JP5310999B2 - Halftone photomask and color filter substrate manufactured using the same - Google Patents

Description

  The present invention relates to a color filter substrate provided with photo spacers and alignment control protrusions for maintaining a distance between substrates opposed to a liquid crystal display device.

  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, but the tilt direction is rotationally symmetric for each pixel when viewed from the observation direction. 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 that at least the development process and later be made common. 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 and simultaneously form PS and alignment control protrusions (hereinafter simply referred to as “protrusions”), it is necessary to irradiate different 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, exposure with a half-tone photomask that can be exposed at the same time by arranging a semi-light-shielding film (half-tone film) that can adjust the amount of transmitted light without forming a fine mosaic pattern is possible. This 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, we created a halftone photomask premised on the use of a positive resist and tried to form PS and protrusions in a batch by proximity exposure (proximity exposure) method. In spite of the fact that the resist is difficult to dissolve, there is a problem that another projection added to the projection portion and having a line width of about 12 μm or less elutes and the resolution is hardly resolved. I understood it. Accordingly, the problem of the present invention is that, even when protrusions having different heights and protrusions having different line widths coexist by proximity exposure (proximity exposure) method, protrusions having a line width of 12 μm or less are present. It is an object of the present invention to provide a halftone photomask capable of stably forming photo spacers and alignment control protrusions, including the case where it is included. It is another object of the present invention to provide a color filter substrate having photo spacers and alignment control protrusions produced by exposure and development using this photo mask.

In order to achieve the above object, the invention of claim 1 uses a positive resist, and a photolithographic method using a proximity exposure method, and a photo spacer and an orientation composed of main ribs and branch ribs having different line widths. In the halftone photomask used when forming the control protrusions on the color filter substrate by batch formation, the portion corresponding to the photospacer of the halftone photomask is a light-shielding portion for light transmission , and the rib and a semi-shielding portion corresponding to the branch rib of the alignment control projection consisting of a narrow branch rib line width than the ribs for optical transparency, seen including a portion of the light blocking during said portion of the semi-shielding, the branch rib The halftone photomask is characterized in that the light shielding portion is formed in a groove shape at the center of the semi-light-shielding portion .

  With such a halftone photomask, it is possible to induce interference of light transmitted through the semi-transmissive part and the full-transmissive part, and to vary the intensity of the transmitted light for each location of the exposed part.

Further, such a halftone photomask is suitable for forming a linear alignment control protrusion.

The invention of claim 2 is a color filter substrate, wherein the billing using a halftone photo mask according to claim 1, equipped with a photo-spacers and the alignment control projection is formed by simultaneously forming by photolithography .

According to a third aspect of the present invention, there is provided the color filter substrate according to the second aspect, further comprising an alignment control protrusion having a line width of 12 μm to 5 μm.

  According to the present invention, when a photospacer and alignment control protrusions are formed in a batch by combining a halftone photomask and proximity exposure (proximity exposure), the height is lower than the photospacer and the line width is 12 μm. It is possible to stably form alignment control protrusions that are less than or equal to the extent. As a result, a color filter substrate having protrusions excellent in gap control and liquid crystal alignment control can be provided.

  An example of the shape of the alignment control protrusion 31 that is the subject of the present invention is shown in FIG. Here, 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. Yes. In FIG. 3, 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). The basic unit constituting the zigzag pattern is a long and narrow rectangle (hereinafter simply referred to as “straight line”) in a plan view, a substantially square shape in a sectional view, and ideally an isosceles triangle. On the other hand, the branch ribs are linear in a plan view and ideally a trapezoidal shape in a cross-sectional view. However, if the line width is narrow, a complicated shape may be formed or resolution may not be possible. If the line width of this rib is 10 to 15 μm, the branch rib is set to have a line width narrower than that of this rib, and is 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 terms of its function, it is preferable that it is thin, but a certain height is necessary. Since the purpose is to develop a photomask structure for improving the resolution of the branch rib portion having a line width of about 12 μm or less, the semi-transparent solid pattern shown in FIG. 2A is shown as a mask pattern corresponding to this portion. The pattern shown in FIG. 5B having a straight line 21 and a total light-shielding groove 22 (hereinafter also referred to as “slit”) at the center was formed, and the resolution was compared in the examples. However, in the present invention, the line width to be formed is a problem, and the distinction between the ribs and the branch ribs is not important, and should be applied only to the formation of alignment control protrusions having two types of line widths. It is not a thing. A plurality of protrusions having one type or three or more types of line widths may be mixed.

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

  Hereinafter, the content of the present invention will be described in detail based on examples.

<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. This is because 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.

The zigzag pattern 33 is a core part for controlling the liquid crystal alignment called the main rib. The additional part 33 extends in parallel or perpendicularly from the bent part of the zigzag, and the branch rib 32 having a narrower line width than the main rib. It is a part called. The branch rib 32 serves as a bank for suppressing the flow of the nematic liquid crystal sealed in the substrate, and the line width is set to about 6,70% of the rib. In terms of its function, it is preferable that it is thin, but a certain height is necessary. In FIG. 3, the size of the display pixel 34 is indicated by an alternate long and short dash line in order to indicate the relative size of the alignment control protrusion 31. In general, a plurality of protrusions cross a pixel, but in this embodiment, only one is illustrated (Patent Document 4).

  First, a transparent substrate 1 on which a low reflective chromium film 2 (hereinafter referred to as Cr) 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 in order to form a PS mask pattern and a light shielding pattern for the slit portion. Thereafter, development was performed for 80 seconds using a TMAH solution (low-concentration tetramethylammonium hydroxide solution) of an organic alkali developer, and the resist other than the resist pattern for PS and the light shielding part pattern was removed (FIG. 1B, ( b ′)). 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 PS Cr pattern 6 and the slit light shielding part pattern 6 'were formed (FIGS. 1C and 1C').

  Next, chromium oxide (CrO) as a semi-permeable film material 4 (hereinafter referred to as a half film) is formed on the transparent substrate 1 by a sputtering method to 18.2 nm, and then a novolac positive type is again formed thereon. Resist 3 ′ was coated and pre-baked at 90 ° C. for 10 minutes (FIGS. 1D and 1D ′). Next, pattern drawing was performed again using a krypton laser drawing 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 alignment control semi-shielding portion (FIGS. 1E and 1E). ')). 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 a desired light shielding pattern 6, 6 A desired photomask having a semi-light-shielding pattern 5 was obtained (FIG. 1 (f), (f ′)).

  In the semi-light-shielding pattern portion for forming the branch ribs (FIGS. 2A and 2B), in order to investigate what size the branch rib is resolved, the semi-light-shielding portions having different dimensions are used. Arranged the pattern. As for the linear pattern (FIG. 2A) which is semi-shielded as a whole, a line width W of 5 μm to 13 μm was provided every 2 μm, and the length was 30 μm. For the pattern (FIG. 2B) in which the light shielding slit 22 is provided at the center, the line width W ′ is 1 to 5 μm, and the slit width L is 2 μm and 3 μm, so that comparison can be made. did.

  In addition, the ultraviolet transmittance of 365 nm (i line) and 405 nm (g line) of the CrO half portion having a thickness of 20 nm was 22.4% and 21.8%, respectively, with respect to the transparent substrate.

<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 alkali-free glass having a thickness of 0.7 mm (for example, OA-2: Nippon Electric Glass Co., Ltd.) by a spin coating method. Then, a light-shielding layer having a width of 14 μm and a height of 1.3 μm is formed by performing patterning processing such as exposure and development, and heat treatment.

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.

<Branch rib formation>
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, through the photomask having a plurality of branch rib patterns, the gap is set to 100 μm with respect to the photoresist layer on the color filter substrate so that the exposure amount is 50 mJ at a wavelength of 365 nm and an illuminance of 17 mW. Proximity exposure (proximity exposure) was performed. 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 obtain a PS and alignment control projection resist pattern on the color filter substrate.

<Resolution evaluation>
When each part of the substrate was observed with a microscope, no loss of pattern or poor resolution was found with respect to PS and main ribs, and the thickness and width were as expected. However, a difference in resist shape depending on the design dimension was found for the branch rib portion having a narrow line width. First, in the linear pattern without the light-shielding slit (FIG. 2A), the resist pattern formed from the design line width of the photomask is formed thicker. For the case with the light shielding slit (FIG. 2B), when the design dimension (the total width of the semi-transmissive portion 21 and the light shielding slit 22) is smaller than 9 μm, the obtained resist pattern line width is wider, and the design line width is larger. On the other hand, when the thickness was 11 μm or more, it was formed narrow. Further, when the width L of the light-shielding slit is compared with 2 μm and 3 μm, the line width of the obtained resist pattern is wider when the design dimension is 9 μm or less, but 3 μm is wider when the design dimension is 11 μm or more. Regarding the resist pattern height, the maximum was when the light-shielding width L was 3 μm.

  As a summary, the relationship between the width and film thickness of the formed resist pattern is shown together in FIG. The horizontal axis is the line width of the obtained resist pattern, the vertical axis is the height (film thickness), and the unit is μm. In the figure, ■ represents the result corresponding to the light shielding width L = 3 μm, □ represents L = 2 μm, and ▲ represents only the semi-light-shielding portion (L = 0 μm). From this figure, it is clear that when the finished line width of the branch rib is about 12 μm or less, a branch rib having a higher height can be obtained with the light shielding slit. The resolution was clearly better with slits.

  The above experimental result can be explained by the interference of light transmitted through the semi-shielding portion. This is probably because the light intensity on the resist at the portion corresponding to the central portion of the slit was weakened by the interference. This result was expected from the result of optical simulation of proximity exposure.

  From the above results, it was proved that the resolution was improved when the light-shielding slit was provided in the semi-light-shielding opening, and it was found that the relationship between the line width and the film thickness could be adjusted fairly freely by providing the light-shielding film.

(A)-(f) The figure explaining the manufacturing process of the pattern for photo spacers in a photomask, (a ')-(f') The figure explaining the manufacturing process of the pattern for photo spacers in a photomask, (A) The schematic diagram which shows an example of the transflective pattern for branch rib formation, (b) The schematic diagram which shows an example of the translucent pattern containing the light shielding slit for branch rib formation. The figure which illustrates typically the processus | protrusion for orientation control which consists of a zigzag main rib and a branch rib. The figure explaining the experimental result which investigated the relationship between the height (film thickness) of a branch rib, and the line width about the presence or absence of a slit.

Explanation of symbols

1. Transparent substrate 2, light shielding film 3, 3 'positive resist 4, semi-light-shielding layer 5, semi-light-shielding pattern (branch rib portion)
6. Shading pattern (PS)
6 ', light-shielding slit 21, semi-light-shielding pattern (main rib and branch rib part)
22, groove (slit) portion 31, orientation control protrusion 32, branch rib 33, main rib 34, pixel

Claims (3)

Using the positive type resist, formed by a photolithographic method using a proximity exposure method, in bulk form photo spacers and the alignment control projection consisting of the rib and the branch rib having different line widths on the color filter substrate In the half-tone photomask used for the alignment, the portion corresponding to the photo spacer of the half-tone photomask is a light-shielding portion for light transmission , and the alignment control is composed of the main rib and the branch rib having a line width narrower than the main rib . portions corresponding to the branch rib projections a semi-shielding the light transmittance, viewing including the site of the light-shielding during said portion of the semi-light,
The half-tone photomask according to claim 1, wherein the branch rib light-shielding portion is formed in a groove shape in the center of the semi-light-shielding portion . 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 . The color filter substrate according to claim 2 , further comprising an alignment control protrusion having a line width of 12 μm to 5 μm.