Alex BuzdugaMatt MostellerDNA LithographyIn a continuous attempt to keep up with Moore's Law, the techniques of transferring patterns to silicon wafers have been improved. Starting with UV-light lithography, steps have been taken to reduce the smallest feature size, to the point where the industry and scientists can work at the nanometer scale when designing transistors to be placed on wafers.DNA Lithography is one of the most recent next-generation lithography techniques (which include X-ray lithography, e-beam lithography, EUV lithography, focused ion-beam lithography and others) that are candidates to replacing traditional photolithography, and its variations and improvements. In order to replicate itself, DNA separates into its two strands, which then, with the use of enzymes and other catalysts, create their counterparts through chemical reactions. Similarly, in DNA Lithography, the concept is of replicating patterns on a substrate by using DNA strands that have been engineered in order to create particular shapes and patterns. The original strands can be potentially used to create millions of copies of themselves, and could be used like the Gutenberg movable type, to create a certain pattern on different parts of a wafer.The technique has been researched at multiple centers across the country, including Masachussets Institute of Technology's Supramolecular Nano Materials Group, IBM's Almaden Research Center at the California Institute of Technology, and NimbleGen Systems Inc. in Madison, Wisconsin. At the California Institute of Technology, prof. Paul Rothemund claims he assembled more than 100 billion copies of a desired shape with a pattern on top to which components could be attached in a single drop of water. Resolution wise, spacing between elements was down to about 6nm , and they could align elements with a less than 10 degrees precision – a crucial element in the fabrication process. Fig. 1 (source: http://www.cs.duke.edu/courses/spring06/cps296.5/papers/KKGBSB02.pdf )As Fig. 1 shows, once the pattern is stuck to the substrate, there are various ways to convert the organic material into semiconductors, metals, and insulators. Because of the very small scale of the organic components, they can potentially assemble submicron patterns on semiconductors that exceed the limits of the most optimistic predictions for future photolithographic techniques. Diatoms ( single-celled phytoplankton – algae ) are some of the organisms whose DNA strands are used to create the microscopic patterns. These organisms are one of the most abundant life forms on Earth, and they help reduce CO2 by encasing themselves in patterned silicon dioxide shells as they fall to the bottom of oceans and lakes worldwide. They build their shells by successively depositing submicron-sized lines of silicon dioxide, which makes them very useful for the fabrication of semiconductor microchips. By identifying and genetically engineering the 75 genes that are responsible with silicon fabrication from the DNA of diatoms, scientists are slowly starting to harness the power of this soft lithography technique. Currently, DNA lithography resolution is limited by the genetic engineering tools available to scientists, which means the smallest feature size is around 40nm, but the future is bright – a commercial packaging of the technology could be ready in the next decade, at much better precision than the one available now. While it is clear that there it will still be some time before DNA-assisted lithography moves to the forefront as the prominent mass production technique, the apparent advantages that this method has over present ones is undeniable. Foremost amongst these advantages is the ability of researchers and developers to create patterns with line widths as small 6nm. With current lithography techniques having a maximum precision of around 22nm line width, including the most advanced techniques such as X-ray lithography and electron-beam direct write, the ability of DNA-assisted lithography to make such small details on chips will allow for a dramatic increase in the number of components embedded in each chip. While there are a variety of other physical limitations that must be considered when attempting to make structures that small (parasitic resistances and capacitances, tunneling of gate oxide, etc.) the mere fact that such elements can be constructed gives researchers a vast increase in potential for the future of the semiconductor industry. Though not as essential to the success of DNA-assisted lithography as its improvement in resolution, the throughput rate of this method is also a major advantage, especially when considering the precision obtained through the process. While the construction of the base pattern, the pattern of hybridized DNA that is constructed to create the chip’s layout, is a very time consuming process, after this initial construction the production of wafers of chips boasting this pattern increases dramatically. Since the DNA pattern works essentially as a printing press, copies of this pattern can be produced quickly and with relative ease. This speed of production, coupled with its low manufacturing costs, are projected to make DNA-assisted lithography in excess of ten times more cost-effective than current production methods, leaving it as the clear choice for large scale production upon its inception into the marketplace. Of final note concerning the advantages of DNA-assisted lithography is the ease by which components made using the method can be studied as arrays of individual structures and the ease by which they can be compatibly integrated with one-another to create more complex nanosystems. Overall, the advantages of this technique over pre-existing lithography techniques are outlined below.Method Max. Resolution Cost (startup/manufacturing)DNA-assisted Photo 6 - 22 nm high startup (~$4mil), low afterUV Photolithography 200 nm $ 0.2 millionDUV Photolithography 65 nm $ 0.5 millionE-Beam Direct Write 30 nm $4 millionE-Beam Projection 35 nm $4 millionX-Ray Photography 30 nm > $10 millionIon Projection 25 nm ~ $4 millionWhile the advantages of DNA-assisted lithography are undeniable and clearly outweigh any current draw-backs, such disadvantages still do exist and are therefore worthy of mention. While not a strict draw-back of the process itself, the fact that most researchers still modestly claim that it will be at least ten years before this