Lateral merging epitaxial growth method of low dislocation density GaN film and application

Abstract

The invention discloses a lateral merging epitaxial growth method of a low-dislocation-density GaN film and application of the lateral merging epitaxial growth method. The lateral merging epitaxial growth method comprises the steps that a growth substrate is provided, the surface material is a GaN-doped material, and the doping element comprises Si; carrying out nitriding treatment to enable the dislocation to be self-assembled to form a plurality of SiNx mask structures; and epitaxial growth continues to be carried out to form the low dislocation density GaN thin film. According to the method, enrichment of Si elements is formed at the dislocation position of the GaN material, the SiNx mask structure specifically covers and grows on the dislocation surface through nitriding treatment, shielding and covering for dislocation are formed, the dislocation is prevented from extending into a GaN epitaxial layer in the following GaN longitudinal epitaxial growth and lateral merging epitaxial growth processes, and the yield of the GaN material is improved. Therefore, the dislocation density in the GaN epitaxial layer is greatly reduced, a patterning mask and a corresponding patterning etching process are not needed, the complexity and the cost are relatively low, and the method is suitable for large-scale production and application.

Description

Technical Field

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

[0002] Gallium nitride (GaN), as a wide bandgap semiconductor material, is widely used in 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 performance requirements for power devices and high-frequency electronic devices, how to prepare high-quality and low-defect density GaN materials has become one of the research hotspots.

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

[0004] In order to avoid the impact of a large number of dislocations, common GaN lateral epitaxy methods to reduce dislocations include the following: Selective Area Epitaxy Selective Area Growth (SAG) is a commonly used GaN lateral epitaxy technology. In this method, a layer of mask material (such as SiO2 or SiN x ), and then define specific opening areas on the mask layer through photolithography. GaN crystals are epitaxially grown in 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, thereby 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 is obtained.

[0005] Multi-step Lateral Epitaxy 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 performed to generate the initial epitaxial layer, and then a mask layer is deposited on it and the growth area is redefined for the second step of epitaxy. This multi-step growth method can further reduce the dislocation density and improve the crystal quality of the crystal.

[0006] Semi-polar or non-polar epitaxial technology Since the polarity of GaN materials affects the generation and propagation of dislocations, semi-polar or non-polar lateral epitaxy technology has also been introduced in the prior art. By changing the growth direction of GaN materials (for example, by epitaxy on different crystal planes), the formation of dislocations can be further reduced. This technology can significantly improve the performance of devices in certain specific applications, such as high-power RF devices.

[0007] ELO technology (Lateral Epitaxial Overgrowth, ELO) ELO technology is one of the most mature GaN lateral epitaxy technologies. In ELO technology, an initial GaN epitaxial layer is first grown on a foreign substrate (such as sapphire), and a mask material (such as SiO2 or SiN) is deposited on it. x ), and then the opening areas are defined by photolithography, and GaN begins to grow in these opening areas and expands laterally. Under the mask coverage area, dislocations cannot continue to propagate, thereby significantly reducing the defect density. Finally, through multi-step growth and optimized processes, a large area of ​​low-defect GaN epitaxial layer can be obtained.

[0008] At present, GaN lateral epitaxy (LEO) technology is widely used to reduce the dislocation density in GaN materials and improve crystal quality. In epitaxial growth, this technology limits the growth of GaN to a specific area through a mask layer, and then allows the crystal to grow from the side of these limited areas, thereby reducing the dislocation density and obtaining high-quality GaN crystals.

[0009] Although the above technologies have made significant progress in improving the quality of GaN epilayers and reducing dislocation density, there are still some limitations and challenges: Difficulty in further reducing dislocation density: Although lateral epitaxy can effectively reduce dislocation density, further reduction of dislocation density is still limited in large-area applications. Especially in the application of high-frequency and high-power devices, excessive dislocation density will affect device performance. Mask coverage is random and cannot accurately cover the dislocation position to achieve the purpose of suppressing the upward extension of dislocations.

[0010] Process complexity and cost: Steps such as mask making increase the complexity and cost of the process, limiting the application of this technology in large-scale industrial production. Summary of the invention

[0011] In view of the deficiencies in the prior art, the object of the present invention is to provide a lateral merged epitaxial growth method for a low dislocation density GaN film and its application.

[0012] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes: In a first aspect, the present invention provides a method for lateral merged epitaxial growth of a low dislocation density GaN film, comprising: Providing a growth substrate, wherein the epitaxial surface of the growth substrate is made of a doped GaN material, and the doping element in the doped GaN material includes Si; The epitaxial surface is nitrided to form a plurality of SiN x Mask structure, the SiN x The mask structure covers the dislocation in a targeted manner; 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.

[0013] In a second aspect, the present invention also provides a low dislocation density GaN epitaxial structure obtained by the above-mentioned lateral merged epitaxial growth method, which comprises 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.

[0014] In a third aspect, the present invention also provides the use of the low dislocation density GaN epitaxial structure in the manufacture of power devices, radio frequency devices or optoelectronic devices.

[0015] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention at least include: The lateral merged epitaxial growth method provided by the present invention utilizes Si doping to form Si element enrichment at the dislocation of GaN material, and through appropriate nitridation treatment, SiN x The mask structure specifically covers the surface of the dislocations to form a shield for the dislocations, thereby preventing the dislocations from extending into the GaN epitaxial layer during the subsequent GaN longitudinal epitaxial growth and lateral merged epitaxial growth. This greatly reduces the dislocation density in the GaN epitaxial layer, and at the same time, there is no need for a patterned mask and the corresponding patterned etching process, with low complexity and cost, making it suitable for large-scale production applications.

[0016] 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 them according to the contents of the specification, the following is a description of the preferred embodiments of the present invention in conjunction with detailed drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the state of nitridation treatment in a lateral merged epitaxial growth method provided by a typical implementation case of the present invention; Figure 2 It is a schematic diagram of the state of longitudinal epitaxial growth in the lateral merged epitaxial growth method provided by a typical implementation case of the present invention; Figure 3 It is a schematic diagram of the state of lateral merged epitaxial growth in a lateral merged epitaxial growth method provided by a typical implementation case of the present invention; Figure 4 is an electron microscope photograph of the sample surface after nitridation treatment provided in a typical embodiment of the present invention; Figure 5 This is an electron microscope photograph of the cross-sectional morphology of a sample after nitridation treatment provided in a typical implementation case of the present invention. DETAILED DESCRIPTION

[0018] In view of the deficiencies in the prior art, the inventor of this case has proposed the technical solution of the present invention after long-term research and extensive practice. The technical solution, its implementation process and principle will be further explained as follows.

[0019] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0020] The embodiment of the present invention provides a method for lateral merged epitaxial growth of a low dislocation density GaN film, which comprises the following steps: Providing a growth substrate, wherein the epitaxial surface of the growth substrate is made of a doped GaN material, and the doping element in the doped GaN material includes Si; The epitaxial surface is nitrided to form a plurality of SiN x (wherein the value of x satisfies the chemical valence matching, and the specific value may be affected by the nitridation process conditions and lead to different nitridation degrees, and the present invention has no excessive restrictions on this) mask structure, the SiN x The mask structure covers the dislocation in a targeted manner; 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.

[0021] In the above scheme, in order to solve the randomness problem of mask coverage and avoid the cost problem caused by lithography, coating and other processes involved in mask preparation, a self-assembly mask design was invented. First, the implementation method of this mask can accurately cover the dislocation position. Secondly, it is implemented in the MOCVD epitaxial process and does not require additional process steps and equipment.

[0022] The overall technical idea of ​​the above solution is: Figure 1 As shown in the figure, first, NH3 nitridation treatment is performed on the Si-doped GaN / sapphire template or the pure GaN substrate using MOCVD equipment. Because Si as an impurity is usually enriched at dislocations, the Si concentration at the dislocations may be 1 to 2 orders of magnitude higher than the average doping concentration. During the nitridation process, SiN is preferentially formed at the dislocations on the GaN surface. x The mask enables the self-assembled mask to effectively cover the dislocations.

[0023] Based on the above targeted coverage, dislocations are effectively shielded and non-dislocation regions are retained as the basis for epitaxial growth, thereby achieving epitaxial growth with low dislocation density. The process of epitaxial growth can be seen in Figure 2 and Figure 3 shown.

[0024] As for 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 .

[0025] In some embodiments, at the dislocation, the local doping concentration of the Si element is 1-2 orders of magnitude higher than the average doping concentration.

[0026] In some embodiments, the growth substrate is a pure GaN substrate, or a foreign substrate with a GaN layer formed on the surface.

[0027] In some embodiments, the nitridation treatment is performed at a temperature of 750-850° C. and for a time of 20-30 min.

[0028] In some embodiments, the nitrogen source for the nitridation treatment includes NH 3 .

[0029] In some embodiments, the flow rate of the nitrogen source for the nitridation treatment is 14 to 20 L / min.

[0030] In some embodiments, the pressure of the nitridation treatment is 100-500 mbar.

[0031] Regarding the growth of the epitaxial layer, in some embodiments, 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.

[0032] In some embodiments, 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.

[0033] Of course, the specific method of GaN epitaxial growth is not limited to the specific conditions of the above examples. The growth of GaN epitaxial layer can be realized by using other existing technical solutions or different process conditions designed and developed by the present invention and the targeted dislocation covering SiN x All implementations of using a mask to achieve low dislocation epitaxial growth are within the feasible scope of the present invention.

[0034] The second aspect of the embodiment of the present invention further provides a low dislocation density GaN epitaxial structure obtained by the lateral merged epitaxial growth method provided in any of the above embodiments, which comprises a growth substrate, a SiN epitaxial substrate, and a GaN epitaxial substrate arranged in sequence along a specified direction. x 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 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.

[0035] The embodiments of the present invention also provide the use of the low dislocation density GaN epitaxial structure in manufacturing power devices, radio frequency devices or optoelectronic devices.

[0036] The technical solution of the present invention is further described in detail below through several embodiments and 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.

[0037] Example 1 This embodiment illustrates a growth process of a GaN epitaxial layer, which is specifically as follows: The Si-doped template is grown by itself, and the growth conditions are as follows: In the experiment of epitaxial growth of Si-doped GaN template on sapphire substrate by MOCVD, a c-plane (0001) single crystal sapphire substrate is first selected, and a strict cleaning step is performed, including ultrasonic cleaning of acetone and isopropanol for 5 minutes each, rinsing with deionized water, 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, high-purity nitrogen and hydrogen are used as carrier gases, ammonia (NH3), trimethylgallium (TMGa), triethylaluminum (TEAl) and silane (SiH4) are introduced as reaction gases, and 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, which lasts for 3-5 minutes to optimize the interface state.

[0038] 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 to 20-40 μmol / min, and the growth is continued 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 to 100-150 μmol / min, and the growth time is 60-120 minutes. At 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.

[0039] The Si-doped GaN / sapphire template obtained by the above method was subjected to NH3 nitridation treatment using MOCVD equipment (NH3 flow rate was 17 SLM, nitridation time was 25 min, temperature was 800 °C). Because impurities are enriched at dislocations, the Si concentration at dislocations may be 1 to 2 orders of magnitude higher than the doping concentration. During the nitridation process, SiN is preferentially formed at the dislocations on the GaN surface. x The mask self-assembled can effectively cover the dislocations.

[0040] Using NH3 as the Group V nitrogen source and TMGa as the Group III Ga source, nitrogen-rich growth was achieved when the V / III ratio was set to 4000, the growth temperature was 900°C, and the gas chamber pressure was 600Torr to achieve nucleation and longitudinal growth.

[0041] NH3 is used as the Group V nitrogen source and TMGa is used as the Group III Ga source. When the V / III ratio is 2500, the growth temperature is increased to 1100°C and the gas chamber pressure is 200 torr to grow the film laterally on the islands in the window area. The film thickness is controlled by controlling the length of the growth time.

[0042] Through the above nitriding conditions, such as Figure 4 As shown, the surface of the sample after nitridation was tested by SEM, and irregularly arranged nanopatterns were found on the surface. The surface of the sample was extensively etched by ICP etching technology (Cl2 and BCl3 flow rates were 10 and 20 sccm, respectively, usually only GaN was etched). The cross section after etching is shown in Figure 5 As shown, it shows that the nano-pattern formed by surface nitridation is SiN x It plays the role of a mask, which plays a great role in blocking dislocations from climbing and reducing the dislocation density of the epitaxial layer in subsequent epitaxy.

[0043] Comparative Example 1 This comparative example is substantially the same as Example 1, except that no nitridation treatment is performed, and thus no SiN x Mask.

[0044] Comparative Example 2 This comparative example uses the ELO technology to carry out GaN lateral merged epitaxial growth, and the specific process is as follows: In the masked lateral epitaxy (LEO) process, the GaN / sapphire template is first selected and subjected to strict surface cleaning treatment. It is ultrasonically cleaned with acetone and isopropanol, rinsed with deionized water, and dried in a nitrogen environment. A 0.5-2 micron SiN layer is deposited using PECVD. x Or SiO2, through mask exposure and development to form a periodic mask stripe pattern, the periodic spacing is usually 1-2 microns, to block the epitaxial growth underneath.

[0045] 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 area. Then the substrate is placed in the MOCVD device and the GaN epitaxial layer is grown in an ammonia and trimethylgallium (TMGa) environment. The vertical growth in the initial stage is constrained by the mask pattern and gradually transitions to lateral growth to cover the mask area and achieve a high-quality lateral epitaxial layer. The conditions and parameters during the epitaxial growth process are consistent with those in Example 1.

[0046] By testing the dislocation density of the samples obtained in the above-mentioned Example 1 and Comparative Examples 1-2 through XRD, it was found that the dislocation density of Example 1 was the lowest, and the dislocation density of Comparative Example 1 was the highest, which was about one order of magnitude higher than the dislocation density of Example 1. The dislocation density of Comparative Example 2 was approximately near the middle value of the dislocation density of Example 1 and Comparative Example 1.

[0047] Example 2 This embodiment is substantially the same as Embodiment 1, and the main difference is that: By replacing the growth template with a pure GaN substrate, a low dislocation density GaN epitaxial layer with a dislocation density comparable to that of Example 1 can still be obtained.

[0048] Example 3 This embodiment is substantially the same as Embodiment 1, and the main difference is that: Adjust the doping concentration of Si in the substrate to 5×10 18 , 1×10 19 , 5×10 19 , 2×10 20 , 5×10 21 , 1×10 22 , 2×10 22 .

[0049] Found in 10 19 -10 22 In the doping concentration range of 5×10 21 , which will lead to a higher Si concentration in the non-dislocation area, forming some mask coverage in the non-dislocation area, affecting the growth rate of the GaN epitaxial layer; when the doping concentration is lower than 1×10 19 When the dislocations are not effectively shielded, the dislocation density of the GaN epitaxial layer increases significantly.

[0050] Example 4 This embodiment is substantially the same as Embodiment 1, and the main difference is that: Adjust the process conditions during nitriding treatment: First, a temperature adjustment experiment was carried out, and the temperature was adjusted to 700, 750, 800, 850, 900, and 950°C. Finally, it was found that the suitable process window was 750-850°C.

[0051] Then, the pressure adjustment experiment was carried out, and the pressure was adjusted to 50, 100, 200, 500, and 700 mbar. Finally, it was found that the pressure process window was 100-500 mbar. Under high pressure environment, the decomposition efficiency of ammonia (NH3) was reduced, resulting in a relatively high concentration of NH3 in the growth atmosphere, which may produce excessive nitrides and affect the crystal quality of GaN crystals. Too low pressure will cause ammonia to decompose too quickly, resulting in insufficient nitrogen source, which will cause an increase in nitrogen vacancy defects in GaN and affect the crystal quality of the epitaxial layer.

[0052] The optimal window of nitridation time was 20-30 minutes. Excessive nitridation will affect the subsequent growth mode of GaN, causing it to change from layered growth (2D mode) to island 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, causing the crystal quality to decline, resulting in more dislocations and other structural defects, and failing to form SiN. x Mask.

[0053] Based on the above embodiments and comparative examples, it can be clearly seen that the lateral merged epitaxial growth method provided in the embodiment of the present invention utilizes Si doping to form Si element enrichment at the dislocation of the GaN material, and through appropriate nitridation treatment, SiN x The mask structure specifically covers the surface of the dislocations to form a shield for the dislocations, thereby preventing the dislocations from extending into the GaN epitaxial layer during the subsequent GaN longitudinal epitaxial growth and lateral merged epitaxial growth. This greatly reduces the dislocation density in the GaN epitaxial layer, and at the same time, there is no need for a patterned mask and the corresponding patterned etching process, with low complexity and cost, making it suitable for large-scale production applications.

[0054] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in 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: Providing a growth substrate, wherein the epitaxial surface of the growth substrate is made of a doped GaN material, and the doping element in the doped GaN material includes Si; The epitaxial surface is nitrided to form a plurality of SiN x Mask structure, the SiN x The mask structure covers the dislocation in a targeted manner; 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 lateral merged epitaxial growth method according to claim 1, characterized in that: The average doping concentration of Si element in the doped GaN material is 10 19 -10 21 / cm 3 .

3. The lateral merged epitaxial growth method according to claim 2, characterized in that: At the dislocation, the local doping concentration of the Si element is 1-2 orders of magnitude higher than the average doping concentration.

4. The lateral merged epitaxial growth method 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.

5. The lateral merged epitaxial growth method according to claim 1, characterized in that: The temperature of the nitriding treatment is 750-850°C and the time is 20-30 minutes; And / or, the nitrogen source for the nitridation treatment includes NH3.

6. The lateral merged epitaxial growth method according to claim 1, characterized in that: The flow rate of the nitrogen source for the nitridation treatment is 14-20 L / min; And / or, the pressure of the nitriding treatment is 100-500 mbar.

7. The lateral merged epitaxial growth method 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.

8. The lateral merged epitaxial growth method 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.

9. The low dislocation density GaN epitaxial structure obtained by the lateral merged epitaxial growth method according to any one of claims 1 to 8, 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.

10. Use of the low dislocation density GaN epitaxial structure according to claim 9 in manufacturing power devices, radio frequency devices or optoelectronic devices.

Images