Substrate pretreatment and single crystal film preparation method for growing aluminum nitride

Abstract

The invention belongs to the technical field of nitride material preparation, and provides a substrate pretreatment and single crystal film preparation method for growing aluminum nitride. According to the method, nitrogen is used as a nitrogen source, aluminum particles are used as an aluminum source, and a metal nitridation vapor phase epitaxy (MNVPE) device is used on a sapphire substrate. Wherein a sunken structure is formed on the sapphire substrate through a pretreatment method, and then the growth of the aluminum nitride single crystal film is carried out in three steps. According to the pretreatment and preparation method for the aluminum nitride single crystal film, on one hand, steam generated by heating aluminum has an etching effect on sapphire, nucleation and crystal column closure of aluminum nitride are facilitated, and on the other hand, annihilation of dislocation and stress release can be promoted through three-step growth, so that the yield of the aluminum nitride single crystal film is improved. Therefore, the crystal quality of the aluminum nitride film prepared by the metal nitriding vapor phase epitaxy method is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of nitride material preparation, and relates to a substrate pretreatment and single crystal film preparation method for growing aluminum nitride. Background Art

[0002] Aluminum nitride belongs to the third generation of semiconductor materials. It has excellent physical properties such as large bandgap, high surface acoustic velocity, good thermal conductivity, high temperature resistance and small dielectric constant. It is widely used in the field of high-frequency, high-voltage and high-power optoelectronic devices. Compared with other third generation semiconductor materials, the biggest advantage of aluminum nitride is that its bandgap is as high as 6.20eV. It has unique advantages in the field of deep ultraviolet and vacuum ultraviolet optoelectronic devices and is the preferred material for making deep ultraviolet and vacuum ultraviolet optoelectronic devices.

[0003] Due to the lack of high lattice matching and low-cost substrate materials for the preparation of aluminum nitride-based ultraviolet photoelectric devices, aluminum nitride single crystal films are often prepared on sapphire substrates. However, due to the difference in thermal expansion coefficients between sapphire and aluminum nitride and the weak migration ability of aluminum atoms, the growth of aluminum nitride single crystal films on sapphire substrates has problems such as difficult film formation and low growth rate, which affects the preparation and performance of the device. Summary of the invention

[0004] The main purpose of the present invention is to provide a sapphire substrate pretreatment and film preparation method in the process of preparing aluminum nitride single crystal film by metal nitride vapor phase epitaxy (MNVPE) device, aiming to solve the problem that the existing technology cannot improve the low crystal quality of aluminum nitride single crystal film. Before the growth of aluminum nitride single crystal film, the sapphire is etched with steam generated by heated aluminum particles, a depression is constructed on the substrate surface to accelerate the closing process of crystal islands, and a three-step growth process is used to reduce the dislocation density to improve the crystal quality.

[0005] To achieve the above object, the present invention provides a technical solution for pretreating sapphire and growing aluminum nitride film in three steps in a metal nitride vapor phase epitaxy device, comprising:

[0006] According to a specific embodiment of the present invention, the present invention provides a method for pretreating a sapphire substrate, which further includes the following steps before growing an aluminum nitride film on the substrate:

[0007] placing aluminum particles in a source region of a reaction chamber and placing a sapphire substrate in a growth region of the reaction chamber;

[0008] Argon gas is introduced into the corundum tube in the reaction chamber;

[0009] The source region is heated to 1100-1500°C and the growth region is heated to 1000-1400°C;

[0010] After reaching the preset temperature, the particles are heated to generate steam that blows the sapphire surface, producing an etching effect and starting pretreatment;

[0011] After the preset time is reached, the introduction of the argon gas is stopped to form a depression on the substrate.

[0012] In a possible implementation, the flow rate of the argon gas is in the range of 1 to 2000 sccm.

[0013] In a possible implementation, the pressure in the reaction chamber of the metal nitride vapor phase epitaxy device ranges from 100 to 20,000 Pa.

[0014] In a possible implementation, the preset time is 1 to 1800 s, preferably 60 to 1200 s.

[0015] In a possible implementation, the depth of the depression on the sapphire surface is 0.001-10 μm.

[0016] In a possible implementation, the diameter of the depression on the sapphire surface is 0.001-50 μm.

[0017] According to a specific embodiment of the present invention, the present invention also provides a three-step method for growing an aluminum nitride single crystal thin film, which comprises:

[0018] Pre-treating the sapphire substrate according to the aforementioned method to obtain a substrate surface with a depression;

[0019] Keeping the temperature of the source region constant, heating the growth region to 1100-1600° C., preferably 1100-1200° C., introducing nitrogen into the quartz tube, and keeping the temperature for a certain period of time to grow a buffer layer on the surface of the substrate;

[0020] Keeping the temperature of the source region constant, heating the growth region to 1200-1600° C., preferably 1200-1300° C., adjusting the flow rates of nitrogen and argon, and maintaining the temperature for a certain period of time to grow a transition layer on the buffer layer;

[0021] Keep the source zone temperature unchanged, heat the growth zone to 1300-1600°C, adjust the flow of nitrogen and argon, keep warm for a certain period of time, grow a high-temperature layer on the transition layer, then cool to room temperature to complete the growth of aluminum nitride single crystal film.

[0022] In a possible implementation, the nitrogen flow rate during the growth of the buffer layer is 3000-4000 sccm, and the argon flow rate is 30-1000 sccm, preferably 30-80 sccm;

[0023] In a possible implementation, the insulation time during the growth of the buffer layer is 1 to 20 minutes;

[0024] In a possible implementation, the nitrogen flow rate during the growth of the transition layer is 2000-3000 sccm, and the argon flow rate is 40-1600 sccm, preferably 40-100 sccm;

[0025] In a possible implementation, the insulation time during the growth of the transition layer is 1 to 30 minutes;

[0026] In a possible implementation, the nitrogen flow rate during the growth of the high temperature layer is 1000-2000 sccm, and the argon flow rate is 100-3000 sccm, preferably 100-600 sccm;

[0027] In a possible implementation, the holding time during the growth of the high temperature layer is 0.1 to 6 hours;

[0028] In a possible implementation, the pressure in the reaction chamber during the three-step growth of the aluminum nitride single crystal thin film ranges from 100 to 20,000 Pa, preferably from 10,000 to 20,000 Pa.

[0029] The pretreatment method for preparing aluminum nitride single crystal film of the present invention pretreats the sapphire substrate before growing the aluminum nitride single crystal film. On the one hand, the substrate surface can be cleaned. On the other hand, the steam generated by the heating of aluminum has an etching effect on the sapphire substrate, and depressions can be constructed on the surface to promote the nucleation of aluminum nitride on the substrate and the closing process of crystal islands, thereby improving the crystal quality of the aluminum nitride single crystal film.

[0030] The present invention grows aluminum nitride single crystal film in three steps in a metal nitride vapor phase epitaxy device, adjusts the lateral growth rate and the longitudinal growth rate in different growth stages by step-by-step growing of a buffer layer, a transition layer and a high-temperature layer, promotes the merging and annihilation of dislocations to reduce the dislocation density, flattens the surface, and increases the growth rate of the film. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the examples of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 It is a schematic structural diagram of the reaction formula of the metal nitride vapor phase epitaxy device of the present invention;

[0033] Figure 2 The sapphire surface treated by the pretreatment method provided in Example 1 of the present invention.

[0034] Figure 3 This is the cross section of sapphire after being treated by the pretreatment method provided in Example 1 of the present invention.

[0035] Figure 4 The sample surface pretreated and buffer layer grown according to Example 1 of the present invention

[0036] Figure 5 The sample surface pretreated and grown with a buffer layer and a transition layer provided in Example 1 of the present invention

[0037] Figure 6 The surface of the aluminum nitride single crystal film after the pretreatment and growth of the buffer layer, transition layer, and high-temperature layer provided in Example 1 of the present invention.

[0038] Figure 7 This is the cross section of the aluminum nitride single crystal film after the pretreatment and growth of the buffer layer, transition layer, and high-temperature layer provided in Example 1 of the present invention.

[0039] Figure 8 The rocking curve measurement result of the (0002) surface of the aluminum nitride single crystal thin film after pretreatment and growth of a buffer layer, a transition layer, and a high-temperature layer provided in Example 1 of the present invention.

[0040] Fig. 9 This is the cross section of the aluminum nitride single crystal thin film grown directly on the substrate without pretreatment in Comparative Example 1.

[0041] Fig.10 This is the surface of the aluminum nitride single crystal thin film grown directly on the substrate without pretreatment in Comparative Example 1.

[0042] Fig.11 1 is the rocking curve measurement result of the (0002) plane of the aluminum nitride single crystal thin film grown directly on the substrate without pretreatment in comparative example 1.

[0043] Fig.12 This is the surface of the aluminum nitride single crystal thin film grown directly on the substrate without pretreatment in Comparative Example 2.

[0044] Fig.13 The rocking curve measurement results of the (0002) plane of the aluminum nitride single crystal thin film grown in three steps directly on the substrate without pretreatment in comparative example 2. DETAILED DESCRIPTION

[0045] In order to facilitate the understanding of the present invention, the present invention will be described in more comprehensive and detailed manner in conjunction with the drawings and preferred embodiments of the specification below, but the scope of protection of the present invention is not limited to the following specific embodiments. The components of the embodiments of the present invention generally described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, those skilled in the art should understand that they can still modify the technical solutions of the various embodiments, or make equivalent replacements for some of the technical features therein; and these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention, and all other embodiments obtained without making creative work are within the scope of protection of the present invention.

[0046] According to one embodiment of the present invention, the metal nitride vapor phase epitaxial growth device used is as follows: Figure 1 As shown, the reaction chamber of the device includes a quartz tube and a corundum tube coaxially sleeved in the quartz tube and located at one end of the quartz tube, aluminum particles are placed in the corundum tube as a source area, and a sapphire substrate is placed at the other end of the quartz tube as a growth area. The end of the corundum tube close to the substrate is open, and gas can be passed through and vacuumed in the quartz tube, and gas can be passed into the corundum tube alone; the substrate is placed 5 to 10 cm away from the proximal end of the corundum tube.

[0047] One aspect of an embodiment of the present invention provides a substrate pretreatment method comprising: placing aluminum particles and a sapphire substrate into a source region and a growth region of a metal nitride vapor phase epitaxy device, respectively, and then evacuating the reaction chamber until the pressure drops below 1 Pa. Then, argon gas is introduced into the quartz tube, the source region is heated to 1100-1500°C, and the growth region is heated to 1000-1400°C. After reaching a predetermined temperature, the aluminum particles are heated to generate steam to pretreat the sapphire substrate.

[0048] In some embodiments, the vapor generated by the aluminum particles when heated includes aluminum and aluminum oxide generated by reacting with the aluminum boat.

[0049] Another aspect of the embodiments of the present invention provides a method for growing aluminum nitride single crystal thin film in three steps using a metal nitride vapor phase epitaxy device, including: pre-treating the substrate according to the aforementioned method to obtain a concave substrate surface, then introducing nitrogen into the quartz tube, adjusting the flow rates of nitrogen and argon, heating the source area to 1100-1500°C, and when the growth area is heated to 1100-1600°C, the buffer layer is grown for 1-20 minutes. After that, the temperature of the source area remains unchanged, the growth area is heated to 1200-1600°C, the flow rates of nitrogen and argon are adjusted, and the transition layer is grown for 1-30 minutes. After that, the temperature of the source area remains unchanged, the growth area is heated to 1300-1600°C, the flow rates of nitrogen and argon are adjusted, and the high-temperature layer is grown for 0.1-6 hours, and then the reaction chamber is cooled to room temperature to complete the growth process.

[0050] Example 1

[0051] Using a metal nitride vapor phase epitaxy device, aluminum particles are placed in the source area, sapphire substrates are placed in the growth area, the chamber is evacuated to below 1Pa, argon gas is introduced at a flow rate of 2000sccm, the source area is heated to 1200℃, the growth area is heated to 1100℃, the reaction chamber pressure is maintained at 12000Pa, and the temperature is kept for 900s to perform substrate pretreatment. Then, the nitrogen flow rate is introduced at 3500sccm, the argon flow rate is adjusted to 80sccm, the source area temperature is kept constant, the growth area is heated to 1100℃, and the temperature is kept for 3min to grow a buffer layer. Then, the nitrogen flow rate is adjusted to 2500sccm, the argon flow rate is adjusted to 90sccm, the source area temperature is kept constant, the growth area is heated to 1300℃, and the temperature is kept for 12min to grow a transition layer. Then, the nitrogen flow rate was adjusted to 1800 sccm, the argon flow rate was adjusted to 1800 sccm, the temperature of the source area was kept unchanged, the growth area was heated to 1450°C, and kept warm for 2 hours to grow a high-temperature layer.

[0052] Example 2

[0053] Using a metal nitride vapor phase epitaxy device, aluminum particles are placed in the source area, a sapphire substrate is placed in the growth area, an argon flow rate of 1500sccm is introduced, the source area is heated to 1350℃, the growth area is heated to 1200℃, and the temperature is kept for 300s to pretreat the substrate. Then, a nitrogen flow rate of 3800sccm is introduced, the argon flow rate is adjusted to 50sccm, the source area remains unchanged, the growth area is heated to 1300℃, and the temperature is kept for 18min to grow a buffer layer. Then, the nitrogen flow rate is adjusted to 2100sccm, the argon flow rate is adjusted to 135sccm, the source area remains unchanged, the growth area is heated to 1450℃, and the temperature is kept for 25min to grow a transition layer. Then, the nitrogen flow rate is adjusted to 1600sccm, the argon flow rate is adjusted to 1200sccm, the source area remains unchanged, the growth area is heated to 1580℃, and the temperature is kept for 4h to grow a high-temperature layer.

[0054] Comparative Example 1

[0055] The difference between this comparative example and Example 1 is that the steam generated by the heating of aluminum particles is not used to etch the sapphire substrate, and the high-temperature layer is directly grown on the sapphire substrate in one step (ie, only the high-temperature layer is grown).

[0056] Comparative Example 2

[0057] The difference between this comparative example and Example 1 is that the steam generated by the heating of aluminum particles is not used to etch the sapphire substrate, and a buffer layer, a transition layer and a high-temperature layer are grown on the sapphire substrate in three steps.

[0058] Example 1 The SEM images of the surface and cross section of the sapphire substrate after pretreatment are as follows: Figure 2 , 3 As shown in the figure, it can be seen that an obvious concave structure is formed on its surface. The surface SEM images after the subsequent growth of the buffer layer, the transition layer, and the high-temperature layer, as well as the cross-sectional SEM of the final film are shown in Figure 1. Figure 4 , 5 , 6, and 7, the rocking curve measurement results of the final single crystal film are shown in Figure 8 As shown, it is obvious that the single crystal film prepared in this example has very excellent crystal quality and a flat surface. Figure 9-13 The test images of the films obtained in Comparative Examples 1 and 2 are respectively, and the film surface prepared by the method is uneven and the crystal quality is poor. It can be seen that the pretreatment method of the present invention can be beneficial to the nucleation and closure of the crystal column of aluminum nitride, and the three-step growth of the present invention can promote the annihilation of dislocations and stress release, thereby improving the crystal quality of the aluminum nitride film prepared by the metal nitride vapor phase epitaxy method.

[0059] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0060] The above-mentioned embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments can still be modified, or some of the technical features can be replaced by equivalents. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A method for substrate pretreatment and single crystal film preparation for growing aluminum nitride, characterized in that: include: The sapphire substrate is pretreated in a metal nitride vapor phase epitaxy device to obtain a substrate with a depression on the surface; and an aluminum nitride single crystal thin film is continuously prepared on the obtained substrate with a depression by three-step growth in a reaction chamber, including three stages: In the first stage, nitrogen is introduced into the quartz tube and argon is introduced into the corundum tube, the source area is heated to 1100-1500° C., the growth area is heated to 1100-1600° C., and the buffer layer is grown on the surface of the substrate for 1-20 minutes. In the second stage, the temperature of the source zone remains unchanged, the growth zone is heated to 1200-1600° C., the flow rates of nitrogen and argon are adjusted, and the temperature is kept for 1-30 minutes to grow a transition layer on the buffer layer; In the third stage, the temperature of the source region remains unchanged, the growth region is heated to 1300-1600°C, the flow rates of nitrogen and argon are adjusted, and the temperature is kept for 0.1-6 hours to grow a high-temperature layer on the transition layer; the temperature is lowered to room temperature to obtain an aluminum nitride single crystal film on a sapphire substrate; During the three-step growth process of preparing single crystal thin films, the pressure in the reaction chamber needs to be kept stable.

2. The method for substrate pretreatment and single crystal film preparation for growing aluminum nitride according to claim 1, characterized in that: The pretreatment forms a depression with a depth of 0.001 to 10 μm and a diameter of 0.001 to 50 μm on the sapphire substrate.

3. The method for substrate pretreatment and single crystal film preparation for growing aluminum nitride according to claim 1, characterized in that: The pre-processing comprises: A metal nitride vapor phase epitaxial growth device is used, and a reaction chamber of the device includes a quartz tube and a corundum tube coaxially sleeved in the quartz tube and located at one end of the quartz tube. Aluminum particles are placed in the corundum tube as a source area, and a sapphire substrate is placed at the other end of the quartz tube as a growth area. The end of the corundum tube close to the substrate is open, and gas can pass through and be evacuated in the quartz tube. Gas can be introduced into the corundum tube alone. The reaction chamber is evacuated to below 1 Pa, and the source area and the growth area are heated to form a temperature gradient. The source area is heated to 1100-1500°C, and the growth area is heated to 1000-1400°C. Argon gas, a carrier gas, is introduced into the corundum tube, and the vapor generated by the heated aluminum particles is carried to the growth area by the carrier gas to pretreat the sapphire substrate. This process lasts for a preset time.

4. The method for substrate pretreatment and single crystal film preparation for growing aluminum nitride according to claim 1, characterized in that: The distance between the substrate and the proximal end of the corundum tube is 5 to 10 cm.

5. The method for substrate pretreatment and single crystal film preparation for growing aluminum nitride according to claim 1, characterized in that: The argon gas flow rate is 1-2000 sccm.

6. The method for substrate pretreatment and single crystal film preparation for growing aluminum nitride according to claim 1, characterized in that: The preset time is 1 to 1800 seconds.

7. The method for substrate pretreatment and single crystal film preparation for growing aluminum nitride according to claim 1, characterized in that: In the first stage, the nitrogen flow rate is 3000-4000 sccm, and the argon flow rate is 30-1000 sccm.

8. The method for substrate pretreatment and single crystal film preparation for growing aluminum nitride according to claim 1, characterized in that: In the second stage, the nitrogen flow rate is 2000-3000 sccm, and the argon flow rate is 40-1600 sccm.

9. The method for substrate pretreatment and single crystal film preparation for growing aluminum nitride according to claim 1, characterized in that: In the third stage, the nitrogen flow rate is 1000-2000 sccm, and the argon flow rate is 100-3000 sccm.

10. The method for substrate pretreatment and single crystal film preparation for growing aluminum nitride according to claim 1, characterized in that: The pressure in the reaction chamber during the three-step growth process is 100-20000 Pa.

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