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Submillimeter spectroscopic diagnostics in semiconductor processing plasmas
Yaser H. Helal, Christopher F. Neese, Frank C. De LuciaDepartment of Physics
The Ohio State University
Paul R. Ewing, Phillip J. Stout, Michael D. ArmacostApplied Materials
June 17, 2014
Spectroscopy and industrial plasmas
• Submillimeter spectroscopy of plasmas is a well established technique
• Typical pressure of semiconductor plasma reactors (1-100 mtorr) is especially advantageous
• Many common molecules in processing plasmas have been studied and can be found in literature
• Many molecules are cataloged in astrophysical databases (JPL, Cologne, …)
Semiconductor Chip
http://www.mikeseeman.com/index.php?id=engineering/research
Semiconductor Processing
http://www.atp.nist.gov/eao/gcr03-844/append-a.htm
•Cleaning
•Deposition
•Lithography
•Etching
QuickSyn Synthesizer
9.3 – 13.9 GHz
QuickSynSynthesizer
9.2 – 13.9 GHz
VDI Receiver
x54
VDI Transmitter
x54
+40db
Diode Detector
Lock-In Amplifier
A/D
PC
LO
IF
500-750 GHz
(Amplifiers)
Component Diagram
Phase Shifter(FM)~40 kHz
Application Technique
• Develop a spectroscopic catalog of molecules found in industrial plasmas
• Build “Snippets” from catalog – Jump to frequency of spectral line and sweep through width of line
• Using synthesizers’ frequency agility to focus on useful spectral lines
• Develop spectral scan strategy based on species of interest and make measurements quickly
Transceiver
• Measured spectra with OSU test plasma reactor
Initial tests at OSU0.10
0.08
0.06
0.04
0.02
0.00
-0.02
Sca
led
Fra
ctio
nal A
bsor
ptio
n
CN CN HCN HCN FCN FCN CF2 CF2 NCO NCO COF2 COF2 CO CO NO NO
(0.0154 GHz snippets)
O2, 120 mtorr N2/O2 O2/CF4/CHF3, 104 mtorr N2/O2/CF4/CHF3, 106 mtorr N2/O2/CHF3, 105 mtorr N2/O2/CF4, 65 mtorr N2/CF4/CHF3, 62 mtorr N2/CHF3, 76 mtorr N2/CF4, 62 mtorr CHF3, 10 mtorr, no plasma
With O2
Without O2
• Sharp standing waves in chamber with window• Reflectance/surface of window material 26%• Reflectance/surface of quartz 10%
Applied Materials Reactor
1.2
1.0
0.8
0.6
0.4
0.2
Dio
de D
etec
tor
Vol
tage
(V
)
750700650600550500GHz
Through chamber with window Table top, Open Air
Cl2, HBr, O2 plasma on polysilicon
• Feed gases are the fuel of reactions• SiO (from wafer reaction), HCl and HBr found.
0.5
0.0
-0.5
Sca
led
Fra
ctio
nal A
bsor
ptio
n x1
03
SiO SiO HCl HCl ClO ClO HBr HBr SiH SiH BrO BrO
(0.0154 GHz snippets)
7 mtorr Cl2/HBr/O2 plasma on polysilicon
N2, CH2F2, SF6 plasma on Si
• See CF2, CS, NH3
• Do not see CF, H2S, H2CS, CH2F2 (depleted in plasma)
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
-0.4Sca
led
Fra
ctio
nal A
bsor
ptio
n x1
03
NH3 CH2F2 CH2F2
(0.0154 GHz snippets)
50 mtorr N2/CH2F2/SF6 plasma1.0
0.5
0.0
-0.5
-1.0
Sca
led
Fra
ctio
nal A
bsor
ptio
n x1
03
CS CS
(0.0154 GHz snippets)
50 mtorr N2/CH2F2/SF6 plasma
N2, CH2F2, SF6 plasma on Si (cont.)
• See NS, HCN, FCN, not CN
2
1
0
-1
Sca
led
Fra
ctio
nal A
bsor
ptio
n x1
03
NS NS CN CN HCN HCN FCN FCN
(0.0154 GHz snippets)
50 mtorr N2/CH2F2/SF6 plasma
NH3 plasma
• NH3 abundance decreases with increasing power
• NH2 observed
8
6
4
2
0
-2
-4
Sca
led
Fra
ctio
nal A
bsor
ptio
n x1
03
NH3 (572.49815 GHz) NH2 (644.33912 GHz)
(0.0307 GHz snippets)
20 mtorr NH3 plasma, relative power: 1x 3x 5x 10x 20x
-0.4
-0.3
-0.2
-0.1
0.0
0.1
Sca
led
Fra
ctio
nal A
bsor
ptio
n x1
03
NH2 (644.33912 GHz)
(0.0307 GHz snippets)
NH2 measured
• A wider NH2 snippet shows 3 lines surrounding the center we used from Splatalogue
0.2
0.1
0.0
-0.1
-0.2
Sca
led
Fra
ctio
nal A
bsor
ptio
n x1
03
644.37644.36644.35644.34644.33644.32GHz
20 mtorr NH3 plasma, relative power: 1x 3x 5x
NH2 measured
• Hyperfine splitting resolved by Müller et al. and available in Cologne Database
0.3
0.2
0.1
0.0
-0.1
-0.2
Sca
led
Fra
ctio
nal A
bsor
ptio
n x1
03
644.37644.36644.35644.34644.33644.32GHz
20 mtorr NH3 plasma, relative power: 1x 3x 5x Splatalogue Cologne
• NH3 and NH2 measurable in an NH3 pulsed plasma
Pulsed Plasma10
8
6
4
2
0
-2
-4
Sca
led
Fra
ctio
nal A
bsor
ptio
n x1
03
NH3 (572.49815 GHz) NH2 (644.33912 GHz)
(0.0614 GHz snippets)
NH3 pulsed plasma, 20 mtorr base duty cycle increased duty cycle
-0.2
-0.1
0.0
0.1
0.2
Sca
led
Fra
ctio
nal A
bsor
ptio
n x1
03
NH2 (644.33912 GHz)
(0.0614 GHz snippets)
Flow Ratio2.5
2.0
1.5
1.0
0.5
0.0
Sca
led
Fra
ctio
nal A
bsor
ptio
n x1
03
0.250.200.150.100.050.00NH3/Ar flow ratio
20 mtorr plasma NH3 Absorption
Power + Pressure
• Suggests that a larger fraction of NH3 is dissociated as pressure increases
8
6
4
2
0
Sca
led
Fra
ctio
nal A
bsor
ptio
n x1
03
Relative Plasma Power
NH3/Ar plasma 80 mtorr 20 mtorr
Summary
• Prototype for a packaged submillimeter spectrometer
• Need for an expanded catalog applicable to industrial plasma products
• Submillimeter spectroscopy allows for the ability to compare how densities correlate with flow, power, pressure, and feed gas
Acknowledgements
• Jennifer A. Holt, OSU• Mark A. Patrick, OSU• Wei Liu, AM• This work is supported by Semiconductor
Research Corporation (SRC) through Texas Analog Center of Excellence at the University of Texas at Dallas (Task ID:1836.126)