Abstract:
A light-emitting device is disclosed. The light-emitting device comprises a substrate, wherein an ion implanted layer on the top surface of the substrate; a thin silicon film disposing on the ion implanted layer; and a light-emitting stack layer on the thin silicon film. This invention also discloses a method of manufacturing a light-emitting device comprising providing a substrate; forming an ion implanted layer on the top surface of the substrate; providing a light-emitting stack layer; forming a thin silicon film on the bottom surface of the light-emitting stack layer; and bonding the light-emitting stack layer to the substrate with the anodic bonding technique.

Description:
REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the right of priority based on TW application Ser. No. 097124823, filed “Jul. 1, 2008”, entitled “Light-emitting Device and Method for Manufacturing the Same” and the contents of which are incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The application relates to a light-emitting device, and more particularly to a light-emitting diode having an ion implanted layer on the top surface of a substrate. 
       BACKGROUND 
       [0003]    The light-emitting diode (LED) emits light by transforming the energy released from the electrons moving between the n-type semiconductor and the p-type semiconductor so the mechanism is different from that of the incandescent lamp. Thus, the LED is called cold light source. In addition, because the LED has advantages like high reliability, long lifetime, compact size, low power consumption, and so on, the current illumination market expects the LED to be an illuminant tool of the new generation. 
         [0004]    The conventional LED structure is a semiconductor epitaxial structure formed on a substrate, wherein the quality of the epitaxy in the semiconductor epitaxial structure has critical influence on the internal quantum efficiency of the LED, and whether the lattice constant of the substrate can match with that of the material of the epitaxial structure is important to the quality of the epitaxy. Therefore, the choice of the substrate materials for the LED is limited. 
         [0005]    In addition, to improve the light extraction efficiency and heat-dissipation of the LED, the technique of transferring the substrate of the LED comes up gradually. Referring to  FIG. 1A  to  FIG. 1G , a flowchart for a conventional substrate transfer process is illustrated. As shown in  FIG. 1A , a first substrate  10  is provided, and an epitaxial structure  12  is provided as shown in  FIG. 1B . Referring to  FIG. 1C , then a second substrate  14  is provided, and an adhesive layer  16  is, referring to  FIG. 1D , formed on the second substrate  14 . Later, referring to  FIG. 1E , the structure illustrated in  FIG. 1A  is flipped to attach the epitaxial structure  12  with the second substrate  14  with the adhesive layer  16  by pressed lamination, wherein the material of the adhesive layer  16  can be metal or polymers like PI, BCB, PFCB, and combinations thereof. After that, referring to  FIG. 1F , the substrate  10  is removed so as to form a conventional light-emitting diode structure illustrated in  FIG. 1G . 
       SUMMARY 
       [0006]    The present application provides a light-emitting device including an epitaxial structure and a substrate wherein the substrate of the LED has an ion implanted layer to alter refractive index of the substrate surface. Therefore, the refractive index has a gradual distribution between the epitaxial structure and the substrate so as to reduce total internal reflection effect. 
         [0007]    The present application provides a method for manufacturing LED by bonding the epitaxial structure to the substrate with the anodic bonding technology. 
         [0008]    Other features and advantages of the present application and variations thereof will become apparent from the following description, drawing and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The accompanying drawings incorporated herein provide a further understanding of the invention therefore constitute a part of this specification. The drawings illustrating embodiments of the invention, together with the description, serve to explain the principles of the invention. 
           [0010]      FIGS. 1A-1G  are the diagrams illustrating the manufacturing procedure of the conventional light-emitting diode. 
           [0011]      FIGS. 2A-2H  are the diagrams illustrating the manufacturing procedure of the light-emitting diode in accordance with one embodiment of the present application. 
           [0012]      FIGS. 3A-3E  are the diagrams illustrating the manufacturing procedure of the light-emitting diode in accordance with another embodiment of the present application. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0013]      FIGS. 2A-2H  are the diagrams illustrating the manufacturing procedure in accordance with one embodiment of the present application, including the following steps: as shown in  FIG. 2A , providing a first substrate  30 , and as shown in  FIG. 2B , forming a light-emitting stack layer  32  by MOCVD (Metal Organic Chemical Vapor Deposition), wherein the light-emitting stack layer  32  includes at least a firs-type conductivity semiconductor layer  320 , a lighting-emitting layer  322 , and a second-type conductivity semiconductor layer  324  from top to bottom, wherein the material of the light-emitting stack layer  32  can be semiconductor materials such as GaAlAs, AlGaInP, GaP or GaN series and combinations thereof. The material of the first substrate  30  can be materials having lattice constant matching with the lattice constant of the light-emitting stack layer  32 , such as Sapphire, SiC, GaAs, and so on. In this embodiment, a substrate of SiC and a light-emitting stack layer of GaN are adopted for exemplifying. 
         [0014]    Thereafter, as shown in  FIG. 2C , a thin silicon film  34  is formed on the light-emitting stack layer  32  by PECVD (Plasma-enhanced Chemical Vapor Deposition), wherein the material of the thin silicon film  34  in this embodiment is amorphous silicon with a width of 200 nm. 
         [0015]    As shown in  2 D, the manufacturing procedure further comprises the following steps: providing a second substrate  36 , wherein the material of the second substrate  36  could be Oxides such as Sapphire or ZnO, and a Sapphire substrate is used as exemplary in this embodiment, and form an ion implanted layer  38  by implanting sodium ions from the upper side into the second substrate  36  through ion implantation technique, wherein sodium ions in the ion implanted layer  38  are combined with oxygen ions of the Sapphire substrate to form Na x O molecules. 
         [0016]    After that, as shown in  FIG. 2E , the manufacturing procedure further comprises the steps of flipping the structure shown in  FIG. 2C , disposing it on the ion implanted layer  38  to contact the thin silicon layer  34  with the ion planted layer  38 ; and providing a voltage between the thin silicon layer  34  and the ion implanted layer  38  wherein the voltage is about 500 to 1200 volts, and the electric potential of the thin silicon layer  34  is higher than the electric potential of the ion implanted layer  38 . Due to the electric potential difference between the thin silicon layer  34  and the ion planted layer  38 , the oxygen ions of the Na x O molecules in the ion planted layer  38  are forced to move toward the thin silicon layer  34  and form an oxide layer  40  with the thin silicon layer  34  in the interface between the ion planted layer  38  and the thin silicon layer  34 . Therefore, an adhesive layer  41  is formed by the thin silicon layer  34  and the oxide layer  40 , and the light-emitting stack layer  32  is attached to the second substrate  36 . In this embodiment, the material of the oxide layer  40  is SiO 2 . 
         [0017]    Then, as shown in  FIG. 2F , the manufacturing procedure further comprises the steps of removing the first substrate  30  as shown in  FIG. 2G , etching part of the light-emitting stack layer  32  by lithography technique to expose part of first-type conductivity semiconductor layer  320  as shown in  FIG. 2H , forming a first electrode  42  and a second electrode  44  on the first-type conductivity semiconductor layer  320  and the second-type conductivity semiconductor layer  324  respectively for electrical connection so as to form a light-emitting diode chip  200 . 
         [0018]    Moreover, in the step of forming the ion implanted layer  38 , the second substrate  36  can be disposed in an oxygen-containing environment so the concentration of the Na x O molecules in the ion planted layer  38  is increased. In a preferred embodiment, the second substrate  36  is disposed in an environment with sufficient oxygen to perform the step of forming the ion implanted layer  38 . In addition, after forming the ion planted layer  38 , the second substrate  36  can be disposed in an oxygen-containing environment for moving the oxygen ions into the ion implanted layer  38  to increase the content of Na x O molecules in the ion planted layer  38  by thermal driving method, wherein a preferred embodiment of above thermal driving step is performed with the second substrate  36  disposed in an environment with sufficient oxygen. 
         [0019]    In this embodiment, the refractive index of the light-emitting stack layer  32  is about 3.4, the refractive index of the second sapphire substrate  36  is about 1.78, and the refractive index of the ion implanted layer  38  implanted by sodium ions is between the refractive indexes of the light-emitting stack layer  32  and the second sapphire substrate  36 , for example, about 1.8 to 2.0. Accordingly, when a light is emitted from the light-emitting stack layer  32 , it is out of the LED chip  200  after passing the ion implanted layer  38  and the second sapphire substrate  36 . Therefore, the refractive index of above light path is gradually altered from higher value to lower one so as to reduce the total internal reflection effect of light and raise the light extraction efficiency of the LED chip  200 . 
         [0020]      FIGS. 3A-3E  are the diagrams illustrating the manufacturing procedure in accordance with another embodiment of the present application. As shown in  FIG. 3A , the manufacturing procedure comprises the steps of providing a second substrate  36  and forming a patterned ion implanting layer  50  on the surface of the second substrate  36 . The patterned ion implanting layer  50  has regular symmetry or irregular asymmetry patterns, wherein a regular symmetry patterned ion planting layer is defined as a patterned ion planting layer showing identical reduplicating characteristics in any direction of the surface of the second sapphire substrate  36 , and the term “regular” could be defined as periodic, varied periodic, quasiperodicity or combinations thereof. The irregular asymmetry patterned ion planting layer is defined as a patterned ion planting layer unable to show identical reduplicating characteristics in any direction of the surface of the second sapphire substrate  36 . Additionally, in this embodiment, the ion planting layer  50  covers about 15% to 85% of the surface area of the second substrate  36 , and the better is 30% to 60% of the surface area. Furthermore, in this ion implanted step, ion source at least comes from sodium ions and the ion source sodium ions forms Na x O molecules in the patterned ion planting layer  50 . 
         [0021]    After that, as shown in  FIG. 3B , the manufacturing procedure further comprises the steps of flipping the structure illustrated in  FIG. 2C  to contact the thin silicon layer  34  with the second substrate  36  and the patterned ion planting layer  50 ; providing a voltage among the patterned ion implanting layer  50 , the thin silicon layer  34  and the second substrate  36 , wherein the voltage is about 500 to 1200 volts in this step, and the electric potential of the thin silicon layer  34  is higher than the electric potential of the patterned ion implanting layer  50 . Due to the electric potential difference between the thin silicon layer  34  and the patterned ion implanting layer  50 , the oxygen ions of the Na x O molecules in the patterned ion implanting layer  50  are forced to move toward the thin silicon layer  34  and form an oxide layer  52  in the interface between the patterned ion implanting layer  50  and the thin silicon layer  34 . Therefore, an adhesive layer  53  is formed by the thin silicon layer  34  and the oxide layer  52 , and the light-emitting stack layer  32  is attached to the second substrate  36 . In this embodiment, the material of the oxide layer  52  is SiO 2 . 
         [0022]    Then, as shown in  FIG. 3C , the manufacturing procedure further comprises the steps of removing the first substrate  30 ; etching part of the light-emitting stack layer  32 , as shown in  FIG. 3D , to expose part of the first-type conductivity semiconductor layer  320  by lithography technique. Finally, as shown in  FIG. 3E , forming a first electrode  42  and a second electrode  44  on the first-type conductivity semiconductor layer  320  and the second-type conductivity semiconductor layer  324  respectively for electrically connecting the first electrode with the first conductivity semiconductor layer and the second electrode with the second conductivity semiconductor layer so as to form a light-emitting diode chip  300 . 
         [0023]    In this embodiment, the material of the second substrate  36  is Sapphire with the refractive index of about 1.78, and the refractive index of the patterned ion implanting layer  50  implanted by sodium ions, for example, on the surface of the second sapphire substrate  36 , is about 1.8 to 2.0. The refractive index difference between the material of the second substrate  36  and the patterned ion implanting layer  50  reduces the total internal reflection effect of light emitted from the light-emitting stack layer  32  in the LED chip  300  so as to further increase the luminescent extraction efficiency. 
         [0024]    The foregoing description has been directed to a specific embodiment of this invention. It will be apparent; however, that other variations and modifications may be made to the described embodiments, with the attainment of some or all of their advantages. Therefore, it is the object of the appended claims to cover all such variations and modifications that fall within the spirit and scope of the invention.