As the world generates and consumes more data than ever before, there is an ongoing push to make electronic devices smaller and more efficient, capable of storing ever-larger volumes of information. The demand for denser data storage is insatiable, driven not only by traditional applications like computers and smartphones but also by the rapid rise of artificial intelligence, which requires massive amounts of data to function effectively. To meet these needs, researchers are collaborating in a public-private partnership to explore new approaches to data storage, especially at the atomic scale. One of the most promising areas of research is the development of 3D NAND flash memory, a type of non-volatile storage that offers the potential for significant gains in storage density.
The Promise of 3D NAND Flash Memory
NAND flash memory is a non-volatile data storage technology, meaning that it retains data even when power is lost. Most consumers are familiar with it through memory cards used in digital cameras, USB drives, and the storage inside mobile phones and computers. Traditionally, NAND flash memory stores data in a single, flat layer of memory cells, each of which can be either “on” or “off,” representing binary data. While this has served well for years, the need for more data storage—particularly as applications like AI, machine learning, and big data analytics continue to grow—has led researchers to look for ways to pack more data into the same space.
This is where 3D NAND flash memory comes into play. Rather than relying on a single layer of cells, 3D NAND involves stacking multiple layers of memory cells on top of each other. The resulting storage structure is much denser and can store far more data in the same footprint, much like how constructing a multi-story building can house more people in the same space as a single-story house. However, creating these vertical stacks of memory requires a complex and highly refined manufacturing process, particularly in etching tiny, vertical holes into the materials that form the core of the memory cells.
The Challenges of Etching Tiny, Precise Holes
In 3D NAND flash memory, a critical part of the manufacturing process involves creating narrow, deep holes that run vertically through layers of materials like silicon oxide and silicon nitride. These holes are essential for connecting the different layers of memory cells and ensuring the flow of electrical signals. The process of creating these holes, known as reactive ion etching (RIE), uses plasma, which is a form of ionized gas, to remove material and etch the necessary patterns.
The goal is to etch these holes as precisely as possible—narrow and deep, with smooth, vertical sides. Achieving this precision at the scale required for 3D NAND memory has been challenging. Researchers have spent years testing different techniques, temperatures, and chemical ingredients to refine the etching process and improve both speed and quality.
Cryo Etching: A New Approach to Faster, Better Etching
One of the most promising advances in this field has been the development of a new technique called cryo etching. Traditional etching methods use separate gases—hydrogen and fluorine—to etch the necessary holes. However, cryo etching takes a different approach by using a single compound, hydrogen fluoride (HF), to create the plasma. This new method has shown significant improvements over previous processes.
The research team, which included scientists from Lam Research, the University of Colorado Boulder, and the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL), compared the performance of the traditional cryo etching method with the new HF-based cryo etching process. The results were impressive: the etching rate—the speed at which the holes were carved—more than doubled, increasing from 310 nanometers per minute to 640 nanometers per minute. For perspective, a human hair is about 90,000 nanometers thick, so the etching process is incredibly precise, even at high speeds.
The Impact of Key Chemical Ingredients
In addition to cryo etching, the researchers also focused on understanding the impact of various chemical compounds used during the etching process. One of these is phosphorus trifluoride (PF3), a gas commonly used in semiconductor manufacturing. In this study, the researchers found that adding PF3 to the etching process had a significant effect. Specifically, it quadrupled the etch rate for silicon dioxide (SiO2), one of the materials used in 3D NAND memory, although the impact on silicon nitride was less pronounced.
Another key compound explored in the research was ammonium fluorosilicate. This substance forms during the etching process when silicon nitride reacts with hydrogen fluoride. The researchers found that while ammonium fluorosilicate can slow down the etching process, it can be countered by the presence of water, which weakens the chemical bonds of the fluorosilicate. Adding water allowed the etching process to proceed more efficiently, even in the presence of this potentially inhibitive compound.
Doubling the Etch Rate and Improving Quality
The improvement in etching speed is one of the most significant outcomes of the study. By using hydrogen fluoride plasma and other refinements, the etching rate for silicon oxide and silicon nitride layers was more than doubled. This means that semiconductor manufacturers could etch more wafers in less time, improving the overall efficiency of the manufacturing process.
Moreover, the quality of the etch was also improved. A more consistent and uniform etching process is crucial for creating the precise, deep, vertical holes required for 3D NAND flash memory. The researchers found that the new method not only increased speed but also improved the precision of the etching, making it possible to manufacture memory with higher density and greater reliability.
A Collaborative Effort in Advancing Semiconductor Manufacturing
The significance of this research extends beyond the technical advances in etching processes. The study demonstrates the power of collaboration between different sectors—industry, academia, and national laboratories. By bringing together experts from diverse fields, the team was able to make crucial advancements in the way 3D NAND flash memory is manufactured, ultimately benefiting a wide range of industries reliant on high-density data storage.
Igor Kaganovich, a principal research physicist at PPPL, emphasized the importance of such collaboration. “This research shows how scientists in industry, academia, and national laboratories can work together to answer important questions in the field of microelectronics. It highlights the value of integrating experimental data with theoretical models to build a better understanding of complex semiconductor manufacturing processes.”
The Road Ahead: Scaling Up for the Future
As the demand for more powerful and efficient data storage grows, innovations like those explored in this research will be essential in meeting future challenges. The ability to create denser, more reliable memory with faster manufacturing processes will be critical as industries across the board—from mobile computing to artificial intelligence—demand increasingly large volumes of data storage.
At the same time, the improvements in etching speed and quality demonstrated in this study represent just one step in the ongoing evolution of semiconductor manufacturing. As researchers continue to refine these processes, we can expect even greater advances in storage technology, pushing the limits of what is possible in terms of data density and efficiency.
In conclusion, the research into refining the processes for creating 3D NAND flash memory is not only a significant technical achievement but also a demonstration of the power of interdisciplinary collaboration. As we continue to push the boundaries of data storage, innovations like these will play a crucial role in shaping the future of electronics, helping to meet the ever-growing demand for faster, denser, and more efficient data storage solutions.
Reference: Thorsten Lill et al, Low-temperature etching of silicon oxide and silicon nitride with hydrogen fluoride, Journal of Vacuum Science & Technology A (2024). DOI: 10.1116/6.0004019