Composite Si / Al buffer layer and preparation method and application thereof
By employing a composite Si/Al buffer layer structure in nitride semiconductor HEMT devices, the defect problem caused by lattice mismatch was solved, thereby improving the reliability and high-frequency characteristics of the devices.
Patent Information
- Application Number
- CN202410598171.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-05-14
- Publication Date
- 2025-11-18
AI Technical Summary
In existing nitride semiconductor HEMT devices, the lattice mismatch between the grown semiconductor material and the substrate leads to a large number of defects, affecting the reliability and high-frequency characteristics of the device.
A composite Si/Al buffer layer structure is adopted. By forming alternating high and low surface energy regions on the substrate surface, and by heat treatment to combine Al and Si atoms with N source to form a composite microstructure of AlN and SiN hybrid, a buffer layer with a high gradient difference is formed, which shields dislocations from extending upward and improves the two-dimensional electron gas density and mobility of the channel layer.
It effectively shields dislocation extension, improves the stress distribution uniformity of the nitride buffer layer, enhances the growth quality of the nitride epitaxial layer, and improves the reliability and high-frequency characteristics of the device.
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Figure CN120977862A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to a composite Si / Al buffer layer, a preparation method and application thereof, and belongs to the technical field of semiconductors. BACKGROUND
[0002] High Electron Mobility Transistor (HEMT) is an important semiconductor device, which has a wide range of applications in wireless communication, radar systems, solar cells and other fields. With the rapid development of mobile communication and radio frequency technology, the demand for high frequency, high power and low noise is becoming higher and higher, and nitride semiconductor HEMT devices have become the focus of research due to their excellent characteristics.
[0003] Nitride semiconductor materials have a large energy gap, high electron mobility and high saturated electron drift speed. In addition, nitride semiconductors also have good thermal stability and radiation resistance, and are suitable for working in high-power and high-temperature environments. Therefore, nitride semiconductor materials are widely used in the preparation of HEMT devices and have a wide application prospect.
[0004] Due to the lattice mismatch between the grown semiconductor material and the substrate, the prepared semiconductor material has many defects. Growing a buffer layer between the substrate and the semiconductor material can alleviate the defect problem in heteroepitaxy to some extent, but there are still a large number of defects (> 10 8 cm -2 ) extending to the channel layer and forming a leakage channel, and heteroepitaxy also affects the switching speed and high-frequency characteristics of the semiconductor device, reducing the reliability of the semiconductor device. These problems limit the application of heteroepitaxy in high electron mobility transistors. SUMMARY
[0005] The main purpose of the present application is to provide a composite Si / Al buffer layer, a preparation method and application thereof, so as to overcome the deficiencies in the prior art.
[0006] In order to achieve the above-mentioned purpose of the application, the technical scheme adopted by the present application comprises:
[0007] The first aspect of the embodiment of the present application provides a preparation method of a composite buffer layer structure, comprising:
[0008] The step of preparing a composite buffer layer structure precursor, the composite buffer layer structure precursor comprising two or more Al layers and one or more Si layers stacked;
[0009] Furthermore, under the condition of at least the presence of an N source, the precursor is subjected to heat treatment, causing partial Al atoms in two or more Al layers to undergo mutual dissolution and diffusion with partial Si atoms in one or more Si layers, and causing the Al atoms and Si atoms in the precursor of the composite buffer layer structure to combine with the N atoms provided by the N source to form AlN and SiN, respectively, thereby forming a composite buffer layer structure, wherein the composite buffer layer structure has a composite microstructure of SiN and AlN intermingled.
[0010] A second aspect of the present invention provides a composite buffer layer structure, comprising: two or more AlN layers and one or more SiN layers stacked together, wherein one of the SiN layers is distributed between two adjacent AlN layers, and a plurality of SiN microstructures are distributed within the AlN layer, wherein the SiN microstructures are integral with the SiN layers adjacent to the AlN layer in which they are located, and a plurality of AlN microstructures are also distributed within the SiN layer, wherein the AlN microstructures are integral with the AlN layers adjacent to the SiN layer in which they are located.
[0011] A third aspect of the present invention provides a composite substrate structure comprising:
[0012] A substrate having a first region and a second region on its surface, wherein the surface energy of the first region is higher than the surface energy of the second region;
[0013] The first AlN layer is distributed in a second region on the surface of the substrate;
[0014] One or more of the composite buffer layer structures are stacked on the first region of the surface of the substrate and the first AlN layer.
[0015] A fourth aspect of this invention provides a method for preparing a composite substrate structure, comprising:
[0016] S1. A substrate having a first region and a second region on its surface is provided, wherein the surface energy of the first region is higher than that of the second region, and Al is deposited on the surface of the substrate under a first temperature and a first pressure to form a first Al layer.
[0017] S2. Under the conditions of first temperature and first pressure, the first Al layer is subjected to a first heat treatment, so that the Al atoms distributed in the first region move to the second region to form a first Al atom layer deposition structure.
[0018] S3. A composite buffer layer structure is formed on the surface of the substrate and the first Al atomic layer deposition structure, specifically including:
[0019] S31. Under the conditions of a second temperature and a second pressure, Al is deposited on the first region of the substrate and the first Al atomic layer deposition structure to form a second Al layer;
[0020] S32. Under the conditions of a third temperature and a third pressure, Si is deposited on the second Al layer to form a Si layer;
[0021] S33. Under the fourth temperature and fourth pressure conditions, Al is deposited on the Si layer to form a third Al layer, thereby obtaining a precursor for a composite buffer layer structure.
[0022] S34. Under the conditions of the fifth temperature and the fifth pressure, and in the presence of an N source, the composite buffer layer structure precursor and the first Al atomic layer deposition structure are subjected to a second heat treatment, at least causing some Al atoms in the second Al layer and the third Al layer to undergo mutual dissolution and diffusion with some Si atoms in the Si layer, and causing the Al atoms and Si atoms in the composite buffer layer structure precursor and the first Al atomic layer deposition structure to combine with the N atoms provided by the N source to form AlN and SiN, respectively, thereby transforming the first Al atomic layer deposition structure into a first AlN layer, and transforming the composite buffer layer structure precursor into a composite buffer layer structure, wherein the composite buffer layer structure has a composite microstructure of SiN and AlN intermingled.
[0023] A fifth aspect of the present invention provides an epitaxial wafer comprising: the composite buffer layer structure or the composite substrate structure.
[0024] In a more specific implementation, the epitaxial wafer is a nitride HEMT epitaxial wafer, which includes the composite buffer layer structure or the composite substrate structure, a gallium nitride buffer layer, a gallium nitride channel layer, an aluminum gallium nitride barrier layer and a gallium nitride capping layer stacked sequentially.
[0025] A sixth aspect of the present invention provides a semiconductor device comprising the aforementioned epitaxial wafer.
[0026] Compared with the prior art, the advantages of the present invention include: The present invention forms a composite microstructure by controlling the diffusion process layer on the substrate surface with high surface energy regions and low surface energy regions through a buffer layer process. On the one hand, by forming a composite buffer layer with highly gradient differences on the substrate with different surface energy regions, the composite microstructure with highly gradient differences can enhance the lateral epitaxial growth of the nitride buffer layer, delay the healing process of the nitride epitaxial layer, thereby shielding the upward extension of dislocations and enabling the dislocations to fully redirect and achieve self-annihilation, thus improving the two-dimensional electron gas density and mobility of the channel layer. On the other hand, under the action of the micro-nano scale composite microstructure, the different stress regions of the nitride buffer layer grown on it are more likely to reach equilibrium through the interaction during the delayed healing process, thereby improving the stress distribution uniformity of the epitaxial wafer and reducing the residual stress in the epitaxial layer, which is applicable to the growth of large-size epitaxial wafers. Attached Figure Description
[0027] Figure 1 This is a schematic diagram of the structure of a nitride HEMT epitaxial wafer provided in a typical embodiment of the present invention;
[0028] Figure 2 This is a partial electron microscope image of a composite Si / Al buffer layer in a nitride HEMT epitaxial wafer provided in a typical embodiment of the present invention;
[0029] Figures 3-12 These are schematic diagrams of the intermediate structure formed during the preparation of a nitride HEMT epitaxial wafer, as provided in a typical embodiment of the present invention. Detailed Implementation
[0030] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate this technical solution, its implementation process, and its principles.
[0031] Explanation Notes: The surface of the substrate has high surface energy regions and low surface energy regions, which are distributed alternately. The size of the high surface energy regions and low surface energy regions is 0.2μm-3μm. It is difficult for atomic aggregation to form on the surface of the high surface energy regions, while it is easy for atomic aggregation to form on the surface of the low surface energy regions.
[0032] The conditions under which a substrate surface has both high surface energy regions and low surface energy regions include:
[0033] a. The substrate surface is a substrate surface, wherein the substrate chamfer angle is >0.5°, or the substrate surface has a periodically distributed pattern structure; or the substrate surface has undergone etching or ion treatment of periodically spaced regions of the surface.
[0034] When the substrate chamfer angle is greater than 0.5°, increasing the substrate chamfer angle can effectively reduce the mesa width, which is beneficial to realize the epitaxial step flow growth mode on the substrate surface, and enables atoms to effectively aggregate at the step position with a smaller migration length.
[0035] When the substrate surface undergoes periodic etching or ion treatment, the high surface energy region and the low surface energy region are periodically distributed on the substrate surface through etching and ion treatment. It is difficult for atomic aggregation to form on the surface of the high surface energy region, while atomic aggregation is formed on the surface of the low surface energy region.
[0036] b. The substrate surface is a heterogeneous composite layer surface disposed on the substrate, wherein the heterogeneous composite layer surface is a surface formed by etching or ion treatment of periodically spaced regions or a surface with a periodic pattern structure.
[0037] When a surface undergoes periodic interval etching or ion treatment, the areas with high and low surface energies are periodically distributed by etching and ion treatment. In the high surface energy areas, it is difficult for atoms to form an aggregated distribution, while in the low surface energy areas, atoms are aggregated.
[0038] When the surface is a periodic pattern structure, the surface energy of the pattern structure surface is different from that of the adjacent patterns. It is difficult for atomic aggregation to form in the high surface energy region, while atomic aggregation is distributed in the low surface energy region.
[0039] The above methods for forming high surface energy regions or low surface energy regions on the substrate surface are known to those skilled in the art, and are not specifically limited or explained here.
[0040] The first aspect of this invention provides a method for preparing a composite buffer layer structure, comprising:
[0041] The step of fabricating a precursor for forming a composite buffer layer structure includes two or more Al layers and one or more Si layers stacked together, wherein one of the Si layers is distributed between two adjacent Al layers;
[0042] Furthermore, under the condition of at least the presence of an N source, the precursor is subjected to heat treatment, causing partial Al atoms in two or more Al layers to undergo mutual dissolution and diffusion with partial Si atoms in one or more Si layers, and causing the Al atoms and Si atoms in the precursor of the composite buffer layer structure to combine with the N atoms provided by the N source to form AlN and SiN, respectively, thereby forming a composite buffer layer structure, wherein the composite buffer layer structure has a composite microstructure of SiN and AlN intermingled.
[0043] Furthermore, the heat treatment temperature is 800℃-1000℃ and the pressure is 1000 torr-500 torr.
[0044] Furthermore, the heat treatment time is 30s-180s.
[0045] Furthermore, the composite microstructure includes multiple AlN microstructures and multiple SiN microstructures.
[0046] Furthermore, the SiN microstructure is formed by Si atoms and N atoms diffusing from the Si layer into the adjacent Al layer and combining with each other, and the AlN microstructure is formed by Al atoms and N atoms diffusing from the Al layer into the adjacent Si layer.
[0047] Furthermore, the thickness of the Si layer is greater than the thickness of the adjacent Al layer. When the composite buffer layer precursor is heat-treated, Si atoms in the Si layer also diffuse to the side surface of the adjacent Al layer opposite to the Si layer.
[0048] In a more specific implementation, the composite buffer layer structure precursor includes a second Al layer, a Si layer and a third Al layer stacked sequentially, wherein the thickness of the second Al layer is 2nm-30nm, the thickness of the Si layer is 5nm-100nm, and the thickness of the third Al layer is 2nm-50nm.
[0049] Furthermore, the SiN microstructure is formed by Si atoms and N atoms diffusing from the Si layer into the second Al layer or the third Al layer, and the AlN microstructure is formed by Al atoms and N atoms diffusing from the second Al layer and / or the third Al layer into the Si layer.
[0050] A second aspect of the present invention provides a composite buffer layer structure, comprising: two or more AlN layers and one or more SiN layers stacked together, wherein one of the SiN layers is distributed between two adjacent AlN layers, and a plurality of SiN microstructures are distributed within the AlN layer, wherein the SiN microstructures are integral with the SiN layers adjacent to the AlN layer in which they are located, and a plurality of AlN microstructures are also distributed within the SiN layer, wherein the AlN microstructures are integral with the AlN layers adjacent to the SiN layer in which they are located.
[0051] Furthermore, the AlN microstructure is completely distributed inside the SiN layer.
[0052] Furthermore, a portion of the SiN microstructure is exposed from the surface of the AlN layer opposite to the SiN layer, and the surface of the exposed portion of the SiN microstructure is flush with the surface of the AlN layer opposite to the SiN layer, or a portion of the SiN microstructure is also distributed on the surface of the AlN layer opposite to the SiN layer.
[0053] Furthermore, the composite buffer layer structure includes a second AlN layer, a SiN layer, and a third AlN layer stacked sequentially. The SiN layer also contains a plurality of AlN microstructures, and the second AlN layer and the third AlN layer also contain a plurality of SiN microstructures. The AlN microstructures are integral with the second AlN layer or the third AlN layer, and the SiN microstructures are integral with the SiN layer.
[0054] Furthermore, the AlN microstructure is completely distributed inside the SiN layer.
[0055] Furthermore, a portion of the SiN microstructure is exposed from the surface of the second AlN layer or the third AlN layer opposite to the SiN layer, and the surface of the exposed portion of the SiN microstructure is flush with the surface of the second AlN layer or the third AlN layer opposite to the SiN layer, or a portion of the SiN microstructure is also distributed on the surface of the second AlN layer and / or the third AlN layer opposite to the SiN layer.
[0056] A third aspect of the present invention provides a composite substrate structure comprising:
[0057] A substrate having a first region and a second region on its surface, wherein the surface energy of the first region is higher than the surface energy of the second region;
[0058] The first AlN layer is distributed in a second region on the surface of the substrate;
[0059] One or more of the composite buffer layer structures are stacked on the first region of the surface of the substrate and the first AlN layer.
[0060] Furthermore, the surface of the composite buffer layer structure facing away from the substrate has a patterned structure with a high gradient difference.
[0061] Furthermore, the thickness of each AlN layer and each SiN layer in the composite buffer layer structure is uniform.
[0062] Furthermore, in the composite buffer layer structure, the side surface of each AlN layer and each SiN layer facing away from the substrate has a pattern structure with a high gradient difference.
[0063] A fourth aspect of this invention provides a method for preparing a composite substrate structure, comprising:
[0064] S1. A substrate having a first region and a second region on its surface is provided, wherein the surface energy of the first region is higher than that of the second region, and Al is deposited on the surface of the substrate under a first temperature and a first pressure to form a first Al layer.
[0065] S2. Under the conditions of first temperature and first pressure, the first Al layer is subjected to a first heat treatment, so that the Al atoms distributed in the first region move to the second region to form a first Al atom layer deposition structure.
[0066] S3. A composite buffer layer structure is formed on the surface of the first region of the substrate and the first Al atomic layer deposition structure, specifically including:
[0067] S31. Under the conditions of a second temperature and a second pressure, Al is deposited on the first region of the substrate and the first Al atomic layer deposition structure to form a second Al layer;
[0068] S32. Under the conditions of a third temperature and a third pressure, Si is deposited on the second Al layer to form a Si layer;
[0069] S33. Under the fourth temperature and fourth pressure conditions, Al is deposited on the Si layer to form a third Al layer, thereby obtaining a precursor for a composite buffer layer structure.
[0070] S34. Under the conditions of the fifth temperature and the fifth pressure, and in the presence of an N source, the composite buffer layer structure precursor and the first Al atomic layer deposition structure are subjected to a second heat treatment, at least causing some Al atoms in the second Al layer and the third Al layer to undergo mutual dissolution and diffusion with some Si atoms in the Si layer, and causing the Al atoms and Si atoms in the composite buffer layer structure precursor and the first Al atomic layer deposition structure to combine with the N atoms provided by the N source to form AlN and SiN, respectively, thereby transforming the first Al atomic layer deposition structure into a first AlN layer, and transforming the composite buffer layer structure precursor into a composite buffer layer structure, wherein the composite buffer layer structure has a composite microstructure of SiN and AlN intermingled.
[0071] Furthermore, the first temperature is 500℃-900℃ and the first pressure is 100 torr-200 torr.
[0072] Furthermore, the duration of the first heat treatment is 10s-30s.
[0073] Furthermore, the second temperature is 500℃-900℃ and the second pressure is 20 torr-100 torr.
[0074] Furthermore, the third temperature is 500℃-900℃, and the third pressure is 20 torr-100 torr.
[0075] Furthermore, the third temperature is 500℃-900℃, and the third pressure is 20 torr-100 torr.
[0076] Furthermore, the fourth temperature is 500℃-900℃, and the fourth pressure is 20 torr-100 torr.
[0077] Furthermore, the fifth temperature is 800℃-1000℃, and the fifth pressure is 100 torr-500 torr.
[0078] Furthermore, the duration of the second heat treatment is 30s-180s.
[0079] Furthermore, the thickness of the Si layer is greater than the thickness of the second Al layer and the third Al layer.
[0080] Furthermore, the thickness of the second Al layer is 2nm-30nm.
[0081] Furthermore, the thickness of the Si layer is 5nm-100nm.
[0082] Furthermore, the thickness of the third Al layer is 2nm-50nm.
[0083] In some more specific embodiments, the method for preparing the composite substrate structure further includes: repeating S31-S34 once or more to form two or more composite buffer layer structures, wherein the two or more composite buffer layer structures are sequentially stacked on the substrate and the first AlN layer.
[0084] In a more specific embodiment, the method for preparing the composite substrate structure specifically includes:
[0085] S1. A substrate with a high surface energy region (i.e., the aforementioned first region) and a low surface energy region (i.e., the aforementioned second region) is placed in a growth chamber. The temperature in the growth chamber is maintained at 500℃-900℃ and the pressure is maintained at 100 torr-200 torr. An Al source is introduced into the growth chamber at a flow rate of 5 sccm-50 sccm to deposit and form a first Al layer on the surface of the substrate.
[0086] S2. Maintain the temperature and pressure conditions in the growth chamber unchanged, interrupt the Al source supply, and perform the first heat treatment on the formed first Al layer for 10s-30s. Al atoms in the high surface energy region move to the low surface energy region, thereby forming a patterned first Al atomic layer deposition structure.
[0087] S3. A composite buffer layer structure is formed on the surface of the substrate and the first Al atomic layer deposition structure, specifically including:
[0088] S31: Set the temperature in the growth chamber to 500℃-900℃ and the pressure to 20 torr-100 torr. Introduce an Al source into the growth chamber at a flow rate of 20 sccm-100 sccm. Form a continuous second Al layer with a thickness of 2nm-30nm in the high surface energy region on the surface of the first Al layer and the substrate surface.
[0089] S32: Set the temperature in the growth chamber to 500℃-900℃ and the pressure to 20 torr-100 torr. Introduce a Si source into the growth chamber at a flow rate of 10 sccm-300 sccm to form a Si layer with a thickness of 5 nm-100 nm on the surface of the second Al layer.
[0090] S33: Set the temperature in the growth chamber to 500℃-900℃ and the pressure to 20 torr-100 torr. Introduce an Al source into the growth chamber at a flow rate of 50 sccm-300 sccm. Form a third Al layer with a thickness of 2nm-50nm on the surface of the Si layer. The third Al layer, the Si layer, and the second Al layer form a composite buffer layer structure precursor.
[0091] S34: Continuously introduce an Al source into the growth chamber, setting the temperature inside the growth chamber to 800℃-1000℃ and the pressure to 100 torr-500 torr. Simultaneously, introduce an N source into the growth chamber at a flow rate of 1 slm-25 slm and maintain this flow for 30s-180s. Perform a second heat treatment on the first Al atomic layer deposition structure and the composite buffer layer structure to transform the first Al atomic layer deposition structure in situ into a first AlN layer and to transform the precursor of the composite buffer layer structure into a composite buffer layer structure. The Al source includes TMAl, the Si source includes SiH4, and the N source includes NH3.
[0092] S35: Repeat steps S31-S34 1-15 times periodically to form a composite substrate structure.
[0093] A fifth aspect of the present invention provides an epitaxial wafer comprising: the composite buffer layer structure or the composite substrate structure.
[0094] In a more specific implementation, the epitaxial wafer is a nitride HEMT epitaxial wafer, which includes the composite buffer layer structure or the composite substrate structure, a gallium nitride buffer layer, a gallium nitride channel layer, an aluminum gallium nitride barrier layer and a gallium nitride capping layer stacked sequentially.
[0095] A sixth aspect of the present invention provides a semiconductor device comprising the aforementioned epitaxial wafer.
[0096] The following will provide further explanation of the technical solution, its implementation process, and its principles, using specific implementation cases as examples.
[0097] Please refer to a more specific implementation plan. Figure 1 A nitride HEMT epitaxial wafer includes a substrate, a first AlN layer disposed in a low surface energy region on the substrate surface, a composite Si / Al buffer layer disposed in a high surface energy region on the substrate surface and on the first AlN layer, and a GaN buffer layer, a GaN channel layer, an AlGaN barrier layer, and a GaN capping layer sequentially stacked on the composite Si / Al buffer layer along a selected direction.
[0098] Please refer to the following for details. Figure 2 The composite Si / Al buffer layer includes at least one periodic structure. Each periodic structure includes a second AlN layer, a SiN layer, and a third AlN layer stacked sequentially along a selected direction. Furthermore, multiple AlN microstructures are distributed within the SiN layer, and multiple SiN microstructures are also distributed within the second AlN layer and the third AlN layer. The AlN microstructures are integral with the second AlN layer or the third AlN layer, and the SiN microstructures are integral with the SiN layer.
[0099] Specifically, the grain boundaries of the composite microstructure formed by multiple AlN microstructures and multiple SiN microstructures can relax and release the stress of the composite Si / Al buffer layer. Under the action of the composite microstructure, the different stress regions of the nitride buffer layer grown on the composite Si / Al buffer layer are more likely to reach equilibrium through the interaction during the delayed healing process, thereby improving the uniformity of stress distribution in the epitaxial wafer, reducing the residual stress in the epitaxial wafer, and thus realizing the growth of large-size epitaxial wafers.
[0100] Specifically, the plurality of AlN microstructures are spaced apart within the SiN layer, and the height of the AlN microstructures is less than the thickness of the SiN layer in the thickness direction. More specifically, a portion of the plurality of AlN microstructures is integral with the second AlN layer, and another portion is integral with the third AlN layer.
[0101] Specifically, a portion of the plurality of SiN microstructures is spaced apart within the second AlN layer, and another portion is spaced apart within the third AlN layer. More specifically, the thickness of the SiN layer is greater than the thickness of either the second or third AlN layer, and the height of the SiN microstructure is less than, greater than, or equal to the thickness of either the second or third AlN layer. More specifically, a portion of the SiN microstructure is exposed from the surface of the second or third AlN layer opposite to the SiN layer, and the surface of the exposed portion of the SiN microstructure is flush with the surface of the second or third AlN layer opposite to the SiN layer; or, a portion of the SiN microstructure is uniformly distributed on the surface of the second and / or third AlN layers opposite to the SiN layer. The SiN layer also acts as a surface roughening mask for the second AlN layer and / or the third AlN layer, thereby further enhancing the lateral epitaxial growth of the nitride buffer layer, delaying the healing process of the nitride epitaxial wafer, and thus shielding the upward extension of dislocations, allowing the dislocations to fully turn and achieve self-annihilation. This not only has a more positive effect on improving the two-dimensional electron gas density and mobility of the channel layer, but also improves the crystal quality of the nitride buffer wafer.
[0102] Specifically, the thicknesses of the second AlN layer, SiN layer, and third AlN layer are all uniform. Due to the presence of the first AlN layer, any structural layer in the second AlN layer, SiN layer, and third AlN layer, as well as the composite Si / Al buffer layer, have a pattern structure with a high gradient difference. Under the action of the specific pattern structure, the residual stress in the epitaxial wafer can be better eliminated.
[0103] For a more specific implementation plan, please refer to Figures 3-12 A method for preparing a nitride HEMT epitaxial wafer includes the following steps:
[0104] (1) Provide a substrate, such as Figure 3 As shown, the substrate surface has high surface energy regions and low surface energy regions. The substrate is surface-treated in a reducing gas atmosphere at a temperature of 1050℃-1200℃ and a pressure of 50 torr-500 torr. This surface treatment not only cleans the substrate but also repairs defects and damage on the substrate surface, providing a support surface for epitaxial wafer growth.
[0105] (2) Growing a first Al atomic layer deposition structure on the substrate, specifically including:
[0106] 21) Place the substrate in the growth chamber. Under conditions of 500℃-900℃ and 100 torr-200 torr, introduce an Al source into the growth chamber at a flow rate of 5 sccm-50 sccm and maintain this flow for 10-60 seconds to form the first Al layer on the substrate surface. Figure 4 As shown;
[0107] 21) Maintaining the temperature and pressure conditions of step 21), interrupt the Al source and maintain this for 10-30 seconds; after surface heat treatment of the first Al layer, metal atoms located in the high surface energy region of the substrate move to the low surface energy region and diffuse sufficiently, thus forming a patterned first Al atomic layer deposition structure with Al atomic layer deposition only in the low surface energy region of the substrate, such as... Figure 5 As shown.
[0108] It should be noted that the thickness of the first Al atomic layer deposition structure needs to be above 2nm, preferably 2nm-8nm. If the thickness of the first Al atomic layer deposition structure is less than 2nm, the thickness gradient of the subsequently formed second Al layer, Si layer and third Al layer will be too small, and the enhanced lateral epitaxial growth effect of the nitride buffer layer brought about by the pattern structure with a high gradient difference cannot be reflected. Furthermore, under the action of a specific pattern structure, as the thickness continues to increase, the interaction between different stress regions of the nitride buffer layer grown on it to achieve equilibrium during the delayed healing process limits the effect of the residual stress in the epitaxial wafer. Moreover, a thicker nitride buffer layer is required to obtain an epitaxial wafer with a smooth surface, which increases the process growth cycle and increases the process cost.
[0109] (3) Growing a composite Si / Al buffer layer on the substrate and the first Al atomic layer deposition structure, specifically including:
[0110] 31) Set the temperature of the growth chamber to 500℃-900℃ and the pressure to 20 torr-100 torr. Introduce an Al source into the growth chamber at a flow rate of 20 sccm-100 sccm and maintain this flow for 30-150 seconds. This forms a second Al layer with a thickness of 2nm-30nm on the surface of the first Al atomic layer deposition structure and in the high surface energy region of the substrate. The thickness of the second Al layer is uniform. Figure 6 As shown;
[0111] 32) Set the temperature of the growth chamber to 500℃-900℃ and the pressure to 20 torr-100 torr. Introduce a Si source into the growth chamber at a flow rate of 10 sccm-300 sccm and maintain for 20-120 seconds. This will form a Si layer with a thickness of 5nm-100nm on the surface of the second Al layer. The Si layer thickness is uniform. Figure 7 As shown;
[0112] 33) Under conditions of 500℃-900℃ and 20 torr-100 torr in the growth chamber, an Al source is introduced into the growth chamber at a flow rate of 50 sccm-300 sccm and maintained for 10-30 seconds. A third Al layer with a thickness of 2nm-50nm is formed on the surface of the Si layer. The thickness of the third Al layer is uniform, thus forming a composite Si / Al buffer layer precursor, such as... Figure 8 As shown.
[0113] Step 33) Without interrupting the Al source, a uniformly distributed Al deposition layer can be formed in both high and low surface energy regions under relatively high Al source flow conditions.
[0114] 34) Continuously introduce an Al source into the growth chamber at a flow rate of 50-300 sccm, under conditions of 800-1000℃ and 100-500 torr. Simultaneously, introduce an N source into the growth chamber at a flow rate of 1-25 slm, maintaining this flow for 30-180 seconds. This process transforms the first Al atomic layer deposition structure into the first AlN layer (also known as the AlN buffer layer), and transforms the precursor of the composite Si / Al buffer layer into the composite Si / Al buffer layer. Figure 9 As shown.
[0115] The third Al layer undergoes N-source heat treatment in step 34). On one hand, the continuous supply of the Al source prevents regional migration of Al atoms before the N source is introduced in step 34), thus avoiding the diffusion of atoms from the high surface energy region of the third Al layer in step 33) to the low surface energy region. This results in a uniformly distributed buffer layer structure with a highly gradient nanoscale pattern, enhancing the lateral epitaxial growth of the nitride buffer layer, delaying the healing process of the nitride epitaxial layer, and shielding dislocations from upward extension, allowing them to fully redirect and self-annihilate, thereby increasing the two-dimensional electron gas density and mobility of the channel layer. On the other hand, during the N-source heat treatment process, some Al atoms in the second and third Al layers of the composite Si / Al buffer layer precursor react with the S... Some Si atoms in the i-layer undergo mutual dissolution and diffusion. The Al atoms and Si atoms in the first Al atomic layer deposition structure and the precursor of the composite Si / Al buffer layer combine with the N atoms provided by the N source to form AlN and SiN, respectively, thereby forming the first AlN layer and the composite Si / Al buffer layer. The composite Si / Al buffer layer has a composite microstructure of SiN and AlN intermingled. The composite microstructure formed by nitrogen thermal treatment can release the stress of the buffer layer by relaxing multiple microstructure grain boundaries. Under the action of the composite microstructure, the different stress regions of the nitride buffer layer grown on it are more likely to reach equilibrium through the interaction during the delayed healing process, thereby improving the stress distribution uniformity of the epitaxial wafer and reducing the residual stress in the epitaxial layer. It is suitable for the growth of large-size epitaxial wafers.
[0116] It should be noted that the thickness of the Si layer is greater than that of the second and third Al layers. This allows Si atoms to diffuse across the second and third Al layers. On one hand, after nitriding, spaced SiN microstructures will form within the second and third AlN layers, introducing multiple grain boundaries into the composite buffer layer. Stress can be released through relaxation between these interfaces, forming a low-stress buffer layer growth template and reducing epitaxial wafer stress. On the other hand, Si atoms may also accumulate on the surfaces of the second and third Al layers. After nitriding, SiN microstructures will also form on these surfaces. These SiN microstructures act as a roughening mask for the AlN layer surface, further enhancing the lateral epitaxial growth of the nitride buffer layer, delaying the healing process of the nitride epitaxial layer, and thus shielding dislocations from upward extension, allowing them to fully redirect and self-annihilate, thereby improving the crystal quality of the nitride buffer layer. Furthermore, the formation of SiN microstructures on the surfaces of the second and third AlN layers further enhances the lateral epitaxial growth of the nitride buffer layer, slows down the healing process of the nitride epitaxial layer, and has a more positive effect on shielding the upward extension of dislocations so that they can fully turn and achieve self-annihilation, thereby improving the two-dimensional electron gas density and mobility of the channel layer.
[0117] 3) Under conditions of 1000℃-1200℃ and 200 torr-200 torr, a GaN buffer layer with a thickness of 1μm-20μm is grown on the composite Si / Al buffer layer, such as... Figure 10 As shown.
[0118] 4) Under conditions of temperature 1050℃-1250℃ and pressure 100 torr-500 torr, grow GaN channel layers with a thickness of 100nm-1000nm on the surface of the GaN buffer layer, such as... Figure 11 As shown.
[0119] 5) Under conditions of 1050℃-1250℃ and 100 torr-200 torr, an AlGaN barrier layer with a thickness of 10nm-50nm is grown on the surface of the GaN channel layer, with an Al composition of 0.2-0.6. Figure 12 As shown.
[0120] 6) Under conditions of temperature 1050℃-1250℃ and pressure 100 torr-500 torr, a GaN capping layer with a thickness of 1nm-3nm is grown on the surface of the AlGaN barrier layer, such as... Figure 1 As shown.
[0121] Example 1
[0122] A method for preparing a nitride HEMT epitaxial wafer includes:
[0123] 1) Provide a substrate with sapphire patterns, and perform surface treatment on the substrate in an H2 gas atmosphere at a temperature of 1110℃ and a pressure of 200 torr (the patterned surface area is a high surface energy area, and the area between the patterns is a low surface energy area).
[0124] 2) Growth of a composite Si / Al buffer layer on a sapphire substrate:
[0125] S21: Place the substrate in the growth chamber, and under the conditions of 550℃ and 120 torr, introduce TMAl at a flow rate of 20 sccm and maintain for 20s to form the first Al layer on the substrate surface.
[0126] S22: Maintain the temperature and pressure conditions of step S21 unchanged, interrupt TMAl, and heat-treat the first Al layer for 15 seconds;
[0127] S23: Under the conditions of temperature 550℃ and pressure 80 torr, TMAl is introduced at a flow rate of 80 sccm and held for 45s to form a second Al layer in the high surface energy region of the first Al layer and the substrate.
[0128] S24: Under conditions of 550℃ and 80 torr, SiH4 is introduced at a flow rate of 120 sccm and held for 60s to form a Si layer on the surface of the second Al layer.
[0129] S25: Under conditions of 550℃ and 50 torr, TMAl is introduced at a flow rate of 200 sccm and held for 15s to form a third Al layer on the surface of the Si layer.
[0130] S26: Continuously introduce TMAl, and under the conditions of temperature 915℃ and pressure 200 torr, introduce NH3 at a flow rate of 20 slm for 65s.
[0131] 3) A GaN buffer layer with a thickness of 2 μm was grown on the surface of the composite Si / Al buffer layer under the conditions of temperature 1115℃ and pressure 150 torr.
[0132] 4) A GaN channel layer with a thickness of 600 nm was grown on the surface of the GaN buffer layer under the conditions of temperature 1090℃ and pressure 200 torr.
[0133] 5) An AlGaN barrier layer with a thickness of 25 nm was grown on the surface of the GaN channel layer under the conditions of temperature 1215℃ and pressure 150 torr, with an Al composition of 0.3.
[0134] 6) A GaN capping layer with a thickness of 1.5 nm was grown on the surface of the AlGaN barrier layer under the conditions of temperature 1105℃ and pressure 150 torr.
[0135] Example 2
[0136] A method for preparing a nitride HEMT epitaxial wafer includes:
[0137] 1) Provide a substrate with sapphire patterns, and perform surface treatment on the substrate in an H2 gas atmosphere at a temperature of 1110℃ and a pressure of 200 torr (the patterned surface area is a high surface energy area, and the area between the patterns is a low surface energy area).
[0138] 2) Growth of a composite Si / Al buffer layer on a sapphire substrate:
[0139] S21: Place the substrate in the growth chamber, and under the conditions of 550℃ and 120 torr, introduce TMAl at a flow rate of 20 sccm and maintain for 20s to form the first Al layer on the substrate surface.
[0140] S22: Maintain the temperature and pressure conditions of step S21 unchanged, interrupt TMAl, and heat-treat the first Al layer for 15 seconds;
[0141] S23: Under the conditions of temperature 550℃ and pressure 80 torr, TMAl is introduced at a flow rate of 80 sccm and held for 45s to form a second Al layer in the high surface energy region of the first Al layer and the substrate.
[0142] S24: Under conditions of 550℃ and 80 torr, SiH4 is introduced at a flow rate of 120 sccm and held for 60s to form a Si layer on the surface of the second Al layer.
[0143] S25: Under conditions of 550℃ and 50 torr, TMAl is introduced at a flow rate of 200 sccm and held for 15s to form a third Al layer on the surface of the Si layer.
[0144] S26: TMAl is continuously introduced, and NH3 is introduced at a temperature of 915℃ and a pressure of 200 torr. The flow rate of NH3 is 20slm and maintained for 65s.
[0145] Repeat steps S23-S26 once.
[0146] 3) A GaN buffer layer with a thickness of 2 μm was grown on the surface of the composite Si / Al buffer layer under the conditions of temperature 1115℃ and pressure 150 torr.
[0147] 4) A GaN channel layer with a thickness of 600 nm was grown on the surface of the GaN buffer layer under the conditions of temperature 1090℃ and pressure 200 torr.
[0148] 5) An AlGaN barrier layer with a thickness of 25 nm was grown on the surface of the GaN channel layer under the conditions of temperature 1215℃ and pressure 150 torr, with an Al composition of 0.3.
[0149] 6) A GaN capping layer with a thickness of 1.5 nm was grown on the surface of the AlGaN barrier layer under the conditions of temperature 1105℃ and pressure 150 torr.
[0150] Comparative Example 1
[0151] Comparative Example 1 is basically the same as Example 1, except that: in Comparative Example 1, AlN / SiN / AlN is sequentially stacked on the substrate as a composite buffer layer, and the thickness of the composite buffer layer is the same as the thickness of the composite Si / Al buffer layer in Example 1.
[0152] The performance of the nitride HEMT epitaxial wafers obtained in Example 1, Example 2 and Comparative Example 1 were tested using the same testing equipment and process. The test results are shown in Table 1.
[0153] Table 1. Performance test results of nitride HEMT epitaxial wafers obtained in Examples 1, 2 and Comparative Example 1.
[0154] 002 face diffraction peak half-width 102 face diffraction peak half-width Area density / cm 2 ]] mobility Example 1 98 145 9.8 x 10 12 ]] 1985 Example 2 96 149 9.6 x 10 12 ]] 1991 Comparative Example 1 101 202 6.7 x 10 12 ]]> 1682
[0155] The full width at half maximum (FWHM) of the diffraction peaks on the 002 and 102 planes of the material were measured by X-ray diffraction (XRD), which can characterize the crystal quality of the material.
[0156] This invention utilizes a buffer layer process to control the formation of a diffusion process layer on a substrate surface with high and low surface energy regions, creating a composite microstructure. On one hand, by forming a composite buffer layer with highly gradient microstructures on substrates with different surface energy regions, this highly gradient microstructure enhances the lateral epitaxial growth of the nitride buffer layer, delays the healing process of the nitride epitaxial layer, and thus shields dislocations from upward extension, allowing them to fully redirect and self-annihilate, thereby increasing the two-dimensional electron gas density and mobility of the channel layer. On the other hand, under the influence of the micro / nano structure, the different stress regions of the nitride buffer layer grown on it are more likely to reach equilibrium through the interaction during the delayed healing process, thereby improving the uniformity of stress distribution in the epitaxial wafer and reducing residual stress in the epitaxial layer. This method is applicable to the growth of large-size epitaxial wafers.
[0157] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.
Claims
1. A method for preparing a composite buffer layer structure, characterized in that, include: The step of fabricating a precursor for forming a composite buffer layer structure includes two or more Al layers and one or more Si layers stacked together, wherein one of the Si layers is distributed between two adjacent Al layers; Furthermore, under the condition of at least the presence of an N source, the precursor is subjected to heat treatment, causing partial Al atoms in two or more Al layers to undergo mutual dissolution and diffusion with partial Si atoms in one or more Si layers, and causing the Al atoms and Si atoms in the precursor of the composite buffer layer structure to combine with the N atoms provided by the N source to form AlN and SiN, respectively, thereby forming a composite buffer layer structure, wherein the composite buffer layer structure has a composite microstructure of SiN and AlN intermingled.
2. The method for preparing the composite buffer layer structure according to claim 1, characterized in that: The heat treatment temperature is 800℃-1000℃ and the pressure is 1000 torr-500 torr; Preferably, the heat treatment time is 30s-180s; Preferably, the composite microstructure includes multiple AlN microstructures and multiple SiN microstructures; Preferably, the SiN microstructure is formed by Si atoms and N atoms diffused from the Si layer into the adjacent Al layer and combining with each other; the AlN microstructure is formed by Al atoms and N atoms diffused from the Al layer into the adjacent Si layer and combining with each other. Preferably, the thickness of the Si layer is greater than the thickness of the adjacent Al layer. When the composite buffer layer structure precursor is heat-treated, Si atoms in the Si layer also diffuse to the side surface of the adjacent Al layer opposite to the Si layer. Preferably, the composite buffer layer structure precursor includes a second Al layer, a Si layer and a third Al layer stacked sequentially, wherein the thickness of the second Al layer is 2nm-30nm, the thickness of the Si layer is 5nm-100nm, and the thickness of the third Al layer is 2nm-50nm. Preferably, the SiN microstructure is formed by Si atoms and N atoms diffused from the Si layer into the second Al layer or the third Al layer, and the AlN microstructure is formed by Al atoms and N atoms diffused from the second Al layer and / or the third Al layer into the Si layer.
3. A composite buffer layer structure, characterized in that, include: The system comprises two or more AlN layers and one or more SiN layers stacked together, wherein one of the SiN layers is distributed between two adjacent AlN layers, and a plurality of SiN microstructures are distributed within the AlN layer. The SiN microstructures are integral with the SiN layers adjacent to the AlN layer in which they are located.
4. The composite buffer layer structure according to claim 3, characterized in that: The AlN microstructure is completely distributed inside the SiN layer; Preferably, a portion of the SiN microstructure is exposed from the surface of the AlN layer opposite to the SiN layer, and the surface of the exposed portion of the SiN microstructure is flush with the surface of the AlN layer opposite to the SiN layer; or, a portion of the SiN microstructure is distributed on the surface of the AlN layer opposite to the SiN layer. Preferably, the composite buffer layer structure includes a second AlN layer, a SiN layer, and a third AlN layer stacked sequentially, and the SiN layer further contains a plurality of AlN microstructures, the second AlN layer and the third AlN layer further contain a plurality of SiN microstructures, wherein the AlN microstructures are integral with the second AlN layer or the third AlN layer, and the SiN microstructures are integral with the SiN layer; Preferably, the AlN microstructure is completely distributed inside the SiN layer; Preferably, a portion of the SiN microstructure is exposed from the surface of the second AlN layer or the third AlN layer opposite to the SiN layer, and the surface of the exposed portion of the SiN microstructure is flush with the surface of the second AlN layer or the third AlN layer opposite to the SiN layer; or, a portion of the SiN microstructure is distributed on the surface of the second AlN layer and / or the third AlN layer opposite to the SiN layer.
5. A composite substrate structure, characterized in that, include: A substrate having a first region and a second region on its surface, wherein the surface energy of the first region is higher than the surface energy of the second region; The first AlN layer is distributed in a second region on the surface of the substrate; One or more composite buffer layer structures as described in any one of claims 3-4, wherein the composite buffer layer structures are stacked on a first region of the surface of the substrate and the first AlN layer.
6. The composite substrate structure according to claim 5, characterized in that: The surface of the composite buffer layer structure facing away from the substrate has a patterned structure with a high gradient difference. Preferably, the thickness of each AlN layer and each SiN layer in the composite buffer layer structure is uniform; Preferably, in the composite buffer layer structure, the side surface of each AlN layer and each SiN layer facing away from the substrate has a pattern structure with a high gradient difference.
7. A method for preparing a composite substrate structure, characterized in that, include: S1. Provide a substrate having a first region and a second region on its surface, wherein the surface energy of the first region is higher than that of the second region, and deposit Al on the surface of the substrate under a first temperature and a first pressure condition to form a first Al layer; S2. Under the conditions of first temperature and first pressure, the first Al layer is subjected to a first heat treatment, so that the Al atoms distributed in the first region move to the second region to form a first Al atom layer deposition structure. S3. A composite buffer layer structure is formed on the surface of the substrate and the first Al atomic layer deposition structure, specifically including: S31. Under the conditions of a second temperature and a second pressure, Al is deposited on the first region of the substrate and the first Al atomic layer deposition structure to form a second Al layer; S32. Under the conditions of a third temperature and a third pressure, Si is deposited on the second Al layer to form a Si layer; S33. Under the fourth temperature and fourth pressure conditions, Al is deposited on the Si layer to form a third Al layer, thereby obtaining a precursor for a composite buffer layer structure. S34. Under the conditions of the fifth temperature and the fifth pressure, and in the presence of an N source, the composite buffer layer structure precursor and the first Al atomic layer deposition structure are subjected to a second heat treatment, at least causing some Al atoms in the second Al layer and the third Al layer to undergo mutual dissolution and diffusion with some Si atoms in the Si layer, and causing the Al atoms and Si atoms in the composite buffer layer structure precursor and the first Al atomic layer deposition structure to combine with the N atoms provided by the N source to form AlN and SiN, respectively, thereby transforming the first Al atomic layer deposition structure into a first AlN layer, and transforming the composite buffer layer structure precursor into a composite buffer layer structure, wherein the composite buffer layer structure has a composite microstructure of SiN and AlN intermingled.
8. The method for preparing the composite substrate structure according to claim 7, characterized in that: The first temperature is 500℃-900℃, and the first pressure is 100 torr-200 torr; And / or, the duration of the first heat treatment is 10s-30s; And / or, the second temperature is 500℃-900℃, and the second pressure is 20 torr-100 torr; And / or, the third temperature is 500℃-900℃, and the third pressure is 20 torr-100 torr; And / or, the third temperature is 500℃-900℃, and the third pressure is 20 torr-100 torr; And / or, the fourth temperature is 500℃-900℃, and the fourth pressure is 20 torr-100 torr; And / or, the fifth temperature is 800℃-1000℃, and the fifth pressure is 100 torr-500 torr; And / or, the duration of the second heat treatment is 30s-180s; Preferably, the thickness of the Si layer is greater than the thickness of the second Al layer and the third Al layer; Preferably, the thickness of the second Al layer is 2nm-30nm; Preferably, the thickness of the Si layer is 5nm-100nm; Preferably, the thickness of the third Al layer is 2nm-50nm; Preferably, the method for preparing the composite substrate structure further includes: repeating S31-S34 once or more to form two or more composite buffer layer structures, wherein the two or more composite buffer layer structures are sequentially stacked on the substrate and the first AlN layer.
9. An epitaxial wafer, characterized in that, include: The composite buffer layer structure according to any one of claims 3-4 or the composite substrate structure according to any one of claims 5-6; Preferably, the epitaxial wafer is a nitride HEMT epitaxial wafer, which includes the composite buffer layer structure or the composite substrate structure, a gallium nitride buffer layer, a gallium nitride channel layer, an aluminum gallium nitride barrier layer and a gallium nitride capping layer stacked sequentially.
10. A semiconductor device, characterized in that, include: The epitaxial wafer as described in claim 9.