Method for manufacturing a photomask and a display device.

Abstract

To provide a photomask having excellent transfer performance for transferring a fine hole pattern on a body to be transferred, by exposing with mid-ultraviolet exposure light.SOLUTION: There is provided a photomask for producing a display device to form a hole pattern on a substrate by using mid-ultraviolet exposure light, wherein the phase difference θ between a transmissive portion and a phase shift film with respect to light of a reference wavelength λ1 contained in the mid-ultraviolet exposure light for exposing the photomask is within the range of 180±15 degrees; the numerical aperture NA of the projection optical system of the exposure apparatus in which the photomask is used is 0.08 or more and 0.20 or less; the mid-ultraviolet exposure light has intensity peaks at two or more wavelengths among 313 nm, 334 nm, and 365 nm; and the reference wavelength λ1 is 313 nm or 334 nm.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD

[0001] The present invention relates to a photomask, particularly a photomask advantageous for manufacturing high-definition display devices, and a method for manufacturing a display device using the same.

BACKGROUND ART

[0002] Patent Document 1 describes a phase shift mask blank for manufacturing display devices, and a phase shift mask manufactured from the phase shift mask blank. It further describes that the phase shift mask is exposed with composite light including i-line, h-line, and g-line.

[0003] Patent Document 2 describes a phase shift mask blank for manufacturing display devices, which is provided with a phase shift film exhibiting optical properties with suppressed wavelength dependency on exposure light, wherein the phase shift film has a transmittance in the range of 3.5% to 8% at a wavelength of 365 nm, a phase difference in the range of 160 degrees to 200 degrees at a wavelength of 365 nm, and a wavelength-dependent variation in transmittance within 5.5% in the wavelength range of 365 nm to 436 nm.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

[0004]

PATENT DOCUMENT 1

PATENT DOCUMENT 2

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0005] In recent years, there has been a growing need for display devices, including LCDs (liquid crystal displays) and OLEDs (organic light-emitting diodes), to offer not only bright and high-definition display performance, but also power efficiency and fast video response times. Therefore, the patterns of the photomasks used in the manufacturing process of these display devices are increasingly miniaturized and highly integrated. Furthermore, there is a demand for technologies that can precisely resolve the patterns of the photomasks onto the transfer target (display panel substrate, etc.).

[0006] Incidentally, if the transfer pattern of the photomask cannot be optically resolved on the transfer surface, a display device with the intended fine pattern cannot be constructed. Here, the spatial resolution of the optical image can be expressed by Rayleigh's resolution criterion, i.e., equation (1) below.

[0007] δ = k1 × λ / NA ···(1) Here, δ is the minimum resolution linewidth, λ is the exposure wavelength, NA is the numerical aperture of the optical system of the exposure device, and k1 is a coefficient also called the k1 factor.

[0008] In the field of display devices (hereinafter also referred to as FPDs (Flat Panel Displays)), a specific wavelength range of high-pressure mercury lamps is used as light for exposure. That is, light containing multiple wavelengths and a wavelength band that mixes them (hereinafter also referred to as broadband) is used, and in particular, the application of exposure light containing three wavelengths of light contained in high-pressure mercury lamp light, namely the g-line (436 nm), h-line (405 nm), and i-line (365 nm), is known (see Patent Documents 1 and 2).

[0009] On the other hand, according to equation (1) above, in order to improve the resolution for fine patterns (i.e., to reduce the minimum resolution linewidth δ), it is effective to reduce λ or increase the NA. However, according to equation (2) below, improving the NA reduces the depth of focus, which can be seen as relatively worsening the stability of the lithography process. Equation (2) is also known as Rayleigh's depth of focus equation.

[0010] DOF = k² × λ / NA 2 ...(2) Here, DOF (Depth of Focus) refers to the depth of focus, and k2 is the coefficient.

[0011] The relationship between the magnitude of the value on the left side of equation (2) and the resolution criterion equation (equation (1)) is reversed. In other words, while a small value on the left side is preferable in equation (1), a large value is desirable in equation (2).

[0012] Therefore, there is a trade-off correlation between the minimum resolution linewidth δ and DOF. However, since the DOF expressed in equation (2) deteriorates in proportion to the square of the NA, it can be said that shortening the wavelength of the exposure light is more rational than increasing the NA if the same level of resolution improvement is assumed. In other words, it is possible to improve resolution while suppressing the decrease in DOF.

[0013] From the broadband exposure environment described above, one possible method to easily achieve shorter wavelengths is to switch to exposure using a single i-line wavelength instead of mixed-wavelength exposure including the g-line, h-line, and i-line, thereby effectively reducing the wavelength. However, this method eliminates the contributions of two of the three wavelengths, meaning that the amount of work per unit time drops to one-third in simple calculations. In the field of FPD production, in addition to the resolution mentioned above, another important factor is production efficiency, so there are circumstances that make adopting single-wavelength exposure difficult.

[0014] Therefore, a method can be considered that maintains a broadband exposure environment while shifting its center of gravity to the shorter wavelength side. In high-pressure mercury lamp light, there are several wavelength groups with peaks in light intensity on the shorter wavelength side than the i-line, so the above method utilizes the light of these wavelength groups as exposure energy.

[0015] The inventors of this invention diligently investigated what kind of photomask would be suitable for a new broadband exposure environment, which shifts the wavelength range used by conventional exposure light to the shorter wavelength side, and exhibit excellent transferability, and have completed this invention. [Means for solving the problem]

[0016] A first aspect of the present invention is: A photomask for manufacturing a display device, for forming a hole pattern with size Dp and Dp ≤ 3 μm on a transfer surface using mid-ultraviolet exposure light, A transparent substrate has a transfer pattern including a hole pattern, The hole pattern in the aforementioned transfer pattern consists of translucent areas surrounded by halftone regions. With respect to the light of a reference wavelength contained in the mid-ultraviolet exposure light for exposing the photomask, the phase difference θ between the light-transmitting portion and the halftone region is approximately 180 degrees, The transmittance T of the halftone region with respect to the reference wavelength of light is 10% ≤ T ≤ 35%. It is a photomask.

[0017] A second aspect of the present invention is: The hole pattern in the transfer pattern consists of light-transmitting portions in which the transparent substrate is exposed, formed by patterning a phase-shift film formed on the transparent substrate. The halftone region is formed by forming the phase shift film on the transparent substrate. The phase-shift film is a photomask according to the first embodiment, having a phase shift amount of approximately 180 degrees with respect to light of the reference wavelength, and having a transmittance T such that 10% ≤ T ≤ 35%.

[0018] A third aspect of the present invention is: A photomask for manufacturing a display device, for forming a hole pattern with size Dp and Dp ≤ 3 μm on a transfer surface using mid-ultraviolet exposure light, A transfer pattern including a hole pattern is provided on a transparent substrate, The hole pattern in the transfer pattern consists of a light-transmitting portion surrounded by a halftone region, When the reference wavelength is λ1 and λ1<365 nm, the phase difference θ between the light-transmitting portion and the halftone region with respect to light of the wavelength λ1 is 180 degrees, and The transmittance T of the halftone region for light of the wavelength λ1 satisfies 10%≦T≦35%, This is a photomask.

[0019] A fourth aspect of the present invention is The hole pattern in the transfer pattern is constituted by the light-transmitting portion where the transparent substrate is exposed, which is formed by patterning a phase shift film formed on the transparent substrate, The halftone region is formed by forming the phase shift film on the transparent substrate, The photomask according to the third aspect described above, wherein the phase shift film has a phase shift amount of 180 degrees with respect to light of the wavelength λ1, has a transmittance T, and satisfies 10%≦T≦35%.

[0020] A fifth aspect of the present invention is The photomask according to any one of the first to fourth aspects described above, wherein the transfer pattern includes an isolated hole pattern.

[0021] A sixth aspect of the present invention is The photomask according to any one of the first to fifth aspects described above, wherein the transfer pattern has a proximity hole pattern including two or more hole patterns located at a proximity distance.

[0022] A seventh aspect of the present invention is The photomask according to the sixth aspect described above, wherein the distance between the centers of gravity of the two hole patterns included in the proximity hole pattern is 9 μm or less.

[0023] An eighth aspect of the present invention is The photomask is one of the first to seventh embodiments described above, wherein the size of the hole pattern in the transfer pattern is Dm, and Dm > Dp.

[0024] A ninth aspect of the present invention is: This is the photomask described in the eighth embodiment above, wherein Dm / Dp is 1.1 or more and 1.8 or less.

[0025] A tenth aspect of the present invention is: The photomask is according to any one of the first to ninth embodiments, wherein the reference wavelength is 313 nm or 334 nm.

[0026] An eleventh aspect of the present invention is: A method for manufacturing a display device, A step of preparing a photomask according to any one of the first to tenth embodiments described above, The process includes an exposure step in which the photomask is exposed using mid-ultraviolet exposure light. The aforementioned mid-ultraviolet exposure light includes a wavelength range where the wavelength λ satisfies 200 nm ≤ λ ≤ 400 nm, and does not include wavelengths where λ > 400 nm and λ < 200 nm. This is a method for manufacturing a container.

[0027] A twelfth aspect of the present invention is: The method for manufacturing a display device according to the 11th embodiment, wherein the exposure step forms a hole pattern with a size Dp ≤ 3 μm on the transfer object. [Effects of the Invention]

[0028] The photomask of the present invention has excellent transfer performance, transferring a fine hole pattern onto a transfer target by exposure using mid-ultraviolet exposure light as described later. [Brief explanation of the drawing]

[0029] [Figure 1] Figure 1 is a schematic plan view of the first photomask 10 of the present invention. [Figure 2]Figure 2(a) is a schematic plan view of the second photomask 20 of the present invention. Figure 2(b) is a schematic cross-sectional view of the resist pattern formed by exposure of the second photomask 20. [Figure 3] Figure 3(a) is a schematic plan view of the photomask of Reference Example 1. Figure 3(b) is a schematic cross-sectional view of the resist pattern formed by exposure of the photomask of Reference Example 1. [Figure 4] Figure 4(a) is a schematic plan view of the photomask of Reference Example 2. Figure 4(b) is a schematic cross-sectional view of the resist pattern formed by exposure of the photomask of Reference Example 2. [Figure 5] Figure 5 shows the characteristics of the films related to Example 1 and Reference Examples 1 to 4. [Figure 6] Figure 6 shows the results of the optical simulations related to Example 1 and Reference Examples 1 to 4. [Figure 7] Figure 7(a) is a schematic plan view of the photomask of Reference Example 3. Figure 7(b) is a schematic cross-sectional view of the resist pattern formed by exposure of the photomask of Reference Example 3. [Figure 8] Figure 8(a) is a schematic plan view of the photomask of Reference Example 4. Figure 8(b) is a schematic cross-sectional view of the resist pattern formed by exposure of the photomask of Reference Example 4. [Figure 9] Figure 9(a) is a schematic plan view of the photomask of Reference Example 5. Figure 9(b) is a schematic cross-sectional view of the resist pattern formed by exposure of the photomask of Reference Example 5. [Figure 10] Figure 10(a) is a schematic plan view of the photomask of Reference Example 6. Figure 10(b) is a schematic cross-sectional view of the resist pattern formed by exposure of the photomask of Reference Example 6. [Figure 11] Figure 11 shows the results of the optical simulations related to Reference Examples 5 and 6. [Modes for carrying out the invention]

[0030] <First Embodiment of the Invention> The photomask of the present invention is a photomask for mid-ultraviolet exposure, and is a photomask for applying mid-ultraviolet light as exposure light. Here, mid-ultraviolet light refers to exposure light having a wavelength range that includes multiple wavelengths in the wavelength range of 200 to 400 nm, and does not include wavelengths less than 200 nm or greater than 400 nm. As the light source for the above exposure light, for example, an appropriate portion of the wavelength range of a high-pressure mercury lamp can be suitably used. In this case, for example, it is preferable to apply broadband wavelengths that include two or more of 313 nm, 334 nm, and 365 nm (i-line) which have intensity peaks, but do not include h-line and g-line. In this specification, "A to B" means a numerical range of "A or more and B or less".

[0031] Such exposure light can be broadband light with a wavelength range shifted to the shorter wavelength side compared to the wavelength range including i-line, h-line, and g-line conventionally used in exposure equipment for manufacturing display devices. According to the inventor's research, this is particularly advantageous in terms of resolution when used for hole pattern formation, and does not result in inefficiencies such as single-wavelength exposure (e.g., reduced production efficiency).

[0032] The photomask of the present invention is A photomask for manufacturing a display device, for forming a hole pattern with size Dp and Dp ≤ 3 μm on a transfer surface using mid-ultraviolet exposure light, A transparent substrate has a transfer pattern including a hole pattern, The hole pattern in the aforementioned transfer pattern consists of translucent areas surrounded by halftone regions. With respect to the light of a reference wavelength included in the mid-ultraviolet exposure light for exposing the photomask, the phase difference θ between the transmitted light of the light-transmitting portion and the transmitted light of the halftone region is approximately 180 degrees, The transmittance T of the halftone region with respect to the reference wavelength of light is 10% ≤ T ≤ 35%.

[0033] Figure 1 illustrates the first photomask 10 of the present invention. The transfer pattern of the first photomask 10 has an isolated hole pattern consisting of a translucent area 12 surrounded by a halftone area 11. An isolated hole pattern means that no other hole patterns exist within a predetermined proximity distance (details described later) from one hole pattern.

[0034] Furthermore, Figure 2(a) illustrates a second photomask 20 of the present invention. The second photomask 20 consists of a light-transmitting portion 12 surrounded by a halftone region 11, and has a proximity hole pattern in which a plurality of hole patterns spaced apart at a predetermined proximity distance are arranged side by side. In Figure 2(a), two hole patterns spaced apart at a predetermined proximity distance are arranged side by side, and such a hole pattern is also called a double hole pattern. Here, an example is given in which the two hole patterns are the same shape (square) and the same size and are arranged side by side. Figure 2(b) is an example of the cross-sectional shape of a resist pattern formed by exposing the second photomask 20 of the present invention.

[0035] Proximity distance refers to the distance at which, when exposed to light, the transmitted light from two hole patterns interacts optically with each other.

[0036] Furthermore, in the following, the hole pattern of the transfer pattern of the photomask may be referred to as the mask hole pattern in order to distinguish it from the hole pattern formed on the transfer surface.

[0037] By exposing the mask hole pattern of the photomask of this embodiment to an exposure apparatus having the above-mentioned light source, a hole pattern with size Dp can be formed on the transfer target (such as a display panel substrate). Here, the effects of the present invention are particularly evident when forming fine holes such as Dp ≤ 3 μm. Furthermore, as the trend toward further miniaturization progresses, the present invention can be usefully applied to forming holes with Dp ≤ 2 μm or Dp ≤ 1.5 μm. In addition, it is preferable that Dp ≤ 0.5 μm.

[0038] Such transfer patterns are useful for layers (e.g., hole layers) that provide the contact holes necessary for the configuration of display panel substrates of display devices (including liquid crystal and organic EL displays). When the hole pattern formed on the transfer substrate is circular, its diameter is denoted as Dp. For other shapes, Dp is denoted as the diameter obtained when the pattern is approximated (converted) to a circle with the same shape and area.

[0039] When Dp exceeds 3 μm, a predetermined resolution performance for obtaining a desired hole pattern on a transfer target using a conventional exposure apparatus for manufacturing display devices can be obtained by using a conventional photomask (e.g., a binary mask). However, the inventors have focused on the problem that when the size Dp of the hole pattern to be obtained on the transfer target is 3 μm or less, a transfer image with sufficient resolution cannot be obtained with a conventional photomask.

[0040] In this embodiment of the photomask, a transfer pattern can be formed on the main surface of a transparent substrate, which is made of a transparent material such as quartz that has been processed to be flat and smooth.

[0041] In the first photomask 10 and second photomask 20 of this embodiment, the mask hole pattern of the transfer pattern is a rectangular cutout pattern enclosed on all four sides, and can be formed as a translucent portion 12 in which the transparent substrate is exposed. The four corners of the rectangle do not need to be perfect 90 degrees, and the four corners and their vicinity may form an arc shape as long as the effects of the present invention are not impaired.

[0042] The shape of the mask hole pattern is preferably quadrilateral (square or rectangle), and more preferably square. When the diameter or side size of the mask hole pattern is Dm, Dm ≤ 3.5 μm. If the shape of the mask hole pattern is square, the length of one side (e.g., CD-X) and the length of the side perpendicular to it (CD-Y) are equal, and this length is taken as Dm. If the shape of the mask hole pattern is rectangular, the longer side (e.g., CD-X) is taken as Dm. The effects of the present invention are particularly pronounced when Dm ≤ 2.0 μm. Furthermore, in a quadrilateral mask hole pattern, the effects of the present invention are particularly pronounced when both CD-X and CD-Y are 2 μm or less. Note that CD is also referred to as Critical Dimension, and in this specification, CD-X means the dimension of the pattern in the X direction, and CD-Y means the dimension of the pattern in the Y direction. Here, the X direction means one direction on the main surface of the photomask, and the Y direction means the other direction perpendicular to the X direction.

[0043] Furthermore, this mask hole pattern (an isolated hole pattern as exemplified in the first photomask 10, or a nearby hole pattern as exemplified in the second photomask 20) ​​is surrounded by a halftone region 11 on the transparent substrate. The halftone region 11 in this embodiment is formed by creating a phase-shift film on the main surface of the transparent substrate, and this phase-shift film has a phase shift of approximately 180 degrees with respect to exposure light of reference wavelength λ1. Therefore, the light-transmitting portion 12 and the halftone region 11 have a phase difference θ of approximately 180 degrees with respect to exposure light of reference wavelength λ1. Here, approximately 180 degrees is within the range of 180 ± 60 degrees, more preferably within the range of 180 ± 30 degrees, and even more preferably within the range of 180 ± 15 degrees. The phase difference θ (the amount of phase shift of the phase-shift film) should be approximately 180 degrees, but it is even more preferable if it is 180 degrees (meaning exactly 180 degrees). The reference wavelength λ1 will be described in detail later.

[0044] Furthermore, the transmittance T of the halftone region 11 with respect to exposure light at the reference wavelength λ1 satisfies 10% ≤ T ≤ 35%. In other words, the phase-shift film in the halftone region 11 of this embodiment has a transmittance T with respect to exposure light at the reference wavelength λ1. If the value of T is excessively large, the resist pattern formed on the transfer substrate by exposure of the photomask is likely to be damaged, and if it is excessively small, the required exposure amount tends to increase. The transmittance T of the halftone region 11 with respect to exposure light at the reference wavelength λ1 is preferably 12% ≤ T ≤ 30%, and more preferably 14% ≤ T ≤ 25%. Note that, unless otherwise specified, the transmittance (%) in this specification means the value converted with the transmittance of the transparent substrate as the reference (100%).

[0045] In the case of a transfer pattern that includes an isolated hole pattern (for example, the first photomask 10), the transmittance of the halftone region 11 is preferably 10% ≤ T ≤ 35%, more preferably 10% ≤ T ≤ 25%, and even more preferably 12% ≤ T ≤ 25%. In the case of a transfer pattern that includes a nearby hole pattern (for example, the second photomask 20), it is more preferably 10% ≤ T ≤ 22%. That is, considering the case in which a transfer pattern provided by a single photomask includes both an isolated hole pattern and a nearby hole pattern, the transmittance of the halftone region 11 is preferably 10% ≤ T ≤ 22%, more preferably 12% ≤ T ≤ 22%, and even more preferably 15% ≤ T ≤ 22%.

[0046] In the above, the reference wavelength λ1 for the phase shift amount and transmittance can be any wavelength included in the wavelength range of the mid-ultraviolet exposure light (200~400nm) described above. The reference wavelength λ1 can more preferably be 250nm≦λ1≦400nm, and even more preferably 250nm<λ1<400nm. It is preferable that the reference wavelength λ1 be shorter than the i-line wavelength. Specifically, the reference wavelength λ1 can be λ1<365nm, preferably 200nm≦λ1<365nm, more preferably 250nm≦λ1<365nm, and even more preferably 250nm<λ1<365nm. In this embodiment, as an example, a wavelength of 334nm is used as the reference wavelength λ1. This wavelength is close to the weighted average considering the intensity distribution in the mid-ultraviolet wavelength range mentioned above, and in the spectrum of a high-pressure mercury lamp, it has a predetermined intensity (peak height). This makes it not only suitable as a reference related to the phase shift effect, but also the most advantageous for obtaining the DOF (depth of focus) improvement effect described later. Furthermore, setting the reference wavelength λ1 to 313 nm is also advantageous because it makes it easier to obtain the DOF improvement effect described later.

[0047] The transfer pattern of this embodiment is particularly effective when it includes a proximity hole pattern, such as in the second photomask 20. In the proximity hole pattern, the distance between the mask hole patterns is preferably such that the distance between their centroids (hereinafter also referred to as pitch P) is 9 μm or less, and preferably 2 μm ≤ P ≤ 9 μm. More preferably, the advantages of the present invention are greater when the pitch P is 2 μm ≤ P ≤ 6 μm, and when the pitch P is 2 μm ≤ P ≤ 4 μm.

[0048] Furthermore, the design of the transfer pattern is not limited to the transfer pattern designs of the first photomask 10 and the second photomask 20. In particular, if the photomask has a proximity hole pattern, additional proximity hole patterns may be formed in addition to the double hole pattern described above. For example, three or more proximity hole patterns of the same shape may be arranged regularly in one direction at a pitch P, or they may be arranged regularly in two dimensions at a constant pitch P. Alternatively, the pitch P does not necessarily have to be constant.

[0049] Furthermore, the individual hole patterns may not be of the same size, but may also contain a mixture of hole patterns of different sizes.

[0050] However, as mentioned above, the effect of the invention is greater when the distance between the centroids of adjacent hole patterns (pitch P) is 9 μm or less.

[0051] Furthermore, it is necessary that the hole patterns do not come into contact with each other, and preferably, the shortest distance d between the edges (outer edges) of the holes is 0.5 to 2.0 μm.

[0052] The first photomask 10 and the second photomask 20 in this embodiment are photomasks for manufacturing display devices, and can be, for example, a rectangular transparent substrate with sides of 300 to 1800 mm and a thickness of 5 to 16 mm, on which a transfer pattern is formed on the main surface.

[0053] This photomask is intended to be exposed by an exposure apparatus used for manufacturing display devices. For example, the numerical aperture (NA) of the projection optical system of the exposure apparatus is approximately 0.08 to 0.20, and its exposure light source is in the mid-ultraviolet region as described above.

[0054] The photomask of this embodiment can be obtained by patterning a phase-shift film formed on a transparent substrate to form a cutout pattern corresponding to the mask hole pattern. For example, in the second photomask 20 of Figure 2(a), a double-hole pattern is formed where two cutout patterns are in close proximity. The mask hole pattern portion is a translucent portion 12 where the transparent substrate is exposed, and the surrounding area is a halftone region 11 where a phase-shift film is formed on the transparent substrate.

[0055] In this embodiment, the size Dm of the mask hole pattern is preferably larger than Dp (Dm > Dp). That is, it is preferable to form a Dm with dimensions equal to the size Dp of the hole pattern formed on the transfer target, plus a mask bias β (β = Dm - Dp).

[0056] The mask bias β is preferably set such that, for example, Dm / Dp is 1.1 to 1.8. In particular, in the case of a transfer pattern including adjacent hole patterns (here, double holes), it is more preferable to set Dm / Dp to 1.2 to 1.7, and even more preferable to set it to 1.25 to 1.65. At this time, it is preferable to set the transmittance T of the phase shift film to 10 to 22%, and more preferably to 12 to 22%. By doing so, when the photomask is exposed, not only are the DOF and required exposure amount within a suitable range, but as shown in Figure 2(b), the partition wall 13 (details described later) formed between the double hole patterns in the resist pattern formed on the transfer target (here, a positive-type photoresist) is not damaged, and the inconvenience of the double hole patterns becoming connected is less likely to occur. [Examples]

[0057] The second photomask 20 shown in Figure 2(a) was designated as Example 1, and optical simulations were performed on the transfer characteristics of each to compare it with the binary mask of Reference Example 1 shown in Figure 3(a) and the halftone phase shift mask of Reference Example 2 shown in Figure 4(a) (with the reference wavelength being the i-line).

[0058] In the second photomask 20 of Example 1, the phase-shift film used in the halftone region 11 had a phase shift of 180 degrees and a transmittance of 16.1% with respect to the mid-ultraviolet exposure wavelength (reference wavelength 334 nm) (see "Mid-ultraviolet PSM (Phase Shift Mask)" in Figure 5).

[0059] Furthermore, in the photomask of Reference Example 1, a light-shielding film (a film that substantially does not transmit exposure light) was formed in the region corresponding to the halftone region 11 in Example 1 (light-shielding region 14), rather than a phase-shift film.

[0060] In Reference Example 2, a phase-shifted film with a phase shift of 180 degrees relative to the reference wavelength i-line (365 nm) and a transmittance of 5.2% was formed in the halftone region 11 of Example 1 (see "i-line PSM" in Figure 5). This was based on the fact that the transmittance of the phase-shifted film was approximately 5-6% as described in the above-mentioned document (Patent Document 2).

[0061] To evaluate the transfer performance of the photomask with the above film structure, a transfer pattern was designed as a close-proximity (double) mask hole pattern. The goal was to form a double hole pattern with a diameter of 1.5 μm on the transfer target, and the following items were evaluated. The shapes of the transfer patterns in Example 1, Reference Example 1, and Reference Example 2 are shown in Figures 2(a), 3(a), and 4(a), respectively. The film characteristics of the halftone region 11 (light-shielding region 14 in the binary mask of Reference Example 1) are shown in Figure 5.

[0062] (1) Exposure amount (mJ / cm 2 ) The exposure amount here indicates the required exposure amount to obtain a pattern of the target size on the transfer surface. A smaller required exposure amount is preferable, for example, 50 mJ / cm². 2 The following is preferable:

[0063] (2) DOF (μm) Here, DOF refers to the depth of field that is within ±10% of the target CD value. A larger DOF is preferable, for example, 15 μm or more is preferable.

[0064] (3) MEEF (Mask Error Enhancement Factor) MEEF represents the ratio of the CD error of the transferred image formed on the substrate to the CD error of the photomask. A smaller MEEF is preferable. The CD error of the photomask refers to the actual CD error (amount of deviation) on the photomask relative to the target CD value on the photomask. The CD error of the transferred image formed on the substrate refers to the actual CD error (amount of deviation) of the transferred image relative to the target CD value of the transferred image formed on the substrate.

[0065] Figure 6 shows the optical simulation results of the transfer characteristics in Example 1, Reference Example 1, and Reference Example 2. Furthermore, Figures 2(b), 3(b), and 4(b) show the cross-sectional shapes of the resist patterns formed on the transfer substrate in Example 1, Reference Example 1, and Reference Example 2, respectively.

[0066] Reference Example 1 (binary mask) is a reference mask, and will be referred to as "reference" hereafter. As shown in Figure 3(b), in the photomask of Reference Example 1, a partition of sufficient height and thickness (hereinafter referred to as partition wall 13) is formed between the double-row hole patterns in the resist pattern (here, a positive-type photoresist pattern) formed on the transfer substrate. On the other hand, as shown in Figure 6, the photomask of Reference Example 1 has a small DOF of less than 15 μm, resulting in insufficient process margins for display device manufacturing.

[0067] In Reference Example 2, an improvement in DOF (Depth of Field) is observed, similar to the effect obtained with existing halftone phase-shift masks. However, as shown in Figure 6, in Reference Example 2, the required exposure amount is about 150% of that in Reference Example 1, which reduces the production efficiency of the display device, making it unsuitable for mass production.

[0068] In Example 1, as shown in Figure 6, sufficient DOF can be obtained, and the exposure dose can be significantly reduced compared to Reference Examples 1 and 2 (50 mJ / cm²). 2 As shown below, and as shown in Figure 2(b), the partition walls 13 between adjacent holes are appropriately formed in the cross-sectional shape of the resist pattern, indicating that it is extremely useful. In Example 1, a reduction effect was also observed in the MEEF value. In Example 1, the hole size on the mask was set to 2.1 μm, compared to the target hole size of 1.5 μm formed on the material to be transferred. That is, a mask bias β was applied such that Dm / Dp was 1.4.

[0069] Here, for confirmation, we also verified whether the transferability improved when the same bias as in Example 1 was applied to Reference Example 1 and Reference Example 2. In Reference Example 1, the mask hole pattern size was set to 2.1 μm by applying a bias, which was designated as Reference Example 3 (Figure 7(a)), and in Reference Example 2, the bias was similarly applied, which was designated as Reference Example 4 (Figure 8(a)). The results of optical simulations of the transfer performance of each are also shown in Figure 6.

[0070] According to the optical simulation results for Reference Examples 3 and 4, in Reference Example 3, although the exposure amount could be reduced by applying a bias, the DOF decreased to a level below that of the reference (Reference Example 1). Also, as shown in Figure 7(b), when examining the cross-section of the resist pattern in Reference Example 3, the partition walls 13 between the double hole patterns could not be sufficiently formed, and the double hole patterns became connected to each other. Furthermore, according to Reference Example 4, not only was the DOF improvement effect smaller than that of the reference, but as shown in Figure 8(b), it was found from the cross-section of the resist pattern that the partition walls 13 between the double hole patterns were very thin and easily damaged. In order to obtain a circuit pattern without defects in the display device to be obtained, it is most preferable that the partition walls 13 of the resist pattern do not lose the initial thickness of the resist, but it is preferable that at least 50% or more of the thickness of the partition walls 13 remains relative to the initial thickness, and it is more preferable that 60% or more of the thickness remains.

[0071] Based on the above, it was confirmed that the transfer performance of this form of photomask is excellent. [Examples]

[0072] The photomask of Reference Example 5 shown in Figure 9(a) and the photomask of Reference Example 6 shown in Figure 10(a) are photomasks having a nearby (double) hole pattern, and were formed in the same manner as in Example 1, except that the transmittance of the phase-shift film in the halftone region 11 was changed. In Reference Examples 5 and 6, the goal is to form a nearby (double) hole pattern of 1.5 μm size on the transfer substrate, similar to Example 1.

[0073] Optical simulations of transfer performance were also performed for Reference Examples 5 and 6 in the same manner as in Example 1. The evaluation items in the optical simulations were the same as in Example 1. The results of the optical simulations are shown in Figure 11. In addition, the cross-sectional shapes of the resist patterns formed on the transfer substrate in Reference Examples 5 and 6 are shown in Figures 9(b) and 10(b), respectively.

[0074] Reference Example 5 uses a phase-shift film with a transmittance of 8% (based on an exposure light wavelength of 334 nm) for the halftone region 11. Simulation results show no particular problems with the DOF value or the cross-sectional shape of the resist pattern, but almost no reduction in the required exposure amount is achieved.

[0075] Furthermore, in Reference Example 6, when the transmittance of the phase-shift film in the halftone region 11 (based on a wavelength of 334 nm) was set to 25%, no particular problems were observed with exposure, DOF, or MEEF. However, as shown in Figure 10(b), the partition walls 13 between the hole patterns could not be sufficiently formed in the cross-sectional shape of the resist pattern.

[0076] Therefore, it is preferable that the transmittance of the halftone region 11 in a double-neighboring-hole pattern be smaller than that shown in Reference Example 6 (specifically, 22% or less), while in an isolated-hole pattern, it is considered that a transmittance of about 25% as shown in Reference Example 6 may be perfectly usable for practical purposes.

[0077] The photomasks of the present invention, as exemplified by the first photomask 10, the second photomask 20, etc., can be manufactured using a lithography process. That is, they can be manufactured using a photomask blank in which a phase-shift film is deposited on the main surface of a substrate made of a transparent material such as quartz. When forming the phase-shift film on the transparent substrate, known means such as sputtering can be used. This phase-shift film (forming the halftone region 11) is, for example, designed to have a phase inversion effect in the mid-ultraviolet wavelength range. Then, a desired patterning is performed on this phase-shift film based on the device to be obtained.

[0078] There are no particular restrictions on the material of the phase-shift film applied to the first photomask 10 and the second photomask 20. For example, transition metal silicides are preferably used. For example, molybdenum silicide (MoSi) and its compounds (MoSiO, MoSiN, MoSiC, MoSiON, MoSiCN, MoSiCO, MoSiCON, etc.) are desirable.

[0079] Alternatively, the material of the phase-shift film may be chromium (Cr) or a compound thereof (CrO, CrN, CrC, CrON, CrCN, CrCO, CrCON, etc.).

[0080] Furthermore, examples of materials for phase-shift films include those containing Ta (tantalum), Zr (zirconium), or Ti as metallic components (e.g., Zr silicide, silicide containing Mo and Zr), or compounds thereof (oxides, nitrides, carbides, etc., as listed above).

[0081] In this embodiment, the first photomask 10 and the second photomask 20 were simulated assuming the use of a MoSi compound for the phase-shift film. The thickness of this phase-shift film can be 100-200 nm and can be formed by known deposition methods such as sputtering. Furthermore, while either dry etching or wet etching may be used for patterning the phase-shift film, wet etching may be advantageous for large photomasks used in the manufacture of display devices.

[0082] In the first photomask 10 and the second photomask 20 described above, a phase-shift film that inverts the exposure light in the mid-ultraviolet region was used in the halftone region 11. However, photomasks with different configurations can also be used. For example, the halftone region 11 may use a semi-transparent film with a transmittance T (e.g., 10% ≤ T ≤ 35%) to the exposure light, which has substantially no phase inversion effect. Substantially no phase inversion effect means that the phase shift amount with respect to the reference wavelength λ1 is 90 degrees or less, preferably 60 degrees or less. On the other hand, the light-transmitting portion 12 that constitutes the mask hole pattern can be formed as a recessed portion in which the surface of the transparent substrate is recessed by a predetermined thickness. This makes it possible to set the phase difference θ between the light-transmitting portion 12 and the halftone region 11 to approximately 180 degrees (or exactly 180 degrees), and the effects of the present invention can be obtained even with such a photomask.

[0083] Furthermore, an additional film (such as a reflection control film or an etching prevention film) may be formed on the transparent substrate of the photomask described above, to the extent that it does not impair the effects of the present invention.

[0084] The present invention includes a method for manufacturing a display device using the above-described photomask. Here, the term "display device" includes the devices that constitute the display device.

[0085] For exposure in the present invention, a projection exposure apparatus that performs 1:1 or reduced exposure with an NA of approximately 0.08 to 0.20 can be used. The NA can preferably be 0.08 to 0.18, and more preferably 0.08 to 0.15.

[0086] The illumination system of the exposure apparatus can use normal illumination. Alternatively, a different type of illumination may be used, namely modified illumination (where the normally incident component is removed from the light incident on the photomask).

[0087] In recent high-resolution OLED (organic light-emitting diode) display circuits, the increased resolution of the circuits has led to a greater need for transfer patterns with two or more adjacent hole patterns. The photomask according to the present invention addresses these new technological challenges.

[0088] Although embodiments of the present invention have been specifically described above, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. [Explanation of Symbols]

[0089] 10. First Photomask 11 Halftone Range 12 Translucent part 13 Division wall 14 Shading area 20. Second Photomask

Claims

1. A photomask for manufacturing a display device for forming a hole pattern on a transfer surface using mid-ultraviolet exposure light, A transparent substrate is provided with a phase-shift film having a transfer pattern, The transfer pattern is a light-transmitting portion in which the transparent substrate formed by patterning the phase-shift film is exposed, and includes a mask hole pattern for forming the hole pattern. With respect to the light of a reference wavelength λ1 contained in the mid-ultraviolet exposure light for exposing the photomask, the phase difference θ between the light-transmitting portion and the phase-shift film is within the range of 180 ± 15 degrees. The transmittance T of the phase-shift film with respect to light at the reference wavelength λ1 is 10% ≤ T ≤ 35%. The numerical aperture (NA) of the projection optical system of the exposure apparatus using the aforementioned photomask is 0.08 or more and 0.20 or less. The aforementioned mid-ultraviolet exposure light has an intensity peak at a wavelength of 334 nm, and also has an intensity peak at one or more wavelengths among 313 nm and 365 nm. The reference wavelength λ1 is 334 nm. Photomask.

2. A photomask for manufacturing a display device for forming a hole pattern on a transfer surface using mid-ultraviolet exposure light, A phase-shift film having a transfer pattern is provided on a transparent substrate. The transfer pattern is a light-transmitting portion in which the transparent substrate formed by patterning the phase-shift film is exposed, and includes a mask hole pattern for forming the hole pattern. With respect to the light of a reference wavelength λ1 contained in the mid-ultraviolet exposure light for exposing the photomask, the phase difference θ between the light-transmitting portion and the phase-shift film is within the range of 180 ± 15 degrees. The transmittance T of the phase-shift film with respect to light at the reference wavelength λ1 is 10% ≤ T ≤ 35%. The numerical aperture (NA) of the projection optical system of the exposure apparatus using the aforementioned photomask is 0.08 or more and 0.20 or less. The aforementioned mid-ultraviolet exposure light has intensity peaks at two or more wavelengths among 313 nm, 334 nm, and 365 nm, and does not include wavelengths exceeding 400 nm. The reference wavelength λ1 is 313 nm or 334 nm. Photomask.

3. The photomask according to claim 1 or 2, wherein the transfer pattern includes an isolated hole pattern which is an isolated mask hole pattern.

4. The photomask according to any one of claims 1 to 3, wherein the transfer pattern has two or more proximity hole patterns which are the mask hole patterns located in close proximity.

5. The photomask according to claim 4, wherein the distance between the centroids of two mask hole patterns included in the proximity hole pattern is 2 μm or more and 9 μm or less.

6. The photomask according to claim 5, wherein the shortest distance between the edges of the two mask hole patterns is 0.5 μm or more and 2.0 μm or less.

7. The photomask according to any one of claims 1 to 6, wherein the size Dm of the mask hole pattern is 3.5 μm or less.

8. A method for manufacturing a display device, A step of preparing a photomask according to any one of claims 1 to 7, The method includes an exposure step in which an exposure apparatus having a projection optical system with a numerical aperture (NA) of 0.08 or more and 0.20 or less is used to expose the photomask with mid-ultraviolet exposure light. The aforementioned mid-ultraviolet exposure light includes a wavelength range where the wavelength λ satisfies 200 nm ≤ λ ≤ 400 nm, and does not include wavelengths where λ > 400 nm and λ < 200 nm. The reference wavelength λ1 of the mid-ultraviolet exposure light is 313 nm or 334 nm. A method for manufacturing a display device.

9. The method for manufacturing a display device according to claim 8, wherein the exposure step forms the hole pattern of size Dp (0.5 μm ≤ Dp ≤ 3 μm) on the transfer object.

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