KR100321561B1 - Method of Manufacturing Ferroelectric Thin Film of Mixed Oxides Containing Volatile Components - Google Patents

Abstract

The present invention provides a method for producing a multi-component oxide ferroelectric thin film, particularly a ferroelectric thin film of bismuth layered oxide, which reduces the loss of volatile components by maintaining a pressure in a vacuum chamber in which sputtering occurs during RF magnetron sputtering at 200 to 300 millitorr (mTorr). To provide. The present invention also provides a method of manufacturing a ferroelectric thin film using the RF magnetron sputtering method, which gives a good ferroelectric property by placing the substrate 3 to 5 cm away from the target center line when sputtering. In addition, the present invention provides a method for producing a ferroelectric thin film using the RF magnetron sputtering method, which gives excellent ferroelectric characteristics by setting the angle of the substrate surface to 30 ° to 60 ° with respect to the target surface during sputtering.

Description

Method of Manufacturing Ferroelectric Thin Film of Mixed Oxides Containing Volatile Components

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a ferroelectric thin film used in a nonvolatile memory device, and in particular, a ferroelectric of a multi-component oxide using a radio frequency magnetron sputtering method compatible with existing semiconductor device manufacturing processes. A method for producing a thin film.

A nonvolatile ferroelectric memory device is a device using a residual polarization phenomenon in which polarization formed by an electric field applied to electrodes formed above and below a ferroelectric thin film removes an electric field. When the residual polarization is used for the information storage method, the loss of the stored information can be prevented even when the electric field is removed, so it is called a nonvolatile memory device.

Ferroelectric materials used in nonvolatile memory devices include Pb (Zr, Ti) O ₃ , a perovskite structure, and Strontium-Bismuth-Tantalate, SrBi ₂ Ta ₂ , a layered perovskite structure. O ₉ ; hereinafter referred to as SBT).

Since the publication of the concept of ferroelectric memory by the University of Colorado, JF Scott in the late '80s, several researchers have conducted research for commercialization. Bismuth layered ferroelectrics, such as SBT, are considered to be very suitable for storage. .

The ferroelectric thin films of bismuth-based layered perovskite structures have been mainly manufactured by the sol-gel method, organometallic chemical vapor deposition method, pulse laser ablation method, and the like. However, in consideration of high integration and large area wafer devices, compatibility with existing semiconductor production processes is required. Therefore, studies on the manufacturing method using the RF magnetron sputtering method with excellent compatibility with the existing semiconductor process is active. In particular, the RF magnetron sputtering method is considered to be excellent as a method of manufacturing a newly proposed SBT thin film for improving the lifetime of the ferroelectric thin film capacitor.

However, when forming a multicomponent oxide thin film by the RF magnetron sputtering method, there is a loss of volatile components such as bismuth, barium, strontium and lead during sputtering. In order to solve this, a method of excessively adding a volatile component to the multicomponent oxide target, co-sputtering using an additional target, or the like is used.

The loss of volatile components during RF magnetron sputtering when forming a multi-component oxide thin film is mainly controlled using methods such as over-addition of expected components, RF power control, and argon gas inflow change [K. Suu, A. Osawa, N. Tani, 'Lead content control of PLZT thin films prepared by RF magnetron sputtering', Integrated Ferroelectrics, 1997, Vol. 14, pp. 59-68]. However, in the case of the SBT thin film, even if a target containing excess bismuth was used, the volatile content could not be controlled by this method.

Therefore, there is a need for a method for reducing the loss of volatile components generated during the RF sputtering process and improving the ferroelectric properties in the production of the multi-component oxide ferroelectric thin film.

Accordingly, an object of the present invention is to provide a method for producing a ferroelectric thin film made of a multi-component oxide, which reduces the loss of volatile components and imparts excellent ferroelectric properties while using an RF magnetron sputtering method compatible with existing semiconductor device manufacturing processes. will be.

1 is a schematic diagram illustrating a high frequency (RF) magnetron sputtering apparatus used in the present invention.

Figure 2 is a characteristic diagram showing the change in the X-ray diffraction pattern of the SBT thin film according to the sputtering pressure change.

3 is a graph showing the change in the composition of the components of the SBT thin film according to the sputtering pressure change.

Figure 4a is a graph showing the change in the characteristics of the polarization-field curve before and after the fatigue test of the platinum electrode using SBT thin film capacitor prepared at 300 millitorr sputtering pressure according to the present invention.

Figure 4b is a graph showing the fatigue characteristic curve according to the number of switching of the SBT thin film capacitor using a platinum electrode prepared at 300 millitorr sputtering pressure according to the present invention.

5 is a schematic diagram illustrating various locations of a substrate relative to a target in a high frequency magnetron sputtering system.

FIG. 6A is a graph illustrating changes in polarization-field curve characteristics of a capacitor using a SBT thin film and a platinum electrode manufactured at a target-substrate distance of 5 cm and an outer surface (57 of FIG. 5) according to the present invention.

Figure 6b is a graph showing the polarization-field curve characteristics change of the capacitor using the SBT thin film and the platinum electrode prepared in the target-substrate distance 3.5 cm, medium (56 in Figure 5) according to the present invention.

FIG. 6C is a graph showing changes in polarization-field curve characteristics of a capacitor using an SBT thin film and a platinum electrode prepared at a target-substrate distance of 2.2 cm and a center (55 in FIG. 5).

FIG. 7A is a graph showing changes in polarization-field curve characteristics of a capacitor using an SBT thin film and a platinum electrode prepared with the substrate 4 cm away from the target centerline and having a target-substrate angle of 90 °. FIG.

FIG. 7B is a graph showing changes in polarization-field curve characteristics of a capacitor using the SBT thin film and the platinum electrode according to the present invention prepared with the substrate 4 cm away from the target centerline and having a target-substrate angle of 45 °. FIG.

<Explanation of symbols for the main parts of the drawings>

11: sputtering chamber

12: substrate holder

13: substrate

14: plasma

15: Target

16: RF power

17: cathode

51: target

52, 53: magnet

54: etching center

55, 56, 57: substrate

The present invention is a method of forming a multi-component oxide thin film on a substrate by sputtering a target made of a multi-component oxide by using a high frequency (RF) magnetron sputtering method and then post-heat treatment to produce a ferroelectric thin film, in a vacuum chamber in which sputtering occurs It provides a method for producing a multi-component oxide ferroelectric thin film characterized in that the pressure is maintained at 200 to 300 millitorr (mTorr) to reduce the loss of volatile components of the thin film during sputtering.

The present invention also provides a method for producing a multi-component oxide ferroelectric thin film using the RF magnetron sputtering method, which gives a superior ferroelectric property by placing the substrate 3 to 5 cm apart from the target center line when sputtering. to provide.

In addition, the present invention provides a method for producing a multi-component oxide ferroelectric thin film using the RF magnetron sputtering method, which gives excellent ferroelectric characteristics by setting the angle of the substrate surface to 30 ° to 60 ° with respect to the target surface during sputtering.

The multi-component oxide ferroelectric thin film that can be produced according to the present invention can be prepared from a multi-component oxide target containing at least one element selected from bismuth, barium, strontium and lead as a volatile component. Specific examples of the multi-component oxide ferroelectric thin film that can be prepared according to the present invention include SrBi ₂ (Ta, Nb) O ₉ , Pb (Zr, Ti) O ₃ , (Pa, La) TiO ₃ , (Pb, La) ( Zr, Ti) O ₃ thin film.

The conditions used for RF magnetron sputtering in the formation of a conventional oxide thin film are for a 2-inch target, the sputtering pressure is 60 millitorr, the distance between the target and the substrate is 5 cm, and the angle between the target surface and the substrate surface is 0 °. In this condition, it is known that the thin film growth rate is the fastest.

1 schematically illustrates an RF magnetron sputtering apparatus used in the present invention. In FIG. 1, the sputtering chamber 11 uses a rotary pump and a turbo pump to maintain high vacuum. After the target 15 is attached to the cathode 17 and the RF power source 16 is applied, the plasma 14 is formed between the target 15 and the substrate 13. When argon ions in the plasma state hit the target, the target material is sputtered and coated on the substrate. In such a deposition method, sputtering is generally performed at a pressure of about 60 mTorr in order to improve the quality of the thin film, but at this vacuum degree, the loss of volatiles occurring during sputtering is large. For SBT targets, the loss of bismuth is large.

In the present invention, various conditions of the RF magnetron sputtering are changed to obtain an excellent multicomponent oxide ferroelectric thin film.

In one aspect of the present invention, in the above RF magnetron sputtering method, the pressure in the vacuum chamber is increased to 200 to 300 millitorr so that the sputtered particles lose kinetic energy due to collision with gas and reach the substrate only by diffusion phenomenon. As a result, the loss of volatiles generated during RF sputtering in the multi-component oxide thin film containing volatile elements can be prevented. For example, it is possible to reduce the loss of bismuth that occurs during RF sputtering of the SBT target.

In addition, the present invention controls the ferroelectric properties of the thin film obtained by changing the position of the substrate in the chamber and the angle with the target at a constant sputtering pressure.

Illustrating a preferred embodiment according to the present invention, the SBT target used is a disc of 2 inches in diameter with a composition of Sr _1.1 Bi _2.6 Ta ₂ O ₉ . As the RF sputtering condition, the sputtering gas is 50% / 50% of oxygen / argon gas, the RF power is 1 to 3 W / cm ² , the spacing between the target and the substrate is 3 to 5 cm, and the temperature at which sputtering is performed at room temperature to be. After forming a thin film by sputtering, it is heat-treated 10 to 60 minutes in an oxygen atmosphere, 650-800 degreeC, for crystallization and crystal growth.

The change in the X-ray diffraction pattern of the SBT thin film obtained when the sputtering pressure was changed is shown in FIG. 2. As the sputtering pressure is increased from 2.5 to 300 mTorr, the loss of bismuth component generated during sputtering of the SBT thin film is reduced, so that when the sputtering pressure is 300 mTorr, diffraction by the high quality SBT 115 plane can be observed. When the sputtering pressure is lowered, bismuth is lost during sputtering, and diffraction peaks due to the pyrochlore phase and strontium tantalum oxide are observed.

Figure 3 shows the change in concentration of each component in the SBT thin film according to the sputtering pressure change. As the sputtering pressure increases, the amount of bismuth component in the deposited SBT thin film is close to the stoichiometric value and is present in excess of 30% at 300 mTorr. The strontium and tantalum components do not change significantly with the sputtering pressure change. Therefore, the sputtering pressure according to the present invention for reducing the loss of volatiles is about 200 to 300 mTorr, more preferably about 300 mTorr.

4A and 4B show the results obtained in a fatigue test of a capacitor using an SBT thin film prepared at a sputtering pressure of 300 mTorr according to the present invention. The polarization field hysteresis curve of the capacitor using the SBT thin film and the platinum electrode manufactured using the low vacuum sputtering pressure is saturated as shown in FIG. 4A. In addition, there is no change in the polarization-field characteristics before and after the fatigue test. 4B shows the change of the residual polarization value by application of a 1 MHz +/- 3 V square switching pulse. From this, it can be seen that the SBT thin film prepared according to the present invention has excellent fatigue characteristics that the residual polarization value does not decrease even after 10 ¹¹ switching.

5 is a schematic diagram illustrating various positions of a substrate relative to a target in RF sputtering according to the present invention. 6A, 6B, and 6C show polarization of a capacitor using a thin film and platinum electrode obtained by placing a substrate at various positions shown in FIG. 5, using a sputtering pressure of 100 mTorr, a 2 inch target, and applying RF power of 3 W / cm ² . -It shows the characteristic change of electric field curve. Referring to FIG. 5, the etching of the constant portion 54 is increased by the magnetic field generated by the magnets 52, 53 attached to the back of the multicomponent oxide target 51, and the sputtering speed is increased. Therefore, according to the change in the distance between the target and the substrate, it is possible to form a thin film of various characteristics.

The polarization-field hysteresis curve of the capacitor using the platinum electrode and the SBT thin film 5 cm away from the target and farthest from the target center as shown in (57) of FIG. 5 is shown in FIG. 6A. If the distance to the target is close to 3.5 cm as shown in (56) of FIG. 5 and the substrate is placed in the middle of the target center and the outer region, the polarization-field hysteresis characteristic of the final capacitor does not show a big difference compared to the far distance as shown in FIG. . However, if the distance to the target is close to 2.2 cm and the substrate is placed on the target center line as shown in (55) of FIG. 5, the residual polarization value of the final capacitor is drastically reduced as shown in FIG. 6C. Considering the magnetic force distribution from the magnet behind the target in RF sputtering, it can be seen that the further the distance from the substrate and the farther from the center of the magnetic lines, the better the SBT thin film.

The distance between the target and the substrate varies depending on the target size, which is expressed in terms of the distance to the unit target diameter. Unless stated otherwise herein, the specification is based on a 2-inch diameter target. In the preferred sputtering of the present invention, the position of the substrate in the chamber is 3 to 5 cm away from the target and the outer side far from the target center line.

On the other hand, when the sputtering pressure is low and the target surface and the substrate surface are parallel, that is, when the deposition speed is high, such as when the angle between the target surface and the substrate surface is 0 °, but many volatile components are lost, changing the angle of the substrate The ferroelectric properties of the thin film obtained by reducing the loss of bismuth can be improved. However, as the angle between the target surface and the substrate surface increases, the deposition rate decreases. When the angle between the target surface and the substrate surface is 30 ° to 60 ° can be obtained a multi-component oxide ferroelectric thin film excellent in overall deposition rate and ferroelectric properties.

7A and 7B show the change in the ferroelectric properties of the SBT thin film according to the change in angle between the target surface and the substrate surface when the distance between the target and the substrate is 5 cm and the substrate is located 4 cm away from the target center line. As shown in FIG. 7A, sputtering in a state where the target surface and the substrate surface are maintained at an angle of 90 °, that is, when the target surface and the substrate surface are perpendicular, shows good polarization-field characteristics with a residual polarization of 7 µC / cm 2. However, the deposition rate is reduced compared to when the angle between the target surface and the substrate surface is 0 degrees. When the angle between the target and the substrate surface is 45 °, the residual polarization value decreases as shown in Fig. 7B, but the polarization saturation state is improved.

Hereinafter, preferable embodiment of this invention is illustrated concretely. However, the present invention is not limited by these examples.

<Example>

Example 1

SBT was used as an SBT target and Pt / Ti / SiO ₂ / Si was used as a substrate for SBT _1.1 Bi _2.6 Ta ₂ O ₉ , and SBT was used as a RF sputtering method in a self-produced plasma deposition (PVD) system. Ferroelectric thin films were prepared. The sputtering gas is 50% / 50% oxygen / argon, the pressure in the sputtering chamber is 300 mTorr, the RF power is 13.56 MHz, the sputtering temperature is 3 W / cm ² , the sputtering temperature is room temperature, and the substrate is placed on the target center line. The space | interval was 5 cm and the angle of the board | substrate was 0 degree with respect to the target surface.

When the thickness of the deposited SBT thin film reached 200 nm, sputtering was completed, and the ferroelectric thin film was formed by post-heat treatment at 750 ° C. for 60 minutes in an oxygen atmosphere.

Comparative Example 1

An SBT ferroelectric thin film was manufactured under the same conditions as in Example 1 except that the pressure in the sputtering chamber was 100 mTorr.

Crystal structure characteristics of the SBT ferroelectric thin films prepared in Example 1 and Comparative Example 1 are shown in FIG. 2. It can be seen that the loss of bismuth was reduced in the ferroelectric thin film prepared by the method of the present invention.

Example 2

A SBT ferroelectric thin film was manufactured under the same conditions as in Example 1 except that the distance between the substrate and the target was 3.5 cm and the sputtering pressure was 100 mTorr.

Comparative Example 2

An SBT ferroelectric thin film was manufactured under the same conditions as in Example 2, except that the distance between the substrate and the target was 2.2 cm.

P-E hysteresis characteristics of the SBT ferroelectric thin films prepared in Example 2 and Comparative Example 2 are shown in FIGS. 6B and 6C. Improvement in SBT ferroelectric properties for each substrate position according to the present invention can be confirmed.

Example 3

The SBT ferroelectric thin film was prepared under the same conditions as in Example 1 except that the angle of the substrate surface was 45 ° to the target surface, the sputtering pressure was 100 mTorr, and the substrate was deposited at a distance of 4 cm from the target center line. Prepared.

Comparative Example 3

An SBT ferroelectric thin film was manufactured under the same conditions as in Example 3, except that the angle of the substrate surface was set to 90 ° with respect to the target surface.

P-E hysteresis characteristics of the SBT thin films prepared in Example 3 and Comparative Example 3 are shown in FIGS. 7A and 7B. In the present invention, the volatile component of the SBT thin film was adjusted by adjusting the angle between the target surface and the substrate surface, thereby improving ferroelectric properties.

Through the present invention, a method of controlling the loss of volatile components generated when forming a volatile component-containing multi-component oxide thin film by RF magnetron sputtering method. By controlling the sputtering pressure and the position of the substrate and the angle between the target and the sputtering pressure according to the present invention, the component compensation and ferroelectric characteristics of the multicomponent oxide ferroelectric thin film to be manufactured are greatly improved.

Claims (7)

A method of forming a multicomponent oxide thin film on a substrate by sputtering a target made of a multicomponent oxide by using a high frequency (RF) magnetron sputtering method, and then performing a post-heat treatment to produce a multicomponent oxide ferroelectric thin film. A method for producing a multi-component oxide ferroelectric thin film, characterized in that the pressure is maintained at 200 to 300 millitorr (mTorr) to reduce the loss of volatile components of the thin film during sputtering. The method of claim 1, wherein the pressure in the vacuum chamber is maintained at 300 mTorr. A method of forming a multicomponent oxide thin film on a substrate by sputtering a target made of a multicomponent oxide by using a high frequency (RF) magnetron sputtering method, and then performing a post-heat treatment to produce a multicomponent oxide ferroelectric thin film. The method of manufacturing a multi-component oxide ferroelectric thin film, characterized in that the distance of 3 to 5 cm and to position the substrate off the target center line. A method of forming a multicomponent oxide thin film on a substrate by sputtering a target made of a multicomponent oxide by using a high frequency (RF) magnetron sputtering method, and then performing a post-heat treatment to produce a multicomponent oxide ferroelectric thin film. A method for producing a multicomponent oxide ferroelectric thin film, characterized in that the angle of the substrate surface is set to 30 ° to 60 °. The method according to any one of claims 1 to 4, wherein the ferroelectric thin film is a bismuth-based multicomponent oxide having a layered perovskite structure. 6. The method of claim 5, wherein the ferroelectric thin film is made of strontium-bismuth-tantalum oxide (SrBi ₂ Ta ₂ O ₉ ). The method according to any one of claims 1 to 4, wherein the volatile component is at least one element selected from bismuth, barium, strontium, and lead.