Oct 25-29, 1999, AVS National Symposium, Seattle Chemical Sensing and Sensor-based Metrology Using Mass Spectrometry in Multi-Component Reaction Systems Y. Xu, T. Gougousi, N. Gupta, J. N. Kidder, Jr., and G. W. Rubloff
Why Real-Time Chemical Sensing? Provides a wealth of useful information regarding the time evolution of the process and reaction mechanism Provides the basis to achieve real-time thin film thickness metrology, and process control. Enables simultaneous fault management. 2
Chemical Sensing Issues in Multi-component Chemical Process Challenges in chemical sensing Sensor choice (Mass Spectrometer, FTIR, Acoustic, etc) Sensor placement (downstream or direct sampling) Selection of appropriate species for metrology development. Wall Chemistry Reactions Reagent condensation Sensor Chemistry Reactions in the ionizer region of the mass spectrometer 3
Multi-Component Chemical Process: W CVD from / Selective W CVD process Dynamic equipment and process* simulation Sensor study Chemical sensing and film thickness metrology in W CVD process WF + H W + 6 HF 6 3 2 * Based on Hsieh s model J. J. Hsieh, "Kinetic model for the chemical vapor deposition of tungsten in the silane reduction process", J. Vac. Sci. Technol. A 11 (6), pp. 3040-46, (Nov/Dec 1993). 4
Multi-Component Chemical Process: W CVD from / Chemical Sensing using mass spectrometry in W CVD on Ulvac ERA-100 P=0.5 Torr BP 300µ orifice 60µ orifice 30µ orifice P=10-6 Torr QMS Pressure control valve Reactor exhaust Baratron Ion gauge to drag stage Turbo pump 50 l/s WF + H W + 6 HF 6 3 2 5
Process Issues for Metrology Our Process Ulvac ERA-100 selective W CVD Selective process at pressure less than 1 Torr Initially, less than 1% reactant conversion rate ( and ) Simulations indicated better reactant utilization at low flow rates: Industry standard NOVELLUS, AMAT blanket W CVD Blanket process at pressure of about 40 Torr About 50% reactant conversion rate Conversion rate (%) 60 50 40 30 20 10 0 : 200 sccm Temp. :400 0 C Pres. : 0.5 Torr Simulation results Low / ratio required for conformal film deposition 2 4 6 8 10 12 14 16 18 20 22 / flow rate ratio 5X flow rate reduction Conversion rate (%) 60 50 40 30 20 10 0 : 40 sccm Temp. :400 0 C Pres. : 0.5 Torr Simulation results Low / ratio required for conformal film deposition 2 4 6 8 10 12 14 16 18 20 22 / flow rate ratio 6
Selection of Species for Mass Spectrometry-based Metrology Product generation : HF generation Significant background due to reaction in ionizer of the mass spectrometry Reactant depletion : depletion and/or depletion Significant background due to low conversion rate WF + H W + 6 HF 6 3 2 7
Multiple Reaction Regions in WCVD process from / Process reaction Sensor (ionizer)reactions Example + 3 W + 6HF 6HF + e 6HF + + 2e + e WF 5+ + F +2e + e + + 2e F + H + 2 HF + + H Hot wafer in Reactor WF H 6 2 Mass Spec. HF HF Cold wafer in Reactor WF H 6 2 Mass Spec. HF 8
Cold wafer cycle to calibrate background and sensor drift H2 40sccm 40sccm 40sccm WF6 0sccm 10sccm 0sccm Pressure 0.5Torr 0.5Torr 0.5Torr Temperature. Ion current for (Amp) 8.00E-011 6.00E-011 4.00E-011 2.00E-011 HF 40sccm 200sccm 10sccm 0sccm 0.5Torr 0.5Torr Step 1 Step 2 Step 3 Step 4 Step 5 flush Cold wafer cycle Heating Hot wafer cycle depletion HF generation Cooling 1.20E-011 9.00E-012 6.00E-012 3.00E-012 Ion current for HF(Amp) 0.00E+000 0.00E+000 0 400 800 1200 1600 Time(sec.) 9
Mass Spectrometry-based deposition rate metrology 2.5E-10 Conditioning cycle 1st wafer 2nd wafer 3rd wafer 1.2E-11 Recipe Temp.:400 0 C Pres. :0.5 Torr : 40sccm : 10sccm Ion current for (Amp) 2E-10 1.5E-10 1E-10 HF Cold Hot Cold Hot Cold C Hot D 9E-12 6E-12 3E-12 Ion current for HF(Amp) 5E-11 A B 0 0 1000 2000 3000 4000 5000 6000 Time(Sec.) 0 Film Thickness B-A A * Dep. time Film Thickness C-D C Dep. * time 10
Mass Spectrometry-based deposition rate metrology Metrology from HF Signal 3000 W film thickness (A) 2500 2000 1500 1000 Thickness=537.6(+/- 20.1)* S (HF) +315.6(+/- 46.6) R 2 =0.95 SD=127A 500 0 Initial nucleation of W seed layer by Si reduction of 0 1 2 3 4 HF signal * Dep. Time (Min.) 11
Mass Spectrometry-based deposition rate metrology Metrology from Signal 3000 W film thickness (A) 2500 2000 1500 1000 Thickness= 5719(+/- 477)S H2 +471(+/- 90) R 2 =0.79 SD=260A 500 Initial nucleation of W seed layer by Si reduction of 0 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 signal * Dep. Time (Min.) 12
Conclusions and Acknowledgment In multi-component CVD process, different species could be chosen for metrology. Reactant depletion (, ) Product generation (HF) Mass spectrometry-based thickness metrology has been demonstrated About 6-7% accuracy from HF signal Expected to be better for higher conversion rates blanket W CVD process (industry standard) Cold wafer cycle implemented for metrology Calibrate sensor drift, measure background In-situ sensor calibration system under development-results promising Conditioning cycle before actual deposition process reduced the wall effects. Acknowledgments: NIST/Dr. Charles Tilford Leybold Inficon/Dr. Bob Ellefson, Dr. Louis Frees NSF SRC/TI 13