JPH10172348A - Lead ferrolelectric film and solution for forming thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower a temperature for obtaining the tetragonal system perovskite structure, in comparison with a conventional case, by using a solution composed of organic derivative of metal selected from lead, lanthanum, zirconium and titanium, including cerium compound for keeping a mol ratio of the cerium oxide/lead composite oxide within a specific range after the heat treatment, for forming a lead ferroelectric film. SOLUTION: In a solution for forming a thin liquid film on a base, and heat treating the same in an oxidizing atmosphere to form a ferrolelectric film of (Pbx La1-x )(Zry Ti1-y )O3 (0<x<=1, 0<Y<=1), a mol ratio of cerium oxide/ lead composite oxide after the heat treatment, is controlled to be 0.0001-0.05. To realize the above-mentioned mol ratio, the organic derivative of the metal selected from lead, lanthanum, zirconium and titanium, including a cerium compound, is used. On this occasion, the organic derivative of lead, lanthanum, zirconium, titanium or the like, is metallic carboxylate, metallic alkoxide or the like, for example, lead acetate, lead octylic acid, or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead-based ferroelectric film and a solution for forming the film. More particularly, the present invention relates to a lead-based ferroelectric film containing a limited amount of cerium oxide and a solution for forming the film.

[0002]

2. Description of the Related Art In recent years, a ferroelectric film is used for a nonvolatile memory or the like utilizing its spontaneous polarization. The ferroelectric memory element forms a transistor layer on a silicon substrate,
Further, a capacitor layer is formed thereon. The lead-based ferroelectric layer is used for a capacitor layer. The ferroelectric memory device is shown in FIG.

[0003]

FIG.

Techniques for forming a lead-based ferroelectric film include physical vapor deposition, chemical vapor deposition, sol-gel method, MOD
(Metal Organic Decomposition
ion) method. Among these techniques, the sol-gel method and the MOD method are easy to control the composition ratio and the dopant,
This is a film forming method that can easily obtain in-plane uniformity of a substrate and can cope with mass production. In the sol-gel method and the MOD method, a liquid film is formed on a wafer by spinning, dipping, spraying, or the like a film forming solution. Mist CVD (hereinafter LSCV)
D) forms a liquid film by adsorbing the atomized solution for film formation on the substrate. The thin film of the composite oxide obtained by heat-treating the liquid film formed on the substrate by each of these coating methods is used to form a tetragonal perovskite structure.
It was necessary to perform crystallization annealing at 00 to 800 ° C.
Conventionally, aluminum wiring is generally used as a wiring material of an IC element, and a PSG film or the like is used as an interlayer insulating film. These are known to undergo significant thermal degradation when exposed to temperatures above 550 ° C. Therefore, it is required that the heat treatment temperature is preferably 550 ° C. or less for manufacturing semiconductor devices.

Proceedings of the 57th Autumn Meeting of the Japan Society of Applied Physics, Academic Lecture Meeting of the 57th Autumn Meeting, p389 "8p-F-4 Preparation of highly oriented sol-gel PZT thin film by introducing a new process Saitama University Faculty of Engineering Gota Monji et al." It was disclosed that an orientation film was obtained at a temperature of 500 ° C. or less by using a forming material and introducing a novel process to the sol-gel method. There is no known document that a crystallization temperature of 550 ° C. or less has been achieved by a typical process.

[0006]

In a more general process, there is a strong demand for a method capable of reducing the heat treatment temperature to a lower temperature, preferably 550 ° C. or less, as compared with the conventional 600 to 800 ° C. Accordingly, an object of the present invention is to provide a lead-based ferroelectric film having a tetragonal perovskite structure at a lower temperature than the conventional ferroelectric film by containing a specific component, and a film forming solution for forming the film. That is.

[0007]

Means for Solving the Problems In order to form a lead-based ferroelectric film on a substrate at a low temperature, the present inventors have earnestly studied a method for producing a lead-based ferroelectric film by a sol-gel method and a MOD method. Have been considering. As a result, in a lead-based ferroelectric containing cerium oxide, when the molar ratio of cerium oxide / lead-based composite oxide is 0.0001 to 0.05, the tetragonal perovskite is formed in an oxidizing atmosphere at a lower temperature than before. The inventors have found that the present invention has a structure, and have completed the present invention. The present invention
A lead-based ferroelectric film containing cerium oxide.
The lead-based ferroelectric film is characterized in that the molar ratio of the lead-based composite oxide is 0.0001 to 0.05, and the temperature at which a tetragonal perovskite structure is formed is lower than before. Further, the present invention is heat-treated in an oxidizing atmosphere to make a thin liquid film on a substrate _{(Pb x La 1-x)} (Zr y Ti 1-y) O
_{3 In} the solution for forming a ferroelectric film (here, 0 <x ≦ 1, 0 <y ≦ 1), the molar ratio of the cerium oxide / lead composite oxide after the heat treatment is 0.0001 to 0.05. This is a film forming solution containing an organic derivative of a metal selected from lead, lanthanum, zirconium, and titanium containing a cerium compound. Here, the organic derivative of a metal is a compound in which a metal element and an organic group are bonded.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The film-forming solution of the present invention comprises a mixture of an organic derivative of a metal selected from lead, lanthanum, zirconium and titanium and a cerium compound, a product solution thereof, and an organic solvent.

The organic derivatives such as lead, lanthanum, zirconium and titanium used in the present invention include metal carboxylate, metal alkoxide, metal β-diketonate and the like.
For example, lead acetate, lead octylate, diisopropoxy lead, lanthanum acetate, isopropoxy lanthanum, tris (dipivaloylmethanato) lanthanum, tetranormal butoxy zirconium, diacetylacetonato diisopropoxy zirconium, tetra normal butoxy titanium, diacetyl acetoacetate And natodiisopropoxytitanium.

The cerium compound used in the present invention is cerium nitrate, cerium acetate, triisopropoxycerium, tris (dipivaloylmethanato) cerium and the like. In particular, when added to a lead-based organic derivative mixed solution, those which dissolve uniformly are preferred.

The organic solvent used in the present invention is an organic solvent which dissolves organic derivatives of lead, lanthanum, zirconium, titanium and mixtures thereof. For example, acetates such as ethyl acetate, n-butyl acetate, and amyl acetate; alcohols such as ethyl alcohol, isopropyl alcohol, and butyl alcohol;
Glycol esters such as -methoxyethanol and 2-ethoxyethanol; and cyclic ethers such as tetrahydrofuran and 1,4-dioxane. These organic solvents can be used even if they are mixed.

In the present invention, the molar ratio of cerium oxide / lead composite oxide is 0.0001 to 0.05, preferably 0.001 to 0.05.

In the present invention, the heat treatment in an oxidizing atmosphere for forming the film into a tetragonal perovskite structure may be performed at a lower temperature for a long time, at a higher temperature for a short time, A heating method can be used.
In any case, as long as the heat treatment method is the same, a lower temperature may be used as compared with the conventional composition in which the cerium compound is not added. Even at the same heat treatment temperature, it may be performed in a shorter time. According to the present invention, the heat treatment temperature can be reduced to 500 ° C. or less, which is preferable for manufacturing a semiconductor device.

In the present invention, the step of applying a solution on a substrate includes a spin method, a dipping method, a spray method, and an LSCV method.
Method D or the like can be used.

In the present invention, in the step of crystallizing the lead-based composite oxide film on the substrate, an atmosphere containing an oxidizing gas is generally used. Examples of the oxidizing gas include oxygen, N ₂ O, and ozone.

[0016]

Example 1 20.2 g of tetra-n-butoxytitanium
(0.059 mol), 20.3 g (0.067 mol) of tetra-n-butoxyzirconium, and 41.0 g of lead acetate
g (0.126 mol) of the mixture was heated at 160 ° C. for 3 hours to form a liquid, and acetylacetone 18.1 was added.
g (0.181 mol), 26.1 g of octylic acid (0.
181 mol) and heated at 160 ° C. for 2 hours to obtain a reddish brown transparent liquid. This solution was treated with n-butyl acetate 23.
After dilution with 2.5 g, cerium nitrate hexahydrate 0.1
Ethanol solution containing 30 (0.0003 mol) 7
7.5 g was added to obtain a solution for film formation. This solution was coated on a silicon wafer on which platinum was deposited using a spinner. The film manufactured by such a procedure is
It was dried by heating at 0 ° C. for 5 minutes, and further heat-treated at 250 ° C. for 30 minutes. Then, heat treatment was performed at 500 ° C. for 3 hours in an oxygen atmosphere. As a result of analyzing this film by X-ray diffraction, it was found to be lead zirconate titanate having a perovskite structure. The composition of this film is CeO ₂ / Pb _1.0 Zr _0.53 Ti _0.47
The molar ratio of O ₃ was 0.002.

[0017]

Comparative Example 1 The same processing as in Example 1 was performed except that cerium nitrate was not added. As a result of X-ray diffraction analysis, the crystals were found to have a pyrochlore structure. Example 1
Table 1 shows the results of Comparative Example 1.

[0018]

[Table 1]

[0019]

Comparative Example 2 When the same treatment as in Comparative Example 1 was performed except for the heat treatment temperature, a heat treatment temperature of 600 ° C. was required to obtain the same X-ray diffraction analysis result as in Example 1.

[0020]

Comparative Example 3 The same treatment as in Example 1 was performed, except that the amount of cerium nitrate added was 3.474 g (0.008 mol). As a result, a pyroglomer structure and a perovskite structure were mixed. The reason is that C
The molar ratio of eO ₂ / Pb _1.0 Zr _0.53 Ti _0.47 O ₃ is 0.0635, which is 0.0 in the present invention.
It is to exceed 5.

[0021]

According to the present invention, the sol-gel method, MOD
There is an effect that a lead-based ferroelectric film can be manufactured by a low-temperature treatment using a method and an LSCVD method.

[Brief description of the drawings]

FIG. 1 is a structural diagram of a ferroelectric memory device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 p or n well 3 Source 4 Gate 5 Drain 6 Oxide film 7 Insulating layer 8 Lower electrode 9 PZT thin film 10 Upper electrode 11 Metal wiring layer 12 CMOS transistor layer 13 Ferroelectric process layer

Claims (2)

[Claims] 1. A lead-based composite oxide containing cerium oxide (Pb)
_{x La 1-x) (Zr} y Ti 1-y) O 3 ( where 0 <
wherein x ≦ 1, 0 <y ≦ 1) and a molar ratio of cerium oxide / lead-based composite oxide is 0.0001 to 0.05. 2. A heat-treated in an oxidizing atmosphere to make a thin liquid film on a substrate _{(Pb x La 1-x)} (Zr y Ti 1-y)
O ₃ (where 0 <x ≦ 1, 0 <y ≦ 1) In the liquid for forming the ferroelectric film, the molar ratio of the cerium oxide / lead-based composite oxide after the heat treatment is 0.0001 to 0.1. A film forming solution containing an organic derivative of a metal selected from lead, lanthanum, zirconium, and titanium, containing a cerium compound so as to be 05.