JPH0987848A - Production of bismuth layer ferroelectric thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a bismuth layer ferroelectric thin film ABi2 B2 O9 (where A is Cr or Ba and B is Nb or Ta) to be used in a nonvolatile memory, etc., by chemical vapor deposition. SOLUTION: The double ethoxide or double isopropoxide shown by A(B(OR)6 )2 as the raw material for A and B is vaporized or sublimated and introduced into a hot CVD device, bismuth tertiary-butoxide or bismuth tertiary- pentoxide is sublimated and introduced as the raw material for Bi, the raw gases are supplied on a heated substrate, the contact part between the raw gases and substrate is irradiated with UV to decompose and grow the raw gases, and then the product is heat-treated in an atmosphere contg. oxygen. The composition and crystal structure of the film are easily controlled by using the method, and the yield in the production of a semiconductor device is improved.

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, the present invention relates to a method for producing the thin film by vapor phase epitaxy by using a specific double alkoxide and a bis-master alkaryoxide as a raw material and irradiating with ultraviolet rays.

[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 has solved the biggest problem of the ferroelectric memory to date, that is, fatigue, that the characteristics of the film deteriorate when the polarization inversion is repeated.

The thin film is formed by an ordinary chemical vapor deposition method (hereinafter referred to as CV).
The technique created by the D method) is the 4th spring 1995.
Proceedings of the 2nd Joint Lecture on Applied Physics p522 "3
1a-D-1 Thin film growth of Bi layered ferroelectric by MOCVD method. Chiba Isobe et al., Sony Central Research Laboratories ”. Among them, tantalum ethoxide Ta (OC ₂
H ₅ ) ₅ and triphenylbismuth Bi (C ₆ H ₅ ) ₃ and strontium bis (dipivaloylmethanato) tetraene complex Sr (dpm) ₂ . Using three kinds of raw materials of tetraen ₂ , oxygen gas was introduced, and by the low pressure CVD method,
By optimizing the pressure, substrate temperature, gas supply amount, etc., Pt / T
SrBi ₂ having a film thickness of 200 nm and a composition ratio Sr / Bi / Ta = 1 / 2.2 / 2.5 on an i / SiO ₂ / Si substrate.
A Ta ₂ O ₉ film is obtained. It is decomposed and deposited at a substrate temperature of 600 to 750 ° C., and then annealed at 800 ° C. in an oxygen atmosphere. The method needs to optimize and control the feed rates of the three raw materials.

The present inventors have invented a patent for a method of using a specific double alkoxide having the same composition ratio of A and B as the raw material as a raw material when the thin film is formed by the MOCVD method (patent application). No. 7-120350). It also discloses the use of Bismaster Chaributoxide or Bismaster Charipentoxide as the Bi raw material. According to this previous patent application, it suffices to control the supply amounts of the two kinds of raw materials, and it is possible to form a thin film having excellent performance.

[0005]

In producing the thin film according to the prior patent application, the substrate should be made to have the same A / B element ratio of the double alkoxide used as the raw material and the A / B element ratio of the film. It was found that the temperature is preferably 500 ° C. or lower. If the temperature is higher than 500 ° C., it is estimated that the ratio of A / B in the decomposition and deposition differs from the ratio of the raw material because the raw material double alkoxide gas is dissociated before reaching the substrate. Yet another raw material, bis-master charialkoxide, decomposes and deposits at 250-400 ° C. Therefore, it is desirable to avoid heating the two raw materials to a high temperature due to heat from the substrate before reaching the substrate.
That is, it is preferable to perform the CVD method with the substrate temperature kept as low as possible. Therefore, a CVD method which is more convenient than the conventional thermal CVD method is desired. Further, in the CVD method at a low temperature of around 300 ° C., since a large amount of residual carbon is common, it is necessary to reduce this residual carbon.

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

[0007]

DISCLOSURE OF THE INVENTION The inventors of the present invention have earnestly studied a method for producing a metal alkoxide and its physical properties, and a method for producing a bismuth layered ferroelectric thin film by a CVD method. As a result, it was found that the particular double alkoxide and bis-master alkali alkoxide in which the two elements A and B have the same composition ratio as the film absorbs ultraviolet rays, and the ultraviolet rays accelerate the decomposition reaction to complete the present invention. I arrived. The feature of the present invention is that a CV is obtained by using a specific double alkoxide and a specific bis-master alkoxide.
When the ferroelectric thin film is formed by the D method, the contact portion between the raw material gas and the substrate is irradiated with ultraviolet rays.

The double alkoxide of the present invention includes S
r [Ta (OEt) ₆ ] ₂ , Sr (Ta (OiP
r) ₆ ] ₂ , Sr [Nb (OEt) ₆ ] ₂ , Sr [Nb
(OiPr) ₆ ] ₂ , Ba [Ta (OEt) ₆ ] ₂ , B
a [Ta (OiPr) ₆ ] ₂ , Ba [Nb (OE
t) ₆ ] ₂ , Ba [Nb (OiPr) ₆ ] ₂ and mixtures thereof (in the above, OEt represents an ethoxy group and OiPr represents an isopropoxy group). Further, the bismaster charialkoxide is bismaster chaributoxide or bismaster charipentoxide.

The present inventors, as the raw material alkoxide,
Sr [Ta (OiPr) ₆ ] ₂ , Bi (OtPen) ₃
The absorption characteristics of light in the visible and ultraviolet regions were measured and are shown in FIG. As shown in FIG. 1, the molecular absorption coefficient at 248 nm is 494 (1 · mo) for Sr [Ta (OiPr) ₆ ] _2.
l ⁻¹ · cm ⁻¹ ), Bi (OtPen) ₃ is 630
It is calculated as (1 · mol ⁻¹ · cm ⁻¹ ). In this way, each alkoxide has a large absorption in the ultraviolet region,
This indicates that the decomposition reaction may be accelerated.

Therefore, the inventors of the present invention performed 254 nm and 185 nm while performing CVD using an ordinary CVD apparatus.
Low-pressure mercury lamp with a spectrum of 193, or 193
nm ArF excimer laser light or 248 nm
The KrF excimer laser light of 1 was irradiated to the contact portion between the raw material gas and the substrate. As a result, these alkoxides
Even if it is not irradiated with light, it is thermally decomposed even at a low temperature of about 300 ° C to form a thin film, but when it is irradiated with light from a low-pressure mercury lamp or excimer laser light, the growth rate of the film is several times that when it is not irradiated. Therefore, they have found that a film can be formed even at a lower temperature, and have completed the present invention.

According to the present invention, the substrate temperature during decomposition and deposition can be lowered. As a result, the temperature at which the source gas is heated by the heat of the substrate decreases before it reaches the substrate, so that the amount of the source gas that dissociates or thermally decomposes before reaching the substrate is reduced, and it is substantially decomposed and deposited on the substrate. , The ratio of the two elements A and B of the double alkoxide is equal to the composition ratio of the two elements A and B of the formed film.

As a gas for diluting and mixing the raw materials, argon, nitrogen, or argon or nitrogen containing an oxidizing gas containing an oxygen element is used. Here, the oxidizing gas containing oxygen element means oxygen, ozone, nitrous oxide N
₂ O and the like. However, when UV irradiation is performed in an atmosphere containing these oxidizing gases, decomposition of the raw material gas is promoted more than in the case where UV irradiation is performed in an atmosphere not containing them, but uniform nuclei in the gas phase The probability of generating increases,
Degradation and deposition on the substrate is not always increased. Therefore, in order to form an optimal film, it is necessary to optimize the operating factors such as the wavelength and intensity of ultraviolet rays, the partial pressure of the oxidizing gas, and the substrate temperature.

As the ultraviolet light source of the present invention, 185n
A low pressure mercury lamp with emission lines at m and 254 nm is used. Most of the light intensity of this lamp is at 254 nm.

Further, as the ultraviolet light source of the present invention, 1
An excimer laser that oscillates in the range of 93 nm and 248 nm is used. For example, ArF oscillating at 193 nm
Excimer laser or KrCl oscillating at 222 nm
Examples include an excimer laser or a KrF excimer laser that oscillates at 248 nm.

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.

[0016]

Example 1 10 g of Sr [Ta (OiPr) 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 180 ° C., and argon was kept at 90 m.
At 1 / min, the vapor was sublimated with Sr [Ta (OiPr) ₆ ] ₂ and was sent to a pyrolysis furnace. At the same time, 10 g of Bi [OC (CH ₃ ) ₂ C ₂ H ₅ ] ₃ was placed in another raw material container.
And keep the container at a constant temperature of 80 ° C.
0 ml / min was introduced, and the sublimated vapor was entrained and sent to the pyrolysis furnace. In a pyrolysis furnace, Pt / SiO ₂ / Si
The substrate is heated to 280 ° C., the above two kinds of gases are mixed and guided onto the substrate, and the substrate surface is irradiated with ultraviolet rays of mainly 185 nm and 254 nm from a low-pressure mercury lamp, and decomposed and deposited for 20 minutes. I tightened it up. Finally, crystallization treatment was performed at 750 ° C. for 30 minutes while flowing a mixed gas of oxygen and argon. Thus, a thin film having a thickness of 250 nm was obtained on the substrate. As a result of XRD analysis of this crystal structure, it was SrBi ₂ Ta ₂ O ₉ .

[0017]

Example 2 using a KrF excimer laser that oscillates ultraviolet 248nm instead of the low-pressure mercury lamp, except that the substrate temperature of 270 ° C. performs the same operation as in Example 1, 250 nm SrBi ₂ Ta ₂ O of ₉ films were obtained.

[0018]

[Comparative example] The substrate temperature was set to 3 without using the low-pressure mercury lamp.
The same operation as in Example 1 was performed except that the temperature was set to 20 ° C. to obtain a SrBi ₂ Ta ₂ O ₉ film having a thickness of 250 nm. Element ratio Sr / Ta / of the film when the experiment under the same conditions is repeated
Bi had more variation in the comparative example than in the first and second examples.

[0019]

According to the present invention, when a Bi layered ferroelectric thin film is produced by a CVD method using a specific double alkoxide and a specific bismuth alkoxide as raw materials,
By irradiating the contact portion between the source gas and the substrate with ultraviolet rays,
A good thin film can be obtained. By using this method, the composition and crystal structure of the film can be easily controlled. Further, in semiconductor device manufacturing, the yield is improved, which is a great advantage.

[Brief description of drawings]

FIG. 1 shows Sr [Ta [O used as a raw material of the present invention.
CH (CH ₃ ) ₂ ] ₆ ] ₂ and Bi [OC (CH ₃ ) ₂ C
₂ H ₅ ] ₃ light absorption characteristics

[Explanation of symbols]

A = Sr [Ta (OiPr) ₆ ] ₂ (5.0 × 10 ⁻³ mol / 1) B = Bi (OtPen) ₃ (3.0 × 10 ⁻³ mol / 1)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H01L 21/314 H01L 27/10 451 27/10 451 H01G 4/06 102 27/108 H01L 27/10 651 21/8242

Claims (3)

[Claims] 1. ABi ₂ B ₂ O ₉ (where A = S
A bismuth layered ferroelectric thin film represented by r, Ba, B = Nb, or Ta) is used as a raw material for A and B. A [B (OR) ₆ ] ₂ (where R is C ₂ H ₅ , CH
(CH ₃ ) ₂ ) and a bis-master charibtoxide or a bis-master charipentoxide as a raw material of Bi in the vapor phase growth method, the raw material gas is contacted with the substrate. A method for producing a bismuth layered ferroelectric thin film, which comprises irradiating a portion with ultraviolet light. 2. The ultraviolet light sources are 185 nm and 254 nm
The method for producing a bismuth layered ferroelectric thin film according to claim 1, which is a low-pressure mercury lamp having a bright line at the bottom. 3. The ultraviolet light sources are 193 nm and 248 nm.
The method of manufacturing a bismuth layered ferroelectric thin film according to claim 1, wherein the excimer laser oscillates in the range of.