Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1998-06-25
2001-08-21
Prenty, Mark V. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S532000
Reexamination Certificate
active
06278152
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device and a method of manufacturing the semiconductor device, and more particularly a semiconductor device featuring the electrode structure of a capacitor and a method of manufacturing the semiconductor device.
In recent years, large-scale integrated circuits (LSIS) have been widely used in the important sections of computers and communication equipment. The performance of the entire equipment is closely related to the performance of each LSI.
Especially in such semiconductor memory devices as DRAMs, as the minimum process dimension decreases, the area of a single memory cell become increasingly small. This makes the capacitor area in a memory cell much smaller.
The smaller memory cell makes the capacitance of the capacitor (storage capacitance: Cs) smaller. The capacitance cannot be made very small because of the sensitivity and errors in software. Namely, as the memory cell area becomes smaller, it is more difficult to secure the necessary capacitance of the capacitor.
To solve this problem, the following two methods have been studied. One method is to form a capacitor three-dimensionally to make the capacitor surface area as large as possible with a smaller cell area, thereby securing the capacitance of the capacitor. The other method is to use an insulating film with high permittivity (what is called a high &egr; film) for a capacitor insulating film.
With the coming generation of design rules of the order of 0.15 microns (or the coming generation of 1-Gbit DRAMs), the process of manufacturing complex three-dimensional storage nodes would become more difficult.
Consequently, as for a method of gaining the capacitance of the capacitor, a method of using an insulating film with higher permittivity (a high-permittivity insulating film) than that of an oxide film for the capacitor insulating film is very important. Typical high-permittivity insulating films include a (Ba, Sr)TiO
3
film.
In the case of a (Ba, Sr)TiO
3
film, use of an RU film that presents the conductivity of metal even when oxidized in the course of processing or a stacked film of an RuO
2
film/Ru film has been studied (refer to S. Yamamichi, et al., IEDM Technical Digest, pp. 119-122, 1995).
FIG. 1
shows a sectional view of a conventional stacked DRAM memory cell using a stacked film of an RuO
2
film/Ru film as a storage node.
Explanation will be given according to the manufacturing processes. First, an element isolating insulating film
82
is formed on a p-type silicon substrate
81
.
Next, after a gate insulating film
83
, a gate electrode (word line)
84
, a gate cap layer
85
, and a low-impurity-concentration n-type source/drain diffused layer
86
have been formed, interlayer insulating films
87
,
88
are deposited and the surface is flattened.
Then, after polycrystalline silicon films
89
,
90
have been formed in a storage node contact area and a bit line contact area in such a manner that they are embedded in the areas, a bit line
91
is formed.
Then, after an interlayer insulating film
92
has been deposited and its surface has been flattened, a storage node contact hole is made. In the hole, a high-impurity-concentration polycrystalline silicon film
93
is embedded.
Next, after a TiSi
x
(titanium silicide) film
94
, aTiN film
95
, an Ru film
96
, and an RuO
2
film
97
have been formed in that order, this stacked film is patterned by ordinary lithography using photoresist (not shown) and RIE techniques to form a storage node
98
. Thereafter, the photoresist is peeled.
Finally, a capacitor insulating film
99
and a plate electrode (e.g., a single layer film of an Ru film or a stacked film of an Ru film/TiN film)
100
which are composed of a high-permittivity insulating film, such as a (Ba, Sr)TiO
3
film, are formed in that order on the entire surface in such a manner that they cover the side face and top face of the storage node
98
.
The stacked DRAM using this type of storage node
98
, however, has the following problem.
Firstly, because the RuO
2
film
97
with a higher film stress than that in the Ru film
96
occupies most of the storage node
98
, the film stress in the storage node
98
becomes higher, resulting in an increase in the leakage current in the capacitor insulating film
99
causes by the film stress.
Secondly, because the TiSi
x
film
94
, TiN. film
95
, Ru film
96
, and RuO
2
film
97
have appeared on the side face of the storage node
98
, this increases leakage current in the capacitor insulating film
99
. The reason for this is that the interface between the TiSi
x
film
94
and the TiN film
95
, the interface between the TiN film
95
and the Ru film
96
, and the interface between the Ru film
96
and the RuO
2
film
97
act as paths for leakage currents.
Lastly, because the corners of the top (RuO
2
film
97
) of the storage node
98
have an acute angle of about 90° and electric fields are liable to concentrate there, this increases leakage current in the capacitor insulating film
99
.
BRIEF SUMMARY OF THE INVENTION
A first object of the present invention is to provide a semiconductor device with a capacitor capable of reducing leakage current and a method of manufacturing the semiconductor device.
A second object of the present invention is to provide a semiconductor device with an electrode which is composed of Ru, the oxide of Ru, or both of these and whose surface area is easily made larger and a method of manufacturing the semiconductor device.
According to a first aspect of the present invention which achieves the first object, there is provided a semiconductor device comprising: a first lower capacitor electrode formed of a first conductive film and having a top face and side face; a second lower capacitor electrode formed of a second conductive film covering at least an upper portion of the side face of the first lower capacitor electrode; a capacitor insulating film provided on the second lower capacitor electrode; and an upper capacitor electrode provided on the capacitor insulating film, wherein film stress of the first conductive film is lower than that of the second conductive film and a volume of the first conductive film is larger than that of the second conductive film.
It is desirable that the second conductive film forming the second lower capacitor electrode further covers the top face of the first conductive film.
With such a structure, even when a material whose film stress is high is used as the second lower capacitor electrode, the film stress in the lower capacitor electrode is low on the whole. As a result, the increase of leakage current in the capacitor insulating film resulting from the film stress in the lower capacitor electrode is suppressed, helping reduce leakage current.
It is desirable that the first conductive film is a Ta film and the second conductive film is an Ru film.
With this structure, an Ru film can be used which presents high film stress as the second lower capacitor electrode but has the property of presenting conductivity even after oxidation, which is favorable in terms of processing.
It is desirable that the capacitor insulating film is a high-permittivity insulating film.
It is desirable that the capacitor insulating film is a high-permittivity dielectric film containing Ba, Sr, and Ti.
With such a structure, leakage current can be reduced and the necessary capacitance of a capacitor can be secured easily even in further miniaturization.
It is desirable that a lower portion of the side face of the first lower capacitor electrode is covered with an insulating film.
With such a structure, because there is no capacitor insulating film at the corners of the undersurface of the first lower capacitor electrode, the concentration of electric fields at the corners of the undersurface of the first lower capacitor electrode is less liable to produce leakage current in the capacitor insulating film. Therefore, it is possible to reduce leakage current in the capacitor insulating film more effectively.
The second lower cap
Aoyama Tomonori
Eguchi Kazuhiro
Hieda Katsuhiko
Imai Keitaro
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Prenty Mark V.
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