Society of Vacuum Coaters, TechCon 2013, Providence, RI, April 22-25, 2013

Helicons are RF plasmas in a magnetic field

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Prf %

200 16%

400 21%

600 35%

800 38%

1000 42%

Density increase over ICP

Helicon sources usually use heavy magnets

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The MØRI source of Plasma Materials Technologies, Inc.

Use permanent magnets instead

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-16

-14

-12

-10

-8

-6

-4

-2

0

2

4

6

8

-10 -8 -6 -4 -2 0 2 4 6 8 10

NdFeB ring magnet3” ID, 5” OD, 1” high

Stagnation point

Put plasma here

or here, to adjust B-field

The far-field is fairly uniform

Single-tube setup

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Optimized discharge tube: 2” x 2”

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1. Diameter: 2 inches

2. Height: 2 inches

3. Aluminum top

4. Material: quartz

5. “Skirt” to prevent eddy currents canceling the antenna current

5.1 cm

10 cm

5 cmANTENNA

GAS INLET (optional)

The antenna is a simple loop, 3 turns for 13 MHz, 1 turn for 27 MHz. The antenna must be as close to the exit aperture as possible.

Antenna: 1/8” diam tube, water-cooled

Experimental chamber

UCLAGate Valve

To Turbo Pump

PUMP BAFFLE AND GROUND PLANE

WALL MAGNETS

Port 1

Port 3

Port 2

38

46

6.8

16.9

27.2

19 cm

Langmuir probes at three ports

A few data

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Radial density profiles at the 3 ports

Low temperature at Port 3

Center density vs. RF power at Port 1

Note that a high B-field does not match this density range.

Side view of an array source

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165 cm

30 cm

15 cm

Probe ports

Aluminum sheetHeight can be adjusted electrically if desired

The source requires only 6” of vertical space above the process chamber. Two tubes are shown.

Z1

Z2

65"

21"

7"

7"

7"

7"29"

3.5"

12"

7"3/4” aluminum

Endplates: gas feed and probe port at each end.

Tubes set in deeply (½ inch)

1/2" aluminum

Medusa 2, an 8-tube array

Possible positions shown for 8 tubes.

Substrate motion

Two arrangements of array

Staggered array

Covers large area uniformly for substrates moving in the y-direction

165 cm

53.3 cm

17.8

17.8

17.8

35.6 cm

x

y

165 cm

53.3 cm

17.8

17.8

17.8

x

yTop view 17.8 Compact array

Gives higher density, but uniformity suffers from

end effects.

Operation with cables and wooden magnet tray

It’s best to have at least 3200W (400W per tube) to get all tubes lit equally.

An adjustable wooden magnet tray

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The top gas feed did not improve operation.

A rectangular 50 transmission line

50-W line with ¼” diam Cu pipe for cooled center conductor

Operation with rectangular transmission line

Radial profile between tubes at Z2

0

0.5

1

1.5

2

2.5

3

3.5

-25 -20 -15 -10 -5 0 5 10 15 20 25r (cm)

n (1

01

1 c

m-3

) n

KTe

Density profiles along the chamber

Staggered configuration, 2kW

Bottom probe array

0

1

2

3

4

5

-8 -6 -4 -2 0 2 4 6 8 10 12 14 16x (in.)

n (1

011 c

m-3

)

-3.5

0

3.5

Staggered, 2kW, D=7", 20mTorr

y (in.)

Argon

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Density profiles along the chamber

Compact configuration, 3kW

Bottom probe array

0

2

4

6

8

10

-8 -6 -4 -2 0 2 4 6 8 10 12 14 16

x (in.)

n (

10

11 c

m-3

)

3.5-03.5

Compact, 3kW, D=7", 20mTorr

y (in)

Data by Humberto Torreblanca, Ph.D. thesis, UCLA, 2008.

An 8-tube array for round substrates

UCLANo center tube is necessary!

Compact modules

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END VIEW

Matching circuit

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The end

Thank you

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