Reverse Photomask that Phase-Shift Film Pattern is used for Reflective pattern, and Blankmask for manufacturing the same

Abstract

In a reverse photomask, the hole pattern of the photomask functions as a light-blocking pattern and the dot pattern functions as a reflection pattern. A reverse blank mask for fabricating a reverse photomask includes a reflective film formed on a substrate and a phase inversion film formed on the reflective film. The phase inversion film has a relative reflectance with respect to the reflective film exceeding 15% for EUV exposure light of a wavelength of 13.5 nm, a phase inversion amount of 110-150° or 220-250°, and a thickness of less than 45 nm. When a wafer with a negative photoresist applied is exposed using the reverse photomask, the hole and dot patterns of the photomask form hole and dot patterns on the wafer, respectively.

Description

Technology Field

[0001] The present invention relates to a blank mask and a photomask, and more specifically, to a reverse photomask in which a phase inversion film pattern is used as a reflection pattern, and a blank mask for producing the same. Background Technology

[0003] Blank masks used in EUV lithography generally consist of two thin films on a substrate: a reflective film that reflects EUV light and an absorbing film that absorbs EUV light. Recently, phase-inversion blank masks capable of achieving higher resolution compared to binary blank masks equipped with such absorbing films are being developed. Phase-inversion blank masks have a higher Normalized Image Log Slope (NILS) compared to binary blank masks, which can reduce stochastic defects caused by the Shot Noise Effect during wafer printing. Additionally, phase-inversion blank masks enable the realization of a low Dose to Space (DtS), thereby increasing semiconductor productivity.

[0004] FIG. 1 is a diagram illustrating the basic structure of a phase inversion blank mask for extreme ultraviolet lithography. The phase inversion blank mask for extreme ultraviolet lithography comprises a substrate (102), a reflective film (104) formed on the substrate (102), a capping film (105) formed on the reflective film (104), a phase inversion film (108) formed on the capping film (105), and a resist film (120) formed on the phase inversion film (108).

[0005] FIG. 2 is a drawing illustrating a photomask fabricated using the blank mask of FIG. 1. After patterning the resist film (120) of the blank mask of FIG. 1, the phase inversion film (108) is patterned using the patterned resist film (120) as an etching mask. Then, by removing the pattern of the resist film (120) on the phase inversion film (108), the fabrication of a photomask in which a phase inversion film pattern (108a) and a reflective film pattern (104a) are formed is completed. When EUV exposure light is incident on this photomask, the incident light incident on the reflective film pattern (104a) is reflected and irradiated onto the wafer, and the incident light incident on the phase inversion film pattern (108a) is irradiated onto the wafer after a significant portion is extinguished by destructive interference. The photoresist on the wafer is patterned by the contrast difference of the reflected light irradiated onto the wafer.

[0006] FIGS. 3 to 6 are drawings sequentially illustrating the process of patterning a wafer using the photomask of FIG. 2, and in particular, drawings showing the process of patterning a wafer (W) in which a positive photoresist (positive PR) is employed.

[0007] In the examples of FIGS. 3 to 6, for convenience of illustration and explanation, only parts of the reflective film (104) and the phase inversion film pattern (108a) among the thin films of the photomask of FIG. 2 are illustrated, and the incident light incident on the photomask is omitted from illustration, and only the reflected light is illustrated. In FIG. 3, the dot portion protruding for patterning on the photomask, i.e., the phase inversion film pattern (108a), is labeled as d1, and the recessed portion, i.e., the hole portion where the phase inversion film (108) is removed and the reflective film (104) is exposed, is labeled as h1. In FIG. 6, the dot portion protruding from the pattern after the wafer (W) patterning is completed is labeled as d2, and the recessed hole portion is labeled as h2.

[0008] As shown in FIG. 3, EUV exposure light is reflected from a photomask and irradiated onto a wafer (W). At this time, the EUV exposure light is reflected in the hole (h1) portion where a reflective film pattern (104a) is formed and blocked in the dot (d1) portion where a phase inversion film pattern (108a) is formed. As the patterned reflected light is irradiated onto the wafer (W), the regions of the positive resist exposed to the reflected light are removed as shown in FIG. 4, and the positive resist is patterned. The wafer (W) is etched using the patterned positive resist as an etching mask as shown in FIG. 5, and the positive photoresist is removed after the etching is completed, thereby obtaining a patterned wafer (W) as shown in FIG. 6.

[0009] FIGS. 7 to 10 are drawings sequentially illustrating the process of patterning a wafer using the photomask of FIG. 2, and in particular, drawings showing the process of patterning a wafer (W) in which a negative photoresist (negative PR) is employed.

[0010] When a negative photoresist is used as in FIG. 7, the areas of the negative photoresist exposed to reflected light as in FIG. 8 remain, and the remaining parts are removed. A wafer (W) is etched as in FIG. 9 using the patterned negative photoresist as an etching mask, and after the etching is completed, the negative photoresist is removed to obtain a patterned wafer (W) as in FIG. 10.

[0011] When performing an exposure process on a wafer using a general photomask, when patterning a wafer (W) that has a positive resist, as in FIGS. 3 and 6, the holes (h1) of the photomask form holes (h2) in the wafer (W) and the dots (d1) of the photomask form dots (d2) in the wafer (W). Conversely, when patterning a wafer (W) that has a negative resist, as in FIGS. 7 to 10, the holes (h1) of the photomask form dots (d2) in the wafer (W) and the dots (d1) of the photomask form holes (h2) in the wafer (W).

[0012] Generally, negative photoresist has the advantage of being thinner than positive photoresist and capable of forming fine patterns even at a low dose, thus showing superior performance compared to positive photoresist. Therefore, a method of actively applying negative photoresist to a wafer (W) is being considered. When negative photoresist is applied to a wafer (W), as described above, the holes (h1) of the photoresist form dots (d2) on the wafer (W).

[0013] However, among the photolithography processes for fabricating semiconductor devices, the final photolithography process is always to form a hole (h2) on the wafer (W), which means that after the process of forming a dot (d2) on the wafer (W), one or more additional processes for forming a hole (h2) are always involved. Therefore, positive photoresist must be used in the final photolithography process, and consequently, the dose reduction achieved by applying negative photoresist in the previous photolithography process does not immediately lead to an increase in production volume considering the entire process.

[0014] If a negative photoresist is to be applied to the wafer (W) even in the final exposure process, the dot (d1) pattern of the photomask must be used to form a hole (h2) on the wafer (W). However, in this case, due to technical limitations in processing the photomask pattern, i.e., the phase inversion film pattern (108a), it is impossible to reduce the pattern size to a level equivalent to the required size of the hole (h1). Additionally, pattern defects in the form of footing may be induced at the bottom of the pattern by the exposure light reflected from the reflective film (104), thereby reducing the uniformity of the size of the hole (h2) formed on the wafer (W).

[0015] Due to these problems, the application of negative photoresist in actual wafer (W) patterning processes has been limited despite the advantages of negative photoresist.

[0016] In the two examples described above, among the patterns formed in the photomask, the hole (h1) was used as a reflection pattern that reflects the exposure light, and the dot (d1) was used as a light-blocking pattern that blocks the exposure light. Conversely, a method is being studied in which the exposure light is blocked in the area on the wafer (W) corresponding to the hole (h1) of the photomask, and the exposure light is irradiated in the area on the wafer (W) corresponding to the dot (d1) of the photomask, so that, as a result, from the perspective of the wafer (W), the hole (h1) functions as a light-blocking pattern and the dot (d1) functions as a reflection pattern. A photomask of this type is referred to as a "reverse photomask" below. When a reverse photomask is used in the exposure process, when a negative photoresist is applied to the wafer (W), the dot pattern of the photomask forms a dot pattern on the wafer (W), and the hole pattern of the photomask forms a hole pattern on the wafer (W). Therefore, all of the aforementioned problems can be resolved while still obtaining the advantages of negative photoresist.

[0017] To fabricate such a reverse photomask, the characteristics of the blank mask serving as the photomask material must be entirely different from those of a conventional blank mask. However, to date, the composition of the blank mask required to fabricate a reverse photomask is unknown. The problem to be solved

[0019] The present invention has been devised to solve the above-mentioned problems, and the objective of the present invention is to provide a reverse photomask in which exposure light is blocked in an area on the wafer corresponding to the reflective film pattern of the photomask and exposure light is irradiated in an area on the wafer corresponding to the phase inversion film pattern of the photomask, so that, as a result, from the perspective of the wafer, the hole pattern of the photomask functions as a light-blocking pattern and the dot pattern functions as a reflective pattern.

[0020] Another objective of the present invention is to provide a blank mask that can be used to fabricate such a reverse photomask. means of solving the problem

[0022] A reverse blank mask for extreme ultraviolet lithography according to the first aspect of the present invention comprises a substrate, a reflective film formed on the substrate, and a phase inversion film formed on the reflective film, wherein the phase inversion film has a relative reflectance with respect to the reflective film exceeding 15% with respect to EUV exposure light of a wavelength of 13.5 nm, and the amount of phase inversion of reflected light reflected from the phase inversion film upon incidence of the EUV exposure light is 110-150° or 220-250°.

[0023] A reverse blank mask for extreme ultraviolet lithography according to the first aspect of the present invention comprises a substrate, a reflective film formed on the substrate, and a phase inversion film formed on the reflective film, wherein the phase inversion film is characterized by having a relative reflectance with respect to the reflective film exceeding 15% with respect to EUV exposure light of a wavelength of 13.5 nm and having a thickness of less than 45 nm.

[0024] Various configurations as follows can be added or limited to the reverse blank masks of the first and second sides mentioned above.

[0025] It is preferable that the above phase inversion film has a relative reflectance of less than 35%.

[0026] The above phase inversion film preferably has a thickness of less than 35 nm, and more preferably less than 30 nm.

[0027] The above phase inversion membrane can be configured to satisfy one of the following formulas.

[0028] 1) 32.5% < R < 35%, -0.1275n + 0.1305 < k < -6.6692n 2 + 12.1540n - 5.5071

[0029] 2) 27.5% < R < 32.5%, -0.1500n + 0.1530 < k < -6.0311n 2 + 10.9240n - 4.9149

[0030] 3) 22.5% < R < 27.5%, -0.1875n + 0.1900 < k < -4.2609n 2 + 7.6028n - 3.3581

[0031] 4) 17.5% < R < 22.5% : -0.2362n + 0.2376 < k < -2.5346n 2 + 4.3613n - 1.8379

[0032] 5) 15% < R < 17.5% : -0.3112n + 0.3108 < k < -7.9010n 2 + 14.1850n - 6.3175

[0033] Here, R, k, and n represent the relative reflectance, extinction coefficient, and refractive index, respectively, for the EUV exposure light.

[0034] It may also be configured to satisfy any one of the following formulas 6) to 10) as a more limited range compared to the above formulas 1) to 5).

[0035] 6) 32.5% < R < 35%, -0.1275n + 0.1305 < k < -1.6193n 2 + 2.8439n - 1.2255

[0036] 7) 27.5% < R < 32.5%, -0.1500n + 0.1530 < k < -1.3636n 2 + 2.3341n - 0.9713

[0037] 8) 22.5% < R < 27.5%, -0.1875n + 0.1900 < k < -1.7045n 2 + 2.9001n - 1.2006

[0038] 9) 17.5% < R < 22.5% : -0.2362n + 0.2376 < k < -0.9554n 2 + 1.4681n - 0.5146

[0039] 10) 15% < R < 17.5% : -0.3112n + 0.3108 < k < -0.7670n 2 + 0.9870n - 0.2242

[0040] In addition to the ranges of the above formulas 1) to 10), the ranges of the following formulas 11) to 14) are also possible.

[0041] 11) 32.5% < R < 35%, n=0.92±0.01, -0.1275n + 0.1305 < k < 0.03

[0042] 12) 27.5% < R < 32.5%, n=0.89±0.01 or n=0.92±0.01, -0.1500n + 0.1530 < k < 0.03

[0043] 13) 22.5% < R < 27.5%, n=0.92±0.01, -0.1875n + 0.1900 < k < 0.03

[0044] 14) 15% < R < 17.5% : For n=0.90±0.01, -0.3112n + 0.3108 < k < 0.05

[0045] According to another aspect of the present invention, a reverse photomask for extreme ultraviolet lithography is provided using a blank mask having the configuration as described above.

[0046] According to another aspect of the present invention, a wafer exposure method is provided, characterized by comprising the steps of: fabricating a reverse photomask using a blank mask as described above; and exposing a wafer using the reverse photomask.

[0047] Preferably, a negative photoresist is used on the wafer during the exposure step. Effects of the invention

[0049] According to the present invention, a reverse photomask is provided in which a phase inversion film pattern and a reflection film pattern function as a reflection pattern and a light-blocking pattern, respectively, for EUV incident light, and a blank mask used for fabricating such a photomask is provided. When the photomask of the present invention is used for the exposure of a wafer to which a negative photoresist is applied, the hole pattern of the photoresist can be used to form a hole pattern on the wafer. Accordingly, the advantages of the negative photoresist can be obtained while solving the problems associated with using conventional photomasks. Brief explanation of the drawing

[0051] FIG. 1 is a diagram illustrating the basic structure of a conventional phase-inversion blank mask for extreme ultraviolet lithography. FIG. 2 is a drawing illustrating a photomask produced using the blank mask of FIG. 1. FIGS. 3 to 6 are drawings sequentially illustrating the process of patterning a wafer to which a positive photoresist is applied using the photomask of FIG. 2. FIGS. 7 to 10 are drawings sequentially illustrating the process of patterning a wafer to which a negative photoresist is applied using the photomask of FIG. 2. FIG. 11 is a drawing illustrating a blank mask for fabricating a reverse photomask according to the present invention. FIG. 12 is a drawing illustrating a photomask produced using the blank mask of FIG. 11. FIG. 13 is a diagram illustrating the diffraction of reflected light. FIG. 14 is a diagram showing the change in light intensity occurring in each region of the wafer due to reflected light and diffracted light reflected from the photomask of FIG. 12. FIGS. 15 to 19 are graphs illustrating the properties required for a phase inversion film for implementing the reverse blank mask of the present invention, as ranges related to the refractive index (n) and extinction coefficient (k) for EUV exposure light for each reflectance range. FIGS. 20 to 24 are graphs showing a reduced range compared to each range shown in FIGS. 15 to 19. FIGS. 25 to 28 are drawings sequentially illustrating the process of patterning a wafer to which a positive photoresist is applied using a reverse photomask according to the present invention. FIGS. 29 to 32 are drawings sequentially illustrating the process of patterning a wafer to which a negative photoresist is applied using a reverse photomask according to the present invention. Specific details for implementing the invention

[0052] The present invention will be described in more detail below with reference to the drawings.

[0053] FIGS. 11 and FIGS. 12 respectively illustrate a reverse blank mask and a reverse photomask according to the present invention. The basic configuration of the blank mask and photomask according to the present invention is identical to that of the blank mask and photomask of the prior art described with reference to FIGS. 1 and FIG. 2. Accordingly, in the following description of the present invention, the basic configuration of the blank mask and photomask is described schematically, and the description of the blank mask and photomask of the prior art described with reference to FIGS. 1 and FIG. 2 is used by reference.

[0054] As illustrated in FIG. 11, the blank mask of the present invention comprises a substrate (202), a reflective film (204) formed on the substrate (202), a capping film (205) formed on the reflective film (204), a phase inversion film (208) formed on the capping film (205), and a resist film (220) formed on the phase inversion film (208). A photomask is fabricated using this blank mask. The photomask of FIG. 12 has a phase inversion film pattern (208a) and a reflective film pattern (204a) patterned using a resist film (120).

[0055] Meanwhile, if another thin film, such as an etching stop film or a hard mask film, remains above and / or below a specific thin film that performs the main phase inversion function and has the same pattern as the phase inversion film pattern (208a), the entire thin film including this specific thin film and the other thin film performs the phase inversion function. Therefore, in cases where multiple thin films that perform the phase inversion function remain as a pattern within the photomask in this manner, the phase inversion film (208) refers to the entire stacked structure of these thin films.

[0056] Even in the reverse photomask, the absolute reflectance of the phase inversion film pattern (208a) is lower than the absolute reflectance of the reflection film pattern (204a). Accordingly, the incident light incident on the photomask is reflected by the reflective film pattern (204a) and blocked by the phase inversion film pattern (208a), which is the same as in a conventional photomask. (More precisely, a contrast difference occurs because the reflectance in the phase inversion film pattern (208a) is lower than the reflectance in the reflective film pattern (204a), and the incident light is reflected after being patterned due to this contrast difference.) However, as described in detail below, in the reverse photomask of the present invention, the reflected light and the diffracted light undergo interference in the path that is reflected by the photomask and then irradiated onto the wafer (W), and accordingly, the exposure light is blocked in the area on the wafer corresponding to the reflective film pattern (204a) of the photomask and the exposure light is irradiated in the area on the wafer corresponding to the phase inversion film pattern (208a) of the photomask. As a result, from the perspective of the wafer, the hole pattern of the photomask functions as a light-blocking pattern, and the dot pattern of the photomask functions as a reflection pattern.

[0057] For the convenience of explanation in consideration of these points, in the following description of the reverse photomask of the present invention, 'phase inversion film pattern' and 'reflection pattern' are used as terms having the same meaning, and 'reflection film pattern' and 'light-blocking pattern' are used as terms having the same meaning. Furthermore, names having the same meaning are cited using the same reference numerals.

[0059] Below, the principle of the reverse photomask of the present invention, in which the phase inversion film pattern (208a) functions as a reflection pattern and the reflection film pattern (204a) functions as a light-blocking pattern is described as above.

[0060] The basic principle of a reverse photomask is to use the diffracted light of reflected light from one pattern (e.g., a dot pattern) within the photomask to cause destructive interference with the reflected light of another pattern (e.g., a hole pattern).

[0061] Figure 13 is a diagram illustrating the diffraction of reflected light.

[0062] When exposure light is reflected from a reflective surface, diffraction occurs in the reflected light. The reflected light along the main path of the incident light is called the zeroth-order diffracted light (D0), and the diffracted light forming a diffraction angle (θ) with respect to the main path is called the first-order diffracted light (D1). Furthermore, since diffraction occurs symmetrically throughout space, there exists a -1st-order diffracted light (-D1) that is symmetric to the first-order diffracted light (D1). Although not shown in FIG. 21, there are diffracted lights that are symmetric to each other in the direction penetrating the surface of FIG. 21 and in the direction penetrating the surface of FIG. 21. That is, diffracted light occurs in all directions on the plate surface of the reflective surface. Additionally, although not shown in FIG. 13, there exists a second-order diffracted light that is diffracted at a second-order diffraction angle (e.g., θ2) exceeding the diffraction angle (θ), and in this manner, an n-th-order diffracted light exists. In the description of the principle of the present invention utilizing diffraction, the illustration and description of the n-th order diffracted light and the -1st order diffracted light (-D1) are omitted.

[0063] The reverse photomask induces destructive interference between the zero-order diffracted light and the first-order diffracted light by causing the first-order diffracted light of the exposure light reflected from the photomask to be generated at a position separated by an integer multiple of the half-pitch of the pattern relative to the generation position of the zero-order diffracted light on the wafer (W). Here, the 'generation position' refers to the position where the intensity peak of the diffracted light occurs. By utilizing this, a reversal effect can be produced such that, from the perspective of the wafer (W) irradiated with reflected light, the reflectance in the reflective film pattern (204a) is actually lower than the reflectance in the phase inversion film pattern (208a). That is, the effect can be obtained where the exposure light is blocked in the region on the wafer (W) corresponding to the hole (h1) of the photomask, and the exposure light is irradiated in the region on the wafer (W) corresponding to the dot (d1) of the photomask.

[0064] FIG. 14 is a drawing for specifically explaining these effects, showing the change in the intensity of light diffracted when exposure light is reflected by the photomask of FIG. 12. In FIG. 14, three reflection patterns (208a-1, 208a-2, 208a-3) among the reflection patterns (208a) of FIG. 12 are shown in enlarged view. Between the three reflection patterns (208a-1, 208a-2, 208a-3), there are two light-blocking patterns (204a-1, 204a-2). In FIG. 14, the capping film (205) is omitted for convenience of explanation. In FIG. 14, each graph (Rh, Rd) of the intensity change of reflected light and diffracted light is divided and illustrated to correspond to the area where each pattern (208a-1, 208a-2, 208a-3, 204a-1, 204a-2) on the photomask is formed.

[0065] Rh is a graph showing reflected light (zero-order diffracted light) and first-order diffracted light in the shielding patterns (204a-1, 204a-2), among which Rh-1 is a graph showing the zero-order diffracted light and first-order diffracted light in the left shielding pattern (204a-1), and Rh-2 is a graph showing the zero-order diffracted light and first-order diffracted light in the right shielding pattern (204a-2). And, Rd is a graph showing the reflected light (0th-order diffracted light) and 1st-order diffracted light in the reflection patterns (208a-1, 208a-2, 208a-3), among which Rd-1 is a graph showing the 0th-order diffracted light and 1st-order diffracted light in the left reflection pattern (208a-1), Rd-2 is a graph showing the 0th-order diffracted light and 1st-order diffracted light in the middle reflection pattern (208a-2), and Rd-3 is a graph showing the 0th-order diffracted light and 1st-order diffracted light in the right reflection pattern (208a-3).

[0066] In FIG. 14, the regions (W1, W2, W3) partitioned for each graph are not regions on the photomask, but regions on the wafer (W) corresponding to each region on the photomask. For example, region W2 is a region on the wafer (W) corresponding to the region where the center reflection pattern (208a-2) of the photomask in FIG. 14 is formed, and regions W1 and W3 are regions on the wafer (W) corresponding to the regions where the left light-blocking pattern (204a-1) and the right light-blocking pattern (204a-2) of the photomask in FIG. 14 are formed, respectively.

[0067] In each graph of Rh and Rd, the zero-order diffracted light exists in the region on the wafer (W) corresponding to the area where the pattern is formed, and the first-order diffracted light exists in the regions on the wafer (W) corresponding to the left and right sides of the area where the pattern is formed. For example, regarding the reflected light from the left light-blocking pattern (204a-1), the zero-order diffracted light exists in the W1 region, and the first-order diffracted light exists in the left region and right region (W2) of the W1 region, respectively. Similarly, regarding the reflected light from the center reflection pattern (208a-2), the zero-order diffracted light exists in the W2 region, and the first-order diffracted light exists in the left region (W1) and right region (W3) of the W2 region, respectively.

[0068] For each pattern (208a-1, 208a-2, 208a-3, 204a-1, 204a-2), the n-th order diffracted light of the second order or higher has been omitted from the illustration. This is because the n-th order diffracted light is very small in magnitude and therefore has minimal influence on the destructive and constructive interference described below. Additionally, for the sake of understanding, each graph (Rh, Rd) in FIG. 14 is illustrated as having a phase difference of approximately π between each region (W1, W2, W3) on the wafer (W), but this does not represent an absolute phase difference. The actual phase difference may differ from FIG. 14, provided that the intensity of light irradiated on one region (e.g., W2) becomes greater than the intensity of light irradiated on the left and right regions (e.g., W1, W2) due to destructive and constructive interference as described below.

[0069] In the Rh graph, which is the first graph in FIG. 14, Rh-1 represents the change in intensity in each region of the wafer (W) when reflected light reflected by the left shading pattern (204a-1) is irradiated onto the wafer (W). The zero-order diffracted light of the left shading pattern (204a-1) has an intensity distribution that is strongest in the central part of region (W1) and weakens toward the edges. In regions adjacent to region (W1) (the left region of W1, and W2), a change in intensity occurs due to the first-order diffracted light. The first-order diffracted light has a lower intensity compared to the zero-order diffracted light and has a distribution that is strongest approximately in the central part of each region and weakens toward the edges. The phase of the first-order diffracted light is opposite to that of the zero-order diffracted light.

[0070] Rh-2 represents the change in intensity in each region of the wafer (W) when reflected light reflected by the right shading pattern (204a-2) is irradiated onto the wafer (W). The zero-order diffracted light of the right shading pattern (204a-2) has an intensity distribution that is strongest in the central part of region (W3) and weakens toward the edges. In regions adjacent to region (W3) (W2, and the right region of W3), a change in intensity occurs due to the first-order diffracted light. The first-order diffracted light has a lower intensity than the zero-order diffracted light and has a distribution that is strongest approximately in the central part of each region and weakens toward the edges. The phase of the first-order diffracted light is opposite to that of the zero-order diffracted light.

[0071] The rightward diffracted light of Rh-1 and the leftward diffracted light of Rh-2 overlap in the W2 region and undergo constructive interference. Therefore, the magnitude of the sum of the first-order diffracted lights in the W2 region is approximately twice the magnitude of each first-order diffracted light.

[0072] In the second graph of FIG. 14, the Rd graph, Rd-2 represents the change in intensity in each region (W1, W2, W3) of the wafer (W) when reflected light reflected from the central reflection pattern (208a-2) is irradiated onto the wafer (W). The zeroth-order diffracted light of the central reflection pattern (208a-2) has an intensity distribution that is strongest in the central part of region (W2) and weakens toward the edges. In the regions (W1, W3) adjacent to region (W2), changes in intensity occur due to the first-order diffracted light. The first-order diffracted light has a lower intensity than the zeroth-order diffracted light and has a distribution that is strongest approximately in the central part of each region and weakens toward the edges. The phase of the first-order diffracted light is opposite to that of the zeroth-order diffracted light.

[0073] Rd-1 and Rd-3 represent changes in intensity in each region of the wafer (W) when reflected light reflected from the regions of the left reflection pattern (208a-1) and the right reflection pattern (208a-3), respectively, is irradiated onto the wafer (W). Rd-1 and Rd-3 have the same shape as Rd-2, and zero-order diffracted light exists in the left region of the W1 region and the right region of the W3 region, respectively, while first-order diffracted light exists in the W1 region and the W3 region, respectively. Accordingly, in the W1 region, the first-order diffracted light of Rd-1 and the first-order diffracted light of Rd-2 overlap to cause constructive interference, and in the W3 region, the first-order diffracted light of Rd-3 and the first-order diffracted light of Rd-2 overlap to cause constructive interference. Therefore, the magnitude of the sum of the first-order diffracted lights in the W1 and W3 regions is approximately twice the magnitude of each first-order diffracted light.

[0074] The Rh + Rd graph, which is the third graph in Fig. 14, shows the distribution of light (combination of Rh and Rd) irradiated to each region (W1, W2, W3) of the wafer (W). In each region (W1, W2, W3), destructive interference occurs due to the overlap of Rh and Rd, and as a result, the intensity of light irradiated to the region (W2) corresponding to the central reflection pattern (208a-2) is higher than the intensity of light irradiated to the regions (W1, W3) corresponding to the light-blocking patterns (204a-1, 204a-2) on both sides. The phase of the W2 region is opposite to that of the W1 and W3 regions.

[0075] Since the reflective film (204) has a higher absolute reflectance than the phase inversion film (208), the phase inversion film (208) has a lower intensity of light that is directly reflected compared to the reflective film (204). Therefore, the intensity of light that is directly reflected from each reflection pattern (208a-1, 208a-2, 208a-3) constituting Rd is basically lower than the intensity of light that is directly reflected from each light-blocking pattern (204a-1, 204a-2) constituting Rh. However, the intensity of the irradiation light combining the zero-order diffracted light and the first-order diffracted light becomes greater in W2 than in W1 and W3 due to destructive and constructive interference as described above. Accordingly, the exposure light is blocked in the regions (W1, W3) on the wafer (W) corresponding to the hole pattern (reflective film pattern (204a)) in the photomask, and the exposure light is reflected in the region (W2) on the wafer (W) corresponding to the dot pattern (phase inversion film pattern (208a)) in the photomask. (More precisely, since the intensity of the light irradiated on W2 is greater than that of W1 and W2, patterned exposure light having a contrast difference is irradiated on the wafer (W).) Accordingly, the reverse photomask of the present invention is implemented.

[0076] Meanwhile, in the illustration and description of FIG. 14, the case where the reflection pattern (208a) and the light-blocking pattern (204a) are line patterns was illustrated. Accordingly, FIG. 14 illustrates that the first-order diffracted light of each pattern (204a, 208a) is generated in the left and right regions, respectively, of the zero-order diffracted light generation area. However, if the light-blocking pattern (204a) is not a line pattern but a hole pattern (i.e., when the photomask of FIG. 14 is illustrated in a planar view and viewed from above to below, the light-blocking pattern (204a) has the shape of a hole), the light-blocking pattern (204a) is surrounded on all sides by the reflection pattern (208a). In this state, Rd includes constructive interference by four first-order diffracted lights instead of two. In this case, the magnitude of Rd in regions W1 and W3 increases by approximately twofold compared to the case in Fig. 14 due to doubling of constructive interference. Consequently, the effect of destructive interference on Rh in regions W1 and W3 increases, and the magnitude of Rh + Rd in regions W1 and W3 becomes smaller than that shown in Fig. 14. As a result, the contrast between regions W1 and W3 and region W2 increases further.

[0078] Below, the specific configuration of a reverse photomask based on the above-mentioned principle is described.

[0079] In order to implement the reverse photomask of the present invention, the distance between the position of diffracted light and the position of reflected light must match an integer multiple of the half-pitch of the pattern to be formed on the wafer (W) as described above. However, this is a factor that must be controlled through the setting of the exposure device performing the exposure process; for example, by adjusting the distance between the photomask and the wafer (W), the focusing position can be adjusted to meet this requirement. Therefore, this can be considered a factor to be reflected in the actual use of the photomask rather than a factor regarding the specifications of the photomask. However, when using a conventional photomask, a reverse effect cannot be obtained even if the distance from the wafer (W) is adjusted, and in order to be used as a reverse photomask, a blank mask must be manufactured with the specifications described below.

[0080] In order to implement the reverse photomask of the present invention, destructive and constructive interference must occur effectively. To achieve this, the phase inversion film (208) must have a high reflectance so that the intensity of the diffracted light increases. According to research conducted by the inventors of the present invention, for the implementation of the reverse photomask, the phase inversion film (208) must have a reflectance exceeding at least 15%. However, the inventors of the present invention discovered that if the reflectance is excessively high, it becomes difficult to implement the reverse function. The preferred reflectance of the phase inversion film (208) is less than 35%. Here, reflectance refers to the reflectance for EUV exposure light of a wavelength of 13.5 nm, and also refers to the relative reflectance, which is the ratio of the absolute reflectance of the phase inversion film (208) to the absolute reflectance of the reflective film (204).

[0081] Meanwhile, a conventional phase inversion film must effectively generate destructive interference between reflected light reflected from the upper and lower parts of the phase inversion film, respectively, and accordingly, the phase inversion amount is set to be around 180°. Conventional phase inversion films typically have a target phase inversion amount set within the range of 160-210°. However, the inventors of the present invention have discovered that the reverse photomask can effectively implement the phase inversion amount of the phase inversion film (208) in a range different from the phase inversion amount pursued by a conventional photomask. According to the research conducted by the inventors of the present invention, the reverse function is not effectively implemented when the phase inversion amount is in the range of 150-220°, and the reverse function is effectively implemented when the phase inversion amount is in the range of 110-150° or 220-250°.

[0082] In order for the phase inversion film (208) to have the reflectance and phase inversion amount as described above, the material constituting the phase inversion film (208) must have an appropriate extinction coefficient (k) and an appropriate refractive index (n).

[0083] The above-described appropriate reflectance can be controlled by the extinction factor (k) of the phase inversion film (208) and the corresponding thickness (t). However, in order for the photomask formed with the phase inversion film (208) having the thickness (t) and extinction factor (k) determined in consideration of this to satisfy the above-described range of phase inversion amount and to have maximum performance in terms of NILS, DtS, etc., a corresponding refractive index (n) is required. That is, for the implementation of a desirable reverse function, the phase inversion film (208) must have an appropriate optical constant (N = n-ik). However, the refractive index (n) and the extinction factor (k), which represent the optical characteristics of the thin film, are each components constituting the optical constant (N), which is a complex refractive index, and are not mutually independent in terms of exhibiting maximum performance of the phase inversion film (208). The requirements for the phase inversion film considering all such aspects must be expressed as a function that defines the relationship between k and n.

[0084] Furthermore, the inventor of the present invention has discovered that a function defining the interrelationship between k and n for a phase inversion film for implementing a reverse function must vary according to the target reflectance range. That is, a phase inversion film (208) having a reflectance of a specific range and a phase inversion film (208) having a reflectance of a different range require different ranges of values ​​for k and n. In addition, reflectance generally needs to be implemented to meet the requirements of individual exposure processes. For example, some exposure processes may require a reflectance of 20%, while others may require a reflectance of 25%. The phase inversion film (208) must be manufactured to have a reflectance that meets these requirements. When the required reflectance differs in this way, the ranges of n and k of the phase inversion film (208) for implementing the reverse function change.

[0085] Considering these various aspects, it is preferable that the range of values ​​of n and k of the phase inversion film (208) for implementing the reverse photomask of the present invention be determined as different functions for each reflectance range.

[0086] FIGS. 15 to 19 are graphs illustrating the physical properties required for a phase inversion film to implement the reverse photomask of the present invention, as ranges related to the refractive index (n) and extinction factor (k) for EUV exposure light for each reflectance range. FIGS. 15 to 19 show the ranges of n and k values ​​at which the reverse function is implemented for reflectance ranges of 32.5 < R < 35%, 27.5 < R < 32.5%, 22.5 < R < 27.5%, 1.75 < R < 22.5%, and 15 < R < 17.5%, respectively. In these graphs, the horizontal axis represents the refractive index (n) for EUV exposure light of 13.5 nm wavelength, and the vertical axis represents the extinction factor (k) for EUV exposure light of 13.5 nm wavelength. The range indicated by the shape of a partial arc in each graph represents the range in which the reverse photomask of the present invention can be implemented. For materials outside this range, it is difficult to implement the reverse function, or even if implemented, it is difficult to satisfy other required performance specifications, such as DtS (Dose to Space) or NILS (Normalized Image Log Slope).

[0087] Each range of FIGS. 15 to 19 can be expressed by the following formulas.

[0088] 32.5% < R < 35% : -0.1275n + 0.1305 < k < -6.6692n 2 + 12.1540n - 5.5071

[0089] 27.5% < R < 32.5% : -0.1500n + 0.1530 < k < -6.0311n 2 + 10.9240n - 4.9149

[0090] 22.5% < R < 27.5% : -0.1875n + 0.1900 < k < -4.2609n 2 + 7.6028n - 3.3581

[0091] 17.5% < R < 22.5% : -0.2362n + 0.2376 < k < -2.5346n 2 + 4.3613n - 1.8379

[0092] 15% < R < 17.5% : -0.3112n + 0.3108 < k < -7.9010n 2 + 14.1850n - 6.3175

[0093] (R : Relative reflectance of the phase inversion film for EUV exposure light of 13.5 nm wavelength,

[0094] k : extinction coefficient of the phase inversion film for EUV exposure light of 13.5 nm wavelength,

[0095] n : Refractive index of the phase-inversion film for EUV exposure light of 13.5 nm wavelength)

[0096] The formula may be satisfied by using only materials within the range described above, or a compound may be satisfied by combining multiple materials outside this range. Additionally, the effective optical constant (eff. N) of the entire phase inversion film (208) may be satisfied by forming a multi-layer structure of phase inversion film (208) each containing a single material or a compound of multiple materials outside this range.

[0097] The effective optical constant (eff. N) in the case of two layers is defined by the following equation.

[0098] eff. N=(n1 x t1 + n2 x t2) / (t1 + t2) - i(k1 x t1 + k2 x t2) / (t1 + t2)

[0099] (n1, k1, t1 : Refractive index of layer 1, extinction factor, thickness,

[0100] n2, k2, t2 : Refractive index, extinction factor, thickness of layer 2)

[0101] The phase inversion film (208) may additionally include light element materials such as N, O, C, B, and H in addition to metal, and the refractive index (n) and extinction coefficient (k) of the phase inversion film (208) are also determined by the presence and content of these light element materials. Therefore, by adjusting the content of each metal and light element included in the phase inversion film (208), a reverse photomask having the above-mentioned n and k values ​​can be realized.

[0102] Meanwhile, in order to secure a high reflectivity of the phase inversion film (208), it is desirable for the phase inversion film (208) to have a thin thickness. On the other hand, when pursuing a high reflectivity, the thickness of the phase inversion film (208) can be reduced, so, for example, an effect of reducing the 3D effect can be obtained. If a material with a high refractive index (n) and a low extinction factor (k) is used, for example, an effective reverse function satisfying the above requirements can be implemented even with a thick thickness of 60 nm. However, if the formula for the values ​​of R, n, and k presented in the present invention is satisfied, the reverse function is implemented more easily when the phase inversion film (208) has a thickness of less than 45 nm, and in this case, an additional effect of reducing the 3D effect can also be obtained. Furthermore, it is desirable for the thickness of the phase inversion film (208) to be less than 35 nm, and it is even more desirable for it to be less than 30 nm. It will be obvious that the phase inversion film (208) must have a minimum thickness to function as a thin film for phase inversion.

[0103] FIGS. 20 to 24 are graphs illustrating reduced ranges compared to the respective ranges shown in FIGS. 15 to 19. FIGS. 20 to 24 illustrate ranges identical to the ranges of reflectance in FIGS. 15 to 19, and it has been confirmed that the performance of the reverse photomask of the present invention is superior in the somewhat reduced ranges shown in FIGS. 20 to 24 compared to the respective ranges shown in FIGS. 15 to 19. The formulas corresponding to each reflectance indicated in each figure are as follows.

[0104] 32.5% < R < 35%, -0.1275n + 0.1305 < k < -1.6193n 2 + 2.8439n - 1.2255

[0105] 27.5% < R < 32.5%, -0.1500n + 0.1530 < k < -1.3636n 2 + 2.3341n - 0.9713

[0106] 22.5% < R < 27.5%, -0.1875n + 0.1900 < k < -1.7045n 2 + 2.9001n - 1.2006

[0107] 17.5% < R < 22.5% : -0.2362n + 0.2376 < k < -0.9554n 2 + 1.4681n - 0.5146

[0108] 15% < R < 17.5% : -0.3112n + 0.3108 < k < -0.7670n 2 + 0.9870n - 0.2242

[0109] In the above equations corresponding to each of FIGS. 20 to 24, the formula defining the lower limit of the k value is the same as the formula described above for FIGS. 15 to 19, and the area allowed by the formula defining the upper limit of the k value is reduced compared to the formula described above for FIGS. 15 to 19. Therefore, when a blank mask is manufactured to satisfy these formulas, the performance as a reverse photomask is superior and the possibility of defects due to product-specific tolerances during the manufacturing process is reduced.

[0110] Meanwhile, the inventor of the present invention discovered that there exists a specific range in which the reverse photomask of the present invention can be fabricated even outside the range expressed by the above-mentioned formulas. In FIGS. 20 to 22 and 24, this specific range is illustrated as a point shape at a location outside the area indicated by the partitioned region in each figure. For example, in FIG. 20, a location is indicated where n is approximately 0.92 and k is slightly smaller than approximately 0.03. This specific range exists as one region in FIG. 20, two regions in FIG. 21, one region in FIG. 22, and one region in FIG. 24, but did not exist in FIG. 23. When this specific range is expressed in correspondence with the reflectance range of each figure, it is as follows.

[0111] 32.5% < R < 35%, n=0.92±0.01, -0.1275n + 0.1305 < k < 0.03

[0112] 27.5% < R < 32.5%, n=0.89±0.01 or n=0.92±0.01, -0.1500n + 0.1530 < k < 0.03

[0113] 22.5% < R < 27.5%, n=0.92±0.01, -0.1875n + 0.1900 < k < 0.03

[0114] 15% < R < 17.5% : For n=0.90±0.01, -0.3112n + 0.3108 < k < 0.05

[0115] Meanwhile, the formulas for FIGS. 15 to 19 and FIGS. 20 to 24 described above must satisfy at least one of the conditions regarding the phase inversion amount of the phase inversion film (208) and the thickness of the phase inversion film (208) as described above of the present invention. That is, the phase inversion amount of the phase inversion film (208) is required to be 110-150° or 220-250°, and the thickness of the phase inversion film (208) is required to be 45 nm or less, preferably less than 35 nm, and more preferably less than 30 nm. However, the reverse photomask of the present invention can be manufactured even if only one of these two conditions is satisfied, and if both of these conditions are satisfied, the performance of the reverse photomask of the present invention can be further guaranteed.

[0117] Hereinafter, an exposure process using a reverse photomask according to the present invention is described.

[0118] FIGS. 25 to 28 are drawings sequentially illustrating the process of patterning a wafer using a reverse photomask according to the present invention, and are drawings showing the process of patterning a wafer (W) in which a positive photoresist (positive PR) is employed.

[0119] As described above, in the reverse photomask of the present invention, the phase inversion film pattern (208a) functions as a reflection pattern for incident light, and the reflection film pattern (204a) functions as a light-blocking pattern for incident light. With this in mind, FIGS. 25 to 28 illustrate that incident light is reflected from the phase inversion film pattern (208a) and incident light is blocked from the reflection film pattern (204a) in order to clearly explain the patterning process of the reverse photomask from a conceptual perspective.

[0120] When a positive photoresist is used as in FIG. 25, the areas of the positive photoresist exposed to reflected light as in FIG. 26 are removed, and the remaining portion is retained. A wafer (W) is etched as in FIG. 27 using the patterned positive photoresist as an etching mask, and after the etching is completed, the positive photoresist is removed to obtain a patterned wafer (W) as in FIG. 28.

[0121] As can be seen in FIGS. 25 and 28, when patterning a wafer (W) that has a positive resist using a reverse photomask, the holes (h1) of the photomask form dots (d2) on the wafer (W), and the dots (d1) of the photomask form holes (h2) on the wafer (W).

[0122] FIGS. 29 to 32 are drawings sequentially illustrating the process of patterning a wafer using a reverse photomask according to the present invention, and are drawings showing the process of patterning a wafer (W) in which a negative photoresist (negative PR) is employed.

[0123] When a negative photoresist is used as in FIG. 29, the areas of the negative photoresist exposed to reflected light as in FIG. 30 remain, and the remaining parts are removed. A wafer (W) is etched as in FIG. 31 using the patterned negative photoresist as an etching mask, and a patterned wafer (W) is obtained as in FIG. 32 by removing the negative photoresist after the etching is completed.

[0124] As can be seen in FIGS. 29 and 32, when patterning a wafer (W) that has a negative resist using a reverse photomask, the holes (h1) of the photomask form holes (h2) in the wafer (W), and the dots (d1) of the photomask form dots (d2) in the wafer (W).

[0125] Thus, when performing an exposure process on a wafer using a reverse photomask according to the present invention, when patterning a wafer (W) that has a positive resist, the holes (h1) of the photomask form a dot (d2) on the wafer (W), and the dots (d1) of the photomask form a hole (h2) on the wafer (W). Conversely, when patterning a wafer (W) that has a negative resist, the holes (h1) of the photomask form a hole (h2) on the wafer (W), and the dots (d1) of the photomask form a dot (d2) on the wafer (W).

[0126] In short, when a wafer (W) with a negative photoresist is exposed using a reverse photomask, the holes (h1) and dots (d1) of the photomask correspond to the holes (h2) and dots (d2) of the wafer (W), respectively, so the pattern of the photomask and the pattern of the wafer (W) become identical. Therefore, by using a reverse photomask, the negative photoresist can be applied even to form the holes (h2) in the final exposure process of the entire exposure process for the wafer (W).

[0128] Although the present invention has been specifically described above through embodiments with reference to the drawings, the embodiments are used merely for the purpose of illustrating and explaining the invention and are not intended to limit the meaning or the scope of the invention as described in the claims. Therefore, those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible from the embodiments, and the true scope of protection of the invention should be determined by the technical details of the claims.

Claims

Claim 1 A reverse blank mask for extreme ultraviolet lithography comprising a substrate, a reflective film formed on the substrate, and a phase inversion film formed on the reflective film, wherein the phase inversion film has a relative reflectance with respect to the reflective film that exceeds 15% and is less than 35% with respect to EUV exposure light of a wavelength of 13.5 nm, and the amount of phase inversion of reflected light reflected from the phase inversion film upon incidence of the EUV exposure light is 110-150° or 220-250°. Claim 2 delete Claim 3 A reverse blank mask for extreme ultraviolet lithography according to claim 1, wherein the phase inversion film satisfies any one of the following formulas 1) to 5): 1) 32.5% < R < 35%, -0.1275n + 0.1305 < k < -6.6692n 2 + 12.1540n - 5.50712) 27.5% < R < 32.5%, -0.1500n + 0.1530 < k < -6.0311n 2 + 10.9240n - 4.91493) 22.5% < R < 27.5%, -0.1875n + 0.1900 < k < -4.2609n 2 + 7.6028n - 3.35814) 17.5% < R < 22.5% : -0.2362n + 0.2376 < k < -2.5346n 2 + 4.3613n - 1.83795) 15% < R < 17.5% : -0.3112n + 0.3108 < k < -7.9010n 2 + 14.1850n - 6.3175(For the above EUV exposure light, R is the relative reflectance, k is the extinction factor, and n is the refractive index) Claim 4 delete Claim 5 delete Claim 6 delete Claim 7 delete Claim 8 A reverse blank mask for extreme ultraviolet lithography according to claim 1, wherein the phase inversion film satisfies any one of the following formulas 6) to 10): 6) 32.5% < R < 35%, -0.1275n + 0.1305 < k < -1.6193n 2 + 2.8439n - 1.22557) 27.5% < R < 32.5%, -0.1500n + 0.1530 < k < -1.3636n 2 + 2.3341n - 0.97138) 22.5% < R < 27.5%, -0.1875n + 0.1900 < k < -1.7045n 2 + 2.9001n - 1.20069) 17.5% < R < 22.5% : -0.2362n + 0.2376 < k < -0.9554n 2 + 1.4681n - 0.514610) 15% < R < 17.5% : -0.3112n + 0.3108 < k < -0.7670n 2 + 0.9870n - 0.2242(for the above EUV exposure light, R is the relative reflectance, k is the extinction factor, and n is the refractive index) Claim 9 delete Claim 10 delete Claim 11 delete Claim 12 delete Claim 13 A reverse blank mask for extreme ultraviolet lithography according to claim 1, wherein the phase inversion film satisfies any one of the following formulas 11) to 14): 11) 32.5% < R < 35%, n=0.92±0.01, -0.1275n + 0.1305 < k < 0.0312) 27.5% < R < 32.5%, n=0.89±0.01 or n=0.92±0.01, -0.1500n + 0.1530 < k < 0.0313) 22.5% < R < 27.5%, n=0.92±0.01, -0.1875n + 0.1900 < k < 0.0314) 15% < R < 17.5% : For n=0.90±0.01, -0.3112n + 0.3108 < k < 0.05 (for the above EUV exposure light, R is relative reflectance, k is extinction factor, and n is refractive index). A reverse blank mask for extreme ultraviolet lithography characterized in that the phase inversion film satisfies the following formula: 32.5% < R < 35%, n=0.92±0.01, -0.1275n + 0.1305 < k < 0.03 (for the above EUV exposure light, R is relative reflectance, k is extinction factor, and n is refractive index). Claim 14 delete Claim 15 delete Claim 16 delete Claim 17 A reverse blank mask for extreme ultraviolet lithography, characterized in that, in any one of claims 1, 3, 8, and 13, the phase inversion film has a thickness of less than 45 nm and has a minimum thickness for functioning as a thin film for phase inversion. Claim 18 A reverse blank mask for extreme ultraviolet lithography according to claim 17, characterized in that the phase inversion film has a thickness of less than 35 nm. Claim 19 A reverse blank mask for extreme ultraviolet lithography according to claim 17, characterized in that the phase inversion film has a thickness of less than 30 nm. Claim 20 A reverse photomask for extreme ultraviolet lithography produced using a blank mask of any one of claims 1, 3, 8, and 13. Claim 21 A wafer exposure method characterized by comprising: a step of fabricating a reverse photomask according to claim 20; and a step of exposing a wafer using the reverse photomask. Claim 22 A wafer exposure method according to claim 21, characterized in that a negative photoresist is used on the wafer during the exposure step. Claim 23 A reverse blank mask for extreme ultraviolet lithography comprising a substrate, a reflective film formed on the substrate, and a phase inversion film formed on the reflective film, wherein the phase inversion film has a relative reflectance with respect to the reflective film that exceeds 15% and is less than 35% with respect to EUV exposure light of a wavelength of 13.5 nm, and has a thickness of less than 45 nm and has a minimum thickness for functioning as a thin film for phase inversion. Claim 24 A reverse blank mask for extreme ultraviolet lithography according to claim 23, characterized in that the phase inversion film has a thickness of less than 35 nm. Claim 25 A reverse blank mask for extreme ultraviolet lithography according to claim 23, characterized in that the phase inversion film has a thickness of less than 30 nm. Claim 26 delete Claim 27 A reverse blank mask for extreme ultraviolet lithography according to claim 23, wherein the phase inversion film satisfies any one of the following formulas 1) to 5): 1) 32.5% < R < 35%, -0.1275n + 0.1305 < k < -6.6692n 2 + 12.1540n - 5.50712) 27.5% < R < 32.5%, -0.1500n + 0.1530 < k < -6.0311n 2 + 10.9240n - 4.91493) 22.5% < R < 27.5%, -0.1875n + 0.1900 < k < -4.2609n 2 + 7.6028n - 3.35814) 17.5% < R < 22.5% : -0.2362n + 0.2376 < k < -2.5346n 2 + 4.3613n - 1.83795) 15% < R < 17.5% : -0.3112n + 0.3108 < k < -7.9010n 2 + 14.1850n - 6.3175(For the above EUV exposure light, R is the relative reflectance, k is the extinction factor, and n is the refractive index) Claim 28 delete Claim 29 delete Claim 30 delete Claim 31 delete Claim 32 A reverse blank mask for extreme ultraviolet lithography according to claim 23, wherein the phase inversion film satisfies any one of the following formulas 6) to 10): 6) 32.5% < R < 35%, -0.1275n + 0.1305 < k < -1.6193n 2 + 2.8439n - 1.22557) 27.5% < R < 32.5%, -0.1500n + 0.1530 < k < -1.3636n 2 + 2.3341n - 0.97138) 22.5% < R < 27.5%, -0.1875n + 0.1900 < k < -1.7045n 2 + 2.9001n - 1.20069) 17.5% < R < 22.5% : -0.2362n + 0.2376 < k < -0.9554n 2 + 1.4681n - 0.514610) 15% < R < 17.5% : -0.3112n + 0.3108 < k < -0.7670n 2 + 0.9870n - 0.2242(for the above EUV exposure light, R is the relative reflectance, k is the extinction factor, and n is the refractive index) Claim 33 delete Claim 34 delete Claim 35 delete Claim 36 delete Claim 37 In claim 23, a reverse blank mask for extreme ultraviolet lithography characterized in that the phase inversion film satisfies any one of the following formulas 11) to 14): 11) 32.5% < R < 35%, n=0.92±0.01, -0.1275n + 0.1305 < k < 0.0312) 27.5% < R < 32.5%, n=0.89±0.01 or n=0.92±0.01, -0.1500n + 0.1530 < k < 0.0313) 22.5% < R < 27.5%, n=0.92±0.01, -0.1875n + 0.1900 < k < 0.0314) 15% < R < 17.5% : For n=0.90±0.01, -0.3112n + 0.3108 < k < 0.05 (for the above EUV exposure light, R is relative reflectance, k is extinction factor, and n is refractive index). A reverse blank mask for extreme ultraviolet lithography characterized in that the phase inversion film satisfies the following formula: 32.5% < R < 35%, n=0.92±0.01, -0.1275n + 0.1305 < k < 0.03 (for the above EUV exposure light, R is relative reflectance, k is extinction factor, and n is refractive index). Claim 38 delete Claim 39 delete Claim 40 delete Claim 41 A reverse photomask for extreme ultraviolet lithography produced using a blank mask of any one of claims 23, 24, 25, 27, 32, and 37. Claim 42 A wafer exposure method characterized by comprising: a step of fabricating a reverse photomask according to claim 41; and a step of exposing a wafer using the reverse photomask. Claim 43 A wafer exposure method according to claim 42, characterized in that a negative photoresist is used on the wafer during the exposure step.

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