Abstract:
A light emitting diode and its fabricating method are disclosed. A light emitting diode epitaxy structure is formed on a substrate, and then the light emitting diode epitaxy structure is etched to form a recess. The recess is then filled with a transparent dielectric material. An adhesive layer is utilized to adhere a conductive substrate and the light emitting diode epitaxy structure. Next, the substrate is removed.

Description:
CLAIM PRIORITY 
     This application is a divisional of U.S. application Ser. No. 11/109,345, filed Apr. 19, 2005, which claims the right of priority based on Taiwan Patent Application No. 094101801 filed on Jan. 21, 2005. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a light emitting diode and its fabricating method, especially to an AlGaInN light emitting diode and its fabricating method. 
     BACKGROUND OF THE INVENTION 
     Since Light emitting diodes (LEDs) have the advantage of low production cost, simple structure, less consuming power, small size and easy installation, they are widely applied in light sources and display devices. In the market of blue-light light emitting diode, AlGaIhnN light emitting diodes gain more attentions then others. 
     Traditionally, an AlGaInN LED epitaxy structure is first formed on a substrate, and then a conductive substrate is bonded to the AlGaInN LED epitaxy structure by an adhesive layer. The substrate is removed subsequently. To obtain the AlGaInN LED epitaxy structure of high quality, the preferred material of the substrate is sapphire. Traditionally, the sapphire substrate may be removed from the AlGaInN LED structure by using a laser beam. The laser beam passes through the sapphire substrate, and decomposes the n-type semiconductor layer of the AlGaInN LED epitaxy structure, contacting the substrate, into Ga and N.sub.2. Then, Ga is melted by heat of a designated temperature, making the sapphire substrate easily removed from the AlGaInN LED epitaxy structure. During the removing step, the adhesive layer might be decomposed, if the laser beam ever illuminates the adhesive layer, making the conductive substrate separating from the AlGaInN LED epitaxy structure. This is a possible drawback. 
     Yoo et al. of U.S. Pat. No. 6,818,531, which disclosed a method for manufacturing vertical GaN LED, has overcome the drawback mentioned above. Referring to  FIG. 1 , an AlGaInN LED epitaxy structure  125  has a residue  125   a  of an n-type semiconductor layer. A conductive substrate  131  is bonded to the AlGaInN LED epitaxy structure  125  by an adhesive layer  124 . As a laser beam is employed on lower surface of the substrate  121  to remove the substrate  121  from the AlGaInN LED epitaxy structure  125 , the residue  125   a  of the n-type semiconductor layer prevents melting of the adhesive layer  124 , and avoids peeling between the conductive substrate  131  and the AlGaInN LED epitaxy structure  125 . However, according to the method disclosed in U.S. Pat. No. 6,818,531, the thickness of the residue  125   a  of the n-type semiconductor layer should be so controlled as to ensure that the laser beam would not pass through the substrate to the adhesive layer  124 . The residue  125   a  of the n-type semiconductor layer must be easy to remove as well. Therefore, the etching parameters must be controlled carefully to ensure the thickness of the residue  125   a  of the n-type semiconductor layer. 
     In addition, as the laser beam is employed on the sapphire substrate, the increase of the strain between the adhesive layer  124  and the AlGaInN LED epitaxy structure  125  results in instability of the AlGaInN LED epitaxy structure, which also causes peeling between each layer of the epitaxy structure. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention is to provide a method of fabricating a light emitting diode. In the steps of removing the substrate, the transparent dielectric layer protects the light emitting diode epitaxy structure, and improves the adhesion of the conductive substrate and the light emitting diode epitaxy structure, so that the conductive substrate will not peel from the light emitting diode epitaxy structure. 
     Another aspect of the present invention is to provide a light emitting diode having a transparent dielectric layer on the sidewall of the light emitting diode epitaxy structure to protect the light emitting diode epitaxy structure, and to avoid peeling occurrence between each layer of the light emitting diode epitaxy structure. 
     Still another aspect of the present invention is to provide a light emitting diode having a transparent dielectric layer on the sidewall of the light emitting diode epitaxy structure to enhance the sidewall output of the light from the light emitting diode. 
     The method of fabricating a light emitting diode of the present invention comprises the following steps. A light emitting diode epitaxy structure is formed on a substrate. The light emitting diode epitaxy structure is then etched to form a recess. A transparent dielectric layer is formed in the recess, and then a conductive substrate is bonded to the light emitting diode epitaxy structure. The substrate is subsequently removed. 
     The light emitting diode of the present invention includes a conductive substrate, a light emitting diode epitaxy structure and a transparent dielectric layer. The light emitting diode epitaxy structure is on the conductive substrate, and the transparent dielectric layer is on the sidewall of the light emitting diode epitaxy structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is the structure of light emitting diode of the prior art. 
         FIG. 2A-2E  is the flow chart of fabricating one embodiment of the light emitting diode of the present invention. 
         FIG. 2F  is one embodiment of the light emitting diode of the present invention. 
         FIG. 3  is another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 2A , a LED epitaxy structure  201  is first fabricated on a substrate  200 . The LED epitaxy structure  201  mentioned herein includes an AlGaInP LED epitaxy structure and an AlGaInN LED epitaxy structure. To obtain an epitaxy structure of high quality, the selected material of the substrate  200  depends on the types of the LED epitaxy structure. As for the AlGaInP LED epitaxy structure, the preferred material of the substrate  200  is Ge, GaAs or InP. As for the AlGaInN LED epitaxy structure, the preferred material of the substrate  200  is sapphire, SiC, Si, LiAlO.sub.2, ZnO or GaN. The steps of fabricating the LED epitaxy structure  201  includes sequentially forming an n-type semiconductor layer  202 , an active layer  204 , and a p-type semiconductor layer  206  on the substrate  200 . The active layer  204  includes a homo-structure, a single hetero-structure, a double hetero-structure or a multi-quantum well structure. 
     Referring to  FIG. 2B , the LED epitaxy structure  201  is then etched to form a plurality of recesses  207  by using conventional lithography and etching technique. The distance between recesses  207  depends on the designed width of the LED epitaxy structure  201 . The designed width of the LED epitaxy structure  201  is preferably the width of the final LED  20  (as shown in  FIG. 2F ). Since the materials of the LED epitaxy structure and the substrate are different, the only consideration for the etching agent is the capability to selectively etch different materials. Therefore, controlling process parameters to monitor the etching rate of the LED epitaxy structure described in the prior art is not necessary. An embodiment disclosed in  FIG. 2B  shows that the recesses  207  are formed and the substrate  200  is exposed. In other embodiment, the substrate  200  is optionally exposed. 
     The transparent dielectric material is then filled in the recess  207 , as shown in  FIG. 2C , to form the transparent dielectric layer  208 . The transparent dielectric layer  208  includes a material of SiO 2 , Si 3 N 4 , benzocyclobutene or polyimide. In one embodiment, the transparent dielectric material may form a transparent dielectric liner  308  along the sidewall of the LED epitaxy structure  201  in the recess  207 , as shown in  FIG. 3 , so that the sidewall of the LED epitaxy structure  201  will be clad in the transparent dielectric liner  308 . In a preferred embodiment, the recess  207  is filled up with the transparent dielectric material, so that the transparent dielectric layer  208  is thick enough for following cutting step. In addition, with the thick transparent dielectric layer  208 , the sidewall output of the light from the LED will increase. 
     A conductive substrate  212  is next bonded to an upper surface of the LED epitaxy structure  201 , as shown in  FIG. 2D , by first forming an adhesive layer  210  on the conductive substrate  212 , and then the adhesive layer  210  is attached to the LED epitaxy structure  201  by thermal compression technique. The adhesive layer  210  is one of the materials of Au, Sn, In, Ag, Ge, Cu, Pb or the alloy thereof. Since the conductive substrate  212  is metal or alloy with high reflectivity, the light generated by the LED epitaxy structure  201  will emit toward a same direction. Therefore, any other additional reflective layers will not be necessary. 
     As shown in  FIG. 2E , the step of removing the substrate  200  is performed. AlGaInN LED epitaxy structure is used as an example. As a laser beam (arrow icon L) is irradiated on the lower surface of the substrate  200 , the laser beam passes through the substrate  200 , decomposes the AlGaInN LED epitaxy structure  201 , contacting the substrate, into Ga and N.sub.2, and then melts Ga by heat of a designated temperature. Thus the substrate  200  is easily removed from the AlGaInN LED epitaxy structure  201 . In addition, peeling between each layer of the LED epitaxy structure  201  will degrade, since the transparent dielectric layer  208  affixes the LED epitaxy structure  201 . The transparent dielectric layer  208  facilitates the bonding of the conductive substrate  212  and the LED epitaxy structure  201 , therefore peeling between the adhesive layer  210  and the LED epitaxy structure  201  will be avoided. 
     Finally, the anode  214  is fabricated on the top of the LED epitaxy structure  201  and the cathode  216  is fabricated under the conductive substrate  212 , respectively, and then the transparent dielectric layer  208  is cut by a conventional cutting step to form a final structure of the LED  20 , as shown in  FIG. 2F . 
     The LED  20 , shown in  FIG. 2F , has the transparent dielectric layer  208  on the sidewall. Since the index of reflection of semiconductor material in the LED epitaxy structure  201  (e.g. the index of reflection of GaN is about 2.4) is different from that of the external medium of the LED  20  (e.g. the index of reflection of air is about 1.5), the light from the LED  20  will be reflected at the sidewall interface of the LED  20 . However, the transparent dielectric layer  208  has high transparency, and the index of reflection of the transparent dielectric layer  208  is such that full reflection of light is avoided. The sidewall light from the LED  20  can easily pass through the transparent dielectric layer  208  to the external medium of the LED  20 . Therefore, the transparent dielectric layer  208  enhances the sidewall outside of the light from the LED  20 . 
     By means of the detailed descriptions of what is presently considered to be the most practical and preferred embodiments of the subject invention, it is the expectation that the features and the gist thereof are plainly revealed. Nevertheless, these above-mentioned illustrations are not intended to be construed in a limiting sense. Instead, it should be well understood that any analogous variation and equivalent arrangement is supposed to be covered within the spirit and scope to be protected and that the interpretation of the scope of the subject invention would therefore as much broadly as it could apply.