Patent Publication Number: US-2003228417-A1

Title: Evaporation method and manufacturing method of display device

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of Invention  
       [0002] This invention relates to an evaporation method and a manufacturing method of a display device, especially to an evaporation method and the manufacturing method of a display device for providing pixel elements with improved display qualities.  
       [0003] 2. Description of the Related Art  
       [0004] EL (electroluminescent) display devices with an EL element have been gathering attention as a display device substituting a CRT and an LCD. The development effort for the EL display device with a thin film transistor (referred to as TFT hereinafter) as a switching device for driving the EL element has been made accordingly.  
       [0005]FIG. 11 is a plan view showing the vicinity of a display pixel of an organic EL display device. FIG. 12A shows a cross-sectional view of the device along the A-A cross-sectional line, and FIG. 12B shows a cross-sectional view of the device along the B-B cross-sectional line in FIG. 11.  
       [0006] As seen from FIGS. 11, 12A, and  12 B, the display pixel  115  is formed in an area surrounded with a gate signal line  51  and a drain signal line  52 . The display pixels are disposed as a matrix configuration.  
       [0007] An organic EL element  60 , which is a light-emitting device, a switching TFT  30  for controlling the timing of supplying electric current to the organic EL element  60 , a driving TFT  40  for supplying electric current to the organic EL element  60 , and a storage capacitance element  56  are disposed in the display pixel  115 . The organic EL element  60  includes an anode  61 , a hole transport layer  62 , an emissive layer  63 , an electron transport layer  64  and a cathode  65 .  
       [0008] The switching TFT  30  is disposed near the crossing of the signal lines  51 ,  52 . A source  33   s  of the TFT  30  functions also as a capacitance electrode  55  that forms capacitance with a storage capacitance electrode line  54 , and is connected to a gate  41  of the EL element driving TFT  40 . A source  43   s  of the second TFT is connected to the anode  61  of the organic EL element  60  and a drain  43   d  is connected to a driving source line  53  that is the source of the electric power supplied to the organic EL element  60 .  
       [0009] The storage capacitance electrode line  54  is disposed in parallel with the gate signal line  51 . The storage capacitance electrode line  54  is made of chrome and forms capacitance by accumulating electric charge with the capacitance electrode  55  connected to the source  33   s  of the TFT through a gate insulating film  12 . A storage capacitance element  56  is disposed to store the voltage applied to a gate electrode  41  of the second TFT  40 .  
       [0010] The TFTs  30 , 40  and the organic EL element  60  are sequentially disposed on a substrate  10 , which may be a glass substrate, a resin substrate, a conductive substrate or a semiconductor substrate, as shown FIGS. 11A and 11B. When the conductive substrate or the semiconductor substrate is used as the substrate  10 , an insulating film made of SiO 2  or SiN should be disposed on the substrate first. Then TFTs  30 ,  40  and the organic EL element are formed. Both TFTs  30 , 40  have a top-gate configuration, where the gate electrode is located above an active layer with the gate insulating film between them.  
       [0011] The explanation on the switching TFT will be made hereinafter.  
       [0012] As shown in FIG. 12A, an amorphous silicon film (referred to as a-Si film hereinafter) is formed through a CVD method on the insulating substrate  10 , which is made of a quartz glass or a non-alkaline glass. A laser beam is lead to the a-Si film for re-crystallization from melt, forming a poly-crystalline silicon film (referred to as a p-Si film, hereinafter). This functions as the active layer  33 . Single layer or multiple layers of a SiO 2  film and a SiN film are formed on the p-Si film as the insulating film  12 , on which the gate signal line  51  also working as the gate electrode  31  made of a metal with a high-melting point such as Cr and Mo and the drain signal line  52  made of Al are disposed. The driving source line  53  made of Al that is the source of the driving power of the organic EL element is also disposed.  
       [0013] A SiO 2  film, a SiN film and a SiO 2  film are sequentially disposed to form an interlayer insulating film  15  on the entire surface of the gate insulating film  32  and the active layer  33 . A drain electrode  36 , which is formed by filling a contact hole formed corresponding to the drain  33   d  with a metal such as Al, is disposed, and a flattening insulating film  17  made of an organic resin for flattening the surface is formed on the entire surface.  
       [0014] Next, the description on the TFT  40  for driving the organic EL element, will be provided. As shown in FIG. 12B, an active layer  43 , which is formed by illuminating with the laser beam for poly-crystallization, a gate insulating film  12 , and a gate electrode  41  made of a metal with a high-melting point such as Cr and Mo are sequentially disposed on the insulating substrate  10 , which is made of a quartz glass or a non-alkaline glass. A channel  43   c , and a source  43   s  and a drain  43   d  located both sides of the channel  43   c  are formed in the active layer  43 . A SiO 2  film, a SiN film and a SiO 2  film are sequentially disposed to form the interlayer insulating film  15  on the entire surface of the gate insulating film  12  and the active layer  43 . The driving source line  53 , which is connected to the driving source by filling a contact hole formed corresponding to the drain  43   d  with a metal such as Al, is disposed. Furthermore, the flattening insulating film  17  made of an organic resin for flattening the surface is formed on the entire surface. A contact hole corresponding to the location of the source  43   s  is formed in the flattening film  17 . A transparent electrode made of ITO (indium tin oxide) that is the anode  61  of the organic EL element making a contact with the source  43   s  through the contact hole is formed on the flattening film  17 . The anode  61  is formed separately, forming an island for each of the display pixel .  
       [0015] The organic EL element  60  includes the anode  61  made of the transparent electrode such as ITO, a hole transportation layer  62  including a first hole transportation layer made of MTDATA (4,4-bis (3-mathylphenylphenylamino)biphenyl) and a second hole transportation layer made of TPD (4,4,4-tris (3-methylphenylphenylamino) triphenylanine), an emissive layer  63  made of Bebq2 (bis(10-hydroxybenzo[h]quinolinato)beryllium) including quinacridone derivative, an electron transportation layer  64  made of Bebq2, and the cathode  65  made of either magnesium-indium alloy, aluminum, or aluminum alloy.  
       [0016] In the organic EL element  60 , a hole injected from the anode  61  and an electron injected from the cathode  65  are recombined in the emissive layer and an exciton is formed by exciting an organic module of the emissive layer  63 . Light is emitted from the emissive layer  63  in a process of relaxation of the exciton and then released outside after going through the transparent anode  61  and the transparent insulating substrate  10 .  
       [0017] This technology is described in, for example, Japanese Laid-Open Patent Publication No. H 11-283182.  
       [0018] The organic EL material used in the hole transportation layer  62 , the emissive layer  63 , and the electron transportation layer  64  of the organic EL element  60  has a low anti-solvent property and it is vulnerable to water. Therefore, the photolithographic technology of the semiconductor process can not be utilized. Thus, the hole transportation layer  62 , the emissive layer  63 , and the electron transportation layer  64  of the organic EL element  60  are formed by evaporation using a shadow mask.  
       [0019] Next, the pattern forming method through evaporation of the organic EL material will be explained by referring to FIGS.  13 - 16 . The reference numeral  100  indicates a vacuum evaporation device, the reference numeral  101  an exhaust system attached to the vacuum evaporation device, and the reference numeral  110  a supporting table in the chamber of the vacuum evaporation device. A shadow mask (an evaporation mask)  111  made of magnetic material such as nickel (Ni) or invar alloy (Fe64Ni36) is disposed on the supporting table  110 . A plurality of opening portions  112  is formed in the predetermined locations of the shadow mask  111 .  
       [0020] A magnet  120 , which is movable in vertical direction, is disposed on the shadow mask  111  on the supporting table  110 . The reference numeral  130  indicates a glass substrate known as a mother glass inserted between the magnet  120  and the shadow mask  111 . The reference numeral  140  denotes an evaporation source located underneath the shadow mask  111  and movable in the horizontal direction along the shadow mask  111 .  
       [0021] The chamber of the vacuum evaporation device  100  is evacuated by the exhaust system  101 , in FIG. 13. The glass substrate  130  is inserted between the magnet  120  and the shadow mask  111  by a transportation system not shown in the figure. Then the glass substrate  130  is placed on the shadow mask  111  by the transportation system as seen from FIG. 14.  
       [0022] Then, the magnet  120  is moved downwards to touch the upper surface of the glass substrate  130  as shown in FIG. 15. The shadow mask  111 , receiving magnetic power from the magnet  120 , is tightly placed to the lower surface of the glass substrate  130 , on which a pattern will be formed.  
       [0023] The evaporation source  140  is moved in the horizontal direction from left edge to the right edge of the glass substrate  130 , as seen from FIG. 16, by a moving system not shown in the figure. While the evaporation source is moving, the organic EL material or the material for the cathode  65  (for example, aluminum) evaporates and is deposited on the surface of the glass substrate  130  through the opening portions  112  of the shadow mask  111 . The evaporation source  140  is a crucible extended in the vertical direction of the FIG. 15. The evaporation material in the crucible is heated by a heater for evaporation.  
       [0024] The magnet  120  moves upwards when the evaporation is finished. The glass substrate  130  is lifted from the shadow mask  111  and moved to the location of the next operation by the transportation system. This completes the pattern forming of the organic El element  60 .  
       [0025] A multi-chamber method, where each layer is formed through the above evaporation method inside each chamber, has been employed for forming the hole transportation layer  62 , the emissive layer  63 , and the electron transportation layer  64  on the anode  61  made of ITO.  
       [0026] However, the hole transportation layer  62 , the emissive layer  63  and the electron transportation layer  64  can not be formed continuously in the same chamber by the conventional evaporation method described above. Therefore, the interface of the layers may be contaminated, leading to the unstable property and the deterioration of the organic El element.  
       [0027] Also, the thickness of and the material for each layer can not be adjusted for each pixel of R, G, or B, in case of a full color organic El element display device that has the display pixel for each R, G, and B.  
       [0028] Therefore, this invention is directed to the continuous pattering through the formation of a plurality of the evaporation layers made of different materials and the evaporation method capable of achieving the most effective thickness for each of the evaporation layers and accommodating the most effective material for each of the evaporation layers.  
       SUMMARY OF THE INVENTION  
       [0029] The invention provides an evaporation method that includes introducing an evaporation mask and a substrate into a vacuum chamber, evacuating the vacuum chamber to create a vacuum, and placing the evaporation mask on a surface of the substrate. The method also includes moving a first evaporation source having a first evaporation material therein in the vacuum along a first direction to deposit the first evaporation material on the surface of the substrate, and moving a second evaporation source having a second evaporation material therein in the vacuum along a second direction to deposit the second evaporation material on the first evaporation material deposited on the surface of the substrate.  
       [0030] The invention also provides a manufacturing method of a display device including an electroluminescent element. The method includes introducing an insulating substrate and an evaporation mask having openings corresponding to a pixel pattern of the display device into a vacuum chamber, evacuating the vacuum chamber to create a vacuum, and placing the evaporation mask on a surface of the insulating substrate. The method also includes moving a first evaporation source having a first constituent material of the electroluminescent element therein in the vacuum along a first direction to deposit the first constituent material on the surface of the insulating substrate, and moving a second evaporation source having a second constituent material of the electroluminescent element therein in the vacuum along a second direction to deposit the second constituent material on the first constituent material deposited on the surface of the insulating substrate.  
       [0031] The invention further provides a manufacturing method of a display device including electroluminescent elements corresponding to multiple colors. The method includes providing a deposition apparatus comprising a first evaporation chamber, a second evaporation chamber and a third evaporation chamber, introducing an insulating substrate and a pixel mask for a first color having openings corresponding to a pixel pattern of the first color into the first evaporation chamber, and placing the pixel mask for the first color on a surface of the insulating substrate. The method further includes moving a first evaporation source of the first color having therein a first constituent material of the electroluminescent element corresponding to the first color along a first direction to deposit the first constituent material of the first color on the surface of the insulating substrate and moving a second evaporation source of the first color having therein a second constituent material of the electroluminescent element corresponding to the first color along a second direction to deposit the second constituent material of the first color on the first constituent material of the first color deposited on the surface of the insulating substrate. The method also includes moving the insulating substrate from the first evaporation chamber to the second evaporation chamber, introducing a pixel mask for a second color having openings corresponding to a pixel pattern of the second color into the second evaporation chamber, and placing the pixel mask for the second color on the surface of the insulating substrate. The method further includes moving a first evaporation source of the second color having therein a first constituent material of the electroluminescent element corresponding to the second color along a third direction to deposit the first constituent material of the second color on the surface of the insulating substrate, and moving a second evaporation source of the second color having therein a second constituent material of the electroluminescent element corresponding to the second color along a fourth direction to deposit the second constituent material of the second color on the first constituent material of the second color deposited on the surface of the insulating substrate. The method also includes moving the insulating substrate from the second evaporation chamber to the third evaporation chamber, introducing a pixel mask for a third color having openings corresponding to a pixel pattern of the third color into the third evaporation chamber, and placing the pixel mask for the third color on the surface of the insulating substrate. The method further includes moving a first evaporation source of the third color having therein a first constituent material of the electroluminescent element corresponding to the third color along a fifth direction to deposit the first constituent material of the third color on the surface of the insulating substrate, and moving a second evaporation source of the third color having therein a second constituent material of the electroluminescent element corresponding to the third color along a sixth direction to deposit the second constituent material of the third color on the first constituent material of the third color deposited on the surface of the insulating substrate. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0032]FIG. 1 shows a step of a manufacturing method of an organic EL display device of the first embodiment of this invention.  
     [0033]FIG. 2 is a top view of an evaporation apparatus shown in FIG. 1.  
     [0034]FIG. 3 shows a step of the manufacturing method of an organic EL display device of the first embodiment following the step of FIG. 1.  
     [0035]FIG. 4 shows a step of the manufacturing method of an organic EL display device of the first embodiment following the step of FIG. 3.  
     [0036]FIG. 5 shows a step of the manufacturing method of an organic EL display device of the first embodiment following the step of FIG. 4.  
     [0037]FIG. 6 shows a step of the manufacturing method of an organic EL display device of the first embodiment following the step of FIG. 5.  
     [0038]FIG. 7 is a cross-sectional view of the organic EL element of the first embodiment.  
     [0039]FIG. 8 shows a vacuum evaporation device used in a manufacturing method of an organic EL display device of the second embodiment of the invention.  
     [0040]FIG. 9 is a cross-sectional view of the organic EL element of the second embodiment.  
     [0041]FIGS. 10A and 10B are a plain views of another deposition devices applicable to the first and second embodiments.  
     [0042]FIG. 11 is a plan view showing a conventional EL display device.  
     [0043]FIG. 12A is a cross-sectional view of the EL display device along with the A-A line in FIG. 11, and FIG. 12B is a cross-sectional view of the EL display device along with the B-B line in FIG. 11.  
     [0044] FIGS.  13 - 16  show steps of a conventional manufacturing method of an organic EL display device. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0045] The first embodiment of this invention will be explained by referring to FIGS.  1 - 7 . The same components in the figures as those in FIGS.  13 - 16  are given the same reference numerals.  
     [0046] A glass substrate  130  is inserted between a magnet  120  and a shadow mask  111  in a chamber of a vacuum evaporation device  100  in FIG. 1. FIG. 2 is a top view of the evaporation device  100  of FIG. 1.  
     [0047] This embodiment employs two evaporation sources  140 ,  141  that are movable by a moving system (not shown in the figure) in a horizontal direction along the main surface of the glass substrate  130  in the chamber of the vacuum evaporation device  100 . The evaporation sources  140 ,  141  are crucibles extending in a direction perpendicular to its propagation direction and evaporation materials placed in the crucibles. The evaporation material in the crucible is heated by a heater for evaporation.  
     [0048] The evaporation source  140  remains at the left edge of the glass substrate  130  and the evaporation source  141  remains at the right edge of the glass substrate  130  before the evaporation begins. The material for an emissive layer is stored in the evaporation source  140  and the material for an electron transportation layer is stored in the evaporation source  141 . Other configurations are the same as those shown in FIG. 12. Although they are not shown in the figures, the TFTs, the interlayer insulating film, the planarization film, and the anode made of a transparent electrode such as ITO have been disposed on the pattern forming surface of the glass substrate  130 . Also, a hole transportation layer has been formed on the anode through the evaporation method described as a conventional example.  
     [0049] The chamber of the vacuum evaporation device  100  is evacuated by an exhaust system  101  in FIG. 1. The glass substrate  130  is inserted between the magnet  120  and the shadow mask  111  by a transportation system not shown in the figure.  
     [0050] The glass substrate  130  is placed on the shadow mask  111  by the transportation system, as shown in FIG. 3.  
     [0051] Then, the magnet  120  moves downwards till it makes a contact with the upper surface of the glass substrate  130 , as shown in FIG. 4. The shadow mask  111 , receiving a magnetic power of the magnet  120 , is tightly placed on the lower surface, that is the pattern forming surface, of the glass substrate  130 .  
     [0052] The material for the emissive layer is disposed through evaporation on the surface of the glass substrate  130  through openings  112  formed in the shadow mask  111  while the evaporation source  140  is moved by the moving system not shown in the figure from the left edge to the right edge of the glass substrate  130 , as seen from FIG. 5. In this case, the evaporation source  140  includes two evaporation materials, i.e., a host and a dopant.  
     [0053] The evaporation source  140  stops at the right edge of the glass substrate  130 , as shown in FIG. 6. Then, the material for the electron transportation layer is disposed through evaporation on the surface of the glass substrate  130  through the same openings  112  formed in the shadow mask  111  while the evaporation source  141  moves in a horizontal direction to the left. The evaporation completes when the evaporation source  141  reaches the left edge of the glass substrate  130 .  
     [0054] The emissive layer and the electron transportation layer are continuously disposed by sequentially moving two evaporation sources  140 ,  141 , in this embodiment. Then, the magnet  120  moves upwards. The glass substrate  130  is lifted from the shadow mask  111  and moves to the location for the next process by the transportation system.  
     [0055] The two evaporation sources  140 ,  141  may move simultaneously to form the emissive layer and the electron transportation layer consecutively. The same material as the material for the emissive layer or the material for the electron transportation layer may be stored in each of the two evaporation sources  140 ,  141 . Further, the material for an electrode, such as the cathode, may be stored in the evaporation sources  140 ,  141 .  
     [0056]FIG. 7 is a cross-sectional view of the organic EL element formed by the evaporation method described above. The reference numeral  1  denotes a planarization layer formed on the glass substrate, and the reference numeral  2  an anode made of ITO, and the reference numeral  3  a hole transportation layer. The hole transportation layer  3  is commonly used for all the pixels, and formed in the entire display region. The emissive layer  4  and a first electron transportation layer  5  are consecutively disposed on the hole transportation layer  3 . Furthermore, a second electron transportation layer  6  is disposed on the first electron transportation layer  5  in the entire display region for commonly used by all the pixels.  
     [0057] According to this embodiment, the emissive layer  4  and the first electron transportation layer  5  are continuously disposed, leading to the improved emissive property of the organic EL element. Also, it is possible to adjust the thickness of and the material for the emissive layer as well as the electron transportation layer for each pixel of R, G, or B. Therefore, it is possible to induce the property of each of the organic EL element of R, G, and B most effectively.  
     [0058] Next, the second embodiment will be explained by referring to FIGS.  8 - 9 . FIG. 8 shows a vacuum evaporation device  300  with multiple chambers. This vacuum evaporation device  300  has five chambers  301 ,  302 ,  303 ,  304 ,  305 . The evaporation of the hole transportation layer  3  on the glass substrate  130  is performed in the chamber  301 . Then, the glass substrate  130  is transported to the chamber  302 , where the evaporation of the emissive layer and the electron transportation layer for the R pixel is performed. After this, the glass substrate  130  is transported to the chamber  303 , where the evaporation of the emissive layer and the electron transportation layer for the G pixel is performed.  
     [0059] Then, the glass substrate  130  is transported to the chamber  304 , where the evaporation of the emissive layer and the electron transportation layer for the B pixel is performed. The glass substrate  130  is then transported to the chamber  305 , where the evaporation of the electron transportation layer commonly used for all the pixels is further performed.  
     [0060] Evaporation sources  150  and  157  are disposed in the chambers  301  and  305  respectively. Each of the chambers  302 ,  303  and  304  corresponding to the pixels of R, G and B has two evaporation sources ( 151 ,  152 ), ( 153 ,  154 ), and ( 155 ,  156 ) respectively. Each set of the two evaporation sources moves consecutively or simultaneously to dispose the emissive layer and the electron transportation layer for each pixel through evaporation as in the evaporation method of the first embodiment.  
     [0061]FIG. 9 shows a cross-sectional view of the organic EL element formed through the evaporation method described above. Organic El elements  70 ,  80 , and  90  for the R pixel, the G pixel and the B pixel, respectively, are shown. in the figure, and the TFT for driving is omitted in the figure for the sake of simplicity.  
     [0062] The emissive layer  72  and the electron transportation layer  73  are continuously disposed on the common hole transportation layer  3  formed on the anode  71  in the organic EL element of the R pixel. The common electron transportation layer  6  is further disposed over these layers. Likewise the emissive layer  82  and the electron transportation layer  83  are continuously disposed on the common hole transportation layer  3  formed on the anode  81  in the organic EL element of the G pixel. The common electron transportation layer  6  is further disposed over these layers.  
     [0063] Also, the emissive layer  92  and the electron transportation layer  93  are continuously disposed on the common hole transportation layer  3  formed on the anode  91  in the organic EL element of the B pixel. The common electron transportation layer  6  is further disposed over these layers.  
     [0064] Therefore, according to this embodiment, the emissive layer and the electron transportation layer can be continuously disposed for each of pixels of R, G, and B, leading to the improvement of the emissive property. Also, it is possible to change the thickness and the material of these layers in order to induce the most favorable condition for each of the pixels of R, G, and B.  
     [0065] Although there are provided two evaporation sources, and two layers are continuously disposed in the these embodiments, it is also possible to provide more than three evaporation sources for continuously disposing more than three layers.  
     [0066] For example, as shown in FIG. 10A, each of the three evaporation sources  140 ,  141  and  142  moves consecutively or simultaneously to continuously dispose three layers through evaporation. Here, the material for the emissive layer is stored in each of the evaporation sources  140  and  141  and the material for the electron transportation layer is stored in the evaporation source  142 . Furthermore, the material for the hole transportation layer may be stored in the evaporation sources  140 , the material for the electron transportation layer may be stored in the evaporation sources  141  and the material for the emissive layer may be stored in the evaporation source  142 .  
     [0067] Further, four evaporation sources may be used as shown in FIG. 10B. Each of the four evaporation sources  140  , 141 ,  142  and  143  moves consecutively or simultaneously to continuously dispose four layers through evaporation. For example, the material for the hole transportation layer is stored in the evaporation sources  140 , the material for the electron transportation layer is stored in the evaporation sources  141  , the material for the orange color emissive layer is stored in the evaporation source  142 , and the material for the blue color emissive layer is stored in the evaporation source  143  in order to form a white color EL element. In this white color EL element, the orange color emissive layer and the blue color emissive layer are stacked on the hole transportation layer.