JPH1192937A - Synthesizing method of plzt thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely synthesize a thin film of good quality without intrusion of foreign matters even in a large area by MOCVD method by using an org. metal source material containing Pb, La, Zr and Ti which does not cause nuclear producing reaction in a gas phase and which exhibits excellent step coverage. SOLUTION: When a PLZT thin film is synthesized by MOCVD method, an org. metal source material described below is used as the source material. The org. metal source material contains Pb, La, Zr, Ti which constitute the thin film, does not cause nuclear producing reaction in a gas phase and has about >=80% step coverage. As for the org. metal source material, for example, Pb(C2 H5 )4 , La(C11 H19 O2 )3 , Zr(C11 H19 O2 )4 and Ti(C11 H1 9O2 )2 (OCH3 )2 are preferably used as the Pb source, La source, Zr source and Ti source, respectively. The synthesis is carried out under conditions of >=500 deg.C, preferably 500 to about 700 deg.C, under <=5 Torr, preferably <=1 Torr pressure. Thereby, a PLZT thin film with excellent characteristics can be obtd. without post-annealing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for synthesizing a PLZT thin film by a chemical vapor deposition method using an organic metal material.

[0002]

2. Description of the Related Art PLZT [(Pb, La) (Zr, T
i) O ₃ ] ferroelectric thin film is made of PbTiO ₃ , PZT [P
Like other PZT-based ferroelectric thin films such as b (Zr, Ti) O ₃ ], it has been put to practical use in various fields by utilizing its pyroelectricity, piezoelectricity, ferroelectricity, electro-optic effect and the like. ing. Recently, as a method of manufacturing this PLZT ferroelectric thin film,
OCVD (Metalorganic Chemical)
Attempts have been made to adopt the 1 Vapor Deposition method.

[0003] The MOCVD method is a technique in which an organic metal compound as a raw material is sent as gas molecules to a reaction chamber, and a thin film is deposited on a substrate by a chemical reaction. PL
When synthesizing an oxide film containing multiple elements such as a ZT ferroelectric thin film, the MOCVD method is different from a physical film forming method such as a sputtering method or a laser ablation method, and an oxygen partial pressure is arbitrarily selected. It is possible to form a film under extremely mild conditions without containing high energy particles. Another feature is that the deposition rate is higher than that of a deposition method such as a sputtering method or a laser ablation method.

Incidentally, a PLZT-based thin film needs to use, as starting materials (source materials), four organometallic materials each containing Pb, La, Zr, and Ti constituting the thin film.
Conventionally, when a general PLZT-based thin film is synthesized by the MOCVD method, the combination is performed as shown in Table 1 below.

[0005]

[Table 1]

The synthesis temperature of a PLZT-based thin film is generally 50
Although the temperature is set to 0 to 700 ° C., when a raw material that causes a nucleation reaction in the gas phase in this temperature range is included, foreign matter generated by nucleation is mixed into the film, and a high quality PL is formed.
ZT-based thin films cannot be synthesized.

Here, the nucleation reaction will be briefly described. Before the organometallic raw material gas reaches the substrate, it is decomposed (reacted) in the gas phase by the radiant heat of the substrate, and the oxide nucleus (powder) is formed. ) Is called a "nucleation reaction in the gas phase". Originally, the source gas reaches the substrate surface,
The film grows by the reaction, but when a nucleation reaction occurs in the gas phase, the nucleus of the oxide is mixed into the film and the quality of the film is significantly deteriorated.

The nucleation reaction is described, for example, in "Electronic Ceramics", July 1993, No. 49-
It is reported in a special article on page 54, "Techniques for manufacturing thin films by the CVD method", and in particular, on page 51, right column, lines 6 to 5
The 2, left column line 10 and Table _{2, Zr (t-OC 4} H 9) 4 is used as a raw material for Zr takes place nucleation reactions in the gas phase, it is not able to form a good quality PLZT-based thin film I have.

[0009] Therefore, in the prior art, of the four combinations shown in Table 1 above, the combination is d at present. However, in the shift to a large-sized substrate for mass production, Ti (i-OC ₃ H ₇₎ used as a Ti raw material, which has conventionally been considered not to cause a nucleation reaction due to an increase in radiation heat from the substrate. ₄ )
It has been found that the nucleation reaction occurs, which is problematic.

When a PLZT-based thin film is synthesized,
The step coverage is a problem. And the step coverage, for example, when the step portion 1 as shown in FIG. 7 (A), covered with a coating 2 as shown in FIG. (B), the most to the thickness d _max of the thickest portion of the film 2 The ratio of the thickness d _mim of the thin portion, that is, (d _mim / d
_max ) × 100 (%), usually, d _max is the thickness covering the plane portion of the step portion 1, and d _mim is the thickness covering the vertical side _surface of the step portion 1. The larger the value, the better.

As described above, the synthesis temperature of the PLZT-based thin film is generally set at 500 to 700 ° C., but this temperature is the crystal growth temperature of the PLZT-based thin film. It is known that the synthesis temperature becomes higher as the substitution amount increases.

In general, in order to obtain a film having a large step coverage, it is more preferable to synthesize in a temperature range where the surface reaction is controlled more than the material supply is controlled as shown in FIG. 6, for example. I have. Also, (Pb _1-y La _y )
(Zr _x Ti _1-x ) _{1-y / 4} O ₃ (y = 0.15, x =
Although the synthesis temperature of 0.45) is 650 ° C. or higher,
The step coverage in the conventional raw material combinations b, c, and d shown in Table 1 was 70%, 70%, and 53%, respectively.
It has not cleared 80% of the practical level.

On the other hand, there has been attempted a method of forming a film at a low synthesis temperature up to a temperature region (surface reaction rate-determining region) where a relatively large step coverage can be obtained. However, in this temperature region, the PLZT-based thin film does not sufficiently crystallize, so that post-annealing (heat treatment) is required (the film will have deteriorated characteristics without post-annealing), and the number of steps will increase accordingly. Such a problem becomes a problem particularly in a region where the amount of La and the amount of Zr are large.

The present invention has been made in consideration of the above-mentioned matters, and an object thereof is to provide a high-quality PLZ even in a large area.
An object of the present invention is to provide a method for synthesizing a PLZT-based thin film that can reliably synthesize a T-based thin film.

[0015]

According to the present invention, there is provided a method for synthesizing a PLZT-based thin film by MOCVD, comprising the steps of: forming an organic material containing Pb, La, Zr, and Ti constituting the PLZT-based thin film; A metal raw material does not cause a nucleation reaction in the gas phase, and a raw material excellent in step coverage is used.

More specifically, Pb (C
₂ H _{5) 4} and, La material as _{La (C 11 H 19 O 2} ) 3
And Zr (C ₁₁ H ₁₉ O ₂ ) ₄ as a Zr raw material and Ti (C ₁₁ H ₁₉ O ₂ ) ₂ (OCH ₃ ) ₂ as a Ti raw material, respectively. Combined.

According to the method for synthesizing a PLZT-based thin film,
No foreign matter is mixed into the PLZT-based thin film, and a high-quality film can be synthesized in a large amount.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

Example 1 First, a TiO ₂ film was formed on the surface of a 6-inch diameter Si substrate at a synthesis temperature of 250 to 700 ° C. using various Ti raw materials, and the presence or absence of a nucleation reaction was examined. A film was formed on a pattern having an aspect ratio of 0.5 or more, and the step coverage was measured. The Ti raw material used here is T
_{i (i-OC 3 H 7} ) 4, Ti (C 11 H 19 O 2)
_{2 (i-OC 3 H 7} ) 2, Ti (C 11 H 19 O 2) 2 C
l ₂ , Ti (C ₁₁ H ₁₉ O ₂ ) ₂ (OCH ₃ ) ₂ .

FIG. 1 shows Ti from various Ti raw materials.
It shows the relationship between the deposition rate of the O ₂ film and the substrate temperature, and the numbers in the figure correspond to the Ti raw materials, respectively. From this figure, Ti (i-OC ₃ H ₇ ) indicated by a number
₄ was found to cause nucleation reaction in the gas phase at a synthesis temperature of more than 500 ° C.. The step coverage of these steps was also examined. Table 2 below shows the presence or absence of a nucleation reaction of various Ti raw materials and the measurement results of the step coverage. The numbers in Table 2 correspond to the numbers in FIG.

[0021]

[Table 2]

From Table 2 above, it can be seen that Ti (C ₁₁ H ₁₉ O ₂ )
_{It was found that 2} (OCH ₃ ) ₂ did not cause a nucleation reaction and was excellent in step coverage, which reached a practical level of 80% or more.

A comparative experiment was carried out for each of the raw materials Zr, Pb and La in the same manner as for the Ti raw material. That is, as the Zr raw material, Zr (C ₁₁ H ₁₉ O ₂ ) ₄ ,
Zr (t-OC ₄ H ₉ ) ₄ , as a Pb raw material,
Pb (C ₂ H ₅ ) ₄ and Pb (C ₁₁ H ₁₉ O ₂ ) ₂ are converted to L
a) As a raw material, La (C ₁₁ H ₁₉ O ₂ ) ₃ was used, and a 6-inch diameter Si was used at a synthesis temperature of 250 to 700 ° C.
A ZrO ₂ film, a PbO film, and a La ₂ O ₃ film are formed on the surface of the substrate, and the presence or absence of a nucleation reaction is examined.
Films were formed on five or more patterns, and the step coverage was measured.

FIG. 2 shows the relationship between the deposition rate of the ZrO ₂ film from various Zr raw materials and the substrate temperature.
Shows the relationship between the deposition rate of the PbO film from various Pb materials and the deposition rate of the La ₂ O ₃ film from the La material and the substrate temperature. In addition, Tables 3 to 5 below show the presence or absence of a nucleation reaction of various Zr raw materials, various Pb raw materials, and La raw materials, and measurement results of step coverage. The numbers in Tables 3 to 5 correspond to the numbers in FIGS. 2 and 3.

[0025]

[Table 3]

[0026]

[Table 4]

[0027]

[Table 5]

From the above measurement results, Zr raw material was Zr.
(C ₁₁ H ₁₉ O ₂ ) ₄ becomes Pb (C
₂ H ₅ ) ₄ is used as La (C ₁₁ H ₁₉ O ₂ ) ₃
Was found to be optimal.

Therefore, Pb (C ₂ H ₅ )
₄ as La material, La (C ₁₁ H ₁₉ O ₂ ) ₃ as Zr
A PLZT-based thin film was synthesized using Zr (C ₁₁ H ₁₉ O ₂ ) ₄ as a raw material and Ti (C ₁₁ H ₁₉ O ₂ ) ₂ (OCH ₃ ) ₂ as a Ti raw material. PLZT of this embodiment
Pb (C
₂ H _{5) 4} and, La material as _{La (C 11 H 19 O 2} ) 3
, Zr (t-OC ₄ H ₉ ) ₄ as a Zr raw material, Ti
Material as _{Ti (i-OC 3 H 7} ) 4 was synthesized PLZT-based thin film was formed using respectively.

Table 6 below shows the results of the synthesis of the PLZT-based thin film of the above-described embodiment (indicated by the symbol I in the table) and the PLZT-based thin film of the comparative example (indicated by the symbol II in the table). .

[0031]

[Table 6]

From Table 6 above, it can be seen that the PLZT-based thin film of this example has very favorable characteristics.
That is, Pb, La, Z constituting the PLZT thin film
The organometallic raw materials containing r and Ti do not cause a nucleation reaction in the gas phase, and by using raw materials having excellent step coverage, and by setting the synthesis temperature to 500 ° C. or higher, a large area can be obtained. Even in this case, a high-quality PLZT-based thin film can be synthesized, and therefore, mass production of sensor devices such as a pyroelectric infrared thin film element for detecting infrared rays and various memories has become possible.

Next, the relationship between the deposition rate of the film and the substrate temperature when the pressure during film formation was variously changed, and the PLZ
The composition, synthesis conditions, and step coverage of the T-based thin film were examined. This will be described as Example 2.

Example 2 Ti (C ₁₁
Using H ₁₉ O ₂ ) ₂ (OCH ₃ ) ₂ , the pressure at the time of film formation was changed variously, and Ti was formed on a Si substrate having a diameter of 6 inches.
O ₂ was deposited.

FIG. 4 shows Ti (C) used in the present invention.₁₁H₁₉
O_Two)_Two(OCH_Three)_TwoFrom TiO _TwoWhen forming a film
It shows the relationship between deposition rate and substrate temperature at
According to the figure, by reducing the pressure during film formation,
The surface reaction rate-limiting region can be shifted to higher temperatures
You can see that. That is, the pressure during film formation is 10 Torr.
5 Torr or 1 Torr than when
Is better. This means that Pb (C
_TwoH_Five)_Four, La (C₁₁H₁₉O_Two)_Three, Zr (C₁₁H₁₉
O_Two)_FourTo form a PbO film and La, respectively._TwoO_Threefilm,
ZrO_TwoThe same is true when a film is formed, and FIG.
Pb (C used in the invention_TwoH_Five)_FourA PbO film from
The relationship between the synthesis temperature and the deposition temperature
You.

Next, when the composition of the PLZT-based thin film and the synthesis conditions (synthesis temperature, pressure during film formation) were variously changed, the step coverage was examined. The results shown in Table 7 below were obtained. . The temperature was set to 500 to 700 ° C., which is preferable as the synthesis temperature of the PLZT-based thin film, and the step coverage was measured by forming a film on a pattern having an aspect ratio of 0.5.

[0037]

[Table 7]

From Table 7 above, it can be seen that, at the same synthesis temperature, the lower the pressure during film formation, the more excellent step coverage can be obtained. In particular, the pressure during film formation is 1 Torr
Or less than this, PLZ with excellent step coverage
A T-based thin film can be obtained. As described above, by reducing the pressure at the time of film formation, a film with good step coverage can be formed at the crystal growth temperature of the PLZT-based thin film. Thus, a PLZT-based thin film having excellent characteristics can be synthesized without post-annealing, and a PLZT-based thin film can be synthesized more easily than in the past.

[0039]

As described above, according to the present invention, P
In the method for synthesizing an LZT-based thin film, the organometallic material comprising Pb, La, Zr, and Ti constituting the PLZT-based thin film does not cause a nucleation reaction in a gas phase and has excellent step coverage. Since foreign materials are not used in the PLZT-based thin film, a high-quality film can be synthesized in large quantities. Therefore, various sensor devices and various memories using the PLZT-based thin film can be mass-produced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a deposition rate of a TiO ₂ film from various Ti raw materials and a substrate temperature.

FIG. 2 is a diagram showing a relationship between a deposition rate of a ZrO ₂ film from various Zr raw materials and a substrate temperature.

FIG. 3 is a diagram showing a relationship between a deposition rate of a PbO film from various Pb raw materials and a deposition rate of a La ₂ O ₃ film from a La raw material and a substrate temperature.

FIG. 4 shows Ti (C ₁₁ H ₁₉ O ₂ ) ₂ (O
FIG. 4 is a diagram showing a relationship between a deposition rate and a substrate temperature when changing a reactor pressure when a TiO ₂ film is formed from CH ₃ ) ₂ .

FIG. 5 shows Pb (C ₂ H ₅ ) ₄ to Pb used in the present invention.
FIG. 3 is a diagram illustrating a relationship between a synthesis temperature and a deposition temperature when a reactor pressure when an O film is formed is changed.

FIG. 6 is a diagram showing a relationship between a general deposition rate of a thin film and a synthesis temperature.

FIG. 7 is a diagram for explaining step coverage.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Katsuhiko Tomita, the inventor, 2nd Higashi-cho, Kichijoin-miya, Kyoto, Kyoto, Japan Inside the Horiba Seisakusho Co., Ltd. HORIBA, Ltd.

Claims (3)

[Claims] 1. A method for synthesizing a PLZT-based thin film by MOCVD, wherein an organometallic raw material containing Pb, La, Zr, and Ti constituting the PLZT-based thin film does not cause a nucleation reaction in a gas phase, and A method for synthesizing a PLZT-based thin film, comprising using a raw material having excellent step coverage. 2. Pb (C ₂ H ₅ ) ₄ as a Pb raw material;
La (C ₁₁ H ₁₉ O ₂ ) ₃ as a La raw material, Zr (C ₁₁ H ₁₉ O ₂ ) ₄ as a Zr raw material, and Ti as a Ti raw material
(C ₁₁ H ₁₉ O ₂ ) ₂ (OCH ₃ ) ₂
The PL according to claim 1, which is synthesized under a temperature condition of 00 ° C or higher.
A method for synthesizing a ZT-based thin film. 3. The method for synthesizing a PLZT-based thin film according to claim 2, wherein the pressure at the time of film formation is 5 Torr or less.