Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2000-08-21
2002-12-24
McDonald, Rodney G. (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192120, C204S192100, C204S298030, C204S298120, C204S298130
Reexamination Certificate
active
06497797
ABSTRACT:
TECHNICAL FIELD
The invention pertains to methods of forming sputtering targets, and further encompasses the targets formed by the methods.
BACKGROUND OF THE INVENTION
A sputtering method is described with reference to
FIG. 1
, which illustrates a sputtering target
10
spaced from a substrate
12
by a distance T/S. Distance TIS is referred to as the target substrate distance. Substrate
12
can comprise, for example, a semiconductive material wafer. Target
10
can comprise numerous materials known to persons of ordinary skill in the art, such as, for example, metallic materials (e.g. one or more of aluminum, copper, titanium, tantalum, tungsten, cobalt, nickel, etc.), or ceramic materials (e.g., BaTiO
3
, Pb(Zr, Ti)O
3
, BiSrTaO
3
, etc.). Also, target
10
can comprise numerous shapes. For instance,
FIG. 2
illustrates that target
10
can comprise a circular shape
Referring again to
FIG. 1
, a shield
14
is provided over a peripheral region of target
10
. Shield
14
can comprise, for example, stainless steel or aluminum.
In operation, material from target
10
is sputter-deposited onto substrate
12
. More specifically, target
10
has a face surface
16
which is exposed to high energy ions and/or atoms. The high energy ions and/or atoms eject atoms from surface
16
, and the ejected atoms are subsequently deposited onto substrate
12
. Shield
14
protects peripheral edges of target
16
from being exposed to the high energy ions and/or atoms. One of the goals in target fabrication is to deposit a uniform film of material over substrate
12
. One aspect of achieving a uniform film is to have an appropriate T/S distance between target surface
16
and substrate
12
, as well as to maintain a substantially common T/S distance from the entirety of the sputtered target face
16
and substrate
12
. Shield
14
is provided to alleviate problems which could occur if the sloped regions of target
10
were exposed to high energy ions and/or atoms during a sputtering process.
FIG. 3
illustrates target
10
after the target has been subjected to the wear of having material sputtered therefrom. Specifically,
FIG. 3
illustrates a wear profile formed across sputtered face surface
16
. The illustrated wear profile is for exemplary purpose only. The shape of an actual wear profile can depend on, for example, the magnet type and target life of materials used in a sputtering process. A dashed line
18
is provided in
FIG. 3
to illustrate the starting position of the face surface when target
10
was new (i.e., the face surface shown in FIG.
1
). As shown in
FIG. 3
, a number of troughs (i.e., sputter tracks) are formed within face surface
16
during the sputtering operation. Accordingly, the target does not wear uniformly across the surface
16
.
Attempts have been made to improve target lifetime by adding additional material to a target to compensate for the uneven wear pattern of FIG.
3
. For instance,
FIG. 4
illustrates a target
20
which attempts to compensate for the uneven wear of FIG.
3
. Target
20
is shown with a dashed line
18
illustrating the position of original face
16
in the target
10
of
FIGS. 1-3
.
FIG. 4
also shows additional material
22
provided over original position
18
, and in locations which compensate for the uneven wear profile of FIG.
3
. Accordingly, target
20
has a face surface
24
which effectively comprises a mirror image of the wear profile of FIG.
3
.
FIG. 4
is one embodiment of prior art processes for compensating for the uneven wear profile of FIG.
3
. Another embodiment is to simply form additional material
22
over various regions of
18
, without necessarily creating a mirror image of the wear of FIG.
3
. Regardless of which of the prior art techniques is utilized, the result is a target having relatively large peaks at positions in which wear has been most significant in prior targets. A difficulty with the processing of
FIG. 4
is that target
20
has large variations in thickness across its surface, and accordingly a T/S distance relative to face
24
of target
20
varies significantly across the face. Accordingly, the uniformity of:film deposition from target
20
can be significantly less than the uniformity of film deposition from a target having a planar face. Thus, even though lifetime can be improved utilizing the target
20
of
FIG. 4
instead of the target
10
of
FIGS. 1-3
, the loss in uniformity can render target
20
less desirable than previous targets
10
of
FIGS. 1-3
.
It would be desirable to develop techniques for forming targets having improved lifetimes, and which can be utilized to uniformly sputter-deposit materials on substrates.
SUMMARY OF THE INVENTION
In one aspect, the invention encompasses a method of forming a sputtering target. A wear profile for a sputtering target surface is determined. The wear profile corresponds to a shape of the target surface after the target is subjected to the wear of having material sputtered therefrom. It can be preferred to determine a wear profile from a target which has been exposed to an anticipated semiconductor wafer fabrication process (specifically, an anticipated sputtering process), for a maximum anticipated lifetime of the target. The maximum anticipated lifetime can vary depending on, for example, the sputtering chamber configuration, the target composition, and the target configuration. The wear profile is divided amongst a plurality of datapoints across the target surface. A difference in height of the target surface after the wear relative to a height of the target surface prior to the wear is calculated. The difference in height calculations generate a plurality of wear definition datapoints. Target lifetime datapoints are calculated using the wear definition datapoints, and sputtering uniformity datapoints are also calculated using the wear definition datapoints. A difference between the target lifetime datapoints and sputtering uniformity datapoints is calculated. A constant corresponding to the difference between a target lifetime datapoint and a sputtering uniformity datapoint is added to the sputtering uniformity datapoints to generate a desired profile for a sputtering target sputtering surface. A sputtering target is formed having a sputtering surface with the desired profile.
The invention encompasses another method of forming a sputtering target. A wear profile for a sputtering target surface is determined. The wear profile is divided amongst a plurality of datapoints to generate datapoints {S
1
. . . S
i
}, where “i” is a positive integer. Also, datapoints are generated to define the target surface prior to the wear, with the datapoints being {R
1
. . . Ri}. Difference datapoints {A
1
. . . A
i
} are generated, with each datapoint A
n
being defined as R
n
−S
n
. Target lifetime datapoints {B
1
. . . B
i
} are calculated. Each datapoint B
n
is defined as ((A
n
* y)+Q); where y is a constant greater than 0, and Q is a constant which can be 0. Sputtering uniformity datapoints {C
1
. . . C
i
} are calculated, with each datapoint C
n
being defined as ((A
n
*z)+P); where z is a constant greater than 0 and less than y, and where P is a constant which can be 0. Difference datapoints {D
1
. . . D
i
} are calculated, with each difference datapoint D
n
, being defined as (B
n
−C
e
). The difference datapoint having the greatest magnitude is determined, and is defined as D
max
. A desired profile dataset {E
1
. . . E
i
} is generated, with each datapoint E
n
being defined as (C
n
+D
max
). A sputtering target is formed to have a sputtering surface with a profile corresponding to the desired profile dataset.
REFERENCES:
patent: 5215639 (1993-06-01), Boys
patent: 5428882 (1995-07-01), Makowiecki et al.
patent: 6068742 (2000-05-01), Daxinger et al.
patent: 6086735 (2000-07-01), Gilman et al.
patent: 61-099674 (1986-05-01), None
patent: 63-042369 (1988-02-01), None
patent: 01-132757 (1989-05-01), None
patent: 06-306597 (1994-01
Honeywell International , Inc.
McDonald Rodney G.
Wells St. John P.S.
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