Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1999-02-25
2001-02-27
Nguyen, Nam (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S298210, C204S298410, C204S298220, C204S298230, C204S298140, C204S192380, C204S298150, C204S298160, C204S298060, C204S298090, C204S298270, C204S298280, C204S298290
Reexamination Certificate
active
06193853
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for applying coatings by magnetron sputtering.
BACKGROUND OF THE INVENTION
Magnetron sputtering is a well known process for applying thin coatings onto objects. Sputtering is implemented by creating an electrical plasma over the surface of an target emitter material in a low-pressure gas atmosphere. Gas ions from the plasma are accelerated by electrical fields to bombard and thereby eject atoms from the surface of the emitter. These atoms travel through the gas environment until they impact the surface of the object to be coated, where they bond to the object, creating the coating layer.
A standard method of improving the efficiency of sputtering has been to use magnetic fields to confine electrons to the glow region in the vicinity of the emitter surface. The addition of such magnetic fields increases the rate of ionization which in turn increases the ion energy and the number of ions in the plasma. The increased ion energy and number of ions increases the overall sputtering rate.
Cylindrical magnetron sputtering devices are known which utilize elongated emitters and solenoid coils which produce flux lines parallel to the axis of the emitter. A significant drawback to such cylindrical sputtering devices is that they suffer from undesirable end effects. In a cylindrical magnetron, the direction of the electron drift velocity vector causes the electrons to orbit around the longitudinal axis of the emitter. However, the electrons tend to leak out or escape their orbits near each end of the emitter, resulting in lower ionization intensities and therefore lower sputtering rates at each end of the emitter. As a result, the portions of the object to be coated in the vicinity of the ends of the emitter may receive little or no coating.
Another drawback to cylindrical magnetrons is that in order to uniformly coat long objects such as pipes, a corresponding long vacuum chamber, emitter and solenoid coil must be provided, adding to the complexity and expense of the apparatus.
Therefore, there is a need in the art for apparatuses and methods suitable for uniformly coating long cylindrical objects such as pipes and the like.
SUMMARY OF THE INVENTION
In general terms, the invention comprises magnetron sputtering methods and apparatuses which may uniformly coat either the interior or exterior of elongated cylindrical workpieces. The invention includes configurations where the workpiece is oriented vertically or horizontally. In a preferred embodiment, means to heat the workpiece in the area being sputtered are provided as well as means for tensioning the workpiece to prevent warping as a result of the heat.
In one aspect of the invention, the invention comprises a sputtering process for applying a coating onto an elongate, hollow cylindrical workpiece having an internal surface and an external surface, said process comprising the steps of:
a) providing a vacuum chamber and introducing a sputtering gas into a low pressure environment in the vacuum chamber;
b) providing an elongate emitter and positioning the emitter substantially parallel to the surface of the workpiece to be coated, positioning the workpiece so the surface of the workpiece to be coated is in the low pressure environment;
c) creating a plasma field between the emitter and the workpiece by providing a power supply connected to the emitter and the workpiece; and
d) creating a magnetic field around the emitter having flux lines substantially and uniformly parallel along a length of the emitter by providing a solenoid coil in a configuration of a coiled tubular conductor connected to a high current/low voltage power supply, wherein an area of overlap between the magnetic field and the plasma field defines a coating zone.
In an embodiment of the invention, the method is applicable to coating the internal surface of the workpiece, where the workpiece itself is used as the vacuum chamber, the emitter is coaxial with the workpiece and has a length less than the workpiece and the coating zone is moved by moving the emitter along the centroidal axis of the workpiece. Preferably, the solenoid has a coiled length approximately equal to the length of the emitter and the coating zone is moved by moving both the solenoid and the emitter along the length of the workpiece in a synchronized fashion.
Alternatively, the solenoid has a coiled length approximately equal to the length of the workpiece and remains stationary while the emitter moves. In another alternative embodiment, the emitter has a length approximately equal to the length of the workpiece and the coating zone is moved by moving the solenoid along the length of the workpiece.
In another embodiment, the method is applicable to coating the external surface of the workpiece, wherein the solenoid coil surrounds the vacuum chamber, the emitter is adjacent and parallel to the workpiece within the vacuum chamber and has a length less than the workpiece and the coating zone is moved by moving the emitter along an axis parallel to the workpiece while the workpiece is rotated along its centroidal axis.
Preferably, the solenoid may have a coiled length approximately equal to the length of the emitter and the coating zone is moved by moving both the solenoid and the emitter along the length of the workpiece in a synchronized fashion. Alternatively, the solenoid may have a coiled length approximately equal to the length of the workpiece and remains stationary while the emitter moves. In another alternative embodiment wherein the external surface of the workpiece is coated, the emitter is adjacent and parallel to the workpiece and has a length approximately equal to the length of the workpiece, the coating zone is moved by moving the solenoid along the length of the workpiece.
With any of these alternative embodiments, the method preferably includes a step wherein the solenoid heats the workpicce in the vicinity of the coating zone and the workpiece is subjected to a tensioning force.
In another aspect of the invention, the invention comprises an apparatus for sputter deposition of a coating onto an internal surface of an elongate, hollow cylindrical workpiece, said workpiece defining an internal chamber, said apparatus comprising:
a) an elongate emitter coaxial to the workpiece to be coated;
b) end plates for sealing the open ends of the workpiece including means to evacuate the chamber and means for introducing a sputtering gas into the chamber;
c) a power supply connected to the emitter and the workpiece for creating a plasma field between the emitter and the workpiece;
d) a solenoid coil in a configuration of a coiled tubular conductor surrounding the workpiece and a high current/low voltage power supply connected to the coiled tubular conductor for creating a magnetic field within the chamber having flux lines substantially and uniformly parallel to the longitudinal axis of the emitter; and
e) wherein an area of overlap between the magnetic field and the plasma field defines a coating zone.
Preferably, the emitter has a length less than the length of the workpiece and the means for moving the coating zone comprises means for moving the emitter along the centroidal axis of the workpiece. More preferably, the coiled length of the solenoid is approximately equal to the length of the emitter and the means for moving the coating zone further comprises means for moving the solenoid together with the emitter in a synchronized manner.
Alternatively, the coiled length of the solenoid is approximately equal to the length of the workpiece and no means for moving the solenoid coil relative to the workpiece are provided. In another alternative embodiment, the length of the emitter is approximately the same as the workpiece and the means for moving the coating zone comprises means for moving the solenoid coil along the length of the workpiece.
Preferably, the apparatus is configured such that the solenoid heats the workpiece and further comprises means for tensioning the workpiece longitudinally.
In another aspect of the in
Ioumchtyk Michael
Yumshtyk Gennady
Cametoid Limited
Chacko-Davis Daborah
Hill & Schumacher
Nguyen Nam
Schymacher Lynn C.
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