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Top-Down Nanomanufacturing. David T. Shaw State University of New York at Buffalo. Contents. Process Overview Lithography Vacuum basics Photolithography basics Photomasks Exposure Tools X-ray lithography Immersion lithography Nano-imprint lithography
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Top-Down Nanomanufacturing David T. Shaw State University of New York at Buffalo
Contents • Process Overview • Lithography • Vacuum basics • Photolithography basics • Photomasks • Exposure Tools • X-ray lithography • Immersion lithography • Nano-imprint lithography • Other techniques - Dip pen, AFM, FIB • Electron Beam lithography • Thin Film Deposition • Etching
Lithography, although imperfect, can generate complex 3-D nanostructures
Brief History of Chip Making Based on Photonic Lithographic Fabrication Photonics lithographic fab is driven by electronics • 1947 - First transistor invented at Bell by Bardeen, Brattain and Shockley • 1958 - First integrated circuit at Texas Instruments by Jack Kilby • 1959 – Planar technology on Si substrate using SiO2 as insulation layers • More than three decades of exponential miniaturization in sizes and costs based on a top-down processing • Dimensions move into nanoscale range at the beginning of the 21st century • Top-down technology is facing three fundamental design limits: • Transistor scalability • Performance • Power dissipation
Top-down Nanostructures • Top down fabrication can be likened to sculpt-ing from a block of stone. • A piece of the base material is gradually eroded until the desired shape is achieved, i.e., you start at the top of the blank piece and work your way down removing material from where it is not required. • Nanotechnology techniques for top down fab-rication vary but can be split into physical and chemical fabrication techniques
Top-down Fabrication of Nanodots Stacking Ge nano–islands on Si(001) (a) AFM image and (b) cross sectional TEM of a typical Ge/Si heterostructure. G. Capellini elat, Appl. Phys. Lett. 82, (2003) 1772-1774
Top-down Fabricating Nanowires With Alternating Diameters or Compositions (ii) Generation of PR pattern
Top-down Fabricating Nanowires With Alternating Compositions • Preparing an array of GaAs wires with a triangular cross section from a GaAs(100) wafer patterned with mask stripes along the (011) direction and anisotropically etched in an aqueous solution, • Patterning the resultant wire array (after removal of the etch mask stripes) with photoresist lines perpendicular to the orientation of the GaAs wires, • Etching the GaAs wires using the photoresist as a mask to generate wires with alternating widths, or • Depositing metals through the photoresist pattern to create GaAs wires with segments alternating in composition. Y. Sun et al, Small,1(11)1052(2005)
Combining top-down and bottom-up A lamellar-forming block copolymer on 2D surfaces chemically patterned with a square array of spots form 3D bicontinuous morphologies. K. C. Daoulas et al, PRL,96,036104(2006)
Integration of Top-down and Bottom-up nanomanufacturing Integrated multifunctional nano-assembly onto bio-MEM devices and lead to scalable and cost effective nanomanufacturing X. Zhang et al, Journal of Nanoparticle Research 6: 125–130, 2004.
Future Integrated Nano-Systems Bottom-up (sensors, memories, etc.) will be integrated with top-down nanocomponents C. Sun, X. Zhang UC Berkeley
Top – Down Nanomanufacturing Derived directly from the chip-making processes Single Silicon Crystal Growth
Vacuum Circuit Liu, UCD Phy250-2, 2006
Conductance of a Straight Tube Liu, UCD Phy250-2, 2006
Outgassing rates for common materials (millibar-liter/sec-cm2) Common vacuum materials Construction Materials which are compatible with UHV OFHC copper, Be-Cu alloy, phosphor bronze, 304 SS, 310 series SS, 340 SS (magnetic), Teflon, MACOR (machinable glass composite), 6061 Al (essentially pure aluminum), 2024 Al (harder alloy), quartz, Pyrex (gassy), alumina (careful with glazed ceramics), molybdenum, tungsten "mu-metal" magnetic shielding (Co, Ni, Fe), polyimide (Vespel), Sn-Ag solder Construction Materials which are compatible with UHV Zn, Cd--Especially be careful of fasteners and bolts, brass, certain solders
Photolithograpy • The most important part of top down fabrication technique is nanolithography. • In this process, required material is protected by a mask and the exposed material is etched away. • Depending upon the level of resolution required for features in the final product, etching of the base material can be done chemically using acids or physically using ultraviolet light, x-rays or electron beams. • This is the technique applied to the manufacture of computer chips.
Diminishing Lithographic Wavelengths E. Chen, Harvard
Contact Lithography Disadvantages • Good contact difficult to achieve • Sensitive to particular contaminants • Hard to get below 2µm • DUV requires quartz mask • Alignment can be difficult
