Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1998-06-04
2001-04-10
Prenty, Mark V. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S411000
Reexamination Certificate
active
06215146
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device and manufacturing method thereof. More specifically, the present invention relates to a semiconductor device and manufacturing method thereof in which a nitrided oxide film is used as a gate insulating film.
2. Description of the Background Art
Demand of semiconductor devices has been rapidly increasing along with remarkable spread of information equipment such as computers. As for the function, devices having large storage capacity and capable of high speed operation are in demand. Accordingly, technical efforts have been made to realize higher degree of integration, higher speed of response and higher reliability of the semiconductor devices.
A DRAM (Dynamic Random Access memory) has been generally known as one of the semiconductor devices that allows random input/output of memory information. The DRAM includes a memory cell array as a storage region storing a number of pieces of memory information, and peripheral circuitry necessary for external input/output.
The memory cell array is formed by a plurality of memory cells each storing a unit memory information arranged in a matrix of rows and columns. The memory cell generally includes one MOS transistor.
FIG. 45
is a cross section of an MOS transistor used in a conventional DRAM. Referring to
FIG. 45
, n type source·drain regions
202
a
and
202
b
are formed in a p type silicon substrate
201
. A region between the source·drain regions
202
a
and
202
b
is a p type channel region
201
a
. A gate electrode
204
is formed on channel region
201
a
with a gate insulating film
203
formed of a silicon oxide interposed.
When the MOS transistor structured in this manner is operated, a voltage is applied to gate electrode
204
. Then, channel region
201
a
is inverted to n type, and therefore current flows through the source·drain regions
202
a
and
202
b.
When the size of the MOS transistor is reduced, thickness of gate insulating film
203
is reduced, and the distance between the source·drain regions
202
a
and
202
b
is also reduced. Even in that case, the voltage applied to gate electrode
204
and the voltage applied to source·drain regions
202
a
and
202
b
are not much different from those used conventionally. Therefore, when miniaturized, electric field in the longitudinal direction of channel
201
a
(longitudinal direction of
FIG. 45
) becomes higher. This lowers effective mobility &mgr;
eff
of electrons in channel region
201
a
, degrading drivability of the transistor.
Further, since electric field in the lateral direction of the channel region
201
a
(direction from source·drain region
202
a
to source·drain region
202
b
) becomes higher, and carriers (electrons) are accelerated, promoting entrance of carriers into gate insulating film
203
. This undesirably makes shorter the hot carrier life of the transistor.
Further, since gate insulating film
203
is made thinner, electric field attains higher also in gate insulating film
203
. Accordingly, insulation of gate insulating film is degraded, resulting in sharp lowering of dielectric breakdown life T
bd
against TDDB (Time Dependent Dielectric Breakdown) of the transistor.
In order to solve these problems, a transistor using a silicon nitrided oxide as the gate insulating film has been proposed in Japanese Patent Publication No. 7-28041.
FIG. 46
is a cross section of the transistor using a silicon nitrided oxide as the gate insulating film. In the transistor shown in
FIG. 45
, silicon oxide was used for the gate insulating film, while in the transistor shown in
FIG. 46
, silicon nitrided oxide
103
is used as the gate insulating film.
Other than this point, an element isolating insulating film
104
is formed on a silicon substrate
101
, and an interlayer insulating film
107
is formed on element isolating insulating film
104
. Source·drain regions
106
are formed at the surface of silicon substrate, and a gate electrode
105
is formed with silicon nitrided oxide
103
interposed, on the surface of silicon substrate
101
. An interlayer insulating film
107
is formed to cover gate electrode
105
, and an aluminum electrode
108
reaching source·drain regions
106
is formed on interlayer insulating film
107
.
In the semiconductor device structured as described above, effective mobility &mgr;
eff
of electrons is improved. However, the problems of degraded hot carrier life and dielectric breakdown life are not solved.
U.S. Pat. No. 5,237,188 also discloses a transistor utilizing a nitrided oxide as the gate insulating film. However, this transistor does not solve the problems of degraded hot carrier life and dielectric breakdown life, either.
SUMMARY OF THE INVENTION
Therefore, the invention was made to solve the above described problems and its object is to provide a semiconductor device having high reliability and capable of high speed operation, having superior characteristics of effective mobility &mgr;
eff
, hot carrier life and dielectric breakdown life.
The inventors made various experiments to improve effective mobility, hot carrier life and dielectric breakdown life, and reached the following conclusion.
(1) In order to improve effective mobility, it is necessary to adapt silicon nitrided oxide (SiON) as the gate insulating film.
(2) The silicon nitrided oxide film is formed by nitriding a silicon oxide formed by thermal oxidation. Thermal oxidation includes dry oxidation using dry oxygen and wet oxidation using steam. When oxidation is performed at the same temperature, longer dielectric breakdown life is obtained by nitriding the silicon oxide formed by wet oxidation.
(3) In order to improve dielectric breakdown life and hot carrier life, distribution of nitrogen in the silicon nitrided oxide and state of bonding of nitrogen must be optimized.
Based on these findings, the semiconductor device of the present invention includes a silicon substrate, silicon nitrided oxide film formed on the silicon substrate, and a gate electrode formed on the silicon nitrided oxide film. Nitrogen is distributed only in the vicinity of an interface between the silicon substrate and the silicon nitrided oxide film. Near the interface, all nitrogen atoms are bonded to two silicon atoms and one oxygen atom. This bonding is represented by the following chemical formula.
In such a semiconductor device, effective mobility is improved as the silicon nitrided oxide film is used as the gate insulating film. Further, since distribution of nitrogen and state of bonding of nitrogen atoms are optimized, the dielectric breakdown life and the hot carrier life are improved. As a result, a semiconductor device having highly reliability and capable of high speed operation can be provided.
It is preferred that the gate electrode is a floating gate electrode, and that the semiconductor device further includes a control gate electrode formed on the floating gate electrode with a dielectric film interposed. In that case, a non-volatile semiconductor memory device having high reliability and capable of high speed operation can be provided.
According to another aspect of the present invention, the semiconductor device includes a silicon substrate, a silicon nitrided oxide film formed on the silicon substrate, and a gate electrode formed on the silicon nitrided oxide film. Nitrogen is distributed only in the vicinity of an interface between the silicon substrate and the silicon nitrided oxide film. A nitrogen atom bonded to three silicon atoms exist only near the interface and preferably, it exist only at a portion very close to the interface, that is, a portion where the silicon nitrided oxide film is next to the interface. The bonding is expressed by the following chemical formula.
In such a semiconductor device, effective mobility is improved as the silicon nitrided oxide film is used as the gate insulating film. Further, since distribution of nitrogen and the state of bonding of nitrogen atoms are optimized, the dielectric breakdown life and the hot ca
Kurokawa Hiroshi
Ogata Tamotsu
Tamura Hiroaki
Umeda Hiroshi
McDermott & Will & Emery
Mitsubishi Kenki Kabushiki Kaisha
Prenty Mark V.
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