Submillimeter spectroscopic diagnostics in a semiconductor
processing plasmaYaser H. Helal, Christopher F. Neese, Jennifer A. Holt,
Frank C. De LuciaDepartment of Physics
The Ohio State University
Paul R. Ewing, Phillip J. Stout, Michael D. ArmacostApplied MaterialsSunnyvale, CA
June 19, 2013
Outline
• Semiconductor processing
• Spectroscopy
• The plasma
• Spectroscopic measurements
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
Spectroscopy• The plasma is transparent to and unaltered
by mm/smm radiation, background and clutter free
• 10-100 mtorr pressure is ideal for high sensitivity and specificity
• Species of interest must have a dipole moment
• Long wavelength is diffraction limited, restraining spatial resolution
• Combinations of argon, oxygen, and octofluorocyclobutane (C4F8) gases are flowed through a vacuum chamber.
• Plasma is initiated through an induction coil by an rf generator typically with 100 W power.
• The plasmas generated contain many ions, radicals, and molecules, most notably: CF2, CO, COF2, and CF*.
The Plasma
What are the variables?
• Flow rates for Ar, O2, and C4F8.
• Power delivered to plasma
• Pressure
What can be measured?
• Abundances of plasma products which have dipole moments
• Temperature
Oxygen Flow
-60
-50
-40
-30
-20
x10-3
188.954188.952188.950188.948188.946GHz
0 sccm .50 sccm 1.0 sccm 2.0 sccm 5.0 sccm
CF2 CO
COF2
CF
18.5 mtorr22.3 mtorr24 mtorr29 mtorr42 mtorr
O2: variableC4F8: 20 sccmAr: 12 sccm100 W
185.9885 194.114132 230.538 206.8505(GHz)
Re
lativ
e I
nte
nsi
ty
(arb
itra
ry z
ero
)
(frequency snippets)
Ar : 30 sccmC4F8 : variableO2 : 0 sccm100 W
600
400
200
0
-200
x10-6
8.0 sccm, 30.0 mtorr 4.0 sccm, 20.3 mtorr 2.0 sccm, 18.8 mtorr 1.0 sccm, 18.0 mtorr 0.5 sccm, 17.5 mtorr
CF2 Spectra vs. C4F8 Flow
307.7252275 GHz
Sca
led
Fra
ctio
nal A
bso
rban
ce
Optical Emission Spectroscopy
Ar : 10 sccmC4F8 : 10 sccm O2 : 10 sccm20.1 mtorr100 W
• Industry standard instrument
• Can see atoms
• Cannot measure densities
800
600
400
200
0
-200
-400
x10-6
Ar : 10 sccmC4F8 : 10 sccm O2 : 10 sccm20.1 mtorr100 W
CO COF2CF2
Calculated Densities:CO: 1.65 x 1013 cm-3
CF2: 1.23 x 1013 cm-3
COF2: 1.73 x 1013 cm-3
DensitiesS
cale
d F
ract
iona
l Ab
sorb
ance
345.7959899 307.7252275 311.7487602(GHz)
(frequency snippets)
CF2 Density vs. C4F8 Flow
CO, CF2, COF2 Densities vs. O2 Flow
0.8
0.6
0.4
0.2
0.0
-0.2
-0.4
300.04300.03300.02300.01300.00GHz
C4F8: 13 sccmO2: 13 sccmAr: 13 sccm
150 W (18 W reflected)13.1 mtorr
Reference Line
COF2 as a thermometer for rotational temperature
(frequency snippets)
Sca
led
Fra
ctio
nal A
bso
rban
ce
Boltzmann Plot
Temperature vs. Power
Summary• SMM absorption spectroscopy can be used as an
in situ probe of the conditions of semiconductor processing plasmas
• Density measurements can be made to further study the behavior of plasma production
• Rotational temperature measurement demonstrated
• Advantages of SMM spectroscopy over industry standard optical emission spectrometer have been demonstrated