Electricity: measuring and testing – Determining nonelectric properties by measuring electric...
Reexamination Certificate
2002-10-30
2004-07-13
Pert, Evan (Department: 2829)
Electricity: measuring and testing
Determining nonelectric properties by measuring electric...
C257S048000
Reexamination Certificate
active
06762597
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to interconnect technology in integrated circuit fabrication, and more particularly, to an interconnect structure, a system, and a method for assessing the permeability of layer material within interconnect such as a diffusion barrier layer material at a via bottom for example.
BACKGROUND OF THE INVENTION
Common components of a monolithic IC (integrated circuit) include interconnect structures such as metal lines for electrically connecting integrated circuit devices formed on a semiconductor substrate, as known to one of ordinary skill in the art of integrated circuit fabrication. A long-recognized important objective in the constant advancement of monolithic IC (Integrated Circuit) technology is the scaling-down of IC dimensions. Such scaling-down of IC dimensions reduces area capacitance and is critical to obtaining higher speed performance of integrated circuits. Moreover, reducing the area of an IC die leads to higher yield in IC fabrication. Such advantages are a driving force to constantly scale down IC dimensions.
Thus far, aluminum has been prevalently used for metallization within integrated circuits. However, as the width of metal lines are scaled down to smaller submicron and even nanometer dimensions, aluminum metallization is more prone to electromigration failure. Electromigration failure, which may lead to open and extruded metal lines, is now a commonly recognized problem. Moreover, as dimensions of metal lines further decrease, metal line resistance increases substantially, and this increase in line resistance may adversely affect circuit performance.
Given the concerns of electromigration and line resistance with smaller metal lines and vias, copper is considered a more viable metal for smaller metallization dimensions. Copper has lower bulk resistivity and potentially higher electromigration tolerance than aluminum. Both the lower bulk resistivity and the higher electromigration tolerance improve circuit performance.
Unfortunately, copper is a mid-bandgap impurity in silicon, silicon dioxide, and other dielectric materials. Thus, copper may diffuse easily into these common integrated circuit materials to degrade the circuit performance of integrated circuits. To prevent such undesired diffusion of copper, a diffusion barrier layer material is deposited to surround the copper interconnect at the interface between the copper interconnect and the surrounding material, as known to one of ordinary skill in the art of integrated circuit fabrication.
As device dimensions including dimensions of the copper interconnect are further scaled down, the thickness of the diffusion barrier layer material surrounding the interconnect is minimized to in turn minimize the resistance of the interconnect. However, with such thinner diffusion barrier layer material surrounding the interconnect, the material of the interconnect may undesirably move through the thin diffusion barrier layer material due to electron wind force. Such flux divergence is especially prevalent with higher current density through the interconnect as dimensions of the interconnect are further scaled down.
Such an attribute of the diffusion barrier layer material surrounding an interconnect wherein material of the interconnect moves through the diffusion barrier layer material due to electron wind force is termed the “permeability” of the diffusion barrier layer material that is said to be “permeable”. The flux of material of the interconnect through the diffusion barrier layer material may lead to interconnect failure from formation of voids within the interconnect. Thus, the permeability of the diffusion barrier layer material is desired to be characterized.
FIG. 1
shows an interconnect test structure
100
of the prior art for characterizing electromigration failure of a test line
102
. The test line
102
is comprised of copper for example, and in that case, the test line
102
is surrounded by a diffusion barrier layer material
104
. The test line
102
is coupled to a first feeder line
106
by a first via
108
, and the test line
102
is coupled to a second feeder line
110
by a second via
112
. The first via
108
and the second via
112
are part of the dual damascene structure of the test line
102
, and the diffusion barrier layer material
104
surrounds the first via
108
and the second via
112
.
The first and second feeder lines
106
and
110
are comprised of copper for example, and in that case, the first and second feeder lines
106
and
110
are surrounded by diffusion barrier layer materials
114
and
116
, respectively. The first feeder line
106
is coupled to a first test pad
118
, and the second feeder line
110
is coupled to a second test pad
120
. During characterization of the interconnect test structure
100
of the prior art, electrons flow from the first feeder line
106
through the test line
102
to the second feeder line
110
when current is applied to flow through the interconnect test structure
100
via the first and second test pads
118
and
120
.
In the interconnect test structure
100
of the prior art, the width of the feeder lines
106
and
110
(i.e., the dimension of the lines
106
and
110
going into the drawing page of
FIG. 1
) is significantly larger (i.e., more than ten times larger for example) than the width of the test line
102
(i.e., the dimension of the test line
102
going into the drawing page of FIG.
1
). Thus, even when the diffusion barrier layer material
104
at the interface of interest
122
between the first via
108
and the first feeder line
106
is significantly permeable, the effect of the flux of material of the first feeder line
106
through such diffusion barrier layer material
104
into the test line
102
is not noticeable because the volume of such flux of material of the first feeder line
106
through the diffusion barrier layer material
104
into the test line
102
is negligible compared to the total volume of the first feeder line
106
.
However, the permeability of the diffusion barrier layer material is desired to be characterized because flux of material of the interconnect through the diffusion barrier layer material may lead to interconnect failure from formation of voids within the interconnect. Thus, a mechanism is desired for assessing the permeability of the diffusion barrier layer material within interconnect.
SUMMARY OF THE INVENTION
Accordingly, in a general aspect of the present invention, a novel interconnect test structure is formed to assess the permeability of layer material within interconnect.
In one embodiment of the present invention, an interconnect test structure for assessing electromigration permeability of a layer material within an interconnect includes a feeder line comprised of a conductive material and having a first current density, J
1
, and a first length, L
1
. In addition, the interconnect test structure includes a cathode line comprised of a conductive material and coupled to the feeder line, and the cathode line is a source of electrons flowing into the feeder line. Furthermore, the interconnect test structure includes a test line comprised of a conductive material and coupled to the feeder line and having a second current density, L
2
, and a second length, L
2
, and the test line is a sink of electrons flowing from the feeder line. Additionally, the interconnect test structure includes a no-flux structure disposed between the cathode line and the feeder line. The layer material is disposed between the feeder line and the test line.
A product of the first current density and the first length of the feeder line, J
1
*L
1
, is less than a critical Blech length constant, (J*L)
CRIT1
for the feeder line. In addition, a product of the second current density and the second length of the test line, J
2
*L
2
, is greater than a critical Blech length constant, (J*L)
CRIT2
for the test line. An occurrence of a void within the feeder line indicates that the layer material is permeable, and an occurrence of a void withi
Hau-Riege Christine
Hau-Riege Stefan
Marathe Amit P.
Choi Monica H.
Pert Evan
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