Abstract:
An improved method of creating LEDs is disclosed. Rather than using a dielectric coating to separate the bond pads from the top surface of the LED, this region of the LED is implanted with ions to increase its resistivity to minimize current flow therethrough. In another embodiment, a plurality of LEDs are produced on a single substrate by implanting ions in the regions between the LEDs and then etching a trench, where the trench is narrower than the implanted regions and positioned within these regions. This results in a trench where both sides have current confinement capabilities to reduce leakage.

Description:
[0001]    This application claims priority of U.S. Provisional Patent Application Ser. No. 61/327,931, filed Apr. 26, 2010, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     FIELD 
       [0002]    This invention relates to fabrication of light emitting diodes (LEDs) and, more particularly, to ion implantation of LEDs. 
       BACKGROUND 
       [0003]    Ion implantation is a standard technique for introducing conductivity-altering impurities into a workpiece. A desired impurity material is ionized in an ion source, the ions are accelerated to form an ion beam of prescribed energy, and the ion beam is directed at the surface of the workpiece. The energetic ions in the beam penetrate into the bulk of the workpiece material and are embedded into the crystalline lattice of the workpiece material to form a region of desired conductivity. 
         [0004]    LEDs are built on a substrate and are doped with impurities to create a p-n junction. A current flows from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction. Electrons and holes flow into the p-n junction from electrodes with different voltages. If an electron meets a hole, it falls into a lower energy level and releases energy in the form of a photon. The wavelength of the light emitted by the LED and the color of the light may depend on the band gap energy of the materials forming the multiple quantum well (MQW). 
         [0005]      FIG. 6  is a cross-sectional side view of a vertical LED structure. The LED  700  has p electrodes (or p mirrors)  701  (illustrated by the hash marks). These p electrodes  701  function as a p-ohmic contact and/or an optical reflection mirror. In other words, the p electrodes  701  serve to reflect light back toward the upper surface (i.e. above the n-type layer  705 ). 
         [0006]    A p-type layer  703  is disposed on the p electrodes  701 . A multiple quantum well (MQW)  704  is disposed on the p-type layer  703 . An n-type layer  705  is disposed on the MQW  704 . Finally, n electrodes  706  are disposed on the n-type layer  705 . This LED  100  may be mounted on a metal alloy in one instance. The p-type layer  703  and n-type layer  705  may be, for example, GaN or AlGaInP. The MQW  704  may be GaInN or AlGaInP. 
         [0007]    Some LED structures have optical reflection problems while others have leakage current problems. Dielectric coatings  710 , such as SiO 2  or SiN x , have been used as isolation layers or to isolate bond pads  711  within LEDs. For example, such a dielectric coating  710  may be formed under the bond pads, as shown in  FIG. 6 . These dielectric coatings  710  also have been formed around mesa perimeters for current confinement. This dielectric coating  710  forces the current toward the electrodes  706  and away from the bond pads  711 , because the bond pads  711  tend to block the light that is being emitted. However, formation of a dielectric coating  710  may lower LED manufacturing throughput and add cost and complexity to manufacturing. 
         [0008]    Accordingly, there is a need in the art for an improved LED structure and methods of LED ion implantation. 
       SUMMARY 
       [0009]    An improved method of creating LEDs is disclosed. Rather than using a dielectric coating to separate the bond pads from the top surface of the LED, this region of the LED is implanted with ions to increase its resistivity to minimize current flow therethrough. In another embodiment, a plurality of LEDs are produced by implanting ions to generate isolation regions first between the individual LEDs and then fabricate mesas, where the trench of mesa etch is narrower than the implanted regions and positioned within these regions. This results in a trench where both sides have current confinement capabilities to reduce leakage. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    For a better understanding of the present disclosure, reference is made to the accompanying drawings, which are incorporated herein by reference and in which: 
           [0011]      FIGS. 1A-C  are cross-sectional side views of a first embodiment of ion implantation into an vertical structure LED; 
           [0012]      FIG. 2  is a top perspective view of a vertical LED; 
           [0013]      FIG. 3  is a cross-sectional side view of an embodiment of a flip chip LED; 
           [0014]      FIG. 4  is a cross-sectional side view of an embodiment of a p-side up lateral structure LED; 
           [0015]      FIGS. 5A-C  are cross-sectional side views of a second embodiment of ion implantation into an LED; 
           [0016]      FIG. 6  is a cross-sectional side view of a vertical LED of the prior art. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The method is described herein in connection with ion implantation of LEDs. However, the method can be used with other semiconductor manufacturing processes. A beam-line ion implanter, plasma doping ion implanter, or other ion implantation system known to those skilled in the art may be used in the embodiments described herein. Furthermore, the embodiments described herein may apply to vertical LEDs, lateral LEDs, flip chip LEDs, p-side up LEDs, or other LED architectures known to those skilled in the art. Thus, the invention is not limited to the specific embodiments described below. 
         [0018]    Ion implantation may be used to improve current confinement or reduce leakage through a sidewall of an LED. This may improve the current and light efficiency of the LED. Ion implantation also may isolate a bond pad or confine current to an effective emission area by isolating the semiconductor under the bond pads. Consequently, an improved LED may be manufactured using ion implantation. 
         [0019]      FIG. 1A  is a cross-sectional side view of a first embodiment using ion implantation to create isolation within an LED. This embodiment is used in conjunction with a vertical LED with the N side up. The LED  100  has a p-type layer  101  disposed on a multiple quantum well (MQW)  102 . The MQW  102  is disposed on an n-type layer  103 , which in turn is disposed on a substrate  104 . Various methods of creating such a LED are well known and will not be described herein. The p-type layer  101  and n-type layer  103  may be, for example, GaN or AlGaInP. In one particular embodiment of  FIG. 1A , the LED  100  may be one mesa. 
         [0020]    In  FIG. 1A , a mask  106  has been placed on the p-type layer  101 . This mask  106  may be a hard or soft mask on the LED  100  made of, for example, photoresist, an oxide, or a metal. In an alternate embodiment, the mask  106  is a shadow mask or stencil mask that is upstream of the LED  100 , between the ions  105  and the LED  100 , and may or may not be disposed directly on the LED  100 . After placement of the mask  106 , ions  105  are implanted into the LED  100 . The ions  105  may be implanted at, for example, a current of between approximately 50 μA to 10 mA and an energy of between approximately 10 eV to 5 MeV, although other currents and energies may be used. These ions  105  may be, for example, H, N, He, Ar, O, Cr, Fe, Ne, F, Ti, C, B, P, Si, or other species known to those skilled in the art. The ions  105  are implanted into the LED  100  in areas exposed by the mask  106 . Thus, the mask  106  prevents implantation in the regions beneath the mask  106 . 
         [0021]    Implant regions  107  (shaded black in  FIG. 1 ) are formed using the ions  105  and mask  106 . These implant regions  107  may be at a depth such that ions are implanted into both the p-type layer  101  and MQW  102 . The energy of the ions  105  may be configured to enable the desired implant depth. Higher implant energy typically means a greater implant depth. 
         [0022]    The ions  105  change the resistivity within the implant regions  107  in the LED  100 . This resistivity in one instance increases by approximately five orders of magnitude. Therefore, the implanted regions  107  will not conduct current as well as the other regions of the LED  100 . These implant regions  107  may be around the mesa or die perimeter or in the region where the bond pad will be located to confine current within the effective device emission area of the LED  100  to improve efficiency of the LED  100 . 
         [0023]    In  FIG. 1B , the LED  100  in  FIG. 1A  has been turned over, and the substrate  104  has been removed. The LED  100  is then placed on a p mirror (or p electrode)  109 , and a second mask  108  has been applied to the n-type layer  103 . This second mask  108  may be a hard or soft mask on the LED  100 , but in an alternate embodiment, the second mask  108  is a shadow mask or stencil mask that is upstream of the LED  100  and may or may not be disposed directly on the LED  100 . Ions  112  are implanted into the regions of the LED  100  exposed by the mask  108 . The ions  109  may be the same as the ions  105  in  FIG. 1A . This may extend the implant regions  107  into the n-type layer  103 . 
         [0024]    In  FIG. 1C , at least one n-finger electrode  110  has been applied to the n-type layer  103  in the LED  100 . In addition, at least one bond pad  111  (shown in crosshatch) has been applied to the n-type layer  103 . The implant regions  107  provide electron confinement within the LED  100 . Furthermore, the implant regions  107  are located beneath the bond pads  111 , thereby forcing the current away from the portions of the LED  100  beneath the bond pads  111 , where emitted light would be blocked by the bond pad  111 . 
         [0025]    In an alternate embodiment, a single or chained implant of ions  105  at a higher energy than illustrated in  FIG. 1A  may form implant regions  107  in the p-type layer  101 , MQW  102 , and n-type layer  103 . 
         [0026]    In yet another alternate embodiment, a single or chained implant of ions  112  at a higher energy than illustrated in  FIG. 1B  may form implant regions  107  in the n-type layer  103 , MQW  102  and p-type layer  101 . 
         [0027]    In other embodiments, a single or chained implant, such as is shown in either  FIG. 1A  or  FIG. 1B , is performed so as to create implant regions  107  in the MWQ  102 , and in one of the p-type layer  101  or the n-type layer  103 . In other words, the implant regions  107  may be in the p-type layer  101  and the MQW  102  (in the case of  FIG. 1A ) or in the n-type layer  103  and the MQW  102  (in the case of  FIG. 1B ). In these embodiments, the other layer is not implanted. 
         [0028]      FIG. 2  is a top perspective view of an LED  120 . A metal frame  125  includes bond pad regions  126  and finger electrodes  127 . The metal frame  125  has multiple finger electrodes  127 , which are disposed on the exposed surface of the LED  120 . Bond pads may be attached to the metal frame  125 , such as along one or more edges. These bond pads may tend to block any light being emitted by the LED  120  in the regions below the bond pad. Therefore, implanted regions  107  (shown in crosshatch) are created in the regions beneath the outer edge of the metal frame  125 . Thus, after the bond pads are attached, current is forced through the metal frame  125  toward the finger electrodes  127 , where the regions below have not been implanted. By using ion implantation to create implant regions  107 , it is not necessary to deposit a dielectric coating on the top surface of the LED  120  to isolate the bond pad regions  126  from the top surface. 
         [0029]    Therefore, the LED is made by creating a device having a p-type layer  101 , a MQW  102  and the n-type layer  103 . One or more ion implants is performed to introduce ions into the MQW  102  and at least one of the n-type layer  103  and the p-type layer  101 . These implants create implant regions  107  through which isolate the current flowing through. These implant regions  107  are introduced into regions of the device where the bond pads will be attached at a later step of the manufacturing process. The metal frame  125  is then attached to the top of the device, without the use of a dielectric coating. As noted above, the dielectric coating is not needed since the implanted regions  107  are directly beneath the bond pads and do not conduct current well. This forces the current passing through the metal frame  125  to flow through the finger electrodes  127 . This improves the current distribution and improves light efficiency. 
         [0030]      FIG. 3  is a cross-sectional side view of an embodiment of a flip chip LED. The LED  130  has an n-type layer  103  disposed on the MQW  102 . The p-type layer  101  is disposed between the MQW  102  and p mirror (or p electrode)  109 . This flip chip LED may be manufactured using techniques similar to those used in  FIG. 1 . Ions are implanted at an energy so that implant regions  107  are formed on either side of the p-type layer  101  and MQW  102 . This implant is preferably performed prior to the attachment of the p mirror  109 . These implant regions  107  provide electron confinement within the LED  130 . 
         [0031]      FIG. 4  is a cross-sectional side view of an embodiment of a p-side up lateral LED. The LED  140  has an n-type layer  103  disposed on the substrate  104 . An MQW  102  is disposed on the n-type layer  103  and the p-type layer  101  is disposed between the MQW  102  and a transparent-conductive layer (TCL)  113 . This LED may be manufactured using techniques similar to those used in  FIG. 1 . A bond pad  121  sits on this TCL  113 . Implant regions  107  are formed on either side of the p-type layer  101  and MQW  102  but could also be any depth into the layer stack of LED. In this particular embodiment, one implant region  107  is formed in the region under the bond pad  121  and has an approximately similar width as the bond pad  121  or slightly wider than the bond pad  121 , as was shown in  FIG. 2 . These implant regions  107  provide electron confinement within the LED  140 . The implant regions  107  also may isolate the bond pad  121 . Isolating the bond pad  121  will prevent current from running through the LED  140  in areas covered by the bond pad  121 , which may be opaque. Thus, the current may be forced into the effective emission areas of the LED  140  and the efficiency of the LED  140  may be improved. 
         [0032]      FIGS. 5A-C  are cross-sectional side views of a second embodiment of ion implantation into an LED. In  FIG. 5A , the n-type layer  103  in LED  150  is disposed on the substrate  104 . An MQW  102  is disposed on the n-type layer  103  and the p-type layer  101  is disposed on the MQW  102 . A mask  106  has been placed on the p-type layer  101 . This mask  106  may be a hard or soft mask on the LED  150 , but in an alternate embodiment, the mask  106  is a shadow mask or stencil mask that is upstream of the LED  150  and may or may not be disposed directly on the LED  150 . Ions  114  are implanted into the LED  150  to form the implanted regions  107 . These ions  114  may be, for example, H, N, He, Ar, O, Cr, Fe, Ne, F, Ti, or other species known to those skilled in the art. The ions  114  are implanted into the LED  150  in areas exposed by the mask  106  and form the implant regions  107 . Thus, the mask  106  prevents implantation of ions  114  under the mask  106 . These implant regions  107  provide electron confinement within the LED  150 . This step may be performed in the fabrication of both vertical and lateral LEDs. 
         [0033]      FIG. 5B  depicts a subsequent processing step in the creation of a lateral LED. In  FIG. 5B , a mesa etch is performed form the lateral LED. This etching process forms trenches  155 . This operation is performed such that part of the implanted regions  107  is etched away, while leaving some portion of the implanted regions  107  on either side of the trench  155 . In other words, the trench  155  is narrower than the implanted region  107 , and positioned within that implanted region  107 . The trenches  155  extend downward to at least the depth of the implanted region  107 , but may go deeper into the n-type layer  103 . A portion of the implanted regions  107  remains on the side of the mesas  119  with the implanted regions  107  removed at the bottom of the trenches  155 . This creates implanted sidewalls on either side of the trench  155  using a single or chained ion implant while having the bottom still conducting for n electrode contact. 
         [0034]      FIG. 5C  depicts a subsequent processing step in the creation of a vertical LED. In  FIG. 5C , a mesa etch occurs to form a vertical LED. This may be a second etch performed after that shown in  FIG. 5B  or may be a single etch to the depth illustrated in  FIG. 5C . The trenches  155  are etched through the n-type layer  103 . Part of the implanted regions  107  are etched away, but a portion of the implanted regions  107  remain on the side of the mesas  119  or on the surfaces of the trenches  155 . In other words, the trench  155  is narrower than the implanted region  107 , and positioned within that implanted region  107 , as described above. 
         [0035]    Ion implantation confinement or bond pad isolation forms bulk volumes around or inside a mesa or LED that may keep current away from a sidewall or from the shadows under bond pads. This may improve LED performance. Implantation also may eliminate isolation layers under a bond pad, which may be a dielectric coating. Removing this isolation layer may improve LED integrity and reliability and reduce manufacturing costs. Current confinement along the mesa or LED perimeter may provide leakage current isolation and provide current confinement in the bulk of the LED. This also improves LED integrity and reliability. 
         [0036]    The implants used in the embodiments disclosed herein may have different profiles. For example, a Gaussian profile may be formed using a single dose implant. A box profile may be formed using a multiple dose implant. Other implant profiles may be formed by varying the parameters of the implant or the anneal. 
         [0037]    The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Furthermore, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. 
         [0038]    Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.