Manufacturing method of metal structure

Abstract

The invention discloses a manufacturing method of a metal structure. The method comprises the following steps: forming a cushion layer on a substrate; forming a first pattern layer on the cushion layer, wherein the first pattern layer comprises a first window; a second pattern layer is formed on the first pattern layer, the second pattern layer comprises a second window communicated with the first window, and the second window and the first window define the metal structure; the projection area of the second window on the substrate is larger than that of the first window on the substrate so as to form a step surrounding the first window; the center of the second window and the center of the first window are located on the same straight line, and the straight line is perpendicular to the substrate; and electroplating in the first window and the second window to form the metal structure. Through the method, the problem of undercutting can be solved.

Description

TECHNICAL FIELD

[0001] The present application relates to a manufacturing method of a semiconductor component, in particular to a manufacturing method of a metal structure. BACKGROUND

[0002] In the manufacturing of a metal structure of MEMS, there is often an undercut problem. The undercut problem will fundamentally affect the mechanical performance, introduce uncertainty and risk of electrical performance, and make subsequent processes difficult to perform, eventually leading to device failure or shortened life.

[0003] Therefore, it is necessary to solve the undercut problem in the manufacturing process of the metal structure. SUMMARY

[0004] The present application aims to provide a manufacturing method of a metal structure, which is beneficial to avoid the undercut problem of the metal structure.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: the manufacturing method of the metal structure comprises the following steps:

[0006] forming a pad layer on a substrate;

[0007] forming a first pattern layer on the pad layer, the first pattern layer comprising a first window;

[0008] forming a second pattern layer on the first pattern layer, the second pattern layer comprising a second window in communication with the first window, the second window and the first window defining the metal structure; the projection area of the second window on the substrate is greater than the projection area of the first window on the substrate to form a step around the first window; the center of the second window and the center of the first window are located on the same straight line, and the straight line is perpendicular to the substrate;

[0009] electroplating in the first window and the second window to form the metal structure.

[0010] In some embodiments, the first pattern layer is formed by a positive photoresist, and the second pattern layer is formed by a negative photoresist.

[0011] In some embodiments, the negative photoresist is SU-8 glue, or KMPR1000 glue, and / or the positive photoresist is AZ photoresist.

[0012] In some embodiments, in the direction parallel to the substrate, the width of the step is w, 0.5 μm ≦ w ≦ 1.5 μm.

[0013] In some embodiments, the thickness of the second pattern layer is greater than the thickness of the first pattern layer in a direction perpendicular to the substrate.

[0014] In some embodiments, the thickness of the second pattern layer is H, 3μm≦H≦220μm in a direction perpendicular to the substrate.

[0015] In some embodiments, the thickness of the first pattern layer is h, 0.2μm≦h≦1.5μm.

[0016] In some embodiments, the second pattern layer is directly formed on the first pattern layer; and / or, the method of manufacturing the metal structure is applied in a MEMS process.

[0017] In some embodiments, the process condition of forming the second pattern layer on the first pattern layer comprises:

[0018] The glue coating step: the rotation speed of the glue coating is 300rpm-5000rpm; the time of keeping the rotation speed is 15s-25s;

[0019] The pre-baking step: the pre-baking temperature is 80℃-105℃, and the pre-baking time is 3min-15min;

[0020] The exposure step: the energy dose is 20mj / cm²-200mj / cm²;

[0021] The hardening step: the temperature is 80℃-105℃, and the time is 1min-8min;

[0022] The developing step: the developing time is 1min-8min.

[0023] In some embodiments, the first pattern layer is formed on the pad layer by using a photolithography process, and the first window is formed by using the photolithography process, comprising:

[0024] The glue coating step: the first pattern layer is formed on the pad layer by using a coating method; the rotation speed of the spin coating is 3500rpm-5000rpm, and the time of keeping the rotation speed is 25s-35s;

[0025] The pre-baking step: the coated first pattern layer is pre-baked, the pre-baking temperature is 70℃-90℃, and the pre-baking time is 55-70s;

[0026] The exposure step: the energy dose is 80mj / cm²-110mj / cm²;

[0027] The post-baking step: the post-baking temperature is 110℃-130℃, and the post-baking time is 55s-70s;

[0028] The developing step: the developing time is 55s-70s.

[0029] It can be understood that the manufacturing method of the metal structure has at least the following beneficial effects:

[0030] For the manufacturing method of the metal structure, by locating the center of the first window and the center of the second window on the same straight line, the first window and the second window form a step. If undercut problem occurs, the glue solution will flow from the step to the root of the second window, filling the gap caused by the undercut. Therefore, the structure formed by the first window and the second window has no undercut problem. Further, the space formed by the first window and the second window can be considered as a mold for electroplating. In this mold, the metal will only grow from the seed layer (pad layer) exposed by the first window. Since the second window is larger (i.e., there is a step), the electroplated metal will expand horizontally while growing vertically. Finally, the mold has no undercut problem, and a metal structure with no undercut problem is naturally formed. For example, in some cases, the bottom of the metal structure is chamfered by 0.5-1 microns, which is only a black line in vision and does not affect the appearance. In addition, the presence of the step, the solidification of the first pattern layer and the root of the second window of the second pattern layer are closely combined, which is beneficial to form a pattern with vertical sidewall and high aspect ratio. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a schematic diagram of forming a pad layer on a substrate;

[0032] Figure 2 is a schematic diagram of forming a first pattern layer on the pad layer and forming a first window after exposure and development;

[0033] Figure 3 is a schematic diagram of forming a second pattern layer;

[0034] Figure 4 is a schematic diagram of the second exposure;

[0035] Figure 5 is a schematic diagram of developing on the basis of Figure 4 , the first window and the second window are connected;

[0036] Figure 6 is a schematic diagram of forming a metal structure after electroplating and removing glue. DETAILED DESCRIPTION

[0037] In order to describe the technical content, structural features, achieved purposes and effects of the application in detail, the technical solutions in the embodiments of the application will be described below in combination with the drawings in the embodiments of the application. Obviously, the described embodiments are only some of the embodiments of the application, rather than all the embodiments. In the following description, for the purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of various exemplary embodiments or implementations of the application. However, various exemplary embodiments can also be practiced without these specific details or with one or more equivalent arrangements. In addition, various exemplary embodiments can be different, but not necessarily mutually exclusive. For example, the specific shape, structure and characteristics of an exemplary embodiment can be used or implemented in another exemplary embodiment without departing from the inventive concept.

[0038] Hereinafter, the terms "first", "second", and the like are used only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second", and the like can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specified.

[0039] In addition, in the present application, spatial relative terms such as "under", "below", "lower", "down", "above", "upper", "on", "higher", "side" (for example, as in "side wall") and the like are used to describe the relationship between one element and another (other) element as shown in the drawings. The spatial relative terms are intended to include different orientations of the device in use, operation and / or manufacture in addition to the orientation depicted in the drawings. For example, if the device in the drawings is turned over, the element described as "below" or "under" the other element or feature will then be positioned "above" the other element or feature. Therefore, the exemplary term "below" can include both upward and downward orientations. In addition, the device can be positioned otherwise (for example, rotated 90 degrees or at other orientations), and accordingly the spatial relative descriptions used herein are interpreted accordingly.

[0040] In the present application, unless otherwise explicitly specified and limited, the term "connection" should be understood broadly, for example, "connection" can be fixed connection, or detachable connection, or integral; can be directly connected, or indirectly connected through an intermediate medium.

[0041] Referring to Figures 1 to 6 The present application discloses a metal structure manufacturing method, which is applied in a MEMS process, that is, as a step of manufacturing a MEMS device. Of course, it can also be applied in other processes, and the method comprises the following steps:

[0042] Referring to Figure 1 A pad layer 2 is formed on the substrate 1. The material of the substrate 1 and the pad layer 2 is not limited, and the pad layer 2 is, for example, copper. The method of forming the pad layer 2 is not limited, and the pad layer 2 is formed, for example, by electroplating.

[0043] Referring to Figure 2 A first pattern layer 3 is formed on the pad layer 2, and the first pattern layer 3 includes a first window 31. The material of the first pattern layer 3 is not limited to a layer formed of a positive photoresist as described below. The first pattern layer 3 and the first window 31 can be formed by any process, for example, a photolithography process.

[0044] Referring to Figure 3 , Figure 4 and Figure 5 A second pattern layer 4 is formed on the first pattern layer 3, and the second pattern layer 4 covers the first pattern layer 3 and covers the first window 31. The formation is not limited to direct formation as described below, and there can be other layers between the first pattern layer 3 and the second pattern layer 4. The second pattern layer 4 includes a second window 41 in communication with the first window 31, and the second window 41 and the first window 31 define the metal structure. Referring to Figure 5 The projection area of the second window 41 on the substrate 1 is greater than the projection area of the first window 31 on the substrate 1 to form a step 42 around the first window 31. The center of the second window 41 and the center of the first window 21 are located on the same straight line, and the straight line is perpendicular to the substrate 1. Comparing Figure 4 and Figure 5 It can be seen that electroplating is performed in the first window 31 and the second window 42 to form the metal structure 5. The process and metal of electroplating are not limited, and the electroplated metal is, for example, Ni, the temperature is 40-45°C (the temperature cannot be too high, and a high temperature affects the vertical appearance of the pattern); the PH value is 4-4.5, the current density is 3.5-4.5 A / dm 2 2, the stirring speed is 100-120 r / min, the pulse frequency is 40-50 Hz, the duty cycle is 50-60%, and the plating solution composition is nickel sulfate, nickel chloride, and boric acid.

[0045] As set forth above, by the center of the first window 31 and the center of the second window 41 being located on the same straight line, the first window 31 and the second window 41 form a step 42, if the undercut problem occurs, the glue solution will flow from the step 42 to the root of the second window 41, filling into the gap caused by the undercut, therefore, the structure formed by the first window 414 and the second window 42 has no undercut problem, that is, the existence of the step can avoid the problem of undercut of the metal structure. Further, the space formed by the first window 41 and the second window 42 can be considered as a mold for electroplating, on which the metal will only grow from the seed layer (pad layer) exposed by the first window 41. Since the second window 42 is larger (that is, there is a step), the electroplated metal will expand horizontally while vertically growing, and finally, the mold has no undercut problem, and the metal structure 5 with no undercut problem is naturally formed, for example, in some cases, the bottom of the metal structure 5 is chamfered by 0.5-1 microns, which is only a black line in vision and does not affect the appearance. In addition, the existence of the step 42, the solidification of the first pattern layer 3 is closely combined with the root of the second window 41 of the second pattern layer 4, which is beneficial to form a pattern with vertical sidewall and high aspect ratio.

[0046] In some embodiments, the first pattern layer 3 is formed by a positive photoresist (also referred to as positive resist), and the second pattern layer 4 is formed by a negative photoresist (also referred to as negative resist). The specific composition of the positive photoresist and the specific composition of the negative photoresist are not limited.

[0047] As set forth above, since the second pattern layer is located on the first pattern layer, in the case that the first pattern layer is formed by a positive photoresist and the second pattern layer is formed by a negative photoresist, at least the following beneficial effects are achieved: a three-dimensional structure with high aspect ratio and vertical sidewall is realized, more specifically, the positive photoresist is easy to obtain a thin layer pattern with high resolution, no residual glue, and steep sidewall; the negative photoresist can form a thick (up to hundreds of microns), vertical sidewall, high aspect ratio, and solid structure, the present application first makes a fine two-dimensional "blueprint" on the pad layer by positive photoresist, and then "grows upward" on the basis of this blueprint by negative photoresist, to copy and extend the tall metal structure 5, so that a metal structure 5 with fine features on the plane and in the vertical direction is obtained, avoiding the undercut problem, the pattern with high aspect ratio and vertical sidewall, and ensuring the good appearance of the metal structure 5.

[0048] In some embodiments, the negative photoresist is SU-8 photoresist. Both SU-8 photoresist and KMPR1000 photoresist have good lateral swelling, can achieve vertical sidewall, and have good aspect ratio capability, which is conducive to solving the undercut problem. In yet some embodiments, the positive photoresist is AZ photoresist. The AZ photoresist is not limited, for example, AZ4620 photoresist, AZ10XT photoresist, or AZ50XT photoresist. Among them, the AZ4620 photoresist is more resistant to etching by plating solution than the negative photoresist. The AZ10XT photoresist has high resistance, and the AZ50XT photoresist has high adhesion. The respective characteristics of these positive photoresists in combination with the negative photoresist can achieve high aspect ratio and vertical sidewall, and solve the undercut problem. In addition, the AZ photoresist has good resolution and CD control, a wide process window, and good ease of use, excellent adhesion to the pad 2, and as a sacrificial layer (can be easily and completely removed by various common solvents (such as acetone, special stripping solution) without attacking the plated metal.

[0049] As described above, the combination of the negative photoresist and the positive photoresist is adopted, the positive photoresist has the advantages of high contrast, high photosensitivity, high adhesion, high resistance to plating process, etc., and the negative photoresist establishes a high aspect ratio vertical wall around the first window 31, therefore, the combination of the two functions is complementary, which is more conducive to forming a "mold" for forming a metal structure composed of the first window 31 and the second window 41, and the mold has a high aspect ratio and vertical sidewall, which can better solve the undercut problem. In particular, when the negative photoresist is su-8 photoresist, the su-8 photoresist has good mechanical properties, chemical corrosion resistance, and thermal stability; it is cross-linked after receiving ultraviolet radiation, is a chemical expansion negative photoresist, and can form complex pattern structures such as steps; it can be directly used as an insulator during plating, and also overcomes the problem of insufficient depth-to-width ratio of ordinary photoresist using UV lithography, has low light absorption in the near-ultraviolet light (365nm-400nm) range, the exposure amount obtained by the entire photoresist layer is uniform, and thick film patterns with vertical sidewall and high aspect ratio (such as 6:1 or less) can be obtained.

[0050] In some embodiments, the width of the step 42 in the direction parallel to the substrate 1 is w, 0.5 μm≦w≦1.5 μm, such as 0.5 μm, 0.55 μm, 0.57 μm, 0.59 μm, 0.6 μm, 0.63 μm, 0.65 μm, 0.67 μm, 0.69 μm, 0.7 μm, 0.72 μm, 0.73 μm, 0.75 μm, 0.8 μm, 0.83 μm, 0.85 μm, 0.88 μm, 0.9 μm, 0.92 μm, 0.95 μm, 0.98 μm, 1 μm, 1.05 μm, 1.1 μm, 1.12 μm, 1.15 μm, 1.18 μm, 1.2 μm, 1.23 μm, 1.25, 1.27 μm, 1.3 μm, 1.33 μm, 1.35 μm, 1.37 μm, 1.4 μm, 1.45 μm, 1.48 μm or 1.5 μm. That is, overall, the second window 41 is larger than the first window 31 by 2±0.5 microns.

[0051] As set forth above, due to 0.5 μm≦w≦1.5 μm, if w is too small, the channel for the reflow of the glue (such as AZ photoresist) is too narrow, the material cannot fill the entire undercut gap well, leading to incomplete repair, possible defects at the root, and failure to solve the undercut problem; if w is too large, the volume to be filled is too large, the AZ photoresist may not have enough quantity or fluidity to completely fill the large gap, forming an unfilled "hole" or leading to excessive deformation of the AZ photoresist layer, again failing to solve the undercut problem.

[0052] Furthermore, for the vertical sidewall, w defines the transition region from full exposure to full non-exposure at the time of exposure, thereby forming an extremely steep chemical change boundary from soluble to insoluble inside the second window 41, which is the basis for forming the vertical sidewall. In summary, there is no undercut problem at the root (step 42) of the second window 41, and the metal structure 5 grows from there as a starting point, naturally forming a vertical sidewall.

[0053] For high aspect ratio, w in the above range provides support for the second window 41, too narrow will limit the efficiency of the developer flowing in and the waste liquid flowing out, leading to incomplete development, residue at the bottom, and pattern failure. Too wide, although the fluid exchange is smooth, but it will sacrifice the verticality of the sidewall and the mechanical strength. Therefore, w in the above range ensures the best balance between sufficient exchange of developer and maintenance of structure strength and verticality, which is beneficial to the formation of high aspect ratio patterns.

[0054] Referring to Figure 3 , Figure 4 and Figure 5In the direction perpendicular to the substrate 1, the thickness of the second pattern layer 4 is greater than the thickness of the first pattern layer 3, such as, Figure 3 H > h.

[0055] As set forth above, the thickness of the second pattern layer 4 is greater than the thickness of the first pattern layer 3, at least has the following beneficial effects: 1) more conducive to solve the undercut problem, and more conducive to obtain vertical sidewall and high aspect ratio pattern, more specifically, the first pattern layer as a two-dimensional, precision better patterned reference layer; the second pattern layer 4 as a functional three-dimensional structure layer, therefore, on the precision better two-dimensional structure more easily form the vertical sidewall and high aspect ratio pattern, solve the undercut problem. For example, a metal structure shape can refer to Figure 6 2) provide excellent mechanical strength and stability, facilitate electroplating to form the metal structure 5, more specifically, the second window 41 and the first window 31 as a mold, in the subsequent electroplating, the second pattern layer 4 is thicker so that the mold is thicker, such a mold can resist the impact of the electroplating liquid flow and the internal stress generated in the electroplating process, and will not be deformed or collapsed, thereby ensuring the precision of the metal structure, ensuring high aspect ratio pattern and vertical sidewall, and solving the undercut problem.

[0056] In some embodiments, referring to Figure 3 and Figure 6 In the direction perpendicular to the substrate 1, the thickness of the second pattern layer 4 is H, 3 μm ≦ H ≦ 220 μm, such as 3 μm, 5 μm, 10 μm, 15 μm, 18 μm, 20 μm, 25 μm, 30 μm, 35 μm, 38 μm, 40 μm, 45 μm, 50 μm, 55 μm, 58 μm, 60 μm, 65 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 115 μm, 120 μm, 130 μm, 135 μm, 140 μm, 150 μm, 155 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, 210 μm or 220 μm.

[0057] As set forth above, since 3 μm ≦ H ≦ 220 μm, it is easier to form a vertical sidewall, a high aspect ratio pattern, thereby ensuring the topography of the metal structure 5. For example, if H is greater than 220 μm, the steepness of the sidewall formed is not good.

[0058] In some embodiments, referring to Figure 3 and Figure 6, the first pattern layer 3 has a thickness h, 0.2 pm≦h≦1.5 pm, such as 0.2 pm, 0.22 pm, 0.25 pm, 0.28 pm, 0.3 pm, 0.33 pm, 0.35 pm, 0.38 pm, 0.4 pm, 0.43 pm, 0.45 pm, 0.48 pm, 0.5 pm, 0.52 pm, 0.55 pm, 0.58 pm, 0.6 pm, 0.62 pm, 0.65 pm, 0.68 pm, 0.7 pm, 0.72 pm, 0.75 pm, 0.78 pm, 0.8 pm, 0.83 pm, 0.85 pm, 0.88 pm, 0.9 pm, 0.92 pm, 0.95 pm, 0.98 pm, 1 pm, 1.02 pm, 1.05 pm, 1.08 pm, 1.1 pm, 1.13 pm, 1.15 pm, 1.18 pm, 1.2 pm, 1.23 pm, 1.25 pm, 1.28 pm, 1.3 pm, 1.33 pm, 1.35 pm, 1.38 pm, 1.4 pm, 1.43 pm, 1.45 pm, 1.48 pm, or 1.5 pm.

[0059] Generally, the thinner the first pattern layer 3, the better. As set forth above, because 0.2 μm≦h≦1.5 μm, the negative photoresist closely adheres to the positive photoresist during the hardening step, and so on, so that it is easier to form a vertical sidewall, a high aspect ratio pattern, and so on, thereby ensuring the topography of the metal structure 5. In addition, it has at least the following beneficial effects: 1) excellent overlay accuracy is achieved, and more specifically, when performing overlay alignment of the second layer pattern 4, the alignment system of the photolithography machine needs to "see through" the second pattern layer 4 to recognize and align the alignment marks on the first pattern layer 3. If the first pattern layer 3 is too thick, its sidewall will form a deep "shadow" or "trench", and after the second pattern layer 4 is filled, it will interfere with the optical alignment signal, such as scattering, diffraction, resulting in poor signal quality and difficult alignment. 2) provides an ideal foundation for the second pattern layer 4, ensuring that its sidewall is vertical, and more specifically, after the second pattern layer 4 is applied, its bottom is in contact with the pattern of the first pattern layer 3. If the sidewall of the pattern of the first pattern layer 3 is not steep or there is residue at the bottom, the topography of the bottom pattern of the second pattern layer 4 will also be destroyed. The first pattern layer 3 of the above thickness provides a better foundation platform for the second pattern layer 4, and the second pattern layer 4 can form its own vertical sidewall on this platform without being deviated by the irregular pattern of the bottom layer; 3) minimizes pattern distortion at the interface of the double layers, and more specifically, during the subsequent pre-baking and hardening processes of the second pattern layer 4, heat will be conducted to the underlying first pattern layer 3. A thinner first pattern layer 3 has a smaller volume and thermal mass. When heated, the stress that can exist inside it is smaller, and the tendency to flow or deform is much lower than that of a thick photoresist layer. This maximizes the change in the size (CD) of the bottom pattern due to the thermal process, ensuring the stability of the overlay reference. 4) fusion with the second pattern layer 4 can better solve the undercut problem, and more specifically, a thinner first pattern layer 3 is more likely to be "modified": during the hardening process of the second pattern layer 4 and the like, heat and possible chemical interactions will cause the surface of the thinner first pattern layer 3 to slightly reflow, interdiffuse or blend, thereby filling the small Undercut that can be generated at the root of the second pattern layer 4 due to acid diffusion or development attack. If the first pattern layer 3 is very thick, it is difficult to effectively fuse the interface with the second pattern layer 4 through post-baking. The first pattern layer 3 of the above thickness is more likely to be affected by the thermal process, thereby actively participating in and facilitating the interface repair process, and ultimately forming a smooth, vertical transition at the root of the second pattern layer 4, better solving the undercut problem.

[0060] Referring to Figures 3 to 6 , the second pattern layer 4 directly covers the first pattern layer 3. Of course, in other embodiments, there can be other layers between the second pattern layer 4 and the first pattern layer 3, in which case the second window 41 also penetrates the other layers.

[0061] As the above setting, since the second pattern layer 4 directly covers the first pattern layer 3, at least the following beneficial effects are achieved:

[0062] 1) Fewer processes, conducive to achieving vertical sidewall, high aspect ratio pattern through negative photoresist photolithography process;

[0063] 2) In the process of hardening the film, the flowability of the photoresist film makes the positive photoresist and the negative photoresist fuse, and the combination of the positive photoresist and the negative photoresist is more closely than the combination of the negative photoresist and the wafer, finally, ensuring the appearance of the metal structure 5. There are other layers between the second pattern layer 4 and the first pattern layer 3, although one step HMDS can be done to increase the bonding force between the positive photoresist and the negative photoresist, but the high temperature in the HMDS process may damage and distort the positive photoresist pad layer pattern, affecting the negative photoresist pattern layer overlay;

[0064] 3) Even if the underlying pad 2 has a slight unevenness, the uniform first pattern layer 3 can "smooth" it, providing a smooth surface for the second pattern layer 4. The direct contact between the negative photoresist and the positive photoresist prevents the pattern of the second pattern layer 4 from falling off in subsequent severe processes (such as electroplating, wet etching);

[0065] 4) By directly covering the first pattern layer 3 with the second pattern layer 4, the interface fusion process between the two effectively fills and repairs the undercut defects that may occur at the root of the second pattern layer 4, forming a smooth and solid transition zone between the pattern of the second pattern layer 4 and the first pattern layer 3. This is equivalent to giving the second pattern layer 4 a solid "foundation", making its sidewall from bottom to top remain vertical, greatly improving the mechanical stability of the structure, and well solving the undercut problem.

[0066] As follows, some steps of the method for manufacturing the metal structure of the present application are described:

[0067] The process conditions for forming the second pattern layer 4 on the first pattern layer 3 include:

[0068] Referring to Figure 3, the glue coating step: the glue coating rotation speed: 300rpm-5000rpm, the rotation speed value is 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, 4000, 4100, 4200, 4300, 4400, 4500, 4600, 4700, 4800, 4900 or 5000; the time of keeping the rotation speed: 15s-25s, for example, the time value is 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 or 25; after the glue coating, the second pattern layer 4 also covers the first window 31. This step has at least the following beneficial effects:

[0069] 1) It is beneficial to ensure the film thickness uniformity and cover the bottom layer pattern (such as the first pattern layer 3), specifically, the above process parameters make the glue film leveling dynamic force and the centrifugal force reach a balance, which can at least uniformly cover the step of the bottom layer pattern (the first pattern layer 3), which is crucial for obtaining the vertical sidewall and high aspect ratio structure subsequently.

[0070] 2) It is beneficial to optimize the intrinsic quality of the glue film, specifically, the above process parameters help the stretch and stress release of the glue molecules, thereby, the internal stress generated in the subsequent baking and exposure process can be reduced, so as to reduce the risk of glue film cracking or peeling from the substrate, and the surface flatness can also be improved, so as to obtain a mirror-like flat surface, which is very important for the focus depth control and vertical sidewall in the exposure process. The uneven surface will lead to uneven exposure energy and line width variation in different areas.

[0071] Pre-baking step: pre-baking temperature: 80-105°C, for example, the temperature value is 80, 83, 85, 88, 90, 93, 95, 98, 100, 102, 103 or 105, pre-baking time: 3-15min, for example, the time value is 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15; this step has at least the following beneficial effects: if the pre-baking temperature exceeds or approaches the transition temperature of the AZ positive photoresist, the first pattern layer 3 softens, flows, deforms, resulting in the destruction of the first pattern layer 3, and the overlay is meaningless. Strictly control the temperature at 80-105°C and optimize the time, in order to achieve the best balance between ensuring the dryness of the negative photoresist (such as SU-8 glue) and guaranteeing the bottom layer topography. The process parameters of the pre-baking step and the process parameters in the hardening step combine to protect the pattern of the first pattern layer of the bottom layer from thermal deformation, which is beneficial to ensure the overlay accuracy.

[0072] Referring to Figure 4 , exposure step: exposure I line, energy dose: 20-200mj / cm², for example, the energy value is 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190 or 200. In addition, other G lines (436nm) and H lines (405nm), deep ultraviolet DUV such as KrF excimer laser (248nm) can also be used, and the energy dose can also be in this range. This exposure dose, combined with the conditions in the subsequent hardening step, is sufficient to ensure that the pattern is fully cross-linked from top to bottom, resistant to lateral erosion of the developer, and in addition, the negative photoresist itself is a negative photoresist with extremely high contrast and low viscosity, which is naturally prone to form vertical sidewalls, so the above process parameters are conducive to realizing vertical sidewalls and high aspect ratio patterns.

[0073] Hardening step: temperature: 80-105°C, for example, the temperature value is 80, 83, 85, 88, 90, 93, 95, 98, 100, 102, 103 or 105, time: 1-8min, for example, the time value is 1, 1.2, 1.5, 1.7, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6, 6.2, 6.5, 6.8, 7, 7.2, 7.5, 7.8 or 8. This process parameter can cause the bottom of the negative photoresist to slightly interdiffuse and physically mix with the pattern surface of the adjacent positive photoresist, forming a transition zone. This transition zone can effectively fill and repair the Undercut defect at the root, forming a more vertical sidewall from the bottom to the top.

[0074] Referring to Figure 5 Developing step: developing time: 1min-8min, such as, the numerical value of time is: 1, 1.5, 1.8, 2, 2.2, 2.3, 2.5, 2.8, 3, 3.1, 3.3, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6, 6.2, 6.5, 6.7, 7, 7.2, 7.5, 7.8 or 8; this step removes the unexposed area of the negative photoresist, forming the final structure for defining the metal topography.

[0075] In summary, through the above steps and process conditions, vertical sidewall, high aspect ratio pattern can be realized, the topography of metal structure 5 is good, such as, 3-220 microns vertical sidewall, high aspect ratio pattern can be realized.

[0076] Referring to Figure 1 and Figure 2 , the first pattern layer 3 is formed on the pad layer 2 by using photolithography process, and the first window 31 is formed, including:

[0077] Gluing step: the first pattern layer 3 is formed on the pad layer 2 by using coating method; the rotation speed of spin coating is: 3500rpm-5000rpm, such as, the numerical value of rotation speed is 3500, 3600, 3700, 3800, 3900, 4000, 4100, 4200, 4300, 4400, 4500, 4600, 4700, 4800, 4900 or 5000, the time of maintaining the rotation speed is: 25s-35s, such as, the numerical value of time is 25, 25.5, 25.8, 26, 26.2, 26.5, 26.8, 27, 27.2, 27.5, 27.7, 28, 28.2, 28.5, 28.8, 29, 29.2, 29.5, 29.8, 30, 30.2, 30.5, 30.8, 31, 31.2, 31.5, 31.8, 32, 32.5, 33, 33.5, 34, 34.5 or 35; this process condition. This step has at least the following beneficial effects:

[0078] 1) to realize and accurately control the thickness of the first pattern layer 3, more specifically, the higher the rotation speed, the greater the centrifugal force generated, the thinner and more uniform the photoresist can be spun. The foregoing process parameters utilize the high viscosity characteristics of positive photoresist to stretch it into a very thin but extremely uniform film by force.

[0079] 2) Improve film thickness uniformity, more specifically, the above duration ensures that the whole system has enough time to reach dynamic equilibrium, thus forming nanometer-level thickness consistency on the surface of the whole pad 2, especially the central active area. Film thickness uniformity is the prerequisite for subsequent consistent exposure dose and CD control. If the thickness of the glue is not uniform, even if the exposure energy is accurate, the line width in different areas will be different.

[0080] 3) Lay a good foundation for pre-baking, more specifically, the above process parameters make the initial solvent content of the glue film lower and more stable when entering the pre-baking step. This means that pre-baking (70-90°C, 55-70s) can focus more on completing the final solvent removal and glue film stabilization, without the need to correct an uneven initial state, thus reducing the process difficulty and defect risk of pre-baking.

[0081] Pre-baking step: pre-baking of the coated first pattern layer 3, pre-baking temperature: 70-90°C, for example, the temperature value is 70, 73, 75, 77, 79, 80, 83, 85, 87 or 90, pre-baking time: 55-70s, for example, the time value is 55, 57, 59, 60, 62, 64, 65, 67, 69 or 70. This step lays the foundation for the success of all subsequent processes, because this step has at least the following beneficial effects:

[0082] 1) Accurately control the thickness of the photoresist, lay the foundation for the first pattern layer 3 to be a thin layer pattern, specifically, after coating, the photoresist contains a large amount of solvent and is in a viscous liquid state. The main purpose of pre-baking is to evaporate this part of the solvent by heating, so that the photoresist changes from a liquid state to a solid thin film. 70-90°C is the temperature for the solvent (usually ethylene glycol ethyl ether acetate) to evaporate effectively, and 55-70 seconds of time ensures that the evaporation process is controllable and uniform. This prevents excessive shrinkage or stress concentration of the glue film caused by excessive temperature or time, helping you achieve the goal of "thin enough" and uniform thickness of the glue film.

[0083] 2) Ensure good adhesion to the substrate and prevent pattern shedding, more specifically, a moderate and sufficient pre-baking can form a firm adhesion between the photoresist and the substrate (such as a silicon wafer or glass), so that the first pattern layer 3 adheres firmly to the pad 2.

[0084] 3) Optimize photosensitive performance and prepare for accurate exposure, more specifically, appropriate pre-baking removes the solvent and forms a stable solid state environment, so that the absorption and reaction of the photoacid generator to light energy during exposure is more consistent and controllable. This creates conditions for using an accurate exposure dose of 80-110 mJ / cm² in the next step, and if pre-baking is insufficient, residual solvent will interfere with the photo reaction, resulting in uneven photosensitivity and CD deviation.

[0085] 4) Obtaining high-quality pattern sidewalls: More specifically, pre-baking determines the physical structure of the photoresist film. Over-baking (too high a temperature or too long a time) will cause the photoresist to partially cross-link or harden prematurely, resulting in a slower dissolution rate during development, potentially leading to residual photoresist or sloping sidewalls. Under-baking, on the other hand, will make the photoresist film too easily eroded in the developer, resulting in rough pattern sidewalls and "drilling." The window of 70℃-90℃ and 55s-70s strikes a balance, ensuring the photoresist film has sufficient mechanical strength while maintaining good solubility, which helps to form clear, steep pattern sidewalls after development. In short, this step allows subsequent exposure, post-baking, and development steps to proceed on an ideal basis, ultimately achieving the desired "qualified CD" and "residue-free pattern."

[0086] Exposure steps: Expose the I line with an energy dose of 80 mJ / cm²-110 mJ / cm², for example, the dose values ​​can be 80, 82, 85, 87, 90, 92, 95, 98, 100, 102, 105, 108, or 110; in addition, other G lines (436 nm) and H lines (405 nm), as well as deep ultraviolet DUV such as KrF excimer laser (248 nm), can also be used, and the energy dose can also be within this range. This step has at least the following beneficial effects:

[0087] 1) Ensuring complete reaction and thorough removal of photoresist residue is crucial. Specifically, positive photoresist needs to absorb sufficient light energy to complete the photochemical reaction, converting the photosensitizer into a compound soluble in the developer. If the exposure dose is below this range, the underlying photoresist layer or localized areas may not receive enough photons, resulting in incomplete photoreaction. Energy levels of 80 mJ / cm²-110 mJ / cm² ensure a sufficient and uniform photochemical reaction throughout the entire thickness of the first pattern layer 3. This is the primary prerequisite for achieving "residue-free" results. Sufficient energy allows the developer to cleanly and thoroughly dissolve the affected area.

[0088] 2) Achieving precise critical dimension (CD) control: More specifically, if the dose is too low, the pattern may not develop completely, or the lines may be wider than designed (because the edge areas lack energy and are not fully modified). If the dose is too high, excess light will scatter into areas that should not be exposed, causing these areas to be partially modified and etched away during development, resulting in lines that are narrower than designed. 80 mJ / cm²-110 mJ / cm² is the optimized "optimal dose point." Within this window, the effects of optical proximity are minimized, ensuring that the linewidth (CD) of the developed pattern is highly consistent with the design dimensions of the mask, thus achieving a "qualified CD."

[0089] 3) Obtaining steep, vertical sidewalls: More specifically, the spatial distribution of light intensity is not an ideal rectangle, but rather contains a transition zone from light to dark (i.e., the "sidewall" region). Optimal exposure doses make this transition zone very steep, so that within the aforementioned dose range, the transition of the positive photoresist from "completely soluble" to "completely insoluble" occurs over an extremely short distance. This directly results in a steep, clear sidewall after development.

[0090] Post-drying step: Post-drying temperature: 110℃-130℃, for example, temperatures of 110, 113, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, or 130℃; Post-drying time: 55s-70s, for example, times of 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, or 70 seconds; This step has at least the following beneficial effects:

[0091] 1) Significantly improves image contrast and completely eliminates residual adhesive. More specifically, the heat from post-baking causes the acid catalyst to continue working in the exposed areas, resulting in an extremely fast dissolution rate (up to hundreds of times), while the unexposed areas remain almost unchanged. Within this range, a good contrast in dissolution rate is provided. During development, the exposed areas are cleanly and efficiently removed, leaving almost no adhesive particles (achieving residue-free operation), while the unexposed areas remain rock-solid, resisting the erosion of the developing solution.

[0092] 2) Obtaining steep, consistent pattern sidewalls for precise CD control: More specifically, if the temperature is too low or the time is too short, insufficient acid diffusion will lead to uneven reaction and rough sidewalls. If the temperature is too high or the time is too long, the acid will diffuse excessively from the exposed area to the unexposed area, causing partial reaction of the pattern that should have been preserved, resulting in CD changes (usually narrower linewidth) and tilted sidewalls.

[0093] The above process parameters found a balance point, providing sufficient heat energy for the acid to complete an effective reaction without causing excessive diffusion of the acid. Thus, CD (Curve Difference) is precisely controlled, the pattern size is highly consistent with the design value, and steep, vertical, and smooth pattern sidewalls are formed.

[0094] Developing steps: Developing time is 55-70 seconds, for example, values ​​such as 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, or 70 seconds. This time provides at least the following beneficial effects:

[0095] 1) It allows for more precise control of the photomask (CD). Specifically, if the development time is too short, the photoresist in the exposed area may not be completely dissolved and removed, resulting in residual photoresist. If the development time is too long, the developer will not only dissolve the parts that should be dissolved, but will also begin to laterally etch (drill) the photoresist in the unexposed areas that should be preserved. The 55-70 second time window ensures that the exposed area is completely removed, while minimizing lateral attack on the sidewalls of the unexposed area pattern. This results in the final CD being highly consistent with the design dimensions of the mask, with good CD controllability and high repeatability.

[0096] 2) To obtain steep, clear pattern sidewalls, more specifically, the development process of positive photoresist proceeds from top to bottom and from the center to the edges. Excessive development time allows the developer more time to dissolve the pattern laterally, resulting in hollowing out the bottom of the pattern and forming undesirable sidewall contours such as "undercuts." The aforementioned time helps to quickly stop the etching process, thus contributing to the formation of more vertical sidewalls.

[0097] 3) Effectively avoids residual photoresist. More specifically, time ensures that the photoresist in all exposed areas on the entire surface of pad 2 can be fully removed, exposing a clean surface of pad 2, thereby achieving "residual-free patterning".

[0098] As described above, through the above steps and process conditions, it can be ensured that the thickness of the first graphic layer 3 is thin enough, and the above parameters can produce qualified CD (critical dimension or feature dimension), residual adhesive graphics, and ensure the integrity of the graphics.

[0099] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope. The scope of protection of the present invention is defined by the appended claims, specification, and their equivalents.

Claims

1. A method for manufacturing a metal structure, characterized in that: The method includes the following steps: A padding layer is formed on the substrate; A first graphic layer is formed on the padding layer, the first graphic layer including a first window; A second graphic layer is formed on the first graphic layer, the second graphic layer including a second window communicating with the first window, the second window and the first window defining the metal structure; the projected area of ​​the second window on the substrate is larger than the projected area of ​​the first window on the substrate to form a step around the first window; the center of the second window and the center of the first window are located on the same straight line, the straight line being perpendicular to the substrate. Electroplating is performed within the first and second windows to form the metal structure.

2. The method for manufacturing a metal structure according to claim 1, characterized in that, The first patterned layer is formed of positive photoresist, and the second patterned layer is formed of negative photoresist.

3. The method for manufacturing a metal structure according to claim 2, characterized in that, The negative photoresist is SU-8 photoresist, or KMPR1000 photoresist, and / or the positive photoresist is AZ photoresist.

4. The method for manufacturing a metal structure according to claim 1, characterized in that, In the direction parallel to the substrate, the width of the step is w, 0.5μm≦w≦1.5μm.

5. The method for manufacturing a metal structure according to claim 1, characterized in that, In a direction perpendicular to the substrate, the thickness of the second patterned layer is greater than the thickness of the first patterned layer.

6. The method for manufacturing a metal structure according to claim 1 or 5, characterized in that, In the direction perpendicular to the substrate, the thickness of the second patterned layer is H, where 3μm≦H≦220μm.

7. The method for manufacturing a metal structure according to claim 1 or 5, characterized in that, The thickness of the first patterned layer is h, where 0.2μm≦h≦1.5μm.

8. The method for manufacturing a metal structure according to claim 1, characterized in that, The second graphics layer directly overlays the first graphics layer; And / or, the manufacturing method of the metal structure is applied in MEMS processes.

9. The method for manufacturing a metal structure according to claim 1, characterized in that, The process conditions for forming the second pattern layer on the first pattern layer include: Adhesive application steps: Spindle speed: 300rpm-5000rpm; Duration of maintaining the specified speed: 15s-25s; Pre-drying steps: Pre-drying temperature: 80℃-105℃, Pre-drying time: 3min-15min; Exposure steps: Energy dose: 20mj / cm²-200mj / cm²; Hardening process: Temperature: 80℃-105℃, Time: 1min-8min; Development steps: Development time: 1 min - 8 min; 10. The method for manufacturing a metal structure according to claim 1, characterized in that, The first patterned layer is formed on the pad layer using a photolithography process, and the first window is formed, including: Adhesive application step: Form the first patterned layer on the pad by coating; Spin coating speed: 3500rpm-5000rpm, holding the speed for 25s-35s; Pre-baking step: Pre-baking the coated first pattern layer, pre-baking temperature: 70℃-90℃, pre-baking time: 55s-70s; Exposure steps: Energy dose: 80mj / cm²-110mj / cm²; Post-drying steps: Post-drying temperature: 110℃-130℃, Post-drying time: 55s-70s; Development steps: Development time: 55s-70s.

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