Abstract:
A method of patterning an indium tin oxide (ITO) layer is performed on a glass substrate. First, using sputtering, an amorphous ITO layer is deposited on the glass substrate. Then, using excimer laser annealing (ELA), the amorphous ITO layer within a predetermined pattern is turned into a crystalline ITO layer. Finally, using an etch solution, the amorphous ITO layer outside the predetermine pattern is removed.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a method of patterning a transparent electrode of Indium Tin Oxide (ITO) and, more particularly, to a method of crystallizing the transparent electrode of ITO.  
           [0003]    2. Description of the Related Art  
           [0004]    A transparent conductive layer of Indium Tin Oxide (ITO) is practically applied to the fabrication of a contact of contact panel, an electrode of liquid crystal display (LCD), a thermal reflective coating, a gas-sensing sensor, a static electricity-resistance coating, and an abrasion-resistance coating of glass. The ITO layer may be formed by a chemical film-forming method, such as spray, chemical evaporation, or dipping. Alternatively, the ITO layer may be formed by a physical film-forming method, such as vacuum evaporation or sputtering. Generally, sputtering can form an ITO layer of a low resistance and a uniform thickness on a substrate. However, when the ITO layer is then patterned by conventional photolithography and etching with oxalic acid, the patterned ITO layer cannot fit in with the requirements for product properties.  
           [0005]    [0005]FIG. 1 is a flow chart of a conventional method of patterning an ITO layer. First, at step  10  of sputtering, an amorphous ITO layer is deposited on a substrate. Then, conventional photolithography, which comprises a step  12  of photoresist coating, a step  14  of soft baking, a step  16  of exposure, a step  18  of developing, a step  20  of hard baking, a step  22  of etching by oxalic acid, and a step  22  of photoresist stripping, is carried out on the amorphous ITO layer. The step  14  of soft baking drives out the solvents existing in the photoresist. The step  16  of exposure makes the photoresist absorb appropriate energy so as to proceed with photochemical transformation. The step  18  of developing forms the potential pattern that is transferred to the photoresist. The step  20  of hard baking is used to further reduce the solvent remaining in the photoresist and fix the profile of the patterned photoresist. The step  22  of etching by oxalic acid removes the amorphous ITO layer not covered by the patterned photoresist, thus forming the pattern of the amorphous ITO layer. Finally, at step  26 , annealing is performed in an oven to turn the amorphous ITO layer into a crystallized ITO layer. Thus the ITO layer can achieve the expected resistance and transparency.  
           [0006]    However, at the step  10  of sputtering with H 2 O, when the amorphous ITO layer is continuously deposited to reach a thickness of more than 800 Å, the process temperature is lower than the process temperature in the subsequent step  20  of hard baking. Thus, the higher temperature in the step  20  of hard baking causes a microcrystalline phenomenon on the surface of the amorphous ITO layer. Also, when the process temperature is improperly controlled in sputtering or photolithography, the microcrystalline phenomenon can be formed. Since oxalic acid is not the excellent etchant for etching crystallized materials, the step  22  of etching cannot completely remove the crystalline area of the ITO layer and this decreases the accuracy of patterning the ITO layer.  
           [0007]    In addition, in the series of steps  12 ˜ 24 , exposured photoresist and developer solution are easily remained on the substrate, thus effecting the properties of the subsequent etching or deposition. Also, the complicated steps  12 ˜ 26  have high production costs and may cause the substrate to be bended, damaged or contaminated if man-made carelessness and improper process control occur.  
           [0008]    Thus, a method of patterning an ITO layer solving the aforementioned problems is called for (desired).  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention provides a method of patterning an ITO layer to pattern and crystallize the amorphous ITO layer at the same time so as to simplify the procedure.  
           [0010]    The method of patterning an indium tin oxide (ITO) layer is performed on a glass substrate. First, using sputtering, an amorphous ITO layer is deposited on the glass substrate. Then, using excimer laser annealing (ELA), the amorphous ITO layer within a predetermined pattern is turned into a crystalline ITO layer. Finally, using an etch solution, the amorphous ITO layer outside the predetermine pattern is removed.  
           [0011]    Accordingly, it is a principle object of the invention to provide excimer laser annealing for replacing the conventional photolithography process.  
           [0012]    It is another object of the invention to use excimer laser annealing to pattern and crystallize the amorphous ITO layer at the same time.  
           [0013]    Yet another object of the invention is to simply the method of patterning the ITO layer.  
           [0014]    It is a further object of the invention to accurately pattern the ITO layer.  
           [0015]    These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a flow chart of a conventional method of patterning an ITO layer.  
         [0017]    [0017]FIG. 2 is a flow chart of the method of patterning an ITO layer according to the present invention.  
         [0018]    [0018]FIG. 3 is a schematic diagram of an ELA apparatus for patterning the ITO layer. 
     
    
       [0019]    Similar reference characters denote corresponding features consistently throughout the attached drawings.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    The present invention provides a method of patterning an ITO layer that is suitable for fabricating the products, such as thin film transistor (TFT), liquid crystal display (LCD), organic light emitting diode (OLED), and plasma display panel (PDP). Hereinafter, the method of patterning an ITO layer is applied to the formation of a transparent electrode in LCD. FIG. 2 is a flow chart of the method of patterning an ITO layer according to the present invention. First, at step  30  of sputtering with H 2 O, an amorphous ITO layer of 200˜800 Å thickness is deposited on a glass substrate. Then, at step  32  of excimer laser annealing (ELA), a high-energy pulsed laser directs laser radiation at selected regions of the amorphous ITO layer to expose the amorphous ITO layer to very high temperatures for short durations. Thus, the amorphous ITO layer is crystallized without damage to the underlying glass substrate, and the crystalline ITO layer achieves the expected resistance and transparency. Finally, the step  34  of etching by oxalic acid removes the amorphous ITO layer outside the selected regions, thus precisely forming the expected pattern of the ITO layer.  
         [0021]    [0021]FIG. 3 is a schematic diagram of an ELA apparatus for patterning the ITO layer. In an ELA apparatus  40 , laser emitter  42  emits a pulsed beam  44  that passes through a beam homogenizer  46 . The pulsed beam  44  is a high-energy coherent radiation at a selective wavelength. The use of laser depends on the required design (parameters), for example, XeCl lasers emit UV radiation at a wavelength of 308 nm; KrF lasers operate at a wavelength of 248 nm. The beam homogenizer  46  installed below the laser emitter  42  is an optical system that produces a substantially uniform beam profile. After the pulsed beam  44  passes through the beam homogenizer  46 , a homogenized beam  47  of a size between 10 mm 2  and 50 mm 2  is emerged.  
         [0022]    Next, the homogenized beam  47  passes through a patterned photo mask disposed on a reticle scanning stage  48 , and then is centralized by a lens  50  to direct irradiate selected regions of an amorphous ITO layer  38  deposited on a glass substrate  36 . Thus, the selected regions of the amorphous ITO layer  38  is exposed to very high temperatures for short durations, resulting crystallization in selected regions of the amorphous ITO layer  38 .  
         [0023]    The glass substrate  36  is placed on a movable stage  52  that can move the glass substrate  36  to a proper position to ensure that the homogenized beam  47  accurately radiates the selected regions on the amorphous ITO layer  38 . Alternatively, the movable stage  52  can redirect the pulsed beam  44  to aim it at different target regions on the glass substrate by moving the laser emitter  42  and related optics to a fixed stage. The power level of the laser emitter  42 , the duration of the pulsed beam  44 , and the size of the homogenized beam  47  determine the number of exposures to the selected region on the glass substrate  36 . The ELA apparatus  40  is readily programmed to perform multiple exposures to properly anneal and crystallize the amorphous ITO layer  38 . Generally, the power level of the laser emitter  42  is 50˜200 mJ/cm 2 .  
         [0024]    In the present invention, the step  32  of ELA replaces the conventional photolithography process. Thus the series of complicated steps of photoresist coating, soft baking, exposure, developing, hard baking, and photoresist stripping are omitted. Also, at the same time when the ITO layer is patterned, the amorphous ITO is turned into crystalline ITO. Therefore, the process of patterning the ITO layer is simplified, and the disadvantages of remaining photoresist, remaining developer solution, bended substrate, and contaminated ITO layer caused by man-made carelessness and improper process control are avoided. Further, compared with performing hard baking on the glass substrate, the present invention exposes the selected regions of the amorphous ITO layer to the high-temperature laser beam for short durations to crystallize the amorphous ITO layer. This can prevent a microcrystalline phenomenon on the surface of the amorphous ITO layer, and therefore the ITO layer is accurately patterned in the subsequent step of etching by oxalic acid.  
         [0025]    It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.