JP2011005404A - Wiring forming device, wiring forming method and wiring forming material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily form a wiring with high aspect ratio with respect to a technology for forming the wiring by applying coating liquid containing a wiring material on the surface of a substrate.SOLUTION: The substrate W is placed on a cool plate 31 and for example, cooled to a liquid nitrogen temperature and moved to the X-direction in this state while discharging the coating liquid containing the wiring material from a discharge nozzle 52. The coating liquid applied on the substrate W becomes highly viscous by being cooled to keep the shape when discharged. The coating liquid on the substrate is irradiated with a UV light to be photo-cured to form the wiring which has the shape kept when discharged and a high aspect ratio.

Description

  The present invention relates to a wiring forming apparatus and a wiring forming method for forming a wiring by applying a coating liquid containing a wiring material on a substrate surface, and a wiring forming material that can be used in the apparatus and method.

  For example, in a manufacturing technique of a photoelectric conversion device that receives light and generates an electromotive force, such as a solar cell, it is necessary to arrange a current collecting electrode or wiring on a light receiving surface of a substrate. As a technique for forming such a wiring, there are a technique for depositing a metal as a wiring material on the surface of a substrate, a technique for printing a coating liquid containing a conductive material by screen printing or an inkjet method, and the like. The wiring for the photoelectric conversion device is preferably one that shields incident light as much as possible and does not reduce the photoelectric conversion efficiency, and has a low electrical resistance. A high height ratio is desirable. However, since the above technique generally forms a thin-film wiring, a high aspect ratio cannot always be obtained.

  In order to solve this problem, there is a technique that employs a so-called nozzle scan method in which a wiring material having a relatively high viscosity is discharged from a nozzle and applied to a substrate. For example, in the techniques described in Patent Document 1 and Patent Document 2, a groove is engraved in the substrate in advance, and an electrode material is poured into the groove from a nozzle to form an electrode having a narrow width and a large thickness. Yes. In the technique described in Patent Document 3, a grid line (wiring) material having fluidity with respect to the substrate surface and a sacrificial material discharged so as to sandwich both sides thereof are coextruded from a nozzle, and then the substrate is heat treated. By evaporating the sacrificial material, high aspect ratio grid lines are obtained.

Japanese Patent Laid-Open No. 2004-281813 (for example, FIG. 4) JP 2006-54374 A (for example, FIG. 1) Japanese Patent Laid-Open No. 2008-118150 (for example, FIGS. 1 and 5)

  The techniques described in Patent Documents 1 and 2 described above have preliminary processing of providing grooves in the substrate in advance, and the process is complicated and the manufacturing cost increases, and in addition to meet the recent demand for thinner substrates. Is difficult. Further, the technique described in Patent Document 3 requires a complicated process of applying and removing a sacrificial material that is not necessary for the final device, and it is impossible to suppress an increase in manufacturing cost.

  Thus, a technique for reliably forming a high aspect ratio wiring at a low cost has not been established so far.

  The present invention has been made in view of the above problems, and in an apparatus and method for forming a wiring by applying a coating liquid containing a wiring material on a substrate surface, and a wiring forming material that can be used in these apparatuses and methods, It is an object of the present invention to provide a technique capable of easily forming a high aspect ratio wiring.

  In order to achieve the above object, a wiring forming apparatus according to the present invention scans and moves a discharge nozzle that discharges a coating liquid containing a wiring material relative to a substrate surface, and the discharge nozzle relative to the substrate surface. A moving mechanism and a thickening means for increasing the viscosity of the coating liquid immediately after being discharged onto the substrate surface from the discharge nozzle are provided.

  In the invention configured as described above, in a wiring forming apparatus that employs a so-called nozzle scan method in which a coating liquid containing a wiring material is discharged onto a substrate surface from a discharge nozzle that moves relative to the substrate surface, the coating is applied to the substrate surface. It has a means for increasing the viscosity of the coating liquid immediately after. When applying the coating liquid containing the wiring material discharged from the discharge nozzle to the substrate surface, it is desirable that the viscosity of the coating liquid is low from the viewpoint of smoothly discharging the coating liquid from the discharge nozzle, while the coating liquid is applied to the substrate surface. From the viewpoint of maintaining a high aspect ratio without spreading the coating solution to the surroundings, there is a conflicting requirement that a higher viscosity of the coating solution is desirable. Therefore, by providing a means for increasing the viscosity of the coating liquid immediately after discharge, it becomes possible to achieve both good coating properties and an effect of suppressing the spread of the coating liquid after coating, thereby facilitating wiring with a high aspect ratio. It becomes possible to form.

  Here, the discharge nozzle further includes light irradiation means for discharging the coating liquid containing a photocurable material and irradiating the coating liquid whose viscosity is increased on the surface of the substrate to be cured. Also good. By doing so, the coating liquid containing the wiring material can be reliably cured, and a stable wiring having a high aspect ratio can be formed.

  As the thickening means, for example, one having a substrate cooling unit that cools the substrate while holding the substrate can be used. In general, the coating solution containing the wiring material has a lower viscosity as the temperature is lower. By cooling the substrate to which the coating solution is applied, the viscosity of the coating solution immediately after coating is increased and is prevented from spreading to the surroundings. If the coating liquid is irradiated with light in this state and cured, the wiring material can be cured while maintaining a high aspect ratio. In addition, if the coating liquid itself is cooled in advance, problems such as a decrease in fluidity in the discharge nozzle and solidification of the coating liquid around the discharge port of the discharge nozzle may occur. On the other hand, if the substrate is cooled, the viscosity of only the coating solution in contact with the substrate increases, so that such a problem does not occur.

  In particular, when the discharge nozzle discharges the coating liquid containing the wiring material and the solvent, it is preferable that the substrate cooling unit cools the substrate to a temperature below the freezing point of the solvent. By doing so, the coating liquid applied to the substrate surface is almost solidified in a short time, and curing by light irradiation occurs while maintaining a shape close to that immediately after being discharged from the discharge nozzle. Thereby, the spreading of the coating solution after coating hardly occurs, and it becomes possible to obtain a wiring having a high aspect ratio.

  On the other hand, a substrate heating unit that heats the substrate while holding the substrate may be provided as the thickening means. By applying the coating liquid on the surface of the heated substrate, the volatilization of the solvent component is promoted in the coating liquid touching the substrate. Thus, the viscosity of the coating liquid increases due to the loss of the solvent component. Therefore, the spread of the coating liquid after coating can be suppressed.

  Here, the discharge nozzle may discharge the coating liquid containing the wiring material and a solvent, and the substrate heating unit may heat the substrate to a temperature not higher than the boiling point of the solvent. When the substrate is heated to a temperature higher than the boiling point of the solvent, there is a possibility that the solvent contained in the coating solution touching the surface of the substrate will violently evaporate or boil and the shape immediately after coating may be destroyed. Therefore, when the substrate is heated, the temperature of the substrate does not exceed the boiling point of the solvent, so that the shape of the wiring can be prevented from collapsing.

  In the invention configured to heat the substrate, the moving mechanism moves the discharge nozzle relative to the substrate surface so that the coating liquid is applied multiple times to the same portion of the substrate surface. You may make it move. When a coating solution is applied to a heated substrate, the solvent component volatilizes in a short time, so the fluidity of the coating solution is extremely lowered. For this reason, it is possible to apply in the same place. By doing so, the thickness of the wiring can be increased.

  In this case, it is desirable that the coating amount in the subsequent coating does not exceed the coating amount in the previous coating. By doing this, since the subsequent coating liquid does not overflow from the region where the coating liquid has been previously applied, only the thickness can be increased without increasing the width of the wiring. Moreover, when hardening wiring by light irradiation after application | coating, it is desirable to perform light irradiation after apply | coating repeatedly. By doing so, it is possible to integrally cure each layer that has been overcoated, and to form a wiring having a stronger structure.

  In addition, in order to achieve the above object, the wiring forming material according to the present invention contains conductive particles and an organic vehicle, and 10 wt% or more and 90 wt% or less of the solvent content in the organic vehicle. Is an organic solvent having a boiling point of 80 ° C. or lower. As will be described in detail later, the wiring forming material having such a composition has high fluidity in a sealed environment, that is, has a low viscosity, and thus is suitable for a coating operation. On the other hand, the solvent starts to volatilize immediately after being discharged into the external space, and the viscosity increases in a short time and changes to a low fluidity state. For this reason, for example, as soon as it is applied to the substrate, the fluidity is low and it does not spread to the surroundings. Therefore, for example, it can be suitably used as a wiring forming material used in an apparatus and method for forming a wiring by coating the substrate surface from a discharge nozzle.

  In this case, as the organic solvent, any one of acetone, ethyl acetate and methyl ethyl ketone can be used. According to experiments by the inventors of the present application, it has been confirmed that these materials can be suitably used for the wiring forming material of the present invention. In addition, in order to make it possible to form a stronger wiring, a photocurable material may be further contained.

  According to a first aspect of the wiring forming method of the present invention, in order to achieve the above object, a step of applying a coating liquid containing a wiring material and a photocurable material to the substrate surface, and the substrate surface And irradiating the coating liquid applied to the substrate with light, and curing the substrate at a predetermined temperature at least from the time when the coating liquid is applied to the substrate surface until the light is irradiated. It is characterized by cooling.

  In the invention configured as described above, since the substrate is cooled until the coating solution containing the wiring material and the photocurable material and applied to the substrate is cured by light irradiation, the applied coating solution is applied. Increases in viscosity and is prevented from flowing out to the surroundings. And since a coating liquid hardens | cures by light irradiation in this way, the state with a high viscosity is maintained, A wiring with a high aspect ratio can be formed easily.

  In addition, the second aspect of the wiring forming method according to the present invention includes a step of heating the substrate to a predetermined temperature and a wiring material and a solvent for the heated substrate surface in order to achieve the above object. And a step of applying a coating solution. In the invention configured as described above, by heating the substrate, the solvent contained in the coating solution applied to the substrate is volatilized in a short time, so that the spread of the coating solution can be suppressed. Therefore, as described above, a wiring having a high aspect ratio can be easily formed.

  Also in this wiring formation method, it is possible to apply the coating solution in a plurality of times on the same location on the substrate surface. Thereby, it is possible to form a wiring having a greater thickness, that is, a higher aspect ratio.

  In addition, a coating liquid containing a photo-curable material is used, and after the application of the coating liquid to the substrate surface is completed, the coating liquid is further irradiated with light to be cured and further strengthened. It is also possible to obtain wiring. In this case, as described above, when the coating liquid is applied in a plurality of times, it is desirable to perform light irradiation after the coating is completed.

  According to the wiring forming apparatus and the wiring forming method of the present invention, since the viscosity of the coating liquid containing the wiring material is increased on the substrate surface after coating, the coating property by nozzle discharge is excellent, and the The spread of the coating liquid can be suppressed and a high aspect ratio wiring can be easily formed. In addition, the wiring forming material according to the present invention has a high aspect ratio when applied to an apparatus and method for forming a wiring by applying it to a substrate surface because the solvent evaporates in a short time immediately after application and the viscosity increases. Ratio wiring can be easily formed.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows 1st Embodiment of the wiring formation apparatus concerning this invention. It is an enlarged view which shows the structure of a head part in detail. It is a figure which shows typically the mode of discharge of the wiring material from a head part. It is a figure which shows the relationship between the temperature of a coating liquid, and a viscosity. It is a flowchart which shows the wiring formation process in 1st Embodiment. It is a figure which shows 2nd Embodiment of the wiring formation apparatus concerning this invention. It is a figure which shows the relationship between the solvent density | concentration in a coating liquid, and a viscosity. It is a flowchart which shows the wiring formation process in 2nd Embodiment. It is a figure which shows the result of having evaluated the composition and the property of the coating liquid. It is a figure which shows the modification of 2nd Embodiment.

<First Embodiment>
FIG. 1 is a view showing a first embodiment of a wiring forming apparatus according to the present invention. The wiring forming apparatus 1 is an apparatus for forming a conductive wiring on a substrate W such as a single crystal silicon wafer having a photoelectric conversion layer formed on the surface thereof, and manufacturing a photoelectric conversion device used as a solar cell, for example. It is. The apparatus 1 can be suitably used for an application in which a collecting electrode is formed on a light incident surface of a photoelectric conversion device, for example.

  In this wiring forming apparatus 1, a stage moving mechanism 2 is provided on a base 11, and a stage 3 that holds a substrate W can be moved in the XY plane shown in FIG. 1 by the stage moving mechanism 2. A frame 12 is fixed to the base 11 so as to straddle the stage 3, and the head unit 5 is attached to the frame 12.

  A cool plate 31 for cooling the substrate W to a predetermined temperature is installed on the upper surface of the stage 3. The temperature of the cool plate 31 is controlled by the cooling unit 32. As will be described in detail later, the cooling capacity required for the cool plate 31 is about minus several tens of degrees, and the cooling principle is not particularly limited as long as such a low temperature can be obtained. For example, a device using an electronic refrigeration technique or a device that allows a refrigerant such as liquid nitrogen to pass through can be used.

  The stage moving mechanism 2 includes an X direction moving mechanism 21 that moves the stage 3 in the X direction from the lower stage, a Y direction moving mechanism 22 that moves the stage 3 in the Y direction, and a θ rotation mechanism 23 that rotates about an axis that faces the Z direction. Have. The X-direction moving mechanism 21 has a structure in which a ball screw 212 is connected to a motor 211 and a nut 213 fixed to the Y-direction moving mechanism 22 is attached to the ball screw 212. When the guide rail 214 is fixed above the ball screw 212 and the motor 211 rotates, the Y-direction moving mechanism 22 moves smoothly along the guide rail 214 in the X direction along with the nut 213.

  The Y-direction moving mechanism 22 also has a motor 221, a ball screw mechanism, and a guide rail 224. When the motor 221 rotates, the θ-rotation mechanism 23 moves in the Y direction along the guide rail 224 by the ball screw mechanism. The θ rotation mechanism 23 rotates the stage 3 about the axis facing the Z direction by the motor 231. With the above configuration, the relative movement direction and orientation of the head unit 5 with respect to the substrate W can be changed.

  The head unit 5 includes a discharge nozzle 52 that discharges a liquid coating liquid onto the substrate W and a light irradiation unit 53 that irradiates UV light (ultraviolet rays) toward the substrate W on the lower surface of the base 51. A supply pipe 522 having a check valve 521 is attached to 52. The supply pipe 522 is branched, one is connected to the pump 523, and the other is connected to the tank 525 storing the coating liquid containing the wiring material via the control valve 524. The light irradiation unit 53 is connected to a light source unit 532 that generates ultraviolet rays via an optical fiber 531.

  Each motor of the stage moving mechanism 2, the pump 523, the control valve 524, the light source unit 532, and the cooling unit 32 are connected to the control unit 6, and these components are controlled by the control unit 6, whereby the substrate formed by the wiring forming apparatus 1. A wiring pattern is formed on W.

  FIG. 2 is an enlarged view showing the configuration of the head portion in more detail. More specifically, FIG. 2A is a diagram showing the shape near the tip of the discharge nozzle when the head unit 5 is viewed from the side, and FIG. 2B is a diagram of the head unit 5 viewed from below. As shown in FIG. 2A, the inside of the discharge nozzle 52 is a cylindrical cavity 52a, and the lower end opens obliquely to the right in the figure to form a discharge port 52b. The coating liquid transported from the tank 525 via the supply pipe 522 is discharged toward the substrate W from the discharge port 52 b at the lower end of the discharge nozzle 52.

  Further, a lens 533 is provided at the tip of the light irradiation unit 53, and the UV light from the light source unit 532 is configured to be condensed on the coating liquid discharged from the first discharge unit 52 onto the substrate W. ing.

  As shown in FIG. 2B, a plurality of discharge ports 52b are arranged at substantially equal intervals in the Y direction. The lens 533 at the lower end of the light irradiation unit 53 is formed in an oval shape so as to cover all the positions where the discharge ports 52b are arranged in the Y direction.

  The number of discharge ports 52b is not particularly limited, but may be, for example, 256. Also, the material of the discharge nozzle 52 is not particularly limited, but for example, silicon or zirconia crystals can be used from the viewpoint that contaminants are not mixed into the discharge liquid and fine processing can be performed.

  FIG. 3 is a diagram schematically showing how the coating liquid is discharged from the head portion. More specifically, FIG. 3A is a side view of the state in which the coating liquid is discharged from the head unit 5. FIG. 3B is a view of the same viewed from obliquely above. In FIG. 3B, the light irradiation unit 53 is not shown in order to make it easier to see the state of discharge from the discharge nozzle 52. Hereinafter, the basic operation of wiring formation by the wiring forming apparatus 1 will be described with reference to FIGS. 1 to 3.

  The discharge of the coating liquid from the discharge nozzle 52 is performed by the check valve 521, the pump 523, and the control valve 524 shown in FIG. First, the pump 523 performs a suction operation with the control valve 524 being opened under the control of the control unit 6. At this time, since the check valve 521 prevents the backflow of the coating liquid, the coating liquid is drawn from the tank 525 to the pump 523. Next, the control valve 524 is closed under the control of the control unit 6, and the pump 523 performs an extrusion operation. Thereby, the coating liquid A1 is continuously discharged from each of the plurality of discharge ports 52b of the discharge nozzle 52.

  When the coating liquid is discharged, the control unit 6 drives and controls each motor of the stage moving mechanism 2 and controls the surface of the substrate W to move in the (+ X) direction below the head unit 5. . In other words, the head unit 5 moves in the (−X) direction while relatively scanning the surface of the substrate W. Thereby, the coating liquid is applied to the surface of the substrate W in a streak shape along the X direction. At this time, the coating liquid A1 is discharged from the discharge port 52b toward the rear in the scanning movement direction, and the discharged liquid is prevented from staying in the vicinity of the discharge port 52b.

  On the rear side (right side in FIG. 3A) of the discharge nozzle 52 in the relative movement direction of the head unit 5 with respect to the substrate W, the UV light L is irradiated from the light irradiation unit 53 to the discharged coating liquid A1. When the coating liquid A1 contains a photocurable resin material, a crosslinking reaction occurs due to the irradiation with the UV light L, and solidification starts. As a result, as shown in FIG. 3B, parallel streak-like structures B1 formed by solidifying the coating liquid A1 discharged from the discharge ports 52b are formed on the substrate W.

  Next, a specific mode of wiring formation on the substrate W by the wiring forming apparatus 1 configured as described above will be described. In this embodiment, a wiring is formed by discharging a coating liquid containing a wiring material from the discharge nozzle 52 and applying it to the surface of the substrate W. At this time, the substrate W is cooled to a low temperature of about several tens of degrees below freezing. This is a major feature. This is to prevent the coating liquid discharged from the nozzle and applied to the substrate surface from spreading on the substrate surface, thereby forming a wiring having a narrow width but a high height, that is, a high aspect ratio.

  In order to smoothly discharge the coating liquid from the discharge nozzle 52 through the supply pipe 522 from the tank 525, it is desirable that the viscosity of the coating liquid is low. However, when such a low-viscosity liquid is applied to the substrate surface, the coating liquid flows and spreads to the surroundings, resulting in a wiring having a wide width and low height, that is, a low aspect ratio. . In order to prevent this, if a high-viscosity coating liquid is used, a high-definition pattern cannot be formed due to the liquid remaining in the supply pipe 525 or solidifying near the tip of the discharge nozzle 52. Sometimes. This embodiment can avoid such a problem.

  FIG. 4 is a diagram showing the relationship between the temperature and viscosity of the coating solution. In the coating liquid containing conductive particles (for example, metal fine particles) as a wiring material and a solvent, as shown in FIG. 4, the lower the liquid temperature, the higher the viscosity and the lower the fluidity. In particular, the change in viscosity is large near the freezing point (fp) of the solvent. In addition, since there is a freezing point drop, the coating liquid does not always freeze at a temperature below the freezing point of the solvent. However, even if it is not completely frozen near the freezing point, the viscosity of the liquid is about several hundred thousand cP, and its fluidity is sufficiently low. That is, in this state, the coating liquid applied to the substrate surface hardly spreads and maintains the initial shape. In this way, if light irradiation is performed with the fluidity of the coating liquid suppressed and the photocuring reaction of the coating liquid proceeds, the wiring material can be solidified while maintaining the shape immediately after coating to obtain a wiring with a high aspect ratio. it can.

  As described above, the substrate temperature may be about the freezing point of the solvent contained in the coating solution or lower. For example, when the substrate temperature is a liquid nitrogen temperature (−196 ° C., 77 K), it is sufficiently lower than the freezing point of a general organic solvent, so that the coating liquid discharged on the substrate is solidified in a short time and almost immediately after discharge. The shape is maintained. However, as shown in FIG. 4, since the viscosity increases as the temperature decreases, the effect of suppressing the spread of the coating solution can be obtained by cooling the substrate from room temperature even at the freezing point or higher. Therefore, for example, even if the substrate is cooled by the principle of a heat exchange type refrigerator using a refrigerant or an electronic refrigerator using the Peltier effect, it is sufficiently practical.

  FIG. 5 is a flowchart showing a wiring formation process in this embodiment. First, an unprocessed substrate W is carried into the apparatus 1 (step S101) and placed on the cool plate 31 on the stage 3. Next, the cooling unit 32 is operated to cool the substrate W to a predetermined temperature (step S102). Then, the stage 3 is moved in the X direction while discharging the coating liquid containing the wiring material from the discharge nozzle 52 (step S103). At this time, UV light is irradiated from the light irradiation unit 53 to the coating liquid immediately after coating. As a result, as illustrated in FIG. 3B, stripe-like wiring along the X direction is drawn on the surface of the substrate W.

  After the wiring is formed up to the vicinity of the edge of the substrate W and drawing is continued until the stage 3 reaches a predetermined end position (step S104), the discharge of the coating liquid, the movement of the stage, the irradiation of the UV light, and the cooling of the substrate are stopped. Then (step S105), the substrate is unloaded (step S106), and the processing for one substrate W is completed. Since the applied wiring material has already undergone a curing reaction by light irradiation, the cross-sectional shape of the wiring does not collapse even when the substrate W is returned to room temperature.

  As described above, in this embodiment, the substrate is cooled in advance when the coating liquid is applied to the substrate surface. For this reason, the viscosity of the coating liquid increases greatly immediately after coating, and a shape close to the cross-sectional shape at the time of coating is temporarily held. Then, while maintaining this shape by maintaining a low temperature state, the wiring material is irreversibly cured by light irradiation to form a high aspect ratio wiring close to the cross-sectional shape at the time of application on the substrate W. Can do.

  Although it is conceivable to cool the coating solution in advance or place the entire apparatus at a low temperature, this will increase the viscosity of the coating solution before discharging, clogging the supply pipe and nozzle, Problems such as difficulty in forming a simple wiring may occur. It can be said that it is most reasonable to cool only the substrate W so that the coating liquid is cooled by touching the substrate.

  In the first embodiment of the present invention described above, a coating liquid is applied to a cooled substrate, and the coating liquid is cooled and cured by light irradiation in a state where the viscosity is increased, thereby obtaining a high aspect ratio wiring. I am trying to do it. On the contrary, in the second embodiment of the present invention described below, the coating liquid is applied while the substrate is heated.

Second Embodiment
FIG. 6 is a view showing a second embodiment of the wiring forming apparatus according to the present invention. The basic configuration and operation of the coating apparatus 1a in this embodiment are substantially the same as those in the first embodiment described above. However, a hot plate 35 for heating the substrate is provided on the stage 3 instead of the cool plate 31 of the first embodiment, and a heating unit 36 for controlling the hot plate 35 is provided instead of the cooling unit. Except for this point, the apparatus configuration is the same as that of the first embodiment.

  FIG. 7 is a graph showing the relationship between the solvent concentration in the coating solution and the viscosity. Naturally, the higher the solvent concentration in the coating solution is, the lower the viscosity is, but this is not a simple decrease. As shown in FIG. 7, the viscosity greatly changes before and after the threshold Cth of a certain solvent concentration. . From this, if the solvent concentration of the coating liquid before discharge is made higher than the threshold value Cth and the solvent concentration is rapidly decreased to the threshold value Cth or less after discharge, the viscosity of the coating liquid increases rapidly. Spreading on the substrate can be prevented, and high aspect ratio wiring can be formed.

  Therefore, in this embodiment, the coating liquid is applied to the preheated substrate W, and the solvent is rapidly volatilized from the coating liquid touching the heated substrate W to reduce the concentration of the coating liquid. I try to suppress the spread. If a curing reaction is caused by light irradiation in a state where the solvent concentration is lowered in this way, a stronger cross-linked structure excluding the solvent can be formed, and the strength of the wiring can be increased.

  In addition, as the coating liquid containing the wiring material, conductive pastes that have already been commercialized can be used, and such conductive paste is of a type that is solidified only by volatilization of the solvent without being photocured. Is also present. In the wiring forming apparatus 1a of this embodiment, even when such a type of coating solution is used, the evaporation of the solvent is promoted by heating the substrate. Is possible. In this case, light irradiation from the light irradiation unit 53 may be omitted.

  In addition, this embodiment is also effective when it is desired to apply the coating liquid to the same location on the substrate W in order to form a wiring having a higher height. This is because, unlike the increase in viscosity due to cooling in the first embodiment, the increase in viscosity due to the volatilization of the solvent is an irreversible change. This is because the new coating solution forms a new layer on the solidified layer of the previous coating solution because it is solidified so as not to be mixed with.

  In this case, if a new coating solution overflows from the previously applied layer, a wiring with a high aspect ratio cannot be obtained. In order to prevent this, it is desirable that the amount of the coating liquid to be applied later does not exceed the amount applied in the previous application, and for example, it is preferable to reduce the amount applied in the subsequent application step. If it does in this way, the coating liquid after that will not spread beyond the breadth of the liquid in previous application | coating, and an application layer can be piled up every time it coats, and thickness can be increased.

  When coating is performed using a method of solidifying by light irradiation after coating, light irradiation may be performed for each coating, but more preferably, light irradiation is not performed at the time of coating each layer. It is preferable to perform light irradiation after completing the layer coating. When light irradiation is performed for each coating, solidification by cross-linking reaction proceeds in each layer, but bonding between different layers becomes weak and the strength when viewed as the whole wiring is inferior. On the other hand, when the light irradiation is performed after finishing the coating of all the layers, the entire coated layer is solidified by a crosslinking reaction, so that the strength of the wiring can be further increased.

  The temperature of the substrate can be set based on, for example, the following concept. The higher the substrate temperature, the more the solvent volatilization is promoted. On the other hand, if the temperature is too high and the coating liquid boils inside, bubbles will be generated inside it and it will be able to bounce, thereby disturbing the shape and electrical characteristics of the wiring. Therefore, it is desirable that the temperature is lower than the temperature at which the coating liquid boils. If the boiling point of a commercially available coating solution is specified, it may be based on the temperature; otherwise, it is slightly lower based on, for example, the boiling point of the main solvent contained in the coating solution. It is better to keep the temperature of For example, in the case of a coating solution containing acetone having a boiling point of about 56 ° C. as a main solvent, the substrate temperature may be about 50 ° C. Other major organic solvents have boiling points of about several tens of degrees Celsius, and therefore, the substrate temperature may be a temperature that is several degrees lower than their boiling points.

  FIG. 8 is a flowchart showing the wiring formation process in this embodiment. Here, the wiring formation process in the case of using a coating liquid premised on curing by light irradiation, that is, using a photopolymerization initiator as a component will be described. When using a coating solution that is not photo-curable, the light irradiation process in step S207 described later may be omitted.

  First, an unprocessed substrate W is carried into the apparatus 1a (step S201) and placed on the hot plate 35 on the stage 3. Next, the heating unit 36 is operated to heat the substrate W to a predetermined temperature (step S202). Then, the stage 3 is moved in the X direction while discharging the coating liquid containing the wiring material from the discharge nozzle 52 (step S203). As a result, as illustrated in FIG. 3B, stripe-like wiring along the X direction is drawn on the surface of the substrate W. At this time, light irradiation from the light irradiation unit 53 is not performed. Since the substrate is heated, the solvent of the coating solution evaporates and solidifies, but the wiring at this point remains extremely brittle.

  After the wiring is formed up to the vicinity of the end of the substrate W and drawing is continued until the stage 3 reaches a predetermined end position (step S204), the discharge of the coating liquid and the movement of the stage 3 are stopped (step S205). When the coating liquid is applied repeatedly, the above steps S203 to S205 are repeated until the predetermined number of times is reached (step S206).

  When the number of coating times reaches a predetermined number, the substrate W coated with the coating liquid is irradiated with light, and the coating liquid is photocured to complete the wiring (step S207). Specifically, by stopping the discharge of the coating liquid from the discharge nozzle 52, while the UV light is emitted from the light irradiation unit 53, the stage 3 is scanned and moved in the X direction by the stage moving mechanism 2. The entire coating solution on the substrate W is irradiated with UV light. When the light irradiation is completed, the substrate W is unloaded (step S208), whereby the processing for one substrate W is completed.

  As described above, in this embodiment, the substrate is heated in advance when the coating liquid is applied to the substrate surface. For this reason, the concentration of the solvent rapidly decreases immediately after application and the viscosity increases greatly, and the coating liquid maintains a shape close to the cross-sectional shape at the time of application. Although this change is irreversible, a wiring with a high aspect ratio close to the cross-sectional shape at the time of application can be formed on the substrate W by further irradiating light to cure the wiring material.

<Composition example of coating solution>
The two embodiments described above are contradictory in that one is for cooling the substrate while the other is for heating the substrate, but “by rapidly increasing the viscosity of the coating solution on the substrate surface. This is common in the technical idea of “maintaining the shape immediately after application”. The inventors of the present application have also studied the composition of a coating solution suitable for such purposes. The composition examples described below can be suitably applied to the wiring forming apparatuses of the first and second embodiments, and are particularly suitable for the wiring forming apparatus 1a of the second embodiment. However, the present invention is not limited to these apparatuses, and can be suitably applied to a wiring forming apparatus and a wiring forming method that form a wiring by discharging from a discharge nozzle onto a substrate.

A coating liquid suitable for the above purpose is a liquid having a property that viscosity is low and fluidity is good when sealed in a container, but the viscosity immediately increases when it is opened to the external space. As a result of various experiments, the present inventors have found that a coating liquid having such properties is preferably provided with the following conditions. The condition is:
(1) including conductive particles and an organic vehicle (a mixture of solvent, resin, thickener, etc.),
(2) Of the solvent components contained in the organic vehicle, the ratio of the organic solvent having a boiling point of 80 ° C. or less to the total solvent is 10 to 90 weight percent.
These are two points. Below, a part of experimental result by the inventors of the present application is shown.

  FIG. 9 is a diagram showing the results of evaluating the composition and properties of the coating solution. Coating solutions having various composition ratios were experimentally prepared, and the characteristics as the coating solution were evaluated. There are two evaluation items: line width and continuous discharge. Among these, “line width” is an evaluation item related to the spread of the wiring on the substrate, and the coating liquid is ejected from the ejection nozzle having an inner diameter of 50 μm onto the substrate at a speed of 20 mm / sec and allowed to stand at room temperature for 5 minutes. The spread width of the liquid is evaluated. Those with the spread remaining at 100 μm or less are represented by “◯” marks, those having 110 μm or more are represented by “X” marks, and the middle of them is represented by “Δ” marks.

  “Continuous discharge” represents the ease of discharge from the nozzle, and the solid in the nozzle and around the discharge port after the operation of turning the discharge on and off 100 times is repeated. This is an evaluation of the presence or absence of adhesion of objects. The symbol “◎” indicates that no deposit was observed, the symbol “◯” indicates that a small amount of deposit was observed, and the symbol “×” indicates that a relatively large amount of deposit was generated. Such deposits obstruct the flow of the coating solution and disturb the shape of the wiring.

  Silver powder was used as the conductive particles constituting the coating solution. As the organic vehicle, one containing ethyl cellulose as a resin material and an organic solvent was used. As the organic solvent, terpionele (boiling point is about 200 ° C, slightly different depending on the structural isomer) is used as the high boiling point solvent, acetone (boiling point is about 56 ° C), ethyl acetate (77 ° C) and methyl ethyl ketone (same as above). 79 ° C). In addition, a small amount of glass frit was added. In this experiment, the contents of silver powder, glass frit and ethyl cellulose were fixed, and only the composition of the solvent occupying the balance was changed, and the above two evaluation items were evaluated.

  As shown in FIG. 9, the coating solution using only the high boiling point terpione as the solvent has good continuous discharge property but has a problem in the line width. This is considered due to the slow evaporation of the solvent. The line width is gradually improved by increasing the ratio of solvents having a lower boiling point such as acetone, ethyl acetate, methyl ethyl ketone, etc., but when the ratio of the low boiling point solvent is increased to 90% or more, the continuous discharge property is decreased. . This is presumably because the coating liquid was dried too quickly and the coating liquid was solidified in the vicinity of the ejection port immediately after ejection.

  As the low boiling point solvent, in addition to those shown here, tetrahydrofuran (boiling point: about 66 ° C.), hexane (69 ° C.) and the like are good and solubility in the resin is slightly inferior, but ethyl alcohol (78 ° C.) is used. Next to this. Further, the same tendency is observed in a composition containing no glass frit and a composition containing a slight amount of a photopolymerization initiator. From these results, it can be said that those meeting the above conditions (1) and (2) have properties preferable as a coating solution.

<Others>
As described above, in each of the above embodiments, the discharge nozzle 52 functions as the “discharge nozzle” of the present invention, and the stage moving mechanism 2 functions as the “moving mechanism” of the present invention. The light irradiation unit 53 functions as the “light irradiation means” of the present invention. The cool plate 31 in the first embodiment functions as the “substrate cooling unit” of the present invention, while the hot plate 32 in the second embodiment functions as the “substrate heating unit” of the present invention. All correspond to the “thickening means” of the present invention.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, the composition of the coating liquid described above is a partial example, and the present invention is not limited to this. Other combinations of the materials listed above may be used. In addition, a coating liquid other than the above-described composition may be applied to the above-described wiring forming apparatuses 1 and 1a, and the coating liquid having the above composition is applied to a wiring forming apparatus having a configuration different from that of the wiring forming apparatuses 1 and 1a. May be.

  Moreover, in the said 1st Embodiment, although the light irradiation part 53 was provided in the head part 5 holding the discharge nozzle 52 and UV light was irradiated to the coating liquid immediately after apply | coating to a board | substrate, in 2nd Embodiment. Similarly to the apparatus, the light irradiation may be performed after the application to the entire substrate is completed. In this case, the light irradiation does not need to be performed by this apparatus, and may be performed by moving the substrate to another apparatus under the condition that the low temperature state is maintained. The same applies to the second embodiment, and the substrate after coating may be moved to another light irradiation device to perform light irradiation. In such a case, it is not necessary to provide the light irradiation function in the wiring forming apparatuses 1 and 1a.

  FIG. 10 is a diagram showing a modification of the second embodiment. In the second embodiment, as shown in FIG. 10, a gas discharge nozzle 59 for sending gas to the coating liquid applied on the substrate W from the discharge nozzle 52 is provided, and dry air or inert is supplied from the nozzle 59. Gas may be allowed to flow around the coating solution on the substrate surface. In this way, since the solvent component evaporated from the coating solution is replaced with dry air or inert gas, the evaporation of the solvent is further promoted, and the viscosity increases rapidly. In this case, it is more effective to discharge a preheated gas. Such a method is also applicable to a technique that does not heat the substrate. That is, even in a configuration in which the hot plate 35 is not provided, by discharging a gas (preferably warmed) to the coating solution immediately after coating, the evaporation of the solvent is promoted to increase the viscosity of the coating solution. The spread can be suppressed.

  In each of the above embodiments, the wiring is formed only on one surface of the substrate W. However, the present invention can be applied to the case where the wiring is formed on both surfaces of the substrate W.

  In each of the above embodiments, a photoelectric conversion device as a solar cell is manufactured by forming wiring on a silicon substrate, but the substrate is not limited to silicon. For example, the present invention can also be applied when forming a wiring in a thin film solar cell formed on a glass substrate or a device other than the solar cell.

  The present invention relates to a wiring forming apparatus and a wiring forming device for forming a wiring having a thin line width, that is, a high aspect ratio required on a substrate, such as a collecting electrode provided on a light receiving surface of a solar cell. It can be suitably applied to a method.

1, 1a Wiring forming device 2 Stage moving mechanism (moving mechanism)
6 Control unit (control means)
21 X direction moving mechanism 22 Y direction moving mechanism 23 θ rotation mechanism 31 Cool plate (substrate cooling unit, thickening means)
35 Hot plate (substrate heating part, thickening means)
52 Discharge nozzle 53 Light irradiation part (light irradiation means)
W substrate

Claims (13)

A discharge nozzle for discharging a coating liquid containing a wiring material to the substrate surface;
A moving mechanism that scans and moves the discharge nozzle relative to the substrate surface;
And a thickening means for increasing the viscosity of the coating liquid immediately after being discharged from the discharge nozzle onto the substrate surface. The discharge nozzle discharges the coating liquid containing a photocurable material,
The wiring forming apparatus according to claim 1, further comprising a light irradiation unit configured to irradiate the coating liquid whose viscosity has been increased on the substrate surface to cure the coating liquid.   The wiring forming apparatus according to claim 2, wherein the thickening unit includes a substrate cooling unit that cools the substrate while holding the substrate.   The wiring forming apparatus according to claim 3, wherein the discharge nozzle discharges the coating liquid containing the wiring material and a solvent, and the substrate cooling unit cools the substrate to a temperature not higher than a freezing point of the solvent.   The wiring forming apparatus according to claim 1, wherein the thickening unit includes a substrate heating unit that heats the substrate while holding the substrate.   The wiring forming apparatus according to claim 5, wherein the discharge nozzle discharges the coating liquid containing the wiring material and a solvent, and the substrate heating unit heats the substrate to a temperature not higher than a boiling point of the solvent.   The wiring forming apparatus according to claim 5, wherein the moving mechanism moves the discharge nozzle relative to the substrate surface so that the coating liquid is applied to the same location on the substrate surface a plurality of times. . Conductive particles;
An organic vehicle and
A wiring forming material, wherein 10 to 90 weight percent of the solvent contained in the organic vehicle is an organic solvent having a boiling point of 80 ° C. or less.   The wiring forming material according to claim 8, which contains any one of acetone, ethyl acetate, and methyl ethyl ketone as the organic solvent. Applying a coating liquid containing a wiring material and a photocurable material to the substrate surface;
A step of irradiating the coating liquid applied to the substrate surface with light and curing the coating liquid,
A wiring forming method, wherein the substrate is cooled to a predetermined temperature at least from when the coating solution is applied to the substrate surface until the light is irradiated. Heating the substrate to a predetermined temperature;
And a step of applying a coating solution containing a wiring material and a solvent to the heated substrate surface.   The wiring forming method according to claim 11, wherein the coating solution is applied in a plurality of times on the same location on the substrate surface. The wiring forming method according to claim 11 or 12, further comprising a step of using a liquid containing a photocurable material as the coating liquid and irradiating the coating liquid applied to the substrate surface with light to cure.

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