Evaluation of alternative development process for high-aspect-ratio poly(methylmethacrylate) microstructures in deep x-ray lithography

Abstract

The development of very thick commercial sheets of poly(methyl methacrylate) (PMMA) resist patterned by deep x-ray lithography was investigated. The development characteristics were explored, with the alternative methyl-iso-butyl-ketone (MIBK)-based developer systems, MIBK and MIBK/ iso-propyl-alcohol (IPA) 1:3, being compared with the “GG” developer system (2-butoxyethoxy-ethanol, morpholine, 2-aminoethanol, and water) more generally used. In particular, the influence of various parameters were studied: PMMA characteristics (resist thickness, pre-exposure thermal treatment), exposure conditions (x-ray incident energy, dose at the bottom of the resist, rate of dose deposition, distribution of dose inside the resist), development conditions (temperature, megasonic-assistance, length of cycle into developer and rinse baths), postexposure treatments (storage, thermal treatment), etc. The study also focused on surface finish of the parts corresponding to different exposure and development conditions. Using MIBK/IPA megasonic assisted development and postexposure treatment at 40 °C resulted in the best conditions, faster development rate, as well as smoother developed surfaces.

Fabrication Approaches for Generating Complex Micro- and Nanopatterns on Polymeric Surfaces

“…Development can be accelerated by moderately increasing the temperature of the developing solution, 26 reducing the exposure time and consequently the cross-linking degree, 27 or agitation. Stirring of the developer solution enhances diffusion, which increases the development rate.…”

X-ray lenses fabricated by deep x-ray lithography

“…Typical exposures were carried out at 100 mA beam current, providing a total estimated dose of 8,000-12,000 joules/cc in 8-12 hours. After exposure, the sheets of PMMA were developed and rinsed at 25°C in the GG development system, 9,10 until the lens structures were developed through. The developed sheets were dried after a final deionized water rinse.…”

Deep-UV exposure of poly(methyl methacrylate) at 254 nm using low-pressure mercury vapor lamps

“…Poly͑methyl methacrylate͒ ͑PMMA͒ is a transparent thermoplastic with important applications as a positive resist for various radiation sources, such as electron beam lithography, [1][2][3][4][5] x-ray lithography, [6][7][8][9][10][11][12] and deep-UV lithography. 13 Radiation sensitivity is due to polymer chain scissions caused by the absorbed radiation.…”

“…2,3,10 Another commonly used developer is GG developer, [7][8][9][10][11][12] which is a mixture of water, butoxyethoxyethanol, tetrahydro-oxazine, and aminoethanol. Popular solvent systems involve cosolvent mixtures of methyl isobutyl ketone ͑MIBK͒ and isopropanol ͑IPA͒, 2,3,5,8,10 and cosolvent mixtures of IPA and water.…”