Sputtering apparatus and process for high rate coatings

• US 6,365,010 B1
• Filed: 09/16/1999
• Issued: 04/02/2002
• Est. Priority Date: 11/06/1998
• Status: Expired due to Fees

• Current Assignee: Winsky Technology Limited
• Original Assignee: Scivac
• Inventors: Hollars, Dennis R.
• Primary Examiner(s): Nguyen, Nam
• Assistant Examiner(s): VerSteeg, Steven H.
• Application Number:
  US09/397,445
• Time in Patent Office: 929 Days
• Field of Search: 204/192.12, 204/298.09, 204/298.12, 204/298.15, 204/298.21, 204/298.22, 204/298.26, 204/298.28
• US Class Current: 204/192.12
• CPC Class Codes: C23C 14/35 by application of a magnetic field, e.g. magnetron sputtering C23C14/3457 takes precedence
• CPC Class Codes: C23C 14/352 using more than one target C23C14/56 takes precedence
• CPC Class Codes: C23C 14/568 Transferring the substrates through a series of coating stations C23C14/562 takes precedence
• CPC Class Codes: H01J 37/3405 Magnetron sputtering

Abstract

A sputtering apparatus and method for high rate deposition of electrically insulating and semiconducting coatings with substantially uniform stoichiometry. Vertically mounted, dual rotatable cylindrical magnetrons with associated vacuum pumps form semi-isolated sputtering modules, which can be independently controlled for the sequential deposition of layers of similar or different materials. Constant voltage operation of AC power with an optional reactive gas flow feedback loop maintains constant coating stoichiometry during small changes in pumping speed caused by substrate motion. The coating method is extremely stable over long periods (days) of operation, with the film stoichiometry being selectable by the voltage control point. The apparatus may take the form of a circular arrangement of modules for batch coating of wafer-like substrates, or the modules may be arranged linearly for the coating of large planar substrates.

Claims

1. A magnetron system for eroding and depositing target material on a substrate, comprising:

a first and a second cylindrical tubular target, each having a longitudinal axis and an outside surface and a fixed length, each cylindrical tubular target rotatable about the longitudinal axis of the cylindrical tubular target, wherein the second rotatable cylindrical tubular target is positioned relative to the first target such that axes of the first and second targets are parallel to each other and the outside surfaces of the first and second cylindrical tubular targets are in close proximity; and

a first and a second magnetic assembly respectively disposed within and along the length of the first and the second tubular target, each magnetic assembly configured to provide a magnetic field racetrack over the outer surface of each tubular target, the magnetic field racetrack confining a plasma gas to erode the target material of each target from a pair of substantially parallel erosion zones along the length of the each tubular target, each pair of erosion zones defining a source plane for each target and being separated by a distance therebetween, and each magnetic assembly configured to fix the distance between the parallel erosion zones in each target to create a combined area of target material flux for each tubular target,

wherein a greater fraction of the target flux from each target is utilized to deposit target material on the substrate than from a single zone on each target, and

wherein the magnetic assemblies are oriented relative to each other such that, at the substrate, an included angle is formed between a pair of planes, normal to the source planes and passing through the axis of each target, and the target flux of each of the targets combines to create an area of substantially uniform flux at the substrate.

2. A magnetron assembly as recited in claim 1, wherein the tubular target includes

a target support assembly for holding the target material and for enabling the target material to be rotated with respect to the magnet assembly.

3. A magnetron assembly as recited in claim 2,

wherein each tubular target rotates at a determinable speed and the plasma gas has a determinable density;

and

wherein the speed of rotation and the density of the plasma gas at the erosion zones substantially prevent target material from accumulating on the target at a location away from the erosion zones during a rotation of the tubular target.

4. A magnetron assembly as recited in claim 2,

wherein each tubular target rotates at a determinable speed;

and

wherein the speed of rotation is in a range of about 10 to 100 RPM.

5. A magnetron assembly as recited in claim 1, further comprising:

a first ungrounded electrode in electrical contact with the first tubular target and

a second ungrounded electrode in electrical contact with the second tubular target; and

wherein the first electrode receives electric power from a first pole of an ac electric source and the second electrode receives electric power from a second pole of the ac electric source, and

wherein the first and second tubular targets alternately become active and inactive to deposit target material on the substrate as the poles of the ac electric source alternate in polarity, the inactive target and the plasma providing a low and substantially constant electrical resistance return path back to the ac electric source.

6. A magnetron assembly as recited in claim 5, wherein:

the first tubular target becomes active to deposit target material on the substrate when the first pole of the ac electric source is negative with respect to the second pole; and

the second tubular target becomes active to deposit target material on the substrate when the second pole of the ac electric source is negative with respect to the first pole.

7. A magnetron assembly as recited in claim 5,

wherein the ac source provides an rms voltage to the first and second ungrounded electrodes;

and

wherein the rms voltage provided by the ac source is substantially constant.

8. A magnetron assembly as recited in claim 1, wherein the outside surfaces of the tubular targets are separated by a distance in a range of about one-half inch to one inch.

9. A magnetron assembly as recited in claim 1, wherein the two planes normal to the source planes intersect in a line common to both planes;

and

wherein the substrate is positioned at a distance proximate to, but not at, the intersecting line of the two planes normal to the source planes.

10. A magnetron assembly as recited in claim 9, wherein the substrate is positioned at a distance nearer to the targets than the intersecting line.

11. A magnetron assembly as recited in claim 9, wherein the substrate is positioned at a distance farther from the targets than the intersecting line.

12. A magnetron assembly as recited in claim 9, wherein the intersecting line is a few inches from the tubular targets.

13. A magnetron assembly as recited in claim 1,

wherein the target flux has a determinable distribution at the substrate;

and

wherein the target flux at the source plane from a single erosion zone has a distribution of a Gaussian-like curve having a center of distribution and a width, the width of the Gaussian-like curve being a distance between two one-half points on the curve.

14. A magnetron assembly as recited in claim 13, wherein the distance between the parallel erosion zones on each target is approximately equal to the width of the Gaussian-like curve for a single erosion zone, the target flux at the substrate from the pair of erosion zones being substantially uniform over a field larger than that from a single erosion zone and having a center of distribution at a point where the Gaussian-like curves for the zones intersect.

15. A magnetron assembly as recited in claim 14,

wherein the included angle between the normal planes of the first and second targets is such that the center of the distributions from each target are separated by twice the width of a single Gaussian-like curve at the substrate such that there is a substantially uniform field of target flux from both targets, and

wherein the field from the pair of targets includes a substantial fraction of the flux from both targets.

16. A magnetron assembly as recited in claim 15, wherein the field from the pair of targets includes about 75% of the flux from both targets.

17. A magnetron assembly as recited in claim 13, wherein the distance between the parallel erosion zones on each target is approximately twice the width of the Gaussian curve for a single erosion zone, the target flux at the substrate from the pair of erosion zones having a center of distribution at a point where the Gaussian curves for the erosion zones intersect.

18. A magnetron assembly as recited in claim 17,

wherein the included angle between the normal planes of the first and second targets is such that the centers of distribution from each target are separated by the width of a single Gaussian-like curve at the substrate such that there is a substantially uniform field of target flux from both targets, and

wherein the field from the pair of targets includes a substantial fraction of the flux from both targets.

19. A magnetron assembly as recited in claim 18, wherein the field from the pair of targets includes about 75% of the flux from both targets.

20. A magnetron system for eroding and depositing target materials on a substrate, comprising:

a first and a second cylindrical tubular target, each having a longitudinal axis and an outside surface and a fixed length, the first target composed of a material and the second target composed of a material that are different from each other, each tubular target rotatable about the longitudinal axis of the cylindrical target, wherein the second rotatable cylindrical tubular target is positioned relative to the first target such that axes of the first and second targets are parallel to each other and the surfaces of the first and second cylindrical tubular targets are in close proximity;

a first and a second magnetic assembly respectively disposed within and along the length of the first and the second tubular target,

each magnetic assembly configured to provide a magnetic field racetrack over an outer surface of each tubular target, the magnetic field racetrack confining a plasma gas to erode the material of each target from a pair of substantially parallel erosion zones along the length of the each tubular target, each pair of erosion zones defining a source plane for each target and being separated by a distance therebetween,

each magnetic assembly configured to fix the distance between the erosion zones in each target to combine the flux from each zone so as to create an area at the substrate of substantially uniform target flux for each tubular target,

wherein a greater fraction of the target flux from each target is utilized to deposit target material on the substrate than from a single erosion zone on each target; and

a baffle disposed between the tubular targets and separating the areas of target flux from each target at the substrate such that the substrate receives first target material to form a first layer on the substrate and then receives second target material to form a second layer over the first layer on the substrate as the substrate is moved past the area of target flux from each target.

21. A method of operating a sputtering process to deposit material from a pair of targets onto a stationary substrate to achieve a given coating stoichiometry, the method comprising the steps of:

introducing a flow of sputtering gas into an evacuated chamber in which the substrate and target material reside;

introducing a flow of reactive gas into the evacuated chamber to cause the deposition of a combination of the target material and the reactive gas onto the substrate, the sputtering gas and reactive gas being pumped into the chamber at a specified speed;

connecting each target material to a voltage source that provides a voltage to cause sputtering gas ions to erode each target material;

forming an intense magnetic field over each target material to confine the sputtering gas ions over a pair of substantially parallel erosion zones on each target material, target material from the erosion zones combining to create an area of substantially uniform target material flux at the substrate,

maintaining the sputtering gas flow, the voltage and the pumping speed approximately constant; and

scanning the magnetic field synchronously over each target material to sweep the target material flux from each target across the substrate.

22. A magnetron for eroding a target and depositing target material onto a substrate, comprising:

a cylindrical tubular target having a longitudinal axis, an inside surface and outside surface and a fixed length, the inside and outside surfaces having a certain inner and outer circumference, respectively, said target being rotatable about said longitudinal axis, said tubular target including

a target material supporting assembly having;

a target support tube;

a cylindrical target backing tube for holding the tubular target material;

first and second target backing tube supports, one at each end of the cylindrical target backing tube, the first tube support for holding the target backing tube in place over and coaxial with the target support tube, a cylindrical chamber being formed by the target backing tube and the target backing tube supports; and

means for receiving rotational drive to rotate target material supporting assembly; and

a magnetic assembly, disposed within and along the length the cylindrical tubular target, configured to provide a magnetic field racetrack over the outside surface of the tubular target, the magnetic field racetrack confining a plasma gas to erode the target material from a pair of substantially parallel erosion zones extending along the length of the tubular target, said assembly being configured to fix the distance between the erosion zones to create an area of substantially uniform target material flux at the substrate, wherein a greater fraction of the target flux is utilized to deposit target material uniformly on the substrate than with a single erosion zone.

23. A magnetron as recited in claim 22, further comprising an electrode in electrical contact with the tubular target, wherein the electrode receives power from an external power source to charge the target at a potential sufficient for deposition of the target material onto the substrate.

24. A magnetron as recited in claim 22, wherein means for receiving rotational drive is a pulley.

25. A magnetron as recited in claim 22, wherein means for receiving rotational drive is a gear.

26. A magnetron as recited in claim 25, further comprising:

a secondary tube fitted within the target support tube and extending from the second tube backing support through the backing tube and through the target support tube; and

an electric commutator mounted on the secondary tube, in electrical contact with the secondary tube to provide a charge sufficient for the target material to act as a cathode during the depositing of the target material onto the substrate.

27. A magnetron as recited in claim 26, wherein the magnet assembly is mounted to the secondary tube.

28. A magnetron as recited in claim 26, further comprising a coolant tube having a first end near the second backing tube support and a second end, fitted within the secondary tube,

the coolant tube having an input orifice near the first end of the cooling tube for receiving an injected coolant, and

wherein the coolant is ejected from an output orifice of the coolant tube near second end.

29. A magnetron as recited in claim 28,

wherein the magnet assembly is mounted to the secondary tube;

and

wherein the magnet assembly is cooled by from the coolant tube.

30. A magnetron for eroding a target and depositing target material onto a substrate, comprising:

a cylindrical tubular target having a longitudinal axis, an inside surface and outside surface and a fixed length, the inside and outside surfaces having a certain inner and outer circumference, respectively, said target being rotatable about said longitudinal axis;

a magnetic assembly, disposed within and along the length the cylindrical tubular target, configured to provide a magnetic field racetrack over the outside surface of the tubular target, the magnetic field racetrack confining a plasma gas to erode the target material from a pair of substantially parallel erosion zones extending along the length of the tubular target, said assembly being configured to fix the distance between the erosion zones to create an area of substantially uniform target material flux at the substrate, wherein a greater fraction of the target flux is utilized to deposit target material uniformly on the substrate than with a single erosion zone, said magnetic assembly including

a backing plate constructed from a magnetic alloy;

a semi-circular non-magnetic housing having a curved portion fitted within a portion of the inner circumference of the tubular target, resting on and sealed to the backing plate and defining a plurality of magnet cavities between the housing and the backing plate, a plurality of cooling cavities formed between the inside surface of the tubular target and the curved portion of the housing;

a plurality of magnets disposed within the cavities for creating the magnetic field over the target material; and

a dark space shield having a tubular shape and fitted over the tubular targets, a gap of a fixed size existing between the shield and the tubular target, the shield having an opening for exposing the tubular target to the plasma gas to define the erosion zone of the tubular target subject to erosion by the plasma gas.

31. A magnetron as recited in claim 30, wherein the magnets are fabricated from a rare earth material having a very high energy density.

32. A magnetron as recited in claim 31, wherein the rare earth material is NeFeB.

33. A magnetron as recited in claim 30, wherein each magnet of the plurality of magnets includes an array of individual smaller magnets and wherein each magnet has a pole piece to smooth out the magnetic field produced from the array.

34. A magnetron as recited in claim 30, wherein the plurality of magnets comprises a center group and two outside groups that are spaced a certain distance from the center group,

each outside group and the center group having a certain polarity so as to define a pair of magnetic arches each spanning the distance between the center and outside groups over the tubular target, an apex of each of the pair of magnetic arches separated by a certain spacing, which is defined by the distances between the magnet groups.

35. A magnetron as recited in claim 30, wherein the plurality of magnets comprises two center groups and two outside groups,

each outside group adjacent to a center group and spaced a certain distance therefrom,

each outside group and its adjacent center group having a certain polarity so as to define a pair of magnetic arches each spanning the distance between each outside group and its adjacent center group over the tubular target, an apex of each of the pair of magnetic arches separated by a certain spacing which is defined by the distances between the magnet groups and the apexes of the magnetic field arches having a spacing that is greater than the spacing between the apexes when only one group of center magnets is used.

36. A magnetron as recited in claim 30, wherein the plurality of magnets comprises:

two center groups being separated by a certain distance; and

two outside groups,

each outside group adjacent to a center group and spaced a certain distance therefrom,

each outside group and its adjacent center group having a certain polarity so as to define a pair of magnetic arches each spanning the distance between each outside group and its adjacent center group over the tubular target the apexes of the magnetic field arches having a spacing that is defined by the distances between the magnet groups, the spacing being greater than the spacing between the apexes when the two groups of center magnets have no space between them.

37. A sputtering module for depositing a target material on a substrate, comprising;

a sputtering enclosure;

a vacuum system mounted on the enclosure for evacuating gases from the sputtering enclosure;

a pair of cylindrical magnetrons disposed proximate and parallel one to the other within the enclosure, each magnetron including;

a cylindrical tubular target having a longitudinal axis and an outside surface and a fixed length, rotatable about the longitudinal axis of the cylindrical target; and

a magnetic assembly disposed within and along the length of the cylindrical tubular target, the magnetic assembly configured to provide a magnetic field racetrack over an outer surface of the tubular target, the magnetic field racetrack confining a plasma gas to erode the target material from a pair of substantially parallel erosion zones along the length of the tubular target, each pair of erosion zones defining a source plane for each target and being separated by a distance therebetween, and the magnetic assembly configured to fix the distance between the erosion zones to create an area of substantially uniform target material flux at the substrate, wherein a greater fraction of the target flux is utilized to deposit target material uniformly on the substrate than with a single zone;

wherein the magnetic assemblies are oriented relative to each other such that, at the substrate, an included angle is formed between a pair of planes, normal to the source planes and passing through the axis of each target, and the target flux of each of the targets combines to create a wider area of uniform flux at the substrate than from each target separately; and

wherein each magnetron has an electrode so that an electric field can be established between the magnetrons to enable the plasma gas of a certain density to form;

rotation means for imparting to each of the tubular targets a speed of rotation with respect to the magnetic assemblies so that a substantial fraction of the outside surface is caused to pass by the magnetic assemblies in a single rotation, wherein the speed of rotation and the density of the plasma gas in the erosion zones are such as to substantially prevent accumulation of target material on regions of the target away from the sputtering zones during a rotation of the tubular target; and

an alternating current electrical power supply having a first and second pole that alternate in polarity, the first pole being connected to the electrode of one of the magnetrons and the second pole being connected to the electrode of the other of the magnetrons, and the alternating current electrical power supply being operated at a preselected constant voltage, wherein each magnetron alternately deposits target material on the substrate as the poles alternate in polarity.

38. A sputtering module as recited in claim 37,

wherein there is a linear array of magnetrons; and

wherein the enclosure includes a baffle and shielding means for linear arrays of magnetrons.

39. A sputtering module as recited in claim 37, wherein the magnetrons are mounted vertically in the sputtering enclosure.

40. A sputtering module as recited in claim 37, wherein a reactive gas having a certain flow is introduced into the sputtering enclosure and the flow of the reactive gas is maintained constant.

41. A sputtering module as recited in claim 37, wherein a reactive gas having a certain flow is introduced into the sputtering enclosure and the flow of the reactive gas is servo-controlled to maintain constant electrical current.

42. A sputtering module as recited in claim 37, wherein each of the magnetic assemblies includes a device for independently scanning the magnetic assemblies in a predetermined pattern with respect to a fixed substrate position.

43. A sputtering module as recited in claim 37, wherein the alternating current power supply having a certain frequency is operated in a frequency range of ten to several hundreds of kilohertz.

44. A sputtering module as recited in claim 37,

wherein the rotation means provides rotational speeds for the magnetrons in a range of 10 to 100 RPM, and

wherein the magnetrons contain no dynamic vacuum-to-coolant seals.

45. A sputtering module as recited in claim 37, wherein different target materials and a baffle are used to form an epitaxial target material layer over a preceding target material layer on the substrate.

46. A batch sputtering machine for depositing insulating and semiconducting films on wafer-like substrates, comprising:

one or more of the sputtering modules as recited in claim 37, disposed in a vacuum chamber and having a deposition region;

a removable rotating substrate holder disposed in the vacuum chamber, which carries substrates sequentially and repeatedly past the deposition region of the sputtering module; and

shutter means for isolating substrates from the rotatable cylindrical magnetrons during startup.

47. A batch sputtering machine as recited in claim 46, wherein the substrate holder forms dynamic seals between the sputtering modules which enable the depositing of different materials sequentially and simultaneously.

48. A batch sputtering machine as recited in claim 46, wherein the substrate holder contains internal passages and feed through means for passing, a coolant fluid through the substrate holder during coating operations.

49. An in-line sputtering machine for depositing insulating and semiconducting films on substrates, comprising;

one or more of the sputtering modules as recited in claim 37 disposed in a vacuum chamber;

linear transport means for passing substrates past the sputtering modules; and

vacuum load and unload means for passing substrates from air to vacuum for processing and back to air in a continuous flow.

50. An in-line sputtering machine as recited in claim 49, wherein the sputtering modules are mounted vertically and disposed in pairs opposite each other for coating both sides of substrates simultaneously.

51. A magnetron assembly comprising:

a tubular target having an inner and outer surface;

a target supporting assembly for supporting the tubular target, the target support assembly including;

means for receiving rotation from an external drive source;

a first and second tubular target support for holding the tubular target, the first tubular target support fastened to one opening of the tubular target and the second tubular target support fastened to the other opening;

a target support tube that connects the rotation receiving means to the first tubular target support;

a first and second set of sealing static O-rings for sealing the first and second tubular target supports, respectively, against the tubular target; and

a set of bearings disposed in an annular ring between the rotation receiving means and the target tube support tube to permit rotation therebetween;

a mounting assembly for securing the target supporting assembly for rotation, the mounting assembly including;

insulated mounting flange having a bore and fastened to a stationary support plane;

a rotary vacuum feedthrough having a bore and disposed within the bore of the mounting flange, the bore of the rotary vacuum feedthrough receiving the target support tube, the first tubular target support positioned against one opening of the feedthrough bore and the rotation receiving means positioned near the other opening of the feedthrough bore;

a set of static O-rings for sealing the feedthrough against the mounting flange;

a set of O-ring seals for sealing the feedthrough against the target support tube disposed within the feedthrough bore;

a first and second set of bearings disposed with a first and second annular rings, respectively, between the rotary vacuum feedthrough and the target support tube for rotation therebetween; and

an insulating alignment flange for receiving, within a cylindrical pocket in the flange and supporting for rotation, the second tubular target support, the insulating alignment flange having a set of bearings disposed within the annular ring between the flange pocket and the lower tubular target support;

a magnet assembly disposed within the tubular target and along its length, the magnet assembly for providing magnetic field over the tubular target defining an erosion zone of the tubular target and having a passage through which a cooling fluid flows to cool the assembly;

a stationary assembly including;

secondary support tube disposed within the target support tube and concentrically within the tubular target and along the length of the tubular target;

an electrical commutator connected to the secondary support tube and making electrical contact with the rotation receiving means;

at least two magnet assembly support clamps fastened about the secondary support tube to support the magnet assembly in proximity to the inner surface of the tubular target; and

a first and second set of bearings disposed in first and second annular gaps between the secondary support tube and the first and second target supports, respectively, to permit rotation of the first and second target supports relative to the secondary support tube; and

a cooling assembly including;

a cooling tube disposed within and along the length of the secondary support tube, the cooling tube connected to the cooling passage in the magnet assembly to convey cooling fluid through the magnet assembly and near the erosion zone of the tubular target; and

a fluid input and output port for injecting cool fluid and extracting the heated fluid from the cooling tube.

52. The magnetron assembly as recited in claim 51,

wherein seals for sealing the feedthrough against the target support tube are ferrofluidic type seals.

53. The magnetron assembly as recited in claim 51,

wherein the mounting assembly is fastened to a horizontal plane so that the tubular target is oriented vertically in space.

54. The magnetron assembly as recited in claim 51, wherein the tubular target includes a carrier tube connected to the first and second target supports and having an outer surface covered with the target material.

55. The magnetron assembly as recited in claim 51,

wherein the cooling tube has a first opening connected to one end of the passage in the magnet assembly and a second opening connected to the other end of the passage in the magnet assembly.

56. A method of operating a sputtering process to deposit target material onto a moving substrate to achieve a given coating stoichiometry, the method comprising the steps of:

introducing a flow of a sputtering gas into an evacuated chamber in which the substrate and target material reside;

introducing a flow of reactive gas into the evacuated chamber to cause the deposition of a combination of the target material and the reactive gas onto the substrate;

connecting the target material to a voltage source that provides a voltage to cause sputtering gas ions to erode the target material, said voltage source maintaining an electric current in the sputtering gas ions;

forming an intense magnetic field over the target material to confine the sputtering gas ions over a pair of substantially parallel erosion zones on the target material, the target material from the erosion zones combining to create an area of substantially uniform target material flux at the substrate;

maintaining the sputtering gas flow and the voltage approximately constant; and

controlling the reactive gas flow with a feedback loop to maintain the electric current approximately constant and to compensate for coating variations caused by the variations in pumping speed due to the moving substrate.

57. A method of operating a sputtering process as recited in claim 56,

wherein the voltage source has a power indicator that provides an indication of the power consumed by the sputtering process; and

wherein a feedback loop controls the reactive gas flow to maintain the power constant.

58. A method of operating a sputtering process as recited in claim 56,

wherein the target material has a cylindrical form of a certain length with a longitudinal axis, an axis of rotation being defined by the longitudinal axis of the cylindrical form;

and

further comprising the step of rotating the target material about the axis of rotation and relative to the magnetic field over the target to improve target material utilization.

59. A method of operating a sputtering process to alternately deposit layers from first material and second material from first and second targets, respectively, onto a stationary substrate, the method comprising the steps of:

introducing a flow of sputtering gas into an evacuated chamber in which the substrate and first and second target material reside, the sputtering gas being pumped into the chamber at a specified speed;

connecting the first and second target each to a voltage source that provides a voltage to cause sputtering gas ions to erode the target material, the voltage source alternately activating each target to alternately deposit layers from first and second material onto the substrate;

forming an intense magnetic field over the first target material to confine the sputtering gas ions over a pair of substantially parallel erosion zones on the first target material;

forming an intense magnetic field over the second target material to confine the sputtering gas ions over a pair of substantially parallel erosion zones on the second target material, the erosion zones on each target material combining to create an area of substantially uniform target material flux at the substrate;

maintaining the sputtering gas flow, the voltage and the pumping speed approximately constant; and

scanning separately each magnetic field over the target that is activated to sweep the target material flux across the substrate and alternately deposit layers from the first and second target material onto the substrate.

60. A method of operating a sputtering process as recited in claim 59, further comprising:

introducing a flow of reactive gas into the evacuated chamber, the layers from the first and second target material being a combination of the target material and the reactive gas; and

maintaining the reactive gas flow approximately constant.