UCLA

Optimization of Source Modulesin ICP-Helicon Multi-Element Arrays for

Large Area Plasma Processing

John D. Evans & Francis F. Chen

UCLA Dept of Electrical Engineering

LTPTL - Low Temperature Plasma Technology Laboratory

AVS 2002, Denver, Co, November 4, 2002

ELECTROSTATIC CHUCK

WAFER

PE

RM

AN

EN

T M

AG

NE

T A

RR

AY

UCLA

ELECTROSTATIC CHUCK

WAFER

PE

RM

AN

EN

T M

AG

NE

T A

RR

AY

Conceptual multitube m=0 helicon source for large area processing

UCLAUCLAOne-tube configuration using large-area Bo-field

coils and radially scannableLangmuir probes

QUARTZ TUBE

PVC PIPE

ANTENNA

MAGNET WINDING

7 cm

5 cm

13 cm

BNC connector

5 mm

17 mm

1 cm

1 cm

10 cm

COIL COIL

Single source tube with individual solenoidal Bo

UCLAUCLASchematic proof of low-field Helicon mode; RH-t-III antenna

Helicity pitch sense B up (down) launches m=+1 up (down) Np and VL enhanced in region that m=+1 mode propagates towards

B m = -1

m = +1

B m = +1

m = -1

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RH 1/2-helical antenna

0

2

4

6

8

10

0 50 100 150 200 250

B (Gauss)N

(10

11cm

-3)

down

up

B direction

Dependence of N(B) on the direction of B reverses when the sense of the helicity of the antenna is reversed; thus it is

m = +1 helicon mode

Sense of helicity

“LH” “RH”

0

2

4

6

8

10

0 50 100 150 200 250

B (Gauss)

N (1

011

cm-3

)

up

down

B direction

LH 1/2-helical antenna

Experimental evidence: Half-helical antennas launch m = +1Helicon mode from source tube when “low field peak” is present.

UCLA

Verification of Low-field Helicon Excitation

Low-field “peak” in N vs B plot

Dependence of occurrence of peak on B-field direction

Dependence of N vs B on B-direction reverses with antenna helicity

UCLA

Low-field peak increases, broadens and shifts to higher B at higher Po.

Po = 25 mTorr

0

2

4

6

8

10

0 50 100 150 200 250

B (Gauss)

N (1

011

cm-3

)

down

up

B direction

Po = 10 mTorr

0

2

4

6

8

10

0 50 100 150 200 250

B (Gauss)

N (1

011

cm-3

)downup

B direction

Po = 5 mTorr

0

2

4

6

8

10

0 50 100 150 200 250

B (Gauss)

N (1

011

cm-3

)

down

up

B direction

Po = 1 mTorr

0

2

4

6

8

10

0 50 100 150 200 250

B (Gauss)

N (1

011

cm-3

)

down

up

B direction

UCLAUCLALeft Hand (LH) Helical Antenna Nomenclature Defined

Lant = Physical length of active antenna element

ant = Antenna Wavelength - pitch of helical straps

Half Helix

Lant = 10 cm

ant = 20 cm

Full Helix

Lant = 10 cm ant = 10 cm

2Double Helix

ant = 5 cmLant = 10 cm

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Radial Np profiles for 3 RH-helical antennas

1kW, 13.56MHz, 15mT Ar, 150G, z=3cm, next slide

Same antenna length, but different “antenna wavelengths”

Top: double-helix; Middle: full-helix; Bottom: half-helix

Wider profiles observed in “B-down” configuration in all cases

Most total downstream Np produced in full-helix case

More total downstream Np produced in “B-down” case

m=1 helicon mode enhances profile width as well as Np

UCLA

0

2

4

6

8

10

0 4 8 12 16 20

R (cm)

N (

10

11 c

m-3) down

up

B direction

Lant =10cm

ant =20cm

EdgeRtube

0

2

4

6

8

10

N (

10

11 c

m-3)

down

up

B direction

Lant =10cm

ant =10cm

0

2

4

6

8

10N

(1011 c

m-3)

down

up

B direction

Lant =10cm

ant = 5cm

Radial Np profiles for 3 “antenna wavelengths”

UCLA

Radial Np profiles for 3 RH-helical antennas

1kW, 13.56MHz, 15mT Ar, 150G, z=3cm, next slide

Same antenna length, but different “antenna wavelengths”

Top: double-helix; Middle: full-helix; Bottom: half-helix

Wider profiles observed in “B-down” configuration in all cases

Most total downstream Np produced in full-helix case

More total downstream Np produced in “B-down” case

m=1 helicon mode enhances profile width as well as Np

UCLAUCLA

Half-helical m = +1 antenna

Lant = 10cm, ant = 20cmLangmuir Probe @ z = 3 cm

below mouth of source tube

0

2

4

6

8

10

-10 -5 0 5 10 15 20R (cm)

Np

m=+1

m= -1

B orientation

EdgeCenter

Lant = 10 cm

1kW, 15mT, 150G

UCLAUCLA

0

2

4

6

8

10

-10 -5 0 5 10 15 20R (cm)

Np

m=+1

m= -1

B orientation

EdgeCenter

Full-helical m = +1 antenna

Lant = 10cm, ant = 10cm

Langmuir Probe @ z = 3 cmbelow mouth of source tube

QUARTZ TUBE

ant = 10 cm

BNCconnector

Lant = 10 cm

UCLAUCLA

0

2

4

6

-10 -5 0 5 10 15 20R (cm)

Np

m=+1

m= -1

B orientation

EdgeCenter

Double-helical m = +1 antenna

Lant = 10cm, ant = 5 cm

Langmuir Probe @ z = 3 cmbelow mouth of source tube

ANTENNA

ant = 5 cmLant = 10 cm

UCLAUCLA

1kW, 10mT Ar, 13.56MHz, Lant =10cm = lant, z=3cm, 150G

0

2

4

6

8

10

-12 -8 -4 0 4 8 12 16 20

R (cm)

N (

1011

cm-3

)

down

up

B direction

EdgeCenter

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M = 0 radial profiles

4 equispaced source tubes,Enough for uniform plasma?

YES, for axial distance z > 10cm from source tubes

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Schematic of multi-turn loop “m=0” source element

54 mm

2.4 mm

6.4 mm10 cm

2.5

cm

antenna

Pyrex

UCLANumerical label convention: 7 tube source, aerial view

“w,x,y,z” = Antennas # W, X, Y, Z “ON”, others “OFF”

PROBE

12

3 4

5

67

“1,2,4,6”

PROBE

12

3 4

5

67

“1,2,4,5”

UCLA

0

2

4

6

8

10

12

-22.5 -15 -7.5 0 7.5 15 22.5R (cm)

N (

1011

cm-3

)

1,2,4,5

1,2,4,6

Tubes

PROBE

123 4

567

“1,2,4,6”PROBE

123 4

567

“1,2,4,5”

UCLA

Np radial nonuniformity vs axialdistance z from source tubes

Broad/flat cannot be explained by streaming of plasma along B-lines and normal diffusion

PROBE

12

3 4

5

67

“1,2,4,5”

UCLA

0

2

4

6

8

10

-22.5 -15 -7.5 0 7.5 15 22.5R (cm)

N (

1011

cm-3

) 3

10

Z (cm)

N(R) vs Z for 3-turn loops, 4 symmetric (1,2,4,6)

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CONCLUSIONS

4 equispaced source tubes good enough,due to Helicon-enhanced uniformity

Multitube concept appears to be applicable to arbitrarily large area.