Poly degradation patterns

Asano, M.,Fukuzaki,H., Yoshida, M., Kumakura, M., Mashimo, T., Yuasa, H., Imai, K., Yamanaka, H., Kawaharada, U., Suzuki, K. (1991). In vivo controlled release of a luteinizing hormone-releasing hormone agonist from poly(DL-lactic acid) formulation of varying degradation pattern. Int. J. Pharm., 67,61-11. 

The positive image so formed had a pattern width of 0.5 p and a y-value of 5. Thus, the degraded polymer was found to achieve an approximately equal resolution at a lower exposure dose, as compared with poly(methyl methacrylate) (PMMA) known as a conventional image forming material (26). 

Initial processing experiments showed however, that under typical O2 RIE conditions (power 0.1 to 0.2 W/cm self-bias — —250 to —350 V, pressure — 5 to 20 mTorr O2), these resists are not very resistant, particularly under prolonged etching. Effective pattern transfer may require etch times of 15 to 30 min (11,12). which are sufficient to cause extensive degradation of the resist. Such behavior is reminiscent of poly (olefin sulfone)s such as the well-known PBS e-beam resist, which is etched 5-7 times faster than polystyrene in an oxygen plasma (5). 

We became interested in poly(l-trimethylsilyl-l-propyne) [poly(TMSP)] after the initial report of its synthesis (9). Poly(TMSP) possesses many of the qualities needed in a practical deep-UV resist material a high silicon content (—25%) thermal stability excellent film-forming properties and a chromo-phore, the conjugated backbone, that absorbs strongly in the deep-UV region. Our initial work with poly(TMSP) showed that it had one serious drawback its sensitivity toward degradation by deep-UV radiation was poor, and doses of >1 J/cm are required for the definition of a positive-tone pattern. 

The same authors have also studied the effects of particle size on the rate of production of monomer during thermal degradation of poly(methyl methacrylate) and observed that the rate increases with particle size for particles smaller than about 50 mesh but it does fall away for larger particles. The study of the effect of layer thickness on the rate of mononrer production has also revealed the similar pattern of behavior of the polymer towards (tegradation. Several reasons for this behavior of the (tegradation are mentioned. "ITiese are ... 

The reactivity of the maleimide monomer was dependent on the substitution pattern of the phenyl ring, with the substituents in the ortho position tending to lower the molecular weight of the polymer formed. The THP substituent is readily removed either chemically or thermally to yield poly(iV-(hydroxyphenyl)maleimides). All polymers exhibited excellent thermal stability and showed no evidence of degradation below 360 °C. Reaction occurs between the phenolic ring of the polyimide and HMTA, to form benzoxazine-type derivatives. These reactions have been studied comprehensively using the monomeric model systems, Ai-(hydroxyphenyl)succinimides (Figure 8) . 

Spiropyran molecules have also been utilized as reverse wettable surfaces, whereby, a hydrophilic surface may be photomodulated to a hydrophobic surface and vice versa. Lygeraki et al. utilized the polar (mercocyanine, zwitterionic open-form) and nonpolar (spiropyran closed-form) properties of the spiropyran-merocyanine photo-chromic transformation to photomodulate surface wettability. 6-N02 BIPS (10 wt %) was added to a poly(methy 1 methacrylate) host matrix and patterned to produce reverse wettable surfaces. However, reversibility is limited to 6-8 irradiation cycles because of degradative photooxidation [22], Reverse wettable surfaces are commercially important as they may enhance drug delivery or function as a self-cleaning surface. 

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