JPH03271360A - Production of thin film of ferroelectric substance - Google Patents

Abstract

PURPOSE:To produce a high quality thin film of PZT type ferroelectric substance at low substrate temp. with high throughput by using a metal as simple substance as an evaporation source and introducing oxygen gas into a vapor deposition reaction chamber. CONSTITUTION:A thin film of PZT type ferroelectric substance, such as lead titanate, lead titanate-lanthavate, lead zirconate-titanate, and lead titavate- zirconate-lanthavate, is produced by a multicomponent vapor deposition method. In the above producing method, respective compositions of metallic elements are independently controlled by using metals as simple substances, such as titanium and lead, or the oxides of single metals as evaporation sources. Further, at the time of introducing oxygen gas as a reactant gas into a vapor deposition reaction chamber, this oxygen gas is preferentially introduced onto a substrate. At this time, it is preferable that a part or the whole of the oxygen gas is introduced after ionization and the substrate surface is irradiated with the resulting ions, if necessary, in the accelerated state. By this method, reaction at the substrate surface can be accelerated, and the high quality this film of ferroelectric substance can be formed efficiently at low temp.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for manufacturing a PZT-based ferroelectric FiJ film, and is applicable to non-volatile random access memory, optical memory, ultrasonic transducer, pyroelectric Used for manufacturing devices, etc.

[Summary of the invention]

The present invention uses the vapor deposition method as the method for forming PZT-based ferroelectric thin films, resulting in an inexpensive, safe, and high-speed film forming process, improves quality reproducibility using the multi-source vapor deposition method, and uses oxygen gas or ions. By introducing this method, a high quality ferroelectric thin film can be obtained.

[Conventional technology]

PZT-based ferroelectric materials have a high Curie point and large spontaneous polarization, so they have been applied to various functional elements such as piezoelectric elements and electro-optical elements, mainly in the form of ceramics, but in recent years, they have been applied to LSI etc. Advances in thin film manufacturing methods have made it possible to obtain thin films, and they are now being applied to semiconductor memories.

Conventionally, methods for manufacturing this type of ferroelectric thin film include
There are CVD methods, sol-gel methods, sputtering methods, etc. For example, as an example of film formation by sputtering method, Croteau e
t aljpn, J, ^ppl, Phys,, 26
Supplement26-2. (1987) 18.

[Problem to be solved by the invention]

High-temperature sputtering, which is often used among conventional techniques because it is easy to obtain ferroelectric properties, has a complicated equipment configuration and a slow film deposition rate of about 2 (nm) per minute, making it difficult to mass-produce at least LSI devices. It's not the right direction.

Although the CVD method has a high film formation rate, it has problems such as poor film thickness distribution and the use of toxic gas. The sol-gel method is 1
In one coating process, a thickness of only about 300 (/110) can be obtained. For example, in order to obtain a film thickness of 1 (ns+), it is necessary to repeat the process three times, and the yield rate due to dust adhesion, etc. Problems such as cracking of the film when removing the alkyl group by filing have also been pointed out.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention uses a reactive multi-component vapor deposition method to produce a PZT-based film! A lf dielectric thin film is formed. In addition, in order to improve the quality of the thin film, oxygen, which is a reactive gas, is ionized as necessary.

[Effect]

If a PZT-based ferroelectric film is formed according to the present invention, first,
The unique characteristics of the vapor deposition method are that the film formation rate is high, the equipment configuration is simple, and there is little contamination. In addition, by employing multi-component deposition, the composition of each metal element is independently controlled to obtain the optimum metal composition, and by introducing oxygen gas, reactive oxygen is supplied or supplied to the substrate surface. Furthermore, by supplying ionized oxygen to be introduced, reactions on the substrate surface are promoted, and crystals grow even at relatively low temperatures.

〔Example〕

Embodiments of the present invention will be described based on the drawings.

FIG. 1 shows a binary vapor deposition apparatus used to carry out the method of manufacturing a PZT-based ferroelectric thin film according to the present invention.

A substrate 2 is placed in a vacuum chamber 1. Lead evaporation source 3. Titanium evaporation64. The oxygen ion sources 5 are arranged so that the particles or ions are directed toward the surface of the substrate 2. The substrate 2 is rotated by a motor 6 so that the film thickness distribution and thickness are uniform. Also, the board 2 has power ll! 7 and a substrate heater vA9 connected via a brush 8, the substrate is heated evenly.

Using the above apparatus, the temperature of the substrate 2 was set to 400 ('C), a (100) oriented PT was used as the substrate 2, and the oxygen gas flow rate was set to 20 (cd) per minute converted to standard conditions. Created. The composition ratio of lead and titanium is approximately 1
It is desirable to have a one-on-one relationship, but in order to achieve this,
The present inventors monitored the bottom film using a quadrupole mass spectrometer and independently controlled the amounts of lead and titanium evaporated from the lead evaporation H3 and the titanium evaporation source 4, respectively. Oxygen ions were accelerated to 3000 nm by a grid (not shown) in the oxygen ion source 5.

When a film of lead titanate was formed under the conditions controlled as described above, a transparent film was formed and a film formation rate of 50 (nm) per minute was obtained. This is more than 10 times the sputtering method. When the film structure was analyzed from the X-ray analysis pattern, it was found that PbTi0z
A pattern corresponding to the above was observed, and in particular, the (1001) orientation of tetrabutyl accounted for 70%, indicating that epitaxial growth was successful. The present inventors attached an Au upper electrode to the sample prepared by the above method to a thickness of 1(-), and added a so-called Sawyer-
When the electrical hysteresis curve was measured using the Tower circuit, a residual polarization (i15 (μC/cya-'')) was obtained. This value is sufficient for application to highly integrated random access memory.

In sputtering and CVD methods, a substrate temperature of approximately 550 (°C) or higher is required to obtain good crystallinity and ferroelectricity through epitaxial growth as in this example. The (001) orientation of PbTiOs was observed even at a substrate temperature of 300 ('t: ).

The reason why epitaxial film formation can be performed at a lower temperature in this way is thought to be because oxygen ions act as active reaction radicals, and in the case of this example.

Gives kinetic energy by accelerating oxygen ions,
This further promotes surface reactions. Oxygen ions with a certain kinetic energy exist even in normal reactive sputtering methods, but in the case of reactive sputtering methods, sputtering using only oxygen gas has poor sputtering efficiency (i.e., it is difficult to obtain a constant film formation rate). For this reason, it is common to mix argon gas with several 10% oxygen gas.In such cases, it is thought that the oxidation reaction of the metal is inhibited by the collision of argon ions on the substrate surface. However, in the present invention, since the vapor deposition method is used,
In such surface reactions, unnecessary and harmful inert gases and ions are not present, but rather a sufficient amount of oxygen is supplied for the oxidation reaction of the metal. This effect is noticeable even if oxygen is not necessarily ionized, and in fact, the present inventors provided a nozzle for simply introducing oxygen gas instead of the oxygen ion source 5 and supplied the oxygen gas to the surface of the substrate 2. Even when the film is formed at a substrate temperature of 300 (T:) or higher
It was confirmed that bTiO3 could be epitaxially grown.

For mass production of I, SI, etc. using PZT-based ferroelectric materials,
The process becomes unstable due to oxidation of the surface of the metal placed in each of the evaporation sources 3 and 4 in the film-forming chamber 1, but as the evaporation source 3.4, PbO or TiO□ is used instead of a single metal. Not only is there no problem if a metal oxide is used, but the quality of the thin film can be further improved by oxidizing the metal in advance.

The delay plate 10 was provided to suppress unnecessary reactions in the gas phase.

In Figure 1, lead and titanium ball sources 3 and 4 are placed at different distances in the radial direction within the vacuum chamber 1, but in order to make the m-component distribution uniform, these and oxygen ion It is also effective to arrange the source 5 concentrically within the chamber 1.

Although this example describes a film formation method for lead titanate, the same method can be applied to the formation of other PZT-based thin films, such as lead titanate, lead zirconate titanate, and lanthanum lead zirconate titanate. have an effect.

[Effects of the Invention] As described above, according to the present invention, a PZT-based ferroelectric thin film can be obtained at low substrate temperature, high sloop, and high quality.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of the ferroelectric yi film manufacturing apparatus of the present invention. Vacuum chamber substrate Lead evaporation source Titanium evaporation source Oxygen ion source and above

Claims (5)

[Claims] (1) In a method for producing ferroelectric thin films of lead titanate, lanthanum lead titanate, lead zirconate titanate, or lanthanum lead zirconate titanate using a multi-source vapor deposition method, an elemental metal is used as each vapor deposition source, and oxygen gas is used. A method for producing a ferroelectric thin film, the method comprising: introducing a ferroelectric thin film into a vapor deposition reaction chamber. (2) A method for producing a ferroelectric thin film according to claim 1, characterized in that a single metal oxide is used as each vapor deposition source. (3) A method for manufacturing a ferroelectric thin film according to claims 1 and 2, characterized in that oxygen gas is preferentially introduced onto the substrate. (4) Claims 1 and 2, characterized in that part or most of the oxygen gas is ionized and introduced.
3. A method for producing a ferroelectric thin film according to items 1 and 3. (5) A method for manufacturing a ferroelectric thin film according to claim 4, characterized in that ionized oxygen is accelerated and irradiated onto the substrate surface.