Immersion lithography resurrects an age-old microscopy method to extend 193-nanomerter light down to the 7-to-8 nanometer circa 2024.
It was the end of the semiconductor roadmap for 193-nanometer lithography--the next generation would have to go to 157-nanometer light.
Jim Blatchford, Texas Instrument's manager of front-end processing, had just finished negotiating for a leading edge 157-nanometer photolithography system, but he was still worried about the unproven technology, so he went to an SPIE (Society of Photo-Optical Instrumentation Engineers) session on 157-nanometer lithography.
When he arrived, however, he was surprised to find the room nearly empty. The rain was pouring down outside making a lonley pitter patter without the usual crowd noises to mask it. Something was wrong at 157-nanometer.
"I remember it so well. We had just finished negotiations on our 157-nanometer tool, but when I walked into a 157-nanmoter session at SPIE 2004 the room was almost completely empty. The sound of the rain pouring down on the roof was eery. I knew right away that something was wrong," said Blatchford.
The mystery was solved when Blatchford found out that the attendees were crowded into the immersion lithography session for 193-nanometer, where presenters were claiming that engineers didn't need to risk going to 157-nanometer. All they had to do was immerse the reduction lens nearest the wafer in water to decrease feature sizes by its index-of-refractionn (1.44). And with higher index fluids, it should be possible to extend 193-nanometer lithography evern further.
"What was most surprising to me was just how quickly everyone adopted immersion lithography. Once it was established as a feasible technology, everybody got on-board immediately," said Blatchford.
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Light at 193 nm has a resolution limit on the order of 65 nm, but
immersion lithography uses the same light source and yet realizes a
semiconductor process at precisions as high as 40-45nm. (Source: Nikon)