Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1997-03-04
2002-10-15
McDonald, Rodney G. (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192130, C204S298030, C204S298200, C204S298190
Reexamination Certificate
active
06464841
ABSTRACT:
The disclosure of U.S. Pat. No. 5,130,005 entitled MAGNETRON SPUTTER COATING METHOD AND APPARATUS WITH ROTATING MAGNET CATHODE filed Dec. 13, 1990 is hereby incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to a cathode used in a sputtering process, and more particularly, to a sputtering cathode assembly with a variable magnetic configuration that compensates for variations in deposition film thickness caused by erosion of a sputtering target.
BACKGROUND OF THE INVENTION
In a sputtering process, sputtering cathode assemblies are commonly used to deposit metal or other conductive material as a thin film onto a surface of a substrate such as a semiconductor wafer. Sputtering cathode assemblies include a vacuum chamber in which a sputtering target is positioned in close proximity to the substrate. As energy is applied to the target, atoms are ultimately sputtered or dislodged from the surface of the target and deposited on substrate.
Frequently, non-uniformities in a film are a result of there being more of a target structure (i.e. a sputtering source) located near a center of a substrate than at an outer edge of the substrate. In theory, with all other parameters being equal, an infinitely large target with a uniform erosion profile would be capable of overcoming film non-uniformity due to the target size. Therefore, it is desirable to make the target large with respect to the surface of the substrate being coated. There are, however, practical limitations on the size of the sputtering target which may be used. Usually, a compromise is made by providing a target having a diameter that is approximately one-half larger than that of the substrate being coated. Nonetheless, with this compromise, use of a target which is eroded uniformly still results in the formation of a film whose thickness increases when moving from the edge of the substrate toward the center of the substrate.
In many commercial processes, such as those where a high rate of deposition is a consideration, magnetron enhanced plasma generation and shaping techniques are utilized to establish a desired erosion profile of the sputtering target. More recently, sputter coating equipment manufacturers have provided sputter coating target and cathode assemblies in which rotating magnet packages are used to assist in magnetron enhancement of the plasma. One such rotating magnet cathode assembly is described and illustrated in U.S. Pat. No. 5,130,005 entitled MAGNETRON SPUTTER COATING METHOD AND APPARATUS WITH ROTATING MAGNET CATHODE which is assigned to Materials Research Corporation.
Designs for cathode assemblies have been optimized to shape the erosion profiles of the targets to compensate for the thinner edge coating effect and other factors contributing to non-uniformity of the film. This is frequently achieved by selectively configuring the magnet assemblies used to shape the plasma. For example, in order to compensate for thinness of a film at the substrate edge, magnet assemblies are often designed to produce a greater duration of plasma around the target edge. This causes the target to erode at a higher rate near the target edge to compensate for reduced target exposure near the substrate edge.
Referring to
FIGS. 1 and 2
, a rotating magnet assembly is shown. A magnet carrier plate
20
is arranged to be rotatable around center axis
26
on shaft
18
. The plate
20
includes an array of magnetic material
28
having a fixed predetermined shape. In particular, the magnetic material
28
is selectively configured so that there are portions positioned at various radii from the center axis
26
in an irregular partially-formed loop. In this configuration, magnetic material
28
is oriented such that a north magnetic pole is at an outer perimeter face
32
while a south magnetic pole is at inner perimeter face
34
. The shape of the sputtering plasma and the resultant erosion of first target
72
adjacent magnetic material
28
is defined by a magnetic flux path
76
extending between the north
32
and south
34
magnetic poles which create a closed loop magnetic field tunnel on the face of the first target
72
.
When the magnetic material
28
is rotated with respect to first target
72
, an erosion profile
74
is formed in first target
72
. The profile
74
includes a substantially circular “bulls eye” pattern wherein the deeper and shallower portions of profile
74
are formed by the particular pattern shape of magnetic material
28
. A first outermost portion
78
of profile
74
is dominated by a rotational dwell of outermost areas
79
of the magnetic material
28
, while the depth of erosion of a central portion
82
of the first target
72
is dominated by center areas
84
of magnetic material
28
. Similarly, an erosion of an intermediate portion
86
between the first outermost portion
78
and the center portion
82
results from a rotational dwell of intermediate areas
88
of magnetic material
28
.
The shape of the profile
74
, in addition to other factors such as the size of the first target
72
and substrate
92
and the spacing between first target
72
and substrate
92
are some factors which determine film thickness uniformity. Further, thickness uniformity is not constant during the life of the target. When first target
72
is new, an initial sputtering surface
90
is substantially flat and at a known distance from the substrate
92
which is to be coated with sputtered material. As erosion progresses, the surface
90
gradually assumes the shape of profile
74
. Together with the erosion, the distance between the surface
90
and substrate
92
increases.
The effect of these changes is shown in FIG.
3
.
FIG. 3
illustrates sputtered material thickness across a diameter of a six-inch substrate. Curve
94
illustrates sputtered material thickness obtained when first target
72
is new and surface
90
is substantially flat. As target erosion progresses, uniformity degrades as illustrated by curve
96
at the mid-point of target life. As first target
72
approaches the end of life, the thickness of sputtered material degrades to that illustrated by curve
98
. The progression of sputtered material thickness as first target
72
erodes, indicates a reduction of film thickness towards the edge of substrate
92
.
These deficiencies may be corrected by periodically replacing the magnetic material
28
with magnetic material having a different shape adapted to provide a higher dwell time in the outermost areas
79
, thereby causing increased sputtering in the first outermost portion
78
of the first target
72
. However, replacement of magnetic material
28
requires removal of the plate
20
and shutdown of sputtering system, resulting in increased costs and reduced productivity.
Further, it is known that sputtering targets of different materials or crystal structures perform differently in the sputtering process. Referring to
FIG. 4A
, an angular distribution of material
120
sputtered from a location
122
on a second target
124
fabricated from aluminum is illustrated. This distribution shows that a majority of material sputtered is located predominantly normal to the target surface. Referring to
FIG. 4B
, an angular distribution of material
132
sputtered from a location
126
on a third target
128
fabricated from terbium or gold is shown. Here the sputtered material is distributed at lower angles along lobes
130
than that shown in FIG.
4
A. Optimizing the deposition uniformity for these and other materials requires replacement of the magnet structure. However, as previously described, this requires undesirable shutdown of the sputtering system.
SUMMARY OF THE INVENTION
A sputtering system for depositing a thin film onto a substrate is disclosed wherein the system includes an evacuatable chamber which includes the substrate. In particular, the system includes a target positioned within the chamber, wherein the target includes a back surface and a sputtering surface. Further, the system includes plasma for eroding the target to provide material fo
Hurwitt Anne
Hurwitt Steven
Hurwitt Anne
McDonald Rodney G.
Tokyo Electron Limited
Wood Herron & Evans L.L.P.
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