Abstract:
The present disclosure relates to a III-nitride semiconductor light-emitting device including: a plurality of III-nitride semiconductor layers having a first III-nitride semiconductor layer having a first conductivity type, a second III-nitride semiconductor layer having a second conductivity type different from the first conductivity type, and an active layer disposed between the first III-nitride semiconductor layer and the second III-nitride semiconductor layer and generating light by recombination of electrons and holes; a bonding pad electrically connected to the plurality of III-nitride semiconductor layers; a protection film disposed over the bonding pad; and a buffer pad disposed between the bonding pad and the protection film and formed to expose the bonding pad.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of PCT Application No. PCT/KR2009/007169 filed on Dec. 2, 2009, which claims the benefit and priority to Korean Patent Application No. 10-2008-0121156, filed Dec. 2, 2008. The entire disclosures of the applications identified in this paragraph are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates generally to a III-nitride semiconductor light-emitting device, and, more particularly, to a III-nitride semiconductor light-emitting device which can prevent a loss of a bonding pad-side protection film. 
         [0003]    The III-nitride semiconductor light-emitting device means a light-emitting device, such as a light-emitting diode including a compound semiconductor layer composed of Al (x) Ga (y) In (1-x-y) N (0≦x≦1, 0≦y≦1, 0≦x+y≦1), and may further include a material composed of other group elements, such as SiC, SiN, SiCN and CN, and a semiconductor layer made of such materials. 
       BACKGROUND 
       [0004]    This section provides background information related to the present disclosure which is not necessarily prior art. 
         [0005]      FIG. 1  is a view illustrating one example of a conventional III-nitride semiconductor light-emitting device. The III-nitride semiconductor light-emitting device includes a substrate  100 , a buffer layer  200  grown on the substrate  100 , an n-type III-nitride semiconductor layer  300  grown on the buffer layer  200 , an active layer  400  grown on the n-type III-nitride semiconductor layer  300 , a p-type III-nitride semiconductor layer  500  grown on the active layer  400 , a p-side electrode  600  formed on the p-type III-nitride semiconductor layer  500 , a p-side bonding pad  700  formed on the p-side electrode  600 , an n-side electrode  800  formed on the n-type III-nitride semiconductor layer exposed by mesa-etching the p-type III-nitride semiconductor layer  500  and the active layer  400 , and a protective film  900 . 
         [0006]    In the case of the substrate  100 , a GaN substrate can be used as a homo-substrate. A sapphire substrate, a SiC substrate or a Si substrate can be used as a hetero-substrate. However, any type of substrate that can have a nitride semiconductor layer grown thereon can be employed. In the case that the SiC substrate is used, the n-side electrode  800  can be formed on the surface of the SiC substrate. 
         [0007]    The nitride semiconductor layers epitaxially grown on the substrate  100  are usually grown by metal organic chemical vapor deposition (MOCVD). 
         [0008]    The buffer layer  200  serves to overcome differences in lattice constant and thermal expansion coefficient between the hetero-substrate  100  and the nitride semiconductor layers. U.S. Pat. No. 5,122,845 describes a technique of growing an AlN buffer layer with a thickness of 100 to 500 Å on a sapphire substrate at 380 to 800° C. In addition, U.S. Pat. No. 5,290,393 describes a technique of growing an Al (x) Ga (1-x) N (0≦x&lt;1) buffer layer with a thickness of 10 to 5000 Å on a sapphire substrate at 200 to 900° C. Moreover, U.S. Publication No. 2006/154454 describes a technique of growing a SiC buffer layer (seed layer) at 600 to 990° C., and growing an In (x) Ga (1-x) N (0&lt;x≦1) thereon. In particular, it is provided with an undoped GaN layer with a thickness of 1 micron to several microns (μm) on the AlN buffer layer, the Al (x) Ga (1-x) N (0≦x&lt;1) buffer layer or the SiC/In (x) Ga (1-x) N (0&lt;x≦1) layer. 
         [0009]    In the n-type nitride semiconductor layer  300 , at least the n-side electrode  800  formed region (n-type contact layer) is doped with a dopant. In some embodiment, the n-type contact layer is made of GaN and doped with Si. U.S. Pat. No. 5,733,796 describes a technique of doping an n-type contact layer at a target doping concentration by adjusting the mixture ratio of Si and other source materials. 
         [0010]    The active layer  400  generates light quanta by recombination of electrons and holes. For example, the active layer  400  contains In (x) Ga (1-x) N (0&lt;x≦1) and has a single layer or multi-quantum well layers. 
         [0011]    The p-type III-nitride semiconductor layer  500  is doped with an appropriate dopant such as Mg, and has p-type conductivity by an activation process. U.S. Pat. No. 5,247,533 describes a technique of activating a p-type nitride semiconductor layer by electron beam irradiation. Moreover, U.S. Pat. No. 5,306,662 describes a technique of activating a p-type III-nitride semiconductor layer by annealing over 400° C. U.S. Publication No. 2006/157714 describes a technique of endowing a p-type nitride semiconductor layer with p-type conductivity without an activation process, by using ammonia and a hydrazine-based source material together as a nitrogen precursor for growing the p-type nitride semiconductor layer. 
         [0012]    The p-side electrode  600  is provided to facilitate current supply to the p-type III-nitride semiconductor layer  500 . U.S. Pat. No. 5,563,422 describes a technique associated with a light-transmitting electrode composed of Ni and Au formed over almost the entire surface of the p-type nitride semiconductor layer  500  and in ohmic-contact with the p-type III-nitride semiconductor layer  500 . In addition, U.S. Pat. No. 6,515,306 describes a technique of forming an n-type superlattice layer on a p-type nitride semiconductor layer, and forming a light-transmitting electrode made of indium tin oxide (ITO) thereon. 
         [0013]    The p-side electrode  600  can be formed so thick as to not transmit but rather to reflect light toward the substrate  100 . This technique is called the flip chip technique. U.S. Pat. No. 6,194,743 describes a technique associated with an electrode structure including an Ag layer with a thickness over 20 nm, a diffusion barrier layer covering the Ag layer, a bonding layer containing Au and Al, and covering the diffusion barrier layer. 
         [0014]    The p-side bonding pad  700  and the n-side electrode  800  are provided for current supply and external wire-bonding. U.S. Pat. No. 5,563,422 describes a technique of forming an n-side electrode with Ti and Al. 
         [0015]    The protection film  900  can be made of SiO 2 . U.S. Pat. No. 5,563,422 describes a technique for forming a transparent and electrically insulative protective film between a p-side bonding pad and an n-side electrode, or on the top surface of a light-emitting device other than the p-side bonding pad and a wire bonding portion of the n-side electrode. 
         [0016]    The n-type nitride semiconductor layer  300  or the p-type nitride semiconductor layer  500  can be constructed as a single layer or as plural layers. Vertical light-emitting devices are introduced by separating the substrate  100  from the nitride semiconductor layers using a laser technique or wet etching. 
         [0017]      FIG. 2  is a photograph of an example of the bonding pad-side protection film of the conventional III-nitride semiconductor light-emitting device. Because of poor adhesion between the p-side bonding pad  700  and the protection film  900 , the protection film  900  is easily broken or separated (A). Bonding a wire to the bonding pad  700  for package fabrication may cause a connection defect between the bonding pad  700  and the wire. 
       SUMMARY 
       [0018]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0019]    There is provided a III-nitride semiconductor light-emitting device, including: a plurality of III-nitride semiconductor layers having a first III-nitride semiconductor layer having a first conductivity type, a second III-nitride semiconductor layer having a second conductivity type different from the first conductivity type, and an active layer disposed between the first III-nitride semiconductor layer and the second III-nitride semiconductor layer and generating light by recombination of electrons and holes; a bonding pad electrically connected to the plurality of III-nitride semiconductor layers; a protection film disposed on the bonding pad; and a buffer pad disposed between the bonding pad and the protection film and formed to expose the bonding pad. 
         [0020]    According to a III-nitride semiconductor light-emitting device of the present disclosure, the adhesion between the bonding pad and the protection film can be improved. 
         [0021]    Also, according to III-nitride semiconductor light-emitting device of the present disclosure, the wire can be bonded to the bonding pad and improve the adhesion between the bonding pad and the protection film at the same time. 
         [0022]    Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0023]    The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
           [0024]      FIG. 1  is a view of an example of a conventional III-nitride semiconductor light-emitting device. 
           [0025]      FIG. 2  is a photograph of an example of a bonding pad-side protection film of the conventional III-nitride semiconductor light-emitting device. 
           [0026]      FIG. 3  is a view of an embodiment of a III-nitride semiconductor light-emitting device according to the present disclosure. 
           [0027]      FIG. 4  is a view of an embodiment of a method for fabricating a III-nitride semiconductor light-emitting device according to the present disclosure. 
           [0028]      FIG. 5  is a photograph of an example of a bonding pad-side protection film of the III-nitride semiconductor light-emitting device according to the present disclosure. 
       
    
    
       [0029]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0030]    Hereinafter, the present disclosure will be described in detail with reference to the accompanying drawings. 
         [0031]      FIG. 3  is a view of an embodiment of a III-nitride semiconductor light-emitting device according to the present disclosure. The III-nitride semiconductor light-emitting device includes a substrate  10 , a buffer layer  20  grown on the substrate  10 , an n-type III-nitride semiconductor layer  30  grown on the buffer layer  20 , an active layer  40  grown on the n-type III-nitride semiconductor layer  30  and generating light by recombination of electrons and holes, a p-type III-nitride semiconductor layer  50  grown on the active layer  40 , a p-side electrode  60  formed on the p-type III-nitride semiconductor layer  50 , a p-side bonding pad  70  formed on the p-side electrode  60 , an n-side electrode  80  formed on the n-type III-nitride semiconductor layer  30  exposed by etching at least the p-type III-nitride semiconductor layer  50  and the active layer  40 , buffer pads  78  and  88  formed on the p-side bonding pad  70  and the n-side electrode  80 , and a protection film  900  formed on the light-emitting device. Here, the n-side electrode  80  not only supplies electricity to the n-type III-nitride semiconductor layer  30  but also functions as a bonding pad for wire-bonding. 
         [0032]    The protection film  90  may be formed of an oxide film, such as, for example, SiO 2 , TiO 2  and Al 2 O 3 . 
         [0033]    The p-side bonding pad  70  is provided for the connection to the p-side electrode  60  and wire-bonding. For example, the p-side bonding pad  70  may be formed of a Cr layer  72 , a Ni layer  74 , and an Au layer  76  sequentially stacked on the p-side electrode  60 . 
         [0034]    The buffer pad  78  is provided on the p-side bonding pad  70  to improve low adhesion between the p-side bonding pad  70  and the protection film  90  and formed of a material which can be adhered, or coupled to the p-side bonding pad  70  and the protection film  90 . That is, if the p-side bonding pad  70  is formed of a metal and the protection film  90  is formed of an oxide film, then the buffer pad  78  may be formed of an oxidizable metal. For example, if a top surface of the p-side bonding pad  70  is formed of an Au layer  76  and the protection film  90  is formed of SiO 2 , then the buffer pad  78  may be formed of Ni or Cr, which is an oxidizable metal, to be sufficiently adhered to SiO 2  as well as Au. 
         [0035]    The buffer pad  78  is formed in an annular shape to expose a central portion  70   c  of the p-side bonding pad  70  so that bonding can occur between the p-side bonding pad  70  and the wire. In some particular embodiments, the buffer pad  78  is formed at a top outer portion of the p-side bonding pad  70  in order to secure the maximum bonding area between the p-side bonding pad  70  and the wire. 
         [0036]    The n-side electrode  80  is provided for the connection to the n-type III-nitride semiconductor layer  30  and wire-bonding. For example, the n-side electrode  80  may be formed of a Cr layer  82 , a Ni layer  84 , and an Au layer  86  sequentially stacked on the n-type III-nitride semiconductor layer  30 , wherein the buffer pad  88  formed on the n-side electrode  80  may have the same structure as that of the buffer pad  78  formed on the p-side bonding pad  70 . 
         [0037]    The protection film  90  is formed over the buffer pads  78  and  88  on the light-emitting device, wherein the p-side bonding pad  70  remains exposed by the buffer pad  78  and the n-side electrode  80  remain exposed by the buffer pad  88  so that wire-bonding can occur to the p-side bonding pad  70  and the n-side electrode  80 . 
         [0038]    Hereinafter, a method for fabricating a III-nitride semiconductor light-emitting device according to the present disclosure will be described in detail. 
         [0039]      FIG. 4  is a view of an embodiment of a method for fabricating a III-nitride semiconductor light-emitting device according to the present disclosure. 
         [0040]    A plurality of III-nitride semiconductor layers  20 ,  30 ,  40 , and  50  are grown over a substrate  10  (see  FIG. 4(   a )). 
         [0041]    The p-type III-nitride semiconductor layer  50  and the active layer  40  are etched in order to expose the n-type III-nitride semiconductor layer  30  (see  FIG. 4(   b )). 
         [0042]    A p-side electrode  60  is formed (see  FIG. 4(   b )). The p-side electrode  60  may be formed on the entire top surface or the partial top surface of the p-type III-nitride semiconductor layer  50 . The p-side electrode  60  may be formed prior to the etching of the p-type III-nitride semiconductor layer  50  and the active layer  40 . 
         [0043]    A p-side bonding pad  70  and an n-side electrode  80  are formed (see  FIG. 4(   c )). Here, the p-side bonding pad  70  and the n-side electrode  80  may be formed by separate processes, respectively. The p-side electrode  60  may be formed by a separate process prior to the etching of the p-type III-nitride semiconductor layer  50  and the active layer  40 . For example, the p-side bonding pad  70  may be formed at a thickness of 1 μm to 2 μm by sequentially stacking Cr, Ni, and Au layers on the p-side electrode  60  using electron beam (E-beam) evaporation. The n-side electrode  80  may be formed in the same manner. 
         [0044]    A buffer pad  78  is formed on the p-side bonding pad  70  (see  FIG. 4(   d )). For example, the buffer pad  78  may be formed of a Ni layer having a thickness of 10 Å to 200 Å on the p-side bonding pad  70  using E-beam evaporation. The buffer pad  88  may be formed in the same manner. 
         [0045]    A protection film  90  is formed. For example, the protection film  90  may be formed of SiO 2 , TiO 2 , and Al 2 O 3  (see  FIG. 4(   d )). 
         [0046]    Parts of the protection film  90  located on top surfaces of the buffer pads  78  and  88  are removed (see  FIG. 4(   e )). The protection film  90  may be removed by dry etching or by wet etching. For example, if the protection film  90  is formed of SiO 2 , it may be dry-etched for about 250 sec. using a gas containing CF 4 , or wet-etched for about 1 to about 2 min. using a solution containing HF. 
         [0047]    The buffer pads  78  and  88  exposed by the removal of the protection film  90  are removed (see  FIG. 4(   f )). The exposed buffer pads  78  and  88  may be removed by wet etching. For example, if the exposed buffer pads  78  and  88  are formed of a Ni layer, they may be wet-etched for a few tens of seconds using a solution containing HCl. 
         [0048]    The resulting structure is subjected to annealing. For example, the resulting structure may be annealed at 425° C. for about 1 min. 
         [0049]      FIG. 5  is a photograph of an example of the bonding pad-side protection film of the III-nitride semiconductor light-emitting device according to the present disclosure. The p-side bonding pad  70  has the central portion exposed by the buffer pad  78 , and the protection film  90  formed on the buffer pad  78  is seldom separated. 
         [0050]    Hereinafter, various exemplary embodiments of the present disclosure will be described. 
         [0051]    (1) A III-nitride semiconductor light-emitting device including a buffer pad between a protection film and a bonding pad. This prevents an adhesion defect between the bonding pad and the protection film. 
         [0052]    (2) A III-nitride semiconductor light-emitting device including a band-shaped pad on a bonding pad. This allows wire-bonding to the bonding pad. 
         [0053]    (3) A III-nitride semiconductor light-emitting device including an oxidizable metal layer between a bonding pad and a protection film. This improves the adhesion between the bonding pad formed of a metal layer and the protection film formed of an oxide film. 
         [0054]    (4) A III-nitride semiconductor light-emitting device including a Ni layer between a bonding pad and a protection film. This improves the adhesion between the bonding pad formed of a metal layer and the protection film formed of SiO 2 . 
         [0055]    (5) A III-nitride semiconductor light-emitting device including a Cr layer between a bonding pad and a protection film. This improves the adhesion between the bonding pad formed of a metal layer and the protection film formed of SiO 2 . 
         [0056]    The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention. 
         [0057]    The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.