Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2000-03-29
2003-08-19
Ver Steeg, Steven H. (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
Reexamination Certificate
active
06607640
ABSTRACT:
This invention relates to an improved method of controlling the temperature of a substrate clamped to a substrate support in a deposition chamber.
BACKGROUND OF THE INVENTION
As semiconductor substrates become larger, and devices formed therein become smaller, new materials and processes must be developed for making these devices. For example, the use of aluminum, which has long been used to make conductive paths and contacts, is being supplanted by copper, which is more conductive and thus has a lower resistivity. Further, copper has superior electromigration properties than does aluminum, even, for example, aluminum doped with silicon. Thus copper has some superior properties for integrated circuits.
A problem with using larger substrates, e.g., silicon wafers, is that processing uniformities are more difficult to maintain across the larger wafer; processing must be uniform across the diameter of the wafer in order to produce devices that are the same across the wafer, irrespective of their position on the wafer. As 8 inch diameter wafers are replaced with wafers of approximately 12 inches in diameter (200 mm diameter), this is not a trivial task.
In preparation for the deposition of copper onto a previously deposited and etched dielectric insulative or other layer, conventionally a barrier layer is deposited between the previously deposited film and the copper layer. The barrier layer can be made of Ta, TaN, W, WN
x
and the like. A seed layer of copper is then deposited onto the barrier layer by sputter deposition, which is followed by electroplating of copper onto the substrate to a finished thickness.
The morphology of the copper seed layer is very important; if the seed layer is rough or bumpy or non-uniform in thickness across the layer, the overlying electroplated copper layer will also be non-uniform, particularly since the copper layers deposited inside the vias and contact openings may be very thin.
A seed layer of copper can be deposited in a sputter deposition reactor. A suitable sputter deposition reactor has a biasable substrate support electrode that can be cooled or heated with a flow of chilled or heated fluid therethrough. The wafer temperature can be maintained close to that of the support electrode by a flow of backside gas, such as about 15 sccm of argon or other inert gas which is passed between the wafer support and the wafer.
A suitable chamber for depositing a copper seed layer is shown in
FIG. 1
in a schematic cross sectional view. This chamber is known as an ionized metal plasma (IMP™) a trademark of Applied Materials, Inc. chamber
The IMP™ chamber
100
as shown in
FIG. 1
comprises a target
104
comprising the material to be sputtered, i.e., copper or other metal, which is mounted on the lid
102
of the chamber. Magnets
106
are mounted on the lid
102
behind the target
104
. A substrate support
112
is movable vertically within the chamber and includes an upper support surface
105
for supporting a substrate
110
. The support member
112
is mounted on an elevator
113
connected to a motor
114
that raises and lowers the support
112
between a lowered loading/unloading position and a raised, processing position. An opening
108
in the chamber wall permits entry and egress of the substrate prior to and after processing. A lift motor
118
raises and lowers pins
120
mounted in the substrate support
112
, which in turn raise and lower the substrate
110
to and from the upper support surface
105
of the substrate support
112
.
A coil
122
provides inductive magnetic fields in the chamber to generate and maintain a higher density plasma between the target
104
and the substrate
110
than would be possible with standard magnetron sputtering of the target
104
. The coil
122
is preferably a flat surface facing inward to the chamber and composed of the same material as the target, as it too will be sputtered to provide deposition material to the substrate. A clamp ring
128
is mounted between the coil
122
and the substrate support
112
which shields an outer edge and the backside of the substrate
110
from sputtered material in the chamber when the substrate
110
is raised into a processing position. In the processing position, the substrate support
112
is raised upwardly into the clamp ring
128
.
Three power sources are used in the chamber
100
. A first power source
130
delivers power to the target
104
to cause the formation of a plasma from a processing gas through gas inlet
136
. A second power source
132
, preferably an RF power source, supplies power to the coil
122
to increase the density of the plasma. A third power source
134
biases the substrate support
112
and thereby provides directional attraction of the ionized sputtered target material toward the substrate
110
. A vacuum pump
146
coupled to an exhaust pipe
148
, in combination with an argon supply (including argon passing under the substrate to and into the chamber) maintain the desired pressure in the chamber.
A controller
149
controls the functions of the power supplies, lift motors, vacuum pump and other chamber components and functions.
In operation, a robot delivers a substrate
110
to the chamber
100
through the opening
108
. The pins
120
are extended upwardly to lift the substrate
110
from the robot, which is then retracted from the chamber
100
. The opening
108
is then sealed. The pins
120
lower the substrate
110
to the upper surface
105
of the substrate support
112
. The substrate support
112
is then raised so that the substrate
110
engages the clamp ring
128
. One or more plasma gases are introduced into the chamber
100
through gas inlet
136
and a plasma is generated between the target
104
and the substrate support
112
with power from the first power source
130
.
The second power source
132
delivers power to the coil
122
to densify the plasma and ionize at least an additional portion of the sputtered target material from the target
104
. The substrate support
112
is then biased by the third power source
134
, so that the sputtered ionized particles are accelerated towards the substrate
110
. A flow of gas is initiated in the substrate support to heat or cool the substrate
110
during deposition. After deposition is complete, the substrate support is lowered to permit retrieval of the processed substrate and to deliver another substrate for processing.
The substrate support
112
also includes a passage for the flow of an inert gas to the surface
105
of the support
112
. The gas can be supplied from a single opening in the support
112
, or the gas can be led through channels in the support surface
105
(not shown) to permit more uniform heating or cooling of the substrate
110
.
However, the chamber
100
produces a non-uniform deposit of a seed layer of copper onto the substrate. The deposited copper seed layer is essentially smooth at the center of the substrate, but is very rough nearer the edges of the substrate. It was believed that this non-uniformity was caused by heating of the clamp ring
128
over time (to 300-400° C.). However, the rough deposits extend up to 2.5 inches from the edge of the substrate, far more than the width that the clamp ring rests on the substrate. Thus the temperature of the clamp ring does not explain the problem or suggest a solution.
A method for improving the uniformity of a deposited copper seed layer across a substrate would be highly desirable.
SUMMARY OF THE INVENTION
We have found that by maintaining a minimum pressure of the temperature control gas between the substrate support and the substrate of at least 15 torr, improved uniformity of the thickness and morphology of a sputter deposited layer metal seed can be achieved.
REFERENCES:
patent: 5178739 (1993-01-01), Barnes et al.
patent: 5266524 (1993-11-01), Wolters
patent: 5513594 (1996-05-01), McClanahan et al.
patent: 5830533 (1998-11-01), Lin et al.
patent: 533254 (1993-03-01), None
Angelo Darryl
Ding Peijun
Sundarrajan Arvind
Yao Tse-Yong
Applied Materials Inc.
Morris Birgit E.
Ver Steeg Steven H.
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