Fundamental Aspects of Atomic Layer Deposition (ALD) and Molecular Layer Deposition (MLD) Steven M. George 1,2,3, Victor M. Bright 1,4,Y. C. Lee 1,4 1 DARPA Center on Science and Technology for Integrated Micro/Nano-Electromechanical Transducers (imint) 2 Department of Chemistry and Biochemistry 3 Department of Chemical and Biological Engineering 4 Department of Mechanical Engineering University of Colorado, Boulder, CO 80309, USA Steven.George@colorado.edu d Victor.Bright@colorado.edu leeyc@colorado.edu DARPA/MTO Workshop Materials and Technologies for 21st Century MEMS and NEMS Miami, FL; January 8, 2008 1
Contents Atomic Layer Deposition - ALD for micro-scaled devices - ALD for nano-scaled devices - ALD for barrier coating Molecular Layer Deposition - Nylon 66 Progress, Opportunities and Challenges Summary 2
Atomic Layer Deposition Viscous Flow Reactor N 2 H 2 O Gas Switching Valves Heated Substrates Quartz Microbalance Sample Loading Clean Area Class 100 TMA Flow Tube Heaters Throttle Valve Pump 3
ALD Atomic Layer Deposition A: Al-OH* + Al(CH 3 ) 3 Al-O-Al-(CH 3 ) 2* + CH 4 Trimethyl Aluminum (TMA) A) Al(CH 3 ) 3 A) OH OH OH CH 3 Al CH 3CH3 CH 4 CH 3 Al CH 3 CH CH 3 3 CH Al 3 CH Al 3 OH OH OH B: Al-CH 3* + H 2 O Al-OH * + CH 4 CH 3 Water B) Al Al CH 3 CH CH3 Al CH 3 3 H 2 O CH 3 OH OH OH H 2 O CH 4 H 2 O OH Al CH CH OH OH 3 3 CH CHAl 3CH3 Al CH 3 3 OH OH OH 4
Thickness (Å) 4000 3500 3000 2500 2000 1500 1000 500 Al 2 O 3 ALD Film Thickness Measured Using Ellipsometer and Stylus Profiler Ellipsometer Stylus Profiler Temperature = 177 C Timing = 1-5-1-5 Si(100) Substrates Al 2 O 3 Growth Rate = 1.29Å/cycle Å/Cycle Precise thickness control Excellent step coverage Conformal deposition i on high aspect ratio structures Pinhole-free deposition Extendible to larger substrates No particle generation Low temperature process (< 150 or even 70 o C) Nano-scale multi-layer structures 0 0 500 1000 1500 2000 2500 3000 AB Cycles M. Ritala et al., Chem. Vap. Depositions, 5, 7 (1999). 5
ALD on MEMS Poly 0 Nitride 3.5 μm Poly1 + Poly2 100nm ZnO ALD Layer N. Hoivik, PhD Thesis, CU-Boulder, 2002 Si Substrate 60nm Al 2 O 3 ALD Layer Note: Sample cut by FIB, re-deposition occurs under P1+P2 structure Excellent conformal interface and adhesive bond between the ALD deposited material and the polysilicon layers. The uniformity and thickness control of the ALD process is far superior to most common deposition processes. 6
ALD-Enabled MEMS? High Quality Coatings with Precise Surface Properties Resistivity of High quality coatings 10 17 ALD ZnO/Al 2 O 3 Alloy Films achieved easily: Resistiv vity (Ohm cm) 10 15 10 13 10 11 10 9 10 7 10 5 10 3 10 1 10-1 10-3 Four Point Probe Mercury Probe 0 20 40 60 80 100 Zn Content, Zn/(Zn+Al) (%) ALD for Electrical l Insulation ALD for Dielectric Contact ALD for Anti-Stiction ALD for Charge Dissipation ALD for Optical Reflectivity ALD for Wear-Resistance ALD for Creep-Resistance ALD for Corrosion-Resistance ALD for Crack-Resistance 108 Reference: J.W. Elam, D. Routkevitch and S.M. George, "Properties of ZnO/Al 2 O 3 Alloy Films Grown Using Atomic Layer Deposition Techniques", J. Electrochem. Soc. 150, G339-G347 (2003). 7
ALD-Enabled NEMS? Yes! CVD or other Coatings on MEMS ALD on MEMS 25 to 100 nm ALD Coating Coating variations on NEMS unacceptable! ALD on NEMS 8
Contents Atomic Layer Deposition - ALD for micro-scaled devices - ALD for nano-scaled devices - ALD for barrier coating Molecular Layer Deposition - Nylon 66 Progress, Opportunities and Challenges Summary 9
ALD HfO2 for 45-nm Microprocessors On Nov. 12, 2007, Intel shipped the first 45-nanometer microprocessors using high-k metal-gate technology. Gordon Moore describes the innovations as "the biggest change in transistor technology since the introduction of polysilicon-gate MOS transistors in the late 1960s. " 11/14/2007. http://www w.eetimes.eu/ /203101162D Don Scansen n EE Times 10
ALD-Enabled Nanotube/Nanowire/Graphene Devices NO2 Treatment D.B. Farmer and R.G. Gordon, Nano Lett., 6, 699 (2006). MBE GaN Nanowires on Si(111) with ~70nm ALD alumina 5 μm Al 2 O 3 ALD on Highly Ordered Pyrolytic Graphite 11
ALD-Enabled Nanotube/Nanowire/Graphene Devices GaN: GaN nanowire with E GaN =330GPa BN ALD coating α 32 GaN =3.2x10-6 K -1 could match the thermal expansion coefficient of silicon, 2.6x10-6 K -1 BN: E BN =700GPa α BN =1.2x10-6 K -1 Electrical, l thermal and mechanical interfaces n n n 500 nm p p p GaN NWs on Si Substrate for LED or FET 12
Contents Atomic Layer Deposition - ALD for micro-scaled devices - ALD for nano-scaled devices - ALD for barrier coating Molecular Layer Deposition - Nylon 66 Progress, Opportunities and Challenges Summary 13
ALD-Based Barrier Coating (Moisture and Oxygen Permeation) 10 1 Polymer Film WVTR (g/m2/day) HTO test Perm meation Rate 0.1 0.01 ALD-on-Polymer Film 0.001 0.0001 Organic LEDs; organic solar cells; polymer sensors; hermetic polymer 100X packaging for MEMS 0 5 10 15 20 25 30 Alumina ALD Thickness (nm) 14
Bending Radius = 0 mm Cracking of SiO x N y and Organic/Inorganic Barrier Films on Polymer Substrates σi = E i Z i R Z m optimal Bending Radius = 5 mm safe design space Grego, et al., 2007, Thin Solid Films, Vol. 515, pp. 4745-4752; Cordero, N., Yoon, J., and Suo, Z., 2007, Applied Physics Letters, Vol. 90, 111910. 15
Molecular Layer Deposition (MLD) for Multilayer Barrier 2nm ALD Alumina 20 nm SiOxNy Layer 20-nm Polymer 2nm MLD Polymer 3X mechanically improved toughness?x chemically improved toughness due to covalent bonds between polymer and alumina layers 16
Contents Atomic Layer Deposition - ALD for micro-scaled devices - ALD for nano-scaled devices - ALD for barrier coating Molecular Layer Deposition - Nylon 66 Progress, Opportunities and Challenges Summary 17
Polymer Molecular Layer Deposition (A) (B) 18
Precursors for Nylon 66 MLD 16H 1,6-Hexanediamine: i H H N CH 2 CH 2 CH 2 CH 2 CH N H 2 H CH 2 2 Adipoyl Chloride: O Cl CH 2 CH 2 C C CH 2 CH Cl 2 O 19
Nylon Molecular Layer Deposition 20
Nylon Molecular Layer Deposition 21
Nylon Molecular Layer Deposition 22
Nylon Molecular Layer Deposition 23
Nylon Molecular Layer Deposition 24
Nylon Molecular Layer Deposition 25
Integrated Absorbance Increase versus Number of AB Cycles at 83 C 60 SiO 2 Powder Substrate, 83 o C Integrated Absorbance 50 40 30 20 10 Start End Combined Absorbance of Amide I and II Bands is Linear with Number of AB Cycles 0 0 2 4 6 8 10 12 14 16 18 20 22 Number of AB Cycles Y. Du & S.M. George, J. Phys. Chem. C 111, 8509 (2007). 26
Contents Atomic Layer Deposition - ALD for micro-scaled devices - ALD for nano-scaled devices - ALD for barrier coating Molecular Layer Deposition - Nylon 66 Progress, Opportunities and Challenges Summary 27
Atomic Layer Deposition: Progress, Opportunities and Challenges ALD at CU-Boulder (George Research Group) Alumina (Al 2 O 3 ) Tungsten (W) Ruthenium (Ru) Aluminum Nitride (AlN) Tantalum Nitride (TaN) Tin Oxide (SnO 2 ) Silicon Dioxide id (SiO 2 ) Hafnium Oxide (HfO 2 ) Zinc Oxide (ZnO) Titanium Oxide (TiO 2 ) Magnesium Oxide (MgO) Manganese Oxide (MnO 2 ) Hydrophobic Layers ALD processes are well developed. d CVD with binary reactions ALD possible. ALD for MEMS - high quality coatings - manufacturable now - quality (yield/defect)? - reliability? ALD for NEMS - enabling technologies for devices and interfaces - improved processes for novel applications, NT/NW/graphene. 28
Atomic and Molecular Layer Deposition: Progress, Opportunities and Challenges Nylon 66 MLD First report by CU in Summer 2006, Others: NC State and Helsinki Institute of Technology Poly(p-Phenylene Ph l Terephthalamide) [PPTA] Kevlar MLD Demonstrated by CU in Spring 2007. Higher Thermal Stability Polyamide Polymer Alucone MLD: Novel Hybrid Organic/Inorganic g Polymer. Published by CU and University of Oslo in Summer 2007. New Nanocomposite Flexible Polymer. MLD of ABC Polymers. Novel Hybrid Organic/Inorganic Polymer based on ABC Reaction Sequence. Demonstrated by CU in Fall 2007. Enlarges Material Set for Nanocomposite Films. ALD/MLD processes are new and good for a large number of inorganic/organic combinations. ALD/MLD for MEMS - > 10X in quality and reliability - new surface properties resulting from polymer layers. ALD/MLD for NEMS - exciting enabling technologies og es for devices and interfaces - organic molecules essential to NEMS; multiple inorganic/organic layers with molecular precision. applications, science and technology? 29
Opportunity: ALD/MLD-Enabled Highly Selective, Stable and Manufacturable Biosensors Wei Tan, Xiohua Du, Steven M. George and Y. C. Lee Universal Functionalization Platform Application-Specific p Receptors MLD PEG ALD Alumina ALD Alumina-on-NW NW/NT/MEMS Devices ALD Alumina-on-NT PEG for anti-fouling to reduce false alarms: Single layer PEG coating? density? Multi-layer PEG coating? Conformation? MLD PEG can give us a precise number of high-quality anti-fouling layers for a quantitative understanding leading to highly selective, stable and manufacturable 5 μm biosensors. ALD Alumina-on-MEMS 30
Summary Atomic Layer Deposition - ALD for micro-scaled devices - ALD for nano-scaled devices - ALD for barrier coating Molecular Layer Deposition - Nylon 66 Progress, Opportunities and Challenges - ALD for MEMS: manufacturing, quality and reliability - ALD for NEMS: enabling technologies for devices and interfaces for system integration - ALD/MLD for MEMS: >10X improvement over ALD in quality and reliability - ALD/MLD for NEMS: Exciting inorganic/organic multilayers for repeatable, predictable and reliable NEMS. 31