EUV-transmissive film, pellicle, and exposure method

Abstract

Provided is an EUV-transmissive film that exhibits a high EUV transmittance. The EUV-transmissive film (10) is a three-layer structure comprising: a metal beryllium layer (12) having a first surface and a second surface; a first nitride layer (14a) that covers the first surface (12a) of the beryllium layer (12) and contains at least one selection from the group consisting of silicon nitride, beryllium nitride, boron nitride, and zirconium nitride; and a second nitride layer (14b) that covers the second surface (12b) of the beryllium layer (12) and contains at least one selection from the group consisting of silicon nitride, beryllium nitride, boron nitride, and zirconium nitride. The EUV-transmissive film (10) has an EUV transmittance of at least 88% at a wavelength of 13.5 nm.

Description

EUV transmitting film, pellicle, and exposure method

[0001] The present disclosure relates to an EUV transmitting film, a pellicle, and an exposure method.

[0002] Miniaturization in semiconductor manufacturing processes continues to advance year by year, resulting in various improvements at each step. In particular, in photolithography processes, EUV (extreme ultraviolet) light with a wavelength of 13.5 nm has begun to be used instead of the 193 nm wavelength used in conventional ArF exposure. As a result, the wavelength has suddenly decreased to less than one-tenth of its original wavelength, resulting in completely different optical characteristics. However, due to the lack of a material with high transmittance for EUV light, there are still no practical pellicles, which are used to prevent particle adhesion on photomasks (reticles). For this reason, device manufacturers are currently unable to use pellicles while manufacturing semiconductor devices.

[0003] Therefore, pellicle films have been developed, and it is considered desirable to use Si, Be, Y, Zr, etc., which have high EUV transmittance, as the core material of the pellicle film. Patent Document 1 (Japanese Patent No. 6858817) discloses a pellicle film including a core layer containing a material that is substantially transparent to EUV radiation, such as (poly)Si, and a cap layer containing a material that absorbs IR radiation.

[0004] Furthermore, Patent Document 2 (JP 2020-98227 A) discloses a pellicle film stretched over one end surface of a pellicle frame, the pellicle film having a main layer of single-crystal Si and graphene on one or both sides of the main layer. It is believed that the presence of graphene in the main layer prevents damage to the pellicle film during pellicle fabrication and ensures sufficient mechanical strength.

[0005] Japanese Patent No. 6858817 Japanese Patent Application Laid-Open No. 2020-98227

[0006] However, the core materials used in pellicle films, which have high EUV transmittance, form a few nanometers of natural oxide on their surfaces in the atmosphere. This oxide absorbs EUV light, reducing the EUV transmittance of the pellicle film. Be, in particular, is a material with high EUV transmittance, but it is said that a 2-3 nm natural oxide film forms on its surface, resulting in a significant transmittance loss of 6-9%. Furthermore, the process of fabricating pellicle films may involve treatments using gases other than atmospheric gases, such as fluorine and chlorine, or acid or alkaline solutions. This can lead to the formation of a side reaction film on the surface of the core material, which can reduce the EUV transmittance. Therefore, it is desirable to form a protective layer on the surface of the core material to suppress the formation of these films.

[0007] However, although a significant decrease in the EUV transmittance of the pellicle film can be prevented by applying a reaction-suppressing protective layer to the surface of a core material such as Si or Be, such a protective layer still has a lower EUV transmittance than the pure core material, leading to a decrease in the EUV transmittance of the pellicle film as a whole. For example, Ru can be used as a protective layer for a Be core material, but when considering a pellicle film with a three-layer structure (Ru / Be / Ru) in which 1-2 nm of Ru is provided on the front and back surfaces of the Be core material, the Ru protective layer causes a loss in EUV transmittance of approximately 3-6%, significantly reducing the performance of the pellicle film.

[0008] The present inventors have now discovered that by employing a three-layer structure of nitride layer / metallic beryllium layer / nitride layer, it is possible to provide an EUV transmitting film that exhibits high EUV transmittance.

[0009] Therefore, an object of the present invention is to provide an EUV transmitting film or pellicle that exhibits high EUV transmittance. Another object of the present invention is to provide an exposure method using an EUV transmitting film.

[0010] The present disclosure provides the following aspects. [Aspect 1] An EUV transmission film having a three-layer structure comprising: a metallic beryllium layer having a first surface and a second surface; a first nitride layer covering the first surface of the beryllium layer and containing at least one selected from the group consisting of silicon nitride, beryllium nitride, boron nitride, and zirconium nitride; and a second nitride layer covering the second surface of the beryllium layer and containing at least one selected from the group consisting of silicon nitride, beryllium nitride, boron nitride, and zirconium nitride, wherein the EUV transmission film has an EUV transmittance of 88% or more at a wavelength of 13.5 nm. [Aspect 2] The EUV transmission film according to Aspect 1, wherein the EUV transmission film has a thickness of 7 to 30 nm. [Aspect 3] The EUV transmission film according to Aspect 1 or 2, wherein the beryllium layer has a thickness of 5 to 25 nm. [Aspect 4] The EUV transmission film according to any one of Aspects 1 to 3, wherein the first nitride layer and the second nitride layer each have a thickness of 1 to 5 nm. [Aspect 5] A pellicle comprising: a substrate having a first surface and a second surface and a cavity in the center; an amorphous carbon layer covering the first surface of the substrate; and the EUV transmitting film according to any one of Aspects 1 to 4, covering the surface of the amorphous carbon layer opposite the substrate and exposed as a free-standing film constituting the bottom surface of the cavity at the same height as the surface of the amorphous carbon layer. [Aspect 6] The pellicle according to Aspect 5, wherein the amorphous carbon layer has a thickness of 1 to 15 nm. [Aspect 7] The pellicle according to Aspect 5 or 6, wherein the substrate is a Si substrate. [Aspect 8] The pellicle according to any one of Aspects 5 to 7, further comprising a mask layer covering the second surface of the substrate. [Aspect 9] The mask layer is SiO ２a pellicle according to Aspect 8, wherein the pellicle is a three-layer pellicle having a protective layer containing amorphous carbon on each side of the EUV transmitting film according to any one of Aspects 1 to 4, a five-layer composite film having a protective layer containing amorphous carbon on each side of the EUV transmitting film, a five-layer composite film being mounted in an apparatus that generates hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals, a five-layer composite film being brought into contact with the hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals, thereby removing the protective layer, and a three-layer EUV transmitting film having a protective layer removed being mounted in an EUV exposure apparatus, and allowing EUV light to pass through the EUV transmitting film, thereby performing pattern exposure on a photosensitive substrate in the EUV exposure apparatus.

[0011] The present invention relates to an EUV transmitting film, an EUV light emitting film, an EUV light emitting device, an EUV light emitting element ...

[0012] EUV Transmission Film FIG. 1 shows a schematic cross-sectional view of an EUV transmission film 10 according to one embodiment of the present invention. The EUV transmission film 10 is a three-layer film consisting of a metal beryllium layer 12, a first nitride layer 14a, and a second nitride layer 14b. The metal beryllium layer 12 has a first surface 12a and a second surface 12b. The first nitride layer 14a is a layer covering the first surface 12a of the metal beryllium layer 12 and containing at least one element selected from the group consisting of silicon nitride, beryllium nitride, boron nitride, and zirconium nitride. The second nitride layer 14b is a layer covering the second surface 12b of the metal beryllium layer 12 and containing at least one element selected from the group consisting of silicon nitride, beryllium nitride, boron nitride, and zirconium nitride. The EUV transmission film 10 has an EUV transmittance of 88% or more at a wavelength of 13.5 nm. In this way, by adopting a three-layer structure of first nitride layer 14a / metallic beryllium layer 12 / second nitride layer 14b, it is possible to provide an EUV transmitting film 10 that exhibits high EUV transmittance.

[0013] As mentioned above, core materials with high EUV transmittance may form a few nanometers of natural oxide film on their surface in the atmosphere. Furthermore, the process of fabricating a pellicle film may involve treatment with gases other than the atmosphere, such as fluorine or chlorine, or with acid or alkaline solutions, which can result in the formation of a side reaction film on the surface of the core material. The formation of such a film reduces the EUV transmittance of the pellicle film. Therefore, it is desirable to form a protective layer on the surface of the core material to suppress the formation of such a film. However, applying a reaction-suppressing protective layer to the surface of the core material leads to a decrease in the EUV transmittance of the pellicle film as a whole. To address this issue, it is conceivable to provide an amorphous carbon layer on both sides of the EUV-transmitting film as a protective film that can be removed by contacting the film with hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals. The aforementioned natural oxide film and side reaction film are formed on the pellicle film during the process from fabrication to installation in an EUV exposure tool and exposure process. However, providing an amorphous carbon layer as a protective layer on both sides of the EUV-transmitting film 10 can prevent the formation of such a film. In particular, the amorphous carbon layer is effective in protecting the EUV-transmitting film 10 from various chemicals (e.g., highly reactive fluorine-based etchants) used in the pellicle film fabrication process (e.g., the self-supporting film fabrication step). Furthermore, if the amorphous carbon layer were provided directly on the metal beryllium layer 12, the amorphous carbon and the metal beryllium might react to form beryllium carbide. However, by providing a three-layer structure of the first nitride layer 14a / metal beryllium layer 12 / first nitride layer 14a and providing the amorphous carbon layer on the nitride layers 14a and 14b, the undesirable reaction between the amorphous carbon and the metal beryllium can be prevented. On the other hand, after serving as a protective layer in the pellicle film fabrication process (e.g., the self-supporting film fabrication step), the amorphous carbon layer becomes an unnecessary layer in terms of reducing EUV transmittance. Therefore, the EUV transmittance can be improved by removing the amorphous carbon layer by contacting it with hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals.The EUV transmitting coating 10 thus obtained has a three-layer structure consisting of the metal beryllium layer 12, the first nitride layer 14a, and the second nitride layer 14b, and since it no longer has a protective layer (amorphous carbon layer), it is possible to avoid a decrease in EUV transmittance due to the protective layer. As a result, the EUV transmitting coating 10 can maximize the high transmittance inherent in the three-layer structure consisting of the metal beryllium layer 12, the first nitride layer 14a, and the second nitride layer 14b, that is, it is possible to exhibit high EUV transmittance during exposure.

[0014] As described above, the EUV transmitting film 10 has a high EUV transmittance. The EUV transmitting film 10 has an EUV transmittance at a wavelength of 13.5 nm of 88% or more, preferably 92% or more, more preferably 93% or more, even more preferably 94% or more, particularly preferably 95% or more, and most preferably 96% or more. The higher the EUV transmittance of the EUV transmitting film 10, the more desirable it is, and its upper limit is not particularly limited and is ideally 100%, but is typically 99% or less, more typically 98% or less.

[0015] The metal beryllium layer 12 is a layer containing metal beryllium as a main component. Here, the "main component" of the metal beryllium layer 12 means a component that accounts for 50 mol % or more of the metal beryllium layer 12, preferably 70 mol % or more, more preferably 80 mol % or more, and even more preferably 90 mol % or more. The metal beryllium layer 12 may also contain impurities in addition to metal beryllium as the main component. Thus, the metal beryllium layer 12 may consist of metal beryllium and inevitable impurities. The thickness of the metal beryllium layer 12 is preferably 5 to 25 nm, more preferably 7 to 20 nm, and even more preferably 9 to 15 nm.

[0016] Each of the first nitride layer 14a and the second nitride layer 14b contains at least one nitride selected from the group consisting of silicon nitride, beryllium nitride, boron nitride, and zirconium nitride. A particularly preferred nitride is silicon nitride. The advantages of providing the first nitride layer 14a and the second nitride layer 14b on both sides of the metal beryllium layer 12 are as described above. In this specification, the terms "silicon nitride," "beryllium nitride," "boron nitride," and "zirconium nitride" refer to Si ３ N ４ , Be ３ N ２ , BN, and ZrN, as well as stoichiometric compositions such as Si ３ N ４－ｘ (wherein 0<x<4), Be ３ N ２－ｘ (wherein 0<x<2), BN ｘ (wherein 0<x<1), ZrN ｘ This term refers to a comprehensive composition that also allows for non-stoichiometric compositions such as (where 0<x<1). The thickness of each of the first nitride layer 14a and the second nitride layer 14b is preferably 1 to 5 nm, and more preferably 1 to 3 nm.

[0017] The first nitride layer 14a, the metal beryllium layer 12, and the second nitride layer 14b alone constitute the EUV transmitting film 10. These layers contribute to achieving high EUV transmittance while ensuring the basic functions of a pellicle film (such as preventing particle adhesion). The thickness of the EUV transmitting film 10 is preferably 7 to 30 nm, more preferably 9 to 26 nm, and even more preferably 11 to 21 nm.

[0018] When each of the first nitride layer 14a and / or the second nitride layer 14b contains beryllium nitride, the EUV transmitting film 10 preferably has a nitrogen concentration gradient region in which the nitrogen concentration decreases toward the metal beryllium layer 12. That is, as described above, the composition of beryllium nitride contains Be. ３ N ２ From the stoichiometric composition ３ N ２－ｘWhile non-stoichiometric compositions such as x (where 0<x<2) are possible, it is preferable for the beryllium nitride constituting the beryllium nitride layer to have a gradient composition that approaches a beryllium-rich composition toward the metal beryllium layer 12. This improves adhesion between the nitride layers 14a and 14b (i.e., the beryllium nitride layers) constituting the EUV transmitting film 10 and the metal beryllium layer 12, and also reduces stress caused by differences in thermal expansion between these layers. This improves adhesion between these layers to suppress peeling, and acts as a thermal expansion buffer layer between these layers to prevent peeling when the layers absorb EUV light and become hot. The thickness of the nitrogen concentration gradient region is preferably smaller than the thickness of each of the nitride layers 14a and 14b. In other words, the entire thickness of each of the nitride layers 14a and 14b does not need to be a nitrogen concentration gradient region. For example, it is preferable that only a portion of the thickness of each of the nitride layers 14a and 14b, for example, a region of 10 to 70% of the thickness of each of the nitride layers 14a and 14b, is a nitrogen concentration gradient region, and more preferably a region of 15 to 50%.

[0019] The EUV transmitting film 10 preferably has a main region for transmitting EUV in the form of a free-standing film. That is, like a pellicle 11 shown in Fig. 2B(k) described later, it is preferable that the substrate 20 or the like (e.g., a Si substrate) used during film formation remains as a border only at the outer edge of the EUV transmitting film 10. In other words, it is preferable that no substrate or the like (e.g., a Si substrate) remains in the main region other than the outer edge, that is, the main region is made up of only three layers: the first nitride layer 14a, the metal beryllium layer 12, and the second nitride layer 14b.

[0020] The EUV transmitting film or pellicle according to the present invention can be fabricated by forming a five-layer composite film on a Si substrate, with protective layers containing amorphous carbon on both sides of the EUV transmitting film, and then removing unnecessary portions of the Si substrate and the protective layers by etching to form a free-standing film. Therefore, as described above, the main part of the EUV transmitting film is in the form of a free-standing film with no Si substrate remaining.

[0021] (1) Preparation of Si Substrate First, as shown in FIG. 2B , a Si substrate 28 is prepared on which a composite film will be formed. After forming a composite film consisting of the second protective layer 16b, the second nitride layer 14b, the metal beryllium layer 12, the first nitride layer 14a, and the first protective layer 16a on the Si substrate 28, the main region (i.e., the region to be a free-standing film) other than the outer edge is removed by etching. Therefore, to efficiently perform etching in a short time, it is desirable to thin the thickness of the Si substrate in the region to be a free-standing film in advance. Therefore, it is desirable to form a mask corresponding to the EUV-transmitting shape on the Si substrate using a conventional semiconductor process, and then etch the Si substrate by wet etching to thin the thickness of the main region of the Si substrate to a predetermined thickness. The Si substrate that has undergone wet etching is then washed and dried to prepare a Si substrate having a cavity formed by wet etching. The wet etching mask may be made of any material that is corrosion-resistant to the wet etching solution for Si, such as SiO . ２ The wet etching solution is not particularly limited as long as it can etch Si. For example, TMAH (tetramethylammonium hydroxide) is preferred because it can perform very good anisotropic etching of Si when used under appropriate conditions.

[0022] (2) Formation of Composite Film A composite film consisting of the second protective layer 16b, the second nitride layer 14b, the metal beryllium layer 12, the first nitride layer 14a, and the first protective layer 16a is formed in this order on the Si substrate. The composite film may be formed by any film formation method. A preferred example of the film formation method is sputtering. The metal beryllium layer 12 is preferably formed by sputtering using a pure Be target.

[0023] The first nitride layer 14a and the second nitride layer 14b are also preferably formed by sputtering. For example, (i) a Si, Be, B, or Zr film may be formed by sputtering using a Si, Be, B, or Zr target, and then nitrogen plasma may be applied to cause a nitriding reaction of the Si, Be, B, or Zr, thereby forming the nitride layers 14a and 14b. Alternatively, (ii) the first nitride layer 14a and the second nitride layer 14b may be formed by reactive sputtering. This reactive sputtering can be performed, for example, by introducing nitrogen gas into the chamber during sputtering using a Si, Be, B, or Zr target, thereby causing a reaction between the Si, Be, B, or Zr and nitrogen to produce silicon nitride, beryllium nitride, boron nitride, or zirconium nitride. Alternatively, (iii) Si ３ N ４ , Be ３ N ２ Alternatively, the nitride layers 14a, 14b may be directly formed by sputtering using a BN or ZrN target. Nitrogen gas may be introduced into the chamber during this sputtering, thereby promoting the reaction of nitrogen with Si, Be, B or Zr to form silicon nitride, beryllium nitride, boron nitride or zirconium nitride, as in the reactive sputtering described above in (ii).

[0024] Each of the first protective layer 16a and the second protective layer 16b is a layer containing amorphous carbon. A layer containing amorphous carbon exhibits high protective performance against various chemicals (e.g., highly reactive fluorine-based etching agents) used in the pellicle film fabrication process (e.g., the self-supporting film formation process). In addition, the layer containing amorphous carbon is advantageous in that the residue left behind when the protective layers 16a and 16b are removed has little effect on the EUV transmitting film 10, and the protective layers 16a and 16b are easily removed. The first protective layer 16a and the second protective layer 16b preferably contain amorphous carbon as a main component, and more preferably are composed of amorphous carbon. Amorphous carbon generally does not have a completely random atomic arrangement, and while it has a microscopic crystalline structure (i.e., it has microcrystals), these microcrystals are often arranged randomly, resulting in an amorphous structure overall. Among these, those containing many microcrystals with a three-dimensional four-coordinate structure like diamond are called DLC (diamond-like carbon), and those containing many microparticles with a planar three-coordinate structure like graphite are called GLC (graphite-like carbon). The first protective layer 16a and the second protective layer 16b may be carbon having a completely irregular atomic arrangement, or may be carbon having irregular microcrystals. Furthermore, they may be amorphous carbon that is not completely dense and contains fine pores. Here, the "main component" in the first protective layer 16a and the second protective layer 16b refers to a component that accounts for 50 wt% or more, preferably 60 wt% or more, more preferably 70 wt% or more, and even more preferably 80 wt% or more of the total weight of the first protective layer 16a or the second protective layer 16b. However, the first protective layer 16a and the second protective layer 16b may be composed solely of amorphous carbon. The thickness of each of the first protective layer 16a and the second protective layer 16b is preferably 1 to 15 nm, more preferably 2 to 12 nm, and even more preferably 3 to 10 nm. The amorphous carbon layers as the first protective layer 16a and the second protective layer 16b are preferably formed by sputtering using a graphite target.

[0025] The methods for forming the metal beryllium layer 12, the nitride layers 14a, 14b, and the protective layers 16a, 16b are not limited to these. The metal beryllium layer 12, the nitride layers 14a, 14b, and the protective layers 16a, 16b may be formed in a single-chamber sputtering apparatus, as in the examples described below, or the metal beryllium layer 12, the nitride layers 14a, 14b, and the protective layers 16a, 16b may be formed in separate chambers using a sputtering apparatus with multiple chambers.

[0026] When the first nitride layer 14a and the second nitride layer 14b are beryllium nitride layers containing a nitrogen concentration gradient region, i.e., when forming a nitrogen concentration gradient region in an EUV transmitting film 10 having a three-layer structure of beryllium nitride / beryllium / beryllium nitride, the beryllium nitride film and the metal beryllium film are deposited by introducing nitrogen gas into the chamber and continuing sputtering using a pure Be target, while stopping the introduction of nitrogen gas midway and switching to metal beryllium film deposition. In this way, a region in which the nitrogen concentration in the deposited film decreases along the thickness direction is formed as the concentration of nitrogen gas in the chamber decreases. On the other hand, when switching from metal beryllium to beryllium nitride, the nitrogen concentration gradient region can be formed by continuing sputtering and then starting the introduction of nitrogen gas midway. The thickness of the nitrogen concentration gradient region can be controlled by adjusting the time for changing the nitrogen gas concentration.

[0027] (3) Formation of a freestanding film The unnecessary parts of the Si substrate 28 on which the composite film is formed, except for the outer edge part to be left as a border, are removed by etching to form the composite film into a freestanding film. The etching of Si may be performed by any method, but it is preferable to use XeF ２ Next, the exposed portions of the first protective layer 16a and the second protective layer 16b are removed to obtain the EUV transmitting film 10 having a three-layer structure consisting of the metal beryllium layer 12, the first nitride layer 14a, and the second nitride layer 14b in the form of a pellicle 11. In particular, the above-mentioned XeF ２After the freestanding film formation process using a fluorine-based etchant such as fluorine-based etchant, the first protective layer 16a and the second protective layer 16b no longer require strong protective properties against the fluorine-based etchant and become unnecessary films in terms of reducing EUV transmittance. Therefore, after forming the composite film into a freestanding film, removing the protective layers 16a and 16b can further increase EUV transmittance. The amorphous carbon layers of the first protective layer 16a and the second protective layer 16b are preferably removed by placing the composite film including the EUV transmitting film 10 in an apparatus that generates hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals, and contacting the composite film with the hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals. By exposing the amorphous carbon layers of the first protective layer 16a and the second protective layer 16b to a hydrogen plasma and / or hydrogen radical atmosphere or an oxygen plasma and / or oxygen radical atmosphere, C on the surface of the amorphous carbon layer reacts with H, thereby removing the amorphous carbon layer. As a result, the entire first protective layer 16 a and the exposed portion of the second protective layer 16 b can be eliminated, while the second protective layer 16 b interposed between the Si substrate 28 and the second protective layer 16 b remains as it is, constituting the amorphous carbon layer 16 of the pellicle 11.

[0028] 2B(k), the EUV transmitting film 10 is preferably provided in the form of a pellicle 11. The pellicle 11 comprises a substrate 20, an amorphous carbon layer 16, and the EUV transmitting film 10. The substrate 20 has a first surface 20a and a second surface 20b, and has a cavity 26 in the center. The substrate 20 is preferably a Si substrate or a Si border. The first surface 20a of the substrate 20 is covered with the amorphous carbon layer 16. The EUV transmitting film 10 covers the surface of the amorphous carbon layer 16 opposite the substrate 20, and is exposed as a free-standing film that forms the bottom surface of the cavity 26 at the same height as the surface of the amorphous carbon layer 16.

[0029] The amorphous carbon layer 16 is a layer containing amorphous carbon. The amorphous carbon layer 16 (i.e., the second protective layer 16b) located directly below the second nitride layer 14b contributes to improving the strength of the second nitride layer 14b. That is, the amorphous carbon layer 16 contributes to improving the crystallinity of the second nitride layer 14b formed thereon, thereby increasing the density and strength of the second nitride layer 14b. That is, if the second nitride layer 14b were formed directly on the substrate 20 without the amorphous carbon layer 16, the crystallinity of the nitride would be poor in the initial stage of film formation, leading to reduced density and strength of the nitride. In contrast, by forming the second nitride layer 14b on the substrate 20 via the amorphous carbon layer 16, a film with good nitride crystallinity can be obtained as the second nitride layer 14b. Since the amorphous carbon layer 16 corresponds to the second protective layer 16b described above, the above description of the second protective layer 16b also applies to the amorphous carbon layer 16. Therefore, the thickness of the amorphous carbon layer 16 is preferably 1 to 15 nm, more preferably 2 to 12 nm, and even more preferably 3 to 10 nm.

[0030] The pellicle 11 may further include a mask layer 22a covering the second surface 20b of the substrate 20. The mask layer 22a is made of SiO ２ Preferably it is a layer.

[0031] Exposure Method According to a preferred embodiment of the present invention, the following exposure method using the EUV transmitting film 10 is provided. In this method, as shown in FIG. 2B(j), a five-layer composite film is first prepared, with a first protective layer 16a and a second protective layer 16b containing amorphous carbon on both sides of the EUV transmitting film 10. Next, the five-layer composite film is placed in an apparatus that generates hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals, and the five-layer composite film is then exposed to the hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals, thereby removing the exposed portions of the first protective layer 16a and the second protective layer 16b. At this time, as shown in FIG. 2B(k), the second protective layer 16b interposed between the Si border 20 and the second nitride layer 14b is left intact, forming the amorphous carbon layer 16 of the pellicle 11. The pellicle 11 including the three-layer EUV transmitting film 10 from which the first protective layer 16a and the second protective layer 16b have been removed is then attached to an EUV exposure device, and EUV is allowed to pass through the EUV transmitting film 10 to perform pattern exposure on a photosensitive substrate in the EUV exposure device.

[0032] The present invention will be explained in more detail by the following examples, but the present invention is not limited to the following examples.

[0033] Example 1 (Reference) Following the procedure shown in FIGS. 2A and 2B, a five-layer composite freestanding film (having protective layers 16 a, 16 b provided on both sides of EUV transmitting film 10) of amorphous carbon / silicon nitride / Be / silicon nitride / amorphous carbon was fabricated as follows.

[0034] (1) Preparation of Si Substrate An Si wafer 20 having a diameter of 8 inches (20.32 cm) was prepared (FIG. 2A(a)). SiO was formed on both sides of the Si wafer 20 by thermal oxidation. ２ A resist was applied to both sides of the Si wafer 20, and exposure and development were performed to form a resist hole of 110 mm x 145 mm on one side, forming a SiO ２ A resist mask 24 for etching was formed (FIG. 2A(c)). One surface of this substrate was wet-etched with hydrofluoric acid to remove SiO ２The exposed portions of film 22 are etched away to leave SiO ２ The mask was fabricated as a mask layer 22a (FIG. 2A(d)). ２ The resist mask 24 for etching was removed using an ashing device (FIG. 2A(e)). After that, the Si was wet-etched using TMAH solution. The etching rate was measured in advance, and the etching was carried out for the time required to achieve the target Si substrate thickness of 50 μm (FIG. 2A(f)). Finally, the SiO 2 formed on the Si surface that was not etched was removed. ２ The film 22 was removed and washed with hydrofluoric acid to prepare a Si substrate 28 (FIG. 2B(g)). The Si substrate may be diced with a laser 30 (FIG. 2B(h)) to obtain a desired shape (FIG. 2B(i)), if necessary. In this way, a 110 mm x 145 mm cavity 26 was provided in the center of the 8-inch (20.32 cm) Si wafer 20, and a Si substrate 28 with a Si thickness of 50 μm at the cavity 26 portion was prepared.

[0035] (2) Formation of Composite Film A composite film having a five-layer structure of amorphous carbon / silicon nitride / Be / silicon nitride / amorphous carbon was formed on the Si substrate 28 provided with the cavity 26 obtained in (1) above as follows (FIG. 2B(i)). First, the Si substrate 28 was set in a multi-target sputtering apparatus, and a graphite target, Si ３ N ４ A target and a pure Be target were attached. The chamber was evacuated, and sputtering was performed using a graphite target at an internal pressure of 0.3 Pa and argon gas only. Sputtering was terminated when a 2 nm film of DLC (Diamond-like Carbon) was formed as amorphous carbon. Next, the chamber was evacuated again, and Si ３ N ４ Using a target, sputtering was performed with an internal pressure of 0.7 Pa and argon gas only. ３ N ４The sputtering was terminated when a 2 nm thick film of beryllium was formed. The chamber was then evacuated again, and sputtering was performed using a pure Be target at an internal pressure of 0.5 Pa and argon gas only. The sputtering was terminated when a 20 nm thick film of beryllium was formed. Next, the chamber was evacuated again, and the Si ３ N ４ Using a target, sputtering was performed with an internal pressure of 0.7 Pa and argon gas only. ３ N ４－ｘ Sputtering was then terminated when the time came for the amorphous carbon (C) 2 nm film to be formed. Thereafter, sputtering was performed using a graphite target in the same manner as in the first step, and sputtering was terminated when the time came for the amorphous carbon (C) 2 nm film to be formed. ３ N ４－ｘ ) 2 nm / beryllium (Be) 20 nm / silicon nitride (Si ３ N ４－ｘ A composite film of 2 nm of beryllium (B) and 2 nm of amorphous carbon (C) was formed. That is, this composite film had a five-layer structure consisting of an EUV transmitting film 10 made up of three layers: a first nitride layer 14 a, a metal beryllium layer 12, and a second nitride layer 14 b, and a first protective layer 16 a and a second protective layer 16 b, each containing amorphous carbon as a main component, formed on either side of the EUV transmitting film 10.

[0036] (3) Freestanding film: XeF capable of processing 8-inch (20.32 cm) substrates ２ The Si substrate 28 with the composite film prepared in (2) above was set in the chamber of the etcher. The chamber was evacuated sufficiently. At this time, if moisture remained in the chamber, XeF ２ The reaction with the gas produces hydrofluoric acid, which can cause corrosion of the etcher or unexpected etching, so sufficient vacuuming was performed. If necessary, the chamber was repeatedly evacuated and nitrogen gas was introduced to reduce residual moisture. Once sufficient vacuuming was achieved, XeF ２ The valve between the source cylinder and the auxiliary chamber was opened. ２ sublimated and XeF ２ Gas has accumulated. There is enough XeF２ Once the gas has accumulated, the valve between the auxiliary chamber and the chamber is opened and XeF ２ The gas was introduced into the chamber: XeF ２ The gas decomposes into Xe and F, and the F reacts with Si to form SiF ４ SiF ４ Since the boiling point of SiF is -95°C, the generated SiF ４ The XeF rapidly evaporated, causing a reaction between the newly exposed Si substrate and the F. As the Si etching progressed and the F in the chamber decreased, the chamber was evacuated and XeF was again added. ２ The gas was introduced into the chamber and etching was carried out. ２ Gas introduction and etching were repeated until the Si substrate 28 corresponding to the portion to be made into a freestanding film was completely removed. Etching was stopped when the unnecessary Si substrate was completely removed. In this way, a five-layer composite freestanding film having a Si border 20 was obtained (FIG. 2B(j)).

[0037] Example 2 (Reference) A composite freestanding film (having protective layers 16a, 16b on both sides of the EUV transmitting film 10) having a Si border 20 was fabricated in the same manner as in Example 1. Thereafter, the amorphous carbon layers exposed on both sides of the composite freestanding film were etched with hydrogen plasma to reduce the thickness of each amorphous carbon layer to 1 nm. In this way, a 1 nm amorphous carbon (C) / silicon nitride (Si) film having a Si border 20 was fabricated. ３ N ４－ｘ ) 2 nm / beryllium (Be) 20 nm / silicon nitride (Si ３ N ４－ｘ A composite free-standing film with a five-layer structure consisting of 2 nm of ZnO (SiO2) and 1 nm of amorphous carbon (C) was obtained (FIG. 2B(j)).

[0038] Example 3 A composite free-standing film (in which protective layers 16a, 16b are provided on both sides of the EUV transmitting film 10) having a Si border 20 was produced in the same manner as in Example 1. Thereafter, the amorphous carbon layers exposed on both sides of the EUV transmitting film 10 were etched with hydrogen plasma to remove the amorphous carbon layers except for the amorphous carbon layer 16 in the portion sandwiched between the EUV transmitting film 10 and the Si border 20. In this way, a silicon nitride (Si ３ N ４－ｘ ) 2 nm / beryllium (Be) 20 nm / silicon nitride (Si ３ N ４－ｘ ) A three-layer composite free-standing film (i.e., EUV transmitting film 10) having a thickness of 2 nm was obtained in the form of a pellicle 11 (FIG. 2B(k)).

[0039] Example 4 In the above (2), the film formation times of amorphous carbon and silicon nitride were changed to obtain a film of amorphous carbon (C) 12 nm / silicon nitride (Si ３ N ４－ｘ ) 1 nm / beryllium (Be) 20 nm / silicon nitride (Si ３ N ４－ｘ A composite free-standing film (with protective layers 16a, 16b provided on both sides of the EUV transmitting film 10) having a Si border 20 was fabricated in the same manner as in Example 1, except that a composite film of 1 nm silicon nitride (Si) / 12 nm amorphous carbon (C) was formed. Thereafter, the amorphous carbon layers exposed on both sides of the EUV transmitting film 10 were etched with hydrogen plasma to remove each amorphous carbon layer except for the amorphous carbon layer 16 in the portion sandwiched between the EUV transmitting film 10 and the Si border 20. In this way, a silicon nitride (Si ３ N ４－ｘ ) 1 nm / beryllium (Be) 20 nm / silicon nitride (Si ３ N ４－ｘ ) A three-layer composite free-standing film (i.e., EUV transmitting film 10) consisting of 1 nm thick was obtained in the form of a pellicle 11 (FIG. 2B(k)).

[0040] EUV Transmittance and Its In-Plane Uniformity The freestanding films serving as EUV transmitting films prepared in Examples 1 to 3 were irradiated with EUV light at an output of 600 W in a hydrogen atmosphere at 20 Pa for 15 minutes, and the transmitted EUV light intensity was then measured using a sensor. The EUV transmittance was calculated by comparing the obtained measurement value with the EUV light intensity directly measured using a sensor without an EUV transmitting film, and the results shown in Table 1 were obtained. The EUV light spot used for the transmittance measurement had an elliptical shape of 0.5 mm × 0.2 mm, and the EUV transmittance at a wavelength of 13.5 nm was measured within this spot size. Therefore, to evaluate the in-plane uniformity of EUV transmittance, the EUV transmittance was measured at each location by moving the EUV light spot, and the in-plane variation was calculated from the data as three times the standard deviation. Therefore, a smaller in-plane variation indicates better in-plane uniformity of EUV transmittance.

[0041]

[0042] As can be seen from the above results, when the amorphous carbon layer is left as in Examples 1 and 2, the in-plane variation in EUV transmittance is small, i.e., the in-plane uniformity is excellent, but the EUV transmittance is low. In contrast, when the amorphous carbon layer is etched away as in Examples 3 and 4, the transmittance can be increased while maintaining an acceptable in-plane uniformity. Although a small in-plane variation in EUV transmittance has the advantage of making the in-plane exposure amount more uniform and improving the homogeneity of the device, a higher EUV transmittance allows exposure to be completed in a shorter time, i.e., improves throughput. In other words, according to the present invention, an EUV transmitting film exhibiting high EUV transmittance can be provided.

[0043] In addition, Example 4 is an embodiment in which the protective function against fluorine-based etching agents is enhanced by setting the thickness of the amorphous carbon layers serving as first protective layer 16a and second protective layer 16b to 12 μm, which is thicker than the thickness (2 μm) of the amorphous carbon layers in Examples 1 to 3. As shown in Table 1, in the present invention, high EUV transmittance can be achieved by finally removing protective layers 16a and 16b, and therefore, the protective function can be enhanced by thickening the amorphous carbon layers serving as protective layers 16a and 16b, as in Example 4.

Claims

1. a metallic beryllium layer having a first surface and a second surface; a first nitride layer covering a first surface of the beryllium layer and including at least one selected from the group consisting of silicon nitride, boron nitride, and zirconium nitride; a second nitride layer covering a second surface of the beryllium layer and including at least one selected from the group consisting of silicon nitride, boron nitride, and zirconium nitride; An EUV transmitting film having a three-layer structure consisting of: The EUV transmitting film has an EUV transmittance of 88% or more at a wavelength of 13.5 nm.

2. 2. The EUV transmitting film according to claim 1, wherein the thickness of the EUV transmitting film is 7 to 30 nm.

3. 3. The EUV transmitting film according to claim 1, wherein the beryllium layer has a thickness of 5 to 25 nm.

4. 3. The EUV transmitting film according to claim 1, wherein the first nitride layer and the second nitride layer each have a thickness of 1 to 5 nm.

5. a substrate having a first surface and a second surface and a central cavity; an amorphous carbon layer covering a first surface of the substrate; the EUV transmitting film according to claim 1 or 2, which covers a surface of the amorphous carbon layer opposite to the substrate and is exposed as a free-standing film constituting a bottom surface of the cavity at the same height as the surface of the amorphous carbon layer; A pellicle comprising:

6. 6. The pellicle of claim 5, wherein the amorphous carbon layer has a thickness of 1 to 15 nm.

7. The pellicle of claim 5 , wherein the substrate is a Si substrate.

8. The pellicle of claim 5 , further comprising a masking layer covering the second surface of the substrate.

9. The mask layer is made of SiO ２ The pellicle of claim 8 which is a layer.

10. a step of preparing a five-layer composite film having protective layers containing amorphous carbon on both sides of the EUV transmitting film according to claim 1 or 2; a step of installing the five-layer composite film in an apparatus that generates hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals; contacting the five-layer composite film with hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals, thereby removing the protective layer; a step of attaching the three-layer EUV transmitting film from which the protective layer has been removed in an EUV exposure apparatus, and allowing EUV to pass through the EUV transmitting film to perform pattern exposure on a photosensitive substrate in the EUV exposure apparatus; An exposure method comprising: