A preparation method of a micro coaxial transmission line with a sapphire as an inner conductor support layer

Abstract

The present invention discloses a preparation method of a micro coaxial transmission line with a sapphire as an inner conductor support layer, comprising: laser processing on the surface of a first sapphire wafer to form a sapphire inner conductor support layer; forming a first inner conductor layer and a first outer conductor layer on the sapphire inner conductor support layer, and forming a first top cover layer on the first outer conductor layer; bonding a second wafer to the first top cover layer, and thinning the first sapphire wafer until the sapphire inner conductor support layer is exposed; forming a second inner conductor layer and a second outer conductor layer on the side of the sapphire inner conductor support layer away from the second wafer, and forming a second top cover layer on the second outer conductor layer; removing the first sacrificial layer, the second sacrificial layer and the second wafer to form a micro coaxial transmission line. The present application uses a sapphire wafer as a preparation substrate, and directly forms a sapphire inner conductor support layer on the sapphire wafer, ensuring that the inner conductor support layer is more firm and not easily deformed, and improving the preparation efficiency of the micro coaxial transmission line.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of micro coaxial transmission lines, and particularly relates to a method for preparing a micro coaxial transmission line with a sapphire as the inner conductor support layer. Background Art

[0002] A micro coaxial transmission line is a basic circuit unit of a radio frequency device prepared by using MEMS process technology, and has a tiny rectangular micro coaxial structure with an air cavity surrounding the inner conductor. This micro transmission line has many advantages in radio frequency applications: such as small volume, light weight, low loss, high isolation, good heat dissipation, etc., and is a research hotspot of millimeter wave radio frequency technology in recent years.

[0003] In the prior art, there are already various methods for preparing the micro coaxial transmission line structure, which are basically micro process cycle processing methods such as thick film lithography, electroplating, and planarization. The metal copper inner conductor in the air cavity needs to be suspended and fixed by an inner conductor support structure. And the materials of the inner conductor support structure in the prior art generally include organic materials such as SU8 photoresist and shape memory polymer. For example, Patent CN110311205A discloses using SU8 photoresist as the inner conductor support material. Patent CN116505220A discloses using shape memory polymer as the inner conductor support material.

[0004] The excellent performance of the micro coaxial transmission line in radio frequency is attributed to the formation of a nearly air cavity rectangular micro coaxial structure in its structure. The metal inner conductor can be suspended and fixed inside the rectangular cavity because a periodic dielectric strip is used to support and fix the inner conductor. This dielectric strip is generally processed by micro process means, and the dielectric strip itself needs to meet the basic requirements of the micro coaxial transmission line in electrical performance, mechanical performance, and heat dissipation characteristics. The existing manufacturing technologies of these micro coaxial structures all need to introduce an inner conductor support material through a special process in the preparation process, making the manufacturing technology of the micro coaxial structure cumbersome and the process longer, indirectly increasing the manufacturing cost and production cycle of the micro coaxial structure. Summary of the Invention

[0005] The present invention aims to solve at least one of the problems in the related technologies to some extent. For this purpose, the object of the present invention is to provide a method for preparing a micro coaxial transmission line, using a sapphire wafer as the preparation substrate, and directly forming a sapphire inner conductor support layer on the sapphire wafer, ensuring that the inner conductor support layer is more firm and not easily deformed, and the preparation method of the present application simplifies the formation process of the inner conductor support layer and improves the preparation efficiency of the micro coaxial transmission line.

[0006] To achieve the above object, the present application adopts the following technical solutions:

[0007] A preparation method of a micro coaxial transmission line with a sapphire as the inner conductor support layer, comprising:

[0008] Laser process the surface of the first sapphire wafer to form a sapphire inner conductor support layer;

[0009] Form a first inner conductor layer and a first outer conductor layer on the sapphire inner conductor support layer. In the direction perpendicular to the extension direction of the micro coaxial transmission line, the first outer conductor layer is located on both sides of the first inner conductor layer, and the height of the first outer conductor layer is greater than the height of the first inner conductor layer; a first sacrificial layer is filled between the first outer conductor layer and the first inner conductor layer;

[0010] Form a first top cover layer on the first outer conductor layer; the first top cover layer covers the first inner conductor layer and the first outer conductor layer;

[0011] Bond the second wafer to the first top cover layer, and thin the first sapphire wafer until the sapphire inner conductor support layer is exposed;

[0012] Form a second inner conductor layer and a second outer conductor layer on the side of the sapphire inner conductor support layer away from the second wafer. In the direction perpendicular to the extension direction of the micro coaxial transmission line, the second outer conductor layer is located on both sides of the second inner conductor layer, and the height of the second outer conductor layer is greater than the height of the second inner conductor layer; a second sacrificial layer is filled between the second outer conductor layer and the second inner conductor layer;

[0013] Form a second top cover layer on the second outer conductor layer; the second top cover layer covers the second inner conductor layer and the second outer conductor layer;

[0014] Remove the first sacrificial layer, the second sacrificial layer and the second wafer to form a micro coaxial transmission line.

[0015] Further, laser processing the surface of the first sapphire wafer to form a sapphire inner conductor support layer specifically includes:

[0016] Use femtosecond laser to laser process the first sapphire wafer, remove the part outside the sapphire inner conductor support layer, and form a sapphire inner conductor support layer on the surface of the first sapphire wafer.

[0017] Further, forming a first inner conductor layer and a first outer conductor layer on the sapphire inner conductor support layer specifically includes:

[0018] Deposit a first inner conductor layer in the middle of the sapphire inner conductor support layer by means of a sacrificial layer mask, and deposit a first lower outer conductor layer on both sides of the first inner conductor layer respectively. The first lower outer conductor layer is simultaneously located on the sapphire inner conductor support layer and the surface of the first sapphire wafer; a first lower sacrificial layer is filled between the first inner conductor layer and the first lower outer conductor layer;

[0019] Deposit a first upper outer conductor layer on the first lower outer conductor layer by means of a sacrificial layer mask; a first upper sacrificial layer is filled between the first upper outer conductor layers on both sides; the first upper outer conductor layer and the first lower outer conductor layer overlap to form a first outer conductor layer with a height greater than that of the first inner conductor layer.

[0020] Further, deposit a first inner conductor layer in the middle of the sapphire inner conductor support layer by means of a sacrificial layer mask, specifically including:

[0021] Deposit a transition layer and a copper seed layer in sequence on one side of the first sapphire wafer where there is a sapphire inner conductor support layer;

[0022] Perform electroplating of a copper layer by means of a sacrificial layer mask to form a first inner conductor layer and first lower outer conductor layers on both sides of the first inner conductor layer; the surfaces of the first inner conductor layer, the first lower outer conductor layer, and the first lower sacrificial layer are flush;

[0023] Deposit a transition layer and a copper seed layer on the surfaces of the first inner conductor layer, the first lower outer conductor layer, and the first lower sacrificial layer in sequence;

[0024] Perform electroplating of a copper layer by means of a sacrificial layer mask to form a first upper outer conductor layer on the first lower outer conductor layer; the surfaces of the first upper outer conductor layer and the first upper sacrificial layer are flush.

[0025] Further, form a first top cover layer on the first outer conductor layer, specifically including:

[0026] Deposit a transition layer and a copper seed layer on the surfaces of the first upper outer conductor layer and the first upper sacrificial layer in sequence;

[0027] Perform electroplating of a copper layer by means of a sacrificial layer mask to form a first top cover layer covering the first inner conductor layer and the first outer conductor layer.

[0028] Further, also include: perform planarization treatment on the first inner conductor layer, the first lower outer conductor layer, and the first lower sacrificial layer so that the thicknesses of the first inner conductor layer and the first lower outer conductor layer are 30 - 60 μm;

[0029] Perform planarization treatment on the first upper outer conductor layer and the first upper sacrificial layer so that the thicknesses of the first inner conductor layer and the first lower outer conductor layer are 90 - 110 μm;

[0030] Perform planarization treatment on the first top cover layer so that the thickness of the first top cover layer is 90 - 110 μm.

[0031] Further, the transition layer is a Ti metal layer, and the thickness of the transition layer is 15 - 25 nm; the thickness of the copper seed layer is 750 - 850 nm.

[0032] Further, a second inner conductor layer and a second outer conductor layer are formed on a side of the sapphire inner conductor support layer away from the second wafer, specifically including:

[0033] The second inner conductor layer is deposited in the middle of the sapphire inner conductor support layer by means of a sacrificial layer mask, and second lower outer conductor layers are respectively deposited on both sides of the second inner conductor layer. The second lower outer conductor layers are simultaneously located on the surfaces of the sapphire inner conductor support layer and the second wafer; a second lower sacrificial layer is filled between the second inner conductor layer and the second lower outer conductor layers;

[0034] The second upper outer conductor layer is deposited above the second lower outer conductor layer by means of a sacrificial layer mask; a second upper sacrificial layer is filled between the second upper outer conductor layers on both sides; the second upper outer conductor layer and the second lower outer conductor layer overlap to form a second outer conductor layer with a height greater than that of the second inner conductor layer.

[0035] Further, the second wafer is bonded to the first top cover layer, specifically including:

[0036] The sacrificial layer is respectively spin-coated on the surface of the second wafer and the surface of the first top cover layer;

[0037] The sacrificial layers in the second wafer and the first top cover layer are subjected to alignment thermocompression bonding.

[0038] Further, the first sacrificial layer, the second sacrificial layer and the second wafer are removed to form a micro coaxial transmission line, specifically including:

[0039] The sacrificial layer is removed by a stripping solvent, so that the second wafer is separated from the micro coaxial transmission line. Meanwhile, an air gap is formed between the first inner conductor layer and the first outer conductor layer, and an air gap is formed between the second inner conductor layer and the second outer conductor layer.

[0040] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art: The present application uses a sapphire wafer as a preparation substrate, and directly forms a sapphire inner conductor support layer on the sapphire wafer. The sapphire material is α-Al2O3 single crystal, which has excellent material properties. Its elastic modulus is 435 GPa, the fracture strength can reach 400 MPa, the thermal conductivity is 24 W / m·K, the temperature resistance can reach above 1000 °C, and the chemical stability is high. Compared with organic materials such as SU8, the mechanical indexes such as compressive strength, tensile strength and Young's modulus are more than one order of magnitude higher. Therefore, the formed inner conductor support is more firm and not easy to deform.

[0041] In this application, the heat dissipation capacity of the inner conductor layer of the supported microcoaxial transmission line is better. Since the microcoaxial transmission line must form an air cavity structure, except for a few periodic positions where the inner conductor layer is directly in contact with the inner conductor support layer, the rest of the surface is wrapped by air. This structure greatly limits the heat dissipation of the inner conductor layer during use. In the prior art, the organic medium has a thermal conductivity coefficient one order of magnitude lower than that of sapphire and a temperature resistance of less than 300 °C. The sapphire inner conductor layer has excellent thermal conductivity and high temperature tolerance, and metal copper itself also has high heat dissipation capacity. Therefore, the metal copper microcoaxial transmission line with sapphire as the inner conductor support layer is extremely suitable for applications in high-power and high-temperature environments.

[0042] In this application, the sapphire material is extremely stable and will not be damaged in any organic solvents or strong alkaline aqueous solutions. Therefore, when removing the photoresist sacrificial layer of the microcoaxial transmission line finally, it is less restricted by the solvent temperature and removal time, avoiding the problem that the general organic inner conductor support structure is easily eroded and damaged in the high-temperature degluing solvent. At the same time, it can save a large amount of process time for the release of the sacrificial layer, simplify the release process of the microcoaxial transmission line, improve the preparation efficiency of the microcoaxial transmission line, and shorten the production cycle of the microcoaxial transmission line. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings herein are incorporated into the specification and form a part of this specification, showing embodiments consistent with the present invention and, together with the specification, are used to explain the principles of the present invention.

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0045] In the drawings:

[0046] Figure 1 is a schematic diagram of the selected sapphire wafer;

[0047] Figure 2 is a schematic diagram of the inner conductor support structure formed on the first sapphire wafer by using the laser processing technology;

[0048] Figure 3 is a schematic diagram of the completion of the processing of the first inner conductor layer and the first lower outer conductor layer on the first sapphire wafer;

[0049] Figure 4 is a schematic diagram of the completion of the processing of the first upper outer conductor layer on the first sapphire wafer;

[0050] Figure 5Schematic diagram for completing the processing of the first top cover layer on the first sapphire wafer;

[0051] Figure 6 Schematic diagram after bonding the second wafer with the first top cover layer;

[0052] Figure 7 Schematic diagram of the micro - coaxial structure after removing the first sapphire wafer;

[0053] Figure 8 Schematic diagram for completing the processing of the second inner conductor layer and the second lower outer conductor layer on the second wafer;

[0054] Figure 9 Schematic diagram for completing the processing of the second upper outer conductor layer on the second wafer;

[0055] Figure 10 Schematic diagram for completing the processing of the second top cover layer on the second wafer;

[0056] Figure 11 Schematic diagram of the finally formed micro - coaxial structure.

[0057] In the figure: 11, the first sapphire wafer; 12, the sapphire inner conductor support layer; 13, the first inner conductor layer; 14, the first lower outer conductor layer; 15, the first lower sacrificial layer; 16, the first upper outer conductor layer; 17, the first upper sacrificial layer; 18, the first top cover layer; 21, the second wafer; 23, the second inner conductor layer; 24, the second lower outer conductor layer; 25, the second lower sacrificial layer; 26, the second upper outer conductor layer; 27, the second upper sacrificial layer; 28, the second top cover layer. Detailed implementation manners

[0058] For a clearer understanding of the technical features, objectives, and effects of the present invention, the detailed implementation manners of the present invention are now described in detail with reference to the accompanying drawings. In the following description, it should be understood that the orientation or positional relationships indicated by "front", "rear", "upper", "lower", "left", "right", "longitudinal", "transverse", "vertical", "horizontal", "top", "bottom", "inner", "outer", "head", "tail", etc. are based on the orientation or positional relationships shown in the accompanying drawings, and are constructed and operated in a specific orientation. This is only for the convenience of describing the technical solution, rather than indicating that the indicated mechanism or element must have a specific orientation. Therefore, it should not be construed as a limitation to the present invention.

[0059] It should also be noted that, unless otherwise clearly specified and limited, terms such as "installation", "connection", "linkage", "fixation", "setting" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components or the interaction relationship between two components. When a component is referred to as being "on" or "under" another component, the component can be "directly" or "indirectly" located above the other component, or there may also be one or more intermediate components. Terms such as "first", "second", "third", etc. are only for the convenience of describing the technical solution of the present invention, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, features defined with "first", "second", "third", etc. can explicitly or implicitly include one or more of such features. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0060] In the following description, for the purpose of illustration rather than limitation, specific details such as specific system structures, technologies, etc. are presented in order to thoroughly understand the embodiments of the present invention. However, those skilled in the art should clearly understand that the present invention can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, mechanisms, circuits, and methods are omitted to avoid unnecessary details from interfering with the description of the present invention.

[0061] Embodiment 1

[0062] Please refer to Figures 1-11 , a preparation method of a micro coaxial transmission line with a sapphire as an inner conductor support layer provided by the present application includes:

[0063] Laser process a sapphire inner conductor support layer 12 on the surface of the first sapphire wafer 11;

[0064] Form a first inner conductor layer 13 and a first outer conductor layer on the sapphire inner conductor support layer 12. In the direction perpendicular to the extension direction of the micro coaxial transmission line, the first outer conductor layer is located on both sides of the first inner conductor layer 13, and the height of the first outer conductor layer is greater than the height of the first inner conductor layer 13; a first sacrificial layer is filled between the first outer conductor layer and the first inner conductor layer 13;

[0065] Form a first top cover layer 18 on the first outer conductor layer; the first top cover layer 18 covers the first inner conductor layer 13 and the first outer conductor layer;

[0066] Bond the second wafer 21 to the first top cover layer 18, and thin the first sapphire wafer 11 until the sapphire inner conductor support layer 12 is exposed;

[0067] On one side of the sapphire inner conductor support layer 12 away from the second wafer 21, a second inner conductor layer 23 and a second outer conductor layer are formed. In the direction perpendicular to the extension direction of the micro coaxial transmission line, the second outer conductor layer is located on both sides of the second inner conductor layer 23, and the height of the second outer conductor layer is greater than the height of the second inner conductor layer 23; a second sacrificial layer is filled between the second outer conductor layer and the second inner conductor layer 23;

[0068] A second top cover layer 28 is formed on the second outer conductor layer; the second top cover layer 28 covers the second inner conductor layer 23 and the second outer conductor layer;

[0069] The first sacrificial layer, the second sacrificial layer and the second wafer 21 are removed to form a micro coaxial transmission line.

[0070] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art: The present application uses a sapphire wafer as the preparation substrate, and directly forms a sapphire inner conductor support layer on the sapphire wafer. The sapphire material is α - Al2O3 single crystal, which has excellent material properties. Its elastic modulus is 435 GPa, the fracture strength can reach 400 MPa, the thermal conductivity coefficient is 24 W / m·K, the temperature resistance can reach above 1000 °C, and the chemical stability is high. Compared with organic materials such as SU8, the mechanical indexes such as compressive strength, tensile strength, and Young's modulus are more than one order of magnitude higher. Therefore, the formed inner conductor support is more firm and not easily deformed. In the present application, the heat dissipation capacity of the inner conductor layer of the supported micro coaxial transmission line is better. Since the micro coaxial transmission line must form an air cavity structure, except for a few periodic positions where the inner conductor layer directly contacts and connects with the inner conductor support layer, the rest of the surface is wrapped by air. This structure greatly limits the heat dissipation of the inner conductor layer during use. In the prior art, the thermal conductivity coefficient of the organic medium is one order of magnitude lower than that of sapphire, and the temperature resistance is less than 300 °C. The sapphire inner conductor layer has excellent thermal conductivity and high temperature tolerance, and the metal copper itself also has high heat dissipation capacity. Therefore, the metal copper micro coaxial transmission line with a sapphire as the inner conductor support layer is extremely suitable for applications in high - power and high - temperature environments.

[0071] The sapphire material in the present application is extremely stable and will not be damaged in any organic solvents and strong alkali aqueous solutions. Therefore, when removing the photoresist sacrificial layer of the micro coaxial transmission line finally, it is less restricted by the solvent temperature and removal time, avoiding the problem that the general organic inner conductor support structure is easily eroded and damaged in high - temperature de - glue solvents. At the same time, it can save a large amount of process time for sacrificial layer release, simplify the release process of the micro coaxial transmission line, improve the preparation efficiency of the micro coaxial transmission line, and shorten the production cycle of the micro coaxial transmission line.

[0072] Embodiment 2

[0073] Please refer to Figures 1-11 , a preparation method of a micro coaxial transmission line with a sapphire as an inner conductor support layer provided by this application. In this embodiment, all sacrificial layers are photoresist. The method includes:

[0074] S1: Laser process the surface of the first sapphire wafer 11 to form a sapphire inner conductor support layer 12. Specifically, it includes:

[0075] S11: As Figure 1 shown, select a 4-inch first sapphire wafer 11 with a thickness range of 200 ± 5 μm.

[0076] S12: Use femtosecond laser to directly process the sapphire wafer, remove 20 μm of sapphire depth, and retain the sapphire inner conductor support layer 12. The femtosecond laser processing parameters are a central wavelength of 800 nm, a pulse frequency of 35 fs, a repetition frequency of 1.5 kHz, and the set laser power is 15 mW.

[0077] S13: Clean the surface of the first sapphire wafer 11 that has completed laser processing with concentrated sulfuric acid at 120 °C for 20 min, then wash it with pure water at 60 °C for 5 min, wash it with pure water at room temperature for 10 min, and place it in an oven to bake at 110 °C for 20 min.

[0078] S2: Form a first inner conductor layer 13 and a first outer conductor layer on the sapphire inner conductor support layer 12. In the direction perpendicular to the extension direction of the micro coaxial transmission line, the first outer conductor layer is located on both sides of the first inner conductor layer 13, and the height of the first outer conductor layer is greater than the height of the first inner conductor layer 13; a first sacrificial layer is filled between the first outer conductor layer and the first inner conductor layer 13. Specifically, it includes:

[0079] S21: Deposit a transition layer and a copper seed layer in sequence on one side of the first sapphire wafer 11 where the sapphire inner conductor support layer 12 is provided by magnetron sputtering; the transition layer is a Ti metal layer, the thickness of the transition layer is 15 - 25 nm, specifically it can be 20 nm; the thickness of the copper seed layer is 750 - 850 nm, specifically it can be 800 nm.

[0080] S22: As Figure 3As shown, copper is electroplated using a sacrificial layer mask to form a first inner conductor layer 13 and first lower outer conductor layers 14 located on either side of the first inner conductor layer 13. The surfaces of the first inner conductor layer 13, the first lower outer conductor layer 14, and the first lower sacrificial layer 15 are flush. Two first lower outer conductor layers 14 are provided, one on either side of the first inner conductor layer 13. The first lower outer conductor layers 14 are located on both the sapphire inner conductor support layer 12 and the surface of the first sapphire wafer 11, so that the center of the sapphire inner conductor support layer 12 supports the first inner conductor layer 13, while the two sides are embedded within the first lower outer conductor layer 14. The first lower sacrificial layer 15 fills the space between the first inner conductor layer 13 and the first lower outer conductor layer 14.

[0081] The specific operations are as follows:

[0082] S221: Spin-coating 60 μm of AZ125nxt photoresist on the surface of the copper seed layer is performed, and photolithography is performed based on the patterns of the first inner conductor layer 13 and the first lower outer conductor layer 14 required for the micro-coaxial transmission line to form an electroplating master mold of the first inner conductor layer 13 and the first lower outer conductor layer 14 in the micro-coaxial transmission line.

[0083] S222: electroplating a copper layer to a thickness of 65 μm using an acid copper system plating solution.

[0084] S223: Use mechanical polishing to thin the first inner conductor layer 13, the first lower outer conductor layer 14 and the first lower sacrificial layer 15 to 52 μm, and then use chemical mechanical polishing to finally control the first inner conductor layer 13, the first lower outer conductor layer 14 and the first lower sacrificial layer 15 to 50 μm. Figure 3 The structure shown.

[0085] S23: If Figure 4 As shown, a first upper outer conductor layer 16 is deposited on the first lower outer conductor layer 14 by means of a sacrificial layer mask; a first upper sacrificial layer 17 is filled between the first upper outer conductor layers 16 on both sides; the first upper outer conductor layer 16 and the first lower outer conductor layer 14 overlap to form a first outer conductor layer having a height greater than that of the first inner conductor layer 13.

[0086] The specific operations are as follows:

[0087] S231: Deposit a transition layer and a copper seed layer sequentially on the surfaces of the first inner conductor layer 13, the first lower outer conductor layer 14, and the first lower sacrificial layer 15; similar to step S21. The seed layer needs to be re-deposited here because, in this embodiment, electroplating is performed on the globally deposited seed layer. This ensures uniformity and consistency of the electroplated copper layer. If electroplating is performed directly on the first lower outer conductor layer 14, it will be localized electroplating, which is not conducive to the uniform growth of the electroplated copper layer on both sides of the first lower outer conductor layer 14, thereby affecting the uniformity and consistency of the first outer conductor layer.

[0088] S232: Electroplate a copper layer by means of a sacrificial layer mask to form a first upper outer conductor layer 16 on the first lower outer conductor layer 14; the surfaces of the first upper outer conductor layer 16 and the first upper sacrificial layer 17 are flush. The specific operations are as follows: On the surface of the copper seed layer, spin-coat AZ125nxt photoresist with a thickness of 120 μm, and perform photolithography in combination with the pattern of the first upper outer conductor layer 16 required for the microcoaxial transmission line to form an electroplating master pattern of the first upper outer conductor layer 16 inside the microcoaxial transmission line. Here, the pattern of the first upper outer conductor layer 16 completely coincides with the pattern of the first lower outer conductor layer 14, and the two together form the first outer conductor layer.

[0089] S233: Electroplate a copper layer with an acid copper system plating solution to a thickness of 130 μm.

[0090] S234: Use mechanical polishing to thin the first upper outer conductor layer 16 and the first upper sacrificial layer 17 to 115 μm, and then use chemical mechanical polishing to finally control the first upper outer conductor layer 16 and the first upper sacrificial layer 17 to 100 μm. Form the structure as Figure 4 shown.

[0091] S3: As Figure 5 shown, form a first top cover layer 18 on the first outer conductor layer; the first top cover layer 18 covers the first inner conductor layer 13 and the first outer conductor layer. The specific operations are as follows:

[0092] S31: Deposit a transition layer and a copper seed layer on the surfaces of the first upper outer conductor layer 16 and the first upper sacrificial layer 17 in sequence; similar to step S21. The reason for re-depositing the seed layer here is that in this embodiment, electroplating needs to be performed on the globally deposited seed layer, which can ensure the uniformity of the electroplated copper layer. At the same time, in this step, electroplating needs to be performed on the first upper sacrificial layer 17 to form the first top cover layer 18 connecting the first upper outer conductor layers 16 on both sides. Therefore, it is necessary to ensure that the coverage range of the seed layer is consistent with the first upper top cover layer.

[0093] S32: Electroplate a copper layer by means of a sacrificial layer mask to form a first top cover layer 18 on the first upper outer conductor layer 16 and the first upper sacrificial layer 17; the surfaces of the first upper outer conductor layer 16 and the first upper sacrificial layer 17 are flush. The specific operations are as follows: On the surface of the copper seed layer, spin-coat AZ125nxt photoresist with a thickness of 120 μm, and perform photolithography in combination with the pattern of the first top cover layer 18 required for the microcoaxial transmission line to form an electroplating master pattern of the first top cover layer inside the microcoaxial transmission line. Here, the first top cover layer 18 completely covers the first upper outer conductor layers 16 on both sides and the area between the first upper outer conductor layers 16 on both sides.

[0094] S33: Electroplate a copper layer with an acid copper system plating solution to a thickness of 130 μm.

[0095] S34: Use mechanical polishing to thin the first top cover layer 18 and the photoresist to 115 μm, and then use chemical mechanical polishing to finally control the first top cover layer 18 and the photoresist to 100 μm. Form the structure as shown in Figure 5 the figure.

[0096] S4: Bond the second wafer 21 to the first top cover layer 18, and thin the first sapphire wafer 11 until the sapphire inner conductor support layer 12 is exposed. Specifically, it includes:

[0097] S41: Select a 4-inch wafer with a thickness of 500 μm and strong mechanical properties as the second wafer 21, and spin-coat AZ125nxt photoresist on the surface of the second wafer 21 and the surface of the first top cover layer 18 respectively; in this application, the second wafer does not need to form a support layer structure and only serves as a support, and will be completely removed later. Therefore, a sapphire wafer can be selected, or other wafers with greater mechanical strength that can serve as the inner conductor support layer can be selected.

[0098] S42: Align and thermally compress bond the photoresist in the second wafer 21 and the first top cover layer 18. The thermal compression temperature is 90 °C and the pressure is 0.3 MPa to form the structure as shown in Figure 6 the figure.

[0099] S43: Take the second wafer 21 as the fixed surface, use mechanical grinding method, with boron carbide abrasive with a particle size of 60 μm, grind and thin to remove 160 μm of the first sapphire wafer, and then use 20 μm boron carbide abrasive to remove 20 μm of the first sapphire wafer 11. At this time, the metal copper surface and the sapphire support structure embedded in the metal copper structure have been exposed. Use nano-SiO2 particles as the polishing liquid for chemical mechanical polishing to polish this surface until all the sapphire inner conductor support layers 12 are completely exposed.

[0100] S5: Form a second inner conductor layer 23 and a second outer conductor layer on the side of the sapphire inner conductor support layer 12 away from the second wafer 21. In the direction perpendicular to the extension direction of the micro coaxial transmission line, the second outer conductor layer is located on both sides of the second inner conductor layer 23, and the height of the second outer conductor layer is greater than the height of the second inner conductor layer 23; a second sacrificial layer is filled between the second outer conductor layer and the second inner conductor layer 23. Specifically, it includes:

[0101] S51: Deposit a transition layer and a copper seed layer in sequence on the side of the sapphire inner conductor support layer 12 away from the second wafer 21 by means of magnetron sputtering. The transition layer is a Ti metal layer, the thickness of the transition layer is 15 - 25 nm, specifically it can be 20 nm; the thickness of the copper seed layer is 750 - 850 nm, specifically it can be 800 nm.

[0102] S52: As Figure 7 shown, deposit a second inner conductor layer 23 in the middle of the sapphire inner conductor support layer 12 by means of a sacrificial layer mask, and deposit second lower outer conductor layers 24 on both sides of the second inner conductor layer 23 respectively. The second lower outer conductor layers 24 are simultaneously located on the surfaces of the sapphire inner conductor support layer 12 and the second wafer 21; a second lower sacrificial layer 25 is filled between the second inner conductor layer 23 and the second lower outer conductor layers 24. Among them, the second lower outer conductor layers 24 coincide with the first lower outer conductor layers 14.

[0103] The specific operations are as follows:

[0104] S521: On the surface of the copper seed layer, spin - coat AZ125nxt photoresist with a thickness of 60 μm, and perform photolithography in combination with the patterns of the second inner conductor layer 23 and the second lower outer conductor layer 24 required for the micro - coaxial transmission line to form the electroplating master models of the second inner conductor layer 23 and the second lower outer conductor layer 24 in the micro - coaxial transmission line.

[0105] S522: Electroplate a copper layer to a thickness of 65 μm using an acid copper system plating solution.

[0106] S523: Use mechanical lapping to thin the second inner conductor layer 23, the second lower outer conductor layer 24 and the second lower sacrificial layer 25 to 52 μm, and then use chemical mechanical polishing to finally control the second inner conductor layer 23, the second lower outer conductor layer 24 and the second lower sacrificial layer 25 to 50 μm. Form the structure as Figure 8 shown.

[0107] S53: As Figure 9 shown, deposit a second upper outer conductor layer 26 above the second lower outer conductor layer 24 by means of a sacrificial layer mask; a second upper sacrificial layer 27 is filled between the second upper outer conductor layers 26 on both sides; the second upper outer conductor layer 26 and the second lower outer conductor layer 24 overlap to form a second outer conductor layer with a height greater than that of the second inner conductor layer 23.

[0108] The specific operations are as follows:

[0109] S531: Deposit a transition layer and a copper seed layer on the surfaces of the second inner conductor layer 23, the second lower outer conductor layer 24, and the second lower sacrificial layer 25 in sequence; similar to step S21. The reason for redepositing the seed layer here is that in this embodiment, electroplating is required on the globally deposited seed layer, which can ensure the uniformity of the electroplated copper layer. If electroplating is directly performed on the second lower outer conductor layer 24, it will be local electroplating, which is not conducive to the uniform growth of the electroplated copper layer on both sides of the second lower outer conductor layer 24, and thus affects the uniformity of the second outer conductor layer.

[0110] S532: Electroplate a copper layer through the sacrificial layer mask to form a second upper outer conductor layer 26 on the second lower outer conductor layer 24; the surfaces of the second upper outer conductor layer 26 and the second upper sacrificial layer 27 are flush. The specific operation is as follows: On the surface of the copper seed layer, spin-coat AZ125nxt photoresist with a thickness of 120 μm, and perform photolithography in combination with the pattern of the second upper outer conductor layer 26 required for the microcoaxial transmission line to form the electroplating master pattern of the second upper outer conductor layer 26 inside the microcoaxial transmission line. Here, the pattern of the second upper outer conductor layer 26 completely coincides with the pattern of the second lower outer conductor layer 24, and the two together form the second outer conductor layer, and the second outer conductor layer completely coincides with the first outer conductor layer at the same time.

[0111] S533: Electroplate a copper layer with an acid copper system plating solution to a thickness of 130 μm.

[0112] S534: Use mechanical polishing to thin the second upper outer conductor layer 26 and the second upper sacrificial layer 27 to 115 μm, and then use chemical mechanical polishing to finally control the second upper outer conductor layer 26 and the second upper sacrificial layer 27 to 100 μm. Form the structure as shown in Figure 9 shown.

[0113] S6: As shown in Figure 10 shown, form a second top cover layer 28 on the second outer conductor layer; the second top cover layer 28 covers the second inner conductor layer 23 and the second outer conductor layer; and the second top cover layer 28 coincides with the first top cover layer 18 in the vertical direction. The specific operation is as follows:

[0114] S61: Deposit a transition layer and a copper seed layer on the surfaces of the second upper outer conductor layer 26 and the second upper sacrificial layer 27 in sequence; similar to step S21. The reason for redepositing the seed layer here is that in this embodiment, electroplating is required on the globally deposited seed layer, which can ensure the uniformity of the electroplated copper layer. At the same time, in this step, electroplating is required on the second upper sacrificial layer 27 to form the second top cover layer 28 connecting the second upper outer conductor layers 26 on both sides. Therefore, it is necessary to ensure that the coverage range of the seed layer is consistent with the second upper top cover layer.

[0115] S62: The copper plating layer is formed by means of a sacrificial layer mask to form a second top cover layer 28 on the second upper outer conductor layer 26 and the second upper sacrificial layer 27; the surfaces of the second upper outer conductor layer 26 and the second upper sacrificial layer 27 are flush. The specific operation is as follows: On the surface of the copper seed layer, AZ125nxt photoresist is spin-coated with a thickness of 120 μm, and lithography is performed in combination with the pattern of the second top cover layer 28 required by the microcoaxial transmission line to form an electroplating master pattern of the second top cover layer 28 inside the microcoaxial transmission line. Here, the second top cover layer 28 completely covers the second upper outer conductor layers 26 on both sides and the area between the second upper outer conductor layers 26 on both sides.

[0116] S63: The copper plating layer is electroplated with an acid copper system plating solution to a thickness of 130 μm.

[0117] S64: The second top cover layer 28 and the photoresist are thinned to 115 μm by mechanical polishing, and then the second top cover layer 28 and the photoresist are finally controlled to 100 μm by chemical mechanical polishing. The structure shown in Figure 10 is formed.

[0118] S7: The first sacrificial layer, the second sacrificial layer and the second wafer 21 are removed to form a microcoaxial transmission line.

[0119] The specific operation is as follows:

[0120] S71: The AZ125nxt type photoresist serving as the sacrificial layer of the microcoaxial transmission line and the bonding layer is removed by soaking in an NMP degluing solvent heated to 70 °C for more than 3 hours, so that the second wafer 21 is separated from the microcoaxial transmission line. At the same time, an air gap is formed between the first inner conductor layer 13 and the first outer conductor layer, and an air gap is formed between the second inner conductor layer 23 and the second outer conductor layer.

[0121] S72: Then, the copper seed layer is removed with a 10% dilute nitric acid solution, and the Ti metal layer in the seed layer, that is, the transition layer, is removed with 2% HF. After washing and drying, a microcoaxial transmission line with a sapphire as the inner conductor support layer is obtained.

[0122] Since the thickness of the seed layer is relatively thin, during the removal process, the influence on the structure of the microcoaxial transmission line can be ignored.

[0123] Example 3

[0124] The difference between this example and Example 2 is that after depositing the seed layer in step S21, the seed layer is patterned so that the pattern of the seed layer is the same as the shape of the first inner conductor layer 13 and the first lower outer conductor layers 14 on both sides of the first inner conductor layer 13. Then, the copper plating layer is formed by local electroplating to form the first inner conductor layer 13 and the first lower outer conductor layers 14.

[0125] Similarly, step S231 is omitted, and copper plating is directly carried out based on the first lower outer conductor layer 14 to form the first upper outer conductor layer 16.

[0126] Similarly, the seed layer formed in step S31 is patterned so that the pattern of the seed layer is the same as the shape of the first upper cover layer.

[0127] Similarly, after the seed layer is deposited in step S51, the seed layer is patterned so that the pattern of the seed layer is the same as the shape of the second inner conductor layer 23 and the second lower outer conductor layers 24 on both sides of the second inner conductor layer 23, and then a copper plating layer is formed by local electroplating to form the second inner conductor layer 23 and the second lower outer conductor layers 24.

[0128] Similarly, step S531 is omitted, and copper plating is directly carried out based on the second lower outer conductor layer 24 to form the second upper outer conductor layer 26.

[0129] Similarly, the seed layer formed in step S61 is patterned so that the pattern of the seed layer is the same as the shape of the second upper cover layer.

[0130] The difference between this embodiment and Embodiment 2 is that all the copper plating in Embodiment 1 is global copper plating, aiming to ensure the uniformity of copper plating, and the seed layer is removed by wet etching after the sacrificial layer is removed in step S7. All the copper plating in this embodiment is local copper plating, and the uniformity of electroplating at each local position is ensured by controlling multiple electroplating probes and parameters. In this way, since the seed layer has been patterned in advance, finally, only the sacrificial layer needs to be removed in step S7 to obtain the microcoaxial transmission line structure, and there is no need to perform separate wet etching on the seed layer, which can ensure the integrity and accuracy of the microcoaxial transmission line structure.

[0131] This application uses a sapphire wafer as the preparation substrate, and directly forms a sapphire inner conductor support layer on the sapphire wafer. The sapphire material is α - Al2O3 single crystal, which has excellent material properties. Its elastic modulus is 435 GPa, the fracture strength can reach 400 MPa, the thermal conductivity coefficient is 24 W / m·K, the temperature resistance can reach above 1000 °C, and the chemical stability is high. Compared with organic materials such as SU8, the mechanical indexes such as compressive strength, tensile strength, and Young's modulus are more than one order of magnitude higher. Therefore, the formed inner conductor support is more firm and not easily deformed.

[0132] In this application, the heat dissipation capacity of the inner conductor layer of the supported micro coaxial transmission line is better. Since the micro coaxial transmission line must form an air cavity structure, except for a few periodic positions where the inner conductor layer is directly in contact with the inner conductor support layer, the rest of the surface is wrapped by air. This structure greatly limits the heat dissipation of the inner conductor layer during use. In the prior art, the organic medium has a thermal conductivity two orders of magnitude lower than that of sapphire and a temperature resistance of less than 300°C. The sapphire inner conductor layer has excellent thermal conductivity and high temperature resistance, and copper itself also has high heat dissipation capacity. Therefore, the copper micro coaxial transmission line with sapphire as the inner conductor support layer is extremely suitable for applications in high-power and high-temperature environments.

[0133] In this application, the sapphire material is extremely stable and will not be damaged in any organic solvent or strong alkali aqueous solution. Therefore, when removing the sacrificial layer of photoresist in the final micro coaxial transmission line, it is less restricted by the solvent temperature and removal time, avoiding the problem that the general organic inner conductor support structure is easily eroded and damaged in the high-temperature degluing solvent. At the same time, it can save a large amount of process time for the release of the sacrificial layer, simplify the release process of the micro coaxial transmission line, improve the preparation efficiency of the micro coaxial transmission line, and shorten the production cycle of the micro coaxial transmission line.

[0134] It can be understood that the above embodiments only represent the preferred embodiments of the present invention, and the description is relatively specific and detailed, but it should not be construed as a limitation to the scope of the invention patent; it should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, the above technical features can be freely combined, and several deformations and improvements can also be made, which all belong to the protection scope of the present invention; therefore, all equivalent transformations and modifications made to the scope of the claims of the present invention should fall within the scope covered by the claims of the present invention.

Claims

1. A preparation method of a micro coaxial transmission line with a sapphire as an inner conductor support layer, characterized in that, Including: Laser process on the surface of the first sapphire wafer to form a sapphire inner conductor support layer; specifically including: using femtosecond laser to process the first sapphire wafer, removing the part outside the sapphire inner conductor support layer, and forming the sapphire inner conductor support layer on the surface of the first sapphire wafer; Form a first inner conductor layer and a first outer conductor layer on the sapphire inner conductor support layer. In the direction perpendicular to the extension direction of the micro coaxial transmission line, the first outer conductor layer is located on both sides of the first inner conductor layer, and the height of the first outer conductor layer is greater than the height of the first inner conductor layer; a first sacrificial layer is filled between the first outer conductor layer and the first inner conductor layer; Form a first top cover layer on the first outer conductor layer; the first top cover layer covers the first inner conductor layer and the first outer conductor layer; Bond the second wafer to the first top cover layer, and thin the first sapphire wafer until the sapphire inner conductor support layer is exposed; Form a second inner conductor layer and a second outer conductor layer on the side of the sapphire inner conductor support layer away from the second wafer. In the direction perpendicular to the extension direction of the micro coaxial transmission line, the second outer conductor layer is located on both sides of the second inner conductor layer, and the height of the second outer conductor layer is greater than the height of the second inner conductor layer; a second sacrificial layer is filled between the second outer conductor layer and the second inner conductor layer; Form a second top cover layer on the second outer conductor layer; the second top cover layer covers the second inner conductor layer and the second outer conductor layer; Remove the first sacrificial layer, the second sacrificial layer and the second wafer to form a micro coaxial transmission line.

2. The preparation method of a micro coaxial transmission line with a sapphire as the inner conductor support layer according to claim 1, characterized in that, Form a first inner conductor layer and a first outer conductor layer on the sapphire inner conductor support layer, specifically including: Deposit the first inner conductor layer in the middle of the sapphire inner conductor support layer by means of a sacrificial layer mask, and deposit a first lower outer conductor layer on both sides of the first inner conductor layer respectively. The first lower outer conductor layer is simultaneously located on the sapphire inner conductor support layer and the surface of the first sapphire wafer; a first lower sacrificial layer is filled between the first inner conductor layer and the first lower outer conductor layer; Deposit a first upper outer conductor layer on the first lower outer conductor layer by means of a sacrificial layer mask; a first upper sacrificial layer is filled between the first upper outer conductor layers on both sides; the first upper outer conductor layer and the first lower outer conductor layer overlap to form a first outer conductor layer with a height greater than that of the first inner conductor layer.

3. The preparation method of a micro coaxial transmission line with a sapphire as the inner conductor support layer according to claim 2, characterized in that, Deposit the first inner conductor layer in the middle of the sapphire inner conductor support layer by means of a sacrificial layer mask, specifically including: Deposit a transition layer and a copper seed layer in sequence on the side of the first sapphire wafer where the sapphire inner conductor support layer is provided; Perform electroplating of a copper layer by means of a sacrificial layer mask to form the first inner conductor layer and the first lower outer conductor layers on both sides of the first inner conductor layer; the surfaces of the first inner conductor layer, the first lower outer conductor layer and the first lower sacrificial layer are flush; Deposit a transition layer and a copper seed layer on the surfaces of the first inner conductor layer, the first lower outer conductor layer and the first lower sacrificial layer in sequence; Perform electroplating of a copper layer by means of a sacrificial layer mask to form the first upper outer conductor layer on the first lower outer conductor layer; the surfaces of the first upper outer conductor layer and the first upper sacrificial layer are flush.

4. The manufacturing method of a micro coaxial transmission line with a sapphire as the inner conductor support layer according to claim 3, characterized in that, Form a first top cover layer on the first outer conductor layer, specifically including: Deposit a transition layer and a copper seed layer successively on the surfaces of the first upper outer conductor layer and the first upper sacrificial layer; Perform electroplating of the copper layer by means of a sacrificial layer mask to form a first top cover layer covering the first inner conductor layer and the first outer conductor layer.

5. The manufacturing method of a micro coaxial transmission line with a sapphire as an inner conductor support layer according to claim 4, characterized in that, It further includes: planarizing the first inner conductor layer, the first lower outer conductor layer and the first lower sacrificial layer so that the thicknesses of the first inner conductor layer and the first lower outer conductor layer are 30 - 60 μm; Planarize the first upper outer conductor layer and the first upper sacrificial layer so that the thicknesses of the first inner conductor layer and the first lower outer conductor layer are 90 - 110 μm; Planarize the first top cover layer so that the thickness of the first top cover layer is 90 - 110 μm.

6. The preparation method of a micro coaxial transmission line with a sapphire as the inner conductor support layer according to claim 3, characterized in that, The transition layer is a Ti metal layer, and the thickness of the transition layer is 15 - 25 nm; the thickness of the copper seed layer is 750 - 850 nm.

7. The manufacturing method of a micro coaxial transmission line with a sapphire as the inner conductor support layer according to claim 3, characterized in that, Form a second inner conductor layer and a second outer conductor layer on one side of the sapphire inner conductor support layer away from the second wafer, specifically including: Deposit the second inner conductor layer in the middle of the sapphire inner conductor support layer by means of a sacrificial layer mask, and deposit second lower outer conductor layers on both sides of the second inner conductor layer respectively. The second lower outer conductor layers are simultaneously located on the surfaces of the sapphire inner conductor support layer and the second wafer; a second lower sacrificial layer is filled between the second inner conductor layer and the second lower outer conductor layer; Deposit a second upper outer conductor layer above the second lower outer conductor layer by means of a sacrificial layer mask; a second upper sacrificial layer is filled between the second upper outer conductor layers on both sides; the second upper outer conductor layer and the second lower outer conductor layer overlap to form a second outer conductor layer with a height greater than that of the second inner conductor layer.

8. The preparation method of a micro coaxial transmission line with a sapphire as the inner conductor support layer according to claim 1, characterized in that, Bond the second wafer to the first top cover layer, specifically including: Spin - coat the sacrificial layer on the surface of the second wafer and the surface of the first top cover layer respectively; Perform alignment thermal compression bonding on the sacrificial layers in the second wafer and the first top cover layer.

9. The preparation method of a micro coaxial transmission line with a sapphire as the inner conductor support layer according to claim 8, characterized in that, Remove the first sacrificial layer, the second sacrificial layer and the second wafer to form a micro - coaxial transmission line, specifically including: Remove the sacrificial layer with a de - glue solvent so that the second wafer is separated from the micro - coaxial transmission line, and at the same time form an air gap between the first inner conductor layer and the first outer conductor layer, and an air gap between the second inner conductor layer and the second outer conductor layer.

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