m. sorokine, h. hemmen, w.w. stoffels, g.m.w. kroesen
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Suiting a voltage and current sensor for Suiting a voltage and current sensor for a nanoparticle detection in an Ar-Silane a nanoparticle detection in an Ar-Silane
capacitively coupled plasma.capacitively coupled plasma.M. Sorokine, H. Hemmen, W.W. Stoffels, G.M.W. Kroesen
Department of Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
EPGEPGElementary Processes in GasdischargesElementary Processes in Gasdischarges
EPGEPGElementary Processes in GasdischargesElementary Processes in Gasdischarges
TU e/TU e/
IV sensorIV sensor
t
VV v
t
IV i
)(0
0)( jwteII
VV v IV i
t
VV v
t
IV i
)(0
0)( jwteII
VV v IV i
FFT. 0.2% fund. 60% harm.
0.00E+00
1.00E-03
2.00E-03
4.00E-03
5.00E-03
6.00E-03
1 53 measurement
current [V]
0.00E+00
1.00E-04
2.00E-04
4.00E-04
5.00E-04
6.00E-04
1 53 measurement
voltage [V]
first harmonic second harmonic third harmonic fourth harmonic
220 28
0.00E+00
1.00E-03
2.00E-03
4.00E-03
5.00E-03
6.00E-03
1 53 measurement
current [V]
0.00E+00
1.00E-04
2.00E-04
4.00E-04
5.00E-04
6.00E-04
1 53 measurement
voltage [V]
first harmonic second harmonic third harmonic fourth harmonic
220 28
0 . 0 0 %
5 . 0 0 %
1 0 . 0 0 %
1 5 . 0 0 %
2 0 . 0 0 %
2 5 . 0 0 %
3 0 . 0 0 %
0 . 0 E + 0 0 2 . 0 E + 0 3 4 . 0 E + 0 3 6 . 0 E + 0 3 8 . 0 E + 0 3 1 . 0 E + 0 4 1 . 2 E + 0 4 1 . 4 E + 0 4 1 . 6 E + 0 4 1 . 8 E + 0 4
1 / a m p l i t u d e [ 1 / V ]
rel. e
rror
6 9 0 m T o r r
7 9 0 m T o r r
9 0 0 m T o r r
2 2 V
VmV 490
256*2
250
0 . 0 0 %
5 . 0 0 %
1 0 . 0 0 %
1 5 . 0 0 %
2 0 . 0 0 %
2 5 . 0 0 %
3 0 . 0 0 %
0 . 0 E + 0 0 2 . 0 E + 0 3 4 . 0 E + 0 3 6 . 0 E + 0 3 8 . 0 E + 0 3 1 . 0 E + 0 4 1 . 2 E + 0 4 1 . 4 E + 0 4 1 . 6 E + 0 4 1 . 8 E + 0 4
1 / a m p l i t u d e [ 1 / V ]
rel. e
rror
6 9 0 m T o r r
7 9 0 m T o r r
9 0 0 m T o r r
2 2 V
VmV 490
256*2
250
Relative errors
0
1
2
3
4
5
0 28 56 84 112 140
fourier coefficient n
abs
(Y[n
] +
i*X
[n])
690 mTorr oscilloscope
-0.25-0.2
-0.15-0.1
-0.050
0.050.1
0.150.2
0.25
0 50 100 150 200 250
time [2ns]
curr
en
t [V
]
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
volta
ge
[V]
current
voltage
Phase shift. FFT 270. PIM 850
FFT spectrum
Plasma discharges are widely used in many specialized commercial production environments. One of these is the
production of solar cells. The key process in that production is the plasma enhanced silicon layers deposition. Solar cells are known to have a high cost and a poor efficiency. By incorporating nano-
scale particles into the layers, a considerable improvement in product quality is achieved. This project is devoted to a study of the process of nano-particle formation. In this work we present
difficulties one encounters analyzing the RF power characteristics using a voltage and current probe. We report on the problems
associated with the data acquisition itself, as well as on the complications in the data processing and analysis. Measurements in the air discharge plasma are presented to illustrate the given
examples.
While using a commercially made Voltage/Current probe one may encounter a problem of not being able to use the factory calibration data. Reasons for that may be a possible change of the impedance of the measuring circuit while using a different measuring device, in our case it was a digital oscilloscope, a different method or technique used in the factory calibration, or simply because such information is not available. Calibration experiments have been performed in air discharge. Experiments in other gases may eliminate the problems of low amplitude harmonics. A higher bit Analog-Digital Converter will increase the detection limits and signal to noise ratio.
-0.250
measurement [2ns]
cu
rre
nt
[V]
firstharmonic
fourthharmonic
thirdharmonic
second harmonic
fundamentalfrequency
higher harmonics
Fourier transformation
Signal from the sensor
IU
Sensor RF generatorPlasma
IU
Sensor RF generatorPlasma
Power monitoring
V mV
1st
2nd 2nd
1st
fund
fund
V mV
1st
2nd 2nd
1st
fund
fund
We used the original Smart PIM hardware of Scientific Systems to calibrate the readings from the sensor. On the factory a similar procedure has already been done
for the original PIM hardware. So we expected that the two results would match each other.
Calibration principle
Afund
Measured harmonics
A1
A2
PIM readings
0.8
PIM measurement
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
1 462
Voltage [V]
first harmonic second harmonic third harmonic fourth harmonic
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
1 462 PIM measurement
current [A]
144 113 0.8
PIM measurement
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
1 462
Voltage [V]
first harmonic second harmonic third harmonic fourth harmonic
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
1 462 PIM measurement
current [A]
144 1138 bit=256
PIM. 1.9% and 1.6% max.
1.96 mV
Representation of discrete higher harmonic measurement
Table 1. Calibration coefficients p=900mTorr current [A/VI] factory
calibration voltage [V/VV] factory
calibration fundamental 10.66±0.02 5.9849E+04 (8.91±0.01)E+02 8.6707E+02 first harmonic 2.55±0.04 1.1970E+05 (1.43±0.07)E+03 1.7341E+03 second harmonic 20.6±0.9 1.7955E+05 (7.7±0.4)E+02 2.6012E+03 third harmonic 27±8 2.3940E+05 (1.3±0.2)E+03 3.4683E+03 fourth harmonic 55±4 2.9925E+05 (2.5±0.2)E+03 4.3353E+03
Table 2. Phase measurements (degrees) p=900mTorr oscilloscope PIM measured offset factory calibration fundamental -22±3 -85.2±0.5 63 27.098 first harmonic -87±6 71.2±0.8 158 54.196 second harmonic -131±9 -131±1 0 81.294 third harmonic -38±20 -41±2 3 108.392 fourth harmonic -39±20 -77.0±0.4 38 135.49
0.00E+00
1.00E-05
2.00E-05
3.00E-05
4.00E-05
5.00E-05
0.00E+00 2.00E-04 4.00E-04 6.00E-04 8.00E-04 1.00E-03
average amplitude [V]
sta
nd
ard
dev
iatio
n [V
]
690 mTorr
790 mTorr
900 mTorr
Standard deviation
Reasonable agreement for voltage and non for current
Our measurements do not confirm factory offset values
Analysis of the standard deviation in our measurements allows us to say that the big deviation in the results for the low amplitude higher harmonics of voltage is a result of a not sufficiently high 8 bit resolution capability of the scope. You can see on the graph that the standard deviation for most experiments remains constant.
4096 points
8 mks
29th EPS Conference, June 17-21, 2002, Montreux, Switzerland
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