Device improvement by lowering LDD resistance with new...

Details Device improvement by lowering LDD resistance with new... Device improvement by lowering LDD resistance with new...

2001-04-19

2002-03-19

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Forming schottky junction

Using refractory group metal

C257S384000

Reexamination Certificate

active

06358826

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to semiconductor fabrication technology, and, more particularly, to a method of fabricating a semiconductor device such as a transistor.
2. Description of the Related Art
There is a constant drive within the semiconductor industry to increase the operating speed of integrated circuit devices, e.g., microprocessors, memory devices, and the like. This drive is fueled by consumer demands for computers and electronic devices that operate at increasingly greater speeds. This demand for increased speed has resulted in a continual reduction in the size of semiconductor devices, e.g., transistors. That is, many components of a typical field effect transistor (FET), e.g., channel length, junction depths, gate dielectric thickness, and the like, are reduced. For example, all other things being equal, the smaller the channel length of the FET, the faster the transistor will operate. Thus, there is a constant drive to reduce the size, or scale, of the components of a typical transistor to increase the overall speed of the transistor, as well as integrated circuit devices incorporating such transistors. Additionally, reducing the size, or scale, of the components of a typical transistor also increases the density, and number, of the transistors that can be produced on a given amount of wafer real estate, lowering the overall cost per transistor as well as the cost of integrated circuit devices incorporating such transistors.
However, reducing the channel length of a transistor also requires reducing the size and area of electrical contacts to active areas, such as N
+
(P
+
) source/drain regions and a doped-polycrystalline silicon (doped-polysilicon or doped-poly) gate conductor. As the size and area of the electrical contacts to the active areas get smaller, the active area contact resistance increases. Increased active area contact resistance is undesirable for a number of reasons. For example, increased active area contact resistance may reduce device drive current, and source/drain current through the device, and may also adversely affect the overall speed and operation of the transistor.
Typically, depositing titanium (Ti) or cobalt (Co) on the active area electrical contacts may decrease active area contact resistance. The Ti may then be silicided by annealing with a heat-treatment to form titanium silicide (TiSi
2
) at the active area electrical contacts (self-aligned silicidation or salicidation). The salicided TiSi
2
lowers active area contact resistance.
As shown in
FIG. 1
, a metal oxide semiconductor field effect transistor (MOSFET or MOS transistor)
100
may be formed on a semiconducting substrate
105
, such as doped-silicon. The MOS transistor
100
may have a doped-poly gate
110
formed above a gate oxide
115
formed above the semiconducting substrate
105
. The doped-poly gate
110
and the gate oxide
115
may be separated from N
+
-doped (P
+
-doped) source/drain regions
120
of the MOS transistor
100
by dielectric spacers
125
. The dielectric spacers
125
may be formed above N
−
-doped (P
−
-doped) lightly doped drain (LDD) regions
130
.
The N
−
-doped (P
−
-doped) LDD regions
130
are typically provided to reduce the magnitude of the maximum channel electric field found close to the N
+
-doped (P
+
-doped) source/drain regions
120
of the MOS transistor
100
, and, thereby, to reduce the associated hot-carrier effects. The lower (or lighter) doping of the N
−
-doped (P
−
-doped) LDD regions
130
, relative to the N
+
-doped (P
+
-doped) source/drain regions
120
of the MOS transistor
100
, reduces the magnitude of the maximum channel electric field found close to the N
+
-doped (P
+
-doped) source/drain regions
120
of the MOS transistor
100
, but increases the source-to-drain resistances of the N
−
-doped (P
−
-doped) LDD regions
130
.
As shown in
FIG. 2
, a Ti metal layer
235
may be blanket-deposited on the MOS transistor
100
shown in FIG.
1
and then subjected to an initial rapid thermal anneal (RTA) process performed at a temperature ranging from approximately 450-800° C. for a time ranging from approximately 15-60 seconds. At surfaces
240
of active areas
245
, such as the N
+
-doped (P
+
-doped) source/drain regions
120
and the doped-poly gate
110
, exposed Si reacts upon heating with the Ti metal layer
235
to form TiSi
2
at the surfaces
240
of the active areas
245
. The Ti metal layer
235
is not believed to react with the dielectric spacers
125
upon heating.
As shown in
FIG. 3
, a wet chemical strip of the Ti metal layer
235
removes excess, unreacted portions (not shown) of the Ti metal layer
235
, leaving behind the salicided TiSi
2
350
only at and below the surfaces
240
of the active areas
245
. The salicided TiSi
2
350
may then be subjected to a final RTA process performed at a temperature ranging from approximately 800-1000° C. for a time ranging from approximately 10-60 seconds.
However, even though conventional salicided TiSi
2
(or salicided CoSi
2
) lowers the contact resistance of the active areas
245
, such as the N
+
-doped (P
+
-doped) source/drain regions
120
and the doped-poly gate
110
, the N
−
-doped (P
−
-doped) LDD regions
130
continue to degrade the device drive current, and the source/drain current through the device, because of the higher resistances of the N
−
-doped (P
−
-doped) LDD regions
130
. The overall source-to-drain resistance, even with the conventional salicided TiSi
2
350
in the N
+
-doped (P
+
-doped) source/drain regions
120
, is significantly determined by the lower dopings, and, hence, higher resistances, of the N
−
-doped (P
−
-doped) LDD regions
130
.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
SUMMARY OF THE INVENTION
In one aspect of the present invention, a method is provided for fabricating a semiconductor device on a structure, the method including forming a dielectric layer adjacent a gate conductor of the semiconductor device and above an LDD region of the structure and forming a first dielectric spacer adjacent a first portion of the dielectric layer adjacent the gate conductor and above a second portion of the dielectric layer above the LDD region. The method also includes introducing a dopant into a source/drain region of the structure and removing a third portion of the dielectric layer above the gate conductor, the second portion of the dielectric layer above the LDD region, and the first dielectric spacer. In addition, the method includes forming a first conductive layer above the gate conductor, adjacent the first portion of the dielectric layer and above the LDD region, and saliciding the first conductive layer above the gate conductor and above the LDD region to form a salicided first conductive layer.
In another aspect of the present invention, a semiconductor device is provided including a structure, a gate dielectric above the structure and a gate conductor above the gate dielectric. The semiconductor device also includes an LDD region of the structure adjacent the gate dielectric and the gate conductor, a dielectric layer adjacent the gate conductor and the gate dielectric, and a salicided first conductive layer above the gate conductor and above the LDD region.


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