Electron beam resist, molecular weight

Many papers have been published on positive electron-beam resists. These resists are mostly polymers which are degraded upon electron-beam irradiation. The resulting lower molecular weight polymer in the exposed area can be selectively removed by a solvent under certain developing conditions. The development is accomplished by the difference in the rate of dissolution between the exposed and unexposed areas, which is a function of the molecular weight of the polymer. Recently, Willson and his co-workers reported the new type of positive resist, poly(phthalaldehyde), the exposure of which in the presence of certain cationic photoinitiators resulted in the spontaneous formation of a relief image without any development step (/). 

From Table XI, it can be seen that polymers have spectrum of doses necessary to obtain maximum readout efficiency. We will examine in the following example the imaging of a positive electron beam resist as a function of dose and molecular weight-solubility changes. 

A positive electron beam resist image is developed by immersion in a solvent which dissolves the exposed region at a rate (Sf)which is faster (approx. lOX) than the unexposed rate (Si. The rate of dissolution of a linear polymer is related to its molecular weight by the Uberreiter function (26) ... 

Molecular Weight Dependence of Electron-Beam Resist Sensitivity... 

The influence of the gel content in polyisoprene-tackifier blends on creep resistance and peel behaviour have been recently studied [62]. The gel content was achieved by cross-linking the adhesives with electron beam irradiation. The molecular weight of the soluble fraction in the blend was always dominated by that of the initial elastomer. Creep resistance was achieved either through molecular weight increases or gel content increases. However, the peel strength is strongly... 

Figure 1. Dissolution rates of a composite resist made of a diazonaphthoquinone sensitizer and o-chloro-m-cresol-formaldehyde Novolak resin after 5 /cm2 electron beam exposures. Note this kind of an induction period appeared only in the high-molecular-weight fraction resin.

Fig. 8. Molecular weight distributions of electron-beam-exposed MRS resist. Dose 15 yC/cin . (a) before development, (b) after half development (50% remaining).

Recently Nitto Denko developed a battery separator made by a wet process that had high puncture strength and high heat rupture resistance. They used a polyolefin resin with a high-molecular-weight rubber as its main component materials and cross-linked through oxidation in air. The melt rupture temperature, as measured by thermomechanical analysis, was over 200°C in this material. They also tried cross-linking UHMWPE with electron-beam and ultraviolet irradiation, but this had the... 

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