1. Submillimeter spectroscopic diagnostics in a semiconductor processing plasma Yaser H. Helal, Christopher F. Neese, Jennifer A. Holt, Frank C. De Lucia Department of Physics The Ohio State University Paul R. Ewing, Phillip J. Stout, Michael D. Armacost Applied Materials Sunnyvale, CA June 19, 2013

2. Outline Semiconductor processing Spectroscopy The plasma Spectroscopic measurements

3. Semiconductor Chip http://www.mikeseeman.com/index.php?id=engineering/research

4. Semiconductor Processing http://www.atp.nist.gov/eao/gcr03-844/append-a.htm Cleaning Deposition Lithography Etching

5. 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

6. Combinations of argon, oxygen, and octofluorocyclobutane (C 4 F 8 ) 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: CF 2, CO, COF 2, and CF*. The Plasma

7. What are the variables? Flow rates for Ar, O 2, and C 4 F 8. Power delivered to plasma Pressure What can be measured? Abundances of plasma products which have dipole moments Temperature

8. Oxygen Flow 18.5 mtorr 22.3 mtorr 24 mtorr 29 mtorr 42 mtorr O 2 : variable C 4 F 8 : 20 sccm Ar: 12 sccm 100 W 185.9885 194.114132 230.538 206.8505 (GHz) Relative Intensity (arbitrary zero) (frequency snippets)

9. Ar : 30 sccm C 4 F 8 : variable O 2 : 0 sccm 100 W CF 2 Spectra vs. C 4 F 8 Flow 307.7252275 GHz Scaled Fractional Absorbance

10. Optical Emission Spectroscopy Ar : 10 sccm C 4 F 8 : 10 sccm O 2 : 10 sccm 20.1 mtorr 100 W Industry standard instrument Can see atoms Cannot measure densities

11. Ar : 10 sccm C 4 F 8 : 10 sccm O 2 : 10 sccm 20.1 mtorr 100 W COCOF 2 CF 2 Calculated Densities: CO: 1.65 x 10 13 cm -3 CF 2 : 1.23 x 10 13 cm -3 COF 2 : 1.73 x 10 13 cm -3 Densities Scaled Fractional Absorbance 345.7959899 307.7252275 311.7487602 (GHz) (frequency snippets)

12. CF 2 Density vs. C 4 F 8 Flow

13. CO, CF 2, COF 2 Densities vs. O 2 Flow

14. C 4 F 8 : 13 sccm O 2 : 13 sccm Ar: 13 sccm 150 W (18 W reflected) 13.1 mtorr Reference Line COF 2 as a thermometer for rotational temperature (frequency snippets) Scaled Fractional Absorbance

15. Boltzmann Plot

16. Temperature vs. Power

17. 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