CN117637442A - Ultrathin aluminum nitride single crystal composite substrate, preparation method thereof and ultraviolet light-emitting device - Google Patents
Ultrathin aluminum nitride single crystal composite substrate, preparation method thereof and ultraviolet light-emitting device Download PDFInfo
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- PMHQVHHXPFUNSP-UHFFFAOYSA-M copper(1+);methylsulfanylmethane;bromide Chemical compound Br[Cu].CSC PMHQVHHXPFUNSP-UHFFFAOYSA-M 0.000 title claims abstract description 171
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Abstract
An ultrathin aluminum nitride single crystal composite substrate, a preparation method thereof and an ultraviolet light-emitting device belong to the field of composite material preparation. The preparation method comprises the following steps: treating the c-axis oriented sapphire substrate with oxygen plasma to form a modified layer on the surface of the sapphire substrate; depositing a polycrystalline aluminum nitride film layer with the thickness of 30-100 nm on the modified layer, annealing at a high temperature to recrystallize the polycrystalline aluminum nitride, and cooling to obtain an ultrathin aluminum nitride single crystal composite substrate; the surface of the sapphire substrate with the c-axis orientation is treated by oxygen plasma, and the thickness of the polycrystalline aluminum nitride film layer is controlled, so that after the ultra-thin polycrystalline aluminum nitride film layer is annealed and recrystallized at high temperature, the high-quality monocrystalline aluminum nitride film layer which has no black spots and good interface stability can be obtained, and the stress state of the obtained monocrystalline aluminum nitride film layer is tensile stress, so that the tensile stress state is favorable for realizing the subsequent epitaxial preparation of the ultraviolet/deep ultraviolet band light-emitting diode.
Description
Technical Field
The application relates to the field of composite material preparation, in particular to an ultrathin aluminum nitride single crystal composite substrate, a preparation method thereof and an ultraviolet light-emitting device.
Background
Aluminum nitride is yet another wide bandgap semiconductor material with excellent properties following gallium nitride.
However, because the preparation difficulty of the aluminum nitride single crystal bulk material is high and the yield is low, the large-scale industrial application of the aluminum nitride single crystal bulk material is still limited, and particularly, the ultra-thin aluminum nitride single crystal composite substrate (the thickness of a single crystal aluminum nitride film layer in the ultra-thin aluminum nitride single crystal composite substrate is 100 nm) prepared by adopting a high-temperature annealing recrystallization mode has black spots, so that the quality of the ultra-thin aluminum nitride single crystal composite substrate is poor, the interface is unstable and the reliability is poor.
The aluminum nitride has the forbidden band width of 6.2eV and the direct band gap characteristic, so that the aluminum nitride has excellent application prospect in an ultraviolet light-emitting device. For the light-emitting diode with middle ultraviolet/deep ultraviolet band, the high-quality aluminum nitride single crystal substrate is the base of the bottom layer material, and the aluminum nitride single crystal composite substrate prepared by high-temperature annealing recrystallization has strong compressive stress, so that the growth difficulty of the ultraviolet light-emitting device region is increased, the surface of the ultraviolet light-emitting device region is extremely easy to coarsen, the aluminum nitride single crystal composite substrate with tensile stress is highly required to regulate the epitaxial growth of the ultraviolet light-emitting device, and the growth of the aluminum nitride buffer layer region becomes a non-negligible cost source in the deep ultraviolet photoelectric device particularly because the preparation difficulty of aluminum nitride is higher.
Therefore, how to realize the stress state matching and high-quality ultrathin aluminum nitride single crystal composite substrate is an important technical approach in the field of ultraviolet light emitting devices.
Disclosure of Invention
The application provides an ultrathin aluminum nitride single crystal composite substrate, a preparation method thereof and an ultraviolet light-emitting device, which can relieve the technical problems that the quality of the ultrathin aluminum nitride single crystal composite substrate prepared and obtained by the existing high-temperature annealing recrystallization method is poor and the stress state is not in a tensile stress state.
Embodiments of the present application are implemented as follows:
in a first aspect, the present application provides a method for preparing an ultrathin aluminum nitride single crystal composite substrate, comprising: treating the c-axis oriented sapphire substrate with oxygen plasma to form a modified layer on the surface of the sapphire substrate;
depositing a polycrystalline aluminum nitride film layer on the modified layer, performing high-temperature annealing to recrystallize the polycrystalline aluminum nitride into a monocrystalline aluminum nitride film layer, and cooling to obtain an ultrathin aluminum nitride monocrystalline composite substrate;
wherein the thickness of the polycrystalline aluminum nitride film layer is 30nm-100nm.
According to the preparation method of the ultrathin aluminum nitride single crystal composite substrate, the surface of the sapphire substrate with the c-axis orientation is treated by utilizing oxygen plasma before the polycrystalline aluminum nitride film is deposited, and the thickness of the polycrystalline aluminum nitride film is controlled, so that after the ultrathin polycrystalline aluminum nitride film is annealed and recrystallized at a high temperature, the high-quality single crystal aluminum nitride film which has no black spots and good interface stability can be obtained, the stress state of the obtained single crystal aluminum nitride film is tensile stress, the tensile stress state is favorable for realizing the epitaxial preparation of a subsequent middle ultraviolet/deep ultraviolet band light-emitting diode, the growth difficulty of a middle ultraviolet/deep ultraviolet band light-emitting diode region is effectively reduced, the quality of the light-emitting diode region is improved, the preparation method is applicable to industrial production, and the manufacturing cost is effectively reduced.
In some embodiments, the polycrystalline aluminum nitride film layer has a thickness of 30nm to 70nm.
In some embodiments, the oxygen plasma treatment is performed at a chamber vacuum of 0.1Pa-1Pa using pure oxygen gas as an oxygen source gas, wherein the treatment temperature is room temperature and the treatment time is 1min-10min.
In some embodiments, the high temperature anneal is a nitrogen ambient atmosphere for an anneal time of 1500 ℃ to 1800 ℃ and for an anneal time of 1h to 5h.
In some embodiments, the cooling is furnace-wise cooling while maintaining an atmospheric nitrogen atmosphere.
In some embodiments, the method of making comprises: before the sapphire substrate is treated by oxygen plasma, impurities on the surface of the sapphire substrate are removed.
In some embodiments, the polycrystalline aluminum nitride film is prepared using physical vapor deposition.
In a second aspect, the present examples provide an ultra-thin aluminum nitride single crystal composite substrate made by the preparation method provided in the first aspect of the present application; wherein the stress state of the single crystal aluminum nitride film layer is a tensile stress state.
The ultrathin aluminum nitride single crystal composite substrate prepared by the preparation method has the advantages that the single crystal aluminum nitride film layer has better interface stability and high quality, and the stress state is a tensile stress state, so that the epitaxial preparation of the subsequent middle ultraviolet/deep ultraviolet band light-emitting diode is realized, the growth difficulty of the middle ultraviolet/deep ultraviolet band light-emitting diode region is effectively reduced, and the quality of the region is improved.
In some embodiments, the surface state of the single crystal aluminum nitride film layer is atomic step state and the step height is less than or equal to 1nm, and the dislocation density of the single crystal aluminum nitride film layer is 10 7 cm -2 -10 10 cm -2 In the interval, the surface roughness RMS is less than or equal to 0.5nm.
In a third aspect, the present application provides an ultraviolet light emitting device, which includes the ultrathin aluminum nitride single crystal composite substrate provided in each embodiment, and the ultraviolet light emitting device is a mid-ultraviolet band light emitting diode or a deep-ultraviolet band light emitting diode.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered limiting the scope, and that other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic flow chart of a method for preparing an ultrathin aluminum nitride single crystal composite substrate;
FIG. 2 is a graph showing the performance test of the ultra-thin aluminum nitride single crystal composite substrate prepared in example 1;
FIG. 3 is a graph showing the performance test of the ultra-thin aluminum nitride single crystal composite substrate prepared in example 3;
FIG. 4 is a mirror image of a single crystal aluminum nitride film layer in the ultra-thin aluminum nitride single crystal composite substrate prepared in comparative example 1;
FIG. 5 is a graph showing test results of comparative example 2 for preparing an ultra-thin aluminum nitride composite substrate;
FIG. 6 is a graph showing the test results of comparative example 3 for preparing an aluminum nitride single crystal composite substrate.
Detailed Description
Embodiments of the present application will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only for illustration of the present application and should not be construed as limiting the scope of the present application. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
The inventor researches find that in the ultrathin aluminum nitride single crystal composite substrate prepared by adopting a high-temperature annealing recrystallization mode, the reason that black spots appear on the single crystal aluminum nitride film layer is as follows: the thickness of the aluminum nitride film layer in the ultrathin aluminum nitride single crystal composite substrate is too thin, so that the aluminum nitride film layer cannot be decomposed on the surface of the substrate in the high-temperature annealing recrystallization process, bubbling occurs due to the decomposition of the surface of the substrate, black spots in the single crystal aluminum nitride film layer are formed, and the quality of the single crystal aluminum nitride film layer is reduced. In the actual operation process, the inventor finds that the stress state is related to the thickness of the aluminum nitride film layer, and the stress state of the finally formed single crystal aluminum nitride film layer can be effectively controlled by controlling the thickness of the aluminum nitride film layer, so that the stress state is matched with the stress required by the light emitting diode in the middle ultraviolet/deep ultraviolet band.
Based on this, the present application is hereby presented.
The following specifically describes an ultrathin aluminum nitride single crystal composite substrate, a preparation method thereof and an ultraviolet light emitting device according to an embodiment of the application:
as shown in fig. 1, the present application example provides a method for preparing an ultrathin aluminum nitride single crystal composite substrate, which includes:
the c-axis oriented sapphire substrate was treated with oxygen plasma to form a modified layer on the surface of the sapphire substrate.
Depositing a polycrystalline aluminum nitride film layer on the modified layer, performing high-temperature annealing to recrystallize the polycrystalline aluminum nitride into a monocrystalline aluminum nitride film layer, and cooling to obtain an ultrathin aluminum nitride monocrystalline composite substrate;
wherein the thickness of the polycrystalline aluminum nitride film layer is 30nm-100nm.
When the thickness of the polycrystalline aluminum nitride film layer is smaller than 30nm, the polycrystalline aluminum nitride film layer is easy to cause that the polycrystalline aluminum nitride film layer cannot form a single crystal aluminum nitride film layer after high-temperature annealing and an ultrathin aluminum nitride single crystal composite substrate cannot be prepared, so that the thickness of the polycrystalline aluminum nitride film layer is more than or equal to 30nm. In the practical operation process, the inventor finds that the stress state of the multi-single crystal aluminum nitride film layer is related to the thickness of the aluminum nitride film layer, when the thickness of the polycrystalline aluminum nitride film layer is less than or equal to 100nm, the stress state of the prepared single crystal aluminum nitride film layer is tensile stress, and when the thickness is more than 100nm, for example, the thickness is 200nm, the stress state of the prepared single crystal aluminum nitride film layer is compressive stress due to the excessive thickness. Based on the above consideration, the thickness of the polycrystalline aluminum nitride film layer is 30nm-100nm, and the monocrystalline aluminum nitride film layer can be formed in the high-temperature annealing recrystallization process and the stress state is tensile stress.
Illustratively, the polycrystalline aluminum nitride film layer has a thickness of any one of 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm or between any two values.
When the thickness of the polycrystalline aluminum nitride film layer is 30nm-100nm, the surface decomposition of the sapphire substrate cannot be pressed in the high-temperature annealing recrystallization process due to the fact that the thickness is too thin, so that bubbling is easily caused in the high-temperature annealing recrystallization process due to the substrate decomposition, black spots in the monocrystalline aluminum nitride film layer are formed, and the quality of the monocrystalline aluminum nitride film layer is reduced.
The sapphire can be used as a substrate after surface polishing treatment, the polishing can cause the problems that micro-area lattice damage is generated on the surface of the sapphire, and the like, and the component of the sapphire substrate is corundum (aluminum oxide), so that oxygen plasma treatment is adopted, on one hand, impurities can not be introduced into the surface of the sapphire substrate, on the other hand, the surface lattice of the sapphire is firmer, micro-area lattice damage and the like on the surface of the sapphire can be effectively repaired, the polished surface of the sapphire is more stable and is not easy to decompose at high temperature, the preparation of the ultrathin aluminum nitride single crystal composite substrate is realized even in a high-temperature annealing recrystallization mode, the surface decomposition of the substrate is not caused, black spots exist in the formed ultrathin single crystal aluminum nitride film layer, and the quality and interface stability of the ultrathin single crystal aluminum nitride film layer are effectively improved.
In summary, according to the preparation method of the ultrathin aluminum nitride single crystal composite substrate, the surface of the sapphire substrate with the c-axis orientation is treated by utilizing oxygen plasma before the polycrystalline aluminum nitride film is deposited, and the thickness of the polycrystalline aluminum nitride film is controlled, so that after the ultrathin polycrystalline aluminum nitride film is annealed and recrystallized at a high temperature, the high-quality single crystal aluminum nitride film with no black spots and good interface stability can be obtained, the stress state of the obtained single crystal aluminum nitride film is tensile stress, the tensile stress state is favorable for realizing the epitaxial preparation of the subsequent ultraviolet/deep ultraviolet band light-emitting diode, the growth difficulty of the region of the ultraviolet/deep ultraviolet band light-emitting diode is effectively reduced, the quality of the region of the ultraviolet/deep ultraviolet band light-emitting diode is improved, and the preparation method is applicable to industrial production, and the manufacturing cost is effectively reduced.
The diameter of the sapphire substrate includes, but is not limited to, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 inches, etc., and the thickness of the sapphire substrate may be selected according to practical requirements, for example, 300-600 μm, etc.
The polycrystalline aluminum nitride film layer can be formed by adopting a physical vapor deposition method.
Physical vapor deposition (PVD for short) is a process in which a metal, alloy, or compound is vaporized (or sputtered) in a vacuum chamber to deposit the vapor atoms or molecules onto the surface of a workpiece under certain conditions. Reference is made in particular to the related art by controlling specific parameters to achieve the preparation of the amorphous phase.
Physical vapor deposition methods include, but are not limited to, any thin film material growth means, such as magnetron sputtering, reactive magnetron sputtering, molecular beam epitaxy, etc., and those skilled in the art can select according to practical requirements without limitation. Illustratively, the polycrystalline aluminum nitride film layer is prepared by a reactive magnetron sputtering method, wherein the target used in the reactive magnetron sputtering method is an aluminum target with purity of 99.9999% so as to avoid introducing impurities. Specific parameters adopted in the reactive magnetron sputtering method can refer to the related technology, so long as the crystal structure of the deposited aluminum nitride film layer is ensured to be polycrystal.
In some embodiments, the polycrystalline aluminum nitride film layer has a thickness of 30-70nm.
The thickness of the polycrystalline aluminum nitride film layer is controlled within the range, so that the stress state of the prepared ultrathin aluminum nitride single crystal composite substrate is tensile stress, the tensile stress state is favorable for realizing the subsequent epitaxial preparation of the light-emitting diode in the middle ultraviolet/deep ultraviolet band, the growth difficulty of the light-emitting diode in the middle ultraviolet/deep ultraviolet band is effectively reduced, the quality of the light-emitting diode in the middle ultraviolet/deep ultraviolet band is improved, the preparation method is suitable for industrial production, and the preparation cost is effectively reduced.
Illustratively, the polycrystalline aluminum nitride film layer has a thickness of any one of 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm or between any two values.
Oxygen plasma treatment includes treatment with pure oxygen in a plasma machine.
In some embodiments, the oxygen plasma treatment is performed at a chamber vacuum of 0.1Pa-1Pa using pure oxygen gas as an oxygen source gas, wherein the treatment temperature is room temperature and the treatment time is 1min-10min.
It is understood that the above-described chamber refers to a chamber in which a sapphire substrate to be processed is placed in a plasma machine.
The treatment time is limited to 1min-10min because the treatment effect after the treatment time is higher than 10min is almost the same as that after the treatment time is 10min.
The oxygen plasma treatment effect is good, and the sapphire substrate can be effectively restrained from being decomposed during high-temperature annealing recrystallization.
In some embodiments, the high temperature anneal is a nitrogen ambient atmosphere for an anneal time of 1500 ℃ to 1800 ℃ and for an anneal time of 1h to 5h.
Within the above range, the polycrystalline aluminum nitride film layer can be effectively recrystallized to form a single crystal aluminum nitride film layer.
Illustratively, the annealing time is any one value or between any two values of 1500 ℃, 1550 ℃, 1600 ℃, 1650 ℃,1700 ℃, 1750 ℃, 1800 ℃. The annealing time is any one value or between any two values of 1h, 2h, 3h, 4h and 5h, and the annealing time can be selected according to the actual film thickness and the annealing temperature.
In some embodiments, the cooling is furnace-wise cooling while maintaining an atmospheric nitrogen atmosphere.
That is, heating intervention is not needed, and the preparation difficulty is effectively reduced.
In some embodiments, the method of making comprises: before the sapphire substrate is treated by oxygen plasma, impurities on the surface of the sapphire substrate are removed.
The method for removing the impurities on the surface of the sapphire substrate comprises the following steps: sequentially ultrasonically cleaning by adopting an acetone solution, an ethanol solution and deionized water, respectively ultrasonically cleaning for 10min, fishing out, and drying by using nitrogen to keep the surface clean. Through the treatment, the cleanliness of the surface of the sapphire substrate is ensured, and the introduction of impurities is avoided.
The application example provides an ultrathin aluminum nitride single crystal composite substrate, which is prepared by the preparation methods provided by the schemes; wherein the stress state of the single crystal aluminum nitride film layer is a tensile stress state.
That is, the ultrathin aluminum nitride single crystal composite substrate prepared by the preparation method has the advantages that the single crystal aluminum nitride film layer has better interface stability and high quality, and the stress state is tensile stress state, so that the subsequent epitaxial preparation of the light emitting diode in the middle ultraviolet/deep ultraviolet band is facilitated, the growth difficulty of the light emitting diode region in the middle ultraviolet/deep ultraviolet band is effectively reduced, and the quality of the light emitting diode region in the middle ultraviolet/deep ultraviolet band is improved.
In some embodiments, the thickness of the single crystal aluminum nitride film layer is 30nm-70nm, the surface state of the single crystal aluminum nitride film layer is in an atomic step state and the step height is less than or equal to 1nm, and the dislocation density of the single crystal aluminum nitride film layer is 10 7 cm -2 -10 10 cm -2 In the interval, the surface roughness RMS is less than or equal to 0.5nm.
The application example also provides an ultraviolet light-emitting device, which comprises the ultrathin aluminum nitride single crystal composite substrate, wherein the ultraviolet light-emitting device is a middle ultraviolet band light-emitting diode or a deep ultraviolet band light-emitting diode (simply called as a middle ultraviolet/deep ultraviolet band light-emitting diode).
The ultra-thin aluminum nitride single crystal composite substrate, the method of manufacturing the same, and the ultraviolet light emitting device of the present application are described in further detail below with reference to examples.
Example 1
The preparation method of the ultrathin aluminum nitride single crystal composite substrate with the thickness of the single crystal aluminum nitride film layer of 50nm comprises the following steps:
1) Selecting a 2-inch c tangential single-polishing sapphire substrate, wherein the thickness of the sapphire substrate is 430 mu m, chemically cleaning the sapphire substrate, blow-drying the sapphire substrate by nitrogen, and ultrasonically cleaning the sapphire substrate by adopting an acetone solution, an ethanol solution and deionized water in sequence, respectively ultrasonically cleaning the sapphire substrate for 10min, and blow-drying the sapphire substrate by nitrogen after fishing out to keep the surface clean;
2) And (3) treating the surface of the cleaned sapphire substrate by utilizing an oxygen plasma bombardment technology, wherein the vacuum degree of a cavity is 0.5Pa, the treatment temperature is room temperature, the oxygen flow is 30sccm, the surface treatment time of the sapphire substrate is 5min, the treatment power is 2kW, and the sapphire substrate after oxygen plasma treatment is obtained.
3) Growing an aluminum nitride film on the surface of the sapphire substrate subjected to oxygen plasma treatment by utilizing reactive magnetron sputtering, wherein the thickness is 50nm, sputtering gas is mixed gas of nitrogen and argon, the flow rate of the argon is 30sccm, the flow rate of the nitrogen is 200sccm, the vacuum degree of a cavity is 0.8Pa, the sputtering power is 3500W, and the sputtering temperature is 700 ℃;
4) Placing the composite substrate after preparing 50nm aluminum nitride in a high-temperature annealing furnace device, wherein the atmosphere environment of the device is a normal-pressure nitrogen environment, the annealing temperature is set to 1700 ℃, the heating rate is 10 ℃/min, the carrier material is graphite material, and the temperature is kept for 1h at 1700 ℃.
5) After the annealing is finished, taking out the annealed ultrathin aluminum nitride single crystal composite substrate after natural cooling, and cleaning and drying;
FIG. 2 is a graph showing the performance test of the ultra-thin aluminum nitride single crystal composite substrate prepared in example 1, wherein part a in FIG. 2 is the (002) and (102) crystal face rocking curves of the ultra-thin aluminum nitride single crystal composite substrate, and according to the X-ray diffraction rocking curve test, the half widths of the (002) and (102) crystal face rocking curves of the samples obtained in example 1 are 282arcsec and 492arcsec, respectively, and are in a single crystal state. The part b in fig. 2 shows the optical lens result, and according to the optical lens result, the obtained sample has a flat surface and no black spot, which indicates that no sapphire decomposition phenomenon occurs. In FIG. 2, part c is a scanning image of the surface of the monocrystalline aluminum nitride film by a microscope, and the surface state of the film is atomic step state, the step height of the monocrystalline aluminum nitride film is less than or equal to 1nm, and the surface roughness RMS is less than or equal to 0.5nm. In fig. 2, the part d is a stress state diagram, and it can be seen that the stress state of the single crystal aluminum nitride film layer is tensile stress.
Example 2
It differs from example 1 only in that:
3) And growing an aluminum nitride film on the surface of the sapphire substrate subjected to oxygen plasma treatment by utilizing reactive magnetron sputtering, wherein the thickness is 30nm.
The sample obtained in example 2 was flat and free of black spots and was single crystal.
Example 3
It differs from example 1 only in that:
3) And growing an aluminum nitride film on the surface of the sapphire substrate subjected to oxygen plasma treatment by utilizing reactive magnetron sputtering, wherein the thickness is 100nm.
The sample obtained in example 3 was flat and free of black spots. Fig. 3 is a graph showing the performance test of the ultrathin aluminum nitride single crystal composite substrate prepared in example 3, and it can be seen that the stress state of the single crystal aluminum nitride film layer is tensile stress.
Comparative example 1
The preparation method of the aluminum nitride single crystal composite substrate comprises the following steps:
1) Selecting a 2-inch c tangential single-polishing sapphire substrate, wherein the thickness of the sapphire substrate is 430 mu m, chemically cleaning the sapphire substrate, blow-drying the sapphire substrate by nitrogen, and ultrasonically cleaning the sapphire substrate by adopting an acetone solution, an ethanol solution and deionized water in sequence, respectively ultrasonically cleaning the sapphire substrate for 10min, and blow-drying the sapphire substrate by nitrogen after fishing out to keep the surface clean;
2) Growing an aluminum nitride film on the surface of the sapphire substrate which is cleaned and dried by utilizing reactive magnetron sputtering, wherein the thickness is 50nm, sputtering gas is mixed gas of nitrogen and argon, the flow rate of the argon is 30sccm, the flow rate of the nitrogen is 200sccm, the vacuum degree of a cavity is 0.8Pa, the sputtering power is 3500W, and the sputtering temperature is 700 ℃;
3) Placing the composite substrate after preparing 50nm aluminum nitride in a high-temperature annealing furnace device, wherein the atmosphere environment of the device is a normal-pressure nitrogen environment, the annealing temperature is set to 1700 ℃, the heating rate is 10 ℃/min, the carrier material is graphite material, and the temperature is kept for 1h at 1700 ℃.
4) After the annealing is finished, taking out the annealed ultrathin aluminum nitride single crystal composite substrate after natural cooling, and cleaning and drying;
the tensile stress of the single crystal aluminum nitride film layer in the ultra-thin aluminum nitride single crystal composite substrate prepared in comparative example 1 is shown in fig. 4, which is a mirror image of the single crystal aluminum nitride film layer in the ultra-thin aluminum nitride single crystal composite substrate prepared in comparative example 1, and as can be seen from fig. 4, black spots appear on the surface of the sample obtained in comparative example 1, thus indicating that the substrate decomposition occurs during annealing of the sapphire on which has not undergone oxygen plasma treatment surface, and thus bubbling occurs, forming black spots, thus indicating the importance of oxygen plasma treatment in preparing the ultra-thin aluminum nitride single crystal composite substrate.
Comparative example 2
The preparation method of the ultrathin aluminum nitride composite substrate comprises the following steps:
1) Selecting a 2-inch c tangential single-polishing sapphire substrate, wherein the thickness of the sapphire substrate is 430 mu m, chemically cleaning the sapphire substrate, blow-drying the sapphire substrate by nitrogen, and ultrasonically cleaning the sapphire substrate by adopting an acetone solution, an ethanol solution and deionized water in sequence, respectively ultrasonically cleaning the sapphire substrate for 10min, and blow-drying the sapphire substrate by nitrogen after fishing out to keep the surface clean;
2) Treating the surface of the cleaned sapphire substrate by utilizing an oxygen plasma bombardment technology, wherein the vacuum degree of a cavity is 0.5Pa, the treatment temperature is room temperature, the oxygen flow is 30sccm, the surface treatment time of the sapphire substrate is 5min, the treatment power is 2kW, and the sapphire substrate after oxygen plasma treatment is obtained;
3) Growing an aluminum nitride film on the surface of the sapphire substrate subjected to oxygen plasma treatment by utilizing reactive magnetron sputtering, wherein the thickness is 25nm, sputtering gas is a mixed gas of nitrogen and argon, the flow rate of the argon is 30sccm, the flow rate of the nitrogen is 200sccm, the vacuum degree of a cavity is 0.8Pa, the sputtering power is 3500W, and the sputtering temperature is 700 ℃;
4) Placing the composite substrate after preparing the 25nm aluminum nitride in a high-temperature annealing furnace device, wherein the atmosphere environment of the device is a normal-pressure nitrogen environment, the annealing temperature is set to 1700 ℃, the heating rate is 10 ℃/min, the carrier material is graphite material, and the temperature is kept for 1h at 1700 ℃.
5) After the annealing is finished, taking out the annealed 25nm ultrathin aluminum nitride composite substrate after natural cooling, and cleaning and drying;
FIG. 5 is a graph showing the test results of the ultra-thin aluminum nitride composite substrate prepared in comparative example 2, in which the diffraction peak is not seen in the diffraction crystal plane of aluminum nitride (002) as shown in part a of FIG. 5, and the result of the transmission electron microscope in part b of FIG. 5 shows that the sample obtained in comparative example 2 is in a polycrystalline state, not in a single crystal state, thus indicating that the formation of an aluminum nitride single crystal film cannot be ensured due to the excessively thin thickness of the aluminum nitride film.
Comparative example 3
The preparation method of the aluminum nitride single crystal composite substrate with the thickness of the single crystal aluminum nitride film layer of 200nm comprises the following steps:
1) Selecting a 2-inch c tangential single-polishing sapphire substrate, wherein the thickness of the sapphire substrate is 430 mu m, chemically cleaning the sapphire substrate, blow-drying the sapphire substrate by nitrogen, and ultrasonically cleaning the sapphire substrate by adopting an acetone solution, an ethanol solution and deionized water in sequence, respectively ultrasonically cleaning the sapphire substrate for 10min, and blow-drying the sapphire substrate by nitrogen after fishing out to keep the surface clean;
2) Treating the surface of the cleaned sapphire substrate by utilizing an oxygen plasma bombardment technology, wherein the vacuum degree of a cavity is 0.5Pa, the treatment temperature is room temperature, the oxygen flow is 30sccm, the surface treatment time of the sapphire substrate is 5min, the treatment power is 2kW, and the sapphire substrate after oxygen plasma treatment is obtained;
3) Growing an aluminum nitride film on the surface of the sapphire substrate subjected to oxygen plasma treatment by utilizing reactive magnetron sputtering, wherein the thickness is 200nm, sputtering gas is a mixed gas of nitrogen and argon, the flow rate of the argon is 30sccm, the flow rate of the nitrogen is 200sccm, the vacuum degree of a cavity is 0.8Pa, the sputtering power is 3500W, and the sputtering temperature is 700 ℃;
4) Placing the composite substrate after preparing the 25nm aluminum nitride in a high-temperature annealing furnace device, wherein the atmosphere environment of the device is a normal-pressure nitrogen environment, the annealing temperature is set to 1700 ℃, the heating rate is 10 ℃/min, the carrier material is graphite material, and the temperature is kept for 1h at 1700 ℃.
5) After the annealing is finished, taking out the annealed 200nm aluminum nitride single crystal composite substrate after natural cooling, and cleaning and drying;
FIG. 6 is a graph showing the performance test of the aluminum nitride single crystal composite substrate prepared in comparative example 3.
As can be seen from fig. 6, although the half-widths of the (002) and (102) crystal plane rocking curves of the obtained samples shown in the left-hand drawing of fig. 6 are 73arcsec and 242arcsec, respectively, the obtained samples are in a single crystal state, but as can be seen from the right-hand drawing of fig. 6, they are in a compressive stress state, and in practical application, a serious roughening phenomenon occurs on the surface of the mid uv/deep uv light emitting diode which is used as the subsequent epitaxy of the substrate, which means that an excessive thickness of the aluminum nitride film layer can cause the aluminum nitride stress state to exhibit a significant compressive stress state, and is not suitable for the tensile stress state of the downstream mid uv/deep uv photodiode epitaxy.
The foregoing is merely a specific embodiment of the present application and is not intended to limit the application, and various modifications and variations may be made to the present application by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.
Claims (10)
1. The preparation method of the ultrathin aluminum nitride single crystal composite substrate is characterized by comprising the following steps of:
treating the c-axis oriented sapphire substrate with oxygen plasma to form a modified layer on the surface of the sapphire substrate;
depositing a polycrystalline aluminum nitride film layer on the modified layer, performing high-temperature annealing to recrystallize the polycrystalline aluminum nitride into a monocrystalline aluminum nitride film layer, and cooling to obtain an ultrathin aluminum nitride monocrystalline composite substrate;
wherein the thickness of the polycrystalline aluminum nitride film layer is 30nm-100nm.
2. The method of claim 1, wherein the polycrystalline aluminum nitride film layer has a thickness of 30nm to 70nm.
3. The method according to claim 1, wherein the oxygen plasma treatment is performed at a chamber vacuum of 0.1Pa to 1Pa using pure oxygen gas as an oxygen source gas, wherein the treatment temperature is room temperature and the treatment time is 1min to 10min.
4. A method according to any one of claims 1 to 3, wherein the high temperature annealing atmosphere is a nitrogen atmospheric atmosphere, the annealing time is 1500 ℃ to 1800 ℃, and the annealing time is 1h to 5h.
5. The method according to claim 4, wherein the cooling is carried out in a furnace while maintaining an atmospheric nitrogen atmosphere.
6. A method of preparation according to any one of claims 1 to 3, wherein the method of preparation comprises: and removing impurities on the surface of the sapphire substrate before the sapphire substrate is treated by adopting the oxygen plasma.
7. A method according to any one of claims 1 to 3, wherein the polycrystalline aluminum nitride film is produced by physical vapor deposition.
8. An ultrathin aluminum nitride single crystal composite substrate, characterized by being produced by the production method according to any one of claims 1 to 7;
wherein the stress state of the single crystal aluminum nitride film layer is a tensile stress state.
9. The ultra-thin aluminum nitride single crystal composite substrate according to claim 8, wherein the surface state of the single crystal aluminum nitride film layer is atomic step state and the step height is 1nm or less, and the dislocation density of the single crystal aluminum nitride film layer is 10 7 cm -2 -10 10 cm -2 In the interval, the surface roughness RMS is less than or equal to 0.5nm.
10. An ultraviolet light-emitting device, characterized by comprising the ultrathin aluminum nitride single crystal composite substrate according to any one of claims 8-9, wherein the ultraviolet light-emitting device is a medium ultraviolet band light-emitting diode or a deep ultraviolet band light-emitting diode.
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