Lithographic technique

Three steps are important for the success of photolithography and for forming microelectrode arrays  

Although a scanned aperture can be used to write arbitrary patterns, the predominant use of photolithography is in replicating a pattern on a mask into a layer of photoresist. Such a mask, also called photo mask, is either a nearly optical flat glass, which is transparent to near UV or a quartz plate, transparent to deep UV covered with a metal absorber pattern (about 800 A thick chromium layer). Such a mask is either placed in physical contact with the resists (contact mode), or an image of the mask is reduced and projected into the resists with an optical system (projection mode). 

2 Other lithographic techniques (X-ray, electron-beam, ion-beam) 

The improvement in optical resolution can be achieved either by inaeasing the numerical aperture or by reducing the wavelength of the illuminating light. This is a consequence of equation 10.7. The theoretical resolution of an optical system for projection printing is limited by Rayleigh diffraction  

In contrast, ion-beam lithography has a better resolution than electron beam lithography because the secondary electrons produced by an ion beam are of lower energy and have a shorter diffusion range so that hardly any back scattering occurs. The ion-beam spot has the 

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Traditional methods for fabricating nano-scaled arrays are usually based on lithographic techniques. Alternative new approaches rely on the use of self-organizing templates. Due to their intrinsic ability to adopt complex and flexible conformations, proteins have been used to control the size and shape, and also to form ordered two-dimensional arrays of nanopartides. The following examples focus on the use of helical protein templates, such as gelatin and collagen, and protein cages such as ferritin-based molecules. 

Abstract This article is a review of the chemical and physical nature of patternable block copolymers and their use as templates for functional nanostructures. The patternability of block copolymers, that is, the ability to make complex, arbitrarily shaped submicron structures in block copolymer films, results from both their ability to self-assemble into microdomains, the bottom-up approach, and the manipulation of these patterns by a variety of physical and chemical means including top-down lithographic techniques. Procedures for achieving long-range control of microdomain pattern orientation as well... 

The use of top-down lithographic techniques to topographically pattern substrates and thereby control the film thickness has been used to create submicron patterns that contain oriented microdomains. This approach is generally described as the graphoepitaxy method and will be discussed in further detail in Sect. 4.1, with other methods which use top-down approaches to control the bottom-up block copolymer patterns. 

In addition to the aforementioned methods for controlling substrate-polymer interactions uniformly across the entire surface, the use of top-down lithographic techniques to chemically pattern substrates provides spatial control over these substrate-polymer interactions and therefore provides even... 

The photoresponsive properties of molecular glasses also have been applied in the design of resists for semiconductor lithography. In a resist, irradiation changes the solubility of the materials, making it more or less soluble (positive or negative resist, respectively). The search for new resist materials follows the development of lithographic techniques toward deep-UV and electron beam... 

One of the most successful lithographic techniques is nanoimprint hthography (NIL), mainly because both its working principle and operation are quite simple (Chou et al, 1996). A schematic diagram of the NIL technique is shown in Fig. 3.22. 

Dip-pen nanolithography (Jiang and Stupp 2005) and soft lithography (Hung and Stupp 2007) have been used to control the placement and orientation of PA nanofibers on two-dimensional substrates. The soft lithographic technique is the more... 

To implement this strategy, multilayered semiconductor structures were grown by MOCVD and then processed using lithographic techniques to create trenches of 10-20 p-m. Trenches of 10 pm were used to create arrays of 34 interdigitated LED/photodiode pairs, as shown in Fig. 8. As molecules adsorb onto the surfaces of these semiconducting materials, the electronic properties of the surfaces can be altered and thus changes in current can be observed when molecules such as ammonia and sulfur dioxide adsorb onto the surfaces of the diodes. 

Molecular Self-Assembly. Reductive techniques, such as those used in the microelectronics industry, can produce structural features smaller than about 200 nm. The use of proximal probes and other nanomanipulative techniques can be considered to be a hybrid of the reductive lithographic techniques and die synthetic strategies of assembling functional nanostructures atom by atom, or molecule by molecule. The organization of nanostructures and devices by the self-assembly of the component atoms and molecules, a ubiquitous phenomenon in biological systems, forms die noncovalent synthetic approach to nanotechnology. 

Optical gene chips dense arrays of oligonucleotides have been successfully applied to detect transcriptional profiling and SNP discovery, where massively parallel analysis is required. However, the fluorescence-based readout of these chips involves not only highly precise and expensive instrumentation but also sophisticated numerical algorithms to interpret the data, and therefore these methods have been commonly limited to use in research laboratories. In this way, thin-film arrays of 14, 20, 25, 48 and 64 electrodes have already been fabricated [12,15,39,40,44,48], using lithographic techniques. Readout systems for these arrays based on electrical detection have also been developed. 

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