TWI395353B - Method for manufacturing vertical light -emitting diodes - Google Patents

Description

Vertical light emitting diode manufacturing method

The present invention relates to a method of fabricating a light-emitting diode, and more particularly to a method of fabricating a GaN-based vertical light-emitting diode.

Conventional lateral structure GaN-based light-emitting diode (LED), because the use of sapphire (Al ₂ O ₃ , sapphire) substrate with poor conductivity and thermal conductivity, the two electrodes should be placed on the same side of the epitaxial structure, resulting in effective light-emitting area Small and current flow paths are too long, causing their series resistance values to be high and deriving severe current crowding. Moreover, the lateral structure GaN-based LED is prone to high temperatures under high power operation, which will result in a loss of luminance and efficiency, a change in the wavelength of the emission, a decrease in reliability, and a shortened life of the LED.

At present, there is a vertical structure GaN-based LED, which replaces the sapphire substrate with a high-conductivity and thermal-conducting replacement substrate. It has been experimentally confirmed that the above problems can be effectively improved to enhance the application of the GaN-based LED in the high-power field. Among them, the sapphire substrate is stripped by a laser lift-off (LLO), and a plated metal substrate having high heat dissipation and low series resistance is integrated, or wafer bonding is performed using a semiconductor substrate or a metal substrate. Substrate technology has been widely used in the fabrication of high power vertical structure GaN-based LEDs. However, the above process of the vertical structure GaN-based LED has the following disadvantages: (1) the metal substrate technology mainly based on electroplating, and the LED epitaxial wafer must be subjected to steps such as pickling, deionized water washing and electroplating, and the process is quite complicated. . (2) Copper, nickel or other alloy substrates commonly used in wafer bonding technology in the industry are subject to thermal stress and stability problems due to their different thermal expansion coefficients from GaN-based materials. (3) In addition, the wafer bonding process involves high temperature (200 ~ 550 ° C) and high voltage, in order to make the metal electrode on the LED wafer and the new substrate instead of the sapphire substrate bonding and ohmic contact. Taking Au-Si (gold-ruthenium) bonding as an example (that is, the bonding of the Au electrode and the replacement germanium substrate), the required process temperature and pressure are 350 to 380 ° C and 20 to 35 kg / cm ^{2 , respectively} . The process of high temperature and high pressure is difficult to control, the contact resistance of components is high, and severe micro-cracks are caused, resulting in low product yield and poor photoelectric characteristics.

As can be seen from the above description, the process of the above vertical GaN-based LED still needs to be improved.

Accordingly, it is an object of the present invention to provide a method of manufacturing a vertical light-emitting diode that can improve process yield, reduce contact resistance, and maintain good photoelectric characteristics of components.

A method of manufacturing a vertical light-emitting diode according to the present invention comprises the following steps (1) of preparing a conversion substrate.

(2) A buffer layer is coated on the conversion substrate.

(3) A light-emitting unit is coated on the buffer layer.

(4) A metal contact layer unit is coated on the light emitting unit.

(5) coating an adhesion reflective layer unit on the metal contact layer unit.

(6) Forming an anisotropic conductive adhesive layer on the adhesion reflective layer unit.

(7) A supporting substrate is adhered to the anisotropic conductive adhesive layer.

(8) The conversion substrate and the buffer layer are removed.

(9) An electrode is coated on the light emitting unit.

The attached reflective layer unit of the step (5) is deposited on the metal contact layer unit by evaporation, sputtering or ion plating, and the attached reflective layer unit comprises four layers of an attached reflective layer. The adhesion reflective layer is selected from the group consisting of titanium (Ti), aluminum (Al), gold (Au), nickel (Ni), silver (Ag), platinum (Pt), palladium (Pd), gold/zinc ( Au/Zn), Au/Be, Au/Ge, Au/Ge/Ni, In (In), Tin (Sn), Zinc (Zn) The group formed, and any combination thereof.

The anisotropic conductive adhesive layer of the step (6) is formed by coating an anisotropic conductive film (ACF) material on the surface of the adhesion reflective layer unit, and the anisotropic conductive adhesive film material is The resin is composed of conductive particles, which has the functions of unidirectional conduction and gluing, and has good thermal stability and elasticity. The anisotropic conductive adhesive layer is used as an adhesive layer to facilitate the press-bonding of the subsequent supporting substrate. Sticky work. The elasticity of the anisotropic conductive layer can be judged by the Young's modulus E value, which is the stress (E=stress/strain) required to produce a strain per unit. The smaller the E value, the softer and more buffering. Suitable as the anisotropic conductive adhesive layer of the present invention, which is 4×10 ⁹ Pa (Pa, ie, N/m ² )≦E≦8×10 ⁹ Pa (Pa), which can provide appropriate elasticity to withstand subsequent processes. The pressure.

The thickness of the anisotropic conductive adhesive layer is d, preferably 5 μm≦d≦20 μm, because the anisotropic conductive adhesive layer is too thin and less than 5 μm, the pressure buffering capacity is weakened, and the thickness is too thick. Will increase the parasitic series resistance.

The support substrate of the step (7) may be a flexible substrate or a non-flexible substrate. The flexible substrate is, for example, a metal film: aluminum foil, copper foil, iron cobalt nickel alloy (stainless steel), gold foil, silver foil, iron foil or any combination thereof, or a plastic polymer sheet. The material of the non-flexible thick film substrate is, for example, a semiconductor substrate such as germanium, gallium nitride, gallium arsenide or tantalum carbide, and a metal substrate such as nickel, copper, copper nickel or copper tungsten.

In the step (7), the test piece of the steps (1) to (6) and the support substrate are pressed and adhered to each other by a wafer bonding machine. The adhesive pressure is P, the adhesive temperature is T, and the adhesive time is t, preferably 9 kg/cm ² ≦P ≦ 25 kg/cm ² , 25 ° C ≦ T ≦ 180 ° C, 5 seconds ≦ t ≦ 900 seconds. When the operating temperature is too low, the curing degree is insufficient, so that the robustness of the component is lowered. When the adhesive pressure is too low and less than 9 kg/cm ² , or the adhesion time is too short, the adhesion is insufficient. If the adhesion time is too long or the temperature is too high, it will cause changes in the colloidal properties.

Step (8) is to remove the conversion substrate by using a laser lift-off method, and the laser light source used is an excimer laser.

The above and other technical contents, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments.

Referring to FIG. 1 , a preferred embodiment of a method for fabricating a vertical LED is used to fabricate a vertical LED. The LED includes: a support substrate 26 and a support layer. An anisotropic conductive adhesive layer 28 on the substrate 26 and an attached reflective layer on the anisotropic conductive adhesive layer 28 A metal contact layer unit 24 on the attached reflective layer unit 25, a light-emitting unit 23 on the metal contact layer unit 24, and an electrode 27 on the light-emitting unit 23 are provided.

Referring to Figures 2, 3 and 4, the method of fabricating a vertical light-emitting diode of the present invention comprises the following steps: (1) performing step 11: preparing a sapphire (Al ₂ O ₃ ) conversion substrate 21.

(2) Step 12: A layer of gallium nitride (GaN) buffer layer 22 is coated on the conversion substrate 21.

(3) performing step 13: coating the light-emitting unit 23 on the GaN buffer layer 22, firstly growing a first cladding layer 231 made of n-type gallium nitride (n-GaN) on the GaN buffer layer 22, Further, an active layer 232 having a multi-quantum well structure is grown on the first cladding layer 231, and finally a layer made of p-type gallium nitride (p-GaN) is grown on the active layer 232. Two cladding layers 233. The active layer 232 may be a homogenous structure, a heterostructure, or a quantum well structure covering a GaN-based material. Therefore, the present invention mainly provides a GaN-based vertical light-emitting diode.

(4) Step 14: coating the metal contact layer unit 24 on the light-emitting unit 23, first performing the activation of the test piece of the steps 11 to 13 at a high temperature to make the carrier of the p-GaN second cladding layer 233 Increased concentration, increased conductivity, and reduced contact resistance. Next, the Al ₂ O ₃ conversion substrate 21 is thinned and polished, and after the test piece is cleaned, the metal contact layer unit 24 can be deposited. The deposition method is an electron beam (E-beam) evaporation method, and a nickel metal contact layer 241 made of nickel (Ni) is sequentially grown on the second cladding layer 233, and a layer is made of gold (Au). The gold metal contact layer 242 is formed, and the test piece is annealed in an oxygen atmosphere at a temperature of 520 ° C for 15 minutes to form a nickel-gold metal oxide (oxidized-Ni/Au), thereby completing p-type ohmic contact. . This step allows a good ohmic contact between the second cladding layer 233 and the subsequently bonded support substrate 26.

(5) Performing step 15: coating the adhesion reflective layer unit 25 on the metal contact layer unit 24 by means of E-beam evaporation, in the order of depositing a layer of titanium (Ti) adhesion reflective layer on the gold metal contact layer 242. 251, a layer of aluminum (Al) adhesion reflective layer 252, a layer of titanium adhesion reflective layer 253, and a layer of gold adhesion reflective layer 254. The adhesion reflection layer unit 25 has a function of light reflection, and can reflect the light generated by the active layer 232 toward the support substrate 26 toward the electrode 27, thereby increasing the luminous efficiency of the LED. Moreover, between the adhesion reflective layer unit 25 and the metal contact layer unit 24, and between the subsequently formed anisotropic conductive adhesive layer 28, there is good ohmic contact and adhesion bonding force.

(6) Performing step 16: forming an anisotropic conductive adhesive layer 28 by applying an anisotropic conductive film on the surface of the gold-attached reflective layer 254 by spin-coating. , ACF) material, in this embodiment, has a thickness of about 10-15 μm.

(7) performing step 17: adhering the support substrate 26, placing the test piece completing the foregoing steps on a wafer bonding machine, and then placing the supporting substrate 26 on the surface of the anisotropic conductive adhesive layer 28, using the wafer bonding machine The test piece and the support substrate 26 are pressed against each other to perform an adhesive bonding operation, and thus the structure shown in FIG. 3 is obtained. The wafer bonding machine of this embodiment is an instrument of the model "ATS P-bond 100" supplied by "Juchang Technology Co., Ltd.". The support substrate 26 is made of 304-L stainless steel. The parameters of adhesion pressure, temperature and time in step 17 are related to the material type of the anisotropic conductive adhesive layer 28. In this embodiment, the anisotropy of Young's modulus E is about 4×10 ⁹ Pa·8×10 ⁹ Pa. Conductive film materials, the typical process parameters are, the adhesion pressure is 25 kg / cm ² , the adhesion temperature is 180 ° C, the adhesion time lasts 15 seconds.

(8) Step 18: The conversion substrate 21 and the buffer layer 22 are removed, and the test piece is irradiated with KrF excimer laser light to perform a laser liftoff to remove the conversion substrate 21. Then, the GaN buffer layer 22 is removed by etching using an inductively coupled plasma (ICP) to obtain the structure shown in FIG.

Referring to FIG. 5, in order to complete the top view of the test piece after the laser stripping process of step 18, the size of the components can be defined by a photomask. Through the elastic flexibility of the anisotropic conductive adhesive layer 28 used in the present invention, the GaN-based epitaxial film after completion of the block laser stripping process (each square block as shown) remains intact. There is no conventional conventional wafer bonding technique for the phenomenon of epitaxial fracture after laser stripping.

(9) performing step 19: depositing an electrode 27 on the surface of the first cladding layer 231 of the light emitting unit 23, the electrode 27 may be composed of a stack of a plurality of different materials, and may be one of materials such as titanium, aluminum, gold, or the like. Any combination is formed, thereby forming an n-type contact, thus completing the fabrication of the vertical light-emitting diode structure of FIG.

6 is a current-voltage characteristic diagram of a vertical LED and a conventional lateral LED according to the present invention, and the element size is 600 μm×600 μm. The figure shows that when the current operation is 50 mA, the forward bias voltage is 2.99 V. Electricity When the current is 300 mA, the forward bias is 3.82V. The forward bias voltages of the conventional lateral LEDs at 50 mA and 300 mA are 3.46 V and 4.8 V, respectively, so the forward bias of the present invention is smaller than that of the conventional lateral LED. While Figure 7 shows that the present invention has better optical output power than conventional lateral LEDs. Because the vertical LED of the present invention has a shorter vertical conduction path than the conventional lateral LED, and a larger light-emitting area, and the bonding technology of the anisotropic conductive adhesive layer 28, the LED produced by the present invention has good quality. The n-GaN first cladding layer 231 exposed by laser lift-off also has a lower sheet resistance, so that current spreading performance is better. Therefore, the vertical LED of the present invention has better photoelectric characteristics, low forward voltage drop, low parasitic series resistance, and high luminous efficiency.

Referring to FIG. 8, the LED obtained in the present embodiment has a current-dominant wavelength measured after undeflected (effective length L=24 mm) and after deflection (effective length L=15 mm). Characteristic curve. It can be seen that under the operating conditions of 30 mA, the original dominant wavelength of the LED without external stress (L=24 mm) is 465.3 nm, while the LED of the deflection (L=15 mm) is the main The wavelength is 465.0 nm and its wavelength shift is only 0.3 nm. It is apparent that the LED produced by the present invention has excellent luminescence properties in the case of substrate deflection.

In summary, by using the anisotropic conductive adhesive layer 28 as an adhesive layer, the process of bonding the support substrate 26 can be simplified, and a preferred bonding method of the support substrate 26 is provided, which facilitates the step of peeling off the conversion substrate 21. Perform to avoid the phenomenon of epitaxial fracture caused by laser peeling. Moreover, the good elasticity of the anisotropic conductive adhesive layer 28 buffers the adhesive pressure in the process, thereby improving the process yield and effectively reducing the contact resistance. Furthermore, the adhesive work of the present invention The temperature is 180 ° C or less, and the present invention is a lower temperature process than the conventional wafer bonding process at least 200 ° C or higher, which reduces the thermal stress problem and can maintain good photoelectric characteristics of the device. Moreover, the present invention uses a lower adhesive pressure and also helps to increase the bond yield of the wafer. At the same time, the vertical conduction of the anisotropic conductive adhesive layer 28 and the anisotropic conductive property of the lateral insulation suppress the series resistance increased by the current diffusion on the path, thereby effectively improving the photoelectric performance of the component.

The above is only the preferred embodiment of the present invention, and the scope of the invention is not limited thereto, that is, the simple equivalent changes and modifications made by the scope of the invention and the description of the invention are All remain within the scope of the invention patent.

11~19‧‧‧Steps

21‧‧‧ Conversion substrate

22‧‧‧ Buffer layer

23‧‧‧Lighting unit

231‧‧‧First coating

232‧‧‧ active layer

233‧‧‧Second coating

24‧‧‧Metal contact unit

241‧‧‧ Nickel metal contact layer

242‧‧‧ Gold metal contact layer

25‧‧‧Adhesive reflector unit

251‧‧‧Titanium attached reflective layer

252‧‧‧Aluminum attached reflective layer

253‧‧‧Titanium attached reflective layer

254‧‧‧ gold-attached reflective layer

26‧‧‧Support substrate

27‧‧‧Electrode

28‧‧‧ anisotropic conductive adhesive layer

1 is a schematic view of a vertical light emitting diode (LED); FIG. 2 is a flow chart showing the steps of a preferred embodiment of the method for fabricating the vertical light emitting diode of the present invention, which produces the method shown in FIG. FIG. 3 is a schematic view of the light emitting diode during the manufacturing process; FIG. 4 is a schematic view similar to FIG. 3, showing a conversion substrate and a buffer layer being removed; FIG. 5 is a preferred embodiment. FIG. 6 is a current-voltage characteristic diagram of a vertical LED and a conventional lateral LED according to the present invention; FIG. 7 is a light output function of the vertical LED and the conventional lateral LED of the present invention; The rate-current characteristic graph; and FIG. 8 is a current-principal wavelength characteristic curve measured by the vertical LED of the present invention in an undeflected state and a flexed state.

11~19‧‧‧Steps

Claims (11)

A method for manufacturing a vertical light-emitting diode comprises the steps of: (1) preparing a conversion substrate; (2) coating a buffer layer on the conversion substrate; and (3) coating a light-emitting unit on the buffer layer (4) coating a metal contact layer unit on the light emitting unit; (5) coating an attached reflective layer unit on the metal contact layer unit; (6) forming an anisotropy on the attached reflective layer unit; a conductive adhesive layer; (7) a support substrate is adhered to the anisotropic conductive adhesive layer; (8) the conversion substrate and the buffer layer are removed; and (9) an electrode is coated on the light-emitting unit; wherein (7) The adhesive pressure is P, the adhesive temperature is T, and 9 kg/cm ² ≦P ≦ 25 kg/cm ² , 25 ° C ≦ T ≦ 180 ° C. The method for manufacturing a vertical light-emitting diode according to claim 1, wherein the adhesion time of the step (7) is t, and 5 seconds ≦t ≦ 900 seconds. The method for manufacturing a vertical light-emitting diode according to claim 1 or 2, wherein the step (6) is to apply an anisotropic conductive film material to the surface of the adhesion reflective layer unit to form the difference. Square conductive adhesive layer. The method for manufacturing a vertical light-emitting diode according to claim 3, wherein the anisotropic conductive adhesive layer has a Young's modulus of E, and 4×10 ⁹ Pa≦E≦8×10 ⁹ Pa. The method for manufacturing a vertical light-emitting diode according to the fourth aspect of the invention, wherein the thickness of the anisotropic conductive adhesive layer is d, and 5 μm ≦d≦20μm. The method of manufacturing a vertical light-emitting diode according to claim 5, wherein the support substrate is a flexible substrate made of a metal thin film or a plastic polymer polymer sheet. The method for manufacturing a vertical light-emitting diode according to claim 5, wherein the material of the support substrate is selected from the group consisting of germanium, gallium nitride, gallium arsenide, tantalum carbide, nickel, copper, A group of copper nickel and copper tungsten. The method for manufacturing a vertical light-emitting diode according to claim 5, wherein the adhesion reflective layer unit is selected from the group consisting of titanium, aluminum, gold, nickel, silver, platinum, palladium, gold/zinc. , gold/铍, gold/锗, gold/锗/nickel, indium, tin, zinc, and any combination thereof. The method for manufacturing a vertical light-emitting diode according to claim 5, wherein the attached reflective layer unit comprises four layers of attached reflective layers, the attached reflective layers being made of titanium, aluminum, titanium, and gold, respectively. . A method of manufacturing a vertical light-emitting diode according to claim 5, wherein the step (8) is to remove the conversion substrate by a laser lift-off method. The method of manufacturing a vertical light-emitting diode according to claim 5, wherein the light-emitting unit is made of a gallium nitride-based material.