Blank mask and photomask

Abstract

The photomask according to the embodiment includes a substrate and a plurality of patterns disposed on the substrate. The patterns include a first layer and a second layer having different electrical conductivities, and the electrical conductivity of the patterns is 500 S / cm to 2000 S / cm.

Description

Technical Field

[0001] The embodiments relate to a blank mask and a photomask.

Background Art

[0002] Semiconductor integrated circuit (Large Scale Integration: LSI) devices and flat panel display (Flat Panel Display: hereinafter, FPD) devices are manufactured by a photolithography process that transfers a pattern using a photomask.

[0003] The blank mask has a structure in which a metal film or a metal compound film containing a metal substance and a photoresist film are formed on a transparent substrate containing synthetic quartz glass. The photomask includes a metal pattern or a metal compound pattern formed by patterning the thin film of the blank mask.

[0004] The thin film includes a light-shielding film, an antireflection film, a phase inversion film, a semitransparent film, or a reflection film depending on required optical characteristics. The blank mask includes at least one or more of the thin films, and the thin films are patterned into a required form to manufacture a photomask including a transfer pattern.

[0005] On the other hand, the photomask transfers a pattern by a contact or non-contact photolithography process, whereby a structure constituting a device can be formed on a substrate to be transferred.

[0006] At this time, for the photomask repeatedly used in the photolithography process, as the number of uses increases, the electrostatic charges charged on the photomask accumulate. When the charge difference between patterns exceeds the breakdown voltage, electrostatic charges are generated between the patterns, damaging the patterns on the photomask. In particular, the more isolated a pattern is, the higher the potential difference with adjacent patterns becomes, resulting in more damage caused by electrostatic discharge current. This leads to problems where the photomask with damaged patterns has to be newly corrected or discarded.

[0007] Therefore, there is a need for a photomask with a new structure that can reduce the electrostatic discharge current of the photomask as described above.

Summary of the Invention

Problems to be Solved by the Invention

[0008] The embodiment provides a photomask that can reduce the discharge current generated by the static electricity of the pattern and increase the discharge voltage.

Means for Solving the Problems

[0009] The photomask according to the embodiment includes a substrate and a plurality of patterns disposed on the substrate. The patterns include a first layer and a second layer with different electrical conductivities, and the electrical conductivity of the patterns is 500 S / cm to 2000 S / cm.

Effects of the Invention

[0010] The blank mask according to the embodiment includes a conductive layer having a conductivity within a set range. Thereby, the photomask manufactured by the blank mask is formed with patterns having a conductivity within a set range.

[0011] As a result, the discharge voltage of the pattern of the photomask increases. Also, when static electricity is generated between adjacent patterns, the magnitude of the discharge current due to the static electricity decreases. Therefore, the magnitude of the heat generation temperature due to the discharge current decreases. Thereby, it is possible to prevent the pattern of the photomask from being damaged by the heat generation of the discharge current generated between adjacent patterns.

[0012] That is, the electrical conductivity of the conductive layer of the blank mask used in the manufacture of the photomask is reduced, and the electrical conductivity of the pattern of the photomask manufactured by the blank mask also decreases.

[0013] Therefore, the current density of the discharge current, which is proportional to the magnitude of the electrical conductivity and the magnitude of the electric field, decreases. Therefore, when static electricity is generated between adjacent patterns, the magnitude of the discharge current generated by the static electricity decreases. Therefore, the magnitude of the heat generation temperature due to the discharge current decreases.

[0014] Therefore, the blank mask according to the embodiment can manufacture a photomask having improved reliability. Also, the photomask according to the embodiment can prevent damage to the pattern and form a circuit pattern having a uniform and fine line width on the wafer, and can increase the life of the photomask.

Brief Description of the Drawings

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Figure 1

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Figure 2

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Figure 3

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Figure 4

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Figure 7

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Figure 8

Mode for Carrying Out the Invention

[0022] Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in detail. However, the technical idea of the present invention is not limited to some of the described embodiments, but can be embodied in various different forms, and within the scope of the technical idea of the present invention, one or more of the components between the embodiments can be selectively combined and replaced for use. Also, the terms (including technical and scientific terms) used in the embodiments of the present invention can be interpreted as meanings generally understood by those with ordinary knowledge in the technical field to which the present invention belongs, unless specifically defined and described otherwise, and terms generally used like those defined in a dictionary can be interpreted considering their meanings in the context of the related technology.

[0023] Also, the terms used in the embodiments of the present invention are for the purpose of explaining the embodiments and do not limit the present invention. In this specification, the singular form can also include the plural form unless otherwise specifically mentioned in a phrase, and when described as "at least one (or one or more) of A and (or) B, C", it can include one or more of all combinations that can be combined with A, B, and C.

[0024] In addition, when explaining the components of the present invention, terms such as first, second, A, B, (a), (b), etc. can be used. Such terms are merely for distinguishing the components from other components and are not limited to the essence, order, or sequence of the components by such terms.

[0025] And when a certain component is described as "connected", "coupled", or "connected" to another component, that component can include not only the case where it is directly connected, coupled, or connected to the other component, but also the case where it is "connected", "coupled", or "connected" by another component between that component and the other component.

[0026] Also, when it is described that it is formed or arranged "above or below" each component, above or below includes not only the case where two components are in direct contact with each other, but also the case where one or more other components are formed or arranged between the two components.

[0027] Also, when expressed as "above or below", it can include not only the upward direction but also the downward direction with respect to one component.

[0028] Hereinafter, with reference to the drawings, a photomask according to an embodiment will be described.

[0029] FIG. 1 is a drawing showing a cross-sectional view of a blank mask according to an embodiment.

[0030] Referring to FIG. 1, the blank mask 1000 according to the embodiment includes a substrate 100 and a conductive layer 200.

[0031] The substrate 100 includes a transparent substrate. For example, the substrate 100 may be a quartz glass, soda lime, glass substrate, alkali-free glass substrate, or low thermal expansion glass substrate. For example, the substrate 100 includes a quartz substrate.

[0032] The conductive layer 200 is disposed on the entire surface of the substrate 100. The conductive layer 200 has a set range of electrical conductivity. Thereby, the pattern of the photomask manufactured by the blank mask also has a set range of electrical conductivity. Therefore, damage to the pattern of the photomask manufactured by the blank mask can be prevented.

[0033] The conductive layer 200 includes a metal. Specifically, the conductive layer 200 includes a metal oxide. Specifically, the conductive layer 200 includes a chromium oxide. More specifically, the conductive layer 200 includes a chromium oxide containing at least one of chromium, carbon, oxygen, and nitrogen. Even more specifically, the conductive layer 200 includes a chromium oxide containing at least one of CrO, CrON, CrCO, and CrCON.

[0034] Referring to FIG. 2, the conductive layer 200 includes a plurality of layers. For example, the conductive layer 200 includes a first layer 210 and a second layer 220. Specifically, the second layer 220 is disposed on at least one of the upper and lower surfaces of the first layer 210.

[0035] In FIG. 2, an example where the conductive layer 200 is formed of three layers is illustrated, but the embodiment is not limited thereto. The conductive layer 200 may be formed of two layers or four or more layers.

[0036] The first layer 210 and the second layer 220 have different compositions from each other. Also, the first layer 210 and the second layer 220 have different composition ratios from each other. Further, the first layer 210 and the second layer 220 have physical properties different from each other.

[0037] For example, the first layer 210 contains a chromium element, a carbon element, and an oxygen element. Also, the second layer 220 contains a chromium element, a carbon element, an oxygen element, and a nitrogen element.

[0038] Also, the first layer 210 and the second layer 220 have different oxygen contents. That is, the composition ratio of oxygen in the metal oxide of the first layer 210 is different from the composition ratio of oxygen in the metal oxynitride of the second layer 220.

[0039] The electrical conductivity of the conductive layer 200 is adjusted by controlling the oxygen contents of the first layer 210 and the second layer 220.

[0040] Also, the first layer 210 and the second layer 220 have different magnitudes of electrical conductivity. For example, the electrical conductivity of the first layer 210 is greater than the electrical conductivity of the second layer 220. Or, the electrical conductivity of the second layer 220 is greater than the electrical conductivity of the first layer 210.

[0041] Also, the first layer 210 and the second layer 220 have different thicknesses. Specifically, the thickness of the first layer 210 is greater than the thickness of the second layer 220.

[0042] When patterning the blank mask to form a photomask, the first layer 210 is defined as the light-shielding layer of the photomask. Also, the second layer 220 is defined as the antireflection layer of the photomask.

[0043] FIG. 3 is a drawing showing a cross-sectional view of the photomask formed by the blank mask.

[0044] The photomask 2000 is formed by applying a photoresist to the blank mask 1000 and then performing exposure and development using an electron beam. That is, the exposure and development processes are carried out using an electron beam according to the desired semiconductor circuit information. Subsequently, after etching the chromium, the photoresist is removed.

[0045] As a result, a plurality of patterns P having semiconductor circuit information are formed on the photomask. For example, the photomask 2000 includes a plurality of patterns having a set line width and interval. Specifically, the photomask 2000 includes a plurality of patterns P having a line width greater than 0 μm and less than or equal to 20 μm, and an interval greater than 0 μm and less than or equal to 20 μm.

[0046] That is, in the region where the pattern P is formed on the photomask 2000, light is blocked, and in the substrate 100 where no pattern is formed, light is transmitted. Thus, by placing the photomask on the wafer, it is possible to form the circuit pattern of the semiconductor circuit information held by the photomask on the surface of the wafer through exposure, development, and etching processes.

[0047] On the other hand, the plurality of patterns P of the photomask have a fine line width and are arranged adjacent to each other. As a result, a discharge current may flow between adjacent patterns due to the electrostatic phenomenon occurring in the patterns. Such a discharge current induces heat generation, and damage may occur to the patterns due to such heat generation temperature.

[0048] FIG. 4 is a drawing for explaining that when static electricity is generated in a pattern on a photomask, the pattern is damaged.

[0049] Referring to FIG. 4, a plurality of patterns are arranged on the substrate 100. For example, a first pattern P1 and a second pattern P2 having circuit information and adjacent to each other are arranged on the substrate 100.

[0050] During the manufacturing process or handling process of the photomask, electrostatic charges accumulate on the respective patterns P1 and P2. As a result, free electrons due to the electrostatic charges are emitted from the first pattern P1 or the second pattern P2. At this time, when the air between the patterns reaches the breakdown strength, the air between the patterns becomes a conductor and forms a conductive path. Thereby, the free electrons emitted from the first pattern P1 or the second pattern P2 move. For example, the free electrons emitted from the first pattern P1 move along the conductive path to the second pattern P2. Thereby, a conductive path is formed between the first pattern P1 and the second pattern P2, and a current flows along the conductive path. Such a phenomenon is defined as pattern discharge, and the current flowing along the conductive path is defined as the discharge current. Also, the voltage at which the discharge current is generated by static electricity is defined as the discharge voltage.

[0051] The discharge current induces heat generation. Such a heat generation temperature is proportional to the discharge current. Therefore, as the magnitude of the discharge current increases, the heat generation temperature also increases. That is, when the discharge current between the first pattern P1 and the second pattern P2 increases, the heat generation temperature between the first pattern P1 and the second pattern P2 also increases. Therefore, due to the increase in the heat generation temperature, there is a risk that the first pattern P1 and the second pattern P2 will be damaged.

[0052] Therefore, due to damage to the pattern of the photomask, when forming a circuit pattern on a wafer using the photomask, an accurate circuit pattern cannot be formed on the wafer. Also, when forming a circuit pattern on a wafer, the line width of the circuit pattern becomes non-uniform.

[0053] The discharge current generated between the first pattern P1 and the second pattern P2 is proportional to the current density J of the first pattern P1 and the second pattern P2. Also, the current density J is proportional to the electrical conductivity σ and the electric field (e-field) E. Specifically, the current density J is defined by the following mathematical formula.

[0054] [Mathematical formula] Current density J = Electrical conductivity σ × Electric field (E-field) E

[0055] Therefore, in order to reduce the discharge current generated between the first pattern P1 and the second pattern P2, the current density J must be decreased. Also, in order to decrease the current density J, the magnitude of either the electrical conductivity or the electric field must be decreased.

[0056] On the other hand, the magnitude of the electrical conductivity does not affect the electric field.

[0057] Figures 5 and 6 are drawings for explaining the changes in the electric field and the current density when the electrical conductivity is varied. Figures 5 and 6 are drawings showing the changes in the electric field and the current density in Experimental Example 1 and Experimental Example 2 where the electrical conductivities are different from each other. Experimental Example 1 is a photomask including a pattern with low electrical conductivity, and Experimental Example 2 is a photomask with relatively higher electrical conductivity than Experimental Example 1.

[0058] Referring to Figure 5, the magnitudes of the electric fields (E-filed) in Experimental Example 1 and Experimental Example 2 have no relation to the electrical conductivity. That is, referring to Figure 5, it can be seen that the electric field magnitudes in Experimental Example 1 and Experimental Example 2 with different electrical conductivities are approximately similar.

[0059] On the other hand, referring to Figure 6, it can be seen that the magnitude of the current density is related to the electrical conductivity. Referring to Figure 6, it can be seen that the current densities of patterns P1 and P2 in Experimental Example 2 with high electrical conductivity are larger than the current densities of patterns P1 and P2 in Experimental Example 1 with low electrical conductivity.

[0060] Referring to Figures 5 and 6, the magnitude of the electrical conductivity does not affect the magnitude of the electric field, and the electrical conductivity is proportional to the current density. Therefore, when the electrical conductivity of the pattern is decreased, the current density can be decreased. Also, when the current density is decreased, the magnitude of the discharge current can be decreased.

[0061] Therefore, the photomask 2000 according to the embodiment controls the electrical conductivity of the pattern within a set range. Thereby, the magnitude of the discharge current generated between the adjacent patterns due to the generation of static electricity is reduced. Therefore, since the heat generation temperature generated by the discharge current is reduced, damage to the pattern of the photomask can be reduced.

[0062] On the other hand, the electrical conductivity of the pattern is controlled by adjusting the oxygen content of the pattern. Specifically, it is formed by adjusting the oxygen content of the conductive layer 200 of the blank mask. More specifically, it is formed by adjusting the oxygen content of the first layer 210 which is a light-shielding layer and / or the second layer 220 which is an antireflection layer. For example, the electrical conductivity range of the conductive layer 200 is set, and the oxygen content can be increased to an amount that satisfies the electrical conductivity range. The magnitude of the electrical conductivity of the first layer 210 and the second layer 220 is inversely proportional to the oxygen content. Therefore, by increasing the oxygen content of the first layer 210 and the second layer 220, the electrical conductivity of the first layer 210 and the second layer 220 can be reduced.

[0063] Thereby, the electrical conductivity of the conductive layer 200 of the blank mask 1000 according to the embodiment is 500 S / cm or more. Specifically, the electrical conductivity of the conductive layer 200 is 500 S / cm to 2000 S / cm. More specifically, the electrical conductivity of the conductive layer 200 is 1200 S / cm to 1600 S / cm.

[0064] Also, the electrical conductivity of the pattern P of the photomask 2000 according to the embodiment is 500 S / cm or more. Specifically, the electrical conductivity of the pattern P is 500 S / cm to 2000 S / cm. More specifically, the electrical conductivity of the pattern P is 1200 S / cm to 1600 S / cm.

[0065] When the electrical conductivity of the conductive layer 200 and the pattern P is between 500 S / cm and 2000 S / cm, the current density of the pattern P decreases. Therefore, when static electricity is generated in the pattern P, the magnitude of the discharge current generated between the patterns P decreases. Therefore, it is possible to reduce damage to the pattern P when static electricity is generated.

[0066] When the electrical conductivity of the conductive layer 200 and the pattern P is less than 500 S / cm, the light-shielding characteristics of the conductive layer 200 and the pattern P decrease. That is, as the oxygen content of the conductive layer 200 and the pattern P increases, the light transmittance of the conductive layer 200 and the pattern P increases. As a result, when forming a circuit pattern on a wafer using the photomask, a uniform line width and an accurate circuit pattern cannot be formed. That is, the characteristics of the photomask decrease.

[0067] Also, when the electrical conductivity of the conductive layer 200 and the pattern P exceeds 2000 S / cm, the increase in the electrical conductivity of the pattern P causes an increase in the current density of the discharge current. As a result, the heat generation temperature increases between adjacent patterns, and damage such as cracks may occur in the patterns. As a result, when forming a circuit pattern on a wafer using the photomask, a uniform line width and an accurate circuit pattern cannot be formed. That is, the characteristics of the photomask decrease.

[0068] Also, the discharge voltage of the pattern P of the photomask 2000 according to the embodiment is 400 V or more. Specifically, the discharge voltage of the pattern P is between 400 V and 550 V. Also, the discharge current of the pattern P of the photomask 2000 according to the embodiment is 0.5 mA or more. Specifically, the discharge current of the pattern P is between 0.5 mA and 2 mA.

[0069] Since the pattern P has the above-described electric conductivity range, the magnitude of the discharge voltage at which static electricity is generated in the pattern P increases, and the magnitude of the discharge current decreases. Therefore, since the magnitude of the discharge voltage of the pattern P increases, the generation of static electricity that can occur in the pattern P decreases. Also, since the magnitude of the discharge current of the pattern P decreases, when static electricity that can occur in the pattern P is generated, damage to the pattern can be reduced.

[0070] Hereinafter, the present invention will be described in more detail via the discharge voltage and discharge current corresponding to the electric conductivity of the pattern of the photomask according to the examples and comparative examples. Such examples are merely presented as illustrations for explaining the present invention in more detail. Therefore, the present invention is not limited to such examples.

[0071] <Example 1> A quartz substrate is prepared. Subsequently, a conductive layer is formed on the quartz substrate.

[0072] The conductive layer is formed by laminating at least one first layer and at least one second layer on the quartz substrate. The first layer contains chromium oxide containing chromium, oxygen, and carbon. Also, the second layer contains chromium oxynitride containing chromium, oxygen, carbon, and nitrogen.

[0073] Subsequently, the oxygen content of the first layer and / or the second layer is controlled to control the electric conductivity of the conductive layer. Thereby, a conductive layer having an (average) electric conductivity of 1399 S / cm is formed.

[0074] Subsequently, the conductive layer is patterned to manufacture a photomask.

[0075] Subsequently, the discharge current and the discharge voltage are measured between the patterns of the photomask.

[0076] <Example 2> A conductive layer was formed in the same manner as in Example 1. Thereby, a conductive layer having an (average) electric conductivity of 1274 S / cm was formed.

[0077] Subsequently, the conductive layer was patterned to fabricate a photomask.

[0078] Subsequently, the discharge current and discharge voltage were measured between the patterns of the photomask.

[0079] <Comparative Example 1> A conductive layer was formed in the same manner as in Example 1. As a result, a conductive layer having an (average) electrical conductivity of 16700 S / cm was formed.

[0080] Subsequently, the conductive layer was patterned to fabricate a photomask.

[0081] Subsequently, the discharge current and discharge voltage were measured between the patterns of the photomask.

[0082] <Comparative Example 2> A conductive layer was formed in the same manner as in Example 1. As a result, a conductive layer having an (average) electrical conductivity of 2690 S / cm was formed.

[0083] Subsequently, the conductive layer was patterned to fabricate a photomask.

[0084] Subsequently, the discharge current and discharge voltage were measured between the patterns of the photomask.

[0085]

Table 1

[0086] FIG. 7 is a graph showing the discharge voltage and discharge current of the patterns according to the examples and comparative examples.

[0087] Referring to FIG. 7, the discharge voltages of the patterns according to Example 1 and Example 2 are higher than those of the comparative examples. Specifically, the discharge voltage of the pattern according to Example 1 is 500 V, the discharge voltage of the pattern according to Example 2 is 450 V, the discharge voltage of the pattern according to Comparative Example 1 is 200 V, and the discharge voltage of the pattern according to Comparative Example 2 is 250 V.

[0088] Therefore, for the patterns according to Example 1 and Example 2, since the work function, which is the minimum energy for generating static electricity, is large, discharge occurs at a high voltage. That is, the discharge voltage is high.

[0089] Also, the discharge currents of the patterns according to Example 1 and Example 2 are smaller than those of the comparative examples. Specifically, the discharge current of the pattern according to Example 1 is 0.9 mA, the discharge current of the pattern according to Example 2 is 1.02 mA, the discharge current of the pattern according to Comparative Example 1 is 12.69 mA, and the discharge current of the pattern according to Comparative Example 2 is 2.5 mA.

[0090] That is, the patterns according to Example 1 and Example 2 have low electrical conductivity. Therefore, the patterns according to Example 1 and Example 2 have a low current density. As a result, the magnitude of the discharge current flowing between the patterns is also small.

[0091] Therefore, since the patterns according to Example 1 and Example 2 have a small discharge current, when static electricity is generated, the magnitude of the heat generation temperature generated between the patterns decreases.

[0092] FIG. 8 is an optical image showing damage to the patterns of the photomasks according to the examples and comparative examples when static electricity is generated.

[0093] Referring to FIG. 8, for the photomasks according to Example 1 and Example 2, when static electricity is generated in the patterns, since the magnitude of the discharge current flowing between the patterns is small, pattern deformation occurs only in local regions and the degree of pattern deformation is not large.

[0094] For the photomasks according to the reverse side, Comparative Example 1, and Comparative Example 2, when static electricity is generated in the pattern, since the magnitude of the discharge current flowing between the patterns is large, the area where pattern deformation occurs is large and the degree of pattern deformation is large.

[0095] That is, for the photomasks according to Example 1 and Example 2, the discharge voltage of the pattern having an electrical conductivity within a set range is high and the discharge current is small. Therefore, when static electricity is generated in the pattern and a discharge current flows between the patterns accordingly, the heat generation temperature due to this decreases. Thereby, it is possible to prevent the pattern from being damaged by the heat generation temperature generated between the patterns. Therefore, the photomask according to the example has improved reliability and can improve the service life.

[0096] Also, referring to Table 1, the patterns according to Example 1 and Example 2 have an optical density of 3 or more in the wavelength range of 450 nm. Therefore, the patterns according to Example 1 and Example 2 have improved light-shielding characteristics.

[0097] Also, the pattern according to the example has an etching rate of 600 seconds or less. Also, the pattern according to the example has an etching deviation of 200 nm or less. Here, the etching deviation is defined by the deviation from the line width of the pattern to be set. Therefore, the photomask according to the example includes a pattern having a fine line width and improved etching characteristics.

[0098] Therefore, the photomask according to the example can improve the line width and uniformity of the pattern and reduce the magnitude of the discharge current generated by static electricity between adjacent patterns.

[0099] Thereby, a circuit pattern having a uniform and fine line width can be formed on the wafer by the photomask according to the example, and the service life and reliability of the photomask can be improved.

[0100] The features, structures, effects, etc. described in the foregoing embodiments are included in at least one embodiment of the present invention and are not necessarily limited to only one embodiment. Furthermore, the features, structures, effects, etc. exemplified in each embodiment can be combined or modified and implemented in other embodiments by those with ordinary knowledge in the field to which the embodiment belongs. Therefore, the content related to such combinations and modifications should be construed as being included in the scope of the present invention.

[0101] In addition, although the description has centered on the embodiments above, this is merely an illustration and does not limit the embodiments. It can be understood that those with ordinary knowledge in the field to which the embodiments belong can make various modifications and applications not exemplified above without departing from the essential characteristics of these embodiments. For example, each component specifically shown in the embodiments can be implemented with modifications. And the differences related to such modifications and applications should be construed as being included in the scope of the embodiments set forth in the appended claims.

Claims

1. A substrate, and a conductive layer disposed on the substrate, wherein the conductive layer includes a first layer and a second layer having different electrical conductivities, and the electrical conductivity of the conductive layer is 500 S / cm to 2000 S / cm, a blank mask.

2. The blank mask according to claim 1, wherein the electrical conductivity of the conductive layer is 1200 S / cm to 1600 S / cm.

3. The first layer includes a metal oxide containing chromium element, carbon element and oxygen element, and the second layer includes a metal oxynitride containing chromium element, carbon element, oxygen element and nitrogen element, the blank mask according to claim 1.

4. A substrate, and a plurality of patterns disposed on the substrate, wherein the patterns include a first layer and a second layer having different electrical conductivities, and the electrical conductivity of the patterns is 500 S / cm to 2000 S / cm, a photomask.

5. The photomask according to claim 4, wherein the electrical conductivity of the patterns is 1200 S / cm to 1600 S / cm.

6. The photomask according to claim 4, wherein the discharge voltage of the patterns is 400 V to 550 V.

7. The photomask according to claim 4, wherein the discharge current of the patterns is 0.5 mA to 2 mA.

8. The photomask according to claim 4, wherein the oxygen content of the first layer is different from the oxygen content of the second layer.

9. The photomask according to claim 4, wherein the electrical conductivity of the first layer is different from the electrical conductivity of the second layer.

10. The photomask according to claim 4, wherein the thickness of the first layer is greater than the thickness of the second layer.

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