Mixture systems of copolymer of methyl methacrylate-methacrylic acid P(MMA-MA) and terpolymer of methyl methacrylate-methacrylic acid-methacryloyl chloride P (MMA-MA-C1MA) have been synthesized and investigated as a positive electron resist. These resists form intermolecular acid anhydride bonds after baking, resulting in improved sensitivity and thermal stability while maintaining high resolution as compared with poly(methyl methacrylate). The polymer containing 5 mole percent (m/o) methacrylic acid (MA) and 0.5 m/o methacryloyl chloride (C1MA) has a sensitivity of 1.9 • 10 -5 C/cm2 at an accelerating voltage of 30 kV, a thermal stability even above 140~ The sensitivity of the polymer containing 0.36 m/o C1MA is 8 • 10 -8 C/cm 2, which is 20 times that of PMMA.Electron beam lithography has been widely investigated and accepted as a means of fabricating microelectronic devices. Properties such as electron sensitivity, resolution, thermal stability, and process tolerance are important factors in determining resist performance. In general, a positive resist has higher resolution than a negative resist which conversely has poor resolution.Many investigations have been carried out to improve the sensitivity of a positive resist while maintaining the other properties. Poly(methyl methacrylate), PMMA, is widely used, but its sensitivity is insufficient. The sensitivity of PMMA, which is fractionated in a mixture of methyl isobutyl ketone (MIBK) and isopropyl alcohol (IPA) to obtain high molecular weight materials with low dispersivity, and developed in a fractional solvent, is better than that of unfractionated or standard-developed PMMA (1). The sensitivity is also improved by copolymerization with highly radiation susceptible groups. Acrylonitrile (2), isobutylene (3), methacrylic acid (4), and a-chloromethacrylate (5) were incorporated into PMMA. On the other hand, polymers of methacrylic esters (4) and methacrylic esters containing halogens (6) were reported as making a more highly sensitive positive electron resist than PMMA. These highly sensitive resists, however, will not be so thermostable as PMMA.To obtain higher sensitivity and thermal stability than methacrylic esters such as PMMA, polymers incorporating methacrylic acid and methacryloyl chloride were synthesized and evaluated. These polymeric resists will form intermolecular anhydride bonds after heating. Polymeric resist, which is cross-linked by anhydride bridges among methacrylate chains, has been shown to have advantageous properties such as higher sensitivity and thermal stability than PMMA in cross-linked methacrylic esters such as ethyl-, isobutyl-, cyclohexyl-, etc. methacrylate. This modified type methyl methacrylate resist is reported by Roberts (7). It has greater thermal stability than PMMA, but the electron sensitivity is not much improved. The sensitivity obtained by MIBK development is 6-8 • 10-6 C/cm 2 at 10 kV after baking at 115~ for 30 min. Measured at 30 kV, the sensitivity is roughly estimated to be 2 X 10-~ C/cm 2 (8).We have examined...

Decay of ions trapped in γ-irradiated poly(methyl methacrylate) (PMMA)-containing ion scavengers was examined. Cations in PMMA migrate through diffusion and by a hopping transfer of the charge. They encounter anions, combine, and thereby decay. The diffusion of cations was confirmed by a comparison of decay of ions in PMMA-containing pyrene and that in a copolymer of methyl methacrylate and 1-pyrenylmethyl methacrylate. Cations in the former sample decay faster than those in the latter sample. The ions in the copolymer are chemically bonded to the polymer chains, preventing the diffusion of the ions. However, the dependence of the decay of the ions on the concentration of pyrenyl groups indicated that the ions decay through a hopping transfer of the charge on pyrenyl groups. The hopping transfer was suppressed by triphenylamine. The suppression is ascribed to structural difference in neutral triphenylamine and its cation. Anions in PMMA are ketyl-type anions at the side chains of the polymer. Their migration is suppressed, since they are connected to the polymer chains and the structures of the neutral state and its anion are different.