Euv transmission film and method of processing the same, and exposure method

Abstract

The present application provides an EUV transmission film, which has a high EUV transmission rate and excellent in-plane uniformity of the EUV transmission rate, although it has protective layers on both sides. The EUV transmission film (10) is composed of five layers, including: a metal beryllium layer (12) having a first side and a second side; a first nitride layer (14a) and a first protective layer (16a) containing amorphous carbon, which successively cover the first side (12a) of the metal beryllium layer (12), the first nitride layer (14a) containing at least one selected from the group consisting of silicon nitride, beryllium nitride, boron nitride and zirconium nitride; a second nitride layer (14b) and a second protective layer (16b) containing amorphous carbon, which successively cover the second side (12b) of the metal beryllium layer (12), the second nitride layer (14b) containing at least one selected from the group consisting of silicon nitride, beryllium nitride, boron nitride and zirconium nitride. The EUV transmission film has an EUV transmission rate of 85% or more at a wavelength of 13.5 nm.

Description

Technical Field

[0001] This invention relates to EUV-permeable films, their processing methods, and exposure methods. Background Technology

[0002] Semiconductor manufacturing processes are becoming increasingly miniaturized, with various improvements being made to each step. In particular, the photolithography process has begun using EUV (Extreme Ultraviolet) light with a wavelength of 13.5 nm to replace the previous 193 nm wavelength used in ArF exposure. As a result, the wavelength is now less than one-tenth of the original wavelength, leading to completely different optical properties. However, there are no materials with high transmittance for EUV light; therefore, protective components, such as pellicles used as anti-particle films in photomasks (reticles), are not yet practical. Consequently, device manufacturers currently manufacture semiconductor devices without using protective components.

[0003] Therefore, in developing protective films, the core materials preferably used are those with high EUV transmittance, such as Si, Be, Y, and Zr. Patent Document 1 (Japanese Patent No. 6858817) discloses a protective film comprising: a core layer containing a material such as (Poly)Si that is substantially transparent to EUV radiation; and an upper cover layer containing a material that absorbs IR radiation.

[0004] Furthermore, Patent Document 2 (Japanese Patent Application Publication No. 2020-98227) discloses a protective film that is stretched and disposed on one end face of a protective frame and has a main layer of single-crystal Si, with graphene on one or both sides of the main layer. Because the main layer contains graphene, the protective film will not break during the fabrication of the protective component, thus exhibiting sufficient mechanical strength.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent No. 6858817

[0008] Patent Document 2: Japanese Patent Application Publication No. 2020-98227 Summary of the Invention

[0009] However, the core materials used in the protective film, which have high EUV transmittance, will form a natural oxide film of several nm on their surface in the atmosphere. This oxide film absorbs EUV, leading to a decrease in the EUV transmittance of the protective film. In particular, Be is a material with high EUV transmittance, but a natural oxide film of 2-3 nm will form on its surface, resulting in a transmittance loss of up to 6-9%. In addition, during the manufacturing process of the protective film, treatments are sometimes carried out using gases such as fluorine or chlorine, acid solutions, or alkaline solutions other than atmospheric gases. Therefore, side reaction films may also form on the surface of the core material, leading 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.

[0010] However, while setting a reaction-inhibiting protective layer on the surface of core materials such as Si and Be can prevent a significant decrease in the EUV transmittance of the protective film, such a protective layer has a lower EUV transmittance compared to the pure core material, leading to a decrease in the overall EUV transmittance of the protective film. For example, Ru can be used as a protective layer for Be core materials. However, considering the three-layer structure (Ru / Be / Ru) protective film obtained by setting 1-2 nm of Ru on the surface and back of the Be core material, the EUV transmittance loss due to the Ru protective layer is about 3-6%, which significantly reduces the performance of the protective film. Therefore, a protective layer with less EUV transmittance loss is desired. On the other hand, for protective films, it is also desirable to have not only 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, and the better the homogeneity of the device manufactured by EUV exposure.

[0011] The inventors of this invention recently 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 exhibits high EUV transmittance despite having protective layers on both sides, and also has excellent in-plane uniformity of EUV transmittance.

[0012] Therefore, an object of the present invention is to provide an EUV-transmitting film that, although having protective layers on both sides, 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 the EUV-transmitting film. Furthermore, a further object of the present invention is to provide an exposure method using the EUV-transmitting film.

[0013] According to the present invention, the following solution is provided.

[0014] [Option 1]

[0015] An EUV permeable membrane, which is composed of the following 5 layers:

[0016] The five-layer structure includes:

[0017] A beryllium metal layer having a first surface and a second surface;

[0018] A first nitride layer covers a first surface of the metal beryllium layer and comprises at least one selected from the group consisting of silicon nitride, beryllium nitride, boron nitride and zirconium nitride.

[0019] A second nitride layer covers the second side of the metal beryllium layer and comprises at least one selected from the group consisting of silicon nitride, beryllium nitride, boron nitride and zirconium nitride.

[0020] A first protective layer, which covers the side of the first nitride layer opposite to the beryllium metal layer, and comprises amorphous carbon; and

[0021] A second protective layer covers the side of the second nitride layer opposite to the beryllium metal layer and contains amorphous carbon.

[0022] The EUV-permeable membrane is characterized in that...

[0023] The EUV-transmitting membrane has an EUV transmittance of over 85% at a wavelength of 13.5 nm.

[0024] [Option 2]

[0025] The EUV permeable membrane according to Scheme 1 is characterized in that,

[0026] The first nitride layer, the beryllium metal layer, and the second nitride layer constitute the main layer of the EUV permeable membrane, and the thickness of the main layer is 7-30 nm.

[0027] [Option 3]

[0028] The EUV permeable membrane according to Scheme 1 or 2 is characterized in that,

[0029] The thickness of the beryllium layer is 5–25 nm.

[0030] [Option 4]

[0031] The EUV permeable membrane according to any one of claims 1 to 3 is characterized in that,

[0032] The thickness of the first nitride layer and the second nitride layer is 1 to 5 nm.

[0033] [Option 5]

[0034] The EUV permeable membrane according to any one of claims 1 to 4 is characterized in that,

[0035] The thickness of the first protective layer and the second protective layer is 1 to 10 nm.

[0036] [Option 6]

[0037] According to the EUV permeable membrane described in Scheme 5, it is characterized in that,

[0038] The thickness of the first protective layer and the second protective layer is 2 to 7 nm.

[0039] [Option 7]

[0040] According to the EUV permeable membrane described in Scheme 5, it is characterized in that,

[0041] The thickness of the first protective layer and the second protective layer is greater than 1 nm and less than 2 nm.

[0042] [Option 8]

[0043] A method for processing an EUV-permeable membrane, characterized by comprising the following steps:

[0044] The EUV permeable membrane described in any of schemes 1 to 7 is installed in a device that generates hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals; and

[0045] The first and second protective layers are thinned by bringing hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals, into contact with the EUV permeable membrane.

[0046] [Option 9]

[0047] An exposure method, characterized by comprising the following steps:

[0048] The EUV permeable membrane described in any of the schemes 1 to 7 is installed in a device that generates hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals.

[0049] Contacting the EUV-permeable membrane with hydrogen plasma and / or hydrogen radicals, or oxygen plasma and / or oxygen radicals, thereby thinning the first and second protective layers; and

[0050] The first protective layer and the second protective layer, which have been thinned, are installed in the EUV exposure apparatus so that EUV passes through the EUV transmission membrane to expose the photosensitive substrate in the EUV exposure apparatus. Attached Figure Description

[0051] Figure 1 This is a simplified cross-sectional view showing one aspect of the EUV permeable membrane of the present invention.

[0052] Figure 2A This is a process flow diagram showing the first half of the manufacturing steps of the EUV permeable membrane in the embodiment.

[0053] Figure 2B This is a process flow diagram showing the latter half of the manufacturing steps of the EUV permeable membrane in the embodiment. Detailed Implementation

[0054] EUV permeable membrane

[0055] Figure 1 The diagram shows a simplified cross-sectional view of an EUV permeable membrane 10 according to one embodiment of the present invention. The EUV permeable membrane 10 is a membrane consisting 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 material 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 material 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 surface of the first nitride layer 14a opposite to the beryllium metal layer 12 and comprising amorphous carbon. The second protective layer 16b is a layer that covers the side of the second nitride layer 14b opposite to the beryllium layer 12 and contains amorphous carbon. The EUV-transmitting membrane 10 has an EUV transmittance of 85% or more at a wavelength of 13.5 nm. By employing a five-layer structure of first protective layer 16a (amorphous carbon layer) / first nitride layer 14a / beryllium layer 12 / second nitride layer 14b / second protective layer 16b (amorphous carbon layer), it is possible to provide an EUV-transmitting membrane 10 that exhibits high EUV transmittance and excellent in-plane uniformity of EUV transmittance, even though it has protective layers 16a and 16b on both sides.

[0056] 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, during the manufacturing process of the protective film, treatment with gases such as fluorine or chlorine (other than atmospheric gases), acid solutions, or alkaline solutions is sometimes performed, which can also lead to the formation of a secondary reaction film on the surface of the core material. The formation of such films reduces the EUV transmittance of the 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, by setting a reaction-inhibiting protective layer on the surface of the core material, the overall EUV transmittance of the protective film decreases. On the other hand, for the protective film, it is also desirable to have not only 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, and the better the homogeneity of the device manufactured by EUV exposure. These problems are successfully solved with the EUV-transmitting film according to the present invention. That is, the EUV-transmitting membrane of the present invention comprises a main layer 11 including 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. In this case, these protective layers 16a and 16b can prevent the formation of natural oxide films and side reaction films that might occur on the surface of the main layer 11 before the manufactured protective component is mounted on the EUV exposure apparatus and subjected to the exposure process (if there were no protective layers 16a and 16b). Furthermore, the EUV transmittance loss of the protective layers 16a and 16b, which contain amorphous carbon, is relatively small. Therefore, although the EUV-transmitting membrane 10 of the present invention is composed of five layers including protective layers 16a and 16b, it can exhibit high EUV transmittance. Furthermore, the EUV-transmitting film 10, consisting of five layers including protective layers 16a and 16b, has the following advantages: compared to a single main layer consisting of three layers without protective layers 16a and 16b, it exhibits superior in-plane uniformity of EUV transmittance. This is believed to be because the protective layers 16a and 16b are formed on both sides, resulting in more uniform unevenness on both sides of the three-layer main layer. Based on this advantage, in EUV exposure using the EUV-transmitting film 10, the in-plane exposure is uniform, improving the homogeneity of devices manufactured by EUV exposure.

[0057] As described above, the EUV permeable membrane 10 has a high EUV transmittance. The EUV permeable membrane 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. The higher the EUV transmittance of the EUV permeable membrane 10, the more desirable it is. There is no particular upper limit, but ideally it is 100%, however, typically it is 95% or less, more typically 94% or less, for example, 93.5% or less.

[0058] The beryllium layer 12 is a layer containing beryllium as the main component. Here, the "main component" in the beryllium layer 12 refers to a component that occupies 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. In addition to containing beryllium as the main component, the beryllium layer 12 may also contain impurities. Therefore, the beryllium layer 12 can be composed of 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.

[0059] 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 beryllium layer 12 are explained below. For example, if an amorphous carbon protective layer is directly provided on the beryllium layer, i.e., the main layer, the amorphous carbon and beryllium may sometimes react to form beryllium carbide. Therefore, by providing a three-layer configuration of the main layer (first nitride layer 14a / 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 amorphous carbon and beryllium can be prevented, i.e., the reaction between the main layer and the protective layer is suppressed. It should be noted that the terms "silicon nitride," "beryllium nitride," "boron nitride," and "zirconium nitride" in this specification refer to: not only stoichiometric compositions such as Si3N4, Be3N2, BN, and ZrN are permissible, but also Si3N... 4-x (where 0 < x < 4), Be3N 2-x (where 0 < x < 2), BN x (where 0 < x < 1), ZrN x (where 0 < x < 1) is a general composition of non-stoichiometric composition. The thickness of the first nitride layer 14a and the second nitride layer 14b is preferably 1 to 5 nm, more preferably 1 to 3 nm.

[0060] The first nitride layer 14a, the beryllium layer 12, and the second nitride layer 14b constitute the main layer 11 of the EUV-transmitting membrane. The main layer 11 ensures the basic functions of a protective membrane (such as preventing particle adhesion) and contributes to achieving high EUV transmittance. The thickness of the main layer 11 is preferably 7–30 nm, more preferably 9–26 nm, and even more preferably 11–21 nm.

[0061] When the first nitride layer 14a and / or the second nitride layer 14b each contain beryllium nitride, the main layer 11 preferably has a nitrogen concentration gradient region where the nitrogen concentration decreases as it approaches the metallic beryllium layer 12. That is, as described above, the beryllium nitride composition may contain stoichiometric compositions ranging from Be3N2 to Be3N... 2-x In the case of a non-stoichiometric composition (where 0 < x < 2), the beryllium nitride constituting the beryllium nitride layer is preferably configured as a gradient composition approaching a beryllium-rich composition as it approaches the metallic beryllium layer 12. This improves the adhesion between the nitride layers 14a and 14b (i.e., the beryllium nitride layers) constituting the main layer 11 and the metallic beryllium layer 12, and mitigates stress caused by the thermal expansion difference between these layers. That is, it can improve the adhesion between these layers to suppress peeling, or act as a thermal expansion mitigation layer when absorbing EUV light and reaching high temperatures, making peeling difficult. The thickness of the nitrogen concentration gradient region is preferably smaller than the thickness of each of the nitride layers 14a and 14b. That is, the entire region where the thickness of each of the nitride layers 14a and 14b is not required is 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, such as 10 to 70% of the thickness of each of the nitride layers 14a and 14b, is a nitrogen concentration gradient region, and more preferably 15 to 50% of the region is a nitrogen concentration gradient region.

[0062] The first protective layer 16a and the second protective layer 16b are both layers containing amorphous carbon. Regarding the layers containing amorphous carbon, in addition to exhibiting higher protective performance compared to various agents (e.g., highly reactive fluorine-based etchants) used in the protective film manufacturing process (e.g., self-supporting film formation process), they are also advantageous in terms of high EUV transmittance, less impact of residue 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. The first protective layer 16a and the second protective layer 16b preferably contain amorphous carbon as the main component, and more preferably are composed of amorphous carbon. Generally, amorphous carbon rarely has a completely irregular atomic arrangement; it often has a crystalline structure (i.e., microcrystals) at the microscopic level, and in such cases, the irregular arrangement of these microcrystals makes the overall structure amorphous. The material containing numerous three-dimensional 4-coordinate microcrystals, like diamond, is called DLC (diamond-like carbon), and the material containing numerous planar 3-coordinate particles, like graphite, is called GLC (graphite-like carbon). The first protective layer 16a and the second protective layer 16b can be carbon with a completely irregular atomic arrangement or carbon with irregularly arranged microcrystals. Furthermore, they can be amorphous carbon containing fine pores and not completely dense. Here, the "main component" in the first protective layer 16a and the second protective layer 16b refers to a component that occupies 50% or more by weight, preferably 60% or more by weight, more preferably 70% or more by weight, and even more preferably 80% or more by weight in 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 be composed solely of amorphous carbon.

[0063] The thickness of each of the first protective layer 16a and the second protective layer 16b is preferably 1 to 10 nm, 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, if a thicker protective layer 16a and 16b is desired to protect the EUV-transmitting film 10 (especially the main layer 11) from damage by various agents (e.g., highly reactive fluorine-based etchants) used in the protective film manufacturing process (e.g., the self-supporting film formation process), then increasing the film thickness will decrease the EUV transmittance of the EUV-transmitting film 10. In this respect, a film thickness within the aforementioned range allows for a good balance between high protective performance and high EUV transmittance relative to various agents. However, to achieve higher EUV transmittance while ensuring minimum protective performance, it is also effective to make the thickness of each of the first protective layer 16a and the second protective layer 16b very thin, preferably 1 nm or more and less than 2 nm, more preferably 1 nm or more and less than 1.5 nm.

[0064] The EUV permeable membrane 10 is preferably in the form of a self-standing membrane in the main area for EUV transmission. That is, preferably only the substrate (e.g., Si substrate) used during film formation is left as a border at the outer edge of the EUV permeable membrane 10. In other words, preferably no substrate (e.g., Si substrate) is left in the main area other than the outer edge. That is, the main area is composed only of the main layer 11 and the protective layers 16a and 16b.

[0065] Manufacturing method

[0066] The EUV-transmitting film of the present invention can be fabricated as follows: after forming a laminated film to be used as the EUV-transmitting film on a Si substrate, the unwanted portions of the Si substrate are removed by etching to achieve self-standing film formation, thereby fabricating the EUV-transmitting film. Therefore, as described above, the main part of the EUV-transmitting film is a self-standing film morphology without any residual Si substrate.

[0067] (1) Preparation of Si substrate

[0068] First, a Si substrate for forming a multilayer film is prepared. After forming a multilayer film including a second protective layer 16b, a second nitride layer 14b, a beryllium layer 12, a first nitride layer 14a, and a first protective layer 16a on the Si substrate, the main area (i.e., the area where a self-standing film is to be formed) except for the outer edge is removed by etching. Therefore, in order to perform etching efficiently in a short time, it is preferable to thin the thickness of the Si substrate in the area where a self-standing film is to be formed beforehand. Therefore, it is desirable to form a mask corresponding to the EUV transmission shape on the Si substrate using conventional semiconductor processes, and to etch the Si substrate using wet etching to thin the thickness of the main area of ​​the Si substrate to a specified thickness. The wet-etched Si substrate is cleaned and dried, thereby preparing a Si substrate having cavities formed by wet etching. It should be noted that as the wet etching mask, any material that is corrosion-resistant to the wet etching solution for Si is acceptable, for example, SiO2 is preferred. In addition, as the wet etching solution, there is no particular limitation as long as it can etch Si. For example, if TMAH (tetramethylammonium hydroxide) is used under appropriate conditions, etching can be performed very well with anisotropic etching of Si, and is therefore preferred.

[0069] (2) Formation of laminated films

[0070] A multilayer film comprising a second protective layer 16b, a second nitride layer 14b, a beryllium layer 12, a first nitride layer 14a, and a first protective layer 16a is sequentially formed on a Si substrate. The multilayer film can be formed using any film-forming method. As a preferred example of a film-forming method, sputtering is employed. The beryllium layer 12 is preferably fabricated using sputtering with a pure Be target. The amorphous carbon film serving as the first protective layer 16a and the second protective layer 16b is preferably fabricated using sputtering with a graphite target.

[0071] The first nitride layer 14a and the second nitride layer 14b are preferably fabricated using sputtering. For example, (i) the nitride layers 14a and 14b can be formed by sputtering a Si, Be, B, or Zr film using a Si, Be, B, or Zr target, followed by irradiation with nitrogen plasma to induce a nitriding reaction in the Si, Be, B, or Zr. Alternatively, (ii) the first nitride layer 14a and the second nitride layer 14b can be fabricated using reactive sputtering. This reactive sputtering can be performed as follows: for example, in sputtering using a Si, Be, B, or Zr target, nitrogen gas is introduced into the chamber to react with Si, Be, B, or Zr to generate silicon nitride, beryllium nitride, boron nitride, or zirconium nitride. Or, (iii) the nitride layers 14a and 14b can be directly formed using sputtering using a Si3N4, Be3N2, BN, or ZrN target. In this sputtering process, by introducing nitrogen gas into the chamber, nitrogen can react with Si, Be, B or Zr to promote the formation of silicon nitride, beryllium nitride, boron nitride or zirconium nitride, as in the reactive sputtering described in (ii) above.

[0072] It should be noted that the methods for forming the beryllium layer 12, nitride layers 14a, 14b, and protective layers 16a, 16b are not limited to these methods. Furthermore, the beryllium layer 12, nitride layers 14a, 14b, and protective layers 16a, 16b can be formed using a single-chamber sputtering apparatus as described in the embodiments below, or multiple-chamber sputtering apparatuses can be used to form the beryllium layer 12, nitride layers 14a, 14b, and protective layers 16a, 16b separately in each chamber.

[0073] When the first nitride layer 14a and the second nitride layer 14b are beryllium nitride layers containing a nitrogen concentration gradient region—that is, when a nitrogen concentration gradient region is formed in the main layer 11 of a three-layer structure of beryllium nitride / beryllium / beryllium nitride—during the deposition of beryllium nitride and metallic beryllium films, nitrogen gas is continuously introduced into the chamber for sputtering using a pure Be target, and the nitrogen introduction is stopped midway to switch to metallic beryllium film deposition. Accordingly, as the nitrogen concentration in the chamber decreases, a region in the formed film where the nitrogen concentration decreases along the thickness direction is formed. On the other hand, when switching from metallic beryllium to beryllium nitride, conversely, if nitrogen gas is introduced midway while sputtering continues, a nitrogen concentration gradient region can be formed. By adjusting the time for changing the nitrogen concentration, the thickness of the nitrogen concentration gradient region can be controlled.

[0074] (3) Self-standing membrane formation

[0075] The unwanted portions of the Si substrate with the composite film formed, excluding the outer edge portion remaining in the form of a boundary, are removed by etching to achieve self-standing film formation of the composite film. The etching of Si can be performed by any method, however, etching using XeF2 is preferred.

[0076] Processing methods

[0077] The manufactured EUV permeable membrane 10 can be processed to be thinner as desired. As described above, by thinning the first protective layer 16a and the second protective layer 16b, a higher EUV transmittance can be achieved while ensuring a minimum level of protection. In particular, after the self-standing film formation process using fluorine-based etchants such as XeF2 described above, the first protective layer 16a and the second protective layer 16b no longer need to have a strong protective function relative to the fluorine-based etchant; it can be said that a stable protective function such as oxidation resistance is sufficient. Therefore, after the EUV permeable membrane 10 has been self-standing film formed, it becomes advantageous to further improve the EUV transmittance by thinning the protective layers 16a and 16b. The process of thinning the EUV permeable membrane 10 is preferably carried out as follows: the EUV permeable membrane 10 is installed in a device that generates hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals, so that the hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals, come into contact with the EUV permeable membrane 10, thereby thinning it. By exposing the first protective layer 16a and the second protective layer 16b, i.e., the amorphous carbon film, to hydrogen plasma and / or a hydrogen free radical atmosphere or an oxygen plasma and / or an oxygen free radical atmosphere, the C and H on the surface of the amorphous carbon film react, thereby partially removing the amorphous carbon film. As a result, the first protective layer 16a and the second protective layer 16b can be thinned.

[0078] Exposure method

[0079] As described above, by thinning the first protective layer 16a and the second protective layer 16b, higher EUV transmittance can be achieved while ensuring minimum protective performance. Therefore, it is preferable to thin the first protective layer 16a and the second protective layer 16b during exposure. From this point of view, a preferred exposure method includes the following steps: mounting the EUV-transmitting film 10 in an apparatus for generating hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals; contacting the hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals, with the EUV-transmitting film 10, thereby thinning the first protective layer 16a and the second protective layer 16b; and mounting the thinned EUV-transmitting film 10 with the first protective layer 16a and the second protective layer 16b in an EUV exposure apparatus, allowing EUV to pass through the EUV-transmitting film 10 to perform pattern exposure on the photosensitive substrate in the EUV exposure apparatus.

[0080] Example

[0081] The invention will be further illustrated by the following examples. However, the invention is not limited to these examples.

[0082] Example 1

[0083] according to Figure 2A and Figure 2B The steps shown are as follows to fabricate a composite self-standing membrane (EUV-permeable membrane) consisting of 5 layers: amorphous carbon / silicon nitride / Be / silicon nitride / amorphous carbon.

[0084] (1) Preparation of Si substrate

[0085] Prepare to produce 8-inch (20.32cm) diameter Si wafers 20 ( Figure 2A (a)). On both sides of the Si wafer 20, a SiO2 film 22 with a thickness of 50 nm is formed by thermal oxidation. Figure 2A (b)). A photoresist is coated on both sides of the Si wafer 20, and exposure and development are performed to form a photoresist mask 24 for SiO2 etching, enabling the formation of 110mm × 145mm photoresist holes on one side. Figure 2A (c)). One side of the substrate is wet-etched using hydrofluoric acid, thereby removing the exposed portion of the SiO2 film 22 and fabricating a SiO2 mask 22a. Figure 2A (d) The resist mask 24 used for SiO2 etching is removed using an ashing device. Figure 2A (e) Then, the Si was wet-etched using TMAH solution. The etching rate was determined beforehand, and the etching was carried out at an etching time set for a target Si substrate thickness of 50 μm. Figure 2A (f) Finally, the SiO2 film 22 formed on the side without Si etching is removed and cleaned with hydrofluoric acid to prepare the Si substrate 28. Figure 2B (g)). Regarding the shape of the Si substrate, it can be cut using laser 30 as needed. Figure 2B (h)), set to the desired shape ( Figure 2B (i)). This prepares a Si substrate 28 with a 110mm × 145mm cavity 26 in the center of an 8-inch (20.32cm) Si wafer 20 and a Si thickness of 50μm in the cavity 26 portion.

[0086] (2) Formation of composite membrane

[0087] The Si substrate 28 with cavity 26 obtained in (1) above is formed as follows: a composite film with a 5-layer structure of amorphous carbon / silicon nitride / Be / silicon nitride / amorphous carbon is formed. Figure 2B(i) First, a Si substrate 28 is fixed to 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 a graphite target at an internal pressure of 0.3 Pa, with only argon gas. Sputtering is completed in 2 nm of amorphous carbon (DLC). Next, the chamber is evacuated again, and sputtering is performed using a Si3N4 target at an internal pressure of 0.3 Pa, with argon gas containing 20% ​​nitrogen. Sputtering is completed in 2 nm of Si3N4. Then, the chamber is evacuated again, and sputtering is performed using a pure Be target at an internal pressure of 0.5 Pa, with only argon gas. Sputtering is completed in 20 nm of beryllium. Finally, the chamber is evacuated again, and sputtering is performed using a Si3N4 target at an internal pressure of 0.3 Pa, with argon gas containing 20% ​​nitrogen. Sputtering is completed in 2 nm of Si3N4. Then, sputtering was performed using a graphite target in the same manner as initially, ending after a 2nm amorphous carbon film was formed. In this way, a 2nm amorphous carbon (C) / silicon nitride (Si3N) film was formed. 4-x 2nm / Beryllium (Be) 20nm / Silicon Nitride (Si3N) 4-x A composite film of 2nm silicon nitride / 2nm amorphous carbon (C) is used as EUV permeable film 10. That is, the EUV permeable film 10 is composed of a main layer consisting of three layers: a first silicon nitride layer, a beryllium metal layer and a second silicon nitride layer, and a first protective layer and a second protective layer containing amorphous carbon as the main component formed on both sides of the main layer.

[0088] (3) Self-supporting membrane formation

[0089] Inside the chamber of an XeF2 electro-etcher capable of processing 8-inch (20.32 cm) substrates, a Si substrate 28 with an EUV-permeable membrane 10 prepared in step (2) is fixed. The chamber is then fully evacuated. If moisture remains in the chamber, it reacts with the XeF2 gas to produce hydrofluoric acid, causing corrosion of the electro-etcher or unexpected etching. Therefore, a full vacuum is required. The chamber is repeatedly evacuated and nitrogen is introduced as needed to reduce residual moisture. After a full vacuum is achieved, the valve between the XeF2 raw material bottle and the preparation chamber is opened. As a result, XeF2 sublimates, and XeF2 gas is also accumulated in the preparation chamber. After XeF2 gas has been fully accumulated in the preparation chamber, the valve between the preparation chamber and the chamber is opened to introduce XeF2 gas into the chamber. XeF2 gas decomposes into Xe and F. F reacts with Si to form SiF4. The boiling point of SiF4 is -95℃, therefore, the generated SiF4 evaporates rapidly, and the newly exposed Si substrate reacts with F. Si etching is performed, and after the F in the chamber is reduced, the chamber is evacuated, and XeF2 gas is introduced into the chamber again for etching. This process of evacuation, XeF2 gas introduction, and etching is repeated until the Si substrate 28 corresponding to the self-standing film disappears. Etching ends after the unwanted portion of the Si substrate disappears. Thus, a five-layer composite self-standing film with a Si border 20 is obtained as the EUV permeable membrane 10. Figure 2B (j)).

[0090] Example 2

[0091] Similar to Example 1, an EUV-transmitting film 10 with Si boundary 20 was fabricated. Then, the amorphous carbon films exposed on both sides of the EUV-transmitting film 10 were etched using hydrogen plasma, thereby reducing the thickness of each amorphous carbon layer to 1 nm. This yields a film with Si boundary 20 comprising 1 nm of amorphous carbon (C) and silicon nitride (Si3N). 4-x 2nm / Beryllium (Be) 20nm / Silicon Nitride (Si3N) 4-x A composite self-standing membrane consisting of 5 layers of 2nm amorphous carbon (C) and 1nm amorphous carbon (C) is used as an EUV permeable membrane 10.

[0092] Example 3 (Compare)

[0093] Similar to Example 1, an EUV-transmitting film 10 with Si boundary 20 is fabricated. Then, the amorphous carbon films exposed on both sides of the EUV-transmitting film 10 are etched using hydrogen plasma, thereby removing each amorphous carbon layer. This yields a silicon nitride (Si3N) film with Si boundary 20. 4-x 2nm / Beryllium (Be) 20nm / Silicon Nitride (Si3N)4-x A composite self-standing membrane consisting of three layers with a diameter of 2nm is used as an EUV permeable membrane 10.

[0094] EUV transmittance and its in-plane uniformity

[0095] For the self-standing membranes used as EUV-transmitting films in Examples 1-3, EUV light was irradiated for 15 minutes at an output power of 600 W in a hydrogen atmosphere at 20 Pa. Afterwards, the amount of transmitted EUV light was measured using a sensor. The EUV transmittance was calculated by comparing the measured value with the value obtained by directly measuring the EUV light amount without the EUV-transmitting film using the sensor. The results are shown in Table 1. The EUV light spot used for transmittance measurement was an oblong shape of 0.5 mm × 0.2 mm, and the EUV transmittance within this spot size was measured. Therefore, to evaluate the in-plane uniformity of EUV transmittance, the EUV transmittance was measured while moving the EUV light spot. The EUV transmittance at each location was measured, and the in-plane deviation was calculated as three times the standard deviation based on these data. Therefore, the smaller the in-plane deviation, the better the in-plane uniformity of EUV transmittance.

[0096] Table 1

[0097] Table 1

[0098]

[0099] *: indicates a comparison example.

[0100] The results above show that if an amorphous carbon film is left in advance as in Examples 1 and 2, although the EUV transmittance decreases somewhat, the in-plane deviation of the EUV transmittance is small, i.e., 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 deviation of the EUV transmittance is large, i.e., the in-plane uniformity deteriorates. In this sense, it can be said that by thinning the amorphous carbon film as in Example 2 and leaving it in place, a high EUV transmittance close to that of Example 3 can be maintained, and the in-plane uniformity of the EUV transmittance is improved compared to Example 3. A high EUV transmittance has the advantage of short exposure time and good throughput; however, a small in-plane deviation of the EUV transmittance results in uniform exposure throughput and improved device homogeneity. That is, according to the present invention, an EUV-transmitting film suitable for achieving high EUV transmittance and improving device homogeneity can be provided.

Claims

1. An EUV permeable membrane, comprising the following five layers: The five-layer structure includes: A beryllium metal layer having a first surface and a second surface; A first nitride layer covers a first surface of the metal beryllium layer and comprises at least one selected from the group consisting of silicon nitride, beryllium nitride, boron nitride and zirconium nitride. A second nitride layer covers the second side of the metal beryllium layer and comprises at least one selected from the group consisting of silicon nitride, beryllium nitride, boron nitride and zirconium nitride. A first protective layer, which covers the side of the first nitride layer opposite to the beryllium metal layer, and comprises amorphous carbon; and A second protective layer covers the side of the second nitride layer opposite to the beryllium metal layer and contains amorphous carbon. The EUV-permeable membrane is characterized in that... The EUV-transmitting membrane has an EUV transmittance of over 85% at a wavelength of 13.5 nm.

2. The EUV permeable membrane according to claim 1, characterized in that, The first nitride layer, the beryllium metal layer, and the second nitride layer constitute the main layer of the EUV permeable membrane, and the thickness of the main layer is 7-30 nm.

3. The EUV permeable membrane according to claim 1 or 2, characterized in that, The thickness of the beryllium layer is 5–25 nm.

4. The EUV permeable membrane according to claim 1 or 2, characterized in that, The thickness of the first nitride layer and the second nitride layer is 1 to 5 nm.

5. The EUV permeable membrane according to claim 1 or 2, characterized in that, The thickness of the first protective layer and the second protective layer is 1 to 10 nm.

6. The EUV permeable membrane according to claim 5, characterized in that, The thickness of the first protective layer and the second protective layer is 2 to 7 nm.

7. The EUV permeable membrane according to claim 5, characterized in that, The thickness of the first protective layer and the second protective layer is greater than 1 nm and less than 2 nm.

8. A method for processing an EUV-permeable membrane, characterized in that, The process includes the following steps: The EUV permeable membrane of claim 1 or 2 is installed in a device for generating hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals; and The first and second protective layers are thinned by bringing hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals, into contact with the EUV permeable membrane.

9. An exposure method, characterized in that, The process includes the following steps: The EUV permeable membrane of claim 1 or 2 is installed in a device that generates hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals. By bringing hydrogen plasma and / or hydrogen free radicals, or oxygen plasma and / or oxygen free radicals, into contact with the EUV permeable membrane, the first protective layer and the second protective layer are thinned. as well as The first protective layer and the second protective layer, which have been thinned, are installed in the EUV exposure apparatus so that EUV passes through the EUV transmission membrane to expose the photosensitive substrate in the EUV exposure apparatus.

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