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Nanolithography: Processing Methods for Nanofabrication Development Ruchita, Richa Srivastava* & B.C.Yadav Department of Applied Physics, M.Tech

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Nanolithography: Processing Methods for Nanofabrication Development Ruchita, Richa Srivastava* & B.C.Yadav Department of Applied Physics, M.Tech Imperial Journal of Interdisciplinary Research (IJIR) Vol-2, Issue-6, 2016 ISSN: 2454-1362, http://www.onlinejournal.in Nanolithography: Processing Methods for Nanofabrication Development Ruchita, Richa Srivastava* & B.C.Yadav Department of Applied Physics, M.Tech. Nano-Optoelectronics Programme, Babasaheb Bhimrao Ambedkar University (A Central University), Lucknow-226025 Abstract: The present review article deals with the Nanolithography includes the various mask or detailedintroduction and classification of mask less, top-down or bottom-up, beam or tip- lithography techniques. Nanolithography is the based, resist-based or resist-less and serial or branch of nanotechnology through which parallel methods. So based on these particular nanofabrication of the patterns or structures can be methods, nanolithography techniques may done very easily. Nanolithography can be include [2] -photolithography, electron-beam considered as a revolutionizing advancement in lithography, nano-imprint lithography, micro- nanotechnology. Nanolithography has various contact lithography, scanning probe techniques and each technique has its own lithography, X-ray lithography etc. advantages and applications in different fields. These nanolithography techniques have This review also summarizes different types of been widely used in the semiconductor and IC direct and indirect techniques of fabrications using industries and play a vital role in manufacturing various substrates, photo resists and photo masks. nanoelectro-mechanical systems (NEMS) and The present article helps to know about the micro electro-mechanical system (MEMS) different methods or ways of fabricating nano devices.Besides this, nanolithography is useful patterns with ease or difficulty depending upon the in fabricating nanoscale photo detectors and technique. Also in this review, the advantages, ring transistors. It also includes various disadvantages and applications of each lithography applicationsin cell biology, microelectronics, techniques are discussed. surface chemistry, micromachining, patterning Keywords: Nanolithography, photolithography, cells, patterning DNA and patterning protein. electron beam lithography, micro-contact 2. Types, Advantages, Disadvantages printing, nano-imprint lithography, X-ray lithography, fabrication. and Applications of Lithography 2.1 Photolithography 1. Introduction Photolithography, as the name depicts is Nanolithography, as the name depicts is again derived from the Greek words in which basically derived from the Greek words in the words 'photo', 'litho', and 'graphy' all have which “nanos”, means dwarf; “lithos”, means the Greek meanings as 'light', 'stone' and rock or stone; and “graphy” means to write. 'writing'. Photolithography is basically a Thus, the literal translation can be illustrated as conventional and classical technique and it is "tiny writing on stone". Nanolithography is the also termed as optical lithography or UV branch of nanotechnology, which is concerned lithography.In the 1820s, NicephoreNiepce with the study and application of the structures invented a photographic process that used or the patterns which are fabricated at Bitumen of Judea, a natural asphalt as the first nanometer scale [1]. Therefore, it means the photo resist. In 1940, Oskar Suß created a nano patterning with at least one lateral positive photo resist by using dimension between the size of an individual diazonaphthoquinone. Later in 1954, Louis atom and approximately 100 nm. Plambeck Jr. developed the Dycryl polymeric Nanolithography is considered to be the letterpress plate, which made the plate making most advanced technique in patterning the process faster. ultra-high-resolution patterns of arbitrary A photolithography system generally shapes to a minimum feature size of a few consists of a light source, a mask, and an optical nanometers. Thus, nanolithography is basically projection system. This technique basically concerned with the fabrication of different utilizes the exposure of photo-resist to patterns and on different substrates as required. ultraviolet light to obtain the desired pattern. Imperial Journal of Interdisciplinary Research (IJIR) Page 275 Imperial Journal of Interdisciplinary Research (IJIR) Vol-2, Issue-6, 2016 ISSN: 2454-1362, http://www.onlinejournal.in For the procedure to start, it is required to project UV pattern from an excimer laser prepare a wafer or substrate with an oxide layer (wavelength of 193 or 248 nm) on the on it. The process further continues with the photo-resist. This enables pattern-size spin coating of photo resist on the substrate. reduction by 2-10 times. This system is Generally, the commonly used photo resist is capable in fabricating high-resolution polymethyl methacrylate (PMMA). The PMMA patterns as small as a few tens of is a polymer of methyl methacrylate with a nanometers (37 nm) and at a high chemical formula (C5H8O2)n. It is basically a throughput of (60-80 wafers/hr). This linear thermoplastic polymer with a melting system has a very expensive set up as it point of 130oC and glass temperature of 100- requires precision control systems of 105oC.Now, the UV light with wavelengths temperature and position and also requires generally ranging from 193-436 nm is a typical optical lens system. Thus, it is illuminated through the photo mask.This photo helpful in manufacturing advance IC and mask usually consists of the opaque features on CPU chips. a transparent substrate (e.g., quartz, glass) to make an exposure on a photo-resist. The exposed area of photo-resist break down which results in more soluble in a chemical solution called developer. Subsequently, the exposed photo-resist is removed to form the desired photo-resist pattern [3-8]. The technique of photolithography can be further explained with the help of a diagram as shown in Fig.1. Figure 2.The three forms of Photolithography (a) Contact printing, (b) Proximity printing, (c) Projection printing Advantages of Photolithography The advantages of Photolithography are given as under: i. The process of photolithography is less expensive and highly efficient in fabricating extremely small incisions on a substrate. Figure 1.Various steps involved in ii. This technique does not require any Photolithography technique. additional tool or material for etching patterns to form an integrated circuit The system of Photolithographycan exist in andonly a single beam of UV light is three forms [9] - sufficient for this task. Contact Printing: In the contact printing iii. The determination of exact shape and size the photo mask is placed in direct contact of any substrate can be monitored by using with the photo resist. Photolithography the process of photolithography. uses these printings in most of research works. Disadvantages of Photolithography Proximity Printing: Proximityprinting is Along with the advantages, Photolithography almost similar to the method of contact has various disadvantages given as follows: printing. In this, photo mask is not in direct i. The process of photolithography requires a contact but with a closed proximity with clean room environment free from all the photo resist. liquids, contaminants and environmental Projection Printing: A projection printing hazards. system uses an optical lens system to Imperial Journal of Interdisciplinary Research (IJIR) Page 276 Imperial Journal of Interdisciplinary Research (IJIR) Vol-2, Issue-6, 2016 ISSN: 2454-1362, http://www.onlinejournal.in ii. In order to fabricate effective patterns, this technique requires a completely flat substrate. iii. This technique is inefficient in producing flat objects. Applications of Photolithography Photolithography has numerous applications which include the following: i. Photolithography can fabricate integrated circuits and other internal computer parts. ii. This technique can be used for the fabrication of microcircuits [10], NEMS, Figure3.Steps involved in the process of Electron MEMS etc. Beam Lithography. iii. Photolithography can also be used to fabricate organic memory devices [11] for Advantages of Electron Beam Lithography an array structure. Electron Beam Lithography has several advantages mentioned as under: 2.2 Electron Beam Lithography i. This technique uses electron beam instead Electron beam lithography is a form of of photons. mask less lithography [12], used for fabricating ii. Pattern can be drawn directly on the nanoscale patterns. The evolution of this substrate with high resolution. technique started in 1960’s where the patterns iii. This technique is helpful in developing were directly written on the wafer with a SEM specialized and prototype devices. type Gaussian beam system with one pixel at a time [13]. Now, during 1970’s IBM introduced the concept of shaped electron beams with Disadvantages of Electron Beam Lithography multiple pixels leading to high throughput and Electron Beam Lithography have also certain manufacturing of large scale semiconductor disadvantages including- chips [14]. i. Machines available for this technique are This technique uses an accelerated beam of costly. electrons to focus on an electron sensitive resist ii. The system is too much complicated. to make an exposure.Now, this electron beam is iii. The process is time taking and inefficient. scanned on the surface of the resist with the diameter as small as a couple of nanometers in a layer by layer fashion to generate the required Applications of Electron Beam Lithography patterns in sequence. Some of the applications of Electron Beam For the process
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