Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1998-01-26
2001-06-19
Everhart, Caridad (Department: 2825)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S631000, C438S633000, C438S692000
Reexamination Certificate
active
06248660
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for forming a metallic plug, for example, in a manufacturing process in a silicon semiconductor device.
BACKGROUND OF THE INVENTION
In order to realize high performance in a silicon semiconductor device, it is necessary to make a device minute and multilayer in structure. However, it has become more difficult to improve reliability in metal wiring, as the device has become smaller. In order to improve reliability in metal wiring, it is particularly necessary to make an extremely large recessed volume of metal small enough in the case of forming a metallic plug that is used for improving reliability at an end connection portion for connecting wires of an upper layer and of a lower layer. Recently, a polishing technique has been introduced into a silicon semiconductor process as a means for reducing a recessed volume.
An example of a conventional method for forming a metallic plug using the polishing technology is explained referring to
FIGS. 8A-8D
as follows. First, an aluminum alloy film is formed on an interlayer dielectric
1
, which insulates an upper wire and a lower wire, by a sputter deposition method or the like. After forming a predetermined resist pattern on the aluminum alloy film by a photolithographic process, the extra aluminum alloy film is eliminated by dry etching and the resist is then also eliminated, thus obtaining a conductive layer
3
as shown in FIG.
8
A. In this case, an example of metal wiring using an aluminum alloy film as the conductive layer
3
is explained, but the conductive layer
3
may be a conductive layer or diffusion layer such as a polycrystalline silicon or the like.
Next, a dielectric that is a silicone oxide film is formed by a CVD method and the dielectric is planarized through a planarization process, thus forming an interlayer dielectric
2
. After forming a predetermined resist pattern on the interlayer dielectric
2
by a photolithographic process, an extra dielectric is eliminated by dry etching and the resist is then also eliminated, thus obtaining an end connection
4
. The end connection
4
is used for connecting the conductive layer
3
and another conductive layer formed thereon, and is open so that the surface of the conductive layer
3
is exposed.
As a next step, an adhesive layer
5
having a layered structure of a titanium nitride film and a titanium film is formed by a sputter deposition method or the like as shown in
FIG. 8B. A
tungsten film
6
as a filling film is then formed using a CVD method so as to fill in the end connection
4
completely as shown in FIG.
8
C. The film thickness of the tungsten film
6
is about 0.3 &mgr;m-1.0 &mgr;m except for the end connection
4
portions.
Finally, a metallic plug
7
is obtained by polishing the tungsten film
6
and the adhesive layer
5
using a polishing device until a part of the interlayer dielectric
2
where the end connection
4
is not formed is completely exposed as shown in FIG.
8
D. In a slurry used in the polish, alumina is used as an abrasive grain, and iron nitrate, a hydrogen peroxide solution, potassium iodate or the like is used for adjusting pH.
There is no big difference of elevation between the surface of the interlayer dielectric
2
exposed and that of the metallic plug
7
, since tungsten is eliminated by polishing. As a result, the recessed volume at the end connection
4
portions after eliminating the tungsten film
6
can be 0.1 &mgr;m or less, thus obtaining a highly reliable conductive layer.
However, in the conventional method mentioned above for forming a metallic plug, when the variation in a polishing rate within a substrate in the case of polishing the tungsten film
6
is not small enough with respect to the variation within a substrate in the case of forming a tungsten film, the polishing time until the interlayer dielectric
2
is exposed is different at different places within the substrate. When the polishing time is different, a portion
8
of the adhesive layer
5
that can not be eliminated is created within the substrate as shown in FIG.
8
D. As mentioned above, in the case where the adhesive layer can not be eliminated, reliability in a semiconductor device decreases, since a short occurs between conductive layers in the same layer.
Furthermore, even in the case where polishing is conducted only for eliminating the whole tungsten film
6
and adhesive layer
5
within the substrate, a difference of elevation (erosion)
9
depending on a pattern density of the end connection
4
occurs on the surface of the interlayer dielectric
2
, since an area having a rapid polishing rate is overpolished. As mentioned above, pattern formation in a photolithography process becomes difficult, when difference of elevation occurs on an interlayer dielectric. Moreover, height of a metallic plug is different according to the difference of elevation of an interlayer dielectric, which causes great variations in resistance at an end connection. As a result, reliability decreases.
SUMMARY OF THE INVENTION
The problem mentioned above can be solved by a method for forming a metallic plug of the present invention. It is an object of the present invention to prevent pattern defects by erosion or a short between conductive layers caused by variation in a polishing rate within a substrate and decrease of reliability in a conductive layer by eliminating a filling film by dry etching beforehand before polishing the filling film such as a tungsten film or the like.
In order to achieve the object mentioned above, a first method for forming a metallic plug of the present invention comprises the following steps: forming an end connection opened in an interlayer dielectric so as to expose the surface of a conductive layer under the interlayer dielectric; forming an adhesive layer on the conductive layer exposed and on the interlayer dielectric; and forming a filling film on the adhesive layer, which fills the end connection completely. The first method for forming a metallic plug of the present invention is characterized by polishing and eliminating the filling film and the adhesive layer using a slurry for polishing a metal after eliminating the filling film by dry etching beforehand.
According to the first method for forming a metallic plug, even in the case of having great variations in a polishing rate within a substrate in the case of polishing the filling film, the variation in the remaining film within the substrate in the case of eliminating the filling film and the adhesive layer completely can be minimized and the volume to be overpolished can be restrained to a low level due to a small volume of the filing film to be polished. As a result, the occurrence of defects due to a short between conductive layers caused by creating a portion where an adhesive layer can not be eliminated can be prevented. In addition, the decrease of reliability in a conductive layer caused by a change of plug resistance due to erosion can be prevented.
In the first method for forming a metallic plug, it is preferable that the adhesive layer has a layered structure of a titanium nitride film and a titanium film. In the case where the adhesive layer has a layered structure as mentioned above, a filling film can adhere to a conductive layer tightly enough.
In addition, it is preferable that the filling film is a tungsten film. In the case of using the tungsten film, the tungsten film can be eliminated by polishing.
Furthermore, it is also preferable that the film thickness of the filling film before being dry etched is in the range of 0.3-1.0 &mgr;m at a portion not having an end connection. In the case where the film thickness is in the range mentioned above, the end connection can be completely filled.
It is further preferable that a volume of the filling film to be eliminated beforehand is 60% or more of the film thickness of the filling film formed. According to such a method for forming a metallic plug, even in the case of having great variations in a polishing rate within a substrate in the case of polishin
Hamanaka Masashi
Ishida Tetsuo
Shishino Masafumi
Everhart Caridad
Matsushita Electronics Corporation
Merchant & Gould P.C.
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