Preparation method of halftone photomask

Abstract

The invention discloses a preparation method of a halftone photomask, which comprises the following steps: S1, a binary mask substrate is subjected to laser photoetching, and a pattern opening on the substrate comprises a binary mask area and a halftone mask area; s2, developing and etching the substrate, removing the photoresist, and cleaning the substrate; s3, coating an ultraviolet light curing adhesive; s4, carrying out ultraviolet laser photoetching on a binary mask region; s5, developing and removing the uncured protection area; and S6, depositing a halftone layer. According to the preparation method disclosed by the invention, the damage to the binary mask chromium layer in the halftone film layer deposition process is reduced, the process yield is improved, the halftone mask region is photoetched, and the binary mask region and the mask region are photoetched at the same time, so that the process flow is simplified, and the process does not need to be returned to a factory for secondary photolithography after being sent out for coating, thereby shortening the process and improving the production efficiency. The nesting precision and the line precision of the halftone mask plate product are improved, the product quality is improved, and the production efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of mask manufacturing, and in particular to a method for preparing a half-tone photomask. Background Art

[0002] In the field of semiconductor display manufacturing, a mask called Half Tone Photomask is often used in the manufacturing process of display panels. It is different from the ordinary binary photomask, which only has a light-shielding area and a fully transparent area (each layer and the quartz substrate, respectively, with a transmittance of 0% and 100%, respectively, for details. Figure 1 ), a new halftone layer (Half Tone) is added to its structure to achieve partial light transmission effect, see Figure 1 , the transmittance of the halftone layer is 10% to 60%. In the traditional manufacturing process (when using a binary mask), a mask can only expose one layer of graphics; if a halftone photomask is used, two layers of structure can be made in one exposure, which reduces the number of exposure machines required, shortens the manufacturing process, improves manufacturing efficiency, and reduces manufacturing costs. Therefore, the halftone photomask is a very important material for semiconductor display panel manufacturing.

[0003] Conventional half-tone mask manufacturing process Figure 2 As shown in, specifically:

[0004] (1) Laser lithography of binary mask substrate--(2) Development of binary mask substrate--(3) Etching of binary mask substrate--(4) Removal of photoresist from binary mask substrate--(5) Cleaning of binary mask substrate--(6) Delivery to coating factory for deposition of half-tone film layer--(7) Return to mask factory for photoresist coating--(8) Lithography of half-tone mask--(9) Development of half-tone mask--(10) Etching of half-tone mask--(11) Removal of photoresist from half-tone mask--(12) Cleaning and shipment of half-tone mask.

[0005] Since the transmittance of the halftone layer is specified by customer needs and is variable, it is necessary to send it to a third-party coating factory to deposit the specified halftone film layer after the binary mask layer is completed. However, the above traditional preparation methods have the following disadvantages: 1. Since the process of depositing the halftone film layer is a magnetron sputtering mode, during the sputtering bombardment process, the impurities in the target material are easy to damage the chrome film of the substrate itself, forming a fully transparent white defect, resulting in the need for additional repairs or direct scrapping of the product; 2. The mask for semiconductor display is usually large in size, with a maximum length * width = 1.62 * 1.78 meters and a weight of more than 120Kg. The longer it is placed horizontally, the greater the droop deformation caused by gravity in the middle part, and the more difficult it is to recover. Since it needs to be sent to a third-party coating factory for coating, the time span for transportation and scheduling at the third-party coating factory is relatively long, resulting in a long wait for the second photolithography. During this period, the mask substrate is prone to deformation, and the difference in the accuracy of the two-layer pattern will increase. 3. During the second etching, due to the penetration of the etching solution, the first layer of chromium film absorption layer may be slightly corroded, affecting the line accuracy.

[0006] In view of this, this patent application is filed. Summary of the invention

[0007] In order to solve the above-mentioned defects of the existing half-tone mask preparation method, the present invention provides a half-tone photomask preparation method.

[0008] The object of the present invention is to provide a method for preparing a halftone photomask, comprising the following steps:

[0009] S1: Laser lithography of a binary mask substrate, wherein the pattern opening on the substrate includes a binary mask area and a half-tone mask area;

[0010] S2: substrate development, etching, photoresist removal, substrate cleaning;

[0011] S3: Apply UV curing adhesive;

[0012] S4: UV laser lithography binary mask area;

[0013] S5: developing and removing the uncured protected area;

[0014] S6: Depositing a halftone layer.

[0015] In the present invention, in step S1, not only the half-tone mask area is photolithographically processed, but also the binary mask area is photolithographically processed, so that the binary mask area and the half-tone mask area are photolithographically processed and etched out at the same time during the first photolithography, thereby saving an etching process. In step S4, a negative photoresist is used, and the part photolithographically processed by the ultraviolet laser absorbs energy to undergo a cross-linking polymerization reaction to form a solidified layer, which has much stronger strength and thickness than a positive photoresist, and can protect the chromium absorption area from damage during the subsequent film deposition process.

[0016] In the present invention, there is no need to return to the mask plate factory for secondary lithography after coating in a third-party coating factory. There is no round-trip logistics time and waiting time for scheduling in the third-party coating factory. The process time is shorter and the deformation of the mask plate substrate is small. Therefore, the position accuracy during the secondary alignment lithography will be higher. At the same time, since there is no second etching process, the line accuracy is only related to the accuracy of the first lithography and etching. There is no sidewall corrosion caused by inconsistent etching rates in the second etching process. In the present invention, binary mask lithography is first performed and then the halftone layer is deposited. There is no need to consider the damage to the binary mask too much, which simplifies the process flow and process difficulty.

[0017] As a preferred design, in step S1, laser lithography is performed on both the binary mask area and the half-tone mask area.

[0018] As a preferred design, the process conditions of laser lithography in step S1 are: coating a positive photoresist on a chrome-plated quartz substrate, the thickness of the photoresist being The wavelength of the photolithography laser is 413nm, and the energy is 50-70mJ / sq.cm. GRX-220&237 series, AZ-1500 series, TFP-650 series positive photoresist can be used

[0019] The exposure principle of positive photoresist is that the area irradiated by laser or energy is activated to generate photoacid, and this area can be removed by the corresponding developer. Different from the conventional halftone mask production method, in the preparation method of the present invention, the binary mask area and the halftone mask area are photolithographically completed together during the first photolithography; while the conventional halftone mask only lithographs the halftone mask area during the first photolithography. The advantage of the present invention of lithographing the binary mask area and the halftone area at one time is that the pattern is formed at one time, the position accuracy between the two is more accurate, and the edge exposure phenomenon of the halftone area is improved (see Figure 8 When the conventional method separates the halftone area and the binary mask into two parts for forming, there is usually a fluctuation position accuracy deviation of about 0.5 to 1 um between the two, which easily leads to the phenomenon of wing bias in the halftone area.

[0020] As a preferred design, in step S2, the developing operation is: using a developer to remove the portion activated by the laser, exposing the underlying chromium absorption layer, while retaining the portion not activated by the laser.

[0021] As a preferred design, the developer is a 1.83-2% tetramethylammonium hydroxide solution or a 0.5% potassium hydroxide solution, and the developing time is controlled at 60s-90s. After developing, it is necessary to rinse with ultrapure water for more than 180s and spin dry. Then enter the etching stage.

[0022] As a preferred design, the etching process in step S2 is: using an etching solution to corrode the chromium absorption layer exposed during the development process, exposing the quartz glass layer at the bottom, and forming a 100% light-transmitting area;

[0023] And / or when removing the photoresist in step S2, a demolding process is used to remove residual photoresist.

[0024] As a preferred design, in step S3, when applying the UV curing glue, first clean the mask substrate with the binary mask area and the halftone area, and then apply negative UV photoresist such as AZ nlof 2035 or SU-8 2000, the temperature is controlled at 23±0.5℃, the viscosity is controlled at 10-20mPa·s, and the glue thickness is controlled at The rotation speed is controlled at 500-800RPM; after the glue coating is completed, it is baked at 95℃ for 5 minutes, and then naturally cooled for 30 minutes. When the temperature returns to 23℃, the next photolithography process is entered;

[0025] In the process of ultraviolet laser lithography of the binary mask area in step S4, a laser with a wavelength of 365nm is used for lithography, and the energy is controlled at 90-105mJ / sq.cm. Through the photolithography cross-linking reaction of the negative ultraviolet photoresist, an excellent mechanical protection layer is formed on the upper layer of the binary mask area to protect the bottom chromium layer and resist the ion bombardment damage of the subsequent coating deposition process. The area not lithographically lasered is removed by using AZ 326MIF or SU-8Developer for development, and the development time is controlled at 60-90s. After the development is completed, it is rinsed and dried, and then packaged and sent for coating.

[0026] As a preferred design, the binary mask area in step S4 includes a chromium absorption layer and a quartz full light-transmitting area.

[0027] As a preferred design, the deposition of the halftone layer in step S6 is sent to a third-party coating factory for processing.

[0028] As a preferred design, it also includes removing all residual photoresist after depositing the halftone layer.

[0029] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0030] The method for preparing a half-tone photomask provided by the present invention reduces the damage to the binary mask chrome layer (absorption layer) during the deposition of the half-tone film layer, thereby improving the process yield; while photolithography is performed on the half-tone mask area, photolithography is also performed on the binary and mask areas, thereby reducing one etching process and reducing the process and equipment costs; at the same time, the present invention does not need to be returned to the mask plate factory for secondary photolithography after being plated in a third-party coating factory, the process time is shorter, the deformation of the mask plate substrate is small, the fitting accuracy of the half-tone mask plate product is improved, and the cancellation of the second etching process improves the line accuracy and improves the product quality; at the same time, the logistics time of returning the mask plate factory from the external coating factory can be reduced, the production cycle is shortened, and the production efficiency is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0032] Figure 1 Schematic diagram of the structure of each layer of a common binary mask and a halftone mask.

[0033] Figure 2 This is a process flow chart for traditional half-tone mask manufacturing.

[0034] Figure 3 A diagram of a method for preparing a half-tone photomask provided by the present invention.

[0035] Figure 4 A preparation flow chart of a half-tone photomask provided by the present invention.

[0036] Figure 5 It is a comparison diagram of the externally deposited halftone layer of the preparation method of the present invention and the existing preparation method.

[0037] Figure 6 It is a comparison diagram of laser lithography between the preparation method of the present invention and the existing preparation method.

[0038] Figure 7 It is a comparison diagram of the development step in the preparation method of the present invention and the etching step in the existing preparation method.

[0039] Figure 8The figure is a comparison of the edge leakage of the halftone area of ​​the mask obtained by the existing method and the preparation method of the present invention.

[0040] Fig. 9 Schematic diagram of substrate deformation under the current preparation method.

[0041] Fig.10 It is a schematic diagram of the deformation of the substrate under the preparation method of the present invention. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. The illustrative embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0043] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0044] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0045] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0046] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0047] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0048] like Figure 3 As shown in , a method for preparing a half-tone photomask of the present invention is:

[0049] 1. First, perform laser lithography on the substrate of the binary mask. At this time, the graphic opening needs to include the binary mask area and the half-tone mask area. The photoresist is the positive photoresist that comes with the raw material, and the part that is laser lithographed will be activated.

[0050] In the existing technical solutions, only the half-tone mask area is photolithographically processed in this step, and the binary mask area is temporarily retained and removed during the second photolithography and etching. Therefore, the original technical solution needs to rely on two etchings. In the present invention, the binary mask area and the half-tone mask area are photolithographically processed and etched out at the same time during the first photolithography, so an etching process can be saved.

[0051] 2. Use developer to remove the laser-activated part, exposing the underlying chromium absorption layer (also called chromium opaque layer or simply chromium layer), and retain the part that is not activated by the laser.

[0052] 3. Use etching solution to corrode the exposed chromium absorption layer to expose the quartz glass layer at the bottom, forming a 100% light-transmitting area.

[0053] 4. Remove the residual photoresist through the stripping process.

[0054] 5. Clean the binary mask substrate.

[0055] 6. Apply UV curing glue. This type of photoresist is a negative photoresist. The part lithographed by the UV laser absorbs energy to undergo cross-linking polymerization reaction to form a cured layer. The part not lithographed by the laser does not react and can be removed by the developer. The negative UV curing glue is used in the present invention to replace the current common positive photoresist. As the UV curing glue receives the energy of ultraviolet light, a cross-linking polymerization reaction occurs inside. The strength and thickness of the cured layer formed are much stronger than those of the positive photoresist, and the chromium absorption area can be protected from damage during the subsequent coating deposition process.

[0056] 7. Use UV laser to photolithography the binary mask area (chromium absorption layer and quartz full light-transmitting area) to form a solidified protective layer; retain the halftone area.

[0057] In the present invention, since there is no need to return to the mask factory for secondary lithography after coating in a third-party coating factory, the secondary lithography is performed immediately after the cleaning and gluing process is completed in the mask factory. There is no round-trip logistics time and scheduling waiting time at the third-party coating factory. The process time is shorter and the deformation of the mask substrate is small. Therefore, the position accuracy during the secondary alignment lithography will be higher.

[0058] 8. Develop and remove the photoresist (uncured) in the halftone area, exposing the quartz glass at the bottom.

[0059] Since there is no second etching process in the present invention, its line accuracy is only related to the accuracy of the first photolithography and etching. There is no side wall corrosion caused by inconsistent etching rate in the second etching process. Therefore, the half-tone mask produced by this technical solution will have higher line accuracy.

[0060] 9.Send to a third-party coating factory to deposit the halftone layer.

[0061] When the half-tone coating layer is deposited in the present invention, the binary mask area (chromium absorption layer and quartz full light-transmitting area) is protected by ultraviolet curing adhesive and is not exposed under the target particles, so impurities in the target particles will not damage the binary mask area.

[0062] 10. Remove residual photoresist.

[0063] 11. Clean, package and ship.

[0064] Among them, the degumming and cleaning processes in the present invention are relatively simple and can be entrusted to a third-party coating factory to complete, further shortening the logistics turnover time and improving the delivery efficiency.

[0065] like Figure 4 The preparation process of a new half-tone mask is also shown.

[0066] The novel preparation method of the present invention is compared with the existing preparation methods. Figure 5 ,6 , as shown in 7.

[0067] First, in the current preparation method, in step (6), the halftone layer is deposited externally, which is easy to cause damage to the chrome layer and light leakage, such as Figure 5 (a) shows light leakage spots, while in the present invention, the halftone layer is deposited externally in step (9), which only damages the photocured photoresist without damaging the chrome and preventing light leakage.

[0068] Secondly, in the current preparation method, laser lithography is performed in step (8). During this process, due to the long waiting time for the secondary lithography, the substrate will be slightly bent and deformed due to the influence of gravity, which is likely to cause a slight displacement of the pattern during the subsequent secondary lithography, thereby affecting the alignment accuracy of the two-layer pattern. However, in the present invention, ultraviolet laser lithography of the binary mask area is performed in step (7). Before this process, no external waiting time is required, and the substrate is basically not deformed, so the alignment accuracy of the two-layer pattern is good.

[0069] Thirdly, in the current preparation method, the second etching process is performed in step (10). Due to the difference in etching rates between the halftone layer and the chrome layer, the chrome layer is easily over-etched, resulting in sidewall corrosion, which affects the line accuracy of the final product. In the process of developing in step (8) of the present invention, since the second etching is not required, the sidewall of the chrome layer will not be corroded, so the line accuracy of the final product is better.

[0070] The preparation process of the half-tone mask of the present invention is described in more detail below in combination with specific implementation examples.

[0071] 1. First, apply on the chrome-plated substrate GRX220 or AZ1500 positive photoresist is used for lithography with a 413nm wavelength laser. The first lithography pattern contains a binary mask area and a halftone area pattern, and the lithography energy is 65mJ / sq.cm.

[0072] 2. Then develop with 1.83-2% tetramethylammonium hydroxide for 60-90 seconds, and then etch with a mixture of 2%-5% ammonium nitrate and 7% perchloric acid for 90-120 seconds.

[0073] 3. Then use 70-90% concentrated sulfuric acid and 10-30% hydrogen peroxide mixed solution to remove the glue and clean and dry. Then apply AZ nlof 2035 or SU-8 2000 negative UV photoresist, control the temperature at 23±0.5℃, the viscosity at 10-20mPa·s, and the coating thickness at The speed is controlled at 500-800RPM.

[0074] 4. After the glue coating is completed, bake at 95°C for 5 minutes, and then cool naturally for 30 minutes. After the temperature returns to 23°, enter the next photolithography process. In the photolithography process, a laser with a wavelength of 365nm is used for photolithography, and the energy is controlled at 90-105mJ / sq.cm. Only the binary mask area is lithographed in the photolithography area.

[0075] 5. After photolithography, use AZ 326MIF or SU-8Developer for 60 to 90 seconds, then rinse, dry and package. The above process can be completed within 24 to 48 hours.

[0076] 6. The packaged boards to be coated are transported to a third-party coating factory for coating. The fastest single transportation time is usually 24 hours. Then, according to the production schedule of the coating factory, half-tone film deposition coating is carried out online. This process usually takes 48 to 72 hours. Then, a mixture of 70 to 90% concentrated sulfuric acid and 10 to 30% hydrogen peroxide is used to remove the photoresist, and then the boards are cleaned, dried, and packaged for shipment. The entire process takes about 7 days.

[0077] The current preparation method requires that after the coating is completed at a third-party coating factory, it takes another 24 hours to transport it back to the mask factory for coating, and then schedule production and processing at the mask factory, which takes 12 to 48 hours. Only then can it be packaged and shipped, and the entire process takes about 10 days. At the same time, since there is a 3 to 5 day interval between the first and second photolithography, the deformation of the glass substrate is greater. As a result, the fitting accuracy during the second photolithography will have a deviation of about 0.7 to 1.5um. Fig. 9 It is the deformation of the substrate under the current preparation method, indicating that the position accuracy deformation range is 0.728μm in the X direction and 1.148μm in the Y direction. Due to long-term placement, the middle part of the glass substrate has a slight deformation. Fig.10 It is the deformation of the substrate under the method of the present invention. The interval time of the secondary lithography is short. The position accuracy deformation range is 0.504μm in the X direction and 0.565μm in the Y direction. The interval time of the secondary lithography is short, there is basically no deformation in the middle, and the fitting accuracy is good.

[0078] By means of the half-tone mask preparation method provided by the present invention, the damage to the binary mask chrome layer (absorption layer) during the deposition of the half-tone film layer is reduced, thereby improving the process yield; while the half-tone mask area is photolithographically processed, the binary and mask areas are also photolithographically processed, thereby reducing one etching process and reducing the process and equipment costs; at the same time, the present invention does not need to be returned to the mask plate factory for secondary photolithography after being plated in a third-party coating factory, the process time is shorter, the deformation of the mask plate substrate is small, the fitting accuracy of the half-tone mask plate product is improved, and the cancellation of the second etching process improves the line accuracy and improves the product quality; at the same time, the logistics time of returning the mask plate factory from the external coating factory can be reduced, the production cycle is shortened, and the production efficiency is improved.

[0079] The above specific implementation methods further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific implementation methods of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a half-tone photomask, characterized in that: The following steps are involved: S1: Laser lithography of a binary mask substrate, wherein the pattern opening on the substrate includes a binary mask area and a half-tone mask area; S2: substrate development, etching, photoresist removal, substrate cleaning; S3: Apply UV curing adhesive; S4: UV laser lithography binary mask area; S5: developing and removing the uncured protected area; S6: Depositing a halftone layer.

2. The method for preparing a halftone photomask according to claim 1, characterized in that: In the step S1, laser lithography is performed on both the binary mask area and the half-tone mask area.

3. The method for preparing a halftone photomask according to claim 1, characterized in that: The process conditions of laser lithography in step S1 are: coating a positive photoresist on a chrome-plated quartz substrate, the thickness of the photoresist being The wavelength of the photolithography laser is 413nm and the energy is 50-70mJ / sq.cm.

4. The method for preparing a half-tone photomask according to claim 1, characterized in that: In step S2, the developing operation is: using a developing solution to remove the portion activated by the laser, exposing the underlying chromium absorption layer, and retaining the portion not activated by the laser.

5. The method for preparing a half-tone photomask according to claim 4, characterized in that: The developer is a tetramethylammonium hydroxide solution with a concentration of 1.83-2% or a potassium hydroxide solution with a concentration of 0.5%, and the developing time is 60s-90s.

6. The method for preparing a half-tone photomask according to claim 1, characterized in that: The etching process in step S2 is: using an etching solution to corrode the chromium absorption layer exposed during the development process, exposing the quartz glass layer at the bottom, and forming a 100% light-transmitting area; And / or when removing the photoresist in step S2, a demolding process is used to remove residual photoresist.

7. The method for preparing a half-tone photomask according to claim 1, characterized in that: In step S3, when coating the UV curing glue, a negative UV photoresist is coated, the temperature is controlled at 23±0.5°C, the viscosity is controlled at 10-20 mPa·s, and the coating thickness is controlled at The speed is controlled at 500-800RPM; After the coating is completed, baking is performed at 95°C for 3 minutes; in step S4, the UV laser lithography binary mask area has a lithography wavelength of 365nm and an energy of 90-105mJ / sq.cm.

8. The method for preparing a half-tone photomask according to claim 1, characterized in that: The binary mask region in step S4 includes a chromium absorption layer and a quartz full light-transmitting region.

9. The method for preparing a half-tone photomask according to claim 1, characterized in that: The deposition of the halftone layer in step S6 is carried out by sending it to a third-party coating factory.

10. The method for preparing a half-tone photomask according to any one of claims 1 to 9, characterized in that: It also includes removing any residual photoresist after depositing the halftone layer.

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