Step and repeat

Figure 9. Bilayer imaging of PCHMS using a 10 1 excimer laser step-and-repeat tool at 248 nm. 170 nm PCHMS over 1.0 pm of a hardbaked AZ-type photoresist 125 mJ/cm2. C>2-RIE image transfer, 0.4-pm images.

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)...

Figure 7. Schematic of a reduction step and-repeat system.

Figure 40. Operating modes for electron beam systems left — raster scan coupled with continuous table motion right — vector scan, step and repeat.

Several other successful machines have also been reported using raster scanning. The IBM EL-1 is a step-and-repeat type system that exposes a 5 mm x 5 mm field. These small fields are then stitched together to form the complete circuit. The EL-1 systems use a 2.5 /im x 2.5 fim square beam and are used to manufacture custom circuits. 

Figure 2. Modulation Transfer Functions (MTF s) for the Perkin Elmer Micralign cameras operating at 250 nm, 300 nm and 400 nm, and for a step-and-repeat camera lens with a numerical aperture of 0.35.

If distortions of the sample are truly isotropic, the only errors that remain after magnification is corrected are residual distortions in the optics, and mask errors. The easiest way to reduce mask errors is to go to 5X or 10X step and repeat systems, but eventually, it should be possible with electron beams to reduce mask errors to insignificant levels. Distortion in the optics of the model 500 is already below 0.1 pm and 3[Pg.15]

Step-and-repeat (S/R) cameras use refractive lenses with numerical apertures of 0.2 to 0.4. The best lenses expose a field of about 2 cm x 2 cm at a numerical aperture of 0.3. Higher numerical aperture is available for smaller field-size. The field-size and numerical aperture for many of the lenses used in microcircuit cameras are shown in Figure 3. Most lenses are designed to operate at a single wavelength that corresponds to a strong line in the mercury spectrum (365 nm, 405 nm, or 436 nm), but lenses have also been corrected for two wavelengths (405 nm and 436 nm) in order to reduce the effects of... 

Refractive lenses must always be used in the step-and-repeat mode because the field size they cover is very much smaller than a silicon wafer. Sample position is either tracked by a laser interferometer, after an initial reticle to wafer alignment, or the reticle and sample are aligned with respect to each other at every chip site (12-17). Alignment at every chip avoids errors... 

Figure 8. Electron micrographs of a trilevel aluminum lift off process employing a typical polysilane as the 02-RIE barrier. Key left, electron-beam imaged and right, optically imaged Mann step and repeat.

In non-ruminants, the malonyl CoA is combined with an acyl carrier protein (ACP) which is part of a six-enzyme complex (molecular weight c. 500 kDa) located in the cytoplasm. All subsequent steps in fatty acid synthesis occur attached to this complex through a series of steps and repeated cycles, the fatty acid is elongated by two carbon units per cycle (Figure 3.8, see also Lehninger, Nelson and Cox, 1993). 

Deep-UV source brightness is another issue, because the power output of a 1-kW mercury-xenon lamp in the 200-250-nm range is only 30-40 mW. For this reason, excimer lasers (such as KrCl and KrF), which can deliver several watts of power at the required wavelengths, are being considered as alternatives (7). In fact, a deep-UV step-and-repeat projection system with an all-quartz lens and a KrF excimer laser with an output at 248 nm has been reported (8). Even the laser-based systems require resists with a sensitivity of 30-70 mj/cm2. 

Blawas AS, Oliver TF, Pirrung MC et al (1998) Step-and-repeat photopatteming of protein features using caged/biotin-BSA characterization and resolution. Langmuir 14 4243 250 Conrad DW, Golightley SK, Bart JC (1998) Photoactivatable o-nitrobenzyl polyethylene glycol-silane for the production of patterned biomolecular arrays. US Patent 5,773,308... 

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