Formation of junctions by diffusion from a doped film at...

Details Formation of junctions by diffusion from a doped film at... Formation of junctions by diffusion from a doped film at...

1998-11-06

2001-05-29

Wilczewski, Mary (Department: 2822)

Semiconductor device manufacturing: process

Making field effect device having pair of active regions...

Having insulated gate

C438S683000, C438S372000, C438S558000, C438S560000

Reexamination Certificate

active

06238986

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method of manufacturing a semiconductor device comprising refractory metal silicide contacts to source/drain and silicon gate regions. The present invention has particular applicability in manufacturing reliable high density semiconductor devices with submicron design features, shallow junction depths and cobalt silicide contacts to source/drain regions.
BACKGROUND ART
Current demands for high density and performance associated with ultra large scale integration require design rules of about 0.18 microns and under, increased transistor and circuit speeds and improved reliability. As device scaling plunges into the deep sub-micron ranges, it becomes increasingly difficult to maintain performance and reliability.
In the manufacture of conventional complementary metal oxide semiconductor (CMOS) devices, referring to
FIG. 1A
, isolation regions
110
, called field oxide regions, are formed in a semiconductor substrate
100
of silicon dioxide by local oxidation of silicon (LOCOS) or by shallow trench isolation (STI). A conductive gate
130
, such as polysilicon, is also formed on substrate
100
, with a gate oxide layer
120
in between. Dielectric spacers
140
are formed on sidewalls of the gate
130
, and source/drain regions
150
are formed on either side of gate
130
by implantation of impurities.
As gate lengths are reduced to below 0.5&mgr;, refractory metal silicide layers, such as titanium silicide, are typically formed over source/drain regions
150
and gate
130
to reduce the sheet resistance of these components, thereby improving device performance. Referring to
FIG. 1B
, a titanium layer
160
is deposited, as by sputtering, over the entire substrate
100
as well as field oxide
110
, gate
130
and spacers
140
. A low temperature rapid thermal anneal (RTA) reaction creates a first-phase titanium silicide (C49) on the exposed silicon of gate
130
and source/drain regions
150
. The unreacted titanium over field oxide
110
and spacers
140
is then removed, and a high temperature RTA reaction changes the first-phase titanium silicide into a low-resistance second-phase titanium silicide
170
(C54), as shown in FIG.
1
C. Since the titanium silicide does not form on field oxide
110
or spacers
140
, it is self-aligned to the gate
130
and source/drain regions
150
. Hence, the titanium silicide formed in this process is known as “titanium salicide” (self-aligned silicide).
Titanium salicide is effective in decreasing sheet resistance if the gate length is greater than about 0.25&mgr;. At a gate length of about 0.25&mgr; the titanium silicide sheet resistance rises dramatically due to narrow-line effects; that is, the low-resistance silicide C54 does not completely form because first-phase C49 grains are very large (about 0.5&mgr;), and hence there are fewer nucleation sites on the gate to nucleate the low resistance silicide C54 during the high temperature RTA.
To maintain low sheet resistance as gate lengths are decreased in scale below about 0.25&mgr;, cobalt is typically used instead of titanium in silicide formation. Cobalt silicide does not display the undesirable narrow-line effects of titanium silicide because the conversion from its first-phase cobalt silicide to its low-resistance second-phase cobalt silicide is a diffusion reaction, rather than the nucleation and growth reaction as with titanium silicide and, therefore, the relationship of grain size to gate size is not a limiting factor.
However, the cobalt salicide process has a drawback in that cobalt silicide is more likely than titanium silicide to cause source and drain junction leakage, which can result in unacceptably high power dissipation as well as functional failure. This problem becomes especially critical as gate lengths are scaled below 0.25&mgr;, and source and drain junctions are typically made shallower to prevent transistor short-channel effects. Since shallow junctions are more susceptible to junction leakage than deep junctions, cobalt silicide related junction leakage effectively limits CMOS device scaling.
A cause of this junction leakage, referring to
FIG. 2
, is the unevenness of the interface between the cobalt silicide
210
and the silicon source/drain regions
220
, which results in an insufficient distance between portions of the bottom of the cobalt silicide
210
and source/drain junctions
220
a.
When a junction
220
a
is biased, a depletion region (i.e., an area depleted of free carriers) is formed which extends on either side of the junction
220
a.
Since the distance the depletion region spreads from the junction
220
a
is inversely proportional to the doping of the region, and source/drain region
220
is more heavily doped than substrate
200
, the depletion region spreads mainly into substrate
200
. Nevertheless, if cobalt silicide
210
extends into the depletion spread, leakage can occur as carriers are swept across this highly charged region. Junction integrity can be maintained by providing a large enough distance between junction
220
a
and the interface of silicide
210
and source/drain region
220
; i.e., by reducing the thickness of cobalt silicide
210
. However, reducing its thickness increases the sheet resistance of cobalt silicide
210
, thus reducing its effectiveness.
There exists a need for a method of manufacturing a semiconductor device with a low-resistance refractory metal silicide layer over its source/drain regions which does not cause junction leakage.
SUMMARY OF THE INVENTION
An advantage of the present invention is a method of manufacturing a semiconductor device having a metal silicide layer over its source/drain regions which does not adversely affect junction integrity.
Additional advantages and other features of the present invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other advantages are achieved in part by a method of manufacturing a semiconductor device, which method comprises forming a metal layer on a main surface of a semiconductor substrate containing silicon; forming a cap layer on the metal layer; heating to form a layer of metal silicide; etching to remove the cap layer; forming a doped layer having impurities on the metal silicide layer; and heating to reduce the resistivity of the silicide and to diffuse the impurities through the metal silicide layer into the substrate to form source/drain regions having a junction depth below the metal silicide layer.
Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the invention. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.


REFERENCES:
patent: 4378628 (1983-04-01), Levinstein et al.
patent: 5352631 (1994-10-01), Sitaram et al.
patent: 5899720 (1999-05-01), Mikagi
patent: 5980265 (1999-11-01), Tischler
patent: 5981372 (1999-11-01), Goto et al.
patent: 5985768 (1999-11-01), Speranza et al.
Materials and Bulk Processes, “Doping Technologies,” The National Technology Roadmap for Semiconductors (1994), pp. 118-121.
H. Jiang, et al., “Ultra Shallow Junction Formation Using Diffusion form Silicides,” J. Electrochem. Soc., vol. 139, No. 1, Jan. 1992, pp. 196-218.

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