CN118147578A - Aluminum nitride coating with different preferred orientations and preparation method thereof - Google Patents

Abstract

An aluminum nitride coating containing different preferred orientations and a preparation method thereof, wherein the preparation method comprises the following steps: feeding the substrate cleaned by the plasma into a reaction cavity, and depositing a first preferred orientation aluminum nitride coating on the surface of the substrate by adopting a magnetron sputtering mode; feeding the deposited substrate into a static placing chamber, and cooling to a preset temperature; delivering the cooled substrate into a transition chamber in vacuum pumping, bombarding the first preferred orientation aluminum nitride coating by adopting a gas ion source, and depositing the first preferred orientation aluminum nitride coating to form an amorphous aluminum nitride transition layer; and (3) sending the substrate after amorphization into a reaction cavity, and depositing a second preferred orientation aluminum nitride coating on the surface of the amorphous aluminum nitride transition layer by adopting a magnetron sputtering mode. According to the invention, aluminum nitride coatings with different preferred orientations are compounded on the same substrate by adopting an ion source bombardment technology to replace a single aluminum oxide coating, so that the performance compounding is realized, and the mechanical property, the insulation barrier property and the corrosion resistance of the CVD Mask are improved.

Description

Aluminum nitride coating with different preferred orientations and preparation method thereof

Technical Field

The invention relates to the technical field of material surface treatment, and in particular to an aluminum nitride coating containing different preferred orientations and a preparation method thereof.

Background technique

In recent years, flexible OLED display technology is gradually becoming the mainstream display technology, and high-quality chemical vapor deposition mask (CVD Mask) is the key to achieving high-quality OLED packaging performance. Because CVD Mask has very strict requirements on position accuracy, in order to avoid position deformation caused by temperature changes, CVD Mask is generally prepared using Invar alloy. In order to improve the barrier insulation and corrosion resistance of CVD Mask, a layer of Al ₂ O ₃ film is usually prepared on its surface, but the thermal expansion coefficient of Invar alloy is very different from that of Al ₂ O ₃ , which can easily cause deformation of CVD Mask during the deposition of thin films, and the accuracy of CVD Mask cannot be guaranteed. In addition, the large internal stress may even lead to demolding failure.

Summary of the invention

Based on this, the purpose of the present invention is to provide an aluminum nitride coating containing different preferred orientations and a preparation method, by adopting a composite structure of aluminum nitride coating containing different preferred orientations to replace the single aluminum oxide coating, so as to improve the mechanical properties, insulation barrier properties and corrosion resistance of CVDMask.

In a first aspect, the present invention provides an aluminum nitride coating containing different preferred orientations, formed on the surface of a substrate, including a first preferred orientation aluminum nitride coating located on the surface of the substrate, an amorphous aluminum nitride transition layer located on the surface of the first preferred orientation aluminum nitride coating, and a second preferred orientation aluminum nitride coating located on the surface of the amorphous aluminum nitride transition layer, wherein the preferred orientations of the second preferred orientation aluminum nitride coating and the first preferred orientation aluminum nitride coating are different.

Furthermore, the thickness of the first preferentially oriented aluminum nitride coating is 1 to 3 um, the thickness of the amorphous aluminum nitride transition layer is 50 to 200 nm; and the thickness of the second preferentially oriented aluminum nitride coating is 1 to 3 um.

Furthermore, the preferred orientation of the aluminum nitride coating is the preferred crystal plane orientation of aluminum oxide crystals.

Furthermore, the preferred crystal plane has wurtzite as a main crystal structure, showing growth in the a-axis direction or the c-axis direction.

In a second aspect, the present invention provides a method for preparing an aluminum nitride coating having different preferred orientations, comprising the following steps:

Step S10, placing the plasma-cleaned substrate into a reaction chamber, and depositing a first preferentially oriented aluminum nitride coating on the surface of the substrate by magnetron sputtering, with the substrate moving at a first preset speed;

Step S11, sending the deposited substrate into a static chamber to cool it to a preset temperature;

Step S12, sending the cooled substrate into a vacuum transition chamber, bombarding the first preferentially oriented aluminum nitride coating with a gas ion source, so as to deposit an amorphous aluminum nitride transition layer on the first preferentially oriented aluminum nitride coating;

In step S13, the amorphized substrate is fed into a reaction chamber, and a second preferentially oriented aluminum nitride coating is deposited on the surface of the amorphous aluminum nitride transition layer by magnetron sputtering. The substrate moves at a second preset speed, which is different from the first preset speed.

Furthermore, in step S10 and step S13, the power source used for magnetron sputtering is a medium frequency power source, the voltage is 300-600V, the working gas is argon, and the reaction gas is nitrogen.

Furthermore, in step S11, the preset temperature is 20-50°C.

Further, in step S12, the gas ion source is a linear anode ion source, the working gas is argon, the voltage is adjustable in the range of 50 to 300 V, and the bombardment time is 10 to 30 minutes.

Further, in step S10, the substrate is mounted on a translation track in the reaction chamber, and the translation track drives the substrate to reciprocate;

The translation track is provided with a pulse bias power supply for applying a negative bias voltage to the substrate and a heating device for heating the substrate.

Furthermore, the voltage range of the pulse bias power supply is 0-500V, the heating temperature range of the heating device is 50-200°C, and the movement speed range of the translation track is 0-200mm/s.

Furthermore, before step S10, the preparation method further comprises:

The substrate is transferred to the positioning stand by a soft-contact electric forklift, and the substrate is automatically sent to the cleaning equipment for ultrasonic cleaning and drying by a manipulator;

The dried substrate is automatically transferred to the vacuum chamber by a robot, and after the vacuum is evacuated to a preset vacuum degree, the working gas is continuously introduced;

A gas ion source is used to bombard the substrate surface to perform plasma cleaning on the substrate.

Furthermore, the gas ion source is a linear anode ion source, the working gas is argon, the voltage can be adjusted in the range of 800 to 1000 V, and the bombardment time is 10 to 30 minutes.

Compared with the prior art, in the present invention, aluminum nitride coatings with different preferential orientations are composited on the same substrate by adopting ion source bombardment technology to replace the single aluminum oxide coating, thereby achieving performance composite, so as to improve the mechanical properties, insulation barrier properties and corrosion resistance of the CVD Mask.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the structure of an aluminum nitride coating having different preferred orientations in the present invention;

FIG2 is a flow chart of a method for preparing aluminum nitride coatings having different preferred orientations according to the present invention;

FIG3 is a schematic diagram of the hcp-AlN crystal structure of the present invention;

FIG4 is an XRD diffraction pattern of the aluminum nitride coating substrate and coating prepared at different translational orbital motion speeds (0 mm/s, 5 mm/s and 200 mm/s, the samples are named AlN-0, AlN-5, AlN-20, respectively) in the present invention;

FIG5 is a surface and interface morphology of samples prepared at different translational orbital motion speeds (0 mm/s, 5 mm/s and 200 mm/s, the samples are named AlN-0, AlN-5, AlN-20, respectively) in the present invention;

FIG6 is a graph showing the surface resistivity and dielectric strength test results of aluminum nitride coatings with different preferred orientations prepared on the surface of Invar alloy in the present invention;

FIG7 is a Tafel curve of aluminum nitride coatings with different preferred orientations prepared on the surface of Invar alloy in the present invention in a 1 mol/L NaF solution and a fitted corrosion potential and corrosion current density curve;

FIG8 is an XRD diffraction spectrum of the composite, upper and lower layers of aluminum nitride coatings with different preferred orientations on the surface of Invar alloy in the present invention;

FIG. 9 is a cross-sectional morphology diagram of two different composite sequences of aluminum nitride coatings with different preferred orientations on the surface of Invar alloy in the present invention.

The following specific implementation manner will further illustrate the present invention in conjunction with the above-mentioned drawings.

Detailed ways

In order to facilitate understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. Several embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

Please refer to Figure 1. In the first aspect, the present invention provides an aluminum nitride coating containing different preferred orientations, which is formed on the surface of a substrate, including a first preferred orientation aluminum nitride coating located on the surface of the substrate, an amorphous aluminum nitride transition layer located on the surface of the first preferred orientation aluminum nitride coating, and a second preferred orientation aluminum nitride coating located on the surface of the amorphous aluminum nitride transition layer. The preferred orientations of the second preferred orientation aluminum nitride coating and the first preferred orientation aluminum nitride coating are different, so that the two aluminum nitride coatings with different preferred orientations can be combined.

It should be noted that, in the present application, the thickness of the first preferentially oriented aluminum nitride coating is 1 to 3 um, the thickness of the amorphous aluminum nitride transition layer is 20 to 200 nm; the thickness of the second preferentially oriented aluminum nitride coating is 1 to 3 um.

Furthermore, the preferred orientation of the aluminum nitride coating is the preferred crystal plane orientation of the aluminum oxide crystal, and the preferred crystal plane has wurtzite as the main crystal structure, showing growth in the a-axis direction or the c-axis direction.

Referring to FIG. 2 , in a second aspect, the present invention provides a method for preparing an aluminum nitride coating having different preferred orientations, comprising the following steps:

Step S10, placing the plasma-cleaned substrate into a reaction chamber, and depositing a first preferentially oriented aluminum nitride coating on the surface of the substrate by magnetron sputtering, with the substrate moving at a first preset speed;

In this step, the power source used for magnetron sputtering is a medium frequency power source with a voltage of 300-600V, the working gas is argon, and the reaction gas is nitrogen.

It should be noted that in this step, the substrate is mounted on a translation track in the reaction chamber, and the translation track drives the substrate to reciprocate to perform reciprocating coating, and the first preset speed is set according to the preferred orientation of the desired aluminum nitride coating;

The translation track is provided with a pulse bias power supply for applying a negative bias voltage to the substrate and a heating device for heating the substrate.

The voltage range of the pulse bias power supply is 0-500V, the heating temperature range of the heating device is 50-200°C, and the movement speed range of the translation track is 0-200mm/s. The sputtering voltage is preferably 400-500V, and the standard flow rate of the introduced reaction gas is preferably 10sccm or more and 20sccm or less to ensure that the sputtering process is carried out under transition conditions to obtain an aluminum nitride coating with a standard stoichiometric ratio.

Step S11, sending the deposited substrate into a static chamber to cool it to a preset temperature;

In this step, the preset temperature is 20-50°C.

Step S12, sending the cooled substrate into a vacuum transition chamber, bombarding the first preferentially oriented aluminum nitride coating with a gas ion source, so as to deposit an amorphous aluminum nitride transition layer on the first preferentially oriented aluminum nitride coating;

It should be noted that, in this step, the gas ion source is used to bombard the first preferentially oriented aluminum nitride coating in order to form an amorphous aluminum nitride transition layer, so as to realize the composite of aluminum nitride coatings with different preferential orientations on the same substrate.

Specifically, in this step, the gas ion source is a linear anode ion source, the working gas is argon, the voltage is adjustable in the range of 50 to 300 V, and the bombardment time is 10 to 30 minutes.

In step S13, the amorphized substrate is fed into a reaction chamber, and a second preferentially oriented aluminum nitride coating is deposited on the surface of the amorphous aluminum nitride transition layer by magnetron sputtering. The substrate moves at a second preset speed, which is different from the first preset speed.

Furthermore, before step S10, the preparation method further comprises:

The substrate is transferred to the positioning stand by a soft-contact electric forklift, and the substrate is automatically sent to the cleaning equipment for ultrasonic cleaning and drying by a manipulator;

The dried substrate is automatically transferred to the vacuum chamber by a robot, and after the vacuum is evacuated to a preset vacuum degree, the working gas is continuously introduced;

It should be noted that in this step, the vacuum degree in the vacuum chamber needs to be evacuated to below 8×10 ⁻⁴ Pa in advance, in order to minimize the influence of background residual gas on the subsequent reactive sputtering process.

A gas ion source is used to bombard the substrate surface to perform plasma cleaning on the substrate.

It should be noted that the gas ion source used is a linear cation source, and the working gas is argon. The ion source voltage is preferably 800-1000V, and the ion source bombardment time is preferably 10-30min, the purpose of which is to remove the residual water molecule film and organic matter in the substrate to be coated area, to activate the substrate and improve the film-substrate bonding force.

In summary, in the present invention, aluminum nitride coatings with different preferential orientations are composited on the same substrate by adopting ion source bombardment technology to replace the single aluminum oxide coating, thereby achieving performance composite, so as to improve the mechanical properties, insulation barrier properties and corrosion resistance of the CVD Mask.

It should be noted that the preparation method of the present application can be applied to the surfaces of different substrates, and is suitable for aluminum oxide coatings, yttrium oxide coatings, and the like.

The following is a specific description with examples:

First, preprocessing:

In the Class 1000 dust-free workshop, a soft-contact electric forklift is used to transfer the CVD Mask substrate to the positioning stand. After the substrate is adjusted to the appropriate position, a forklift is used to transfer the substrate to the cleaning equipment.

The barcode scanner is used to extract the product's external dimensions. The automated cleaning and transmission section adaptively adjusts the positions of the manipulator, lifting fixture, and transmission wheel according to the product's dimensions. The forklift lifts the substrate to the front section of the cleaning machine where the manipulator grabs it. The manipulator automatically transfers the substrate to the cleaning equipment for cleaning, which includes: ultrasonic liquid cleaning - 1 ultrasonic rinse - 2 ultrasonic rinses - scanning spray - clean air removal of water - vacuum dehydration - cleanliness inspection;

In order to prevent the cleaned CVD Mask substrate from being attached by tiny particles, this stage is transferred to a fully automatic transfer process, including: tray connection - tray transmission - robot grabbing - substrate rack receiving substrate - substrate rack transmission to the cleaning area in the vacuum chamber.

Second, preparation of aluminum nitride coatings with different preferred orientations

The first type of preferentially oriented aluminum nitride coating deposition: vacuuming - gas plasma surface cleaning - high-speed online detection of particles (≥10um) - adjusting the distance between the sputtering cathode and the substrate to 8cm, setting the moving speed of the translational track where the substrate is located to 200mm/s, sputtering aluminum nitride - online monitoring of the thickness and temperature of the aluminum nitride coating, after reaching a thickness of 1um, transporting it to a static room for cooling and cooling it to 25°C;

Amorphous aluminum nitride transition layer deposition: the substrate is transferred from the static chamber to the transition chamber - vacuum pumping - linear ion source low-energy argon ion bombardment;

The second preferentially oriented aluminum nitride coating deposition: sent to the reaction chamber again - adjust the substrate rack moving speed to 0mm/s, and keep other parameters unchanged, and deposit the second preferentially oriented aluminum nitride coating facing the sputtering target - after standing for 10 hours, the CVD Mask product is transferred to the automated transmission section through the transition chamber - transferred from the substrate rack to the unloading robot position - the robot grabs the product - the forklift moves to the fixed position to receive the product - the robot detaches from the product, and the forklift receives it.

Third, shipment inspection

Check whether the sheet surface is wrinkled, the cell position accuracy, the sheet droop, the edge aluminum nitride coating integrity, and whether the aluminum nitride coating resistance meets the requirements. After passing the inspection, transfer it into the nitrogen protection storage box for shipment.

Specifically, AlN thin film was prepared on the surface of Invar alloy by medium frequency reactive magnetron sputtering, the medium frequency power supply power was set to 500W, the frequency was set to 20kHz, the duty cycle was set to 40%, the flow ratio of the introduced working gas Ar to the reactive gas _N2 was set to 32:12sccm, the substrate temperature was heated to 200℃, and sputtering was continued for 60min at this temperature. The substrate movement speed was used as a variable to control the substrate to move back and forth between the twin cathode sputtering targets. The substrate movement speed was set to 0, 5 and 200mm/s respectively, and AlN thin films were prepared and named: AlN-0, AlN-5, AlN-20.

Please refer to Figure 3. It should be noted that crystalline AlN is mainly hexagonal wurtzite (hcp), with a lattice constant of There are two types of Al-N bonds in hcp-AlN: _B1 type and _B2 type. The bond length of _B1 type covalent bond is/> Its formation energy is less than the bond length / > _B2 -type ionic bonds. In the hcp-AlN crystal structure, a single Al (or N) atom combines with four adjacent N (or Al) atoms to form a regular tetrahedron, and further forms a triangular prism with _C3V symmetry with different atoms with the _B2 bond as the coaxis (as shown in 4). The direction of the B2 bond is the c _- axis. When the c-axis is perpendicular to the substrate, AlN presents a c-axis orientation, and the surface parallel to the substrate is a close-packed surface, such as the (002) surface; when the c-axis is parallel to the substrate, it presents an a-axis orientation, and the surface parallel to the substrate is a loosely packed surface, such as the (100) surface. The (002) plane is composed of _B1 and _B2 type bonds, and the (100) plane is composed only of _B1 type bonds. Studies have confirmed that the kinetic energy of the adsorbed atoms will greatly affect the formation of the orientation, and the formation of the combination of _B1 and _B2 bonds requires high energy. This is also the reason why high-energy deposition conditions are required to form the (002) plane, while lower energy conditions are suitable for the formation of the (100) plane.

Please refer to Figure 4. The dotted box contains the diffraction peaks of AlN, while the unmarked diffraction peaks belong to the Invar alloy substrate. The XRD diffraction peaks in the box all match the standard ICSD (00-025-1133), indicating that the crystal structure belongs to hcp-AlN. The diffraction peaks with 2θ values of 33.2°, 36.0°, and 59.4° correspond to the (100), (002), and (110) orientations, respectively. From the XRD diffraction spectrum, it can be seen that when the substrate movement speed is 200mm/s, AlN-20 has the highest intensity diffraction peak at 2θ=33.2°, indicating that the preferred orientation of the film is (100), which belongs to the a-axis orientation; when the movement speed drops to 5mm/s, AlN-5 has a preferred orientation of (002) and a certain intensity of (100) diffraction peak; when the movement speed is 0mm/s, AlN-0 has a preferred orientation of (002), and the intensity is higher than that of 5mm/s, indicating that the crystallinity is improved. It can be seen that when preparing AlN film, stillness is conducive to the growth of (002) orientation, while the increase of movement speed will be conducive to the growth of (100) orientation and inhibit the (002) orientation.

Based on the XRD diffraction pattern, the grain size of the prepared AlN film was calculated using the Scherrer formula, and the grain size calculation results of the aluminum nitride film prepared at different rotation speeds were obtained. The results showed that the grain size of the aluminum nitride film prepared at 0 mm/s was 25.31 nm; the grain size corresponding to the (002) orientation in the aluminum nitride film prepared at 5 mm/s was 30.20 nm, and the grain size corresponding to the (100) orientation was 32.19 nm; the grain size of the aluminum oxide film prepared at 20 mm/s was 40.06 nm. Therefore, it is concluded that the increase in the moving speed will increase the grain size of the AlN film, and the grain size of the (002) orientation is smaller than the grain size of the (100) orientation.

Please refer to Figure 5, the surface of the AlN film is dense without obvious cracks or pores. It can be seen that with the increase of the substrate movement speed, the grains of the prepared aluminum nitride film become coarser and more uneven. The aluminum nitride film structure under the condition of 200mm/s is in a columnar crystal state, and the aluminum nitride film structure prepared under the conditions of 0mm/s and 5mm/s is dense without obvious columnar crystal structure.

Combining the XRD and SEM results, the surface grain size of the film with (100) preferred orientation is larger, and the cross section has a more obvious columnar crystal structure; while the surface grain size of the film with (002) preferred orientation is smaller, the columnar crystal structure of the cross section is not obvious, and the film layer is more dense. The SEM characterization results match the grain size trend calculated based on XRD, and also show that the film quality of the AlN film with (002) preferred orientation is better than that of the film with (100) preferred orientation. EDS energy spectrum analysis was performed on the AlN film, and the film thickness and aluminum-nitrogen ratio of the aluminum nitride films prepared at different movement speeds were obtained: the film thicknesses of AlN-0, AlN-5, and AlN-20 were 1050, 1180, and 1060 nm, respectively, and the corresponding deposition rates were 17.5, 19.7, and 17.7 nm/min; the aluminum-nitrogen atomic percentages of AlN-0, AlN-5, and AlN-20 were 48.23:51.77, 51.35:48.65, and 50.54:49.46, respectively, indicating that the AlN film prepared under this deposition condition basically meets the standard stoichiometric aluminum-nitrogen ratio of 1:1.

Please refer to Figure 6. As the protective coating of the Mask, the good insulation performance of the AlN film is an important condition to ensure that it does not spark and break down when in contact with the conductive glass. The surface resistance is measured using a concentric hammer electrode and converted into surface resistivity. As shown in Figure 6, the average surface resistivity of AlN (100) is 2.1×10 ¹³ Ω, and that of AlN (002) is 1.3×10 ¹⁴ Ω. The average surface resistivity of the (002) orientation is 6.2 times that of the (100) orientation. The two different orientations of the AlN film are both orders of magnitude higher than the surface resistivity of 2×10 ¹² Ω of Al ₂ O ₃ on the surface of Invar alloy. The dielectric strength test results of the AlN film on the surface of Invar alloy show that the dielectric strength of the two preferred orientations is not much different. Compared with the dielectric strength of 45V/μm of the Al ₂ O ₃ film on the surface of Invar alloy, the insulation performance and breakdown resistance of the AlN film are significantly improved. The results show that (002) preferred oriented AlN films have better insulation properties and are more suitable as insulating barriers.

Please refer to Figure 7. The Tafel polarization curve of AlN potentiodynamic polarization in 1 mol/L NaF solution system was measured, and the corrosion potential and corrosion current density results were obtained by fitting the curve. The results show that the corrosion potential E _corr of the Invar alloy substrate is 0.2663V, and the corrosion current density I _corr is 1.62× ^10-9 A/ ^cm2 ; the corrosion potential E _corr of the (100) preferentially oriented AlN film is 0.3411V, and the corrosion current density I _corr is 5.49× ^10-7 A/ ^cm2 ; the corrosion potential E _corr of the (002) preferentially oriented AlN film is 0.3191V, and the corrosion current density I _corr is 1.95× ^10-8 A/ ^cm2 ; It can be clearly seen from Figure 6 that the preparation of AlN film effectively improves the corrosion resistance of Invar alloy, and the corrosion resistance of AlN(100) is significantly better than that of AlN(002). By analyzing the fitted corrosion current density and corrosion potential data results, the corrosion current density of AlN (002) is 12 times that of AlN (100). The results show that the (100) preferred orientation AlN film has better F ^- corrosion resistance.

Please refer to Figure 1. Considering that the performance advantages of AlN films with different preferred orientations have different focuses, combined with ion source bombardment technology, a composite AlN coating with (100) and (002) preferred orientations is deposited on an Invar alloy substrate to achieve a combination of their advantageous properties. The (002) preferred orientation improves wear resistance and insulation properties, and the (100) preferred orientation improves corrosion resistance.

Please refer to FIG8 . In a preferred embodiment of the present application, the XRD diffraction pattern of the AlN composite coating with different preferred orientations deposited on the Invar alloy substrate shows that the scheme achieves the composite preparation of (100) and (002) preferred oriented AlN films on the same substrate.

Please refer to FIG. 9 . In another preferred embodiment of the present application, different composite sequences may be used to prepare AlN films having both (100) and (002) preferred orientations according to different application scenarios and requirements for AlN film performance.

In summary, the present invention couples and regulates the preparation parameters of the substrate to achieve the regulation of the preferred orientation of the aluminum nitride coating, realizes the conversion of the c-axis orientation and the a-axis orientation of the aluminum nitride coating on the surface of Invar alloy, and combines the ion source bombardment technology to composite coatings of the same material with different preferred orientations on the same substrate to achieve performance composite, providing a new solution and theoretical guidance for the preparation technology of the mask protective coating in the OLED evaporation process.

In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other. The above-mentioned embodiments only express several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims (10)

1. An aluminum nitride coating containing different preferred orientations, formed on the surface of a substrate, characterized in that it includes a first preferred orientation aluminum nitride coating located on the surface of the substrate, an amorphous aluminum nitride transition layer located on the surface of the first preferred orientation aluminum nitride coating, and a second preferred orientation aluminum nitride coating located on the surface of the amorphous aluminum nitride transition layer, wherein the preferred orientations of the second preferred orientation aluminum nitride coating and the first preferred orientation aluminum nitride coating are different. 2. The aluminum nitride coating containing different preferred orientations according to claim 1 is characterized in that the thickness of the first preferred orientation aluminum nitride coating is 1~3um, the thickness of the amorphous aluminum nitride transition layer is 50~200nm; the thickness of the second preferred orientation aluminum nitride coating is 1~3um. 3. The aluminum nitride coating with different preferred orientations according to claim 1, characterized in that the preferred orientation of the aluminum nitride coating is the preferred crystal plane orientation of the aluminum oxide crystal. 4. The aluminum nitride coating with different preferred orientations according to claim 3 is characterized in that the preferred crystal plane has wurtzite as the main crystal structure and exhibits growth in the a-axis direction or the c-axis direction. 5. A method for preparing an aluminum nitride coating having different preferred orientations, characterized in that it comprises the following steps: Step S10, placing the plasma-cleaned substrate into a reaction chamber, and depositing a first preferentially oriented aluminum nitride coating on the surface of the substrate by magnetron sputtering, with the substrate moving at a first preset speed; Step S11, sending the deposited substrate into a static chamber to cool it to a preset temperature; Step S12, sending the cooled substrate into a vacuum transition chamber, bombarding the first preferentially oriented aluminum nitride coating with a gas ion source, so as to deposit an amorphous aluminum nitride transition layer on the first preferentially oriented aluminum nitride coating; In step S13, the amorphized substrate is fed into a reaction chamber, and a second preferentially oriented aluminum nitride coating is deposited on the surface of the amorphous aluminum nitride transition layer by magnetron sputtering. The substrate moves at a second preset speed, which is different from the first preset speed. 6. The method for preparing an aluminum nitride coating having different preferred orientations according to claim 5, characterized in that, in step S10 and step S13, the power source used for magnetron sputtering is a medium frequency power source, the voltage is 300-600V, the working gas is argon, and the reaction gas is nitrogen; In step S11, the preset temperature is 20 to 50°C; In step S12, the gas ion source is a linear anode ion source, the working gas is argon, the voltage is adjustable in the range of 50 to 300 V, and the bombardment time is 10 to 30 min. 7. The method for preparing an aluminum nitride coating having different preferred orientations according to claim 5, characterized in that, in step S10, the substrate is mounted on a translation track in a reaction chamber, and the translation track drives the substrate to reciprocate; The translation track is provided with a pulse bias power supply for applying a negative bias voltage to the substrate and a heating device for heating the substrate. 8. The method for preparing an aluminum nitride coating with different preferred orientations according to claim 7, characterized in that the voltage range of the pulse bias power supply is 0 ~ 500 V, the heating temperature range of the heating device is 50 ~ 200 ° C, and the movement speed range of the translation track is 0 ~ 200 mm/s. 9. The method for preparing an aluminum nitride coating having different preferred orientations according to claim 5, characterized in that before step S10, the method further comprises: The substrate is transferred to the positioning stand by a soft-contact electric forklift, and the substrate is automatically sent to the cleaning equipment for ultrasonic cleaning and drying by a manipulator; The dried substrate is automatically transferred to the vacuum chamber by a robot, and after the vacuum is evacuated to a preset vacuum degree, the working gas is continuously introduced; A gas ion source is used to bombard the substrate surface to perform plasma cleaning on the substrate. 10. The method for preparing an aluminum nitride coating with different preferred orientations according to claim 9, characterized in that the gas ion source is a linear anode ion source, the working gas is argon, the voltage is adjustable in the range of 800 to 1000 V, and the bombardment time is 10 to 30 min.