Patent Application
20070007130
The invention concerns sputtering targets and in particular concerns sputtering targets enhanced for improved performance in magnetron sputtering systems.
Diode sputtering systems are used to apply a film of target material to the surface of a substrate. An electric field is applied between a target and the substrate to generate a plasma within a sputter chamber. Ions from the plasma collide with the target and dislodge atoms of the target material. The dislodged atoms adhere to the surface of the substrate forming a film thereon.
Magnetron sputtering systems improve the sputter rates of diode sputtering systems by using a magnetic field in addition to the electric field. Magnetron sputtering systems arrange a magnetic array behind the sputter target to generate a magnetic field over the active surface of the target. The magnetic field traps ions in the plasma near the active surface of the target, thereby increasing the plasma density and improving the sputter rate. However, the benefits provided by magnetron sputtering systems are reduced or lost when sputtering ferromagnetic target materials.
The deposition of magnetic materials such as ferromagnetic cobalt and nickel alloys is used in applications such as magnetic data storage. The high magnetic permeability and low pass-through flux characteristics of these materials make sputtering in a magnetron sputtering system difficult. Specifically, most or all of the magnetic field generated by the magnetic array of the magnetron sputtering system is shunted through the interior of the target rather than out through and over the active surface of the target.
Attempts have been made by target manufacturers to address the sputtering difficulties associated with ferromagnetic target materials. For example, strain has been induced in targets via hot or cold working of the material in efforts to raise the pass-through flux and lower the magnetic permeability of the target material. However, the ability to improve these characteristics is limited. Alternative solutions have included modifying the settings or configurations of magnetron sputtering systems to increase the magnetic field generated. These solutions are also not ideal.
Accordingly, a need exists for an improved magnetron sputtering target that improves sputtering efficiency of ferromagnetic materials without requiring extensive modification to existing magnetron sputtering systems.
The present invention addresses the foregoing deficiencies of conventional sputtering targets by embedding magnets in the sputtering target. Specifically, one or more magnets are embedded in a back surface of the sputtering target and are oriented to increase the magnetic field passing through the sputtering target into the sputter chamber. By increasing the magnetic field in the sputter chamber, plasma density is increased which improves sputter rates and operating voltages can be reduced.
According to one aspect of the invention, a sputtering target is provided for use in a magnetron sputtering system. The sputtering target includes an active surface from which target material is sputtered and a back surface opposite the active surface. At least one magnet is embedded in the back surface of the sputtering target. The magnet is further oriented to increase the magnetic field passing through the active surface of the target. The sputtering target typically comprises ferromagnetic materials, however, non-ferromagnetic materials may be used as well.
Preferably, the embedded magnet is a rare earth magnet and is aligned within -the center of a sputter track of the magnetron sputtering system. In addition, the magnet is preferably embedded in the target at a depth from the active surface greater than the maximum depth of the sputter track.
The enhanced sputtering target may also include a backing plate bonded to the back surface of the target. Magnets may be embedded in the backing plate, the target material or both.
The foregoing summary of the invention has been provided so that the nature of the invention can be understood quickly. A more detailed and complete understanding of the preferred embodiments of the invention can be obtained by reference to the following detailed description of the invention together with the associated drawings.
To sputter the target material from sputtering target 11, the sputter chamber is filled with a working gas such as Argon and an electric field is applied between sputtering target 11 and substrate 12. The electric field breaks down the working gas to generate a plasma in the sputter chamber. Ions in the plasma are attracted to and collide with active surface 11a of sputtering target 11. These collisions dislodge atoms of the target material which then travel and adhere to the surface of substrate 12 to form a film thereon.
Magnetron sputtering system 10 uses a magnetic array, depicted as magnets 14a to 14c in
The penetration of the magnetic field through sputtering target 11 shown in
Magnets 25a and 25b are oriented within sputtering target 21 to block the shunting of magnetic field through the interior of the target and increase the amount of magnetic field penetrating active surface 21a into the sputter chamber. To achieve the results, one embodiment of the invention orients the magnetic poles of magnets 25a and 25b with those of the magnetic array represented by magnets 24a to 24c. Specifically, the magnetic poles of 25a and 25b are oriented parallel to those of the magnetic array. It is to be understood that this orientation represents one embodiment of the invention, and that alternative orientations that increase the magnetic field penetrating sputtering target 21 fall within the scope of the invention.
The shape and configuration of the embedded magnets are dependent on the configuration of the magnetic array in the magnetron sputtering system used for sputtering the target material. The configuration of the magnetic array defines the location of one or more sputter tracks in active surface 21a. A sputter track represents an erosion pattern formed in active surface 21 a as the target material is sputtered. Representative sputter tracks are shown in
One advantage of embedding magnets 25a and 25b in sputtering target 21, rather than simply placing them externally on back surface 21b, is to place the magnets 25a and 25b closer to active surface 21a. This increases the amount of magnetic field penetrating active surface 21a into the sputter chamber, thereby improving the sputtering process. According to one embodiment of the invention, magnets 25a and 25b are embedded at a depth from active surface 21a just below the maximum depth of the sputter track. This allows the magnets to be close to active surface 21a, while preventing contamination caused by sputtering the magnets themselves.
Magnets 25a and 25b are embedded in back surface 21b using any of a number of methods known to those skilled in the art. For example, conventional machining techniques may be used to bore holes for each of the magnets. The magnets may then either be pressure fitted into the holes, bonded using known bonding techniques or a combination of these methods.
Similar to
An advantage to embedding the magnets in the backing plate is that when the sputtering target has been consumed, the backing plate can be removed and bonded to a new sputtering target. Alternative embodiments of the two-part sputtering target include embedding magnets 35a and 35b in sputtering target 31 (similar to that shown in
As described above, the present invention provides a novel way to enhance sputtering targets for use in magnetron sputtering systems. A significant advantage provided by the invention is that the enhancements are made to the target itself rather than requiring extensive modifications to the magnetron sputtering system. The invention has been described in the context of sputtering targets made of ferromagnetic sputtering material. It is to be understood, however, that the invention is equally applicable to non-ferromagnetic sputtering targets to improve sputter rates. Furthermore, the invention is not limited to sputtering targets having specific shapes. For example, the sputtering targets may be circular, rectangular, etc.
The foregoing detailed description is intended to illustrate preferred embodiments of the invention. However, the examples set forth above are not intended to limit the scope of the invention, which should be interpreted using the claims set forth below. It is to be understood that various modifications to the illustrated examples of the invention can be made without departing from the spirit and scope of the invention.
