Patent Publication Number: US-2006013970-A1

Title: Method for providing a layer, wiring substrate, elector-optical device, and electronic equipment

Description:
BACKGROUND  
      The present invention relates to a method for providing a layer, wiring substrate, electro-optical device and electronic equipment.  
      A method for manufacturing a wiring substrate using an additive process of printing has drawn attention. This is because the additive process requires fewer costs than another method for manufacturing a wiring substrate involving repetitive processes of thin-film application and photolithography.  
      Techniques for providing a metal wiring by ink jetting applicable to this additive process have been developed. Japanese Unexamined Patent Publication No. 2004-6578 is an example of related art.  
      To form a pattern of a film or layer on a substance by ink jetting, the degree of spread of a discharged material on the substance must be made different from one part to another, in some cases, depending on the shape of the pattern. For example, it is preferably that a material that has landed on a substance does not spread very much to form a layer boundary. This way the layer boundary can be clearly defined. For another example, a material that has landed on a substance may spread when forming an inner portion of the same layer.  
      Forming an insulating layer having a contact hole, for example, requires a liquid material of a comparatively high concentration. This is because such a material takes a comparatively short time to lose its liquidity due to the vaporization of its solvent after being discharged, and thus it is easy to define the outer shape of an opening serving as the contact hole.  
      However, such a liquid material does not spread broadly after it has landed. Therefore, it is difficult for such a liquid material to provide a layer with a flat surface that eliminates an underlying step.  
     SUMMARY  
      An advantage of the present invention is to provide an insulating layer with a flat surface that eliminates an underlying step and having a contact hole by ink jetting.  
      A method for providing a layer according to an aspect of the invention is used for manufacturing a wiring substrate by ink jetting. The method includes: 
          (a) discharging a first liquid insulating material of a first concentration on a surface of a first level so that a side of a first conductive layer placed on the surface is covered by the first insulating material;     (b) providing a first insulating layer facing the first conductive layer by activating or drying the first insulating material that has been discharged;     (c) discharging a second liquid insulating material of a second concentration on the first conductive layer and the first insulating layer, the second concentration being higher than the first concentration; and     (d) providing a second insulating layer covering the first conductive layer and the first insulating layer by activating or drying the second insulating material that has been discharged.        

      This method makes it easy to provide the flat insulating layer covering the first conductive layer by ink jetting.  
      It is preferable that the first conductive layer is a copper wiring.  
      In this case, it is possible to provide the insulating layer on a widely available wiring substrate by ink jetting.  
      It is preferable that the method for providing a layer also includes: 
          (e) discharging a first liquid conductive material on the surface; and     (f) providing the first conductive layer by activating or drying the first conductive material that has been discharged.        

      This method makes it possible to apply ink jetting to providing the conductive layer.  
      It is more preferable that (e) includes discharging the first conductive material containing silver.  
      This method makes it easy to provide the conductive layer by ink jetting.  
      It is preferable that (c) includes discharging the second insulating material so that the second insulating material defines a contact hole that exposes part of the first conductive layer, and (d) includes providing the second insulating layer having the contact hole by activating or drying the second insulating material that has been discharged.  
      This method makes it possible to providing the insulating layer having the contact hole by ink jetting.  
      It is preferable that the method for providing a layer also includes: 
          (g) providing a second conductive layer facing the first conductive layer in the contact hole.        

      It is preferable that (g) includes discharging a second liquid conductive material in the contact hole, and providing the second conductive layer by activating or drying the second conductive material that has been discharged.  
      This method makes it possible to providing the conductive layer filling up the contact hole by ink jetting.  
      A method for providing a layer according to another aspect of the invention is used for providing a layer that covers a first part and a second part facing the first part by ink jetting. The method includes: 
          (a) discharging a first liquid insulating material of a first concentration on the first part; and     (b) discharging a second liquid insulating material of a second concentration on the second part after (a).        

      This method makes it possible to make the degree of spread of the liquid materials partly different on a substance. Therefore, it is easy to provide layer boundary and inner parts.  
      A wiring substrate according to yet another aspect of the invention is manufactured by any of the above-described methods for providing a layer.  
      Accordingly, the wiring substrate is manufactured by ink jetting.  
      An electro-optical device according to a further aspect of the invention is manufactured by any of the above-described methods for providing a layer.  
      Accordingly, the electro-optical device is manufactured by ink jetting.  
      Electronic equipment according to a still further aspect of the invention is manufactured by any of the above-described methods for providing a layer.  
      Accordingly, the electronic equipment is manufactured by ink jetting. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will be described with reference to the accompanying drawings, wherein like numbers refer to like elements, and wherein:  
       FIG. 1  is a schematic of a layer-deposition unit;  
       FIG. 2  is a schematic of a discharge device included in the layer-deposition unit;  
       FIGS. 3A and 3B  are schematics of a head included in the discharge device;  
       FIG. 4  is a functional block diagram of a controller included in the discharge device;  
       FIGS. 5A through 5D  illustrate a manufacturing method according to a first embodiment of the invention;  
       FIGS. 6A through 6E  illustrate the manufacturing method according to the first embodiment of the invention;  
       FIGS. 7A through 7D  illustrate the manufacturing method according to the first embodiment of the invention;  
       FIGS. 8A through 8E  illustrate a manufacturing method according to a second embodiment of the invention;  
       FIG. 9  is a schematic of a mobile phone; and  
       FIG. 10  is a schematic of a personal computer. 
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
     First Embodiment  
      A wiring substrate according to a first embodiment of the invention is made with a tape-like base substrate. Here the base substrate is made of polyimide and also called a flexible substrate. On the base substrate, a metal wiring is provided by a manufacturing process that will be described in detail later. After the metal wiring is provided, the base substrate is pressed to cut out a plurality of substrates. Thus, a plurality of substrates each of which is provided with a metal wiring are made out of the base substrate. According to the present embodiment, every metal wiring provided to the plurality of substrates has the same pattern. The substrate provided with the metal wiring is referred to as a “wiring substrate”.  
      A. Layer-Deposition Unit  
      The wiring substrate according to the present embodiment is manufactured by a layer-deposition process performed with six layer-deposition units. These six layer-deposition units have fundamentally the same structure and function. Therefore, the structure and function of one representative unit out of the six layer-deposition units will be described below to prevent redundancy.  
      A layer-deposition unit  10  shown in  FIG. 1  is a unit for providing a conductive or insulating layer on a surface placed at a certain level. The layer-deposition unit  10  includes a pair of reels W 1 , a discharge device  10 A, and an oven  10 B. The discharge device  10 A and the oven  10 B included in the layer-deposition unit  10  process a base substrate  1   a  while the base substrate  1   a  is reeled out from one of the reels W 1  and then reeled in to the other of the reels W 1 . This processing is also called “reel-to-reel”.  
      The discharge device  10 A discharges a liquid material onto a surface placed at a certain level of the base substrate  1   a . The oven  10 B heats and activates the liquid material supplied or applied by the discharge device  10 A.  
      Six discharge devices (each corresponding to the discharge device  10 A) included in six layer-deposition units (each corresponding to the layer-deposition unit  10 ) are hereinafter referred to as follows for the sake of convenience: a first discharge device  11 A, a second discharge device  12 A, a third discharge device  13 A, a fourth discharge device  14 A, a fifth discharge device  15 A, and a sixth discharge device  16 A. In the same manner, six ovens (each corresponding to the oven  10 B) are hereinafter referred to as follows for the sake of convenience: a first oven  11 B, a second oven  12 B, a third oven  13 B, a fourth oven  14 B, a fifth oven  15 B, and a sixth oven  16 B.  
      The six discharge devices  11 A,  12 A,  13 A,  14 A,  15 A, and  16 A have fundamentally the same structure and function. Therefore, the structure and function of the first discharge device  11 A will be described below to prevent redundancy as a representative of the six discharge devices  11 A,  12 A,  13 A,  14 A,  15 A, and  16 A.  
      B. Structure of the Discharge Device  
      The first discharge device  11 A shown in  FIG. 2  is an inkjet device. The first discharge device  11 A includes a tank  101  for storing a liquid material  111 , a tube  110 , and a discharge scanner  102  for supplying the liquid material  111  from the tank  101  through the tube  110 . The discharge scanner  102  includes a ground stage GS, a discharge head  103 , a stage  106 , a first position controller  104 , a second position controller  108 , a controller  112 , and a support  104   a.    
      The discharge head  103  holds a head  114  shown in  FIG. 3 . The head  114  discharges droplets of the liquid material  111  based on a signal from the controller  112 . The head  114  held by the discharge head  103  is coupled to the tank  101  by the tube  110 . Accordingly, the liquid material  111  is supplied from the tank  101  to the head  114 .  
      The stage  106  provides a flat surface for fixing the base substrate  1   a . The stage  106  also fixes the position of the base substrate  1   a  by suction.  
      The first position controller  104  is fixed by the support  104   a  at a certain height from the ground stage GS. The first position controller  104  moves the discharge head  103  in the X-axis direction and the Z-axis direction perpendicular thereto, based on a signal from the controller  112 . Furthermore, the first position controller  104  rotates the discharge head  103  around an axis parallel to the Z axis. In the present embodiment, the Z-axis direction is parallel to the vertical direction (i.e., the direction of gravitational acceleration).  
      The second position controller  108  moves the stage  106  on the ground stage GS in the Y-axis direction based on a signal from the controller  112 . Here, the Y-axis direction is perpendicular to the X-axis and Z-axis directions.  
      The structures of the first position controller  104  and the second position controller  108  are available by using a known XY robot employing a linear motor or servomotor. Here, a detailed description thereof is omitted. The first position controller  104  and the second position controller  108  are hereinafter also referred to as “robot” or “scanner”.  
      As described above, the first position controller  104  moves the discharge head  103  in the X-axis direction. In addition, the second position controller  108  moves the base substrate  1   a  together with the stage  106  in the Y-axis direction. As a result, the relative position of the head  114  to the base substrate  1   a  changes. Specifically, the discharge head  103 , the head  114  or a nozzle  118  (shown in  FIG. 3 ) moves, in other words scans, in the X-axis and Y-axis directions relatively to the base substrate  1   a  while maintaining a certain distance therefrom in the Z-axis direction. Moving or scanning relatively refers to moving at least one of one side discharging the liquid material  111  relatively to the other side (recipient) onto which the discharged material has landed.  
      The controller  112  receives discharge data (e.g. bitmap data) representing a relative position to which the liquid material  111  should be discharged from an external information processor. The controller  112  stores the discharge data it has received in an internal memory, and controls, based on the stored discharge data, the first position controller  104 , the second position controller  108 , and the head  114 .  
      The first discharge device  11 A having the above-described structure moves the nozzle  118  (shown in  FIG. 3 ) of the head  114  relatively to the base substrate  1   a  based on bitmap data, and discharges the liquid material  111  from the nozzle  118  onto a recipient. The bitmap data are used for providing a material on the base substrate  1   a  with a predetermined pattern. Note that the relative movement of the head  114  and discharging of the liquid material  111  from the head  114  in the first discharge device  11 A may be collectively referred to as “application scan” or “discharge device”.  
      Here, the recipient means an area onto which droplets of the liquid material  111  land and spread. Furthermore, the recipient is formed by surface modification of an underlying substance, so that the liquid material  111  will be discharged with a desired angle of contact. Here, if the surface of an underlying substance is preferably lyophobic or lyophilic to the liquid material  111  without such surface modification (i.e. the liquid material  111  has landed on the surface of the underlying substance with a desired angle of contact), the surface of the underlying substance may serve as the recipient. The recipient is hereinafter also referred to as “target” or “receptive part”.  
      C. Head  
      As shown in  FIGS. 3A and 3B , the head  114  included in the first discharge device  11 A is an inkjet head having a plurality of nozzles  118 . The head  114  includes an oscillating plate  126  and a nozzle plate  128  that defines the opening of each nozzle  118 . Provided between the oscillating plate  126  and the nozzle plate  128  is a reservoir  129 . The reservoir  129  is always filled with the liquid material  111  supplied from an external tank (not shown) through a hole  131 .  
      Also provided between the oscillating plate  126  and the nozzle plate  128  are a plurality of partition walls  122 . An area surrounded by the oscillating plate  126 , the nozzle plate  128 , and a pair of partition walls  122  is a cavity  120 . Provided correspondingly to the nozzles  118 , cavities  120  are provided in the same number as the nozzles  118 . The liquid material  111  is supplied from the reservoir  129  to each of the cavities  120  through a supply opening  130  placed between a pair of partition walls  122 . The diameter of each nozzle  118  is approximately 27 μm in the present embodiment.  
      On the oscillating plate  126 , oscillators  124  are provided correspondingly to the cavities  120 . Each of the oscillators  124  includes a piezoelectric element  124 C and a pair of electrodes  124 A and  124 B that sandwich the piezoelectric element  124 C. The controller  112  provides a driving voltage in between the pair of electrodes  124 A and  124 B, making droplets D of the liquid material  111  be discharged from a correspondent nozzle  118 . Here, the volume of the material discharged from the nozzle  118  is variable from 0 to 42 picoliters. The shape of the nozzle  118  is adjusted, so that droplets D of the liquid material  111  are discharged from the nozzle  118  in the Z-axis direction.  
      A portion including one nozzle  118 , a cavity  120  corresponding to the nozzle  118 , and an oscillator  124  corresponding to the cavity  120  is hereinafter also referred to as “discharge portion  127 ”. Accordingly, one head  114  includes the same number of nozzles  118  and discharge portions  127 . The discharge portion  127  may include an electrothermal converting element instead of the piezoelectric element. In other words, the discharge portion  127  may have a structure for discharging a material by means of the thermal expansion of the material with the electrothermal converting element.  
      D. Controller  
      The structure of the controller  112  will now be described. As shown in  FIG. 4 , the controller  112  includes an input buffer memory  200 , a memory  202 , a processor  204 , a scan driver  206 , and a head driver  208 . The input buffer memory  200  and the processor  204  are coupled, so that they can communicate to each other. The processor  204  and the memory  202  are coupled, so that they can communicate to each other. Also, the processor  204  and the scan driver  206  are coupled, so that they can communicate to each other. Furthermore, the processor  204  and the head driver  208  are coupled, so that they can communicate to each other. The scan driver  206  is coupled to the first position controller  104  and the second position controller  108 , so that they can communicate to each other. In the same manner, the head driver  208  is coupled to the head  114 , so that they can communicate to each other.  
      The input buffer memory  200  receives discharge data for discharging droplets D of the liquid material  111  from a host computer (not shown) outside the first discharge device  11 A. The input buffer memory  200  provides the processor  204  with the discharge data. The processor  204  then stores the discharge data in the memory  202 . In the example shown in  FIG. 4 , the memory  202  is a random access memory (RAM).  
      The processor  204  provides the scan driver  206  with data showing the relative position of the nozzle  118  to a recipient base on the discharge data in the memory  202 . The scan driver  206  provides the second position controller  108  with a stage drive signal based on the data and the cycle of discharge. As a result, the head  114  moves relatively to the recipient. Meanwhile, the processor  204  provides, base on the discharge data stored in the memory  202 , the head  114  with a discharge signal required for discharging the liquid material  111 . Consequently, a corresponding nozzle  118  in the head  114  discharges droplets D of the liquid material  111 .  
      The controller  112  may be a computer provided with a central processing unit (CPU), read only memory (ROM), random access memory (RAM), and bus. In this case, the above-described function of the controller  112  is provided by a software program that is executed by a computer. Alternatively, the controller  112  may be provided by an exclusive circuit (hardware).  
      E. Liquid Material  
      The liquid material  111  means a viscid material that can be discharged as droplets from the nozzle  118  of the head  114 . The liquid material  111  can be either a water- or oil-based material. It is sufficient to have a certain fluidity (viscosity) with which the material can be discharged from the nozzle  118 . The material can even contain a solid matter as long as it is fluid as a whole.  
      The viscosity of the liquid material  111  is preferably from 1 to 50 mPa·s. A viscosity of 1 mpa·s or more prevents an area around the nozzle  118  from being contaminated by the outflow of the liquid material  111  while discharging droplets D of the liquid material  111 . Meanwhile, a viscosity of 50 mPa·s or less reduces the possibility of clogging of the nozzle  118 , and provides smooth droplet discharge.  
      First, second, and third conductive materials that will be described later are examples of the liquid material  111 . The first conductive material is discharged from the first discharge device  11 A, the second conductive material from the fourth discharge device  14 A, and the third conductive material from the fifth discharge device  15 A.  
      In the present embodiment, the first, second, and third conductive materials include silver particles whose average diameter is about 10 nm, a dispersion medium, and an organic solvent. The silver particles are covered by the dispersion medium in these conductive materials. The silver particles covered by the dispersion medium are stably dispersed in the organic solvent. Here, the dispersion medium is a compound that is capable of being coordinated with silver atoms. Examples of such a dispersion medium include amine, alcohol, and thiol.  
      Particles whose average diameter is about 1 to several hundred nanometers are also called nanoparticles. Accordingly, the first, second, and third conductive materials include silver nanoparticles.  
      Furthermore, first, second, and third insulating materials that will be described later are also examples of the liquid material  111 . The first insulating material is discharged from the second discharge device  12 A, while the second insulating material is discharged from the third discharge device  13 A. The third insulating material is discharged from the sixth discharge device  16 A. Here, the first and third insulating materials are identical.  
      In the present embodiment, the first and second insulating materials are solutions including a polyimide precursor and N-methyl-2-pyrrolidone that is a solvent (diluent). In both the first and second insulating materials, the concentration of the polyimide precursor is set at predetermined values. In the present embodiment, the concentration of the polyimide precursor contained in the first insulating material is lower than that in the second insulating material. In general, the higher the concentration of a polyimide precursor is, the shorter it takes for the first and second insulating materials to substantially lose their fluidity. Meanwhile, the lower the concentration of the polyimide precursor is, the longer the first and second insulating materials can maintain their fluidity.  
      The concentration of the polyimide precursors contained in the first and second insulating materials corresponds to the concentration of an insulating material according to the present invention. If an insulating layer is provided by agglomerating insulating particles instead of polymerization, the concentration or weight percent of such insulating particles corresponds to the concentration of an insulating material according to the invention.  
      F. Manufacturing Method  
      A method for providing, that is, manufacturing a layer will now be described.  
      A first conductive layer  21  is provided on almost the same level of the base substrate  1   a.    
      First, the base substrate  1   a  is placed on the stage  106  included in the first discharge device  11 A as shown in  FIG. 5A . Consequently, the first discharge device  11 A provides, based on first bitmap data, a first conductive material layer  21 B on a recipient on the base substrate  1   a.    
      More specifically, the relative position of the nozzle  118  to the base substrate  1   a  is changed two dimensionally, i.e. in the X-axis and Y-axis directions. When the nozzle  118  reaches at a position corresponding to a pattern to be formed, the first discharge device  11 A discharges droplets of a first conductive material  21 A from the nozzle  118 . The discharged droplets of the first conductive material  21 A land on a recipient on the base substrate  1   a . As the droplets of the first conductive material  21 A land on the recipient, the first conductive material layer  21 B is provided on the recipient on the base substrate  1   a.    
      The first bitmap data are a kind of discharge data. The discharge data include information representing a relative position (discharge position) on which droplets are to be discharged from the nozzle  118  and information representing the volume of the droplets to be discharged onto each discharge position. The discharge data are supplied from an external information processor or host computer (not shown) to a memory in the controller  112  included in the first discharge device  1 A. The controller  112  controls, based on the provided discharge data, moving of the head  114  by the first position controller  104  and discharge of droplets by the head  114 .  
      After providing the first conductive material layer  21 B, the first conductive material layer  21 B is activated. For this purpose, the base substrate  1   a  is placed inside the first oven  1 B in the present embodiment. By heating the first conductive material layer  21 B, silver micro particles in the first conductive material layer  21 B are sintered or welded. As a result of the activation, a first conductive layer  21  having a first pattern is provided on the base substrate  1   a  as shown in  FIG. 5B .  
      The first conductive layer  21  having the first pattern includes a wiring  25 A, a wiring  25 B, and a wiring  25 C as shown in  FIG. 5C . The wirings  25 A,  25 B, and  25 C are laid out on recipients on the base substrate  1   a . This means that the wirings  25 A,  25 B, and  25 C are positioned on a surface L 1  on almost the same level. The wirings  25 A,  25 B, and  25 C are physically separated from each other on the surface L 1 . The wirings  25 A and  25 B are electrically coupled to each other in a later step. Meanwhile, the wiring  25 C is electrically isolated from both of the wirings  25 A and  25 B.  
      F 2 . First Insulating Layer  
      As the first conductive layer  21  having the first pattern is provided, a step is developed to the thickness of the first conductive layer  21  on the base substrate  1   a . Therefore, a first insulating layer  31  is provided on part of the base substrate  1   a  in which the first conductive layer  21  has not been provided as shown in  FIG. 5D  in the present embodiment. The first insulating layer  31  covers the side of the first conductive layer  21 , and thereby eliminating the step accompanying the first conductive layer  21 .  
      First, the base substrate  1   a  provided with the first conductive layer  21  is placed on the stage  106  included in the second discharge device  12 A as shown in  FIG. 5D . Consequently, the second discharge device  12 A provides, based on second bitmap data, a first insulating material layer  31 B on a recipient on the base substrate  1   a.    
      More specifically, the relative position of the nozzle  118  to the base substrate  1   a  is changed two dimensionally. When the nozzle  118  reaches at a position corresponding to the recipient, the second discharge device  12 A discharges droplets of a first insulating material  31 A from the nozzle  118 . The discharged droplets of the first insulating material  31 A land on the recipient on the base substrate  1   a . As the droplets of the first insulating material  31 A land on the recipient, the first insulating material layer  31 B is provided on the recipient on the base substrate  1   a.    
      Here, the concentration of the first insulating material  31 A is set sufficiently low, so that after the first insulating material  31 A has landed it can maintain its fluidity until it spreads to cover the side of the first conductive layer  21 . Accordingly, the first insulating material  31 A that has landed on the recipient forms a layer (first insulating material layer  31 B) to an even thickness on the recipient.  
      After providing the first insulating material layer  31 B, the first insulating material layer  31 B is activated. For this purpose, the base substrate  1   a  is placed inside the second oven  12 B in the present embodiment. By heating the first insulating material layer  31 B, a polyimide precursor in the first insulating material layer  31 B is polymerized to provide a polyimide layer. As a result of the activation, a first insulating layer  31  (polyimide layer) is provided on the base substrate  1   a  as shown in  FIG. 6A .  
      Providing the first insulating layer  31  eliminates a step developed on the base substrate  1   a  accompanying the first conductive layer  21 . This is because the surface of the first conductive layer  21  and the surface of the first insulating layer  31  are on almost the same level. The surface consisting of the surfaces of the first conductive layer  21  and the first insulating layer  31  is hereinafter also called “second level surface”.  
      F 3 . Second Insulating Layer  
      After providing the first insulating layer  31 , a second insulating layer that covers the first conductive layer  21  and the first insulating layer  31  is provided.  
      As shown in  FIG. 6B , the base substrate  1   a  provided with the first conductive layer  21  and the first insulating layer  31  is placed on the stage  106  included in the third discharge device  13 A. Consequently, the third discharge device  13 A provides, based on third bitmap data, a second insulating material layer  32 B that covers the first conductive layer  21  and the first insulating layer  31 .  
      Specifically, the relative position of the nozzle  118  to the base substrate  1   a  is changed two dimensionally. When the nozzle  118  reaches at a position corresponding to a recipient on the first conductive layer  21  and a recipient on the first insulating layer  31 , the third discharge device  13 A discharges droplets of a second insulating material  32 A from the nozzle  118 . The discharged droplets of the second insulating material  32 A land on the recipients on the first conductive layer  21  and the first insulating layer  31 . As the droplets of the second insulating material  32 A land on the recipients, the second insulating material layer  32 B that covers the first conductive layer  21  and the first insulating layer  31  is provided.  
      Here, the droplets of the second insulating material  32 A are discharged in a way that a contact hole  35  is formed on each of the wirings  25 A and  25 C. In other words, the droplets of the second insulating material  32 A are discharged in a way that the outer shape of the contact hole  35  is defined by the second insulating material  32 A that has landed. Therefore, the droplets of the second insulating material  32 A are not discharged onto an area to be reserved for the contact hole  35 .  
      The concentration of the second insulating material  32 A is higher than that of the first insulating material  31 A. Accordingly, it takes a shorter time for the second insulating material  32 A that has landed on the first conductive layer  21  to lose its fluidity than for the first insulating material  31 A to lose its fluidity. As a result, the second insulating material  32 A is more suitable for defining the contact hole  35  than the first insulating material  31 A. In the present embodiment, an area to be reserved for the contact hole  35  is left as an opening even before the second insulating material layer  32 B is activated.  
      After providing the second insulating material layer  32 B, the second insulating material layer  32 B is activated. For this purpose, the base substrate  1   a  is placed inside the third oven  13 B in the present embodiment. By heating the second insulating material layer  32 B, a polyimide precursor in the second insulating material layer  32 B is polymerized to provide a polyimide layer. As a result of the activation, a second insulating layer  32  (polyimide layer) that covers the first conductive layer  21  and the first insulating layer  31  is provided as shown in  FIG. 6C . As described above, the second insulating layer  32  has the contact hole  35  on each of the wirings  25 A and  25 C.  
      While the concentration of the second insulating material  32 A is high, the surface of the second insulating layer  32  made of the second insulating material  32 A is flat. This is because the surface of the recipient (second level surface) onto which the second insulating material  32 A lands is a flat surface consisting of the first conductive layer  21  and the first insulating layer  31 .  
      The first insulating material  31 A and the second insulating material  32 A are provided as follows. First, the second insulating material  32 A of a concentration suitable for defining the contact hole  35  is provided by adjusting a polyimide precursor concentration in a solution. Then, the first insulating material  31 A is provided by adding a certain amount of solvent to the second insulating material  32 A to dilute the second insulating material  32 A. Here, N-methyl-2-pyrrolidone or N,N-dimethylacetamide may be used as the solvent.  
      F 4 . Second Conductive Layer  
      After the second insulating layer  32  is provided, a second conductive layer is provided to penetrate the contact hole  35  provided to the second insulating layer  32 .  
      First, the base substrate  1   a  is placed on the stage  106  included in the fourth discharge device  14 A as shown in  FIG. 6D . Consequently, the fourth discharge device  14 A provides, based on fourth bitmap data, a second conductive material layer  22 B that penetrates the contact hole  35  provided to the second insulating layer  32 .  
      Specifically, the relative position of the nozzle  118  to the second insulating layer  32  is changed two dimensionally. When the nozzle  118  reaches at a position corresponding to the contact hole  35 , the fourth discharge device  14 A discharges droplets of a second conductive material  22 A from the nozzle  118 . The discharged droplets of the second conductive material  22 A land on a recipient on the first conductive layer  21  that is exposed by the contact hole  35 . As the droplets land and fill up the contact hole  35 , the second conductive material layer  22 B penetrating the contact hole  35  is provided.  
      After providing the second conductive material layer  22 B, the second conductive material layer  22 B is activated. For this purpose, the base substrate  1   a  is placed inside the fourth oven  14 B in the present embodiment. By heating the second conductive material layer  22 B, silver micro particles in the second conductive material layer  22 B are sintered or welded. As a result of the activation, the wirings  25 A and  25 C in the first conductive layer  21  are electrically and physically coupled, and a second conductive layer  22  that penetrates the contact hole  35  is provided as shown in  FIG. 6E .  
      F 5 . Third Conductive Layer  
      After providing the second conductive layer  22 , a third conductive layer  23  is provided on the second insulating layer  32  and the second conductive layer  22 .  
      First, the base substrate  1   a  is placed on the stage  106  included in the fifth discharge device  15 A as shown in  FIG. 7A . Consequently, the fifth discharge device  15 A provides, based on fifth bitmap data, a third conductive material layer  23 B with a second pattern on a recipient on the second insulating layer  32  and on a recipient on the second conductive layer  22 . The second pattern is to link each second conductive layer  22  provided to two contact holes  35 .  
      More specifically, the relative position of the nozzle  118  to the base substrate  1   a  is changed two dimensionally, i.e. in the X-axis and Y-axis directions. When the nozzle  118  reaches at a position corresponding to a pattern to be formed, the fifth discharge device  15 A discharges droplets of a third conductive material  23 A from the nozzle  118 . The discharged droplets of the third conductive material  23 A land on recipients on the second insulating layer  32  and the second conductive layer  22 . As the droplets of the third conductive material  23 A land on the recipients, the third conductive material layer  23 B is provided on the recipients on the second insulating layer  32  and the second conductive layer  22 .  
      After providing the third conductive material layer  23 B, the third conductive material layer  23 B is activated. For this purpose, the base substrate  1   a  is placed inside the fifth oven  15 B in the present embodiment. By heating the third conductive material layer  23 B, silver micro particles in the third conductive material layer  23 B are sintered or welded. As a result of the activation, the third conductive layer  23  electrically coupled to each second conductive layer  22  provided to two contact holes  35  is provided as shown in  FIG. 7B .  
      The third conductive layer  23  electrically couples the wirings  25 A and  25 C included in the first conductive layer  21 . Meanwhile, the wiring  25 B also included in the first conductive layer  21  is electrically isolated from both the wirings  25 A and  25 C.  
      F 6 . Third Insulating Layer  
      After providing the third conductive layer  23 , a third insulating layer  33  that covers the third conductive layer  23  is provided.  
      First, the base substrate  1   a  is placed on the stage  106  included in the sixth discharge device  16 A as shown in  FIG. 7C . Consequently, the sixth discharge device  16 A provides, based on sixth bitmap data, a third insulating material layer  33 B that covers the third conductive layer  23 .  
      More specifically, the relative position of the nozzle  118  to the base substrate  1   a  is changed two dimensionally, i.e. in the X-axis and Y-axis directions. When the nozzle  118  reaches at a position corresponding to a pattern to be formed, the sixth discharge device  16 A discharges droplets of a third insulating material  33 A from the nozzle  118 . The discharged droplets of the third insulating material  33 A land on recipients on the second insulating layer  32  and the third conductive layer  23 . As the droplets of the third insulating material  33 A land on the recipients, the third insulating material layer  33 B is provided. In the present embodiment, the third insulating material  33 A and the first insulating material  31 A are identical.  
      After providing the third insulating material layer  33 B, the third insulating material layer  33 B is activated. For this purpose, the base substrate  1   a  is placed inside the sixth oven  16 B in the present embodiment. By heating the third insulating material layer  33 B, a polyimide precursor in the third insulating material layer  33 B is polymerized to provide a polyimide layer. As a result of the activation, a third insulating layer  33  that covers the third conductive layer  23  is provided as shown in  FIG. 7D .  
      As mentioned above, the present embodiment provides a wiring substrate having a three-dimensional wiring configuration by ink jetting.  
      In particular, even if a step is developed on a first level surface, the surface of the next (second) level can be flattened by discharging the first insulating material  31 A whose concentration is comparatively low on the first level surface. Furthermore, the present embodiment provides the contact hole  35  having a clearly defined shape by discharging the second insulating material  32 A whose concentration is higher than that of the first insulating material  31 A on the second level surface. In other words, the present embodiment provides an insulating layer that is flat and provided with the contact hole  35  having a clearly defined shape by discharging a liquid material (insulating material). Moreover, since the first insulating layer  31  and the second insulating layer  32  are made of the same material, they have the same coefficient of linear expansion, which makes it hard to produce stress due to thermal expansion.  
     Second Embodiment  
      A method for providing a layer according to a second embodiment of the invention is substantially the same as the method for providing a layer of the first embodiment, except for how to provide a second insulating layer. Therefore, only a step to provide the second insulating layer will be described below in order to prevent redundancy.  
      G. Second Insulating Layer  
      First, the first conductive layer  21  and the first insulating layer  31  are provided on the base substrate  1   a  by the method for providing a layer of the first embodiment. Then, a second insulating layer that covers the first conductive layer  21  and the first insulating layer  31  is provided.  
      Specifically, the second discharge device  12 A and the third discharge device  13 A form, based on their bitmap data, a second insulating material layer on recipients on the first conductive layer  21  and the first insulating layer  31 . The second insulating material layer is activated in a later step to be a second insulating layer.  
      The second insulating material layer to be the second insulating layer consists of a layer boundary part and a layer inner part. The layer boundary part is an outermost portion in the second insulating material layer or the second insulating layer. The layer inner part is a portion surrounded by the layer boundary part. Note that if the layer boundary part defines the outer shape of a contact hole or via hole in the second insulating material layer, the layer boundary part is surrounded by the layer inner part. At any rate, the layer boundary part and the layer inner part are close to each other.  
      In the present embodiment, a recipient on the first conductive layer  21  or the first insulating layer  31  that corresponds to the layer boundary part is hereinafter also called “first part  41 ”. Also, a recipient on the first conductive layer  21  or the first insulating layer  31  that corresponds to the layer inner part is hereinafter also called “second part  42 ”. The first part  41  is an outermost portion in the recipient. The second part  42  is a portion surrounded by the first part  41 . The first part  41  and the second part  42  are close to each other. While the first part  41  and the second part  42  are on surfaces on the same level (second level) in the present embodiment, the first part  41  and the second part  42  may be on surfaces on different levels.  
      G 1 . Layer Boundary Part (Discharge onto the First Part  41 )  
      How to provide the second insulating layer will now be described in greater detail. As shown in  FIG. 8B , the third discharge device  13 A changes the relative position of the nozzle  118  (shown in  FIG. 3 ) to the base substrate  1   a  in the Y-axis positive direction at a relative rate V. When the nozzle  118  reaches at a position corresponding to the first part  41 , the head  114  discharges droplets of the second insulating material  32 A.  
      By repeating the relative movement of the head  114  in the X-axis and Y-axis directions, the third discharge device  13 A makes droplets of the second insulating material  32 A land on the entire area of the first part  41  on the base substrate  1   a . Accordingly, the second insulating material layer (layer boundary part)  32 B that covers the first part  41  is provided.  
      The concentration of the second insulating material  32 A is higher than that of the first insulating material  31 A described in the first embodiment. Accordingly, it takes a shorter time for the second insulating material  32 A that has landed on the first conductive layer  21  to lose its fluidity than for the first insulating material  31 A to lose its fluidity. As a result, the second insulating material  32 A is more suitable for defining the layer boundary part than the first insulating material  31 A. This way the layer boundary part on the first part  14  can maintain an opening to be the contact hole  35  until the layer boundary part is activated and hardened, if the first part  41  is located correspondingly to the outer shape of the contact hole  35  as shown in  FIGS. 8B and 8C , for example.  
      After providing the layer boundary part of the second insulating material layer  32 B, the layer boundary part is activated. For this purpose, the base substrate  1   a  is placed inside the third oven  13 B. By heating the base substrate  1   a , the layer boundary part of the second insulating material layer  32 B is hardened to provide a layer boundary part of the second insulating layer  32  as shown in  FIG. 8C .  
      G 2 . Layer Inner Part (Discharge onto the Second Part  42 )  
      After providing the layer boundary part of the second insulating layer  32 , the layer inner part is provided. As shown in  FIG. 8D , the second discharge device  12 A changes the relative position of the nozzle  118  (shown in  FIG. 3 ) to the base substrate  1   a  in the Y-axis positive direction at a relative rate V. When the nozzle  118  reaches at a position corresponding to the second part  42 , the head  114  discharges droplets of the first insulating material  31 A. As described in the first embodiment, the concentration of the first insulating material  31 A is set sufficiently low. Therefore, the first insulating material  31 A that has landed on the second part  42  spreads sufficiently broadly.  
      By repeating the relative movement of the head  114  in the X-axis and Y-axis directions, the second discharge device  12 A fills the area (second part  42 ) surrounded by the layer boundary part with the first insulating material  31 A. As a result, the second discharge device  12 A provides the layer inner part of the second insulating material layer  32 B.  
      After providing the layer inner part of the second insulating material layer  32 B, the layer inner part of is activated. For this purpose, the base substrate  1   a  is placed inside the second oven  12 B. By heating the base substrate  1   a , the layer inner part of the second insulating material layer  32 B is hardened to provide a layer inner part of the second insulating layer  32 . Now that the layer boundary part of the second insulating layer  32  has been already provided, the activation with the second oven  12 B completes the second insulating layer  32 . Specifically, the second insulating layer  32  (polyimide layer) that covers the first conductive layer  21  and the first insulating layer  31  is provided as shown in  FIG. 8E  after the activation with the second oven  12 B. Also as described above, the second insulating layer  32  has the contact hole  35  on each of the wirings  25 A and  25 C.  
      Thus, the second discharge device  12 A and the third discharge device  13 A can make the degree of spread of the liquid material  111  partly different on a substance, even if surface modification is uniformly provided on the substance.  
      The wiring substrates exemplified in the first and second embodiments are wiring substrates coupled to a liquid crystal panel included in a liquid crystal display. Thus, the methods according to the first and second embodiments are applicable to manufacturing of liquid crystal displays.  
      Furthermore, the methods according to the first and second embodiments are applicable to manufacturing not only of liquid crystal displays but also of various electro-optical devices. Here, the electro-optical devices are not limited to devices utilizing changes in optical characteristics (so-called electro-optical effects) such as changes in birefringence, optical rotatory power, or light scattering, and include all devices that emit, transmit, or reflect light in accordance with the application of a signal voltage.  
      Examples of such electro-optical devices include liquid crystal displays, electroluminescent displays, plasma displays, surface-conduction electron-emitter displays (SED), and field emission displays (FED).  
      In addition, the methods according to the first and second embodiments are applicable to manufacturing of various electronic equipment. For example, the methods according to the first and second embodiments are applicable to manufacturing of a mobile phone  50  having a liquid crystal display  52  shown in  FIG. 9  and of a personal computer  60  having a liquid crystal display  62  shown in  FIG. 10 .  
      First Modification  
      The first insulating layer  31  and the second insulating layer  32  according to the first and second embodiments are made of polyimide. Note that other polymer materials can also be used instead of polyimide. If the first insulating layer  31  and the second insulating layer  32  are made of other polymer materials, the first insulating material  31 A and the second insulating material  32 A may include a corresponding polymer precursor instead of the polyimide precursor.  
      Second Modification  
      The insulating layers made of the first insulating material  31 A and the second insulating material  32 A include polyimide having the same structure, that is, polymer materials having the same structure. Therefore, the structure of the polymer precursor contained in the first insulating material  31 A is the same as that in the second insulating material  32 A. However, the structure of the polymer precursor contained in the first insulating material  31 A may differ from that in the second insulating material  32 A, as long as they produce insulating layers having nearly equal coefficients of linear expansion. This is because the above-described effects are available only if the concentration of the first insulating material  31 A is lower than that of the second insulating material  32 A, even when the first insulating material  31 A and the second insulating material  32 A contain polymer precursors of different structures.  
      Third Modification  
      Metal wirings are provided on the base substrate  1   a  made of polyimide according to the first and second embodiments. Instead of this base substrate  1   a , ceramics, glass, epoxy, glass epoxy, or silicon substrates may be used to achieve the same effects in the first and second embodiments. When a silicon substrate is used, a passivation film may be deposited on the surface of the substrate before the conductive materials are discharged. Even if any substrates or films are used, an area onto which the liquid material  111  lands from the nozzle  118  corresponds to the “recipient”.  
      Fourth Modification  
      While the conductive materials used in the first and second embodiments contain silver nanoparticles, nanoparticles of other metals may be used instead. Examples of such metals may include gold, platinum, copper, palladium, rhodium, osmium, ruthenium, iridium, iron, tin, zinc, cobalt, nickel, chromium, titan, tantalum, tungsten, and indium. Any one of or an alloy of two or more of these materials may be used. Note that using a conductive material containing silver nanoparticles is preferable for ink jetting, since silver is easy to handle with a comparatively low reduction temperature.  
      Also, the conductive materials may contain organic metal compounds instead of metal nanoparticles. Here, the organic metal compounds mean compounds with which metal is separated out through decomposition by heat (i.e. activation). Examples of such organic metal compounds may include chlorotriethylphosphine gold (I), chlorotrimethylphosphine gold (I), chlorotriphenylphosphine gold (I), silver (I) 2,4-pentanedionato complexes, trimethylphosphine (hexafluoroacetylacetonato) silver (I) complexes, and copper (I) hexafluoropentane dionato cyclooctadiene complexes.  
      This way metal contained in the conductive materials can be in the form of either particles such as nanoparticles or compounds such as organic metal compounds.  
      Fifth Modification  
      According to the first and second embodiments, the conductive and insulating material layers are activated by heat with the ovens  11 B,  12 B,  13 B,  14 B,  15 B, and  16 B. In addition to heating, the conductive or insulating material layers may be activated by irradiating the layers with light with ultraviolet- or visible-light-wavelengths, or electromagnetic waves such as microwaves. Instead of this activation, the conductive or insulating material layers may be simply dried. This is because leaving the conductive and insulating material layers that have been provided as they are can develop the conductive and insulating layers, respectively. Note that it takes a shorter time to make the conductive or insulating layers by means of some kind of activation than simply drying the conductive or insulating material layers. Therefore, the conductive or insulating layers are preferably activated.  
      Sixth Modification  
      While the first conductive layer is a silver wiring provided by ink jetting according to the first and second embodiments, the first conductive layer may be a copper wiring provided by photolithography.  
      Seventh Modification  
      According to the first and second embodiments, the first insulating material  31 A is discharged from the second discharge device  12 A, while the second insulating material  32 A is discharged from the third discharge device  13 A. However, the first insulating material  31 A and the second insulating material  32 A may be discharged not separately from the second discharge device  12 A and the third discharge device  13 A, but from a single discharge device. Also according to the first and second embodiments, polymer precursors contained in the first insulating material  31 A and the second insulating material  32 A are identical. Therefore, there is no need to clean a flow path such as the tank  101  and the tube  110  in switching the first insulating material  31 A and the second insulating material  32 A. Therefore, the number of discharge devices can be reduced without increasing a step for washing the flow path in the devices.