Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
2000-06-02
2001-07-24
Nguyen, Tuan H. (Department: 2823)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S239000, C438S238000, C438S256000, C257S306000, C257S308000, C257S486000
Reexamination Certificate
active
06265262
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device including a capacitor buried in an insulating film formed on a semiconductor substrate and a method of fabricating the semiconductor device.
In accordance with refinement of semiconductor devices such as a dynamic random access memory (DRAM), stored charge per unit area, namely, electrostatic capacity, has been increased by forming a capacitor three-dimensionally against a transistor by employing a stack type or trench type memory cell structure instead of a planar type structure.
Now, a conventional semiconductor device will be described with reference to FIG.
12
.
As is shown in
FIG. 12
, on a semiconductor substrate
50
where a transistor (not shown) constituting a memory cell is formed, a first insulating film
51
is formed, and a plug
52
connected to the semiconductor substrate
50
(specifically, a diffused layer of the transistor) is formed in the first insulating film
51
. The plug
52
includes a polysilicon film
52
a
and a barrier layer
52
b
successively buried in the first insulating film
51
.
Furthermore, a second insulating film
53
is formed on the first insulating film
51
, and a capacitor
54
connected to the plug
52
is formed in the second insulating film
53
. The capacitor
54
includes a bottom electrode
54
a
, a capacitor dielectric film
54
b
and a top electrode
54
c
successively buried in the second insulating film
53
.
In the conventional semiconductor device, since the barrier layer
52
b
is formed on the polysilicon film
52
a
in the plug
52
, the polysilicon film
52
a
of the plug
52
and the bottom electrode
54
a
of the capacitor
54
can be prevented from being in contact with each other. As a result, the electric characteristic of the plug
52
can be prevented from degrading through oxidation of the polysilicon film
52
a
of the plug
52
during the formation of the capacitor
54
.
In the conventional semiconductor device, however, there arises a first problem that the electric resistance of the plug
52
mainly including the polysilicon film
52
a
is increased as the diameter of the plug is reduced in accordance with refinement.
Moreover, the conventional semiconductor device has a second problem that the reliability of the capacitor
54
cannot be guaranteed because the bottom electrode
54
is contaminated or the first insulating film
51
or the second insulating film
53
is excessively etched during the formation of the capacitor
54
.
In order to overcome the first problem, the present inventors have examined silicidation of a polysilicon film included in a plug for the purpose of reducing the resistance of the plug connected to the capacitor. Specifically, the polysilicon film included in the plug is silicided by using titanium.
Now, a method of siliciding a polysilicon film included in a plug by using titanium will be described with reference to FIGS.
13
(
a
) through
13
(
d
) and
14
(
a
) through
14
(
d
).
First, as is shown in FIG.
13
(
a
), a contact hole
62
formed in a first interlayer insulating film
61
formed on a silicon substrate
60
is filled with a polysilicon film
63
, and then, an upper portion of the polysilicon film
63
filled in the contact hole
62
is removed, thereby forming a recess
62
a
on the polysilicon film
63
in the contact hole
62
as is shown in FIG.
13
(
b
).
Next, as is shown in FIG.
13
(
c
), a titanium film
64
is deposited on the silicon substrate
60
so as to cover the top surface of the polysilicon film
63
, and then, the titanium film
64
is subjected to a heat treatment for silicidation, thereby forming a titanium silicide layer
65
as is shown in FIG.
13
(
d
).
The aspect ratio of the recess
62
a
is set to approximately 0.5 through 1.0 (namely, the recess has a depth of approximately 50 through 100 nm and a diameter of approximately 100 through 200 nm), so that a void cannot be formed within a barrier layer
67
subsequently formed on the titanium silicide layer
65
(as shown in FIG.
14
(
c
). At this point, as is shown in FIG.
13
(
c
), the titanium film
64
is continuously formed not only inside but also outside of the recess
62
a
. Furthermore, as is shown in FIG.
13
(
d
), the titanium silicide layer
65
is formed not only in the surface portion of the polysilicon film
63
but also in the wall and the outside portion of the recess
62
a
. In other words, the titanium silicide layer
65
is formed also in the vicinity of the opening of the recess
62
a
, namely, in the vicinity of the opening of the contact hole
62
.
Next, as is shown in FIG.
14
(
a
), an unreacted portion of the titanium film
64
is selectively removed by wet etching, and, as is shown in FIG.
14
(
b
), for example, a TiN film
66
is deposited on the titanium silicide layer
65
so as to completely bury the recess
62
a.
Then, as is shown in FIG.
14
(
c
), portions of the TiN film
66
and the titanium silicide layer
65
outside of the recess
62
a
are removed by the CMP, so that the barrier layer
67
can be formed from the TiN film
66
inside of the titanium silicide layer
65
within the recess
62
a
. In this manner, a plug
68
including the polysilicon film
63
, the titanium silicide layer
65
and the barrier layer
67
is formed in the contact hole
62
.
Next, as is shown in FIG.
14
(
d
), a second interlayer insulating film
69
is deposited on the first interlayer insulating film
61
, a recess
70
is formed in the second interlayer insulating film
69
so as to expose the top surface of the plug
68
, and then, a conductive film
71
serving as a capacitor bottom electrode is deposited on the second interlayer insulating film
69
so as to cover the wall and the bottom of the recess
70
.
Subsequently, although not shown in the drawings, a portion of the conductive film
71
outside of the recess
70
is removed, so as to form the capacitor bottom electrode from the conductive film
71
on the wall and the bottom of the recess
70
, and thereafter, a capacitor dielectric film and a capacitor top electrode are successively formed on the capacitor bottom electrode.
In this fabrication method, however, the titanium silicide layer
65
and the conductive film
71
are directly in contact with each other (as shown in FIG.
14
(
d
)) when the heat treatment is carried out for improving the electric characteristic of the conductive film
71
after the deposition thereof. Therefore, the titanium silicide layer
65
and the conductive film
71
are reacted with each other, resulting in siliciding the conductive film
71
, namely, the capacitor bottom electrode. Furthermore, when the capacitor dielectric film including oxygen is formed on the capacitor bottom electrode, the titanium silicide layer
65
of the plug
68
is oxidized, which increases the resistance of the plug
68
. As a result, the plug
68
cannot be utilized.
SUMMARY OF THE INVENTION
In consideration of the aforementioned conventional problems, a first object of the invention is reducing the resistance of a plug by forming a silicide layer in the plug and preventing contact between the silicide layer of the plug and a capacitor bottom electrode, and a second object is improving the reliability of a capacitor.
The present inventors have variously studied the cause of the direct contact between the titanium silicide layer
65
and the conductive film
71
in the conventional method shown in FIGS.
13
(
a
) through
13
(
d
) and
14
(
a
) through
14
(
d
), namely, the reason why the titanium silicide layer
65
is formed not only in the surface portion of the polysilicon film
63
but also in the vicinity of the opening of the recess
62
a
. As a result, it has been found that the titanium silicide layer
65
is formed also in the vicinity of the opening of the recess
62
a
because when the silicidation is caused between the titanium film
64
and the polysilicon film
63
, silicon atoms constituting the polysilicon film
63
are diffused into titanium atoms constituting the titanium film
64
continuous
Mori Yoshihiro
Okuno Yasutoshi
Tsuzumitani Akihiko
Lee Hsien-Ming
Matsushita Electric - Industrial Co., Ltd.
Nguyen Tuan H.
Nixon & Peabody LLP
Robinson Eric J.
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