JP4631748B2 - Electrostatic adsorption method - Google Patents

Description

  The present invention relates to a method for continuously adsorbing a substrate such as a glass substrate from an air atmosphere to a vacuum atmosphere using an electrostatic chuck.

For example, as an embodiment using a glass substrate, a liquid crystal display panel has a structure in which liquid crystal is interposed between two glass substrates.
Such a liquid crystal panel can be manufactured by placing liquid crystal on one glass substrate under vacuum and stacking another glass substrate on the liquid crystal.

  On the other hand, what is disclosed in Patent Document 1 is known as an electrostatic chuck for adsorbing a semiconductor wafer under vacuum. This electrostatic chuck accumulates charges opposite to the charges on the attracting surface on the surface of the semiconductor wafer, and attracts the semiconductor wafer by Coulomb force (Johnsen-Rahbek force).

  The electrostatic chuck using the above-described Coulomb force (Johnsen-Rahbek force) cannot adsorb a glass substrate and cannot be used for manufacturing a liquid crystal display panel. Thus, Patent Document 2 proposes an electrostatic chuck that attracts a glass substrate by a completely different attracting mechanism using a gradient force.

Further, a method disclosed in Patent Document 3 has been proposed as a method for adsorbing a glass substrate by Coulomb force (Johnsen-Rahbek force). In this method, the temperature of the glass substrate is raised and the volume resistivity of the glass substrate is changed to 10 ¹⁴ Ω · cm or less for adsorption.

  Further, it is well known that the adsorption force changes depending on changes in atmospheric conditions such as the degree of vacuum and humidity, and Patent Documents 4 to 7 are known as means for reducing and stabilizing the change in the adsorption force.

  The content disclosed in Patent Document 4 is a method of sending dry air to the adsorption surface to make the atmospheric conditions constant, and the content disclosed in Patent Document 5 is a method of placing in an evacuated and vacuum environment in an adsorption state. The content disclosed in Document 6 is a method for controlling the applied voltage by measuring the adsorption force, and the content disclosed in Patent Document 7 is a method for controlling the applied voltage by measuring humidity.

Japanese Patent Laid-Open No. 10-206876 JP 2000-332091 A JP 2005-32858 A JP 11-260899 A JP 2000-21963 A JP-A-6-334024 JP 7-210104 A

  Some electrostatic chucks disclosed in Patent Document 1 cannot adsorb an insulator such as a glass substrate. According to the electrostatic chuck disclosed in Patent Document 2 and Patent Document 3, an insulator such as a glass substrate can be adsorbed.

However, the suction force with a gradient force in Patent Document 2 is weaker compared to the adsorption force by the Coulomb force ^{20~50g / cm 2 (2000g / cm} 2 or higher). In the method proposed in Patent Document 3, the glass substrate must be heated.

  Also, as disclosed in Patent Documents 4 to 7, even if dry air is sent to the adsorption surface, or even if the applied voltage is changed according to the humidity to make the adsorption force (gradient force) constant, the adsorption force is not increased. Therefore, for example, when a glass substrate is carried into the vacuum chamber from a vacuum suction state and vacuum suction does not work under reduced pressure, the electrostatic suction force is insufficient and the glass substrate is There is a risk of falling from the chuck.

The present inventors have obtained knowledge that the adsorption force of the electrostatic chuck varies depending on the atmospheric humidity, and that the variation further varies depending on the surface roughness of the adsorption surface of the electrostatic chuck.
Based on such knowledge, the invention according to claim 1 uses an electrostatic chuck in which the average roughness (Ra) of the attracting surface is less than 0.7 μm, and the electrostatic chuck continuously from the atmospheric atmosphere to the vacuum atmosphere. In adsorbing a substrate made of glass or a polymer film having an electrically insulating property on the surface to be attracted to the electrostatic chuck, the substrate is placed in an air atmosphere in which the relative humidity of the air atmosphere is 35% or more and 73% or less. Mounted on the electrostatic chuck, and then, in this air atmosphere, the adsorption water on the substrate surface remains between the adsorption surface side of the substrate to the electrostatic chuck and the adsorption surface of the electrostatic chuck. Depressurize, vacuum-suck the substrate, apply a voltage to the electrostatic chuck in an air atmosphere, ionize the water adsorbed on the substrate surface by an electric field, and the surface of the substrate on the suction surface side to the electrostatic chuck Anti was lowered, after adsorbed by the suction force with a gradient force and Johnsen-Rahbek force, and so that the vacuum atmosphere.

  The substrate is a transparent glass substrate (elementary glass), a transparent electrode: ITO (Indium Tin Oxide) film formed on one side of the substrate, and the three primary colors of red, green, and blue on the transparent glass substrate. Color filters (CF) in which patterns are regularly arranged, polymer films, etc. can be applied.

As the structure of the electrostatic chuck, the dielectric constant of the dielectric serving as the attracting surface is 10 ¹⁰ Ω · cm or more, the thickness of the dielectric layer is 0.3 mm to 1.0 mm, and the electrodes are alternately provided in the dielectric layer. By making the width of 0.5 mm to 1 mm and the distance between the electrodes 0.5 mm to 1 mm, a gradient force sufficient to adsorb the glass substrate can be generated.

Further, the degree of vacuum between the suction surface of the substrate to the electrostatic chuck and the suction surface of the electrostatic chuck may be 5 Pa or more, or the vacuum atmosphere may be 5 Pa or more and 50 Pa or less. Conceivable.

  According to the method of the present invention, an insulating substrate such as a glass substrate can be processed from an air atmosphere to a vacuum atmosphere while being held by one electrostatic chuck. Therefore, it is extremely advantageous in manufacturing a liquid crystal display panel.

  DESCRIPTION OF EMBODIMENTS Embodiments for carrying out the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic view of an apparatus used for measuring the maximum static frictional force of an electrostatic chuck used for carrying out the method of the present invention. The basic adsorption force and the residual adsorption force were measured under the following conditions.

(Measurement of basic adsorption force)
・ Set the outside of the chamber to an arbitrary humidity, and remove the static electricity from the glass substrate with the electrostatic chuck and ITO film formed on one side with an ionizer. ・ Vacuum adsorption of the glass substrate (start measurement)
・ Apply the specified voltage to the electrode (elapsed time 60 seconds)
・ The chamber is evacuated (elapsed time: 65 seconds)
・ Stop the vacuum suction of the substrate and make it the same pressure as in the chamber (after reaching the vacuum degree in the chamber of 200 Pa)
・ Measure the adsorption force with a load cell (elapsed time 360 seconds, vacuum 10 Pa)

(Measurement of residual adsorption power)
・ The outside of the chamber is set to an arbitrary humidity, and the glass substrate with the electrostatic chuck and ITO film formed on one side is removed with an ionizer. 2) Vacuum adsorption of the glass substrate (start of measurement)
3) Apply a specified voltage to the electrodes (elapsed time 60 seconds)
4) The inside of the chamber is evacuated (elapsed time: 65 seconds)
5) Stop the vacuum suction of the substrate and make it the same pressure as in the chamber (after reaching the vacuum degree of 200 Pa in the chamber) ・ Turn off the voltage (elapsed time 360 seconds, vacuum degree 10 Pa)
・ After 10 seconds, measure the adsorption force with the load cell.

(Test conditions)
The test conditions for the measurement of basic adsorption force and residual adsorption force are as follows.
Electrode: Width 2mm, spacing 1mm
Dielectric layer: 375 μm thick
Glass substrate: 100 mm x 100 mm, thickness 0.7 mm
Applied polarity: Fixed (fixes the polarity of the voltage applied to the internal electrode)
Invert (the polarity of the voltage is inverted every measurement)
Applied voltage: ± 3kV
Atmosphere outside chamber: Adjustable in the range of 30% to 90% humidity

FIG. 2 is a graph showing the relationship between the humidity outside the chamber and the basic adsorption force, and FIG. 3 is a graph showing the relationship between the humidity outside the chamber and the residual adsorption force. In any case, compared to the maximum static friction force of the atmosphere is about 0.2 gf / cm ^2, the maximum static friction force (gf / cm ²⁾ tends to increase.

  The reason why the maximum static frictional force is increased is that the glass substrate is covered with surface adsorbed water in the atmosphere. When a voltage is applied in the air to adsorb the substrate, the surface adsorbed water is ionized by the generated electric field and vacuum Even if it becomes atmosphere, it remains as it is, and it acts like a conductive material, so it is thought that the adsorption power increases. Since the amount of water adsorbed on the surface also changes due to changes in humidity, the amount of ionization also changes, and the adsorption force is considered to fluctuate.

  Table 1 shows the results of experiments on the relationship between the surface roughness Ra (μm), the relative humidity, and the maximum static frictional force. . The evaluation was the same as in the above apparatus except that the glass substrate was adsorbed downward, and the presence or absence of the substrate was evaluated when the relative humidity in the air atmosphere was 55%. When the surface roughness Ra was smaller than 0.7 μm, no substrate was dropped.

Next, FIG. 4 shows the results of experiments on the relationship between the relative humidity and the maximum static frictional force when the surface roughness Ra is 0.3 μm and 0.7 μm. In order to prevent the substrate from falling when the substrate is continuously held from the atmosphere to the vacuum, the substrate may basically be within a range in which the specific gravity of the substrate can be maintained, so that it is 0.2 gf / cm ² or more. Good. Desirably, when the influence of the remaining pressure (back pressure) in the exhaust flow path for vacuum chucking of the electrostatic chuck is taken into consideration when the atmosphere is changed to the vacuum atmosphere (the apparatus in FIG. However, it is considered that a maximum static friction force of approximately 1 gf / cm ² or more is sufficient as a value capable of maintaining the substrate holding.

Therefore, from FIG. 4, when Ra is 0.3 μm, the condition that the maximum static frictional force of 1 gf / cm ² or more can be exhibited is that the relative humidity of the atmospheric atmosphere at the time of vacuum adsorption is 35 to 73%. From the results, when Ra is 0.7 μm which may cause the substrate to fall, it is 35 to 46%. In addition, when Ra is 0.3 μm, the change in the adsorption force is small with respect to the change in humidity, and it is easy to control with the apparatus. On the other hand, when Ra is 0.7 μm, the adsorption force varies greatly with a slight change in humidity. It is difficult to control. Therefore, it is understood that the roughness (Ra) of the adsorption surface should be less than 0.7 μm in order to effectively increase the adsorption force increased by the humidity of the atmospheric atmosphere and not to make a large difference in the fluctuation of humidity.

  Therefore, if Ra is less than 0.7 μm, the adsorption force can be maintained at a value sufficient to hold the substrate even when the relative humidity changes due to changes in temperature conditions. There is no need to do it strictly. Furthermore, if the relationship between the attractive force and the relative humidity shown in FIG. 4 is grasped, the load on the electrostatic chuck can be reduced by adjusting the applied voltage to a low voltage after being applied to the vacuum atmosphere of the chamber.

  FIG. 5 is a schematic diagram of an apparatus used for measuring the vertical chucking force of the electrostatic chuck used for carrying out the method of the present invention. The basic chucking force and the residual chucking force were measured under the following conditions.

(Measurement of basic adsorption force)
・ Set the outside of the chamber to an arbitrary humidity, and neutralize the glass substrate with the electrostatic chuck and ITO film on one side with an ionizer. ・ Apply a specified voltage to the electrode (start measurement).
・ The chamber is evacuated (elapsed time: 5 seconds)
・ Adsorbing force is measured with a load cell (elapsed time 300 seconds, vacuum 10 Pa)

(Measurement of residual adsorption power)
・ Set the outside of the chamber to an arbitrary humidity, and neutralize the electrostatic chuck and glass substrate with an ionizer. 2) Apply the specified voltage to the electrode (start measurement)
3) The chamber is evacuated (elapsed time: 5 seconds)
4) Turn off the voltage (elapsed time 300 seconds, vacuum 10 Pa)
5) Measure the adsorptive power with a load cell after 10 seconds

The test conditions are the same as described above except that the applied voltage is ± 1 kV. FIG. 6 is a graph showing the relationship between the humidity outside the chamber and the basic adsorption force, and FIG. 7 is a graph showing the relationship between the humidity outside the chamber and the residual adsorption force. In either case, the maximum static frictional force (gf / cm ² ) tends to increase.

  Further, the vertical suction force was also tested for the relationship between the suction surface roughness and the relative humidity, and the result was the same as in FIG.

FIG. 8 shows the relationship between the electrostatic chuck surface roughness Ra and the relative humidity when the type of the substrate is changed, and the evaluation method was based on the measurement of the basic adsorption force.
As the substrate, a color filter (CF) and a glass substrate (elementary glass) were used.

  When the electrostatic chuck surface roughness Ra is 0.3 μm for both the color filter and the raw glass, it exhibits a stable adsorption force up to a relative humidity of 35% to about 75%. Is greatly influenced by. In the case of bare glass, by reducing the electrostatic chuck surface roughness Ra, it is possible to secure the necessary adsorption force within a wide range of relative humidity by the adsorption force of the adsorbed water even if the applied voltage is reduced.

Table 2 shows an example in which a polymer film is used as a substrate to be adsorbed, showing a change in adsorption force when a voltage is applied after the degree of vacuum in the chamber is changed from atmospheric to vacuum. As a measuring method, the chamber is evacuated in a state where the electrostatic chuck and the polymer film are previously left in the chamber of the apparatus shown in FIG. 1 (the state in the chamber of FIG. 1), and the degree of vacuum is 50 Pa. After reaching 5 Pa, a specified voltage is applied to the electrostatic chuck, and after the application time, the polymer film is pulled with a load cell, and the maximum static frictional force (gf / cm ² ) at which the polymer film starts to move is measured as an adsorption force. .

If the degree of vacuum is the same, the adsorption force is substantially constant regardless of the application time, and the lower the degree of vacuum, the higher the adsorption force at a lower applied voltage. This tendency is because the amount of water in the chamber decreases as the degree of vacuum increases, and the surface adsorbed water intervening between the polymer film before voltage application and the electrostatic chuck surface is also taken away. . For this reason, it is considered that the lower the degree of vacuum with the larger amount of surface adsorbed water, the higher the adsorptive power as in the above-described evaluation of the substrate such as the glass substrate.

  Next, FIG. 9 to FIG. 16 show an example in which the method of the present invention is used for laminating liquid crystal panels. The laminating apparatus arranges a mounting table 2 on the bottom surface in the chamber 1 and places it on the ceiling. An electrostatic chuck 3 is disposed, and an opening 4 for loading and unloading the glass substrate W is formed on the side surface of the chamber 1. The opening 4 is opened and closed by a door 5. The connecting pipe 6 is provided with a pipe 7 for supplying air, nitrogen gas or the like on the ceiling.

  A through hole 21 is formed in the mounting table 2, and a pin 23 that is moved up and down by the cylinder unit 22 is accommodated in the through hole 21.

  The electrostatic chuck 3 is moved up and down by a cylinder unit 31, and its lower surface is a suction surface 32, and a vacuum suction hole 33 is opened on this suction surface, and the surface roughness (Ra) of the suction surface 32 is further determined. The thickness is less than 0.7 μm.

  In the above, first, as shown in FIG. 9, air is introduced into the chamber 1 from the pipe 6 to bring the inside of the chamber 1 to atmospheric pressure. At this time, the relative humidity of the introduced air is controlled to 35% or more by a dehumidifier or a humidifier. If the relative humidity is 35% or more, it can contribute to the removal of the influence of static electricity. Preferably, the relative humidity is 50 or more at which the charging voltage is lowered.

  Next, as shown in FIG. 10, the door 5 is opened, the glass substrate W is inserted into the chamber 1 from the opening 4 by the arm 8, and the pin 23 is raised by the cylinder unit 22 as shown in FIG. The glass substrate W is received from 8.

  Thereafter, as shown in FIG. 12, the arm 8 moves backward, and the pin 23 is lowered to place the glass substrate W on the upper surface of the placement table 2.

  Then, as shown in FIG. 13, the nozzle 9 is inserted into the chamber 1 to supply liquid crystal to the surface of the glass substrate W. The liquid crystal supply may be completed outside the chamber 1 in advance.

  Next, another glass substrate W is carried into the chamber 1 by the arm 8 as shown in FIG. 14, and the electrostatic chuck 3 is lowered by the cylinder unit 31 as shown in FIG. The surface 32 is pressed against the upper surface of the glass substrate W. Incidentally, at this time, adsorbed water is attached to the surface of the glass substrate W.

  Then, as shown in FIG. 16, the arm 8 is retracted from the chamber 1 and the opening 4 is hermetically closed with the door 5, and then the pressure inside the chamber 1 is reduced to about 5 to 50 Pa through the pipe 7. The gas dissolved in the liquid crystal is removed by this reduced pressure. Thereafter, the electrostatic chuck 3 is lowered and the two glasses are bonded together with a liquid crystal in between.

  As mentioned above, although the example which utilized this invention for bonding of a liquid crystal panel was shown, as mentioned above, the method of this invention is applicable to various board | substrates, and is effective for the manufacturing apparatus using those board | substrates. Is the method.

Schematic diagram of an apparatus used to measure the maximum static frictional force of an electrostatic chuck used to implement the method of the present invention Graph showing the relationship between humidity outside the chamber and basic adsorption force Graph showing the relationship between humidity outside the chamber and residual adsorption power The figure which shows the result of having experimented about the relation of the adsorption surface roughness, relative humidity, and the maximum static friction force Schematic diagram of an apparatus used to measure the vertical chucking force of an electrostatic chuck used to implement the method of the present invention Graph showing the relationship between humidity outside the chamber and basic adsorption force Graph showing the relationship between humidity outside the chamber and residual adsorption power Graph showing the relationship between humidity outside the chamber and basic adsorption force The figure which shows the example which utilized this invention method for bonding of a liquid crystal panel The figure which shows the example which utilized this invention method for bonding of a liquid crystal panel The figure which shows the example which utilized this invention method for bonding of a liquid crystal panel The figure which shows the example which utilized this invention method for bonding of a liquid crystal panel The figure which shows the example which utilized this invention method for bonding of a liquid crystal panel The figure which shows the example which utilized this invention method for bonding of a liquid crystal panel The figure which shows the example which utilized this invention method for bonding of a liquid crystal panel The figure which shows the example which utilized this invention method for bonding of a liquid crystal panel

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Chamber, 2 ... Mounting table, 21 ... Through-hole, 22 ... Cylinder unit, 23 ... Pin, 3 ... Electrostatic chuck, 31 ... Cylinder unit, 32 ... Suction surface, 33 ... Hole for vacuum suction, 4 ... Opening, 5 ... door, 6, 7 ... piping, 8 ... arm, W ... glass substrate.

Claims (3)

Using an electrostatic chuck average roughness of the suction surface (Ra) of was less than 0.7μm with holes for vacuum suction by the suction surface to open, the static continuously until a vacuum atmosphere at the electrostatic chuck from the atmosphere When adsorbing a substrate made of glass or polymer film that shows electrical insulation on the suction surface side to the electric chuck ,
The substrate is mounted on the electrostatic chuck in an air atmosphere in which the relative humidity of the air atmosphere is 35% or more and 73% or less, and then the suction surface side of the substrate to the electrostatic chuck in the air atmosphere Between the suction surface of the electrostatic chuck and the suction surface of the electrostatic chuck so that the water adsorbed on the substrate surface remains, vacuum-suck the substrate, and then apply a voltage to the electrostatic chuck in an air atmosphere, Water adsorbed on the surface is ionized by an electric field, the surface resistance of the substrate to the electrostatic chuck is lowered, and the surface is adsorbed by an adsorption force based on a gradient force and a Johnsen-Rahbek force. A characteristic electrostatic adsorption method. The electrostatic chucking method according to claim 1, wherein a degree of vacuum of 5 Pa or more is set between the chucking surface side of the substrate to the electrostatic chuck and the chucking surface of the electrostatic chuck. The electrostatic adsorption method according to claim 1, wherein the vacuum atmosphere has a degree of vacuum of 5 Pa or more and 50 Pa or less.

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