Spatially Distributed Experimentation to Understand ALD Process Chemistry

1. Spatially Distributed Experimentation to Understand ALD Process Chemistry Rubloff Research Group Accomplishments

2. Accomplishment Designed and implemented ALD reactor to achieve spatial distribution of impingement fluxes Demonstrated spatial gradients in thickness and material properties Significance Atomic layer deposition (ALD) is widely sought for its atomic-scale thickness control and unprecedented uniformity and conformality Precursor dose permutations add complexity to ALD process recipes, where underlying surface chemistry is not well understood Spatially distributed ALD enables rapid investigation of ALD process/dose recipes and optimization of material properties Researchers involved Laurent Henn-Lecordier, Gary W. Rubloff Support NSF IMI, PAT-IRST MicroCombi, Laboratory for Physical Sciences, MKS Instruments Spatially Distributed Atomic Layer Deposition (ALD) Rubloff: Spatially distributed atomic layer deposition

3. Intellectual merit Atomic layer deposition (ALD) enables atomic-level control of ultrathin film deposition over 3-D surfaces. It relies on alternating doses of molecules that saturate surface sites to achieve these benefits. ALD surface chemistry is not well-understood, so finding suitable dose recipes is hampered by the numerous permutations available. We have designed and implemented an ALD reactor design that uses cross-flow of precursor gases to achieve combinatorial variation of surface reaction conditions across a 4” wafer. We have demonstrated the fabrication of spatial gradients in thickness and material properties for an Al2O3 ALD process. Coupled with rapid characterization of across-wafer material and electrical properties, the cross-flow ALD reactor provides a platform for addressing the relation of ALD process chemical conditions to resulting material properties. Spatially Distributed Atomic Layer Deposition (ALD) Rubloff: Spatially distributed atomic layer deposition

4. Broader Impacts Atomic layer deposition (ALD) is widely sought for its atomic-scale thickness control and unprecedented uniformity and conformality, key benefits for existing technologies (e.g. semiconductors) and for a broad set of nanotechnology applications. The numerous precursor dose permutations inhibits fundamental understanding of ALD surface chemistry and process applications. Our cross-flow ALD design and associated material characterization provide a platform for rapid learning in ALD process behavior and enhanced development of ALD applications. Close collaboration with Italy group (FBK-irst) has been essential in chemical, compositional, and structural characterization of ALD layers. TMA dose Optimal properties saturating doses H2O dose Spatially Distributed Atomic Layer Deposition (ALD) Rubloff: Spatially distributed atomic layer deposition

5. Metal precursor exposure Purge Initial surface L L M M L L L L LH L L L L L L L M M M M M L L L L L L L L L L O O O O OH OH OH OH OH SUBSTRATE H2O H2O LH H2O Growth of 1 monolayer of metal oxide OH OH OH OH OH M M M OH M M L O O O O O O O O O Purge Water exposure Atomic Layer Deposition (ALD) • Alternating doses of chemical precursors, repeated approximately once per atomic layer • Self-limiting adsorption/reaction for each dose 08/25/05 5 Rubloff: Spatially distributed atomic layer deposition

6. ALD mini- reactor Cross-Flow ALD Reactor Z-axis pneumatic actuator UHV chamber 10-5torr Moveable cap 100 mm wafer 0.1 torr MKS RGA Substrate heater 50µm orifice Gas Outlet Gas Inlet L. Henn-Lecordier - 54th AVS TF-Mo M10 - 10/15/07 6 Rubloff: Spatially distributed atomic layer deposition

7. 2 . 2 0 E - 0 1 0 1 8 0 2 . 0 0 E - 0 1 0 1 6 0 1 . 8 0 E - 0 1 0 1 4 0 1 . 6 0 E - 0 1 0 1 2 0 1 . 4 0 E - 0 1 0 1 0 0 1 . 2 0 E - 0 1 0 8 0 0 2 4 6 8 1 0 0 2 4 6 8 1 0 P o s i t i o n a c r o s s w a f e r [ c m ] P o s i t i o n a c r o s s w a f e r [ c m ] 8 . 8 1 . 7 4 8 . 6 8 . 4 1 . 7 2 8 . 2 8 . 0 1 . 7 0 7 . 8 7 . 6 1 . 6 8 7 . 4 7 . 2 1 . 6 6 7 . 0 6 . 8 1 . 6 4 0 2 4 6 8 1 0 0 2 4 6 8 1 0 P o s i t i o n a c r o s s w a f e r [ c m ] Across-Wafer Al2O3 ALD Film Properties Under-dose H2O conditions (0.8µmol) Thickness (Å) Capacitance (F) Permittivity Refractive index P o s i t i o n a c r o s s w a f e r [ c m ] Rubloff: Spatially distributed atomic layer deposition

8. Saturating H2O dose (1.25 μmol) Al2O3 ALD: TMA under-dosing • Moderate under-dosing TMA causes uniformity degradation & depletion • Larger under-dosing TMA condition generates very strong nonuniformity, nearly discontinuous profile • Enhance growth rate at inlet with dramatic depletion at outlet • Possibly OH oversaturation at inlet which getters and reacts the under-dosed TMA 8 Rubloff: Spatially distributed atomic layer deposition

9. Under-dosed TMA (0.33 μmol) 1 Å/cycle Al2O3 ALD: H2O under-dosing • H2O/TMA < 2 • improved uniformity but mean thickness decreases due to insufficient reactant supply • H2O/TMA > 2 • profound nonuniformity at front and rear, with limited uniformity at middle 9 Rubloff: Spatially distributed atomic layer deposition