CN117587510A - Epitaxial structure for forming high-quality AlN film, preparation method and application - Google Patents
Epitaxial structure for forming high-quality AlN film, preparation method and application Download PDFInfo
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- 238000002360 preparation method Methods 0.000 title claims abstract description 23
- 239000000758 substrate Substances 0.000 claims abstract description 58
- 239000010408 film Substances 0.000 claims description 83
- 238000000034 method Methods 0.000 claims description 62
- 238000005229 chemical vapour deposition Methods 0.000 claims description 17
- 238000000137 annealing Methods 0.000 claims description 16
- 239000000463 material Substances 0.000 claims description 16
- 229910052594 sapphire Inorganic materials 0.000 claims description 16
- 239000010980 sapphire Substances 0.000 claims description 16
- 239000010409 thin film Substances 0.000 claims description 13
- 229910052782 aluminium Inorganic materials 0.000 claims description 9
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 9
- 239000004065 semiconductor Substances 0.000 claims description 9
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 6
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 6
- 230000007547 defect Effects 0.000 claims description 6
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 3
- 229910021529 ammonia Inorganic materials 0.000 claims description 3
- 239000001257 hydrogen Substances 0.000 claims description 3
- 229910052739 hydrogen Inorganic materials 0.000 claims description 3
- 229910052757 nitrogen Inorganic materials 0.000 claims description 3
- 238000004519 manufacturing process Methods 0.000 claims description 2
- PMHQVHHXPFUNSP-UHFFFAOYSA-M copper(1+);methylsulfanylmethane;bromide Chemical compound Br[Cu].CSC PMHQVHHXPFUNSP-UHFFFAOYSA-M 0.000 description 226
- 230000008569 process Effects 0.000 description 19
- 230000000052 comparative effect Effects 0.000 description 13
- 230000003746 surface roughness Effects 0.000 description 11
- 238000006243 chemical reaction Methods 0.000 description 10
- 238000002488 metal-organic chemical vapour deposition Methods 0.000 description 9
- JLTRXTDYQLMHGR-UHFFFAOYSA-N trimethylaluminium Chemical group C[Al](C)C JLTRXTDYQLMHGR-UHFFFAOYSA-N 0.000 description 7
- 238000009826 distribution Methods 0.000 description 6
- 238000001816 cooling Methods 0.000 description 5
- 238000005240 physical vapour deposition Methods 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- 230000008859 change Effects 0.000 description 3
- 239000013078 crystal Substances 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 238000005498 polishing Methods 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 238000004544 sputter deposition Methods 0.000 description 3
- 238000002441 X-ray diffraction Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
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- 238000010438 heat treatment Methods 0.000 description 2
- 239000013067 intermediate product Substances 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 238000012876 topography Methods 0.000 description 2
- PIGFYZPCRLYGLF-UHFFFAOYSA-N Aluminum nitride Chemical compound [Al]#N PIGFYZPCRLYGLF-UHFFFAOYSA-N 0.000 description 1
- 238000004630 atomic force microscopy Methods 0.000 description 1
- 238000010923 batch production Methods 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 230000032798 delamination Effects 0.000 description 1
- 238000000151 deposition Methods 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000001534 heteroepitaxy Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
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- 238000000926 separation method Methods 0.000 description 1
- 239000013077 target material Substances 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 238000007740 vapor deposition Methods 0.000 description 1
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- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/12—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a stress relaxation structure, e.g. buffer layer
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
- C30B25/02—Epitaxial-layer growth
- C30B25/18—Epitaxial-layer growth characterised by the substrate
- C30B25/183—Epitaxial-layer growth characterised by the substrate being provided with a buffer layer, e.g. a lattice matching layer
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/40—AIIIBV compounds wherein A is B, Al, Ga, In or Tl and B is N, P, As, Sb or Bi
- C30B29/403—AIII-nitrides
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/40—AIIIBV compounds wherein A is B, Al, Ga, In or Tl and B is N, P, As, Sb or Bi
- C30B29/403—AIII-nitrides
- C30B29/406—Gallium nitride
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- H01L33/0062—Processes for devices with an active region comprising only III-V compounds
- H01L33/0066—Processes for devices with an active region comprising only III-V compounds with a substrate not being a III-V compound
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- H01L33/26—Materials of the light emitting region
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Abstract
The invention discloses an epitaxial structure for forming a high-quality A1N film, a preparation method and application. The epitaxial structure comprises a substrate, a buffer layer, a first A1N layer and a second A1N layer which are sequentially stacked; the lattice mismatch degree of the buffer layer and the A1N is lower than that of the buffer layer and the substrate; the first A1N layer is provided with a plurality of island structures; the second A1N layer is connected with the island-shaped structure to form a continuous film layer, so that a high-quality A1N film is formed; the growth temperature of the first A1N layer is smaller than that of the second A1N layer, and the growth temperature of the second A1N layer is 1000-1200 ℃. According to the invention, the problem of large lattice mismatch is solved by inserting the buffer layer, on the basis of the introduction of the first A1N layer grown at the first temperature with lower temperature, the second A1N film can be grown at the second temperature lower than the second temperature in the prior art, the second A1N layer with high quality and thicker thickness can be formed, and the surface of the second A1N layer is free from cracks under the condition of thicker thickness.
Description
Technical Field
The invention relates to the technical field of semiconductors, in particular to an epitaxial structure for forming a high-quality AlN film, a preparation method and application.
Background
Aluminum nitride (AlN) materials are used for the preparation of photoelectric devices such as ultraviolet detectors, ultraviolet Light Emitting Diodes (LEDs), and ultraviolet lasers, and are commonly used as a growth base for semiconductor material layers for epitaxial growth. However, the high quality AlN single crystal substrate is very expensive, and the existing technical route mostly selects the growth of a high quality AlN thin film on a substrate such as sapphire as a growth basis.
The reasons for influencing the growth of the high-quality AlN film at present are mainly as follows: 1. when the conventional method uses Metal organic chemical vapor deposition (Metal-organic Chemical Vapor Deposition, MOCVD) to grow the AlN film, the hetero-epitaxy of the sapphire substrate and AlN has the problems of large lattice mismatch (13.3%) and large thermal mismatch (44%), the AlN film has poor crystal quality and large dislocation density (up to 1 multiplied by 10) 11 /cm 2 Left and right), and as the thickness increases, the internal stress increases, and cracks appear on the surface; 2. at present, the AlN film needs higher temperature (1200 ℃ -1300 ℃) for growth and has higher requirements on equipment; 3. at present, a physical vapor deposition (Physical Vapor Deposition, PVD) sputtering method is mainly adopted to obtain a high-quality AlN film, but the thickness of the AlN film which can be grown is limited, the PVD sputtered AlN film produced by a general batch process is about 20nm-100nm, if the thicker AlN film is continuously deposited, the thicker AlN layer on a target material is caused to be deposited along with the elongation of the process time, the sputtering difficulty of the subsequent process is increased, the process stability and the accuracy are more difficult to ensure, and the limit of the deposition thickness of the AlN film is difficult to meet the use requirements of different devices in the growing mode.
It can be seen that the current prior art still has great difficulty in growing AlN films with relatively high thickness and quality.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide an epitaxial structure for forming a high-quality AlN film, a preparation method and application.
In order to achieve the purpose of the invention, the technical scheme adopted by the invention comprises the following steps:
in a first aspect, the present invention provides an epitaxial structure for forming a high quality AlN film, including a substrate, a buffer layer, a first AlN layer, and a second AlN layer, which are sequentially stacked in a first direction; the lattice mismatch degree of the buffer layer and the first AlN layer is lower than that of the substrate and the first AlN layer; the first AlN layer has a plurality of island-like structures extending in the first direction; the second AlN layer is connected with a plurality of island structures along a second direction perpendicular to the first direction and forms a continuous film layer, and at least the continuous film layer forms the high-quality AlN film; the growth temperature of the first AlN layer is smaller than that of the second AlN layer, and the growth temperature of the second AlN layer is 1000-1200 ℃.
Further, the average height of the island-shaped structures is 10-12nm;
the second AlN layer has a continuous surface with a roughness of less than 0.25 nm;
and/or, when the thickness of the second AlN layer is 200nm or more, the defect density of the second AlN layer is 5X 10 8 /cm 2 The following is given.
Further, the thickness of the first AlN layer is 10-30nm;
and/or the thickness of the second AlN layer is 200-500nm;
and/or the material of the buffer layer comprises any one or more than two of u-type GaN and n-type GaN;
and/or the material of the substrate comprises any one or more than two of sapphire and Si, siC, gaN.
In a second aspect, the present invention also provides a method for preparing a high quality AlN film, including:
providing a substrate with a buffer layer covered on the surface;
growing a first AlN layer on the surface of the buffer layer under a first set condition;
growing a second AlN layer on the surface of the first AlN layer under a second set condition;
wherein the lattice mismatch degree of the buffer layer and the first AlN layer is lower than that of the substrate and the first AlN layer;
the first temperature in the first setting condition is smaller than the second temperature in the second setting condition, and the second temperature is 1000-1200 ℃.
Further, the first setting condition further includes a first V/III ratio, the second setting condition further includes a second V/III ratio, and the preparation method includes:
under the conditions that the temperature is the first temperature and the V/III ratio is the first V/III ratio, adopting a chemical vapor deposition method to grow the first AlN layer on the surface of the buffer layer;
under the conditions that the temperature is the second temperature and the V/III ratio is the second V/III ratio, growing the second AlN layer on the surface of the first AlN layer by adopting a chemical vapor deposition method;
wherein the first temperature is 450-900 ℃; the first V/III ratio is 1000 or less and the second V/III ratio is 500 or less.
Further, the buffer layer comprises a u-type GaN layer and/or an n-type GaN layer, the providing a substrate with a buffer layer covered on the surface comprises:
providing the substrate;
growing the u-type GaN layer and/or the n-type GaN layer on the surface of the substrate by adopting a chemical vapor deposition method;
and carrying out high-temperature annealing treatment on the u-type GaN layer and/or the n-type GaN layer under a third set condition, wherein the third set condition comprises a third temperature.
Further, the third setting condition comprises a third temperature of 950-1150 ℃ and a time of 2-5min, and the atmosphere is a mixed atmosphere of hydrogen and ammonia;
the first V/III ratio is 300-1000, and the second V/III ratio is 100-500;
the method further comprises the steps of:
and before the first AlN layer is grown, linearly reducing the growth temperature of the substrate from the third temperature to the first temperature.
Further, the growth of the buffer layer, the first AlN layer and the second AlN layer is continuously carried out in the same chemical vapor deposition equipment;
the growth atmosphere of the chemical vapor deposition method comprises a gaseous aluminum source and a nitrogen source, and the flow rate of the aluminum source for growing the first AlN layer is lower than that of the aluminum source for growing the second AlN layer.
In a third aspect, the present invention also provides a high quality AlN film prepared by the above-described preparation method.
In a fourth aspect, the present invention also provides a semiconductor device comprising the above epitaxial structure or the above high quality AlN film.
Based on the technical scheme, compared with the prior art, the invention has the beneficial effects that:
according to the technical scheme provided by the invention, the problem of large lattice mismatch between the AlN film and the substrate is solved through the insertion of the buffer layer, on the basis, the second AlN film can be grown at a second temperature lower than the second temperature in the prior art by matching with the introduction of the first AlN layer grown at the first temperature, the second AlN layer (for example, 1 mu m) with high quality and thicker thickness can be grown by the growth method, and cracks can not appear on the surface of the second AlN layer under the condition of thicker thickness.
The above description is only an overview of the technical solutions of the present invention, and in order to enable those skilled in the art to more clearly understand the technical means of the present application, the present invention may be implemented according to the content of the specification, the following description is given of the preferred embodiments of the present invention with reference to the accompanying drawings.
Drawings
FIG. 1 is a schematic diagram of an epitaxial structure according to an exemplary embodiment of the present invention;
FIG. 2 is a schematic diagram of an intermediate structure formed by a partial flow of a preparation method according to an exemplary embodiment of the present invention;
FIG. 3 is a schematic illustration of an intermediate structure formed by another partial flow of a preparation method according to an exemplary embodiment of the present invention;
FIG. 4 is an optical image of the surface topography of a high quality AlN film provided by an exemplary embodiment of the invention;
FIG. 5 is an optical image of the surface topography of a high quality AlN film provided by an exemplary comparative case of the present invention;
fig. 6 is a schematic structural diagram of an ultraviolet LED device according to another exemplary embodiment of the present invention.
Reference numerals illustrate:
11. a substrate; 12. a buffer layer; 13. a first AlN layer; 14. and a second AlN layer.
Detailed Description
In view of the shortcomings in the prior art, the inventor of the present invention has long studied and practiced in a large number of ways to propose the technical scheme of the present invention. The technical scheme, the implementation process, the principle and the like are further explained as follows.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, however, the present invention may be practiced otherwise than as described herein, and therefore the scope of the present invention is not limited to the specific embodiments disclosed below.
Moreover, relational terms such as "first" and "second", and the like, may be used solely to distinguish one from another component or method step having the same name, without necessarily requiring or implying any actual such relationship or order between such components or method steps.
Referring to fig. 1, an epitaxial structure for forming a high quality AlN film according to an embodiment of the present invention includes a substrate 11, a buffer layer 12, a first AlN layer 13, and a second AlN layer 14, which are sequentially stacked.
The degree of lattice mismatch of the buffer layer 12 and the first AlN layer 13 is lower than the degree of lattice mismatch of the substrate 11 and the first AlN layer 13; the first AlN layer 13 has a plurality of island-like structures extending in the first direction; the second AlN layer 14 is connected with the island-shaped structure along a second direction perpendicular to the first direction and forms a continuous film layer, and at least the continuous film layer forms a high-quality AlN film; the growth temperature of the first AlN layer 13 is smaller than that of the second AlN layer 14, and the growth temperature of the second AlN layer 14 is 1000-1200 ℃.
The epitaxial structure as a whole may be an intermediate product in a semiconductor process, for example, epitaxial growth may be continued on the surface of the intermediate product, and the surface quality of the second AlN layer 14 is utilized to obtain excellent subsequent epitaxial quality; the product can be sold in a commodity form, and after buying the epitaxial structure, the buyer continues to peel off the film or grow epitaxially; in any case, it is within the scope of the present invention to form or utilize the epitaxial structure provided by the present invention during the implementation.
It should be noted that the high-quality AlN film generally refers to a combination of the first AlN layer 13 and the second AlN layer 14, but is not limited thereto, and may be a high-quality AlN film product if the first AlN layer 13 is removed by a certain technique such as polishing, and all or a part of the second AlN layer 14 remains.
Based on the technical scheme, the invention provides an epitaxial structure and a method capable of improving the quality of an AlN film and the growth thickness thereof and having lower growth temperature from the perspective of reducing the lattice mismatch and the thermal mismatch to the film quality of the AlN film; the solution is that by introducing a double-layer buffer structure of the buffer layer 12 and the first AlN layer 13 and purposefully reducing the growth temperature of the first AlN layer 13, the second AlN layer 14 with thicker thickness and higher film quality can be grown at a lower temperature.
The average height of the island-like structure in the first AlN layer 13 is 10-12nm due to low-temperature growth, the distance is far, and usually several nm to several tens nm, and statistics cannot be accurately performed, which is significantly different from the size and distribution characteristics of the first AlN layer 13 formed under conventional growth conditions. The island-like structures obtained under such growth conditions are larger in average size and more sparsely distributed (i.e., more widely spaced) than conventional growth conditions. It should be noted that, the heights obtained in the embodiments of the present invention are statistical average values, the height distribution of the island-shaped structures under the general conditions is similar to the normal distribution, and the height distribution is a range, but the average heights of the island-shaped structures obtained in most cases are not limited to the above range, and in some cases are beyond the above range of average heights, but still conform to the larger size and more sparse distribution compared with the conventional growth conditions.
Thus, in some embodiments, the second AlN layer 14 can have a continuous surface with a roughness below 0.25nm.
In some embodiments, when the thickness of the second AlN layer 14 is 200nm or more, the defect density of the second AlN layer 14 can be 5×10 8 /cm 2 The following is given. Specifically, for example, the above-mentioned test criteria for roughness and dislocation density are the surface roughness and dislocation density obtained by statistics in a square field of view having a test window of 4 μm×4 μm; in the preferred embodiment, the roughness values measured are < 0.25nm and the dislocation density is less than 5X 10 8 /cm 2 . The technical scheme provided by the invention has the technical effects of low defect and no cracking in a thicker film layer, and the characteristics are obvious characteristics of the epitaxial structure provided by the invention and the high-quality AlN film obtained by the epitaxial structure, and are difficult to realize in the existing technical schemes.
With respect to the material and thickness of each portion, in some embodiments, the thickness of the first AlN layer 13 may be 10-30nm.
In some embodiments, the thickness of the second AlN layer 14 may be 200-500nm, but is not limited thereto, and the above thickness is only a preferable thickness range for maintaining the optimal film quality, and in actual growth, a thicker high-quality film, for example, 1 μm and above, may be obtained.
In some embodiments, the material of the buffer layer 12 may include any one or a combination of two or more of u-type GaN and n-type GaN, and is not limited thereto.
In some embodiments, the material of the substrate 11 may include any one or more of sapphire and Si, siC, gaN, and is not limited thereto, and the key of the technical scheme provided by the present invention is that the combination of the buffer layer 12 and the first AlN layer 13 and the growth temperature of the first AlN layer 13 and the second AlN layer 14, and the specific material of the substrate 11 and the material of the buffer layer 12 matched with the same may be properly adjusted, so that the corresponding functions may be achieved.
Referring to fig. 2-3, the embodiment of the invention also provides a preparation method of the high-quality AlN film, which includes the following steps:
s1: a substrate 11 is provided, the surface of which is covered with a buffer layer 12 as shown in fig. 2.
S2: under a first set condition, a first AlN layer 13 as shown in fig. 3 is grown on the surface of the buffer layer 12.
The degree of lattice mismatch of the buffer layer 12 and the first AlN layer 13 is lower than the degree of lattice mismatch of the substrate 11 and the first AlN layer 13.
S3: under the second set condition, a second AlN layer 14 is grown on the surface of the first AlN layer 13, and finally an epitaxial structure as shown in fig. 1 is formed.
The first temperature in the first setting condition is less than the second temperature in the second setting condition, and the second temperature is 1000-1200 ℃.
The buffer layer 12 is provided with a solution that is different from most of the prior art at least in that the growth conditions of the first AlN layer 13 and the second AlN layer 14 are different, for example, in the present invention, the growth temperature of each AlN layer is significantly lower than the common temperature range in the prior art.
The main reason for the difference is that the present invention aims at the above-mentioned technical problems, by redesigning the epitaxial structure, introducing the GaN buffer layer 12, and improving the growth conditions of the two AlN layers, the dislocation density formed during the growth of the AlN film is reduced, so as to achieve an AlN film with higher quality and no surface cracks at a lower temperature and with simpler process.
The first AlN layer 13 grown at a lower temperature is prone to a 3D growth mode, has a discontinuous island growth state, can avoid dislocation extension, and further reduces the influence caused by lattice mismatch on the basis of the buffer layer 12; after forming the first AlN layer 13, the second AlN layer 14 is grown continuously at a second temperature that is somewhat higher relative to the first AlN layer 13 (but still lower than conventional growth temperatures in the prior art), which can significantly reduce the risk of cracking of the film due to thermal mismatch as compared to conventional growth temperatures, thereby enabling a relatively thicker and better quality second AlN layer 14.
In addition, some of the prior art methods use an AlN layer as the buffer layer 12 on the sapphire substrate 11 by sputtering, and the process is complex, and the in-situ growth cannot be performed in the same equipment; the invention adopts the mode of growing the GaN buffer layer 12 to simplify the process, the MOCVD process is used in the whole process, and the obtained AlN film has higher quality, and is specifically expressed in that: if an AlN layer is grown directly on the sapphire substrate 11, lattice mismatch and thermal mismatch are excessive, but this problem can be solved after the GaN buffer layer 12 is interposed. The lattice mismatch of the GaN buffer layer 12 and AlN is much smaller, and the GaN buffer layer is suitable for being used as a transition layer, so that the dislocation density of the first AlN layer 13 is smaller, the stress is smaller, and the growth of the second AlN layer 14 is facilitated; the second AlN layer 14 is matched with a lower growth temperature so as not to crack easily, so that a thicker cracking-free film layer is obtained, the requirement on equipment is lower, and continuous growth in the same vapor deposition equipment can be realized.
It should be noted that the preparation method provided by the present invention is essentially for forming a high-quality AlN film (the film at least includes the second AlN layer 14), and whether the high-quality AlN film is separated from the substrate 11, the buffer layer 12 and the first AlN layer 13 or not falls within the scope of the preparation method.
It will be appreciated that after separation of the second AlN layer 14, a separate high quality AlN film product is obtained as described below, which, when not separated, corresponds to the epitaxial structure (in this case the preparation method may also be understood as the preparation method of the epitaxial structure).
With respect to the specific growth conditions of the present invention, other conditions may be set in combination to further optimize the film quality based on the above temperature difference, for example, in some embodiments, the first set of conditions further includes a first V/III ratio, the second set of conditions further includes a second V/III ratio, and the first V/III ratio is preferably set to be greater than the second V/III ratio; the preparation method can comprise the following steps:
al) and growing a first AlN layer 13 on the surface of the buffer layer 12 by adopting a chemical vapor deposition method under the conditions that the temperature is a first temperature and the V/III ratio is a first V/III ratio.
The first temperature is 450-900 ℃, and the first V/III ratio is below 1000.
A2 Under the conditions that the temperature is the second temperature and the V/III ratio is the second V/III ratio, the second AlN layer 14 is grown on the surface of the first AlN layer 13 by adopting a chemical vapor deposition method.
The second temperature is 1000-1200 deg.C, and the second V/III ratio is below 500.
In some embodiments, the buffer layer 12 comprises a u-type GaN layer and/or an n-type GaN layer, and the step of providing the substrate 11 with the buffer layer 12 covered on the surface may comprise, for example, the steps of:
b1 A substrate 11 is provided.
B2 A chemical vapor deposition method is used to grow a u-type GaN layer and/or an n-type GaN layer on the surface of the substrate 11.
B3 Under a third set condition, carrying out high-temperature annealing treatment on the u-type GaN layer and/or the n-type GaN layer.
The third setting condition comprises that the third temperature is 950-1150 ℃ and the time is 2-5min, and the atmosphere is the mixed atmosphere of hydrogen and ammonia.
B4 After the annealing operation is performed, the temperature of the reaction chamber of the MOCVD equipment is linearly reduced from the third temperature to the first temperature.
It should be noted that, in order to implement the technical solution provided by the present invention, the substrate with the buffer layer 12 on the surface may be prepared by itself by adopting the specific process, or the corresponding substrate meeting the requirements may be directly purchased or prepared by entrusting, and both embodiments are within the protection scope of the present invention.
And more specific manufacturing conditions are, for example, in some embodiments, a first V/III ratio of 300 to 1000 and a second V/III ratio of 100 to 500.
In some embodiments, the growth atmosphere of the chemical vapor deposition method includes a gaseous aluminum source and a nitrogen source, and the flow rate of the aluminum source for growing the first AlN layer 13 is lower than the flow rate of the aluminum source for growing the second AlN layer 14.
This is because, under the conditions of low temperature, low V/III ratio, also in the case where the Al source flow rate is small, the small mobility of Al atoms results in the first AlN layer 13 being more prone to grow in the vertical direction rather than moving in the horizontal direction than in the conventional growth conditions, forming an island-like structure that is smaller in volume and sparser in distribution.
As some typical application examples of the above technical solutions, the above preparation method may be implemented by the following specific steps:
1) A u-type GaN layer having a thickness of 1-4.5 μm was grown on the cleaned sapphire substrate 11 by MOCVD.
The u-type GaN layer is used to form a relatively flat buffer layer 12 on the sapphire substrate 11, so as to reduce a large number of dislocations caused by lattice mismatch between the subsequently grown AlN thin film and the sapphire substrate 11 (the lattice mismatch between AlN and sapphire is relatively large, about 13.3%, and the lattice mismatch between GaN and AlN is only 2.5%).
2) At NH 3 And H 2 And (3) carrying out high-temperature annealing on the u-type GaN layer in atmosphere, wherein the temperature is 950-1150 ℃.
Due to the introduction of H only 2 Into the reaction chamber of the MOCVD apparatus, the GaN material is decomposed at high temperature, thus at H 2 Is doped with NH 3 As a shielding gas; the effect of the high temperature anneal is to remove impurities and merge small grains into larger grains to reduce dislocation density.
3) A low temperature AlN buffer layer 12 (i.e., a first AlN layer 13) is grown on top of the u-GaN layer.
The conditions for growing the low-temperature AlN buffer layer 12 include: the V/III ratio is 300-1000, and the growth temperature is 450-900 ℃; the thickness of the low temperature AlN buffer layer 12 is preferably 10-30nm.
Further, the low-temperature AlN buffer layer 12 mainly tends to be 3D-grown, and in the case where V/III is relatively small and the temperature is low, al atoms migrate relatively slowly, mainly grow in the vertical direction to form an island-like structure, which is very beneficial to release the stress generated by lattice mismatch.
4) A high temperature AlN thin film layer (i.e., second AlN layer 14) is grown on the low temperature AlN buffer layer 12 formed in the previous step.
The conditions for growing the high temperature AlN buffer layer 12 include: the V/III ratio is between 100 and 500, and the growth temperature is between 1000 and 1200 ℃; the thickness of the high temperature AlN buffer layer 12 is 200-500nm or higher.
Further, the high temperature AlN buffer layer 12 is a high quality AlN film that is actually grown, and under the conditions of a lower V/III ratio than that of the conventional AlN layer, and a second temperature that is higher than that of the first AlN layer 13 but lower than that of the conventional AlN layer, the second AlN layer 14 mainly tends to grow in two dimensions, achieving the purpose of merging island-like structures, and eventually forming a flat surface with small roughness.
By adopting the preparation process, compared with the traditional MOCVD method, the method has lower growth temperature and can grow thicker AlN film without crack. It should be noted that the technical solution provided by the present invention is not only the adjustment of the growth condition of a single film layer, but also the optimization of the coordination between the growth conditions of each film layer in the whole growth process, at least comprising a first temperature which is significantly lower and a second temperature which is lower than that conventionally used in the prior art, and more optionally comprising the quantitative relationship and specific range between the first V/III ratio and the second V/III ratio.
In some of the above application examples, the substrate 11 is not limited to the exemplary sapphire substrate, but may be replaced by a substrate made of other materials such as Si, siC, gaN, and is not limited to the specific example of the present invention.
In some embodiments, the growth temperature at which the substrate 11 is grown is linearly reduced from the third temperature to the first temperature prior to growing the first AlN layer 13. In a general multi-step epitaxial growth process, the temperature change between layers is usually heated with a fixed heating power or directly turned off to naturally cool the layers until the set temperature is reached, and the heating curve is not intentionally controlled, so that the temperature change curves of the substrate 11 and the buffer layer 12 are not linear but are generally concave curves when the temperature is reduced. The purpose of this is to avoid defects of the buffer layer 12, such as microcracks, caused by the change of the cooling rate by linear cooling, thereby improving the grain quality of the buffer layer 12 and further improving the growth quality of the AlN layer.
In some embodiments, buffer layer 12, first AlN layer 13, and second AlN layer 14 are all continuously grown in the same chemical vapor deposition apparatus, which avoids contamination and substantial cooling after the material is removed from the growth chamber, which is clearly advantageous for improving growth quality.
Regarding the application forms of the high-quality AlN film, the above-mentioned epitaxial structure including the second AlN layer 14 may be used as the application forms by continuing the growth of the subsequent semiconductor material layer, or at least the second AlN layer 14 may be peeled off and transferred to other substrates or applied as a new growth substrate alone, and not only in the semiconductor field, but also in other fields such as optics, precision instruments, etc. having higher requirements for AlN layer and quality may take advantage of the technical advantages of the present invention to generate corresponding values; namely, the preparation method can further comprise the following steps:
c1 The substrate 11 and the buffer layer 12 are peeled off by a laser peeling process to obtain an epitaxial layer including the buffer layer 12, the first AlN layer 13, and the second AlN layer 14, which are stacked.
C2 Polishing the epitaxial layer to obtain a first AlN layer 13 and a second AlN layer 14 as high-quality AlN thin films.
Correspondingly, the embodiment of the invention also provides the high-quality AlN film prepared by the preparation method. The high quality AlN film may be, for example, in particular, a stripped, separate second AlN layer 14.
It is understood that the structure of the high quality AlN film is not limited thereto, and in other embodiments, the first AlN layer 13 and the second AlN layer 14 may be peeled off, and the second AlN layer 14 may be obtained as a high quality AlN film. Alternatively, the substrate 11 and the buffer layer 12 may be peeled off to obtain a high-quality AlN film, that is, a high-quality AlN film including the buffer layer 12, the first AlN layer 13, and the second AlN layer 14 stacked, and the like, but in these cases, at least all or part of the second AlN layer 14 is included.
As a further application of the above technical solutions, the present examples also provide a semiconductor device including the epitaxial structure provided by any one of the above embodiments or the high quality AlN thin film provided by any one of the above embodiments.
The technical scheme of the invention is further described in detail below through a plurality of embodiments and with reference to the accompanying drawings. However, the examples are chosen to illustrate the invention only and are not intended to limit the scope of the invention.
Example 1
The first embodiment of the present invention relates to a growth process of an epitaxial structure for forming a high quality AlN film, specifically as follows:
1) And (3) growing a u-type GaN layer on the clean sapphire substrate by using an MOCVD method, wherein the thickness of the u-type GaN layer is about 4.5 mu m.
2) At NH 3 And H 2 And (3) carrying out high-temperature annealing on the u-type GaN layer in the atmosphere with the volume ratio of 1:3, wherein the annealing temperature is 1050 ℃, and the annealing time is 5min.
3) And growing a low-temperature AlN buffer layer on the u-type GaN layer, wherein the V/III ratio is 400, the used Al source is Trimethylaluminum (TMAL), the flow rate of the Al source is 300sccm, the growth temperature is 500 ℃, and the thickness of the low-temperature AlN buffer layer is 30nm.
4) And growing a high-temperature AlN film layer on the low-temperature AlN buffer layer formed in the previous step, wherein V/III is 300, TMAL flow is 400sccm, the growth temperature is 1100 ℃, and the thickness of the high-temperature AlN film layer is 200nm.
The low-temperature AlN buffer layer and the high-temperature AlN thin film layer form a high-quality AlN thin film.
The epitaxial structure samples formed in this example were tested, including X-ray diffraction (XRD) testing (002) and (102) crystal planes and atomic force microscopy (Atomic Force Microscope, AFM) testing.
The XRD data measured were: (002) 110arcsec, (102) =290 arcsec, the dislocation density was estimated to be 2.6x10 8 /cm 2 The method comprises the steps of carrying out a first treatment on the surface of the And AFM showed a surface roughness (4 μm x 4 μm) of 0.2nm.
The surface morphology of the high-quality AlN film prepared in this example is shown in fig. 4, and it can be seen that the surface is smooth and crack-free.
Example 2
This example also illustrates a growth process for forming an epitaxial structure of high quality AlN film, as follows:
1) And (3) growing a u-type GaN layer on the clean sapphire substrate by using an MOCVD method, wherein the thickness of the u-type GaN layer is about 4.5 mu m.
2) At NH 3 And H 2 And (3) carrying out high-temperature annealing on the u-type GaN layer in the atmosphere of which the volume ratio is 1:3, wherein the annealing temperature is 950 ℃, and the annealing time is 5min.
3) And a low-temperature AlN buffer layer is grown on the u-type GaN layer, the V/III ratio is 1000, the TMAL flow is 300sccm, the growth temperature is 450 ℃, and the thickness of the low-temperature AlN buffer layer is 10nm.
4) And growing a high-temperature AlN film layer on the low-temperature AlN buffer layer formed in the previous step, wherein V/III is 500, TMAL flow is 500sccm, the growth temperature is 1200 ℃, and the thickness of the high-temperature AlN film layer is 500nm.
The dislocation density of the second AlN layer formed in this example was 3X 10 8 /cm 2 The method comprises the steps of carrying out a first treatment on the surface of the The surface roughness (4 μm. Times.4 μm) was 0.25nm.
Example 3
This example also illustrates a growth process for forming an epitaxial structure of high quality AlN film, as follows:
1) And (3) growing a u-type GaN layer on the clean sapphire substrate by using an MOCVD method, wherein the thickness of the u-type GaN layer is about 4.5 mu m.
2) At NH 3 And H 2 And (3) carrying out high-temperature annealing on the u-type GaN layer in the atmosphere with the volume ratio of 1:3, wherein the annealing temperature is 1150 ℃, and the annealing time is 2min.
3) And a low-temperature AlN buffer layer is grown on the u-type GaN layer, the V/III ratio is 300, the TMAL flow is 300sccm, the growth temperature is 900 ℃, and the thickness of the low-temperature AlN buffer layer is 20nm.
4) And growing a high-temperature AlN film layer on the low-temperature AlN buffer layer formed in the previous step, wherein V/III is 100, TMAL flow is 500sccm, the growth temperature is 1000 ℃, and the thickness of the high-temperature AlN film layer is 400nm.
The dislocation density of the second AlN layer formed in this example was 3X 10 8 /cm 2 The method comprises the steps of carrying out a first treatment on the surface of the The surface roughness (4 μm. Times.4 μm) was 0.23nm.
Example 4
This embodiment is similar to embodiment 2, except that: the thickness of the high temperature AlN thin film layer in the step 4) is 1 μm.
The dislocation density of the second AlN layer formed in this example was 3.4X10 8 /cm 2 The method comprises the steps of carrying out a first treatment on the surface of the The surface roughness (4 μm. Times.4 μm) was 0.28nm.
And the film grown in this example still maintains a crack-free surface.
Example 5
This example illustrates the preparation of a high quality AlN thin film after delamination, as follows:
based on the embodiment 2, a laser stripping method is adopted to strip the substrate and the u-type GaN layer, so as to obtain an epitaxial layer; and polishing the epitaxial layer to remove the u-type GaN layer, so as to obtain a high-quality AlN film which can be used for growing an ultraviolet detector, an ultraviolet LED or an ultraviolet laser.
Example 6
This embodiment is substantially the same as embodiment 1, except that:
in the steps 2) to 3), a program-controlled linear cooling mode is adopted instead of the natural cooling mode in the embodiment 1, so that the temperature in the reaction chamber is linearly reduced from the annealing temperature of 1050 ℃ to the growth temperature of 500 ℃ under the time span of 8 min. The rest of the reaction process and conditions remained unchanged.
The dislocation density of the second AlN layer formed was 2.3X10 8 /cm 2 The method comprises the steps of carrying out a first treatment on the surface of the The surface roughness (4 μm. Times.4 μm) was 0.19nm.
Example 7
The preparation process of the semiconductor device of this embodiment is specifically as follows:
the structure of the ultraviolet LED device prepared in this embodiment is shown in fig. 6, and the ultraviolet LED device includes an N electrode, a first AlN layer 13, a second AlN layer 14, an electron-providing layer, a light-emitting layer, a hole-providing layer, an electron-blocking layer, and a P electrode, and the high-quality AlN film provided in this embodiment of the present invention is used as a growth substrate to perform growth of each layer, and the thicknesses, materials, and growth processes of other film layers and electrodes except the high-quality AlN film need only be conventional methods for preparing an ultraviolet LED device. The photoelectric conversion efficiency of the device was finally measured to be 19.4%.
Comparative example 1
This comparative example is substantially the same as example 1, with the main difference that:
in the step 3), the growth temperature of the first AlN layer is 1200 ℃; in step 4), the growth temperature of the second AlN layer is 1500 ℃.
The comparative example was grown using common AlN layer growth conditions, and the dislocation density of the finally obtained second AlN layer was 8X 10 8 /cm 2 The surface roughness was 0.5nm.
And the corresponding device is manufactured by continuing to grow by adopting the same growth method as in the example 5, and finally the photoelectric conversion efficiency of the device is 16.1%.
Comparative example 2
This comparative example is substantially the same as example 1, with the main difference that:
in step 3), the growth temperature of the first AlN layer is adjusted to 1000 ℃.
The dislocation density of the finally obtained second AlN layer was 6.7X10 8 /cm 2 The surface roughness was 0.42nm.
And the corresponding device is manufactured by continuing to grow by adopting the same growth method as in the example 5, and finally the photoelectric conversion efficiency of the device is 14.2%.
Comparative example 3
This comparative example is substantially the same as example 1, with the main difference that:
in step 4), the growth temperature of the second AlN layer was adjusted to 1350 ℃.
The dislocation density of the finally obtained second AlN layer was 2.7X10 8 /cm 2 The surface roughness was 0.22nm.
And the corresponding device is manufactured by continuing to grow by adopting the same growth method as in the example 5, and finally the photoelectric conversion efficiency of the device is 22.7%.
Comparative example 4
The comparative example is substantially the same as example 1, with the main difference that: steps 1) and 2) are omitted, i.e., the low-temperature AlN buffer layer is directly grown on the sapphire substrate, and then the high-temperature AlN buffer layer is grown again, and the high-quality AlN film prepared by this scheme has cracks, as shown in fig. 5.
The dislocation density of the finally obtained second AlN layer was 9.7X10 8 /cm 2 The surface roughness was 0.68nm.
And the corresponding device is manufactured by continuing to grow by adopting the same growth method as in the example 5, and finally the photoelectric conversion efficiency of the device is 14.3%.
Comparative example 5
The comparative example is substantially the same as example 1, with the main difference that: the step of high temperature annealing of step 2) is omitted.
The dislocation density of the finally obtained second AlN layer was 5.7X10 8 /cm 2 The surface roughness was 0.39nm.
And the corresponding device is manufactured by continuing to grow by adopting the same growth method as in the example 5, and finally the photoelectric conversion efficiency of the device is 17.3%.
Based on the above embodiments and comparative examples, it is clear that the growth process and the obtained epitaxial structure provided by the embodiments of the present invention solve the problem of large lattice mismatch between the AlN thin film and the substrate by inserting the buffer layer, and on this basis, the introduction of the first AlN layer grown at the first temperature, which is lower than the prior art, can be used to grow the second AlN thin film at the second temperature, which is lower than the prior art, and the growth method can grow to form the second AlN layer with high quality and thicker thickness, and the surface of the second AlN thin film will not crack when the thickness is thicker.
It should be understood that the above embodiments are merely for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the present invention and implement the same according to the present invention without limiting the scope of the present invention. All equivalent changes or modifications made in accordance with the spirit of the present invention should be construed to be included in the scope of the present invention.
Claims (10)
1. An epitaxial structure for forming a high-quality AlN thin film, characterized by comprising a substrate, a buffer layer, a first AlN layer and a second AlN layer which are laminated in sequence along a first direction;
the lattice mismatch degree of the buffer layer and the first AlN layer is lower than that of the substrate and the first AlN layer;
the first AlN layer has a plurality of island-like structures extending in the first direction;
the second AlN layer is connected with a plurality of island structures along a second direction perpendicular to the first direction and forms a continuous film layer, and at least the continuous film layer forms the high-quality AlN film;
the growth temperature of the first A1N layer is smaller than that of the second AlN layer, and the growth temperature of the second A1N layer is 1000-1200 ℃.
2. Epitaxial structure according to claim 1, characterized in that the island-like structure has an average height of 10-12nm;
the second A1N layer has a continuous surface with a roughness below 0.25 nm;
and/or, when the thickness of the second A1N layer is 200nm or more, the defect density of the second AlN layer is 5×10 8 /cm 2 The following is given.
3. The epitaxial structure of claim 2, wherein the first AlN layer has a thickness of 10-30nm;
and/or the thickness of the second AlN layer is 200-500nm;
and/or the material of the buffer layer comprises any one or more than two of u-type GaN and n-type GaN;
and/or the material of the substrate comprises any one or more than two of sapphire and Si, siC, gaN.
4. The preparation method of the high-quality AlN film is characterized by comprising the following steps of:
providing a substrate with a buffer layer covered on the surface;
growing a first AlN layer on the surface of the buffer layer under a first set condition;
growing a second AlN layer on the surface of the first AlN layer under a second set condition;
wherein the lattice mismatch degree of the buffer layer and the first AlN layer is lower than that of the substrate and the first AlN layer;
the first temperature in the first setting condition is smaller than the second temperature in the second setting condition, and the second temperature is 1000-1200 ℃.
5. The method according to claim 4, wherein the first setting condition further includes a first V/III ratio, the second setting condition further includes a second V/III ratio, the method comprising:
under the conditions that the temperature is the first temperature and the V/III ratio is the first V/III ratio, adopting a chemical vapor deposition method to grow the first AlN layer on the surface of the buffer layer;
under the conditions that the temperature is the second temperature and the V/III ratio is the second V/III ratio, growing the second AlN layer on the surface of the first AlN layer by adopting a chemical vapor deposition method;
wherein the first temperature is 450-900 ℃; the first V/III ratio is 1000 or less and the second V/III ratio is 500 or less.
6. The method according to claim 5, wherein the buffer layer comprises a u-type GaN layer and/or an n-type GaN layer, the providing a substrate surface-coated with the buffer layer comprises:
providing the substrate;
growing the u-type GaN layer and/or the n-type GaN layer on the surface of the substrate by adopting a chemical vapor deposition method;
and carrying out high-temperature annealing treatment on the u-type GaN layer and/or the n-type GaN layer under a third set condition, wherein the third set condition comprises a third temperature.
7. The method according to claim 6, wherein the third setting condition includes a third temperature of 950-1150 ℃ for 2-5min, and an atmosphere of a mixed atmosphere of hydrogen and ammonia;
the first V/III ratio is 300-1000, and the second V/III ratio is 100-500;
the method further comprises the steps of:
and before the first AlN layer is grown, linearly reducing the growth temperature of the substrate from the third temperature to the first temperature.
8. The method according to claim 6, wherein the growth of the buffer layer, the first AlN layer, and the second AlN layer is continuously performed in the same chemical vapor deposition apparatus;
the growth atmosphere of the chemical vapor deposition method comprises a gaseous aluminum source and a nitrogen source, and the flow rate of the aluminum source for growing the first AlN layer is lower than that of the aluminum source for growing the second AlN layer.
9. A high quality AlN film produced by the production method according to any one of claims 5 to 8.
10. A semiconductor device comprising the epitaxial structure of any one of claims 1-4 or the high quality AlN film of claim 9.
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