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

Outline Semiconductor processing Spectroscopy The plasma Spectroscopic measurements

Semiconductor Chip

Semiconductor Processing Cleaning Deposition Lithography Etching

Spectroscopy The plasma is transparent to and unaltered by mm/smm radiation, background and clutter free 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 (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

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

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 (GHz) Relative Intensity (arbitrary zero) (frequency snippets)

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

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

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 cm -3 CF 2 : 1.23 x cm -3 COF 2 : 1.73 x cm -3 Densities Scaled Fractional Absorbance (GHz) (frequency snippets)

CF 2 Density vs. C 4 F 8 Flow

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

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

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