Forming method of filter

Abstract

A forming method of a filter comprises the following steps: after forming a first mask for covering an initial electrode finger in an edge region, removing partial thickness of an initial interdigital electrode at the side part of a first mask layer, and forming a bus bar of a bus region and electrode fingers of a central region and the edge region, a piston structure located at the top of an electrode finger is formed at the intersection of the first mask layer and the electrode finger of the edge area; the first mask layer covers the initial electrode finger in the edge area, and the projection of the first mask layer on the substrate intersects with the projection of the initial electrode finger on the substrate, namely, the edge of the first mask layer is self-aligned with the side wall of the initial electrode finger in the edge area, so that the side wall of the piston structure is aligned with the side wall of the electrode finger; and the appearance quality of the interdigital electrode and the alignment precision of the electrode fingers and the piston structure are improved, so that the clutter suppression effect of the filter is improved.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to the field of semiconductor manufacturing, and in particular, to a forming method of a filter. BACKGROUND

[0002] A piezoelectric surface acoustic wave (SAW) filter is a kind of filter device made by using the piezoelectric effect and the physical characteristics of the propagation of the surface acoustic wave, and is widely used in various fields, such as the radio frequency field. The surface acoustic wave is an elastic wave whose energy is concentrated near the surface.

[0003] In the current design of the surface acoustic wave product, the SAW filter will generate a transversely propagating acoustic wave, which will cause the SAW filter to have a transverse resonant mode, that is, to generate a spurious wave in the passband and near the passband, which will increase the loss of the SAW filter and cause the quality factor value (Q value) to fluctuate greatly, thereby reducing the performance of the SAW filter.

[0004] Therefore, how to suppress the transversely propagating acoustic wave has become a problem to be solved urgently. SUMMARY

[0005] The problem solved by embodiments of the present application is to provide a forming method of a filter, which is beneficial to improve the performance of the filter.

[0006] To solve the above problem, embodiments of the present application provide a forming method of a filter, comprising: providing a substrate, the substrate comprising a center region, a convergence region and an edge region between the center region and the convergence region, the center region, the edge region and the convergence region being arranged in sequence along a first direction; forming an initial interdigital electrode on the substrate in the center region, the edge region and the convergence region, the initial interdigital electrode comprising an initial convergence strip located in the convergence region, and initial electrode fingers located in the center region and the edge region, the initial electrode fingers extending along the first direction and being arranged in intervals along a second direction, the initial convergence strip extending along the second direction and connecting each of the initial electrode fingers, the first direction intersecting the second direction; forming a first mask layer covering the initial electrode fingers in the edge region, the first mask layer extending along the second direction, a projection of the first mask layer on the substrate intersecting a projection of the initial electrode fingers on the substrate; removing a part of thickness of the initial interdigital electrode located at a side of the first mask layer, to form a convergence strip located in the convergence region, and electrode fingers located in the center region and the edge region, and to form a piston structure located at a top of the electrode finger at an intersection of the first mask layer and the electrode finger of the edge region, the convergence strip, the piston structure and the electrode finger constituting an interdigital electrode.

[0007] Compared with the prior art, the technical scheme of the embodiment of the present application has the following advantages: The embodiment of the present application provides a filter forming method, which comprises the following steps: providing a substrate, wherein the substrate comprises a center region, a convergence region and an edge region between the center region and the convergence region, and the center region, the edge region and the convergence region are arranged in sequence along a first direction; forming an initial interdigital electrode on the substrate in the center region, the edge region and the convergence region, wherein the initial interdigital electrode comprises an initial convergence strip in the convergence region and initial electrode fingers in the center region and the edge region, the initial electrode fingers extend along the first direction and are arranged in the second direction, the initial convergence strip extends along the second direction and is connected with each of the initial electrode fingers, and the first direction intersects with the second direction; forming a first mask layer in the edge region, wherein the first mask layer covers the initial electrode fingers and extends along the second direction, and a projection of the first mask layer on the substrate intersects with a projection of the initial electrode fingers on the substrate; removing a partial thickness of the initial interdigital electrode on the side of the first mask layer to form a convergence strip in the convergence region, electrode fingers in the center region and the edge region and a piston structure on the top of the electrode fingers at the intersection of the first mask layer and the electrode fingers in the edge region, and the convergence strip, the piston structure and the electrode fingers constitute an interdigital electrode; in the embodiment, since the first mask layer covers the initial electrode fingers in the edge region, and the projection of the first mask layer on the substrate intersects with the projection of the initial electrode fingers on the substrate, that is, the edge of the first mask layer is self-aligned with the side wall of the initial electrode fingers in the edge region, therefore, in the process of removing the partial thickness of the initial interdigital electrode on the side of the first mask layer and forming the piston structure on the top of the electrode fingers at the intersection of the first mask layer and the electrode fingers in the edge region, the side wall of the piston structure is aligned with the side wall of the electrode fingers, which is beneficial to improving the appearance quality of the interdigital electrode and the alignment accuracy of the electrode fingers and the piston structure, thereby enhancing the function of the filter in suppressing spurs and improving the performance of the filter. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1 is a top view of the step of providing a substrate in the filter forming method of the embodiment of the present application; Figure 2 is a top view of the step of forming an interdigital electrode material layer in the filter forming method of the embodiment of the present application; Figure 3 is a top view of the step of forming an interdigital electrode material layer in the filter forming method of the embodiment of the present application, Figure 2 is a sectional view along the direction of AA1; Figure 4This is a top view of a filter forming method according to an embodiment of the present invention, wherein a patterned second mask layer is formed on the interdigitated electrode material layer in the central region, the busbar region, and the edge region. Figure 5 In a filter formation method according to an embodiment of the present invention, Figure 4 A sectional view along the AA1 direction; Figure 6 This is a top view of the initial interdigitated electrodes formed in a filter forming method according to an embodiment of the present invention; Figure 7 In a filter formation method according to an embodiment of the present invention, Figure 6 Top view along the AA1 direction; Figure 8 This is a top view of a filter forming method according to an embodiment of the present invention, in which a filling layer is formed between adjacent initial interdigitated electrodes, and a first mask layer covering the initial electrode fingers is formed in the edge region; Figure 9 In a filter formation method according to an embodiment of the present invention, Figure 8 A sectional view along the AA1 direction; Figure 10 This is a top view of a filter forming method according to an embodiment of the present invention, showing the formation of a busbar, electrode fingers, and piston structure. Figure 11 In a filter formation method according to an embodiment of the present invention, Figure 10 A cross-sectional view along the BB1 ​​direction. Detailed Implementation

[0009] As can be seen from the background technology, it is currently difficult to suppress transversely propagating sound waves in SAW filters.

[0010] There are generally two methods to suppress transversely propagating sound waves in a SAW filter. One method is to thicken the ends of the interdigital electrodes of the SAW filter to form a piston structure; the other method is to thicken the ends of the interdigital electrodes to form a hammerhead structure. Both methods increase the mass of the ends of the interdigital electrodes, thereby reducing the propagation speed of transversely propagating sound waves in that region and thus suppressing transversely propagating sound waves in the SAW filter.

[0011] Research has found that when using the method of forming a piston structure, the electrode fingers of the SAW filter are first formed, and then the piston structure is formed at the top of both ends of the electrode fingers. That is, the electrode fingers and piston structure are formed in two steps. Due to the limitations of photolithography process conditions, the alignment accuracy between the sidewall of the piston structure and the sidewall of the electrode fingers is easily reduced, which in turn makes the morphology quality of the interdigitated electrode formed by the piston structure and the electrode fingers poor.

[0012] To address the aforementioned technical problems, embodiments of the present invention provide a method for forming a filter, comprising: providing a substrate, the substrate including a central region, a bus region, and an edge region located between the central region and the bus region, the central region, the edge region, and the bus region being arranged sequentially along a first direction; forming initial interdigitated electrodes on the substrate of the central region, the edge region, and the bus region, the initial interdigitated electrodes including initial bus bars located in the bus region and initial electrode fingers located in the central region and the edge region, the initial electrode fingers extending along the first direction and spaced apart along a second direction, the initial bus bars extending along the second direction and connecting each of the initial electrode fingers. The electrode finger is formed in the edge region, where the first direction intersects the second direction; a first mask layer is formed to cover the initial electrode finger, the first mask layer extends along the second direction, and the projection of the first mask layer on the substrate intersects the projection of the initial electrode finger on the substrate; a portion of the thickness of the initial interdigitated electrode located on the side of the first mask layer is removed to form a busbar located in the busbar region, and electrode fingers located in the center region and the edge region, and a piston structure is formed at the intersection of the first mask layer and the electrode fingers in the edge region, the busbar, the piston structure and the electrode fingers constituting an interdigitated electrode.

[0013] In the scheme disclosed in this embodiment of the invention, a portion of the thickness of the initial interdigitated electrode located on the side of the first mask layer is removed, and a piston structure is formed at the intersection of the first mask layer and the electrode fingers in the edge region, located at the top of the electrode fingers. Since the first mask layer covers the initial electrode fingers in the edge region, and the projection of the first mask layer on the substrate intersects with the projection of the initial electrode fingers on the substrate, that is, the edge of the first mask layer is self-aligned with the sidewall of the initial electrode fingers in the edge region, therefore, in the process of removing a portion of the thickness of the initial interdigitated electrode located on the side of the first mask layer and forming the piston structure at the intersection of the first mask layer and the electrode fingers in the edge region, the sidewall of the piston structure is aligned with the sidewall of the electrode fingers. This is beneficial to improving the morphological quality of the interdigitated electrode and the alignment accuracy of the electrode fingers and the piston structure, thereby enhancing the filter's ability to suppress clutter and thus improving the filter's performance.

[0014] To make the above-mentioned objects, features and advantages of the embodiments of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0015] Figures 1 to 11 This is a schematic diagram of the structure corresponding to each step in one embodiment of the filter formation method of the present invention. Specifically, Figure 1 It provides a top view of the base. Figure 2 This is a top view of the formation of the interdigitated electrode material layer. Figure 3 yes Figure 2 A cross-sectional view along the AA1 direction. Figure 4 This is a top view of a patterned second mask layer formed on the interdigitated electrode material layer within the central region, the busbar region, and the edge region. Figure 5 yes Figure 4 A cross-sectional view along the AA1 direction. Figure 6 This is a top view showing the formation of the initial interdigitated electrodes. Figure 7 yes Figure 6 Top view along the AA1 direction, Figure 8 This is a top view showing the formation of a fill layer between adjacent initial interdigitated electrodes and the formation of a first mask layer in the edge region to cover the initial electrode fingers. Figure 9 yes Figure 8 A cross-sectional view along the AA1 direction. Figure 10 This is a top view of the busbar, electrode fingers, and piston structure. Figure 11 yes Figure 10 A cross-sectional view along the BB1 ​​direction.

[0016] refer to Figure 1 A substrate 500 is provided, the substrate 500 including a central region I, a confluence region II and an edge region III located between the central region I and the confluence region II, the central region I, the edge region III and the confluence region II being arranged sequentially along a first direction X.

[0017] The substrate 500 provides a fabrication platform for subsequent surface acoustic wave (SAW) filters. SAW filters are specialized filtering devices made using the piezoelectric effect and the physical characteristics of surface acoustic wave propagation. In a SAW filter, the signal undergoes two electro-acoustic-electro-electric conversions, thus achieving frequency selectivity. SAW filters offer advantages such as high operating frequency, simple manufacturing process, low manufacturing cost, and high frequency response consistency, and are therefore widely used in various electronic devices.

[0018] In this embodiment, the substrate 500 is a piezoelectric substrate, so that the subsequent surface acoustic wave filter structure can utilize the piezoelectric effect for filtering.

[0019] The substrate 500 may be made of lithium niobate (LiNbO3), lithium tantalate (LiTaO3), quartz, or piezoelectric ceramic. As an example, the substrate 500 may be made of lithium niobate. In other embodiments, the substrate may also be a piezoelectric on insulator (POI) substrate.

[0020] The busbar region II provides space for the subsequent formation of the busbar strip, the edge region III provides space for the subsequent formation of the piston structure and electrode fingers, and the center region I provides space for the subsequent formation of the electrode fingers.

[0021] refer to Figures 2 to 7 Initial interdigitated electrodes 501 are formed on the substrate 500 of the central region I, edge region III, and busbar region II (e.g., Figures 6 to 7 As shown), the initial interdigitated electrode 501 includes an initial bus bar 502 located in the bus region II (as shown). Figure 6 As shown), and the initial electrode fingers 503 located in the central region II and the edge region III (as shown). Figure 6 As shown in the figure, the initial electrode fingers 503 extend along the first direction X and are spaced apart along the second direction Y, and the initial busbar 502 extends along the second direction Y and connects each of the initial electrode fingers 503, and the first direction X and the second direction Y intersect.

[0022] The initial interdigitated electrode 501 is used to form the interdigitated electrode, the initial bus bar 502 is used to form the bus bar, and the initial electrode finger 503 is used to form the electrode finger.

[0023] As an example, the first direction X is perpendicular to the second direction Y. It is understood that in other embodiments, the angle between the first and second directions may be other angles, depending on actual needs.

[0024] As an example, the initial electrode finger 503 of edge region III is also used to form the piston structure in the interdigitated electrode.

[0025] In the step of forming the initial interdigitated electrode 501 on the substrate 500 of the central region I, edge region III and confluence region II, the initial interdigitated electrode 501 is a stacked structure or a single-layer structure.

[0026] In this embodiment, the initial interdigitated electrode 501 has a stacked structure.

[0027] refer to Figure 7As an example, when the initial interdigitated electrode 501 is a stacked structure, the initial interdigitated electrode 501 includes: a third initial interdigitated electrode 504 attached to the substrate 500, a second initial interdigitated electrode 505 located on the third initial interdigitated electrode 504, and a first initial interdigitated electrode 506 located on the second initial interdigitated electrode 505.

[0028] In another embodiment, the initial interdigitated electrode can have two layers. For example, the initial interdigitated electrode can include only the third initial interdigitated electrode and the second initial interdigitated electrode, or it can include the third interdigitated electrode and the first initial interdigitated electrode, or it can include the second initial interdigitated electrode and the first initial interdigitated electrode.

[0029] In other embodiments, the initial interdigitated electrode may be a single-layer structure, or the initial interdigitated electrode may have more than three layers.

[0030] Specifically, the step of forming the initial interdigitated electrode 501 on the substrate 500 of the central region I, edge region III, and busbar region II includes: referencing Figures 2 to 3 An interdigitated electrode material layer 507 is formed on the substrate 500 of the central region I, the busbar region II, and the edge region III; Reference Figures 4 to 5 In the central region I, the busbar region II, and the edge region III, a patterned second mask layer 508 is formed on the interdigitated electrode material layer 507. The second mask layer 508 includes a first mask portion 509 and a second mask portion 510. The first mask portion 509 is located on the interdigitated electrode material layer 507 in the busbar region II. The first mask portion 509 extends along the second direction Y and connects each of the second mask portions 510. The second mask portions 510 extend along the first direction X and are spaced apart along the second direction Y. The second mask portions 510 are located on the interdigitated electrode material layers 507 in the central region I and the edge region II. (Reference) Figures 6 to 7 Using the second mask layer 508 as a mask, the interdigitated electrode material layer 507 is patterned (e.g., ...). Figure 4 As shown, the interdigitated material layer 507 of the busbar region II is patterned as an initial busbar 502 corresponding to the first mask portion 509, and the interdigitated material layer 507 of the center region I and the edge region III is patterned as an initial electrode finger 503 corresponding to the second mask portion 510.

[0031] The interdigitated electrode material layer 507 is used to form the initial interdigitated electrode 501.

[0032] In this embodiment, the process of forming interdigitated electrode material layer 507 on the substrate 500 of the central region I, the busbar region II and the edge region III includes sputtering, atomic layer deposition or vapor deposition.

[0033] It should be noted that sputtering, atomic layer deposition, or vapor deposition processes can improve the film quality of the interdigital electrode material layer 507, thereby improving the film quality of the initial interdigital electrode 501.

[0034] As an example, the process of forming the interdigitated electrode material layer 507 on the substrate 500 of the central region I, the busbar region II and the edge region III is a sputtering process.

[0035] It should be noted that in this embodiment, the initial interdigital electrode 501 has a stacked structure, and correspondingly, the interdigital electrode material layer 507 also has a stacked structure. (See reference...) Figure 3 As an example, the interdigital electrode material layer 507 includes a third interdigital electrode material layer 511 on a substrate, a second interdigital electrode material layer 512 on the third interdigital electrode material layer 511, and a first interdigital electrode material layer 513 on the second interdigital electrode material layer 512.

[0036] Specifically, the third interdigital electrode material layer 511 is used to improve the adhesion between the substrate 500 and the second interdigital electrode material layer 512, the second interdigital electrode material layer 512 is used to improve the conductivity of the filter, and the first interdigital electrode material layer 513 is used to increase the quality of the filter.

[0037] In this embodiment, in the step of forming an interdigitated electrode material layer 507 on the substrate 500 of the central region I, the choke region II and the edge region III, the interdigitated electrode material layer 507 is a stacked structure, the topmost interdigitated electrode material layer 507 is the first interdigitated electrode material layer 513, and another interdigitated electrode material layer 507 located at the bottom of the first interdigitated electrode material layer 513 is the second interdigitated electrode material layer 512. There is a removal selectivity ratio between the first interdigitated electrode material layer 513 and the second interdigitated electrode layer 512.

[0038] It should be noted that there is a removal selectivity between the first interdigital electrode material layer 513 and the second interdigital electrode material layer 512. In the subsequent process of patterning the first interdigital electrode material layer 513 using the second mask layer 508 as a mask, this helps to improve the consistency of the rate of removing the exposed first interdigital electrode material layer 513, thereby improving the accuracy of patterning the first interdigital electrode material layer 513 and correspondingly improving the accuracy of patterning the second interdigital electrode material layer 512.

[0039] In this embodiment, in the step of forming interdigitated electrode material layers 507 on the substrate 500 of the central region I, the confluence region II and the edge region III, the thickness of the first interdigitated electrode material layer 513 is greater than the thickness of the second interdigitated electrode material layer 512.

[0040] It should be noted that the thickness of the first interdigital electrode material layer 513 is greater than the thickness of the second interdigital electrode material layer 512, which is beneficial to increase the quality of the formed interdigital electrode and improve the conductivity of the interdigital electrode.

[0041] As an example, the thickness of the first interdigital electrode material layer 513 is 3 to 5 times the thickness of the second interdigital electrode material layer 512. In other embodiments, the ratio of the thickness of the first interdigital electrode material layer to the thickness of the second interdigital electrode material layer is set according to actual process requirements.

[0042] The material of the second interdigital electrode material layer 512 includes an aluminum-copper alloy or aluminum.

[0043] It should be noted that aluminum-copper alloys or aluminum have good electrical conductivity; therefore, aluminum-copper alloys or aluminum can improve the conductivity of the filter. As an example, the material of the second interdigital electrode material layer 512 is an aluminum-copper alloy.

[0044] The material of the first interdigital electrode material layer 513 includes tungsten or molybdenum.

[0045] It should be noted that tungsten or molybdenum has a large mass; therefore, tungsten or molybdenum can reduce the propagation speed of transversely propagating sound waves in the filter, thereby reducing the characteristic dimension (CD) value of the interdigital electrodes. As an example, the material of the first interdigital electrode material layer 513 is tungsten.

[0046] In this embodiment, when the interdigital electrode material layer is a stacked structure, the interdigital electrode material layer 507 further includes a third interdigital electrode material layer 511 attached to the substrate 500, wherein the adhesion of the third interdigital electrode material layer 511 to the substrate 500 is greater than the adhesion of the second interdigital electrode material layer 512 to the substrate 500.

[0047] As an example, the third interdigital electrode material 511 is the bottommost interdigital electrode material layer 507, and the adhesion of the third interdigital electrode material 511 to the substrate 500 is greater than the adhesion of the adjacent interdigital electrode material layer 507 to the substrate 500.

[0048] The material of the third interdigital electrode material layer 511 includes titanium, chromium, titanium nitride, aluminum nitride, or titanium tungsten.

[0049] It should be noted that titanium, chromium, titanium nitride, aluminum nitride, or titanium tungsten have good adhesion; therefore, titanium, chromium, titanium nitride, aluminum nitride, or titanium tungsten can improve the adhesion between the substrate 500 and the second interdigital electrode material layer 512. As an example, the material of the third interdigital electrode material layer 511 is titanium.

[0050] The second mask layer 508 is used as a mask layer for forming the initial interdigitated electrode 501. Specifically, the first mask portion 509 is provided with a pattern corresponding to the initial busbar 502, and the first mask portion 509 is used as a mask layer for forming the initial busbar 502. The second mask portion 510 is provided with a pattern corresponding to the initial electrode finger 503, and the second mask portion 510 is used as a mask layer for forming the initial electrode finger 503.

[0051] It should be noted that the morphology of the second mask layer 508 is arranged as a first mask portion 509 and multiple second mask portions 510, which is beneficial for defining the position and shape of the initial busbar 502 and the initial electrode finger 503 formed subsequently.

[0052] In this embodiment, the material of the second mask layer 508 includes photoresist. Photoresist has high resolution, allowing for precise control of the area to be removed; simultaneously, photoresist is easy to remove, thereby reducing process complexity and improving production efficiency. In other embodiments, the second mask layer may also be made of other materials that can serve as etching masks and are easy to remove.

[0053] In this embodiment, the process of patterning the interdigitated electrode material layer 507 using the second mask layer 508 as a mask includes a dry etching process.

[0054] It should be noted that the dry etching process has anisotropic etching characteristics, which is beneficial to improving the morphology quality of the initial interdigitated electrode 501.

[0055] Specifically, the step of patterning the interdigitated electrode material layer 507 using the second mask layer 508 as a mask includes: using the second interdigitated electrode material layer 512 as a stop layer and using the second mask layer 508 as a mask to pattern the first interdigitated electrode material layer 513 to form a first initial interdigitated electrode 506; and using the second mask layer 508 and the first initial interdigitated electrode 506 as masks to pattern the second interdigitated electrode material layer 512 to form a second initial interdigitated electrode 505.

[0056] It should be noted that using the second interdigital electrode material layer 512 as a stop layer helps to precisely control the rate of removing the first interdigital electrode material layer 513, thereby improving the consistency of the rate of removing the first interdigital electrode material layer 513, thus improving the accuracy of patterning the first interdigital electrode material layer 513. Consequently, in the subsequent process of patterning the second interdigital electrode material layer 512 using the second mask layer 508 and the first initial interdigital electrode 506 as masks, it is beneficial to further improve the accuracy of patterning the second interdigital electrode material layer 512.

[0057] In the step of forming the first initial interdigitated electrode 506 by patterning the first interdigitated electrode material layer 513 using the second interdigitated electrode material layer 512 as the stop layer and the second mask layer 508 as the mask, the removal selectivity ratio between the first interdigitated electrode material layer 513 and the second interdigitated electrode material layer 512 should not be too small. If the removal selectivity ratio between the first interdigitated electrode material layer 513 and the second interdigitated electrode material layer 512 is too small, it is easy to make the uniformity of the removal rate of the first interdigitated electrode material layer 513 poor, thereby making the feature size uniformity of the first initial interdigitated electrode 506 poor. Therefore, in this embodiment, the removal selectivity ratio between the first interdigitated electrode material layer 513 and the second interdigitated electrode material layer 512 is greater than or equal to 10:1.

[0058] In this embodiment, after patterning the interdigitated electrode material layer 507 using the second mask layer 508 as a mask, the method further includes: removing the second mask layer 508.

[0059] It should be noted that removing the second mask layer 508 is to prepare for the subsequent formation of a first mask layer in the edge region III that covers the initial electrode finger 503.

[0060] Specifically, the second mask layer 508 is removed by wet desmearing or ashing process.

[0061] refer to Figures 8 to 9 In this embodiment, before forming a first mask layer covering the initial interdigitated electrodes 503 in the edge region III, the method further includes forming a filling layer 514 between adjacent initial interdigitated electrodes 501.

[0062] The filler layer 514 is used to form a flat surface with the initial interdigitated electrode 501 and also to protect the substrate 500.

[0063] In this embodiment, in the step of forming a filling layer 514 between adjacent initial interdigital electrodes 501, the filling layer 514 also covers the top of the initial interdigital electrodes 501.

[0064] It should be noted that the filling layer 514 also covers the top of the initial interdigitated electrode 501. On the one hand, during the subsequent formation of the first mask layer covering the initial electrode fingers 503 in the edge region III, it helps to reduce the probability of damage to the initial interdigitated electrode 501. On the other hand, during the subsequent formation of the piston structure, the filling layer 514 and the first mask layer work together to further protect the initial interdigitated electrode 501 in the edge region III. In addition, the filling layer 514 has good leveling properties, which can ensure that the formed surface has high flatness, thereby providing a better flat surface for subsequent processes such as coating, exposure, and development of the first mask layer, and thus ensuring the uniformity of subsequent processes, such as ensuring the consistency of parameters such as critical dimensions (CD) and thickness.

[0065] In this embodiment, the process of forming a filling layer 514 between adjacent initial interdigitated electrodes 501 includes a spin coating process.

[0066] It should be noted that the spin coating process has good coverage, and therefore, a filling layer 514 with uniform thickness and good quality can be formed between adjacent initial interdigitated electrodes 501.

[0067] In this embodiment, in the step of forming a filling layer 514 between adjacent initial interdigitated electrodes 501, the material of the filling layer 514 includes a bottom anti-reflective material.

[0068] It should be noted that the bottom anti-reflective material has good leveling properties, and therefore can fill well between adjacent initial interdigitated electrodes 501.

[0069] In other embodiments, during the step of forming a fill layer between adjacent initial interdigitated electrodes, the top of the fill layer is flush with the top of the initial interdigitated electrodes.

[0070] Specifically, the step of forming a fill layer between adjacent initial interdigitated electrodes includes: forming a fill material layer between adjacent initial interdigitated electrodes, the fill material layer also covering the top of the initial interdigitated electrodes; planarizing the fill material layer, removing the fill material layer above the top of the initial interdigitated electrodes, and using the remaining fill material layer as the fill layer.

[0071] Continue to refer to Figures 8 to 9 A first mask layer 515 is formed in the edge region III to cover the initial electrode finger 503. The first mask layer 515 extends along the second direction Y, and the projection of the first mask layer 515 on the substrate 500 intersects the projection of the initial electrode finger 503 on the substrate 500.

[0072] The first mask layer 515 is used as a mask for forming the piston structure.

[0073] It should be noted that, since the first mask layer 515 covers the initial electrode finger 503 in the edge region III, and the projection of the first mask layer 515 on the substrate 500 intersects with the projection of the initial electrode finger 503 on the substrate 500, that is, the edge of the first mask layer 515 is self-aligned with the sidewall of the initial electrode finger 503 in the edge region III, therefore, by removing part of the thickness of the initial interdigitated electrode 501 located on the side of the first mask layer 515, the process of forming a piston structure at the top of the electrode finger at the intersection of the first mask layer 515 and the electrode finger 503 in the edge region III, makes the sidewall of the piston structure aligned with the sidewall of the electrode finger, which is beneficial to improving the morphological quality of the interdigitated electrode and the alignment accuracy of the electrode finger and the piston structure, thereby enhancing the filter's ability to suppress clutter and thus improving the filter's performance.

[0074] like Figure 8 As shown, in this embodiment, in the edge region III on one side of the central region II, the first mask layer 515 covers each initial electrode finger 503 along the second direction Y, that is, the same first mask layer 515 covers multiple initial electrode fingers 503.

[0075] In other embodiments, the first mask layer may correspond one-to-one with the initial electrode finger in the edge region on one side of the central region, or each first mask layer may cover a portion of the multiple initial electrode fingers.

[0076] In this embodiment, the material of the first mask layer 515 includes photoresist. Photoresist has high resolution, allowing for precise control of the area to be removed; simultaneously, photoresist is easy to remove, thereby reducing process complexity and improving production efficiency. In other embodiments, the second mask layer may also be made of other materials that can serve as etching masks and are easily removable.

[0077] In this embodiment, the step of forming a first mask layer 515 covering the initial electrode finger 503 in the edge region III includes: forming a first mask layer 515 extending along the second direction Y on top of the filling layer 514 in the edge region III, wherein the first mask layer 515 also covers the initial electrode finger 503, which is beneficial to increasing the process window that aligns the sidewall of the piston structure with the sidewall of the electrode finger.

[0078] refer to Figures 10 to 11A portion of the thickness of the initial interdigitated electrode 501 located on the side of the first mask layer 515 is removed to form a busbar 516 located in the busbar region I and electrode fingers 517 located in the central region II and the edge region III. A piston structure 518 is formed at the intersection of the first mask layer 515 and the electrode fingers 517 in the edge region II, located at the top of the electrode fingers 517. The busbar 516, the piston structure 518 and the electrode fingers 517 constitute the interdigitated electrode 519.

[0079] Remove a portion of the thickness of the initial interdigitated electrode 501 located on the side of the first mask layer 515, i.e., form the piston structure 518 and electrode finger 517 in the same step, so that the sidewall of the piston structure 518 is aligned with the sidewall of the electrode finger 517.

[0080] It should be noted that both the busbar 516 and the electrode finger 517 are formed from the remaining thickness of the initial interdigitated electrode 501. Specifically, the busbar 516 is formed from the remaining initial busbar 502, and the electrode finger 517 is formed from the initial electrode finger 503.

[0081] The interdigitated electrode 519 is used to realize the mutual conversion between electrical signals and acoustic signals, so that the surface acoustic wave filter can filter the signal.

[0082] Busbar 516 is used to transmit electrical signals from the input to the output of the filter.

[0083] Electrode 517 is used to realize the mutual conversion between electrical signals and acoustic signals.

[0084] The piston structure 518 is used to suppress transversely propagating sound waves in the filter. Specifically, the piston structure 518 increases the mass of the interdigitated electrode 517 located in edge region III, thereby reducing the propagation speed of transversely propagating sound waves in this region and thus suppressing transversely propagating sound waves in the filter.

[0085] It should be noted that the interdigital electrode 519 is arranged as a bus bar 516 and multiple electrode fingers 517. A piston structure 518 is formed on the electrode fingers 517, which helps to reduce the area of ​​the interdigital electrode 519 while enhancing the acoustic-to-electric conversion efficiency of the filter.

[0086] In this embodiment, the busbar 516 includes a first busbar 520 and a second busbar 521 disposed opposite to each other along the first direction X, and both the first busbar 520 and the second busbar 521 extend along the second direction Y; the electrode finger 517 includes a first electrode finger 522 connected to the first busbar 520 and a second electrode finger 523 connected to the second busbar 521, and the first electrode finger 522 and the second electrode finger 523 are arranged in a cross pattern.

[0087] It should be noted that the first busbar 520 and the second busbar 521 are arranged opposite each other along the first direction X, and the first electrode finger 522 and the second electrode finger 523 are arranged in a cross pattern. This allows the busbar 516 and the electrode finger 517 to make full use of the space formed, resulting in a higher pattern density and saving space area without interfering with each other.

[0088] Specifically, when the first busbar 520 and the first electrode finger 522 serve as input terminals, the second busbar 521 and the second electrode finger 523 serve as output terminals. The input terminals are used to convert electrical signals into acoustic signals, and the output terminals are used to convert acoustic signals into electrical signals, thereby achieving filtering. In other embodiments, the first busbar and the first electrode finger can also serve as output terminals, and the second busbar and the second electrode finger can serve as input terminals.

[0089] In this embodiment, when the initial interdigitated electrode 501 is a stacked structure, the step of removing part of the thickness of the initial interdigitated electrode 501 located on the side of the first mask layer 515 includes: removing part of the thickness of the top layer initial interdigitated electrode 501 on the side of the first mask layer 515, the remaining thickness of the top layer initial interdigitated electrode 501 serving as the top layer electrode finger 517, and forming a piston structure 518 at the intersection of the first mask layer 515 and the electrode finger 517 of the edge region III, the piston structure 518 being an integral structure with the top layer electrode finger 517.

[0090] It should be noted that by removing part of the thickness of the initial interdigitated electrode 501 on the side of the first mask layer 515, the top electrode finger 515 and the piston structure 518 are formed. Consequently, the piston structure 518 and the top electrode finger 517 are integrated into one structure. On the one hand, this helps to simplify the process steps and improve production efficiency. On the other hand, it can enhance the stability between the piston structure 518 and the top electrode finger 517, thereby reducing the probability of separation between the piston structure 518 and the top electrode finger 517.

[0091] In other embodiments, when the initial interdigital electrode is a single-layer structure, the piston structure and the interdigital electrode of full thickness are an integral structure.

[0092] In this embodiment, the process of removing part of the thickness of the initial interdigitated electrode 501 located on the side of the first mask layer 515 includes one or both of reactive plasma etching and ion beam etching.

[0093] It should be noted that both reactive plasma etching and ion beam etching processes have good directionality and high resolution, which can accurately remove part of the thickness of the initial interdigitated electrode 501 located on the side of the first mask layer 515. At the same time, both reactive plasma etching and ion beam etching processes have good etching uniformity, which results in high uniformity of the thickness of the remaining initial interdigitated electrode 501 in the central region I and the busbar region II.

[0094] As an example, the process of removing a portion of the thickness of the initial interdigitated electrode 501 located on the side of the first mask layer 515 is an ion beam etching process.

[0095] It should be noted that the thickness of the initial interdigitated electrode 501 located on the side of the first mask layer 515 can be precisely controlled by the ion beam etching process, thereby precisely controlling the thickness of the formed piston structure 518.

[0096] In the step of removing a portion of the thickness of the initial interdigitated electrode 501 located on the side of the first mask layer 515, the thickness of the initial interdigitated electrode 501 removed should not be too large or too small. If the thickness of the initial interdigitated electrode 501 removed is too large, the height of the piston structure 518 will be too large, which may cause the operating frequency of the filter to fail to meet the actual design requirements; if the thickness of the initial interdigitated electrode 501 removed is too small, the height of the piston structure 518 will be too small, which may cause the piston structure 518 to have a poor effect in suppressing harmonics. Therefore, in this embodiment, in the step of removing a portion of the thickness of the initial interdigitated electrode 501 located on the side of the first mask layer 515, the thickness of the initial interdigitated electrode 501 removed is 0.25λ micrometers to 1λ micrometers.

[0097] It should be noted that λ refers to the wavelength of the elastic wave determined by the electrode period of the interdigitated electrode.

[0098] In this embodiment, the step of removing a portion of the thickness of the initial interdigitated electrode 501 located on the side of the first mask layer 515 includes: using the first mask layer 515 and the filling layer 514 as masks, removing a portion of the thickness of the initial interdigitated electrode 501 in the central region I and the busbar region II, forming a protruding piston structure 518 on the initial electrode finger 501 in the edge region III, using the remaining thickness of the initial busbar 502 in the busbar region II as a busbar 516, and using the remaining thickness of the initial electrode finger 503 in the central region I and the edge region III as an electrode finger 517.

[0099] It should be noted that, since the filling layer 514 is located between adjacent initial interdigitated electrodes 501, that is, the filling layer 514 covers the substrate 500 between adjacent initial interdigitated electrodes 501, and the first mask layer 515 is located on the initial electrode fingers 503 in the edge region III, it is beneficial to reduce the probability of the initial electrode fingers 503 in the substrate 500 and the edge region III being damaged during the process of removing a portion of the initial interdigitated electrodes 501 in the central region I and the bus region II using the first mask layer 515 and the filling layer 514 as masks.

[0100] In this embodiment, the step of removing a portion of the thickness of the initial interdigitated electrode 501 located on the side of the first mask layer 515 further includes: using the first mask layer 515 and the filling layer 514 as masks, before removing a portion of the thickness of the initial interdigitated electrode 501 in the central region I and the bus region II, using the first mask layer 515 as a mask, removing a portion of the thickness of the filling layer 514, so that the top of the initial interdigitated electrode 510 is exposed.

[0101] It should be noted that by using the first mask layer 515 as a mask to remove part of the thickness of the fill layer 514, the top of the initial interdigitated electrode 510 is exposed, which helps to reduce the difficulty of the subsequent process of removing part of the thickness of the initial interdigitated electrode 501 located on the side of the first mask layer 515.

[0102] In the step of removing a portion of the filler layer 514 using the first mask layer 515 as a mask, the removal selectivity ratio between the filler layer 514 and the first mask layer 515 should not be too small. If the removal selectivity ratio between the filler layer 514 and the first mask layer 515 is too small, the probability of the first mask layer 515 being removed during the removal of a portion of the filler layer 514 using the first mask layer 515 as a mask will easily increase, thereby easily leading to poor protection of the initial electrode fingers 501 of the edge region III by the first mask layer 515, resulting in poor morphological quality of the formed piston structure 518. Therefore, in this embodiment, in the step of removing a portion of the filler layer 514 using the first mask layer 515 as a mask, the removal selectivity ratio between the filler layer 514 and the first mask layer 515 is greater than or equal to 3.

[0103] In this embodiment, the process of removing a portion of the thickness of the filler layer 514 using the first mask layer 515 as a mask includes a dry etching process.

[0104] It should be noted that because the dry etching process can achieve anisotropic etching and has the characteristics of adjustable etching rate and etching time, the thickness and morphology of the removed filler layer 514 can be precisely controlled.

[0105] Continue to refer to Figure 10 In this embodiment, after forming the busbar 516, electrode finger 517 and piston structure 518, the method further includes removing the first mask layer 515 and the filler layer 514.

[0106] It should be noted that removing the first mask layer 515 and the filler layer 514 is to prepare for subsequent processes.

[0107] In this embodiment, a process combining ashing and wet adhesive removal is used to remove the first mask layer 515 and the filler layer 514.

[0108] It should be noted that both the ashing process and the wet desmearing process use neutral solutions, thus effectively removing the first mask layer 515 and the filler layer 514 without damaging the interdigitated electrode 517.

[0109] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for forming a filter, characterized in that, include: A substrate is provided, the substrate including a central region, a confluence region and an edge region located between the central region and the confluence region, the central region, the edge region and the confluence region being arranged sequentially along a first direction; Initial interdigitated electrodes are formed on the substrate of the central region, edge region, and bus region. The initial interdigitated electrodes include an initial bus bar located in the bus region and initial electrode fingers located in the central region and edge region. The initial electrode fingers extend along a first direction and are spaced apart along a second direction. The initial bus bar extends along the second direction and connects each of the initial electrode fingers. The first direction intersects the second direction. A first mask layer is formed in the edge region to cover the initial electrode finger. The first mask layer extends along a second direction, and the projection of the first mask layer on the substrate intersects with the projection of the initial electrode finger on the substrate. A portion of the thickness of the initial interdigitated electrode located on the side of the first mask layer is removed to form a busbar in the busbar region and electrode fingers in the center region and the edge region. A piston structure is formed at the top of the electrode fingers at the intersection of the first mask layer and the electrode fingers in the edge region. The busbar, piston structure and electrode fingers constitute the interdigitated electrode.

2. The method for forming a filter as described in claim 1, characterized in that, Before forming the first mask layer covering the initial electrode fingers in the edge region, the method further includes: A fill layer is formed between adjacent initial interdigitated electrodes; The step of forming a first mask layer in the edge region that covers the initial electrode finger includes: forming a first mask layer extending in the second direction on top of the fill layer in the edge region, the first mask layer also covering the initial electrode finger; The step of removing a portion of the thickness of the initial interdigitated electrode located on the side of the first mask layer includes: using the first mask layer and the filling layer as masks, removing a portion of the thickness of the initial interdigitated electrode in the central region and the busbar region, forming a protruding piston structure on the initial electrode finger in the edge region, using the remaining thickness of the initial busbar in the busbar region as a busbar, and using the remaining thickness of the initial electrode finger in the central region and the edge region as an electrode finger; After forming the busbar, electrode fingers and piston structure, the process further includes: removing the first mask layer and filler layer.

3. The method for forming a filter as described in claim 2, characterized in that, In the step of forming a fill layer between adjacent initial interdigitated electrodes, the fill layer also covers the top of the initial interdigitated electrodes; The step of removing a portion of the thickness of the initial interdigitated electrode located on the side of the first mask layer further includes: using the first mask layer and the fill layer as masks, before removing the portion of the thickness of the initial interdigitated electrode in the central region and the bus region, using the first mask layer as a mask, removing a portion of the thickness of the fill layer, so that the top of the initial interdigitated electrode is exposed.

4. The method for forming a filter as described in claim 3, characterized in that, In the step of removing a portion of the thickness of the filler layer using the first mask layer as a mask, the removal selectivity ratio between the filler layer and the first mask layer is greater than or equal to 3.

5. The method for forming a filter as described in claim 3, characterized in that, The process of removing a portion of the thickness of the filler layer using the first mask layer as a mask includes a dry etching process.

6. The method for forming a filter as described in claim 2, characterized in that, The process of forming a filler layer between adjacent initial interdigitated electrodes includes a spin coating process.

7. The method for forming a filter as described in claim 2, characterized in that, In the step of forming a fill layer between adjacent initial interdigitated electrodes, the material of the fill layer includes a bottom anti-reflective coating material.

8. The method for forming a filter as described in claim 2, characterized in that, The first mask layer and filler layer are removed using a combination of ashing and wet desmearing processes.

9. The method for forming a filter as described in claim 1, characterized in that, The process for removing a portion of the thickness of the initial interdigitated electrode located on the side of the first mask layer includes one or both of reactive plasma etching and ion beam etching.

10. The method for forming a filter as described in claim 1, characterized in that, In the step of removing a portion of the thickness of the initial interdigitated electrode located on the side of the first mask layer, the thickness of the initial interdigitated electrode is removed from 0.25λ micrometers to 1λ micrometers, where λ refers to the wavelength of the elastic wave determined by the electrode period of the interdigitated electrode.

11. The method for forming a filter as described in claim 1, characterized in that, In the step of forming the initial interdigitated electrode on the substrate of the central region, edge region and bus region, the initial interdigitated electrode is a stacked structure or a single-layer structure; Wherein, when the initial interdigitated electrode is a stacked structure, the step of removing part of the thickness of the initial interdigitated electrode located on the side of the first mask layer includes: removing part of the thickness of the top layer initial interdigitated electrode on the side of the first mask layer, the remaining thickness of the top layer initial interdigitated electrode serving as the top layer electrode finger, and forming a piston structure at the intersection of the first mask layer and the electrode finger of the edge region at the top of the top layer electrode finger, the piston structure being an integral structure with the top layer electrode finger.

12. The method for forming a filter according to any one of claims 1 to 11, characterized in that, The step of forming the initial interdigitated electrode on the substrate of the central region, the edge region, and the busbar region includes: forming an interdigitated electrode material layer on the substrate of the central region, the busbar region, and the edge region; In the central region, the busbar region, and the edge region, a patterned second mask layer is formed on the interdigitated electrode material layer. The second mask layer includes a first mask portion and a second mask portion. The first mask portion is located on the interdigitated electrode material layer in the busbar region. The first mask portion extends along the second direction and connects each of the second mask portions. The second mask portions extend along the first direction and are spaced apart along the second direction. The second mask portions are located on the interdigitated electrode material layers in the central region and the edge region. Using the second mask layer as a mask, the interdigitated electrode material layer is patterned, and the interdigitated material layer of the busbar region is patterned into an initial busbar corresponding to the first mask portion. The interdigitated material layers of the central region and the edge region are patterned into initial electrode fingers corresponding to the second mask portion.

13. The method for forming a filter as described in claim 12, characterized in that, In the step of forming an interdigitated electrode material layer on the substrate of the central region, the confluence region and the edge region, the interdigitated electrode material layer is a stacked structure, the topmost interdigitated electrode material layer is the first interdigitated electrode material layer, another interdigitated electrode material layer located at the bottom of the first interdigitated electrode material layer is the second interdigitated electrode material layer, and there is a removal selectivity ratio between the first interdigitated electrode material layer and the second interdigitated electrode material layer. The step of patterning the interdigitated electrode material layer using the second mask layer as a mask includes: using the second interdigitated electrode material layer as a stop layer and using the second mask layer as a mask to pattern the first interdigitated electrode material layer to form a first initial interdigitated electrode; The second interdigitated electrode material layer is patterned using the second mask layer and the first initial interdigitated electrode as a mask to form the second initial interdigitated electrode.

14. The method for forming a filter as described in claim 13, characterized in that, In the step of forming interdigitated electrode material layers on the substrate of the central region, the confluence region, and the edge region, the thickness of the first interdigitated electrode material layer is greater than the thickness of the second interdigitated electrode material layer.

15. The method for forming a filter as described in claim 14, characterized in that, The thickness of the first interdigital electrode material layer is 3 to 5 times the thickness of the second interdigital electrode material layer.

16. The method for forming a filter as described in claim 13, characterized in that, In the step of forming a first initial interdigitated electrode by using the second interdigitated electrode material layer as a stop layer and the second mask layer as a mask to pattern the first interdigitated electrode material layer, the removal selection ratio between the first interdigitated electrode material layer and the second interdigitated electrode material layer is greater than or equal to 10:

1.

17. The method for forming a filter as described in claim 13, characterized in that, When the interdigitated electrode material layer is a stacked structure, the interdigitated electrode material layer further includes: a third interdigitated electrode material layer attached to the substrate, wherein the adhesion of the third interdigitated electrode material layer to the substrate is greater than the adhesion of the second interdigitated electrode material layer to the substrate.

18. The method for forming a filter as described in claim 17, characterized in that, The material of the third interdigital electrode layer includes titanium, chromium, titanium nitride, aluminum nitride, or titanium tungsten; the material of the second interdigital electrode layer includes an aluminum-copper alloy or aluminum; and the material of the first interdigital electrode layer includes tungsten or molybdenum.

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