Polymers Constituted by Methyl Methacrylate, Methacrylic Acid, and Methacryloyl Chloride as a Positive Electron Resist

Abstract

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...

Effects of Heat‐Treatment on Electron Beam Sensitivities and Chain Scission Efficiencies of Poly(MMA‐co‐t‐BMA)

“…But thermal properties (glass transition temperature, Tg, and thermal degradation point, Td) are lower than other resists (8). Moreover, copolymers of methyl methacrylate and methacrylic acid (9) or methacryloyl chloride (10) were reported, and the sensitivity improvement of these copolymers were concluded with the formation of methacrylic anhydride by prebaking above 200~…”

A Cross‐Linked Positive Resist Derived from Poly(Methacrylonitrile‐co‐Methacrylic Acid)

“…Cross-linked positive resists were suggested to attain high sensitivity and good resolution (1)(2)(3)(4). In cross-linked positive resists, linear polymers are cross-linked in situ on the substrate by heat or light to form an insoluble gel before the exposure.…”