WO2007007980A1 - Light emitting diode device comprising a diffusion barrier layer and method for preparation thereof - Google Patents
Light emitting diode device comprising a diffusion barrier layer and method for preparation thereof Download PDFInfo
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- WO2007007980A1 WO2007007980A1 PCT/KR2006/002653 KR2006002653W WO2007007980A1 WO 2007007980 A1 WO2007007980 A1 WO 2007007980A1 KR 2006002653 W KR2006002653 W KR 2006002653W WO 2007007980 A1 WO2007007980 A1 WO 2007007980A1
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- Prior art keywords
- light emitting
- emitting diode
- layer
- electrically conductive
- binder
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- 238000009792 diffusion process Methods 0.000 title claims description 34
- 230000004888 barrier function Effects 0.000 title claims description 25
- 238000002360 preparation method Methods 0.000 title description 2
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- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 claims description 17
- 229910052737 gold Inorganic materials 0.000 claims description 17
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- 229910001218 Gallium arsenide Inorganic materials 0.000 description 1
- 229910000673 Indium arsenide Inorganic materials 0.000 description 1
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- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/36—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the electrodes
- H01L33/40—Materials therefor
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- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/005—Processes
- H01L33/0093—Wafer bonding; Removal of the growth substrate
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- H—ELECTRICITY
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- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
- H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
- H01L2224/42—Wire connectors; Manufacturing methods related thereto
- H01L2224/44—Structure, shape, material or disposition of the wire connectors prior to the connecting process
- H01L2224/45—Structure, shape, material or disposition of the wire connectors prior to the connecting process of an individual wire connector
- H01L2224/45001—Core members of the connector
- H01L2224/45099—Material
- H01L2224/451—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and polonium (Po), and alloys thereof
- H01L2224/45138—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and polonium (Po), and alloys thereof the principal constituent melting at a temperature of greater than or equal to 950°C and less than 1550°C
- H01L2224/45144—Gold (Au) as principal constituent
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- H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
- H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
- H01L2224/42—Wire connectors; Manufacturing methods related thereto
- H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
- H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
- H01L2224/4805—Shape
- H01L2224/4809—Loop shape
- H01L2224/48091—Arched
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- H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
- H01L2224/42—Wire connectors; Manufacturing methods related thereto
- H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
- H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
- H01L2224/484—Connecting portions
- H01L2224/48463—Connecting portions the connecting portion on the bonding area of the semiconductor or solid-state body being a ball bond
- H01L2224/48465—Connecting portions the connecting portion on the bonding area of the semiconductor or solid-state body being a ball bond the other connecting portion not on the bonding area being a wedge bond, i.e. ball-to-wedge, regular stitch
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- H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
- H01L2224/42—Wire connectors; Manufacturing methods related thereto
- H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
- H01L2224/49—Structure, shape, material or disposition of the wire connectors after the connecting process of a plurality of wire connectors
- H01L2224/491—Disposition
- H01L2224/49105—Connecting at different heights
- H01L2224/49107—Connecting at different heights on the semiconductor or solid-state body
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- H01L2224/80—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected
- H01L2224/83—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a layer connector
- H01L2224/83001—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a layer connector involving a temporary auxiliary member not forming part of the bonding apparatus
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- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/01—Chemical elements
- H01L2924/01019—Potassium [K]
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- H01L2924/01079—Gold [Au]
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- H01L2924/10—Details of semiconductor or other solid state devices to be connected
- H01L2924/102—Material of the semiconductor or solid state bodies
- H01L2924/1025—Semiconducting materials
- H01L2924/10251—Elemental semiconductors, i.e. Group IV
- H01L2924/10253—Silicon [Si]
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- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/20—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a particular shape, e.g. curved or truncated substrate
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- H—ELECTRICITY
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- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/26—Materials of the light emitting region
- H01L33/30—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table
- H01L33/32—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table containing nitrogen
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/48—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
- H01L33/52—Encapsulations
- H01L33/54—Encapsulations having a particular shape
Definitions
- the present invention relates to a light emitting diode device which is provided, between an ohmic contact metal layer 12 and a binder layer 17, with an electrically conductive layer capable of preventing components of a binder layer 17 from diffusing into the ohmic contact metal layer during high- temperature heat treatment, thereby securing stability and product uniformity, and a fabricating method thereof.
- a light emitting diode (LED) device is a semiconductor device which generates light by allowing a forward current to flow through a PN junction.
- a sapphire substrate 8 is mainly used for growing gallium nitride-based compound semiconductors for the manufacture of a light emitting diode.
- Sapphire substrates are electrically insulators, so that the cathode 1 and anode 2 of LED are formed on the front face of a wafer.
- a low-power GaN-based light emitting diode is manufactured in such a manner that a sapphire substrate 8, on which a crystal structure is grown, is put on a lead frame 4 and then the two electrodes 1, 2 are connected to an upper portion of the sapphire substrate 8. At this time, in order to improve a heat dissipation efficiency, the sapphire substrate 8 is bonded onto the lead frame 4 after reducing its thickness to become approximately 100 ⁇ m or less.
- Thermal conductivity of sapphire substrates 8 is approximately 50 W/m • K. Therefore, even if the thickness is reduced to be about 100 //in, it has a high thermal resistance. On the contrary, in a case of a high-power gallium nitride-based light emitting diode, there is a tendency to mainly use a flip chip bonding method in order to more improve a heat dissipation characteristic.
- a chip with an LED structure is bonded onto a sub-mount 10, such as silicon wafer (150 W/m • K) having superior thermal conductivity or an AIN ceramic substrate (about 180 W/m • K) , with its inner surface facing out, and FIG. 2 schematically shows this method.
- a sub-mount 10 such as silicon wafer (150 W/m • K) having superior thermal conductivity or an AIN ceramic substrate (about 180 W/m • K) , with its inner surface facing out
- FIG. 2 schematically shows this method.
- a flip chip structure since heat is emitted through the sub-mount substrate 10, a heat dissipation efficiency is improved as compared with a case of heat dissipation through the sapphire substrate 8, but there is a problem in that its manufacturing process is complicated and the heat dissipation still leaves more to be desired.
- a Laser Lift-Off (LLO) -type manufacturing method of a light emitting diode comes into the spotlight.
- Manufacturing an LED by means of the laser lift-off method is known to generate the most excellent structure for enhancing the heat dissipation efficiency by irradiating laser toward a sapphire substrate 8, on which the LED has grown, and removing the sapphire substrate 8 from the LED' s crystal structure before packaging.
- the LED manufactured by the laser lift-off method has a better light extraction property because the light emitting area becomes almost equal to the size of chips (in a case of the flip chip, the light emitting area corresponds to about 60 % of the size of chips) .
- the LLO-type method requires a technology for bonding a p-type ohmic contact metal layer surface of a light emitting diode section onto a substrate, for example, a sub- mount.
- a substrate for example, a sub-mount.
- metals for binding are deposited on upper surfaces of the p-type ohmic contact metal and the sub-mount, respectively and then the two surfaces are oppositely bonded onto each other.
- the LLO-type method also requires a process of separating a sapphire substrate from the light emitting diode section by irradiating laser toward the light emitting diode section.
- the sapphire substrate when an interface between the sapphire substrate and the light emitting diode section grown thereon absorbs laser energy, the sapphire substrate applies a force to the light emitting diode section left on the opposite side while being detached from the light emitting diode section. At this time, if the light emitting diode section is improperly bonded onto the sub-mount, the light emitting diode section is also detached from the sub-mount. Thus, the light emitting diode section must be firmly bonded onto the sub-mount in order not to be detached from the sub-mount.
- binder materials that is, binders include PdIn 3 , which has been studied out by the University of California, Berkeley, and Sn-based metal used in the flip chip light emitting diode device.
- the melting points of PdIn 3 and Sn-based metal are below 664 °C and 500 °C , respectively.
- These binders enable the light emitting diode section and the sub-mount to be easily bonded onto each other by forming metal compounds at a low temperature of about 300 ° C, but cannot maintain the bonding state if they are further treated at a high temperature. That is, if an n-type ohmic contact metal layer is deposited on n-type gallium nitride exposed after removing the sapphire substrate by the laser irradiation and then heat treatment is performed at a temperature between
- FIG. 1 is a sectional view showing a structure of a low- power GaN-based light emitting diode device
- FIG. 2 is a sectional view showing a structure of a high-power GaN-based flip chip light emitting diode device
- FIG. 3 is a sectional structural view of a GaN-based LLO light emitting diode unit chip which is provided with an electrically conductive layer for preventing diffusion between a binder layer and an ohmic contact metal layer according to the present invention
- FIG. 4 is a schematic view showing a method for fabricating a high-power LLO light emitting diode device according to the present invention.
- FIG. 5 is a schematic view showing a process of bonding a light emitting diode section onto a second substrate (sub- mount) according to the present invention.
- the present inventors have attempted to bond the light emitting diode section surface onto the substrate (sub-mount) by using gold (Au) or gold-containing alloy, which can be subjected to heat treatment at a temperature of 600 ° C to 800 ° C by virtue of its melting point of 1070 ° C and has high thermal conductivity and superior oxidation resistance, as a binder.
- the present inventors have recognized that when the heat treatment of the n-type ohmic contact metal layer is progressed on the n-type layer exposed after removing the sapphire substrate by the laser irradiation, components (e.g., Au) of the binder layer diffuse into the p- type ohmic contact metal layer adjacent thereto through the high-temperature heat treatment and such a inter-diffusion between the binder layer and the p-type ohmic contact metal layer causes an increase of ohmic contact resistance and weakening of the bonding force of the binder.
- components e.g., Au
- a light emitting diode device in which (a) a substrate; (b) a binder layer; (c) an ohmic contact metal layer; and (d) a light emitting diode section are stacked in sequence, wherein the light emitting diode device has an electrically conductive layer for preventing components of the binder layer from diffusing into the ohmic contact metal layer and being formed between the ohmic contact metal layer and the binder layer.
- a method for fabricating a light emitting diode device comprising the steps of: (a) depositing an ohmic contact metal layer on one surface of a light emitting diode section; (b) forming a diffusion barrier layer on the ohmic contact metal layer by using an electrically conductive material having no defect and higher density than that of a binder; (c) forming a binder layer on the electrically conductive diffusion barrier layer by using the binder; and (d) bonding the binder layer surface of the light emitting diode section onto a substrate.
- a light emitting diode device preferably, a Laser Lift- Off (LLO) light emitting diode device according to the present invention is characterized in that an electrically conductive layer capable of preventing components of a binder layer from diffusing into an ohmic contact metal layer adjacent thereto is provided between the ohmic contact metal layer and the boding layer.
- LLO Laser Lift- Off
- a heating and pressing process or heat treatment of an n-type ohmic contact metal layer is performed in a state where a binder layer for bonding a light emitting diode section onto a substrate neighbors a p-type ohmic contact metal layer formed in the light emitting diode section, a gold
- (Au) component of the binder layer characteristically diffuses into the p-type ohmic contact metal layer, and particularly is more readily mixed with Ag or Al metal which is used as a reflection layer of the light emitting diode section.
- the binder layer and the p-type ohmic contact metal layer come to lose their respective functions, that is, ohmic contact resistance of the p-type ohmic contact metal layer is increased and a bonding force of the binder layer is weakened.
- the diffusion of the binder layer components can be fundamentally suppressed during the heating and pressing process or the heat treatment of the n- type ohmic contact metal layer by interposing, between the binder layer and the p-type ohmic contact metal layer, an electrically conductive layer which is stable even during the heat treatment and thus can prevent the mixing of the two layers.
- the two metal layers of the binder layer and the p-type ohmic contact metal layer come to fulfill their own basic functions, so a light emitting diode device having stable and uniform properties can be secured.
- the present invention can improve characteristics of the light emitting diode device by enabling the heat treatment of the n- type ohmic contact metal layer, which is to be performed in the LLO-type manufacturing method.
- the conductive diffusion barrier layer according to the present invention which is interposed between the ohmic contact metal layer (c) and the binder layer (b), and prevents the binder layer components from diffusing into the ohmic contact metal layer even if the heat treatment is carried out at a high temperature of 500 ° C or more, preferably, 600 ° C to 800 ° C corresponding to a heat treatment range of the n-type ohmic contact metal layer, may consist of electrically conductive materials.
- a non-limitative example of the electrically conductive layer materials includes ordinary transition metals or ceramics known in the art, and a specific example of the transition metals includes Ni, Ti, Ru, Ta, W, Zr, Mo or a mixture thereof.
- the diffusion barrier layer For preventing diffusion, first of all, it is requisite that the diffusion barrier layer must be thermodynamically stable. That is, it is ideal that no chemical reaction occurs, and a reaction rate must be slow, if any.
- the diffusion barrier layer has few defects therein, preferably has a defect of 1 or less per unit area ( ⁇ I/cm 2 ) of the diffusion barrier layer. That is, since if a defect exists within the diffusion barrier layer, the defect becomes a diffusion passage to promote the diffusion, as few as possible defects are advantageous. Particularly, when linear defects exist in a vertical direction of the diffusion barrier layer, diffusion occurs more readily, so it is preferred to prevent diffusion by interposing diffusion inhibiting materials between the vertical linear defects.
- the diffusion barrier layer has high density. This is because the higher a degree of filling of the diffusion barrier layer, the more slowly other atoms diffuse.
- the diffusion barrier layer of the present invention has higher density than that of the gold (Au) 'component of the binder layer, that is, a diffusion-causing factor.
- the electrically conductive layer preferably consists of a material having a different recrystallization temperature range from that of the gold (Au) component of the binder layer.
- the electrically conductive layer preferably consists of a material having a crystallization temperature different from, in particular, higher than that of gold (Au) .
- the electrically conductive layer consists of a ductile material. If the ductile material is used as the component of the electrically conductive layer, the light emitting diode section can be rearranged parallel to the substrate (second substrate), e.g., the sub-mount through the heating and pressing process even if it is not flatly, but slopingly arranged on the substrate.
- the substrate second substrate
- the light emitting diode section in the form of a unit chip does not slope, but parallels to the substrate in this way, laser beams can be uniformly irradiated toward the unit chip because the laser beams are perpendicular to the chip surface.
- the sapphire substrate is removed through uniform absorption of laser at an interface between the light emitting diode section and the sapphire substrate, a flat and uniform surface having low roughness can be obtained. Such a flat and uniform surface plays an important role in securing product uniformity in the subsequent deposition process of the n-type ohmic contact metal layer and the other processes after that deposition process.
- the sapphire substrate applies an impact onto the light emitting diode section while removed by the laser irradiation. However, since the impact applied onto the light emitting diode section is easily absorbed when the electrically conductive layer has ductility, the light emitting diode section can not be separated from the sub-mount.
- the electrically conductive layer preferably has a thickness of 50 A or more for the impact absorption.
- the light emitting diode section (d), the other component of the light emitting diode device according to the present invention, may be formed with a p-type layer, an active layer (light emitting layer) and an n-type layer using ordinary Groups H-- V compounds known in the art, and a non-limitative example of the compounds includes GaAs, GaP, GaN, InP, InAs, InSb, GaAlN, InGaN, InAlGaN or a mixture thereof.
- the p-type layer and the n-type layer may not be doped with a p-type dopant and an n-type dopant, respectively, but are preferably doped with those dopants if possible.
- the active layer may be of a single quantum well structure or a multiple quantum well (MQW) structure.
- another buffer layer may be included.
- the ohmic contact metal layer (c) of the light emitting diode section is located adjacent to the electrically conductive layer, and may be an n-type ohmic contact metal layer or a p-type contact metal layer according to the manufacturing types of the light emitting diode device, for example, manufacturing types for a low-power device, a mid-power device and a high-power device or a Laser Lift-Off (LLO) manufacturing type.
- Ordinary metals known in the art such as Ni, Au, Pt and the like, may be used as the ohmic contact metal, and a metal layer for reflecting light, such as an Ag layer, an Al layer or a Cr layer, may be further used. Also, there is no specific limitation on the shape and the thickness of the ohmic contact metal.
- the binder layer (b, 17), another component of the light emitting diode device according to the present invention, is preferably made of gold (Au) or gold-containing alloy which not only can be subjected to heat treatment at a temperature between 600 ° C and 800 ° C , but also has high thermal conductivity and superior oxidation resistance as stated above.
- Ordinary sub-mounts 10 known in the art may be used as the substrate for mounting the light emitting diode section thereon, and the substrate may consist of CuW, Si, AlN ceramic, Al 2 O 3 ceramic or the like.
- the size of the substrate may be larger than that of the light emitting diode section or may be equal to or larger than that of a sapphire substrate when the light emitting diode section is grown onto the sapphire substrate .
- FIG. 3 shows a sectional structure of a light emitting diode (LED) device in accordance with a preferred embodiment of the present invention.
- An electrically conductive pad section for example, a p-type electrically conductive pad section 16 is located on an insulation layer 20 which is formed on one surface of a substrate, that is, a sub-mount 10, and a binder layer 17, an electrically conductive layer 14 and a p-type ohmic contact metal layer 12 of a light emitting diode section exist on the p-type electrically conductive pad section 16 in a state where they are bonded onto each other.
- a p-type layer 7, an active layer (light emitting layer) 6 and an n-type layer 5 of the light emitting diode section are sequentially formed in a stack structure on the p-type ohmic contact metal layer 12.
- an n-ohmic contact metal layer 13 is bonded onto a light emitting diodes section surface adjacent to the n-type layer 5.
- the p-type electrically conductive pad section 16 and the n-ohmic contact metal layer 13 are electrically connected to an external power source, that is, a lead frame 4 through a wire 9, respectively.
- the so-constructed light emitting diode device may be operated according to the following principle. That is, if a specific voltage is applied to the light emitting diode device through the wire 9 connected to the external power source, a cathode of the light emitting diode device is connected to the external power source through the n-type ohmic contact metal layer 13 and the n-type layer 5, and an anode of the light emitting diode device is connected to the external power source through the p-type electrically conductive pad section 16, the binder layer 17, the electrically conductive layer 14, the p-type ohmic contact metal layer 12 and the p-type layer 7, so an electric current flows through the light emitting diode device.
- the light emitting diode device which is provided with an electrically conductive layer between the binder layer and the ohmic contact metal layer according to the present invention can be fabricated by a conventional method known in the art, except that a diffusion barrier layer is formed between the binder layer and the ohmic contact metal layer by using an electrically conductive material having few defect and higher density than that of the binder.
- the light emitting diode device can be fabricated by mounting a sapphire substrate having a grown light emitting diode crystal structure onto a sub-mount, removing the sapphire via laser irradiation; and forming electrodes and connecting each of them to an external electric power source.
- a general process of manufacturing the light emitting diode device according to the present invention will be explained in more detail. Particularly, characteristics of the present invention discriminated clearly from the prior art, for example, formation and bonding of conductive diffusion barrier layer will be explained.
- FIG. 4 is a schematic view showing a Laser Lift-Off (LLO) -type method for fabricating a light emitting diode device according to the present invention
- FIG. 5 is a schematic view showing a process of bonding a light emitting diode section onto a second substrate (sub-mount) according to the present invention.
- LLO Laser Lift-Off
- Step of growing the LED section onto sapphire substrate An n-type layer, an active layer (light emitting layer) and a p-type layer are grown in sequence onto a sapphire substrate (first substrate) by means of metal organic chemical vapor deposition (MOCVD) , liquid phase epitaxy (LPE) , molecular beam epitaxy (MBE) or the like to form a light emitting diode section.
- MOCVD metal organic chemical vapor deposition
- LPE liquid phase epitaxy
- MBE molecular beam epitaxy
- a p-type ohmic contact metal layer is formed on an upper p-type surface (e.g., p-type GaN surface) of the wafer by vacuum deposition and then heat treatment is performed to complete a p-type ohmic contact.
- a diffusion barrier layer is formed on the ohmic contact metal layer.
- a diffusion barrier layer consists of an electrically conductive material which has few defect and higher density than that of a binder, for example, transition metal such as Ni, Ti, Ru, Ta, W and the like or ceramic.
- transition metal such as Ni, Ti, Ru, Ta, W and the like or ceramic.
- the diffusion barrier layer may be formed by deposition methods known to the art in a case of using metal as its material, and may be formed various coating methods in a case of using ceramic as its material.
- a binder layer is formed on the electrically conductive layer by using gold or gold-containing alloy having a higher melting point as a binder.
- the light emitting diode section and a substrate, preferably, an electrically conductive pad section located on the substrate consist of the same material as that of the binder layer, that is, gold or gold-containing alloy.
- the binder layer may be formed by conventional methods known in the art, for example, a deposition method.
- the light emitting diode crystal structure is grown onto the sapphire substrate with a thickness of about 430 j ⁇ n.
- the sapphire substrate is thinned to a thickness of about 80 ⁇ m to 100 ⁇ m through a lapping/polishing process, if necessary.
- a sub-mount substrate may be used in order to enhance a heat dissipation efficiency. That is, the light emitting diode section is turned upside down over the sub-mount substrate such that the polished sapphire substrate climbs upward, and the binder layer surface is bonded onto the sub-mount substrate, preferably, the electrically conductive pad section located on the sub-mount substrate.
- the binder later surface is bonded onto the substrate by high-temperature pressing.
- Ranges of temperature and pressure during the high-temperature pressing are 250 ° C to 500 ° C and 1 Mpa to 100 Mpa, respectively, but they are not limited to such ranges .
- FIG. 5 is a sectional structural view showing a method of bonding the light emitting diode section onto the substrate, e.g., a sub-mount.
- the substrate that is, the sub-mount 10 is put on a heater 30, the binder layer 17 of the light emitting diode section is positioned face-to-face with the electrically conductive pad section, for example, a p-type electrically conductive pad section 16, and then a press 40 is located on the other surface of the light emitting diode section or a sapphire substrate surface in a case where the light emitting diode section is grown onto the sapphire substrate.
- the electrically conductive pad section for example, a p-type electrically conductive pad section 16
- Temperature and pressure of the heater 30 and the press 40 may be adjusted in the above-mentioned ranges, respectively, but heating and pressing by the heater 30 and the press 40 is preferably performed at a temperature of 300 ° C and a pressure of 10 Mpa.
- a Teflon film known in the art may be used between the light emitting diode section and the press 40. At this time, there is no specific limit to the thickness of the Teflon film, but the thickness is preferably between 70 ⁇ m to 150 ⁇ m. (7) Step of forming the unit chip
- the sub-mount substrate and the light emitting diode crystal structure may be diced into unit LED chips.
- Typical methods generally known in the art such as dicing, scribing and breaking processes, can be performed in order to separate the unit chips.
- Step of bonding the unit chip to lead frame The unit chips are bonded onto a lead frame. At this time, the binder layer surface may be bonded directly onto the lead frame, with omission of the step of bonding the sub-mount and/or the step of forming the unit chip.
- Step of irradiating the laser (see FIG. 4c)
- the sapphire substrate is removed by irradiating laser such as excimer laser.
- the wavelength of laser is preferably below 365 nm.
- Laser beams transmitting the sapphire substrate are absorbed into a gallium nitride section to decompose gallium nitride existing in an interface region between the sapphire substrate and the gallium nitride section.
- the sapphire substrate is separated from the light emitting diode crystal structure while metal gallium and nitrogen gas are produced.
- an n-type ohmic contact metal layer is deposited on the n-type layer (e.g., n-type GaN surface), which is exposed as the sapphire substrate is removed.
- heat treatment is performed at a temperature of 600 "C to 800 ° C in order to reduce resistances of the n-type ohmic contact metal layer and the n-type layer.
- Gold wire bonding for the n-type surface and/or the p- type surface, preferably, the n-type surface and the electrically conductive pad section on the sub-mount is performed.
- Step of treating a molding material A molding material such as epoxy or a molding material mixed with a fluorescent substance is coated to complete the fabrication of the light emitting diode device. At this time, it is possible to properly change the order of the step of forming the unit chip in order to promote facilitation and simplification of the fabrication method.
- the light emitting diode device may be applied to all kinds of light emitting diode devices regardless of their fabricating types, power grades and light emitting ranges so long as they are provided with the electrically conductive layer between the binder layer and the ohmic contact metal layer, but is preferably applied to a Laser lift-Off (LLO) light emitting diode device which requires heat treatment, for example, n-type ohmic contact metal heat treatment.
- LLO Laser lift-Off
- the present invention provides a light emitting unit with a light emitting diode device which has the above-mentioned structure or is manufactured by the above- mentioned method.
- the light emitting unit includes all kinds of light emitting unit having a light emitting diode device, for example, an illuminator, an indicating unit, a germicidal lamp, a display unit and so forth.
- a light emitting diode device is provided with an electrically conductive diffusion barrier layer which is interposed between an ohmic contact metal layer and a binder layer of a light emitting diode section, thereby improving characteristics of the light emitting diode device through n- type ohmic contact metal heat treatment and enhancing stability and product uniformity of an LLO-type fabricating method.
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Abstract
Disclosed is a light emitting diode device in which (a) a substrate; (b) a binder layer; (c) an ohmic contact metal layer; and (d) a light emitting diode section are stacked in sequence, wherein the light emitting diode device has an electrically conductive layer for preventing components of the binder layer from diffusing into the ohmic contact metal layer, and being formed between the ohmic contact metal layer and the binder layer. In such a light emitting diode device, the electrically conductive layer capable of preventing the binder layer components from diffusing into the ohmic contact metal layer is formed between the ohmic contact metal layer and the binder layer, so stability and product qualities of the light emitting diode device can be improved.
Description
LIGHT EMITTING DIODE DEVICE COMPRISING A DIFFUSION BARRIER LAYER AND METHOD FOR PREPARATION THEREOF
Technical Field The present invention relates to a light emitting diode device which is provided, between an ohmic contact metal layer 12 and a binder layer 17, with an electrically conductive layer capable of preventing components of a binder layer 17 from diffusing into the ohmic contact metal layer during high- temperature heat treatment, thereby securing stability and product uniformity, and a fabricating method thereof.
Background Art
A light emitting diode (LED) device is a semiconductor device which generates light by allowing a forward current to flow through a PN junction.
A sapphire substrate 8 is mainly used for growing gallium nitride-based compound semiconductors for the manufacture of a light emitting diode. Sapphire substrates are electrically insulators, so that the cathode 1 and anode 2 of LED are formed on the front face of a wafer. In general, a low-power GaN-based light emitting diode is manufactured in such a manner that a sapphire substrate 8, on which a crystal structure is grown, is put on a lead frame 4 and then the two electrodes 1, 2 are connected to an upper portion of the sapphire substrate 8. At this time, in order to improve a heat dissipation efficiency, the sapphire substrate 8 is bonded onto the lead frame 4 after reducing its thickness to become approximately 100 βm or less. This is schematically shown in FIG. 1. Thermal conductivity of sapphire substrates 8 is approximately 50 W/m • K. Therefore, even if the thickness is reduced to be about 100 //in, it has a high thermal resistance. On the contrary, in a case of a high-power
gallium nitride-based light emitting diode, there is a tendency to mainly use a flip chip bonding method in order to more improve a heat dissipation characteristic.
In the flip-chip bonding method, a chip with an LED structure is bonded onto a sub-mount 10, such as silicon wafer (150 W/m • K) having superior thermal conductivity or an AIN ceramic substrate (about 180 W/m • K) , with its inner surface facing out, and FIG. 2 schematically shows this method. In such a flip chip structure, since heat is emitted through the sub-mount substrate 10, a heat dissipation efficiency is improved as compared with a case of heat dissipation through the sapphire substrate 8, but there is a problem in that its manufacturing process is complicated and the heat dissipation still leaves more to be desired. In order to solve the above-mentioned problems, a Laser Lift-Off (LLO) -type manufacturing method of a light emitting diode comes into the spotlight. Manufacturing an LED by means of the laser lift-off method is known to generate the most excellent structure for enhancing the heat dissipation efficiency by irradiating laser toward a sapphire substrate 8, on which the LED has grown, and removing the sapphire substrate 8 from the LED' s crystal structure before packaging. Also, the LED manufactured by the laser lift-off method has a better light extraction property because the light emitting area becomes almost equal to the size of chips (in a case of the flip chip, the light emitting area corresponds to about 60 % of the size of chips) .
Meanwhile, the LLO-type method requires a technology for bonding a p-type ohmic contact metal layer surface of a light emitting diode section onto a substrate, for example, a sub- mount. In a general bonding technology, metals for binding are deposited on upper surfaces of the p-type ohmic contact metal and the sub-mount, respectively and then the two
surfaces are oppositely bonded onto each other. Also, the LLO-type method also requires a process of separating a sapphire substrate from the light emitting diode section by irradiating laser toward the light emitting diode section. At this time, only the sapphire substrate must be removed and the remaining portions must be left on the sub-mount, by reason of which it is required to bond the light emitting diode section and the sub-mount onto each other as stated above. For reference, when an interface between the sapphire substrate and the light emitting diode section grown thereon absorbs laser energy, the sapphire substrate applies a force to the light emitting diode section left on the opposite side while being detached from the light emitting diode section. At this time, if the light emitting diode section is improperly bonded onto the sub-mount, the light emitting diode section is also detached from the sub-mount. Thus, the light emitting diode section must be firmly bonded onto the sub-mount in order not to be detached from the sub-mount.
Conventionally, binder materials, that is, binders include PdIn3, which has been studied out by the University of California, Berkeley, and Sn-based metal used in the flip chip light emitting diode device. The melting points of PdIn3 and Sn-based metal are below 664 °C and 500 °C , respectively. These binders enable the light emitting diode section and the sub-mount to be easily bonded onto each other by forming metal compounds at a low temperature of about 300 °C, but cannot maintain the bonding state if they are further treated at a high temperature. That is, if an n-type ohmic contact metal layer is deposited on n-type gallium nitride exposed after removing the sapphire substrate by the laser irradiation and then heat treatment is performed at a temperature between
600 °C and 800 °C in order to reduce resistances of the n-type ohmic contact metal layer and the n-type gallium nitride,
there occurs a problem that the bonding between the light emitting diode section and the sub-mount becomes weakened and thus the stability of the light emitting diode device is lowered. However, if the high-temperature heat treatment of the n-type ohmic contact metal layer is not performed in order to prevent the weakening of the bonding between the light emitting diode section and the sub-mount, there also occurs a problem that the product quality of the finished light emitting diode device is lowered. Therefore, contrary to the flip chip bonding method in which a low-temperature bonding process is possible because the bonding is performed after the heat treatment of the ohmic contact metal layer, it is essentially desired to develop a binder capable of being subjected to the high-temperature heat treatment in a case of the LLO-type method in which the heat treatment of the n-type ohmic contact metal layer is performed after the laser irradiation.
Brief Description of the Drawings The foregoing and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:
FIG. 1 is a sectional view showing a structure of a low- power GaN-based light emitting diode device;
FIG. 2 is a sectional view showing a structure of a high-power GaN-based flip chip light emitting diode device;
FIG. 3 is a sectional structural view of a GaN-based LLO light emitting diode unit chip which is provided with an electrically conductive layer for preventing diffusion between a binder layer and an ohmic contact metal layer according to the present invention;
FIG. 4 is a schematic view showing a method for fabricating a high-power LLO light emitting diode device according to the present invention; and
FIG. 5 is a schematic view showing a process of bonding a light emitting diode section onto a second substrate (sub- mount) according to the present invention. <Brief Description of the indications in the drawings>
5: n-GaN
6: multiple quantum well (MQW) 7: p-GaN
8 : sapphire substrate
10 sub mount 12 p-ohmic contact layer 13 n-ohmic contact layer 14 electrically conductive layer 16 p-electrically conductive pad section 17 binder layer
30: the heater 40: the press
Disclosure of the Invention
Considering the above-mentioned problems, the present inventors have attempted to bond the light emitting diode section surface onto the substrate (sub-mount) by using gold (Au) or gold-containing alloy, which can be subjected to heat treatment at a temperature of 600 °C to 800 °C by virtue of its melting point of 1070 °C and has high thermal conductivity and superior oxidation resistance, as a binder. Through this attempt, for the first time, the present inventors have recognized that when the heat treatment of the n-type ohmic contact metal layer is progressed on the n-type layer exposed after removing the sapphire substrate by the laser irradiation, components (e.g., Au) of the binder layer diffuse into the p-
type ohmic contact metal layer adjacent thereto through the high-temperature heat treatment and such a inter-diffusion between the binder layer and the p-type ohmic contact metal layer causes an increase of ohmic contact resistance and weakening of the bonding force of the binder.
Accordingly, it is an object of the present invention to provide a light emitting diode device which can improve its characteristics through heat treatment of an ohmic contact metal layer and sustain a bonding force of a binder layer to enhance its uniformity by providing, between the ohmic contact metal layer and the binder layer, an electrically conductive layer capable of preventing components of the binder layer from diffusing into the ohmic contact metal layer during high- temperature heat treatment, and a fabricating method thereof. To achieve this objective, in accordance with one aspect of the present invention, there is provided a light emitting diode device in which (a) a substrate; (b) a binder layer; (c) an ohmic contact metal layer; and (d) a light emitting diode section are stacked in sequence, wherein the light emitting diode device has an electrically conductive layer for preventing components of the binder layer from diffusing into the ohmic contact metal layer and being formed between the ohmic contact metal layer and the binder layer.
In accordance with another aspect of the present invention, there is provided a method for fabricating a light emitting diode device, the method comprising the steps of: (a) depositing an ohmic contact metal layer on one surface of a light emitting diode section; (b) forming a diffusion barrier layer on the ohmic contact metal layer by using an electrically conductive material having no defect and higher density than that of a binder; (c) forming a binder layer on the electrically conductive diffusion barrier layer by using
the binder; and (d) bonding the binder layer surface of the light emitting diode section onto a substrate.
Hereinafter, the present invention will be described in more detail. A light emitting diode device, preferably, a Laser Lift- Off (LLO) light emitting diode device according to the present invention is characterized in that an electrically conductive layer capable of preventing components of a binder layer from diffusing into an ohmic contact metal layer adjacent thereto is provided between the ohmic contact metal layer and the boding layer.
If a heating and pressing process or heat treatment of an n-type ohmic contact metal layer is performed in a state where a binder layer for bonding a light emitting diode section onto a substrate neighbors a p-type ohmic contact metal layer formed in the light emitting diode section, a gold
(Au) component of the binder layer characteristically diffuses into the p-type ohmic contact metal layer, and particularly is more readily mixed with Ag or Al metal which is used as a reflection layer of the light emitting diode section. On account of this, the binder layer and the p-type ohmic contact metal layer come to lose their respective functions, that is, ohmic contact resistance of the p-type ohmic contact metal layer is increased and a bonding force of the binder layer is weakened.
In the present invention, the diffusion of the binder layer components can be fundamentally suppressed during the heating and pressing process or the heat treatment of the n- type ohmic contact metal layer by interposing, between the binder layer and the p-type ohmic contact metal layer, an electrically conductive layer which is stable even during the heat treatment and thus can prevent the mixing of the two layers. Thus, the two metal layers of the binder layer and
the p-type ohmic contact metal layer come to fulfill their own basic functions, so a light emitting diode device having stable and uniform properties can be secured. Also, the present invention can improve characteristics of the light emitting diode device by enabling the heat treatment of the n- type ohmic contact metal layer, which is to be performed in the LLO-type manufacturing method.
As described above, the conductive diffusion barrier layer according to the present invention, which is interposed between the ohmic contact metal layer (c) and the binder layer (b), and prevents the binder layer components from diffusing into the ohmic contact metal layer even if the heat treatment is carried out at a high temperature of 500 °C or more, preferably, 600 °C to 800 °C corresponding to a heat treatment range of the n-type ohmic contact metal layer, may consist of electrically conductive materials.
A non-limitative example of the electrically conductive layer materials includes ordinary transition metals or ceramics known in the art, and a specific example of the transition metals includes Ni, Ti, Ru, Ta, W, Zr, Mo or a mixture thereof.
For preventing diffusion, first of all, it is requisite that the diffusion barrier layer must be thermodynamically stable. That is, it is ideal that no chemical reaction occurs, and a reaction rate must be slow, if any. Secondly, the diffusion barrier layer has few defects therein, preferably has a defect of 1 or less per unit area (< I/cm2) of the diffusion barrier layer. That is, since if a defect exists within the diffusion barrier layer, the defect becomes a diffusion passage to promote the diffusion, as few as possible defects are advantageous. Particularly, when linear defects exist in a vertical direction of the diffusion barrier layer, diffusion occurs more readily, so it is preferred to prevent
diffusion by interposing diffusion inhibiting materials between the vertical linear defects. Thirdly, in order to prevent migration of atoms, it is advantageous that the diffusion barrier layer has high density. This is because the higher a degree of filling of the diffusion barrier layer, the more slowly other atoms diffuse. Thus, it is preferred that the diffusion barrier layer of the present invention has higher density than that of the gold (Au) 'component of the binder layer, that is, a diffusion-causing factor. In addition, the electrically conductive layer preferably consists of a material having a different recrystallization temperature range from that of the gold (Au) component of the binder layer. As an example, gold (Au) has a melting point of 1070 °C, but its recrystallization temperature is only half of the melting point, that is, about 500 °C , and rearrangement of gold atoms occurs during the recrystallization at that temperature. Consequently, if the light emitting diode section is heated to above 500 °C, the gold (Au) component of the binder layer is recrystallized to easily diffuse into the p-type ohmic contact metal layer adjacent thereto. Therefore, the electrically conductive layer preferably consists of a material having a crystallization temperature different from, in particular, higher than that of gold (Au) .
Moreover, it is preferred that the electrically conductive layer consists of a ductile material. If the ductile material is used as the component of the electrically conductive layer, the light emitting diode section can be rearranged parallel to the substrate (second substrate), e.g., the sub-mount through the heating and pressing process even if it is not flatly, but slopingly arranged on the substrate. When the light emitting diode section in the form of a unit chip does not slope, but parallels to the substrate in this way, laser beams can be uniformly irradiated toward the unit
chip because the laser beams are perpendicular to the chip surface. By virtue of this, stability and uniformity can be secured in the process of removing the sapphire substrate, which usually has a higher fraction defective than those of other processes. Furthermore, since the sapphire substrate is removed through uniform absorption of laser at an interface between the light emitting diode section and the sapphire substrate, a flat and uniform surface having low roughness can be obtained. Such a flat and uniform surface plays an important role in securing product uniformity in the subsequent deposition process of the n-type ohmic contact metal layer and the other processes after that deposition process. In addition, the sapphire substrate applies an impact onto the light emitting diode section while removed by the laser irradiation. However, since the impact applied onto the light emitting diode section is easily absorbed when the electrically conductive layer has ductility, the light emitting diode section can not be separated from the sub-mount.
There is no limit to the thickness of the electrically conductive layer, but the electrically conductive layer preferably has a thickness of 50 A or more for the impact absorption.
The light emitting diode section (d), the other component of the light emitting diode device according to the present invention, may be formed with a p-type layer, an active layer (light emitting layer) and an n-type layer using ordinary Groups H-- V compounds known in the art, and a non-limitative example of the compounds includes GaAs, GaP, GaN, InP, InAs, InSb, GaAlN, InGaN, InAlGaN or a mixture thereof. The p-type layer and the n-type layer may not be doped with a p-type dopant and an n-type dopant, respectively, but are preferably doped with those dopants if possible. The active layer (so called light emitting layer) may be of a single quantum well
structure or a multiple quantum well (MQW) structure. In addition to the above-mentioned p-type, active and n-type layers, another buffer layer may be included. By adjusting a composition of Groups IH- Vcompounds, light emitting diodes with a long wavelength to a short wavelength can be freely manufactured, through which the present invention can be applied to all kinds of light emitting diodes without being limited to a blue nitride-base light emitting diode with a wavelength of 460 ran . The ohmic contact metal layer (c) of the light emitting diode section, another component of the light emitting diode device according to the present invention, is located adjacent to the electrically conductive layer, and may be an n-type ohmic contact metal layer or a p-type contact metal layer according to the manufacturing types of the light emitting diode device, for example, manufacturing types for a low-power device, a mid-power device and a high-power device or a Laser Lift-Off (LLO) manufacturing type. Ordinary metals known in the art, such as Ni, Au, Pt and the like, may be used as the ohmic contact metal, and a metal layer for reflecting light, such as an Ag layer, an Al layer or a Cr layer, may be further used. Also, there is no specific limitation on the shape and the thickness of the ohmic contact metal.
The binder layer (b, 17), another component of the light emitting diode device according to the present invention, is preferably made of gold (Au) or gold-containing alloy which not only can be subjected to heat treatment at a temperature between 600 °C and 800 °C , but also has high thermal conductivity and superior oxidation resistance as stated above. Ordinary sub-mounts 10 known in the art may be used as the substrate for mounting the light emitting diode section thereon, and the substrate may consist of CuW, Si, AlN ceramic, Al2O3 ceramic or the like. The size of the substrate may be
larger than that of the light emitting diode section or may be equal to or larger than that of a sapphire substrate when the light emitting diode section is grown onto the sapphire substrate . Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned by practicing the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings .
Hereinafter, the present invention will be explained in more detail in connection with preferred embodiments. However, it should be noted that the present invention is not limited to these embodiments.
FIG. 3 shows a sectional structure of a light emitting diode (LED) device in accordance with a preferred embodiment of the present invention. An electrically conductive pad section, for example, a p-type electrically conductive pad section 16 is located on an insulation layer 20 which is formed on one surface of a substrate, that is, a sub-mount 10, and a binder layer 17, an electrically conductive layer 14 and a p-type ohmic contact metal layer 12 of a light emitting diode section exist on the p-type electrically conductive pad section 16 in a state where they are bonded onto each other. A p-type layer 7, an active layer (light emitting layer) 6 and an n-type layer 5 of the light emitting diode section are sequentially formed in a stack structure on the p-type ohmic contact metal layer 12. At this time, an n-ohmic contact metal layer 13 is bonded onto a light emitting diodes section surface adjacent to the n-type layer 5. The p-type
electrically conductive pad section 16 and the n-ohmic contact metal layer 13 are electrically connected to an external power source, that is, a lead frame 4 through a wire 9, respectively.
The so-constructed light emitting diode device may be operated according to the following principle. That is, if a specific voltage is applied to the light emitting diode device through the wire 9 connected to the external power source, a cathode of the light emitting diode device is connected to the external power source through the n-type ohmic contact metal layer 13 and the n-type layer 5, and an anode of the light emitting diode device is connected to the external power source through the p-type electrically conductive pad section 16, the binder layer 17, the electrically conductive layer 14, the p-type ohmic contact metal layer 12 and the p-type layer 7, so an electric current flows through the light emitting diode device. By this, light with energy corresponding to a band gap or an energy level difference of the active layer is emitted from the light emitting diode device while electrons and holes are recombined with each other in the active layer. The light emitting diode device which is provided with an electrically conductive layer between the binder layer and the ohmic contact metal layer according to the present invention can be fabricated by a conventional method known in the art, except that a diffusion barrier layer is formed between the binder layer and the ohmic contact metal layer by using an electrically conductive material having few defect and higher density than that of the binder. In one embodiment of the method, the light emitting diode device can be fabricated by mounting a sapphire substrate having a grown light emitting diode crystal structure onto a sub-mount, removing the sapphire via laser irradiation; and forming electrodes and connecting each of them to an external electric power source.
Hereinafter, a general process of manufacturing the light emitting diode device according to the present invention will be explained in more detail. Particularly, characteristics of the present invention discriminated clearly from the prior art, for example, formation and bonding of conductive diffusion barrier layer will be explained. FIG. 4 is a schematic view showing a Laser Lift-Off (LLO) -type method for fabricating a light emitting diode device according to the present invention, and FIG. 5 is a schematic view showing a process of bonding a light emitting diode section onto a second substrate (sub-mount) according to the present invention.
(1) Step of growing the LED section onto sapphire substrate An n-type layer, an active layer (light emitting layer) and a p-type layer are grown in sequence onto a sapphire substrate (first substrate) by means of metal organic chemical vapor deposition (MOCVD) , liquid phase epitaxy (LPE) , molecular beam epitaxy (MBE) or the like to form a light emitting diode section.
(2) Step of forming the p-type ohmic contact metal layer (cf. FIG. 4a)
After a wafer, in which the light emitting diode crystal structure (e.g., GaN-based) is grown onto the sapphire substrate, is initially washed out, a p-type ohmic contact metal layer is formed on an upper p-type surface (e.g., p-type GaN surface) of the wafer by vacuum deposition and then heat treatment is performed to complete a p-type ohmic contact.
(3) Step of forming the electrically conductive diffusion barrier layer (cf. FIG. 4a)
A diffusion barrier layer is formed on the ohmic contact metal layer. Such a diffusion barrier layer consists of an electrically conductive material which has few defect and
higher density than that of a binder, for example, transition metal such as Ni, Ti, Ru, Ta, W and the like or ceramic. At this=τ= time, the diffusion barrier layer may be formed by deposition methods known to the art in a case of using metal as its material, and may be formed various coating methods in a case of using ceramic as its material.
(4) Step of forming the binder layer (see FIG. 4a)
A binder layer is formed on the electrically conductive layer by using gold or gold-containing alloy having a higher melting point as a binder. At this time, in order to facilitate the bonding of the binder, it is preferred that the light emitting diode section and a substrate, preferably, an electrically conductive pad section located on the substrate consist of the same material as that of the binder layer, that is, gold or gold-containing alloy. Also, the binder layer may be formed by conventional methods known in the art, for example, a deposition method.
(5) Step of polishing the sapphire substrate
In general, the light emitting diode crystal structure is grown onto the sapphire substrate with a thickness of about 430 jωn. In order to form a mirror surface enabling laser beams to easily transmit the sapphire substrate, the sapphire substrate is thinned to a thickness of about 80 μm to 100 μm through a lapping/polishing process, if necessary. (6) Step of bonding the sapphire substrate surface to second substrate (sub-mount) (see FIG. 4b)
For example, in a case of a high-power light emitting diode, a sub-mount substrate may be used in order to enhance a heat dissipation efficiency. That is, the light emitting diode section is turned upside down over the sub-mount substrate such that the polished sapphire substrate climbs upward, and the binder layer surface is bonded onto the sub-
mount substrate, preferably, the electrically conductive pad section located on the sub-mount substrate.
The binder later surface is bonded onto the substrate by high-temperature pressing. Ranges of temperature and pressure during the high-temperature pressing are 250 °C to 500 °C and 1 Mpa to 100 Mpa, respectively, but they are not limited to such ranges .
FIG. 5 is a sectional structural view showing a method of bonding the light emitting diode section onto the substrate, e.g., a sub-mount.
In one example of the bonding method as shown in FIG. 5, the substrate, that is, the sub-mount 10 is put on a heater 30, the binder layer 17 of the light emitting diode section is positioned face-to-face with the electrically conductive pad section, for example, a p-type electrically conductive pad section 16, and then a press 40 is located on the other surface of the light emitting diode section or a sapphire substrate surface in a case where the light emitting diode section is grown onto the sapphire substrate. Temperature and pressure of the heater 30 and the press 40 may be adjusted in the above-mentioned ranges, respectively, but heating and pressing by the heater 30 and the press 40 is preferably performed at a temperature of 300 °C and a pressure of 10 Mpa. In order to uniformly deliver the bonding pressure to the sub- mount and the light emitting diode section, a Teflon film known in the art may be used between the light emitting diode section and the press 40. At this time, there is no specific limit to the thickness of the Teflon film, but the thickness is preferably between 70 μm to 150 μm. (7) Step of forming the unit chip
If necessary, the sub-mount substrate and the light emitting diode crystal structure may be diced into unit LED chips. Typical methods generally known in the art, such as dicing,
scribing and breaking processes, can be performed in order to separate the unit chips. In addition, it is also possible to irradiate laser beam so as to separate the unit chips.
(8) Step of bonding the unit chip to lead frame The unit chips are bonded onto a lead frame. At this time, the binder layer surface may be bonded directly onto the lead frame, with omission of the step of bonding the sub-mount and/or the step of forming the unit chip.
(9) Step of irradiating the laser (see FIG. 4c) The sapphire substrate is removed by irradiating laser such as excimer laser. At this time, the wavelength of laser is preferably below 365 nm. For example, Laser beams transmitting the sapphire substrate are absorbed into a gallium nitride section to decompose gallium nitride existing in an interface region between the sapphire substrate and the gallium nitride section. Thus, the sapphire substrate is separated from the light emitting diode crystal structure while metal gallium and nitrogen gas are produced.
(10) Step of forming the n-type ohmic contact metal layer
If necessary, an n-type ohmic contact metal layer is deposited on the n-type layer (e.g., n-type GaN surface), which is exposed as the sapphire substrate is removed. After the deposition of the n-type contact metal layer, heat treatment is performed at a temperature of 600 "C to 800 °C in order to reduce resistances of the n-type ohmic contact metal layer and the n-type layer.
(11) Wire bonding step
Gold wire bonding for the n-type surface and/or the p- type surface, preferably, the n-type surface and the electrically conductive pad section on the sub-mount is performed.
(12) Step of treating a molding material
A molding material such as epoxy or a molding material mixed with a fluorescent substance is coated to complete the fabrication of the light emitting diode device. At this time, it is possible to properly change the order of the step of forming the unit chip in order to promote facilitation and simplification of the fabrication method.
The above-mentioned embodiments of the fabricating method of the light emitting diode device are only preferred examples, and the present invention should not be limited to them.
The light emitting diode device according to the present invention may be applied to all kinds of light emitting diode devices regardless of their fabricating types, power grades and light emitting ranges so long as they are provided with the electrically conductive layer between the binder layer and the ohmic contact metal layer, but is preferably applied to a Laser lift-Off (LLO) light emitting diode device which requires heat treatment, for example, n-type ohmic contact metal heat treatment. In addition, the present invention provides a light emitting unit with a light emitting diode device which has the above-mentioned structure or is manufactured by the above- mentioned method. The light emitting unit includes all kinds of light emitting unit having a light emitting diode device, for example, an illuminator, an indicating unit, a germicidal lamp, a display unit and so forth.
The forgoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teachings can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.
Industrial Applicability
As described above, a light emitting diode device according to the present invention is provided with an electrically conductive diffusion barrier layer which is interposed between an ohmic contact metal layer and a binder layer of a light emitting diode section, thereby improving characteristics of the light emitting diode device through n- type ohmic contact metal heat treatment and enhancing stability and product uniformity of an LLO-type fabricating method.
Claims
1. A light emitting diode device in which (a) a substrate; (b) a binder layer; (c) an ohmic contact metal layer; and (d) a light emitting diode section are stacked in sequence, wherein the light emitting diode device has an electrically conductive layer for preventing components of the binder layer from diffusing into the ohmic contact metal layer, and being formed between the ohmic contact metal layer and the binder layer.
2. The light emitting diode device as claimed in claim 1, wherein the electrically conductive layer prevents the components of the binder layer from diffusing into the ohmic contact metal layer during high-temperature heat treatment.
3. The light emitting diode device as claimed in claim 2, wherein the temperature of the high-temperature heat treatment is in a range of 600 °C to 800 °C .
4. The light emitting diode device as claimed in claim 1, wherein the electrically conductive layer is made of a material having a defect of 1 or less per unit area of the electrically conductive layer
5. The light emitting diode device as claimed in claim 1, wherein the electrically conductive layer is made of a material having higher density than that of the binder
6. The light emitting diode device as claimed in claim 1, wherein the electrically conductive layer is made of a material having recrystallization temperature different from those of the binder layer components.
7. The light emitting diode device as claimed in claim 1, wherein the electrically conductive layer is made of a ductile material.
8. The light emitting diode device as claimed in claim 1, wherein the electrically conductive layer is made of at least one kind of metal or ceramic selected from the group consisting of Ni, Ti, Ru, Ta, W, Zr and Mo.
9. The light emitting diode device as claimed in claim 1, wherein the thickness of the electrically conductive layer is 50 A or more.
10. The light emitting diode device as claimed in claim 1, wherein the binder layer is made of gold or gold-containing alloy.
11. The light emitting diode device as claimed in claim 1, wherein the light emitting diode section is fabricated by means of a Laser Lift-Off (LLO) method.
12. A light emitting unit including the light emitting diode device as claimed in any one of claims 1 to 11.
13. A method for fabricating a light emitting diode device, the method comprising the steps of:
(a) depositing an ohmic contact metal layer on one surface of a light emitting diode section; (b) forming a diffusion barrier layer on the ohmic contact metal layer by using an electrically conductive material having higher density than that of a binder; (c) forming a binder layer on the electrically conductive diffusion barrier layer by using the binder; and
(d) bonding the binder layer surface of the light emitting diode section onto a substrate.
14. The method as claimed in claim 13, wherein the electrically conductive diffusion barrier layer is made of at least one kind of ceramic or metal selected from the group consisting of NI, Ti, Ru, Ta, W, Zr and Mo.
15. The method as claimed in claim 13, wherein in step (d) , the binder layer surface of the light emitting diode section is bonded onto an electrically conductive pad section located on the substrate.
16. The method as claimed in claim 13, wherein the bonding in step (d) is performed by heating and pressing at a temperature of 250 °C to 500 °C and a pressure of 1 Mpa to 100 Mpa .
17. The method as claimed in claim 13, comprising the steps of:
(a) depositing a p-type ohmic contact metal layer on a p-type layer of a light emitting diode section grown onto a first substrate;
(b) forming a diffusion barrier layer on the p-type ohmic contact metal layer by using electrically conductive material having higher density than that of a binder;
(c) forming a binder layer on the electrically conductive diffusion barrier layer by using the binder;
(d) bonding the binder layer surface of the light emitting diode section onto a second substrate; (e) irradiating laser toward the light emitting diode section to remove the first substrate; and
(f) depositing an n-type ohmic contact metal layer on an n-type layer of the light emitting diode section, which is exposed as the first substrate is removed, and then carrying out heat treatment.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR10-2005-0060989 | 2005-07-07 | ||
| KR1020050060989A KR20070006027A (en) | 2005-07-07 | 2005-07-07 | Light emitting diode device comprising a diffusion barrier layer and method for preparation thereof |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| WO2007007980A1 true WO2007007980A1 (en) | 2007-01-18 |
Family
ID=37637319
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/KR2006/002653 WO2007007980A1 (en) | 2005-07-07 | 2006-07-07 | Light emitting diode device comprising a diffusion barrier layer and method for preparation thereof |
Country Status (3)
| Country | Link |
|---|---|
| KR (1) | KR20070006027A (en) |
| TW (1) | TW200707811A (en) |
| WO (1) | WO2007007980A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113841261A (en) * | 2021-06-10 | 2021-12-24 | 天津三安光电有限公司 | Light emitting diode and manufacturing method thereof |
Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH1140852A (en) * | 1997-07-16 | 1999-02-12 | Sanyo Electric Co Ltd | Electrode on n-type nitride semiconductor semiconductor device provided with it, and manufacture thereof |
| WO2003041234A1 (en) * | 2001-11-05 | 2003-05-15 | Nichia Corporation | Semiconductor element |
| US6639354B1 (en) * | 1999-07-23 | 2003-10-28 | Sony Corporation | Light emitting device, production method thereof, and light emitting apparatus and display unit using the same |
| EP1471583A1 (en) * | 2002-01-28 | 2004-10-27 | Nichia Corporation | Nitride semiconductor device having support substrate and its manufacturing method |
| US20050133797A1 (en) * | 2003-12-23 | 2005-06-23 | Samsung Electronics Co., Ltd. | Flip-chip light emitting diode and method of manufacturing the same |
| KR20050068402A (en) * | 2003-12-30 | 2005-07-05 | 서울옵토디바이스주식회사 | P-type ohmic contact in gan-based led |
-
2005
- 2005-07-07 KR KR1020050060989A patent/KR20070006027A/en not_active Application Discontinuation
-
2006
- 2006-07-06 TW TW095124624A patent/TW200707811A/en unknown
- 2006-07-07 WO PCT/KR2006/002653 patent/WO2007007980A1/en active Application Filing
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH1140852A (en) * | 1997-07-16 | 1999-02-12 | Sanyo Electric Co Ltd | Electrode on n-type nitride semiconductor semiconductor device provided with it, and manufacture thereof |
| US6639354B1 (en) * | 1999-07-23 | 2003-10-28 | Sony Corporation | Light emitting device, production method thereof, and light emitting apparatus and display unit using the same |
| WO2003041234A1 (en) * | 2001-11-05 | 2003-05-15 | Nichia Corporation | Semiconductor element |
| EP1471583A1 (en) * | 2002-01-28 | 2004-10-27 | Nichia Corporation | Nitride semiconductor device having support substrate and its manufacturing method |
| US20050133797A1 (en) * | 2003-12-23 | 2005-06-23 | Samsung Electronics Co., Ltd. | Flip-chip light emitting diode and method of manufacturing the same |
| KR20050068402A (en) * | 2003-12-30 | 2005-07-05 | 서울옵토디바이스주식회사 | P-type ohmic contact in gan-based led |
Also Published As
| Publication number | Publication date |
|---|---|
| TW200707811A (en) | 2007-02-16 |
| KR20070006027A (en) | 2007-01-11 |
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