Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2000-02-07
2004-05-11
Flynn, Nathan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S296000, C257S288000, C257S213000
Reexamination Certificate
active
06734488
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device including a capacitor used in a dynamic random access memory (DRAM) or the like, and a method of manufacturing the same.
2. Description of the Background Art
A semiconductor device provided with a DRAM having a capacitor for storing signal information as charges has been used conventionally. Hereinafter, a structure of such a conventional semiconductor device provided with a DRAM having a capacitor will be described with reference to FIG.
18
. In the conventional semiconductor device including the DRAM with the capacitor, as shown in
FIG. 18
, a source/drain region
101
is formed below a main surface of a semiconductor substrate
120
with a prescribed depth. An interlayer oxide film
102
is formed to cover semiconductor substrate
120
including source/drain region
101
. A contact hole is formed which penetrates interlayer oxide film
102
to reach source/drain region
101
. A storage electrode consisting of a polycrystalline silicon (hereinafter, referred to as “polysilicon”) film
103
with an n type impurity introduced therein is formed to fill in the contact hole as well as to continuously cover the upper surface of interlayer oxide film
102
. A capacitor dielectric film consisting of a tantalum oxide film
104
, expressed as a chemical formula Ta
2
O
5
, is formed to continuously cover the surface of polysilicon film
103
as well as a portion of the upper surface of interlayer oxide film
102
. A cell plate electrode consisting of a titanium nitride film
105
, expressed as TiN, is formed by chemical vapor deposition (CVD) to cover the upper surface of tantalum oxide film
104
.
In the conventional semiconductor device as described above, if a negative bias voltage is applied to the cell plate electrode, electrons in titanium nitride film
105
being the cell plate electrode are introduced into tantalum oxide film
104
being the capacitor dielectric film, whereby a leakage current is generated. This introduction of electrons from the cell plate electrode to the capacitor dielectric film causing the leakage current occurs when energy needed for electrons to exceed a potential barrier, which is determined by a work function of titanium nitride film
105
forming the cell plate electrode, is provided to the electrons within titanium nitride film
105
. The fact that the leakage current is generated when the titanium nitride film, the work function of which is 4.95 eV, is used as the electrode means that a material having a work function that is greater than 4.95 eV needs to be used to form the electrode.
Further, in the manufacturing method of the conventional semiconductor device as described above, the step of forming tantalum oxide film
104
being the capacitor dielectric film is followed by the step of depositing titanium nitride film
105
that is to be the cell plate electrode. In this step of depositing titanium nitride film
105
, ammonia (NH
3
) gas causing reduction is used, and thus, oxygen atoms that are components of tantalum oxide film
104
are eliminated. This causes a deficiency of oxygen atoms in tantalum oxide film
104
, which in turn causes generation of a leakage current in the capacitor dielectric film.
The amount of charges stored in the capacitor reduces over time, due to the leakage current generated in the capacitor as described above. As a result, the charge retaining capability of the capacitor is diminished, which results in the degradation of refresh performance of the capacitor.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor device provided with a capacitor with an improved charge retaining capability, by suppressing generation of a leakage current in the capacitor dielectric film.
The semiconductor device according to a first aspect of the present invention includes: a contact plug including a tungsten film in the upper portion thereof, formed on a semiconductor substrate; a storage electrode including a tantalum nitride film formed on and contacting an upper surface of the tungsten film; a capacitor dielectric film including a tantalum oxide film formed on and contacting an upper surface of the tantalum nitride film; and a cell plate electrode including a tantalum nitride film formed on and contacting an upper surface of the tantalum oxide film.
In such a structure, the storage electrode and the cell plate electrode are formed of tantalum nitride film, the work function of which is greater than that of the titanium nitride film used to form the cell plate electrode of the capacitor in the conventional semiconductor device. This restricts introduction of electrons into the tantalum oxide film forming the capacitor dielectric film. Thus, it is possible to suppress generation of a leakage current in the capacitor dielectric film.
Further, the contact plug is formed using the tungsten film. Therefore, it is possible to prevent oxidation of the upper surface of the contact plug, which would be inevitable during a manufacturing process when a polysilicon film is used to form the storage electrode as in the case of the conventional semiconductor device. This prevents formation of additional capacitance because of the oxidation of the upper surface of the contact plug. As a result, reduction of capacitance of the capacitor is suppressed.
Moreover, the tantalum nitride film offering an effective barrier is formed on the tungsten film. Thus, counter diffusion between the tungsten film and the tantalum nitride film is prevented. This restricts generation of a leakage current in the capacitor dielectric film due to the counter diffusion between the contact plug and the storage electrode. As a result, the charge retaining capability of the capacitor is improved.
The semiconductor device according to a second aspect includes: a storage electrode including a tantalum nitride film formed on a semiconductor substrate; a capacitor dielectric film including a tantalum oxide film formed on and contacting an upper surface of the tantalum nitride film; and a cell pate electrode including a tantalum nitride film formed on and contacting an upper surface of the tantalum oxide film and a copper film formed on and contacting an upper surface of the tantalum nitride film.
In such a structure, the copper film used for the cell plate electrode is highly conductive, which increases drift speed of electrons within the cell plate electrode. Therefore, a capacitor can respond to the signal charges given to the capacitor at a greater response speed. As a result, the operating speed of the semiconductor device is increased. In addition, a part of the cell plate electrode is formed of the tantalum nitride film offering a good barrier, which prevents counter diffusion between the tantalum nitride film and the copper film. Thus, generation of a leakage current in the capacitor dielectric film due to the counter diffusion within the cell plate electrode is restricted. As a result, it is again possible to improve the charge retaining capability of the capacitor when the copper film is used as a portion of the cell plate electrode to increase the conductivity of the cell plate electrode.
The semiconductor device according to a third aspect of the present invention includes: a storage electrode including an indium oxide film formed on a semiconductor substrate; a capacitor dielectric film including a tantalum oxide film formed on and contacting an upper surface of the indium oxide film; and a cell plate electrode including an indium oxide film formed on and contacting an upper surface of the tantalum oxide film.
In such a structure, the storage electrode and the cell plate electrode are formed of indium oxide film, which minimizes the likelihood of a reductive elimination reaction of the tantalum oxide film forming the capacitor dielectric film occurring during the manufacturing process. Accordingly, possibility of elimination of oxygen atoms within the tantalum oxide film due to the reductive reaction is reduced. Thus, a
Aihara Kazuhiro
Inaba Yutaka
Tsuchimoto Junichi
Wakao Kazutoshi
Flynn Nathan
McDermott & Will & Emery
Mondt Johannes
Renesas Technology Corp.
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