KR100480501B1 - Process for the formation of pzt thin film by metal-organic chemical vapor deposition - Google Patents

Abstract

The present invention relates to a method for preparing a lead zirconate titanate (PZT) thin film using an organometallic chemical vapor deposition method, Pb (methd) ₂ represented by the following Chemical Formula 1, Zr (methd) ₄ represented by the following Chemical Formula 2, and the following Chemical Formula 3 According to the method of the present invention comprising vaporizing a single mixed precursor solution comprising Ti (mpd) (methd) ₂ and then depositing it on a substrate in a temperature range of 360 to 560 ° C., PZT having the required composition Thin films can be easily produced:

Description

PROCESS FOR THE FORMATION OF PZT THIN FILM BY METAL-ORGANIC CHEMICAL VAPOR DEPOSITION}

The present invention relates to a method for preparing a lead zirconate titanate (PZT) thin film by metal organic chemical vapor deposition (MOCVD). And a process for producing PZT thin films of desired composition by using them as and introducing them into the reactor in the form of a single mixed solution.

Recently, semiconductor technology has been continuously growing by pursuing more advanced technology through miniaturization of semiconductor devices, and researching suitable thin film materials and processing technologies, in particular, applying it to ferroelectric random access memory (FRAM) Research on PZT thin film as a suitable thin film is actively underway.

Ferroelectric thin films have been using sputtering methods in the 70's, so RF magnetron sputtering, ion beam sputtering, reactive co-evaporation, and metal organic decomposition ( Metal Organic Decomposition (MOD), Liquid Souce Misted Chemical Decomposition (LSMCD), Laser Ablation, and Organic Metal Deposition (MOCVD). In particular, the organic metal chemical vapor deposition method has emerged as a competitive process due to the advantages such as high deposition rate and excellent step coverage (step coverage).

Organometallic chemical vapor deposition is a method of synthesizing a thin film of a solid material from a gaseous organic metal raw material through a chemical reaction, and is a process of arranging atoms on a substrate using a precursor material as a chemical raw material. The low decomposition temperature of the organometallic compounds used allows low temperature processes, and the composition and deposition rate of the thin film can be controlled by controlling the introduction amount of the raw material and the amount of transport gas. In addition, since the surface of the substrate is not damaged, an excellent thin film can be obtained. For these reasons, processes using organometallic chemical vapor deposition have attracted attention to produce excellent oxide films in the DRAM and FRAM fields.

Important factors to consider in the CVD process include the selection of the appropriate precursor, the design of the precursor supply system, the design of the reactor, the establishment of the operating conditions, but the selection of the appropriate precursor and the efficient transport of the precursor are the most important factors that can determine the success or failure of the chemical vapor deposition process. It is one of the important factors. Initially, mainly chloride or hydroxy-based compounds were used as precursor materials, but organometallic compounds are mainly used due to poor physical properties such as contamination of thin films by halogen atoms. In general, organic compounds have a higher vapor pressure than inorganic compounds, have a low decomposition temperature, and in particular, can change physical and chemical properties of raw materials by changing ligand structure.

As the precursor material for MOCVD, a material having a high vapor pressure at a low temperature, having a large difference between the vaporization temperature and the decomposition temperature, leaving no residue of organic matter in the thin film, and having a stable and nontoxic condition is preferable. Organometallic compounds used to deposit metal oxide thin films, including PZT thin films, can be classified into metal alkyl, metal alkoxide and metal diketonate systems. The metal alkyl system has a high vapor pressure of the raw material but high toxicity, and the alkoxide system is relatively easy to synthesize and has been well studied for its decomposition process. However, it is very sensitive to moisture, so that the hydrolysis or hydration reactions occur easily. While the system is not sensitive to moisture and is easy to handle, it is difficult to synthesize with high purity and has a disadvantage of being expensive. Among them, diketonate-based precursors, which exist mainly in the solid phase but have excellent properties, are mainly used. Representative diketonate-based ligands are TMHD (2,2,6,6-tetramethyl-3,5-heptanedione). Recently, a number of chemical precursor companies have proposed various methods to have a higher vapor pressure by forming a monomer as a precursor based on TMHD. For example, there is a method to obtain a high vapor pressure of the precursor material by forming a complex of another ligand having an N or O donor having a non-covalent electron pair, and another method is to use a larger substituent on the substituent. There is a method using a steric effect that effectively masks central metal ions by substitution (Chem. Vap. Deposition, 1998, 4 , No. 5, p169). On the other hand, attempts have been made to induce monomers by coordinating central metal ions using long-bridged ligands containing elements with large numbers of unshared electron pairs in the substituents themselves (J. Mater. Res., 1999, 14 , No. 10, p3988).

In addition to research on improving precursor properties, research on efficient transport of precursors has also been of interest. Recently, in consideration of reproducibility, attention has been focused on solution transport rather than bubbling transport. In the case of a three-component complex oxide, there are a method of transporting each precursor individually when transporting a solution, and a method of transporting three precursors in the form of a single mixed solution. In the latter case, reproducible supply of the precursor is possible and the composition of the thin film can be easily controlled by controlling the composition of a single mixed solution. And the three precursor materials should have good solubility in the solvent.

Accordingly, it is an object of the present invention to provide a method for easily preparing a PZT thin film having a desired composition from a single mixed solution.

In order to achieve the above object, the present invention includes Pb (methd) ₂ represented by the following formula (1), Zr (methd) ₄ represented by the following formula (2) and Ti (mpd) (methd) ₂ represented by the formula (3) To provide a method for producing a lead zirconate titanate (PZT) thin film comprising vaporizing a single mixed precursor solution and then depositing on a substrate in a temperature range of 360 to 560 ℃:

Formula 1

Formula 2

Formula 3

Hereinafter, the present invention will be described in detail.

In the present invention, Pb (methd) ₂ , Zr (methd) ₄ and Ti (mpd) (methd) ₂ are used as Pb, Zr, and Ti precursor materials, respectively, wherein methd is methoxyethoxy. Tetramethylheptanedione (methoxyethoxytetramethylheptanedione), mpd means methylpentanedione (methylpentanedione).

The methd ligand is a modified form of the TMHD ligand, which forms a lasso structure containing oxygen atoms containing a lone pair of electrons at the end of the substituent. Oxygen atoms having such unshared electron pairs may improve coordination of the central metal ions to stabilize the precursor molecules and increase the probability of being present as monomers during vaporization. In addition, precursor molecules based on methd have a characteristic of hardly remaining residues during vaporization.

The Pb (methd) ₂ precursor used in the present invention has the form of a white solid at room temperature, and the Zr (methd) ₄ and Ti (mpd) (methd) ₂ precursors each have the form of a yellow liquid at room temperature.

1 is a schematic view of an example of an organometallic chemical vapor deposition apparatus that can be used in the present invention, according to the method for producing a PZT thin film of the present invention, three metal precursor materials, that is, Pb (methd) ₂ , Zr (methd) ₄ And dissolving Ti (mpd) (tmhd) ₂ in an organic solvent to prepare a single mixed solution 1 having a desired composition, and injecting the resulting mixed solution into the vaporizer 2 in an argon gas atmosphere as a carrier gas 3. After vaporization and vaporization, the PZT thin film can be deposited by injecting the obtained vapor with the oxygen-containing gas 4 into the reactor 5 to grow a film on various substrates under internal temperature conditions of 360 to 560 ° C.

Each of the metal precursor materials may be separately injected into the vaporizer 2, but in order to transfer reproducible precursor materials, the metal precursor materials are dissolved in an organic solvent by a liquid delivery method and then mixed in an appropriate ratio having a desired composition. It is preferable to inject in the form of a single mixed solution.

The mixing ratio between the precursor materials is preferably mixed in an appropriate ratio for forming a PZT thin film having a desired composition. In particular, by controlling the ratio of Pb content and (Zr / Ti), a thin film having a desired composition can be easily obtained. Preferably, the composition ratio [Pb / (Zr + Ti)] of the precursor material is in the range of 0.4 to 1.1. In this case, the mixing ratio of Zr: Ti is preferably set to 3: 7 to 5: 5.

As in the method of the present invention, in the case of preparing a single mixed solution by dissolving three or more metal precursor materials in a solvent, it is necessary to satisfy the condition that mutual reactions between precursor molecules do not occur in the mixed solution. Precursor combinations consisting of Pb (methd) ₂ , Zr (methd) ₄ and Ti (mpd) (methd) ₂ are suitable for use in the form of a single mixed solution since no reaction occurs between the precursors.

As the solvent used in the present invention, all solvents commonly used in the art may be used, for example, n-heptane, n-octane, tetrahydrofuran (THF) and mixtures thereof may be used. When the mixed solution is injected into the vaporizer 2, a controller capable of precisely controlling the flow of the solution may be used, and specific examples thereof include a liquid flow meter (LFM) and a syringe pump. .

The vaporization process of the precursor mixed solution (1) may be carried out at 200 to 300 ℃.

The vaporized precursor material is preferably deposited on the substrate in the temperature range of 360 to 560 ℃, when the deposition is carried out at a temperature lower than the above range, the deposition rate of Ti and Zr is too low, at a temperature higher than the above range In the case of deposition, the Pb content in the thin film is drastically reduced due to the volatility of Pb and PbO, and also adversely affects the uniformity of the thin film due to the gas phase reaction.

As the substrate of the PZT thin film that can be used in the present invention, any conventional one can be used, and typically, Si, Pt, Ir, Ru, IrO ₂ , RuO _2, and the like.

According to the present invention, PZT thin films of various compositions can be prepared by changing the concentration of constituent precursor materials in a single mixed solution.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

Example

Deposition of PZT Thin Films

Example 1

Using the organometallic chemical vapor deposition apparatus shown in FIG. 1, Pb (methd) ₂ , Zr (methd) ₄ and Ti (mpd) (methd) ₂ on a (111) Pt / TiO ₂ / SiO ₂ / Si substrate A PZT thin film was formed from the precursor material.

First, each precursor material was dissolved in n-octane at a concentration of 0.1 M to prepare a single precursor solution, and then the composition of the precursor mixed solution was fixed at [Zr: Ti] _sol = 3: 7 and [Pb / (Zr + Ti)] _sol = 0.9 so that each single precursor solution was mixed in volume ratio. The obtained mixed solution (1) was injected into the vaporizer (2) having an internal temperature of 230 ° C. and a pressure of 7 torr at a rate of 0.15 ml / min, at which time Ar 80 sccm and an oxygen-containing gas were used as the transport gas (3). 400 sccm of O ₂ was flowed together as (4). Vaporized vapor was then injected into the reactor 5 at a rate of 0.15 mL / min. During the film growth, the internal pressure in the reactor 5 was maintained at 1 torr, and the temperature was in the range of 360 to 560 ° C.

Comparative Example 1

A PZT thin film was grown on the substrate by the same procedure as in Example 1 except that Ti (mpd) (tmhd) ₂ was used instead of Ti (mpd) (methd) ₂ as the Ti precursor material.

NMR spectral analysis of a single mixed solution

In order to confirm the presence of constituent precursor material interactions to form the PZT thin film, NMR spectral results of a single mixed solution are shown in FIGS. 2A and 2B, respectively. 2A and 2B, in the case of a single mixed solution used in the present invention, no peaks are observed even after one week has elapsed as the precursors do not react with each other (FIG. 2B), and Ti (mpd) (methd ) use of a ₂ instead of Ti (mpd) (tmhd) ₂ to include Pb (tmhd) ₂ is formed with a peak (Fig. 2a) ligand therefrom between Pb (methd) ₂ and Ti (mpd) (tmhd) ₂ precursor mutual It can be seen that an exchange reaction occurs.

Example 2

In order to observe the effect of the change of Pb content in the precursor mixture solution on the deposition rate, the composition of the precursor mixture solution was fixed at [Zr: Ti] _sol = 3: 7 and [Pb / (Zr + Ti)] _sol = A PZT thin film was grown on the substrate by the same procedure as in Example 1 except that the deposition was performed to 0.6.

Example 3

In order to observe the effect of the change of Pb content in the precursor mixture solution on the deposition rate, the composition of the precursor mixture solution was fixed at [Zr: Ti] _sol = 3: 7 and [Pb / (Zr + Ti)] _sol = A PZT thin film was grown on the substrate by the same procedure as in Example 1 except that the deposition was performed to 0.4.

Example 4

In order to observe the effect of the change of the Pb content in the precursor mixture solution on the deposition rate, except that the deposition was carried out so that the composition of the precursor mixture solution was [Pb: Zr: Ti] _sol = 11: 5: 5, The PZT thin film was grown on the substrate by the same procedure as in Example 1.

Example 5

In order to observe the effect of the change of the Pb content in the precursor mixture solution on the deposition rate, except that the deposition was carried out so that the composition of the precursor mixture solution was [Pb: Zr: Ti] _sol = 11: 3: 7, The PZT thin film was grown on the substrate by the same procedure as in Example 1.

Example 6-8

The PZT thin film was deposited on the substrate by the same procedure as in Example 1, except that the injection rate of the resulting precursor mixture solution was maintained at 0.20 ml / min, 0.25 ml / min and 0.30 ml / min instead of 0.15 ml / min. Grown.

Deposition Properties Analysis of Thin Films

3 is a graph showing a change in deposition rate according to deposition temperature and solution composition in the reactor 5 of the PZT thin films formed in Examples 1 to 3, respectively. As shown in FIG. 3, as the deposition temperature is increased, the deposition rate of the thin film is reduced as a whole. In particular, it can be seen that the thickness of the thin film is rapidly decreased at 500 ° C. or higher. In addition, as the relative content of Pb in the precursor composition increases, the thickness of the thin film decreases, which may be interpreted as the formation of the thin film is inhibited as the deposition temperature increases due to the high volatility of PbO.

4 shows the change in the composition of the thin film according to the change of the deposition temperature and the solution composition in the reactor 5 of the PZT thin films formed in Examples 3 to 5, respectively. The composition of the precursor mixed solution was (a) [Pb: Zr: Ti] _sol = 11: 3: 7 (Example 5), (b) [Pb: Zr: Ti] _sol = 11: 5: 5 (Example 4) and (c) [Pb: Zr: Ti] _sol = 4: 3: 7 (Example 3), the Pb content in the PZT thin film gradually decreases as the deposition temperature increases, which is as described above. And the volatility of PbO increases with temperature. 4 (b) and 4 (c), it can be seen that as the Pb content in the precursor solution increases, the Pb content in the grown PZT thin film also increases. In the case of [Zr: Ti] _sol = 3: 7 (c), the Pb content in the thin film decreases rapidly with increasing temperature, whereas in case of [Zr: Ti] _sol = 5: 5 (b), the Pb in the thin film It can be seen that the content is gradually reduced while maintaining a substantially constant. From FIG. 4, it is much easier to obtain a thin film having a desired composition by appropriately adjusting the ratio of Pb content and [Zr / Ti] in the mixed precursor solution.

Figure 5 shows the change in deposition rate by changing the injection rate of a single mixed solution according to Examples 6 to 8, from which the deposition rate increases linearly as the injection rate of the precursor solution is increased. Able to know. That is, the thickness of the thin film can be adjusted by controlling the injection rate of the solution.

As can be seen from the above, according to the method for producing a PZT thin film of the present invention, by controlling the mixing ratio of the precursor constituent material, it is possible to grow a PZT thin film having a desired composition, for example, [Pb: Zr: Ti] _sol = 11 A PZT thin film close to [Pb / (Zr + Ti)] = 1 can be prepared by depositing a vapor formed from a precursor mixed solution having a composition of 5: 5 on a substrate at a deposition temperature of 400 to 480 ° C. in a reactor. have.

Crystallinity Analysis of the Formed Thin Film

6, which shows the crystallinity change of the PZT thin film according to the deposition temperature, it can be seen that a PZT thin film having a relatively high intensity perovskite phase is formed at a deposition temperature of 480 ° C. FIG.

As described above, according to the method of the present invention, using a chemical vapor deposition method from a single mixed solution containing Pb (methd) ₂ , Zr (methd) ₄ and Ti (mpd) (methd) ₂ as precursor materials, The ferroelectric PZT thin film fabricated so as to be applied as a capacitor dielectric material can be applied.

Simple modifications or changes of the present invention can be easily carried out by those skilled in the art, and all such modifications or changes can be seen to be included in the scope of the present invention.

1 is a schematic diagram of an organometallic chemical vapor deposition apparatus used in the present invention;

2A and 2B show NMR spectra of the precursor mixed solution prepared in Comparative Example 1 and Example 1 according to the present invention, respectively;

3 is a view showing a change in deposition rate according to the deposition temperature and the solution composition of the PZT thin film formed in Examples 1 to 3 according to the present invention, respectively;

4 is a view showing a change in the composition in the thin film according to the change in the deposition temperature and the solution composition of the PZT thin films formed in Examples 3 to 5 according to the present invention;

5 is a view showing a change in deposition rate according to the change in the injection rate of the PZT precursor mixed solution prepared in Example 1 and Example 6-8 according to the present invention;

6 is a view showing the crystallinity change according to the deposition temperature of the PZT thin film prepared according to the present invention.

Explanation of symbols for the main parts of the drawings

1: precursor mixed solution 4: oxygen-containing gas

2: vaporizer 5: deposition reactor

3: carrier gas

Claims (7)

After vaporizing a single mixed precursor solution comprising Pb (methd) ₂ represented by the following Chemical Formula 1, Zr (methd) ₄ represented by the following Chemical Formula 2 and Ti (mpd) (methd) ₂ represented by the following Chemical Formula 3, Method for producing a lead zirconate titanate (PZT) thin film, comprising depositing on a substrate in the temperature range of 360 to 560 ℃: Formula 1 Formula 2 Formula 3 The method of claim 1, And wherein the composition ratio [Pb / (Zr + Ti)] of the metal precursor material in the mixed precursor solution is in the range of 0.4 to 1.1. The method of claim 2, The mixing ratio of Zr: Ti ranges from 3: 7 to 5: 5. The method of claim 1, Wherein the mixed precursor solution is prepared by dissolving each precursor material in an organic solvent. The method of claim 4, wherein Wherein the organic solvent is selected from n-heptane, n-octane, tetrahydrofuran (THF) and mixtures thereof. The method of claim 1, Wherein the substrate is selected from Si, Pt, Ir, Ru, IrO ₂ and RuO ₂ . The method of claim 1, The vaporization process is carried out in a temperature range of 200 to 300 ℃.