CN109065438B - Preparation method of AlN thin film - Google Patents
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Abstract
A preparation method of an AlN thin film comprises the following steps: step 1: annealing the substrate for epitaxy; step 2: growing a first AlN layer on the substrate, wherein the growth temperature is the same as the annealing temperature in the step 1; and step 3: growing a second AlN layer on the first AlN layer, wherein the growth temperature and the Al source flow of the second AlN layer are gradually changed; and 4, step 4: and growing a third AlN layer with constant temperature and constant source on the second AlN layer. The method has simple process, and can realize the preparation of the low-dislocation AlN epitaxial material with high stability and high repeatability.
Description
Technical Field
The invention relates to the technical field of semiconductor epitaxial growth, in particular to a preparation method for preparing a high-quality AlN thin film by adopting metal organic chemical vapor deposition.
Background
The AlN semiconductor material has the forbidden band width of 6.2eV, belongs to the third generation wide forbidden band semiconductor material, has the advantages of high breakdown voltage, high electron saturation velocity, stability, corrosion resistance and the like, has stronger spontaneous and piezoelectric polarity and very high surface acoustic wave velocity, can form AlGaN alloy to realize continuous change of the band gap, and can be used for preparing a heterojunction device structure. Therefore, the aluminum nitride-based wide bandgap material is widely favored in the research field of front-edge photoelectron and microelectronic devices by virtue of excellent semiconductor characteristics, is a semiconductor material with important applications in the aspects of solid-state ultraviolet light sources, photoelectric detectors, high-temperature high-power electronics and the like, and the demand for the AlN-based high-aluminum nitride semiconductor material is continuously increased along with the wide application of third-generation semiconductor devices and chips.
At present, the quality of AlN materials is difficult to meet the high performance requirement of devices, the main reason is that heterogeneous substrate epitaxy such as sapphire is mainly adopted due to the lack of high-quality large-size homogeneous substrates, and a large amount of defects such as dislocation are generated due to the existence of huge lattice mismatch and thermal mismatch. Secondly, AlN has strict requirements on the conditions of the epitaxial growth process, and various defects are easily formed in the nucleation and growth process of AlN due to poor migration capability of Al atoms on the epitaxial surface and strong pre-reaction of a reaction source. Therefore, the existing AlN epitaxial technology process mainly focuses on substrate treatment, medium-low temperature nucleation and high-temperature growth. However, the direct high-temperature rapid growth on the medium-low temperature nucleation layer or the secondary epitaxial layer is not beneficial to relieving strain, reducing threading dislocation density and even generating new dislocation sources, so that a proper transitional growth process is needed in the middle no matter the high-temperature AlN growth on the in-situ medium-low temperature buffer layer or the secondary epitaxy on the sputtering AlN or epitaxial AlN thick-layer substrate, the stress is further reduced, and the defect density is reduced.
Disclosure of Invention
The invention solves the technical problem of overcoming the defects of the prior art, provides a preparation method for preparing a high-quality AlN thin film, and particularly provides a transition epitaxy technology for converting a substrate into high-temperature AlN growth.
In order to solve the technical problems, the invention adopts the technical scheme that:
the invention provides a preparation method of an AlN thin film, which comprises the following steps:
step 1: annealing the substrate for epitaxy;
step 2: growing a first AlN layer on the substrate, wherein the growth temperature is the same as the annealing temperature in the step 1;
and step 3: growing a second AlN layer on the first AlN layer, wherein the growth temperature and the Al source flow of the second AlN layer are gradually changed;
and 4, step 4: and growing a third AlN layer with constant temperature and constant source on the second AlN layer.
The technical scheme of the invention has the following advantages and beneficial effects: by utilizing the method, the stress is further reduced, the defect density of high-temperature AlN is reduced, and the surface is smooth through proper transition treatment and transition layer growth processes on the substrate. Compared with the prior general method, under the condition of the same growth process conditions and thickness, the half-height width of XRD scanning (102) of the AlN epitaxial film obtained by the method is obviously improved, 100-fold and 200arcsec is reduced, and (002) the half-height width is also improved, which shows that the density of screw-type and edge-type dislocation in the AlN epitaxial film is reduced. The method has simple process, and can realize the preparation of the low-dislocation AlN epitaxial material with high stability and high repeatability.
Drawings
For better understanding of the objects, technical solutions and advantages of the present invention, the following detailed description is provided in conjunction with the embodiments and the accompanying drawings, in which:
FIG. 1 is a block diagram illustrating the steps of a method for preparing an AlN thin film according to the present invention;
fig. 2 shows a schematic diagram of the AlN structure grown by the present method in example 1 of the present invention.
DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION
The invention provides a preparation method of an AlN film, which is a preparation process for growing the AlN film by adopting Metal Organic Chemical Vapor Deposition (MOCVD), wherein a reaction source adopts hydride NH3Gas and organicMetallic Al sources, such as TMAl and TEAl, are epitaxially grown in an MOCVD reactor at a temperature, pressure and atmosphere. Referring to fig. 1, the present invention provides a method for preparing an AlN film, including the following steps:
step 1: carrying out high-temperature annealing on the substrate 10 for epitaxy, wherein the temperature for annealing the substrate 10 is 950-1150 ℃, the annealing time is 5-15 minutes, and the annealing atmosphere is NH3、H2Atmosphere, NH3As a shielding gas. The substrate 10 includes but is not limited to an AlN bulk single crystal substrate; or AlN buffer layer formed by magnetron sputtering or in-situ growth on sapphire, silicon carbide or silicon substrate; or AlN, GaN or gallium oxide and the like epitaxial layer template; the high-temperature annealing of the substrate can enable the crystal grains of the medium-low temperature buffer layer to be combined and grown to a proper degree, and the dislocation density is reduced. And for secondary epitaxy, high-temperature annealing can enable the surface to be clean, atomic steps on the surface to be smooth and clear, and secondary epitaxy crystal quality is promoted.
Step 2: after high-temperature annealing, growing a first AlN layer 11 on the substrate 10, wherein the growth temperature is the same as the high-temperature annealing temperature in the step 1, and the thickness of the first AlN layer 11 is 5-30 nm; the first AlN layer 11 is typically grown at a lower temperature than the subsequent material growth temperature, so that there is a relatively low temperature AlN doped layer for the subsequent high temperature growth, which is beneficial to blocking dislocations and relieving substrate stress.
And step 3: growing a second AlN layer 12 on the first AlN layer 11, the growing temperature and the Al source flow of the second AlN layer 12 being gradually changed, the temperature change range when growing the second AlN layer 12 being: gradually changing from the temperature at which the first AlN layer 11 is grown to the temperature at which the third AlN layer 13 is grown; the variation range of the Al source flow is: the flow rate of the Al source for growing the first AlN layer 11 is gradually changed to the flow rate of the Al source for growing the third AlN layer 13, and the thickness of the second AlN layer 12 is 10-100 nm; the innovative characteristic of the layer is that the growth temperature is gradually changed from low temperature to high temperature, and simultaneously the reaction source V/III is gradually changed from high temperature to low temperature (NH)3Source is unchanged, organic Al source is gradually increased), growth temperature is gradually increased, and AlN growth is facilitated to be changed from surface roughening to flattening. The reaction source V/III changes from high to low and can gradually regulate and control Al atomsThe diffusion length of the growth surface is such that growth from a three-dimensional-like growth with a shorter diffusion length is favored over a quasi-two-dimensional growth with a longer diffusion length. The superposition of the two effects of temperature gradient and reaction source gradient effectively bends and annihilates the dislocation, so that the dislocation is cut off and penetrates upwards, thereby reducing the dislocation density of the subsequent upward epitaxial layer and being beneficial to gradually releasing and relieving the stress.
And 4, step 4: and growing a constant-temperature and constant-source third AlN layer 13 on the second AlN layer 12, wherein the growth temperature of the third AlN layer 13 is 1000-1500 ℃. And at high temperature, the surface migration capability of Al atoms is stronger, rapid two-dimensional growth is realized, and the AlN epitaxial layer material with low dislocation density, no crack and smooth surface can be obtained.
Wherein NH in the growth of the first AlN layer 11, the second AlN layer 12 and the third AlN layer 133The gas flow and the gas carrying capacity of the reaction source are kept constant. The stability of the airflow in the reaction chamber is kept, the stability of a concentration field and a temperature field is favorably kept, the uniformity of the material is improved, and the defect density is reduced.
Wherein the reaction pressure at the time of growing the first AlN layer 11, the second AlN layer 12, and the third AlN layer 13 is kept constant. The range is 30-100torr, and the lower growth pressure is favorable for reducing the parasitic reaction of the source and improving the crystal quality.
The preparation method adopts Metal Organic Chemical Vapor Deposition (MOCVD) epitaxial growth.
Wherein the steps 1-4 are grown continuously without a transition or stop layer in process between steps.
Wherein said steps 1-4 can be grown in multiple cycles.
The present invention will be described in further detail below with reference to specific embodiments and with reference to the attached drawings.
The first embodiment is as follows:
as shown in fig. 2:
(1) sputtering 75nm AlN on a (0001) plane sapphire substrate to be used as a substrate 10; heating the sputtered AlN substrate 10 to 1100 ℃ in an MOCVD reaction chamber, and annealing at high temperature in the atmosphere of NH3And H2Atmosphere, annealing time 5 minutes.
(2) Keeping the temperature at 1100 ℃ constant and the pressure at 50torr, NH3The flow rate was unchanged, TMAl source was introduced at a V/III ratio of 1280, and a first AlN layer 11 was grown to a thickness of 15 nm.
(3) Raising the temperature from 1100 ℃ to 1250 ℃, gradually raising the temperature, and keeping the temperature for 5 minutes; simultaneously, the gas carrying capacity of a reaction source is unchanged, the pressure is kept unchanged at 50torr, and NH is added3The flow rate was kept constant, and the TMAl source flow was increased to gradually decrease from a V/III ratio of 1280 to 640, to grow a second AlN layer 12 with an AlN growth thickness of 50 nm.
(4) The third AlN layer 13 was grown at a growth rate of 600nm/h for 1 hour while maintaining the temperature at 1250 ℃ and the pressure at 50 torr.
The AlN epitaxial layer obtained in the embodiment is flat in surface and has the root-mean-square roughness smaller than 1nm when observed under an Atomic Force Microscope (AFM), two-dimensional step growth can be observed, the half width at half maximum of a (002) plane rocking curve is lower than 200arcsec when the X-ray diffraction (XRD) scans, and the half width at half maximum of a (102) plane is lower than 650 arcsec, compared with AlN which is grown without the method, namely, the temperature is directly increased on a sputtering AlN substrate, the half width at half maximum of the (102) plane is obviously improved, 100-shaped and 200arcsec is reduced, and the half width at half maximum of 002 is also improved, and the screw-shaped and edge-shaped dislocation density in the high-temperature epitaxial AlN layer is obviously reduced by. At a thickness of about 600nm, a higher crystalline quality and a smooth and flat surface are obtained.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (9)
1. A preparation method of an AlN thin film comprises the following steps:
step 1: annealing the substrate for epitaxy;
step 2: growing a first AlN layer on the substrate, wherein the growth temperature is the same as the annealing temperature in the step 1;
and step 3: growing a second AlN layer on the first AlN layer, the second AlN layer having a growth temperature and an Al source flow that are graded, the growth temperature of the second AlN layer being a temperature graded from the growth temperature of the first AlN layer to the third AlN layer, the Al source flow of the second AlN layer being an Al source flow graded from the Al source flow of the first AlN layer to the third AlN layer;
and 4, step 4: and growing a third AlN layer with constant temperature and constant source on the second AlN layer.
2. The method for preparing the AlN thin film according to claim 1, wherein the step 1 anneals the substrate at 950-1150 ℃ for 5-15 minutes in NH3And H2An atmosphere.
3. The method of producing an AlN thin film according to claim 1, wherein the thickness of the first AlN layer is 5-30 nm.
4. The method of producing an AlN thin film according to claim 1, wherein the second AlN layer has a thickness of 10-100 nm.
5. The method for preparing an AlN thin film according to claim 1, wherein the growth temperature of the third AlN layer is 1000-1500 ℃.
6. The method for producing an AlN thin film according to claim 1, wherein NH is generated when the first AlN layer, the second AlN layer and the third AlN layer are grown3The gas flow and the gas carrying capacity of the reaction source are kept constant.
7. The method of producing an AlN thin film according to claim 6, wherein the reaction pressure at the time of growing the first AlN layer, the second AlN layer and the third AlN layer is kept constant.
8. The method for producing an AlN thin film according to claim 1, wherein the base comprises an AlN bulk single-crystal substrate; or a buffer layer of magnetron sputtered AlN or in-situ grown A1N on a sapphire, silicon carbide or silicon substrate; or AlN, GaN, or gallium oxide epitaxial layer templates.
9. The method for preparing an AlN film according to claim 1, wherein the method for preparing is epitaxial growth using Metal Organic Chemical Vapor Deposition (MOCVD).
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| CN109727847A (en) * | 2018-12-28 | 2019-05-07 | 华中科技大学鄂州工业技术研究院 | AlN film and preparation method based on Sapphire Substrate |
| CN110098287B (en) * | 2019-03-19 | 2020-07-31 | 华灿光电股份有限公司 | AlN template and method for manufacturing light-emitting diode epitaxial wafer |
| CN111146078B (en) * | 2019-12-27 | 2022-11-15 | 中国电子科技集团公司第十三研究所 | Preparation method of AlN thin film |
| CN111341645B (en) * | 2020-03-31 | 2023-04-07 | 江西力特康光学有限公司 | Method for manufacturing aluminum nitride semiconductor film and structure thereof |
| CN111509093A (en) * | 2020-04-24 | 2020-08-07 | 苏州紫灿科技有限公司 | AlN thin film with gradual change insertion layer and preparation method thereof |
| CN111676451A (en) * | 2020-06-28 | 2020-09-18 | 中国科学院半导体研究所 | Preparation method of polarity-controllable high-quality AlN template |
| CN114381699A (en) * | 2020-10-21 | 2022-04-22 | 中国科学院苏州纳米技术与纳米仿生研究所 | Metal single crystal film and preparation method thereof |
| CN113451457A (en) * | 2021-06-25 | 2021-09-28 | 中国科学院半导体研究所 | Preparation method of AlN thin film |
| CN115579434B (en) * | 2022-12-09 | 2023-02-07 | 埃特曼(苏州)半导体技术有限公司 | Epitaxial wafer of semiconductor optoelectronic device and manufacturing method and application thereof |
| CN116741854A (en) * | 2023-08-11 | 2023-09-12 | 至芯半导体(杭州)有限公司 | AlN film and preparation method and application thereof |
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| US8629065B2 (en) * | 2009-11-06 | 2014-01-14 | Ostendo Technologies, Inc. | Growth of planar non-polar {10-10} M-plane gallium nitride with hydride vapor phase epitaxy (HVPE) |
| CN103361718A (en) * | 2012-04-09 | 2013-10-23 | 中国科学院物理研究所 | Method for growing aluminium nitride monocrystal by using physical vapor transport method |
| JP2014179544A (en) * | 2013-03-15 | 2014-09-25 | Asahi Kasei Corp | AlN THIN FILM MANUFACTURING METHOD AND AlN THIN FILM |
| CN105762247A (en) * | 2016-03-02 | 2016-07-13 | 厦门乾照光电股份有限公司 | Nitride buffer layer manufacturing method in composite structure |
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