Method for forming fine titanium nitride film and method for fabricating semiconductor element using the same

A method for forming a fine titanium nitride film and a method for fabricating a semiconductor element using this method. The method for forming a fine titanium nitride film includes the steps of depositing a titanium nitride film on a semiconductor substrate such as with a reactive sputtering method, introducing oxygen into the columnar structured grain boundaries of the titanium nitride film such as by exposing the titanium nitride film to atmosphere, depositing a titanium film on the titanium nitride film having oxygen stuffed therein, converting the titanium film into a fine titanium nitride film by subjecting the titanium film to two times of a heat treatment process. In case a COB DRAM element bit line is formed of tungsten, the fine titanium nitride film and the underlying oxygen-stuffed titanium nitride film, serving as barriers for preventing high temperature diffusion of the tungsten, allow a tungsten bit line having excellent contact and barrier properties. In case the fine titanium nitride film is used as an MOS transistor gate, a gate which can satisfy the thermal stability of a polysilicon as well as the low resistivity of a silicide may be obtained.

FIELD OF THE INVENTION 
This invention relates to methods for forming titanium nitride films having 
a low resistivity, and more particularly to a method for forming a fine 
titanium nitride film which is suitable as a diffusion barrier layer 
between a metal layer of, such as, tungsten, and a silicon substrate, and 
a method for fabricating a semiconductor element using this method. 
BACKGROUND OF THE INVENTION 
As the design rule for elements in products such as dynamic random access 
memories (DRAMs) becomes more stringent, a greater restraint has been 
imposed on using materials having high resistivity, such as 
polycrystalline silicon as a gate electrode of the elements. In order to 
overcome this restraint, many studies for lowering the resistivity of the 
gate electrode have been carried out. 
First, metals, such as tungsten or molybdenum, having a low reactivity with 
a gate oxide film of, such as, a silicon oxide film, have been 
investigated for use as the gate electrode. Second, a silicide film of, 
such as, tantalum silicide TaSi.sub.2 or molybdenum silicide MoSi.sub.2, 
deposited on the gate oxide film also have been investigated for use as 
the gate electrode. These methods, however, have problems in that the 
properties of the gate oxide film may deteriorate and/or the material of 
the gate electrode may peel off of the gate oxide film by the reaction of 
the gate oxide film with the gate electrode. Particularly, in case of a 
ultra-large scale integrated element having a gate oxide film of several 
tens of angstroms (.ANG.) in thickness, the element can suffer from 
radiation damage. That is, the stability of the polycrystalline film 
sometimes cannot be assured with the foregoing methods. 
Third, polycides having resistivities as low as the above metals and 
silicides, as well as stabilities as stable as the polycrystalline silicon 
film, have been investigated for use as the gate electrode. As for methods 
for forming the polycides, there is a self-aligned silicide (salicide) 
method using a chemical vapor deposition (CVD) method or with a sputtering 
method. 
FIGS. 1A and 1B are sectional views illustrating a semiconductor element 
illustrating a conventional polycide film formed with the salicide method. 
Referring to FIG. 1A, a gate oxide film and a layered gate electrode have 
been formed by forming thin oxide film 11 and polycrystalline silicon film 
12 on silicon substrate 10, and by forming polycide film 13 thereon with 
the salicide method, and subjecting these layers to a patterning. 
However, in case the polycide film is formed on a polycrystalline silicon 
film with the salicide method, the interface between polycrystalline 
silicon film 12 and polycide film 13 making up the gate electrode is 
unstable. As a result, problems of agglomeration and penetration of 
polycide 13 into underlying polycrystalline film 12 may occur as 
illustrated in FIG. 1B due to a subsequent heat treatment process. 
FIGS. 2A and 2B are sectional views of a semiconductor element illustrating 
a conventional polycide film formed with a CVD method or a sputtering 
method. 
As illustrated in FIG. 2A, in the case of a layered gate electrode having 
layers of polycrystalline film 22 and polycide film 23 formed on gate 
oxide film 21 on substrate 20, with the layers formed with a CVD method or 
a sputtering method, steps may form between polycrystalline silicon film 
22 and polycide 23 of the gate electrode and/or polycide film 23 may peel 
off from polycrystalline silicon film 22 due to shrinkage of polycide film 
23 in a subsequent heat treatment process due to the instability of the 
interface between polycrystalline silicon film 22 and polycide film 23. 
Moreover, in case the polycide film is used as the gate electrode of an 
ultra-large scale integrated element on the order of 0.1 .mu.m, there has 
been a limit in using such a polycide film as a gate electrode due to a 
sharp increase of the resistivity. 
Fourth, a titanium nitride film formed with a reactive sputtering method 
has been investigated for use as an inactive gate electrode. 
As illustrated in FIG. 3A, in case titanium nitride film 32 is used as the 
gate electrode, the ultra-large scale integrated element having very thin 
gate oxide film 31 on substrate 30 can suffer from radiation damage. 
Moreover, the properties of titanium nitride film 32 deposited with a 
sputtering method may be altered due to immigration of impurities 34 along 
the grain boundaries between columns of the columnar structured titanium 
nitride film in a subsequent heat treatment process as illustrated in FIG. 
3B. 
When the Gibbs free energies of the titanium oxide film and the silicon 
oxide film are compared, since the energy of the titanium oxide film is 
substantially greater than the energy of the silicon oxide film, titanium 
nitride film 32 may react with gate oxide film 31 of silicon oxide in a 
subsequent heat treatment process. Therefore, a problem may occur in that 
the gate oxide film is spoiled due to reaction of the titanium nitride 
film of the gate electrode with the gate oxide film to be altered into a 
titanium oxide film and a titanium silicide. 
Fifth, a composite silicide film has been investigated for use as the gate 
electrode. 
As illustrated in FIG. 4, in order to solve the problem of the third method 
wherein the polycide film is used as the gate electrode, a composite 
polycide structured gate electrode is formed by depositing both titanium 
nitride film 43 on polycrystalline silicon film 42 as a barrier and 
titanium silicide TiSi.sub.2 film 44 thereon. Reference numbers 40 and 41 
in the drawing represent a silicon substrate and a gate oxide film, 
respectively. However, since the method also utilizes a sputtering method 
in forming the titanium silicide, like the previous case, the problems of 
shrinkage and contamination by impurities of the silicide have been caused 
in a subsequent heat treatment process. 
FIG. 5 is a sectional view of a general COB (Capacitor On Bit line) 
structured DRAM element having bit lines formed of polycide. 
Referring to FIG. 5, in general, the conventional COB structured DRAM 
element has used polycide, for example, tungsten silicide WSi.sub.2 
/polycrystalline silicon films 52 and 51, as bit lines. In case the bit 
lines are formed of polycide, though advantageous in terms of excellent 
thermal stability, such may have a problem of low operation speed of the 
element due to the high resistivity of the tungsten silicide film being 
about 50.about.200 .mu..OMEGA..multidot.cm and the resistivity of the 
polycrystalline silicon film being about 200 .mu..OMEGA..multidot.cm. 
Moreover, the polycrystalline silicon film of the bit line doped with n+ 
type impurities can form a contact only to n+ type or n- type region 53 or 
54. Therefore, in order to form a contact for capacitor 57 to a bit line 
to p+ type region 55 in a final wiring process, a poor process of etching 
insulation film 59 at a portion having an aspect ratio of more than 3 
should have been carried out. 
That is, in case wiring 56-2 and 56-1 are formed with contacts to n+ type 
region 53 and p+ type region 55, respectively, a contact to region 53 
having a substantially smaller aspect ratio than the contact to p+ type 
region 55 can be formed due to a bit line formed of polycrystalline 
silicon film 51 and tungsten silicide film 52 on n+ type region 53. 
At this time, in case the bit line is formed of a metal, the process can be 
simple since the bit line can be formed irrespective of the conduction 
type of the impurity region, but, as illustrated in FIG. 5, in case the 
bit line is formed of a polycrystalline silicon film, there has been a 
problem in that the processes are substantially complicated and difficult, 
since a contact to p+ type region 55 having a much greater aspect ratio 
may be required. 
Moreover, the thermal processes for fabricating the COB structured DRAM 
element performed at an elevated temperature of over 800.degree. C. 
repeated several times after the processes for forming gate electrodes 58 
and the bit lines is equivalent to a process performed under an elevated 
temperature such as about 870.degree. C. for 9 hours. 
Therefore, an effective barrier layer that can inhibit reaction of the bit 
line metal with the silicon substrate is required in case a metal like 
tungsten is used as the bit line material. 
Referring to FIG. 6A, for the conventional COB structured DRAM element, 
titanium nitride and titanium films 63 and 62 have been used as a barrier 
layer for preventing high temperature diffusion of the bit line tungsten. 
That is, in order to prevent diffusion of the bit line tungsten in the 
processes performed under elevated temperatures after the formation of 
tungsten bit line 64, a barrier layer formed of titanium nitride and 
titanium films 63 and 62 has been formed between bit line 64 and silicon 
substrate 60. Reference number 61 in the drawing is a thick insulation 
film formed of an oxide film. 
However, as has been explained, since the titanium nitride film has a 
columnar structure with many voids, the barrier layer formed of the 
titanium nitride film/titanium film can be spoiled as illustrated in FIG. 
6B. 
Therefore, there has been a problem in that the element can be spoiled due 
to reaction of the tungsten with the substrate through the spoiled barrier 
to form tungsten silicide 65. 
Moreover, there has been a problem in that the resistivity of the foregoing 
titanium nitride film deposited with the reactive sputtering method 
becomes very high (up to about 200-1000 .mu..OMEGA..multidot.cm) due to 
the grain structure illustrated in FIG. 3B, compared to a resistivity of 
about 23 .mu..OMEGA..multidot.cm of a single crystal titanium nitride film 
at room temperature. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide a fine structured titanium 
nitride film with a thermal nitridation process. 
Other objects of this invention include providing a method for forming a 
fine titanium nitride film having low resistivity as well as excellent 
thermal stability. 
Another object of this invention is to provide a fine titanium nitride film 
suitable for a barrier that can prevent high temperature diffusion of a 
bit line metal. 
A further object of this invention is to provide a method for fabricating 
an MOS transistor utilizing the method for forming a fine titanium nitride 
film. 
A still further object of this invention is to provide a method for 
fabricating a COB structured DRAM element utilizing the method for forming 
a fine titanium nitride film. 
These and other objects and features of this invention may be achieved by 
providing a method for forming a fine titanium nitride film, including 
steps for depositing a titanium nitride film on a semiconductor substrate 
with a reactive sputtering method, stuffing oxygen into columnar 
structured grain boundaries of the titanium nitride film by exposing the 
titanium nitride film to atmosphere, depositing a titanium film on the 
titanium nitride film having oxygen stuffed therein, converting the 
titanium film into a fine titanium nitride film by subjecting the titanium 
film to two times of a heat treatment process. 
These and other objects and features of this invention may be achieved by 
providing a method for fabricating a semiconductor element, including 
steps for forming a gate oxide film on a semiconductor substrate, forming 
a polysilicon film on the gate oxide film, depositing a titanium nitride 
film on the polysilicon film, stuffing oxygen into grain boundaries of the 
titanium nitride film by exposing the titanium nitride film to atmosphere, 
depositing a titanium film on the titanium nitride film, converting the 
titanium film into a fine titanium nitride film by subjecting the titanium 
film to rapid thermal annealing, forming a gate by subjecting the fine 
titanium nitride film and the underlying titanium nitride film to 
patterning successively, and forming impurity regions in the substrate by 
subjecting the substrate to second conduction type impurity ion injection 
with the gate used as a mask. 
These and other objects and features of this invention may be achieved by 
providing a method for fabricating a semiconductor element, including 
steps for forming a second conduction type impurity region in a first 
conduction type semiconductor substrate, forming an insulation film on the 
semiconductor substrate having the impurity region formed therein, forming 
a contact hole to the impurity region by removing a part of the insulation 
film on the impurity region, depositing a first titanium film on the 
overall substrate and stuffing oxygen into grain boundaries of the first 
titanium film by exposing the first titanium film to atmosphere, 
depositing a titanium nitride film on the first titanium film and exposing 
the titanium nitride film to atmosphere, depositing a second titanium film 
on the titanium nitride film, converting the second titanium film into a 
fine titanium nitride film by subjecting the second titanium film to rapid 
thermal annealing, forming a bit line metal layer on the titanium nitride 
film, forming a bit line so as to make contact to the impurity region 
through the contact hole by subjecting the titanium nitride film and the 
metal layer to patterning successively, and forming a capacitor by 
carrying out a general capacitor forming process. 
As such, in case the fine titanium nitride film is utilized as an MOS 
transistor gate, a gate satisfying the thermal stability of a polysilicon 
film as well as the low resistivity of a silicide can be obtained. 
As such, in case a COB DRAM element bit line is formed of tungsten, a 
tungsten bit line having excellent contact properties as well as barrier 
properties can be obtained because the fine titanium nitride film and the 
underlying oxygen stuffed titanium nitride film serve as barriers that can 
prevent high temperature diffusion of the tungsten in following capacitor 
forming process.

DETAILED DESCRIPTION OF THE INVENTION 
A method for forming a fine titanium nitride film in accordance with a 
first embodiment of this invention and processes for fabricating a 
semiconductor element utilizing the method are to be explained 
hereinafter, referring to the attached drawings. 
FIGS. 7A to 7D illustrate processes for forming the fine titanium nitride 
film in accordance with the first embodiment of this invention. 
Referring to FIGS. 7A and 7B, thin oxide film 71 is formed on silicon 
substrate 70, and titanium nitride film 72 is formed thereon to a 
thickness of about 50-500 .ANG. with a reactive sputtering method. After 
forming titanium nitride film 72 with a reactive sputtering method, the 
wafer is exposed to atmosphere. That is, titanium nitride film 72 is 
exposed to atmosphere containing oxygen. 
Titanium nitride film 72 exposed to atmosphere absorbs oxygen to stuff 
oxygen into (or introduce into) the grain boundaries of the titanium 
nitride film. Therefore, due to the oxygen stuffed in the voids between 
the grain boundaries of the titanium nitride film, transfer of material 
through the voids of the titanium nitride film is inhibited. Thus, the 
titanium nitride film stuffed with oxygen can serve as a good diffusion 
barrier. 
Titanium film 73 is formed on titanium nitride film 72 to a thickness of 
about 200-2000 .ANG. as illustrated in FIG. 7C, and is subjected to 
nitridation with more than one time of rapid thermal annealing. As a 
result, the titanium film can be converted into fine titanium nitride film 
74 as illustrated in FIG. 7D. As an example, it has been determined that 
nitridation resulting in nitrogen atoms in the titanium film of an amount 
of up to or below about 40% may give good results. 
Titanium nitride film 72 stuffed with oxygen, serving as a diffusion 
barrier inhibiting reaction between titanium film 73 and substrate 70, can 
prevent underlying thin oxide film 71 from being spoiled. 
Of the two (or more) times of rapid thermal annealing done in this 
invention, the first one may be conducted at about 500.degree. C. for 
about 40 seconds and the second one may be conducted at about 800.degree. 
C. for about 30 seconds. 
Properties of the conventional titanium nitride film having the grain 
boundaries stuffed with no oxygen formed by a reactive sputtering method 
and the fine titanium nitride film in accordance with this invention are 
illustrated in FIG. 12. 
As illustrated in FIG. 12, in case two titanium nitride films each having a 
thickness of about 1000 .ANG. are subjected to rapid thermal annealing at 
about 650.degree. C. for about 30 seconds for comparison of the two 
titanium nitride films, the fine titanium nitride film obtained through 
the foregoing processes exhibits an almost constant sheet resistivity of 
about 0.3 .OMEGA./.quadrature. irrespective of the duration of the heat 
treatment with a resistivity of about 30 .mu..OMEGA..multidot.cm, whereas, 
compared to this invention, the conventional titanium nitride film 
deposited by a reactive sputtering method exhibits a substantially greater 
sheet resistivity of about 28 .OMEGA./.quadrature. with a resistivity of 
about 280 .mu..OMEGA..multidot.cm. 
As a result of additional heat treatment done with a varied duration at a 
temperature of about 950.degree. C. in order to investigate thermal 
stability of fine titanium nitride film 74 in accordance with this 
invention, it is found that sheet resistivity Rs of the fine titanium 
nitride film in accordance with this invention is almost constant 
irrespective of the duration of the heat treatment, whereas it is found 
that the conventional titanium nitride film exhibits spoiling of the 
element at the moment when the duration of the additional heat treatment 
exceeds one minute due to a sharp increase of the sheet resistivity to a 
significantly greater value. 
Accordingly, it has been found that the fine titanium nitride film in 
accordance with this invention can satisfy the thermal stability of a 
polycide as well as the low resistivity of a silicide. 
Even though the foregoing embodiment has been explained based on a titanium 
film and a titanium nitride film, it is evident that the embodiment of 
this invention may be applicable not limited to the above, but also may be 
applicable to refractory metals including IVB (Ti, Zr, and Hf) and VB (V, 
Nb, and Ta) groups of the transition metals of the periodic table. 
FIGS. 8A to 8H illustrate processes for fabricating an MOS transistor 
utilizing the method for forming a fine titanium nitride film of FIGS. 7A 
and 7D, having a gate thereof formed of the fine titanium nitride film. 
Referring to FIGS. 8A and 8B, thin gate oxide film 81 having a thickness of 
about 80 .ANG. is formed on silicon substrate 80, and doped polysilicon 
film 82 having a thickness of about 500 .ANG. is deposited thereon. 
Referring to FIG. 8C, titanium nitride film 83 is deposited to a thickness 
of about 100 .ANG. with a reactive sputtering method, and the wafer is 
exposed to atmosphere. That is, titanium nitride film 83 is exposed to 
atmosphere. At this time, grain boundaries of titanium nitride film 83 
exposed to atmosphere are stuffed with oxygen. 
As illustrated in FIG. 8D, by depositing titanium film 84 on titanium 
nitride film 83 to a thickness of about 1000 .ANG., and by subjecting them 
to nitridation/rapid thermal annealing as above as illustrated in FIG. 8E, 
fine titanium nitride film 85 can be formed. 
As illustrated in FIG. 8F, by subjecting fine titanium nitride film 85, 
underlying oxygen-stuffed titanium nitride film 83, and polysilicon film 
82 to patterning, gate 86 made up of fine titanium nitride film 85, oxygen 
stuffed titanium nitride film 83, and polysilicon film 82 can be formed. 
As illustrated in FIG. 8G and 8H, by forming side wall spacers 87 at the 
sides of gate 86, and by injecting impurities having a conductivity 
opposite to substrate 80 into substrate 80 with gate 86 and side wall 
spacers 87 used as masks, impurity regions 88 for the source/drain regions 
are formed. Thus, an MOS transistor having the fine titanium nitride film 
utilized as a gate can be fabricated. At this time, since the fine 
titanium nitride film utilized as a gate has a sheet resistivity of about 
3 .OMEGA./.quadrature., a good gate electrode can be formed. 
FIGS. 9A and 9B illustrate processes for forming a fine titanium nitride 
film in accordance with a second embodiment of this invention. 
Referring to FIG. 9A, titanium film 91, titanium nitride film 92, and 
titanium film 93 are deposited on silicon substrate 90, successively. At 
this time, overlying titanium film 93, titanium nitride film 92, and 
underlying titanium film 91 are deposited to thicknesses of about 200-2000 
.ANG., about 50-500 .ANG., and below about 200 .ANG., respectively. 
Titanium film 91, titanium nitride film 92, and titanium film 93 are not 
deposited on substrate 90 continuously, but are exposed to atmosphere 
after deposition of each of the films in order to stuff the grain 
boundaries with oxygen. That is, on finishing deposition of underlying 
titanium film 91, titanium film 91 is exposed to atmosphere, on finishing 
deposition of titanium nitride film 92, titanium nitride film 92 is 
exposed to atmosphere, and thereafter overlying titanium film 93 is 
deposited. Thus, titanium nitride film 92 stuffed with oxygen can serve as 
a good diffusion barrier. 
As illustrated in FIG. 9B, upon nitridation of overlying titanium film 93 
by subjecting it to more than one time of rapid thermal annealing, 
titanium film 93 is converted into fine titanium nitride film 94. 
Underlying titanium film 91, converted into a titanium silicide TiSi.sub.2 
film through reaction with substrate 90, forms an ohmic contact to improve 
the contact properties. 
Titanium nitride film 92 stuffed with oxygen serving as a diffusion barrier 
isolates the reaction between overlying titanium film 93 and underlying 
titanium film 91. 
Of the two times of rapid thermal annealing also performed in the second 
embodiment of this invention, the first one may be conducted at about 
500.degree. C. for about 40 seconds and the second one may be conducted at 
about 800.degree. C. for about 30 seconds. 
Like the first embodiment of this invention, it is found that the fine 
titanium nitride film in accordance with the second embodiment of this 
invention has the properties as illustrated in FIG. 12. 
Even though the second embodiment has been explained based on a titanium 
film and a titanium nitride film, it is evident that the embodiment of 
this invention may be applicable not limited to the above, but also may be 
applicable to refractory metals including IVB (Ti, Zr, and Hf) and VB (V, 
Nb, and Ta) groups of the transition metals of the periodic table. 
FIGS. 10A to 10E illustrate processes for fabricating a DRAM element 
utilizing the method for forming a fine titanium nitride film of FIGS. 9A 
and 9B. 
Referring to FIG. 10A, impurity region 101 is formed in silicon substrate 
100, and thick oxide film 102 is deposited on substrate 100 having 
impurity region 101 formed therein to a thickness of about 5000 .ANG.. Bit 
line contact 103 to impurity region 101 is formed by etching oxide film 
102 on impurity region 101. 
Titanium film 104, titanium nitride film 105, and titanium film 106 are 
deposited on the overall substrate including bit line contact 103 to 
thicknesses of below about 400 .ANG., about 100 .ANG., and about 100 
.ANG., respectively. 
Titanium film 104, titanium nitride film 105, and titanium film 100 are not 
deposited on substrate 100 continuously, but are exposed to atmosphere 
after deposition of each of the films in order to stuff the grain 
boundaries with oxygen. 
As illustrated in FIG. 10C, upon nitridation of overlying titanium film 106 
by subjecting it to more than one time of rapid thermal annealing, 
titanium film 106 is converted into fine titanium nitride film 107. 
Of underlying titanium film 104, the part in contact with substrate 100 
converts into titanium silicide TiSi.sub.2 film 108 through reaction with 
silicon of substrate 100 and forms an ohmic contact to improve the contact 
properties. Since titanium film 104 in contact with oxide film 102 does 
not react with the oxide film, titanium film 104 remains otherwise in a 
substantially unaltered form. 
Titanium nitride film 105 stuffed with oxygen serving as a diffusion 
barrier isolates the reaction between overlying titanium film 106 and 
underlying titanium film 104. 
Of the two times of rapid thermal annealing conducted, the first one may be 
conducted at about 500.degree. C. for about 40 seconds and the second one 
may be conducted at about 800.degree. C. for about 30 seconds. 
Referring to FIGS. 10D and 10E, bit line 110 is formed by depositing 
tungsten film 109 to a thickness of about 1000 .ANG. with a chemical vapor 
deposition method, and subjecting tungsten film 109, fine titanium nitride 
film 107, oxygen stuffed titanium nitride film 105, and titanium film 104 
to a patterning. 
After forming the bit line, a COB-structured DRAM element may be fabricated 
by carrying out a capacitor forming process. 
Though the fabrication process for forming the COB structured DRAM element 
after formation of the bit line is equivalent to carrying out a heat 
treatment process at about 870.degree. C. for about 9 hours, prevention of 
diffusion of the tungsten even in such high temperature conditions may be 
achieved by the excellent barrier properties of fine titanium nitride film 
107, oxygen stuffed titanium nitride film 105, and titanium film 104. That 
is, tungsten diffusion through the barrier as illustrated in FIG. 6B may 
not occur. It also has an effect that the sheet resistivity is not changed 
even after the additional heat treatment process as illustrated in FIG. 
12. 
FIG. 11 illustrates a section of a COB-structured DRAM element utilizing 
the method for forming a bit line of FIGS. 10A to 10E. 
As illustrated in FIG. 11, different from the polysilicon film, metal bit 
line 110 may be formed on all kinds of impurity regions, irrespective of 
the conduction type of impurity regions 112 and 113. 
Comparing FIG. 5 and FIG. 11, in case a bit line is formed of a metal as 
with this invention, since the aspect ratio of a contact formed for 
following wiring process may be smaller by 1/2, the following processes 
become much easier. Since the titanium silicide formed at the bit line 
contact forms an ohmic contact, the contact resistance can be reduced as 
compared with the case in which the bit line is formed of a polysilicon 
film. 
This invention as explained above can provide a titanium nitride film 
having an excellent thermal stability, a low resistivity, and a fine 
structure by a nitridation process using a heat treatment process. 
Therefore, since the fine titanium nitride film, serving as an excellent 
barrier, prevents the bit line metal from diffusing, a DRAM element having 
excellent properties may be fabricated. In case the fine titanium nitride 
film is used as an MOS transistor gate, the gate may satisfy the thermal 
stability of a polysilicon as well as the low resistivity of a silicide. 
Although the invention has been described in conjunction with specific 
embodiments, it is evident that many alternatives and variations will be 
apparent to those skilled in the art in light of the foregoing 
description. Accordingly, the invention is intended to embrace all of the 
alternatives and variations that fall within the spirit and scope of the 
appended claims.