Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
1999-10-27
2001-09-11
Meeks, Timothy (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S255320, C427S377000, C204S192180, C204S192200, C204S192220
Reexamination Certificate
active
06287637
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to ferroelectric films. More particularly, the present invention relates to a ferroelectric film having improved electrical characteristics and the corresponding fabrication method for producing the ferroelectric film.
Ferroelectric films are typically used as the dielectric material for a ferroelectric capacitor in a ferroelectric memory cell. For proper memory operation, it is critical that the ferroelectric film achieves desirable electrical performance evidenced by the ability to liberate a detectable charge in response to the application of an externally applied electrical field. It has been shown in the laboratory that crystal growth characteristics and film orientation are critical to achieving this desirable electrical performance. Typically, the ferroelectric film is deposited on a conducting electrode surface, such as the bottom electrode of the ferroelectric capacitor. The bottom electrode can be fabricated from a variety of films such as: platinum, iridium, iridium oxide, ruthenium oxide, palladium, as well as other noble metals and their oxides, or other suitable conductive materials known in the art. Each of these electrodes has a unique surface with changing roughness, and/or conductivity, which dramatically impacts the sticking coefficients for the various components of a subsequently deposited ferroelectric film. As the sticking coefficients vary, the composition of the ferroelectric film varies. As the electrode surface begins to accept a layer of ferroelectric film, the sticking coefficients for the constituents change and dictate the composition of the bulk film. Therefore, the composition required for optimum electrical performance cannot be obtained using a single fixed set of sputtering conditions or solution chemistry.
For subsequent comparison to the improved ferroelectric film of the present invention, a typical prior art ferroelectric PZT film (lead zirconate titanate) having a thickness of about 2400Angstroms and deposited with a single step deposition has roughly 75% of the crystal domains oriented in the <111> crystal orientation. The “switched charge” liberated using a three-volt pulse [“Qsw(3 v)”] was measured at about 21 micro-Coulombs per centimeter squared. The applied voltage at which the switched charge of the ferroelectric capacitor is 90% saturated [“V(90%)”] was measured at about 4.5 volts.
What is desired is a ferroelectric film having optimized electrical performance in which specific adjustments in deposition conditions are made to compensate for the electrode variables described above and to dictate a desired film composition profile.
SUMMARY OF THE INVENTION
It is, therefore, a principal object of the present invention to achieve an optimized composition profile in a ferroelectric film in order to enhance electrical performance.
According to the present invention a thin nucleation layer of a specific composition is implemented to optimize ferroelectric crystal orientation and is markedly different from the composition required in the bulk of the ferroelectric film. The bulk film utilizes the established nucleation layer as a foundation for its crystalline growth. Because of these composition requirements, a multi-step deposition process is implemented to achieve the desired composition profile. The method of the present invention also allows for an optional third composition adjustment near the upper surface of the film to ensure compatibility with an upper electrode interface and to compensate for interactions resulting from subsequent processing.
The foregoing and other objects, features and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment of the invention, which proceeds with reference to the accompanying drawing figure.
REFERENCES:
patent: 5206788 (1993-04-01), Larson et al.
patent: 5397446 (1995-03-01), Ishihara et al.
patent: 5407855 (1995-04-01), Maniar et al.
patent: 5426075 (1995-06-01), Perino et al.
patent: 5519566 (1996-05-01), Perino et al.
patent: 5714194 (1998-02-01), Komai et al.
patent: 5719417 (1998-02-01), Roeder et al.
patent: 5811847 (1998-09-01), Joshi et al.
patent: 5817170 (1998-10-01), Desu et al.
patent: 2 314 348 A (1997-12-01), None
patent: 62161953 (1987-07-01), None
patent: 05-347229 (1993-12-01), None
patent: 06228736 (1994-08-01), None
patent: 7-62933 (1995-03-01), None
patent: 07168119 (1996-12-01), None
patent: 08340085 (1996-12-01), None
patent: 08181358 (1998-01-01), None
patent: 10012832 (1998-01-01), None
patent: 10050960 (1998-02-01), None
patent: 08215467 (1998-02-01), None
patent: WO 94/10704 (1994-05-01), None
Jung et al., J. Appl. Phys. 79(12), pp. 9245-9249, Jun. 15, 1996.*
“Influence of Buffer Layers and Excess Pb/Zr+Ti Ratios on Fatigue Characteristics of Sol-Gel Derived Pb(Zr,Ti)03 Thin Films” DOI H. et al., Japanese Journal of Applied Physics May 24-27, 1995, vol. 34 No. 9B, pp. 5105-5112.
Patent Abstracts of Japan, vol. 018, No. 604 (C-1275), Nov. 17, 1994 & JP 06 228736 a TDK Corp., Aug. 16, 1994.
Jung, H.J. et al. “Electrical Characteristics of Heteroprocessed Pb(Zr0.52Ti0.48)03 Films” Journal of Applied Physics, USA, vol. 79, No. 12, Jun. 15, 1996, pp. 9245-9249.
Chu Fan
Eastep Brian
Fox Glen
Burton Esq. Carol W.
Kubida, Esq. William J.
Meeks Timothy
Meza, Esq. Peter J.
Ramtron International Corporation
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