Method for cleaning focal plane microbridge structure of wafer

Abstract

The invention belongs to the technical field of chip cleaning, and discloses a cleaning method of a wafer focal plane microbridge structure, which comprises the following steps of: (1) putting a wafer into absolute ethyl alcohol added with a fluorocarbon surfactant to clean for the first time; (2) carrying out two-fluid spray cleaning on the wafer cleaned for the first time by adopting isopropanol and compressed gas; and (3) drying the wafer cleaned by the two-fluid spray. According to the cleaning method, the number of foreign matters remaining on pixels after the wafer is scribed can be effectively reduced, the qualified rate and reliability of products are improved, the imaging quality of the detector is optimized, and the detector shows more excellent performance in practical application.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of chip cleaning, and particularly relates to a cleaning method for a focal plane micro-bridge structure of a wafer, and is especially suitable for the precision cleaning of a micro-bridge structure in the manufacturing of a non-cooled infrared focal plane detector. BACKGROUND

[0002] In the field of non-cooled infrared focal plane detector manufacturing, the processing technology of the micro-bridge structure is a core link that determines the performance of the detector. In the traditional process flow, the wafer needs to be first cut after the micro-bridge structure is completed, and then the suspended micro-bridge is formed by releasing the sacrificial layer. However, silicon chips, metal particles and organic residues generated in the dicing process will adhere to the surface of the micro-bridge or embed in the structure gap. The existing cleaning technology cannot completely remove these foreign matters, resulting in a significant reduction in the yield of the device. The foreign matter residues after dicing increase the micro-bridge breakage rate, and the residues are prone to cause micro-bridge collapse, thermal crosstalk abnormalities and other problems in the subsequent process, directly affecting the imaging uniformity and sensitivity of the detector.

[0003] The current industry generally adopts the process route of "dicing first and then releasing". This scheme has inherent defects: the combined action of the cooling liquid and mechanical stress during dicing will exacerbate the generation and adhesion of foreign matters. Especially when the sacrificial layer has not been released, the semi-closed cavity structure formed by the micro-bridge and the substrate will hinder the penetration of the cleaning liquid, resulting in the bottom of the groove and the bridge leg connection being the most affected area of foreign matter accumulation.

[0004] In view of the above problems, the existing technology such as CN202311136804.X proposes to use a spray- soaking collaborative cleaning method to ensure the integrity of the micro-bridge structure while ensuring the cleaning environment by using a method of spray and soaking collaboration. However, this scheme still has the following technical problems: 1) for the wafer with a groove structure, the surface tension of the cleaning liquid causes the formation of a gas blocking effect inside the micro-bridge structure, and the actual measurement shows that the cleaning coverage rate at the bottom of the groove is insufficient; 2) too many processes, frequent change of cleaning environment is required for multi-process switching, and the single wafer processing time is long, which affects the production line efficiency. SUMMARY

[0005] The present application aims to provide a cleaning method for a focal plane micro-bridge structure of a wafer to solve at least one technical problem in the background art.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present application is: A cleaning method for a focal plane micro-bridge structure of a wafer, comprising the following steps: (1) placing the wafer into anhydrous ethanol added with fluorocarbon surfactant for first cleaning; (2) using isopropyl alcohol and compressed gas to perform two-fluid spray cleaning on the wafer after the first cleaning; (3) drying the wafer after the two-fluid spray cleaning.

[0007] Further, in step (1), the fluorocarbon surfactant is at least one of perfluoropolyether carboxylate, perfluoroalkyl sulfonate, modified perfluoropolyether, fluorocarbon-carbon hydrogen complex surfactant.

[0008] Further, in step (1), the fluorocarbon surfactant is at least one of perfluoropolyether carboxylate, perfluoroalkyl sulfonate, modified perfluoropolyether, fluorocarbon-carbon hydrogen complex surfactant.

[0009] Further, in step (1), the fluorocarbon surfactant is at least one of perfluoropolyether carboxylate, perfluoroalkyl sulfonate, modified perfluoropolyether, fluorocarbon-carbon hydrogen complex surfactant.

[0010] Further, in step (1), the fluorocarbon surfactant is at least one of perfluoropolyether carboxylate, perfluoroalkyl sulfonate, modified perfluoropolyether, fluorocarbon-carbon hydrogen complex surfactant.

[0011] Further, in step (1), the fluorocarbon surfactant is at least one of perfluoropolyether carboxylate, perfluoroalkyl sulfonate, modified perfluoropolyether, fluorocarbon-carbon hydrogen complex surfactant.

[0012] Further, in step (2), the compressed gas is compressed nitrogen, compressed argon or compressed air.

[0013] Further, in step (2), the wafer is subjected to two-fluid spray cleaning in a rotating state; the rotating speed during the cleaning is 500-2000 r / min.

[0014] Further, in step (2), the wafer is subjected to two-fluid spray cleaning in an ultrasonic state; the ultrasonic frequency is 20-100 kHz, and the ultrasonic cleaning time is 3-8 min.

[0015] Further, in step (2), the wafer is placed on a support during the cleaning, and the wafer has an inclination angle of 0-60° with respect to the horizontal plane; further preferably, the inclination angle is 35-45°.

[0016] Further, in step (2), the two-fluid spray cleaning direction has an angle of 130-150° with respect to the wafer; the spray pressure is 0.15-0.3 MPa.

[0017] Further, in step (3), the drying method is rotary drying; the rotary drying speed is 500-2000 r / min; and the drying time is 5-10 min.

[0018] Compared with the prior art, the present application has the following advantages: (1) The cleaning method can effectively reduce the number of foreign matters remaining on the pixel after the wafer is scribed, greatly improve the pass rate and reliability of the product, optimize the imaging quality of the detector, and make the detector show more excellent performance in actual application.

[0019] (2) The two-step method replaces the traditional multi-step method, shortens the single wafer processing time, improves the cleaning and production efficiency, and simplifies the process without frequent replacement of cleaning liquid.

[0020] (3) The contaminants are removed more thoroughly, the surface tension is reduced by fluorocarbon surfactant, combined with reverse immersion and ultrasonic, and the cleaning coverage rate of the groove bottom is improved.

[0021] (4) The micron-sized droplets are formed by gas-liquid synergistic atomization, which can reduce the impact force on the structure with deep groove while ensuring the cleaning effect, reduce the damage to the precision structure, realize the "high efficiency and low damage" cleaning of the micro-bridge structure, avoid the mechanical stress caused by high-pressure spraying, and further ensure the uniform stress of the micro-bridge during the cleaning process through inclination and rotation and ultrasonic, the structure is strong in protection, and the risk of micro-bridge fracture and collapse is greatly reduced. BRIEF DESCRIPTION OF DRAWINGS

[0022] The accompanying drawings are included to provide a further understanding of the application, and constitute a part of the specification, together with the embodiments of the application, to explain the application, and do not constitute a limitation on the application.

[0023] In the drawings: Figure 1 It is a two-fluid spray cleaning schematic diagram in example 1.

[0024] Figure 2 It is an OM microscope detection diagram (5 times) of the wafer before cleaning in example 1.

[0025] Figure 3 It is an OM microscope detection diagram (5 times) of the wafer after cleaning in example 1. DETAILED DESCRIPTION

[0026] The application provides a cleaning method for a wafer focal plane micro-bridge structure, comprising the following steps: (1) Put the wafer into anhydrous ethanol added with fluorocarbon surfactant for the first cleaning; the first cleaning is low surface tension solution penetration cleaning.

[0027] In specific embodiments, the fluorocarbon surfactant is selected from one or more of a combination of perfluoropolyether carboxylate (PFPE-COONa), perfluoroalkyl sulfonate (PFAS), modified perfluoropolyether (PFPE), and fluorocarbon-hydrocarbon composite surfactant. For the removal of particle contaminants in wafer cleaning, the present application selects perfluoropolyether carboxylate (PFPE-COONa) as the preferred solution, which can efficiently remove particle residues, organic contaminants and metal impurities on the wafer surface, and is particularly suitable for deep cleaning of high aspect ratio microstructures (such as deep hole bottoms and micro-bridge structures involved in the present application). Perfluoroalkyl sulfonate (PFAS) and modified perfluoropolyether (PFPE) have significant stripping effect on hydrocarbon-based organic contaminants due to their oleophobic properties, while fluorocarbon-hydrocarbon composite surfactants exhibit stronger affinity for metal contaminants.

[0028] In specific embodiments, the amount of fluorocarbon surfactant added is 0.08-0.15wt% of the anhydrous ethanol.

[0029] In specific embodiments, the surface tension of the anhydrous ethanol to which the fluorocarbon surfactant is added is 18-22mN / m.

[0030] The addition of fluorocarbon surfactant can lower the surface tension of the solution to below 22.1mN / m of conventional anhydrous ethanol, and by utilizing the ultra-low surface tension characteristics, the capillary penetration ability of the solution to sub-micron gaps is enhanced, breaking through the air resistance effect of traditional cleaning solutions and achieving effective wetting of the trench bottom and bridge leg junctions.

[0031] In specific embodiments, the wafer is placed in an inverted manner in the anhydrous ethanol to which the fluorocarbon surfactant is added.

[0032] In specific embodiments, the first cleaning is performed by first static soaking and then ultrasonic cleaning, with an ultrasonic frequency of 20-100kHz and a first cleaning duration of 5-10min. The core of ultrasonic cleaning is cavitation, which occurs when ultrasonic waves propagate in the cleaning solution. In the negative pressure phase, many small bubbles are formed in the liquid as cavitation bubbles. These cavitation bubbles collapse violently in the positive pressure phase, generating a large local pressure and shock wave, thereby stripping the dirt attached to the surface of the object.

[0033] At the same time, surface tension directly affects the formation and collapse process of cavitation bubbles. Higher surface tension hinders the formation of cavitation bubbles, reducing cavitation efficiency; while lower surface tension is conducive to the formation and collapse of cavitation bubbles, improving cleaning efficiency.

[0034] Further, the wafer is placed in an inverted manner in the anhydrous ethanol to which the fluorocarbon surfactant is added, and cleaning is performed by a combination of static soaking and ultrasonic cleaning.

[0035] Wafer reverse immersion can achieve full surface contact. After immersion, the glue dissolves, and during reverse, the photoresist and foreign matter naturally sink due to gravity after separating from the wafer surface, reducing secondary adhesion. Ultrasonic cleaning produces micro-bubble breakage through cavitation effect, stripping stubborn particle contaminants, while avoiding micro-bridge mechanical stress damage caused by prolonged ultrasonic cleaning.

[0036] (2) Isopropyl alcohol and compressed gas are used to spray clean the wafer after the first cleaning.

[0037] Isopropyl alcohol, as a medium-polar solvent, can effectively dissolve residual ethanol and non-ionic organic contaminants, and compressed gas can achieve physical removal of ionic residues and microparticles through high-speed impact. While enhancing the dissolution and flushing effect, the isopropyl alcohol's azeotropic property (boiling point about 78℃) and the dispersion effect of the gas flow are used to simultaneously improve the solvent evaporation efficiency, effectively avoiding surface residue risks.

[0038] In specific embodiments, the wafer is sprayed and cleaned in a rotating state; further preferably, the rotation speed during cleaning is 500-2000 r / min.

[0039] In specific embodiments, the wafer is sprayed and cleaned in an ultrasonic state, i.e., ultrasonic waves are applied in the path of the spray cleaning: first, ultrasonic waves can refine droplet size, improve impact force and coverage uniformity; second, droplet impact on the wafer is accompanied by cavitation effect, effectively removing sub-micron particles and organic residues. Further improving cleaning effect.

[0040] More specifically, the ultrasonic frequency is 20-100 kHz, and the ultrasonic cleaning time is 3-8 min, combined with a rotating flow field, further strengthening the cavitation effect, achieving all-around cleaning of the micro-bridge bottom and sides.

[0041] In specific embodiments, the wafer is placed on a stage during cleaning, and the inclination angle of the wafer to the horizontal plane is 0-60°. Further preferably, it is 35-45°, and more preferably, it is 40°.

[0042] In specific embodiments, the included angle between the wafer and the spray cleaning direction is adjusted to 130-150°, and a spiral flow field is formed in combination with the rotating state. The inclined design causes the cleaning liquid to flow along the wafer surface gradient under the action of centrifugal force, especially producing directional flushing force on deep trench structures, removing residual particles in the gaps.

[0043] In specific embodiments, the compressed gas is compressed nitrogen, compressed argon, or compressed air, etc.

[0044] In specific embodiments, the spray pressure of the two-fluid spray cleaning is 0.15-0.3 MPa.

[0045] (3) Dry the wafer after two-fluid spray cleaning.

[0046] In a specific embodiment, a spin-drying method is used, with a rotation speed of 500-2000 r / min and a drying time of 5-10 min. The surface residual liquid is quickly removed by centrifugal force, avoiding water marks or re-deposition of pollutants caused by traditional static drying.

[0047] In order to facilitate the understanding of the present application, the following will be a more comprehensive and detailed description of the present application in conjunction with the preferred embodiments, but the protection scope of the present application is not limited to the following specific embodiments.

[0048] Unless otherwise defined, all the professional terms used in the following are the same as the meanings commonly understood by those skilled in the art. The professional terms used in this paper are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present application.

[0049] Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0050] Example 1 (1) First cleaning: prepare anhydrous ethanol containing 0.1wt% fluorocarbon surfactant, and the fluorocarbon surfactant is perfluoropolyether carboxylate (PFPE-COONa). The surface tension of anhydrous ethanol after adding fluorocarbon surfactant is measured to be 18.2 mN / m.

[0051] Place the wafer (12 inches, micro-bridge structure groove depth 10 μm, width 1 μm) upside down in the cleaning tank, first soak for 5 min, then start ultrasonic cleaning (frequency 20 kHz) for 3 min, so that the solution fully penetrates the micro-bridge gap and dissolves the organic contaminants.

[0052] (2) As shown in Figure 1 , fix the wafer on the stage, adjust the inclination angle to 40°, rotate at a speed of 1000 r / min, use isopropanol and compressed high-purity nitrogen to perform two-fluid spray cleaning on the wafer, the spray pressure is 0.2 MPa, the two-fluid spray cleaning direction is at an angle of 140° with the wafer, and ultrasonic waves (frequency 20 kHz) are applied in the spray cleaning path. The cleaning time is 3 min, and the residual particles and metal ions are removed by centrifugal force and cavitation effect.

[0053] (3) Drying: spin-dryer at 1000 r / min for 5 min to completely dry the wafer surface without liquid residue.

[0054] Use an OM microscope to detect the wafer before and after cleaning, respectively as Figure 2 and 3As shown, it can be seen that there are obvious particle contaminants on the wafer surface before cleaning, and no obvious particle contaminants are observed after cleaning, which shows that the cleaning method can effectively reduce the number of particle contaminants remaining on the wafer surface after scribing.

[0055] Example 2 Example 2 is basically the same as Example 1, and the difference lies in the different amounts of surfactant and surface tension in step (1). Specifically: Anhydrous ethanol containing 0.05wt% fluorocarbon surfactant is configured, and the fluorocarbon surfactant is perfluoropolyether carboxylate (PFPE-COONa). The surface tension of the anhydrous ethanol after adding the fluorocarbon surfactant is measured to be 20mN / m.

[0056] Example 3 Example 3 is basically the same as Example 1, and the difference lies in the different amounts of surfactant and surface tension in step (1). Specifically: Anhydrous ethanol containing 0.15wt% fluorocarbon surfactant is configured, and the fluorocarbon surfactant is perfluoropolyether carboxylate (PFPE-COONa). The surface tension of the anhydrous ethanol after adding the fluorocarbon surfactant is measured to be 16mN / m.

[0057] Example 4 Example 4 is basically the same as Example 1, and the difference lies in that step (1) does not use the inverted mode. Specifically: The wafer (12 inches, micro-bridge structure groove depth 10μm, width 1μm) is placed vertically in the cleaning tank.

[0058] Example 5 Example 5 is basically the same as Example 1, and the difference lies in that isopropanol (analytical pure) and compressed argon gas are used for two-fluid spray cleaning of the wafer in step (2).

[0059] Example 6 Example 6 is basically the same as Example 1, and the difference lies in that the angle between the wafer and the two-fluid spray cleaning direction is 130° in step (2).

[0060] Example 7 Example 7 is basically the same as Example 1, and the difference lies in that the rotation speed is 1200r / min during cleaning in step (2).

[0061] Example 8 Example 8 is basically the same as Example 1, and the difference lies in that the wafer is fixed on the stage in step (2), and the inclination angle is adjusted to 0°.

[0062] Example 9 Example 8 is basically the same as Example 1, except that in step (2), the wafer is fixed on a stage, and the tilt angle is adjusted to 60°.

[0063] Comparative Example 1 Comparative Example 1 is basically the same as Example 1, except that in step (1), no surfactant is added.

[0064] Comparative Example 2 Comparative Example 2 is basically the same as Example 1, except that in step (1), a hydroxylamine solution is selected, i.e., the wafer is placed in a hydroxylamine solution with fluorocarbon surfactant added, and the first cleaning is performed. That is: The first cleaning: a hydroxylamine solution with a mass concentration of 1-5% is taken, a hydroxylamine solution with a concentration of 3.5wt% containing 0.1wt% fluorocarbon surfactant is prepared, and the fluorocarbon surfactant used is perfluoropolyether carboxylate (PFPE-COONa). The surface tension of the hydroxylamine solution after adding the fluorocarbon surfactant is measured to be 22mN / m.

[0065] The wafer (12 inches, micro-bridge structure trench depth 10μm, width 1μm) is placed upside down in the cleaning tank, first soaked for 5min, then ultrasonic cleaning (frequency 20kHz) is started for 3min, so that the solution fully penetrates the micro-bridge gap and dissolves the organic contaminants.

[0066] Comparative Example 3 Comparative Example 3 is basically the same as Example 1, except that in step (2), a high-pressure spray cleaning method is selected. Specifically: The wafer is fixed on a stage, the tilt angle is adjusted to 40°, and the wafer is rotated at a speed of 1000r / min. Isopropyl alcohol is used to clean the wafer by high-pressure spraying, the spraying pressure is 0.2MPa, the spraying direction makes an angle of 140° with the wafer, and ultrasonic waves (frequency 20kHz) are applied in the path of the spray cleaning. The cleaning time is 3min, and the centrifugal force and cavitation effect are used to remove residual particles and metal ions.

[0067] Comparative Example 4 Comparative Example 4 is basically the same as Example 1, except that in step (2), an immersion ultrasonic cleaning method is selected. Specifically: The wafer is fixed on a stage, the tilt angle is adjusted to 30°, and the wafer is rotated at a speed of 1000r / min. Isopropyl alcohol is used to clean the wafer by immersion, and ultrasonic cleaning (frequency 20kHz) is started for 3min. The centrifugal force and cavitation effect are used to remove residual particles and metal ions.

[0068] Comparative Example 5 Comparative Example 5 is CN202311136804.X which proposes a spray- soaking synergistic cleaning method by using a method of spray and soaking working in cooperation. The wafer cleaned in Comparative Example 5 is the same as that in Example 1.

[0069] Specifically, firstly, spraying the wafer with a solution containing hydroxylamine at a pressure of 1 Mpa, and then soaking the wafer with the solution containing hydroxylamine for 50 min, while performing the first cleaning of the wafer; firstly, spraying the wafer with isopropyl alcohol solvent at a pressure of 1 Mpa, and then soaking the wafer with the isopropyl alcohol solvent for 10 min, while performing the second cleaning of the wafer; firstly, spraying the wafer with deionized water at a pressure of 1 Mpa, and then soaking the wafer with the deionized water for 8 min, while performing the third cleaning of the wafer; firstly, spraying the wafer with isopropyl alcohol solvent at a pressure of 1 Mpa, and then soaking the wafer with the isopropyl alcohol solvent for 10 min, while performing the fourth cleaning of the wafer; drying the cleaned wafer: drying at room temperature for 30 min, and then baking in an oven at 120℃ for 3 min.

[0070] Test Example The cleaning time of the record example and the comparative example was recorded, and the cleaned wafer in the example and the comparative example was tested: Particle density detection: using KLA-Tencor SP2 surface particle detector, scanning 10 1cm×1cm areas in the center area of the wafer, and calculating the average particle density.

[0071] Structural integrity test: using a scanning electron microscope (SEM) to observe the surface of the micro-bridge and the connection of the bridge legs, and counting the proportion of fracture or collapse.

[0072] The data is shown in Table 1. Table 1 As can be seen from Table 1, by surface tension regulation, multi-dimensional cleaning and process parameter optimization, the present application significantly shortens the cleaning time, realizes high cleanliness cleaning of the micro-bridge structure, effectively solves the problems of residual pollutants, easy damage of structure and low efficiency in the traditional technology, and is suitable for large-scale industrial production.

[0073] The above merely provides the preferred embodiments of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the principles and technical scope of the present application shall fall into the scope of the present application.

Claims

1. A method for cleaning a microbridge structure on a wafer focal plane, characterized in that: The following steps are involved: (1) Place the wafer in anhydrous ethanol with fluorocarbon surfactant for the first cleaning; (2) Using isopropyl alcohol and compressed gas to perform two-fluid spray cleaning on the wafer after the first cleaning; (3) Drying the wafer after two-fluid spray cleaning.

2. The cleaning method according to claim 1, wherein In step (1), the fluorocarbon surfactant is at least one of perfluoropolyether carboxylate, perfluoroalkyl sulfonate, modified perfluoropolyether, and fluorocarbon-hydrogen composite surfactant; the amount of the fluorocarbon surfactant added is 0.05-0.15 wt% of the anhydrous ethanol; and the surface tension of the anhydrous ethanol to which the fluorocarbon surfactant is added is 18-22 mN / m.

3. The cleaning method according to claim 1, wherein In step (1), the wafer is placed upside down in anhydrous ethanol to which a fluorocarbon surfactant is added.

4. The cleaning method according to claim 1, wherein In step (1), the first cleaning process includes a static soaking step and an ultrasonic cleaning step in sequence, wherein: the ultrasonic frequency range is 20~100kHz, and the first cleaning time is 5~10min.

5. The cleaning method according to claim 1, wherein In step (2), the wafer is cleaned by a two-fluid spray while rotating; the rotation speed during cleaning is 500~2000r / min.

6. The cleaning method according to claim 1, wherein In step (2), the wafer is cleaned by two-fluid spray under ultrasonic conditions; the ultrasonic frequency is 20-100 kHz, and the ultrasonic cleaning time is 3-8 minutes.

7. The cleaning method according to claim 1, wherein In step (2), the wafer is placed on a carrier during cleaning, and the inclination angle of the wafer to the horizontal plane is 0-60°; preferably 35-45°.

8. The cleaning method according to claim 7, wherein In step (2), the angle between the two-fluid spray cleaning direction and the wafer is 130~150°; the spray pressure is 0.15~0.3MPa.

9. The cleaning method according to claim 1, wherein In step (2), the compressed gas is compressed nitrogen, compressed argon or compressed air.

10. The cleaning method according to claim 1, wherein In step (3), the drying method is spin drying; the rotation speed of the spin drying is 500~2000r / min; and the drying time is 5~10min.

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