Reflective photomask blanks and reflective photomasks

Abstract

To provide reflection type photomask blanks and a reflection type photomask having high resistance to a hydrogen radical with improved transferability while suppressing a projection effect to the minimum.SOLUTION: A reflection type photomask blank 10 includes a substrate 1, a reflection part 7 and a low reflection part 8. The low reflection part 8 is a laminate structure body composed of an absorption layer 4 and an outermost surface layer 5. The absorption layer 4 includes one or more kinds selected from a first material group, by 50 atom% or more in total. The outermost surface layer 5 includes one or more kinds selected from a second material group, by 80 atom% or more in total. The first material group includes tin, tellurium, cobalt, nickel, platinum, silver, copper, zinc, and bismuth, and oxide, nitride, and oxynitride thereof. The second material group includes tantalum, aluminum, ruthenium, molybdenum, zirconium, titanium, zinc, indium, and vanadium, and oxide, nitride, and oxynitride thereof.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a reflective photomask and a reflective photomask blank for manufacturing the same.

Background Art

[0002] In the manufacturing process of semiconductor devices, with the miniaturization of semiconductor devices, the requirements for the miniaturization of photolithography technology are increasing. In photolithography, the minimum development dimension of the transfer pattern greatly depends on the wavelength of the exposure light source, and the shorter the wavelength, the smaller the minimum resolution dimension can be. For this reason, in the manufacturing process of semiconductor devices, the exposure light source using the conventional ArF excimer laser light with a wavelength of 193 nm has been replaced by an EUV exposure light source with a wavelength of 13.5 nm.

[0003] Since EUV light has a short wavelength, most substances have high light absorbability. For this reason, a photomask for EUV (EUV mask) is a reflective mask, different from the conventional transmissive mask (see, for example, Patent Document 1 and Patent Document 2). Patent Document 1 discloses that in a reflective exposure mask used for EUV lithography, a multilayer film in which two or more types of material layers are periodically laminated is formed on a base substrate, and a pattern made of a metal film containing nitrogen or a mask pattern composed of a laminated structure of a metal nitride film and a metal film is formed on the multilayer film. Further, Patent Document 2 discloses a reflective EUV mask including, as an absorber film on a multilayer reflective film, a phase control film and a laminated structure in which a high refractive index material layer and a low refractive index material layer are alternately laminated on the phase control film.

[0004] Since refractive optical systems that utilize light transmission cannot be used in EUV lithography as described above, the optical system members of the exposure apparatus are mirrors instead of lenses. For this reason, there is a problem that the incident light and the reflected light on the EUV photomask cannot be designed to be coaxial. Usually, in EUV lithography, a method is adopted in which the optical axis is tilted by 6 degrees from the vertical direction of the EUV photomask to irradiate EUV light, and the reflected light reflected at an angle of minus 6 degrees is irradiated onto the semiconductor substrate. In this way, since EUV lithography tilts the optical axis, there may occur a problem called the "projection effect (shadowing effect)", in which the EUV light incident on the EUV photomask creates a shadow of the pattern (absorbing layer pattern) of the EUV photomask, resulting in deteriorated transfer performance.

[0005] Regarding this problem, Patent Document 1 discloses a method that can reduce the projection effect by adopting a material with an attenuation coefficient k of 0.03 or more for EUV as the material constituting the phase control film and the low refractive index material layer, enabling the formation of an absorber layer with a thinner film thickness (film thickness of 60 nm or less) than before. Also, Patent Document 2 discloses a method of reducing the film thickness and the projection effect by adopting a compound material with high absorbability (attenuation coefficient k) for EUV light for a conventional absorber layer or phase shift film mainly composed of Ta.

[0006] In current EUV exposure apparatuses, hydrogen radical cleaning is often performed to prevent contamination in the chamber due to the mixing of impurities, so-called contamination. Since photomasks are often exposed to a hydrogen radical environment, if the durability against hydrogen radicals is low, the life of the photomask may be shortened. Therefore, photomasks need to be formed of a compound material with high hydrogen radical resistance.

[0007] However, the methods in Patent Document 1 and Patent Document 2 do not mention the hydrogen radical resistance, and it is not clear whether they can withstand long-term use as photomasks. Also, in the method of Patent Document 2, a method of forming a low-reflection film (low-reflection portion) for EUV light on the absorption layer is described, but there is no mention at all about the increase in the projection effect due to the increase in the total film thickness of the absorber layer and the low-reflection film by forming the low-reflection portion, and it is not clear whether it is an EUV photomask with high transferability.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] An object of the present invention is to provide an EUV photomask blank (reflection type photomask blank) and an EUV photomask (reflection type photomask) that have high resistance to hydrogen radicals and improve transferability by minimizing the projection effect.

Means for Solving the Problems

[0010] To achieve the above object, a reflective photomask blank according to one aspect of the present invention includes a substrate, a reflective portion formed on the substrate to reflect incident light, and a low-reflection portion formed on the reflective portion to absorb incident light. The low-reflection portion is at least a two-layer or more stacked structure composed of an absorption layer and a topmost layer. At least one layer of the absorption layer contains 50 atomic% or more in total of one or more selected from the first material group. The topmost layer contains 80 atomic% or more in total of at least one or more selected from the second material group. The first material group is tin (Sn), tellurium (Te), cobalt (Co), nickel (Ni), platinum (Pt), silver (Ag), copper (Cu), zinc (Zn), and bismuth (Bi), and their oxides, nitrides, and oxynitrides. The second material group is tantalum (Ta), aluminum (Al), ruthenium (Ru), molybdenum (Mo), zirconium (Zr), titanium (Ti), zinc (Zn), indium (In), and vanadium (V), and their oxides, nitrides, and oxynitrides, which is characterized by this.

[0011] Further, the absorption layer may be divided into a plurality of layers. Even when it is divided into a plurality of layers, the total film thickness is within the range of 17 nm or more and 47 nm or less, and the OD value (Optical Density) may be 1.0 or more. Further, the film thickness of the low-reflection portion is 60 nm or less, and the film thickness of the topmost layer may be 1.0 nm or more.

[0012] To achieve the above object, a reflective photomask according to one aspect of the present invention includes a substrate, a reflective portion formed on the substrate for reflecting incident light, and a low-reflection portion formed on the reflective portion for absorbing incident light. The low-reflection portion is at least a two-layer or more stacked structure composed of an absorption layer and a topmost layer. At least one layer of the absorption layer contains a total of 50 atomic% or more of one or more selected from the first material group, and the topmost layer contains a total of 80 atomic% or more of at least one or more selected from the second material group. The first material group includes tin (Sn), tellurium (Te), cobalt (Co), nickel (Ni), platinum (Pt), silver (Ag), copper (Cu), zinc (Zn), and bismuth (Bi), as well as their oxides, nitrides, and oxynitrides. The second material group includes tantalum (Ta), aluminum (Al), ruthenium (Ru), molybdenum (Mo), zirconium (Zr), titanium (Ti), zinc (Zn), indium (In), and vanadium (V), as well as their oxides, nitrides, and oxynitrides, and is characterized in that.

Effect of the Invention

[0013] According to one aspect of the present invention, by forming a low-reflection portion composed of a compound material having high absorbency to EUV and a compound material having high hydrogen radical resistance on the outermost layer, the dimensional accuracy and shape accuracy of the pattern transferred onto the wafer are improved, and it becomes possible to use the photomask for a long period of time. That is, according to one aspect of the present invention, it is possible to provide an EUV photomask blank (reflective photomask blank) and an EUV photomask (reflective photomask) that have high resistance to hydrogen radicals and improve transferability by minimizing the projection effect.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0015] Hereinafter, with reference to the drawings, each configuration of the reflective photomask blank and the reflective photomask according to the present invention will be described. FIG. 1 is a schematic cross-sectional view showing a reflective photomask blank 10 according to an embodiment of the present invention. Further, FIG. 2 is a schematic cross-sectional view showing a reflective photomask 20 according to an embodiment of the present invention. Here, the reflective photomask 20 according to the embodiment of the present invention shown in FIG. 2 is formed by patterning a low-reflection portion 8 of the reflective photomask blank 10 according to the embodiment of the present invention shown in FIG. 1.

[0016] (Overall Structure) As shown in FIG. 1, a reflective photomask blank 10 according to an embodiment of the present invention includes a substrate 1, a multilayer reflective film 2 formed on the substrate 1, and a capping layer 3 formed on the multilayer reflective film 2. Accordingly, a reflective portion 7 having the multilayer reflective film 2 and the capping layer 3 is formed on the substrate 1. The reflective photomask blank 10 according to the embodiment of the present invention includes a low-reflection portion 8 on the reflective portion 7. The low-reflection portion 8 is composed of at least two or more layers. One of the layers is an absorption layer 4, and the outermost layer 5 is provided on the absorption layer 4. (Substrate) For the substrate 1 according to the embodiment of the present invention, for example, a flat Si substrate, a synthetic quartz substrate, or the like can be used. Further, a low-thermal-expansion glass added with titanium can be used for the substrate 1. However, as long as the material has a small coefficient of thermal expansion, the present invention is not limited thereto.

[0017] (Reflective portion) (Multilayer reflective film) The multilayer reflective film 2 according to the embodiment of the present invention only needs to be one that reflects EUV light (extreme ultraviolet light), which is exposure light. A multilayer reflective film formed by a combination of materials having significantly different refractive indices for EUV light is preferable. The multilayer reflective film 2 is preferably formed by repeatedly laminating about 40 cycles of layers in a combination such as Mo (molybdenum) and Si (silicon), or Mo (molybdenum) and Be (beryllium).

[0018] (Capping layer) The capping layer 3 according to the embodiment of the present invention is formed of a material having resistance to dry etching performed when forming a pattern on the absorption layer 4, and functions as an etching stopper for preventing damage to the multilayer reflective film 2 when etching and forming a low-reflection portion pattern described later. Here, depending on the material of the multilayer reflective film 2 and the etching conditions, the capping layer 3 may not be provided. Further, although not shown, a backside conductive film can be formed on the surface of the substrate 1 where the multilayer reflective film 2 is not formed. The backside conductive film is a film for fixing the reflective photomask 20 described later to an exposure machine using the principle of an electrostatic chuck.

[0019] Low-reflection portion As shown in FIG. 2, the low-reflection portion 8 according to the embodiment of the present invention is a layer in which a low-reflection portion pattern 8a is formed by removing a part of the low-reflection portion 8 of the reflective photomask blank 10. In EUV lithography, EUV light is incident obliquely and reflected by the reflection portion 7. However, due to the projection effect in which the low-reflection portion pattern 8a obstructs the optical path, the transfer performance onto the wafer may deteriorate. This deterioration of the transfer performance is reduced by thinning the thickness of the low-reflection portion 8 that absorbs EUV light. In order to thin the thickness of the low-reflection portion 8, it is preferable to apply a material having a higher absorbability to EUV light than conventional materials, that is, a material having a high extinction coefficient k with respect to a wavelength of 13.5 nm, to the absorption layer 4.

[0020] <Absorption layer> The extinction coefficient k of tantalum (Ta), which is the main material of the conventional absorption layer 4, is 0.041. If it is a compound material having a larger extinction coefficient k than that, it is possible to reduce the thickness of the absorption layer 4 (low-reflection portion 8) as compared with the conventional case. FIG. 3 shows a graph of the optical constants of tantalum (Ta) and the first material group described later. From FIG. 3, it can be seen that the materials included in the first material group each have a larger extinction coefficient k than the conventional materials and can reduce the projection effect.

[0021] Here, the "first material group" in the present embodiment means a material group composed of tin (Sn), tellurium (Te), cobalt (Co), nickel (Ni), platinum (Pt), silver (Ag), copper (Cu), zinc (Zn), and bismuth (Bi), as well as their oxides, nitrides, and oxynitrides. That is, at least one layer constituting the absorption layer 4 in the present embodiment contains 50 atomic% or more in total of one or more selected from the material group composed of tin (Sn), tellurium (Te), cobalt (Co), nickel (Ni), platinum (Pt), silver (Ag), copper (Cu), zinc (Zn), and bismuth (Bi), as well as their oxides, nitrides, and oxynitrides. Since the materials constituting the first material group have a large attenuation coefficient k, when at least one layer constituting the absorption layer 4 is formed of the materials constituting the first material group, the transfer performance can be improved. Among the first material group, tin (Sn) is particularly preferable because its thermal stability is enhanced by oxidation and it can be easily processed by reactive gases.

[0022] For the absorption layer 4 of the present embodiment, a compound material in which at least one material selected from the above-described first material group is mixed with another material can be used. However, in order to reduce the projection effect, the total film thickness (overall film thickness) of the absorption layer 4 is preferably 47 nm or less. When the total film thickness (overall film thickness) of the absorption layer 4 exceeds 47 nm, pattern transfer may not be improved due to the projection effect. When the total film thickness (overall film thickness) of the absorption layer 4 is less than 17 nm, the OD value may be less than 1, and pattern transfer may not be improved.

[0023] Also, the mixing ratio of the materials constituting the absorption layer 4 of the present embodiment needs to be a mixing ratio calculated so that the OD value is 1 or more in order to maintain a contrast enabling pattern transfer. The lower limit value of the mixing ratio of the materials constituting the absorption layer 4 of the present embodiment cannot be generally determined because it depends on the optical constants of the other materials to be mixed. However, in order to reduce the projection effect compared to the conventional film, it is desirable that the compound material contains at least 50 atomic% or more of the materials constituting the first material group.

[0024] Furthermore, in order to transfer a fine pattern, it is desirable that the contrast in the intensity of the light reflected from the reflection portion 7 and the low reflection portion 8 be high. Therefore, it is more preferable that the OD value of the absorption layer 4 be 1.5 or more. The absorption layer 4 is formed on the capping layer 3, for example, by sputtering. However, for the roughness of the absorption layer pattern after etching, the in-plane dimensional uniformity, or the in-plane uniformity of the transferred image, the film quality of the absorption layer 4 is preferably sufficiently amorphous. Therefore, the absorption layer 4 may be formed of a compound material containing less than 50 atomic% of at least one material selected from boron (B), nitrogen (N), silicon (Si), germanium (Ge), hafnium (Hf), and their oxides, nitrides, and oxynitrides.

[0025] In addition to the first material group, the absorption layer 4 may be formed by mixing another material, for example, for the purpose of improving amorphousness, improving cleaning resistance, preventing mixing, improving the contrast of inspection light, phase shift, etc. Note that the absorption layer 4 may have a single-layer structure or a layer structure divided into a plurality of layers. When the absorption layer 4 has a layer structure divided into a plurality of layers, each layer may be formed with a different composition. For example, the lowermost layer of the absorption layer 4 may be formed of the material having the largest extinction coefficient k among the materials constituting the first material group, and may be laminated so that the extinction coefficient k of the materials constituting the first material group decreases sequentially. Also, the lowermost layer of the absorption layer 4 may be formed of the material having the smallest extinction coefficient k among the materials constituting the first material group, and may be laminated so that the extinction coefficient k of the materials constituting the first material group increases sequentially.

[0026] <Outermost layer> As described above, in an EUV exposure apparatus, since the photomask is often exposed to a hydrogen radical environment, it is necessary to extend the life of the photomask by using a compound material with high hydrogen radical resistance. As shown in FIG. 4, when the hydrogen flow rate is 10 19 at / (cm 2s), and in a hydrogen radical environment excited under the condition that the electrode distance is 18 mm using 40 MHz CCP (Capacitively Coupled Plasma), a compound material with a film reduction rate of 0.1 nm / s or less is used as a material with high hydrogen radical resistance in this embodiment.

[0027] The outermost layer 5 contains at least one or more selected from the second material group described later, totaling 80 atomic% or more. The materials in the second material group are materials that satisfy the conditions as the above-mentioned materials with high radical resistance. The compound material of the outermost layer 5 can be mixed with, for example, another material in addition to the second material group. However, in order not to reduce the radical resistance, it is desirable that the outermost layer 5 is composed of a compound material containing at least 80 atomic% or more of the materials in the second material group.

[0028] Here, the "second material group" in this embodiment means a material group composed of tantalum (Ta), aluminum (Al), ruthenium (Ru), molybdenum (Mo), zirconium (Zr), titanium (Ti), zinc (Zn), indium (In), and vanadium (V), and their oxides, nitrides, and oxynitrides. That is, the outermost layer 5 in this embodiment contains 80 atomic% or more in total of one or more selected from the material group composed of tantalum (Ta), aluminum (Al), ruthenium (Ru), molybdenum (Mo), zirconium (Zr), titanium (Ti), zinc (Zn), indium (In), and vanadium (V), and their oxides, nitrides, and oxynitrides.

[0029] Since the low reflection portion 8 has the combined film thickness of the absorption layer 4 and the outermost layer 5, there is a concern that the projection effect increases. Therefore, it is desirable that the total film thickness of the absorption layer 4 and the outermost layer 5 is 60 nm or less. Further, when a compound material with sufficient hydrogen radical resistance is used as the outermost layer 5, in order to obtain a stable film thickness distribution, the film thickness of the outermost layer 5 is preferably 1.0 nm or more. Also, in order to minimize the shadowing effect, the film thickness of the outermost layer 5 is preferably 10 nm or less.

[0030] The outermost layer 5 is formed on the absorption layer 4, for example, by sputtering. However, due to the roughness of the outermost layer pattern after etching, the in-plane dimensional uniformity, or the in-plane uniformity of the transferred image, the film quality of the outermost layer 5 is preferably sufficiently amorphous. Therefore, the outermost layer 5 may be formed of a compound material containing at least one element selected from boron (B), nitrogen (N), germanium (Ge), hafnium (Hf), and their oxides, nitrides, and oxynitrides in a composition ratio of less than 20%.

[0031] In the absorption layer 4 of the conventional EUV reflective photomask, a compound material mainly composed of Ta has been applied as described above. In this case, to obtain an optical density OD (Equation 1), which is an index representing the contrast of the light intensity between the reflective portion 7 and the low-reflective portion 8, of 1 or more, a film thickness of 40 nm or more is required, and to obtain an OD value of 2 or more, a film thickness of 70 nm or more is required. OD = -log(Ra / Rm) ···(Equation 1)

[0032] In the conventional EUV reflective photomask, as described above, a compound material mainly composed of Ta has a film thickness of 60 nm, the reflectance from the low-reflective portion 8 is about 2%, and when converted to the OD with the reflective portion 7, it is about 1.5. A larger OD value results in better contrast and higher transferability. An OD value > 1 is required for pattern transfer, but compared with the above conventional case, an OD of 1.5 or more is more preferable.

[0033] Hereinafter, examples of the reflective photomask blanks and photomasks according to the present invention will be described with reference to figures and tables. [Example 1] First, a method for manufacturing the reflective photomask blank 100 will be described with reference to FIG. 5. First, as shown in FIG. 5, a multilayer reflective film 12 is formed by laminating 40 pairs of a laminated film of silicon (Si) and molybdenum (Mo) on a substrate 11 of synthetic quartz having low thermal expansion characteristics. The film thickness of the multilayer reflective film 12 was set to 280 nm. In FIG. 5, for simplicity, the multilayer reflective film 12 is illustrated as several pairs of laminated films. Next, a capping layer 13 made of ruthenium (Ru) as an intermediate film was formed on the multilayer reflective film 12 so that its film thickness became 2.5 nm. As a result, a reflective portion 17 having the multilayer reflective film 12 and the capping layer 13 was formed on the substrate 11.

[0034] Next, an absorption layer 14 made of tin oxide (SnO) was formed on the capping layer 13 so that its film thickness became 25 nm. The atomic number ratio of tin (Sn) to oxygen (O) was 1:1.6 as measured by XPS (X-ray photoelectron spectroscopy). Note that for chemical stabilization, it is preferable that Sn is bonded with O / Sn > 1. Further, when the crystallinity of the absorption layer 14 was measured by XRD (X-ray diffractometer), it was found to be amorphous although slight crystallinity was observed.

[0035] Next, the outermost layer 15 made of tantalum oxide (TaO) was formed on the absorption layer 14 so that its film thickness became 2 nm. As a result, a low-reflection portion 18 having the absorption layer 14 and the outermost layer 15 was formed on the reflective portion 17. Next, a back surface conductive film 16 made of chromium nitride (CrN) was formed to a thickness of 100 nm on the side of the substrate 11 where the multilayer reflective film 12 was not formed, and the reflective type photomask blank 100 of Example 1 was manufactured. For forming each film (layer formation) on the substrate 11, a multi-source sputtering apparatus was used. The film thickness of each film was controlled by the sputtering time.

[0036] Next, a method for manufacturing the reflective type photomask 200 will be described with reference to FIGS. 6 to 9. First, as shown in FIG. 6, a positive chemically amplified resist (SEBP9012: manufactured by Shin-Etsu Chemical Co., Ltd.) was spin-coated to a film thickness of 120 nm on the low-reflection portion 18 provided in the reflective type photomask blank 100, and baked at 110° C. for 10 minutes to form a resist film 19. Next, a predetermined pattern was drawn on a resist film 19 formed of a positive chemically amplified resist using an electron beam lithography machine (JBX3030, manufactured by JEOL Ltd.). Thereafter, a baking treatment was performed at 110°C for 10 minutes, and then spray development (SFG3000, manufactured by Sigma Meltech Co., Ltd.) was carried out. As a result, a resist pattern 19a was formed as shown in FIG. 7.

[0037] Next, using the resist pattern 19a as an etching mask, dry etching mainly using a fluorine-based gas was performed to pattern the outermost layer 15, and an outermost layer pattern was formed on the outermost layer 15 as shown in FIG. 8. Next, dry etching mainly using a chlorine-based gas was performed to pattern the absorption layer 14, and an absorption layer pattern was formed. As a result, a low reflection portion pattern 18a was formed as shown in FIG. 9. Next, the remaining resist pattern 19a was removed, and a reflective photomask 200 according to this example was fabricated.

[0038] Next, it was immersed in sulfuric acid at 80°C for 10 minutes, and then immersed in a cleaning solution prepared by mixing ammonia, hydrogen peroxide water, and water at a ratio of 1:1:20 for 10 minutes using 500 W of megasonic, and rinsed with running water for 10 minutes for cleaning. In this example, the film thickness was measured by AFM and compared with the film thickness during film formation, but no change was observed. Note that, as the cleaning resistance required for the photomask in this example, a material and structure with a film thickness reduction amount of 1 nm or less by the above cleaning process are considered to have high cleaning resistance.

[0039] In this example, the low reflection portion pattern 18a formed in the low reflection portion 18 includes a line width 64 nm LS (line and space) pattern, a line width 200 nm LS pattern for measuring the film thickness of the absorption layer using AFM, and a 4 mm square low reflection portion removal portion for EUV reflectivity measurement on the reflective photomask 200 for transfer evaluation. In this example, the line width 64 nm LS pattern was designed in the x direction and the y direction as shown in FIG. 10 so that the influence of the projection effect by EUV irradiation could be more easily seen.

[0040] [Example 2] The absorption layer 14 was formed of a compound material in which tin oxide (SnO) and silicon oxide (SiO) were homogeneous at a ratio of 50:50, and the film was formed so that its film thickness became 47 nm. Silicon oxide (SiO) was selected because it has high transparency to EUV light, that is, it is the compound material with the lowest EUV absorption among the first material group described above. Next, on the absorption layer 14, the outermost layer 15 formed of tantalum oxide (TaO) was formed so that its film thickness became 1.5 nm. As a result, the total film thickness of the low reflection portion 18 became 48.5 nm. In addition, except for the film formation of each of the absorption layer 14 and the outermost layer 15, the reflective photomask blank 100 and the reflective photomask 200 of Example 2 were produced by the same method as in Example 1.

[0041] [Example 3] The absorption layer 14 was formed of a compound material in which tin oxide (SnO) and silicon oxide (SiO) were homogeneous at a ratio of 50:50, and the film was formed so that its film thickness became 47 nm. Next, on the absorption layer 14, the outermost layer 15 formed of molybdenum (Mo) was formed so that its film thickness became 13 nm. As a result, the total film thickness of the low reflection portion 18 became 60 nm. In addition, except for the film formation of each of the absorption layer 14 and the outermost layer 15, the reflective photomask blank 100 and the reflective photomask 200 of Example 3 were produced by the same method as in Example 1.

[0042] [Example 4] The absorption layer 14 was formed of tin oxide (SnO), and the film was formed so that its film thickness became 17 nm. Next, on the absorption layer 14, the outermost layer 15 formed of tantalum oxide (TaO) was formed so that its film thickness became 1.5 nm. As a result, the total film thickness of the low reflection portion 18 became 18.5 nm. In addition, except for the film formation of each of the absorption layer 14 and the outermost layer 15, the reflective photomask blank 100 and the reflective photomask 200 of Example 4 were produced by the same method as in Example 1.

[0043] [Example 5] The absorption layer 14 was formed of a compound material in which tin oxide (SnO) and silicon oxide (SiO) were homogeneous at a ratio of 50:50, and a film was formed so that its film thickness became 35 nm. Next, on the absorption layer 14, the outermost layer 15 formed of tantalum oxide (TaO) was formed so that its film thickness became 1.5 nm. As a result, the total film thickness of the low reflection portion 18 became 36.5 nm. In addition, except for the film formation of each of the absorption layer 14 and the outermost layer 15, the reflective photomask blank 100 and the reflective photomask 200 of Example 5 were produced in the same manner as in Example 1.

[0044] [Example 6] The absorption layer 14 was formed of tin oxide (SnO), and a film was formed so that its film thickness became 16 nm. Next, on the absorption layer 14, the outermost layer 15 formed of tantalum oxide (TaO) was formed so that its film thickness became 0.8 nm. As a result, the total film thickness of the low reflection portion 18 became 16.8 nm. In addition, except for the film formation of each of the absorption layer 14 and the outermost layer 15, the reflective photomask blank 100 and the reflective photomask 200 of Example 6 were produced in the same manner as in Example 1.

[0045] [Example 7] The absorption layer 14 was formed of tin oxide (SnO), and a film was formed so that its film thickness became 17 nm. Next, on the absorption layer 14, the outermost layer 15 formed of tantalum oxide (TaO) was formed so that its film thickness became 0.8 nm. As a result, the total film thickness of the low reflection portion 18 became 17.8 nm. In addition, except for the film formation of each of the absorption layer 14 and the outermost layer 15, the reflective photomask blank 100 and the reflective photomask 200 of Example 7 were produced in the same manner as in Example 1.

[0046] [Comparative Example 1] The absorption layer 14 was formed of tantalum nitride (TaN) and deposited to a film thickness of 58 nm. Also, the outermost layer 15 was formed of tantalum oxide (TaO) and deposited to a film thickness of 2 nm. This comparative example assumes a reflective photomask of an existing film mainly composed of conventional tantalum (Ta). Note that, except for the film formation of the absorption layer 14 and the outermost layer 15, the reflective photomask blanks 100 and the reflective photomasks 200 of Comparative Example 1 were fabricated in the same manner as in Example 1.

[0047] [Comparative Example 2] The absorption layer 14 was formed of a compound material in which tin oxide (SnO) and silicon oxide (SiO) are homogeneous at a ratio of 40:60, and deposited to a film thickness of 42 nm. Next, on the absorption layer 14, the outermost layer 15 formed of tantalum oxide (TaO) was deposited to a film thickness of 1.5 nm. As a result, the total film thickness of the low reflection portion 18 became 43.5 nm. Note that, except for the film formation of the absorption layer 14 and the outermost layer 15, the reflective photomask blanks 100 and the reflective photomasks 200 of Comparative Example 2 were fabricated in the same manner as in Example 1.

[0048] [Comparative Example 3] The absorption layer 14 was formed of tin oxide (SnO) and deposited to a film thickness of 25 nm. Also, the outermost layer 15 was not formed. Note that, except for that, the reflective photomask blanks 100 and the reflective photomasks 200 of Comparative Example 3 were fabricated in the same manner as in Example 1. The reflectance Rm in the reflection layer region and the reflectance Ra in the low reflection portion region of each of the reflective photomasks 200 fabricated in the above-described Examples and Comparative Examples were measured using a reflectance measuring apparatus for EUV light. The measurement of the reflectance Rm was performed in the absorption layer removal portion with a 4 mm square. From the measurement results, the OD value was calculated using the above-described formula (1).

[0049] (Hydrogen Radical Resistance) As shown in FIG. 4, using a 40 MHz CCP (Capacitively Coupled Plasma), a flow rate of 10 19 at / (cm 2The hydrogen in (s) was excited in chamber 300 to generate hydrogen plasma, and each reflective photomask 200 fabricated in the examples and comparative examples, which is sample 302, was placed on one of the electrodes 301 with an electrode - to - electrode distance of 18 mm, and the hydrogen radical resistance of each sample 302 was measured. The measurement of the hydrogen radical resistance was performed by confirming the film - thickness change of the low - reflection portion 18 after hydrogen radical treatment using an atomic force microscope (AFM). Also, the measurement of the hydrogen radical resistance was performed using a 200 - nm line - width LS pattern.

[0050] (Wafer Exposure Evaluation) Using an EUV exposure apparatus (NXE3300B, manufactured by ASML), the low - reflection portion pattern 18a of each reflective photomask 200 fabricated in the examples and comparative examples was transferred and exposed onto a semiconductor wafer coated with an EUV positive - type chemically amplified resist. At this time, the exposure dose was adjusted so that the LS pattern in the x - direction shown in FIG. 10 was transferred as designed. Specifically, in this exposure test, the LS pattern (line - width 64 nm) in the x - direction shown in FIG. 10 was exposed so that the line - width on the semiconductor wafer was 16 nm. The transferred resist pattern was observed and the line - width was measured using an electron - beam dimensional measurement machine to confirm the resolution. The results of these evaluations are shown in Table 1.

[0051]

Table 1

[0052] In Table 1, in Comparative Example 1, the absorption layer 14 is formed of tantalum nitride (TaN) with a film - thickness of 58 nm, and the outermost layer 15 is formed of tantalum oxide (TaO) with a film - thickness of 2 nm. The mask characteristics of the reflective photomask 200 equipped with a tantalum (Ta) - based existing film and the resist pattern dimensions on the wafer are shown. The resist pattern dimensions on the wafer are the numerical values described as "H - V bias" in the "Pattern Transferability" column.

[0053] In the case of the reflective photomask 200 of Comparative Example 1, the OD value was 1.5, and a contrast enabling pattern transfer was obtained. Further, as a result of patterning with EUV light, the pattern dimension in the y direction was 9 nm, and the H-V bias (horizontal-vertical dimension difference) was 7 nm, enabling resolution but resulting in a low transferability due to a large influence of the shadowing effect. In this example, conditions of materials and structures having a bias value smaller than the H-V bias of the existing tantalum (Ta)-based film are defined as conditions with improved transferability.

[0054] In Table 1, in Example 1, the absorption layer 14 is formed of tin oxide (SnO) with a film thickness of 25 nm, and the outermost layer 15 is formed of tantalum oxide (TaO) with a film thickness of 2 nm, showing the mask characteristics of the reflective photomask 200 provided with the low-reflection portion 18 and the resist pattern dimensions on the wafer. In the case of the reflective photomask 200 of Example 1, no film thickness change was observed with respect to hydrogen radicals, resulting in good results. The OD value was 2.0, providing a sufficiently high contrast. As a result of patterning with EUV light, the H-V bias was 4 nm, which was the best result among those evaluated this time.

[0055] In Table 1, in Example 2, the absorption layer 14 is formed of a compound material (mixing ratio 1:1) of tin oxide (SnO) and silicon oxide (SiO) with a film thickness of 47 nm, and the outermost layer 15 is formed of tantalum oxide (TaO) with a film thickness of 1.5 nm, showing the mask characteristics of the reflective photomask 200 provided with the low-reflection portion 18 and the resist pattern dimensions on the wafer. In the case of the reflective photomask 200 of Example 2, no film thickness change was observed with respect to hydrogen radicals, resulting in good results. The OD value was 1.7, providing a sufficient contrast. Silicon oxide (SiO) is a material with low absorption with respect to EUV light, and the mixing ratio is also 1:1, i.e., the content of the material in the first material group is 50 atomic%, but a sufficient contrast was obtained with a film thickness of 47 nm. As a result of patterning with EUV light, the H-V bias was 5 nm, and compared with Comparative Example 1, the effect of shadowing was reduced and the pattern transferability was improved.

[0056] In Table 1, in Example 3, the absorption layer 14 is formed of a compound material (mixing ratio 1:1) of tin oxide (SnO) and silicon oxide (SiO), its film thickness is 47 nm, the outermost layer 15 is formed of molybdenum (Mo), and its film thickness is 13 nm. The mask characteristics of the reflective photomask 200 having the low reflection portion 18 and the resist pattern dimensions on the wafer are shown. In the case of the reflective photomask 200 of Example 3, no film thickness change was observed for hydrogen radicals. The OD value was 1.6, which was sufficient contrast. As a result of patterning with EUV light, the H-V bias was 6 nm and patterning was possible. When the film thicknesses of the absorption layer 14 and the outermost layer 15 were totaled, the film thickness of the low reflection portion 18 was 60 nm. However, by combining the compound material of the absorption layer 14 and the material of the outermost layer 15, the effect of shadowing could be reduced and the pattern transferability could be improved.

[0057] In Table 1, in Example 4, the absorption layer 14 is formed of tin oxide (SnO), its film thickness is 17 nm, the outermost layer 15 is formed of tantalum oxide (TaO), and its film thickness is 1.5 nm. The mask characteristics of the reflective photomask 200 having the low reflection portion 18 and the resist pattern dimensions on the wafer are shown. In the case of the reflective photomask 200 of Example 4, no film thickness change was observed for hydrogen radicals. The OD value was 1.0. As a result of patterning with EUV light, the H-V bias was 6 nm and patterning was possible.

[0058] In Table 1, in Example 5, the absorption layer 14 is formed of a compound material (mixing ratio 1:1) of tin oxide (SnO) and silicon oxide (SiO), its film thickness is 35 nm, the outermost layer 15 is formed of tantalum oxide (TaO), and its film thickness is 1.5 nm. The mask characteristics of the reflective photomask 200 having the low reflection portion 18 and the resist pattern dimensions on the wafer are shown. In the case of the reflective photomask 200 of Example 5, no change in film thickness was observed for hydrogen radicals. The OD value was 1.0. As a result of patterning with EUV light, the H-V bias was able to transfer the pattern at 6 nm. From this result, it was found that in the case of the absorption layer 14 with the content of the material in the first material group being 50 atomic %, its film thickness could be thinned to 35 nm.

[0059] In Table 1, in Example 6, the absorption layer 14 was formed of tin oxide (SnO) with a film thickness of 16 nm, and the outermost layer 15 was formed of tantalum oxide (TaO) with a film thickness of 0.8 nm. The mask characteristics of the reflective photomask 200 provided with the low-reflection portion 18 and the resist pattern dimensions on the wafer are shown. In the case of the reflective photomask 200 of Example 6, a slight change in film thickness was observed for hydrogen radicals. The film thickness of the outermost layer 15 was thin, and uniform film formation could not be achieved. It is considered that the absorption layer was selectively thinned due to film formation unevenness. The OD value was 0.99, which was not sufficient as a transferable contrast. As a result of patterning with EUV light, the H-V bias was able to transfer the pattern at 6 nm, but due to the lack of contrast, the line edge roughness increased.

[0060] In Table 1, in Example 7, the absorption layer 14 was formed of tin oxide (SnO) with a film thickness of 17 nm, and the outermost layer 15 was formed of tantalum oxide (TaO) with a film thickness of 0.8 nm. The mask characteristics of the reflective photomask 200 provided with the low-reflection portion 18 and the resist pattern dimensions on the wafer are shown. In the case of the reflective photomask 200 of Example 7, a slight change in film thickness similar to that in Example 6 was observed for hydrogen radicals. The OD value was 1.0. As a result of patterning with EUV light, the H-V bias was able to transfer the pattern at 6 nm. Since the contrast was higher than that in Example 6, no deterioration of the line edge roughness was observed.

[0061] In Table 1, in Comparative Example 2, the absorption layer 14 is formed of a compound material (mixing ratio 2:3) of tin oxide (SnO) and silicon oxide (SiO), its film thickness is 42 nm, and the outermost layer 15 is formed of tantalum oxide (TaO) with a film thickness of 1.5 nm. The mask characteristics of the reflective photomask 200 provided with the low reflection portion 18 and the resist pattern dimensions on the wafer are shown. In the case of the reflective photomask 200 of Comparative Example 2, the OD value was 1.0. As a result of patterning with EUV light, no transfer occurred in the y direction. When the content ratio of the first material group was less than 50 atomic%, sufficient contrast could not be obtained without increasing the film thickness of the absorption layer 14. When the film thickness was increased to obtain contrast, the projection effect increased and the transferability deteriorated. Note that the evaluation of hydrogen radical resistance was not performed.

[0062] In Table 1, in Comparative Example 3, the absorption layer 14 is formed of tin oxide (SnO) with a film thickness of 25 nm, and the mask characteristics of the reflective photomask 200 without forming the outermost layer 15 and the resist pattern dimensions on the wafer are shown. In the case of the reflective photomask 200 of Comparative Example 2, an OD value of 1.7 provided sufficient contrast. As a result of patterning with EUV light, the H-V bias was 4 nm and high transferability was obtained. However, as a result of the hydrogen radical resistance evaluation, a change in film thickness was observed before and after the treatment.

[0063] In Table 1, each evaluation result is marked with "○" when it is evaluated to have excellent characteristics, "△" when it is evaluated to have characteristics without problems in use, and "×" when it is evaluated to have problems with that characteristic in use. Comparing Examples 1 to 5 with the existing film (Comparative Example 1), it is clear that the hydrogen radical resistance is comparable and the pattern transferability is improved. Also, comparing Examples 1 to 7 with Comparative Example 3, it is clear that the low reflection portion 18 formed of a material containing at least one kind from the second material group has higher hydrogen radical resistance than the low reflection portion 18 formed only of the absorption layer 14.

[0064] Also, in any of the reflective photomasks 200 of Examples 1 to 7 and Comparative Examples 1 to 3 in Table 1, there was no change in film thickness before and after the cleaning treatment, and the cleaning resistance was high. Thus, it is clear that the reflective photomask 200 formed with the outermost layer 15 containing 80 atomic % or more of the compound material composed of the second material group on the absorption layer 14 containing 50 atomic % or more of the compound material composed of the first material group is excellent in transferability and hydrogen radical resistance, reduces the projection effect, and is a reflective photomask with a long lifespan and high transfer performance.

Industrial Applicability

[0065] The reflective photomask blanks and reflective photomasks according to the present invention can be suitably used for forming fine patterns by EUV exposure in manufacturing processes such as semiconductor integrated circuits.

Explanation of Reference Numerals

[0066] 1... Substrate 2... Multilayer reflective film 3... Capping layer 4... Absorption layer 5... Outermost layer 7... Reflective portion 8... Low-reflection portion 8a... Low-reflection portion pattern 10... Reflective photomask blank 20... Reflective photomask 11... Substrate 12... Multilayer reflective film 13... Capping layer 14... Absorption layer 15... Outermost layer 16... Backside conductive film 17... Reflective portion 18... Low-reflection portion 18a... Low-reflection portion pattern 19... Resist film 19a... Resist pattern 100... Reflective photomask blank 200... Reflective photomask 300... Chamber 301... Electrode 302... Sample

Claims

1. A substrate, a reflective portion formed on the substrate for reflecting incident light, and a low-reflection portion formed on the reflective portion for absorbing incident light, wherein the low-reflection portion is at least a two-layer or more laminated structure composed of an absorption layer and a topmost layer, at least one layer of the absorption layer contains 50 atomic% or more in total of one or more selected from the first material group, the topmost layer contains 80 atomic% or more in total of at least one or more selected from the second material group, the first material group is tellurium (Te), cobalt (Co), copper (Cu), zinc (Zn), and bismuth (Bi), and their oxides, nitrides, and oxynitrides, the second material group is tantalum (Ta), aluminum (Al), ruthenium (Ru), molybdenum (Mo), zirconium (Zr), titanium (Ti), zinc (Zn), indium (In), and vanadium (V), and their oxides, nitrides, and oxynitrides, characterized by a reflective photomask blank.

2. A substrate, a reflective portion formed on the substrate for reflecting incident light, and a low-reflection portion formed on the reflective portion for absorbing incident light, wherein the low-reflection portion is at least a two-layer or more laminated structure composed of an absorption layer and a topmost layer, at least one layer of the absorption layer contains 50 atomic% or more in total of one or more selected from the first material group, the topmost layer contains 80 atomic% or more in total of at least one or more selected from the second material group, the first material group is tin (Sn), tellurium (Te), cobalt (Co), nickel (Ni), platinum (Pt), silver (Ag), copper (Cu), zinc (Zn), and bismuth (Bi), and their oxides, nitrides, and oxynitrides, The second material group is characterized by being aluminum (Al), ruthenium (Ru), molybdenum (Mo), zirconium (Zr), titanium (Ti), indium (In), and vanadium (V), and their oxides, nitrides, and oxynitrides, for a reflective photomask blank.

3. The first material group is tellurium (Te), cobalt (Co), and copper (Cu), and their oxides, nitrides, and oxynitrides, The second material group is ruthenium (Ru), molybdenum (Mo), zirconium (Zr), titanium (Ti), indium (In), and vanadium (V), and their oxides, nitrides, and oxynitrides, for the reflective photomask blank according to claim 1 or claim 2.

4. The absorption layer is formed of only tin oxide, or only tin oxide and silicon oxide, The outermost layer is formed of only molybdenum, for the reflective photomask blank according to claim 2.

5. The absorption layer is formed of only tin oxide and silicon oxide, The outermost layer is formed of only molybdenum, for the reflective photomask blank according to claim 2.

6. The absorption layer has a total film thickness in the range of 17 nm or more and 47 nm or less, and an OD value (Optical Density) of 1.0 or more, for the reflective photomask blank according to any one of claims 1 to 5.

7. The film thickness of the low reflection portion is 60 nm or less, and the film thickness of the outermost layer is 1.0 nm or more, for the reflective photomask blank according to any one of claims 1 to 6.

8. A substrate, A reflective portion formed on the substrate to reflect incident light, a low-reflection portion formed on the reflection portion to absorb incident light; The low-reflection portion is at least a two-layer or more stacked structure composed of an absorption layer and a topmost layer; At least one layer of the absorption layer contains 50 atomic% or more in total of one or more selected from the first material group; The topmost layer contains 80 atomic% or more in total of at least one or more selected from the second material group; The first material group is tellurium (Te), cobalt (Co), copper (Cu), zinc (Zn), and bismuth (Bi), and their oxides, nitrides, and oxynitrides; The second material group is tantalum (Ta), aluminum (Al), ruthenium (Ru), molybdenum (Mo), zirconium (Zr), titanium (Ti), zinc (Zn), indium (In), and vanadium (V), and their oxides, nitrides, and oxynitrides, and a reflective photomask characterized by this.

9. a substrate; a reflection portion formed on the substrate to reflect incident light; a low-reflection portion formed on the reflection portion to absorb incident light; The low-reflection portion is at least a two-layer or more stacked structure composed of an absorption layer and a topmost layer; At least one layer of the absorption layer contains 50 atomic% or more in total of one or more selected from the first material group; The topmost layer contains 80 atomic% or more in total of at least one or more selected from the second material group; The first material group is tin (Sn), tellurium (Te), cobalt (Co), nickel (Ni), platinum (Pt), silver (Ag), copper (Cu), zinc (Zn), and bismuth (Bi), and their oxides, nitrides, and oxynitrides; The second material group is aluminum (Al), ruthenium (Ru), molybdenum (Mo), zirconium (Zr), titanium (Ti), indium (In), and vanadium (V), and their oxides, nitrides, and oxynitrides, and is characterized by a reflective photomask.

10. The first material group is tellurium (Te), cobalt (Co), and copper (Cu), and their oxides, nitrides, and oxynitrides, The second material group is ruthenium (Ru), molybdenum (Mo), zirconium (Zr), titanium (Ti), indium (In), and vanadium (V), and their oxides, nitrides, and oxynitrides, and is characterized by the reflective photomask according to claim 8 or claim 9.

11. The absorption layer is formed of only tin oxide, or only tin oxide and silicon oxide, The outermost layer is formed of only molybdenum, and is characterized by the reflective photomask according to claim 9.

12. The absorption layer is formed of only tin oxide and silicon oxide, The outermost layer is formed of only molybdenum, and is characterized by the reflective photomask according to claim 9.

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