Photomask and manufacturing method thereof

Abstract

To provide a production method of a photomask capable of improving patterning accuracy.SOLUTION: A production method of a photomask 100 includes the steps of: a step of forming a phase shift film 2, an etching stopper film 3 and an upper layer film 4 on a transparent substrate 1; a step of forming a resist pattern 5a; a first etching step of selectively etching the upper layer film 4 with a mask of the resist pattern 5a; a second etching step of selectively etching the etching stopper film 3; a third etching step of selectively etching the phase shift film 2 and the upper layer film 4; and a fourth etching step of selectively etching the etching stopper film 3. The phase shift film 2 and the upper layer film 4 are composed of a same kind of a substance, and the etching stopper film 3 is composed of a substance different from that of the phase shift film 2. In the third etching step, the phase shift film 2 is etched, and the upper layer film 4 is side-etched to form a rim part 6 in a self-alignment manner and a width of the rim part is determined.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] For flat panel displays such as liquid crystal panels, there is a demand for finer patterns to improve image quality, etc. To meet such demands, a method is known in which a phase shift region (sometimes referred to as a rim portion) that inverts the phase of the exposure light (shifts the phase by approximately 180°) is formed around the periphery of a light-shielding pattern, thereby improving the intensity distribution of the exposure light on the exposure object and increasing patterning accuracy. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-13283 Summary of the Invention [Problem to be solved by the invention]

[0004] As disclosed in Patent Document 1, in order to form a phase shift region around a light-shielding region, it is necessary to pattern a light-shielding film, then form a phase shift film, and pattern the phase shift film. When patterning a phase shift film, if there is an alignment error with respect to the pattern of the light-shielding film, the width of the phase shift region will vary, which will make it difficult to achieve the effect of improving the patterning accuracy using a photomask on the object to be exposed.

[0005] In view of the above problems, an object of the present invention is to provide a photomask in which a rim portion is formed in a self-aligned manner, thereby enabling improvement in pattern precision, and a method for manufacturing the same. [Means for solving the problem]

[0006] The method for manufacturing a photomask according to the present invention includes the steps of: forming a phase shift film on a transparent substrate; forming an etching stopper film on the phase shift film; forming an upper layer film on the etching stopper film; forming a resist pattern on the upper layer film; a first etching step of selectively etching the upper layer film using the resist pattern as a mask; a second etching step of selectively etching the etching stopper film; a third etching step of selectively etching the phase shift film and the upper layer film; a fourth etching step of selectively etching the etching stopper film, the phase shift film and the upper layer film are made of the same kind of material, and the etching stopper film is made of a material different from that of the phase shift film, In the third etching step, the phase shift film is etched and the upper layer film is side-etched to form a rim portion in a self-aligned manner, and the width of the rim portion is determined.

[0007] In addition, in the above configuration, The laminate of the phase shift film, the etching stopper film, and the upper film may form a light-shielding region.

[0008] Such a photomask manufacturing method enables the rim portion to be formed in a self-aligned manner, which contributes to improving patterning accuracy.

[0009] In addition, in the above configuration, In the third etching step, the width of the rim portion may be determined by the difference in etching rate between the phase shift film and the upper layer film.

[0010] By using such a method for manufacturing a photomask, the width of the rim portion can be controlled, and a rim portion with a fine width can be formed.

[0011] In addition, in the above configuration, The upper layer film may be configured to be a semi-permeable film.

[0012] By using this method of manufacturing a photomask, it is possible to obtain an optimum control range and high control accuracy for the width of the rim portion when forming the rim portion by utilizing the difference in etching speed. Furthermore, it is possible to simultaneously suppress the reflectance of the light-shielding region and suppress the influence of multiple scattering caused by the exposure tool.

[0013] In addition, in the above configuration, In the third etching step, the phase shift film is just etched. It may be configured as follows.

[0014] By using such a method for manufacturing a photomask, the rim portion can be easily formed.

[0015] In addition, in the above configuration, The transmittance of the upper layer film may be determined based on data relating to the correlation between the transmittance of the upper layer film and the width of the rim portion.

[0016] Such a method for manufacturing a photomask can contribute to facilitating the manufacture of photomasks.

[0017] The photomask according to the present invention comprises: It has a light-shielding pattern and a rim portion, the rim portion is provided with a uniform width around the entire periphery of the light-shielding pattern, the light-shielding pattern is composed of a phase shift film, an etching stopper film, and a semi-transparent film; the rim portion is made of the phase shift film, the phase shift film and the semi-transparent film are made of the same kind of material, The etching stopper film is made of a material different from that of the phase shift film and the semi-transparent film.

[0018] A photomask having such a configuration can contribute to improving patterning accuracy. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a photomask in which a rim portion is formed in a self-aligned manner, enabling improved pattern precision, and a method for manufacturing the same. [Brief explanation of the drawings]

[0020] [Figure 1] 1A to 1C are cross-sectional views of a photomask 100 illustrating the main steps of manufacturing the photomask. [Figure 2] 2A to 2C are cross-sectional views of the photomask 100 illustrating the main steps of manufacturing the photomask. [Figure 3] 3A to 3C are cross-sectional views of the photomask 100 illustrating the main steps of manufacturing the photomask. [Figure 4] Figure 4(A) is a cross-sectional view schematically showing the dimensional relationship between the semi-transparent film pattern 4b and the phase shift film pattern 2a, and Figure 4(B) is a plan view schematically showing the dimensional relationship between the semi-transparent film pattern 4b and the rim portion 6. [Figure 5] FIG. 5(A) shows a comparison of the reflectance of the etching stopper film 3, the semi-transparent film 4, and the laminated layer of the anti-reflection film and the light-shielding film for the g-line, and FIG. 5(B) shows a comparison of the reflectance of the etching stopper film 3, the semi-transparent film 4, and the laminated layer of the anti-reflection film and the light-shielding film for the i-line. [Figure 6] FIG. 6 shows the etching rates of the semi-transparent film 4 and the phase shift film 2. [Figure 7] Figure 7(A) shows the etching time dependence of the width (side etching amount) of the rim portion 6 of the semi-transparent film 4, and Figure 7(B) shows the transmittance dependence of the width (side etching amount) of the rim portion 6 of the semi-transparent film 4. [Figure 8]Figure 8(A) shows the relationship between the film thickness of the photoresist film exposed using the photomask 100 and the optical density (OD) of the laminated structure of the phase shift film 2, the etching stopper film 3 and the semi-transparent film 4, and Figure 8(B) shows the relationship between the DOF (depth of focus) at which the photoresist film is exposed and the optical density (OD) of the laminated structure of the phase shift film 2, the etching stopper film 3 and the semi-transparent film 4. [Figure 9] FIG. 9A shows the relationship between the transmittance and film thickness of the semi-transparent film 4, and FIGS. 9B and 9C are cross-sectional views illustrating the transmittance dependency of the side etching amount of the semi-transparent film 4. DETAILED DESCRIPTION OF THE INVENTION

[0021] 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.

[0022] Furthermore, terms used in this specification that specify shapes, geometric conditions, and their degrees, such as "parallel," "orthogonal," and "identical," as well as values ​​of lengths and angles, are not to be construed as being bound by strict meanings, but rather as including a range within which similar functions can be expected.

[0023] (Embodiment 1) A method for manufacturing the photomask 100 will now be described with reference to the drawings. 1, 2 and 3 are cross-sectional views of a photomask 100 showing the main steps of manufacturing the photomask.

[0024] First, as shown in FIG. 1(A), a phase shift film 2 is formed on a transparent substrate 1 such as quartz by a film formation method such as PVD or CVD, and then an etching stopper film 3 is formed on the phase shift film 2. The phase shift film 2 can be made of, for example, a Cr film, a Cr compound (oxide, nitride, oxynitride, etc.), a Si compound (oxide, nitride, oxynitride, etc.), or a metal silicide (Mo silicide, etc.).

[0025] The thickness of the phase shift film 2 can invert the phase of the exposure light (e.g., i-line, h-line, g-line, or any mixture of these) used in the lithography process using the photomask 100, and can be set to a thickness that achieves the desired phase shift amount (e.g., 180°±60°). Here, inversion indicates that the phase difference with respect to the i-line, h-line, g-line, or any mixed light selected from these is approximately 180°, and although approximately 180° is preferably within the range of 180°±20°, it is not limited to this range and naturally also includes the desired phase shift amount. The thickness of the phase shift film 2 can be set to, for example, 70 nm to 170 nm, typically 120 nm. The etching stopper film 3 is made of a substance (material) with etching characteristics different from those of the phase shift film 2. For example, a Cr-based film can be selected as the phase shift film 2, and a Ni-based film can be selected as the etching stopper film. The thickness of the etching stopper film 3 can be set to, for example, 1 nm to 70 nm. In particular, a Ni film can be etched using a mixture of sulfuric acid and hydrogen peroxide, and is easier to handle than hydrofluoric acid, which is used to etch Si-based films. The thickness of the etching stopper film 3 is smaller than the thickness of the phase shift film 2 (thickness of the etching stopper film 3<thickness of the phase shift film 2).

[0026] 1(B), a semi-transparent film 4 is formed on the etching stopper film 3 by a film formation method such as PVD or CVD. The semi-transparent film 4 is made of the same type of substance (material) as the phase shift film 2. Therefore, the semi-transparent film 4 and the phase shift film 2 are made of films having the same etching characteristics. The transmittance of the semi-transparent film 4 itself can be, for example, 5% to 60%, preferably 5% to 30%, with respect to the exposure light, and further, the film thickness is set to ensure light blocking properties (for example, an optical density in the range of 2 to 3) in the laminated structure of the phase shift film 2, etching stopper film 3 and semi-transparent film 4. For example, semi-transparent film 4 may be a Cr film of 10 nm to 50 nm, phase shift film 2 may be a Cr film of 70 nm to 170 nm, and etching stopper film 3 may be a Ni film of 1 nm to 70 nm. A substrate in which a phase shift film 2, an etching stopper film 3, and a semi-transparent film 4 are laminated in this order on a transparent substrate 1 can be prepared as a photomask blank 200.

[0027] FIG. 5(A) shows a comparison of the reflectance of an etching stopper film 3, a semi-transparent film 4, and a light-shielding film having an anti-reflection film on top (hereinafter referred to as a stack of an anti-reflection film and a light-shielding film) for g-line, and FIG. 5(B) shows a comparison of the reflectance of an etching stopper film 3, a semi-transparent film 4, and a stack of an anti-reflection film and a light-shielding film for i-line. α indicates the reflectance of the etching stopper film 3, β indicates the reflectance of the semi-transparent film 4, and γ indicates the thickness of the anti-reflection film and the light-shielding film. The etching stopper film 3 is a Ni film of 30±10 nm, the semi-transparent film 4 is a Cr film of 30±10 nm, and the laminate of the anti-reflection film and the light-shielding film is 30±20 nm. The laminate of the anti-reflection film and the light-shielding film is shown for comparison of reflectance. The light-shielding film with the anti-reflection film is made of known materials, for example, the anti-reflection film is a chromium oxide film with a thickness of about 15 nm, and the light-shielding film is a chromium film with a thickness of about 80 nm.

[0028] As shown in FIG. 5, the etching stopper film 3 has a high reflectance, but the semi-transparent film 4 has a low reflectance. By forming the semi-transparent film 4 on the etching stopper film 3, the reflectance can be significantly reduced. Conventionally, light-shielding films have been used in the light-shielding area, but the reflectance of light-shielding films is high. Therefore, in order to reduce the reflectance, it is necessary to use a laminate of an anti-reflection film and a light-shielding film, as shown in Figure 5. The anti-reflection film with this laminated structure usually needs to be made of a material with a high extinction coefficient. When patterning a laminated structure that employs a light-shielding film and an anti-reflection film made of different materials, the etching characteristics of each film are different, which requires different etching processes for each film, increasing the number of manufacturing steps.

[0029] However, as in the present invention, by using a semi-transmitting film 4 as the top film formed in the light-shielding region, instead of a laminate of an anti-reflection film and a light-shielding film, it is possible to effectively reduce the reflectance. Furthermore, by constructing the topmost semi-transparent film 4 and the bottommost phase shift film 2 from the same type of substance (material), and using a material with a large extinction coefficient, such as a chromium-based material, it is possible to prevent an increase in manufacturing steps during patterning. In this specification, a homogeneous substance refers to a substance that can be etched with the same etchant and has approximately the same etching characteristics, such as etching rate, and can be said to be a homogeneous substance if it contains at least the same element or each of the components that make up the substance is the same element.

[0030] The etching stopper film 3 has a high reflectance (for example, 30% or more) for g-line and i-line exposure light, but the semi-transparent film 4 has a low reflectance (for example, 10% to 15%). As described above, the surface reflectance can be reduced by forming the semi-transparent film 4 as an upper layer on the surface of the etching stopper film 3. In this way, when the semi-transparent film 4 is formed on the etching stopper film 3 having high reflectance, the influence of multiple scattering between the photomask 100 and the lens of the exposure machine can be suppressed when performing exposure processing using the photomask 100. Furthermore, since light-shielding films generally have high surface reflectance, by forming a semi-transparent film 4 instead of a light-shielding film on the top layer, the surface reflectance can be suppressed, while the laminated structure of the phase shift film 2, etching stopper film 3, and semi-transparent film 4 can ensure light-shielding properties. By preventing exposure of the etching stopper film 3 and covering the surface with a semi-transparent film having low reflectivity, the surface reflectivity of the photomask 100 is reduced, and reflection from the photomask 100 into the exposure device during the exposure process when manufacturing products using the photomask 100 is prevented, thereby contributing to improved patterning accuracy.

[0031] Next, as shown in FIG. 1(C), a photoresist film 5 is formed on the semi-transparent film 4 by a coating method or the like.

[0032] Next, as shown in FIG. 1(D), the photoresist film 5 is patterned by a lithography process to form a photoresist film pattern 5a (referred to as a resist pattern 5a).

[0033] Next, as shown in FIG. 2(A), the semi-transparent film 4 is etched using the resist pattern 5a as an etching mask to form a first semi-transparent film pattern 4a (first etching step). Since the semi-transparent film 4 and the etching stopper film 3 have different etching characteristics, the semi-transparent film 4 can be selectively etched relative to the etching stopper film 3. For example, the semi-transparent film 4 can be suitably selectively etched by wet etching. As an etching solution, a known chemical solution, for example, a ceric ammonium nitrate solution, can be used. In particular, wet etching can achieve a high etching selectivity ratio, and the etching selectivity ratio of the semi-transparent film 4 to the etching stopper film 3 can be several tens of times or more.

[0034] The etching time can be set to the time required for exposing the top surface of the etching stopper film 3 (just etching). Note that when setting the time for just etching, the etching time can be set taking into consideration the uniformity of the film thickness of the film to be etched. The setting of the etching time is similar to that for the just etching described below. In this first etching step, the phase shift film 2 provided below the etching stopper film 3 is not etched. Furthermore, as shown in FIG. 2(A), the sidewall surfaces of the resist pattern 5a and the first semi-transparent film pattern 4a are flush with each other (aligned in the vertical direction).

[0035] Next, as shown in FIG. 2(B), the etching stopper film 3 is etched using the resist pattern 5a and the first semi-transparent film pattern 4a as an etching mask to form a first etching stopper film pattern 3a (second etching step). Since the etching stopper film 3 and the semi-transparent film 4 have different etching characteristics, the etching stopper film 3 can be selectively etched with respect to the semi-transparent film 4. For example, the etching stopper film 3 can be suitably selectively etched by wet etching.

[0036] The etching time can be set to the time (just etching) until the outermost surface of the phase shift film 2 is exposed and the etching stopper film 3 is removed using the semi-transparent film 4 as a mask. As shown in Figure 2(B), the sidewall surfaces of the first etching stopper film pattern 3a and the first semi-transparent film pattern 4a become flush with each other (aligned vertically).

[0037] Next, as shown in FIG. 2(C), the phase shift film 2 is etched using the resist pattern 5a and the first etching stopper film pattern 3a as an etching mask to form a phase shift film pattern 2a (third etching step). Since the phase shift film 2 and the etching stopper film 3 have different etching characteristics, the phase shift film 2 can be selectively etched relative to the etching stopper film 3 .

[0038] The etching time can be set to the time required for just etching to expose the top surface of the transparent substrate 1. As shown in FIG. 2(C), the sidewall surfaces of the phase shift film pattern 2a and the first etching stopper film pattern 3a become flush with each other (aligned vertically). In the third etching step, since the phase shift film 2 and the semi-transparent film 4 are made of the same (homogeneous) material, the sidewall surface of the first semi-transparent film pattern 4a is etched (side-etched) in this etching step to form the second semi-transparent film pattern 4b, whose sidewall surface is recessed from the end face of the first etching stopper film pattern 3a. Furthermore, by just etching the phase shift film 2, the pattern shape of the phase shift film pattern 2a becomes the shape determined by the resist pattern 5a (or the same shape), making it unnecessary to size the resist pattern 5a in consideration of side etching of the phase shift film pattern 2a.

[0039] Next, as shown in FIG. 2(D), the resist pattern 5a is removed by a known method such as ashing.

[0040] Next, as shown in FIG. 3, the first etching stopper film pattern 3a is selectively etched using the second semi-transparent film pattern 4b as an etching mask to form a second etching stopper film pattern 3b (fourth etching step). This step exposes the surface of the phase shift film pattern 2a that is not covered with the second semi-transparent film pattern 4b.

[0041] As in the second etching step, the etching stopper film 3 has different etching characteristics from the semi-transparent film 4 and the phase shift film 2, so the etching stopper film 3 can be etched selectively with respect to the semi-transparent film 4 and the phase shift film 2. The etching time is set to a time until the outermost surface of the phase shift film 2 is exposed (just etching). As shown in FIG. 3, the sidewall surfaces of the second etching stopper film pattern 3b and the second semi-transparent film pattern 4b are flush with each other (aligned in the vertical direction).

[0042] In the third etching process, the sidewalls of the first semi-transmissive film pattern 4a are side-etched and recede. Therefore, as shown in FIG. 3, the width (L2) of the second semi-transmissive film pattern 4b is shorter than the width (L1) of the phase shift film pattern 2a (L2 < L1), and a region (rim portion 6) where the second semi-transmissive film pattern 4b does not exist is formed above the phase shift film pattern 2a. Accordingly, the rim portion 6 is self-aligned around the laminated region (three-layer region) of the phase shift film pattern 2a (lower layer film) having light-shielding properties, the second etching stopper film pattern 3b (intermediate film), and the second semi-transmissive film pattern 4b (upper layer film). This laminated region constitutes a light-shielding region (light-shielding pattern). Also, since the width of the rim portion 6 is determined by the side-etching amount of the first semi-transmissive film pattern 4a, it is determined by the third etching process.

[0043] The rim portion 6 is composed of the phase shift film 2 and has the phase shift amount of the phase shift film 2. On the photomask 100, a phase shift region formed by the rim portion 6 in contact with the light-shielding region is self-alignedly provided over the entire periphery of the light-shielding region. The phase shift region has the effect of improving the intensity distribution of the exposure light and improving the pattern accuracy of the exposure pattern by the light-shielding region at the periphery of the light-shielding region.

[0044] FIG. 4(A) is a cross-sectional view schematically showing the dimensional relationship between the second semi-transmissive film pattern 4b and the phase shift film pattern 2a, and FIG. 4(B) is a plan view schematically showing the dimensional relationship between the second semi-transmissive film pattern 4b and the rim portion 6. FIG. 4 illustrates the case where the resist pattern 5a is a line pattern, but is not limited thereto. For example, the same applies when forming a hole pattern. As shown in FIG. 4(B), for example, when the resist pattern 5a is a line pattern, if the line width of the phase shift film pattern 2a is L1 and the line width of the second semi-transmissive film pattern 4b is L2, the width W of the rim portion 6 is (L1 - L2) / 2, for example, W = 0.5 μm. 2(C), the width of the rim portion 6 can be controlled by controlling the amount of side etching of the semi-transparent film 4. The width of the rim portion 6 can be set to, for example, 0.1 μm to 2 μm, typically 0.2 to 0.8 μm. The rim portion 6 is formed by isotropically side-etching the first semi-transparent film pattern 4a, and is therefore formed with a uniform width W around the entire periphery of the light-shielding patterns of the phase shift film pattern 2a, the second etching stopper film pattern 3b, and the second semi-transparent film pattern 4b.

[0045] As described above, the etching process for the phase shift film 2 and the side etching process for the semi-transparent film 4 are performed in the same process. A method for achieving a desired amount of side etching of the semi-transparent film 4 in the third etching process set to the just-etching time for the phase shift film 2 will be described below.

[0046] FIG. 6 shows the etching rates of the semi-transparent film 4 and the phase shift film 2. In FIG. 6, the horizontal axis represents the etching time (seconds) and the vertical axis represents the amount of side etching. In the figure, ● and ▲ indicate data for the semi-transparent film 4 with transmittances of 10% and 30%, respectively. In the figure, ◆ indicates data for the phase shift film 2 (PS). Figure 7(A) shows the etching time dependence of the width (side etching amount) of the rim portion 6 of the semi-transparent film 4, and Figure 7(B) shows the transmittance dependence of the width (side etching amount) of the rim portion 6 of the semi-transparent film 4. In Figure 7(A), the horizontal axis is etching time (seconds) and the vertical axis is the width (μm) of the rim portion 6, and in the figure, ◆, ○, ▲, and □ represent data for semi-transparent films 4 with transmittances of 5%, 10%, 15%, and 30%, respectively. In Figure 7(B), the horizontal axis represents the transmittance (%) of the semi-transparent film 4, and the vertical axis represents the width (μm) of the rim portion 6. In the figure, ○, ◆, □, and ▲ represent data for etching times of 150 seconds, 170 seconds, 190 seconds, and 210 seconds, respectively. The data shown in FIG. 7 is an example and is not limited to this.

[0047] As shown in Figure 6, even with the same etching time, the amount of side etching differs between the semi-transparent film 4 and the phase shift film 2. This difference in the amount of side etching allows the formation of the rim portion 6. In other words, there is a difference in the etching rate between the semi-transparent film 4 and the phase shift film 2, and this difference in etching rate can be used to control and determine the width of the rim portion 6 (rim width). It is also apparent that the amount of side etching (etching rate) differs depending on the transmittance of the semi-transparent film 4. Therefore, the rim width can be controlled by controlling the etching time and transmittance.

[0048] For example, when the transmittance is 10%, the semi-transparent film 4 reaches the just-etched state in the first etching step. Furthermore, if the etching time in the third etching step is 178 seconds, the etching rate of the semi-transparent film 4 is 8.8 nm / s, and therefore the side etching amount of the semi-transparent film 4 is 1.57 μm. On the other hand, the phase shift film 2 reaches just etching in 147 seconds in the third etching step, and the etching rate is 5.3 nm / s, and therefore the side etching amount is 0.16 μm. Therefore, the difference between the pattern line width of the phase shift film 2 and the pattern line width of the semi-transparent film 4 is 1.41 μm (= 1.57 μm - 0.16 μm), and half of that corresponds to the rim width on one side. In this way, the rim portion 6 of the phase shift film 2 having a width of approximately 0.7 μm can be formed. The etching rate can be adjusted by the transmittance of the semi-transparent film 4, which allows for delicate control of the amount of side etching, and also makes it possible to form a rim portion 6 with a fine width.

[0049] 7(A), it can be seen that the width of the rim portion 6 increases linearly with the etching time. It can also be seen that the side etching rate (the rate at which the width of the rim portion 6 is formed) decreases as the transmittance of the semi-transparent film 4 to the exposure light increases. Furthermore, as shown in Figure 7(B), the inventors have found that as the transmittance of the semi-transparent film 4 increases, the width of the rim portion 6 decreases, and there is a correlation between the width of the rim portion 6 and the transmittance of the semi-transparent film 4. For example, in Figure 7(B), it is observed that the correlation between the width of the rim portion 6 and the transmittance of the semi-transparent film 4 is approximately linear. Therefore, the side etching rate can be controlled by the transmittance of the semi-transparent film 4. For example, if the etching rate of the phase shift film 2 is 5 nm / s and the side etching rate of the semi-transparent film 4 can be controlled within a range of, for example, 5 to 10 nm / s, then it is possible to control the width of the rim portion 6 by controlling the side etching rate of the semi-transparent film 4.

[0050] As described above, the side etching time of the semi-transparent film 4 that forms the rim portion 6 is determined by the just etching time of the phase shift film 2 (third etching step). The desired width (size) of the rim portion 6 can be controlled and managed by previously obtaining the correlation between the width of the rim portion 6 (amount of side etching of the semi-transparent film 4), the etching time, and the transmittance of the semi-transparent film 4, calculating the transmittance of the semi-transparent film 4 from this correlation, and determining the film formation conditions for the semi-transparent film 4. In this way, the desired width of the rim portion 6 can be achieved without adding a special etching process to adjust the width of the rim portion 6. As a result, this contributes to shortening the manufacturing time for the photomask 100 and enables precise patterning.

[0051] Figure 8(A) shows the relationship between the film thickness of the photoresist film exposed using the photomask 100 and the optical density (OD) of the laminated structure of the phase shift film 2, the etching stopper film 3 and the semi-transparent film 4, and Figure 8(B) shows the relationship between the DOF (depth of focus) at which the photoresist film is exposed and the optical density (OD) of the laminated structure of the phase shift film 2, the etching stopper film 3 and the semi-transparent film 4. Figure 8 shows the simulation results for an example of exposing a positive photoresist film, where NA=0.1, the phase shift amount of the rim portion 6 (phase shift film 2) is 180°, the transmittance is 5%, and the optical densities are 1.7, 2.0, 3.0, and infinity.

[0052] From FIG. 8(A), it can be seen that the thickness of the photoresist film is maximum when the optical density is 3, but the film thickness tends to decrease as the optical density decreases. On the other hand, the depth of focus tends to increase as the optical density decreases: the depth of focus at an optical density of 3.0 or less is greater than the depth of focus at an optical density of infinity. 8(A) and 8(B), in the exposure process using the photomask 100, by preferably setting the optical density in the range of 2 to 3, the loss of film thickness of the photoresist can be reduced, and a good shape of the exposed photoresist can be stably obtained, thereby improving the exposure performance (patterning performance). In the laminated structure of the phase shift film 2, etching stopper film 3, and semi-transparent film 4, by using the semi-transparent film 4 as the top film, the optical density can be controlled within an optimal range. If a light-shielding film is used as the top film, the optical density becomes large, and it is difficult to control the optical density to such an optimum value (2 to 3).

[0053] FIG. 9(A) shows the relationship between the transmittance and film thickness of the semi-transparent film 4, and FIGS. 9(B) and 9(C) are cross-sectional views illustrating the transmittance dependency of the side etching amount of the semi-transparent film 4. 9(B) and 9(C) respectively show the etching effect when the semi-transparent film 4 is thick and thin. The arrows in Fig. 9(B) and (C) symbolically indicate the supply of etchant.

[0054] As shown in FIG. 9(A), the transmittance tends to decrease as the film thickness increases, and the change in the amount of side etching is thought to be due to a geometric change caused by the film thickness. In the third etching step, for example, if wet etching is employed, the photomask 100 in the manufacturing process is immersed in a chemical bath containing an etching solution (etchant). As shown by the arrows in Figures 9(B) and (C), the etching solution is supplied to the exposed sidewall surface of the semi-transparent film 4. Compared to the case of Figure 9(C), in the case of Figure 9(B), the semi-transparent film 4 is thicker, so the area subjected to the etching action is larger, and the amount of etchant supplied to the surface increases, the reaction rate increases, and the etching rate increases. As shown in FIG. 9(A), the slope of the graph tends to decrease as the transmittance increases, and it can be seen that the relationship between the transmittance and the film thickness is nonlinear.

[0055] By previously obtaining the correlation between the transmittance and film thickness of the semi-transparent film 4 shown in FIG. 9(A) through experiments, it is possible to form a semi-transparent film 4 that achieves a desired transmittance. For example, the film thickness can be easily controlled by the film formation time, etc. Because the phase shift film 2 and the semi-transparent film 4 are made of the same type of material, they can be formed using the same equipment. Furthermore, by controlling the film thickness of the semi-transparent film 4 by changing the film formation time, the side etching characteristics can be controlled, which simplifies production management of the photomask 100.

[0056] On the other hand, transmittance can be directly measured using an optical instrument. Since it is easier to measure than film thickness, using transmittance has the advantage of making it easier to manage the production of the semi-transparent film 4. Furthermore, as described above, the transmittance of the semi-transparent film 4 required to achieve the required width of the rim portion 6 can be easily calculated (by simple arithmetic operations, etc.) based on the correlation shown in Figure 7. 7, the width of the rim portion 6 can be efficiently controlled by utilizing the correlation between the etching time and the transmittance and the width of the rim portion 6 in the production management of the photomask 100. This correlation can be stored as data in a storage device such as a control device or production management device used in the production process management, etc.

[0057] It should be noted that this does not exclude the use of film thickness instead of the transmittance of the semi-transparent film 4 as data relating to the correlation with the width of the rim portion 6. When film thickness is normally used for management in the photomask manufacturing process, the correlation between the width of the rim portion 6 (amount of side etching of the semi-transparent film 4), the etching time, and the film thickness of the semi-transparent film 4 may be stored as data in a storage device such as a control device or production management device.

[0058] Note that if the transmittance of the semi-transparent film 4 is changed to achieve the desired width of the rim portion 6, the optical density of the laminated structure of the phase shift film 2, etching stopper film 3, and semi-transparent film 4 will change. However, the optical characteristic (transmittance) of the etching stopper film 3 is set so that the optical density of the laminated structure of the phase shift film 2, etching stopper film 3, and semi-transparent film 4 can achieve a required value (e.g., 3 or more) within the transmittance range of the semi-transparent film 4 being used. For example, for the semi-transparent film 4 with the highest transmittance, the thickness of the etching stopper film 3 is adjusted so that the optical density of the laminated structure of the phase shift film 2, etching stopper film 3, and semi-transparent film 4 is, for example, 3 or more. The etching stopper film 3 does not exist on the phase shift film pattern 2a (rim portion 6), and therefore does not affect the characteristics of the phase shift film pattern 2a.

[0059] (Embodiment 2) The manufacturing process, including the determination of the film configuration specifications of the photomask 100, will be described below.

[0060] First, the width of the rim portion 6 required for patterning the electronic circuit based on the product specifications is determined. The width of the rim portion 6 can be determined from information obtained by simulation of the lithography process, experiments, or the like.

[0061] Next, the film formation conditions (transmittance or film thickness) of the semi-transparent film 4 are determined to achieve the width of the rim portion 6. The specifications of the semi-transparent film 4 (semi-transmittance or film thickness) are determined from the correlation between the transmittance of the semi-transparent film 4 and the width of the rim portion 6, or the correlation between the film thickness of the semi-transmittance 4 and the width of the rim portion 6, which have been obtained in advance.

[0062] Next, in the step shown in FIG. 1(B), a semi-transparent film 4 having the above-determined specifications is formed on the etching stopper film 3.

[0063] Thereafter, the photomask 100 is manufactured through the steps shown in FIGS. 1(C) to 3.

[0064] Therefore, a plurality of photomask blanks each having a laminate of a transparent substrate 1, a phase shift film 2 and an etching stopper film 3 obtained by the process shown in FIG. 1(A) may be prepared in advance. As a result, the manufacturing period of the photomask 100 can be shortened, and the photomask 100 suited to the product specifications can be manufactured. [Industrial Applicability]

[0065] According to the present invention, a photomask that enables precise patterning can be obtained, and can also contribute to shortening delivery times, and thus has great industrial applicability. [Explanation of symbols]

[0066] 1 Transparent substrate 2 Phase shift film 2a Phase shift film pattern 3 Etching stopper film 3a First etching stopper film pattern 3b Second etching stopper film pattern 4 Semi-transparent membrane (upper layer membrane) 4a First semi-transparent film pattern 4b Second semi-transparent film pattern 5 Photoresist film 5a Photoresist film pattern (resist pattern) 6 Rim 100 Photomasks 200 Photomask blanks L1 Width of the phase shift film pattern L2 Width of semi-transparent film pattern W Rim width

Claims

1. forming a phase shift film on a transparent substrate; forming an etching stopper film on the phase shift film; forming a semi-transparent film on the etching stopper film; forming a resist pattern on the semi-transparent film; a first etching step of selectively etching the semi-transparent film using the resist pattern as a mask; a second etching step of selectively etching the etching stopper film; a third etching step of selectively etching the phase shift film and the semi-transparent film; a fourth etching step of selectively etching the etching stopper film, each component of the phase shift film and the semi-transparent film is made of the same element, and the etching stopper film is made of a material different from that of the phase shift film; the semi-transparent film has a transmittance of 5 to 30% with respect to the exposure wavelength; A method for manufacturing a photomask, characterized in that in the third etching step, the rim portion is formed in a self-aligned manner by etching the phase shift film and the semi-transparent film based on data regarding the correlation between the transmittance of the semi-transparent film, etching time, and the width of the rim portion, which data is obtained in advance using the correlation between the thickness and transmittance of the semi-transparent film obtained by changing the film formation time of the semi-transparent film.

2. 2. The method for manufacturing a photomask according to claim 1, wherein a laminate of said phase shift film, said etching stopper film and said semi-transparent film forms a light-shielding region.

3. The optical density of the light-shielding area is in the range of 2 to 3.

3. The method for manufacturing a photomask according to claim 2.

4. The transmittance of the semi-transparent film is controlled by the film thickness.

2. The method for manufacturing a photomask according to claim 1.

5. The semi-permeable film is made of a chromium-based material, the reflectance of the semi-transparent film is lower than the reflectance of the etching stopper film, The reflectance of the semi-transparent film is 10% to 15% with respect to the exposure wavelength, and the reflectance of the etching stopper film is 30% or more with respect to the exposure wavelength.

2. The method for manufacturing a photomask according to claim 1.

Images