Optimization method of high-thickness hafnium-based piezoelectric film device

Abstract

The invention belongs to the technical field of microelectronic devices, and discloses an optimization method of a high-thickness hafnium-based piezoelectric film device, the thickness of a hafnium-based piezoelectric functional layer of the high-thickness hafnium-based piezoelectric film device is not less than 20nm, and the hafnium-based piezoelectric functional layer is of a superlattice structure formed by alternately laminating hafnium oxide and zirconium oxide; the piezoelectric performance of the high-thickness hafnium-based piezoelectric film device is optimized by depositing a third oxide layer at the interface of two adjacent superlattice units every other preset thickness in the hafnium-based piezoelectric functional layer; the third oxide layer is selected from an aluminum oxide layer and a silicon oxide layer. The third oxide layer is inserted into the superlattice laminated structure formed by alternately laminating high-thickness hafnium oxide and zirconium oxide, so that the formation of large grains in the hafnium-based piezoelectric film can be inhibited, the formation of an m-phase structure without piezoelectric property in the hafnium-based film is inhibited, the increase of non-centrosymmetric o-phase structures in the film is promoted, and the piezoelectric property of the film is improved. Therefore, the piezoelectric coefficient of the whole device is improved, and the piezoelectric property of the high-thickness hafnium-based piezoelectric film device is optimized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of microelectronic devices, and more particularly, to an optimization method of high-thickness hafnium-based piezoelectric thin film devices. BACKGROUND

[0002] With the development and changes of the information age, the Internet of Things and artificial intelligence have long been integrated into modern life and gradually become the development trend and direction of the future. Among them, the perception and processing of a large number of physical signals in nature are particularly important in applications such as wearable devices. As the basic structure of mechanical and acoustic signal perception, piezoelectric thin films have become one of the research focuses of multi-modal information devices.

[0003] Piezoelectric materials are a class of materials that can generate spontaneous polarization under strain. The reason is that the crystal lattice presents a non-central symmetric structure, and the positive and negative charge centers in the unit cell will separate during the deformation of the unit cell. Traditional piezoelectric materials include aluminum nitride (AlN) materials, perovskite materials (Pb(Zr,Ti)O3, SrBi2Ta2O9) and organic piezoelectric materials. The integration of perovskite materials is difficult to improve because their piezoelectric properties are inhibited below 100 nm in thickness. AlN materials are easily partially oxidized in the process, which weakens their piezoelectric properties, so the vacuum degree in the process is very high. Perovskite and organic materials are not compatible with CMOS technology, making it difficult to integrate on existing silicon-based production lines. Therefore, traditional piezoelectric materials are limited in integrated circuit technology with a thickness of 10 nm-100 nm, and are generally used in micro-electro-mechanical systems (MEMS). However, once in nanoelectromechanical systems (NEMS), it is difficult to function. Hafnium oxide-based materials can be applied to high-integration NEMS devices due to their high silicon compatibility and large piezoelectric properties at the nanometer scale. However, most NEMS devices require piezoelectric thin films with a thickness of about 10 nm-100 nm. When the thickness of hafnium-based materials is more than 20 nm, the piezoelectric properties will be inhibited due to changes in the stability of each crystal phase, so a method is needed to improve the piezoelectric properties above 20 nm in thickness to enable hafnium-based piezoelectric thin films to be applied in most NEMS devices.

[0004] HfO2 materials can form three common crystal phases at room temperature, which are monoclinic phase (m-phase), tetragonal phase (t-phase) and orthorhombic phase (o-phase). Only the non-centrosymmetric o-phase can exhibit large piezoelectric properties. When the hafnium-based material thin film is heat treated to crystallize, the three crystal phases can become the most stable crystalline phase respectively due to different process parameters. In the deposited amorphous hafnium-based piezoelectric thin film, there are many o / t phase small grains at first, and the grains gradually grow and phase change to o, t or m phase during the heat annealing process and stabilize during the cooling process of heat treatment. The crystallization kinetics process is related to many factors. R. Materlik et al. calculated the HfO2 0.5 Zr 0.5 O2 solid solution thin film of different thicknesses on the stability of each crystal phase (R. Materlik et al. The origin of ferroelectricity in Hf 1-x Zr x O2: A computational investigation and a surface energy model, Journal of Applied Physics, 2015, 117, 134109). Among them, in the thin film with small thickness (<2 nm), the t-phase is the stable phase, in the thin film with large thickness (>6 nm), the m-phase is the stable phase, and the required o-phase is between the t-phase and the m-phase. Therefore, the film thickness that can exhibit piezoelectric properties is usually controlled to be less than 20 nm in the literature to achieve the purpose of inhibiting monoclinic m-phase and promoting piezoelectric o-phase formation.

[0005] On the other hand, the relatively thin (about 10 nm) piezoelectric thin film has many limitations when actually applied to devices. The relatively thin piezoelectric thin film is more seriously affected by the substrate template effect, and in practical application, most of the lattice inside the thin film will be affected by the substrate stress, resulting in incomplete relaxation and affecting the piezoelectric response. Secondly, in the piezoelectric sensing NEMS device with cantilever structure, due to the frequent reciprocating vibration process of the cantilever, the low mechanical strength of the relatively thin piezoelectric thin film on the cantilever can easily affect the durability of the overall device, and the reliability and robustness of the device are reduced. At the same time, in the acoustic wave device (SAW\BAW) using piezoelectric thin film, due to the matching problem of thin film thickness and acoustic wave amplitude, it is generally hoped that the piezoelectric material maintains piezoelectric properties in a series of thicknesses of 10-100 nm, so that different frequency acoustic wave resonators can be made to be used as filters and other devices, and if the piezoelectric thin film performance decreases greatly or even disappears when the thickness reaches 20 nm or more, it will limit the application of acoustic wave frequency of the device. Therefore, finding a method to optimize the piezoelectric properties of hafnium-based thin film with higher thickness can make the application of hafnium-based material in piezoelectric devices more widely.

[0006] In addition to controlling the thickness, making hafnium-based thin films into superlattice stack structures of HfO2 and doped element oxides can also promote the o-phase content and improve the durability. Some studies have improved the performance of hafnium-based superlattice thin films by adjusting various sub-layer parameters (sub-layer thickness, sub-layer type, and the number ratio of multiple sub-layers) of the superlattice structure. For example, the invention patent: A hafnium oxide-based ferroelectric crystal phase modulation method based on a superlattice structure (publication number CN119781192A) discloses a method for adjusting the crystal phase of ferroelectric hafnium oxide thin films by changing the thickness ratio of HfO2 sub-layers and doped element layers. However, most of the above inventions do not focus on the blocking effect of interlayer strain between superlattice sub-layers on crystal grains and domains, thereby ignoring the role of superlattice structures in optimizing the performance of thick hafnium-based thin films. SUMMARY

[0007] In view of the above defects or improvement needs of the prior art, the purpose of the present application is to provide an optimization method for high-thickness hafnium-based piezoelectric thin film devices. By inserting a third oxide layer (such as an aluminum oxide layer or a silicon oxide layer) into the superlattice stack structure formed by the alternating stack of high-thickness hafnium oxide and zirconium oxide, the formation of large crystal grains in the hafnium-based piezoelectric thin film can be inhibited, thereby inhibiting the formation of m-phase structures without piezoelectric properties in the hafnium-based thin film, promoting the increase of o-phase structures without central symmetry in the thin film, and thereby improving the piezoelectric coefficient of the entire device, optimizing the piezoelectric performance of the high-thickness hafnium-based piezoelectric thin film device, and enhancing the piezoelectric response. Compared with the prior art, the present application can stabilize the piezoelectric phase in a larger thickness hafnium-based piezoelectric thin film, and provides a new idea for improving the performance of high-thickness hafnium-based piezoelectric thin film devices.

[0008] To achieve the above-mentioned purpose, according to one aspect of the present application, an optimization method for high-thickness hafnium-based piezoelectric thin film devices is provided. The high-thickness hafnium-based piezoelectric thin film device comprises a substrate, a bottom electrode, and a hafnium-based piezoelectric functional layer from bottom to top. The thickness of the hafnium-based piezoelectric functional layer is not less than 20 nm, and is a superlattice structure formed by the alternating stack of hafnium oxide and zirconium oxide. The superlattice structure comprises a plurality of superlattice units, and each superlattice unit is formed by stacking a hafnium oxide layer and a zirconium oxide layer from bottom to top. The characteristic is that a third oxide layer is deposited at the interface between two adjacent superlattice units at a predetermined thickness interval in the hafnium-based piezoelectric functional layer, thereby optimizing the piezoelectric performance of the high-thickness hafnium-based piezoelectric thin film device. The third oxide layer is selected from an aluminum oxide layer and a silicon oxide layer.

[0009] As a further preferred embodiment of the present application, the predetermined thickness interval is specifically every 10-16 nm;

[0010] The thickness of each third oxide layer is 0.5-2 nm.

[0011] As a further preferred embodiment of the present application, a third oxide layer is also deposited on the top surface of the hafnium-based piezoelectric functional layer.

[0012] As a further preferred embodiment of the present application, the optimized high-thickness hafnium-based piezoelectric thin film device uses a zirconium oxide layer or a third oxide layer as a capping layer for air contact, and does not have a top electrode.

[0013] As a further preferred embodiment of the present application, the thickness of the hafnium-based piezoelectric functional layer before optimization is 30-36 nm.

[0014] As a further preferred embodiment of the present application, the hafnium-based piezoelectric functional layer before optimization is based on Hf x Zr y O2, where x is a positive number greater than 0, y is a positive number greater than 0, and x+y≤2;

[0015] Preferably, the Hf x Zr y O2, x:y is preferably 1:1;

[0016] The superlattice structure has n superlattice units, including n hafnium oxide layers and n zirconium oxide layers, and each hafnium oxide layer and each zirconium oxide layer has a thickness of 1-6 nm;

[0017] Where n is a positive integer greater than or equal to 2 and less than or equal to 12;

[0018] Preferably, each hafnium oxide layer and each zirconium oxide layer has a thickness of 2 nm;

[0019] The every preset thickness is specifically a thickness of every 12 nm.

[0020] As a further preferred embodiment of the present application, the material of the substrate is selected from intrinsic Si, p-Si, n-Si, and SiO2.

[0021] The material of the bottom electrode is selected from Pt, TiN, W, Au, TaN, and RuO2, and is preferably TiN.

[0022] As a further preferred embodiment of the present application, it specifically includes the following steps:

[0023] (1) Depositing a bottom electrode on a clean and dry substrate;

[0024] (2) Depositing a plurality of superlattice units on the bottom electrode, each superlattice unit being formed by stacking a hafnium oxide layer and a zirconium oxide layer from bottom to top;

[0025] (3) When the deposition thickness of step (2) reaches a preset thickness interval, depositing a third oxide layer;

[0026] (4) repeating step (2) and step (3) so that a third oxide layer is formed at the interface between two adjacent superlattice units at every preset thickness in the superlattice structure, until the sum of the thicknesses of the superlattice structure parts is not less than 20 nm, thereby forming an optimized hafnium-based piezoelectric functional layer;

[0027] (5) rapid thermal annealing, so as to obtain an optimized high-thickness hafnium-based piezoelectric thin film device; wherein the rapid thermal annealing is performed in vacuum or N2, the annealing temperature is 400-700℃, and the annealing time is 30-60s;

[0028] Preferably, in the step (5), the rapid thermal annealing is performed in vacuum, and the vacuum degree is less than or equal to 5.0*10 -2 hPa, and more preferably less than or equal to 2.0*10 -2 hPa.

[0029] According to another aspect of the present application, the present application provides an optimized high-thickness hafnium-based piezoelectric thin film device obtained by using the above-mentioned optimization method.

[0030] Compared with the prior art, by inserting an Al2O3 layer or a SiO2 layer in the hafnium-zirconium-oxygen piezoelectric thin film of the HfO2 / ZrO2 superlattice stack structure to cut off the continuity of the grain growth, the present application can effectively improve the piezoelectric performance of the high-thickness hafnium-based piezoelectric thin film (thickness greater than 20 nm). The third oxide interlayer (i.e., the aluminum oxide interlayer or the silicon oxide interlayer) introduced in the present application can interrupt the growth of the grains in the hafnium-based thin film, thereby inhibiting the formation of m phase.

[0031] The present application can inhibit monoclinic m phase in thicker hafnium-based piezoelectric thin film (i.e. hafnium-based piezoelectric functional layer with thickness not less than 20 nm before optimization, such as 30-42 nm) and promote more non-centrosymmetric o phase formation, which can exhibit good piezoelectric response. The present application inserts Al2O3 layer or SiO2 layer in thicker thin film, which can effectively cut off grain growth in thicker thin film. For high thickness hafnium-based piezoelectric thin film device, when the thickness of the thin film increases, the interface layer inhibition effect of HfO2 and ZrO2 phase matching is difficult to prevent the formation of larger grains. The present application can further cut off large grains by inserting an Al2O3 layer or a SiO2 layer every preset thickness, which can inhibit the phase transition of crystal phase to m phase in the thin film, thereby increasing the proportion of o phase in the thin film and enhancing the piezoelectric properties and piezoelectric response of the device. Because the lattice constants and common crystal phase structures of HfO2 and ZrO2 are close, the interface layer in thicker laminated thin film device may not be significant, so that larger grains may appear in the thin film. The insertion of thin Al2O3 dielectric layer or SiO2 dielectric layer can prevent the formation of large grains in the thin film, and the lattice mismatch of Al2O3 dielectric layer (or SiO2 dielectric layer) can cut off the crystal growth in the thin film and inhibit the formation of large grains across multiple layers in the thin film.

[0032] The present application can inhibit and cut off the growth of large grains in hafnium-based piezoelectric thin film by introducing alumina intercalation structure or silicon oxide intercalation structure into the hafnium-based piezoelectric thin film of superlattice laminated structure, combined with rapid thermal annealing, which can control the stable phase in the thin film to o phase and inhibit the increase of m phase caused by the increase of the thickness of the thin film, thereby improving the piezoelectric response of the hafnium-based piezoelectric thin film device.

[0033] The piezoelectric properties of hafnium-based materials come from the asymmetric crystal phase o phase in the material, which is a metastable phase at room temperature. Thermodynamic model shows that the difference in surface energy of different crystal phases in different size grains determines the crystallization kinetics process of hafnium-based materials during heat treatment, and it is generally believed that hafnium-based materials will be stabilized in the crystalline phase with the lowest surface energy in a certain size of grain. According to theoretical calculation, o phase is most stable in 2-6 nm size grain, and the thickness of practical piezoelectric thin film is usually greater than 20 nm, so the application of hafnium-based piezoelectric materials in actual high thickness devices is limited.

[0034] The present application forms a third oxide intercalation structure with alumina and silica as the third oxide, and it is found that the lattice mismatch between the superlattice stack structure and the sublayer of the third oxide intercalation and the interlayer potential barrier can block the grain growth during heat treatment, refine the grain and domain structure, thereby obtaining a hafnium-based piezoelectric film with high piezoelectric phase content, large piezoelectric response, and the ability to maintain piezoelectric properties at a relatively thick thickness. The lattice type and lattice constant of the alumina and silica material and the fluorite-type hafnium oxide and zirconium oxide layer are quite different, which can form an interlayer transverse grain boundary. This interface can effectively cut off the grain growth of the piezoelectric layer and thus control the grain size, and also can act as a potential barrier to block the migration of leaking carriers, thereby improving the electrical performance of the device and reducing power consumption. Moreover, the alumina and silica as high elastic constant intercalation layers can introduce interlayer tensile stress, which further stabilizes the o phase in the piezoelectric layer during heat treatment. On this basis, the two materials of alumina and silica have high compatibility with existing processes; the deposition method is the same as that of hafnium oxide material; the deposition process parameters are similar to those of hafnium oxide material, so they can be inserted into the superlattice stack structure of the present application without destroying the original process atmosphere, effectively preventing adverse effects on the piezoelectric film caused by switching the process atmosphere. Therefore, the present application optimizes the hafnium-based piezoelectric film with superlattice stack structure using alumina intercalation or silica intercalation, promotes the piezoelectric phase transition and enhances its piezoelectric performance, and the optimization method enables the hafnium-based piezoelectric film to maintain large piezoelectric performance even at a relatively thick thickness. The hafnium-based piezoelectric device optimized by this method can better match the thickness required by NEMS devices, and provides a new idea for the application of hafnium-based materials in acoustic devices and sensor devices.

[0035] In addition, the present application is directed to a high-thickness hafnium-based piezoelectric thin film device (the thickness of the hafnium-based piezoelectric functional layer is not less than 20 nm, and the hafnium oxide layer contacts the bottom electrode), and a third oxide layer is inserted at a predetermined thickness interval to obtain an optimized device with a zirconium oxide layer or a third oxide layer as a capping layer (no need to make a top electrode, and no need for the positive effect of electrode capping on crystallization). That is, the optimization method of the present application can also deposit a third oxide layer on the top surface of the hafnium-based piezoelectric functional layer without the need for an additional top electrode. Even if a third oxide layer is not deposited on the top surface of the hafnium-based piezoelectric functional layer, in the present application, due to the use of a stack structure, the topmost ZrO2 or third oxide layer can replace the top metal electrode capping to exert an out-of-plane stress on the film during annealing, promote the formation of piezoelectric phase in the film, eliminate the subsequent wet etching step of the metal electrode, simplify the process flow, and reduce the preparation cost of the hafnium-based piezoelectric device. That is, the optimized device of the present application can be quickly heat annealed after depositing the piezoelectric functional layer with oxide intercalation during preparation, and the topmost ZrO2 or third oxide capping layer can replace the top electrode capping to exert a stress effect on the overall device, so that a larger piezoelectric performance can be induced without depositing a top electrode.

[0036] In summary, the present application can improve the piezoelectric performance of high-thickness hafnium-based piezoelectric thin film devices by optimizing the high-thickness hafnium-based piezoelectric thin film devices, and can still maintain excellent piezoelectric characteristics when the thickness of the thin film is increased to more than 40 nm, thereby providing a method for subsequent application of hafnium-based thin film materials to NEMS devices and the like. The present application proves that the introduction of a dielectric interlayer structure into the HfO2 / ZrO2 superlattice stack structure can effectively improve the piezoelectric characteristics and longitudinal piezoelectric response of the hafnium-based piezoelectric thin film, thereby providing a new idea for the optimization direction of subsequent piezoelectric thin films. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a device structure schematic diagram corresponding to embodiment 1 of the present application; the deposition method is to alternately stack and grow 2nm-thick HfO2 and 2nm-thick ZrO2 to form a 12nm thin film, and then perform rapid thermal annealing.

[0038] Figure 2 is a device structure schematic diagram corresponding to comparative example 1 of the present application; the deposition method is to cyclically deposit HfO2 and ZrO2 with a total thickness of 12nm, so that the overall thin film presents a doped solid solution structure rather than a layered structure, and then perform rapid thermal annealing.

[0039] Figure 3 is a device structure schematic diagram corresponding to embodiment 2 of the present application; the deposition method is to alternately stack and grow 2nm-thick HfO2 and 2nm-thick ZrO2, and insert an Al2O3 thin film (1nm thick) every 12nm thin film (6 sublayers), so that the final total thickness is (12+1)nm x 3, i.e. 39nm (the sum of the thicknesses of the superlattice structure part is 36nm), and then perform rapid thermal annealing.

[0040] Figure 4 is a device structure schematic diagram corresponding to comparative example 2 of the present application; the deposition method is to alternately stack and grow 2nm-thick HfO2 and 2nm-thick ZrO2, and the final total thickness is 36nm, and then perform rapid thermal annealing. Comparative example 2 does not contain an Al2O3 layer or a SiO2 layer.

[0041] Figure 5 is a device structure schematic diagram corresponding to comparative example 3 of the present application; the deposition method is to cyclically deposit HfO2 and ZrO2 with a total thickness of 36nm, so that the overall thin film presents a doped solid solution structure rather than a layered structure, and then perform rapid thermal annealing. Comparative example 3 does not contain an Al2O3 layer or a SiO2 layer.

[0042] Figure 6is the surface grain morphology of the device of Example 1 and Comparative Example 1 of the present application. The surface morphology can be obtained by taking high resolution scanning electron microscope (SEM) images of the film surface after annealing. The grain size analysis is performed.

[0043] Figure 7 is the fitting curve of the statistical results of the grain segmentation and diameter statistics of Example 1 and Comparative Example 1 using the watershed algorithm. The statistical results show that the average grain size of the device of Example 1 using the superlattice structure is smaller than that of Comparative Example 1.

[0044] Figure 8 is the diffraction curve of the crystal phase structure of Example 1 and Comparative Example 1 characterized by grazing incidence X-ray diffraction (GIXRD). The results show that the m phase content in the superlattice stack structure film is significantly reduced, and the o / t phase content is significantly increased.

[0045] Figure 9 is the fitting curve of the amplitude-excitation test results and the piezoelectric coefficient d 33,eff of the film of Example 2, Comparative Example 2 and Comparative Example 3, and the slope value of the fitting curve is the longitudinal piezoelectric coefficient d 33,eff of the corresponding device. The results show that the 39nm thick device of Example 2 using the stack and oxide interlayer optimization has the largest piezoelectric response, while the piezoelectric response of the 36nm thick Comparative Example 2 with only the stack structure is smaller than that of Example 2 with an aluminum oxide interlayer, and the piezoelectric response of Comparative Example 3 with a solid solution structure is the smallest, proving that the optimization method of the present application can enable the hafnium-based piezoelectric film to maintain a larger piezoelectric response when the thickness is increased to about 40nm.

[0046] Figure 10 is the diffraction curve of the crystal phase structure of Example 2, Comparative Example 2 and Comparative Example 3 characterized by grazing incidence X-ray diffraction (GIXRD). The results show that the m phase content in the interlayer-optimized superlattice structure film is significantly reduced, and the o / t phase content is significantly increased. Combined with the piezoelectric performance characterization, it can be judged that the hafnium-based piezoelectric film using the interlayer-optimized superlattice stack structure can inhibit the m phase transition and form more o phases, and therefore has a larger piezoelectric response. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical scheme and advantages of the present application clearer and more apparent, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0048] In the present application, the optimized hafnium-based piezoelectric thin film device includes, from bottom to top, a substrate layer, a bottom electrode layer, and a piezoelectric layer. The piezoelectric layer adopts a HfO2 / ZrO2 stacked structure. The present application is directed to a thicker HfO2 / ZrO2 stacked structure, in which an Al2O3 layer is inserted.

[0049] Similar to the nano-laminated superlattice structure known in the prior art, the HfO2 / ZrO2 laminated structure used in the following examples or comparative examples refers to the formation of an alternating stacked film structure by alternating deposition of HfO2 and ZrO2 at a sub-10 nm thickness, and the HfO2 layer contacts the bottom electrode and the ZrO2 layer contacts the air, so that the HfO2 layer forms a template effect at the interface with the bottom electrode to guide the overall film crystallization. That is, for the HfO2 / ZrO2 stacked structure, the thickness of the HfO2 layer is equal to that of the ZrO2 layer, and the specific thickness is 1 nm-6 nm, and the HfO2 layer contacts the bottom electrode, and the two materials are alternately stacked, and finally the ZrO2 layer is at the topmost layer. The present application is directed to a thicker HfO2 / ZrO2 stacked structure, for example, one Al2O3 layer can be deposited for every 6 layers of HfO2 / ZrO2 layers. In the following examples, the HfO2 / ZrO2 corresponds to a piezoelectric thin film structure of an alternating laminated nano-layer structure of HfO2 and ZrO2, denoted as [HfO2 / ZrO2] x Zr y O2 corresponds to a piezoelectric thin film structure of an alternating laminated nano-layer structure of HfO2 and ZrO2, denoted as [HfO2 / ZrO2] n structure, wherein n is a positive integer greater than or equal to 2, i.e., having n superlattice units, including n hafnium oxide layers and n zirconium oxide layers, and the total number of layers is 2n layers.

[0050] The following examples and comparative examples are all taken as an example of using TiN as the bottom electrode layer. Taking the TiN / HfO2 / ZrO2 laminated device as an example, it can be prepared by the following process flow:

[0051] First, select and clean the substrate. The substrate can be any substrate capable of carrying semiconductor components, such as intrinsic silicon, silicon oxide, doped silicon (such as p-Si, n-Si), etc. The following examples and comparative examples all use Si / SiO2 substrate. The substrate is ultrasonically cleaned with acetone and alcohol organic solvents, and then washed with deionized water.

[0052] The bottom electrode and the piezoelectric layer are deposited on the substrate in sequence. Among them, the bottom electrode layer is deposited by electron beam evaporation or magnetron sputtering, and then the hafnium-based piezoelectric functional layer is grown by atomic layer deposition.

[0053] Finally, a rapid thermal annealing furnace is used for rapid thermal annealing, the annealing temperature can be set to 400-700°C, and the annealing time can be 30-60s (e.g., 30s), so that the piezoelectric film is crystallized as a whole. Similar to conventional rapid thermal annealing, the temperature program of the annealing process includes, in order, a temperature rising stage for rising to the target annealing temperature, a temperature holding stage for keeping the temperature at the target annealing temperature, and a temperature falling stage for falling from the target annealing temperature. The following examples and comparative examples are all rapid thermal annealed at 600°C for 30s in a vacuum atmosphere.

[0054] The following are specific examples:

[0055] Example 1: Growth of a 12nm-thick HfO2 / ZrO2 piezoelectric film device in a stacked structure (no third oxide layer used in this example)

[0056] Example 1 is a hafnium-based piezoelectric film in a stacked structure, in which the total thickness of the piezoelectric film is 12nm, and each of the HfO2 and ZrO2 layers is 2nm. The structure is as shown in Figure 1 , in which the HfO2 layer contacts the bottom TiN electrode layer, and the ZrO2 layer contacts the top air; it is a HfO2 / ZrO2 superlattice stacked structure obtained by using atomic layer deposition cycles to deposit 2nm-thick HfO2 and 2nm-thick ZrO2, which are alternately stacked in turn.

[0057] Comparative Example 1: 12nm-thick Hf 0.5 Zr 0.5 O2 piezoelectric film device in a solid solution structure (no third oxide layer used in this example)

[0058] Comparative Example 1 is basically the same as Example 1 in the overall device structure, and the main difference is that the piezoelectric layer of Comparative Example 1 is a solid solution Hf 0.5 Zr 0.5 O2 layer doped with ZrO2, and the structure is as shown in Figure 2 . By using atomic layer deposition cycles to deposit ~0.08nm-thick HfO2 and ~0.08nm-thick ZrO2 (i.e., performing one pulse dose of hafnium source and oxygen source reaction growth, and then performing one pulse dose of zirconium source and oxygen source reaction growth, which are alternately and cyclically deposited), the oxide grown by one pulse reaction presents a nanometer island shape and does not form a film on the surface, and the two oxides are uniformly mixed to form a solid solution without a superlattice multilayer stacking structure inside.

[0059] Example 2: 39nm-thick HfO2 / ZrO2 / Al2O3 piezoelectric film device with intercalation optimization

[0060] Example 2 is an intercalated Al2O3 dielectric interlayer optimized stacked hafnium-based piezoelectric thin film device with a 39 nm thick piezoelectric layer, 2 nm thick layers of HfO2and ZrO2, and a 1 nm thick layer of Al2O3 intercalated every 6 layers, as shown in Figure 3 The process is similar to Example 1, with the exception that a 1 nm thick layer of Al2O3 is deposited after every 12 nm thick [HfO2 / ZrO2] layer. The 1 nm thick layer of Al2O3 is an amorphous film prepared by atomic layer deposition.

[0061] Comparative Example 2: 36 nm thick HfO2 / ZrO2 piezoelectric thin film device grown in a stacked structure (no third oxide layer used in this example)

[0062] Comparative Example 2 is a 36 nm thick hafnium-based piezoelectric thin film device in a superlattice stacked structure with 2 nm thick layers of HfO2and ZrO2, as shown in Figure 4 The process is similar to Example 1, with the exception that the superlattice stacked structure is thicker.

[0063] Comparative Example 3: 36 nm thick HfO2 / ZrO2 piezoelectric thin film device in a solid solution structure (no third oxide layer used in this example) 0.5 Zr 0.5 O2

[0064] Comparative Example 3 is a 36 nm thick ZrO2-doped HfO2 solid solution HfZrO2 device, as shown in 0.5 Zr 0.5 O2 Figure 5 The process is similar to Comparative Example 1, with the exception that the solid solution structure is thicker.

[0065] Example 3: 26 nm thick HfO2 / ZrO2 / Al2O3 piezoelectric thin film device with intercalated Al2O3 dielectric interlayer optimization

[0066] Example 3 is an intercalated Al2O3 dielectric interlayer optimized superlattice stacked hafnium-based piezoelectric thin film device with a 26 nm thick piezoelectric layer, as shown in Example 2, with the exception that each layer of HfO2and ZrO2is 1 nm thick, and a 1 nm thick layer of Al2O3 is intercalated every 12 layers (i.e., 12 nm thick), and the process is similar to Example 2.

[0067] Comparative Example 4: 24 nm thick HfO2 / ZrO2 piezoelectric thin film device in a solid solution structure (no third oxide layer used in this example) 0.5 Zr 0.5 O2

[0068] Comparative Example 4 is a 24 nm thick ZrO2-doped HfO2 solid solution HfZrO2 device.0.5 Zr 0.5 O2 device, without internal superlattice multilayer stack structure, process similar to Comparative Example 1, except the solid solution structure is thicker.

[0069] Example 4: Interlayer-optimized 39 nm thick HfO2 / ZrO2 / Al2O3 piezoelectric thin film device

[0070] Example 4 is an interlayer-optimized superlattice stack structure hafnium-based piezoelectric thin film device with a 39 nm thick piezoelectric layer, similar to Example 2, except each layer of HfO2 and ZrO2 is 6 nm, and every 2 layers of the stack (12 nm thick) is interlayered with a 1 nm thick layer of Al2O3, and the process is similar to Example 2.

[0071] Example 5: Interlayer-optimized 37.5 nm thick HfO2 / ZrO2 / Al2O3 piezoelectric thin film device

[0072] Example 5 is an interlayer-optimized superlattice stack structure hafnium-based piezoelectric thin film device with a 37.5 nm thick piezoelectric layer, similar to Example 2, except each layer of HfO2 and ZrO2 is 2 nm, and every 6 layers of the stack (12 nm thick) is interlayered with a 0.5 nm thick layer of Al2O3, and the process is similar to Example 2.

[0073] Example 6: Interlayer-optimized 42 nm thick HfO2 / ZrO2 / Al2O3 piezoelectric thin film device

[0074] Example 6 is an interlayer-optimized superlattice stack structure hafnium-based piezoelectric thin film device with a 42 nm thick piezoelectric layer, similar to Example 2, except each layer of HfO2 and ZrO2 is 2 nm, and every 6 layers of the stack (12 nm thick) is interlayered with a 2 nm thick layer of Al2O3, and the process is similar to Example 2.

[0075] Example 7: Interlayer-optimized 39 nm thick HfO2 / ZrO2 / SiO2 piezoelectric thin film device

[0076] Example 7 is an interlayer-optimized superlattice stack structure hafnium-based piezoelectric thin film device with a 39 nm thick piezoelectric layer, similar to Example 2, except every 12 nm thick superlattice structure is interlayered with a 1 nm thick layer of SiO2, which is grown using an atomic layer deposition process, and the process is similar to Example 2.

[0077] All examples and comparative examples are subjected to rapid thermal annealing at 600 °C for 30 s under N2 atmosphere using a rapid annealing furnace.

[0078] With the samples obtained from Example 1 and Comparative Example 1 as examples, the average grain of Example 1 and Comparative Example 1 is analyzed and counted by using a scanning electron microscope and a watershed method, and it is found that the average grain size of the piezoelectric film with the superlattice stack structure in Example 1 is smaller than that of the piezoelectric layer with the solid solution structure in Comparative Example 1. The crystal phase of the film of Example 1 and Comparative Example 1 is analyzed by using a grazing incidence X-ray diffraction method, and it is found that the m-phase content of the device with the superlattice stack structure is significantly reduced, and the o / t-phase content is significantly increased, which verifies the effect of the small grain formed by the superlattice stack on inhibiting the m-phase and promoting the o / t-phase.

[0079] Further, the piezoelectric performance of Example 2, Comparative Example 2 and Comparative Example 3 is tested by using a piezoelectric force atomic force microscope (PFM), and the test results show that the longitudinal piezoelectric coefficient d 33,eff of Example 2, Comparative Example 2 and Comparative Example 3 is about 6.06 pm / V, about 4.03 pm / V and about 1.04 pm / V respectively, which proves that the piezoelectric performance and piezoelectric response of the device of Example 2 optimized by the method of the application are significantly improved compared with the solid solution device (Comparative Example 3), and compared with the device with only the superlattice stack structure (Comparative Example 2), the piezoelectric performance of the hafnium-based piezoelectric layer with the superlattice structure is further optimized by the aluminum oxide interlayer structure used in the application.

[0080] The crystal phase structure of Example 2, Comparative Example 2 and Comparative Example 3 is characterized by using a grazing incidence X-ray diffraction method, and the results are shown in Figure 10 It can be seen that the o / t-phase content of Example 2 with the interlayer structure optimization is significantly increased compared with the unoptimized examples (Comparative Example 2 and Comparative Example 3), and since the piezoelectric performance is the largest, it can be proved that the reason for the increase of the peak area ratio is the increase of the o-phase content, which proves that the optimization method of the application can increase the o-phase ratio in the thin film with a higher thickness.

[0081] In addition, the piezoelectric performance of Example 3 described above is improved compared with Comparative Example 4, but the improvement amplitude is smaller than that of Example 2 compared with Comparative Example 3. The piezoelectric performance of Examples 4-7 described above is also improved compared with Comparative Example 2 and Comparative Example 3 (of course, the improvement effect of Example 2 is the most obvious; the improvement effect of Example 7 is not as good as that of Example 2, mainly because the elastic constant of the SiO2 layer is not as good as that of Al2O3, so the interlayer tensile stress introduced is not as good as that of Al2O3).

[0082] It can be seen that, by comparing the Hf 0.5 Zr 0.5 O2 piezoelectric thin film device with the superlattice stack structure with the traditional Hf 0.5 Zr 0.5The piezoelectric film device of the O2 solid solution structure is annealed at 600 DEG C for 30s in N2 atmosphere, and compared with the HfO2 / ZrO2 piezoelectric film device of the present application using the laminated structure and the interlayer optimization, the experimental results prove that under the condition of high thickness, the laminated structure and the interlayer optimization of the present application can obtain higher piezoelectric performance, and maintain higher piezoelectric characteristics, which proves that the interlayer optimization can promote the formation of the piezoelectric phase, and provides a thought for the application of the hafnium-based film in the piezoelectric device under high thickness.

[0083] The above examples are only examples, for example, Figure 3 The topmost layer is an Al2O3 layer (corresponding to the third oxide layer), but the third oxide on the top surface is an optional structure, and a zirconium oxide layer can also be directly used as a capping layer to contact air. In addition, the rapid thermal annealing can also be performed according to other rapid thermal annealing conditions reported in the prior art, for example, the annealing atmosphere can also be N2 atmosphere in addition to vacuum, and the annealing effect is equivalent.

[0084] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present application, and is not intended to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for optimizing a high thickness hafnium-based piezoelectric thin film device, the high thickness hafnium-based piezoelectric thin film device comprising, from bottom to top, a substrate, a bottom electrode, and a hafnium-based piezoelectric functional layer, wherein, The thickness of the hafnium-based piezoelectric functional layer is not less than 20 nm. It is a superlattice structure formed by alternating layers of hafnium oxide and zirconium oxide, including multiple superlattice units. Each superlattice unit is formed by stacking a hafnium oxide layer and a zirconium oxide layer from bottom to top. The key feature is that a third oxide layer is deposited at the interface between two adjacent superlattice units at predetermined thicknesses inside the hafnium-based piezoelectric functional layer, thereby optimizing the piezoelectric performance of the high-thickness hafnium-based piezoelectric thin film device. The third oxide layer is selected from aluminum oxide layer and silicon oxide layer.

2. The optimization method of claim 1, wherein, The preset thickness interval specifically refers to a thickness interval of 10nm-16nm; The thickness of each third oxide layer is 0.5nm-2nm.

3. The optimization method of claim 1, wherein, A third oxide layer is also deposited on the top surface of the hafnium-based piezoelectric functional layer.

4. The optimization method of claim 1, wherein, The optimized high-thickness hafnium-based piezoelectric thin film device uses a zirconium oxide layer or a third oxide layer as a capping layer for contact with air, and does not have a top electrode.

5. The optimization method as described in claim 1, characterized in that, Before optimization, the thickness of the hafnium-based piezoelectric functional layer was 30nm to 36nm.

6. The optimization method as described in claim 1, characterized in that, Before optimization, the hafnium-based piezoelectric functional layer is based on Hf x Zr y O2 piezoelectric material, wherein x is a positive number greater than 0, y is a positive number greater than 0, and x+y≤2; Preferably, the Hf x Zr y In O2, x:y is preferably 1:1; The superlattice structure has n superlattice units, including n hafnium oxide layers and n zirconium oxide layers, with each hafnium oxide layer and each zirconium oxide layer having a thickness of 1 nm to 6 nm; Where n is a positive integer greater than or equal to 2 and less than or equal to 12; Preferably, the thickness of each hafnium oxide layer and each zirconium oxide layer is 2 nm; The preset thickness interval specifically refers to a thickness interval of 12 nm.

7. The optimization method as described in claim 1, characterized in that, The substrate is made of materials selected from: intrinsic Si, p-Si, n-Si, and SiO2; The bottom electrode is made of materials selected from: Pt, TiN, W, Au, TaN, RuO2; preferably TiN.

8. The optimization method as described in claim 1, characterized in that, Specifically, the following steps are included: (1) Deposit the bottom electrode on a clean and dry substrate; (2) A plurality of superlattice units are deposited on the bottom electrode, each superlattice unit being formed by stacking a hafnium oxide layer and a zirconium oxide layer from bottom to top; (3) When the deposition thickness in step (2) reaches the preset thickness interval, a third oxide layer is deposited; (4) Repeat steps (2) and (3) to deposit a third oxide layer at the interface between two adjacent superlattice units at a predetermined thickness in the superlattice structure until the sum of the thicknesses of the superlattice structure is not less than 20 nm, thereby forming an optimized hafnium-based piezoelectric functional layer. (5) Rapid thermal annealing yields the optimized high-thickness hafnium-based piezoelectric thin film device; wherein the rapid thermal annealing is performed under vacuum or N2, the annealing temperature is 400℃-700℃, and the annealing time is 30s-60s; Preferably, in the step (5), the rapid thermal annealing is performed under vacuum condition, the vacuum degree is less than or equal to 5.0*10 -2 hPa, more preferably less than or equal to 2.0*10 -2 hPa.

9. An optimized high-thickness hafnium-based piezoelectric thin film device obtained by the optimization method described in any one of claims 1-8.

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