JPH0717713A - Thin film having high dielectric constant - Google Patents

Abstract

PURPOSE:To make a thin film excellent in leakage property and to make a thin film capacitor small in size and high in capacity by controlling a perovskite oxide having a specified compsn. range. CONSTITUTION:A palladium film is formed as a lower electrode 2 on a substrate 1 such as sapphire, and a gold film is formed as an upper electrode 4 thereon. A dielectric layer 3 is formed by ion-beam sputtering method with a powdery target composed of BaCO3, SrCO3, and TiO2 as the start source materials so as to obtain the compsn. expressed by formula (y satisfies 1.00<=y<=1.20), and calcined at about 900 deg.C between electrodes 2 and 4. Then the substrate 1 is disposed in vacuum at about 650 deg.C to obtain a thin film having as high as >=500 dielectric const. As necessary, one or more elements of Mn, Pb and rare earth elements are added to the compsn. expressed by the formula by <=10mol% to obtain a thin film having high dielectric const.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high dielectric constant thin film used for a thin film capacitor.

[0002]

2. Description of the Related 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. Conventionally, materials such as SiO ₂ and Si ₃ N ₄ have been used for thin film capacitors used in integrated circuits and the like. These materials have high insulation, but have a dielectric constant of 10
Small and small. The capacitance of a capacitor is proportional to the dielectric constant and the electrode area, and inversely proportional to the film thickness. In order to make a thin film capacitor having a certain amount of capacitance by reducing the electrode area by miniaturizing the integrated circuit, it is necessary to use a material having a high dielectric constant or to reduce the film thickness. However, the thinness of the film is limited due to problems such as insulation, so it is necessary to develop a dielectric thin film having a large dielectric constant in order to miniaturize the thin film capacitor.

BaTiO ₃ , SrTiO ₃ and PbTi which are perovskite type oxides represented by the chemical formula ABO _3.
It is known that materials mainly composed of O ₃ etc. have a dielectric constant of 100 to 10000 in single crystal or ceramic, and thinning of these materials is extremely effective for the purpose of miniaturizing the above-mentioned thin film capacitor. Is. Considering the application to a capacitive insulating film such as a DRAM, it is preferable to use a paraelectric material rather than a ferroelectric material at an operating temperature. Therefore, a paraelectric material having a relatively high dielectric constant, SrTiO ₃ , (Ba, S
r) Attention has been paid to TiO ₃ thin films. Above all (Ba,
Since Sr) TiO ₃ has a higher dielectric constant than SrTiO _3, and a thin film having a higher dielectric constant can be obtained by changing the ratio of Ba and Sr, it has been actively researched. An example of that is the 1990 I-E-E-No. 7
Annual Proceedings of International Symposium on Applications of Ferroelectrics (Proceedings of 1990)
IEEE 7th International S
ymposium on Applicationsso
f Ferroelectrics 121-124), a (Ba _{1 -x} Sr _x ) TiO 3 film having a thickness of 400 to 500 nm formed by a sputtering method.
₃ thin films, the dielectric constant shows the maximum at x = 0.5, and the dielectric constant is 8
There is a report that a value of 70 was obtained.

[0004]

As described above, (Ba, S
r) A TiO ₃ -based thin film having a high dielectric constant can be obtained by changing the ratio of Ba and Sr.
It is a relatively thick film of 00 nm, and when the film thickness is made thinner, a film having a dielectric constant value like the above example cannot be obtained,
Leakage current increases.

The present invention is practical as a thin film capacitor.
200 nm with a dielectric constant of 00 or more and good leak characteristics
The purpose is to realize a small-sized thin film capacitor by producing a dielectric film having the following film thickness.

[0006]

[Means for Solving the Problems] Conventional (Ba, Sr) Ti
In the O ₃ thin film, Ti: (Ba +
We have developed a thin film with a high dielectric constant by making the Sr) ratio 1: 1 and changing the ratio of Ba and Sr. In the present invention, the ratio of Ti and (Ba + Sr) is shifted from the chemical composition ratio, and a certain amount of (Ba + Sr) is excessive with respect to Ti.
is characterized in that it has at r) _y TiO ₃ and a composition range of 1.00 <y ≦ 1.20. Especially 1.03 <y <
In the composition range of 1.16, a dielectric film having a higher dielectric constant can be obtained. Further, in the above composition range, (Ba, Sr) _y T
By adding Mn, Pb, a rare earth element or the like to iO ₃ , a dielectric film having better insulating properties can be obtained. At this time, the ratio of Ba and Sr is Ba / Sr = 0.4 to 0.7.
The composition range of is desirable.

[0007]

【Example】

(Embodiment 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 palladium film is formed as a lower electrode 2 on a substrate 1 such as sapphire, and a gold film is formed as an upper electrode 4 on the palladium film. The dielectric layer 3 is made of starting materials BaCO ₃ , SrCO ₃ , and TiO ₂ (Ba
_{0. 5, Sr 0. 5} ) y TiO 3 in y = 0.80,0.
90, 0.95, 1.00, 1.05, 1.10, 1.
Weighed to the composition of 15.1.20, 1.30, 1.50,
It was formed by an ion beam sputtering method using a powder target calcined at 900 ° C. The film thickness of the dielectric film was 150 nm for each composition. Substrate temperature was 650 ℃, Ar: 1.4 × 10 - 4 torr, O 2: 8.0 ×
10 ^- the deposition was carried out in ⁵ torr of atmosphere.

The dielectric constant of the dielectric film manufactured as in the above-mentioned embodiment changed as shown in FIG. 2 with respect to the composition of the target. When the composition of the film was confirmed by ICP analysis,
The ratio of (Ba + Sr) to Ti is (Ba, Sr) _y Ti
Regarding the value of y of O ₃ , the value of the film was slightly lower than the value of the target, and the value of the film formed using the target of y = 1.05 was y = 1.01.

[0009] As shown in FIG. 2 (Ba _{0. 5,} Sr
_0.5) dielectric constant _y TiO ₃ film depends on the composition, 1 <y
In the composition range of ≦ 1.20, the dielectric constant shows a value of 500 or more, which is a practical value for a thin film capacitor. Moreover, the leak current characteristic, that is, the current-voltage characteristic was sufficiently high enough to be put to practical use.

(Embodiment 2) As in Embodiment 1 above, FIG.
As shown in, the lower electrode 2 is formed on the substrate 1 such as sapphire.
Then, a palladium film is formed thereon, and a gold film is formed thereon as the upper electrode 4. The dielectric layer 3 contains BaCO ₃ , SrCO ₃ , and TiO ₂ as starting materials (Ba 0.5, S) _{.
r 0. 5) 1. 2} 0 TiO 3 and (Ba _{0. 5,} Sr
_{0. 5) 1. 2 0 TiO} 3 + xMn (x = 0.05,
0.10, 0.11) was weighed and formed by an ion beam sputtering method using a powder target calcined at 900 ° C. The film thickness of the dielectric film is 15 for each composition.
It was 0 nm. The substrate temperature is 650 ° C. and Ar: 1.
^{4 × 10 - 4 torr, O} 2: 8.0 × 10 - 5 tor
Film formation was performed in an atmosphere of r.

The current-voltage characteristics of the dielectric film produced as in the above embodiment are as shown in FIG. (B
_{a 0. 5, Sr 0.} 5) 1. 2 0 TiO 3 + 0.05M
n film of the current - voltage characteristic _{(.. Ba 0 5, Sr} 0 5)
_{. 1 2 0} TiO ₃ film of current - have achieved constant current region to a higher voltage than the voltage characteristic, the dielectric breakdown voltage becomes higher. _{Further, (Ba 0. 5, Sr} 0. 5) 1. 2 0 Ti
The dielectric constant of the O ₃ + 0.05Mn film (Ba _{0. 5,} Sr
_{0.5) 1.} It was similar to _{2 0} TiO ₃ film. (B
_{a 0. 5, Sr 0. 5} ) 1. 2 0 TiO 3 + 0.10M
n film of the current - voltage characteristic _{(.. Ba 0 5, Sr} 0 5)
_{. 1 2 0} TiO ₃ film of current _-. Is good compared to the voltage _{characteristic, (.. Ba 0 5,} Sr 0 5) 1 2 0 TiO 3 +
Insulating properties of 0.11Mn film (Ba _{0. 5,} S
_{r 0. 5) 1. 2} 0 worse than TiO ₃ film, the dielectric constant was reduced.

[0012]

As described above, according to the present invention, 20
A dielectric thin film having a film thickness of 0 nm or less and a dielectric constant of 500 or more and good leak characteristics can be manufactured, and miniaturization and high capacitance can be realized as compared with a conventional thin film capacitor.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a thin film capacitor.

[2] _{(Ba 0. 5, Sr 0} . 5) is a diagram showing the relationship between the composition y and dielectric constant of the _y TiO ₃ film.

[3] _{(Ba 0. 5, Sr 0} . 5) 1. 2 0 TiO 3
_{Film, (Ba 0. 5, Sr} 0. 5) 1. 2 0 TiO 3 +
0.05Mn _{film, (Ba 0. 5, Sr} 0. 5) 1. 2 0
TiO ₃ + 0.10Mn film and (Ba _{0. 5,} Sr
_{.. 0 5) 1 2 0} TiO 3 + 0.11Mn film of current - is a graph showing voltage characteristics.

[Explanation of symbols]

 1 substrate 2 lower electrode 3 dielectric film 4 upper electrode

Claims (2)

[Claims] 1. A perovskite type oxide represented by the chemical formula of (Ba, Sr) _y TiO ₃ , wherein 1.00 <y
A high dielectric constant thin film having a composition of ≦ 1.20. 2. A substance obtained by adding at least one of Mn, Pb, and a rare earth element to the substance of claim 1 (B
a, Sr) _y TiO ₃ is added in a range of up to 10 mol% and has a high dielectric constant thin film.