Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2000-10-04
2001-12-25
Flynn, Nathan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S306000, C257S308000, C361S321400, C438S396000
Reexamination Certificate
active
06333534
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device and method of fabricating it, and, in more detail, relates to a semiconductor device and method of fabrication provided with a capacitor of a simple stacked structure in which a ferroelectric film or insulating film of high relative permittivity is employed as the capacitor insulating film.
2. Description of the Related Art
In recent years, advances have been made in achieving higher integration and higher densities of semiconductor devices such as for example DRAMs (Dynamic Random Access Memories). Increasing the density and increasing the integration of a semiconductor device tends to decrease capacitance, lowering the reliability of the semiconductor device.
An effective method of increasing the capacitance of a capacitor of small area is to employ a ferroelectric film or insulator film of high relative permittivity as the capacitor insulating film. Ta
2
O
5
, SrTiO
3
, (Ba
(x)
Sr
(1−x)
) TiO
3
etc. are considered promising as insulator films of high relative permittivity used for capacitor insulating films. These insulating films have no hysteresis characteristic and have extremely high relative permittivity. The necessary capacitance can thereby be ensured, without making the construction of the capacitor device complicated, by employing these as the capacitor insulating film.
A known example of the construction of a capacitor in which a high relative permittivity insulating film is employed as the capacitor insulating film is shown in FIG. 1 of Y. Ohno et al, “A Memory Cell Capacitor With Ba
(x)
Sr
(1−x)
TiO
3
(BST) Film For Advanced DRAMs” 1994 Symposium on VLSI Technology Digest of Technical Papers, 11.1, p. 149.
A method of fabricating a capacitor as disclosed in this article will now be described with reference to FIG.
9
.
First of all, a contact plug
902
is formed in a prescribed position of inter-layer insulating film
901
, using the ordinary photolithographic technique and deposition techniques. This contact plug
902
is employed as a contact for the lower electrode (corresponding to the storage node).
Next, a laminated film
903
is formed (see FIG.
9
(A)) on the surface of inter-layer insulating film
901
so as to contact this contact plug
902
. This laminated film
903
is processed in a subsequent step to form the lower electrode. Laminated film
903
is constituted of an adhesive layer
904
to prevent peeling of the lower electrode from the inter-layer insulating film
901
, a barrier layer
905
for preventing diffusion of carrier within the lower electrode, and an electrode layer
906
. For example, a titanium (Ti) film can be employed for adhesive layer
904
, a titanium nitride (TiN) film can be employed for the barrier layer, and a ruthenium (Ru) film can be employed for the lower electrode layer
906
.
Next, lower electrode
907
is formed by patterning of laminated film
903
by RIE (Reactive Ion Etching) or a similar technique. After this, a side wall
908
(see FIG.
9
(B)) is formed on the side face of lower electrode
907
by etching using RIE etc. after deposition of an insulating material on the entire surface of inter-layer insulating film
901
.
Next, capacitor insulating film
909
is formed by depositing a Ta
2
O
5
, SrTiO
3
or (Ba
(x)
Sr
(1−x)
)TiO
3
on the surface of inter-layer insulating film
901
, lower electrode
907
and side wall
908
. The capacitor is completed (see FIG.
9
(C)) by forming an upper electrode
910
by depositing for example Ru on the entire surface of insulating film
909
.
FIG.
9
(D) is a view showing part of the capacitor of FIG.
9
(C) to a larger scale. In this capacitor, the step coverage of insulating film
909
is improved by forming side walls
908
on the side faces of lower electrode
907
, thereby preventing short circuiting of lower electrode
907
and upper electrode
910
, Also, oxidation of adhesive layer
904
by annealing performed in a subsequent step is prevented by the provision of these side walls
908
.
However, this gives rise to the drawback that, if a side wall
908
is formed on the side face of lower electrode
903
, the capacitance of the capacitor is lowered, since the contact area of electrode
903
and insulating film
909
becomes small.
If a side wall
908
is provided, only the upper surface of lower electrode
907
acts as a storage node; the side face does not act as a storage node (see FIG.
9
(D)). That is, since the area of the storage node is decreased to the extent of the area of the side face, the capacitance is lowered to that extent. Consequently, even by employing a ferroelectric film or high relative permittivity insulating film as capacitor insulating film
909
, it was still not possible to raise the capacitance sufficiently.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor device and method of fabricating it whereby short circuiting of the upper electrode and lower electrode can be prevented, oxidation of the adhesive layer in the annealing step can be prevented, and whereby a capacitor can be provided that is of small area yet sufficiently large capacitance.
Also, a further object of the present invention is to provide a semiconductor device and method of fabricating it whereby oxidation of the adhesive layer can be prevented and a capacitor whereby sufficiently large capacitance can be obtained can be formed with small area and low cost.
A semiconductor device according to the present invention has a capacitor comprising a lower electrode having a laminated layer including an adhesive layer formed on an insulating film, a barrier layer formed so as to cover the upper surface of the adhesive layer, a nitride side formed so as to cover the side surface of the adhesive layer, and an electrode formed so as to cover the upper surface of the barrier layer, a capacitor insulating film formed so as to cover the upper surface and side surface of the lower electrode, and an upper electrode formed so as to cover the surface of the capacitor insulating film. With a semiconductor device according to the present invention, oxidation of the adhesive layer is prevented since the upper surface of the adhesive layer is covered by the barrier layer and the side surface of the adhesive layer is covered by the nitride side. Consequently, oxidation of the adhesive layer can be prevented even without the provision of a side wall. Since a side wall is not provided, the side face of the laminated layer can be employed as a storage node, so the capacitance can be increased. In a desirable mode of this invention, the lower electrode is further provided with a side electrode covering the side face of the laminated layer. By means of this side electrode, the step coverage of the capacitor insulating film can be increased, thereby preventing short circuiting of the lower electrode and upper electrode. Also, thanks to the provision of a side electrode, the area of the storage node can be further increased and so capacitance can be further increased.
A method according to the present invention of fabricating a semiconductor device includes a capacitor fabricating process comprising: a lower electrode forming process having a step of depositing a film for forming an adhesive layer using a non-nitrided conducting material on an insulating film, a step of depositing a film for forming a barrier layer using a conductive material formed by nitriding said non-nitrided conductive material on the surface of said non-nitrided conductive material film, a step of depositing a film for forming an electrode layer using a conductive material that is difficult to nitride on the surface of said nitrided conductive material film, a step of forming said adhesive layer, said barrier layer and said electrode layer by patterning these films, and a step of forming a nitride side on the side face of said adhesive layer by heating these layers in an atmosphere of nitrogen gas; a process of forming a capacitor insulating film by depositing an
Flynn Nathan
Forde Remmon R.
OKI Electric Industry Co., Ltd.
Volentine & Francos, PLLC
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