28.09.2014
Science, Technology and Medicine open access publisher.Publish, read and share novel research. NanolithographyGunasekaran Venugopal1 and Sang-Jae Kim2[1] Karunya University, Department of Nanosciences and Technology, Tamil Nadu, India[2] Jeju National University, Department of Mechatronics Engineering, Jeju, South Korea1. Aarhus University generates and shares knowledge that contributes to solving complex social and global challenges. Students participating in a formal exchange programme between their home university and Aarhus University.
Circular Dichroism (CD) spectroscopy measures the difference in absorption between left and right handed circularly polarized light in chiral molecules. Actor Karan who was busy as a lead actor, is back with Uchathula Shiva which is produced by his wife Devi Karan.
After Jackson Durai, director Dharanidharan is planning to do a film with actor Shirish which is a murder thriller mystery with rain as a main backdrop. Lakshmi Menon says that, no one approached her to play the lead role in Kumki2 till now and if she gets a chance, she will accept that role since, Kumki film gave her a major break in Kollywood.
Actress Angana Rai is roped in Kadaisi Bench Karthik film in which Actor Bharath is playing the lead role. After a long gap, actor Nepolean has made a come back in the film Kidaari in which Sasikumar played the lead role. Vishal, Tamannah and Vadivelu are busy with the dubbing work of their upcoming film Kaththi Sandai which is directed by Suraj. Introduction Nanolithography is the branch of nanotechnology concerned with the study and application of the nanofabrication of nanometer-scale structures, meaning nanopatterning with at least one lateral dimension between the size of an individual atom and approximately 100 nm.
AcknowledgementsThe authors would like to acknowledge the supports from the National Research Foundation of Korea Grant under contract number 2011-0015829 and 2011 Jeju Sea Grant College Program funded by the Ministry of Land, Transport and Maritime Affairs (MLTM), Republic of Korea. C Davis, 2003Chemomechanical surface patterning and functionalization of silicon surfaces using an atomic force microscope.
It is running successfully all over and Nepolean’s performance became one of the major highlight.
A part of this work was carried out at the Research Instrument Center (RIC) at Jeju National University, Jeju, and Republic of Korea.
The size of the meniscus, which is controlled by relative humidity, affects the ODT transport rate, the effective tip-substrate contact area and DPN resolution. Therefore the literal translation is "tiny writing on stone", however nowadays one understands something different whenever this term is associated with nanotechnology. Also the author (G.V) would like to thank the management of Karunya University for continuing this research through their KSTG seed money grant No. This technology can be suitable to use in nanofabrication of various semiconducting Integrated Circuits (ICs), NEMS and for various applications in research. The modification in semiconductor chips at the nano-scale (in the range of 10-9 meter) is also possible. The positive photo-resist (AZ 5214) was spin-coated over the graphene flakes on the substrate. Nanofabrication is the method in which the devices can be designed and manufactured with the dimensions in nanometers [Kim, 1999; Venugopal, 2011a, 2011b, 2011c).
By using photolithography (Mask Aligner MDA- 400M; MIDAS), the graphene flakes were patterned through Cr mask for electrode formation.
The conventional fabrication techniques like Focused Ion Beam (FIB) and wet etching methods are able to remove or etch the parts in the range to micron scale (Kim, 2001).
Then the gold (99.99 %) electrodes of 100 nm- thick were formed through thermal evaporation technique and structured by lift-off using acetone.
However, in recent days, patterning and etching have to be done in nanoscale for specific applications. Nanomanupulation is a technique in which some specific tools are used to manipulate the objects in nanoscale (Parikh, 2008). Then lift-off process is carried out (using acetone) to get the final pattern for device characterization. At present, Scanning Probe microscopic methods involved in AFM [Davis, 2003) and Scanning Tunneling Microscopy (STM) are being used to manipulate the objects in nanometer scale.
Specifically, AFM is being used to move the atoms, carbon nanotubes, nanoparticles, various nano-scale objects and also to test integrated circuits. Instruments used in nanolithography include the Scanning Probe Microscope (SPM) and the AFM. Focused ion beam 3-D fabrication technique Miniaturization is the central theme in modern fabrication technology.
Either the SPM or the AFM can be used to etch, write, or print on a surface in single-atom dimensions (Venugopal, 2012). The main drawbacks in the existing lithographic techniques will be carefully analyzed in this chapter. Here, the focused ion beam (FIB) direct milling technique will be discussed with the focus on fabricating devices at the micrometer to nano-scale level. Also the need of nano-patterning for the low-cost, high throughput surface patterning technologies will be presented in this chapter. Because of the very short wavelength and very large energy density, the FIB has the ability for direct fabrication of structures that have feature sizes at or below 1 ?m. In addition, the complete coverage of nanolithographic process which includes Introduction, Resists and Masks, Photon-based Lithography, Electron Beam Lithography, Ion Beam Lithography and emerging nanolithographic techniques will be discussed in detail. As a result, the FIB has recently become a popular candidate in making high-quality microdevices or high-precision microstructures (Kim, 2008). However, the alternate nanolithography techniques like Micro-contact printing, Nanoimprint Lithography, Scanned Probe Lithography, Dip-pen Lithography will also be discussed in detail in this chapter2. The FIB has been a powerful tool in the semiconductor industry mainly for mask repairing, device modification, failure analysis and integrated circuit debugging.
Two basic working modes, ion beam direct write and ion beam projection, have been developed for these applications. Nowadays it becomes a standard in biomaterials engineering and for fundamental research on cellular biology by mean of soft lithography. The ion beam direct write process, also known as FIB milling (FIBM), is the process of transferring patterns by direct impingement of the ion beam on the substrate. It is a large collection of microfabrication techniques that removes materials from a substrate and has been successfully used for fabricating various three-dimensional (3D) micro structures and devices from a wide range of materials.


The batch fabrication of microstructures requires a low-cost, high throughput surface patterning technology. For the ion beam projection process, a collimated beam of ions passes through a stencil mask and the reduced image of the mask is projected onto the substrate underneath. For example, it is important to design nanodevices such as nano-transistors and nanodiodes, nanoswitches and nanologic gates, in order to design nanoscale computers with tera-scale capabilities. The ion beam projection process is also known as focused ion beam lithography (FIBL) and can serve as an alternative to conventional optical lithography (Kim, 1999). All living biological systems function due to molecular interactions of different subsystems. For example, to develop the graphite stacked-junctions, planar-type nanostructures, a high-resolution FIB instrument (SII SMI-2050) can be used. The molecular building blocks (proteins and nucleic acids, lipids and carbohydrates, DNA and RNA) can be viewed as inspiring possible strategy on how to design high-performance NEMS and MEMS that possess the properties and characteristics needed. In addition, analytical and numerical methods are available to analyze the dynamics and three-dimensional geometry, bonding, and other features of atoms and molecules. So, electromagnetic and mechanical, as well as other physical and chemical properties can be studied. Figure 5.The photograph image of FIB unit and schematic of FIB machineThe 3-D etching technique can be followed by tilting the substrate stage up to 90° automatically for etching thin graphite flake. The clear axes of the FIB process configurations with in-plane (x–y) and vertical axes (as z direction) are indicated in an axis diagram in Figure. Photolithography – A conventional and classical methodLithography consists of patterning substrate by employing the interaction of beams of photons or particles with materials.
The in-plane area was defined by tilting the sample stage by 30° anticlockwise with respect to the ion beam and milling along the ab-plane. The process of IC manufacturing consists of a series of 10-20 steps or more, called mask layers where layers of materials coated with resists are patterned then transferred onto the material layer. A photolithography system consists of a light source, a mask, and an optical projection system. Photoresists are radiation sensitive materials that usually consist of a photo-sensitive compound, a polymeric backbone, and a solvent. The out of plane or the c-axis plane was fabricated by rotating the sample stage by an angle of 180°, then tilting by 60° anticlockwise with respect to the ion beam, and milling along the c-axis direction (Saini, 2010). Resists can be classified upon their solubility after exposure into: positive resists (solubility of exposed area increases) and negative resists (solubility of exposed area decreases).
1 shows the schematic of lithographic process in order to make the pattern on the desired substrate. Patterning graphene device using photolithographyAs mechanically exfoliated graphene sheets are in a mesoscopic scale, a lithographic technique is required to make metallic contacts on the sheet. Highly oriented pyrolytic graphite (HOPG) was used as the source material for graphene fabrication. The number of elementary junctions in the stack will vary depends on the height of the junction.
If junction height is more, the more number of elementary junctions exists which provide larger more resistance in c-axis characteristics. X- ray lithography This lithography processes involve the category of nanolithographic techniques, through which transistors with smaller features can be patterned. It uses X-rays to transfer a geometric pattern from a mask to a light-sensitive chemical photoresist, or simply "resist," on the substrate. A series of chemical treatments then engraves the produced pattern into the material underneath the photoresist. X-ray lithography can be extended to an optical resolution of 15 nm by using the short wavelengths of 1 nm for the illumination.
The extension of the method relies on Near Field X-rays in Fresnel diffraction: a clear mask feature is "demagnified" by proximity to a wafer that is set near to a "Critical Condition".
This Condition determines the mask-to-wafer Gap and depends on both the size of the clear mask feature and on the wavelength. This technique originated as a candidate for next-generation lithography for the semiconductor industry, with batches of microprocessors successfully produced. Having short wavelengths (below 1 nm), X-rays overcome the diffraction limits of optical lithography, allowing smaller feature sizes. If the X-ray source isn't collimated, as with a synchrotron radiation, elementary collimating mirrors or diffractive lenses are used in the place of the refractive lenses used in optics.
The X-rays are broadband, typically from a compactsynchrotron radiation source, allowing rapid exposure. Deep X-ray lithography (DXRL) uses yet shorter wavelengths on the order of 0.1 nm and modified procedures such as the LIGA process, to fabricate deep and even three-dimensional structures. Stage – 5: Removal of wafer Now put off Vacuum contact button Then bring down the stage by using Micrometer handle Remove mask holder carefully Then press substrate vac. X-rays are usually generate secondary electrons as in the cases of extreme ultraviolet lithography and electron beam lithography. In this process, the UV-unexposed parts (in case of positive PR) the photo-resist will be dissolved in the developer solution and show clear electrode pattern fabricated via mask. Then put the wafer in DI water bath for 1 min and do air- drying to clean the wafer thoroughly. Stage – 7: Pattern Analysis After developing, Put the developed wafer again in wafer stage and press substrate Vac. E-beam lithography Electron Beam Lithography uses a tightly focussed beam of electrons scanned over the surface of a substrate. Typically, electron beam lithography with ultra high resolution (UHR) is used at the very beginning of a multiple technique and a multiple step process in a top down approach in order to transfer the nanostructure into the substrate or subsequently build up a device in a layer by layer fashion.
E-beam applicationsThis E-beam lithographic technique is mainly having following advantages in research field: Research and Development Advanced processing techniquesFuture processing equipment Can convert SEM to be used as an EBL machine Minimum resolution is slightly larger Used with photolithography and X-ray lithography to create next generation devices. For nanolithography with ultra high resolution down to sub10nm feature sizes, complete dedicated e-beam writer systems or converted scanning electron microscopes (SEM) can be used. With the help of a design editor and a pattern generator, the electron beam is guided over the substrate surface, which is covered with electron beam sensitive resist such as PMMA, in order to generate a resist mask which then can be further used for nanopattern transfer. Resist Preparation In this Process, the PMMA solution is spin coated onto the sample and baked to harden the film and remove any remaining solvent.
Exposure Selected areas of sample are exposed to a beam of high energy electrons Development Sample is immersed in developer solution to selectively remove resist from the exposed area.


E-Beam Lithography Disadvantages Not an efficient process for industrial processing Takes multiple hours to pattern entire wafer Machines are costly Greater than 5 million dollars System is more complex than photolithography systemScattering and over exposure result in minimum feature being largerSlow throughput 3.5. Micro-contact printing (soft lithography) This is known as soft lithography that usually uses the relief patterns on a PDMS (poly-dimethylsiloxane) stamp in order to form patterns of self-assembled monolayers (SAMs) of ink on the surface of a substrate through conformal contact. This technique has wide range of application in cell biology, microelectronics, surface chemistry, micromachining, Patterning cells, patterning DNA and Patterning protein.
No need clean room facilityUsing single master, multiple stamps can be made Reliability of individual stamps which can be used for many times. Nano-imprint lithographyNanoimprint lithography (NIL) is an emerging process that can produce sub-10nm features. After embossing the resist, compressed resist material is removed using anisotropic etching and the substrate exposed. It can produce features at extremely small resolutions that cover a large area with a high throughput and relatively low cost, which is main advantage of this technique. It can be adapted to transfer all components needed to create a thin film transistor on a plastic substrate.
This has high throughput and is relatively inexpensive compared to developing extreme deep UV lithography for commercial viability. It is also flexible enough to be used at chip level with several layers or at the wafer level when single layer is required. One of the current barriers to production at these resolutions is the development of mould.
It can be used for fabricating nanoscale photo- detectors, silicon quantum-dot, quantum wire and ring transistors (Chou, S.Y.
Scanning Probe Lithography (SPL) SPL is an emerging area of research in which the scanning tunneling microscope (STM) or the atomic force microscope (AFM) is used to pattern nanometer-scale features. The patterning methods include mechanical pattering such as scratching or nano-indentation, or local heating with sharp tip (Dagata, 1995). When a voltage bias is applied between a sharp probe tip and a sample, an intense electric field is generated in the vicinity of the tip (Ref. This process can make arbitrary patterns by controlling the trajectory of AFM tip.This process involves small scan area, Low throughout. SPL method is a recognized as a lithographic tool in the deep sub-micron regime, as it is compatible with standard semiconductor processing. There are four main factors which dictate the viability of SPL as a known patterning method for the semiconductor industry. In this method, another technique describes a SPL technique which is known as Dip Pen Nanolithography. Dip Pen Nanolithography - in this process, the patterning is done by directly transferring chemical species to the surface. Dip Pen Nanolithography (DPN)Dip Pen Nanolithography (DPN) is known as a soft-lithography technique that uses an AFM scanning probe tip to draw nanostructures. In this process, a probe tip is coated with liquid ink, which then flows onto the surface to make patterns wherever the tip makes contact.
This kind of directwrite technique provides high-resolution patterning capabilities for a number of molecular and biomolecular “inks” on a variety of substrates. Some of the applications of the DPN technique include sol gel templates that are used to prepare nanotubes and nanowires, and protein nanoarrays to detect the amount of proteins in biological samples such as blood. This process was first developed by Professor Chad Mirkin at Northwestern University Nanotechnology Institute for depositing thin organic films in patterns with feature sizes of around 10 nm ( about 20 times better than the best optical lithography) (Mirkin, 1999). In DPN technology, the ink on a sharp object is transported to a paper substrate via capillary forces.
The capillary transport of molecules from the AFM tip to the solid substrate is used in DPN to directly “write” pattern consisting of a relatively small collection of molecules in nanometer dimesions.
An AFM tip is used to write alkanethiols with 30-nm line width resolution on a gold thin film in a manner analogous to that of a dip pen. Chemisorption and self-assembly of the molecules can be used to limit the diffusion of the molecules after deposition. Relative humidity seems to affect the resolution of the lithographic process by controlling the rate of ODT transport from the tip to the substrate. The size of the water meniscus that bridges the tip and substrate depends on relative humidity. For example, the 30-nm wide line required 5 min to generate in a 34% relative humidity environment, whereas the 100-nm line required 1.5 min to generate in a 42% relative humidity environment. DPN application on semiconductor surfacesDip-Pen Nanolithography can not only apply to gold surface using alkyl or aryl thiols as inks, but also to semiconductor surfaces, such as silicon and gallium arsenide.
Hexamethyldisilazane (HMDS) is used as the ink to pattern and modify (polarity) the surface of semiconductors. Lateral force microscopy (LFM) can be used to differentiate between oxidized semiconductor surfaces and patterned areas with the deposited monolayers of HMDS.
The choice of the silazane ink is a critical component of the process since the traditional adsorbates such as trichlorosilanes are incompatible with the water meniscus and polymerize during ink deposition. This work provides insight into additional factors, such as temperature and adsorbate reactivity, that control the rate of the DPN process and paves the way for researchers to interface organic and biological structures generated via DPN with electronically important semiconductor substrates (Ivanisevic, 2001).
DPN application on magnetic materials: Approach to high density recording and storageOver the past decade, there has been considerable interest in methods for synthesizing and patterning nanoscale magnetic materials. These nanomaterials show novel size-dependent properties, are potentially useful for high-density recording.
The conventional top-down approach in recording media is plagued by the difficulties of etching and patterning novel hard magnetic systems, especially as the individual recording elements approach the super paramagnetic limit at room temperature operations. This method utilizes a conventional atomic force microscope tip, coated with the BaFe precursor solution, to generate patterns that can be post-treated at elevated temperature to generate magnetic features consisting of barium ferrite in its hexagonal magnetoplumbite (M-type) structure. Conclusion In conclusion, the complete nanolithographic processes which include introduction, resists and masks, Photon-based lithography, electron beam lithography, ion beam lithography and emerging nanolithographic techniques like the alternate nanolithography techniques Micro-contact printing, Nanoimprint Lithography, Scanned Probe Lithography, Dip-pen Lithography were briefly discussed in this chapter. As a conclusion, the following table can presents the complete scenerio of the nanolithographic process.



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