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