KR20180086663A - Conformal deposition method and device of lithium phosphate thin film electrolytes for 3D solid state batteries by MOCVD - Google Patents

Abstract

The present invention relates to a method and an apparatus for uniformly depositing a lithium phosphate thin film electrolyte for a 3D solid-state battery by metal-organic chemical vapor deposition. The present invention provides the method for depositing the lithium phosphate thin film electrolyte, comprising a step of depositing on a substrate using lithium as a precursor, a phosphate precursor and water as an activator through the metal-organic chemical vapor deposition.

Description

Technical Field [0001] The present invention relates to a method and apparatus for uniformly depositing a lithium phosphate thin film electrolyte for a three-dimensional solid-state battery by metal-organic chemical vapor deposition,

The present invention relates to a method and apparatus for depositing a lithium phosphate thin film electrolyte and a lithium phosphate thin film produced thereby.

The repeated downscaling of microsystems such as micro-sensors, implantable medical devices and micro-electro-mechanical systems has increased interest in ultra-thin Li-ion batteries as an on-board power source. However, the demand for high energy and power density for on-board power requires the development of three-dimensional (3D) structure thin-film batteries. 3D structured solid state batteries can be a solution to improve the performance of existing 2D solid state batteries. The biggest advantage of a 3D structured battery over 2D is that it has a high specific surface area, a high energy density, a short diffusion path for fast charging and discharging with improved power density. The large surface area promotes an increase in the amount of active material for high storage capacity. High Stability Solid electrolytes enable the battery to operate with an extended lifetime of up to 10000 times the charge and discharge cycles.

A typical thin-film Li-ion battery consists of three thin layers: a cathode, an anode, and an electrolyte separating them. Electrolytes play an important role, not only preventing electrons from leaking into the inside, but also conducting Li-ions for battery operation. Lithium phosphate based electrolytes are the most popular solid electrolytes for thin film Li-ion batteries due to their many beneficial properties. For a Li ₃ PO ₄ 10 ^-7 Scm ^-1 and LiPON - having a relatively high ionic conductivity of up to 10 ^-6 Scm ^-1 for (nitrogen-doped lithium phosphate), has a high electrochemical stability window (0 to 4.7 V vs. Li / Li ⁺ ).

Lithium phosphate thin film electrolytes were synthesized by several deposition methods such as sputtering, e-beam deposition and pulsed laser deposition. However, these physical techniques are limited to flat substrates. That is, they can not uniformly deposit on the 3D geometry. In order to deposit uniform films on 3D structures, atomic layer deposition (ALD) and metal-organic chemical vapor deposition (MOCVD) techniques have been commonly used to deposit uniform films on 3D structures.

Recently, atomic layer deposition (ALD) has been used to form highly uniform lithium phosphate and LiPON thin films on 3D structures. However, the relatively low growth rates of about 1 A per cycle of 90 s and about 0.7 A per cycle of 8 s, as well as complex device requirements due to sequential processing, have limited the application of ALD to use in high volume production environments.

Deposition of lithium phosphate based electrolytes by metal-organic chemical vapor deposition has also been reported, but this report did not include the possibility of MOCVD for deposition on 3D structures. Xie et al. Developed a MOCVD process for depositing a lithium phosphate thin film using lithium tert-butoxide, trimethyl phosphate and oxygen as precursors. However, this electrolyte could not be uniformly deposited on the 3D structure, because the deposition took place in the mass transport limited regime.

It is an object of the present invention to provide a method and apparatus for depositing a lithium phosphate thin film electrolyte capable of uniformly depositing even on a 3D structure, and a lithium phosphate thin film produced thereby.

In order to accomplish the above object, the present invention provides a method for depositing a lithium phosphate thin film electrolyte comprising depositing a lithium precursor, a phosphate precursor and water as an activator on a substrate through a metal-organic chemical vapor deposition method to provide.

In the present invention, the lithium precursor may be lithium dipivaloyl methanate.

In the present invention, the phosphate precursor may be triethyl phosphate.

In the present invention, the substrate may be a three-dimensional structure substrate having a concavo-convex pattern with an aspect ratio of 5: 1 or more.

In the present invention, the deposition temperature may be 300 ° C to 450 ° C.

In the present invention, the activation energy of the deposition step may be 10 kJ mole ^{-1 or} more.

The present invention also relates to a plasma processing apparatus comprising: a reaction chamber in which deposition is performed; And a lithium precursor bubbler connected to the reaction chamber through a line and having a tube of a bent structure.

In the present invention, the tube may include two or more bending structures.

In the present invention, the lithium precursor bubbler can be made of glass.

In the present invention, the lithium precursor bubbler may contain paraffin oil as a heating medium.

Further, the present invention provides a lithium phosphate thin film having a three-dimensional structure having a concavo-convex pattern with an aspect ratio of 5: 1 or more and having a step-coverage of 40% or more.

The ionic conductivity of the lithium phosphate thin film according to the present invention may be 1 × 10 ^-8 S cm ^{-1 or} more.

Percentages of lithium, phosphorus, and oxygen at a depth of 1 nm or more from the surface of the lithium phosphate thin film according to the present invention can maintain a deviation of +/- 10% along the depth, respectively.

The carbon percentage at a depth of 1 nm or more from the surface of the lithium phosphate thin film according to the present invention may be 5% or less.

According to the present invention, the lithium phosphate thin film can be uniformly deposited also on the 3D structure.

FIG. 1 schematically shows a configuration of an experimental apparatus for depositing a lithium phosphate membrane.
2 is a SEM image of a surface of a Li ₃ PO ₄ thin film deposited at (a) 300 ° C., (b) 350 ° C., (c) 400 ° C., and (d) 450 ° C.
Figure 3 shows a proposed mechanism for the formation of a lithium phosphate structure.
Figure 4 shows the dependence of the growth rate on the deposition temperature, and the internal image shows the Arrhenius plot for the growth rate.
Figure 5 shows the GIXRD pattern of Li ₃ PO ₄ thin films deposited at 300 ° C to 500 ° C.
FIG. 6 shows a high-resolution XPS spectrum of Li 1s, P 2p, O 1s and C 1s of Li ₃ PO ₄ thin films deposited at 300 ° C and 400 ° C.
Figure 7 shows the elemental depth profile of Li ₃ PO ₄ thin films deposited at (a) 300 ° C and (b) 400 ° C with an etch depth of 10 nm.
Figure 8 shows the Nyquist plot for the EIS spectra of Li ₃ PO ₄ films deposited at (a) 300 ° C, (b) 350 ° C, (c) 400 ° C, and (d) 450 ° C.
9 is a cross-sectional SEM image of a Li ₃ PO ₄ thin film deposited on a Si substrate comprising a groove with an aspect ratio of 6: 1.

Hereinafter, the present invention will be described in detail.

[Deposition method]

The method of depositing a lithium phosphate thin film electrolyte according to the present invention may include depositing a lithium precursor, a phosphate precursor and water as an activator on a substrate.

As the lithium precursor, lithium dipivaloyl methanate (Li (DPM)), lithium tert-butoxide, lithium bis (trimethylsilyl) amide and the like can be used, and Li (DPM) can be preferably used. Li (DPM) has a higher vaporization temperature than other conventional lithium precursors, but is preferred because it has better stability in an air atmosphere.

As the phosphate precursor, triethyl phosphate (TEP), trimethyl phosphate and the like can be used, and TEP can be preferably used.

As the activating agent, water, ammonia, and oxygen can be used, and preferably water can be used. Water is both an activator and an oxygen precursor. Water plays an important role in the formation of Li ₃ PO ₄ , and in the absence of water, deposition does not occur even at a high temperature of 600 ° C. As the water, distilled water, deionized water and the like can be used.

As the deposition method, a chemical vapor deposition (CVD) method or the like can be used, and a metal-organic chemical vapor deposition (MOCVD) method can be preferably used. The lithium phosphate thin film can be uniformly deposited on the three-dimensional substrate using the MOCVD method.

As the substrate, a silicon substrate or the like can be used. In particular, the present invention can uniformly deposit a lithium phosphate thin film on not only a conventional two-dimensional substrate but also a substrate having a three-dimensional structure. The three-dimensional structure may include geometric rules or all irregular structures except a two-dimensional flat structure. For example, the three-dimensional structure may include irregularities, grooves, protruding structures, etc., and the size or area of these structures may be small, and it is not necessary to be regular. Preferably, the substrate may be a three-dimensional structure substrate having a concavo-convex pattern with an aspect ratio of 5: 1 or more. The upper limit of the aspect ratio may be, for example, 20: 1 or 15: 1.

The deposition temperature may be 300 ° C to 450 ° C, preferably 325 ° C to 425 ° C, more preferably 350 ° C to 400 ° C, and properties such as ion conductivity can be improved in this range. In the present invention, it is possible to deposit at a low temperature, and it is possible to solve problems such as gas generation occurring at a high temperature deposition of 600 ° C or more.

The activation energy of the deposition step may be at least 10 kJ mole ^-1 , preferably at least 20 kJ mole ^-1 , more preferably at least 30 kJ mole ^-1 . The upper limit of the activation energy is not particularly limited, and may be, for example, 100 kJ mole ^-1 or less or 50 kJ mole ^-1 or less.

[Deposition Apparatus]

1, the apparatus for depositing a lithium phosphate thin film electrolyte according to the present invention includes a reaction chamber (reactor), a lithium precursor bubbler, a phosphate precursor bubbler, a water bubbler, a heating unit, a transfer line, .

The reaction chamber is where the deposition takes place, and the substrate is placed inside. The reaction chamber can be heated by being provided with a heating unit inside and / or outside the chamber, and a cooling unit (cooling water or the like) is provided inside and / or outside the chamber wall for cooling. In addition, a vacuum can be formed inside the reaction chamber by being connected to a vacuum pump or the like.

The lithium precursor bubbler may be one which has been specially manufactured in accordance with the present invention in order to secure a stable supply of the precursor to the reaction chamber. To this end, the lithium precursor bubbler of the present invention can be made of glass, can have a bent structure, and can contain paraffin oil as a heating medium.

In particular, the tube may comprise two or more, preferably three or more, bending structures. The bending direction may be an up-down (vertical) direction and / or a left-right (horizontal) direction. FIG. 1 illustrates a generally W-shaped tube configuration having a two-loop structure, but the present invention is not limited thereto and various modifications are possible. The tube with a flexure configuration ensures a sufficiently long residence time of the carrier gas within the bubbler, thereby ensuring that the carrier gas is completely saturated with the vaporized lithium precursor. As a result, the lithium precursor is continuously transferred to the reactor at a fixed ratio, so that a thin film having a uniform composition can be obtained and reproducibility can be improved.

By using glass bubbler and paraffin oil, you can observe the internal parts of the bubbler to see if the line is not clogged by the condensed precursor. Paraffin oil has the advantage that it can provide a uniform temperature as a heating medium. The paraffin oil may be wholly or partially filled into the bubbler, and the bending structure tube may be inserted into the bubbler to surround the paraffin oil. A plurality of ceramic particles (alumina balls) may be inserted into the tube for temperature uniformity and heat capacity increase, and a filter may be inserted into the tube to prevent leakage of alumina balls. A heating device may be installed inside and / or outside the bubbler for heating, and a separate supply line may be connected to the tube for precursor supply and the like.

The phosphate precursor bubbler and the water bubbler may have the same configuration as the lithium precursor bubbler described above, and may have a simple vessel structure without any separate tube, heating medium or the like as illustrated in the drawings. The phosphate precursor bubbler and the water bubbler can be made of metal, for example stainless steel.

Each precursor bubbler is connected to a carrier gas supply line, and each precursor can be transported to the reaction chamber via a carrier gas. As the carrier gas, an inert gas such as nitrogen can be used, and the flow rate of the precursor and the carrier gas can be controlled by the mass flow rate controller.

Each precursor bubbler is connected to the reaction chamber via a separate supply line, and each precursor supply line may be individually connected to the reaction chamber, or merged as illustrated in the figure, and finally one supply line may be connected to the reaction chamber have. The precursor feed lines are equipped with line heaters and can be heated during transport of the precursor.

[Lithium phosphate thin film]

The lithium phosphate thin film formed using the above-described method and apparatus has a three-dimensional structure having a concavo-convex pattern with an aspect ratio of 5: 1 or more, and can have a step-coverage of 40% or more.

The aspect ratio of the lithium phosphate thin film may be 5: 1 or more, preferably 6: 1 or more. The upper limit of the aspect ratio may be, for example, 20: 1 or 15: 1.

The step-coverage of the lithium phosphate thin film may be at least 40%, preferably at least 45%. The upper limit value of the step-coverage is not particularly limited, and may be, for example, 100%, 80% or 60%. The step-coverage can mean a coating step in terms of thin film uniformity, and can in particular mean the percentage of the minimum thickness to the maximum thickness of the deposited film.

The ionic conductivity of the lithium phosphate thin film may be not less than 1 x 10 ^-8 S cm ^-1 , preferably not less than 2 x 10 ^-8 S cm ^-1 , more preferably not less than 5 x 10 ^-8 S cm ^-1 . The upper limit of the ionic conductivity is not particularly limited and may be, for example, 1 x ^10-6 S cm ^-1 or less or 1 x ^10-7 S cm ^-1 or less.

Percentages of lithium, phosphorus, and oxygen at depths of 1 nm or more from the surface of the lithium phosphate thin film can each maintain a deviation of +/- 10% along the depth. That is, in the lithium phosphate thin film deposited according to the present invention, the concentrations of lithium, phosphorus, and oxygen can be uniform along the depth of the lithium phosphate thin film.

At a depth of 1 nm or more from the surface of the lithium phosphate thin film, the carbon percentage can be 5% or less. That is, the lithium phosphate thin film deposited according to the present invention may contain little carbon.

The thickness of the lithium phosphate thin film is not particularly limited, and may be, for example, 10 to 1000 nm, preferably 50 to 500 nm.

Hereinafter, the present invention will be described more specifically by way of examples.

[Example]

In this embodiment, the lithium phosphate thin film is uniformly deposited on the 3D structure by MOCVD using lithium dipivaloylmethanate (Li (DPM)), triethylphosphate (TEP) and water (H ₂ O) as precursors Respectively. The effect of deposition temperature on the properties of lithium phosphate thin films was investigated. We also proposed and implemented a new bubbler design that stably transfers the solid precursor (Li (DPM)) to the reactor. To investigate the feasibility of 3D deposition by the developed method, a lithium phosphate thin film was deposited on a trenched substrate. Finally, mechanisms for thin film formation and a description of uniform deposition on 3D structures are presented.

1. Experiment

Lithium phosphate thin films were deposited by MOCVD technique. The reactor system included a custom cold wall low pressure MOCVD chamber. (DPM) (Sigma Aldrich, 98%), triethylphosphate (TEP) (Sigma Aldrich, 99.8%) and deionized water (H ₂ O) were used as precursors. Li (DPM), TEP and H ₂ O were maintained at 170 ° C, 25 ° C and 25 ° C, respectively, in each bubbler. The TEP and water were housed in a commercially available stainless steel bubbler and the bubbler for the solid Li (DPM) precursor was customized to glass according to the design proposed by Andre et al. To ensure a stable supply of the solid precursor to the reaction chamber (Fig. 1). The bubbler used paraffin oil as the heating medium to provide a uniform temperature. The two-loop tube configuration inside the bubbler ensured a long residence time of the carrier gas inside the bubbler, so that it was completely saturated with the Li (DPM) precursor. The use of glass bubbler and paraffin oil has other advantages, that is, by observing the internal components of the bubbler, it can be determined whether the line is not blocked by the condensed precursor. Li (DPM) has a higher vaporization temperature than other conventional lithium precursors such as lithium tert-butoxide, lithium bis (trimethylsilyl) amide, but was selected in this example due to better stability in an air atmosphere. This precursor was delivered to the reaction chamber by N ₂ as a carrier gas. The Li (DPM) line was maintained at 180 [deg.] C to prevent premature condensation of Li (DPM) inside the transfer tube. The substrate temperature was varied from 300 캜 to 450 캜. The flow rates of Li (DPM), TEP and H ₂ O, and carrier gas were controlled by a mass flow controller. Reaction pressure was monitored with a Convectron pressure gauge (Grandville-Phillips 275). The reactor base pressure was maintained at 50 mTorr and the typical operating pressure was maintained at 1.2 Torr. Fig. 1 schematically shows a configuration of an experimental apparatus for depositing a lithium phosphate film. A preliminary parameter variation experiment was performed first to confirm the basic operating conditions illustrated in Table 1. Table 1 shows experimental MOCVD conditions for Li ₃ PO ₄ deposition.

parameter unit value Li (DPM) carrier gas flow rate
TEP carrier gas flow rate
H ₂ O carrier gas flow rate
Base pressure
Working pressure
Li (DPM) bubbler temperature
TEP bubbler temperature
Water bubbler temperature
Line temperature sccm
sccm
sccm
mTorr
Torr
℃
℃
℃
℃ 100
50
10
50
1.2
170
25
25
180

Li ₃ PO ₄ was deposited on the silicon substrate for measurement of shape, element composition and bonding state. However, in order to measure crystallinity, a Li ₃ PO ₄ film was deposited on Corning XG glass to prevent the substrate peak from appearing in the XRD pattern of the thin film. For 3D deposition, a lithium phosphate film was deposited on the grooved silicon substrate. The silicon substrate was etched to obtain grooves of 135 탆 depth and 22.5 탆 width (aspect ratio 6: 1), 100 탆 depth and 10 탆 width (aspect ratio 10: 1), respectively. For the measurement of electrochemical impedance spectroscopy (EIS), a sandwich structure of Inconel / Li ₃ PO ₄ / Inconel was fabricated on a 2 × 2 mm 2 silicon substrate. The Inconel layer was deposited to a thickness of 200 nm by DC sputtering. The thicknesses of the lithium phosphate thin films deposited at 300 ° C, 350 ° C, 400 ° C and 450 ° C for 5 hours of deposition time were 90 nm, 180 nm, 300 nm and 440 nm, respectively.

The morphology and cross-sectional microstructure of Li ₃ PO ₄ thin films were examined by scanning electron microscopy (SEM, Hitachi S-4800). The crystallinity of the thin film was measured by an X-ray diffractometer (XRD, PANalytical, X'Pert-PRO MPD) in a grazing incidence mode (GIXRD) mode. Element composition and bonding state were measured by X-ray photoelectron spectroscopy (XPS, Thermo Scientific, K-Alpha). For the XPS depth profile, Ar sputtering was applied prior to measurements for surface layer removal of the film. The elemental ratio of Li: P was calculated from the inductively coupled plasma photoemission spectrometer (ICP-OES, Shimadzu ICPS-8100). Samples were digested with a solution of nitric acid and hydrochloric acid with a HNO ₃ : HCl ratio of 20: 1. EIS measurements were performed using Autolab PGSTAT302N (Metrohm, Netherlands).

2. Results and Discussion

Figure 2 shows a surface SEM image of a lithium phosphate film deposited at different temperatures. The film surface was smooth and pinhole free at all deposition temperatures. As the temperature increased, the grain became clear at 450 ° C as the surface became rougher. The crystalline film of the lithium phosphate-based electrolyte has a much lower ionic conductivity than the amorphous film of the same composition. Therefore, the vapor deposition temperature window of the Li ₃ PO ₄ film was selected at 300 캜 to 450 캜. In the absence of water, no deposition occurred at high temperatures (eg, 600 ° C.), which implies that water plays an important role in the formation of Li ₃ PO ₄ . This is consistent with previous reports on the deposition of lithium phosphate based electrolytes. In these studies, NH ₃ or O ₂ was used as an activator, but little of the effect of these activators on the formation of the lithium phosphate structure was noted. In the present invention, a mechanism of forming a lithium phosphate structure in the presence of water is proposed. Hodges et al. Reported that a nucleophilic attack on OP (OCH ₃ ) ₃ in the meteoroid occurs mainly in carbon instead of phosphorus, resulting in the displacement of CH ₃ O ^- from the structure. Thus, decomposition of (C ₂ H ₅ O) ₂ POO ^- from TEP with the aid of H ₂ O follows the same steps as in FIG. Lithium from the decomposition of the Li (DPM) is _{(C 2 H 5 O) 2} POO - to form in combination with _{(C 2 H 5 O) 2} POOLi. This process continues until all C ₂ H ₅ ⁺ groups have been replaced by Li ⁺ to form a PO (LiO) ₃ or Li ₃ PO ₄ structure. This proposed mechanism describes the formation of lithium phosphate based electrolytes in recent published documents. In these studies, NH ₃ or O ₂ played the same role as H ₂ O and dissolved R-OP bonds.

Figure 4 shows the dependence of the growth rate of the thin film on the deposition temperature. The deposition rate increased monotonically with increasing temperature. The activation energy was calculated from the Arrhenius plot for growth rate as follows.

[Equation 1]

G = Aexp. (- E _a / RT)

Here, G (nm h ^-1) is the growth rate, A is a constant, E _a (kJ mol ^-1) is the activation ^{energy, R (8.314 J mol - 1} K - 1) is the gas constant, T (K) is deposited Temperature. The active energy calculated from the line slope of the ln (G) versus reciprocal temperature (K) plot was 38.32 kJ mol ^-1 . In general, there is no exact range of activation energies that determine the process as motion- or diffusion-controlled (in many cases, reactions with an activation energy of less than 20 kJ mol ^-1 can be considered diffusion controlled). However, in an existing report where deposition occurred in the diffusion rate region, the measured activation energy was 1.14 kJ mol ^-1 . Therefore, in the present invention, the MOCVD process is operated in a nearly kinetic limited regime.

Figure 5 shows the GIXRD pattern of a Li ₃ PO ₄ film deposited at a temperature of 300 ° C to 500 ° C. At 300 캜, the Li ₃ PO ₄ thin film exhibited a broad band in the XRD pattern, indicating a typical amorphous phase. As the temperature was increased to 350 캜 and 400 캜, the XRD pattern of the film showed a specific peak indicating crystalline lithium phosphate at 2? = 23.1 (110), 24.8 (102), 33.9 (022) and 28.8 Pattern 01-072-1963). This peak was quite wide with low intensity. This indicates that the film is partially crystallized, or that these crystals have a small particle size. At 450 캜, a sharp sharp peak of Li ₃ PO ₄ appeared. All the peaks of the films deposited at 350 캜 and 400 캜 appeared to have high strength. As can be seen from the XRD, the films deposited at 300 ° C were amorphous and partially crystallized at higher temperatures. This is consistent with the morphological change of the surface SEM image of FIG. At 500 ° C, a specific peak corresponding to crystalline Li ₄ P ₂ O ₇ appeared, indicating that there was a phase transition of the film in the range of 450 ° C to 500 ° C. Therefore, it is desirable to limit the temperature of the deposition process to less than 450 캜. The compositional change of the thin film will be discussed later.

6 shows XPS spectra of lithium phosphate films deposited at 300 ° C and 400 ° C, respectively. Measurements were made at the surface (black curve) of the sample and at a depth of 10 nm (red curve) from the surface to evaluate and eliminate the influence of the air environment on the XPS results of the film. XPS irradiation confirmed the presence of Li, P, O, and C on the film surface. In phosphorus, there was no difference between the spectrum on the surface and inside of the film. P 2p spectra can be Pollution (deconvoluted) to see Deacon P 2p _1/2 and P 2p _3/2. In all the deposition range, P 2p _3/2 peak was observed at 133.4 eV, which was similar to the standard _{Li 3 PO 4 (133.6 eV)} . This result confirms that the phosphorus in the film exists in the same chemical bonding state as the standard Li ₃ PO ₄ . Carbon was also detected at the film surface in the form of organic compounds (285 eV) and -OC = O- (288.9 eV) at all deposition temperatures. However, at a depth of 10 nm, the carbon signal disappeared, which was demonstrated by the disappearance of the corresponding peak. This confirms that the carbon detected at the surface came from organic contamination of the surface and is not present inside the vapor-deposited film. The lack of carbon in the Li ₃ PO ₄ film even at low temperatures of 300 ° C can be attributed to the use of water, which is described in the proposed mechanism. The water attack not only reduced the deposition temperature but also eliminated carbon contamination by promoting the collapse of the PO-C ₂ H ₅ bond. Compared with the previous results using ammonia, carbon remained in the film at 500 ° C. Due to the high electronegativity of oxygen, water can be described as being more active than ammonia.

At 300 캜, there was a change in the XPS spectrum of O 1s and Li 1s when going from the surface to the inside of the film. In the case of Li 1s, there was a variation from 55.4 eV (Li ₃ PO ₄ ) to 55.6 eV (Li ₂ O) when comparing the Li 1s spectrum at 10 nm inside the surface and the film. However, since these peaks are too close to each other, it is not appropriate to deconvolute them, and conclusions can not be derived based on this fluctuation. For O 1s, the peak at 531.5 eV of Li ₃ PO ₄ was still observed in both cases, but there was another peak at 528.4 eV in the intracellular spectrum, indicating oxygen at Li ₂ O. This peak did not appear on the film surface. This represents the formation of Li ₂ O in the film at low deposition temperatures. The absence of the O 1s peak of Li ₂ O in the surface spectrum can be explained by the fact that Li ₂ O reacts with CO ₂ in the air to form Li ₂ CO ₃ . The O 1s of Li ₂ CO ₃ showed a binding energy at 531.5 eV, which overlapped with the O 1s peak of Li ₃ PO ₄ . In 400 ℃, a peak indicating the oxygen of Li ₂ O natjiman still displayed, and the intensity is much lower than the deposited film at 300 ℃. Thus, the formation of the Li ₂ O phase appeared to decrease with increasing temperature.

Figure 7 shows the elemental depth profile of Li ₃ PO ₄ thin films deposited at 300 ° C and 400 ° C, respectively. The percentage of carbon in the membrane was significantly reduced from 20% to 1% at about 1 nm depth in both cases. This result confirms again that there is no carbon in the vapor-deposited film. When the temperature was changed from 300 ° C to 400 ° C, the average Li: O ratio in the film slightly increased. In addition, the percentages of Li, P, and O were almost constant along the film depth, indicating that the film had a uniform composition. This was due to the advantages of bubbler design. The sufficiently long residence time of the carrier gas in the bubbler due to the two-loop structure of the tube ensured that the carrier gas was completely saturated with the vaporized lithium precursor. Thus, all the precursors were continuously delivered to the reactor at a fixed rate, so that the theorem of the deposited film was fixed. Reproducibility is one of the major problems of the MOCVD process using a solid precursor. The bubbler design of the present invention can help solve this problem.

Since the XPS sensitivity factor for lithium is very low, the elemental composition measurement of the Li ₃ PO ₄ film using this method is not sufficiently accurate. Thus, inductively coupled plasma mass spectrometry (ICP-MS) measurements were performed to determine the Li to P ratio in the film. Along with the P-to-O ratio specified by XPS, this data provided more reliable results. Table 2 shows the element composition with different results for the lithium phosphate film deposited at different temperatures. Specifically, Table 2 shows the growth rate, film thickness, composition and ionic conductivity of the lithium phosphate film deposited at 300 ° C, 350 ° C, 400 ° C and 450 ° C.

Temperature (℃) Growth rate
(nm hr ^-1) Film thickness
(nm) Furtherance Ion conductivity
(S cm ^-1 ) 300 18 90 Li _{3 . 7} PO _{4 .35} 5.6 × 10 ^-10 350 36 180 Li _{3 . 1} PO _{4 .05} 2.3 × 10 ^-8 400 60 300 Li _{2 . 9} PO _{3 .95} 5.0 × 10 ^-8 450 88 440 Li _{2 . 9} PO _{3 .95} 5.5 × 10 ^-9

Li P ratio for when the film is deposited at 300 ℃ and 350 ℃ I larger than 3, this means that lithium is present in the other compounds other than Li ₃ PO _4. This result is consistent with the XPS depth profile data and indicates that Li ₂ O is present in the deposited film at low deposition temperatures. The lithium concentration decreased with increasing deposition temperature, especially at 300 캜 to 350 캜. Lithium phosphate is commonly referred to as (Li ₂ O) _x (P ₂ O ₅ ) _y . Thus, in the present invention, the x to y ratio decreased from 3.7 (ultra-phosphate) to 2 (pyro-phosphate) as the temperature increased from 300 ° C to 500 ° C. This observation trend can be explained as follows. At low temperatures, TEP is decomposed into PO ₄ ^3- at low reaction rates, whereas the formation of Li ⁺ from Li (DPM) is rapid. There is therefore not enough PO ₄ ^3- and Li ⁺ present in the form of Li ₂ O. Kozen et al. Reported the deposition of Li ₂ O from lithium tert-butoxide and H ₂ O by ALD at temperatures higher than 240 ° C. As the temperature increased, the Li fragments were partially vaporized, while the amount of PO ₄ ^3- rapidly increased, forming a -POP-bond with each other, i. E. Less Li ⁺ in the membrane.

Figure 8 shows the Nyquist plot for the EIS spectrum of Li ₃ PO ₄ deposited at different temperatures. The ionic conductivity was calculated as follows.

&Quot; (2) "

σ = d / RA

Where σ (cm ^-1 ) is the ionic conductivity, d (cm) is the thickness of the Li ₃ PO ₄ film, R (Ω) is the resistance measured by measuring the diameter of the semicircle in the Nyquist plot, A Lt; / RTI > Table 2 shows the ionic conductivity. As described above, when the temperature was increased, there were two factors influencing the ion conductivity, namely, the element composition and the crystallinity. The highest conductivity (5.0 × 10 ^-8 S cm ^-1 ) was obtained in the films deposited at 400 ° C. In 300 ℃ to 400 ℃, the ionic conductivity up to at the lowest ^{(5.6 × 10 -10 S cm -1} ) - was significantly improved by ^{(5.0 × 10 -8 S cm 1} ). In this region, the element composition plays a more important role because the film is almost amorphous. In this case, the ionic conductivity increased with decreasing Li: P ratio, which was in stark contrast to previous reports on Li ₃ PO ₄ and LiPON deposition. Improved ionic conductivity with increasing Li: P ratio is only effective at rates of less than 3. At a ratio greater than 3, the tendency was the opposite as in the present invention. In other words, the ionic conductivity of Li ₃ PO ₄ was highest when the Li: P ratio was close to 3. This conclusion is valid in recent reports. Another aspect that can explain this tendency membrane than ionic conductivity with by forming a thick Li ₂ CO ₃ layer receives more effect by the CO ₂ in the film is air having a high Li ₂ O ratio, low Li ₂ O ratio Will be more dramatically reduced. At 400 ° C to 450 ° C, ionic conductivity decreased. Since the film compositions are similar, it can be understood that the high crystallinity of the film deposited at 450 ° C reduces the ionic conductivity. At 500 캜, the ionic conductivity could not be measured due to the high crystallinity and partial formation of Li ₄ P ₂ O ₇ .

A grooved silicon substrate was used to demonstrate the feasibility of Li ₃ PO ₄ deposition on the 3D structure by MOCVD. From the above discussion, a temperature of 400 DEG C must be selected for the 2D deposition. However, for 3D deposition, the temperature must be lower to drive the process in the reaction rate rate range. Thus, the selected temperature is 350 [deg.] C, at which the growth rate and ionic conductivity are still sufficiently high. The silicon substrate contained a depth of 135 탆 and a width of 22.5 탆 (aspect ratio 6: 1) and a groove of 100 탆 depth and 10 탆 width (aspect ratio 10: 1). In a 10: 1 aspect ratio groove, the Li ₃ PO ₄ film was not successfully deposited. The film became discontinuous at about 60 nm from the top. 9 shows a cross-sectional SEM image of a Li ₃ PO ₄ thin film deposited for 5 hours on a trench having an aspect ratio of 6: 1. The most important issue for deposition on 3D geometry is membrane continuity. Very small cracks or holes can cause contact between the electrodes, resulting in a short circuit. As shown in Figure 9, the Li ₃ PO ₄ film was continuous on all surfaces of the grooves. As the distance from the top increased, the thickness of the film decreased very steadily. At the bottom, the film thickness was 100 nm, which was about 46% of the thickness at the top. When applied to a 3D battery, the ion diffusion time through the electrolyte may be different at the top of the groove and at the bottom of the groove, but battery performance is believed not to be significantly affected. The EIS measurement of the film could be performed with a thickness as thin as 90 nm, indicating dense film and no pinholes. Compared to the most recent report on Li ₃ PO ₄ deposition by MOCVD using O ₂ , the present invention exhibits substantially superior performance. The Li ₃ PO ₄ film was uniformly deposited with 46% step-coverage on a very high aspect ratio 3D substrate. This can be explained by the fact that the MOCVD process used in the present invention is in the reaction rate-rate region due to the proper activation of H ₂ O. This also means that the transfer of the precursor to the surface occurs rapidly. Thus, there was a small difference in reactant concentration between the top and bottom of the groove. Since the temperature fluctuations can be ignored, the film thickness was similar between the top and bottom of the groove of the 3D substrate. In addition, when the active energy of the present invention is compared with that of the existing report, the activity of various activating gases can be classified as O ₂ > H ₂ O> NH ₃ . The use of O ₂ as activator dramatically increases the reaction rate. Thus, the deposition process that occurs in the diffusion rate region results in low step-coverage. Using NH ₃ for LiPON deposition is expected to yield better step-coverage over the 3D geometry than the results of this process. These results confirm the feasibility of MOCVD in Li ₃ PO ₄ deposition, or that any material is generally available on a 3D structure as long as the process occurs in the reaction rate rate region.

3. Conclusion

High quality Li ₃ PO ₄ films were successfully deposited by MOCVD using Li (DPM), TEP and H ₂ O as precursors. As the temperature increased, the growth rate increased and the lithium concentration decreased. The films were mainly amorphous at deposition temperatures lower than 400 ° C and then became partially crystalline when the temperature increased. The concentrations of Li, P and O were constant along the film depth. Films with the highest ionic conductivity (5.0 x 10 ^-8 S cm ^-1 ) were obtained at deposition temperatures of 400 ° C. Water played an important role in the deposition process, not only promoting the decomposition of TEP for the formation of lithium phosphate structure, but also reducing the carbon concentration in the film at 300 ° C. In addition, the appropriate activity of water helped to reduce the rate of the reaction so that the process took place in the reaction rate-rate range, which was measured as the measured activation energy of 38.32 kJ mol ^-1 . The film was uniformly deposited at 350 [deg.] C on a grooved substrate with an aspect ratio of 6: 1 and exhibited step coverage of 46%.

Claims (14)

A method of depositing a lithium phosphate thin film electrolyte comprising depositing a lithium precursor, a phosphate precursor and water as an activator on a substrate through a metal-organic chemical vapor deposition process. The method according to claim 1,
Wherein the lithium precursor is lithium dipivaloylmethanate. ≪ RTI ID = 0.0 > 11. < / RTI > The method according to claim 1,
Wherein the phosphate precursor is triethyl phosphate. ≪ RTI ID = 0.0 > 11. < / RTI > The method according to claim 1,
Wherein the substrate is a three-dimensional structure substrate having a concavo-convex pattern with an aspect ratio of 5: 1 or more. The method according to claim 1,
Wherein the deposition temperature is 300 ° C. to 450 ° C. 5. A method for depositing a lithium phosphate thin film electrolyte according to claim 1, The method according to claim 1,
Wherein the activation energy of the deposition step is 10 kJ mole ^-1 or more. A reaction chamber in which deposition is performed; And
And a lithium precursor bubbler connected to the reaction chamber through a line and having a tube of a bent structure. 8. The method of claim 7,
Wherein the tube comprises at least two bent structures. ≪ RTI ID = 0.0 > 11. < / RTI > 8. The method of claim 7,
Wherein the lithium precursor bubbler is made of glass. 8. The method of claim 7,
Wherein the lithium precursor bubbler comprises paraffin oil as a heating medium. Dimensional structure having an asperity pattern with an aspect ratio of 5: 1 or more,
A lithium phosphate thin film having a step-coverage of at least 40%. 12. The method of claim 11,
Wherein the lithium phosphate thin film has an ion conductivity of 1 x 10 < ^-8 > Scm < ^-1 > or more. 12. The method of claim 11,
Wherein the percentage of lithium, phosphorus, and oxygen at a depth of 1 nm or more from the surface of the lithium phosphate thin film maintains a deviation of +/- 10% along the depth, respectively. 12. The method of claim 11,
Wherein the carbon percentage at a depth of 1 nm or more from the surface of the lithium phosphate thin film is 5% or less.

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