Interdigital transducer and preparation method therefor, and surface acoustic wave filter

Abstract

The present invention is applicable to the technical field of wireless communications, and particularly relates to an interdigital transducer and a preparation method therefor, and a surface acoustic wave filter. The preparation method comprises the following steps: performing two rounds of photoresist spin-coating and two rounds of a hard-baking treatment on a wafer, performing an exposure treatment, developer spin-coating and a film deposition treatment, and stripping a photoresist, so as to obtain an interdigital transducer. Compared with the prior art, in the present invention, two layers of photoresist are applied to a wafer, wherein the physical properties of the two layers of photoresist are different, such that in a subsequent developer spin-coating process, the remaining structure of the upper layer of photoresist is larger than that of the lower layer of photoresist, thereby forming a T-shaped-like photoresist structure. Therefore, when film deposition is performed on the wafer, a gap is formed between a metal film and the lower layer of photoresist, thereby effectively preventing the photoresist from adhering to the periphery of the metal film, which causes incomplete stripping, and thus the electrical performance and reliability of an interdigital transducer and a surface acoustic wave filter thereof are effectively improved.

Description

Interdigital transducer and preparation method thereof, and surface acoustic wave filter TECHNICAL FIELD

[0001] The present application is suitable for the field of wireless communication technology, and particularly relates to an interdigital transducer and a preparation method thereof, and a surface acoustic wave filter. BACKGROUND

[0002] With the maturity of the fifth generation wireless communication technology solution, smart phones need to increase filters to support the increasing number of frequency bands, and the dense frequency bands make the interference problem between the uplinks in the system prominent. In order to ensure high-quality data communication between frequency spectrums, a typical high-end smart phone needs to be equipped with at least 50 radio frequency front-end filters. With the continuous upgrading of communication technology (5G mobile phones) and the deployment of new technologies such as carrier aggregation (CA) and multiple-input multiple-output (MIMO), the number of communication frequency bands is increasing, and this number will show a sustained and fierce growth trend.

[0003] A surface acoustic wave (SAW) resonator is a kind of transduction passive band-pass filter made by using the piezoelectric effect and the physical characteristics of surface acoustic wave propagation. The SAW resonator is increasingly valued in communication circuit design due to its small size, strong radiation resistance, high speed, low power consumption and high reliability. The resonant frequency of the SAW resonator can be accurately tuned in a wide range through photolithography technology, and it has a small shape factor, low connection loss and low cost, and is very suitable for monolithic integration of different frequency filters.

[0004] At present, there are two kinds of stripping and etching in the mainstream SAW processing technology, and the main difference between the two is the order of uniform coating and film plating. The stripping process is after uniform coating, a series of exposure and development, the photoresist is patterned, then film plating and stripping are carried out, and finally the interdigital transducer is obtained. Compared with the etching process, it is widely used by international leading manufacturers due to its better resolution.

[0005] However, the stripping process currently also has certain technical defects, mainly manifested in the phenomenon of incomplete stripping. The main reason is that during the film plating process, the temperature of the evaporated aluminum film material is relatively high, and after falling on the wafer surface, the photoresist will be further heated, so that its adhesion is further strengthened compared with the development after baking, especially in the contact area of the interdigital transducer and the photoresist, the excessive adhesion is easy to cause the phenomenon of incomplete stripping, which will greatly affect the electrical performance and reliability of the filter.

[0006] Therefore, a new interdigital transducer and a preparation method thereof, and a surface acoustic wave filter are needed to solve the above problems. SUMMARY

[0007] The application provides an interdigital transducer and a preparation method thereof and a surface acoustic wave filter, aiming at completely stripping off photoresist attached to the interdigital transducer during preparation, so as to improve the reliability and electrical performance of the interdigital transducer.

[0008] In a first aspect, the application provides a preparation method of an interdigital transducer, comprising the following steps:

[0009] S1, cleaning the surface of a wafer to obtain a first wafer;

[0010] S2, spin-coating a first photoresist on the surface of the first wafer to obtain a second wafer coated with the first photoresist;

[0011] S3, performing first hard baking on the second wafer to obtain a third wafer; wherein the baking time of the second wafer during the first hard baking is 20-45 seconds, and the baking temperature is 70-100℃;

[0012] S4, spin-coating a second photoresist on the surface of the first photoresist of the third wafer and performing second hard baking to obtain a fourth wafer coated with two layers of photoresist;

[0013] S5, performing exposure treatment on the fourth wafer to obtain a fifth wafer;

[0014] S6, spin-coating a developing solution on the surface of the fifth wafer to remove the unexposed area on the fifth wafer to obtain a sixth wafer; wherein the remaining structure of the second photoresist of the sixth wafer is more than that of the first photoresist of the sixth wafer;

[0015] S7, performing plating film treatment on the sixth wafer to obtain a seventh wafer;

[0016] S8, stripping the photoresist on the seventh wafer by a preset chemical solvent to obtain an interdigital transducer.

[0017] Preferably, in step S4, the following sub-steps are included:

[0018] S41a, spin-coating a second photoresist on the surface of the first photoresist of the third wafer, and the sensitivity of the second photoresist is lower than that of the first photoresist;

[0019] S42a, performing second hard baking on the third wafer after spin-coating the second photoresist to obtain the fourth wafer, wherein the baking time of the third wafer during the second hard baking is 20-45 seconds, and the baking temperature is 70-100℃.

[0020] Preferably, the sensitivity of the first photoresist is 1.3-2.0 times that of the second photoresist.

[0021] Preferably, the first photoresist sensitivity ranges from 10-1000 mJ / cm 2 .

[0022] Preferably, in step S4, the following sub-steps are included:

[0023] S41b, spin-coating the first photoresist on the surface of the first layer of photoresist of the third wafer to form a second layer of photoresist;

[0024] S42b, performing a second hard baking treatment on the third wafer after spin-coating the first photoresist through a heating platform to obtain the fourth wafer; wherein the baking time during the second hard baking treatment is 20-45 seconds, and the baking temperature during the second hard baking treatment is higher than the baking temperature during the first hard baking treatment.

[0025] Preferably, the baking temperature during the second hard baking treatment is 5-30℃ higher than the baking temperature during the first hard baking treatment.

[0026] Preferably, the preset chemical solvent includes N-methyl pyrrolidone and tetramethylammonium hydroxide.

[0027] The mass of the N-methyl pyrrolidone accounts for 5%-30% of the total mass of the preset chemical solvent, the mass of the tetramethylammonium hydroxide accounts for 2.5% of the total mass of the preset chemical solvent, and the rest is water.

[0028] Preferably, in step S1, the surface of the wafer is cleaned by ultrasonic waves; in step S2, a first layer of photoresist is spin-coated on the surface of the first wafer by a high-speed homogenizer; in step S3, the second wafer is subjected to a first hard baking treatment by a heating platform; in step S5, the fourth wafer is subjected to an exposure treatment by a deep ultraviolet light source through a mask; and in step S7, the sixth wafer is subjected to a film plating treatment by an electron beam evaporation.

[0029] In a second aspect, the present application further provides an interdigital transducer, which is prepared by the preparation method of the interdigital transducer as described in the above embodiments.

[0030] In a third aspect, a surface acoustic wave filter includes an interdigital transducer as described in the above embodiments.

[0031] Compared with existing technologies, this invention coats the wafer with two layers of photoresist. Due to the difference in properties between the two layers of photoresist, the top layer of photoresist will have more residual structure than the bottom layer during the subsequent spin coating and development process, forming a T-shaped photoresist structure. This allows a gap to be formed between the metal film and the bottom layer of photoresist during wafer deposition, effectively preventing photoresist from adhering to the periphery of the metal film and causing incomplete peeling. This effectively improves the electrical performance and reliability of the interdigital transducer and its surface acoustic wave filter. Attached Figure Description

[0032] The present invention will now be described in detail with reference to the accompanying drawings. The above and other aspects of the present invention will become clearer and more readily understood through the detailed description following the accompanying drawings. In the drawings:

[0033] Figure 1 is a flowchart of the fabrication method of the interdigital transducer provided in an embodiment of the present invention;

[0034] Figure 2 is a schematic diagram of the interface between the metal film and the photoresist in the fabrication method of the interdigital transducer provided in the embodiment of the present invention;

[0035] Figure 3 is a cross-sectional schematic diagram of the preparation process of a specific embodiment 1 of the preparation method of the interdigital transducer provided in this invention;

[0036] Figure 4 is a cross-sectional schematic diagram of the preparation process of a specific embodiment 2 of the preparation method of the interdigital transducer provided in this invention.

[0037] In the figure, 1 is the first wafer, 2 is the second wafer, 3 is the third wafer, 4 is the fourth wafer, 5 is the fifth wafer, 6 is the sixth wafer, 7 is the seventh wafer, 8 is the interdigitated transducer, 11 is the first photoresist, 12 is the second photoresist, 13 is the photomask, and 14 is the metal film. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0039] Implementation Method 1

[0040] Please refer to Figures 1-4. This invention provides a method for fabricating an interdigital transducer, the method comprising the following steps:

[0041] S1. The surface of the wafer is cleaned to obtain the first wafer 1.

[0042] In this embodiment of the invention, the surface of the wafer is cleaned using ultrasonic waves.

[0043] S2. Spin-coat a layer of first photoresist 11 onto the surface of the first wafer 1 to obtain a second wafer 2 coated with the first layer of photoresist.

[0044] In this embodiment of the invention, the sensitivity range of the first photoresist 11 is 10-1000 mJ / cm. 2 The first photoresist 11 is uniformly spin-coated onto the first wafer 1 using a high-speed homogenizer.

[0045] S3. Perform a first hardening process on the second wafer 2 to obtain a third wafer 3; wherein, the baking time for the first hardening process of the second wafer 2 is 20-45 seconds and the baking temperature is 70-100℃.

[0046] In this embodiment of the invention, the second wafer 2 is subjected to a first hardening process by a heating platform. The first hardening process removes some of the residual moisture in the first photoresist 11, forming a first photoresist 11 after the first hardening process, which improves the adhesion and stability between the first photoresist 11 and the surface of the second wafer 2.

[0047] S4. A second layer of photoresist is spin-coated onto the surface of the first layer of photoresist on the third wafer 3 and a second hardening treatment is performed to obtain a fourth wafer 4 coated with two layers of photoresist.

[0048] In this embodiment of the invention, the physical properties of the second photoresist layer are different from those of the first photoresist layer. Furthermore, due to the different physical properties (such as sensitivity, hardness, viscosity, etc.) between the two photoresist layers after the second hardening process, the remaining structure of the second photoresist layer after spin coating with the developer in the subsequent step S6 will be greater than the remaining structure of the first photoresist layer.

[0049] S5. Exposure processing is performed on the fourth wafer 4 to obtain the fifth wafer 5.

[0050] In this embodiment of the invention, the fourth wafer 4 is exposed using a deep ultraviolet light source through a mask 13. The exposure time of the fourth wafer 4 by the deep ultraviolet light source (DUV) through the mask 13 can be set according to the actual situation.

[0051] S6. Spin-coating developer onto the fifth wafer 5 to remove unexposed areas on the fifth wafer 5, resulting in a sixth wafer 6; wherein the remaining structure of the second photoresist layer of the sixth wafer 6 is greater than the remaining structure of the first photoresist layer of the sixth wafer 6.

[0052] In this embodiment of the invention, due to the difference in physical properties between the second layer of photoresist and the first layer of photoresist, there is a difference in the development effect of the developing solution, resulting in the remaining structure of the second layer of photoresist on the sixth wafer 6 being greater than the remaining structure of the first layer of photoresist on the sixth wafer 6.

[0053] S7. The sixth wafer 6 is coated to obtain the seventh wafer 7.

[0054] In this embodiment of the invention, the sixth wafer 6 is coated by electron beam evaporation. Since the second layer of photoresist has more remaining structure than the first layer of photoresist, a gap is formed between the second layer of photoresist and the first layer of photoresist when the metal film 14 is coated. This effectively avoids the photoresist from adhering to the periphery of the metal film 14 and causing incomplete peeling.

[0055] S8. The photoresist on the seventh wafer 7 is stripped using a preset chemical solvent to obtain the interdigital transducer 8.

[0056] In this embodiment of the invention, the preset chemical solvent includes N-methylpyrrolidone (NMP) and tetramethylammonium hydroxide (TMAH); based on the total mass of the preset chemical solvent, the mass of N-methylpyrrolidone accounts for 5%-30% of the total mass of the preset chemical solvent, and the mass of tetramethylammonium hydroxide accounts for 2.5% of the total mass of the preset chemical solvent.

[0057] Compared with existing technologies, this invention coats the wafer with two layers of photoresist. Due to the difference in properties between the two layers of photoresist, the top layer of photoresist will have more residual structure than the bottom layer during the subsequent spin coating and development process, forming a T-shaped photoresist structure. This allows a gap to be formed between the metal film and the bottom layer of photoresist during wafer deposition, effectively preventing photoresist from adhering to the periphery of the metal film and causing incomplete peeling. This effectively improves the electrical performance and reliability of the interdigital transducer and its surface acoustic wave filter.

[0058] To better illustrate the technical effects achieved by the embodiments of the present invention, two specific embodiments will be described in detail below:

[0059] Specific Implementation Example 1

[0060] Please refer to Figure 3, which is a cross-sectional schematic diagram of the preparation process of the interdigital transducer 8 provided in the embodiment of the present invention, specifically embodiment 1.

[0061] S1. The surface of the wafer is cleaned to obtain the first wafer 1.

[0062] In this embodiment of the invention, the surface of the wafer is cleaned using ultrasonic waves.

[0063] S2. Spin-coat a layer of first photoresist 11 onto the surface of the first wafer 1 to obtain a second wafer 2 coated with the first layer of photoresist.

[0064] In this embodiment of the invention, the sensitivity range of the first photoresist 11 is 10-1000 mJ / cm. 2 The first photoresist 11 is uniformly spin-coated onto the first wafer 1 using a high-speed homogenizer.

[0065] S3. Perform a first hardening process on the second wafer 2 to obtain a third wafer 3; wherein the baking time for the first hardening process of the two wafers is 20-45 seconds and the baking temperature is 70-100℃.

[0066] In this embodiment of the invention, the second wafer 2 is subjected to a first hardening process by a heating platform. The first hardening process removes some of the residual moisture in the first photoresist 11, forming the first photoresist 11 after the first hardening, which improves the adhesion and stability between the first photoresist 11 and the surface of the second wafer 2.

[0067] S4. A second layer of photoresist is spin-coated onto the surface of the first layer of photoresist on the third wafer 3 and a second hardening treatment is performed to obtain a fourth wafer 4 coated with two layers of photoresist.

[0068] In this embodiment of the invention, step S4 includes the following sub-steps:

[0069] S41a, a second photoresist 12 is spin-coated onto the surface of the first layer of photoresist on the third wafer 3, and the sensitivity of the second photoresist 12 is lower than that of the first photoresist 11.

[0070] Specifically, the second photoresist 12 has a sensitivity range of 10-1000 mJ / cm. 2 Furthermore, the sensitivity of the first photoresist 11 is 1.3-2.0 times that of the second photoresist 12. When the sensitivity of the photoresist during the two spin coatings is small, the exposure time and exposure dose in step S5 can be adjusted appropriately.

[0071] S42a. The third wafer 3 after spin coating the second photoresist 12 is subjected to a second hardening process to obtain the fourth wafer 4. The baking time of the third wafer 3 during the second hardening process is 20-45 seconds and the baking temperature is 70-100℃.

[0072] Specifically, due to the difference in sensitivity between the two photoresist layers after the second hardening process, when spin-coating the developer in the subsequent step S6, the remaining structure of the second photoresist layer after spin-coating the developer will be more than the remaining structure of the first photoresist layer, and the overall photoresist will form a T-shaped structure.

[0073] S5. Exposure processing is performed on the fourth wafer 4 to obtain the fifth wafer 5.

[0074] In this embodiment of the invention, the fourth wafer 4 is exposed using a deep ultraviolet light source through a mask 13. The exposure time of the fourth wafer 4 by the deep ultraviolet light source (DUV) through the mask 13 can be set according to the actual situation.

[0075] S6. Spin-coating developer onto the fifth wafer 5 to remove unexposed areas on the fifth wafer 5, resulting in a sixth wafer 6; wherein the remaining structure of the second photoresist layer of the sixth wafer 6 is greater than the remaining structure of the first photoresist layer of the sixth wafer 6.

[0076] In this embodiment of the invention, due to the difference in sensitivity between the second layer of photoresist and the first layer of photoresist, there is a difference in the development effect of the developing solution, resulting in more remaining structures of the second layer of photoresist on the sixth wafer 6 than the remaining structures of the first layer of photoresist on the sixth wafer 6.

[0077] S7. The sixth wafer 6 is coated to obtain the seventh wafer 7.

[0078] In this embodiment of the invention, the sixth wafer 6 is coated by electron beam evaporation. Since the second layer of photoresist has more remaining structure than the first layer of photoresist, a gap is formed between the second layer of photoresist and the first layer of photoresist when the metal film 14 is coated. This effectively avoids the photoresist from adhering to the periphery of the metal film 14 and causing incomplete peeling.

[0079] S8. The photoresist on the seventh wafer 7 is stripped using a preset chemical solvent to obtain the interdigital transducer 8.

[0080] In this embodiment of the invention, the preset chemical solvent includes N-methylpyrrolidone (NMP) and tetramethylammonium hydroxide (TMAH); based on the total mass of the preset chemical solvent, the mass of N-methylpyrrolidone accounts for 5%-30% of the total mass of the preset chemical solvent, and the mass of tetramethylammonium hydroxide accounts for 2.5% of the total mass of the preset chemical solvent.

[0081] Specific Implementation Example 2

[0082] Please refer to Figure 4, which is a cross-sectional schematic diagram of the preparation process of the interdigital transducer 8 provided in embodiment 2 of the present invention.

[0083] S1. The surface of the wafer is cleaned to obtain the first wafer 1.

[0084] In this embodiment of the invention, the surface of the wafer is cleaned using ultrasonic waves.

[0085] S2. Spin-coat a layer of first photoresist 11 onto the surface of the first wafer 1 to obtain a second wafer 2 coated with the first layer of photoresist.

[0086] In this embodiment of the invention, the sensitivity range of the first photoresist 11 is 10-1000 mJ / cm. 2 The first photoresist 11 is uniformly spin-coated onto the first wafer 1 using a high-speed homogenizer.

[0087] S3. Perform a first hardening process on the second wafer 2 to obtain a third wafer 3; wherein the baking time for the first hardening process of the two wafers is 20-45 seconds and the baking temperature is 70-100℃.

[0088] In this embodiment of the invention, the second wafer 2 is subjected to a first hardening process by a heating platform. The first hardening process removes some of the residual moisture in the first photoresist 11, thereby improving the adhesion and stability between the first photoresist 11 and the surface of the second wafer 2.

[0089] S4. A second layer of photoresist is spin-coated onto the surface of the first layer of photoresist on the third wafer 3 and a second hardening treatment is performed to obtain a fourth wafer 4 coated with two layers of photoresist.

[0090] In this embodiment of the invention, step S4 includes the following sub-steps:

[0091] S41b: Spin-coat the surface of the first layer of photoresist on the third wafer 3 to form a second layer of photoresist;

[0092] S42b, the third wafer 3 after spin coating of the first photoresist 11 is subjected to a second hardening process through the heating platform to obtain the fourth wafer 4; wherein, the baking time during the second hardening process is 20-45 seconds, and the baking temperature during the second hardening process is higher than the baking temperature during the first hardening process, and is 5-35°C higher.

[0093] Specifically, due to the difference in hardness and viscosity between the two photoresist layers after the second hardening process, when spin-coating the developer in the subsequent step S6, the remaining structure of the second photoresist layer after spin-coating the developer will be greater than the remaining structure of the first photoresist layer, forming a T-shaped photoresist as a whole.

[0094] S5. Exposure processing is performed on the fourth wafer 4 to obtain the fifth wafer 5.

[0095] In this embodiment of the invention, the fourth wafer 4 is exposed using a deep ultraviolet light source through a mask 13. The exposure time of the fourth wafer 4 by the deep ultraviolet light source (DUV) through the mask 13 can be set according to the actual situation.

[0096] S6. Spin-coating developer onto the fifth wafer 5 to remove unexposed areas on the fifth wafer 5, resulting in a sixth wafer 6; wherein the remaining structure of the second photoresist layer of the sixth wafer 6 is greater than the remaining structure of the first photoresist layer of the sixth wafer 6.

[0097] In this embodiment of the invention, due to the difference in physical properties between the second layer of photoresist and the first layer of photoresist, there is a difference in the development effect of the developing solution, resulting in the remaining structure of the second layer of photoresist on the sixth wafer 6 being greater than the remaining structure of the first layer of photoresist on the sixth wafer 6.

[0098] S7. The sixth wafer 6 is coated to obtain the seventh wafer 7.

[0099] In this embodiment of the invention, the sixth wafer 6 is coated by electron beam evaporation. Since the second layer of photoresist has more remaining structure than the first layer of photoresist, a gap is formed between the second layer of photoresist and the first layer of photoresist when the metal film 14 is coated. This effectively avoids the photoresist from adhering to the periphery of the metal film 14 and causing incomplete peeling.

[0100] S8. The photoresist on the seventh wafer 7 is stripped using a preset chemical solvent to obtain the interdigital transducer 8.

[0101] In this embodiment of the invention, the preset chemical solvent includes N-methylpyrrolidone (NMP) and tetramethylammonium hydroxide (TMAH); based on the total mass of the preset chemical solvent, the mass of N-methylpyrrolidone accounts for 5%-30% of the total mass of the preset chemical solvent, and the mass of tetramethylammonium hydroxide accounts for 2.5% of the total mass of the preset chemical solvent.

[0102] Implementation Method 2

[0103] The present invention also provides an interdigital transducer, which is manufactured by the interdigital transducer manufacturing method described above. Since the interdigital transducer in this embodiment is manufactured by the interdigital transducer manufacturing method in Embodiment 1, the interdigital transducer in this embodiment can also achieve the technical effects achieved by the interdigital transducer manufacturing method in Embodiment 1, and will not be elaborated further here.

[0104] Implementation Method 3

[0105] The present invention also provides a surface acoustic wave (SAW) filter, which includes the interdigital transducer described in Embodiment 2. Since the SAW filter in this embodiment includes the interdigital transducer in Embodiment 2, the SAW filter in this embodiment can also achieve the technical effects achieved by the interdigital transducer in Embodiment 2, and will not be elaborated further here.

[0106] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0107] The embodiments of the present invention have been described above with reference to the accompanying drawings. The disclosed embodiments are merely preferred embodiments of the present invention. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many equivalent changes in form without departing from the spirit and scope of the claims of the present invention, and all such changes are within the protection scope of the present invention.

Claims

1. A method of fabricating an interdigital transducer, characterized by, The preparation method comprises the following steps: S1, cleaning the surface of a wafer to obtain a first wafer; S2, spin coating a first photoresist on the surface of the first wafer to obtain a second wafer coated with the first photoresist; S3, performing a first hard baking treatment on the second wafer to obtain a third wafer; wherein the baking time of the second wafer during the first hard baking treatment is 20-45 seconds, and the baking temperature is 70-100℃; S4, spin coating a second photoresist on the surface of the first photoresist of the third wafer and performing a second hard baking treatment to obtain a fourth wafer coated with two layers of photoresist; S5, performing an exposure treatment on the fourth wafer to obtain a fifth wafer; S6, spin coating a developing solution on the surface of the fifth wafer to remove the unexposed areas on the fifth wafer to obtain a sixth wafer; wherein the remaining structure of the second photoresist of the sixth wafer is more than that of the first photoresist of the sixth wafer; S7, performing a plating film treatment on the sixth wafer to obtain a seventh wafer; S8, stripping the photoresist on the seventh wafer by a preset chemical solvent to obtain an interdigital transducer.

2. The method for preparing the interdigital transducer as described in claim 1, characterized in that, In step S4, the following sub-steps are included: S41a, spin coating a second photoresist on the surface of the first photoresist of the third wafer, and the sensitivity of the second photoresist is lower than that of the first photoresist; S42a, performing a second hard baking treatment on the third wafer after spin coating the second photoresist to obtain the fourth wafer; wherein the baking time of the third wafer during the second hard baking treatment is 20-45 seconds, and the baking temperature is 70-100℃.

3. The method for preparing the interdigital transducer as described in claim 2, characterized in that, The sensitivity of the first photoresist is 1.3-2.0 times that of the second photoresist.

4. The method for preparing the interdigital transducer as described in claim 3, characterized in that, The first photoresist sensitivity ranges from 10 to 1000 mJ / cm 2 .

5. The method for preparing the interdigital transducer as described in claim 1, characterized in that, In step S4, the following sub-steps are included: S41b, spin coating the first photoresist on the surface of the first photoresist of the third wafer to form a second layer of photoresist; S42b, performing a second hard baking treatment on the third wafer after spin coating the first photoresist by a heating platform to obtain the fourth wafer; wherein the baking time of the second hard baking treatment is 20-45 seconds, and the baking temperature of the second hard baking treatment is higher than that of the first hard baking treatment.

6. The method for preparing the interdigital transducer as described in claim 5, characterized in that, The baking temperature of the second hard baking treatment is 5-30℃ higher than that of the first hard baking treatment.

7. The method for preparing the interdigital transducer as described in claim 1, characterized in that, The preset chemical solvent comprises N-methyl pyrrolidone and tetramethylammonium hydroxide; In terms of the total mass of the preset chemical solvent, the mass of the N-methyl pyrrolidone accounts for 5%-30% of the total mass of the preset chemical solvent, the mass of the tetramethylammonium hydroxide accounts for 2.5% of the total mass of the preset chemical solvent, and the balance is water.

8. The method for preparing the interdigital transducer as described in claim 1, characterized in that, In step S1, the surface of the wafer is cleaned by ultrasonic waves; in step S2, a first photoresist is spin-coated on the surface of the first wafer by a high-speed homogenizer; in step S3, the second wafer is subjected to a first hard-baking treatment by a heating platform; in step S5, the fourth wafer is subjected to an exposure treatment by a mask through a deep ultraviolet light source; and in step S7, the sixth wafer is subjected to a film plating treatment by electron beam evaporation.

9. An interdigital transducer, characterized by The interdigital transducer is prepared by the method of claim 1-8.

10. A surface acoustic filter, characterized by, The surface acoustic wave filter comprises the interdigital transducer of claim 9.

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