JPH0629462A - Formation of dielectric thin film - Google Patents

Abstract

(57) [Summary] [Object] To provide a method for forming a high dielectric constant thin film, which can realize a higher dielectric constant even when the formed dielectric film is thin. [Structure] The growth of a single dielectric crystal and the interruption of the growth are repeated a predetermined number of times to form a thin film having a predetermined thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a dielectric thin film. More specifically, the present invention relates to a method of forming a thin film having a high dielectric constant such as used as a capacitor of a high density memory device.

[0002]

2. Description of the Related Art At present, the densification is being promoted in the field of various electronic devices, but in a dynamic memory device (DRAM), in order to prevent soft error due to α rays, the signal charge amount per memory cell is Even if the cell area is miniaturized, it cannot be significantly reduced. Further, in the 64 Mbit memory currently under development, one memory cell area is as small as about 1.5 μm ² and, in addition, low voltage operation is required to suppress an increase in power consumption.
Since the signal charge amount is the product of the electrostatic capacity and the operating voltage, it is necessary to compensate for the decrease in the power supply voltage by the increase in the electrostatic capacity.

One of the measures usually taken to increase the capacitance of the capacitor of a memory device is to reduce the thickness of the capacitive insulating film. However, the thinning of the capacitance insulating film is facing a physical limit.

Si ₃ N which has been conventionally used as a capacitive insulating film
_{In the 4} / SiO ₂ laminated film, if the thickness is reduced to 5 nm or less in terms of SiO ₂ film, the leak current will increase. Therefore, in order to realize a high density memory of 64 Mbits, a new capacitive insulating film that can be thinned to 4 nm or less in terms of SiO ₂ film is required as a capacitive insulating film. Research institutions are developing oxide-based high dielectric constant thin films such as PZT, STO, PbTiO ₃ , and BaTiO ₃ . These thin films can be produced by various methods that are convenient, but in all of these methods, the growth of the film is carried out continuously until a predetermined film thickness is reached. There is no known technique for repeatedly forming a film.

[0005]

As a general tendency in producing such a dielectric thin film, the crystal grain size becomes smaller as the film thickness becomes thinner.
It is known that the relative permittivity of thin films also decreases. As an example, FIG. 4 and FIG. 5 show the relationship between the film thickness and the crystal grain size and the relationship between the film thickness and the relative dielectric constant when a PZT thin film was formed by the rf magnetron sputtering method. As is clear from these figures, when the film thickness becomes 1 μm or less,
It can be seen that both the crystal grain size and the relative dielectric constant are significantly reduced.

This phenomenon that the relative dielectric constant decreases as the film becomes thinner, this phenomenon is considered to be used as a capacitive insulating film of a high density memory device. PZT, STO, PbTiO ₃ , BaTi
It is inconvenient for thin films of dielectrics such as O ₃ .

An object of the present invention is to provide a method for forming a dielectric thin film which can realize a higher dielectric constant even when the formed dielectric film is thin.

[0008]

The method of forming a dielectric thin film according to the present invention is characterized in that the growth of a single dielectric crystal and the interruption of the growth are repeated a predetermined number of times to form a thin film of a predetermined thickness. And

The dielectric material capable of forming a thin film by the method of the present invention is mainly of an oxide type, such as PZT.
(Pb (Ti, Zr) O ₃ ), STO (SrTiO ₃ ), PbTiO ₃ , Ba
TiO _{3 and the} like.

The film forming method for growing the dielectric thin film by the method of the present invention can be appropriately selected according to the dielectric to be grown. Further, the crystal growth can be interrupted easily by keeping the growth atmosphere and stopping the supply of the raw material. For example, when forming a PZT thin film, the growth can be interrupted by growing the thin film using a sputtering method and closing the shutter.

The number of times the crystal growth is interrupted depends on the thickness of the film to be grown and the thickness of the film obtained in one growth operation. In general, the better the number of interruptions, the better the results obtained, but if the number of interruptions is more than a certain number, the remarkable effect is not seen. Therefore, it is preferable to determine a convenient number of interruptions according to the growth conditions and the conditions of the apparatus.

It has been found that the ratio of the growth time to the interruption time also affects the relative dielectric constant of the film. Generally, when the interruption time is longer than the growth time, that is, when the ratio of the interruption time and the growth time is 1 or more, a film having a larger relative dielectric constant can be obtained. The ratio of the suspension time to the growth time is more preferably 1.2 or more. When the number of interruptions is two or more, it is possible to change the ratio between the interruption time and the growth time without uniformly setting it.

[0013]

In the method for forming a high dielectric constant thin film of the present invention, the crystal growth is interrupted because the crystal grains formed on the substrate move on the surface of the substrate during the film growth process, particularly in the initial stage of film growth. Allows the grains to coalesce into larger grains. The larger individual crystal grains suppress the decrease in the relative permittivity even when the film thickness is thin, thus making it possible to realize a thin film having a higher permittivity.

Increasing the ratio of the film growth interruption time to the growth time makes the obtained crystal grains larger and thus the film relative permittivity larger. Until this ratio reaches approximately 1, the crystal grain size increases almost in proportion to this ratio, but the increase in the crystal grain size slows down when this ratio exceeds 1, and becomes approximately 1.2. Almost leveled off when exceeded. Therefore, the ratio of the interruption time to the growth time in the present invention is preferably 1 or more, more preferably 1.
It is 2 or more.

[0015]

The present invention will be further described with reference to the following examples.

A 1000 Å SiO ₂ film was formed on the surface of the substrate by thermally oxidizing the silicon substrate. On top of this, D
A 3000 Å Pt film was formed by the C sputtering method.

Next, a PZT thin film was grown on the Pt film by the rf magnetron sputtering method. Sinter-molded PZT powder was used as a target, and 100% oxygen was used as a sputtering gas. rf output is 250
W, gas pressure is 50 mTorr, and substrate temperature is 650 ° C.
And

The thickness of one growth of the film is 50 to 250 Å, and there is a break of more than the growth time, 0.1 to 2.5 μm.
Of various thicknesses were grown. Growth interruption is r
f The shutter of the magnetron sputtering device was closed.

A graph of FIG. 1 shows the relationship between the ratio of the interruption time to the growth time and the size of the obtained crystal grains for the PZT thin film having a film thickness of 2.5 μm. As is clear from this figure, the larger the ratio of the suspending time to the growing time, the larger the crystal grain size. Will not be recognized. Similar results were obtained for PZT thin films having other thicknesses.

The relationship between the film thickness and the crystal grain size and the relationship between the film thickness and the relative permittivity are shown in the graphs of FIGS. 2 and 3, respectively, when the ratio of the interruption time to the growth time is 1.2. Show. In these figures, the broken line shows an example of the prior art in which film formation was continuously performed without interruption. As is clear from these figures, compared to the case without interruption during the film formation,
When the growth and the interruption are repeated, the crystal grain size increases, and the relative permittivity also increases accordingly, and the relative permittivity 530 is realized with the film thickness of 0.5 μm.

[0021]

As described above, according to the present invention,
Since the grain size of grown crystal grains can be made larger,
The relative dielectric constant of the formed film can be increased.
Therefore, even if the formed film is thin, a higher dielectric constant can be realized, so that it is considered that the method of the present invention can be applied to the fabrication of capacitors for future high density memories.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the grain size and the ratio of the PZT thin film growth interruption time to the growth time.

FIG. 2 is a graph showing the relationship between the film thickness and the crystal grain size of the PZT thin film according to the present invention in comparison with the conventional example.

FIG. 3 is a graph showing the relationship between the film thickness of the PZT thin film according to the present invention and the relative dielectric constant in comparison with the conventional example.

FIG. 4 is a graph showing the relationship between the film thickness and the crystal grain size of a PZT thin film formed by a conventional method.

FIG. 5 is a graph showing the relationship between the film thickness and the relative dielectric constant of a PZT thin film formed by a conventional method.

Claims (3)

[Claims] 1. A method of forming a dielectric thin film, which comprises repeating the growth of a single dielectric crystal and the interruption of the growth a predetermined number of times to form a thin film having a predetermined thickness. 2. The method according to claim 1, wherein the ratio of the time for stopping the growth of the thin film to the growth time is 1 or more. 3. The method according to claim 1, wherein the interruption of the growth is performed by stopping the supply of the growth gas.