Active solid-state devices (e.g. – transistors – solid-state diode – Test or calibration structure
Reexamination Certificate
2000-03-27
2002-05-14
Jackson, Jr., Jerome (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Test or calibration structure
C257S767000, C257S773000
Reexamination Certificate
active
06388269
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a metal interconnection structure for evaluation on electromigration appeared therein, and more particularly to a metal interconnection structure for evaluation on reliability of a semiconductor device.
The electromigration has been known to be a phenomenon that metal ions in the metal interconnection in the semiconductor device are moved by exchange in momentum between electrons as current carriers flowing through the metal interconnection and the metal ions in the metal interconnection under an increased current density of the metal interconnection and/or an increased device temperature due to an increased power for each chip. The electromigration may cause a local formation of voids in the metal interconnection, whereby a resistance of the metal interconnection is increased and a disconnection to the metal interconnection appears. Namely, the electromigration deteriorates the reliability of the semiconductor device. For those reasons, it is important to do an evaluation on the electromigration of the metal interconnection of the semiconductor device.
FIG. 1
is a fragmentary plane view illustrative of a metal interconnection and a plug interconnection for connection to an electrode pad to conduct an electromigration-evaluation test. A plug interconnection
22
made of aluminum has a width wider than a metal interconnection
21
made of aluminum as a sample for evaluation on electromigration. The test is made by applying a current through the plug interconnection
22
and the metal interconnection
21
, whereby electrons
25
move in a direction from the plug interconnection
22
to the metal interconnection
21
, and also aluminum atoms
26
are moved by exchange in momentum with the electrons
25
. Namely, the aluminum atoms
26
flow from the plug interconnection
22
to the metal interconnection
21
. As described above, the plug interconnection
22
is wider than the metal interconnection
21
. The plug interconnection
22
serves as a large aluminum atom donor which supplies aluminum atoms
26
to the metal interconnection
21
. Supply of aluminum atoms
26
from the plug interconnection
22
to the metal interconnection
21
compensates electromigration of the metal interconnection
21
, thereby disturbing the evaluation on electromigration.
In order to suppress that the aluminum atoms
26
in the plug interconnection
22
are moved into the metal interconnection
21
, it was proposed that opposite ends of the metal interconnection
21
are terminated with other metal than aluminum.
FIG. 2A
is a fragmentary plane view illustrative of another connection structure of plug vias between an aluminum interconnection for evaluation on electromigration and an aluminum plug interconnection.
FIG. 2B
is a fragmentary cross sectional elevation view illustrative of the other connection structure of plug vias between an aluminum interconnection for evaluation on electromigration and an aluminum plug interconnection as shown in FIG.
2
A. An aluminum interconnection
21
for evaluation on electromigration is connected through tungsten plug vias
24
to an aluminum plug interconnection
22
. A current is applied from the aluminum plug interconnection
22
to the aluminum interconnection
21
. The current causes aluminum atoms in the aluminum plug interconnection
22
to move toward one end thereof which is connected through the tungsten plug vias
24
to the aluminum interconnection
21
. The aluminum atoms do not move through the tungsten plug vias
24
to the aluminum interconnection
21
. The current flows from the aluminum plug interconnection
22
through the tungsten plug vias
24
to the aluminum interconnection
21
. Aluminum atoms
26
in the aluminum interconnection
21
are moved by the electromigration without any supply of aluminum atoms from the aluminum plug interconnection
22
. A discontinuation in flow of aluminum atoms causes the electromigration in the boundary between the aluminum interconnection and the tungsten plug vias. This electromigration forms voids. The movement of aluminum atoms by the electromigration is due to a drift of aluminum atoms in the aluminum interconnection.
The first test pattern shown in
FIG. 1
has the following problems. The aluminum interconnection
21
to be evaluated on electromigration is connected with the wide aluminum plug interconnection
22
which is connected with the electrode pad not illustrated. Crystal grains
23
exist in not only the aluminum interconnection
21
but also the aluminum plug interconnection
22
. Namely, aluminum atoms are likely to move along the crystal grains
23
not only in the aluminum interconnection
21
but also in the aluminum plug interconnection
22
. The aluminum atoms flow from the aluminum plug interconnection
22
into the aluminum interconnection
21
. This means that the aluminum atoms are supplied from the aluminum plug interconnection
22
into the aluminum interconnection
21
, whereby even aluminum atoms in the aluminum interconnection
21
are moved by the electromigration, the supply of the aluminum atoms from the aluminum plug interconnection
22
compensate the electromigration in the aluminum interconnection
21
, whereby an electromigration life-time is made long. Particularly, if the aluminum interconnection is abutted with a titanium layer, a TiAl alloy exists in the boundary between the aluminum interconnection and the titanium layer. Aluminum atoms are easy to move through a Ti—Al interface. Namely, the aluminum atoms are easily to be supplied into the aluminum interconnection to be evaluated on electromigration. As a result, even the electromigration appears in the aluminum interconnection, externally supplied aluminum atoms may compensate the electromigration to suppress formation of voids in the aluminum interconnection. Further external supply of aluminum atoms into the aluminum interconnection to be evaluated on electromigration results in increase in volume of the aluminum interconnection and in reduction in resistance of the aluminum interconnection.
The second test pattern shown in
FIG. 2
has a similar structure to the actual interconnection layout pattern, whereby an accurate evaluation on electromigration life-time of the aluminum interconnection. The second test pattern shown in
FIG. 2
is, however, disadvantage in a complicated structure which needs a longer time necessary for forming the test pattern than the first test pattern of FIG.
1
. As illustrated in
FIG. 2B
, the aluminum interconnection
21
to be evaluated on electromigration is formed at a different level from the aluminum plug interconnection
22
. Further, the aluminum interconnection
21
and the aluminum plug interconnection
22
are connected to each other through the tungsten plug vias
24
.
FIG. 3
is a diagram illustrative of variations in resistance of the metal interconnections of the first and second test patterns shown in FIGS.
1
and
2
A-
2
B versus time of electromigration test. The first test pattern remains in resistance due to supply of aluminum atoms from the aluminum plug interconnection and then decreases in resistance due to excess supply of aluminum atoms from the aluminum plug interconnection. Namely, the electromigration appeared in the aluminum interconnection is compensated by the supply of aluminum atoms from the aluminum plug interconnection. The wide aluminum interconnection has a large number of crystal grains which make it easy for aluminum atoms to move through the aluminum interconnection. Aluminum atoms are moved toward an anode whilst voids are moved toward a cathode. The voids are, however, filled up with the aluminum atoms supplied from the aluminum plug interconnection. The second test pattern remains in resistance before the electromigration appears but after the electromigration appears, the resistance increases apparently.
In order to prevent compensation to electromigration by external supply of aluminum atoms, the aluminum interconnection to be evaluated on electromigration is terminate
Jackson, Jr. Jerome
NEC Corporation
Young & Thompson
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