A HfO2-based ferroelectric thin film and its preparation method

Abstract

The present invention provides an HfO2-based ferroelectric thin film, comprising a substrate layer, wherein the upper surface of the substrate layer is sequentially provided with a bottom electrode layer, a first HfO2-based thin film layer, an HfSe2 scattered sheet layer, a second HfO2-based thin film layer and a top electrode layer from bottom to top. The present invention also provides a method for preparing the above-mentioned HfO2-based ferroelectric thin film. Compared with the existing technology, the present invention has the following advantages: the present invention significantly improves the polarization strength of the HfO2 ferroelectric thin film by fixing oxygen vacancies at the interface of the two-dimensional HfSe2 embedding layer and introducing asymmetric ferroelectric phase nuclei through regular lattice dislocations, which is specifically manifested in that the polarization value of the HfO2 ferroelectric thin film is increased to a value close to the theoretical value.

Description

Technical Field

[0001] The present invention relates to the field of ferroelectric thin films, and in particular to an HfO2-based ferroelectric thin film and a preparation method thereof. Background Art

[0002] In recent years, HfO2 has garnered increasing attention as a novel ferroelectric oxide. Compared to traditional perovskite ferroelectric materials, HfO2 exhibits a lower dielectric constant and ultrathin nanometer-scale thickness. The ferroelectric properties of HfO2 can be maintained in an ultrathin state, making it highly attractive for the miniaturization of integrated circuits. Furthermore, HfO2 is well known for its wide applications in microelectronics processes, such as high-k insulator gates and non-volatile memory. In this process, HfO2 has developed excellent compatibility with CMOS industrial processes and highly mature ultrathin conformal manufacturing techniques. Therefore, the new ferroelectric phenomenon observed in HfO2 will significantly expand the application range of ferroelectric polarization.

[0003] Generally speaking, non-centrosymmetric crystal structures are the cause of ferroelectricity. Oxygen vacancy defects contribute to the formation of non-centrosymmetric crystal structures. However, HfO2 films with a high number of oxygen vacancies are often sensitive to oxidation, which leads to a decrease in ferroelectric properties and instability. Summary of the Invention

[0004] The purpose of the present invention is to provide an HfO2-based ferroelectric film, which significantly improves the polarization strength of the HfO2 ferroelectric film by fixing oxygen vacancies at the interface of the two-dimensional HfSe2 embedding layer and introducing asymmetric ferroelectric phase nuclei through regular lattice dislocations, thereby increasing the polarization value of the HfO2 ferroelectric film to a value close to the theoretical value.

[0005] To achieve the above-mentioned purpose, the present invention provides an HfO2-based ferroelectric film, including a substrate layer, the upper surface of which is provided with a bottom electrode layer, a first HfO2-based thin film layer, an HfSe2 scattered sheet layer, a second HfO2-based thin film layer and a top electrode layer in sequence from bottom to top.

[0006] Another object of the present invention is to provide a method for preparing the HfO2-based ferroelectric thin film, the method specifically comprising the following steps: S1, pre-cleaning the substrate layer;

[0007] S2, depositing a bottom electrode layer on the substrate layer cleaned in step S1;

[0008] S3, depositing a first HfO2-based thin film layer on the bottom electrode layer deposited in step S2;

[0009] S4, covering the first HfO2-based thin film layer deposited in step S3 with a HfSe2 bulk layer;

[0010] S5, depositing a second HfO2-based thin film layer on the covered HfSe2 bulk layer in step S4;

[0011] S6, performing annealing treatment on the surface of the second HfO2-based thin film layer deposited in step S5;

[0012] S7, depositing a top electrode layer on the second HfO2-based thin film layer annealed in step S6 to obtain a HfO2-based ferroelectric thin film.

[0013] Preferably, in step S1, the material of the substrate layer is silicon, and the substrate layer is cleaned using an RCA cleaning method.

[0014] Preferably, in step S2 and step S7, the materials of the bottom electrode layer and the top electrode layer are both Pt, and the bottom electrode layer and the top electrode layer are both deposited by electron beam evaporation, and the process parameters of the electron beam evaporation method are as follows: vacuum degree is 7Pa, and beam current is 10A.

[0015] Preferably, in step S2 and step S7, the thickness of the bottom electrode layer and the top electrode layer are both 30 nm.

[0016] Preferably, in step S3, the first HfO2-based thin film layer is deposited by atomic layer deposition, and the process parameters are as follows: deposition temperature is 250°C, deposition time is 15-30 min, and deposition thickness is 3-5 nm.

[0017] Preferably, during the atomic layer deposition process, the precursor is Hf[N(CH3)C2H5]4 and the oxidation source precursor is O3.

[0018] Preferably, in step S4, the bulk HfSe2 synthesized by the chemical vapor transport (CVT) method of the purchased HfSe2 single-layer bulk flakes is mechanically exfoliated by standard mechanical exfoliation of the HfSe2 flakes. The specific steps are: the flaky HfSe2 is cleaned by soaking in acetone / propanol, and then detached using a low-residue thermal release tape (Nitto-Denko Revalpha) in a nitrogen environment in a glove box with O2 and H2O <3ppm.

[0019] Preferably, in step S5, the second HfO2-based thin film layer is deposited by atomic layer deposition, and the process parameters are as follows: deposition temperature is 250°C, deposition time is 15-30 min, and thickness is 3-5 nm.

[0020] Preferably, during the atomic layer deposition process, the precursor is Hf[N(CH3)C2H5]4 and the oxidation source precursor is O3.

[0021] Preferably, in step S6, the annealing treatment specifically includes the following steps: heating to 150°C at a heating rate of 5°C / min under a nitrogen protective atmosphere and keeping warm for 5 minutes, heating to 250°C at a heating rate of 3°C / min and keeping warm for 5 minutes, heating to 400°C at a heating rate of 23°C / min and keeping warm for 5 minutes, heating to 450°C at a heating rate of 10°C / min and keeping warm for 5 minutes, and finally heating to 800°C at a heating rate of 10°C / min and keeping warm for 2 minutes, and finally cooling to room temperature.

[0022] Compared with the prior art, the present invention has the following advantages: the present invention fixes oxygen vacancies at the interface of the two-dimensional HfSe2 embedding layer and introduces asymmetric ferroelectric phase nuclei through regular lattice dislocations, thereby significantly improving the polarization strength of the HfO2 ferroelectric film. Specifically, the polarization value of the HfO2 ferroelectric film is increased to a value close to the theoretical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the structure of the HfO2-based ferroelectric thin film of the present invention;

[0024] Figure 2 A flow chart for preparing the HfO2-based ferroelectric thin film of the present invention;

[0025] Figure 3 TEM structure diagram of the HfO2-based ferroelectric thin film prepared in Example 2 of the present invention;

[0026] Figure 4 This is a piezoelectric force microscopy (PFM) response diagram of the HfO2-based ferroelectric film prepared in Example 2 of the present invention;

[0027] Figure 5 This is a polarization characteristic diagram of the HfO2-based ferroelectric thin film prepared in Example 2 of the present invention.

[0028] Description of reference numerals:

[0029] 1-substrate layer; 2-bottom electrode layer; 3-first HfO2-based thin film layer; 4-HfSe2 bulk layer, 5-second HfO2-based thin film layer; 6-top electrode layer. DETAILED DESCRIPTION

[0030] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0031] Example 1

[0032] like Figure 1As shown, a HfO2-based ferroelectric film includes a substrate layer 1, and the upper surface of the substrate layer 1 is provided with a bottom electrode layer 2, a first HfO2-based thin film layer 3, an HfSe2 scattered sheet layer 4, a second HfO2-based thin film layer 5 and a top electrode layer 6 in sequence from bottom to top.

[0033] In the present invention, HfSe2 is a Hf-based two-dimensional semiconductor material. The HfSe2 / HfO2 interface has similar properties to Si / SiO2. Specifically, HfO2 acts as a natural oxide layer on HfSe2, creating a good interface between the two. Furthermore, the introduction of Se can effectively fix oxygen vacancies and form stress with the surrounding Hf-O chemical structure, promoting the formation of a non-centrosymmetric crystal structure phase.

[0034] like Figure 2 As shown, the preparation method of the HfO2-based ferroelectric thin film specifically includes the following steps:

[0035] S1, pre-cleaning the substrate layer 1, the material of the substrate layer 1 is silicon, and the substrate layer 1 is cleaned by RCA cleaning method;

[0036] S2, depositing a bottom electrode layer 2 on the substrate layer 1 cleaned in step S1;

[0037] S3. Depositing a first HfO2-based thin film layer 3 on the bottom electrode layer 2 deposited in step S2 by atomic layer deposition, wherein the precursor is Hf[N(CH3)C2H5]4, the oxidation source precursor is O3, and the process parameters of the atomic layer deposition are as follows: deposition temperature is 250°C, deposition time is 15 minutes, and deposition thickness is 3 nm;

[0038] S4, covering the first HfO2-based thin film layer 3 deposited in step S3 with a HfSe2 bulk layer 4;

[0039] S5. Depositing a second HfO2-based thin film layer 5 on the HfSe2 bulk layer 4 covered in step S4 by atomic layer deposition, wherein the precursor is Hf[N(CH3)C2H5]4, the oxidation source precursor is O3, and the process parameters of the atomic layer deposition are as follows: deposition temperature is 250°C, deposition time is 15 minutes, and deposition thickness is 3-5 nm;

[0040] S6. Anneal the surface of the second HfO2-based thin film layer 5 deposited in step S5, specifically: heat to 150°C at a heating rate of 5°C / min under a nitrogen protective atmosphere and keep warm for 5 minutes, heat to 250°C at a heating rate of 3°C / min and keep warm for 5 minutes, heat to 400°C at a heating rate of 23°C / min and keep warm for 5 minutes, heat to 450°C at a heating rate of 10°C / min and keep warm for 5 minutes, finally heat to 800°C at a heating rate of 10°C / min and keep warm for 2 minutes, and finally cool to room temperature.

[0041] S7 , depositing a top electrode layer 6 on the second HfO 2 -based thin film layer 5 annealed in step S6 to obtain a HfO 2 -based ferroelectric thin film.

[0042] In step S1, the RCA standard cleaning method was first invented by Kern, Puotinen and others in 1965 at the RCA laboratory in Princeton, NJ, and got its name from this. RCA cleaning is a typical and widely used wet chemical cleaning method. It is an effective method for removing various types of contaminants on the surface of silicon wafers. The cleaning equipment used is mostly a multi-tank processing cleaning system.

[0043] The cleaning system mainly includes the following liquids:

[0044] (1) SPM: H2SO4 / H2O2 120-150°C SPM has a high oxidizing ability. It can oxidize metals and dissolve them in the cleaning solution. It can also oxidize organic matter to produce CO2 and H2O. Using SPM to clean silicon wafers can remove heavy organic contamination and some metals on the silicon wafer surface. However, when the organic contamination is particularly severe, it will carbonize the organic matter and become difficult to remove.

[0045] (2) HF (DHF): HF (DHF) at 20-25°C DHF can remove the natural oxide film on the surface of the silicon wafer. Therefore, the metal attached to the natural oxide film will be dissolved into the cleaning solution. At the same time, DHF inhibits the formation of the oxide film. Therefore, it is easy to remove metals such as Al, Fe, Zn, Ni on the surface of the silicon wafer. DHF can also remove metal hydroxides attached to the natural oxide film. When cleaning with DHF, while the natural oxide film is corroded, the silicon on the surface of the silicon wafer is almost not corroded.

[0046] (3) APM (SC-1): NH4OH / H2O2 / H2O 30-80°C Due to the action of H2O2, a natural oxide film (SiO2) forms on the surface of the silicon wafer, which is hydrophilic. The cleaning solution can penetrate between the surface of the silicon wafer and the particles. Since the natural oxide layer on the surface of the silicon wafer and the Si on the surface of the silicon wafer are corroded by NH4OH, the particles attached to the surface of the silicon wafer fall into the cleaning solution, thereby achieving the purpose of particle removal. While NH4OH corrodes the surface of the silicon wafer, H2O2 forms a new oxide film on the surface of the oxidized silicon wafer.

[0047] (4) HPM (SC-2): HCl / H2O2 / H2O at 65-85°C is used to remove metal contaminants such as sodium, iron, and magnesium from the surface of silicon wafers. HPM can remove Fe and Zn at room temperature.

[0048] In this embodiment, in step S2 and step S7, the materials of the bottom electrode layer 2 and the top electrode layer 6 are both Pt, and the bottom electrode layer 2 and the top electrode layer 6 are both deposited by electron beam evaporation. The process parameters of the electron beam evaporation method are as follows: the vacuum degree is 7 Pa, the beam current is 10 A, and the thickness of the bottom electrode layer 2 and the top electrode layer 6 are both 30 nm.

[0049] In this embodiment, in step S4, HfSe2 single-layer bulk flakes are mechanically exfoliated from bulk HfSe2 synthesized by a chemical vapor transport (CVT) method. The HfSe2 flakes are exfoliated by standard mechanical exfoliation. Specifically, the HfSe2 flakes are cleaned by immersion in acetone / propanol, and then released using a low-residue thermal release tape (Nitto-Denko Revalpha) in a nitrogen environment in a glove box with O2 and H2O <3ppm.

[0050] Example 2

[0051] like Figure 1 As shown, the structure of the HfO2-based ferroelectric film of this embodiment is the same as that of the HfO2-based ferroelectric film of Example 1, except that the preparation method is as follows. Figure 2 As shown, the method for preparing the HfO2-based ferroelectric thin film in this embodiment includes the following steps:

[0052] S1, pre-cleaning the substrate layer 1, the material of the substrate layer 1 is silicon, and the substrate layer 1 is cleaned by RCA cleaning method;

[0053] S2, depositing a bottom electrode layer 2 on the substrate layer 1 cleaned in step S1;

[0054] S3. Depositing a first HfO2-based thin film layer 3 on the bottom electrode layer 2 deposited in step S2 by atomic layer deposition, wherein the precursor is Hf[N(CH3)C2H5]4, the oxidation source precursor is O3, and the process parameters of the atomic layer deposition are as follows: deposition temperature is 250°C, deposition time is 20 minutes, and deposition thickness is 4 nm;

[0055] S4, covering the first HfO2-based thin film layer 3 deposited in step S3 with a HfSe2 bulk layer 4;

[0056] S5. Depositing a second HfO2-based thin film layer 5 on the HfSe2 bulk layer 4 covered in step S4 by atomic layer deposition, wherein the precursor is Hf[N(CH3)C2H5]4, the oxidation source precursor is O3, and the process parameters of the atomic layer deposition are as follows: deposition temperature is 250°C, deposition time is 22 minutes, and deposition thickness is 4 nm;

[0057] S6. Anneal the surface of the second HfO2-based thin film layer 5 deposited in step S5, specifically: heat to 150°C at a heating rate of 5°C / min under a nitrogen protective atmosphere and keep warm for 5 minutes, heat to 250°C at a heating rate of 3°C / min and keep warm for 5 minutes, heat to 400°C at a heating rate of 23°C / min and keep warm for 5 minutes, heat to 450°C at a heating rate of 10°C / min and keep warm for 5 minutes, finally heat to 800°C at a heating rate of 10°C / min and keep warm for 2 minutes, and finally cool to room temperature.

[0058] S7 , depositing a top electrode layer 6 on the second HfO 2 -based thin film layer 5 annealed in step S6 to obtain a HfO 2 -based ferroelectric thin film.

[0059] In this embodiment, in step S2 and step S7, the materials of the bottom electrode layer 2 and the top electrode layer 6 are both Pt, and the bottom electrode layer 2 and the top electrode layer 6 are both deposited by electron beam evaporation. The process parameters of the electron beam evaporation method are as follows: the vacuum degree is 7 Pa, the beam current is 10 A, and the thickness of the bottom electrode layer 2 and the top electrode layer 6 are both 30 nm.

[0060] Example 3

[0061] like Figure 1 As shown, the structure of the HfO2-based ferroelectric film of this embodiment is the same as that of the HfO2-based ferroelectric film of Example 1, except that the preparation method is as follows. Figure 2 As shown, the method for preparing the HfO2-based ferroelectric thin film in this embodiment includes the following steps:

[0062] S1, pre-cleaning the substrate layer 1, the material of the substrate layer 1 is silicon, and the substrate layer 1 is cleaned by RCA cleaning method;

[0063] S2, depositing a bottom electrode layer 2 on the substrate layer 1 cleaned in step S1;

[0064] S3. Depositing a first HfO2-based thin film layer 3 on the bottom electrode layer 2 deposited in step S2 by atomic layer deposition, wherein the precursor is Hf[N(CH3)C2H5]4, the oxidation source precursor is O3, and the process parameters of the atomic layer deposition are as follows: deposition temperature is 250°C, deposition time is 30 minutes, and deposition thickness is 5 nm;

[0065] S4, covering the first HfO2-based thin film layer 3 deposited in step S3 with a HfSe2 bulk layer 4;

[0066] S5. Depositing a second HfO2-based thin film layer 5 on the HfSe2 bulk layer 4 covered in step S4 by atomic layer deposition, wherein the precursor is Hf[N(CH3)C2H5]4, the oxidation source precursor is O3, and the process parameters of the atomic layer deposition are as follows: deposition temperature is 250°C, deposition time is 30 minutes, and deposition thickness is 5 nm;

[0067] S6. Anneal the surface of the second HfO2-based thin film layer 5 deposited in step S5, specifically: heat to 150°C at a heating rate of 5°C / min under a nitrogen protective atmosphere and keep warm for 5 minutes, heat to 250°C at a heating rate of 3°C / min and keep warm for 5 minutes, heat to 400°C at a heating rate of 23°C / min and keep warm for 5 minutes, heat to 450°C at a heating rate of 10°C / min and keep warm for 5 minutes, finally heat to 800°C at a heating rate of 10°C / min and keep warm for 2 minutes, and finally cool to room temperature.

[0068] S7 , depositing a top electrode layer 6 on the second HfO 2 -based thin film layer 5 annealed in step S6 to obtain a HfO 2 -based ferroelectric thin film.

[0069] In this embodiment, in step S2 and step S7, the materials of the bottom electrode layer 2 and the top electrode layer 6 are both Pt, and the bottom electrode layer 2 and the top electrode layer 6 are both deposited by electron beam evaporation. The process parameters of the electron beam evaporation method are as follows: the vacuum degree is 7 Pa, the beam current is 10 A, and the thickness of the bottom electrode layer 2 and the top electrode layer 6 are both 30 nm.

[0070] The inventors have characterized the performance of the HfO2-based ferroelectric thin film obtained in Example 2. The characterization results are as follows: Figure 3 、 Figure 4 and Figure 5 As shown, Figure 3Transmission electron microscopy (TEM) image of the HfO2-based ferroelectric film obtained in Example 2. Gallium ions were used for milling before TEM characterization. TEM images were obtained using a calibrated FEI Titan at 300 kV. Figure 3 Good HfSe2 / HfO2 contact interface characteristics can be observed; Figure 4 The piezoelectric force microscope (PFM) response diagram of the HfO2-based ferroelectric film prepared in Example 2, wherein the horizontal axis is the voltage amplitude applied to the top electrode, the right vertical axis is the PFM response amplitude value of the HfO2-based ferroelectric film, and the left vertical axis is the PFM response phase value of the HfO2 film. Figure 4 It can be seen that the PFM amplitude and phase response hysteresis of the HfO2-based ferroelectric film of the present invention are clear, proving the existence of domain polarization reversal. The maximum displacement of polarization switching can be known from the PFM amplitude response, and the domain type is a multi-domain structure from the PFM phase response. Figure 5 The polarization characteristic diagram of the HfO2-based ferroelectric film obtained in Example 2, the horizontal axis is the voltage applied to the top electrode, and the vertical axis is the polarization value of the HfO2-based ferroelectric film. Figure 5 It can be seen that the HfO2-based ferroelectric film of the present invention has very excellent polarization performance. When loaded with 8V, the residual polarization intensity is close to 60μC / cm 2 , which is much higher than most preparation levels (approximately 50μC / cm 2 ), the polarization performance of the HfO2-based ferroelectric thin film prepared by the process of the present invention is significantly enhanced.

[0071] Although the present disclosure is disclosed as above, the protection scope of the present disclosure is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A HfO2-based ferroelectric thin film, characterized in that It comprises a substrate layer (1), the upper surface of which is A bottom electrode layer (2), a first HfO2-based thin film layer (3), an HfSe2 scattered sheet layer (4), and a second HfO2-based thin film layer (5) are sequentially arranged on the top. and a top electrode layer (6), the method for preparing the HfO2-based ferroelectric thin film specifically comprises the following steps: S1, pre-cleaning the substrate layer (1); S2, depositing a bottom electrode layer (2) on the substrate layer (1) cleaned in step S1; S3, depositing a first HfO2-based thin film layer (3) on the bottom electrode layer (2) deposited in step S2; S4, covering the first HfO2-based thin film layer (3) deposited in step S3 with a HfSe2 scattered sheet layer (4); S5, depositing a second HfO2-based thin film layer (5) on the covered HfSe2 bulk layer (4) in step S4; S6, performing annealing treatment on the surface of the second HfO2-based thin film layer (5) deposited in step S5; S7, depositing a top electrode layer (6) on the second HfO2-based thin film layer (5) that has been annealed in step S6 to obtain a HfO2-based ferroelectric thin film; In step S4, the preparation method of HfSe2 single-layer loose flakes is as follows: the bulk HfSe2 synthesized by the chemical vapor transport method is mechanically exfoliated, and the HfSe2 flakes are exfoliated by standard mechanical exfoliation, specifically the following steps: the HfSe2 flakes are cleaned by immersion in acetone / propanol, and then released using a low-residue thermal release tape in a glove box with O2 and H2O <3ppm under a nitrogen environment; In step S6, the annealing treatment specifically includes the following steps: heating to 150°C at a heating rate of 5°C / min and keeping warm for 5 minutes under a nitrogen protective atmosphere, heating to 250°C at a heating rate of 3°C / min and keeping warm for 5 minutes, heating to 400°C at a heating rate of 23°C / min and keeping warm for 5 minutes, heating to 450°C at a heating rate of 10°C / min and keeping warm for 5 minutes, and finally heating to 800°C at a heating rate of 10°C / min and keeping warm for 2 minutes, and finally cooling to room temperature.

2. The HfO2-based ferroelectric thin film according to claim 1, wherein In the step S1, the material of the substrate layer (1) is silicon, and the substrate layer (1) is cleaned by using an RCA cleaning method.

3. The HfO2-based ferroelectric thin film according to claim 1, wherein In step S2 and step S7, the materials of the bottom electrode layer (2) and the top electrode layer (6) are both Pt, and the bottom electrode layer (2) and the top electrode layer (6) are both deposited by electron beam evaporation. The process parameters of the electron beam evaporation method are as follows: the vacuum degree is 7 Pa and the beam current is 10 A.

4. The HfO2-based ferroelectric thin film according to claim 2, wherein In the step S2 and the step S7, the thickness of the bottom electrode layer (2) and the top electrode layer (6) are both 30 nm.

5. The HfO2-based ferroelectric thin film according to claim 1, wherein In the step S3, the first HfO2-based thin film layer (3) is deposited by atomic layer deposition, and the process parameters are as follows: deposition temperature is 250°C, deposition time is 15-30 minutes, and deposition thickness is 3-5 nm.

6. The HfO2-based ferroelectric thin film according to claim 4, wherein During the atomic layer deposition process, the precursor is Hf[N(CH3)C2H5]4 and the oxidation source precursor is O3.

7. The HfO2-based ferroelectric thin film according to claim 1, wherein In the step S5, the second HfO2-based thin film layer (5) is deposited by atomic layer deposition, and the process parameters are as follows: deposition temperature is 250°C, deposition time is 15-30 minutes, and thickness is 3-5 nm.

8. The HfO2-based ferroelectric thin film according to claim 7, wherein During the atomic layer deposition process, the precursor is Hf[N(CH3)C2H5]4 and the oxidation source precursor is O3.

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