JPH0977592A - Production of bismuth laminar ferroelectric thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a forming method of a bismuth laminar ferroelectric thin film ABi2 B2 O9 (wherein A is Sr or Ba and B is Nb or Ta) used for a nonvolatile memory by chemical vapor phase growing method. SOLUTION: A double ethoxide expressed by A[B(OC2 H5 )6 ]2 as the source material of A and B is vaporized or sublimated and introduced into a thermal CVD device, while bismuth tertiary butoxide or bismuth tertiary pentoxide as the source material of Bi is sublimated and introduced into the device. These source materials are decomposed and grown on a heated substrate and then heat treated in an atmosphere containing oxygen. By this method, the compsn. and the crystal structure of the film can easily be controlled, and a general CVD device having high mass productivity for the production of semiconductor devices can be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a bismuth layered ferroelectric thin film. More specifically, it relates to a method for producing the thin film by a vapor phase growth method using a specific double ethoxide as a raw material.

[0002]

2. Description of the Related Art In recent years, bismuth layered ferroelectric thin films have been used in non-volatile memories and the like which make use of their spontaneous polarization. In particular, SrBi ₂ Ta ₂ O ₉ is an excellent thin film that solves the biggest problem of the ferroelectric memory to date, namely, fatigue, that the characteristics of the film deteriorate with repeated polarization inversion.

The following two methods are known as methods for producing a thin film of a bismuth layered ferroelectric substance. The first method is M
OD (Metal Organic Deposition)
on) method, for example, Proceedings of the 55th Autumn Meeting of the Applied Physics Society of Japan in the fall of 1994 P394 “20P-M-
19 Development of Y1 system (Bi layer) ferroelectric thin film (II)
/ Materials and film formation method ". In this method, alkoxides, carboxylates, etc. of each metal composing the thin film are applied according to the composition ratio by spin coating, and dried and baked to thermally decompose organic matter and anneal in an oxygen atmosphere. Crystallize.

The second method is LS-MCVD (Liqui).
d Source-Misted Chemical V
apor Deposition) method, for example, 19
Autumn 1994 Proceedings of 55th Annual Meeting of the Japan Society of Applied Physics
P393 "Preparation and evaluation of ferroelectric thin film by 20P-M-16 LSMCVD method" and the like. Similar to the spin coating method, this method atomizes a raw material whose composition is stoichiometrically adjusted, transports it to a vacuum chamber with a carrier gas, deposits it on a substrate, and then heats organic matter by a dry baking process. It is decomposed and crystallized by annealing in an oxygen atmosphere.

[0005]

There is a case where a usual chemical vapor deposition method (hereinafter referred to as a CVD method) is required from a series of mass productivity in a semiconductor device manufacturing process, and the conventional method cannot always satisfy this purpose. The reason why it was difficult to prepare a good bismuth layered ferroelectric thin film by the ordinary CVD method was that it was difficult to obtain a stable volatile stable raw material compound, and three elements A, Bi and B were used. It is not easy to accurately control the composition ratio of (3) to the stoichiometric ratio.

An object of the present invention is to provide a method for producing a bismuth layered ferroelectric thin film by a CVD method.

[0007]

Means for Solving the Problems The present inventors have been conducting research for many years on the synthesis of metal alkoxides. In addition, we have continued to study earnestly about making oxides by decomposition. As a result, when an oxide ferroelectric thin film having a bismuth layer structure is formed by the CVD method, if a double alkoxide containing two elements A and B is used as a raw material, the element ratio of the film can be easily controlled, and good results can be obtained. The inventors have found that a film exhibiting electrical characteristics can be formed and completed the present invention. A feature of the present invention is that when a bismuth layered ferroelectric thin film is manufactured by a CVD method, a specific double alkoxide in which the two elements A and B have the same composition ratio as that of the film is used.

The double alkoxide of the present invention is easy to synthesize, separate and purify during its production, and is stable during heating for vaporization or sublimation supply in a CVD apparatus,
It is an ethoxide that decomposes cleanly on the substrate.

A preferred double ethoxide is Goel,
M. S. , Goel, A .; B. and Mehrotr
a.R. C. , Synth. React. Inorg.
Met. -Org. Chem. vol6,251-63
(1976) and Mehtra, R .; C. , Ad
v. Inorg. Chem. & Radiochem.
The following four are described in vol26, p326 (1983). Sr [Ta (OEt) ₆ ] ₂ , Sr [Nb (OE
t) ₆ ] ₂ , Ba [Ta (OEt) ₆ ] ₂ , Ba [Nb
(OEt) ₆ ] ₂ (in the above, OEt represents an ethoxy group)

Further, Sr [Ta _x Nb _1-x (OEt)
₆ ] ₂ (where 0 <x <1), a complex ethoxide in which A and B each consist of two elements can be regarded as a combination compound of the above four compounds and can be preferably used. Sr
[Ta (OEt) ₆ ] ₂ and Sr [Nb (OE
t) ₆ ] ₂ is a preferable double alkoxide because it is a liquid at a high temperature and can be supplied to a CVD apparatus by evaporation.

These are ferroelectric SrBi ₂ T, respectively.
a ₂ O ₉ , SrBi ₂ Nb ₂ O ₉ , BaBi ₂ Ta ₂ O
₉ , BaBi ₂ Nb ₂ O ₉ can be used in the manufacture of the film.
Of these, Sr [Ta (OEt) ₆ ] ₂ is particularly stable,
It has excellent evaporation characteristics and is suitable for forming a film of SrBi ₂ Ta ₂ O ₉ .

The production method of the double ethoxide used in the present invention is Ta (OEt) ₅ or Nb (OEt) ₅
Metal strontium or metal barium is added to the ethanol solution described in (1) above, and 1/2 of tantalum or niobium atom is added, and the mixture is heated and refluxed sufficiently to completely react with strontium or barium to double-alkoxide. Or separately synthesized strontium ethoxide Sr (OEt)
Stoichiometric amount of ₂ or barium ethoxide Ba (OEt) ₂ is added to an ethanol solution of Ta (OEt) ₅ or Nb (OEt) ₅ and heated under reflux sufficiently. Then, ethanol is distilled off, and the powder remaining in the reactor is transferred to a distillation apparatus or a sublimation apparatus and distilled or sublimated under vacuum.

In the raw material supply system of the CVD reactor, Sr [Ta (OEt) ₆ ] ₂ and Sr [Nb kept at a high temperature are used.
(OEt) ₆ ] _{2 in} the feed cylinder, free Ta
In order to prevent (OEt) ₅ and Nb (OEt) _{5 from} being formed and evaporating, Sr (OEt) ₂ may be present in an amount slightly higher than the equivalent amount of double ethoxide formation.

The bismuth alkoxide used in the present invention is bismuth alkoxide, which has good thermal stability at the time of supply and high volatility.
H ₃ ) ₃ ] ₃ or Bismaster Charipentoxide B
i _{[OC (CH 3) 2 C 2} H 5 ] ₃ are preferred. Other bismuth alkoxides are partially decomposed at a temperature at which the sublimation pressure or vapor pressure is preferable, so that it is difficult to control the supply amount and the deposition amount. With triphenylbismuth, the decomposition temperature is high, and the amount of deposition greatly depends on the amount of oxygen, so it is difficult to control the composition.

As the CVD method in the present invention, thermal CV is used.
The D method, the photo CVD method, the plasma CVD method, or the like can be adopted.

Examples of the present invention will be described below. It should be understood that the following embodiments are examples of the present invention, and the present invention is not limited to these embodiments.

[0017]

[Examples] 50.4 g of tantalum ethoxide Ta (OEt) _{5 and} 0.2 l of ethanol were placed in a flask equipped with a condenser.
Was charged, then 5.6 g of metal strontium Sr was added, and the mixture was heated to reflux. The strontium was completely reacted in about 0.5 hours. Then, the mixture was heated under reflux for 10 hours to thoroughly carry out double alkoxide formation. Then ethanol was distilled off and the product powder was vacuum dried. This powder was placed in a distillation apparatus, and the pressure was reduced to 0.3 Torr and heated, whereby it melted at around 130 ° C. As an initial fraction, 3.0 g was collected, and then a colorless transparent liquid was recovered as a main fraction at a distillation temperature of 165 to 170 ° C. The liquid solidified immediately upon cooling with air and weighed 42.0 g. The melting point was 125 ° C. by thermal analysis. As a result of elemental analysis and organic group analysis, this white crystal was found to be double ethoxide Sr [Ta (OE
t) ₆ ] ₂ . Calculated value Sr 8.85%, Ta3
6.5%, whereas the analytical value Sr 8.81%, Ta
The yield was 35.5% and the yield was 68%.

Next, thermal CVD was performed using the obtained distilled product. 25 g of Sr [Ta (OEt) ₆ ] ₂ was filled in a raw material container of a low pressure thermal CVD apparatus system (total pressure 5 Torr), the container was kept at a constant temperature of 150 ° C., and argon was 40 ml / m 2.
Introduced by bubbling, Sr [Ta (OEt) ₆ ] ₂
Was sent to the pyrolysis furnace. At the same time, Bi [OC (CH ₃ ) ₂ C ₂ H ₅ ] ₃ 2 was placed in another raw material container.
5 g was charged, the container was kept at a constant temperature of 80 ° C., argon was introduced at 30 ml / min, and sublimated vapor was entrained,
It was sent to the pyrolysis furnace. In the pyrolysis furnace, Pt / SiO ₂ /
The Si substrate was heated to 340 ° C., and the above-mentioned two kinds of gases were mixed and introduced onto this substrate to cause thermal decomposition deposition. Finally, while flowing a mixed gas of oxygen and argon,
Crystallization treatment was performed at 50 ° C. for 60 minutes. Thus, a thin film having a thickness of 200 nm was obtained on the substrate. This crystal structure is X
As a result of RD analysis, it was SrBi ₂ Ta ₂ O ₉ .

[0019]

According to the present invention, when the Bi layered ferroelectric thin film is manufactured by the CVD method, the double ethoxide represented by A [B (OEt) ₆ ] ₂ is used to obtain good characteristics. A thin film can be obtained. By using this raw material, the composition and crystal structure of the film can be easily controlled. In addition, since an ordinary CVD apparatus with high mass productivity can be used in the manufacture of semiconductor devices, this is a great advantage.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication location H01L 27/108 H01L 27/10 651 21/8242

Claims (2)

[Claims] 1. ABi ₂ B ₂ O ₉ (where A = S
r, Ba, B = Nb, or Ta), in the case of producing a bismuth layered ferroelectric thin film represented by the vapor phase epitaxy method, A [B (OC ₂ H
₅ ) ₆ ] A method for producing a bismuth layered ferroelectric thin film, which comprises using the double ethoxide represented by the formula ₂ ). 2. The method for producing a bismuth layered ferroelectric thin film according to claim 1, wherein the Bi raw material is bismaster schalibutoxide or bismaster schalipentoxide.