Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified material other than unalloyed aluminum
Reexamination Certificate
2000-06-01
2004-11-16
Quach, T. N. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
C257S752000, C257S764000, C257S766000
Reexamination Certificate
active
06818991
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device and a method of forming the same, and more particularly to a copper-alloy interconnection structure formed in an inter-layer insulator in a semiconductor device and a method of forming the same.
In recent years, the degree of integration of semiconductor devices such as LSI has been on the increase in response to the requirements for improvement in functions of electronic devices and for scaling down and reduction in weight as well as improvement in high speed performance. In order to realize the increase in the degree of integration of the semiconductor devices, it is essential to reduce a width of the interconnection. The majority of the conventional interconnection comprises an aluminum interconnection because aluminum is low in electrical resistance and is superior in adhesiveness with a silicon dioxide film as well as superior in formability.
The aluminum interconnection raises serious problems in electromigration, stressmigration, and formation of voids particularly as the width of the aluminum interconnection is reduced for realizing the increase in the degree of integration of the semiconductor devices. In these circumstances, recently, other available materials than aluminum have been investigated as the interconnection materials free from the above problems.
Copper is attractive as the interconnection material reduced in width. Copper is lower in electric resistance than aluminum. Namely, the electric resistance of copper is about two third of the electric resistance of aluminum. For this reason, the copper interconnection allows a higher current density than the aluminum interconnection. Further, copper is higher in melting point than aluminum by not less than 400° C. This means that the copper interconnection is higher in stability to electromigration than the aluminum interconnection. The copper interconnection is, thus, attractive as the interconnection material for the advanced semiconductor device such as LSI.
If, however, the width of the copper interconnection is reduced to about 0.3 micrometers, then an electromigration is caused, and the copper interconnection is made deteriorated due to an electromigration. In order to reduce the electromigration of the copper interconnection having a reduced with of about 0.3 micrometers, it is effective to enlarge crystal grain sizes of copper of the copper interconnection. The enlargement in crystal grain size of copper causes grain boundaries of the crystal grain to be diffused, thereby suppressing movement of copper atoms through the copper interconnection. The suppression of the movement of copper atoms through the copper interconnection means suppression of electromigration. In Japanese laid-open patent publication No. 4-326521, it is disclosed that a copper interconnection has a copper crystal grain size of not less than 1 micrometer. This copper interconnection may be formed by a deposition of a copper film on an insulation film on a semiconductor substrate by either a molecular beam epitaxy or a sputtering method, and subsequent patterning the copper film by a dry etching process. Similar conventional techniques are also disclosed in Japanese laid-open patent publication No. 5-47760 and 10-60633.
In order to realize the reduction in width of the interconnection, it is required to accurately and conveniently form the interconnection. For this purpose, in place of the above method of deposition of the copper film and subsequent patterning the same by a dry etching process, the following method has been proposed. A groove is formed in an insulation film on a semiconductor substrate. A copper film is filled within the groove for subsequent heat treatment to form a copper interconnection in the groove. This conventional method is suitable for forming a fine copper interconnection with a reduced width. It is not so difficult to accurately control the width of the groove in the insulation film. This means it not so difficult to accurately control the width of the copper interconnection in the groove.
FIG. 1A
is a fragmentary cross sectional elevation view illustrative of a conventional copper interconnection formed in a trench groove in an insulation film over a semiconductor substrate, taken along a plane vertical to a longitudinal direction of the copper interconnection.
FIG. 1B
is a fragmentary perspective view illustrative of the conventional copper interconnection of FIG.
1
A.
FIG. 1C
is a fragmentary cross sectional elevation view illustrative of the conventional copper interconnection, taken along a B-B′ line of FIG
1
B, wherein the B-B′ line is parallel to the longitudinal direction of the copper interconnection.
FIGS. 2A through 2D
are fragmentary cross sectional elevation views illustrative of sequential steps involved in a conventional method of forming a copper interconnection formed in a trench groove in an insulation film over a semiconductor substrate, taken along a plane vertical to a longitudinal direction of the copper interconnection.
A copper interconnection
400
comprises a copper layer
41
and a barrier material layer
2
. The copper interconnection
400
is formed in a trench groove formed in an inter-layer insulator
10
formed on a semiconductor substrate
0
. The barrier metal layer
2
is formed on a bottom and side walls of the trench groove and the copper layer
41
is formed on the barrier metal layer
2
to fill the trench groove. A top surface
400
a
of the copper film
41
of the copper interconnection
400
is planarized to be leveled to the top surface of the inter-layer insulator
10
. The copper interconnection
400
may be formed as follows.
With reference to
FIG. 2A
, a trench groove
10
a
is formed in an inter-layer insulator
10
on a semiconductor substrate
0
.
With reference to
FIG. 2B
, a barrier metal layer
2
is entirely formed on the top surface of the inter-layer insulator
10
and on a bottom and side wails of the trench groove
10
a.
With reference to
FIG. 2C
, a copper layer
12
is entirely deposited on the barrier metal layer
2
so that the trench groove
10
a
is completely filled with the copper layer
12
and also the copper layer
12
exists over the top surface of the inter-layer insulator
10
.
With reference to
FIG. 2D
, a chemical mechanical polishment is carried out to the copper layer
12
and the barrier metal layer
2
so that the copper layer
12
and the barrier metal layer
2
remain only with in the trench groove
10
a
to form a copper layer
41
within the trench groove
10
a
. A heat treatment is carried out to the copper layer
41
so as to cause re-arrangement of copper atoms of the copper layer
41
, thereby to form a copper interconnection
400
in the trench groove in the inter-layer insulator
10
.
As a modification, it is possible that the heat treatment is carried out prior to the chemical mechanical polishment.
This conventional copper interconnection has the following problems. As described above, the trench groove
10
a
is formed in the inter-layer insulator and then the copper layer is filled within the trench groove prior to the heat treatment to the copper layer for re-arrangement of the copper atoms in the copper layer. If the copper interconnection is required to have a reduced width, it is necessary to form the trench groove with a reduced width corresponding to the required reduced width of the copper interconnection. The narrow width of the trench groove suppress the growth of the copper crystal grain, whereby the copper crystal grain is likely to have a small size. The small size of the crystal grain allows existence of many crystal grain boundaries
43
. During the current flow through the copper interconnection, a mass-transfer of copper frequently appears through crystal grain boundaries having the lowest energy, whereby the electromigration frequently appears. This electromigration may cause a disconnection or a crack of the copper interconnection. As a result, the electromigration reduces the reliability of
McGinn & Gibb PLLC
Quach T. N.
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