Pellicle for EUV lithography

Abstract

To provide a pellicle in which peeling or fusion of a filter is suppressed even at high temperature such as 500°C or higher for example in EUV lithography.SOLUTION: A pellicle used in EUV lithography comprises a frame having an opening, and a pellicle film extensionally supported on one end face side of the frame so as to cover the opening, where vent holes for ventilation and filter covering the vent holes are provided for the frame, and the filters are made of quartz fiber, metal fiber, ceramic fiber, carbon fiber, sintered metal or sintered ceramic.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pellicle for EUV lithography. [Background technology]

[0002] In the manufacturing process of semiconductor devices such as large-scale integrated circuits (LSIs) and ultra-LSIs, as well as liquid crystal display panels, patterning is performed by irradiating light onto a photosensitive layer through a mask (also called an exposure master or reticle). If foreign matter adheres to the mask, the light is absorbed by the foreign matter or is reflected and bent by the surface of the foreign matter. As a result, the formed pattern may be deformed or have rough edges, resulting in problems such as impaired dimensions, quality, and appearance after patterning.

[0003] To solve this problem, a method has been adopted in which a pellicle with a light-transmitting pellicle film is attached to the surface of the mask to prevent foreign matter from adhering. A pellicle generally has a frame (pellicle frame), a pellicle film, which is a transparent thin film, arranged on one side of the frame, and an adhesive layer, which is arranged on the other side of the frame (the side opposite the pellicle film of the pellicle frame), for attaching it to the photomask.

[0004] The wavelength of light used in lithography is becoming shorter, and the use of EUV (Extreme Ultra Violet) light is being considered for next-generation lithography technology. EUV light refers to light with a wavelength in the soft X-ray or vacuum ultraviolet region, specifically, light rays with a wavelength of approximately 13.5 nm ± 0.3 nm.

[0005] EUV light is easily absorbed by all materials. If the pellicle film absorbs EUV light, it not only causes exposure defects but can also be damaged by heat generated by the energy of the EUV light.

[0006] Since exposure is performed under vacuum, ventilation holes are installed to reduce the pressure difference between the inside and outside of the closed space formed by the pellicle and the photomask, and a filter is placed to cover the ventilation holes to prevent foreign matter from entering the pellicle. Conventionally, such filters have been made of polytetrafluoroethylene (PTFE) (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-057804 Summary of the Invention [Problem to be solved by the invention]

[0008] However, during EUV exposure, the pellicle film absorbs light, causing the temperature of the pellicle film to rise to over 500°C. In an EUV exposure environment where temperatures reach over 500°C, PTFE filters can peel off or melt, creating a problem.

[0009] The present invention has been proposed in view of the above-described conventional situation, and an object of the present invention is to provide a pellicle in which peeling or melting of the filter is suppressed even at high temperatures, such as 500°C or higher, in EUV lithography. [Means for solving the problem]

[0010] [1] A pellicle for use in EUV lithography, comprising: a frame having an opening; and a pellicle membrane stretched and supported on one end face side of the frame so as to cover the opening, The frame is provided with a ventilation hole for ventilation and a filter that covers the ventilation hole, A pellicle characterized in that the filter is made of quartz fiber, metal fiber, ceramic fiber, carbon fiber, sintered metal or sintered ceramic. [2] The pellicle according to [1], wherein the filter is made of sintered metal or sintered ceramic. [3] The pellicle according to [1], wherein the metal fibers are titanium fibers. [4] The pellicle according to any one of [1] to [3], wherein the frame is made of titanium or a titanium alloy, and the filter is made of titanium fiber or sintered titanium. [5] The pellicle according to [1], wherein the frame is made of a carbon material and the filter is made of carbon fiber. [6] The pellicle according to [1] or [2], wherein the frame is made of ceramic and the filter is made of ceramic fiber or sintered ceramic. [7] The pellicle according to any one of [1] to [6], wherein the pellicle membrane is made of a carbon material. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a pellicle in which peeling or melting of the filter is suppressed even at high temperatures, for example, 500° C. or higher. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing an example of a configuration of a pellicle. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, a description will be given of an embodiment of the present invention (hereinafter abbreviated as "embodiment") with reference to the drawings. The present invention is not limited to the following embodiment, and various modifications can be made within the scope of the gist of the present invention.

[0014] An overview of the pellicle according to this embodiment will be described below. Fig. 1(a) is a top view showing a pellicle 1, and Fig. 1(b) is a longitudinal cross-sectional view. In the following description, the upper side of each figure will be referred to as "top" and the lower side as "bottom."

[0015] In this specification, EUV light refers to light with a wavelength of 5 nm or more and 30 nm or less. The wavelength of EUV light is preferably 5 nm or more and 14 nm or less, and specifically, EUV light refers to light with a wavelength of about 13.5 nm±0.3 nm.

[0016] [Pellicle] The pellicle 1 is a structure that protects a photomask from dust in photolithography, etc. The pellicle 1 includes a frame 2, a pellicle film 3, an adhesive layer 4, and a release film 5.

[0017] <frame> The frame 2 (frame body) can have any shape that allows the pellicle membrane 3 to be stretched over the frame 2. For example, the frame 2 can have an outer shape such as a rectangle, a square, a rectangle, or an ellipse when viewed from the front. The rectangle can be a square, a rectangle, or the like, and can have both right-angled corners and a roughly rectangular shape with rounded corners (FIG. 1). The polygon can be a triangle, a trapezoid, a parallelogram, a pentagon, a hexagon, or the like.

[0018] The size of the frame 2 and its opening can be determined according to the size of the photomask. When the frame 2 has a rectangular shape consisting of a pair of long sides and a pair of short sides in a front view, the long side length can be 80 mm to 300 mm, the short side length can be 50 mm to 250 mm, the widths of the long sides and the short sides can each be 1.0 mm to 10.0 mm, and / or the height of the frame 2 can be 1.0 to 6.0 mm.

[0019] As shown in Fig. 1, the frame 2 has edges. The edges can have rod-shaped edge members that extend linearly. A pair of edge members can be arranged parallel to each other with a gap between them, and similarly, another pair of edge members can be arranged parallel to each other with a gap between them. The ends of two contacting edge members can be connected so that they form approximately a right angle with each other.

[0020] The frame 2 can be made of known materials such as aluminum, aluminum alloys (e.g., 5000 series, 6000 series, 7000 series, etc.), titanium, titanium alloys (e.g., Ti-Al-V, Ti-V-Cr-Sn-Al, etc.), steel, stainless steel, magnesium alloys, ceramics (e.g., SiC, AlN, Al2O3, etc.), ceramic-metal composites (e.g., Al-SiC, Al-AlN, Al-Al2O3, etc.), engineering plastics such as PE, PA, PC, PEEK, etc., fiber composites such as GFRP, CFRP, etc., carbon materials, or combinations thereof. Among these, titanium, titanium alloys, carbon materials, or ceramics are preferred.

[0021] Titanium, titanium alloys, carbon materials, or ceramics have excellent heat resistance and high strength, so by constructing the frame 2 from the above materials, deformation of the frame 2 and wrinkles in the pellicle film 3 can be more reliably prevented even at high temperatures during EUV lithography.

[0022] The carbon material is not particularly limited, but examples thereof include graphite, carbon nanotubes, carbon fibers, and glassy carbon, and among these, graphite or glassy carbon is preferred.

[0023] <Ventilation holes> The frame 2 is provided with ventilation holes 10. By providing the ventilation holes 10, the difference in air pressure between the inside and outside of the closed space formed by the pellicle 1 and the photomask can be eliminated, and swelling or denting of the pellicle film 3 can be prevented.

[0024] The arrangement, number, and size of the ventilation holes 10 are not particularly limited as long as the above-mentioned purpose can be achieved, but Fig. 1 shows a case where one ventilation hole 10 is provided near the center of each side of the frame 2. As for the size, the diameter is, for example, about 0.3 to 0.7 mm.

[0025] <filter> Furthermore, a dust filter 11 is provided to cover the ventilation hole 10. The filter 11 is formed to be larger than the ventilation hole 10. This prevents foreign matter from entering the closed space between the pellicle 1 and the photomask from the outside through the ventilation hole 10.

[0026] The filter 11 is preferably made of quartz fiber, metal fiber, ceramic fiber, carbon fiber, sintered metal or sintered ceramic, and more preferably made of sintered metal or sintered ceramic.

[0027] Quartz fibers are preferable because they have high heat resistance and are fine-meshed, so they can be used in EUV exposure at temperatures of 500° C. or higher, and they can reliably capture foreign matter.

[0028] The metal constituting the metal fibers is not particularly limited, but examples thereof include aluminum and titanium, with titanium being preferred.

[0029] Ceramics have high heat resistance and do not cause problems such as outgassing. The ceramic that constitutes the ceramic fiber is not particularly limited, but examples thereof include titania, zirconia, ferrite, alumina, zircon, and mullite.

[0030] Carbon fiber has a fast adsorption rate and generates significantly less dust than granular carbon filters. Examples of carbon materials that form carbon fibers include graphene and activated carbon.

[0031] These quartz fibers, metal fibers, and carbon fibers are configured as entangled fiber bodies such as wool bodies and nonwoven fabrics.

[0032] Sintered metal is produced, for example, by sintering metal powder (powder metallurgy), and is a porous body having minute pores inside, and has extremely high filtering ability and excellent durability.

[0033] The sintered metal may be a powder sintered metal obtained by sintering a powder, a sintered wire mesh obtained by sintering a wire mesh, or a fiber sintered metal obtained by sintering a fiber (metal fiber).

[0034] The material of the sintered metal is not particularly limited, but examples thereof include stainless steel, Hastelloy, Monel, Inconel, titanium, nickel, etc., of which titanium is preferred. The metal may be a pure metal or an alloy, and a small amount of a non-metal may be added.

[0035] Examples of sintered ceramics include ceramics such as titania, zirconia, ferrite, alumina, zircon, and mullite.

[0036] In the pellicle 1, the frame 2 is preferably made of titanium or a titanium alloy, and the filter 11 is preferably made of titanium fiber or sintered titanium.

[0037] In addition, in the pellicle 1, it is preferable that the frame 2 is made of a carbon material and the filter 11 is made of carbon fiber.

[0038] In addition, in the pellicle 1, it is preferable that the frame 2 is made of ceramic and the filter 11 is made of ceramic fiber or sintered ceramic.

[0039] By constructing the frame 2 and the filter 11 from the same type of material as described above, the coefficients of linear thermal expansion of the frame 2 and the filter 11 become similar, and peeling or deformation of the filter 11 due to differences in the coefficients of linear thermal expansion when exposed to high temperatures can be more effectively suppressed.

[0040] The thickness of the filter 11 is not particularly limited, but is preferably 0.1 to 1.0 mm.

[0041] The filter 11 is installed so as to cover the ventilation hole 10 provided in the frame 2. In this case, the filter 11 may be installed using a known organic adhesive, but there are concerns that the filter may peel off or that outgas may be generated if the frame 2 becomes hot due to exposure. Therefore, if the frame 2 and the filter 11 are made of a metal material, the filter 11 may be continuously and integrally attached to the frame 2 by welding. In this way, since no adhesive is used, the problems of peeling off and outgassing can be avoided.

[0042] If necessary, an adhesive (e.g., acrylic, vinyl acetate, silicone, rubber-based adhesive, etc.) or grease (e.g., silicone-based, fluorine-based grease, etc.) may be applied to the inner surface or entire surface of the frame 2 to capture foreign matter. Additionally, the frame 2 may be provided with a jig hole or the like for attaching the pellicle 1 to a photomask, if necessary.

[0043] <Pellicle membrane> The pellicle film 3 is a transparent thin film having a thickness of 2 μm or less, and is formed so as to sufficiently transmit light emitted from a light source in photolithography.

[0044] The material constituting the pellicle film 3 is preferably a carbon film containing a carbon structure obtained by heating carbon or a compound containing carbon atoms. Carbon, graphene, carbon nanotubes (CNT), graphite, etc. are preferred as carbon films. Carbon nanotube films are particularly preferred from the viewpoints of heat resistance and transmittance. Furthermore, a reinforcing material may be present from the viewpoints of handling and light resistance. Preferred reinforcing materials are SiC or SiN-based compounds, or metals such as Mo, Ru, and Rh.

[0045] The carbon film is produced by, for example, including a step (step I) of depositing a film containing carbon atoms on a substrate, a step (step II) of heating the film deposited on the substrate at 800 to 1400°C in a nitrogen atmosphere to form a carbon film, and a step (step III) of peeling the carbon film from the substrate.

[0046] In (Step I), the compound containing carbon atoms is not particularly limited as long as it is carbonized by heating, and is preferably an organic material.

[0047] The compound containing carbon atoms is more preferably at least one selected from the group consisting of polyimide compounds, polybenzoxazine compounds, polyacrylonitrile compounds, polyisocyanate compounds, polyamide compounds, heteroaromatic ring compounds, polyphenylene resins, polyether resins, liquid crystal polymer resins, polyparaxylylene resins, phenolic resins, epoxy resins, and furan resins. The compound containing carbon atoms is more preferably at least one selected from the group consisting of polyimide compounds and polybenzoxazine compounds.

[0048] The substrate is not particularly limited as long as it has a melting point higher than 800 to 1400°C, which is the heating temperature when forming the carbon film, and for example, a silicon substrate (hereinafter also referred to as Si substrate) whose surface layer contains silicon dioxide (SiO2) is preferred. By producing a carbon film on a Si substrate, a carbon film with excellent in-plane film thickness uniformity can be produced without film breakage.

[0049] Known techniques can be applied to form carbon or a compound containing carbon atoms into a film, and arc plasma deposition (APD) is a preferred method for forming carbon into a film on a substrate, while spin coating is a preferred method for forming a compound containing carbon atoms into a film on a substrate. These methods make it possible to produce a carbon film with excellent in-plane film thickness uniformity.

[0050] In (Step II), the heating temperature is 800 to 1400° C., preferably 900 to 1300° C., and more preferably 1000 to 1200° C. Heating can be carried out using a heat treatment furnace or the like.

[0051] The heating time is preferably 1 minute to 10 hours, more preferably 10 minutes to 3 hours, and even more preferably 30 minutes to 2 hours, from the viewpoint of sufficiently converting carbon atoms into a turbostratic carbon structure.

[0052] In (Step III), the specific method for the step of peeling the carbon film from the substrate is not particularly limited, and examples thereof include a method including: a step of spin-coating a composition containing an acrylic resin or the like onto the carbon film obtained by heating to form a support film; a step of peeling the substrate by a hydrofluoric acid treatment or the like; a step of attaching a support frame to the peripheral edge of the carbon film of the structure consisting of the carbon film and the support film; and a step of removing the support film by an etching treatment or the like.

[0053] The thickness of the carbon film constituting the pellicle film 3 is preferably less than 1500 nm. The thickness of the carbon film is the thickness of the film as used in the ordinary sense. The upper limit of the thickness of the carbon film is more preferably 1200 nm or less, even more preferably 1000 nm or less, and even more preferably 500 nm or less. By making the thickness of the carbon film less than 1500 nm, it is possible to obtain a carbon film that does not develop cracks during production. The lower limit of the thickness of the carbon film is not particularly limited as long as it is greater than 0 nm.

[0054] The thickness of the carbon film can be controlled, for example, by adjusting the thickness of a film containing carbon atoms when the film is laminated on a substrate in the method for producing the pellicle film 3.

[0055] As shown in FIG. 1( b ), the pellicle film 3 is adhered and fixed to one end of the frame 2 with an adhesive (not shown), and covers the frame 2 .

[0056] <Adhesive layer> As shown in FIG. 1(b), an adhesive layer 4 for attaching the pellicle 1 to the photomask is disposed on the other end side of the frame 2 (the side of the frame 2 opposite to the pellicle film 3).

[0057] The adhesive layer 4 is made of an adhesive such as an acrylic, rubber, vinyl, epoxy, or silicone adhesive, and more preferably made of an acrylic, rubber, or silicone adhesive, etc. The thickness of the adhesive layer 4 is preferably, for example, 0.1 mm to 1.0 mm.

[0058] <Release film> A release film 5 (liner) is disposed so as to cover the adhesive layer 4. This release film 5 protects the adhesive layer 4 when not in use, and is peeled off from the adhesive layer 4 when the pellicle 1 is in use.

[0059] A film of polyester or the like having a thickness of about 30 to 200 μm is generally used for the release film 5. If the peeling force required to peel the release film 5 from the adhesive layer 4 is too great, the adhesive layer 4 may be deformed during peeling. Therefore, the surface of the film that comes into contact with the adhesive may be subjected to a release treatment such as silicone or fluorine to achieve an appropriate peeling force.

[0060] In the pellicle 1 of this embodiment having such a configuration, the filter 11 is made of quartz fiber, metal fiber, ceramic fiber, carbon fiber, sintered metal, or sintered ceramic, so that peeling or melting of the filter 11 is suppressed even at high temperatures, and the pellicle has excellent structural stability, making it suitable as a pellicle for EUV lithography.

[0061] Although the embodiment of the present invention has been described above, the present invention is not limited to this and can be modified as appropriate within the scope of the invention. [Example]

[0062] The present invention will now be described in more detail with reference to examples and comparative examples. However, the present invention is not limited to the following examples as long as it does not deviate from the gist of the present invention.

[0063] [Fabrication of pellicle] Example 1 (1) Preparation of adhesive frame A frame (melting temperature: 1668°C, 0.2% yield strength at 300°C: 900 MPa, Young's modulus: 78 GPa) made of β-type Ti alloy (Ti-15V-3Cr-3Sn-3Al) with an outer diameter of 149 mm x 115 mm x height of 3 mm and width of 2 mm was prepared, and an acrylic adhesive was attached to its lower end surface to create an adhesive-coated frame. A 0.5 mm diameter air hole was provided in the frame, and a filter made of quartz fiber was attached with an adhesive so as to cover the air hole.

[0064] (2) Preparation of carbon film A 15 wt% solution of a polyimide precursor (BPDA-ODA) synthesized from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BDPA) and 4,4'-diaminodiphenyl ether (ODA) in N-methylpyrrolidone was spin-coated onto a Si substrate and imidized at 300°C for 1 hour under a nitrogen atmosphere to form a 400 nm thick polyimide film.

[0065] Subsequently, the substrate was placed in a heat treatment furnace and heated in an N2 flow atmosphere at 1100°C for 1 hour to carbonize it, thereby obtaining a carbon film with a thickness of 200 nm.

[0066] The substrate was then spin-coated at 500 rpm with a 15 wt% solution of polymethyl methacrylate (PMMA) in acetone to form a support film. The substrate was then immersed in a 40 wt% aqueous solution of hydrogen fluoride, and the PMMA-coated carbon film was peeled off from the substrate and washed with water. The PMMA-coated carbon film was then immersed in a 1:1 (weight ratio) solution of acetone and isopropyl alcohol to dissolve the PMMA. The carbon film was then transferred to the isopropyl alcohol solution using a glass substrate. The carbon film was then removed and dried to obtain a carbon film.

[0067] The obtained carbon film was attached to the upper end surface of the adhesive-attached frame via an adhesive to form the pellicle of Example 1.

[0068] <Example 2> A pellicle was prepared in the same manner as in Example 1, except that a filter made of stainless steel fibers was used instead of the quartz fibers.

[0069] Example 3 A pellicle was produced in the same manner as in Example 1, except that a ceramic fiber filter was used instead of the quartz fiber.

[0070] Example 4 A pellicle was produced in the same manner as in Example 1, except that a filter made of titanium fiber was used instead of the quartz fiber.

[0071] <Example 5> A pellicle was fabricated in the same manner as in Example 1, except that a frame made of a titanium alloy was used instead of an aluminum alloy, and a filter made of titanium fiber was used instead of quartz fiber.

[0072] Example 6 A pellicle was fabricated in the same manner as in Example 1, except that a frame made of a titanium alloy was used instead of an aluminum alloy, and a filter made of sintered titanium was used instead of quartz fiber. Example 7 A pellicle was produced in the same manner as in Example 1, except that a frame made of carbon was used instead of an aluminum alloy and a filter made of carbon fiber was used instead of quartz fiber. Example 8 A pellicle was fabricated in the same manner as in Example 1, except that a ceramic frame was used instead of the aluminum alloy and a sintered ceramic filter was used instead of the quartz fiber.

[0073] <Comparative Example 1> A pellicle was produced in the same manner as in Example 1, except that a filter made of polytetrafluoroethylene (PTFE) was used instead of the quartz fiber.

[0074] <Comparative Example 2> A pellicle was produced in the same manner as in Example 1, except that a frame made of a titanium alloy was used instead of an aluminum alloy, and a filter made of polytetrafluoroethylene (PTFE) was used instead of quartz fiber.

[0075] [Evaluation of frame properties] The filtering performance of the pellicles of the examples and comparative examples prepared as described above was evaluated as follows.

[0076] <Foreign matter collection ability> The foreign matter capturing ability of the filter was investigated under the following conditions. Equipment: TSI filter test equipment 3160 ·Particle: PAO 0.5μm ·Surface speed: 5.3cm / s

[0077] <Heat resistance test> The obtained pellicle was attached to a quartz substrate (6025) and stored in an oven at 200°C for 24 hours. After that, the condition of the filter was visually observed. If the filter was severely deformed or peeled off, it was marked with ×; if there was some deformation but no practical problem, it was marked with ◯; if there was no change in appearance, it was marked with ⊚.

[0078] Table 1 shows the evaluation results of the filter performance (foreign matter capture ability, heat resistance test) of the pellicles of the examples and comparative examples.

[0079] [Table 1]

[0080] As is clear from Table 1, in the comparative example using PTFE as a filter, deformation and peeling occurred during the heat resistance test, but in Examples 1 to 8 using filters made of quartz fiber, metal fiber (stainless steel fiber, titanium fiber), ceramic fiber, or sintered metal (sintered titanium), sufficient collection performance of more than 95% was achieved and no significant deformation was observed during the heat resistance test. In particular, Examples 5 to 8, in which the filter and frame were made of the same material, obtained better results.

[0081] Although the embodiment of the present invention has been described above, the present invention is not limited to this and can be modified as appropriate within the scope of the invention. [Industrial Applicability]

[0082] By using the pellicle according to the present invention, peeling or melting of the filter can be suppressed even at high temperatures of, for example, 500°C or higher, and the pellicle can be widely used as a pellicle for EUV lithography. [Explanation of symbols]

[0083] 1: Pellicle 2: Frame 3: Pellicle membrane 4:Adhesive layer 5: Release film 10: Ventilation hole 11: Filter

Claims

1. A pellicle for use in EUV lithography, comprising: a frame having an opening; and a pellicle membrane stretched and supported on one end face side of the frame so as to cover the opening, The frame is provided with a ventilation hole for ventilation and a filter that covers the ventilation hole, the frame is made of titanium, a titanium alloy, or a carbon material; the filter is made of quartz fiber, metal fiber, carbon fiber, or sintered metal; A pellicle characterized in that the frame and the filter are made of the same type of material.

2. The pellicle of claim 1 , wherein the filter is made of sintered metal.

3. The pellicle of claim 1 , wherein the metal fibers are titanium fibers.

4. 4. The pellicle according to claim 1, wherein the frame is made of titanium or a titanium alloy, and the filter is made of titanium fiber or sintered titanium.

5. The pellicle of claim 1 , wherein the frame is made of a carbon material and the filter is made of carbon fiber.

6. The pellicle according to any one of claims 1 to 5, wherein the pellicle membrane is made of a carbon material.

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