Pellicle frame and pellicle

Abstract

Provided is a frame-like pellicle frame 1 that has: a pellicle frame body 1; a polymer layer 1b covering the pellicle frame body 1; and an inorganic layer 1c formed on the polymer layer 1b. The pellicle frame according to the present invention is provided with a coating in which a polymer layer and an inorganic layer are layered together, whereby it is possible to provide a pellicle frame and a pellicle that have excellent hydrogen radical resistance during EUV exposure and good foreign matter inspectability.

Description

Pellicle Frame and Pellicle

[0001] The present invention relates to a pellicle frame and a pellicle attached as a foreign matter removal device to a photomask for lithography.

[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) by a mercury lamp to KrF excimer laser (248 nm), ArF excimer laser (193 nm), etc., and furthermore, EUV (Extreme Ultra Violet) exposure using EUV light with a main wavelength of 13.5 nm is being studied.

[0003] In the manufacture of semiconductors such as LSIs and super LSIs or the manufacture of liquid crystal display panels, light is irradiated onto a semiconductor wafer or a raw plate for liquid crystal to form a pattern. In this case, if foreign matter adheres to the photomask for lithography and the reticle (hereinafter collectively referred to as the "exposure original plate"), since this foreign matter absorbs light or bends light, the transferred pattern is deformed, the edge becomes rough, and in addition, the substrate is blackened and contaminated, resulting in problems such as damage to dimensions, quality, appearance, etc.

[0004] These operations are usually carried out 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 a foreign matter removal device to the surface of the exposure original plate is generally adopted. In this case, since the foreign matter does not directly adhere to the surface of the exposure original plate but adheres to the pellicle, if the focus is adjusted to the pattern of the exposure original plate during lithography, the foreign matter on the pellicle becomes irrelevant to the transfer.

[0005] The basic structure of this pellicle consists of a pellicle frame made of aluminum or titanium, with a pellicle film that has high transmittance to the light used for exposure stretched across its upper surface, and an airtight gasket formed on its lower surface. The airtight gasket generally uses an adhesive layer, and a protective sheet is attached to protect this 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] In particular, since EUV exposure is performed under high vacuum, the EUV pellicle is exposed to pressure changes from atmospheric pressure to vacuum and vice versa. During this process, air moves through the vents provided in the pellicle frame. In EUV pellicles, air movement occurs inside the pellicle, which was not present in ArF pellicles, increasing the risk of foreign matter adhering to the pellicle frame surface falling onto the exposure plate. Therefore, EUV pellicles require stricter foreign matter inspection than ArF pellicles.

[0007] Furthermore, in EUV lithography, hydrogen gas is introduced to remove foreign matter generated from the light source. This hydrogen gas is excited by EUV light, generating hydrogen radicals. Therefore, pellicles for EUV lithography also require resistance to hydrogen radicals.

[0008] The inside of an EUV lithography system is a very special and harsh environment, consisting of a vacuum and a hydrogen radical environment. Concerns about adverse effects during EUV lithography under such harsh conditions have led to the fact that EUV lithography pellicle frames have often not been coated, leaving the base material, such as single-crystal silicon, titanium, or aluminum alloy, exposed on the surface.

[0009] However, when the base material is exposed, processing scratches that occur during the shaping process will inevitably be present on the surface. Since surface scratches make it difficult to inspect for foreign objects on the pellicle frame, surface scratch removal is necessary. Common surface scratch removal methods include manual polishing and blasting.

[0010] In conventional KrF and ArF lithography, the problematic foreign matter size was μm, and the aforementioned scratch removal treatment allowed the material to be used as a pellicle without any problems. However, in EUV lithography, nm-sized foreign matter is becoming a problem. With conventional scratch removal treatments, it is difficult to completely eliminate nm-level polishing residue because the surface irregularities are physically scraped off.

[0011] Conventionally, to solve this problem, methods have been proposed such as forming a polymer layer on the surface of the pellicle frame, as described in Patent Documents 1 to 3 below, or forming an inorganic layer on the surface of the pellicle frame, as described in Patent Document 4 below.

[0012] Japanese Patent Publication No. 2007-333910, Japanese Patent Publication No. 2012-073610, Japanese Patent Publication No. 2017-040688, Japanese Patent Publication No. 2018-049043

[0013] Forming a polymer layer on the pellicle frame surface as described in Patent Documents 1 to 3 allows the polymer layer to completely cover the base material surface, thus eliminating the risk of polishing residue falling during pellicle use and making it an effective measure against foreign matter. However, this method has the drawback that the polymer layer can be damaged by hydrogen radicals.

[0014] Furthermore, when an inorganic layer, as described in Patent Document 4, is formed on the surface of the pellicle frame, although the inorganic layer is not damaged by hydrogen radicals, it is not possible to make the layer thicker, and scratches and irregularities on the frame surface remain, resulting in the disadvantage of poor foreign object inspection compared to a polymer layer. In this case, it is technically possible to increase the thickness of the layer by stacking inorganic layers, but when stress is applied to the inorganic layer, such as due to thermal expansion of the frame, there is a concern that the coating may peel off due to poor adhesion between the stacked inorganic layers.

[0015] The present invention has been made in view of the above circumstances, and aims to provide a pellicle frame that can achieve good foreign matter inspection performance without causing problems due to hydrogen radicals, and a pellicle using the pellicle frame.

[0016] The inventors of the present invention have conducted diligent studies to achieve the above objectives and have found that by forming a polymer layer, preferably with a thickness of 1 μm or more, on the pellicle frame body, made of, for example, acrylic resin, epoxy resin, fluororesin, or polyimide resin, and further forming an inorganic layer, such as metal, metal oxide film, ceramics, or Si compound, on this polymer layer, a pellicle frame can be obtained that has good hydrogen radical resistance and can achieve good foreign object inspection performance without being affected by the shape of the pellicle frame surface, such as scratches or irregularities, and have thus completed the present invention.

[0017] Accordingly, the present invention provides the following pellicle frame and a pellicle using the pellicle frame. 1. A frame-shaped pellicle frame having a pellicle frame body, a polymer layer covering the pellicle frame body, and an inorganic layer formed on the polymer layer. 2. The pellicle frame according to 1, wherein the thickness of the polymer layer is 1 μm or more. 3. The pellicle frame according to 1 or 2, wherein the polymer layer is made of acrylic resin, epoxy resin, fluororesin, or polyimide resin. 4. The pellicle frame according to any one of 1 to 3, wherein the inorganic layer is made of metal, metal oxide film, ceramics, or Si compound. 5. A pellicle comprising the pellicle frame according to any one of 1 to 4 and a pellicle film provided on the upper end surface of the pellicle frame via an adhesive. 6. The pellicle according to 5, used for EUV exposure. 7. The pellicle according to 5 or 6, wherein the height of the pellicle is 2.5 mm or less.

[0018] According to the present invention, by applying a coating to the surface of the pellicle frame in which a polymer layer and an inorganic layer are laminated, it is possible to provide a pellicle frame and pellicle that have excellent hydrogen radical resistance during EUV exposure and good foreign matter inspection properties.

[0019] Figure 1(A) is a perspective view showing an example of the pellicle frame of the present invention, and Figure 1(B) is a cross-sectional view of the frame along E-E. This is a schematic diagram showing the pellicle of the present invention mounted on a photomask.

[0020] The present invention will be described in more detail below. The pellicle frame of the present invention is a frame-shaped pellicle frame having an upper end surface on which a pellicle film is provided and a lower end surface facing a photomask.

[0021] If the pellicle frame is frame-shaped, its shape corresponds to the shape of the photomask on which the pellicle is attached. Generally, it is a rectangular or square frame, as shown in Figure 1. The corners (edges) of the pellicle frame may remain sharp (pointed), or they may be chamfered, such as with R-chamfering or C-chamfering, to create other shapes such as curved shapes.

[0022] Furthermore, the pellicle frame has a surface for attaching the pellicle film (referred to here as the upper end surface) and a surface that contacts the photomask when the photomask is attached (referred to here as the lower end surface).

[0023] As shown in Figure 2, for example, the pellicle film 2 is usually attached to the upper end surface of the pellicle frame via adhesive 4, and an adhesive 5 for attaching the pellicle to the photomask 3 is provided on the lower end surface. However, the method of attaching the pellicle film 2 and the method of attaching it to the photomask 3 are not limited to the method using adhesive 4 and adhesive 5, and any appropriate method can be adopted.

[0024] The dimensions of the pellicle frame are not particularly limited, but if the height of the EUV pellicle is limited to 2.5 mm or less, the thickness of the EUV pellicle frame is preferably smaller than that, less than 2.5 mm. In particular, considering the thickness of the pellicle film and the adhesive for the photomask, the thickness of the EUV pellicle frame is preferably 1.5 mm or less. Furthermore, the lower limit of the thickness of the pellicle frame is preferably 1.0 mm or more.

[0025] The pellicle frame of the present invention comprises a pellicle frame body, a polymer layer covering the pellicle frame body, and an inorganic layer formed on the polymer layer.

[0026] Figure 1(A) shows a pellicle frame 1 according to an example of the present invention, where 11 is the inner surface of the pellicle frame, 12 is the outer surface of the pellicle frame, 13 is the upper end surface of the pellicle frame, and 14 is the lower end surface of the pellicle frame. As shown in Figure 1(B), the pellicle frame 1 has a frame-shaped pellicle frame body 1a which is a base material, a polymer layer 1b which covers the pellicle frame body 1a, and an inorganic layer 1c which is further formed on the polymer layer 1b.

[0027] Although not shown in Figure 1, tool holes can be provided on the sides of the pellicle frame 1, particularly on the longer sides, for handling and for separating the pellicle from the photomask. The size of the tool holes is preferably 0.5 to 1.0 mm in length in the thickness direction of the frame (or diameter in the case of a circular shape). There are no restrictions on the shape of the holes; they may be circular or rectangular.

[0028] In addition to the jig holes, ventilation openings may be provided to prevent the membrane from bending when there are pressure changes inside and outside the pellicle. There are no restrictions on the shape, number, or location of the ventilation openings. Notches may be provided on the end faces to serve as ventilation openings. Filters may be provided in the ventilation openings as needed. Although the jig holes mentioned above are usually holes that do not penetrate from the outer surface to the inner surface, they can also be made to penetrate and used as ventilation holes.

[0029] Furthermore, the pellicle frame may be provided with projections facing outward or inward. By using such projections, a filter can be formed on the projections. In addition, by providing a connection mechanism (screws, adhesive, etc.) to the exposure master plate on the outward-facing projection, the adhesive for the photomask, which will be described later, can be omitted.

[0030] There are no restrictions on the material of the pellicle frame body 1a described above, and known materials can be used. However, especially for pellicle frames used in EUV applications, materials with a low coefficient of thermal expansion are preferred because they may be exposed to high temperatures. Examples include Si, SiO2, SiN, quartz, Invar, titanium, titanium alloys, and aluminum alloys. Among these, titanium, titanium alloys, and aluminum alloys are preferred due to their ease of processing and light weight. Furthermore, from the viewpoint of a low coefficient of thermal expansion, materials with a linear expansion coefficient of 10 × 10⁻¹⁰ are preferred. -6 It is preferable that the metal has a (1 / K) or lower ratio, and more preferably that it be selected from titanium or a titanium alloy.

[0031] The pellicle frame body 1a described above is preferably subjected to scratch removal and cleaning treatments as needed after being processed into a frame shape. Although this step is not essential to the present invention, it is preferable to perform these treatments to make the frame surface smooth and clean in order to uniformly apply the polymer layer 1b described above to the surface. For scratch removal treatment, manual polishing with alumina abrasives, physical polishing, blasting, chemical polishing with chemicals, etc. may be used. In addition, a coloring process for the frame may be added to improve foreign matter inspection, or an oxide film may be formed on the surface by anodizing, etc. For cleaning, pure water, neutral detergent, acid / alkaline cleaning, ultrasonic cleaning, etc. can be used.

[0032] There are no particular restrictions on the material of the polymer layer 1b, and known polymer materials can be used. For example, acrylic resin, epoxy resin, fluororesin, or polyimide resin can be suitably used. The thickness of the polymer layer 1b is preferably 1 μm or more in order to fill in the irregularities on the surface of the pellicle frame body 1a, which is the base material, with the polymer and make the surface smooth. A thickness of 5 μm or more is particularly preferable because it can smooth out even large irregularities on the frame surface. There are no particular restrictions on the method of forming the polymer layer 1b, and known methods can be used. For example, electrodeposition coating, dip coating, and spray coating can be suitably used. Among these, electrodeposition coating and dip coating are particularly preferred because they can completely coat the inside of the ventilation parts provided in the pellicle frame body 1a.

[0033] In this invention, an inorganic layer 1c is formed on the surface of the polymer layer 1b, and the surface of the polymer layer 1b is coated with this inorganic layer 1c. The material of the inorganic layer 1c must be resistant to hydrogen radicals, and for example, metals, metal oxides, ceramics, or Si compounds such as SiO2 or SiO2 can be used. There are no particular restrictions on the method of forming the inorganic layer 1c, and known methods can be used. For example, vapor deposition, dipping coating, spray coating, etc., are suitably used. The thickness of the inorganic layer 1c is preferably 0.5 μm or less to prevent peeling of the coating, and from the viewpoint of work efficiency, it is preferable that it be 0.1 μm or less, as long as it covers the polymer layer.

[0034] As described above, the pellicle frame 1 of the present invention is used as a pellicle by having a pellicle film stretched over its upper end surface 13.

[0035] Figure 2 shows a pellicle 10 using the pellicle frame 1 of the present invention, in which the pellicle film 2 is adhered and stretched to the upper end surface 13 (see Figure 1A) of the pellicle frame 1 with adhesive 4. This pellicle 10 is then peelably attached to the photomask 3 via adhesive 5 on the lower end surface 14 (see Figure 1A) of the pellicle frame 1, protecting the patterned surface on the photomask 3.

[0036] There are no restrictions on the material of the pellicle film 2 described above; materials with high transmittance at the wavelength of the exposure light source and high light resistance are preferably used as appropriate. For example, for EUV exposure, ultrathin silicon films or carbon films (graphene, diamond-like carbon, carbon nanotubes, etc.) are used. If the pellicle film is difficult to handle on its own, a pellicle film supported by a frame made of silicon or the like can be used. In that case, for example, the pellicle can be easily manufactured by bonding the frame region and the pellicle frame together.

[0037] There are no restrictions on the adhesive 4; any adhesive that can reliably adhere the pellicle film 2 to the upper end surface 13 of the pellicle frame 1 is acceptable, and can be appropriately selected from known adhesives. In that case, an adhesive with strong adhesive strength is preferably used to firmly hold the pellicle film. Alternatively, a strong adhesive can be used as the adhesive 4 for attaching the pellicle film 2.

[0038] The adhesive 5 used on the lower end surface 14 of the pellicle frame 1 for attachment to the photomask 6 is preferably provided around the entire circumference of the lower end surface 14 of the pellicle frame 1. Any known adhesive can be appropriately selected and used as the adhesive 5, and acrylic adhesives, silicone adhesives, rubber adhesives, etc., are preferably used. The adhesive may be processed into any shape as needed.

[0039] A release layer (separator) to protect the adhesive 5 may be attached to the lower end surface of the adhesive 5, that is, between the adhesive 5 and the photomask 3. The material of the release layer is not particularly limited, but for example, polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA), polyethylene (PE), polycarbonate (PC), polyvinyl chloride (PVC), polypropylene (PP), etc. may be used. In addition, 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] The pellicle frame and pellicle of the present invention are not particularly limited, but can be suitably used in EUV exposure. In this case, they can be used not only as protective members to prevent foreign matter from adhering to the exposure plate in the EUV exposure apparatus, but also as protective members to protect the exposure plate during storage and transportation. In addition to the method of attaching the pellicle to the exposure plate such as a photomask to manufacture an exposure plate with a pellicle, methods such as electrostatic adsorption and mechanical fixing can also be employed.

[0041] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0042] [Evaluation Test of Hydrogen Radical Resistance] Samples (1) to (7) below were prepared, and their resistance to hydrogen radicals was evaluated using the method described below. The results are shown in Table 1. [Samples] (1) A 40 mm square, 0.3 mm thick titanium plate was prepared. (2) A 40 mm square, 0.3 mm thick aluminum plate was prepared. (3) The titanium plate from (1) was washed with pure water and electroplated with acrylic resin (Elecoat Frosty W-2 (manufactured by Shimizu Corporation)) to a thickness of 10 μm. (4) The acrylic resin coated titanium plate from (3) was coated with SiO2 to a thickness of 10 nm at room temperature by atomic layer deposition (Cool ALD Co., Ltd.). (5) The acrylic resin coated titanium plate from (3) was coated with SiO2 to a thickness of 100 μm by high-density plasma CVD (Cellvac Co., Ltd.). (6) 100 parts by mass of silicone adhesive (X-40-3264 manufactured by Shin-Etsu Chemical Co., Ltd.) was mixed with 1 part by mass of curing agent (PT-56 manufactured by Shin-Etsu Chemical Co., Ltd.), and the mixture was diluted with an isoparaffinic solvent. This mixture was then applied to the acrylic resin coated titanium plate from (3) by spin coating to a thickness of 500 μm, and then heated and cured at 100°C for 30 minutes. (7) A titanium plate from (1) was prepared by coating it with SiON using high-density plasma CVD (Selvac Co., Ltd.) to a thickness of 100 μm.

[0043] [Test Method] First, the weight of each sample was measured immediately after heating the sample at 100°C for 10 minutes to remove the adsorbed water on the sample surface. Then, hydrogen plasma irradiation was performed under the following conditions, and the weight change of each sample was measured. (Hydrogen Plasma Irradiation Conditions) Apparatus: FlexAL manufactured by Oxford Instruments Plasma source: ICP (Inductively Coupled Plasma) Treatment conditions: Pressure 80 mTorr, H2 amount 50 sccm Power: 200 W Treatment temperature: 100°C Treatment time: 600 s

[0044]

[0045] From the results in Table 1, no weight loss was confirmed for metals such as titanium and aluminum and inorganic layers such as SiO2 and SiON. When a polymer layer such as an acrylic resin was applied, weight loss was confirmed, indicating that the polymer layer was damaged. However, it was found that by forming an inorganic layer on top of the polymer layer, damage from hydrogen radicals could be prevented.

[0046] [Comparative Example 1] A titanium-made pellicle frame body (outer dimensions 150 mm × 118 mm × height 1.5 mm, frame width 4.0 mm) was fabricated. On the outer surface of the long side of this pellicle frame body, two jig holes with a diameter of 1 mm × depth 1.2 mm were provided at a position 104 mm by central distribution. After processing, in order to remove the processing scratches on the surface, it was manually polished with alumina abrasive, and then degreased and washed with an alkaline aqueous solution.

[0047] The above-mentioned pellicle frame body was precisely cleaned with a neutral detergent. On the upper end surface 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 as an adhesive for the pellicle film to a thickness of 0.1 mm over the entire width except for the notch portion. Also, on the lower end surface 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.) and stirring was applied over the entire circumference to a thickness of 0.1 mm over the entire width.

[0048] Subsequently, the pellicle frame was heated at 90°C for 12 hours to cure the adhesive on the upper and lower end surfaces. Next, an ultra-thin silicone film was pressed onto the adhesive formed on the upper end surface of the frame to form the pellicle film. Meanwhile, a protective cover (outer dimensions 151 mm x 117 mm, width 6 mm, thickness 0.13 mm) was added to the mask adhesive to protect it during transport, thus completing the pellicle.

[0049] [Comparative Example 2] A pellicle was prepared in the same manner as in Comparative Example 1, except that the titanium frame was treated to remove scratches, degreased and cleaned, and then electrolytically coated with acrylic resin (Elecoat Frosty W-2 (manufactured by Shimizu Corporation)) to a thickness of 10 μm.

[0050] [Comparative Example 3] A pellicle was prepared in the same manner as in Comparative Example 1, except that the titanium frame was subjected to a scratch removal treatment, degreased and cleaned, and then coated with SiON at room temperature using atomic layer deposition (Cool ALD Co., Ltd.) to a film thickness of 10 μm.

[0051] [Example] A pellicle was prepared in the same manner as in Comparative Example 1, except that a titanium frame was treated to remove scratches, degreased and cleaned, then electrolytically coated with acrylic resin (Elecoat Frosty W-2 (manufactured by Shimizu Corporation)) to a thickness of 10 μm, and then coated with SiO2 to a thickness of 10 μm using room temperature atomic layer deposition (Cool ALD Co., Ltd.).

[0052] [Foreign Matter Inspection Test] For each pellicle frame in Comparative Examples 1, 2, and 3 and the Examples, a 10 μm polystyrene standard particle was attached to one location on the inner wall surface. Visual inspection was performed in a dark room using a focusing lamp, and the inspectability of each pellicle frame was evaluated by determining whether only the standard particle could be detected according to the following criteria. The results are shown in Table 2. In addition, the results of the hydrogen radical resistance test (results in Table 1) corresponding to each pellicle frame are also shown in Table 2. (Evaluation Criteria) ○: Only the standard particle glowed under focusing light and could be detected visually. ×: Even in areas where no standard particle was attached, the irregularities on the frame surface glowed under focusing light, and it was not possible to visually detect only the standard particle.

[0053]

[0054] As shown in Tables 1 and 2, it was confirmed that forming a polymer layer on the surface of the frame body, and then forming an inorganic layer on top of the polymer layer, makes it possible to provide a pellicle with good foreign matter inspection properties and hydrogen radical resistance. Furthermore, by applying a coating to the frame surface, the exposure of the base material is prevented, eliminating the risk of nanometer-sized polishing residue, which is difficult to detect by visual inspection, falling off during pellicle use.

[0055] 1. Pellicle frame 1a. Pellicle frame body 1b. Polymer layer 1c. Inorganic layer 2. Pellicle film 3. Photomask 4. Adhesive or bonding agent for pellicle film 5. Adhesive or bonding agent for photomask 10. Pellicle 11. Inner surface of pellicle frame 12. Outer surface of pellicle frame 13. Upper end surface of pellicle frame 14. Lower end surface of pellicle frame

Claims

1. A pellicle frame in the shape of a frame, characterized by comprising a pellicle frame body, a polymer layer covering the pellicle frame body, and an inorganic layer formed on the polymer layer.

2. The pellicle frame according to claim 1, wherein the thickness of the polymer layer is 1 μm or more.

3. The pellicle frame according to claim 1, wherein the polymer layer is made of acrylic resin, epoxy resin, fluororesin, or polyimide resin.

4. The pellicle frame according to claim 1, wherein the inorganic layer is made of a metal, a metal oxide film, a ceramic, or a Si compound.

5. A pellicle comprising a pellicle frame as described in claim 1 and a pellicle film provided on the upper end surface of the pellicle frame via an adhesive.

6. The pellicle according to claim 5, used for EUV exposure.

7. The pellicle according to claim 5, wherein the height of the pellicle is 2.5 mm or less.

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