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

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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

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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.

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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)

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NH3 CH2F2 CH2F2

(0.0154 GHz snippets)

50 mtorr N2/CH2F2/SF6 plasma1.0

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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

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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

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NH3 (572.49815 GHz) NH2 (644.33912 GHz)

(0.0307 GHz snippets)

20 mtorr NH3 plasma, relative power: 1x 3x 5x 10x 20x

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NH2 (644.33912 GHz)

(0.0307 GHz snippets)

NH2 measured

• A wider NH2 snippet shows 3 lines surrounding the center we used from Splatalogue

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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

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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

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NH3 (572.49815 GHz) NH2 (644.33912 GHz)

(0.0614 GHz snippets)

NH3 pulsed plasma, 20 mtorr base duty cycle increased duty cycle

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NH2 (644.33912 GHz)

(0.0614 GHz snippets)

Flow Ratio2.5

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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

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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)