Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2000-04-18
2002-11-05
Dang, Trung (Department: 2823)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S627000, C438S637000, C438S653000, C438S656000
Reexamination Certificate
active
06475907
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device having a barrier metal layer made of a refractory metal film and a method for manufacturing the same and, more particularly to, the semiconductor device having the barrier metal layer with a barrier property which is improved by inhibiting crystallization of the barrier metal layer and the method for manufacturing the same.
2. Description of the Related Art
With the increasing integration density of Large Scale Integrations (LSIs), contact holes need to be more and more finely patterned, thus increasing an aspect ratio, i.e. a value of a depth of the contact hole divided by its diameter. With this, a layer made of aluminum or other metal formed by a conventional sputtering method, which has rather poor step coverage, may cause an increase in contact resistance at a contact hole or, possibly, disconnection at it. Even if wiring is possible, moreover, there might occur such an electro-migration phenomenon that a current flow would cause migration of aluminum atoms, so that the wiring is liable to be disconnected, thus problematically lowering a reliability.
To solve this problem, such a method has been employed that metal having good step coverage is buried in the contact hole.
A typical one of such methods is a tungsten-plug method whereby a tungsten layer excellent in step coverage formed by a Chemical Vapor Deposition (CVD) method is buried in the contact hole. According to this tungsten-plug method, first a titanium film is formed in the contact hole by a sputtering method to reduce connection resistance (contact resistance) of the contact hole, then, a barrier metal film made of titanium nitride is formed in the contact hole by the sputtering method to enhance adherence between this titanium film and the tungsten layer as well as to prevent the tungsten layer from penetrating into a substrate, and then the tungsten layer is buried into the contact hole by the CVD method, and then the tungsten layer is etched back overall to be left only in the contact hole, thus forming a tungsten plug. With this method also, as the fine patterning of the contact hole advances and therefore its aspect ratio is increased, the sputtering method becomes unable to form the titanium film or titanium nitride film, i.e. barrier metal layer, to a desired thickness in the contact hole. This may lead to increase in contact resistance or destruction of circuit elements by the tungsten layer.
To guard against this, it has been attempted to form the titanium film and the titanium nitride film by the CVD method. This thermal-reaction CVD method is widely used because the titanium film nitride formed by such CVD method as utilizing thermal reaction is most excellent in step coverage. Note here that the contact hole is filled with the titanium film, the titanium nitride film, and a tungsten film, all three of which are formed by the CVD method.
First, as shown in
FIG. 3A
, on a silicon substrate
301
on which element-isolating regions are defined by field insulator films (not shown), a silicon oxide film
302
is formed as an inter-layer insulator film to a thickness of 1.5 &mgr;m by the CVD method.
Next, as shown in
FIG. 3B
, a photo-resist film
303
is formed on the silicon oxide film
302
and then patterned by typical photolithography so as to make an opening at positions where a contact hole
304
is to be formed. Using this photo-resist film
303
as a mask, dry etching is performed to form the contact hole
304
in this silicon film
302
which reaches the silicon substrate
301
. This contact hole
304
has a diameter of approximately 0.4 &mgr;m.
Next, as shown in
FIG. 3C
, the photo-resist film
303
is removed and then a titanium film
305
is formed. Specifically, this titanium film
305
is formed to a thickness of 10 nm by the CVD method, whereby a plasma is generated by flowing a gas mixture containing 10 sccm (standard cubic centimeter per minute) of titanium tetra-chloride and 1000 sccm of argon (Ar), setting an intra-chamber pressure at 20 Torr and a wafer temperature at 500° C. or higher, and applying several hundreds of watts of high-frequency power between the opposing electrodes of the silicon substrate
301
.
Next, as shown in
FIG. 3D
, a first titanium nitride film
306
is formed on the titanium film
305
to a thickness of 60 nm. Specifically, this first titanium nitride film
306
can be formed by flowing 50 sccm of titanium tetra-chloride, 100 sccm of ammonia, and 50 sccm of nitrogen, setting the intra-chamber pressure at 30 Torr, and heating a susceptor so that the wafer temperature would be 600° C.
Next, as shown in
FIG. 3E
, a tungsten film
307
is formed overall by the CVD method to fill the contact hole
304
. In fact, the tungsten film
307
is formed in two steps of nucleation and hole filling. Specifically, after the semiconductor substrate
301
is heated to 450° C., a gas mixture is introduced which contains 10 sccm of mono-silane, 20 sccm of tungsten hexa-fluoride, 800 sccm of argon, and 1000 sccm of hydrogen and setting the intra-chamber pressure at 30 Torr by use of a pressure regulating valve to perform the tungsten film
307
formation for about 10 seconds.
After nucleation is thus performed on the silicon substrate
301
, continuously a gas mixture is introduced which contains 95 sccm of tungsten hexa-fluoride, 600 sccm of argon, and 1000 sccm of hydrogen and setting the intra-chamber pressure at 90 Torr to perform the tungsten film
307
formation for about 50 seconds in order to fill the contact hole
304
. Under these conditions, the tungsten film
307
is formed to a thickness of about 5000 Å on the silicon oxide film
302
.
Next, as shown in
FIG. 3F
, part of the tungsten film
307
in the contact hole
304
being left as is, the other part of the tungsten film is etched back and removed by use of a gas containing sulfur hexa-fluoride, to expose the surface of the first titanium nitride film
306
.
Next, as shown in
FIG. 3G
, an aluminum-alloy film
308
is deposited overall by the sputtering method and patterned into a desired wiring by photolithographic and dry etching methods, to complete an aluminum wiring.
According to the above-mentioned prior-art technologies, however, the first titanium nitride film
306
formed by the thermal CVD method is of a prismatic polycrystalline construction and so has a lot of grain boundaries with insufficient barrier nature. To improve the barrier property, it is effective to increase the thickness of the first titanium nitride film
306
, which may destroy a diffused layer formed in the silicon substrate
301
surface and also may result in increase in the aspect ratio of the contact hole
304
into which tungsten plug
309
is to be buried. When the titanium nitride film
306
is formed by the CVD method, in particular, the titanium nitride film
306
titanium nitride film
306
is subject to larger stress, which may cause cracking in the first titanium nitride film
306
or its flaking-off, thus reducing manufacturing yield.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to provide a semiconductor device having a barrier metal layer which can improve a barrier property and prevent lowering of manufacturing yield without destruction of diffused layers in a substrate surface nor deterioration of an aspect ratio of contact holes and a method for manufacturing a same.
According to a first aspect of the present invention, there is provided a semiconductor device having a barrier metal layer, including:
a semiconductor substrate;
an insulator film having a through hole therein formed on the semiconductor substrate;
a first refractory metal nitride film which is formed on an inside surface of the through hole in the insulator film and a surface of which is oxidized or in a surface of which oxygen is absorbed; and
a second refractory metal nitride film which is formed on the first refractory metal nitride film and which has taken in oxygen.
In the foregoing, the
Dang Trung
Hayes & Soloway PC
Kebede Brook
NEC Corporation
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