Pellicle for EUV exposure

Abstract

To provide a pellicle frame which can effectively prevent the formation of wrinkles in the pellicle frame, and the peeling, rupturing, breaking of a pellicle film from the pellicle frame, when a fine pattern of 10 nm or less is formed in a photoresist film using the EUV exposure technique, and is lightweight and has low damage risk, and a pellicle using the same.SOLUTION: There are provided a pellicle frame which is composed of metal or an alloy with a coefficient of linear expansion of 10×10-6(1 / K) or less and a density of 4.6 g / cm3 or less, and a pellicle containing the pellicle frame as a component.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pellicle for lithography used as a dust protection device when manufacturing semiconductor devices such as LSIs and VLSIs, printed circuit boards, liquid crystal displays, and the like. [Background technology]

[0002] When manufacturing semiconductor devices such as LSIs and ultra-LSIs, or liquid crystal displays, patterns are created by irradiating light onto semiconductor wafers or liquid crystal master plates. However, if dust adheres to the photomasks or reticles (hereinafter referred to simply as "photomasks") used in this process, the edges of the patterns become rough and the underlying surface becomes blackened, which can cause problems such as impairing the dimensions, quality, and appearance of the resulting products.

[0003] For this reason, pattern production work is usually carried out in a clean room, but even so, it is difficult to keep the photomask clean at all times. Therefore, a pellicle is attached to the surface of the photomask to protect it from dust before exposure. In this case, foreign particles do not adhere directly to the surface of the photomask, but rather to the pellicle film. Therefore, if the focus is aligned on the photomask pattern during lithography, foreign particles on the pellicle film will not affect the transfer.

[0004] Generally, a pellicle is made by applying a transparent pellicle film made of nitrocellulose, cellulose acetate, fluororesin, or the like, which has good light transmission, to the upper surface of a pellicle frame made of aluminum, stainless steel, polyethylene, or the like, with a good solvent for the pellicle film, and then air-drying and adhering the film (see Patent Document 1), or by adhering the film with an adhesive such as acrylic resin or epoxy resin (see Patent Documents 2 and 3).Furthermore, the lower end of the pellicle frame is provided with an adhesive layer made of polybutene resin, polyvinyl acetate resin, acrylic resin, silicone resin, or the like, for adhering to a photomask, and a release layer (separator) for protecting the adhesive layer.

[0005] When such a pellicle is attached to the surface of a photomask and a photoresist film formed on a semiconductor wafer or liquid crystal original plate is exposed through the photomask, foreign matter such as dust will adhere to the surface of the pellicle and not directly to the surface of the photomask. Therefore, if the exposure light is irradiated so that its focus is positioned on the pattern formed on the photomask, it is possible to avoid the effects of foreign matter such as dust.

[0006] In recent years, semiconductor devices and liquid crystal displays have become increasingly highly integrated and miniaturized. Currently, technology for forming fine patterns of approximately 32 nm on photoresist films is becoming practical. Patterns of approximately 32 nm can be achieved using immersion lithography, in which the space between the semiconductor wafer or LCD master and the projection lens is filled with a liquid such as ultrapure water, and the photoresist film is exposed to an argon fluoride (ArF) excimer laser, or by using improved excimer laser techniques such as double exposure.

[0007] However, next-generation semiconductor devices and liquid crystal displays require even finer patterning of 10 nm or less, and improvements to conventional exposure technology using excimer lasers are no longer sufficient to achieve this.

[0008] Therefore, EUV exposure technology, which uses EUV (Extreme Ultra Violet) light with a dominant wavelength of 13.5 nm, is seen as the most promising method for forming patterns of 10 nm or less. When using this EUV exposure technology to form fine patterns of 10 nm or less in a photoresist film, it is necessary to resolve technical issues such as what type of light source, photoresist, and pellicle to use. Of these technical issues, development is progressing and various proposals have been made regarding new light sources and new photoresist materials.

[0009] Regarding pellicles, which affect the yield of semiconductor devices or liquid crystal displays, for example, Patent Document 3 describes a 0.1 to 2.0 μm thick silicon film that is transparent and does not cause optical distortion as a pellicle membrane to be used in EUV lithography. However, there are still unresolved issues that must be resolved before it can be applied in practice, which is currently a major obstacle to putting EUV exposure technology into practical use.

[0010] Conventionally, the material of the pellicle frame that constitutes the pellicle has been selected based solely on its rigidity and processability when exposed to i-line (wavelength 365 nm), krypton fluoride (KrF) excimer laser light (wavelength 248 nm), or argon fluoride (ArF) excimer laser light (wavelength 193 nm), and is typically aluminum, stainless steel, polyethylene, etc.

[0011] On the other hand, the material of the photomask is usually quartz glass, and the pellicle film is a transparent film depending on the light source, such as nitrocellulose, cellulose acetate, or fluororesin for i-line, KrF, or ArF, or silicone for EUV.

[0012] However, when using EUV exposure technology to form fine patterns of 10 nm or less in a photoresist film, using conventional pellicles can cause the pellicle film to wrinkle, peel off from the pellicle frame, tear, or crack.

[0013] In Patent Document 4, it was discovered that the occurrence of wrinkles and damage to the pellicle film is caused by expansion and contraction and distortion of the pellicle frame, which can occur due to a temperature rise caused by light energy during exposure, and that the linear expansion coefficient is 10 × 10 -6 It is proposed to use materials below (1 / K) for the frame.

[0014] However, materials with low thermal expansion coefficients, such as Si, SiO2, SiC, and SiN, are brittle and difficult to process. In particular, EUV pellicles must be 2.5 mm or less in height due to the limited space available for pellicle placement within EUV exposure equipment.

[0015] In addition, the side of the pellicle frame of the pellicle is usually provided with tool holes used for handling and peeling the pellicle from the photomask, as well as ventilation holes to alleviate the pressure difference between the inside and outside of the pellicle. In EUV lithography, the inside of the exposure tool is made vacuum, so the EUV pellicle needs to withstand the pressure change from atmospheric pressure to vacuum, and the ventilation holes of the EUV pellicle must have a large area.

[0016] For example, the thickness of the pellicle frame of an EUV pellicle will be less than 2.5 mm, but if you try to create a 1 mm diameter hole in the side of a pellicle frame made of materials such as Si, SiO2, SiC, or SiN, the thickness of the pellicle frame near the hole may become small, making it more likely that the pellicle frame will be damaged when drilling the hole or peeling off the pellicle. If a larger area is required for the ventilation part, the possibility of damage will increase even further.

[0017] Therefore, it is possible to consider using a metal such as Invar as a material with a low thermal expansion coefficient. Metals and alloys are easy to process and will not be damaged even if holes are drilled in the side of the pellicle frame.

[0018] Incidentally, the width of the pellicle frame is preferably as small as possible to ensure a wide exposure area, and has traditionally been around 2 mm. However, in the case of EUV pellicles, the width of the pellicle frame is limited by the pellicle membrane, and it has been found that it needs to be increased to around 3 to 4 mm.

[0019] Furthermore, in recent years, there has been a demand for faster movement of the mask stage in order to improve the throughput of EUV manufacturing, and the total weight of the pellicle must be 15 g or less.

[0020] However, when the width is increased from 2 mm to 4 mm, the volume of the pellicle frame roughly doubles, and even at 3 mm it increases by approximately 1.5 times, making it clear that a pellicle frame made of Invar would be too heavy. [Prior art documents] [Patent documents]

[0021] [Patent Document 1] Japanese Patent Application Publication No. 58-219023 [Patent Document 2] U.S. Patent No. 4,861,402 [Patent Document 3] Special Publication No. 63-27707 [Patent Document 4] Japanese Patent Application Laid-Open No. 2016-200616 Summary of the Invention [Problem to be solved by the invention]

[0022] The present invention has been made in consideration of the above circumstances, and aims to provide a pellicle frame and a pellicle using the same that can effectively prevent the pellicle film from wrinkling, peeling off, tearing, or cracking from the pellicle frame when forming fine patterns of 10 nm or less in a photoresist film using EUV exposure technology, and that is lightweight and has little risk of breakage. [Means for solving the problem]

[0023] The present inventors have developed a pellicle frame having a linear expansion coefficient of 10 × 10 -6 (1 / K) or less, and the density is 4.6 g / cm 3 The inventors have discovered that the use of the following metals or alloys prevents wrinkles or damage to the pellicle membrane, and is lightweight, making them ideal for the latest EUV exposure technology, leading to the creation of the present invention.

[0024] Accordingly, the present invention provides the following pellicle frame and pellicle. 1. Linear expansion coefficient is 10 x 10 -6 (1 / K) or less, and the density is 4.6 g / cm 3 A pellicle frame characterized by being made of the following metal or alloy: 2. The pellicle frame according to 1, wherein the metal or alloy is titanium or a titanium alloy. 3. The pellicle frame according to 1 or 2, having a thickness of less than 2.5 mm. 4. A pellicle frame according to any one of 1 to 3, having one or more holes formed on the side surface. 5. A pellicle comprising the pellicle frame according to any one of 1 to 4 as a constituent element. [Effects of the Invention]

[0025] According to the pellicle frame and pellicle of the present invention, even if the temperature of the pellicle frame rises due to the light energy from exposure, the expansion and contraction and distortion of the pellicle frame can be kept small, and wrinkles and damage do not occur in the pellicle film. Furthermore, the pellicle frame and pellicle of the present invention have excellent processability, which is expected to improve yield, and the area of ​​the ventilation part can be made large. Furthermore, there is little risk of damage when the pellicle is removed, and because they are lightweight, they can be applied to the latest EUV exposure technology. [Brief explanation of the drawings]

[0026] [Figure 1] 1A and 1B are schematic diagrams (examples) showing one embodiment of the pellicle frame of the present invention, in which (A) is a view from the bottom end surface side, (B) is a view from the long side outer surface side, and (C) is a view from the short side outer surface side. [Figure 2] 1A and 1B are schematic diagrams showing another embodiment of the pellicle frame of the present invention, where (A) is a view from the bottom end surface side, (B) is a view from the long side outer surface side, and (C) is a view from the short side outer surface side. DETAILED DESCRIPTION OF THE INVENTION

[0027] The pellicle frame of the present invention typically has an upper end surface on which a pellicle membrane is provided and a lower end surface facing the photomask. Its shape corresponds to the shape of the photomask on which the pellicle is mounted. It is generally a quadrilateral (rectangular or square) frame.

[0028] The pellicle frame has an upper end surface for providing the pellicle film and a lower end surface that faces the photomask when the photomask is attached. Typically, the pellicle film is provided on the upper end surface via an adhesive or the like, and an adhesive or the like is provided on the lower end surface for attaching the pellicle to the photomask, but this is not limited to this.

[0029] The dimensions of the pellicle frame are not particularly limited, but since the height of an EUV pellicle is limited to 2.5 mm or less, the thickness of an EUV pellicle frame is smaller than that, i.e., less than 2.5 mm. In practice, taking into account the thickness of the pellicle film, mask adhesive, etc., the thickness is preferably 2.0 mm or less, and more preferably 1.6 mm or less.

[0030] Furthermore, to fully function as a pellicle, a height of 1.5 mm or more is required, and therefore, taking into account the thickness of the pellicle film, mask adhesive, etc., the thickness of the pellicle frame for EUV is preferably 1.0 mm or more.

[0031] Furthermore, the side of the pellicle frame is usually provided with tool holes used for handling and peeling the pellicle from the photomask, as well as ventilation holes to alleviate the pressure difference between the inside and outside of the pellicle. In EUV lithography, the inside of the exposure device is made vacuum, so the EUV pellicle must be able to withstand the pressure change from atmospheric pressure to vacuum, and it is therefore preferable that the ventilation holes of the EUV pellicle have as large an area as possible.

[0032] Therefore, holes are preferably provided on the side surfaces of the pellicle frame, and the size of the jig holes and vent holes is 0.5 to 1.0 mm in length in the thickness direction of the frame (diameter if circular). There are no restrictions on the shape of the holes, and they may be circular or rectangular. Also, jig holes are usually holes that do not penetrate from the outer surface to the inner surface, while vent holes are holes that penetrate from the outer surface to the inner surface.

[0033] When drilling holes in the side of a pellicle frame, a margin of at least 0.2 mm is required around the drilled hole to accommodate processing constraints and maintain the strength of the frame. If a jig hole or vent hole measuring 1.0 mm or more in the thickness direction of the frame is to be drilled, the frame thickness should preferably be 1.4 mm or more.

[0034] The dimensions of the EUV pellicle frame are usually 145 to 152 mm in outer dimensions for the long side, 113 to 120 mm in outer dimensions for the short side, 1.0 to 2.0 mm in thickness, and 3.0 to 4.0 mm in width. The volume of the pellicle frame is 3.2 cm 3 Preferably less than 2.6cm 3 More preferably, it is:

[0035] In the present invention, the material of the pellicle frame has a linear expansion coefficient of 10 × 10 -6 (1 / K) or less and density is 5g / cm 3 The following metals or alloys are used:

[0036] In the present invention, by using a metal or alloy as the material for the pellicle frame, it is possible to drill holes in the side surface with a margin of only 0.2 mm. For example, a hole with a diameter of 1.0 mm can be drilled in the side surface of a pellicle frame with a thickness of 1.5 mm. In this case, the margin above and below the hole is 0.25 mm.

[0037] Furthermore, when forming holes in a pellicle frame made of a brittle material such as single crystal silicon, a margin of at least 0.5 mm is required around the hole. Therefore, only holes up to 0.5 mm in diameter can be formed on the side of a 1.5 mm thick pellicle frame. This may result in an insufficient ventilation area for an EUV pellicle. Furthermore, to reliably hold and peel the pellicle using a 0.5 mm diameter jig hole, the number of holes must be increased, reducing yield. Furthermore, even with a 0.5 mm margin, there is a high possibility of breakage when a large force is applied, such as during peeling.

[0038] In the present invention, the linear expansion coefficient of the material of the pellicle frame is 10 × 10 -6 (1 / K) or less, and within this range, the expansion / contraction and distortion of the pellicle frame that can occur due to the temperature rise caused by the light energy during exposure can be kept sufficiently small, preventing wrinkles and damage to the pellicle membrane.

[0039] In the present invention, the density of the metal or alloy that is the pellicle frame material is 4.6 g / cm 3 Within this density range, the volume is 3.2 cm 3 The weight of the following pellicle frame can be reduced to 15 g or less. However, if the volume of the pellicle frame is 2.6 cm 3 If the volume exceeds 2.6 cm, the weight of the pellicle film and mask adhesive other than the pellicle frame must be 3 g or less. Therefore, the volume of the pellicle frame is 2.6 cm. 3 The density is preferably 4.5 g / cm or less. 3 The following is the result.

[0040] Examples of such metals or alloys include titanium and titanium alloys such as Ti-V-Al alloys and Ti-V-Cr-Sn-Al alloys, and it is preferable to use these.

[0041] In the pellicle of the present invention, a pellicle membrane is provided on the upper end surface of the pellicle frame via a pressure-sensitive adhesive or adhesive. There are no limitations on the materials for the pressure-sensitive adhesive or adhesive, and known pressure-sensitive adhesives can be used. For example, a good solvent for the pellicle membrane may be applied, followed by air drying and adhesion, or an adhesive or pressure-sensitive adhesive such as an acrylic resin, a silicone resin, or an epoxy resin may be used.

[0042] Furthermore, although there are no limitations on the material of the pellicle film, a material with high transmittance and high light resistance at the wavelength of the exposure light source is preferred. For example, amorphous fluoropolymers can be used for excimer lasers. Examples of amorphous fluoropolymers include Cytop (trade name, manufactured by Asahi Glass Co., Ltd.) and Teflon (registered trademark) AF (trade name, manufactured by DuPont Co., Ltd.).

[0043] For EUV exposure, an ultrathin silicon film made of single crystal silicon, polycrystalline silicon, or amorphous silicon, or a carbon film, etc., is used. The pellicle film may be provided with a protective film such as SiC, SiO2, Si3N4, SiON, Y2O3, YN, Mo, Ru, or Rh.

[0044] Furthermore, an adhesive for attaching the pellicle frame to a photomask is formed on the lower end surface of the pellicle frame. Known mask adhesives can be used, including adhesives made of polybutene resin, polyvinyl acetate resin, SEBS (poly(styrene-ethylene-butadiene-styrene)) resin, acrylic resin, silicone resin, etc. Adhesives made of acrylic resin and silicone resin are particularly preferred.

[0045] The pellicle film adhesive and mask pressure-sensitive adhesive can be applied, for example, by dipping, spraying, brushing, or by using a dispenser coating device, but application using a dispenser coating device is preferred from the standpoints of stability, workability, yield, etc.

[0046] Furthermore, the adhesive or glue is generally formed over the entire circumferential circumference of the end face of the pellicle frame, with a width equal to or less than the width of the pellicle frame.

[0047] Furthermore, if the viscosity of the pellicle film adhesive and mask adhesive is high and application using an application device is difficult, aromatic solvents such as toluene and xylene, aliphatic solvents such as hexane, octane, isooctane and isoparaffin, ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, ether solvents such as diisopropyl ether and 1,4-dioxane, or mixed solvents of these can be added as needed.

[0048] A release layer (separator) may be attached to the lower end surface of the mask adhesive to protect the adhesive. The material of the release layer is not particularly limited, but examples include polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polyethylene (PE), polycarbonate (PC), polyvinyl chloride (PVC), and polypropylene (PP). 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.

[0049] When a hole penetrating from the outer surface to the inner surface is provided in the pellicle frame, a dust filter may be provided for the purpose of removing particles. The filter may be installed inside the hole or on the side surface so as to cover the opening of the hole.

[0050] In the EUV pellicle frame, the total area of ​​the ventilation hole openings is 5mm 2 It is preferable that the thickness is 10 mm or more. 2 The ventilation holes may be formed, for example, from the outer surface to the inner surface so as to form a recess in the lower end surface.

[0051] 1 and 2 show an example of a pellicle 1 that includes a pellicle frame 2 of the present invention as a component. A pellicle film 3 is adhered and stretched to the upper end surface of the pellicle frame 2 with an adhesive 5. A pressure-sensitive adhesive 4 is provided on the lower end surface of the pellicle frame 2 for attaching it to a photomask (not shown). In the figures, reference numeral 6 denotes an air vent, and the pellicle frame of FIG. 2, unlike that of FIG. 1, is formed so that the air vent forms a recess 6 on the lower end surface. Reference numeral 7 denotes a jig hole that is typically formed to peel the pellicle from the photomask using a jig. [Example]

[0052] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0053] [Example 1] Titanium (linear expansion coefficient: 8.4 x 10 -6 (1 / K), density: 4.5g / cm 3 A pellicle frame (external dimensions: 150 mm × 118 mm × 1.5 mm, frame width: 3.0 mm) was fabricated from PET.

[0054] Two jig holes, each 1 mm in diameter and 1.2 mm deep, were drilled on the outer surface of the long side of the pellicle frame, 52 mm from the center toward the corner. In addition, six through-holes were drilled at 10 mm, 30 mm, and 65 mm from the center of the long side toward the corner, and four at 10 mm and 30 mm from the center of the short side toward the corner.

[0055] After washing the pellicle frame with a neutral detergent and pure water and drying it, a silicone adhesive (X-40-3264 manufactured by Shin-Etsu Chemical Co., Ltd.) was applied to the entire periphery of the upper and lower end surfaces of the frame.

[0056] The pellicle frame was then heated at 90°C for 12 hours to harden the adhesive on the top and bottom edges. An ultrathin silicon film was then pressed onto the adhesive on the top edge of the frame to complete the pellicle.

[0057] Here, the volume of the pellicle frame is approximately 2.4 cm 3 The total weight of the pellicle membrane and adhesive is approximately 3.1 g.

[0058] [Example 2] The material of the pellicle frame is Ti-Al6-V4 titanium alloy (linear expansion coefficient: 8.8 × 10 -6 (1 / K), density: 4.4g / cm 3 ) was used. Otherwise, a pellicle was produced in the same manner as in Example 1.

[0059] [Comparative Example 1] The material of the pellicle frame is silica glass (SiO2) (linear expansion coefficient: 0.5 × 10 -6 (1 / K), density: 2.2g / cm 3 ) was used. Otherwise, a pellicle was produced in the same manner as in Example 1.

[0060] In this case, when forming the jig holes or through holes in the pellicle frame, 7 out of 10 were damaged. Furthermore, after the heat cycle test described below, when an attempt was made to peel the pellicle from the quartz substrate using a peeling jig, the jig holes were damaged.

[0061] Comparative Example 2 The material of the pellicle frame is silicon nitride (Si3N4) (linear expansion coefficient: 2.8 × 10 -6 (1 / K), density: 3.2g / cm 3 ) was used. Otherwise, a pellicle was produced in the same manner as in Example 1.

[0062] In this case, when forming the jig holes or through holes in the pellicle frame, 9 out of 10 were damaged. Furthermore, after the heat cycle test described below, when an attempt was made to peel the pellicle from the quartz substrate using a peeling jig, the jig holes were damaged.

[0063] Comparative Example 3 The material of the pellicle frame is Invar (Fe-Ni36) (linear expansion coefficient: 1.5 × 10-6 (1 / K), density: 8.1g / cm 3 ) was used. Otherwise, a pellicle was produced in the same manner as in Example 1.

[0064] Comparative Example 4 The material of the pellicle frame is aluminum (Al) (linear expansion coefficient: 23 × 10 -6 (1 / K), density: 2.7g / cm 3 ) was used. Otherwise, a pellicle was produced in the same manner as in Example 1.

[0065] The following heat cycle tests were carried out on the pellicles produced in Examples 1 and 2 and Comparative Examples 1 to 4. Table 1 shows the processability of each material as a pellicle frame, the heat cycle test results, the pellicle weight, and the overall evaluation results for each pellicle.

[0066] [Heat cycle test] The pellicle attached to the quartz substrate was heated to 200°C in an oven and left to stand for 24 hours, then left to stand at room temperature for another 24 hours. This cycle was repeated five times, and the condition of the pellicle was then visually inspected.

[0067] [Table 1]

[0068] According to the results in Table 1, the pellicles of Examples 1 and 2 were excellent in both heat cycle test results and processability, and the pellicle weight could be kept to 15 g or less. On the other hand, the pellicles of Comparative Examples 1 and 2 had problems with processability, and it was difficult to form holes in the side surfaces. The pellicle of Comparative Example 3 was excellent in both heat cycle test results and processability, but the pellicle weight exceeded 15 g, making it unsuitable for EUV lithography. The pellicle frame of Comparative Example 4 underwent large expansion and contraction during the heat cycle test, resulting in cracks in the pellicle film. [Explanation of symbols]

[0069] 1 Pellicle 2 Pellicle Frame 3 Pellicle membrane 4 Photomask adhesive 5. Pellicle membrane adhesive 6 ventilation holes 7 Jig Hole

Claims

1. In a pellicle for EUV lithography in which a pellicle film is provided on the upper end surface of a pellicle frame via an adhesive or an adhesive agent, the pellicle frame has a thickness of less than 2.5 mm, a width of 3 to 4 mm, and a material having a linear expansion coefficient of 10 × 10 -6 (1 / K) or less and a density of 4.6 g / cm 3 or less, and is made of titanium or a titanium alloy, and the pellicle film is a silicon film or a carbon film. A pellicle for EUV lithography, characterized by the above.

2. The pellicle for EUV exposure according to Claim 1, wherein the pellicle film is an ultrathin silicon film composed of single crystal silicon, polycrystalline silicon, or amorphous silicon.

3. The pellicle for EUV exposure according to Claim 1 or 2, wherein the pellicle film is provided with a protective film made of a material selected from the group consisting of SiC, SiO2, Si3N4, SiON, Y2O3, YN, Mo, Ru, and Rh.

4. The pellicle for EUV exposure according to Claim 1 or 2, wherein the weight of the pellicle frame is 15 g or less.

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