WO2007046656A1

WO2007046656A1 - Method of producing light emitting diode having vertical structure

Info

Publication number: WO2007046656A1
Application number: PCT/KR2006/004279
Authority: WO
Inventors: Woo-Beom Choi; Sang-Won Seo; Seung-Woo Choi; Sang-Yong Park
Original assignee: Bnp Science
Priority date: 2005-10-20
Filing date: 2006-10-20
Publication date: 2007-04-26
Also published as: KR100752348B1; KR20070043296A

Abstract

Disclosed is a fabricating method for light emitting diodes (LEDs) having vertical structure, improved regarding a sapphire substrate removal step which is essential for the fabrication of the LEDs. According to the embodiments of the present invention, in order to minimize damage of an epitaxial layer when removing the sapphire substrate from the epitaxial layer, the removal of the sapphire substrate is performed in two steps, that is, polishing or etching, and laser beam projection. First, the sapphire substrate is processed into a thin layer by the polishing or etching, so that the epitaxial layer can be avoided from directly contacting with etching solution. Accordingly, increase of roughness and generation of pinholes on a surface of the epitaxial layer can be prevented.

Description

METHOD OF PRODUCING LIGHT EMITTING DIODE HAVING VERTICAL STRUCTURE

Technical Field

[1] The present invention relates to a light emitting diode (LED) and a method for producing the LED. More particularly, the present invention relates to an improved method for producing an LED having vertical structure, and an LED produced using the method.

[2]

Background Art

[3] A light emitting diode (LED) is a generally known semiconductor device that converts electric currents to light, by the combination of electrons with holes. Color of the light emitted from the LED depends on the semiconductor materials used in the LED because wavelength of the emitted light is determined by a band gap which refers to energy difference between electrons in the valence band and electrons in the conduction band. To be more specific, photons with low-energy and long- wavelength are generated from a smaller band gap, and photons with high-energy and short- wavelength from a larger band gap.

[4] When a nitride is used as a luminous material in the thin film structure of the LED, sapphire is usually adopted as a base substrate since the sapphire having similar lattice constant and crystal structure causes less crystal defects during epitaxial growth.

[5] FIG. 1 is a sectional view showing an example of a conventional LED having horizontal structure. More specifically, the LED of FIG. 1 is a GaN LED 100 having horizontal structure. The GaN LED 100 comprises a sapphire substrate 110 and a GaN luminous structure 150 formed on the sapphire substrate 110.

[6] The GaN luminous structure 150 is constructed by successive lamination of an n- type GaN clad layer 152, an active layer 154 having a Multi-Quantum Well structure, and a p-type GaN clad layer 156. Growth of the luminous structure 150 is achieved by generally-known processings such as Metal Organic Chemical Vapor Deposition (MOCVD), Liquid-Phase Epitaxy (LPE), and Molecule Beam Epitaxy (MBE). Therefore, the luminous structure 150 is also referred to as an epitaxial layer. A buffer layer (not shown) comprising AlN/GaN may be further provided to improve lattice matching between the sapphire substrate 110 and the luminous structure 150, before the growth of the n-type GaN clad layer 152.

[7] Predetermined areas of the p-type GaN clad layer 156 and the active layer 154 are dry-etched, so that an upper surface of the n-type GaN clad layer 152 is partly exposed. Then, an n-type electrode 190 and a p-type electrode 170 are formed on the exposed areas. Generally, a transparent electrode 160 may be formed on the p-type GaN clad layer 156 before forming the p-type electrode 170, so that a current injection area can be increased without deteriorating luminance of the LED.

[8] Since the above- structured GaN LED 100 uses the sapphire substrate 110 which is an insulant, however, the electric current flow from the n-type electrode 190 to the p- type electrode 170 through the active layer 154 should be formed narrow in a horizontal direction. Such narrow electric current flow increases forward voltage of the GaN LED 100, thereby deteriorating current efficiency. Furthermore, the insulant barely discharges static electricity induced from the outside, and thus increases defect rate of the device due to the static electricity.

[9] In addition, although much heat is generated as current density is increased, heat discharge efficiency of the sapphire substrate 110 is unsatisfactory due to low thermal conductivity. Therefore, as the heat accumulates, mechanical stress may be generated between the sapphire substrate 110 and the GaN luminous structure 150. Consequently, stability of the device is deteriorated and application of high current for high output is restricted.

[10] In order to form the n-type electrode 190, a part of the active layer 154 not less than the area of the n-type electrode 190 needs to be partially removed. As a luminous area is decreased, the luminous efficiency corresponding to the ratio of the luminance to the element size is deteriorated. Furthermore, productivity of chips per wafer is restricted because it is hard to reduce a chip size of the LED 100 due to the formation of both the n-type electrode 190 and the p-type electrode 170 on the upper part of the LED 100.

[11] FIG. 2 is a sectional view of an exemplary LED having vertical structure, for overcoming demerits of the horizontally structured conventional LED.

[12] In FIG. 2, a GaN LED 200 having vertical structure comprises a luminous structure

250, that is, an epitaxial layer constituted by a p-type GaN clad layer 252, an active layer 254, and an n-type GaN clad layer 256.

[13] As shown in FIG. 2, the vertically structured LED 200 utilizes a conductive substrate such as a silicon substrate 220 as a receptor substrate for the epitaxial layer 250, so that upper and lower parts thereof electrically communicate with each other. As a result, the heat discharge efficiency of the LED 200 can be improved. The forward voltage can be reduced since the electric current flows through a wider area than in the horizontally structured LED. In addition, static electricity problem is effectively prevented from being generated, and high output of LED 200 is obtainable by applying high current thereto.

[14] With regard to the manufacturing processes, the process for forming the transparent electrode is not required since current density distribution is improved highly enough. Also, the sapphire substrate which is firm can be omitted, thereby simplifying the process of cutting the structure by the unit device. Unlike the horizontally structured LED, partial etching of the active layer is not required, thereby enhancing luminance by securing a wider luminous area. Production of chips per wafer can also be increased by reducing the chip size of the unit LED.

[15] FIG. 3 through FIG. 9 show steps of the conventional process for fabricating the

LED having vertical structure shown in FIG. 2, respectively.

[16] In the step of FIG. 3, an epitaxial layer, that is, a luminous structure 350 of GaN single crystal layers is formed on a sapphire substrate 310 which is used as a sacrificial layer. In the step of FIG. 4, the luminous structure 350 is separated into the size of unit LED. In the step of FIG. 5, a conductive substrate 320 such as a silicon substrate is bonded to an upper surface of the luminous structure 350 being separated, using a conductive adhesive layer 340.

[17] In the step of FIG. 6 or FIG. 7, the sapphire substrate 310 is removed. As shown in

FIG. 6, a laser beam may be used in separating the sapphire substrate 310 from the luminous structure 350. Alternatively, mechanical polishing, wet-etching, or dry- etching may be used for removal of the sapphire substrate 310 as shown in FIG. 7.

[18] In the step of FIG. 8, electrodes 370 and 390 are formed on opposite sides of the resultant structure, respectively. In the step of FIG. 9, the resultant structure is cut by the unit LED size, that is, the size of the separated luminous structure 350, to obtain a final form of the LED having vertical structure.

[19] Although the sapphire substrate 310 is required for growth of the epitaxial layer

350, the sapphire substrate 310 should be replaced by the conductive substrate 320 since an insulant such as the sapphire substrate 310 is inappropriate as a receptor substrate for an LED.

[20] When removing the sapphire substrate 310 using the laser beam as shown in FIG. 6, the laser beam being projected moves within a certain small area determined by size and shape of a focus of the laser beam, rather than being simultaneously projected onto the whole surface of the wafer on which a plurality of the luminous structures 350 are formed. This causes great stress on the boundary of the laser-projected area.

[21] Referring to FIG. 7, in addition, when polishing and etching are used for removing the sapphire substrate 310, selectivity of etching solution with respect to the sapphire substrate 310 and the epitaxial layer, that is, the GaN luminous structure 350 is unfavorable. Therefore, the epitaxial layer is obtained with uneven thickness, rough surface, and pinholes generated thereon.

[22] According to the above conventional methods for removing the sapphire substrate

310, the epitaxial layer 350 is degraded due to the stress, surface defection and the pinholes. As a consequence, the whole performance as well as the luminous efficiency of the LED should be deteriorated.

[23] Although the vertically structured LED is much more advantageous than the horizontally structured LED, the above problems caused in the sapphire substrate removal step which is essential for the fabrication of the vertically structured LED still remain unsolved.

[24]

Disclosure of Invention Technical Problem

[25] The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a fabricating method for a light emitting diode (LED) having vertical structure, capable of effectively removing a sapphire substrate 310 and minimizing deterioration of an epitaxial layer 350, and an improved LED having vertical structure fabricated by the method. More particularly, it is an object of the present invention to provide a removal process for a sapphire substrate 310 after bonding the sapphire substrate 310 and the conductive receptor substrate 320, in fabricating the LED having vertical structure, without deteriorating the epitaxial layer 350.

[26]

Technical Solution

[27] According to an aspect of the present invention, there is provided a method for fabricating light emitting diodes (LEDs) having vertical structure, comprising steps of forming a luminous structure on a device substrate; providing a receptor substrate; bonding the luminous structure to the receptor substrate; reducing thickness of the device substrate; generating unit devices by etching the structure on the receptor substrate, the structure comprising the device substrate and the luminous structure; and removing the remaining respective device substrates from the respective unit devices by projecting a laser beam.

[28] According to another embodiment of the present invention, there is provided a method for fabricating LEDs having vertical structure comprising steps of forming a luminous structure on a device substrate; forming a reflection layer on the luminous structure; forming an adhesive layer on the reflection layer; etching the luminous structure, the reflection layer, and the adhesive layer formed on the device substrate by the unit device size; providing a receptor substrate; bonding the luminous structure to the receptor substrate using the adhesive layer; reducing thickness of the receptor substrate; forming electrodes on both surfaces of the receptor substrate; and separating the receptor substrate into the unit device size.

[29] According to yet another embodiment of the present invention, there is provided a method for fabricating LEDs having vertical structure comprising steps of forming a luminous structure on a device substrate; separating the structure formed on the device substrate including the luminous structure by etching by the unit device size; providing a conductive receptor substrate having a pattern for separating the respective devices formed by predetermined depth; bonding the luminous structure to the conductive receptor substrate; reducing thickness of the device substrate; separating the device substrate from the luminous structure using a laser beam; forming an electrode on the luminous structure being separated by the unit device size; fixing the unit devices using a fixing means; exposing the pattern by processing a back surface of the conductive receptor substrate; forming another electrode on the back surface of the conductive receptor substrate; and separating the unit devices from the fixing means. [30]

Advantageous Effects

[31] According to the embodiments of the present invention, in order to minimize damage on an epitaxial layer when removing a sapphire substrate from the epitaxial layer, the removal of the sapphire substrate is performed in two steps. One is mechanical polishing or etching and the other is laser beam projection.

[32] First, the sapphire substrate is processed into a thin layer by the polishing or etching, so that the epitaxial layer can be avoided from directly contacting with etching solution. Consequently, increase of roughness and generation of pinholes on a surface of the epitaxial layer can be prevented.

[33] Next, by projecting a laser beam onto the thinly processed sapphire substrate, the sapphire substrate can be separated without stressing and damaging the LEDs. Here, the sapphire substrate being separated is thinner than in a conventional laser processing. Therefore, the stress generated by the laser beam during the separation is reduced, thereby restraining deterioration of the epitaxial layer.

[34] Applying the process according to the embodiments of the present invention, disadvantages from the polishing and etching processes of the conventional LED fabrication method, for example, unevenness in thickness, increase of roughness, and generation of pinholes on the epitaxial layer can be prevented. Moreover, unlike the conventional laser processing, damage and stress applied to the epitaxial layer around the laser projection area can be highly reduced.

[35] According to the present invention, deterioration of the epitaxial layer is minimized, thereby improving luminous efficiency of the LED. Consequently, reliability of the LED is enhanced.

[36] While the invention has been shown and described with reference to certain embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. For example, the method for removing a sapphire substrate according to the present invention can be adopted not only by the LED fabricating process of the present invention, but also by other various fabricating processes such as a laser diode fabricating process, which include a step of separating an insulant substrate, for example, the sapphire substrate from an epitaxial layer.

[37]

Brief Description of the Drawings

[38] 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:

[39] FIG. 1 is a sectional view of a conventional light emitting diode (LED) having horizontal structure;

[40] FIG. 2 is a sectional view of a conventional LED having vertical structure;

[41] FIG. 3 through FIG. 9 show respective steps of the fabricating process for the conventional LED having vertical structure;

[42] FIG. 10 through FIG. 24 show respective steps of the fabricating process for an

LED having vertical structure according to a first embodiment of the present invention;

[43] FIG. 25 through FIG. 32 show respective steps of the fabricating process for an

LED having vertical structure according to a second embodiment of the present invention; and

[44] FIG. 33 through FIG. 43 show respective steps of the fabricating process for an

LED having vertical structure according to a third embodiment of the present invention.

[45]

Mode for the Invention

[46] Reference will now be made in detail to exemplary embodiments of the present invention.

[47] <First Embodiment

[48] FIG. 10 through FIG. 24 show respective steps of the fabricating process for an

LED having vertical structure according to a first embodiment of the present invention.

[49] As shown in FIG. 10, a luminous structure 420 is formed on a device substrate 410, for example, a sapphire substrate 410. The device substrate 410 is also referred to as a sacrificial substrate or a growth substrate for the luminous structure 420. An n-type GaN clad layer, an active layer, and a p-type GaN clad layer are successively formed by epitaxial growth, thereby constructing an epitaxial layer , that is, the GaN luminous structure 420. In case where the sapphire substrate 410 having the luminous structure 420 thereon is offered in advance to an LED fabricating process, the step for forming the luminous structure 420 can be omitted from the LED fabricating process.

[50] In order to improve lattice matching between the sapphire substrate 410 and the epitaxial layer 420, an optional buffer layer (not shown) comprising AlN/GaN can be provided. Also, a reflection layer 430 can be optionally formed to reflect light discharged from the active layer in the GaN luminous structure 420. The reflection layer 430 may comprise Ni, Al, Ag, Au, Pt, or an alloy of the aforementioned materials. Other various materials generally used for a reflection layer in the art can also be adopted for the reflection layer 430. Although it is preferred to include the reflection layer 430, luminance can be somewhat improved without forming the reflection layer 430 because a first conductive adhesive layer 442 in the present invention usually comprises metal or alloy having relatively high reflectivity.

[51] Afterwards, the first conductive adhesive layer 442 is formed to facilitate bonding between a device substrate and the receptor substrate such as a silicon substrate. The receptor substrate is also referred to as a host substrate in the art. The silicon substrate is generally used in the LED having vertical structure. However, except an insulant such as sapphire, other materials such as Ge, SiC, ZnO, diamond, and GaAs may be adopted. The first conductive adhesive layer 442 may be formed of an adhesive pad which is a conductive material having adhesive property. A metal adhesive using Au is adequate as the conductive material, while other materials such as Au-Sn, Sn, In, Au- Ag, Ag-Ge, Ag-Cu, and Pb-Sn may be used.

[52] When using a receptor substrate 450 as shown in FIG. 11, a second adhesive layer

444 is formed on an upper part of the receptor substrate 450 comprising a silicon single crystal. The second adhesive layer 444 formed on the receptor substrate 450 and the first adhesive layer 442 formed on the device substrate 410 are formed of the same material and in the same form.

[53] The steps of FIG. 10 and FIG. 11 can be exchanged and even simultaneously performed. When the device substrate 410 and the receptor substrate 450 are bonded to each other using a single adhesive layer, one of steps for forming the first adhesive layer 442 and forming the second adhesive layer 444 can be omitted.

[54] Referring to FIG. 12, the device substrate 410 and the receptor substrate 450 are bonded to each other using thermo-compression, in a manner that the first adhesive layer 442 and the second adhesive layer 444 face each other. Through the thermo- compression, the two adhesive layers 442 and 444 are combined into a substantially single adhesive layer 440.

[55] Referring to FIG. 13, the device substrate 410 such as the sapphire substrate 410 is processed into tens of D, preferably, less than 50D in thickness by polishing, etching or combination thereof. By processing the sapphire substrate 410 thin, direct contact between the etching solution and the epitaxial layer 420 can be avoided. As a consequence, increase in roughness and generation of pinholes caused to the epitaxial layer of the conventional art can be prevented. Chemical Mechanical Polishing (CMP), for example, may be adopted when performing the polishing. Dry-etching using Reactive Ion Etching (RIE) or Induced Coupled Plasma/RIE (ICP/RIE), for example, may be adopted when performing the etching. Otherwise, wet-etching may be performed, using hydrochloric acid, nitric acid, potassium hydroxide, sodium hydroxide, sulfuric acid, phosphoric acid or mixed liquid of the aforementioned etchants as the etching solution.

[56] In the steps in FIG. 14 through FIG. 20, the epitaxial layer is separated into unit

LEDs through photo-etching using an oxide film as a mask.

[57] Referring to FIG. 14, a material capable of resisting the etching and serving as a mask, such as an oxide film 460 and a nitride film, is deposited on the sapphire substrate 410 and a photoresist 470 is deposited thereon.

[58] In the step of FIG. 15, the photoresist 470 is patterned by the unit device size. In the step of FIG. 16, the oxide film 460 is patterned by etching. In the step of FIG. 17, the photoresist 470 is removed. In the step of FIG. 18, the sapphire substrate 410 and the epitaxial layer 420 are patterned by dry-etching or wet-etching, using the oxide film 460 as a mask. Next, the reflection layer 430 and the adhesive layer 440 are etched in the step of FIG. 19. The oxide film 460 is removed by dry-etching or wet-etching in the step of FIG. 20.

[59] In the step of FIG. 21, the sapphire substrate 410 is removed using a laser beam.

Having already been laminated through the polishing and the etching, the sapphire substrate 410 can be removed by the unit device size without inducing any stress and damage to the epitaxial layer 420 of the LED. The laser beam is projected onto a plurality of the unit devices simultaneously. Here, a boundary of the laser beam is controlled to be disposed between the boundaries of the respective unit devices, so that the unit devices are minimally stressed.

[60] In the step of FIG. 22, an n-type electrode 480 is formed on the LED. In the step of

FIG. 23, a silicon substrate 450 is polished into a thin layer, and a p-type electrode 490 is deposited on the polished silicon substrate 450. Finally, in the step of FIG. 24, the silicon substrate 450 is cut by the unit device size.

[61] <Second Embodiment

[62] FIG. 25 through FIG. 32 show respective steps for fabricating an LED having vertical structure according to a second embodiment of the present invention.

[63] As shown in FIG. 25, a luminous structure 520, an optional buffer layer (not shown), an optional reflection layer 530, and a first conductive adhesive layer 542 are successively formed on a device substrate 510 such as a sapphire substrate. Instead of the above steps, a ready-made substrate having the above luminous structure thereon may be provided.

[64] In the step of FIG. 26, the epitaxially grown luminous structure 520, the reflection layer 530, and the first conductive adhesive layer 542 are separated into unit LEDs through photo-etching process.

[65] As shown in FIG. 27, a second adhesive layer 544 is formed on an upper part of a receptor substrate 550 comprising a silicon single crystal. The two substrates 510 and 550 are bonded to each other using thermo-compression in a manner that the first adhesive layer 542 and the second adhesive layer 544 face each other. When the device substrate 510 and the receptor substrate 550 are bonded using a single adhesive layer, one of steps for forming the first adhesive layer 542 and forming the second adhesive layer 544 can be omitted. When one adhesive layer is selected to be formed, the other adhesive layer may be omitted. However, both layers cannot be omitted at the same time

[66] Next, in the step of FIG. 28, the device substrate 510 such as the sapphire substrate

510 is processed into tens of D, preferably, less than 50D in thickness by polishing and etching. In the step of FIG. 29, the sapphire substrate 510 is removed using a laser beam. Since having already been processed thin through polishing and etching, the sapphire layer 510 can be clearly removed by the unit device size without stressing and damaging the LED device including the luminous structure 520, that is, an epitaxial layer.

[67] In FIG. 30, the adhesive layers 542 and 544 are removed using wet-etching, for example. In FIG. 31, the receptor substrate 550 such as a silicon substrate is polished into a thin layer, and electrodes 580 and 590 are formed on the upper surface and the lower surface of the LED, respectively. In FIG. 32, finally, the receptor substrate 550 whereon the electrode 590 is formed is cut by the unit device size.

[68] <Third Embodiment

[69] FIG. 33 through FIG. 40 show respective steps of the fabricating process for an

LED having vertical structure according to a third embodiment of the present invention. In the third embodiment, a patterning step is further included, for patterning a silicon substrate to facilely separate the LED structure into unit devices.

[70] As shown in FIG. 33, a luminous structure 620, an optional buffer layer (not shown), an optional reflection layer 630, and a first conductive adhesive layer 642 are formed on an upper part of a device substrate 610 such as a sapphire substrate. As in the previous embodiments, this step can be omitted by providing a ready-made substrate having the above structure thereon.

[71] In FIG. 34, the luminous structure 620, the reflection layer 630, and the first conductive adhesive layer 642 are separated into unit LEDs through photo-etching process.

[72] The receptor substrate 650 comprising a silicon single crystal is etched to form patterns for separating the respective devices by a predetermined depth using dry- etching as shown in FIG. 35. Selectively, in this step, a second conductive adhesive layer 644 can be formed on the receptor substrate 650 whereon the patterns are formed.

[73] In FIG. 36, the two substrates 610 and 650 are bonded to each other using thermo- compression, in a manner that the first adhesive layer 642 and the second adhesive layer 644 face each other.

[74] In FIG. 37, the device substrate 610 such as the sapphire substrate 610 is processed into tens of D, preferably, less than 50D in thickness by polishing and etching. In the step of FIG. 38, the sapphire substrate 610 is removed by a laser beam. In FIG. 39, an electrode 680 is formed on the luminous structure 620. In FIG. 40, a fixative tape 670, for example, an ultraviolet (UV) tape or a dicing tape is applied to fix the LED devices.

[75] As the back surface of the conductive receptor substrate 650 is processed by polishing and etching, the patterns for separating the devices are gradually exposed, and the structure on the receptor substrate 650 is clearly separated as shown in FIG. 41. In FIG. 42, another electrode 690 is formed on the receptor substrate 650 being exposed. In FIG. 43, finally, the unit LED devices are separated from the fixative tape 680.

[76]

Industrial Applicability

[77] The present invention is applicable to various fields of semiconductor device fabrication accompanied by a process of separating a device substrate, that is, a sacrificial substrate such as a sapphire substrate from an epitaxial layer. For example, the present invention can be applied to fabrication of a light emitting diode (LED) and a laser diode.

[78]

Claims

[1] A method for fabricating light emitting diodes (LEDs) having vertical structure, comprising steps of: providing a device substrate on which a luminous structure is formed; providing a receptor substrate; bonding the luminous structure to the receptor substrate; reducing thickness of the device substrate; generating unit devices by etching the structure on the receptor substrate, the structure comprising the device substrate and the luminous structure; and removing the remaining respective device substrates from the respective unit devices by projecting a laser beam. [2] The method of claim 1, further comprising a step of forming a reflection layer on the luminous structure after the step of providing the device substrate on which the luminous structure is formed. [3] The method of claim 1, further comprising a step of forming electrodes on the opposite surfaces of the unit device from which the remaining device substrate is removed. [4] The method of claim 1, wherein the bonding step comprises bonding the luminous structure and the receptor substrate to each other by providing a conductive adhesive layer to at least one of the luminous structure and the receptor substrate. [5] The method of claim 4, wherein the bonding step comprises bonding the conductive adhesive layer by thermo-compression. [6] The method of claim 1, wherein the reducing step comprises processing the device substrate into tens of D, preferably, less than 50D in thickness. [7] The method of claim 1, wherein the reducing step comprises reducing thickness of the device substrate by at least one of polishing and etching. [8] The method of claim 7, wherein the reducing step comprises at least one of polishing and etching the device substrate into a thickness capable of preventing direct contact of etching solution with the luminous structure. [9] The method of claim 1, wherein the generating step comprises steps of: depositing an oxide film on the device substrate; applying photoresist on the oxide film; patterning the photoresist by the unit device size; patterning the oxide film by etching; and etching the device substrate and the luminous structure by the unit device size using the oxide film as a mask. [10] The method of claim 1, wherein the removing step comprises projecting the laser beam onto the plurality of the unit devices simultaneously, in a manner that a boundary of the laser beam is disposed on the space between the respective unit devices. [11] The method of claim 1, wherein the removing step comprises projecting the laser beam so that the laser beam may not induce any substantial stress onto the luminous structure. [12] The method of claim 3, wherein the electrode forming step comprises steps of: forming an electrode on the upper surface of the unit device from which the remaining device substrate is removed; reducing thickness of the receptor substrate by processing the back surface thereof; forming another electrode on the back surface of the receptor substrate; and separating the receptor substrate into unit device size.

[13] The method of claim 1, wherein the device substrate is a sapphire substrate.

[14] An LED having vertical structure fabricated by a method of one of claims 1 to

13. [15] A method for removing a sapphire substrate from an epitaxial layer grown on the sapphire substrate, comprising steps of: reducing thickness of the sapphire substrate using at least one of polishing and etching; and projecting a laser beam onto the sapphire substrate reduced in thickness. [16] A method for fabricating LEDs having vertical structure comprising steps of: providing a device substrate on which a luminous structure is formed; forming a reflection layer on the luminous structure; forming an adhesive layer on the reflection layer; etching the luminous structure, the reflection layer, and the adhesive layer formed on the device substrate, by the unit device size; providing a receptor substrate; bonding the luminous structure to the receptor substrate using the adhesive layer; reducing thickness of the receptor substrate; forming electrodes on both surfaces of the receptor substrate; and separating the receptor substrate into the unit device sizes. [17] The method of claim 16, wherein the bonding step comprises: forming another adhesive layer on the receptor substrate; and bonding the adhesive layer on the reflection layer to the adhesive layer on the receptor substrate by thermo-compression. [18] The method of claim 16, the reducing step comprises processing the device substrate into tens of D, preferably, less than 50D in thickness, by at least one of polishing and etching. [19] An LED having vertical structure fabricated by a method of one of claims 16 to

18.

[20] An LED having vertical structure fabricated by the method of claim 15.

[21] A method for fabricating LEDs having vertical structure comprising steps of: providing a device substrate on which a luminous structure is formed; separating the structure formed on the device substrate including the luminous structure by etching by the unit device size; providing a conductive receptor substrate having a pattern for separating the respective devices formed by a predetermined depth; bonding the luminous structure to the conductive receptor substrate; reducing thickness of the device substrate; separating the device substrate from the luminous structure using a laser beam; forming an electrode on the luminous structure being separated by the unit device size; fixing the unit devices using a fixing means; separating the unit devices by processing a back surface of the conductive receptor substrate; forming another electrode on the back surface of the conductive receptor substrate; and separating the unit devices from the fixing means. [22] The method of claim 21, wherein the bonding step comprises: providing a conductive adhesive layer respectively to the luminous structure and the conductive receptor substrate; and bonding the two adhesive layers by thermo-compression. [23] The method of claim 21, wherein the reducing step comprises processing the device substrate into tens of D, preferably, less than 50D in thickness, by at least one of polishing and etching.

[24] The method of claim 21, wherein the fixing means is a fixative tape.

[25] The method of claim 21, wherein the device substrate is a sapphire substrate.

[26] An LED having vertical structure fabricated by a method of one of claims 21 to

25. [27] A laser diode fabricated by the method of claim 15.