Glass substrate for euvl, and mask blank for euvl

Abstract

A technology is provided to suppress the flatness of the central region of the main surface of a glass substrate for EUVL to less than 10.0 nm. A glass substrate for EUVL has a first rectangular main surface on which a conductive film is formed, and a second rectangular main surface opposite to the first main surface on which an EUV reflective film and an EUV absorbing film are formed in that order. Among the first main surfaces, if the coordinates of a point in the central area of ​​a square with a vertical length of 142 mm and a horizontal length of 142 mm, excluding the rectangular frame-shaped main area, are represented as (x,y,z(x,y)), the maximum difference between the heights of the surface, which is a set of coordinates (x,y,z3(x,y)) calculated using equations (1) to (3) in the specification, is less than 10.0 nm.

Description

Technology Field

[0001] The present disclosure relates to a glass substrate for Extreme Ultra-Violet Lithography (EUVL) and a mask blank for EUVL. Background Technology

[0002] Conventionally, photolithography technology has been used in the manufacture of semiconductor devices. In photolithography technology, light is irradiated onto a circuit pattern on a photomask using an exposure device, and the circuit pattern is reduced and transferred onto a resist film.

[0003] Recently, in order to enable the transfer of fine circuit patterns, the use of short-wavelength exposure light, such as ArF excimer laser light and further EUV (Extreme Ultra-Violet) light, is being considered.

[0004] Here, EUV (extreme ultraviolet) refers to light that includes soft X-rays and vacuum ultraviolet rays, specifically having a wavelength of about 0.2 nm to 100 nm. At present, EUV with a wavelength of about 13.5 nm is mainly being considered.

[0005] A photomask for EUVL is obtained by forming a circuit pattern on an EUVL mask blank.

[0006] A mask blank for EUVL comprises a glass substrate, a conductive film formed on a first main surface of the glass substrate, and an EUV reflective film and an EUV absorbing film formed on a second main surface of the glass substrate. The EUV reflective film and the EUV absorbing film are formed in this order.

[0007] The EUV reflective film reflects EUV. The EUV absorbing film absorbs EUV. An aperture pattern, which is a circuit pattern, is formed on the EUV absorbing film. The conductive film is adsorbed to the electrostatic chuck of the exposure device.

[0008] High flatness is required for EUVL mask blanks to improve the transfer precision of circuit patterns. This flatness is primarily determined by the flatness of the EUVL glass substrate. Therefore, high flatness is also required for the EUVL glass substrate.

[0009] The EUVL mask blank described in Patent Document 1 has a central region and an outer region on the main surface opposite to the glass substrate in the conductive film. The central region is a square region of 142 mm in height and 142 mm in width, excluding the rectangular frame-shaped outer region surrounding the central region. In the central region, the flatness of the component having a degree of Legendre polynomial of 3 or more and 25 or less is 20 nm or less.

[0010] In addition, the EUVL mask blank described in Patent Document 2 has a difference between the highest and lowest heights within the calculation area of ​​the difference data between the composite surface shape and the virtual surface shape of 25 nm or less. The calculation area is the inner area of ​​a circle with a diameter of 104 mm. The composite surface shape is obtained by synthesizing the surface shape of a multilayer reflective film and the surface shape of a conductive film. The virtual surface shape is defined by a Zernike polynomial expressed in polar coordinates. Prior art literature

[0011] Japanese Patent Publication No. 6229807 Japanese Patent Publication No. 6033987 The problem to be solved

[0012] As mentioned above, glass substrates for ELVL require high flatness. Therefore, in the central region of the main surface of the glass substrate for EUVL, polishing, local processing, and finishing polishing are generally performed in this order. Methods for local processing include, for example, the GCIB (Gas Cluster Ion Beam) method or the PCVM (Plasma Chemical Vaporization Machining) method.

[0013] In the finishing polishing process, the EUVL glass substrate and the polishing plate are rotated separately, and the EUVL glass substrate is pressed against the polishing plate. The central region of the main surface of the EUVL glass substrate is finished polished approximately axially with respect to its center, but is not finished axially symmetrically, and after finishing polishing, it contains an axially symmetric component and the remaining deformed component.

[0014] The deformation component includes a saddle-shaped component. This saddle-shaped component is generated by finishing polishing. It is preferable to express this saddle-shaped component using Zernike polynomials rather than Legendre polynomials. This is because, unlike Legendre polynomials, Zernike polynomials are expressed in polar coordinates, making them suitable for excluding components that are axially symmetric.

[0015] However, unlike Legendre polynomials, Zernike polynomials can only represent circular regions. The main surface of a glass substrate for EUVL is rectangular, and its central region is also rectangular; consequently, the four corners of the rectangle cannot be represented by Zernike polynomials. Consequently, conventionally, it has been impossible to accurately identify the deformation components occurring during finishing polishing.

[0016] As a result, it was difficult to suppress the flatness of the central region of the main surface of a conventional EUVL glass substrate to less than 10.0 nm.

[0017] One aspect of the present disclosure provides a technique for suppressing the flatness of the central region of the main surface of a glass substrate for EUVL to less than 10.0 nm. means of solving the problem

[0018] A glass substrate for EUVL according to one embodiment of the present disclosure has a first rectangular main surface on which a conductive film is formed, and a second rectangular main surface opposite to the first main surface on which an EUV reflective film and an EUV absorbing film are formed in that order. Among the first main surfaces, if the coordinates of a point in the central area of ​​a square with a length of 142 mm and a width of 142 mm, excluding the rectangular frame-shaped peripheral area, are represented as (x,y,z(x,y)), the maximum difference between the heights of the surface, which is a set of coordinates (x,y,z3(x,y)) calculated using the following equations (1) to (3), is less than 10.0 nm.

[0019]

[0020] In the above coordinates (x,y,z(x,y)), x represents the horizontal coordinate, y represents the vertical coordinate, and z represents the height coordinate, and the horizontal, vertical, and height directions are perpendicular to each other. Effects of the invention

[0021] According to one embodiment of the present disclosure, the flatness of the central region of the main surface of a glass substrate for EUVL can be suppressed to less than 10.0 nm. Brief explanation of the drawing

[0022] FIG. 1 is a flowchart illustrating a method for manufacturing a mask blank for EUVL according to one embodiment. FIG. 2 is a cross-sectional view showing a glass substrate for EUVL according to one embodiment. FIG. 3 is a plan view showing a glass substrate for EUVL according to one embodiment. FIG. 4 is a cross-sectional view showing a mask blank for EUVL according to one embodiment. Figure 5 is a cross-sectional view showing an example of a photomask for EUVL. FIG. 6 is a perspective view showing an example of a double-sided grinder, and is a perspective view showing a part of the double-sided grinder broken apart. Figure 7 is a drawing showing an example of the height distribution of the central region of the first main surface after finishing polishing. FIG. 8 is a plan view showing an example of the arrangement of multiple points set in a central area. Figure 9 is a diagram showing the height distribution of the component extracted from the height distribution of Figure 7 using Equation (1). Figure 10 is a diagram showing the height distribution of the component extracted from the height distribution of Figure 7 using Equation (2). Figure 11 is a diagram showing the height distribution of the component extracted from the height distribution of Figure 7 using Equation (3). Specific details for implementing the invention

[0023] Hereinafter, embodiments for implementing the present disclosure will be described with reference to the drawings. In each drawing, identical or corresponding components are denoted by the same reference numerals, and descriptions may be omitted. Within the specification, "to" indicating a numerical range means that the values ​​described before and after it are included as lower and upper limits.

[0024] As shown in FIG. 1, the method for manufacturing a mask blank for EUVL has steps S1 to S7. Using the EUVL glass substrate (2) shown in FIG. 2 and FIG. 3, the EUVL mask blank (1) shown in FIG. 4 is manufactured. Hereinafter, the EUVL mask blank (1) is also referred to simply as the mask blank (1). In addition, the EUVL glass substrate (2) is also referred to simply as the glass substrate (2).

[0025] As shown in FIGS. 2 and 3, the glass substrate (2) includes a first main surface (21) and a second main surface (22) in a direction opposite to the first main surface (21). The first main surface (21) is rectangular in shape. In this specification, a rectangular shape includes a shape in which chamfering is performed on the corners. Also, a rectangle includes a square. The second main surface (22) is in a direction opposite to the first main surface (21). The second main surface (22) is also rectangular in shape, just like the first main surface (21).

[0026] Additionally, the glass substrate (2) includes four end surfaces (23), four first chamfered surfaces (24), and four second chamfered surfaces (25). The end surfaces (23) are perpendicular to the first main surface (21) and the second main surface (22). The first chamfered surfaces (24) are formed at the boundary between the first main surface (21) and the end surfaces (23). The second chamfered surfaces (25) are formed at the boundary between the second main surface (22) and the end surfaces (23). In this embodiment, the first chamfered surfaces (24) and the second chamfered surfaces (25) are so-called C chamfered surfaces, but they may also be R chamfered surfaces.

[0027] The glass of the glass substrate (2) is preferably quartz glass containing TiO2. Quartz glass has a smaller coefficient of linear expansion and smaller dimensional changes due to temperature changes compared to ordinary soda-lime glass. Quartz glass may contain 80 mass% to 95 mass% of SiO2 and 4 mass% to 17 mass% of TiO2. If the TiO2 content is 4 mass% to 17 mass%, the coefficient of linear expansion near room temperature is approximately zero, and almost no dimensional changes occur near room temperature. Quartz glass may contain a third component or impurity other than SiO2 and TiO2.

[0028] When viewed in a flat plane, the size of the glass substrate (2) is, for example, 152 mm in height and 152 mm in width. The height and width dimensions may be 152 mm or larger.

[0029] The glass substrate (2) has a central region (27) and a peripheral region (28) on the first main surface (21). The central region (27) is a square area with a vertical length of 142 mm and a horizontal length of 142 mm, excluding the rectangular frame-shaped peripheral region (28) surrounding the central region (27), and is an area processed to a desired flatness by steps S1 to S4. The four sides of the central region (27) are parallel to the four end surfaces (23). The center of the central region (27) coincides with the center of the first main surface (21).

[0030] Additionally, although not shown, the second main surface (22) of the glass substrate (2) also has a central area and a peripheral area, just like the first main surface (21). The central area of ​​the second main surface (22) is a square area with a vertical length of 142 mm and a horizontal length of 142 mm, just like the central area of ​​the first main surface (21), and is an area processed to a desired flatness by steps S1 to S4 of FIG. 1.

[0031] First, in Step S1, the first main surface (21) and the second main surface (22) of the glass substrate (2) are polished. In this embodiment, the first main surface (21) and the second main surface (22) are polished simultaneously with a double-sided polisher (9) described later, but they may also be polished sequentially with a single-sided polisher not shown. In Step S1, the glass substrate (2) is polished while supplying a polishing slurry between the polishing pad and the glass substrate (2).

[0032] As a polishing pad, for example, a urethane-based polishing pad, a non-woven polishing pad, or a suede-based polishing pad is used. The polishing slurry includes an abrasive and a dispersion medium. The abrasive is, for example, cerium oxide particles. The dispersion medium is, for example, water or an organic solvent. The first main surface (21) and the second main surface (22) may be polished multiple times with an abrasive of a different material or particle size.

[0033] In addition, the abrasive used in Step S1 is not limited to cerium oxide particles. For example, the abrasive used in Step S1 may be silicon oxide particles, aluminum oxide particles, zirconium oxide particles, titanium oxide particles, diamond particles, or silicon carbide particles.

[0034] Next, in step S2, the surface shape of the first main surface (21) and the second main surface (22) of the glass substrate (2) is measured. For measuring the surface shape, a non-contact measuring instrument, such as a laser interference type, is used to prevent scratches on the surface. The measuring instrument measures the surface shape of the central region (27) of the first main surface (21) and the central region of the second main surface (22).

[0035] Next, in step S3, the first main surface (21) and the second main surface (22) of the glass substrate (2) are locally processed to improve flatness by referring to the measurement results of step S2. The first main surface (21) and the second main surface (22) are locally processed in sequence. The order may be either one first and is not particularly limited. The method of local processing is, for example, the GCIB method or the PCVM method. The method of local processing may be a polishing method using a magnetic fluid or a polishing method using a rotary polishing tool.

[0036] Next, in step S4, the first main surface (21) and the second main surface (22) of the glass substrate (2) are polished. In this embodiment, the first main surface (21) and the second main surface (22) are polished simultaneously with a double-sided polisher (9) described later, but they may also be polished sequentially with a single-sided polisher not shown. In step S4, the glass substrate (2) is polished while supplying a polishing slurry between the polishing pad and the glass substrate (2). The polishing slurry contains an abrasive. The abrasive is, for example, colloidal silica particles.

[0037] Next, in step S5, a conductive film (5) as shown in FIG. 4 is formed in the central region (27) of the first main surface (21) of the glass substrate (2). The conductive film (5) is used to adsorb a photomask for EUVL to the electrostatic chuck of the exposure device. The conductive film (5) is formed, for example, from chromium nitride (CrN), etc. As a method for forming the conductive film (5), a sputtering method is used, for example.

[0038] Next, in step S6, an EUV reflective film (3) shown in FIG. 4 is formed in the central region of the second main surface (22) of the glass substrate (2). The EUV reflective film (3) reflects EUV. The EUV reflective film (3) may be a multilayer reflective film, for example, in which a high refractive index layer and a low refractive index layer are alternately stacked. The high refractive index layer is formed, for example, of silicon (Si), and the low refractive index layer is formed, for example, of molybdenum (Mo). As a method for forming the EUV reflective film (3), a sputtering method such as an ion beam sputtering method or a magnetron sputtering method is used.

[0039] Finally, in step S7, an EUV absorption film (4) shown in FIG. 4 is formed on the EUV reflection film (3) formed in step S6. The EUV absorption film (4) absorbs EUV. The EUV absorption film (4) is formed, for example, by a single metal, alloy, nitride, oxide, oxynitride, etc., comprising at least one element selected from tantalum (Ta), chromium (Cr), and palladium (Pd). As a method for forming the EUV absorption film (4), for example, a sputtering method is used.

[0040] Additionally, steps S6 and S7 are performed after step S5 in this embodiment, but may be performed before step S5.

[0041] By the above steps S1 to S7, a mask blank (1) shown in FIG. 4 is obtained. The mask blank (1) has a first main surface (11) and a second main surface (12) in a direction opposite to the first main surface (11), and has a conductive film (5), a glass substrate (2), an EUV reflective film (3), and an EUV absorbing film (4) in this order from the side of the first main surface (11) to the side of the second main surface (12).

[0042] The mask blank (1), although not shown, has a central region and a peripheral region on the first main surface (11), just like the glass substrate (2). The central region is a square area of ​​142 mm in height and 142 mm in width, excluding the rectangular frame-shaped peripheral region surrounding the central region. Additionally, the mask blank (1) also has a central region and a peripheral region on the second main surface (12), just like the glass substrate (2). The central region is a square area of ​​142 mm in height and 142 mm in width, excluding the rectangular frame-shaped peripheral region surrounding the central region.

[0043] In addition, the mask blank (1) may include other films in addition to the conductive film (5), the glass substrate (2), the EUV reflective film (3), and the EUV absorbing film (4).

[0044] For example, the mask blank (1) may further include an anti-reflective film. The anti-reflective film is formed on the EUV absorption film (4). Subsequently, a circuit pattern (41) is formed on both the anti-reflective film and the EUV absorption film (4). The anti-reflective film is used for inspection of the circuit pattern (41) and has a lower reflection characteristic than the EUV absorption film (4) with respect to inspection light. The anti-reflective film is formed, for example, from TaON or TaO. As a method for forming the anti-reflective film, for example, a sputtering method is used.

[0045] Additionally, the mask blank (1) may further include a protective film. The protective film is formed between the EUV reflective film (3) and the EUV absorbing film (4). The protective film protects the EUV reflective film (3) so that the EUV reflective film (3) is not etched when the EUV absorbing film (4) is etched to form a circuit pattern (41) on the EUV absorbing film (4). The protective film is formed of, for example, Ru, Si, or TiO2. As a method for forming the protective film, for example, a sputtering method is used.

[0046] As shown in FIG. 5, a photomask for EUVL is obtained by forming a circuit pattern (41) on an EUV absorption film (4). The circuit pattern (41) is an aperture pattern, and photolithography and etching methods are used to form it. Accordingly, a resist film used to form the circuit pattern (41) may be included in the mask blank (1).

[0047] However, the mask blank (1) requires high flatness to improve the transfer precision of the circuit pattern (41). The flatness is mainly determined by the flatness of the glass substrate (2). Therefore, the glass substrate (2) also requires high flatness.

[0048] Therefore, on the glass substrate (2), polishing (step S1), local processing (step S3), and finishing polishing (step S4) are performed in this order as described above. In the finishing polishing, the glass substrate (2) and the polishing plate are rotated respectively while the glass substrate (2) is pressed against the polishing plate. For the finishing polishing, for example, a double-sided polishing machine (9) shown in FIG. 6 is used.

[0049] The double-sided polishing machine (9) has a lower platen (91), an upper platen (92), a carrier (93), a sun gear (94), and an internal gear (95). The lower platen (91) is arranged horizontally, and a lower polishing pad (96) is attached to the upper surface of the lower platen (91). The upper platen (92) is arranged horizontally, and an upper polishing pad (97) is attached to the lower surface of the upper platen (92). The carrier (93) holds and supports a glass substrate (2) horizontally between the lower platen (91) and the upper platen (92). Each carrier (93) holds and supports one glass substrate (2), but may hold and support multiple substrates. The carrier (93) is positioned on the outer side in the radial direction of the sun gear (94) and is also positioned on the inner side in the radial direction of the internal gear (95). The carriers (93) are spaced apart and arranged in multiple numbers around the sun gear (94). The sun gear (94) and the internal gear (95) are arranged concentrically and mesh with the outer gear (93a) of the carrier (93).

[0050] The double-sided polishing machine (9) is, for example, a 4-way type, and the lower polishing plate (91), the upper polishing plate (92), the sun gear (94), and the internal gear (95) rotate around the same vertical centerline of rotation. The lower polishing plate (91) and the upper polishing plate (92) rotate in opposite directions, pressing the lower polishing pad (96) against the lower surface of the glass substrate (2) and also pressing the upper polishing pad (97) against the upper surface of the glass substrate (2). In addition, at least one of the lower polishing plate (91) and the upper polishing plate (92) supplies a polishing slurry to the glass substrate (2). The polishing slurry is supplied between the glass substrate (2) and the lower polishing pad (96) to polish the lower surface of the glass substrate (2). In addition, the polishing slurry is supplied between the glass substrate (2) and the upper polishing pad (97) to polish the upper surface of the glass substrate (2).

[0051] For example, the lower platen (91), the sun gear (94), and the internal gear (95) rotate in the same direction when viewed in a plane. Their rotational direction is opposite to the rotational direction of the upper platen (92). The carrier (93) rotates while orbiting. The orbital direction of the carrier (93) is the same direction as the rotational direction of the sun gear (94) and the internal gear (95). Meanwhile, the rotational direction of the carrier (93) is determined by the magnitude of the product of the rotational speed of the sun gear (94) and the pitch circle diameter, and the product of the rotational speed of the internal gear (95) and the pitch circle diameter. If the product of the rotational speed of the internal gear (95) and the pitch circle diameter is greater than the product of the rotational speed of the sun gear (94) and the pitch circle diameter, the rotational direction of the carrier (93) and the orbital direction of the carrier (93) become the same direction. Meanwhile, if the product of the rotational speed of the internal gear (95) and the pitch circle diameter is smaller than the product of the rotational speed of the linear gear (94) and the pitch circle diameter, the rotational direction of the carrier (93) and the orbital direction of the carrier (93) become opposite.

[0052] By means of a double-sided polisher (9), the first main surface (21) and the second main surface (22) of the glass substrate (2) are finished polished approximately axially with respect to their respective centers. The first main surface (21) and the second main surface (22) tend to be polished plane-symmetrically with respect to the center plane in the plate thickness direction of the glass substrate (2). The first main surface (21) and the second main surface (22) tend to be polished into convex curved surfaces or polished into concave curved surfaces. Additionally, for the finishing polishing, a single-sided polisher not shown above may be used.

[0053] FIG. 7 shows an example of the height distribution of the central region (27) of the first main surface (21) after finishing polishing. Here, the height distribution after tilt correction is shown. The central region (27) shown in FIG. 7 is a convex curved surface where the height of the center is higher than the height of the four corners. In FIG. 7, the unit of the numerical value representing the height is nm, and the higher the numerical value, the higher the height. Also, the height distribution of the central region of the second main surface (22) after finishing polishing is the same as the height distribution in FIG. 7, so it is omitted from illustration.

[0054] The height distribution shown in FIG. 7 was measured using an UltraFlat200Mask manufactured by Corning Tropel. Here, in order to exclude the influence of gravity, the glass substrate (2) was set up approximately vertically, and the glass substrate (2) was supported so that both the first main surface (21) and the second main surface (22) of the glass substrate (2) did not come into contact with other members such as a stage, and the height distribution was measured.

[0055] As is evident from FIG. 7, the central region (27) of the first main surface (21) after finishing polishing is not perfectly axially symmetric and includes an axially symmetric component and the remaining deformed component. The deformed component includes a saddle-shaped component as shown in FIG. 11, which will be described in detail later. This saddle-shaped component is generated by finishing polishing.

[0056] It is preferable to express the components of this bird shape using Zernike polynomials rather than Legendre polynomials. This is because, unlike Legendre polynomials, Zernike polynomials are expressed in polar coordinates, making them suitable for excluding components that are axially symmetric.

[0057] However, unlike Legendre polynomials, Zernike polynomials can only represent circular regions. The central region (27) is rectangular, and the four corners of the rectangle cannot be represented by Zernike polynomials. Therefore, it was not possible to accurately identify the deformation components that occur during conventional finishing polishing.

[0058] Therefore, in this embodiment, the coordinates of a point in the central area (27) of a square with a height of 142 mm and a width of 142 mm are represented as (x,y,z(x,y)), and the deformation component is determined using the following equations (1) to (3).

[0059]

[0060] In the above coordinates (x,y,z(x,y)), x represents the horizontal coordinate, y represents the vertical coordinate, and z represents the height coordinate, and the horizontal, vertical, and height directions are perpendicular to each other.

[0061] FIG. 8 shows an example of the arrangement of multiple points set in the central area (27). In FIG. 8, the X-axis direction is the horizontal direction and the Y-axis direction is the vertical direction. The origin, which is the intersection point of the X-axis and the Y-axis, is the center of the central area (27).

[0062] As is evident from FIG. 8, z1(x,y) in Equation (1) is the average value of the heights of two points that are symmetrical twice around the origin. FIG. 9 shows the height distribution of a plane, which is a set of coordinates (x,y, z1(x,y)). In FIG. 9, the unit of the numerical value representing the height is nm, and the higher the numerical value, the higher the height. The height distribution shown in FIG. 9 includes, in addition to the axially symmetrical component, a saddle-shaped component and a 4-times symmetrical component rotated around the origin. This 4-times symmetrical component is rotated counterclockwise, for example, as shown by the dashed line in FIG. 9.

[0063] As is evident from FIG. 8, z2(x,y) in Equation (2) is the average value of the heights of four points that are symmetrical four times around the origin. FIG. 10 shows the height distribution of a plane, which is a set of coordinates (x,y, z2(x,y)). In FIG. 10, the unit of the numerical value representing the height is nm, and the higher the numerical value, the higher the height. The height distribution shown in FIG. 10 includes, in addition to the axially symmetrical component, a 4-times symmetrical component rotated around the origin. This 4-times symmetrical component is rotated counterclockwise, for example, as shown by the dashed line in FIG. 10.

[0064] z3(x,y) in Equation (3) is the difference between z1(x,y) in Equation (1) and z2(x,y) in Equation (2). The height distribution of a surface, which is a set of coordinates (x,y, z3(x,y)), is shown in FIG. 11. In FIG. 11, the unit of the numerical value representing the height is nm, and the higher the numerical value, the higher the height. The height distribution shown in FIG. 11 is the difference between the height distribution shown in FIG. 9 and the height distribution shown in FIG. 10, and mainly includes a saddle-shaped component. As is evident from FIG. 11, the saddle-shaped component is a component that is symmetrically rotated about the origin.

[0065] The inventors have found, through experiments and the like, that if the maximum height difference Δz3 (Δz3≥0) of a plane that is a set of coordinates (x,y,z3(x,y)) is less than 10.0 nm, the flatness PV (PV≥0) of the central region (27) can be suppressed to less than 10.0 nm.

[0066] In the present disclosure, the flatness PV of the central region (27) refers to the maximum difference in height of the remaining components excluding the component represented by a quadratic function from the entire component of the height distribution of the central region (27). The quadratic function is represented by the following equation (4).

[0067]

[0068] In the above equation (4), a, b, c, d, e, f are zfit It is a constant determined such that the sum of the squares of the differences between (x,y) and z(x,y) is minimized, and it is a constant obtained by the least squares method.

[0069] The component of the quadratic function is a component that can be automatically corrected in the exposure device. Therefore, the component of the quadratic function does not affect the transfer precision of the circuit pattern (41). Thus, when calculating the flatness PV of the central region (27), the component of the quadratic function is excluded from the entire component of the height distribution of the central region (27).

[0070] In order to suppress Δz3 to less than 10.0 nm, the inventor first performs the treatment of steps S1 to S4 on another glass substrate (2) in advance, and uses the following formula (5) to determine the difference in height z at each point of the central region (27) before and after finishing polishing. dif (x,y) was calculated. Next, using the following equation (6), z 2_dif (x,y) was calculated.

[0071]

[0072] In the above equation (5), z after (x,y) is the height at coordinates (x,y) after final polishing, and z before (x,y) is the height at coordinates (x,y) after local processing and before final polishing. z after (x,y) and z before The difference between (x,y) is z dif Since it is (x,y), z dif (x,y) represents the distribution of the amount of polishing for the finishing polishing.

[0073] z of the above equation (6) 2_dif (x,y) is the average value of two points reflected twice around the origin. Therefore, z in the above equation (6) 2_dif (x,y) is a component that is symmetric twice among the above deformation components, and corresponds to z3(x,y) of Equation (3).

[0074] The inventors, a previously calculated z 2_dif It was found that by using (x,y) to correct the target height of each point of the central region (27) in the local processing (step S3), Δz3 can be suppressed to less than 10.0 nm. As a result, a glass substrate (2) with a PV of less than 10.0 nm could be obtained.

[0075] Here, the target height after correction is the target height set based on the measurement result of Step S2 and the pre-calculated z 2_dif It is obtained from the difference of (x,y). In other words, the target machining amount after correction is the target machining amount set based on the measurement result of Step S2 and the pre-calculated z 2_dif It is obtained from the sum of (x,y). The z used for these corrections 2_dif (x,y) is preferably the average value of a plurality of glass substrates (2). z 2_dif The average value of (x,y) is calculated for each finishing polishing condition (e.g., type of abrasive, type of polishing pad, polishing pressure, and rotational speed).

[0076] In order to reduce the saddle-shaped component as shown in FIG. 11 after finishing polishing, it is effective to increase the ratio of the rotational speed of the carrier (93) to the rotational speed of the lower platen (91) during finishing polishing. The ratio is preferably 20% to 40%, and more preferably 25% to 35%. By increasing the speed of the carrier (93) rotation, Δz3 can be suppressed to 7.0 nm or less, and PV can be suppressed to less than 8.0 nm.

[0077] In addition, when reducing the saddle-shaped component by increasing the speed of rotation of the carrier (93), the correction of the target height or target processing amount in local processing is given by z of the above equation (6). 2_dif Instead of (x,y), z of the following equation (7) 4_dif Use (x,y).

[0078]

[0079] z of the above equation (7) 4_dif (x,y) is the average value of 4 points resulting from 4-fold reflection. z is the average value of 2 points resulting from 2-fold reflection. 2_dif Instead of (x,y), z is the average of the 4 points 4_dif By using (x,y), the number of samples can be increased, which can reduce the error.

[0080] Also, z, the average value of the 4 points of 4-fold symmetry 4_dif (x,y) does not contain a saddle-shaped component as shown in FIG. 11, but this is not a problem. This is because the saddle-shaped component as shown in FIG. 11 is reduced when the rotation of the carrier (93) is accelerated.

[0081] When the rotational speed of the carrier (93) is large, the target height after correction is the target height set based on the measurement result of step S2 and the pre-calculated z 4_dif It is obtained from the difference of (x,y). In other words, the target machining amount after correction is the target machining amount set based on the measurement result of Step S2 and the pre-calculated z 4_dif It is obtained from the sum of (x,y). The z used for these corrections 4_dif (x,y) is preferably the average value of a plurality of glass substrates (2). z 4_dif The average value of (x,y) is calculated for each finishing polishing condition (e.g., type of abrasive, type of polishing pad, polishing pressure and rotation speed, etc.).

[0082] Although the central region (27) of the first main surface (21) of the glass substrate (2) has been described above, the same applies to the central region of the second main surface (22) of the glass substrate (2). If Δz3 is suppressed to less than 10.0 nm in the central region of the second main surface (22), the PV can be suppressed to less than 10.0 nm.

[0083] In addition, the flatness of the first main surface (11) of the mask blank (1) is determined by the flatness of the first main surface (21) of the glass substrate (2). Accordingly, if the central region of the first main surface (11) also has Δz3 suppressed to less than 10.0 nm, the PV can be suppressed to 15.0 nm or less, preferably less than 10.0 nm.

[0084] In addition, the flatness of the second main surface (12) of the mask blank (1) is determined by the flatness of the second main surface (22) of the glass substrate (2). Accordingly, if the central region of the second main surface (12) also has Δz3 suppressed to less than 10.0 nm, the PV can be suppressed to 15.0 nm or less, preferably less than 10.0 nm.

[0085] [Example]

[0086] Among Examples 1 to 7, steps S1 to S4 shown in FIG. 1 were performed under the same conditions, except for the conditions below, to produce a glass substrate (2), and Δz3 and PV were measured for the central region (27) of the first main surface (21). In addition, in Examples 1 to 3, during finishing polishing, the ratio of the rotational speed of the carrier (93) to the rotational speed of the lower platen (91) was controlled to 30%, and also a previously calculated z 4_dif The target height of the local processing was corrected using the average value of (x,y). In addition, in Example 4, during finishing polishing, the ratio of the rotational speed of the carrier (93) to the rotational speed of the lower platen (91) was controlled to 10%, and also a previously calculated z 2_dif The target height of the local processing was corrected using the average value of (x,y). Meanwhile, in Examples 5 to 7, during the finishing polishing, the ratio of the rotational speed of the carrier (93) to the rotational speed of the lower platen (91) was controlled to 10%, and also a previously calculated z 2_difThe target height for local processing was set using the measurement result of Step S2, without using the average value of (x,y). Examples 1 to 4 are examples, and Examples 5 to 7 are comparative examples. The results are shown in Table 1.

[0087]

[0088] As is evident from Table 1, in Examples 1 to 3, the carrier is rotated at high speed during finishing polishing, and also a predetermined z 4_dif Since the target height of the local processing was corrected using the average value of (x,y), Δz3 could be suppressed to 7.0 nm or less, and PV could be suppressed to less than 8.0 nm. In addition, in Example 4, the carrier was rotated at a low speed during the finishing polishing, and also the previously calculated z 2_dif Since the target height of the local processing was corrected using the average value of (x,y), Δz3 could be suppressed to less than 10.0 nm and PV could be suppressed to less than 10.0 nm. Meanwhile, in Examples 5 to 7, the carrier was rotated at a low speed during the finishing polishing, and also the previously calculated z 2_dif Since the target height for local processing was set using the measurement result of step S2 without using the average value of (x,y), Δz3 became 10.0 nm or more and PV became 10.0 nm or more.

[0089] Next, a mask blank (1) for EUVL was fabricated using the glass substrates (2) of Examples 1 to 4, Example 6, and Example 7, excluding Example 5. First, a CrN film of 100 nm was formed as a conductive film by ion beam sputtering on the first main surface (21) (the surface where Δz3 and PV were measured) of the glass substrate (2). Next, a multilayer reflective film (EUV reflective film) was formed by ion beam sputtering on the second main surface (22) of the glass substrate (2). The multilayer reflective film consisted of stacking a Si film of about 4 nm and a Mo film of about 3 nm alternately for 40 cycles, and finally stacking a Si film of about 4 nm. Subsequently, a Ru film of 2.5 nm was deposited on the multilayer reflective film by sputtering as a protective film. Next, as an absorption film (EUV absorption film), a TaN film of 75 nm and a TaON film of 5 nm were deposited on the protective film by sputtering. In this way, an EUVL mask blank (1) having a conductive film (5), a glass substrate (2), an EUV reflective film (3), and an EUV absorption film (4) in this order was obtained.

[0090] Δz3 and PV were measured for the central region of the first main surface (11) (the side facing the conductive film (5)) of the EUVL mask blank (1) fabricated using the glass substrates (2) of Examples 1 to 4, Examples 6 and 7. The results are shown in Table 2.

[0091]

[0092] As shown in Table 2, in Examples 1 to 4, for the central region of the first main surface (11) of the EUVL mask blank (1), Δz3 could be suppressed to less than 10.0 nm and PV could be suppressed to 15.0 nm or less. In Examples 6 and 7, for the central region of the first main surface (11) of the EUVL mask blank (1), Δz3 became 10.0 nm or more and PV became larger than 15.0 nm.

[0093] Although the glass substrate for EUVL and the mask blank for EUVL according to the present disclosure have been described above, the present disclosure is not limited to the above embodiments. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope described in the claims. These also naturally fall within the technical scope of the present disclosure. Explanation of the symbols

[0094] 2: Glass substrate 21: First major surface 22: Second major surface 27: Central area 28: Main Character Area 3: EUV reflective film 4: EUV absorption membrane 5: Challenge Stage

Claims

Claim 1 A glass substrate for EUVL having a first rectangular main surface on which a conductive film is formed, and a second rectangular main surface opposite to the first main surface on which an EUV reflective film and an EUV absorbing film are formed in this order, wherein, among the first main surfaces, the coordinates of a point in the central region of a square of 142 mm in height and 142 mm in width, excluding the rectangular frame-shaped peripheral region, are represented as (x,y,z(x,y)), and the maximum difference between the heights of the surface is less than 10.0 nm, and the flatness PV of the central region of the first main surface is 15.0 nm or less. In the above coordinates (x,y,z(x,y)), x represents the horizontal coordinate, y represents the vertical coordinate, and z represents the height coordinate, and the horizontal, vertical, and height directions are perpendicular to each other. Claim 2 A glass substrate for EUVL having a first rectangular main surface on which a conductive film is formed, and a second rectangular main surface opposite to the first main surface on which an EUV reflective film and an EUV absorbing film are formed in this order, wherein, among the second main surfaces, the maximum difference between the heights of a surface is less than 10.0 nm, and the flatness PV of the central region of the second main surface is 15.0 nm or less, wherein if the coordinates of a point in the central region of a square of 142 mm in height and 142 mm in width, excluding the rectangular frame-shaped peripheral region, are represented as (x,y,z(x,y)), the maximum difference between the heights of the surface is less than 10.0 nm, and the flatness PV of the central region of the second main surface is 15.0 nm or less. In the above coordinates (x,y,z(x,y)), x represents the horizontal coordinate, y represents the vertical coordinate, and z represents the height coordinate, and the horizontal, vertical, and height directions are perpendicular to each other. Claim 3 An EUVL mask blank having a first rectangular main surface and a second rectangular main surface opposite to the first main surface, and having a conductive film, a glass substrate, an EUV reflective film, and an EUV absorbing film in this order from the side of the first main surface to the side of the second main surface, wherein among the first main surfaces, the maximum difference between the heights of a surface is less than 10.0 nm, and the flatness PV of the central region of the first main surface is 15.0 nm or less, wherein the coordinates of a point in the central region of a square with a height of 142 mm and a width of 142 mm, excluding the rectangular frame-shaped peripheral region, are represented as (x,y,z(x,y)), and the set of coordinates (x,y,z3(x,y)) calculated using the following formulas (1) to (3). In the above coordinates (x,y,z(x,y)), x represents the horizontal coordinate, y represents the vertical coordinate, and z represents the height coordinate, and the horizontal, vertical, and height directions are perpendicular to each other. Claim 4 An EUVL mask blank having a first rectangular main surface and a second rectangular main surface opposite to the first main surface, and having a conductive film, a glass substrate, an EUV reflective film, and an EUV absorbing film in this order from the side of the first main surface to the side of the second main surface, wherein among the second main surfaces, if the coordinates of a point in a central area of ​​a square with a vertical length of 142 mm and a horizontal length of 142 mm excluding the rectangular frame-shaped peripheral area are represented as (x,y,z(x,y)), the maximum difference between the heights of the surface is less than 10.0 nm, and the flatness PV of the central area of ​​the second main surface is 15.0 nm or less. In the above coordinates (x,y,z(x,y)), x represents the horizontal coordinate, y represents the vertical coordinate, and z represents the height coordinate, and the horizontal, vertical, and height directions are perpendicular to each other.

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