Feeding a growing need for shrinking devices

New material could improve processes for sub-microscopic manufacturing.

The increasing demand for miniaturization of electronic devices, such as semiconductors and transistors, down to nanoscale dimensions is pushing the capacity of the optical lithography processes used to produce them. There is a strong need for new light-sensitive materials, known as photoresists, that can meet the demands of more advanced micro photolithographic techniques.

Micro-photolithography is used in the fabrication of super-miniature and highly complex patterns such as those on integrated circuit boards. It allows for patterns that are only a few tens of nanometers in size to be etched or deposited onto photoresists.

Among the critical components of photoresists are photoacid generators (PAGs). These produce the strong acids required to engrave or deposit patterns on to substrates. More efficient PAGs could lead to improvements in the performance of micro-photolithographic processes, but also of rapid prototyping (3D printing) and photocuring systems. 

Nara Institute of Science and Technology (NAIST) researchers have been investigating a new type of PAG by irradiating photochromic triangle terarylenes with ultraviolet ight, inducing an electrocyclic reaction that produces a closed-ring structure and triggers the release of methanesulfonic acid by the PAG.  By introducing hydrogen atoms and the acid’s conjugate base to both sides of the structure a self-contained PAG was formed.

“We had already developed highly efficient photo- quantitative compounds based on compounds with a triangle terarylene structure,” explains Tsuyoshi Kawai, from NAIST’s Photonic Molecular Science Laboratory. “Although this new type of PAG only achieved a quantum yield of 52% during the study, it promises the possibility of super-efficient photoresists in the future with quantum yields close to 100%.”

PAGs with higher quantum yields are more efficient at producing photoacids andcould lead to better performing photoresists and improvements in photolithographic processes. The PAG developed in the study was also capable of photoinitiating the cationic polymerization of cyclohexene oxide — an epoxy monomer.

This could lead to improvements in 3D printing as well as in photocuring processes that produce materials used for such products as sealants, protective gloves and rubber stoppers for pharmaceuticals.

“Although photochromic reactions that lower the pH of photoacids have been reported, they are not able to generate sufficiently strong and reactive acids for cationic polymerization to occur,” Kawai
says. “Employing the PAG as a phototrigger of cationic polymerization indicates that the new PAG is compatible with photopolymer systems and represents another significant outcome from our research.”

This article was first published in the NAIST Research Highlights 2016 Booklet.. Read the original article here