Manufacturing method for EUV transmitting film and pellicle

Abstract

Provided is a method for efficiently producing a high-quality EUV-transmissive film or pellicle in which a mask layer is prevented from remaining in an eave-like shape extending toward a cavity and particles are unlikely to occur. The method includes: a step in which a substrate having a first surface and a second surface is prepared; a step in which the entire area of the first surface and a peripheral area not including a cavity area positioned in the center of the second surface are covered by a mask layer; a step in which the substrate exposed in the cavity area is partially removed by etching and a cavity is formed; a step in which the mask layer covering the first surface is removed by etching; a step in which an EUV-transmissive film is formed on the surface of the substrate on the cavity side and on the surface of the mask layer covering the second surface; and a step in which the substrate is removed from the first surface by etching until the EUV-transmissive film is exposed on the opposite side from the cavity and the EUV-transmissive film is made to be self supporting in the cavity area.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an EUV transmitting film and a pellicle. [Background technology]

[0002] Miniaturization in semiconductor manufacturing processes continues to advance year by year, with various improvements being made to each process. In particular, in the photolithography process, extreme ultraviolet (EUV) 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 dropped to less than one-tenth of the original wavelength, and its optical properties have become completely different. However, because there are no materials with high transmittance to EUV light, there are still no practical pellicles, for example, which are used to prevent particle adhesion on photomasks (reticles). As a result, device manufacturers are currently unable to use pellicles while manufacturing semiconductor devices.

[0003] Therefore, poly-Si-based pellicle films have been proposed. For example, 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. However, when the poly-Si-based pellicle film is made thick enough to maintain film strength, its EUV transmittance does not reach the target 90%, and it is not yet practical.

[0004] Additionally, carbon nanotube (CNT)-based pellicle membranes have also been developed (for example, Patent Document 2 (JP 2018-194840 A)), which are expected to have higher EUV transmittance. However, CNT-based pellicle membranes are not durable in the pellicle usage environment (low-pressure hydrogen atmosphere), and if the pellicle membrane is coated with metal to enhance durability, the EUV transmittance decreases, making it impossible to achieve a practical level of transmittance.

[0005] Various methods for manufacturing pellicle films have been proposed. For example, Non-Patent Document 1 (Dario L. Goldfarb, "Fabrication of a full-size EUV pellicle based on silicon nitride," Volume 31, Issue 12, PHOTOMASK, SPIE, 2015) discloses a method for manufacturing a free-standing SiNx film as a pellicle film. The basic method is as follows: First, a SiNx film to serve as the pellicle film is formed on both sides of a Si substrate (Step A). Next, a reactive ion etching (RIE) mask for etching the formed SiNx film is formed on only one side (Step B). Part of the SiNx is removed by RIE to expose the Si substrate (Step C). Both sides of the Si substrate are coated with amorphous Si, and then the Si substrate is diced to form an outer shape (Step D). Finally, the Si substrate is wet-etched using the SiNx film as a mask to form a free-standing SiNx film (Step E). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6858817 [Patent Document 2] Japanese Patent Application Laid-Open No. 2018-194840 [Non-patent literature]

[0007] [Non-Patent Document 1] Dario L. Goldfarb, "Fabrication of a full size EUV pellicle based on silicon nitride", Volume 31, Issue 12, PHOTOMASK, SPIE, 2015 Summary of the Invention

[0008] When attempting to fabricate an EUV-transmitting film as a pellicle membrane using a conventional manufacturing method such as that disclosed in Non-Patent Document 1, one possible approach is to form an EUV-transmitting film on a substrate and then etch away unnecessary portions of the substrate to create a freestanding film. Figures 4A and 4B show an example of such a conventional manufacturing process. In this conventional process, a substrate 110 such as a Si wafer is first prepared (Figure 4A(a)). A mask layer 112 such as an SiO2 layer is formed on both sides of the substrate 110. Resist is applied to one or both sides of the substrate 110, and exposure and development are performed to form a resist mask (not shown) for etching, so that a hole of a predetermined size is formed in the resist on one side. One side of the substrate 110 is etched to remove the exposed portion of the mask layer 112, forming an opening corresponding to the cavity region C (Figure 4A(c)). After removing the resist mask, the substrate 110 is etched with an etching solution such as TMAH (tetramethylammonium hydroxide) solution to thin the cavity region C of the substrate 110 to a desired thickness, thereby forming a cavity 114 (FIG. 4A(d)). The mask layer 112 present on the surface opposite the cavity 114 is etched away to obtain a cavity substrate 115 (FIG. 4B(e)). An EUV-transmitting film 116 is formed on the surface of the cavity substrate 115 opposite the cavity 114 (FIG. 4B(f)). Finally, the substrate 110 corresponding to the portion to be made into a free-standing film is etched away to make the EUV-transmitting film 116 a free-standing film (FIG. 4B(g)). In this way, a pellicle 118 is obtained, which includes a frame 117 including the substrate 110 and the mask layer 112 remaining in a frame shape, and the EUV-transmitting film 116.

[0009] However, in the pellicle 118 thus fabricated, the inner edge 112a of the frame-shaped mask layer 112 remains in an eave-like shape extending toward the cavity 114, as shown in FIGS. 4B(g) and 4C. This is because, when the substrate 110, such as a Si wafer, used to form the cavity 114 is etched from below, side etching also occurs laterally as the etching progresses upward in the figure. If the mask layer 112 is left in this eave-like state toward the cavity 114, the eave-like inner edge 112a, which is weak in strength, breaks, generating particles (dust), which are likely to adhere to the EUV transmitting film 116. If particles adhere to the EUV transmitting film 116, the particles block EUV light during exposure, resulting in exposure defects in which the mask pattern is not accurately transferred. On the other hand, it is possible to remove the mask layer 112 after etching the substrate 110, but this would require additional steps and costs, and since the EUV transmitting film 116 has already been formed into a free-standing film, it would be an additional process that carries a high risk of damaging the free-standing film. Therefore, a manufacturing method is desired that prevents the mask layer 112 from remaining in a eaves-like shape extending from the cavity 114.

[0010] The present inventors have now discovered that by forming an EUV transmitting film on the cavity-side surface of the substrate and then etching away the substrate from the surface opposite the cavity to form the EUV transmitting film as a free-standing film, it is possible to prevent the mask layer from remaining in the shape of an overhang extending toward the cavity, and to manufacture a high-quality EUV transmitting film or pellicle by an efficient method that is less likely to generate particles.

[0011] Therefore, an object of the present invention is to manufacture a high-quality EUV-transmitting film or pellicle using an efficient method that is less likely to generate particles, by avoiding the mask layer remaining in a eaves-like shape extending toward the cavity.

[0012] According to one aspect of the present invention, providing a substrate having a first side and a second side; covering the entire area of the first surface and a peripheral area of the second surface other than a cavity area located at the center thereof with a mask layer; etching away a portion of the substrate exposed in the cavity region to form a cavity; Etching away the mask layer covering the first surface; forming an EUV transmitting film on the surface of the mask layer that covers the cavity side surface of the substrate and the second surface; etching the substrate from the first surface until the EUV transmitting film is exposed on the side opposite the cavity, thereby forming the EUV transmitting film in the cavity region into a free-standing film; A method for producing an EUV transmitting film is provided, comprising:

[0013] According to another aspect of the present invention, providing a substrate having a first side and a second side; covering the entire area of the first surface and a peripheral area of the second surface other than a cavity area located at the center thereof with a mask layer; etching away a portion of the substrate exposed in the cavity region to form a cavity; etching away the mask layer covering the first surface and the mask layer covering the peripheral region of the second surface; forming an EUV transmitting film on the surface of the substrate facing the cavity; etching the substrate from the first surface until the EUV transmitting film is exposed on the side opposite the cavity, thereby forming the EUV transmitting film in the cavity region into a free-standing film; A method for producing an EUV transmitting film is provided, comprising:

[0014] According to another aspect of the present invention, a substrate having a first surface and a second surface and a central cavity; a mask layer covering the second surface of the substrate; an EUV transmitting film that continuously covers a surface of the mask layer and an inner surface of the cavity of the substrate and is exposed as a free-standing film that forms a bottom surface of the cavity at the same height as the first surface; A pellicle is provided comprising:

[0015] According to another aspect of the present invention, a substrate having a first surface and a second surface and a central cavity; an EUV transmitting film that continuously covers the second surface of the substrate and the inner surface of the cavity and is exposed as a free-standing film that forms the bottom surface of the cavity at the same height as the first surface; A pellicle is provided comprising: [Brief explanation of the drawings]

[0016] [Figure 1A] 1A to 1C are diagrams illustrating an example of the first half of a process in a method for manufacturing an EUV transmitting film according to one embodiment of the present invention. [Figure 1B] 1B is a diagram showing an example of a second half step following FIG. 1A in a method for producing an EUV transmitting film according to one embodiment of the present invention. [Figure 1C] 1B is a diagram showing another example of the latter half of the process following FIG. 1A in the method for producing an EUV transmitting film according to one embodiment of the present invention. [Figure 2A] 10A to 10C are diagrams showing another example of the first half of the steps in the method for producing an EUV transmitting film according to the present invention. [Figure 2B] 2B is a diagram showing an example of the latter half of the process following FIG. 2A in the method for producing an EUV transmitting film according to the present invention. [Figure 3A] 1A to 1C are diagrams showing an example of the first half of the steps in the method for manufacturing an EUV transmitting film using an SOI substrate according to the present invention. [Figure 3B] 3B is a diagram showing an example of the latter half of the process following FIG. 3A in the method for manufacturing an EUV transmitting film using an SOI substrate according to the present invention. [Figure 4A] 1A to 1C are diagrams showing the first half of the steps in a conventional method for manufacturing an EUV transmitting film. [Figure 4B]4B is a diagram showing the latter half of the process following FIG. 4A in the method for manufacturing an EUV transmitting film according to the prior art. [Figure 4C] This is an SEM image of a portion of the pellicle shown in FIG. 4B(g) (area 4C surrounded by a solid line) observed from the mask layer toward the bottom of the cavity. DETAILED DESCRIPTION OF THE INVENTION

[0017] Manufacturing method for EUV transmitting film The method for manufacturing an EUV-transmitting film according to the present invention includes the steps of (1) preparing a substrate, (2) forming a mask layer, (3) forming a cavity, (4) removing the mask layer, (5) forming an EUV-transmitting film, and (6) forming a free-standing EUV-transmitting film. In the present invention, an EUV-transmitting film is formed on the surface of the substrate facing the cavity, and the substrate is etched away from the surface opposite the cavity to form a free-standing EUV-transmitting film. This prevents the mask layer from remaining in a eaves-like shape extending toward the cavity, making it possible to manufacture a high-quality EUV-transmitting film or pellicle using an efficient method that is less likely to generate particles. Details of this method will be explained below.

[0018] 1A to 4B show methods for producing EUV transmitting films according to several embodiments of the present invention. Each step will be described below with reference to these drawings.

[0019] (1) Preparing the circuit board As shown in FIGS. 1A(a) and 2A(a), a substrate 10 is prepared. The substrate 10 has a first surface 10a and a second surface 10b. The second surface 10b is the side on which a cavity will be formed in a later process, and the first surface 10a is the side on which no cavity will be formed in a later process. The substrate 10 serves as a support for forming an EUV-transmitting film 16 thereon. Ultimately, the cavity region C is etched away to form the EUV-transmitting film 16 as a freestanding film, while the other peripheral region P is left as a frame. Therefore, the substrate 10 is desirably made of a material that provides a desirable base for forming the EUV-transmitting film 16 and can be etched away. While there are no particular limitations on the substrate 10, it is preferably a Si substrate (e.g., a Si wafer).

[0020] The substrate 10 may be an SOI (Silicon on Insulator) substrate. As shown in FIG. 3A(a), the SOI substrate 10′ is composed of a Si substrate 10c, a SiO layer 10d, and a Si layer 10e, with the SiO layer 10d interposed between the Si substrate 10c and the Si layer 10e. In this case, the first surface 10a is the surface of the Si layer 10e, and the second surface 10b is the surface of the Si substrate 10c. By using the SOI substrate 10′, etching of the Si substrate 10c (Si etching) can be accurately stopped at the SiO layer 10d. This has the advantage of easily avoiding problems caused by excessive Si etching (e.g., loosening of the free-standing film due to the substrate 10 becoming too thin).

[0021] (2) Formation of mask layer As shown in FIGS. 1A(b) and 1A(c) and 2A(b) and 2A(c), the entire region of the first surface 10a of the substrate 10 and the peripheral region P of the second surface 10b other than the cavity region C located at the center thereof are covered with a mask layer 12. The material of the mask layer 12 is not particularly limited as long as it is corrosion-resistant to the wet etching solution used to etch the substrate 10 (e.g., TMAH used in Si etching). A preferred mask layer 12 is a SiO2 film. The mask layer 12 may be formed by any method. For example, the SiO2 film is preferably formed by chemical vapor deposition (CVD) or thermal oxidation. The thickness of the SiO2 film is preferably 100 to 1000 nm.

[0022] The mask layer 12 can be formed as follows. First, the mask layer 12 is formed on the first surface 10a and the second surface 10b of the substrate 10 (FIGS. 1A(b) and 2A(b)). Next, a resist is applied to the first surface 10a and the second surface 10b, and is exposed and developed to form an opening in the resist corresponding to the cavity region C on the second surface 10b side, forming a resist mask (not shown). The size of the cavity region C corresponds to the size of the EUV-transmitting film 16 to be fabricated. After wet etching with an etching solution such as hydrofluoric acid, the exposed portions of the mask layer 12 in the openings in the resist mask are etched away, and the resist mask is then removed. In this way, the mask layer 12 having an opening in the cavity region C is obtained (FIGS. 1A(c) and 2A(c)).

[0023] (3) Cavity formation As shown in FIGS. 1A(d) and 2A(d), the substrate 10 exposed in the cavity region C is partially etched away to form the cavity 14. That is, the cavity region C of the substrate 10 is removed by etching after the EUV-transmitting film 16 is formed thereon. Therefore, to efficiently perform etching in a short time, it is desirable to thin the thickness of the substrate 10 in the region where the freestanding film is to be formed (i.e., the cavity region C) in advance. Therefore, the cavity 14 is formed by etching the substrate 10 through the opening in the mask layer 12, thereby thinning the cavity region C of the substrate 10. The etching of the substrate 10 may be either wet etching or dry etching, and is not particularly limited. The etchant is not particularly limited as long as it can etch the substrate 10. For example, when etching is performed using the DeepRIE method, which is a dry process, the Si substrate is etched perpendicular to the mask layer 12, as shown in FIG. 1A(d), which is preferable because it prevents the mask layer 12 from remaining in an eave-like shape. When wet etching a Si substrate, a TMAH (tetramethylammonium hydroxide) solution is preferred. Using a TMAH solution under appropriate conditions allows for very good anisotropic etching of Si. In particular, anisotropic etching is advantageous over isotropic etching in that it allows etching to proceed linearly in the thickness direction of the substrate 10 (less likely to wrap around to just below the mask layer 12) when forming the cavity 14, making it less likely for the mask layer 12 to remain in an eave-like shape. Nevertheless, when wet etching is performed, as shown in FIG. 2A(d), the Si substrate is etched not only vertically but also laterally due to the etching solution wrapping around, so the mask layer 12 may temporarily remain in an eave-like shape. However, in the embodiment shown in FIGS. 2A and 2B, this can be prevented in a subsequent process by removing the eave-like shape shown in FIG. 2. B Since the mask layer 12 is removed as shown in (e), it is possible to prevent the mask layer 12 from remaining in an overhanging shape.

[0024] When using an SOI substrate 10', the cavity 14 is preferably formed by first etching away the Si substrate 10c until the cavity 14 reaches the SiO2 layer 10d (FIG. 3A(d)), and then separately etching away the SiO2 layer 10d from the cavity 14 (FIG. 3B(e)), as shown in FIGS. 3A(d) and 3B(e). Etching of the Si substrate 10c may be performed by either dry etching or wet etching, as described above. In this embodiment, etching can be accurately stopped at the SiO2 layer 10d, thereby avoiding problems caused by excessive Si etching (e.g., loosening of the free-standing film due to the substrate 10 becoming too thin). Subsequent etching of the SiO2 layer 10d exposed in the cavity 14 is preferably performed using hydrofluoric acid. Thus, the Si layer 10e is exposed as a free-standing film in the cavity 14.

[0025] (4) Removal of the mask layer As shown in FIG. 1B(e), the mask layer 12 covering the first surface 10a is etched away. In this way, a substrate 10 having a cavity 14 (i.e., a cavity substrate 15) is obtained. As described above, the mask layer 12 can be etched away by wet etching using an etching solution such as hydrofluoric acid. In this way, a cavity substrate 15 having a cavity 14 is obtained. The mask layer 12 covering the peripheral region P of the second surface 10b can be left as it is. That is, in the subsequent film formation step, an EUV-transmitting film 16 can be formed from on top of the mask layer 12 covering the peripheral region P of the second surface 10b. This makes it possible to omit the mask removal process.

[0026] However, as a modified embodiment, the mask layer 12 covering the peripheral region P of the second surface 10b may also be etched away. That is, as shown in FIG. 1C(e') and FIG. 2B(e), both the mask layer 12 covering the first surface 10a and the mask layer 12 covering the peripheral region P of the second surface 10b may be etched away. By also etching away the mask layer 12 covering the peripheral region P of the second surface 10b, the mask layer 12 no longer exists, which makes it possible to prevent the mask layer 12 from remaining in an overhanging shape.

[0027] Even when an SOI substrate 10' is used, as shown in FIG. 3B(f), the mask layer 12 covering the first surface 10a may be removed by etching in the same manner as above.

[0028] (5) Formation of EUV-transmitting film As shown in Figure 1B(f), an EUV-transmitting film 16 is formed on the surface of the substrate 10 on the cavity 14 side and on the surface of the mask layer 12 that covers the second surface 10b. Alternatively, in modified embodiments shown in Figures 1C(f') and 2B(f), the EUV-transmitting film 16 is formed on the surface of the substrate 10 on the cavity 14 side. That is, in conventional methods, the EUV-transmitting film 16 is formed on the flat surface opposite the surface on which the cavity 14 is formed, but in the present invention, the film is formed on the uneven surface on the side on which the cavity 14 is formed of the substrate 10 (on top of the mask layer 12, if present there). The advantages associated with this will be described later in the next step.

[0029] The EUV transmitting film 16 preferably has a main layer composed of at least one metal selected from the group consisting of Ni, Al, Be, Cr, and Ga. These metals have the advantage of being resistant to erosion by XeF gas when etching away a substrate 10, such as a Si substrate, with XeF gas to form a freestanding EUV transmitting film 16. This is supported by the fact that the boiling points of the fluorides of Ni, Al, Be, Cr, and Ga are significantly higher than the boiling point of XeF, which is 114°C: 1750°C (NiF), 1260°C (AlF), 1169°C (BeF), 1100°C (CrF), and 950°C (GaF). High boiling points mean lower vapor pressures, which translates into resistance to etching by XeF. From the perspective of an EUV transmitting film, a particularly preferred main layer is composed of Be (metallic beryllium). Be has a higher EUV transmittance than Si or C, and therefore exhibits a practically high EUV transmittance (for example, 93% or more). Furthermore, it is preferable that the EUV transmitting film 16 further include a protective layer covering at least one side (preferably both sides) of the main layer in order to protect the main layer. When the main layer is made of Be, preferred examples of materials for the protective layer include beryllium nitride, beryllium oxide, and beryllium fluoride.

[0030] The EUV transmitting film 16 may be formed by any film formation method. Examples of preferred film formation methods include sputtering and CVD (chemical vapor deposition). As described above, in the present invention, film formation is performed on the non-flat surface of the substrate 10 on the side where the cavity 14 is formed. However, even if a film formation method with poor wraparound, such as sputtering, is used, the thickness of the substrate 10, such as a Si substrate, is usually 1 mm or less, so that even on the inner surface of the cavity 14, there is no significant difference in film thickness compared to when a film is formed on a flat surface.

[0031] For example, when fabricating a three-layer structure of beryllium nitride / beryllium / beryllium nitride, it is preferable to fabricate the beryllium film as the main layer by sputtering using a pure Be target, and the beryllium nitride film as the protective layer by reactive sputtering. This reactive sputtering can be performed, for example, by introducing nitrogen gas into the chamber during sputtering using a pure Be target, causing the beryllium and nitrogen to react and produce beryllium nitride. As described below, the beryllium nitride film may have a gradient composition layer (a layer composed of a nitrogen concentration gradient region, described below) in which the nitrogen concentration decreases toward the beryllium nitride film. A preferred example of the procedure in this case is as follows: First, a beryllium nitride film is formed by Be sputtering while introducing nitrogen gas in addition to the normally used Ar atmospheric gas. After a beryllium nitride film of a predetermined thickness is formed, a gradient composition layer is formed by Be sputtering while reducing the amount of nitrogen gas. After the gradient composition layer is formed, the introduction of nitrogen gas is stopped, and a beryllium layer is formed to a predetermined thickness. Thereafter, a gradient composition layer is formed again while increasing the amount of nitrogen gas introduced, and a beryllium nitride film is formed again as the outermost layer by reactive sputtering.

[0032] As another method, beryllium nitride can be produced by forming a beryllium film and then irradiating it with nitrogen plasma to cause a nitriding reaction of the beryllium to produce beryllium nitride. In any case, the synthesis method of beryllium nitride is not limited to these. It is preferable to use separate beryllium targets for forming the beryllium nitride film and beryllium targets for forming the beryllium film, but it is also possible to use the same target for forming the beryllium nitride film and the beryllium film. The beryllium nitride film and the beryllium film may be formed in a single-chamber sputtering apparatus, as in the examples described below, or the beryllium nitride film and the beryllium film may be formed in separate chambers using a two-chamber sputtering apparatus.

[0033] Even when an SOI substrate 10′ is used, as shown in FIG. 3B(g), an EUV transmitting film 16 may be formed in the same manner as described above on the surface of the SOI substrate 10′ on the cavity 14 side and on the surface of the mask layer 12 that covers the second surface 10b.

[0034] (6) Freestanding EUV-transmitting film 1B(g), 1C(g'), and 2B(g), the substrate 10 is etched away from the first surface 10a until the EUV transparent film 16 is exposed on the side opposite the cavity 14, thereby forming the EUV transparent film 16 in the cavity region C into a free-standing film. In this way, etching of the substrate 10 (e.g., a Si substrate) to form the EUV transparent film 16 into a free-standing film is performed from the flat surface of the substrate 10 opposite the cavity 14, unlike the conventional process in which etching of the substrate 10 is performed from the inner surface of the cavity 14. This brings about the following several advantages.

[0035] First, because the EUV-transmitting film 16 is resistant to etchants (or has a protective film resistant to etchants), it functions as a protective film on the surface of the cavity 14 of the substrate 10, such as a Si substrate, and prevents side etching of the substrate 10 inside the cavity 14. This prevents the mask layer 12 from remaining in an eave-like shape. As mentioned above, in conventional processes, side etching occurs on the side surfaces of the cavity 14, resulting in the problem of the mask layer 112 remaining in an eave-like shape extending toward the cavity 114, as shown in FIGS. 4B(g) and 4C. If this state is left as it is, the weak inner edge 112a of the eave-like shape breaks, generating particles (dust), which are likely to adhere to the EUV-transmitting film 116. If particles adhere to the EUV-transmitting film 116, the particles block EUV light during exposure, resulting in exposure defects in which the mask pattern is not accurately transferred. In contrast, in the method of the present invention, the cavity 14 and mask layer 12 are covered with the EUV-transmitting film 16, so side etching does not occur, and as a result, it is possible to prevent the mask layer 12 from remaining like an overhang. While it is possible to remove the mask layer 12 after etching the substrate 10, this would require additional steps and costs, and since the EUV-transmitting film 16 has already been formed into a free-standing film, it would require an additional process that carries a high risk of damaging the free-standing film. The method of the present invention does not require such an additional process.

[0036] Second, because etching of substrate 10 proceeds on a flat surface that does not have cavity 14, etching unevenness due to differences in the shapes of flat and non-flat portions (corners, etc.) is less likely to occur compared to etching from the surface of substrate 10 facing cavity 14, enabling uniform etching. That is, in conventional processes where etching is performed from the inner surface of cavity 14, uneven etching occurs depending on the location due to uneven diffusion of etchant, etc., but with the method of the present invention, etching of a flat surface can form EUV transmitting film 16 into a free-standing film, making it less likely to cause uneven etching. Therefore, the method of the present invention can produce a high-quality EUV transmitting film 16 or pellicle 18.

[0037] Thus, the method of the present invention makes it possible to prevent the mask layer 12 from remaining in a eaves-like shape extending toward the cavity 14, and to manufacture a high-quality EUV-transmitting film or pellicle using an efficient method that is less likely to generate particles.

[0038] The etching of the substrate 10 to make the EUV transmitting film 16 a freestanding film is preferably performed by an etching method that does not erode the EUV transmitting film 16. For example, when etching a Si substrate, it is preferable to perform the etching with XeF2 gas.

[0039] Even when the SOI substrate 10′ is used, the B As shown in (h), the EUV transparent film 16 can be made into a free-standing film by etching away the SOI substrate 10' (specifically, the Si layer 10e) from the first surface 10a in the same manner as above until the EUV transparent film 16 is exposed on the side opposite the cavity 14. As a result of making the EUV transparent film 16 in the cavity region C into a free-standing film in this manner, the free-standing portion of the EUV transparent film 16 and the SiO2 layer 10d are exposed on the same plane on the side opposite the cavity 14. In this embodiment, because the SiO2 layer 10d exists below the Si layer 10e, the etching can be stopped at the SiO2 layer 10d without strict control of the etching time in the XeF2 etching for removing the Si layer 10e.

[0040] As a result of etching away the substrate 10 or SOI substrate 10' in this way, the EUV-transmitting film 16 in the cavity region C becomes a free-standing film. Meanwhile, in the peripheral region P outside the cavity region, three layers (substrate 10, mask layer 12, and EUV-transmitting film 16) (FIG. 1B(g)), two layers (substrate 10 and EUV-transmitting film 16) (FIGS. 1C(g') and 2B(g)), or four layers (SiO2 layer 10d, Si substrate 10c, mask layer 12, and EUV-transmitting film 16) (FIG. 3B(h)) remain, forming a frame 17 for supporting the free-standing film. In this way, a pellicle 18 having the EUV-transmitting film 16 (pellicle film) and frame 17 is obtained.

[0041] Pellicle As described above, an EUV transmitting film and a pellicle including the same are manufactured by the manufacturing method of the present invention.

[0042] 1B(g), a pellicle 18 according to one embodiment of the present invention includes a substrate 10, a mask layer 12, and an EUV-transmitting film 16. The substrate 10 has a first surface 10a and a second surface 10b, and has a cavity 14 in its center. The mask layer 12 covers the second surface 10b of the substrate 10. The EUV-transmitting film 16 continuously covers the surface of the mask layer 12 and the inner surface of the cavity 14 in the substrate 10, and is exposed as a free-standing film that forms the bottom surface of the cavity 14 at the same height as the first surface 10a.

[0043] As shown in FIG. 1C(g') and FIG. 2B(g), a pellicle 18' according to another embodiment of the present invention includes a substrate 10 and an EUV-transmitting film 16. The substrate 10 is The substrate 10 has a first surface 10a and a second surface 10b, and has a cavity 14 in the center. The EUV transmitting film 16 continuously covers the second surface 10b of the substrate 10 and the inner surface of the cavity 14, and is exposed as a free-standing film that forms the bottom surface of the cavity 14 at the same height as the first surface 10a.

[0044] In either embodiment, the substrate 10 may be composed of two layers, a Si substrate 10c and an SiO2 layer 10d, as in the pellicle 18'' shown in FIG. 3B(h). This is a typical layer configuration for a pellicle 18'' manufactured using an SOI substrate 10'.

[0045] As described above, the pellicle 18, 18′, or 18″ has an EUV-transmitting film 16 (pellicle film) and a frame 17. The frame 17 may be made up of three layers: a substrate 10, a mask layer 12, and an EUV-transmitting film 16 (FIG. 1B(g)), two layers: a substrate 10 and an EUV-transmitting film 16 (FIG. 1C(g') and FIG. 2B(g)), or three or four layers: a SiO2 layer 10d, a Si substrate 10c, a mask layer 12 (optional), and an EUV-transmitting film 16 (FIG. 3B (h)).

[0046] Preferred embodiment of EUV transmitting film As described above, a preferred embodiment of the EUV transmitting film comprises a main layer and a protective layer covering at least one side (preferably both sides) of the main layer. In this embodiment, the main layer is preferably made of metal beryllium, while the protective layer is preferably made of beryllium nitride. By combining a main layer made of metal beryllium with a protective layer made of beryllium nitride in this way, it is possible to provide an EUV transmitting film that combines a practically high EUV transmittance (e.g., 93% or more) with durability in a low-pressure hydrogen atmosphere environment.

[0047] The main layer according to this embodiment is preferably made of metallic beryllium. However, the main layer does not need to be made entirely of metallic beryllium; it is sufficient that the main layer is preferably made of at least 99% by weight, more preferably at least 99.5% by weight, and even more preferably at least 99.8% by weight of metallic beryllium. This contributes to the realization of a practically high level of EUV transmittance while ensuring the basic functions of a pellicle film (such as the function of preventing particle adhesion). From this perspective, the thickness of the main layer is preferably 10 to 70 nm, more preferably 15 to 50 nm, and even more preferably 20 to 35 nm.

[0048] The protective layer in this embodiment is a layer for protecting the main layer, which is a metal beryllium layer. Therefore, the protective layer only needs to cover at least one side of the main layer, but it is preferable to cover both sides of the main layer with the protective layer. The protective layer is preferably composed of beryllium nitride. However, the main layer does not need to be entirely composed of beryllium nitride; it is sufficient that 99% by weight or more, preferably 99.5% by weight or more, and more preferably 99.8% by weight or more of the main layer is composed of beryllium nitride. Because beryllium nitride has a high EUV transmittance, it has a higher EUV transmittance than a beryllium film with a Ru layer formed thereon at the same thickness. According to theoretical calculations, the transmittance of a 30-nm-thick beryllium film with a 3-nm-thick Ru film formed on both sides is 85.8%, while the transmittance of a 30-nm-thick beryllium film with a 3-nm-thick beryllium nitride film formed on both sides is 91.1%. When a 2-nm-thick beryllium nitride layer and a 1-nm-thick gradient composition layer (a layer composed of a nitrogen concentration gradient region, described below) are formed on both sides of a 30-nm-thick beryllium film, the transmittance exceeds 91.1%. Forming dense beryllium nitride layers on both sides of the beryllium layer suppresses reaction with the XeF2 gas used in etching the Si substrate, described below. Furthermore, because beryllium is a highly reactive material, it easily oxidizes to form beryllium oxide, but the formation of beryllium nitride suppresses this oxidation. As described above, the benefits of using a beryllium nitride layer as a protective layer include increased EUV transmittance, protection of the beryllium film (main layer) during the etching process, and prevention of oxidation.

[0049] The thickness of the protective layer in this embodiment is preferably 5 nm or less, more preferably 3 nm or less. Considering that protective layers of 3 nm in thickness are formed on both sides of the main layer, a 3 nm thick beryllium nitride film has an EUV transmittance of 95%, which is significantly higher than the 90% of a Ru film. There is no particular lower limit to the thickness of the protective layer, but if it is too thin, it may be difficult to cover the entire main layer, or the crystallinity of the beryllium nitride may be poor, making it difficult to obtain the physical properties of beryllium nitride. In this specification, the term "beryllium nitride" refers not only to a stoichiometric composition such as Be3N2, but also to a beryllium nitride having a stoichiometric composition such as Be3N2-x It means an inclusive composition that allows a non-stoichiometric composition such as (where 0 < x < 2).

[0050] The protective layer preferably has a nitrogen concentration gradient region where the nitrogen concentration decreases as it approaches the main layer. That is, as described above, the composition of beryllium nitride constituting the protective layer includes non-stoichiometric compositions such as Be3N from the stoichiometric composition such as Be3N2 to Be3N 2-x Since it can include non-stoichiometric compositions such as (where 0 < x < 2), the beryllium nitride constituting the protective layer preferably has a gradient composition that approaches a beryllium-rich composition as it approaches the main layer. By doing so, the adhesion between the protective layer (i.e., the beryllium nitride layer) and the main layer (i.e., the metallic beryllium layer) can be improved, and the generation of stress caused by the difference in thermal expansion between the two layers can be alleviated. That is, it is possible to improve the adhesion between the two layers to suppress peeling, or to make it difficult to peel as a thermal expansion relaxation layer between the two layers when it absorbs EUV light and becomes high temperature. The thickness of the nitrogen concentration gradient region is preferably smaller than the thickness of the protective layer. That is, it is not necessary for the entire thickness of the protective layer to be the nitrogen concentration gradient region. For example, it is preferable that only a part of the thickness of the protective layer, for example, preferably 10 to 70% of the thickness of the protective layer, more preferably 15 to 50% of the thickness of the protective layer is the nitrogen concentration gradient region.

[0051] The EUV transmission film 16 according to this aspect can have a high EUV transmittance at a practical level, preferably having an EUV transmittance of 91% or more, more preferably 92% or more, and even more preferably 93% or more. Since the higher the EUV transmittance, the more desirable it is, the upper limit value is not particularly limited, but the EUV transmittance of the EUV transmission film 16 according to this aspect can typically be 99% or less, more typically 98% or less, and even more typically 95% or less.

Examples

[0052] The present invention will be further specifically described by the following examples.

[0053] Example 1 According to the procedure shown in FIGS. 1A and 1B, a composite free-standing film (EUV-transmitting film) having a three-layer structure of beryllium nitride / beryllium / beryllium nitride was fabricated as follows.

[0054] (1) Preparation of the cavity substrate An 8-inch (20.32 cm) diameter Si wafer was prepared as the substrate 10 (Fig. 1A(a)). A 1 μm thick SiO2 layer was formed on both sides of the Si wafer by thermal oxidation as a mask layer 12 (Fig. 1A(b)). Resist was applied to both sides of the Si wafer with the SiO2 layer formed, and a resist mask (not shown) for SiO2 etching was formed by exposure and development so that a 110 mm × 140 mm hole in the resist was formed on one side as a cavity region C. One side of the substrate was wet-etched with hydrofluoric acid to remove the exposed portion of the SiO2 film in the cavity region C, exposing the Si wafer. The resist mask was then removed using an ashing device (Fig. 1A(c)). Subsequently, the Si wafer was dry-etched (anisotropically etched) in the thickness direction using reactive ion etching from the exposed portion of the cavity region C to form a cavity 14 (Fig. 1A(d)). At this time, the etching time was calculated in advance from the etching rate so that the thickness of the Si wafer remaining as the bottom of the cavity 14 would be about 10 μm, and etching was performed for that etching time. The SiO2 layer on the surface opposite the cavity 14 was removed and cleaned with hydrofluoric acid to prepare a cavity substrate 15 for forming an EUV-transmitting film (FIG. 1B(e)).

[0055] (2) Formation of composite membrane A three-layer composite film of beryllium nitride / beryllium / beryllium nitride was formed on the cavity 14-forming surface of the cavity substrate 15 obtained in (1) above, covering the entire area, including not only the cavity region C (the inner surface of the cavity 14) but also the peripheral region P (SiO2 layer), as follows (Figure 1B(f)). First, the cavity substrate 15 was placed in a sputtering apparatus and a pure Be target was attached. The chamber was evacuated, and reactive sputtering was performed at an internal pressure of 0.5 Pa with an argon gas to nitrogen gas flow ratio adjusted to 1:1. The reactive sputtering was terminated when a 2 nm layer of beryllium nitride was formed. Next, sputtering was performed using only argon gas without introducing nitrogen gas, and the sputtering was terminated when a 25 nm layer of beryllium nitride was formed. After that, reactive sputtering was performed again with nitrogen gas introduced as in the first step, and the reactive sputtering was terminated when a 2 nm layer of beryllium nitride was formed. In this way, a composite film of beryllium nitride 2 nm / beryllium 25 nm / beryllium nitride 2 nm was formed as the EUV transmitting film 16 .

[0056] (3) Self-supporting film The cavity substrate 15 with the EUV-transmitting film 16 obtained in (2) above was placed in the chamber of a XeF2 etcher so that the surface opposite the cavity 14 (i.e., the exposed surface of the Si substrate 10) would be etched with XeF2. The chamber was then thoroughly evacuated. Residual moisture in the chamber reacted with the XeF2 gas to produce hydrofluoric acid, which could corrode the etcher or cause unexpected etching. The chamber was evacuated thoroughly, and nitrogen gas was introduced repeatedly as needed to reduce residual moisture. Once the chamber was sufficiently evacuated, the valve between the XeF2 source cylinder and the auxiliary chamber was opened. As a result, XeF2 sublimated, and XeF2 gas accumulated in the auxiliary chamber. Once a sufficient amount of XeF2 gas had accumulated in the auxiliary chamber, the valve between the auxiliary chamber and the chamber was opened, and XeF2 gas was introduced into the chamber. The XeF2 gas reacted with Si to produce SiF4 and Xe. Because the boiling point of SiF4 is -95°C, the generated SiF4 quickly evaporated, triggering a reaction of F with the newly exposed Si substrate. As the Si etching progressed and the XeF2 gas in the chamber decreased, the chamber was evacuated and XeF2 gas was again introduced into the chamber to continue etching. This process of evacuation, XeF2 gas introduction, and etching was repeated until the Si substrate 10 corresponding to the portion to be formed into a freestanding film was completely removed. Etching was terminated when the unnecessary portion of the Si substrate was removed. In this way, a pellicle 18 was obtained, comprising a composite freestanding film of EUV-transmitting film 16 and a frame 17 supporting the composite freestanding film (Figure 1B(g)). The EUV transmittance of the resulting beryllium nitride / beryllium / beryllium nitride three-layer composite freestanding film was measured and found to be 92.8%.

[0057] Example 2 According to the procedure shown in FIGS. 2A and 2B, a composite free-standing film (EUV-transmitting film) having a three-layer structure of beryllium nitride / beryllium / beryllium nitride was fabricated as follows.

[0058] (1) Preparation of the cavity substrate An 8-inch (20.32 cm) diameter Si wafer was prepared as the substrate 10 (Fig. 2A(a)). A 1 μm thick SiO2 layer was formed on both sides of the Si wafer by thermal oxidation as a mask layer 12 (Fig. 2A(b)). Resist was applied to both sides of the Si wafer with the SiO2 layer formed, and exposure and development were performed to form a resist mask (not shown) for SiO2 etching so that a 110 mm × 140 mm hole in the resist was formed on one side as a cavity region C. One side of the substrate was wet-etched with hydrofluoric acid to remove the exposed portion of the SiO2 film in the cavity region C, exposing the Si wafer. The resist mask was then removed with an ashing device (Fig. 2A(c)). Subsequently, the Si wafer was wet-etched in the thickness direction (anisotropic etching) using TMAH solution from the exposed portion of the cavity region C to form a cavity 14 (Fig. 2A(d)). The etching time was calculated in advance from the etching rate so that the thickness of the Si wafer remaining at the bottom of the cavity 14 would be approximately 10 μm, and etching was performed for that duration. The etching using the TMAH solution is anisotropic, proceeding primarily upward in the figure, but also laterally. Therefore, the mask layer 12 forms an overhanging structure, as shown in Figure 2A(d). Therefore, the mask layer 12 on both sides of the substrate was removed and cleaned with hydrofluoric acid to prepare a cavity substrate 15' for forming an EUV-transmitting film (Figure 2B(e)).

[0059] (2) Formation of composite membrane A three-layer composite film of beryllium nitride / beryllium / beryllium nitride was formed as an EUV-transmitting film 16 on the cavity 14-forming surface of the cavity substrate 15' obtained in (1) above, over the entire area including not only the cavity region C (the inner surface of the cavity 14) but also the peripheral region P, in the same manner as in Example 1 (Figure 2B(f)).

[0060] (3) Self-supporting film The cavity substrate 15' with the EUV-transmitting film 16 obtained in (2) above was placed in the chamber of a XeF etcher so that the surface opposite the cavity 14 (i.e., the exposed surface of the Si substrate 10) was etched with XeF. XeF etching was performed in the same manner as in Example 1. In this way, the Si substrate 10 at the bottom of the cavity 14 was etched away, yielding a pellicle 18' comprising a composite freestanding film of the EUV-transmitting film 16 and a frame 17 supporting the composite freestanding film (Figure 2B(g)). Unlike Example 1, in Example 2, the mask layer 12 was removed, eliminating the overhanging structure of the mask layer 12, preventing damage to the mask layer 12 and the generation of particles. The EUV transmittance of the resulting composite freestanding film with a three-layer structure of beryllium nitride / beryllium / beryllium nitride was measured and found to be 93.1%.

[0061] Example 3 According to the procedure shown in FIGS. 3A and 3B, a composite free-standing film (EUV-transmitting film) having a three-layer structure of beryllium nitride / beryllium / beryllium nitride was fabricated as follows.

[0062] (1) Preparation of the cavity substrate An SOI substrate 10' was prepared, which consisted of a Si substrate 10c on which a 1-μm-thick SiO2 layer 10d (insulator layer) and a 10-μm-thick Si layer 10e (SOI layer) were sequentially formed (FIG. 3A(a)). On both sides of this SOI substrate 10', 1-μm-thick SiO2 layers were formed as mask layers 12 by thermal oxidation (FIG. 3A(b)). Resist was applied to both sides of the SOI substrate 10' on which the SiO2 layers were formed, and exposure and development were performed to form a resist mask (not shown) for SiO2 etching so that a 110 mm × 140 mm hole in the resist was formed on one side as a cavity region C. One side of this substrate was wet-etched with hydrofluoric acid to etch away the exposed portion of the SiO2 film in the cavity region C, exposing the SOI substrate 10'. The resist mask was then removed using an ashing device (FIG. 3A(c)). Thereafter, the Si substrate 10c was dry-etched (anisotropically etched) in the thickness direction using reactive ion etching from the exposed portion of the cavity region C until the SiO2 layer 10d was exposed, forming the cavity 14 (FIG. 3A(d)). The exposed SiO2 layer 10d was etched away with hydrofluoric acid to expose the Si layer 10e (FIG. 3B(e)). Thereafter, the mask layer 12 (SiO2 layer) on the surface opposite the cavity 14 was etched away with hydrofluoric acid to prepare a cavity substrate 15'' for forming an EUV-transmitting film (FIG. 3B(f)).

[0063] (2) Formation of composite membrane On the cavity 14-forming surface of the cavity substrate 15'' obtained in (1) above, a three-layer composite film of beryllium nitride / beryllium / beryllium nitride was formed as an EUV-transmitting film 16 over the entire area, including not only the cavity region C (the inner surface of the cavity 14) but also the peripheral region P (SiO2 layer), in the same manner as in Example 1 (Figure 3B(g)).

[0064] (3) Self-supporting film The cavity substrate 15'' with the EUV-transmitting film 16 obtained in (2) above was placed in the chamber of a XeF etcher so that the surface opposite the cavity 14 (i.e., the exposed surface of the Si layer 10e) was etched with XeF. XeF etching was performed in the same manner as in Example 1. The Si layer 10e at the bottom of the cavity 14 was then etched away, yielding a pellicle 18'' (Figure 3B(h)) comprising a composite freestanding film of the EUV-transmitting film 16 and a frame 17 supporting the composite freestanding film. Unlike Example 1, Example 2 contains an SiO layer 10d below the Si layer 10e. Therefore, the etching can be stopped at the SiO layer 10d without strict control of the etching time during the XeF etching to remove the Si layer 10e. This is advantageous in that excessive etching can be prevented. The EUV transmittance of the resulting beryllium nitride / beryllium / beryllium nitride three-layer composite freestanding film was measured and found to be 93.3%.

[0065] Results and Discussion In Examples 1 to 3, both the mask layer (SiO2 layer in Examples 1 to 3) used to form the cavity in the substrate and the inner surface of the cavity are covered with a beryllium nitride / beryllium / beryllium nitride composite film, so the inner surface of the cavity is not etched by XeF2 etching. In other words, side etching does not occur. In Examples 1 to 3, the silicon thickness at the bottom of the cavity is 10 μm. Conventional methods would have resulted in side etching of approximately 10 μm, resulting in an overhanging structure in which the mask layer extends toward the cavity. If the mask layer were to form an overhanging structure, the mask layer would be composed of SiO2, which is only 1 μm thick, and therefore weak and easily damaged. Furthermore, damage generates particles (dust) that adhere to the freestanding film. When a freestanding film is used as a pellicle film, adhesion of particles to the freestanding film blocks EUV light during exposure, resulting in inaccurate transfer of the mask pattern and poor exposure. In contrast, the freestanding film fabricated in the present invention does not form an overhanging structure, eliminating the problem of the overhanging structure breaking and adhering to the freestanding film.

Claims

1. providing a substrate having a first side and a second side; covering the entire area of the first surface and a peripheral area of the second surface other than a cavity area located at the center thereof with a mask layer; etching away a portion of the substrate exposed in the cavity region to form a cavity; Etching away the mask layer covering the first surface; forming an EUV transmitting film on a surface of the mask layer that covers the cavity side surface of the substrate and the second surface; etching the substrate from the first surface until the EUV transmitting film is exposed on a side opposite the cavity, thereby forming the EUV transmitting film in the cavity region into a free-standing film; A method for producing an EUV transmitting film, comprising:

2. providing a substrate having a first side and a second side; covering the entire area of the first surface and a peripheral area of the second surface other than a cavity area located at the center thereof with a mask layer; etching away a portion of the substrate exposed in the cavity region to form a cavity; etching away the mask layer covering the first surface and the mask layer covering the peripheral region of the second surface; forming an EUV transmitting film on the surface of the substrate facing the cavity; etching the substrate from the first surface until the EUV transmitting film is exposed on a side opposite the cavity, thereby forming the EUV transmitting film in the cavity region into a free-standing film; A method for producing an EUV transmitting film, comprising:

3. 3. The method for producing an EUV transmitting film according to claim 1, wherein the EUV transmitting film includes a main layer made of metallic beryllium.

4. The method for producing an EUV transmitting film according to claim 3 , wherein the EUV transmitting film comprises a protective layer covering at least one surface of the main layer.

5. The method for producing an EUV transmitting film according to any one of claims 1 to 4, wherein the substrate is a Si substrate.

6. The substrate is an SOI substrate, and the SOI substrate comprises a Si substrate, a Si layer, and a SiO 2 layer interposed between the Si substrate and the Si layer. ２ a layer, the first surface being a surface of the Si layer, and the second surface being a surface of the Si substrate.

7. The formation of the cavity is performed by filling the cavity with the SiO ２ The Si substrate is etched away until the SiO ２ The EUV transmitting film is then removed from the cavity by etching away the free-standing film portion and the SiO ２ The method of claim 6 , wherein the layer is exposed on a same plane opposite the cavity.

8. a substrate having a first surface and a second surface and a central cavity; a mask layer covering the second surface of the substrate; an EUV transmitting film that continuously covers a surface of the mask layer and an inner surface of the cavity of the substrate and is exposed as a free-standing film that forms a bottom surface of the cavity at the same height as the first surface; A pellicle comprising:

9. a substrate having a first surface and a second surface and a central cavity; an EUV transmitting film that continuously covers the second surface of the substrate and the inner surface of the cavity and is exposed as a free-standing film that forms a bottom surface of the cavity at the same height as the first surface; A pellicle comprising:

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