Researchers find a faster way to etch deep holes for 3D NAND Plasma-based cryo-etching technique doubles etch speed, improving efficiency Faster etching might mean cheaper storage, but real-world impact is TBD
3D NAND flash memory is different from traditional single-layer NAND because it vertically stacks memory cells to cram more storage into smaller spaces.
The process involves carving precise, deep holes into alternating layers of silicon oxide and silicon nitride, and this has always been a bit slow, until now.
A team of researchers from Lam Research, the University of Colorado Boulder, and the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) has developed a plasma-based technique that can etch the deep, narrow holes required for 3D NAND memory at a much faster rate, a paper published in the Journal of Vacuum Science & Technology A
Will it benefit end users?
The team’s approach uses a cryogenic etching process using hydrogen fluoride plasma rather than the traditional method.
“Cryo etch with the hydrogen fluoride plasma showed a significant increase in the etching rate compared to previous cryo-etch processes, where you are using separate fluorine and hydrogen sources,” said Thorsten Lill of Lam Research. Using the new method saw etching rates for the layers soar from 310 nanometers per minute to 640 nanometers per minute – more than doubling the efficiency.
“The quality of the etch seems to have improved as well, and that’s significant,” Lill added.
The researchers also looked at the impact of phosphorus trifluoride. Adding it during the process quadrupled the etch rate for silicon dioxide, but it only had marginal impact on the silicon nitride layer. They also looked at ammonium fluorosilicate, a chemical which forms during the etching process when silicon nitride reacts with hydrogen fluoride. This slows down the etching process, but adding water was found to counteract this.
While the technical achievement is to be applauded, the practical implications are less clear. Faster, better etching rates may simplify and speed up production, but whether these savings trickle down to better or cheaper storage devices remains to be seen.
“Most people are familiar with NAND flash memory because it’s the kind that is in the memory cards for digital cameras and thumb drives. It is also used in computers and mobile phones. Making this type of memory denser still – so that more data can be packed into the same footprint – will be increasingly important as our data storage needs grow due to the use of artificial intelligence,” explained Igor Kaganovich, a principal research physicist at PPPL.
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