Patent Application
20070012939
The application claims the benefit of Korea Patent Application No. 2005-0036958 filed with the Korea Industrial Property Office on May 3, 2005, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a flip chip light emitting diode and a method of manufacturing the same, and more specifically, to a flip chip light emitting diode in which a plurality of mesas for forming an n-type electrode are formed, a plurality of grooves are formed by etching predetermined regions between the mesas, and a large amount of current is accordingly caused to flow into the center of a light emitting section to thereby obtain a current-spreading effect, and a method of manufacturing the same.
2. Description of the Related Art
In general, a light emitting diode (LED) is such an element that converts an electrical signal into the form of infrared rays, ultraviolet rays or light so as to send and receive signals by using the characteristics of a compound semiconductor such as the recombining of electrons and holes.
A light emitting diode is generally used in home appliances, remote controls, electronic display boards, markers, automation equipments, optical communication devices, and the like. The light emitting diode is roughly divided into an IRED (infrared emitting diode) and VLED (visible light emitting diode).
In a light emitting diode, the frequency (or wavelength) of emitted light is utilized as a band-gap function of a material used in the semiconductor device. When a semiconductor material having a small band gap is used, a photon having low energy and a long wavelength is generated. When a semiconductor material having a large band gap is used, a photon having a short wavelength is generated. Accordingly, a semiconductor material is selected according to the type of light which is desired to be emitted.
In the case of a red light emitting diode, a material such as AlGaInP is used. In the case of a blue light emitting diode, silicon carbide (SiC) and gallium nitride (GaN) as a nitride semiconductor of the group III are used. Recently, as a nitride semiconductor used in a blue light emitting diode, (AlxIn1-x)yGa1-yN (0<x<1 and 0<y<1) has been widely used.
Among them, since bulk single-crystal GaN cannot be formed in a gallium-base light emitting diode, a substrate suitable for the growth of GaN crystal should be used. Sapphire is representatively used.
In the GaN light emitting structure 8, a p-type nitride semiconductor layer 4 and an active layer 3 are mesa-etched to expose a portion of the upper surface of an n-type nitride semiconductor layer 2. On the exposed upper surface of the n-type nitride semiconductor layer 2 and the unetched upper surface of the p-type nitride semiconductor layer 4, a p-type electrode 6 and an n-type electrode 7 are respectively formed so as to apply a predetermined voltage. In general, in order not to have a bad influence on the brightness of light generated while increasing a current injection area, a transparent electrode 5 can be formed on the upper surface of the p-type nitride semiconductor layer 4 before the p-type electrode 6 is formed.
In the GaN-based light emitting diode having such a construction, a light emitting diode package can be manufactured through a die bonding process by a chip-side-up method. In this case, light emits in the direction where the p-type electrode 6 and the n-type electrode 7 are formed. In the portion where the electrodes 6 and 7 are formed, light cannot be emitted. Further, the radiation of heat generated in a chip when light is emitted is reduced due to low heat conductivity of sapphire, thereby reducing the lifetime of the light emitting diode.
In order to solve the problems, the GaN-based light emitting diode can be constructed in the form of a flip chip in which the light emitting diode 9 of
In such a flip chip light emitting diode, predetermined regions of the grown active layer and p-type nitride semiconductor layer are etched to expose a plurality of regions of the n-type nitride semiconductor layer, in order to form more than one n-type electrode. In this case, the exposed portion is referred to as a mesa. On the mesa, the n-type electrode and insulating body are formed to thereby manufacture a light emitting diode chip.
In the above-described flip chip light emitting diode according to the related art, however, the length of the current path increases as the current path is gradually distant from the n-type electrode. Then, the resistance of N—GaN increases. As a result, electric current is concentrated and flows in a portion adjacent to the n-type electrode, thereby reducing a current-spreading effect.
An advantage of the present invention is that it provides a flip chip light emitting diode in which an active layer and a p-type nitride semiconductor layer are etched so that an n-type nitride semiconductor layer in a light emitting structure positioned between mesas is exposed to form a plurality of grooves and an insulating layer is formed on the surface of the groove so as to induce the flow of current to the center portion, thereby improving the light emission efficiency of the center portion of a light emitting diode chip, and a method of manufacturing the same.
Another advantage of the invention is that it provides a flip chip light emitting diode in which, when the plurality of grooves are formed, intervals between the grooves are designed to change so that a large amount of current, which has been concentrated toward an n-type electrode in the related art, can flow into the center of a light emitting section, thereby obtaining a current spreading effect, and a method of manufacturing the same.
Additional aspects and advantages of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept.
According to an aspect of the invention, a method of manufacturing a flip chip light emitting diode includes sequentially forming an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer on an optically-transparent substrate; etching predetermined regions of the active layer and p-type nitride semiconductor layer and exposing a plurality of regions of the n-type nitride semiconductor layer so as to form a plurality of mesas; etching predetermined regions of the active layer and p-type nitride semiconductor layer positioned between the formed mesas and exposing the plurality of regions of the n-type nitride semiconductor layer so as to form a plurality of grooves; forming an insulating layer on the surface of the groove; forming a p-type electrode across the insulating layer formed on the upper portion of the p-type nitride semiconductor layer and the surface of the groove; and forming an n-type electrode on the formed mesa.
In forming the mesas or forming the grooves, etching is performed by an RIE method.
In forming the mesas or forming the grooves, the predetermined regions of the active layer and p-type nitride semiconductor layer are etched.
In forming the grooves, etching is performed so that the width of the groove corresponds to the range of 1 to 50 μm.
In forming the grooves, etching is performed so that intervals between the plurality of grooves are reduced as the intervals approach the mesa.
In forming the grooves, etching is performed so that an angle between the bottom and side surfaces of the groove is in the range of 90° to 165°.
In forming the p-type electrode, p-type ohmic metal, barrier metal, and bonding metal are sequentially laminated.
In forming the n-type electrode, n-type ohmic metal is laminated.
According to another aspect of the invention, a flip chip light emitting diode includes an optically-transparent substrate; a light emitting structure that is formed by sequentially forming an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer on the substrate, the light emitting structure including: a plurality of mesas that are formed by exposing a plurality of regions of the n-type nitride semiconductor layer so that the regions have a predetermined width; and a plurality of grooves that are formed by exposing a plurality of regions of the n-type nitride semiconductor layer positioned between the mesas so that the regions have a predetermined width; a groove insulating layer that is formed across the surface of the groove of the light emitting structure; a p-type electrode that is formed across the insulting layer formed on the upper portion of the p-type nitride semiconductor layer and the surface of the groove in the light emitting structure; and an n-type electrode that is formed on the plurality of mesas of the light emitting structure.
The light emitting structure is formed by the reactive ion etching (RIE) of the active layer and p-type nitride semiconductor layer.
The width of the groove positioned in the light emitting structure is in the range of 1 to 50 μm.
The plurality of grooves formed in the light emitting structure are formed so that the intervals between the grooves are reduced as the intervals approach the mesa on which the n-type electrode is formed.
The plurality of grooves formed in the light emitting structure are formed so that an angle between the bottom and side surfaces of the groove is in the range of 90° to 165°.
The p-type electrode is formed by sequentially laminating p-type ohmic metal, barrier metal, and bonding metal.
The n-type electrode is formed by laminating n-type ohmic metal.
These and/or other aspects and advantages of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept by referring to the figures.
Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.
The light emitting structure 44, which is formed by sequentially laminating the n-type nitride semiconductor layer 31, the active layer 32, and the p-type nitride semiconductor layer 33 on the sapphire substrate 30 used as an optically-transparent substrate, can be manufactured by using a MOCVD (metal organic chemical vapor deposition) method or the like. In the MOCVD method, a material composed of a volatile alkyl compound which is an organic metal compound of the group III and a hydrogen compound of the group V is vapor-thermally decomposed into a III-V group compound. Such a method is preferably used in manufacturing a high-brightness light emitting diode, because a very thin growth layer corresponding to the MBE level can be grown and a thin film with good quality can be reproduced and mass-produced, even though the used material is poisonous and explosive. At this time, before the n-type nitride semiconductor layer 31 is grown, a buffer layer (not shown) composed of AIN/GaN can be formed, in order to improve the lattice matching with the sapphire substrate 30.
In general, the active layer 32 has such structures as a double hetero structure and a single or multi quantum well structure. In the double hetero structure, the active layers 32 of a light emitting region are grown to have a thickness of 10 to 100 nm, and a donor and acceptor are co-doped so that the active layers are radiatively recombined from the donor-acceptor pair (DAP). In the single or multi quantum well structure, light emitting layers are manufactured with a thickness of 1 to 10 nm so as to form a quantum well structure and thus are radiatively recombined through the band-to-band transition. It is preferable to manufacture a thin light emitting diode having a quantum structure in which the thickness of the active layer 32 does not exceed a pseudomorphic critical layer thickness where an electric potential is not generated due to dislocation caused by the lattice mismatch between respective semiconductor thin layers.
The mesa formed in the light emitting structure 41 is formed as follows: the active layer 32 and the p-type nitride semiconductor layer 33 are grown across the overall portion of the n-type nitride semiconductor layer 31, and predetermined regions of the grown active layer 32 and p-type nitride semiconductor layer 33 are etched. In the mesa formed in such a manner, the n-type electrode 39 is positioned. Further, predetermined regions of the active layers and p-type nitride semiconductor layers positioned between the mesas are etched to thereby form the plurality of grooves.
As an etching method when the mesas and grooves are formed, an RIE method is preferably used. In the RIE method, the mesa and groove can be accurately etched to have a desired shape, compared with a wet etching method. Further, an angle with respect to the cross-section of the mesa and groove, which will be described below, can be easily adjusted to thereby improve light emission efficiency.
On the other hand, a portion of an insulating body as well as the n-type electrode can be formed on the mesa, the insulating body protecting a light emitting diode. In this case, the mesa needs to have a width of 25 to 50 μm, because the width of the n-type electrode corresponds to 15 to 30 μm and the width of the portion of the insulating body corresponds to 10 to 20 μm.
On each surface of the plurality of grooves formed in the light emitting structure 41, the groove insulating layer 34 is formed, by which the flow of current concentrated on a portion close to the n-type electrode 39 can be dispersed into the center portion thereof which is distant from the n-type electrode 39. Preferably, the groove insulating layer 34 can be formed of SiO2. In addition to that, an insulating material such as Si3N4, Al2O3, or the like can be used.
The p-type electrode 38 includes the p-type ohmic metal 35, the barrier metal 36, and the bonding metal 37, which are sequentially laminated across the upper surface of the p-type nitride semiconductor layer 33 and the insulating layer 34 formed on the groove.
The p-type ohmic metal 35 is formed of a material selected from a group composed of Pt, Rh, Pd/Ni/Al/Ti/Au, Ni—La solid solution/Au, Pd/Au, Ti/Pt/Au, Pd/Ni, Zn—Ni solid solution/Au, InGaN, Ni/Pd/Au, Ni—La solid solution/Au, Pd/Au, Ti/Pt/Au, Pd/Ni, Pt/Ni/Au, Ta/Ti, Ru/Ni, and Au/Ni/Au.
The barrier metal 36 is laminated, in order to prevent metal for ohmic contact and the uppermost metal layer for wiring from being alloyed. The barrier metal 36 can be typically formed of an alloy of Cr/Ni or Ti and W.
The bonding metal 37 is bonded to an electrode formed on a silicon submount (refer to
On the other hand, the n-type electrode 39 formed on the mesa which is formed by mesa-etching has the n-type ohmic metal laminated therein. The n-type ohmic metal is formed of a material selected from a group composed of Ti/Ag, Ti/Al, Pd/Al, Ni/Au, Si/Ti, ITO, Ti/Al/Pt/Au, ITO/ZnO, Ti/Al/Ni/Au, and Al.
The upper portions of the p-type electrode 38 and n-type electrode 39 are protected by an insulating body composed of a transparent nonconductor film. In this case, a portion of the insulating body is etched so that portions or the overall electrodes 38 and 39 are exposed. In other words, the insulating body is etched in the substantially same form (where the insulating body has the substantially same width and length as those of the electrodes) as the electrodes in the position corresponding to the formed electrodes 38 and 39.
The groove 40 is etched so that the width d of the groove 40 corresponds to the range of 1 to 50 μm. If the groove 40 is etched so that the width d of the groove 40 is larger than 50 μm, a portion of the entire light emitting area, occupied by the groove 40 which does not contribute to the light emission, becomes so wide that the light emission efficiency is reduced. Therefore, it is preferable that the width d of the groove 40 should be less than 50 μm.
As shown in
In a general flip chip light emitting diode, the resistance of the n-type nitride semiconductor layer 31 increases as it becomes distant from the n-type electrode 39, so that electric current is concentrated and flows in a portion adjacent to the n-type electrode 39. As in the embodiment of the invention, when the intervals between the grooves formed of an insulating body are gradually narrowed as they approach the n-type electrode 39, the cross-sectional area of the current path in a portion adjacent to the n-type electrode 39 is reduced due to the groove insulating layer 34, and the resistance of the portion adjacent to the n-type electrode 39 is increased due to a resistance effect. Accordingly, the overall resistance of the light emitting section becomes averagely constant. Therefore, electric current spreads and flows into the overall light emitting section, thereby obtaining the current-spreading effect. The resistance effect can be defined by the following equation:
R=ρl/S(R: resistance [Ω], ρ: specific resistance[Ωcm], l: length [m], S: cross-sectional area [m2]). Since the cross-sectional area of the current path is reduced, the resistance of the portion adjacent to the n-type electrode 39 is increased by the above equation.
As shown in
That is, the manufacturing method includes a cleaning process (S1) in which contaminants on a wafer are removed, an activation process (S2) in which cathodic treatment for discharging or increasing electrons is performed and P—GaN, the n-type nitride semiconductor layer, and the active layer are grown, a forming process (S3) in which the mesas and grooves are formed, a forming process (S4) in which the insulating layer is formed on the surface of the formed groove, forming processes (S5 to S7) in which the p-type electrode is formed across the upper portion of the p-type nitride semiconductor layer and the insulating layer formed on the surface of the groove, that is, in which the p-type ohmic metal is formed, the barrier metal is formed on the p-type ohmic metal, and the boding metal is formed on the barrier metal, a forming process (S8) in which the n-type electrode is formed on the mesa, that is, the n-type ohmic metal is formed, an etching process (S9) in which, after the upper portions of the p-type and n-type nitride semiconductor layers in which the p-type and n-type electrodes are formed are insulated, etching is performed so that predetermined regions of the p-type and n-type electrodes are exposed. Through the manufacturing method, a light emitting diode chip according to the present invention is completed.
The mesas and grooves are formed through a cleaning process, a photo process, an etching process, a stripping process, and a thickness adjusting process. The p-type ohmic metal, the n-type ohmic metal, the barrier metal, and the bonding metal are formed through a cleaning process, a photo process, preprocessing, a lift-off process, and an annealing process. The groove insulating layer and the insulating layer are formed through a cleaning process, a photo process, an etching process, a stripping process, and a cleaning process.
The n-type ohmic metal is formed the same as the p-type ohmic metal is formed (not shown).
According to the flip chip light emitting diode and the method of manufacturing the same, predetermined regions of the grown active layer and p-type nitride semiconductor layer positioned between the mesas are etched, a plurality of regions of the n-type nitride semiconductor layer are exposed outside to form the plurality of grooves, and the insulating layer is formed on the surface of the groove to thereby induce the flow of current to the center portion. Further, the plurality of grooves are formed so that intervals between the grooves are designed to be gradually narrowed as they approach the n-type electrode, thereby reducing the cross-section of the current path. As a result, a large amount of current, which has been concentrated toward the n-type electrode in the related art, can flow into the center of the light emitting section, which makes it possible to obtain a current-spreading effect.
While the present invention has been described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications in form and detail may be made therein without departing from the scope of the present invention as defined by the following claims.
According to the flip chip light emitting diode and the method of manufacturing the same, predetermined regions between the mesas as well as the mesas are etched to form the plurality of grooves, and the insulating layer is formed thereon, which makes it possible to induce the flow of current to the center of the light emitting section.
Furthermore, the plurality of grooves are formed so that intervals between the grooves are designed to be gradually narrowed as they approach the n-type electrode, thereby reducing the cross-section of the current path. As a result, a large amount of current, concentrated toward the n-type electrode, can flow into the center of the light emitting section, which makes it possible to obtain a current-spreading effect.
Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2005-0036958 | May 2005 | KR | national |
