Metal stripping process

Abstract

The invention provides a metal stripping process which comprises the following steps: S1, a substrate is provided, the surface of the substrate is provided with a high step structure, and the maximum height of the high step structure is a first height; s2, a first photoresist layer with a first thickness is formed on the surface of the substrate, the first photoresist layer is positive photoresist, and full exposure processing is carried out; s3, a second photoresist layer with a second thickness is formed on the surface of the first photoresist layer, the second photoresist layer is negative photoresist, and graphical exposure processing is carried out; s4, carrying out developing treatment on the first photoresist layer and the second photoresist layer; s5, depositing metal on the surface of the substrate by adopting a metal evaporation process; and S6, removing the residual photoresist to form a metal structure on the surface of the high-step structure. According to the technology, in the photoetching process, the step is filled with the positive photoresist, then the negative photoresist is used for covering, and complete covering of a high-step structure and complete stripping of a metal structure are achieved.

Description

Technical Field

[0001] The present invention relates to the field of microelectronic manufacturing, and particularly to a lift-off process for metals. Background Art

[0002] In the field of microelectronic manufacturing, the lithography process is one of the key processes. The traditional lift-off process usually uses a single negative photoresist to construct patterns. The process flow includes coating a negative photoresist on a substrate, forming a predetermined pattern through lithographic exposure, then performing metal evaporation, and finally stripping the photoresist to form a metal structure. However, when facing complex structures with high steps, a single type of photoresist often has difficulty achieving complete coverage of the steps, resulting in incomplete metal stripping or incomplete patterns. This is because there are certain physical limitations to the viscosity of the negative photoresist, and it is impossible to effectively cover high-step structures by simply increasing the thickness of the photoresist. Therefore, the existing technology has obvious limitations in dealing with high-step structures, and there is an urgent need to develop a new method to overcome this technical problem. Summary of the Invention

[0003] To solve all or part of the above problems in the prior art, the present invention provides a lift-off process for metals. This process realizes complete coverage of high-step structures and complete stripping of metal structures by first filling the steps with a positive photoresist and then covering it with a negative photoresist during the lithography process.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] A lift-off process for metals, comprising the following steps:

[0006] S1. Provide a substrate, the surface of the substrate having a high-step structure, the maximum height of the high-step structure being a first height;

[0007] S2. Form a first photoresist layer with a first thickness on the surface of the substrate, the first photoresist layer being a positive photoresist, and perform full exposure treatment;

[0008] S3. Form a second photoresist layer with a second thickness on the surface of the first photoresist layer, the second photoresist layer being a negative photoresist, and perform patterned exposure treatment;

[0009] S4. Develop the first photoresist layer and the second photoresist layer;

[0010] S5. Deposit metal on the surface of the substrate by using a metal evaporation process;

[0011] S6. Remove the remaining photoresist to form a metal structure on the surface of the high-step structure.

[0012] The first height is greater than the maximum thickness that the first photoresist layer can form.

[0013] The first height is greater than the maximum thickness that the second photoresist layer can form.

[0014] The first thickness is less than the first height, and the sum of the first thickness and the second thickness is greater than the first height.

[0015] The difference between the sum of the first thickness and the second thickness and the first height is 2 - 3 times the metal thickness.

[0016] The difference between the sum of the first thickness and the second thickness and the first height is 1.5 μm.

[0017] The first height is 5 - 6 μm, the first thickness is 4 ± 0.5 μm, and the second thickness is 3.5 ± 0.5 μm.

[0018] In step S3, the exposure energy for the patterned exposure is 600 - 800 mJ / cm 2 .

[0019] In step S5, the thickness of the metal evaporation is 0.1 - 0.6 μm, and the metal material is selected from one or more of gold, platinum, or titanium.

[0020] In step S6, a stripping solution or mechanical stripping is used to remove the remaining photoresist.

[0021] The present invention has at least the following beneficial effects:

[0022] 1) By adopting a combined process of positive photoresist and negative photoresist, the problem in the prior art that a single photoresist is difficult to cover high-step structures is solved. Due to its excellent fluidity and coating performance, the positive photoresist can fully fill the bottom of the high-step structure, providing a flatter surface for subsequent processes; while the negative photoresist shows higher stability during exposure and development, capable of forming clear and stable graphic structures.

[0023] 2) By controlling the differences between the thicknesses of the positive photoresist, negative photoresist and the height of the high-step structure, the exposure energy, and the development conditions, the present invention not only achieves complete coverage of the high-step structure, but also optimizes the complete stripping and patterning effects of the metal structure, significantly reducing corner residues. It is particularly suitable for the field of high-precision metal patterning, with remarkable practicality and innovation. Description of the Drawings

[0024] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the following will briefly introduce the accompanying drawings required for the description of the embodiments. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0025] Figure 1 It is a flowchart of a metal stripping process according to an embodiment of the present invention.

[0026] Figure 2 It is a schematic diagram of the process flow of a metal stripping process according to an embodiment of the present invention.

[0027] Figure 3 It is a schematic diagram of a substrate with a high-step structure in step S1 of a metal stripping process according to an embodiment of the present invention.

[0028] Figure 4 It is an optical microscope diagram after metal evaporation in step S5 of a metal stripping process according to an embodiment of the present invention.

[0029] Figure 5 It is a cross-sectional view after metal evaporation in step S5 of a metal stripping process according to an embodiment of the present invention.

[0030] Figure 6 It is an optical microscope diagram after removing photoresist in step S6 of a metal stripping process according to an embodiment of the present invention.

[0031] Reference numerals: 1, substrate; 2, high-step structure; 3, first photoresist layer; 4, second photoresist layer; 5, metal. Specific embodiments

[0032] The following will clearly and completely describe the technical solutions in the specific embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0033] In the embodiments of the present invention, with reference to Figures 1 to 6 as shown, a metal stripping process is provided, including the following steps:

[0034] S1. As Figure 2 shown in a, provide a substrate 1, the surface of the substrate 1 has a high-step structure 2, and the maximum height of the high-step structure 2 is the first height;

[0035] S2. As Figure 2As shown in Fig. b, a first photoresist layer 3 with a first thickness is formed on the surface of the substrate 1. The first photoresist layer 3 is a positive photoresist, and a full exposure process is performed.

[0036] S3. As Figure 2 As shown in Fig. c, a second photoresist layer 4 with a second thickness is formed on the surface of the first photoresist layer 3. The second photoresist layer 4 is a negative photoresist, and a patterned exposure process is performed.

[0037] S4. As Figure 2 As shown in Fig. d, the first photoresist layer 3 and the second photoresist layer 4 are developed.

[0038] S5. As Figure 2 As shown in Fig. e, a metal 5 is deposited on the surface of the substrate 1 by a metal evaporation process.

[0039] S6. As Figure 2 As shown in Fig. f, the remaining photoresist is removed to form a metal structure on the surface of the high-step structure 2.

[0040] Through the above process steps, the present invention can effectively solve the problem that a single photoresist in the prior art is difficult to cover the high-step structure 2, thereby realizing the complete peeling and patterning of the metal structure on the surface of the high-step structure 2.

[0041] In the present invention, to ensure that the first photoresist layer 3 and the second photoresist layer 4 can effectively cover the high-step structure 2 and realize the complete peeling of the metal structure, the thicknesses of the three need to satisfy a specific relationship. Considering the material properties of the photoresist, such as viscosity and leveling property, and process limitations, such as coating uniformity and exposure resolution, there is a maximum thickness limit for a single photoresist layer. When the height of the high-step structure 2 exceeds this limit, a single photoresist layer cannot completely cover it. The present invention is directed to such high-step structures 2, and through the cooperation of a double-layer photoresist, the coverage effect is ensured to meet the requirements for the complete peeling of the metal structure.

[0042] Specifically, as described above, based on the characteristics of existing photoresist materials and process limitations, there is a process upper limit for the maximum formable thickness of a single photoresist layer. However, the maximum height (i.e., the first height) of the high-step structure 2 in this embodiment exceeds this upper limit. Therefore, the existing lithography process cannot achieve complete coverage of it through a single photoresist layer. In this embodiment, that is, the first height is greater than the maximum thickness that the first photoresist layer 3 can form, and is also greater than the maximum thickness that the second photoresist layer 4 can form. The first thickness (i.e., the thickness of the first photoresist layer 3) is less than the first height. The sum of the first thickness and the second thickness (i.e., the total thickness of the photoresist layer) is greater than the first height to ensure that the overall thickness can completely cover the high-step structure 2. The difference between the sum of the first thickness and the second thickness and the first height is 2 to 3 times the metal thickness. This height difference ensures that the metal film can break naturally after deposition, so that the subsequent stripping liquid can enter. Specifically, in this embodiment, it is 1.5 μm.

[0043] In this embodiment, the first height is specifically 5 - 6 μm, the first thickness is specifically 4 ± 0.5 μm, and the second thickness is specifically 3.5 ± 0.5 μm. The positive photoresist is one of AR89 and IP5700, and the negative photoresist is one of SU-8 and E3502B. The thickness of the photoresist has a great relationship with the viscosity. Here, the viscosity of the positive photoresist with the first thickness is about 60 cP, and the viscosity of the negative photoresist with the second thickness is about 50 cP.

[0044] In step S2, a first photoresist layer 3 with a thickness of 4 μm (the positive photoresist is IP5700) is formed on the surface of the substrate 1, and full exposure treatment is performed using a SUSS device. The exposure energy range is 1000 - 1500 mJ / cm 2 .

[0045] In step S3, a second photoresist layer 4 with a thickness of 3.5 μm (the negative photoresist is E3502B) is formed on the surface of the first photoresist layer 3, and patterned exposure treatment is performed using a STEP device. The exposure energy is 600 - 800 mJ / cm 2 , and this energy range can effectively reduce the problem of corner residues.

[0046] In step S5, the thickness of the evaporated metal 5 is 0.1 μm of titanium, 0.2 μm of platinum, and 0.3 μm of gold.

[0047] In step S6, the remaining photoresist is removed using a stripping solution or mechanical stripping. In this embodiment, a stripping solution is specifically used for removal. Specifically, an NMP stripping solution is selected, the temperature is 80 °C, and the treatment time is 10 min.

[0048] Through the precise control of the above process steps and parameters, this embodiment can effectively solve the problem that a single photoresist in the prior art is difficult to cover the high-step structure 2. By optimizing the material selection, exposure energy, and stripping process of the photoresist, the complete stripping and patterning of the metal structure on the surface of the high-step structure 2 are achieved, while reducing the problem of corner residues.

[0049] By adopting a combined process of positive photoresist and negative photoresist, the present invention can effectively solve the filling and covering problems of the high-step structure 2, and then achieve the complete stripping of the metal structure. First, a layer of positive photoresist is formed on the surface of the substrate 1. Due to its excellent fluidity and coating performance, the positive photoresist can fully fill the bottom of the high-step structure 2, providing a flatter surface for subsequent processes. On the basis of the positive photoresist layer, a layer of negative photoresist is further formed. The negative photoresist has higher stability during the exposure and development processes and can form clear and stable graphic structures. By precisely controlling the thickness, exposure energy, and development conditions of the positive photoresist and the negative photoresist, the stability and reliability of the process are further improved.

[0050] It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A metal stripping process, characterized in that: The following steps are involved: S1. Providing a substrate, wherein the substrate surface has a high step structure, and the maximum height of the high step structure is a first height; S2. forming a first photoresist layer having a first thickness on the surface of the substrate, wherein the first photoresist layer is a positive photoresist, and performing a full exposure process; S3. forming a second photoresist layer having a second thickness on the surface of the first photoresist layer, wherein the second photoresist layer is a negative photoresist, and performing a patterned exposure process; S4. developing the first photoresist layer and the second photoresist layer; S5. Depositing metal on the surface of the substrate by a metal evaporation process; S6. removing the remaining photoresist to form a metal structure located on the surface of the high-step structure.

2. The process according to claim 1, characterized in that The first height is greater than a maximum thickness that the first photoresist layer can form.

3. The process according to claim 1, characterized in that The first height is greater than a maximum thickness that the second photoresist layer can form.

4. The process according to claim 1, characterized in that The first thickness is smaller than the first height, and the sum of the first thickness and the second thickness is larger than the first height.

5. The process according to claim 4, characterized in that The difference between the sum of the first thickness and the second thickness and the first height is 2-3 times the metal thickness.

6. The process according to claim 5, characterized in that The difference between the sum of the first thickness and the second thickness and the first height is 1.5 μm.

7. The process according to claim 4, characterized in that The first height is 5-6 μm, the first thickness is 4±0.5 μm, and the second thickness is 3.5±0.5 μm.

8. The process according to claim 1, characterized in that In step S3, the exposure energy of the patterned exposure is 600-800 mJ / cm 2 .

9. The process according to claim 1, characterized in that In the step S5, the thickness of the metal evaporation is 0.1-0.6 μm, and the metal material is selected from one or more of gold, platinum or titanium.

10. The process according to claim 1, characterized in that In the step S6, a stripping solution or mechanical stripping is used to remove the remaining photoresist.

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