JP2015219290A5 - - Google Patents

Description

Photomask manufacturing method and photomask substrate

  The present invention relates to a photomask manufacturing method in which a transfer pattern is formed by patterning an optical film formed on a transparent substrate, and a photomask substrate used in the manufacturing method. The present invention particularly relates to a photomask manufacturing method advantageously used for manufacturing a display device and a photomask substrate used therefor. The present invention also relates to a method for manufacturing a display device using a photomask manufactured by the method for manufacturing a photomask.

  As electronic device products such as display devices become more precise, there is an increasing demand for stricter dimensional control of transfer patterns provided in photomasks used in the manufacture of such devices.

  In relation to this, Patent Document 1 describes a method of performing dimensional control more accurately for the pattern of the light shielding film. That is, the light shielding film is etched using the resist pattern as a mask. After the light shielding film not covered with the resist pattern is removed and the etching is stopped, light is irradiated from the back surface of the substrate to expose the resist not shielded by the light shielding film. In addition, a method is described in which the edge position of the light shielding film is grasped by developing and the additional etching time is determined.

JP 2010-169750 A

  At present, image quality (sharpness, brightness), operation speed, and power saving required for display devices (for example, mobile terminals such as smartphones and tablets) are increasing more than ever. In order to meet these needs, there is a strong demand for miniaturization and higher density of a transfer pattern for a photomask used for manufacturing a display device.

  In manufacturing a display device, a photomask having a desired transfer pattern is manufactured using a photolithography process. That is, a resist film is formed on an optical film formed on a transparent substrate, drawn on the resist film with energy rays (laser light, etc.) and developed, and the resist pattern obtained as a mask is used as an optical film. Etch. If necessary, another optical film is formed, and the photolithography process is repeated to form a final transfer pattern. The optical film here includes, for example, a light-shielding film that shields exposure light to the photomask, a semi-transparent film that partially transmits, or a functional film such as a phase shift film and an etching stopper film.

  The display device manufacturing photomask is larger in size (for example, 300 mm or more on one side) than the semiconductor manufacturing photomask (generally 5 to 6 inches), and various sizes exist. Therefore, in the etching of the optical film when manufacturing a photomask for manufacturing a display device, when wet etching is applied rather than dry etching that requires a vacuum chamber, the burden on the etching device and the etching process is small. There is an advantage that it is easy to control.

  However, it is not always easy to precisely control the dimensional accuracy of the finally obtained transfer pattern through these steps. For example, regarding an allowable range for the target dimension, if there is an allowable range of about ± 100 nm with respect to the target value, even if it can be achieved without great difficulty by strict management of each process such as drawing, development, etching, etc. In order to set the target value within an allowable range of about ± 50 nm, and further within the allowable range of about ± 20 nm with respect to the target value, a new technical problem arises.

  For example, a process of manufacturing a binary mask having a transfer pattern having a light transmitting part and a light shielding part will be described with reference to a flow shown in FIG.

  First, as shown in FIG. 1A, an optical film is formed on a transparent substrate by a film forming means such as a sputtering method, and a photoresist film is applied on the surface thereof. Prepare a photomask substrate. Here, the optical film is a light shielding film containing chromium as a main component.

  Next, as shown in FIG. 1B, a predetermined pattern is drawn using a laser drawing apparatus. Here, laser light having a wavelength of 413 nm emitted from a light source mounted on an FPD (Flat Panel Display) drawing machine is used as drawing light.

  Next, as shown in FIG. 1C, the resist film after drawing is developed to form a resist pattern.

Next, as shown in FIG. 1D, the optical film is wet-etched using the formed resist pattern as a mask to form an optical film pattern . Although the optical film in a portion where the light-transmitting portion is set the etching time to be fully etched away, whereby the nature of the wet etching, side etching progresses. Therefore, as shown in FIG. 1D, the edge of the optical film after etching (cross-section to be etched) is hidden under the resist pattern. For this reason, in the drawing data when drawing is performed in the step shown in FIG. 1B, it is necessary to preliminarily incorporate the dimension change due to the side etching (sizing).

  Next, as shown in FIG. 1E, the resist pattern is removed, and a binary mask including an optical film pattern and having a transfer pattern is completed.

  In order to finally obtain an optical film pattern that matches the target dimension, it is necessary to precisely determine the etching time. For this reason, in order to reach a desired pattern dimension, it is necessary to quantitatively grasp the etching rate (etching amount per unit time) of a predetermined optical film. However, even if the etching rate can be grasped, it is not always easy to accurately determine the etching end point.

  An example of a resist pattern serving as an etching mask is shown in FIG. FIG. 2 shows a resist pattern cross-sectional SEM photograph formed by drawing and developing a pattern on a resist film formed on an optical film (here, a light-shielding film). This corresponds to the shape of the resist pattern at the time of FIG.

  As shown in FIG. 2, the formed resist pattern has a thickness of about 300 to 1000 nm and is considerably thicker than the optical film. In addition, the side surface is not perpendicular to the substrate, has a slight inclination, and skirting is also seen at the edge of the contact portion with the optical film. Such a three-dimensional shape of the resist pattern is affected by various condition fluctuations at the time of drawing and development, and does not necessarily have complete reproducibility. Therefore, after performing etching for a preset time using the resist pattern as a mask, the dimension of the optical film pattern does not always reach the target dimension.

  Therefore, it is conceivable to measure the dimension of the resist pattern first before starting the etching and determine the etching time for the optical film based on this. In measurement, it is theoretically possible to determine the edge position of the resist by irradiating the inspection light and detecting the reflected light or transmitted light. However, as described above, it is difficult to measure the optical dimension of the resist pattern due to the thickness of the resist pattern, the slanted cross-sectional shape, etc., and the detected inspection light indicates the position on the optical film. This is unclear and the reliability of measurement accuracy is not sufficient.

  Next, wet etching of the optical film is performed using this resist pattern as a mask, and the dimension of the optical film pattern at the time when the etching has progressed to the middle is grasped. From the dimensions and the etching rate of the optical film, addition to the optical film is performed. Consider an etching time and additional etching of the optical film.

  In general, dry etching has an anisotropic etching property, whereas wet etching has an isotropic etching property. Therefore, as described above, as the optical film to be etched is etched in the thickness direction, the etching also proceeds from the side surface. For this reason, when the end of etching approaches, the dimension of the optical film pattern does not match the dimension of the resist pattern serving as an etching mask, and becomes smaller. That is, the edge of the optical film pattern enters the resist pattern side from the edge of the resist pattern and is hidden under the resist pattern. FIG. 3 shows an SEM photograph of the cross-sectional shape of the optical film pattern (pattern of the light shielding film shown in FIG. 3) after wet etching using the resist pattern as an etching mask. This SEM photograph corresponds to the cross-sectional shape of FIG.

  At this time, when the dimensions of the optical film pattern as shown in FIG. 3 are to be measured, the surface side of the substrate (of the main surface of the substrate, the side on which the pattern is formed is referred to as the surface or the first main surface. Therefore, even if it is intended to detect the reflected light or transmitted light by irradiating the inspection light, the resist pattern is obstructed and the reading accuracy of the dimension of the optical film pattern cannot be obtained. Therefore, when the inspection light is irradiated from the rear surface side (the main surface of the substrate opposite to the front surface side of the substrate) and the transmitted light is detected on the front surface side, the resist pattern also becomes an obstacle. Further, when the inspection light is irradiated from the back side and the dimension of the optical film pattern is measured by detecting the reflected light, the transparent substrate becomes an obstacle.

  Incidentally, in Patent Document 1, in the state shown in FIG. 3, exposure is performed from the back side of the substrate, and the resist exposed from the end of the optical film when viewed from the back side is exposed and eluted by development. In addition, a method is described in which line width measurement is performed after matching the edge position of the resist pattern and the optical film.

  In this case, since the optical film pattern shape that is the same shape as the resist pattern shape is theoretically formed, the dimension is measured from the resist pattern side, and the additional etching time can be calculated based on the dimension measurement result. In this case, an optical film pattern having a target dimension can be obtained.

  However, even with this method, it is not easy to satisfy the extremely strict dimensional accuracy required for recent display devices. Because, in the dimension measurement of the optical film pattern by the method of Patent Document 1, the dimension of the optical film is not directly measured, but the dimension of the optical film is indirectly obtained from the resist pattern dimension. The measurement accuracy is not sufficient. Note that when the measurement of the dimension of the optical film pattern is to be reflected from the lower side (the back side of the substrate), the thickness of the transparent substrate also hinders the measurement.

  The shape of the resist pattern is affected by the development temperature of the resist and the developer concentration, and it is not easy to keep them constant. Considering the above situation, in order to perform patterning with high dimensional accuracy, it is not easily affected by the above fluctuation factors, and it is suitable for the exact etching time until the etching end point (that is, the etching amount required for the optical film) It is useful to obtain a method for grasping the etching time.

  As mentioned above, display devices typified by liquid crystal and organic EL tend to increase those having a finer structure than before. This tendency is common to each part of the display device such as a thin film transistor (TFT) substrate and a color filter (photo spacer, color plate). However, in these display devices, the fineness of the image, the speed of operation, It is related to needs such as brightness and power saving.

  As a result, the demand for accuracy of CD (Critical Dimension: hereinafter referred to as pattern line width) of a transfer pattern of a photomask for manufacturing a display device has become strict. This is the same whether it is a line and space pattern, a hole pattern, or a TFT substrate channel structure. For example, the CD accuracy of the transfer pattern is required to be a target value ± 50 nm or less, and further to a target value ± 20 nm or less depending on specifications.

  In order to satisfy these requirements, it is required that in-plane CD variation in the formation of the transfer pattern is suppressed and that the absolute value is finished to the limit as designed. In other words, the center value of the CD of the formed transfer pattern needs to match the target value with high accuracy. Therefore, an object of the present invention is to obtain a photomask manufacturing method capable of forming a transfer pattern with high dimensional accuracy.

  In order to solve the above-described problem, in the isotropic etching, the CD center value of the dimension of the optical film to be patterned reaches the target value, and at the same time, the etching is stopped. Therefore, it is important to accurately detect the timing for stopping etching (end point detection).

  In order to solve the above problems, the present invention has the following configuration. The present invention provides a photomask manufacturing method characterized by the following configurations 1 to 5 and 8 to 11, a photomask substrate characterized by the following configurations 6, 7, 12, and 13, A manufacturing method of a display device characterized by being configured 14.

(Configuration 1)
In the first aspect of the present invention, an optical film for forming a transfer pattern and a reflective thin film having etching selectivity with respect to the optical film are laminated on a transparent substrate, and a resist film is further formed on the outermost surface. A step of preparing a formed photomask substrate with resist, a resist pattern forming step of forming a resist pattern by drawing and developing a predetermined pattern on the resist film using a drawing apparatus, and the resist Etching the reflective thin film using a pattern as a mask to form a reflective thin film pattern, a thin film etching step, a step of removing the resist pattern, and a dimension measuring step of measuring a dimension of the reflective thin film pattern; The reflective thin film pattern is masked based on the etching time of the optical film determined based on the measured dimensions. An optical film etching step for performing wet etching of the optical film, and a step for removing the reflective thin film. In the dimension measuring step, an inspection light is applied to the measuring portion of the reflective thin film pattern. The photomask manufacturing method is characterized in that the dimension measurement is performed by irradiating and detecting reflected light of the inspection light.

(Configuration 2)
Configuration 2 of the present invention is the photomask manufacturing method according to Configuration 1, wherein the thickness of the reflective thin film is smaller than the thickness of the optical film.

(Configuration 3)
In the configuration 3 of the present invention, the surface reflectance Rt (%) of the reflective thin film with respect to the inspection light is higher than the surface reflectance Ro (%) of the optical film, and the difference (Rt−Ro) is 5 (%). 3) The photomask manufacturing method according to Configuration 1 or 2, wherein the method is as described above.

(Configuration 4)
The configuration 4 of the present invention is the photomask according to any one of the configurations 1 to 3, wherein the surface reflectance Rt of the reflective thin film with respect to the inspection light is 20 (%) or more. It is a manufacturing method.

(Configuration 5)
Configuration 5 of the present invention is the photomask manufacturing method according to any one of Configurations 1 to 4, wherein light having a wavelength in the range of 300 to 1000 nm is used as the inspection light.

(Configuration 6)
Configuration 6 of the present invention includes: a photomask substrate for forming a transfer mask for manufacturing a display device; an optical film for forming a transfer pattern on a transparent substrate; and the optical film A reflective thin film made of a material having etching selectivity is laminated, and the thickness of the reflective thin film is smaller than that of the optical film, and the surface reflectance Rt of the reflective thin film with respect to light having a wavelength of 500 nm. Is a photomask substrate characterized in that it is 20 (%) or higher and is higher than the surface reflectance Ro (%) of the optical film.

(Configuration 7)
In the configuration 7 of the present invention, the surface reflectance Rt (%) of the reflective thin film with respect to the light having the wavelength of 500 nm is higher than the surface reflectance Ro (%) of the optical film, and the difference (Rt−Ro). The photomask substrate according to Structure 6, wherein the ratio is 5 (%) or more.

(Configuration 8)
In the configuration 8 of the present invention, an optical film for forming a transfer pattern and a transparent thin film having etching selectivity with respect to the optical film are laminated on a transparent substrate, and a resist film is further formed on the outermost surface. A step of preparing a formed photomask substrate with resist, a resist pattern forming step of forming a resist pattern by drawing and developing a predetermined pattern on the resist film using a drawing apparatus, and the resist Using the pattern as a mask, the transmissive thin film is etched to form a transmissive thin film pattern, and the optical film is wet etched using at least the transmissive thin film pattern as a mask to form a preliminary optical film pattern An optical film preliminary etching step, a dimension measuring step for measuring the dimension of the optical film preliminary pattern, and a measurement An optical film additional etching step of additionally etching the optical film based on the additional etching time of the optical film determined based on the measured dimensions, and a step of removing the transparent thin film, In the dimension measuring step, the dimension measurement is performed by irradiating the measurement part of the optical film preliminary pattern with inspection light transmitted through the transparent thin film.

(Configuration 9)
The ninth aspect of the present invention is the photomask manufacturing method according to the eighth aspect, wherein the film thickness of the transmissive thin film is smaller than the film thickness of the optical film.

(Configuration 10)
According to a tenth aspect of the present invention, in the photomask manufacturing method according to the eighth or ninth aspect, the transmittance Tt of the transmissive thin film with respect to the inspection light is 50% or more.

(Configuration 11)
Configuration 11 of the present invention is characterized in that, at the end of the optical film preliminary etching step, an edge of the optical film is located inside the transmissive thin film pattern when viewed from the surface side of the photomask. It is the manufacturing method of the photomask in any one of the structures 8-10.

(Configuration 12)
Configuration 12 of the present invention includes a photomask substrate for forming a transfer mask for manufacturing a display device, an optical film for forming a transfer pattern on a transparent substrate, and the optical film. And a transparent thin film made of a material having etching selectivity. The film thickness of the transparent thin film is smaller than the film thickness of the optical film, and the light transmittance Tt of the transparent thin film with respect to a wavelength of 500 nm. Is a photomask substrate characterized by being 50% or more.

(Configuration 13)
Structure 13 of the present invention is the photomask substrate according to Structure 12, wherein the optical film has a light transmittance To of 50% or less with respect to light having a wavelength of 500 nm.

(Configuration 14)
According to the present invention, in the constitution 14 of the present invention, a photomask produced by the production method according to any one of the constitutions 1 to 5 and the constitutions 8 to 11 is prepared, and the photomask is exposed using an exposure apparatus. And a step of transferring the transfer pattern onto a transfer target.

  According to the photomask manufacturing method of the present invention, it is possible to control precise pattern dimension accuracy in photomask manufacturing.

It is a cross-sectional schematic diagram which shows an example of the manufacturing process (a) of a photomask. It is a cross-sectional schematic diagram which shows an example of the manufacturing process (b) of a photomask. It is a cross-sectional schematic diagram which shows an example of the manufacturing process (c) of a photomask. It is a cross-sectional schematic diagram which shows an example of the manufacturing process (d) of a photomask. It is a cross-sectional schematic diagram which shows an example of the manufacturing process (e) of a photomask. It is an example of the SEM photograph of the cross-sectional shape of a resist pattern corresponding to the process shown in FIG.1 (c). 2 is an example of an SEM photograph of a cross-sectional shape of an optical film pattern (light-shielding film pattern) after wet etching using a resist pattern as an etching mask, corresponding to the step shown in FIG. It is a cross-sectional schematic diagram which shows the manufacturing process (a) of the 1st aspect of this invention. It is a cross-sectional schematic diagram which shows the manufacturing process (b) of a 1st aspect. It is a cross-sectional schematic diagram which shows the manufacturing process (c) of a 1st aspect. It is a cross-sectional schematic diagram which shows the manufacturing process (d) of a 1st aspect. It is a cross-sectional schematic diagram which shows the manufacturing process (e) of a 1st aspect. It is a cross-sectional schematic diagram which shows the manufacturing process (f) of a 1st aspect. It is a cross-sectional schematic diagram which shows the manufacturing process (g) of a 1st aspect. It is a cross-sectional schematic diagram which shows the manufacturing process (h) of a 1st aspect. It is a cross-sectional schematic diagram which shows the manufacturing process (a) of the 2nd aspect of the manufacturing method of the photomask of this invention. It is a cross-sectional schematic diagram which shows the manufacturing process (b) of a 2nd aspect. It is a cross-sectional schematic diagram which shows the manufacturing process (c) of a 2nd aspect. It is a cross-sectional schematic diagram which shows the manufacturing process (d) of a 2nd aspect. It is a cross-sectional schematic diagram which shows the manufacturing process (e) of a 2nd aspect. It is a cross-sectional schematic diagram which shows the manufacturing process (f) of a 2nd aspect. It is a cross-sectional schematic diagram which shows the manufacturing process (g) of a 2nd aspect. It is a cross-sectional schematic diagram which shows the manufacturing process (h) of a 2nd aspect. It is a cross-sectional schematic diagram which shows the manufacturing process (i) of a 2nd aspect. It is explanatory drawing which shows the dimension measuring method of a reflective thin film pattern. It is explanatory drawing which shows the dimension measuring method of the optical film pattern in the dimension measuring process shown in FIG.5 (g). It is a figure which shows an example of the correlation with etching time and CD variation | change_quantity.

(First aspect)
The manufacturing method of the photomask of the 1st aspect of this invention is a manufacturing method of the photomask applied to forming a pattern with a predetermined method with respect to the optical film of the photomask substrate with a resist. Specifically, the photomask manufacturing method of the present invention includes a step of preparing a photomask substrate with a resist, a resist pattern forming step, a thin film etching step, a step of removing the resist pattern, a dimension measuring step, An optical film etching step and a step of removing the reflective thin film. In the step of preparing a photomask substrate with a resist, an optical film for forming a transfer pattern and a reflective thin film having etching selectivity with respect to the optical film are laminated on a transparent substrate, and the outermost surface A resist film is formed. In the resist pattern forming step, a resist pattern is formed by drawing and developing a predetermined pattern on the resist film using a drawing apparatus. In the thin film etching process, the reflective thin film is etched using the resist pattern as a mask to form a reflective thin film pattern. In the step of removing the resist pattern, the resist pattern is removed. In the dimension measuring step, the dimension of the reflective thin film pattern is measured. In this dimension measuring step, the dimension measurement is performed by irradiating the measuring portion of the reflective thin film pattern with inspection light and detecting the reflected light of the inspection light. In the optical film etching step, wet etching of the optical film is performed using the reflective thin film pattern as a mask based on the etching time of the optical film determined based on the measured dimensions.

  With reference to FIG. 4, the 1st aspect of the manufacturing method of the photomask of this invention is demonstrated concretely.

  As shown in FIG. 4A, a photomask substrate is prepared (step of preparing a photomask substrate with resist).

  The photomask substrate can be a photomask blank having the following configuration. As will be described later, the photomask substrate of the present invention is not necessarily a photomask blank, but in this embodiment, the photomask blank shown in FIG. 4A will be described below.

  In FIG. 4A, “Resist” refers to a resist, and “Qz” refers to a transparent substrate such as synthetic quartz. These terms are the same in other drawings.

  As a transparent substrate used for manufacturing a photomask substrate, a substrate made of synthetic quartz or the like is polished flat and smooth. The first main surface is a rectangle having a side of 300 mm to 1400 mm and a thickness of about 5 to 13 mm.

  On this substrate, an optical film is formed on the first main surface of the transparent substrate by a known film forming method such as sputtering.

  As the optical film, for example, a light shielding film (optical density OD with respect to exposure light when using a photomask is 3 or more) can be used. Further, the optical film may be a semi-transparent film that partially transmits exposure light. The exposure light transmittance of the semi-transparent film is exemplified by 3 to 60%.

  For example, it may be a phase shift film that has a transmittance of 3 to 30% for exposure light and shifts the phase of the representative wavelength contained in the exposure light by approximately 180 degrees. About 180 degrees means an angle in the range of 150 to 210 degrees.

  Furthermore, the optical film is a semi-transparent film that has a light transmittance of 3 to 60% with respect to the exposure light and shifts the phase of the representative wavelength contained in the exposure light within a range of 5 to 90 degrees. be able to. Such a semi-transparent film is used instead of the light shielding film or together with the light shielding film when forming a fine space pattern or hole pattern, to assist the amount of light transmitted through the photomask, and to form a resist on the transferred object. The light quantity auxiliary pattern used for the purpose of reaching the photosensitive threshold value can be obtained.

  The film thickness of the optical film is determined by its function, but can be 10 to 300 nm. When the thickness is about 100 to 150 nm, the effect of the present invention is remarkable. For example, when the optical film is a light shielding film, the film thickness can be suitably set.

  The optical film can be wet-etched. Examples of the material for the optical film include a film containing chromium (Cr). For example, it may be a film containing any of chromium oxide, nitride, carbide, oxynitride, and oxynitride carbide.

  Furthermore, an optical film made of a metal other than chromium, for example, Mo, Ta, W, Zr, Nb, Ti, or a compound thereof can also be applied. For example, a metal silicide or a material containing an oxide, nitride, carbide, oxynitride, or oxynitride carbide thereof can be used. Examples of the metal silicide include molybdenum silicide and tantalum silicide.

  The optical film preferably has a surface reflectance Ro of 15 (%) or less with respect to inspection light used for dimension measurement using reflected light, which will be described later. For example, when light having a wavelength of 500 nm is used as the inspection light, it is preferable that the surface reflectance Ro500 of the optical film with respect to this wavelength is 15 (%) or less. More preferably, it is 10 (%) or less, More preferably, it is 8% or less.

  The optical film preferably includes an antireflection layer for suppressing light reflectance on the surface thereof. In that case, for example, in an optical film containing chromium as a main component, the antireflection layer has a composition in which the surface layer of the chromium compound (oxide, nitride, carbide, etc.) changes in the thickness direction of the optical film. It is preferable to become. The composition change may be a step change or a continuous change. This antireflection layer has a function of suppressing reflection with respect to exposure light used when a photomask is used, but also has an action of suppressing surface reflection in dimension measurement described later.

  Further, the photomask substrate of the present invention is not limited to a photomask blank, and is a film other than the optical film of the present invention and the reflective thin film of the present invention on the transparent substrate, as long as the effects of the present invention are not hindered. It may be a photomask intermediate having a film pattern, and further comprising the optical film of the present invention and a reflective thin film. Examples of the film other than the reflective thin film or the pattern of the film include functional films (those that provide electrical properties such as conductivity and insulation, and those that have an etching stopper function). In the second embodiment, the transmittance measurement) is not affected.

  Next, a reflective thin film is formed on the optical film by a known film formation method such as sputtering. The reflective thin film is a thin film having a property of reflecting light having a wavelength emitted from the inspection device for dimension measurement in the dimension measurement process.

  As the material of the reflective thin film, a material having etching selectivity with respect to the optical film is used. Etching selectivity means having resistance to an etchant that etches the other film. Preferably, the etching rate of the other film with respect to the etching agent is 1/10 or less, preferably 1/50 or less, more preferably 1/100 or less of the etching rate of the other film with respect to the etching agent.

  The reflective thin film preferably has a surface reflectance Rt of 20 (%) or more with respect to inspection light used for dimension measurement described later. For example, when light having a wavelength of 500 nm is used as the inspection light, the reflectance Rt500 of the reflective thin film with respect to the inspection light is preferably 20 (%) or more, and more preferably 50 (%).

  Further, it is desirable that the reflective thin film has an excessive reflectance with respect to the drawing light in the drawing process. For this reason, it is preferable that the surface reflectance Rw with respect to the drawing light wavelength (for example, 413 nm) of the reflective thin film is 10 (%) or less.

The surface reflectance Rt with respect to the inspection light reflective thin film is preferably higher than the surface reflectivity Rw for drawing light reflective film. For example, the difference between the surface reflectance Rt500 for a wavelength of 500 nm and the surface reflectance Rw413 for a wavelength of 413 nm of the reflective thin film is preferably about 5 (%).

  Furthermore, the surface reflectance Rt (%) of the reflective thin film with respect to the inspection light of the reflective thin film is higher than the surface reflectance Ro (%) of the optical film, and the difference (Rt−Ro) is 5 (%) or more. Preferably there is. When a wavelength of 500 nm is used as the inspection light, the difference in reflectance (Rt500-Ro500) between the reflective thin film and the optical film with respect to the wavelength of 500 nm is 5 (%) or more, preferably 10 (% ) Or more, more preferably 20% or more.

  Examples of the material of the reflective thin film include a metal containing Mo, Ti, W, Ta, or Zr, or a compound thereof. Examples of the compound include oxides, nitrides, carbides, and oxynitrides. Alternatively, silicides of these metals, oxides, nitrides, carbides, oxynitrides, or oxynitride carbides thereof may be used. If the optical film is a material other than Cr, a material containing Cr may be used for the reflective thin film. However, among the above, a material not containing Si can be said to be a more preferable material because of its high adhesion to the resist film.

  The material of the reflective thin film is a material that can obtain etching selectivity with the optical film as described above.

  The thickness of the reflective thin film is preferably smaller than that of the optical film. The thickness of the reflective thin film is 5 to 100 nm, more preferably 5 to 20 nm.

  If the reflective thin film is too thick, the etching time becomes excessive, and the dimensional measurement accuracy described later tends to be insufficient. If the reflective thin film is too thin, the in-plane film thickness variation tends to increase. In order to prevent side etching of the reflective thin film from affecting the measurement described later, the thickness of the reflective thin film is preferably smaller than the thickness of the optical film. For example, the thickness of the optical film is 1/10 or less, more preferably 1/20 or less. When the thickness of the reflective thin film is reduced to this level, it is advantageous that the sizing amount can be reduced when the side etching amount of the reflective thin film is reflected in the drawing data in advance (sizing). When the sizing amount is large, there is a disadvantage that the minimum resolution dimension is approached (or reached) in the extraction pattern (hole pattern, space pattern, etc.). That is, the small thickness of the reflective thin film is particularly important when a fine punch pattern (for example, CD is 2 μm or less) is formed.

  As a photomask substrate that can be used in the photomask manufacturing method of the first aspect of the present invention, an optical film for forming a transfer pattern on a transparent substrate, and an etching selectivity with respect to the optical film are provided. What is laminated | stacked in this order with the reflective thin film which consists of a material which has can be used preferably. As described above, the thickness of the reflective thin film is smaller than that of the optical film, the surface reflectance Rt of the reflective thin film with respect to light having a wavelength of 500 nm is 20 (%) or more, and the surface reflection of the optical film. It is preferable that the rate is higher than Ro (%). Further, as described above, the surface reflectance Rt (%) of the reflective thin film with respect to the inspection light is higher than the surface reflectance Ro (%) of the optical film, and the difference (Rt−Ro) is 5 (%) or more. Preferably there is.

  As a photomask substrate used in the method for producing a photomask of the present invention, a photomask substrate with a resist in which a resist film is further formed on a reflective thin film can be used. In order to form the resist film, a resist serving as a raw material for the resist film can be applied onto the transparent substrate by a known coating apparatus such as a slit coater or a spin coater. The thickness of the resist film is preferably 300 to 1000 nm.

  Here, the resist film will be described as a positive photoresist for laser drawing. However, a negative photoresist may be used as the resist film, and when drawing is performed with an electron beam, an electron beam resist may be used.

  Next, as shown in FIG. 4B, a desired pattern is drawn on the resist film (drawing in a resist pattern forming step). As a drawing apparatus used for drawing a pattern, an FPD laser drawing machine can be used. As the drawing light, laser light having a wavelength of 413 nm is generally used. In FIG. 4B, irradiation with laser light for drawing is schematically shown by a plurality of arrows.

  The drawing data used here is sized so that it is set slightly smaller (under direction) than the target space width dimension (CD2 in FIG. 4G) of the optical film pattern.

  Next, as shown in FIG. 4C, the resist film is developed with a developer to form a resist pattern (development in a resist pattern forming step).

  Next, as shown in FIG. 4D, the reflective thin film is etched using the formed resist film as a mask to form a reflective thin film pattern (thin film etching process). This etching is preferably wet etching, but may be dry etching.

  In general, a photomask for a display device has a size (for example, one side of 300 mm to 1400 mm) larger than a photomask for semiconductor manufacturing (5 to 6 inches), and various sizes. Therefore, it is more advantageous to perform wet etching than to perform dry etching such as a vacuum chamber that places a heavy burden on apparatus control. Here, as an example of a method for forming the reflective thin film pattern, wet etching will be described.

  An etching solution (etching agent) for performing wet etching can be selected from known materials depending on the material of the reflective thin film. For example, ceric ammonium nitrate can be used for a reflective thin film containing Cr. When the reflective thin film is a metal silicide-based material, buffered hydrofluoric acid or the like is appropriately used.

  By etching the reflective thin film, the surface of the optical film corresponding to the etched reflective thin film is exposed.

  Next, as shown in FIG. 4E, the resist pattern remaining on the reflective thin film pattern is removed (step of removing the resist pattern).

  Next, as shown in FIG.4 (f), the dimension measurement of a reflective thin film pattern is performed (dimension measurement process). The dimension measurement may be performed at any part of the reflective thin film pattern. For example, if it is a line and space pattern, the width of a line part may be measured and a space part may be measured. FIG. 4F illustrates a case where CD1 in the space portion is measured. In the transfer pattern to be finally obtained, a portion requiring particularly high accuracy is set as a guarantee portion, and the width of this portion is measured. The object to be measured may be either the width of the reflective thin film pattern (for example, the width of the light shielding portion) or the gap of the reflective thin film pattern (the width of the light transmitting portion such as a hole or a slit).

  A method for measuring the dimension of the reflective thin film pattern is illustrated in FIG. As the inspection light, light within a wavelength range of 300 to 1000 nm can be used. For example, when using inspection light with a wavelength of 400 to 600 nm for dimension measurement, the measurement sensitivity is high, and when using inspection light with a wavelength of 300 to 500 nm, high resolution is obtained because of high resolution. . Here, an inspection light of about 500 nm is exemplified as the inspection light. As described above, since there is a detectable contrast between the reflectance of the reflective thin film with respect to the inspection light and the reflectance of the optical film with respect to the inspection light, the accuracy of dimension measurement is ensured.

  The wavelength of the inspection light preferably has a certain wavelength difference from the wavelength of the drawing light. The wavelength difference between the inspection light and the drawing light is preferably 50 nm or more, more preferably 80 nm or more.

  Here, the etching time applied to the etching of the optical film is set using the measured value of CD1 and the etching rate of the optical film ascertained in advance.

  As described above, the etching rate of the optical film can be obtained by obtaining the correlation between the etching time and the CD change amount as illustrated in FIG. That is, the etching amount per unit time when using the etching solution used for the optical film having the same film material and film thickness as the optical film pattern to be obtained is obtained as data.

  Next, as shown in FIG. 4G, wet etching for a set etching time is performed using the reflective thin film pattern as a mask (optical film etching step). When this etching is completed, side etching of the optical film proceeds, and when viewed from the first main surface (pattern forming surface) side of the photomask, the edge (cross section to be etched) of the optical film pattern is the reflective thin film. Hidden under the pattern.

However, the edge position of the optical film pattern after the etching is correctly controlled, and the target dimension CD2 is obtained.

  Next, as shown in FIG. 4H, the reflective thin film is removed (step of removing the reflective thin film).

  According to the above method, since the dimension measurement using the reflective thin film is performed and the etching time is determined, the CD accuracy of the optical film is higher than when the optical film is etched using the resist pattern as a mask. It becomes possible to do. The thickness of the reflective thin film to be dimensionally measured is 1/50 or less compared to the thickness of the resist pattern, and having physical properties suitable for reflective optical measurement also contributes to the improvement of CD accuracy.

  Of course, the manufacturing method of the present invention includes a case where a photomask having a more complicated structure is formed by further forming and patterning after the optical film pattern as described above is formed.

(Second aspect)
The photomask manufacturing method according to the second aspect of the present invention is a photomask manufacturing method applied to forming a pattern by a predetermined method on an optical film of a resist-coated photomask substrate. Specifically, the photomask manufacturing method of the present invention includes a step of preparing a photomask substrate with a resist, a resist pattern forming step, a thin film etching step, an optical film preliminary etching step, a dimension measuring step, an optical A film additional etching step and a step of removing the permeable thin film. Specifically, in the step of preparing a photomask substrate with a resist, an optical film for forming a transfer pattern and a transparent thin film having etching selectivity with respect to the optical film are laminated on a transparent substrate. is, the resist film is formed on the further the outermost surface. In the resist pattern forming step, a resist pattern is formed by drawing and developing a predetermined pattern on the resist film using a drawing apparatus. In the thin film etching process, the transparent thin film is etched using the resist pattern as a mask to form a transparent thin film pattern. In the optical film preliminary etching step, the optical film is wet-etched using at least the transmissive thin film pattern as a mask to form an optical film preliminary pattern. In the dimension measuring step, the dimension of the optical film preliminary pattern is measured. In this dimension measurement step, the dimension measurement is performed by irradiating the measurement portion of the optical film preliminary pattern with inspection light transmitted through the transparent thin film. In the optical film additional etching step, the optical film is additionally etched based on the additional etching time of the optical film determined based on the measured dimensions. In the step of removing the permeable thin film, the permeable thin film is removed.

  The second aspect of the photomask manufacturing method of the present invention will be specifically described with reference to FIG.

  As shown in FIG. 5A, here, a photomask substrate using a transmissive thin film instead of the reflective thin film used in the first aspect is prepared.

  In the photomask manufacturing method of the second aspect, for example, first, a photomask blank shown in FIG. 5A is prepared (step of preparing a photomask substrate with resist). The photomask substrate of this embodiment is the same as the photomask blank of the first embodiment except that a transmissive thin film is provided instead of the reflective thin film.

  As the transparent substrate of the second aspect, the same transparent substrate as that of the first aspect can be used.

  As the optical film of the second aspect, the same optical film as that of the first aspect can be used. However, the optical film of the second aspect preferably has a transmittance To of 50 (%) or less with respect to the inspection light used for dimension measurement by transmitted light, as will be described later. For example, when light having a wavelength of 500 nm is used as the inspection light, it is preferable that the transmittance To500 of the optical film with respect to this wavelength is in the above range. Further, the reflectance Ro of the optical film with respect to the inspection light is preferably 15% or less. More preferably, the reflectance Ro of the optical film is 8% or less.

  In the photomask manufacturing method according to the second aspect, a transmissive thin film is formed on the optical film by a known film formation method such as sputtering. The transmissive thin film is a thin film having a property of transmitting light having a wavelength emitted from the inspection apparatus for dimension measurement in the dimension measurement process.

  The material of the transmissive thin film is the same as that of the first aspect in that it has etching selectivity with the material of the optical film. Further, as in the case of the reflective thin film of the first aspect, the film thickness of the transmissive thin film is preferably smaller than the film thickness of the optical film.

  The transmissive thin film preferably has a transmittance Tt of 50 (%) or more with respect to inspection light used for dimension measurement described later. The transmittance Tt with respect to the inspection light of the transmissive thin film is more preferably 70 (%) or more, and still more preferably 80 (%) or more. For example, when light having a wavelength of 500 nm is used as the inspection light, the transmittance Tt500 with respect to the inspection light of the transmissive thin film is preferably in the above range. Here, the transmittance Tt500 is a value when the transmittance of the inspection light in the air is 100 (%).

  The transmittance To (%) of the optical film with respect to the inspection light is preferably lower than the transmittance Tt (%) of the transmissive thin film with respect to the inspection light. The difference (Tt−To) between the transmittance Tt (%) of the transparent thin film with respect to the inspection light and the transmittance To (%) of the optical film may be 20 (%) or more, more preferably 30% or more. More preferred.

  In the drawing process, it is desirable that the reflectance of the transparent thin film with respect to the drawing light is not excessive. For this reason, it is preferable that the surface reflectance Rw with respect to the drawing light wavelength (for example, 413 nm) of the transparent thin film is 10 (%) or less.

  Examples of the material for the transmissive thin film include metals containing Mo, Ti, W, Ta, or Zr, and compounds thereof. Examples of the compound include oxides, nitrides, carbides, and oxynitrides. Alternatively, silicides of these metals or oxides, nitrides, carbides, oxynitrides, oxynitride carbides, or the like of the silicides may be used. Furthermore, it can be an oxide, nitride, or oxynitride of Si. However, among the above, a material not containing Si can be said to be a more preferable material because of its high adhesion to the resist film. In view of these, Ta, Ti, or Zr oxides, nitrides, oxynitrides, carbonitrides, and the like are particularly preferable. Of these materials, those having the above-described light transmittance can be selected and used.

  However, the permeable thin film is a material that can provide etching selectivity with the optical film as described above.

  The film thickness of the transmissive thin film is smaller than that of the optical film, and the film thickness is desired to be 5 to 100 nm, more preferably 5 to 50 nm, and still more preferably 5 to 20 nm.

  In order to reduce the influence of side etching, the thickness of the transmissive thin film is preferably 1/10 or less, more preferably 1/20 or less of the thickness of the optical film, as in the first embodiment.

  As a photomask substrate that can be used in the photomask manufacturing method of the second aspect of the present invention, an optical film for forming a transfer pattern on a transparent substrate, and etching selectivity with respect to the optical film What laminated | stacked the transparent thin film which consists of material which has can be used preferably. As described above, the thickness of the transmissive thin film is preferably smaller than that of the optical film, and the light transmittance Tt of the transmissive thin film with respect to light having a wavelength of 500 nm is preferably 50 (%) or more. Furthermore, the light transmittance To of the optical film with respect to light having a wavelength of 500 nm is preferably 50% or less.

  As the resist film used in the second embodiment, the same resist film as that of the first embodiment can be used.

  Next, as shown in FIG. 5B, a desired pattern is drawn on the resist film (drawing in a resist pattern forming step). The drawing of the pattern of the second mode is the same as that of the first mode. However, the drawing data to be used is preferably sized so as to be set slightly smaller (under direction) with respect to the dimension of the space portion of the target optical film pattern (CD5 in FIG. 5H). In FIG. 5B, irradiation with laser light for drawing is schematically shown by a plurality of arrows.

  Next, as shown in FIG. 5C, the resist film is developed with a developer to form a resist pattern (development in a resist pattern forming step).

  Next, as shown in FIG. 5D, the transmissive thin film is etched using the formed resist pattern as a mask to form a transmissive thin film pattern (thin film etching process). This etching is preferably wet etching, but may be dry etching. Here, wet etching is used. The etching solution applicable for forming the transmissive thin film pattern in the second aspect is the same as that in the case of the etching for forming the reflective thin film pattern of the first aspect.

  By etching the transmissive thin film, the surface of the optical film corresponding to the etched transmissive thin film is exposed. The dimension (CD) of the part is set to CD3.

  Next, as shown in FIG. 5E, the exposed optical film is wet-etched using the transmissive thin film pattern as a mask (optical film preliminary etching step). Here, the etching time is a time shorter than the etching time necessary for obtaining the final dimension (CD5) of the optical film pattern, that is, an etching time in which the etching stops under. In this specification, this etching is referred to as “preliminary etching”. Since the optical film is etched away by the preliminary etching and side etching proceeds at the same time, the dimension of the side etched portion becomes CD4 larger than CD3. At this time, the edge (cross section to be etched) of the optical film is located below the transmissive thin film pattern. That is, at the end of the optical film preliminary etching step, the edge of the optical film is located inside the transmissive thin film pattern (the transmissive thin film region) when viewed from the surface side of the photomask.

  Next, as shown in FIG. 5F, the resist is removed.

Next, as shown in FIG. 5G, the edge position of the optical film is detected and CD4 is measured (dimension measuring step). A dimension measuring method is shown in FIG.

  The transmissive thin film is sufficiently transmissive to inspection light (for example, light having a wavelength of about 500 nm). Therefore, when inspection light is incident from the back surface (second main surface) side of the transparent substrate and the transmitted light is detected on the front surface (first main surface) side, the edge of the optical film between the transparent thin film and the transparent substrate Can be detected. As a result, the dimension (CD4) of the edge portion of the optical film can be measured with sufficient accuracy.

  As described above, since the dimension (CD4) of the edge portion of the optical film is slightly under-etched (under direction) with respect to the target dimension (CD5), it reaches the target dimension CD5 by the subsequent additional etching. can do. For the additional etching, the additional etching time until the target dimension CD5 is reached is calculated based on the measured CD4 dimension and the etching rate of the transmissive thin film that has been grasped in advance.

  Next, as shown in FIG. 5H, additional etching for the calculated time is performed (optical film additional etching step).

  Next, as shown in FIG. 5I, the transparent thin film is removed (step of removing the transparent thin film).

  Thus, the photomask is completed. Of course, as in the first embodiment, a photomask having a more complicated structure may be manufactured by further film formation and patterning.

This photomask has excellent CD accuracy with respect to the target dimension (CD5), and the etching end point is accurately determined with respect to the target value, so that the in-plane center value of the CD is highly consistent.

  In the manufacturing method of the second aspect, the resist pattern shown in FIG. 5 (f) may be removed before the optical film is etched in FIG. 5 (e).

  There are no particular restrictions on the use of the photomask according to the production method of the present invention. The photomask produced by the production method of the present invention can be used particularly advantageously as a photomask for producing a display device. For example, the photomask according to the manufacturing method of the present invention is a layer in which CD accuracy is particularly important, such as each layer used in a display device (for example, a source / drain layer, a pixel layer of a TFT array, a photospacer layer of a color filter). ) Can be used advantageously.

  Therefore, the present invention is a method for manufacturing a display device using a photomask manufactured by the above-described manufacturing method of the present invention. Specifically, the manufacturing method of the display device of the present invention includes a step of preparing a photomask manufactured by the manufacturing method of the first aspect or the second aspect of the present invention described above, and an exposure apparatus. Exposing to a photomask and transferring the transfer pattern onto a transfer medium. Since the display device can be manufactured by using the photomask whose precise pattern dimensional accuracy can be controlled by the display device manufacturing method of the present invention, the precise pattern dimensional accuracy is also obtained in the manufactured display device. Can be controlled.

  For example, when manufacturing a display device, the line width of the transfer pattern is about 1 to 100 μm, and the present invention is particularly applicable to a photomask in which a portion (measurement part) of 2 to 30 μm is a target for dimension measurement. The effect of this photomask manufacturing method is remarkable.

  Therefore, as an exposure machine used when transferring the transfer pattern provided in the photomask manufactured by the manufacturing method of the present invention to the transfer object, a so-called FPD exposure apparatus (or liquid crystal exposure apparatus) is used. A projection exposure apparatus of equal magnification or a proximity exposure apparatus can be used.

  At this time, the exposure light is light used when exposed by an exposure machine when using a photomask, and a light source in a wavelength region including i-line, h-line, and g-line is used in manufacturing a display device. It is done. Further, in the present application, the representative wavelength can be any wavelength light included therein, for example, h-line.

  As the optical system of the exposure apparatus, in the case of a projection exposure apparatus, the NA (numerical aperture) is 0.08 to 0.10, and the coherency factor (σ) is in the range of 0.5 to 1.0. Can be preferably used. However, there is a need for a higher-resolution exposure apparatus. For example, it is possible to use an exposure apparatus having an NA of 0.08 to 0.14.

  The photomask manufacturing method of the present invention can be applied to manufacturing all kinds of photomasks having at least one optical film on a transparent substrate.

  For example, the present invention can be preferably applied when manufacturing a binary mask using an optical film as a light shielding film. Further, it can be applied to a method of manufacturing a phase shift mask (so-called Levenson mask or halftone type phase shift mask) using an optical film as a phase shift film.

  Further, the present invention can also be applied to forming a multi-tone photomask including a translucent portion and a light-shielding portion and a semi-transparent portion using the optical film of the present invention in the transfer pattern. In this case, by using a film that partially transmits the exposure light without changing the phase (the phase shift amount is 90 degrees or less) (transmittance is, for example, 20 to 60%) as the optical film, And The formed transfer pattern can form a three-dimensional resist pattern having a step on the transfer target body, which can increase the efficiency of manufacturing a display device or the like.

  Further, as the optical film, a film that partially transmits the exposure light without phase inversion (transmittance is, for example, 2 to 50%) is used, and the semi-transparent part thereby is adjacent to the translucent part. It is also possible to apply to a light quantity auxiliary mask that compensates for the shortage of transmitted light quantity of the fine slit.

  The present invention also includes a photomask substrate on which an optical film and a reflective thin film or a transmissive thin film are formed, for example, a photomask blank, for use in the manufacturing method.

In either case of the first aspect or the second aspect, the part (measurement unit) that is the target of dimension measurement in the dimension measurement process is performed at a plurality of positions so that the tendency of the entire main surface of the photomask substrate can be grasped. It is preferable. Further, it is preferable that the measurement unit is provided in the vicinity of each of the four sides and / or in the vicinity of each of the four corners of the substrate having at least a quadrangle main surface. Furthermore, when a grid that equally divides the main surface into a certain area is drawn, it is preferable that a measurement unit is disposed in each of the sections equally divided into the grid. In this case, the in-plane line width fluctuation tendency that occurs during development and etching can be accurately grasped. Alternatively, the dimensions obtained at these multiple points can be subjected to appropriate calculations such as taking an average value, and can be quantitatively analyzed.

Claims (14)

An optical film for forming a transfer pattern on a transparent substrate, a reflective thin film having etching selectivity with respect to the optical film, and a resist film formed on the outermost surface. Preparing a mask substrate;
A resist pattern forming step of forming a resist pattern by drawing and developing a predetermined pattern on the resist film using a drawing apparatus;
Using the resist pattern as a mask, etching the reflective thin film to form a reflective thin film pattern, a thin film etching step,
Removing the resist pattern;
A dimension measuring step for measuring the dimension of the reflective thin film pattern; and
An optical film etching step of performing wet etching of the optical film using the reflective thin film pattern as a mask, based on the etching time of the optical film determined based on the measured dimensions;
Removing the reflective thin film,
In the dimension measurement step, the dimension measurement is performed by irradiating the measurement portion of the reflective thin film pattern with inspection light and detecting the reflected light of the inspection light. Photomask manufacturing method.   2. The method of manufacturing a photomask according to claim 1, wherein the thickness of the reflective thin film is smaller than the thickness of the optical film.   The surface reflectance Rt (%) of the reflective thin film with respect to the inspection light is higher than the surface reflectance Ro (%) of the optical film, and the difference (Rt−Ro) is 5 (%) or more. A method for producing a photomask according to claim 1 or 2.   The method for manufacturing a photomask according to claim 1, wherein the surface reflectance Rt of the reflective thin film with respect to the inspection light is 20 (%) or more.   The photomask manufacturing method according to claim 1, wherein light having a wavelength in a range of 300 to 1000 nm is used as the inspection light. In a photomask substrate for making a photomask provided with a transfer pattern for manufacturing a display device,
An optical film for forming a transfer pattern and a reflective thin film made of a material having etching selectivity with respect to the optical film are laminated on a transparent substrate,
The film thickness of the reflective thin film is smaller than the film thickness of the optical film,
The photomask substrate, wherein the reflective thin film has a surface reflectance Rt of 20 (%) or more and higher than a surface reflectance Ro (%) of the optical film with respect to light having a wavelength of 500 nm. The surface reflectance Rt (%) of the reflective thin film with respect to the 500 nm wavelength light is higher than the surface reflectance Ro (%) of the optical film, and the difference (Rt−Ro) is 5 (%) or more. The photomask substrate according to claim 6, wherein the photomask substrate is provided. An optical film for forming a transfer pattern on a transparent substrate, a transparent thin film having etching selectivity with respect to the optical film, and a resist film formed on the outermost surface. Preparing a mask substrate;
A resist pattern forming step of forming a resist pattern by drawing and developing a predetermined pattern on the resist film using a drawing apparatus;
Using the resist pattern as a mask, etching the transparent thin film to form a transparent thin film pattern, and a thin film etching step,
An optical film preliminary etching step of wet-etching the optical film using at least the transmissive thin film pattern as a mask to form an optical film preliminary pattern; and
A dimension measuring step of measuring the dimension of the optical film preliminary pattern; and
An optical film additional etching step of additionally etching the optical film based on the additional etching time of the optical film determined based on the measured dimensions;
Removing the permeable thin film,
In the dimension measuring step, the dimension measurement is performed by irradiating the measurement portion of the optical film preliminary pattern with the inspection light transmitted through the transmissive thin film, and the method for manufacturing a photomask.   9. The method of manufacturing a photomask according to claim 8, wherein the thickness of the transmissive thin film is smaller than the thickness of the optical film.   10. The photomask manufacturing method according to claim 8, wherein a transmittance Tt of the transparent thin film with respect to the inspection light is 50 (%) or more. 11.   The optical film pre-etching step is completed, and the edge of the optical film is located inside the transmissive thin film pattern when viewed from the surface side of the photomask. 2. A method for producing a photomask according to claim 1. In a photomask substrate for making a photomask provided with a transfer pattern for manufacturing a display device,
An optical film for forming a transfer pattern and a transparent thin film made of a material having etching selectivity with respect to the optical film are laminated on a transparent substrate,
The film thickness of the transmissive thin film is smaller than the film thickness of the optical film,
A photomask substrate, wherein a light transmittance Tt of the transparent thin film with respect to a wavelength of 500 nm is 50 (%) or more.   The photomask substrate according to claim 12, wherein a light transmittance To of the optical film with respect to a wavelength of 500 nm is 50 (%) or less. Preparing a photomask manufactured by the manufacturing method according to any one of claims 1 to 5 and claims 8 to 11;
Exposing to the photomask using an exposure apparatus, and transferring the transfer pattern to a transfer target.
Manufacturing method of display device.