CN103268882A - A kind of high-voltage LED chip with microstructure anti-reflection film - Google Patents

Abstract

The invention belongs to the field of semiconductor emitting device manufacturing, and particularly relates to a high-voltage LED chip with a microstructural antireflection film. The high-voltage LED chip with the microstructural antireflection film comprises a sapphire substrate, a buffering layer, a N-type layer, a quantum well layer, a P-type layer, an electrode on the P-type layer, an electrode on the N-type layer, a cross structure, an ITO layer and an antireflection film body, wherein the antireflection film body covers the ITO layer and is provided with a cylindrical microstructure. The high-voltage LED chip with the microstructural antireflection film can effectively reduce reflection losses when an LED emerges light, and meanwhile light ray total reflection from the chip to the air can be reduced through the microstructure. Meanwhile, the antireflection film can restrain dampness of the chip and diffusion of impurities, and a final protective function is achieved.

Description

A kind of high-voltage LED chip with microstructure anti-reflection film

technical field

The invention belongs to the field of manufacturing semiconductor light-emitting devices, and in particular relates to a high-voltage LED chip with a microstructure anti-reflection film.

Background technique

LED is an energy-saving, environmentally friendly, long-life, and pollution-free light-emitting device. Its energy consumption is only 10% of incandescent lamps and 50% of fluorescent lamps. The luminous efficiency of the existing known high-power LEDs can reach 160lm/w, the stable working environment is a DC current of 350mA, and the working voltage is generally 3V, which cannot be directly driven by commercial power. In order to overcome the above-mentioned technical problems, high-voltage LEDs emerged as a new type of LED structure. The driving current of the high-voltage LED is generally 20mA, and the working voltage is generally 45-50V. Generally, 4 high-voltage LEDs are directly connected in series to reach the working voltage of 220V, which is convenient for direct driving of the mains. Existing known high-voltage LEDs generally consist of a sapphire substrate, a buffer layer, an N-type layer, a quantum well layer, a P-type layer, electrodes on the P layer and the N layer, a connecting bridge, an ITO layer, and the like. Due to the high refractive index of the ITO layer, a large amount of light is converted into heat and lost due to total internal reflection. At the same time, the sudden change of the interface refractive index causes the reflection loss of light, which adversely affects the light extraction efficiency of the high-voltage LED.

The structure of the known common process high-voltage LED chip is an array structure, which divides a 45*45mil chip into several small chip particles (generally 15-17) on an epitaxial wafer. The main structure includes: a sapphire substrate, a buffer layer, an N-type layer, a quantum well layer, a P-type layer, an electrode on the P layer and the N layer, a connecting bridge, and an ITO layer. Without considering the light absorption of the material, when the active layer emits light and the photons reach the interface between the chip and the air, due to the change of the refractive index, a large amount of light energy is reflected back into the chip and finally turned into heat and emitted. . At the same time, due to the change of the refractive index between the interfaces, when the light is emitted from the chip to the outside, the occurrence of total reflection further reduces the light effect. It directly leads to the low external quantum effect.

Currently commonly used anti-reflection film materials mainly include silicon nitride (SiN _x ), silicon dioxide (SiO ₂ ), silicon oxynitride (SiON _x ), and metal oxide films are also used. Among them, silicon dioxide film has the lowest cost, but its structure is relatively loose, its vacuum density is high, and its ability to resist moisture and metal ion pollution is relatively poor. Silicon nitride (generally Si ₃ N ₄ ) films have obvious advantages over silicon dioxide in terms of resistance to impurity diffusion and water vapor penetration, but there are a large number of interface charges and defects between the silicon nitride film and the chip interface, resulting in The electrical properties of the device have a serious impact (see Liu Baofeng, Li Hongfeng, Jin Liguo. "Study on the Preparation and Properties of Passivation Layer Si ₃ N ₄ Films for Semiconductor Devices" [J]. Journal of Harbin University of Science and Technology, 2003, 8(6 ): 10). And the refractive index of silicon dioxide and silicon nitride are 1.45 and 2.0 respectively, and the best AR coating material should have a refractive index as close to 1.58 as possible. Therefore, the former two are not anti-reflection coating materials with better transmission properties. The refractive index of SiON can be adjusted within the range of 1.6-1.7 (generally 1.58-1.71). Therefore, SiON is currently the most excellent anti-reflection coating material, which can achieve better anti-reflection performance.

Contents of the invention

In order to overcome the internal total reflection and reflection loss of high-voltage LEDs in ordinary technology and improve light extraction efficiency, the invention provides a high-voltage LED chip with a microstructure anti-reflection film. The anti-reflection coating can effectively reduce the reflection loss caused by sudden changes in the refractive index. And its surface microstructure can effectively reduce the total internal reflection of light, thereby improving the light extraction efficiency.

Technical scheme of the present invention comprises:

A high-voltage LED chip with a microstructure anti-reflection film, including a plurality of light-emitting units, each light-emitting unit sequentially includes a gem substrate 1, a buffer layer 2, an N-type layer 3, a quantum well layer 4, and a P-type layer from bottom to top 5 and ITO layer 6, each light-emitting unit also includes an electrode 7 on the P-type layer and an electrode 8 on the N-type layer, and the electrodes between adjacent light-emitting units are connected by a connecting bridge 9, and each light-emitting unit also includes an electrode covering the The anti-reflection film 10 on the ITO layer, the top surface of the anti-reflection film above the ITO layer 6 has a cylindrical microstructure.

Further optimized, the anti-reflection wavelength corresponding to the anti-reflection coating is consistent with the emission wavelength of the active layer of the chip. At present, high-voltage chips are mainly based on blue light, and the light-emitting wavelength is about 455nm. SiON is selected as the film material, and its refractive index is adjustable within the range of 1.6-1.7 (generally 1.58-1.71).

Further optimized, the thickness of the anti-reflection film is a quarter of the light emitting wavelength of the LED.

Further optimized, the thickness of the microstructure is 1/10 of the thickness of the antireflection film.

Further optimized, in addition to covering the top of the ITO layer, the anti-reflection film also covers the side between the upper surface of the ITO layer and the electrode 8 on the N-type layer, and only the anti-reflection film above the ITO layer has a cylindrical microstructure.

Further optimized, the antireflection covers the entire outer surface of the ITO layer of the chip.

Further optimized, the cylindrical microstructure has a base radius of 1.5um and a height of 100 angstroms.

Further optimized, the distance between the centers of adjacent cylindrical bottom surfaces of the cylindrical microstructure is 4um-6um.

Further optimized, the anti-reflection film is formed by depositing SiON film by PECVD (Plasma Enhanced Chemical Vapor Deposition), and the cylindrical microstructure is etched by ICP (Inductively Coupled Plasma-Inductively Coupled Plasma).

For further optimization, the SiON film is deposited by reaction with SiH ₄ , N ₂ O, and NH ₃ , and the refractive index of the SiON film is 1.58-1.71.

Among the currently existing solutions, some use SiO ₂ as an anti-reflection coating. Although its cost is low, its compactness is poor, and its ability to resist moisture and metal ion contamination is relatively poor. Some use SiON as the anti-reflection coating material, but its surface does not have a microstructure. Although it can effectively reduce the reflected energy and increase the transmission, due to the existence of the total reflection angle, the outgoing energy is only 39.1% of the original, which is not really effective. Improve light extraction efficiency. There are also random passivated metal oxide films used as antireflection film materials, which use tin oxide, aluminum oxide, magnesium oxide, zinc aluminum oxide, indium oxide, tin dioxide, indium tin oxide, antimony trioxide, diantimony trioxide Bismuth is one of several materials used as an anti-reflection and anti-reflection coating. However, the cost of metal materials is high, and the refractive index is not easy to control, so the anti-reflection effect cannot be really achieved.

Compared with the prior art, the present invention has the following advantages and technical effects:

(1) Compared with the high-voltage LED of ordinary technology, it can effectively reduce the reflection loss inside the chip and improve the light output efficiency;

(2) Through the microstructure of the surface, the total reflection inside the chip can be effectively destroyed, and the outgoing energy can be effectively increased;

(3) The microstructure adopts a cylindrical shape and the height does not exceed 100 angstroms, which can maintain the flatness of the upper light-emitting surface, thereby ensuring the effectiveness of the anti-reflection coating.

Description of drawings

FIG. 1 is a schematic cross-sectional view of a high-voltage LED chip structure. In the figure, 1-sapphire substrate, 2-buffer layer, 3-N-type layer, 4-quantum well layer, 5-P-type layer, 7, 8-P layer and electrodes on the N layer, 9-connection bridge, 6-ITO layer, 10-anti-reflection coating.

Detailed ways

The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings and examples, but the implementation and protection of the present invention are not limited thereto.

Please refer to Figure 1, a high-voltage LED chip with a microstructure anti-reflection film, including multiple light-emitting units, each light-emitting unit includes a gem substrate 1, a buffer layer 2, an N-type layer 3, and a quantum well layer from bottom to top. 4. P-type layer 5 and ITO layer 6, each light-emitting unit also includes an electrode 7 on the P-type layer and an electrode 8 on the N-type layer, the electrodes between adjacent light-emitting units are connected by a connecting bridge 9, and each light-emitting unit The unit also includes an anti-reflection film 10 covering the ITO layer, and the top surface of the anti-reflection film above the ITO layer 6 has a cylindrical microstructure.

Generally, the main luminescent wavelength of a blue-ray chip is 455nm, so the thickness of the anti-reflection film is about 1140 angstroms. In the actual process, it should be greater than 1140 angstroms in order to etch the microstructure on the surface of the anti-reflection film.

The thickness of the anti-reflection coating should be 1/4 of the main wavelength of light. When light enters the film from the chip, one reflection occurs, which is set as reflected ray A. Then the light will have a second reflection between the film and the outside world, reflecting ray B. Taking direct light as an example, light B travels twice the distance of the film thickness compared with light A, and when light A and light B destructively interfere, the anti-reflection effect of the anti-reflection coating reaches the maximum. Then the film thickness d satisfies the formula:

$\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; k\&lambda;</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}$

Generally take k=0, then the film thickness is

If the light of the chip exits directly, according to the Fresnel reflectivity formula:

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}$

Light is emitted from the inside of the chip into the air, n ₁ =1 (refractive index of air), n ₂ =2.54 (refractive index of GaN), and the calculated reflection loss is nearly 19%. When the anti-reflection coating is added, the light reaches the anti-reflection coating from the chip, and then the anti-reflection coating is emitted.

When the light reaches the AR coating from the chip, since the refractive index of silicon oxynitride is about 1.6, n ₁ =1.6 at this time, and the reflection loss can be calculated as 5.1% from the Fresnel reflectivity. That is, t ₁ =94.9% of the energy reaches the AR coating. When the light exits from the AR coating, the reflection loss can be calculated to be 5.3%, and the transmission energy t ₂ =94.7%. Then the total outgoing energy is t=t ₁ *t ₂ =89.9%. In contrast, when the light is directly incident from the chip into the air, the reflection loss is 19%, the output energy t ₀ is 81% of the original, and the light extraction efficiency is increased by (tt ₀ )/t ₀ =11%.

On the other hand, in the absence of microstructures, total internal reflection occurs when light emerges from the surface of silicon oxynitride. From the total reflection formula:

${\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; all</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

Among them, n ₁ =1, n ₂ =1.6, the calculation can get θ _all =38.7°. By the formula:

Then it can be calculated that the energy emitted from the front of the chip is only 39.1% of the energy within the range of 2π solid angle above the interface between the chip and the air. After adding the cylindrical surface microstructure, the original total internal reflection will be destroyed, thereby increasing its outgoing energy.

The invention discloses a manufacturing process of the above structure. The anti-reflection coating material is SiON, and its coating thickness is 1/4 of the main light emission wavelength, about 1100 angstroms. The specific process includes:

(1) Clean the chips that have completed other process steps through the QDR cleaning process;

(2) Put the chip into PECVD and place the coating material;

(3) Carry out the coating process according to the set procedure;

(4) After the coating is completed, check the thickness of the coating. The thickness of the coating should be greater than 1100 angstroms in order to etch the microstructure on the surface of the coating;

(5) Use ICP etching process to etch a cylindrical microstructure on the surface of the film layer;

(6) Clean the etched chip and check the etching quality under an optical microscope.

The invention improves the light extraction efficiency of the high-voltage LED chip by more than 11%. The above descriptions are only specific embodiments of the present invention, and are not intended to limit the protection scope of the present invention. All other modifications and modifications that do not depart from the scope of the claims should be included in the scope of the present invention. .

Claims (10)

1. A high-voltage LED chip with a microstructure anti-reflection film, comprising a plurality of light-emitting units, each light-emitting unit comprises a gem substrate 1, a buffer layer 2, an N-type layer 3, a quantum well layer 4, a P type layer 5 and ITO layer 6, each light emitting unit also includes an electrode 7 on the P type layer and an electrode 8 on the N type layer, and the electrodes between adjacent light emitting units are connected by a connecting bridge 9, which is characterized in that each light emitting unit The unit also includes an anti-reflection film 10 covering the ITO layer, and the top surface of the anti-reflection film above the ITO layer 6 has a cylindrical microstructure. 2. A high-voltage LED chip with a microstructure anti-reflection film according to claim 1, wherein the anti-reflection film is made of SiON material. 3. A high-voltage LED chip with a microstructure anti-reflection film according to claim 1, wherein the thickness of the anti-reflection film is 1/4 of the light-emitting wavelength of the LED. 4. A high-voltage LED chip with a microstructure antireflection film according to claim 3, wherein the thickness of the microstructure is 1/10 of the thickness of the antireflection film. 5. A kind of high voltage LED chip with microstructure anti-reflection film according to claim 1, characterized in that the anti-reflection film also covers the electrode on the upper surface of the ITO layer to the N-type layer in addition to covering the top of the ITO layer 8, and only the AR coating above the ITO layer has a cylindrical microstructure. 6. A high-voltage LED chip with a microstructure anti-reflection film according to claim 1, characterized in that the anti-reflection coating covers the entire outer surface of the ITO layer of the chip. 7. A high-voltage LED chip with a microstructure anti-reflection film according to claim 1, characterized in that the radius of the bottom surface of the cylindrical microstructure is 1.5 um and the height is 100 angstroms. 8. A high-voltage LED chip with a microstructure anti-reflection film according to claim 1, characterized in that the distance between the centers of adjacent cylindrical bottom surfaces of the cylindrical microstructure is 4um~6um. 9. The microstructure anti-reflection film for improving the light extraction efficiency of high-voltage LEDs according to claim 1, characterized in that: the anti-reflection film is formed by depositing a SiON film by PECVD, and the cylindrical microstructure is etched by ICP. 10. The microstructure anti-reflection coating for improving the light extraction efficiency of high-voltage LEDs according to claim 9, characterized in that: the SiON film is deposited by reaction of SiH ₄ and N ₂ O, NH ₃ , and the refractive index of the SiON film is 1.58~1.71 .

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