A Micro LED pixel point for solving lateral etching and a preparation method thereof

Abstract

A method for preparing Micro LED pixel points to solve lateral etching, belonging to the technical field of semiconductor devices and their processing technologies. By changing the method for preparing the mask, two gases, Ar2 and N2, are added on the basis of the etching gases Cl2 / BCl3. After adjusting the optimal ratio, the etching selectivity ratio of SiO2 to AlGaInP can reach more than 15:1 from 5:1, and no lateral etching problem occurs during the etching process, obtaining pixel points with high selectivity, smooth sidewalls, and no lateral etching. The present invention solves the serious lateral etching problem existing in the N + GaAs heavily doped layer and the P-type GaP layer during the etching process, solves the problem of discontinuous coverage of the subsequent passivation layer due to the existence of lateral etching, can effectively improve the problem of rough sidewalls and bottoms during etching, extremely increases the etching selectivity ratio of the hard mask, and further improves the luminous efficiency of Micro LED.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor devices and processing techniques thereof, and specifically relates to a method for preparing Micro LED pixels that solves the problem of lateral etching. Background Art

[0002] Micro LED displays have outstanding high-quality features such as low power consumption, high brightness, high contrast and short response time. The related technical applications of this type of device cover wearable electronic devices, electronic device screens, lensless microscopes, visible light communications, etc. The aluminum gallium indium phosphide (AlGaInP) quaternary material is currently a high-brightness, high-efficiency material for preparing red and yellow light Micro LEDs, and is an indispensable part of realizing the full color of Micro LEDs. However, the development time of AlGaInP-based devices is shorter than that of gallium nitride (GaN)-based devices, and there are few reports on related process methods and they are still in the research stage. Among them, the preparation of AlGaInP-based pixels is the most critical link in the entire Micro LED device preparation process, and is a key factor affecting the luminous efficiency and brightness of MicroLEDs.

[0003] AlGaInP-based devices are epitaxially grown on gallium arsenide (GaAs) substrates. The lattice growth law must be strictly matched between the multilayer materials. AlGaInP-based devices are composed of a multilayer structure, from bottom to top, GaAs substrate, N + GaAs heavily doped layer, N-type AlGaInP layer, MQWs quantum well layer, P-type AlGaInP layer and P-type GaP layer. AlGaInP-based devices usually require the GaAs substrate to be peeled off and then eutectic bonded with a Si-based CMOS substrate (digital circuit chip). The device structure after eutectic bonding consists of a Si-based CMOS substrate, a bonding metal layer (composed of four layers of Cr-Au-Sn-Ti deposited in sequence), a P-type GaP layer, a P-type AlGaInP layer, an MQWs quantum well layer, an N-type AlGaInP layer and an N-type GaP layer. + GaAs heavily doped layer. In the etching process, the etching rate of each layer of material is not exactly the same, such as N +The two current spreading layers, the GaAs heavily doped layer and the P-type GaP layer, have a large difference in etching rate with the AlGaInP material, so they are prone to lateral etching problems during the etching process, which seriously affects the continuity of the current spreading layer and thus affects the electrical performance of the ohmic contact, resulting in poor photoelectric conversion efficiency. At the same time, the defects of lateral etching affect the process of subsequent processes, such as the coverage of the subsequent passivation layer, which leads to leakage problems at the defects. In addition, the etching process also needs to meet the requirements of smooth etching side walls, achieving an ideal etching angle, and achieving an ideal ratio of etching selectivity between the mask and the etching material, which puts higher requirements on the etching process of Micro LED pixels. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing Micro LED pixels that solves the problem of lateral etching.

[0005] The Micro LED pixel point for solving lateral etching of the present invention is composed of a 100-500nm thick P-type GaP layer, a 100-500nm thick P-type AlGaInP layer, a 5-80nm thick MQWs quantum well layer, a 100-500nm thick N-type AlGaInP layer, and a 5-80nm thick N-type GaP layer. + It consists of a heavily doped GaAs layer and a 50~700nm thick SiO2 film; among them, the upper surface diameter of the Micro LED pixel is 5~7μm, the lower surface diameter is 6~8μm, and the pixel pitch is 4~6μm; from bottom to top, the bonding metal layer is composed of four layers of Cr-Au-Sn-Ti metal deposited in sequence, with a total thickness of 100~800nm; the bonding metal layer is prepared on a Si-based CMOS substrate, and the thickness of the Si-based CMOS substrate is 300~1000μm.

[0006] The present invention changes the mask preparation method and increases the passivation gas in the etching to obtain a Micro LED pixel with an ideal etching morphology of high etching selectivity, smooth sidewalls, and no lateral etching. This method enables the subsequent processes to proceed smoothly and improves the luminous power of the Micro LED pixel.

[0007] The common pixel preparation method is to use the inductively coupled plasma (ICP) method for etching. The ICP etching method has a high degree of anisotropy, and the etching gas is mainly Cl2 / BCl3 or SiCl4. The present invention adds Ar2 and N2 gases on the basis of the common etching gas Cl2 / BCl3. After adjusting the optimal ratio, the etching selectivity ratio of SiO2 and AlGaInP can be increased from 5:1 to more than 15:1, and no lateral etching problem will occur during the etching process.

[0008] The present invention generates a passivation layer on the side wall of the pixel point during the etching process by adding appropriate concentrations of N2 and Ar2. The passivation layer covers the entire etching table, reduces the consumption of the mask during the etching process, greatly improves the etching selectivity, and protects the side wall from lateral etching. When increasing N2, a certain proportion of Ar2 must be added. Ar2 helps reduce the excessive generation of the passivation layer during the etching process. Secondly, the etching direction of Ar2 is nearly vertical, which will consume the passivation layer at the bottom of the etching, thereby not affecting the further downward etching of Cl2 / BCl3.

[0009] The AlGaInP hard mask etching process is similar to "copying", that is, the size and shape of the patterned mask are "copied" to the pixel through etching. The reason for using a hard mask is that the hard mask is not easily changed in shape by a strong plasma etching gas, so the mask can be copied to the pixel almost 1:1. The common AlGaInP-based pixel mask preparation method uses hard mask patterning. The hard mask material is usually SiO2. The SiO2 patterning method uses patterned metal or patterned photoresist to prepare (在BCl中对AlGaInP激光结构进行选择性蚀刻 3 / Cl 2 电感耦合等离子体 , G T Edwards、D I Westwood和P M Smowton,7 2006年3月 • 2006 IOP Publishing Ltd半导体科学与技术, 第21卷,第4期) .

[0010] The method of the present invention adopts a patterned photoresist to prepare a SiO2 mask, and the patterned photoresist adopts different post-baking methods to obtain a photoresist with smooth side walls. Baking at a certain temperature can make the side walls of the photoresist reflux smooth without changing the size of the photoresist too much, and is relatively more resistant to etching, thereby etching a smooth SiO2 cylinder. The present invention does not use metal to prepare a patterned SiO2 mask because the side walls are rough after the metal evaporation stripping photoresist, and SiO2 will replicate the shape of the metal mask, resulting in rough side walls, and finally resulting in rough pixels, and secondly, the residual shading of the metal mask is also avoided. Finally, the AlGaInP-based device is etched by a smooth SiO2 cylinder to obtain a Micro LED pixel with smooth side walls.

[0011] The present invention provides a method for preparing a Micro LED pixel that solves lateral etching, such as Figure 2 As shown, the steps are as follows:

[0012] (a) Hard mask deposition: The AlGaInP-based device after eutectic bonding with the Si-based CMOS substrate was ultrasonically cleaned with acetone, isopropanol, and deionized water for 10 to 20 minutes, and then the surface moisture was blown dry; then the AlGaInP-based device N was deposited using PECVD equipment. +A 50~700nm thick SiO2 film is deposited on the surface of the GaAs heavily doped layer; the deposition power is 40~60W, the vacuum degree is 150~300Pa, the silane (SiH4) flow rate is 40~60sccm, the nitrous oxide (N2O) flow rate is 400~600sccm, and the deposition time (Time) is 50~400s;

[0013] (b) Exposure: Spin-coat positive photoresist on the surface of the SiO2 film, and perform UV mask exposure after curing; the shape of the photoresist mask is the same as the shape of the Micro LED pixel to be prepared, that is, the photoresist mask is a periodically arranged circular through-hole structure, and the area outside the circular through-hole structure is a light-transmitting part. The photoresist in the area outside the circular through-hole structure is exposed to UV light; the aperture of the circular through-hole is 4~6μm, and the center interval of the circular through-hole is 4~6μm; after exposure, the AlGaInP-based device is placed in the developer and soaked for a period of time (1~3min), then taken out and placed in a container filled with deionized water for flushing (3~8min), the exposed positive photoresist is removed, and the AlGaInP-based device is blown dry after the flushing process is completed;

[0014] (c) Post-baking: The AlGaInP-based device after drying is post-baked at 80-180°C for 10-15 minutes to allow the unexposed positive photoresist to reflow into a trapezoidal shape and then cool to room temperature. At this time, the sidewalls of the photoresist are smooth.

[0015] (d) SiO2 etching; using ICP-F-based equipment, pure CHF3 as the reactive etching gas, and the cooled photoresist as a mask to etch the SiO2 film, a patterned SiO2 hard mask is obtained after etching; the CHF3 flow rate is 80~120sccm, the chamber pressure is 5~10mTorr, the ICP power is 600~1000W, and the ICP temperature is 15~25℃. The patterned SiO2 hard mask presents a cylindrical structure, and the diameter of the cylinder replicates the diameter of the photoresist, which is 5~7μm;

[0016] (e) Removing the photoresist: Use a degumming solution and deionized water ultrasonic cleaning for 15 to 30 minutes and 8 to 15 minutes respectively to remove the photoresist on the patterned SiO2 hard mask, and then blow dry the moisture on the surface of the AlGaInP-based device; at this time, the surface of the AlGaInP-based device is not covered with photoresist, but only with the patterned SiO2 hard mask;

[0017] (f) Pixel etching: Using ICP-Cl-based equipment, the patterned SiO2 hard mask is used as a mask to etch for 5-15 minutes to obtain Micro LED pixels on the bonding metal layer. From bottom to top, the Micro LED pixel consists of a P-type GaP layer, a P-type AlGaInP layer, an MQWs quantum well layer, an N-type AlGaInP layer, and an N-type AlGaInP layer. +The etching gases used are Cl2, BCl3, Ar2 and N2, with Cl2 and BCl3 as the main reaction gases, Ar2 as the cleaning gas, and N2 as the passivation gas; the Cl2 flow rate is 40~60sccm, the BCl3 flow rate is 40~60sccm, the Ar flow rate is 15~30sccm, the N2 flow rate is 5~10sccm, and the ratio of the Ar flow rate to the N2 flow rate is 2.5~3.5:1; the upper surface diameter of the Micro LED pixel is 5~7μm, the lower surface diameter is 6~8μm, and the pixel pitch is 4~6μm.

[0018] Beneficial effects of the present invention:

[0019] First, the present invention solves the problem of the current expansion layer N + The serious lateral etching problem of GaAs heavily doped layer and P-type GaP layer during the etching process solves the problem of discontinuous coverage of the subsequent passivation layer due to the existence of lateral etching; secondly, the process method provided by the present invention can effectively improve the problems of uneven etching side walls and rough bottoms, greatly increase the etching selectivity of the hard mask, and to a certain extent can reduce side wall etching damage, reduce active dangling bonds on the side walls, thereby reducing non-radiative recombination and thus improving the luminous efficiency of Micro LEDs. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 : A schematic diagram of the structure of the Micro LED pixel of the present invention;

[0021] Figure 2 : Schematic diagram of the preparation process of the Micro LED pixel of the present invention;

[0022] Figure 3 : Scanning electron microscope images (SEM) of pixels prepared by different etching methods. DETAILED DESCRIPTION

[0023] Embodiment 1:

[0024] like Figure 1 As shown, the Micro LED pixel point for solving lateral etching described in the present invention is composed of a 300nm thick P-type GaP layer 3, a 300nm thick P-type AlGaInP layer 4, a 35nm thick MQWs quantum well layer 5, a 300nm thick N-type AlGaInP layer 6, and a 35nm thick N-type GaP layer 7 prepared on a bonding metal layer 2 from bottom to top. +The micro-LED chip is composed of a heavily doped GaAs layer 7 and a 300nm thick SiO2 film 8; wherein, the upper surface diameter of the Micro LED pixel is 5.5μm, the lower surface diameter is 7μm, and the pixel pitch is 5μm; from bottom to top, the bonding metal layer 2 is composed of four layers of Cr-Au-Sn-Ti metal deposited in sequence, with a total thickness of 400nm; the bonding metal layer 2 is prepared on a Si-based CMOS substrate 1, and the thickness of the Si-based CMOS substrate 1 is 600μm.

[0025] The steps for preparing the Micro LED pixel that solves the lateral etching are as follows:

[0026] (a) Hard mask deposition: The AlGaInP-based device after eutectic bonding with the Si-based CMOS substrate was ultrasonically cleaned with acetone, isopropanol, and deionized water for 20 min, 20 min, and 10 min, respectively, and then the surface moisture was blown dry; then, the AlGaInP-based device N + A 300nm thick SiO2 film was deposited on the surface of the heavily doped GaAs layer using PECVD equipment; the deposition parameters were: power (Power): 50W; vacuum (Pressure): 200Pa; silane (SiH4) flow rate: 50sccm; nitrous oxide (N2O) flow rate: 500sccm; deposition time (Time): 300s;

[0027] (b) Exposure: Spread the SiO2 film surface of the AlGaInP-based device (positive photoresist PL117) at a speed of 4000 r / s for 50 s, pre-bake at 110°C for 2 min, transfer the AlGaInP-based device to the exposure machine, select the program and expose it at 300 mj / cm 2 The shape of the mask is the same as the shape of the Micro LED pixel to be prepared, that is, the mask is a periodically arranged circular through-hole structure, the area outside the circular through-hole structure is a light-transmitting part, and the photoresist outside the circular through-hole structure is exposed to ultraviolet light; the aperture of the circular through-hole is 5 microns, and the center interval of the circular through-hole is 5 microns; after the AlGaInP-based device is transmitted, the AlGaInP-based device is placed in the developer and soaked for 1 minute, then taken out and placed in a container filled with deionized water for 5 minutes, and the exposed positive photoresist is removed. After the flushing process is completed, the surface of the AlGaInP-based device is blown dry, and the diameter of the developed photoresist is observed under a microscope. The theoretical requirement for the photoresist size is 5μm, and the actual measurement is 5.5μm. The diameter is in the range of 5±1μm, and the photolithography meets the standard;

[0028] (c) Post-development baking: Bake at 120°C for 12 minutes and then cool, so that the unexposed positive photoresist reflows into a trapezoidal shape and then cools to room temperature. At this time, the sidewalls of the photoresist are smooth;

[0029] (d) SiO2 etching: ICP-F was used with photoresist as mask, CHF3 was used as reactive etching gas, CHF3 flow rate was 100 sccm, chamber pressure was 8 mTorr, ICP power was 800 W, ICP temperature was 20°C, and the etched SiO2 showed a cylindrical structure, the diameter of which replicated the diameter of the photoresist, which was 5.5 μm.

[0030] (e) Removing photoresist: Use a degumming solution and deionized water to perform ultrasonic cleaning for 20 minutes and 10 minutes respectively to remove the photoresist on the patterned SiO2 hard mask, and then manually blow dry the moisture on the device surface; at this time, the surface of the AlGaInP-based device is not covered with photoresist, only the patterned SiO2 hard mask;

[0031] (f) Pixel etching: Using ICP-Cl-based equipment, the patterned SiO2 hard mask is used as a mask to etch for 10 minutes to obtain Micro LED pixels on the bonding metal layer. From bottom to top, the Micro LED pixel consists of a P-type GaP layer, a P-type AlGaInP layer, an MQWs quantum well layer, an N-type AlGaInP layer, and an N-type AlGaInP layer. + The surface of the AlGaInP-based device is mainly affected by Ar2, thereby becoming rough and weakening the passivation effect. The upper surface diameter of the obtained Micro LED pixel is 5.5μm, the lower surface diameter is 7μm, and the pixel pitch is 5μm.

[0032] Figure 3 (a) and (c) are the conventional Cl2 / BCl3 gas etching technology ( 对……的选择性蚀刻 在BCl中AlGaInP激光结构 3 / Cl 2 电感耦合等离子体 , G T Edwards, D I Westwood和P M Smowton,2006年3月7日 • 2006 IOP Publishing Ltd半导体科学与技术,第21卷,第4期 ) Scanning electron microscope image (SEM) of the prepared pixel; Figure 3 (b) and (d) are scanning electron microscope images (SEM) of pixel points prepared by etching using the method of the present invention; Figure 3 (a) in the figure shows that the etching conditions other than those of the method of the present invention will cause the N + Lateral etching of the heavily doped GaAs layer occurs. Figure 3 (b) in the figure shows that the etching method of the present invention can solve the problem of N +Lateral etching problem of GaAs heavily doped layer; Figure 3 (c) in the figure shows that the etching conditions not in the method of the present invention will cause the GaP layer indicated by the arrow to be etched laterally. Figure 3 (d) in the figure shows that the etching method of the present invention can solve the lateral etching problem of the GaP layer, thereby preparing a Micro LED pixel that solves the lateral etching problem.

Claims

1. A method for preparing a Micro LED pixel that solves the problem of lateral etching, characterized in that: The steps are as follows: (a) Hard mask deposition: The AlGaInP-based device after eutectic bonding with the Si-based CMOS substrate was ultrasonically cleaned with acetone, isopropanol, and deionized water for 10 to 20 minutes, and then the surface moisture was blown dry; then, the AlGaInP-based device N + A 50-700nm thick SiO2 film is deposited on the surface of the heavily doped GaAs layer; (b) Exposure: Spin-coat a positive photoresist on the surface of the SiO2 film, and perform UV mask exposure after curing. The shape of the photoresist mask is the same as the shape of the Micro LED pixel to be prepared. After exposure, the AlGaInP-based device is placed in a developer and soaked for a period of time, then taken out and placed in a container filled with deionized water for flushing. The exposed positive photoresist is removed. After the flushing process is completed, the AlGaInP-based device is blown dry. (c) Post-baking: The AlGaInP-based device after drying is post-baked at 80-180°C for 10-15 minutes to allow the unexposed positive photoresist to reflow into a trapezoidal shape and then cool to room temperature. At this time, the sidewalls of the photoresist are smooth. (d) SiO2 etching: The SiO2 film is etched using the cooled photoresist as a mask to obtain a patterned SiO2 hard mask; (e) Removing the photoresist: Use a degumming solution and deionized water ultrasonic cleaning for 15 to 30 minutes and 8 to 15 minutes respectively to remove the photoresist on the patterned SiO2 hard mask, and then blow dry the moisture on the surface of the AlGaInP-based device; at this time, the surface of the AlGaInP-based device is not covered with photoresist, but only with the patterned SiO2 hard mask; (f) Pixel etching: After etching for 5-15 minutes using a patterned SiO2 hard mask as a mask, a Micro LED pixel is obtained on the bonding metal layer. From bottom to top, the Micro LED pixel consists of a P-type GaP layer, a P-type AlGaInP layer, an MQWs quantum well layer, an N-type AlGaInP layer, and an N-type AlGaInP layer. + The GaAs heavily doped layer is composed; the etching gases used are Cl2, BCl3, Ar2 and N2, the flow rate of Cl2 is 40~60sccm, the flow rate of BCl3 is 40~60sccm, the flow rate of Ar is 15~30sccm, the flow rate of N2 is 5~10sccm, and the ratio of Ar flow rate to N2 flow rate is 2.5~3.5:

1.

2. A method for preparing a Micro LED pixel that solves lateral etching according to claim 1, characterized in that: In step (1), the AlGaInP-based device after eutectic bonding of the Si-based CMOS substrate is composed of a 300-1000 μm thick Si-based CMOS substrate, a 100-800 nm thick bonding metal layer, a 100-500 nm thick P-type GaP layer, a 100-500 nm thick P-type AlGaInP layer, a 5-80 nm thick MQWs quantum well layer, a 100-500 nm thick N-type AlGaInP layer, and a 5-80 nm thick N-type GaP layer. + GaAs heavily doped layer.

3. A method for preparing a Micro LED pixel that solves lateral etching according to claim 1, characterized in that: In step (1), a PECVD device is used to deposit a SiO2 film; the deposition power is 40-60 W, the vacuum degree is 150-300 Pa, the silane flow rate is 40-60 sccm, the nitrous oxide flow rate is 400-600 sccm, and the deposition time is 50-400 s.

4. A method for preparing a Micro LED pixel that solves lateral etching according to claim 1, characterized in that: In step (b), the photoresist mask is a periodically arranged circular through-hole structure, the area outside the circular through-hole structure is a light-transmitting part, and the photoresist outside the circular through-hole structure is ultraviolet exposed; the aperture of the circular through-hole is 4~6μm, and the center spacing of the circular through-hole is 4~6μm.

5. The method for preparing a Micro LED pixel that solves lateral etching according to claim 1, characterized in that: In step (d), an ICP-F-based device is used to etch the SiO2 film, and pure CHF3 is used as the reactive etching gas; the CHF3 flow rate is 80-120 sccm, the chamber pressure is 5-10 mTorr, the ICP power is 600-1000 W, the ICP temperature is 15-25°C, and the patterned SiO2 hard mask presents a cylindrical structure, and the diameter of the cylinder replicates the diameter of the photoresist.

6. The method for preparing a Micro LED pixel that solves lateral etching according to claim 1, characterized in that: In step (f), the upper surface diameter of the Micro LED pixel is 5~7μm, the lower surface diameter is 6~8μm, and the pixel pitch is 4~6μm.

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