AU2020101866A4

AU2020101866A4 - A method for preparing ferroelectric thin film by magnetron sputtering and ferroelectric thin film

Info

Publication number: AU2020101866A4
Application number: AU2020101866A
Authority: AU
Inventors: Jiajia Liao; Yichun ZHOU
Original assignee: Xiangtan University
Current assignee: Xiangtan University
Priority date: 2020-08-18
Filing date: 2020-08-18
Publication date: 2020-09-24
Anticipated expiration: 2028-08-18

Abstract

The method for preparing ferroelectric thin films by low-temperature magnetron sputtering comprises the following steps: Si, placing a single sputtering target and a substrate in a reaction chamber with high vacuum. S2, supplying a power to sputter the target material at room temperature and obtain atoms and/or atomic groups from target surface. S3, depositing the atoms and/or atomic groups between the target and the substrate onto the substrate under the action of an electric field and a magnetic field to obtain a preformed amorphous thin film. S4, annealing the amorphous ferroelectric thin film to obtain a ferroelectric thin film. The ferroelectric thin film is prepared by setting a single sputtering target in the reaction chamber, sputtering at room temperature and performing magnetron sputtering deposition. The method solves the problems that there is a high requirement for the temperature in single target sputtering and a strict requirement for instrument in double target co-sputtering in the prior art. 1/9 4 3 2 1 FIG, 1 20 25 30 35 40 45 50 55 20 (degree) FIG. 2

Description

1/9

4

3 2 1

FIG, 1

25 30 35 40 45 50 55 20 (degree)

FIG. 2

A method for preparing ferroelectric thin film by magnetron sputtering and ferroelectric thin film

TECHNICAL FIELD

[01] The invention relates to the technical field of thin film material preparation, in particular to a method for preparing a ferroelectric thin film by magnetron sputtering and the ferroelectric thin film.

BACKGROUND

[02] Ferroelectric thin film is the core material of ferroelectric memory devices, and its performance and preparation process determine the cost and performance reliability of its integrated devices. Traditional hafnium oxide thin films and their doped series have been widely used as gate dielectric materials in metal-oxide-semiconductor field- effect transistor (MOSFET), which have strong process compatibility with complementary metal-oxide-semiconductor (CMOS) process. On the one hand, the breakdown electric field, remanent polarization, coercive electric field and other properties of hafnium oxide thin films are comparable to or even better than those of traditional perovskite ferroelectric thin films; on the other hand, the preparation process and scaling down properties of hafnium oxide thin films overcome the shortcomings of traditional perovskite thin films. In a word, the novel hafnium oxide-based ferroelectric thin film brings good news to the design and integration of ferroelectric memory devices with high density and low power consumption

[03] At present, the preparation methods of hafnium oxide-based ferroelectric thin films include Atomic layer deposition, Metal organic chemical vapor deposition, Chemical solution deposition and other methods based on precursor reaction. Although hafnium oxide-based ferroelectric thin films with excellent performance have been obtained, there are still some problems, for example, impurities such as carbon and hydrogen in the precursor reaction may be embedded in the thin films, which may cause uncontrollable doping to the hafnium oxide-based thin films, thus affecting the reliability performances. In recent years, the deposition based on Physical vapour deposition are investigated. As one of the important thin film preparation methods in

CMOS process, magnetron sputtering has the advantages of large-area deposition, compatibility with low-temperature process and good film quality. At present, there are two main preparation processes for hafnium oxide-based ferroelectric thin films deposition- one is to realize controllable element doping induced ferroelectric thin films by double target co-sputtering; the other one is to sputter the zirconium doped hafnium oxide target at high temperature (-500°C). However, no matter which technology is

used, there are certain defects. For example, double target co-sputtering requires higher demands for equipment, which raises the process difficulties However, single target sputtering requires sputtering at high temperature, which increases the thermal budget of the device and damages the structure and performance of the structures prepared by the previous process.

SUMMARY

[04] (1) The Purpose of Invention

[05] The invention aims to provide a method for preparing a ferroelectric thin film by magnetron sputtering and the ferroelectric thin film prepared by the method. The ferroelectric thin film is prepared by setting a single sputtering target in the reaction chamber, sputtering at room temperature and performing magnetron deposition to prepare a ferroelectric thin film. It avoids the high requirement of temperature in single target sputtering method and the strict requirement of instrument in double target co sputtering method. Therefore, it is used to reduce the film deposition cost while maintaining the same electrical performances.

[06] (2) Technical Scheme

[07] In order to solve the above problems, the first aspect of the present invention provides a method for preparing a ferroelectric thin film by magnetron sputtering, including the following steps.

[08] S1. Placing a single sputtering target and a substrate in a reaction chamber under high vacuum.

[09] S2. Supplying a power to sputter the target material at room temperature to obtain atoms and/or atomic groups from target surface.

[010] S3. Depositing the atoms and/or atomic groups between the target and the substrate on the substrate under the action of an electric field and a magnetic field to obtain a preformed amorphous thin film.

[011] S4. Annealing the preformed amorphous thin film to obtain a ferroelectric thin film.

[012] Further, the target material is a ceramic target material; the substrate is one of semiconductor materials, metal materials or dielectric materials.

[013] Further, the ceramic target comprises a hafnium oxide-based ceramic target doped with zirconium, aluminium, silicon, yttrium, strontium, lanthanum, lutetium, gold, scandium, neodymium, germanium and/or nitrogen.

[014] Further, the semiconductor materials include silicon, germanium, gallium arsenide and gallium nitride; the metal electrode comprises titanium nitride, tantalum nitride, tungsten, platinum, iridium and iridium oxide; the dielectric material comprises hafnium oxide, zirconium oxide, silicon oxide, aluminium oxide, hafnium nitride and silicon nitride.

[015] Further, after the step Sl, the following steps are also included: 1) pumping down the reaction chamber to 10-4-10-6 Pa; 2) introducing sputtering gas to adjust the pressure to 0.4-3.5 Pa and adjust the power to 50-150 W, wherein the sputtering gas comprises argon, krypton and/or oxygen and/or nitrogen.

[016] Further, the step S2 specifically includes:

[017] S21: ionize the sputtering gas under the pressure of 0.4-3.5 Pa and the power of 50-150 W to form plasma.

[018] S22: bombard the target surface with the plasma, and sputter the atoms and/or atomic groups escaped from the target surface.

[019] Further, the step S4 specifically includes the following steps:

[020] S41: put the preformed amorphous thin film to an annealing furnace, raise the temperature of the annealing furnace to 300-1000 °C at a speed of 15-200 °C/s, and keep the temperature constant for 1-1800 s to anneal the preformed thin film.

[021] S42: cool the annealing furnace to room temperature to obtain the ferroelectric thin film and take it out.

[022] Furthermore, the thickness of the ferroelectric thin film is 1-50 nm.

[023] Further, the step SI, step S2 and/or step S3 further comprise the step of adjusting the distance between the target and the substrate to be 10-150 mm.

[024] According to another aspect of the present invention, it provides a ferroelectric thin film prepared by any one of the above methods.

[025] Summary of Technical Scheme

[026] Magnetron sputtering belongs to the category of glow discharge, and the film is prepared by cathode sputtering principle. Film particles come from glow discharge, and the target atoms are sputtered down by argon ion sputtering on the cathode target, and then deposited on the substrate surface to form the required film. The magnetic control principle of the application is that the special distribution of the orthogonal electromagnetic field is adopted to control the electron motion track in the electric field, so that the electrons become cycloidal motion in the orthogonal electromagnetic field, thus greatly increasing the probability of collision with gas molecules.

[027] Under the action of electric field, electrons move toward the substrate. During the movement, electrons collide with the charged carrier gas atoms, so that plasma and a new electron are obtained by ionization. The new electron also moves toward the substrate under the action of electric field, and the obtained plasma bombard the target material with high energy under the acceleration of electric field. The target material is sputtered out from the surface in the form of neutral atoms and atomic groups. Under the control of electric field and magnetic control, after multiple collisions, hafnium atoms, zirconium atoms, hafnium oxide atomic groups and zirconium oxide atomic groups with lower energy will be deposited on the substrate surface, and will nucleate and grow on the substrate surface due to certain energy. The film deposited at first is amorphous state and crystallized after rapid thermal annealing. Wherein, orthorhombic phase (ferroelectric phase) is formed during crystallization.

[028] (3) Beneficial Effects

[029] The ferroelectric thin film is prepared by setting a single sputtering target in the reaction chamber, sputtering at room temperature and performing magnetron deposition. It avoids the high requirement of temperature in single target sputtering and the strict requirement of instrument in double target sputtering. The increasing of the thermal budget of the device caused by high temperature and the structural damage of the device prepared by the previous process are prevented. In addition, the hafnium oxide-based ferroelectric thin film prepared by the invention has the characteristics of large remanent polarization, and switchable ferroelectric polarization properties. Besides, the ferroelectric property can be further improved by adjusting parameters in the deposition process, such as pressure, sputtering power, sputtering gas and so on.

BRIEF DESCRIPTION OF THE FIGURES

[030] Fig. 1 is a structural diagram of a ferroelectric thin film prepared by the magnetron sputtering method of the present invention;

[031] Fig. 2 is an X-ray diffraction pattern of metal-ferroelectric-metal (MFM) structure with hafnium oxide-based ferroelectric thin films prepared in examples 1 and 2;

[032] Fig. 3 is a polarization-voltage (P-V) results of MFM structure of hafnium oxide-based ferroelectric thin films prepared in examples 1 and 2;

[033] Figs. 4a- 4c are piezoelectric-force microscope (PFM) diagrams of hafnium oxide-based ferroelectric thin films prepared in example 2;

[034] Figs. 5a- 5d are polarization-voltage (P-V) results of MFM structure of hafnium oxide-based ferroelectric thin films in examples 3-6;

[035] Figs. 6a and 6b are schematic diagrams of metal -HZO ferroelectric layer silicon (MFS) structures prepared in example 7, respectively;

[036] Fig. 7 is a capacitance-voltage (C-V) characteristics of the MFS structure prepared in example 7;

[037] Fig. 8 is a flow chart of a method for preparing a ferroelectric thin film by magnetron sputtering according to an embodiment of the present application;

[038] Fig. 9 is a flow chart of a method for preparing a ferroelectric thin film by magnetron sputtering according to another embodiment of the present application;

[039] Fig. 10 is a flow chart of a specific method of magnetron sputtering according to an embodiment of the present application;

[040] Fig. 11 is a flow chart of a specific method for annealing a preformed ferroelectric thin film according to an embodiment of the present application;

[041] Fig. 12 is a flow chart of a specific method for cleaning a silicon substrate according to an embodiment of the application.

[042] Reference number:

[043] 1. n*-Si substrate, 2. titanium nitride electrode, 3. hafnium oxide-based ferroelectric thin films, 4. Au electrode, 5. Al, 6. p-Si substrate, 7. iridium electrode.

DESCRIPTION OF THE INVENTION

[044] The

[045] An

[046] In order to make the object, technical scheme and advantages of the present invention clearer, the present invention will be further described in detail with reference to the specific embodiments and drawings. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the invention. Furthermore, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily obscuring the concepts of the present invention.

[047] Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative labor should belong to the protection scope of the present invention.

[048] In addition, the technical features involved in different embodiments of the invention described below can be combined with each other as long as they do not conflict with each other.

[049] Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. In the various figures, the same elements are denoted by similar reference numerals. For the sake of clarity, various parts in the drawings are not drawn to scale.

[050] Please refer to Fig. 8, which is a flowchart of a method for preparing ferroelectric thin films by magnetron sputtering according to an embodiment of the present application.

[051] An embodiment of the present invention, as shown in Fig. 8, provides a method for preparing ferroelectric thin films by magnetron sputtering at low temperature, which comprises the following steps.

[052] Si. Placing a single sputtering target and a substrate in a reaction chamber with high vacuum.

[053] S2. Sputtering the target material at room temperature to obtain atoms and/or atomic groups from the target surface.

[054] S3. Depositing the atoms and/or atomic groups between the target and the substrate on the substrate under the action of an electric field and a magnetic field to obtain a preformed amorphous thin film.

[055] S4. Annealing the preformed amorphous thin film to obtain a ferroelectric thin film.

[056] In this embodiment, Si, S2 and S3 do not represent the performed order. For example, step S2 and step S3 can be performed simultaneously or sequentially. Wherein, the atoms sputtered in step S3 are neutral atoms, and only atoms or only atomic groups may be sputtered according to different target materials; or it may be a mixture of atoms and atomic groups. In this embodiment, only a single target is used in the sputtering process, and only the temperature of the reaction chamber needs to be adjusted to room temperature during sputtering, thereby reducing the deposition temperature and improving the quality of the ferroelectric thin film. Single target doping can reduce the requirements for equipment, and the price of double target sputtering equipment is obviously much more expensive than that of single target sputtering equipment. Moreover, in the preparation process of single target, the cost of target is simplified, and the deposition parameters are well-controlled compared with those of double target, for example, there is only one sputtering power or pressure, so there is no need to consider the switching period of the two targets, and the operation is simpler and more convenient. In addition, the sputtering process in this application can be realized at room temperature. In the preparation of devices, ferroelectric thin films are usually deposited in partially completed devices. If the deposition temperature in this step is too high, the thermal budget of the devices will be increased, which may cause damage to some areas of the previous devices, such as the source and drain regions of transistors and the gate dielectric layer.

[057] In this application, magnetron sputtering has another advantage, that is, it can have the advantage of uniform deposition in a large area (12 inches). The ferroelectric thin film obtained has the advantages of large area, fast deposition rate, suppressed impurity, single target and low temperature.

[058] In an alternative embodiment, the target is a ceramic target; the substrate is one of semiconductor material, metal material or dielectric material.

[059] In this embodiment, the ceramic target can be a semiconductor material, a metal electrode or a dielectric material, and a compound oxide target is preferably used, and the target in this application is a single target. Ferroelectric thin films were prepared by using compound oxides as target materials, and their highly scaling down characteristics overcome the shortcomings of traditional perovskite thin films. The traditional ferroelectric materials mainly include strontium bismuth tantalate, lead zirconate titanate, etc., the ferroelectricity degrades greatly when the thickness of the ferroelectric thin film is reduced below 10 nm. Besides, since they cannot be prepared by the existing CMOS process, the special process lines are constructed, which increases the cost for ferroelectric memory.

[060] The ferroelectric thin film prepared by the application can be compatible with CMOS process, and can also be used for preparing memory devices with high storage density and low power consumption.

[061] In an alternative embodiment, the ceramic target comprises a hafnium oxide-based ceramic target doped with zirconium, aluminum, silicon, yttrium, strontium, lanthanum, lutetium, gold, scandium, neodymium, germanium and/or nitrogen.

[062] In this embodiment, the hafnium oxide-based ceramic target can be doped with one element or two elements, but not limited to the above lists. For example, the chemical formulas of hafnium oxide-based ceramic targets doped with zirconium, lanthanum, yttrium and aluminum are HfZryO2, HfLayO2, HfxYyO2, HfxAlyO2. But it is not limited to the above list.

[063] In an alternative embodiment, the semiconductor material includes silicon, germanium, gallium arsenide and gallium nitride. The metal electrode includes titanium nitride, tantalum nitride, tungsten, platinum, iridium and iridium oxide. The dielectric materials include hafnium oxide, zirconium oxide, silicon oxide, aluminum oxide, hafnium nitride and silicon nitride. The substrate is preferably made of silicon material in semiconductor, specifically n*-Si(100), wherein n*-Si(100) is an heavily doped N type silicon substrate with (100) crystal plane.

[064] Please refer to Fig. 9, which is a flow chart of a method for preparing ferroelectric thin films by magnetron sputtering according to another embodiment of the present application.

[065] In an alternative embodiment, as shown in fig. 9, the following steps are further included after step Si.

[066] 1) Pumping down the reaction chamber to 10-410-6 pa.

[067] 2) Introducing carrier gas to adjust the pressure to 0.4-3.5 Pa and adjust the power to 50-150 W.

[068] In this embodiment, when pumping down the reaction chamber, which includes two processes, mechanical pumping in the first stage and mechanical pumping and molecular pumping in the second stage, wherein the molecular pump can only work under the condition of mechanical pumping and a certain degree of vacuum, otherwise the molecular pump blades will be broken by high-concentration air molecules. For example, a mechanical pump can be used to obtain the chamber pressure of 10-2 Pa, and then a molecular pump can be used to pump down to below 10-4 Pa, so as to ensure the vacuum degree in the reaction chamber and pump away the air in the chamber, which contains oxygen, nitrogen, carbon dioxide, dust impurities and other air components. The higher the basic vacuum degree is, the higher the quality of the deposited film is. Generally, vacuum equipment (such as magnetron sputtering) needs to start sputtering at 10 -4- 1 0 -7 Pa. The vacuum pressure value is preferably 10-7 Pa. Then, a sputtering gas is introduced into the reaction chamber, and the pressure is stabilized by controlling the mass flow of sputtering gas to ensure stable environment in the reaction chamber and the sputtering pressure is preferably 1 Pa, such as 1.2 Pa, 1.4 Pa, 1.5 Pa, 1.6 Pa, 1.8 Pa, 2 Pa, 2.2 Pa, 2.4 Pa, 2.5 Pa, 2.6 Pa, 2.8 Pa or 3 Pa, but is not limited to the above list. Wherein the optimal is 2 Pa. After adjusting to the sputtering pressure, simultaneously adjust the sputtering power to 50 -150 W, preferably 60 -100 W, such as 60 W, 65 W, 70 W, 75 W, 80 W, 85 W, 90 W, 95 W or 100 W, but not limited to the above list, wherein the optimal power value is 80 W. Within the pressure range of this application, gas can be ionized to form glow discharge and generate plasma. If the pressure is too small, the plasma density will be too low, the deposition rate will be slow, and even the plasma cannot be generated. If the pressure is too high, the sputtered atoms will collide many times in the high concentration plasma, and the deposition rate will also slow down, and this process will also affect the deposition quality and growth mode of thin films.

[069] In an alternative embodiment, the sputtering gas comprises argon, krypton and/or oxygen, and/or nitrogen.

[070] In this embodiment, after the vacuum degree of the reaction chamber is adjusted, a sputtering gas is introduced to adjust the pressure in the reaction chamber to sputtering pressure, wherein the sputtering gas can be argon alone, krypton alone, or a mixture of these gases, such as argon and oxygen doped or used at the same time, or krypton and oxygen doped or introduced at the same time, but not limited to the above list.

[071] Please refer to Fig. 10, which is a flow chart of a specific method of magnetron sputtering according to an embodiment of the present application.

[072] In an optional embodiment, as shown in Fig. 10, step S2 specifically includes:

[073] S21: ionizing the carrier gas under the pressure of 0.4-3.5 Pa and the power of 50-150 W to form plasma.

[074] S22: bombarding the surface of the target with plasma to sputter atoms and/or atomic groups from the surface of the target.

[075] In this embodiment, when the sputtering gas is, for example, oxygen or argon, it ionizes under the action of an electric field to form plasma and each ion bombards the surface of the sputtering target continuously under the action of the electric field, and since the ions are charged, they are collected to the surface of the target . Atoms and/or atomic groups on the surface of the target can be sputtered out. The sputtered atoms and/or atomic groups and other sputtered neutral particles with certain energy and charged ions move to the surface of the substrate layer by layer under the control of magnetic field.

[076] Please refer to Fig. 11, which is a flow chart of a specific method for annealing a preformed ferroelectric thin film according to an embodiment of the present application.

[077] In an alternative embodiment, as shown in Fig. 11, step S4 specifically includes the following steps:

[078] S41: transferring the preformed ferroelectric thin film to an annealing furnace, raising the temperature of the annealing furnace to 300-1000 °C at a speed of

-200 °C/s, andkeeping the temperature constant for 1-1800 s to anneal the preformed

amorphous thin film into ferroelectric phase.

[079] S42: cooling the annealing furnace to room temperature and take it out.

[080] In this embodiment, the preformed ferroelectric thin film just formed by sputtering deposition is amorphous, has no ferroelectricity, and needs to undergo rapid thermal annealing to form crystalline states. Wherein, grains with orthorhombic phase exhibit ferroelectricity. The rate of rapid annealing is preferably 30-100 °C/s, for

example, 30 °C/s, 35 °C/s, 40 °C/s, 45 °C/s, 50 °C/s, 55 °C/s, 60°C/s, 65 °C/s, 70 °C/s,

°C/s, 80 °C/s, 85 °C/s, 90 °C/s, 95 °C/s or 100 °C/s, but it not limited to the above

list and the optimal heating rate is 50 °C/s. In this embodiment , annealing causes the

preformed amorphous film to form a crystalline state at a temperature of 300-1000 0 C,

preferably 450-650C, and more preferably is at 500-600 0 C, for example, 5100 C,

520 0C, 5300C, 5400C, 5500C, 5600 C, 570C, 580C, 590C or 600C,but it not limited

to the above list and the optimal temperature is 550C. After reaching the annealing

temperature, in order to ensure the stability of the crystalline state, the annealing temperature should be kept constant for 1-1800 s, preferably 30-300 s, and most preferably is 60 s.

[081] In an alternative embodiment, the thickness of the ferroelectric thin film is 1-50 nm; the area of the ferroelectric thin film is no more than 12 inches.

[082] Please refer to Fig. 12, which is a flow chart of a specific method for cleaning a silicon substrate according to an embodiment of the application.

[083] In an optional embodiment, as shown in Fig. 12, before the step Sl when the silicon substrate is prepared, the method further comprises:

[084] S01: clean the substrate with a mixed solution of sulfuric acid and hydrogen peroxide for 10 minutes.

[085] S02: clean the substrate again with diluted hydrofluoric acid solution for 8 s.

[086] In this embodiment, when the substrate material is a silicon substrate, the process of adopting this method is to clean the substrate with a mixed solution of H2SO4 and H202at room temperature for 10 minutes to remove the organic matter and particles on the surface of the substrate. After rinsing it with deionized water, soak the substrate in HF solution for 8-15 s to remove the oxide layer on the surface of the substrate. Finally, the clean silicon substrate is placed in the reaction chamber. If the substrate is not clean, it will affect the electrical properties of the deposited thin film, and further affect the device performances. When different substrate materials are selected, the cleaning method can be appropriately adjusted, which is not limited to the above list.

[087] In an alternative embodiment, the sulfuric acid is concentrated sulfuric acid with a concentration of 98%; hydrogen peroxide is with a concentration of 30%. Concentrated sulfuric acid and hydrogen peroxide are mixed according to the ratio of :5. The solution concentration of hydrofluoric acid is 1%.

[088] In an optional embodiment, step Sl, step S2 and/or step S3 further comprise the step adjusting the distance between the target and the substrate to be 10-150 mm.

[089] In this embodiment, the distance between the target and the substrate in the reaction chamber can be controlled manually. In order to improve the sputtering efficiency, the distance between the target and the substrate can be adjusted before, after or in step Sl to keep the distance between them at 10-150 mm, preferably 30-65 mm, such as 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm or 65 mm, but not limited to the above list, for example, it also can be 32 mm, 38 mm, 56 mm, 62 mm, etc., wherein the optimal distance value is 55 mm. If the distance is too large, target atoms and atomic groups may take longer to move on the substrate, and undergo more collisions. Thus the deposition rate of thin films will be reduced and the deposition quality may also be affected. If the distance is too small, the electric field and magnetic field have not enough distance to control and screen the directions of the atoms, atomic groups and particles.

[090] According to another embodiment of the present invention, there is provided a ferroelectric thin film prepared by any one of the above methods.

[091] The following examples will verify the excellent performance of ferroelectric thin films prepared by the deposition method of this application. Refer to Fig. 1- Fig. 7 to analyse the excellent performance of ferroelectric thin films in the following examples.

[092] Example 1

[093] The n'-Si (100) substrate was cleaned with a mixture ratio of 98% H2SO4 and 30%H202 of 5: 5 for 10 minutes to remove the organics and particles on the substrate surface. After rinsed with deionised water, it was soaked in 1% HF solution for 8 s to remove the surface oxide layer. A clean n*-Si(100) substrate and a zirconium doped hafnium oxide-based ceramic target are placed in a reaction chamber. Adjusting the vacuum degree of the reaction chamber. Firstly vacuumizing the reaction chamber to 10-2 Pa by a mechanical pump, and then pumping down the reaction chamber to 10 ' Pa by a mechanical pump and a molecular pump at the same time; then argon and oxygen with a flow ratio of 10:1 were introduced into the reaction chamber to adjust the pressure of the reaction chamber to 2 Pa and the power to 60 W. Under the conditions of pressure and power, the sputtering gas is ionized to generate high-density plasma.. The reactive plasma is used to bombard the surface of zirconium-doped hafnium oxide ceramic target, and hafnium atoms, zirconium atoms, oxygen atoms, hafnium oxide atomic groups, zirconium oxide atomic groups and atomic groups mixed with the above atomic groups are sputtered from the surface of the target. While adjusting the distance between the zirconium-doped hafnium oxide-based ceramic target and the n*-Si (100) substrate to 55 mm, an electric field and a magnetic field are introduced, so that hafnium atoms, zirconium atoms, oxygen atoms, hafnium oxide atomic groups, zirconium oxide atomic groups and atomic groups mixed with the above atomic groups are deposited on the silicon substrate to form a preformed zirconium doped hafnium oxide film with a thickness of 10 nm. Transferring the film to an annealing furnace for annealing, heating the annealing furnace at a heating rate of 30°C

/s until the temperature of the annealing furnace rises to 550°C, keeping the temperature

constant for 30 s for rapid thermal annealing, and then cooling to room temperature to and take it out

[094] It should be noted that in order to verify the ferroelectricity of the prepared ferroelectric thin film, a zirconium-doped hafnium oxide-based ceramic target is placed in the reaction chamber, at the same time, a titanium nitride target is placed in. The titanium nitride is sputtered and deposited under certain conditions to form a titanium nitride thin film with a thickness of 60 nm as the bottom electrode. After obtaining a 10 nm zirconium doped hafnium oxide ferroelectric thin film, Au electrode was deposited on the ferroelectric thin film by thermal evaporation covering a shadow mask to form a top electrode with a thickness of 40 nm and an area of 24*104cm 2 to form a MFM capacitor, which was tested by hysteresis loop (P-E curve), X-ray diffraction (XRD) and piezoelectric microscope (PFM).

[095] Example 2

[096] The n*-Si (100) substrate was cleaned with a mixture ratio of 98% H2SO4 and 30%H202 of 1: 1 for 10 minutes to remove the organic matter and particles on the surface. After rinsed with deionized water, it was soaked in 1% HF solution for 10 s to remove the silicon surface oxide layer. A clean n*-Si (100) substrate and a zirconium doped hafnium oxide-based ceramic target are placed in a reaction chamber. The distance between zirconium-doped hafnium oxide-based ceramic target and n*-Si (100) substrate was adjusted to 55 mm. Adjusting the vacuum degree of the reaction chamber. Firstly, vacuumizing the reaction chamber to 10-2Pa by a mechanical pump, and then vacuumizing the reaction chamber to 10-6 Pa by a mechanical pump and a molecular pump at the same time; then pure argon was introduced into the reaction chamber to adjust the pressure of the reaction chamber to 2 Pa and the power to 60 W. Under the conditions of pressure and power, the plasma source is lighted to ionize the introduced gas to form ion flow. The ion current is used to bombard the surface of zirconium-doped hafnium oxide-based ceramic target, and hafnium atoms, zirconium atoms, oxygen atoms, hafnium oxide atomic groups, zirconium oxide atomic groups and atomic groups mixed with the above atomic groups are sputtered from the surface of the target. An electric field and a magnetic field are introduced, so that hafnium atoms, zirconium atoms, oxygen atoms, hafnium oxide atomic groups, zirconium oxide atomic groups and atomic groups mixed with the above atomic groups are deposited on the silicon substrate to form a preformed zirconium-doped hafnium oxide film with a thickness of 1Onm. Transferring the film to an annealing furnace for annealing, heating the annealing furnace at a heating rate of 30°C/s until the temperature of the annealing furnace rises to 550°C, keeping the temperature constant for 30s for rapid thermal annealing, and then lowering the temperature of the annealing furnace to room temperature to obtain and take out a zirconium-doped hafnium oxide ferroelectric film with a thickness of nm.The ferroelectric thin film has a crystalline state.

[097] The method to verify the ferroelectricity of the prepared ferroelectric thin film is the same as Example 1.

[098] Example 3 to 6

[099] In Example 3 to Example 6, the n+-Si (100) substrate was washed with a mixture of 98% H2SO4and 30%H202for 10 minutes to remove the organic matter and particles on the surface. After rinsed with deionized water, it was soaked in 1% HF solution for 10s to remove the silicon surface oxide layer. A clean n+-Si(100) substrate is placed in a reaction chamber. The distance between zirconium-doped hafnium oxide based ceramic target and n*-Si (100) substrate was adjusted to 55 mm. Adjusting the vacuum degree of the reaction chamber. Firstly vacuumizing the reaction chamber to -2Pa by a mechanical pump, and then vacuumizing the reaction chamber to 106 Pa by a mechanical pump and a molecular pump at the same time; then pure argon was introduced into the reaction chamber to adjust the pressure of the reaction chamber to 2Pa and the power to 50 W, 60 W,70 W and 80 W, respectively. Under the conditions of pressure and power, the plasma source is lighted to ionize the introduced gas to form ion flow. The ion current is used to bombard the surface of zirconium-doped hafnium oxide-based ceramic target, and hafnium atoms, zirconium atoms, oxygen atoms, hafnium oxide atomic groups, zirconium oxide atomic groups and atomic groups mixed with the above atomic groups are sputtered from the surface of the target. An electric field and a magnetic field are introduced, so that hafnium atoms, zirconium atoms, oxygen atoms, hafnium oxide atomic groups, zirconium oxide atomic groups and atomic groups mixed with the above atomic groups are deposited on the silicon substrate to form a preformed zirconium-doped hafnium oxide film with a thickness of 16nm. Transferring the film to an annealing furnace for annealing, heating the annealing furnace at a heating rate of 30°C/s until the temperature of the annealing furnace rises to 550°C, keeping the temperature constant for 30s for rapid thermal annealing, and then lowering the temperature of the annealing furnace to room temperature to obtain and take out a zirconium-doped hafnium oxide ferroelectric film with a thickness of 16nm.The ferroelectric thin film has a crystalline state.

[0100] The method to verify the ferroelectricity of the prepared ferroelectric thin film is the same as Example 1.

[0101] Example 7:

[0102] The p-Si (100) substrate was cleaned with a mixed solution of 98% H2SO4 and 30%H202 for 10 minutes to remove organic matter and particles on the surface. After being rinsed with deionized water, it was soaked in 1% HF solution for 15 seconds to remove the oxide layer on the silicon surface. A clean p-Si substrate is placed in a reaction chamber. Meanwhile, titanium nitride (electrode target), iridium target (electrode target) and zirconium-doped hafnium oxide-based ceramic target (ferroelectric thin film target) were placed in the reaction chamber, and the reaction chamber was evacuated to 10-5 Pa. At first, under the conditions of power of 80 W and pressure of 2 Pa, argon is introduced into the reaction chamber, and the zirconium doped hafnium oxide-based ceramic target is sputtered, and the distance between the zirconium-doped hafnium oxide-based ceramic target and the silicon substrate is adjusted to 55 mm during deposition. The deposited zirconium doped hafnium oxide film is 12 nm. Then, switch the target to titanium nitride target and adjust the pressure to 0.58 Pa and the power to 400 W, , start sputtering titanium nitride target and deposit nm titanium nitride film. Then, the target material was switched to iridium metal target, and the pressure and power were adjusted to 0.7 Pa and 100 W, respectively, and nm iridium electrode was deposited. After sputtering of hafnium oxide doped with zirconium, titanium nitride and iridium is completed, the sample is taken out and annealed in a thermal annealing furnace. Heating the annealing furnace at a heating rate of 30°C/s until the temperature of the annealing furnace rises to 650°C, and performing rapid thermal annealing at the constant temperature for 30 s, so that the preformed ferroelectric thin film was crystallized. The photoresist was spin coated on the above samples, and it was baked on a hot plate at 90°C for 90 s and then exposed to ultraviolet light by lithography, then developed in a developing solution for 40 s, and finally post baked on a hot plate at 120°C for 3 minutes. After transferring the pattern on the reticle to the photoresist by the above steps, etching is carried out for 5 minutes by using a reactive ion etching machine under the conditions of Ar/Cl2flow rate of 50sc cm and sc cm respectively and power of 50 W. Finally, acetone is used to remove the residual photoresist. The area of titanium nitride/iridium electrode formed by etching is 10 4 cm 2

, forming a capacitance sample, which is characterized by capacitance-voltage (C-V) test.

[0103] The preparation process of example 7 is shown in Figs. 6a and 6b, in which Fig. 6a shows the structure diagram of capacitor; Fig. 6b is a structural diagram of a capacitor sample with electrodes which is formed by etching. Fig. 7 shows the capacitance-voltage (C-V) curve of measuring the metal-ferroelectric layer-silicon (MFS) capacitor. With the voltage sweeps from -5 V to 3 V, the memory window of about 0.22 V is obtained. it's the hysteresis direction is consistent with that caused by the reversal of ferroelectric polarization. This example proves that the hafnium oxide based thin film prepared by magnetron sputtering on silicon substrate still shows good ferroelectricity.

[0104] It can be seen from the X-ray diffraction (XRD) results in Fig. 2 and Fig. 1, table 1 that the peak intensity of the orthorhombic phase (111) / tetragonal phase (01It) of the hafnium oxide-based ferroelectric thin film obtained in this embodiment 1 is obviously increased. The peak at the position of 20 at 30.80 is generally regarded as the crystalline phase of asymmetric orthogonal ferroelectric phase, which is the origin for the ferroelectric polarization. Therefore, the higher the proportion of orthorhombic ferroelectric phases in the films, the larger the ferroelectric polarization and the stronger the ferroelectricity. At the same time, the peak intensity of monoclinic phase (-11Im) is suppressed, which also proves that the ferroelectric properties of hafnium oxide-based ferroelectric thin films are improved. since the monoclinic phase indicates paraelectric properties rather than ferroelectric properties. From the crystal structure analysis, reducing the oxygen concentration of sputtering gas promotes the formation of orthorhombic phase and inhibits the formation of monoclinic phase.

[0105] Fig. 3 shows the P-E characteristics of the fabricated capacitors in Examples 1 and 2. It can be seen that the hafnium oxide-based ferroelectric thin film prepared in Example 2 has better ferroelectric properties, which are represented by larger remanent polarization and better saturation. Under the applied electric field of 4.3 MV/cm, the remanent polarization 2Pr is about 30 [C/cm2 .

[0106] In order to further determine the ferroelectric properties of the hafnium oxide-based ferroelectric thin film prepared by the method provided by the invention, Figure 4 shows the PFM diagram of the sample in Example 2, and Figure 4a shows that the hafnium oxide-based ferroelectric thin film has good crystallinity and uniform grain size. Fig. 4b and Fig. 4c are the initial piezoelectric response amplitude and phase of the hafnium oxide-based ferroelectric thin film in the out-of-plane direction, respectively. Then, a box-shaped electric field is applied to the film through the conductive tip. The square areas of 3 mx3 m and 1.5 [mx1.5 m were written by applying tip bias voltages of

[0107] -30V and 30V respectively. The PFM phase diagram clearly shows the polarization with direction of up and down, as shown by the piezoelectric response amplitude in Figure 4b, and the dark and bright areas in the phase diagram in Figure 4c. The results show that the polarization of the hafnium oxide-based ferroelectric thin film prepared by the method of the invention can be reversed, which proves good ferroelectricity.

[0108] Fig. 5a-5d are the polarization-electric field (P-E) hysteresis of MFM structure of hafnium oxide-based ferroelectric thin films prepared with power of 50-80 W, respectively. Corresponding to the examples 3-6, the sputtering power was increased from 50 W to 80 W successively, which results in the film thickness of 16 nm. The results show that the ferroelectricity is improved when the deposition power is increased. This may be due to the stronger bond between Hf-, Zr- and 0- atoms caused by higher energy atomic clusters, which enhanced the crystallization of hafnium oxide and ferroelectric phase.

Examples Thickness of HZO film (nm) Sputtering power (w) Sputtering gas 1 10 60 Ar, 02 2 10 60 Ar 3 16 50 Ar 4 16 60 Ar 5 16 70 Ar 6 16 80 Ar

[0109] The invention aims to protect a method for preparing a ferroelectric thin film by low-temperature magnetron sputtering and the ferroelectric thin film. The ferroelectric thin film is prepared by setting a single sputtering target in the reaction chamber, sputtering at room temperature and performing magnetron deposition. It avoids the high requirement of temperature in single target sputtering and the strict requirement of instrument in double target sputtering. The increasing of the thermal budget of the device caused by high temperature and damaging of the structure of the device prepared by the previous process are prevented. In addition, the hafnium oxide based ferroelectric thin film prepared by the invention has the characteristics of high remanent polarization, switchable ferroelectric polarization and the like, and the ferroelectric property of the thin film can be further improved by adjusting parameters in the deposition process, such as pressure, sputtering power, sputtering gas and the like.

[0110] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, and do not constitute a limitation of the present invention. Therefore, any modification, equivalent substitution, improvement, etc. made without departing from the spirit and scope of the present invention shall be included in the protection scope of the present invention. Furthermore, the appended claims of the present invention are intended to cover all changes and modifications that fall within the scope and boundaries of the appended claims, or equivalents of such scope and boundaries.

[0111] Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms, in keeping with the broad principles and the spirit of the invention described herein.

[0112] The present invention and the described embodiments specifically include the best method known to the applicant of performing the invention. The present invention and the described preferred embodiments specifically include at least one feature that is industrially applicable

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A method for preparing ferroelectric thin films by magnetron sputtering is characterized by comprising the following steps.

Si. Placing a single sputtering target and a substrate in a reaction chamber under high vacuum.

S2. Sputtering the target material at room temperature to obtain atoms and/or atomic groups from target surface.

S3. Depositing the atoms and/or atomic groups between the target and the substrate on the substrate under the action of an electric field and a magnetic field to obtain a preformed amorphous thin film.

S4. Annealing the preformed amorphous thin film to obtain a ferroelectric thin film.

2. The method according to claim 1 is characterized in that the target material is a ceramic target material; the substrate is one of semiconductor material, metal material or dielectric material.

3. The method according to claim 2 is characterized in that the ceramic target comprises a hafnium oxide-based ceramic target doped with zirconium, aluminium, silicon, yttrium, strontium, lanthanum, lutetium, gold, scandium, neodymium, germanium and/or nitrogen.

4. The method according to claim 2 is characterized in that the semiconductor material comprises silicon, germanium, gallium arsenide and gallium nitride; the metal electrode comprises titanium nitride, tantalum nitride, tungsten, platinum, iridium and yttrium oxide; the dielectric material comprises hafnium oxide, zirconium oxide, silicon oxide, aluminum oxide, hafnium nitride and silicon nitride.

5. The method according to claim 1 is characterized in that it further comprises the following steps after step Si.

1) Vacuumizing the reaction chamber to 10-4-10-6 pa;

2) Introducing carrier gas to adjust the pressure to 0.4-3.5Pa and adjust the power to 50-150W; and the carrier gas comprises argon, krypton and/or oxygen.

6. The method according to claim 5 is characterized in that the step S2 specifically comprises

S21: ionize the carrier gas at a pressure of 0.4-3.5Pa and a power of 50-150W to form an ion flow;

S22: bombarding the target surface with the ion current, and sputtering the atoms and/or atomic groups from the target surface.

7. The method according to claim 1 is characterized in that the step S4 specifically comprises the following steps:

S41: transferring the preformed ferroelectric thin film to an annealing furnace, raising the temperature of the annealing furnace to 300-1000 °C at a speed of 15-200 °C

/s, and keeping the temperature constant for is-1800s to anneal the preformed ferroelectric thin film;

S42: reducing the temperature of the annealing furnace to room temperature to obtain the ferroelectric thin film and take it out.

8. The method according to claim 1 or 7 is characterized in that the thickness of the ferroelectric thin film is 1-50nm.

9. The method according to claim 1 is characterized in that the steps Si, S2 and/or S3 further comprise the step to adjust the distance between the target and the substrate to be 10-150mm.

10. A ferroelectric thin film is characterized in that it is prepared by the method according to any one of claims I to 9.

Intensity (a.u.)

20 25 -111m

30 011t/111o

35 1/9

FIG. 2 FIG, 1 Au 111

40 021m 112o

2 (degree) 211m

45 50 实施例1 实施例2