Preparation method of high-quality gallium nitride film based on porous silicon nitride insertion layer

Abstract

The invention provides a preparation method of a high-quality gallium nitride film based on a porous silicon nitride insertion layer. The preparation method comprises the following steps: firstly, sequentially depositing a GaN low-temperature buffer layer and a u-GaN layer subjected to compression strain on a patterned sapphire substrate; a porous SiNx insertion layer is deposited on the u-GaN layer in situ, a nanoscale hole structure penetrating in the thickness direction is formed in the porous SiNx insertion layer, and the u-GaN layer is exposed at holes; then GaN nanorods vertically grow at the holes, finally, growth conditions are regulated and controlled to enable the GaN nanorods to transversely grow and combine to form a flat high-quality GaN thin film, and a gap is formed between the porous SiNx insertion layer and the GaN thin film. According to the method, the internal stress of the GaN film can be effectively reduced, the dislocation density is reduced, the film quality is improved, the process is simple, and the method is suitable for large-scale and low-cost industrial production of the GaN film.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of semiconductor thin films, and particularly relates to a method for preparing high-quality gallium nitride thin films based on a porous silicon nitride insertion layer. Background Art

[0002] Gallium nitride (GaN) is a semiconductor material with wide bandgap characteristics. With its excellent electrical, optical, and thermal properties, it has been widely used in high-power, high-frequency electronic devices, and optoelectronic device fields. The high breakdown voltage and high electron mobility of GaN give it significant advantages over traditional silicon (Si) materials in high-power and high-frequency applications. The growth of GaN thin films usually relies on the metalorganic chemical vapor deposition (MOCVD) process, which successfully prepares GaN thin films through epitaxial growth under high-temperature conditions.

[0003] However, there are large lattice mismatches and differences in thermal expansion coefficients between the current GaN material and common substrate materials (such as sapphire). This will cause stress accumulation during the growth process, which in turn affects the physical properties of the thin film (carrier mobility, bandgap width, etc.), and further affects its electrical, optical, and thermal properties. The stress generated due to the mismatch not only affects the crystal quality of the GaN thin film but may also cause problems such as lattice defects, dislocations, and surface roughness during the growth process, and even lead to performance degradation. Especially in high-power and high-frequency applications, these defects may seriously affect the performance of the device and cannot meet the requirements of high-power electronic devices, high-frequency electronic devices, and high-efficiency LEDs, etc.

[0004] Currently, there have been studies to improve the quality of GaN thin films by applying masking techniques and adjusting growth conditions. The masking technique effectively improves the quality of GaN thin films by locally regulating the growth environment and reducing stress concentration. Specifically, the mask can control the thickness, morphology, and stress distribution of the GaN thin film, reduce the formation of cracks, and promote crystal growth. However, existing masking techniques usually require complex micro-nano processing techniques such as photolithography and electron beam lithography. These process steps not only increase the production complexity, significantly increase the cost and time consumption, but may also introduce etching damage during the etching process, affecting the crystal quality of the GaN thin film. This poses certain challenges to the large-scale industrial production of GaN thin films. Summary of the Invention

[0005] To solve the deficiencies of the above-mentioned existing technologies, the present invention provides a method for preparing high-quality gallium nitride thin films based on a porous silicon nitride insertion layer, aiming to use in-situ grown porous silicon nitride as a mask to promote the high-quality growth of gallium nitride thin films, effectively reduce the internal stress of the GaN thin film, and improve the film quality.

[0006] The present invention adopts the following technical solutions to achieve the purpose:

[0007] Preparation method of high-quality gallium nitride thin film based on porous silicon nitride insertion layer, characterized in that: firstly, a GaN low-temperature buffer layer and a compressed-strained u-GaN layer are sequentially deposited on a patterned sapphire substrate; then a porous SiN x insertion layer is in-situ deposited on the u-GaN layer, and the porous SiN x insertion layer is formed with a nanoscale hole structure penetrating along the thickness direction, and the u-GaN layer is exposed at the holes; then GaN nanocolumns are vertically grown at the holes, and finally the growth conditions are adjusted to make the GaN nanocolumns grow laterally and merge to form a flat high-quality GaN thin film, and a gap is formed between the porous SiN x insertion layer and the GaN thin film, and the gap is formed above the non-hole position of the porous SiN x insertion layer.

[0008] Furthermore, the patterned sapphire substrate is (0001)c-plane oriented, and the GaN low-temperature buffer layer, u-GaN layer, GaN nanocolumns and GaN thin film grown based on it are all (0001)c-plane oriented.

[0009] Furthermore, the size of the nanoscale hole structure in the porous SiN x insertion layer is 10 - 300 nm. The diameter of the GaN nanocolumns is the same as the hole size of the porous SiN x layer. The SiN x layer can not only serve as a mask for the subsequent growth of GaN nanocolumns, but also as a dislocation blocking layer to improve the crystal quality of the GaN thin film.

[0010] Furthermore, during the lateral growth of the GaN nanocolumns, the growth rate from the top to the bottom of the GaN nanocolumns shows a decreasing trend, so that an inverted trapezoidal structure with a wider top and a narrower bottom is generated during the merging process, and after the merging, a gap that fails to be completely merged is formed between the porous SiN x insertion layer and the GaN thin film and above the non-hole position of the porous SiN x insertion layer.

[0011] Furthermore, the preparation method of the high-quality gallium nitride thin film based on the porous silicon nitride insertion layer is specifically as follows: in an MOCVD system, using TMGa or TEGa as the gallium source, NH3 as the nitrogen source, SiH4 as the silicon source, and a mixed gas of nitrogen and hydrogen as the carrier gas, layer-by-layer deposition is carried out, including the following steps:

[0012] Step 1, pre-treat the substrate

[0013] Place the patterned sapphire substrate into an MOCVD equipment, and heat-treat it in a mixed atmosphere of NH3 and N2 (flow ratio 1:1) at 1000 - 1200 °C for 10 - 15 minutes.

[0014] Step 2: Deposit a GaN low-temperature buffer layer

[0015] Under the conditions of a temperature of 700 - 900 °C, a pressure of 50 - 80 Torr, and a V / III ratio of 900 - 1000, grow a GaN low-temperature buffer layer with a thickness of 20 - 50 nm on the sapphire substrate; the V / III ratio refers to the molar ratio of the group V source and the group III source introduced into the reaction chamber. The role of the buffer layer is to relieve the lattice mismatch between sapphire and gallium nitride, reduce stress accumulation, and improve the crystallization quality of the gallium nitride thin film.

[0016] Step 3: Deposit a u-GaN layer

[0017] Under the conditions of a temperature of 1000 - 1100 °C, a pressure of 130 - 170 Torr, and a V / III ratio of 1050 - 1100, grow a u-GaN layer with a thickness of 1 - 2 μm on the GaN low-temperature buffer layer obtained in Step 2. This layer is the basic layer of gallium nitride and is the basis for the subsequent growth of gallium nitride, and is under the action of compressive strain.

[0018] Step 4: In-situ deposit porous SiN x Insertion layer

[0019] Under the conditions of a temperature of 800 - 1000 °C and a pressure of 80 - 120 Torr, in-situ deposit porous SiN on the u-GaN layer obtained in Step 3 x Insertion layer, and the deposition time is 6 - 10 minutes. By controlling the deposition time, the density of the holes in the porous SiN x Insertion layer can be regulated, so as to be able to act as a mask to guide the vertical and horizontal growth of gallium nitride, and play a certain role in blocking dislocations, reducing the dislocation density of the upper thin film. This mask has good selectivity and can optimize the stress distribution during the growth process while controlling the growth area.

[0020] Step 5: Vertically grow GaN nanocolumns

[0021] Under the conditions of 850 - 950 °C, a pressure of 180 - 220 Torr, and a V / III ratio of 20 - 40, vertically grow GaN nanocolumns with a height of 0.5 - 1 μm at the holes of the porous SiN x Insertion layer. Under the masking effect of the porous SiN x Insertion layer, gallium nitride begins to grow vertically. Due to the guiding effect of the mask, gallium nitride forms a high-quality vertical structure in the specified area. This process can effectively control the crystal structure of the thin film and improve the uniformity and performance of the material.

[0022] Step 6: Lateral merging of GaN nanocolumns to form a film

[0023] Adjust the temperature to 1000 - 1100 °C, the gas pressure to 180 - 220 Torr, and the V / III ratio to 3000 to promote the lateral merging and vertical planar growth of the GaN nanocolumns obtained in Step 5 until a high-quality GaN film with a thickness of 1.5 - 2 μm is formed on the porous SiN x insertion layer. After the vertical growth is completed, the gallium nitride material will undergo lateral merging. By controlling the growth temperature and atmosphere, the gallium nitride layer will merge horizontally with the help of the mask to form a large-area film, further reducing the internal stress and improving the material uniformity.

[0024] Compared with the existing technologies, the present invention provides a method for promoting the growth of gallium nitride thin films through a porous silicon nitride mask, which can effectively reduce the internal stress of the GaN thin film, improve the film quality, and provide a new solution for the production of wide-bandgap semiconductor devices. The beneficial effects of the present invention are specifically reflected in:

[0025] 1. The present invention uses the in-situ deposited porous SiN x insertion layer as a mask, and by controlling the growth conditions, effectively guides the vertical and horizontal growth of the GaN thin film, greatly avoiding the direct growth of the GaN thin film on the patterned sapphire substrate with lattice mismatch, and effectively reducing the internal stress suffered by the GaN thin film. At the same time, the non-porous positions of the porous SiN x insertion layer can act as a dislocation blocking layer to prevent the dislocations at the bottom from extending upward into the upper GaN thin film, improving the film quality. And by using the porous structure of the SiN x insertion layer, it can promote the growth of the GaN thin film in a low-stress state, improving the film quality and uniformity. This method not only improves the quality of the GaN thin film, but also reduces the formation of cracks and defects, and has broad application prospects, especially in the manufacturing of high-power electronic devices and LED devices.

[0026] 2. Compared with the existing mask technologies, the porous SiN x insertion layer in the present invention can be directly grown in-situ on GaN without going through complex pre-treatment steps such as lithography, simplifying the production process and reducing the manufacturing cost. And through the in-situ grown SiN x mask, the stress distribution of the thin film can be better controlled, and the etching damage that may occur during the traditional lithography process can be avoided, thereby improving the quality and stability of the GaN thin film, and being suitable for large-scale and low-cost industrial production. Description of the Drawings

[0027] Figure 1 It is a schematic structural diagram of the high-quality GaN thin film provided by the present invention.

[0028] Figure 2 is porous SiN x Schematic diagram of the insertion layer.

[0029] Figure 3 is porous SiN x Schematic diagram of the blocking effect of the insertion layer on dislocations.

[0030] Figure 4 Flow chart of the preparation method of high-quality gallium nitride thin film based on porous silicon nitride insertion layer.

[0031] Figure 5 is the porous SiN in Example 1 x SEM images when the deposition time of the insertion layer is 8 minutes and 10 minutes respectively, and GaN nanocolumns are vertically grown on it for 5 minutes.

[0032] Figure 6 is with or without porous SiN in Example 1 x Raman shift comparison chart of the grown GaN thin films with or without the porous SiN insertion layer.

[0033] Figure 7 is with or without porous SiN in Example 1 x XRD rocking curve comparison chart of the grown GaN thin films with or without the porous SiN insertion layer along the (002) direction. Detailed implementation mode

[0034] The following will describe the embodiments of the present invention in detail with reference to the accompanying drawings. The following embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given.

[0035] Example 1

[0036] As Figure 1 shown, this example provides a structure of a high-quality GaN thin film, which is sequentially deposited from bottom to top on a patterned sapphire substrate: a GaN low-temperature buffer layer, a u-GaN layer, a porous SiN x insertion layer and a high-quality GaN thin film. Its preparation method is as follows: First, a GaN low-temperature buffer layer and a compressively strained u-GaN layer are sequentially deposited on the patterned sapphire substrate; then a porous SiN x insertion layer is in-situ deposited on the u-GaN layer to act as a mask for the subsequent growth process. The porous SiN x insertion layer is formed with a nanoscale hole structure penetrating along the thickness direction, and the u-GaN layer is exposed at the holes. Since the adhesion coefficient of Ga to SiNx is very low, GaN cannot directly nucleate on the SiN x site surface. By controlling the epitaxial conditions (growth temperature, pressure, V / III ratio, etc.), GaN first grows from SiNx GaN nanocolumn structures grow vertically upward in the holes of the insertion layer. Next, the growth conditions are changed to inhibit the vertical growth of the GaN nanocolumns and promote the lateral growth. The adjacent GaN nanocolumns merge laterally to form a continuous GaN thin film, and there is a void formed between the porous SiN x insertion layer and the GaN thin film, and this void is formed in the porous SiN x above the non-hole positions of the insertion layer. The GaN thin film continues to grow to an appropriate thickness. This thin film has the characteristics of low stress, low dislocation density, and high crystal quality.

[0037] As Figure 2 shown, this embodiment shows the schematic diagram of the hole structure of the porous SiN x insertion layer, where the holes are randomly distributed and the sizes vary from dozens of nanometers to hundreds of nanometers.

[0038] As Figure 3 shown, this embodiment shows the blocking effect of the porous SiN x insertion layer as a mask on dislocations. Due to the large lattice mismatch between the hetero-substrates, the GaN thin film is subjected to compressive strain from the bottom layer, which will cause a large number of dislocations to be generated inside the GaN thin film. As the epitaxial process proceeds, the dislocations continuously extend upward. At this time, the SiN x acts as a mask and plays a certain blocking role on the dislocations. Some dislocations are blocked and annihilated under the SiN x mask, reducing the dislocation density of the upper-layer thin film and improving the crystal quality.

[0039] As Figure 4 shown, this embodiment also provides a method for preparing a high-quality gallium nitride thin film based on a porous silicon nitride insertion layer. The entire preparation process is completed in a MOCVD system, using TMGa as the gallium source, NH3 as the nitrogen source, SiH4 as the silicon source, and a mixed gas of nitrogen and hydrogen (flow ratio of 5:1) as the carrier gas, and performing layer-by-layer deposition, including the following steps:

[0040] Step 1, pre-treat the substrate

[0041] Put a 4-inch c-plane patterned sapphire substrate into the MOCVD equipment and treat it in a mixed gas of NH3 and N2 (flow ratio 1:1) at 1100 °C for 10 minutes.

[0042] Step 2, deposit a GaN low-temperature buffer layer

[0043] Grow a 20-nm-thick GaN low-temperature buffer layer on the sapphire substrate obtained in Step 1 under the conditions of a temperature of 800 °C, a pressure of 65 Torr, and a V / III ratio of 1000.

[0044] Step 3, deposit the u-GaN layer

[0045] Under the conditions of a temperature of 1050 °C, a pressure of 150 Torr, and a V / III ratio of 1000 - 1100, a 2-μm-thick u-GaN layer is grown on the GaN low-temperature buffer layer obtained in Step 2.

[0046] Step 4: In-situ deposition of porous SiN x Insertion layer

[0047] Under the conditions of a temperature of 900 °C and a pressure of 100 Torr, porous SiN is in-situ deposited on the u-GaN layer obtained in Step 3. x Insertion layer, and the deposition time is 8 minutes.

[0048] Step 5: Vertically grow GaN nanocolumns

[0049] Under the conditions of a temperature of 950 °C, a pressure of 200 Torr, and a V / III ratio of 30, GaN with a height of about 1 μm is vertically grown in the holes of the porous SiN x insertion layer to form a nanocolumn structure. The diameter of the GaN nanocolumns is the same as the hole size of the porous SiN x insertion layer.

[0050] Step 6: Horizontally merge GaN nanocolumns into a film

[0051] Adjust the temperature to 1050 °C, the pressure to 200 Torr, and the V / III ratio to 300 to promote the horizontal merging and vertical planar growth of the GaN nanocolumns obtained in Step 5 until a high-quality GaN thin film with a thickness of 1.5 - 2 μm is formed on the porous SiN x insertion layer.

[0052] As Figure 5 shown, this embodiment shows the SEM images when the deposition times of the porous SiN x insertion layer are 8 minutes and 10 minutes respectively, and GaN nanocolumns are vertically grown on it for 5 minutes. Since the GaN deposition time is short, the GaN islands have just grown out of the holes, and the surface morphology of the porous SiN x insertion layer can be clearly observed. It can be seen that as the SiN x deposition time increases, the density of the GaN islands decreases, indicating that the hole density of the porous SiN x insertion layer gradually decreases. Therefore, the thickness of the porous SiN x insertion layer should not be too thick.

[0053] For comparison, this embodiment also grows a GaN thin film under the condition of no porous SiN x insertion layer, that is, directly grows a GaN thin film with a thickness of 1.5 - 2 μm on the u-GaN layer according to the conditions of Step 6.

[0054] As shown Figure 6 in the figure, this embodiment provides a Raman shift comparison diagram of GaN thin films grown with and without a porous SiN x insertion layer. It can be seen that the orange dashed line at a wavenumber of 567.5 cm -1 marks the unstrained position of the E2(high) phonon mode of GaN. The residual biaxial stress can be determined based on the shift of the Raman peak from this unstrained position. Accordingly, it can be concluded that the GaN thin film grown based on the porous SiN x insertion layer has a smaller Raman peak shift compared to the GaN thin film without the porous SiN x insertion layer, and the stress in the film is fully released.

[0055] As shown Figure 7 in the figure, this embodiment also provides a comparison diagram of XRD rocking curves of GaN thin films grown with and without a porous SiN x insertion layer along the (002) direction. The full width at half maximum (FWHM) of the XRD rocking curve of the GaN thin film along the (002) direction can be used to evaluate the dislocation density in the film. It can be concluded that the GaN thin film grown based on the porous SiN x insertion layer has a narrower FWHM of the rocking curve compared to the GaN thin film without the porous SiN x insertion layer, and the dislocation density in the film is fully reduced.

[0056] The above are only exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-quality gallium nitride thin film based on a porous silicon nitride interlayer, characterized in that: First, a GaN low-temperature buffer layer and a compressively strained u-GaN layer are sequentially deposited on a patterned sapphire substrate; then a porous SiN x insertion layer is in-situ deposited on the u-GaN layer. The porous SiN x insertion layer is formed with a nanoscale hole structure penetrating in the thickness direction, and the u-GaN layer is exposed at the holes; then GaN nanocolumns are vertically grown at the holes, and finally the growth conditions are adjusted to make the GaN nanocolumns grow laterally and merge to form a flat and high-quality GaN thin film, and a gap is formed between the porous SiN x insertion layer and the GaN thin film, and the gap is formed above the non-hole position of the porous SiN x insertion layer.

2. The preparation method according to claim 1, characterized in that: The patterned sapphire substrate is c-plane oriented.

3. The preparation method according to claim 1, characterized in that: The GaN low-temperature buffer layer, u-GaN layer, GaN nanocolumns, and GaN thin film are all c-plane oriented.

4. The preparation method according to claim 1, wherein: During the lateral growth of the GaN nanocolumns, the growth rate from the top to the bottom of the GaN nanocolumns shows a decreasing trend, thereby generating an inverted trapezoidal structure with a wider top and a narrower bottom during the merging process, and after the merging, making the porous SiN x insertion layer is between the GaN thin film and is located in the porous SiN x gaps that are not fully merged are formed above the non-porous positions of the insertion layer.

5. The preparation method according to any one of claims 1 to 4, characterized in that, In an MOCVD system, using TMGa or TEGa as the gallium source, NH3 as the nitrogen source, SiH4 as the silicon source, and a mixed gas of nitrogen and hydrogen as the carrier gas, layer-by-layer deposition is carried out, including the following steps: Step 1. Pretreat the substrate Put the patterned sapphire substrate into the MOCVD equipment, and heat-treat it in a mixed atmosphere of NH3 and N2 at 1000 - 1200 °C for 10 - 15 minutes; Step 2. Deposit the GaN low-temperature buffer layer Under the conditions of a temperature of 700 - 900 °C, a pressure of 50 - 80 Torr, and a V / III ratio of 900 - 1000, grow a GaN low-temperature buffer layer with a thickness of 20 - 50 nm on the sapphire substrate; Step 3. Deposit the u-GaN layer Under the conditions of a temperature of 1000 - 1100 °C, a pressure of 130 - 170 Torr, and a V / III ratio of 1050 - 1100, grow a u-GaN layer with a thickness of 1 - 2 μm on the GaN low-temperature buffer layer obtained in Step 2; Step 4, in-situ deposition of porous SiN x Insertion layer Under the conditions of a temperature of 800 to 1000 °C and a gas pressure of 80 to 120 Torr, a porous SiN is in-situ deposited on the u-GaN layer obtained in step 3 x Insertion layer, and the deposition time is 6 to 10 minutes; Step 5. Vertically grow GaN nanocolumns Under the conditions of 850 - 950 °C, a gas pressure of 180 - 220 Torr, and a V / III ratio of 20 - 40, GaN nanocolumns with a height of 0.5 - 1 μm are vertically grown at the pores of the porous SiN x insertion layer; Step 6. Horizontally merge the GaN nanocolumns into a film Adjust the temperature to 1000 - 1100 °C, the pressure to 180 - 220 Torr, and the V / III ratio to 3000 to promote the lateral merging and vertical planar growth of the GaN nanocolumns obtained in step 5 until a high-quality GaN thin film with a thickness of 1.5 - 2 μm is formed on the porous SiN x insertion layer.

6. A high-quality gallium nitride thin film based on a porous silicon nitride insertion layer prepared by the preparation method according to any one of claims 1 - 5.

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