Beyond Ultraviolet Light, a New Lithographic Resist Material Could Help Keep Moore's Law on Track

Researchers from Johns Hopkins University, the East China University of Science and Technology, Stony Brook University, the Brookhaven National Laboratory, Soochow University, the École Polytechnique Fédérale de Lausanne (EPFL), and Lawrence Berkeley National Laboratory have come up with a process and the necessary materials that, they say, could help keep Moore's Law on track by making it possible to continue shrinking semiconductor feature sizes — using a lithographic process "beyond extreme ultraviolet radiation."

"Companies have their roadmaps of where they want to be in 10 to 20 years and beyond," explains co-corresponding author Michael Tsapatsis, professor of chemical and biomolecular engineering at Johns Hopkins University, by way of background to the team's work. "One hurdle has been finding a process for making smaller features in a production line where you irradiate materials quickly and with absolute precision to make the process economical."

The march of technology has seen, historically, the number of transistors on a leading-edge semiconductor chip trend towards a doubling roughly every two years — an observation by Intel co-founder Gordon Moore, which has become a must-hit target for the industry. To achieve that without ballooning processors to the size of football pitches, the transistors and other components have to get smaller — but today, in the world of single-digit nanometer feature sizes, that's a real challenge.

In order to create chips with ultra-small feature sizes, the lithographic process has by necessity taken a turn for the energetic: leading-edge chips are today built using extreme ultraviolet (EUV) lithography — but even that has its limits, which is where team's work comes into play: beyond extreme ultraviolet lithography (B-EUV).

There are two key parts to the lithographic process. The first is the laser, and the second is the resist — a material that reacts with the laser radiation to etch patterns into the silicon. Traditional resists don't work well with high-energy B-EUV laser sources — but resists made from imidazole-based metal-organic materials do. The team's key contribution: a way to coat the silicon wafer with this new imidazole-based resist, dubbed chemical liquid deposition (CLD), and a path to easy experimentation to discover other materials that could work for B-EUV semiconductor production.

"By playing with the two components (metal and imidazole), you can change the efficiency of absorbing the light and the chemistry of the following reactions. And that opens us up to creating new metal-organic pairings," Tsapatsis explains. "The exciting thing is there are at least 10 different metals that can be used for this chemistry, and hundreds of organics. Because different wavelengths have different interactions with different elements, a metal that is a loser in one wavelength can be a winner with the other. Zinc is not very good for extreme ultraviolet radiation, but it's one of the best for the B-EUV."

The team's work has been published under closed-access terms in the journal Nature Chemical Engineering.