Oligomeric methyl silsesquioxane (O‐MSSQ) precursors were prepared from methyl trimethoxysilane (MTMS) in a mixed solvent of methyl isobutyl ketone and tetrahydrofuran by variations in the pH and molar ratio of water to MTMS (R1). The molecular structures of O‐MSSQ were controlled by the reaction conditions. At a fixed pH value, the percentage of the end group, SiOCH3, decreased with increasing R1, but that of SiOH increased. With the pH increasing, the ratio of SiOCH3 groups to SiOH groups was enhanced, but ratio of the molecular weights was reduced. The molecular weight distribution was progressively broader as the pH value decreased. These results were explained by the effects of R1 and pH on the hydrolysis and condensation reactions. The prepared O‐MSSQ precursors consisted of mixed cage and network structures. The ratio of cage structures to network structures increased at low pH and high R1 values. Highly uniform thin films were spin‐coated from the O‐MSSQ precursors, and this was followed by multistep curing. The content of cage structures in O‐MSSQ films decreased with increasing curing temperatures, whereas the network content in O‐MSSQ films showed the opposite trend. Such a structural transformation resulted in significant variations in the physical properties. Both the refractive index and dielectric constant decreased with higher cage/network ratios because of changes in the molar volume. The prepared O‐MSSQ has potential applications as a low dielectric constant material. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1560–1571, 2002

Because of the everlasting promotion of micro/nano-fabrication techniques, the measurement of the feature contour of micro/nano-fabricated structures become an important issue. Atomic force microscopy (AFM) is a high accuracy measurement instrument that has been frequently used in measuring of micro/nano-fabricated structures. However, most conventional AFM systems use a single probe with a monotonic tilting angle to scan all kinds of sample profiles. This type of AFM design easily suffers from the so-called "side wall effect", and the scanning result will induce a distortion phenomenon at the corner part. To solve this problem, a novel dual probe AFM system is proposed in this paper. A highly flexible system structure is adopted in this work to create different tilting angle of each probe. With the method developed for obtaining the appropriate tilting angle, we set up the so-called "effective tilting angles" under different scanning scenarios. In addition, a useful merging method has been developed to stitch together the scanning results from two different probes out of two different scanning units. For scanning a standard grating, the error of sidewall angle from the scan image decreases form 27.3 % to 4.5 % when our method is compared with a traditional scan. Finally, by integrating the proposed scan method with a new raster based local scan strategy, we can achieve a high-throughput precision scan. In the scan of human blood cells, we not only can remove unnecessary scan area up to 61.04 % but also can improve sidewall distortion. A comprehensive series of experiments have been conducted to validate the scanning capability of the proposed methods on our self-developed AFM system.

No abstract

No abstract

No abstract