Chemistry: electrical and wave energy – Apparatus – Coating – forming or etching by sputtering
Reexamination Certificate
2001-06-29
2002-05-28
McDonald, Rodney G. (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Coating, forming or etching by sputtering
C204S298120, C204S298200, C204S298230, C204S298270, C204S298280, C204S298290, C204S192110
Reexamination Certificate
active
06395156
ABSTRACT:
BACKGROUND OF INVENTION
This invention relates to sputtering systems, and more particularly to target movement for improved uniformity.
Thin films for electronic or optical devices can be deposited onto a substrate in a low-pressure sputtering chamber or machine. An ion-beam generator or source directs ions to the surface of a target, causing some target atoms or ions to be ejected from the target's surface. These target ions then travel through the low-pressure chamber until reaching the surface of the substrate. A thin film of the target material, or a compound form of the target material, is deposited on the surface of the substrate.
Each target can be used many times, depositing films on many substrates that are loaded and unloaded into the chamber. Eventually the target becomes worn and must be replaced with a new target. Such target replacement may halt production runs and require a skilled technician. Minimizing target replacement is desirable; however, film quality is critical so targets are often replaced frequently to improve film uniformity.
FIG. 1A
is a front view of a worn sputtering target. Repeated deposition runs using the same target results in removal of target material from target
10
. Spot
12
is formed on the surface of target
10
where the ion beam impacts target
10
. The size and shape of spot
12
can vary with the angle of the ion beam to target
10
, and the type and beam-shape of ion-beam generator used. The location of spot
12
can be off-center of target
10
as shown.
FIG. 1B
is a side view of a worn sputtering target. Depression
14
is formed on target
10
where spot
12
impacted the surface of target
10
. The target material that was in depression
14
was ejected by the ion beam impacting the surface of target
10
in the region of depression
14
.
More complex shapes of the ion-beam spot on the target are possible.
FIGS. 2A
,
2
B show complex wear of a sputtering target. Spot
12
has several annular rings that are caused by the ion beam being somewhat non-uniform. Regions of the ion beam with a higher beam density or energy can sputter portions of target
10
at higher rates. Dimples
16
may be formed on the surface of target
10
where the beam has a higher energy or density. Dimples
16
may be ring-shaped or somewhat irregular.
FIG. 3A
shows sputtering of a new target. Ion source
18
generates an ion beam that is directed onto target
10
. Target ions or atoms are ejected from target
10
and travel to the surface of substrate
20
, depositing a film on substrate
20
. Substrate
20
can be removed and replaced with another substrate and deposition repeated many times with many different substrates before target
10
is replaced.
FIG. 3B
shows sputtering of a worn target. After many depositions runs, dimples
16
have formed on the surface of target
10
where the ion beam from ion source
18
has impacted the surface. Since the surface of target
10
is no longer smooth but rough, some scattering of the ion beam can occur. The angle that target atoms or ions are ejected can vary with the surface roughness. Some ejected target atoms may not reach the surface of substrate
20
, resulting in a lower deposition rate and possibly a less-uniform deposition across the surface of substrate
20
. Since such scattering is undesirable, target
10
is often replaced more frequently to avoid such problems.
Since target replacement may require downtime of the sputtering machine, spare targets are sometimes included within the sputtering chamber to minimize such downtime. Target replacement can be automated, allowing
2
or
3
targets to be used up before all targets are replaced at one time.
FIG. 4A
shows a top view of a sputtering chamber with multiple targets. Target
10
is mounted on target mount
22
. Spare targets
15
,
17
are also mounted on target mount
22
. A motor can be activated to turn shaft
28
, allowing a different or spare target
15
to be rotated into the position that was occupied by target
10
, so that the ion beam from ion source
18
impacts spare target
15
, which deposits a film onto substrate
20
.
Shaft
28
can be rotated by one-third of a revolution, or
120
degrees, to exchange targets. Spare targets
15
,
17
can be of the same target material as target
10
, or can be of an entirely different target material. The sputtering machine can be programmed with a recipe that rotates shaft
28
to select one of the three targets for each deposition step. Multi-layer films can then be deposited.
FIG. 4B
is a side view of a sputtering chamber with multiple targets. Ion-beam source
18
sends an ion beam that impacts target
10
. Target atoms or ions ejected from target
10
travel to substrate
20
and are deposited on its surface. To improve film uniformity, substrate
20
can be rotated by a motor (not shown).
Spare target
15
(an another spare target hidden from view) and selected target
10
are mounted on target mount
22
. Shaft
28
can rotate target mount
22
to select the desired target for sputtering. Motor
24
and gearbox
26
are activated to rotate shaft
28
by the desired amount. Motor
24
is mounted outside the low-pressure chamber
30
to minimize contamination.
Targets
10
,
15
and substrate
20
can be heated or cooled as desired. Channels for cooling water can be formed on the backing plates to targets
10
,
15
. Motor
24
can also be operated during deposition to slightly rock target
10
. Shaft
28
rocks back and forth by about
3
degrees to slightly vary the surface angle of the ion beam to target
10
during deposition. This rocking may improve uniformity.
Although target wear may be improved by such rocking, a mechanism to move the target is desired to improve uniformity. Rotation or spinning of targets has been used as one way to improve target wear. However, such target rotation may not sufficiently spread the wear over the target surface. A more aggressive way to move the target during deposition is thus desired to reduce target wear and improve uniformity of deposition.
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patent: 6051113 (2000-04-01), Moslehi
Hsueh Paul
Ma Abraham C.
Auvinen Stuart T.
McDonald Rodney G.
Super Light Wave Corp.
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