WO1998037569A1

WO1998037569A1 - Magnetic circuit for magnetron sputtering

Info

Publication number: WO1998037569A1
Application number: PCT/US1998/002658
Authority: WO
Inventors: Andrew L. Nordquist
Original assignee: Novellus Systems, Inc.
Priority date: 1997-02-24
Filing date: 1998-02-13
Publication date: 1998-08-27

Abstract

A magnetic circuit and a magnetron sputtering apparatus including the magnetic circuit are disclosed. The magnetic circuit is configured for generating a high magnetic flux density and plasma discharge at a target sputtering surface located relatively far from the magnetic circuit, and relatively far from the axis of rotation of the magnetic circuit, thereby reducing target waste. Thicker targets may be used, thereby increasing target life.

Description

IN THE UNITED STATES PATENT AND TRADEMARK OFFICE

APPLICATION FOR PATENT

MAGNETIC CIRCUIT FOR MAGNETRON SPUTTERING

The present invention relates generally to magnetron sputtering devices, and particularly to an improved magnetic circuit for use in magnetron sputtering devices . More particularly , the present invention relates to an improved magnetic circuit that is con_figured to generate a controlled plasma discharge near the perimeter of a sputtering target in a magnetron sputtering device.

Magnetron sputtering devices have long been used by the semiconductor processing industry to coat substrates (e.g. / silicon wafers) with various materials (e.g. , aluminum, titanium, gold, etc. ) during the manufacture of integrated circuits . Generally, in a spu_ttering device, the material to be deposited or spu_ttered on he substrate is contained in a target. _The substrate is placed on a substrate support table in a sputtering chamber. Air in the sputtering chamber is evacuated and replaced with an inert gas such as argon, preferably at a low pressure . An electric field is es_tablished between an anode such as the walls that line the sputtering chamber and the target . The targe^t acts as an electron source, or a cathode . Ions are formed when electrons collide with the inert gas. The ions are then drawn toward the target by the electric field. The ions impact the target with sufficient energy to dislodge, or sputter, atoms of target material into the sputtering chamber. The sputtered atoms travel from the target sputtering surface to the substrate, coating the substrate with a thin film of target material. The target erodes more quickly in regions where more ions impact the target. The cloud of free electrons, inert gas atoms, inert gas ions and sputtered atoms that exists near the target sputtering surface is termed a "plasma discharge."

The location of plasma discharge is controlled by introducing a magnetic field adjacent^"to the sputtering surface of the target in the sputtering chamber. The magnetic field is generated by a rotating magnetic circuit located near the back surface of the target. The magnetic field acts to trap electrons in a desired region so that ionization is concentrated in that region. Creation of such a region adjacent to the target sputtering surface results in a corresponding region of plasma discharge near the target sputtering surface. The region of plasma discharge forms a closed loop path that corresponds to the closed loop shape of the magnetic circuit as viewed from the target. Stated differently, the plasma discharge has a parallel cross- sectional shape that corresponds to the parallel cross- sectional shape of the magnetic circuit. Generally, a parallel cross-section is a cross-section taken along a plane parallel to the target sputtering surface, and a perpendicular cross-section is a cross-section taken • along a plane perpendicular to the target sputtering surface .

During operation, the closed loop path of plasma discharge near the target sputtering surface rotates with the magnetic circuit about an axis that is perpendicular to the target sputtering surface. The rotating closed loop path of plasma discharge sweeps an area of the target surface where sputtering occurs. The swept area of the target sputtering surface is the area in which controlled target erosion occurs. The magnetron sputtering device has an absolute plasma reach that is defined as the maximum radius (as measured from the axis of rotation of the magnetic circuit) at which a controlled plasma discharge exists near the target sputtering surface. Likewise, the rotating magnetic circuit has a magnetic circuit sweep perimeter that is located at a distance from the axis of rotation of the magnetic circuit that is the distance between the axis of rotation and the point on the magnetic circuit that is farthest from that axis of rotation. The relative plasma reach is defined as the difference between the absolute plasma reach and the radius at which the magnetic circuit sweep perimeter is located. A magnetic circuit having an increased relative plasma reach establishes a controlled plasma discharge closer to the perimeter of a target.

Generally, a magnetic circuit that generates a stronger magnetic field in a direction parallel to the target sputtering surface produces a stronger electron trap that increases the intensity of plasma discharge near the target sputtering surface , thereby increasing target erosion in a region adj acent to the trap . As the distance between the magnetic circuit and the target sputtering surface increases , the strength of the electron trap decreases , thereby decreasing the intensity of the plasma discharge at the target sputtering surface and decreasing target erosion in the region adj acent to the trap . Therefore, a target having a sputtering surface that is located farther from the magnetic circuit requires a stronger magnetic field to sustain a plasma discharge comparable to that sustained at the sputtering surface of a target that is located closer to the magnetic circuit . Target sputtering surfaces located farther from a magnetic circuit provide more space between the target sputtering surface and the magnetic circuit . The additional space provides for the use of thicker targets or other items that can fit in the space such as a cooling plate. It is desirable in magnetron sputtering to use thicker targets that have longer lives thereby requiring less down-time in replacing targets during the operation of the device . It is also desirable in magnetron sputtering to provide a strong magnetic field at a more distant target sputtering surface without using additional magnetic material . It is also desirable in magnetron sputtering to control the- location of the plasma discharge on the target sputtering surface so that target material is not wasted. In particular, establishing a plasma discharge closer to the target perimeter utilizes more available target material and reduces waste . Finally, it is desirable to achieve these characteristics without having to manage a dual plasma discharge through use of a complex magnetic circuit construction such as that disclosed in U. S . Pat . No . 5, 242 , 566. A dual plasma discharge exists when a magnetic circuit contributes the same amount of magnetic flux to two parallel electron trap regions . Such a situation is unstable unless the two trap regions are connected to each other so that they form a closed loop, effectively becoming a single trap region. Managing a dual plasma discharge by connecting the trap regions together adds undesirable complexity to the magnetic circuit .

_Previously known magnetron sputtering devices use magnetic circuits having a variety of configurations to generate magnetic fields near target sputtering surfaces . Some magnetic circuits have a strong magnetic field at the target sputtering surface an_d a low relative plasma reach, providing a plasma discharge located relatively close to the axis of rotation of the magnetic circuit (and relatively far from the target perimeter) , both when operating with targets having sputtering surfaces located relatively far from the magnetic circuit and when operating with targets having sputtering surfaces located relatively near _the magnetic circuit . Other magnetic circuits have a weak magnetic field at the target sputtering surface and a high relative plasma reach, providing a plasma discharge located farther from the axis of rotation of the magnetic circuit (and closer to the perimeter of targets) having sputtering surfaces relatively near the magnetic circuit . However, there remains a need for a magnetic circuit having high relative plasma reach that sustains a plasma discharge relatively far from the axis of rotation of the magnetic circuit (and relatively near the perimeter of targets) having sputtering surfaces located relatively far from the magnetic circuit, thereby (1) increasing the available space between the magnetic circuit and the target sputtering surface,, enabling use of thicker targets or other items in the additional space and (2) providing a controlled plasma discharge closer to the perimeter of targets .

It would be desirable to provide a magnetic circuit for use in a magnetron sputtering device wherein the magnetic circuit has a high relative plasma reach and a magnetic field of sufficient strength to sustain a plasma discharge at a target sputtering surface located relatively far from the magnetic circuit, thus providing a controlled plasma discharge relatively near the perimeter of a target located relatively far from the magnetic circuit.

It would also be desirable to provide a magnetic circuit for use in a magnetron sputtering device wherein the magnetic circuit has a high relative plasma reach and a magnetic field of sufficient strength to sustain a plasma discharge at a target sputtering surface located relatively far from the magnetic circuit, thus providing a controlled plasma discharge relatively near the perimeter of a target located relatively far from the magnetic circuit without utilizing additional magnetic material to generate the required magnetic field .

It would further be desirable to provide a magnetic circuit for use in a magnetron sputtering device wherein the magnetic circuit has a high relative plasma reach and a magnetic field of sufficient strength to sustain a plasma discharge at a target sputtering surface located relatively far from the magnetic circuit , thus providing a controlled plasma discharge relatively near the perimeter of a target located relatively far from the magnetic circuit, and having a design that does not require the complex construction necessary to manage a dual plasma discharge .

summary of the Invention It is an object of the present invention to provide a magnetic circuit for use in a magnetron sputtering device wherein the magnetic circuit has a high relative plasma reach and a magnetic field of sufficient strength to sustain a plasma discharge at a target sputtering surface located relatively far from the magnetic circuit, thus providing a controlled plasma discharge relatively near the perimeter of a target located relatively far from the magnetic circuit . It is another obj ect of the present invention to provide a magnetic circuit for use in a magnetron sputtering device wherein the magnetic circuit has a high relative plasma reach and a magnetic field of

1 sufficient strength to sustain a plasma discharge at a target sputtering surface located relatively far from the magnetic circuit, thus providing a controlled plasma discharge relatively near the perimeter of a target located relatively far from the magnetic circuit without utilizing additional magnetic material to generate the required magnetic field.

It is a further object of the present invention to provide a magnetic circuit for use in a magnetron sputtering device wherein the magnetic circuit has a high relative plasma reach and a magnetic field of sufficient strength to sustain a plasma discharge at a target sputtering surface located relatively far from the magnetic circuit, thus providing a controlled plasma discharge relatively near the perimeter of a target located relatively far from the magnetic circuit, and having a design that does not require the complex construction necessary to manage a dual plasma discharge. The magnetron sputtering apparatus of the present invention includes an anode, a target and rotating magnet assembly. The target serves as a cathode which in conjunction with the anode generates an electric field. The rotating magnet assembly contains a magnetic circuit having a magnet array and a magnet array pole base . The magnet array forms a closed loop and has a top side, a bottom side opposite the top side, a gap side and an interior side opposite the gap side . The magnet array pole base forms a closed loop and has a contact surface, a top surface, a gap surface and an outer surface . The magnet array and

Z the magnet array pole base are oriented such that the contact surface of the magnet array pole base magnetically connects the magnet array pole base to the bottom side of the magnet array and such that the magnet array pole base forms a single gap between the gap side of the magnet array and the gap surface of the magnet array pole base.

FIG. 1 is a cross-sectional view of a rotating magnetron sputtering apparatus having a magnet assembly in accordance with the present invention;

FIG. 2 is an exploded perspective view of the magnet assembly shown in FIG. 1;

FIG. 3 is a plan view of the magnet assembly shown in FIG. 2;

FI_G. 4 is a fragmented cross-sectional view of the magnet assembly shown in FIG. 3 , taken along line 4-4 of FIG. 3 ;

FIG. 5 is a cross -sectional view of a previously known magnetic circuit, showing simulated magnetic flux lines near a target sputtering surface; FIG. 6 is a cross-sectional view of another previously known magnetic circuit, showing simulated magnetic flux lines near a target sputtering surface; FIG. 7 is a cross -sectional view of yet another previously known magnetic circuit, showing simulated magnetic flux lines near a target sputtering surface; FIG.. 8 is another cross-sectional view of the magnetic circuit of the present invention, showing simulated magnetic flux lines near a target sputtering surface; FIG. 9 is a graph depicting simulated magnetic field strengths and predicted relative plasma intensity along a target sputtering surface for the previously known magnetic circuit shown in FIG. 5; FIG. 10 is a graph depicting simulated magnetic field strengths and predicted relative plasma intensity along a target sputtering surface for the previously known magnetic circuit shown in FIG. 6;

FIG. 11 is a graph depicting simulated magnetic field strengths and predicted relative plasma intensity along a target sputtering surface for the previously known magnetic circuit shown in FIG. 7; and

FIG. 12 is a graph depicting simulated magnetic field strengths and predicted relative plasma intensity along a target sputtering sxirface for the magnetic circuit of the present invention shown in FIG. 8.

Referring first to FIG. 1, a cross-sectional view of a magnetron sputtering apparatus 20 in accordance with the principles of the present invention is described. Sputtering apparatus 20 includes metal housing 22, housing cover 24, and substrate support table 28 for supporting substrate 30. Substrate 30 has an upper surface 21 that is intended to be^' sputter coated with a thin film of material by sputtering apparatus 20 . Substrate 30 may be , for example , a semiconductor wafer.

Target assembly 23 may be a large diameter target assembly (e . g. , about fourteen inches or more) which facilitates sputtering a film of material having a highly uniform thickness on upper surface 21 of substrate 30 . Target assembly 23 includes target 32 which has a sputtering surface 33 and a back surface 43 . Target 32 may be a monolithic target or a composite target . Target assembly 23 also includes a cooling plate 57 bonded to target 32 . Details of cooling plate 57 may be found in copending U.S . patent Application Ser. No . of Eartsough et al . entitled INTERNALLY COOLED TARGET ASSEMBLY FOR

MAGNETRON SPUTTERING, filed concurrently herewith, which is hereby incorporated by reference in its entirety.

Sputtering takes place in sputtering chamber 26. Target sputtering surface 33 is located inside sputtering chamber 26. Substrate 30 is also within sputtering chamber 26. A vacuum system (not shown⁾ is connected to sputtering chamber 26. The vacuum system acts to remove air from sputtering chamber 26 so that air may be replaced with an inert gas such as argon at low pressure. The inert gas provides the medium for ionization. Sputtering apparatus 20 generates electric fields, using a power supply and electrical connections (not shown) , to create regions of high electron density between target 32 and substrate 30 which facilitate ionization of the inert gas. Inert gas pressures il ranging from 0 .1 millitorr to 5 millitorr are typical The gas is introduced into sputtering chamber 26 via inlet tube 40 . O-rings 42 , 44 and 51 serve to maintain the pressure differential between sputtering chamber 26 and the atmosphere .

As mentioned above, sputtering^' apparatus 20 establishes an electric field in sputtering chamber 26 that is required to sputter target 32 . Target 32 is placed at a negative potential through a connection to a power supply (not shown) . Target 32 thus acts as a cathode . The magnitude of the negative potential can be adjusted within the range from about 0 Volts to about 1500 Volts . Sputtering typically takes place in the range from about 250 Volts to about 800 Volts . Dark space ring 50 surrounding sputtering chamber 26 is placed at ground potential, acting as an anode . Dark space ring 50 is grounded through an electrical contact with housing 22. Dark space ring 50 is maintained at ground potential so that an electric field is established between dark space ring 50 and target 32. Dark space ring 50 , which is preferably made of stainless steel to withstand cleaning, is electrically connected to housing 22 via conductive springs 52. Ceramic insulator 56 is secured between target 32 and dark space ring 50 to provide electrical insulation therebetween . Substrate support table 28 also contributes to the electric field, but because substrate support table 28 is not grounded and is electrically isolated from housing 22 and target 32 , its contribution to the electric field is not as great as that of dark space ring 50. The electric field intersects target 32 at an angle that is substantially normal to target sputtering surface 33 to create a plasma discharge in which ionized gas atoms are forced into target sputtering surface 33 with sufficient energy to sputter the target atoms. Some of the sputtered target atoms land on substrate 30 and form a thin film of target material on upper surface 21 of substrate 30. Sputtering apparatus 20 also includes magnet assembly 36. Magnet assembly 36 is used to control the location of plasma discharge at target sputtering surface 33. Magnet assembly 36 is secured for rotation on magnet assembly mounting plate 66. Motor 38 rotates magnet assembly 36 through magnet assembly mounting plate 66. Magnet assembly mounting plate 66 is supported for rotation about axis 72. Plastic insulating wall 76 surrounds magnet assembly 36, electrically isolating magnet assembly 36 from housing 22, which is at ground potential.

Coolant for target assembly 23 is provided through coolant connectors 58 and 59 and coolant hoses 60 and 61. Coolant hoses 60 and 61 are connected to external hoses (not shown) which supply coolant to sputtering apparatus 20. From their connections to the external coolant hoses (not shown) , coolant hoses 60 and 61 extend around the perimeter of sputtering apparatus 20 until they terminate at coolant connectors 58 and 59, respectively. Dark space ring 50 may also be cooled by coolant flowing through a cooling channel (not shown) in dark space ring 50. A typical coolant is water.

Substrate support table 28 contains a heat transfer apparatus 86 for controlling the temperature of substrate 30 which is clamped to the substrate support table 28 by a clamp (not shown) . For some sputtering processes, gas may be introduced between substrate 30 and substrate support table 28 to aid in heat transfer. It is also known to use electrostatic clamping as an alternative to mechanical clamping. The top surface of substrate support table 28 is positionable from about 1 inch to about 4 inches below target sputtering surface 33. The distance between the top surface of substrate support table 28 and target 32 may be set by adjusting the size of dark space ring 50, and by raising or lowering substrate support table 28.

Sputtering apparatus 20 also includes port 92 which serves as an inlet/outlet for transferring substrates into and out of sputtering chamber 26 in a conventional manner. Port 92 is sealable by a conventional gate valve (not shown) . In addition, sputtering apparatus 20 contains a barrel shaped deposition shield 94 which is maintained at ground potential and serves to accumulate sputtered atoms which do not land on substrate 30. Deposition shield 94 is easily cleaned.

FIG. 2 is an exploded perspective view of magnet assembly 36 in accordance with the present invention. Referring to FIG. 2, magnet assembly 36 comprises magnetic circuit 82, including magnet array 78 and magnet array pole base 80, counterweight

\Λ 84 , counterweight mounting plate 96, cover 98 and foam spacers 100 , 102 and 104. The combination of magnet array 78 and magnet array pole base 80 forms magnetic circuit 82. _Magnetic circuit 82 has a parallel cross- sectional shape forming a closed loop that results in a desired sputter deposition distribution. Factors which determine the parallel cross-sectional shape of magnetic circuit 82 are described in U.S . Patent No. 5 , ₂₅₂, ₁₉4 , which is incorporated herein by reference. _In general , magnetic circuit 82 is placed off -axis in ma_gne_t assembly 36, the resulting imbalance in weight _bein_g counterbalanced by counterweight 84 as depicted in _FIG. ₂. Counterweight 84 is secured to coun_terweight mounting plate 96. Counterweight moun_ting plate 96 is secured to magnet array pole base ₈₀ , foam spacer 102 and cover 98 by locking screws and washers 130.

_Magnet assembly 36, through use of magnetic circuit ₈₂, generates a magnetic field having arcuate magnetic field lines that intersect target sputtering surface ₃₃ (shown in FIG. 1) . Arcuate magnetic field lines enclose a closed loop path adjacent to target sputtering surface 33 (shown in FIG. 1) . A corresponding plasma discharge forming a closed loop pa_th is established near the target sputtering surface ₃₃ (shown in FIG. 1) . It is well known that magnetic field lines enclosing a closed loop path near a target sputtering surface are required in order to sustain a con_trolled plasma discharge in a magnetron sputtering device . h Magnet assembly 36 as well as magnetic circuit 82 positioned therein, is rotated about axis 72 (shown in FIG. 1) such that a closed loop path of plasma discharge sweeps an area of target sputtering surface 33 to be sputtered. The rotating magnetic circuit 82 has a magnetic circuit sweep perimeter that is located at a distance from axis 72 (shown in FIG. 1) that is the distance between the axis 72 and the point on magnetic circuit 82 that is farthest from axis 72. The absolute plasma reach of magnetic circuit 82 is defined as the maximum radius (as measured from axis 72) at which a controlled plasma discharge exists near target sputtering surface 33 (shown in FIG. 1) . The relative plasma reach of magnetic circuit 82 is the difference between the absolute plasma reach and the radius (as measured from axis 72) at which the magnetic circuit sweep perimeter is located.

The physical reach of magnet array 78 and magnet array pole base 80 in the direction of the perimeter of target 32 (shown in FIG. 1) may be limited by the confines of insulator 76 (shown in FIG. 1) and the presence of cover 98. However, as is described below, the perpendicular cross-sectional design of magnetic circuit 82 of the present invention extends the reach of the generated magnetic field in the direction of the perimeter of target 32 (shown in FIG. 1) , thus facilitating a plasma discharge near the perimeter of target 32, especially when utilizing target sputtering surfaces located farther away from magnet assembly 36. Referring to FIG. 3 , a plan view of magnet assembly 36 as viewed from the side closest to target 32 (shown in FIG. 1⁾ is described. Magnet array 78 preferably includes a single series of magnets, each individual magnet therein having a shape that is determined by factors disclosed in U.S . Patent No . 5 , 252 , 194 . FIG. 3 shows two general types of magnets, square magnets 108 and triangular magnets 110. The north sides of magnets 108 and 110 contact cover 98 (shown more clearly in FIG. 2) , and the south sides of' magnets 108 and 110 contact a single 'magnet array pole base 80 (shown in FIG. 2) . Although the preferred mode of contact between magnet array 78 and magnet array pole base 80 is direct- physical contact, indirect magnetic contact will suffice . For purposes of this invention, the north-south orientation is irrelevant as long as all magnets 108 and 110 are oriented the same way. Therefore, the south sides of magnets 108 and 110 may contact cover 98 instead of the north sides of magnets 108 and 110.

Magnets 108 and 110 may be composed of any magnetic material known in the art . Rare earth magnets composed of neodymium, iron and boron are used in the preferred embodiment . Smaller magnets may be stacked together to form individual magnets 108 and 110. In the embodiment depicted in FIGS . 2 and 3 , magnets 108 and 110 all have about the same strength, 35 million Gauss -Oersteds (MGO) .

FIG. 4 is a fragmented cross-sectional view of the magnet assembly of FIG. 3 taken along line 4-4. Referring to FIG. 4 , magnet array 78 is shown contacting magnet array pole base 80 . Magnet array 78 has a top side 112 which contacts cover 98 and faces back surface 43 of target 32 (shown in FIG. 1) , a bottom side 113 which contacts magnet array pole base 80 , a gap side 114 , and an interior side 116 that is opposite the gap side 114. Magnet array pole base 80, which is made of iron, has a contact surface 120 , a top surface 124 , a bottom surface 125 , an outer surface ₁26 , an interior surface 127 and a gap surface ₁28 . Magnet array 78 is placed in magnetic contact with magnet array pole base 80 such that bottom side ₁₁₃ of magnet array 78 magnetically contacts contact surface 120 of magnet array pole base 80. Magnet array 78 is preferably in direct physical contact with magnet array pole base 80 . Top surface ₁2₄ contacts cover 98 and faces back surface 43 of target ₃₂ (shown in FIG. 1) . Outer surface 126 is perpendicular to target sputtering surface 33 (shown in FIG. ₁₎ and faces the target perimeter. Gap surface ₁₂₈ has a side portion 131 that faces the gap side 114 of magnet array 78 , a rounded portion 133 , a bottom portion 135 , and a flush portion 137 that is flush with the gap side 114 of magnet array 78.

Pedestal 139 is defined by flush portion 137 of gap surface 128, contact surface 120 and interior surface 127. Magnet array 78 is in magnetic contact, and preferably is in direct physical contact, with pedestal 139 of magnet array pole base 80. Magnet array pole base extension 141 is bounded by top surface 124 , outer surface 126, bottom surface 125, side portion ₁3₁ of gap surface 128 , rounded portion 133 of

IS gap surface 128 and bottom portion 135 of gap surface 128. Top surface 124 of magnet array pole base 80 is also the top side of magnet array pole base extension 141. In the embodiment depicted, top surface 124 is coplanar with top side 112 of magnet array 78-. In the preferred embodiment, top surface 124 does not directly contact a magnet array. Magnetic circuit gap 129 is formed between gap surface 128 and gap side 114. The magnetic circuit gap width of magnetic circuit 82 is the distance between the side portion 131 of gap surface 128 and gap side 114 of magnet array 78.

Magnetic circuit 82 has a parallel cross- sectional shape that is a closed loop. Likewise, magnet array 78, magnet array pole base 80, all the components of the magnet array pole base 80 and the magnetic circuit gap 129 have parallel cross-sectional shapes that are closed loops. In addition, magnetic circuit 82 as well as all the components therein maintain substantially the same parallel cross- sectional configuration throughout the closed loop.

Referring again to FIG. 4, foam spacer 100 is shown abutting magnet array 78 on interior side 116 of magnet array 78. Foam spacer 102 is shown filling magnetic circuit gap 129. Foam spacers 100 and 102 act to prevent lateral movement of magnet array 78 on magnet array pole base 80. Foam spacer 104 contacts outer surface 126 of magnet array pole base 80 as well as the outer edge of cover 98. Cover 98 is bonded to magnet array 78, foam spacers 100, 102 and 104, and to magnet array pole base 80.

Jl Continuing with FIG. 4, the total height of magnet array pole base 80, as measured from bottom surface 125 to top surface 124, is 34.5 mm. The total width of magnet array pole base 80, as measured from outer surface 126 to interior, surface 127, is 43 mm.

The width of top surface 124 of magnet array pole base

80, as measured from outer surface 126 to side position

131 of gap surface 128, is 5 mm. The radius of curvature of rounded portion 133 of gap surface 128 is 8 mm. The width of magnet array 78, as measured from gap side 114 to interior side 116, is 19 mm. The height of magnet array 78, as measured from bottom side

113 to top side 112 is 16.2 mm. Cover 98 is 0.5 mm thick. The width of magnetic circuit gap.129 at top surface 124 and top side 112, as measured from side portion 131 of gap surface 128 to gap side 114, is

19 mm. Before sputtering, target 32 (shown in FIG. 1) is 18 mm thick, measured from back surface 43 to target sputtering surface 33 (shown in FIG. 1) , and target sputtering surface 33 is 25.8 mm away from top surface

124 of magnet array pole base 80. The ratio of the distance between target sputtering surface 33 and top surface 124 (or top side 112) to the width of magnetic circuit gap 129 is 25.8 / 19.0 = 1.35. Top surface 124 of magnet array pole base 80 and top side 112 of magnet array 78 together are referred to as the top side of magnetic circuit 82.

Each of FIGS. 5-7 is a prediction of the locations of relevant magnetic flux lines resulting from a simulation of a previously known magnetic circuit acting near a target sputtering surface. FIG. fro 8 is a prediction of the location of relevant magnetic flux lines resulting from a simulation of a magnetic circuit having a perpendicular cross-section in accordance with the present invention . More particularly, each of FIGS . 5-8 show the perpendicular cross -section of a magnetic circuit taken along a plane through the portion of the magnetic circuit at which the outer surface of the magnetic circuit is located farthest from the axis of rotation of the magnetic circuit . As discussed in detail below, each of FIGS . 5 -8 show magnetic flux lines resulting from a simulation of a magnetic circuit in which the distance between the target sputtering surface and the top side of the magnetic circuit is 1.6 times the magnetic circuit gap width. In addition, the magnetic circuits represented in FIGS . 5-8 also have straight -shaped parallel cross-sections which extend in the direction perpendicular to the plane of the perpendicular cross- sections depicted in FIGS . 5-8 . FIGS . 9-12 are graphs showing simulated magnetic field strengths and predicted relative plasma discharge strengths of magnetic circuits having the perpendicular cross-sections depicted in FIGS . 5-8 , respectively, and having straight-shaped parallel cross -sections . All magnetic field strengths are measured in Gauss , and all levels of plasma intensity are relative .

TABLES 1-3 below, summarize information obtained from simulations of magnetic circuits having the perpendicular cross -sectional shapes depicted in

FIGS . 5 -8 . TABLE 1 summarizes the relevant information contained in FIGS . 9-12. TABLE 2 relates to simulations of magnetic circuits having circular-shape_d parallel cross -sections . TABLE 3 relates to simulations of magnetic circuits having parallel cross- sections like the magnetic circuits referenced in TABL_E 1, in addition to the magnetic circuits being located closer to the target sputtering surfaces .

FIG. 5 is a cross -sectional view of a previously known magnetic circuit 500 , showing simulated magnetic flux lines 522 indicative of the magnetic field generated by magnetic circuit 500 near target 512. Magnet array pole pieces 502 and 504 contact magnet array 506, all three components forming magnetic circuit 500. Magnetic circuit 500 is located near target 510 , target 510 having a target sputtering surface 512 and a back surface 514. The top side 530 of magnetic circuit 500 is 'the surface closest to target 5₁0. Point 516 is located on the outer surface 518 of magnet array pole piece 504, outer surface 518 also being the outer surface of magnetic circuit 500. Point 516 is the origin of an x-y-z coordinate system that is oriented as depicted by axes 515, and is the point on the magnetic circuit 500 that is located farthest from the axis of rotation of magnetic circuit 500. The z-axis (not shown) is oriented perpendicular to the x-y plane . The simulated magnetic circuit of FIG. 5 extends infinitely in the z-direction. The perimeter of the target is in the positive x-direction. The axis of rota_tion of magnetic circuit 500 is in the negative x-direction. Lines 522 are magnetic flux lines that pass through target sputtering surface 512. Point 524 is located on the inside of magnet array pole piece 502, and point 526 is located on the inside of magnet array pole piece 504. The distance between point 524 and point 526 represents the width of the magnetic circuit gap of magnetic circuit 500.

FIG. 6 is a cross-sectional view of another previously known magnetic circuit 600 showing simulated magnetic flux lines 622 indicative of the magnetic field generated by magnetic circuit 600 near target 612. Magnet array pole pieces 602 and 604 contact magnet array 606, all three components forming magnetic circuit 600. Magnetic circuit 600 is located near target 610 that has a target sputtering surface 612 and a back surface 614. The top side 630 of magnetic circuit 600 is the set of surfaces on magnetic circuit 600 that is closest to target 610. Point 616 is located on the outer surface 618 of magnet array pole piece 604, outer surface 618 also being the outer surface of magnetic circuit 600. Point 616 is the origin of an x-y-z coordinate system oriented as depicted by axes 615, and is the point on the magnetic circuit 600 that is located farthest from the axis of rotation of magnetic circuit 600. The z-axis (not shown₎ is oriented perpendicular to the x-y plane. The perimeter of the target is in the positive x-direction. The axis of rotation of the magnetic circuit is in the negative x-direction. Lines 622 are a magnetic flux lines that pass through target sputtering surface 612. Point 624 is located on the gap side of magnet array pole piece 602, and point 626 is located on the gap side of magnet array pole piece 604. The distance between point 624 and point 626 represents the magnetic circuit gap width of magnetic circuit 600.

FIG. 7 is a cross-sectional view of another previously known magnetic circuit 700 showing simulated magnetic flux lines 722 indicative of the magnetic field generated by magnetic circuit 700 near target 712. Magnet array 704 has a top side 701, a bottom side 703 and at least two gap sides 705. Magnet array pole piece 702 contacts bottom side 703 of magnet array 704, magnet array 704 and magnet array pole piece 702 forming magnetic circuit 700. Magnet array pole piece 702 has an inner surface 708 and an outer surface 709, inner surface 708 forming two gaps on either side of magnet array 704. The portion of outer surface 709 that is nearest to the perimeter of target 710 is also referred to as the outer surface of magnetic circuit 700. The perimeter of target 710 is in the positive x- direction. The axis of rotation of magnetic circuit 700 is in the negative x-direction. Magnetic circuit 700 is located near a target 710 that has a target sputtering surface 712 and a back surface 714. The top side 730 of magnetic circuit 700 is the set of surfaces on magnetic circuit 700 that is closest to target 710. Magnet array pole piece 702 has a point 716 on outer surface 709 that is the origin of an x-y-z coordinate system oriented as depicted by coordinate axes 718. The z-axis (not shown) passes through point 716 and is oriented perpendicular to the x-y plane. Point 716 is the point on magnetic circuit 700 located farthest from the axis of rotation of magnetic circuit 700. Lines 722 are magnetic flux lines that pass through target sputtering surface 712. Point 724 is located on the gap side 705 that is nearest the target perimeter, and point 726 is located on inner surface 708 of magnet array pole piece 702. The distance between point 724 and point 726 represents the magnetic circuit gap width of magnetic circuit 700.

FIG. 8 is a cross-sectional view of magnetic circuit 800 of the present invention, showing simulated magnetic flux lines 822 indicative of the magnetic field generated by magnetic circuit 800 near target 812. Magnet array 804 has a top side 801, a bottom side 803, a gap side 805 and an interior side 807. Magnet array pole base 802 is attached to bottom side 803 of magnet array 804, magnet array 804 and magnet array pole base 802 forming magnetic circuit 800.

Magnet array pole base 802 has a gap surface 808 and an outer surface 809. Outer surface 809 is also the outer surface of magnetic .circuit 800. Magnetic circuit 800 is located near target 810 that has a target sputtering surface 812 and a back surface 814. The top side 830 of magnetic circuit 800 is the set of surfaces on magnetic circuit 800 that is closest to target 810. Magnet array pole base 802 has a point 816 on outer surface 809 that is the origin of an x-y-z coordinate system oriented as depicted by coordinate axes 818.

The z-axis (not shown) passes through point 816 and is oriented perpendicular to the x-y plane. Point 816 is the point on magnetic circuit 800 that is located farthest from the axis of rotation of magnetic circuit 800. The perimeter of the target is in the positive x- direction. The axis of rotation of magnetic circuit 800 is in the negative x-direction. Lines 822 are magnetic flux lines that pass through target sputtering surface 812. Point 824 is located on gap side 805 of magnet array 804, and point 826 is located on gap surface 808 . The distance between point 824 and point 826 represents the magnetic circuit gap width of magnetic circuit 800. As will be described in greater detail below, magnetic circuit 800 generates a magnetic flux density that is capable of sustaining a plasma discharge farther from the axis of rotation of the magnetic circuit and closer to the target perimeter than do the previously known magnetic circuits depicted in FIGS . 5-7.

FIG. 9 is a graph that provides information that is summarized in TABLE 1 below, and that is used to determine the "Plasma Reach" and the relative strengths and locations of the simulated magnetic field and peak plasma discharge associated with magnetic circuit 500 of FIG. 5. Line 902 represents the simulated magnetic field strength in the positive x- direction, "Bx* , along target sputtering surface 512 (F_IG. ₅) , and at the location in the x-direction as indicated by axes 515 (FIG. 5) with origin at point 516 (FIG. 5) . Line 904 represents the simulated magnetic field strength in the positive y-direction, By^Λ , along target sputtering surface 512 (FIG. 5) , and at the location in the x-direction as indicated by axes 515 (FIG. 5) . Line 906 represents the vectored sum of lines ₉₀₂ and 904. Line 908 represents the' predicted intensity of the plasma discharge associated with magnetic circuit 500 of FIG. 5. FIG. 10 is a graph that provides information that is summarized in TABLE 1 below, and that is used to determine "Plasma Reach" and the relative strengths and locations of the simulated magnetic field and peak plasma discharge associated with magnetic circuit 600 at FIG. 6. Line 1002 represents the simulated magnetic field strength in the positive x-direction, Bx", along target sputtering surface 612 (FIG. 7) and at the location in the x-direction as indicated by axes 615 (FIG. 6) with origin at point 616 (FIG. 6) . Line 1004 represents the simulated magnetic field strength in the positive y-direction, "By", along target sputtering surface 612 (FIG. 6) and at the location in the x-direction as indicated by axes 615 (FIG. 6) . Line 1006 represents ^' the vectored sum of lines 1002 and

1004. Line 1008 represents the predicted intensity of the plasma discharge associated with magnetic circuit

600 of FIG. 6.

FIG, 11 is a graph that provides information that is summarized in TABLE 1 below, and that is used to _de_termine "Plasma Reach" and the relative strengths an_d locations of the simulated magnetic field and peak plasma _discharge associated with magnetic circuit 700 at FI_G. ₇. Line 1102 represents the simulated magnetic fiel_d strength in the positive x-direction, "Bx" , along target sputtering surface 712 (FIG. 7) and at the location in the x-direction as indicated by axes 718 (FI_G. ₇) with origin at point 716 (FIG. 7) . Line 1104 represents the simulated magnetic field strength in the positive y-direction, By" , along target sputtering surface ₇12 (FIG. 7) and at the location in the x-direction as indicated by axes 718 (FIG . 7) . Line 1106 represents the vectored sum of lines 1102 and 1104 . Line 1108 represents the simulated intensity of the plasma discharge associated with magnetic circuit 700 of FIG. 7.

FIG. 12 is a graph that provides information that is summarized in TABLE 1 below, and that is used to determine "Plasma Reach" and the relative strengths and locations of the simulated magnetic field and peak plasma discharge associated with the magnetic circuit of the present invention (as depicted in FIG. 8) . Line 1202 represents the simulated magnetic field strength in the positive x-direction, "Bx", along target sputtering surface 812 (FIG. 8) and at the location in the x-direction as indicated by axes 818 (FIG. 8⁾ with origin at point 816 (FIG. 8) . Line 1204 represents the simulated magnetic field strength in the positive y- direction, "By", along target sputtering surface 812 (FIG. 8) and at the location in the x-direction as indicated by axes 818 (FIG. 8) . Line 1306 represents the vectored sum of lines 1202 and 1204. Line 1208 represents the predicted intensity of the plasma discharge associated with magnetic circuit 800 of

FIG 8. For magnetron sputtering devices, it is generally known that a controlled plasma discharge will only exist in regions where the magnitude of the magnetic field adjacent to the target sputtering surface and in the direction perpendicular to the target sputtering surface (the y-direction of FIGS. 5- 8₎ is approximately less than or equal to the magnitude of the magnetic field in the direction parallel to the target sputtering surface (the x-direction of FIGS. 5- 8) . In other words, a controlled plasma discharge can only be sustained when the magnitude of By is approximately less than or equal to the magnitude of Bx. It is also known that a controlled plasma discharge will not be sustained in regions where the strength of the magnetic field in the direction parallel to the target sputtering surface (the x- direction of FIGS. 5-8) is less than approximately 200 Gauss. Therefore, the relative plasma reach, or the reach of the region of controlled plasma discharge at the target sputtering surface beyond the magnetic circuit sweep perimeter is approximately defined by the minimum distance of (1) the distance between the magnetic circuit sweep perimeter and the region at the target sputtering surface that is farthest from the magnetic circuit's axis of rotation and that is located where the magnitude of By is approximately equal to the magnitude of Bx and (2) the distance between the magnetic circuit sweep perimeter and the region at the target sputtering surface that is farthest from the magnetic circuit's axis of rotation and that is located where the magnetic field strength in the direction parallel to the target sputtering surface (the x- direction of FIGS. 5-8) is approximately 200 Gauss.

TABLE 1 summarizes relevant information depicted in FIGS. 9-12 and shows the relative strengths and locations of the magnetic fields, and the relative locations of the peak plasma discharges and the relative plasma reach associated with magnetic circuits having the perpendicular cross-sections depicted in FIGS. 5-8 when (1) the target sputtering surface is located at a distance from the top side of the magnetic circuit that is 1.6 times the magnetic circuit gap width, and (2) the magnetic circuit is assumed to extend infinitely in the z-direction (as shown in FIGS. 5-8) without curving. Note that the magnetic circuit of FIG. 7 has two gaps, and in that instance the target sputtering surface is located at a distance from the top side of the magnetic circuit of FIG. 7 that is 1.6 times the width of one of the gaps.

TABLE 2 is a summary similar to that of TABLE 1, showing information obtained through simulations of magnetic circuits in which each magnetic circuit has a circular-shaped parallel cross-section and a perpendicular cross-section as depicted in FIGS. 5-8 and as discussed above in reference to FIGS. 5-8. The top sides of the magnetic circuits of the simulations summarized in TABLE 3 were located a distance away from the target sputtering surface that is 1.6 times the magnetic circuit gap width.

TABLE 3 is a summary similar to that of TABLE 1, showing information obtained through simulations of magnetic circuits in which each magnetic circuit has a straight-shaped parallel cross-section like the magnetic circuits discussed in reference to TABLE 1, and wherein each magnetic circuit has a perpendicular cross-section as depicted in FIGS. 5-8 and as discussed above in reference to FIGS. 5-8. The top sides of the magnetic circuits of the simulations summarized in TABLE 3 were located a distance away from the target sputtering surface that is equal to the magnetic circuit gap widths.

For the simulations represented in TABLES l- 3 , distances represent distances in the x-direction of FIGS. 5-8 and are measured at the target sputtering surfaces with the origin located at the point of the magnet circuit that is farthest from the axis of rotation of the magnetic circuit. Magnetic field strength is measured in Gauss and is determined at the target sputtering surface. Each individual magnet of the simulated magnetic circuits has a strength of 35 MGO and has a length in the x-direction of FIGS. 5-8 of 1 inch, and width in the y-direction of FIGS. 5-8 of 1 inch.

TABLE 3

Referring to TABLES 1-3 , the columns labeled "Bx = By" refer to the distance between the magnetic circuit sweep perimeter and the region at the target sputtering surface that is farthest from the magnetic circuit' s axis of rotation and that is located where the magnitude of Bx is approximately equal to the magnitude of By. The columns labeled "Bx = 200 Gauss" refer to the distance between the magnetic circuit sweep perimeter and the region at the target sputtering surface that is farthest from the magnetic circuit' s axis of rotation and that is located where the magnetic flux in the direction parallel to the target sputtering surface (the x-direction of FIGS . 5-8) is approximately 200 Gauss . The columns labeled "Plasma Reach" refer to the relative plasma reach of the magnetic circuits. The relative plasma reach is the distance beyond the magnetic circuit sweep perimeter (in the positive x- direction of FIGS . 5-8 , and away from the axis of rotation of the magnetic circuit) at which a controlled plasma discharge is sustained. The columns labeled "Peak Plasma" refer to the distance in the x-direction of FIGS . 5-8 at which the predicted highest intensity plasma discharge exists . The columns labeled "Max Bx" refer to the most positive distance in the x-direction of _FI_GS . 5-8 at which the strength of the magnetic field in a direction parallel to the target sputtering surface and located at the target sputtering surface is a maximum. Finally, the columns labeled "Max Bx

3J (Gauss) " refer to the strength of the magnetic field that occurs at the "Max Bx" distance and that is in a direction parallel to the target sputtering surface and is located at the target sputtering surface. TABLES 1-3 clearly depict some of the a_dvantages of the magnetic circuit of the present invention. Referring to TABLES 1 and 2, the simulated relative plasma reach (0.61 inches in TABLE 1, and 0.57 inches in TABLE 2) of the magnetic circuit having the perpen_dicular cross-section of the present invention is greater than the simulated relative plasma reach of the ma_gne_tic circuits having the perpendicular cross - sections of FIGS . 5-7. The superior relative plasma reac_h of the magnetic circuit of the present invention ena_bles a controlled plasma discharge at a distance farther from the axis of rotation of the magnetic circuit (and magnet assembly) and closer to the perimeter of a target having a sputtering surface relatively far from the magnetic circuit. Sputtering closer to the perimeter of targets reduces target material waste. In addition, sputtering closer to target perimeters may provide for more uniform _deposition of sputtered material on the substrate.

In general, as long as the magnetic field of the magnetic circuit of the present invention has sufficient strength at the target sputtering surface to sustain a controlled plasma discharge, and as long as the distance between the target sputtering surface and the magne_tic circuit is greater than approximately 1.3⁰ times the magnetic circuit gap width, the magnetic circui_t of the present invention has a greater relative plasma reach than the magnetic circuits of FIGS . ₅-₇. In addition, the top side of the magnet array and the top surface of the magnet array pole base need not be coplanar in order to achieve the advantages described. In fact, as long as the magnetic circuit has sufficient strength to sustain a controlled plasma discharge, a further increase in relative plasma reach may be achieved by recessing the magnet array closer to the bottom surface of the magnet array pole base. Recessing the top surface of the magnet array pole base relative to the top side of the magnet array may increase the strength of the maximum magnetic field at the target sputtering surface.

Referring to- TABLES 1, 2 and 3 , the simulated maximum strength of the magnetic field generated in the x-_direction ("Max Bx") by the magnetic circuit having the perpendicular cross -section of the present invention (FIG. 8) is greater than the simulated maximum strengths of the magnetic fields generated in the x-direction ("Max Bx" ) by the magnetic circuits of _FIGS . ₆ and 7. Greater maximum field strength in the x-direction enables a controlled plasma discharge at increased distances between the target sputtering surface and the magnetic circuit. Enabling increased distances between the target sputtering surface and the magne_tic circuit permits use of other components in the increased space . For example, a thicker target may be used, or a target having a cooling plate may be used. Thicker targets are desirable because they provide for longer magnetron operating times before the system must _be s_hu_t-down for a target change . Finally, as can be seen in TABLES 1, 2 and 3 the displacement of the peak plasma discharge as well as the displacement of the location of the maximum magnetic field ("Max Bx") by the magnetic circuit of the present invention results in a strong plasma discharge farther from the axis of rotation of the magnetic circuit and closer to the perimeter of the target. In addition to the advantages discussed above, the magnetic circuit of the present invention has the benefit of a less complex construction than that of the magnetic circuit of FIG. 7. The magnetic circuit of FIG. 7 requires complex magnetic circuit variation at the ends of the dual gap region in order to link the gaps together. The magnetic circuit of the present invention maintains substantially the same perpendicular cross-section throughout the entire closed loop parallel cross-sectional shape of magnetic circuit, whereas the magnetic circuit of FIG. 7 does not maintain the same perpendicular cross-section throughout the entire magnetic circuit.

The magnetic circuit and magnet assembly disclosed is not limited to use in a magnetron sputtering apparatus with a planar target. The magnetic circuit of the present invention may be used with nonplanar targets, the shape of the magnetic circuit conforming to the nonplanar target in a manner that permits rotation about a central axis. The magnet assembly can also be used in etching apparatus devices that are well known in the art. Thus an improved magnetic circuit configured to σenerate a controlled plasma discharge near the perimeter of a sputtering target in a magnetron sputtering device is provided. One skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments, which are presented for illustration and not limitation, and the present invention is limited only by the claims which follow.

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Claims

We claim:

1. A magnetron sputtering apparatus comprising : an anode; a target having a sputtering surface and a back surface, said target serving as a cathode which in combination with said anode generates an electric field between said target and said anode; and a rotating magnet assembly mounted for rotation and positioned behind said back surface for generating a magnetic field adjacent to said sputtering surface, said magnet assembly having a magnetic circuit, said magnetic circuit having a magnet array and a magnet array pole base, said magnet array forming a closed loop and having a top side, a bottom side opposite said top side, a gap side and an interior side opposite said gap side, said magnet array pole base forming a closed loop and having a magnet contact surface, a top surface, a gap surface and an outer surface, said magnet contact surface magnetically connecting said magnet array pole base to said bottom side of said magnet array, said magnet array pole base forming a single gap between said gap side of said magnet array and said gap surface of said magnet array pole base.

2. A method of making a magnetron sputtering apparatus comprising the steps of: providing an anode; providing a target having a sputtering surface and a back surface, said target serving as a cathode which in combination with said anode generates an electric field between said target and said anode; and providing a rotating magnet assembly moun_te_d for rotation and positioned behind said back sur_face for generating a magnetic field adjacent to sai_d sputtering surface, said magnet assembly having a ma_gne_tic circuit, said magnetic circuit having a magnet array an_d a magnet array pole base, said magnet array _forming a closed loop and having a top side, a bottom si_de opposite said top side, a gap side and an interior si_de opposite said gap side, said magnet array pole _base _forming a closed loop and having a magnet contact surface, a top surface, a gap surface and an outer surface, said magnet contact surface magnetically connec_ting said magnet array pole base to said bottom si_de of said magnet array, said magnet array pole base forming a single gap between said gap side of said magnet array and said gap surface of said magnet array pole base.

3. A magnetic circuit for use in a magnetron sputtering apparatus comprising: a magnet array forming a closed loop and having a top side, a bottom side opposite said top side, a gap side and an interior side opposite said gap side; and a magnet array pole base forming a closed loop and having a magnet contact surface, a top side, a gap surface and an outer surface, said bottom side of said magnet array magnetically connected to said magnet array pole base at said contact surface, said magnet array pole base forming a single gap between said gap side of said magnet array and said gap surface of said magnet array pole base.

Ho

4 . A method of making a magnetic circuit for use in a magnetron sputtering apparatus comprising the steps of : providing a magnet array forming a closed loop and having a top side, a bottom side opposite said top side, a gap side and an interior side opposite said gap side; and providing a magnet array pole base forming a closed loop and having a magnet contact surface, a top side, a gap surface and an outer surface, said bottom side of said magnet array magnetically connected to said magnet array pole base at said contact surface, said magnet array pole base forming a single gap between said gap side of said magnet array and said gap surface of said magnet array pole base.

τι

5. A magnetic circuit for use in a magnetron sputtering apparatus comprising: a magnet array pole base having an outer surface, a top surface and a pedestal, said outer surface forming a closed loop, said top surface forming a closed loop interior to said outer surface and said pedestal forming a closed loop interior to said top surface; and a magnet array having a bottom side, a top side opposite said bottom side, said bottom side contacting said pedestal, said top side of said magnet array being substantially coplanar with said top surface of said magnet array.

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6. A method of making a magnetic circui_t for use in a magnetron sputtering apparatus comprising the steps of : providing a magnet array pole base having an outer surface, a top surface and a pedestal, said outer surface forming a closed loop, said top surface forming a closed loop interior to said outer surface and said pedestal forming a closed loop interior to said top surface; and providing a magnet array having a bottom side, a top side opposite said bottom side, said bottom side contacting said pedestal, said top side of said magnet array being substantially coplanar with said top surface of said magnet, array.

13

7. A magnetron sputtering apparatus comprising : an anode; a target having a sputtering surface and a back surface, said target serving as a cathode which in combination with said anode generates an electric field between said target and said anode; and a rotating magnet assembly mounted for rotation and positioned behind said back surface for generating a magnetic field adjacent to said sputtering surface, said magnet assembly having a magnetic circuit, said magnetic circuit having a magnet array pole base and a magnet array, said magnet array pole base having an outer surface, a top surface and a pedestal, said outer surface forming a closed loop, said top surface forming a closed loop interior to said outer surface and said pedestal forming a closed loop interior to said top surface, said magnet array having a bottom side, a top side opposite said bottom side, said bottom side contacting said pedestal, said top side of said magnet array being substantially coplanar with said top surface of said magnet array.

HH

8. A method of making a magnetron sputtering apparatus comprising the steps of: providing an anode; providing a target having a sputtering surface and a back surface, said target serving as a cathode which in combination with said anode generates an electric field between said target and said anode; and providing a rotating magnet assembly mounte_d for rotation and positioned behind said back surface for generating a magnetic field adjacent to sai_d spu_ttering surface, said magnet assembly having a magnetic circuit, said magnetic circuit having a magnet array po_le base and a magnet array, said magnet array pole _base having an outer surface, a top surface and a pe_des_ta_l, said outer surface forming a closed loop, sai_d top surface forming a closed loop interior to said outer surface and said pedestal forming a closed loop interior _to said top surface, said magnet array having a _bottom side, a top side opposite said bottom side, sai_{d b}o_ttom side contacting said pedestal, said top si_de of said magnet array being substantially coplanar with said top surface of said magnet array.

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