EUV permeating membrane, its processing method and exposure method

Abstract

An EUV-transmitting film is provided, having protective layers on both sides, exhibiting high EUV transmittance and excellent in-plane uniformity of EUV transmittance. This EUV-transmitting film comprises five layers: a beryllium metal layer having a first side and a second side; a first nitride layer covering the first side of the beryllium metal layer and comprising at least one element selected from the group consisting of silicon nitride, beryllium nitride, boron nitride, and zirconium nitride; a second nitride layer covering the second side of the beryllium metal layer and comprising at least one element selected from the group consisting of silicon nitride, beryllium nitride, boron nitride, and zirconium nitride; a first protective layer covering the side opposite to the first nitride layer of the beryllium metal layer and comprising amorphous carbon; and a second protective layer covering the side opposite to the second nitride layer of the beryllium metal layer and comprising amorphous carbon. This EUV-transmitting film exhibits an EUV transmittance of 85% or higher at a wavelength of 13.5 nm.

Description

[Technical Field]

[0001] This disclosure relates to EUV penetrating films and their processing and exposure methods. [Previous Technology]

[0002] Miniaturization in semiconductor manufacturing processes is progressing year by year, with various improvements being made to each step. In particular, in the photolithography step, EUV (Extreme Ultraviolet) light with a wavelength of 13.5 nm has begun to be used instead of the previous 193 nm ArF exposure. As a result, the wavelength suddenly becomes less than 1 / 10, and its optical properties become completely different. However, since there are no materials with high transmittance to EUV light, for example, pellicles, which serve as anti-particle films for photomasks, are still not practical. Therefore, equipment manufacturers cannot currently use pellicles to manufacture semiconductor devices.

[0003] Therefore, people have been developing photomask protective films and expect that the core material of the photomask protective film should use materials with high EUV transmittance such as Si, Be, Y, and Zr. Patent document 1 (Japanese Patent No. 6858817) discloses a photomask protective film having a core layer and a capping layer, wherein the core layer is a core layer containing a material that is substantially transparent to EUV radiation such as poly(Si), and the capping layer is a capping layer containing a material that absorbs IR radiation.

[0004] Furthermore, Patent Document 2 (Japanese Patent Application Publication No. 2020-98227) discloses a photomask protective film, which is a photomask protective film stretched on one end face of a photomask protective film frame, having a monocrystalline Si main layer and graphene on one or both sides of the main layer. By having graphene in the main layer, sufficient mechanical strength can be achieved without damaging the photomask protective film during fabrication. [Prior Art Documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent No. 6858817 [Patent Document 2] Japanese Patent Application Publication No. 2020-98227 [Summary of the Invention]

[0006] However, the core material used for the photomask protective film, which has high EUV transmittance, forms a natural oxide film of several nm on its surface in the atmosphere. This oxide film reduces the EUV transmittance of the photomask protective film by absorbing EUV. In particular, Be is a material with high EUV transmittance, but it is said that a natural oxide film of 2-3 nm forms on its surface, resulting in a transmittance loss of 6-9% due to this oxide film. In addition, the manufacturing process of the photomask protective film may involve the use of gases such as fluorine and chlorine, or solutions such as acids and alkalis, which are not part of the atmosphere. Therefore, side reaction films are generated on the surface of the core material, which may also lead to a decrease in EUV transmittance. Therefore, it is desirable to form a protective layer on the surface of the core material to inhibit the formation of these films.

[0007] However, although a significant decrease in EUV transmittance of the photomask can be prevented by attaching a reaction-inhibiting protective layer to the surface of the core material such as Si or Be, the EUV transmittance of such a protective layer is still lower than that of the pure core material, resulting in a decrease in the overall EUV transmittance of the photomask. For example, Ru can be used as a protective layer for the Be core material, but considering that a 1-2 nm layer of Ru in a three-layer structure (Ru / Be / Ru) photomask is applied to the surface and back of the Be core material, the Ru protective layer will cause an EUV transmittance loss of about 3-6%, significantly reducing the performance of the photomask. Therefore, a protective layer with low EUV transmittance loss is desired. In addition, it is desirable for the photomask to not only have high EUV transmittance but also excellent in-plane uniformity of EUV transmittance. This is because the better the in-plane uniformity of EUV transmittance, the more uniform the in-plane exposure becomes, and the better the homogeneity of the device manufactured by EUV exposure.

[0008] The inventors have discovered that by employing a five-layer structure consisting of an amorphous carbon layer, a nitride layer, a beryllium metal layer, a nitride layer, and an amorphous carbon layer, an EUV-transmitting film can be provided that has protective layers on both sides, exhibits high EUV transmittance, and also has excellent in-plane uniformity of EUV transmittance.

[0009] Therefore, an object of the present invention is to provide an EUV-transmitting film having protective layers on both sides, exhibiting high EUV transmittance, and also exhibiting excellent in-plane uniformity of EUV transmittance. Furthermore, another object of the present invention is to provide a method for processing the EUV-transmitting film. Further, yet another object of the present invention is to provide an exposure method using the EUV-transmitting film.

[0010] According to this disclosure, the following embodiments are provided. [Implication 1] An EUV-transmitting film, which is an EUV-transmitting film composed of five layers formed as follows: a beryllium metal layer having a first side and a second side; a first nitride layer covering the first side of the aforementioned beryllium metal layer and comprising at least one of the group consisting of silicon nitride, beryllium nitride, boron nitride and zirconium nitride; a second nitride layer covering the second side of the aforementioned beryllium metal layer and comprising at least one of the group consisting of silicon nitride, beryllium nitride, boron nitride and zirconium nitride; a first protective layer covering the side opposite to the aforementioned beryllium metal layer of the aforementioned first nitride layer and comprising amorphous carbon; a second protective layer covering the side opposite to the aforementioned beryllium metal layer of the aforementioned second nitride layer and comprising amorphous carbon, wherein the aforementioned EUV-transmitting film has an EUV transmittance of 85% or more at a wavelength of 13.5 nm. [Sample 2] The EUV penetrating film as described in Sample 1, wherein the aforementioned first nitride layer, the aforementioned beryllium layer, and the aforementioned second nitride layer constitute the main layer of the EUV penetrating film, and the thickness of the aforementioned main layer is 7-30 nm. [Sample 3] The EUV penetrating film as described in Sample 1 or 2, wherein the thickness of the aforementioned beryllium layer is 5-25 nm. [Sample 4] The EUV penetrating film as described in any of Samples 1-3, wherein the thickness of each of the aforementioned first nitride layer and the aforementioned second nitride layer is 1-5 nm. [Sample 5] The EUV penetrating film as described in any of Samples 1-4, wherein the thickness of each of the aforementioned first protective layer and the aforementioned second protective layer is 1-10 nm or less. [Sample 6] The EUV penetrating film as described in Sample 5, wherein the thickness of each of the aforementioned first protective layer and the aforementioned second protective layer is 2-7 nm. [Sample 7] The EUV penetrating film as described in Sample 5, wherein the thickness of each of the aforementioned first protective layer and the aforementioned second protective layer is 1 nm or more but less than 2 nm. [Sample 8] A method for processing an EUV-transmitting membrane includes: installing the EUV-transmitting membrane as described in any of Samples 1 to 7 in an apparatus for generating hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals; and contacting the EUV-transmitting membrane with hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals, thereby thinning the first protective layer and the second protective layer. [Sample 9] An exposure method comprising: installing an EUV-transmitting film as described in any of Samples 1 to 7 in an apparatus for generating hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals; contacting the EUV-transmitting film with hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals, thereby thinning the first protective layer and the second protective layer; installing the thinned EUV-transmitting film of the first protective layer and the second protective layer in an EUV exposure apparatus, allowing EUV to penetrate the EUV-transmitting film, and performing pattern exposure on a photosensitive substrate in the EUV exposure apparatus.

Implementation Method

[0012] [Form for Implementing the Invention] Figure 1 shows a schematic cross-sectional view of an EUV permeation membrane 10 according to one form of the present invention. The EUV permeation membrane 10 is a membrane composed of five layers: a beryllium metal layer 12, a first nitride layer 14a, a second nitride layer 14b, a first protective layer 16a, and a second protective layer 16b. The beryllium metal 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 beryllium metal layer 12 and comprising at least one layer 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 beryllium metal layer 12 and comprising at least one layer selected from the group consisting of silicon nitride, beryllium nitride, boron nitride, and zirconium nitride. The first protective layer 16a is a layer covering the side of the first nitride layer 14a opposite to the beryllium layer 12 and contains amorphous carbon. The second protective layer 16b is a layer covering the side of the second nitride layer 14b opposite to the beryllium layer 12 and contains amorphous carbon. The EUV transmitting film 10 has an EUV transmittance of over 85% at a wavelength of 13.5 nm. In this way, by using a five-layer structure consisting of the first protective layer 16a (amorphous carbon layer), the first nitride layer 14a, the beryllium layer 12, the second nitride layer 14b, and the second protective layer 16b (amorphous carbon layer), an EUV transmitting film 10 can be provided that has protective layers 16a and 16b on both sides, exhibits high EUV transmittance, and also has excellent in-plane uniformity of EUV transmittance.

[0013] As mentioned above, core materials with high EUV transmittance sometimes form a natural oxide film of several nm on their surface in the atmosphere. Furthermore, the manufacturing process of the photomask protective film may involve the use of gases such as fluorine and chlorine, or solutions such as acids and alkalis, which may generate side reaction films on the surface of the core material. The formation of such films reduces the EUV transmittance of the photomask protective film. Therefore, it is desirable to form a protective layer on the surface of the core material to inhibit the formation of these films. However, attaching a reaction-inhibiting protective layer to the surface of the core material leads to a decrease in the EUV transmittance of the photomask protective film as a whole. On the other hand, it is desirable for the photomask protective film to not only have high EUV transmittance but also excellent in-plane uniformity of EUV transmittance. This is because the better the in-plane uniformity of EUV transmittance, the more uniform the in-plane exposure becomes, and the higher the homogeneity of the device manufactured after EUV exposure. The EUV-transmitting film according to the present invention successfully solves these problems. That is, the EUV-transmitting film of the present invention comprises: a main layer 11 formed by a first nitride layer 14a with high EUV transmittance, a beryllium layer 12, and a second nitride layer 14b, and a first protective layer 16a and a second protective layer 16b covering both sides of the main layer 11. These protective layers 16a and 16b prevent the formation of natural oxide films and side reaction films on the surface of the main layer 11 (if the protective layers 16a and 16b were not present) until the photomask protective film is mounted on the EUV exposure apparatus during the exposure process. Furthermore, since the protective layers 16a and 16b containing amorphous carbon have minimal EUV transmittance loss, the EUV-transmitting film 10 of the present invention can exhibit high EUV transmittance even when it has five layers of protective layers 16a and 16b. Furthermore, the EUV-transmitting film 10, consisting of five layers including protective layers 16a and 16b, offers superior in-plane uniformity of EUV transmittance compared to a main layer consisting of only three layers without protective layers 16a and 16b. This is presumably because forming protective layers 16a and 16b on both sides makes the unevenness of the three-layer main layer smoother. This advantage results in more uniform in-plane exposure during EUV exposure through the EUV-transmitting film 10, improving the homogeneity of the device manufactured using EUV exposure.

[0014] The EUV transmitting film 10 described above has a high EUV transmittance. The EUV transmitting film 10 has an EUV transmittance of 85% or more at a wavelength of 13.5 nm, preferably 90% or more, more preferably 91% or more, and even more preferably 92% or more. It is desirable for the EUV transmitting film 10 to have a higher EUV transmittance, and there is no particular upper limit. Ideally, it would be 100%, but typically it is below 95%, more typically below 94%, for example, below 93.5%.

[0015] The beryllium layer 12 is a layer containing beryllium as the main component. Here, "main component" in the beryllium layer 12 refers to a component accounting for 50 mol% or more, preferably 70 mol% or more, more preferably 80 mol% or more, and even more preferably 90 mol% or more of the beryllium layer 12. Furthermore, the beryllium layer 12 may contain impurities other than beryllium as the main component. Therefore, the beryllium layer 12 can be formed from beryllium and unavoidable impurities. The thickness of the beryllium layer 12 is preferably 5 to 25 nm, more preferably 7 to 20 nm, and even more preferably 9 to 15 nm.

[0016] The first nitride layer 14a and the second nitride layer 14b each comprise at least one nitride selected from the group consisting of silicon nitride, beryllium nitride, boron nitride, and zirconium nitride. Silicon nitride is particularly preferred. 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 below. For example, if an amorphous carbon protective layer is directly provided on the main layer of the metal beryllium layer, the amorphous carbon may react with the metal beryllium to form beryllium carbide. Therefore, by making the main layer a three-layer structure of the first nitride layer 14a / metal beryllium layer 12 / first nitride layer 14a, and providing the 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, that is, the reaction between the main layer and the protective layer can be suppressed. Furthermore, the terms "silicon nitride," "beryllium nitride," "boron nitride," and "zirconium nitride" used in this specification not only allow stoichiometric compositions of materials such as Si3N4, Be3N2, BN, and ZrN, but also allow composite compositions of non-stoichiometric compositions such as Si3N4-x (where 0 < x < 4), Be3N2-x (where 0 < x < 2), BNx (where 0 < x < 1), and ZrNx (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 beryllium metal layer 12, and the second nitride layer 14b constitute the main layer 11 of the EUV transmission film. The main layer 11 can ensure the basic functions of the photomask protective film (such as preventing particle adhesion) while contributing to the achievement of high EUV transmittance. The thickness of the main layer 11 is preferably 7~30nm, more preferably 9~26nm, and even more preferably 11~21nm.

[0018] When the first nitride layer 14a and / or the second nitride layer 14b each contain beryllium nitride, the main layer 11 is preferably provided with a nitrogen concentration sloping region where the nitrogen concentration decreases as it approaches the metal beryllium layer 12. That is, although the composition of the beryllium nitride as described above may include stoichiometric compositions ranging from Be3N2 to non-stoichiometric compositions such as Be3N2-x (where 0 < x < 2), the beryllium nitride constituting the beryllium nitride layer is preferably provided with a sloping composition where the composition approaches the beryllium-rich composition as it approaches the metal beryllium layer 12. In this way, the adhesion between the nitride layers 14a, 14b (i.e., the beryllium nitride layer) constituting the main layer 11 and the metal beryllium layer 12 can be improved, while the stress generated by the thermal expansion difference between these layers can also be mitigated. That is, in cases where these layers are subjected to high temperatures due to increased adhesion and peeling, or where the layers absorb EUV light, this layer can act as a thermal expansion buffer, making them difficult to peel off. The thickness of the nitrogen concentration tilted region is preferably smaller than the thickness of each of the nitride layers 14a and 14b. That is, the entire thickness of each of the nitride layers 14a and 14b does not need to be a nitrogen concentration tilted region. For example, it is preferable that only a portion of the thickness of each of the nitride layers 14a and 14b is a nitrogen concentration tilted region; more preferably, 15% to 50% of the thickness of each of the nitride layers 14a and 14b is a nitrogen concentration tilted region.

[0019] The first protective layer 16a and the second protective layer 16b each comprise a layer of amorphous carbon. The layers comprising amorphous carbon not only provide protection against various chemicals (e.g., highly reactive fluorine-based etchants) used in the photomask protective film fabrication process (e.g., self-supporting film formation step), but also offer the following advantages: high EUV transmittance, minimal impact of residues from thinning or removing the protective layers 16a and 16b on the main layer 11, and ease of thinning or removing the protective layers 16a and 16b. It is preferable that the first protective layer 16a and the second protective layer 16b contain amorphous carbon as their main component, and more preferably they are composed of amorphous carbon. Amorphous carbon generally rarely has a completely irregular atomic arrangement; although it has a crystalline structure at the microscopic level (i.e., it has microcrystals), these microcrystals are mostly irregularly arranged, making the whole amorphous. Among them, microcrystals containing a large number of diamond-like three-dimensional 4-coordination structures are called DLC (Diamond-like Carbon), and microparticles containing a large number of graphite-like planar 3-coordination structures are called GLC (Graphite-like Carbon). The first protective layer 16a and the second protective layer 16b can be carbon with completely irregular atomic arrangements or carbon with irregular microcrystals. Further, they can also be amorphous carbon that is not completely dense and contains micropores. Here, the "main component" in the first protective layer 16a and the second protective layer 16b refers to the component that accounts for more than 50% by weight, more preferably more than 60% by weight, more preferably more than 70% by weight, and even more preferably more than 80% by weight 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 can also be formed 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 achieved more effectively. Furthermore, in order to protect the EUV-transmitting film 10 (especially the main layer 11) from the effects of various chemicals (e.g., highly reactive fluorine-based etchants) used in the photomask protective film fabrication process (e.g., self-supporting film formation step), it is desirable for the protective layers 16a and 16b to be relatively thick. However, if the film thickness increases, the EUV transmittance of the EUV-transmitting film 10 will decrease. In this respect, if the film thickness is within the above-mentioned range, a good balance can be achieved between high protection against various chemicals and high EUV transmittance. However, in order to ensure minimum protection performance while achieving higher EUV penetration, the thickness of the first protective layer 16a and the second protective layer 16b can be very thin, for example, preferably 1 nm or more but less than 2 nm, and more preferably 1 nm or more but less than 1.5 nm.

[0021] The EUV-transmitting film 10 is preferably a self-supporting film in the main area for EUV transmission. That is, it is preferable that the substrate (e.g., a Si substrate) used during film formation is left as a border only at the outer edge of the EUV-transmitting film 10. In other words, the substrate (e.g., a Si substrate) is not left in the main area outside the outer edge. That is, it is preferable that the main area is composed only of the main layer 11 and the protective layers 16a and 16b.

[0022] Manufacturing Method The EUV-transmitting film of the present invention can be fabricated by etching and removing unwanted portions of the Si substrate after forming a laminated film that serves as an EUV-transmitting film on a Si substrate. Therefore, as described above, the main portion of the EUV-transmitting film becomes a self-supporting film that does not leave any residue on the Si substrate.

[0023] (1) Preparation of Si substrate First, a Si substrate for forming a laminated film thereon is prepared. The Si substrate is removed by etching the main area (i.e., the area that should serve as a self-supporting film) outside its outer edge after forming a laminated film thereon consisting of a second protective layer 16b, a second nitride layer 14b, a beryllium metal layer 12, a first nitride layer 14a, and a first protective layer 16a. Therefore, in order to perform etching more efficiently in a short time, it is desirable to pre-thin the thickness of the Si substrate in the area that should serve as a self-supporting film. Therefore, it is desirable to use a conventional semiconductor process to form a mask corresponding to the EUV transmission shape on the Si substrate, and to thin the thickness of the main area of ​​the Si substrate to a predetermined thickness by wet etching the Si substrate. By cleaning and drying the wet-etched Si substrate, a Si substrate with voids formed by wet etching is prepared. In addition, as the wet etching mask, any material that is resistant to wet etching solution of Si can be used, for example, SiO2 is suitable. Furthermore, there are no particular limitations on the wet etching solution, as long as it can etch Si. For example, TMAH (tetramethylammonium hydroxide) is preferred because it can perform very good anisotropic etching of Si under appropriate conditions.

[0024] (2) Formation of the laminated film On the Si substrate, a laminated film consisting of a second protective layer 16b, a second nitride layer 14b, a beryllium metal layer 12, a first nitride layer 14a, and a first protective layer 16a is formed sequentially. The laminated film can be formed by any film formation method. Sputtering is an example of a preferred film formation method. The beryllium metal layer 12 is preferably formed by sputtering using a pure Be target. The amorphous carbon film used as the first protective layer 16a and the second protective layer 16b is preferably formed by sputtering using a graphite target.

[0025] The first nitride layer 14a and the second nitride layer 14b are preferably fabricated by sputtering. For example, (i) after forming a Si, Be, B, or Zr film by sputtering using a Si, Be, B, or Zr target, the Si, Be, B, or Zr can be nitrided by irradiating with nitrogen plasma to form nitride layers 14a and 14b. Furthermore, (ii) the first nitride layer 14a and the second nitride layer 14b can be fabricated by reactive sputtering. This reactive sputtering, for example, can be performed by introducing nitrogen gas into a chamber during sputtering using a Si, Be, B, or Zr target, causing Si, Be, B, or Zr to react with nitrogen to generate silicon nitride, beryllium nitride, boron nitride, or zirconium nitride. Alternatively, (iii) nitride layers 14a and 14b can be directly formed by sputtering using Si3N4, Be3N2, BN, or ZrN targets. In this sputtering, nitrogen gas can be introduced into the chamber, as in reactive sputtering as described in (ii) above, to react Si, Be, B, or Zr with nitrogen, promoting the formation of silicon nitride, beryllium nitride, boron nitride, or zirconium nitride.

[0026] Furthermore, the methods for forming the beryllium metal layer 12, the nitride layers 14a, 14b, and the protective layers 16a, 16b are not limited to these. Alternatively, the beryllium metal layer 12, the nitride layers 14a, 14b, and the protective layers 16a, 16b can be formed in a single-chamber sputtering apparatus as described in the embodiments below, or a sputtering apparatus with multiple chambers can be used to form the beryllium metal layer 12, the nitride layers 14a, 14b, and the protective layers 16a, 16b in individual chambers.

[0027] When the first nitride layer 14a and the second nitride layer 14b are beryllium nitride layers containing nitrogen concentration tilt regions, that is, when nitrogen concentration tilt regions are formed in the main layer 11 of the three-layer structure of beryllium nitride / beryllium / beryllium nitride, during the deposition of beryllium nitride film and metal beryllium film, nitrogen gas can be introduced into the chamber to continue sputtering using a pure Be target, but the introduction of nitrogen gas is stopped midway, and the deposition of metal beryllium film is switched. In this way, as the nitrogen gas concentration in the chamber decreases, a region in which the nitrogen concentration decreases in the thickness direction is formed in the film. On the other hand, when switching from metal beryllium to beryllium nitride, sputtering is continued in the opposite way, but if nitrogen gas is introduced midway, nitrogen concentration tilt regions can be formed. The thickness of the nitrogen concentration tilt regions can be controlled by adjusting the time of nitrogen concentration change.

[0028] (3) Self-supporting film formation: Self-supporting film formation of composite film is performed by etching and removing unwanted portions of the Si substrate on which the composite film is formed, except for the outer edge portion which remains as a boundary. The etching of Si can be performed by any method, but it is preferred to perform the etching using XeF2.

[0029] The EUV-transmitting film 10 can be processed to be thinner, depending on the desired method. As mentioned above, by thinning the first protective layer 16a and the second protective layer 16b, a minimum level of protection can be ensured while achieving a higher EUV transmittance. In particular, after the self-supporting film formation step using the aforementioned fluorine-based etchant such as XeF2, the strong protective function of the first protective layer 16a and the second protective layer 16b against the fluorine-based etchant is no longer required; stable protective functions such as oxidation resistance are sufficient. Therefore, after the EUV-transmitting film 10 is self-supporting, it is advantageous to further improve the EUV transmittance by thinning the protective layers 16a and 16b. The thinning of the EUV penetrating membrane 10 is preferably performed by installing the EUV penetrating membrane 10 in a device that generates hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals, thereby bringing the EUV penetrating membrane 10 into contact with the hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals. This is achieved by exposing the amorphous carbon film, which serves as the first protective layer 16a and the second protective layer 16b, to a hydrogen plasma and / or hydrogen free radical environment or an oxygen plasma and / or oxygen free radical environment, causing the C and H on the surface of the amorphous carbon film to react and removing a portion of the amorphous carbon film. As a result, the first protective layer 16a and the second protective layer 16b can be thinned.

[0030] As described above, by thinning the first protective layer 16a and the second protective layer 16b, a minimum level of protection can be ensured while achieving a higher EUV transmittance. Therefore, it is preferable to thin the first protective layer 16a and the second protective layer 16b during exposure. From this viewpoint, a preferred exposure method includes: installing the EUV-transmitting film 10 within an apparatus for generating hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals; thinning the first protective layer 16a and the second protective layer 16b by reacting the EUV-transmitting film 10 with hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals; and installing the thinned EUV-transmitting film 10 with the first protective layer 16a and the second protective layer 16b within an EUV exposure apparatus, allowing EUV to penetrate the EUV-transmitting film 10, and performing pattern exposure on the photosensitive substrate within the EUV exposure apparatus.

[0031] [Examples] The present invention will be further illustrated by the following examples. However, the present invention is not limited to the following examples.

[0032] Example 1 Following the order shown in Figures 2A and 2B, a composite self-supporting membrane (EUV penetration membrane) consisting of 5 layers of amorphous carbon / silicon nitride / Be / silicon nitride / amorphous carbon is fabricated as follows.

[0033] (1) Preparation of Si substrate: Prepare an 8-inch (20.32 cm) diameter Si wafer 20 (Figure 2A(a)). On both sides of the Si wafer 20, form a 50 nm thick SiO2 film 22 by thermal oxidation (Figure 2A(b)). Coat both sides of the Si wafer 20 with resist, and expose and develop it to form a resist mask 24 for SiO2 etching by forming a 110 mm × 145 mm resist hole on one side. By wet etching one side of this substrate with hydrofluoric acid, etch away the exposed part of the SiO2 film 22 to make a SiO2 mask 22a (Figure 2A(d)). Remove the resist mask 24 for SiO2 etching using an ashing device (Figure 2A(e)). Then, wet etch Si with TMAH liquid. In this etching process, the etching rate is determined beforehand, and only sufficient etching time is performed to achieve a target Si substrate thickness of 50 μm (Figure 2A(f)). Finally, the SiO2 film 22 formed on the unetched Si surface is removed and cleaned with hydrofluoric acid to prepare the Si substrate 28 (Figure 2B(g)). The Si substrate shape can be cut using a laser 30 (Figure 2B(h)) to achieve the desired shape (Figure 2B(i)). Thus, a 110 mm × 145 mm cavity 26 is formed in the center of an 8-inch (20.32 cm) Si wafer 20, preparing a Si substrate 28 with a Si thickness of 50 μm for the cavity 26 portion.

[0034] (2) Formation of the composite film On the Si substrate 28 having the voids 26 obtained in (1) above, a composite film with a five-layer structure of amorphous carbon / silicon nitride / Be / silicon nitride / amorphous carbon is formed in the following manner (Figure 2B(i)). First, the Si substrate 28 is set in a multi-target sputtering apparatus, and a graphite target, a Si3N4 target and a pure Be target are mounted. The chamber is evacuated, and sputtering is performed using the graphite target at an internal pressure of 0.3 Pa and only with argon gas. The time for the amorphous carbon DLC (Diamond-like Carbon) film to form 2 nm is calculated, and the sputtering is completed. Next, the chamber is evacuated again, and sputtering is performed using the Si3N4 target at an internal pressure of 0.3 Pa and with argon gas plus 20% nitrogen gas. The time for the Si3N4 film to form 2 nm is calculated, and the sputtering is completed. Furthermore, the chamber was evacuated again, and sputtering was performed using a pure Be target at an internal pressure of 0.5 Pa with only argon gas. The time required for the beryllium film to form a 20 nm film was calculated, and the sputtering was completed. Next, the chamber was evacuated again, and sputtering was performed using a Si3N4 target at an internal pressure of 0.3 Pa with argon gas and 20% nitrogen gas. The time required for the Si3N4 film to form a 2 nm film was calculated, and the sputtering was completed. Afterward, in the same manner as before, sputtering was performed using a graphite target, and the time required for the amorphous carbon film to form a 2 nm film was calculated, and the sputtering was completed. In this way, a composite film of 2 nm amorphous carbon (C) / 2 nm silicon nitride (Si3N4-x) / 20 nm beryllium (Be) / 2 nm silicon nitride (Si3N4-x) / 2 nm amorphous carbon (C) was formed as the EUV transmission film 10. That is, the EUV penetrating film 10 is composed of 5 layers formed as follows: a main layer consisting of 3 layers, namely a first silicon nitride layer, a beryllium metal layer and a second silicon nitride layer; a first protective layer and a second protective layer, which are respectively formed on both sides of the main layer and contain amorphous carbon as the main component.

[0035] (3) Self-supporting film formation: In the chamber of an XeF2 etching machine capable of processing 8-inch (20.32cm) substrates, a Si substrate 28 with an EUV-transmitting film 10 prepared in (2) above is placed. The chamber is fully evacuated. If there is residual moisture in the chamber, it will react with XeF2 gas to produce hydrofluoric acid, causing corrosion of the etching machine and accidental etching. Therefore, it is necessary to fully evacuate. As needed, the chamber is evacuated and nitrogen gas is introduced repeatedly to reduce residual moisture. Once the chamber is fully evacuated, the valve between the XeF2 raw material bottle and the spare chamber is opened. As a result, XeF2 sublimates and XeF2 gas accumulates in the spare chamber. After sufficient accumulation of XeF2 gas in the spare chamber, the valve between the spare chamber and the chamber is opened to introduce XeF2 gas into the chamber. XeF2 gas decomposes into Xe and F, and F reacts with Si to generate SiF4. SiF4 has a boiling point of -95°C. The generated SiF4 evaporates rapidly, causing the newly exposed Si substrate to react with F. Si etching is performed to reduce the F in the chamber. The chamber is then evacuated, and XeF2 gas is introduced into the chamber again for etching. This process of evacuation, introduction of XeF2 gas, and etching is repeated until the portion of the Si substrate 28 corresponding to the self-supporting film disappears. The etching is complete when the unwanted portion of the Si substrate disappears. In this way, a composite self-supporting film consisting of 5 layers with a Si border 20 is obtained as the EUV transmission film 10 (Figure 2B(j)).

[0036] Example 2: Similar to Example 1, an EUV-transmitting film 10 with Si boundary 20 was fabricated. Then, the thickness of each amorphous carbon layer was reduced to 1 nm by etching the exposed amorphous carbon films on both sides of the EUV-transmitting film 10 using hydrogen plasma. Thus, a composite self-supporting film consisting of 5 layers—1 nm of amorphous carbon (C), 2 nm of silicon nitride (Si3N4-x), 20 nm of beryllium (Be), 2 nm of silicon nitride (Si3N4-x), and 1 nm of amorphous carbon (C)—was obtained as the EUV-transmitting film 10.

[0037] Example 3 (Comparison) Similar to Example 1, an EUV-transmitting film 10 with Si boundary 20 was fabricated. Then, the amorphous carbon layers exposed on both sides of the EUV-transmitting film 10 were removed by hydrogen plasma etching. Thus, a composite self-supporting film consisting of three layers, namely Si boundary 20, silicon nitride (Si3N4-x) 2nm / beryllium (Be) 20nm / silicon nitride (Si3N4-x) 2nm, was obtained as the EUV-transmitting film 10.

[0038] EUV transmittance and its in-plane uniformity: For the self-supporting films of the EUV-transmitting films prepared as Examples 1-3, EUV light was irradiated with EUV light at an output power of 600W for 15 minutes in a hydrogen environment at 20 Pa, and the amount of transmitted EUV light was measured using a sensor. The obtained measured value was compared with the value of EUV light directly measured by the sensor without the EUV-transmitting film, and the EUV transmittance was calculated, as shown in Table 1. At this time, the spot of the EUV light used for transmittance measurement was an elliptical shape of 0.5 mm × 0.2 mm, and the EUV transmittance within its spot size was measured. Therefore, in order to evaluate the in-plane uniformity of EUV transmittance, the EUV transmittance was measured while moving the spot of the EUV light, and the EUV transmittance at each position was measured. From these data, the in-plane variation value was calculated as three times the standard deviation. Therefore, the smaller the in-plane variation value, the better the in-plane uniformity of EUV transmittance.

[0039] [Table 1] Composition and thickness (nm) of each layer EUV characteristics First protective layer First Nitride layer Metal beryllium layer second Nitride layer second protective layer EUV penetration rate (%) EUV penetration rate In-plane changes (%) C Si3N 4-x Be Si3N 4-x C Example 1 2 2 20 2 2 91.1 0.2 Example 2 1 2 20 2 1 92.6 0.3 Example 3* none 2 20 2 none 93.8 0.5 *: indicates a comparison example.

[0040] As can be understood from the above results, if the amorphous carbon film is retained as in Examples 1 and 2, although the EUV transmittance will be slightly lower, the in-plane variation of the EUV transmittance is small, that is, the in-plane uniformity is excellent. On the other hand, if the amorphous carbon film is etched away as in Example 3, although the transmittance increases, the in-plane variation of the EUV transmittance is large, that is, the in-plane uniformity deteriorates. In this sense, it can be said that by retaining a thinner amorphous carbon film as in Example 2, a high EUV transmittance close to that of Example 3 can be maintained, and the in-plane uniformity of the EUV transmittance can be further improved compared to Example 3. Although a high EUV transmittance has the advantage of being able to complete exposure in a short time, that is, improving productivity, a small in-plane variation of the EUV transmittance results in a more uniform exposure amount in the plane, improving the homogeneity of the device. That is, according to the present invention, an EUV transmitting film suitable for achieving high EUV transmittance while improving the homogeneity of the device can be provided. [Simplified Explanation of the Diagram]

[0011] Figure 1 is a schematic cross-sectional view showing one aspect of the EUV-transmitting membrane of the present invention. Figure 2A is a flowchart showing the first half of the manufacturing sequence of the EUV-transmitting membrane in the embodiment. Figure 2B is a flowchart showing the second half of the manufacturing sequence of the EUV-transmitting membrane in the embodiment.

Claims

1. An EUV-transmitting film comprising five layers: a beryllium metal layer having a first side and a second side; a first nitride layer covering the first side of the beryllium metal layer and comprising at least one of the group consisting of silicon nitride, boron nitride, and zirconium nitride; a second nitride layer covering the second side of the beryllium metal layer and comprising at least one of the group consisting of silicon nitride, boron nitride, and zirconium nitride; a first protective layer covering the side opposite to the first nitride layer of the beryllium metal layer and comprising amorphous carbon; and a second protective layer covering the side opposite to the second nitride layer of the beryllium metal layer and comprising 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 penetrating membrane as described in claim 1, wherein the aforementioned first nitride layer, the aforementioned beryllium metal layer and the aforementioned second nitride layer constitute the main layer of the aforementioned EUV penetrating membrane, and the thickness of the aforementioned main layer is 7~30nm.

3. The EUV-transmitting film as described in claim 1 or 2, wherein the thickness of the aforementioned beryllium layer is 5 to 25 nm.

4. The EUV-transmitting film as described in claim 1 or 2, wherein the thickness of the first nitride layer and the second nitride layer is 1 to 5 nm respectively.

5. The EUV-transmitting film as described in claim 1 or 2, wherein the thickness of the first protective layer and the second protective layer is 1 to 10 nm respectively.

6. The EUV-transmitting film as described in claim 5, wherein the thickness of the first protective layer and the second protective layer is 2 to 7 nm respectively.

7. The EUV-transmitting film as described in claim 5, wherein the thickness of the first protective layer and the second protective layer is 1 nm or more but less than 2 nm.

8. A method for processing an EUV-transmitting membrane, comprising: The steps of installing the EUV penetrating membrane as described in claim 1 or 2 in an apparatus for generating hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals; and the steps of contacting the aforementioned EUV penetrating membrane with hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals, thereby thinning the aforementioned first protective layer and the aforementioned second protective layer.

9. An exposure method, comprising: The steps of installing the EUV-transmitting film described in claim 1 or 2 in an apparatus for generating hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals; contacting the aforementioned EUV-transmitting film with hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals, thereby thinning the aforementioned first protective layer and the aforementioned second protective layer; and installing the thinned EUV-transmitting film of the aforementioned first protective layer and the aforementioned second protective layer in an EUV exposure apparatus, allowing EUV to penetrate the aforementioned EUV-transmitting film, and performing pattern exposure on a photosensitive substrate in the aforementioned EUV exposure apparatus.

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