Photomask, photomask blank and method for producing photomask

Abstract

To provide a photomask and a photomask blank capable of preventing electrostatic breakdown of an exposure pattern.SOLUTION: A photomask includes a transparent substrate and has a conductive pattern and a transfer pattern on the transparent substrate, where the width of the conductive pattern is below the resolution limit of the exposure light, and at least a part of the transfer pattern is located on the conductive pattern. The transfer pattern is electrically connected to the conductive pattern. The shape of the conductive pattern may be a geometric pattern. Additionally, the conductive pattern may be semi-transparent.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a photomask, a photomask blank, and a method for manufacturing a photomask. [Background technology]

[0002] Photomasks used in lithography processes have various exposure patterns formed on an insulating, transparent substrate such as quartz. For example, a pattern formed using a metal light-shielding film constitutes a capacitor. When static electricity is generated during the photomask manufacturing process, the amount of charge increases, especially in large-area patterns. When charged isolated patterns are adjacent to each other, discharge can occur between the isolated patterns, causing electrostatic damage. As pattern line widths become increasingly finer, the risk of electrostatic discharge (ESD) increases. To address this problem, a method has been proposed in which a transparent conductive film is formed on the transparent substrate of the photomask, and isolated patterns are electrically connected by the transparent conductive film to prevent electrostatic breakdown. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-241921 [Patent Document 2] Patent Publication No. 2014-232330 [Patent Document 3] Japanese Patent Application Publication No. 3-255421 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-25894 Summary of the Invention [Problem to be solved by the invention]

[0004] The transparent conductive film used for antistatic purposes must be made of a material that has high transmittance to the exposure light used in the lithography process using a photomask. However, if ITO or the like is used as the transparent conductive film, the material itself may be expensive. Furthermore, it is necessary to prepare new film forming equipment, etching equipment, etc. for forming the transparent conductive film, which increases the manufacturing cost and requires the development of a manufacturing process.

[0005] In view of the above problems, an object of the present invention is to provide a photomask, a photomask blank, and a method for manufacturing a photomask that can prevent electrostatic damage to a transfer pattern for exposure. [Means for solving the problem]

[0006] The photomask according to the present invention comprises: a transparent substrate, and a conductive pattern and a transfer pattern on the transparent substrate; the width of the conductive pattern is equal to or less than the resolution limit of the exposure light; At least a portion of the transfer pattern is located on the conductive pattern and is in electrical contact with the conductive pattern.

[0007] By configuring the photomask in this way, the conductive pattern can prevent electrostatic breakdown of the transfer pattern transferred onto the exposure target in the lithography process using the photomask.

[0008] Furthermore, the photomask according to the present invention has the above-mentioned configuration, The conductive pattern may have a geometric shape.

[0009] By configuring the photomask in this way, electrostatic breakdown can be prevented, and the conductive pattern can achieve high transmittance for exposure light.

[0010] Furthermore, the photomask according to the present invention has the above-mentioned configuration, The conductive pattern may be semi-transparent.

[0011] By configuring the photomask in this way, it is possible to prevent electrostatic breakdown and further prevent the transfer of the conductive pattern to the exposure target.

[0012] Furthermore, the photomask according to the present invention has the above-mentioned configuration, The conductive pattern may have a honeycomb shape.

[0013] By configuring the photomask in this way, it is possible to prevent electrostatic breakdown and set the transmittance of the conductive pattern to a high level.

[0014] Furthermore, the photomask according to the present invention has the above-mentioned configuration, the transfer pattern is a laminate of an intermediate film and an upper layer film formed on the intermediate film, The intermediate film and the upper film may be electrically conductive.

[0015] Furthermore, the photomask according to the present invention has the above-mentioned configuration, the intermediate film has etching selectivity with respect to the conductive pattern; The upper layer film may have etching selectivity with respect to the intermediate film.

[0016] Such a photomask configuration allows the intermediate film to function as an etching stopper, and also improves the degree of freedom in etching processing in the photomask manufacturing process.

[0017] Furthermore, the photomask according to the present invention has the above-mentioned configuration, the transfer pattern is composed of an upper layer film, The upper layer film may be conductive.

[0018] Furthermore, the photomask according to the present invention has the above-mentioned configuration, The upper layer film may have etching selectivity with respect to the conductive pattern.

[0019] Such a photomask configuration reduces the number of layers to be formed, which contributes to reducing the number of steps in the photomask manufacturing process.

[0020] Furthermore, the photomask according to the present invention has the above-mentioned configuration, The upper film may be a semi-transparent film or a phase shift film.

[0021] By configuring the photomask in this way, a halftone mask, a phase shift mask, or a halftone type phase shift mask can be obtained.

[0022] Furthermore, the photomask according to the present invention has the above-mentioned configuration, the conductive pattern is formed of an underlayer film, the underlayer film being a phase shift film; the transfer pattern is composed of an upper layer film and is formed on the lower layer film; The edge of the transfer pattern may have a rim portion formed by the underlayer film.

[0023] By configuring the photomask in this way, a rim-type phase shift mask can be obtained. In particular, in the case of a fine pattern such as a rim-type phase shift mask, electrostatic breakdown is more likely to occur, so the effect of preventing electrostatic breakdown is even greater.

[0024] The photomask blank according to the present invention comprises: a transparent substrate and a conductive pattern on the transparent substrate; The width of the conductive pattern is equal to or less than the resolution limit of the exposure light. It is characterized by:

[0025] Such a photomask blank configuration makes it possible to accommodate a variety of transfer pattern designs while preventing electrostatic damage to the transfer pattern, and also allows for rapid start of photomask manufacturing in response to customer orders.

[0026] The method for manufacturing a photomask according to the present invention includes the steps of: forming a conductive film on a transparent substrate; patterning the conductive film to form a conductive pattern having a width equal to or less than the resolution limit of exposure light; forming an intermediate film having conductivity on the conductive pattern; forming an upper layer film having electrical conductivity on the intermediate film; The method is characterized by including a step of patterning the intermediate film and the upper layer film to form a transfer pattern constituted by laminating the intermediate film and the upper layer film, and exposing a part of the conductive pattern.

[0027] By using such a photomask manufacturing method, it is possible to manufacture a photomask having a transfer pattern with a layered structure, which is capable of preventing electrostatic breakdown.

[0028] The method for manufacturing a photomask according to the present invention includes the steps of: forming a conductive film on a transparent substrate; patterning the conductive film to form a conductive pattern having a width equal to or less than the resolution limit of exposure light; forming an upper layer film having conductivity on the conductive pattern; and patterning the upper layer film to form a transfer pattern made of the upper layer film and exposing a portion of the conductive pattern. It is characterized by:

[0029] By using such a photomask manufacturing method, it is possible to manufacture a photomask having a single-layer transfer pattern that can prevent electrostatic breakdown, which can contribute to reducing the number of steps in the photomask manufacturing process. [Effects of the Invention]

[0030] According to the present invention, it is possible to obtain a photomask, a photomask blank, and a method for manufacturing a photomask that can prevent electrostatic damage to an exposure pattern. [Brief explanation of the drawings]

[0031] [Figure 1] 1A to 1C are cross-sectional views showing the main manufacturing steps of a photomask 100 according to the first embodiment. [Figure 2] 2A to 2C are cross-sectional views showing the main manufacturing steps of the photomask 100 according to the first embodiment. [Figure 3] FIG. 3 is a plan view of a photomask 100 having a conductive pattern 2a and a laminated pattern Pt on a transparent substrate 1. As shown in FIG. [Figure 4] FIG. 4 is a schematic diagram for calculating the occupancy of conductive pattern 2a in the shape of a rectangular lattice pattern and conductive pattern 2a in the shape of a hexagonal lattice pattern. [Figure 5] 5A to 5C are cross-sectional views showing the main manufacturing steps of the photomask 100 according to the second embodiment. [Figure 6] 6A to 6C are cross-sectional views and plan views showing the main manufacturing steps of the photomask 100 according to the third embodiment. [Figure 7] 7A to 7C are cross-sectional views and plan views showing the main manufacturing steps of the photomask 100 according to the third embodiment. [Figure 8] FIG. 8 is a graph schematically showing the correlation between the pitch of the unit shape (the pitch of the conductive pattern 2a) and the pixel area ratio (occupancy rate) of the transfer pattern. DETAILED DESCRIPTION OF THE INVENTION

[0032] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the following embodiments are not intended to limit the scope of the present invention. Furthermore, the same or similar components will be designated by the same reference numerals, and their description may be omitted.

[0033] (Embodiment 1) Hereinafter, a method for manufacturing the photomask 100 according to the first embodiment will be described with reference to the drawings. 1 and 2 are cross-sectional views showing the main manufacturing steps of a photomask 100 according to the first embodiment.

[0034] (Photomask blanks preparation process) As shown in FIG. 1(A), a transparent substrate 1 such as synthetic quartz glass is prepared, and a conductive film 2 (underlayer film 2) made of a conductive material such as, but not limited to, a metal film of Cr, Ni, Mo, etc., a Cr-based metal compound, or a metal silicide compound of Mo, etc. is formed on the transparent substrate 1 by sputtering, vapor deposition, or the like. Thereafter, a first photoresist film 3 is formed on the conductive film 2 by a coating method, a spray method or the like.

[0035] The thickness of the conductive film 2 can be set to, for example, but not limited to, 1 to 10 nm. As the material of the conductive film 2, for example, Cr, which has low resistivity, can be suitably used, but other materials with low resistivity such as Ni can also be used. In particular, Cr and Ni are materials commonly used in the manufacturing process of photomasks and have low resistivities of 125 nΩm and 69.3 nΩm, respectively. The conductive film 2 may be a semi-transparent film having a transmittance of 30% or more, preferably 60% or more, and more preferably 80 to 90%. As will be described later, it is possible to effectively prevent the conductive pattern 2a formed by the conductive film 2 from being transferred to the exposure target. Each optical characteristic is defined with respect to the representative wavelength of exposure light in the lithography process (for example, but not limited to, i-line, h-line, g-line, or any mixture of these light).

[0036] Furthermore, the conductive film 2 may be set to have a small phase shift (approximately 0°, for example, 0 to 20°) and a high transmittance (70 to 90%). In a lithography process using the photomask 100, the influence of exposure light passing through the conductive film 2 can be suppressed.

[0037] Next, as shown in FIG. 1(B), the first photoresist film 3 is patterned by exposure using laser drawing or the like and development to form a first photoresist pattern 3a (first etching mask pattern).

[0038] Next, as shown in Fig. 1(C), the conductive film 2 is etched using the first photoresist pattern 3a as an etching mask to form a conductive pattern 2a (lower layer pattern 2a). The conductive pattern 2a is, for example, a lattice-shaped wiring pattern, as will be described later with reference to Fig. 3. The conductive pattern 2a is formed over the entire surface of the photomask 100, or at least over the entire region where a transfer pattern to be transferred to an exposure target in a lithography process of the photomask 100 is to be disposed.

[0039] Furthermore, if it is known from the shape of the transfer pattern that there is a high risk of electrostatic breakdown occurring in a specific region, the conductive pattern 2a may be provided only in that region (high-risk region) where there is a high risk of electrostatic breakdown occurring.

[0040] The etching can be suitably performed by known wet etching, but may also be performed by dry etching. For example, when Cr is used as the conductive film 2 and wet etching is used as the etching method, cerium ammonium nitrate, for example, can be used as the etchant. When Ni is used as the conductive film 2, sulfuric acid, nitric acid, or a compound thereof can be used as the etchant. When MoSi is used as the conductive film 2, hydrogen fluoride, for example, can be used as the etchant.

[0041] The width of the linear portion of the conductive pattern 2a (hereinafter simply referred to as the width of the conductive pattern 2a) is equal to or less than the resolution limit of the exposure light (exposure device) in the lithography process using the photomask 100, and is, for example, but not limited to, 0.1 to 1 μm. To narrow the width of the conductive pattern 2a, the conductive film 2 may be patterned using the first photoresist pattern 3a as an etching mask, and then the conductive pattern 2a may be further side-etched by wet etching, so that the width of the conductive pattern 2a can be made smaller than the width of the first photoresist pattern 3a. Even if the conductive film 2 has low transmittance and light-blocking properties, the width of the conductive pattern 2a can be set to be equal to or less than the resolution limit of the exposure light (exposure device) in the lithography process, thereby preventing the conductive pattern 2a from being transferred to the exposure target. As will be described later with reference to Figure 4, by optimizing the shape of the conductive pattern 2a, it is possible to set the light transmittance of the entire conductive pattern 2a high even if the conductive film 2 has low transmittance such as a light-shielding film.

[0042] The pattern shape (in top view) of the conductive pattern 2a is a geometric pattern (for example, a shape composed of intersecting lines, such as, but not limited to, a mesh), and openings can be defined. The conductive pattern 2a can be, for example, a grid pattern, as described below. The shape of each unit constituting the grid pattern can be, for example, but not limited to, a triangle, a rectangle, a hexagon, a circle, etc. The conductive pattern 2a can also be a combination of units having multiple shapes, for example, a combination of a hexagon and a pentagon, or any combination of multiple shapes such as a hexagon, a pentagon, a triangle, etc. The conductive pattern 2a may have any pattern shape, and is not limited to a regular pattern shape, but may be composed of an irregular pattern shape, or may be a pattern shape that combines regular and irregular patterns. The conductive pattern 2a may also be composed of a plurality of units of different shapes, and the arrangement of each unit may also be arbitrary. Each unit has an opening (unit opening) of an arbitrary shape that is isolated therein. By forming the conductive pattern 2a in such a grid pattern, it is possible to reduce the area occupied by the conductive film 2 and improve the transmittance of the conductive pattern 2a to the exposure light. The transmittance of the conductive pattern 2a can be set to, for example, 70% or more.

[0043] Next, as shown in FIG. 1(D), the first photoresist pattern 3a is removed by ashing or the like. A plurality of transparent substrates 1 having conductive patterns 2a as shown in FIG. 1(D) may be prepared as photomask blanks and stored. By using the above-described photomask blanks, it is possible to quickly start manufacturing photomasks in response to customer orders.

[0044] Next, as shown in Fig. 1(E), an intermediate film 4 is formed on the transparent substrate 1 and the conductive pattern 2a by a sputtering method, a vapor deposition method, or the like, to a thickness of, for example, but not limited to, 1 to 70 nm. The intermediate film 4 is made of a conductive material. At least a part of the bottom of the intermediate film 4 is in contact with the conductive pattern 2a. The material of the intermediate film 4 is different from that of the conductive film 2, and has etching selectivity with respect to the conductive pattern 2a. In other words, the material of the intermediate film 4 is a material that can be selectively etched with respect to the conductive pattern 2a, and the intermediate film 4 functions as an etching stopper. The material of the intermediate film 4 can be selected from known materials such as, for example, but not limited to, metal films of Cr, Ni, etc., Cr-based metal compounds, metal silicide compounds of Mo, etc., and Si-based materials. For example, when Cr is used for the conductive film 2, Ni, Mo, or the like can be used for the intermediate film 4.

[0045] 1(F), an upper layer film 5 is formed on the intermediate film 4 by sputtering, vapor deposition, or the like, for example, but not limited to, a thickness of 60 to 120 nm. The bottom of the upper layer film 5 is in contact with the intermediate film 4. The upper layer 5 is made of a conductive material different from that of the intermediate film 4, and the upper layer 5 can have etching selectivity with respect to the intermediate film 4. For example, when Ni or Mo is used for the intermediate film 4, Cr can be used for the upper film 5. Moreover, the upper layer 5 can be a light-shielding film.

[0046] Alternatively, the intermediate film 4 and the upper layer film 5 may each be semi-transparent films, and the laminated film of the intermediate film 4 and the upper layer film 5 may have light-blocking properties. For example, the optical density (OD value) of the light-shielding film can be 2-5. Furthermore, the laminated film of the intermediate film 4 and the upper layer film 5 may be semi-transparent or may be a phase shift film (for example, with a phase shift amount of 160° to 200°). The optical properties of the intermediate film 4, the upper layer film 5, and the laminated film of the intermediate film 4 and the upper layer film 5 can be appropriately set depending on the application of the photomask 100.

[0047] It is also possible to prepare and store a plurality of photomask blanks each having a conductive pattern 2a, an intermediate film 4 and an upper layer film 5 as shown in FIG. 1(F).

[0048] Next, as shown in FIG. 2(G), a second photoresist film 6 is formed by coating, spraying, or the like.

[0049] Next, as shown in FIG. 2(H), the second photoresist film 6 is patterned by exposure using laser drawing or the like and development to form a second photoresist pattern 6a (second etching mask pattern). Thereafter, the upper layer film 5 is selectively etched with respect to the intermediate film 4 using the second photoresist pattern 6a as an etching mask to form an upper layer pattern 5a. The etching can be suitably performed by known wet etching, but may also be performed by dry etching. For example, when Cr is used for the upper layer film 5, Ni is used for the intermediate film 4, and wet etching is used as the etching method, cerium ammonium nitrate can be used as the etchant.

[0050] 2(I), the intermediate film 4 is selectively etched with respect to the conductive pattern 2a using the second photoresist pattern 6a as an etching mask to form an intermediate pattern 4a. As a result, a laminated pattern Pt consisting of the intermediate pattern 4a and the upper layer pattern 5a is formed. Since the intermediate pattern 4a and the upper layer pattern 5a each have conductivity, the laminated pattern Pt also has conductivity. The etching can be preferably a known wet etching, but can also be dry etching. For example, when Cr is used as the conductive film 2 and Ni is used as the intermediate film 4, and wet etching is used as the etching method, a mixture of sulfuric acid and hydrogen peroxide solution can be used as the etchant.

[0051] Even if the conductive film 2 and the upper layer film 5 are made of the same material, the intermediate film 4 functions as an etching stopper, so the conductive pattern 2a is not etched in the step shown in Fig. 2(H). In this case, the same film forming apparatus and etching apparatus can be used for the conductive film 2 and the upper layer film 5.

[0052] Next, as shown in FIG. 2(J), the second photoresist pattern 6a is removed by ashing or the like. A photomask 100 having a laminated pattern Pt in contact with the conductive pattern 2a can be obtained. In a lithography process using the photomask 100, an exposure target can be patterned by a laminated pattern Pt, which is a transfer pattern.

[0053] The upper layer pattern 5a may be further patterned on the intermediate pattern 4a of the laminated pattern Pt to expose the intermediate pattern 4a. The transfer pattern may have a single layer pattern composed only of the intermediate film 4, and a laminated pattern Pt composed of the intermediate film 4 and the upper layer film 5. This can improve the degree of freedom in designing the transfer pattern of the photomask 100.

[0054] Alternatively, the laminated pattern Pt may have light-shielding properties, and the intermediate film 4 may be a semi-transparent phase shift film that inverts the phase. For example, as shown in FIG. 2(K), a single-layer pattern made of the intermediate film 4 may be configured as a rim portion Rm around the laminated pattern Pt. This configuration allows the photomask 100 to be a rim-type phase shift mask. The rim portion Rm sharpens the profile of the exposure light around the laminated pattern Pt on the resist film to be transferred. As a result, the patterning accuracy of the laminated pattern Pt can be improved. The phase shift amount of the intermediate film 4 can be, for example, 120° to 240°, and the transmittance can be, for example, 1 to 10%. The rim portion Rm is intended to improve the patterning accuracy of the laminated pattern Pt, and the combination of the rim portion Rm and the laminated pattern Pt may also be referred to as a transfer pattern.

[0055] As shown in Figure 2(K), after the process of Figure 2(J), a third resist pattern (not shown) may be additionally formed on the upper layer pattern 5a, and the third resist pattern may be used as an etching mask to etch the upper layer pattern 5a selectively with respect to the conductive pattern 2a and the intermediate pattern 4a. For example, by making the intermediate film 4 a semi-transparent film that inverts the phase and the upper film 5 a light-shielding film, a rim portion Rm consisting of the intermediate pattern 4a can be formed around the laminated pattern Pt, thereby providing a rim-type phase shift mask. Furthermore, by making the intermediate film 4 and the upper film 5 semi-transparent films, it is possible to provide a multi-tone photomask.

[0056] In addition, in the process of Figure 2(I), after forming the stacked pattern Pt, it is also possible to form the rim portion Rm without using an additional mask by selectively side-etching the upper layer pattern 5a with respect to the conductive pattern 2a and the intermediate pattern 4a, for example, by isotropic etching (preferably wet etching).

[0057] Fig. 3 is a plan view of a photomask 100 having a conductive pattern 2a and a laminated pattern Pt on a transparent substrate 1. Fig. 3 shows the pattern shape of the conductive pattern 2a. Fig. 3(A) shows an example of a conductive pattern 2a having a lattice pattern (sometimes referred to as a rectangular lattice pattern) formed by repeating units each having a rectangular pattern. Fig. 3(B) shows an example of a conductive pattern 2a having a lattice pattern (sometimes referred to as a hexagonal lattice pattern) formed by repeating units each having a hexagonal pattern. The patterns surrounded by dotted lines in Figs. 3(A) and (B) show enlarged views of the units Un that make up each pattern.

[0058] As shown in Figure 3, the conductive pattern 2a is a connected pattern, and has a geometric shape in which wiring patterns are combined. Any two points on the conductive pattern 2a are connected to each other by a line. That is, all points on the conductive pattern 2a are connected to each other both physically and electrically. In the region where the laminated pattern Pt, which is the transfer pattern, is formed, the conductive pattern 2a is provided below the laminated pattern Pt, so that the charge generated by static electricity is dispersed over the entire surface of the photomask 100. As a result, the potential difference between the isolated laminated patterns Pt disappears, preventing electrostatic breakdown. The conductive pattern 2a is sometimes called a bridge pattern because it connects the isolated laminated patterns Pt.

[0059] In this way, by forming the conductive pattern 2a in a mesh-like pattern, it is possible to secure multiple current paths that electrically connect two points. Furthermore, by using a low-resistance metal film as the conductive film 2, it is possible to achieve quick charge transfer. As a result, it is possible to prevent electrostatic breakdown caused by charge concentration in, for example, a small, isolated transfer pattern. Furthermore, by arranging the conductive pattern 2a evenly over the entire area, it is possible to obtain the effect of preventing electrostatic breakdown regardless of the design of the transfer pattern (even if the pattern is complicated). Therefore, the photomask 100 having the conductive pattern 2a can meet the diverse needs (or diverse circuits) of customers.

[0060] 3, the conductive pattern 2a has openings OP. The transparent substrate 1 is exposed through the openings OP, and does not affect the exposure of the transfer pattern in the lithography process using the photomask 100. The transmittance of the conductive pattern 2a can be controlled by the occupancy rate of the opening OP.

[0061] 3(A) and 3(B) , a grid pattern consisting of a regular arrangement of units Un (unit patterns), which are the smallest components, can be easily designed to determine the ratio (occupancy) of the area of ​​the openings OP to the area of ​​the conductive pattern 2a. Furthermore, by using such a pattern, uniform transmittance can be achieved on the photomask 100, and excellent electrostatic breakdown prevention can be achieved by uniformly distributing electric charges.

[0062] The photomask 100 illustrated in FIGS. 3(A) and 3(B) has a plurality of laminated patterns Pt1 to Pt8, and each of the laminated patterns Pt1 to Pt8 is in contact with the conductive pattern 2a at its bottom surface. Without the conductive pattern 2a, the laminated patterns Pt1 to Pt8 would be isolated patterns spaced apart from one another, but the conductive pattern 2a forms an interconnection pattern that electrically connects the laminated patterns Pt1 to Pt8 to one another. Therefore, even if the designed transfer patterns (laminate patterns Pt1 to Pt8) are isolated patterns, they are electrically connected to the conductive pattern 2a, and therefore electrostatic breakdown can be avoided. The size (Lx, Ly) (sometimes referred to as unit size) of the unit shapes that make up the shape of the conductive pattern 2a may be set so that the transfer patterns (laminate patterns Pt1 to Pt8) come into contact with the conductive pattern 2a.

[0063] For example, the unit size of the conductive pattern 2a can be determined in accordance with the design rules and occupancy rate of the transfer pattern. Figure 8 shows a graph that schematically illustrates the correlation between the pitch of the unit shapes (pitch of the conductive pattern 2a) and the pixel area rate (occupancy rate) of the transfer pattern. In Figure 8, the vertical axis represents the pitch of the unit shapes (pitch of the conductive pattern 2a), and the horizontal axis represents the pixel area rate of the transfer pattern. 8, when the pixel area ratio of the transfer pattern is large, the interval between isolated patterns tends to become small. Therefore, the pitch (or unit size) of the unit shapes can be made larger (toward the "H" in the figure) as the pixel area ratio of the transfer pattern becomes larger. Furthermore, when the pixel area ratio of the transfer pattern is small, the spacing between isolated patterns tends to become larger. Therefore, the smaller the pixel area ratio of the transfer pattern, the smaller the pitch (or unit size) of the unit shapes can be made (toward the "L" side in the figure). 8 is an example, and the present invention is not limited to this example. The conductive pattern 2a can be determined according to the actual transfer pattern.

[0064] FIG. 4 is a schematic diagram for calculating and comparing the occupancy rates of conductive pattern 2a in a rectangular lattice pattern shape and conductive pattern 2a in a hexagonal lattice pattern shape. Fig. 4(A) is a top view schematically showing a conductive pattern 2a in a rectangular lattice pattern shape. Fig. 4(B) is an enlarged view of the area indicated by dotted line Z in Fig. 4(A). Fig. 4(C) is a top view schematically showing a conductive pattern 2a in a hexagonal lattice pattern shape. Fig. 4(D) is an enlarged view of the area indicated by dotted line Z in Fig. 4(C). The area indicated by dotted line Z is a region (referred to as unit area region Z) that defines a unit area for calculating transmittance. In FIG. 4, the solid lines schematically show the shape of the conductive pattern 2a.

[0065] In Figures 4(A) and (B), w is the length of one side of a square, which is a unit that makes up a rectangular lattice pattern, and in Figures 4(C) and (D), w is the length of one side of a regular hexagon, which is a unit that makes up a hexagonal lattice pattern.

[0066] The shading rate (=1-transmittance) of exposure light by the conductive pattern 2a in a unit area region Z is defined as the ratio between the area of ​​the conductive pattern 2a and the area of ​​the unit area region Z as follows, and the shading rates of the rectangular lattice pattern and the hexagonal lattice pattern are compared. Light blocking rate = [area of ​​conductive pattern 2a] / [area of ​​unit area region Z] (Equation 1)

[0067] 4(A) and 4(B), when the width of the conductive pattern 2a is d, the area of ​​the conductive pattern 2a in the unit area region Z is 2×d×w. Since the area of ​​the unit area region Z is w×w, the light blocking rate is 2×(d / w).

[0068] 4(C) and 4(D), when the width of the conductive pattern 2a is d, the area of ​​the conductive pattern 2a in the unit area region Z is 3×d×w / 2. Since the area of ​​the unit area region Z is (((√3)×w×w / 2) / 2)×3, the light blocking rate is (2 / (√3))×(d / w). For example, when w=100 μm and d=0.6 μm, the light blocking rate of the rectangular lattice pattern is 1.2%, and the light blocking rate of the hexagonal lattice pattern is 0.693%. Therefore, the light blocking rate of the hexagonal lattice pattern is lower than that of the rectangular lattice pattern. That is, the hexagonal lattice pattern has a higher transmittance, and therefore the hexagonal lattice pattern (honeycomb pattern) can be suitably used as the shape of the conductive pattern 2a.

[0069] The light blocking rate can be set by the geometric parameters of the grid pattern, for example, the length (w) of the side of the unit pattern and the width (d) of the conductive pattern 2a. Therefore, by determining the geometric parameters of the grating pattern in accordance with the required transmittance (1-light blocking rate), it is easy to ensure a transmittance of, for example, 70% or more. Even when the conductive film 2 is made of a light-shielding film, the transmittance of a photomask blank having a conductive pattern 2a can be set to 70% or more by optimizing the shape of the grid pattern and the geometric parameters of the grid pattern (e.g., d, w). Furthermore, by configuring the conductive film 2 as a semi-transparent film, the transmittance of the photomask blank can be further improved. It is also possible to expand the degree of freedom (setting range) in setting the shape of the grating pattern and the geometric parameters of the grating pattern.

[0070] As described above, by setting the width (d) of the conductive pattern 2a to be equal to or less than the resolution limit of the exposure light in the lithography process using the photomask 100, the conductive pattern 2a will not be transferred to the exposure target. The area shielded by the conductive pattern 2a is controlled by geometric parameters, ensuring a sufficiently high transmittance, for example, 70% or more. Furthermore, the transparent substrate 1 is exposed in the area (openings OP) other than the linear portion of the conductive pattern 2a, and this does not affect the transmittance or the amount of phase shift, so there is no effect on the exposure of the laminated pattern Pt to the exposure target.

[0071] (Embodiment 2) In the first embodiment, the transfer pattern of the photomask 100 is composed of a laminated pattern Pt. The transfer pattern may also be composed of a single layer pattern of an upper film. The manufacturing process of the photomask 100 according to the second embodiment will be described below. 5A to 5C are cross-sectional views showing the main manufacturing steps of the photomask 100 according to the second embodiment.

[0072] As shown in Figure 5(A), after the process shown in Figure 1(D), a conductive upper layer film 7 (functional film) is formed on a photomask blank having a conductive pattern 2a on a transparent substrate 1 by a sputtering method, a vapor deposition method, or the like. The upper layer film 7 is made of a material different from that of the conductive pattern 2a (conductive film 2), and has etching selectivity with respect to the conductive pattern 2a. Moreover, the upper layer film 7 may be a light-shielding film, a semi-transparent film, or a phase shift film that inverts the phase of exposure light. For example, a multi-tone photomask can be provided by forming the upper layer film 7 from a semi-transparent film, which can reduce the number of lithography steps in the manufacturing process of liquid crystal panels and the like, thereby contributing to a reduction in manufacturing costs. Furthermore, by forming the upper layer 7 from a phase shift film, it is possible to provide a half-tone phase shift mask, which inverts the phase of the exposure light and improves the resolution of the transferred pattern due to the phase shift effect. For example, Cr may be used as the material for the conductive film 2, and Ni, Mo, Mo silicide, or the like may be used as the material for the upper film 7, or vice versa.

[0073] It is also possible to prepare and store a plurality of transparent substrates 1 each having a conductive pattern 2a and an upper layer film 7 as shown in FIG. 5(A) as photomask blanks.

[0074] Next, as shown in FIG. 5(B), a third photoresist film 8 is formed by coating, spraying, or the like.

[0075] Next, as shown in FIG. 5(C), the third photoresist film 8 is patterned by exposure using laser drawing or the like and development to form a third photoresist pattern 8a (third etching mask pattern).

[0076] 5(D), the upper layer film 7 is selectively etched with respect to the conductive pattern 2a using the third photoresist pattern 8a as an etching mask to form an upper layer pattern 7a. Wet etching is preferably used for the etching, but dry etching may also be used. Thereafter, the third photoresist pattern 8a is removed by ashing or the like. It is possible to obtain a photomask 100 having an upper layer pattern 7a in contact with the conductive pattern 2a. The transfer pattern is composed of a single upper layer pattern 7a. In a lithography process using the photomask 100, the upper layer pattern 7a, which is a transfer pattern, can be used to pattern an exposure target.

[0077] By using a light-shielding film as the upper layer film 7, a binary mask can be obtained. Furthermore, by employing a semi-transparent film or a phase shift film as the upper layer film 7, it is possible to obtain a half-tone mask, a phase shift mask, or a half-tone type phase shift mask. The optical properties (transmittance, phase shift amount) of the upper layer film 7 may be determined according to the application.

[0078] (Embodiment 3) The lower layer film 2 may be made of a phase shift film, and a single layer pattern made of the lower layer film 2 may be configured as the rim portion Rm of the laminated pattern Pt. The manufacturing process of the photomask 100 according to the third embodiment will be described below with reference to Fig. 6 and Fig. 7. Figs. 6(A), (C), (D), 7(E), and (F) are cross-sectional views showing the main manufacturing process of the photomask 100, and Figs. 6(B) and 7(G) are plan views showing the main manufacturing process of the photomask 100.

[0079] As shown in the cross-sectional view of Figure 6(A) and the plan view of Figure 6(B), a conductive film 2 (underlayer film 2) is formed on a transparent substrate 1, and a first photoresist film 3 is formed on the conductive film 2 by a coating method, a spraying method, or the like. Thereafter, the first photoresist film 3 is patterned by exposure using laser drawing or the like and development to form first photoresist patterns 3a and 3a' (first etching mask patterns).

[0080] The conductive film 2 is made of a phase shift film that inverts the phase, with a phase shift amount of approximately 180° (90° to 270°) and a transmittance of, for example, 3 to 30%.The film thickness is, for example, 70 nm to 170 nm. As described above, the conductive film 2 can be made of a metal film such as Cr, Ni, or Mo, or a metal compound.

[0081] The first photoresist patterns 3a and 3a' have a shape that is a combination of the bridge pattern and transfer pattern of the conductive pattern 2a of the above-described embodiment 1. The first photoresist pattern 3a corresponds to the bridge pattern, and the first photoresist pattern 3a' corresponds to the transfer pattern. The shape of the first photoresist pattern 3a' can be, for example, a shape including the laminated pattern Pt and the rim portion Rm. As a design pattern, a bridge pattern (a geometric pattern) is prepared in advance as the conductive pattern 2a, and a transfer pattern that realizes the product specifications of a customer or the like can be synthesized (overlaid) using a design support tool such as CAD (software). Therefore, the pattern data required for manufacturing photomasks 100 for various purposes can be quickly generated.

[0082] Thereafter, as shown in FIG. 6(C), the conductive film 2 is etched by, for example, wet etching using the first photoresist patterns 3a and 3a' as an etching mask to form conductive patterns 2a and 2a'.

[0083] 6(D), the first photoresist patterns 3a and 3a' are removed by ashing, etc. Thereafter, an upper layer film 7 is formed on the conductive patterns 2a and 2a'. The upper layer 7 is made of a material different from that of the conductive film 2 and is made of a material that can be selectively etched relative to the conductive film 2.

[0084] 7(E), a third photoresist film 8 is formed. Thereafter, the third photoresist film 8 is patterned by exposure using laser drawing or the like and development to form a third photoresist pattern 8a. The third photoresist pattern 8a defines the laminated pattern Pt.

[0085] 7(F) and 7(G), the third photoresist pattern 8a is used as an etching mask to selectively etch the upper layer film 7 with respect to the conductive pattern 2a by, for example, wet etching, to form the upper layer pattern 7a. The third photoresist pattern 8a is then removed by ashing or the like. A rim portion Rm made of a single-layer conductive pattern 2a (conductive film 2) is formed at the edge of the upper layer pattern 7a. That is, the rim portion Rm can be formed around the laminated pattern Pt. The width of the rim portion Rm can be determined by the third photoresist pattern 8a. In the example shown in FIG. 7, rims Rm are formed only on the left and right sides of upper layer pattern 7a, but rims Rm can also be formed above and below upper layer pattern 7a. The width of the rim portion Rm can be set appropriately, and can also be set depending on the pattern shape.

[0086] The rim portion Rm inverts the phase of the exposure light, making the exposure light distribution at the edge of the laminated pattern Pt steeper, and can improve the patterning accuracy of the laminated pattern Pt. The photomask 100 can be used as a rim-type phase shift mask in a lithography process. The rim portion Rm is provided around the laminated pattern Pt depending on the accuracy of the pattern, and the width of the rim portion Rm can be set appropriately depending on the shape, size, etc. of the laminated pattern Pt.

[0087] In order to generate the conductive pattern 2a shown in Figures 6(A) and (B), the transfer pattern to be combined with the bridge pattern is composed of a combination of a laminated pattern Pt and an appropriately formed rim portion Rm. As shown in FIGS. 7(F) and 7(G), a part of the conductive pattern 2a forms a rim portion Rm, and further forms a conductive pattern 2a' (lower layer pattern 2a') below the laminated pattern Pt.

[0088] It should be noted that the photomask 100 of the third embodiment can be interpreted as having the upper layer pattern 7a of the laminated pattern Pt formed as a transfer pattern on the conductive pattern 2a.

[0089] It is also possible to provide a multi-tone photomask by using a semi-transparent film as the upper layer film 7. [Industrial Applicability]

[0090] According to the present invention, a conductive pattern is provided on a transparent substrate, and a transfer pattern, which is a conductive exposure pattern, is formed on the conductive pattern, so that electrostatic damage to the photomask can be prevented. The conductive pattern is not transferred to the exposure target in the lithography process and can be set to have a high transmittance, so it does not affect the lithography process and can be applied to various photomasks. Furthermore, the conductive pattern can be made using known materials used in the photomask manufacturing process and existing photomask manufacturing equipment can be used, making the present invention highly applicable to industry. [Explanation of symbols]

[0091] 100 Photomasks 1 Transparent substrate 2 Conductive film (underlayer film) 2a, 2a' Conductive pattern (lower layer pattern) 3 First photoresist film 3a, 3a' First photoresist pattern (first etching mask pattern) 4 Interlayer 4a Intermediate pattern 5 Upper membrane 5a Upper layer pattern 6 Second photoresist film 6a Second photoresist pattern (second etching mask pattern) 7 Upper layer membrane (functional membrane) 7a Upper layer pattern 8. Third photoresist film 8a Third photoresist pattern (third etching mask pattern) Pt, Pt1 to Pt8 laminated pattern

Claims

1. A transparent substrate, and a conductive pattern and a transfer pattern on the transparent substrate, The width of the conductive pattern is less than or equal to the resolution limit of the exposure light. At least a portion of the transfer pattern is located on the conductive pattern and is in electrical contact with the conductive pattern. A photomask characterized by the following features.

2. The shape of the conductive pattern is a geometric pattern. The photomask according to claim 1, characterized in that it is a photomask.

3. The conductive pattern is semi-permeable. A photomask according to claim 1 or 2, characterized by the above.

4. The conductive pattern has a honeycomb shape. A photomask according to claim 1 or 2, characterized by the above.

5. The transfer pattern is a lamination of an interlayer and an upper layer formed on the interlayer. The interlayer and the upper layer are electrically conductive. A photomask according to claim 1 or 2, characterized by the above.

6. The interlayer has etching selectivity with respect to the conductive pattern, The upper layer film has etching selectivity with respect to the intermediate film. The photomask according to claim 5, characterized in that it is a photomask.

7. The aforementioned transfer pattern is composed of an upper layer film. The upper layer film is conductive. A photomask according to claim 1 or 2, characterized by the above.

8. The upper layer film has etching selectivity with respect to the conductive pattern. The photomask according to claim 7, characterized by its features.

9. The photomask according to claim 7, characterized in that the upper layer film is a semipermeable film or a phase-shift film.

10. The conductive pattern is composed of an underlying film, and the underlying film is a phase-shift film. The aforementioned transfer pattern is composed of an upper layer film and is formed on the lower layer film. The edges of the transfer pattern have a rim portion formed by the underlying film. The photomask according to claim 1, characterized in that it is a photomask.

11. A transparent substrate and a conductive pattern having been placed on the transparent substrate, The width of the conductive pattern is less than or equal to the resolution limit of the exposure light. A photomask blank characterized by the following features.

12. A process of forming a conductive film on a transparent substrate, The process involves patterning the conductive film to form a conductive pattern having a width less than or equal to the resolution limit of the exposure light, A step of forming a conductive interlayer on the conductive pattern, A step of forming a conductive upper layer on the interlayer, The process includes patterning the interlayer and the upper layer to form a transfer pattern formed by lamination of the interlayer and the upper layer, and exposing a portion of the conductive pattern. A method for manufacturing a photomask, characterized by the following:

13. A process of forming a conductive film on a transparent substrate, The process involves patterning the conductive film to form a conductive pattern having a width less than or equal to the resolution limit of the exposure light, A step of forming a conductive upper layer film on the conductive pattern, The process includes patterning the upper layer film to form a transfer pattern composed of the upper layer film, and exposing a portion of the conductive pattern. A method for manufacturing a photomask, characterized by the following:

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