Method for manufacturing a surface acoustic wave filter and surface acoustic wave filter

Abstract

The application is suitable for the field of semiconductor processing and manufacturing, and provides a manufacturing method of a surface acoustic wave filter and the surface acoustic wave filter. The surface acoustic wave filter is composed of multiple cavities. The cavity comprises a substrate, the surface of the substrate has multiple grooves; a bus bar is fixed in the groove, and the top surface of the bus bar is higher than the surface of the substrate; and a plating layer covers the surface of the substrate between the exposed surfaces of adjacent bus bars. The application uses ion beam etching to etch the substrate under the bus bar to a certain depth, and then fills metal material through ion beam evaporation or electroplating to form a bus bar with a certain depth. As a result, the bus bar edge has an etching cross section, the continuous potential energy surface in the original sound propagation direction is eliminated, the transverse surface acoustic wave generated by the bus bar is reduced and eliminated, the in-band jitter is reduced, and the in-band performance of the surface acoustic wave filter is improved.

Description

Technical Field

[0001] This invention is applicable to the field of semiconductor processing and manufacturing, and particularly relates to a method for manufacturing a surface acoustic wave (SAW) filter and the SAW filter itself. Background Technology

[0002] Surface acoustic wave (SAW) filters are a widely used filter technology. Their basic principle involves using piezoelectric materials, such as lithium niobate (LiNbO3) or lithium tantalate (LiTaO3) crystals, to convert electromagnetic signals into mechanical vibrations. These vibrations are then filtered through mechanical resonance, targeting the waveband near the mechanical resonance frequency. Because the wavelength of mechanical waves at the same frequency is much shorter than that of electromagnetic waves (only one three-hundred-thousandth of the wavelength), SAW filters are smaller and have a higher roll-off than traditional cavity filters, making them widely used in mobile phones, base stations, and other terminal applications.

[0003] In the prior art, the standard surface acoustic wave filter single cavity structure is as follows: Figure 1 As shown, it consists of an interdigital transducer (IDT), a busbar connecting the IDT, and reflective gratings on both sides of the IDT. The IDT is used for the interconversion of electroacoustic signals, the busbar connects and conducts electricity to the IDT, and the reflective gratings enhance the energy concentration of sound waves to improve the resonant Q value. By connecting multiple cavities electrically or acoustically in a certain way, a complete filter can be obtained, realizing the function of filtering electromagnetic waves of a specific frequency.

[0004] In surface acoustic wave (SAW) filters, transverse modes—vibrational modes perpendicular to the acoustic propagation direction of the inductively coupled transducer (IDT)—are vibrational modes that need to be suppressed. This is because transverse modes cause discontinuities in acoustic wave propagation and introduce stray waves, increasing the jitter in the filter's passband and affecting the final filter performance. Some transverse modes are caused by the diffraction of acoustic waves propagating within the IDT; another part is caused by the busbars, which are conductive and placed on top of a piezoelectric crystal, and the SAW waves excited by the busbars also become part of the transverse modes.

[0005] Existing technologies typically employ a method of adding a layer of heavy metal to the tips of the interdigitated fingers to disrupt the continuous potential energy surface, thereby suppressing transverse modes. However, the existing methods, due to the excessively narrow width of the interdigitated finger structure in the IDT, impose higher requirements on process alignment and design, making it difficult to quickly and easily reduce the transverse modes of the filter. Summary of the Invention

[0006] This invention provides a method for manufacturing a surface acoustic wave (SAW) filter and a SAW filter, aiming to solve the problems of existing methods for suppressing transverse modes being limited by the width of the interdigital structure and having high process requirements.

[0007] In a first aspect, embodiments of the present invention provide a method for manufacturing a surface acoustic wave filter, the method comprising the following steps:

[0008] S1. Cover the surface of the substrate with photoresist;

[0009] S2. Use a light shield with through holes to cover the photoresist, and then perform photolithography to remove the photoresist outside the through hole location;

[0010] S3. Remove the light shield and perform a plating on the surface of the processed surface;

[0011] S4. Remove the photoresist that was not removed in step S3 to expose the area of ​​the processing surface that is not covered by the coating, and etch the area of ​​the processing surface that is not covered by the coating to form a trench on the substrate.

[0012] S5. Fill the trench with metal to form a busbar;

[0013] S6. Re-cover the photoresist on the processed surface, so that the photoresist covers the adjacent busbars and the coating between the adjacent busbars;

[0014] S7. Remove the coating layer not covered by the photoresist on the processing surface by etching. Then, remove all the photoresist to obtain the cavity structure. Combine the different cavity structures according to their electrical characteristics to obtain the surface acoustic wave filter.

[0015] Furthermore, in step S3, the thickness of the coating is not greater than the thickness of the photoresist.

[0016] Furthermore, in step S4, the coating is aluminum.

[0017] Furthermore, in step S4, the metal is filled into the trench by ion beam evaporation or ion beam electroplating.

[0018] Furthermore, in step S5, the metal is filled into the trench by ion beam evaporation or ion beam electroplating.

[0019] Furthermore, in step S5, the metal is aluminum or an aluminum-copper alloy.

[0020] Secondly, embodiments of the present invention also provide a surface acoustic wave filter, comprising at least two cavity structures stacked or cascaded together, wherein the cavity structure includes:

[0021] Substrate, the surface of which has multiple trenches;

[0022] A busbar, the busbar being fixed in the trench, and the top surface of the busbar being higher than the surface of the substrate; and,

[0023] A coating that covers the surface of the substrate between the exposed surfaces of adjacent busbars;

[0024] The surface acoustic wave filter is manufactured by the surface acoustic wave filter manufacturing method described in any one of the above embodiments.

[0025] The beneficial effects achieved by this invention are due to the use of ion beam etching to etch the substrate under the busbar to a certain depth, and then using ion beam evaporation or electroplating to fill the metal material to form a busbar with a certain depth. This method makes the edge of the busbar have an etched cross section, eliminating the continuous potential energy surface in the original sound propagation direction. Ultimately, the transverse surface acoustic wave generated by the busbar is reduced or eliminated, reducing jitter in the passband and thus improving the passband performance of the surface acoustic wave filter. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a single cavity structure of a surface acoustic wave filter in the prior art;

[0027] Figure 2 This is a flowchart of the manufacturing method of the surface acoustic wave filter provided in the embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram of the manufacturing process of a single cavity of a surface acoustic wave filter provided in an embodiment of the present invention;

[0029] Figure 4 This is a schematic diagram of the cavity structure of the surface acoustic wave filter provided in an embodiment of the present invention;

[0030] Figure 5 This is a schematic diagram of the surface acoustic wave filter provided in an embodiment of the present invention. Detailed Implementation

[0031] 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.

[0032] Please refer to Figure 2 , Figure 2 This is a flowchart illustrating the steps of a surface acoustic wave (SAW) filter manufacturing method provided in an embodiment of the present invention. The manufacturing method includes the following steps:

[0033] S1. Cover the surface of the substrate with photoresist.

[0034] Photoresist is a type of etchant material whose solubility changes when exposed to ultraviolet light, electron beams, ion beams, X-rays, etc. Its function is to protect areas that do not need to be processed during the photolithography process.

[0035] S2. Use a light shield with through holes to cover the photoresist, and then perform photolithography to remove the photoresist outside the through hole location.

[0036] The light shield used in this embodiment of the invention is used to determine the location of the trench.

[0037] S3. Remove the light shield and perform a coating on the surface of the processed surface.

[0038] After removing the light shield, the substrate surface is exposed, but a portion of the photoresist is still retained. The remaining photoresist is used to protect the trenches from being covered by the coating.

[0039] S4. Remove the photoresist that was not removed in step S3 to expose the area of ​​the processing surface that is not covered by the coating, and etch the area of ​​the processing surface that is not covered by the coating to form a trench on the substrate.

[0040] S5. Fill the groove with metal to form a busbar.

[0041] In this embodiment of the invention, multiple trenches can be etched at once in the same set of processes. Similarly, the operation of filling metal to form a busbar can also be completed multiple times in the same set of processes.

[0042] S6. Re-cover the photoresist on the processed surface, so that the photoresist covers the adjacent busbars and the coating between the adjacent busbars.

[0043] Specifically, the process schematic diagram of a single cavity of the surface acoustic wave filter provided in this embodiment of the invention is as follows: Figure 3 As shown, for a surface acoustic wave filter cavity with a specific filtering function, the IDT formed is located between two busbars. Therefore, the coating can be removed where the IDT does not need to be constructed, reducing the consumption of raw materials in the manufacturing process.

[0044] S7. Remove the coating layer not covered by the photoresist on the processing surface by etching. Then, remove all the photoresist to obtain the cavity structure. Combine the different cavity structures according to their electrical characteristics to obtain the surface acoustic wave filter.

[0045] Furthermore, in step S4, the thickness of the coating is not greater than the thickness of the photoresist.

[0046] Furthermore, in step S4, the coating is aluminum (Al).

[0047] Furthermore, in step S4, the etching method used to etch the processing surface not covered by the coating is ion beam etching.

[0048] Furthermore, in step S5, the metal is filled into the trench by ion beam evaporation or ion beam electroplating.

[0049] Furthermore, in step S5, the metal is aluminum (Al) or an aluminum-copper alloy (AlCu).

[0050] The beneficial effects achieved by this invention are due to the use of ion beam etching to etch the substrate under the busbar to a certain depth, and then using ion beam evaporation or electroplating to fill the metal material to form a busbar with a certain depth. This method makes the edge of the busbar have an etched cross section, eliminating the continuous potential energy surface in the original sound propagation direction. Ultimately, the transverse surface acoustic wave generated by the busbar is reduced or eliminated, reducing jitter in the passband and thus improving the passband performance of the surface acoustic wave filter.

[0051] This invention also provides a surface acoustic wave filter, which includes at least two cavity structures stacked or cascaded together. Please refer to [reference needed]. Figure 4 , Figure 4 This is a schematic diagram of the cavity structure of the surface acoustic wave filter provided in an embodiment of the present invention. The cavity structure 100 includes:

[0052] Substrate 1, the surface of which has a plurality of trenches 11;

[0053] Busbar 2, the busbar 11 being fixed in the trench 11, and the top surface of the busbar 11 being higher than the surface of the substrate 1; and,

[0054] A coating 3, which covers the surface of the substrate 1 between the exposed surfaces of adjacent busbars 2;

[0055] The surface acoustic wave filter is manufactured using the surface acoustic wave filter manufacturing method described in the previous embodiment.

[0056] The surface acoustic wave filter provided in this embodiment of the invention has an etched cross section on the edge of the busbar of the cavity, which eliminates the continuous potential energy surface in the original direction of sound propagation. This ultimately reduces and eliminates the transverse surface acoustic wave generated by the busbar, reduces jitter in the passband, and thus improves the passband performance.

[0057] Please refer to Figure 5 , Figure 5This is a schematic diagram of the surface acoustic wave (SAW) filter provided in an embodiment of the present invention. The SAW filter is composed of multiple cascaded resonators (1-6), wherein each resonator is connected via a connection provided in this embodiment of the present invention. Figure 4 The cavity structure shown is formed by arranging resonators with different characteristics according to certain electrical rules, such as... Figure 5 After being cascaded together, a complete surface acoustic wave (SAW) filter structure can be formed. It should be noted that... Figure 5 The connection method described is merely an example of an embodiment of the present invention and is not intended to limit the specific structure of the surface acoustic wave filter of the present invention.

[0058] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. The storage medium can be a magnetic disk, optical disk, read-only memory (ROM), or random access memory (RAM), etc.

[0059] 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.

[0060] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk), and includes several instructions to cause a terminal (which may be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in the various embodiments of the present invention.

[0061] 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 for manufacturing a surface acoustic wave filter, characterized in that, The manufacturing method includes the following steps: S1. Cover the surface of the substrate with photoresist; S2. Use a light shield with through holes to cover the photoresist, and then perform photolithography to remove the photoresist outside the through hole location; S3. Remove the light shield and apply a coating to the surface of the processed surface, wherein the coating is aluminum; S4. Remove the photoresist that was not removed in step S3 to expose the area of ​​the processing surface that is not covered by the coating, and etch the area of ​​the processing surface that is not covered by the coating to form a trench on the substrate. S5. Fill the trench with metal to form a busbar; S6. Re-cover the photoresist on the processed surface, so that the photoresist covers the adjacent busbars and the coating between the adjacent busbars; S7. Remove the coating layer not covered by the photoresist on the processing surface by etching. Then, remove all the photoresist to obtain the cavity structure. Combine the different cavity structures according to their electrical characteristics to obtain the surface acoustic wave filter.

2. The method for manufacturing a surface acoustic wave filter as described in claim 1, characterized in that, In step S3, the thickness of the coating is not greater than the thickness of the photoresist.

3. The method for manufacturing a surface acoustic wave filter as described in claim 1, characterized in that, In step S4, the etching method used to etch the area of ​​the processing surface not covered by the coating is ion beam etching.

4. The method for manufacturing a surface acoustic wave filter as described in claim 1, characterized in that, In step S5, the metal is filled into the trench by ion beam evaporation or ion beam electroplating.

5. The method for manufacturing a surface acoustic wave filter as described in claim 1, characterized in that, In step S5, the metal is aluminum or an aluminum-copper alloy.

6. A surface acoustic wave filter, characterized in that, It includes at least two cavity structures that are stacked or cascaded together, the cavity structure comprising: Substrate, the surface of which has multiple trenches; A busbar, the busbar being fixed in the trench, and the top surface of the busbar being higher than the surface of the substrate; and, A coating that covers the surface of the substrate between the exposed surfaces of adjacent busbars; The surface acoustic wave filter is manufactured by the method of manufacturing a surface acoustic wave filter according to any one of claims 1-5.

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