Coating method for improving rotation MURA of TFT-LCD color filter

Abstract

The invention discloses a coating method for improving rotation MURA of a TFT-LCD color filter. The coating method comprises the following steps of photoresist preparation, wherein photoresist with the viscosity ranging from 2.8 cP to 3.2 cP is provided; the photoresist is dropwise added to the surface of the glass substrate, spin coating is carried out at the rotation speed N, the rotation speed N is cooperated with the viscosity of the photoresist, and the rotation speed reduction amplitude of the rotation speed N relative to the original rotation speed N is controlled within the range of 50-100 rpm. Therefore, the viscosity of the photoresist is reduced, and the rotating speed of coating is synchronously reduced, so that the viscosity of the photoresist and the rotating speed of coating are cooperatively matched, the viscous resistance of a photoresist solution can be reduced, the excessive stretching effect of a centrifugal force is weakened, the formation of a film thickness gradient is avoided, and the defects of bright and dark stripes of a rotating MURA are greatly reduced; and meanwhile, the film thickness uniformity can be improved without modifying existing equipment, the stability of subsequent procedures is guaranteed, and the manufacturing cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of display technology, and in particular to a coating method for improving the rotating MURA of TFT-LCD color filters. Background Technology

[0002] In the manufacturing process of TFT-LCD color filters (CF), RGB photoresist coating is one of the core steps. Currently, the industry commonly uses spin coating to achieve uniform photoresist coverage: the centrifugal force generated by high-speed rotation evenly distributes the photoresist on the surface of the glass substrate. During spin coating, if the photoresist viscosity and rotation speed are not properly matched, the photoresist solution can easily form concentric or radial film thicknesses on the substrate surface, resulting in spin MURA defects. These defects manifest as ring-shaped or radial uneven brightness in the panel display, directly affecting display quality and product yield.

[0003] Traditional coating processes typically use high-viscosity photoresists and apply them at a fixed rotation speed. However, due to poor matching between the photoresist viscosity and rotation speed, the photoresist solution spreads unevenly during centrifugal coating, resulting in poor film thickness uniformity and a high rate of rotational mutagenesis (MMURA) defects. Furthermore, simply adjusting the viscosity or rotation speed cannot fundamentally improve rotational mutagenesis defects, making it difficult to meet mass production yield requirements.

[0004] In view of the above, an improved coating method for rotating MURA of TFT-LCD color filters is proposed. Summary of the Invention

[0005] The purpose of this invention is to overcome at least one deficiency in the prior art and provide an improved coating method for rotating MURA of TFT-LCD color filters. By synergistically adapting the photoresist viscosity to the rotation coating speed, the uniformity of the photoresist film thickness is improved, thereby effectively suppressing rotating MURA defects and increasing the production yield.

[0006] The objective of this invention is achieved through the following technical solution: A coating method for improving the rotating MURA of a TFT-LCD color filter, characterized by comprising the following steps: Photoresist preparation: Provide photoresist with a viscosity of 2.8 cP~3.2 cP; Spin coating: The photoresist is dropped onto the surface of a glass substrate and spin-coated at a rotation speed N, wherein the rotation speed N is coordinated with the viscosity of the photoresist, and the reduction in rotation speed N relative to the original rotation speed N0 is controlled within the range of 50 rpm to 100 rpm.

[0007] In one embodiment, the original rotational speed N0 is 300 rpm to 500 rpm, and the rotational speed N is 200 rpm to 450 rpm.

[0008] In one embodiment, the original rotational speed N0 is 350 rpm, the rotational speed N is reduced from the original rotational speed N0 to 280 rpm, and the photoresist viscosity is 3.0 cP.

[0009] In one embodiment, prior to the spin coating step, the following steps are also included: Substrate pretreatment: Cleaning and drying the glass substrate.

[0010] In one embodiment, during the substrate pretreatment step: The glass substrate is cleaned by washing with water. The drying temperature is 110℃ and the drying time is 130s.

[0011] In one embodiment, after the spin coating step, the following steps are further included: Curing process: The photoresist coated on the glass substrate is thermally cured to form a photoresist film layer.

[0012] In one embodiment, during the curing process step: The thermosetting temperature is 230℃ and the thermosetting time is 30min.

[0013] In one embodiment, after the curing process step, the following steps are further included: Testing and verification: The uniformity of the thickness of the photoresist film layer on the glass substrate is tested.

[0014] In one embodiment, during the detection and verification step: The thickness of the photoresist film on the glass substrate was measured using a film thickness gauge. Thickness data were collected at nine measurement points. The uniformity of the photoresist film thickness was calculated using the following formula: (max-min) / (max+min)×100%; Where: max is the maximum thickness of the photoresist film layer among the 9 measurement points, and min is the minimum thickness of the photoresist film layer among the 9 measurement points.

[0015] In one embodiment, the photoresist is any one of RGB photoresists.

[0016] Compared with the prior art, the present invention has at least the following advantages: 1. The improved coating method for rotating MURA of TFT-LCD color filters of the present invention abandons the traditional process of using 4cP high-viscosity photoresist with a fixed high rotation speed, and adopts a 2.8cP~3.2cP low-viscosity photoresist with a low rotation speed. On the one hand, it can reduce the internal viscosity resistance of the photoresist solution, weaken fluid disturbance and local accumulation phenomenon. On the other hand, by reducing the coating rotation speed, the rotation speed is reduced synchronously from the original rotation speed, thereby weakening the excessive stretching effect of centrifugal force and avoiding the formation of concentric and radial film thickness gradients. This reduces the defects of bright and dark stripes in rotating MURA, significantly reducing the product defect rate from the industry average of 8%~12% to an extremely low level, and significantly improving the display quality of the panel and the yield of finished products.

[0017] 2. The improved coating method for rotating MURA of TFT-LCD color filters of the present invention solves the unrepairable rotating MURA defect from the source, reduces the scrap of defective substrates, reduces raw material and production capacity losses, and does not require modification of existing coating equipment, saving high hardware upgrade costs and debugging cycles, significantly reducing the manufacturing cost of a single substrate and improving production efficiency.

[0018] 3. The improved coating method for rotating MURA of TFT-LCD color filters of the present invention coordinates and adapts the viscosity of the optical adhesive to the rotation speed of the coating process, simultaneously solving the problems of thin film at the edges of low-viscosity adhesives and uneven film thickness in the center at low rotation speeds. This achieves uniform adhesive spreading across the entire substrate area, improves film thickness uniformity, and ensures stable subsequent processes and consistent optical adhesive film performance. Furthermore, it enables process standardization, ease of control, and high fault tolerance, allowing for adaptation to existing production lines without complex debugging, thus overcoming industry equipment optimization bottlenecks. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below.

[0020] Figure 1 This is a schematic diagram of the steps in an embodiment of the present invention to improve the coating method of rotating MURA for TFT-LCD color filters; Figure 2 This is a schematic diagram of the rotating flow of photoresist. Figure 3 This is a schematic diagram of rotating MURA on a glass substrate. Detailed Implementation

[0021] To facilitate understanding of the present invention, a more comprehensive description of the present invention will be given below with reference to the accompanying drawings. This embodiment is only used to explain the present invention and is not intended to limit the scope of protection of the present invention.

[0022] Comparative example (traditional process): High viscosity photoresist with a viscosity of 4.0±0.2cP is used, combined with high-speed coating at 300rpm~500rpm.

[0023] The above traditional processes can create uneven thickness of the photoresist film layer on the substrate surface, forming concentric or radial patterns, resulting in rotating mura and causing bright and dark stripes on the display screen. The product defect rate is as high as 8%-12%. (See also...) Figure 2 The diagram illustrates the rotational flow of photoresist. A glass substrate is placed on a rotating disk of a spin coating apparatus. After photoresist is applied to the glass substrate, the rotating disk drives the substrate, causing the photoresist to distribute onto the substrate surface under centrifugal force. However, due to the large thickness uniformity error of the photoresist film after spin coating, rotational MURA occurs. Please refer to [link to relevant documentation]. Figure 3 The diagram shows a radiating pattern of light and dark stripes on a glass substrate. Rotational MURA is an unrepairable defect, and defective substrates must be scrapped. Furthermore, to address these issues, the industry primarily focuses on upgrading equipment hardware, such as improving the rotation mechanism and increasing the coating time. However, these modifications are costly, time-consuming, and fail to fundamentally solve the problem of uneven centrifugal distribution of high-viscosity adhesive.

[0024] Example 1: A coating method for improving the rotating MURA of a TFT-LCD color filter, comprising the following steps: Photoresist preparation: Provide photoresist with a viscosity of 2.8 cP~3.2 cP; Spin coating: The photoresist is dropped onto the surface of a glass substrate and spin-coated at a rotation speed N, wherein the rotation speed N is coordinated with the viscosity of the photoresist, and the reduction in rotation speed N relative to the original rotation speed N0 is controlled within the range of 50 rpm to 100 rpm.

[0025] In the above embodiments, the viscosity of the photoresist is replaced from the high viscosity photoresist of 4±0.2 cP in the traditional process to a low viscosity photoresist of 2.8 cP~3.2 cP. Simultaneously, the rotation speed needs to be matched with the photoresist viscosity. The high rotation speed N0 of 300 rpm~500 rpm in the traditional process is synchronously reduced, with the reduction controlled within the range of 50 rpm~100 rpm. For example, if the original rotation speed N0 is 300 rpm~500 rpm, after synchronous reduction, the rotation speed N is 200 rpm~450 rpm, thereby achieving a photoresist film thickness deviation of less than or equal to 2%. That is, simply changing the photoresist viscosity without changing the coating rotation speed, or simply changing the coating rotation speed without changing the photoresist viscosity, cannot improve the uniformity of the photoresist film thickness, and therefore cannot solve the defect of rotational MURA in the color filter substrate. The experimental test data comparison is shown in Table 1 below:

[0026] In Table 1 above, the photoresist viscosity was measured at room temperature (25±1℃) using a viscometer. The photoresist supplier adjusted the viscosity of the photoresist from 4cP to 3±0.2cP and monitored the incoming material using a viscometer. A rotational viscometer can be used as the viscometer. The inspection method of rotating MURA: The color filter substrate is lit up, and the inspection is carried out by optical MURA inspection equipment or visual inspection. The rotating MURA inspection method is existing technology and will not be described in detail here. After the batch inspection is completed, the percentage of defective products by rotating MURA is calculated. Method for detecting film thickness uniformity: The thickness of the photoresist film layer on the glass substrate is measured using a film thickness gauge. Thickness data of the photoresist film layer are collected at 9 measurement points. The film thickness uniformity of the photoresist film layer is calculated according to the following formula: (max-min) / (max+min)×100%; Where: max represents the maximum thickness of the photoresist film layer among the 9 measurement points, and min represents the minimum thickness of the photoresist film layer among the 9 measurement points. The smaller the number calculated by the above formula, the smaller the thickness deviation of the optical photoresist film layer, the better the film thickness uniformity, and the lower the rotational MURA failure rate; conversely, the larger the number calculated by the above formula, the larger the thickness deviation of the optical photoresist film layer, the worse the film thickness uniformity, and the higher the rotational MURA failure rate.

[0027] Comparing Table 1 above, the film thickness uniformity is poor under both the condition of reducing viscosity without reducing rotation speed and the condition of reducing rotation speed without reducing viscosity, and the defect rate of rotational MURA is also high. Furthermore, reducing photoresist viscosity has a significant impact on film thickness uniformity. The optimal film thickness uniformity and the lowest rotational MURA defect rate are achieved when both rotation speed and viscosity are reduced simultaneously, ensuring that the thickness deviation of the photoresist film layer on the glass substrate is less than or equal to 2%. Therefore, it can be concluded that while reducing photoresist viscosity, the rotation speed N of the coating spinner must be reduced simultaneously. Only when the photoresist viscosity and rotation speed N are synergistically matched can better film thickness uniformity be obtained, thereby greatly reducing the defect rate of rotational MURA for color filters. Therefore, low-viscosity photoresist and low rotation speed must be used in combination to avoid uneven coating or insufficient edge thickness caused by adjusting a single parameter. Experimental tests show that after adopting this invention, the rotational MURA defect rate decreased from 8-12% to 0.5-1%, reducing defect losses by more than 90%.

[0028] The principle of this invention: The core improvement of this invention is based on the fundamental principles of fluid mechanics and thin film formation, and addresses the unique process requirements of color filter substrates in the TFT-LCD industry: Optimization of the flow field for low-viscosity photoresist: reducing the internal viscous resistance of the photoresist, making it easier to form a uniform and smooth flow during rotation, and reducing local accumulation caused by viscosity differences; Control of centrifugal force at low rotation speed: reducing excessive stretching of the photoresist by centrifugal force, avoiding excessive ejection of the photoresist at the edges to form thickness gradients, while ensuring uniform distribution of the photoresist in the central area of ​​the glass substrate; By simultaneously establishing a synergistic matching mechanism between photoresist viscosity and rotation speed, the problem of insufficient edge thickness caused by low-viscosity photoresist can be solved, while the problem of uneven thickness in the center caused by low rotation speed can also be solved, achieving a dual improvement in photoresist thickness uniformity.

[0029] It should also be noted that the photoresist is any one of the RGB photoresists, that is, the photoresist is an RGB three-color photoresist, which is suitable for 4.5-5 generation TFT-LCD glass substrates, and the amount of photoresist applied to a single substrate is controlled at 30ml.

[0030] Further, the original rotational speed N0 is 350 rpm. Preferably, the rotational speed N is reduced from the original rotational speed N0 to 280 rpm, and the photoresist viscosity is 3.0 cP. The experimental test data comparing a rotational speed N of 280 rpm and a photoresist viscosity in the range of 2.8 cP to 3.2 cP with an original rotational speed N0 of 350 rpm and a traditional photoresist viscosity of 4.0 cP are shown in Table 2 below.

[0031] In Table 2, the test methods are the same as in Table 1, and will not be repeated here. The photoresist viscosity is controlled between 2.8 cP and 3.2 cP, and the rotation speed N is controlled between 200 and 450 rpm. Taking the original rotation speed N0 as 350 rpm as an example, the reduction in rotation speed N needs to be controlled within the range of 50-100 rpm. Therefore, when the photoresist viscosity is between 2.8 cP and 3.2 cP, the preferred rotation speed N is between 260 rpm and 300 rpm. That is, as shown in Table 2, when the photoresist viscosity is 2.8 cP, the rotation speed N is 260 rpm; when the photoresist viscosity is 3.0, the rotation speed N is 280 rpm; and when the photoresist viscosity is 3.2, the rotation speed N is 300 rpm.

[0032] Example 2 adds a substrate pretreatment step to Example 1, that is, before the spin coating step, it further includes the following steps: Substrate pretreatment: The glass substrate is cleaned and dried. In this step: The glass substrate is cleaned by washing with water; the drying temperature is 110℃ and the drying time is 130s. It should be noted that the drying temperature and drying time can be adjusted according to actual needs, with the preferred drying temperature being 110℃ and the drying time being 130s.

[0033] In this way, by removing impurities and moisture from the surface of the glass substrate, the impurities are prevented from affecting the photoresist spreading effect, thereby further improving the uniformity of film thickness and thus improving the product yield.

[0034] Example 3 adds a curing step to Example 1 or Example 2, that is, after the spin coating step, it further includes the following steps: Curing process: The photoresist coated on the glass substrate is thermally cured to form a photoresist film layer. In this step: The thermosetting temperature is 230℃, and the thermosetting time is 30 minutes. It should be noted that the thermosetting temperature and time can be adjusted according to actual conditions, but the preferred thermosetting temperature is 230℃ and the thermosetting time is 30 minutes.

[0035] Example 4 adds a detection and verification step to Example 3, that is, after the curing process, it also includes the following steps: Testing and Verification: The uniformity of the photoresist film thickness on the glass substrate is tested. In this step: In the detection and verification step: the thickness of the photoresist film layer on the glass substrate is measured using a film thickness gauge. Nine measurement points are selected to collect the thickness data of the photoresist film layer. The uniformity of the photoresist film layer thickness is calculated according to the following formula: (max-min) / (max+min)×100%; Where: max represents the maximum thickness of the photoresist film layer among the 9 measurement points, and min represents the minimum thickness of the photoresist film layer among the 9 measurement points. Other methods can also be used to calculate the uniformity of the film thickness. When using the formula in this embodiment, the smaller the calculated result, the smaller the film thickness deviation of the photoresist film layer at each location on the glass substrate surface, the more uniform the film thickness distribution, and the lower the rotational MURA defect rate. Conversely, the larger the calculated result, the larger the film thickness deviation of the photoresist film layer at each location on the glass substrate surface, the more uneven the film thickness distribution, and the higher the rotational MURA defect rate.

[0036] This embodiment includes complete process steps, including substrate pretreatment to remove impurities, curing to shape the optical adhesive film layer, and quality control through testing and verification. The synergistic effect of low-viscosity photoresist and low-speed coating rotation can effectively avoid rotational MURA defects and significantly reduce the rotational MURA defect rate. It does not require modification of existing coating equipment, greatly reducing manufacturing costs. At the same time, the process is standardized, easy to operate, and can be directly adapted to existing production lines, thereby enhancing product competitiveness.

[0037] Please see Figure 1 As shown, a coating method for improving the rotating MURA of a TFT-LCD color filter specifically includes the following steps: S100 substrate pretreatment: cleaning and drying of the glass substrate; S200 photoresist preparation: Provide photoresist with a viscosity of 2.8 cP~3.2 cP; S300 spin coating: The photoresist is dropped onto the surface of a glass substrate and spin-coated at a rotation speed N, wherein the rotation speed N is coordinated with the viscosity of the photoresist, and the reduction in rotation speed N relative to the original rotation speed N0 is controlled within the range of 50 rpm to 100 rpm. S400 curing process: The photoresist coated on the glass substrate is thermally cured to form a photoresist film layer; S500 Inspection and Verification: This procedure inspects the uniformity of the photoresist film thickness on a glass substrate.

[0038] The present invention has the following beneficial effects: 1. The improved coating method for rotating MURA of TFT-LCD color filters of the present invention abandons the traditional process of using 4cP high-viscosity photoresist with a fixed high rotation speed, and adopts a 2.8cP~3.2cP low-viscosity photoresist with a low rotation speed. On the one hand, it can reduce the internal viscosity resistance of the photoresist solution, weaken fluid disturbance and local accumulation phenomenon. On the other hand, by reducing the coating rotation speed, the rotation speed is reduced synchronously from the original rotation speed, thereby weakening the excessive stretching effect of centrifugal force and avoiding the formation of concentric and radial film thickness gradients. This reduces the defects of bright and dark stripes in rotating MURA, significantly reducing the product defect rate from 8%~12% in the industry to 0.5-1%, reducing defect losses by more than 90%, and significantly improving the display quality of the panel and the yield of finished products.

[0039] 2. The improved coating method for rotating MURA of TFT-LCD color filters of the present invention solves the unrepairable rotating MURA defect from the source, reduces the scrap of defective substrates, reduces raw material and production capacity losses, and does not require modification of existing coating equipment, saving high hardware upgrade costs and debugging cycles, significantly reducing the manufacturing cost of a single substrate and improving production efficiency.

[0040] 3. The improved coating method for rotating MURA of TFT-LCD color filters of the present invention coordinates and adapts the viscosity of the optical adhesive to the rotation speed of the coating process, simultaneously solving the problems of thin film at the edges of low-viscosity adhesives and uneven film thickness in the center at low rotation speeds. This achieves uniform adhesive spreading over the entire substrate, comprehensively improving film thickness uniformity and ensuring stable subsequent processes and consistent optical adhesive layer performance. Furthermore, it achieves process standardization, ease of control, and high fault tolerance, adapting to existing production lines without complex debugging, thus overcoming industry hardware optimization bottlenecks.

[0041] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this invention should be determined by the appended claims.

Claims

1. A coating method for improving the rotating MURA of a TFT-LCD color filter, characterized in that, Includes the following steps: Photoresist preparation: Provide photoresist with a viscosity of 2.8 cP~3.2 cP; Spin coating: The photoresist is dropped onto the surface of a glass substrate and spin-coated at a rotation speed N, wherein the rotation speed N is coordinated with the viscosity of the photoresist, and the reduction in rotation speed N relative to the original rotation speed N0 is controlled within the range of 50 rpm to 100 rpm.

2. The coating method for improving the rotating MURA of TFT-LCD color filters according to claim 1, characterized in that, The original rotational speed N0 is 300 rpm to 500 rpm, and the rotational speed N is 200 rpm to 450 rpm.

3. The coating method for improving the rotating MURA of TFT-LCD color filters according to claim 2, characterized in that, The original rotational speed N0 was 350 rpm, the rotational speed N was reduced from the original rotational speed N0 to 280 rpm, and the photoresist viscosity was 3.0 cP.

4. The coating method for improving the rotating MURA of TFT-LCD color filters according to claim 1, characterized in that, Prior to the spin coating step, the following steps are also included: Substrate pretreatment: Cleaning and drying the glass substrate.

5. The coating method for improving the rotating MURA of TFT-LCD color filters according to claim 4, characterized in that, In the substrate pretreatment step: The glass substrate is cleaned by washing with water. The drying temperature is 110℃ and the drying time is 130s.

6. The coating method for improving the rotating MURA of TFT-LCD color filters according to claim 1 or 5, characterized in that, Following the spin coating step, the following steps are also included: Curing process: The photoresist coated on the glass substrate is thermally cured to form a photoresist film layer.

7. The coating method for improving the rotating MURA of TFT-LCD color filters according to claim 6, characterized in that, In the curing process step: The thermosetting temperature is 230℃ and the thermosetting time is 30min.

8. The coating method for improving the rotating MURA of TFT-LCD color filters according to claim 6, characterized in that, Following the curing process, the following steps are also included: Testing and verification: The uniformity of the thickness of the photoresist film layer on the glass substrate is tested.

9. The coating method for improving the rotating MURA of a TFT-LCD color filter according to claim 8, characterized in that, In the detection and verification steps: The thickness of the photoresist film on the glass substrate was measured using a film thickness gauge. Thickness data were collected at nine measurement points. The uniformity of the photoresist film thickness was calculated using the following formula: (max-min) / (max+min)×100%; Where: max is the maximum thickness of the photoresist film layer among the 9 measurement points, and min is the minimum thickness of the photoresist film layer among the 9 measurement points.

10. The coating method for improving the rotating MURA of a TFT-LCD color filter according to claim 1, characterized in that, The photoresist can be any type of RGB photoresist.

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