KR100239008B1 - Oxide thin film fabrication method by using n2o reactive gas - Google Patents

Abstract

A method of manufacturing a ferroelectric oxide thin film, comprising by generating an inert gas with a plasma of the reaction gas in a constant rate releasing the particles from the target of the composition of interest was grown by depositing the particles on a substrate, a reaction gas N ₂ O Provided is a method for producing a ferroelectric oxide thin film, which is used.

Description

Oxide thin film deposition method using NO reaction gas

The present invention relates to a method for producing a ferroelectric oxide thin film using an N ₂ O reaction gas, and a ferroelectric oxide thin film produced by the method. Specifically, the present invention relates to a ferroelectric, electro-thin film or high-capacity DRAM of 256 Mbit or more for use in nonvolatile ferroelectric random access memory (NVFeRAM or NVFRAM), or devices using related characteristics such as piezoelectric and pyroelectric nonlinear optics. It relates to a method for producing a capacitor thin film or a dielectric thin film outside these application ranges.

Ferroelectric thin films have high dielectric constant, excellent piezoelectricity and superconductivity, and excellent optical properties, and are being used as DRAM (Dynamic Random Access Memory) devices, micro piezoelectric devices, infrared detectors, and other optical devices. Along with the rapid development of process technology, it is gaining attention as a major part of nonvolatile ferroelectric memory devices.

In order to use the ferroelectric thin film as a main part of a nonvolatile ferroelectric memory device, which is one of those currently commercialized as a representative application using a ferroelectric thin film, a high residual polarization value, a low leakage current value, and a residual time change And the spontaneous polarization value should not change. In addition, the fatigue properties should be excellent and the dielectric loss should be small.

To date, ferroelectric thin films of nonvolatile ferroelectric memory devices include Pb (Zr _1-x Ti _x ) O ₃ , various layered compounds (SrBi ₂ Ta ₂ O ₉ , BaBi ₂ Ta ₂ O ₉ , Bi ₄ Ti ₃ O _12, etc.), Pb _1-x La _x (Zr _1-y Ti _y ) O ₃ and the like have been studied, and research on thinning and related properties for making a thin film having excellent characteristics has been actively conducted.

The most widely used method of such a thinning method is the sputtering deposition method. In the conventional sputtering deposition method, oxygen is used as the reaction gas. In the sputtering deposition method, the deposition is generated by self-biasing inside the plasma formed of the introduced inert gas (eg, argon gas) and the added reactive gas, and sputtered by colliding with the target by argon particles accelerated by the bias. Through the growth of particles. Thin films deposited by the sputtering method have significant energy when they are separated from the target by argon-accelerated particles, causing stress to the film during the initial deposition, and electrons and anions in the plasma are also accelerated to the substrate to affect the film. Crazy In depositing an oxide thin film by the spattering method, it is common to add an excess of oxygen gas for sufficient oxidation of the deposited film even when an oxide target is used. The added oxygen gas is ionized in the plasma formed by the argon gas to deposit while reacting with atoms or atoms sputtered from the target. At this time, the ionization of the added oxygen source as easily as possible affects the ultimate physical properties of the deposited oxide film as a necessary condition for a smooth oxidation reaction to occur.

However, in the case of forming a thin film by the sputtering deposition method using oxygen as a reaction gas, the composition control of the thin film is not easy, and therefore, it is particularly difficult to deposit a thin film containing Pb, Bi, or the like which is highly volatile.

In addition, defect films such as oxygen vacancies or cation (eg, Pb ³⁺ ) vacancies exist in thin films formed by the conventional spattering deposition method using oxygen as a reaction gas, and such defect structures have a space charge. Since the layer is formed, a deterioration in switching characteristics in which the voltage direction changes periodically may occur.

In addition, in the process of forming a thin film by a conventional spatter deposition method using oxygen as a reaction gas, the thinner the thickness, the lower the film characteristics due to residual stress caused by the reduction of the particle size of the deposited film or the difference in thermal expansion coefficient due to the influence of the substrate. Occurs. In particular, in the case of deposition of a Pb (Zr _1-x Ti _x ) O ₃ thin film, the thinner the thickness, the more severe the deterioration of characteristics of the film.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thin film manufacturing method for producing a homogeneous ferroelectric thin film having improved electrical properties by solving the above problems of a thin film manufactured by a conventional spattering deposition method.

It is also an object of the present invention to provide a ferroelectric thin film having improved and homogeneous electrical properties produced by the process of the present invention, in particular having a thickness of 1000 kPa or less.

1A and 1B are graphs showing residual polarization values (Pr) and constant electric field values (Ec) of ferroelectric thin films produced by a conventional method using O ₂ as a reaction gas, respectively.

2a and 2b are graphs showing the residual polarization value (Pr) and the constant electric field value (Ec) of the ferroelectric thin film produced by the method of the present invention using N ₂ O as the reaction gas, respectively.

3a is a graph showing the residual polarization value (Pr) and the electric field value (Ec) of an as-grown thin film deposited by a conventional method using O ₂ as a reaction gas and a thin film subjected to post-heat treatment. .

FIG. 3b is a graph showing the residual polarization values (Pr) and the electric field values (Ec) of the as-grown thin films deposited by the method of the present invention using N ₂ O as the reaction gas and the thin films subjected to post-heat treatment.

The present invention provides a method for producing a ferroelectric thin film comprising generating a plasma of a constant ratio of an inert gas and a reaction gas to release particles from a target having a desired composition, and growing and depositing the particles on a substrate. _It provides a ferroelectric thin film manufacturing method using ₂ O.

According to the method of the present invention, during deposition, the reaction of the N ₂ O gas with the particles sputtered out of the target proceeds much more sufficiently than the reaction of the O ₂ gas with the particles in the conventional method, and also the crystalline phase Enhancement also occurs much more fully than with O ₂ . Thus, in the method of the present invention, no separate post-treatment is required after deposition.

In the method of the present invention, the use ratio of the reaction gas to the inert gas is 1 to 100%.

Preferred targets for use in the process of the present invention are Pb (Zr _1-x Ti _x ) O ₃ , SrBi ₂ Ta ₂ O ₉ , BaBi ₂ Ta ₂ O ₉ , Bi ₄ Ti ₃ O ₁₂ , Pb _1-x La (Zr _1-y Ti _y ) O ₃ , BST, TiO ₂ , Ta ₂ O ₅ .

According to the method of the present invention, even if the thickness is 1000 GPa or less, the characteristics of the ferroelectric thin film are good.

Hereinafter, this invention is illustrated as an Example. However, the present invention is not limited by this embodiment.

Example 1

A Pt / Ti / SiO ₂ / Si (100) wafer was mounted as a substrate in a reaction chamber having a target composition of Pb (Zr _0.52 Ti _0.48 ) O ₃ , and the pump was operated so that the vacuum degree was 5 × 10 ⁻⁶ torr. The mounted substrate was then heated to 520 ° C. using a tungsten-halogen lamp.

After 30 minutes of heating, the plasma was generated by adjusting the flow rate so that the ratio of Ar and N ₂ O gas was 80:20 to deposit a thin film having a thickness of 1000 Pa. At this time, the degree of vacuum was 1 × 10 ⁻² torr, the distance between the target and the substrate was 5 cm, and the size of the target was 10 cm.

By repeating the above process, thin films having thicknesses of 2000 mV, 3000 mV and 4000 mV were deposited, respectively.

Residual polarization values Pr and constant electric field values Ec were evaluated for the deposited thin films of each thickness, and the results are shown in FIGS. 2A and 2B, respectively.

Example 2

After the thin film was deposited in the same manner as in Example 1, it was further heat treated at a temperature of 500 to 700 ° C. Residual polarization values and constant electric field values were evaluated for the thin films of the thicknesses thus heat treated, and the results are shown in FIG. 3B.

Example 3

The thin film was deposited in a manner similar to that of Example 1, except that O ₂ gas was used as the reaction gas.

Regarding the thin films of each thickness, the residual polarization value and the electric field value were evaluated, and the results are shown in FIGS. 1A and 1B.

Example 4

After the thin film was deposited in the same manner as in Example 3, it was further heat treated at a temperature of 500 to 700 ° C. Residual polarization values and constant electric field values were evaluated for the thin films of the thicknesses thus heat treated, and the results are shown in FIG. 3A.

It can be seen from FIG. 1A and FIG. 2A that the improvement of the residual polarization value is noticeable when the N ₂ O gas is used compared with the case where O ₂ is used. In addition, it can be seen that compared to the case from Fig. 1b and 2b, the case of using the N ₂ O gas with O _2, even if the film thickness change there is a tendency that the change of the coercive field value is constant.

3A and 3B show that the thin film deposited by using N ₂ O gas as the reactive gas compared to the thin film deposited using oxygen as the reactant gas, has the residual polarization and the electric field characteristics between the ag-grown thin film and the post-heat treated thin film. It can be seen that there is almost no difference. This demonstrates that when depositing using N ₂ O gas as the reaction gas, a sufficient oxidation reaction and crystal phase enhancement already occur during deposition to form a stable oxide.

Example 5

In this embodiment, the film quality was evaluated by measuring the survival probability of the electrode for the thin film deposited using N ₂ O gas as a reaction gas and the thin film deposited using O ₂ gas according to the prior art. .

To this end, an electrode having a metal (lower electrode) -thin film-metal (upper electrode) structure was formed. Here, the lower electrode uses a platinum film deposited on a silicon wafer, and after depositing a PZT thin film on the thickness of 1000 Å and 700 따라 according to the present invention and the prior art, the upper electrode is 0.3 mm in diameter using a shadow mist. It was formed by depositing platinum dots.

At this time, platinum was deposited by DC spattering at a pressure of 10 mtorr at about 30 sccm of argon gas to maintain a platinum target mounting condition of 10 to 20 W, followed by deposition for about 15 minutes, to a thickness of 800 to 1000 kPa. It was deposited at room temperature.

An electric field was applied to each electrode thus formed. The number of dots in which an electrode was broken and an electrical short was generated without showing the residual polarization of an appropriate value with respect to the applied electric field was measured, and the survival probability was calculated from the number.

The results are shown in Table 1 below.

As can be seen from Table 1, when using N ₂ O gas according to the present invention as a reaction gas, even if the thickness is reduced to 1000 kPa, the survival probability of the electrode having a diameter of 300 ㎛ size of 47.8% to 67.3% The survival rate increased from 20.8% to 37.9% even though the thickness was significantly reduced to 700Å, indicating that membrane quality was accompanied.

Forming a ferroelectric oxide thin film by the spatter deposition method using N ₂ O gas as the reaction gas, a thinner and more homogeneous thin film can be obtained than the conventional method using oxygen gas, and the deterioration of properties is further improved, Crystallinity improvement occurs during deposition.

Claims (3)

By generating a plasma of the inert gas and the reactive gas having a ratio of the reactive gas to the inert gas of 1 to 100%, Pb (Zr _1-x Ti _x ) O ₃ , SrBi ₂ Ta ₂ O ₉ , BaBi ₂ Ta ₂ Emission of particles from a target which is O ₉ , Bi ₄ Ti ₃ O ₁₂ , Pb _1-x La (Zr _1-y Ti _y ) O ₃ , BST, TiO ₂ or Ta ₂ O ₅ , which are grown on a substrate and deposited A method for producing a ferroelectric oxide thin film by sputtering, comprising: N ₂ O is used as a reaction gas. The method of claim 1 wherein the ratio of inert gas to reactive gas is 80:20. The method of claim 1, wherein the thin film has a thickness of 1000 GPa or less.

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