Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1998-11-04
2001-08-07
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S295000, C257S296000, C257S309000
Reexamination Certificate
active
06271559
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a semiconductor memory, more particularly, to a semiconductor memory having an information storage capacitance device comprising at least a precious metal electrode film and a ferroelectric film or an oxide film having a high dielectric constant.
The area of the information storage capacitance device has become smaller and smaller in recent years with miniaturization of semiconductor devices and the absolute value of a capacitance also tends to decrease. The capacitance C is determined by the following equation (1) in the case of a parallel flat sheet electrode structure, for example:
C=&egr;·S/d (1)
where &egr; is a dielectric constant of dielectrics, S is the area of an electrode and d is a film thickness of the dielectrics (distance between electrodes).
To secure the capacitance without increasing the area S of the electrodes used for the information storage capacitance device, it is necessary either to use dielectrics having a high dielectric constant &egr; or to reduce the film thickness d of the dielectrics.
Because an inherent limit exists to the reduction of the film thickness of the dielectrics, however, technology of securing the capacitance without increasing the planar area of an insulating film used for the information storage capacitance device has been proposed as typified by a semiconductor memory using a ferroelectric such as PZT (Pb(Zr
x
Ti
1−x
)O
3
), etc, as the dielectrics that is described in JP-A-3-256358.
Since these ferroelectric materials are oxides and film formation is conducted under condition at a temperature of hundreds of Centigrades (° C.), single-crystal silicon for fabricating a transistor, for example, cannot be used as a capacitance electrode. This is because the oxidation-reduction reaction takes place in the interface between silicon and the ferroelectric material during the film formation process or in subsequent process steps, thereby film quality of the ferroelectric film is very likely to get deteriorated.
Therefore, those materials which are difficultly oxidized even at high temperature must be used for the electrode of the ferroelectric material. The materials such as PZT have ferroelectricity only when their crystal structure is a perovskite structure. It is known empirically that crystallinity of the thin films in general having the perovskite structure is greatly affected by an underlay material.
In other words, because the material of the bottom electrode must have a function such that the perovskite thin film can grow epitaxially with the (111) or (001) texture, the lower electrode material is limited from the aspect of the crystal structure.
With the background described above, precious metal materials having a face-centered cubic structure such as platinum have been examined as the bottom electrode material. However, when a precious metal electrode is used for semiconductors, an electrically conductive film such as TiN (titanium nitride) or Ti (titanium) is necessary as a barrier layer for preventing silicon diffusion in order to prevent a silicidation reaction (chemical reaction between silicon and other metals).
SUMMARY OF THE INVENTION
A high temperature of not lower than about 500° C. is necessary for forming the PZT thin film having the perovskite structure.
However, conduction failures have often occurred in the past in the information storage capacitance device structures whose ferroelectric thin film such as PZT is formed at a temperature higher than about 500° C.
Because the related technology has not clarified the cause for the occurrence of the conduction failures, effective measures have not yet been established to solve the conduction failures.
It is an object of the present invention to accomplish a semiconductor memory which restricts the occurrence of conduction failure in an information storage capacitance device using a ferroelectric film or an oxide film having a high dielectric constant as dielectrics, and which operates stably.
(1) To accomplish this object, the semiconductor memory according to the present invention employs the following structure. A semiconductor memory having a structure in which an information storage capacitance device comprising a ferroelectric film or an oxide film having a high dielectric constant formed on a bottom electrode including at least one layer of a precious metal layer in such a manner as to keep contact with the bottom electrode and a top electrode formed on the ferroelectric film or on the oxide film is electrically connected to a silicon (Si) substrate either directly or through an electrically conductive film, wherein the precious metal layer contains at least one kind of additional elements, at least one kind of the additional elements is an element having a smaller atomic radius than the atomic radius of the precious metal element, and interatomic bond energy between this element and the precious metal element is within ±20% of interatomic bond energy between the precious metal elements.
(2) Preferably, in the item (1) described above, the precious metal layer comprises platinum (Pt) containing at least element selected from the group consisting of nickel (Ni), cobalt (Co), vanadium (V), iron (Fe) and chromium (Cr).
(3) Preferably, in the item (1) described above, the precious metal layer comprises gold (Au) containing at least one element selected from the group consisting of copper (Cu), palladium (Pd), chromium (Cr), iron (Fe), cobalt (Co) and nickel (Ni).
(4) Preferably, in the item (1) described above, the precious metal layer comprises silver (Ag) containing at least one element selected from the group consisting of copper (Cu), palladium (Pd), chromium (Cr) and gold (Au).
(5) Preferably, further, in the item (1) described above, the concentration of the additional element to the precious metal element is from 0.05 to 50 at %.
The inventors of the present invention have clarified for, the first time, the cause for the occurrence of conduction defects in the information storage capacitance device.
In other words, the present inventors have found out that when an oxide thin film is formed at high temperature of not lower than about 500° C. the oxygen atoms diffuse through the crystal grain boundary of the precious metal film, so that the electrically conductive film as a barrier layer between the precious metal film and the Si substrate is oxidized and delamination occurs between the conductive film and the precious metal film to thereby invite the conduction defects.
It can be appreciated from this finding that in order to prevent the conduction defect, the grain boundary diffusion of the oxygen atoms in the precious metal film must be restricted.
Therefore, the present inventors have clarified that when the additional elements are contained in the precious metal film, at least one kind of these additional elements is the one that has a smaller atomic radius than that of the main constituent element of the precious metal film, and when interatomic bond energy between this element and the main constituent element is within ±20% of interatomic bond energy between the main constituent elements, the grain boundary diffusion in the precious metal film can be restricted.
Incidentally, the term “main constituent element” of the precious metal film hereby means an element that is contained in the greatest amount in the precious metal film.
REFERENCES:
patent: 5471363 (1995-11-01), Mihara
patent: 5471364 (1995-11-01), Summerfelt et al.
patent: 5612574 (1997-03-01), Summerfelt et al.
patent: 5708284 (1998-01-01), Onishi
patent: 6020233 (2000-02-01), Kim
patent: 3-256358 (1991-11-01), None
Iwasaki Tomio
Miura Hideo
Antonelli Terry Stout & Kraus LLP
Fenty Jesse A.
Hitachi Ltd
Lee Eddie
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