Abstract:
A light-emitting diode (LED) is provided, wherein the LED comprises an epitaxial structure, a bonding layer and a composite substrate. The composite substrate comprises a patterned substrate having a pattern and a conductive material layer disposed around the patterned substrate. The bonding layer is formed on the composite substrate. The epitaxial structure is formed on the bonding layer.

Description:
RELATED APPLICATIONS 
       [0001]    The present application is a divisional of application Ser. No. 11/232,633, filed on Sep. 22, 2005, which claimed the benefit of Taiwan Application Serial Number 94115424, filed May 12, 2005, the disclosures of which are hereby incorporated by reference herein in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a light-emitting diode (LED), and more particularly relates to an LED that has good thermal conductivity and good processability. 
       BACKGROUND 
       [0003]    An LED is composed of an epitaxial structure such as a homo-structure, a single hetero-structure, a double hetero-structure or a multiple quantum well. An LED having a p-n junction interface that can emit light with various wavelengths has several characteristics, such as a low electrical power consumption, low heat generation, long operational life, small volume, good impact resistance, fast response and excellent stability; thus the LED has been popularly used in electrical appliances and electronic devices as a light source. 
         [0004]    Typically, an LED is composed of an epitaxial structure having a substrate, an n-type cladding layer formed over the substrate, a p-type cladding layer and an active layer formed between the n-type cladding layer and the p-type cladding layer. Light is emitted as current flows through the epitaxial structure. The light wavelength can be altered by varying the composition of the epitaxial structure material. 
         [0005]    To improve performance, an LED requires some downstream processes to increase its brightness, thermal conductivity or the effectiveness of current diffusion. The downstream processes, such as a cutting process, may require a substrate transferring technology or a wafer bonding technology for forming additional substrates made of metal or III-V semiconductor materials. Either copper having good thermal conductivity or silicon with good process abilities (for example, with high rigidity and low coefficient of thermal expansion) is appropriate for forming the additional substrates. However, applying copper or silicon individually cannot improve both the yield of the downstream processes and the performance of an LED simultaneously, even though copper has good thermal conductivity and silicon has good processability. The process yield can be improved with copper due to its high thermal conductivity, but its poor rigidity and large coefficient of thermal expansion creates bad processability, particularly when a thinner copper substrate is required. Meanwhile, the performance of an LED can be improved with silicon since its coefficient of thermal expansion compliments downstream processes, but its poor thermal conductivity creates poor process yield. 
         [0006]    It is desired, therefore, to provide a method for forming an LED having good thermal conductivity and good processability so as to improve the yield and performance thereof. 
       SUMMARY 
       [0007]    One of the objectives of the present invention is to provide an LED having good thermal conductivity and good processability. The LED comprises an epitaxial structure, a bonding layer and a composite substrate. The composite substrate comprises a patterned substrate having a pattern and a conductive material layer disposed around the patterned substrate. The bonding layer is formed on the composite substrate. The epitaxial structure is formed on the bonding layer. 
         [0008]    Accordingly, the feature of the present invention is to provide a composite substrate having good thermal conductivity and good processability via the composite substrate, so as to resolve the prior art problems by improving processing yield and the performance of an LED. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    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: 
           [0010]      FIG. 1  illustrates a cross-sectional view of an LED structure in accordance with the first embodiment of the present invention. 
           [0011]      FIG. 2  illustrates a cross-sectional view of an epitaxial structure for forming the LED structure in accordance with the first embodiment of the present invention. 
           [0012]      FIG. 3   a  illustrates a cross-sectional view of a patterned second substrate for forming the LED structure in accordance with the first embodiment of the present invention. 
           [0013]      FIG. 3   b  illustrates a top view of the second substrate after the patterning process is conducted in accordance with the first embodiment of the present invention. 
           [0014]      FIG. 4  is a cross-sectional view of the structure after the patterned second substrate is adhered to the epitaxial structure in accordance with the first embodiment of the present invention. 
           [0015]      FIG. 5  is a cross-sectional view of the structure after a portion of the patterned second substrate is removed in accordance with the first embodiment of the present invention. 
           [0016]      FIG. 6  is a cross-sectional view of the structure after a metal layer is formed over the patterned silicon layer in accordance with the first embodiment of the present invention. 
           [0017]      FIG. 7  illustrates a cross-sectional view of an LED structure in accordance with the second embodiment of the present invention. 
           [0018]      FIG. 8  illustrates a cross-sectional view of an epitaxial structure for forming the LED structure in accordance with the second embodiment of the present invention. 
           [0019]      FIG. 9  is a cross-sectional view of the structure after a second substrate is adhered to the epitaxial structure in accordance with the second embodiment of the present invention. 
           [0020]      FIG. 10   a  is a cross-sectional view of the structure after a portion of the second substrate is removed in accordance with the second embodiment of the present invention. 
           [0021]      FIG. 10   b  illustrates a top view of the second substrate after the patterned silicon layer is formed in accordance with the second embodiment of the present invention. 
           [0022]      FIG. 11  is a cross-sectional view of the structure after a metal layer is formed over the patterned silicon layer in accordance with the second embodiment of the present invention. 
           [0023]      FIG. 12  is a cross-sectional view of the structure after a first electrode and a second electrode are formed on the epitaxial structure in accordance with the first embodiment of the present invention. 
           [0024]      FIG. 13  is a cross-sectional view of another structure after a first electrode and a second electrode are formed on the epitaxial structure in accordance with the first embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]    The feature of the present invention is to provide a composite substrate having good thermal conductivity via copper and good processability via silicon, so as to improve processing yield and the performance of an LED. 
         [0026]    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. 
         [0027]      FIG. 1  illustrates a cross-sectional view of an LED structure in accordance with the first embodiment of the present invention. The LED comprises an epitaxial structure  102 , a bonding layer  104  and a composite substrate  300 . The bonding layer  104 , located over one side of the epitaxial structure  102 , is used for adhering the composite substrate  300  to the epitaxial structure  102 . The composite substrate  300  comprises a patterned silicon layer  106   a  penetrated through by at least one opening  103  and a metal layer  108  covering the patterned silicon layer  106   a , wherein a portion of the metal layer  108  is filled in the openings  103 . 
         [0028]      FIG. 2  illustrates a cross-sectional view of an epitaxial structure for forming the LED structure in accordance with the first embodiment of the present invention. According to the first embodiment of the present invention, forming the LED structure comprises the following steps: 
         [0029]    First, the epitaxial structure  102  is formed on a first substrate  100 . The epitaxial structure  102  is formed over the first substrate  100 . In various embodiments of the present invention, the epitaxial structure  102  comprises a homo-structure, a single hetero-structure, a double hetero-structure, a multiple quantum well or any arbitrary combination thereof. In the present embodiment, the epitaxial structure  102  includes an n-type cladding layer  112  made of AlGaInP, an active layer  114  and a p-type cladding layer  116  made of AlGaInP deposited sequentially over the first substrate  100  by an epitaxial process, wherein the active layer  114  is a multiple quantum well made of AlGaInP. In the present embodiment, the epitaxial structure  102  further comprises a contact layer  109  formed over the p-type cladding layer  116  and a reflection layer  110  formed over the contact layer  109 . 
         [0030]      FIG. 3   a  illustrates a cross-sectional view of a patterned second substrate  106  for forming the LED structure in accordance with the first embodiment of the present invention. In the present invention, the second substrate  106  made of silicon and having a first surface  111  and a second surface  115 . Then, a patterning process, such as an etch process, is conducted on the first surface  111  to form a plurality of openings  103 . 
         [0031]      FIG. 3   b  illustrates a top view of the second substrate after the patterning process is conducted. In various embodiments of the present invention, the shapes of the openings  103  are circular, triangular, rectangular, polygonal, irregular or any arbitrary combination thereof, and the openings are arranged regularly or irregularly. In the present embodiment, the openings  103  are circular and arranged regularly. 
         [0032]    Next, an adhering process is conducted to adhere the first surface  111  of the second substrate  106  to the side of the epitaxial structure  102  away from the first substrate  100 . 
         [0033]      FIG. 4  is a cross-sectional view of the structure after the patterned second substrate is adhered with the epitaxial structure  102  in accordance with the first embodiment of the present invention. In the present embodiment, the adhering process is conducted by the following steps. First, the bonding layer  104  is formed on the reflection layer  110  of the epitaxial structure  102 . For example, the bonding layer  104  including organic material, such as B-staged bisbenzocyclobutene (BCB) resin, metal material, such as AuBe/Au alloy or the combination thereof is formed on the reflection layer  110  of the epitaxial structure  102  by a spin coating process. Subsequently, a bonding process follows to adhere the first surface  111  of the patterned second substrate  106  to the bonding layer  104 . 
         [0034]    A portion of the patterned second substrate  106  is removed after the adhering process is conducted. 
         [0035]      FIG. 5  is across-sectional view of the structure after a portion of the patterned second substrate  106  is removed in accordance with the first embodiment of the present invention. In the present embodiment, a portion of the patterned second substrate  106  is removed by an etch process or a chemical mechanical polishing process to form at least one through-hole penetrating through the openings  103  and exposing a portion of the bonding layer  104  through the through-holes. The remaining portion of the patterned second substrate  106  formed as the patterned silicon layer  106   a  has a thickness that is substantially between 1 μm and 200 μm. 
         [0036]    Then, a metal layer  108  is formed over the patterned silicon layer  106   a.    
         [0037]      FIG. 6  is a cross-sectional view of the structure after the metal layer  108  is formed over the patterned silicon layer  106   a  in accordance with the first embodiment of the present invention. A sputtering process, anodic oxidation process or the combination thereof forms the metal layer  108 . The thickness of the metal layer  108  is substantially between 0.5 μm and 100 μm. In addition, a portion of the metal layer  108  is filled into the through-holes penetrating through the openings  103  and contacts the bonding layer  104 . 
         [0038]    The structure of the metal layer  108  depends on the steps of sputtering process selected for forming thereof. For example, the metal layer  108  can be a single metal layer structure, multi-hetero metal interlace structure, single layer alloy structure or any combination thereof and depends on the various sputtering steps, such as co-deposition, interlaced deposition and single deposition, and the material used for the sputtering process. The material of the metal layer  108  can be Cu, Ni, CuO or Cu/Ni alloy and is deposited over the patterned silicon layer  106   a . In the present embodiment, the metal layer  108  is made of copper. The metal layer  108  comprises a single copper structure, a Cu/Ni interlace structure or a Cu/Ni alloy structure. 
         [0039]    Next, the first substrate  100  is removed to produce the structure illustrated in  FIG. 1 . 
         [0040]    Another method for forming the LED structure is disclosed by the second embodiment. The method of the second embodiment is substantially similar to the first embodiment, merely varying in the methods for forming the patterned silicon layer  106   a.    
         [0041]      FIG. 7  illustrates a cross-sectional view of an LED structure in accordance with the second embodiment of the present invention. The LED comprises an epitaxial structure  202 , a bonding layer  204  and a composite substrate  400 . The bonding layer  204 , located over one side of the epitaxial structure  202 , is used for adhering the composite substrate  400  to the epitaxial structure  202 . The composite substrate  400  comprises a patterned silicon layer  206   a  penetrated by at least one opening  203 , and a metal layer  208  covering the patterned silicon layer  206   a , wherein a portion of the metal layer  208  is filled in the openings  203 . 
         [0042]      FIG. 8  illustrates a cross-sectional view of an epitaxial structure  202  for forming the LED structure, in accordance with the second embodiment of the present invention. According to the second embodiment of the present invention, forming the LED structure comprises the following steps: 
         [0043]    First, an epitaxial structure  202  is formed on a first substrate  200 . The epitaxial structure  202  is formed over the first substrate  200 . In various embodiments of the present invention, the epitaxial structure  202  comprises a homo-structure, a single hetero-structure, a double hetero-structure, a multiple quantum well or any arbitrary combination thereof. In the present embodiment, the epitaxial structure  202  includes an n-type cladding layer  212  made of AlGaInP, an active layer  214  and a p-type cladding layer  216  made of AlGaInP deposited sequentially over the first substrate  200  by an epitaxial process, wherein the active layer  214  is a multiple quantum well made of AlGaInP. In the present embodiment, the epitaxial structure  202  further comprises a contact layer  209  formed over the p-type cladding layer  216  and a reflection layer  210  formed over the contact layer  209 . 
         [0044]    Simultaneously, a second substrate  206  is provided. In the present invention, the second substrate  206  is made of silicon and has a first surface  211  and a second surface  215 . Then, an adhering process is conducted to adhere the first surface  211  of the second substrate  206  to the side of the epitaxial structure  202  away from the first substrate  200 . 
         [0045]      FIG. 9  is a cross-sectional view of the structure after the second substrate  206  is adhered to the epitaxial structure in accordance with the second embodiment of the present invention. In the present embodiment, the adhering process is conducted by the following steps: 
         [0046]    First, a bonding layer  204  is formed on the reflection layer  210  of the epitaxial structure  202 . For example, the bonding layer  204  including organic material, such as B-staged bisbenzocyclobutene (BCB) resin, metal material, such as AuBe/Au alloy, or the combination thereof is formed on the reflection layer  210  of the epitaxial structure  202  by a spin coating process. 
         [0047]    Subsequently, a bonding process follows to adhere the first surface  211  of the second substrate  206  to the bonding layer  204 . 
         [0048]    A portion of the second substrate  206  is removed after the adhering process is conducted. 
         [0049]      FIG. 10   a  is a cross-sectional view of the structure after a portion of the second substrate  206  is removed in accordance with the second embodiment of the present invention. In the present embodiment, a portion of the second substrate  206  is removed by an etch process or a chemical mechanical polishing process to form at least one penetrating opening  203  exposing a portion of the bonding layer  204 . The remaining portion of the patterned second substrate  206  formed as a patterned silicon layer  206   a  has a thickness that is substantially between 1 μm and 200 μm. 
         [0050]      FIG. 10   b  illustrates a top view of the second substrate  206  after the patterned silicon layer  206   a  is formed. In some embodiments of the present invention, the shapes of the penetrating openings  203  are circular, triangular, rectangular, polygonal, irregular or any arbitrary combination thereof, and the penetrating openings  203  are arranged regularly or irregularly. In the present embodiment, the penetrating openings  203  are circular and arranged regularly. 
         [0051]    Next, a metal layer  208  is formed over the patterned silicon layer  206   a.    
         [0052]      FIG. 11  is a cross-sectional view of the structure after the metal layer  208  is formed over the patterned silicon layer  206   a  in accordance with the second embodiment of the present invention. A sputtering process, anodic oxidation process or the combination thereof forms the metal layer  208 . The thickness of the metal layer  208  is substantially between 0.5 μm and 100 μm. In addition, a portion of the metal layer  208  is filled into the through-holes penetrating through the openings  203  and contacts the bonding layer  204 . 
         [0053]    The structure of the metal layer  208  depends on the steps of sputtering process selected for forming thereof. For example, the metal layer  208  is a single metal layer structure, multi-hetero metal interlace structure, single layer alloy structure or any combination thereof depending on the various sputtering steps, such as co-deposition, interlaced deposition and single deposition, and the material used for the sputtering process. The material of the metal layer  208  can be Cu, Ni, CuO or Cu/Ni alloy and is deposited over the patterned silicon layer  206   a . In the present embodiment, the metal layer  208  is made of copper. The metal layer  208  comprises a single copper structure, a Cu/Ni interlace structure or a Cu/Ni alloy structure. 
         [0054]    Then, the first substrate  200  is removed to produce the structure illustrated in  FIG. 7 . 
         [0055]    In the preferred embodiments of the present invention, the LED structure further comprises a first electrode and a second electrode. 
         [0056]      FIG. 12  is a cross-sectional view of the structure after the first electrode and the second electrode are formed on the epitaxial structure in accordance with the first embodiment of the present invention. In the present embodiment, the first electrode  130  and the second electrode  140  are located on the epitaxial structure  102  on the same side of the patterned silicon layer  106   a.    
         [0057]    The following steps form the first electrode  130  and the second electrode  140 : 
         [0058]    First, an etch process is conducted from the n-type cladding layer  112  downward through the active layer  114  to the p-type cladding layer  116 , so that a portion of the p-type cladding layer  116  is exposed. Then, the first electrode  130  and the second electrode  140  are formed on the n-type cladding layer  112  and the p-type cladding layer  116 , respectively, by a deposition process. 
         [0059]    In another preferred embodiment, the first electrode  130  and the second electrode  140  are connected on the epitaxial structure  102  and, respectively, located on different sides of the patterned silicon layer  106   a.    
         [0060]      FIG. 13  is a cross-sectional view of another structure after the first electrode and the second electrode are formed on the epitaxial structure in accordance with the first embodiment of the present invention. In the present embodiment, the metal layer  108  acts as the second electrode  140 , and the first electrode  130  is formed on the n-type cladding layer  112  by a deposition process. 
         [0061]    Accordingly, the advantage of the present invention is to provide a composite substrate having good thermal conductivity via copper and good processability via silicon, so as to resolve the prior art problems to improve the processing yield and performance of an LED. 
         [0062]    As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrated 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.