Preparation method for reducing angle of inverted trapezoidal isolation column of photoresist

Abstract

The invention provides a preparation method for reducing the angle of a photoresist inverted trapezoidal isolation column, which comprises the following steps: preparing a crystal violet solution with the concentration of 50-200mg / L in a yellow light environment; the photoresist added with the crystal violet solution is obtained; the crystal violet solution and the polysorbate-20 solution are added into the photoresist; placing the photoresist added with the crystal violet solution and the polysorbate-20 solution in a refrigerator at 1-10 DEG C for 20-30 hours, and screening out the photoresist without precipitation as the final photoresist; the final inverted trapezoidal isolation column is prepared; according to the method, the chamfer angle of the exposed pattern can be effectively increased, so that the side wall is changed into a more inclined slope shape from a steep shape.

Description

Technical Field

[0001] This invention relates to a method for preparing inverted trapezoidal isolation pillars for reducing the angle of photoresist, belonging to the field of photolithography technology. Background Technology

[0002] Currently, in the practical application of passive matrix organic light-emitting diode (PMOLED) displays, inverted trapezoidal photoresist structures are fabricated to isolate the vapor-deposited materials. To create these inverted trapezoidal photoresist structures, negative photoresist is typically used for exposure. The exposed negative photoresist is then developed and retained, while the negative photoresist in the unexposed areas is removed by the developer. Traditional processes theoretically can form inverted trapezoidal structures through a single exposure and by utilizing the diffraction effect of light.

[0003] However, due to limitations in exposure equipment and photoresist properties, the light diffraction area is small, resulting in an excessively steep tilt angle for the manufactured isolation pillars. The measured angles are approximately 79° and 80°, close to right angles. The insufficient tilt slope makes it impossible to effectively isolate the vapor-deposited material and fails to meet process requirements. Summary of the Invention

[0004] The purpose of this invention is to provide a method for reducing the angle of inverted trapezoidal isolation pillars in photoresist, thereby solving the problem of excessively steep tilt angles of isolation pillars in the prior art.

[0005] The technical solution of this invention is: A method for fabricating inverted trapezoidal isolation pillars for reducing the angle of photoresist includes the following steps: Step 1: Prepare a crystal violet solution with a concentration of 50-200 mg / mL in a yellow light environment; Step 2: Mix the crystal violet solution and photoresist at a ratio of 150ml-250ml:1 gallon to obtain the photoresist after adding the crystal violet solution; Step 3: Add 3-5 ml of polysorbate-20 solution to the photoresist after adding crystal violet solution to obtain the photoresist after adding crystal violet solution and polysorbate-20 solution; Step 4: Place the photoresist after adding crystal violet solution and polysorbate-20 solution in a refrigerator at 1-10℃ for 20-30 hours to obtain the final photoresist; Step 5: After the final photoresist is fed into the inverted trapezoidal isolation pillar production line for cleaning, coating, exposure, and development, the final inverted trapezoidal isolation pillar is obtained.

[0006] Further, a crystal violet solution with a concentration of 100 mg / L was prepared.

[0007] Further, in step 1, a crystal violet solution with a concentration of 50-200 mg / mL is prepared by adding a diluent to a beaker, placing a magnetic rotor at the bottom of the beaker, and rotating the beaker on a magnetic rotating base to pour the crystal violet powder into the beaker until the powder is completely dissolved.

[0008] Furthermore, in step 1, the diluent is a mixture of propylene glycol ethyl ether (PGME) and propylene glycol methyl ether acetate (PGMEA) in a volume ratio of 7:3, and the water content of the diluent is less than 0.05%.

[0009] Furthermore, in step 2, the ratio of crystal violet solution to photoresist is 200 ml: 1 gallon.

[0010] Furthermore, in step 3, the polysorbate-20 solution is 4 ml.

[0011] The beneficial effects of this invention are as follows: This method for preparing inverted trapezoidal isolation pillars for reducing the angle of photoresist, by adding crystal violet and polysorbate-20 solution (i.e., Tween 20 solution) to negative photoresist, and mixing them evenly before applying them to the photoresist for exposure and development, can effectively increase the chamfer angle of the pattern after exposure, making the sidewalls change from a relatively steep straight shape to a more inclined slope, thereby effectively isolating the vapor-deposited material, reducing defects such as line runs caused by insufficient isolation pillar angle, and improving production yield. This method uses photoresist with added dye to produce products with relatively good chamfer angle stability, making it easier to adjust T-shaped isolation pillars with the required chamfer angle, and providing a larger process window. Attached Figure Description

[0012] Figure 1 This is a schematic flowchart of a method for preparing a photoresist inverted trapezoidal isolation pillar for reducing the angle of the isolation pillars, according to an embodiment of the present invention. Detailed Implementation

[0013] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0014] The embodiment provides a method for fabricating inverted trapezoidal isolation pillars of photoresist to reduce their angle, such as Figure 1 This includes the following steps: Step 1: Prepare a crystal violet solution with a concentration of 50-200 mg / L in a yellow light environment.

[0015] Step 2: Mix the crystal violet solution and photoresist at a ratio of 150ml-250ml:1 gallon to obtain the photoresist with added crystal violet solution.

[0016] Step 3: Add 3-5 ml of polysorbate-20 solution to the photoresist after adding crystal violet solution to obtain the photoresist after adding crystal violet solution and polysorbate-20 solution.

[0017] Step 4: After adding crystal violet solution and polysorbate-20 solution, place the photoresist in a refrigerator at 1-10℃ for 20-30 hours, and then screen out the photoresist without precipitation as the final photoresist.

[0018] Step 5: After the final photoresist is fed into the inverted trapezoidal isolation pillar production line for cleaning, coating, exposure, and development, the final inverted trapezoidal isolation pillar is obtained.

[0019] This method for preparing inverted trapezoidal isolation pillars in photoresist involves adding crystal violet and polysorbate-20 solution (i.e., Tween 20 solution) to negative photoresist. After uniform mixing, the mixture is used for coating, exposure, and development. This effectively increases the chamfer angle of the exposed pattern, changing the sidewalls from steep to more sloping. This effectively isolates the vapor-deposited material, reduces defects such as line runs caused by insufficient isolation pillar angle, and improves production yield. This method uses photoresist with added dye to produce products with relatively good chamfer angle stability, making it easier to adjust T-shaped isolation pillars with the required chamfer angle and providing a wider process window.

[0020] The fabrication method for reducing the angle of the inverted trapezoidal isolation pillars in the embodiment was experimentally tested as follows: The negative photoresist ENPI300 from Taiwan Yongguang Chemical Industry Co., Ltd., pure crystal violet powder from Shanghai Jizhi Biochemical Technology Co., Ltd., diluent from Jiangsu Kewotai Materials Technology Co., Ltd., and pure Tween-20 solution from Shandong Tuopu Bioengineering Co., Ltd. were used in this preparation. The preparation must be carried out in a yellow light laboratory without ultraviolet irradiation.

[0021] Step 1: Place 1L of diluent in a beaker, place the magnetic rotor at the bottom of the beaker, and put the beaker on the magnetic rotating base. Turn on the rotation. Pour 100g of crystal violet powder into the beaker. After the powder is completely dissolved, turn off the magnetic rotating switch to obtain a crystal violet solution. The above method prepares a 100 mg / mL solution of crystal violet powder with the diluent. The diluent consists of propylene glycol ethyl ether (PGME) and propylene glycol methyl ether acetate (PGMEA) in a 7:3 ratio, and the water content of the diluent is less than 0.05%.

[0022] Step 2: Prepare five portions of each of the following five crystal violet solutions: 50ml, 100ml, 150ml, 200ml, and 250ml. Also prepare 25 bottles of 1-gallon ENPI300 negative photoresist. Mix the crystal violet solution and photoresist separately. Mixing method: Use a measuring cup to add 50ml of crystal violet solution to the photoresist each time. Shake the photoresist repeatedly for 3 minutes after each addition. This will yield 25 bottles of photoresist with 50ml, 100ml, 150ml, 200ml, and 250ml of solution added, with 5 portions of each solution. Step 3: For each type of photoresist with added crystal violet solution concentration, keep one bottle of each. To add the remaining photoresist: using a burette, add 2ml, 3ml, 4ml, and 5ml of Tween-20 solution to the photoresist with each of the five crystal violet solution concentrations. After each addition, shake the photoresist repeatedly for 3 minutes. This will result in photoresist with different Tween-20 solution concentrations. Each type of photoresist with added crystal violet solution concentration will have five different Tween-20 solution concentrations (including the one without added crystal violet solution). Step 4: Place the 25 bottles of prepared photoresist in a refrigerator at 1-10℃ for 24 hours. After 24 hours, remove them and observe them under a Na lamp to check for any precipitates, as shown in Table 1. Table 1. Results of precipitates with different amounts of crystal violet photoresist solution added.

[0023] Because deposits in the photoresist can lead to foreign matter on the film surface after subsequent coating, affecting pattern formation and causing anomalies such as side etching, excessive addition of Tween-20 solution may cause problems: it can excessively reduce the surface tension of the photoresist, affecting coating uniformity. During spin coating, excessively low surface tension can cause the photoresist to spread excessively on the substrate surface, forming an uneven coating thickness. Especially in the substrate edge area, a "thick edge" phenomenon is prone to occur, that is, the adhesive layer at the edge is significantly thicker than that in the center area. To address the above issues, the photoresist without deposits in Table 1 was used to prepare the coated samples to ensure that the subsequent coated film surface is free of foreign matter, and the dry film thickness was measured using a film thickness gauge. Here, the photoresist uniformity standard of the substrate film should not be less than 95%. The film thickness uniformity needs to be calculated using the measured intra-wafer maximum value Hmax and intra-wafer minimum value Hmin, and the calculation formula is: 1 - ((Hmax-Hmin) / (Hmax+Hmin)). The fabrication process parameters are shown in Table 2: Table 2. Process parameters for photoresist fabrication and coating

[0024] After the above steps, sample preparation and film thickness measurement were performed, and the results are shown in Table 3: Table 3. Film thickness of photoresist with different amounts of Tween-20 solution added.

[0025] Based on the above measurement results, the Tween-20 solution addition schemes with the best film thickness uniformity corresponding to different amounts of crystal violet solution were selected, as shown in Table 4: Table 4. Uniformity of film thickness in photoresist coating with different amounts of Tween-20 solution.

[0026] Step 5: Too little crystal violet will have an insignificant effect, while too much will lead to excessive light absorption, resulting in insufficient exposure at the bottom of the photoresist and inadequate cross-linking, potentially causing defects such as delamination or pattern undercutting. Furthermore, excessive crystal violet may cause localized aggregation in the photoresist, leading to uneven stress distribution and reduced overall adhesion. Lateral light scattering and excessive gradient changes may slightly reduce the pattern's limiting resolution. To address these issues, five bottles of photoresist prepared as shown in Table 4 and one bottle of photoresist without added crystal violet solution were used in the inverted trapezoidal isolation pillar fabrication line for cleaning, coating, exposure, and development. To obtain the required top width of 10µm (critical linewidth) after development, adjustments were made to EXP (exposure) and PEB (post-exposure baking) as shown in Table 5. Cleaning, IR, coating, development, and post-baking were performed under the same conditions as shown in Table 6. The process parameters are as follows: Table 5. Process parameters for preparing inverted trapezoidal isolation columns

[0027] Table 6 Process parameters for cleaning, IR, coating, developing, and post-baking

[0028] After sample preparation following the above process, the critical linewidth data after development corresponding to different amounts of crystal violet solution added are shown in Tables 7 and 8. Here, the top and bottom width values ​​and corresponding differences of the critical linewidths at five locations on the substrate produced under each condition are recorded.

[0029] Table 7. Key linewidth data after development for different amounts of crystal violet solution added.

[0030] Table 8. Data on the difference between the top and bottom critical linewidths after development for different amounts of crystal violet solution added.

[0031] Based on past debugging experience, if the difference between the top and bottom of the critical linewidth after development is less than 3µm, there is a risk of an excessively steep chamfer angle, which would fail to stably and effectively isolate the vapor-deposited material. Therefore, samples prepared with 0ml, 50ml, and 100ml of crystal violet solution do not meet production requirements.

[0032] SEM cross-sectional analysis was performed on inverted trapezoidal isolation column samples prepared with crystal violet solution additions of 150ml, 200ml, and 250ml, as shown in Table 9. Based on previous debugging experience, to ensure stable and effective isolation of the vapor-deposited material after substrate development during production, the chamfer angle of the sample sheet is preferably less than 70°.

[0033] Table 9. SEM cross-sectional analysis results of the inverted trapezoidal isolation column

[0034] Conduct a cross-cut test: Place the test pieces prepared under the corresponding conditions of 200ml and 250ml crystal violet solution additions on a marble platform. Under a magnifying glass, use a cross-cut blade to draw approximately 1mm x 1mm squares in the test area (exposing the underlying glass). Measure the squares with a ruler to confirm their dimensions. After drawing the squares, gently brush away any impurities from the scratched surface with a soft brush and inspect the cut edges. Intersect the original cut lines at 90° to form a grid pattern, with 10 squares in each direction, for a total of 100 small square areas. Press the center of 3M tape onto the grid and quickly tear the sealant at a 45° angle. The product's cross-cut test result must be ≥4B. Cross-cut test results: Test pieces prepared under the corresponding conditions of 200ml and 250ml crystal violet solution additions showed no peeling, meeting production requirements.

[0035] Resolution confirmation: The mask used for sample preparation had lines with a width of 1-20 μm. After development, it was confirmed that the lines with a width of 1-20 μm were 4-20 μm and 6-20 μm respectively, prepared under the conditions of 200 ml and 250 ml of crystal violet solution addition, respectively. Therefore, the sample prepared under the condition of 200 ml of crystal violet solution addition had higher resolution.

[0036] Based on the above experiments, it has been confirmed that by adding 200 ml of crystal violet solution and 4 ml of Tween-20 solution to 1 gallon of negative photoresist ENPI300, and following the methods in Tables 5 and 6, isolation columns with a chamfer angle within 65°, adhesion reaching 5B, and good resolution can be prepared. Furthermore, these columns do not crystallize when stored at 1-10℃ and have a film thickness uniformity of over 95%.

[0037] This method for preparing inverted trapezoidal isolation pillars in photoresist utilizes crystal violet, chemically known as methyl violet. As a triphenylmethane dye, crystal violet strongly absorbs light of specific wavelengths, exhibiting multiple characteristic absorption peaks in the ultraviolet-visible region, with absorption characteristics extending across the 200-800 nm range. In photolithography, this characteristic creates a top-to-bottom light intensity gradient, resulting in a higher degree of cross-linking at the top of the photoresist compared to the bottom. During development, this cross-linking gradient transforms into a sloping sidewall profile. Simultaneously, crystal violet dye absorbs reflected light, effectively suppressing standing wave effects, thus achieving smoother, more uniform sidewalls and improving chamfer quality. The crystal violet molecule contains multiple aromatic rings and polar groups. These structures can form stronger intermolecular forces with resin molecules in the photoresist, including π-π stacking, hydrogen bonding, and dipole-dipole interactions, thereby enhancing the adhesion between the photoresist and the substrate and strengthening the adhesion mechanism.

[0038] The principle behind this method for preparing inverted trapezoidal isolation pillars in photoresist, using the addition of crystal violet dye to negative photoresist, is explained as follows: 1) The main function of crystal violet is to selectively absorb photons of the exposure wavelength. This causes the light intensity to gradually decrease as it penetrates the photoresist, thus creating a top-to-bottom light intensity gradient in the vertical direction (Z-axis) of the photoresist. The top is the strongest illuminated area, and the bottom is the weakest, creating a light intensity gradient; 2) In negative photoresist, the illuminated area undergoes a cross-linking reaction and becomes insoluble. Due to the light intensity gradient, the degree of cross-linking at the top of the photoresist is much higher than at the bottom, forming a cross-linking degree gradient; 3) During development, although the cross-linked parts are insoluble, the sidewall edges form a transition zone where the cross-linking density gradually decreases from top to bottom. The developer slightly erodes the top edge area with lower cross-linking degree, thus etching out a slanted angle. The more significant the light intensity gradient, the larger the chamfer angle, resulting in a slanted chamfer.

[0039] This method for preparing photoresist inverted trapezoidal isolation pillars addresses the issue that, based on the physicochemical properties of crystal violet, its precipitation temperature in propylene glycol methyl ether acetate (PGMEA) typically occurs at a low temperature of 4-10°C as its concentration increases. When the temperature decreases, the solubility of crystal violet decreases significantly, leading to supersaturation and ultimately crystal precipitation. Since photoresist is stored at 1-10°C, this necessitates increasing solution stability. Therefore, adding a surfactant is employed. Surfactant molecules can adsorb onto the surface of the forming microcrystals, hindering further crystal growth and acting as a "crystal inhibitor."

[0040] Meanwhile, Tween-20 is a polyoxyethylene nonionic surfactant, chemically named polyoxyethylene sorbitan monolaurate. Its molecular structure contains approximately 20 ethylene oxide units, with the hydrophobic end being laurate and the hydrophilic end being a polyoxyethylene chain. As a nonionic surfactant, Tween-20 does not carry a charge and does not electrostatically interact with PGMEA. This nonionic property allows it to be compatible with various solvent systems without interfering with the system's chemical equilibrium. Tween-20 is mainly used as a wetting agent and leveling agent in photolithography processes. Its mechanisms of action include: reducing surface tension: by adsorbing at the solid-liquid interface, it reduces the surface tension of the photoresist, improving wettability to the substrate; improving coating performance: it promotes uniform spreading of the photoresist on the substrate surface, reducing coating defects such as pinholes and thick edges; and enhancing adhesion: by improving wetting properties, it indirectly improves the adhesion between the photoresist and the substrate.

[0041] The advantages of adding Tween-20 to photoresists are as follows: Good chemical stability: unaffected by acids, alkalis, and salts, and has good compatibility with other components in the photoresist; Low foaming: does not foam during the photolithography process, which is beneficial to process stability; Mildness: will not have a destructive effect on the resin and photosensitizer in the photoresist; Improved resolution: obtains clearer pattern edges by improving wettability; Enhanced uniformity: reduces defects such as uneven coating and thick edges; Improved process window: expands the operating window of the photolithography process and improves process stability.

[0042] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing photoresist inverted trapezoidal isolation pillars, characterized in that: Includes the following steps, Step 1: Prepare a crystal violet solution with a concentration of 50-200 mg / L in a yellow light environment; Step 2: Mix the crystal violet solution and photoresist at a ratio of 150ml-250ml:1 gallon to obtain the photoresist after adding the crystal violet solution; Step 3: Add 3-5 ml of polysorbate-20 solution to the photoresist after adding crystal violet solution to obtain the photoresist after adding crystal violet solution and polysorbate-20 solution; Step 4: After adding crystal violet solution and polysorbate-20 solution, place the photoresist in a refrigerator at 1-10℃ for 20-30 hours, and then screen out the photoresist without precipitation as the final photoresist. Step 5: After the final photoresist is fed into the inverted trapezoidal isolation pillar production line for cleaning, coating, exposure, and development, the final inverted trapezoidal isolation pillar is obtained.

2. The method for preparing photoresist inverted trapezoidal isolation pillars as described in claim 1, characterized in that: Prepare a crystal violet solution with a concentration of 100 mg / L.

3. The method for preparing photoresist inverted trapezoidal isolation pillars as described in claim 1, characterized in that: In step 1, a crystal violet solution with a concentration of 50-200 mg / L is prepared by adding the diluent to a beaker, placing a magnetic rotor at the bottom of the beaker, and rotating the beaker on a magnetic rotating base to pour the crystal violet powder into the beaker until the powder is completely dissolved.

4. The method for preparing photoresist inverted trapezoidal isolation pillars as described in claim 3, characterized in that: In step 1, the diluent is a mixture of propylene glycol ethyl ether (PGME) and propylene glycol methyl ether acetate (PGMEA) in a volume ratio of 7:3, and the water content of the diluent is less than 0.05%.

5. The method for preparing photoresist inverted trapezoidal isolation pillars as described in any one of claims 1-3, characterized in that: In step 2, the ratio of crystal violet solution to photoresist is 200 ml to 1 gallon.

6. The method for preparing photoresist inverted trapezoidal isolation pillars as described in any one of claims 1-3, characterized in that: In step 3, the polysorbate-20 solution is 4 ml.

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