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