Dry etching durability of positive electron resists

Abstract

SynopsisThe effects of positive electron resist structures and G values for scission on dry etching durability have been studied with regard to plasma etching, reactive sputter etching, and plasma ashing.Polymers of aromatic methacrylates, especially poly(a-methylstyrene), all of which contain a benzene ring in the side chain, exhibit superior durability for each etching system. On the other hand, polymers of fluorinated and chlorinated methacrylates show low durability compared with the nonsubstituted polymethacrylates. In addition, they vary in durability with respect to the etching gas used. The sputtering effect which is induced by ion bombardment in flat bed-type reactors produces a significant loss in thickness of positive resists. Rough correlations between dry etching rates and Gs(scission) as the indication of sensitivity were obtained. The large dispersion of the correlaticns implies the possibility of more useful positive electron resists of high durability and high sensitivity.

Performance Control of Positive-Working Electron Beam Resists by Copolymerization and Blending

“…The bent point was observed about 20°C below Tg of non-halogenated poly(alkyl methacrylate)s, but the correlation between the bent point and Tg did not hold in the case of poly(aromatic methacrylate)s, halogenated polymethacrylates, poly(methyl isopropenyl ketone), and PMSt. 6 The correlation was not observed for the current copolymer systems, either. Quantum yield for the unimolecular chain scission of solid polymers, which is governed by mobility of polymer segments to form a special transition state (e.g., Norrish Type II reaction), is known to increase above Tg rapidly to the same value as that obtained in solution.…”

“…4 · 16 • 17 The Gs-value is reported to be 1.3 4 2.3. 6 Degradation of PMSt at 25°C under vacuum is explained as a random· breaking of skeletal chain bond accompanied by depropagation to split off about 100 monomer units/ 8 and the determined Gsvalue is 0.23 6 Since the PMSt-MMA copolymers, which were prepared by radical polymerization, contained MSt units isolated from each other in the copolymer chain as was deduced theoretically from the copolymerization reactivity ratio of MSt and confirmed Polymer J., Vol. 17, No.…”

“…On the other hand, the PMSt was predominantly syndiotactic, and the stereoregularity was fairly different from those of the PMMAs and the copolymer PMSt-MMAs. Sharma et al reported that isotactic, heterotactic and syndiotactic PMMAs had sensitivities of 20, 60 and 200 ,uC em-2 , respectively, when developed with MIBK [4]+1PA [6] for 60sY The sensitivity of a PMMA, the tacticity of which is it: ht: st = 8.9: 35.7: 55.4, is calculated to be 134 ,uC em-2 from the above-mentioned sensitivity data. Similarly, another PMMA, which has the same tacticity as the PMSt (it: ht: st=0:8.3:91.7), is estimated to be 188,uC cm-2 .…”

“…5 However, it may be unreliable because the bent point on the etching ratetemperature plot appears at a different temperature for each resist polymer. 6 At least it is doubtful that simple additivity is applicable to all the positive-working copolymer resists at any temperature.…”

Pulse Radiolysis Study on a Highly Sensitive Chlorinated Resist ZEP520A

“…On the other hand, the development of main-chain scission type (positive) EB resists exhibiting dry etching resistance is relatively difficult given that their high tendency towards degradation reduces the dry etching resistance [3]. ZEP520A (ZEON) is a relatively recently developed positive EB resist exhibiting high tendency towards degradation and dry etching resistance.…”