Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the structure and fabricating method of a photoelectric device of Group III nitride semiconductor, and relates more particularly to the light emitting structure of a photoelectric device and the fabricating method thereof. 
     2. Description of the Related Art 
     Currently, light emitting diodes made of gallium nitride material or Group III nitride semiconductor material are built upon a sapphire substrate mainly because the degree of lattice mismatch between sapphire and Group III nitride semiconductor material is low (although a buffer layer is still often required to improve the mismatch therebetween). However, sapphire substrates have many disadvantages, such as high insulation characteristics, and due to such characteristics it is not easy to create a light emitting diode made of Group III nitride semiconductor material having a vertical conductive structure. Therefore, technology continues to advance and allow use of other substrate materials, such as silicon carbide, to reduce such disadvantages. Due to its greater conductivity, silicon carbide can be used to produce a conductive substrate, and because the degree of lattice match between silicon carbide and Group III nitride active layer is low, using a buffer layer made of gallium nitride or aluminum gallium nitride, a Group III nitride semiconductor layer can be deposited on a silicon carbide substrate. Moreover, due to its high stability, silicon carbide is becoming more important in such manufacturing processes. Although a Group III nitride semiconductor layer can be deposited on a silicon carbide substrate with the help of a buffer layer made of gallium nitride or aluminum gallium nitride, the degree of lattice match between a Group III nitride semiconductor material and silicon carbide (which is lower than the degree of lattice match between aluminum gallium nitride and silicon carbide) often causes defects in an epitaxial layer even where the buffer layer is formed on a silicon carbide substrate. Furthermore, a silicon carbide substrate is more expensive than substrates made of other materials. 
       FIGS. 1A and 1B  show a method of separating a thin film from a growth substrate, disclosed in U.S. Pat. No. 6,071,795. The method initially forms a separation region  12  and a silicon nitride layer  13  on a sapphire substrate  11 , and then a bonding layer  14  is disposed on the surface of the silicon nitride layer  13 . Next, with the help of the bonding layer  14 , a silicon substrate  15  is bonded to the above-mentioned sapphire substrate  11  with a stacked-layer structure. A laser beam penetrating the sapphire substrate  11  is directed at the separation region  12 , and causes the separation region to decompose. Finally, the remnant material of the decomposed separation region  12  is cleared to obtain a composite including the silicon substrate  15  and the silicon nitride layer  13 . However, because the bonding layer  14  between the silicon substrate  15  and the silicon nitride layer  13  is dielectric, the composite cannot be a basis for building a vertical structure light emitting diode. Moreover, if the material for the bonding layer  14  is disposed incorrectly or selected improperly, the bonding is affected, and defects are formed in the silicon nitride layer  13 . 
       FIG. 2  shows a method of separating two layers of material from one another, disclosed in U.S. Pat. No. 6,740,604. The technology used for the disclosure related to  FIG. 2  is similar to the technology for the disclosure related to  FIGS. 1A and 1B . A laser beam  23  is directed at the interface between a first semiconductor layer  21  and a second semiconductor layer  22 , and initiates the decomposition of the second semiconductor layer  22  at the interface. Finally, the first semiconductor layer  21  is separated from the second semiconductor layer  22 . The second semiconductor layer  22  can be the film layer formed on a substrate. In such process, a substrate replaces the first semiconductor layer  21 , and then both are separated. 
       FIG. 3  shows a structure prior to separation of the substrate, disclosed in U.S. Pat. No. 6,746,889. The method initially grows several epitaxial layers, which comprise the first region  32  of a first conductivity type, a light-emitting p-n junction  33 , and the second region  34  of a second conductivity type, on a substrate  31 . Next, several sawing streets  36  are cut through the epitaxial layers of the first region  32 , light-emitting p-n junction  33  and second region  34  to have a plurality of individual optoelectronic devices or dies  35  formed on the substrate  31 . Thereafter, the second region  34  is bonded to a submount  37 . As shown in the above-mentioned prior art technology, a laser beam, in the same manner, penetrating the substrate  31  causes the substrate  31  to separate from the first region  32 . Separated optoelectronic devices or dies  35  can be removed from the submount  37  and proceed through the packaging processes. Obviously, when the epitaxial layers are cut through, individual optoelectronic devices or dies  35  bonded to the submount  37  squeeze one another by external forces such that die cracks may occur. 
       FIG. 4  is a side view of the laser lift-off process for removing a sapphire substrate, disclosed in U.S. Pat. No. 6,617,261. A gallium nitride layer  42  is initially formed on a sapphire substrate  41 , and then a plurality of grooves  44  are formed by etching process. Next, a silicon substrate  43  is bonded to the surface where the gallium nitride layer  42  is formed and then is etched to form the grooves  44 . Thereafter, an ultraviolet excimer laser  45  emits a laser beam  46  to the sapphire substrate  41 . The laser beam  46  penetrates the transparent sapphire substrate  41  to cause the gallium nitride at the interface to decompose so as to obtain a silicon substrate  43  bonded with the gallium nitride layer  42 . Any residual gallium metal on the surface of the gallium nitride layer  42  is removed by hydrochloric acid. The gallium nitride layer  42  is finally cleaned for subsequent deposition processes. 
     Conventional technologies use high-energy laser beams to separate substrates or light emitting dies. However, those technologies have low throughput and require expensive equipment. Therefore, a new separation technology that has none of the above-mentioned issues, can guarantee the quality of produced light emitting dies, and can be applied to mass production is required by the market. 
     SUMMARY OF THE INVENTION 
     The primary objective of the present invention is to provide a photoelectric device of Group III nitride semiconductor and a fabricating method thereof. The method can employ an insulating original substrate as a base for epitaxy, which is then removed to obtain a photoelectric device of Group III nitride semiconductor having a vertical conductive structure. 
     Another objective of the present invention is to provide a photoelectric device of Group III nitride semiconductor and the fabricating method thereof using conventional processes and equipment so as to minimize manufacturing cost. 
     In order to achieve the above objectives, the present invention proposes a method of fabricating a photoelectric device of Group III nitride semiconductor, with the method comprising the steps of: forming a first Group III nitride semiconductor layer on a surface of an original substrate; forming a patterned epitaxial-blocking layer on the first Group III nitride semiconductor layer; forming a second Group III nitride semiconductor layer on the epitaxial-blocking layer and on the portions of the first Group III nitride semiconductor layer not covered by the epitaxial-blocking layer, and then removing the epitaxial-blocking layer; forming a third Group III nitride semiconductor layer on the second Group III nitride semiconductor layer; depositing or adhering a conductive layer on the third Group III nitride semiconductor layer; and releasing a combination of the third Group III nitride semiconductor layer and the conductive layer apart from the second Group III nitride semiconductor layer. 
     According to one embodiment, the method of fabricating a photoelectric device of Group III nitride semiconductor further comprises a step of forming a metallic mirror layer between the third Group III nitride semiconductor layer and the conductive layer. 
     The material of the epitaxial-blocking layer is preferably silica. 
     According to one embodiment, the conductive layer is formed by electroplating, composite electroplating, or bonding to deposit copper (Cu), nickel (Ni), copper tungsten alloy (CuW), silicon (Si), or silicon carbide (SiC). 
     According to one embodiment, the material of the original substrate comprises sapphire, silicon carbide, silicon, zinc oxide, magnesium oxide, and gallium arsenide. 
     According to one embodiment, the second Group III nitride semiconductor layer is decomposed by wet etching so that the combination of the third Group III nitride semiconductor layer and the conductive layer is separated from the original substrate. 
     According to one embodiment, the method further comprises a step of forming an N-type semiconductor layer, an active layer, and a P-type semiconductor layer between the third Group III nitride semiconductor layer and the metallic mirror layer. 
     According to one embodiment, the epitaxial-blocking layer comprises a plurality of convexes and a plurality of grooves among the convexes. 
     According to one embodiment, the method of fabricating a photoelectric device of Group III nitride semiconductor further comprises a step of disposing an etching protection layer on the conductive layer and the metallic mirror layer. 
     According to one embodiment, the second Group III nitride semiconductor layer comprises a plurality of mushroom blocks or mushroom strips protruding on the first Group III nitride semiconductor layer. The third Group III nitride semiconductor layer is laterally grown from the sides of each of the mushroom blocks or the mushroom strips to join each other. The profile of each of the mushroom blocks or the mushroom strips can be changed by controlling the growth conditions of the third Group III nitride semiconductor layer. 
     The present invention proposes a photoelectric device of Group III nitride semiconductor, which comprises a Group III nitride semiconductor layer, a metallic mirror layer formed on the Group III nitride semiconductor layer; and a conductive layer formed on the metallic mirror layer. 
     According to one embodiment, the material of the Group III nitride semiconductor layer is Al x In y Ga 1-x-y N, wherein 0≦x≦1 and 0≦y≦1. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described according to the appended drawings in which: 
         FIGS. 1A and 1B  show a method of separating a thin film from a growth substrate, disclosed in U.S. Pat. No. 6,071,795; 
         FIG. 2  shows a method of separating two layers of material from one another, disclosed in U.S. Pat. No. 6,740,604; 
         FIG. 3  shows a structure before a substrate is separated, disclosed in U.S. Pat. No. 6,746,889; 
         FIG. 4  is a side view of the laser lift-off process for removing a sapphire substrate, disclosed in U.S. Pat. No. 6,617,261; 
         FIG. 5  is a flow chart showing a process for fabricating a photoelectric device of Group III nitride semiconductor according to one embodiment of the present invention; 
         FIGS. 6A-6G  are schematic diagrams illustrating a process for fabricating a photoelectric device of Group III nitride semiconductor according to one embodiment of the present invention; 
         FIGS. 7A and 7B  are schematic diagrams illustrating a process for fabricating a photoelectric device of Group III nitride semiconductor according to another embodiment of the present invention; and 
         FIGS. 8A-8D  are schematic diagrams illustrating patterned first Group III nitride semiconductor layers according to embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 5  is a flow chart showing a process for fabricating a photoelectric device of Group III nitride semiconductor according to one embodiment of the present invention. In Step S 51 , a first Group III nitride semiconductor layer is formed on a surface of a original substrate, such as a sapphire substrate (i.e. aluminum oxide, Al 2 O 3 ), silicon carbide (SiC) substrate, silicon substrate, zinc oxide (ZnO) substrate, magnesium oxide (MgO) substrate, gallium arsenide (GaAs) substrate, etc. Then, in Step S 52 , using photolithography and etching process to form a patterned epitaxial-blocking layer on the first Group III nitride semiconductor layer. For example a patterned silicon oxide. That is, the epitaxial-blocking layer with a default pattern covers partial surfaces of the first Group III nitride semiconductor layer. 
     Subsequently, a second Group III nitride semiconductor layer is grown on the epitaxial-blocking layer and the exposed portions of the first Group III nitride semiconductor layer, as shown in Step S 53 . Before the second Group III nitride semiconductor layer completely covers the epitaxial-blocking layer, the growth of the second Group III nitride semiconductor layer is stopped. Then, the epitaxial-blocking layer is removed, as shown in Step S 54  and S 55 . 
     In Step S 56 , a third Group III nitride semiconductor layer is grown on the second Group III nitride semiconductor layer. Next, a metallic mirror layer is formed on the third Group III nitride semiconductor layer, as shown in Step S 57 . The metallic mirror layer can reflect the light emitted from the third Group III nitride semiconductor layer. As shown in Step S 58 , a conductive material is deposited on the third Group III nitride semiconductor layer. For example, the conductive layer is formed by electroplating, composite electroplating, or bonding to deposit copper (Cu), nickel (Ni), copper tungsten alloy (CuW), silicon (Si), or silicon carbide (SiC) so that the light emitting diode has a vertical conductive structure. A photoelectric device of Group III nitride semiconductor with a single vertical conductive structure is obtained by releasing the combination of the third Group III nitride semiconductor layer and the conductive layer apart from the second Group III nitride semiconductor layer, as shown in Step S 59 . The second Group III nitride semiconductor layer can be decomposed by an etching step. 
       FIGS. 6A-6G  are schematic diagrams illustrating a process for fabricating a photoelectric device of Group III nitride semiconductor according to one embodiment of the present invention. A first Group III nitride semiconductor layer  62  is formed on the surface of an original substrate  61 . A patterned epitaxial-blocking layer  63  is formed on the first Group III nitride semiconductor layer  62 . A second Group III nitride semiconductor layer  64  is formed on the epitaxial-blocking layer  63  and the surface of the first Group III nitride semiconductor layer  62  not covered by the epitaxial-blocking layer  63 , as shown in  FIG. 6C . The second Group III nitride semiconductor layer  64  is laterally overgrown on the portion of the surface of the first Group III nitride semiconductor layer  62  where the epitaxial-blocking layer  63  does not cover from the middle of each of the openings. Therefore, the defects of threading dislocation are reduced. Furthermore, the direction of a threading dislocation defect occurring in the second Group III nitride semiconductor layer  64  located in the opening is redirected to extend in parallel manner along the surface of the original substrate  61 . This threading dislocation defect will meet another defect propagating in an opposite direction so that the density of vertical threading dislocation is reduced. 
     As shown in  FIG. 6D , the epitaxial-blocking layer  63  is removed by an etching process, and grooves  63 ′ appear. Consequently, the mushroom-blocks or mushroom-strips of the second Group III nitride semiconductor layer  64  are erected on the first Group III nitride semiconductor layer  62 . Afterward, a third Group III nitride semiconductor layer  65  is formed on the mushroom-blocks or mushroom-strips of the second Group III nitride semiconductor layer  64 . The third Group III nitride semiconductor layer  65  is laterally grown from the sides of each of the mushroom members of the second Group III nitride semiconductor layer  64  until the separate segments from each mushroom member join together into one layer. As shown in  FIG. 6E , a metallic mirror layer  66  is formed on the third Group III nitride semiconductor layer  65 . 
     A conductive layer  67  is deposited on or adhered to the metallic mirror layer  66 . For example, copper (Cu), nickel (Ni), copper tungsten alloy (CuW), silicon (Si), or silicon carbide (SiC) is deposited thereon by electroplating, composite electroplating, or bonding. In addition to excellent electrical conductivity, the conductive layer  66  can also improve heat conductivity. Depositing an etching protection layer  68 , for example a silicon dioxide (SiO 2 ) layer, to protect the conductive layer  67  and the mirror metal layer  66  from the corrosion of the etchant. Under the protection of the etching protection layer  68 , the conductive layer  67  and the mirror metal layer  66  will not be exposed to the etchant so as to avoid damage. Consequently, the etchant is brought into the grooves  63 ′ of the second Group III nitride semiconductor layer  64  so that the second Group III nitride semiconductor layer  64  and parts of the third Group III nitride semiconductor layer  65  are decomposed. The combination of the treated third Group III nitride semiconductor layer  65 ′ and the layers stacked on the layer  65 ′ is released from the second Group III nitride semiconductor layer  62 . Next, the etching protection layer  68  is removed so as to obtain a photoelectric device  60  of Group III nitride semiconductor, as shown in FIG.  6 G. 
     The metallic mirror layer  66  is selectable, and depends on the package type of the photoelectric device for reflecting light. The material of the second Group III nitride semiconductor layer  64  and the third Group III nitride semiconductor layer  65  is Al x In y Ga 1-x-y N, wherein 0≦x≦1 and 0≦y≦1 and such material helps the deposition of the silicon doped N-type gallium nitride layer. The third Group III nitride semiconductor layer  65  can include a light emitting structure, and specifically can include an N-type semiconductor layer, an active layer (light emitting layer), and a P-type semiconductor layer, or a light emitting structure can be further formed between the third Group III nitride semiconductor layer  65  and the metallic mirror layer  66 . 
     The profile of each of the mushroom blocks or the mushroom strips can be changed by controlling growth conditions of the second Group III nitride semiconductor layer  64  such as the flow rate of the elements of Group III nitride, temperature and time. Compared with  FIG. 6C , the second Group III nitride semiconductor layer  64 ′ in  FIG. 7A  has flat tops rather than sharp tops. Similarly, after the epitaxial-blocking layer  63  is removed, the third Group III nitride semiconductor layer  65 , metallic mirror layer  66  and etching protection layer  68  are sequentially formed, as shown in  FIG. 7B . The combination of the treated third Group III nitride semiconductor layer  65  and the layers stacked on the layer  65  is released from the second Group III nitride semiconductor layer  62  by using wet etching technology. Furthermore, the etching protection layer  68  is removed so as to obtain a vertical photoelectric device of Group III nitride semiconductor. 
       FIGS. 8A-8D  are schematic diagrams illustrating patterned first Group III nitride semiconductor layers according to embodiments of the present invention. As shown in  FIG. 8A , the epitaxial-blocking layer  63  has a plurality of hexagonal cylinders  631  and a plurality of grooves  632  connected together. As shown in  FIG. 8B , the epitaxial-blocking layer  63  has a plurality of circular cylinders  633  and a plurality of grooves  634  connected together. As shown in  FIG. 8C , the epitaxial-blocking layer  63  has a plurality of rectangular cylinders  635  and a plurality of grooves  636  connected together. As shown in  FIG. 8D , the epitaxial-blocking layer  63  has a plurality of convexes  637  and a plurality of grooves  628  separating the convexes  627 , and the convex  627  can have a strip-like shape. 
     The above-described embodiments of the present invention are intended to be illustrative only. Numerous alternative embodiments may be devised by persons skilled in the art without departing from the scope of the following claims.

Technology Category: 5