Comprehensive X-ray reflectivity (XR) studies were conducted to characterize the structure of thin polyalkylsilicate films made of a poly(methylsilsesquioxane-co-ethylenylsilsesquioxane) precursor containing a star-shaped poly( -caprolactone) as a pore generator (porogen). The films were deposited on silicon wafer substrates by spin-coating and subsequently cured at various temperatures. Such spin-on glasses have a potential application as a low-dielectric-constant material for advanced semiconductors. Because highintensity synchrotron X-ray radiation was used, the XR data could be measured over 9 orders of magnitude in intensity, which facilitated the observation of fine structural details. A hierarchical fitting procedure for modeling the XR data is given. By evaluation of the critical angle of total reflection of the film material, which was observed at smallest angles, in particular the film electron density could be determined with a high accuracy. The films cured at 420 °C show a lower electron density as compared to those cured at 250 °C. This is explained by the fact that at the higher temperature the porogen is calcined and escapes from the films leaving behind a nanoporous structure. Film porosities could be estimated from the observed changes in the electron densities. From the very large number of high-frequency oscillations observed in the XR curves, it is concluded that the films exhibit a homogeneous, well-defined structure with small interface and surface roughness. The film thickness could be determined with an accuracy of (1 Å. The observation of an additional low-frequency modulation of the XR curves revealed a surface skin layer with a thickness of ca. 45 Å and with a slightly increased electron density as compared to the bulk of the film.
New soluble polyimides with improved adhesion to copper were synthesized from 6,4‘-diamino-2-phenylbenzimidazole (BIA) and 2,2‘-bis(trifluoromethyl)-4,4‘-diaminobiphenyl (TFDB) with 3,3‘,4,4‘-benzophenone tetracarboxylic dianhydride (BTDA) via one-pot synthetic method using N-methylpyrrolidone (NMP) as a solvent. Precipitation or gelation did not occur during imidization, and the synthesized polyimides having inherent viscosity values of 0.86−1.74 dL/g were dissolved well in polar aprotic solvents and phenolic solvents. Flexible and fingernail-creasable films were formed on casting. T g values of the polyimides were in the range of 320−351 °C and 5% weight loss in nitrogen occurred above 540 °C in all cases. The polyimides containing an equimolar amount of BIA and TFDB showed good adhesion to copper without any adhesion promoters. Water absorption and dielectric constant of the polyimides were in the ranges of 0.57−1.18% and 2.74−2.94, respectively. The polyimides containing a higher content of benzimidazole rings exhibited higher adhesion to copper.
A two-dimensional liquid chromatography (2D-LC) method, normal phase liquid chromatography (NPLC) for one dimension and reversed phase liquid chromatography (RPLC) for the other dimension, was employed to map the molecular weight distribution (MWD) of the individual blocks of a polystyrene-block-polyisoprene (PS-b-PI) diblock copolymer. The first-dimension (1st-D) NPLC separates PS-b-PI according to the PS block length while the second-dimension (2nd-D) RPLC separates PS-b-PI according to the PI block length. For the first-dimension NPLC separation, the column temperature was controlled to improve the resolution while the 2nd-D RPLC was run isothermally to reduce the separation time. The MWD information of individual blocks provides equivalent information to MWD and chemical composition distribution of a block copolymer. In this analysis, the effluent from the 1st-D LC separation is concentrated before the injection to the 2nd-D LC by use of a trap column, which allows an efficient interface between the two LC separations. Over 200 different block copolymer species could be identified from the 2D-LC chromatogram.
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