Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1999-03-19
2001-03-06
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S653000, C438S906000, C438S679000, C438S630000
Reexamination Certificate
active
06197684
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to the fabrication of semiconductor integrated circuits (ICs), and more particularly to a method for forming a metal/metal nitride layer.
2. Description of the Related Art
As the integration of integrated circuits increases, the surface area of a wafer becomes insufficient for fabrication of required interconnections. In order to meet the surface requirement of the interconnections, multi-layered interconnections have become widely used in highly integrated devices. Typically, a dielectric layer is formed between metallic layers to isolate the metallic layers from each other. A metallic plug is formed to connect the metallic layers to each other. However, in order to improve the adhesion between the metallic plug and other materials as well as to avoid a spike effect between the metallic plug and silicon material, it is necessary to form a barrier layer before the metallic plug.
Titanium nitride (TixNy) is a barrier layer material or a glue layer material frequently used in Very Large Scale Integration (VLSI). In order to improve the ohmic contact between the metallic plug and the silicon material, titanium nitride is usually used with titanium. For example, titanium/titanium nitride (Ti/TiN) are used together as a barrier layer in order to reduce the work function at a junction as well as to prevent the occurrence of the spike effect and electrical migration.
Among all metal materials, tungsten has an advantageous high melting point, heat expansion ratio, and correspondence to silicon. In addition, tungsten deposited by chemical vapor deposition (CVD) does not have a high internal stress, and has a better step coverage. Thus, the manufacture of the metal plug with tungsten deposited by CVD has been widely used in the secondary micrometer process.
FIGS. 1A
to
1
C are schematic, cross-sectional views showing a conventional method of forming a titanium/titanium nitride layer. In
FIG. 1A
, a metal oxide semiconductor (MOS) transistor
102
is formed on a substrate
100
. A patterned dielectric layer
104
is formed on the substrate
100
to cover the MOS transistor
102
. The patterned dielectric layer
104
comprises a contact opening
106
therein. The contact opening
106
exposes a portion of a source/drain region
108
in the substrate
100
.
In
FIG. 1B
, a titanium layer
110
is sputter-deposited on the dielectric layer
104
to cover the exposed source/drain region
108
. The titanium layer
110
is conformal to the contact opening
106
. In order to increase the deposition ability of the titanium layer
110
, a collimator (not shown) is placed between the substrate
100
and a metallic target (not shown) while forming the titanium layer
110
.
In
FIG. 1C
, a titanium nitride layer
112
is formed on the titanium layer
110
by physical vapor deposition (PVD). The titanium nitride layer
112
is conformal to the contact opening
106
. The titanium layer
110
and the titanium nitride layer
112
together form a barrier layer. However, the barrier layer formed by physical vapor deposition on a contact or a via, having a high aspect ratio does not have a sufficient step coverage ability. The titanium layer
110
positioned on the comers of the bottom of the contact opening
106
is exposed, as indicated by reference number
114
shown in
FIG. 1C
, while depositing the titanium nitride layer
112
.
When tungsten metal is deposited in the contact opening
106
as a plug, WF
6
serves as the gas source for CVD. Once the titanium layer
110
is exposed due to the poor step coverage of the titanium nitride layer
12
or any defect in the titanium nitride layer
112
, F atoms released by WF
6
can pass through the titanium nitride layer
112
and react with titanium located below to form TiF
4
. As TiF
4
is a volatile gas, a phenomenon similar to an explosion will occur when tungsten is deposited on the contact opening
106
. This is known as a volcano effect. The occurrence of such an effect results in removal or bending of the titanium nitride layer
112
, allowing tungsten to be deposited on both sides of the titanium nitride
112
layer that are removed. If this occurs on the top end comer of the contact opening or the interlayer opening, there will be a projection of the surface of the tungsten layer. When the projection is too severe, the projection is difficult to remove using a normal reactive etching process. As a result, this leads to the problems of a blind window, a short circuit, wafer pollution, and low production.
SUMMARY OF THE INVENTION
The invention provides a method for forming a metal/metal nitride layer. A dielectric layer is formed on a substrate comprising a conductive region. The dielectric layer comprises an opening exposing a portion of the conductive region. A conformal metal layer is formed on the dielectric layer by physical vapor deposition using collimator to cover the exposed conductive region. A metal nitride layer is formed on the metal layer. A part of the metal layer may be exposed due to poor step coverage. An implanting process is performed on the metal nitride layer and on the exposed metal layer using a nitric gas.
The invention performs the implanting process to reinforce the metal nitride layer. The exposed metal layer can react with the nitric gas to form metal nitride to cover the exposed metal layer. Tungsten can be deposited in the opening without a volcano effect.
REFERENCES:
patent: 5401675 (1995-03-01), Lee et al.
patent: 5547881 (1996-08-01), Wang et al.
patent: 5600182 (1997-02-01), Schinella et al.
patent: 5804505 (1998-09-01), Yamada et al.
patent: 5885896 (1999-03-01), Thakur et al.
Anya Igwe U.
Oppenheimer Wolf & Donnelly LLP
Smith Matthew
United Microelectronics Corp.
LandOfFree
Method for forming metal/metal nitride layer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for forming metal/metal nitride layer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for forming metal/metal nitride layer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2479605