Research Bits: Feb. 10

Speeding up 3D NAND etch

Researchers from Lam Research, the University of Colorado Boulder, and Princeton Plasma Physics Laboratory (PPPL) investigated ways to speed up the cryogenic reactive ion etching process for 3D NAND by using a combined hydrogen fluoride gas to create the plasma.

“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, R&D collaborations at Lam Research, in a statement. “The quality of the etch seems to have improved as well, and that’s significant.”

The rate when simultaneously etching both the alternating silicon oxide and silicon nitride layers that make up a 3D NAND stack more than doubled, increasing from 310 nanometers per minute to 640 nanometers per minute.

The researchers also found that adding phosphorus trifluoride quadrupled the etch rate for silicon dioxide, though it only marginally increased the silicon nitride etch rate. They also investigated ammonium fluorosilicate, which forms during the etching process when the silicon nitride reacts with the hydrogen fluoride. They found that while it can slow down etching, water can offset the effect. [1]

Xenon in CVD

Researchers at Linköping University found that using the noble gas xenon in chemical vapor deposition helps create a more even material coating in the deep, narrow holes of high-density memories.

Henrik Pedersen, professor of inorganic chemistry at Linköping University, noted in a statement one of the key challenges in memory manufacturing: “The problem is getting the material into the holes and coating the surface inside the hole evenly. You don’t want more material at the opening of the hole – it clogs the opening, and you can’t fill the rest of the hole. The molecules that carry the atoms for the material must be able to get all the way to the bottom.”

This can be achieved by lowering the temperature to slow down the chemical reactions, but doing so can result in the material having poorer properties. By adding xenon, the researchers were able to use high enough temperatures to achieve really good material quality.

“We don’t yet know exactly how this actually works. We believe that the xenon gas helps ‘push’ the molecules into the hole. This was a genius move by my doctoral student Arun Haridas Choolakkal. He had studied some basic formulas for how gases move and put forward the hypothesis that this should work. Together we set up a number of experiments to test it, and it worked,” added Pedersen.

The technology has been patented and sold to a Finnish company that intends to develop it further. [2]

Cache management

Researchers from Chalmers University of Technology and the University of Gothenburg proposed a method to improve cache memory’s access to information about how and where data is processed in the system, enabling better data management.

“Our solution enables computers to retrieve data significantly faster than before, as the cache can manage far more processing elements (PEs) than most existing systems. This makes it possible to meet the demands of tomorrow’s powerful computers,” said Per Stenström, professor at the Department of Computer Science and Engineering at Chalmers University of Technology and the University of Gothenburg, in a press release.

Developed as part of the European Processor Initiative, the components will be in a European high-performance computing system planned for 2030. The researchers believe the technology could also be integrated into standard computers within a few years.

References

[1] Thorsten Lill, Mingmei Wang, Dongjun Wu, Youn-Jin Oh, Tae Won Kim, Mark Wilcoxson, Harmeet Singh, Vahid Ghodsi, Steven M. George, Yuri Barsukov, Igor Kaganovich; Low-temperature etching of silicon oxide and silicon nitride with hydrogen fluoride. J. Vac. Sci. Technol. A 1 November 2024; 42 (6): 063006. https://doi.org/10.1116/6.0004019

[2] Choolakkal, A.H., Niiranen, P., Dorri, S. et al. Competitive co-diffusion as a route to enhanced step coverage in chemical vapor deposition. Nat Commun 15, 10667 (2024). https://doi.org/10.1038/s41467-024-55007-1