Nanolithography Techniques MSE 505 / MSNT 505 P. Coane
Outline What Is Nanotechnology? The Motivation For Going Small Nanofabrication Technologies Basic Techniques Nano Lithography
NANOTECHNOLOGY Nanotechnology is the design and engineering of components or structures that have at least one physical dimension the size of 100 nanometers or less. For perspective, the diameter of a human hair is roughly 100,000 nanometers. A single walled carbon nanotube has a diameter of about one nanometer. For the microelectronics industry, device structure dimensions are being reduced using top down methods scale down minimum feature size. True nanotechnology is when devices or structures are crafted by using bottom up methods i.e., by building structures up molecule by molecule.
Device Size (nm) Development Time Characteristic feature sizes that lie in the intermediate range between isolated atoms and bulk materials (one to 100 nanometers) often display physical attributes substantially different from those displayed by either atoms or bulk materials.
NANOTECHNOLOGY Motivation To Go Small To make novel devices that leverage the special properties of nanoscale building blocks consisting of a small collection of atoms. In contrast to bulk materials, having properties that are dominated by novel quantum phenomena and/or the effects of surface energy. What has been gained in the last 50 years with device shrinkage will be surpassed by the benefits of nanomaterials and their arrangement into devices. Superior selectivity for interaction, enhanced sensitivity to detection, and novel programmability for added structural and functional control (i.e. biosensors). Revolutionary new products using new materials and substances not accessible with other technologies
Nanotechnology (Nano-imprint lithography) (E-beam and X-ray Nano lithography) (Dip Pen Nano lithography)
Nanomanufacturing Nanoassembly Techniques Layer-by-Layer Assembly Molecular Recognition-Based Self-Assembly Self-Assembled Monolayers (SAM) Nanoassembly by Step-Wise Polymerization Nanopatterning Techniques X-ray Lithography E-beam Lithography Nanoimprint Lithography Molecular Imprinting Electroless Deposition Techniques With Charged Nanoparticles Protein Nanoengineering Techniques Computer-Aided Peptide Design Automated Abiotic Peptide Synthesis Biotic Peptide Synthesis in Host Organism
Nanomanufacturing Not Just an Engineering Process For Atomic Scale precision and control, fundamental principles of physics and chemistry must be applied. Nanoscale Manufacturing is Multidisciplinary Involving but not limited to mechanics, electrical engineering, physics, chemistry, biology, and biomedical engineering. Nanomanufacturing is the Integration of Engineering, Science and Biology
Nanofabrication * Lithography In General Terms lithography can be viewed as a physical process involving image transfer or patterning into various types of media using Visible and UV Light Electron Beam Ion Beam Laser X-rays Precision Machining Printing * For Nano Fabrication A key consideration is Resolution
Information Flow in the Optical Lithographic Process Process Bias Every process step creates an opportunity to lose information or distort the desired pattern.
Optical Lithography represents the relative improvement in moving to the next generation wave length Wavelengths for optical lithography. Resolution W min uses k1 = 0.3 and DOF uses k3 = 1, assuming NA = 0.9 for all wavelengths except EUV, which assumed NA = 0.25. J. Vac. Sci. Technol. B, Vol. 21, No. 6, Nov/Dec 2003
Optical Lithography Fundamental Limits to going below 193 nm For 157 nm - Single crystal calcium fluoride lenses required - Oxygen and water vapor absorb at this wavelength - Cost estimates are in the range of $20 million per scanner For EUV - Multi coated reflective mirrors required up to 40 layers - Reflective masks are required and must have a surface flatness of 50 nm or less from edge to edge - Mask surfaces can be damaged by oxidation. - Cost estimates are from $40 to $70 million per scanner
JBX-3030MV JBX-5000LS/E JBX-6000FE/E JBX-9000MV JBX-9300FS Electron Beam Systems Emitter Accelerating Voltage Min. Beam Size Beam Shape LaB6 single crystal 25 kv and 50 kv Variable LaB6 single crystal 25 kv and 50 kv 8nm Spot LaB6 single crystal 25 kv and 50 kv 5nm Spot LaB6 single crystal 50 kv Variable ZrO/W (Schottkey) 100 kv / 50 kv 4nm (100 kv) 7nm (50 kv) Spot Deflection Vector scan Vector scan Vector scan Vector scan Vector scan
Electron Beam Systems
Electron Beam Systems
Electron Beam Size Limits Electrons have a finite quantum mechanical wavelength: λ = 1.2 V b -1/2 Which gives a diffraction limited beam size expressed as: d d = 0.6 α λ Add all contributions to calculate theoretical minimum beam size: d d = ( d g 2 + ds 2 + dc 2 + dd 2 ) 1/2
Electron Beam Nanolithography 15 nm wide gold palladium lines, 50 nm periodicity, PMMA resist, fabricated by lift-off on a thin silicon nitride membrane IBM 1. RES. DEVELOP. VOL. 32 NO. 4 JULY 1988
Nanofabrication Electron Beam Lithography
E-Beam Exposures in Hydrogen Silsesquioxane Resist 30 nm period grating exposed in 30-nm-thick HSQ resist on Si; (a) overall gratings, and (b) higher magnification view of ~10 nm lines at 30 nm period exposed at 2200 nc/cm. 27 nm period lines exposed in 30 nm HSQ resist on Si; (a) overall gratings and (b) higher magnification view of individual lines in the 27 nm period grating exposed at a double-pass line dose of 1650 nc/cm. J. Vac. Sci. Technol. B 21, No 6., Nov/Dec 2003
Nanometer Gratings by E-beam lithography Width of individual lines vs dose for 30, 40, and 50 nm periodicity gratings exposed in 30 nm of Hydrogen Silsesquioxane resist. J. Vac. Sci. Technol. B, Vol. 21, No. 6, Nov/Dec 2003
Nanolithography Process Window Constraints Plot of linewidth variation from nominal (i.e. developed for the time required to clear features) for up to 50% overdevelopment. Isolated features stay within a +/- 10% process window for features as small as 30 nm. Dense (line:space ratio of 1:3 or greater) features remain in the process window for features as small as 45 nm.
Nanofabrication Electrochemically Grown Wires for Sensor Array Applications Schematic diagram of a structure used for the electrochemical wire growth. (a) Electrodeposited wire connected between electrodes. (b) Cross-sectional view of the Si substrate, silicon nitride (1 um), Au contacts, and thermally evaporated SiO. Channels for the electrolyte solution are formed between electrodes by e-beam patterning of the SiO. Nano Lett., Vol. 4, No. 3, 2004
Nano-patterning by X-ray Lithography Scanning electron micrographs of device patterns with feature sizes less than 40 nm achieved by x-ray nanolithography followed by liftoff. The x-ray mask is shown on top and the lifted-off pattern is on the bottom.
X-ray Nanolithography
Nano-machining By using sub-nanometer control afforded by AFM technology the nm1300 employs a subtractive photomask repair technique. The current system is focused on meeting requirements for the 130- nanometer design rule node, but the technique is extendable to the 100 nm node and beyond. RAVE LLC
Nano-machining of MoSi on Quartz Phase Shifting Photo Mask
Mechanical Lithography by AFM Process sequence of mechanical AFM lithography, lift-off and pattern transfer J. Vac. Sci. Technol. B, Vol. 16, No. 5, Sep/Oct 1998
Nanolithography AFM Nanografting of Thiols on a Au(111) Surface The sample is the surface of a gold crystal (Au(111)) covered with a self assembled monolayer (SAM) of decanethiol (CH3(CH2)9SH). Imaging was done under liquid in a solution containing octadecanethiol (CH3(CH2)17SH). The lithography was done by applying an approximately 10X higher force during writing. This displaced the decanethiol molecules, which were then replaced in the SAM by the longer octadecanethiol molecules. The surface is higher where written because the tails of the octadecanethiol molecules stick up above the average height of the SAM. Total size of the spirals is 620nm. Average line spacing is 40nm and average line-widths (FWHM) are 15 to 20nm. M. Liu and G. Liu, UC Davis
Nanolithography using Anodic Oxidation When the AFM tip is brought close to the surface, water from the ambient humidity forms a droplet between the tip and the substrate. To drive the anodic oxidation process, a voltage (5 to 15 volts) is applied between the tip and the substrate. The high electric field ionizes the water droplet and the OH- ions produced provide the oxidant for the chemical reaction.
Nanolithograpy Anodic Oxidation The Notre Dame logo shows 2nm thick oxide grown on a Ti film. Oxidation is performed by applying a potential to a conducting AFM tip and using the condensed water droplet at the tip as an electrochemical cell. The oxidized region grows, resulting in raised surface features. EE Department Univ. of Notre Dame
Nanolithography using AFM Anodic Oxidation on Ti Substrate Width at the bottom of the trench is about 80nm EE Department Univ. of Notre Dame
Nanolithography using AFM Anodic Oxidation - Ti Substrate The width at the top of the lines is about 70nm EE Department Univ. of Notre Dame
Nanolithography using an STM (1) The oxide layer within the e-beam-exposed area is decomposed and reduced (2) The reduced SiO is changed to volatile SiO and evaporated from the surface at elevated temperatures. Schematic diagram of the experimental set-up for silicon oxide removal by field emitted electron beam irradiation at an elevated temperature using a Scanning Tunneling Microscope (STM). Nanotechnology 14 (2003) R55 R62
Nanolithography on SiO 2 using an STM Smallest linewidth = 25 nm The quantum yield for impact-induced SiO 2 decomposition as a function of the e-beam kinetic energy with beam currents of 10 na ( ), 20 na ( ), 30 na (), 40 na () and 50 na ( ). The solid curve represents the substantial yield. Nano-fabrication of patterns by PC control of the STM tip position. Nanotechnology 14 (2003) R55 R62
Nanofabrication on the Molecular Scale STM image of a polypropylene molecule on graphite.
Nanofabrication on the Molecular Scale
Nanofabrication SAM of Phenylene-Based Conjugated Molecules in an FET geometry The electronic transport characteristics of self-assembled monolayers of phenylene-based ð- conjugated molecules were measured in a three terminal device geometry. The short (1 nm) molecules were connected between two gold electrodes with a nearby Al 2 O3/Al gate electrode. It was possible to fabricate working devices using three of the five molecules investigated. The other two types of molecules led to devices where the Au electrodes were shorted together. For devices with 1,3-benzenedithiol, a weak gate effect was observed. (a) Schematic diagram of the device. The suspended bridge consists of hard baked photoresist or SiO2, and evaporated Si (or SiN). (b) Scanning-electron- microscope (SEM) image of the device that has a contact area of 400 nm2. For clarity in SEM imaging, samples were tilted 45. (c) SEM image that shows that the top surface is far away from the substrate (> 500 nm) and that the supporting middle layer features a large undercut. Thus, we can measure the transport properties of the devices without a liftoff step in the fabrication. Nano Lett., Vol. 3, No. 2, 2003
Nanofabrication on the Atomic Scale
Scanning Tunneling Microscope In the constant tunneling current mode of operation, a voltage Vz is applied to the Z piezoelectric element by means of the control unit CU to keep the tunneling current constant while the tip is scanned across the surface by altering Vx and Vy. The trace of the tip, a y-scan, generally resembles the surface topography. Electronic inhomogeneities also produce structure in the tip trace, as illustrated on the right above with two surface atoms having excessive negative charge.
Nanopatterning on the Atomic Scale Using a Scanning Tunneling Microscope (STM) Xenon Atoms IBM 1990
290 nm Conducting Polymers 100 nm Protein Nanoarrays 65 nm Small Organic Molecules Silicon Nanostructures Dip-Pen Nanolithograpy 4µm Ultrahigh Density DNA Arrays Prototype Probe Arrays 1 µm Single Nanoparticle Lines 290 nm Sol Gel Structures
Bottom-Up Nanofabrication via Dip-Pen Nanolithograpy Building Blocks DPN-Generated Surface Templates Addressable Materials with Well-Defined Superstructures and Orientations
DPN: A Versatile Tool For Nanofabrication Life Sciences Microelectronics science & technology science & technology single molecule studies structure/function drug discovery ultra-high density gene chips proteomics/peptide arrays cell processes (adhesion) virus/protein crystallization (Bio)sensor Devices molecular electronics nanoscale surface phenomena organic etch resists printed nanocatalysts combinatorial materials discovery CNT, nanowire devices additive photomask repair circuit edit spintronic devices gas/chemosensors CONVERGENCE of fields from the BOTTOM UP
Two Fundamental Types of Dip-Pen Nanolithography Methods Direct Write write the molecule of interest directly onto the surface as the ink Templating write out an ink pattern in order to fabricate or attach something else
Dip-Pen Nanolithography Florida State University
Dip-Pen Nanolithography / SAM 16-mercaptohexadecanoic acid (MHA) Procedure for preparing functionalized DPN-generated nanostructures using thiol-containing molecules
Dip-Pen Nanolithography / SAM AFM topographic images of the etched MHA/Au/Ti/SiOx /Si nanostructures, lines (A) and dots (B), based on the DPN of MHA on a gold surface
Dip-Pen Nanolithography / SAM AFM topographic images of individual Au nanoparticles adsorbed on HS-SAM-modified nanopatterns of lines (A, with high-resolution image inserted) and dots (B).
~1.3 Million DPN Pen Array MEGApede (courtesy of NanoInk, Inc.)
MEGApede - DPNStamper MEGApede probe array Fluorescent arrays deposited by a MEGApede DPNStamper
Nanofabrication Using Self Assembly Polar Molecular Patterns Non-Polar Region Substrate Surface Functionalization SWCNT Suspension The substrate is functionalized with organic molecules to produce polar and non-polar regions. Carbon nanotubes in solution are attracted to the polar regions and selectively self assemble on the substrate following the lithographically defined patterns. SWCNT Self Assembly Mass production of carbon nanotube based circuit structures is possible
Imprint Lithography Fabrication sequence for three different varieties of imprint lithography.
Nanofabrication Using Step-and Flash Imprint Lithography 1. Using a precise piezo-driven dispense head, a silicon-rich, low-viscosity, photocurable, monomer solution is dispensed onto the substrate in the region where the pattern is to be printed. 2. The template is then pressed into contact with the wafer using very low pressures (<1psi) to spread the liquid across the field and fill the template's relief. 3. UV light is irradiated through the back of the template, curing the monomer. 4. The template, pre-coated with a fluorocarbon release agent, is removed, leaving the cured, patterned resist layer behind. 5. Finally, a breakthrough etch passing through the residual etch barrier and a transfer layer (any organic spin-coated resin such as an antireflective coating, ARC) transfers the high aspect ratio pattern to the substrate. Solid State Technology February 2004
Step and Flash Nano-Imprint Lithography Template pattern transfer sequence for 30 nm features. 100, 60, 30, and 20 nm features defined using the ITO-based process. J. Vac. Sci. Technol. B, Vol. 21, No. 6, Nov/Dec 2003
Step and Flash Nano-Imprint Lithography Printed features in the acrylate-based etch barrier. (a) Top-down SEMs. (b) Cross-sectional images of both single tier and multi-tiered features. J. Vac. Sci. Technol. B, Vol. 21, No. 6, Nov/Dec 2003
Imprint Lithography for Application to Integrated Circuit Fabrication Multi-tiered structures formed by iterating the fabrication process.