Engineering

Polymer chemistry

Resist

Ketone

Materials science

Solubility

Layer (electronics)

Polymethyl methacrylate

Methyl isobutyl ketone

Fractionation

Methacrylate

Methyl methacrylate

Chemical engineering

Isopropyl alcohol

Dissolution

Polymer

Nanotechnology

Organic chemistry

Copolymer

Enzyme

Composite material

Gel permeation chromatography

Chemistry

Molar mass distribution

Monomer

Size-exclusion chromatography

Journal of The Electrochemical Society

The effect of the molecular‐weight distribution of polymethyl methacrylate on its performance as a resist material for electron beam exposure is investigated with the aid of gel‐permeation chromatography. The solubility of PMMA in a developer comprising a 3:1 ratio of isopropyl alcohol to methyl isobutyl ketone is determined, and the need for post‐development washing of substrates in isopropyl alcohol is shown to be due, in part, to the liberation of insoluble polymer molecules from the film during development. Removal of very high molecular weight molecules, which are dominant in determining intrinsic viscosity, is found to lend considerable improvement to the rate of dissolution of PMMA in solvents, ease of filtration, and quality of spin‐coated films. The optimum molecular‐weight distribution is determined as being one which contains very few molecules with weights below about 50,000 or above a few hundred thousand. The preparation of PMMA with such a distribution by fractionation is outlined, and 10% concentrations of the resulting fractions are found to dissolve in methyl isobutyl ketone at 21°C in 2–3 min. The effectiveness of fractionated PMMA as a resist against chemical etchants is also found to be considerably better than that of broadly distributed polymers. Baking of films prior to exposure is considered with regard to its effects on substrate adhesion, molecular‐weight distribution, and the rate at which films dissolve in solvents. Preliminary results on the use of polymer hydrolysis as a method of improving adhesion of the polymer to substrates are reported, an order of magnitude improvement being easily achieved.

Polymethyl Methacrylate as an Electron Sensitive Resist