Abstract:
A method for manufacturing a light-emitting diode is described, comprising the following steps. A substrate is provided. An illuminant epitaxial structure is formed on the substrate, wherein the illuminant epitaxial structure comprises a first conductivity type semiconductor layer, an active layer and a second conductivity type semiconductor layer stacked on the substrate in sequence, a surface of the second conductivity type semiconductor layer includes at least one epitaxial defect formed therein, and the first conductivity type semiconductor layer and the second conductivity type semiconductor layer are opposite conductivity types. Then, an insulation layer is formed to fill into the epitaxial defect in the second conductivity type semiconductor layer. A transparent electrode layer is formed on the surface of the second conductivity type semiconductor layer.

Description:
RELATED APPLICATIONS  
       [0001]     The present application is based on, and claims priority from, Taiwan Application Serial Number 94132908, filed Sep. 22, 2005, the disclosure of which is hereby incorporated by reference herein in its entirety.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to a method for manufacturing a light-emitting diode, and more particularly, to a method for manufacturing a light-emitting diode of high electrostatic discharge (ESD).  
       BACKGROUND OF THE INVENTION  
       [0003]      FIG. 1  illustrates a cross-sectional view of a conventional light-emitting diode structure. Typically, in the fabrication of a light-emitting diode structure  114 , a substrate  100  is provided for the growth of the material layers formed sequentially. An N-type semiconductor material layer  102  is form to cover the substrate  100  by an epitaxial method. Next, an active layer  104  is formed to cover the N-type semiconductor material layer  102  by an epitaxial method, wherein the active layer  104  may be a multiple quantum well (MQW) structure. A P-type semiconductor material layer  106  is formed on the active layer  104  by an epitaxial method, similarly. Usually, epitaxial defects are produced in a surface structure of the semiconductor material, such as epitaxial defects  108  formed in the P-type semiconductor material layer  106 , due to the lattice arrangement direction of the semiconductor material. These epitaxial defects  108  may be V-shaped, such as shown in  FIG. 1 .  
         [0004]     After the P-type semiconductor material layer  106  is formed, a transparent electrode layer  110  is formed to cover the P-type semiconductor material layer  106  by a deposition method. Because the surface structure of the P-type semiconductor material layer  106  includes the epitaxial defects  108 , the transparent electrode layer  110  is deposited on the uneven surface of the P-type semiconductor material layer  106 . Then, a metal electrode pad  112  is formed on a portion of the transparent electrode layer  110  by a deposition method. A high temperature anneal treatment is performed to complete the fabrication of a light-emitting diode structure  114 , such as shown in  FIG. 1 .  
         [0005]     However, because the P-type semiconductor material layer  106  has the epitaxial defects  108 , the epitaxial defects  108  are filled with the material of the transparent electrode layer  110 . As a result, the conductive material is close to the active layer  104 , even contacts the active layer  104 . When the high temperature anneal treatment is performed sequentially, the metal in the transparent electrode layer  110  and/or the metal electrode layer  112  diffuses into the active layer  104 . Therefore, the electrostatic discharge protection of the light-emitting diode device may be inactive when operating at a working voltage by a low current or at a high voltage, thereby greatly reducing the reliability and operating stability of the light-emitting diode device.  
       SUMMARY OF THE INVENTION  
       [0006]     Therefore, one objective of the present invention is to provide a method for manufacturing a light-emitting diode by filling surface defects of an epitaxial layer with an insulation material before depositing a transparent electrode or a metal electrode, so as to isolate an active layer and the conductive electrode material. As a result, the electrode material can be prevented from diffusing to the active layer during the following high temperature anneal process, thereby avoiding the inactivity of the electrostatic discharge when the device is at low operating current or high operating voltage.  
         [0007]     Another objective of the present invention is to provide a method for manufacturing a light-emitting diode by using an insulation material to repair surface defects of an epitaxial material layer, thereby improving a connection surface between an electrode layer formed sequentially and the epitaxial material layer.  
         [0008]     Still another objective of the present invention is to provide a method for manufacturing a light-emitting diode, which can increase the efficiency of the electrostatic discharge of the light-emitting diode and can enhance the operating reliability of stability of the device.  
         [0009]     According to the aforementioned objectives, the present invention provides a method for manufacturing a light-emitting diode, comprising the following steps. A substrate is provided. An illuminant epitaxial structure is formed on the substrate, wherein the illuminant epitaxial structure comprises a first conductivity type semiconductor layer, an active layer and a second conductivity type semiconductor layer stacked on the substrate in sequence, a surface of the second conductivity type semiconductor layer includes at least one epitaxial defect formed therein, and the first conductivity type semiconductor layer and the second conductivity type semiconductor layer are opposite conductivity types. Then, an insulation layer is formed to fill into the epitaxial defect in the second conductivity type semiconductor layer. A transparent electrode layer is formed on the surface of the second conductivity type semiconductor layer.  
         [0010]     According to a preferred embodiment of the present invention, a material of the insulation layer may be oxide or nitride, such as silicon dioxide (SiO 2 ) or silicon nitride (Si 3 N 4 ). The step of forming the insulation layer further comprises forming an insulation material layer on the surface of the second conductivity type semiconductor layer, and performing a removing step to remove the insulation material layer beyond the epitaxial defect. In the present invention, the step of forming the insulation material layer may use an electron beam evaporation method, a thermal oxidation method, a physical vapor deposition method, or a chemical vapor deposition method, and the removing step may use a wet etching process, a dry etching process or a chemical mechanical polishing process.  
         [0011]     By filling the insulation material into the epitaxial defect, the epitaxial defect can be modified to have an insulating epitaxial surface state, thereby preventing the metal elements in the transparent electrode or the metal electrode pad formed sequentially from diffusing to the active layer, to increase the efficiency of the electrostatic discharge of the light-emitting diode and enhance the operating reliability of stability of the light-emitting diode device. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0013]      FIG. 1  illustrates a cross-sectional view of a conventional light-emitting diode structure; and  
         [0014]      FIGS. 2 through 5  are schematic flow diagrams showing the process for manufacturing a light-emitting diode in accordance with a preferred embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]     The present invention discloses a method for manufacturing a light-emitting diode by filling an insulation material into epitaxial defects in an epitaxial material layer to isolate an active layer and a following conductive material layer, so as to improve the reliability and stability of the light-emitting diode device. In order to make the illustration of the present invention more explicit and complete, the following description is stated with reference to  FIGS. 2 through 5 .  
         [0016]      FIGS. 2 through 5  are schematic flow diagrams showing the process for manufacturing a light-emitting diode in accordance with a preferred embodiment of the present invention. In the present invention, when the light-emitting diode is manufactured, a substrate  200  is provided for the growth of material layers formed thereon. A first conductivity type semiconductor layer  202  is grown on the substrate  200  by, for example, an epitaxial method. A material of the first conductivity type semiconductor layer  202  may be composed of a GaN-based or GaP-based material. Next, an active layer  204  is growth on the first conductivity type semiconductor layer  202  by, for example, an epitaxial method. A material of the active layer  204  may be composed of a GaN-based or GaP-based material, and the active layer  204  may include a multiple quantum well structure. After the growth of the active layer  204  is completed, a second conductivity type semiconductor layer  206  is grown on the active layer  204  by, for example, an epitaxial method. A material of the second conductivity type semiconductor layer  206  may be composed of a GaN-based or GaP-based material. In the present invention, the first conductivity type semiconductor layer  202  and the second conductivity type semiconductor layer  206  are opposite conductivity types. That is, when the first conductivity type semiconductor layer  202  is N-type, the second conductivity type semiconductor layer  206  is P-type; conversely, when the first conductivity type semiconductor layer  202  is P-type, the second conductivity type semiconductor layer  206  is N-type. The first conductivity type semiconductor layer  202 , the active layer  204  and the second conductivity type semiconductor layer  206  constitute an illuminant epitaxial structure of the light-emitting diode. Due to the lattice arrangement direction of the semiconductor material, an epitaxial layer typically has epitaxial defects. For example, in the structure of the second conductivity type semiconductor layer  206 , one or more epitaxial defects  208  may be produced. In some examples, these epitaxial defects  208  may be in V-shaped, such as shown in  FIG. 2 .  
         [0017]     After the illuminant epitaxial structure is completed, as shown in  FIG. 3 , an insulation material layer  210  is formed to cover a surface of the second conductivity type semiconductor layer  206  and to fill into the epitaxial defects  208  in the surface structure of the second conductivity type semiconductor layer  206  by, for example, an electron beam evaporation method, a thermal oxidation method, a physical vapor deposition method, or a chemical vapor deposition method. In the present invention, a material of the insulation material layer  210  may be oxide, such as silicon dioxide, or nitride, such as silicon nitride. A thickness of the insulation material layer  210  is preferably between about 100 Å and about 5000 Å.  
         [0018]     Then, a removing step is performed on the insulation material layer  210  to remove a portion of the insulation material layer  210  and remain the insulation material layer  210  within the epitaxial defects  208 , such as shown in  FIG. 4 . In a preferred embodiment of the present invention, the removing step may include an etch-back process or a chemical mechanical polishing process. The etch-back process may use a dry etching technique or a wet-etching technique. In the etch-back process, a high selectivity etchant and a high load effected are applied to perform an appropriate over etching, so as to completely remove the insulation material layer  210  on the surface of the second conductivity type semiconductor layer  206  beyond the epitaxial defects  208  and form an insulation layer  212  in the epitaxial defects  208  to insulate the active layer  204  and a conductive material deposited sequentially. When the wet-etching technique is applied, an etchane, such as NH 4 F BOE or HF, is used. When the dry-etching technique is applied, an inductively coupled plasma etcher may be used to perform an inductively coupled plasma etch, or a reactive ion etcher may be used to perform a reactive ion etch. When the chemical mechanical polishing process is applied, an end point detection method is used to monitor the polishing process to prevent the excessive polishing phenomenon from occurring and to perform an appropriate over polishing treatment when reaching the polishing end point, so as to ensure that no insulation material layer  210  remains on the surface of the second conductivity type semiconductor layer  206  except the epitaxial defects  208 .  
         [0019]     One feature of the present invention is that an insulation material is filled into epitaxial defects of an epitaxial structure after the illuminant epitaxial structure of the light-emitting diode is completed, thereby can effectively isolate the active layer and the conductive material formed sequentially to enhance the electrical stability of the device.  
         [0020]     After filling the insulation layer  212  into the epitaxial defects  208 , a transparent electrode layer  214  is formed to cover the surface of the second conductivity type semiconductor layer  206 , to fill into the epitaxial defects  208  and to cover the insulation layer  212  by, for example, a chemical vapor deposition method. A material of the transparent electrode layer  214  is, for example, ITO or ZnO. Because the insulation layer  212  has made up a portion of the epitaxial defects  208 , the transparent electrode layer  214  can be formed on the surface smoother than that in the prior art. Then, a metal electrode pad  216  is formed on a portion of the transparent electrode layer  214  by, for example, an evaporation method. Subsequently, a high temperature anneal treatment is performed to improve the electrical contact between the transparent electrode layer  214  and the metal electrode pad  216 , and the fabrication of a light-emitting diode structure  218  is completed, such as shown in  FIG. 5 .  
         [0021]     The epitaxial defects  208  of the second conductivity type semiconductor layer  206  are filled with the insulation layer  212 , which can effectively block the transparent electrode layer  214  and the active layer  204 . As a result, when the anneal treatment is performed, the metal elements, such as In or Sn, in the transparent electrode layer  214  or the metal elements in the metal electrode pad  216  can be prevented from diffusing into the active layer  204 , thereby greatly improving the electrical quality of the light-emitting diode structure  218  to further enhance the reliability and stability of the light-emitting diode device. By blocking the metal elements in the transparent electrode layer  214  and the metal electrode pad  216  from diffusing into the active layer  204 , it can avoid the inactivity of the electrostatic discharge when the light-emitting diode device is operated at low current or high voltage.  
         [0022]     It is noteworthy that the manufacture technique of the present invention can be applied to a light-emitting diode device with a vertically conductive structure and a light-emitting diode device with a horizontally conductive structure.  
         [0023]     According to the aforementioned description, one advantage of the present invention is that the method for manufacturing a light-emitting diode of the present invention fills surface defects of an epitaxial layer with an insulation material before depositing a transparent electrode or a metal electrode, so that an active layer and the electrode material can be effectively isolated to prevent the electrode material from diffusing to the active layer, and to avoid the inactivity of the electrostatic discharge when the light-emitting diode device is operated at low current or high voltage.  
         [0024]     According to the aforementioned description, another advantage of the present invention is that the present method for manufacturing a light-emitting diode uses an insulation material to repair the defects in the epitaxial surface, so that the connecting surface condition between the following electrode layer and the epitaxial material layer is improved.  
         [0025]     According to the aforementioned description, still another advantage of the present invention is that the electrical quality of the light-emitting diode can be enhanced to achieve the object of increasing the operating reliability and stability of the device with the application of the present method for manufacturing a light-emitting diode.  
         [0026]     As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrated of the present invention rather than limiting of the present invention. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structure.