Abstract:
This application discloses a light-emitting device with narrow dominant wavelength distribution and a method of making the same. The light-emitting device with narrow dominant wavelength distribution at least includes a substrate, a plurality of light-emitting stacked layers on the substrate, and a plurality of wavelength transforming layers on the light-emitting stacked layers, wherein the light-emitting stacked layer emits a first light with a first dominant wavelength variation; the wavelength transforming layer absorbs the first light and converts the first light into the second light with a second dominant wavelength variation; and the first dominant wavelength variation is larger than the second dominant wavelength variation.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    A wafer-scaled light-emitting device and manufacturing method thereof is disclosed, especially is related to a wafer-scaled light-emitting diode with narrow dominant wavelength distribution and a method of enabling convergent distribution of dominant wavelength of the wafer-scaled light-emitting device. 
         [0003]    2. Reference to Related Application 
         [0004]    This application claims the right of priority based on TW application Ser. No. 098106259, filed “Feb. 25, 2009”, entitled “LIGHT-EMITTING DEVICE WITH NARROW DOMINANT WAVELENGTH DISTRIBUTION AND METHOD OF MAKING THE SAME” and the contents of which are incorporated herein by reference in its entirety. 
         [0005]    3. Description of the Related Art 
         [0006]    The light-generating mechanism of a light-emitting diode (LED) is that the difference of the energy of electrons moving between an n-type semiconductor and a p-type semiconductor is released through the form of light. This light-generating mechanism of the LED is different from that of incandescent lamps so the LED is titled a cold light source. Besides, LED has advantages like high reliability, long life span, small dimensions, and electricity saving so the LED has been deemed as an illumination source of a new generation. 
         [0007]      FIG. 1A  to  FIG. 1E  show a conventional process flow of manufacturing a light-emitting device. As  FIG. 1A  shows, a substrate  10  is provided. As  FIG. 1B  shows, a plurality of epitaxial stacked layers  12  is formed on the substrate  10 , and the plurality of epitaxial stacked layers  12  is etched by lithography to form a plurality of light-emitting stacked layers  14 , as  FIG. 1C  shows. Next, as  FIG. 1D  shows, electrodes  16  are formed on the plurality of light-emitting stacked layers  14  to form an LED wafer  100 . Finally, as  FIG. 1E  shows, the LED wafer  100  is diced to form LED chips  18 . 
         [0008]    The distribution of the dominant wavelengths of the light-emitting stacked layers  14 , however, is not uniform. The difference of the dominant wavelength can be 15 nm-20 nm or even more so the difference of the dominant wavelength of the LED chips  18  formed by the light-emitting stacked layers  14  is large as well. The problem of non-uniform distribution of the dominant wavelengths further influences the consistency of characteristics of the products utilizing the LED chips  18 . Taking the conventional blue LED chip with the 460 nm dominant wavelength cooperating with the yellow phosphors to generate white light as an example, if the distribution range of the dominant wavelengths of the blue LED chips on the same LED wafer reaches 20 nm, namely the dominant wavelengths are between 450 nm and 470 nm, the distribution of the color temperatures of the white lights formed by mixing the light from the blue LED chips and the yellow wavelength-converting materials having 570 nm excited wavelength is also influenced. 
         [0009]    As  FIG. 2  shows, because the wide distribution of the dominant wavelengths of each light-emitting stacked layer on the LED wafer, the color temperatures of the white lights formed by mixing the light from the LED chips and the wavelength-converting materials distribute between 6500K and 9500K. With the difference of the color temperatures, which is about 3000K, the consistency of the quality of the products is affected significantly. 
         [0010]    To solve the problem of non-uniform distribution of the dominant wavelength of the light-emitting stacked layers  14 , there are probing, sorting, and binning processes in the conventional manufacturing process of the LED chips  18  to screen out the LED chips  18  having similar dominant wavelengths for various application demanding different wavelengths, as  FIG. 3  shows. 
         [0011]    Although the probing, sorting, and binning processes can reduce the influence upon the consistence of the quality caused by non-uniform distribution of the dominant wavelength, when the products to which the LED chips  18  are applied strictly require a tight distribution of the dominant wavelength, such as the back-light unit having the LED chips in the large size display, the ratio of the available LED chips  18  on the LED wafer  100  is low. Besides, sorting and binning processes are time-consuming and laborious, and increase the cost and time of manufacturing the LED chips. 
       SUMMARY 
       [0012]    The present application provides an LED wafer with narrow dominant wavelength distribution including a substrate, a plurality of light-emitting stacked layers formed on the substrate, and a wavelength transforming layer formed on the plurality of light-emitting stacked layers to converge and convert the dominant wavelengths emitted from the light-emitting stacked layers. 
         [0013]    The present application further discloses a method of converging the dominant wavelength distribution of the LED wafer, including the steps of providing a substrate, forming a plurality of light-emitting stacked layers on the substrate, and forming a wavelength transforming layer on the plurality of light-emitting stacked layers to converge the dominant wavelength distribution of each of the plurality of light-emitting stacked layers on the LED wafer. 
         [0014]    The present application also provides a method of manufacturing a light-emitting device, including forming a wavelength transforming layer to converge the variation of the dominant wavelengths of the light-emitting stacked layers to improve the usage efficiency. 
         [0015]    Another purpose of the present application is to provide a method of manufacturing a light-emitting device, including forming a wavelength transforming layer to converge the variation of the dominant wavelengths of the light-emitting stacked layers to eliminate sorting and binning processes in the manufacturing process of LED chips. 
         [0016]    The foregoing aspects and many of the attendant purpose, technology, characteristic, and function of this application will become more readily appreciated as the same becomes better understood by reference to the following embodiments detailed description, when taken in conjunction with the accompanying drawings 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The accompanying drawings are included to provide easy understanding of the application, and are incorporated herein and constitute a part of this specification. The drawings illustrate embodiments of the application and, together with the description, serve to illustrate the principles of the application. 
           [0018]      FIGS. 1A-1E  illustrate a conventional process flow of manufacturing LED chips. 
           [0019]      FIG. 2  illustrates a conventional CIE 1931 chromaticity diagram of a blue LED combining with yellow phosphor powders. 
           [0020]      FIG. 3  illustrates a conventional schematic view of probing of the LED chips. 
           [0021]      FIGS. 4A-4F  illustrate a process flow of manufacturing LED chips in accordance with an embodiment of the present application. 
           [0022]      FIG. 5  illustrates a cross-sectional view of the LED chips in accordance with another embodiment of the present application. 
           [0023]      FIG. 6  illustrates a CIE 1931 chromaticity diagram in accordance with the embodiment of the present application. 
           [0024]      FIG. 7  illustrates a cross-sectional view of the LED chips in accordance with another embodiment of the present application. 
           [0025]      FIGS. 8A-8B  illustrate cross-sectional views of the LED chips in accordance with other embodiments of the present application. 
           [0026]      FIG. 9  illustrates a schematic view of dicing steps in accordance with another embodiment of the present application. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    Reference is made in detail to the preferred embodiments of the present application, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
         [0028]      FIGS. 4A-4F  illustrate a process flow in accordance with an embodiment of the present application. As  FIG. 4A  shows, a substrate  20  is provided, wherein the substrate  20  can be an electrical conductive substrate. As  FIG. 4B  shows, a plurality of epitaxial layers  22  is formed on the substrate  20 , wherein each of the plurality of epitaxial layers  22  at least includes a first conductivity-type semiconductor layer  220 , an active layer  222 , and a second conductivity-type semiconductor layer  224 . The material of the plurality of epitaxial layers  22  can be a material including at least one element of Al, Ga, In, N, P, or As, such as GaN series or AlGaInP series material, for example. The embodiment below takes GaN series material as an example for explanation. 
         [0029]    As  FIG. 4C  shows, a plurality of light-emitting stacked layers  24  is formed on the substrate  20  by etching the plurality of epitaxial layers  22  with lithography. As  FIG. 4D  shows, a plurality of electrodes  26  is formed on the plurality of light-emitting stacked layers  24  by evaporation, and an LED wafer  200  is formed. 
         [0030]    The plurality of light-emitting stacked layers  24  can emit a plurality of first lights  210 , wherein the dominant wavelengths of the first lights  210  are between 390 nm and 430 nm. There is a first difference of the dominant wavelengths between any two first lights  210 , wherein the maximum of the first difference of the dominant wavelengths is a first dominant wavelength variation V 1 . 
         [0031]    As  FIG. 4E  shows, after forming the electrodes  26 , a plurality of wavelength transforming layers  28  is formed to cover the surfaces of the plurality of light-emitting stacked layers  24 , wherein the material of the plurality of wavelength transforming layers  28  contains fluorescent material or phosphor material. In this embodiment, the plurality of wavelength transforming layers  28  can be composed of phosphor powder. The material of the wavelength transforming layer  28  can be blue phosphor powder containing one or more than one materials selected from a group consisting of Si 3 MgSi 2 O 8 :Eu, BaMgAl 10 O 17 :Eu, (SrBaCa) 5 (PO 4 ) 3 Cl:Eu, Sr 3 (Al 2 O 5 )Cl 2 :Eu 2+  and Sr 4 Al 14 O 25 :Eu. The phosphor powder is uniformly or partially spread on the surface of the light-emitting stacked layer  24  so the wavelength transforming layer  28  absorbs substantially the whole first light  210  emitted from the light-emitting stacked layer  24  and converts the first light  210  into a second light  220 . 
         [0032]    In this embodiment, the dominant wavelengths of the second lights  220  are between 450 nm and 470 nm which are blue lights of long wavelength. There is a second difference of the dominant wavelengths between any two second lights  220 , wherein the maximum of the second difference of the dominant wavelengths is a second dominant wavelength variation V 2 . Finally, as  FIG. 4F  shows, the plurality of light-emitting stacked layers  24  is diced to form a plurality of LED chips  30 . 
         [0033]    In the above embodiment, the first dominant wavelength variation V 1  is between 15 nm and 20 nm, and the second dominant wavelength variation V 2  is less than 10 nm, preferably less than 5 nm. The difference of the dominant wavelengths of the lights from any two of the plurality of light-emitting layers  24  can be reduced by forming the plurality of wavelength transforming layers  28  on the plurality of light-emitting stacked layers  24 . The distribution of the dominant wavelengths of the plurality of LED chips  30  from the same LED wafer  200  can be convergent to improve the usage efficiency of the plurality of light-emitting stacked layers  24  on the LED wafer  200 . Moreover, the above embodiment can skip sorting and binning processes in the manufacturing process of the LED chips to further reduce the cost of production. 
         [0034]    In addition, as  FIG. 5  shows, the present application can include the step of forming a wavelength converting layer  32  on the wavelength transforming layer  28  after forming the wavelength transforming layer  28 . The wavelength converting layer  32  includes one or more than one kind of phosphor powders, wherein the phosphor powders include a material selected from a group consisting of yellow phosphor powders including yttrium aluminum garnet (YAG) or alkaline-earth halide aluminate, green phosphor powders including BaMgAl 10 O 17 :Eu, MnBa 2 SiO 4 :Eu, (Sr,Ca)SiO 4 :Eu, CaSc 2 O 4 :Eu, Ca 8 Mg(SiO 4 ) 4 Cl 2 :Eu, Mn, SrSi 2 O 2 N 2 :Eu, LaPO 4 :Tb,Ce, Zn2SiO 4 :Mn, ZnS:Cu, YBO 3 :Ce,Tb, (Ca,Sr,Ba)Al 2 O 4 :Eu, Sr 2 P 2 O 7 :Eu,Mn, SrAl 2 S 4 :Eu, BaAl 2 S 4 :Eu, Sr 2 Ga 2 S 5 :Eu, SiAlON:Eu, KSrPO 4 :Tb, or Na 2 Gd 2 B 2 O 7 :Ce,Tb, and red phosphor powders including Y 2 O 3 :Eu, YVO 4 :Eu, CaSiAlN3:Eu, (Sr,Ca)SiAlN3:Eu, Sr 2 Si 5 N 8 :Eu, CaSiN 2 :Eu, (Y,Gd)BO 3 :Eu, (La,Y) 2 O 2 S:Eu, La 2 TeO 6 :Eu, SrS:Eu, Gd 2 MoO 6 :Eu, Y 2 WO 6 :Eu,Bi, Lu 2 WO 6 :Eu,Bi, (Ca,Sr,Ba)MgSi 2 O 6 :Eu,Mn, Sr 3 SiO 5 :Eu, SrY 2 S 4 :Eu, CaSiO 3 :Eu, Ca 8 MgLa(PO 4 ) 7 :Eu, Ca 8 MgGd(PO 4 ) 7 :Eu, Ca 8 MgY(PO 4 ) 7 :Eu, or CaLa 2 S 4 :Ce. The above phosphor powders are uniformly or partially spread on the wavelength transforming layer  28 . 
         [0035]    In this embodiment, the wavelength converting layer  32  includes at least one yellow phosphor powder. The wavelength converting layer  32  can absorb the second light  220  and convert the second light  220  into third light  230  in yellow color, wherein the dominant wavelength of the third light  230  is about 570 nm. Then, the third light  230  of yellow color and the second light  220  which is not absorbed by the wavelength converting layer  32  are mixed to generate a fourth light  240  in white light. 
         [0036]    Because the dominant wavelength of the second light  220  is about 460 nm and the second dominant wavelength variation V 2  is less than 10 nm, preferably less than 5 nm. In the embodiment, the distribution range of the second dominant wavelengths is between 455 nm and 465 nm.  FIG. 6  illustrates a CIE 1931 chromaticity diagram of the fourth light  240 . As  FIG. 6  shows, the color temperature of the fourth light  240  which is generated by mixing the second light  220  and the third light  230  is about between 6500K and 8500K (the intersection point of the black curve and the solid line in  FIG. 6 ). The difference of the color temperature of the fourth light  240  is less than 2000K, preferably less than 1000K. 
         [0037]    Comparing to the conventional technology that the blue LED whose dominant wavelength is between 450 nm and 470 nm combines with the yellow phosphor powder to generate the white light of which the difference of the color temperature is 3000K (the intersection point of the black curve and the dotted line in  FIG. 6 ), the embodiment of the present application significantly increases the uniformity of the light emitted from each light-emitting stacked layer of an LED wafer. 
         [0038]    Furthermore, although the LED chip which is a vertical structure is taken as an example in the above embodiment, the scope of the present application is not limited to the LED of the vertical structure.  FIG. 7  is a cross-sectional view of another embodiment of the present application. As  FIG. 7  shows, an LED wafer  500  includes a substrate  50 , and a plurality of light-emitting stacked layers  52 , a plurality of first electrodes  54 , a plurality of second electrodes  56 , and a plurality of wavelength transforming layers  58  formed on the substrate  50 , wherein each of the plurality of light-emitting stacked layers  52  at least includes a first conductivity-type semiconductor layer  520 , an active layer  522 , and a second conductivity-type semiconductor layer  524 . Each of the plurality of light-emitting stacked layers  52  includes a plane exposing the second conductivity-type semiconductor layer  524 . Each of the plurality of first electrodes  54  and each of the plurality of second electrodes  56  are located on the first conductivity-type semiconductor layer  520  and the second conductivity-type semiconductor layer  524  respectively. The plurality of wavelength transforming layers  58  covers the plurality of light-emitting stacked layers  52 . 
         [0039]    Moreover,  FIGS. 8A and 8B  are cross-sectional views of other embodiments of the present application. The embodiments can further include an electrical connection structure  60  to connect the adjacent light-emitting stacked layers  52 / 52 ′ in series connection. As  FIG. 8A  shows, the electrical connection structure  60  is a metal wire. The wire bonding technology is utilized to electrically connect the second electrode  56  of a light-emitting stacked layer  52  and the first electrode  54  of another light-emitting stacked layer  52 ′ to form a series connection between different light-emitting stacked layers  52  and  52 ′. As  FIG. 8B  shows, the electrical connection structure  60  can also include an insulating layer  62  formed between the adjacent light-emitting stacked layers  52  and  52 ′, and a metal layer  64  formed on the insulating layer  62  to electrically connect the second electrode  56  of a light-emitting stacked layer  52  and the first electrode  54  of another light-emitting stacked layer  52 ′. Thus, there is a series connection between different light-emitting stacked layers  52  and  52 ′. 
         [0040]    Additionally, as  FIG. 9  shows, each of the plurality of light-emitting stacked layers  52  can be diced along the dicing line A to form the LED chip in the step of dicing the LED wafer. The plurality of light-emitting stacked layers  52  and  52 ′ which are connected by the electrical connection structure  60  in series connection are diced along the dicing line B to form an LED array chip  70 . In general, the voltage drop of each of the plurality of light-emitting stacked layer  52  and  52 ′ is about 3.5V. Fourteen light-emitting stacked layers  52  and  52 ′ which are in series connection are diced to form an LED array chip  70  and can be directly applied to the vehicle application which is  48 V in the alternating current power supply. Moreover, thirty light-emitting stacked layers  52  and  52 ′ connected in series can also be diced to form the LED array chip  70  and can be directly applied to the household application with 100V in the alternating current power supply. Because there is a wavelength transforming layer on each of the light-emitting stacked layers  52  and  52 ′, the dominant wavelengths of each of the light-emitting stacked layers  52  and  52 ′ are more consistent. Thus, the process of sorting and binning based on the distribution of the dominant wavelengths can be eliminated in the conventional manufacturing process of the LED array chip to reduce the cost of production. 
         [0041]    The foregoing description has been directed to the specific embodiments of this application. It will be apparent, however, that other variations and modifications may be made to the embodiments without escaping the spirit and scope of the application.