Commercial helicon sources inject plasma into a field-free region
Commercial helicon sources inject plasma into a field-free region
description
Transcript of Commercial helicon sources inject plasma into a field-free region
![Page 1: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/1.jpg)
![Page 2: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/2.jpg)
Commercial helicon sources inject plasmainto a field-free region
To pump
PROBE 1PROBE 2
The MORI source A helicon injection expt.
![Page 3: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/3.jpg)
We wish to optimize a source which could be part of a large array
ELECTROSTATIC CHUCK
WAFER
MULTI-TUBE HELICON PLASMA SOURCE
PE
RM
AN
EN
T M
AG
NE
T A
RR
AY
Conceptual RF plasma source for etching and depostion of semiconductor wafers and flat-panel display substrates.
Metal or ceramic endplate
Arbitrary antenna
We can use a low-field density peak seen in at B 30G for n 1012 cm-3
![Page 4: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/4.jpg)
The low-B peak has been seen in many different experiments
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 50 100 150 200B (G)
n (1
013 c
m-3
)
Uniform B4 mTorr Ar2.2kW @ 27.12MHz2cm diameter
The field at the peak can range between 10 and 50G, and the peak is much larger in some experiments than in others.
1989, 1" tube
![Page 5: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/5.jpg)
The low-B peak is also seen in a 7-tube array of m = 0 sources
0.0
0.6
1.2
1.8
0 20 40 60 80 100 120 140B (G)
n (1
011 c
m-3
)
200135115857045
Prf (W)
8 mTorr, 13.56 MHz
![Page 6: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/6.jpg)
Computations using Don Arnush's HELIC code predict this peak and show how it varies
a
b
c
Distantconducting shell
antenna
plasma
LLc
dEndplates havearbitrary reflectivity
HELIC calculates waves and loading with• Radial density profile n(r)• Collisional damping• Different (thin) antenna configurations• Antenna coupling• Trivelpiece-Gould modes• Endplates (arbitrary reflectivity)
It requires• Uniform B-field• Uniform n(z)• Cold-plasma dielectric
![Page 7: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/7.jpg)
The plasma loading R() shows a low-B peak which moves with density
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 50 100 150 200B (G)
R (o
hms)
2E+114E+116E+118E+111E+12
n (cm-3)
1011-1012 range
Single-loop m = 0 antenna, 10 cm from endplate, 2 mTorr, Te = 4eV
![Page 8: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/8.jpg)
At high densities, the low-B peak is gone
1012-1013 range
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 50 100 150 200B (G)
R (o
hms)
1.0E+121.5E+122.0E+124.0E+126.0E+1210 E+12
n (cm-3)
Single-loop m = 0 antenna, 10 cm from endplate, 2 mTorr, Te = 4eV
![Page 9: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/9.jpg)
The low-B peak vs. density at constant B
0.0
0.5
1.0
1.5
2.0
2.5
3.0
1E+11 1E+12 1E+13n (cm-3)
R (o
hms)
3050100150200300
B (G)
Single-loop m = 0 antenna, 10 cm from endplate, 2 mTorr, 13.56 MHz
![Page 10: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/10.jpg)
What is the cause of the low-B peak?
• It is not the lower hybrid resonance (1450 G)
• Is it due to a resonance between the helicon mode and the Trivelpiece-Gould mode, when they have comparable radial wavelengths and can interfere constructively?
• Is it due to constructive interference by the wave reflected from the endplate?
Computations show that it is probably the latter.
![Page 11: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/11.jpg)
"Standard" conditions for numerical tests
200 cm
10 12
10Single loop
Half helical
0.0
0.2
0.4
0.6
0.8
1.0
1.2
-1.0 -0.5 0.0 0.5 1.0r / a
n / n
0
B = 10-300 Gno = 1012 cm-3
p = 10 mTorr ArInsulating endplateKTe = 4 eV (affects
collisions only)
f = 13.56 MHz
Radial density profile
![Page 12: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/12.jpg)
The low-B peak sharpens at lower pressure
0
1
2
3
4
5
6
0 50 100 150 200 250 300
B (G)
R (o
hms)
2mTorr10mTorr
p
![Page 13: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/13.jpg)
The peak is sensitive to the density profile
0
1
2
3
4
5
6
0 50 100 150 200 250 300
B (G)
R (o
hms)
UniformFlat with rolloffParabolic
![Page 14: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/14.jpg)
The peak depends on the boundary condition
0
1
2
3
4
5
6
7
8
0 50 100 150 200 250 300
B (G)
R (o
hms)
InsulatingConducting
![Page 15: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/15.jpg)
The peak depends on distance from endplate
0
1
2
3
4
5
6
0 50 100 150 200 250 300
B (G)
R (o
hms)
5 cm10 cmNo bdy
d
![Page 16: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/16.jpg)
The peak depends on the type of antenna
0
1
2
3
4
5
6
0 50 100 150 200 250 300
B (G)
R (o
hms)
Loop, d = 10 cmHH10, d = 10 cmNagoya III
Single loop: m = 0, bidirectionalHH (half-wavelength helical): m = 1, undirectionalNagoya Type III: m = 1, bidirectional
![Page 17: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/17.jpg)
Axial deposition profile of HH10 antenna depends on the sign of the helicity
0.0
0.5
1.0
1.5
2.0
2.5
-1.0 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2z (m)
P(z
)
m = -1m = +1
R = 1.085
R = 0.739
Direction of propagation: (m = +1), (m = -1)
![Page 18: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/18.jpg)
This explains previous data on density enhancement by an aperture limiter
TO PUMP
Block can be solid or have a 1.2-cm diam hole.It can be conducting (carbon) or insulating (boron nitride).It can be moved to various positions behind or under the antenna.
![Page 19: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/19.jpg)
Radial density profile shows enhancement whenever there is a limiter
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0r (cm)
n (1
013 c
m-3
)
C limiterNo holeBN limiterNo limiter
Uniform field
![Page 20: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/20.jpg)
At 800G, the limiter position is not critical
0
2
4
6
-2 -1 0 1 2r (cm)
n (a
rb. u
nits
)
-4-6-8-12-18-28None
z (cm)800 G, 1.8kW, 8mTorr
Carbon block with 1.2 cm diam holez cm behind antenna midplane
![Page 21: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/21.jpg)
The end coils can also be turned off or reversed to form a cusped B-field
to pump
END COILS
The field lines then end on the glass tube, which forms an insulting endplate. An aperture limiter can also be added.
![Page 22: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/22.jpg)
The cusp configuration doubles the amount of plasma created
0.0
0.4
0.8
1.2
1.6
-3 -2 -1 0 1 2 3r (cm)
n
End coils reversedEnd coils offUniform B-field
4mTorr Ar 4 cm diameter
2.23 X
1 X
1.95 X
Integrated density enhancement
![Page 23: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/23.jpg)
Limiter enhancement with and without a magnetic cusp
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0r (cm)
n (1
013 c
m-3
)
C limiterNo holeBN limiterNo limiter
Uniform field
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0r (cm)
n (1
013 c
m-3
)
C lim.BN lim.No lim.
Cusp field
The cusp field greatly enhances the density without a limiter, but adds little when a limiter is already in place.
![Page 24: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/24.jpg)
Density increase with end coil current is larger with a bidirectional antenna
0.0
0.4
0.8
1.2
1.6
2.0
-40 -20 0 20 40End coil voltage
n (1
013 c
m-3
)
Right helicalNagoya III
Antenna
Cusp field Uniform field
![Page 25: Commercial helicon sources inject plasma into a field-free region](https://reader033.fdocuments.in/reader033/viewer/2022051518/56814c3a550346895db94146/html5/thumbnails/25.jpg)
CONCLUSION
For low-field, low-density helicon injection into a large chamber, reflection of waves from an endplate can be designed to optimize plasma production. This phenomenon is probably responsible for previously unexplained density increases with aperture limiters and cusped magnetic fields . This is a significant effect.