Preparation method of flexible electrode

Abstract

The invention provides a preparation method of a flexible electrode, and relates to the technical field of semiconductor materials. The preparation method comprises the following steps: coating the surface of a pretreated substrate with a polyimide coating with a first preset thickness, and curing to form a base layer; sequentially carrying out photoresist coating, exposure treatment and development treatment on the surface of the substrate layer so as to form a patterned photoresist on the upper surface of the substrate layer; performing metal deposition on the substrate layer so as to deposit a metal layer with a second preset thickness on the surface of the patterned photoresist and the surface of the exposed substrate layer; removing the photoresist and the metal layer on the surface of the photoresist by using metal stripping liquid so as to form an alignment mark on the surface of the substrate layer; wherein the metal stripping liquid is an N-methyl pyrrolidone solution, and the second preset thickness ranges from 150 nm to 250 nm. The alignment mark in the flexible electrode is high in definition and high in graph accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor materials, and in particular to a method for preparing a flexible electrode. Background Art

[0002] Brain-computer interface refers to a direct connection created between the human or animal brain and an external device to achieve information exchange between the brain and the device. It is committed to helping disabled people regain hope in life and will start the integration of humans and artificial intelligence. As a bridge connecting humans and computers, the brain-computer interface requires a flexible electrode to be connected in series to achieve the connection between humans and computers. The flexible electrode has good biocompatibility and stability, can better fit the brain, and reduce the impact of brain movement on the electrode. Polyimide has the characteristics of high strength, flexibility, bendability and human compatibility. It is widely used in flexible substrate materials with high biocompatibility requirements. The setting of exposure alignment marks in the semiconductor process based on polyimide substrate is the basis for ensuring the normal superposition of graphics.

[0003] In the prior art, the alignment mark in the flexible electrode is usually set on the surface of the silicon substrate, and a layer of polyimide is covered on the surface of the alignment mark. Although polyimide has a certain degree of transparency, the clarity of the alignment mark covered with polyimide is still affected (refer to Figure 2 ), especially in flexible electrodes with high requirements for polyimide thickness, the clarity of the alignment mark set at the bottom of the polyimide is worse, thus affecting the alignment accuracy of the subsequent layer. Technicians usually reduce the thickness of the polyimide to improve the clarity of the alignment mark. However, the thinning of the polyimide layer will also reduce the strength of the flexible electrode, further affecting the mechanical strength of the flexible electrode. Summary of the invention

[0004] One object of the present invention is to provide a method for preparing a flexible electrode to solve the technical problem of low clarity of alignment marks in flexible electrodes used for brain-computer interfaces in the prior art.

[0005] Another object of the present invention is to improve the structural stability of the flexible electrode.

[0006] According to the purpose of the present invention, the present invention provides a method for preparing a flexible electrode, comprising:

[0007] Coating a polyimide coating of a first preset thickness on the surface of the pretreated substrate, and forming a base layer after curing;

[0008] Sequentially performing photoresist coating, exposure treatment and development treatment on the surface of the base layer to form a patterned photoresist on the upper surface of the base layer;

[0009] Performing metal deposition on the base layer to deposit a metal layer having a second preset thickness on the surface of the patterned photoresist and the exposed surface of the base layer;

[0010] The photoresist and the metal layer on the surface of the photoresist are removed by using a metal stripping liquid to form an alignment mark on the surface of the base layer; wherein,

[0011] The metal stripping solution is N-methylpyrrolidone solution, and the second preset thickness is any value between 150nm and 250nm.

[0012] Optionally, the step of removing the photoresist and the metal layer on the surface of the photoresist by using a metal stripping solution further comprises:

[0013] The substrate, the base layer, the photoresist layer and the metal layer are immersed in the metal stripping solution for a preset time.

[0014] Optionally, the preset time is any value between 10 minutes and 15 minutes.

[0015] Optionally, the metal layer is made of gold or aluminum.

[0016] Optionally, the metal layer is deposited by physical vapor deposition.

[0017] Optionally, a deposition temperature of the metal layer is lower than a curing temperature of the base layer.

[0018] Optionally, the curing temperature of the base layer is any value between 300°C and 400°C.

[0019] Optionally, before the step of sequentially coating the surface of the substrate layer with photoresist, the method further comprises:

[0020] The surface of the base layer is surface treated.

[0021] Optionally, the surface treatment is performed by plasma treatment.

[0022] The present invention sequentially coats a polyimide coating and a photoresist layer on the surface of a substrate from bottom to top, and sequentially performs exposure treatment and development treatment, and performs metal stripping using a metal stripping liquid after metal deposition to remove the photoresist retained after development and the metal layer on the photoresist, and retains the metal layer deposited on the base layer, thereby forming an alignment mark with high definition and better alignment accuracy on the base layer.

[0023] Furthermore, the preset time of the present invention is any value between 10min and 15min. The immersion time of the metal stripping solution is set to any value between 10min and 15min, so that the photoresist layer and the N-methylpyrrolidone in the metal stripping solution are completely reacted and dissolved, and the photoresist layer on the surface of the substrate layer and the metal layer on the surface of the photoresist are completely removed. At the same time, the immersion time is prevented from being too long, which may cause the metal layer on the surface of the substrate layer or the substrate layer to be corroded, thereby ensuring the structural stability of the flexible electrode.

[0024] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Hereinafter, some specific embodiments of the present invention will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings:

[0026] Figure 1 is a schematic flow chart of a method for preparing a flexible substrate according to an embodiment of the present invention;

[0027] Figure 2 It is a schematic structural diagram of an alignment mark in a flexible substrate prepared in the prior art;

[0028] Figure 3 is a schematic structural diagram of an alignment mark in a flexible substrate according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0030] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. It is to be understood that the specific embodiments described herein are only used to explain the present application, rather than to limit the present application. It should also be noted that, for ease of description, only some structures related to the present application are shown in the accompanying drawings, rather than all structures. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0031] The terms "including" and "having" and any variations thereof in this application are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device comprising a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products or devices.

[0032] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0033] Figure 1 is a schematic flow chart of a method for preparing a flexible substrate according to an embodiment of the present invention, Figure 2 is a schematic structural diagram of an alignment mark in a flexible substrate prepared in the prior art. Figure 3 is a schematic structural diagram of an alignment mark in a flexible substrate according to an embodiment of the present invention.

[0034] like Figure 1 As shown, the present invention provides a method for preparing a flexible electrode, comprising:

[0035] Step S100: coating a polyimide coating of a first preset thickness on the surface of the pretreated substrate, and forming a base layer after curing;

[0036] Step S200: performing photoresist coating, exposure treatment and development treatment on the surface of the base layer in sequence to form a patterned photoresist on the upper surface of the base layer;

[0037] Step S300: performing metal deposition on the base layer to deposit a metal layer having a second preset thickness on the surface of the patterned photoresist and the surface of the exposed base layer;

[0038] Step S400: using a metal stripping solution to remove the photoresist and the metal layer on the surface of the photoresist to form an alignment mark on the surface of the substrate layer, wherein the metal stripping solution is an N-methylpyrrolidone solution, and the thickness of the metal layer is any value between 150nm and 250nm.

[0039] In this embodiment, in the preparation process of the flexible electrode, a polyimide coating of a first preset thickness is firstly coated on the surface of the pretreated substrate, and a base layer is formed after curing. Photoresist coating, exposure treatment and development treatment are sequentially performed on the surface of the base layer to form a patterned photoresist on the upper surface of the base layer. Then, metal deposition is performed above the base layer to deposit a metal layer with a second preset thickness on the surface of the patterned photoresist and the surface of the exposed base layer. Finally, the photoresist and the metal layer on the surface of the photoresist are removed by a metal stripping liquid to form an alignment mark on the surface of the base layer, wherein the metal stripping liquid is an N-methylpyrrolidone solution, and the second preset thickness is any value between 150nm and 250nm. Here, the second preset thickness can be 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, 220nm, 240nm or 250nm, or any value between 150nm and 250nm.

[0040] In this embodiment, a polyimide coating and a photoresist layer are sequentially coated on the surface of the substrate from bottom to top, and exposure treatment and development treatment are performed in sequence. After metal deposition, metal stripping is performed using a metal stripping liquid to remove the photoresist retained after development and the metal layer on the photoresist, and the metal layer deposited on the base layer is retained, thereby forming an alignment mark with high definition and better alignment accuracy on the base layer.

[0041] In this embodiment, the thickness of the metal layer is set to any value between 150nm and 250nm, that is, by controlling the metal deposition time and the metal deposition rate, the deposition thickness of the metal layer is set to any value between 150nm and 250nm, which can ensure that the metal layer can provide sufficient conductivity without excessively increasing the rigidity of the electrode, thereby maintaining good flexibility and conductivity of the flexible electrode. At the same time, setting the deposition thickness of the metal layer used to form the alignment mark within the above range can avoid the metal layer being too thin, resulting in the metal pattern being unclearly defined, and can also avoid the metal layer being too thick, resulting in blurring or deformation of the pattern, thereby avoiding affecting the pattern accuracy of the alignment mark and ensuring the pattern accuracy of the alignment mark.

[0042] In this embodiment, the material of the substrate is a silicon substrate, and the pretreatment includes surface cleaning and surface drying of the substrate to remove impurities on the surface of the substrate to prevent the presence of impurities on the surface of the substrate from causing unstable adhesion of the polyimide coating, thereby further improving the structural stability of the flexible electrode.

[0043] In this embodiment, the first preset thickness is any value in the range of 20μm-50μm, that is, the thickness of the polyimide coating can be 20μm, 25μm, 30μm, 35μm, 40μm, 45μm or 50μm, or any value in the range of 20μm-50μm. Setting the thickness of the polyimide coating within the above range can provide strong mechanical strength and maintain a certain degree of flexibility at the same time, and can be applied to the electrical connection between humans and computers in brain-computer interfaces that need to withstand moderate deformation.

[0044] In a further embodiment, step S400 further includes:

[0045] The substrate, base layer, photoresist layer and metal layer are immersed in the metal stripping solution for a preset time.

[0046] In the present embodiment, in the process of removing the photoresist and the metal layer on the surface of the photoresist by using a metal stripping solution, the substrate, the base layer, the photoresist layer and the metal layer need to be immersed in the metal stripping solution for a preset time. Since the material of the substrate is a silicon substrate, the material of the base layer is polyimide, and the metal layer is insoluble in the metal stripping solution, after the above-mentioned multi-structure is placed in the metal stripping solution for a preset time, the N-methylpyrrolidone in the metal stripping solution is an organic solvent, which can dissolve the photoresist and strip the metal layer on the surface of the photoresist, that is, the photoresist layer on the surface of the base layer and the metal layer on the surface of the photoresist can be completely removed, and only the metal layer on the surface of the base layer is retained, thereby forming a metal alignment mark on the surface of the base layer.

[0047] In a further embodiment, the preset time is any value between 10min and 15min, and the immersion time of the photoresist layer, the metal layer and the base layer in the metal stripping solution can be 10min, 11min, 12min, 13min, 14min or 15min, or any value between 10min and 15min. In this embodiment, by setting the immersion time of the metal stripping solution to any value between 10min and 15min, the photoresist layer is completely reacted and dissolved with the N-methylpyrrolidone in the metal stripping solution, and the photoresist layer on the surface of the base layer and the metal layer on the surface of the photoresist are completely removed, while preventing the metal layer on the surface of the base layer or the base layer from being corroded due to the immersion time being too long, thereby ensuring the structural stability of the flexible electrode.

[0048] In a further embodiment, the material of the metal layer is gold or aluminum. In this embodiment, the material of the metal layer can be gold or aluminum, that is, since both gold and aluminum have high reflectivity and chemical stability, they can ensure the clarity of the alignment mark while improving the stability of the metal layer in the metal stripping solution.

[0049] In a preferred embodiment, the material of the metal layer is preferably gold, that is, the material of the metal layer formed on the surface of the base layer is preferably gold. This is because gold has high chemical inertness and will not chemically react with the solute or solvent in the metal stripping solution, thereby further ensuring that the metal layer on the surface of the base layer can be preserved intact.

[0050] In a further embodiment, the metal layer is deposited by physical vapor deposition, which can uniformly deposit the metal layer on a substrate of a larger area and different shapes to form a smooth and uniform film. In addition, the metal layer deposited by physical vapor deposition usually has a higher density and compactness, which can effectively prevent oxygen or moisture in the air from penetrating into the metal layer, improve the stability and durability of the metal film, and provide excellent adhesion, avoiding the problem of unreliable adhesion that may be caused by traditional chemical methods. Here, the metal layer can also be deposited by metal sputtering deposition.

[0051] In a further embodiment, the deposition temperature of the metal layer is lower than the curing temperature of the base layer. In this embodiment, since polyimide is a flexible material with a certain thermal expansion coefficient, the deposition temperature of the metal layer is controlled to be always lower than the curing temperature of the base layer to avoid excessively high deposition temperature during the metal deposition process, which may cause the base layer of the polyimide material to deform or bend slightly, thereby affecting the accuracy of the alignment mark, thereby preventing the base layer from thermally expanding and causing the alignment mark to shift or distort the pattern.

[0052] In a further embodiment, the curing temperature of the base layer is any value between 300°C and 400°C, that is, the curing temperature of the base layer can be 300°C, 320°C, 340°C, 360°C, 380°C or 400°C, or any value between 300°C and 400°C. By setting the curing temperature of the base layer within the above range, the cross-linking degree of the polyimide during the curing process of the base layer is increased, thereby significantly improving the thermal stability of the material, so that it can maintain its structural stability in a high temperature environment and is not prone to deformation or degradation. In addition, the curing temperature within the above range makes the polyimide surface smoother and has a higher surface energy, thereby improving its adhesion to the coating material, and can effectively enhance the adhesion between the polyimide and the substrate, the metal layer and the photoresist.

[0053] In a further embodiment, before step S200, the following steps are further included:

[0054] The surface of the base layer is surface treated.

[0055] In this embodiment, by performing surface treatment on the surface of the base layer and then coating the photoresist, the adhesion of the photoresist to the base layer can be effectively improved, and the risk of unstable adhesion of the photoresist on the base layer causing pattern shifting during subsequent exposure and development processes can be prevented, thereby further improving the pattern accuracy and clarity of the alignment mark.

[0056] In a further embodiment, the surface treatment method is plasma treatment. In this embodiment, the surface of the substrate layer is treated by plasma treatment to increase the roughness of the substrate layer surface by physical means, thereby improving the adhesion of the photoresist to the substrate layer, and further preventing the situation in which the exposure and response may lead to unclear patterns due to unstable adhesion.

[0057] The present application will be further described in detail below with reference to specific embodiments.

[0058] Example 1

[0059] First, a 40 μm polyimide coating is coated on the surface of the pretreated substrate, and a base layer is formed after curing at 300°C. Photoresist coating, exposure treatment and development treatment are performed on the surface of the base layer in sequence to form a patterned photoresist on the upper surface of the base layer. Then, metal deposition is performed above the base layer to deposit a 200 nm metal layer on the surface of the patterned photoresist and the surface of the exposed base layer. The material of the metal layer is gold. Finally, the photoresist and the metal layer on the surface of the photoresist are removed using an N-methylpyrrolidone solution to form an alignment mark on the surface of the base layer.

[0060] like Figure 3 As shown, the clarity of the alignment mark in the flexible electrode plate prepared in Example 1 is significantly higher than the clarity of the alignment mark in the flexible electrode plate prepared in the prior art.

[0061] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0062] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a flexible electrode, characterized in that: include: Coating a polyimide coating of a first preset thickness on the surface of the pretreated substrate, and forming a base layer after curing; Sequentially performing photoresist coating, exposure treatment and development treatment on the surface of the base layer to form a patterned photoresist on the upper surface of the base layer; Performing metal deposition on the base layer to deposit a metal layer having a second preset thickness on the surface of the patterned photoresist and the exposed surface of the base layer; The photoresist and the metal layer on the surface of the photoresist are removed by using a metal stripping liquid to form an alignment mark on the surface of the base layer; wherein, The metal stripping solution is N-methylpyrrolidone solution, and the second preset thickness is any value between 150nm and 250nm.

2. The preparation method according to claim 1, characterized in that: The step of removing the photoresist and the metal layer on the surface of the photoresist by using a metal stripping solution further comprises: The substrate, the base layer, the photoresist layer and the metal layer are immersed in the metal stripping solution for a preset time.

3. The preparation method according to claim 2, characterized in that: The preset time is any value between 10min and 15min.

4. The preparation method according to claim 3, characterized in that: The material of the metal layer is either gold or aluminum.

5. The preparation method according to claim 4, characterized in that: The metal layer is deposited by physical vapor deposition.

6. The preparation method according to claim 5, characterized in that: The deposition temperature of the metal layer is lower than the curing temperature of the base layer.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The curing temperature of the base layer is any value between 300°C and 400°C.

8. The preparation method according to claim 7, characterized in that: Before the step of sequentially coating the surface of the substrate with photoresist, the step further includes: The surface of the base layer is surface treated.

9. The preparation method according to claim 8, characterized in that: The surface treatment method is plasma treatment.

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