Abstract:
A manufacturing method and a structure of a light-emitting diode (LED) chip are disclosed. The method includes the steps of: providing a conductive block; providing an epitaxial block; bonding; removing an epitaxial substrate; making independent LEDs; forming a dielectric layer; and making electrical connection. A first LED, a second LED, and a third LED are formed on the conductive block, wherein the first and second LEDs are electrically connected in series, and the second and third LEDs are electrically connected in parallel. Thus, a basic unit with a flexible design of series- and parallel-connected LEDs can be formed to increase the variety and application of LED chip-based designs.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a method for making a light-emitting diode (LED) chip and the structure of the LED chip. More particularly, the present invention relates to a manufacturing method and a structure of an LED chip configured for illumination purposes. 
     2. Description of Related Art 
     Please refer to  FIG. 1  for a sectional view of a conventional horizontal-structure LED unit  101  with parallel-connected LEDs. Manufacture of the LED unit  101  begins by forming an n-type semiconductor layer  111  on a gallium arsenide (GaAs) dielectric substrate  10 , and a p-type semiconductor layer  112  on the n-type semiconductor layer  111 . Then, an etching process is carried out to form a plurality of LEDs  11 , which are subsequently connected in parallel by a first dielectric material  12  and a conductive layer  13 . The LEDs  11  made by the TD process can only form a parallel-connected structure but cannot form a series-connected structure. 
       FIG. 2  is a sectional view of a conventional horizontal-structure LED unit  102  with parallel-connected LEDs made by the wafer bonding (WB) process. To make the LED unit  102  by the WB process, a second dielectric material  15  is formed on a metal or silicon substrate  14 , then a p-type semiconductor layer  112  is formed on the second dielectric material  15 , and an n-type semiconductor layer  111  is formed on the p-type semiconductor layer  112 . Afterward, a plurality of LEDs  11  is formed by etching, and the LEDs  11  are connected in parallel by a first dielectric material  12  and a conductive layer  13 . Again, the vertical LEDs  11  made by the WB process can form a parallel-connected structure but not a series-connected structure. 
       FIG. 3  is a sectional view of a conventional horizontal-structure LED unit  103  with series-connected LEDs made by the WB process. The WB-based manufacturing process includes forming a second dielectric material  15  on a metal or silicon substrate  14 , forming a p-type semiconductor layer  112  on the second dielectric material  15 , forming an n-type semiconductor layer  111  on the p-type semiconductor layer  112 , forming a plurality of LEDs  11  by etching, and connecting the LEDs  11  in series by a first dielectric material  12  and a conductive layer  13 . 
     According to the above, the conventional horizontal-structure LED unit  101  can only form a structure with parallel-connected LEDs (hereinafter referred to as a parallel-connected LED structure). Likewise, the conventional horizontal-structure LED units  102 ,  103  made by the WB process can only form either a parallel-connected LED structure or a structure with series-connected LEDs (hereinafter referred to as a series-connected LED structure); it is practically impossible to form a structure with series- and parallel-connected LEDs (hereinafter referred to as a series- and parallel-connected LED structure) in a single manufacturing process. As such, the conventional techniques leave much to be desired. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention relates to a manufacturing method and a structure of an LED chip, wherein at least one series- and parallel-connected LED structure is formed on a substrate using a wafer-level manufacturing process. By implementing the present invention, the variety and application of LED chip-based designs can be significantly increased. 
     The present invention provides a manufacturing method of a light-emitting diode (LED) chip, comprising the steps of: providing a conductive block, wherein the conductive block comprises: a conductive substrate having a first region and a second region; a first dielectric layer formed on the first region; and a first metal layer formed on the second region and the first dielectric layer; providing an epitaxial block, wherein the epitaxial block comprises: an epitaxial substrate; an epitaxial layer formed on the epitaxial substrate; and a second metal layer formed on a semiconductor side of the epitaxial layer; bonding, wherein the first metal layer is bonded with the second metal layer so that the conductive block and the epitaxial block are bonded together to form a bonded block; removing the epitaxial substrate, wherein the epitaxial substrate is removed from the bonded block so as to form an LED block; making independent LEDs, wherein the LED block is etched so that at least a first LED is formed on the first region and at least a second LED and at least a third LED are formed on the second region; forming a second dielectric layer, wherein the second dielectric layer is formed between the at least a first LED, the at least a second LED, and the at least a third LED; and making electrical connection, wherein a first conductive layer is formed on the second dielectric layer to series-connect each said first LED and each said second LED, and a second conductive layer is formed on the second dielectric layer to parallel-connect each said second LED and each said third LED. 
     The present invention also provides A light-emitting diode (LED) chip structure, comprising: a conductive block comprising: a conductive substrate having a first region and a second region; a first dielectric layer formed on the first region; and a plurality of first metal layers independently connected to the second region and the first dielectric layer; at least a first LED fixedly provided on the first dielectric layer via bonding between one of a plurality of second metal layers and a said first metal layer; at least a second LED fixedly provided on the second region via bonding between a said second metal layer and a said first metal layer, wherein the at least a second LED is connected in series to the at least a first LED by one of a plurality of second dielectric layers and a first conductive layer; and at least a third LED fixedly provided on the second region via bonding between a said second metal layer and a said first metal layer, wherein the at least a third LED is connected in parallel to the at least a second LED by a said second dielectric layer and a second conductive layer. 
     Implementation of the present invention at least involves the following inventive steps: 
     1. A series- and parallel-connected LED structure can be formed on a conductive block by a simple manufacturing process. 
     2. The variety and application of LED chip-based designs can be substantially increased. 
     The detailed features and advantages of the present invention will be described in detail with reference to the preferred embodiments so as to enable persons skilled in the art to gain insight into the technical disclosure of the present invention, implement the present invention accordingly, and readily understand the objectives and advantages of the present invention by perusal of the contents disclosed in the specification, the claims, and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a sectional view of a conventional horizontal-structure LED unit; 
         FIG. 2  is a sectional view of a conventional horizontal-structure LED unit made by the WB process; 
         FIG. 3  is a sectional view of a conventional series-connected LED unit made by the WB process; 
         FIG. 4  is the flowchart of a method for making an LED chip according to an embodiment of the present invention; 
         FIG. 5A  is a sectional view showing the first aspect of a conductive block in the present invention; 
         FIG. 5B  is a sectional view showing the second aspect of the conductive block in the present invention; 
         FIG. 6  is a sectional view of an epitaxial block according to an embodiment of the present invention; 
         FIG. 7  is a sectional view of a bonded block according to an embodiment of the present invention; 
         FIG. 8  is a sectional view of an LED block according to an embodiment of the present invention, wherein the LED block is formed by removing an epitaxial substrate from the bonded block; 
         FIG. 9  is a sectional view of a plurality of independent LEDs according to an embodiment of the present invention, wherein the LEDs are formed by etching; 
         FIG. 10  is a sectional view showing how a second dielectric layer is formed on the independent LEDs according to an embodiment of the present invention; 
         FIG. 11A  is a sectional view showing the first aspect of using a conductive layer on the second dielectric layer to make series and parallel electrical connection according to the present invention; 
         FIG. 11B  is a sectional view showing the second aspect of using a conductive layer on the second dielectric layer to make series and parallel electrical connection according to the present invention; 
         FIG. 12  is a sectional view of an epitaxial block according to another embodiment of the present invention, wherein the epitaxial block has a reflective layer; and 
         FIG. 13  is a sectional view of an LED chip structure according to an embodiment of the present invention, wherein the LED chip structure has a non-conductive substrate with a plurality of first conductive posts. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Please refer to  FIG. 4  for the flowchart of a method  5200  for making an LED chip according to an embodiment of the present invention. The method includes the steps of: providing a conductive block (step S 10 ), providing an epitaxial block (step S 20 ), bonding (step S 30 ), removing an epitaxial substrate (step S 40 ); making independent LEDs (step S 50 ), forming a second dielectric layer (step S 60 ), and making electrical connection (step S 70 ). 
     The step of providing a conductive block (step S 10 ) is detailed as follows. Referring to  FIG. 5A , a conductive block  20  is provided which includes a conductive substrate  21 . In order to form horizontal-structure LEDs and vertical-structure LEDs at the same time, the conductive substrate  21  is divided into a first region  22  and a second region  23 . A first dielectric layer  24  is formed on the first region  22  to provide the conditions for making horizontal-structure LEDs in a later step. Then, a first metal layer  25  is formed on both the second region  23  and the first dielectric layer  24  to enable the subsequent bonding step. Not only that, the first metal layer  25  on the second region  23  provides the conditions for making vertical-structure LEDs. 
     Referring to  FIG. 5B , the conductive substrate  21  can be a semiconductor wafer substrate, such as a semiconductor conductive substrate made of a group IV-IV, group III-IV, group II-VI, silicon, germanium, gallium nitride, or gallium arsenide. Alternatively, the conductive substrate  21  can be a substrate with high conductivity, such as one made of copper tungsten, molybdenum, copper, tungsten, or manganese. The conductive substrate  21  can also be made by processing a non-conductive substrate such that the non-conductive substrate is rendered conductive. For instance, the conductive substrate  21  includes a non-conductive substrate  26 , and the non-conductive substrate  26  is provided therein with a plurality of first conductive posts  27 . Each first conductive post  27  penetrates and extends through the non-conductive substrate  26  and is electrically connected to the first metal layer  25 . The first conductive posts  27  also provide heat dissipation. 
     The step of providing an epitaxial block (step S 20 ) is now described with reference to  FIG. 6 . An epitaxial block  30  is provided in the form of an LED epitaxial block and includes an epitaxial substrate  31 , an epitaxial layer  32 , and a second metal layer  33 . The epitaxial substrate  31  serves to grow and support LEDs. The epitaxial layer  32  constitutes the LEDs and is formed on the epitaxial substrate  31 . The second metal layer  33  is formed on a semiconductor side  34  of the epitaxial layer  32  (i.e., the side of the epitaxial layer  32  that is opposite the epitaxial substrate  31 ) to facilitate subsequent bonding. 
     Referring to  FIG. 7 , the step of bonding (step S 30 ) is carried out in the following manner. With the first metal layer  25  on the conductive block  20  and the second metal layer  33  on the epitaxial block  30 , the conductive block  20  and the epitaxial block  30  are bonded together by bonding the first metal layer  25  with the second metal layer  33 . This can be easily done thanks to the same material properties of the first and second metal layers  25 ,  33 . After bonding, the conductive block  20  and the epitaxial block  30  jointly form a bonded block  40 . 
     Next, the step of removing the epitaxial substrate (step S 40 ) is performed. Referring to  FIG. 8 , once the conductive block  20  and the epitaxial block  30  form the bonded block  40 , the conductive block  20  replaces the epitaxial substrate  31  as the structural support for the epitaxial layer  32 . In order for subsequently formed LEDs to emit light effectively, the epitaxial substrate  31  must be removed from the bonded block  40 . The removal of the epitaxial substrate  31  also facilitates the manufacture of each LED in the following step. By transferring the epitaxial layer  32  to the conductive block  20  and removing the epitaxial substrate  31 , the bonded block  40  is turned into an LED block  50 . 
     Then, the step of making independent LEDs (step S 50 ) is executed. Referring to  FIG. 9 , an etching process is performed on the LED block  50  formed in the previous step. In order to make a series- and parallel-connected LED structure, the LED block  50  must, to begin with, be etched to form a plurality of independent LEDs. The etching process is conducted no further than the first dielectric layer  24 . As a result, the first metal layer  25  is divided into several independent sections that are electrically disconnected. 
     The etching process is planned as follows. Since the first dielectric layer  24  on the first region  22  provides the conditions for making horizontal structures, at least one first LED  60  must be formed on the first region  22 . On the other hand, now that the first metal layer  25  and the second metal layer  33  on the second region  23  are electrically connected with the conductive substrate  21  and therefore provide the conditions for making vertical structures, a parallel-connected structure including at least one second LED  70  and at least one third LED  80  must be formed on the second region  23 . The at least one first LED  60  will be later connected in series to the parallel-connected second and third LEDs  70 ,  80 , as explained further below. 
     The step of forming a second dielectric layer (step S 60 ) is now described with reference to  FIG. 10 . After the making of the independent LEDs (step S 50 ), a second dielectric layer  90  is formed in the etched-away portions between the first, second, and third LEDs  60 ,  70 ,  80  to provide the necessary electrical isolation for forming a series and parallel circuit in the subsequent step. 
     Lastly, the step of making electrical connection (step S 70 ) is performed, as shown in  FIGS. 11A and 11B . A first conductive layer  91  is formed on the second dielectric layer  90  to connect each first LED  60  and each second LED  70  in series. Additionally, a second conductive layer  92  is formed on the second dielectric layer  90  to connect each second LED  70  and each third LED  80  in parallel. Thus, an LED circuit with both series and parallel connections is formed on the conductive block  20 . 
     Referring to  FIG. 12 , with a view to increasing light emitting efficiency of the LEDs, the epitaxial block  30 ′ is made in such a way that a reflective layer  35  is formed between the semiconductor side  34  of the epitaxial layer  32  and the second metal layer  33 . Reflection of the reflective layer  35  can enhance light emitting efficiency of the LEDs. The reflective layer  35  is generally made of a dielectric material. However, as the second and third LEDs  70 ,  80  must be vertical structures, the semiconductor side  34  of at least the second and third LEDs  70 ,  80  must be electrically connected to the second metal layer  33 . To achieve this end, at least a portion of the reflective layer  35  that corresponds in position to the second and third LEDs  70 ,  80  is formed therein with a plurality of second conductive posts  36  for making electrical connection between the semiconductor side  34  of the second and third LEDs  70 ,  80  and the second metal layer  33 . The second conductive posts  36  also serve to dissipate heat. 
     In order not to complicate the manufacturing process with an additional alignment step, the plural second conductive posts  36  need not be formed only in a portion of the reflective layer  35  that corresponds in position to the first region  22  or the second region  23 . In other words, the second conductive posts  36  can be distributed over a wider area than required to electrically connect the semiconductor side  34  of the first, second, and third LEDs  60 ,  70 ,  80  to the second metal layer  33 . As the portion of the second metal layer  33  that corresponds in position to the at least one first LED  60  has been divided into separate and electrically disconnected sections after the etching process, the aforesaid arrangement of the second conductive posts  36  has no adverse effect on the manufacture of the intended series circuit. 
     Referring again to  FIG. 11A , the present invention also provides an embodiment of an LED chip structure  200  based on the foregoing manufacturing method. In the embodiment shown in  FIG. 11A , the LED chip structure  200  includes a conductive block  20 , at least one first LED  60 , at least one second LED  70 , and at least one third LED  80 . 
     The conductive block  20  includes a conductive substrate  21 , which has a first region  22  and a second region  23 . The first region  22  is covered by a first dielectric layer  24 . The second region  23  and the first dielectric layer  24  are covered by a plurality of separate first metal layers  25 . The first metal layers  25  form independent and electrically disconnected sections as a result of etching and serve a bonding function during the manufacturing process. 
     The conductive substrate  21  can be a semiconductor wafer substrate, such as a semiconductor conductive substrate made of a group IV-IV, group III-IV, group II-VI, silicon, germanium, gallium nitride, or gallium arsenide. Alternatively, the conductive substrate  21  can be a substrate with high conductivity, such as one made of copper tungsten, molybdenum, copper, tungsten, or manganese. 
     The conductive substrate  21  can also be made by processing a non-conductive substrate and thus providing the non-conductive substrate with electrical conductivity. For example, referring to  FIG. 11B , the conductive substrate includes a non-conductive substrate  26 , and the non-conductive substrate  26  is formed therein with a plurality of first conductive posts  27 . Each first conductive post  27  penetrates and extends through the non-conductive substrate  26  and is electrically connected to the corresponding first metal layer  25 . The first conductive posts  27  also provide heat dissipation. 
     The first LED  60  is fixed to the first dielectric layer  24  on the first region  22  via bonding between one of a plurality of second metal layers  33  and one of the first metal layers  25 . 
     Similarly, the second LED  70  is fixedly provided on the second region  23  via bonding between one of the second metal layers  33  and one of the first metal layers  25 . In addition, the second LED  70  and the first LED  60  are connected in series by one of a plurality of second dielectric layers  90  and a first conductive layer  91 . 
     The third LED  80  is fixed on the second region  23  via bonding between another pair of the first and second metal layers  25 ,  33 . Furthermore, the third LED  80  and the second LED  70  are connected in parallel by one of the second dielectric layers  90  and a second conductive layer  92 . 
     As shown in  FIG. 13 , in order to enhance light emitting efficiency of the LEDs, a reflective layer  35  is provided between each of the first, second, and third LEDs  60 ,  70 ,  80  and the corresponding second metal layer  33 . Now that the second LED  70  and the third LED  80  are intended to be vertical structures, at least the reflective layers  35  on the second region  23  must be provided therein with a plurality of second conductive posts  36 , so as for the second LED  70  and the third LED  80  to be respectively and electrically connected to the corresponding second metal layers  33 . The second conductive posts  36  serve a heat dissipating function as well. 
     With the LED chip structure  200  being a product of the foregoing method S 200  for making an LED chip, further details of the LED chip structure  200  as can be known from the description of the method S 200  are not repeated herein. 
     The features of the present invention are disclosed above by the preferred embodiments to allow persons skilled in the art to gain insight into the contents of the present invention and implement the present invention accordingly. The preferred embodiments of the present invention should not be interpreted as restrictive of the scope of the present invention. Hence, all equivalent modifications or amendments made to the aforesaid embodiments should fall within the scope of the appended claims.