Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1999-12-29
2002-11-26
McDonald, Rodney G. (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S298150, C204S298270, C204S298280, C204S298290, C427S255500, C427S248100, C118S728000, C118S729000, C118S730000
Reexamination Certificate
active
06485616
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention applies to the field of coating substrates using processes in which a high level of coating uniformity is required. Such processes may use physical vapor deposition (PVD) or sputtering to apply the coating.
Typical coating processes that achieve a high level of uniformity generally use an arrangement similar to the arrangement shown in
FIG. 1. A
process that uses this arrangement is typically called a “long throw” process, because there is often a considerable distance between the source of coating material and the substrates. In
FIG. 1
, the source
1
is shown as a cylindrical can representative of a vapor source for a PVD process in which the can contains the material being evaporated. The can is substantially a point source of material. In a long throw sputtering process, the source is typically a sputtering target, which is usually larger than the evaporative source. As disclosed by
FIG. 1
, the typical arrangement includes substrates
2
carried by a platen
5
. Several platens may be mounted on a rack
3
.
To achieve a uniform coating on the substrates, two distinct motions are typically applied to the substrates
2
. The first motion is provided by rotation of the rack
3
about the axis
4
. The second motion is provided by rotation of the platen
5
, which holds the substrates, about its axis
6
. The compound motion produced by the combination of the first and second motions is called “planetary rotation”.
In processes employing planetary rotation, the rack and platen have different rates of rotation. Radial reference lines
7
and
8
have been drawn on the rack
3
and platen
5
, respectively and a reference line
9
connects the two axes of rotation. As the rack
3
and platen
5
rotate, the angles that the projections of the lines
7
,
8
and
9
make will change. At a first instant of time the lines
7
and
8
make certain angles with the line
9
. If the motions of rack and platen are generated by mechanical means such as gears or chains connected to the same source of motion, then at some later second instant of time lines
7
and
8
will make the same angles with the line
9
. The time interval between the second and first instants of time (during which both rack and platen will complete a whole number of rotations) may be referred to as the period. The first and second motions are selected such that a large number of revolutions of both rack and platen occurs during the period. This selection causes all substrates mounted at the same distance from the axis
6
of the second rotation to experience almost exactly the same path within the chamber during one period. Therefore, the coating applied to all substrates equidistant from the center will be the same.
In the process disclosed in
FIG. 1
, the uniformity of the coating that is applied to a point on a substrate varies with the distance from that point to the axis of the second motion. In order to achieve a given level of uniformity, the region where the substrates may be placed is limited to the space between circles
10
and
11
. As the requirement for uniformity becomes more stringent, or as the deposition becomes less uniform, the radial distance between the circles decreases, limiting the number and size of substrates that may be coated in a single process.
For processes requiring uniform deposition over a large area, the distance between the source
1
and the substrate
2
is generally considerably greater than the radial distance between circles
10
and
11
. In addition, masks, such a sector masks, which may move in a third motion about the axis of the second rotation
6
, or fixed “wall” masks, may be used to improve uniformity. The large distance between the substrate
2
and the required masks reduces the deposition rate of the process, resulting in a long and expensive process to produce a limited number of coated substrates.
Another process currently employed is commonly referred to as a “short throw” sputtering processes. In a short-throw process, the distance between the source of material (sputtering target) and the substrates is usually only a few inches. These short throw processes include “batch processes” in which the substrates are transported past a source of coating material by a rotating drum and “in-line” processes in which a transporting mechanism carries the substrates past the source in a substantially straight path. Such processes are widely used in industry to apply coatings to substrates. For example, U.S. Pat. No. 5,714,009 to Bartolomei, commonly assigned with the present application, discloses such a process. The Bartolomei patent, incorporated by reference herein, describes arrangements for producing coatings by microwave-assisted sputtering. In the disclosed process, both rotating drums and linear transport mechanisms are used to transport substrates past sputtering targets and microwave energized plasma generators in a reactive sputtering process.
FIG. 2
depicts one of the possible arrangements.
Referring to
FIG. 2
, a sputtering chamber
21
contains a rotatable drum
22
which carries substrates
23
in a first motion parallel to the direction of the arrow
24
past an elongated sputtering target
25
and past an elongated microwave-energized plasma generator
26
. The substrates
23
are arranged in rows that are parallel to the substrate motion and columns perpendicular to that motion. The target
25
and plasma generator
26
are typically mounted on the chamber wall, and are visible in
FIG. 2
because a portion of the wall has been cut away. Other sputtering targets and plasma generators, not shown, may also be mounted on the chamber wall. Usually additional targets and plasma generators will have the same vertical dimensions and will be mounted in the same vertical position as the targets and generators shown in FIG.
2
.
During the sputtering process, material will be sputtered from the sputtering target
25
on to the substrates
23
where it will react with a reacting gas in the chamber to produce the desired coating. It is almost always necessary to assure that all of the substrates receive a coating that has nearly the same properties. In particular, the amount of deposited material per unit area on each substrate must generally be the same within a prescribed limit.
The amount of material deposited on a given substrate depends on the location of the substrate in the direction of the longer length of the target. The arrow
27
indicates this direction, referred to throughout the application as the “z direction”. The deposition of material is highest at the center of the sputtering target and decreases to zero at extreme distances from the center. In
FIG. 2
, the lines
28
and
29
at the ends of arrow
27
, bound the region within which uniformity of deposition remains within tolerance. It is typically necessary to restrict the size of the region in the z direction so that the difference between the deposition on the center substrates and on the end substrates lies within the acceptable tolerance. Thus, the number of substrates in each column is the number that may be mounted between these limits. This number will be reduced in processes in which a tighter tolerance is imposed.
FIG. 3
a
is a graph illustrating the correlation between the amount of deposited material and the position of the substrate along the vertical column (i.e. position in the z direction). Curve
30
in
FIG. 3
a
applies to the batch process of FIG.
2
and shows the amount of deposited material per unit area at substrate locations along the z direction. The target generating the curve disclosed in
FIG. 3
a
is assumed to be “ideal”, that is, it has a uniform rate of sputtering at all locations.
The deposition of material on the substrates is highest at point
31
, which lies opposite the center of the target. At locations
32
that lie opposite the ends of the target the deposition is reduced to approximately half of the center value. Arrows
33
are provided to indicate the tolerance for the process. The limits of
Gray Robert
Howard Bill
Deposition Sciences, Inc.
Duane Morris LLP
McDonald Rodney G.
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