EP0957522A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Semiconductor memory device and method for fabricating the same
Assignee: Panasonic Holdings Corp
•
Filing: 1999-05-12
•
Granted: —
•
Expires: 2019-05-12
Abstract
Abstract A low-leakage-current layer, made of BST in which the content of Ti deviates from its stoichiometric composition, is interposed between a high-dielectric-constant layer, made of BST with the stoichiometric composition, and an upper electrode. And a charge-storable dielectric film is made up of the high-dielectric-constant layer and the low-leakage-current layer. Such a BST film containing a larger number of Ti atoms than that defined by stoichiometry can suppress the leakage current to a larger degree. Also, if such a film is used, then the relative dielectric constant does not decrease so much as a BST film with the stoichiometric composition. Accordingly, the leakage current can be suppressed while minimizing the decrease in relative dielectric constant of the entire charge-storable dielectric film, which is a serial connection of capacitors, thus contributing to the downsizing of a semiconductor memory device. As a result, a semiconductor memory device, including a charge-storable dielectric film with decreased leakage current and enhanced charge storability, can be obtained.
Inventors
- 👤 Michihito Ueda
- 👤 Takashi Ohtsuka
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-27 16:00
CPC Classifications
H; H10; H10B; H10B12/00; H10D; H10D1/00; H10D1/60; H10D1/68; H10D1/682; H10D1/684
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
121 words
A semiconductor memory device comprising a plurality
of cells, each said cell including: a lower electrode; a charge-storable dielectric film, formed on the lower
electrode and made of a dielectric in which information is
storable; and an upper electrode formed on the charge-storable dielectric
film, wherein the charge-storable dielectric film includes: a first dielectric layer made of an oxide containing at
least two metal elements and a dielectric with a high relative
dielectric constant or a ferroelectric; and a second dielectric layer, which is formed over and/or
under the first dielectric layer and made of an oxide containing
at least two metal elements and through which a smaller
amount of leakage current flows than that flowing through the
first dielectric layer.
Claim 2
Dependent Claim
30 words
The device of Claim 1, wherein the first dielectric
layer has an approximately stoichiometric composition, and wherein the second dielectric layer has a composition deviated
from the stoichiometric composition thereof.
Claim 3
Dependent Claim
19 words
The device of Claim 1, wherein the first dielectric
layer contains the three elements of Ba, Sr and Ti.
Claim 4
Dependent Claim
24 words
The device of Claim 3, wherein the first dielectric
layer has a composition expressed by Ba x Sr 1-x TiO 3 , where 0≦x≦1.
Claim 5
Dependent Claim
19 words
The device of Claim 1, wherein the second dielectric
layer contains the three elements of Ba, Sr and Ti.
Claim 6
Dependent Claim
38 words
The device of Claim 5, wherein the number of Ti atoms
accounts for larger than 50% and equal to or smaller than 60%
of the total number of Ba, Sr and Ti atoms in the second dielectric
layer.
Claim 7
Dependent Claim
86 words
The device of Claim 2, wherein the first and second
dielectric layers of the charge-storable dielectric film both
contain the three elements of Ba, Sr and Ti, and wherein the first and second dielectric layers are formed
such that a ratio of the number of Ti atoms to the total number
of Ba, Sr and Ti atoms in the charge-storable dielectric
film is represented as a continuous function of a distance as
measured from the lower surface of the charge-storable dielectric
film in the thickness direction.
Claim 8
Dependent Claim
49 words
The device of Claim 7, wherein the ratio of the number
of Ti atoms to the total number of Ba, Sr and Ti atoms is 50%
in part of the charge-storable dielectric film that corresponds
to at least one half of the total thickness of the
charge-storable dielectric film.
Claim 9
Independent Claim
155 words
A method for fabricating a semiconductor memory device,
comprising the steps of: a) forming a lower electrode over a substrate; b) forming a charge-storable dielectric film on the lower
electrode, the charge-storable dielectric film being made of a
dielectric in which information is storable; and C) forming an upper electrode on the charge-storable dielectric
film, wherein the step b) includes: i) forming a first dielectric layer made of an oxide containing
at least two metal elements and a dielectric with a
high relative dielectric constant or a ferroelectric; and ii) forming a second dielectric layer over and/or under
the first dielectric layer, the second dielectric layer being
made of an oxide containing the same elements as those of the
first dielectric layer but having a different composition than
that of the first dielectric layer, the amount of leakage current
flowing through the second dielectric layer being smaller
than that flowing through the first dielectric layer.
Claim 10
Dependent Claim
85 words
The method of Claim 9, wherein in the step i), the
first dielectric layer is formed to contain the three elements
of Ba, Sr and Ti substantially at a stoichiometric composition,
and wherein in the step ii), the second dielectric layer is
formed to contain the three elements of Ba, Sr and Ti at such
a composition that the number of Ti atoms accounts for larger
than 50% and equal to or smaller than 60% of the total number
of Ba, Sr and Ti atoms.
Claim 11
Dependent Claim
29 words
The method of Claim 9 or 10, wherein a heat treatment
is conducted to heat the substrate at 650°C or more before the
steps i) and ii) are performed.
Claim 12
Dependent Claim
53 words
The method of Claim 10, wherein in the step b), while
the first and second dielectric layers are formed by a metalorganic
chemical vapor deposition process, the temperature of
the substrate is changed, thereby changing the ratio of the
number of Ti atoms to the total number of Ba, Sr and Ti atoms.
Claim 13
Dependent Claim
28 words
The method of Claim 12, wherein in the step b), the
temperature of the substrate is kept constant in the step i),
but changed in the step ii).
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
Maintenance schedule is calculated for granted US utility patents.