SK hynix begins mass production of 375 layer 3D NAND at M15 facility with molybdenum material shift to increase performance and bit productivity
According to industry publication TheElec reported that, SK hynix is reportedly finished the production verification stage for its new 375 layer 3D NAND flash memory, and the company will now roll the technology onto mass production lines. The company has not chosen to construct new fabrication facilities and will pursue conversion investment for its existing M15 facility located in Cheongju. It will produce current 176, 238, and 321 layer products that will give way to the new high density design as they are phased out of the M15 line.
While under development, the future 400 layer class NAND had an internal target of 400 layers. Unfortunately, engineering difficulties associated with very tall stacking made it impossible to drill perfect, aligned channel holes through hundreds of microscopic layers, forcing engineers to alter the final 375 layer target. One industry insider knowledgeable about the roadmap confirmed
"Products that have previously been stated as 400 layer class NAND has been revised to 375 layer and later 480, and 604 layer."
The engineering changes necessitated by extremely dense layering have caused SK hynix to adopt molybdenum and replace a part of the tungsten material used in their metal gate electrodes. When making vertically oriented NAND chips, memory capacity increases with each additional layer of cell and word lines. As the layers get closer and thinner, the high electrical resistance of the tungsten wire hinders signal speed. Molybdenum offers better electrical resistance in thin layers, increasing chip read write speeds.
The physical structure of the deposited layer also provides a slight benefit for the bottom and top of the wafer package. In contrast to the added, blocking liner layer used in Tungsten deposition, Molybdenum does not require one and can be directly deposited, reducing the thickness and the size of the completed package. However, material processing for Molybdenum is proving more complex, as it has to be delivered as a gas and the precursor material is solid at room temperature, necessitating sophisticated heaters to ensure a steady stream.
The material shift to Molybdenum will not be entirely new to the NAND industry; Samsung's 9th generation 286 layer product used Molybdenum and is reportedly working on a 10th generation that exceeds 400 layers. Samsung uses single wafer processing systems, primarily those from Lam Research, to deposit the material whereas SK hynix chose an oven type system made by Tokyo Electron. Ovens that can process approximately 100 wafers simultaneously will provide much lower initial cost, space, and material utilization compared to single wafer systems.
The materials involved include several primary chemical manufacturers such as Merck KGaA, Entegris, and Air Liquide. SK Specialty is also considering supplying, potentially through the existing distribution networks of Air Liquide in order to satisfy the pure supply aspect. Molybdenum will experience rapid demand increase within the next several years; estimations place industry wide usage in excess of 80 tons by the end of this decade.
The implication behind this hardware transition is that profit margins are more important than unit shipment volume. Another industry observer pointed out
"Unlike DRAM, the NAND industry is still concerned more about profits than shipments. The production reduction of low layer NAND and increase of 375 layer NAND is designed to boost bit productivity and reduce costs, rather than expand total production."
