Ferroelectric capacitor and method for fabricating the same

Abstract

In a ferroelectric capacitor comprising: a lower electrode; a ferroelectric film formed on the lower electrode; and an upper electrode formed on the ferroelectric film, variations in composition profile of elements constituting the ferroelectric film are 50% or lower in the thickness direction of the ferroelectric film, and the polarization switching time of the ferroelectric film is 1 μs or less.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C are sectional views showing a method for fabricating a ferroelectric capacitor according to a first embodiment of the present invention in the order of its fabrication process steps.

FIGS. 2A and 2B are sectional views showing the method for fabricating a ferroelectric capacitor according to the first embodiment of the present invention in the order of its fabrication process steps.

FIG. 3A is a sectional view showing the thicknesswise profile of the ferroelectric capacitor according to the first embodiment of the present invention, and FIG. 3B is a sectional view showing the thicknesswise profile of the ferroelectric capacitor according to a conventional example.

FIG. 4 is a graph showing the relation between variations (%) in composition profile of elements constituting the ferroelectric film and the polarization switching speed (nanosecond) in the ferroelectric capacitor according to the first embodiment of the present invention.

FIGS. 5A to 5C are sectional views showing a fabrication method of a ferroelectric capacitor according to a second embodiment of the present invention in the order of its fabrication process steps.

FIGS. 6A and 6B are sectional views showing a fabrication method of a ferroelectric capacitor according to the second embodiment of the present invention in the order of its fabrication process steps.

FIG. 7 is a graph showing the relation between variations (%) in orientation and the polarization switching speed (nanosecond) of the ferroelectric film according to the second embodiment of the present invention.

FIGS. 8A to 8C are sectional views showing a fabrication method of a ferroelectric capacitor made of SBTN(SrBi₂(Ta_1-xNb_x)₂O₉) according to a third embodiment of the present invention in the order of its fabrication process steps.

FIGS. 9A and 9B are sectional views showing the fabrication method of a ferroelectric capacitor made of SBTN according to the third embodiment of the present invention in the order of its fabrication process steps.

FIGS. 10A to 10C are sectional views showing a fabrication method of a ferroelectric capacitor made of PZT according to the third embodiment of the present invention in the order of its fabrication process steps.

FIGS. 11A and 11B are sectional views showing the fabrication method of a ferroelectric capacitor made of PZT according to the third embodiment of the present invention in the order of its fabrication process steps.

FIGS. 12A to 12C are sectional views showing a fabrication method of a ferroelectric capacitor made of BLT according to the third embodiment of the present invention in the order of its fabrication process steps.

FIGS. 13A and 13B are sectional views showing the fabrication method of a ferroelectric capacitor made of BLT((Bi,La)₄Ti₃O₁₂) according to the third embodiment of the present invention in the order of its fabrication process steps.

Claims

1. A ferroelectric capacitor comprising: a lower electrode; a ferroelectric film formed on the lower electrode; and an upper electrode formed on the ferroelectric film, wherein in the thickness direction of the ferroelectric film, variations in composition profile of elements constituting the ferroelectric film are 50% or lower, andthe polarization switching time of the ferroelectric film is 1 μs or less.

2. The capacitor of claim 1, wherein variations in the composition profile are 25% or lower, andthe polarization switching time is 100 ns or less.

3. The capacitor of claim 1, wherein variations in the composition profile are 13% or lower, and the polarization switching time is 20 ns or less.

4. A ferroelectric capacitor comprising: a lower electrode; a ferroelectric film formed on the lower electrode; and an upper electrode formed on the ferroelectric film, wherein variations in orientation of the ferroelectric film are 100% or lower, and the polarization switching time of the ferroelectric film is 1 μs or less.

5. The capacitor of claim 4, wherein variations in orientation of the ferroelectric film are 50% or lower, andthe polarization switching time of the ferroelectric film is 100 ns or less.

6. The capacitor of claim 4, wherein variations in orientation of the ferroelectric film are 20% or lower, andthe polarization switching time of the ferroelectric film is 20 ns or less.

7. A ferroelectric capacitor comprising: a lower electrode; a ferroelectric film formed on the lower electrode; and an upper electrode formed on the ferroelectric film, wherein of elements constituting the ferroelectric film, the content of an element with a relatively high volatility has a smooth distribution in the thickness direction of the ferroelectric film,the content of the element with a relatively high volatility is locally minimum around the center of the thickness of the ferroelectric film, andthe content of the element with a relatively high volatility is locally maximum around the interfaces between the ferroelectric film and the lower electrode and between the ferroelectric film and the upper electrode.

8. The capacitor of claim 7, wherein the ferroelectric film has a Pb-containing ferroelectric crystal structure represented by (Bi2O2)2+ (Am−1BmO3m+1)2− (where A and B represent metal), andthe element with a relatively high volatility is Pb.

9. The capacitor of claim 7, wherein the ferroelectric film has a bismuth-layered ferroelectric crystal structure, andthe element with a relatively high volatility is Bi.

10. A method for fabricating a ferroelectric capacitor which comprises: a lower electrode; a ferroelectric film formed on the lower electrode and having a Pb-containing ferroelectric crystal structure represented by (Bi2O2)2+ (Am−1BmO3m+1)2− (where A and B represent metal); and an upper electrode formed on the ferroelectric film, wherein formation of the ferroelectric film comprises:a first step of forming, on the lower electrode, a first ferroelectric film containing a greater number of Pb in content than the stoichiometric content;a second step of forming, on the first ferroelectric film, a second ferroelectric film containing a smaller number of Pb in content than the stoichiometric content; anda third step of forming, on the second ferroelectric film, a third ferroelectric film containing a greater number of Pb in content than the stoichiometric content.

11. The method of claim 10, wherein formation of the ferroelectric film further comprises, after the third step, the step of performing a thermal treatment at a temperature higher than the crystallization temperatures of the first, second, and third ferroelectric films.

12. A method for fabricating a ferroelectric capacitor which comprises: a lower electrode; a ferroelectric film formed on the lower electrode and having a Bi-containing ferroelectric crystal structure represented by (Bi2O2)2+ (Am−1BmO3m+1)2− (where A and B represent metal); and an upper electrode formed on the ferroelectric film, wherein formation of the ferroelectric film comprises:a first step of forming, on the lower electrode, a first ferroelectric film containing a greater number of Bi in content than the stoichiometric content;a second step of forming, on the first ferroelectric film, a second ferroelectric film containing a smaller number of Bi in content than the stoichiometric content; anda third step of forming, on the second ferroelectric film, a third ferroelectric film containing a greater number of Bi in content than the stoichiometric content.

13. The method of claim 12, wherein formation of the ferroelectric film further comprises, after the third step, the step of performing a thermal treatment at a temperature higher than the crystallization temperatures of the first, second, and third ferroelectric films.