JPH0788219B2 - Method for manufacturing high dielectric constant thin film - Google Patents

Description

The present invention relates to a method for producing a high dielectric constant thin film used in a thin film capacitor.

(Prior Art) With the development of integrated circuit technology, electronic circuits are becoming smaller and smaller, and it is becoming more important to make capacitors, which are indispensable circuit elements for various electronic circuits, smaller. Therefore, thin film capacitors using dielectric thin films are widely used.
First and foremost, the dielectric thin film used for thin film capacitors is required to have high insulation properties, that is, a small leak current. Therefore, materials widely used in the past are SiO ₂ and Si.
It is limited to materials with a dielectric constant of at most 10 such as ₃ N ₄ and Al ₂ O ₃ . However, the progress in miniaturization of circuit elements other than capacitors, in particular, active elements such as transistors is remarkable, and further miniaturization of capacitors is strongly desired.

In order to miniaturize thin film capacitors, it is necessary to develop a dielectric thin film with a large dielectric constant. BaTiO ₃ , SrTi, which is a perovskite type oxide represented by the chemical formula ABO _3.
It is known that a material mainly containing O ₃ , PbTiO ₃ or the like has a dielectric constant of 100 or more and 10,000 or more in a single crystal or a ceramic, and is widely used for a ceramic capacitor. The thinning of these materials is extremely effective for the purpose of miniaturizing the above-mentioned thin film capacitor, and research has been conducted for a long time. Among these, as an example where relatively good characteristics are obtained, the proceeding of
Proceedings of the IEEE
Volume 59, No. 10, pp. 1440-1447, has a paper published on a BaTiO ₃ thin film formed by sputtering and heat treatment.
Dielectric constants of 16 (prepared at room temperature) to 1900 (heat treated at 1200 ° C) have been obtained. Also Proc. 35th Electronic Component
s Conferens pp. _219-225 , a (Ba _0.28 Sr _0.72 ) TiO ₃ thin film (deposited at 700 ° C.) has a dielectric constant of 1100.

(Problems to be Solved by the Invention) As described above, in order to obtain a high dielectric constant with a (Ba, Sr) TiO ₃ -based thin film, a film formation temperature or a heat treatment temperature of 700 ° C. or higher is required. If it is processed at a temperature higher than the film temperature, the insulating property deteriorates, and the leakage current at a practical voltage when used in a thin film capacitor is large, so it has not been put to practical use. The above-mentioned deterioration of the insulating property is caused by a volume change accompanying the crystallization of the film during the high temperature heat treatment, or a minute crack or a void generated in the cooling process due to the difference in the thermal expansion coefficient between the film and the substrate. At least 60 to solve such problems
It is necessary to form a film at a low temperature of 0 ° C. or less. However, for example, when the conventional BaTiO ₃ film is formed at 600 ° C., the dielectric constant is about 200 at most.

An object of the present invention is to realize a small-sized thin film capacitor by producing a film having a dielectric constant of 400 or more, which is practical as a thin film capacitor, at a low temperature of 600 ° C. or lower.

(Means for Solving the Problems) In order to solve the above problems, the method for producing a high dielectric constant film of the present invention is a mixed powder consisting of BaCO ₃ , SrCO ₃ , and TiO ₂ weighed to a predetermined composition and having a temperature of 800 ° C. or higher. It is characterized in that it is prepared by a sputtering method at a substrate temperature of 400 ° C. or more and 600 ° C. or less after being calcined at 1000 ° C. or less and used as a target. Note that any of the RF sputtering method and the ion beam sputtering method is effective as the above-described sputtering method.

Example 1 Next, the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing the structure of an embodiment of the present invention. As shown in FIG. 1, a lower electrode 2 is formed on a substrate 1 such as silicon, silicon having an insulating layer on the surface, or sapphire.
As a film of a material selected from refractory metals such as platinum, palladium, molybdenum or metal silicide,
A dielectric layer 3 is formed thereon, and an aluminum or gold film is further formed thereon as an upper electrode 4. The dielectric layer 3 is composed of starting materials BaCO ₃ , SrCO ₃ , and TiO ₂ (Ba _1-x Sr _x ).
TiO ₃ x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7.0.8, 0.9, 1.
A film thickness of 2000 Å was formed by a sputtering method using a powder target which was weighed to a composition of 0 and calcined at 900 ° C. The substrate temperature was 600 ° C., and a mixed gas of Ar / O ₂ = 90/10 was used as the sputtering gas.

The dielectric constant of the dielectric film manufactured as in the above example changes with the composition of the film as shown in FIG. When the composition of the film was analyzed by Rutherford back scattering (RBS), it was confirmed that it was in agreement with the target composition.

The dielectric constant of the (Ba _1-x Sr _x ) TiO ₃ film depends on the composition, and x = 0.5.
The maximum value was 980.

When manufacturing a thin film capacitor, ε · Eb is expressed as a figure of merit, where ε is the dielectric constant of the dielectric film and Eb is the breaking strength. Currently, a silicon nitride film is used as a dielectric film of a thin film capacitor, but in the future, a capacitor capacity 10 times or more that of a silicon nitride film is desired. The silicon nitride film has a dielectric constant of about 8 and a breaking strength of about 6 MV / cm. On the other hand, since the (Ba, Sr) TiO ₃ film has a breaking strength of about 1 MV / cm, it is necessary to have a dielectric constant of about 500 or more in order to obtain a material index ε · Eb 10 times or more that of a silicon nitride film.

As shown in FIG. 2, (Ba _1-x Sr _x ) TiO ₃ in this example.
The film has a dielectric constant of 500 or more in the composition range of 0.4 ≦ x ≦ 0.7, and satisfies the above material index as a dielectric film for a thin film capacitor.

(Example 2) Next, the effect of the film forming temperature on the dielectric constant and the leakage current was investigated in the composition of (Ba _1-x Sr _x ) TiO ₃ at x = 0.4, 0.5, 0.7.

(Ba _1-x Sr _x ) TiO ₃ Weighed in a composition of x = 0.5 BaCO ₃ , Sr
A mixed powder of CO ₃ and TiO ₂ was calcined at 900 ° C. and used as a target, and was formed by sputtering on a sapphire substrate on which a palladium film was deposited at a substrate temperature of 300 to 900 ° C. The film thickness was 2000Å. Further, a gold electrode was formed on the dielectric film to manufacture a thin film capacitor having the structure shown in FIG. The dielectric constant and the leak current of the dielectric film formed at each substrate temperature are summarized in FIGS. 3 and 4, respectively.
The dielectric constant increases with the substrate temperature, and becomes 500 or more at a substrate temperature of 400 ° C or higher. However, the leak current is 600 ℃
When it exceeds, it increases rapidly and cannot be used as a thin film capacitor. Therefore, it is desirable that the temperature of the substrate on which (Ba, Sr) TiO _{3 is formed} by sputtering is in the range of 400 ° C to 600 ° C.

Example 3 Next, the effect of the calcination temperature of the powder target used in the sputtering method on the dielectric constant of the dielectric film was examined.

(Ba _1-x Sr _x ) TiO ₃ Weighed in a composition of x = 0.5 BaCO ₃ , Sr
A mixed powder of CO ₃ and TiO ₂ was calcined at 500 to 1400 ° C. and used as a target, and a palladium film was deposited at a substrate temperature of 600 ° C. to form a film on a sapphire substrate by a sputtering method. The film thickness was 2000Å. Further, a gold electrode was formed on the dielectric film to manufacture a thin film capacitor having the structure shown in FIG. The dielectric constants when the mixed powder was calcined at each temperature and used as a target are summarized in FIG. The dielectric constant depends on the calcination temperature of the target powder, and is 500 or more at 700 to 1000 ° C. However, the leak current is at a level of 10 ^-8 A / cm ² regardless of the calcination temperature of the target powder. Therefore, the calcination temperature of the target powder is preferably 700 ° C or higher and 1000 ° C or lower.

(Effects of the Invention) As described above, according to the present invention, a dielectric film having a dielectric constant of 500 or more and a high insulating property can be produced at a film forming temperature of 600 ° C. or less, and can be made smaller than a conventional thin film capacitor, Higher capacity can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing the structure of a thin film capacitor, and FIG. 2 is a view showing the relationship between the composition x of a (Ba _1-x Sr _x ) TiO ₃ film and the dielectric constant,
FIG. 3 shows the relationship between the substrate temperature and the dielectric constant during film formation, FIG. 4 shows the relationship between the substrate temperature during film formation and the leakage current, and FIG. 5 shows the calcination temperature of the target powder (Ba _0.5 Sr _0.5 ) TiO ₃
The figure which shows the relationship with the dielectric constant of a film. 1 ... Substrate, 2 ... Lower electrode, 3 ... Dielectric film, 4 ...
Upper electrode.

Claims (1)

[Claims] 1. BaCO ₃ , SrCO ₃ , and TiO ₂ weighed to a predetermined composition.
A method for producing a high dielectric constant thin film, which comprises: calcination of a mixed powder consisting of (4) at a temperature of 800 ° C. or higher and 1000 ° C. or lower to be used as a target, and by sputtering at a substrate temperature of 400 ° C. or higher and 600 ° C. or lower.