KR20080031589A - Measuring apparatus for rubbing angle of alignment layer and method for measuring rubbing angle by using the apparatus - Google Patents

Abstract

An apparatus for measuring an angle of a rubbing axis of an alignment layer and a method of measuring the angle of the rubbing axis by using the apparatus are provided to form a birefringence material layer on the alignment layer formed on a sample substrate to improve measurement accuracy, thereby producing liquid crystal displays with a high contrast ratio. An apparatus for measuring an angle of a rubbing axis of an alignment layer includes a light source(210) for providing light used for measurement, a polarizer(220) for polarizing the light, an optical phase modulator(230) for controlling a retardation value of the light which passes through the polarizer and a sample substrate(240) which transmits the light having the retardation value controlled by the optical phase modulator and has the alignment layer and a liquid crystal layer formed on the alignment layer, a birefringence material forming unit(250) for forming liquid crystal on the alignment layer, a light-detector(260) for detecting the polarization state of the light which passes through the sample substrate, a detector(270) for detecting the light output from the light-detector and measuring the retardation value and a controller(280) for measuring an angle of the rubbing axis of the alignment layer by using the retardation value and controlling the optical phase modulator.

Description

Apparatus for measuring rubbing axis of alignment layer and measuring method for rubbing axis using same {Measuring Apparatus for Rubbing Angle of Alignment Layer and Method for Measuring Rubbing Angle by using the apparatus}

1 is a view showing a cross section of the measurement sample substrate used in the conventional rubbing axis measurement method.

Figure 2 is a block diagram showing the configuration of a rubbing axis measuring apparatus according to an embodiment of the present invention.

3A and 3B are views illustrating a process of forming a liquid crystal layer having a uniform thickness on a substrate by a spin coating method in a rubbing axis measuring apparatus according to an exemplary embodiment of the present invention.

Figure 4 is a view showing a cross section of the measurement sample substrate used in the rubbing axis measuring method of the present invention.

Fig. 5A is a diagram showing the amount of change Δx ₁ of the x value with respect to the amount of change Δy of the y value when the amplitude is small in the fitting function.

Fig. 5B is a diagram showing an amount of change Δx ₂ of the x value with respect to the amount of change Δy of the y value when the amplitude is large in the fitting function.

Fig. 6 is a diagram showing retardation values and deviations when measuring a rubbing axis using a measurement sample substrate coated with only an alignment film.

FIG. 7 is a diagram illustrating retardation values and deviations when a rubbing axis is measured using a measurement sample substrate coated with an OCB (Optically Compensated Birefringence) type liquid crystal on a uniform thickness.

8A and 8B illustrate a process of forming a liquid crystal layer having a uniform thickness on a substrate by a non-spin coating method in a rubbing axis measuring apparatus according to a second exemplary embodiment of the present invention.

9A and 9B illustrate a process of forming a liquid crystal layer having a uniform thickness on a substrate by a printing method in a rubbing axis measuring apparatus according to a third exemplary embodiment of the present invention.

The present invention relates to a rubbing axis measuring method and a rubbing axis measuring device of an alignment layer, which is one of various measuring methods which are carried out for quality control of a liquid crystal display device

In particular, the present invention relates to measuring a rubbing axis by coating a birefringent material such as liquid crystal on an alignment film of a measurement sample substrate.

In the liquid crystal display (LCD), which is the most representative flat panel display, one of the important quality standards required is to secure a high contrast ratio (CR).

The contrast ratio is a value obtained by dividing the luminance in the full white state by the luminance in the full black state, and the luminance in the full black state is sensitive to the contrast ratio.

In order to achieve a high contrast ratio, the LCD needs to implement a full full black state. In order to realize a full black state, it is important to control the rubbing axis of the LCD. That is, the rubbing axis measurement of the alignment layer is one of important measurements for quality control of the liquid crystal display device.

1 is a view showing a cross section of a measurement sample substrate used in a rubbing axis measuring method of a conventional alignment film.

The measurement sample substrate used in the conventional rubbing axis measurement method of the alignment layer is characterized in that the alignment layer 120 is coated on one side of the substrate 110 as shown in FIG.

The substrate 110 generally uses a glass substrate on which no other layer is formed, or a transparent substrate on which a transparent metal such as indium tin oxide (ITO) or indium zinc oxide (IZO) is deposited on the glass substrate. The substrate on which this is formed or the substrate on which the thin film transistor is formed can also be used.

In the rubbing axis measuring method of the conventional alignment film, the retardation of light transmitted through the measurement sample substrate on which the alignment film is coated is measured, and the angle of the rubbing axis of the alignment film was measured using the retardation value.

However, the rubbing axis measurement method of the conventional alignment film has the following problems.

Since the retardation value of the light by the alignment layer has a small value of about 0.2 nm, it may be caused by an error that the measurement sample substrate is distorted when the measurement sample substrate is fixed, or by cutting at an angle when cutting the measurement sample substrate from the original glass. In contrast to the measurement error caused by various factors such as an error or an error due to the characteristics of the detector itself, the measurement value of the retardation is not large, and thus there is a problem in that the precision in measuring the rubbing axis of the alignment layer is poor.

Therefore, the present invention has been proposed to solve the above problems, and in the rubbing axis measurement of the alignment layer carried out for quality control of a liquid crystal display device having a high contrast ratio, a birefringent material on the alignment layer applied to the measurement sample substrate It is an object to improve the accuracy of measuring the rubbing axis of the alignment film by amplifying the retardation value of the light transmitted through the measurement sample substrate by forming the layer.

Rubbing axis measuring apparatus according to an embodiment of the present invention for achieving the above object is

A light source providing light to be used for measurement;

A polarizer for polarizing the light supplied from the light source,

An optical phase modulator for adjusting a retardation value of light passing through the polarizer,

A measurement sample substrate through which light whose retardation value is adjusted by the optical phase modulator is transmitted, an alignment film is coated, and a liquid crystal layer is formed on the alignment film;

A birefringent material forming unit for forming a liquid crystal, which is a birefringent material, in a uniform thickness on the alignment layer coated on the measurement sample substrate;

An analyzer for determining a polarization state of light passing through the measurement sample substrate;

A detector for detecting light passing through the analyzer and measuring retardation;

And a controller for measuring the angle of the rubbing axis of the alignment layer using the retardation value measured by the detector and controlling the optical phase modulator.

In addition, the rubbing axis measuring method of the alignment film according to an embodiment of the present invention for achieving the above object,

Supplying light from the light source to the measuring device,

Polarizing the light supplied from the light source through a polarizer;

Adjusting a retardation value of light passing through the polarizer through an optical phase modulator;

Passing light through the optical phase modulator and having a retardation value adjusted therethrough;

Determining a polarization state of light transmitted through the measurement sample substrate through an analyzer;

Detecting the light passing through the analyzer through a detector and measuring a retardation value of the light;

Measuring the angle of the rubbing axis by fitting a retardation value measured through the detector;

And forming a liquid crystal layer in a uniform thickness on top of the alignment layer applied to the measurement sample substrate.

Hereinafter, the rubbing axis measuring apparatus and the rubbing axis measuring method of the alignment film according to the embodiment of the present invention having the above characteristics will be described in detail with reference to the accompanying drawings.

2 is a block diagram showing a rubbing axis measuring apparatus according to an embodiment of the present invention.

The rubbing axis measuring apparatus shown in FIG. 2 includes a light source 210 for supplying light to the measuring device, a polarizer 220 for polarizing the light supplied from the light source 210, and a polarizer 220. An alignment layer is coated to measure the rubbing axis angle of the alignment layer by using the optical phase modulator 230 capable of adjusting the retardation value of light and the light whose retardation value is adjusted by the optical phase modulator 230. A measurement sample substrate 240 having a liquid crystal layer formed thereon, a birefringent material forming unit 250 for forming the liquid crystal layer to a uniform thickness on an alignment layer applied to the measurement sample substrate 240, and the measurement An analyzer 260 for checking the polarization state of the light passing through the sample substrate 240, a detector 270 for detecting the retardation by detecting the light passing through the analyzer 260, and the optical phase Control modulator 230 and measure at detector 270 A retardation value by using a fitting function comprises a control unit 280 to measure the angle of the alignment layer rubbing axis.

The light source 210 may use a laser light or a metal halide lamp.

The polarizer 220 and the analyzer 260 are perpendicular to the traveling direction of light, and the transmission axis of the polarizer 220 and the transmission axis of the analyzer 260 are perpendicular to each other.

The optical phase modulator 230 generally uses an optical phase modulator using polarization elasticity. That is, when the polarized light passes through the transparent solid material included in the optical phase modulator, when the transparent solid material contracts or expands, the refractive index changes in size so that a difference in speed occurs when the polarized light proceeds in the absence of contraction or expansion. The retardation value of the polarized light can be adjusted to a desired value by using the.

The measurement sample substrate 240 is coated with an alignment layer, and includes a liquid crystal layer formed in a uniform thickness by the birefringent material forming unit 250 on the alignment layer. The liquid crystal layer amplifies the retardation value of the light passing through the measurement sample substrate 240, thereby increasing the precision of the rubbing axis angle measurement of the alignment layer.

The detector 270 detects light passing through the analyzer 260 and outputs an electrical signal to measure retardation.

The controller 280 measures the angle of the rubbing axis of the alignment layer through a fitting function of the measured retardation value and controls the optical phase modulator 230.

The birefringent material forming unit 250 is configured to form a liquid crystal layer with a uniform thickness on the alignment layer applied to the measurement sample substrate by spin coating, and includes a rotatable stage and a dispenser for dropping liquid crystal. do.

3A and 3B illustrate a process of forming a liquid crystal layer with a uniform thickness on an alignment layer applied to a measurement sample substrate by a spin coating method.

As shown in FIG. 3A, the side substrate 310 coated with the alignment layer 320 is disposed on the rotatable stage 340, and the liquid crystal 330 is dropped on the alignment layer using the dispenser 350. Rotate 340.

When the stage rotates, the liquid crystal layer 330 is formed to have a uniform thickness on the alignment layer 320 coated on the substrate 310 as shown in FIG. 3B by centrifugal force.

4 is a view showing a cross section of a measurement sample substrate used in the rubbing axis measurement apparatus of the alignment film according to the embodiment of the present invention.

As can be seen in FIG. 4, in the measurement sample substrate used in this embodiment, the alignment layer 320 is coated on the substrate 310, and the liquid crystal layer 330 is formed on the alignment layer to have a uniform thickness.

The substrate 310 mainly uses a glass substrate on which no layer is formed or a glass substrate on which transparent metals such as indium tin oxide (ITO) or indium zinc oxide (IZO) are deposited, but a color filter layer or a thin film transistor is formed. It is also possible to use a substrate.

Next, the rubbing axis measuring method and measuring principle of the alignment layer according to an embodiment of the present invention will be described.

First, the method of measuring the rubbing axis of the alignment layer will be described with reference to FIG. 2.

When light is supplied from the light source 210 to the measuring device, the light supplied from the light source is polarized while passing through the polarizer 220, and the polarized light passes through the optical phase modulator 230 that can adjust the retardation value. The measurement sample substrate 240 is transmitted through.

The measurement sample substrate 240 is located on a rotatable stage (not shown), and the measurement is performed while the measurement sample substrate is rotated. One side of the measurement sample substrate 240 is coated with an alignment layer, and an upper portion of the alignment layer is a liquid crystal. A layer is formed.

The liquid crystal layer is formed to have a uniform thickness in the birefringent material forming unit 250 by a spin coating method.

The light whose retardation value is adjusted by the optical phase modulator 230 is transmitted through the rotating measurement sample substrate 240, and the light passing through the measurement sample substrate 240 passes through the analyzer 260 to detect the detector ( 270).

The detector 270 detects light and outputs an electric signal. In this case, the electric signal is divided into a DC (Direct Current) component and an AC (Alternative Current) component.

When the angle rotated when the measurement sample substrate is rotated is θ and the retardation value by the measurement sample substrate is B, the voltage of the DC component in the electrical signal output by the detector is expressed by the following equation (1).

In Equation (1), C is a constant, J ₀ is a Bessel function, and A ₀ is a retardation value controlled by an optical phase modulator.

On the other hand, the voltage of the AC component output by the detector is expressed by the following equation (2).

At this time, I _2f Since the following terms are small, it is known that I _AC can be expressed as Equation (3) below.

At this time, I _1f is expressed by the following equation (4).

In (4), C is a constant, J ₁ is a Bessel function, A ₀ is a retardation value controlled by an optical phase modulator, and B is a retardation value by a measurement sample substrate.

When I _AC divided by I _DC from the above equations is a function g (θ), g (θ) is expressed as Equation (5) below.

At this time, it is known that J ₀ (A ₀ ) = 0 when the retardation value A ₀ of the light adjusted by the optical phase modulator is fixed to 0.383 wav, that is, 2.405 nm.

Therefore, when the retardation value A ₀ of the light adjusted in the optical phase modulator is fixed to 2.405 nm, the function g (θ) in Equation (5) is summarized as Equation (6) below.

(단, A₀=2.405nm)

(Where A ₀ = 2.405 nm)

Since A ₀ = 2.405 nm in equation (6), 2J ₁ (A ₀ ) sin (B) is a constant.

Considering the rubbing axis angle of the alignment film applied to the measurement sample substrate in the above function, when the rubbing axis angle of the alignment film is α, the function g (θ) can be rewritten as in the following equation (7).

(단, A=2J₁(A₀)sin(B) 이고 A₀=2.405nm)

(Where A = 2J ₁ (A ₀ ) sin (B) and A ₀ = 2.405 nm)

Since the rotation angle θ of the measurement sample substrate is adjusted in Equation (7), the function becomes a function of the rubbing axis angle α of the alignment layer, and thus can be used as a fitting function for obtaining the rubbing axis angle α.

At this time, A represents the amplitude of the function g (θ), and the larger the value of A of the fitting function, the higher the precision of the fitting value with respect to the angle of the rubbing axis of the alignment film.

5A and 5B show the accuracy of fitting according to the magnitude of A value in fitting the angles of the rubbing axis of the alignment film.

FIG. 5A shows the result of fitting the rubbing axis angle of the alignment film when the A value of the fitting function, that is, the amplitude is A ', and FIG. 5B is the case where the A value of the fitting function, that is, the amplitude is A " This is the result of fitting the rubbing axis angle of the alignment film.

As can be seen from Fig. 5A and Fig. 5B, when comparing the amount of change of the x value fitted to the same Δy, the amount of change Δx ₁ of the value of x when the amplitude is small as A 'is large as shown in Fig. 5A. It can be seen that the change in x value at the time is larger than Δx _2. That is, the larger the amplitude value, the smaller the change in the fitted x value, so that the rubbing axis angle of the measurement sample substrate can be fitted more precisely.

Therefore, in order to increase the accuracy of the rubbing axis measurement, it is necessary to increase the A value of the fitting function, and to increase the A value of the fitting function, it is necessary to greatly amplify the retardation value of the measurement sample substrate.

As such, in order to increase the retardation value of the measurement sample substrate, a liquid crystal layer is formed on the alignment layer applied to the measurement sample substrate.

As the liquid crystal used in the liquid crystal layer, an OCB (Optically Compensated Birefringence) type liquid crystal is preferable, but a TN (Twisted Nematic) type liquid crystal or another type of liquid crystal may be used.

FIG. 6 is a diagram illustrating a result of measuring a rubbing axis of an alignment layer by using a measurement sample substrate coated only with an alignment layer, and FIG. 7 illustrates forming an OCB (Optically Compensated Birefringence) liquid crystal layer on an alignment layer coated on the measurement sample substrate. It is a figure which shows the result when the rubbing axis of an alignment film was measured using the measurement sample board | substrate.

The measurement method was repeated five times using the same measurement sample substrate and the same measuring equipment to obtain the average value.

As can be seen in FIG. 6, the retardation value 610 of the light passing through the measurement sample substrate coated with only the alignment layer is 0.2307 nm, and the deviation 620 between the maximum value and the minimum value from the five measured values is 0.168 deg. Can be. Where deg is the unit of angle.

In contrast, in the case of using the measurement sample substrate in which the OCB liquid crystal layer was formed on the alignment layer, as shown in FIG. 7, the retardation value 610 of transmitted light was 18.7015 nm, and the maximum and minimum values were measured five times. It can be seen that the deviation 620 is 0.043 deg.

That is, the retardation value of transmitted light is increased in comparison with the case where the measurement sample substrate having the OCB liquid crystal layer formed on the alignment layer is used compared to the case where the measurement sample substrate is coated with only the alignment layer. It can be seen that the more accurate measurement is made by reducing the deviation between the maximum value and the minimum value of.

In the embodiment of the present invention, although the liquid crystal is used as a birefringent material used to amplify the retardation value of the measurement sample substrate, a material having a birefringence property and having a uniform thickness on the measurement sample substrate may be used. It's okay.

The rubbing axis measuring apparatus and rubbing axis measuring method of the alignment layer according to the second preferred embodiment of the present invention are as follows.

The rubbing axis measuring apparatus of the alignment layer according to the second preferred embodiment of the present invention uses a liquid crystal as a birefringent material for amplifying the retardation value of the measurement sample substrate in the birefringent material forming unit, and the upper surface of the measurement sample substrate In order to form a liquid crystal layer with a uniform thickness by using a non-spin coating method, a stage in which a measurement sample substrate can be positioned and a scanning sample substrate positioned on the stage are scanned. It is configured to include a nozzle (Nozzle), etc. that can inject a liquid crystal at a uniform pressure, and other configuration is the same as the above-described rubbing axis measuring apparatus will be omitted.

In the rubbing axis measuring method according to the second preferred embodiment of the present invention, the birefringent material forming unit forms a liquid crystal with a birefringent material on the alignment layer coated on the measurement sample substrate with a non-spin coating method in a uniform thickness. Characterized in that it includes, other processes are the same as the embodiment of the above-described rubbing axis measuring method.

8A and 8B illustrate a process of forming a liquid crystal layer with a uniform thickness on a measurement sample substrate by a non-spin coating method using a liquid crystal as a birefringent material.

In the non-spin coating method, as shown in FIG. 8A, the substrate 310 having the alignment layer 320 coated thereon is positioned on the stage 360 of the birefringent material forming unit, and the liquid crystal is uniformly applied without the substrate rotating. When the movable nozzle 370 that sprays scans the measurement sample substrate, the liquid crystal layer 330 is formed to have a uniform thickness over the entire surface of the measurement sample substrate as shown in FIG. 8B.

An OCB (Optically Compensated Birefringence) type liquid crystal is preferable as the liquid crystal, but a twisted nematic (TN) type liquid crystal or another type of liquid crystal may be used.

The rubbing axis measuring apparatus and rubbing axis measuring method of the alignment film according to the third preferred embodiment of the present invention are as follows.

The rubbing axis measuring apparatus of the alignment layer according to the third preferred embodiment of the present invention uses a liquid crystal as a birefringent material for amplifying the retardation value of the measurement sample substrate in the birefringent material forming unit, and the liquid crystal on the upper surface of the measurement sample substrate. In order to form a layer with a uniform thickness in a printing method, a stage for positioning a measurement sample substrate on which an alignment film is applied, a roller for printing liquid crystals at a uniform thickness, and a roller are measurement samples It is configured to include a liquid crystal supply unit for supplying the liquid crystal to the roller so that the liquid crystal can be uniformly printed on the substrate, other configuration is the same as the above-described rubbing axis measuring apparatus will be omitted.

The rubbing axis measuring method according to the third preferred embodiment of the present invention includes forming a liquid crystal with a uniform thickness by printing a birefringent material on the alignment layer applied to the measurement sample substrate in the birefringent material forming unit. The other process is the same as the embodiment of the above-described rubbing axis measuring method.

9A and 9B illustrate a process of forming a liquid crystal layer with a uniform thickness on a measurement sample substrate by a printing method using a liquid crystal as a birefringent material.

In the printing method, as shown in FIG. 9A, the substrate 310 having the alignment layer 320 coated thereon is positioned on the stage 360 of the birefringent material forming unit, and the liquid crystal is uniformly applied to the entire surface by receiving the liquid crystal from the liquid crystal supply unit 390. When the roller 380 is in contact with the measurement sample substrate at a uniform pressure and speed, and rotates in one direction, the liquid crystal uniformly applied to the front surface of the roller 380 is transferred to the measurement sample substrate, The liquid crystal layer 330 having a uniform thickness is formed.

An OCB (Optically Compensated Birefringence) type liquid crystal is preferable as the liquid crystal, but a twisted nematic (TN) type liquid crystal or another type of liquid crystal may be used.

The foregoing has described preferred embodiments of the present invention, and the present invention is not limited to the above embodiments, and various modifications may be made without departing from the spirit of the present invention.

The rubbing axis measuring apparatus and the rubbing axis measuring method using the same according to the present invention has the following effects.

In the conventional rubbing axis measuring method, the measurement accuracy is low by measuring the rubbing axis using a measuring sample substrate on which only an alignment film is coated, but the present invention provides a birefringence for increasing the retardation of light passing through the measuring sample substrate on the alignment film. By forming an additional layer of material material to measure the rubbing axis, it is possible to increase the accuracy of the measurement, and by using the improved rubbing axis measuring method for quality control of the liquid crystal display device, the production of a liquid crystal display device having a high contrast ratio can be pursued. have.

Claims (15)

A light source for supplying light to the measuring device; A polarizer for polarizing light supplied from the light source; An optical phase modulator for adjusting a retardation value of light passing through the polarizer; A measurement sample substrate for measuring a rubbing axis using light passing through the optical phase modulator; A birefringent material forming unit for forming a birefringent material having a uniform thickness on the alignment layer applied to the measurement sample substrate; An analyzer for determining a polarization state of light passing through the measurement sample substrate; A detector for detecting light passing through the analyzer and measuring retardation; And a control unit for determining a rubbing axis of the alignment layer using the retardation value measured by the detector and controlling the optical phase modulator. The method of claim 1, And a liquid crystal is used as the birefringent material. The method of claim 2, And a liquid crystal used in the birefringent material forming unit is an OCB (Optically Compensated Birefringence) type liquid crystal. The method of claim 1, And a TN (Twisted Nematic) type liquid crystal is used as the birefringent material used in the birefringent material forming unit. The method of claim 1, The birefringent material forming unit includes a stage capable of fixing a measurement sample substrate and a rotatable stage, and a dispenser for dropping liquid crystal, in order to form a liquid crystal layer by spin coating. Rubbing axis measuring device. The method of claim 1, The birefringent material forming unit may spray a liquid crystal at a uniform pressure while scanning the measurement sample substrate and a stage for positioning the measurement sample substrate to form a liquid crystal layer by a non-spin coating method. A rubbing axis measuring apparatus for an alignment film, comprising a nozzle having a groove. The method of claim 1, The birefringent material forming unit may transfer a liquid crystal to a pressure at a uniform pressure to a stage for positioning a measurement sample substrate, a liquid crystal supply unit supplying liquid crystal to a roller, and a measurement sample substrate in order to form a liquid crystal layer by a printing method. A rubbing axis measuring apparatus for an alignment film, comprising a roller. Forming a alignment film on the substrate; Forming a birefringent material with a uniform thickness on the alignment layer; And a third step of measuring the angle of the rubbing axis of the alignment film by using the rubbing axis measuring device of the alignment film of claim 1. The method of claim 8, And a liquid crystal is used as the birefringent material. The method of claim 9, And a liquid crystal used in the birefringent material forming unit is an OCB (Optically Compensated Birefringence) type liquid crystal. The method of claim 9, And a liquid crystal used in the birefringent material forming unit is a twisted nematic (TN) type liquid crystal. The method of claim 8, The forming of the birefringent material on the alignment layer may include fixing the substrate to the rotatable stage, dropping liquid crystal through a dispenser on the substrate positioned on the stage, and rotating the substrate to drop the substrate onto the substrate. A rubbing axis measuring method of an alignment layer, comprising a spin coating step of coating a liquid crystal with a uniform thickness. The method of claim 8, The forming of the birefringent material on the alignment layer may include positioning a substrate on a stage, and a movable nozzle capable of injecting liquid crystal at a uniform pressure on the substrate positioned on the stage, scanning the substrate. While measuring the rubbing axis of the alignment layer comprising a non-spin coating (Non-Spin Coating) step of applying a liquid crystal in a uniform thickness. The method of claim 8, Forming a birefringent material on the alignment layer, the step of positioning the substrate on the stage, the liquid crystal is uniformly applied to the liquid crystal supplied on the front surface of the roller and the roller is uniformly applied to the liquid crystal while proceeding in contact with the substrate A rubbing axis measurement method for an alignment film comprising a printing step of applying a thickness. The method of claim 8, The second step includes supplying light from the light source to the measuring device; Polarizing the light supplied from the light source through the polarizer; Adjusting the retardation value of the light passing through the polarizer through the optical phase modulator; Passing through the optical phase modulator and the light with the retardation value is adjusted to pass through the substrate having a birefringent material film on the upper surface, Determining a polarization state of light transmitted through the substrate through an analyzer; Detecting the light passing through the analyzer through a detector and measuring a retardation value of the light; And measuring the angle of the rubbing axis by using the retardation value measured by the detector.

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