Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2000-10-17
2002-10-01
McDonald, Rodney G. (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S298170, C204S298180, C204S298190
Reexamination Certificate
active
06458252
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the magnetron sputtering, and more particularly, to magnetron magnet design for the efficient utilization of a sputtering target.
BACKGROUND OF THE INVENTION
Magnetron sputtering, or magnetically enhanced sputtering, involves the use of a sputtering target to provide coating material for vapor phase deposition in a vacuum onto substrates in a chamber. In sputtering, the sputtering target is energized with a negative potential to act as a cathode in a glow discharge system. In magnetron sputtering, magnets generate a magnetic field in the form of a closed loop magnetic tunnel over the surface of the sputtering target. The magnetic tunnel confines electrons near the surface of the target. The electron confinement allows the formation of a plasma with significantly lower ignition and extinction voltages for a given process pressure, and significantly lower ignition and extinction pressures for a given cathode voltage.
A conventional magnetic tunnel confines near the target surface both thermal electrons and secondary electrons. Thermal electrons are distinguished from secondary electrons by their origins, which give the electrons different characteristics. Thermal electrons are created through an ionizing collision of an atom or ion with another electron. Thermal electrons are much more numerous than secondary electrons but have much lower energy. Secondary electrons are emitted from the target upon impact of the target by an ion.
The tunnel forces the secondary electrons into semicircular orbits along the length of the magnetic tunnel due to the influence of the component of the magnetic field that is parallel to the uneroded target surface in the cross-sectional plane. The component of the magnetic field perpendicular to the uneroded target surface forces secondary electrons moving parallel to the axis of the tunnel to move laterally in the cross-sectional plane toward the magnetic centerline of the tunnel, which is the line on the surface of the target where the magnetic field perpendicular to the uneroded target surface is zero. Thermal electrons, on the other hand, move back and forth in the cross-sectional plane of the tunnel and form helical orbits along the lines of magnetic flux. Because of their low mobility perpendicular to the lines of magnetic flux, thermal electrons are confined to the region of the cathode. Magnetic mirrors created by converging magnetic flux lines at the edge of the magnetic tunnel keeps the thermal electrons reflecting from side to side as the low mobility of the thermal electrons perpendicular to the magnetic flux lines keeps them moving in helical orbits around the flux lines. The mirror effect is strongest at the edges of the magnetic tunnel and vanishes above the magnetic centerline of the tunnel, so that the thermal electrons move horizontally in a one-dimensional potential well that is centered at the magnetic centerline of the tunnel.
The electron confining properties of magnetron sputtering are effective in enhancing plasma density near the target surface and make magnetically enhanced sputtering much more practical than traditional diode sputtering. However, the conventional magnetic tunnel is responsible for low target utilization because the concentration of electrons near the magnetic centerline of the tunnel causes the plasma density to be similarly concentrated, making the erosion rate highest in this region. Further, as the target erodes, the target surface in the area adjacent the centerline erodes into even stronger magnetic fields, which accelerates the concentration of the erosion. In addition, the concentrated erosion produces a V-shaped profile redirecting secondary electrons from the opposite walls to the center of the erosion groove, further concentrating the plasma there. Typically, utilization of a target of uniform thickness has been approximately 25%. Poor target utilization undermines the economics of thin film deposition by increasing the number of expended targets and amount of unused target material as well as the machine downtime required for target changes. Uneroded areas of the target tend to occur near the edges of the magnetic tunnel. Where such areas exist, they tend to accumulate redeposited material that flakes off into the processing chamber to produce particulate contamination of the substrate.
Magnetic tunnels have been employed having nonsymmetrical shapes that are rotated with respect to the target to manipulate the erosion profile. Such rotation is useful in achieving improved film uniformity on the substrate, achieving higher target utilization and eroding points on the target that would otherwise be left uneroded if the magnetic tunnel were static. These rotating arrangements are only convenient for round planar targets. For rectangular and annular targets, only static magnetic arrangements have been practical.
For frusto-conical targets and other annular or ring-shaped targets having other system components located in the center of the target, the magnetron arrangements of the prior art have not provided high target utilization. While magnetically enhanced sputtering has made sputtering a practical and economically viable technique for depositing thin films, its full economic potential has not been realized in the case of static magnetic arrangements.
Accordingly, there remains a need to provide a magnet design that will produce high target utilization with frusto-conical and other annular targets.
SUMMARY OF THE INVENTION
An objective of the present invention is to provide for improved utilization and full face erosion of a frusto-conical target in a magnetron sputtering apparatus. A particular objective of the present invention is to provide for improved utilization of an annular target without restricting availability of the volume within the opening in the center of the target to use for other hardware, such as, for example, an ICP source.
In accordance with the principles of the present invention, a sputtering apparatus that includes an frusto-conical or similar annular sputtering target is provided with a magnetron magnet assembly that causes the erosion of the target to move from the center of the target annulus to inner and outer regions as the target erodes. The magnet assembly is positioned behind the target to produce a plasma confining magnetic field over the target in the shape of an annular tunnel on the surface of the annular target surrounding the opening at the target center. The walls of the target form a truncated cone that is inclined, for example, at about 35° to the plane of the central opening.
In one embodiment of the invention, three permanent magnet rings produce three magnetic tunnels. The relative contributions of the three tunnels produces the effect of magnetic flux lines that are parallel to the surface of the target. For a thin target, and as some point part way through the lives of thicker targets, an inner magnetic tunnel and an outer magnetic interact with a main central magnetic tunnel to produce a resultant magnetic flux parallel to the surface of the uneroded target. With such thicker targets, a main central tunnel dominates early in the target's life to erode the mean radius of the annular target along the target centerline and inner and outer tunnels dominate later in the life of the target to erode areas adjacent the inner and outer rims of the target annulus and spread the erosion groove inward and outward of the target centerline in the same manner as if the flux remained parallel to the uneroded target surface throughout the life of the target.
In the preferred embodiment, a sputtering apparatus, is an ionized physical vapor deposition apparatus that includes a vacuum processing chamber, a substrate support in the processing chamber for supporting a substrate for processing, an annular magnetron sputtering cathode assembly having a central opening and an inductively coupled plasma source behind a dielectric window in the central opening. The magnetron cathode assembly includes a frusto-conical sputteri
McDonald Rodney G.
Tokyo Electron Limited
Wood Herron & Evans L.L.P.
LandOfFree
High target utilization magnetic arrangement for a truncated... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High target utilization magnetic arrangement for a truncated..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High target utilization magnetic arrangement for a truncated... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2958458