In-Situ FTIR Spectroscopy and Metrology of a Tungsten CVD Process A. Singhal, L. Henn-Lecordier and J. N. Kidder Jr. University of Maryland, College Park, MD C.A. Gogol, J.F. Kushneir Inficon, Inc. East Syracuse, NY Research supported by 1 AVS 2001 National Symposium, MS-TuA9
Applications for Gas-Phase Diagnostics Analysis of Process Chemistry Reactants and By-Products Monitoring and Control of Gas-Phase Stoichiometry (upstream) Detection of Reaction Products and Reactant (downstream) Real-Time Rate Metrology and Process Control Fault Detection and Fault Management Mass Spectrometry (Residual Gas Analysis) Fourier Transform Infrared Spectroscopy Acoustic Sensing Ultra-Violet Spectroscopy 2 AVS 2001 National Symposium, MS-TuA9
Fourier Transform Infrared Spectroscopy Advantages Non intrusive to process chemistry Applicable for detection over wide range of partial pressures (1-1000 Torr) Chemically identity and concentration are detectable Drawbacks Cannot detect monoatomic and homonuclear diatomic molecules Cost and size of commercial FTIR systems 3 AVS 2001 National Symposium, MS-TuA9
Quantitative Analysis Using FTIR Transmittance versus frequency obtained from the Fourier transform of an interferogram Sample Cell inlet IR beam outlet Transmittance Absorbance I Intensity with sample in beam I o Intensity with no sample (e.g. N 2 ) ε Absorptivity l Pathlength = log Io log I 10 10 c Concentration = ω ) T A I o A = εlc (Beer s Law) 4 AVS 2001 National Symposium, MS-TuA9
Spectrometer and Gas Sampling Cell To Process Pumps From CVD Reactor O-ring Sealed KBr Window Interferometer (Design & Prototypes) Purge Gas Purge Gas ZnSe Convex Lens (f:25.4 mm, dia 25.4 mm) KBr Biconvex Lens (f: 25.4mm, Dia: 25.4 mm) IR Source 25.4 mm 87 mm 31 mm IR Beam 22 mm 22.5 mm 100mm 241 mm 85 mm 12.5 mm O-ring Sealed KBr Window Aluminum Slits 44.5 mm Sampling Cell 50 mm 54 mm 23 mm MCT Detector 25.4 mm 50 mm 65 mm 132 mm LN2 Cooled Dewar Designs and Prototypes Interferometer In-situ sampling cell and spectrometer components Detector Source Mirror Mirror Detector Beam splitter Source Small size, Cost-Effective 1 cm -1 resolution Mirror Mirror Stainless steel UHV compatible cell O-ring sealed KBr windows with purge KBr, ZnSe convex lenses Detector: MCT LN2 cooled detector Source: Nickel-chrome element mini igniter 5 AVS 2001 National Symposium, MS-TuA9
Initial Experiments SF 6 Transmittance Spectrum Absorbance versus SF 6 partial pressure Transmittance 1.5 P SF6 =868 mtorr 1.0 0.5 948 615 0.0 4000 3500 3000 2500 2000 1500 1000 500 Absorbance ( A.U.) 2.5 2.0 1.5 1.0 0.5 0.0 600 500 400 300 200 150 125 100 91 75 66 55 48 43 pressure (mtorr) 910 920 930 940 950 960 970 Wavenumber (cm -1 ) Wavenumber (cm -1 ) 6 AVS 2001 National Symposium, MS-TuA9
Linearity of Absorbance with Partial Pressure: SF 6 35 5 Absorbance Area of the Peak at 948 cm -1 A: Absorbance Peak Height 30 25 20 15 10 5 A<1 A>1 0 0 200 400 600 800 1000 Pressure of SF 6 in the Optical Cell (mtorr) Absorbance Area of Peak at 615 cm -1 4 3 2 1 R=0.99693 0 0 200 400 600 800 1000 Pressure of SF 6 in the optical cell (mtorr) 7 AVS 2001 National Symposium, MS-TuA9
Integration of FTIR on ULVAC CVD Cluster Tool WF 6, H 2, N 2 WF ( g ) + H ( g ) W ( s ) 6HF( g ) 6 3 2 + N 2 (Heater) Sampling System ULVAC CVD System 10 Torr Diaphragm Pump COMPOSER 100 Torr Window purge (N 2 ) FTIR MFM, variable valve P Process pumps Process pumps 8 AVS 2001 National Symposium, MS-TuA9
Tungsten-CVD Growth Rate Metrology H 2 Reduction W-CVD Process WF ( g ) + H ( g ) W ( s ) 6HF( g 6 3 2 + ) Reaction rate measured via: WF 6 depletion signal HF production signal * Prior approaches: Acoustic Sensing and Mass Spectroscopy * Gougousi et al., J. Vac. Sci.Technol. B 18, 1352-1363 (2000) Henn-Lecordier, et al., J. Vac. Sci.Technol A 19 (2), 621-626 (2001) 9 AVS 2001 National Symposium, MS-TuA9
Absorption Spectrum of WF 6 0.20 WF6 (712.5cm-1 ) 0.15 0.10 0.05 Peak at 712.5 cm -1 used for rate metrology Absorbance (A.U) WF6 (1481.53 cm-1 ) WF6 (1388.26 cm-1 ) WF6 (809.61cm-1 ) WF6 (933.83 cm-1 ) 0.00 3500 3000 2500 2000 1500 1000 Wavenumber(cm -1 ) 10 AVS 2001 National Symposium, MS-TuA9
WF 6 : Absorbance versus partial pressure Absorbance 0.6 0.893 Torr 0.703 Torr 0.5 0.495 Torr 0.355 Torr 0.214 Torr 0.4 0.3 0.2 0.1 0.0 625 650 675 700 725 750 Absorbance at 712.5 cm-1 (peak height) 0.6 0.5 0.4 0.3 0.2 0.1 0.0 R=0.99909 H 2 =60 sccm N 2 =150 sccm N 2 purge=19.8 sccm P CELL =33 Torr 0.0 0.2 0.4 0.6 0.8 1.0 Wavenumber (cm -1 ) WF 6 partial pressure in cell (Torr) 11 AVS 2001 National Symposium, MS-TuA9
Run-to-Run Reproducibility 1.0 WF 6 Absorbance (712.5 cm -1 ) 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 P WF6 = 0.54 Torr Pressure ratio 0.17/0.54 = 0.31 Absorbance ratio 0.14/0.43 = 0.32 P P WF 6 WF 6 = 0.703Torr = 0.214Torr 0.17 Torr 0.0 0 2 4 6 8 10 Process Run Number 12 AVS 2001 National Symposium, MS-TuA9
In-situ FTIR Spectra 0.2 Absorbance HF (3700-4200) During W deposition SiF 4 (1030.8) WF 6 (712.5) N 2 purge 0.0 Unheated wafer 4000 3500 3000 2500 2000 1500 1000 Wavenumber(cm -1 ) 13 AVS 2001 National Symposium, MS-TuA9
WF 6 signal (712.5 cm -1 ) vs. flow conditions 1.0 0.8 N 2 Unheated Wafer During W Deposition Absorbance 0.6 0.4 0.2 0.0 740 720 700 680 Wavenumber (cm -1 ) 14 AVS 2001 National Symposium, MS-TuA9
Deposition Process WF ( g ) + H ( g ) W ( s ) 6HF( g 6 3 2 + ) STEP Time (sec) WF 6 (sccm) H 2 (sccm) N 2 [process] (sccm) N 2 [heater] (sccm) P rxtr (Torr) P cell (Torr) 1 40 36.5 220 200 75 0-10 100 2 600 10 60 0 75 10 100 Window purge in sampling cell: 100 sccm Weight measurement by ex-situ balance 15 AVS 2001 National Symposium, MS-TuA9
WF 6 concentration versus time Absorbance at 712.5 cm -1 (peak height) 1.2 450 o C 1.0 0.8 0.6 0.4 0.2 430 o C 415 o C 410 o C 405 o C 400 o C 395 o C 390 o C 0.0 0 150 300 450 600 750 900 Time (sec) Area under the curve is proportional to the amount of unreacted WF 6 downstream of the wafer 16 AVS 2001 National Symposium, MS-TuA9
Correlation of WF 6 signal to film weight Time Integrated Height at 712.5 cm-1 680 660 640 620 600 580 390 o C 390 o C R=-0.99672 395 o C 395 o C 400 o C 400 o C 405 o C 410 o C 410 o C 0.14 0.15 0.16 0.17 0.18 0.19 0.20 0.21 Mass of deposited tungsten (g) 17 AVS 2001 National Symposium, MS-TuA9
Reaction product: HF HF signal (band) versus time Correlation of time integrated HF signal to deposited mass Absorbance Signal of HF 0.2 0.1 0.0-0.1 450 C 430 C 415 C 410 C 405 C 400 C 395 C 390 o C Integrated HF absorption peak height 200 180 160 140 120 100 80 60 40 20 R 0.92804-0.2 0 200 400 600 800 1000 1200 Time (sec) 0 0.0 0.1 0.2 0.3 Film Mass (g) 18 AVS 2001 National Symposium, MS-TuA9
Reaction product: SiF 4 SiF 4 signal (1030 cm -1 ) versus time Correlation of time integrated SiF 4 signal to deposited mass 30 Height of SiF 4 absorbance (1030 cm -1 ) 0.06 410 C 405 C 0.05 400 C 395 C 0.04 390 C 0.03 0.02 0.01 0.00-0.01-0.02 0 150 300 450 600 750 900 Time (sec) Time Integrated SiF 4 Signal 25 20 15 10 5 R=0.9728 0 0.00 0.05 0.10 0.15 0.20 Mass of Tungsten deposited (g) 19 AVS 2001 National Symposium, MS-TuA9
Conclusion Novel compact FTIR Spectrometer integrated with a W-CVD tool. Linear sensor response to downstream reactant concentration. Signal was stable and reproducible over several process runs. Real-time, in-situ measurements of reactant consumption (WF 6 ) correlated to film thickness with 1% error. Signals for reaction products (HF, SiF 4 ) detected and correlated to thickness but with a higher signal to noise. Next step: Integration of FTIR sensor directly into exhaust line End-point control of film thickness 20 AVS 2001 National Symposium, MS-TuA9
Reaction products: HF and SiF 4 (?) HF Production SiF 4 Production Absorbance (A.U.) 0.10 0.05 0.00 Array of peaks of HF in the region 3700-4200 cm -1 Only N 2 flowing Cold Wafer Step W-deposition process Absorbance (A.U) 0.10 0.08 0.06 0.04 0.02 Peak of SiF 4 at 1030 cm -1 Only N 2 flowing Cold Wafer Step W-deposition process 0.00-0.05 4400 4200 4000 3800 3600 Wavenumber (cm -1 ) -0.02 1080 1060 1040 1020 1000 980 Wavenumber (cm -1 ) Generation of SiF 4 attributed to reaction between HF and quartz component in the reactor 21 AVS 2001 National Symposium, MS-TuA9