Multilayer resolution

Figure 2.16 (a) Pure spectra and some distribution maps coming from global multilayer resolution analysis (b) Plot of the signal contribution (in percentage) from the different constituents in the different layers. 

Recently commercially available X-ray systems for laminography have a spatial resolution limited to hundred microns, which is not enough for modem multilayer electronic devices and assembles. Modem PCBs, flip-chips, BGA-connections etc. can contain contacts and soldering points of 10 to 20 microns. The classical approach for industrial laminography in electronic applications is shown in Fig.2. 

Laminographical approaches can be used for layer-by-layer visualization of the internal microstructure for the flat objects (multilayers, PCBs etc.), that caimot be reconstructed by computerized tomography because of the limited possibilities in rotation. Depth and lateral spatial resolutions are limited by the tube, camera and rotation accuracy. Microfocus X-ray tubes and digital registration techniques with static cameras allow improving resolution. Precision object manipulations and more effective distortion corrections can do further improvement. 

Initial results prove the high potential of LA-based hyphenated techniques for depth profiling of coatings and multilayer samples. These techniques can be used as complementary methods to other surface-analysis techniques. Probably the most reasonable application of laser ablation for depth profiling would be the range from a few tens of nanometers to a few tens of microns, a range which is difficult to analyze by other techniques, e. g. SIMS, SNMS,TXRE, GD-OES-MS, etc. The lateral and depth resolution of LA can both be improved by use of femtosecond lasers. 

The intramembranous domain of Ca -ATPase contains of the mass of the ATPase molecule based on electron microscopy of Ca -ATPase crystals [90,91] and X-ray diffraction analysis of oriented multilayers of sarcoplasmic reticulum [140]. Although in speculative models developed from these reconstructed structures the intramembranous domain was pictured as containing ten transmembrane helices [141,142], at the resolution attainable so far, several alternative transmembrane arrangements would be equally possible. 

Nakamura, M., Kiyohara, S., Saito, K. Sugita, K., and Sugo, T., High resolution of DL-tryptophan at high flow rates using a bovine serum albumin-multilayered porous hollow-fiber membrane, Anal. Chem., 71, 1323, 1999. 

XANES spectroscopy is also the basis of chemically sensitive X-ray imaging, as well as qualitative and quantitative microspectroscopy [306], ptXANES is attractive for chemical analysis, with its spatial resolution down to 10 ptm. Variations on the theme are surface EXAFS (SEXAFS), grazing incidence XAS and in situ time-resolved XAS investigations. Grazing angle XAFS can be used for the study of ultrathin multilayer systems. 

Films of 7 3 mixtures of 1-naphthyl acrylate and ethoxylated bisphenol-A dimethacrylate had better planarizing properties than any of the resins that were examined and may be useful as layers for etchback processing. For use as bottom layers in multilayer-resist structures it will be necessary to bake the films after uv hardening to increase the Tg, and if the exposure wavelength is above 300 nm, an appropriate dye must be added to eliminate substrate reflections that degrade resolution. 

Electron Beam Lithography. LB PMMA films with thicknesses of 6.3 nm (7 layers) are sufficient for patterning a Cr film suitable for photomask fabrication. For ultrathin PMMA films the resolution (see Fig. 1) is limited by the smallest spot diameter available on MEBES I (1/8 pm). However, it is not possible to obtain this resolution if a thicker resist (>100 nm) is used under the same exposure and development conditions, which demonstrates that ultrathin resists are able to minimize the proximity effect. Also, since the radius of gyration of 188,100 Mw PMMA is about 10 nm in the bulk, and the thickness of the 7 layer film (6.3 nm) is less than 10 nm, it is reasonable to assume there must be an alteration of chain configuration in the ultrathin films. This will be particularly true when the post-deposition baking temperature of the multilayer films is less than the glass transition temperature (115°C), as is the case for the present experiments. In such a case, interdiffusion of PMMA chains between the deposited layers may not result in chain configurations characteristic of the bulk. 

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