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

Abstract

The copolymer of methyl methacrylate (MMA) and t-butyl methacrylate (tBMA), CP-3-2 (MMA/tBMA=68/32) showed a high performance (sensitivity 0.3 ~C/cm 2, and resolution 0.3 ~m line) for positive electron beam resist by the heattreatment at 250~ Some heat-treatment effects were observed: weight loss, improvement of thermal properties, and decrease of molecular weight occurred, and the chain scission efficiency (G-value) increased from 1.8 to 3.3 by heat-treatment at 250~ Moreover, the composition changes of the CP-3-2 for the heat-treatment temperature were measured with an FT-IR, 13C-and 1H-NMR. The results showed that t-butyl groups of the tBMA component were eliminated above 220~ and six-membered acid anhydrides were formed. Furthermore, elimination of methoxy groups of the MMA were also observed.Poly(methyl methacrylate) (PMMA) is a well-known electron beam (EB) resist and is probably one of the more widely used positive resists (1). PMMA has high resolution (2) and acceptable resist properties, but sensitivity of >50 ~C/cm ~ at 10-20 keV is inconveniently low (3). In recent years, the search for a more sensitive positive resist has led to the development of other resists, such as poly(butene-1 sulfone) (PBS) (4), poly(fluoroalkyl methacrylate) (5, 6), and poly(chloromethyl methacrylate) (7). The minimum dose required to pattern these resists is generally lower than 10 ~C/cm 2 but higher than 1 ~C/cm ~. PBS, which appears to be the most sensitive as a positive EB resist, requires a minimum dose of 1 ~C/cm 2. 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~It is well known that degradation of a positive resist occurs through the scission of main chain bonds. Methyl methacrylate and other alkyl methacrylate polymers and copolymers are known to be degradable by radiation (11). In a previous paper (8), we reported our studies of methacrylate polymers and copolymers as high sensitivity EB resists. In these polymers, poly(isopropyl methacrylate) and poly(methyl methacrylate-co-isopropyl methacrylate) had high sensitivities to EB radiation. For this copolymer, the main cause of high sensitivity was not an increase of the chain scission efficiency (G-value) of the copolymer, but by a change of solubilities by copolymerization (12). On the other hand, poly(methyl methacrylate-co-t-butyl methacrylate)s were not highly sensitive, but these copolymers were changed to highlysensitive positive EB resists by heat-treatment (13).In this paper, we wish to report our studies of EB resists derived from heat-treated copolymers of methyl methacrylate (MMA) and t-butyl methacrylate (tBMA). Moreover, the composition change of the copolymer by heat-treatment and chain scission efficiencies by EB radiation are also ...

Electron Beam-Mediated Cross-Linking of Blown Film-Extruded Biodegradable PGA/PBAT Blends toward High Toughness and Low Oxygen Permeation

“…These are attributed to the degradation of the esters along the polymer chain backbone and indicate the formation of oxidatively degraded chain scission with terminal carboxylic acids and anhydrides (see Scheme ). This follows previously observed degradation above 250 kGy EBT of other polymers. − The FTIR spectra of the white regions of the films treated at 450 kGy or the other areas of the films treated with 400 and 450 kGy do not show any degradation. This is presumably because after significant irradiation of the film at higher dosages, sufficient scission, cross-linking, and degradation occur on the polymer surface.…”

“…(See Scheme 1) This follows previously observed degradation above 250 kGy EBT of other polymers. [29][30][31] The FTIR spectra of the white regions of the films treated at 450 kGy or the other areas of the films treated with 400 and 450 kGy do not show any degradation. This is presumably because after significant irradiation of the film at higher dosages, sufficient scission, crosslinking, and degradation occurs on the polymer surface.…”