Abstract:
A method for manufacturing a light-emitting diode (LED) is described. The method comprises: providing a temporary substrate; forming an illuminant epitaxial structure on the temporary substrate; forming a first transparent conductive layer on the illuminant epitaxial structure; forming a metal substrate on the first transparent conductive layer; forming an adhesion layer on the metal substrate; providing a supporting substrate, wherein the supporting substrate is connected to the metal substrate by the adhesion layer; removing the temporary substrate, so as to expose a surface of the illuminant epitaxial structure; forming a second transparent conductive layer on the exexposed surface of the illuminant epitaxial structure; and forming an electrode on a portion of the second transparent conductive layer.

Description:
RELATED APPLICATIONS  
       [0001]     The present application is based on, and claims priority from, Taiwan Application Serial Number 93107175, filed Mar. 17, 2004, 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 (LED), and more particularly, to a method for manufacturing a light-emitting diode with a high ability for heat dissipation.  
       BACKGROUND OF THE INVENTION  
       [0003]     Light-emitting diodes are semiconductor illumination devices formed by using semiconductor materials. The light-emitting diodes are one kind of minute solid-state light source that can transform electrical energy into light energy. The semiconductor have many advantages, including small volume, a low driving voltage, rapid response speed, resistance to shock, and long life, and also can meet the light, thin, and miniaturization needs of various apparatuses. Light-emitting diodes have thus have become very popular electric products in daily life.  
         [0004]     In the fabrication of light-emitting diodes, III-nitride-based semiconductors, such as GaN, AlGaN, InGaN and AlInGaN, are common. Usually, epitaxial structures of most of the light-emitting devices made of the III-nitride-based semiconductors are grown on an electrically insulating sapphire substrate, which is different from other light-emitting devices utilizing conductive substrates. The sapphire substrate is an insulator, so an electrode can be directly formed on the sapphire substrate. Electrodes have to be formed to contact respectively a p-type semiconductor layer and an n-type semiconductor layer directly, so that the light-emitting devices of the aforementioned type can be completed.  
         [0005]      FIG. 1  illustrates a cross-sectional view of a conventional light-emitting diode. In the fabrication of the light-emitting diode, a buffer layer  102  is firstly formed on a transparent substrate  100  by deposition. The substrate  100  is typically made of sapphire. An n-type semiconductor layer  104  is epitaxially formed on the buffer layer  102 , in which the n-type semiconductor layer  104  is typically made of III-nitrides. Next, an active layer  106  is epitaxially formed on the n-type semiconductor layer  104 , in which the active layer  106  is typically a multiple quantum well (MQW) structure. A p-type semiconductor layer  108  is epitaxially grown on the active layer  106 , in which the p-type semiconductor layer  108  is typically made of III-nitrides. An illuminant epitaxial structure is composed of the n-type semiconductor layer  104 , the active layer  106  and the p-type semiconductor layer  108 .  
         [0006]     The substrate  100  is made of sapphire, an insulator, so contact electrodes of the light-emitting diode have to be formed to contact respectively the p-type semiconductor layer  108  and the n-type semiconductor layer  104  directly, and cannot be directly formed on the substrate  100  made of sapphire. Accordingly, after the illuminant epitaxial structure is formed, a definition step is performed by photolithography and etching to remove a portion of the active layer  106 , a portion of the p-type semiconductor layer  108  and a portion of the n-type semiconductor layer  104 , so as to expose a portion of the n-type semiconductor layer  104 . Then, an electrode  110  and an electrode  112  are respectively formed on the p-type semiconductor layer  108  and the exposed portion of the n-type semiconductor layer  104  is formed directly by thermal evaporation, E-beam evaporation or ion-sputtering, so that the fabrication of the light-emitting diode is completed.  
       SUMMARY OF THE INVENTION  
       [0007]     One objective of the present invention is to provide a method for manufacturing a light-emitting diode, in which a temporary substrate for support is provided on a metal substrate, to support an illuminant epitaxial structure in the subsequent processes. Therefore, it benefits the proceeding of the subsequent processes, thereby effectively enhancing the process yield.  
         [0008]     Another objective of the present invention is to provide a method for manufacturing a light-emitting diode having a thick metal substrate, so that the light-emitting diode has an excellent capability for heat dissipation.  
         [0009]     According to the aforementioned objectives, the present invention provides a method for manufacturing a light-emitting diode comprising: providing a temporary substrate; forming an illuminant epitaxial structure on the temporary substrate; forming a first transparent conductive layer on the illuminant epitaxial structure; forming a reflective layer on the first transparent conductive layer; forming a metal substrate on the reflective layer; forming an adhesion layer on the metal substrate; providing a supporting substrate, wherein the supporting substrate is connected to the metal substrate by the adhesion layer; removing the temporary substrate, so as to expose a surface of the illuminant epitaxial structure; forming a second transparent conductive layer on the exposed surface of the illuminant epitaxial structure; and forming an electrode on a portion of the second transparent conductive layer.  
         [0010]     According to a preferred embodiment of the present invention, the supporting substrate and the adhesion layer are made of conductors, so that the supporting substrate and the adhesion layer are not necessary to be removed. Therefore, the structural strength of the light-emitting diode device can be increased, and the process can be simplified.  
         [0011]     According to the aforementioned description, a thick metal substrate is provided when a light-emitting diode device is fabricated in the present invention, so that the light-emitting diode device has an excellent capability for heat dissipation. In addition, in the fabrication of the light-emitting diode device, a temporary substrate used for support is provided and located on the metal substrate, to provide a structural support in the subsequent processes and to benefit the subsequent processes, thus achieving the objective of enhancing the process yield. 
     
    
     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.  
         [0014]     FIGS.  2  to  8  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. The method provides a temporary substrate for supporting, so an illuminant epitaxial structure can be supported structurally in the sequent processes, to achieve the objective of increasing the process yield. In order to make the illustration of the present invention more explicit and complete, the following description is stated with reference to FIGS.  2  to  8 .  
         [0016]     FIGS.  2  to  8  are schematic flow diagrams showing the process for manufacturing a light-emitting diode in accordance with a preferred embodiment of the present invention. A temporary substrate  200  is firstly provided, in which a material of the temporary substrate  200  is selected from the materials that can be lattice matched with an epitaxial layer grown thereon sequentially, and a material of the temporary substrate  200  can be sapphire, SiC or GaAs, for example. An illuminant epitaxial structure  202  is grown on the temporary substrate  200  by, for example, epitaxy, so as to form a structure such as illustrated in  FIG. 2 . The illuminant epitaxial structure  202  comprises an n-type semiconductor layer  202   a , an active layer  202   b  and a p-type semiconductor layer  202   c , in which a material of the n-type semiconductor layer  202   a  can be n-type AlGaInP or n-type GaN, the p-type semiconductor layer  202   c  can be p-type AlGaInP or p-type GaN, and the active layer  202   b  can be a multiple quantum well structure, for example.  
         [0017]     After the illuminant epitaxial structure  202  is formed, a transparent conductive layer  204  is formed to cover the illuminant epitaxial structure  202 , so as to form a structure such as illustrated in  FIG. 3 , in which a material of the transparent conductive layer  204  can be, for example, indium tin oxide (ITO), ZnO, cadmium tin oxide (CTO), TiWN, In 2 O 3 , SnO 2 , MgO, ZnGa 2 O 4 , SnO 2 /Sb, Ga 2 O 3 /Sn, AgInO 2 /Sn, In 2 O 3 /Zn, CuAlO 2 , LaCuOS, NiO, CuGaO 2 , or SrCu 2 O 2 . The transparent conductive layer  204  is also called a transparent electrode layer, and the transparent conductive layer  204  not only can have a good ohmic contact with the illuminant epitaxial structure  202 , but also have a current-spreading function.  
         [0018]     Next, a thin reflective layer  206  is formed by evaporation, sputtering, electroplating or electroless electroplating, and a material of the reflective layer  206  can be a reflective material, such as Au, Ag, Al, In, Sn, Pt, Ti, Zn, Pb, AuBe, Ni, PbSn or AuZn. After the reflective layer  206  is formed, a metal substrate  208  of large thickness is formed to form the structure illustrated in  FIG. 4  by evaporation, sputtering, electroplating or electroless electroplating. The thickness of the metal substrate  208  is preferably between 30 μm and 150 μm, and a material of the metal substrate  208  can be, for example, Al, Pt, Pd, Zn, Ni, Ti, In, Cr, Cu, Sn, Ag or an alloy thereof.  
         [0019]     One feature of the present invention is that the metal substrate  208  of large thickness is provided, and the metal substrate  208  has excellent heat conductivity, so the heat dissipation capability of the light-emitting diode device can be greatly enhanced to achieve the objective of increasing the performance of the light-emitting diode device.  
         [0020]     It is worthy of note that if the material of the metal substrate  208  has an excellent reflective capability, the reflective layer  206  can be eliminated.  
         [0021]     Then, an adhesion layer  210  is formed on the metal substrate  208 , and a material of the adhesion layer  210  is preferably selected from the materials that are convenient for adhesion and removal. A material of the adhesion layer  210  can be a non-conductive material, such as wax or epoxy resin, or can be a conductive material, such as Au, AuBe, AuZn, Pt, Pd, Cu, Ni, In, Al, Ag, Cr, Ti, AuSn, InSn, PbSn, SnAgCu, or SnCu. Next, a supporting substrate  212  is provided, and the supporting substrate  212  is connected to the metal substrate  208  by the adhesion layer  210  and a wafer bonding method, so as to formed a structure such as illustrated in  FIG. 5 . A material of the supporting substrate  212  can be selected from conductive materials or nonconductive materials, and the material of the supporting substrate  212  can be selected from materials of higher structural strength. The material of the supporting substrate  212  can be, for example, silicon, or a nonconductive material, such as AlN, BN, Al 2 O 3 , MgO, BeO, TiO 2  or SiO 2 .  
         [0022]     Another feature of the present invention is that the structural strength of the metal substrate  208  is lesser, and the structural strength of the supporting substrate  212  is greater, so the illuminant epitaxial structure  202  can be supported by the supporting substrate  210  in the subsequent processes, thereby reducing damage to the illuminant epitaxial structure  202 . Therefore, the process yield can be greatly increased to solve the problem of low yield in the conventional process.  
         [0023]     After the supporting substrate  212  is adhered to the metal substrate  208 , the temporary substrate  200  and the structural layers formed thereon are reversed. Next, the temporary substrate  200  is removed by, for example, polishing, chemical etching or laser stripping, so as to expose a surface of the illuminant epitaxial structure  202 , as illustrated in  FIG. 6 . The polishing can be, for example, chemical mechanical polishing (CMP), and chemical etching can be dry etching or wet etching. After the temporary substrate  200  is removed, the illuminant efficiency of the light-emitting diode can be increased.  
         [0024]     After the temporary substrate  200  is removed, a transparent conductive layer  214  is formed to cover the exposed surface of the illuminant epitaxial structure  202 , in which a material of the transparent conductive layer  214  can be, for example, indium tin oxide, ZnO, cadmium tin oxide, TiWN, In 2 O 3 , SnO 2 , MgO, ZnGa 2 O 4 , SnO 2 /Sb, Ga 2 O 3 /Sn, AgInO 2 /Sn, In 2 O 3 /Zn, CuAlO 2 , LaCuOS, NiO, CuGaO 2 , or SrCu 2 O 2 . The transparent conductive layer  214  is also called a transparent electrode layer, and the transparent conductive layer  214  not only has a good ohmic contact with the illuminant epitaxial structure  202 , but also has a current-spreading function, to make the current more uniform and increase the illuminant efficiency of the light-emitting diode. Then, an electrode  216  is formed on a portion of the transparent conductive layer  214  by, for example, evaporation or electroplating, so as to form a structure such as the one illustrated in  FIG. 7   a.  A material of the electrode  216  is preferably selected from materials having reflective capability, to reduce light emitted from the illuminant epitaxial structure  202  being absorbed by the electrode  216 . The electrode  216  is preferably a Cu layer, and more preferably a composite structure composed of a Cu layer and an indium (In) layer.  
         [0025]     In another preferred embodiment of the present invention, before the transparent conductive layer  214  is formed, a portion of the n-type semiconductor layer  202   a  and a portion of the active layer  202   b  can be removed firstly by a photolithography process and an etching process until a portion of the p-type semiconductor layer  202   c  is exposed. Then, the transparent conductive layer  214  is formed on the n-type semiconductor layer  202   a  of the illuminant epitaxial structure  202 . Subsequently, the electrode  216  and an electrode  218  are formed on the n-type semiconductor layer  202   a  and a portion of the exposed portion of the p-type semiconductor layer  202   c , respectively, as illustrated in  FIG. 7   b.    
         [0026]     In the present invention, while the adhesion layer  210  and the supporting substrate  212  are made of conductive materials, the adhesion layer  210  and the supporting substrate  212  need not be removed, and thus the fabrication of the light-emitting diode structure according to an embodiment of the present invention is completed. Then, light-emitting diode chips are formed after dicing, and the fabrication of light-emitting diode devices are completed. However, the adhesion layer  210  and the supporting substrate  212  also can be removed when the adhesion layer  210  and the supporting substrate  212  are made of conductive materials. When at least one of the adhesion layer  210  and the supporting substrate  212  is made of conductive materials, the adhesion layer  210  and the supporting substrate  212  have to be removed. After the adhesion layer  210  and the supporting substrate  212  are removed by, for example, a stripping method, a chemical etching method, a polishing method or a laser stripping method, the metal substrate  208  is exposed, to complete the fabrication of the light-emitting diode structure according to another embodiment of the present invention, as illustrated in  FIG. 8 . Then, light-emitting diode chips are formed after dicing, and the fabrication of light-emitting diode devices is completed.  
         [0027]     It is worthy of note that the electrode and the electrode  218  can also be formed by, for example, evaporation or electroplating, after the supporting substrate  212  is removed.  
         [0028]     According to the aforementioned description, one advantage of the present invention is that the light-emitting diode of the present invention has a very thick metal substrate, so that the heat-dissipating capability of the light-emitting diode can be greatly enhanced.  
         [0029]     According to the aforementioned description, one advantage of the present invention is that a supporting substrate having high structural strength is provided on the metal substrate in the fabrication of the light-emitting diode of the present invention, so that the illuminant epitaxial structure is strongly supported in the subsequent processes, to the benefit of the subsequent processes. Therefore, the damage of the illuminant epitaxial structure is reduced, to enhance effectively the process yield and achieve the objective of increasing the quality of the light-emitting diode.  
         [0030]     As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrative 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.