Methyl methacrylate, electron-beam

Methyl methacrylate can also be polymerized by radiation using either a cobalt-60 source or accelerated electrons at dose rates up to 3 megarads/sec. The activation energy for the electron beam polymerization is about 7.0kcal/ mole (Ref 12). Radical polymerization can also occur using diisocyanates or hydroperoxides as the initiating species (Ref 15)... 

Figure 41. A plot of sensitivity to Mo (5.4k) x-ray radiation and 20 kV electron beam radiation for several resists. EPB is epoxidized polybutadiene, P(GMA-EA) is a copolymer of glycidyl methacrylate and ethyl acrylate (COP), PGMA is poly (glycidyl methacrylate), PBS is poly (butene-1 -sulfone), FBM-1 is poly (2,2,3,3-tetrafluoropropyl methacrylate), P(MMA-MA) is a copolymer of methyl methacrylate and methacrylic acid, PMMA is poly (methyl methacrylate). (Reproduced with permission from Ref. 56J...

The incorporation of small percentages (<10%) of 3-oximino-2-butanone methacrylate (4) into poly(methyl methacrylate) (PMMA) (Scheme I) results in a four fold increase in polymer sensitivity in the range of 230-260 nm flO.l 11. Presumably, the moderately labile N-O bond is induced to cleave, leading to decarboxylation and main chain scission (Scheme II). The sensitivity is further enhanced by the addition of external sensitizers. Also, preliminary results indicated that terpolymerization with methacrylonitrile would effect an additional increase. These results complement those of Stillwagon (12) who had previously shown that copolymerization of methyl methacrylate with methacrylonitrile increased the polymer s sensitivity to electron beam irradiation. The mole fraction of the comonomers was kept low in order to insure retention of the high resolution properties of PMMA (3.41. 

In this article we will describe two different types of positive electron-beam resists, which were briefly reported in our previous communications (2,3). One is the homopolymer or copolymer with methyl methacrylate and a-substituted benzyl methacrylate, which forms methacrylic acid units in the polymer chain on exposure to an electron-beam and can be developed by using an alkaline solution developer. In this case, the structural change in the side group of the polymer effectively alters the solubility properties of the exposed polymer, and excellent contrast between the exposed and unexposed areas is obtained. The other is a self developing polyaldehyde resist, which is depolymerized into a volatile monomer upon electron-beam exposure. The sensitivity was extremely high without using any sensitizer. 

The results mentioned here clearly indicate that the enhancement in the sensitivity and 7-value of the poly (a,a-dimethyl benzyl methacrylate) resist over poly(methyl methacrylate) is mainly due to facilitated formation of methacrylic acid units on electron-beam exposure. The exposed area, which contains CH,... 

Figure 7. Difference infrared spectra between the polymethacrylates unexposed and exposed to the electron-beam of 1.6x10 4 C/cm2. (A) poly (methyl methacrylate) (B) poly(a-methylbenzyl methacrylate) (C) atactic poly(a,a-dimethylbenzyl methacrylate) (D) poly(a,a-diphenylethyl methacrylate).

The reaction of poly (methyl methacrylate) on electron-beam exposure has been thoroughly studied and the elimination of methoxycarbonyl group is considered to be the primary mechanism, by which the main-chain scission is initiated (20,21). However, in this work the formation of acid carbonyl group... 

Table IV. Electron-beam Exposure Characteristics of Copolymers of a,a-Diphenylethyl Methacrylatef ) with Methyl Methacrylate ( /2) ...

Table VII the electron-beam exposure characteristics are given for the soluble poly (triphenylmethyl methacrylate-co-methyl methacrylate)s. The sensitivity on alkaline development was strongly influenced by the copolymer composition. The highest sensitivity was obtained on the copolymer containing 93.7 mol% methyl methacrylate. The copolymer of highest sensitivity showed the 7-value of 6.3, which was nearly twice as large as that for poly(methyl methacrylate). Formation of methacrylic acid units on exposure is obvious from the infrared spectrum. However, the mechanism of the occurrence should be different from the case of the a,a-dimethylbenzyl methacrylate polymer since there are no /3-hydrogen atoms in the triphenylmethyl group, and may be similar to the case of poly (methyl methacrylate). This will be explored in the near future.

Other examples include the monitoring of the degradation of poly(methyl methacrylate) (PMMA) by an electron beam [355] or the investigation of the... 

The radiation degradation of poly(2-octyne) occurs only in the presence of oxygen. Its degradation products contain carbonyl and hydroxyl groups, and so dissolve in polar solvents (e.g., acetone). Such solubility change is essential to resist materials. The Gs value (number of main-chain scission per 100 eV of absorbed dose) of poly(2-octyne) is ca. 12. It is noteworthy that this value is higher than that of poly-(methyl methacrylate) (Gs ca. 2)118) which is being used as electron-beam resists. 

Bermudez VM. (1999) Low-energy electron beam effects on poly(methyl methacrylate) resist films. / Vac Sci Technol S 17 2512-2518. 

Gold arrays are prepared by electron beam lithography (EBL) according to the following method. The bare substrate is a glass plate (10 mm X 10 mm) on which a thin indium tin oxide (ITO) substrate is evaporated. The ITO substrate is then spin coated (60 s, at 5000 rpm) with a 100 nm thick Poly methyl-methacrylate (PMMA) polymer,... 

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