“A Design for an efficient cylindrical magnetron cathode with rotating magnets and optical emission incorporated”

Inventors A. Subrahmanyam, Krishna Valleti

IIT Madras, Chennai, INDIA.

Shrikanth V Joshi, G.Sundararajan ARCI, Hyderabad, INDIA.

Patent on,

“A Design for an efficient cylindrical magnetron cathode with rotating magnets and optical emission incorporated”

Inventors A. Subrahmanyam, Krishna Valleti

IIT Madras, Chennai, INDIA.

Shrikanth V Joshi, G.Sundararajan ARCI, Hyderabad, INDIA.

Out look of the presentation:

Brief introduction to sputtering mechanism

Different sputtering techniques – focused on planar & cylindrical

About & limitations of planar magnetrons (circular, rectangular)

Description of existing cylindrical magnetrons

Drawbacks

Present invention design and evaluation

Important references related to present invention

Brief introduction to sputtering mechanism

focused on planar & cylindrical

About & limitations of planar magnetrons (circular, rectangular)

Description of existing cylindrical magnetrons

Present invention design and evaluation

Important references related to present invention

* Effective creation of Argon ions by secondary electron bombardment

Sputtering Process:

Effective creation of Argon ions by secondary electron bombardment

Sputtering

Diode Sputtering

R

R

* The magnetic field confines the glow discharge plasma and increases the length of the path of electrons moving under the influence of the electric field.

Magnetron Sputtering

♦ Planar magnetron sputtering

♦ Cylindrical magnetron sputtering

R electron = 3.37 x E 1/2 (eV) / B (Gauss)

R ion = 911 x E 1/2 (eV) / B (Gauss)

The magnetic field confines the glow discharge plasma and increases the length of the path of electrons moving under the influence of the electric field.

Planar magnetron sputtering

* The cathode includes an array of permanent magnets arranged in a closed loop and mounted in a fixed position in relation to the flat target plate.

* The magnetic confinement of the plasma results in a high rate of erosion of the target along the narrow "race track".

Limitations

* Only a relatively small portion of the total target material is used.

* Limited heat transfer and arcing at the edges and the center of the target.

* The spitting of debris is very high.

* Only planar objects can be coated uniformly.

The cathode includes an array of permanent magnets arranged in a closed loop and mounted in a fixed position in relation to the flat target plate.

The magnetic confinement of the plasma results in a high rate of erosion of the

Only a relatively small portion of the total target material is used.

Limited heat transfer and arcing at the edges and the center of the target.

Only planar objects can be coated uniformly.

Scope of present invention:

Batch of Industrial tool coating cost

effectively (more number in a single run).

For large area glass coatings in the architectural, automotive and display industry.

Defense equipment protection form wear

and corrosion loss (mainly Gun barrels)

architectural, automotive and display industry.

Defense equipment protection form wear

Simple Cylindrical magnetron:

* Electromagnets requires high current which results in enhanced heating Electromagnets requires high current which results in enhanced heating.

* A cathode target assembly in the form of an elongated, cylindrical tube carries a layer of material applied to its outer surface that is to be sputtered.

Existing Cylindrical magnetron designs:

Design reference: US 4,179,351 patent issued on Dec. 18, 1979 to Hawton, Jr. et al.

1

U.S.Army Armament Research, Development and Engineering Center

U.S.Army Armament Research, Development and Engineering Center

A cathode target assembly in the form of an elongated, cylindrical tube carries a layer of material applied to its outer surface that is to be sputtered.

Magnet

Non magnetic Spacer

Existing Cylindrical magnetron designs:

US 4,179,351 patent issued on Dec. 18, 1979 to Hawton, Jr. et al.

2

Vacuum coating technologies, Fairfield

3

Vacuum coating technologies, Fairfield

US ­ 5,047,131 U

S­6375815

* The target tube is rotated about its longitudinal axis. A magnetic structure is arranged inside the tube but does not rotate with it.

* The rotation of the target surface through the stationary plasma sputters the top layer of material from entire surface as that surface is rotated through the magnetic field.

* Any dielectric that is deposited on the target surface is apparently removed by sputtering when it rotates in the region of the magnetic field thereby reducing arcing

* The non uniformity in the deposited films is around 12%.

* Rotating seals are included in this support structure for isolating the electrical contacts and

cooling fluid from the vacuum chamber.

* Rotation of the target (not magnetic arrangement) results in local gas fluctuations.

* Sputtering in rotating target geometry will not allow oblique deposition (which results in

improved depositing film properties).

* Permanent magnets were damaged with time because of coolant water circulation (over

the magnets) and the magnetic field strength decreases slowly.

The target tube is rotated about its longitudinal axis. A magnetic structure is arranged inside

The rotation of the target surface through the stationary plasma sputters the top layer of material from entire surface as that surface is rotated through the magnetic field.

Any dielectric that is deposited on the target surface is apparently removed by sputtering when it rotates in the region of the magnetic field thereby reducing arcing ("self-cleaning" ).

The non uniformity in the deposited films is around 12%.

Rotating seals are included in this support structure for isolating the electrical contacts and

Rotation of the target (not magnetic arrangement) results in local gas fluctuations.

Sputtering in rotating target geometry will not allow oblique deposition (which results in

Permanent magnets were damaged with time because of coolant water circulation (over

the magnets) and the magnetic field strength decreases slowly.

* Electron Confining efficiency;

I = K V n , n = 6.8 ( in the present geometry)

K – function of working pressure and magnetic field strength.

Present Invention:

Cylindrical cathode

Power connection

Magnet arrangement

High torque Motor

Plasma profile

( in the present geometry)

function of working pressure and magnetic field strength.

Cylindrical cathode

Optical fiber port

Cooling water port

0 2 4 6 8

­100

­80

­60

­40

­20

0

20

40

60

80

100 % thickness variation fro

m average value

Distance from one end of CM (cm)

Thickness variation along the cylindrical axis:

Target Utilization:

% 100 ) ( ) (

× = final t initial t U

w

w t

± 3 %

10

Thickness variation along the cylindrical axis:

In the present design;

U t ≈ 90%

* A strip 12.0 cm × 2.5 cm of glass plate is used as substrate.

* Surface profilometry is used for thickness measurements.

Surface at the step

Plasma Emission spectra

Tantalum (atomic) – 696.6 nm

Process control by plasma emission monitoring:

Argon (first ionization) – 750.4 nm

Nitrogen (exited) – 738.5 nm

Process control by plasma emission monitoring:

Over all achievements in the design:

Maximum uniformity in thickness along the length of the cylindrical magnetron is achieved

Maximum target utilization is achieved

Complicated rotation seal mechanism is eliminated

Permanent magnetic material property degradation by corrosion is eliminated

Ease of target loading is achieved

Difficulties in monitoring gas distribution uniformity by gas showers is eliminated

Maximum uniformity in thickness along the length of the cylindrical

Maximum target utilization is achieved

Complicated rotation seal mechanism is eliminated

Permanent magnetic material property degradation by corrosion is eliminated

Difficulties in monitoring gas distribution uniformity by gas showers is

Important references:

1. “Design advances and applications of the rotatable cylindrical magnetron Michael Wright and Terry Beardow – JVST A 4 (1986) 388.

2. “Homogeneous coatings inside cylinders” Technol. 177-178 (2004) 355.

3. “Characterization and Comparison of Magnetron Sputtered and Electroplated Gun Bore Coatings” by Christopher P. Mulligan, Stephen B. Smith and Gregory N. Vigilante Transactions of the ASME 128 (2006) 240.

4. “Advanced generation of rotatable magnetron technology for high performance reactive sputtering” by S.J. Nadel, P. Greene, J. Rietzel, M. Perata, L. Malaszewski, and R. Hill – Thin solid films 502 (2006) 15.

Design advances and applications of the rotatable cylindrical magnetron” by JVST A 4 (1986) 388.

“Homogeneous coatings inside cylinders” by F. Loffler and C. Siewert – Surf. Coat.

“Characterization and Comparison of Magnetron Sputtered and Electroplated Gun by Christopher P. Mulligan, Stephen B. Smith and Gregory N. Vigilante –

“Advanced generation of rotatable magnetron technology for high performance by S.J. Nadel, P. Greene, J. Rietzel, M. Perata, L. Malaszewski, and R. Hill