JP2010008532A - Half tone photomask and color filter substrate produced by using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of occurrence of a recess or recesses in the cross section in one or two parts of the central region dependently on line width of a projection for orientation control when a photospacer and the projection for orientation control are collectively formed via a proximity exposure method by using a half tone photomask. <P>SOLUTION: In the half tone photomask, a region corresponding to a photospacer has light shielding properties as to light transmittance, while a region corresponding to a projection for orientation control has half light shielding properties as to light transmittance and has a phase difference of 45 degrees or less. The color filter substrate has the photospacer and the projection for orientation control collectively formed via a photolithography method by using the half tone photomask. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a photo spacer for maintaining a distance between substrates opposed to a liquid crystal display device and a halftone photo mask for forming alignment control protrusions.

  A liquid crystal display device holds liquid crystal between a pair of substrates. Because the distance between substrates (hereinafter referred to as the cell gap) needs to be maintained accurately over the entire surface as the liquid crystal display device becomes larger, photolithography technology from the conventional method of spraying beads made of resin or glass into the liquid crystal The method has shifted to a method of forming columnar protrusions. Protrusions made of a resist material formed on a substrate by photolithography technology, so-called photo spacers (hereinafter also referred to as “PS”), have a high degree of freedom in arrangement, uniformity in height, It has many advantages over the bead spraying method, such as not moving, and is less contaminated in the process, and is usually disposed on the color filter layer on the color filter substrate side (see Patent Document 1).

  In addition, a large liquid crystal display device is desired to have a high viewing angle so that the color tone is the same when viewed from any direction, but this is not easy due to the geometric anisotropy of liquid crystal molecules. . In order to reduce the viewing angle dependency, the liquid crystal molecules as a whole must have a rotational symmetry in the orientation of the liquid crystal as viewed from the observation direction, rotate within the substrate surface, or have certain restrictions on the alignment state. As well-known alignment control techniques, IPS (In plane switching mode) and VA (Vertical alignment mode) are adopted.

  The liquid crystal alignment required in the VA method is difficult in the bead dispersion method, and the movement of the liquid crystal molecules is usually controlled by forming linear protrusions on the substrate in contact with the liquid crystal. In other words, the liquid crystal molecules are aligned perpendicular to the substrate surface when no voltage is applied, and when the voltage is applied, the liquid crystal molecules are tilted so as to be parallel to the substrate. In order to force the liquid crystal molecules to be maintained, the slope of the protrusion side is utilized.

  Therefore, the protrusions are formed not only on the PS holding the cell gap but also on the substrate surface in contact with the liquid crystal for the purpose of alignment control. Other than the VA mode, even in the OCB (Optically Compensated Bend) mode, a configuration including protrusions is required to easily transfer liquid crystal molecules from the splay state to the bend state (see Patent Document 2). In the ferroelectric liquid crystal, a resin arranged in a stripe shape is used as a spacer.

When the protrusions require a plurality of functions for controlling the orientation of PS or liquid crystal, protrusions having different heights and shapes are necessary, and it is desirable that they are formed simultaneously. That is, for example, when a PS having a certain height is formed by a regular photolithography method, and projections having different heights are formed again by a photolithography method, it is preferable to share at least the development process and thereafter. Regarding the technology for forming a latent image of multiple protrusions with different heights on a resist, a technology that uses two photomasks to change the amount of exposure light, or a mosaic of minute openings in the light-shielding film An example is disclosed in which a technique for forming two types of latent images on a resist with a single exposure is applied to a VA mode liquid crystal display device by changing the amount of exposure light depending on the difference in aperture ratio (for example, (See Patent Document 3 and Patent Document 4).
Japanese Patent Laid-Open No. 11-242225 Japanese Patent Laid-Open No. 10-20284 JP 2001-201750 A JP 2003-75808 A

  In order to expose the same resist layer to simultaneously form PS and alignment control protrusions (hereinafter also simply referred to as “protrusions”), it is necessary to irradiate the corresponding portions with different amounts of ultraviolet light. Exposure by exchanging the photomask has a problem that it takes time to replace the mask and the productivity is lowered. On the other hand, forming a light-shielding mosaic pattern having a size smaller than that required for PS and protrusions on the photomask is problematic from the miniaturization technique, although it depends on the size of the mosaic. Therefore, if possible, collective exposure using a halftone photomask that can be exposed at the same time by placing a semi-light-shielding film (halftone film) that can adjust the amount of transmitted light without forming a fine mosaic pattern. Is the most preferred embodiment.

  In addition, there are two exposure methods: a projection exposure method and a proximity exposure (proximity exposure) method, but the former has a problem that the cost of the apparatus is higher than the latter, and the time required for the exposure process is long. Proximity exposure (proximity exposure) is desirable.

  Therefore, a half-tone photomask was prepared on the premise of using a positive resist, and when PS and alignment control protrusions were collectively formed by a proximity exposure (proximity exposure) method, the protrusions extended in the direction in which the protrusions extended. Therefore, although a trapezoidal shape or a semi-cylindrical shape in cross section is required, such a shape is not necessarily exhibited. Specifically, it has been found that depending on the line width of the protrusion, the central portion may exhibit a cross-sectional shape that is recessed at one or two places. The shape of the inclined surface of the alignment control protrusion is such that the inclination angle of the inclined surface regulates the liquid crystal alignment. Therefore, if the shape is complicated, a desired liquid crystal alignment cannot be obtained, and the image quality of the liquid crystal display device is deteriorated.

  Therefore, the present invention has developed a photomask that can reduce the unevenness on the surface of the alignment control protrusion and make the shape as close to a trapezoid as possible.

  In order to achieve the above object, a first aspect of the present invention provides a halftone photo used when forming photo spacers and alignment control protrusions on a color filter substrate in a batch by a photolithography method using a proximity exposure method. In the mask, the portion corresponding to the photo spacer of the halftone photomask is light-shielding for light transmission, the portion corresponding to the alignment control protrusion is semi-light-shielding for light transmission, and the phase difference is 45 degrees or less. Is a halftone photomask.

  With such a halftone photomask, it is possible to form protrusions with different heights at the same time, and to induce interference between the light transmitted through the semi-light-shielding part and the total transmission part. By controlling the phase difference, it is possible to vary the transmitted light intensity of the exposed resist portion corresponding to the semi-light-shielding portion fairly freely.

  According to a second aspect of the present invention, there is provided a color filter substrate comprising a photo spacer and an alignment control protrusion formed by batch formation by a photolithography method using the halftone photomask according to the first aspect. .

  Since the exposure intensity at a desired location on the photoresist can be made constant, the photoresist is also uniformly exposed.

When forming the photospacer and the alignment control protrusion by batch formation using the halftone photomask according to the present invention, the height of the phase difference of the halftone portion is set to an appropriate range, which is lower than the photospacer. The cross-sectional shape of the alignment control protrusion can be stably trapezoidal. As a result, a color filter substrate having protrusions excellent in gap control between the substrates and liquid crystal alignment control can be provided, so that a liquid crystal display device using the color filter substrate has excellent image quality.

  An example of the shape of the alignment control protrusion which is the subject of the present invention is shown in FIG. In this figure, the zigzag pattern 33 in plan view called the main rib is a core portion for controlling the liquid crystal alignment, and an additional portion called the branch rib 32 extends in parallel or perpendicularly from the bent portion of the main rib. ing. In FIG. 2, the size of the display pixel 34 is indicated by a one-dot chain line in order to show the relative arrangement of the ribs 33 on the pixel. In general, a plurality of zigzag patterns seem to traverse the pixels, but only one is illustrated in this embodiment (see Patent Document 4).

  Further, if the line width of the main rib is set to about 6 to 16 μm, the branch rib is set to have a line width narrower than that of the main rib and is set to about 6,70%. The angle at which the zigzag bends is normally set to 90 degrees. The branch ribs 32 have functions such as preventing the disorder of the liquid crystal alignment at the edge portion of the pixel electrode and serving as a bank for suppressing the flow of the nematic liquid crystal sealed in the substrate.

  In addition, the meaning of “half” of “semi-light-shielding” in the present invention is not limited to a sufficient transmittance with respect to ultraviolet rays for exposure, a light-shielding rate that is half of a complete light-shielding effect, or a light-shielding rate of an intermediate level. It indicates a range (gray tone) and means that it has a light shielding property or a light transmitting property.

  The basic unit constituting the zigzag pattern is a long and narrow rectangle (hereinafter referred to as a “straight line”) in plan view, but a trapezoidal shape having a long or oblique side is ideal in a cross-sectional view. On the other hand, the branch rib has a linear shape in a plan view, a trapezoidal shape in a sectional view, and ideally a rectangular shape. In either case, depending on the line width, a complicated uneven shape is formed, and in the worst case, the image cannot be resolved. An object of the present invention is to improve the cross-sectional shape of the alignment control protrusions so as to form two or three concavo-convex shapes as schematically shown in FIG. The uneven shape is a kamaboko shape or a trapezoidal shape. Hereinafter, the method is demonstrated based on an Example.

<Halftone photomask>
Since this embodiment is based on the premise that photo spacers and protrusions are formed with a positive photoresist, the photomask is, for example, a regular octagonal light-shielding (non-transmissive) Cr pattern (not shown) for PS. And a semi-light-shielding zigzag pattern 32 as an alignment control protrusion 31 as shown in FIG. 3 and branch ribs 33 added thereto. In a positive photoresist, a sufficiently exposed portion is dissolved by development, and an unexposed portion and an insufficiently exposed portion are not dissolved or only partially dissolved and remain on the substrate as a pattern.

  First, a transparent substrate 1 on which a low reflective chromium 2 (hereinafter referred to as Cr) film having a thickness of 500 mm was formed as a light-shielding material was prepared as a starting substrate for manufacturing a photomask.

  Next, a novolac positive resist 3 was coated on the starting substrate 1 and prebaked at 90 ° C. for 10 minutes (FIGS. 1A and 1A). Next, pattern formation was performed using a krypton laser drawing apparatus having a wavelength of 413 nm for PS light-shielding pattern formation. Thereafter, development was performed for 80 seconds using a TMAH solution (low concentration tetramethylammonium hydroxide solution) of an organic alkali developer to remove the resist other than the resist pattern for PS (FIGS. 1B and 1B '). . Next, the exposed Cr layer was also eluted and removed with an aqueous solution of ceric ammonium nitrate (14.3 mass%) / perchloric acid (5.6 mass%). Thus, the Cr pattern 6 for PS was formed (FIG. 1C).

  Next, chromium oxide (CrO) is formed as a semi-permeable film material 4 (hereinafter also referred to as a half film) on the transparent substrate 1 to a predetermined film thickness by sputtering, and a novolak system is formed thereon again. The positive resist 3 ′ was coated and prebaked at 90 ° C. for 10 minutes (FIGS. 1D and 1D ′). Next, pattern writing was performed again using a krypton laser writing apparatus having a wavelength of 413 nm, and development was performed with a TMAH solution for 80 seconds to form a resist pattern corresponding to the semi-light-shielding portion for orientation control (FIG. 1 (e ′)). . Next, the CrO layer 4 exposed with ceric ammonium nitrate / perchloric acid aqueous solution is eluted and removed, and finally the remaining resist layer is peeled off with a potassium hydroxide solution and further washed to obtain the desired light-shielding pattern 6 and half A desired photomask having a light-shielding pattern 5 was obtained (FIGS. 1 (f) and (f ′)).

(Phase difference characteristics of half film)
The design line widths of the half film portions were 6, 9, 13, and 16 μm, and the former two were arranged in a mask portion corresponding to the branch rib, and the latter two were arranged in the mask portion corresponding to the main rib. By setting the film thickness of CrO to a predetermined film thickness, halftone photomasks X, Y, and Z having the following phase differences were obtained.
Condition X: CrO thickness 600Å 118 (365 nm), 111 (405 nm)
Condition Y: CrO thickness 450 mm 83 (365 nm), 80 (405 nm)
Condition Z: CrO thickness 200 mm 40 (365 nm), 34 (405 nm)
Note that the two numerical values on the right are phase differences with respect to the wavelength in parentheses and the unit is degrees.

<Color filter substrate>
Next, a method for manufacturing a color filter substrate will be described (not shown). First, a black photosensitive resist in which carbon black is dispersed in an acrylic resin is applied to a transparent substrate made of 0.7 mm-thick alkali-free glass (for example, OA-2: manufactured by Nippon Electric Glass Co., Ltd.) by spin coating. The light shielding layer having a width of 14 μm and a height of 1.3 μm is formed by applying, performing a patterning process such as exposure and development, and a heating process.

  Next, a red photosensitive resist in which a dianthraquinone pigment is dispersed in an acrylic resin is applied by a spin coating method, a red photosensitive resist layer is formed, and patterning by an exposure / development method using a predetermined exposure mask is performed. Processing and heat treatment were performed to form red colored pixels having a width of 100 μm and a film thickness of 1.3 μm. Similarly, a green photosensitive resist in which a phthalocyanine green pigment is dispersed in an acrylic resin is applied by spin coating to form a green photosensitive resist layer, and patterning processing such as exposure and development using a predetermined exposure mask Then, heat treatment is performed to form a green colored pixel having a width of 100 μm and a film thickness of 1.4 μm. Similarly, a blue photosensitive resist in which a phthalocyanine blue pigment is dispersed in an acrylic resin is applied by a spin coating method to form a blue photosensitive resist layer, and a patterning process such as exposure and development using a predetermined exposure mask, By performing heat treatment, blue colored pixels having a width of 100 μm and a film thickness of 1.3 μm are formed, and a color filter layer in which red, green, and blue colored pixels are arranged can be obtained.

  Next, an indium oxide-based target was sputtered to form a 150 nm thick transparent conductive film 14 on the colored pixels of the color filter substrate. In this case, an overcoat layer may be provided in advance under the transparent conductive film in order to reduce steps between the colored pixels and prevent impurities from being eluted from the coloring material.

<Projection formation for orientation control>
A positive photoresist (LC1800-21, manufactured by Rohm and Haas Electronic Materials) is coated on the color filter substrate on which the transparent conductive film is formed to a thickness of 2.4 μm, and prebaked at 130 degrees for 100 seconds. Processing was performed to obtain a positive photoresist layer to be PS and an alignment control protrusion.

  Next, in order to form a resist pattern for orientation control, a wavelength of 365 nm is applied to the photoresist layer on the color filter substrate through a photomask whose CrO film thickness conditions are X, Y, and Z. Proximity exposure (proximity exposure) with a gap of 100 μm was performed so that the exposure amount was 50 mJ at an illuminance of 17 mW. Thereafter, development processing was performed for 80 seconds with a 6.3 mass% sodium carbonate aqueous solution. Finally, a post-baking process at 230 ° C. for 20 minutes was performed to form PS and alignment control projection resist patterns X ′, Y ′, and Z ′ on the color filter.

<Resolution evaluation>
The film thickness (height) of the developed resist pattern formed on the substrate was measured using a stylus type film thickness meter. There are three types of cross-sectional shapes found in the resist patterns X ′ and Y ′, and their outlines are shown in FIGS. 3 (a), 3 (b), and 3 (c). The lower case alphabets in FIG. 3 indicate the positions (ae) and width (f) at which the film thickness peaks, and specific numerical values are shown in Tables 1 and 2 below.

  When the phase difference induced by the half film is approximately 70 degrees or more from Tables 1 and 2 and the design line width is as narrow as 9 μm or less, the two resist projections on the bottom of the pan bottom valley or the two peaks on the concave bottom It was a pattern. When the design line width was as thick as 13 μm or more, the pattern was three peaks.

  On the other hand, when the phase difference was approximately 40 degrees under the condition Z ′, no irregularities were found and the shape was substantially trapezoidal (not shown). The thicknesses were 0.34, 1.10, 1.67, and 1.70 μm for the design line widths of 6, 9, 13, and 16 μm, respectively. Further, although details of the results are omitted, a simulation of proximity exposure was performed by setting the width of the half part (semi-light-shielding part) to 5.5 μm and 15 μm, the wavelengths to 365 nm and 405 nm, and the phase difference of the semi-light-shielding part was 90. In the case of the degree, the transmitted light intensity distribution at the center was maximum and minimum on both sides, and increased again. When there was no phase difference, it was found that the transmitted light intensity distribution was such that the transmitted light intensity at the center portion was a pan-bottom valley. By combining these results with the above experimental results, it can be said that when the phase difference of the half portion is set to approximately 45 degrees or less, the alignment control projections without irregularities can be formed.

  As described above, the importance of appropriately setting the phase difference of the semi-light-shielding opening has been demonstrated.

FIGS. 5A to 5F are diagrams illustrating a manufacturing process of a photospacer pattern and an alignment control protrusion in a photomask. FIGS. The figure which illustrates typically the processus | protrusion for orientation control which consists of a zigzag main rib and a branch rib. The figure which represented typically the surface shape of the processus | protrusion for orientation control. (A) two ridges having a pan bottom valley, (b) two ridges having a concave valley, (c) three ridges having a concave valley.

Explanation of symbols

1. Transparent substrate 2, light-shielding film 3, 3 'positive resist 4, semi-light-shielding layer (CrO)
5, semi-light-shielding pattern 6, light-shielding Cr pattern (for photo spacer)
31, alignment control protrusion 32, branch rib 33, main rib 34, and pixel pattern

Claims (2)

  The halftone photomask used when forming the photospacer and the alignment control protrusion on the color filter substrate by batch formation by a photolithography method using a proximity exposure method, corresponds to the photospacer of the halftone photomask. A halftone photomask characterized in that a part is light-shielded with respect to light transmission and a part corresponding to the alignment control protrusion is semi-light-shielded with respect to light transmission and has a phase difference of 45 degrees or less.   A color filter substrate comprising a photo spacer and an alignment control protrusion formed by batch formation by a photolithography method using the halftone photomask according to claim 1.

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