Cornell University researchers Christopher Ober and Yi Yi have created new photoacid generator (PAG) compounds for improved photolithography resist performance. Unlike currently available PAGs that contain perfluorooctylsulfonate (PFOS), these new PAGs are PFOS-free, non-toxic and contain low amounts of fluorine. The inventors have taken a new approach to produce these PAGs by using semifluorinated acids comprising one or more carbohydrate or saccharide moieties.
Monosaccharides are the simplest form of carbohydrates and are therefore completely environmentally friendly. Moreover, due to the large size of saccharide groups, these acids have much lower acid diffusion to minimize line edge roughness (LER) of the patterns. Such acids also have high boiling temperatures. The saccharide compounds are abundant and inexpensive and therefore can reduce the cost of the PAGs. Both ionic and non-ionic PAGs have been developed.
Ober also invented new photoacid generator (PAG) compounds that improve photolithography resist performance and sensitivity. Unlike currently available PAGs that contain perfluorooctylsulfonates (PFOS), these new PAGs are PFOS-free, non-toxic, environmentally friendly and contain low amounts of fluorine. Both ionic and non-ionic formulations were developed and are composed of two parts; an acid precursor and a chromophore. The improved formulations introduce new functional groups in perfluorinated acid precursors to control their size and volatility while maintaining their strength. These functional groups are chosen to mimic the groups in the resist side chain so that PAGs better interact with the resist and distribute uniformly.
Potential Applications
* Semiconductor manufacturing, microfabrication
o DUV lithography (248nm and 193nm)
o 193 nm immersion lithography
o EUV lithography
* Coating applications
o Coat curing
Advantages
* PFOS-free and high sensitivity
* Improves photolithographic performance with benchmark resists
* Higher biotic/abiotic degradation and no bioaccumulation
* Reduces amount of fluorine
* Provides uniform acid distribution and well-controlled acid diffusion
* Reduces leaching levels in immersion lithography
* Good solubility in organic solvents
* Thermally stable
Ober further created a new photonic material with a high refractive index (1.68), prepared by two-photon lithography. The material is composed of molecules that include at least one thiirane ring (three membered cyclic sulfides), which subsequently results in a photonic crystal structure.
Up to date, photonic crystals have been restricted to those of low refractive indices (at most 1.6) with the associated limited band gap. Hence, utilizing thiiranes is an appealing solution since they have a high refractive index due to the presence of sulfur atoms. The resulting photonic crystal can be used to control the flow of electromagnetic waves for numerous technological applications.
Potential Applications
- Next generation optical devices utilizing photonic crystals, such as ultra-high efficiency lasers or micro-miniature optical integrated circuits
- Extended applications in micromachine and microreactor technology
- High resolution and structure diversity obtained through two-photon lithography
- High reactivity and high refractive index of thiiranes, suitable for photosensitive materials
- A further heightened refractive index via addition of a brominated epoxy resin
Licensing Contact: Martin Teschl, Technology Commercialization & Liaison Officer: mt439@cornell.edu, Tel: (607) 254-4454
