Iodinated polystyrene (IPS) is obtained by direct iodination of polystyrene and its lithographic characteristics are investigated. The sensitivity of the polymer to electron beams is increased as the result of iodination by a factor of about 10 and reaches 1 μC/cm2. Coated IPS films are very stable and no changes in exposure characteristics are observed even after pre‐baking at 220°C for 10 min. It is found that crosslinking does not proceed in a vacuum after electron beam exposure. The milling rate of IPS under Ar+ bombardment is measured to be 0.25 nm/s. This is lower than that of poly(glycidyl methacrylate‐co‐ethyl acrylate) (0.67 nm/s) and that of permalloy (0.42 nm/s), both obtained under the same conditions. The mechanism of sensitization by iodination is discussed.
We prepared c-axis aligned, large single-domain Nd-Ba-Cu-O (NdBCO) bulk superconductors with the addition of Ag 2 O by the melt-processing technique under a flowing Ar gas atmosphere using Ag-free NdBCO as seed crystals. The melt-processing condition has been elaborated by varying the contents of Ag 2 O and CeO 2 , and the molar ratio of Ba to Cu. We successfully synthesized c-axis aligned, single-domain samples, free from serious cracks or weak links, 30 mm in diameter and 13 mm in thickness in the range of 15-20 wt% Ag 2 O, 0-0.5 wt% CeO 2 and 0.706-0.76 for the Ba to Cu ratio. The largest trapped field of these NdBCO samples was 1.23 T at 77 K and 7.0 T at 42 K, while fracturing of the sample occurred at a further lower temperature. We found that the field trapping performance of the present NdBCO/Ag samples is almost the same as that of our previously reported SmBCO/Ag samples, but the critical stress of fracturing was smaller for NdBCO/Ag.
Poly(4-vinylphenol) sensitized by an aromatic monoazide compound (4-azidochalcone), called MRL (Micro Resist for Longer wavelengths), has been prepared and evaluated as a negative UV resist. The resist is sensitive to radiation in the 300 to 400 nm region. The sensitivity of MRL is comparable to that of a positive quinonediazide photoresist under exposure to unfiltered light from a high pressure Hg lamp. An aqueous base developer removes the unexposed areas of MRL with no evidence of swelling of the exposed areas, indicating its high resolution capability. The main products in the exposure of MRL films are found to be primary and secondary amines. It is concluded that the formation of secondary amines attached to the polymer chain is responsible for the insolubilization of the exposed MRL in the base developer.
Relative rates were measured for polymer film loss in an oxygen plasma environment. Both polymers doped with iodine compounds and iodinated polymers show high resistance to the oxygen plasma. Our ESCA studies on iodinated polystyrenes indicate that the oxygen plasma converts the iodo-substituent to iodine oxides. Through taking advantage of the oxygen plasma resistance of iodine compounds, we have been able to come up with a two-layer photolithography system for microfabrication. In the context of this two-layer process, evaluations were made of a positive photoresist formulated from OFPR-800 (Tokyo Ohka Kogyo Company) and 2,4,6-triiodophenol, as well as a negative deep-UV resist composed of iodinated poly(vinyl phenol) and 3,3'-diazidodiphenyl sulfone.
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