Transition metal fluoride superionic conductor dielectric thin film and method of making same

Abstract

The application discloses a transition metal fluoride super ionic conductor dielectric film and a preparation method thereof. The super ionic conductor dielectric film is prepared by a thermal evaporation method from a transition metal fluoride super ionic conductor. The transition metal fluoride super ionic conductor is selected from scandium fluoride, yttrium fluoride, titanium fluoride, hafnium fluoride, manganese fluoride, ferrous fluoride and nickel fluoride. In the application, the source material of the transition metal fluoride is heated and evaporated into a gaseous state in an evaporation system by the thermal evaporation method. The gaseous fluoride is directly adhered to a substrate placed on the upper side of the source material and recrystallized, so that the thickness of the transition metal fluoride is controllable, the number of defects is controllable and the integration is very high. The super ionic transition metal fluoride dielectric material can show great potential in the design and manufacture of new functional devices.

Description

Transition metal fluoride superionic conductor dielectric thin films and their preparation methods Technical Field

[0001] This invention belongs to the field of semiconductor materials technology, specifically relating to a transition metal fluoride superionic conductor dielectric thin film and its preparation method. Background Technology

[0002] Dielectric materials are among the core materials used in condensed matter physics and advanced electronic devices. As the miniaturization of traditional semiconductor devices approaches its physical limits, a crucial solution to overcome the adverse effects of short-channel effects is to find dielectric materials with stronger control over channel materials. In condensed matter physics research, the manipulation of various strongly correlated electronic phenomena also requires the development of dielectric materials with greater capacitive coupling. Traditional low-dielectric-constant SiO2 dielectric materials and subsequently developed high-dielectric-constant dielectric materials such as HfO2 and ZrO2 often face severe gate leakage problems due to their dielectric breakdown limits, and are gradually failing to meet the field-effect control requirements of electronic states in micro-semiconductor devices or strongly correlated electronic systems. Although researchers have successively developed novel dielectrics with larger capacitive coupling, such as SrTiO3 single-crystal thin-film oxide dielectrics with ultra-high dielectric constants and organic electrolyte materials, these novel dielectrics still have significant problems in practical applications. For example, SrTiO3 single-crystal thin-film oxide dielectrics require transfer to a target substrate or material surface and are not suitable for wafer-level fabrication; while organic electrolyte materials, which mostly exist in liquid or gel form, are difficult to be compatible with traditional semiconductor photolithography processes. In addition, liquid electrolytes also have electrochemical mechanisms that seriously affect the stability and reproducibility of devices. Therefore, it is crucial to find dielectric materials that possess large coupling capacitance, wide bandgap, stable existence in solid-state form, compatibility with traditional semiconductor device processes, and the ability to be grown on a large scale.

[0003] Due to the superionic properties of fluorides, fluoride ions can move rapidly within the crystal and form an electric double-layer effect under an electric field. Therefore, this structural characteristic is highly suitable for use as a solid ionic dielectric in various electronic devices. However, previous studies on the properties of fluorides were based on their powder or solid solution forms, which cannot be directly applied to the fabrication of electronic devices. Therefore, this invention proposes to directly prepare fluoride thin films from fluoride powders. Summary of the Invention

[0004] The purpose of this invention is to provide a superionic conductor dielectric film, obtained from a transition metal fluoride superionic conductor; the conductivity of the superionic conductor dielectric film is 10. -2 -10 -5 S / cm, low-frequency capacitance (0.01Hz) is 0.4-70.3μF / cm 2High-frequency capacitor (10 6 (Hz) is 0.01-0.30 μF / cm 2 Leakage current density less than 10 -5 A / cm 2 The root mean square surface roughness is less than 1 nm, and the fluorine vacancy content is 0.01-15%.

[0005] Furthermore, the transition metal fluoride superionic conductor is scandium fluoride (ScF3), yttrium fluoride (YF3), titanium fluoride (TiF4), hafnium fluoride (HfF4), manganese fluoride (MnF2), ferrous fluoride (FeF2), or nickel fluoride (NiF3).

[0006] The second objective of this invention is to provide a method for preparing the above-mentioned superionic conductor dielectric film, wherein the dielectric film is prepared by thermal growth.

[0007] Furthermore, the preparation method involves: first, grinding the transition metal fluoride superionic conductor, then placing it on the heating column of a thermal evaporation system, and when the system vacuum reaches 10... -5 Evaporation begins when Pa is above a certain level, with transition metal fluorides as... The evaporation rate is adjusted to deposit on the substrate surface until a thickness of 10-20 nm is achieved. Until the target thickness is achieved, the temperature of the substrate is controlled at 200-600K during the vapor deposition process.

[0008] Furthermore, the transition metal fluoride superionic conductor is ground to a particle size of less than 200 mesh.

[0009] Furthermore, the substrate is made of SiO2 / Si, Si, Ge, mica, sapphire, ruby, indium phosphide, indium arsenide, gallium phosphide, gallium nitride, strontium titanate, zirconium oxide, silicon carbide, or quartz glass.

[0010] In the thermal growth of transition metal fluoride superionic conductor thin films, a slow evaporation rate is initially selected to obtain a film with high density. In one embodiment of the present invention, a method is employed... The evaporation rate can be increased once the film thickness reaches a certain value, such as 10 nm, in order to reduce the total evaporation time. Simultaneously, the system's vacuum level needs to be controlled. Theoretically, the better the system vacuum level, the denser and higher the quality of the deposited film. For example, 10 -5 High vacuum on the order of Pa. In addition, in order to form more fluorine vacancies and improve the ionic conductivity of the fluoride film, this invention is designed to use a relatively low substrate temperature, such as 200-600K.

[0011] A third objective of this invention is to provide the application of the aforementioned superionic conductor dielectric thin film in the fabrication of semiconductor devices. Preferably, the semiconductor device is a field-effect transistor, an inverter circuit, a logic gate circuit, or a non-volatile memory device.

[0012] The fourth objective of this invention is to provide a semiconductor device comprising the aforementioned dielectric thin film.

[0013] This invention employs thermal evaporation to deposit transition metal fluoride superionic conductor dielectric films. Thermal evaporation is a simple, low-cost, and large-scale film growth method with controllable film quality and thickness. Because the metal cation lattice framework in transition metal fluorides allows fluoride ions with small ionic radii to move freely within the crystal, and because transition metal fluorides have large band gaps and excellent insulation properties, they are beneficial for suppressing leakage current through the fluoride film dielectric. Through thermal evaporation, the transition metal fluoride source material is heated and evaporated into a gaseous state in the evaporation system. The gaseous fluoride directly adheres to the substrate placed above the source material and recrystallizes, thus enabling controllable thickness and defect number of the transition metal fluoride, and exhibiting high integration. This demonstrates the great potential of superionic transition metal fluoride dielectric materials in the design and manufacture of novel functional devices. Attached Figure Description

[0014] In Figure 1, (a) is a photograph of the transition metal fluoride superion conductor source material, and (b) is a schematic diagram of the thermal evaporation principle.

[0015] Figure 2 shows the EDX spectrum of the NiF3 thin film.

[0016] Figure 3 is a geometric schematic diagram of the capacitance test of a superionic conductor fluoride dielectric film.

[0017] Figure 4 shows the capacitance test results of seven transition metal superionic conductor fluoride films.

[0018] In Figure 5, (a) is a schematic diagram of the bottom-gate MoS2 field-effect transistor based on NiF3 thin-film superionic conductor gate dielectric, and (b) is the transfer characteristic curve at a source-drain voltage of 0.5V. Detailed Implementation

[0019] The preferred embodiments of the present invention will now be described in detail with reference to specific examples. It should be understood that the following examples are given for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications and substitutions to the present invention without departing from its spirit and essence.

[0020] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0021] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0022] The thermal evaporation system used in the following embodiments is the VZZ-300 high vacuum thermal evaporation system from Beijing MicroNano Vacuum Co., Ltd. Other high vacuum thermal evaporation systems can also be used, as long as the vacuum regulation of the thermal evaporation process can be controlled.

[0023] The transition metal fluoride superionic conductors used in the following embodiments are from the following sources:

[0024] Table 1

[0025] Transition Metal Fluorides Company (Country) Purity (%) Scandium Fluoride (ScF3) Shanghai McLean Biotech Co., Ltd. (China) 99.99 Yttrium Fluoride (YF3) Beijing Zhongjin Research New Materials Technology Co., Ltd. (China) 99.99 Titanium Fluoride (TiF4) Shanghai McLean Biotech Co., Ltd. (China) 98 Hafnium Fluoride (HfF4) Shanghai McLean Biotech Co., Ltd. (China) 99.9 Manganese Fluoride (MnF2) Shanghai McLean Biotech Co., Ltd. (China) 99.9 Ferrous Fluoride (FeF2) Shanghai McLean Biotech Co., Ltd. (China) 98 surface

[0026] Example 1

[0027] I. The preparation process of fluoride thin films is as follows:

[0028] 1. Pressing of transition metal fluoride powders

[0029] First, the fluoride powder or lumps are ground into an extremely fine powder of about 200 mesh. The powder is then placed into a stainless steel mold with a diameter of 10 mm for pressing. In this embodiment, the fluoride powder is pressed into a diameter of 10 mm and a length of 10 mm, depending on the size of the selected tungsten boat.

[0030] 2. Thermal growth preparation of transition metal fluoride superionic conductor thin films

[0031] The compressed columnar fluoride material is placed in a tungsten boat, which is then transferred to the heating column of the thermal evaporation system and secured. Simultaneously, the strontium titanate substrate to be deposited is adhered using high-temperature resistant yellow tape, and a substrate baffle is placed directly beneath the substrate to seal the cavity. The pneumatic valve between the vacuum pump and the evaporation system is opened, followed by the mechanical pump to obtain a rough vacuum. When the system vacuum level is better than 5 Pa, the molecular pump is activated until the system reaches 10 Pa. -5 High vacuum in the Pa range.

[0032] Turn on the water cooling system of the substrate. Increase the current flowing through the tungsten boat. When the heating temperature exceeds the melting point of the fluoride, fluoride molecules begin to deposit on the pre-placed substrate to form a fluoride film. Monitor the thickness of the transition metal fluoride film on the strontium titanate substrate surface using a crystal oscillator film thickness gauge. During the evaporation process, first allow the fluoride material to... The material is exhaled at a certain rate, and once the exhaled thickness reaches 10 nm, the baffle between the fluoride material and the substrate is opened. Then, the current flowing through the tungsten boat is reduced, and the reading of the crystal oscillator film thickness gauge is observed to maintain the thickness. The rate of thermal evaporation, maintaining The evaporation rate was increased until the thickness reached 10 nm; finally, the current flowing through the tungsten boat was increased, and the evaporation rate was increased to a certain level by observing the reading of the crystal oscillator film thickness gauge. A faster rate of thermal evaporation, maintaining The rate continues until the target thickness of 200nm is reached.

[0033] The crystal structures, thermal evaporation currents, back vacuum before vapor deposition, and worst vacuum during vapor deposition of different fluorides are summarized in Table 2.

[0034] Table 2

[0035]

[0036] II. Basic Characterization of Transition Metal Fluoride Superionic Conductor Thin Films

[0037] To confirm the actual chemical element ratio of cations and anions in transition metal fluoride films, energy-dispersive X-ray spectroscopy (EDX) was used to characterize different transition metal fluorides. The working principle is to identify the different elements in the test sample by distinguishing the characteristic X-rays emitted by each element. The chemical element ratio of the transition metal fluoride NiF3 was characterized by EDX testing, and the results are shown in Figure 2. Further data analysis yielded the specific chemical element ratio of NiF3, and the results are shown in Table 3.

[0038] Table 3

[0039] Average vacancy concentration (%) for Sample 1 and Sample 2: NiF3 25.1: 74.9 27.1: 72.0 1: 2.8 35.6 surface

[0040] As can be seen, the actual ratio of fluoride ions in the transition metal fluoride superionic conductor film is lower than the 3:1 ratio in the chemical formula. This test result indicates that there are a large number of fluoride ion vacancies in the transition metal fluoride film. It is precisely because of the presence of these fluoride ion vacancies that fluoride ions can migrate rapidly in the lattice framework of the fluoride, thereby giving it high ionic conductivity.

[0041] As shown in Figure 3, the capacitance characteristics of the superionic conductor fluoride were tested using a parallel-plate capacitor structure with a silicon substrate having a 300 nm oxide layer. First, the pattern of the lower electrode was pre-fabricated on the silicon substrate using photolithography. Then, a metal electrode was deposited using an electron beam evaporation system to serve as the lower electrode of the parallel-plate capacitor. Next, a metal fluoride solid solution film was deposited on the pre-fabricated electrode substrate using a thermal evaporation system. Finally, the pattern of the upper electrode was pre-fabricated on the metal fluoride film using photolithography, and a metal electrode was deposited using an electron beam evaporation system to serve as the upper electrode of the parallel-plate capacitor. Electrochemical impedance spectroscopy (EIS) measurements were performed on an electrochemical workstation (Zahner Zennium Pro). Based on the parallel-plate capacitor geometry (metal electrode / fluoride / metal electrode with a 200 nm fluoride film), a 20 mV AC voltage was applied as a perturbation signal, and EIS measurements were performed within a frequency range (f) from 0.01 Hz to 1 MHz to obtain the frequency-dependent impedance Z and phase angle θ. The capacitance C per unit area of ​​a fluoride film is calculated using the following formula:

[0042] C = 1 / 2πfZ ″ S.

[0043] Where f is the frequency, Z″ is the imaginary part of the impedance, and S is the area of ​​the parallel-plate capacitor. Temperature-dependent EIS measurements are performed in a cryogenic system under vacuum conditions.

[0044] To further investigate the capacitive coupling performance of these seven transition metal fluorides, frequency-dependent capacitance was measured at room temperature, with the aim of identifying suitable dielectric materials for various electronic devices. Figure 4 shows the capacitive characteristics of a series of transition metal fluoride films. As can be seen from the figure, most transition metal fluoride films exhibit high capacitive coupling characteristics.

[0045] The table below shows the test results of relevant properties of the transition metal fluoride superionic conductor thin film prepared in this embodiment:

[0046] Table 4

[0047]

[0048] In summary, transition metal fluoride superionic conductors have great potential as dielectric layer materials for field-effect transistors.

[0049] Example 2

[0050] Based on the excellent dielectric properties of the aforementioned transition metal fluoride superionic conductor thin film, the construction of a single transition metal fluoride thin film-based gate dielectric field-effect transistor further demonstrates the advantages of transition metal fluoride superionic conductors as novel dielectric materials in electronic devices. The overall configuration of the two-dimensional semiconductor field-effect transistor based on the transition metal fluoride dielectric thin film adopts a bottom-gate structure. A transition metal fluoride thin film is deposited on a strontium titanate substrate as the dielectric layer material of the field-effect transistor, and the channel material is an n-type doped two-dimensional semiconductor material, MoS2. The fabrication process of the field-effect transistor is as follows:

[0051] (1) Substrate cleaning: First, place the cut strontium titanate substrate into a mixed solution of acetone, ethanol and isopropanol, and clean it in an ultrasonic cleaner for 3-5 minutes to remove impurities attached to the surface. Then rinse with isopropanol solution and treat the surface of the titanate substrate with oxygen plasma to remove residual organic solution, so that it has a clean surface.

[0052] (2) Preparation of bottom gate electrode: The bottom gate electrode pattern is pre-formed on the strontium titanate substrate by photolithography. Titanium gold electrodes (the thickness of the titanium gold metal electrodes is 3 / 9nm) are deposited by electron beam evaporation as the bottom gate. Then, the metal electrodes are stripped in acetone solution and rinsed with isopropanol to obtain a substrate with the bottom gate.

[0053] (3) A transition metal fluoride film is thermally grown on a strontium titanate substrate with a pre-set bottom gate electrode pattern.

[0054] (4) Preparation of two-dimensional channel material: The mechanical peeling method is adopted. First, the layered sheet of two-dimensional material is mechanically peeled off from the bulk MoS2 crystal with tape, and then polydimethylsiloxane (PDMS) is used for further peeling. The sample thickness is determined by optical photographs and suitable thin-layer two-dimensional material samples are found. Then, the MoS2 material sheet is transferred from PDMS to the surface of the metal fluoride film obtained in the third step by dry transfer.

[0055] (5) Deposition of source and drain metal electrodes: Polymethyl methacrylate (PMMA) is spin-coated onto the substrate surface of the transferred sample. Electrode patterns are formed on the MoS2 sample using photolithography. After development, metal electrodes (Ti / Au, 6+45nm) are deposited by electron beam evaporation. Finally, the metal electrodes are stripped in acetone solution and rinsed with isopropanol to obtain the final two-dimensional field-effect transistor device. To improve the interfacial contact resistance of the metal semiconductor, an annealing treatment is usually performed at 200 degrees Celsius under argon-hydrogen gas (95% Ar and 5% H2) for two hours.

[0056] Device testing method: The above-mentioned field-effect transistors were tested for device performance at room temperature. The source-drain voltage and gate voltage were applied using a Keithley 2614B digital source meter, and the source-drain current and gate drain current were measured simultaneously.

[0057] Figure 5(a) shows a schematic diagram of the bottom-gate MoS2 field-effect transistor based on a transition metal fluoride (NiF3) thin-film gate dielectric, with the upper left inset showing an optical photograph of the device. As can be seen from the transfer characteristic curves in Figure 5(b), the MoS2 channel material exhibits n-type doping, and it can be concluded that NiF3 has an excellent modulation effect on the MoS2 bottom-gate field-effect transistor.

Claims

1. A superionic conductor dielectric thin film, characterized in that, The transition metal fluoride superionic conductor was prepared by thermal evaporation. The preparation process was as follows: the transition metal fluoride superionic conductor was first ground, and then placed on the heating column of the thermal evaporation system. When the system vacuum reached 10... -5 Evaporation begins when the pressure is above a certain level (Pa). The transition metal fluoride superionic conductor evaporates and deposits on the substrate surface at a rate of 0.2-0.4 Å / s until a thickness of 10-20 nm is reached. The rate is then adjusted to 0.8-1.0 Å / s until the target thickness is achieved. During the evaporation process, the substrate temperature is controlled at 200-600 K. The conductivity of the superionic conductor dielectric film is 10⁻⁶ K. -5 -10 -2 S / cm, low-frequency capacitance is 0.4-70.3 μF / cm 2 The high-frequency capacitance is 0.01-0.30 μF / cm. 2 Leakage current density less than 10 -5 A / cm 2 The surface roughness root mean square is less than 1 nm, and the fluorine vacancy content is 0.01-15%.

2. The superionic conductor dielectric thin film according to claim 1, characterized in that, The transition metal fluoride superionic conductor is selected from scandium fluoride, yttrium fluoride, titanium fluoride, hafnium fluoride, manganese fluoride, ferrous fluoride, and nickel fluoride.

3. The method for preparing the superionic conductor dielectric thin film according to claim 1 or 2, characterized in that, The superionic conductor dielectric film was prepared by thermal evaporation.

4. The preparation method according to claim 3, characterized in that, The preparation method is as follows: first, the transition metal fluoride superionic conductor is ground, and then it is placed on the heating column of the thermal evaporation system. When the system vacuum reaches 10... -5 When the pressure is above Pa, evaporation begins. The transition metal fluoride superionic conductor evaporates and deposits on the substrate surface at a rate of 0.2-0.4 Å / s until the thickness reaches 10-20 nm. The rate is then adjusted to 0.8-1.0 Å / s until the target thickness is reached.

5. The preparation method according to claim 4, characterized in that, The temperature of the substrate is controlled at 200-600 K during the vapor deposition process.

6. The preparation method according to claim 4, characterized in that, The transition metal fluoride superionic conductor is ground to a particle size of less than 200 mesh.

7. The preparation method according to claim 4, characterized in that, The substrate is made of SiO2 / Si, Si, Ge, mica, sapphire, ruby, indium phosphide, indium arsenide, gallium phosphide, gallium nitride, strontium titanate, zirconium oxide, silicon carbide, or quartz glass.

8. The application of the superionic conductor dielectric thin film according to claim 1 or 2 in the fabrication of semiconductor devices.

9. The application according to claim 8, characterized in that, The semiconductor device is a field-effect transistor, an inverter circuit, a logic gate circuit, or a non-volatile magnetic memory device.

10. A semiconductor device, characterized in that, Includes the superionic conductor dielectric thin film as described in claim 1 or 2; the semiconductor device is a field-effect transistor, an inverter circuit, a logic gate circuit, or a non-volatile magnetic memory device.

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