JP2009165951A - Thin film forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin film forming apparatus capable of forming a thin film by discharging and applying a material solution on a substrate from an inkjet head under a reduced pressure to have a uniform film thickness and each simplified constitution installed without deteriorating the function of a discharge coating. <P>SOLUTION: The thin film forming apparatus is constituted of a plurality of inkjet heads respectively discharging the material solution from a plurality of nozzles formed with a fixed interval on the substrate, a coating solution housing container for supplying the material solution using the water head difference between the nozzle surface and the liquid surface to the inkjet heads, a substrate transporting table for placing the substrate and moving horizontally and a pressure reduced chamber housing the inkjet head, the coating solution housing container and the substrate transporting table and provided with the pressure reduced chamber, wherein the coating solution housing container directly connected to the inkjet head is placed under the same reduced pressure atmosphere. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a thin film forming apparatus for discharging and forming a thin film on a substrate using an ink jet head.

  Various semiconductor devices, display elements, and the like are composed of various thin films. Among liquid crystal display elements that have shown dramatic growth in recent years, as the most important thin film, Examples include membranes.

  A liquid crystal display device having great advantages of thinning, large size, and low power consumption is mainly used in a mobile phone, a personal computer, a thin television, and the like, and has been greatly developed.

  In a liquid crystal display element, a liquid crystal composition is sandwiched between two substrates on which electrodes are formed, and a voltage is applied between the two electrodes, whereby the molecular arrangement of the liquid crystal is twisted and light from the backlight is emitted. The image is displayed in combination with a polarizing plate and a color filter by using a switching phenomenon in which the image is straightly moved or blocked.

  The alignment film functions as a trigger for causing a change in the alignment of the liquid crystal molecules. In order to align the liquid crystal molecules in one direction, a pretilt angle formed by the molecular axis of the liquid crystal molecules and the alignment film needs to be given in advance.

  Specifically, after the alignment film is applied to the substrate, a rubbing process that lightly rubs in a specific direction with a specific cloth is performed to provide a nucleus that becomes a starting point when the alignment of liquid crystal molecules is twisted on the surface of the alignment film. Is formed.

  If a voltage is applied between the electrodes of both substrates, liquid crystal molecular alignment in a certain direction is realized. In order to realize the intended display, the role of the alignment film is extremely important, and the uniformity of the film thickness and composition, which are the basic characteristics of the thin film, is strongly desired.

  In addition, the molecular alignment of the liquid crystal has a deep relationship with the display performance such as the brightness of the screen and the width of the viewing angle. In order to improve these characteristics, the horizontal electric field type alignment (IPS) and the vertical alignment (VA). Has been proposed, and alignment film materials have been developed accordingly. It is an important issue to apply this alignment film material to a substrate to form a thin film uniformly in a large area.

The conventional alignment film formation of a liquid crystal display element is generally performed by offset printing (flexographic printing) described in Patent Document 1. The alignment film material developed on the anilox roller is made to have a uniform thickness with a doctor roller, transferred to a printing plate provided on the plate cylinder, then transferred to the substrate surface, and then subjected to a drying process and a baking process, whereby the alignment film Is formed.
JP 54-21862 A

Since liquid crystal display elements are becoming larger in size year by year, it is very difficult to replace a plate cylinder provided with a printing plate in a clean room with a conventional printing method, and material loss is also large. As described, there is also proposed an inkjet alignment film forming method in which an alignment film material is sprayed from a nozzle and applied to the surface of a substrate, and the alignment film is formed through development, drying and baking processes.
JP 2003-80130 A

  FIG. 10 is a diagram showing an outline of a conventional thin film forming apparatus. The thin film forming apparatus 1b has a substrate transfer table 4 for fixing the substrate 3, and a head 2 in which a plurality of inkjet heads 9 are arranged in a head bracket 2a is supported by a portal frame 2e above the substrate transfer table 4. Provided.

  A plurality of nozzles 9a exist on the lower surface of each inkjet head 9, and the material solution 9d supplied from the application solution storage container 2c through the application solution supply pipe 2d is discharged. Incidentally, the droplet discharge direction of each nozzle 9 a is perpendicular to the surface of the substrate 3.

  The substrate transfer table 4 is moved horizontally by the table moving actuator 6a, and the coating operation is performed while adjusting the movement amount of the substrate 3 on the substrate transfer table 4 and the discharge amount from the inkjet head 9.

  The substrate transfer table 4 is positioned with high accuracy by the stage controller 10f. The position detector 6b acquires the position of the substrate transfer table 4 and feeds it back to the stage controller 10f, whereby the position is controlled to be an accurate position.

  An alignment film is formed by spreading, drying, and firing the material solution 9d ejected from each inkjet head 9 and landed as spherical dots on the surface of the substrate 3 conveyed in a predetermined direction at a predetermined speed. The

  As for the progress of the substrate 3 in the coating operation, a direct moving method in which the position of the ink jet head 9 is fixed and the substrate transport table 4 is moved horizontally, and a position in which the substrate transport table 4 is fixed and the ink jet head 9 is moved horizontally. There is an indirect movement method.

  In the non-contact forming method using the inkjet head proposed for solving the problem in forming the alignment film of the liquid crystal display element by offset printing, the problems related to the use efficiency of the alignment film material and the plate change have been solved. .

  However, there is a big problem in ensuring uniformity of the alignment film thickness. The conventional inkjet method for forming an alignment film is performed under normal pressure (atmospheric pressure), and the amount of droplets used in the inkjet method is extremely small. It is easily affected by the air current and directly affects the dispersion of the landing position on the substrate.

  By ensuring that the gap between the inkjet head and the substrate is as narrow as possible so that the kinetic energy during ejection does not decay, it is possible to maintain the accuracy of the landing position. This becomes a major factor in fluctuations in the thickness of the alignment film formed on the substrate.

  The landing position accuracy occurs when the relative movement speed of the ink jet head and the substrate fluctuates or when the nozzle ejection timing is shifted, but the alignment film forming method using the ink jet method forms a single droplet on the substrate. Since this is a method of obtaining a thin film having a large area by diffusing and developing dots, the positional deviation of the dots is a major factor in film thickness fluctuation.

  Further, the ink jet head is manufactured by a fine process similar to that of a semiconductor, and in order for the material solution to smoothly pass through the flow path that occupies the main part of the device, there is a restriction on viscosity as a fluid property of the material solution. . Furthermore, in order to eject one droplet from the nozzle, there is a restriction on the surface tension of the material solution itself.

  In addition, regarding the inkjet head currently used for industrial use, the viscosity is about 5 to 15 mPa · s and the surface tension is about 25 to 45 mN / m.

  In the case of an alignment film material, polyimide as a main component is a very stable polymer material and is difficult to dissolve. Therefore, a large amount of γ-butyllactone, N-methylpyrrolidone, butyl cellosolve, etc. is used as a solvent. The viscosity is applied by spraying.

  When a solvent-added material solution lands on the substrate, evaporation of the solvent and diffusion development as a liquid occur simultaneously. Finally, when the material is semi-dried, the movement of the substance stops, but the polyimide has a relatively large specific gravity. The molecules diffuse and go to the end, so that a coffee stain phenomenon occurs in which the thickness of the end becomes very large.

  In the process aiming at thin film formation, an abnormal increase in the film thickness at the periphery of the coating area is a fatal trouble in the manufacture of liquid crystal display elements, so it is important to avoid the bulge at the edge. It is.

  In a method for forming a thin film by inkjet, it is effective to perform inkjet coating under a reduced pressure environment lower than atmospheric pressure as a means for obtaining a highly uniform film thickness distribution. However, in order to perform stable discharge coating with the thin film forming apparatus, it is necessary to pay attention to the water head difference between the nozzle surface of the inkjet head and the liquid surface of the coating solution storage container.

  FIG. 11 is a diagram showing the water head difference between the nozzle surface of the inkjet head and the liquid level of the coating solution storage container.

  The shear type ink jet head 9 frequently used in the ink jet coating apparatus has a deformation ejection mechanism using a piezo element approaching just before the nozzle 9a. Therefore, the surface of the nozzle 9a of the ink jet head 9 is a material in the coating solution storage container 2c. The liquid level is higher than that of the solution 9d.

  If the liquid surface of the material solution 9d is higher than the nozzle 9a surface of the ink jet head 9, the material solution 9d is not restrained by the nozzle 9a surface and oozes out. Moreover, if the liquid level of the material solution 9d falls more than necessary, the pumping action of the piezo element will not be achieved, and it will not be applied by discharge.

  When securing the water head difference, taking care not to disturb the movement of the inkjet head and the movement of the substrate transfer table, the supply piping system tends to be redundant, which is a major issue when mounting a thin film forming apparatus under reduced pressure. Become.

  Therefore, the present invention realizes uniformity of the film thickness when forming a thin film by discharging and applying a material solution onto a substrate from an inkjet head under reduced pressure, and each component without impairing the function of discharging and applying. An object of the present invention is to provide a thin film forming apparatus that is simply mounted.

  The material solution that drops out of the inkjet head as a droplet lands on the substrate and then diffuses and develops on the substrate surface. However, when the kinetic energy of the material solution and the frictional resistance against the substrate surface are balanced, Stop.

  In the diffusion process, volatile components such as a solvent continue to evaporate from the surface of the material solution. The evaporation behavior is most actively performed on the free surface of the tip of the droplet.

  When evaporation in this region is accelerated, a flow called Marangoni flow is generated to supply the material solution from the center to the end of the droplet. By repeating this flow, a region having a high concentration is formed at the end portion, and as a result, the film thickness becomes very large.

  FIG. 12 is a diagram showing the influence of the degree of pressure reduction on the final droplet cross-sectional shape when the droplet discharged from the inkjet head is developed on the substrate.

  As shown in the upper part of FIG. 12, the material solution flows and the solvent evaporates and drys simultaneously. The diffusion and development of the material solution on the substrate is determined by the kinetic energy of the droplet and the surface state of the substrate, but the evaporation of the solvent changes its boiling point depending on the degree of decompression, so that the entire flow is controlled.

  Comparing the film formation behavior 13 in the atmosphere with the film formation behavior 13a under reduced pressure, the final surface shape varies greatly depending on the degree of pressure reduction as shown in the lower part of FIG.

  By controlling the diffusion of the material solution and the evaporation of volatile components such as solvents using decompression means, when forming a thin film by connecting droplets by inkjet ejection, the coffee stain phenomenon and film thickness unevenness are eliminated. A uniform film thickness excellent in flatness can be realized.

  Further, the supply of the material solution from the coating solution storage container to the ink jet head uses a water head difference considering gravity.

  With the liquid surface of the coating solution storage container and the nozzle surface of the inkjet head open to the atmosphere, the gravity corresponding to the water head difference and the piping resistance including the inkjet head pipe line are balanced, and the material solution is discharged from the nozzle during discharge suspension. In the discharging operation, the material solution is supplied without stagnation in response to the actuator of the inkjet head.

  FIG. 13 is a diagram showing a state of a water head difference that affects the shape of the solution meniscus at the nozzle tip in the pre-ejection stage.

  If the water head difference is 14, the shape of the meniscus 9e is optimal. If the water head difference is excessive 14a, the material solution 9d becomes a retracted meniscus 9e.

  Therefore, it is necessary to set the water head difference so that the shape of the meniscus 9e of the material solution 9d at the nozzle 9a discharge port of the inkjet head 9 is optimized. In the atmospheric pressure, the surface of the material solution 9d is lowered by about 100 mm with respect to the surface of the nozzle 9a of the inkjet head 9.

  Under reduced pressure, if the coating solution storage container directly connected to the ink jet head is installed outside the decompression chamber, a pressure difference is generated inside and outside the decompression chamber, and it is difficult to cover this with a water head difference. Place the container in a vacuum chamber. It is not necessary to include a coating solution replenishing tank or the like for replenishing the material solution in the coating solution storage container.

  Next, in order to smoothly perform the ink jet spray coating operation, it is required that droplets can be discharged from any nozzle under a reduced pressure environment. Further, for stable ink jetting, it is necessary that the ink jet head and the piping supply system are not clogged.

  In the material solution supply system including the ink jet head, bubbles mixed in due to the inflow of air from the outside and the generation of bubbles from the inside cause pressure interruption, and stable ejection cannot be performed. Note that air bubbles from the outside can be prevented by measures such as sealing.

  Regarding the generation of bubbles from the inside, the solvent contained in the material solution tends to evaporate due to the lowering of the boiling point in a reduced pressure environment, and the bubble generation is accelerated, or the bubbles are inherent in the material solution from the beginning. Water that has been stored, moisture that has been absorbed during storage, or moisture that has condensed on the walls of the piping system or the flow path of the inkjet head may be evaporated by decompression.

  FIG. 14 is a graph showing the solvent component of the liquid crystal alignment film and the vapor pressure of water. Examples of the solvent component used for forming the alignment film include NMP, butyl cellosolve, and γ-butyllactone.

  The vapor pressure diagram 15 is obtained from the equation of Antione showing the relationship between the temperature of the liquid and the vapor pressure, and the effect of the boiling under reduced pressure is greater than the solvent contained in the material solution. The effect is more pronounced.

  At a reduced pressure of 47 kPa, the equilibrium temperature of water is reduced to about 80 ° C., and at 7.4 kPa, it is reduced to about 40 ° C., and the lower limit for vaporization of moisture by reducing pressure at 25 ° C., which is a standard room temperature, is 3.169 kPa. .

  Although depending on the surface state inside the flow path of the ink jet head, stable discharge can be realized if the operation is performed while reducing the pressure within the range between the atmospheric pressure and the lower limit.

  Next, in order to discharge all the nozzles that make up the inkjet head in an atmospheric environment without stagnation, the sum of the air force pushing the material solution and the weight of the material solution corresponding to the water head difference, and the material solution is discharged from the nozzle. The pressure difference between the holding force and the sum of the pipe resistances accompanying the movement of the material solution needs to be appropriate, and when the inkjet head, coating solution piping system and coating environment conditions are determined, the water head difference is optimized. This is a requirement for stable ejection.

  Even under a reduced pressure environment, stable discharge is possible if the difference between the force for releasing the material solution and the force for pressing the material solution is properly maintained. In order to stably maintain the inkjet discharge operation, it is necessary to always maintain a balance between the discharge of the material solution that is the demand and the replenishment of the material solution that is the supply.

  Detects the liquid level drop caused by the use of the material solution, and supplies the material solution corresponding to the amount of decrease. As an apparatus for measuring the liquid level, there are an optical type, a mechanical type using a float or the like, and a type using a sound wave.

  In a situation where the coating solution storage container is contained in the decompression chamber, a mechanism capable of moving the installation moving stage holding the coating solution storage container up and down is attached.

  Next, since the gap between the nozzle surface of the inkjet head and the substrate is usually 1 mm or less, the coating solution storage container is installed below the surface of the substrate transport table holding the substrate in order to ensure a negative water head difference. There is a need to.

  When coating a wide area, it is necessary to move at least one of the inkjet head and the substrate. However, since the coating material storage container cannot be installed within the movable range of the substrate transport table, the coating solution supply pipe must be installed. Have to take long.

  Therefore, if the coating material storage container is disposed in the vicinity of the upper part of the inkjet head, the coating solution supply pipe can be shortened, and an orderly thin film forming apparatus can be configured.

  At the same time, a fine differential pressure adjustment mechanism using an electropneumatic regulator is introduced to shift the negative effect on the effect of the head differential to the positive side. As a result, the problem in supplying the material solution can be solved, and the inkjet head and the coating material storage container can be brought close to each other, thereby enabling efficient mounting.

  Since inkjet discharge is performed in a reduced pressure environment, when the discharged droplets diffuse and expand along with the evaporation of the solvent along the substrate surface, the rise at the edge is reduced and smoothly merges with adjacent droplets. Can be made. As a result, a thin film having a smooth surface shape with small variations in film thickness can be formed.

  By installing the coating solution storage container in the vacuum chamber, the relative water head difference with the nozzle surface of the inkjet head can be handled in the same way as in atmospheric pressure, and the thin film forming apparatus can be miniaturized. Can do.

  By limiting the lower limit of the degree of decompression of the decompressed atmosphere, it is possible to suppress the generation of bubbles in the piping of the ink jet head and in the liquid feeding piping, and the reliability of stable ejection can be improved.

  If the water head difference between the nozzle surface of the inkjet head and the liquid surface of the coating solution storage container is within the allowable range, droplets can be stably ejected, but environmental temperature, environmental humidity, vibration, etc. Taking the influence into consideration, when the material solution is consumed and the liquid level is lowered, the ink solution can be stably ejected by replenishing the material solution and maintaining the optimum water head difference.

  In order to secure the optimum water head difference, the piping system connecting the coating solution storage container and the inkjet head becomes redundant. The coating solution storage container is attached immediately above the inkjet head, and a slight differential pressure adjustment mechanism is provided to provide a water head difference. It can be solved by adjusting. Thereby, miniaturization and simplification of the thin film forming apparatus can be realized, and the reliability can be improved by shortening the pipe length.

  The material solution contains volatile organic compounds (VOC) and the like by adding a solvent, but the thin film forming apparatus is completely partitioned by the decompression chamber, and is evacuated by a vacuum pump and then adsorbed by VOC. Since removal is performed by a removal device, sufficient consideration can be given to the environment.

  The present invention can be applied to the manufacture of functional thin films constituting various display elements including liquid crystals and the manufacture of various thin films of semiconductor devices. Compared with conventional sputtering methods and CVD methods, the coating material In addition to excellent utilization efficiency and throughput, it can be provided at a very low cost.

  Below, based on an accompanying drawing, the thin film formation apparatus which is this invention is demonstrated in detail. An alignment film which is the most important functional thin film of the liquid crystal display element will be described as an example, and the case where an alignment film solution is used as a material solution will be described.

  FIG. 1 is a diagram showing an outline of a thin film forming apparatus according to the present invention. The thin film forming apparatus 1 includes a head 2, a coating solution storage container 2c, a substrate transfer table 4, a decompression chamber 7, and the like.

  The head 2 has a plurality of inkjet heads 9 arranged on a head bracket 2a, is held hollow by a portal frame 2e, and can be moved up and down by a head lifting / lowering actuator 2b.

  In each inkjet head 9, a plurality of nozzles 9a are formed linearly downward at regular intervals in order to eject droplets of the material solution 9d, and in order to supply the material solution 9d, a coating solution A coating solution supply pipe 2d branched from the storage container 2c is connected.

  The substrate transfer table 4 is a table for placing the substrate 3 on which the material solution 9d is applied and moving the substrate 3 horizontally. The substrate 3 can be applied with a vacuum suction method as long as the treatment is performed under atmospheric pressure. However, since the substrate 3 is in a reduced pressure environment, the substrate 3 is fixed to the substrate transfer table 4 by an electrostatic chuck 4a for substrate suction.

  Further, the substrate transport table 4 can be placed on the stage 5 having the lift pin mechanism 5a so that the substrate transport table 4 can be lifted upward when the substrate 3 is carried in or out.

  The substrate transfer table 4 can be moved back and forth along the guide rail 6 by a table moving actuator 6a. It is also possible to appropriately control the amount of movement by measuring the position of the substrate transport table 4 with the position detector 6b.

  The table moving actuator 6a is normally a servo motor and is connected to the stage 5 via a ball screw. However, when low dust generation is required, a linear motor can be used.

  The head 2, the coating solution storage container 2c, and the substrate transfer table 4 are disposed on the base frame 7a in the sealed decompression chamber 7. The head 2 is supported by fixing the portal frame 2e to the base frame 7a, and the substrate transport table 4 is installed with the guide rail 6 laid on the base frame 7a.

  In addition, since each inkjet head 9 of the head 2 supplies the material solution 9d using pressure, the coating solution storage container 2c directly connected to each inkjet head 9 needs to be placed under the same pressure environment.

  Outside the decompression chamber 7, a vacuum exhaust pump 7b for decompressing the decompression chamber 7 and a volatile solvent adsorption processing device 7c for removing volatile organic compounds (VOC) are installed.

  FIG. 2 is a diagram showing a cross-sectional structure of a liquid crystal display element in which an alignment film is formed by the thin film forming apparatus according to the present invention.

  The liquid crystal panel 8 is a liquid crystal display element manufactured by using the substrate 3 coated with the alignment film 8 a in the thin film forming apparatus 1. It consists of a front module, a liquid crystal layer, and a rear module. When light is irradiated from the back backlight, an image can be projected.

  The alignment film 8a applied to the substrate 3 of the front module and the alignment film 8a applied to the substrate 3 of the rear module face each other, and a liquid crystal layer is formed by filling liquid crystal molecules therebetween, and a voltage is applied to the counter electrode and the pixel electrode. As a result, the orientation of the liquid crystal molecules is changed and combined with the polarizing plate to turn on and off the transmitted light. Moreover, the color of light is changed through a color filter.

  FIGS. 3A and 3B are a plan view and a front view showing a layout of a head having pseudo long lines when one-pass coating is performed by the thin film forming apparatus according to the present invention. The upper stage is a plan view of the head 2, and the lower stage is a front view of the head 2.

  The ink jet head 9 is based on a piezo element, and a flow path is formed through which the material solution 9d flows from the material solution supply port 9b to each nozzle 9a. When a voltage is applied to the channel, the shape of the channel expands and contracts due to the piezoelectric effect and functions as a pump, so that droplets can be ejected from the nozzle.

  In order to perform coating for one row, an inkjet head row is formed by arranging the inkjet heads 9 in the longitudinal direction. However, two rows of inkjet heads are prepared, and the first row of inkjet heads 9 and 2 are arranged in parallel. Arranged so that the inkjet heads 9 in the rows are staggered.

  In addition, the inkjet head 9 in the first row and the inkjet head 9 in the right side of the second row are aligned with the positions of the rightmost nozzle 9a in the first row and the leftmost nozzle 9a in the second row. The head 9 and the inkjet head 9 on the left side of the second row align the positions of the leftmost nozzle 9a in the first row and the rightmost nozzle 9a in the second row.

  One row cannot cover the non-nozzle region between the ink jet heads 9, but by compensating the two rows alternately, an equally spaced nozzle pitch can be realized, and two ink jet head rows can be formed with a time difference. It can function as a single line-shaped head 2 in a pseudo manner.

  A coating solution supply pipe 2d is connected to the material solution supply port 9b of each inkjet head 9, and when the material solution 9d is discharged from the nozzle 9a, the material solution 9d is supplied from the coating solution storage container 2c into the inkjet head 9. The

  Each inkjet head 9 is connected to the system controller 10 by a head controller connection cable 9c, and discharge of the material solution 9d from the nozzle 9a is controlled.

  FIG. 4 is a diagram showing a control structure in the coating operation of the thin film forming apparatus according to the present invention. The system control device 10 includes an inkjet head controller 10a, a control computer 10e, a stage controller 10f, a decompression control 10g, and the like.

  The inkjet head controller 10a includes a head drive unit 10b, a memory unit 10c, a control unit 10d, and the like, and controls the operation of each inkjet head 9.

  The control computer 10e is a device that executes a program in which a coating operation control algorithm is assembled. First, a discharge coating pitch and coating pattern information (such as a coating start position, a coating end position, and a coating pattern shape) are set.

  The application pattern shape is created by data such as a bitmap. By making each dot correspond to the nozzle 9a of the inkjet head 9, the ejection can be controlled. The set bitmap data is sent to the memory unit 10c.

  When the application start signal is sent from the control computer 10e to the control unit 10d, the control unit 10d uses the encoder pulse from the stage controller 10f as a trigger signal to give an operation instruction to the head drive unit 10b and the memory unit 10c. put out.

  The memory unit 10c sends application pattern shape data necessary for one application operation from the bitmap data to the head driving unit 10b. That is, when there are two inkjet head rows, data for two rows is sent.

  The head drive unit 10b sends a head drive signal to each inkjet head 9 based on the data of the coating pattern shape. When there are two inkjet head rows, the head drive signal for the first row is sent, and then the head drive signal for the second row is sent after a while.

  In each inkjet head 9, a material solution 9d is discharged from the nozzle 9a to the substrate 3 according to the shape of the application pattern. Since the substrate 3 moves, after the first row is ejected, the second row is ejected so as to fill the vacant space of the first row, and the one row is evenly applied.

  Further, the control computer 10e sends command data (movement start signal, application start position, application end position) for controlling the movement of the substrate 3 to the stage controller 10f simultaneously with the start of application or when performing positioning feedback control. Etc).

  The stage controller 10f operates the table moving actuator 6a to move the substrate transport table 4 at a predetermined speed, and periodically sends encoder pulses to the control unit 10d from the application start position to the application end position.

  When the substrate transfer table 4 is moved, the position detector 6b periodically acquires the position of the substrate transfer table 4, calculates the speed of the substrate transfer table 4, and sends it to the control computer 10e via the stage controller 10f.

  The control computer 10e determines whether or not the moving speed of the substrate transfer table 4 is appropriate. If the moving speed is too fast or too slow, the control computer 10e performs feedback control by urging the stage controller 10f to adjust the moving speed. .

  By properly controlling the relationship between the inkjet head controller 10a that manages the ejection of the inkjet head 9 and the stage controller 10f that manages the movement of the substrate transport table 4, it is possible to apply and form a uniform thin film on the substrate 3. It becomes.

  The control computer 10e also performs a decompression control 10g in the decompression chamber 7. By performing the coating operation in a reduced pressure environment, it is possible to control the evaporation during the diffusion and expansion after the droplets have landed on the substrate 3 and to make the film thickness distribution uniform.

  FIG. 5 is a diagram showing a control structure in the decompression chamber of the thin film forming apparatus according to the present invention. The coating operation is performed by setting the inside of the decompression chamber 7 containing the thin film forming apparatus 1 to a pressure lower than the atmospheric pressure.

  The decompression chamber 7 is provided with a vacuum seal 7d, and a vacuum gauge 7e for measuring the degree of decompression of the decompression chamber 7 and detecting pressure fluctuation is installed. In addition, a valve for pressure adjustment and a valve for opening to the atmosphere are provided, and nitrogen can be taken in through a filter.

  An evacuation pump 7b is connected to depressurize the decompression chamber 7, but a variable pressure regulating valve 7i is provided between the decompression chamber 7 and the evacuation pump 7b in order to keep the pressure level constant at a low degree of vacuum. Controls minute pressure fluctuations.

  When the pressure in the decompression chamber 7 rises and the vacuum gauge 7e detects it, a pressure detection signal is input to the sequencer 7f. The sequencer 7f issues a command to the servo amplifier 7h via the communication means 7g, operates the servo motor 7j that controls the opening / closing of the variable pressure regulating valve 7i, and opens the variable pressure regulating valve 7i.

  When the pressure in the decompression chamber 7 reaches the set value, the servo amplifier 7h closes the variable pressure regulating valve 7i and opens the leak valve 7k in accordance with a command from the sequencer 7f to keep the pressure in the decompression chamber 7 at the set value. .

  If the degree of pressure reduction at which the effect of the diffusion of the landed material solution 9d and the evaporation of the solvent in the material solution 9d on the thickness of the formed thin film is determined is optimal, the decompression chamber 7 can always be set to the optimum pressure. it can.

  In the inkjet coating of the present invention, the coating solution storage container 2c and each inkjet head 9 are connected by a coating solution supply pipe 2d, and due to the water head difference between the liquid level of the coating solution storage container 2c and the nozzle 9a surface of the inkjet head 9. Natural supply using gravity.

  When ink jet application is performed under atmospheric pressure using the shear type ink jet head 9, good discharge is performed when the liquid level of the application solution storage container 2 c is set to be about 100 mm lower than the nozzle 9 a surface of the ink jet head 9.

  In addition, the meniscus 9e of the inkjet head 9 can be made appropriate by making the liquid level of the coating solution storage container 2c moderately low. When the liquid level becomes high, liquid leakage tends to occur, and when the liquid level is too low, it becomes difficult to discharge.

  Further, if the inkjet head 9 is in the decompression chamber 7 and the coating solution storage container 2c is outside the decompression chamber 7, it is necessary to secure a very large water head difference of 10 m or more, and it becomes difficult to configure the apparatus. Therefore, the coating solution storage container 2 c is also installed in the decompression chamber 7.

  Even if the supply of the material solution 9d is good at atmospheric pressure, the boiling point drops when placed in a reduced pressure environment, so that the water content is easily vaporized, and the volume of the vaporized or internal gas increases in inverse proportion to the pressure. Therefore, a discontinuous portion of the material solution 9d occurs in the coating solution supply pipe 2d, and stable discharge becomes impossible.

  Therefore, the degree of decompression of the decompression chamber 7 is in the range of the saturated vapor pressure of water (3.1 kPa) or more and the atmospheric pressure (101.3 kPa) or less at room temperature (25 ° C.) such as a clean room where the thin film forming apparatus 1 is installed. By setting at, it is possible to prevent the inherent moisture from vaporizing and generating bubbles. If the temperature conditions are different, the lower limit (saturated vapor pressure of water) is also changed accordingly.

  FIG. 6 is a view showing a mechanism for optimally maintaining the water head difference between the liquid level of the coating solution storage container and the nozzle surface of the inkjet head in the thin film forming apparatus according to the present invention.

  Ink jet discharge is important for pressure transmission. However, since the ink jet head 9 is placed in a reduced pressure environment, the coating solution storage container 2c is also placed in the reduced pressure chamber 7 in order to perform natural supply due to a water head difference. Must be done in an environment.

  The allowable range of the water head difference is about 10 mm above and below, but the material solution 9d is consumed, so the liquid level gradually decreases. Therefore, a water head difference adjusting mechanism 11 is provided in the thin film forming apparatus 1.

  A storage container lifting / lowering actuator 11a capable of moving the moving stage 11b in the vertical direction is installed in the decompression chamber 7, and the coating solution storage container 2c is placed on the moving stage 11b.

  Further, the liquid level monitoring sensor 11c is attached so as to sandwich the coating solution storage container 2c. When a drop in the liquid level is detected, the coating solution storage container 2c is raised by the storage container lifting / lowering actuator 11a to always maintain a constant water head difference.

  In order to compensate for the shortage of the material solution 9d, a replenishment tank 11d is provided outside the decompression chamber 7, and the material solution 9d is sent to the application solution storage container 2c by the replenishment pump 11e when the application operation is interrupted. You can also.

  FIG. 7 is a diagram showing a configuration in which the coating solution storage container is disposed above the inkjet head in the thin film forming apparatus according to the present invention, and the piping system is made more efficient.

  The set value of the water head difference is obtained from the balance of the force applied to the material solution 9d in the stationary state on the nozzle 9a surface of the inkjet head 9, and the liquid level of the coating solution storage container 2c is lower than the nozzle 9a surface by the optimal set value. There is a need to.

  However, since the coating gap between the inkjet head 9 and the substrate 3 is usually about 0.5 mm, the coating solution storage container 2c cannot be placed on the substrate transport table 4, and is placed at a position higher than the inkjet head 9. I can't.

  For this reason, if the application solution storage container 2c is installed at a position far away from the movable range of the substrate transfer table 4, the application solution supply pipe 2d becomes very long and the pipe resistance also increases.

  Therefore, in the thin film forming apparatus 1a, the coating solution supply pipe 2d is arranged in a short and orderly manner, and the fine differential pressure adjusting mechanism 12 is provided so that the coating solution storage container 2c can be installed at a position higher than the inkjet head 9, thereby ensuring reliability. To do.

  The fine differential pressure adjusting mechanism 12 uses the electropneumatic regulator 12a to generate a negative fine differential pressure between the inkjet head 9 and the coating solution storage container 2c even when the coating solution storage container 2c is at a high position.

  FIG. 8 is a diagram showing a control structure of an electropneumatic regulator installed in the thin film forming apparatus according to the present invention. The electropneumatic regulator 12a has an exhaust valve 12b and an air supply valve 12c, and can be used for both step-up and step-down by properly using both according to the set pressure.

  For example, when a boost input signal is input to the control circuit 12i, the supply solenoid valve 12d is opened, the exhaust solenoid valve 12e is closed, and a part of the supply air is sent to the pilot chamber 12f through the supply solenoid valve 12d. It is done. When the pressure in the pilot chamber 12f rises and acts on the upper surface of the diaphragm 12g, the air supply valve 12c interlocked with the diaphragm 12g opens, and the pressurization by the air supply becomes the output pressure.

  On the other hand, when a depressurization input signal is input to the control circuit 12i, the supply solenoid valve 12d is closed, the exhaust solenoid valve 12e is opened, and exhaust is performed from the pilot chamber 12f. When the pressure in the pilot chamber 12f is lowered, the exhaust valve 12b interlocked with the diaphragm 12g is opened, and the decompression due to the exhaust becomes the output pressure.

  FIG. 9 is a block diagram for realizing control for converging the output pressure of the electropneumatic regulator of the thin film forming apparatus according to the present invention to a constant value.

  When a series of operations are performed by the electropneumatic regulator 12a, the internal pressure of the pilot chamber 12f is detected by the pressure detection sensor 12h and fed back to the control circuit 12i, so that the operation is repeated until the output pressure is proportional to the input signal. To do.

  The electropneumatic regulator 12a can be improved in accuracy by being installed in multiple stages in series or in parallel.

It is a figure which shows the outline | summary of the thin film formation apparatus which is this invention. It is a figure which shows the cross-section of the liquid crystal display element which formed the alignment film with the thin film forming apparatus which is this invention. It is the top view and front view which show the layout of the head which comprised the pseudo elongate line when performing 1 pass application | coating with the thin film forming apparatus which is this invention. It is a figure which shows the control structure in the application | coating operation | movement of the thin film forming apparatus which is this invention. It is a figure which shows the control structure in the decompression chamber of the thin film forming apparatus which is this invention. It is a figure which shows the mechanism which maintains the water head difference of the liquid level of a coating solution storage container and the nozzle surface of an inkjet head optimally with the thin film forming apparatus which is this invention. It is a figure which shows the structure which arrange | positioned the coating solution storage container above the inkjet head with the thin film forming apparatus which is this invention, and made the piping system efficient. It is a figure which shows the control structure of the electropneumatic regulator installed in the thin film forming apparatus which is this invention. It is a block diagram which implement | achieves the control which converges the output pressure of the electropneumatic regulator of the thin film formation apparatus which is this invention to a fixed value. It is a figure which shows the outline | summary of the conventional thin film formation apparatus. It is the figure shown about the water head difference of the nozzle surface of an inkjet head, and the liquid level of a coating solution storage container. FIG. 4 is a diagram illustrating the influence of the degree of pressure reduction on the final droplet cross-sectional shape when droplets discharged from an inkjet head are developed on a substrate. It is the figure shown about the state of the water head difference which affects the shape of the solution meniscus in the nozzle tip in the stage before discharge. It is a graph which shows the vapor pressure of the solvent component and water of a liquid crystal aligning film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Thin film forming apparatus 1a Thin film forming apparatus 1b Thin film forming apparatus 2 Head 2a Head bracket 2b Actuator for raising / lowering head 2c Coating solution storage container 2d Coating solution supply piping 2e Portal frame 3 Substrate 4 Substrate transport table 4a Electrostatic chuck 5 Stage 5a Lift pin Mechanism 6 Guide rail 6a Table moving actuator 6b Position detector 7 Decompression chamber 7a Base frame 7b Vacuum exhaust pump 7c Volatile solvent adsorption processing device 7d Vacuum seal 7e Vacuum gauge 7f Sequencer 7g Communication means 7h Servo amplifier 7i Variable pressure regulating valve 7j Servo motor 7k Leak valve 8 Liquid crystal panel 8a Alignment film 9 Inkjet head 9a Nozzle 9b Material solution supply port 9c Head controller connection cable 9d Material solution 9e Meniscus 9f Liquid dripping DESCRIPTION OF SYMBOLS 10 System controller 10a Inkjet head controller 10b Head drive part 10c Memory part 10d Control part 10e Control computer 10f Stage controller 10g Depressurization control 11 Hydrohead adjustment mechanism 11a Storage container raising / lowering actuator 11b Moving stage 11c Liquid level monitoring sensor 11d For replenishment Tank 11e Replenishment pump 12 Fine differential pressure adjustment mechanism 12a Electro-pneumatic regulator 12b Exhaust valve 12c Intake valve 12d Inlet solenoid valve 12e Exhaust solenoid valve 12f Pilot chamber 12g Diaphragm 12h Pressure detection sensor 12i Control circuit 13 Formation in air Membrane behavior 13a Deposition behavior under reduced pressure 14 Suitable head differential 14a Excessive head differential 14b Insufficient head differential 15 Vapor pressure diagram

Claims (4)

A plurality of inkjet heads for discharging a material solution from a plurality of nozzles formed at regular intervals and applying the solution to a substrate;
A coating solution storage container for supplying a material solution to the inkjet head using a water head difference between a nozzle surface and a liquid surface;
A substrate transfer table for placing and moving the substrate horizontally;
A system controller having an inkjet head controller that controls the ejection of the inkjet head, and a stage controller that moves the substrate transfer table and detects the position and performs feedback control;
A decompression chamber having decompression means for housing the inkjet head, the coating solution storage container, and the substrate transfer table;
The thin film forming apparatus, wherein the coating solution storage container directly connected to the ink jet head is placed under the same reduced pressure environment.   2. The thin film forming apparatus according to claim 1, wherein the pressure in the decompression chamber is in a range from atmospheric pressure (101.3 kPa) to 3.1 kPa which is a saturated vapor pressure of water.   A water head difference adjustment mechanism is provided that detects the liquid level of the coating solution storage container and moves the coating solution storage container up and down to maintain a constant water head difference between the nozzle surface of the inkjet head and the liquid surface of the coating solution storage container. The thin film forming apparatus according to claim 1, wherein the thin film forming apparatus is provided.   A fine differential pressure adjusting mechanism is provided in which the coating solution storage container is installed at a position higher than the inkjet head, and a negative differential pressure is generated between the inkjet head and the coating solution storage container by an electropneumatic regulator. The thin film forming apparatus according to any one of claims 1 to 3.

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