Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2003-05-20
2004-06-22
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S296000, C257S310000, C257S311000, C257S295000, C438S244000, C438S253000, C438S387000, C438S396000
Reexamination Certificate
active
06753566
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device including a capacitor device having a capacitor dielectric film of an oxide dielectric film such as a ferroelectric film and a high dielectric film, and a method for fabricating the semiconductor device.
In a recently accelerated trend in processing and storing massive data resulting from development of digital technology, electronic equipment have been more and more highly developed, and therefore, semiconductor devices used in electronic equipment have been rapidly developed in their refinement.
Accordingly, in order to realize a high degree of integration in a dynamic RAM, a technique to use an oxide dielectric film as a capacitor dielectric film instead of a conventionally used silicon oxide or silicon nitride film has been widely studied and developed.
Also, in order to realize practical use of a nonvolatile RAM capable of operating at a lower voltage and writing/reading data at a higher speed, ferroelectric films having a spontaneous polarization characteristic are earnestly studied.
In a semiconductor memory using a ferroelectric film or a high dielectric film, in order to attain a high degree of integration of a megabit-class, stack-type memory cells are used instead of conventionally used planer-type memory cells. The most significant problem in employing the stack-type memory cells is preventing a contact face between a plug and a lower electrode of a capacitor device from being oxidized in high temperature annealing carried out in an oxygen atmosphere for crystallizing the ferroelectric film or the high dielectric film.
A conventional semiconductor device will now be described with reference to FIG.
6
A.
As shown in
FIG. 6A
, impurity diffusion layers
11
serving as the source and the drain are formed in a semiconductor substrate
10
, and a gate electrode
12
is formed on a region of the semiconductor substrate
10
sandwiched between the impurity diffusion layers
11
. The impurity diffusion layers
11
and the gate electrode
12
together form a transistor.
A protection insulating film
13
is formed on the semiconductor substrate
10
so as to cover the transistor, and a plug
14
of, for example, tungsten connected to one of the impurity diffusion layers
11
is formed in the protection insulating film
13
.
An adhesive layer
15
of titanium having a lower face in contact with the upper face of the plug
14
is formed on the protection insulating film
13
. An oxygen barrier layer
16
of iridium oxide is formed on the adhesive layer
15
, and a capacitor device composed of a capacitor lower electrode
17
, a capacitor dielectric film
18
of a ferroelectric film and a capacitor upper electrode
19
is formed on the oxygen barrier layer
16
. Accordingly, one of the impurity diffusion layers
11
of the transistor is electrically connected to the capacitor lower electrode
17
through the plug
14
.
The oxygen barrier layer
16
has a function to prevent oxidation of the plug
14
, and the adhesive layer
15
has a function to improve adhesion between the oxygen barrier layer
16
and the plug
14
.
In order to crystallize the ferroelectric film used for forming the capacitor dielectric film
18
, it is necessary to carry out annealing at a temperature of 600 through 800 in an oxygen atmosphere. During this annealing, a metal oxide film with high resistance is formed in the vicinity of the interface between the plug
14
and the adhesive layer
15
, which disadvantageously increases the contact resistance between the plug
14
and the lower electrode
17
.
Therefore, the present inventors have variously studied the cause of the formation of the metal oxide film in the vicinity of the interface between the plug
14
and the adhesive layer
15
, resulting in finding the following:
FIG. 6B
shows migration paths of oxygen atoms in the conventional semiconductor device, wherein denotes an oxygen atom and an arrow denotes a migration path of the oxygen atom.
In the annealing for crystallizing the ferroelectric film used for forming the capacitor dielectric film
18
, oxygen atoms included in the oxygen atmosphere are diffused into the capacitor dielectric film
18
, then migrate through a first path for passing through the capacitor lower electrode
17
and the oxygen barrier layer
16
to reach the adhesive layer
15
and through a second path for passing through a side portion of the capacitor dielectric film
18
to reach the adhesive layer
15
, and finally reach the plug
14
.
Although the oxygen barrier layer
16
of iridium oxide is formed on the plug
14
, the oxygen barrier layer
16
cannot definitely prevent the passage of the oxygen atoms because the annealing for crystallization is carried out in an oxygen atmosphere at a high temperature.
Also, when the oxygen atoms reach the adhesive layer
15
, titanium included in the adhesive layer
15
is easily oxidized into titanium oxide, and hence, the oxygen atoms reach the plug
14
after thus oxidizing the adhesive layer. The oxygen atoms having reached the plug
14
oxidize a metal, such as tungsten, included in the plug
14
, which disadvantageously increases the contact resistance between the capacitor lower electrode
17
and the plug
14
.
Furthermore, when the oxygen atoms reach the oxygen barrier layer
16
, pin holes may be formed or the thickness is locally reduced in the oxygen barrier layer
16
. Therefore, in a contact chain used for a test and including thousands or ten thousands of serially connected plugs
14
, the resistance becomes abnormally high when the diameter of each plug
14
is small.
SUMMARY OF THE INVENTION
In consideration of the aforementioned conventional problems, an object of the invention is preventing contact resistance between a capacitor lower electrode and a plug from increasing by definitely preventing oxidation of the plug.
In order to achieve the object, the first semiconductor device of this invention comprises an impurity diffusion layer serving as a source or a drain of a transistor formed in a semiconductor substrate; a protection insulating film covering the transistor; a capacitor lower electrode, a capacitor dielectric film of an oxide dielectric film and a capacitor upper electrode successively formed on the protection insulating film; a plug buried in the protection insulating film for electrically connecting the impurity diffusion layer of the transistor to the capacitor lower electrode; and an oxygen barrier layer formed between the plug and the capacitor lower electrode, and the oxygen barrier layer is made from a composite nitride that is a mixture or an alloy of a first nitride having a conducting property and a second nitride having an insulating property.
In the first semiconductor device of the invention, the oxygen barrier layer formed between the plug and the capacitor lower electrode is made from the composite nitride that is a mixture or an alloy of the first nitride having a conducting property and the second nitride having an insulating property. In an oxygen atmosphere at a high temperature, the second nitride having an insulating property is more highly reactive with oxygen atoms than the first nitride having a conducting property.
Therefore, in crystallizing the capacitor dielectric film of the oxide dielectric film in an oxygen atmosphere at a high temperature, when the oxygen atoms diffuse into the oxygen barrier layer, the second nitride having an insulating property is rapidly reacted with the oxygen atoms to produce an oxide in a surface portion of the oxygen barrier layer. Since an oxide has a smaller particle size than a nitride, when the nitride is changed into the oxide, the migration paths of the oxygen atoms formed in the grain boundary of the nitride becomes complicated and elongated, which makes it difficult for the oxygen atoms to diffuse within the oxygen barrier layer. In other words, since an oxide layer for preventing diffusion of the oxygen atoms is formed in the surface portion of the oxygen barrier layer, the function of the oxygen b
Hayashi Shinichiro
Judai Yuji
Kutsunai Toshie
Mikawa Takumi
Flynn Nathan J.
Matsushita Electric - Industrial Co., Ltd.
Nixon & Peabody LLP
Studebaker Donald R.
Wilson Scott R.
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