MEMS_06 guiren resolution enhancement_01

MEMS_06 guiren resolution enhancement_01 - Chapter 1...

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Unformatted text preview: Chapter 1 Photolithography Resolution Enhancement Technology • Three main technologies: – Resist technology – Mask technology – Exposure tools • All need to be addressed to optimize the resolution • RET was relatively expensive • Short wavelength was selected • Recent much progress in RET Resolution enhancement technology (RET) • Challenges of conventional resists: – Low quantum yield -> fundamental limit on photosensitivity of these resists – +resist 0.2-0.3 –-resist: 0.5-1 – Worse for shorter light wavelength due to unbleachable absorption for +resist – Hard to be used for thicker resist • Methods for improvement – Chemical amplifier resists – Image reversal – Antireflective coating-thin film interference – Thin film imaging Improved resist performance • Chemical amplification: – A single photon initiates a cascade of chemical reaction of sort that characterize a silver halide photographic emulsion system – The amplification is based on the photogeneration of a catalytic photoproduct – The catalytic photoproduct is often an acidic species, that catalyze scission or cross-linking – The catalytic scission or cross linking depends on the post- exposure baking temperature, time and method Improved resist performance • tBOC-based resists – A catalytic deprotection scheme, • use a thermal stable acid-labile tert- butoxycarbonyl group to mask the hydroxyl functionality of poly(vinylphenol) – Development is based on • polarity changes • rather than molecular weight changes • through scission and polymerization – Upon exposure and subsequent baking to • diffuse the photogenerated acid and • complete reaction – The acid cleaves the labile tBOC protecting group to form a polar polyvinyl phenolic polymer • Riston and polyimide can be made thick for thick resist layer Improved resist performance • However, had to obtain high aspect ratio devices due to – resolution limit, – high optical absorbency and – difficulty in obtaining layer thicker than 50 um in a single spin coat Improved resist performance • SU-8 resist – A –resist have advantages to overcome the disadvantage mentioned above – Good thermal and chemical stability – Photoinitiators (e.g. onium salt) could polymerize low cost epoxy resin – Strong lewis acid in the polymer matrix catalyzes...
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This note was uploaded on 10/03/2011 for the course BMEN 589 taught by Professor Wang during the Spring '11 term at South Carolina.

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MEMS_06 guiren resolution enhancement_01 - Chapter 1...

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