CN100568555C - Roughened electrodes are used for high-brightness front-mount LED chips and vertical LED chips - Google Patents

Abstract

The invention discloses a manufacturing process of a high-brightness LED chip, which uses natural photolithography technology and ICP dry etching technology to micronize the transparent conductive film layer of the traditional and vertical gallium nitride-based LED, thereby improving the performance of the LED chip. chip light efficiency. And this roughening inventive method is applied to the front LED structure and the vertical LED structure. Under the condition of not adding new devices, the invention greatly improves the external quantum efficiency and stability of the LED chip.

Description

Roughened electrodes are used in the production process of high-brightness formal LED chips and vertical LED chips and their products

technical field

The invention relates to a process method for manufacturing a high-brightness LED chip by a gallium nitride (GaN) semiconductor, in particular to roughening the surface of a transparent conductive film ITO to improve the light extraction efficiency of the LED chip, and belongs to the technical field of nano-processing and semiconductor lighting.

Background technique

External quantum efficiency is the main technical bottleneck of high-brightness LED chips, and its size is equal to the product of internal quantum efficiency and light escape rate. Currently, the internal quantum efficiency of commercial LEDs is close to 100%, but the external quantum efficiency is only 3-30%. This is mainly due to the low escape rate of light. The factors that cause the low escape rate of light include: the absorption of light by lattice defects; the absorption of light by the substrate; the loss of light at each interface due to total reflection during the exit process.

Indium tin oxide ITO (the mass ratio of In ₂ O ₃ to Sn ₂ O ₃ is 9:1) film has the following advantages: high light transmittance (~90%) in the visible spectrum region; low resistivity (<5 ×10 ^-4 Ωcm). Therefore, ITO thin films are widely used as transparent electrodes and current spreading layers in optoelectronic devices. In commercial LEDs, transparent ITO films are gradually replacing semi-transparent metal films Ni/Au. The brightness of the LED with ITO as the ohmic contact is about 50% higher than that of the translucent Ni/Au as the ohmic contact. However, at the interface between ITO and air, due to the large difference in the refractive index of the two media, a large amount of light still cannot be coupled out. The refractive index of ITO is 2.10, and the maximum reflection angle of light from ITO to air is 28°. Only about less than 20% of the light energy enters the air from the ITO medium, which greatly reduces the external quantum efficiency of the LED device.

Therefore, it is the key to improve the external quantum efficiency to allow the light emitted by the light-emitting layer to be coupled out of the device. The invention relates to a method for improving the light-emitting efficiency of an LED.

Contents of the invention

The object of the present invention is to provide a manufacturing process of an LED chip and its products which are simple in process, low in cost, suitable for industrial production, and capable of improving external quantum efficiency. Specifically, it is to apply nanofabrication technology, that is, natural lithography technology (naturallithography), combined with ICP dry etching technology to micronize the ITO film surface of traditional and vertical GaN-based LED devices, by increasing light from The probability of the ITO medium refracting into the air, thereby improving the external quantum efficiency of the LED device. And the inventive method of roughening the electrode is used in the preparation process of the front-mounted LED chip and the vertical LED chip.

The object of the present invention is achieved in this way: a novel high-brightness light-emitting diode, comprising a sapphire substrate, a GaN buffer layer, an n-type GaN layer, an InGaN/GaN multi-quantum well active layer, a p-type GaN layer, and a p-type ohmic contact Transparent electrodes, p-type metal electrodes and welding pads, n-type metal electrodes and welding pads and metal layer mirrors, characterized in that there is also a p-AlGaN waveguide between the InGaN/GaN multi-quantum well active layer and the p-type GaN layer layer; the p-type ohmic contact transparent electrode material adopts ITO, and utilizes natural photolithography technology and IPC dry etching to roughen the surface of the ITO film, and the particle size range of the polystyrene nanoparticles used in the etching process 350nm-400nm, the mass percentage concentration of the nanoparticles is 1-10%; the metal layer mirror is a single metal or multi-layer metal, with a thickness of 2 to 10 microns;

The above-mentioned novel high-brightness light-emitting diode is prepared by the following method:

(1) Using MOCVD epitaxy to grow GaN-based LED structure epitaxial wafers, and the lower lining is blue sapphire;

(2) Deposit ITO film on the epitaxial wafer by electron beam evaporation;

(3) Apply natural photolithography technology and dry etching on the deposited ITO film to roughen the surface of the ITO film;

(4) Deposit _SiO2 film on the ITO surface as a dry etching mask, and carry out photolithography on this surface;

(5) Use BOE solution: N ₄ HF to HF with a volume ratio of 4:1 to clean the SiO ₂ not protected by the photoresist;

(6) Use an acidic solution: HNO ₃ , HCL, H ₂ O in a volume ratio of 2:1:1 to clean the ITO not protected by the photoresist;

(7) cleaning the photoresist with film remover;

(8) Use ICP to etch the N-face steps and chip-sized scribes to expose the N-GaN mesas;

(9) cleaning SiO ₂ on P-GaN with BOE solution;

(10) Evaporation of P-N electrodes and welding pads with Ni/Au as a metal combination;

(11) Thinning the sapphire from 350 to 450 μm to 200 μm with chemical mechanical polishing equipment;

(12) Divide the epitaxial wafer with electrodes into individual LED devices with a laser scribing machine;

(13) Coating a metal layer mirror on the substrate, the material is single metal or multi-layer metal.

The purpose of the present invention can also be achieved in the following manner: the thickness of the ITO film is 350nm-400nm.

The parameters of the dry etching: bias power supply power: 150-200 watts, ICP electric power supply power: 150-200 watts; gas flow rate: chlorine gas, 30-40 standard cubic centimeters per minute, argon gas, 2-6 standard Cubic centimeters per minute; etching time: 50-300 seconds.

Another structural form of the present invention is: a novel vertical GaN-based high-brightness light-emitting diode, including an n-GaN layer, an InGaN/GaN multi-quantum well active layer, a p-type GaN layer, an n-type transparent electrode, N-type metal electrodes, welding pads and metal layer mirrors are characterized in that: there is also a p-AlGaN waveguide layer between the InGaN/GaN multi-quantum well active layer and the p-type GaN layer; the n-type transparent electrode current diffusion The material of the layer is ITO, and the surface of the ITO film is nano-processed by using natural photolithography technology and dry etching;

The above-mentioned novel vertical structure gallium nitride-based high-brightness light-emitting diode is prepared by the following method:

(1) Using MOCVD to grow LED light-emitting structures on sapphire substrates;

(2) plating a metal layer on the p-GaN layer of the epitaxial layer;

(3) The metal bonding method is reversely bonded on the metal mirror;

(4) Laser peeling off the sapphire substrate substrate;

(5) Depositing an ITO thin film on the stripped n-GaN epitaxial layer by electron beam evaporation;

(6) Apply natural photolithography technology and dry etching on the deposited ITO film to miniaturize the surface of the ITO film;

(7) Deposit _SiO2 film on the surface of ITO as a dry etching mask, and carry out photolithography on this surface;

(8) Use BOE solution: N ₄ HF to HF with a volume ratio of 4:1 to clean the SiO ₂ not protected by photoresist;

(9) Use an acidic solution: HNO ₃ , HCL, H ₂ O in a volume ratio of 2:1:1 to clean the ITO not protected by the photoresist;

(10) cleaning the photoresist with film remover;

(11) Evaporating n-metal electrodes;

(14) Divide the epitaxial wafer with electrodes prepared into individual LED devices with a laser scribing machine.

The invention provides an LED chip manufacturing process and its products which are simple in process, low in cost, suitable for industrialized production, and can improve external quantum efficiency.

Description of drawings

Fig. 1 is novel high brightness LED chip among the present invention;

Fig. 2 is a novel vertical structure GaN-based LED wafer of light-emitting diodes in the present invention;

Fig. 3 is the profile graph of the ITO surface prepared by electron beam evaporation method in the present invention;

Fig. 4 is the contour curve figure of the ITO surface that miniaturizes in the present invention;

Fig. 5 is the luminance contrast (chip wavelength is 468nm) of the LED that the surface miniaturization process has been processed in the present invention and the LED that the surface is not rough;

Fig. 6 is the forward voltage contrast (chip wavelength is 468nm) under the driving current of 20 milliamperes of the LED that the surface is miniaturized and the LED that the surface miniaturization is processed in the present invention;

Detailed ways

One of the novel light-emitting diodes of the present invention, comprising a sapphire substrate 1, a GaN buffer layer 2, an n-type GaN layer 3, an InGaN/GaN multiple quantum well (MQWs) active layer (light-emitting layer) 4, and a p-AlGaN waveguide layer 5 , p-type GaN layer 6, p-type ohmic contact transparent electrode 7, p-type metal electrode 8, n-type ohmic contact electrode 9 and metal layer mirror 10. ITO is used as the p-type ohmic contact transparent electrode material, and the surface of the ITO film is roughened by natural lithography and dry etching.

In order to realize the above-mentioned light-emitting diodes, a method for preparing a high-brightness light-emitting diode of the present invention comprises the following steps:

(1) Using MOCVD epitaxy to grow GaN-based LED structure epitaxial wafers, the lining is sapphire (Al ₂ O ₃ );

(2) Deposit ITO film on the epitaxial wafer by electron beam evaporation;

(3) Apply natural lithography (natural lithography) and dry etching on the deposited ITO film to roughen the surface of the ITO film;

(4) Deposit _SiO2 film on the ITO surface as a dry etching mask, and carry out photolithography on this surface;

(5) Clean the SiO ₂ not protected by photoresist with BOE solution (the volume ratio of N ₄ HF to HF is 4:1);

(6) Clean the ITO not protected by the photoresist with an acidic solution (HNO ₃ , HCL, H ₂ O in a volume ratio of 2:1:1);

(7) cleaning the photoresist with film remover;

(8) Use ICP to etch the N-face steps and chip-sized scribes to expose the N-GaN mesas;

(9) cleaning SiO ₂ on P-GaN with BOE solution;

(10) Evaporation of P-N electrodes and welding pads with Ni/Au as a metal combination;

(11) Thinning the sapphire from 350 to 450 μm to 200 μm with chemical mechanical polishing (CMP) equipment;

(12) Divide the epitaxial wafer with electrodes into individual LED devices with a laser scribing machine;

(13) Coating a metal layer mirror on the substrate. Materials can be single metal or multi-layer metal.

Natural lithography technology and ICP dry etching technology are used for nanofabrication and miniaturization of transparent electrode ITO, including the following steps:

(1) Deposit an ITO film with a certain thickness on the surface of the epitaxial wafer with an electron beam evaporation device; the thickness of the ITO film is 350nm-400nm.

(2) above-mentioned epitaxial wafer is soaked in deionized water, improves the hydrophilic property of ITO thin film on epitaxial wafer surface;

(3) The polystyrene nanoparticles with a particle size range of 350nm-400nm are formulated so that the mass percent concentration of the nanoparticles is 1-10%.

(4) Use a spin coater to evenly spin-coat the above-mentioned suspension on the ITO surface according to certain parameter settings;

(5) naturally dry the epitaxial wafer at room temperature;

(6) Set ICP parameters, bias power supply power: 150-200 watts, ICP electric power supply power: 150-200 watts; gas flow: chlorine gas, 30-40 standard cubic centimeters per minute, argon gas, 3-6 standard cubic centimeters cm/min; etching time: 50-300 seconds. Etching the above-mentioned epitaxial wafer;

(7) Scrub the surface of the epitaxial wafer with a cotton ball soaked in a solvent to remove the nanospheres after ICP etching.

It can be seen from Figure 3 and Figure 4 that the contour curves of the ITO surface before and after micronization treatment, before the micronization treatment, the flatness of the ITO surface is about 3 ~ 4nm, after the micronization treatment, the ITO surface has a great change, its flatness It is about 120-130nm. The corresponding ICP parameters are: bias power supply: 150 watts, ICP electric power supply: 150 watts; gas flow rate: chlorine gas, 36 standard cubic centimeters per minute, argon gas, 4 standard cubic centimeters per minute; etching time: 200 seconds .

It can be seen from Fig. 5 that the brightness contrast between LEDs treated with micronized ITO surface and untreated LEDs on ITO surface (chip wavelength is 468nm). The brightness of miniaturized LEDs is greatly improved compared to untreated LEDs. It can be seen from Fig. 6 that the leakage current of the LED with miniaturization on the ITO surface and the LED with the miniaturization on the surface is driven by a voltage in the direction of 5V (the chip wavelength is 468nm). Compared with the stability of untreated LEDs, the brightness of miniaturized LEDs is greatly improved. Therefore, the present invention provides a manufacturing process of an LED chip that is simple in process, low in cost, suitable for industrial production, and capable of improving external quantum efficiency.

Another light-emitting diode of the present invention is a novel vertical structure GaN-based high-brightness LED as shown in Figure 2, including n-GaN layer 1, InGaN/GaN multiple quantum wells (MQWs) active layer (light-emitting layer) 2, p- AlGaN waveguide layer 3 , p-type GaN layer 4 , n-type transparent electrode 5 , n-type metal electrode 6 and metal layer mirror 7 . ITO is used as the n-type transparent electrode material, and the surface of the ITO film is roughened by natural lithography and dry etching.

In order to realize the above-mentioned novel vertical structure GaN-based LED, the preparation method includes the following steps:

(1) On the sapphire substrate (Al ₂ O ₃ ), the LED light-emitting structure is grown by MOCVD;

(2) plating a metal layer on the p-GaN layer of the epitaxial layer;

(3) The metal bonding method is reversely bonded on the metal mirror;

(4) Laser peeling off the sapphire substrate (Al ₂ O ₃ ) substrate;

(5) Depositing an ITO thin film on the stripped n-GaN epitaxial layer by electron beam evaporation;

(6) Apply natural lithography (natural lithography) and dry etching on the deposited ITO film to micronize the surface of the ITO film;

(7) Deposit _SiO2 film on the surface of ITO as a dry etching mask, and carry out photolithography on this surface;

(8) Cleaning the SiO ₂ not protected by photoresist with BOE solution (the volume ratio of N ₄ HF to HF is 4:1);

(9) Cleaning the ITO not protected by the photoresist with an acidic solution (HNO ₃ , HCL, H ₂ O in a volume ratio of 2:1:1);

(10) cleaning the photoresist with film remover;

(11) Evaporating n-metal electrodes;

(14) Divide the epitaxial wafer with electrodes prepared into individual LED devices with a laser scribing machine.

For the above-mentioned vertical GaN-based high-brightness LED, due to the high conductivity of the N-type highly doped layer, the current can not be crowded around it, and the current can be evenly distributed laterally to the entire device, and the current can flow quasi-vertically from bottom to top. Through the P-type layer and the active layer, and then through the N-type highly doped layer, it flows laterally to the N electrode, the material of the light-emitting layer can be fully applied, the current density is increased, the working voltage and resistance of the LED are reduced, the heat generated is reduced, and the light extraction efficiency is improved. , effectively improving the current distribution, making the heat source distribution and luminous intensity more uniform. Compared with the first high-brightness LED based on the traditional LED, the external quantum efficiency of the chip can be improved.

Claims (6)

1, a kind of novel high brightness LED, comprise Sapphire Substrate, GaN resilient coating, n type GaN layer, InGaN/GaN multiple quantum well active layer, p type GaN layer, p type ohmic contact transparency electrode, p type metal electrode and weld pad, n type metal electrode and weld pad and metal level mirror, it is characterized in that: between InGaN/GaN multiple quantum well active layer and p type GaN layer, also have a p-AlGaN ducting layer; Described p type ohmic contact transparent electrode material adopts ITO, and utilize natural daylight lithography and IPC dry etching that alligatoring is carried out on the ito thin film surface, the particle size range of used polystyrene nanoparticles is 350nm-400nm in the etching technics, and the mass percent concentration that is made into nano particle is 1～10%; Described metal level mirror is monometallic or multiple layer metal, and thickness is at 2 to 10 microns;

Above-mentioned novel high brightness LED adopts following method preparation:

(1) utilization MOCVD epitaxial growth GaN based LED construction epitaxial wafer, substrate is a sapphire;

(2) deposited by electron beam evaporation deposits ito thin film on epitaxial wafer;

(3) application natural daylight lithography and dry etching carry out roughening to the ito thin film surface on the deposition ito thin film;

(4) at ITO surface deposition SiO ₂Film is as the dry etching mask, and carries out photoetching on this surface;

(5) use BOE solution: N ₄HF and HF volume ratio are 4: 1, clean the SiO that is not subjected to the photoresist protection ₂

(6) use acid solution: HNO ₃, HCL, H ₂The O volume ratio is 2: 1: 1, cleans the ITO that is not subjected to the photoresist protection;

(7) use the stripper cleaning photoetching glue;

(8) with the road of drawing of ICP etching N face step and chip size, expose the N-GaN table top;

(9) with the SiO on the BOE solution cleaning P-GaN ₂

(10) evaporation is the P-N electrode and the weld pad of metallic combination with Ni/Au;

(11) with chemical-mechanical polisher sapphire is thinned to 200 μ m by 350～450 μ m;

(12) epitaxial wafer that will perform electrode is divided into single led device with laser scribing means;

(13) metal cladding mirror on substrate, material is monometallic or multiple layer metal.

2, according to the described high brightness LED of claim 1, it is characterized in that: described ito thin film thickness is 350nm-400nm.

3, according to claim 1 or 2 described high brightness LEDs, it is characterized in that: the parameter of described dry etching: grid bias power supply power: 150-200 watt, ICP electricity power: 150-200 watt; Gas flow: chlorine, the 30-40 standard cubic centimeter/minute, argon gas, the 2-6 standard cubic centimeter/minute; Etch period: 50-300 second.

4, a kind of novel vertical structure gallium nitride-based high-brightness light-emitting diode, comprise n-GaN layer, InGaN/GaN multiple quantum well active layer, p type GaN layer, n type transparency electrode, n type metal electrode and weld pad and metal level mirror, it is characterized in that: between InGaN/GaN multiple quantum well active layer and p type GaN layer, also have a p-AlGaN ducting layer; Described n type transparent electrode material adopts ITO, and utilizes natural daylight lithography and IPC dry etching that nanoprocessing is carried out on the ito thin film surface;

Above-mentioned novel vertical structure gallium nitride-based high-brightness light-emitting diode adopts following method preparation:

(1) on Sapphire Substrate with MOCVD growth LED ray structure;

(2) metal cladding on the p-GaN of epitaxial loayer layer;

(3) the legal reverse key of metallic bond is combined on the mirror metal;

(4) laser lift-off falls the Sapphire Substrate substrate;

(5) deposit ito thin film on the n-GaN epitaxial loayer of deposited by electron beam evaporation after peeling off;

(6) application natural daylight lithography and dry etching carry out miniaturization to the ito thin film surface on the deposition ito thin film;

(7) at ITO surface deposition SiO ₂Film is as the dry etching mask, and carries out photoetching on this surface;

(8) use BOE solution: N ₄HF and HF volume ratio are 4: 1, clean the SiO that is not subjected to the photoresist protection ₂

(9) use acid solution: HNO ₃, HCL, H ₂The O volume ratio is 2: 1: 1, cleans the ITO that is not subjected to the photoresist protection;

(10) use the stripper cleaning photoetching glue;

(11) evaporating n-metal electrode;

(14) epitaxial wafer that will perform electrode is divided into single LED device with laser scribing means.

5, according to the described novel vertical structure gallium nitride-based high-brightness light-emitting diode of claim 4, it is characterized in that: described ito thin film thickness is 350nm-400nm.

6, according to claim 4 or 5 described novel vertical structure gallium nitride-based high-brightness light-emitting diodes, it is characterized in that: the parameter of described dry etching: grid bias power supply power: 150-200 watt, ICP electricity power: 150-200 watt; Gas flow: chlorine, the 30-40 standard cubic centimeter/minute, argon gas, the 2-6 standard cubic centimeter/minute; Etch period: 50-300 second.

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