Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1998-11-23
2001-01-16
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S680000, C438S685000, C438S694000, C438S676000, C438S677000
Reexamination Certificate
active
06174805
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a titanium film forming method and, more particularly, to a titanium film forming method of depositing titanium by chemical vapor deposition using a plasma, which can be applied to a semiconductor device manufacturing method including the step of forming a barrier metal.
With an increase in LSI integration degree, the diameter of a contact hole decreases, and the aspect ratio (depth/diameter) increases. Assume that interconnections are to be connected to the source and drain of a MOS transistor through contact holes having such a high aspect ratio. In this case, first, a silicide of a refractory metal such as titanium is formed at the interface doped with an impurity. Second, tungsten is used as a conductive material to be filled into the contact holes.
The first point will be described first. When, for example, aluminum is filled as a plug into a contact hole formed in an impurity region such as a source or drain in a silicon substrate, the aluminum is diffused in the silicon substrate. With an increase in LSI integration degree, impurity regions such as a source and drain are formed more shallowly. For this reason, an aluminum diffusion region reaches a portion deeper than an impurity diffusion region. If the plug material is diffused deeper than the impurity region in this manner, the function of the transistor is impaired.
If, for example, titanium silicide is formed on the bottom portion of the contact hole in advance, and the plug is formed on it, diffusion of the plug material into the silicon substrate can be prevented, thus solving the above problem.
The second point will be described next. A plug must be filled into a contact hole without producing any voids. It is not easy to fill a micropatterned contact hole having a high aspect ratio with a plug without producing any voids as described above. If, for example, aluminum is filled into the contact hole by sputtering, a void is produced in the central portion of the contact hole. For this reason, as is well known, tungsten is filled into the contact hole to form a plug by chemical vapor deposition (CVD). Since the CVD method exhibits excellent step coverage characteristics, the contact hole can be filled without any void. Tungsten is selected as a material which can be deposited by the CVD method and has a low resistance.
As described above, when contacts for connecting interconnections to the source and drain of a micropatterned MOS transistor, a refractory metal silicide such as titanium silicide is formed at the interface between each contact and the silicon substrate, and tungsten is formed on the silicide by the CVD method to fill each contact hole.
A conventional method of manufacturing a semiconductor device having contact holes formed in the above manner will be briefly described below.
The following is a case wherein contacts to be connected to a source and drain are formed.
First of all, as shown in
FIG. 5A
, silicon oxide is deposited on a silicon substrate
501
, on which a MOS transistor is formed, so as to form an insulating interlayer
510
. In this case, the MOS transistor is formed in a region partitioned by an element isolation oxide film
502
in the silicon substrate
501
. This MOS transistor is made up of a gate electrode
504
formed through a gate insulating film
503
and a source and drain
505
formed by doping an impurity having a desired conductivity type into portions of the silicon substrate
501
which are located on the two sides of the gate electrode
504
.
Subsequently, as shown in
FIG. 5B
, contact holes
511
are formed in the insulating interlayer
510
to expose the source and drain
505
formation regions.
As shown in
FIG. 5C
, a titanium film
506
, which is a refractory metal film, is formed on the insulating interlayer
510
including the bottom portions and side surfaces of the contact holes
511
to have a thickness of about 10 nm. This titanium film
506
may be formed by depositing titanium by chemical vapor deposition using titanium tetrachloride, hydrogen, and argon as source gases. This deposition is performed while the silicon substrate
501
is heated to about 500° C. With this process, the titanium film
506
and the silicon substrate
501
are made to react with each other to form a titanium silicide film
507
having a thickness of about 20 nm at the interface therebetween.
If tungsten is deposited on the titanium silicide film
507
to fill the contact holes
511
, interconnections through the contact holes
511
can be formed. However, the deposition of tungsten reduces the titanium silicide film
507
. A tungsten film is formed to fill the contact holes by CVD using WF
6
as a source gas. In this formation of a tungsten film by CVD, since WF
6
is used, the film formation atmosphere contains fluorine. Since this fluorine and titanium readily form a compound, and this titanium fluoride is a gas, the titanium content of this fluoride becomes lower than that of the titanium silicide film
507
. That is, in forming a tungsten film by CVD, titanium silicide is etched. Since almost no titanium film
506
is left on the titanium silicide film
507
, if a tungsten film is directly formed on the titanium silicide film
507
by CVD, the titanium silicide film
507
is reduced.
To prevent this, when titanium silicide is used as a barrier film, and a tungsten film is to be formed on the barrier film by CVD as described above, a titanium nitride film is formed to protect the titanium silicide.
First of all, to form this titanium nitride film on the titanium film
506
, the titanium film
506
is exposed to ammonia to form a titanium nitride film
506
a
. This prevents a newly deposited titanium nitride film from peeling off. This is because a titanium nitride film formed on a titanium film tends to peel off.
With the above process, a new titanium nitride film
508
having a thickness of about 500 nm is formed on the titanium nitride film
506
a
having undergone transformation by nitriding, as shown in FIG.
5
D. This film may be deposited by chemical vapor deposition using titanium tetrachloride, hydrogen, and argon as source gases.
A tungsten film is then formed on the resultant structure by CVD using WF
6
as a source gas. Thereafter, the tungsten film and the titanium nitride films
506
a
and
508
on the insulating interlayer
510
are patterned to form interconnections
520
connected to the source and drain
505
, as shown in FIG.
5
E.
The process described above attaches importance to the thickness of the titanium film
506
which determines the thickness of the titanium silicide film
507
to a certain degree.
If the titanium film
506
is excessively thick, the titanium silicide film
507
also becomes thick. An increase in the thickness of the titanium silicide film
507
leads to an increase in consumption of silicon in the silicon substrate
501
. If the titanium silicide film
507
is excessively thick, the bottom portion of the titanium silicide film
507
extends through the source and drain
505
formation region to come into contact with the silicon substrate
501
. That is, if the titanium film
506
is excessively thick, the interconnections
520
cannot be properly connected to the source and drain
505
.
In contrast to this, if the titanium film
506
is excessively thin, since the titanium silicide film
507
becomes thin, the resistance between the interconnections
520
and the source and drain
505
through the titanium nitride film
508
and the like increases.
The above titanium film is formed by plasma CVD using RF discharge based on titanium chloride gas as a source for the following reasons.
First of all, plasma CVD allows film formation at a temperature lower than that in thermal CVD, and also allows film formation at a proper deposition rate even by using a material that cannot react or react very slowly in a thermal process. According to plasma CVD, therefore, a thin titanium film can be formed while the formation of titanium oxide is suppressed. Titanium exhibits excellent
Berry Renee′ R.
Hutchins, Wheeler & Dittmar
NEC Corporation
Nelms David
LandOfFree
Titanium film forming method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Titanium film forming method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Titanium film forming method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2499493