JPH10251022A - Formation of thin pzt film, and thin pzt film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thin PZT film having high residual polarization, satisfactory flatness, surface properties and crystallinity by formed an underlayer of Pb-Ti oxide having a specified compsn., applying a precursor soln. for forming a thin PZT film on the underlayer and heat-treating it. SOLUTION: An underlayer of PbTix O(2x+1) (where 0.2<=X<=0.8) is formed on a substrate preferably in 2-15nm thickness and the objective thin PZT film is formed on the underlayer preferably by a sol-gel method by which a precursor soln. for forming a thin PZT film is applied on the underlayer and heat-treated. The precursor soln. is prepd. by dissolving a lead carboxylate such as lead acetate trihydrate or a lead compd. such as lead isopropoxide and a titanium alkoxide such as titanium ethoxide or titanium butoxide or a titanium compd. such as a titanium-acetylacetone complex in acetic ester or alcohol to 0.5-3wt.% concn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nonvolatile semiconductor memory device, a thin film capacitor, a pyroelectric (IR) detector,
Ferroelectric devices such as sensors, surface acoustic wave substrate optical waveguides, optical storage devices, spatial light modulators, and frequency doublers for diode lasers, dielectric devices, pyroelectric devices, piezoelectric devices, and electro-optics The present invention relates to a method of forming a PZT (lead zirconate titanate) thin film and a PZT thin film used in an apparatus or the like, and more particularly to a method of forming a PZT thin film in which an underlayer is formed between a substrate and a PZT thin film, and a PZT thin film.

[0002]

2. Description of the Related Art A sol-gel method is known as a method for forming a PZT thin film used for the above-mentioned applications. Also, this P
Upon the ZT thin film formed on a substrate, a method of forming the base layer of PbTiO ₃ by a coating with and heat treatment of PbTiO ₃ precursor solution is described in Japanese Patent Laid-Open No. 3-69512.

That is, as described in the same publication, this PbTiO ₃
Both the underlayer and PZT are made of a perovskite phase, but the crystallinity of PZT is greatly affected by the material of the undersubstrate. In contrast, PbTiO ₃ is the material of the base substrate, since its crystallization degree is not affected, to form a PbTiO ₃ undercoat layer on the substrate,
By forming a PZT thin film on this PbTiO ₃ underlayer, a good PZT film can be obtained without being affected by the material of the underlying layer.
It becomes possible to form a T thin film.

The formation of the PbTiO ₃ underlayer causes the formation of PZ
The surface properties such as the flatness of the surface of the T thin film are also improved.

[0005]

As a result of various studies, it has been found that the remnant polarization of a PZT thin film is reduced when a PbTiO ₃ underlayer is formed, as described in JP-A-3-69512.

An object of the present invention is to prevent a decrease in remanent polarization of a PZT thin film formed on a substrate via an underlayer.

[0007]

According to the method of forming a PZT thin film of the present invention, PbTi _X O _{(2X + 1)} (0.2
.Ltoreq.X.ltoreq.0.8), a precursor solution for forming a PZT thin film is applied on the underlayer, and heat-treated to form a PZT thin film.

That is, the present inventors have conducted various studies to solve the above-mentioned problems, and found that a PbTi _X O _{(2X + 1)} layer having a specific composition is formed as an underlayer to obtain a PZT layer.
The inventors have found that a decrease in the remanent polarization of the T thin film can be prevented, and have arrived at the present invention.

In the present invention, the PbTi _X O _{(2X + 1)} underlayer is formed by applying a precursor solution for forming a PbTi _X O _{(2X + 1)} underlayer on a substrate and then performing a heat treatment. Preferably, the thickness of the underlayer is 2 to 15 nm. _{Further, PbTi X O (2X + 1} ) PbTi X O (2X + 1) of the underlying layer forming precursor solution concentration is preferably from 0.5 to 3 wt%.

The PZT thin film of the present invention is formed by such a method of forming a PZT thin film of the present invention.

[0011]

Embodiments of the present invention will be described below in detail.

In the present invention, P formed as an underlayer is
In the bTi _X O _{(2X + 1)} composition, when X exceeds 0.8, the remanent polarization of the PZT thin film formed thereon is reduced. If X is less than 0.2, the surface roughness of the PZT thin film formed thereon becomes high and the remanent polarization decreases.

When the thickness of the PbTi _X O _{(2X + 1)} underlayer according to the present invention is excessively small, the effect of improving the surface properties, crystallinity, etc. of the PZT thin film due to the formation of the underlayer is sufficiently improved. On the contrary, if the thickness is excessively large, excessive Pb migrates into the PZT thin film and deteriorates the PZT thin film. Therefore, PbTi _X O _{(2X + 1)} (0.2 ≦ X ≦ 0.8)
The thickness of the underlayer is preferably 2 to 15 nm.

Such PbTi _X O _{(2X + 1)} (0.2 ≦
(X ≦ 0.8) The thickness of the PZT thin film formed on the underlayer is usually about 100 to 300 nm. If the film thickness is less than 100 nm, it is difficult to obtain insulation because it is too thin, and if it exceeds 300 nm, grain growth is severe and the surface tends to be rough.

In order to form the PZT thin film of the present invention, first, the above PbTi _X O _{(2X + 1)} (0.2 ≦ X ≦
0.8) Form an underlayer.

Here, the substrate is Pt / Ti / Si
O ₂ / Si substrate, Pt / Ta / SiO ₂ / Si substrate, P
t / SiO ₂ / Si substrate, Ir / IrO ₂ / Si substrate,
Pt / TiN / SiO ₂ / Si substrate, Pt / Ir / Si
O ₂ / Si substrate, (Pt-Ir alloy) / IrO ₂ / Si
A substrate, a Pt / Ir / IrO ₂ / Si substrate, or the like can be used.

PbTi _X O _{(2X + 1)} (0.2 ≦ X ≦ 0.
8) The underlayer is preferably formed by a sol-gel method in which the precursor solution is applied to a substrate and then heat-treated. In this case, the precursor solution may be a carboxylate such as lead acetate / trihydrate. A lead compound such as an alkoxide such as isopropoxide of iron or lead, a titanium alkoxide such as titanium ethoxide or titanium butoxide, or a titanium compound such as an acetylacetone complex of Ti are mixed at a predetermined Pb: Ti ratio, and Pb and Ti are mixed. Total concentration in terms of oxide of PbTi _X O _{(2X + 1)}
What was melt | dissolved in the solvent so that a density | concentration becomes 0.5-3 weight% can be used. If the concentration of the precursor solution is less than 0.5% by weight, the thickness of the formed underlayer is too small, and if it exceeds 3% by weight, the thickness of the formed underlayer is too large. An underlayer having a small thickness cannot be formed.

Examples of the solvent for the precursor solution for forming the underlayer include acetates such as ethyl acetate, propyl acetate, butyl acetate and isoamyl acetate, and alcohols such as ethanol, propanol, butanol and 2-methoxyethanol. Can be

PbTi _X O _{(2X + 1)} (0.2 ≦ X ≦ 0.
8) The base layer is prepared by applying the above-mentioned PbTi _x O _{(2X + 1)} base layer forming precursor solution on a substrate by spin coating or the like, and then pre-baking at 100 to 450 ° C. for about 1 to 15 minutes. It is formed.

The PZT thin film of the present invention is obtained by coating a precursor solution for forming a PZT thin film on a PbTi _X O _{(2X + 1)} (0.2 ≦ X ≦ 0.8) underlayer formed in this manner. It is formed by a sol-gel method of applying and heat-treating.

The precursor solution for forming a PZT thin film includes a lead compound, a zirconium compound and a titanium compound in a predetermined Pb: Zr: Ti ratio, and a mixture of Pb, Zr and Ti.
Can be used as dissolved in a solvent such that the total concentration in terms of oxide is 5 to 20% by weight. If the concentration of the precursor solution is less than 5% by weight, the thickness of the PZT thin film formed by one application is too small, and the PZT thin film having a desired thickness is formed.
The number of coatings for forming the T thin film is undesirably increased. If the concentration exceeds 20% by weight, cracks are likely to occur.

The lead compound, the titanium compound and the solvent of the precursor solution for forming a PZT thin film are the same as the above PbT
i _X O _{(2X + 1)} can be the same as those exemplified in the explanation of the underlying layer forming precursor solution, as the zirconium compound, zirconium ethoxide, zirconium alkoxides such as zirconium butoxide, acetylacetone Zr A complex or the like can be used.

In general, the Pb: Zr: Ti ratio of a PZT thin film is expressed by a molar ratio of Pb: (Zr + Ti) = 1.20 to 1.0.
It is preferable that Zr: Ti = 7 to 2: 3 to 8 at 5: 1.

The PZT thin film of the present invention is made of PbTi _x O
_{(2X + 1)} (0.2 ≦ X ≦ 0.8) The precursor solution for forming a PZT thin film is applied on an underlayer by a spin coating method, and then temporarily calcined at 100 to 450 ° C. for about 1 to 15 minutes. This coating and calcination are repeated as necessary until a desired film thickness is obtained, and finally, calcination is carried out at 550 to 750 ° C. for 1 minute to 1 hour to crystallize.

[0025]

The present invention will be described more specifically below with reference to examples and comparative examples.

Examples 1 to 5 and Comparative Examples 1 to 4 A PZT thin film was formed on a substrate via a PbTi _x O _{(2X + 1)} underlayer.

First, the substrate (Pt / Ti / SiO ₂ / S)
i) A precursor solution for forming a PbTi _X O _{(2X + 1)} underlayer is applied thereon by spin coating at 3000 rpm for 15 seconds and calcined at 400 ° C. for 5 minutes, and then a PZT thin film is formed. The precursor solution for application was applied and calcined under the same conditions as described above, and this application step was further performed 4 times, and after a total of 5 applications, crystallization was performed at 600 ° C. for 1 hour (however, In Comparative Example 1, no underlayer was formed.) PbTi _x O formed
The thickness of the _{(2X + 1)} underlayer is as shown in Table 1, and the thickness of the PZT thin film is 200 nm.

The used precursor solution for forming the PbTi _X O _{(2X + 1)} underlayer was prepared by adding lead acetate and titanium ethoxide to 2-
Pb: Ti ratio and Pb shown in Table 1 in methoxyethanol
This is a solution dissolved to have a Ti _X O _{(2X + 1)} concentration.

The precursor solution for forming a PZT thin film is composed of lead acetate, titanium ethoxide and zirconium ethoxide.
-In methoxyethanol, Pb: Ti: Zr = 1.1:
0.52: 0.48 (molar ratio), a solution in which Pb, Ti and Zr are dissolved to a total concentration of 10% by weight in terms of oxide.

After measuring the remanent polarization of the obtained PZT thin film,
The results are shown in Table 1. Further, the flatness of the surface of the PZT thin film was examined by SEM, and the good (良) or bad (×) is also shown in Table 1.

From Table 1, it can be seen that PbTi _X O _{(2X + 1)} (0.2 ≦
X ≦ 0.8) It can be seen that the PZT thin film formed via the underlayer has good surface properties and large residual polarization.

[0032]

[Table 1]

[0033]

As described above in detail, according to the method for forming a PZT thin film and the PZT thin film of the present invention, flatness, surface properties,
A high-performance PZT thin film having remarkably good crystallinity and the like and large remanent polarization is provided.

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI C30B 29/32 C30B 29/32 Z

Claims (5)

[Claims] An underlayer made of PbTi _X O _{(2X + 1)} (where 0.2 ≦ X ≦ 0.8) is formed on a substrate, and a precursor solution for forming a PZT thin film is formed on the underlayer. And forming a PZT thin film by heat treatment. 2. The method according to claim 1, wherein PbT is formed on the substrate.
i _X O _{(2X + 1)} denoted coating an underlying layer forming precursor solution, characterized by subsequently heat-treated to form the undercoat layer PZ
Method for forming T thin film. 3. The method according to claim 1, wherein the underlayer is formed to have a thickness of 2 to 15 nm. 4. The method according to claim 2, wherein the PbTi _X O
_{(2X + 1)} PbTi _X O _{(2X + 1) in the} underlayer forming precursor solution
PZT having a concentration of 0.5 to 3% by weight
A method for forming a thin film. 5. A PZT thin film formed by the method according to claim 1.