Preparation method of micro-coaxial transmission line with sapphire as inner conductor supporting layer

Abstract

The invention discloses a preparation method of a micro coaxial transmission line with sapphire as an inner conductor supporting layer. The preparation method comprises the following steps: forming the sapphire inner conductor supporting layer on the surface of a first sapphire wafer through laser processing; forming a first inner conductor layer and a first outer conductor layer on the sapphire inner conductor supporting layer, and forming a first top cover layer on the first outer conductor layer; bonding the second wafer with the first top cover layer, and thinning the first sapphire wafer until the sapphire inner conductor supporting layer is exposed; forming a second inner conductor layer and a second outer conductor layer on one side, far away from the second wafer, of the sapphire inner conductor supporting layer, and forming a second top cover layer on the second outer conductor layer; and removing the first sacrificial layer, the second sacrificial layer and the second wafer to form the micro coaxial transmission line. According to the invention, the sapphire wafer is used as the preparation substrate, and the sapphire inner conductor supporting layer is directly formed on the sapphire wafer, so that the inner conductor supporting layer is ensured to be firmer and not easy to deform, and the preparation efficiency of the micro coaxial transmission line is improved.

Description

Technical Field

[0001] The invention relates to the technical field of micro-coaxial transmission line preparation, and in particular to a method for preparing a micro-coaxial transmission line using sapphire as an inner conductor support layer. Background Art

[0002] Micro-coaxial transmission line is a basic circuit unit of RF devices made by MEMS process technology. It has a tiny rectangular micro-coaxial structure with an air cavity surrounding the inner conductor. This kind of micro-transmission line has many advantages in RF applications: small size, light weight, low loss, high isolation, good heat dissipation, etc. It has become a research hotspot in millimeter wave RF technology in recent years.

[0003] There are many methods for preparing micro-coaxial transmission line structures in the prior art, which basically adopt thick-resist photolithography, electroplating, and flattening micro-process cycle processing methods. The metal copper inner conductor in the air cavity needs to adopt an inner conductor support structure to achieve suspended fixation. 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 the use of SU8 photoresist as the inner conductor support material. Patent CN116505220A discloses the use of shape memory polymer as the inner conductor support material.

[0004] The superior performance of micro-coaxial transmission lines in radio frequency performance is attributed to the fact that they form a rectangular micro-coaxial structure that is almost an air cavity. 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-processing methods. The dielectric strip itself must meet the basic requirements of micro-coaxial transmission lines in terms of electrical properties, mechanical properties, and heat dissipation characteristics. The existing manufacturing technologies of these micro-coaxial structures require the introduction of inner conductor support materials through special processes in the preparation process, making the manufacturing technology of the micro-coaxial structure cumbersome and the process long, which indirectly increases 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 art to a certain extent. To this end, the purpose of the present invention is to provide a method for preparing a micro-coaxial transmission line, using a sapphire wafer as a preparation substrate, and directly forming a sapphire inner conductor support layer on the sapphire wafer to ensure that the inner conductor support layer is more solid and not easy to deform, 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] In order to achieve the above purpose, this application adopts the following technical solutions:

[0007] A method for preparing a micro-coaxial transmission line using sapphire as an inner conductor support layer, comprising:

[0008] Forming a sapphire inner conductor support layer by laser processing on the surface of the first sapphire wafer;

[0009] A first inner conductor layer and a first outer conductor layer are formed on the sapphire inner conductor support layer, wherein the first outer conductor layer is located on both sides of the first inner conductor layer in a direction perpendicular to the extension direction of the micro-coaxial transmission line, 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] forming a first cap layer on the first outer conductor layer; the first cap layer covers the first inner conductor layer and the first outer conductor layer;

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

[0012] A second inner conductor layer and a second outer conductor layer are formed on the sapphire inner conductor support layer at a side away from the second wafer, wherein the second outer conductor layer is located on both sides of the second inner conductor layer in a direction perpendicular to the extension direction of the micro-coaxial transmission line, and the height of the second outer conductor layer is greater than that of the second inner conductor layer; and a second sacrificial layer is filled between the second outer conductor layer and the second inner conductor layer;

[0013] forming a second cap layer on the second outer conductor layer; the second cap layer covers the second inner conductor layer and the second outer conductor layer;

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

[0015] Further, a sapphire inner conductor support layer is formed by laser processing on the surface of the first sapphire wafer, specifically comprising:

[0016] The first sapphire wafer is laser processed by using a femtosecond laser to remove the portion outside the sapphire inner conductor support layer, thereby forming a sapphire inner conductor support layer located 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] Depositing a first inner conductor layer in the middle of the sapphire inner conductor support layer by means of a sacrificial layer mask, and depositing first lower outer conductor layers on both sides of the first inner conductor layer, wherein the first lower outer conductor layer is located on the sapphire inner conductor support layer and the surface of the first sapphire wafer at the same time; and a first lower sacrificial layer is filled between the first inner conductor layer and the first lower outer conductor layer;

[0019] A first upper outer conductor layer is deposited 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, depositing a first inner conductor layer in the middle of the sapphire inner conductor support layer by means of a sacrificial layer mask specifically includes:

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

[0022] Electroplating a copper layer by means of a sacrificial layer mask to form a first inner conductor layer and a first lower outer conductor layer located 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] Depositing 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] The copper layer is electroplated by means of a sacrificial layer mask to form a first upper outer conductor layer located 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, forming a first cap layer on the first outer conductor layer specifically includes:

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

[0027] The copper layer is electroplated 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] Furthermore, it also includes: performing a planarization process on the first inner conductor layer, the first lower outer conductor layer and the first lower sacrificial layer, so that the thickness of the first inner conductor layer and the first lower outer conductor layer is 30-60 μm;

[0029] Planarizing the first upper outer conductor layer and the first upper sacrificial layer so that the thickness of the first inner conductor layer and the first lower outer conductor layer is 90-110 μm;

[0030] The first top cover layer is planarized so that the thickness of the first top cover layer is 90-110 μm.

[0031] Furthermore, 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, forming a second inner conductor layer and a second outer conductor layer on a side of the sapphire inner conductor support layer away from the second wafer specifically includes:

[0033] Depositing a second inner conductor layer in the middle of the sapphire inner conductor support layer by means of a sacrificial layer mask, and depositing a second lower outer conductor layer on both sides of the second inner conductor layer, wherein the second lower outer conductor layer is located on the sapphire inner conductor support layer and the second wafer surface at the same time; and a second lower sacrificial layer is filled between the second inner conductor layer and the second lower outer conductor layer;

[0034] A second upper outer conductor layer is deposited on 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, bonding the second wafer to the first top cover layer specifically includes:

[0036] Spin coating the sacrificial layer on the second wafer surface and the first cap layer surface respectively;

[0037] The second wafer and the sacrificial layer in the first cap layer are aligned and thermally pressed and bonded.

[0038] Further, removing the first sacrificial layer, the second sacrificial layer and the second wafer to form a micro-coaxial transmission line specifically includes:

[0039] The sacrificial layer is removed by a debonding solvent, so that the second wafer is separated from the micro-coaxial transmission line, and 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 solution provided in the embodiment of the present application has the following advantages over 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 an α-Al2O3 single crystal, which has excellent material properties, an elastic modulus of 435GPa, a fracture strength of up to 400MPa, a thermal conductivity coefficient of 24W / m·K, a temperature resistance of up to 1000°C, and high chemical stability. Compared with organic materials such as SU8, the mechanical indicators such as compressive strength, tensile strength, and Young's modulus are more than one order of magnitude higher, so the formed inner conductor support is more solid and not easy to deform.

[0041] The inner conductor layer of the micro-coaxial transmission line supported in the present application has better heat dissipation capability. Since the micro-coaxial transmission line must form an air cavity structure, the inner conductor layer is wrapped by air except for a few periodic positions that are directly in contact with the inner conductor support layer. This structure greatly limits the heat dissipation of the inner conductor layer during use. In the prior art, the thermal conductivity of organic media 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 metal copper itself also has high heat dissipation capability. Therefore, the metal copper micro-coaxial transmission line with sapphire as the inner conductor support layer is extremely suitable for applications in high-power and high-heat environments.

[0042] The sapphire material in the present application is extremely stable and will not be damaged in any organic solvent or strong alkaline aqueous solution. Therefore, when the final photoresist sacrificial layer of the micro-coaxial transmission line is removed, it is less restricted by the solvent temperature and removal time, thereby avoiding the problem that the general organic inner conductor support structure is easily corroded and damaged in a high-temperature degumming solvent. At the same time, a large amount of process time for releasing the sacrificial layer can be saved, the release process of the micro-coaxial transmission line is simplified, the preparation efficiency of the micro-coaxial transmission line is improved, and the production cycle of the micro-coaxial transmission line is shortened. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0044] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0045] In the attached figure:

[0046] Figure 1 Schematic diagram of the selected sapphire wafer;

[0047] Figure 2 A schematic diagram of an inner conductor support structure formed on a first sapphire wafer using a laser processing process;

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

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

[0050] Figure 5A schematic diagram of completing the processing of a first top cover layer on a first sapphire wafer;

[0051] Figure 6 is a schematic diagram of bonding the second wafer to the first top cover layer;

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

[0053] Figure 8 A schematic diagram showing the completion of a second inner conductor layer and a second lower outer conductor layer on a second wafer;

[0054] Fig. 9 A schematic diagram of completing processing of a second upper outer conductor layer on a second wafer;

[0055] Fig.10 A schematic diagram of completing the second top cover layer processing on the second wafer;

[0056] Fig.11 Schematic diagram of the final micro-coaxial structure.

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

[0058] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific embodiments 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 directions or positional relationships indicated by "front", "back", "up", "down", "left", "right", "longitudinal", "horizontal", "vertical", "horizontal", "top", "bottom", "inside", "outside", "head", "tail", etc. are based on the directions or positional relationships shown in the accompanying drawings, are constructed and operated in a specific direction, and are only for the convenience of describing the present technical solution, rather than indicating that the mechanism or element referred to must have a specific direction, and therefore cannot be understood as a limitation to the present invention.

[0059] It should also be noted that, unless otherwise clearly specified and limited, the terms such as "installed", "connected", "connected", "fixed", "set" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. When an element is referred to as being "on" or "under" another element, the element can be "directly" or "indirectly" located on the other element, or there may be one or more intermediate elements. The terms "first", "second", "third", etc. are only for the convenience of describing the present technical solution, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", "third", etc. can explicitly or implicitly include one or more of the 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 the specific circumstances.

[0060] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may 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 prevent unnecessary details from obstructing the description of the present invention.

[0061] Example 1

[0062] See also Figure 1-Figure 11 The present application provides a method for preparing a micro-coaxial transmission line with sapphire as an inner conductor support layer, comprising:

[0063] Forming a sapphire inner conductor support layer 12 by laser processing on the surface of the first sapphire wafer 11;

[0064] A first inner conductor layer 13 and a first outer conductor layer are formed on the sapphire inner conductor support layer 12. In a direction perpendicular to the extension 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] A first top cover layer 18 is formed 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] Bonding the second wafer 21 to the first top cover layer 18, and thinning the first sapphire wafer 11 until the sapphire inner conductor support layer 12 is exposed;

[0067] A second inner conductor layer 23 and a second outer conductor layer are formed on the sapphire inner conductor support layer 12 at a side away from the second wafer 21. In a direction perpendicular to the extension 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 solution provided in the embodiment of the present application has the following advantages over 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 an α-Al2O3 single crystal, which has excellent material properties, an elastic modulus of 435GPa, a fracture strength of up to 400MPa, a thermal conductivity coefficient of 24W / m·K, a temperature resistance of up to 1000°C, and high chemical stability. Compared with organic materials such as SU8, the mechanical indicators such as compressive strength, tensile strength, and Young's modulus are more than one order of magnitude higher, so the formed inner conductor support is more solid and not easy to deform. The inner conductor layer of the micro-coaxial transmission line supported in the present application has better heat dissipation capability. Since the micro-coaxial transmission line must form an air cavity structure, the inner conductor layer is wrapped by air except for a few periodic positions that are directly in contact with the inner conductor support layer. This structure greatly limits the heat dissipation of the inner conductor layer during use. In the prior art, the thermal conductivity of organic media 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 metal copper itself also has high heat dissipation capability. Therefore, the metal copper micro-coaxial transmission line with sapphire as the inner conductor support layer is extremely suitable for applications in high-power and high-heat environments.

[0071] The sapphire material in the present application is extremely stable and will not be damaged in any organic solvent or strong alkaline aqueous solution. Therefore, when the final photoresist sacrificial layer of the micro-coaxial transmission line is removed, it is less restricted by the solvent temperature and removal time, thereby avoiding the problem that the general organic inner conductor support structure is easily corroded and damaged in a high-temperature degumming solvent. At the same time, a large amount of process time for releasing the sacrificial layer can be saved, the release process of the micro-coaxial transmission line is simplified, the preparation efficiency of the micro-coaxial transmission line is improved, and the production cycle of the micro-coaxial transmission line is shortened.

[0072] Example 2

[0073] See also Figure 1-Figure 11 The present application provides a method for preparing a micro-coaxial transmission line with sapphire as an inner conductor support layer. In this embodiment, all sacrificial layers are photoresist. It includes:

[0074] S1: forming a sapphire inner conductor support layer 12 by laser processing on the surface of the first sapphire wafer 11. Specifically comprising:

[0075] S11: Figure 1 As shown, a first sapphire wafer 11 of 4 inches and a thickness range of 200±5 μm is selected.

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

[0077] S13: The surface of the first sapphire wafer 11 that has completed laser processing is cleaned with concentrated sulfuric acid at 120° C. for 20 minutes, then cleaned with pure water at 60° C. for 5 minutes, cleaned with pure water at room temperature for 10 minutes, and then placed in an oven and baked at 110° C. for 20 minutes.

[0078] S2: forming a first inner conductor layer 13 and a first outer conductor layer on the sapphire inner conductor support layer 12, wherein the first outer conductor layer is located on both sides of the first inner conductor layer 13 in a direction perpendicular to the extension direction of the micro-coaxial transmission line, 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, the steps include:

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

[0080] S22: Figure 3As shown, the copper layer is electroplated by means of a sacrificial layer mask to form a first inner conductor layer 13 and a first lower outer conductor layer 14 located on both sides 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. There are two first lower outer conductor layers 14, which are located on both sides of the first inner conductor layer 13, and the first lower outer conductor layer 14 is located on the surface of the sapphire inner conductor support layer 12 and the first sapphire wafer 11 at the same time, so that the middle of the sapphire inner conductor support layer 12 is used to support the first inner conductor layer 13, and the two sides are embedded in the first lower outer conductor layer 14; the first lower sacrificial layer 15 is filled 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, and perform photolithography in combination with 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: 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: Depositing a transition layer and a copper seed layer on the surface of the first inner conductor layer 13, the first lower outer conductor layer 14 and the first lower sacrificial layer 15 in sequence; similar to step S21. The reason why the seed layer needs to be re-deposited 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. If electroplating is performed directly on the first lower outer conductor layer 14, it is local electroplating, which is not conducive to the uniform growth of the electroplated copper layer on the first lower outer conductor layer 14 on both sides, thereby affecting the uniformity of the first outer conductor layer.

[0088] S232: Electroplating a copper layer by means of a sacrificial layer mask to form a first upper outer conductor layer 16 located 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 operation is as follows: Spin coating AZ125nxt photoresist 120μm is applied on the surface of the copper seed layer by a spin coating process, and photolithography is performed in combination with the pattern of the first upper outer conductor layer 16 required for the micro-coaxial transmission line to form an electroplating master mold of the first upper outer conductor layer 16 in the micro-coaxial transmission line. Here, the pattern of the first upper outer conductor layer 16 completely overlaps with the pattern of the first lower outer conductor layer 14, and the two together form the first outer conductor layer.

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

[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. Figure 4 The structure shown.

[0091] S3: Figure 5 As shown, a first top cover layer 18 is formed 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 operation is as follows:

[0092] S31: Depositing a transition layer and a copper seed layer on the surface of the first upper outer conductor layer 16 and the first upper sacrificial layer 17 in sequence; similar to step S21. The reason why the seed layer needs to be re-deposited here is that in this embodiment, electroplating needs to be performed on the globally deposited seed layer, so as to ensure the uniformity and consistency of the electroplated copper layer. At the same time, electroplating needs to be performed on the first upper sacrificial layer 17 in this step to form a 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 of the seed layer is consistent with that of the first upper top cover layer.

[0093] S32: Electroplating the copper layer by means of a sacrificial layer mask to form a first top cover layer 18 located 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 operation is as follows: Spin coating AZ125nxt photoresist 120μm is applied on the surface of the copper seed layer by a spin coating process, and photolithography is performed in combination with the pattern of the first top cover layer 18 required for the micro-coaxial transmission line to form an electroplated master mold of the first top cover layer 18 in the micro-coaxial transmission line. Here, the first top cover layer 18 completely covers the first upper outer conductor layer 16 on both sides and the area between the first upper outer conductor layer 16 on both sides.

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

[0095] S34: Use mechanical polishing to thin the first cap layer 18 and the photoresist to 115 μm, and then use chemical mechanical polishing to finally control the first cap layer 18 and the photoresist to 100 μm. Figure 5 The structure shown.

[0096] S4: Bonding the second wafer 21 to the first cap layer 18, and thinning the first sapphire wafer 11 until the sapphire inner conductor support layer 12 is exposed. Specifically including:

[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 the present application, the second wafer does not need to form a supporting layer structure, it 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 an inner conductor support layer can be selected.

[0098] S42: Align the second wafer 21 and the photoresist in the first cap layer 18 by hot pressing and bonding at a hot pressing temperature of 90° C. and a pressure of 0.3 MPa to form a Figure 6 The structure shown.

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

[0100] S5: forming 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, wherein the second outer conductor layer is located on both sides of the second inner conductor layer 23 in a direction perpendicular to the extension of the micro-coaxial transmission line, and the height of the second outer conductor layer is greater than the height of the second inner conductor layer 23; and a second sacrificial layer is filled between the second outer conductor layer and the second inner conductor layer 23. Specifically comprising:

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

[0102] S52: Figure 7 As shown, a second inner conductor layer 23 is deposited in the middle of the sapphire inner conductor support layer 12 by means of a sacrificial layer mask, and a second lower outer conductor layer 24 is deposited on both sides of the second inner conductor layer 23, and the second lower outer conductor layer 24 is located on the surface of the sapphire inner conductor support layer 12 and the second wafer 21 at the same time; a second lower sacrificial layer 25 is filled between the second inner conductor layer 23 and the second lower outer conductor layer 24. The second lower outer conductor layer 24 overlaps with the first lower outer conductor layer 14.

[0103] The specific operations are as follows:

[0104] S521: Spin coating 60 μm of AZ125nxt photoresist on the surface of the copper seed layer, and photolithography is performed 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 mold of the second inner conductor layer 23 and the second lower outer conductor layer 24 in the micro-coaxial transmission line.

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

[0106] S523: Use mechanical polishing 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. Figure 8 The structure shown.

[0107] S53: Fig. 9 As shown, a second upper outer conductor layer 26 is deposited 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 whose height is greater than the second inner conductor layer 23.

[0108] The specific operations are as follows:

[0109] S531: Depositing 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 why the seed layer needs to be re-deposited 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. If electroplating is performed directly on the second lower outer conductor layer 24, it is local electroplating, which is not conducive to the uniform growth of the electroplated copper layer on the second lower outer conductor layer 24 on both sides, thereby affecting the uniformity of the second outer conductor layer.

[0110] S532: Electroplating a copper layer by means of a sacrificial layer mask to form a second upper outer conductor layer 26 located on the second lower outer conductor layer 24; the second upper outer conductor layer 26 and the second upper sacrificial layer 27 are flush with each other. The specific operation is as follows: Spin coating AZ125nxt photoresist 120μm is applied on the surface of the copper seed layer by a spin coating process, and photolithography is performed in combination with the pattern of the second upper outer conductor layer 26 required for the micro-coaxial transmission line to form an electroplating master mold of the second upper outer conductor layer 26 in the micro-coaxial transmission line. Here, the pattern of the second upper outer conductor layer 26 completely overlaps 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 overlaps with the first outer conductor layer at the same time.

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

[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. Fig. 9 The structure shown.

[0113] S6: Fig.10 As shown, 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; and the second top cover layer 28 overlaps with the first top cover layer 18 in the vertical direction. The specific operations are as follows:

[0114] S61: Deposit a transition layer and a copper seed layer on the surface of the second upper outer conductor layer 26 and the second upper sacrificial layer 27 in sequence; similar to step S21. The reason why the seed layer needs to be re-deposited here is that in this embodiment, electroplating needs to be performed on the globally deposited seed layer, so as to ensure the uniformity and consistency of the electroplated copper layer. At the same time, electroplating needs to be performed on the second upper sacrificial layer 27 in this step to form a 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 of the seed layer is consistent with that of the second upper top cover layer.

[0115] S62: Electroplating a copper layer by means of a sacrificial layer mask to form a second top cover layer 28 located 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: Spin coating 120μm of AZ125nxt photoresist is applied on the surface of the copper seed layer, and photolithography is performed in combination with the pattern of the second top cover layer 28 required for the micro-coaxial transmission line to form an electroplated master mold of the second top cover layer 28 in the micro-coaxial transmission line. Here, the second top cover layer 28 completely covers the second upper outer conductor layer 26 on both sides and the area between the second upper outer conductor layer 26 on both sides.

[0116] S63: electroplating a copper layer to a thickness of 130 μm using an acid copper system plating solution.

[0117] S64: Use mechanical polishing to thin the second cap layer 28 and the photoresist to 115 μm, and then use chemical mechanical polishing to finally control the second cap layer 28 and the photoresist to 100 μm. Fig.10 The structure shown.

[0118] S7: removing the first sacrificial layer, the second sacrificial layer and the second wafer 21 to form a micro-coaxial transmission line.

[0119] The specific operations are as follows:

[0120] S71: Use NMP debonding solvent heated to 70°C and soak for more than 3 hours to remove the sacrificial layer and bonding layer of the micro-coaxial transmission line AZ125nxt photoresist, so that the second wafer 21 is separated from the micro-coaxial transmission line, and 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: Use 10% dilute nitric acid solution to remove the copper seed layer, use 2% HF to remove the Ti metal layer, that is, the transition layer in the seed layer, and after washing and drying, obtain a micro-coaxial transmission line with sapphire as the inner conductor support layer.

[0122] Due to the thin thickness of the seed layer, the impact on the micro-coaxial transmission line structure during the removal process can be ignored.

[0123] Example 3

[0124] The difference between this embodiment and Embodiment 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 layer 14 located on both sides of the first inner conductor layer 13, and then the first inner conductor layer 13 and the first lower outer conductor layer 14 are formed by local electroplating of the copper layer.

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

[0126] Likewise, 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 cap layer.

[0127] Similarly, after depositing the seed layer in step S51, the seed layer is patterned so that the pattern of the seed layer is the same as the second inner conductor layer 23 and the second lower outer conductor layer 24 located on both sides of the second inner conductor layer 23, and then the second inner conductor layer 23 and the second lower outer conductor layer 24 are formed by local electroplating of the copper layer.

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

[0129] Likewise, 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 cap layer.

[0130] The difference between this embodiment and embodiment 2 is that: in embodiment 1, all the copper electroplating is global copper electroplating, the purpose is to ensure the uniformity of copper electroplating, and the seed layer is wet-etched and removed after the sacrificial layer is removed in step S7. In this embodiment, all the copper electroplating is local copper electroplating, 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, it is only necessary to remove the sacrificial layer in step S7 to obtain the micro-coaxial transmission line structure, and there is no need to wet-etch the seed layer separately, which can ensure the integrity and accuracy of the micro-coaxial transmission line structure.

[0131] 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 an α-Al2O3 single crystal with excellent material properties. Its elastic modulus is 435GPa, its fracture strength can reach 400MPa, its thermal conductivity is 24W / m·K, its temperature resistance can reach above 1000°C, and its chemical stability is high. Compared with organic materials such as SU8, its mechanical indicators 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 solid and not easy to deform.

[0132] The inner conductor layer of the micro-coaxial transmission line supported in the present application has better heat dissipation capability. Since the micro-coaxial transmission line must form an air cavity structure, the inner conductor layer is wrapped by air except for a few periodic positions that are directly in contact with the inner conductor support layer. This structure greatly limits the heat dissipation of the inner conductor layer during use. In the prior art, the thermal conductivity of organic media is two orders 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 metal copper itself also has high heat dissipation capability. Therefore, the metal copper micro-coaxial transmission line with sapphire as the inner conductor support layer is extremely suitable for applications in high-power and high-heat environments.

[0133] The sapphire material in the present application is extremely stable and will not be damaged in any organic solvent or strong alkaline aqueous solution. Therefore, when the final photoresist sacrificial layer of the micro-coaxial transmission line is removed, it is less restricted by the solvent temperature and removal time, thereby avoiding the problem that the general organic inner conductor support structure is easily corroded and damaged in a high-temperature degumming solvent. At the same time, a large amount of process time for releasing the sacrificial layer can be saved, the release process of the micro-coaxial transmission line is simplified, the preparation efficiency of the micro-coaxial transmission line is improved, and the production cycle of the micro-coaxial transmission line is shortened.

[0134] It can be understood that the above embodiments only express the preferred implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the patent scope of the present invention. It should be pointed out that, for ordinary technicians in this field, the above technical features can be freely combined without departing from the concept of the present invention, and several deformations and improvements can be made, which all belong to the protection scope of the present invention. Therefore, all equivalent changes and modifications made to the scope of the claims of the present invention should belong to the coverage of the claims of the present invention.

Claims

1. A method for preparing a micro-coaxial transmission line with sapphire as an inner conductor support layer, characterized in that: include: Forming a sapphire inner conductor support layer by laser processing on the surface of the first sapphire wafer; A first inner conductor layer and a first outer conductor layer are formed on the sapphire inner conductor support layer, wherein the first outer conductor layer is located on both sides of the first inner conductor layer in a direction perpendicular to the extension direction of the micro-coaxial transmission line, 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; forming a first cap layer on the first outer conductor layer; the first cap layer covers the first inner conductor layer and the first outer conductor layer; Bonding the second wafer to the first top cover layer, and thinning the first sapphire wafer until the sapphire inner conductor support layer is exposed; A second inner conductor layer and a second outer conductor layer are formed on the sapphire inner conductor support layer at a side away from the second wafer, wherein the second outer conductor layer is located on both sides of the second inner conductor layer in a direction perpendicular to the extension direction of the micro-coaxial transmission line, and the height of the second outer conductor layer is greater than that of the second inner conductor layer; and a second sacrificial layer is filled between the second outer conductor layer and the second inner conductor layer; forming a second cap layer on the second outer conductor layer; the second cap layer covers the second inner conductor layer and the second outer conductor layer; The first sacrificial layer, the second sacrificial layer and the second wafer are removed to form a micro coaxial transmission line.

2. The method for preparing a micro-coaxial transmission line with sapphire as an inner conductor support layer according to claim 1, characterized in that: Laser processing is performed on the surface of the first sapphire wafer to form a sapphire inner conductor support layer, specifically comprising: The first sapphire wafer is laser processed by using a femtosecond laser to remove the portion outside the sapphire inner conductor support layer, thereby forming a sapphire inner conductor support layer located on the surface of the first sapphire wafer.

3. The method for preparing a micro-coaxial transmission line with sapphire as an inner conductor support layer according to claim 1, characterized in that: Forming a first inner conductor layer and a first outer conductor layer on a sapphire inner conductor support layer specifically includes: Depositing a first inner conductor layer in the middle of the sapphire inner conductor support layer by means of a sacrificial layer mask, and depositing first lower outer conductor layers on both sides of the first inner conductor layer, wherein the first lower outer conductor layer is located on the sapphire inner conductor support layer and the surface of the first sapphire wafer at the same time; and a first lower sacrificial layer is filled between the first inner conductor layer and the first lower outer conductor layer; A first upper outer conductor layer is deposited 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.

4. The method for preparing a micro-coaxial transmission line with sapphire as an inner conductor support layer according to claim 3, characterized in that: Depositing a first inner conductor layer in the middle of the sapphire inner conductor support layer by means of a sacrificial layer mask specifically includes: Depositing a transition layer and a copper seed layer in sequence on one side of the first sapphire wafer where a sapphire inner conductor support layer is provided; Electroplating a copper layer by means of a sacrificial layer mask to form a first inner conductor layer and a first lower outer conductor layer located 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; Depositing 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; The copper layer is electroplated by means of a sacrificial layer mask to form a first upper outer conductor layer located on the first lower outer conductor layer; the surfaces of the first upper outer conductor layer and the first upper sacrificial layer are flush.

5. The method for preparing a micro-coaxial transmission line with sapphire as an inner conductor support layer according to claim 4, characterized in that: Forming a first cap layer on the first outer conductor layer specifically includes: Depositing a transition layer and a copper seed layer in sequence on the surfaces of the first upper outer conductor layer and the first upper sacrificial layer; The copper layer is electroplated 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.

6. The method for preparing a micro-coaxial transmission line with sapphire as an inner conductor support layer according to claim 5, characterized in that: The method further comprises: performing a planarization process on the first inner conductor layer, the first lower outer conductor layer and the first lower sacrificial layer, so that the thickness of the first inner conductor layer and the first lower outer conductor layer is 30-60 μm; Planarizing the first upper outer conductor layer and the first upper sacrificial layer so that the thickness of the first inner conductor layer and the first lower outer conductor layer is 90-110 μm; The first top cover layer is planarized so that the thickness of the first top cover layer is 90-110 μm.

7. The method for preparing a micro-coaxial transmission line with sapphire as an inner conductor support layer according to claim 4, 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.

8. The method for preparing a micro-coaxial transmission line with sapphire as an inner conductor support layer according to claim 4, characterized in that: Forming a second inner conductor layer and a second outer conductor layer on a side of the sapphire inner conductor support layer away from the second wafer, specifically comprising: Depositing a second inner conductor layer in the middle of the sapphire inner conductor support layer by means of a sacrificial layer mask, and depositing a second lower outer conductor layer on both sides of the second inner conductor layer, wherein the second lower outer conductor layer is located on the sapphire inner conductor support layer and the second wafer surface at the same time; and a second lower sacrificial layer is filled between the second inner conductor layer and the second lower outer conductor layer; A second upper outer conductor layer is deposited on 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.

9. The method for preparing a micro-coaxial transmission line with sapphire as an inner conductor support layer according to claim 1, characterized in that: Bonding the second wafer to the first cap layer includes: Spin coating the sacrificial layer on the second wafer surface and the first cap layer surface respectively; The second wafer and the sacrificial layer in the first cap layer are aligned and thermally pressed and bonded.

10. The method for preparing a micro-coaxial transmission line with sapphire as an inner conductor support layer according to claim 9, characterized in that: The first sacrificial layer, the second sacrificial layer and the second wafer are removed to form a micro-coaxial transmission line, specifically including: The sacrificial layer is removed by a debonding solvent, so that the second wafer is separated from the micro-coaxial transmission line, and 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.

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