Wafer, wafer cleaning method, and cleaning system

Abstract

The application discloses a wafer, a wafer cleaning method and a wafer cleaning system, and relates to the technical field of semiconductors. High-purity oxygen is introduced into a cleaning device, the wafer cleaning system is used for the synergic adjustment of the wavelength and intensity of ultraviolet light, the concentration of ozone generated in the cleaning device is strictly controlled, and the wafer is prevented from being subjected to adverse effects such as overoxidation and thermal damage. The permeability of micro-bubbles is used to realize efficient cleaning of deep holes of the wafer, and the effect of uniform cleaning of the whole wafer is realized. The cleaning method has the characteristics of low input cost, high cleaning efficiency and environmental protection in the cleaning process, and has promotion.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more specifically, to wafers, wafer cleaning methods, and cleaning systems. Background Technology

[0002] The cleanliness of the wafer surface directly affects the electrical performance and yield of devices, making wafer cleaning a critical step in semiconductor manufacturing. Currently, cleaning technology still relies on wet chemical processes, such as RCA cleaning.

[0003] The wet chemical process removes organic residues using an ammonia-hydrogen peroxide mixture (SC1), removes metallic impurities using a hydrochloric acid-hydrogen peroxide mixture (SC2), and uses hydrofluoric acid solution to strip the oxide layer, forming a complete cleaning process. However, it has the following drawbacks: strong acid / alkali solutions can easily damage the metal interconnect layers, posing a risk of material corrosion; the waste liquid contains fluorides and heavy metals, resulting in high treatment costs and environmental pollution; the high aspect ratio structure of the wafer (>10:1) makes it difficult for the cleaning solution to effectively wet the bottom of the holes, resulting in organic residues at the bottom.

[0004] Ozone cleaning technology has attracted attention due to its strong oxidizing properties and the non-polluting nature of its decomposition products. However, the micron-sized bubbles (>10μm) generated by traditional bubbling ozone generators are limited by the size effect and cannot enter the submicron deep pores of the wafer, thus limiting the cleaning effect to the surface.

[0005] Therefore, developing a cleaning technology that can penetrate deep into the micro-nano structure of wafers and has both material compatibility and environmental friendliness is a technical challenge that urgently needs to be solved.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide wafers, wafer cleaning methods, and wafer cleaning systems to solve or improve the aforementioned technical problems.

[0008] This invention is implemented as follows: In a first aspect, the present invention provides a wafer cleaning method, comprising the following steps: The loaded wafers are placed in a cleaning device, and oxygen is introduced into the cleaning device. The applied wavelength is 170nm-200nm and the intensity is 20mW / cm. 2 -100mW / cm 2 Ozone is produced by photolyzing introduced oxygen under ultraviolet light. The gas at the top of the cleaning equipment is introduced into a bubble generator for processing to produce microbubbles with an average particle size of 100nm-500nm. Microbubbles are mixed with cleaning reagents and then sprayed onto the wafer surface through a spraying device to clean the wafer.

[0009] In an optional embodiment, the wafer cleaning process has at least one of the following characteristics: Feature 1: The purity of oxygen is ≥99.9%, the oxygen flow rate is 10SLM-20SLM, and the oxygen introduction time is 0.5min-1.5min. Feature 2: The ozone concentration inside the cleaning equipment is 50ppm-200ppm; Feature 3: The wafer rotates at a speed of 10rpm-50rpm.

[0010] In an optional embodiment, the wafer is mounted on the surface of a rotating tray by vacuum adsorption, with a vacuum level ≤10. -3 Pa; And / or, microbubbles are sprayed onto the wafer surface at a flow rate of 1.0 L / min to 5.0 L / min for cleaning.

[0011] In an optional embodiment, the cleaning agent is selected from at least one of deionized water, ultrapure water, and distilled water; And / or, the bubble generator is selected from at least one of a venturi tube and a microporous membrane plate; the bubble generator is assisted by ultrasonic cavitation technology, and the ultrasonic frequency for preparing microbubbles is 0.8MHz-1.2MHz, and the ultrasonic power density is 5W / cm³. 2 -15W / cm 2 Ultrasonic treatment time: 2-5 seconds; And / or, the aspect ratio of the wafer deep via is ≥30:1.

[0012] In an optional embodiment, the wafer cleaning method further includes post-processing; the post-processing includes drying the wafer after cleaning. During the drying process, the tray rotates at a speed of 80rpm-110rpm and is sprayed with high-purity nitrogen at a speed of 45L / min-55L / min for 50s-80s. And / or, the total time for wafer cleaning is 8 min / batch - 12 min / batch.

[0013] Secondly, the present invention provides a wafer prepared by cleaning it using the wafer cleaning method described in any of the foregoing embodiments.

[0014] In an optional implementation, the particle density on the wafer surface is ≤3.5×10⁻⁶. 10 atoms / cm 2 ; Based on the particle density on the wafer surface, the cleaning rate of particles at the wafer edge is ≥99.3%, and the cleaning rate of particles at the wafer center is ≥85.7%.

[0015] Thirdly, the present invention provides a wafer cleaning system for implementing the wafer cleaning method as described in any of the foregoing embodiments; The wafer cleaning system includes cleaning equipment, trays, ultraviolet generators, bubble generators, spray devices, and sensors; The cleaning equipment is equipped with an oxygen delivery port; The tray is used to hold wafers and is placed in the cleaning equipment during cleaning; the center of the tray has a through hole for the spray device to pass through; The ultraviolet generator is located directly above the cleaning equipment; The sensor is used to monitor the ozone concentration inside the cleaning equipment in real time.

[0016] In an optional implementation, the bubble generator inlet is higher than the cleaning reagent liquid level, and the bubble generator outlet is immersed in the cleaning reagent; And / or, the inlet of the spray device is immersed in the cleaning reagent, and the outlet of the spray device is above the upper surface of the tray.

[0017] In an optional embodiment, a nozzle is detachably installed at the outlet of the spray device; The nozzle has at least two rings of nozzles on its orifice surface, and the multiple rings of nozzles are arranged in a concentric ring from the inside to the outside along the radial direction.

[0018] The present invention has the following beneficial effects: The wafer cleaning method provided in this invention introduces high-purity oxygen into the cleaning equipment and utilizes the synergistic adjustment of ultraviolet light wavelength and intensity by the wafer cleaning system to strictly control the ozone concentration generated within the cleaning equipment, thus avoiding adverse effects such as peroxidation and thermal damage to the wafer. It leverages the permeability of microbubbles to achieve deep and efficient cleaning of deep holes in the wafer, resulting in uniform cleaning across the entire wafer surface. This cleaning method is characterized by low investment cost, high cleaning efficiency, and environmentally friendly process, making it widely applicable. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the cleaning system. Figure 2This is a schematic diagram of particulate matter detection on the wafer surface before wafer cleaning in Example 1; Figure 3 This is a schematic diagram of particulate matter detection on the wafer surface after wafer cleaning in Example 1; Figure 4 This is a schematic diagram of particulate matter detection on the wafer surface before wafer cleaning, as shown in Comparative Example 1. Figure 5 This is a schematic diagram of particulate matter detection on the wafer surface after wafer cleaning, as shown in Comparative Example 1.

[0021] Figure reference numerals: 10-UV generator; 12-Wafer; 14-Tray; 16-Bubble generator; 17-Cleaning reagent surface; 18-Cleaning reagent; 20-Spraying device. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0023] In a first aspect, the present invention provides a wafer 12 cleaning method, comprising the following steps: The loaded wafer 12 was placed in the cleaning equipment, and oxygen was introduced into the cleaning equipment. The applied wavelength is 170nm-200nm and the intensity is 20mW / cm. 2 -100mW / cm 2 Ozone is produced by photolyzing introduced oxygen under ultraviolet light. The gas at the top of the cleaning equipment is introduced into the bubble generator 16 for processing to obtain microbubbles with an average particle size of 100nm-500nm. After the microbubbles are mixed with the cleaning reagent 18, they are sprayed onto the surface of the wafer 12 through the spraying device 20 to clean the wafer 12.

[0024] It should be noted that the present invention introduces high-purity oxygen, which serves as a raw material for ozone synthesis. The high purity of the oxygen ensures the yield and concentration of ozone. The oxygen introduction is carried out under normal pressure conditions.

[0025] A specific wavelength of ultraviolet light is used to directly photolyze O2 to generate high-concentration ozone (O3), achieving a direct and efficient conversion of oxygen to ozone. This activates ozone / water molecules to produce highly reactive free radicals (·OH), enhancing the oxidation capacity of wafer 12 and imparting an interfacial photocatalytic effect to the microbubbles, thereby strengthening the cleaning intensity within the deep pores of wafer 12. The relevant reaction equations are as follows: O2 + hν (specific wavelength) → 2O; O· + O2 → O3.

[0026] If the wavelength is too long, ozone will decompose under the action of ultraviolet light. The relevant reaction equation is as follows: O3 + hν (specific wavelength) → O· + O2.

[0027] Ozone concentration is monitored in real time by sensors, and the oxygen supply is adjusted accordingly to control ozone concentration and prevent excessive oxidation damage to wafer 12. The ultraviolet lamps are located directly above tray 14 and arranged in an array. In other embodiments of the invention, the layout of the ultraviolet lamps is adjusted according to actual needs.

[0028] Bubble generator 16 is assisted by ultrasonic cavitation technology. The two work together to break ozone gas into particles with an average size of 100nm-500nm and a density >10. 8 The microbubbles, with a density of 1 microbubbles per mL and a negative surface charge (Zeta potential ≤ -30 mV), prevent aggregation and enhance permeability within the 12 deep pores of the wafer. The microbubbles generate a microjet effect within the deep pores due to the curvature of the gas-liquid interface. Utilizing the centrifugal force of the rotating tray 14, the microbubbles penetrate deep into the 12 deep pores of the wafer. The hydroxyl radicals (·OH) released upon the bursting of the microbubbles within the deep pores promote the oxidative decomposition of organic residues (such as photosensitive adhesive and carbides) within the 12 deep pores, thereby achieving highly efficient cleaning of the 12 deep pores of the wafer.

[0029] The average particle size of the microbubbles was measured using a Malvern Zetasizer Nano ZS particle size analyzer. This analyzer works by irradiating the suspension with a laser and analyzing the scattered light fluctuations caused by the Brownian motion of the microbubbles to invert the particle size distribution. The density of the microbubbles was measured using a confocal microscope. Specifically, 0.001% Nile Red fluorescent dye was added to stain only the microbubble interfaces to count the number of microbubbles in each region.

[0030] It should be noted that the microbubbles are mainly ozone microbubbles, mixed with a small amount of oxygen microbubbles, but this will not affect the depth cleaning and cleaning effect of ozone on the 12 deep holes of the wafer.

[0031] In other embodiments of the present invention, other suitable testing methods can be selected to test the average particle size and density of microbubbles according to actual needs.

[0032] Furthermore, the wavelength of ultraviolet light is 175nm-190nm, and even further, 185nm. If the wavelength is too short, the cleaning effect is poor; if the wavelength is too long, the ozone yield decreases, and it may even cause decomposition. Long wavelengths promote the generation of hydroxyl radicals, at which point only residual ozone can be utilized, resulting in a decrease in cleaning effect and low oxygen absorption rate. The allowable fluctuation range of wavelength is ±2nm. When the wavelength is >190nm, the cleaning effect decreases significantly.

[0033] Furthermore, the intensity of the ultraviolet light is 40 mW / cm². 2 -80mW / cm 2 Furthermore, the strength is 60 mW / cm. 2 Increased ultraviolet light intensity leads to increased ozone concentration and reduced particulate matter on the wafer 12 surface. However, excessively high intensity can raise the temperature of the elemental wafer 12, inducing thermal damage and affecting the density of microbubbles generated by the bubble generator 16, thus prolonging the cleaning time. The permissible fluctuation range for intensity is 50 mW / cm². 2 -70mW / cm 2 If the strength is >100mW / cm 2 It can induce fever and injury.

[0034] In an optional embodiment, the wafer 12 cleaning process has at least one of the following characteristics: Feature 1: The purity of oxygen is ≥99.9%, the oxygen flow rate is 10SLM-20SLM, and the oxygen introduction time is 0.5min-1.5min; SLM represents the volumetric flow rate of oxygen under standard conditions, with the unit being L / min. Feature 2: The ozone concentration inside the cleaning equipment is 50ppm-200ppm; Feature 3: Wafer 12 rotates at a speed of 10 rpm to 50 rpm. If the speed of wafer 12 is greater than 50 rpm, the microbubbles will not be fully immersed in the deep holes of wafer 12, thus causing the microbubbles to detach from the surface of wafer 12.

[0035] In an optional embodiment, wafer 12 is mounted on the surface of rotating tray 14 by vacuum adsorption, with a vacuum level ≤10. -3 Pa; Vacuum adsorption is used to fix the wafer 12 on the surface of the rotating tray 14, which helps to avoid mechanical damage to the wafer 12. The rotating tray 14 is located above the cleaning reagent liquid surface 17, and a vacuum device is provided on the opposite side of the rotating tray 14 for vacuum adsorption of the wafer 12.

[0036] In an optional embodiment, the tray 14 has a convex shape with a higher center and lower edges. The wafers 12 are uniformly and arrayedly adsorbed on the concave outer surface of the tray 14, and the vacuum device is located on the inner surface of the tray 14. During the cleaning process, the jets sprayed from the spray device 20 uniformly cover the upper surface of the wafers 12 to form a liquid film, while the tray 14 rotates at a certain speed to achieve cleaning of the wafers 12.

[0037] It should be noted that the jetting stream penetrates into the 12 deep holes of the wafer, and after the 12 deep holes of the wafer break, local high pressure is generated, forming a micro-jet inside the deep holes, which promotes the complete decomposition of carbon-based residues by ·OH free radicals, significantly improving the cleaning effect.

[0038] In an optional embodiment, microbubbles are sprayed onto the surface of wafer 12 at a flow rate of 1.0 L / min to 5.0 L / min for cleaning.

[0039] Furthermore, the flow rate of the microbubbles is 2.0 L / min to 3.0 L / min; if the flow rate of the microbubbles is too high, it will cause the jets to splash after being ejected, which will disrupt the uniformity of the liquid film on the surface of wafer 12.

[0040] In an optional embodiment, the cleaning reagent 18 is selected from at least one of deionized water, ultrapure water, and distilled water; since the cleaning reagent 18 is water and no chemical reagents are introduced, the cost is significantly reduced. For example, taking a 12-inch wafer as an example, the cost of chemical reagents for traditional RCA cleaning is 12.8 yuan per wafer, and the waste liquid contains HF / NH4. + Chemical ions require additional investment to process later; the wafer 12 cleaning method of this invention only requires the investment of water and electricity, with a cost of 0.9 yuan per wafer, zero chemical emissions, and no environmental pollutants generated during the entire cleaning process, making it more environmentally friendly and compliant with ISO 14064 standards.

[0041] And / or, the bubble generator 16 is selected from at least one of a venturi tube and a microporous membrane plate; the bubble generator 16 is assisted by ultrasonic cavitation technology, and the ultrasonic frequency for preparing microbubbles is 0.8MHz-1.2MHz, and the ultrasonic power density is 5W / cm³. 2 -15W / cm 2 Ultrasonic treatment time: 2-5 seconds; And / or, the aspect ratio of 12 deep holes on the wafer is ≥30:1.

[0042] It should be noted that the smaller the aspect ratio of the wafer 12, the easier it is to clean. For wafer 12 with a large aspect ratio, the micron-sized bubbles (>10μm) generated by traditional bubble ozone generators are limited by the size effect and cannot enter the submicron deep holes of the wafer 12, thus limiting the cleaning effect to the surface.

[0043] The present invention generates ozone in the cleaning equipment and generates microbubbles using a bubble generator 16. The microbubbles and cleaning reagent 18 are guided and sprayed together onto the surface of the wafer 12 to form a liquid film, thereby cleaning the wafer 12.

[0044] In an optional embodiment, the wafer 12 cleaning method further includes post-processing; the post-processing includes drying the wafer 12 after cleaning. During the drying process, tray 14 rotates at a speed of 80rpm-110rpm and is sprayed with high-purity nitrogen gas at a speed of 45L / min-55L / min for 50s-80s.

[0045] And / or, the total cleaning time for wafer 12 is 8 min / batch - 12 min / batch.

[0046] If the cleaning time for wafer 12 is too long, such as >15 minutes, it will lead to over-oxidation of wafer 12; if the cleaning time is too short, the residual substances in the deep holes of wafer 12 will not be thoroughly cleaned.

[0047] In summary, the wafer 12 cleaning method provided by the embodiments of the present invention includes the following steps:

[0048] (1) Wafer 12 loading and oxygenation Wafer 12 is mounted on the surface of rotating tray 14 by vacuum adsorption, and oxygen is introduced into the cleaning equipment; Among them, vacuum degree ≤10 -3 Pa; oxygen purity ≥ 99.9%, oxygen flow rate 10 SLM-20 SLM, oxygen introduction time 0.5 min-1.5 min; aspect ratio of 12 deep holes on the wafer ≥ 30:1.

[0049] (2) Ultraviolet-induced ozone generation The applied wavelength is 170nm-200nm and the intensity is 20mW / cm. 2 -100mW / cm 2 Ultraviolet light is used to photolyze the introduced oxygen to produce ozone; during this process, sensors are used to monitor in real time to ensure that the ozone concentration in the cleaning equipment is between 50ppm and 200ppm.

[0050] (3) In-situ synthesis of microbubbles The gas from the upper part of the cleaning equipment is introduced into the bubble generator 16 for processing to obtain particles with an average size of 100nm-500nm and a density >10. 9 Microbubbles per mL; Among them, the bubble generator 16 is equipped with ultrasonic cavitation technology. The bubble generator 16 uses a venturi tube, and the device that provides ultrasonic cavitation technology is an ultrasonic transducer; its operating frequency is 0.8MHz-1.5MHz.

[0051] (4) Rotary spray deep hole penetration After the microbubbles are mixed with the cleaning reagent 18, they are sprayed onto the surface of the wafer 12 through the spraying device 20 to clean the wafer 12.

[0052] The wafer 12 rotates at a speed of 10rpm-50rpm, and microbubbles are sprayed onto the surface of the wafer 12 at a flow rate of 1.0L / min-5.0L / min for cleaning.

[0053] (5) Post-processing The post-processing involves purging the wafer 12 on the surface of the rotating tray 14 with nitrogen gas; during the drying process, the tray 14 rotates at a speed of 80 rpm to 110 rpm and is sprayed with high-purity nitrogen gas at a speed of 45 L / min to 55 L / min for 50 s to 80 s. The total cleaning time for wafer 12 is 8 min / batch - 12 min / batch.

[0054] Secondly, the present invention provides a wafer 12, which is prepared by cleaning the wafer 12 using any of the aforementioned embodiments.

[0055] In an optional implementation, the particle density on the wafer surface is ≤3.5×10⁻⁶. 10 atoms / cm 2 ; Based on the particle density on the wafer surface, the cleaning rate of particles at the wafer edge is ≥99.3%, and the cleaning rate of particles at the wafer center is ≥85.7%.

[0056] It should be noted that the types of particulate matter on the wafer 12 surface include carbon particles, residual metal particles, silicon dioxide particles, and dust, etc. In this embodiment of the invention, the device for detecting the particulate matter content on the wafer surface is a Candela 8520; in other embodiments of the invention, the detection device is selected reasonably according to actual needs.

[0057] Centrifugal force results in a thinner liquid film, smaller microbubbles, and a higher ozone concentration at the edge, thus increasing oxidation efficiency. Therefore, the cleaning rate at the edge of wafer 12 is greater than that at the center of wafer 12.

[0058] Cleaning rate (%) = N 清洗后 / N 清洗前 ×100%, N 清洗后 This indicates the content of particulate matter on the surface of wafer 12 after cleaning, N. 清洗前 This indicates the content of particulate matter on the surface of wafer 12 before cleaning.

[0059] Wafer surface particle density = N 清洗后 / S 晶圆 N 清洗后 S represents the content of particulate matter on the surface of wafer 12 after cleaning. 晶圆 This represents the wafer area.

[0060] Thirdly, the present invention provides a wafer 12 cleaning system for implementing the wafer 12 cleaning method as described in any of the foregoing embodiments; The wafer 12 cleaning system includes cleaning equipment, tray 14, ultraviolet generator 10, bubble generator 16, spray device 20, and sensors; The cleaning equipment is equipped with an oxygen delivery port; The tray 14 is used to hold the wafer 12 and is placed in the cleaning equipment during cleaning; the center of the tray 14 has a through hole for the spray device 20 to pass through. The ultraviolet generator 10 is located directly above the cleaning equipment; The sensor is used to monitor the ozone concentration inside the cleaning equipment in real time.

[0061] In an optional embodiment, the inlet of the bubble generator 16 is higher than the cleaning reagent liquid level 17, and the outlet of the bubble generator 16 is immersed in the cleaning reagent 18. And / or, the inlet of the spray device 20 is immersed in the cleaning reagent, and the outlet of the spray device 20 is above the upper surface of the tray 14.

[0062] It should be noted that the installation position of the bubble generator 16 is not particularly limited and can be adjusted reasonably as needed, such as being installed in the center of the tray 14 or on the inner wall of the cleaning equipment, as long as the inlet of the bubble generator 16 is controlled above the cleaning reagent liquid surface 17 and the outlet is below the cleaning reagent 18. The microbubbles output by the bubble generator 16 are introduced into the spray device 20 together with the cleaning reagent 18 and sprayed onto the surface of the wafer 12 for cleaning. In this embodiment of the invention, the outlet of the bubble generator 16 is placed near the inlet of the spray device 20 to ensure that the spray stream contains more microbubbles and improve the cleaning rate.

[0063] In an optional embodiment, a nozzle is detachably mounted at the outlet of the spray device 20; The nozzle has at least two rings of nozzles on its orifice surface, and the multiple rings of nozzles are arranged in a concentric ring from the inside to the outside along the radial direction.

[0064] It should be noted that the nozzle diameter should be selected reasonably according to actual needs; the nozzle is set with multiple rings to facilitate the jet to cover the surface of wafer 12 as comprehensively as possible and to penetrate into the deep holes of wafer 12. After the deep holes of wafer 12 break, local high pressure is generated, forming a micro-jet in the deep holes, which promotes the complete decomposition of carbon-based residues by ·OH free radicals, significantly improving the cleaning effect.

[0065] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0066] Example 1 This embodiment provides a wafer 12 cleaning method, taking silicon carbide wafer 12 as an example, which includes the following steps:

[0067] (1) Wafer 12 loading and oxygenation Wafer 12 is mounted on the surface of rotating tray 14 by vacuum adsorption, and oxygen is introduced into the cleaning equipment; Among them, vacuum degree ≤10 -3Pa; oxygen purity ≥ 99.9%, oxygen flow rate 15 SLM, oxygen introduction time 1.0 min; wafer 12-hole aspect ratio 30:1.

[0068] (2) Ultraviolet-induced ozone generation The applied wavelength is 185 nm and the intensity is 60 mW / cm. 2 Ultraviolet light is used to photolyze the introduced oxygen to produce ozone; during this process, sensors are used to monitor in real time to ensure that the ozone concentration in the cleaning equipment is 152±8ppm.

[0069] (3) In-situ synthesis of microbubbles The gas from the upper part of the cleaning equipment is introduced into the bubble generator 16 for processing to obtain particles with an average size of 200 nm and a density of 8.1 × 10⁻⁶. 8 Microbubbles per mL; Among them, the bubble generator 16 is equipped with ultrasonic cavitation technology. The bubble generator 16 uses a venturi tube, and the device that provides ultrasonic cavitation technology is an ultrasonic transducer; its operating frequency is 1.0MHz.

[0070] (4) Rotary spray deep hole penetration After the microbubbles are mixed with the cleaning reagent 18, they are sprayed onto the surface of the wafer 12 through the spraying device 20 to clean the wafer 12.

[0071] The wafer 12 rotates at 30 rpm, and microbubbles are sprayed onto the surface of the wafer 12 at a flow rate of 2.0 L / min for cleaning.

[0072] (5) Post-processing The post-processing involves purging the surface of the wafer 12 on the rotating tray 14 with nitrogen; during the drying process, the tray 14 rotates at a speed of 100 rpm and is sprayed with high-purity nitrogen at a speed of 50 L / min for 60 seconds. The total cleaning time for wafer 12 is 10 minutes per batch, and the cost is 0.9 yuan per wafer.

[0073] Comparative Example 1 This comparative example provides a wafer 12 cleaning method, using silicon carbide wafer 12 as an example, which includes the following steps:

[0074] (1) SC1 cleaning SC1 cleaning is an alkaline oxidation process. The cleaning reagent 18 is NH4OH, H2O2 and H2O in a volume ratio of 1:1:5. The wafer 12 and the cleaning reagent 18 are placed in an 80°C water bath for 10 minutes.

[0075] (2) First-stage ultrapure water cleaning Wash with ultrapure water (reagent 18) at room temperature for 5 minutes to remove NH4. + And alkaline residue; water consumption > 200L / batch.

[0076] (3) SC2 cleaning SC2 cleaning is an acidic process for removing metal ions, dissolving Fe on wafer 12. 2+ Cu 2+ Metal ions; Cleaning reagent 18 is HCl, H2O2 and H2O in a volume ratio of 1:1:6; Place wafer 12 together with cleaning reagent 18 in a 70℃ water bath for 10 min.

[0077] (4) Secondary ultrapure water cleaning Ultrasonic cleaning at room temperature for 5 minutes is used to remove acidic residues and metal complexes.

[0078] (5) DHF cleaning DHF cleaning is used to remove the native oxide layer on the surface of wafer 12; cleaning reagent 18 is HF and H2O in a volume ratio of 1:50; wafer 12 is immersed in cleaning reagent 18 at 25°C for 60 seconds.

[0079] (6) Drying treatment The wafer 12 is rotated at 2000 rpm and sprayed with hot nitrogen gas; the nitrogen gas temperature is 50°C and the spraying time is 90 seconds.

[0080] The total cleaning time for wafer 12 is ≥45 minutes, and the cost of chemical reagents is 12.8 yuan per wafer.

[0081] Experimental Example 1 This experiment investigated the effect of ultraviolet light wavelength on the cleaning effect. The cleaning method for wafer 12 was the same as in Example 1, except for the ultraviolet light wavelength. The ozone yield, ·OH concentration, and particulate matter content in the deep pores of the wafer were summarized, and the effects of each wavelength were analyzed and summarized. The relevant results are shown in Table 1.

[0082] Among them, ozone yield: the ozone concentration in the outlet gas is measured online using an ozone analyzer (such as 2B Technologies Model 106), and the unit energy yield (g / kWh) is calculated in combination with the UV lamp power.

[0083] ·OH concentration: The fluorescence probe method was used, with terephthalic acid as the ·OH scavenger to generate 2-hydroxyterephthalic acid, which was quantitatively measured by a fluorescence spectrophotometer (excitation wavelength 315 nm, emission wavelength 425 nm).

[0084] Wafer surface particulate matter removal rate (%) = N 清洗后 / N 清洗前 ×100%, N清洗后 This indicates the content of particulate matter on the surface of wafer 12 after cleaning, N. 清洗前 This indicates the content of particulate matter on the wafer surface before cleaning. Wafer surface particulate matter content: measured using a Candela 8520 instrument.

[0085] Table 1. Effect of UV wavelength on cleaning effect

[0086] Experimental Example 2 This experiment investigated the effect of ultraviolet light intensity on the cleaning effect. The cleaning method for wafer 12 was the same as in Example 1, except for the ultraviolet light intensity. The ozone concentration, microbubble density, cleaning time, and residual particulate matter on the wafer surface were summarized, and the relevant results are shown in Table 2.

[0087] Among them, ozone concentration: the gas phase ozone concentration above the cleaning reagent 18 was measured online using an ultraviolet absorption ozone analyzer (based on 254nm absorption, such as Teledyne API465M).

[0088] Microbubble density: The microbubble concentration (cells / mL) was measured using dynamic light scattering (DLS) combined with nanoparticle tracking analysis (NTA) (such as Malvern NanoSight NS300).

[0089] Cleaning time: The cleaning time is determined by real-time optical endpoint detection (change in reflectivity).

[0090] Wafer surface particle density = N 清洗后 / S 晶圆 N 清洗后 S represents the content of particulate matter on the surface of wafer 12 after cleaning. 晶圆 The content of particulate matter on the surface of wafer 12 was measured using a Candela 8520 device, representing the wafer area.

[0091] Table 2. Effect of UV light intensity on cleaning effect

[0092] As can be seen from the data in Table 2, the light intensity ranges from 20 mW / cm². 2 Increased to 80 mW / cm 2 At that time, the ozone concentration and microbubble density both increased significantly, the cleaning time was shortened, and the particulate matter on the wafer 12 surface decreased.

[0093] 50 mW / cm 2 -80 mW / cm 2 To achieve the optimal window for ultraviolet light intensity, the surface particle count of wafer 12 was reduced to 3 × 10⁻⁶. 10 atoms / cm2 The cleaning time is 8-10 minutes.

[0094] The intensity of ultraviolet light is 100 mW / cm 2 Although the time can be further shortened, it leads to a temperature rise of more than 15°C on wafer 12, inducing thermal damage (the particle count on the wafer 12 surface actually increases slightly), so it is not recommended.

[0095] Experimental Example 3 This experiment investigated the effect of UV irradiation time on the cleaning effect. The cleaning method for wafer 12 was the same as in Example 1, except for the UV irradiation time. The cleaning rates under different aspect ratios were summarized, and the relevant results are shown in Table 3.

[0096] Wherein, cleaning rate (%) = N 清洗后 / N 清洗前 ×100%, N 清洗后 This indicates the content of particulate matter on the surface of wafer 12 after cleaning, N. 清洗前 This indicates the content of particulate matter on the wafer surface before cleaning. The particulate matter content on the wafer surface was measured using a Candela 8520 instrument.

[0097] Table 3 Cleaning efficiency under different aspect ratios

[0098] As shown in Table 3, longer illumination time leads to higher deep-hole cleaning rates, but also carries the risk of over-oxidation. The optimal balance is achieved when the UV illumination time is 10 minutes, at which point the cleaning rate reaches 99.2% for an aspect ratio of 20:1 and 95.7% for an aspect ratio of 30:1. While a UV illumination time of 15 minutes results in a cleaning rate close to 100%, excessive oxidation of the wafer surface affects device reliability.

[0099] Test Example 4 This experiment investigated the effect of spraying speed on microbubble penetration. The wafer 12 cleaning method was the same as in Example 1, except for the spraying speed. The average microbubble size, deep hole bottom coverage, and solution utilization were summarized, and the relevant results are shown in Table 4.

[0100] Among them, the microbubble particle size was measured using dynamic light scattering (DLS) or nanoparticle tracking analysis (NTA) to measure the hydrodynamic diameter (nm) of the microbubble.

[0101] Deep hole bottom coverage ratio: The percentage of the area covered by residue at the bottom of the hole was analyzed using SEM cross-section analysis.

[0102] Solution utilization rate: The ratio of the total spray flow rate to the actual contact flow rate on the wafer 12 surface is measured by a flow meter (the splash liquid that does not contact the wafer 12 is collected and the difference is calculated).

[0103] Table 4. Effect of spray velocity on microbubble penetration

[0104] As can be seen from the data in Table 4, when the spraying speed increases from 1.0 L / min to 2.0 L / min, the microbubble particle size decreases (from 320 nm to 210 nm), the coverage ratio of the bottom of the deep hole increases significantly (from 72.5% to 98.3%), and the solution utilization rate decreases slightly (from 95% to 88%).

[0105] The optimal cleaning effect is achieved when the spraying speed is 2.0 L / min, at which point the coverage rate at the bottom of the deep hole reaches 98.3%, and the solution utilization rate is 88%.

[0106] As the spraying speed continues to increase to above 3.0 L / min, although the microbubble particle size becomes smaller, liquid film splashing leads to a decrease in coverage and a sharp drop in solution utilization (from 75% to 65%), so it is not recommended.

[0107] Experimental Example 5 This experiment investigated the effect of wafer 12 rotation speed on cleaning uniformity. The wafer 12 cleaning method was the same as in Example 1, except for the wafer 12 rotation speed. The cleaning rates at the wafer 12 edges, the wafer 12 center, and the uniformity were summarized, and the relevant results are shown in Table 5.

[0108] Wherein, cleaning rate (%) = N 清洗后 / N 清洗前 ×100%, N 清洗后 This indicates the content of particulate matter on the surface of wafer 12 after cleaning, N. 清洗前 This indicates the content of particulate matter on the surface of wafer 12 before cleaning. The particulate matter content on the wafer surface was measured using a Candela 8520 device. Specifically, wafer 12 was divided into concentric rings, with the radius r of the central region of wafer 12 < 50 mm and the radius r of the edge region of wafer 12 > 100 mm.

[0109] Uniformity (1σ): 49 points (7×7 grid) are uniformly selected on the 12-inch surface of the wafer. The cleaning rate at each point is measured, and the ratio of the standard deviation to the mean is calculated (1σ = standard deviation / mean × 100%). This is done using an automated mapping inspection system (such as KLA-Tencor Surfscan). The smaller the 1σ, the better the cleaning uniformity.

[0110] Table 5. Effect of wafer rotation speed on cleaning uniformity

[0111] As can be seen from the data in Table 5, when the wafer rotation speed increases from 10 rpm to 30 rpm, the center cleaning rate increases from 85.7% to 99.1%, and the uniformity improves from ±12.5% ​​to ±1.8%.

[0112] When the wafer rotation speed is 30 rpm, the optimal balance point is: the cleaning rate of both the edge of the wafer and the cleaning rate of the center of the wafer are >99%, and the cleaning uniformity is optimal at this point, 1σ=1.8%.

[0113] When the rotation speed of wafer 12 is 50 rpm, the center cleaning rate decreases (98.5%) because excessive centrifugal force causes microbubbles to be thrown away from the center area of ​​wafer 12; at this time, the uniformity 1σ=1.5%, but the center cleaning effect of wafer 12 deteriorates.

[0114] Analysis example 1 This analysis compares the cleaning time, cost, wafer 12 deep hole cleaning capability, wafer 12 surface damage, and environmental friendliness of Example 1 and Comparative Example 1, and the results are shown in Table 6.

[0115] Table 6 Analysis results of Example 1 and Comparative Example 1

[0116] In summary, the wafer 12 cleaning method provided by this invention introduces high-purity oxygen into the cleaning equipment and utilizes the synergistic adjustment of ultraviolet light wavelength and intensity by the wafer 12 cleaning system to strictly control the ozone concentration generated within the cleaning equipment, thus avoiding adverse effects such as peroxidation and thermal damage to the wafer 12. It utilizes the permeability of microbubbles to achieve deep and efficient cleaning of the deep holes in the wafer 12, achieving uniform cleaning of the entire wafer 12 area. The cleaning method is characterized by low investment cost, high cleaning efficiency, and environmentally friendly cleaning process, making it widely applicable.

[0117] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A wafer cleaning method, characterized in that, Includes the following steps: The loaded wafers are placed in a cleaning device, and oxygen is introduced into the cleaning device. The applied wavelength is 170nm-200nm and the intensity is 20mW / cm. 2 -100mW / cm 2 Ozone is produced by photolyzing introduced oxygen under ultraviolet light. The gas at the top of the cleaning equipment is introduced into a bubble generator for processing to produce microbubbles with an average particle size of 100nm-500nm. The microbubbles are mixed with the cleaning reagent and then sprayed onto the surface of the wafer through a spraying device to clean the wafer.

2. The wafer cleaning method according to claim 1, characterized in that, The wafer cleaning process has at least one of the following characteristics: Feature 1: The purity of oxygen is ≥99.9%, the oxygen flow rate is 10SLM-20SLM, and the oxygen introduction time is 0.5min-1.5min. Feature 2: The ozone concentration inside the cleaning equipment is 50ppm-200ppm; Feature 3: The wafer rotates at a speed of 10rpm-50rpm.

3. The wafer cleaning method according to claim 1, characterized in that, The wafers are mounted on the surface of a rotating tray using a vacuum adsorption method, with a vacuum level ≤10. -3 Pa; And / or, microbubbles are sprayed onto the wafer surface at a flow rate of 1.0 L / min to 5.0 L / min for cleaning.

4. The wafer cleaning method according to claim 1, characterized in that, The cleaning reagent is selected from at least one of deionized water, ultrapure water and distilled water; And / or, the bubble generator is selected from at least one of a venturi tube and a microporous membrane plate; the bubble generator is assisted by ultrasonic cavitation technology, and the ultrasonic frequency for preparing microbubbles is 0.8MHz-1.2MHz, and the ultrasonic power density is 5W / cm³. 2 -15W / cm 2 Ultrasonic treatment time: 2-5 seconds; And / or, the aspect ratio of the wafer deep via is ≥30:

1.

5. The wafer cleaning method according to claim 1, characterized in that, The wafer cleaning method further includes post-processing; the post-processing includes drying the wafer after cleaning. During the drying process, the tray is rotated at a speed of 80rpm-110rpm and sprayed with high-purity nitrogen gas at a speed of 45L / min-55L / min for 50s-80s. And / or, the total time for wafer cleaning is 8 min / batch - 12 min / batch.

6. A wafer, characterized in that, The wafer is prepared by cleaning using the wafer cleaning method described in any one of claims 1-5.

7. The wafer according to claim 6, characterized in that, The particle density on the wafer surface is ≤3.5×10⁻⁶. 10 atoms / cm 2 ; Based on the particle density on the wafer surface, the wafer edge cleaning rate is ≥99.3%, and the wafer center cleaning rate is ≥85.7%.

8. A wafer cleaning system, characterized in that, Implement the wafer cleaning method as described in any one of claims 1-5; The wafer cleaning system includes cleaning equipment, a tray, an ultraviolet generator, a bubble generator, a spray device, and sensors; The cleaning equipment is equipped with an oxygen delivery port; The tray is used to load wafers and is placed in the cleaning equipment during cleaning; the center of the tray has a through hole for the spray device to pass through; The ultraviolet generator is located directly above the cleaning equipment; The sensor is used to monitor the ozone concentration inside the cleaning equipment in real time.

9. The cleaning system according to claim 8, characterized in that, The inlet of the bubble generator is higher than the level of the cleaning reagent, and the outlet of the bubble generator is immersed in the cleaning reagent. And / or, the inlet of the spray device is immersed in the cleaning agent, and the outlet of the spray device is above the upper surface of the tray.

10. The cleaning system according to claim 9, characterized in that, The spray device outlet is detachably equipped with a nozzle; The nozzle has at least two rings of nozzles on its nozzle surface, and the multiple rings of nozzles are arranged in a concentric ring from the inside to the outside along the radial direction.

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