JPH0543242A - Production of lead titanate zirconate-based thin film - Google Patents

Abstract

PURPOSE:To easily obtain a thin film contg. lead titanate zirconate with good reproducibility by sputtering the lead composition in the thin film by a controlled high-frequency power. CONSTITUTION:A thermally oxidized film is formed on a substrate of quartz glass, etc., and then a platinum film, etc., are formed thereon by DC sputtering to obtain a desired substrate. The substrate is heated to <=200 deg.C, and a lead titanate zirconate sintered body as the target is sputtered by the high-frequency magnetron sputtering method to form a thin film on the substrate. The obtained thin film is heat-treated in an oxidizing atmosphere at the heating and cooling rate of <=2 deg.C/min to produce a lead titanate zirconate-based thin film consisting essentially of the lead titanate zirconate Pb(ZrxTi1-x)O3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film containing lead zirconate titanate Pb (Zr _x Ti _1-x ) O ₃ as a main component used in semiconductor integrated circuits, optical elements, pyroelectric elements, piezoelectric elements and the like. Is.

[0002]

2. Description of the Related Art Lead zirconate titanate Pb (Zr _x Ti _1-x ) O ₃
The system solid solution is a ferroelectric substance having a perovskite structure, has large piezoelectricity and pyroelectricity, and is applied to piezoelectric elements, infrared detectors, and the like. Moreover, what replaced a part of lead by La is known as PLZT, and since it is transparent, application to an electro-optic element is tried. Recently, it has been applied to nonvolatile semiconductor memories and DRAMs by utilizing its large relative permittivity and polarization inversion characteristics.

When a thin film of lead zirconate titanate Pb (Zr _x Ti _1-x ) O ₃ type solid solution is formed by the sputtering method, different from ceramics produced by mixing and sintering stoichiometric raw materials,
Due to the difference in the sputtering rate among lead, zirconium, and titanium and the adhesion rate to the substrate, there are many uncertain factors, and a method for obtaining a stoichiometric composition has not been established.

Although the target composition, sputtering conditions, sputtering gas composition, etc. have been investigated for each case, the present situation is that a method for precisely controlling the composition of the thin film has not been established. As a method of controlling the composition of the thin film by changing the sputtering conditions without changing the composition of the target, JP-A-61-88403 describes a method of controlling the composition by the sputtering gas pressure.

[0005]

With the method of controlling the composition by the sputtering gas pressure described in JP-A-61-88403, it is difficult to precisely control the gas pressure. Therefore, the composition can be reproduced with good reproducibility. It is also difficult to control precisely.

[0006]

[Means for Solving the Problems] When a thin film of a lead zirconate titanate solid solution thin film was formed by a sputtering method, the high frequency power dependence of the thin film composition was investigated in detail. It was found to change in proportion to power. By fixing other sputtering conditions and adjusting the high frequency power, a thin film having a desired composition is obtained.

[0007]

Since the high frequency power can be easily and precisely controlled as compared with the gas pressure, a method for precisely and precisely controlling the composition of the thin film of the lead zirconate titanate solid solution is provided.

[0008]

Example A lead zirconate titanate thin film was formed by a high frequency magnetron sputtering method using a lead zirconate titanate (Pb (Zr _0.5 Ti _0.5 ) O ₃ ) sintered body as a target. Zr / Ti
Although the composition ratio of is set to 50/50, it may be set to an appropriate composition ratio according to the intended use. For the substrate, after forming a thermal oxide film with a thickness of about 1000 Å on a quartz glass substrate or a silicon substrate,
A platinum film having a thickness of about 1000 Å was formed on it by DC sputtering.

A mixed gas of argon and oxygen was used as the sputtering gas. The sputtering gas pressure was 15 Pa. The composition of the thin film was analyzed by inductively coupled plasma emission spectroscopy. Figure 1
As shown in Fig. 3, the composition ratio of titanium and zirconium contained in the thin film varies depending on the high frequency power to be sputtered.
The composition ratio of lead to titanium and zirconium is almost the same as that of Get, but the composition ratio of lead to titanium and zirconium is changed in proportion to the high frequency power. Under the sputtering conditions shown in this figure,
If the high frequency power is 360 W, there will be no excess or deficiency in the amount of lead,
A thin film having the same composition as the target can be obtained. If the sputtering conditions other than high-frequency power, such as the sputtering gas pressure or the mixing ratio of oxygen and argon, are changed, the high-frequency power at which the composition ratio of lead to titanium and zirconium is 1 (Pb / Zr + Ti = 1) will change. There is no change in that it changes in proportion to electric power. Therefore, if sputtering is performed with some high-frequency power and the composition of the obtained thin film is analyzed, Pb / Zr +
The high frequency power that Ti = 1 can be determined. By performing the sputtering with the high frequency power thus determined, a thin film having the same composition as the target can be formed.

When the substrate temperature is set to 600 ° C. or higher, an (as-depo) perovskite structure is obtained at the end of sputtering. However, as shown in FIG. 2, the composition change of lead becomes large, and the composition is controlled when sputtering is performed at a low temperature. It becomes more difficult than

A thin film sputtered at 200 ° C. or lower can be heat-treated to obtain a perovskite structure. As shown in FIG. 3, heat treatment may be performed at 590 ° C. or higher. In addition, when heat treatment is performed, if the temperature is rapidly raised or lowered, the thin film may peel off from the substrate. In order to prevent this, the temperature rising / falling rate may be set to 2 ° C./min or less.

The electrical characteristics of the thin film formed by the above method greatly vary depending on the lead composition, as shown in FIG. When viewed by X-ray diffraction, all of the thin films appear to be a single phase of PZT with a perovskite structure, but the reason why they have the same relative permittivity and remanent polarization as that of the sintered body is that there is no excess or deficiency in the Pb composition and Pb Only a film having a composition satisfying / Zr + Ti = 1. Also, the electric field (anti-electric field) required to reverse the polarization is Pb / Zr +
It is constant from the composition that satisfies Ti = 1. Relative permittivity,
The remanent polarization and the magnitude of the coercive electric field are particularly important characteristics when the ferroelectric substance is applied to an electric device. For example, when the ferroelectric thin film is applied to a non-volatile memory, it is necessary to have a large remanent polarization and a small coercive electric field. Also,
When using a ferroelectric thin film as a capacitor insulating film of DRAM, the relative dielectric constant must be large. It is important to control the lead composition in order to obtain desired electrical characteristics, and it has been clarified that the lead composition in the thin film can be precisely controlled by high frequency power during sputtering.

[0013]

By adjusting the high frequency power, it is possible to easily form a thin film of the lead zirconate titanate solid solution having a desired composition with good reproducibility.

[Brief description of drawings]

FIG. 1 is a diagram showing a high frequency power dependency of a composition ratio of a sputtered thin film.

FIG. 2 High frequency power dependence of composition ratio of sputtered thin film (600
It is a figure showing the case (sputtering at ° C).

FIG. 3 is a diagram showing a change in crystal structure due to heat treatment of a sputtered thin film.

FIG. 4 is a diagram showing changes in electrical characteristics of a sputtered thin film depending on the composition.

Front Page Continuation (72) Inventor Eiji Takeda 1-280 Higashi Koikekubo, Kokubunji, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd.

Claims (3)

[Claims] 1. When forming a thin film containing lead zirconate titanate Pb (Zr _x Ti _1-x ) O ₃ as a main component by a high frequency sputtering method, controlling the composition of lead in the thin film by high frequency power. A method for producing a lead zirconate titanate-based thin film, comprising: 2. The method for producing a lead zirconate titanate-based thin film according to claim 1, wherein the sputtering is performed at a substrate temperature of 200 ° C. or lower, and then the heat treatment is performed in an oxidizing atmosphere. 3. The lead zirconate titanate-based thin film according to claim 2, wherein the heat treatment is performed in an oxidizing atmosphere, and the temperature rising rate and the temperature lowering rate are 2 ° C. or less per minute. Manufacturing method.