Over the last year and a half, the major NAND flash makers have started selling their 1X nm class of planar flash memory. According to our sourcing of the devices on the open market, Micron was first with product appearing in February of 2014, followed by SK-Hynix in October. Nearly 6 months later, products sporting Samsung 16 nm or Toshiba 15 nm NAND flash showed up in our laboratories.

There has been much discussion in the literature on the end of lithographic scaling of planar NAND flash, and its replacement with vertically stacked flash such as Samsung’s 3D V-NAND or Toshiba’s BiCS. There is a consensus that planar NAND will end near the 10 nm node, that is, one or two generations into the future from the 15/16 nm NAND flash that we at TechInsights are now completing analysis on. We thought it timely to look at some process features that we see in these 15/16 nm flash memories.

We have been buying NAND flash memory for a number of years for our technical analysis reports shows the process nodes versus year that we acquired them for Micron and SK-Hynix. These two manufacturers were typically the first to market with a process node. A semi-log plot is used to show the roughly 23%/year process shrink (solid black line) that we see for the Micron and Hynix devices.

The rate of process shrinks has slowed dramatically for the 25 nm and smaller product and this likely reflects the difficulties in implementing double patterning lithography and reducing electrical interference between adjacent cells.

Two approaches can be used for double patterning. Litho-etch-litho-etch (LELE) double patterning (DP) that is typically used for logic processes, or self-aligned double patterning (SADP) using sidewall spacers that is used by the memory makers. This has worked for NAND flash devices down to the present 16 nm node but may not make it to the 10 nm class of devices.

But scaling down to planar 10 nm NAND flash is still seen as a significant challenge and this has spurred efforts to develop 3D vertical NAND flash memory.

By: DocMemory
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