Pellicle for EUV lithography

Abstract

To provide a pellicle that can more reliably suppress frame deformation and the occurrence of wrinkles in the pellicle film during EUV lithography. [Solution] A pellicle for use in EUV lithography, comprising a frame having an opening and a pellicle membrane stretched and supported on one end face of the frame so as to cover the opening, characterized in that the frame is made of a carbon material and the pellicle membrane is made of a carbon material.

Description

Technical Field

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

Background Art

[0002] In the manufacturing processes of semiconductor devices such as large-scale integrated circuits (LSIs) and very-large-scale integrated circuits (VLSIs), and liquid crystal display panels, patterning is performed by irradiating a photosensitive layer or the like with light through a mask (also referred to as an exposure master or a reticle). At that time, if foreign matter adheres to the mask, the light is absorbed by the foreign matter, or the light is reflected and bent on the surface of the foreign matter. As a result, problems such as deformation of the formed pattern, rough edges, and deterioration of the dimensions, quality, and appearance after patterning occur. To solve such problems, a method of attaching a pellicle having a pellicle film that transmits light to the surface of the mask to suppress the adhesion of foreign matter is adopted.

[0003] The wavelength of light used in lithography is becoming shorter, and the use of extreme ultraviolet (EUV) light is being considered as the next-generation lithography technology. EUV light refers to light having a wavelength in the soft X-ray region or the vacuum ultraviolet region, specifically, light rays of about 13.5 nm ± 0.3 nm.

[0004] [[ID=2ON]]EUV light is easily absorbed by any substance. When the pellicle film absorbs EUV light, it not only causes exposure failure but may also damage the pellicle film due to heat generation by the energy of EUV light.

[0005] For example, in EUV exposure, the pellicle film absorbs light, and the temperature of the pellicle film rises to 500°C or higher. There are problems such as the heat being transmitted to the frame and the frame being deformed. In addition, due to the difference in the linear expansion coefficients of the frame material and the pellicle film material, there are also problems such as wrinkles forming in the pellicle film during exposure.

[0006] Therefore, conventional pellicle films, such as those used for ArF light, are considered unsuitable for EUV light, and pellicles specifically designed for EUV light have been proposed.

[0007] For example, Patent Document 1 discloses a pellicle in which wrinkles and damage to the pellicle film are suppressed by using a metal or alloy with a low coefficient of thermal expansion and density as the frame. Patent Document 2 discloses a pellicle frame made of a material having a low coefficient of thermal expansion. Patent Document 3 discloses a pellicle frame made of a composite member in which carbon fibers are oriented in the longitudinal direction of each side of the frame. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2019-70745 [Patent Document 2] Patent No. 6370255 [Patent Document 3] Patent No. 5940283 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, the techniques disclosed in the above-mentioned literature are not sufficient to suppress frame deformation or the occurrence of wrinkles in the pellicle film.

[0010] This invention was proposed in view of the above-mentioned conventional circumstances, and the object of this invention is to provide a pellicle that can more reliably suppress frame deformation and the occurrence of wrinkles in the pellicle film in EUV lithography. [Means for solving the problem]

[0011] [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, A pellicle characterized in that the frame is made of carbon material. [2] The pellicle according to [1], wherein the carbon material is graphite or glassy carbon. [3] The pellicle according to [1] or [2], wherein the pellicle film is made of a carbon material. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a pellicle that can more reliably suppress frame deformation and the occurrence of wrinkles in the pellicle film during EUV lithography. [Brief explanation of the drawing]

[0013] [Figure 1] This figure shows an example of a pellicle configuration. [Modes for carrying out the invention]

[0014] The following describes embodiments for carrying out the present invention (hereinafter abbreviated as "embodiments") with reference to the drawings. The present invention is not limited to the following embodiments, and can be implemented in various modifications within the scope of its gist.

[0015] The outline of the pellicle according to this embodiment will be described. Figure 1(a) is a top view showing the pellicle 1, and Figure 1(b) is a longitudinal cross-sectional view. In the following explanation, the upper side of each diagram will be referred to as "top" and the lower side as "bottom."

[0016] Furthermore, in this specification, EUV light refers to light with a wavelength of 5 nm to 30 nm. Preferably, the wavelength of EUV light is 5 nm to 14 nm, and specifically, EUV light refers to light with a wavelength of approximately 13.5 nm ± 0.3 nm.

[0017] [Pericle] The pericle 1 is a structure for preventing dust on a photomask in photolithography or the like. The pericle 1 includes a frame 2, a pericle film 3, an adhesive layer 4, and a release film 5.

[0018] [Frame] The frame 2 (frame body) can have an arbitrary form such that the pericle film 3 can be stretched on the frame 2. For example, when viewed from the front, the frame 2 can have an outer shape such as a square, a polygon, a circle, an ellipse, etc. The square can be a square, a rectangle, etc., and can have both the case where the corners are right angles and the case of a substantially square shape (Figure 1) where the corners are rounded. The polygon can be a triangle, a trapezoid, a parallelogram, a pentagon, a hexagon, etc.

[0019] The size of the frame 2 and its opening can be determined according to the size of the photomask. When the frame 2 is rectangular in shape with a pair of long sides and a pair of short sides in a front view, the length of the long side can be 80 mm to 300 mm, the length of the short side can be 50 mm to 250 mm, the widths of the long side and the short side can be 1.0 mm to 10.0 mm respectively, and / or the height of the frame 2 can be 1.0 mm to 8.0 mm.

[0020] As shown in Figure 1, the frame 2 has an edge. The edge can have a rod-shaped edge member extending linearly. A pair of edge members can be arranged in parallel with a gap between them. Similarly, another pair of edge members can also be arranged in parallel with a gap between them. The ends of two contacting edge members can be connected so as to form a substantially right angle with each other.

[0021] In the pericle 1 of the present invention, the frame 2 is made of a carbon material. <00​

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

[0023] (Graphite) Graphite is a layered form of graphite with a hexagonal plate-like crystalline structure. Graphite has excellent heat resistance and is highly resistant to thermal shock. It also has the advantage of a low coefficient of thermal expansion. By constructing frame 2 from graphite, deformation of frame 2 and wrinkle formation of the pellicle film 3 can be suppressed even at high temperatures during EUV lithography.

[0024] The graphite material may be selected as appropriate, and may be either artificial or natural. It may also be isotropic graphite or SiC-coated graphite material, in which SiC is coated on the surface of the graphite.

[0025] This section describes one example of a common manufacturing method for Frame 2 using graphite. (1) First, finely ground coal coke or other materials are molded into a frame shape to obtain a carbon molded body. (2) Next, the carbon molded body is heated to 800°C to 1000°C in a firing furnace and fired to obtain a fired body. (3) Then, the fired body is removed from the firing furnace and heated to 3000°C in a graphitization furnace to obtain the final product by graphitization. In order to ensure that the orientation of the long and short sides is uniform, CIP molding is preferred for the molding in (1).

[0026] (Glass-like carbon) Glassy carbon is a non-graphitized carbon that combines the properties of glass and ceramic. It is a type of carbon material obtained by carbonizing and firing cured thermosetting resins, and possesses a glassy, ​​highly homogeneous, and dense structure. In addition to the conductivity, chemical stability (especially acid resistance), and heat resistance characteristic of general carbon materials, it also has the unique feature of not pulverizing or flaking off from its surface, making it attractive for various applications.

[0027] Glassy carbon has particularly excellent high-temperature stability and heat resistance, as well as high strength. It also has the advantage of a low coefficient of thermal expansion and strong resistance to thermal shock. By constructing frame 2 from glassy carbon, deformation of frame 2 and wrinkle formation of the pellicle film 3 can be suppressed even at high temperatures during EUV lithography.

[0028] This section describes an example of a general manufacturing method for frame 2 using glassy carbon. (1) First, cellulose, phenolic resin, imide resin, furan resin, or other thermosetting resin is molded into a frame shape and cured. (2) Then, it is obtained by calcining and carbonizing in an inert atmosphere or under vacuum.

[0029] The method for molding the thermosetting resin into a frame shape is not particularly limited. It may be manufactured using molding methods such as pressure molding, injection molding, or compression molding, or it may be manufactured by cutting or machining from a block of thermosetting resin.

[0030] After forming the frame shape, the material is calcined and carbonized to produce glassy carbon. The calcination is carried out under an inert gas atmosphere such as nitrogen gas, helium gas, or argon gas, or under vacuum. The calcination temperature is preferably 700 to 1600°C.

[0031] Ventilation holes may be provided in frame 2. By providing ventilation holes, the pressure difference inside and outside the closed space formed by the pellicle 1 and the photomask can be eliminated, preventing the pellicle membrane 3 from bulging or denting. It is also preferable to attach dust removal filters to the ventilation holes. In this way, foreign matter can be prevented from entering the closed space between the pellicle 1 and the photomask from the outside through the ventilation holes.

[0032] The inner circumferential surface or the entire surface of frame 2 may be coated with an adhesive (e.g., acrylic, vinyl acetate, silicone, or rubber-based adhesive) or grease (e.g., silicone or fluorine-based grease) as needed to trap foreign matter. In addition, the frame 2 may be provided with jig holes or other features as needed for attaching the pellicle 1 to the photomask.

[0033] <Pellicle membrane> The pellicle film 3 is a transparent thin film. The pellicle film 3 has a thickness of 10 μm or less and is formed to sufficiently transmit light emitted from a light source in photolithography.

[0034] The materials constituting the pellicle film 3 are not particularly limited, but examples include silicon films, silicon carbide films, cellulose derivatives, fluoropolymers, and carbon materials, and among these, carbon materials are preferred.

[0035] Because the pellicle film 3 is made of carbon material, the difference in linear thermal expansion coefficients between it and the frame 2, which is also made of carbon material, is reduced. Even when the pellicle film 3 is heated to a high temperature by EUV light, the difference in linear thermal expansion coefficients between the pellicle film 3 and the frame 2 effectively suppresses the formation of wrinkles in the pellicle film 3.

[0036] The pellicle film 3 is preferably a carbon film containing a carbon structure obtained by heating carbon or a compound containing carbon atoms.

[0037] A carbon film is manufactured, for example, by comprising the steps of: laminating a film containing carbon atoms onto a substrate (Step I); heating the film laminated on the substrate at 800 to 1400°C under a nitrogen atmosphere to form a carbon film (Step II); and peeling the carbon film from the substrate (Step III).

[0038] 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.

[0039] The carbon-carbon compound is more preferably one or more 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 carbon-carbon compound is more preferably one or more selected from the group consisting of polyimide compounds and polybenzoxazine compounds.

[0040] The substrate is not particularly limited as long as its melting point is higher than the heating temperature of 800 to 1400°C used when forming the carbon film. For example, a silicon substrate (hereinafter also referred to as a Si substrate) in which the surface layer contains silicon dioxide (SiO2) is preferred. By manufacturing a carbon film on a Si substrate, a carbon film with excellent uniformity of in-plane film thickness can be manufactured without film breakage.

[0041] Known techniques can be applied to form carbon or carbon-containing compounds into films. For forming carbon into films on a substrate, arc plasma deposition (also known as APD) is preferred, and for forming carbon-containing compounds into films on a substrate, spin coating is preferred. These methods allow for the production of carbon films with excellent uniformity of in-plane film thickness.

[0042] 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.

[0043] 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 to a random carbon structure.

[0044] In (Step III), the specific method for peeling the carbon film from the substrate is not particularly limited and includes, for example, a step of spin-coating a composition containing acrylic resin or the like onto the carbon film obtained by heating to form a support film; a step of peeling the substrate by hydrofluoric acid treatment or the like; a step of attaching a support frame to the periphery 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 etching treatment or the like.

[0045] The thickness of the carbon film constituting the pellicle film 3 is preferably less than 150 nm. The thickness of the carbon film is the thickness of the film in the usual sense. The upper limit of the carbon film thickness is more preferably 120 nm or less, even more preferably 100 nm or less, and even more preferably 60 nm or less. By reducing the thickness of the carbon film to less than 150 nm, the transmittance to EUV light can be increased. From the viewpoint of transmittance, thinner films are preferable, but there is no particular lower limit to the thickness of the carbon film as long as it is greater than 0 nm.

[0046] The thickness of the carbon film can be controlled, for example, in a pellicle film manufacturing method, by adjusting the thickness of the film when laminating a film containing carbon atoms onto a substrate.

[0047] As shown in Figure 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.

[0048] <Adhesive layer> As shown in Figure 1(b), an adhesive layer 4 for attaching the pellicle 1 to the photomask is provided on the other end of the frame 2 (the side opposite to the pellicle film 3 of the frame 2).

[0049] The adhesive layer 4 is composed of adhesives such as acrylic, rubber, vinyl, epoxy, and silicone, with acrylic, rubber, and silicone being more preferred constituent materials. The thickness of the adhesive layer 4 is preferably, for example, 0.2 mm to 2.5 mm.

[0050] <Release film> A release film 5 (liner) is positioned to cover the adhesive layer 4. This release film 5 protects the adhesive layer 4 when not in use and peels off from the adhesive layer 4 when the pellicle 1 is used.

[0051] Generally, a film with a thickness of about 30 to 200 μm, such as polyester, is used for the release film 5. Furthermore, if the peeling force when removing the release film 5 from the adhesive layer 4 is too strong, the adhesive layer 4 may deform during removal. Therefore, a release treatment such as silicone or fluorine may be applied to the film surface in contact with the adhesive to ensure an appropriate peeling force.

[0052] In this embodiment of the pellicle 1, the frame 2 is made of a carbon material that has excellent heat resistance and high strength. Therefore, deformation and damage are less likely to occur even at high temperatures, and it has excellent structural stability, making it suitable as a pellicle for EUV lithography. In other words, with the pellicle 1 of this embodiment, deformation of the frame 2 and the occurrence of wrinkles in the pellicle film 3 can be suppressed more reliably in EUV lithography.

[0053] While embodiments of the present invention have been described above, the present invention is not limited thereto and can be modified as appropriate without departing from the spirit of the invention. [Examples]

[0054] Next, this embodiment will be described in more detail with reference to examples and comparative examples. However, this embodiment is not limited to the following examples, unless it deviates from its essence.

[0055] [Making the pellicle] <Example 1> (1) Fabrication of adhesive-backed frame A pellicle frame made of glass-like carbon with an outer diameter of 149mm x 115mm x height of 1.5mm and a width of 3.5mm was prepared, and acrylic adhesive was applied to its lower end surface to create an adhesive-backed frame.

[0056] (2) Fabrication of carbon film A 15 wt% solution of polyimide precursor (BPDA-ODA), synthesized from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BDPA) and 4,4'-diaminodiphenyl AL (ODA), dissolved in N-methylpyrrolidone was applied to a Si substrate by spin coating. The substrate was imidized at 300°C for 1 hour under a nitrogen atmosphere to obtain a polyimide film with a thickness of 200 nm.

[0057] Next, the substrate was placed in a heat treatment furnace and carbonized by N2 flow treatment and heating at 1100°C for 1 hour, obtaining a carbon film with a thickness of 100 nm.

[0058] Subsequently, a support film was formed by spin-coating a 15 wt% acetone solution of polymethyl methacrylate (PMMA) onto the substrate at 500 rpm. The substrate was immersed in a 40 wt% aqueous hydrogen fluoride solution to peel off the PMMA-coated carbon film from the substrate, and then washed with water. Next, the PMMA-coated carbon film was immersed in an acetone:isopropyl alcohol = 1:1 (by weight) solution to dissolve the PMMA, and then the carbon film was transferred to the isopropyl alcohol solution using a glass substrate. The carbon film was then lifted and dried to obtain the carbon film.

[0059] The resulting carbon film was attached to the upper end surface of the adhesive-coated frame via an adhesive to create the pellicle of Example 1.

[0060] <Example 2> The pellicle was fabricated in the same manner as in Example 1, except that a graphite frame was used instead of glassy carbon.

[0061] <Example 3> The pellicle was fabricated in the same manner as in Example 1, except that a silicon pellicle film was used instead of carbon material.

[0062] <Comparative Example 1> The pellicle was fabricated in the same manner as in Example 1, except that a frame made of Al alloy (7075) was used instead of glassy carbon.

[0063] <Comparative Example 2> The pellicle was fabricated in the same manner as in Example 1, except that a frame made of Ti alloy (Ti-6Al-V) was used instead of glassy carbon.

[0064] [Heat resistance evaluation of pellicle] The heat resistance of the fabricated pellicle was evaluated as follows.

[0065] <Frame deformation> The obtained pellicle was attached to a quartz substrate (6025) and left in an oven at 200°C for 24 hours. After that, the condition of the pellicle (deformation of the frame) was observed visually and evaluated as follows. ○: No deformation was observed in the frame. ×: Deformation was observed in the frame.

[0066] <Formation of membrane wrinkles> After conducting the same heating test as described above, the condition of the pellicle (formation of film wrinkles) was visually observed and evaluated as follows. ○: The pellicle film was not wrinkled. △: There were some wrinkles in the pellicle film. ×: The pellicle film was severely wrinkled.

[0067] <Photomask deformation> The deformation of the photomask was evaluated using a FlatMaster200 from Tropel. For the photomask (6025 quartz), the flatness was measured before and after attaching the pellicle, and the difference in flatness before and after attachment was calculated to determine how much the mask (6025 quartz) deformed due to the attachment of the pellicle (measurement range: 135 mm x 110 mm), and the results were evaluated as follows. The pellicle was attached to the quartz using a simple mounter (load: 5 kgf, 60 sec). ○: The amount of deformation of the photomask due to the attachment of the pellicle was less than 40 nm. ×: The deformation of the photomask due to the attachment of the pellicle was 40 nm or more.

[0068] Table 1 summarizes the evaluation results regarding the physical properties of the frame and the heat resistance of the pellicle.

[0069] The evaluation results are summarized in Table 1.

[0070] [Table 1]

[0071] As is clear from Table 1, the example using carbon material showed more reliable suppression of frame deformation and pellicle film wrinkle formation compared to the comparative example using metal material (alloy) for the frame. Furthermore, mask distortion was also kept to a minimum.

[0072] Furthermore, the examples also show that a more significant effect is obtained by using a carbon material as the pellicle film.

[0073] While embodiments of the present invention have been described above, the present invention is not limited thereto and can be modified as appropriate without departing from the spirit of the invention. [Industrial applicability]

[0074] By using the pellicle according to the present invention, it becomes possible to more reliably suppress frame deformation and the occurrence of wrinkles in the pellicle film due to heat generation from the absorption of EUV light, and it can be widely used as a pellicle for EUV lithography. [Explanation of Symbols]

[0075] 1: Pellicle 2: Frame 3: Pellicle membrane 4: Adhesive layer 5: Release film

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 made of carbon material, A pellicle characterized in that the pellicle film is composed of a carbon material.

2. The pellicle according to claim 1, wherein the carbon material constituting the frame is graphite or glassy carbon.

3. The pellicle according to claim 2, wherein the carbon material constituting the frame is glassy carbon.

Images