Pattern transfer fidelity

Dry etching is a well established pattern-transfer technique in IC technology, characterized by a very good ability to pattern fine lines and by a high fidelity of pattern transfer [31]. It has become an important complementary technique for fabricating microstructures, after it has been adapted to the specific requirements of very deep etching. 

In order to support the ever-shrinking device dimensions, a dry etching technique was developed to replace wet chemical etching for high-fidelity pattern transfer by Irving and co-workers ° in 1971 in a process that involved the use of a CF4/O2 gas mixture to etch silicon wafers. Molecular beam epitaxy, developed also in 1971 by Cho, offers the advantage of near-perfect vertical control of composition and doping down to atomic dimensions, and is now applied extensively in the fabrication of photonic devices and quantum effect devices. ... 

Another means of expressing the fidelity of an optical system is in terms of its modulation transfer function. The modulation transfer function describes the ability of the optical system to accurately reproduce an object whose pattern of luminance varies in a sinusoidal manner. An optical system which can precisely duplicate the modulation pattern of the object in the modulation pattern of the image has a modulation transfer function equal to 1.0 this represents the performance of a perfect system. The greater the difference between the modulation pattern in the image compared with that in the object, the lower the modulation transfer function. In practice, the modulation transfer pattern is usually evaluated with a square-wave pattern produced by a periodic array of lines. The modulation transfer function approaches zero as the spatial frequency of the lines increases. The limiting resolution in terms of the modulation transfer function is... 

Role of RNA intermediates (Herbert and Rich, 1999). The mutation rate of a genome is likely to increase when genetic information is passed through RNA whether RNA is a viral genome or a retrotransposon because RNA polymerase reaction is neither edited nor subject to post-replicative repair. In addition, hotspots of a genetic chain in RNA retrotransposons can result from nomandom patterns of a decreased fidelity strand transfer to other templates and untemplated extensions. 

Fig. 7.5 Top Schematic of experimental device during the EHD lithography process under a laterally heterogeneous electric field, (a) A structured upper plate creates a heterogeneous force field focusing the instability towards the protruding structures (b). In (c) a positive replica of the master pattern is transferred into the polymer. In unstructured regions, the film remains stable on a much longer lime scale. Bottom High fidelity EHD lithography showing the robustness of pattern replication with respect to the parameters of the electrode...

Micro-molding in capillaries (MIMIC) represents another form of RM. In MIMIC, a patterned polymeric mold is placed into conformal contact with a surface to form a network of empty channels. When a low-viscosity photocurable fluid (such as PU) is placed at the open ends of the channels, the liquid spontaneously fills the channels by capillary action. After the PU is cured under UV light, the mold is removed to leave behind a network of polymeric features. Although MIMIC is a remarkably simple technique and transfers features with high fidelity, it is limited by the viscosity of the liquid precursors that can fill the channels. Channels having dimensions smaller than 100 nm are difficult to fill by capillary action. Figure 7 illustrates the general process of MIMIC. 

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