JP2002196300A - Liquid crystal coating applicator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably hold substrates to be coated with liquid crystals without the occurrence of uneven temperature and distortion with a liquid crystal coating applicator by a spin coating method. SOLUTION: A chucking table 12 of the liquid crystal coating applicator 10 has a substrate supporting surface 12A of the same shape and size as those of the substrate 16 to be coated and this substrate supporting surface 12A is provided with attraction holes 18 in the segments where outer periphery edges 16A of the substrate 16 are attracted. In addition, the substrate supporting surface 12A is formed as a flat surface and the substrate 16 is attracted and held by negative pressure only at the outer periphery edges 16A of the substrate in the tight contact state of the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal coating apparatus for applying liquid crystal to a substrate in a manufacturing process of a liquid crystal display device or the like.

[0002]

2. Description of the Related Art Liquid crystals are sensitive to temperature, and even when a uniform thin film is formed, the optical characteristics of a completed liquid crystal layer may become uneven due to temperature unevenness during coating.

[0003] This will be described in detail.

[0004] Liquid crystal materials have a self-integrating ability and are known as materials that spontaneously regulate molecular arrangement. In general,
When a thin film is formed by applying a liquid crystal liquid after applying a rubbing treatment to a polyimide film called an alignment film, liquid crystal molecules near the polyimide film interface are aligned according to the alignment force of the alignment film, and alignment control is performed on the entire liquid crystal layer. I'm trying to get Microscopically, individual liquid crystal molecules have some degree of variation, but a liquid crystal film having a uniform molecular arrangement is formed in the entire liquid crystal layer, and a film having characteristics as one optical element is obtained.

The optical characteristics of a liquid crystal as an optical element include birefringence and circular dichroism, which differ depending on the type of liquid crystal phase.

The above characteristics are exhibited by the regular arrangement of liquid crystal molecules. However, depending on the film thickness, the temperature, the state of the interface of the alignment film, and the like, the molecular arrangement is disordered or the regularity is different.

For example, when a nematic liquid crystal is coated on an alignment film to form a thin film, if the film thickness is uneven or the phase is disturbed, the originally transparent nematic liquid crystal film scatters light or has a refractive index. Anisotropy may be non-uniform.

In particular, the cholesteric liquid crystal is a temperature-sensitive material as described above, and the wavelength region of the reflected circularly polarized light changes depending on the temperature when applied to the substrate.

A spin coating method is known in which a liquid crystal is applied on a substrate in a thin film to form a liquid crystal layer.

In this spin coating method, a liquid crystal liquid is spread thinly and uniformly on a substrate while the substrate is held horizontally on a chuck table and rotated in a horizontal plane to form a thin film.

When a liquid crystal solution is applied to a substrate by using a liquid crystal coating device for spin coating as described above, a temperature difference on the surface of the substrate is likely to occur due to the rotation of the substrate.

For example, if the chuck table for holding the substrate horizontally is smaller than the substrate, the portion of the substrate that protrudes from the chuck table is rotated by cutting off the air. When a cholesteric liquid crystal is applied thereto, unevenness occurs in the wavelength region of the reflected circularly polarized light after the thin film is formed, that is, color unevenness occurs.

In the case where a suction hole to which a negative pressure is applied is provided on the chuck base and the substrate is suction-held by the negative pressure,
The temperature of the portion of the substrate located at the suction hole decreases, and therefore the reflection wavelength region of the cholesteric liquid crystal changes only in the portion near the suction hole.

The change in the color (reflection wavelength) of the cholesteric liquid crystal generated as described above is caused by the arrangement of the liquid crystal molecules in the film. The portion where the color has changed once is heated to a temperature at which the cholesteric liquid crystal becomes isotropic. However, since the existing alignment state is not eliminated near the interface with the substrate, there is a problem that the color unevenness is not eliminated even when the liquid crystal is lowered to a temperature showing a cholesteric phase.

On the other hand, for example, Japanese Unexamined Patent Publication No.
As disclosed in Japanese Patent Application Publication No. 88-88, in order to make the temperature of the substrate uniform during spin coating, a heat insulating layer is used between the chuck table and a motor shaft for rotating the chuck table. There is one in which a temperature difference between a portion in contact with the shaft and another portion is not generated.

In order to avoid a decrease in temperature at the suction hole portion, there is an apparatus which supports a substrate by embedding it in a chuck table as disclosed in, for example, Japanese Patent Application Laid-Open No. 6-267836.

Further, there is another type in which the substrate is supported from below by a plurality of pins.

[0018]

However, even if a heat insulating layer is provided between the chuck base and the motor shaft as disclosed in the above-mentioned Japanese Patent Application Laid-Open No. Hei 5-326388, the suction hole portion and the chuck base and the substrate are not provided. Since the heat fluctuation of the contact portion with the substrate is not taken into consideration, there is a problem that the temperature unevenness of the sucked substrate cannot be suppressed.

In the spin coating apparatus disclosed in Japanese Patent Application Laid-Open No. 6-267836, the substrate is held without suction, so that the substrate may not completely adhere to the chuck table. However, there is a problem that a temperature difference occurs between a portion of the substrate that is in contact with the chuck table and a portion that is not, and further, when the substrate is distorted during rotation, the thickness of the applied liquid crystal becomes uneven. .

Further, in the spin coating apparatus in which the substrate is supported by the plurality of pins, the temperature on the entire back side of the substrate (excluding the portion in contact with the tips of the pins) becomes uniform, but the substrate is If the substrate is thin because it is only placed on a plurality of pins, the substrate may be distorted during rotation, and the thickness of the applied liquid crystal may be uneven. In addition, there is a problem that the substrate may be detached from the chuck table or damaged during rotation.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has a rotation coating apparatus capable of holding a substrate by suction and uniformly applying liquid crystal without causing temperature unevenness. The purpose is to provide.

[0022]

SUMMARY OF THE INVENTION The present invention comprises a horizontal substrate supporting surface and a chuck base rotatable about a vertical rotation center, and holds the substrate on the substrate supporting surface. In the liquid crystal coating apparatus, in which the liquid crystal is applied to the upper surface of the substrate by rotating about the rotation center in the state, the substrate support surface of the chuck table is flat and has a size equal to or larger than that of the substrate to be held. The above object is achieved by a liquid crystal coating device having a surface.

Further, in the liquid crystal coating apparatus, a suction hole to which a negative pressure for sucking the substrate is applied is provided in a portion of the substrate supporting surface corresponding to an outer peripheral portion of the substrate to be held. It may be.

Further, in the above-mentioned liquid crystal coating apparatus, the suction hole may be located inward from a position corresponding to an outer peripheral edge of the substrate.
It may be arranged in a range within mm.

In the present invention, since the chuck table for holding the substrate has the same shape or a size larger than that of the substrate and the support surface of the substrate is a flat surface, a part of the substrate is formed. It does not protrude from the chuck table and does not contact the chuck table unevenly.

Furthermore, since only the outer peripheral edge portion of the substrate is adsorbed, there is no temperature unevenness on the adsorbed substrate, and the liquid crystal is uniformly and stably fixed by the adsorption. It can be applied safely.

In addition, in the case of ordinary spin coating, liquid crystal pools are formed on the outer peripheral edge of the substrate, so that the film thickness becomes too thick and becomes a defective portion. Since the peripheral portion is sucked by the suction holes, color unevenness does not occur in the effective portion of the applied liquid crystal even when the temperature is reduced due to the negative pressure.

[0028]

Embodiments of the present invention will be described below in detail with reference to the drawings.

As shown in FIG. 1, a liquid crystal coating apparatus 10 according to an embodiment of the present invention has a horizontal substrate support surface 12A and rotates in a horizontal plane about a vertical spindle 14. A liquid crystal is applied to the upper surface of the substrate 16 by rotating around a rotation center which is the center axis of the spindle 14 while holding the substrate 16 on the substrate support surface 12A. It is like that.

The substrate support surface 1 of the chuck table 12
2A is a flat surface having the same size as the substrate 16, and a plurality of suction holes 18 are formed along the outer peripheral edge 13 of the substrate support surface 12A.

The plurality of suction holes 18 are provided on the substrate support surface 12.
When the substrate 16 is sucked onto A, the outer peripheral portion 16A of the substrate 16 can be sucked.

More specifically, the suction holes 18 are arranged so as to suck a rectangular frame-shaped invalid area 17 within 2 mm from the outer peripheral edge of the substrate 16.

The ineffective area 17 is an area in which, when a liquid crystal is applied to a substrate by a spin coating method, the liquid crystal flows to the outer peripheral portion by the rotation of the substrate and rises, so that effective optical characteristics cannot be obtained. .

A reference numeral 20 in FIGS. 1 and 2 denotes a negative pressure passage formed in the chuck base 12 for supplying a negative pressure to the suction hole 18.

The substrate 1 is formed by the liquid crystal coating apparatus as described above.
When applying liquid crystal to the substrate 6, the substrate 16 is
A is placed on A so that its shape matches, and a negative pressure is applied to the suction hole 18 from the negative pressure passage 20.

As a result, the substrate 16 is placed on the substrate support surface 12A.
The temperature of the outer peripheral edge 16A of the substrate 16 held stably is reduced by the application of a negative pressure to the suction hole 18, but this portion is, as described above, the film thickness of the liquid crystal. Is an invalid area 17 that cannot be controlled, so that there is no problem even if the temperature drops.

Since the substrate support surface 12A is a flat surface and the substrate 16 is held in close contact with the substrate support surface 12A, there is no occurrence of temperature unevenness due to uneven contact between the two.

In the liquid crystal coating apparatus 10 according to the above embodiment, the substrate supporting surface 12A has the same size as the substrate 16, but the present invention is not limited to this. Any material can be used as long as it can adsorb the outer peripheral edge of the substrate by a negative pressure and can adhere the substrate to the substrate supporting surface.

Accordingly, for example, as shown in FIG. 3, the substrate supporting surface 22A having a shape larger than the substrate 16 to be sucked.
May be constituted.

[0040]

EXAMPLE (Example 1) First, a chuck base similar to that in the liquid crystal coating apparatus shown in FIG. 1 was prepared. The chuck base of the present invention is dedicated to a glass substrate of 100 mm × 100 mm × 0.7 mm, and has the same shape as the glass substrate.
The suction holes are arranged on the outer peripheral portion of the substrate (within 2 mm from the end), and all the glass substrate surfaces other than the suction holes can be in close contact with the chuck table.

Here, Delrin was used as the material of the chuck table. A glass substrate of 100 mm × 100 mm × 0.7 mm is provided with an alignment film for aligning cholesteric liquid crystal. The alignment film was obtained by subjecting a polyimide thin film to a rubbing treatment, and the thickness of the polyimide film was 100 nm.

The cholesteric liquid crystal solution was prepared by dissolving the cholesteric liquid crystal in toluene to 33 wt%. Cholesteric liquid crystals include nematic liquid crystal monomers with a chiral agent added, and polymer cholesteric liquid crystals.
Any liquid crystal having a cholesteric phase at any temperature may be used.

The glass substrate was fixed to the chuck table by vacuum suction. The glass substrate has the same shape as the chuck table, and the chuck table and the entire back surface of the glass substrate are in close contact with each other. However, the depressurized air is in contact with the suction holes located at the outer peripheral portion. Next, a cholesteric liquid crystal solution was dropped on the substrate, and the chuck table was rotated. The spin coating condition was 1000 rpm × 15 sec.

After the application, the glass substrate was heated to 90 ° C. on a hot plate to completely remove the solvent, and a cholesteric liquid crystal layer having a uniform reflection color was entirely formed on the surface of the glass substrate other than the outer peripheral portion (except for the adsorption holes). A film could be formed.

Comparative Example 1 A comparative experiment was performed with a conventional liquid crystal coating apparatus. Chuck table 1 in this liquid crystal coating device
Has a circular shape smaller than the substrate size as shown in FIG. 4, and the suction holes 2 are also arranged on the entire substrate supporting surface. The material is Delrin. Using this chuck table 1, a cholesteric liquid crystal was formed under the same cholesteric solution as in Example 1, under the same rotation conditions and drying conditions.

As a result, a cholesteric film was formed in which the shape of the chuck table and the trace of the suction hole were clearly left, unlike the case where the film was formed by the liquid crystal coating apparatus according to the present invention shown in Example 1. The portion of the glass substrate having the suction holes and the portion not in contact with the chuck table had a blue-green reflection color, and did not exhibit the original blue reflection color.

Table 1 shows the results of measuring the temperature distribution of the glass substrate before and after spin coating using a non-contact type thermometer.

[0048]

[Table 1]

Before the application, the temperature of the center part and the end part (the part where the glass substrate and the chuck base are not in contact with each other in the case of the conventional chuck base) of the chuck base of the present invention and the conventional chuck base are the same at 21 ° C. there were. Next, the cholesteric solution was dropped, and the temperature was measured after spin coating. In the liquid crystal coating apparatus of the present invention, the temperature of the substrate was 20 ° C. at both the center and the ends, and although the temperature was lower than before coating, No temperature unevenness occurred in the substrate. On the other hand, in the conventional liquid crystal coating apparatus, the temperature at the center of the substrate after coating is 20 ° C., whereas the temperature at the end of the substrate where the glass substrate is not in contact with the chuck base is 19 ° C. Temperature difference occurred.

(Comparative Example 2) Further, when an experiment was conducted in the same manner as in Comparative Example 1 using an acetone solution instead of a toluene solution as a cholesteric solution, as shown in Table 2, the liquid crystal coating apparatus of the present invention showed a temperature difference. However, in the conventional liquid crystal coating apparatus, the center of the substrate was 17 ° C. and the end was 15 ° C.
Further, the temperature difference became large.

[0051]

[Table 2]

Example 2 A nematic liquid crystal solution was prepared by dissolving a nematic liquid crystal in toluene to a concentration of 20 wt%.

The chuck base shown in FIG. 1 was mounted on the spin coating apparatus, and the glass substrate was fixed by vacuum suction. The glass substrate has the same shape as the chuck table, and the chuck table and the entire back surface of the glass substrate are in close contact with each other. However, the depressurized air is in contact with the suction holes located on the outer peripheral portion. Next, a nematic liquid crystal solution was dropped on the substrate, and the chuck table was rotated. Spin coating condition is 1000rpm × 15se
c.

After the application, the glass substrate was heated to 80 ° C. on a hot plate to completely blow off the solvent. An optically uniform nematic liquid crystal layer was formed on the surface of the glass substrate other than the outer peripheral portion (other than the adsorption holes). A film could be formed. Similar results were obtained with discotic liquid crystals and smectic liquid crystals.

[0055]

According to the present invention, liquid crystal can be applied while holding and rotating the substrate without causing temperature unevenness or distortion, so that a uniform liquid crystal without color unevenness can be obtained. It has an excellent effect that a thin film can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a liquid crystal coating apparatus according to an embodiment of the present invention as a partial cross section.

FIG. 2 is an enlarged plan view showing a part of a substrate supporting surface of the liquid crystal coating apparatus.

FIG. 3 is a perspective view showing a liquid crystal coating apparatus according to another embodiment.

FIG. 4 is a plan view showing an example of a chuck base of a conventional liquid crystal coating apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Liquid crystal coating device 12, 22 ... Chuck table 12A, 22A ... Substrate support surface 13 ... Outer edge 14 ... Spindle 16 ... Substrate 16A ... Outer edge 17 ... Invalid area 18 ... Suction hole 20 ... Negative pressure passage

Claims (3)

[Claims] A chuck base having a horizontal substrate support surface and rotatable around a vertical rotation center;
In a liquid crystal coating apparatus that rotates around the rotation center while holding the substrate on the substrate support surface to apply liquid crystal to the upper surface of the substrate, the substrate of the chuck table that holds the substrate support surface A liquid crystal coating device characterized by having a flat surface having the same shape or larger size. 2. The method according to claim 1, wherein a portion of the substrate support surface corresponding to an outer peripheral edge of the substrate to be held is provided.
A liquid crystal coating apparatus, comprising: a suction hole to which a negative pressure for sucking the substrate is applied. 3. The liquid crystal applicator according to claim 2, wherein the suction holes are arranged within a range of 2 mm inward from a position corresponding to an outer peripheral end of the substrate.