Dielectric element

Details Dielectric element Dielectric element

2000-11-14

2004-04-13

Jones, Deborah (Department: 1775)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S699000, C428S704000

Reexamination Certificate

active

06720096

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dielectric element, and more specifically, it relates to a dielectric element such as a capacitor element employing an oxide-based dielectric film.
2. Description of the Prior Art
Deep study is recently made on a ferroelectric memory as a nonvolatile memory having a high speed and requiring low power consumption.
FIGS. 29 and 30
are sectional views showing representative structures of conventional ferroelectric memories.
In the structure shown in
FIG. 29
, an isolation oxide film
101
, a well region
103
for a MOS transistor
102
, a source region
104
, a source electrode
105
connected with the source region
104
, a gate electrode
106
, a drain region
107
and an interlayer isolation film
114
are formed on an Si substrate
100
. An oxide-based dielectric capacitor
113
is connected to the drain region
107
through a plug
109
.
In the structure shown in
FIG. 30
, an isolation oxide film
101
, a well region
103
for a MOS transistor
102
, a source region
104
, a source electrode
105
connected with the source region
104
, a gate electrode
106
, a drain region
107
, a drain electrode
108
connected with the drain region
107
and an interlayer isolation film
114
are formed on an Si substrate
100
. An oxide-based dielectric capacitor
113
is connected to the gate electrode
106
through a plug
109
. The structure shown in
FIG. 30
is referred to as an FET-type ferroelectric memory.
In each of the structures shown in
FIGS. 29 and 30
, the oxide-based dielectric capacitor
113
is formed by a lower electrode
110
, an oxide-based dielectric film
111
and an upper electrode
112
. The lower electrode
110
is connected with the plug
109
made of polycrystalline silicon (poly-Si) or tungsten (W). The oxide-based dielectric film
111
of PbZr
X
Ti
1−X
O
3
(PZT) or SrBi
2
Ta
2
O
9
(SBT) serving as a ferroelectric film is formed on the lower electrode
110
. The upper electrode
112
is formed on the oxide-based dielectric film
111
. In particular, iridium (Ir), platinum (Pt) or a material containing such a component is widely employed as the material for the lower electrode
110
. This is because this material has low reactivity with the oxide-based dielectric film
111
or excellent high-temperature resistance. The upper electrode
112
is also made of a material such as iridium (Ir) or platinum (Pt), similarly to the lower electrode
110
. In each of the structures shown in
FIGS. 29 and 30
, the upper electrode
112
is formed by an Ir film.
Also in a dynamic random access memory (DRAM), the capacitor size is recently reduced following refinement of cells and hence a capacitor structure employing an oxide-based dielectric film of Ba
X
Sr
1−X
TiO
3
(BST) or the like having a high dielectric constant is required. The capacitor structure of this DRAM is similar to that shown in FIG.
29
.
However, self orientation of Ir or Pt is so strong that crystal grains exhibit a columnar structure when annealed. In this case, grain boundaries align in a direction perpendicular to the substrate. In annealing performed in a high-temperature oxygen atmosphere for sintering the oxide-based dielectric film forming a capacitor insulator film, therefore, oxygen diffuses along the grain boundaries. Thus, poly-Si or W forming an electrode such as a plug is oxidized to form an oxide film. Consequently, the capacitor characteristics are deteriorated or bad influence is exerted on preparation of the capacitor element.
When the plug
109
is prepared from poly-Si and partially oxidized in the element structure shown in
FIG. 29
, for example, a silicon oxide film is formed between the lower electrode
110
and the plug
109
. In this case, the silicon oxide film serves as a capacitor insulator film and is serially connected to the oxide-based dielectric capacitor
113
. When capacitors are serially connected, a bias applied thereto is divided in inverse proportion to the capacitance of each capacitor. The dielectric constant of an oxide-based dielectric film is generally several 10 to several 100 times that of a silicon oxide film, and hence the capacitance of the oxide-based dielectric capacitor
113
is increased.
Therefore, a bias applied in the state serially connecting the oxide-based dielectric capacitor
113
with the silicon oxide capacitor is not much divided to the oxide-based dielectric capacitor
113
. In the case of a ferroelectric memory having the oxide-based dielectric film
111
of a ferroelectric film, for example, its inverted polarization value is reduced to disadvantageously deteriorate the memory characteristics. In the case of a DRAM having the oxide-based dielectric film
111
of a high dielectric film, its charging quantity is reduced to disadvantageously deteriorate the memory characteristics.
When made of W in place of the aforementioned poly-Si in the element structure shown in
FIG. 29
, the plug
109
is partially oxidized to form a tungsten oxide film. In this case, film separation results from volume expansion caused by forming the tungsten oxide film, leading to such a problem that it is difficult to prepare a high-quality capacitor element.
In addition, oxygen diffuses outward from the oxide-based dielectric film
111
along the grain boundaries of Ir or Pt forming the lower electrode
110
or the upper electrode
112
, to disadvantageously deteriorate the characteristics such as the polarization characteristic of the oxide-based dielectric film
111
itself.
In the element structure shown in
FIG. 29
, the Ir film forming the upper electrode
112
is inconveniently oxidized when the oxide-based dielectric film
111
is annealed in an oxygen atmosphere to be sintered.
FIGS. 31 and 32
are schematic sectional views for illustrating problems of the prior art.
When the Ir film forming the upper electrode
112
is oxidized in the annealing performed in the oxygen atmosphere for sintering the oxide-based dielectric film
111
as hereinabove described, a gigantic hillock (projection)
112
a
is readily formed on the surface of the upper electrode
112
, as shown in
FIG. 31
or
32
. When such a hillock
112
a
is formed, a plate line
116
a
is disadvantageously disconnected as shown in FIG.
31
. Or, an upper wire
118
formed on a plate wire
116
b
through an interlayer isolation film
117
is disadvantageously short-circuited to the plate wire
116
b
, as shown in FIG.
32
.
When oxidized, the Ir film forming the upper electrode
112
causes compositional change to inconveniently result in stress change of the Ir film. Therefore, the ferroelectric characteristics also disadvantageously tend to change.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a dielectric element having excellent characteristics by suppressing oxidation of an electrode.
Another object of the present invention is to suppress deterioration of the characteristics of an oxide-based dielectric film in the aforementioned dielectric element.
Still another object of the present invention is to provide a dielectric element capable of inhibiting the surface of an upper electrode from formation of a hillock (projection) by suppressing oxidation of the upper electrode.
A further object of the present invention is to suppress stress change resulting from compositional change of an upper electrode material.
A dielectric element according to an aspect of the present invention comprises an insulator film including an oxide-based dielectric film and an electrode including a first conductor film containing at least a metal and silicon. The aforementioned metal includes at least one metal selected from a group consisting of Ir, Pt, Ru, Re, Ni, Co and Mo. According to the present invention, the dielectric element is a wide concept including not only a capacitor element but also another element employing a dielectric material.
In the dielectric element according to this aspect, the first conductor film serves as a barrier film for stopping diffusion of oxygen du

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