Lateral Merging Epitaxial Growth Method and Application of GaN Thin Films with Low Dislocation Density

Abstract

The present invention discloses a lateral merging epitaxial growth method and application of a GaN thin film with a low dislocation density. The lateral merging epitaxial growth method includes: providing a growth substrate with a surface material being a doped GaN material, and the doping element including Si; performing a nitridation treatment to self-assemble a plurality of SiN x mask structures at dislocation sites; and continuing with epitaxial growth to form a GaN thin film with a low dislocation density. In the present invention, an enrichment of Si elements is formed at the dislocation sites of the GaN material, and through the nitridation treatment, the SiN x mask structures are specifically covered on the surfaces of the dislocations during growth, forming a shielding and covering of the dislocations, so as to avoid the extension of dislocations into the GaN epitaxial layer during the subsequent GaN vertical epitaxial growth and lateral merging epitaxial growth processes. Thereby, the dislocation density in the GaN epitaxial layer is greatly reduced. At the same time, there is no need for a patterned mask and the corresponding patterned etching process, and the complexity and cost are both relatively low, which is suitable for large-scale production applications.

Description

Technical Field

[0001] The present invention relates to the technical field of epitaxial growth of semiconductor materials, and particularly to a lateral merging epitaxial growth method and application of a GaN thin film with a low dislocation density. Background Art

[0002] Gallium nitride (GaN), as a wide-bandgap semiconductor material, is widely used in the fields of high-power devices, radio frequency devices, and optoelectronic devices due to its advantages such as high breakdown field strength, high electron mobility, and high temperature resistance. With the improvement of the performance requirements of power devices and high-frequency electronic devices, how to fabricate high-quality GaN materials with a low defect density has become one of the research hotspots.

[0003] In the traditional epitaxial growth of GaN, hetero-substrates such as sapphire, SiC, or Si are usually used. Due to the lattice mismatch and the difference in thermal expansion coefficient between the substrate and the GaN crystal, a large number of dislocation defects will be generated during the epitaxial process. These defects will greatly affect the device performance and reduce the breakdown voltage, on-resistance, electron mobility, etc. of the material.

[0004] To avoid the influence of a large number of dislocations, common GaN lateral epitaxial methods for reducing dislocations include the following several:

[0005] Selective Area Epitaxy

[0006] Selective Area Growth (SAG) is a commonly used GaN lateral epitaxial technique. In this method, first, a mask material (such as SiO2 or SiN x ) is deposited on the substrate surface, and then specific opening areas are defined on the mask layer through photolithography technology. GaN crystals are epitaxially grown within these opening areas, and then the GaN crystals grow laterally from the opening areas. Due to the existence of the mask area, the defects cannot continue to extend under the mask, thus reducing the dislocation density. The advantage of this method is that the epitaxial growth conditions can be optimized by precisely controlling the opening size and distribution, and finally a high-quality GaN epitaxial layer can be obtained.

[0007] Multi-step Lateral Epitaxy

[0008] The multi-step lateral epitaxy method further optimizes the quality of GaN by growing in multiple steps during the epitaxial growth process. Usually, the first step of growth is carried out to generate an initial epitaxial layer, then a mask layer is deposited on it and the growth area is redefined, and the second-step epitaxy is carried out. This multi-step growth method can further reduce the dislocation density and improve the crystal quality.

[0009] Semi-polar or Non-polar Epitaxial Technology

[0010] Since the polarity of GaN materials can affect the generation and propagation of dislocations, semi-polar or non-polar lateral epitaxial techniques have been introduced in the prior art. By changing the growth direction of GaN materials (e.g., through epitaxy on different crystal planes), the formation of dislocations can be further reduced. In certain specific applications, such as high-power RF devices, this technique can significantly improve the performance of the devices.

[0011] ELO technology (Lateral Epitaxial Overgrowth, ELO)

[0012] ELO technology is one of the most mature GaN lateral epitaxial techniques. In ELO technology, first, an initial GaN epitaxial layer is grown on a hetero-substrate (such as sapphire), and a mask material (such as SiO2 or SiN x ) is deposited on it. Then, the opening areas are defined through photolithography technology, and GaN starts to grow and laterally expand within these opening areas. Under the mask-covered areas, dislocations cannot continue to propagate, thus significantly reducing the defect density. Finally, through multi-step growth and optimized processes, a large-area GaN epitaxial layer with low defects can be obtained.

[0013] Currently, the GaN lateral epitaxial (Lateral Epitaxial Overgrowth, LEO) technology is widely used to reduce the dislocation density in GaN materials and improve the crystal quality. In this epitaxial growth technology, the growth of GaN is limited to specific areas through a mask layer, and then the crystal grows by lateral expansion from the sides of these limited areas, thereby reducing the dislocation density and obtaining high-quality GaN crystals.

[0014] Although the above technologies have made significant progress in improving the quality of GaN epitaxial layers and reducing the dislocation density, there are still some limitations and challenges:

[0015] Difficulty in further reducing the dislocation density: Although lateral epitaxy can effectively reduce the dislocation density, in large-area applications, the further reduction of the dislocation density is still limited. Especially in the applications of high-frequency and high-power devices, too high a dislocation density will affect the device performance. The mask coverage is random and cannot accurately cover the dislocation positions to achieve the purpose of suppressing the upward extension of dislocations.

[0016] Process complexity and cost: Steps such as mask fabrication increase the process complexity and cost, restricting the application of this technology in large-scale industrial production. Summary of the Invention

[0017] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a lateral merging epitaxial growth method and application of a GaN thin film with a low dislocation density.

[0018] To achieve the foregoing invention object, the technical solutions adopted by the present invention include:

[0019] In a first aspect, the present invention provides a lateral merging epitaxial growth method for a low dislocation density GaN thin film, which includes:

[0020] Providing a growth substrate, wherein the material of the epitaxial surface of the growth substrate is a doped GaN material, and the doping element in the doped GaN material includes Si;

[0021] Performing a nitridation treatment on the epitaxial surface so that multiple SiN x mask structures are self-assembled at the dislocations of the epitaxial surface, and the SiN x mask structures specifically cover the dislocations;

[0022] After performing the nitridation treatment, continuously perform vertical epitaxial growth and lateral merging epitaxial growth of GaN material on the epitaxial surface to form the low dislocation density GaN thin film.

[0023] In a second aspect, the present invention further provides a low dislocation density GaN epitaxial structure prepared by the above lateral merging epitaxial growth method, which includes a growth substrate, SiN x mask structure, and low dislocation density GaN thin film arranged in sequence along a specified direction;

[0024] The material of the epitaxial surface of the growth substrate is a doped GaN material, the doping element in the doped GaN material includes Si and there are dislocations in the growth substrate, and the SiN x mask structure specifically covers the dislocations; the low dislocation density GaN thin film is formed by epitaxial growth based on the doped GaN material exposed between adjacent SiN x mask structures.

[0025] In a third aspect, the present invention further provides an application of the above low dislocation density GaN epitaxial structure in manufacturing power devices, radio frequency devices or optoelectronic devices.

[0026] Based on the above technical solutions, compared with the prior art, the beneficial effects of the present invention at least include:

[0027] The lateral merging epitaxial growth method provided by the present invention utilizes the doping of Si to form an enrichment of Si elements at the dislocations of the GaN material. Through appropriate nitridation treatment, SiN xThe mask structure is specifically covered and grown on the dislocation surface to form a shielding for the dislocations, so as to avoid the extension of dislocations into the GaN epitaxial layer during the subsequent GaN vertical epitaxial growth and lateral epitaxial growth by merging. Thereby, the dislocation density in the GaN epitaxial layer is greatly reduced. At the same time, there is no need for a patterned mask and the corresponding patterned etching process, with lower complexity and cost, and is suitable for large-scale production applications.

[0028] The above description is only an overview of the technical solution of the present invention. In order to enable those skilled in the art to more clearly understand the technical means of the present application and implement it in accordance with the content of the specification, the following is a detailed description with reference to the preferred embodiments of the present invention and the accompanying drawings. Brief Description of the Drawings

[0029] Figure 1 It is a schematic diagram of the state during nitridation treatment in the lateral epitaxial growth method by merging provided by a typical embodiment of the present invention;

[0030] Figure 2 It is a schematic diagram of the state during vertical epitaxial growth in the lateral epitaxial growth method by merging provided by a typical embodiment of the present invention;

[0031] Figure 3 It is a schematic diagram of the state during lateral epitaxial growth by merging in the lateral epitaxial growth method by merging provided by a typical embodiment of the present invention;

[0032] Figure 4 It is a scanning electron microscope (SEM) photograph of the surface of a sample after nitridation treatment provided by a typical embodiment of the present invention;

[0033] Figure 5 It is a cross-sectional SEM photograph of a sample after nitridation treatment provided by a typical embodiment of the present invention. Detailed Embodiments

[0034] In view of the deficiencies in the prior art, the inventors of this case have proposed the technical solution of the present invention through long-term research and a large number of practices. The following will further explain the technical solution, its implementation process, principles, etc.

[0035] In the following description, many specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited by the specific embodiments disclosed below.

[0036] The embodiment of the present invention provides a method for lateral epitaxial growth by merging of a GaN thin film with a low dislocation density, which includes the following steps:

[0037] Provide a growth substrate, wherein the material of the epitaxial surface of the growth substrate is doped GaN material, and the doping element in the doped GaN material includes Si;

[0038] Perform nitridation treatment on the epitaxial surface to self-assemble multiple SiN x (where the value of x satisfies valence matching, and the specific value may vary due to different nitridation degrees caused by nitridation process conditions. The present invention does not have excessive limitations on this) mask structures at the dislocations on the epitaxial surface. The SiN x mask structures specifically cover the dislocations;

[0039] After performing the nitridation treatment, continue to perform longitudinal epitaxial growth and lateral epitaxial growth of GaN material on the epitaxial surface in sequence to form the low dislocation density GaN thin film.

[0040] In the above solution, in order to solve the randomness problem of mask coverage and avoid the cost problems caused by processes such as lithography and coating involved in mask preparation, a self-assembled mask design is invented. Firstly, the implementation method of this mask can accurately cover the dislocation positions. Secondly, it is realized during the MOCVD epitaxial process and does not require additional process steps and equipment.

[0041] The overall technical idea of the above solution is: as Figure 1 shown, firstly, perform NH3 nitridation treatment on the Si-doped GaN / sapphire template or pure GaN substrate using MOCVD equipment. Since Si as an impurity usually enriches at dislocations, the Si concentration at dislocations may be 1-2 orders of magnitude higher than the average doping concentration. During nitridation, SiN x masks will be preferentially formed at the dislocations on the GaN surface, enabling the self-assembled masks to effectively cover the dislocations.

[0042] Based on the above targeted coverage, the dislocations are effectively shielded and the non-dislocation regions are reserved as the basis for epitaxial growth, thereby realizing epitaxial growth with a low dislocation density. The process of epitaxial growth can be referred to Figure 2 and Figure 3 shown.

[0043] Regarding some specific implementation details, in some embodiments, the average doping concentration of Si element in the doped GaN material is 10 19 -10 21 / cm 3 .

[0044] In some embodiments, at the dislocations, the local doping concentration of Si element is higher than 1-2 orders of magnitude of the average doping concentration.

[0045] In some embodiments, the growth substrate is a pure GaN substrate or a hetero-substrate with a GaN layer formed on its surface.

[0046] In some embodiments, the temperature of the nitridation treatment is 750 - 850 °C, and the time is 20 - 30 min.

[0047] In some embodiments, the nitrogen source for the nitridation treatment includes NH3.

[0048] In some embodiments, the flow rate of the nitrogen source for the nitridation treatment is 14 - 20 L / min.

[0049] In some embodiments, the pressure of the nitridation treatment is 100 - 500 mbar.

[0050] Regarding the growth of the epitaxial layer, in some embodiments, the V / III ratio of the vertical epitaxial growth is above 3000, the growth temperature is below 1000 °C, and the atmospheric pressure is 300 - 500 torr.

[0051] In some embodiments, the V / III ratio of the lateral coalescence epitaxial growth is 2000 - 3000, the growth temperature is above 1000 °C, and the atmospheric pressure is 100 - 300 torr.

[0052] Of course, the specific GaN epitaxial growth method is not limited to the specific conditions of the above examples. Implementations that use existing other technical solutions or different process conditions designed and developed independently to achieve the growth of the GaN epitaxial layer and utilize the SiN x mask provided by the present invention to achieve low-dislocation epitaxial growth are all within the feasible scope of the present invention.

[0053] The second aspect of the embodiments of the present invention also provides a low-dislocation density GaN epitaxial structure prepared by the lateral coalescence epitaxial growth method provided in any of the above embodiments, which includes a growth substrate, SiN x mask structure, and a low-dislocation density GaN thin film arranged in sequence along a specified direction; the material of the epitaxial surface of the growth substrate is doped GaN material, the doping element in the doped GaN material includes Si, and there are dislocations in the growth substrate. The SiN x mask structure specifically covers the dislocations; the low-dislocation density GaN thin film is formed by epitaxial growth based on the doped GaN material exposed between adjacent SiN x mask structures.

[0054] The embodiments of the present invention also provide the application of the above low-dislocation density GaN epitaxial structure in manufacturing power devices, radio frequency devices, or optoelectronic devices.

[0055] The technical solutions of the present invention will be further described in detail below through several embodiments in conjunction with the accompanying drawings. However, the selected embodiments are only used to illustrate the present invention and do not limit the scope of the present invention.

[0056] Example 1

[0057] This example illustrates the growth process of a GaN epitaxial layer, which is specifically as follows:

[0058] The Si-doped template is grown by itself. The growth conditions are as follows: In the experiment of epitaxially growing a Si-doped GaN template on a sapphire substrate using MOCVD, first, a c-plane (0001) single-crystal sapphire substrate is selected. After strict cleaning steps, including ultrasonic cleaning with acetone and isopropyl alcohol for 5 minutes each, rinsing with deionized water and then drying with high-purity nitrogen, and sintering at 900 °C to remove surface contaminants and improve interface quality. The pressure in the reaction chamber is maintained at 100 - 300 mbar. Using high-purity nitrogen and hydrogen as carrier gases, ammonia (NH3), trimethylgallium (TMGa), triethylaluminum (TEAl), and silane (SiH4) are introduced as reaction gases. The substrate rotation speed is controlled at 300 - 500 rpm. At the beginning of growth, the substrate temperature is raised to 1050 °C for surface nitridation treatment, lasting for 3 - 5 minutes to optimize the interface state.

[0059] Subsequently, a 20 - 30 nm thick low-temperature GaN buffer layer is deposited at 500 - 550 °C. The NH3 flow rate is maintained at 5 slm, the TMGa flow rate is set at 20 - 40 μmol / min, and the growth continues for 5 - 10 minutes to improve the stress state of the crystal structure. The growth of the high-temperature GaN epitaxial layer is carried out at 1050 - 1100 °C, the layer thickness is controlled at 2 - 3 µm, the NH3 flow rate is increased to 10 - 15 slm, the TMGa flow rate is set at 100 - 150 μmol / min, and the growth time is 60 - 120 minutes. In the high-temperature stage, Si doping is achieved by introducing silane (SiH4), and the flow rate is controlled at 0.5 - 1.0 μmol / min to ensure appropriate doping concentration and electrical properties.

[0060] On the Si-doped GaN / sapphire template obtained by the above method, NH3 nitridation treatment is carried out using an MOCVD device (NH3 flow rate is 17 SLM, nitridation time is 25 min, temperature is 800 °C). Since impurities will accumulate at dislocations, the Si concentration at dislocations may be 1 - 2 orders of magnitude higher than the doping concentration, and SiN will preferentially form at the dislocations on the GaN surface during nitridation. x The mask formed by self-assembly of the mask can effectively cover the dislocations.

[0061] Using NH3 as the group-V nitrogen source and TMGa as the group-III Ga source, nitrogen-rich growth is carried out at a V / III ratio of 4000, the growth temperature is 900 °C, and the gas chamber pressure is 600 Torr to achieve nucleation and longitudinal growth.

[0062] With NH3 as the group-V nitrogen source and TMGa as the group-III Ga source, at a V / III ratio of 2500, the growth temperature is increased to 1100 °C, and the gas chamber pressure is 200 Torr. Lateral film growth occurs on the islands in the window area, and the film thickness is controlled by controlling the growth time.

[0063] Under the above nitridation conditions, as Figure 4 shown, the surface of the nitrided sample is tested by SEM, and it is found that irregularly arranged nano-patterns are generated on the surface. The surface of the sample is etched by ICP etching technology (the flow rates of Cl2 and BCl3 are 10 and 20 sccm respectively, and usually only GaN is etched), and the cross-section after etching is as Figure 5 shown, indicating that the nano-patterns formed by surface nitridation are SiN x which plays a role as a mask and is of great significance for subsequent epitaxial blocking of dislocation climb and reducing the dislocation density of the epitaxial layer.

[0064] Comparative Example 1

[0065] This comparative example is generally the same as Example 1, and the main difference is that no nitridation treatment is carried out, so no SiN x mask is formed.

[0066] Comparative Example 2

[0067] In this comparative example, the ELO technology is used for lateral epitaxial growth of GaN. The specific process is as follows:

[0068] In the mask lateral epitaxial overgrowth (LEO) process, first, a GaN / sapphire template is selected and strictly surface-cleaned. After ultrasonic cleaning with acetone and isopropyl alcohol respectively, it is rinsed with deionized water and dried in a nitrogen environment. A 0.5 - 2 μm thick SiN x or SiO2 is deposited by PECVD, and a periodic mask strip pattern is formed through mask exposure and development. The period spacing is usually 1 - 2 μm to block the epitaxial growth below it.

[0069] After the mask pattern is formed, the photoresist in the non-mask area is removed by plasma etching to ensure the cleanliness of the lateral epitaxial region. Then, the substrate is placed into the MOCVD equipment, and the growth of the GaN epitaxial layer is started in an environment of ammonia gas and trimethylgallium (TMGa). The vertical growth in the initial stage is restricted by the mask pattern and gradually transitions to lateral growth to cover the mask area, achieving a high-quality lateral epitaxial layer. The condition parameters during the epitaxial growth process are the same as those in Example 1.

[0070] By testing the dislocation density of the samples obtained in Example 1 and Comparative Examples 1-2 through XRD, it is found that the dislocation density of Example 1 is the lowest, the dislocation density of Comparative Example 1 is the highest, which is about one order of magnitude higher than that of Example 1, and the dislocation density of Comparative Example 2 is approximately near the intermediate value between the dislocation densities of Example 1 and Comparative Example 1.

[0071] Example 2

[0072] This example is generally the same as Example 1, and the main difference lies in:

[0073] By replacing the growth template with a pure GaN substrate, a GaN epitaxial layer with a low dislocation density comparable to that of Example 1 can still be obtained.

[0074] Example 3

[0075] This example is generally the same as Example 1, and the main difference lies in:

[0076] Adjust the doping concentration of Si in the substrate, which is adjusted to 5×10 18 、1×10 19 、5×10 19 、2×10 20 、5×10 21 、1×10 22 、2×10 22 .

[0077] It is found that within the doping concentration range of 10 19 -10 22 , GaN epitaxial layers with low dislocation density can be obtained; however, when the doping concentration is higher than 5×10 21 , it will cause a relatively high Si concentration in the non-dislocation area, forming some mask coverage in the non-dislocation area, which affects the growth rate of the GaN epitaxial layer; when the doping concentration is lower than 1×10 19 , it cannot play an effective role in dislocation shielding, resulting in a significant increase in the dislocation density of the GaN epitaxial layer.

[0078] Example 4

[0079] This example is generally the same as Example 1, and the main difference lies in:

[0080] Adjust the process conditions during nitridation treatment:

[0081] First, conduct a temperature adjustment experiment. Adjust the temperature to 700, 750, 800, 850, 900, 950 °C. Finally, it is found that the appropriate process window is 750 - 850 °C.

[0082] Then, conduct a pressure adjustment experiment. Adjust the pressure to 50, 100, 200, 500, 700 mbar. Finally, it is found that the pressure process window is 100 - 500 mbar. In a high - pressure environment, the decomposition efficiency of ammonia (NH3) decreases, resulting in a relatively higher concentration of NH3 in the growth atmosphere, which may produce excessive nitrides and affect the crystallization quality of GaN crystals. Too low a pressure will cause the ammonia to decompose too quickly, resulting in insufficient nitrogen source, which will increase the nitrogen vacancy defects in GaN and affect the crystal quality of the epitaxial layer.

[0083] And a nitridation time adjustment experiment, 15, 20, 25, 30, 35 min. Finally, it is found that the optimal window for nitridation time is 20 - 30 min. Excessive nitridation will affect the subsequent growth mode of GaN, causing it to change from layer - by - layer growth (2D mode) to island - like growth (3D mode), resulting in an increase in the dislocation density of the epitaxial layer. Insufficient nitridation will affect the initial growth mode of the GaN epitaxial layer, reducing the crystal quality, resulting in more dislocations and other structural defects, and at the same time, it is impossible to form a SiN x mask.

[0084] Based on the above - mentioned embodiments and comparative examples, it can be clearly seen that the lateral - merging epitaxial growth method provided by the embodiments of the present invention uses the doping of Si to form an enrichment of Si elements at the dislocations of the GaN material. Through appropriate nitridation treatment, the SiN x mask structure is specifically covered and grown on the surface of the dislocations to form a shielding and covering of the dislocations, thereby avoiding the extension of dislocations into the GaN epitaxial layer during the subsequent GaN vertical epitaxial growth and lateral - merging epitaxial growth processes. Thus, the dislocation density in the GaN epitaxial layer is greatly reduced. At the same time, there is no need for a patterned mask and the corresponding patterned etching process, with lower complexity and cost, and it is suitable for large - scale production applications.

[0085] It should be understood that the above - mentioned embodiments are only used to illustrate the technical concept and characteristics of the present invention, and their purpose is to enable those familiar with this technology to understand the content of the present invention and implement it accordingly, and cannot be used to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for lateral merged epitaxial growth of a low dislocation density GaN film, characterized in that: include: A growth substrate is provided, wherein the epitaxial surface of the growth substrate is made of a doped GaN material, the doping element in the doped GaN material includes Si, and the average doping concentration of the Si element in the doped GaN material is 10 19 -10 21 / cm 3 , at the dislocation, the local doping concentration of the Si element is 1-2 orders of magnitude higher than the average doping concentration; The epitaxial surface is nitrided to allow the dislocations on the epitaxial surface to self-assemble into a plurality of SiN x Mask structure, the SiN x The mask structure covers the dislocation in a targeted manner, the temperature of the nitridation treatment is 750-850° C., the pressure is 100-500 mbar, the time is 20-30 min, and the nitrogen source of the nitridation treatment includes NH3; After the nitridation treatment, longitudinal epitaxial growth and lateral combined epitaxial growth of GaN material are sequentially performed on the epitaxial surface to form the low dislocation density GaN film.

2. The method for lateral merged epitaxial growth of a low dislocation density GaN film according to claim 1, characterized in that: The growth substrate is a pure GaN substrate, or a heterogeneous substrate with a GaN layer formed on the surface.

3. The method for lateral merged epitaxial growth of a low dislocation density GaN film according to claim 1, characterized in that: The flow rate of the nitrogen source for the nitridation treatment is 14-20 L / min.

4. The method for lateral merged epitaxial growth of a low dislocation density GaN film according to claim 1, characterized in that: The V / III ratio of the longitudinal epitaxial growth is above 3000, the growth temperature is below 1000° C., and the atmosphere pressure is 300-500 torr.

5. The method for lateral merged epitaxial growth of a low dislocation density GaN film according to claim 1, characterized in that: The V / III ratio of the lateral merged epitaxial growth is 2000-3000, the growth temperature is above 1000° C., and the atmosphere pressure is 100-300 torr.

6. The low dislocation density GaN epitaxial structure obtained by the lateral merging epitaxial growth method of a low dislocation density GaN film according to any one of claims 1 to 5, characterized in that: It includes a growth substrate, a SiN x Mask structure and low dislocation density GaN film; The epitaxial surface of the growth substrate is made of doped GaN material, the doping element in the doped GaN material includes Si, and there are dislocations in the growth substrate. x The mask structure covers the dislocation in a targeted manner; the low dislocation density GaN film is adjacent to the SiN x The doped GaN material exposed between the mask structures is formed by epitaxial growth.

7. Use of the low dislocation density GaN epitaxial structure according to claim 6 in the manufacture of power devices, radio frequency devices or optoelectronic devices.

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