with strong ability to remove metal from the surface of the wafer. Therefore, in the RCA cleaning process, the cleaning sequence is usually: SC1-DHF-SC2, that is, according to the characteristics and main functions of various cleaning solutions, first remove organic matter and particle contamination on the surface of the silicon wafer, then remove the oxide film, and finally remove the metal ions.

[0032] Therefore, the traditional RCA cleaning method adopts SC1 cleaning solution + SC2 cleaning solution or DHF combined with ultrasonic cleaning process. HF cleaning removes the natural oxide film on the surface, so the metal attached to the natural oxide film is dissolved in the cleaning solution again, and DHF cleaning can inhibit the formation of the natural oxide film. Therefore, metals such as Al, Fe, Zn, Ni on the surface can be easily removed. However, as the natural oxide film dissolves into the cleaning solution, a part of precious metals such as Cu (with a higher redox potential than hydrogen) will adhere to the silicon surface, making it difficult to remove. Therefore, it is difficult to remove metals such as Cu by DHF cleaning. At the same time, since the oxide film on the surface of the silicon wafer is removed, the surface will be hydrophobic, and the hydrophobic silicon wafer surface is easy to adsorb metals again, resulting in a situation where metal pollution still increases after DHF, and this deterioration needs to be improved.

[0033] The method of the present invention enhances the effect of removing metals such as Cu by adding an appropriate amount of H2O2 to the existing DHF demetallization process, and adds an HCL+O3 process to improve the hydrophilicity of the silicon wafer surface and reduce metal adsorption pollution. In the final rinse, an HNO3 solution is used to reduce Ca surface pollution, thereby improving the overall metal level. By adjusting the concentration and the process steps, the optimal process conditions for removing metals are obtained.

[0034] In this embodiment, since room temperature is used and the solution is not heated during the cleaning process, the amount of hydrogen peroxide volatilized during the cleaning process can be reduced, so that after a cleaning operation on the silicon wafer, only a small amount of hydrogen peroxide needs to be supplemented to meet the cleaning requirements. That is to say, compared with the existing process, the amount of hydrogen peroxide supplemented can be reduced by about 60%, which greatly saves the amount of hydrogen peroxide used and saves costs.

[0035] Second embodiment

[0036] The second embodiment of the present application relates to a cleaning method for improving the metal level on the surface of a silicon wafer. The second embodiment is an improvement made on the basis of the first embodiment, and the specific improvements are:

[0037] Furthermore, in this embodiment, the volume ratio of DHF to hydrogen peroxide is 1:20; the ratio of nitric acid solution is HNO3:water=1:15.

[0038] Furthermore, in this embodiment, the volume ratio of hydrochloric acid to ozone is HCL:water=1:30, and the ozone concentration is 5 ppm.

[0039] Furthermore, in this embodiment, the process of drying the silicon wafer after three rinses and packaging to obtain the final silicon wafer product is as follows:

[0040] The silicon wafers after three rinses are dried with IPA Marangon i; the dried silicon wafers are packaged in inner packaging bags, and nitrogen is filled in the inner packaging bags; the outer packaging bags are packaged outside the inner packaging bags again, and the space between the inner and outer packaging bags is vacuumed to obtain the final silicon wafer products.

[0041] Furthermore, in this embodiment, the temperature of the high-purity water is 20-25°C.

[0042] Furthermore, in this embodiment, during the drying process of IPA Marangon i, the pulling speed is 0.5-2 mm / sec, the flow rate of hot nitrogen is 100-200 L / min, and the drying time is 100-200 s.

[0043] Further, in this embodiment, the process of placing the rinsed silicon wafer into a mixed ozone and hydrochloric acid cleaning tank for cleaning for 270-300 seconds is as follows:

[0044] The method of rapid drainage after soaking and spraying at the same time is adopted: the cleaned silicon wafer is placed in the ozone water cleaning tank in a vertical state and soaked for 270-300s, and then the rapid drainage valve at the bottom of the tank is opened for rapid drainage, and the two nozzles above the cleaning tank are opened while draining, and the nozzles on the nozzles spray both sides of the silicon wafer evenly at the same time.

[0045] Furthermore, in this embodiment, the water spraying pressure of each nozzle is 0.01-0.1 MPa, the flow rate is 0.5-1 L / min, the interval between the silicon wafer and the nozzle is 5-10 cm, and the spraying time is 30-60 s.

[0046] The step division of the above methods is only for the purpose of clear description. When implemented, they can be combined into one step or some steps can be split and decomposed into multiple steps. As long as they include the same logical relationship, they are all within the scope of protection of this patent; adding insignificant modifications to the algorithm or process or introducing insignificant designs without changing the core design of the algorithm and process are all within the scope of protection of this patent.

[0047] Third embodiment

[0048] like Figure 2 As shown, the third embodiment of the present application relates to a cleaning system for improving the metal level on the surface of a silicon wafer, comprising: a first cleaning unit 1, a second cleaning unit 2, a third cleaning unit 3 and a packaging unit 4;

[0049] The first cleaning unit 1 is used to grind the silicon wafer, wash the ground silicon wafer with deionized water, wash the processed silicon wafer with a mixed solution of DHF, ammonia, hydrogen peroxide and water at room temperature, and rinse with high-purity water;

[0050] The second cleaning unit 2 is used to put the rinsed silicon wafer into a mixed cleaning tank of ozone and hydrochloric acid for cleaning, and then perform a rapid secondary rinse with high-purity water;

[0051] The third cleaning unit 3 is used to clean the silicon wafer after the secondary cleaning with a nitric acid solution at room temperature, and then perform three rapid high-purity water cleanings;

[0052] The packaging unit 4 is used to dry the silicon wafers after three rinses and obtain the final silicon wafer products after packaging.

[0053] It is not difficult to find that this embodiment is a system embodiment corresponding to the first embodiment, and this embodiment can be implemented in conjunction with the first embodiment. The relevant technical details mentioned in the first embodiment are still valid in this embodiment, and in order to reduce repetition, they are not repeated here. Accordingly, the relevant technical details mentioned in this embodiment can also be applied in the first embodiment.

[0054] It is worth mentioning that all modules involved in this embodiment are logic modules. In practical applications, a logic unit can be a physical unit, a part of a physical unit, or a combination of multiple physical units. In addition, in order to highlight the innovative part of this application, this embodiment does not introduce units that are not closely related to solving the technical problems proposed by this application, but this does not mean that there are no other units in this embodiment.

[0055] Experimental comparison

[0056] This embodiment conducts metal level verification experiments through different DOE process adjustment experiments to verify the beneficial effects of the present invention. The same batch of silicon wafers are used to conduct experiments under different experimental conditions. Silicon wafers are sampled before and after cleaning for metal determination to confirm the metal level.

[0057] The cleaning machine used in this embodiment has a total of 8 tanks, namely, 1 pure water tank, 2 SC-1 tanks, 3 pure water tanks, 4 DHF tanks, 5 pure water tanks, 6 HCL+O3 tanks, 7 pure water tanks, 8 HNO3 tanks, and 9 pure water tanks, ensuring the consistency of conditions in the comparative experiment; the tank positions and process conditions of the cleaning machine are shown in Figure 1, through adjusting the process parameters such as process time, DHF+H2O2 ratio, HCL+O3 ratio, HNO3 solution ratio and so on, DOE experiment was designed for experimental verification, the particle data was measured by SP1 particle measuring machine, and the particle data was analyzed to obtain the experimental results. The experimental results are as follows: through batch comparison experiments, it can be concluded that the cleaning time is 270s, the DHF+H2O2 ratio is 1:20, the HCL+O3 ratio is HCL: water = 1:30, the introduced O3 concentration is 5ppm, and the HNO3 solution ratio is 1:15. The cleaning effect is the best, and the metal level has an improvement effect of about 50%. The contents of Na, Mg, Al, K, Ca, Cr, Fe, Ni, Cu, and Zn are less than 0.5E9Atoms / cm, and the metal improvement effect is good. The specific cleaning time and temperature obtained from the experiment are shown in Table 1.

[0058] Table 1 Cleaning time and temperature of each step in this embodiment

[0059] step time temperature Pure water cleaning 270s-300s 20℃ SC-1 solution cleaning 270s-300s 70℃ Pure water cleaning 270s-300s 20℃ <![CDATA[Cleaning with hydrofluoric acid + H202 solution]]> 270s-300s 20℃ Pure water cleaning 270s-300s 20℃ <![CDATA[HCL + O3 cleaning]]> 270s-300s 20℃ Pure water cleaning 270s-300s 20℃ <![CDATA[Cleaning with HNO3 solution]]> 270s-300s 20℃ Pure water cleaning 270s-300s 20℃

[0060] From the above experiments, it can be known that the SC-1+DHF cleaning process adopted by the present invention adds a hydrophilic surfactant or a water-soluble metal chelating agent to DHF. Under the action of the surfactant or the hydrophilic chelating agent, after DHF cleaning, the surface of the silicon wafer is still hydrophilic, and metal adsorption pollution no longer recurs. Therefore, it is necessary to improve the DHF process to increase the removal ability of metals such as Cu, add the HCL+O3 process, improve the hydrophilicity of the silicon wafer surface, reduce metal adsorption pollution, and use HNO3 solution in the final rinse to reduce Ca surface contamination, thereby improving the metal level overall, and obtaining the best process conditions for removing metals by adjusting the concentration and the process steps.

[0061] The flow chart or block diagram in the accompanying drawings shows the possible architecture, function and operation of the equipment, method and computer program product according to various embodiments of the present application. In this regard, each box in the flow chart or block diagram can represent a module, a program segment or a part of a code, and the module, the program segment or a part of the code contains one or more executable instructions for realizing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in a different order from the order marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram and / or flow chart, and the combination of the boxes in the block diagram and / or flow chart can be implemented with a dedicated system for hardware that performs a specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions.

[0062] The scope of the present application is defined by the appended claims rather than the above description, and it is intended that all changes that fall within the meaning and scope of the equivalent elements of the claims are included in the present application. Any figure mark in the claims should not be regarded as limiting the claims involved. In addition, it is clear that the word "comprising" does not exclude other units or steps, and the singular does not exclude the plural. Multiple units or devices stated in the device claim may also be implemented by one unit or device through software or hardware. The words "first", "second", etc. are only used to distinguish the description, and do not indicate any particular order, nor can they be understood as indicating or implying relative importance.

[0063] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily mention changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims, and the above embodiments should be regarded as exemplary and non-restrictive.

Claims

1. A cleaning method for improving the metal level on the surface of a silicon wafer, characterized in that: The following steps are involved: Grinding the silicon wafer, washing the ground silicon wafer with deionized water, washing the treated silicon wafer with a mixed solution of DHF, ammonia, hydrogen peroxide and water at room temperature for 270-300 seconds, and then washing with high-purity water for 270-300 seconds, wherein the pH value of the mixed solution is greater than 9; The washed silicon wafer is placed in a mixed ozone and hydrochloric acid cleaning tank for 270-300 seconds, followed by a rapid secondary high-purity water rinse for 270-300 seconds, wherein the pH value of the mixed ozone and hydrochloric acid is less than 1; The silicon wafer after the secondary washing is cleaned with nitric acid solution at room temperature for 270-300 seconds, and then quickly rinsed with high-purity water three times for 270-300 seconds; The silicon wafers after three rinses are dried and packaged to obtain the final silicon wafer products.

2. The cleaning method for improving the metal level on the surface of a silicon wafer according to claim 1, characterized in that: The volume ratio of DHF to hydrogen peroxide is 1:20; the ratio of nitric acid solution is HNO3:water=1:

15.

3. The cleaning method for improving the metal level on the surface of a silicon wafer according to claim 1, characterized in that: The volume ratio of the hydrochloric acid to ozone is HCL:water=1:30, and the ozone concentration is 5 ppm.

4. The cleaning method for improving the metal level on the surface of a silicon wafer according to claim 1, characterized in that: The process of drying the silicon wafer after three rinses and packaging to obtain the final silicon wafer product is as follows: The silicon wafers after three rinses are dried with IPA Marangon i; the dried silicon wafers are packaged in inner packaging bags, and nitrogen is filled in the inner packaging bags; the outer packaging bags are packaged outside the inner packaging bags again, and the space between the inner and outer packaging bags is vacuumed to obtain the final silicon wafer products.

5. The cleaning method for improving the metal level on the surface of a silicon wafer according to claim 1, characterized in that: The temperature of the high-purity water is 20-25°C.

6. The cleaning method for improving the metal level on the surface of a silicon wafer according to claim 5, characterized in that: During the IPA Marangon i drying process, the pulling speed is 0.5-2 mm / sec, the flow rate of hot nitrogen is 100-200 L / min, and the drying time is 100-200 s.

7. The cleaning method for improving the metal level on the surface of a silicon wafer according to claim 1, characterized in that: in, The process of placing the rinsed silicon wafer into a mixed ozone and hydrochloric acid cleaning tank for cleaning for 270-300 seconds is as follows: The method of rapid drainage after soaking and spraying at the same time is adopted: the cleaned silicon wafer is placed in the ozone water cleaning tank in a vertical state and soaked for 270-300s, and then the rapid drainage valve at the bottom of the tank is opened for rapid drainage, and the two nozzles above the cleaning tank are opened while draining, and the nozzles on the nozzles spray both sides of the silicon wafer evenly at the same time.

8. The cleaning method for improving the metal level on the surface of a silicon wafer according to claim 7, characterized in that: in, The water spraying pressure of each nozzle is 0.01-0.1 MPa, the flow rate is 0.5-1 L / min, the distance between the silicon wafer and the nozzle is 5-10 cm, and the spraying time is 30-60 s.

9. A cleaning system for improving the metal level on the surface of a silicon wafer, used for implementing the cleaning method for improving the metal level on the surface of a silicon wafer as claimed in any one of claims 1 to 8, characterized in that: include: A first cleaning unit (1), a second cleaning unit (2), a third cleaning unit (3) and a packaging unit (4); The first cleaning unit (1) is used to grind the silicon wafer, wash the ground silicon wafer with deionized water, wash the processed silicon wafer with a mixed solution of DHF, ammonia, hydrogen peroxide and water at room temperature, and rinse with high-purity water; The second cleaning unit (2) is used to place the rinsed silicon wafer into a mixed cleaning tank of ozone and hydrochloric acid for cleaning, and then perform a rapid secondary rinse with high-purity water; The third cleaning unit (3) is used to clean the silicon wafer after the second cleaning with a nitric acid solution at room temperature, and then perform three rapid cleanings with high-purity water; The packaging unit (4) is used to dry the silicon wafers after three rinses, and obtain the final silicon wafer products after packaging.

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