Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1996-09-27
2002-03-12
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S310000, C438S003000, C438S240000
Reexamination Certificate
active
06355952
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a nonvolatile memory cell having a capacitor formed by the use of a ferroelectric film, and also to a method of manufacturing the same.
With recent progress of the film forming technology, rapid studies are currently advanced in the application of nonvolatile memory cells each using a ferroelectric thin film. In the nonvolatile memory cell, it is possible to perform fast polarization inversion of a ferroelectric thin film and also fast rewriting effected by utilizing the residual polarization of the thin film. The nonvolatile memory cells with ferroelectric thin films being currently studied are broadly classified into a type to detect a change of a stored charge amount in a dielectric capacitor, and a type to detect a resistance change caused by spontaneous polarization of a ferroelectric. The semiconductor memory element related to the present invention belongs to the former type.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a semiconductor memory element of an improved construction so contrived as to suppress diffusion of hydrogen or intrusion of water content into a capacitor having a ferroelectric thin film, and also to provide a method of manufacturing such an improved memory element.
For the purpose of achieving the object mentioned above, the capacitor structure of the semiconductor memory element according to the present invention comprises: (a) a lower electrode formed on a semiconductor substrate; (b) a capacitor part composed of a ferroelectric thin film formed on the lower electrode; and (c) an upper electrode formed on the capacitor part. The capacitor structure further has: (d) a first protective layer consisting of one or more layers formed between the semiconductor substrate and the lower electrode, and composed of a material selected from those of Group IVa transition metal, Group Va transition metal, Group IVa transition metal nitride, Group Va transition metal nitride, silicon nitride, nickel and palladium; and (e) a second protective layer consisting of one or more layers formed on the upper electrode, and composed of a material selected from those of Group IVa transition metal, Group Va transition metal, Group IVa transition metal nitride, Group Va transition metal nitride, nickel and palladium.
In the capacitor structure of the semiconductor memory element of the present invention, it is preferred that the upper electrode covers the capacitor part, the lower electrode and the first protective layer via an insulator layer. In this case, it is further preferred that the second protective layer covers the surface of the upper electrode. Here, the expression of covering the surface of the upper electrode with the second protective layer does not signify that, when the upper electrode functions also as a wiring (e.g. plate line), the second protective layer covers even such wiring as well. This definition applies to the following description also.
A method of forming a capacitor structure of a semiconductor memory element according to a first aspect of the present invention for achieving the above object comprises the steps of: (a) forming, on a semiconductor substrate, a first protective layer consisting of one or more layers composed of a material selected from those of Group IVa transition metal, Group Va transition metal, Group IVa transition metal nitride, Group Va transition metal nitride, silicon nitride, nickel and palladium; (b) forming a lower electrode layer on the first protective layer; (c) forming a lower electrode by patterning the lower electrode layer and the first protective layer; (d) forming a ferroelectric thin film on the lower electrode, and patterning the ferroelectric thin film to thereby form a capacitor part composed of the ferroelectric thin film; (e) forming an insulator layer on the entire surface, and then forming an opening in the insulator layer at a position above the capacitor part; (f) forming an upper electrode layer on the insulator layer inclusive of the opening; (g) forming a second protective layer consisting of one or more layers formed on the upper electrode layer, and composed of a material selected from those of Group IVa transition metal, Group Va transition metal, Group IVa transition metal nitride, Group Va transition metal nitride, nickel and palladium; and (h) forming an upper electrode by patterning the second protective layer and the upper electrode layer.
A method of forming a capacitor structure of a semiconductor memory element according to a second aspect of the present invention for achieving the above object comprises the following steps instead of the steps (f), (g) and (h) defined in the method according to the second embodiment: (i) forming an upper electrode layer on the insulator layer inclusive of the opening, and then patterning the upper electrode layer to thereby form an upper electrode; and (j) forming, on the upper electrode, a second protective layer consisting of one or more layers and composed of a material selected from those of Group IVa transition metal, Group Va transition metal, Group IVa transition metal nitride, Group Va transition metal nitride, nickel and palladium, and then patterning the second protective layer in such a manner that the surface of the upper electrode is covered with the second protective layer.
A method of forming a capacitor structure of a semiconductor memory element according to a third aspect of the present invention for achieving the above object comprises the following steps instead of the steps (c) and (d) defined in the method according to the first embodiment: (k) forming a ferroelectric thin film on the lower electrode layer; and (l) patterning the ferroelectric thin film, the lower electrode layer and the first protective layer to thereby form a capacitor part composed of the ferroelectric thin film, and a lower electrode.
A method of forming a capacitor structure of a semiconductor memory element according to a fourth aspect of the present invention for achieving the above object comprises the steps of: (a) forming, on a semiconductor substrate, a first protective layer consisting of one or more layers composed of a material selected from those of Group IVa transition metal, Group Va transition metal, Group IVa transition metal nitride, Group Va transition metal nitride, silicon nitride, nickel and palladium; (b) forming a lower electrode layer on the first protective layer; (c) forming a ferroelectric thin film on the lower electrode layer; (d) patterning the ferroelectric thin film, the lower electrode layer and the first protective layer to thereby form a capacitor composed of said ferroelectric thin film, and a lower electrode; (e) forming an insulator layer on the entire surface, and then forming an opening in the insulator layer at a position above the capacitor part; (f) forming an upper electrode layer on the insulator layer inclusive of the opening, and then patterning the upper electrode layer to thereby form an upper electrode; and (g) forming, on the upper electrode, a second protective layer consisting of one or more layers and composed of a material selected from those of Group IVa transition metal, Group Va transition metal, Group IVa transition metal nitride, Group Va transition metal nitride, nickel and palladium, and then patterning the second protective layer in such a manner that the surface of the upper electrode is covered with the second protective layer.
In the present invention, an exemplary material for composing the lower electrode may be Pt, RuO
2
, IrO
2
, La—Sr—Co—O (LSCO) having a perovskite structure, or a two-layer structure of LSCO/Pt formed in this order from below. Meanwhile, an exemplary material for composing the upper electrode may be Pt, RuO
2
, IrO
2
or aluminum alloy.
The ferroelectric thin film may be composed of a perovskite type ferroelectric material of a Bi-series layer structure. More specifically, an exemplary material suited for composing the ferroelectric thin film may be Bi
2
SrTa
2
O
9
, Bi
2
SrNb
2
O
9
Ochiai Akihiko
Yamoto Hisayoshi
Sonnenschein Nath & Rosenthal
Sony Corporation
Weiss Howard
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