Lithography optical

1971 Near contact printing Cyclized rubber 1 Kbit DRAM 8 12 

1974 Near contact printing DNQ/Novolac 4 Kbit DRAM 6 

Unfortunately, contact printing was plagued by a number of practical and technical difficulties. Bringing the mask and the wafer into direct contact causes damage to the mask and creates defects, which are reproduced in subsequent exposures. In addition, nonflatness of the wafer and mask results in alignment 

Practical and technical difficulties associated with contact printing led to a modification of the latter technique, such that the mask and the wafer were separated by a small, accurately controlled gap of 10-25 p,m during exposure. Introduced in the early 1970s, this technique, known as proximity printing, minimizes mask and wafer damage caused by contact, but at the expense of resolution. This gap, however, limited resolution because of diffraction. The theoretical resolution of proximity printing is given by 

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Optical glass Optical glasses Optical holography Optical lithography... 

Optical Lithography. Optical Hthography uses visible or ultraviolet light as the exposure media, and is the dominant Hthographic process used for patterning IC wafers. The linewidth limit is near 0.4 p.m, although some narrower features may be possible (34). The masks typically are made from patterned, opaque chromium films on glass. 

Preliminary experiments with electron-beam writing and ion-beam projection lithography have demonstrated that the S-layer may also be patterned by these techniques in the sub-lOO-nm range (nnpnblished resnlts). The combination of ion-beam projection lithography and S-layers as resist might become important in the near fntnre, since ion beams allow the transfer of smaller featnres into S-layer lattices compared to optical lithography. 

Alivisatos and coworkers reported on the realization of an electrode structure scaled down to the level of a single Au nanocluster [24]. They combined optical lithography and angle evaporation techniques (see previous discussion of SET-device fabrication) to define a narrow gap of a few nanometers between two Au leads on a Si substrate. The Au leads were functionalized with hexane-1,6-dithiol, which binds linearly to the Au surface. 5.8 nm Au nanoclusters were immobilized from solution between the leads via the free dithiol end, which faces the solution. Slight current steps in the I U) characteristic at 77K were reflected by the resulting device (see Figure 8). By curve fitting to classical Coulomb blockade models, the resistances are 32 MQ and 2 G 2, respectively, and the junction... 

On the way to more reliability in device fabrication, Kronholz et al. reported on the reproducible fabrication of protected metal nanoelectrodes on silicon chips with <30nm gap width and their electrochemical characterization [33]. For the fabrication of the chips, an optical lithography step and two electron-beam steps are combined (Figure 18). 

Optical lithography, in compound semiconductor processing, 22 193 Optically active citronellol, 24 506 Optically transparent porous gel-silica, 23 75, 76 Optical materials nonlinear, 17 442-460 second-order nonlinear, 17 444—453 third-order nonlinear, 17 453-457 Optical memory, photochromic material application, 6 602 Optical microscopy, 16 467-487 history of, 16 467-469 in kinetic studies, 14 622 liquid immersion, 15 186 Optical mode density, 14 849, 850-852 Optical multichannel analyzers (OMAs), 23 143... 

Ultrathin resists have many technological advantages In optical lithography they offer improved exposure and focus latitude (2), and alleviate the problem of... 

Optical Lithography. For the novolac/PAC films, the PAC concentration was varied rather than the film thickness. Films with 5 % PAC could not withstand the Cr... 

The continued downscaling of transistor sizes is essential to the continuation of Moore s law. Lithography has always been a limiting factor. Optical lithography is limited by the optical resolution... 

However, again this application did not succeed. Optical lithography continues. First by steppers with half or third spacing. Now, a new form of lithography is close to implementation, known as extreme-UV lithography. This uses coherent UV from a plasma of Sn4+ ions, which emits at around 100 eV. 

Figure 3. Schematic of present and potential future optical lithography systems (a) Perkin Elmer Micralign (10), (b) Bell Labs printer (11), (c) reduction step-and-repeat (Censor, Electromask, GCA, Optimetrix, Philips), (d) IX step-and-repeat (Ultratech), (e) IX stripe scan, and (f) reduction step-scan, R indicates object and image orientations. Lenses are indicated only schematically. (Reproduced with permission from Ref. 30)...

We have now discussed qualitatively several concepts which are important in developing an understanding of image projection in optical lithography. These are summarized below ... 

King, M. C. "Principles of Optical Lithography" in VLSI Electronics Microstructure Science, 1981, 7, ed. by Einspruch, N. G., Academic Press, New York, N.Y., p 41-81. 

Institute of Technology (Reese et al., 2003). Using optical lithography to etch away photolithographic resists on stainless steel foils, french pens were designed with a rectangular geometry of 6 p in depfh, 30 p in width with 30 p sidewalls at the tips. To add structural support, the features anterior to the tip were expanded out so that the width of the sidewalls increased to 120 p with a trench width set at 90 p. 

Nonlinear optics, lithography, conductors, semiconductors, piezoelectronic, pyroelectronic, solar energy conversion, electrodes, computer chip circuitry UV absorption, smart materials, nanocomposites, laser, sealants, paints, caulks, lubricants, gaskets... 

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