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

Abstract

ABSTRACT:EB exposure characteristics, such as sensitivity and contrast, and durability against oxygen plasma were measured with linear copolymers and polymer blends of various composition, which were prepared from cx-methylstyrene [MSt] and methyl methacrylate [MMA]. Moreover, new developers were examined for these polymers, since sensitivity and contrast of the positive-working resist system depend largely on dissolution kinetics concerning each combination of the resist polymer and the developer. Methyl isobutyl ketone and isoamyl acetate were used as the developer, though they were developers of excessive dissolving power for PMMA and /or PMSt homopolymers. The copolymers containing 30-50mol% of MSt were as durable as PMSt homopolymer against oxygen plasma and had higher contrast than PMMA. The blend had dryetching durability as large as the copolymer of the same composition, and showed considerably high contrast, while the copolymer had higher sensitivity than the blend. The blends containing 21 mol% or Jess of MSt monomer units were much more durable than PMMA and of contrast as high as PMMA, but Jess sensitive than PMMA.KEY WORDS Sensitivity I Contrast I Durability I Oxygen Plasma I Dry Etching I cx-Methylstyrene I Methyl Methacrylate I Composition I Developer I As the dimensions of electronic devices shrink, the resists for microfabrication are required to have excellent performance such as i) higher contrast, ii) larger dry-etching durability, and iii) higher sensitivity. It is generally said from theoretical consideration and experimental results that positive-working resists are of high contrast. Recently, it has been found out that dry-etching durability and sensitivity are the two contradicting properties in positive-working electron resists; a durable resist such as poly(phenyl methacrylate)[PPhMA] has a low sensitivity, while a sensitive resist such as poly(butene-1 sulfone) [PBS] is not durable enough. 1 This tendency was derived from the study on one-component resist systems composed of degradable linear homopolymers, and does not deny the future development of excellent resist systems which have all the characteristics i), ii), and iii), if the candidates to be investigated are extended toward multi-component, crosslinked polymer, and /or copolymer systems. For example, PPhMA was sensitized by copolymerizing with a small amount of crosslinkable monomer at the slight expense of its large dry-etching durability. 2 The durability of poly( olefin sulfone) was extensively improved by blending with an aromatic resin at a great loss of high sensitivity, as was observed with the poly(2-methyl -1-pentene sulfone )-novo lac system. 3 Sensitivity of poly( methyl methacrylate) was enhanced by copolymerization with a fragile monomer, e.g., methyl chloroac-1091

Influence of the Chemical Structure of Polymers of the Methacrylic Series on the Properties of Positive Resists

“…However, in spite of the fact that PMMA is the predominant polymer for positive electron beam resists, with the aim of increasing their quality, use is very often made of binary and ternary copolymers of MMA with monomers of a different chemical nature, the structure of which makes it possible to modify the properties of the resists [18,19]. In particular, for the given end purpose, the use of emulsion copolymers of MMA with α-methylstyrene (MS) is known, and also of these monomers with a third component N-methacrylamide (MAAm).…”