Filter and forming method thereof

Abstract

The invention provides a filter and a forming method thereof, the filter comprises a substrate and an electrode finger, the electrode finger comprises a first interdigital electrode layer and a second interdigital electrode layer located on the first interdigital electrode layer; and the mass block is located between the first interdigital electrode layer and the second interdigital electrode layer in the edge area, and the mass block and the first interdigital electrode layer are of an integrated structure. According to the invention, transverse propagation sound waves are inhibited, and the problem that transverse diffusion of sound waves may affect device performance is solved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more specifically to a filter and a method for forming the same. Background Technology

[0002] Surface acoustic wave (SAW) filters fabricate input and output electrodes on a piezoelectric substrate. An alternating voltage is applied to the input, utilizing the piezoelectric effect to convert electrical energy into acoustic energy. They offer advantages such as low insertion loss, wide bandwidth, and low cost, and are widely used in communication RF front-end modules. To reduce spurious effects, suppress second harmonics, and improve the filter's passband performance, a common practice is to thicken the regions at both ends of the interdigital electrodes (piston structure) to reduce the propagation speed at the ends.

[0003] In current surface acoustic wave (SAW) product designs, SAW filters generate transversely propagating acoustic waves. These waves cause transverse resonant modes in the SAW filter, resulting in clutter in and around the passband. This clutter increases the loss of the SAW filter, causing significant fluctuations in the quality factor (Q value) and reducing the performance of the SAW filter.

[0004] Therefore, how to suppress transversely propagating sound waves has become an urgent problem to be solved. Summary of the Invention

[0005] The problem solved by this invention is the lateral propagation of sound waves in existing filters.

[0006] To address the above problems, the present invention provides a filter, the filter comprising: 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 bus region and the edge region being arranged along a first direction; Interdigitated electrodes are located on the substrate of the central region, the busbar region, and the edge region. The interdigitated electrodes include a busbar located in the busbar region and a plurality of electrode fingers located in the edge region and the central region. The busbar extends along a second direction and connects each of the electrode fingers. The electrode fingers extend along a first direction and are spaced apart along the second direction. The first direction intersects the second direction. The electrode includes a first interdigitated electrode layer and a second interdigitated electrode layer located on the first interdigitated electrode layer; A mass block is located between the first interdigital electrode layer and the second interdigital electrode layer in the edge region, and the mass block and the first interdigital electrode layer are an integral structure.

[0007] Optionally, the sidewall of the mass block is aligned with the sidewall of the electrode finger.

[0008] Optionally, the material density of the first interdigital electrode layer is greater than the material density of the second interdigital electrode layer.

[0009] Optionally, the thickness of the first interdigital electrode layer is greater than or equal to the thickness of the second interdigital electrode layer.

[0010] Optionally, the material of the first interdigital electrode layer includes tungsten, molybdenum, gold, rhodium, tantalum, platinum, or copper; and / or, the material of the second interdigital electrode layer includes an aluminum-copper alloy, aluminum, or copper.

[0011] Optionally, the interdigitated electrode further includes a fifth interdigitated electrode layer located between the first interdigitated electrode layer and the substrate, wherein the first interdigitated electrode layer and the fifth interdigitated electrode layer have a selective etching ratio to serve as an etching stop layer.

[0012] Optionally, the material of the fifth interdigital electrode layer includes titanium nitride, aluminum, or aluminum nitride.

[0013] Optionally, the electrode may further include a third interdigitated electrode layer located on the second interdigitated electrode layer, wherein the material density of the third interdigitated electrode layer is greater than that of the second interdigitated electrode layer.

[0014] Optionally, the material of the third interdigital electrode layer includes tungsten, molybdenum, gold, rhodium, tantalum, platinum, or copper.

[0015] Optionally, the interdigitated electrode further includes a fourth interdigitated electrode layer, which is attached to the substrate, and the adhesion of the fourth interdigitated electrode layer to the substrate is greater than the adhesion of the first interdigitated electrode layer to the substrate.

[0016] This application also provides a method for forming a filter, including, A substrate is provided, 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 bus region and the edge region being arranged along a first direction; A first metal layer is deposited on the substrate; The first metal layer is partially etched to form an initial mass block in the edge region; A second metal layer is deposited on the side of the substrate where the initial mass block is disposed; The second metal layer, the initial mass block, and the first metal layer are etched to stop at the substrate to form a busbar located in the busbar region, electrode fingers located in the central region and the edge region, and a mass block between the first interdigitated electrode layer and the second interdigitated electrode layer of the electrode fingers located in the edge region. The busbar, the mass block, and the electrode fingers constitute interdigitated electrodes. The electrode fingers extend along the first direction and are spaced apart along the second direction. The busbar extends along the second direction and connects each of the electrode fingers. The first direction intersects the second direction.

[0017] Optionally, partially etching the first metal layer to form an initial mass block in the edge region includes: A patterned first mask is disposed on the first metal layer, and the first mask is disposed on the first metal layer in the edge region; The first metal layer located in the central region and the confluence region is partially etched according to the first mask to form the initial mass block in the edge region; After the initial mass block is formed, the first mask is removed.

[0018] Optionally, etching the second metal layer, the initial mass block, and the first metal layer to stop at the substrate includes: A patterned second mask is provided on the second metal layer. The second mask includes a first mask portion and a second mask portion. The first mask portion is located on the second metal layer of 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 second metal layer of the center region and the edge region and intersect with the orthographic projection of the initial mass block on the substrate. Using the second mask as a mask, the second metal layer, the initial mass block and the first metal layer are etched. The second metal layer and the first metal layer in the busbar region are etched into busbars corresponding to the first mask portion. The second metal layer and the first metal layer in the center region and the edge region are etched into electrode fingers corresponding to the second mask portion. The remaining initial mass block located in the edge region is used as a mass block. After forming the busbar, electrode fingers, and mass block, the second mask portion is removed.

[0019] Optionally, before depositing the first metal layer on the substrate, an etch stop layer is further deposited on the substrate.

[0020] Compared with the prior art, the technical solution of the embodiments of the present invention has the following advantages: 1. In the filter provided in this application embodiment, by placing a mass block between the first interdigital electrode layer and the second interdigital electrode layer, and forming an integral structure with the first interdigital electrode layer, compared with the prior art where the electrode fingers are composed of multiple electrode layers and the mass block formed on the electrode fingers usually also uses the same multi-layer metal material as the electrode layers, this application simplifies the structure of the electrode fingers and the mass block, and can also suppress laterally propagating sound waves, solving the problem that the lateral diffusion of sound waves may affect the device performance. Furthermore, due to the simple structure, the fabrication process is relatively simple.

[0021] 2. In the filter provided in this application embodiment, by setting the material density of the first interdigital electrode layer to be greater than that of the second interdigital electrode layer, the loss of sound wave energy during propagation can be effectively reduced, thereby helping to improve the quality factor (Q value) of the filter and optimize its frequency selection performance and signal processing accuracy.

[0022] 3. In the filter provided in this application embodiment, by setting the thickness of the first interdigital electrode layer to be greater than or equal to the thickness of the second interdigital electrode layer, the denser metal occupies a higher proportion in the total thickness of the electrode fingers. This not only enhances the energy conversion efficiency between the electrodes and the piezoelectric material, thereby effectively improving the electromechanical coupling coefficient of the filter and optimizing its signal transmission performance; at the same time, the reasonable allocation of electrode layer thickness can reduce the overall space occupied by the device, thereby achieving miniaturization of the device.

[0023] 4. In the filter provided in this application embodiment, by setting a fifth interdigital electrode layer as an etch stop layer between the first interdigital electrode layer and the substrate, the substrate can be avoided from being damaged by excessive etching during the fabrication process.

[0024] 5. In the filter provided in this application embodiment, by setting a third interdigital electrode layer on the second interdigital electrode layer, and the material density of the third interdigital electrode layer is greater than that of the second interdigital electrode layer, it is helpful to tune the filter frequency. When there is a gap between the filter frequency and the preset frequency, the filter frequency can be adjusted by adjusting the thickness and uniformity of the top high-density material, thereby ensuring that the filter can work stably in the preset frequency range.

[0025] 6. In the filter formation method provided in this application embodiment, a first metal layer is deposited first, and an initial mass block is formed by etching the first metal layer. Then, a second metal layer is deposited, and the busbar, electrode fingers, and mass block are formed simultaneously by etching. This process only requires two metal deposition and etching operations to simultaneously fabricate the busbar, electrode fingers, and mass block, simplifying the production process. In addition, by placing the mass block between the first interdigital electrode layer and the second interdigital electrode layer, the structure of the electrode fingers and the mass block is simplified, and the transverse propagation of acoustic waves can be suppressed, solving the problem that transverse acoustic wave diffusion may affect device performance. At the same time, combined with the application of self-alignment technology, the stacking accuracy requirements between the mass block and the electrode fingers are effectively guaranteed. Attached Figure Description

[0026] Figure 1 A schematic diagram of the filter structure provided in the embodiments of this application; Figure 2 for Figure 1 The diagram shows another structural schematic of the filter.

[0027] Figure 3 for Figure 1 A top view of the substrate in the filter shown; Figure 4 A schematic flowchart illustrating the filter formation method provided in this application embodiment; Figure 5 for Figure 4 The process flow diagram corresponding to the formation method shown; Figure 6 for Figure 4 The diagram shows the process of forming the initial mass block in the formation method shown. Figure 7 for Figure 4 A schematic diagram of the process for forming interdigitated electrodes in the shown method; Figure 8 A top view after setting the second mask; Figure 9 A top view showing the formation of the interdigitated electrodes; Explanation of reference numerals in the attached figures: 1. Filter; 11. Substrate; 12. First metal layer; 13. Second metal layer; 14. Initial mass block; 15. First mask; 16. Interdigitated electrode; 17. Second mask; 161. Mass block; 162. Electrode finger; 163. Busbar; 1621, First interdigital electrode layer; 1622, Second interdigital electrode layer; 1623, Third interdigital electrode layer; 1624, Fourth interdigital electrode layer; 121. First sub-metal layer; 122. Second sub-metal layer; 131. Third sub-metal layer; 132. Fourth sub-metal layer; 171. First mask portion; 172. Second mask portion; 1721. First end; 1722. Second end; I. Central Area; II. Convergence Area; III. Periphery Area; X, the first direction; Y, the second direction. Detailed Implementation

[0028] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0029] Please see Figures 1 to 3 ,as well as Figure 9 , Figure 1 A schematic diagram of the filter structure provided in the embodiments of this application; Figure 2 for Figure 1 The diagram shows another possible structure of the filter. Figure 3 for Figure 1 The top view of the substrate in the filter shown. Figure 9 This is a top view showing the formation of interdigitated electrodes. An embodiment of this application provides a filter 1, which includes: a substrate 11, the substrate 11 including a central region I, a bus region II, and an edge region III located between the central region I and the bus region II, the central region I, the bus region II, and the edge region III being arranged along a first direction X; and interdigitated electrodes 16 located on the substrate of the central region I, the bus region II, and the edge region III, the interdigitated electrodes 16 including a bus bar 163 located in the bus region II and a plurality of electrode fingers 162 located in the edge region III and the central region I. Busbar 163 extends along the second direction Y and connects each electrode finger 162. The electrode fingers 162 extend along the first direction X and are spaced apart along the second direction Y. The electrode fingers 162 intersect with the mass block 161. The first direction X intersects with the second direction Y. The electrode finger 162 includes a first interdigitated electrode layer 1621 and a second interdigitated electrode layer 1622 located on the first interdigitated electrode layer 1621. The mass block 161 is located between the first interdigitated electrode layer 1621 and the second interdigitated electrode layer 1622 in the edge region III. In this embodiment, by placing the mass block 161 between the first interdigitated electrode layer 1621 and the second interdigitated electrode layer 1622, compared with the prior art where the electrode fingers 162 are composed of multiple electrode layers and the mass block 161 formed on the electrode fingers 162 usually adopts the same multilayer metal material as the electrode layers, this application simplifies the structure of the electrode fingers 162 and the mass block 161, and can also suppress laterally propagating sound waves, solving the problem that the lateral diffusion of sound waves may affect the device performance. Furthermore, due to its simple structure, the preparation process is relatively simple.

[0030] The interdigitated electrode 16 is used to realize the mutual conversion between electrical signals and acoustic signals, so that the filter 1 can filter the signal.

[0031] Busbar 163 is used to transmit telecommunications from the input of the filter to the output.

[0032] Electrode 162 is used to apply an electric field to the substrate surface to make the substrate 11 vibrate, ultimately realizing the electroacoustic-electric conversion.

[0033] Mass block 161 is used to suppress transversely propagating sound waves in the filter. Specifically, mass block 161 increases the mass of the interdigitated electrode 16 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.

[0034] The alignment of the sidewall of mass block 161 with the sidewall of electrode finger 162 is beneficial to improving the morphological quality of interdigitated electrode 16 and the alignment accuracy of electrode finger 162 and mass block 161, thereby improving the filter's ability to suppress clutter and thus improving the performance of filter 1.

[0035] In some embodiments, the mass block 161 is a stacked structure or a single-layer structure. For example, when the mass block 161 is a single-layer structure, the material of the mass block 161 is the same as the material of the first interdigital electrode layer 1621. This arrangement allows the mass block 161 and the first interdigital electrode layer 1621 to be an integral structure, thereby reducing the interface stress and process complexity that may be caused by splicing different materials, and also improving the structural correlation and stability of the two, laying the foundation for subsequent device fabrication and performance optimization.

[0036] The material density of the first interdigital electrode layer 1621 is greater than that of the second interdigital electrode layer 1622, which can effectively reduce the loss of sound wave energy during propagation, thereby helping to improve the quality factor (Q value) of the filter and optimize its frequency selection performance and signal processing accuracy.

[0037] The thickness of the first interdigital electrode layer 1621 is greater than or equal to the thickness of the second interdigital electrode layer 1622. This means that the denser metal occupies a higher proportion in the total thickness of the electrode fingers 162. Specifically, under the premise of ensuring the Q value, at the same frequency, by setting the thickness of the denser first interdigital electrode layer 1621 to the maximum as the main metal, the spacing of the first interdigital electrode layer 1621 can be set to the minimum, thereby increasing the duty cycle and achieving miniaturization of the filter 1.

[0038] The material of the first interdigital electrode layer 1621 includes tungsten, molybdenum, gold, rhodium, tantalum, platinum, or copper. It should be noted that tungsten, molybdenum, gold, rhodium, tantalum, platinum, or copper have a large mass, thus reducing the propagation speed of transversely propagating sound waves in the filter, thereby reducing the characteristic dimension (CD) value of the interdigital electrode 16. As an example, the material of the first interdigital electrode layer 1621 is tungsten.

[0039] The material of the second interdigital electrode layer 1622 includes an aluminum-copper alloy, aluminum, or copper. It is understood that aluminum-copper alloys, aluminum, or copper have good electrical conductivity; therefore, they can improve the conductivity of the filter. Additionally, it should be noted that to ensure the conductivity of the interdigital electrode 16, the thickness of the second interdigital electrode layer 1622 needs to be no less than 50 nm. As an example, the material of the second interdigital electrode layer 1622 is aluminum.

[0040] It is understandable that, since the mass block 161, positioned between the first interdigital electrode layer 1621 and the second interdigital electrode layer 1622, can suppress clutter, the surface of the second interdigital electrode layer 1622 away from the substrate 11 can be designed as a flat surface (e.g., ...). Figure 2 ); or, depending on actual needs, it can be made to naturally form a raised structure in the area corresponding to mass block 161 along with the height of mass block 161 (e.g. Figure 1 Both designs can ensure the clutter suppression effect of mass block 161, while meeting the process and performance requirements of different scenarios.

[0041] Electrode 162 also includes a third interdigitated electrode layer 1623 located on the second interdigitated electrode layer 1622, the material density of the third interdigitated electrode layer 1623 being greater than the material density of the second interdigitated electrode layer 1622. This facilitates frequency tuning of the filter. When there is a difference between the filter frequency and the preset frequency, the filter frequency can be adjusted by adjusting the thickness and uniformity of the top high-density material, thereby ensuring that the filter can operate stably within the preset frequency range and stabilizing the frequency response performance of filter 1.

[0042] In some embodiments, the material of the third interdigital electrode layer 1623 includes tungsten, molybdenum, gold, rhodium, tantalum, platinum, or copper. As an example, the material of the third interdigital electrode layer 1623 is tungsten.

[0043] The interdigitated electrode 16 also includes a fourth interdigitated electrode layer 1624, which is attached to the substrate 11. The adhesion of the fourth interdigitated electrode layer 1624 to the substrate 11 is greater than that of the first interdigitated electrode layer 1621 to the substrate 11. This arrangement can prevent the interdigitated electrode 16 from peeling off or warping from the substrate 11, thereby improving the stability of the filter 1.

[0044] The fourth interdigital electrode layer 1624 is made of titanium, chromium, titanium nitride, aluminum nitride, or titanium tungsten. Titanium, chromium, titanium nitride, aluminum nitride, or titanium tungsten exhibit good adhesion; therefore, they can improve the adhesion between the substrate and the first interdigital electrode layer 1621. As an example, the fourth interdigital electrode layer 1624 is made of titanium.

[0045] The interdigitated electrode 16 also includes a fifth interdigitated electrode layer (not shown) located between the first interdigitated electrode layer 1621 and the substrate 11. A selective etching ratio is used between the first interdigitated electrode layer 1621 and the fifth interdigitated electrode layer to serve as an etching stop layer. It is understood that because the thickness of edge region III differs from other regions, other areas will be etched to the substrate 11 first. To avoid prolonged etching of the substrate 11 in other areas, which could damage the substrate 11 and affect device performance, and to address the issue of uneven etching due to fluctuations in the etching process itself, this embodiment of the application uses a fifth interdigitated electrode layer as an etching stop layer between the first interdigitated electrode layer and the substrate. This avoids excessive etching and damage to the substrate during fabrication.

[0046] The material of the fifth interdigital electrode layer includes titanium nitride, aluminum, or aluminum nitride.

[0047] As an example, the material of mass block 161 is tungsten.

[0048] Please see Figures 4 to 5 , Figure 4 This is a schematic flowchart illustrating the filter formation method provided in an embodiment of this application. Figure 5 for Figure 4 The process flow diagram corresponding to the formation method shown is illustrated. This application embodiment provides a method for forming a filter 1, which includes the following steps: S110. A substrate is provided, 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 bus region and the edge region being arranged along a first direction.

[0049] Substrate 11 provides a fabrication platform for subsequent fabrication of 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 have advantages such as high operating frequency, simple manufacturing process, low manufacturing cost, and high frequency response consistency; therefore, they are widely used in various electronic devices.

[0050] In this embodiment, the substrate 11 is a piezoelectric substrate 11, so that the subsequent filter 1 structure can use the piezoelectric effect for filtering.

[0051] The substrate 11 may be made of lithium niobate (LiNbO3), lithium tantalate (LiTaO3), quartz, or piezoelectric ceramic. As an example, the substrate 11 may be made of lithium niobate. In other embodiments, the substrate 11 may also be a piezoelectric substrate on an insulator.

[0052] The ducting region II provides a spatial location for the subsequent formation of the ducting strip 163, the edge region III provides a spatial location for the subsequent formation of the mass block 161 and the electrode finger 162, and the center region I provides a spatial location for the subsequent formation of the electrode finger 162.

[0053] S120, Deposit a first metal layer on the substrate.

[0054] It should be noted that the first metal layer 12 includes at least one metal structure layer. That is, the first metal layer 12 can be a single metal structure layer, a double metal structure layer, or a stacked structure of multiple metal layers. Specifically, it can be configured one-to-one according to the specific structure and function of the interdigitated electrodes 16, and no specific limitations are made here. In this embodiment, the first metal layer 12 includes a double-layer structure of a first sub-metal layer 121 and a second sub-metal layer 122 stacked together as an example for illustration. This example is only for illustrative purposes and should not be construed as a limitation on the specific structure of the first metal layer 12.

[0055] For example, when the first metal layer 12 is a stacked structure of multiple metal layers, depositing the first metal layer 12 on the substrate 11 may be: depositing a first sub-metal layer 121 to a preset thickness on the surface of the substrate 11, and then depositing a second sub-metal layer 122 to a preset thickness on the first sub-metal layer 121.

[0056] It should be noted that the material of the first sub-metal layer 121 is used to form at least the busbar 163 and electrode fingers 162 in the interdigitated electrodes 16. Specifically, the material of the first sub-metal layer 121 is used to form at least the busbar 163 extending along the second direction Y and the electrode fingers 162 extending along the first direction X, where the first direction X intersects the second direction Y. 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 direction X and the second direction Y can be other angles depending on actual needs.

[0057] In some embodiments, the material of the second sub-metal layer 122 is used to form the mass block 161, electrode fingers 162, and busbar 163 in the interdigitated electrode 16, such that the mass block 161 includes the material of the second sub-metal layer 122, and the busbar 163 and electrode fingers 162 include the materials of the first sub-metal layer 121 and the second sub-metal layer 122. That is, the material of the first sub-metal layer 121 is used to form the fourth interdigitated electrode layer 1624, and the material of the second sub-metal layer 122 is used to form the first interdigitated electrode layer 1621.

[0058] In some embodiments, the material of the first sub-metal layer 121 includes titanium, chromium, titanium nitride, aluminum nitride, or titanium tungsten, and the material of the second sub-metal layer 122 includes tungsten, molybdenum, gold, rhodium, tantalum, platinum, or copper.

[0059] In some embodiments, before depositing the first metal layer 12 on the substrate 11, an etch stop layer is further deposited on the substrate 11. By providing an etch stop layer on the substrate 11, damage to the substrate 11 due to over-etching can be avoided during fabrication.

[0060] S130. Partial etching of the first metal layer to form an initial mass block in the edge region.

[0061] It should be noted that there are multiple feasible implementation methods in the process of forming the initial mass block 14. The embodiments of this application will be described in detail with the following specific examples, but they are not intended to limit the scope of protection of the technical solution of this application.

[0062] For example, please refer to Figure 5 and Figure 6 , Figure 6 for Figure 4 The schematic diagram of the process for forming the initial mass block in the shown method includes, in some embodiments, the etching of the first metal layer 12 to form the initial mass block 14 includes the following steps: S131. A first mask with a pattern is provided on the first metal layer, and the first mask is provided on the first metal layer in the edge region.

[0063] The first mask 15 is used as a mask for forming the initial mass block 14. For example, the first mask 15 extends along the second direction Y and covers the edge region III.

[0064] In this embodiment, the material of the first mask 15 includes photoresist. Specifically, a layer of photoresist is coated on the surface of the second sub-metal layer 122, and the first mask 15 with a preset patterned structure is obtained by exposure and development. The first mask 15 is located on the second sub-metal layer 122 in the edge region III.

[0065] S132. Partial etching of the first metal layer located in the central region and the busbar region is performed according to the first mask to form an initial mass block in the edge region.

[0066] Based on the first mask 15, an etching process suitable for the material of the first metal layer 12, such as dry etching or wet etching, is used to etch the first metal layer 12 that is not covered by the mask, namely the central region I and the busbar region II. During the etching process, the etching parameters are controlled to ensure the etching depth, so as to achieve partial etching of the first metal layer 12.

[0067] In some embodiments, etching the first metal layer 12 located in the central region I and the busbar region II according to the first mask 15 includes etching a portion of the thickness of the first metal layer 12 to form an initial mass block 14 of the remaining thickness of the first metal layer 12 protruding from the edge region III, the remaining thickness of the first metal layer 12 serving as the material layer of the interdigitated electrodes 16. Exemplarily, the second sub-metal layer 122 in the central region I and the busbar region II is partially etched to form a mass block 161 including the second sub-metal layer 122, and a busbar 163 and electrode fingers 162 including the first sub-metal layer 121 and the second sub-metal layer 122.

[0068] It should be noted that the first metal layer 12 may include two or more metal layer structures. Therefore, the etching depth and number of etching layers of the first metal layer 12 can be set according to the specific actual function of the interdigitated electrode 16, and no specific restrictions are imposed here.

[0069] S133. After forming the initial mass block, remove the first mask.

[0070] The first mask 15 remaining after etching is removed by employing a stripping process that matches the material of the first mask 15, such as chemical dissolution or plasma ashing.

[0071] S140. Deposit a second metal layer on the side of the substrate where the initial mass block is located.

[0072] It should be noted that the second metal layer 13 includes at least one metal structure layer, that is, the second metal layer 13 can be a single metal structure layer or a stacked structure of multiple metal layers. In this embodiment, the second metal layer 13 includes a double-layer structure of a third sub-metal layer 131 and a fourth sub-metal layer 132 stacked together as an example. This example is only for illustrative purposes and should not be construed as a limitation on the specific structure of the second metal layer 13.

[0073] The deposition of the second metal layer 13 includes: sequentially depositing a third sub-metal layer 131 and a fourth sub-metal layer 132 on the second sub-metal layer 122 and the initial mass block 14. Specifically, using physical vapor deposition or chemical vapor deposition, the third sub-metal layer 131 is uniformly and continuously deposited on the surface areas of the second sub-metal layer 122 and the initial mass block 14. After the third sub-metal layer 131 is deposited and forms a uniform film, the fourth sub-metal layer 132 is deposited on its surface. The sequential deposition of the third sub-metal layer 131 and the fourth sub-metal layer 132 together constructs the composite metal stack structure of the interdigitated electrode 16, laying the material foundation for the subsequent formation of the interdigitated electrode 16 through an etching process.

[0074] It should be noted that the material of the third sub-metal layer 131 needs to be set by comprehensively considering the electrical conductivity of the filter 1, its compatibility with the second sub-metal layer 122, and the operability of the subsequent etching process. Its thickness needs to be controlled by precise process parameters such as deposition time and power to ensure that it can completely cover the second sub-metal layer 122 and the step interface between it and the initial mass block 14, forming a gapless and dense cover layer, providing a stable conductive and structural substrate 11 for the subsequent interdigitated electrode 16 structure.

[0075] In some embodiments, the material of the third sub-metal layer 131 includes an aluminum-copper alloy, aluminum, or copper.

[0076] In some embodiments, the material of the fourth sub-metal layer 132 includes tungsten, molybdenum, gold, rhodium, tantalum, platinum, or copper.

[0077] It is understandable that when setting the third sub-metal layer 131, since the mass block 161 can suppress clutter when it is placed between the second sub-metal layer 122 and the third sub-metal layer 131, the surface of the third sub-metal layer 131 away from the substrate 11 can be designed as a flat surface; or, according to actual needs, it can be made to naturally form a raised shape in the area corresponding to the initial mass block 14 with the height of the initial mass block 14. Both designs can ensure the clutter suppression effect of the mass block 161 and meet the process and performance requirements under different scenarios.

[0078] S150. The second metal layer, the initial mass block, and the first metal layer are etched to stop on the substrate to form a busbar located in the busbar region, electrode fingers located in the central region and the edge region, and a mass block between the first interdigitated electrode layer and the second interdigitated electrode layer in the electrode fingers located in the edge region. The busbar, the mass block, and the electrode fingers constitute interdigitated electrodes. The electrode fingers extend along the first direction and are spaced apart along the second direction. The busbar extends along the second direction and connects each electrode finger. The first direction and the second direction intersect.

[0079] For example, see again Figure 5 and Figure 7 , Figure 7 for Figure 4 The schematic diagram of the process for forming interdigitated electrodes in the shown method includes, in some embodiments, the etching of the second metal layer 13 to stop at the substrate 11 comprising the following steps: S151. A patterned second mask is provided on the second metal layer. The second mask includes a first mask portion and a second mask portion. The first mask portion is located on the second metal layer of the bus region. The first mask portion extends along a second direction and connects each of the second mask portions. The second mask portions extend along a first direction and are spaced apart along the second direction. The second mask portions are located on the second metal layer of the center region and the edge region and intersect with the orthographic projection of the initial mass block on the substrate.

[0080] Please continue reading. Figure 8 , Figure 8 To obtain a top view after setting the second mask, after depositing the third sub-metal layer 131 and the fourth sub-metal layer 132, the interdigitated electrodes 16 are patterned. Specifically, photoresist is uniformly coated on the surface of the fourth sub-metal layer 132, and the pre-defined interdigitated electrode 16 pattern is set onto the photoresist layer through a photolithography process to form a second mask 17 with a patterned structure. The second mask 17 includes a first mask portion 171 and a second mask portion 172. Specifically, the first mask portion 171 provides a first predetermined pattern corresponding to the busbar 163 and serves as a mask layer for forming the busbar 163. The second mask portion 172 provides a second predetermined pattern corresponding to the electrode fingers 162 and serves as a mask layer for forming the electrode fingers 162 and the mass block 161. The second mask portion 172 includes a first end 1721 connected to the first mask portion 171 and a second end 1722 away from the first end 1721, and the second end 1722 intersects with the orthographic projection of the initial mass block 14 on the substrate 11.

[0081] The predetermined pattern corresponding to the interdigitated electrode 16 is transferred to the second metal layer 13, and the projection of the predetermined pattern on the second metal layer 13 intersects with the initial mass block 14, so that the sidewall of the mass block 161 is aligned with the sidewall of the electrode finger 162. This is beneficial to improve the morphological quality of the interdigitated electrode 16 and the alignment accuracy of the electrode finger 162 and the mass block 161, thereby improving the filter's ability to suppress clutter and thus improving the filter's performance.

[0082] S152. Using the second mask as a mask, etch the second metal layer, the initial mass block and the first metal layer, etch the second metal layer and the first metal layer in the busbar region into busbars corresponding to the first mask portion, etch the second metal layer and the first metal layer in the center region and the edge region into electrode fingers corresponding to the second mask portion, and the remaining initial mass block located in the edge region is used as a mass block.

[0083] Please continue reading. Figure 9 , Figure 9 To form a top view of the interdigitated electrodes, in some embodiments, using a second mask 17 as a mask, patterning the second metal layer 13 and the initial mass block 14 includes: patterning the second metal layer 13, the initial mass block 14, and the remaining thickness of the first metal layer 12; patterning the second metal layer 13 and the first metal layer 12 in the busbar region II as busbars 163 corresponding to the first mask portion 171; patterning the second metal layer 13 and the first metal layer 12 in the center region I and the edge region III as electrode fingers 162 corresponding to the second mask portion 172; and using the remaining initial mass block 14 located in the edge region III as a mass block 161.

[0084] For example, etching to form the interdigitated electrode 16 includes: sequentially etching the fourth sub-metal layer 132, the third sub-metal layer 131, the second sub-metal layer 122, and the first sub-metal layer 121 located in the central region I and the busbar region II until the surface of the substrate 11 is exposed to form the electrode fingers 162 and the busbar 163; and sequentially etching the fourth sub-metal layer 132, the third sub-metal layer 131, the initial mass block 14, the second sub-metal layer 122, and the first sub-metal layer 121 located in the edge region III until the surface of the substrate 11 is exposed to form the electrode fingers 162 and the mass block 161. That is, the electrode fingers 162 and the busbar 163 include a first interdigitated electrode layer 1621 formed by the second sub-metal layer 122, a second interdigitated electrode layer 1622 formed by the third sub-metal layer 131, a fourth interdigitated electrode layer 1624 formed by the first sub-metal layer 121, and a third interdigitated electrode layer 1623 formed by the fourth sub-metal layer 132.

[0085] It should be noted that during the etching process, the etching gas and power parameters can be switched according to the material, thickness and characteristics of each metal layer, and excessive etching damage to the substrate 11 material must be avoided during the etching process.

[0086] It should be noted that the busbar 163 can be a single layer or multiple layers. Therefore, when forming the busbar 163, the fourth sub-metal layer 132, the third sub-metal layer 131, the second sub-metal layer 122 and the first sub-metal layer 121 can be selectively etched according to the actual situation. Alternatively, when setting one of the metal layers, no metal layer can be set in the busbar II.

[0087] S153. After forming the busbar, electrode fingers and mass block, remove the second mask portion.

[0088] Select an appropriate removal process based on the material type of the second mask 17. For example, if it is a photoresist mask, a wet stripping process can be used, immersing the substrate 11 in a dedicated photoresist removal solution to remove residual photoresist through chemical dissolution. For high-precision applications, a plasma ashing process can also be used, utilizing the chemical reaction between oxygen plasma and the photoresist to decompose it into volatile gases, achieving residue-free removal. Additionally, after removing the second mask, cleaning and drying processes are required to ensure no contaminants remain on the surface.

[0089] By first depositing a first sub-metal layer 121 and a second sub-metal layer 122, and then etching the second sub-metal layer 122 to form an initial mass block 14, a third sub-metal layer 131 and a fourth sub-metal layer 132 are deposited sequentially, and interdigitated electrodes 16 and mass blocks 161 are formed simultaneously through etching. This process requires only two metal deposition and etching steps to simultaneously fabricate interdigitated electrodes 16 and mass blocks 161, simplifying the production process. At the same time, the application of self-alignment technology effectively ensures the stacking accuracy requirements between mass blocks 161 and interdigitated electrodes 16.

[0090] 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 filter, characterized in that, The filter includes: 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 bus region and the edge region being arranged along a first direction; Interdigitated electrodes are located on the substrate of the central region, the busbar region, and the edge region. The interdigitated electrodes include a busbar located in the busbar region and a plurality of electrode fingers located in the edge region and the central region. The busbar extends along a second direction and connects each of the electrode fingers. The electrode fingers extend along a first direction and are spaced apart along the second direction. The first direction intersects the second direction. The electrode includes a first interdigitated electrode layer and a second interdigitated electrode layer located on the first interdigitated electrode layer; A mass block is located between the first interdigital electrode layer and the second interdigital electrode layer in the edge region, and the mass block and the first interdigital electrode layer are an integral structure.

2. The filter according to claim 1, characterized in that, The sidewall of the mass block is aligned with the sidewall of the electrode finger.

3. The filter according to any one of claims 1-2, characterized in that, The material density of the first interdigital electrode layer is greater than that of the second interdigital electrode layer.

4. The filter according to claim 3, characterized in that, The thickness of the first interdigital electrode layer is greater than or equal to the thickness of the second interdigital electrode layer.

5. The filter according to claim 4, characterized in that, The material of the first interdigital electrode layer includes tungsten, molybdenum, gold, rhodium, tantalum, platinum, or copper; and / or, the material of the second interdigital electrode layer includes an aluminum-copper alloy, aluminum, or copper.

6. The filter according to any one of claims 1-2, characterized in that, The interdigitated electrode further includes a fifth interdigitated electrode layer located between the first interdigitated electrode layer and the substrate, wherein the first interdigitated electrode layer and the fifth interdigitated electrode layer have a selective etching ratio to serve as an etching stop layer.

7. The filter according to claim 6, characterized in that, The material of the fifth interdigital electrode layer includes titanium nitride, aluminum, or aluminum nitride.

8. The filter according to any one of claims 1-2, characterized in that, The electrode also includes a third interdigitated electrode layer located on the second interdigitated electrode layer, wherein the material density of the third interdigitated electrode layer is greater than that of the second interdigitated electrode layer.

9. The filter according to claim 8, characterized in that, The material of the third interdigital electrode layer includes tungsten, molybdenum, gold, rhodium, tantalum, platinum, or copper.

10. The filter according to any one of claims 1-2, characterized in that, The interdigitated electrode further includes a fourth interdigitated electrode layer, which is attached to the substrate, and the adhesion of the fourth interdigitated electrode layer to the substrate is greater than the adhesion of the first interdigitated electrode layer to the substrate.

11. A method for forming a filter, characterized in that, include, A substrate is provided, 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 bus region and the edge region being arranged along a first direction; A first metal layer is deposited on the substrate; The first metal layer is partially etched to form an initial mass block in the edge region; A second metal layer is deposited on the side of the substrate where the initial mass block is disposed; The second metal layer, the initial mass block, and the first metal layer are etched to stop at the substrate to form a busbar located in the busbar region, electrode fingers located in the central region and the edge region, and a mass block between the first interdigitated electrode layer and the second interdigitated electrode layer of the electrode fingers located in the edge region. The busbar, the mass block, and the electrode fingers constitute interdigitated electrodes. The electrode fingers extend along the first direction and are spaced apart along the second direction. The busbar extends along the second direction and connects each of the electrode fingers. The first direction intersects the second direction.

12. The forming method according to claim 11, characterized in that, The step of partially etching the first metal layer to form an initial mass block in the edge region includes: A patterned first mask is disposed on the first metal layer, and the first mask is disposed on the first metal layer in the edge region; The first metal layer located in the central region and the confluence region is partially etched according to the first mask to form the initial mass block in the edge region; After the initial mass block is formed, the first mask is removed.

13. The forming method according to claim 11, characterized in that, The etching of the second metal layer, the initial mass block, and the first metal layer to stop at the substrate includes: A patterned second mask is provided on the second metal layer. The second mask includes a first mask portion and a second mask portion. The first mask portion is located on the second metal layer of 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 second metal layer of the center region and the edge region and intersect with the orthographic projection of the initial mass block on the substrate. Using the second mask as a mask, the second metal layer, the initial mass block and the first metal layer are etched. The second metal layer and the first metal layer in the busbar region are etched into busbars corresponding to the first mask portion. The second metal layer and the first metal layer in the center region and the edge region are etched into electrode fingers corresponding to the second mask portion. The remaining initial mass block located in the edge region is used as a mass block. After forming the busbar, electrode fingers, and mass block, the second mask portion is removed.

14. The forming method according to claim 11, characterized in that, Before depositing the first metal layer on the substrate, the method further includes depositing an etch stop layer on the substrate.

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