Preparation method of AlN thin film for high-frequency broadband filter and AlN thin film

Abstract

This application provides a method for preparing an AlN thin film for a high-frequency broadband filter and the AlN thin film itself, belonging to the field of semiconductor device technology. The method for preparing the AlN thin film includes the following steps: 1) growing a substrate layer on a Si substrate using MOCVD to obtain a substrate epitaxial wafer; 2) performing low-power PVD sputtering deposition on the substrate epitaxial wafer to grow an AlN intermediate layer; 3) then performing high-power PVD sputtering deposition on the AlN intermediate layer to grow an AlN top layer, thus obtaining the AlN thin film. This application, through the combined use of two PVD sputtering deposition steps, can simultaneously coordinate the warpage, surface roughness, and crystal quality of the AlN thin film, thereby obtaining an AlN thin film with excellent overall performance.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of an AlN film for a high-frequency broadband filter and the AlN film, and belongs to the technical field of semiconductor devices. BACKGROUND

[0002] With the development of 5G communication technology, filters gradually develop in the direction of high frequency, small size and high precision. Traditional filter materials such as piezoelectric ceramic materials are difficult to meet the application conditions of high frequency due to performance limitations, and also have the disadvantages of large size and slow response. As the third generation semiconductor material, AlN has the advantages of good piezoelectric performance, high thermal conductivity and good chemical stability, and the AlN film along the C-axis has an extremely high acoustic wave speed of 11354 m·s -1 Therefore, the AlN film has extremely excellent application prospects in high-frequency broadband filters, can ensure high frequency with small size, and also has fast response speed.

[0003] At present, the AlN piezoelectric film can be grown at low temperature on sapphire, SiC and Si substrates by physical vapor deposition (PVD), such as magnetron sputtering. Compared with other substrates, the Si substrate has the advantages of good electrically conductive and heat conductive performance and low cost, but there is a large lattice mismatch and thermal mismatch between the Si substrate and the AlN film. When the AlN film is grown by the traditional PVD method, there is a strong coupling effect between the AlN and the substrate, which will cause a large in-plane stress on the AlN film, and the use of PVD to grow AlN directly on Si will cause a large number of dislocations due to the lattice mismatch and thermal mismatch, affecting the crystal quality of the AlN film. Therefore, the AlN piezoelectric film sputtered on the Si substrate has poor comprehensive performance, and it is difficult to balance the warpage, surface roughness and crystal quality, and often the surface roughness and crystal quality are deteriorated after the warpage is optimized. This has a great influence on the subsequent growth of other films on the AlN film, such as AlScN film, and on the device process and device performance. SUMMARY

[0004] The first object of the application is to provide a preparation method of an AlN film for a high-frequency broadband filter, which can coordinate the in-plane stress state, surface roughness and crystal quality of the AlN film on the Si substrate, and obtain an AlN film with good comprehensive performance.

[0005] The second object of the application is to provide an AlN film which can simultaneously satisfy low in-plane stress, low surface roughness and high crystal quality, and has good comprehensive performance.

[0006] The preparation method of the AlN film for a high-frequency broadband filter of the application adopts the following scheme:

[0007] A method for preparing an AlN thin film for a high-frequency broadband filter includes the following steps: 1) growing a substrate layer on a Si substrate using MOCVD to obtain a substrate epitaxial wafer; 2) performing low-power PVD sputtering deposition on the substrate epitaxial wafer to grow an AlN intermediate layer; the sputtering power of the low-power PVD sputtering deposition is 1500~1900 W; 3) then performing high-power PVD sputtering deposition on the AlN intermediate layer to grow an AlN top layer, thereby obtaining the AlN thin film; the sputtering power of the high-power PVD deposition sputtering is 2100~3000 W. This application first performs low-power PVD sputtering deposition on the substrate layer. The lower sputtering power makes it easier for the in-plane stress of the AlN film to transform from tensile stress to compressive stress, and the overall warpage changes from concave to convex. The compressive stress on the low-power AlN layer can offset the tensile stress on other AlN film layers, thereby maintaining the overall stress state at a low level. At the same time, the polycrystalline layer generated by the low-power AlN film can relax some of the in-plane stress caused by the strong coupling between the upper AlN film and the substrate layer, thereby reducing residual stress. Then, high-power PVD sputtering deposition is performed. The higher power deposition helps to increase the initial energy of Al atoms when they reach the surface of the epitaxial wafer, thereby increasing the surface mobility of Al atoms. This allows Al atoms to migrate to suitable positions and form bonds, which helps to suppress 3D growth and thus improves the crystal quality and surface roughness of the film. This application uses two PVD sputtering deposition steps in combination. The power coordination between the two steps can simultaneously coordinate the stress state, surface roughness, and crystal quality of the AlN film, thereby obtaining an AlN film with good overall performance, which is beneficial for application in high-frequency broadband filters.

[0008] The MOCVD method described in this application refers to Metal-Organic Chemical Vapor Deposition, and the PVD method refers to Physical Vapor Deposition, primarily DC reactive magnetron sputtering. Before PVD sputtering deposition, this application also employs MOCVD to prepare a substrate layer. Utilizing the advantage of high-temperature MOCVD in preparing high-quality AlN thin films (including ultrathin, crack-free films within 200 nm), a high-quality substrate is provided for the upper PVD-AlN layer, allowing the upper PVD-AlN layer to inherit the advantages of the substrate and improve the overall performance of PVD-AlN. Exemplarily, the substrate layer is an AlN layer.

[0009] Preferably, the sputtering power of the high-power PVD sputtering deposition is P1, and the sputtering power of the low-power PVD sputtering deposition is P2, where 600 W ≤ P1 - P2 ≤ 1100 W. By controlling the power of the high-power and low-power PVD sputtering deposition, the two PVD sputtering deposition steps are closely coordinated. The lower power sputtering conditions can regulate the internal stress state, causing the internal stress to reverse. On this basis, high-power sputtering is beneficial to improving the overall crystal quality of the AlN film. At the same time, the combination of high and low power can effectively offset the internal stress, thereby reducing the residual stress of the overall film and giving the obtained AlN film excellent comprehensive performance.

[0010] Preferably, the conditions for the low-power PVD sputtering deposition include: the sputtering target is an Al target, the substrate temperature is 400~650℃, the gas volumetric flow rate Ar:N2≥1:6, the working gas pressure is 4~10 mTorr; and the thickness of the AlN interlayer is 50~150 nm.

[0011] Preferably, the conditions for the low-power PVD sputtering deposition include: sputtering power of 1600~1800 W, substrate temperature of 450~500℃, gas volumetric flow rate ratio of Ar:N2 of 1:(4~6), working gas pressure of 5~7 mTorr; and the thickness of the AlN interlayer of 65~100 nm.

[0012] Furthermore, the conditions for the low-power PVD sputtering deposition include: sputtering power of 1700 W, substrate temperature of 500 °C, and working pressure of 7 mTorr.

[0013] Preferably, the conditions for high-power PVD sputtering deposition include: an Al sputtering target, a substrate temperature of 650-720°C, a gas volumetric flow rate of Ar:N2 ≤ 1:6, a working pressure of 2-4 mTorr, and a thickness of 200-800 nm for the AlN top layer. This application uses a lower argon-nitrogen ratio, which on the one hand suppresses the growth rate, allowing Al or AlN sufficient time for surface migration; on the other hand, it makes it easier for free Al to collide with N. Since Al has a much larger mass than N, the energy lost in collisions between Al and N is less than the energy lost in collisions between Al and N, thus effectively increasing the energy of Al. Furthermore, at a lower working pressure, Ar ions have a longer mean free path, reducing the probability of collisions before reaching the Al target. Combined with higher sputtering power, this provides sufficient energy for Al ions, increasing their migration length. Additionally, a higher substrate temperature also contributes to increasing the surface migration length. These conditions, combined with high-power sputtering, optimize the surface and crystal quality of the AlN top layer, further improving the overall performance of the AlN thin film.

[0014] Preferably, the conditions for high-power PVD sputtering deposition include: sputtering power of 2400~2700 W, substrate temperature of 680~700℃, gas volumetric flow rate of Ar:N2 of 1:(6~10), working pressure of 2.8~3.2 mTorr, and thickness of the AlN top layer of 300~700 nm.

[0015] Furthermore, the conditions for the high-power PVD sputtering deposition include: a sputtering power of 2550 W, a substrate temperature of 700 °C, and a working pressure of 2.8 mTorr.

[0016] The technical solution adopted in this application for the AlN thin film is as follows:

[0017] The AlN thin film prepared by any of the above methods comprises a substrate layer, an AlN intermediate layer, and an AlN top layer. This application controls the growth process of the AlN thin film through a two-step combination of low-power PVD sputtering deposition and high-power PVD sputtering deposition, adjusting the stress state and growth kinetics of the AlN intermediate layer and the AlN top layer. This improves the internal stress of the AlN thin film, optimizes the stress state, and also enhances the surface and crystal quality of the AlN thin film, achieving a comprehensive performance of low residual stress, low surface roughness, and high crystal quality.

[0018] Preferably, the thickness of the substrate layer is 50-2000 nm; the thickness of the AlN intermediate layer is 50-150 nm; and the thickness of the AlN top layer is 200-800 nm. Using a thinner AlN intermediate layer ensures excellent crystal quality while also relaxing the interfacial stress of the substrate to a certain extent; simultaneously, the thicker AlN top layer ensures both the surface and crystal quality of the AlN film, thus obtaining an AlN film with excellent overall performance.

[0019] Preferably, the thickness of the AlN intermediate layer is 65~100 nm, and the thickness of the AlN top layer is 300~700 nm. Attached Figure Description

[0020] Figure 1 Image showing the warpage of the AlN film in Example 1;

[0021] Figure 2 The image shows the warpage of the AlN film in Comparative Example 1.

[0022] Figure 3 The image shows the warpage of the AlN film in Comparative Example 2.

[0023] Figure 4 An optical microscope image of the AlN thin film in Comparative Example 2;

[0024] Figure 5 An optical microscope image of the AlN thin film in Comparative Example 3;

[0025] Figure 6 The image shows the AFM surface morphology of the AlN thin film in Example 1.

[0026] Figure 7 The image shows the AFM surface morphology of the AlN film in Comparative Example 1.

[0027] Figure 8 The XRD pattern of the AlN thin film in Example 1;

[0028] Figure 9 The image shows the XRD pattern of the AlN thin film in Comparative Example 1. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0030] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, every point or individual value between the endpoints of the range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value or with other lower or upper limits to form a range not explicitly stated.

[0031] In existing technologies, AlN thin films on Si substrates suffer from poor overall performance, including residual stress, surface roughness, and crystal quality, due to the large in-plane stress generated by decoupling. It is also difficult to balance stress state, surface roughness, and crystal quality. Therefore, it is necessary to propose new methods for preparing AlN thin films to coordinate the various performance indicators of AlN thin films and meet the performance requirements of application devices.

[0032] To address the aforementioned problems, this application provides a method for preparing an AlN thin film. The technical solution adopted is as follows: A method for preparing an AlN thin film includes the following steps: 1) growing a substrate layer on a Si substrate using MOCVD to obtain a substrate epitaxial wafer; 2) performing low-power PVD sputtering deposition on the substrate epitaxial wafer to grow an AlN intermediate layer; the sputtering power of the low-power PVD sputtering deposition is 1500~1900 W; 3) then performing high-power PVD sputtering deposition on the AlN intermediate layer to grow an AlN top layer, thereby obtaining the AlN thin film; the sputtering power of the high-power PVD deposition sputtering is 2100~3000 W.

[0033] In some specific embodiments, the low-power PVD sputtering deposition is further preceded by pretreatment of the PVD equipment, Al target, and AlN substrate epitaxial wafer, respectively.

[0034] In some specific embodiments, pretreatment of the PVD equipment includes placing the tray in the PVD furnace and running the production process more than three times. The production process may vary depending on the equipment, and the pretreatment is carried out according to the actual situation. The purpose is to remove water molecules and oxygen adsorbed on the surface of the tray after it has not been used for a long time.

[0035] In some specific embodiments, pretreatment of the Al target material includes introducing Ar gas at 600-700°C for 1-5 minutes, for example, introducing Ar gas at 650°C for 3 minutes. By bombarding the Al target material with Ar ions without introducing N2, the nitrides on the surface of the Al target material are removed, thereby obtaining a stable AlN growth state.

[0036] In some specific embodiments, the pretreatment of the AlN substrate epitaxial wafer includes placing the AlN substrate epitaxial wafer in a PVD furnace and baking it at a high temperature of 650~740°C for 30~300 s, preferably 60 s. The high temperature baking can remove water and oxygen particles and organic impurities on the epitaxial wafer.

[0037] In some specific embodiments, in the high-power PVD sputtering deposition, the upper limit of the sputtering power is selected from any value among 2300 W, 2400 W, 2500 W, 2600 W, 2700 W, 2800 W, 2900 W, and 3000 W, and the lower limit of the sputtering power is selected from any value among 2100 W, 2200 W, 2300 W, 2400 W, 2500 W, 2600 W, 2700 W, 2800 W, and 2900 W. The sputtering power is selected from a range consisting of any value taken from the upper and lower limits. In the low-power PVD sputtering deposition, the upper limit of the sputtering power is selected from any value among 1600 W, 1700 W, 1800 W, and 1900 W, and the lower limit of the sputtering power is selected from any value among 1500 W, 1600 W, 1700 W, and 1800 W. The sputtering power is selected from a range consisting of any value taken from the upper and lower limits.

[0038] In some specific embodiments, the conditions for the low-power PVD sputtering deposition include: the sputtering target is an Al target, the substrate temperature is 400~650℃, the gas volumetric flow rate Ar:N2≥1:6, the working gas pressure is 4~10 mTorr; and the thickness of the AlN interlayer is 50~150 nm.

[0039] In some specific embodiments, in the low-power PVD sputtering deposition conditions, the upper limit of the substrate temperature is selected from any value among 450℃, 500℃, 550℃, 600℃, and 650℃, and the lower limit of the substrate temperature is selected from any value among 400℃, 450℃, 500℃, 550℃, and 600℃. The substrate temperature is selected from a range consisting of any value between the upper and lower limits. The upper limit of the working gas pressure is selected from any value among 5 mTorr, 6 mTorr, 7 mTorr, 8 mTorr, 9 mTorr, and 10 mTorr, and the lower limit of the working gas pressure is selected from any value among 4 mTorr, 5 mTorr, 6 mTorr, 7 mTorr, 8 mTorr, and 9 mTorr. The working gas pressure is selected from a range consisting of any two values ​​between the upper and lower limits. The gas volumetric flow rate Ar:N2 is selected from a range consisting of any two values ​​among 1:1, 1:2, 1:3, 1:4, 1:5, and 1:6.

[0040] In some specific embodiments, the conditions for the high-power PVD sputtering deposition include: the sputtering target is an Al target, the substrate temperature is 650~720℃, the gas volumetric flow rate Ar:N2≤1:6, the working gas pressure is 2~4 mTorr, and the thickness of the AlN top layer is 200~800 nm.

[0041] In some specific embodiments, the high-power PVD sputtering deposition conditions include an upper limit for the substrate temperature selected from any one of 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, and 720°C; a lower limit for the substrate temperature selected from any one of 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, and 710°C; and a substrate temperature range formed by any value taken from the upper and lower limits. The working gas pressure is selected from 2 mTorr, 2.2 mTorr, 2.4 mTorr, 2.5 mTorr, 2.6 mTorr, 2.8 mTorr, 3 mTorr, 3.2 mTorr, 3.4 mTorr, 3.5 mTorr, 3.6 mTorr, 3.8 mTorr, and 4 mTorr. The range consisting of any two values ​​in mTorr; the gas volumetric flow rate Ar:N2 is selected from the range consisting of any two values ​​in 1:6, 1:7, 1:8, 1:9, 1:10, 1:20, and 1:30.

[0042] For example, when the substrate layer is an AlN substrate layer, the growth of the substrate layer using the MOCVD method includes the following steps: pre-depositing an Al atomic layer on a Si substrate, and then sequentially depositing an LT-AlN nucleation layer and an HT-AlN layer to obtain the AlN substrate layer. This application controls the growth of the AlN substrate layer using the MOCVD method, simultaneously preparing an LT-AlN nucleation layer (low-temperature AlN nucleation layer) and an HT-AlN layer (high-temperature AlN layer), which together form a high-quality AlN substrate layer. Using this as the substrate for the PVD-AlN epitaxial film is beneficial for further improving the crystal quality of the PVD-AlN epitaxial film.

[0043] In some specific embodiments, the conditions for pre-depositing the Al atomic layer include: a pre-deposit temperature of 800~900℃, a gas pressure of 50~100 Torr, a TMAl volumetric flow rate of 10~30 sccm, and a pre-deposit time of 30~60 s.

[0044] In some specific embodiments, the Si substrate is further subjected to annealing before the pre-deposition of the Al atomic layer. The annealing conditions include: annealing temperature of 1050~1100℃, annealing pressure of 50~100 Torr, and processing time of 4~6 min.

[0045] Optionally, the deposition conditions of the LT-AlN nucleation layer include: a deposition temperature of 850~900℃, a deposition pressure of 50~100 Torr, a TMAl volumetric flow rate of 190~220 sccm, an NH3 volumetric flow rate of 5~5.2 slm, and a deposition time of 0.5~1.5 min.

[0046] Optionally, the deposition conditions of the HT-AlN layer include: a deposition temperature of 1050~1120℃, a deposition pressure of 30~50 Torr, a TMAl volumetric flow rate of 230~250 sccm, an NH3 volumetric flow rate of 21~23 slm, and a deposition time of 4~5 min.

[0047] Examples

[0048] The technical solution of this application will be described below with reference to specific embodiments. The raw materials used in the following embodiments are all from commercially available products, and the devices or equipment used are all purchased from conventional market sales channels. The PVD sputtering system is purchased from the iTops A230 aluminum nitride sputtering system of North China Electronics Technology Group Co., Ltd.

[0049] Example 1

[0050] The method for preparing the AlN thin film in this embodiment includes the following steps:

[0051] 1) The cleaned Si substrate was placed into the MOCVD reaction chamber. The chamber pressure was maintained at 50 Torr, and annealing was performed at 1050℃ for 4 min. After annealing, the temperature was lowered, and the TMAl volumetric flow rate was controlled at 10 sccm. An Al atomic layer was pre-deposited at 800℃ and 50 Torr for 30 s. Following the pre-deposited Al atomic layer, an LT-AlN nucleation layer was deposited. The deposition conditions for the LT-AlN nucleation layer were: deposition temperature 850℃, deposition pressure 50 Torr, TMAl volumetric flow rate 190 sccm, NH3 volumetric flow rate 5 slm, and deposition time 0.5 min. Next, an HT-AlN layer was deposited. The deposition conditions for the HT-AlN layer were: deposition temperature 1050℃, deposition pressure 30 Torr, TMAl volumetric flow rate 230 sccm, NH3 volumetric flow rate 21 slm, and deposition time 4 min. After the HT-AlN layer was deposited, the AlN substrate epitaxial wafer was obtained.

[0052] 2) Place the tray in the PVD furnace and run the production program more than 3 times. Then, pretreat the Al target material by introducing Ar gas at 650°C for 3 minutes. Next, place the substrate epitaxial wafer in the PVD furnace and bake it at 700°C for 60 seconds. After baking, cool it down.

[0053] 3) The baked substrate epitaxial wafer was subjected to low-power PVD sputtering deposition to grow an AlN intermediate layer. The conditions for low-power PVD sputtering deposition included: sputtering power of 1700 W, substrate temperature of 500℃, gas volume flow rate of Ar:N2=1:4, and working pressure of 6 mTorr.

[0054] 4) Then, high-power PVD sputtering deposition was performed in situ on the AlN intermediate layer to grow the AlN top layer. The conditions for high-power PVD sputtering deposition included: sputtering power of 2550 W, substrate temperature of 700℃, gas volumetric flow rate Ar:N2=1:6, and working pressure of 2.8 mTorr; the power difference between high-power PVD sputtering deposition and low-power PVD sputtering deposition was 850 W.

[0055] 5) After the AlN top layer is grown, the AlN film of this embodiment is obtained. The AlN film includes an AlN base layer, an AlN intermediate layer and an AlN top layer, wherein the thickness of the AlN base layer is 50 nm, the thickness of the AlN intermediate layer is 100 nm and the thickness of the AlN top layer is 700 nm.

[0056] Example 2

[0057] The method for preparing the AlN thin film in this embodiment includes the following steps:

[0058] 1) The cleaned Si substrate was placed into the MOCVD reaction chamber. The chamber pressure was maintained at 50 Torr, and annealing was performed at 1050℃ for 4 min. After annealing, the temperature was lowered, and the TMAl volumetric flow rate was controlled at 10 sccm. An Al atomic layer was pre-deposited at 800℃ and 50 Torr for 30 s. Following the pre-deposited Al atomic layer, an LT-AlN nucleation layer was deposited. The deposition conditions for the LT-AlN nucleation layer were: deposition temperature 850℃, deposition pressure 50 Torr, TMAl volumetric flow rate 190 sccm, NH3 volumetric flow rate 5 slm, and deposition time 0.5 min. Next, an HT-AlN layer was deposited. The deposition conditions for the HT-AlN layer were: deposition temperature 1050℃, deposition pressure 30 Torr, TMAl volumetric flow rate 230 sccm, NH3 volumetric flow rate 21 slm, and deposition time 4 min. After the HT-AlN layer was deposited, the AlN substrate epitaxial wafer was obtained.

[0059] 2) Place the tray in the PVD furnace and run the production program more than 3 times. Then, pretreat the Al target material by introducing Ar gas at 650°C for 3 minutes. Next, place the AlN substrate epitaxial wafer in the PVD furnace and bake it at 650°C for 30 seconds. After baking, cool it down.

[0060] 3) The baked AlN substrate epitaxial wafer was subjected to low-power PVD sputtering deposition to grow an AlN intermediate layer. The conditions for low-power PVD sputtering deposition included: sputtering power of 1500 W, substrate temperature of 400℃, gas volume flow rate of Ar:N2=1:6, and working pressure of 4 mTorr.

[0061] 4) Then, high-power PVD sputtering deposition was performed in situ on the AlN intermediate layer to grow the AlN top layer. The conditions for high-power PVD sputtering deposition included: sputtering power of 2100 W, substrate temperature of 650℃, gas volumetric flow rate Ar:N2=1:10, and working pressure of 2 mTorr; the power difference between high-power PVD sputtering deposition and low-power PVD sputtering deposition was 600 W.

[0062] After the AlN top layer is grown, the AlN film of this embodiment is obtained. The AlN film includes an AlN substrate layer, an AlN intermediate layer and an AlN top layer, wherein the thickness of the AlN substrate layer is 50 nm, the thickness of the AlN intermediate layer is 50 nm and the thickness of the AlN top layer is 200 nm.

[0063] Example 3

[0064] The method for preparing the AlN thin film in this embodiment includes the following steps:

[0065] 1) The cleaned Si substrate was placed into the MOCVD reaction chamber. The MOCVD reaction chamber pressure was maintained at 100 Torr, and annealing was performed at 1100℃ for 6 min. After annealing, the temperature was lowered, and then the volumetric flow rate of TMAl was controlled at 30 sccm. An Al atomic layer was pre-deposited at 100 Torr and 900℃ for 60 s. After the pre-deposited Al atomic layer, an LT-AlN nucleation layer was deposited. The deposition conditions for the LT-AlN nucleation layer were: deposition temperature of 900℃, deposition pressure of 100 Torr, TMAl volumetric flow rate of 220 sccm, NH3 volumetric flow rate of 5.2 slm, and deposition time of 1.5 min. Next, an HT-AlN layer was deposited. The deposition conditions for the HT-AlN layer were: deposition temperature of 1120℃, deposition pressure of 50 Torr, TMAl volumetric flow rate of 250 sccm, NH3 volumetric flow rate of 23 slm, and deposition time of 5 min. After the HT-AlN layer is deposited, an AlN substrate epitaxial wafer is obtained;

[0066] 2) Place the tray in the PVD furnace and run the production program more than 3 times. Then, pretreat the Al target material by introducing Ar gas at 650°C for 3 minutes. Next, place the AlN substrate epitaxial wafer in the PVD furnace and bake it at 740°C for 300 seconds. After baking, cool it down.

[0067] 3) The baked AlN substrate epitaxial wafer was subjected to low-power PVD sputtering deposition to grow an AlN intermediate layer. The conditions for low-power PVD sputtering deposition included: sputtering power of 1900 W, substrate temperature of 650℃, gas volume flow rate Ar:N2=1:4, and working pressure of 10 mTorr.

[0068] 4) Then, high-power PVD sputtering deposition was performed in situ on the AlN intermediate layer to grow the AlN top layer. The conditions for high-power PVD sputtering deposition included: sputtering power of 3000 W, substrate temperature of 720℃, gas volumetric flow rate Ar:N2=1:10, and working pressure of 4 mTorr; the power difference between high-power PVD sputtering deposition and low-power PVD sputtering deposition was 1100 W.

[0069] After the AlN top layer is grown, the AlN film of this embodiment is obtained. The AlN film includes an AlN substrate layer, an AlN intermediate layer and an AlN top layer, wherein the thickness of the AlN substrate layer is 200 nm, the thickness of the AlN intermediate layer is 150 nm and the thickness of the AlN top layer is 600 nm.

[0070] Example 4

[0071] The method for preparing the AlN thin film in this embodiment differs from that in Example 1 only in that:

[0072] Step 3) The conditions for controlling low-power PVD sputtering deposition include: sputtering power of 1800 W, substrate temperature of 450℃, gas volumetric flow rate Ar:N2=1:6, and working gas pressure of 5 mTorr.

[0073] Step 4) The conditions for controlling high-power PVD sputtering deposition include: sputtering power of 2700 W, substrate temperature of 680℃, gas volumetric flow rate Ar:N2=1:10, working gas pressure of 3.2 mTorr; the power difference between high-power PVD sputtering deposition and low-power PVD sputtering deposition is 900 W.

[0074] After the AlN top layer is grown, the AlN film of this embodiment is obtained. The AlN film includes an AlN substrate, an AlN intermediate layer and an AlN top layer, wherein the thickness of the AlN intermediate layer is 65 nm and the thickness of the AlN top layer is 300 nm.

[0075] Example 5

[0076] The method for preparing the AlN thin film in this embodiment differs from that in Example 1 only in that:

[0077] Step 3) The sputtering power of low-power PVD sputtering deposition is 1600 W; Step 4) The sputtering power of high-power PVD sputtering deposition is 2400 W; The power difference between high-power PVD sputtering deposition and low-power PVD sputtering deposition is 800 W.

[0078] Comparative Example 1

[0079] The preparation method of the AlN thin film in this comparative example differs from that in Example 1 only in that:

[0080] Step 3) The sputtering power of low-power PVD sputtering deposition is 1450 W; Step 4) The sputtering power of high-power PVD sputtering deposition is 2550 W; The power difference between high-power PVD sputtering deposition and low-power PVD sputtering deposition is 1100 W.

[0081] Comparative Example 2

[0082] The preparation method of the AlN thin film in this comparative example differs from that in Example 1 only in that:

[0083] Step 3) The sputtering power of low-power PVD sputtering deposition is 1950 W; Step 4) The sputtering power of high-power PVD sputtering deposition is 3050 W; The power difference between high-power PVD sputtering deposition and low-power PVD sputtering deposition is 1100 W.

[0084] Comparative Example 3

[0085] The preparation method of the AlN thin film in this comparative example differs from that in Example 1 only in that steps 1 to 3 are omitted, and high-power PVD sputtering deposition is performed directly on the cleaned Si substrate. The high-power PVD sputtering deposition method is the same as that in Example 1.

[0086] Test case

[0087] The warpage of the AlN films in Examples 1-5 and Comparative Examples 1-2 was tested using a warpage measuring instrument. The maximum warpage of the AlN films in Examples 1-5 and Comparative Examples 1-2 is shown in Table 1 below. The warpage images of Examples 1 and Comparative Examples 1-2 are shown below. Figures 1-3 As shown, by Figures 1-3 It can be seen that Example 1 has high flatness, with a maximum warpage of only 14 nm. Comparative Example 1, with its low-power PVD sputtering power, suffers from severe epitaxial wafer bulging, resulting in a maximum warpage of 93 nm. Comparative Example 2, with its high-power PVD sputtering power, exhibits an overly concave epitaxial wafer, with a maximum warpage of -105 nm. The epitaxial wafers of Comparative Example 2 and Comparative Example 3 were observed using an optical microscope. The optical microscope image of Comparative Example 2 is shown below. Figure 4 As shown, the optical microscope image of Comparative Example 3 is as follows: Figure 5 As shown. By Figure 4 and Figure 5As can be seen, the AlN film in Comparative Example 2 shows a small number of cracks, while the AlN film in Comparative Example 3 shows a large number of cracks on its surface. This indicates that directly performing high-power sputtering deposition without using low-power sputtering results in excessive tensile stress on the PVD-AlN film on the Si substrate, exceeding the film's stress tolerance limit and causing severe surface cracking. In contrast, this application uses low-power growth of the AlN intermediate layer to relax the strong coupling between the upper AlN film and the substrate layer, thereby reducing in-plane stress. Furthermore, the high-power growth of the top AlN layer, combined with the AlN intermediate layer, ensures low warpage and good surface quality of the AlN film.

[0088] The surface roughness of the AlN films in Examples 1-5 and Comparative Examples 1-2 was measured using atomic force microscopy (AFM), and the results are shown in Table 1 below; where, Figure 6 The surface topography of AFM in Example 1 is shown. Figure 7 The AFM surface morphology image of Comparative Example 1 is shown. A comparison reveals that the AlN film prepared by Comparative Example 1 using lower-power PVD sputtering has coarser particles and poorer surface roughness. The calculated root mean square deviation roughness (RMS RSD) of the AlN film reached 3.48 nm, while the RMS RSD roughness of Example 1 was only 0.89 nm, exhibiting significantly lower surface roughness. This indicates that this application, by depositing the AlN top layer with higher power, increases the initial energy of Al atoms reaching the epitaxial wafer surface, which is beneficial for improving the surface mobility of Al atoms. This allows Al atoms to migrate to suitable positions and form bonds, thereby reducing the surface roughness of the AlN film.

[0089] XRD tests were performed on the AlN films of Examples 1-5 and Comparative Examples 1-2, and the full width at half maximum (FWHM) of the (002) plane of each AlN film was calculated. The results are shown in Table 1. For example, the XRD patterns of the AlN films of Example 1 and Comparative Example 1 are shown in Table 1. Figures 8-9 As shown.

[0090] Table 1. Surface roughness of AlN films in Examples 1-5 and Comparative Examples 1-2

[0091]

[0092] As shown in Table 1, compared with Comparative Examples 1 and 2, the warpage of Examples 1-5 was significantly improved, with the maximum absolute value of warpage ranging from 14 to 52 nm. This indicates that the present application coordinates the stress state of the AlN film by combining low-power and high-power PVD sputtering deposition, which is beneficial to improving the warpage of the film and obtaining a flatter AlN film. Furthermore, Examples 1-5 also have lower surface roughness, with root mean square deviation roughness ranging from 0.89 to 2.33 nm. Compared with Comparative Examples 1 and 2, the surface roughness has been significantly reduced. This shows that the low-power and high-power combined deposition sputtering method of the present application is also beneficial to improving the surface roughness of the AlN film. In addition, the half-width at half-maximum (WHM) of the (002) plane of the AlN film of Examples 1-5 was measured to be 1153-1275 sec, which is lower than that of Comparative Examples 1 and 2. This indicates that the AlN obtained by the two-step PVD deposition sputtering process of the present application has a highly preferred orientation, and the crystal quality of AlN is further optimized. As shown in Table 1, this application relaxes part of the interface stress by first performing low-power PVD sputtering deposition, and then uses high-power PVD sputtering deposition to coordinate the internal stress state of the AlN film, thereby optimizing the warpage of the film. It is also beneficial to optimize the surface roughness and crystal quality of the AlN film, making it suitable for preparing high-performance high-frequency broadband filters.

Claims

1. A method for producing an AlN thin film for a high-frequency broadband filter, characterized by, The method comprises the following steps: 1) growing a base layer on a Si substrate by MOCVD to obtain a base epitaxial wafer; 2) performing low-power PVD sputtering deposition on the base epitaxial wafer to grow an AlN intermediate layer; the sputtering power of the low-power PVD sputtering deposition is 1500-1900 W; 3) then performing high-power PVD sputtering deposition on the AlN intermediate layer to grow an AlN top layer, thereby obtaining the AlN film; the sputtering power of the high-power PVD sputtering deposition is 2100-2900 W; the sputtering power of the high-power PVD sputtering deposition is P1, the sputtering power of the low-power PVD sputtering deposition is P2, and 600 W≤P1-P2≤1100 W; the conditions of the low-power PVD sputtering deposition include that the sputtering target is an Al target, the substrate temperature is 400-650 ℃, the gas volume flow ratio Ar:N2 is ≥1:6, and the working pressure is 4-10 mTorr; the thickness of the AlN intermediate layer is 50-150 nm; the conditions of the high-power PVD sputtering deposition include that the sputtering target is an Al target, the substrate temperature is 650-720 ℃, the gas volume flow ratio Ar:N2 is ≤1:6, the working pressure is 2-4 mTorr, and the thickness of the AlN top layer is 200-800 nm.

2. The method of claim 1, wherein the conditions of the low-power PVD sputtering deposition include that the sputtering power is 1600-1800 W, the substrate temperature is 450-500 ℃, the gas volume flow ratio Ar:N2 is 1:(4-6), and the working pressure is 5-7 mTorr; the thickness of the AlN intermediate layer is 65-100 nm.

3. The method of claim 1, wherein the conditions of the high-power PVD sputtering deposition include that the sputtering power is 2400-2700 W, the substrate temperature is 680-700 ℃, the gas volume flow ratio Ar:N2 is 1:(6-10), the working pressure is 2.8-3.2 mTorr, and the thickness of the AlN top layer is 300-700 nm.

4. The AlN thin film prepared according to the method of any one of claims 1 to 3, characterized by The AlN film comprises a base layer, an AlN intermediate layer and an AlN top layer.

5. The AlN film according to claim 4, wherein The thickness of the base layer is 50-2000 nm; the thickness of the AlN intermediate layer is 50-150 nm; and the thickness of the AlN top layer is 200-800 nm.

6. The AlN thin film according to claim 5, characterized by The thickness of the AlN intermediate layer is 65-100 nm, and the thickness of the AlN top layer is 300-700 nm.

Images