Reflective photomask blank, reflective photomask, and method for manufacturing reflective pohotomask
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- TEKSCEND PHOTOMASK CORP
- Filing Date
- 2026-01-23
- Publication Date
- 2026-08-06
Smart Images
Figure JP2026002283_06082026_PF_FP_ABST
Abstract
Description
Reflective photomask blank, reflective photomask, and method for manufacturing a reflective photomask
[0001] The present invention relates to a reflective photomask blank, a reflective photomask, and a method for manufacturing a reflective photomask.
[0002] In semiconductor device manufacturing processes, the miniaturization of semiconductor devices has led to increased demand for miniaturization of photolithography technology. In photolithography, the minimum resolution dimension of the transfer pattern largely depends on the wavelength of the exposure light source; the shorter the wavelength, the smaller the minimum resolution dimension can be. For this reason, in semiconductor device manufacturing processes, exposure light sources using conventional 193 nm ArF excimer laser light are being replaced with 13.5 nm EUV (Extreme Ultra Violet) exposure light sources.
[0003] Because EUV light has a short wavelength, most materials have high light absorption properties. For this reason, EUV photomasks (EUV masks) are reflective masks, unlike conventional transmission masks. Regarding reflective mask technology, for example, there is the one described in Patent Document 1. The reflective mask blank, which is the basis of a reflective mask, has a multilayer reflective layer that exhibits high reflectivity to the exposure light source wavelength and an absorption layer for the exposure light source wavelength sequentially formed on a low thermal expansion substrate, and furthermore, a back-surface conductive film for electrostatic chuck in the exposure machine is formed on the back surface of the substrate. There are also EUV masks that have a buffer layer (capping layer) between the multilayer reflective layer and the absorption layer.
[0004] Japanese Patent Publication No. 2007-273678
[0005] Reflective masks are used in EUV lithography. For example, as shown in Figure 1, the conductive film on the back surface of the reflective mask Y is typically adsorbed onto the stage X of the EUV exposure apparatus. If foreign matter adheres to the back surface of the reflective mask in this usage configuration, it can lead to contamination of the EUV exposure apparatus. Therefore, improving the appearance quality of the back surface of the reflective mask is important. Conventional conductive films on the back surface of reflective masks often use tantalum-based materials (such as TaB) as the material.
[0006] The manufacturing process for reflective masks sometimes includes a step of cleaning the back surface of the reflective mask. When a visual inspection is performed on the back surface of the reflective mask (i.e., the surface of the conductive film on the back surface) after this back surface cleaning process, a large number of foreign matter may be detected. Figure 2 shows an example of the visual quality of the conductive film surface on the back surface of a conventional reflective mask after back surface cleaning. In Figure 2, each dot indicates the foreign matter adhering to (remaining) on the conductive film surface on the back surface of the reflective mask after back surface cleaning. In other words, even though the back surface of a conventional reflective mask is cleaned during the manufacturing process, foreign matter may not be completely removed from the conductive film surface on the back surface, or the removal of foreign matter from the conductive film surface on the back surface may be insufficient.
[0007] This disclosure is made under the circumstances described above, and aims to provide a reflective photomask blank, a reflective photomask, and a method for manufacturing the same that reduces the adhesion of foreign matter to the surface of the back conductive film that may occur during the mask manufacturing process. In other words, this disclosure aims to provide a reflective photomask blank, a reflective photomask, and a method for manufacturing the same that makes it less likely for foreign matter to adhere to the surface of the back conductive film during the mask manufacturing process, thereby improving the appearance quality of the back surface.
[0008] This disclosure has been made to solve the above problems, and one aspect of this disclosure is a reflective photomask blank for making a reflective photomask for pattern transfer using extreme ultraviolet light as a light source, comprising a substrate, a reflective portion formed on the substrate that reflects incident light, a low-reflectivity portion formed on the reflective portion with or without other films, and a back surface conductive film formed on the side of the substrate opposite to the side on which the reflective portion is formed, wherein the surface free energy of the back surface conductive film is 0.8 or less when the surface free energy of amorphous TaN is set to 1.
[0009] Furthermore, a reflective photomask according to one aspect of the present disclosure is a reflective photomask for pattern transfer using extreme ultraviolet light as a light source, comprising: a substrate; a reflective portion formed on the substrate that reflects incident light; a low-reflectivity portion formed on the reflective portion, with or without other films; and a back surface conductive film formed on the side of the substrate opposite to the side on which the reflective portion is formed, wherein the surface free energy of the back surface conductive film is 0.8 or less when the surface free energy of amorphous TaN is set to 1.
[0010] Furthermore, a method for manufacturing a reflective photomask according to one aspect of this disclosure is a method for manufacturing a reflective photomask using a reflective photomask blank according to one aspect of this disclosure, wherein the surface free energy of the back conductive film is 0.8 or less when the surface free energy of amorphous TaN is set to 1.
[0011] A reflective photomask blank according to one aspect of this disclosure makes it possible to provide a reflective photomask blank, a reflective photomask, and a method for manufacturing the same that reduces the adhesion of foreign matter to the surface of the back conductive film, which may occur during the mask manufacturing process. In other words, a reflective photomask blank according to one aspect of this disclosure makes it possible to provide a reflective photomask blank, a reflective photomask, and a method for manufacturing the same that makes it less likely for foreign matter to adhere to the surface of the back conductive film during the mask manufacturing process, thereby improving the appearance quality of the back surface.
[0012] This is a schematic diagram showing a transfer apparatus using EUV light. This is a diagram showing an example of the surface quality of the back surface of a conventional reflective mask. This is a schematic cross-sectional view showing the configuration of a reflective photomask blank according to an embodiment of this disclosure. This is a schematic cross-sectional view showing the configuration of a reflective photomask blank according to a modified example of an embodiment of this disclosure. This is a schematic cross-sectional view showing the configuration of a reflective photomask according to an embodiment of this disclosure. This is a schematic cross-sectional view showing the configuration of a reflective photomask according to a modified example of an embodiment of this disclosure.
[0013] As a result of diligent research, the inventors have revealed that if the surface free energy of the conductive film on the back surface is 0.8 or less (with the surface free energy of amorphous TaN set to 1), then foreign matter is less likely to adhere to the back surface during the manufacturing process of a reflective photomask, and the quality of the back surface appearance is improved. In other words, this disclosure proposes and provides a new design concept for improving the back surface appearance quality of reflective photomask blanks and reflective photomasks. This point will be explained below.
[0014] In conventional design philosophies, in order to improve the surface quality of the back surface of reflective photomask blanks and reflective photomasks, attention has been paid to methods and conditions other than the mask manufacturing process, such as the management methods and conditions for masks and mask blanks, and various methods and conditions have been adjusted to prevent foreign matter from adhering to the surface of the conductive film on the back surface during the mask manufacturing process. Alternatively, in conventional design philosophies, in order to improve the surface quality of the back surface of reflective photomask blanks and reflective photomasks, attention has been paid to the back surface cleaning process, and the type of cleaning solution and cleaning method used in the back surface cleaning process have been adjusted.
[0015] In response to this, the inventors focused on the "surface free energy of the back surface conductive film" and found that by forming the back surface conductive film with a material that has a lower surface free energy than existing materials, foreign matter is less likely to adhere to the back surface during the mask manufacturing process, i.e., the quality of the back surface appearance is improved. Furthermore, the inventors found that by forming the back surface conductive film with a material that has a lower surface free energy than existing materials, even if foreign matter adheres to the back surface conductive film, it can be easily removed by washing.
[0016] Thus, the design philosophy presented in this disclosure differs significantly from conventional design philosophies that focused on methods and conditions for managing masks and mask blanks, or on the types and methods of cleaning solutions. Regarding the aforementioned "foreign matter" adhering to the surface of the back conductive film, its generation mechanism is currently unknown, but it is thought to consist of particles adhering during transport of the mask substrate during drawing, developing, etching, etc., or components resulting from resist flowing to the back during resist coating or developing.
[0017] Hereinafter, an embodiment of this disclosure will be described with reference to the drawings. Herein, the configuration shown in the drawings is schematic, and the relationship between thickness and planar dimensions, the ratio of the thickness of each layer, etc., will differ from reality. Furthermore, the embodiment described below is an example of a configuration to embody the technical idea of this disclosure, and the technical idea of this disclosure is not limited to the materials, shapes, structures, etc. of the components described below. The technical idea of this disclosure can be modified in various ways within the technical scope defined by the claims described in the patent claims.
[0018] (Configuration of Reflective Photomask Blank) Figure 3 is a schematic cross-sectional view showing the configuration of a reflective photomask blank (reflective mask blank) 100 according to an embodiment of the present disclosure. As shown in Figure 3, the reflective photomask blank 100 according to an embodiment of the present disclosure is a reflective photomask blank for making a reflective photomask for pattern transfer using extreme ultraviolet light as a light source, and comprises a substrate 11, a reflective portion 12 formed on the substrate 11 that reflects incident light, a low-reflectivity portion 13 formed on the reflective portion 12 without interposing another film, and a single-layer back surface conductive film 14 formed on the side of the substrate 11 opposite to the side on which the reflective portion 12 is formed. In Figure 3, the low-reflectivity portion 13 formed on the reflective portion 12 without interposing another film has been described, but the present disclosure is not limited thereto. For example, the low-reflectivity portion 13 may be formed on the reflective portion 12 via another film (not shown).
[0019] Figure 4 is a schematic cross-sectional view showing the configuration of a reflective photomask blank (reflective mask blank) 200 according to an embodiment of the present disclosure. As shown in Figure 4, the reflective photomask blank 200 according to an embodiment of the present disclosure is a reflective photomask blank for making a reflective photomask for pattern transfer using extreme ultraviolet light as a light source, and comprises a substrate 11, a reflective portion 12 formed on the substrate 11 that reflects incident light, a low-reflectivity portion 13 formed on the reflective portion 12 without interposing any other film, and two layers of back-surface conductive films 14 with different physical properties formed on the side of the substrate 11 opposite to the side on which the reflective portion 12 is formed. The back-surface conductive film 14 of the reflective photomask blank 200 comprises a lower layer 15 and an upper layer 16. The lower layer 15 of the back-surface conductive film 14 is located on the substrate 11 side of the upper layer 16 of the back-surface conductive film 14.
[0020] Thus, the reflective photomask blank 200 according to the embodiment of this disclosure has a two-layer configuration of the back surface conductive film 14, and corresponds to a modified example of the reflective photomask blank 100 according to the embodiment of this disclosure which has a single layer of back surface conductive film 14. In Figure 4, a low-reflection portion 13 formed on the reflective portion 12 without interposing another film has been described, but this disclosure is not limited thereto. For example, the low-reflection portion 13 may be formed on the reflective portion 12 via another film (not shown).
[0021] The following describes in detail each layer constituting the reflective photomask blank 100 and the reflective photomask blank 200 according to the embodiments of this disclosure.
[0022] (Substrate) The substrate 11 according to the embodiment of this disclosure can be, for example, a flat Si substrate or a synthetic quartz substrate. In addition, a titanium-doped low thermal expansion glass can be used for the substrate 11, but this disclosure is not limited to these materials as long as they have a low coefficient of thermal expansion.
[0023] (Reflective portion) The reflective portion 12 according to the embodiment of this disclosure is formed on one side (surface) of the substrate 11 and is a layer or film that reflects EUV light (extreme ultraviolet light), which is exposure light. For example, it is a multilayer reflective film made of a combination of materials with significantly different refractive indices for EUV light. The multilayer reflective film according to the embodiment of this disclosure may be formed by repeatedly stacking layers of a combination such as Mo (molybdenum) and Si (silicon), or Mo (molybdenum) and Be (beryllium) for about 40 cycles.
[0024] (Capping Layer) In embodiments of this disclosure, a capping layer (not shown) may be provided between the reflective portion 12 and the low-reflectance portion 13. The capping layer according to the embodiments of this disclosure functions as an etching stopper to prevent damage to the multilayer reflective film when etching the low-reflectance portion 13 in the photomask fabrication process. Depending on the material of the multilayer reflective film and the etching conditions, the capping layer may not be formed. The capping layer is made of a material that is resistant to dry etching performed when forming the pattern of the low-reflectance portion 13. The material of the capping layer may be, for example, a material containing ruthenium (Ru) or chromium (Cr).
[0025] (Low-reflection area) As shown in Figure 3, the low-reflection area 13 is a layer formed on the reflective area 12 and is a layer that absorbs EUV light, which is the exposure light. In the embodiments of this disclosure, as will be described later, the absorption pattern (absorption pattern layer) 13a of the reflective photomask 300 is formed by removing a part of the low-reflection area 13 of the reflective photomask blank 100, that is, by patterning the low-reflection area 13. In EUV lithography, EUV light is incident at an oblique angle and reflected by the reflective area 12, but the transfer performance onto the wafer (semiconductor substrate) may deteriorate due to the projection effect in which the absorption pattern 13a obstructs the optical path. This deterioration in transfer performance can be reduced by reducing the thickness of the low-reflection area 13 that absorbs EUV light. In order to reduce the thickness of the low-reflection area 13, it is preferable to use a material that has higher absorption of EUV light than conventional materials, that is, a material with a high extinction coefficient k for a wavelength of 13.5 nm.
[0026] Therefore, it is preferable that the low-reflection portion 13 is formed from a material containing elements with a relatively high extinction coefficient k, such as tantalum (Ta), tin (Sn), nickel (Ni), platinum (Pt), tungsten (W), hafnium (Hf), chromium (Cr), indium (In), iridium (Ir), tellurium (Te), bismuth (Bi), etc. Alternatively, the low-reflection portion 13 may be formed from a material other than those containing the elements with a relatively high extinction coefficient k mentioned above. More specifically, the low-reflection portion 13 may be formed from a material that exhibits a phase shift effect, such as a material containing molybdenum (Mo), ruthenium (Ru), platinum (Pt), iridium (Ir), osmium (Os), rhenium (Re), palladium (Pd), silver (Ag), etc.
[0027] (Back surface conductive film) A back surface conductive film 14 is formed on the other side (back surface) of the substrate 11, that is, the side on which the reflective portion 12 is not formed. The back surface conductive film 14 is a film used to fix a reflective photomask 300, which has been made using the reflective photomask blank 100 according to the embodiment of this disclosure, to an exposure machine using the principle of an electrostatic chuck. The back surface conductive film 14 comprises at least one layer (film), and when the surface free energy of an existing back surface conductive film material is set to 1, the relative surface free energy of the outermost layer of the back surface conductive film 14 is 0.8 or less. If the relative surface free energy of the outermost layer of the back surface conductive film 14 is 0.8 or less, it is possible to suppress the adhesion of foreign matter during the mask manufacturing process. More preferably, if the relative surface free energy is 0.5 or less, it is possible to further suppress the adhesion of foreign matter. As a result, the appearance quality of the surface of the back surface conductive film 14 can be improved.
[0028] Here, in the embodiments of this disclosure, "relative surface free energy" means the ratio of the surface free energy of the outermost layer of the back conductive film 14 to the surface free energy of the existing back conductive film material (surface free energy of the outermost layer of the back conductive film 14 / surface free energy of the existing back conductive film material). Furthermore, in the embodiments of this disclosure, "existing back conductive film material" specifically means amorphous tantalum nitride (amorphous TaN). Furthermore, in the embodiments of this disclosure, "amorphous" means a state in which the degree of crystallinity is 10% or less. The degree of crystallinity in the embodiments of this disclosure can be measured, for example, using density method, X-ray diffraction method, infrared method, NMR method, or thermal analysis method.
[0029] Density methods calculate the proportion of crystalline material (crystallinity) by utilizing the density difference between crystalline and amorphous regions. X-ray diffraction calculates the proportion of crystalline material (crystallinity) from the X-ray diffraction pattern. Infrared spectroscopy measures the ratio of the absorption band intensities of crystalline and amorphous regions using infrared spectroscopy. NMR spectroscopy measures the difference in relaxation times between crystalline and amorphous regions using nuclear magnetic resonance (NMR). Thermal analysis calculates the proportion of crystalline material (crystallinity) from the heat of the endothermic peak due to melting.
[0030] In embodiments relating to this disclosure, the contact angle of water and diiodomethane (CH4) is measured using a contact angle meter. ２ I ２ From the contact angle of the back surface conductive film, the surface free energy of the back surface conductive film and the surface free energy of the existing reference back surface conductive film material (specifically amorphous TaN) are measured. From the measured values of each layer obtained in this way, the relative surface free energy of the outermost layer of the back surface conductive film 14 is determined, with the surface free energy of the existing back surface conductive film material set to 1.
[0031] The back surface conductive film 14 may be formed from a material containing at least one selected from hafnium (Hf), zirconium (Zr), gold (Au), indium (In), tin (Sn), and lead (Pb), or from a material consisting only of hafnium (Hf), zirconium (Zr), gold (Au), indium (In), tin (Sn), or lead (Pb). Furthermore, it is more preferable if the back surface conductive film 14 is formed from a material containing at least one selected from indium (In), lead (Pb), and tin (Sn), or from a material consisting only of indium (In), lead (Pb), or tin (Sn), because the relative surface free energy will be 0.5 or less. In the embodiments of this disclosure, an alloy containing elements other than those mentioned above is also acceptable, as long as the relative surface free energy is 0.8 or less. In addition, the relative surface free energy value in the embodiments of this disclosure can be appropriately adjusted by adjusting the content ratio of each of the above-mentioned elements or the combination of each element.
[0032] As described above, in the embodiments of this disclosure, it is sufficient to suppress the adhesion of foreign matter to the surface of the back conductive film 14. Therefore, it is sufficient to have a layer with a lower relative surface free energy than existing tantalum (Ta)-based materials formed on the surface of the back conductive film 14. For example, as shown in Figure 4, the back conductive film 14 consists of two layers (upper layer 16 and lower layer 15) with different physical properties. The upper layer 16 may be formed on the surface of the lower layer 15, which is made of an existing tantalum (Ta)-based material, and is made of a material containing at least one element selected from hafnium (Hf), zirconium (Zr), gold (Au), indium (In), tin (Sn), and lead (Pb), which have a lower relative surface free energy than existing tantalum (Ta)-based materials. In this way, as long as a layer with a lower relative surface free energy than existing tantalum (Ta)-based materials is formed on the surface of the back conductive film 14, the back conductive film 14 may have a multilayer structure or a single-layer structure.
[0033] Furthermore, if the back conductive film 14 has a multilayer structure, the relative surface free energy of each layer constituting the back conductive film 14 may gradually decrease (for example, linearly) in the direction away from the substrate 11, and the layers may be stacked such that the relative surface free energy at the outermost surface of the back conductive film 14 is 0.8 or less. Alternatively, the relative surface free energy of each layer constituting the back conductive film 14 may gradually increase (for example, linearly) in the direction away from the substrate 11, and the layers may be stacked such that the relative surface free energy at the outermost surface of the back conductive film 14 is 0.8 or less.
[0034] Furthermore, if the back conductive film 14 has a multilayer structure, the relative surface free energy of each layer constituting the back conductive film 14 may gradually decrease (for example, exponentially) in the direction away from the substrate 11, and the layers may be stacked such that the relative surface free energy at the outermost surface of the back conductive film 14 is 0.8 or less. Alternatively, the relative surface free energy of each layer constituting the back conductive film 14 may gradually increase (for example, exponentially) in the direction away from the substrate 11, and the layers may be stacked such that the relative surface free energy at the outermost surface of the back conductive film 14 is 0.8 or less. Of course, the relative surface free energy of each layer constituting the back conductive film 14 may be the same as that of the other layers.
[0035] Furthermore, if the back conductive film 14 has a single-layer structure, the content of at least one element selected from hafnium (Hf), zirconium (Zr), gold (Au), indium (In), tin (Sn), and lead (Pb) in the back conductive film 14 may gradually increase (for example, linearly) in the direction away from the substrate 11, and the relative surface free energy at the outermost surface of the back conductive film 14 may be 0.8 or less. Alternatively, the content of at least one element selected from hafnium (Hf), zirconium (Zr), gold (Au), indium (In), tin (Sn), and lead (Pb) in the back conductive film 14 may gradually decrease (for example, linearly) in the direction away from the substrate 11, and the relative surface free energy at the outermost surface of the back conductive film 14 may be 0.8 or less.
[0036] Also, when the back surface conductive film 14 has a single-layer structure, in the direction away from the substrate 11, the content of at least one element selected from hafnium (Hf), zirconium (Zr), gold (Au), indium (In), tin (Sn), and lead (Pb) contained in the back surface conductive film 14 etc. may gradually (e.g., exponentially) increase, and the relative surface free energy may be 0.8 or less at the outermost surface of the back surface conductive film 14. Alternatively, in the direction away from the substrate 11, the content of at least one element selected from hafnium (Hf), zirconium (Zr), gold (Au), indium (In), tin (Sn), and lead (Pb) contained in the back surface conductive film 14 etc. may gradually (e.g., exponentially) decrease, and the relative surface free energy may be 0.8 or less at the outermost surface of the back surface conductive film 14. Of course, in the back surface conductive film 14, there may be no gradient in the content of at least one element selected from hafnium (Hf), zirconium (Zr), gold (Au), indium (In), tin (Sn), and lead (Pb) etc., and the above elements may be uniformly dispersed in the back surface conductive film 14.
[0037] The back surface conductive film 14 is preferable because conduction can be ensured during the electrostatic chucking of the exposure machine without problems if the sheet resistance is 250 Ω / sq or less. That is, the back surface conductive film 14 is more preferably such that the sheet resistance is 250 Ω / sq or less and the relative surface free energy is 0.8 or less. The film thickness of the back surface conductive film 14 may be 10 nm or more. If the film thickness of the back surface conductive film 14 is 10 nm or more, it is preferable because sufficient conductivity can be ensured.
[0038] Also, when the back surface conductive film 14 has a multilayer structure, it is sufficient that the relative surface free energy is 0.8 or less at the outermost surface of the back surface conductive film 14. For example, in the direction away from the substrate 11, the film thickness of each layer constituting the back surface conductive film 14 may gradually (e.g., stepwise) become thinner, and the film thickness of the layer constituting the outermost surface of the back surface conductive film 14 may be the thinnest among the layers constituting the back surface conductive film 14. Alternatively, in the direction away from the substrate 11, the film thickness of each layer constituting the back surface conductive film 14 may gradually (e.g., stepwise) become thicker, and the film thickness of the layer constituting the outermost surface of the back surface conductive film 14 may be the thickest among the layers constituting the back surface conductive film 14.
[0039] (Configuration of Reflective Photomask) Fig. 5 is a schematic cross-sectional view showing the configuration of a reflective photomask (reflective mask) 300 according to an embodiment of the present disclosure. As shown in Fig. 5, the reflective photomask 300 according to the embodiment of the present disclosure is a reflective photomask for pattern transfer using extreme ultraviolet light as a light source, and includes a substrate 11, a reflective portion 12 formed on the substrate 11 to reflect incident light, a low-reflection portion 13 (patterned low-reflection portion 13a) formed on the reflective portion 12 without an intervening other film, and a single-layer backside conductive film 14 formed on the side opposite to the side where the reflective portion 12 of the substrate 11 is formed. Thus, the reflective photomask 300 according to the embodiment of the present disclosure is manufactured by forming a transfer pattern on the low-reflection portion 13 of the reflective photomask blank 100 according to the embodiment of the present disclosure. In Fig. 5, the "low-reflection portion 13 on which the transfer pattern is formed" is conveniently denoted as "13a".
[0040] Fig. 6 is a schematic cross-sectional view showing the configuration of a reflective photomask 400 according to an embodiment of the present disclosure. As shown in Fig. 6, the reflective photomask 400 according to the embodiment of the present disclosure is a reflective photomask for pattern transfer using extreme ultraviolet light as a light source, and includes a substrate 11, a reflective portion 12 formed on the substrate 11 to reflect incident light, a low-reflection portion 13 formed on the reflective portion 12 without an intervening other film, and two-layer backside conductive films 14 having different physical properties formed on the side opposite to the side where the reflective portion 12 of the substrate 11 is formed. The backside conductive film 14 according to the reflective photomask 400 includes a lower layer 15 and an upper layer 16 of the backside conductive film 14. And the lower layer 15 of the backside conductive film 14 is located closer to the substrate 11 side than the upper layer 16 of the backside conductive film 14.
[0041] Furthermore, the reflective photomask 400 according to the embodiment of this disclosure is manufactured by forming a transfer pattern on the low-reflectivity portion 13 of the reflective photomask blank 200 according to the embodiment of this disclosure. In Figure 6, the "low-reflectivity portion 13 on which the transfer pattern is formed" is conveniently denoted as "13a". Thus, the reflective photomask 400 according to the embodiment of this disclosure has a two-layer configuration of the back surface conductive film 14 and corresponds to a modified example of the reflective photomask 300 according to the embodiment of this disclosure.
[0042] Each layer constituting the reflective photomask 300 and reflective photomask 400 according to the embodiments of this disclosure is the same as each layer constituting the reflective photomask blank 100 and reflective photomask blank 200 according to the embodiments of this disclosure described above. Therefore, a detailed explanation of each layer is omitted here.
[0043] (Method for Manufacturing a Reflective Photomask) The methods for manufacturing the reflective photomask 300 and reflective photomask 400 according to the embodiments of this disclosure will be briefly described below. The method for manufacturing the reflective photomask 300 according to the embodiments of this disclosure is a method for manufacturing a reflective photomask using the reflective photomask blank 100 according to the embodiments of this disclosure, and comprises the steps of: forming a reflective portion 12 that reflects incident light on a substrate 11; forming a low-reflection portion 13 on the reflective portion 12, with or without other films; forming a single layer back surface conductive film 14 on the side of the substrate 11 opposite to the side on which the reflective portion 12 is formed; and forming a transfer pattern on the low-reflection portion 13, wherein the surface free energy of the back surface conductive film 14 is 0.8 or less when the surface free energy of amorphous TaN is set to 1.
[0044] Furthermore, the method for manufacturing the reflective photomask 400 according to the embodiment of the present disclosure is a method for manufacturing a reflective photomask using the reflective photomask blank 200 according to the embodiment of the present disclosure, comprising the steps of: forming a reflective portion 12 that reflects incident light on a substrate 11; forming a low-reflectivity portion 13 on the reflective portion 12, with or without other films; forming a multilayer structure (upper layer 16 and lower layer 15) back surface conductive film 14 on the side of the substrate 11 opposite to the side on which the reflective portion 12 is formed; and forming a transfer pattern on the low-reflectivity portion 13, wherein the surface free energy of the back surface conductive film 14 is 0.8 or less when the surface free energy of amorphous TaN is taken as 1.
[0045] [Examples] The following describes the reflective mask blank and reflective mask according to the embodiments of this disclosure.
[0046] (Example 1) A synthetic quartz substrate with low thermal expansion was used as the substrate. Forty multilayer films, each consisting of a pair of silicon (Si) and molybdenum (Mo), were stacked on the substrate to form a multilayer reflective film (reflective portion). The thickness of the multilayer reflective film was set to 280 nm. Next, a protective film (capping layer) was deposited on the multilayer reflective film using ruthenium (Ru) to a thickness of 2.5 nm. An absorption film (low-reflectance portion) of tin oxide (SnO) was deposited on the protective film to a thickness of 40 nm.
[0047] Next, a single-layer back-side conductive film of zirconium nitride (ZrN) was deposited to a thickness of 120 nm on the side of the substrate where the multilayer reflective film was not formed, using a DC sputtering apparatus. The atomic ratio of zirconium (Zr) to nitrogen (N) in the deposited back-side conductive film was measured by XPS (X-ray photoelectron spectroscopy) and was found to be 70.0:30.0. Next, a contact angle meter was used to measure the difference between water and diiodomethane (CH4). ２ I ２ When the surface free energy of the back surface conductive film in Example 1 was measured from the contact angle, the ratio of the surface free energy (relative surface free energy) to the surface free energy (reference value) of the back surface conductive film in Comparative Example 1, described later, which is set to 1, was 0.77.
[0048] Next, surface resistance measurement was performed on the back conductive film in Example 1 using the four-terminal method, and it was found that the sheet resistance value was 250 Ω / □ or less. Since a sheet resistance value of 250 Ω / □ or less does not pose a problem when using a reflective mask, the "conductivity" was evaluated as "acceptable" in this example. Next, a positive-type chemically amplified resist (SEBP9012: manufactured by Shin-Etsu Chemical Co., Ltd.) was deposited on the absorption film to a thickness of 120 nm by spin coating, and baked at 110 degrees for 10 minutes to form a resist film. Then, a predetermined pattern was drawn on the positive-type chemically amplified resist using an electron beam lithography machine (JBX3030: manufactured by JEOL Ltd.). After that, a bake treatment was performed at 110 degrees for 10 minutes, followed by spray development (SFG3000: manufactured by Sigma Meltec Co., Ltd.). This formed the resist pattern.
[0049] Next, using the resist pattern as an etching mask, the absorption film pattern was formed by dry etching mainly with chlorine-based gas. Then, the remaining resist pattern was peeled off. In this way, an absorption film pattern was formed with the surface and sides of the absorption film exposed. Next, the back surface conductive film was washed for 400 seconds using an ozone cleaning solution. After washing, the back surface appearance inspection was performed using an optical inspection machine. As a result of the back surface appearance inspection, the number of foreign objects with a diameter of 10 μm or more was 0, and the total number of foreign objects detected of all sizes was 55. In this embodiment, the "back surface appearance inspection (back surface appearance quality)" was evaluated as "pass" because if the number of foreign objects with a diameter of 10 μm or more on the back surface of the reflective mask (i.e., the surface of the back surface conductive film) is 0, the possibility of contaminating the EUV exposure apparatus when using the reflective mask is extremely low.
[0050] (Example 2) A reflective mask blank of Example 2 was prepared in the same manner as in Example 1, except that a back surface conductive film of hafnium nitride (HfN) was deposited to a thickness of 120 nm on the side of the substrate where the multilayer reflective film was not formed, using a DC sputtering apparatus. The atomic ratio of hafnium (Hf) to nitrogen (N) in the back surface conductive film of the reflective mask blank of Example 2 was measured by XPS (X-ray photoelectron spectroscopy) and found to be 65.0:35.0. Furthermore, when the surface free energy of the back surface conductive film in Example 2 was measured, the ratio of surface free energy (relative surface free energy) to the surface free energy (reference value) of the back surface conductive film in Comparative Example 1, described later, was 0.68. In addition, when the surface resistance of the back surface conductive film in Example 2 was measured using the four-terminal method, it was found that the sheet resistance value was 250 Ω / □ or less. Therefore, the conductivity was satisfactory. Furthermore, in Example 2, the results of the back surface inspection performed after ozone cleaning showed that there were 0 foreign objects with a diameter of 10 μm or more, and a total of 41 foreign objects of all sizes.
[0051] (Example 3) A reflective mask blank of Example 3 was prepared in the same manner as in Example 1, except that a back-side conductive film of gold (Au) was deposited to a thickness of 120 nm on the side of the substrate where the multilayer reflective film was not formed, using a DC sputtering apparatus. The atomic ratio of gold (Au) to other elements in the back-side conductive film of the reflective mask blank of Example 3 was measured by XPS (X-ray photoelectron spectroscopy) and found to be 100.0:0. Furthermore, when the surface free energy of the back-side conductive film in Example 3 was measured, the ratio of surface free energies (relative surface free energy) to the surface free energy (reference value) of the back-side conductive film in Comparative Example 1 (described later) was set to 1 was 0.54. In addition, when the surface resistance of the back-side conductive film in Example 3 was measured using the four-terminal method, it was found that the sheet resistance value was 250 Ω / □ or less. Therefore, the conductivity was satisfactory. Furthermore, in Example 3, the results of the back surface inspection performed after ozone cleaning showed that there were 0 foreign objects with a diameter of 10 μm or more, and a total of 40 foreign objects of all sizes detected.
[0052] (Example 4) On the side of the substrate where the multilayer reflective film is not formed, indium oxide (In ２ O ３ A reflective mask blank of Example 4 was prepared in the same manner as in Example 1, except that a conductive film was deposited on the back surface using a DC sputtering apparatus to a thickness of 120 nm. The atomic ratio of indium (In) to oxygen (O) in the conductive film on the back surface of the reflective mask blank of Example 4 was measured by XPS (X-ray photoelectron spectroscopy) and found to be 38.0:62.0. The surface free energy of the conductive film on the back surface of Example 4 was measured and found to be 0.25 when the surface free energy (reference value) of the conductive film on the back surface of Comparative Example 1 (described later) was set to 1. Surface resistance measurement of the conductive film on the back surface of Example 4 using the four-terminal method revealed that the sheet resistance value was 250 Ω / □ or less. Therefore, the conductivity was satisfactory. In addition, the results of the back surface appearance inspection performed after ozone cleaning in Example 4 showed that there were 0 foreign objects with a diameter of 10 μm or more, and a total of 20 foreign objects of all sizes.
[0053] (Example 5) On the side of the substrate where the multilayer reflective film is not formed, tin oxide (SnO ２A reflective mask blank of Example 5 was prepared in the same manner as in Example 1, except that a conductive film was deposited on the back surface using a DC sputtering apparatus to a thickness of 120 nm. The atomic ratio of tin (Sn) to oxygen (O) in the conductive film on the back surface of the reflective mask blank of Example 5 was measured by XPS (X-ray photoelectron spectroscopy) and found to be 30.0:70.0. The surface free energy of the conductive film on the back surface of Example 5 was measured and found to be 0.27 when the surface free energy (reference value) of the conductive film on the back surface of Comparative Example 1 (described later) was set to 1. Surface resistance measurement of the conductive film on the back surface of Example 5 using the four-terminal method revealed that the sheet resistance value was 250 Ω / □ or less. Therefore, the conductivity was satisfactory. In addition, the results of the back surface appearance inspection performed after ozone cleaning in Example 5 showed that there were 0 foreign objects with a diameter of 10 μm or more, and a total of 22 foreign objects of all sizes.
[0054] (Example 6) On the side of the substrate where the multilayer reflective film is not formed, lead oxide (PbO ２ A reflective mask blank of Example 6 was prepared in the same manner as in Example 1, except that a conductive film was deposited on the back surface using a DC sputtering apparatus to a thickness of 120 nm. The atomic ratio of lead (Pb) to oxygen (O) in the conductive film on the back surface of the reflective mask blank of Example 6 was measured by XPS (X-ray photoelectron spectroscopy) and found to be 32.0:68.0. The surface free energy of the conductive film on the back surface of Example 6 was measured and found to be 0.21 when the surface free energy (reference value) of the conductive film on the back surface of Comparative Example 1 (described later) was set to 1. Surface resistance measurement of the conductive film on the back surface of Example 6 using the four-terminal method revealed that the sheet resistance value was 250 Ω / □ or less. Therefore, the conductivity was satisfactory. In addition, the results of the back surface appearance inspection performed after ozone cleaning in Example 6 showed that there were 0 foreign objects with a diameter of 10 μm or more, and a total of 25 foreign objects of all sizes.
[0055] (Example 7) A reflective mask blank of Example 7 was prepared in the same manner as in Example 1, except that a back surface conductive film of indium tin oxide (ITO) to a thickness of 120 nm was deposited on the side of the substrate where the multilayer reflective film was not formed, using a DC sputtering apparatus. The atomic ratio of indium (In), tin (Sn), and oxygen (O) in the back surface conductive film of the reflective mask blank of Example 7 was measured by XPS (X-ray photoelectron spectroscopy) and found to be 36.0:60.0:4.0. Furthermore, when the surface free energy of the back surface conductive film in Example 7 was measured, the ratio of surface free energy (relative surface free energy) to the surface free energy (reference value) of the back surface conductive film in Comparative Example 1, described later, was 0.26. In addition, when the surface resistance of the back surface conductive film in Example 7 was measured using the four-terminal method, it was found that the sheet resistance value was 250 Ω / □ or less. Therefore, the conductivity was satisfactory. Furthermore, in Example 7, the results of the back surface inspection performed after ozone cleaning showed that there were 0 foreign objects with a diameter of 10 μm or more, and a total of 18 foreign objects of all sizes.
[0056] (Example 8) A reflective mask blank of Example 8 was produced in the same manner as in Example 1, except that on the side where the multilayer reflective film of the substrate was not formed, a lower layer of the back surface conductive film was formed using a DC sputtering apparatus to a thickness of 120 nm of tantalum nitride (TaN), and an upper layer of the back surface conductive film was formed using a DC sputtering apparatus to a thickness of 120 nm of zirconium nitride (ZrN). The atomic number ratio of tantalum (Ta) to nitrogen (N) in the lower layer of the back surface conductive film provided in the reflective mask blank of Example 8 was 70.0:30.0 when measured by XPS (X-ray photoelectron spectroscopy). Also, the atomic number ratio of zirconium (Zr) to nitrogen (N) in the upper layer of the back surface conductive film provided in the reflective mask blank of Example 8 was 70.0:30.0 when measured by XPS (X-ray photoelectron spectroscopy). Moreover, when the surface free energy of the back surface conductive film in Example 8 was measured, the ratio of the surface free energy (relative surface free energy) when the surface free energy of the back surface conductive film in Comparative Example 1 (reference value) described later was set to 1 was 0.78. In addition, when the surface resistance of the back surface conductive film in Example 8 was measured by the four-terminal method, it was found that the sheet resistance value was 250 Ω / □ or less. Therefore, the conductivity was qualified. Also, as a result of the back surface appearance inspection performed after ozone cleaning in Example 8, the number of detected foreign substances with a diameter of 10 μm or more was 0, and the total number of detected foreign substances of all sizes was 48.
[0057] (Example 9) On the side where the multilayer reflective film of the substrate was not formed, a lower layer of the back surface conductive film was formed using a DC sputtering apparatus to a thickness of 120 nm of tantalum nitride (TaN), and indium oxide (In ２ O ３A reflective mask blank of Example 9 was prepared in the same manner as in Example 1, except that the upper layer of the back conductive film was deposited using a DC sputtering apparatus to a thickness of 7 nm. The atomic ratio of tantalum (Ta) to nitrogen (N) in the lower layer of the back conductive film on the reflective mask blank of Example 9 was measured by XPS (X-ray photoelectron spectroscopy) and found to be 70.0:30.0. The atomic ratio of indium (In) to oxygen (O) in the upper layer of the back conductive film on the reflective mask blank of Example 9 was measured by XPS (X-ray photoelectron spectroscopy) and found to be 39.0:61.0. Furthermore, when the surface free energy of the back conductive film in Example 9 was measured, the ratio of surface free energy (relative surface free energy) to the surface free energy (reference value) of the back conductive film in Comparative Example 1, described later, was 0.25. Furthermore, when the surface resistance of the back conductive film in Example 9 was measured using the four-terminal method, it was found that the sheet resistance value was 250 Ω / □ or less. Therefore, the conductivity was satisfactory. In addition, the results of the back surface inspection performed after ozone cleaning in Example 9 showed that there were 0 foreign objects with a diameter of 10 μm or more, and a total of 24 foreign objects of all sizes detected.
[0058] (Example 10) On the side of the substrate where the multilayer reflective film is not formed, tantalum nitride (TaN) is deposited to a thickness of 120 nm as the underlying layer of the back surface conductive film using a DC sputtering apparatus, and tin oxide (SnO ２A reflective mask blank of Example 10 was prepared in the same manner as in Example 1, except that the upper layer of the back conductive film was deposited using a DC sputtering apparatus to a thickness of 7 nm. The atomic ratio of tantalum (Ta) to nitrogen (N) in the lower layer of the back conductive film on the reflective mask blank of Example 10 was measured by XPS (X-ray photoelectron spectroscopy) and found to be 70.0:30.0. The atomic ratio of tin (Sn) to oxygen (O) in the upper layer of the back conductive film on the reflective mask blank of Example 10 was measured by XPS (X-ray photoelectron spectroscopy) and found to be 34.0:66.0. Furthermore, when the surface free energy of the back conductive film in Example 10 was measured, the ratio of surface free energies (relative surface free energy) to the surface free energy (reference value) of the back conductive film in Comparative Example 1 (described later) was 0.27. Furthermore, when surface resistance measurement was performed on the conductive film on the back surface of Example 10 using the four-terminal method, it was found that the sheet resistance value was 250 Ω / □ or less. Therefore, the conductivity was satisfactory. In addition, the results of the back surface appearance inspection performed after ozone cleaning in Example 10 showed that there were 0 foreign objects with a diameter of 10 μm or more, and a total of 21 foreign objects of all sizes detected.
[0059] (Example 11) On the side of the substrate where no multilayer reflective film is formed, chromium oxynitride (CrON) is deposited to a thickness of 120 nm as the underlying layer of the back surface conductive film using a DC sputtering apparatus, and indium oxide (In ２ O ３A reflective mask blank of Example 11 was prepared in the same manner as in Example 1, except that the upper layer of the back conductive film was deposited using a DC sputtering apparatus to a thickness of 7 nm. The atomic ratio of chromium (Cr), oxygen (O), and nitrogen (N) in the lower layer of the back conductive film on the reflective mask blank of Example 11 was measured by XPS (X-ray photoelectron spectroscopy) and was 85.0:5.0:10.0. The atomic ratio of indium (In) and oxygen (O) in the upper layer of the back conductive film on the reflective mask blank of Example 11 was measured by XPS (X-ray photoelectron spectroscopy) and was 39.0:61.0. Furthermore, when the surface free energy of the back conductive film in Example 11 was measured, the ratio of surface free energies (relative surface free energy) to the surface free energy (reference value) of the back conductive film in Comparative Example 1 (described later) was 0.25. Furthermore, when surface resistance measurement was performed on the conductive film on the back surface in Example 11 using the four-terminal method, it was found that the sheet resistance value was 250 Ω / □ or less. Therefore, the conductivity was satisfactory. In addition, the results of the back surface appearance inspection performed after ozone cleaning in Example 11 showed that there were 0 foreign objects with a diameter of 10 μm or more, and a total of 30 foreign objects of all sizes detected.
[0060] (Example 12) A reflective mask blank of Example 12 was prepared in the same manner as in Example 1, except that a lower layer of chromium oxynitride (CrON) to a thickness of 120 nm was deposited on the side of the substrate where the multilayer reflective film was not formed, using a DC sputtering apparatus, and an upper layer of titanium nitride (TiN) to a thickness of 7 nm was deposited on the upper layer of the back surface conductive film using a DC sputtering apparatus. The atomic ratio of chromium (Cr), oxygen (O), and nitrogen (N) in the lower layer of the back surface conductive film on the reflective mask blank of Example 12 was measured by XPS (X-ray photoelectron spectroscopy) and found to be 85.0:5.0:10.0. The atomic ratio of titanium (Ti) to nitrogen (N) in the upper layer of the back surface conductive film on the reflective mask blank of Example 12 was measured by XPS (X-ray photoelectron spectroscopy) and found to be 70.0:30.0. Furthermore, when the surface free energy of the back conductive film in Example 12 was measured, the ratio of the surface free energy (relative surface free energy) to the surface free energy (reference value) of the back conductive film in Comparative Example 1 (described later) was 0.78. In addition, when the surface resistance of the back conductive film in Example 12 was measured using the four-terminal method, it was found that the sheet resistance value was 250 Ω / □ or less. Therefore, the conductivity was satisfactory. Furthermore, in Example 12, the results of the back surface appearance inspection performed after ozone cleaning showed that there were 0 foreign objects with a diameter of 10 μm or more, and a total of 58 foreign objects of all sizes were detected.
[0061] (Example 13) On the side of the substrate where no multilayer reflective film is formed, chromium oxynitride (CrON) is deposited to a thickness of 120 nm as the underlying layer of the back surface conductive film using a DC sputtering apparatus, and aluminum oxide (Al ２ O ３A reflective mask blank of Example 13 was prepared in the same manner as in Example 1, except that the upper layer of the back conductive film was deposited using a DC sputtering apparatus to a thickness of 5 nm. The atomic ratio of chromium (Cr), oxygen (O), and nitrogen (N) in the lower layer of the back conductive film on the reflective mask blank of Example 13 was measured by XPS (X-ray photoelectron spectroscopy) and was 85.0:5.0:10.0. The atomic ratio of aluminum (Al) and oxygen (O) in the upper layer of the back conductive film on the reflective mask blank of Example 13 was measured by XPS (X-ray photoelectron spectroscopy) and was 35.0:65.0. Furthermore, when the surface free energy of the back conductive film in Example 13 was measured, the ratio of surface free energies (relative surface free energy) when the surface free energy of the back conductive film in Comparative Example 1 (described later) was set to 1 was 0.49. Furthermore, when surface resistance measurement was performed on the conductive film on the back surface of Example 13 using the four-terminal method, it was found that the sheet resistance value was greater than 250 Ω / □. Therefore, the conductivity was unsatisfactory. In addition, the results of the back surface appearance inspection performed after ozone cleaning in Example 13 showed that there were 0 foreign objects with a diameter of 10 μm or more, and a total of 38 foreign objects of all sizes were detected.
[0062] (Comparative Example 1) A reflective mask blank of Comparative Example 1 was prepared in the same manner as in Example 1, except that a tantalum nitride (TaN) back surface conductive film was deposited on the side of the substrate where the multilayer reflective film was not formed, to a thickness of 120 nm, using a DC sputtering apparatus. The atomic ratio of tantalum (Ta) to nitrogen (N) in the back surface conductive film of the reflective mask blank of Comparative Example 1 was measured by XPS (X-ray photoelectron spectroscopy) and found to be 70.0:30.0. The surface free energy of the back surface conductive film of Comparative Example 1 was also measured and the measured value was set to 1 (reference value). Furthermore, when the surface resistance of the back surface conductive film of Comparative Example 1 was measured using the four-terminal method, it was found that the sheet resistance value was 250 Ω / □ or less. Therefore, the conductivity was satisfactory. In addition, the results of the back surface appearance inspection performed after ozone cleaning of Comparative Example 1 showed that 72 foreign objects with a diameter of 10 μm or more were detected, and the total number of foreign objects of all sizes detected was 618. In Comparative Example 1, the tantalum nitride (TaN) film formed was in an amorphous state. Specifically, the content of amorphous tantalum nitride (TaN) in the entire back surface conductive film formed in Comparative Example 1 was 55% by mass, as measured by X-ray diffraction.
[0063] (Comparative Example 2) A reflective mask blank of Comparative Example 2 was prepared in the same manner as in Example 1, except that a platinum (Pt) back surface conductive film was deposited to a thickness of 120 nm on the side of the substrate where the multilayer reflective film was not formed, using a DC sputtering apparatus. The atomic ratio of platinum (Pt) to other elements in the back surface conductive film of the reflective mask blank of Comparative Example 2 was measured by XPS (X-ray photoelectron spectroscopy) and found to be 100.0:0. Furthermore, when the surface free energy of the back surface conductive film of Comparative Example 2 was measured, the ratio of the surface free energy (relative surface free energy) to the surface free energy (reference value) of the back surface conductive film of Comparative Example 1 was set to 1, and the ratio was 0.83. In addition, when the surface resistance of the back surface conductive film of Comparative Example 2 was measured using the four-terminal method, it was found that the sheet resistance value was 250 Ω / □ or less. Therefore, the conductivity was satisfactory. Furthermore, in Comparative Example 2, the results of the back surface inspection performed after ozone cleaning showed that 30 foreign objects with a diameter of 10 μm or more were detected, and the total number of foreign objects detected across all sizes was 297.
[0064] These evaluation results are shown in Table 1.
[0065]
[0066] From the results of the above embodiments, it was found that if a reflective photomask blank has a surface free energy of 0.8 or less when the surface free energy of amorphous TaN is set to 1, then foreign matter is less likely to adhere to the surface of the back conductive film during the mask manufacturing process, and the quality of the back surface appearance is improved. Furthermore, it was found that if a reflective photomask has a surface free energy of 0.8 or less when the surface free energy of amorphous TaN is set to 1, then foreign matter is less likely to adhere to the surface of the back conductive film, and even if foreign matter does adhere to the surface of the back conductive film, it can be easily removed by cleaning.
[0067] Furthermore, for example, the present disclosure can take the following configurations: (1) A reflective photomask blank for making a reflective photomask for pattern transfer using extreme ultraviolet light as a light source, comprising: a substrate; a reflective portion formed on the substrate that reflects incident light; a low-reflectivity portion formed on the reflective portion, with or without other films; and a back surface conductive film formed on the side of the substrate opposite to the side on which the reflective portion is formed, wherein the surface free energy of the back surface conductive film is 0.8 or less when the surface free energy of amorphous TaN is set to 1. (2) The reflective photomask blank according to (1) above, wherein the back surface conductive film is made of a material containing at least one selected from Hf, Zr, Au, In, Sn, and Pb. (3) The reflective photomask blank according to (1) or (2) above, wherein the sheet resistance of the back surface conductive film is 250 Ω / □ or less. (4) The reflective photomask blank according to any one of (1) to (3) above, characterized in that the thickness of the back conductive film is 10 nm or more. (5) A reflective photomask for pattern transfer using extreme ultraviolet light as a light source, comprising: a substrate; a reflective portion formed on the substrate that reflects incident light; a low reflective portion formed on the reflective portion, with or without other films; and a back conductive film formed on the side of the substrate opposite to the side on which the reflective portion is formed, characterized in that the surface free energy of the back conductive film is 0.8 or less when the surface free energy of amorphous TaN is set to 1. (6) A method for manufacturing a reflective photomask using the reflective photomask blank according to any one of (1) to (4) above, characterized in that the surface free energy of the back conductive film is 0.8 or less when the surface free energy of amorphous TaN is set to 1.
[0068] The reflective photomask blank and reflective photomask according to this disclosure can be suitably used to form fine patterns by EUV exposure in the manufacturing process of semiconductor integrated circuits and the like.
[0069] 11...Substrate 12...Reflective area 13...Low-reflective area 13a...Transfer pattern 14...Back surface conductive film 15...Underlayer of back surface conductive film 16...Upper layer of back surface conductive film 100...Reflective photomask blank 200...Reflective photomask blank 300...Reflective photomask 400...Reflective photomask X...Stage Y...Reflective mask
Claims
1. A reflective photomask blank for producing a reflective photomask for pattern transfer using extreme ultraviolet light as a light source, comprising: a substrate; a reflective portion formed on the substrate that reflects incident light; a low-reflectivity portion formed on the reflective portion, with or without other films; and a back surface conductive film formed on the side of the substrate opposite to the side on which the reflective portion is formed, wherein the surface free energy of the back surface conductive film is 0.8 or less when the surface free energy of amorphous TaN is set to 1.
2. The reflective photomask blank according to claim 1, characterized in that the back surface conductive film is made of a material containing at least one selected from Hf, Zr, Au, In, Sn, and Pb.
3. The reflective photomask blank according to claim 1 or 2, characterized in that the sheet resistance of the conductive film on the back surface is 250 Ω / □ or less.
4. The reflective photomask blank according to claim 1 or 2, characterized in that the thickness of the conductive film on the back surface is 10 nm or more.
5. A reflective photomask for pattern transfer using extreme ultraviolet light as a light source, comprising: a substrate; a reflective portion formed on the substrate that reflects incident light; a low-reflectivity portion formed on the reflective portion, with or without other films; and a back surface conductive film formed on the side of the substrate opposite to the side on which the reflective portion is formed, wherein the surface free energy of the back surface conductive film is 0.8 or less when the surface free energy of amorphous TaN is set to 1.
6. A method for manufacturing a reflective photomask using the reflective photomask blank described in claim 1 or claim 2, characterized in that the surface free energy of the conductive film on the back surface is 0.8 or less when the surface free energy of amorphous TaN is set to 1.