A method of forming an interdigital electrode

Abstract

This invention provides a method for forming interdigitated electrodes, wherein the interdigitated electrodes are metal stacks. The method includes: providing a piezoelectric substrate; forming a metal material stack and a composite mask material layer on the piezoelectric substrate; the metal material stack includes a first metal material layer and a second metal material layer; the composite mask material layer includes a first mask material layer and a second mask material layer made of different materials; patterning the composite mask material layer to obtain a composite mask layer; the composite mask layer includes a first mask layer corresponding to the first mask material layer and a second mask layer corresponding to the second mask material layer; etching the first metal material layer using the composite mask layer as a mask to obtain a first metal layer, simultaneously consuming the first mask layer; and etching the second metal material layer using the second mask layer as a mask to obtain a second metal layer. This invention solves the problem that the interdigitated electrode material needs to be coated with a thick photoresist, and the unexpected reduction in photoresist thickness during the etching process makes it difficult to control the morphology of the interdigitated electrodes.

Description

Technical Field

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

[0002] As communication frequency bands advance to higher frequencies, the linewidth of interdigital electrodes is continuously shrinking, while simultaneously placing higher demands on the power tolerance of the electrodes. To improve power tolerance, multilayer metal stacked structures of interdigital electrodes have been developed in existing technologies. With the continuous miniaturization of devices, the thickness of interdigital electrodes is also increasing. The etching depth-to-width ratio of interdigital electrode materials using traditional photoresist methods is large, requiring the coating of thicker photoresist. During the etching process, the photoresist thickness may decrease unexpectedly, making it difficult to control the morphology of the interdigital electrodes. Summary of the Invention

[0003] The problem solved by this invention is that traditional photoresist etching of interdigital electrode materials has a large etching depth-to-width ratio, requiring a thicker layer of photoresist. During the etching process, the photoresist thickness may decrease unexpectedly, making it difficult to control the morphology of the interdigital electrodes.

[0004] To address the aforementioned problems, this invention provides a method for forming interdigitated electrodes, wherein the interdigitated electrodes are metal stacks. The method includes: providing a piezoelectric substrate; forming a metal material stack and a composite mask material layer on the piezoelectric substrate; wherein the metal material stack includes a first metal material layer and a second metal material layer, the second metal material layer being disposed on the piezoelectric substrate and the first metal material layer being disposed on the second metal material layer; the composite mask material layer includes a first mask material layer and a second mask material layer of different materials, the second mask material layer being disposed on the first metal material layer and the first mask material layer being disposed on the second mask material layer; patterning the composite mask material layer to obtain a composite mask layer; the composite mask layer includes a first mask layer corresponding to the first mask material layer and a second mask layer corresponding to the second mask material layer; using the composite mask layer as a mask, etching the first metal material layer to obtain a first metal layer, simultaneously consuming the first mask layer; using the second mask layer as a mask, etching the second metal material layer to obtain a second metal layer, wherein the metal stack includes the first metal layer and the second metal layer.

[0005] By using composite mask layers made of different materials in upper and lower layers, the mask function is relayed for different metal layer etching stages, solving the problem that a single mask cannot simultaneously adapt to multiple etching systems; the complex multilayer metal etching is decomposed into multiple independent and controllable sub-steps, which greatly reduces the difficulty of process development, broadens the process window, and facilitates the control of the morphology of the interdigitated electrodes.

[0006] Furthermore, when etching the second metal material layer using the second mask layer as a mask, the second mask layer undergoes a passivation reaction with the etching gas.

[0007] Furthermore, the material of the second metal layer includes W or Mo; the material of the second mask layer includes TiN; and the etching gas for etching the second metal material layer is SF6-based gas.

[0008] The second metal layer, made of high-density, high-acoustic impedance materials such as W or Mo, can improve the power tolerance of the film. TiN material has extremely high selectivity for etching W or Mo with SF6-based gas. By using the non-volatile TiF4 generated by the reaction of TiN mask with SF6 etching gas, a dense passivation layer is formed in situ on the etching sidewalls of W or Mo layers, effectively blocking the lateral attack of F free radicals on the W or Mo sidewalls, fundamentally solving the problem of side-cutting in the etching of W or Mo layers, and obtaining steep electrode sidewalls.

[0009] Furthermore, the first metal layer is made of Al or AlCu alloy, with the Cu content in the AlCu alloy being <5%; the first mask layer is made of SiO2, and the etching gas used to etch the first metal material layer is a Cl2 / BCl3-based gas.

[0010] The first metal layer uses Al or AlCu alloy as the main conductive layer. SiO2 has an extremely high selectivity for etching Al or AlCu alloy with Cl2 / BCl3-based gas, which can ensure the pattern accuracy of the Al or AlCu alloy layer etching.

[0011] Furthermore, the metal stack also includes a seed layer disposed between the piezoelectric substrate and the second metal layer; correspondingly, after etching the second metal material layer using the second mask layer as a mask, the process further includes: etching the seed material layer using the second mask layer as a mask to obtain the seed layer.

[0012] Furthermore, the seed layer can be made of AlN, Ti, or TiN.

[0013] Setting a seed layer can significantly enhance the bonding force between the second metal layer and the piezoelectric substrate, preventing the electrode from falling off under high-power operating conditions; using the same mask to complete the etching of the second metal layer and the seed layer simplifies the process flow and avoids alignment errors caused by multiple masks.

[0014] Furthermore, the metal stack also includes a first protective layer disposed between the first metal layer and the second metal layer; correspondingly, after etching the first metal material layer using the composite mask layer as a mask, the process further includes: etching the first protective material layer using the composite mask layer as a mask to obtain the first protective layer; and / or, the metal stack also includes a second protective layer disposed on the first metal layer; correspondingly, before etching the first metal material layer using the composite mask layer as a mask, the process further includes: etching the second protective material layer using the composite mask layer as a mask to obtain the second protective layer.

[0015] By setting a first protective layer, the interfacial bonding performance between the second metal layer and the first metal layer can be effectively improved, preventing intermetallic diffusion at high temperatures. At the same time, when a mass load is formed on the first metal layer, the first protective layer can also serve as an etching stop layer for the first metal layer, ensuring that the first metal layer below the mass load and the first metal layers at other locations are etched on the top surface of the first protective layer. This can prevent over-etching of some first metal layers and damage to the second metal layer below, ensuring the thickness uniformity and power tolerance performance of the second metal layer.

[0016] By setting a second protective layer, the interfacial bonding performance between the first mask layer and the first metal layer can be effectively improved, preventing metal-to-metal diffusion at high temperatures; at the same time, the first metal layer is protected from oxidation or damage in subsequent processes, ensuring the thickness uniformity and power tolerance performance of the first metal layer.

[0017] Furthermore, the first protective layer is made of Ti or TiN; and / or the second protective layer is made of Ti or TiN.

[0018] Furthermore, the patterned composite mask layer includes: forming a photoresist layer with an interdigitated pattern on a composite mask material layer; using the photoresist layer as a mask, etching the first mask material layer to obtain a first mask layer with an interdigitated pattern; using the first mask layer as a mask, etching the second mask material layer to obtain a second mask layer with an interdigitated pattern.

[0019] By transferring the interdigitated pattern of the photoresist layer to the first mask layer, which has a higher hardness, and then performing subsequent metal layer etching, the problem of deformation and peeling of the photoresist during long-term dry etching is avoided, which significantly improves the accuracy and stability of the interdigitated pattern transfer.

[0020] Furthermore, the interdigitated pattern on the first mask layer has a trench shape, with the trench being an inverted trapezoidal structure that is wider at the top and narrower at the bottom, and the sidewall angle of the trench is 85-89°.

[0021] The inverted trapezoidal structure with a sidewall angle of 85-89° effectively compensates for the linewidth shrinkage during subsequent metal etching, ensuring that the final electrode linewidth is consistent with the design value and that the etching morphology of the metal stack remains straight. At the same time, it further improves the stability and fidelity of the interdigitated pattern transfer and reduces the serrated defects at the electrode edges.

[0022] In summary, the various technical solutions described above in this application can have one or more of the following beneficial effects: When using the method of this invention to fabricate interdigitated electrodes, different mask layers are used for etching different metal layers of the interdigitated electrodes, achieving mask relay between the two mask layers in the composite mask layer. Using a high-density, high-acoustic impedance material as the electrode power layer material can improve the power tolerance of the interdigitated electrodes, reduce the device center frequency deviation, and effectively reduce insertion loss. Simultaneously, the method of this invention utilizes the characteristics of the mask layer material and the etching gas to form a passivation layer on the sidewall of the electrode power layer, which can make the sidewall of the power layer (i.e., the second metal layer) steeper, effectively reducing lateral side cut-out, reducing electrode linewidth deviation, and improving the overall performance of the interdigitated electrodes. Attached Figure Description

[0023] Figure 1 A flowchart of a method for forming interdigitated electrodes provided by the present invention; Figures 2-8 This is a schematic diagram of the structure corresponding to each step in one embodiment of the method for forming interdigitated electrodes of the present invention.

[0024] Explanation of reference numerals in the attached figures: 100 - Interdigitated electrode; 110 - Photoresist layer; 120 - First mask material layer; 121 - First mask layer; 130 - Second mask material layer; 131 - Second mask layer; 140 - First metal material layer; 141 - First metal layer; 150 - First protective material layer; 151 - First protective layer; 160 - Second metal material layer; 161 - Second metal layer; 170 - Seed material layer; 171 - Seed layer; 180 - Piezoelectric substrate. Detailed Implementation

[0025] The purpose of this invention is to provide a method for forming interdigitated electrodes, which achieves the effect of mask function relay at different metal layer etching stages by using multi-layer masks to ensure high selectivity for each metal layer.

[0026] 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 with reference to the accompanying drawings.

[0027] See Figures 1-8 The present invention provides a method for forming an interdigitated electrode 100, wherein the interdigitated electrode 100 includes a metal stack, and the method for forming the interdigitated electrode includes: Step S1: Provide a piezoelectric substrate 180, and form a metal material stack and a composite mask material layer on the piezoelectric substrate 180; wherein, the metal material stack includes a first metal material layer 140 and a second metal material layer 160, the second metal material layer 160 is disposed on the piezoelectric substrate 180, and the first metal material layer 140 is disposed on the second metal material layer 160; the composite mask material layer includes a first mask material layer 120 and a second mask material layer 130 of different materials, the second mask material layer 130 is disposed on the first metal material layer 140, and the first mask material layer 120 is disposed on the second mask material layer 130; Step S2: Pattern the composite mask material layer to obtain the composite mask layer; the composite mask layer includes a first mask layer 121 corresponding to the first mask material layer 120 and a second mask layer 131 corresponding to the second mask material layer 130; Step S3: Using the composite mask layer as a mask, etch the first metal material layer 140 to obtain the first metal layer 141, and simultaneously consume the first mask layer 121; Step S4: Using the second mask layer 131 as a mask, etch the second metal material layer 160 to obtain the second metal layer 161. The metal stack includes the first metal layer 141 and the second metal layer 161.

[0028] In this embodiment, by using a composite mask layer of different materials in upper and lower layers, the mask function relay of different metal layer etching stages is realized, which solves the problem that a single mask cannot adapt to multiple etching systems at the same time. The complex multilayer metal etching is decomposed into multiple independent and controllable sub-steps, and the process windows of each step are decoupled from each other, which greatly reduces the difficulty of process development and debugging costs, widens the process window, and facilitates the control of the morphology of the interdigitated electrodes.

[0029] In one specific embodiment, when the second metal material layer 160 is etched using the second mask layer 131 as a mask, the second mask layer 131 undergoes a passivation reaction with the etching gas.

[0030] In one specific embodiment, the material of the second metal layer 161 includes W or Mo; the material of the second mask layer 131 includes TiN; and the etching gas for etching the second metal material layer 160 is an SF6-based gas.

[0031] Optionally, the thickness of the second metal layer 161 is 20-600 nm; the thickness of the second mask layer 131 is 30-80 nm.

[0032] The second metal layer 161 is made of a high-density, high-acoustic-impedance material such as W or Mo, which can improve the power tolerance of the film layer.

[0033] When etching metal layers made of W or Mo using SF6-based gas, the isotropic etching characteristics of F radicals easily lead to lateral etching on the sidewalls of the metal layer, resulting in uncontrolled electrode linewidth, deteriorated sidewall morphology, and severely affecting the consistency of device performance. Therefore, this embodiment uses TiN material as the second mask layer 131. On the one hand, TiN material has extremely high selectivity for SF6-based gas etching of W or Mo; on the other hand, the non-volatile TiF4 generated by the reaction of the TiN mask with the SF6 etching gas can form a dense passivation layer in situ on the etched sidewalls of the W or Mo layer, effectively blocking the lateral attack of F radicals on the W or Mo sidewalls. This fundamentally solves the problem of sidewall etching in the W or Mo layer, resulting in steep electrode sidewalls.

[0034] In one specific embodiment, the first metal layer 141 is made of Al or AlCu alloy, wherein the Cu content in the AlCu alloy is <5%; the first mask layer 121 is made of SiO2, and the etching gas for etching the first metal material layer 140 is a Cl2 / BCl3-based gas.

[0035] The first metal layer 141 uses Al or AlCu alloy as the main conductive layer. SiO2 has an extremely high selectivity for etching Al or AlCu alloy with Cl2 / BCl3-based gas, which can ensure the pattern accuracy of the Al or AlCu alloy layer etching.

[0036] In one specific embodiment, the thickness of the first metal layer 141 can be 50-500nm, and the thickness of the first mask layer 121 can be 50-250nm. The aim is to ensure that the first mask layer 121 is basically consumed when the first metal layer 141 is etched, so that no material of the first mask layer 121 remains and affects the etching morphology of the subsequent film layer. At the same time, it avoids the first mask layer 121 being exhausted too early, which would cause the subsequent film layer to be exposed and damaged prematurely.

[0037] In one specific embodiment, the metal stack further includes a seed layer 171, which is disposed between the piezoelectric substrate 180 and the second metal layer 161; correspondingly, after etching the second metal material layer 160 using the second mask layer 131 as a mask, the method further includes etching the seed material layer 170 using the second mask layer 131 as a mask to obtain the seed layer 171.

[0038] In one specific embodiment, the seed layer 171 is made of AlN, Ti, or TiN.

[0039] Optionally, the thickness of the seed layer 171 is 10-50 nm.

[0040] Using a seed layer 171 can significantly enhance the bonding force between the second metal layer 161 and the piezoelectric substrate 180, preventing the electrode from falling off under high-power operating conditions. Using the same mask layer (i.e., the second mask layer 131) to complete the etching of the second metal layer 161 and the seed layer 171 simplifies the process flow and avoids alignment errors caused by multiple masks.

[0041] In one specific embodiment, the metal stack further includes a first protective layer 151, which is disposed between the first metal layer 141 and the second metal layer 161.

[0042] Correspondingly, after etching the first metal material layer 140 using the composite mask layer as a mask, the process further includes etching the first protective material layer 150 using the composite mask layer as a mask to obtain the first protective layer 151.

[0043] It is understandable that the mask material itself will be gradually consumed during dry etching. In this embodiment, the first metal material layer 140 is etched using a composite mask layer as the mask, that is, the first metal material layer 140 is etched using the first mask layer 121 as the mask. After the first metal layer 141 is etched, if the first mask layer 121 is not completely consumed, the first protective material layer 150 is etched using the first mask layer 121 as the mask; if the first mask layer 121 is completely consumed, the first protective material layer 150 is etched using the second mask layer 131 as the mask.

[0044] Optionally, the first mask layer 121 or the second mask layer 131 can be used as the etching mask depending on the material of the first protective layer 151; at the same time, the thickness of the first mask layer 121 also needs to be designed accordingly. For example, if the first mask layer 121 is to be used as the etching mask, the thickness of the first mask layer 121 needs to be designed accordingly to ensure that the first mask layer 121 is consumed simultaneously after the first protective material layer 150 is etched. If the second mask layer 131 is to be used as the etching mask, the thickness of the first mask layer 121 needs to be designed accordingly to ensure that the first mask layer 121 is consumed simultaneously after the first metal material layer 140 is etched.

[0045] Optionally, the thickness of the first protective layer 151 is 10-40 nm.

[0046] In one specific embodiment, the metal stack further includes a second protective layer (not shown in the figure), which is disposed on the first metal layer 141.

[0047] Accordingly, before etching the first metal material layer 140 using the composite mask layer as a mask, the process further includes: etching the second protective material layer using the composite mask layer as a mask to obtain the second protective layer.

[0048] In this embodiment, a composite mask layer is used as a mask to etch the second protective material layer to obtain the second protective layer; that is, the first mask layer 121 is used as a mask to etch the second protective material layer to obtain the second protective layer. Subsequently, the first metal material layer 140 is etched using the first mask layer 121 as a mask to obtain the first metal layer 141. Therefore, the thickness of the first mask layer 121 is at least the mask thickness consumed by etching the second protective material layer and the first metal material layer 140.

[0049] In one specific embodiment, the metal stack includes a first protective layer 151 and a second protective layer, and the second protective material layer, the first metal material layer 140 and the first protective material layer 150 are etched using the first mask layer 121 as a mask. The thickness of the first mask layer 121 is the mask thickness consumed in etching the second protective material layer, the first metal material layer 140 and the first protective material layer 150.

[0050] In the above embodiments, by setting the first protective layer 151, the interfacial bonding performance between the second metal layer 161 and the first metal layer 141 can be effectively improved, preventing intermetallic diffusion at high temperatures. At the same time, when a mass load is formed on the first metal layer 141, the first protective layer can also serve as an etching stop layer for the first metal layer 141, ensuring that the first metal layer 141 below the mass load and the first metal layers 141 at other locations are etched on the top surface of the first protective layer. This can prevent some of the first metal layers 141 from being over-etched and damaging the second metal layer 162 below, ensuring the thickness uniformity and power tolerance performance of the second metal layer 162.

[0051] By setting a second protective layer, the interfacial bonding performance between the first mask layer 121 and the first metal layer 141 can be effectively improved, preventing metal-to-metal diffusion at high temperatures; at the same time, the first metal layer 141 is protected from oxidation or damage in subsequent processes, ensuring the thickness uniformity and power tolerance performance of the first metal layer 141.

[0052] In one specific embodiment, the first protective layer 151 is made of Ti or TiN; and / or, the second protective layer is made of Ti or TiN. Optionally, the second protective layer and the second mask layer 131 are combined into the same TiN layer.

[0053] In one specific embodiment, the patterned composite mask layer includes: forming a photoresist layer 110 with an interdigitated pattern on a composite mask material layer; using the photoresist layer 110 as a mask, etching a first mask material layer 120 to obtain a first mask layer 121 with an interdigitated pattern; removing the photoresist layer 110; and using the first mask layer 121 as a mask, etching a second mask material layer 130 to obtain a second mask layer 131 with an interdigitated pattern.

[0054] Optionally, the material of the first mask layer 121 includes silicon oxide.

[0055] By transferring the interdigitated pattern of the photoresist layer 110 to the first mask layer 121, which has higher hardness, and then performing subsequent metal layer etching, the problem of deformation and peeling of the photoresist during long-term dry etching is avoided, which significantly improves the accuracy and stability of the interdigitated pattern transfer.

[0056] In one specific embodiment, the interdigitated pattern on the first mask layer 121 has a groove shape. The groove is an inverted trapezoidal structure that is wider at the top and narrower at the bottom. The sidewall angle of the groove is 85-89°, such as 85°, 86°, 87°, 88°, 89°, etc., which is not limited here.

[0057] The inverted trapezoidal structure with a sidewall angle of 85-89° effectively compensates for the linewidth shrinkage during subsequent metal etching, ensuring that the final electrode linewidth is consistent with the design value and that the etching morphology of the metal stack remains straight. At the same time, it further improves the stability and fidelity of the interdigitated pattern transfer and reduces the serrated defects at the electrode edges.

[0058] 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 interdigitated electrodes, characterized in that, The interdigitated electrodes are metal stacks, and the method for forming them includes: A piezoelectric substrate is provided, on which a metal material stack and a composite mask material layer are formed; wherein, the metal material stack includes a first metal material layer and a second metal material layer, the second metal material layer being disposed on the piezoelectric substrate, and the first metal material layer being disposed on the second metal material layer; the composite mask material layer includes a first mask material layer and a second mask material layer made of different materials, the second mask material layer being disposed on the first metal material layer, and the first mask material layer being disposed on the second mask material layer; The composite mask material layer is graphically represented to obtain a composite mask layer; the composite mask layer includes a first mask layer corresponding to the first mask material layer and a second mask layer corresponding to the second mask material layer; Using the composite mask layer as a mask, the first metal material layer is etched to obtain the first metal layer, and the first mask layer is consumed simultaneously. Using the second mask layer as a mask, the second metal material layer is etched to obtain the second metal layer. The metal stack includes the first metal layer and the second metal layer.

2. The forming method according to claim 1, characterized in that, When the second mask layer is used as a mask to etch the second metal material layer, the second mask layer undergoes a passivation reaction with the etching gas.

3. The forming method according to claim 2, characterized in that, The material of the second metal layer includes W or Mo; The second mask layer is made of TiN, and the etching gas used to etch the second metal material layer is SF6-based gas.

4. The forming method according to claim 1, characterized in that, The first metal layer can be made of Al or AlCu alloy, wherein the Cu content in the AlCu alloy is <5%; The first mask layer is made of SiO2, and the etching gas used to etch the first metal material layer is a Cl2 / BCl3-based gas.

5. The forming method according to claim 1, characterized in that, The metal stack further includes a seed layer, which is disposed between the piezoelectric substrate and the second metal layer; Accordingly, after etching the second metal material layer using the second mask layer as a mask, the process further includes etching the seed material layer using the second mask layer as a mask to obtain the seed layer.

6. The forming method according to claim 5, characterized in that, The seed layer can be made of AlN, Ti, or TiN.

7. The forming method according to any one of claims 1-6, characterized in that, The metal stack further includes a first protective layer, which is disposed between the first metal layer and the second metal layer; Accordingly, after etching the first metal material layer using the composite mask layer as a mask, the method further includes: etching the first protective material layer using the composite mask layer as a mask to obtain the first protective layer; And / or, the metal stack further includes a second protective layer disposed on the first metal layer; Accordingly, before etching the first metal material layer using the composite mask layer as a mask, the method further includes: etching the second protective material layer using the composite mask layer as a mask to obtain the second protective layer.

8. The forming method according to claim 7, characterized in that, The first protective layer may be made of Ti or TiN; And / or, the material of the second protective layer includes Ti or TiN.

9. The forming method according to any one of claims 1-6, characterized in that, Graphicalizing the composite mask layer includes: A photoresist layer with an interdigitated pattern is formed on the composite mask material layer; Using the photoresist layer as a mask, the first mask material layer is etched to obtain a first mask layer with the interdigitated pattern; Using the first mask layer as a mask, the second mask material layer is etched to obtain a second mask layer with the interdigitated pattern.

10. The forming method according to claim 9, characterized in that, The interdigitated pattern on the first mask layer has a groove shape, and the groove is an inverted trapezoidal structure that is wider at the top and narrower at the bottom, with a sidewall angle of 85-89°.

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