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Diagnostics for large area RF plasma reactors Alan Howling Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland Center for Research in Plasma Physics (CRPP)

start by acknowledging:

Christoph Hollenstein, Laurent Sansonnens, & co.

A. Howling, Nankai University 1 aah March 28 - April 3 (2010)

Schematic drawing of a rectangular parallel plate RF capacitive plasma reactor:

process gas

RF transmission line

plasma process pump

pumping grid

substrate

pumping grids

glass substrate (about 1 m2)

2 aah

loading/unloading port

RF electrode with showerhead

RF inter-electrode voltage in vacuum RF tip and ground tip of the probe measure the RF voltage between the electrodes at each position

oscilloscope (floating)

passive voltage probe, 1/100

3 aah

grounded reactor

RF inter-electrode voltage in vacuum

RF power side connection

4 aah

RF inter-electrode electric field in vacuum using a diode probe J. Appl. Phys. 95 4559 (2004)

probe inserted through holes in a side wall

5 aah

RF inter-electrode electric field in vacuum using a diode probe E-field relative profile at 100 MHz (bench test with scanning probe) 1 0.8 0.6 0.4

Electromagnetic modeling

J0(k0 r)

IN VACUUM

0.2 0 0.4 6 aah

0.2

0

1 metre

0.2

0.4 m

J. Appl. Phys. 95 4559 (2004)

surface electrostatic probes: (i) ion saturated current

81 surface probes for DC voltage and current measurements

reactor 47 x 57 cm2

7 aah


8 aah

surface electrostatic probes: (i) ion saturated current J. Appl. Phys. 95 4559 (2004)

Cylindrical reactor experiment

1 metre

optical emission & surface electrostatic probes 9 aah

surface electrostatic probes: (i) ion saturated current J. Appl. Phys. 95 4559 (2004)

Probe array: ion current normalized to center 1

Parallel Plates for 69 MHz

{J0(εeff0.5k0r)}2

0.75 0.5 0.25 0

10 mTorr 0.4

0.2

100 mTorr 0

0.2

0.4

1 0.75 10 aah

0.5

Teflon Lens for 69 MHz

m


EXPERIMENTS AT 100 MHz probe array ion saturation currents (normalized to the central values)

200 W

0.5 Torr

1

10 mTorr

0.75 0.5 0.25

{J0(3.5 k0 r)}2 0 0.4 11 aah

0.2

0

1 metre

0.2

0.4 m

J. Appl. Phys. 95 4559 (2004)

surface electrostatic probes: (ii) DC floating voltage

DC floating voltages give approx. variation in RF plasma potential DC currents to grounded probes give DC current density profile,

Idc, Vf

12 aah

surface electrostatic probes: (ii) DC floating voltage

perturbation to plasma RF potential due to sidewall area 13 aah

surface electrostatic probes: (iii) DC current, zero bias Small area: ~ U and Uconstant over the electrode area

Blocking capacitor

T ⎡ ⎛ U~ ⎞⎤ Te ⎛ M i ⎞ 1 ⎟ + Te ln ⎢I o ⎜⎜ ⎟⎟⎥ ( J e + J i ) dt = 0 → U = ln⎜⎜ 2 ⎝ 2.3me ⎟⎠ T ∫0 ⎢⎣ ⎝ Te ⎠⎥⎦

Local ambipolarity for 0 time averaged conducting current on the electrode

Large area: U constant, but U~ varying according to the telegraph equation

Equation cannot be satisfied simultaneously over the electrode area

RF electrode

i

e

plasma plasma bulke ground electrode

i circulating current

Ug 0V

14 aah

Vsb

Urf

Ũrf Ũg x

surface electrostatic probes: (iii) DC current, zero bias

15 aah

optical emission intensity: fibre optic probes J. Appl. Phys. 95 4559 (2004)

optical emission & surface electrostatic probes

1 metre

Cylindrical reactor experiment 16 aah

optical emission intensity: fibre optic probes J. Appl. Phys. 95 4559 (2004)

fibre optic telescope

fibre optic telescope, for right-angle view

17 aah

optical emission intensity: fibre optic probes

Optical emission 2D profiles in a rectangular reactor:

Parallel plates

With lens

18 aah

ex situ film thickness measurements

Film thickness measurements, ex situ, telegraph effect

Plasma non-uniformity convoluted with gas flow non-uniformity etc.

telegraph model

19 aah

ex situ film thickness measurements

no lens

Film thickness measurements, ex situ, standing wave correction Plasma non-uniformity convoluted with gas flow non-uniformity etc.

with lens

20 aah

ex situ film thickness measurement: interferogram

21 aah

ex situ film thickness measurement: interferogram

non-uniformity due to powder

37 cm x 47 cm

non-uniformity due to standing wave (VHF frequency) 22 aah

light scattering from powder plasma reactor

vacuum chamber

grids

CCD camera

57 cm 47 cm

interference filter

windows

argon laser beam at 488 nm

23 aah

beam expander

MRS Symp. Proc. Vol. 507 Amorphous and Microcrystalline Silicon Technology, pp547-557 (1998).

OES and electron temperature vs time

H2* emission is only from e+H2 collisions, but H* emission has several sources

24 aah

time