CN116555723A - A method for preparing gallium nitride thin film and Micro-LED device based on patterned graphene mask - Google Patents

Abstract

The invention discloses a method for preparing a gallium nitride film and a Micro-LED device based on a patterned graphene mask. PECVD deposition reaction is carried out on a gallium nitride substrate to obtain a graphene layer, and an etching process is adopted to obtain graphene mask structure patterns which are arranged in a long strip shape or in a square shape and are arranged in a matrix shape; the MOCVD epitaxial process is adopted, and conditions such as temperature, pressure, V/III and the like are changed in the MOCVD growth process, so that step nucleation of gallium nitride along the boundary of a window and a mask is effectively regulated and controlled; and (3) obtaining a gallium nitride film with lower dislocation density and a Micro-LED device with excellent performance through lateral epitaxial growth at different times.

Description

A GaN thin film and Micro-LED device based on a patterned graphene mask method of

technical field

The invention relates to a method for preparing a gallium nitride film and a Micro-LED device based on a patterned graphene mask, and belongs to the technical field of semiconductors.

Background technique

Gallium nitride (GaN), as one of the representative III-nitride materials, has the advantages of large band gap, high carrier saturation migration rate, breakdown field strength, and good thermal conductivity. It has broad prospects in the fields of new generation lighting display, mobile communication and energy Internet. Due to the lack of single crystal GaN in nature, most of the current commercial GaN is obtained by heterogeneous epitaxy of substrates such as sapphire and silicon carbide. The quality deteriorates, and there are more crystal defects, such as dislocations, stacking faults, etc.; there will also be obvious warpage leading to cracking of the epitaxial layer. The existence of these defects greatly reduces the performance of the device and seriously limits the application of GaN and development. Epitaxial lateral growth (ELOG) is currently one of the effective means to reduce the dislocation density inside the crystal. Common mask materials are mainly amorphous silicon dioxide, silicon nitride, etc., but these materials will be wrapped after growth Inside the material, due to its poor thermal conductivity, electrical conductivity and other material properties, it also directly affects the performance of the device; using two-dimensional materials such as graphene as a mask can solve these problems very well, and most of them are currently obtained by wet transfer. Graphene film, but the obtained graphene film will have many defects such as pollution and wrinkles in the material, which will affect the nucleation behavior of GaN, so that high-quality GaN film cannot be obtained by lateral epitaxy.

For GaN display lighting applications, Micro-LED has a very broad application prospect due to its advantages of high brightness, low energy consumption, and wide color gamut. At present, Micro-LED chips of different sizes are mainly obtained by dry etching. However, in the process of device fabrication, it will inevitably cause damage to the sidewall of the chip and destroy the crystal structure, resulting in an increase in the proportion of non-radiative recombination on the chip surface and a decrease in radiative recombination, resulting in a decrease in internal quantum efficiency and external quantum efficiency. The radiation recombination efficiency is mainly affected by the dislocation density inside the material, and the dislocations inside the material will form a non-radiative recombination center, reducing the radiation recombination efficiency of the LED.

Therefore, it is necessary to provide a method for controlling the nucleation of GaN by using a patterned graphene mask, so as to obtain GaN chips and Micro-LED chips with selectively grown low dislocation density, so as to solve the above problems.

Contents of the invention

The present invention aims at the deficiencies in the prior art, and provides a method for preparing GaN thin films based on a patterned graphene mask to obtain high-quality GaN epitaxial layers, and can effectively reduce the dislocation density in different layers of Micro-LEDs. A method for preparing a Micro-LED device that improves device performance.

The technical solution for realizing the purpose of the present invention is to provide a method for preparing a gallium nitride film based on a patterned graphene mask, comprising the following steps:

(1) Perform PECVD deposition reaction on the gallium nitride substrate to obtain a graphene layer, and use an etching process to obtain a strip-shaped or square-shaped graphene mask structure pattern arranged in a matrix;

(2) Using MOCVD epitaxy process, under the conditions of TMGa flux of about 16.1sccm, NH ₃ flux of 24-32slm, V/III of 6000-8000, pressure of 500Torr, and temperature of 950-970℃, the GaN edge is controlled. Cube-shaped or strip-shaped graphene boundary nucleation and growth of GaN islands;

(3) Under the conditions of TMGa flux of 40sccm, NH ₃ flux of 80-100slm, V/III of 8000-10000, pressure of 100-200Torr, and temperature of 1050-1070°C, the growth on the graphene boundary is controlled. The GaN islands are grown laterally until they merge, resulting in GaN thin films.

The technical solution of the present invention also includes a method for preparing a Micro-LED device based on a patterned graphene mask, comprising the following steps:

(1) Perform PECVD deposition reaction on the gallium nitride substrate to obtain a graphene layer, and use an etching process to obtain a square-shaped graphene mask structure pattern arranged in a matrix;

(2) Using MOCVD epitaxy process, under the conditions of TMGa flux of about 16.1sccm, NH ₃ flux of 24-32slm, V/III of 6000-8000, pressure of 500Torr, and temperature of 950-970℃, the GaN edge is controlled. The nucleation and growth of GaN islands on the boundaries of each block-shaped graphene;

(3) Under the conditions of TMGa flux of 20sccm, NH ₃ flux of 40-50slm, V/III of 8000-10000, pressure of 100-200Torr, temperature of 1050-1070°C and growth time of 30-50min, Control the lateral growth of the GaN islands at the growth graphene boundary until they merge, cover the graphene under the u-GaN, and obtain a u-GaN layer with a thickness of 3-5 microns;

(4) Change the growth gas source, deposit n-GaN layer, quantum well layer, AlGaN layer, and P-GaN layer in sequence to obtain Micro-LED devices.

The square-shaped mask in the graphene mask structure pattern described in the technical solution for preparing Micro-LED devices according to the present invention has a side length of 1-5 μm, and the interval between adjacent square-shaped masks is 5-30 μm.

The principle of the present invention is that the graphene mask structure is a square structure perpendicular to the m-plane of GaN, and the selective nucleation of GaN can be regulated by changing the V/III ratio. A higher V/III (about 7000) ratio can Make GaN nucleate along the graphene strip and the steps on both sides of the window (both sides of the groove), and the lower V/III (about 2000) ratio promotes the nucleation of GaN in the window area (groove); the two kinds of formation The combination of nuclei can well complete the selective growth and further merge into a whole GaN strip.

Compared with prior art, the beneficial effect of the present invention is:

1. The invention is based on a patterned graphene mask, adopts two different epitaxy processes, effectively regulates the nucleation behavior of GaN, contributes to the lateral epitaxy of high-quality GaN films, and directly epitaxes the Micro-LED device structure, avoiding the process Pollution and crystal defects caused by

2. In the technical solution provided by the present invention, GaN nucleates at the steps of the graphene mask on both sides of the window. Compared with direct nucleation in the groove of the window, the nucleation method can more effectively reduce the dislocation density.

3. The present invention utilizes the nucleation characteristics of GaN around the patterned graphene to control GaN to grow an independent device structure. The device structure is obtained through lateral epitaxy, wherein the dislocation density is low and the crystal quality is good.

Description of drawings

FIG. 1 is a schematic structural diagram of a striped graphene mask pattern perpendicular to the m-plane of GaN provided by Embodiment 1 of the present invention;

Figure 2 is a schematic diagram of the MOCVD growth principle of GaN nucleation along the window (groove) of the striped graphene mask using the traditional process;

Fig. 3 is a SEM image of the nucleation and growth of GaN along the window region of the striped graphene mask into an independent strip structure using the traditional process;

4 is a schematic diagram of the MOCVD growth principle of GaN nucleation along the steps of a striped graphene mask using the process provided by Embodiment 1 of the present invention;

Figures 5, 6, and 7 respectively show the nucleation and growth of GaN along the steps on both sides of the strip-shaped graphene mask as an independent strip structure, further growth and growth into a triangular strip by using the process provided by Embodiment 1 of the present invention. SEM image;

FIG. 8 is an SEM image of a real GaN thin film prepared by using the process provided in Example 1 of the present invention.

9 is a schematic structural diagram of a square graphene mask pattern provided by Embodiment 2 of the present invention;

10 is a schematic diagram of the MOCVD growth principle of GaN along a square graphene mask using the process provided by Embodiment 2 of the present invention;

Fig. 11 is a SEM image of GaN nucleated and grown into an independent mesa structure along the steps of a square graphene mask using the process provided by Embodiment 2 of the present invention.

Among them: 1 is the graphene mask, 2 is the gallium nitride template (substrate), 3 is the window (groove), 4 is the nucleation of GaN in the window area, and 5 is the further three-dimensional process based on the nucleation of GaN in the window area. Growth, 6 is further two-dimensional growth on the basis of three-dimensional growth, 7 is the final merged GaN film, 8 is the nucleation of GaN along the steps of the graphene mask, and 9 is the rest of the Micro-LED layer structure.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Embodiment one

This embodiment provides a method for preparing a GaN thin film using a graphene mask as a strip pattern mask structure, the steps are as follows:

(1) PECVD growth graphene

Perform PECVD deposition reaction on the gallium nitride template (substrate) to obtain a graphene layer;

(2) Patterned graphene

The graphene mask substrate structure pattern arranged in strips is obtained by etching process, and then the photoresist residue, the oxide layer on the substrate surface and the oxide pollution are removed after organic and inorganic cleaning; see attached drawing 1 for basic The schematic diagram of the structure of the graphene mask substrate arranged in strips provided in the embodiment, including a graphene mask 1, a gallium nitride template 2, and a window 3, wherein the graphene mask is a strip pattern mask structure, the stripe direction is perpendicular to the m-plane of the substrate GaN, the period is 10 μm, the window width is 3 μm, and the mask width is 7 μm.

(3) GaN nucleation and GaN thin films grown by MOCVD

Taking the traditional lateral epitaxy process of MOCVD as a comparison example, see Figure 2, which is a schematic diagram of the MOCVD growth principle of GaN nucleation along the window (groove) of the striped graphene mask using the traditional lateral epitaxy process of MOCVD , using TMGa flux of 55sccm, NH ₃ flux of 28slm, V/III=2000, pressure of 500Torr, and temperature of 970°C to grow gallium nitride thin films, which can control the nucleation of GaN preferentially in the window area4, GaN Nucleation and growth along the window region of the strip-shaped graphene mask is an independent strip structure, and the SEM image of the object is shown in Figure 3; under this condition, the three-dimensional growth is continued for 60min until a stable structure with {11- 22} The triangular strip structure of the crystal plane 5, changing the growth conditions, the TMGa flux is 40sccm, the NH ₃ flux is 80slm, V/III=8000, the pressure is 200Torr, and the temperature is 1080℃, making the triangular strips further two-dimensional grow 6, meet and merge into GaN thin film 7 after growing for 90 minutes.

Referring to accompanying drawing 4, in order to adopt the MOCVD lateral epitaxial process provided by this embodiment, the schematic diagram of the MOCVD growth principle of GaN nucleation along the steps of the striped graphene mask; when the TMGa flux is 16.1 sccm, the _NH flux 30slm, V/III=7500, pressure 500Torr, temperature 970°C, GaN is controlled to nucleate preferentially at the steps on both sides of the graphene mask 8, the actual SEM image is shown in Figure 5 ; Then grow further under this condition, forming two GaN strips in the window area and merging, the SEM image of the actual object is shown in Figure 6; after growing for 60 minutes, a triangular strip with {11-22} crystal plane is obtained Structure 5, its actual SEM image is shown in Figure 7; change the growth conditions, the flux of TMGa is 40sccm, the flux of _NH3 is 80slm, V/III=8000, the pressure is 100Torr, and the temperature is 1080°C, so that the triangular bars The strips were further two-dimensionally grown 6, and after 80 minutes of growth, they met and merged into a GaN film 7. Compared with the film obtained by the traditional lateral epitaxy process in the comparative example, the dislocation density of the finally obtained GaN film was lower, reaching 10 ⁶ cm ^{- 2} order of magnitude, its actual SEM image is shown in Figure 8.

Using the method provided in this embodiment, GaN thin films with different thicknesses can be obtained by controlling the growth time.

In this embodiment, MOCVD is used to perform the first step of GaN nucleation growth under the conditions of 970°C and 500 Torr. At this time, the dislocations under the mask are completely blocked, and only the dislocations in the window region penetrate into the epitaxial layer; change Growth parameters: The second two-dimensional growth of GaN is carried out under the conditions of 1070°C and 100 Torr to promote the lateral growth of GaN strips until they merge into a smooth GaN film. Due to the low V/III ratio growth sample, GaN nucleates in the groove, and the dislocation penetrating from the window undergoes a 90°C bending during the process, changing from a vertical dislocation to a horizontal dislocation, and in In the process of merging, annihilation occurs when encountering, so as to reduce the dislocation density of the epitaxial layer. Through the method provided by the present invention, the dislocation density can be reduced from 5x10 ⁸ cm ^-2 of the substrate to 1x10 ⁷ cm ^-2 , close to 1.5 order of magnitude reduction. At the same time, due to the use of samples grown with a high V/III ratio, the GaN nucleation is at the graphene steps on both sides of the window, and the GaN nucleation islands have a small contact area with the substrate, so the penetration from the substrate to the epitaxial layer There is also less dislocation density. In addition, these GaN islands grow further into GaN strips, and the narrow strips on both sides of the window will meet and merge immediately. Part of the dislocations in the crystal will bend and meet in the process, thereby reacting ; During the lateral growth process, dislocations bend at 90°C, changing from vertical dislocations to horizontal dislocations, and meet and annihilate in the process of merging, reducing the dislocation density of the epitaxial layer again.

In this example, the selective nucleation of GaN is regulated by changing the V/III ratio. A higher V/III (about 7000) ratio can make GaN move along the graphene strip and the steps on both sides of the window (both sides of the groove) Nucleation, the lower V/III (about 2000) ratio promotes the nucleation of GaN in the window region (groove); the combination of the two nucleation methods can well complete the selective growth (both nucleation methods can reduce the epitaxy The dislocation density of the layer, the reduction ability of the first method is stronger), and further merged into a whole GaN strip, and finally a GaN film is obtained.

Embodiment two

This embodiment provides a method for preparing a gallium nitride film and a Micro-LED chip based on a square graphene mask pattern.

Perform PECVD deposition reaction on the gallium nitride template (substrate) to obtain a graphene layer; use an etching process to obtain a graphene mask substrate structure pattern, see accompanying drawing 9, for the square graphene mask provided in this embodiment Schematic diagram of the structure, including graphene mask 1, gallium nitride template 2, and window 3, wherein the graphene mask is a square mask structure in an array, and the direction is chosen to be perpendicular to the m-plane of GaN and parallel to the a-plane, with a period of The size of the window and the mask can be selected according to the size requirements of the actual chip. In this embodiment, the width of the window is 7 μm, and the width of the mask is 3 μm.

After organic and inorganic cleaning, photoresist residue, substrate surface oxide layer and oxide pollution are removed; referring to accompanying drawing 10, in order to adopt the square graphene structure provided by this embodiment, GaN is along the border of square graphene Schematic diagram of nucleated MOCVD growth; under the conditions of TMGa flux of 16.1sccm, NH ₃ flux of 30slm, V/III=7500, pressure of 500Torr, and temperature of 970℃ for 5min, GaN is preferentially grown on square graphite Nucleation 8 is formed at the steps around the ene mask; then change the growth parameters TMGa flux to 20sccm, NH ₃ flux to 40slm, V/III=8000, pressure to 200Torr, and temperature to 1080°C to make the triangular strips further two-dimensional After growing for 30 minutes, the GaN epitaxial layer completely covers the entire mask and forms a GaN periodic mesa structure with smooth sidewalls, and epitaxially generates gallium nitride thin film 7, which is u-GaN. The actual SEM image is shown in Figure 11. Show.

Growing the u-GaN layer under the conditions of 970°C and 7500 higher V/III can make Ga atoms obtain extremely strong mobility, thus forcing Ga atoms to migrate to the steps of the four boundaries of the square graphene for reaction Nucleation, GaN islands grown along the boundaries are obtained, and then the growth parameters are changed to promote the lateral two-dimensional growth of GaN islands, directly covering graphene, and obtaining a complete u-GaN layer.

In the technical solution of the present invention, the graphene mask structure is a square structure perpendicular to the m-plane of GaN. During the first step of nucleation and growth, a higher V/III ratio (about 7000) is used to promote GaN along the graphite The ene mask and the steps around the window are nucleated, and a square GaN mesa structure is formed after further lateral growth. This method is more suitable for substrates with a small mask area. The smaller the mask width, the more conducive to growth around the window. Stepped GaN islands further meet and merge. If the mask width is wider, the GaN grown at the step of the mask boundary will only further fill the window area due to the strong migration ability of Ga atoms on the graphene mask; then change the MOCVD The growth gas source uses trimethylgallium, trimethylaluminum, dicyclopentadienyl magnesium, etc. as metal organic compounds, and further grows n-GaN layer, quantum well, AlGaN layer, p -GaN layer, the basic structure of the micro-LED chip can be obtained, and the selective growth of the periodic chip array is realized; the Micro-LED chip array obtained by photolithography-etching is usually difficult to achieve 5*5μm ² Below, due to exposure and other reasons, the expected pattern structure cannot be obtained, but the direct epitaxy method provided by the present invention can optimize these problems, and the array size obtained by direct epitaxy is small, and the mask width can be between 500nm and 5μm between. The chip obtained by the direct epitaxial growth has a smooth side wall and a good crystal structure, which is conducive to improving the luminous efficiency of the chip and improving the performance of the device.

Claims (3)

1. A method for preparing gallium nitride film based on patterned graphene mask, is characterized in that comprising the steps: (1) Perform PECVD deposition reaction on the gallium nitride substrate to obtain a graphene layer, and use an etching process to obtain a strip-shaped or square-shaped graphene mask structure pattern arranged in a matrix; (2) Using MOCVD epitaxy process, under the conditions of TMGa flux of about 16.1sccm, NH ₃ flux of 24-32slm, V/III of 6000-8000, pressure of 500Torr, and temperature of 950-970℃, the GaN edge is controlled. Cube-shaped or strip-shaped graphene boundary nucleation and growth of GaN islands; (3) Under the conditions of TMGa flux of 40sccm, NH ₃ flux of 80-100slm, V/III of 8000-10000, pressure of 100-200Torr, and temperature of 1050-1070°C, the growth on the graphene boundary is controlled. The GaN islands are grown laterally until they merge, resulting in GaN thin films. 2. A method for preparing a Micro-LED device based on a patterned graphene mask, characterized in that it comprises the steps: (1) Perform PECVD deposition reaction on the gallium nitride substrate to obtain a graphene layer, and use an etching process to obtain a square-shaped graphene mask structure pattern arranged in a matrix; (2) Using MOCVD epitaxy process, under the conditions of TMGa flux of about 16.1sccm, NH ₃ flux of 24-32slm, V/III of 6000-8000, pressure of 500Torr, and temperature of 950-970℃, the GaN edge is controlled. The nucleation and growth of GaN islands on the boundaries of each block-shaped graphene; (3) Under the conditions of TMGa flux of 20sccm, NH ₃ flux of 40-50slm, V/III of 8000-10000, pressure of 100-200Torr, temperature of 1050-1070°C and growth time of 30-50min, Control the lateral growth of the GaN islands at the growth graphene boundary until they merge, cover the graphene under the u-GaN, and obtain a u-GaN layer with a thickness of 3-5 microns; (4) Change the growth gas source, deposit n-GaN layer, quantum well layer, AlGaN layer, and P-GaN layer in sequence to obtain Micro-LED devices. 3. A method for preparing a Micro-LED device based on a patterned graphene mask according to claim 2, characterized in that: the square mask in the graphene mask structure pattern has a side length of 1 ～5 μm, and the interval between adjacent square masks is 5～30 μm.