Abstract:
A light emitting diode having an adhesive layer and a reflective layer and a manufacturing method thereof featured by adhering together a light emitting diode stack and a substrate having a reflective metal layer by use of a transparent adhesive layer so that the light rays directed to the reflective metal layer can be reflected therefrom to improve the brightness of the light emitting diode.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a division of U.S. application Ser. No. 10/604,245 filed Jul. 4, 2003. 
     
    
     BACKGROUND OF INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a light emitting diode and the manufacturing method thereof. More particularly, the invention is directed to a light emitting diode having an adhesive layer and a reflective layer and the manufacturing method thereof.  
         [0004]     2. Description of the Prior Art  
         [0005]     Light emitting diodes can be used in a wide variety of devices, for example, optical displays, traffic lights, data storage devices, communication devices, illumination devices, and medical devices. To manufacture a light emitting diode of higher brightness is an important task of engineers.  
         [0006]     A prior art method for improving LED brightness involves bonding two semiconductor parts together by van der Waals forces. However, it has a disadvantage in that van der Waals forces are too weak to provide a sufficient mechanical bonding strength between the two parts and therefore they are apt to separate.  
         [0007]     In U.S. Pat. No. 5,376,580, a method for bonding an LED stack and a transparent substrate to create an ohmic interface therebetween is disclosed. The transparent substrate can be made of GaP. The light generated from the LED stack can pass through the LED stack as well as the transparent substrate. However, this prior art method has to be carried out at about 1000° C. by exerting a coaxial compressive force on the LED stack and the transparent substrate to form an ohmic interface therebetween. The primary disadvantage of this prior art method lies in that the property of the LED is destroyed by the high temperature during the manufacturing process and this results in an LED of low light emitting efficiency. In addition, the transparent GaP substrate has a color and a transparency of only about 60-70%. It therefore reduces brightness of the LED.  
         [0008]     Another prior art method for improving LED brightness involves a bonding technique using a metal layer to bond an LED stack and a substrate. The metal layer forms a bonding layer and a mirror through its metallic property. Thereby, the light rays emitted from the LED stack can be reflected at the metal layer and re-enter the LED stack without passing through the metal layer and entering the substrate. The disadvantage that the some light rays are absorbed by a substrate can therefore be avoided. In such a manufacturing process, the bonding temperature of the metal layer is only about 300-450° C. The LED property will not be destroyed at these low temperatures. However, this bonding technique involves a few disadvantages. One of the disadvantages lies in that although a low bonding temperature will not cause any reaction between the metal layer and any of the two semiconductor layers to be bonded and therefore a highly reflective metal surface (reflectivity over 90%) and improved light emitting efficiency can be obtained, the bonding effect is not sufficient due to that there is no reaction between the metal layer and any of the semiconductor layers to be bonded, and an ohmic interface cannot be formed between the metal layer and any of the semiconductor layers to be bonded. Nevertheless, in case that a higher bonding temperature is adopted, the bonding between the metal layer and any of the two semiconductor layers to be bonded is good. However, the reflectivity of the reflective metal layer will be greatly reduced and therefore the metal layer cannot provide a good mirror function. This is another disadvantage of the bonding technique.  
         [0009]     To avoid the aforementioned disadvantages, the inventors of the present application got an inventive concept to be explained in the following. In case a transparent adhesive layer is used for adhering a metal layer, as mentioned above, to an LED stack, light rays generated by the LED stack may pass through the transparent adhesive layer, be reflected by the metal layer, and then pass through the LED stack. However, if the metal layer is simply adhered to the LED stack by use of an adhesive layer, the adhesion between them is achieved only by van der Waals forces and peeling is apt to occur at the adhesion interface. The inventive concept lies in that a reaction layer is formed between the transparent adhesive layer and any of the LED stack and the metal layer, wherein a reaction occurs between the reaction layer and the transparent adhesive layer so that hydrogen bonds or ionic bonds are formed to enhance the bonding forces provided by the transparent adhesive layer. Thereby, the transparent adhesive layer can provide an enhanced mechanical strength and thus the above-mentioned disadvantage of peeling can be avoided. In addition, using the transparent adhesive layer can avoid the above-mentioned disadvantage caused by the bonding between the metal layer and the LED stack. Moreover, a transparent conductive layer can be formed between the transparent adhesive layer and the LED stack for improving the efficiency of current spreading and thereby can enhance the brightness of the LED.  
       SUMMARY OF INVENTION  
       [0010]     An object of the invention is to provide a light emitting diode having an adhesive layer and a reflective layer and the manufacturing method thereof. In the manufacturing method, a transparent adhesive layer is used to bond an LED stack and a substrate having a reflective layer so that light can pass through the transparent adhesive layer and reflected at the reflective layer. On each of the upper and lower surfaces of the transparent adhesive layer is formed a reaction layer. The reaction layer creates reaction when it and the transparent adhesive layer is pressurized and heated to enhance the bonding forces at the adhesive surface for improving mechanical strength. The light directed to the reflective layer is reflected out to increase the brightness of the light emitting diode. Additionally, the reflective layer can also be formed between the LED stack and the reaction layer so that the adhesive layer does not have to be limited to a transparent adhesive layer and light directed to the reflective layer can be reflected out even a non-transparent adhesive layer is used. This method does not have any problems relating the decrease in reflectivity and decrease in bonding effect. Thereby, an effect of total reflection can be obtained and the object of increasing the brightness of an LED can be achieved.  
         [0011]     A light emitting diode having an adhesive layer and a reflective layer in accordance with a preferred embodiment of the invention comprises a second substrate, a reflective metal layer formed on the second substrate, a first reaction layer formed on the reflective metal layer, a transparent adhesive layer formed on the first reaction layer, a second reaction layer formed on the transparent adhesive layer, a transparent conductive layer formed on the second reaction layer, wherein the upper surface of the transparent conductive layer consists of a first surface area and a second surface area. A first contact layer is formed on the first surface area. A first cladding layer is formed on the first contact layer. An active layer is formed on the first cladding layer. A second cladding layer is formed on the active layer. A second contact layer is formed on the second cladding layer. A first electrode is formed on the second contact layer. A second electrode is formed on the second surface area.  
         [0012]     The manufacturing method of a light emitting diode in accordance with a preferred embodiment of the invention comprises the following steps: forming in sequence, on a first substrate, a second contact layer, a second cladding layer, an active layer, a first cladding layer, a first contact layer, a transparent conductive layer, a second reaction layer to constitute a first stack; forming a reflective metal layer on a second substrate and forming a first reaction layer on the reflective metal layer to constitute a second stack; providing a transparent adhesive layer and using the transparent adhesive layer to bind together the first stack and the second stack by adhering it to the surface of the second reaction layer and the surface of the first reaction layer to constitute a third stack; removing the first substrate to constitute a fourth stack; suitably etching the fourth stack to the transparent conductive layer to form an exposed surface area of the transparent conductive layer; and forming a first electrode on the second contact layer and a second electrode on the exposed surface area of the transparent conductive layer. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0013]      FIG. 1  is a schematic diagram showing a light emitting diode having an adhesive layer and a reflective layer in accordance with a preferred embodiment of the invention.  
         [0014]      FIG. 2  is a schematic diagram showing a first stack for use in a method for manufacturing a light emitting diode having an adhesive layer and a reflective layer, as shown in  FIG. 1 , in accordance with the invention.  
         [0015]      FIG. 3  is a schematic diagram showing a second stack for use in a method for manufacturing a light emitting diode having an adhesive layer and a reflective layer, as shown in  FIG. 1 , in accordance with the invention.  
         [0016]      FIG. 4  is a schematic diagram showing a third stack formed, after adhesive binding the first stack and the second stack and before removing the first substrate, in a method for manufacturing a light emitting diode having an adhesive layer and a reflective layer, as shown in  FIG. 1 , in accordance with the invention.  
         [0017]      FIG. 5  is a schematic diagram showing a fourth stack formed, after removing the first substrate, in a method for manufacturing a light emitting diode having an adhesive layer and a reflective layer, as shown in  FIG. 1 , in accordance with the invention.  
         [0018]      FIG. 6  is a schematic diagram showing a light emitting diode having an adhesive layer and a reflective layer in accordance with another preferred embodiment of the invention.  
         [0019]      FIG. 7  is a schematic diagram showing a light emitting diode having an adhesive layer and a reflective layer in accordance with yet another preferred embodiment of the invention.  
         [0020]      FIG. 8  is a schematic diagram showing a fifth stack for use in a method for manufacturing a light emitting diode having an adhesive layer and a reflective layer, as shown in  FIG. 7 , in accordance with the invention.  
         [0021]      FIG. 9  is a schematic diagram showing a sixth stack for use in a method for manufacturing a light emitting diode having an adhesive layer and a reflective layer, as shown in  FIG. 7 , in accordance with the invention.  
         [0022]      FIG. 10  is a schematic diagram showing a seventh stack formed, after adhesive binding the first stack and the second stack and before removing the first substrate, in a method for manufacturing a light emitting diode having an adhesive layer and a reflective layer, as shown in  FIG. 7 , in accordance with the invention.  
         [0023]      FIG. 11  is a schematic diagram showing a light emitting diode having an adhesive layer and a reflective layer in accordance with still yet another preferred embodiment of the invention.  
         [0024]      FIG. 12  is a schematic diagram showing a eighth stack for use in a method for manufacturing a light emitting diode having an adhesive layer and a reflective layer, as shown in  FIG. 11 , in accordance with the invention.  
         [0025]      FIG. 13  is a schematic diagram showing a ninth stack for use in a method for manufacturing a light emitting diode having an adhesive layer and a reflective layer, as shown in  FIG. 11 , in accordance with the invention.  
         [0026]      FIG. 14  is a schematic diagram showing a tenth stack formed, after adhesive binding the first stack and the second stack and before removing the first substrate, in a method for manufacturing a light emitting diode having an adhesive layer and a reflective layer, as shown in  FIG. 11 , in accordance with the invention. 
     
    
     DETAILED DESCRIPTION  
       [0027]     Referring to  FIG. 1 , a light emitting diode having an adhesive layer and a reflective layer  1  in accordance with a preferred embodiment of the invention comprises a second substrate  10 , a reflective metal layer  11  formed on the second substrate  10 , a first reaction layer  22  formed on the reflective metal layer  11 , a transparent adhesive layer  12  formed on the first reaction layer  22 , a second reaction layer  23  formed on the transparent adhesive layer  12 , a transparent conductive layer  21  formed on the second reaction layer  23 , wherein the upper surface of the transparent conductive layer  21  consists of a first surface area and a second surface area. A first contact layer  13  is formed on the first surface area. A first cladding layer  14  is formed on the first contact layer  13 . An active layer  15  is formed on the first cladding layer  14 . A second cladding layer  16  is formed on the active layer  15 . A second contact layer  17  is formed on the second cladding layer  16 . A first electrode  19  is formed on the second contact layer  17 . A second electrode  20  is formed on the second surface area.  
         [0028]     Referring to FIGS.  1  to  5 , the manufacturing method of the light emitting diode  1  comprises the following steps: forming in sequence, on a first substrate  18 , a second contact layer  17 , a second cladding layer  16 , an active layer  15 , a first cladding layer  14 , a first contact layer  13 , a transparent conductive layer  21 , a second reaction layer  23  to constitute a first stack  2 ; forming a reflective metal layer  11  on a second substrate  10  and forming a first reaction layer  22  on the reflective metal layer  11  to constitute a second stack  3 , as shown in  FIG. 3 ; providing a transparent adhesive layer  12  and using the transparent adhesive layer  12  to bind together the first stack  2  and the second stack  3  by adhering it to the surface of the second reaction layer  23  and the surface of the first reaction layer  22  to constitute a third stack  4 , as shown in  FIG. 4 ; removing the first substrate  18  to constitute a fourth stack  5 , as shown in  FIG. 5 ; suitably etching the fourth stack  5  to the transparent conductive layer  21  to form an exposed surface area of the transparent conductive layer  21 ; and forming a first electrode  19  on the second contact layer  17  and a second electrode  20  on the exposed surface area of the transparent conductive layer  21 .  
         [0029]     A light emitting diode having an adhesive layer and a reflective layer  6  in accordance with another preferred embodiment of the invention is shown in  FIG. 6 . The LED structure and manufacturing method of this LED  6  is similar to that in accordance with the aforementioned preferred embodiment except that the reflective metal layer  11  is replaced by a reflective oxide layer  611  by which the light directed to the reflective oxide layer  611  can be reflected and taken out.  
         [0030]     Referring to  FIG. 7 , a light emitting diode having an adhesive layer and a reflective layer  7  in accordance with yet another preferred embodiment of the invention comprises a reflective metal substrate  710 ; a first reaction layer  722  formed on the reflective metal substrate  710 ; a transparent adhesive layer  712  formed on the first reaction layer  722 ; a second reaction layer  723  formed on the transparent adhesive layer  712 ; a transparent conductive layer  721  formed on the second reaction layer  723 ; wherein the transparent conductive layer  721  comprises a first surface area and a second surface area; a first contact layer  713  formed on the first surface area; a first cladding layer  714  formed on the first contact layer  713 ; an active layer  715  formed on the first cladding layer  714 ; a second cladding layer  716  formed on the active layer  715 ; a second contact layer  717  formed on the second cladding layer  716 ; a first electrode  719  formed on the second contact layer  717 ; and the second electrode  720  formed on the second surface area.  
         [0031]     Referring to FIGS.  7  to  10 , the manufacturing method of the LED  7  comprises the following steps: forming in sequence, on a first substrate  718 , a second contact layer  717 , a second cladding layer  716 , an active layer  715 , a first cladding layer  714 , a first contact layer  713 , a transparent conductive layer  721 , a second reaction layer  723  to constitute a fifth stack  8 ; forming a first reaction layer  722  on a reflective metal substrate  710  to constitute a sixth stack  9 ; bonding the surface of the second reaction layer of the first stack with the surface of the first reaction layer of the sixth stack by use of a transparent adhesive layer  712 ; removing the first substrate  718  to leave a seventh stack  100 ; suitably etching the seventh stack  100  to form an exposed surface area of the transparent conductive layer  721 ; and forming a first electrode  719  and a second electrode  720  respectively on the second contact layer  717  and the exposed surface area of the transparent conductive layer  721 .  
         [0032]     Referring to  FIG. 11 , a light emitting diode  110  in accordance with another preferred embodiment of the invention comprises a second substrate  1110 ; a first reaction layer  1122  formed on the second substrate  1110 ; an adhesive layer  1112  formed on the first reaction layer  1122 ; a second reaction layer  1123  formed on the adhesive layer  1112 ; a reflective metal layer  1111  formed on the second reaction layer  1123 ; a transparent conductive layer  1121  formed on the reflective metal layer  1111 , wherein the transparent conductive layer  1121  comprises a first surface area and a second surface area; a first contact layer  1113  formed on the first surface area; a first cladding layer  1114  formed on the first contact layer  1113 ; an active layer  1115  formed on the first cladding layer  1114 ; a second cladding layer  1116  formed on the active layer  1115 ; a second contact layer  1117  formed on the second cladding layer  1116 ; a first electrode  1119  formed on the second contact layer  1117 ; and a second electrode  1120  formed on the second surface area.  
         [0033]     Referring to FIGS.  12  to  14 , a method for manufacturing the light emitting diode  110  comprises the following steps: forming, in sequence, on a first substrate  1118 , a second contact layer  1117 , a second cladding layer  1116 , an active layer  1115 , a first cladding layer  1114 , a first contact layer  1113 , a transparent conductive layer  1121 , a reflective metal layer  1111 , a second reaction layer  1123  to constitute an eighth stack  120 ; forming a first reaction layer  1122  on a second substrate  1110  to constitute a ninth stack  130 ; bonding together the surface of the second reaction layer  1123  of the eighth stack  120  and the surface of the first reaction layer  1122  of the ninth stack  130  by use of a adhesive layer  1112 ; removing the first substrate  1118  to constitute a tenth stack  140 ; suitably etching the tenth stack  140  to the transparent conductive layer  1121  to form an exposed surface area of the first contact layer  1113 ; and forming a first electrode  1119  and a second electrode  1120  respectively on the second contact layer  1117  and the exposed surface area of the first contact layer  1113 .  
         [0034]     The first substrate  18 ,  718 , or  1118  comprises at least a material selected from the group consisting of GaP, GaAs, and Ge. The second substrate  10  or  1110  comprises at least a material selected from the group consisting of Si, GaAs, SiC, Al 2 O 3 , glass, GaP, GaAsP, and AlGaAs. The transparent adhesive layer  12  or  1112  comprises at least a material selected from the group consisting of polyimide (PI), benzocyclobutene (BCB), perfluorocyclobutane (PFCB), and the like. The first reaction layer  22 ,  722 , or  1122  comprises at least a material selected from the group consisting of SiN x , Ti, and Cr. The second reaction layer  23 ,  723 , or  1123  comprises at least a material selected from the group consisting of SiN x , Ti, and Cr, and the like. The reflective metal substrate  710  comprises at least a material selected from the group consisting of Sn, Al, Au, Pt, Zn, Ag, Ti, Pb, Pd, Ge, Cu, AuBe, AuGe, Ni, PbSn, AuZn, and the like. The first contact layer  13 ,  713 , or  1113  comprises at least a material selected from the group consisting of GaP, GaAs, GaAsP, InGaP, AlGaInP, and AlGaAs. The reflective oxide layer  611  comprises at least a material selected from the group consisting of SiN x , SiO 2 , Al 2 O 3 , TiO 2 , MgO, and the like. The reflective metal layer  11  or  1111  comprises at least a material selected from the group consisting of In, Sn, Al, Au, Pt, Zn, Ag, Ti, Pb, Pd, Ge, Cu, AuBe, AuGe, Ni, PbSn, AuZn, and the like. Each of the first cladding layer  14 ,  714 , or  1114 , the active layer  15 ,  715 , or  1115 , and the second cladding layer  16 ,  716 , or  1116  comprises AlGaInP. The second contact layer  17 ,  717 ,  1117  comprises at least a material selected from the group consisting of GaP, GaAs, GaAsP, InGaP, AlGaInP, and AlGaAs. The transparent conductive layer  21 ,  721 , or  1121  comprises at least a material selected from the group consisting of indium tin oxide, cadmium tin oxide, antimony tin oxide, zinc oxide, and zinc tin oxide.  
         [0035]     Although the preferred embodiments of the invention has been illustrated and described in the above, it will be obvious to those skilled in the art that various modifications may be made without departing from the scope and spirit of the invention defined by the appended claims.