Electron beams using poly

The intensity of the electron beam used to examine thin crystalline polymer films by electron microscopy is usually of sufficient intensity to induce cross-linking. It is not surprising, therefore, after initial examination in the crystalline state, that thin films of poly(amides) and polyethylene display ordered structures when subsequently examined in the molten state by this technique. These observations are to be expected. They cannot be construed as evidence that, in general, the liquid state in polymers is an ordered one.(33) The partially ordered liquid represents an interesting, unique situation that results from the nature of the chain arrangement at the time of network formation. 

Thickness Measurement. The thickness of poly(I) at different coverages was obtained using a Tencor alpha-step 100 surface profile measuring system. Electrodes used were glass slides coated with Pt by electron beam evaporation. In order to produce a "step" across which the stylus of the surface profiler was drawn, Apiezon N grease was applied to part of the electrode surface and was removed with CH2CI2 after derivatization with poly(I). 

Interest in solution inhibition resist systems is not limited to photoresist technology. Systems that are sensitive to electron-beam irradiation have also been of active interest. While conventional positive photoresists may be used for e-beam applications (31,32), they exhibit poor sensitivity and alternatives are desirable. Bowden, et al, at AT T Bell Laboratories, developed a novel, novolac-poly(2-methyl-l-pentene sulfone) (PMPS) composite resist, NPR (Figure 9) (33,34). PMPS, which acts as a dissolution inhibitor for the novolac resin, undergoes spontaneous depolymerization upon irradiation (35). Subsequent vaporization facilitates aqueous base removal of the exposed regions. Resist systems based on this chemistry have also been reported by other workers (36,37). 

Poly(methylmethacrylate), PMMA, Is a well-known degradable polymer in the radiation chemistry of macromolecule (1). Hatzkis reported that PMMA is an excellent resist material usable in the microfabrication technology for manufacturing the microelectronic devices where X-rays and electron beams are used as radiation sources (2). 

An early commercial interest in poly (olefin sulfones) was sparked by the low raw materials cost, but this interest waned when it became apparent that thermal instability is a general characteristic of this class of materials. In 1970 Brown and O Donnell reported that poly (butene-1-sulfone) is degraded by gamma radiation with a G(s) approaching 10, making it one of the most radiation-sensitive polymers known (38-39). The potential for use of this radiation sensitivity in the design of electron beam resists was quickly realized by several members of the electronics industry. Bell Laboratories, RCA, and IBM published studies demonstrating the potential of poly (alkene... 

The flue gas from municipal waste incinerator boilers contains SO2, and HCl. To remove these harmful components simultaneously by dry process, electron beam treatment method was investigated. The pilot-scale test was conducted in Matsudo, Japan, in 1992 with a flue gas of 1000 m /hr [34]. Recently, dioxins, namely, poly-chlorinated-di-benzo-paradioxins (PCDDs) and poly-chrorinated-di-benzo-furan (PCDFs), from incinerators have become a very serious problem because of their high toxicity. Pilot-scale tests to decompose dioxins by electron beam irradiation were conducted in Karlsruhe, Germany [35], and in Takahama, Japan [36], using almost the same capacity of flue gas, 1000 m /hr. Very promising results were obtained with decomposing more than 90% of dioxins. 

Okano et al. [51] applied poly(IPAAm) to modifying the surface of commercial polystyrene1 culture dishes for bovine aortic endothelial cells as well as for rat hepatocytes. Graft polymerization of IPAAm onto the polystyrene dishes was carried out by using an electron beam. The thickness of the poly(IPAAm)-grafted layer in aqueous systems was 0.5 pm at 37 °C and 0.6 pm at 15 °C. After endothelial cells were cultured at 37 °C for 2 days, the temperature was decreased to 10 °C and the number of cells that were detached from the surface was counted. Okano et al. observed that 100% of cells were detached from the poly(IPAAm)grafted surface. 

Ito has also extended this type of photochemistry to the electron-beam-induced catalytic acidolysis of acid-labile main chain acetal linkages in polyphthaldehyde. These polymers, like the poly(2-methylpentene-l-suIfone) (PMPS) sensitizer in NPR resist described earlier have ceiling temperatures on the order of -40 °C. As normally used, the polyaldehydes are end-capped by acylation or alkylation and are thus quite stable. The main chain bonds are very sensitive to acid-catalyzed cleavage which in turn allows the whole chain to revert to monomer in an unzipping sequence similar to that occuring in irradiated PMPS. Irradiation of polyphthaldehyde containing 10% of a suitable sensitizer such as triphenylsulfonium hexafluoroarsenate with either deep UV... 

Development of Resist Patterns. Development was done in AZ2401 developer diluted with 2 to 5 times its volume of water AZ2401 is an aqueous solution of KOH with a surfactant. When the resist films were exposed to electron beam doses of 5 iC/cm2 at 25 keV, it usually took 1.5 to 2.0 min for complete development of the images using a diazo-naphthoquinone sensitizer with o-chloro-cresol-formaldehyde Novolak resin in (1 3) AZ2401/water developer. With poly(2-methyl-l-pentene sulfone) the chlorinated Novolak resin exposed to I juC/cm2, it took 2.0 min in (1 4) AZ2401 developer for complete image development. 

For further enhancement of electron beam sensitivity, the chlorinated Novolak resin was studied using poly (2-methyl-1-pentene sulfone) as a dissolution inhibitor. The chlorinated Novolak resin mixed well with the polysulfone, and there was no phase separation observed when the films were spin-coated. With 13 wt% of the polysulfone, the chlorinated Novolak resist cast from a cellosolve acetate solution yielded fully developed images with R/Ra = 9.2 after exposure to 2 / 2. It gave fully developed images with R/R0 = 3.2 at a dose of 1 / 2, as shown in Figure 3. There are some problems with this resist system some cracking of the developed resist images... 

Positive Electron-beam Resist of Poly (a-substituted Benzyl Methacrylate). The electron-beam resist behaviors of poly(a-substituted benzyl methacrylate)s are given in Table III. When the exposed resist films were developed with a mixture of MIBK and IPA, the sensitivities of these polymers were on the order of 10-4 C/cm2. When a dilute solution of sodium methoxide in methanol was used as a developer, the sensitivity was enhanced as compared with the former case, and increased with an increase in the bulkiness of the ester group of the polymer except for poly(a,a-diphenylethyl methacrylate). 

Spectral subtraction usually provides a sensitive method for detecting small changes in the sample. Figure 5 shows the difference spectra between the atactic poly(a,a-dimethylbenzyl methacrylate) s unexposed and exposed to electron-beam at several doses. The positive absorption at 1729 cm-1 is due to the ester carbonyl group consumed on the exposure and the negative ones at 1700 and 1760 cm-1 to the acid and acid anhydride carbonyl groups formed, respectively. The formation of methacrylic acid units was more easily detected using the difference spectrum However, these difference spectra could not be used for the quantitative determination because the absorptions overlap somewhat. 

For calibrating the accelerator, poly(vinyl chloride) films and a simple water calorimeter are used in addition to monitoring and controlling the electrical parameters of the accelerator which affect the dose output and, in turn, the absorbed dose. The poly(vinyl chloride) is used primarily for establishing the depth dose in samples irradiated with the scanned electron beam. This film is relatively thin when compared with the range of 10... 

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