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] This invention relates to a lithography pellicle used as a dust filter when manufacturing semiconductor devices such as LSIs and ultra-large-scale integrated circuits (ULSIs), printed circuit boards, liquid crystal displays, and the like. [Background technology]

[0002] When manufacturing semiconductor devices such as LSIs and ultra-large-scale integrated circuits (ULSIs) and liquid crystal displays, patterns are created by irradiating semiconductor wafers or liquid crystal master plates with light. However, if dust adheres to the photomask or reticle (hereinafter simply referred to as "photomask") used in this process, the edges of the pattern become rough, the base material becomes blackened, and other problems arise, such as damage to the dimensions, quality, and appearance of the resulting product.

[0003] For this reason, pattern creation is usually performed in a cleanroom, but even then, it is difficult to keep the photomask clean at all times. Therefore, a pellicle is attached to the surface of the photomask as a dust filter before exposure. In this case, foreign matter does not adhere directly to the surface of the photomask but adheres to the pellicle film, so if the focus is set on the pattern on the photomask during lithography, the foreign matter on the pellicle film will not be affected by the transfer.

[0004] Generally, a pellicle is formed by bonding a transparent pellicle film, made of nitrocellulose, cellulose acetate, fluororesin, etc., which transmits light well, to the upper surface of a pellicle frame made of aluminum, stainless steel, polyethylene, etc., after applying a suitable solvent for the pellicle film and air-drying it (see Patent Document 1), or by bonding it 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, etc., for attachment to a photomask, and a release layer (separator) for protecting the adhesive layer.

[0005] Furthermore, when such a pellicle is attached to the surface of a photomask and a photoresist film formed on a semiconductor wafer or liquid crystal master is exposed via the photomask, foreign matter such as dust adheres to the surface of the pellicle and not directly to the surface of the photomask. Therefore, by irradiating the exposure light so that the focal point is located on the pattern formed on the photomask, it becomes possible to avoid the effects of foreign matter such as dust.

[0006] Incidentally, in recent years, semiconductor devices and liquid crystal displays have been becoming increasingly integrated and miniaturized. Currently, technology for forming fine patterns of about 32 nm on photoresist films is being put into practical use. Patterns of about 32 nm can be achieved using immersion lithography, which involves filling the space between the semiconductor wafer or liquid crystal master and the projection lens with a liquid such as ultrapure water, and exposing the photoresist film using an argon fluoride (ArF) excimer laser, or by improving conventional excimer laser techniques such as double exposure.

[0007] However, next-generation semiconductor devices and liquid crystal displays require even finer pattern formation of 10nm or less, and it is no longer possible to achieve such finer pattern formation of 10nm or less with improvements to conventional excimer laser exposure technology.

[0008] Therefore, EUV (Extreme Ultra Violet) lithography, which uses EUV light with a dominant wavelength of 13.5 nm, is considered the most promising method for forming patterns smaller than 10 nm. When using this EUV lithography technology to form fine patterns smaller than 10 nm on a photoresist film, it is necessary to solve technical challenges such as what kind of light source to use, what kind of photoresist to use, and what kind of pellicle to use. Of these technical challenges, development is progressing and various proposals have been made for new light sources and new photoresist materials.

[0009] Regarding the pellicle, which is crucial for the yield of semiconductor devices or liquid crystal displays, for example, Patent Document 3 describes a transparent, optically distortion-free silicon film with a thickness of 0.1 to 2.0 μm as a pellicle film for use in EUV lithography. However, unresolved issues remain for practical application, which pose a significant obstacle to the practical implementation of EUV exposure technology.

[0010] Conventionally, when selecting the material for the pellicle frame that constitutes the pellicle, in exposure using i-line (wavelength 365nm), krypton fluoride (KrF) excimer laser light (wavelength 248nm), and argon fluoride (ArF) excimer laser light (wavelength 193nm), the material has been selected based solely on its rigidity and processability, and typically aluminum, stainless steel, and polyethylene have been used.

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

[0012] However, when using EUV lithography technology to form fine patterns of 10 nm or less on a photoresist film, using conventional pellicles can result in wrinkles in the pellicle film, peeling off the pellicle frame, tearing, or cracking.

[0013] Patent Document 4 found that wrinkles and damage to the pellicle film are caused by expansion and contraction and distortion of the pellicle frame due to the temperature rise caused by light energy during exposure, and that the coefficient of linear expansion is 10 × 10 -6 It has been suggested that materials with a (1 / K) or lower ratio be used for the frame.

[0014] However, materials such as Si, SiO2, SiC, and SiN with low thermal expansion coefficients have problems of being brittle and difficult to process. In particular, for EUV pellicles, due to the small pellicle placement space in the EUV exposure apparatus, it is necessary to make the height 2.5 mm or less.

[0015] Also, usually, on the side surface of the pellicle frame of the pellicle, jig holes used when handling or peeling the pellicle from the photomask and ventilation parts for relaxing the pressure difference inside and outside the pellicle are provided. Further, in EUV lithography, in order to make the inside of the exposure apparatus vacuum, the EUV pellicle needs to withstand the pressure change from atmospheric pressure to vacuum, and the ventilation part of the EUV pellicle is required to have a large area.

[0016] For example, although the thickness of the pellicle frame of the EUV pellicle becomes smaller than 2.5 mm, when trying to provide a hole with a diameter of 1 mm on the side surface of the pellicle frame made of materials such as Si, SiO2, SiC, and SiN, the thickness near the hole of the pellicle frame may become smaller, and there is a high possibility that the pellicle frame will be damaged during hole processing or pellicle peeling. If a large area of the ventilation part is required, the possibility of damage will further increase.

[0017] Therefore, it is also conceivable to use a metal such as invar as a material with a low thermal expansion coefficient. Metals and alloys are easy to process and do not break even when holes are provided on the side surface of the pellicle frame.

[0018] By the way, the width of the pellicle frame is preferably as small as possible in order to widen the exposure area, and conventionally it was about 2 mm. However, in the case of EUV pellicles, it has been found that the width of the pellicle frame is restricted by the pellicle film and needs to be increased to about 3 - 4 mm.

[0019] In recent years, for the purpose of improving the throughput of EUV manufacturing, faster movement of the mask stage has been required, and the total weight of the pellicle is required to be 15 g or less.

[0020] However, when the width becomes 2 mm to 4 mm, the volume of the pellicle frame becomes about twice or about 1.5 times even at 3 mm. As a result, it was found that the pellicle frame made of invar becomes too heavy.

Prior Art Documents

Patent Documents

[0021]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0022] The present invention has been made in view of the above circumstances, and when forming a fine pattern of 10 nm or less on a photoresist film using EUV exposure technology, it can effectively prevent the situation where wrinkles occur in the pellicle film, the pellicle film peels off, breaks, or cracks from the pellicle frame. Moreover, an object of the present invention is to provide a pellicle frame that is lightweight and has a low risk of damage, and a pellicle using the same.

Means for Solving the Problems

[0023] The inventor of the present invention uses a frame-shaped pellicle frame having an upper end surface provided with a pellicle film and a lower end surface facing a photomask, and a metal or alloy 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 has found that it is optimal for the latest EUV exposure technology because it does not cause wrinkles or damage to the pellicle film and is lighter in weight, thus arriving at the present invention.

[0024] Accordingly, the present invention provides the following pellicle frame and pellicle. 1. The coefficient of linear expansion is 10 × 10 -6 (1 / K) or less, and density of 4.6 g / cm³ 3 A pellicle frame characterized by being made of the following metals or alloys. 2. The pellicle frame according to claim 1, wherein the above metal or alloy is titanium or a titanium alloy. 3. A pellicle frame as described in 1 or 2, with a thickness of less than 2.5 mm. 4. A pellicle frame as described in any of 1 to 3, having one or more holes on its side. A pellicle characterized by including a pellicle frame as described in any of sections 5.1 to 5.4 as a component. [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 to a minimum, preventing wrinkles and damage to the pellicle film. Furthermore, the pellicle frame and pellicle of the present invention offer excellent processability, leading to improved yield, and allow for a larger ventilation area. Moreover, they have a low risk of damage during pellicle peeling and are lightweight, making them applicable to the latest EUV exposure technology. [Brief explanation of the drawing]

[0026] [Figure 1] This is a schematic diagram (example) showing one embodiment of the pellicle frame of the present invention, where (A) is a view from the lower end side, (B) is a view from the outer side of the long side, and (C) is a view from the outer side of the short side. [Figure 2] This is a schematic diagram showing another embodiment of the pellicle frame of the present invention, where (A) is a view from the lower end side, (B) is a view from the outer side of the long side, and (C) is a view from the outer side of the short side. [Modes for carrying out the invention]

[0027] The pellicle frame of the present invention typically has an upper end surface for mounting the pellicle film and a lower end surface facing the photomask. Its shape is frame-like, corresponding to the shape of the photomask on which the pellicle is attached. Generally, it is a rectangular (or square) frame shape.

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

[0029] The dimensions of the pellicle frame are not particularly limited, but since the height of the pellicle for EUV is limited to 2.5 mm or less, the thickness of the pellicle frame for EUV is smaller than that, less than 2.5 mm. In practice, considering the thickness of the pellicle film and mask adhesive, it is preferable that it be 2.0 mm or less, and more preferably 1.6 mm or less.

[0030] Furthermore, in order for the pellicle to function properly, a height of 1.5 mm or more is required. Therefore, considering the thickness of the pellicle frame for EUV, it is preferable that the thickness be 1.0 mm or more, taking into account the thickness of the pellicle film and mask adhesive.

[0031] Furthermore, the sides of the pellicle frame are typically provided with jig holes used for handling and detaching the pellicle from the photomask, as well as ventilation openings to mitigate pressure differences between the inside and outside of the pellicle. In addition, since the exposure apparatus is kept under vacuum in EUV lithography, the EUV pellicle must withstand the pressure change from atmospheric pressure to vacuum, and it is preferable that the ventilation openings of the EUV pellicle have as large an area as possible.

[0032] Therefore, it is preferable to provide holes on the side surface of the pellicle frame. The size of the jig holes and ventilation holes is such that the length in the thickness direction of the frame (diameter in the case of a circle) is 0.5 to 1.0 mm. There is no limitation on the shape of the holes, and they can be circular or rectangular. Also, usually, the jig holes are holes that do not penetrate from the outer surface to the inner surface, and the ventilation holes are holes that penetrate from the outer surface to the inner surface.

[0033] When providing holes on the side surface of the pellicle frame, in order to maintain processing constraints and the strength of the frame, at least a 0.2 mm margin is required around the processed holes. If a jig hole or ventilation hole with a length in the thickness direction of the frame of 1.0 mm or more is to be provided, the thickness of the frame is preferably 1.4 mm or more.

[0034] The dimensions of the EUV pellicle frame are usually such that the length of the long side in the outer dimensions is 145 to 152 mm, the length of the short side is 113 to 120 mm, the thickness is 1.0 to 2.0 mm, and the width is 3.0 to 4.0 mm. Also, the volume of the pellicle frame is preferably 3.2 cm 3 or less, and more preferably 2.6 cm 3 or less.

[0035] In the present invention, for the material of the pellicle frame, a metal or alloy with a linear expansion coefficient of 10×10 -6 (1 / K) or less and a density of 5 g / cm 3 or less is used.

[0036] In the present invention, by using a metal or alloy as the material of the pellicle frame, holes can be provided on the side surface even with a 0.2 mm margin. For example, a hole with a diameter of 1.0 mm can be provided on the side surface of a pellicle frame with a thickness of 1.5 mm. At this time, the margin above and below the hole is 0.25 mm.

[0037] Furthermore, when forming holes in a pellicle frame made of brittle material such as silicon single crystal, 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 insufficient ventilation for an EUV pellicle, and to reliably hold or detach the frame with 0.5 mm diameter jig holes, the number of holes must be increased, which reduces the yield. Moreover, even with a 0.5 mm margin, there is a high possibility of breakage when large forces are applied, such as during detachment.

[0038] In this invention, the coefficient of thermal expansion of the pellicle frame material is 10 × 10 -6 The temperature is below (1 / K), and within this range, the expansion and contraction and distortion of the pellicle frame that may occur due to the temperature rise caused by the light energy during exposure can be sufficiently suppressed, preventing wrinkles and damage to the pellicle film.

[0039] Furthermore, in this invention, the density of the metal or alloy that is the pellicle frame material is 4.6 g / cm³. 3 The following applies: Within this density range, the volume is 3.2 cm³. 3 The following pellicle frames can have a weight of 15g or less. However, the volume of the pellicle frame must be 2.6cm³. 3 If this is exceeded, the weight of the pellicle film and mask adhesive other than the pellicle frame must be 3g or less. Therefore, the volume of the pellicle frame must be 2.6cm³. 3 The following is preferable, and the density is more preferably 4.5 g / cm³. 3 The following applies:

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

[0041] In the pellicle of the present invention, a pellicle film is provided on the upper end surface of the pellicle frame via an adhesive or bonding agent. There are no restrictions on the material of the adhesive or bonding agent; known materials can be used. For example, the pellicle film may be bonded by applying a good solvent and then air-drying it, or adhesives or bonding agents such as acrylic resin, silicone resin, or epoxy resin may be used.

[0042] Furthermore, while there are no restrictions on the material of the pellicle film, it is preferable to use a material with high transmittance at the wavelength of the exposure light source and high light resistance. For example, amorphous fluoropolymers can be used for excimer lasers. Examples of amorphous fluoropolymers include Cytop [manufactured by Asahi Glass Co., Ltd.: product name] and Teflon® AF [manufactured by DuPont Japan Ltd.: product name].

[0043] Furthermore, for EUV lithography, ultrathin silicon films or carbon films composed of single-crystal silicon, polycrystalline silicon, or amorphous silicon are used. The pellicle film may also include protective films made of SiC, SiO2, Si3N4, SiON, Y2O3, YN, Mo, Ru, and Rh.

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

[0045] The pellicle film adhesive and mask adhesive can be applied by, for example, dipping, spraying, brushing, or using a dispenser application device, but application using a dispenser application device is preferred in terms of stability, workability, and yield.

[0046] Furthermore, adhesives and bonding agents are generally formed over the entire circumference of the pellicle frame end face, 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 by a coating 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 mixtures thereof may 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 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.

[0049] If the pellicle frame has holes that penetrate from the outer surface to the inner surface, a dust filter may be provided for the purpose of removing particles. The filter may be installed inside the holes, or it may be installed on the side so as to cover the openings of the holes.

[0050] In addition, for EUV pellicle frames, the total area of ​​the ventilation openings is 5 mm². 2 It is preferable to have a minimum of 10 mm 2 The above is more preferable. The ventilation holes may, for example, penetrate from the outer surface to the inner surface so that a recess is formed on the lower end surface.

[0051] Here, Figures 1 and 2 show an example of a pellicle 1 that includes the pellicle frame 2 of the present invention as a component. The pellicle film 3 is bonded and stretched to the upper end surface of the pellicle frame 2 with adhesive 5. Adhesive 4 for attaching to a photomask (not shown) is provided on the lower end surface of the pellicle frame 2. In the figures, reference numeral 6 denotes a ventilation hole, and unlike Figure 1, the pellicle frame in Figure 2 is formed so that the ventilation hole is recessed 6 on the lower end surface. Reference numeral 7 denotes a jig hole that is usually formed to peel the pellicle from the photomask using a jig. [Examples]

[0052] 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.

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

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

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

[0056] Next, the pellicle frame was heated at 90°C for 12 hours to cure the adhesive on the upper and lower end surfaces. Subsequently, an ultra-thin silicone film was pressed onto the adhesive formed on the upper end surface of the frame to complete the pellicle.

[0057] Here, the volume of the pellicle frame is approximately 2.4 cm³. 3 The total weight of the pellicle film and adhesive is approximately 3.1g.

[0058] [Example 2] The pellicle frame is made of Ti-Al6-V4 titanium alloy, an alloy of titanium, aluminum, and vanadium (coefficient of thermal expansion: 8.8 × 10⁻⁶). -6 (1 / K), density: 4.4g / cm 3 ) was used. Otherwise, the pellicle was prepared in the same manner as in Example 1.

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

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

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

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

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

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

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

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

[0067] [Table 1]

[0068] According to the results in Table 1, the pellicles of Examples 1 and 2 showed good results in both heat cycle tests and processability, and the pellicle weight was kept below 15g. On the other hand, the pellicles of Comparative Examples 1 and 2 had problems with machinability, making it difficult to create holes in the side surfaces. Although the pellicle of Comparative Example 3 showed good results in both heat cycle testing and processability, it could not be applied to EUV lithography because its pellicle weight exceeded 15g. In Comparative Example 4, the pellicle frame underwent significant expansion and contraction during the heat cycle test, resulting in cracks in the pellicle film. [Explanation of Symbols]

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

Claims

1. In an EUV exposure pellicle in which a pellicle film is provided on the upper end surface of a pellicle frame via an adhesive or bonding agent, the pellicle frame has a thickness of less than 2.5 mm, a width of 3 to 4 mm, a weight of 15 g or less, and its material has a coefficient of thermal expansion of 10 × 10 -6 (1 / K) or less, and density of 4.6 g / cm³ 3 A pellicle for EUV exposure, characterized in that it is made of titanium or a titanium alloy, has multiple holes of 1.0 mm or more in length in the thickness direction of the pellicle frame formed on its side surface, and the pellicle film is a silicon film or a carbon film.

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, and amorphous silicon.

3. The above pellicle film contains SiC and SiO 2 Si 3 N 4 , SION, Y 2 O 3 The pellicle for EUV exposure according to claim 1 or 2, comprising a protective film made of a material selected from the group consisting of YN, Mo, Ru, and Rh.

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