A doped aluminum nitride ferroelectric thin film, a ferroelectric device and a preparation method thereof

Abstract

This invention discloses a doped aluminum nitride ferroelectric thin film, a ferroelectric device, and its fabrication method. The doped aluminum nitride ferroelectric thin film has a wurtzite crystal structure and forms an atomic layer structure with periodically modulated doping concentration along the polarization axis [0001]. This structure is composed of alternating stacks of highly doped and low-doped atomic sublayers, with a period length as small as one unit cell length. The vertical spacing between cation and anion layers in different sublayers varies, thus introducing localized polarization differences at the atomic scale. By controlling the sputtering parameters, a periodic distribution of doping elements along the film thickness direction can be achieved. Under external electric field or electron beam excitation, the thin film exhibits non-collective step-like polarization reversal dynamics, which is beneficial for reducing the polarization reversal energy barrier and improving ferroelectric switching performance. This invention also provides a ferroelectric device based on this thin film and its fabrication method, which has good process compatibility and application prospects.

Description

Technical Field

[0001] This invention belongs to the field of microelectronic materials and devices technology, specifically relating to a doped aluminum nitride ferroelectric thin film, a ferroelectric device, and a method for preparing the same. Background Technology

[0002] Ferroelectric materials, due to their spontaneous polarization and the ability to reverse polarization direction with an external electric field, have broad application prospects in non-volatile memories, field-effect transistors, piezoelectric devices, and neuromorphic computing. Traditional ferroelectric materials are typically composed of perovskite oxides, such as lead zirconate titanate and barium titanate. The ferroelectric polarization reversal behavior of these materials can be described using classical frameworks such as the Ginzburg-Landau-Devrheim theory and soft-mode theory. However, as semiconductor process nodes evolve towards the nanoscale, the bottlenecks of traditional ferroelectric materials in terms of CMOS process compatibility, thermal stability, and miniaturization characteristics are becoming increasingly prominent.

[0003] In recent years, the large remanent ferroelectric polarization characteristics discovered in doped wurtzite aluminum nitride (AlN) materials have attracted widespread attention from academia and industry. This material, due to its excellent polarization intensity, high thermal stability, and good scalability, is considered a highly promising candidate material for next-generation non-volatile memories. Currently, research on doped aluminum nitride mainly focuses on optimizing macroscopic storage performance, such as adjusting doping concentration and electrode type. However, research on device performance regulation based on thin film atomic structure arrangement remains insufficient, hindering further improvements in device performance. Therefore, there is an urgent need to design a performance optimization strategy to improve the performance of doped aluminum nitride ferroelectric thin films and ferroelectric devices from an atomic scale perspective. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a doped aluminum nitride ferroelectric thin film, a ferroelectric device, and a method for preparing the same. By controlling the preparation process, the dopant elements are orderly distributed in the wurtzite aluminum nitride lattice, resulting in an atomic layer structure with periodically modulated doping concentration along the polarization axis. This introduces localized polarization differences at the atomic scale, regulates the polarization reversal dynamics, and thereby improves polarization reversal efficiency and ferroelectric performance.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A doped aluminum nitride ferroelectric thin film has a wurtzite crystal structure. The characteristic feature is that the doped aluminum nitride ferroelectric thin film forms an atomic layer structure with periodically modulated doping concentration along the polarization axis

[0001] . The atomic layer structure includes alternating highly doped and low-doped atomic sublayers along the

[0001] direction. In the highly doped atomic sublayer, the cation layer is occupied by highly doped elements and aluminum atoms, and in the low-doped atomic sublayer, the cation layer is occupied by low-doped elements and aluminum atoms. The anion layers are all occupied by nitrogen atoms. The doping elements are Sc, B, Ga, Y, Zr, or Hf. The thickness of the doped aluminum nitride ferroelectric thin film is 20-100 nm.

[0007] Furthermore, in the highly doped atomic sublayer, the vertical distance between the center of the cation layer and the center of the adjacent anion layer along the

[0001] direction is Δr1; in the low-doped atomic sublayer, the vertical distance between the center of the cation layer and the center of the adjacent anion layer along the

[0001] direction is Δr2, and Δr1 and Δr2 are different. Since different sublayers have different local polarization intensities, a local polarization structure that changes periodically along the polarization axis direction is formed.

[0008] Furthermore, the periodically modulated atomic layer structure has a period length ranging from 0.5 to 5 nm.

[0009] A ferroelectric device, characterized in that: from bottom to top, it comprises a substrate, a bottom electrode, a ferroelectric thin film layer, and a top electrode, wherein the ferroelectric thin film layer is the doped aluminum nitride ferroelectric thin film according to any one of claims 1 to 3; wherein, the substrate is selected from one of Si / SiO2, Si(110), Si(111), Al2O3, and GaN; and the bottom electrode and the top electrode are selected from one or more of Pt, W, Al, Mo, and TiN.

[0010] Furthermore, the ferroelectric device is a ferroelectric capacitor, a ferroelectric diode, or a ferroelectric field-effect transistor.

[0011] A method for fabricating a ferroelectric device includes the following steps:

[0012] Step 1: Clean and pretreat the substrate;

[0013] Step 2: Deposit a bottom electrode layer on the substrate;

[0014] Step 3: A magnetron sputtering process is used to deposit a doped aluminum nitride ferroelectric thin film on the bottom electrode layer. Under vacuum conditions of 200-500°C, an aluminum element target and a doped element target are used in a mixed atmosphere of argon and nitrogen. The doped aluminum nitride ferroelectric thin film is deposited on the formed bottom electrode by dual-target DC co-sputtering. The sputtering power of the aluminum target is fixed at 20 to 200W. By adjusting the time period from 30 seconds to 10 minutes and the sputtering power of the target position from 10W to 200W, the dynamic distribution control of the doped element during the film growth process is realized. This results in a periodically modulated doping concentration structure along the

[0001] direction of the doped aluminum nitride ferroelectric thin film, which is composed of alternating high-doped atomic sublayers and low-doped atomic sublayers. The doped element is Sc, B, Ga, Y, Zr or Hf.

[0015] Step 4: Remove the silicon substrate with the deposited bottom electrode and aluminum nitride doped film, attach a hard mask with the electrode pattern to the substrate surface, and use magnetron sputtering to prepare the top electrode on the substrate surface with the hard mask attached.

[0016] Further, step one specifically involves ultrasonically cleaning the substrate sequentially with acetone solution, anhydrous ethanol, and deionized water for 10-15 minutes to remove surface organic matter and particulate contamination. Then, the substrate is dried with a high-purity nitrogen gun and immediately sent into the magnetron sputtering chamber.

[0017] Furthermore, step two specifically involves depositing a bottom electrode on the pretreated silicon substrate using magnetron sputtering, with the bottom electrode having a thickness of 20-200 nm.

[0018] Furthermore, in step three, an aluminum elemental target and a doped elemental target are used to prepare a doped aluminum nitride thin film by dual-target co-sputtering in a mixed gas of argon and nitrogen. The doping concentration in the film is controlled by fixing the power of the aluminum elemental target and adjusting the power of the doped elemental target. Alternatively, an aluminum nitride ceramic target and a doped elemental nitride ceramic target are used to prepare a doped aluminum nitride thin film by dual-target co-sputtering in a mixed gas of argon and nitrogen. The doping concentration in the film is controlled by fixing the power of the aluminum nitride ceramic target and adjusting the power of the doped elemental nitride ceramic target. By adjusting the sputtering power and deposition time, the periodic enrichment and depletion of the doped element in the thickness direction of the film are achieved, thereby obtaining the periodic modulated atomic layer structure.

[0019] Furthermore, step four specifically involves: depositing a top electrode on the doped aluminum nitride ferroelectric thin film using DC magnetron sputtering; defining the top electrode pattern using a hard mask that has been fabricated to create the electrode pattern; and ensuring that the top electrode pattern is square with a minimum size of 100 × 100 μm. 2 The maximum size is 500×500 μm. 2 Preferably, the thickness of the top electrode is 20-100 nm.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1) This invention breaks through the existing technical path of relying mainly on uniform doping and macroscopic parameter optimization for doped aluminum nitride ferroelectric thin films, and proposes a new structural design scheme based on periodic modulation of atomic-scale doping concentration; by controlling the doping concentration distribution along the polarization axis

[0001] , a periodic atomic structure is formed by alternating stacking of highly doped atomic sublayers and low-doped atomic sublayers.

[0022] 2) Under external electric field or electron beam excitation, the thin film exhibits non-collective step-like polarization reversal dynamics. Since the potential barrier overcome by each step of this multi-step reversal behavior is low, polarization reversal is easier to occur, thereby improving polarization reversal efficiency and ferroelectric switching characteristics.

[0023] 3) A reactive co-sputtering process is employed, using an aluminum elemental target and a doped elemental target, or an aluminum nitride ceramic target and a doped element nitride ceramic target, for co-sputtering. By adjusting the sputtering power and deposition time, the doping concentration in the thin film can be precisely controlled, achieving periodic enrichment and depletion of the doped element along the film thickness direction, thereby obtaining a high-quality doped aluminum nitride thin film with the aforementioned periodic atomic structure. This preparation method is compatible with existing semiconductor processes, has good repeatability, and is suitable for large-scale production. Attached Figure Description

[0024] Figure 1 The aluminum nitride ferroelectric thin film of the present invention is along

[11] High-resolution iDPC-STEM atomic images in the [0] direction;

[0025] Figure 2 This is a schematic diagram of the structure of the aluminum nitride-doped ferroelectric thin film-based ferroelectric device of the present invention;

[0026] Figure 3 This is a comparison chart of the ferroelectric curves of the control group and the control group in the aluminum nitride doped ferroelectric capacitor device of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] See Figure 1-3 This invention proposes a doped aluminum nitride ferroelectric thin film, a ferroelectric device, and a method for preparing the same, comprising the following steps:

[0029] Step 1: Clean and pretreat the Si(100) / SiO2 substrate;

[0030] Specifically, the Si(100) / SiO2 substrate was ultrasonically cleaned for 15 min in sequence with acetone solution, anhydrous ethanol and deionized water to remove surface organic matter and particulate contamination. Then, the substrate was dried with a high-purity nitrogen gun and immediately sent into the magnetron sputtering chamber.

[0031] Step 2: Deposit a bottom electrode Pt with a thickness of 100 nm on the pretreated silicon substrate using magnetron sputtering;

[0032] Step 3: Preparation of doped aluminum nitride ferroelectric thin films;

[0033] Specifically, under high-temperature vacuum conditions of 400 degrees Celsius, aluminum and scandium targets were used to deposit an aluminum nitride ferroelectric thin film on the bottom electrode formed in step two via dual-target DC co-sputtering in a mixed atmosphere of argon and nitrogen. The aluminum target sputtering power was fixed at 200 W, while the scandium target power was alternated between 150 W and 170 W for the control group. The deposition time under each power condition was 30 seconds, the sputtering pressure was 3 mTorr, and the N2 gas flow rate was 10 sccm. By controlling these process parameters, periodic enrichment and depletion of dopants along the film thickness direction were achieved, thereby obtaining a periodically modulated atomic layer structure. Figure 1 As shown, the doped aluminum nitride ferroelectric thin film of the present invention is along

[11] High-resolution iDPC-STEM atomic images along the

[0001] direction show that the vertical spacing between the center of the cation layer and the center of the adjacent anion layer in the highly doped atomic sublayer along the

[0001] direction is Δr1; the vertical spacing between the center of the cation layer and the center of the adjacent anion layer in the low-doped atomic sublayer along the

[0001] direction is Δr2, and Δr1 and Δr2 are different. Δr1 and Δr2 show obvious longitudinal alternation, indicating that there is a periodic modulation structure in the film with alternating stacking of highly doped and low-doped atomic sublayers along the polarization axis

[0001] . As a control group, the scandium target power was fixed at 160W, the sputtering pressure was 3 mTorr, the N2 gas flow rate was 10 sccm, and the other process conditions were the same as those of the control group.

[0034] Step 4: Deposit the top electrode on the doped aluminum nitride ferroelectric thin film. A schematic diagram of the device structure is shown below. Figure 2 As shown in the figure: 1 is the Si(100) / SiO2 substrate; 2 is the bottom electrode layer; 3 is the ferroelectric functional layer; 4 is the top electrode layer.

[0035] Specifically, a top electrode is deposited on the doped aluminum nitride ferroelectric thin film obtained in step three using DC magnetron sputtering. The top electrode pattern is defined by a hard mask with a pre-fabricated electrode pattern. The top electrode pattern is square, with a minimum size of 100 × 100 μm. 2 The maximum size is 500×500 μm. 2 Thus, a ferroelectric capacitor device based on doped aluminum nitride ferroelectric thin film was obtained.

[0036] Figure 3 The figures show the ferroelectric curves of the control group and the control group. The coercivity field of the control group is lower than that of the control group, indicating that the periodic modulation structure is beneficial to reducing the difficulty of polarization reversal.

[0037] Obviously, the embodiments described above are merely some embodiments of this application, and not all embodiments. This application can be implemented in many different forms; rather, the purpose of providing these embodiments is to make the disclosure of this application more thorough and comprehensive. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing specific embodiments, or make equivalent substitutions for some of the technical features. Any equivalent structures made using the content of this application's specification and drawings, directly or indirectly applied to other related technical fields, are similarly within the scope of protection of this application.

Claims

1. A doped aluminum nitride ferroelectric thin film having a wurtzite crystal structure, characterized in that, The doped aluminum nitride ferroelectric thin film forms an atomic layer structure with periodically modulated doping concentration along the polarization axis [0001]. The atomic layer structure includes alternating highly doped atomic sublayers and low-doped atomic sublayers along the [0001] direction. The cation layer in the highly doped atomic sublayer is occupied by highly doped elements and aluminum atoms, the cation layer in the low-doped atomic sublayer is occupied by low-doped elements and aluminum atoms, and the anion layer is occupied by nitrogen atoms. The doping elements are Sc, B, Ga, Y, Zr, or Hf. The thickness of the doped aluminum nitride ferroelectric thin film is 20-100 nm.

2. The doped aluminum nitride ferroelectric thin film according to claim 1, characterized in that, The vertical distance between the center of the cation layer and the center of the adjacent anion layer in the highly doped atomic sublayer along the [0001] direction is Δr1; the vertical distance between the center of the cation layer and the center of the adjacent anion layer in the low-doped atomic sublayer along the [0001] direction is Δr2, and Δr1 and Δr2 are different. Since different sublayers have different local polarization intensities, a local polarization structure that changes periodically along the polarization axis direction is formed.

3. The doped aluminum nitride ferroelectric thin film according to claim 1, characterized in that, The periodically modulated atomic layer structure has a period length ranging from 0.5 to 5 nm.

4. A ferroelectric device, characterized in that, From bottom to top, it comprises a substrate, a bottom electrode, a ferroelectric thin film layer, and a top electrode, wherein the ferroelectric thin film layer is the doped aluminum nitride ferroelectric thin film according to any one of claims 1 to 3; wherein the substrate is selected from one of Si / SiO2, Si(110), Si(111), Al2O3, and GaN; and the bottom electrode and the top electrode are selected from one or more of Pt, W, Al, Mo, and TiN.

5. The ferroelectric device according to claim 4, characterized in that, The ferroelectric device is a ferroelectric capacitor, a ferroelectric diode, or a ferroelectric field-effect transistor.

6. A method for preparing a ferroelectric device, characterized in that, Includes the following steps: Step 1: Clean and pretreat the substrate; Step 2: Deposit a bottom electrode layer on the substrate; Step 3: A magnetron sputtering process is used to deposit a doped aluminum nitride ferroelectric thin film on the bottom electrode layer. Under vacuum conditions of 200-500°C, an aluminum element target and a doped element target are used in a mixed atmosphere of argon and nitrogen. The doped aluminum nitride ferroelectric thin film is deposited on the formed bottom electrode by dual-target DC co-sputtering. The sputtering power of the aluminum target is fixed at 20 to 200W. By adjusting the time period from 30 seconds to 10 minutes and the sputtering power of the target position from 10W to 200W, the dynamic distribution control of the doped element during the film growth process is realized. This results in a periodically modulated doping concentration structure along the [0001] direction of the doped aluminum nitride ferroelectric thin film, which is composed of alternating high-doped atomic sublayers and low-doped atomic sublayers. The doped element is Sc, B, Ga, Y, Zr or Hf. Step 4: Remove the silicon substrate with the deposited bottom electrode and aluminum nitride doped film, attach a hard mask with the electrode pattern to the substrate surface, and use magnetron sputtering to prepare the top electrode on the substrate surface with the hard mask attached.

7. The method for preparing the ferroelectric device according to claim 6, characterized in that, Step one is as follows: The substrate is ultrasonically cleaned with acetone solution, anhydrous ethanol and deionized water for 10-15 minutes in sequence to remove surface organic matter and particulate contamination. Then, the substrate is dried with a high-purity nitrogen gun and immediately sent into the magnetron sputtering chamber.

8. The method for preparing the ferroelectric device according to claim 6, characterized in that, Step two specifically involves depositing a bottom electrode on the pretreated silicon substrate using magnetron sputtering, with the bottom electrode having a thickness of 20-200 nm.

9. The method for preparing the ferroelectric device according to claim 6, characterized in that, Step 3 involves using an aluminum elemental target and a doped elemental target for dual-target co-sputtering in a mixture of argon and nitrogen to prepare a doped aluminum nitride thin film. The doping concentration in the film is controlled by fixing the power of the aluminum elemental target and adjusting the power of the doped elemental target. Alternatively, an aluminum nitride ceramic target and a doped elemental nitride ceramic target are used for dual-target co-sputtering in a mixture of argon and nitrogen to prepare a doped aluminum nitride thin film. The doping concentration in the film is controlled by fixing the power of the aluminum nitride ceramic target and adjusting the power of the doped elemental nitride ceramic target. By adjusting the sputtering power and deposition time, the periodic enrichment and depletion of the doped element in the film thickness direction are achieved, thereby obtaining the periodic modulated atomic layer structure.

10. The method for preparing the ferroelectric device according to claim 6, characterized in that, Step four specifically involves depositing a top electrode on the doped aluminum nitride ferroelectric thin film using DC magnetron sputtering. The top electrode pattern is defined by a hard mask that has been fabricated to create the electrode pattern. The top electrode pattern is square, with a minimum size of 100 × 100 μm. 2 The maximum size is 500×500 μm. 2 The thickness of the top electrode is 20-100 nm.

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