Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2003-01-27
2004-11-02
VerSteeg, Steven (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S298030, C073S086000
Reexamination Certificate
active
06811657
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to sputter deposition on substrate surfaces. More specifically, the present invention relates to methods and apparatus for measuring the profile of a sputtering target.
2. State of the Art
A thin film of metallic material may be deposited on a substrate using a sputter deposition process wherein a metallic target is attacked with ions causing atoms or small particles of the target to be ejected from the target and deposited on the substrate surface.
FIG. 1
illustrates a cross-sectional schematic of a typical sputtering apparatus
10
comprising a vacuum chamber
12
having a gas inlet
14
and a gas outlet
16
. The sputtering apparatus
10
further comprises a substrate support pedestal
24
and a metallic target
22
attached to a sputtering cathode assembly
18
, each located within the vacuum chamber
12
. The pedestal
24
may be configured to secure a substrate
26
thereto with a biasable electrostatic chuck, a vacuum chuck, a clamping structure, or a combination of methods. The substrate
26
may be transported to and from the pedestal
24
manually or with a robotic arm or blade (not shown).
During the sputtering process, the vacuum chamber
12
is filled with an inert gas, such as argon, through the gas inlet
14
and then reduced to a near vacuum through the gas outlet
16
. The target
22
is negatively charged to cause electrons to be emitted from an exposed surface
23
of the target
22
and move toward an anode (not shown). A portion of the moving electrons strike atoms of the inert gas, causing the atoms to become positively ionized and move towards the negatively charged target
22
. The electrons, inert gas atoms, and ions form a plasma which is typically intensified and confined over the target surface
23
by a magnetic field generated by a magnet assembly
20
located proximate the target
22
. The magnet assembly
20
may comprise one or more permanent magnets or electromagnets located behind and/or to the side of the target
22
. A portion of the ions discharging from the plasma strike the target surface
23
at a high velocity, causing atoms or small particles of the target
22
material to be ejected from the target surface
23
. The ejected atoms or small particles then travel through the vacuum chamber
12
until they strike a surface, such as the surface of the substrate
26
, forming a thin metallic film thereon.
The magnetic field formed over the target surface
23
by the magnet assembly
20
confines the electrons emitted from the target
22
to an area near the target surface
23
. This greatly increases the electron density and the likelihood of collisions between the electrons and the atoms of the inert gas in the space near the target surface
23
. Therefore, there is a higher rate of ion production in plasma regions near the target surface
23
where the magnetic field intensity is stronger. Varying rates of ion production in different plasma regions causes the target surface
23
to erode unevenly. Typically, the configuration of the magnet assembly
20
produces a radial variation of thick and thin areas, or grooves, within a diameter of the target surface
23
.
FIG. 2
illustrates a cross-sectional perspective view of a typical erosion profile of a cylindrical metallic target
22
, such as the metallic target
22
shown in
FIG. 1
, which has been used in a sputtering process.
FIG. 2
illustrates a target surface
23
before erosion has occurred as well as a target surface
32
that has eroded unevenly across the length of a diameter bounded by an outside edge
25
of the target
22
. Due to the geometry of a magnetic field surrounding the target
22
, the target surface
32
has eroded nearly symmetrically about a center line
30
dividing the length of the diameter.
Referring now to
FIGS. 1 and 2
, the target
22
may comprise a rare metal, such as gold, platinum, palladium or silver, or may comprise, for example, aluminum, titanium, tungsten or any other target material conventionally employed in the semiconductor industry. Therefore, it is advantageous to consume as much of the target
22
material during sputter deposition processes as possible before replacing an eroded target
22
. Further, replacing an eroded target
22
before the end of its useful life may be a difficult and time-consuming task. However, it is important to replace the target
22
before a groove “punches through” the target
22
material and exposes portions of the cathode assembly
18
to erosion, causing damage to the cathode assembly
18
and contaminating the sputtering apparatus
10
. For example, the target
22
material in the area of groove
28
shown in
FIG. 2
may erode before the remainder of the target
22
material and expose the cathode assembly
18
to ionic bombardment from the surrounding plasma.
The useful life of a metallic sputtering target
22
is typically estimated by determining the cumulative deposition time for the target
22
. A deposition time is chosen to guarantee that the target
22
material will never be completely removed at any given location and may take into account the thickness of the target
22
, the material used for the target
22
, and the effect of intensifying and confining the plasma over the target surface
32
by a magnetic field generated by the magnet assembly
20
in a predetermined configuration. However, if the characteristics of the plasma distribution change due to, for example, reconfiguring the magnet assembly
20
to produce a magnetic field with a different geometry, the erosion of the target surface
32
may be changed and could result in localized enhanced metal removal and the possible punching through to the cathode assembly
18
before the expiration of the estimated deposition time.
Directly measuring the target surface
23
is difficult and time consuming. Opening the vacuum chamber
12
to inspect the target surface
23
requires several hours of idle time while the vacuum chamber
12
is baked out under post-vacuum inspection. Accurate measurement of the target surface
23
while the sputtering apparatus
10
is under vacuum is difficult because the gap distance d between the target
22
and the pedestal
24
may be as small as 25 millimeters. Typical measurement devices are too large to be inserted into the gap d between the target
22
and the pedestal
24
to profile the target surface
23
while the vacuum chamber
12
is under vacuum. Further, measurement devices placed near the target
22
during a sputtering process may be damaged by exposure to metal deposition.
In view of the shortcomings in the art, it would be advantageous to prevent premature replacement and overconsumption of the target
22
by providing a technique and device to measure the target surface
23
while the vacuum chamber
12
is under vacuum.
BRIEF SUMMARY OF THE INVENTION
The present invention relates to methods and apparatus for measuring the erosion of a metallic sputtering target.
An apparatus according to one embodiment of the present invention comprises a sensor configured to emit an energy beam toward a target surface and to detect a reflection of the energy beam from the target surface. The sensor may be coupled to a thin profile arm configured to move or transport the sensor over the target surface between the target and a substrate support pedestal to a plurality of measurement locations. The arm may be configured to attach to a robotic device. The sensor and the arm are configured, positioned and sized to be inserted into a narrow gap existing between the target surface and the pedestal. The arm may also be configured to remove the sensor from the gap and to shield the sensor during a sputtering process.
In another embodiment of the present invention, the sensor comprises a source element configured to emit a collimated light beam and a plurality of detectors arranged in a linear array. The source element may be positioned so as to emit the collimated light beam at an acute angle with respect to the linear
Micro)n Technology, Inc.
TraskBritt
VerSteeg Steven
LandOfFree
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