In-Situ FTIR Spectroscopy and Metrology of a Tungsten CVD Process

Transcription

1 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

2 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

3 Fourier Transform Infrared Spectroscopy Advantages Non intrusive to process chemistry Applicable for detection over wide range of partial pressures ( 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

4 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 c Concentration = ω ) T A I o A = εlc (Beer s Law) 4 AVS 2001 National Symposium, MS-TuA9

5 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

6 Initial Experiments SF 6 Transmittance Spectrum Absorbance versus SF 6 partial pressure Transmittance 1.5 P SF6 =868 mtorr Absorbance ( A.U.) pressure (mtorr) Wavenumber (cm -1 ) Wavenumber (cm -1 ) 6 AVS 2001 National Symposium, MS-TuA9

7 Linearity of Absorbance with Partial Pressure: SF Absorbance Area of the Peak at 948 cm -1 A: Absorbance Peak Height A<1 A> Pressure of SF 6 in the Optical Cell (mtorr) Absorbance Area of Peak at 615 cm R= Pressure of SF 6 in the optical cell (mtorr) 7 AVS 2001 National Symposium, MS-TuA9

8 Integration of FTIR on ULVAC CVD Cluster Tool WF 6, H 2, N 2 WF ( g ) + H ( g ) W ( s ) 6HF( g ) 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

9 Tungsten-CVD Growth Rate Metrology H 2 Reduction W-CVD Process WF ( g ) + H ( g ) W ( s ) 6HF( g ) 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, (2000) Henn-Lecordier, et al., J. Vac. Sci.Technol A 19 (2), (2001) 9 AVS 2001 National Symposium, MS-TuA9

10 Absorption Spectrum of WF WF6 (712.5cm-1 ) Peak at cm -1 used for rate metrology Absorbance (A.U) WF6 ( cm-1 ) WF6 ( cm-1 ) WF6 (809.61cm-1 ) WF6 ( cm-1 ) Wavenumber(cm -1 ) 10 AVS 2001 National Symposium, MS-TuA9

11 WF 6 : Absorbance versus partial pressure Absorbance Torr Torr Torr Torr Torr Absorbance at cm-1 (peak height) R= H 2 =60 sccm N 2 =150 sccm N 2 purge=19.8 sccm P CELL =33 Torr Wavenumber (cm -1 ) WF 6 partial pressure in cell (Torr) 11 AVS 2001 National Symposium, MS-TuA9

12 Run-to-Run Reproducibility 1.0 WF 6 Absorbance (712.5 cm -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 Process Run Number 12 AVS 2001 National Symposium, MS-TuA9

13 In-situ FTIR Spectra 0.2 Absorbance HF ( ) During W deposition SiF 4 (1030.8) WF 6 (712.5) N 2 purge 0.0 Unheated wafer Wavenumber(cm -1 ) 13 AVS 2001 National Symposium, MS-TuA9

14 WF 6 signal (712.5 cm -1 ) vs. flow conditions N 2 Unheated Wafer During W Deposition Absorbance Wavenumber (cm -1 ) 14 AVS 2001 National Symposium, MS-TuA9

15 Deposition Process WF ( g ) + H ( g ) W ( s ) 6HF( g ) STEP Time (sec) WF 6 (sccm) H 2 (sccm) N 2 [process] (sccm) N 2 [heater] (sccm) P rxtr (Torr) P cell (Torr) Window purge in sampling cell: 100 sccm Weight measurement by ex-situ balance 15 AVS 2001 National Symposium, MS-TuA9

16 WF 6 concentration versus time Absorbance at cm -1 (peak height) o C o C 415 o C 410 o C 405 o C 400 o C 395 o C 390 o C 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

17 Correlation of WF 6 signal to film weight Time Integrated Height at cm o C 390 o C R= o C 395 o C 400 o C 400 o C 405 o C 410 o C 410 o C Mass of deposited tungsten (g) 17 AVS 2001 National Symposium, MS-TuA9

18 Reaction product: HF HF signal (band) versus time Correlation of time integrated HF signal to deposited mass Absorbance Signal of HF C 430 C 415 C 410 C 405 C 400 C 395 C 390 o C Integrated HF absorption peak height R Time (sec) Film Mass (g) 18 AVS 2001 National Symposium, MS-TuA9

19 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 ) C 405 C C 395 C C Time (sec) Time Integrated SiF 4 Signal R= Mass of Tungsten deposited (g) 19 AVS 2001 National Symposium, MS-TuA9

20 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

21 Reaction products: HF and SiF 4 (?) HF Production SiF 4 Production Absorbance (A.U.) Array of peaks of HF in the region cm -1 Only N 2 flowing Cold Wafer Step W-deposition process Absorbance (A.U) Peak of SiF 4 at 1030 cm -1 Only N 2 flowing Cold Wafer Step W-deposition process Wavenumber (cm -1 ) 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