Growth and Properties of Multiwalled Carbon Nanotubes What are Carbon Nanotubes? What are they good for? Why are we interested in them? - Interconnects of the future? - our vision Where do we stand - our results - how to make them... -...in the right place... -...first results... Page 1 Conclusion
What are Carbon Nanotubes? just roll up a graphene sheet and you will get a single wall carbon nanotube (SWNT) Page 2
What are Carbon Nanotubes? Page 3 07.08.2001 multi-wall tubes (MWNT)
What are Nanotubes good for? prominent features: length: microns to millimeters diameter: 1-30 nm electrical conductivity: metallic (ballistic transport) energy gap depends on diameter or semiconducting depending on chirality operating current density > 10 9 A/cm 2 (Cu~ 10 6 A/cm 2 ) thermal conductivity ~ 6000 W/Km (Cu~ 400W/Km) gravimetric surface: > 1500 m 2 /g maximum strain: 0.11 % @ 1Volt (Ferroelectr. 0.11 % @ 100 V) e-modulus 1000 GPa, elastic elongation of 40% huge hydrogen storage capacity of >6 weight percent Page 4
Carbon Nanotubes applications transistor 3d-wiring via-interconnect actuators, sensors carbon-nanotubes nanocontainer Page 5 biomolecular applications gas sensors hydrogen storage batteries flat panel displays
Why are CNTs interesting for us? Nanotubes: a possible solution for roadmap problems? red areas: no known solutions! Page 6 source:http://public.itrs.net/files/2000updatefinal/2kudfinal.cfm
Our Vision Vision: smallest contact hole of the world filled with highly conductive carbon nanotube Vision Metal 2 CNT Dielectric Catalyst Metal 1 Page 7
Where we stand - our results how to make them CVD-growth of Carbon Nanotubes Page 8 The catalyst support, i.e., the substrate is also very important.
Where we stand - our results how we make them Preparation of the samples by lift-off technique CVD-growth of Carbon Nanotubes i-line or e-beam resist substrate resist patterning by i-line or e-beam substrate deposition of catalytic materials by evaporation, sputtering or spin-on methods substrate lift-off with solvents and ultrasonification CVD-growth of multiwall carbon nanotubes Page 9
Where we stand - our results Task Identify: suitable catalyst suitable catalyst support suitable CVD-process to get good quality nanotubes with processes compatible with semiconductor backend of line Page 10
Pure Metal (PVD) Where we stand - our results how we make them CVD of Multi-walled Nanotubes - Table of catalysts tested Carbonyl Chloride Acetylacetonate (spin-on) Oxalate Carbonyl in cellulose nitrate (spin-on) (spin-on) (spin-on) (spin-on) Fe Excellent Excellent Excellent Excellent Good None Ni None - None Poor - - Co None None Single None - None Ru - None None - - - Mo - None - - - - Ir - - - - - - Pt None - - - - - Page 11 Suitable substrates include: Silicon, Silicon Oxide, Silicon Nitride, Poly-Si,Tantalum, Tantalum Nitride, Titanium, Aluminum, Nickel (poor). Unsuitable Substrates: Gold, Platinum, Tungsten. The interaction between substrate and catalyst is crucial.
Where we stand - our results how we make them 100µm x 100µm blocks of carbon nanotubes on a SiO 2 substrate Page 12
Where we stand - our results how we make them Selective Growth of Carbon Nanotubes on Metal Electrodes Page 13
Where we stand - our results how we make them- first attempt Objective: Use selective growth of Carbon Nanotubes for high aspect ratio nanoscale vias Vision Status Metal 2 CNTs Dielectric Catalyst Metal 1 Page 14
Where we stand - our results First electrical characterization of self-aligned grown CNT Array of vertically aligned CNTs grown out of a 30x5 µm 2 wide via. The tops of the nanotubes are contacted by tungsten. tungsten pad deposited by FIB W-contact R CNT R sum Nanotubes Page 15 ~10 Ω R Pt+Si Si-oxide Pt & catalyst Si- Substrate
Where we stand - our results First electrical Characterization of self-aligned grown CNT 1,0m Total Resistance = 11 O Contact Resistance =10 O Resistance of CNT Bundle = 1 O Contact Area = 5 x 30 µm 2 Number of CNTs ~ 10,000 Quantum Resistance = 13 ko (one state, electron spins up and down) current [A] 500,0µ 0,0-500,0µ -1,0m -10,0m -5,0m 0,0 5,0m 10,0m Voltage [V] Resistance per CNT ~ 10 ko R CNT W-contact Page 16 R sum ~10 Ω R Pt+Si Nanotubes Si-oxide Pt & catalyst Si-Substrate
Carbon Nanotubes First electrical Characterization of a Single MW-CNT Single Carbon Nanotube in Contact with two Au-electrodes IV Curve for Single Nanotube 40 Au-contact nanotube Au-contact 30 20 10 Current /µa 0-10 -20-30 -40-10 -8-6 -4-2 0 2 4 6 8 10 Voltage /V Page 17 The resistance obtained is 380kO and mainly determined by the contact resistances. The measured current density is 2 10 7 A/cm 2. Coherent Spin Transport Spintronics
Carbon Nanotubes First electrical Characterization of a coiled MW-CNT Single Carbon Nanotube grown between two Pt-electrodes Au-contact nanotube Au-contact Page 18 The resistance obtained is 2 MO and mainly determined by the contact resistances.the measured current density is 3 10 6 A/cm 2.
Conclusion Summary of the talk basics of Carbon Nanotubes possible general applications of CNTs Nanotubes as interconnects Vision: The nanotube via Identification of suitable catalysts suitable catalyst support suitable CVD-process first electrical results of vias made out of CNT arrays Page 19
The Nanotube-Team at CPR Franz Kreupl Andrew Graham Eugen Unger Maik Liebau Support from: Peter Meis CFE FA 5 (FIB) Hans Cerva Siemens CT MM7 (TEM) Page 20