Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1999-12-02
2003-03-11
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S412000
Reexamination Certificate
active
06531749
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a field effect transistor having a gate electrode with a multilayered structure of silicon and copper, and a method of manufacturing the field effect transistor.
In recent years, further shrinkage in feature size of LSIs has been studied to increase the performance and degree of integration. For such shrinkage in feature size, the resistance of the gate electrode of a field effect transistor must be decreased to attain high performance. For this purpose, use of a two-layered structure of a metal and polysilicon for a gate electrode has been examined.
A gate electrode having a two-layered structure of polysilicon and copper has been proposed because of the low electrical resistance and better workability or chemical stability than that of gold or silver.
The conventional field effect transistor will be described. As shown in
FIG. 6
, first, a lower gate electrode
1403
of polysilicon is formed on a silicon substrate
1401
via a gate insulating film
1402
. An upper gate electrode
1405
of copper is formed on the lower gate electrode
1403
via a barrier film
1404
of, e.g., titanium nitride. A barrier film
1406
of, e.g., titanium nitride is formed on the upper gate electrode
1405
. The lower gate electrode
1403
and upper gate electrode
1405
form the gate electrode of the transistor.
A side wall
1407
of silicon oxide is formed to cover the side surface of the gate electrode. A lightly doped impurity region
1408
is formed in the silicon substrate
1401
under the side wall
1407
. The silicon substrate
1401
has a source
1409
and drain
1410
which sandwich the lightly doped impurity region
1408
.
The gate electrode comprising the lightly doped impurity region
1408
, source
1409
, drain
1410
, gate insulating film
1402
, and the gate electrode (comprising lower gate electrode
1403
and upper gate electrode
1405
) form a field effect transistor having an LDD structure. This LDD structure suppresses the single channel effect.
This transistor is covered with an interlayer insulating film
1411
of silicon oxide. A gate electrode interconnection
1412
and source electrode interconnection
1413
formed from, e.g., aluminum are formed on the interlayer insulating film
1411
. The gate electrode interconnection
1412
is connected to the upper gate electrode
1405
via the barrier film
1406
by a plug
1414
in the through hole formed in the interlayer insulating film
1411
. The plug
1414
is formed from tungsten. A barrier film
1414
a
of, e.g., titanium nitride is formed on the side and bottom surfaces of the plug
1414
.
The source electrode interconnection
1413
is connected to the source
1409
by a plug
1415
in the contact hole formed in the interlayer insulating film
1411
. The plug
1415
is also formed from tungsten. A barrier film
1415
a
of, e.g., titanium nitride is formed on the side and button surfaces of the plug
1415
.
Barrier films
1412
a
and
1413
a
of, e.g., titanium nitride are formed on the gate electrode interconnection
1412
and source electrode interconnection
1413
, respectively. A protective insulating film
1416
is formed on the interlayer insulating film
1411
to cover the interconnections such as the gate electrode interconnection
1412
and source electrode interconnection
1413
.
As described above, when the gate electrode has a two-layered structure of polysilicon and copper to reduce the resistance, the upper electrode
1405
of copper has the barrier films
1404
and
1406
on the lower and upper surfaces to suppress diffusion of copper to the lower polysilicon layer or upper metal interconnection formed from copper.
However, copper is diffused into the silicon oxide film and therefore diffused through the side wall
1407
and interlayer insulating film
1411
, which are formed from silicon oxide. When copper is diffused to the silicon substrate
1401
, a junction leakage current is generated, the ON current of the transistor is decreased, or the threshold value varies. When copper is diffused to the upper interconnection layer, a leakage current between the interconnection is generated.
SUMMARY OF THE INVENTION
It is therefore a principal object of the present invention to allow use of copper for the gate electrode of a field effect transistor without degrading the characteristics of the transistor.
In order to achieve the above object, according to the present invention, there is provided a field effect transistor comprising a lower gate electrode formed from silicon on a silicon substrate via a gate insulating film, an upper gate electrode formed from copper above the lower gate electrode, a first barrier film having a conductivity capable of supplying to the lower gate electrode a current enough to drive a channel portion and formed to cover a lower surface of the upper gate electrode and impede diffusion of copper, a second barrier film having a lower end in contact with the first barrier film and formed to cover side surfaces of the upper gate electrode and impede diffusion of copper, a third barrier film having an end portion in contact with the second barrier film and formed to cover an upper surface of the upper gate electrode and impede diffusion of copper, and a source and drain formed in the silicon substrate to sandwich a region under the lower gate electrode.
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Matsuki Takeo
Shinmura Toshiki
Chaudhuri Olik
NEC Corporation
Pham Hoai
Young & Thompson
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