Filter, method of forming a filter, and electronic device

Abstract

The application discloses a filter and a forming method thereof and an electronic device. In the forming method, a frequency modulation layer with a first opening is formed on an interdigital transducer, a pad is formed in the first opening, a passivation layer covering the frequency modulation layer and the pad is formed after thinning treatment is performed on the frequency modulation layer in a predetermined region, damage to the passivation layer is avoided, the film layer quality of the passivation layer is higher, the protection of the passivation layer on the pad and the frequency modulation layer is guaranteed, and therefore the reliability of the filter is improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing, and more particularly to a filter, a method for forming the filter, and an electronic device. Background Technology

[0002] Radio frequency (RF) front-end chips in wireless communication devices include power amplifiers, antenna switches, RF filters, multiplexers, and low-noise amplifiers. Among these, RF filters include surface acoustic wave (SAW) filters, bulk acoustic wave (BAW) filters, micro-electro-mechanical system (MEMS) filters, and integrated passive device (IPD) filters.

[0003] SAW filters have a high quality factor (Q value) and are used to create radio frequency filters with low insertion loss and high out-of-band rejection. As one of the most widely used filters in current wireless communication devices, the high reliability of SAW filters can extend the lifespan of electronic devices and expand their application range.

[0004] Currently, the performance of SAW filters still needs improvement. Summary of the Invention

[0005] The problem solved by the embodiments of the present invention is to provide a filter, a method for forming a filter, and an electronic device, which is beneficial to improving the reliability of the filter.

[0006] To address the aforementioned problems, embodiments of the present invention provide a method for forming a filter, comprising: providing a substrate, wherein an interdigital transducer is formed on the substrate, the interdigital transducer including a connecting portion; forming a frequency modulation layer having a first opening on the substrate, the frequency modulation layer covering the interdigital transducer, and the first opening exposing at least a portion of the surface of the connecting portion; forming a pad in the first opening, the pad being electrically connected to the connecting portion; after forming the pad, thinning a predetermined area of ​​the frequency modulation layer; and after thinning the predetermined area of ​​the frequency modulation layer, forming a passivation layer covering the frequency modulation layer and the pad.

[0007] Optionally, the step of forming a pad in the first opening includes: forming a first mask layer having a first mask opening on the frequency modulation layer; wherein the first mask opening is connected to the first opening formed in the frequency modulation layer, and the first mask opening exposes the connection portion through the first opening; forming a pad material layer in the first opening, the pad material layer also being located on the first mask layer; removing the first mask layer and the pad material layer located on the first mask layer, the remaining pad material layer located in the first opening serving as a pad.

[0008] Optionally, the step of forming a frequency modulation layer with a first opening on the substrate includes: forming the frequency modulation layer covering the substrate and the interdigital transducer; patterning the frequency modulation layer and forming the first opening in the frequency modulation layer; before patterning the frequency modulation layer, forming a first mask layer with a first mask opening on the frequency modulation layer, the first mask opening exposing the frequency modulation layer covering the connection portion; in the step of patterning the frequency modulation layer, removing the frequency modulation layer at the bottom of the first mask opening and forming a first opening in the frequency modulation layer that communicates with the first mask opening.

[0009] Optionally, the process for forming the frequency modulation layer covering the substrate and the interdigital transducer includes physical vapor deposition, chemical vapor deposition, or atomic layer deposition.

[0010] Optionally, the process of thinning a predetermined area of ​​the frequency modulation layer includes a trimming process.

[0011] Optionally, after forming a passivation layer covering the frequency modulation layer and the pad, the method further includes: forming a second opening in the passivation layer, the second opening exposing at least a portion of the surface of the pad; forming a solder ball in the second opening, and the solder ball being electrically connected to the pad.

[0012] Optionally, the step of forming solder balls in the second opening includes: forming a second mask layer having a second mask opening on the passivation layer; wherein the second mask opening is connected to the second opening formed in the passivation layer, and the second mask opening exposes the solder pad through the second opening; forming the solder ball in the second mask opening and the second opening; after forming the solder ball, the forming method further includes: removing the second mask layer.

[0013] Optionally, the step of forming a second opening in the passivation layer includes: forming a second mask layer having a second mask opening on the passivation layer, the second mask opening exposing the passivation layer covering the pad; using the second mask layer as a mask, removing the passivation layer at the bottom of the second mask opening, and forming a second opening in the passivation layer that communicates with the second mask opening.

[0014] Optionally, the process for forming the passivation layer covering the frequency modulation layer and the pads includes physical vapor deposition, chemical vapor deposition, or atomic layer deposition.

[0015] Accordingly, embodiments of the present invention also provide a filter, comprising: a substrate; an interdigital transducer located on the substrate, the interdigital transducer including a connection portion; a frequency modulation layer covering the substrate and the interdigital transducer, wherein the frequency modulation layer exposes at least a portion of the surface of the connection portion, the surface of the connection portion exposed by the frequency modulation layer serving as a first interconnection region of the connection portion, the frequency modulation layer including a frequency modulation region and a non-frequency modulation region, the thickness of the frequency modulation layer located in the frequency modulation region being less than the thickness of the frequency modulation layer located in the non-frequency modulation region; a pad located on the side of the frequency modulation layer and covering the first interconnection region of the connection portion, the pad being electrically connected to the connection portion; and a passivation layer covering the frequency modulation layer and the pad.

[0016] Optionally, the passivation layer exposes at least a portion of the surface of the pad, and the surface of the pad exposed by the passivation layer serves as a second interconnect region of the pad; the filter further includes: solder balls located on the side of the passivation layer and covering the second interconnect region of the pad, the solder balls being electrically connected to the pad.

[0017] Optionally, the interdigital transducer includes interdigital electrodes, each interdigital electrode including the connecting portion and electrode fingers located on the side of the connecting portion, and the connecting portion is electrically connected to the electrode fingers.

[0018] Accordingly, the present invention also provides an electronic device including the filter described in any embodiment of the present invention. Compared with the prior art, the technical solution of the embodiments of the present invention has the following advantages: In a filter formation method provided by this invention, after forming a frequency modulation layer with a first opening on an interdigital transducer, a pad is formed in the first opening. Subsequently, the frequency modulation layer in the predetermined area is thinned to form a passivation layer covering the frequency modulation layer and the pad, thereby avoiding damage to the passivation layer and resulting in a high-quality passivation layer. Consequently, the protective effect of the passivation layer on the pad and the frequency modulation layer is guaranteed, thereby improving the reliability of the filter.

[0019] This invention provides a filter in which the surface of the exposed connection portion of the frequency modulation layer serves as the first interconnect region of the connection portion. The thickness of the frequency modulation layer in the frequency modulation region is less than the thickness of the frequency modulation layer in the non-frequency modulation region. The pads are located in the first interconnect region, and a passivation layer covers the frequency modulation layer and the pads. That is, the passivation layer is formed after the frequency modulation layer is thinned, thereby avoiding damage to the passivation layer and resulting in a high-quality passivation layer. Consequently, the protective effect of the passivation layer on the pads and the frequency modulation layer is guaranteed, thereby improving the reliability of the filter. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a filter structure; Figures 2 to 12 This is a schematic diagram of the structure corresponding to each step in the filter formation method of the present invention; Figure 13 This is a schematic diagram of the structure of an embodiment of the filter of the present invention. Detailed Implementation

[0021] Currently, the reliability of filters still needs improvement. This paper analyzes the reasons why filter performance needs further improvement, using a schematic diagram of one such filter.

[0022] Figure 1 This is a schematic diagram of a filter structure.

[0023] refer to Figure 1 The filter includes: a substrate 10; an interdigital transducer 11 located on the substrate 10, the interdigital transducer 11 including interdigital electrodes 14, the interdigital electrodes 14 including the connecting portion 11a and electrode fingers 11b located on the side of the connecting portion 11a, and the connecting portion 11a being electrically connected to the electrode fingers 11b; a pad 12 located on top of the connecting portion 11a, and the pad 12 being electrically connected to the connecting portion 11a; and a frequency modulation layer 13 covering the substrate 10, the interdigital transducer 11, and the pad 12. The frequency modulation layer 13 exposes at least a portion of the surface of the pad 12. The surface of the pad 12 exposed by the frequency modulation layer 13 serves as the interconnect region i of the pad 12. The frequency modulation layer 13 includes a frequency modulation region (not shown in the figure) and a non-frequency modulation region (not shown in the figure). The thickness of the frequency modulation layer 13 located in the frequency modulation region is less than the thickness of the frequency modulation layer 13 located in the non-frequency modulation region. Solder balls 15 are located on the side of the frequency modulation layer 13 and cover the interconnect region i of the pad 12. The solder balls 15 are electrically connected to the pad 12.

[0024] It should be noted that the electrical connection between the connecting part 11a and the electrode finger 11b is not shown in the figure. In the actual design, the connecting part 11a and the electrode finger 11b are electrically connected in other areas of the filter.

[0025] Specifically, the frequency tuning region refers to the working area of ​​the interdigital transducer 11 (e.g., the area where the electrode finger 11b is located, or the electrode finger area of ​​the interdigital electrode 14 and the adjacent acoustic wave propagation channel), and the non-frequency tuning region refers to the non-working area of ​​the interdigital transducer 11 (e.g., the area where the connection portion 11a is located, or the area where the connection portion 11a and the pad 12 are located).

[0026] Research revealed that, on the one hand, the frequency modulation layer 13 covers the substrate 10, the interdigital transducer 11, and the pads 12, with at least a portion of the surface of the pads 12 exposed. The frequency modulation layer 13 includes a frequency modulation region (not shown in the figure) and a non-frequency modulation region (not shown in the figure). The thickness of the frequency modulation layer 13 located in the frequency modulation region is less than the thickness of the frequency modulation layer 13 located in the non-frequency modulation region. That is, the frequency modulation region is formed by locally thinning the frequency modulation layer 13, thus the frequency modulation layer in the frequency modulation region... Defects such as microcracks, rough surfaces, or insufficient thickness may exist in the frequency modulation layer 13, which reduces the protection effect of the frequency modulation layer 13 on the interdigital transducer 11, thereby reducing the reliability of the filter. On the other hand, the frequency modulation layer 13 exposes at least part of the surface of the pad 12 so that test probes can directly contact the pad 12 in the wafer-level testing process to achieve electrical performance testing of the filter. However, this filter adds the process of patterned frequency modulation layer 13 in the wafer-level process stage, which increases the complexity of the wafer-level process stage.

[0027] Wafer-level testing refers to the testing of the electrical performance of a filter chip when it is in the form of a whole wafer before it is diced and packaged.

[0028] To address the aforementioned technical problems, embodiments of the present invention provide a method for forming a filter, comprising: providing a substrate, on which an interdigital transducer is formed, the interdigital transducer including a connecting portion; forming a frequency modulation layer having a first opening on the substrate, the frequency modulation layer covering the interdigital transducer, and the first opening exposing at least a portion of the surface of the connecting portion; forming a pad in the first opening, the pad being electrically connected to the connecting portion; after forming the pad, thinning a predetermined area of ​​the frequency modulation layer; and after thinning the predetermined area of ​​the frequency modulation layer, forming a passivation layer covering the frequency modulation layer and the pad.

[0029] In the scheme disclosed in the embodiments of the present invention, after forming a frequency modulation layer with a first opening on the interdigital transducer, a pad is formed in the first opening. Subsequently, the frequency modulation layer in the predetermined area is thinned to form a passivation layer covering the frequency modulation layer and the pad, thereby avoiding damage to the passivation layer and making the film quality of the passivation layer high. Correspondingly, the protective effect of the passivation layer on the pad and the frequency modulation layer is guaranteed, thereby improving the reliability of the filter.

[0030] 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.

[0031] Figures 2 to 12 This is a schematic diagram of the structure corresponding to each step in the filter formation method of the present invention.

[0032] refer to Figure 2 A substrate 100 is provided, on which an interdigital transducer 101 is formed, the interdigital transducer 101 including a connecting portion 102.

[0033] It should be noted that the electrical connection between the connecting part 102 and the interdigital transducer 101 is not shown in the figure. In the actual design, the connecting part 102 and the interdigital transducer 101 are electrically connected in other areas of the filter.

[0034] Substrate 100 is used to provide a process platform for forming filters.

[0035] In some embodiments, a surface acoustic wave (SAW) filter is used as an example for illustration. A SAW filter is a specialized filtering device made using the piezoelectric effect and the physical characteristics of surface acoustic wave propagation. In a SAW filter, the signal undergoes two conversions: electro-acoustic and electro-acoustic, thereby 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.

[0036] Accordingly, the substrate 100 is a piezoelectric substrate, thereby enabling the subsequent surface acoustic wave filter structure to utilize the piezoelectric effect for filtering.

[0037] The substrate 100 is made of materials including lithium niobate, lithium tantalate, quartz, or piezoelectric ceramics. As an example, the substrate 100 is made of lithium niobate.

[0038] The interdigital transducer 101 is used to convert between electrical signals and acoustic signals, thereby enabling the surface acoustic wave (SAW) filter to filter the signals. In some embodiments, the formed filter is a SAW filter; therefore, the interdigital transducer 101 is correspondingly an interdigital electrode 103, which includes the connecting portion 102 and electrode fingers 104 located on the side of the connecting portion 102, and the connecting portion 102 is electrically connected to the electrode fingers 104. Specifically, the interdigital transducer 101 is a metal interdigital transducer (IDT).

[0039] The connection part 102 is used to realize the electrical connection between the electrode finger 104 and the pad, thereby realizing the electrical connection between the interdigital transducer 101 and the external circuit structure.

[0040] The electrode fingers 104 and the connector 102 are both made of one or more of molybdenum, aluminum, platinum, tungsten, gold, nickel, and silver. In some embodiments, the electrode fingers 104 and the connector 102 are both made of aluminum. Specifically, the electrode fingers 104 and the connector 102 are formed by depositing a metal film on the substrate 100 and patterning the metal film using photolithography and etching processes.

[0041] refer to Figures 3 to 5 A first opening 105 is formed on the substrate 100 (e.g., Figure 5 The frequency modulation layer 106 (shown) covers the interdigital transducer 101, and the first opening 105 exposes at least a portion of the surface of the connection portion 102.

[0042] The frequency modulation layer 106 can not only protect the interdigital transducer 101, the connector 102, and the substrate 100 in subsequent processes, but also be used to adjust the operating frequency of the interdigital transducer 101. Specifically, the operating frequency of the interdigital transducer 101 is adjusted by changing the thickness of the frequency modulation layer 106 according to the target operating frequency.

[0043] The frequency modulation layer 106 has a first opening 105 that exposes at least a portion of the surface of the connection portion 102. Therefore, the frequency modulation layer 106 can also be used to define the area where the connection portion 102 connects to the pads.

[0044] In some embodiments, the first opening 105 exposes at least a portion of the surface of the connection portion 102, which helps to reduce the difficulty of making an electrical connection between the connection portion 102 and the pad. As an example, the first opening 105 exposes a portion of the top surface of the connection portion 102.

[0045] In some embodiments, the material of the frequency modulation layer 106 includes silicon oxide or silicon nitride.

[0046] It should be noted that silicon oxide or silicon nitride has relatively stable physical and chemical properties. In subsequent process manufacturing, silicon oxide or silicon nitride is not easily removed, which can effectively protect the interdigital transducer 101.

[0047] As an example, the material of the frequency modulation layer 106 is silicon oxide.

[0048] The steps for forming a frequency modulation layer 106 with a first opening 105 on the substrate 100 are described in detail below with reference to the accompanying drawings.

[0049] refer to Figure 3 This forms the frequency modulation layer 106 covering the substrate 100 and the interdigital transducer 101.

[0050] In some embodiments, the process of forming the frequency modulation layer 106 covering the substrate 100 and the interdigital transducer 101 includes physical vapor deposition, chemical vapor deposition, or atomic layer deposition.

[0051] It should be noted that physical vapor deposition (PVD), chemical vapor deposition (CVD), or atomic layer deposition (ALD) processes have the characteristic of high film deposition density. Therefore, the frequency modulation layer 106 formed by PVD, CVD, or ALD processes has higher density, which is beneficial to improving the density of the subsequently formed frequency modulation layer 106. In addition, PVD, CVD, or ALD processes have high step coverage, so that the sidewalls of the interdigital transducer 101 can also be covered by the frequency modulation layer 106.

[0052] refer to Figure 4 Before graphically representing the frequency modulation layer 106, a first mask layer 108 with a first mask opening 107 is formed on the frequency modulation layer 106, the first mask opening 107 exposing the frequency modulation layer 106 covering the connection portion 102.

[0053] The first mask opening 107 is used to define the position and shape of the subsequent pads, and also facilitates the removal of the frequency modulation layer 106 at the bottom of the first mask opening 107 along the first mask opening 107.

[0054] The first mask opening 107 exposes the frequency modulation layer 106 covering the connection portion 102, making it easier to remove the frequency modulation layer 106 covering the connection portion 102 so that the connection portion 102 is exposed, thereby enabling the pads to electrically connect to the connection portion 102.

[0055] The first mask layer 108 is used as a mask for forming the patterned frequency modulation layer 106 and pads.

[0056] In some embodiments, the material of the first mask layer 108 includes photoresist. Photoresist has high resolution, allowing precise control of the opening size of the first mask opening 107; simultaneously, photoresist is easy to remove, thereby reducing process complexity and improving production efficiency. In other embodiments, the first mask layer may also be made of other materials suitable for use as etching masks and easily removable.

[0057] refer to Figure 4 In some embodiments, during the step of forming a first mask layer 108 with a first mask opening 107 on the frequency modulation layer 106, the angle A between the sidewall of the first mask opening 107 and the top surface of the connecting portion 102 is an acute angle.

[0058] The sidewall of the first mask opening 107 refers to the sidewall of the first mask layer 108.

[0059] It should be noted that the angle A between the sidewall of the first mask opening 107 and the top surface of the connecting portion 102 is an acute angle, that is, the inclination of the sidewall of the first mask layer 108 is large. During the process of forming the pad material layer, the pad material layer is not easy to form on the sidewall of the first mask layer 108. Therefore, it is easy to operate when removing the pad material layer on the top of the first mask layer 108.

[0060] refer to Figure 5 The frequency modulation layer 106 is graphically represented, and a first opening 105 is formed in the frequency modulation layer 106.

[0061] The first opening 105 provides space for an electrical connection between the pad and the connector 102.

[0062] Specifically, in the step of graphically representing the frequency modulation layer 106, the frequency modulation layer 106 at the bottom of the first mask opening 107 is removed, and a first opening 105 communicating with the first mask opening 107 is formed in the frequency modulation layer 106.

[0063] It should be noted that the first mask layer 108 serves as the mask for forming the patterned frequency modulation layer 106 and the pads. That is, the patterned frequency modulation layer 106 and the pads share a single photomask. Compared with the scheme of using two photomasks to form the first opening and the pads respectively, the number of photomasks is reduced, thereby simplifying the process and reducing production costs. At the same time, the alignment accuracy between the first opening 105 and the pads is improved, which correspondingly improves the electrical connection reliability between the pads and the connection portion 102, thereby helping to improve the performance of the filter. In addition, the patterned frequency modulation layer 106 and the pads share the first mask layer 108, which reduces the number of times the mask layer is formed, thereby reducing the probability of residues from the first mask layer 108 on the surface of the frequency modulation layer 106, and thus improving the formation quality of the passivation layer.

[0064] In some embodiments, the process of removing the frequency modulation layer 106 at the bottom of the first mask opening 107 includes a dry etching process. The dry etching process has anisotropic etching characteristics, and the etching is more directional, which is beneficial to improving the morphology and dimensional accuracy of the first opening 105.

[0065] In other embodiments, after forming a frequency modulation layer with a first opening on the substrate, a first mask layer with a first mask opening can be formed on the frequency modulation layer, that is, different mask layers can be used to form the first opening and form the pad.

[0066] refer to Figures 5 to 7 A pad 109 is formed in the first opening 105, and the pad 109 is electrically connected to the connection portion 102.

[0067] The solder pad 109 is used to electrically connect the connection part 102 so as to realize the electrical connection between the connection part 102 and the solder ball.

[0068] In some embodiments, the material of pad 109 includes one or more of aluminum, copper, gold, titanium, nickel, silver, and tungsten. It should be noted that aluminum, copper, gold, titanium, nickel, silver, and tungsten all have good electrical conductivity. As an example, the material of pad 109 is aluminum.

[0069] Specifically, the step of forming the pad 109 in the first opening 105 includes: referring to Figure 5 A first mask layer 108 with a first mask opening 107 is formed on the frequency modulation layer 106; wherein the first mask opening 107 communicates with a first opening 105 formed in the frequency modulation layer 106, and the first mask opening 107 exposes the connection portion 102 through the first opening 105; (refer to reference) Figure 5 and Figure 6 A pad material layer 110 is formed in the first mask opening 107 and the first opening 105, and the pad material layer 110 is also located on the first mask layer 108; referring to the reference Figure 6 and Figure 7 Remove the first mask layer 108 and the pad material layer 110 located on the first mask layer 108, and the remaining pad material layer 110 located in the first opening 105 serves as the pad 109.

[0070] The first mask opening 107 is connected to the first opening 105 formed in the frequency modulation layer 106. No additional alignment steps are required between the first opening 105 and the first mask opening 107. When forming the pad 109, the pad material layer 110 can be deposited directly in the first mask opening 107 and the first opening 105, thereby simplifying the process and reducing defects caused by alignment errors.

[0071] The pad material layer 110 is used to form the pad 109.

[0072] Specifically, removing the first mask layer 108 serves two purposes: firstly, it facilitates subsequent thinning of a predetermined area (not shown in the figure) of the frequency modulation layer 106; secondly, it provides space for the subsequent formation of a passivation layer on the frequency modulation layer 106 and the pads 109. In some embodiments, after the pads 109 are formed, a predetermined area (not shown in the figure) of the frequency modulation layer 106 is thinned.

[0073] Specifically, the predetermined region refers to the working area of ​​the interdigital transducer 101 (e.g., the area where the electrode fingers 104 are located, or the area of ​​the electrode fingers 104 of the interdigital electrodes 103 and the adjacent acoustic wave propagation channel). Thinning the predetermined region removes a portion of the thickness of the frequency modulation layer 106 within that region, thereby forming a frequency modulation region on the frequency modulation layer 106. The thickness of the frequency modulation layer 106 located in the frequency modulation region is less than the thickness of the frequency modulation layer 106 located in the non-frequency modulation region.

[0074] It should be noted that since the patterned frequency modulation layer 106 and the pads 109 share the first mask layer 108, the surface of the frequency modulation layer 106 is covered by the first mask layer 108 and cannot be thinned before the pads 109 are formed. After the pads 109 are formed and the first mask layer 108 is removed, the surface of the frequency modulation layer 106 is exposed, thereby enabling thinning of a predetermined area of ​​the frequency modulation layer 106 to adjust the operating frequency of the filter.

[0075] It should also be noted that the predetermined area of ​​the frequency modulation layer 106 is thinned to change the thickness of the frequency modulation layer 106, thereby changing the mass load on the surface acoustic wave propagation path, compensating for the influence of process deviations on the filter operating frequency, and thus improving the consistency of the filter operating frequency.

[0076] In some embodiments, the process of thinning a predetermined region (not shown) of the frequency modulation layer 106 includes a trimming process.

[0077] It should be noted that the trimming process has the characteristics of high precision and high controllability. Therefore, it can accurately remove the thickness of the frequency modulation layer 106 in the predetermined area, thereby accurately adjusting the operating frequency of the filter.

[0078] refer to Figure 8 After thinning a predetermined area of ​​the frequency modulation layer 106, a passivation layer 112 is formed covering the frequency modulation layer 106 and the pad 109.

[0079] Passivation layer 112 is used to protect frequency modulation layer 106 and pad 109.

[0080] It should be noted that after forming a frequency modulation layer 106 with a first opening 105 on the interdigital transducer 101, a pad 109 is formed in the first opening 105. Subsequently, the frequency modulation layer 106 in the predetermined area is thinned to form a passivation layer 112 covering the frequency modulation layer 106 and the pad 109, thereby avoiding damage to the passivation layer 112 and resulting in a higher film quality of the passivation layer 112. Consequently, the protective effect of the passivation layer 112 on the pad 109 and the frequency modulation layer 106 is guaranteed, thereby improving the reliability of the filter.

[0081] In some embodiments, the process of forming the passivation layer 112 covering the frequency modulation layer 106 and the pad 109 includes physical vapor deposition, chemical vapor deposition or atomic layer deposition.

[0082] Physical vapor deposition (PVD), chemical vapor deposition (CVD), or atomic layer deposition (ALD) processes all feature high film density and uniformity, as well as good step coverage. Therefore, the passivation layer 112 formed by PVD, CVD, or ALD processes has high density, uniform thickness, and can effectively cover the sidewalls of pad 109.

[0083] As an example, the process for forming the passivation layer 112 covering the frequency modulation layer 106 and the pads 109 is a physical vapor deposition process.

[0084] In some embodiments, the material of the passivation layer 112 includes silicon oxide or silicon nitride.

[0085] It should be noted that silicon oxide or silicon nitride has relatively stable physical and chemical properties. In subsequent process manufacturing, silicon oxide or silicon nitride is not easily removed, which can effectively protect the pads 109 and the frequency modulation layer 106.

[0086] In some embodiments, the passivation layer 112 has a thickness of 5 nanometers to 15 nanometers.

[0087] It should be noted that by controlling the thickness of the passivation layer 112 to between 5 nanometers and 15 nanometers, the uniformity of the passivation layer 112 film thickness can be ensured, and the test probe can be allowed to directly penetrate the passivation layer 112 and make electrical contact with the pad 109 during the wafer-level testing process. This eliminates the need to open a test window in the passivation layer 112, simplifying the wafer-level process steps.

[0088] Wafer-level testing refers to the testing of the electrical performance of a filter chip when it is in the form of a whole wafer before it is diced and packaged.

[0089] refer to Figures 9 to 10 After forming a passivation layer 112 covering the frequency modulation layer 106 and the pads 109, the method further includes: forming a second opening 113 in the passivation layer 112 (e.g., ...). Figure 10 As shown), the second opening 113 exposes at least a portion of the surface of the pad 109.

[0090] A second opening 113 is formed in the passivation layer 112, and the second opening 113 exposes at least a portion of the surface of the pad 109. Therefore, the passivation layer 112 can also define the area where the solder ball 114 is connected to the pad 109 in the packaging process.

[0091] Specifically, a second opening 113 is formed in the passivation layer 112. The second opening 113 is formed during the packaging process stage, rather than during the wafer-level process stage.

[0092] In some embodiments, the second opening 113 exposes at least a portion of the surface of the pad 109, which helps to reduce the difficulty of making an electrical connection between the pad 109 and the solder ball 114. As an example, the second opening 113 exposes a portion of the top surface of the pad 109.

[0093] The steps for forming the second opening 113 in the passivation layer 112 are described in detail below with reference to the accompanying drawings.

[0094] refer to Figure 9 A second mask layer 116 with a second mask opening 115 is formed on the passivation layer 112, the second mask opening 115 exposing the passivation layer 112 covering the pad 109.

[0095] The second mask opening 115 is used to define the position and shape of subsequent solder balls, and also facilitates the removal of the passivation layer 112 at the bottom of the second mask opening 115.

[0096] The second mask opening 115 exposes the passivation layer 112 covering the pad 109, which facilitates the removal of the passivation layer 112 covering the pad 109 to expose the pad 109, thereby enabling the solder balls to electrically connect to the pad 109.

[0097] The second mask layer 116 is used as a mask for forming the passivation layer 112 with the second opening 113 and the solder ball.

[0098] In some embodiments, the material of the second mask layer 116 includes photoresist. Photoresist has high resolution, allowing precise control of the opening size of the second mask opening 115; 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 suitable for use as etching masks and easily removable.

[0099] refer to Figure 10 Using the second mask layer 116 as a mask, the passivation layer 112 at the bottom of the second mask opening 115 is removed, and a second opening 113 communicating with the second mask opening 115 is formed in the passivation layer 112.

[0100] The second opening 113 provides space for an electrical connection between the solder ball and the pad 109.

[0101] It should be noted that the second mask layer 116 serves as the mask for forming the passivation layer 112 with the second opening 113 and the solder balls. That is, the passivation layer 112 with the second opening 113 and the solder balls share a single photomask. Compared with the scheme of using two photomasks to form the second opening and the solder balls separately, the number of photomasks is reduced, thereby simplifying the process and reducing production costs. At the same time, the alignment accuracy between the second opening 113 and the solder balls is improved, which in turn improves the electrical connection reliability between the solder balls and the pads 109, thereby improving the performance of the filter.

[0102] In other embodiments, after forming the second opening on the passivation layer, a second mask layer with the second mask opening can be formed on the passivation layer, that is, different mask layers can be used to form the second opening and the solder ball.

[0103] refer to Figures 10 to 11 Solder balls 114 are formed in the second opening 113 (e.g., Figure 11 As shown), the solder ball 114 is electrically connected to the solder pad 109.

[0104] Solder ball 114 is used to electrically connect pad 109 to enable electrical connection between pad 109 and external circuitry.

[0105] In some embodiments, the material of the solder ball 114 includes tin solder, silver solder, or gold-tin alloy solder.

[0106] Specifically, the step of forming solder balls 114 in the second opening 113 includes: referring to Figure 10 A second mask layer 116 having a second mask opening 115 is formed on the passivation layer 112; wherein the second mask opening 115 communicates with a second opening 113 formed in the passivation layer 112, and the second mask opening 115 exposes the pad 109 through the second opening 113; Reference Figure 11 Solder balls 114 are formed in the second mask opening 115 and the second opening 113.

[0107] The second mask opening 115 is connected to the second opening 113 formed in the passivation layer 112. No additional alignment steps are required between the second opening 113 and the second mask opening 115. When forming the solder ball 114, the solder ball 114 can be formed directly in the second mask opening 115 and the second opening 113, thereby simplifying the process and reducing defects caused by alignment errors.

[0108] Reference Figure 11 and Figure 12 After forming the solder ball 114, the forming method further includes: removing the second mask layer 116.

[0109] Specifically, the second mask layer 116 is removed using a wet desmearing or ashing process.

[0110] Accordingly, the present invention also provides a filter. Figure 13 This is a schematic diagram of the structure of an embodiment of the filter of the present invention.

[0111] refer to Figure 13 The filter includes: a substrate 100; an interdigital transducer 101 located on the substrate 100, the interdigital transducer 101 including a connection portion 102; a frequency modulation layer 106 covering the substrate 100 and the interdigital transducer 101, the frequency modulation layer 106 exposing at least a portion of the surface of the connection portion 102, the surface of the connection portion 102 exposed by the frequency modulation layer 106 serving as a first interconnect region I of the connection portion 102, the frequency modulation layer 106 including a frequency modulation region (not shown) and a non-frequency modulation region (not shown), the thickness of the frequency modulation layer 106 located in the frequency modulation region being less than the thickness of the frequency modulation layer 106 located in the non-frequency modulation region; a pad 109 located on the side of the frequency modulation layer 106 and covering the first interconnect region I of the connection portion 102, the pad 109 being electrically connected to the connection portion 102; and a passivation layer 112 covering the frequency modulation layer 106 and the pad 109.

[0112] Substrate 100 is used to provide a process platform for forming filters.

[0113] In some embodiments, a surface acoustic wave (SAW) filter is used as an example for illustration. A SAW filter is a specialized filtering device made using the piezoelectric effect and the physical characteristics of surface acoustic wave propagation. In a SAW filter, the signal undergoes two conversions: electro-acoustic and electro-acoustic, thereby 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.

[0114] Accordingly, the substrate 100 is a piezoelectric substrate, thereby enabling the subsequent surface acoustic wave filter structure to utilize the piezoelectric effect for filtering.

[0115] The substrate 100 is made of materials including lithium niobate, lithium tantalate, quartz, or piezoelectric ceramics. As an example, the substrate 100 is made of lithium niobate.

[0116] The interdigital transducer 101 is used to convert between electrical signals and acoustic signals, thereby enabling the surface acoustic wave (SAW) filter to filter the signals. In some embodiments, the formed filter is a SAW filter; therefore, the interdigital transducer 101 is correspondingly an interdigital electrode 103, which includes the connecting portion 102 and electrode fingers 104 located on the side of the connecting portion 102, and the connecting portion 102 is electrically connected to the electrode fingers 104. Specifically, the interdigital transducer 101 is a metal interdigital transducer.

[0117] It should be noted that the electrical connection between the connecting part 102 and the electrode finger 104 is not shown in the figure. In the actual design, the connecting part 102 and the electrode finger 104 are electrically connected in other areas of the filter.

[0118] The connection part 102 is used to realize the electrical connection between the electrode finger 104 and the pad 109, thereby realizing the electrical connection between the interdigital transducer 101 and the external circuit structure.

[0119] The electrode finger 104 and the connecting portion 102 are both made of one or more of molybdenum, aluminum, platinum, tungsten, gold, nickel, and silver. In some embodiments, the electrode finger 104 and the connecting portion 102 are both made of aluminum.

[0120] The frequency modulation layer 106 not only protects the interdigital transducer 101, the connecting part 102, and the substrate 100, but also adjusts the operating frequency of the interdigital transducer 101. Specifically, the operating frequency of the interdigital transducer 101 is adjusted by changing the thickness of the frequency modulation layer 106 according to the target operating frequency.

[0121] Specifically, the frequency modulation layer 106 has a first opening 105, which exposes the first interconnect region I.

[0122] Therefore, the frequency modulation layer 106 can also be used to define the area where the connection portion 102 connects to the pad 109, that is, to define the first interconnect region I. Specifically, the first opening 105 is used to provide space for the electrical connection between the pad 109 and the connection portion 102.

[0123] In some embodiments, the frequency modulation layer 106 exposes at least a portion of the surface of the connection portion 102, which helps to reduce the difficulty of achieving an electrical connection between the connection portion 102 and the pad 109. As an example, the frequency modulation layer 106 exposes a portion of the top surface of the connection portion 102.

[0124] In some embodiments, the material of the frequency modulation layer 106 includes silicon oxide or silicon nitride.

[0125] It should be noted that silicon oxide or silicon nitride has relatively stable physical and chemical properties. In subsequent process manufacturing, silicon oxide or silicon nitride is not easily removed, which can effectively protect the interdigital transducer 101.

[0126] As an example, the material of the frequency modulation layer 106 is silicon oxide.

[0127] Specifically, the frequency tuning region refers to the working area of ​​the interdigital transducer 101 (e.g., the area where the electrode finger 104 is located, or the area of ​​the electrode finger 104 of the interdigital electrode 103 and the adjacent acoustic wave propagation channel), and the non-frequency tuning region refers to the non-working area of ​​the interdigital transducer 101 (e.g., the area where the connection portion 102 is located, or the area where the connection portion 102 and the pad 109 are located).

[0128] In some embodiments, the thickness of the frequency modulation layer 106 located in the frequency modulation zone is less than the thickness of the frequency modulation layer 106 located in the non-frequency modulation zone. That is, changing the thickness of the frequency modulation layer 106 in the frequency modulation zone changes the mass load on the surface acoustic wave propagation path, correspondingly compensating for the influence of process deviations on the filter's operating frequency, thereby improving the consistency of the operating frequency between the frequency modulation zone and the non-frequency modulation zone.

[0129] The pad 109 is used to electrically connect the connector 102 to achieve electrical connection between the connector 102 and the solder ball 114.

[0130] In some embodiments, the material of pad 109 includes one or more of aluminum, copper, gold, titanium, nickel, silver, and tungsten. It should be noted that aluminum, copper, gold, titanium, nickel, silver, and tungsten all have good electrical conductivity. As an example, the material of pad 109 is aluminum.

[0131] Passivation layer 112 is used to protect frequency modulation layer 106 and pad 109.

[0132] It should be noted that the surface of the connection portion 102 exposed by the frequency modulation layer 106 serves as the first interconnect region I of the connection portion 102. The thickness of the frequency modulation layer 106 in the frequency modulation region is less than the thickness of the frequency modulation layer 106 in the non-frequency modulation region. The pad 109 is located in the first interconnect region I, and the passivation layer 112 covers the frequency modulation layer 106 and the pad 109. That is, the passivation layer 112 is formed after the frequency modulation layer 106 is thinned, thereby avoiding damage to the passivation layer 112 and resulting in a higher film quality of the passivation layer 112. Consequently, the protective effect of the passivation layer 112 on the pad 109 and the frequency modulation layer 106 is guaranteed, thereby improving the reliability of the filter.

[0133] In some embodiments, the material of the passivation layer 112 includes silicon oxide or silicon nitride.

[0134] It should be noted that silicon oxide or silicon nitride has relatively stable physical and chemical properties. In subsequent process manufacturing, silicon oxide or silicon nitride is not easily removed, which can effectively protect the pads 109 and the frequency modulation layer 106.

[0135] In some embodiments, the passivation layer 112 has a thickness of 5 nanometers to 15 nanometers.

[0136] It should be noted that by controlling the thickness of the passivation layer 112 to between 5 nanometers and 15 nanometers, the uniformity of the passivation layer 112 film thickness can be ensured, and the test probe can be allowed to directly penetrate the passivation layer 112 and make electrical contact with the pad 109 during the wafer-level testing process. This eliminates the need to open a test window in the passivation layer 112, thus simplifying the process steps.

[0137] Wafer-level testing refers to the testing of the electrical performance of a filter chip when it is in the form of a whole wafer before it is diced and packaged.

[0138] In some embodiments, the passivation layer 112 exposes at least a portion of the surface of the pad 109, and the surface of the pad 109 exposed by the passivation layer 112 serves as the second interconnect region II of the pad 109.

[0139] Specifically, the passivation layer 112 has a second opening 113, which exposes the second interconnect region II.

[0140] A second opening 113 is formed in the passivation layer 112, and the second opening 113 exposes at least a portion of the surface of the pad 109. Therefore, the passivation layer 112 can also define the area where the solder ball 114 is connected to the pad 109 in the packaging process.

[0141] Specifically, a second opening 113 is formed in the passivation layer 112. The second opening 113 is formed during the packaging process stage, rather than during the wafer-level process stage.

[0142] In some embodiments, the passivation layer 112 exposes at least a portion of the surface of the pad 109, which helps to reduce the difficulty of achieving electrical connection between the pad 109 and the solder ball 114. As an example, the passivation layer 112 exposes a portion of the top surface of the pad 109.

[0143] In some embodiments, the filter further includes: solder balls 114 located on the side of the passivation layer 112 and covering the second interconnect region II of the pad 109, the solder balls 114 being electrically connected to the pad 109.

[0144] Solder ball 114 is used to electrically connect pad 109 to enable electrical connection between pad 109 and external circuitry.

[0145] In some embodiments, the material of the solder ball 114 includes tin solder, silver solder, or gold-tin alloy solder.

[0146] Accordingly, embodiments of the present invention also provide an electronic device, which includes the filter described in any embodiment of the present invention.

[0147] Filters can be integrated into various electronic devices. As the foregoing analysis shows, filters have high reliability, which in turn enables the development of highly reliable electronic devices. These electronic devices can also include personal computers, smartphones and other mobile terminals, media players, navigation devices, video game consoles, game controllers, tablet computers, wearable devices, security access control systems, POS terminals, medical devices, flight simulators, and more.

[0148] The filter structure of this embodiment can be formed using the filter structure formation method of the aforementioned embodiment, or it can be formed using other filter structure formation methods, which will not be described again in this embodiment.

[0149] 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 on which an interdigital transducer is formed, the interdigital transducer including a connecting portion; A frequency modulation layer with a first opening is formed on the substrate, the frequency modulation layer covering the interdigital transducer, and the first opening exposing at least a portion of the surface of the connection portion; A pad is formed in the first opening, and the pad is electrically connected to the connection portion; After the pads are formed, the predetermined area of ​​the frequency modulation layer is thinned. After thinning a predetermined area of ​​the frequency modulation layer, a passivation layer is formed covering the frequency modulation layer and the pads.

2. The method for forming a filter as described in claim 1, characterized in that, The step of forming a pad in the first opening includes: forming a first mask layer having a first mask opening on the frequency modulation layer; wherein the first mask opening is connected to the first opening formed in the frequency modulation layer, and the first mask opening exposes the connection portion through the first opening; A pad material layer is formed in the first mask opening and the first opening, and the pad material layer is also located on the first mask layer; Remove the first mask layer and the pad material layer located on the first mask layer, and the remaining pad material layer located in the first opening serves as the pad.

3. The method for forming a filter as described in claim 2, characterized in that, The step of forming a frequency modulation layer with a first opening on the substrate includes: forming the frequency modulation layer covering the substrate and the interdigital transducer; and patterning the frequency modulation layer to form the first opening in the frequency modulation layer. Before the frequency modulation layer is graphically visualized, a first mask layer with a first mask opening is formed on the frequency modulation layer, the first mask opening exposing the frequency modulation layer covering the connection portion; In the step of graphically representing the frequency modulation layer, the frequency modulation layer at the bottom of the first mask opening is removed, and a first opening communicating with the first mask opening is formed in the frequency modulation layer.

4. The method for forming a filter according to any one of claims 1 to 3, characterized in that, The process for forming the frequency modulation layer includes physical vapor deposition, chemical vapor deposition, or atomic layer deposition.

5. The method for forming a filter as described in claim 1, characterized in that, The process of thinning a predetermined area of ​​the frequency modulation layer includes a trimming process.

6. The method for forming a filter as described in claim 1, characterized in that, After forming a passivation layer covering the frequency modulation layer and the pads, the method further includes: forming a second opening in the passivation layer, the second opening exposing at least a portion of the surface of the pads; Solder balls are formed in the second opening, and the solder balls are electrically connected to the pads.

7. The method for forming a filter as described in claim 6, characterized in that, The step of forming solder balls in the second opening includes: forming a second mask layer having a second mask opening on the passivation layer; wherein the second mask opening is connected to the second opening formed in the passivation layer, and the second mask opening exposes the solder pad through the second opening; The solder ball is formed in the second mask opening and the second opening; After forming the solder balls, the forming method further includes removing the second mask layer.

8. The method for forming a filter as described in claim 7, characterized in that, The step of forming a second opening in the passivation layer includes: forming a second mask layer having a second mask opening on the passivation layer, the second mask opening exposing the passivation layer covering the pad; Using the second mask layer as a mask, the passivation layer at the bottom of the second mask opening is removed, and a second opening communicating with the second mask opening is formed in the passivation layer.

9. The method for forming a filter as described in claim 1, characterized in that, The process for forming the passivation layer covering the frequency modulation layer and the pads includes physical vapor deposition, chemical vapor deposition, or atomic layer deposition.

10. A filter, characterized in that, include: Base; An interdigital transducer is located on the substrate, and the interdigital transducer includes a connecting portion; A frequency modulation layer covers the substrate and the interdigital transducer, and the frequency modulation layer exposes at least a portion of the surface of the connection portion. The surface of the connection portion exposed by the frequency modulation layer serves as a first interconnection region of the connection portion. The frequency modulation layer includes a frequency modulation region and a non-frequency modulation region. The thickness of the frequency modulation layer located in the frequency modulation region is less than the thickness of the frequency modulation layer located in the non-frequency modulation region. A pad is located on the side of the frequency modulation layer and covers the first interconnect area of ​​the connection portion; the pad is electrically connected to the connection portion. A passivation layer covers the frequency modulation layer and the pads.

11. The filter as claimed in claim 10, characterized in that, The passivation layer exposes at least a portion of the surface of the pad, and the surface of the pad exposed by the passivation layer serves as a second interconnect region of the pad; The filter further includes: solder balls located on the side of the passivation layer and covering the second interconnect region of the pad, the solder balls being electrically connected to the pad.

12. The filter as claimed in claim 10, characterized in that, The interdigital transducer includes interdigital electrodes, each interdigital electrode including the connecting portion and electrode fingers located on the side of the connecting portion, and the connecting portion is electrically connected to the electrode fingers.

13. An electronic device, characterized in that, Includes the filter as described in any one of claims 10 to 12.

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