Contoured sputtering target

A contoured sputtering target includes a target member of sputtering material having a top surface, a bottom surface and an outer peripheral surface. One or more contoured annular regions are formed on the top surface of the target member that extend radially inwardly from the outer peripheral surface and away from the bottom surface. The target member may further include planar, concave or central recessed regions formed in the top surface that are surrounded by the one or more contoured annular regions. The configuration of the target member reduces generation of contaminating particles from nodules that may form near the outer peripheral surface of the target during a sputtering operation. Methods of forming a contoured sputtering target are also disclosed.

FIELD OF THE INVENTION 
The present invention relates generally to sputtering systems and, more 
particularly, to sputtering targets for use in processing a substrate or 
wafer in a sputtering system. 
BACKGROUND OF THE INVENTION 
Sputter coating refers to a process for coating a substrate, such as a 
semiconductor wafer, within a vacuum processing chamber of a sputtering 
system. In the sputter coating process, an applied electric field 
positively biases the wafer relative to an oppositely mounted, negatively 
biased target made of sputtering material. Once the processing chamber is 
evacuated, an inert gas is introduced into the chamber at a low pressure, 
and the applied electric field ionizes the process gas. As a result, 
positive ions from the gas bombard the target to cause sputtering of the 
target material onto the wafer in a thin film. A magnet or electromagnet 
may be located behind the target to provide a magnetic field above the 
surface of the target facing the wafer to confine the ion "plasma" 
adjacent the target, and thereby enhance the sputter coating operation. 
Sputtering targets are typically formed as a generally circular disk of 
target material, such as aluminum alloys, gold, silver, copper, titanium, 
titanium-tungsten or platinum. The disk of target material may be soldered 
or otherwise bonded to a supporting target backplate to form a replaceable 
sputtering target assembly. During the sputtering operation, material is 
sputtered from the top surface of the target and deposited on the wafer. 
The sputtering material typically erodes unevenly across the width or face 
of the target exposed to the wafer, with some areas of the target eroding 
more quickly than other areas. 
To overcome this problem, some sputtering equipment employs a variation of 
the magnetic field, or multiple, non-planar erosion zones on the target, 
or both, to create a generally uniform sputtering rate across the face of 
the target. Typically, the outer radial region of the target has been made 
thicker than the central region of the target. The target may include a 
concave region formed in the target face or even a hole formed through the 
center of the target. Sputtering material is eroded from the target until 
the target is no longer able to provide the desired coating features on 
the wafer. At that time, the target assembly, consisting of the eroded 
target and backplate, is replaced by a new target assembly. 
In titanium nitride (TiN) sputtering, for example, a titanium sputtering 
target and backplate assembly is mounted in the vacuum processing chamber 
with exposed surface of the target facing a wafer. The vacuum chamber is 
evacuated, and then filled with nitrogen gas that ionizes in the presence 
of the applied electric field. Positive ions from the plasma process gas 
bombard the top surface of the target and cause titanium particles to be 
sputtered toward the wafer. During the sputtering process, the titanium 
particles chemically react with the nitrogen process gas to form a thin 
film of titanium nitride on the wafer surface. 
An important aspect in sputter coating of wafers is the purity of the film 
deposited onto the wafer. As the amount of contaminants within the sputter 
processing chamber increases, the wafer product yield decreases as 
impurities are formed on the wafer. For example, in titanium nitride 
sputtering, TiN nodules are known to form on the sputtering face of the 
target as material from the central portion of the target is sputtered and 
redeposited on the outer peripheral edge of the target face rather than on 
the wafer. During the sputtering operation, the TiN nodules have a 
tendency to flake and generate contaminating particles that adversely 
affect the purity of the deposited titanium nitride film on the wafer. 
Since TiN particle generation becomes worse with increasing use of the 
target, the target must be periodically conditioned to maintain an 
acceptable device yield. 
Target conditioning is achieved by conducting titanium-only sputtering on 
non-product substrates. The titanium-only sputtering causes the TiN 
nodules held on the target to be released and deposited on the non-product 
substrates. While the periodic conditioning prolongs the usable life of 
the target by removing the contaminating TiN nodules, it requires stoppage 
of the wafer coating production line and results in downtime of the 
sputtering system. Thus, notwithstanding known contouring of sputtering 
targets and modifications to operation of sputtering systems, nodule 
formation on targets has been a problem, particularly in titanium nitride 
sputter deposition. 
In the past, one-piece sputtering targets have been made that include 
steep-angled bevels formed adjacent the outer edge of the target to reduce 
redeposition of TiN particles near the outer surface of the target. In 
U.S. Pat. No. 5,538,603, for example, bevels are formed adjacent the outer 
edge of the target that taper at an angle of at least 30.degree. with 
respect to the planar face of the target, and preferably at a greater 
angle, i.e., 70.degree. , such that the trajectory of the backscattered 
atoms will cause the atoms to miss the outer surface of the target 
altogether. The steep angles of the bevels are also chosen to reduce the 
thickness of the target adjacent its outer peripheral edge to increase the 
sputter deposition rate near the tapered target edge. Thus, backscattered 
TiN particles that collide and redeposit on the target are more likely to 
be resputtered onto the wafer or substrate. However, the steep tapered 
targets are single-piece targets that do not encounter the same TiN nodule 
formation problems associated with sputtering targets mounted to a target 
backplate. 
Accordingly, there is a need for a sputtering target and backplate assembly 
that reduces generation of contaminating particles from nodules that may 
form during a sputtering operation. There is also a need for a sputtering 
target and backplate assembly that requires less periodic conditioning 
during the life of the target, thereby resulting in less system downtime 
and a reduction in preventative maintenance. 
SUMMARY OF THE INVENTION 
The present invention overcomes the foregoing and other shortcomings and 
drawbacks of the sputtering targets heretofore known. While the invention 
will be described in connection with certain embodiments, it will be 
understood that the invention is not limited to these embodiments. On the 
contrary, the invention includes all alternatives, modifications and 
equivalents as may be included within the spirit and scope of the present 
invention. 
In accordance with the principles of the present invention, a contoured 
sputtering target is provided that includes a target member of sputtering 
material having a top surface or face designed to be exposed to, and 
confront, the wafer or substrate being coated, a planar bottom surface 
typically bonded or otherwise joined to a conventional target backplate, 
and an outer peripheral surface. During a sputtering operation in a 
processing chamber, sputtered material is ejected from the top surface of 
the target member and deposited on the substrate in a thin coating or 
film. 
In one embodiment of the present invention, the target member has a 
contoured annular region formed on the top surface that extends radially 
inwardly a predetermined distance from the outer peripheral surface and 
away from the bottom surface. The contoured annular region may include a 
planar surface, or a radiused surface that extends radially inwardly and 
away from the bottom surface. The target member may further include a 
planar, concave or central recessed region formed in the top surface of 
the target that is surrounded by the contoured annular region. 
In an alternative embodiment of the present invention, at least two 
contoured annular regions may be formed on the top surface of the target 
member. One of the contoured annular regions is formed radially inwardly 
from the other contoured annular region. One, or both, of the contoured 
annular regions may include a planar surface or a radiused surface that 
extends radially inwardly and away from the bottom surface. The target 
member may further include a planar, concave or central recessed region 
formed in the top surface of the target that is surrounded by the 
contoured annular regions. 
The shape or profile of the contoured annular regions on the target member 
is particularly advantageous to reduce accumulation of redeposition at the 
target edge. Additionally, the contoured sputtering target of the present 
invention is particularly profiled to reduce the sputtering or erosion 
rate of the target member near the outer peripheral surface. As nodules 
(not shown) form at or near the outer peripheral surface during a 
sputtering operation, the lower plasma intensity existing near the formed 
annular regions on the target, and the reduced sputtering rate created by 
the profile of the target, prevents the nodules from flaking or 
resputtering during a sputtering operation. The contoured annular regions 
formed on the target member advantageously stabilize the nodules that may 
form on the target member to significantly reduce resputtering or flaking 
of the nodules during a sputtering operation. 
The contoured sputtering target of the present invention therefore reduces 
accumulation of nodules during a sputtering operation, and further reduces 
generation of contaminating particles from any nodules that may form 
during the sputtering operation. The contoured sputtering target of the 
present invention also requires less periodic conditioning during the life 
of the target, thereby resulting in less system downtime and a reduction 
in preventative maintenance. 
The above features and advantages of the present invention will be better 
understood with reference to the accompanying figures and detailed 
description.

DETAILED DESCRIPTION OF THE INVENTION 
With reference to the figures, and to FIG. 1 in particular, a contoured 
sputtering target assembly 10 in accordance with one embodiment of the 
present invention is shown. Sputtering target assembly 10 includes a 
target member 12 of sputtering material that may be soldered or otherwise 
joined to a target backplate 14 for use in a sputtering system (not 
shown). As those skilled in the art will appreciate, sputtering target 
assembly 10 is mounted within a vacuum processing chamber (not shown) of 
the sputtering system (not shown) through fasteners (not shown) and a 
centrally threaded shaft 16. The sputtering system (not shown) may be of 
the type shown in U.S. Pat. Nos. 4,909,695 and 5,130,005, both assigned to 
the assignee of the present invention, which are expressly incorporated 
herein by reference in their entirety. 
Target member 12 may be formed as a generally circular disk of sputtering 
material, including, but not limited to, titanium, titanium-tungsten, 
platinum, aluminum alloys, gold, silver, copper or refractory metal 
silicides. The diameter of target member 12 will vary, typically between 
ten and fourteen inches depending on the size of the wafer to be 
sputtered. For example, a ten inch diameter target may be used to sputter 
coat a six inch diameter wafer, while a twelve inch target may be used to 
sputter coat an eight inch wafer. While target member 12 will be described 
in detail herein as a circular disk with a diameter of about ten inches, 
it will be appreciated by those skilled in the art that other 
configurations and sizes of target member 12 are possible without 
departing from the spirit and scope of the present invention. 
As best understood with reference to FIGS. 1 and 2, target member 12 has a 
precisely machined face or top surface 18, a planar bottom surface 20, and 
an outer peripheral surface 22. Preferably, as shown in the figures, the 
outer peripheral surface 22 is formed generally perpendicularly to the 
planar bottom surface 20. During a sputtering operation, target member 12 
is mounted within the sputtering process chamber (not shown) with the top 
surface 18 of the target 12 facing the wafer (not shown). Sputtering 
material is caused to be ejected from the top surface 18 of target member 
12 and deposited onto the wafer (not shown) in a thin film as is well 
known in the art. 
In accordance with one embodiment of the present invention, as best 
understood with reference to FIGS. 1, 1A and 2, target member 12 is 
contoured to reduce generation of contaminating particles from nodules 
(not shown) that may form near the outer peripheral surface 22 of the 
target during a sputtering operation. Top surface 18 of target member 12 
is formed with a contoured annular region 24 that extends radially 
inwardly from the outer peripheral surface 22 and away from the bottom 
surface 20. For a ten inch diameter target, for example, the contoured 
annular region 24 may extend to an annular boundary 26 that lies radially 
inwardly from the outer peripheral surface 22 in a range between about 
0.195 in. and about 0.975 in. 
The profile of contoured annular region 24 is particularly chosen to reduce 
accumulation of redeposition at or near the outer peripheral surface 22. 
The profile of contoured annular region 24 is also chosen to reduce the 
sputtering or erosion rate of target member 12 near the outer peripheral 
surface 22. Thus, as nodules (not shown) form at or near that location, 
the reduced sputtering rate created by the profile of target member 12 and 
lower plasma intensity existing near the outer peripheral surface 22 
stabilizes the nodules (not shown) and prevents them from flaking and 
generating contaminating particles within the processing chamber (not 
shown) that may adversely affect the sputtered film on the substrate or 
wafer (not shown). While the contour of target member 12 reduces 
generation of contaminating particles from nodules that may form on target 
member 12, particularly in titanium nitride sputtering processes, those 
skilled in the art will appreciate that the present invention is 
applicable to other sputtering processes as well without departing from 
the spirit and scope of the present invention. 
The contoured annular region 24 is inclined from the outer peripheral 
surface 22 to the radially inward annular boundary 26. The contoured 
annular region 24 may be inclined at an angle ".alpha." (FIG. 1A) in a 
range between about 5.degree. and about 20.degree. relative to a plane 28 
(FIG. 1A) that is parallel to the planar bottom surface 20 of the target. 
In one embodiment of the present invention, contoured annular region 24 
may include a planar surface 30 (FIGS. 1, 1A and 2). Alternatively, as 
shown in FIG. 1B, the contoured annular region 24 may include a radiused 
surface 32 that extends radially inwardly from the outer peripheral 
surface 22 to the annular boundary 26 and away from the bottom surface 20 
of the target 12. In either embodiment of the contoured annual region 24 
as shown in FIGS. 1A and 1B, the configuration of target member 12 reduces 
generation of contaminating particles from nodules that may form near the 
outer peripheral surface 22 during a sputtering operation. 
In accordance with the principles of the present invention, target member 
12 may include a planar region (not shown) formed on the top surface 18 
that is surrounded by the contoured annular region 24. The planar region 
(not shown) is formed generally parallel to the planar bottom surface 20 
of target 12. In another embodiment of the present invention, as best 
understood with reference to FIGS. 1 and 2, the target member 12 may 
include a substantially concave region 34 formed in the top surface 18 
that is surrounded by the contoured annular region 24. The circumferential 
edge of the concave region 34 may be coincident with the annular boundary 
26. 
In yet another embodiment of the present invention, as best understood with 
reference to FIGS. 5, 5A, 5B, 5C and 6, the target member 12 may include a 
planar region 36 formed in the top surface 18 that is surrounded by the 
annular region 24. The planar region 36 is generally parallel to the 
planar bottom surface 20 of the target. The planar region 36 includes a 
central recessed region 38 formed in the top surface 18 that reduces the 
thickness of the target member 12 between the planar region 36 and the 
bottom surface 20 of the target 12 by about 5% to about 20%. 
For a ten inch diameter target, for example, central recessed region 38 is 
preferably formed in the about 0.195 in. to about 3.10" central portion of 
the top surface 18. As best understood with reference to FIGS. 5 and 5A, 
the central recessed region 38 may include a 45.degree. step 40 that 
extends from the planar region 36 to a recessed planar region 42 formed in 
the top surface 18. Alternatively, the step transition from the planar 
region 36 to the recessed planar region 42 may be formed as a 90.degree. 
step 44 (FIG. 5B) or a radiused step 46 (FIG. 5C). The formation of 
concave region 34 of FIGS. 1 and 2, and the central recessed regions 38 of 
FIGS. 5, 5A, 5B, 5C and 6, in combination with the contoured annular 
region 24, further reduce generation of contaminating particles from 
nodules that may form near the outer peripheral surface 22 of the target 
12 during a sputtering operation. 
With reference now to FIGS. 3, 3A, 3B and 4, an alternative embodiment of 
target member 12 is shown, designated target member 112. Target member 112 
has a face or top surface 118, a planar bottom surface 120, and an outer 
peripheral surface 122 that preferably extends perpendicularly to planar 
bottom surface 120. 
As best understood with reference to FIGS. 3 and 4, top surface 118 of 
target member 112 is formed with a first contoured annular region 124 that 
extends radially inwardly from the outer peripheral surface 122 and away 
from the bottom surface 120. For a ten inch diameter target, for example, 
the contoured annular region 124 may extend to an annular boundary 126 
that lies radially inwardly from the outer peripheral surface 122 in a 
range between about 0.0195 in. and about 0.195 in. 
In this embodiment of the present invention, top surface 118 of target 
member 112 is also formed with a second contoured annular region 224 that 
extends radially inwardly from the first annular region 124 and away from 
the bottom surface 120. For a ten inch diameter target, for example, the 
second contoured annular region 224 may extend to an annular boundary 226 
that lies radially inwardly from the annular boundary 126 in a range 
between about 0.1755 in. and about 0.995 in. 
The contoured annular region 124 is inclined at an angle ".beta." (FIG. 3A) 
in a range between about 30.degree. and about 60.degree. relative to a 
plane 128 (FIG. 3A) that is parallel to the planar bottom surface 120 of 
the target. In one embodiment of the present invention, contoured annular 
region 124 includes a planar surface 130 (FIGS. 3 and 3A) that is inclined 
from the outer peripheral surface 122 to the radially inward annular 
boundary 126. Alternatively, as shown in FIG. 3B, the contoured annular 
region 124 may include a radiused surface 132 that extends radially 
inwardly from the outer peripheral surface 122 to the annular boundary 126 
and away from the bottom surface 120. 
The contoured annular region 224 is inclined at an angle ".alpha." (FIG. 
3A) in a range between about 5.degree. and about 20.degree. relative to a 
plane 228 (FIG. 3A) that is parallel to the planar bottom surface 120 of 
target 112. In one embodiment of the present invention, contoured annular 
region 224 may include a planar surface 230 (FIGS. 3 and 4) that is 
inclined from the contoured annular region 124 to the radially inward 
annular boundary 226. Alternatively, the contoured annular region 224 may 
include a radiused surface (not shown) that extends radially inwardly from 
the annular boundary 126 to the annular boundary 226 and away from the 
bottom surface 120. In each embodiment of the contoured annual regions 124 
and 224 as shown in FIGS. 3A and 3B, the configuration of target member 
112 reduces generation of contaminating particles from nodules that may 
form near the outer peripheral surface 122 of the target 112 during a 
sputtering operation. 
In accordance with the principles of the present invention, target member 
112 may include a planar region (not shown) formed on the top surface 118 
that is surrounded by the annular regions 124 and 224. The planar region 
(not shown) is formed generally parallel to the bottom surface 120. In 
another embodiment of the present invention, as best understood with 
reference to FIGS. 3 and 4, the target member 112 may include a 
substantially concave region 134 formed in the top surface 118 that is 
surrounded by the annular regions 124 and 224. In yet another embodiment 
of the present invention, as best understood with reference to FIGS. 7 and 
8, the target member 112 may include a planar region 136 formed in the top 
surface 118 that is surrounded by the annular regions 124 and 224. Planar 
region 136 is formed generally parallel to the bottom surface 120. The 
planar region 136 includes a central recessed region 138 formed in the top 
surface 118 that is similar to the central recess region 38 described in 
detail above with reference to FIGS. 5, 5A, 5B and 5C. 
As best understood with reference to FIG. 7, the central recessed region 
138 may include a 45.degree. step 140 that extends from the planar region 
136 to a recessed planar region 142 formed in the top surface 118. 
Alternatively, the step transition from the planar region 136 to the 
recessed planar region 142 may be formed as a 90.degree. step (not shown) 
or a radiused step (not shown) as described in detail above with reference 
to FIGS. 5B and 5C. The formation of the concave region 134 of FIGS. 3 and 
4, and the central recessed regions 138 of FIGS. 7 and 8, further reduce 
generation of contaminating particles from nodules that may form near the 
outer peripheral surface 122 of the target 112 during a sputtering 
operation. 
From the above disclosure of the general principles of the present 
invention and the preceding detailed description of preferred embodiments, 
those skilled in the art will readily comprehend the various modifications 
to which the present invention is susceptible. For example, the central 
recessed regions 38 and 138 may be replaced with central holes (not shown) 
extending through the thickness of the target member. Moreover, it will be 
appreciated that for sputtering targets of greater or lesser diameter than 
the ten inch diameter target member 12 discussed herein, the dimensions 
set forth above with respect to the radially inward extent of contoured 
annular regions 24, 124 and 224 will be increased or decreased 
proportionally. The invention in its broader aspects is therefore not 
limited to the specific details and illustrative example shown and 
described. Accordingly, departures may be made from such details without 
departing from the spirit or scope of Applicants general inventive 
concept. Therefore, Applicants desire to be limited only by the scope of 
the following claims and equivalents thereof: