Visible light nanoscaling enhances photolithography
"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 multi-photon 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 polymerisation of 3D materials on-chip. Using what is called Multi-photon Absorption Polymerisation (MAP), the team has fabricated tiny inductors on chips. RAPID is a follow-on effort to use multi-photon 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, realising 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 commercialisation in about 10 years.
Figure 1: Microinductor created using multi-photon absorption polymerisation (MAP) followed by selective metallisation.
R. Colin Johnson