EUV transmissive film, method for processing same, and light exposure method

Abstract

The present invention provides an EUV transmissive film that has a protective layer on both surfaces, and still has high EUV transmittance and excellent in-plane uniformity of the EUV transmittance. An EUV transmissive film (10) has a five-layer configuration that comprises: a metal beryllium layer (12) that has first and second surfaces; a first nitride layer (14a) that contains at least one substance selected from the group consisting of silicon nitride, beryllium nitride, boron nitride, and zirconium nitride, and a first protective layer (16a) that contains amorphous carbon, the first nitride layer (14a) and the first protective layer (16a) sequentially covering the first surface (12a) of the metal beryllium layer (12); and a second nitride layer (14b) that contains at least one substance selected from the group consisting of silicon nitride, beryllium nitride, boron nitride, and zirconium nitride, and a second protective layer (16b) that contains amorphous carbon, the second nitride layer (14b) and the second protective layer (16b) sequentially covering the second surface (12b) of the metal beryllium layer (12). This EUV transmissive film has an EUV transmittance of 85% or more at a wavelength of 13.5 nm.

Description

EUV transmitting film, its processing method, and exposure method

[0001] The present disclosure relates to an EUV transmitting film, a processing method thereof, 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, while applying a reaction-suppressing protective layer to the surface of a core material such as Si or Be can prevent a significant decrease in the EUV transmittance of the pellicle film, 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. However, 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 of EUV transmittance of approximately 3-6%, significantly reducing the performance of the pellicle film. Therefore, a protective layer with a small EUV transmittance loss is desired. Meanwhile, pellicle films are desired not only to have high EUV transmittance but also to have excellent in-plane uniformity of EUV transmittance. This is because the more uniform the in-plane uniformity of EUV transmittance, the more uniform the in-plane exposure dose and the improved homogeneity of devices manufactured through EUV exposure.

[0008] The present inventors have now discovered that by employing a five-layer structure of amorphous carbon layer / nitride layer / metallic beryllium layer / nitride layer / amorphous carbon layer, it is possible to provide an EUV transmitting film that has high EUV transmittance and excellent in-plane uniformity of EUV transmittance, even while having protective layers on both sides.

[0009] Therefore, an object of the present invention is to provide an EUV transmitting film that has protective layers on both sides and yet exhibits high EUV transmittance and excellent in-plane uniformity of EUV transmittance. Another object of the present invention is to provide a method for processing an EUV transmitting film. Still 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 five-layer structure comprising: a metal beryllium layer having a first surface and a second surface, a first nitride layer covering the first surface of the metal beryllium layer and containing at least one selected from the group consisting of silicon nitride, beryllium nitride, boron nitride, and zirconium nitride, a second nitride layer covering the second surface of the metal beryllium layer and containing at least one selected from the group consisting of silicon nitride, beryllium nitride, boron nitride, and zirconium nitride, a first protective layer covering the surface of the first nitride layer opposite to the metal beryllium layer and containing amorphous carbon, and a second protective layer covering the surface of the second nitride layer opposite to the metal beryllium layer and containing amorphous carbon, wherein the EUV transmission film has an EUV transmittance of 85% or more at a wavelength of 13.5 nm. [Aspect 2] The EUV transmitting film according to Aspect 1, wherein the first nitride layer, the metal beryllium layer, and the second nitride layer constitute a main layer of the EUV transmitting film, and the main layer has a thickness of 7 to 30 nm. [Aspect 3] The EUV transmitting film according to Aspect 1 or 2, wherein the metal beryllium layer has a thickness of 5 to 25 nm. [Aspect 4] The EUV transmitting 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] The EUV transmitting film according to any one of Aspects 1 to 4, wherein the first protective layer and the second protective layer each have a thickness of 1 to 10 nm or less. [Aspect 6] The EUV transmitting film according to Aspect 5, wherein the first protective layer and the second protective layer each have a thickness of 2 to 7 nm. [Aspect 7] The EUV transmitting film according to Aspect 5, wherein the first protective layer and the second protective layer each have a thickness of 1 nm or more and less than 2 nm. [Aspect 8] A method for processing an EUV transmitting film, comprising the steps of: installing the EUV transmitting film according to any one of Aspects 1 to 7 in an apparatus that generates hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals; and contacting the EUV transmitting film with hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals, thereby thinning the first protective layer and the second protective layer.[Aspect 9] An exposure method comprising the steps of: installing the EUV transmitting film according to any one of Aspects 1 to 7 in an apparatus that generates hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals; bringing the EUV transmitting film into contact with hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals, thereby thinning the first protective layer and the second protective layer; and installing the EUV transmitting film with the first protective layer and the second protective layer thinned in an EUV exposure apparatus, allowing EUV to pass through the EUV transmitting film, and performing pattern exposure on a photosensitive substrate in the EUV exposure apparatus.

[0011] 1 is a schematic cross-sectional view showing one embodiment of an EUV transmitting film according to the present invention, and FIG. 2 is a process flow diagram showing the first half of a manufacturing procedure for an EUV transmitting film in an example, and FIG. 3 is a process flow diagram showing the second half of a manufacturing procedure for an EUV transmitting film in an example.

[0012] EUV Transmitting Film FIG. 1 shows a schematic cross-sectional view of an EUV transmitting film 10 according to one embodiment of the present invention. The EUV transmitting film 10 is a five-layer film consisting of a metal beryllium layer 12, a first nitride layer 14a, a second nitride layer 14b, a first protective layer 16a, and a second protective layer 16b. 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 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 selected from the group consisting of silicon nitride, beryllium nitride, boron nitride, and zirconium nitride. The first protective layer 16a is a layer containing amorphous carbon that covers the surface of the first nitride layer 14a opposite the metal beryllium layer 12. The second protective layer 16b is a layer containing amorphous carbon that covers the surface of the second nitride layer 14b opposite the metal beryllium layer 12. The EUV transmitting coating 10 has an EUV transmittance of 85% or more at a wavelength of 13.5 nm. By adopting this five-layer structure of the first protective layer 16a (amorphous carbon layer), first nitride layer 14a, metal beryllium layer 12, second nitride layer 14b, and second protective layer 16b (amorphous carbon layer), it is possible to provide an EUV transmitting coating 10 that exhibits high EUV transmittance and excellent in-plane uniformity of EUV transmittance, even though it has the protective layers 16a and 16b on both sides.

[0013] As mentioned above, core materials with high EUV transmittance may form a native oxide film several nanometers thick on their surfaces 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. On the other hand, pellicle films are desired not only to have high EUV transmittance but also to have excellent in-plane uniformity of EUV transmittance. This is because the more uniform the in-plane uniformity of EUV transmittance, the more uniform the exposure dose within the surface, improving the homogeneity of devices manufactured through EUV exposure. These problems are successfully solved by the EUV transmitting film of the present invention. That is, the EUV transmitting film of the present invention comprises a main layer 11 made of a first nitride layer 14a, a metal beryllium layer 12, and a second nitride layer 14b, each of which has a high EUV transmittance, and a first protective layer 16a and a second protective layer 16b covering both sides of the main layer 11, and these protective layers 16a and 16b can prevent the formation of a natural oxide film or a side reaction film that would occur on the surface of the main layer 11 (if the protective layers 16a and 16b were not present) during the time period until the fabricated pellicle is loaded into an EUV exposure tool and subjected to an exposure process. Furthermore, because the protective layers 16a and 16b, which contain amorphous carbon, have a small loss in EUV transmittance, the EUV transmitting film 10 of the present invention can exhibit high EUV transmittance despite having a five-layer structure including the protective layers 16a and 16b. Furthermore, the EUV transmitting film 10 having a five-layer structure including the protective layers 16 a and 16 b has the advantage of being superior in in-plane uniformity of EUV transmittance compared to a three-layer main layer structure without the protective layers 16 a and 16 b. This is thought to be because the protective layers 16 a and 16 b formed on both sides more even out the irregularities on both sides of the three-layer main layer. This advantage allows for a uniform in-plane exposure dose during EUV exposure through the EUV transmitting film 10, thereby improving the uniformity of devices manufactured through EUV 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 85% or more, preferably 90% or more, more preferably 91% or more, and even more preferably 92% 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 95% or less, more typically 94% or less, for example 93.5% 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 explained as follows. For example, if an amorphous carbon protective layer is provided directly on the main layer, which is a metal beryllium layer, the amorphous carbon may react with the metal beryllium to form beryllium carbide. Therefore, by providing the main layer with a three-layer structure of the first nitride layer 14a / metal beryllium layer 12 / first nitride layer 14a and providing amorphous carbon protective layers 16a and 16b on the nitride layers 14a and 14b, the reaction between the amorphous carbon and the metal beryllium can be prevented, i.e., the reaction between the main layer and the protective layer can be suppressed. Note that, in this specification, the terms "silicon nitride," "beryllium nitride," "boron nitride," and "zirconium nitride" refer to silicon nitride. ３ N ４ , Be ３ N２ , 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 constitute the main layer 11 of the EUV transmitting film. The main layer 11 contributes to realizing high EUV transmittance while ensuring the basic functions of a pellicle film (such as preventing particle adhesion). The thickness of the main layer 11 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 main layer 11 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 main layer 11 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 delamination, and acts as a thermal expansion buffer layer between these layers to prevent delamination 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] Each of the first protective layer 16a and the second protective layer 16b is a layer containing amorphous carbon. Amorphous carbon-containing layers exhibit high protection 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), and are also advantageous in that they have high EUV transmittance, minimize the impact of residues on the main layer 11 when the protective layers 16a and 16b are thinned or removed, and are easily thinned or removed. The first protective layer 16a and the second protective layer 16b preferably contain amorphous carbon as a primary 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 irregularly, 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 with a completely irregular atomic arrangement, or carbon with 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 16 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.

[0020] The thickness of each of the first protective layer 16a and the second protective layer 16b is preferably 1 to 10 nm or less, more preferably 2 to 7 nm, and even more preferably 3 to 5 nm. Within these ranges, high EUV transmittance and improved in-plane uniformity of EUV transmittance can be more effectively achieved. Furthermore, thicker protective layers 16a and 16b are desirable for protecting the EUV transmitting film 10 (particularly the main layer 11) from various chemicals (e.g., highly reactive fluorine-based etching agents) used in the pellicle film fabrication process (e.g., the self-supporting film fabrication process). However, increasing the thickness of the protective layers 16a and 16b reduces the EUV transmittance of the EUV transmitting film 10. In this regard, a thickness within the above range can achieve a good balance between high protection performance against various chemicals and high EUV transmittance. However, in order to achieve even higher EUV transmittance while ensuring a minimum level of protective performance, it is also effective to make each of the first protective layer 16 a and the second protective layer 16 b extremely thin, preferably at least 1 nm but less than 2 nm, and more preferably at least 1 nm but less than 1.5 nm.

[0021] The EUV transmitting film 10 preferably has a main region for transmitting EUV in the form of a free-standing film. That is, it is preferable that the substrate (e.g., 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 (e.g., Si substrate) remains in the main region other than the outer edge, that is, the main region is composed only of the main layer 11 and the protective layers 16 a and 16 b.

[0022] The EUV transmitting film according to the present invention can be produced by forming a laminated film to be used as the EUV transmitting film on a Si substrate, and then removing unnecessary portions of the Si substrate 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.

[0023] (1) Preparation of Si Substrate First, a Si substrate is prepared on which a laminated film is to be formed. After forming a laminated 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, 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.

[0024] (2) Formation of a Laminated Film A laminated 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 laminated 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. The amorphous carbon films serving as the first protective layer 16a and the second protective layer 16b are preferably formed by sputtering using a graphite target.

[0025] 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).

[0026] 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.

[0027] 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 a main layer 11 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.

[0028] (3) Formation of a freestanding film The unnecessary parts of the Si substrate on which the composite film is formed are removed by etching, except for the outer edge part that will remain as a border, to form the composite film into a freestanding film. Si etching can be performed by any method, but XeF ２ This can be preferably performed by etching using

[0029] Processing Method If desired, the manufactured EUV transmitting film 10 may be processed to be thin. As described above, by thinning the first protective layer 16a and the second protective layer 16b, it is possible to achieve a higher EUV transmittance while ensuring a minimum level of protective performance. In particular, the above-mentioned XeF ２After undergoing the freestanding film formation process using a fluorine-based etchant such as HCl, the first protective layer 16a and the second protective layer 16b no longer require strong protective properties against the fluorine-based etchant; a mild protective property such as oxidation resistance is sufficient. Therefore, after forming the EUV transmitting film 10 into a freestanding film, it may be advantageous to further increase the EUV transmittance by making the first protective layer 16a thinner than the protective layers 16a and 16b. The thinning of the EUV transmitting film 10 is preferably performed by placing 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 EUV transmitting film 10 with the hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals. By exposing the amorphous carbon films 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 film reacts with H, resulting in partial removal of the amorphous carbon film. As a result, the first protective layer 16a and the second protective layer 16b can be made thin.

[0030] Exposure Method As described above, by thinning the first protective layer 16 a and the second protective layer 16 b, it is possible to achieve even higher EUV transmittance while ensuring a minimum level of protective performance. Therefore, it is preferable to thin the first protective layer 16 a and the second protective layer 16 b during exposure. From this perspective, a preferred exposure method includes the steps of: installing the EUV transmitting film 10 in an apparatus that generates hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals; bringing the EUV transmitting film 10 into contact with the hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals, thereby thinning the first protective layer 16 a and the second protective layer 16 b; and installing the EUV transmitting film 10 with the thinned first protective layer 16 a and the second protective layer 16 b in an EUV exposure apparatus, allowing EUV light to pass through the EUV transmitting film 10, and performing pattern exposure on a photosensitive substrate in the EUV exposure apparatus.

[0031] The present invention will be explained in more detail by the following examples, but the present invention is not limited to the following examples.

[0032] Example 1 According to the procedure shown in FIGS. 2A and 2B, a five-layer composite free-standing film (EUV-transmitting film) of amorphous carbon / silicon nitride / Be / silicon nitride / amorphous carbon was prepared as follows.

[0033] (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 ２ The exposed portions of film 22 are etched away to leave SiO ２ A mask 22a was fabricated (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.

[0034] (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 ４A 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 0.3 Pa and a gas mixture of argon gas and 20% nitrogen gas. ３ N ４ The 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 0.3 Pa and a gas mixture of argon gas and 20% nitrogen gas. ３ N ４ 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 silicon nitride (SiN) and 2 nm of amorphous carbon (C) was formed as the EUV transmitting film 10. That is, this EUV transmitting film 10 has a five-layer structure consisting of a main layer made up of three layers, namely, a first silicon nitride layer, a metal beryllium layer, and a second silicon nitride layer, and a first protective layer and a second protective layer, each containing amorphous carbon as a main component, formed on both sides of the main layer.

[0035] (3) Freestanding film: XeF capable of processing 8-inch (20.32 cm) substrates ２The Si substrate 28 with the EUV transmitting film 10 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 chamber was evacuated sufficiently to avoid the reaction with the gas to generate hydrofluoric acid, which could cause corrosion of the etcher or unexpected etching. If necessary, the chamber was repeatedly evacuated and nitrogen gas was introduced to reduce residual moisture. Once the chamber was evacuated sufficiently, 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 XeF ２ 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 free-standing film was completely removed. Etching was stopped when the unnecessary Si substrate was completely removed. In this way, a five-layer composite free-standing film having a Si border 20 was obtained as the EUV transmitting film 10 (FIG. 2B(j)).

[0036] Example 2 An EUV transmitting film 10 having a Si border 20 was fabricated in the same manner as in Example 1. Thereafter, the amorphous carbon film exposed on both sides of the EUV transmitting film 10 was etched with hydrogen plasma to reduce the thickness of each amorphous carbon layer to 1 nm. In this way, an EUV transmitting film 10 having a Si border 20 and a thickness of 1 nm of amorphous carbon (C) / silicon nitride (Si ３ N ４－ｘ) 2 nm / beryllium (Be) 20 nm / silicon nitride (Si ３ N ４－ｘ A composite free-standing film having a five-layer structure consisting of 2 nm of SiO 2 and 1 nm of amorphous carbon (C) was obtained as the EUV transmitting film 10.

[0037] Example 3 (Comparative) An EUV transmitting film 10 having a Si border 20 was produced in the same manner as in Example 1. Thereafter, the amorphous carbon films exposed on both sides of the EUV transmitting film 10 were etched with hydrogen plasma to remove each amorphous carbon layer. 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 having a thickness of 2 nm was obtained as the EUV transmitting film 10.

[0038] 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 with a sensor. The EUV transmittance was calculated by comparing the obtained measurement value with the EUV light intensity directly measured with 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 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.

[0039]

[0040] As can be seen from the above results, when the amorphous carbon film is left as in Examples 1 and 2, the EUV transmittance is slightly lowered, but the in-plane variation in EUV transmittance is small, i.e., the in-plane uniformity is excellent. On the other hand, when the amorphous carbon film is etched away as in Example 3, the transmittance is increased, but the in-plane variation in EUV transmittance is large, i.e., the in-plane uniformity is poor. In this sense, it can be said that by leaving the amorphous carbon film thin as in Example 2, it is possible to generally maintain a high EUV transmittance close to that of Example 3 while improving the in-plane uniformity of EUV transmittance compared to Example 3. While a higher EUV transmittance has the advantage of completing exposure in a shorter time, i.e., improving throughput, a smaller in-plane variation in EUV transmittance results in a more uniform in-plane exposure amount and improves device uniformity. In other words, according to the present invention, an EUV transmitting film suitable for improving device uniformity while realizing a high EUV transmittance can be provided.

Claims

1. An EUV transmitting film having a five-layer structure comprising: a metal beryllium layer having a first surface and a second surface; a first nitride layer covering the first surface of the metal beryllium layer and containing at least one selected from the group consisting of silicon nitride, beryllium nitride, boron nitride, and zirconium nitride; a second nitride layer covering the second surface of the metal beryllium layer and containing at least one selected from the group consisting of silicon nitride, beryllium nitride, boron nitride, and zirconium nitride; a first protective layer covering the surface of the first nitride layer opposite to the metal beryllium layer and containing amorphous carbon; and a second protective layer covering the surface of the second nitride layer opposite to the metal beryllium layer and containing amorphous carbon, wherein the EUV transmitting film has an EUV transmittance of 85% or more at a wavelength of 13.5 nm.

2. The EUV transmitting film according to claim 1, wherein the first nitride layer, the metal beryllium layer, and the second nitride layer constitute a main layer of the EUV transmitting film, and the thickness of the main layer is 7 to 30 nm.

3. The EUV transmitting film according to claim 1 or 2, wherein the thickness of the metallic beryllium layer is 5 to 25 nm.

4. The EUV transmitting film according to claim 1 or 2, wherein the first nitride layer and the second nitride layer each have a thickness of 1 to 5 nm.

5. The EUV transmitting film according to claim 1 or 2, wherein the thickness of each of the first protective layer and the second protective layer is 1 to 10 nm or less.

6. The EUV transmitting film according to claim 5, wherein the first protective layer and the second protective layer each have a thickness of 2 to 7 nm.

7. The EUV transmitting film according to claim 5, wherein the thickness of each of the first protective layer and the second protective layer is 1 nm or more and less than 2 nm.

8. A method for processing an EUV transmitting film, comprising the steps of: installing the EUV transmitting film according to claim 1 or 2 in an apparatus that generates hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals; and bringing the EUV transmitting film into contact with hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals, thereby thinning the first protective layer and the second protective layer.

9. An exposure method comprising the steps of: installing the EUV transmitting film according to claim 1 or 2 in an apparatus that generates hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals; bringing the EUV transmitting film into contact with hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals, thereby thinning the first protective layer and the second protective layer; and installing the EUV transmitting film with the first protective layer and the second protective layer thinned in an EUV exposure apparatus, allowing EUV to pass through the EUV transmitting film, and performing pattern exposure on a photosensitive substrate in the EUV exposure apparatus.

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