le

ac

, M

hnolo

ne 31

the p

l dep

ncy o

modern high-current power supplies, particularly when we

field. Third, a coupling fixture provides a vacuum seal

higher power operation based on the use of non-soluble

interruption for vent or maintenance. Rotating and static

seals and surfaces must provide reliable vacuum interfaces

6-month to 1-year

Thin Solid Films 502 (200move from DC or pulsed DC to mid-frequency AC supplies.

First, the end block support structures provide the

mechanical and vacuum connections for target rotation,

cooling water and power feed. The enhanced end block

presented here has been designed from first principles to

sustain greater than 300 A DC or AC current, at up to 1100

V DC or 2500 V AC plasma ignition strike voltages.

Second, the target tube provides the deposition material,

including features to compensate for differing erosion rates

at the center and turn-around sections of the magnetic

material. Provisions for controlling the magnet to target

surface distance allow optimization of the local magnetic

field strength at the target surface. Thin film uniformity can

be tuned through this method.

Modern cylindrical magnetrons are expected to operate

reliably at power densities up to 20 W/mm of racetrack

circumference, in either DC, pulsed DC or MF modes.

Taking advantage of the target utilization offered by the

cylindrical magnetrons, traditional production campaigns

are extended from typical 2 week up to 3 or 4 weeks withouttesting and production systems are presented. Critical performance features including current handling capability, seal lifetime, and process

uniformity are discussed.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Sputtering; Deposition process; Optical coatings

1. Introduction

A rotating cylindrical magnetron can be broken down

into four key components. Each component requires

optimization for maximum performance when utilizing

between the target tube and the end blocks. In this design,

the end blocks connect to the target tube with an improved,

non-proprietary fixation that provides more reliable O-ring

compression and eliminates the risk of target-to-spindle

leaks. Finally, the water-cooled magnetic array allowsfixtures and process control results in stable, high deposition ratessputter deposition is now based upon reactive sputtering of rotatable cylindrical magnetrons using AC power supplies. A new generation of

rotatable sputter magnetrons is based upon design from first principles for optimized use with high current mid-frequency AC sputtering

power supplies. Improved target designs result in more robust vacuum sealing and greater than 90% material utilization. Improved magnet

for reactive sputtering with 3% uniformity range. Results from lifetimeAdvanced generation of rotatab

performance re

S.J. Nadel *, P. Greene, J. Rietzel

VACUUM COATING Tec

Available onli

Abstract

Magnetron performance is ultimately the determining factor in

density, target utilization and efficiency, coating uniformity, materia

around and ease of maintenance all contribute to the overall efficie0040-6090/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.tsf.2005.07.227

* Corresponding author.

E-mail address: steve.nadel@vact.com (S.J. Nadel).magnetron technology for high

tive sputtering

. Perata, L. Malaszewski, R. Hill

gies, Fairfield, CA, USA

August 2005

roductivity of glass sputter coating technology. Maximum power

osition rates, vacuum reliability, arc and debris control, quick turn-

f any magnetron sputter source. The state of the art in magnetron

6) 15 21

www.elsevier.com/locate/tsfunder such conditions for at least areplacement cycle. Increasing demands for productivity and

quality improvement require thin film uniformity control

within a 4% range of average film thickness at the highest

deposition speeds possible with mass flow or advanced

closed loop control of reactive processes. Magnetic field and

target tube designs must cooperate to achieve materials

utilization of 70% or greater while minimizing or eliminat-

ing non-sputtered surfaces to reduce arcing and debris

generation.

This paper reports the results of an enhanced cylindrical

magnetron design incorporating these features and capa-

bilities [1].

2. End block structure

The schematic in Fig. 1 shows the water and power input

side of the end block support mechanism. A primary design

objective was to minimize inductive heating generated by

300 A current for the typical 2580 kHz operating

life at the minimum rating of 300 A.

However, the successes and improvements in AC

sputtering of cylindrical magnetrons have encouraged the

introduction of an enhanced generation of MF power

supplies, capable of delivering up to 180 kW AC power.

Previous end block designs have been current limited to

200300 A, preventing users from taking full advantage of

the available power capabilities. The current end block

design has accumulated over 500 h operation at 400 A with

S.J. Nadel et al. / Thin Solid Films 502 (2006) 152116frequencies of modern AC magnetron sputtering power

supplies. Lip seals, bearings, energizers and retaining rings

were all evaluated to eliminate inductive current loops.

Further heat management is provided by water-cooling the

spindle and using a multi-layer, electrically insulated heat

shield to protect the end block.

The companion drive side end block is shown Fig. 2.

Differentially pumped redundant seals [2] are used in both

end blocks to reduce the pressure on the vacuum-side seals to

near zero. Fig. 3 shows the seal cavity, differentially pumped

to 60 Torr. Due to the force of atmospheric pressure on the air-

side seal, this seal should fail first, causing a pressure rise in

the cavity. The pressure monitor on the differentially pumped

line will then offer an alarm signal, prior to a vacuum-side

leak that can affect deposition processes. The pump and alarm

manifold shown in Fig. 4 provides the user with notification

and assistance in troubleshooting leaks at the next convenient

maintenance cycle.Fig. 1. Water/power end block.Testing of this end block design was carried out on the G-

85 coating system and a test tank. Both systems used a C-

MAGR 6000 modular cathode designed for 2.5 m substratewidths. Testing at 300 A AC was carried out for 21,000 h

without seal failures. DC testing at 96,000 kW h was run

using high-voltage DC processes. Stand-alone off-line

accelerated testing for seal life was done for over 10,000

h on the main drive spindle. No visible wear was seen on the

hard coated spindle surfaces. Lips seals were tested over

2400 h with no visible wear.

After the in-house testing, more than 30 dual AC

cylindrical magnetrons were installed and monitored in the

field. Following the first 5000 h operation, wear on seals is

under 20%, leading to a projected seal life of 10,000 h. This

fulfills the first design criteria of 1-years production seal

Fig. 2. Drive end block.Fig. 3. Seal cavity.

no failures. Further testing is underway to verify the

operational lifetime of the seals at 400 A. The end block

brittleness and manufacturing problems limit the extent to

An alternative design places a ring of relatively slow

sputtering metal in the high erosion position [7]. Fig. 5

shows the end of a target with a slow sputtering metal ring.

Through the use of the Ti ring at the turn around, sputter-

through of the end material before the center material is

eliminated. This leads to nearly 100% utilization of the

target material available in the center. Target utilization is

now limited only by the initial concentricity of the target

and the uniformity of the sputter erosion over target life.

Two experiments were conducted to demonstrate that

metal sputtered from the end ring would not contaminate the

coated product. Fig. 6 shows the first experimental

conditions, in which a stainless steel ring was attached to

a Ti tube. Fe levels in the deposited Ti films were monitored

by Energy Dispersive X-ray Analysis. Substrates placed

Fig. 4. Differentially pumped end blocks.

S.J. Nadel et al. / Thin Solid Films 502 (2006) 1521 17which the dog-bone solution can be used.design limit is theoretically 600 A.

3. High utilization target design

Inherent in all linear magnetron designs is a variation in

magnetic field intensity and shape at the end and turn-

around relative to the center. The magnetic field variations

result in corresponding changes in plasma intensity that

effect the erosion rates along the magnetron. Typically, this

results in areas of deeper erosion within or immediately

adjacent to the corners of the racetrack. The rotation of the

cylindrical magnetron enhances this difference; in the worst

case, a deep groove can erode at the end of the tube while

significant target material remains in the center. (By design,

these high erosion areas of the magnetron are at least 10(25 cm) from the edge of the glass substrate to avoid

distortion of the uniformity profiles.)

Previous solutions for reducing the excess erosion

include weakening or spreading out the magnetic field [4]

or increasing the available material (dog-bone) [5,6] at

the ends of the target tube. There are limits to weakening the

magnetic field without a significant increase in the escape of

electrons at the turn-around, which can further distort the

uniformity and eventually extinguish the plasma. MaterialFig. 5. Slow sputtering metal end ring.Fig. 6. Configuration for SST ring on Ti tube to test for contamination ofdeposited film.

Fig. 7. Sampling configuration for evaluation of TiO2 films deposited from

targets with Ti rings.

In the second experiment, Ti rings were placed on a

sensitive to manufacturing tolerances or operator assembly.

Fig. 9 shows the first design to offer a full flat face sealing

surface for maximum reliable O-ring compression.

5. Magnet array design

The final component key to magnetron performance is

the combination of pole piece and magnet array, clamped to

the water support bar. Water-cooled magnets are required for

Table 1

Film thickness and optical constants of TiO2 films deposited from target

with Ti rings

Sample Location Thickness

(nm)

n at 550

nm

k at 550

nm

1 0.5W 614 2.4602 0.000002 1.5W 621 2.4596 0.001153 2.5W 629 2.4590 0.000844 50- 631 2.4332 0.00189

5 97.5W 649 2.4499 0.007246 98.5W 645 2.4526 0.000487 99.5W 639 2.4591 0.00000

Fig. 9. Flat surface O-ring compression for target to spindle seal.

S.J. Nadel et al. / Thin Solid Films 502 (2006) 152118ceramic sub-stoichiometric TiOx target. Nominal sputtering

conditions for high rate, non-absorbing TiO2 films utilize a

gas ratio of 96% Argon/4% Oxygen. In these conditions, the

Ti metal ring should actually sputter an absorbing film faster

than the target material, giving a worst-case and easily

identifiable condition for potential contamination. Fig. 7

shows the position of samples located across a full-width

2.5 m substrate, and extending past the edge of the substrate.

Table 1 shows the film thickness and optical constants (n, k

at 550 nm) across the sampling positions. No change in

index or absorption is seen on any films taken from the edge

of the glass, compared to the center. There is no indication

of metallic Ti in any films. This is demonstrated in the

absorption spectra shown in Fig. 8.

4. Target fixation

The interface between the target and the end block is the

component most frequently accessed by the user, and

therefore most critical for robust design. The clampingdirectly under the metal rings showed nearly 40% Fe

content. However, moving inwards until we reach the edge

of a full size substrate, the Fe content drops to below 0.5%

(see positions F, G, H in Fig. 6). These values represent the

detection limits of Fe via EDX analysis.

A Hanging off edge 612 2.4643 0.00207

B Hanging off edge 638 2.4557 0.00326between the spindle and target tube must provide a

repeatable and reliable sealing surface, which is not

Fig. 8. Absorption spectra in visible region for TiO2 films deposited from

targets with Ti rings.the highest power operation of the magnetron. Thus, non-

soluble SmCo is used. Magnetic field uniformity is

optimized by first saturating and treating the magnets to

their target value. Then magnets are sorted into lots with

tolerances of +1.5% of target value for each magnet bar.

Tolerances between different arrays are +3%. Stainless steelFig. 10. SmCo magnet array protected by stainless steel caps.

Fig. 11. Mid-span support structure attached to magnet array.

f Si3N

S.J. Nadel et al. / Thin Solid Films 502 (2006) 1521 19caps protect the magnets from mechanical damage when the

array is removed from the tube during a target change (Fig.

10). The array can easily be oriented for sputter up or down

application. The high field intensity of the SmCo magnets

allows easy ignition of the plasma, even with targets up to

6.5W (16.5 cm) diameter. This allows the use of thicker dog-bone style targets.

The magnet array has been extended to sputter out to the

end of the target tube, without the heat generated by the

plasma affecting the end block and seals. All previous

cylindrical magnetron designs suffered from re-deposition

and condensate build up in the last few inches of the un-

Fig. 12. Cross magnetron width uniformity osputtered target area. Unless properly shielded, this could

lead to debris generation or arcing. Traditionally, this was

Fig. 13. Cross magnetron (full and cut size lite) uniformity of SiO2solved through the use of target end shields that formed a

dark space between the shield and the target. However, the

need for close spacing to form a dark shield, required a

complex set of end shields optimized for varying target

thicknesses achieved with different materials and manufac-

turing processes. By sputtering to the end of the target tube,

the new array eliminates this complexity.

As cylindrical magnetrons reach lengths of 3.8 m for

European style jumbo 3.2 m flat glass, controlling the

deflection of the magnet bar becomes critical. Maintaining a

constant distance between the magnets and the target surface

is necessary for simple and repeatable optimization of the

4 films deposited on full and cut size lites.sputtered thin film uniformity. A Mid-span Support

structure shown in Fig. 11 is clamped to the magnet array

films. Vertical graph shows uniformity in direction of travel.

Various enhancements described above have been

s depo

S.J. Nadel et al. / Thin Solid Films 502 (2006) 152120combined to produce the following results for reactive

depositions processes in open loop mode. Reactive to

inert gas ratios are controlled via mass flow controllers.to fix this spacing [3]. The rollers shown ride on the inside

surface of the target tube, maintaining a constant spacing.

6. Results for reactive deposition processes

Fig. 14. SnO2 film uniformity aUniformity is adjusted through modification of magnetic

field strength (using shims to adjust magnet bar spacing)

Fig. 15. TiO2 uniformity on full size (one vand reactive/inert gas ratio (using segmented gas distribu-

tion bars).

Figs. 1216 show uniformity profiles generated for

standard materials deposited on 2.5-m-wide flat glass. All

materials were deposited using Robicon AC power supplies.

The TiO2 films were deposited from ceramic targets. Film

thickness was determined optically, based upon measure-

ments of optical constants used to generate models of film

side b* color values versus film thickness. Measurements

are taken every 10 cm across the glass, to within 50 mm of

sited on full and cut size lites.the edge of the glass. Uniformity profiles are plotted as the

percent deviation of film thickness at any point on the glass,

s. two magnetrons) and cut size lites.

ty on

S.J. Nadel et al. / Thin Solid Films 502 (2006) 1521 21from the average thickness across the full width. Deposition

speeds are calculated based upon measurements of the

average thickness across the glass and the line speed.

Cross-width profiles are shown for all materials for both

full and cut size lites run consecutively. For Si3N4 and TiO2,

the effect of running two magnetrons to deposit the layer are

shown. For SiO2, the front to back uniformity is also shown.

Generally, the uniformity profiles on all slow sputtering

materials were within a 3% thickness range across the full

and cut size lites, out to 50 mm from the edge. For the faster

sputtering materials such as SnO2 and ZnO, this increased

slightly, but is still better than 4% range, including cut size

lite. The front to back uniformity is also within a 3% range.

Fig. 16. ZnO uniformiThe uniformity range and deposition speeds are summarized

in Table 2.

7. Conclusion

More than 45 dual AC magnetrons are currently in

production incorporating the features described above.

These magnetrons are capable of operating at levels of at

least 300 A/120 kW AC with a seal life of at least 1 year.

With the use of dog-bone or Metal-ring targets,

material utilizations of 90100% can be achieved.

Table 2

Deposition rates and corresponding thin film uniformity ranges

Material Rate

(nm m/min)

kW

(AC)

Thickness range

(% average thickness)

SiO2 30 70 3

Si3N4 70 60 3

TiO2 50 90 3

SnO2 95 60 4

ZnO 120 75 4Improved magnet arrays allow simple uniformity tuning

to achieve thickness uniformity of 34% or better on full

and cut size glass. Routine maintenance can now be under

the complete control of the user through in-house main-

tenance. Improved target clamping increases reliability and

up time, and is freely available to all target vendors to

simplify procurement and reduce materials costs. The

combination of high operating powers, simplified uniform-

ity tuning, reduced debris and arc generation, increased

materials utilization and higher reliability provide higher

yields and improved quality films at reduced operating

costs.full and cut size lites.References

[1] R. Barrett, U.S. Patent No. 6736948, 18 May 2004.

[2] Patent applied for.

[3] Patent applied for.

[4] K. Hartig, A. Dietrich, J. Szczyrbowski, U.S. Pat. #5,364,518,

November 15, 1994.

[5] W. De Boscher, G. Gobin, R. De Gryse, Proc. 3rd ICCG, 2000,

p. 59.

[6] J. Vanderstraeten, U.S. Pat. #5,853,816, December 28, 1998.

[7] E. R. Dickey, E. Bjornard, U.S. Pat. #5,725,746, March 10, 1998.

Advanced generation of rotatable magnetron technology for high performance reactive sputteringIntroductionEnd block structureHigh utilization target designTarget fixationMagnet array designResults for reactive deposition processesConclusionReferences