Method for manufacturing pellicle frame

Abstract

The present invention provides a method for manufacturing a pellicle frame, the method being characterized by comprising the following steps (1) and (2): (1) a step for forming a frame shape; and (2) a step for ultrasonically cleaning the frame formed in step (1). According to this manufacturing method, deburring can be performed without changing the state of the frame surface by performing deburring processing using ultrasonic waves. As a result, the number of defective products can be reduced in the pellicle frame manufacturing process.

Description

Method for manufacturing a pellicle frame

[0001] The present invention relates to a method for manufacturing a pellicle frame that is attached to a photomask for lithography as dust removal.

[0002] In recent years, the design rules of LSIs have been miniaturized to sub-quarter microns, and accordingly, the short wavelength of exposure light sources has been progressing. That is, the exposure light source has shifted from g-line (436 nm) and i-line (365 nm) using a mercury lamp to KrF excimer laser (248 nm), ArF excimer laser (193 nm), etc., and further, EUV (Extreme Ultra Violet) light with a main wavelength of 13.5 nm is being considered for EUV exposure.

[0003] In the manufacture of semiconductors such as LSIs and super LSIs or in the manufacture of liquid crystal display panels, light is irradiated onto a semiconductor wafer or a raw plate for liquid crystals to create a pattern. In this case, if dust adheres to the photomask for lithography and the reticle (hereinafter collectively referred to as the "exposure original plate"), this dust absorbs light or bends light, resulting in problems such as the transferred pattern being deformed, the edges being rough, and the substrate being blackened and soiled, thereby impairing dimensions, quality, appearance, etc.

[0004] These operations are usually performed in a clean room, but it is still difficult to always keep the exposure original plate clean. Therefore, a method of performing exposure after attaching a pellicle as dust protection on the surface of the exposure original plate is generally adopted. In this case, foreign substances do not directly adhere to the surface of the exposure original plate but adhere to the pellicle. Therefore, if the focus is set on the pattern of the exposure original plate during lithography, the foreign substances on the pellicle become irrelevant to the transfer.

[0005] The basic structure of this pellicle consists of a pellicle film with high transmittance to the light used for exposure stretched across the upper end surface of the pellicle frame, and an airtight gasket formed on the lower end surface. The airtight gasket generally uses an adhesive layer. The pellicle film is made of nitrocellulose, cellulose acetate, fluorine-based polymers, etc., which transmit light used for exposure well (g-line (436 nm), i-line (365 nm) from a mercury lamp, KrF excimer laser (248 nm), ArF excimer laser (193 nm), etc.), but for EUV exposure, ultrathin silicon films and carbon films are being considered as pellicle films.

[0006] Since the purpose of the pellicle is to protect the exposure plate from the adhesion of foreign matter, a very high degree of cleanliness is required for the pellicle. Therefore, in the pellicle manufacturing process, it is necessary to inspect the pellicle film, pellicle frame, adhesive, and protective sheet before shipment to ensure that no foreign matter is present.

[0007] Typically, foreign object inspection of a pellicle frame involves focusing light onto the frame in a darkroom and visually detecting scattered light from the foreign object. Alternatively, a foreign object inspection device is used to irradiate the pellicle frame with a laser, such as a He-Ne laser or semiconductor laser, and detect the scattered light from the foreign object using a semiconductor detector (CCD) or similar device.

[0008] If burrs are present on the surface of the pellicle frame, these burrs can generate scattered light, making it difficult to determine whether the detected scattered light originates from foreign matter or from the frame's burrs.

[0009] Conventionally, surface treatment of the pellicle frame has been a common practice to remove burrs from it. For example, Patent Document 1 proposes anodizing as a surface treatment for an aluminum alloy pellicle frame. Patent Document 2 proposes applying a polymer coating as a surface treatment for an aluminum alloy pellicle frame. Furthermore, Patent Document 3 proposes blasting or chemical polishing the frame surface.

[0010] It was possible to remove burrs by applying the surface treatments described in these patent documents. However, burrs often remained even after the frame surface treatment. In addition, there was a problem in that the condition of the frame surface (material, appearance, color, roughness, etc.) changed significantly before and after the frame treatment.

[0011] Furthermore, in the case of mass-produced frame products where burrs are found in products whose surface condition has already been determined, it is extremely difficult to perform additional surface treatment to remove burrs, as the same quality frame is maintained and produced in large quantities. As a result, the frame products have no choice but to be discarded as defective, which poses a significant industrial challenge.

[0012] Japanese Patent Publication No. 5943076, Japanese Unexamined Patent Publication No. 2007-333910, Japanese Unexamined Patent Publication No. 2022-000709

[0013] The present invention has been made in view of the above circumstances, and aims to provide a method for manufacturing a pellicle frame that can deburr without changing the surface condition of the pellicle frame.

[0014] As a result of diligent research to achieve the above objective, the inventors discovered that by performing ultrasonic cleaning as a deburring treatment on the frame after it has been processed into a frame shape during the manufacturing process of the pellicle frame, burrs can be cleanly removed without changing the surface condition of the pellicle frame, leading to the present invention.

[0015] Accordingly, the present invention provides the following methods for manufacturing a pellicle frame: 1. A method for manufacturing a pellicle frame comprising the following steps (1) and (2): (1) a step of forming a frame shape; (2) a step of ultrasonically cleaning the frame formed in (1). 2. The method for manufacturing a pellicle frame according to 1, wherein the material of the frame in step (1) is metal. 3. The method for manufacturing a pellicle frame according to 1 or 2, wherein in step (2), a chemical solution containing water is used as the ultrasonic cleaning solution. 4. The method for manufacturing a pellicle frame according to 1 or 2, further comprising a step of chemically polishing the frame formed in (1).

[0016] According to the manufacturing method of the present invention, deburring can be performed without changing the surface condition of the frame by applying ultrasonic deburring treatment. This makes it possible to reduce defective products in the manufacturing process of pellicle frames.

[0017] The present invention will be described in more detail below. The method for manufacturing a pellicle frame of the present invention is characterized by comprising the following steps (1) and (2): (1) a step of forming a frame shape, and (2) a step of ultrasonically cleaning the frame formed in (1).

[0018] Step (1) described above is a process of processing the base material of the pellicle frame to form a predetermined frame shape. The base material of the pellicle frame is preferably a metal. There are no restrictions on the type of metal, and known metals can be used. Since pellicle frames for EUV may be exposed to high temperatures, a material with a small coefficient of thermal expansion is preferred. Examples include Invar, titanium, titanium alloys, and aluminum alloys, and among these, titanium, titanium alloys, and aluminum alloys are preferred from the viewpoint of ease of processing and light weight.

[0019] The frame shape described above is typically a rectangular (or square) frame. However, it does not need to be a perfectly rectangular frame; each side of the rectangular frame may have a partial protrusion. For example, when using an image alignment function to position the pellicle frame, the frame needs a structurally distinctive marker. In this case, a partial protrusion may be provided on the outside or inside of the side to serve as an alignment marker. Furthermore, it is preferable to provide the protrusion on the outside of the frame so as not to obstruct the exposure area.

[0020] Furthermore, the rectangular frame shape of the frame can be chamfered in various ways, such as C-chamfering, R-chamfering, or thread chamfering.

[0021] In step (1) above, after processing the frame into a predetermined shape, a step may be provided to form jig holes on the side surface of the frame, which are used for handling and peeling the pellicle from the photomask. The size of the jig holes is usually 0.5 to 1.0 mm in length in the thickness direction of the pellicle frame (diameter in the case of a circular shape). There are no particular restrictions on the shape of the jig holes, and they may be circular or rectangular. Typically, the jig holes are holes that do not penetrate from the outer surface to the inner surface of the pellicle frame.

[0022] Furthermore, in addition to the jig holes, ventilation openings may be provided on the sides of the frame to prevent the pellicle membrane from bending when pressure changes occur inside and outside the pellicle. There are no particular restrictions on the shape, number, or location of the ventilation openings. For example, through holes or notches may be provided on one end face to serve as ventilation openings. Filters may also be provided in the ventilation openings as needed.

[0023] Burrs tend to form on the ends (side edges) of the jig holes, through holes, and notches, as well as on the inner edges of the bottom of the recesses. Therefore, in this invention, by providing a step of deburring using ultrasound as described later, burrs present on the ends of the jig holes, through holes, and notches can be effectively removed without changing the surface condition of the frame, and a high-quality pellicle frame can be provided as a product.

[0024] Step (2) described above is a step of ultrasonically cleaning the frame that has been processed into a predetermined shape by step (1). This step is performed with the aim of thoroughly removing burrs present on the surface of the frame by ultrasonic cleaning.

[0025] The ultrasonic cleaning described above involves immersing the pellicle frame in a chemical solution and applying ultrasonic waves. During ultrasonic cleaning, bubbles repeatedly form and disappear in the chemical solution. When bubbles form, the chemical solution is instantaneously pushed out of the bubbles, while when bubbles disappear, the chemical solution is instantaneously pulled back to where the bubbles were. This instantaneous movement of the chemical solution causes the burrs on the frame surface to vibrate instantaneously, leading to fatigue failure at the base of the burrs and allowing for their complete removal. There are no particular restrictions on the frequency of ultrasonic cleaning, but frequencies of 20 kHz or higher are preferred for their high deburring effect. Furthermore, in order to completely remove burrs with a length of approximately 0.4 mm or more from the frame surface, it is necessary to ensure a frequency within the range of 20 kHz or higher and less than 40 kHz, preferably 20 to 30 kHz, and even more preferably 20 to 25 kHz. For example, when using a wide-range multi-wave oscillator as the ultrasonic device, it is preferable to set the fundamental frequency within the range of 20 kHz or higher and less than 40 kHz. A wide-range multi-wave oscillator is a device that changes the magnitude of the sound pressure change of ultrasound by synergistically adding numerous harmonic components to a fundamental frequency within a specific range. If the ultrasound frequency is 40 kHz or higher, even if burrs less than approximately 0.4 mm in length can be removed, larger burrs may not be sufficiently removed.

[0026] There are no particular restrictions on the type of chemical solution used for ultrasonic cleaning, but it is preferable to use a chemical solution with a high specific gravity for deburring. Specifically, it is preferable to use a chemical solution with a specific gravity of 0.8 or higher, preferably 0.9 or higher. The higher the specific gravity of the chemical solution, the greater the impact applied to the burrs, thus improving the deburring effect. Also, since the chemical solution may splash during ultrasonic cleaning, water is preferred from a safety standpoint. If the frame is noticeably dirty, detergent may be added to the water. The chemical solution may be heated to improve cleaning performance.

[0027] The timing for deburring using ultrasonic cleaning is preferably after the frame has been processed into its shape and before the adhesive is applied to the frame. In particular, it is preferable to perform ultrasonic cleaning immediately after processing into the frame shape, or immediately after processing into the frame shape and performing chemical polishing. If processing is performed on the frame after deburring, new burrs will be generated. Also, if deburring is performed after the adhesive has been applied, the performance of the adhesive may be impaired. If surface treatment is applied to the frame, there are no particular restrictions on the timing of the deburring process; it can be done before or after the surface treatment process.

[0028] Regarding the ultrasonic cleaning time, in order to fully obtain the effects of the present invention, it is preferably 3 minutes or more, more preferably 5 minutes or more, and even more preferably 30 minutes or more. The upper limit is within 24 hours, preferably within 10 hours, and more preferably within 5 hours. If the processing time is too long, the manufacturing time of the pellicle frame will increase, reducing productivity, and the surface of the frame may be damaged by the action of ultrasound, which is undesirable.

[0029] Furthermore, the present invention may include a step of performing a surface treatment on the frame formed by (1) above. There are no particular limitations on the method of this surface treatment, and various surface treatments can be performed, such as degreasing by immersion in an alkaline solution, anodizing, black nickel plating, blackening the frame surface by doping the oxide film with carbon, chemical polishing, and electrolytic polishing.

[0030] The pellicle frame manufactured by the above manufacturing process has a surface for attaching the pellicle film (referred to here as the "upper end surface") and a surface that faces the photomask when the photomask is attached (referred to here as the "lower end surface").

[0031] The upper and lower ends, inner and outer surfaces of the pellicle frame do not need to be flat; grooves, steps, and chamfers may be added as needed.

[0032] Typically, a pellicle film is attached to the upper end surface of the pellicle frame via an adhesive, and an adhesive for attaching the pellicle to the photomask is attached to the lower end surface.

[0033] The dimensions of the pellicle frame are not particularly limited, but since the height of the EUV pellicle is limited to less than 2.5 mm, the thickness of the EUV pellicle frame is smaller than that, less than 2.5 mm.

[0034] Furthermore, the thickness of the pellicle frame for EUV is preferably 1.5 mm or less, taking into account the thickness of the pellicle film, photomask adhesive, etc.

[0035] A pellicle can be obtained by attaching a pellicle film to the upper end surface of the above-mentioned pellicle frame via an adhesive or bonding agent. There are no particular restrictions on the material of the pellicle film, but it is preferable to use a material with high transmittance at the wavelength of the exposure light source and high light resistance. For example, for EUV exposure, an ultrathin silicon film or carbon film can be used.

[0036] Furthermore, the pellicle film does not need to be made of only one material. For example, one method for producing an ultrathin silicon film involves first forming a self-supporting pellicle film layer on a silicon wafer, and then etching the portion of the silicon wafer that will become the self-supporting film, thereby producing an ultrathin silicon self-supporting film supported by the frame of the silicon wafer. In such a case, in this invention, the frame of the silicon wafer is also included in the definition of the pellicle film.

[0037] As described above, an adhesive or bonding agent is formed on the upper end surface of the pellicle frame to hold the pellicle film. There are no restrictions on the material of the adhesive or bonding agent; known materials can be used, and acrylic adhesives and silicone adhesives are preferably used. The adhesive or bonding agent may be processed into any shape as needed. To firmly hold the pellicle film, an adhesive or bonding agent with strong adhesive strength is preferred.

[0038] On the other hand, an adhesive for attaching to a photomask is formed on the lower end surface of the pellicle frame. Generally, it is preferable that the photomask adhesive is provided over the entire circumference of the pellicle frame. As the photomask adhesive, known ones can be used, and acrylic adhesives and silicone adhesives can be preferably used. The adhesive may be processed into an arbitrary shape as required.

[0039] Furthermore, a release layer (separator) for protecting the adhesive may be attached to the lower end surface of the photomask adhesive. The material of the release layer is not particularly limited. For example, polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), polyethylene (PE), polycarbonate (PC), polyvinyl chloride (PVC), polypropylene (PP), etc. can be used. Also, if necessary, a release agent such as a silicone-based release agent or a fluorine-based release agent may be applied to the surface of the release layer.

[0040] [Examples 1, Comparative Examples 1 to 3] Hereinafter, examples and comparative examples will be shown to specifically explain the present invention, but the present invention is not limited to the following examples.

[0041] [Comparative Example 1] A titanium pellicle frame (outer dimensions 150 mm × 118 mm × 1.5 mm, frame width 4.0 mm) was produced. On the outer surface of the long side of the pellicle frame, two jig holes with a diameter of 1 mm × depth of 1.2 mm were provided at a position 104 mm by center distribution.

[0042] The intervals between the holes described below indicate the distance between the centers of the holes. Six through-holes with a diameter of 0.8 mm were provided at intervals of 10 mm so as to be symmetric from the center of the side between the jig holes on the long side. On the short side, four through-holes with a diameter of 0.8 mm were provided at intervals of 20 mm so as to be symmetric from the center of the side. Therefore, a total of 20 through-holes exist in the entire pellicle.

[0043] After frame processing, it was immersed in an alkaline solution for degreasing treatment. Then, the frame was immersed in a chemical polishing solution for chemical polishing treatment.

[0044] [Conditions of Chemical Polishing Treatment] - Chemical solution: "Esclean S-22" manufactured by Sasaki Chemical Co., Ltd. - Temperature: 30°C - Treatment time: 10 seconds

[0045] After the chemical polishing treatment, the pellicle frame was precisely cleaned with a neutral detergent and pure water. On the upper end face of the frame, a mixture obtained by adding 1 part by mass of a curing agent ("PT-56" manufactured by Shin-Etsu Chemical Co., Ltd.) to 100 parts by mass of a silicone adhesive ("X-40-3264" manufactured by Shin-Etsu Chemical Co., Ltd.) and stirring was applied over the entire circumference to a thickness of 0.1 mm. Also, on the lower end face of the frame, a mixture obtained by adding 0.1 part by mass of a curing agent (L-45 manufactured by Soken Chemical & Engineering Co., Ltd.) to 100 parts by mass of an acrylic adhesive ("SK Dyn 1495" manufactured by Soken Chemical & Engineering Co., Ltd.) as a photomask adhesive and stirring was applied over the entire circumference to a thickness of 0.1 mm.

[0046] Then, the pellicle frame was heated at 90°C for 12 hours to cure the adhesives on the upper and lower end faces of the frame. Subsequently, an ultrathin silicon film was pressure-bonded to the adhesive formed on the upper end face of the frame as a pellicle film to complete the pellicle.

[0047] When the completed pellicle was inspected for foreign matter while irradiating it with a condenser lamp in a dark room, bright spots resembling foreign matter were confirmed at the ends of five through-holes, so it was judged as不合格 as a process defective product. When the bright spot locations were observed with a scanning electron microscope (hereinafter referred to as "SEM") at a magnification of 150 times, burrs were confirmed at the ends of the through-holes.

[0048] Next, in order to remove the burrs, attempts were made to remove the burrs by ultrasonic cleaning (Example 1), remove the burrs using an abrasive (Comparative Example 2), and remove the burrs by blasting (Comparative Example 3).

[0049] [Example 1] After the chemical polishing treatment of Comparative Example 1, a burr removal step by ultrasonic cleaning was introduced. All other steps were the same as in Comparative Example 1.

[0050] [Conditions of Ultrasonic Burr Removal] - Apparatus: "PERION-HDB-20" manufactured by Blue Star R&D Co., Ltd. - Oscillator: 2 kHz fundamental frequency to 275 kHz simultaneous wideband multiple-wave oscillator - Transducer output density: 2 W / cm 2 0 [Chemical solution: Water - Liquid temperature: Room temperature - Treatment time: 60 minutes

[0051] When the completed pellicle was inspected for foreign matter in a darkroom under the illumination of a focusing lamp, no bright spots were observed, indicating good quality. Furthermore, when the through-hole was observed with a SEM at 150x magnification, no burrs were found. Additionally, when the inner surface of the frame was observed with a SEM at 1000x magnification, there were no significant changes compared to Comparative Example 1.

[0052] [Comparative Example 2] In Comparative Example 2, a deburring process using an abrasive was introduced after the chemical polishing treatment of Comparative Example 1. In the above deburring process, 3M Corporation's sponge abrasive "Microfine 5085" was used as the abrasive material, and the entire frame was polished. All other processes were the same as in Comparative Example 1.

[0053] When the completed pellicle was inspected for foreign objects in a darkroom under the illumination of a focusing lamp, a bright spot resembling a foreign object was found at the edge of one through-hole, and it was judged to be a defective product and therefore rejected. When the bright spot was observed at a magnification of 150x using a SEM, a burr was found at the edge of the through-hole. Furthermore, when the inner surface of the frame was observed at a magnification of 1000x using a SEM, small particles of about 3 to 10 μm were found, and EDX analysis of these particles revealed that they were aluminum oxide contained in the sponge abrasive material. Therefore, it was found that deburring with abrasive material does not completely remove the burrs, and some of the abrasive material remains on the frame.

[0054] [Comparative Example 3] In Comparative Example 3, a deburring process using blasting was introduced before the chemical polishing process in Comparative Example 1. All other processes were the same as in Comparative Example 1.

[0055] [Deburring conditions by blasting] ・Abrasive: Glass beads manufactured by Fuji Seisakusho Co., Ltd. (center particle size ≤ 30 μm) ・Discharge pressure: 7 kgf / cm 2 Time: 30 seconds

[0056] When the completed pellicle was inspected for foreign matter in a darkroom under the illumination of a focusing lamp, no bright spots were found, indicating good quality. When the through-hole was observed with a SEM at 150x magnification, no burrs were found. However, when the inner surface of the frame was observed with a SEM at 1000x magnification, numerous irregularities were observed compared to Comparative Example 1. It was found that the marks left by the blast particles remained on the frame surface. Since the surface condition of the frame changes, it is difficult to apply this to mass-produced products where the surface condition is already determined.

[0057] The results for Example 1 and Comparative Examples 1-3 are shown in Table 1 below. The "Frame Manufacturing Process" column in Table 1 below shows the main process steps from frame processing to before adhesive application.

[0058]

[0059] Based on the above results, it was possible to remove burrs from the frame without changing the surface condition of the frame by applying ultrasonic deburring treatment to the frame. Therefore, the manufacturing method of the present invention makes it possible to provide a burr-free pellicle frame and a pellicle equipped with said pellicle frame without changing the surface condition of the frame.

Claims

1. A method for manufacturing a pellicle frame, comprising the following steps (1) and (2): (1) a step of forming a frame shape; and (2) a step of ultrasonically cleaning the frame formed in (1).

2. The method for manufacturing a pellicle frame according to claim 1, wherein in step (1) above, the material of the frame is metal.

3. The method for manufacturing a pellicle frame according to claim 1, wherein in step (2) above, a chemical solution containing water is used as the ultrasonic cleaning solution.

4. A method for manufacturing a pellicle frame according to claim 1, comprising the step of chemically polishing the frame formed by (1) above.

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