Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1999-12-03
2003-02-25
McDonald, Rodney G. (Department: 2786)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S298030, C118S663000, C118S664000, C118S665000, C118S730000, C427S008000, C427S009000, C700S116000
Reexamination Certificate
active
06524449
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to methods and apparatus for producing thin films on substrates by vapor deposition (e.g., sputtering). The invention pertains to improving the accuracy of the deposited film thickness across the substrate (e.g., by improving the uniformity of the film thickness across the substrate where it is desired to deposit a film having uniform thickness).
2. Discussion of the Related Art
Thin film coatings are typically produced by various vapor deposition methods (such as sputtering, CVD, and electron beam evaporation) in which the substrate to be coated is passed through a vapor of the coating material and accumulates a thin film through condensation of the vapor. For many applications, such as optical films for EUV (extreme ultra violet) lithography, it is desirable that the coating be very uniform in thickness (e.g., with no more than 0.1% variation in thickness across the coated substrate). Multilayer coatings for EUV optics are commonly applied using DC magnetron sputtering.
FIG. 1
is a side cross-sectional view of a DC magnetron sputtering system, and
FIG. 2
is a cross-sectional view of the
FIG. 1
system taken along line 2—2 of FIG.
1
. The system of
FIGS. 1 and 2
, described in pending U.S. patent application Ser. No. 08/607,054, filed Feb. 22, 1996 by Vernon and Ceglio (assigned to the assignee of the present application), includes housing
10
(which has a cylindrical sidewall) and two rectangular sources (of sputtered atoms) located 180 degrees apart (relative to the system's vertical central axis through the center of shaft
6
) at opposite sides of housing
10
. One source is surrounded by chimney
2
; the other is surrounded by chimney
2
A. Chimneys
2
and
2
A limit the deposition zone for each source (in which sputtered atoms can be deposited on substrate
11
or
12
) to the area directly above the target (
3
or
3
A) of each source. The two substrates (
11
and
12
) are held face down on rotatable platter
5
above the sources, at locations 90 degrees apart with respect to the axis of shaft
6
.
Multilayers (alternating layers of two different materials) can be deposited on each of substrates
11
and
12
by sweeping the substrates across the sources (by controlled rotation of shaft
6
and hence platter
5
relative to the stationary housing
10
and the stationary sources).
More specifically, the system of
FIGS. 1 and 2
includes a first source comprising magnetron
1
, chimney
2
, and target
3
positioned within chimney
2
in the electric and magnetic fields produced by element
1
(such that ions present within chimney
2
, e.g., ions created within chimney
2
, will accelerate toward and be incident on target
3
). In response to collisions of the ions (which can be argon ions) with target
3
, a vapor of sputtered atoms
4
is produced in the volume surrounded by chimney
2
. Some of atoms
4
will be deposited on the downward-facing surface of substrate
11
(or
12
), when the substrate (
11
or
12
) is exposed to sputtered atoms
4
in chimney
2
.
Similarly, the system also includes a second source comprising magnetron
1
A, chimney
2
A, and target
3
A positioned within chimney
2
A in the electric and magnetic fields produced by element
1
A (such that ions created within chimney
2
A will accelerate toward and be incident on target
3
A). In response to collisions of the ions with target
3
A, a vapor of sputtered atoms
4
A is produced in the volume surrounded by chimney
2
A. Some of atoms
4
A will be deposited on the downward-facing surface of substrate
11
(or
12
), when the substrate (
11
or
12
) is exposed to sputtered atoms
4
A in chimney
2
A.
Each of two substrate holders
9
(only one of which is visible in
FIG. 1
) is fixedly mounted to the lower end of one of shafts
8
(only one of which is visible in
FIG. 1
) so as to fit in an orifice extending through platter
5
. Substrate
11
is mounted on substrate holder
9
, with a downward facing surface to be coated. Shaft
8
is rotatably connected to spinner
7
, so that spinner
7
can cause shaft
8
, holder
9
, and substrate
11
to rotate as a unit relative to platter
5
, whether or not platter
5
is itself rotating relative to housing
10
. Similarly, substrate
12
(shown in
FIG. 2
only) is mounted on a substrate holder
9
(not visible in
FIGS. 1 and 2
) in turn fixedly mounted to a shaft
8
, and the shaft is rotatably connected to a spinner (identical to spinner
7
). During operation, elements
1
,
2
,
3
,
1
A,
2
A, and
3
A remain stationary within housing
10
, while platter
5
rotates to sweep substrates
11
and
12
sequentially across chimneys
2
and
2
A (typically while substrates
11
and
12
are rotated about their centers by the spinners relative to platter
5
).
To deposit typical multilayer coatings on the substrates, atoms
4
(in chimney
2
) are different (i.e., have a different atomic weight) than atoms
4
A in chimney
2
A. In some implementations, atoms
4
are Molybdenum atoms and atoms
4
A are silicon (or beryllium) atoms (and magnetrons
1
and
1
A produce a plasma of ultrapure Argon ions at a pressure of about 1.00 mTorr, with source powers of 360 W and 170 W, respectively, for magnetrons
1
A and
1
). Platter
5
is rotated within housing
10
(at a first rotational speed) while each substrate spins (at a speed much greater than the first rotational speed) relative to platter
5
. During each revolution of platter
5
relative to housing
10
, each of substrates
11
and
12
sweeps sequentially across chimney
2
and chimney
2
A, so that one layer of atoms
4
and then one layer of atoms
4
A condenses on each substrate. The thickness of each layer is determined by the time that the substrate is exposed to the vapor (
4
or
4
A), which is in turn determined by the substrate transit velocity. The arrangement of substrates
11
and
12
and chimneys
2
and
2
A is such that no more than one substrate is over one source at any time. Therefore, the two substrates can be independently coated with identical or completely different multilayer structures.
By rapidly spinning substrate
11
(or
12
) about its own axis of symmetry relative to platter
5
, better azimuthal uniformity of the condensed coating can be achieved. However, radial non-uniformities in coating thickness typically result.
To compensate for radial non-uniformities in coating thickness, a carefully shaped mask can be inserted between each substrate and the sputtered atom vapor to which the substrate is exposed. However, such a masking operation requires tedious iteration to determine the optimal shape of each mask, and can be impractical for cases in which very high uniformity is required. Use of masks also prevents independent deposition of two different coating distributions on a masked substrate as the masked substrate sweeps sequentially across two sources during a single platter rotation. Also, a mask is not suitable for a substrate whose center must be coated, since the mask cannot be perfectly positioned at the center of rotation of a spinning substrate, and thus a small spot at the center of the masked substrate will be coated with the wrong thickness.
Another approach is to use a “baffle” which is a shaped piece of metal that is stationary with respect to the source (unlike a mask which moves together as a unit with the substrate, as the substrate moves relative to the source) and is present between the substrate and the sputtered atom vapor to which the substrate is exposed. Use of baffles allows independent deposition of two different coating distributions on a masked substrate as the masked substrate sweeps sequentially across two sources during a single platter rotation. However, use of baffles prevents independent deposition of different coating distributions on two substrates, each of which sweeps sequentially across a source during a single platter rotation. As will be apparent from the description below of the invention, the present invention avoids use of ba
Folta James A.
Montcalm Claude
Walton Christopher
McDonald Rodney G.
Sierra Patent Group Ltd.
Smith Andrew V.
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