Abstract:
Disclosed herein are technologies for forming a plurality of known good die (KGD)-light emitting diode (LED) components into a larger size optically coherent LED chips or devices. This Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority of U.S. Provisional Patent Application Ser. No. 61/977,384 filed Apr. 9, 2014, and U.S. patent application Ser. No. 14/338,327 filed Jul. 22, 2014. 
     
    
     BACKGROUND 
       [0002]    Light emitting diodes (LEDs) are gaining wide acceptance in a variety of area-illumination applications such as in architectural lighting, residential illumination, industrial lighting, outdoor lighting, and the like. 
         [0003]    A typical LED is made of semiconducting materials doped with impurities to create a p-n junction. As in other diodes, current flows easily from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction. Charge-carriers such as electrons and holes may flow into the p-n junction from electrodes with different voltages. When an electron meets a hole, for example, it falls into a lower energy level and releases energy in the form of a photon. 
         [0004]    For high-brightness applications, a large LED chip size is preferable. More importantly, with larger LED chip size, higher brightness may be achieved at much lower current density which leads to less degradation of efficacy. However simply increasing the die size of LEDs causes significant yield loss and thus hinders the adoption of big-chip LEDs. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The detailed description is described with reference to accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components. 
           [0006]      FIG. 1  is a diagram of an example metal organic chemical vapor deposition (MOCVD) stack as described in present implementations herein. 
           [0007]      FIG. 2  is a diagram of an example etching of a gallium nitride (GaN) as described in present implementations herein. 
           [0008]      FIG. 3  is a diagram of an example etching of a GaN as described in present implementations herein. 
           [0009]      FIG. 4  is a diagram of an example formation of a metal contact for the n-type GaN as described in present implementations herein. 
           [0010]      FIG. 5  is a diagram of an example formation of a metal contact for the p-type GaN as described in present implementations herein. 
           [0011]      FIG. 6  is a diagram of an example formation of a dielectric material for isolation purposes. 
           [0012]      FIG. 7  is a diagram of an example etching of a dielectric to expose a metal contact as described in present implementations herein. 
           [0013]      FIG. 8  is a diagram of an example patterning of probe pads onto metal contacts as described in present implementations herein. 
           [0014]      FIG. 9  is a diagram of an example optional step of electroplating of a solder bump. 
           [0015]      FIG. 10  is a diagram of an example process of thinning down, roughening, and singulating KGD-LED components. 
           [0016]      FIG. 11  is a diagram of an example mounting substrate upon which the singulated KGD-LED components may be attached or mounted. 
           [0017]      FIG. 12  is a diagram of an example multiple mounting configurations on a substrate wafer floor plan. 
           [0018]      FIG. 13  is a diagram of an example process of aligning and placing KGD-LED components to the mounting substrate to form a plurality of joined KGD-LED components. 
           [0019]      FIG. 14  is a diagram of an example process of filling gaps and spaces in between the mounted KDG-LED components and the mounting substrate. 
           [0020]      FIG. 15  is a diagram of an example method-flowchart of joining a plurality of KGD-LED components as described in present implementations herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Described herein are processes and method of forming a plurality of known good die (KGD)-light emitting diode (LED) components into a larger size optically coherent LED chips or devices. 
         [0022]    In an implementation, a wafer testing may provide a multiple of KGD-LED components. In this implementation, the KGD-LED components are singulated and flip chip bonded onto a mounting substrate, which includes redistribution layers (RDLs) that facilitate electrical connections between the KGD-LED components and an operating device. For example, the electrical connections facilitated by the RDLs may include series or parallel connections of the KGD-LED components to a circuitry, power source, or components of the operating device. 
         [0023]    With the KGD-LED components bonded onto the mounting substrate, a gap and spaces in between the bonded KGD-LED components are under-filled with a transparent material (e.g., silicon or epoxy). The gap, for example, is configured to include a measurement such that it facilitates free flowing of the transparent under-filling materials (e.g., equal or less than 100 um) in between the aligned and mounted KGD-LED components. After a curing process, a surface of the transparent filling material may be roughened for purposes of light extraction. Similarly, an upper surface and a lower surface of a substrate in a stack of LED layers that forms the KGD-LED component are roughened and patterned, respectively, for purposes of this light extraction (e.g., about 1-3 um in roughness). The transparent material filling the gap is transparent to the light wavelength that is emitted by the LED components. The transparent material may be customized as to not absorb the LED light wavelength, otherwise there may be poor light output by the device. In addition, the gap dimension between the KGD-LED components, the shape of the KGD, pattern of the KGD, or combination, may be configured to facilitate free flowing of the transparent under-filling material. 
         [0024]    The formed or joined plurality of KGD-LED components above may allow for scalability to increasingly larger LED chip or device size; high efficacy; high brightness; high yield; and low cost. 
         [0025]      FIGS. 1-15  depict one illustrative method of joining a plurality of KGD-LED components including into a larger size optically coherent LED chips or devices. 
         [0026]    For example,  FIGS. 1-5  initially depict an illustrative situation where metal contacts are formed into the n-type and p-type gallium nitride (GaN) surfaces of stack of LED layers. 
         [0027]      FIG. 1 , in this example, shows a MOCVD stack  100  (i.e., stack of LED layers) that includes a substrate  102 , n-type GaN  104 , a MQW  106 , and a p-type GaN  108 . 
         [0028]    In accordance with embodiment described herein, the sequential formation of the n-type GaN  104 , MQW  106 , and the p-type GaN  108  into or above the substrate  102  may be implemented via any suitable processes and materials. For example, the substrate  102  may include a crystalline material such as in the case of sapphire or silicon carbide (SiC) substrates where the crystalline material is lattice matched to the GaN materials (i.e., n-type GaN  104  and p-type GaN  108 ). In this example, the substrate  102  may have a microstructured surface. On the other hand, the n-type GaN  104  and the p-type GaN  108  may include the same or different semiconducting materials and they may either be doped or undoped, or doped with different dopant materials. In general, the semiconducting materials n-type GaN  104  and the p-type GaN  108  may be formed by forming a hard mask (not shown) such as, for example, a silicon nitride hard mask. 
         [0029]    The MQW  106 , for example, may include different band-gaps and thicknesses depending upon their number of quantum wells and barriers. According to the present disclosure, the number of quantum wells and barriers, and their thicknesses may be adjusted to controllably vary the intensity ratio of the emitted photons of different energies (wavelengths). As a consequence, the MQW  106  may be tailored so as to emit light of multiple wavelength bands which are combinable to yield a light of a desired color. It is to be appreciated that embodiments in accordance with the present description may suit other types of LEDs that includes different materials. 
         [0030]      FIG. 2  illustrates an example etching in the GaN to define a device area which may be patterned using a first mask i.e., mask layer  1 . 
         [0031]    For example, portions of the sequentially formed n-type GaN  104 , MQW  106 , and the p-type GaN  108  are etched away via inductively coupled plasma reactive ion etching (RIE), or other suitable process. In this example, the etching may result to a new dimension of the MOCVD stack  100 . That is, an outer perimeter (i.e., upper surface) of the substrate  102  is cleared of the sequentially formed n-type GaN  104 , MQW  106 , and the p-type GaN  108 . For example, a photolithography (i.e., mask layer  1 ) and a strip photoresist are used to clear a width of 30 um (i.e., shown in width  200 ) measured from an outer perimeter of the substrate  102 . In this example, the sequentially formed n-type GaN  104 , MQW  106 , and the p-type GaN  108  may appear as a single unit (e.g., square) on top of the substrate  102 , which may also have a square configuration (e.g., 600 um by 600 um die size). 
         [0032]      FIG. 3  is illustrates an example etching of the GaN which may be patterned using a second mask, i.e., mask layer  2 . 
         [0033]    For example, an etching process is performed that removes materials of the p-type GaN  108 , MQW  106 , and a portion of the n-type GaN  104  in the stack of LED layers. At the end of the etching process, a width of 40 um (i.e., shown as width  300 ) may be removed from an outer perimeter of the stack of LED layers: p-type GaN  108 , MQW  106 , and portion of the n-type GaN  104 . For example, after the etching process, the stack of LED layers—p-type GaN  108 , MQW  106 , and the n-type GaN  104 —may appear as a square on top of the n-type GaN  104 . In this example, a new truncated dimension of the n-type GaN  104  may include a lower base such as the 540 um base dimension as a result of the process in  FIG. 2 , and an upper base that is defined by removal of the outer perimeter (i.e., shown in width  300 ) of the n-type GaN  104 . 
         [0034]      FIG. 4  illustrates an example formation of a metal contact for the n-type GaN which may be formed using a third mask, i.e., mask layer.  FIG. 4  involves another process performed on previous  FIG. 3  and to this end, the previously defined materials, removed portions, and/or processes may not be shown again to simplify the presentation. 
         [0035]    For example,  FIG. 4  illustrates formation of metal contacts  400  in the n-type GaN  104 . Particularly, the metal contacts  400  are disposed on top of a planar upper surface of the lower base and within the perimeter defined by the width  300 . For example, the metal contacts  400  includes a width of about 30 um and the metal contacts  400  may surround the upper base of the n-type GaN  104 . In this example, the 30 um metal contacts  400  lie within the perimeter defined by the width  300 . 
         [0036]    In accordance with implementations described herein, the illustrated formation shown in  FIG. 4  may be via any suitable processes and materials. For example, a deposition process using an electron beam (“e-beam”) utilizes 15 nm Ti/200 nm Al/40 nm Ni/50 nm Au to form the metal contacts  400 . Furthermore, a rapid thermal anneal (RTA) at 900° C. for 30 secs in a N2 environment may be utilized in the formation of the metal contacts  400 . In this example, the utilized photoresists may be removed by organic solvents. 
         [0037]      FIG. 5  illustrates an example formation of a metal contact for the p-type GaN which may be formed using a fourth mask, i.e., mask “layer  4 .  FIG. 5  involves another process performed on previous  FIG. 4  and to this end, the previously defined materials, removed portions, and/or processes may not be shown again to simplify the presentation. 
         [0038]    For example,  FIG. 5  illustrates formation of metal contacts  500  on a top planar surface of the p-type GaN  108 . In this example, the metal contacts  500  may form a square within an area defined by the upper planar surface of the p-type GaN  108 . The square formed by the metal contacts  500 , for example, has a side measurement of 450 um while the square formed by the p-type GaN  108  has a side measurement of 460 um (i.e., larger by 5 um). A top-view diagram as shown in  FIG. 5  may illustrate the configuration of the metal contacts  400  and  500 . 
         [0039]    In an implementation, the following techniques or process may be implemented to form the metal contacts  500 : photolithography to expose the metal contact formation regions, roughening of the p-type GaN surface to induce, enhance, and/or optimize diffusive reflection; E-beam evaporate 20 nm Pd (or Ni)/500 nmAl/40 nm Ni/50 nm Au to form the metal contacts  500 ; liftoff of the photoresist by organic solvents; and annealing process that utilizes nitrogen at 550° C. for 5 minutes. 
         [0040]      FIG. 6  illustrates an example formation of a dielectric  600  for isolation purposes.  FIG. 6  involves another process performed on previous  FIG. 5  and to this end, the previously defined materials, removed portions, and/or processes may not be shown again to simplify the presentation. 
         [0041]    For example, the formation of the dielectric  600  may involve depositing 500 nm of silicon dioxide (SiO2) with a uniform coverage on the top and step side walls of the resulting stack of LED layers or materials. In this example, the selection of particular dielectric material and process control is implemented to obtain low stress and step coverage. 
         [0042]      FIG. 7  illustrates an example etching of the formed dielectric  600  to expose metal contacts which may be patterned using a fifth mask, i.e., “mask layer  5 .”  FIG. 7  involves another process performed on previous  FIG. 6  and to this end, the previously defined materials, removed portions, and/or processes may not be shown again to simplify the presentation. 
         [0043]    In an implementation, a photolithographic process, a wet and/or dry etching processes may be used to selectively etch the dielectric  600  from the top surfaces of the resulting stack of LED layers. For example, a first opening width  700  defines a width of the etched dielectric  600  that exposes the metal contacts  400 . In this example, the first opening width may include about 20 um in measurement. 
         [0044]    In another example, a second opening width  702  defines a width of the etched dielectric  600  that exposes the metal contacts  500 . In this example, the second opening width  702  may be less than 100 um in measurement. 
         [0045]      FIG. 8  illustrates an example patterning of probe pads onto the metal contacts using a sixth mask, i.e., “mask layer  6 .”  FIG. 8  involves another process performed on previous  FIG. 7  and to this end, the previously defined materials, removed portions, and/or processes may are not discussed again to simplify the presentation. 
         [0046]    In an implementation, the probe pads may include a plurality of interface pads connected to the metal contacts  400  and  500 . For example, probe pads  800 - 2 ,  800 - 4 ,  800 - 6  and  800 - 8  may include the interface pads that are bonded with the metal contact  400 . In another example, the probe pad  802  may include the interface pad that is bonded with the metal contact  500 . 
         [0047]    To form the probe pads  800  and  802 , the following may be implemented: photolithography to expose regions where the probe pads may be formed; E-beam that utilizes 20 nm Ti/300 nm Al/200 nmNi/300 nm Au to form the bonding pads; and liftoff of the photoresist by organic solvents. 
         [0048]    With continuing reference to  FIG. 8 , the probe pads  800  may be disposed at each corner of the metal contact  400  while a single probe pad  802  may be disposed at the metal contact  500 . For example, the probe pads  800  and  802  may have a similar width of about 100 um. 
         [0049]      FIG. 9  illustrates an example of an optional step of electroplating of a solder bump. The solder bumps (not shown), for example, may be formed on top of the probe pads  800  and  802 . 
         [0050]    In general, structures of solder bumps may be formed by performing one or more deposition processes to deposit one or more layers of barrier materials (not shown) and/or seed layers, e.g., Ti/1 um Cu, a copper seed layer, etc. above the probe pads  800  and  802 . Thereafter, the solder bump structures may be subjected to one or more chemical mechanical planarization (CMP) processes to remove excess materials such as excess materials which are above 60 um in height. 
         [0051]    In an implementation, the formed stack of LED layers, metal contacts, and the probe pads may constitute a structure of an LED device. In this implementation, a testing of dies on the wafer is performed to generate a known good die (KGD) map. The KGD map may include KGD-LED components that may be combined to form a plurality of KGD-LED components as further discussed below. 
         [0052]      FIG. 10  illustrates an example process of thinning down, roughening, and singulating KGD-LED components  1000 . 
         [0053]    In certain implementations, the substrate  102  of the stack of LED layers may be maintained at its originally provided thickness. In other implementations, the substrate  102  may be thinned to a desired thickness. For example, the substrate  102  may be grinded down to a thickness of about 200 um and subsequently polished with grit 4000 to 8000 to roughen the sapphire surface (i.e., upper surface of the substrate  102 ) leaving or forming a surface roughness of 1-3 micrometers. In this example, the thinning and polishing may be performed before or after a partial or full singulation/dicing process. The roughening, for example, enhances light extraction through and out of the sapphire substrate  102 . 
         [0054]    With continuing reference to singulated KGD-LED component  1000  as shown in  FIG. 12 , the singulation may utilize laser scribing that utilizes 5 um precision and 15 um kerf. Before the singulation process is performed, the front side of the multiple KGD-LED components  1000  to be singulated may be coated and protected with photoresists. In other implementations, etching, sawing, lasing, or other conventional singulation technique may be utilized to produce singulated KGD-LED components  1000 - 2 ,  1000 - 4 ,  1000 - 6  and  1000 - 8 . 
         [0055]      FIG. 11  illustrates an example mounting substrate  1100  upon which the singulated KGD-LED components  1000  may be attached or mounted. The following process may be implemented to form the mounting substrate  1100 . For example, a growth substrate is mounted with conductive vias  1102  and  1104  to allow interconnection of the singulated KGD-LED components  1000  to other components, circuits, power supply, etc. (not shown). In this example, the mounting substrate  1100  may include re-distributed layers (RDL) (not shown) to provide electrical connections and/or to route or re-route the multiple electrodes of the KGD-LED components  1000  to positive (+) and negative (−) electrodes of the power supply. The positive and negative electrodes, for example, are illustrated by positive electrode  1102  and negative electrode  1104 , respectively. 
         [0056]      FIG. 12  illustrates an example multiple mounting configurations on a substrate floor plan. Each site, shown as a discrete square in  FIG. 12 , may be configured to accept the KGD-LED component  1000 . The KGD-LED component  100 , for example, may be derived through IC testing procedures. Thus, varying sizes of LED devices may be obtained by orienting multiple KDG-LED components  1000  in relatively close proximity, such as in a 1×2, 2×2, 3×3, 4×4 or any suitable matrix. 
         [0057]      FIG. 13  illustrates an example process of aligning and placing the KGD-LED components  1000  to the mounting substrate  1100  to form a plurality of joined KGD-LED components. 
         [0058]    In an implementation, the singulated KGD-LED components  1000  are aligned and bonded to the mounting substrate  1100 . In this example, the bonding may include soldering such as dipping a flux to the optional solder bump as described in  FIG. 9  above. In another implementation, the bonding and electrical connection may be achieved by a mass reflow process, which may be implemented according to the reflow profile of the solder (e.g., SAC 305 or eutectic solder SnPb 63/37). 
         [0059]      FIG. 14  illustrates an example process of filling gaps and spaces in between the mounted KDG-LED components  1000  and the mounting substrate  1100 . The gaps (i.e., gaps  1400 - 2 ,  1400 - 4 , etc.), for example, may include a length and/or width measurement that is large enough to facilitate free flowing of transparent under-filling materials  1402 . 
         [0060]    In an implementation, the transparent filling material  1402 , e.g., silicone or epoxy, SU-8, with or without filler may be inserted into the gaps  1400  that are located in between the mounted KGD-LED components  1000 . In this implementation, areas or spaces in between individual KGD-LED component  1000  may be filled as well with the transparent filling material  1402  to prevent voids. The gaps  1400 , for example may have about 100 um or less in measurement to make sure that no interruption in the under-filling of transparent filling material  1402  may arise in the process. 
         [0061]    For example, a commercially available under-filling material  1402  with 0.2 um size SiO 2  particles (n˜1.5) dispersed in an epoxy (n˜1.4) may be applied at once in the gaps  1400 . In this example, the under-filling material  1402  may have a refractive index close to a refractive index of the substrate  102  of the KGD-LED component  1000 . For example, a 1.78 refractive index that is close to the refractive index of the sapphire substrate  102  may be utilized as the under-filling transparent material  1402 . 
         [0062]    For extracting light emitted from sapphire side edges, the transparent filling material  1402  may include a roughened surface after curing process. Furthermore, a roughened upper surface  1404  at a planar surface of the thinned substrate  102  may be formed for further light extraction. 
         [0063]    As shown, a patterned lower surface  1406  is formed at an other planar side of the thinned substrate  102 . The patterned lower surface  1406  may be disposed in between the thinned substrate  102  and the n-type GaN  104 . 
         [0064]    In an implementation, the under-filling process may include small particles of metal oxide that may be interspersed within the epoxy matrix. For example, the transparent underfill material  1402  may be applied in a vacuum to ensure proper coverage and then may be cured in a pressurized oven. Once the epoxy or other material is cured, the entire surface may be plasma etched to increase surface roughness, thereby further enhancing the light extraction characteristics of the transparent underfill material  1402 . 
         [0065]    With continuing reference to  FIG. 14 , a multi-layer RDL  1408  (or RDL  1408 ) may facilitate connection of multiple KGD-LED components  1000  to other components, power sources, circuits, or devices. For example, the RDL  1408  may facilitate series and/or parallel connections between the KGD-LED components  1000  to a particular circuitry. In this example, the series and/or parallel connections may be based upon desired intensity of the KGD-LED components  200  because amount of currents may be manipulated through series and/or parallel connections. 
         [0066]      FIG. 14  further illustrates a multiple under bump metallization (UBM) layer  1410  that is electrically connected to the probe pads  800 . The probe pads  800 , for example, may include reflective electrical conductor. The probe pads  800 , in this example, may be coupled to the UBM layer  1410  through a solder  1410 . 
         [0067]      FIG. 15  shows an example process flowchart  1500  illustrating an example method for joining multiple KGD-LED components in a device. The order in which the method is described is not intended to be construed as a limitation, and any number of the described method blocks may be combined in any order to implement the method, or alternate method. Additionally, individual blocks may be deleted from the method without departing from the spirit and scope of the subject matter described herein. Furthermore, the method may be implemented in any suitable hardware, software, firmware, or a combination thereof, without departing from the scope of the invention. 
         [0068]    At block  1502 , testing a wafer for KGD-LED component is performed. For example, the KGD-LED component  1000  includes a thinned substrate  102  with a rough upper surface and a patterned lower surface. In this example, the rough upper surface (i.e., about 0.3-3 um in roughness) is disposed on exposed planar surface of the substrate  102  while the patterned lower surface is disposed in between the other planar surface (i.e., opposite side of the rough surface) of the substrate  102  and the n-type GaN  104 . The rough surface is utilized, for example, for light extraction while the patterned surface may be utilized to correspond to a desired light wavelength such as 450 nm for blue or 550 nm for green. 
         [0069]    At block  1504 , flip chip bonding of KGD-LED component onto a substrate is performed. For example, multiple KGD-LED components  1000  are mounted into the mounting substrate  1100 . In this example, the mounting substrate  1100  may include the RDL  1408  that facilitates series and/or parallel connections between the mounted KGD-LED components  1000  and a power source of another circuits or operating device. 
         [0070]    At block  1506 , under-filling a gap and spaces in between the KGD-LED components with a transparent material is performed. For example, the transparent filling material, e.g., silicone or epoxy, SU-8, w/ or w/o filler may be inserted into the gaps  1400  and spaces that are located in between the mounted KGD-LED components  1000 . In this example, the transparent filling material covers the gap and spaces in between KGD-LED components  1000  at once to prevent voids. The gaps  1400 , for example may have about 100 um or less in measurement to make sure that no interruption in the under-filling flow may arise in the process. 
         [0071]    After curing of the formed transparent material, a surface of the formed transparent material is roughened. Furthermore, the formed transparent material is configured to include a refractive index that is close to a refractive index of the thinned substrate  102 .