Reflective mask blank and reflective mask

Abstract

Provided is a reflective mask in which a fine absorption film pattern can be formed even when a high-absorbing material is used as an absorption film of an EUV mask, thereby enabling reduction of a projection effect and performing electron beam corrected etching, and a reflective mask blank for manufacturing the same. The reflective mask blank (10) according to the present embodiment includes a substrate (1), a multilayer reflective film (2) having a multilayer film structure and reflecting EUV light formed on the substrate (1), a capping layer (3) formed on the multilayer reflective film (2) and protecting the multilayer reflective film (2), and an absorption film (4) formed on the capping layer (3) and absorbing EUV light, the absorption film (4) containing 50 atomic % or more of an element constituting at least one of tin oxide (SnO) and indium oxide (InO) and containing a material that is easily etched by a fluorine-based gas or a chlorine-based gas.

Description

TECHNICAL FIELD

[0001] The present application relates to a reflective mask blank and a reflective mask. BACKGROUND

[0002] In a manufacturing process of a semiconductor device, as the semiconductor device is miniaturized, the miniaturization of a lithography technique is also required. In lithography, the minimum resolution size of a transferred pattern greatly depends on the wavelength of an exposure light source, and the shorter the wavelength, the smaller the minimum resolution size. Therefore, in the manufacturing process of a semiconductor device, the exposure light source is switched from a conventional exposure light source using an ArF excimer laser having a wavelength of 193 nm to an EUV (Extreme Ultra Violet) exposure light source having a wavelength of 13.5 nm.

[0003] Since the EUV light has a short wavelength, almost all substances have high light absorption. Therefore, unlike the conventional transmissive mask, the EUV mask is a reflective mask (see, for example, Patent Literature 1, Patent Literature 2). In Patent Literature 1, it is disclosed that, in a reflective exposure mask used in EUV lithography, a multilayer film is formed by periodically stacking two or more material layers on a base substrate, and a pattern composed of a metal film containing a nitride or a mask pattern composed of a stacked structure of a metal film and a nitride metal film is formed on the multilayer film. In addition, in Patent Literature 2, a reflective EUV mask is disclosed in which a pattern composed of a metal film containing an ion-implanted element is formed as an absorption film on a multilayer reflective film.

[0004] In addition, the EUV lithography cannot use a refractive optical system that uses transmission of light as described above, and therefore the optical system component of an exposure apparatus does not use a lens but uses a mirror. Therefore, there is a problem that the incident light and the reflected light toward the EUV mask cannot be designed on the same axis, and in the EUV lithography, a method is generally adopted in which the optical axis is tilted by 6 degrees with respect to the vertical direction of the EUV mask to incident EUV light, and the reflected light reflected at an angle of -6 degrees is irradiated onto a semiconductor substrate.

[0005] Thus, in the EUV lithography, since the optical axis is tilted, the EUV light incident to the EUV mask forms a shadow of the pattern (absorption film pattern) of the EUV mask, and therefore there is a problem of a so-called "projection effect" in which the transfer performance is sometimes deteriorated.

[0006] In order to solve this problem, in Patent Literature 2, a method is disclosed in which by ion-implanting a material having a high extinction coefficient k in the absorption film, the absorption of the EUV light can be increased, and the EUV reflectance can be suppressed, so that the film thickness of the absorber layer (60 nm or less) can be made thinner than conventional.

[0007] With the development of miniaturization, dry etching has become common in the patterning of the light-shielding film of a transmissive photomask, and can also be applied to the patterning of the absorbing film in an EUV mask. However, the material with a high extinction coefficient k for EUV used in Patent Literature 2 is generally a material with a low dry etching rate. Therefore, the processability of the absorbing film deteriorates, and it is necessary to make the resist that becomes an etching mask thicker, and as a result, there is a problem that it is difficult to form a fine absorbing film pattern with a highly absorptive material.

[0008] In addition, in the defect correction process of the photomask manufacturing process, when performing electron beam correction etching, a material with a high extinction coefficient k is a material with an extremely slow etching rate, and it is difficult to correct defects, which can become a major problem.

[0009] Prior Art Documents

[0010] Patent Literature

[0011] Patent Literature 1: Japanese Patent Application Publication No. 2004-6798

[0012] Patent Literature 2: Japanese Patent Application Publication No. 2015-73013 SUMMARY

[0013] Problems to be Solved by the Invention

[0014] The present application was made to solve the above problems, and has an object to provide a reflective mask in which a fine absorbing film pattern can be formed even when a highly absorptive material is used as an absorbing film of an EUV mask, and in which a projection effect can be mitigated and electron beam correction etching can be performed, and a reflective mask blank for manufacturing the reflective mask.

[0015] Means for Solving the Problems

[0016] To achieve the above object, one embodiment of the present application relates to a reflective mask blank having a substrate, a reflective film having a multilayer film structure and reflecting EUV light formed on the substrate, a protective film formed on the reflective film and protecting the reflective film, and an absorbing film formed on the protective film and absorbing EUV light, characterized in that the absorbing film contains 50 atomic% or more of an element constituting at least one of tin oxide and indium oxide, and contains a material that is easily etched by a fluorine-based gas or a chlorine-based gas.

[0017] In addition, one aspect of the present invention relates to a reflective mask comprising: a substrate, a reflective film having a multilayer film structure and reflecting EUV light formed on the substrate, a protective film formed on the reflective film and protecting the reflective film, and an absorbing film formed on the protective film and absorbing EUV light, characterized in that the absorbing film contains more than 50 atomic percent of an element constituting at least one of tin oxide and indium oxide, and contains a material that is easily etched by fluorine-based gases or chlorine-based gases.

[0018] Effects of the present invention

[0019] According to one aspect of the present invention, a reflective mask and a reflective mask preform for fabricating the reflective mask utilize an absorbent film with high EUV light absorption and capable of dry etching. Therefore, a thinner resist film thickness than conventional methods can be used to form fine high-absorption film patterns. As a result, projection effects can be mitigated, and linewidth errors and pattern positional offsets on the wafer can be reduced. Furthermore, electron beam correction etching is possible.

[0020] Thus, if the reflective mask and the reflective mask blank used to fabricate the reflective mask are according to an aspect of the present invention, it is possible to provide a reflective mask and a reflective mask blank used to fabricate the reflective mask that can form fine absorption film patterns even when using a highly absorbent material as the absorption film of the EUV mask, thereby reducing the projection effect and enabling electron beam corrected etching. Attached Figure Description

[0021] [ Figure 1 [Illustration 1] is a schematic cross-sectional view showing the structure of a reflective photomask blank according to an embodiment of the present invention.

[0022] [ Figure 2 [Illustration 1] is a schematic cross-sectional view showing the structure of a reflective photomask according to an embodiment of the present invention.

[0023] [ Figure 3 [This is a graph showing the optical constants of various metals at the wavelength of EUV light.]

[0024] [ Figure 4 [1] is a graph showing the simulation results of the reflectivity of EUV light of a reflective photomask blank according to an embodiment of the present invention.

[0025] [ Figure 5 [1] is a graph showing the simulation results of the OD value of the reflective photomask blank at the wavelength of EUV light according to an embodiment of the present invention.

[0026] [ Figure 6This is a schematic cross-sectional view showing the side etching after electron beam corrected etching of a monolayer absorber film made of tin oxide.

[0027] [ Figure 7 [Illustration 1] is a schematic cross-sectional view showing the structure of a reflective photomask blank according to an embodiment of the present invention.

[0028] [ Figure 8 [Illustrated cross-sectional view] is a schematic cross-sectional view showing the manufacturing process of a reflective photomask according to an embodiment of the present invention.

[0029] [ Figure 9 [Illustrated cross-sectional view] is a schematic cross-sectional view showing the manufacturing process of a reflective photomask according to an embodiment of the present invention.

[0030] [ Figure 10 [Illustrated cross-sectional view] is a schematic cross-sectional view showing the manufacturing process of a reflective photomask according to an embodiment of the present invention.

[0031] [ Figure 11 [Illustrated cross-sectional view] is a schematic cross-sectional view illustrating the correction process of a reflective photomask according to an embodiment of the present invention. Detailed Implementation

[0032] Hereinafter, the reflective photomask blank and the various components of the reflective photomask involved in the present invention will be described with reference to the accompanying drawings.

[0033] (Overall structure)

[0034] Figure 1 This is a schematic cross-sectional view showing the structure of the reflective photomask blank (reflective photomask blank) 10 according to an embodiment of the present invention. Additionally, Figure 2 This is a schematic cross-sectional view showing the structure of a reflective photomask (reflective mask) 20 according to an embodiment of the present invention. Here, Figure 2 The reflective photomask 20 involved in the embodiment of the present invention shown is obtained by... Figure 1 The absorption film 4 of the reflective photomask blank 10 shown in the embodiment of the present invention is formed by patterning.

[0035] like Figure 1 As shown, the reflective photomask blank 10 according to an embodiment of the present invention includes: a multilayer reflective film (reflective film) 2 on a substrate 1, and a capping layer (protective layer) 3 on the multilayer reflective film 2. Thus, the multilayer reflective film 2 and the capping layer 3 are formed on the substrate 1. The capping layer 3 has an absorption film 4, and the absorption film 4 is composed of at least one layer.

[0036] (Substrate)

[0037] The substrate 1 according to the embodiment of the present application can use a flat Si substrate or a synthetic quartz substrate, or the like. In addition, the substrate 1 can use low thermal expansion glass to which titanium is added, but the present application is not limited to these as long as the material has a small thermal expansion rate.

[0038] (Multilayer reflective film)

[0039] The multilayer reflective film 2 according to the embodiment of the present application is a film that reflects EUV light (extreme ultraviolet light) as exposure light, and is composed of a multilayer reflective film in which materials having a large difference in refractive index for EUV light are combined. The multilayer reflective film 2 can be formed, for example, by repeatedly laminating a combination layer of Mo (molybdenum) and Si (silicon), or Mo (molybdenum) and Be (beryllium) for about 40 cycles.

[0040] (Capping layer)

[0041] The capping layer 3 according to the embodiment of the present application is formed of a material that has resistance to dry etching performed when the pattern of the absorption film 4 is formed, and functions as an etching stopper layer that prevents damage to the multilayer reflective film 2 when the absorption film pattern is etched. Here, depending on the material of the multilayer reflective film 2 and the etching conditions, the capping layer 3 can not be provided. In addition, although not shown, a back surface conductive film can be formed on the surface of the substrate 1 on which the multilayer reflective film 2 is not formed. The back surface conductive film is a film that is fixed using the principle of an electrostatic chuck when the reflective photomask 20 is set on an exposure machine.

[0042] As shown in FIG. 1, the reflective photomask blank 10 includes a substrate 1, a multilayer reflective film 2, a capping layer 3, and an absorption film 4. The substrate 1 is formed of a material that has a small thermal expansion rate, and is formed in a circular shape. The multilayer reflective film 2 is formed on the substrate 1, and is a film that reflects EUV light as exposure light. The capping layer 3 is formed on the multilayer reflective film 2, and is a film that has resistance to dry etching performed when the pattern of the absorption film 4 is formed. The absorption film 4 is formed on the capping layer 3, and is a film that absorbs EUV light. Figure 2 As shown in FIG. 1, the reflective photomask blank 10 includes a substrate 1, a multilayer reflective film 2, a capping layer 3, and an absorption film 4. The substrate 1 is formed of a material that has a small thermal expansion rate, and is formed in a circular shape. The multilayer reflective film 2 is formed on the substrate 1, and is a film that reflects EUV light as exposure light. The capping layer 3 is formed on the multilayer reflective film 2, and is a film that has resistance to dry etching performed when the pattern of the absorption film 4 is formed. The absorption film 4 is formed on the capping layer 3, and is a film that absorbs EUV light.

[0043] Figure 3 is a graph showing the optical constants of each metal material for EUV light having a wavelength of 13.5 nm. Figure 3The horizontal axis represents the refractive index n, and the vertical axis represents the extinction coefficient k. Tantalum (Ta), the main material of the conventional absorption film 4, has an extinction coefficient k of 0.041. If a compound material with an extinction coefficient k greater than Ta is used, the thickness of the absorption film 4 can be reduced compared to the conventional method. By using a material with an extinction coefficient k of 0.06 or higher as the main component, the thickness of the absorption film 4 can be sufficiently reduced, thereby minimizing the projection effect.

[0044] Materials that satisfy the combination of optical constants (nk values) as described above, such as Figure 3 As shown, materials such as silver (Ag), indium (In), tin (Sn), nickel (Ni), and tellurium (Te) have extinction coefficients k ranging from 0.07 to 0.08. With any of these materials, the extinction coefficient k can be significantly increased to approximately twice that of tantalum (Ta), a traditional absorbent film material, which has an extinction coefficient of 0.041, thus achieving high light absorption. However, these highly absorbent materials have poor dry etching properties (in other words, the halides of these elements have low volatility), making them difficult to process into masks, or their low melting points prevent them from withstanding the heat during mask fabrication or EUV exposure, rendering them almost impractical as masks.

[0045] To avoid such drawbacks, the absorption film 4 of the reflective photomask blank 10 and the absorption film pattern 14a of the reflective photomask 20 involved in this embodiment are formed from tin oxide (SnO) film or indium oxide (InO) film. Tin (Sn) and indium (In) have relatively low melting points, around 230°C and 160°C respectively, posing problems with thermal stability. However, by forming tin oxide (SnO) film or indium oxide (InO) film, their respective melting points can be significantly increased. Multiple tin oxide (SnO) films were actually fabricated using reactive sputtering, and their melting points were measured using a thermal analysis device. The results showed that the tin oxide (SnO) film had a melting point of 1630°C, and the indium oxide (InO) film had a melting point of 1910°C, both higher than their respective elemental melting points.

[0046] Furthermore, tin oxide (SnO) and indium oxide (InO) films are chemically stable, making them difficult to etch with fluorine-based gases (such as fluorine-containing etching gases like CF4 or SF6) or chlorine-based gases (such as chlorine-containing etching gases like Cl2 or HCl) commonly used in dry etching. In this case, due to the low dry etching rate, the resist formed on the absorption film 4 needs to be thickened, resulting in difficulty in forming fine absorption film patterns 14a.

[0047] On the contrary, by mixing a material having a property of being easily etched by a fluorine-based gas or a chlorine-based gas in a tin oxide (SnO) film or an indium oxide (InO) film, respectively, the etching rate when using a fluorine-based gas or a chlorine-based gas can be improved. Thus, the resist film thickness on the absorption film 4 can be reduced, and as a result, the difficulty of forming a fine absorption film pattern 14a with a highly absorptive material can be reduced.

[0048] Generally, in dry etching, a gas introduced into a plasma collides with electrons, and active radicals and various forms of reactive ions are generated to cause etching, but the more volatile products with low boiling points are formed on the etching surface, the more easily etching is performed. Then, as an index thereof, the boiling point and the vapor pressure of a reaction product formed by the etched material and the introduced gas are used. That is, the more the reaction product with a low boiling point is vaporized, and the higher the vapor pressure is, the more easily the gas is exhausted.

[0049] Hereinafter, the definitions of the above-described "easily etched" and "difficult to be etched" in the etching of the absorption film 4 of the reflective photomask blank 10 will be described.

[0050] The case of being easily etched by a chlorine-based gas means that the boiling point of at least one chlorine-based compound generated by etching is 250°C or lower, and the case of being difficult to be etched by a chlorine-based gas means that the boiling point of a stoichiometrically obtainable form of chloride is 300°C or higher. Note that the same applies to a fluorine-based gas.

[0051] The absorption film 4 provided in the reflective photomask blank 10 and the absorption film pattern 14a provided in the reflective photomask 20 according to the embodiment of the present application are a tin oxide (SnO) film or an indium oxide (InO) film containing a mixed material that is easily etched by a fluorine-based gas or a chlorine-based gas, and are a film in which the atomic ratio of the above-described mixed material to tin oxide (SnO) or indium oxide (InO) is more than 0% and is within a range of 45% or less. That is, a film in which the atomic ratio of tin oxide (SnO) or indium oxide (InO) is more than 50% and is less than 100%. As long as the compound material is within the range, the refractive index as an optical constant for EUV light is almost not changed. In addition, the extinction coefficient k varies depending on the atomic ratio, but for the absorption film 4 (absorption film pattern 14a), a film thickness of 45 nm or less and an EUV reflectance of 3% or less can be achieved. Thus, the tin oxide (SnO) film or the indium oxide (InO) film containing the mixed material that is easily etched by a fluorine-based gas or a chlorine-based gas can achieve higher light absorbance than the existing absorption film formation material, i.e., tantalum (Ta).

[0052] In fact, when a plurality of silicon (Si) -containing tin oxide (SnO) film samples having a content of tin oxide (SnO) in a range of more than 50% and less than 100% and a content of various metals varied are produced and reflectance at an EUV light wavelength (13.5 nm) is measured, it is possible to achieve EUV reflectance of 3% or less with a film thickness thinner than the film thickness (about 60 nm) of the existing tantalum (Ta) absorption film.

[0053] That is, the reflection-type mask blank 10 according to the present embodiment has a substrate 1, a reflection film 2 having a multilayer film structure and reflecting EUV light formed on the substrate 1, a cap layer 3 formed on the reflection film 2 and protecting the reflection film 2, and an absorption film 4 formed on the cap layer 3 and absorbing EUV light, the absorption film 4 containing 50 atomic % or more of an element constituting at least one of tin oxide (SnO) and indium oxide (InO) and containing a material that is easily etched by a fluorine-based gas or a chlorine-based gas.

[0054] In addition, the reflection-type mask 20 according to the present embodiment has a substrate 11, a reflection film 12 having a multilayer film structure and reflecting EUV light formed on the substrate 11, a cap layer 13 formed on the reflection film 12 and protecting the reflection film 12, and an absorption film pattern 14a formed on the cap layer 13 and absorbing EUV light, the absorption film pattern 14a containing 50 atomic % or more of an element constituting at least one of tin oxide (SnO) and indium oxide (InO) and containing a material that is easily etched by a fluorine-based gas or a chlorine-based gas.

[0055] In order to achieve the above-described etching process, it is desirable to use a substance having a low boiling point of a fluorine-based compound or a chlorine-based compound, which is a material that is easily etched by a fluorine-based gas or a chlorine-based gas, as the material mixed in the absorption film 4 (absorption film pattern 14a). That is, as the material mixed in the absorption film 4 (absorption film pattern 14a), it is desirable to select a substance whose boiling point becomes lower in a fluorinated or chlorinated state.

[0056] Table 1 shows the boiling points of tin (Sn), indium (In), and halogen compounds of metals as preferred as the absorbing material (main component) of the reflective photomask 20 according to the present embodiment, and as the mixed material. The values in Table 1 are a summary of values found in various literatures (CRC Handbook of Chemistry and Ohysics, 97th Edition (2016) and the like) and websites. As shown in Table 1, as the mixed material that is easily etched by a fluorine-based gas, silicon, antimony, iridium, osmium, rhenium, tungsten, germanium, arsenic, vanadium, selenium, molybdenum, and tantalum are desirable. As the mixed material that is easily etched by a chlorine-based gas, silicon, chromium, germanium, arsenic, vanadium, titanium, tantalum, aluminum, and the like are desirable. In addition, oxides, nitrides, oxynitrides, or boron nitrides of these mixed materials can also be used. In addition, as the etching gas, a mixed gas of a fluorine-based gas and a chlorine-based gas can also be used, and a non-halogen gas such as oxygen and hydrogen can also be included in order to promote the reaction.

[0057] [Table 1]

[0058]

[0059] Not limited to EUV exposure, in achieving transfer using projection exposure, the optical property required for a photomask is first mask contrast. In general, in a transmissive mask, the mask contrast is evaluated by the following formula (1) when the transmittance of the transparent substrate portion is set to To, and the transmittance of the pattern portion including the light shielding film is set to T.

[0060] OD = -log (T / To) (1)

[0061] Here, OD is called optical density, and indicates the degree of light shielding of the light shielding film.

[0062] In an EUV mask, the mask contrast can also be evaluated in the same manner, when the reflectance of the high reflection portion composed of the multilayer reflection film 12 and the protective film 13 is set to Ro, and the reflectance from the low reflection portion including the absorbing film pattern 14a is set to R (refer to Figure 2 ), and is evaluated by the following formula (2) in the same manner as the transmissive mask.

[0063] OD = -log (R / R0) (2)

[0064] In the reflective photomask blank 10 and the reflective photomask 20, in general, the higher the OD value is, the better. Figure 4 EUV light reflectance and Figure 5The shown OD values are calculated using the optical constants (refractive index, extinction coefficient) and film thicknesses of the respective layers for a reflective photomask blank 10 in which a capping layer (protective layer) 3 of Ru having a thickness of 2.5 nm is present below each absorption film 4, further a multilayer reflective film 2 of a stack of layers of Si and Mo is present below the same, a plurality of pairs (for example, 40 pairs) of which are stacked, a flat synthetic quartz substrate (substrate 1) is present below the same, and a back surface conductive film of CrN is further present on the back surface of the synthetic quartz substrate. That is, the OD values are calculated on the basis of the following formula (1) in which the back surface conductive film is not taken into account. Figure 1 The reflective photomask blank 10 shown above and Figure 2 The back surface of the substrate 1 of each of the reflective photomask 20 shown above is provided with a back surface conductive film. However, the materials and film thicknesses of the multilayer reflective film 2, 12, the capping layer 3, 13, the back surface conductive film, and the substrate 1, 11 of the reflective photomask blank 10 and the reflective photomask 20 according to the present embodiment are not limited thereto.

[0065] As is apparent from Figure 4 As is apparent from the above, the SnO film containing Si can greatly reduce the EUV light reflectance with respect to the Ta film at the same film thickness. In addition, the SnO film containing Si can greatly reduce the film thickness with respect to the Ta film at the same reflectance. Thus, the SnO film containing Si is effective as a constituent element of a high-absorption film at the wavelength of EUV light.

[0066] As is apparent from Figure 5 As is apparent from the above, in order to obtain an OD value of 1 or more, the Ta film requires a film thickness of at least about 40 nm, whereas the SnO film containing Si can have a film thickness of about 18 nm. As is apparent from the above, the SnO film containing Si is effective as a constituent element that can reduce the overall thickness of the absorption film 4 with respect to the Ta film from the viewpoint of the OD value.

[0067] In addition, in order to obtain an OD value of 2 or more, the Ta film requires a film thickness of at least about 70 nm, whereas the SnO film containing Si can have a film thickness of 33 nm. As is apparent from the above, the SnO film containing Si is also effective as a constituent element that can reduce the overall thickness of the absorption film 4 with respect to the Ta film in an OD value of 2 or more. In conventional absorption films, a Ta film having a film thickness of about 70 nm (OD value of 2) is used as a standard.

[0068] Thus, by using the tin oxide (SnO) film containing silicon (Si) as the absorption film 4 (absorption film pattern 14a), it is possible to keep the OD value, which indicates the basic performance of the reflective photomask blank 10 and the reflective photomask 20, constant, and to thin the absorption film 4 (absorption film pattern 14a).

[0069] Next, in order to evaluate the influence of the projection effect, the change in the HV bias value when the film thickness is changed was compared by simulation for the tantalum (Ta) film and the tin oxide (SnO) film containing silicon (Si), respectively. The HV bias value is the line width difference of the transfer pattern depending on the direction of the mask pattern, that is, the difference between the line width in the horizontal (Horizontal: H) direction and the line width in the vertical (Vertical: V) direction. The line width in the H direction indicates the line width of a linear pattern orthogonal to a plane formed by incident light and reflected light (hereinafter, sometimes referred to as "incident plane"), and the line width in the V direction indicates the line width of a linear pattern parallel to the incident plane. That is, the line width in the H direction is the length in the direction parallel to the incident plane, and the line width in the V direction is the length in the direction orthogonal to the incident plane.

[0070] The line width in the H direction is influenced by the projection effect, and the contrast of the edge portion of the transfer pattern decreases and the line width in the H direction decreases. The pattern influenced by the projection effect has a line width after transfer that is smaller than the desired line width. On the other hand, the line width in the V direction is hardly influenced by the projection effect. Therefore, the line width of the transfer pattern in the direction perpendicular to the incident plane and the line width of the transfer pattern in the direction parallel to the incident plane produce a line width difference (HV bias).

[0071] Here, the HV bias values of the existing tantalum (Ta) film (film thickness 60 nm) and the tin oxide (SnO) film containing silicon (Si) (film thickness 26 nm) were compared, and the results are shown in Table 2. The HV bias value was very large, 7.3 nm, in the tantalum (Ta) film, but could be greatly reduced to 4.0 nm in the tin oxide (SnO) film containing silicon (Si), and was improved. Thus, in the reflective photomask blank 10 and the reflective photomask 20 of the present embodiment, by using the tin oxide (SnO) film containing silicon (Si) as the material for forming the absorption film 4 (absorption film pattern 14a), it is possible to greatly reduce the influence of the projection effect (HV bias).

[0072] As described above, in order to have heat resistance, the material used in the absorption film 4 (absorption film pattern 14a) is more desirably an oxide than a single substance. In order to have heat resistance, it is necessary to be in a state where a single substance is reliably bonded with oxygen. That is, as the tin oxide (SnO) film, the indium oxide (InO) film used in the absorption film 4 (absorption film pattern 14a) of the present embodiment, it is preferable that the atomic ratio (O / Sn) of oxygen (O) to tin (Sn) of the tin oxide (SnO) film be between 1.5 or more and 2.5 or less, and the atomic ratio (O / In) of oxygen (O) to indium (In) of the indium oxide (InO) film be between 1.0 or more and 2.0 or less.

[0073] Figure 6 is a schematic cross-sectional view showing the absorption film pattern 14a after the electron beam correction etching process when tin oxide (SnO) is selected as a main component (formation material) for forming the absorption film 14 to manufacture the reflective photomask 20.

[0074] In the electron beam correction etching, for example, by supplying an etching gas such as a fluorine-based gas (XeF2) while irradiating an electron beam to the etching site, the reactivity of the etchant of fluorine is promoted to etch the tin oxide (SnO). However, the tin oxide (SnO) has strong etching resistance to the fluorine-based gas, and it takes a very long time to etch, and thus, damage called side etching BS perpendicular to the etching direction as shown in 14b can occur. When the side etching BS is large, the line width of the site where the electron beam correction etching is performed is greatly shifted, and thus, it takes a very long time to etch due to the strong etching resistance to the etching gas, which becomes one of the reasons for the correction failure. Figure 6

[0075] Here, by using the tin oxide (SnO) containing a material whose boiling point is 250°C or less, which is easily etched by the fluorine-based gas, that is, a fluorine compound, as the absorption film 4 (absorption film pattern 14a), it is possible to improve the correction etching rate, and suppress the side etching BS to 2 nm or less, and thus, it is possible to improve the success rate of the electron beam correction etching. Therefore, in the case where the correction side etching BS is 2 nm or less by the fluorine-based gas, it can be considered that the material is fast in the correction etching rate. The same is true for the case where the indium oxide (InO) is used as the absorption film 4 (absorption film pattern 14a).

[0076] ​In addition, in the case where the protective film 13 of the substrate is etched by electron beam correction etching using a fluorine-based gas, electron beam correction etching can be performed using a chlorine-based gas (NOCl). Indium oxide (InO) is difficult to be etched by a chlorine-based gas, and thus side etching BS can also occur. In this case, by using indium oxide (InO) containing a material that is easily etched by a chlorine-based gas, i.e., a material having a boiling point of a chlorine compound of 250°C or less, as the absorption film 4 (absorption film pattern 14a), the correction etching rate can be improved, and side etching BS can be suppressed, and thus the success rate of electron beam correction etching can be improved.

[0077] In order to achieve the above-described etching process, the material mixed in the absorption film 4 (absorption film pattern 14a) is desirably a material that can be subjected to electron beam correction etching using a fluorine-based gas or a chlorine-based gas, i.e., a material having a boiling point of a fluorine compound or a chlorine compound of 250°C or less. Specifically, as a mixed material that is easily etched by a fluorine-based gas, silicon, antimony, iridium, osmium, rhenium, tungsten, germanium, arsenic, vanadium, selenium, molybdenum, and tantalum are desirable, as shown in Table 1. As a mixed material that is easily etched by a chlorine-based gas, silicon, chromium, germanium, arsenic, vanadium, titanium, tantalum, aluminum, and the like are desirable. In addition, oxides, nitrides, oxynitrides, or boron nitrides of these mixed materials can also be used. In addition, a mixed gas of a fluorine-based gas and a chlorine-based gas can also be used as the etching gas.

[0078] Thus, the absorption film 4 (absorption film pattern 14a) according to the present embodiment contains a material having a faster correction etching rate at the time of electron beam correction than an absorption film (absorption film pattern) composed of only at least one of tin oxide (SnO) and indium oxide (InO). Here, the "material having a faster correction etching rate at the time of electron beam correction" refers to the above-described "material that can be subjected to electron beam correction etching using a fluorine-based gas or a chlorine-based gas".

[0079] In addition, since the use of the above-described mixed material reduces the resistance to chemical solutions such as SPM (sulfuric acid / hydrogen peroxide water mixed solution) and APM (ammonia / hydrogen peroxide water mixed solution) that are typically used for mask cleaning, the absorption film surface becomes rough, and disadvantages such as adverse effects on reflectivity occur, in the above-described case, a layer having cleaning resistance of about 1 to 5 nm can be provided on the absorption film 4 (absorption film pattern 14a). As another method, a coating film having cleaning resistance can be provided to cover the absorption film 4 (absorption film pattern 14a) exposed on the mask surface, or the cap layer 3, 13.

[0080] As the material used for the layer or coating film having cleaning resistance, for example, a material containing at least one of SiO2, SiON, TaO, TaN, TaBN, CrN, CrON, CrO, TiO2, and the like can be listed.

[0081] [Example 1]

[0082] Hereinafter, embodiments of the reflective photomask blank and photomask involved in the present invention will be described using figures and tables.

[0083] like Figure 7 As shown, a multilayer reflective film 12, consisting of 40 layers of silicon (Si) and molybdenum (Mo) stacked together, is formed on a synthetic quartz substrate 11 with low thermal expansion properties. The thickness of the multilayer reflective film 12 is set to 280 nm.

[0084] Next, a capping layer 13 made of ruthenium (Ru) as an intermediate film is formed on the multilayer reflective film 12 with a thickness of 2.5 nm. Thus, a reflective portion having the multilayer reflective film 12 and the capping layer 13 is formed on the substrate 11. An absorption film 14 made of tin oxide (SnO) and silicon (Si) is formed on the capping layer 13 with a thickness of 26 nm. The atomic ratio of tin (Sn), oxygen (O), and silicon (Si) was measured by XPS (X-ray photoelectron spectroscopy) and the result was 31.7:63.3:5.0. Furthermore, XRD (X-ray diffraction) was performed, and although slight crystallinity was observed, the material was amorphous.

[0085] Next, a back conductive film 15 formed of chromium nitride (CrN) with a thickness of 100 nm is formed on the side of the substrate 11 where the multilayer reflective film 12 is not formed, thereby fabricating a reflective photomask blank 100.

[0086] The films on the substrate 11 were formed using a multi-element sputtering apparatus. The thickness of each film was controlled by the sputtering time.

[0087] Regarding the aforementioned tin oxide (SnO) film containing silicon (Si), the reflectivity R0 of the reflective layer region and the reflectivity R of the absorption film region were measured using an EUV light reflectance measuring device. Based on the measurement results, the OD value as a mask characteristic was calculated, and the results are shown in Table 2. It is possible to fabricate a mask with an EUV reflectivity of 0.08% and an OD value of 2.9.

[0088] Next, use Figure 8 to Figure 10 The fabrication method of the reflective photomask 200 is explained.

[0089] like Figure 8 As shown, a positive chemical amplification resist (SEBP9012: manufactured by Shin-Etsu Chemical Co., Ltd.) with a film thickness of 120 nm is formed on the absorption film 14 of the reflective photomask blank 100 using a spin coater, and then baked at 110°C for 10 minutes to form a resist film 16.

[0090] Next, a predetermined pattern is drawn on the resist film 16 formed of a positive chemical amplification resist using an electron beam drawing machine (JBX3030: manufactured by JEOL Ltd.). Then, a baking treatment is performed at 110°C for 10 minutes, and then a spray development (SFG3000: manufactured by "SIGMA MECHANICAL TECHNOLOGY LTD.") is performed. Thus, as shown in FIG. 1, the resist pattern 16a is formed. Figure 9

[0091] Next, as shown in FIG. 2, the resist pattern 16a is used as an etching mask, and the absorption film 14 is patterned by dry etching using a mixed gas of a chlorine-based gas and a fluorine-based gas as a main component, thereby forming an absorption film pattern 14a. Figure 9

[0092] As shown in Table 2, it is found that the resist selectivity of the present base is improved compared to the SnO 100% film.

[0093] Next, as shown in FIG. 3, the resist pattern 16a is peeled off to form the absorption film pattern 14a, thereby producing the reflective photomask 200 of Example 1. In Example 1, the absorption film pattern 14a formed of the absorption film 14 that functions as a low reflection layer is a line width 64 nm LS (line width and pitch) pattern. The line width 64 nm LS pattern is designed in the x direction and the y direction, respectively, in a manner that the influence of the projection effect due to EUV irradiation is easily observed. Figure 10

[0094] ​​​An EUV exposure device (NXE3300B: manufactured by ASML) was used to transfer exposure of the absorption film pattern 14a of the reflective photomask 200 produced in each of the examples described below and each of the comparative examples described below to a semiconductor wafer on which an EUV positive chemically amplified resist was applied. At this time, the exposure amount was adjusted so that the x-direction LS pattern was transferred as designed. Observation and line width measurement of the resist pattern after transfer were performed using an electron beam size measuring instrument, and the resolution and HV deviation were confirmed. More specifically, in Example 1, the y-direction LS pattern was properly transferred, and the magnitude of the HV deviation when compared with the case in which a conventional tantalum (Ta) mask was used was evaluated. That is, a case in which the y-direction LS pattern was transferred as designed and the HV deviation was smaller than when a conventional tantalum (Ta) mask was used was rated as "pass" in a state in which the exposure amount was adjusted so that the x-direction LS pattern was transferred as designed; a case in which the y-direction LS pattern was not transferred as designed (a case in which the y-direction LS pattern was not resolved) or the HV deviation was larger than when a conventional tantalum (Ta) mask was used was rated as "fail". As shown in Table 2, the y-direction LS pattern size was 12.0 nm with respect to a design value of 16.0 nm, and the HV deviation was 4.0 nm. That is, the reflective photomask 200 of Example 1 had a pattern transfer property that was not problematic in use.

[0095] Note that, regarding the "conventional tantalum (Ta) mask" described above, "Reference Example" is described in Table 2.

[0096] Figure 11 An enlarged view of a portion of the absorption film pattern 14a in the reflective photomask 200 is shown. Here, a specific method for electron beam correction etching with respect to the absorption film pattern 14a formed using the resist pattern 16a and by dry etching processing is explained. First, an electron beam correction machine (MeRiT MG45: manufactured by Carl Zeiss) was used to irradiate the absorption film pattern 14a as the topmost layer with an electron beam in a gas atmosphere in which a fluorine-based gas and oxygen were mixed to perform electron beam correction etching. The fluorine gas flow at this time was performed using a cold trap technique with temperature control. With respect to the temperature, the fluorine was -26°C (hereinafter, referred to as the control temperature), and the oxygen was -43°C. The line width was measured using an SEM (LWM9045: manufactured by ADVANTEST), and it was confirmed that the side etching BS at this time was less than 1 nm.

[0097] Note that, in the "determination" column of Table 2, a case in which an advantage was observed in both the OD value and the transfer property compared with the conventional tantalum (Ta) mask was indicated as "0"; a case in which an advantage was not observed in at least one of the OD value and the transfer property was indicated as "A"; and a case in which at least one of the OD value and the transfer property was deteriorated was indicated as "X".

[0098] [Table 2]

[0099]

[0100] [Example 2]

[0101] The absorption film 14 was formed of tin oxide (SnO) and silicon (Si) and was formed so that the film thickness thereof became 45 nm. The atomic ratio of tin (Sn) to oxygen (O) to silicon (Si) was measured by XPS (X-ray photoelectron spectroscopy) and was 16.7:33.3:50.0. The method of forming other films and the method of making a mask were the same as in Example 1. The etching selectivity with respect to the resist film 16 (resist selectivity) was calculated and it was found that the film was better than 100% tin oxide (SnO).

[0102] In addition, measurement was performed by a reflectance measuring device that utilizes EUV light and the OD value as a mask characteristic was calculated and the results are shown in Table 2. It was found that the EUV reflectance was 1.8% and the OD value was 1.6.

[0103] In the transferability evaluation using EUV exposure, the LS pattern size in the y direction was 10.7 nm with respect to the design value of 16.0 nm and the HV deviation was 5.3 nm. That is, the reflective photomask 200 of Example 2 had pattern transferability that was not problematic in use.

[0104] In the electron beam etching correction, the control temperature of the fluorine gas flow was set to -20°C and that of oxygen was set to -43°C. It was confirmed that the side etching BS at this time was less than 1 nm.

[0105] [Comparative Example 1]

[0106] The absorption film 14 was formed of tin oxide (SnO) and silicon (Si) and was formed so that the film thickness thereof became 45 nm. The atomic ratio of tin (Sn) to oxygen (O) to silicon (Si) was measured by XPS (X-ray photoelectron spectroscopy) and was 10.0:20.0:70.0. The method of forming other films and the method of making a mask were the same as in Example 1. The etching selectivity with respect to the resist film 16 (resist selectivity) was calculated and it was found that the film was better than 100% tin oxide (SnO).

[0107] In addition, measurement was performed by a reflectance measuring device that utilizes EUV light and the OD value as a mask characteristic was calculated and the results are shown in Table 2. It was found that the EUV reflectance was 5.1% and the OD value was 1.1. That is, the EUV light reflectance was higher than that of the existing tantalum (Ta) mask.

[0108] In the transferability evaluation using EUV exposure, the LS pattern size in the y direction was 12.9 nm with respect to the design value of 16.0 nm, and the HV deviation was 3.1 nm.

[0109] In the electron beam etching correction, the control temperature of the fluorine gas flow was set to -20°C, and that of the oxygen was set to -43°C. It was confirmed that the side etching BS at this time was less than 1 nm.

[0110] [Example 3]

[0111] The absorption film 14 was formed of indium oxide (InO) and molybdenum (Mo), and was formed so that the film thickness thereof became 27 nm. The atomic ratio of indium (In) to oxygen (O) to molybdenum (Mo) was measured by XPS (X-ray photoelectron spectroscopy), and the result was 38.0:57.0:5.0. The film formation method and the mask production method of the other films were the same as in Example 1. The etching selectivity with respect to the resist film 16 (resist selectivity) was calculated, and it was found that the film was better than the 100% indium oxide (InO) film.

[0112] In addition, the reflectance measurement device using EUV light was used for measurement, and the OD value as a mask characteristic was calculated, and the result is shown in Table 2. It was found that the EUV reflectance was 1.0%, and the OD value was 1.8.

[0113] In the transferability evaluation using EUV exposure, the LS pattern size in the y direction was 12.9 nm with respect to the design value of 16.0 nm, and the HV deviation was 3.1 nm.

[0114] In the electron beam etching correction, the control temperature of the fluorine gas flow was set to -20°C, and that of the oxygen was set to -43°C. It was confirmed that the side etching BS at this time was less than 1 nm.

[0115] [Example 4]

[0116] The absorption film 14 was formed of indium oxide (InO) and molybdenum (Mo), and was formed so that the film thickness thereof became 34 nm. The atomic ratio of indium (In) to oxygen (O) to molybdenum (Mo) was measured by XPS (X-ray photoelectron spectroscopy), and the result was 24.0:36.0:40.0. The film formation method and the mask production method of the other films were the same as in Example 1. The etching selectivity with respect to the resist film 16 (resist selectivity) was calculated, and it was found that the film was better than the 100% indium oxide (InO) film.

[0117] In addition, the reflectance measuring device using EUV light was used for measurement, and the OD value as a mask characteristic was calculated, and as a result, as shown in Table 2, it was found that the EUV reflectance was 2.3% and the OD value was 1.4.

[0118] In the transferability evaluation using EUV exposure, the LS pattern size in the y direction was 11.0 nm with respect to the design value of 16.0 nm, and the HV deviation was 5.0 nm. That is, the reflective photomask 200 of Example 4 had pattern transferability that was not problematic in use.

[0119] In the electron beam etching correction, the control temperature of the fluorine gas flow was set to -20°C, and the oxygen was set to -43°C. It was confirmed that the side etching BS at this time was less than 1 nm.

[0120] [Comparative Example 2]

[0121] The absorption film 14 was formed of indium oxide (InO) and molybdenum (Mo), and was formed so that the film thickness thereof was 42 nm. The atomic ratio of indium (In) to oxygen (O) to molybdenum (Mo) was measured by XPS (X-ray photoelectron spectroscopy), and the result was 24.0:36.0:40.0. The method of forming the other films and the method of making the mask were the same as in Example 1. The etching selectivity with respect to the resist film 16 (resist selectivity) was calculated, and as a result, it was found that the film was better than the indium oxide (InO) 100%.

[0122] In addition, the reflectance measuring device using EUV light was used for measurement, and the OD value as a mask characteristic was calculated, and as a result, as shown in Table 2, it was found that the EUV reflectance was 1.0% and the OD value was 1.8.

[0123] In the transferability evaluation using EUV exposure, the LS pattern size in the y direction was 7.0 nm with respect to the design value of 16.0 nm, and the HV deviation was 9.0 nm. That is, the pattern transferability of the reflective photomask 200 of Comparative Example 3 was worse than that of the existing tantalum (Ta) mask, and no advantage was observed.

[0124] In the electron beam etching correction, the control temperature of the fluorine gas flow was set to -20°C, and the oxygen was set to -43°C. It was confirmed that the side etching BS at this time was less than 1 nm.

[0125] [Comparative Example 3]

[0126] The absorption film 14 was formed of indium oxide (InO) and molybdenum (Mo) and was formed so that the film thickness thereof became 50 nm. The atomic ratio of indium (In) to oxygen (O) to molybdenum (Mo) was measured by XPS (X-ray photoelectron spectroscopy) and was 24.0:36.0:40.0. The method of forming other films and the method of making a mask were the same as in Example 1. The etching selectivity with respect to the resist film 16 (resist selectivity) was calculated and it was found that the film was better than 100% of indium oxide (InO).

[0127] In addition, measurement was performed by a reflectance measuring device using EUV light and the OD value as a mask characteristic was calculated and the results are shown in Table 2. It was found that the EUV reflectance was 0.7% and the OD value was 2.0.

[0128] In the transferability evaluation using EUV exposure, the LS pattern size in the y direction could not be resolved with respect to the design value of 16.0 nm. That is, the pattern transferability of the reflective photomask 200 of Comparative Example 4 was worse than that of the existing tantalum (Ta) mask and no advantage was observed.

[0129] In the electron beam etching correction, the control temperature of the fluorine gas flow was set to -20°C and that of oxygen was set to -43°C. It was confirmed that the side etching BS at this time was less than 1 nm.

[0130] [Comparative Example 4]

[0131] The absorption film 14 was formed of indium oxide (InO) and molybdenum (Mo) and was formed so that the film thickness thereof became 45 nm. The atomic ratio of indium (In) to oxygen (O) to molybdenum (Mo) was measured by XPS (X-ray photoelectron spectroscopy) and was 16.0:24.0:60.0. The method of forming other films and the method of making a mask were the same as in Example 1. The etching selectivity with respect to the resist film 16 (resist selectivity) was calculated and it was found that the film was better than 100% of indium oxide (InO).

[0132] In addition, measurement was performed by a reflectance measuring device using EUV light and the OD value as a mask characteristic was calculated and the results are shown in Table 2. It was found that the EUV reflectance was 6.6% and the OD value was 1.0. That is, the EUV light reflectance was higher than that of the existing tantalum (Ta) mask.

[0133] In the transferability evaluation using EUV exposure, the LS pattern size in the y direction was 6.4 nm with respect to the design value of 16.0 nm and the HV deviation was 9.6 nm. That is, the pattern transferability of the reflective photomask 200 of Comparative Example 5 was worse than that of the existing tantalum (Ta) mask and no advantage was observed.

[0134] In the electron beam etching correction, the control temperature of the fluorine gas flow was set to -20°C and that of the oxygen to -43°C. It was confirmed that the side etching BS at this time was less than 1 nm.

[0135] Industrial applicability

[0136] The reflective photomask according to the present application is applicable to formation of a fine pattern by EUV exposure in a manufacturing process of a semiconductor integrated circuit or the like.

[0137] Explanation of symbols

[0138] 1 … substrate

[0139] 2 … multilayer reflective film

[0140] 3 … capping layer

[0141] 4 … absorption film

[0142] 10 … reflective photomask blank (reflective mask blank)

[0143] 11 … substrate

[0144] 12 … multilayer reflective film

[0145] 13 … capping layer

[0146] 14 … absorption film

[0147] 14a … absorption film pattern

[0148] 14b … electron beam correction etching site in the absorption film pattern

[0149] 15 … back surface conductive film

[0150] 16 … resist film

[0151] 16a … resist pattern

[0152] BS … side etching

[0153] 20 … reflective photomask (reflective mask)

[0154] 100 … reflective photomask blank (reflective mask blank)

[0155] 200 … reflective photomask (reflective mask)

Claims

1. A reflective mask blank, comprising: a substrate, a reflective film having a multilayer film structure and reflecting EUV light formed on the substrate, a protective film formed on the reflective film and protecting the reflective film, and an absorbing film formed on the protective film and absorbing EUV light, characterized in that: the absorbing film contains 50 atomic% or more of an element constituting indium oxide, and contains a material that is easily etched by a fluorine-based gas or a chlorine-based gas, the material that is easily etched by the fluorine-based gas is at least one selected from the group consisting of antimony, iridium, osmium, rhenium, tungsten, germanium, vanadium, selenium, molybdenum, and oxides, nitrides, oxynitrides, and boron nitride compounds thereof, and the material that is easily etched by the chlorine-based gas is at least one selected from the group consisting of germanium, vanadium, titanium, aluminum, and oxides, nitrides, oxynitrides, and boron nitride compounds thereof.

2. The reflective mask blank according to claim 1, characterized in that: a film thickness of the absorbing film is 45 nm or less, and an OD value (Optical Density) is 1.0 or more.

3. The reflective mask blank according to claim 1 or claim 2, characterized in that: an atomic ratio (O / In) of oxygen (O) to indium (In) in the absorbing film is in a range of 1.0 or more and 2.0 or less.

4. The reflective mask blank according to any one of claims 1 to 3, characterized in that: the absorbing film contains a material that has a faster correction etching rate at electron beam correction than an absorbing film composed of only at least one of tin oxide and indium oxide.

5. A reflective mask, characterized by comprising: a substrate, a reflective film having a multilayer film structure and reflecting EUV light formed on the substrate, a protective film formed on the reflective film and protecting the reflective film, and an absorbing film formed on the protective film and absorbing EUV light, the absorbing film contains 50 atomic% or more of an element constituting indium oxide, and contains a material that is easily etched by a fluorine-based gas or a chlorine-based gas, the material that is easily etched by the fluorine-based gas is at least one selected from the group consisting of antimony, iridium, osmium, rhenium, tungsten, germanium, vanadium, selenium, molybdenum, and oxides, nitrides, oxynitrides, and boron nitride compounds thereof, and the material that is easily etched by the chlorine-based gas is at least one selected from the group consisting of germanium, vanadium, titanium, aluminum, and oxides, nitrides, oxynitrides, and boron nitride compounds thereof.

6. The reflective mask according to claim 5, characterized in that: a film thickness of the absorbing film is 45 nm or less, and an OD value (Optical Density) is 1.0 or more.

7. The reflective mask according to claim 5 or claim 6, characterized in that: an atomic ratio (O / In) of oxygen (O) to indium (In) in the absorbing film is in a range of 1.0 or more and 2.0 or less.

8. The reflective mask according to any one of claims 5 to 7, characterized in that: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The absorption film contains a material whose correction etching rate at the time of electron beam correction is faster than that of an absorption film composed only of at least one of tin oxide and indium oxide. The absorption film contains a material whose correction etching rate at the time of electron beam correction is faster than that of an absorption film composed only of at least one of tin oxide and indium oxide.

Images