Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
1999-06-10
2002-05-14
Everhart, Caridad (Department: 2825)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S396000, C438S640000, C438S978000, C438S726000
Reexamination Certificate
active
06387752
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a semiconductor memory device and a method of fabricating the same, and more particularly to a semiconductor memory device having a cylindrical accumulation electrode and a method of fabricating the same.
2. Description of the Related Art
Among memory cells used for a highly integrated semiconductor memory or DRAM, a memory cell comprised of a single transistor and a single capacitor has the small number of constituents and can be readily reduced in an area, and hence, has been widely employed.
Since an output voltage produced by a memory cell is in proportion to a capacity of a capacitor included in a memory cell, it would be necessary for the capacitor to have a sufficient capacity in order to ensure stable operation of the memory cell, even when the memory cell is designed to be small-sized and highly integrated. As a capacitor designed to have a sufficiently great capacity is known a capacitor including a cylindrical accumulation electrode.
For instance, such a capacitor including a cylindrical accumulation electrode is disclosed in Japanese Unexamined Patent Publications Nos. 5-218332, 6-151747, 8-153858, and 8-316435.
FIGS. 1
to
4
are cross-sectional views of a memory cell including a cylindrical accumulation electrode, illustrating respective steps of a method of fabricating a cylindrical accumulation electrode, disclosed in the above-mentioned Japanese Unexamined Patent Publication No. 5-218332.
The method of a fabricating a cylindrical accumulation electrode is explained hereinbelow with reference to
FIGS. 1
to
4
.
First, as illustrated in
FIG. 1
, a transistor and a capacitor is fabricated on a semiconductor substrate
10
in accordance with a conventional method of fabricating a semiconductor device. At this stage, a resultant semiconductor device is covered at a surface thereof with a lower interlayer insulating film
11
.
Then, a nitride film
12
and an oxide film
13
are successively deposited on the lower interlayer insulating film
11
. The nitride film
12
and the oxide film
13
cooperate with each other to thereby form an insulating film
14
. Then, as illustrated in
FIG. 2
, openings
15
are formed throughout the insulating film
14
in areas where accumulation electrodes are to be fabricated. The openings
15
reach the lower interlayer insulating film
11
.
Then, as illustrated in
FIG. 3
, a thin polysilicon film
16
is formed on an inner sidewall and a bottom of each of the openings
15
. The thin polysilicon film
16
is designed to have such a thickness that the thickness is sufficient as a sidewall of a cylindrical accumulation electrode and that the openings
15
are not filled with the polysilicon film
16
. By designing the polysilicon film
16
to have such a thickness, there are formed recesses
16
a
surrounded by the polysilicon film
16
.
Then, as illustrated in
FIG. 3
, the recesses
16
a
are filled with oxide films
17
.
Then, a portion
16
b
(illustrated with broken lines) of the polysilicon film
16
formed on the oxide film
13
is etched back by dry etching for removal. Thereafter, the oxide film
13
is removed by etching.
Thus, there is obtained a cylindrical accumulation electrode
18
. Then, as illustrated in
FIG. 4
, the cylindrical accumulation electrode
18
is entirely covered with a capacity plate or an opposing electrode
19
. In the thus fabricated cylindrical accumulation electrode
18
, a capacity C is defined by the capacity plate
19
and an outer surface
20
of a sidewall of the cylindrical accumulation electrode
18
, acting as a capacity film.
In accordance with the cylindrical accumulation electrode
18
, an outer surface and an inner surface of a cylinder are effective areas for defining a capacity C. Hence, a capacity C could be increased relatively to an accumulation electrode in the form of a rectangular parallelopiped block.
However, the conventional cylindrical accumulation electrode
18
is accompanied with a problem of structural stability in a sidewall of a cylinder. That is, the sidewall of the cylinder might be fallen down in a process carried out subsequent to the formation of the cylinder. Such structural instability of the cylinder is a hindrance to smoothly carrying out a process of fabricating a semiconductor memory device.
To the contrary, if the cylindrical accumulation electrode
18
is designed to have a sidewall having a great thickness for ensuring structural stability, there would be paused another problem that an area defined within an inner surface of a sidewall of the cylinder cannot avoid from being small, resulting in a smaller capacity.
The reason why the above-mentioned problems are caused is that the conventional cylindrical accumulation electrode
18
is designed to have a sidewall and a bottom which have the same thickness. Specifically, since the polysilicon film
16
is formed in the opening
15
in a single step in the conventional method of fabricating the cylindrical accumulation electrode
18
, a thickness of a sidewall of the cylinder is unavoidably always the same as a thickness of a bottom of the cylinder.
As a result, when an area of a memory cell is to be reduced, a thickness of a sidewall of the cylinder had to be reduced in the conventional cylindrical accumulation electrode so that opposing portions of a sidewall do not make contact with each other. Since a thickness of a sidewall is always equal to a thickness of a bottom in the conventional cylindrical accumulation electrode, if a thickness of a sidewall is reduced, a thickness of a bottom is also reduced, resulting in structural instability of a cylindrical accumulation electrode.
In particular, since a thickness of a portion through which a sidewall is connected to a bottom is also reduced, the sidewall is likely to fall down from the bottom at the portion.
SUMMARY OF THE INVENTION
In view of the above-mentioned problems in the conventional cylindrical accumulation electrode, it is an object of the present invention to provide a semiconductor memory device and a method of fabricating the same, both of which are capable of independently determining thicknesses of a sidewall and a bottom of a cylindrical accumulation electrode, and differentiating the thicknesses from each other.
In one aspect of the present invention, there is provided a semiconductor memory device including (a) a memory cell including a transistor and a capacitor, and (b) a cylindrical accumulation electrode constituted of a sidewall and a bottom, a first thickness of the sidewall and a second thickness of the bottom of the cylindrical accumulation electrode being different from each other.
There is further provided a semiconductor memory device including (a) a memory cell including a transistor and a capacitor, and (b) a cylindrical accumulation electrode constituted of a sidewall and a bottom, a first thickness of the sidewall being smaller than a second thickness of the bottom.
In the semiconductor memory device, a bottom of a cylindrical accumulation electrode is designed to have a greater thickness than a thickness of a sidewall of the cylindrical accumulation electrode. This ensures much reduction in probability in fall-down of a sidewall, and enhances structural stability in a sidewall of a cylindrical accumulation electrode. In addition, it would be possible to accomplish a semiconductor memory device capable of readily increasing a capacity thereof.
The reason why a bottom of a cylindrical accumulation electrode can have a greater thickness than a thickness of a sidewall of the cylindrical accumulation electrode is that a bottom and a sidewall of a cylindrical accumulation electrode are independently formed in accordance with the present invention, and hence, thicknesses of a bottom and a sidewall can be independently determined, unlike the conventional cylindrical accumulation electrode.
It is preferable that the first thickness is greater at a location closer to the bottom. Namely, a sidewall of the cylindrical accumulation electrode may be tap
Everhart Caridad
Luu Chuong Anh
NEC Corporation
Scully Scott Murphy & Presser
LandOfFree
Semiconductor memory device and method of fabricating the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor memory device and method of fabricating the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor memory device and method of fabricating the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2872257