MRS meeting- 2011-Moataz (2)

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1 Moataz Bellah M. Mousa , C.J. Oldham, J.S. Jur and G.N . Parsons Department of Chemical and Biomolecular Engineering North Carolina State University MRS/ASM/AVS Meeting NCSU- 2011 Effect of Flow dynamics on Atomic Layer Deposition of Al 2 O 3 and ZnO at Atmospheric Pressure

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2 Introduction Atomic Layer Deposition (ALD) Importance of Atmospheric Pressure Atomic Layer Deposition AP-ALD Flow-tube Reactor Results and Analysis Temperature window for ZnO and Al 2 O 3 ( Ellipsometry measurements) In situ growth study of ZnO and Al 2 O 3 (quartz crystal microbalance) Extra growth? - Gas flow dynamics model Summary Outline Atmospheric Pressure Atomic Layer Deposition (AP-ALD) Is the growth process the same as at low pressure?

Atomic Layer Deposition (ALD): 

Atomic Layer Deposition (ALD) Trimethyl Aluminum (TMA) OH Surface 3 Qing P., et al. Nano Letters, 7 , 719-722 (2007)

Atomic Layer Deposition (ALD) in Semiconductors Industry: 

Atomic Layer Deposition (ALD) in Semiconductors Industry www.nanotechia.org www.greencentrecanada.com Flat-Panel Displays (Thin-Film Electroluminescent) Ritala, M. et al., Chem. Vap. Deposition 1999, 5, 7 Integrated Circuits www. gizmowatch.com Batch vacuum Processing 4

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Printed electronics and Organic solar cells ALD applications can get expanded to Continuous Atmospheric processing 5 http://www.tii.se/projects/ http://www.plusplasticelectronics.com http://flexdisplay.asu.edu/

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6 Isolation Valves To Ventilation To Pump Flow Tube Reactor Heater or Time Pressure, Torr N 2 N 2 N 2 N 2 pump pump Real data at 760 Torr Pressure Control 1-760 Torr Flow tube reactor with variable pressure delivery Tube diam. = 3.5 cm 2 Torr , 0.5 slm Ave. velocity ~ 4m/s TMA H 2 O

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7 0.5slm 760 Torr ZnO 100 °C DEZ/N 2 /H 2 O/N 2 = 2/45/2/45 s Quartz Crystal Microbalance (QCM) at different pressures and flow rates Jur , J. S. & Parsons, G. N. ACS Applied Materials & Interfaces 3 , 299-308 (2011) time (sec) At 5slm residence time drops to 8s, but the extra growth is still observed

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Possible reasons for Extra Deposition… Change in species adsorption/desorption rate (surface reaction kinetics) Insufficient Precursor/ products purge (CVD component) 8

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9 Al 2 O 3 TMA/N 2 /water/N 2 = 2/45/2/45 s (100 cycles) 760 Torr 2 Torr

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10 ZnO DEZ/N 2 /water/N 2 = 2/45/2/45 s (100 cycles) 760 Torr 2 Torr The pressure dependence of “extra growth” is temperature independent between 40-210 0 C

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Possible reasons for Extra Deposition… Change in species adsorption/desorption rate (surface reaction kinetics) Insufficient Precursor/ products purge (CVD component) 11

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12 * Boundary layer for flat surface outside pipe *Organometallic Vapor-Phase Epitaxy, 2 nd edition, Academic press, 1999 * Time needed for species to diffuse through Boundary Layer: t D  BL 2 / D H2O-N2 ; t D  P At fixed flow, Pressure ↑, Density ↑, but U ∞ ↓ BL independent of P Fick’s first law: D H2O-N2  1/P H 2 O Flux from surface during purge step (molecules/cm 2 sec) High Pressure, need to: Increase purge time and/or Increase gas velocity, U ∞ Substrate y z D H2O BL Gas flow U ∞

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14 Levy’s system- new ALD reactor design approach Substrate TMA H 2 O N 2 Levy et al, APL 92, 192101 2008 Levy Flow space: 30-100 m m

AP-ALD Al2O3 on Cotton Hydrophilic to Hydrophobic surface: 

AP-ALD Al2O3 on Cotton Hydrophilic to Hydrophobic surface 2 cycles, 760 Torr , 5 slm N 2 Front Back 2 cycles, 2 Torr , 500 sccm N 2 Hyde et al, Langmuir 2009, 26, 2550. 15

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Summary and Conclusions Flow reactor at 760 Torr: Excess growth for Al 2 O 3 and ZnO Not dependent on substrate temperature: 40 - 210  C Boundary layer, diffusivity are important to understand pressure effects. Increasing flow velocity lead to a more efficient ALD process under atmospheric pressure. New design for AP-ALD reactors is required to account for the required high velocity without the need for huge impractical gas flow rate. CMMI Nanomanufacturing 16

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The Parsons’ Group and Dr. Jesse Jur Acknowledgment 17

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Now Near future Through Continuous Fast Atm. ALD

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19 Runs Ellipsometry (A 0 ) (per cycle) QCM ( ng /cm 2 ) (per cycle) 2 torr , 100 cycles 1.024 53.3 Atm. , 50cycles, 5slm 1.612 66 Atm , 50cycles, 10slm 1.516 62 Combining Ellipsometry and QCM measurements (Al 2 O 3 ) Runs Ellipsometry (A 0 ) (per cycle) QCM ( ng /cm 2 ) (per cycle) Density ( gm /cm 3 ) (Calculated) 2 torr , 100 cycles 1.024 53.3 5.21 Atm. , 50cycles, 5slm 1.612 66 4.09 Atm , 50cycles, 10slm 1.516 62 4.09 Different species (more parasitic components)??

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Atomic Force Microscopy (AFM)

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