CN114743876A - Preparation method of buffer layer of epitaxial structure and preparation method of gallium nitride epitaxial layer - Google Patents

Preparation method of buffer layer of epitaxial structure and preparation method of gallium nitride epitaxial layer Download PDF

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CN114743876A
CN114743876A CN202210249322.4A CN202210249322A CN114743876A CN 114743876 A CN114743876 A CN 114743876A CN 202210249322 A CN202210249322 A CN 202210249322A CN 114743876 A CN114743876 A CN 114743876A
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aluminum nitride
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邢国兵
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Semiconductor Manufacturing Electronics Shaoxing Corp SMEC
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Abstract

The invention provides a preparation method of a buffer layer of an epitaxial structure and a preparation method of a gallium nitride epitaxial layer. The first aluminum nitride layer is prepared by performing the atomic layer deposition process at least twice, and before each atomic layer deposition process, the surface of the current film layer is subjected to micro-etching treatment to remove defects, particles and the like existing on the surface of the current film layer, so that the lattice quality of the current film layer can be effectively improved, a better growth environment is provided for the growth of the subsequent film layer, the pre-reaction problem existing in the prior art when the aluminum nitride layer is prepared by using the MOCVD process is also avoided, the various defects caused by the pre-reaction problem can be reduced, and the crystal quality is improved.

Description

Preparation method of buffer layer of epitaxial structure and preparation method of gallium nitride epitaxial layer
Technical Field
The invention relates to the technical field of semiconductors, in particular to a preparation method of a buffer layer of an epitaxial structure, a preparation method of a gallium nitride epitaxial layer and a preparation method of a gallium nitride-based power device.
Background
In the field of semiconductor technology, in order to optimize device performance, meet the manufacturing requirements of high-frequency high-power devices, and the like, an epitaxial growth technology is widely applied, and specifically, an epitaxial layer with a certain thickness is grown on the surface of a substrate by using an epitaxial process. For example, some III-V compounds have promising application due to their advantages of large forbidden bandwidth, high breakdown electric field, high thermal conductivity, high electron saturation rate, etc., and are generally epitaxially grown on a foreign substrate (e.g., a silicon substrate). However, there are problems of lattice mismatch and thermal mismatch between the III-V compound and the foreign substrate, so that the heteroepitaxially grown III-V compound usually has many defects including cracks, dislocations, impurities, and the like.
Currently, to reduce defects in the final grown top epitaxial layer, a buffer layer is typically formed between the substrate and the top epitaxial layer. For example, in a gallium nitride epitaxial process, an aluminum nitride layer may be preferentially epitaxially grown as a buffer layer before growing the gallium nitride epitaxial layer, which is commonly grown by Metal-organic Chemical Vapor Deposition (MOCVD) in the prior art. However, the MOCVD vapor phase epitaxy growth process has very strict process requirements, and is prone to pre-reaction, so that the utilization efficiency of a reaction source is greatly reduced, and various defects are easily formed to affect the crystal quality.
Disclosure of Invention
The invention aims to provide a preparation method of a buffer layer of an epitaxial structure, which aims to solve the problem that a pre-reaction phenomenon is easy to occur when an MOCVD (metal organic chemical vapor deposition) process is carried out to epitaxially grow aluminum nitride in the prior art.
In order to solve the above technical problem, the present invention provides a method for preparing an epitaxial structure, comprising: providing a substrate; and performing at least two atomic layer deposition processes to form a first aluminum nitride layer on the substrate, and performing micro-etching treatment on the surface of the current film layer before each atomic layer deposition process.
Optionally, the micro etching process includes: and introducing micro-etching gas into the process chamber with the substrate to corrode defects and particles on the surface of the film layer.
Optionally, before each atomic layer deposition, introducing ammonia gas into the process chamber in which the substrate is placed, so as to perform micro-etching treatment on the surface of the current film layer by using the ammonia gas; and continuously introducing ammonia gas and introducing an aluminum source in the process of performing the atomic layer deposition to form the aluminum nitride film.
Optionally, during the preparation of the first aluminum nitride layer, the substrate is always in a nitrogen-containing atmosphere.
Optionally, during the interval between adjacent atomic layer deposition processes, the process chamber in which the substrate is placed is continuously purged with nitrogen and/or ammonia.
Optionally, after the last atomic layer deposition is performed, stopping introducing the aluminum source, continuously introducing ammonia gas and nitrogen gas, and performing staged cooling.
Optionally, before preparing the first aluminum nitride layer, the method further includes: a chemical vapor deposition process is performed to form a first silicon nitride layer on the substrate.
Optionally, before the first silicon nitride layer is formed, a micro-etching process is performed on the surface of the substrate.
Optionally, after the forming of the first aluminum nitride layer, the method further includes: and performing an MOCVD process to form a second aluminum nitride layer at a temperature higher than a first predetermined temperature, which is higher than a process temperature of the atomic layer deposition process.
Optionally, the method for forming the second aluminum nitride layer includes: starting to perform MOCVD deposition by taking the first temperature as an initial temperature, continuously raising the temperature in the deposition process until the temperature is raised to a second temperature, and stopping the deposition process to form the second aluminum nitride layer.
Optionally, after forming the second aluminum nitride layer, the method further includes: and performing an MOCVD process to form a second silicon nitride layer on the second aluminum nitride layer, wherein a pore structure is formed in the second silicon nitride layer.
Optionally, after forming the second silicon nitride layer, the method further includes: and performing an MOCVD process to form a third aluminum nitride layer at a temperature higher than a second predetermined temperature, which is higher than the first predetermined temperature.
Optionally, the method for forming the third aluminum nitride layer includes: starting to perform MOCVD deposition by taking the third temperature as an initial temperature, continuously raising the temperature in the deposition process until the temperature is raised to the fourth temperature, and stopping the deposition process to form the third aluminum nitride layer.
The invention also provides a preparation method of the gallium nitride epitaxial layer, which comprises the following steps: by adopting the preparation method, the aluminum nitride buffer layer is formed on the substrate, and the gallium nitride epitaxial layer is formed above the aluminum nitride buffer layer.
Optionally, the preparation method of the gallium nitride epitaxial layer further comprises: and forming at least one layer of gallium nitride aluminum buffer layer and at least one layer of gallium nitride buffer layer on the aluminum nitride buffer layer, and epitaxially growing a gallium nitride epitaxial layer on the gallium nitride buffer layer at the top layer.
The invention also provides a preparation method of the gallium nitride-based power device, which comprises the following steps: and forming a gallium nitride epitaxial layer by adopting the preparation method of the gallium nitride epitaxial layer, and preparing a power device on the gallium nitride epitaxial layer. The power device includes, for example, a HEMT device.
In the preparation method of the buffer layer of the epitaxial structure, the first aluminum nitride layer is prepared by executing the atomic layer deposition process at least twice, so that the pre-reaction problem existing in the prior art when the aluminum nitride layer is prepared by utilizing the MOCVD process is effectively avoided, various defects caused by the pre-reaction problem can be reduced, and the crystal quality is improved. And before each atomic layer deposition process, the surface of the current film layer is subjected to micro-etching treatment to remove defects, particles and the like (for example, incomplete crystals and the like on the surface) existing on the surface of the current film layer, so that the lattice quality of the current film layer can be effectively improved, and a better growth environment is provided for the growth of the subsequent film layer.
Furthermore, before the first aluminum nitride layer is prepared by utilizing the atomic layer deposition process, a first flat and pore-free silicon nitride layer can be formed on the substrate by utilizing the chemical vapor deposition process, the surface of the substrate can be completely covered, the defects in the substrate can be better buried, the phenomenon of lattice mismatch between the substrate and the first aluminum nitride layer can be improved, and the stress can be effectively relieved. In addition, on the basis of the flat and pore-free first silicon nitride layer, the first aluminum nitride layer formed on the basis of the atomic layer deposition process can flatly cover the first silicon nitride layer, and the flatness of the whole epitaxial structure is improved.
Drawings
Fig. 1 is a schematic flow chart illustrating a method for preparing a buffer layer in an epitaxial structure according to an embodiment of the invention.
Fig. 2 is a schematic diagram of an epitaxial structure in an embodiment of the invention.
Wherein the reference numbers are as follows: 100-a substrate; 210-a first silicon nitride layer; 220-a second silicon nitride layer; 310-a first aluminum nitride layer; 311-a first layer of aluminum nitride film; 312-a second layer of aluminum nitride film; 313-a third aluminum nitride film; 320-a second aluminum nitride layer; 330-third aluminum nitride layer.
Detailed Description
The epitaxial structure and the preparation method thereof, and the preparation method of the gallium nitride-based power device, which are provided by the present invention, are further described in detail below with reference to fig. 1-2 and specific examples. Fig. 1 is a schematic flow chart of a method for preparing a buffer layer in an epitaxial structure according to an embodiment of the present invention, and fig. 2 is a schematic view of an epitaxial structure according to an embodiment of the present invention. The advantages and features of the present invention will become more apparent from the following description. It is to be noted that the drawings are in a very simplified form and are not to precise scale, which is merely for the purpose of facilitating and distinctly claiming the embodiments of the present invention. It will be understood that relative terms, such as "above," "below," "top," "bottom," "above," and "below," may be used in relation to various elements shown in the figures. These relative terms are intended to encompass different orientations of the elements in addition to the orientation depicted in the figures. For example, if the device were inverted relative to the view in the drawings, an element described as "above" another element, for example, would now be below that element.
First, as shown in fig. 1 and 2, a substrate 100 is provided. The substrate 100 is, for example, a silicon substrate.
Further, prior to performing the epitaxial process on the substrate 100, the substrate 100 may be preferentially cleaned to remove contaminants, particles, etc. on the surface of the substrate. In an exemplary embodiment, the substrate 100 may be sequentially and cyclically cleaned by an organic solution, such as an isopropyl alcohol (IPA) solution, and a clean water, such as deionized water, without limitation. In this embodiment, the substrate 100 may be placed in a thermostatic bath containing isopropyl alcohol, and the surface cleaning may be performed by circulating water at a temperature of 50 to 300 ℃. In addition, after the substrate 100 is cleaned with the organic solution and the clean water, the substrate 100 may be also subjected to ultrasonic cleaning.
In this embodiment, with continuing reference to fig. 1 and fig. 2, before forming the first aluminum nitride layer, the method further includes: a chemical vapor deposition process is performed to form a first silicon nitride layer 210 on the substrate 100. For example, the thickness of the first silicon nitride layer 210 is, for example, 1nm to 30 nm.
Optionally, before depositing the first silicon nitride layer 210, the method further includes: the surface of the substrate 100, particularly the surface on which a silicon nitride layer is to be formed, is subjected to a micro-etching process to remove defects, particles, and the like on the surface of the substrate (e.g., to remove incomplete crystals, etc. on the surface). In particular, the microetching process may be performed using a microetching gas that tends to selectively etch from defect sites (e.g., dislocation defects, etc.). Thus, the lattice quality of the surface of the substrate 100 can be effectively improved, and a better growth environment is provided for the subsequent growth of the first silicon nitride layer. In particular embodiments, ammonia (NH) may be utilized3) The surface of the substrate 100 is subjected to a micro-etching process.
The first silicon nitride layer 210 is formed on the surface of the substrate after the microetching. The first silicon nitride layer 210 in this embodiment is specifically prepared by a PECVD process, and compared with a silicon nitride layer prepared by an MOCVD process, the first silicon nitride layer 210 formed in this embodiment has better flatness, higher compactness and uniformity, so that the surface of the substrate 100 can be completely covered, and defects in the substrate 100 can be better buried.
It should be noted that, in some schemes, an MOCVD process is used to prepare the silicon nitride layer, so that the formed silicon nitride layer is in a porous structure and partially exposes the surface of the substrate, and on the basis, a low-temperature MOCVD process is used to grow the aluminum nitride layer, so that the aluminum nitride layer can be epitaxially grown in a three-dimensional (3D) manner from the pores exposed in the substrate, thereby reducing bit line defects in the epitaxially grown aluminum nitride layer.
In the present embodiment, the first aluminum nitride layer 310 is formed by an atomic layer deposition process in a subsequent process, so that the first silicon nitride layer 210 can be prepared by a conventional chemical vapor deposition process (e.g., PECVD) to improve the flatness of the entire epitaxial structure. And, the first silicon nitride layer 210 is prepared by using a conventional chemical vapor deposition process (e.g., PECVD), and the formed first silicon nitride layer 210 can be planarized to cover the surface of the substrate 100, so that when the atomic layer deposition process (ALD) is used to form the first aluminum nitride layer 310 in a subsequent process, the first aluminum nitride layer 310 can grow layer by layer in an atomic layer manner to have better flatness, and the quality of a film layer can be better controlled, and the problem of pre-reaction occurring when aluminum nitride is prepared by using MOCVD is also overcome.
Further, in the chemical vapor deposition process (e.g., PECVD) for forming the first silicon nitride layer 210, Silane (SiH) may be specifically used4) As the silicon source, ammonia (NH) gas is used3) As a nitrogen source. And, the temperature of the PECVD process may be 200-500 ℃.
In this embodiment, the micro-etching process on the substrate surface and the deposition of the first silicon nitride layer 210 may be performed in the same process chamber. For example: firstly, a substrate 100 is placed in a process chamber of a chemical vapor deposition process, the temperature in the process chamber is raised to a set temperature range (for example, 200 ℃ to 500 ℃), and then the surface of the substrate 100 can be baked to remove moisture and the like on the surface; then, introducing a micro etching gas (e.g., ammonia gas, etc.) into the process chamber to etch the incomplete crystals on the surface of the substrate 100; thereafter, a silicon source gas is introduced (e.g., silane is introduced at a controlled flow rate of, for example, 10sccm to 200sccm), and a carrier gas (e.g., nitrogen gas, etc.) is introduced along with the silicon source gas, so as to deposit a first silicon nitride layer 210 on the surface of the substrate 100. That is, in the present embodiment, the microetching gas and the sink for microetching the surface of the substrate 100The nitrogen sources deposited on the first silicon nitride layer 210 may each include ammonia (NH)3)。
Next, with continued reference to fig. 1 and 2, at least two Atomic Layer Deposition (ALD) processes are performed to form a first aluminum nitride Layer 310 on the first silicon nitride Layer 210. In this embodiment, the atomic layer deposition process is used to form the first aluminum nitride layer 310, which can effectively overcome the pre-reaction problem existing in the conventional process when the MOCVD process is performed to prepare the aluminum nitride layer.
Since the surface of the first silicon nitride layer 210 is flat, the first aluminum nitride layer 310 formed by the atomic layer deposition process can conform to the surface of the first silicon nitride layer 210 to cover the first silicon nitride layer 210. In this embodiment, the first silicon nitride layer 210 covers the surface of the substrate 100 flatly and is interposed between the first aluminum nitride layer 310 and the substrate 100, so as to achieve effective transition between the substrate 100 and the first aluminum nitride layer 310, improve the problem of lattice mismatch between the substrate 100 and the first aluminum nitride layer 310, relieve the larger stress between the substrate 100 and the first aluminum nitride layer 310 due to the lattice mismatch, and better improve the dislocation and the thermal expansion coefficient between the substrate 100 and the first aluminum nitride layer 310. In addition, lateral relaxation of stress may also be achieved with the first silicon nitride layer 210, further reducing stress and dislocation defects (e.g., including threading dislocations and edge dislocations, etc.).
Further, before each atomic layer deposition process is performed, a micro-etching process may be performed on the surface of the current film layer to remove defects and particles on the surface of each film layer, so as to improve the overall crystal quality of the finally formed first aluminum nitride layer 310. The specific method for micro-etching treatment comprises the following steps: a microetching gas (e.g., including ammonia) is introduced into the process chamber in which the substrate 100 is placed to etch the surface of the film.
In this embodiment, before the performing the first atomic layer deposition process, the method includes: the surface of the first silicon nitride layer 210 is micro-etched to remove defects, particles, etc. on the surface of the first silicon nitride layer 210 (e.g., to remove crystals with poor quality on the surface, etc.), and to improve the surface of the first silicon nitride layer 210The lattice quality provides a better growth environment for the subsequent first aluminum nitride layer 310, and improves the crystal quality of the subsequently formed first aluminum nitride layer 310. In particular embodiments, ammonia (NH) may be utilized3) The surface of the first silicon nitride layer 210 is subjected to a micro-etching process.
In a specific embodiment, a plurality of atomic layer deposition processes may be performed to sequentially form a plurality of aluminum nitride films on the first silicon nitride layer 210, wherein each of the aluminum nitride films may have a thickness ranging from 1nm to 50 nm. For example, it is schematically shown in fig. 2 that three atomic layer deposition processes are performed to form three aluminum nitride films, a first aluminum nitride film 311, a second aluminum nitride film 312, and a third aluminum nitride film 313.
In the atomic layer deposition process for forming the first aluminum nitride layer 310, Trimethylaluminum (TMAL) may be used as an aluminum source, and ammonia (NH) may be used3) As a nitrogen source. And the temperature of the atomic layer deposition process can be controlled between 100 ℃ and 500 ℃.
An example is given below to specifically describe a method for forming the first aluminum nitride layer 310 by an atomic layer deposition process, which includes the following steps, for example.
In the first step, the temperature of the process chamber is set to 100-500 ℃, and then a predetermined time (e.g., 3-10 min, etc.) may be waited to keep the chamber stable and to remove undesired gas impurities, etc. from the chamber.
In the second step, a micro-etching gas (e.g., ammonia gas, etc.) is introduced into the process chamber to etch particles, incomplete crystals, etc. on the surface of the first silicon nitride layer 210. In this stage, the flow rate of the introduced micro-etching gas and the micro-etching time can be adjusted according to specific conditions, for example, the flow rate of the micro-etching gas can be controlled to be 10sccm to 500sccm, the micro-etching time can be controlled to be 1min to 5min, and then the next step is performed.
And step three, introducing aluminum source gas and nitrogen source gas to deposit an aluminum nitride film. In this embodiment, ammonia (NH) gas may be continuously introduced3) For constituting a nitrogen source, wherein the flow rate of the ammonia gas is, for example, 10sccm to 500 sccm; and, using Trimethylaluminum (TMAL) as the aluminum sourceThe flow rate of the trimethylaluminum can be adjusted to 10sccm to 500 sccm. Further, a carrier gas (e.g., nitrogen, etc.) may be introduced into the process chamber. Thus, the first atomic layer deposition process is performed, and the thickness of the first aluminum nitride film 311 is 1nm to 50 nm.
And a fourth step of stopping the introduction of the aluminum source and the nitrogen source, continuously introducing a carrier gas (such as nitrogen gas and the like), and waiting for a predetermined time (such as 3min-10min and the like) to remove gas impurities and the like in the process chamber.
Fifth, the second to third steps as described above are repeatedly performed to form a second aluminum nitride film 312 on the first aluminum nitride film 311. Namely: introducing micro etching gas (such as ammonia gas and the like) again to corrode particles, incomplete crystals and the like on the surface of the first aluminum nitride film 311; then, the continuous introduction of ammonia gas is maintained, and trimethylaluminum gas and carrier gas are introduced to form a second aluminum nitride film 312 with a thickness of 1nm to 50 nm.
If the aluminum nitride film is required to be deposited subsequently, the fourth step is executed, namely: the introduction of the aluminum source and the nitrogen source is stopped, the introduction of the carrier gas (e.g., nitrogen gas, etc.) is continued, and a predetermined time (e.g., 3min to 10min, etc.) is waited to remove the gaseous impurities from the process chamber in preparation for the next atomic deposition. When the next atomic deposition is performed, i.e., the second to third steps as described above are returned to be performed, for example, in the present embodiment, the third aluminum nitride film 313 having a thickness of 1nm to 50nm is formed by the third atomic layer deposition.
After the last atomic layer deposition, the aluminum source can be closed, the continuous introduction of the nitrogen source (such as ammonia gas and the like) and the nitrogen gas can be kept at the moment, and the set time (such as 1min-5min and the like) is waited; then, the temperature is reduced in a staged manner, for example, 20 ℃ to 80 ℃ at intervals of 1min to 5 min. Further, the nitrogen source (e.g., ammonia gas, etc.) may be turned off at any stage of the second stage-the fourth stage of the temperature decrease until the temperature is cooled. In this embodiment, after the aluminum source is turned off, ammonia gas is continuously introduced, so that on one hand, the ammonia gas can be used to micro-etch particles, incomplete crystals, and the like on the surface of the first aluminum nitride layer 310; on the other hand, the stability of the first aluminum nitride layer 310 may be improved.
Specifically, in the process of forming the first aluminum nitride layer 310, a nitrogen-containing gas, such as nitrogen and/or ammonia, is continuously introduced into the process chamber, so that the formed aluminum nitride film is always in a nitrogen-containing atmosphere, and the problem of nitrogen precipitation of the formed aluminum nitride film due to unstable performance is effectively solved. That is, a nitrogen-containing gas (e.g., a continuous flow of nitrogen and/or ammonia) is continuously introduced into the process chamber in which the substrate is disposed during the atomic layer deposition process and during the interval between adjacent atomic layer deposition processes. Moreover, after the atomic layer deposition process is completed, nitrogen is continuously introduced, and the temperature is lowered in a staged manner, so that the stability of the first aluminum nitride layer 310 formed by the atomic layer deposition process is improved.
In this embodiment, the substrate 100 at the bottom is covered with the first silicon nitride layer 210 and the first aluminum nitride layer 310 to serve as a bottom buffer layer, so that the epitaxial defect is improved and the threading dislocation is effectively reduced.
In a further aspect, the method further comprises: a second aluminum nitride layer 320, a second silicon nitride layer 220, a third aluminum nitride layer 330, and the like are sequentially formed on the first aluminum nitride layer 310.
Referring specifically to fig. 1 and 2, after the first aluminum nitride layer 310 is formed, the method further includes: the MOCVD process is performed at higher than the first predetermined temperature to form the second aluminum nitride layer 320. Wherein the first predetermined temperature is higher than a process temperature of the atomic layer deposition process, for example higher than 500 ℃.
Further, the second aluminum nitride layer 320 may be formed, for example, by: the MOCVD deposition is started at the first temperature, and the temperature is continuously increased during the deposition process until the temperature is increased to the second temperature, and then the deposition process is stopped, so that the second aluminum nitride layer 320 with gradually changing temperature (i.e., from the first temperature to the second temperature) can be formed. The process of raising the temperature from the first temperature to the second temperature may be a stepwise temperature raising method or a continuous temperature raising method. It is considered that the aluminum nitride material is transformed from the three-dimensional growth mode to the two-dimensional growth mode at the time of depositing the second aluminum nitride layer 320 to further reduce dislocation defects. Wherein the temperature range from the first temperature to the second temperature may be selected from the range of 500 ℃ to 1800 ℃, such as 600 ℃ for the first temperature, 1300 ℃ for the second temperature, and the like.
With continuing reference to fig. 1 and 2, after forming the second aluminum nitride layer 320, further comprising: an MOCVD process is performed to form the second silicon nitride layer 220. The second silicon nitride layer 220 has a pore structure to block epitaxy of the second aluminum nitride layer 320 thereunder by the second silicon nitride layer 220. Specifically, the method for forming the second silicon nitride layer 220 includes, for example: the MOCVD process is performed under the conditions that the growth temperature is 600 to 1000 ℃ and the growth pressure is 50 to 200mbar to form the second silicon nitride layer 220 having a thickness of 1 to 10 nm.
With continuing reference to fig. 1 and 2, after forming the second silicon nitride layer 220, the method further includes: an MOCVD process is performed at higher than the second predetermined temperature to form the third aluminum nitride layer 330. Wherein the second predetermined temperature may be further higher than the first predetermined temperature.
Further, the forming method of the third aluminum nitride layer 330 includes, for example: the MOCVD deposition is started at the third temperature as the starting temperature, and the temperature is continuously increased during the deposition process until the temperature is increased to the fourth temperature, and then the deposition process is stopped, so that the third aluminum nitride layer 330 with gradually changing temperature (i.e., from the third temperature to the fourth temperature) can be formed. The process of raising the temperature from the third temperature to the fourth temperature may be a stepwise temperature raising method or a continuous temperature raising method. The third temperature may be higher than the first temperature, and the fourth temperature may be higher than the second temperature, in this embodiment, the temperature range from the third temperature to the fourth temperature may be selected from a region range of 800 ℃ to 1800 ℃, for example, the third temperature is 1000 ℃, the fourth temperature is 1400 ℃, and the like.
That is, the second aluminum nitride layer 320 is transformed from the three-dimensional growth mode to the two-dimensional growth mode; the third aluminum nitride layer 330 continues to change from the three-dimensional growth mode to the two-dimensional growth mode from the second silicon nitride layer 220 in the grid shape until the two-dimensional growth mode is changed, so as to reduce dislocation defects and quickly repair the epitaxial layer, thereby forming an aluminum nitride layer with better quality.
In summary, in the preparation method of the buffer layer provided in this embodiment, the first silicon nitride layer 210 at the bottom layer can be used to better bury the defects in the substrate 100, and realize effective transition between the substrate 100 and the first aluminum nitride layer 310, so as to improve the lattice mismatch phenomenon between the substrate 100 and the first aluminum nitride layer 310, effectively relieve stress, greatly reduce the defects such as cracks and threading dislocations caused by lattice mismatch, and provide a better growth basis for the subsequent epitaxial growth.
In particular, in the preparation process of the gallium nitride epitaxial layer, aluminum nitride crystals and gallium nitride crystals have very close lattice constants and thermal expansion coefficients, so that the aluminum nitride crystals and the gallium nitride crystals are the preferred materials for the buffer layer below the aluminum nitride crystals in the epitaxial growth of the gallium nitride.
In this embodiment, the buffer layer of the epitaxial structure may be applied to a process for preparing a gallium nitride epitaxial layer. Specifically, a silicon nitride buffer layer and an aluminum nitride buffer layer may be formed on the substrate by the method described above, where the aluminum nitride buffer layer corresponds to, for example, the "first aluminum nitride layer 310" described above, or may also correspond to the "first aluminum nitride layer 310 and the second aluminum nitride layer 320" described above, or may also correspond to the "first aluminum nitride layer 310, the second aluminum nitride layer 320, and the third aluminum nitride layer 330" described above.
In a further aspect, at least one aluminum gallium nitride buffer layer (GaAlN) and at least one gallium nitride buffer layer (GaN) may be formed on the aluminum nitride buffer layer, and a gallium nitride epitaxial layer may be epitaxially grown on the gallium nitride buffer layer on the top layer. Based on this, a gallium nitride epitaxial layer with low defects can be formed.
When the gallium nitride epitaxial layer is applied to the gallium nitride-based power device, the performance of the formed power device can be improved. Namely, a method for preparing a gallium nitride-based power device specifically comprises the following steps: the preparation method of the gallium nitride epitaxial layer is adopted to form the gallium nitride epitaxial layer, and the power device is prepared on the gallium nitride epitaxial layer. The power device includes, for example, a HEMT device, i.e., a High Electron Mobility Transistor (HEMT).
It should be noted that, although the present invention has been described with reference to the preferred embodiments, the present invention is not limited to the embodiments. It will be apparent to those skilled in the art that many changes and modifications can be made, or equivalents employed, to the presently disclosed embodiments without departing from the intended scope of the invention. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the protection scope of the technical solution of the present invention, unless the content of the technical solution of the present invention is departed from.
It should be further understood that the terms "first," "second," "third," and the like in the description are used for distinguishing between various components, elements, steps, and the like, and are not intended to imply a logical or sequential relationship between various components, elements, steps, or the like, unless otherwise indicated or indicated.
It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention. It must be noted that, as used herein and in the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. For example, reference to "a step" or "an apparatus" means a reference to one or more steps or apparatuses and may include sub-steps as well as sub-apparatuses. All conjunctions used should be understood in the broadest sense. And, the word "or" should be understood to have the definition of a logical "or" rather than the definition of a logical "exclusive or" unless the context clearly dictates otherwise.

Claims (17)

1. A method for preparing a buffer layer of an epitaxial structure is characterized by comprising the following steps:
providing a substrate;
and performing at least two atomic layer deposition processes to form a first aluminum nitride layer on the substrate, and performing micro-etching treatment on the surface of the current film layer before each atomic layer deposition process.
2. A method of preparing a buffer layer of an epitaxial structure according to claim 1, characterized in that the microetching treatment comprises: and introducing micro-etching gas into the process chamber with the substrate to corrode defects and particles on the surface of the film layer.
3. The method for preparing a buffer layer of an epitaxial structure according to claim 2 wherein, before each atomic layer deposition, ammonia gas is introduced into the process chamber in which the substrate is placed, so as to perform a micro-etching treatment on the surface of the current film layer by using the ammonia gas; and continuously introducing ammonia gas and introducing an aluminum source in the process of performing the atomic layer deposition to form the aluminum nitride film.
4. The method of preparing a buffer layer for an epitaxial structure according to claim 1 wherein the substrate is always in a nitrogen-containing atmosphere during the preparation of the first aluminum nitride layer.
5. A method of preparing a buffer layer of an epitaxial structure according to claim 4 characterised in that the introduction of nitrogen and/or ammonia into the process chamber in which the substrate is placed is continued during the interval between adjacent atomic layer deposition processes.
6. The method of claim 1, wherein after the last deposition of the atomic layer is performed, the introduction of the aluminum source is stopped, and the introduction of the ammonia gas and the nitrogen gas is continued, and the temperature is lowered in a stepwise manner.
7. The method of preparing a buffer layer of an epitaxial structure of claim 1 further comprising, prior to preparing the first aluminum nitride layer: performing a chemical vapor deposition process to form a first silicon nitride layer on the substrate.
8. The method of preparing a buffer layer of an epitaxial structure according to claim 7 wherein the surface of the substrate is subjected to a microetching treatment prior to forming the first silicon nitride layer.
9. The method of preparing a buffer layer for an epitaxial structure according to any of claims 1 to 8 further comprising, after forming the first aluminum nitride layer: and performing an MOCVD process to form a second aluminum nitride layer at a temperature higher than a first predetermined temperature, which is higher than a process temperature of the atomic layer deposition process.
10. The method of preparing a buffer layer of an epitaxial structure of claim 9 wherein the method of forming the second aluminum nitride layer comprises: starting to perform MOCVD deposition by taking the first temperature as an initial temperature, continuously raising the temperature in the deposition process until the temperature is raised to a second temperature, and stopping the deposition process to form the second aluminum nitride layer.
11. The method of preparing a buffer layer for an epitaxial structure of claim 9 further comprising, after forming the second aluminum nitride layer: and performing an MOCVD process to form a second silicon nitride layer on the second aluminum nitride layer, wherein a pore structure is formed in the second silicon nitride layer.
12. The method of preparing a buffer layer for an epitaxial structure of claim 11 further comprising, after forming the second silicon nitride layer: and performing an MOCVD process to form a third aluminum nitride layer at a temperature higher than a second predetermined temperature, which is higher than the first predetermined temperature.
13. The method of preparing a buffer layer of an epitaxial structure of claim 12 wherein the third aluminum nitride layer is formed by a method comprising: starting to perform MOCVD deposition by taking the third temperature as an initial temperature, continuously raising the temperature in the deposition process until the temperature is raised to the fourth temperature, and stopping the deposition process to form the third aluminum nitride layer.
14. A method for preparing a gallium nitride epitaxial layer is characterized by comprising the following steps: forming an aluminum nitride buffer layer on a substrate and forming a gallium nitride epitaxial layer on the aluminum nitride buffer layer by using the manufacturing method according to any one of claims 1 to 13.
15. The method for preparing a gallium nitride epitaxial layer according to claim 14, further comprising: and forming at least one layer of gallium nitride aluminum buffer layer and at least one layer of gallium nitride buffer layer on the aluminum nitride buffer layer, and epitaxially growing a gallium nitride epitaxial layer on the gallium nitride buffer layer at the top layer.
16. A preparation method of a gallium nitride-based power device is characterized by comprising the following steps: forming a gallium nitride epitaxial layer by the method for preparing a gallium nitride epitaxial layer according to claim 14 or 15, and preparing a power device on the gallium nitride epitaxial layer.
17. The method of fabricating a gallium nitride-based power device according to claim 16, wherein the power device comprises a HEMT device.
CN202210249322.4A 2022-03-14 2022-03-14 Preparation method of buffer layer of epitaxial structure and preparation method of gallium nitride epitaxial layer Pending CN114743876A (en)

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