A method for developing a thick film negative photoresist
By combining static development and short-time ultrasonic treatment with isopropanol cleaning, the problem of difficult removal of photoresist at the gaps of folded waveguides was solved, achieving tight adhesion between the photoresist and the substrate and pattern integrity, thus ensuring the smooth progress of subsequent processing.
Patent Information
- Application Number
- CN202210866049.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-07-22
- Publication Date
- 2025-12-19
- Estimated Expiration
- 2042-07-22
AI Technical Summary
Existing technologies struggle to completely remove photoresist residue from the gaps in folded waveguides during the development process while maintaining tight adhesion between the photoresist and the substrate. This is especially true when the gap size is less than 40μm-50μm, as traditional methods can easily lead to photoresist swelling, detachment, or pattern oscillation.
A method combining static development with short-term ultrasonic treatment and isopropanol cleaning is adopted. After static development for 10-15 minutes, ultrasonic treatment is performed for a very short time of 10-20 seconds. The photoresist is then intermittently transferred to isopropanol for cleaning, and finally rinsed with deionized water and dried with nitrogen gas to ensure tight adhesion between the photoresist and the substrate.
It effectively removes photoresist residue at the gaps of the folded waveguide, ensuring the integrity of the photoresist pattern and its tight adhesion to the substrate, avoiding the problems of photoresist swelling and detachment, and ensuring the smooth progress of subsequent processing.
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Figure CN115437226B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of microfabrication of vacuum electron devices. More particularly, it relates to a developing method of thick-film negative photoresist. BACKGROUND
[0002] The most basic feature of terahertz vacuum devices is high frequency and high voltage. In this frequency band, vacuum devices outperform solid-state devices, and have irreplaceability in radar, communication, electronic countermeasures, etc. With the continuous increase of the working frequency of terahertz vacuum devices, the size of its components has been reduced to tens of microns, and higher requirements have been put forward for the surface roughness. The continuous reduction of components means that traditional precision machining methods cannot produce samples that meet the size accuracy requirements. In order to meet the requirements of size accuracy and surface finish, microfabrication means is usually introduced to manufacture the slow wave structure of vacuum electron devices, which is where electrons and electromagnetic waves interact, and generally adopts a folded waveguide form (as shown in Figure 1 In the process of microfabrication technology manufacturing, the photoetching process is the basis and key step of the whole process. Generally, the photoetching process mainly includes the steps of coating, pre-baking, exposure, post-baking, development, etc.
[0003] With the continuous optimization of the folded waveguide structure, the gap size at the folding place has been smaller than the narrow edge width, and the narrowest gap width is only 40-50 μm. Compared with the development result of the traditional folded waveguide Figure 1 The absolute depth of this folded waveguide is large, and the photoresist film thickness is 300-400 μm. In particular, the photoresist at the folding gap of the folded waveguide is more difficult to dissolve than other positions, and the development process is more difficult. Simply increasing the development time not only cannot completely remove the residual photoresist at the gap, but also causes the photoresist film to swell and fall off due to the excessive soaking time in the development solution. Although the addition of ultrasonic cleaning increases the pressure on the surface of the photoresist, it can accelerate diffusion and development at the gap, but ultrasonic waves are extremely easy to cause pattern oscillation, and thus accelerate the cracking and falling off of the photoresist film. Therefore, how to develop without residual photoresist on the basis of tight adhesion of the photoresist to the substrate has become a challenge in the photoetching process of the folded waveguide. SUMMARY
[0004] To solve the above technical problems, the present application provides a developing method for microfabrication process in the field of vacuum electron technology, which can completely remove the photoresist difficult to dissolve at the gap of the folded waveguide, and also ensure the tight adhesion of the photoresist to the substrate.
[0005] To achieve the above purpose, the present application provides a developing method of thick-film negative photoresist, which comprises the following steps:
[0006] (1) Put the sample coated with photoresist to be developed into the developing solution for static development;
[0007] (2) The sample after static development continues to be treated with ultrasound in the developing solution for 10s-20s;
[0008] (3) The sample after ultrasound treatment is moved to isopropanol solution for cleaning;
[0009] (4) Steps (2) and (3) are repeated 2-3 times in turn;
[0010] (5) Rinse with deionized water and dry with nitrogen.
[0011] In the above method, the sample after static development is treated with ultrasound for a very short time, and the intermittent time between the two ultrasonic treatments is used for isopropanol cleaning operation. The role of the isopropanol cleaning operation has three effects: first, the continuous ultrasound process will produce a strong force on the sample, and setting the ultrasound intermittent time can avoid the deformation and falling of the photoresist caused by too long ultrasound time; second, the intermittent period avoids the swelling and falling of the photoresist caused by the photoresist contacting the developing solution for too long; third, the intermittent period uses isopropanol to clean the sample, and the characteristics of isopropanol dissolved in water can ensure that there is no impurity residue in the deionized water rinsing stage.
[0012] Further, the sample to be developed is used to prepare a folded waveguide. It can be understood that the sample to be developed is obtained after the substrate is coated with photoresist and then undergoes pre-baking, exposure and post-baking. Alternatively, the substrate is an oxygen-free copper substrate with a thickness of 5-10 mm.
[0013] Further, in step (1), the gap width of the folded waveguide at the folding part is 40-50 μm.
[0014] Further, in step (1), the thickness of the photoresist in the sample to be developed is 300-400 μm. It can be understood that the thickness of the photoresist here refers to the thickness of the photoresist coated on the sample.
[0015] Further, in step (1), the photoresist is a negative photoresist of the SU8-2000 series, which has high viscosity. Alternatively, the negative photoresist of the SU8-2000 series includes but is not limited to SU8-2000, SU8-2100 or SU8-2150, etc.
[0016] Further, in step (1), the main component of the developing solution is 1-methoxy-2-propyl acetate, ethyl lactate or dipropyl ketone alcohol.
[0017] Furthermore, in step (1), the static development time is 10-15 minutes. The short static development time allows the photoresist in the non-exposed area to dissolve in the developer solution, while ensuring that the photoresist in the exposed area remains tightly adhered to the substrate. If manual or mechanical shaking and stirring are added during the static development process, the photoresist film will loosen faster.
[0018] Optionally, in step (1), placing the sample upside down in the developing solution can ensure that the dissolved photoresist can be removed from the surface in time.
[0019] Furthermore, in step (2), the power of the ultrasonic treatment is 250W-300W. The ultrasonic treatment conditions of this invention can avoid problems such as pattern oscillation, accelerated photoresist cracking, and detachment caused by excessively long ultrasonic duration or excessive power.
[0020] Furthermore, in step (3), the cleaning time is 3-5 minutes.
[0021] Furthermore, in step (5), the resistivity of the deionized water is 18 MΩ·cm. This resistivity of deionized water results in fewer impurities and non-corrosiveness, ensuring the integrity and stability of the photoresist pattern structure.
[0022] Optionally, the rinsing time with deionized water is 3-5 minutes.
[0023] Furthermore, the method also includes observing the development results using an optical microscope.
[0024] Optionally, the criteria for judging clean development are that there is no residual photoresist in the gaps of the photoresist film under a microscope and the photoresist is tightly bonded to the copper substrate.
[0025] Furthermore, unless otherwise specified, any range described in this invention includes the endpoints, any values between the endpoints, and any sub-ranges formed by the endpoints or any values between the endpoints. There are no particular limitations on the purity of any raw materials used in this invention; however, analytical grade is preferred. The sources and abbreviations of all raw materials used in this invention are conventional sources and abbreviations in the art, and are clearly understood within the scope of their relevant uses. Those skilled in the art can obtain them from commercially available sources or prepare them using conventional methods based on their abbreviations and corresponding uses.
[0026] The beneficial effects of this invention are as follows:
[0027] 1. The development method provided by the present invention combines static development with multiple intermittent, short-time, low-power ultrasonic treatment processes to cleanly develop the photoresist that is difficult to remove from the fold gaps of small-sized folded waveguides.
[0028] 2、The developing method provided by the application effectively balances the problems of developing and photoresist peeling, clean photoresist film patterns closely adhered to the substrate can be obtained, and then the subsequent processing process is ensured to be carried out smoothly. BRIEF DESCRIPTION OF DRAWINGS
[0029] The specific embodiments of the application will be further described in detail below with reference to the accompanying drawings.
[0030] Figure 1 The developing results of a conventional folded waveguide sample are shown;
[0031] Figure 2 The developing results of the folded waveguide sample of Example 1 are shown;
[0032] Figure 3 The developing results of the folded waveguide sample of Comparative Example 1 are shown;
[0033] Figure 4 The developing results of the folded waveguide sample of Comparative Example 2 are shown;
[0034] Figure 5 The developing results of the folded waveguide sample of Comparative Example 3 are shown;
[0035] Figure 6 The developing results of the folded waveguide sample of Comparative Example 4 are shown. DETAILED DESCRIPTION
[0036] In order to further understand the application, the preferred embodiments of the application are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the application and are not a limitation on the patent claims of the application.
[0037] Example 1
[0038] A developing method of a thick film negative photoresist, comprising the following steps:
[0039] First step: prepare a 4-inch oxygen-free copper sheet with a thickness of 10 mm, spin coat 350 μm of SU8-2150 negative photoresist, and sequentially perform pre-baking, exposure, and post-baking processes. The negative photoresist exposure area is insoluble in the developing solution due to cross-linking reaction during post-baking, and the unexposed area is soluble in the developing solution during developing. After post-baking, a sample of the folded waveguide to be developed (the gap width at the folded part is 50 μm) is obtained, and the sample is inverted in an acetic acid-1-methoxy-2-propyl ester developing solution and left for 15 min.
[0040] Second step: ultrasonic treatment is performed on the sample soaked in the developing solution, the ultrasonic wave power is 300 W, and the ultrasonic treatment time is 15 s.
[0041] Third step: the sample is taken out of the developing solution, soaked in isopropyl alcohol, and inverted for 3 min.
[0042] Fourth step: transfer the sample from isopropyl alcohol to the developing solution, continue to ultrasonic for 15s, then take out and soak in isopropyl alcohol for 3min.
[0043] Fifth step: transfer the sample from isopropyl alcohol to the developing solution, ultrasonic for 10s, then take out and soak in isopropyl alcohol for 3min.
[0044] Sixth step: take out the sample from isopropyl alcohol, and rinse the surface of the sample with deionized water for 5min.
[0045] Seventh step: dry the sample with nitrogen, and observe the developing result by optical microscope.
[0046] The developing result is shown in Fig. 1, which shows that the photoresist at the gap of the folded waveguide is completely dissolved, the photoresist film pattern is clean, and the photoresist film is tightly adhered to the substrate. Figure 2
[0047] Example 2
[0048] A developing method of a thick film negative photoresist, comprising the following steps:
[0049] First step: prepare a 4-inch oxygen-free copper sheet with a thickness of 10mm, and spin-coat 400μm SU8-2150 negative photoresist. Perform the processes of pre-baking, exposure, and post-baking in sequence. The negative photoresist in the exposed area is insoluble in the developing solution after the cross-linking reaction in the post-baking process, and the unexposed area is soluble in the developing solution. After the post-baking process, obtain a sample of the folded waveguide to be developed (the gap width at the folded part is 50μm), and place the sample upside down in the 1-methoxy-2-propyl acetate developing solution for 15min.
[0050] Second step: ultrasonic the sample soaked in the developing solution, with an ultrasonic power of 300W and for 20s.
[0051] Third step: take out the sample from the developing solution, and soak it in isopropyl alcohol upside down for 3min.
[0052] Fourth step: transfer the sample from isopropyl alcohol to the developing solution, continue to ultrasonic for 20s, then take out and soak in isopropyl alcohol for 3min.
[0053] Fifth step: transfer the sample from isopropyl alcohol to the developing solution, ultrasonic for 10s, then take out and soak in isopropyl alcohol for 3min.
[0054] Sixth step: take out the sample from isopropyl alcohol, and rinse the surface of the sample with deionized water for 5min.
[0055] Seventh step: dry the sample with nitrogen, and observe the developing result by optical microscope.
[0056] The developing result is similar to that of Example 1.
[0057] Example 3
[0058] A developing method of thick-film negative photoresist, comprising the following steps:
[0059] First step: prepare 4-inch oxygen-free copper sheet with a thickness of 10 mm, spin-coat 300 μm SU8-2150 negative photoresist, and sequentially perform pre-baking, exposure, and post-baking processes. The exposed area of the negative photoresist is insoluble in the developing solution due to cross-linking reaction during post-baking, and the unexposed area is soluble in the developing solution during development. After post-baking, a sample of the folded waveguide to be developed (with a gap width of 50 μm at the folding part) is obtained, and the sample is inverted in an acetic acid-1-methoxy-2-propyl ester developing solution for 10 min.
[0060] Second step: ultrasonic treatment is performed on the sample immersed in the developing solution, with an ultrasonic power of 250 W and an ultrasonic time of 10 s.
[0061] Third step: the sample is taken out of the developing solution and immersed in isopropyl alcohol for 3 min.
[0062] Fourth step: the sample is transferred from isopropyl alcohol to the developing solution, and after 10 s of ultrasonic treatment, the sample is taken out and immersed in isopropyl alcohol for 3 min.
[0063] Fifth step: the sample is transferred from isopropyl alcohol to the developing solution, and after 10 s of ultrasonic treatment, the sample is taken out and immersed in isopropyl alcohol for 3 min.
[0064] Sixth step: the sample is taken out of isopropyl alcohol, and the surface of the sample is washed with deionized water for 5 min.
[0065] Seventh step: the sample is dried with nitrogen, and the developing result is observed by an optical microscope.
[0066] The developing result is similar to that of Example 1.
[0067] Comparative Example 1
[0068] A developing method of thick-film negative photoresist, comprising the following steps:
[0069] First step: prepare 4-inch oxygen-free copper sheet with a thickness of 10 mm, spin-coat 350 μm SU8-2150 negative photoresist, and sequentially perform pre-baking, exposure, and post-baking processes. The exposed area of the negative photoresist is insoluble in the developing solution due to cross-linking reaction during post-baking, and the unexposed area is soluble in the developing solution during development. After post-baking, a sample of the folded waveguide to be developed (with a gap width of 50 μm at the folding part) is obtained, and the sample is inverted in an acetic acid-1-methoxy-2-propyl ester developing solution for 20 min.
[0070] Second step: the sample is taken out of the developing solution and immersed in isopropyl alcohol for 3 min.
[0071] Third step: take out the sample from isopropyl alcohol, rinse the sample surface with deionized water for 5 min, dry the sample with nitrogen, and observe the development result with an optical microscope.
[0072] The development result is shown in FIG. 1, which shows that the photoresist at the gap of the folded waveguide cannot be dissolved, and the photoresist pattern is not clean. Moreover, due to the long soaking time in the developer, the adhesion of the photoresist pattern is reduced, and the photoresist is partially peeled off. Figure 3
[0073] Comparative Example 2
[0074] A development method of a thick film negative photoresist, comprising the following steps:
[0075] First step: prepare a 4-inch oxygen-free copper sheet with a thickness of 10 mm, spin-coat 350 μm of SU8-2150 negative photoresist, and sequentially perform pre-baking, exposure, and post-baking processes. The negative photoresist in the exposed area is cross-linked and insoluble in the developer during post-baking, and the unexposed area is soluble in the developer during development. After post-baking, a sample of a folded waveguide to be developed (the gap width at the folded part is 50 μm) is obtained, and the sample is inverted in an ethyl acetate-1-methoxy-2-propyl ester developer for ultrasonic treatment for 3 min (the ultrasonic power is 300 W).
[0076] Second step: let the sample soaked in the developer stand for 12 min.
[0077] Third step: perform ultrasonic treatment on the sample soaked in the developer, with an ultrasonic power of 250 W and for 10 s.
[0078] Fourth step: take out the sample from the developer, and soak it in isopropyl alcohol for 3 min.
[0079] Fifth step: transfer the sample from isopropyl alcohol to the developer, continue ultrasonic treatment for 10 s, and then take it out and soak it in isopropyl alcohol for 3 min.
[0080] Sixth step: transfer the sample from isopropyl alcohol to the developer, perform ultrasonic treatment for 10 s, and then take it out and soak it in isopropyl alcohol for 3 min.
[0081] Seventh step: take out the sample from isopropyl alcohol, and rinse the sample surface with deionized water for 5 min.
[0082] Eighth step: dry the sample with nitrogen, and observe the development result with an optical microscope.
[0083] The development result is shown in FIG. 1, which shows that the photoresist at the gap of the folded waveguide cannot be dissolved, and the photoresist pattern is not clean. Moreover, due to the long soaking time in the developer, the adhesion of the photoresist pattern is reduced, and the photoresist is partially peeled off. Figure 4
[0084] Comparative Example 3
[0085] A developing method of thick-film negative photoresist, comprising the following steps:
[0086] Step 1: Prepare a 4-inch oxygen-free copper sheet with a thickness of 10 mm, spin-coat 350 μm of SU8-2150 negative photoresist, and sequentially perform pre-baking, exposure, and post-baking processes. The exposed area of the negative photoresist is insoluble in the developing solution due to cross-linking reaction during post-baking, and the unexposed area is soluble in the developing solution during development. After post-baking, a sample of the folded waveguide to be developed (with a gap width of 50 μm at the folding part) is obtained, and the sample is inverted in an acetic acid-1-methoxy-2-propyl ester developing solution for 15 min.
[0087] Step 2: Ultrasonically treat the sample immersed in the developing solution, with an ultrasonic power of 300 W and ultrasonic treatment for 15 s.
[0088] Step 3: Take out the sample from the developing solution, immerse it in isopropyl alcohol, and invert it for 3 min.
[0089] Step 4: Rinse the surface of the sample with deionized water for 5 min, dry the sample with nitrogen, and observe the development result with an optical microscope.
[0090] The development result is shown in FIG. 1, which shows that the adhesion of the photoresist to the substrate is good, but the development at the gap is incomplete and the photoresist film is not clean. Figure 5
[0091] Comparative Example 4
[0092] A developing method of thick-film negative photoresist, comprising the following steps:
[0093] Step 1: Prepare a 4-inch oxygen-free copper sheet with a thickness of 10 mm, spin-coat 350 μm of SU8-2150 negative photoresist, and sequentially perform pre-baking, exposure, and post-baking processes. The exposed area of the negative photoresist is insoluble in the developing solution due to cross-linking reaction during post-baking, and the unexposed area is soluble in the developing solution during development. After post-baking, a sample of the folded waveguide to be developed (with a gap width of 50 μm at the folding part) is obtained, and the sample is inverted in an acetic acid-1-methoxy-2-propyl ester developing solution for 15 min.
[0094] Step 2: Ultrasonically treat the sample immersed in the developing solution, with an ultrasonic power of 300 W and ultrasonic treatment for 15 s.
[0095] Step 3: Take out the sample from the developing solution, immerse it in isopropyl alcohol, and invert it for 30 s.
[0096] Step 4: Transfer the sample from isopropyl alcohol to the developing solution, continue ultrasonic treatment for 15 s, then take it out and immerse it in isopropyl alcohol for 30 s.
[0097] Step 5: The sample was transferred from isopropanol to the developing solution, and after 10 seconds of ultrasonic treatment, the sample was taken out and soaked in isopropanol for 30 seconds.
[0098] Step 6: The sample was taken out from isopropanol and the surface of the sample was rinsed with deionized water for 5 minutes.
[0099] Step 7: The sample was dried with nitrogen, and the developing result was observed by optical microscope.
[0100] The developing result is shown in Fig. 1. Figure 6 It can be seen from the figure that the adhesion between the photoresist and the substrate is good, but the photoresist dissolved on the surface of the pattern has not completely separated from the substrate, and the cleaning is not complete.
[0101] Obviously, the above-mentioned embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. For those skilled in the art, other different forms of changes or variations can be made on the basis of the above description, and it is impossible to enumerate all the embodiments here. Any obvious changes or variations derived from the technical solutions of the present application still fall within the protection scope of the present application.
Claims
1. A method for developing a thick-film negative photoresist for microfabrication processes in the field of vacuum electronics, characterized in that, The method comprises the following steps: (1) inverting a sample to be developed coated with photoresist in a developing solution to perform static development, the time of the static development being 10-15 min; wherein the thickness of the photoresist in the sample to be developed is 300-400 μm; the sample to be developed is obtained after the photoresist is coated on a substrate and then the substrate is subjected to pre-baking, exposure and post-baking; the substrate is oxygen-free copper substrate; (2) continuing to place the sample after static development in the developing solution to perform ultrasonic treatment for 10-20 s, the power of the ultrasonic treatment being 250-300 W; (3) inverting the sample after ultrasonic treatment to immerse in an isopropyl alcohol solution for 3-5 min; (4) repeating steps (2) and (3) for 2-3 times in turn; (5) rinsing with deionized water and blowing dry with nitrogen; the sample to be developed is used to prepare a folded waveguide; the gap width of the folded waveguide at the folded part is 40-50 μm.
2. The method of claim 1, wherein, In step (1), the photoresist is SU8-2000 series negative photoresist.
3. The method of claim 1, wherein, In step (1), the main component of the developing solution is 1-methoxy-2-propyl acetate, ethyl lactate or diacetone alcohol.
4. The method of claim 1, wherein, In step (5), the resistivity of the deionized water is 18 MΩ·cm.
5. The method of claim 1, wherein, The method further comprises observing the development result by an optical microscope.
Citation Information
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