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Technique promises nanoscale resolution with visible light

Posted: 11 Feb 2011 ?? ?Print Version ?Bookmark and Share

Keywords:multiphoton photoresists? Resolution Augmentation through Photo-Induced Deactivation? nanoscale resolution?

A research team at the University of Maryland is promoting the use of multiphoton photoresists to enable visible light to achieve nanoscale resolution that is inversely dependent on exposure time. The proposal is being forwarded in view of photolithography research's continued focus on extremely short wavelengths of UV light.

"Most approaches to getting higher resolution with photolithography involve using light of ever shorter wavelengths," said professor John Fourkas. "Our goal is to use visible light to produce nanoscale features."

The new multiphoton technique, called Resolution Augmentation through Photo-Induced Deactivation (RAPID), uses one laser to initiate exposure in the photoresist and a second to complete it, allowing full exposure of only the nanoscale overlapping areas of the two focused beams.

"If we take a laser beam and focus it through a microscope objective, we can confine absorption to this very tiny region right at the focal volume of the laser," Fourkas said.

The researchers have already perfected the technique for use in the selective polymerization of 3D materials on-chip. Using what is called Multi-photon Absorption Polymerization (MAP), the team has fabricated tiny inductors on chips. RAPID is a follow-on effort to use multiphoton absorption with photoresists to achieve nanoscale resolution with focused visible light, delaying or possibly eliminating the need to move to extreme UV (EUV) light sources.

The technique works at normal atmospheric pressure, unlike EUV, which requires processing in a vacuum. Instead, a special photo-initiator in the resist is activated by one laser, then deactivated by a second, realizing a phenomenon the researchers call proportional velocity (PROVE), which yields smaller features for higher exposures.

Next the researchers plan to test their technique on the wafer scale, in contrast to the point-by-point demonstrations they have given so far. The team estimates that RAPID will be ready for commercialization in about 10 years.

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Figure 1: Microinductor created using multiphoton absorption polymerization (MAP) followed by selective metallization.

R. Colin Johnson
EE Times

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