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Intel maps out plans for 3D NAND

Posted: 28 May 2013 ?? ?Print Version ?Bookmark and Share

Keywords:NAND flash? memory IC? p-BiCS? IM Flash Technologies?

The joint venture of Intel Corp. and Micron Technology Inc., IM Flash Technologies LLC (IMFT), is mapping out how it will transition its NAND flash memory ICs into 3D. However, the company estimates that its development of a 20nm memory cell has bought it a generation or two of 2D scaling.

Speaking at the IMEC Technology Forum, Keyvan Esfarjani, vice president technology & manufacturing at Intel and co-CEO of IMFT revealed some of the reasoning behind IMFT's 3D NAND strategy.

An industry-wide transition for the non-volatile NAND flash memory technology from memory cells in a 2D array to strings of NAND transistors integrated monolithically in the vertical direction is now anticipated. These 3D memories are expected to be arranged as a 2D array of vertical semiconductor channels with many levels of gate-all-around (GAA) structures forming the multiple voltage level memory cell transistors.

Toshiba is leading the charge towards 3D NAND processes with its pipe-shaped Bit Cost Scalable (p-BiCS) technology, which it has presented at numerous learned conferences over several years. Towards the end of last year Toshiba announced that it had 16-layer devices based on a 50nm diameter vertical channel. Samples are due this year and volume production in 2015. Toshiba's p-BiC technology arranges the transistor string in a U-shape.

3D NAND transition

The transition to 3D NAND according to Esfarjani.

But Esfarjani, while acknowledging there is a scaling limit for 2D NAND flash, indicated in one of his slides that 2D NAND flash can scale to two more nodes at about 15- and 10nm. The slide showed that the first 3D NAND generation is likely to be brought up alongside that 15nm 2D node. Esfarjani added that 16-layer NAND flash ICs will not be enough to provide an economic benefit. "You need 64 or at least 32 layers," he said.

According to Esfarjani, the planar floating-gate high-K metal gate cell introduced by IMFT at the 20nm node to replace a "wrap-around" cell used at 34- and 25nm would scale further. IMFT introduced a 128Gb NAND flash memory at the 20nm in 2012, leveraging its HKMG experience gained in logic circuits.

Keyvan Esfarjani

Esfarjani: New materials are being developed for 3D NAND.

Among the techniques being used to extend the 2D NAND flash generation are the addition of a nitride film and nanodots, Esfarjani said. "But a working cell is not enough. You also need high endurance of 10^5 cycles and higher," he told the IMEC Technology Forum audience.

"The transition to 3D is not limited by lithography," Esfarjani said indicating that a 40nm diameter semiconductor channel was about right. The challenges are in metrology, in finding materials that can withstand the temperatures of multilayer semiconductor processing and the high aspect ratio etch to drive in the vertical channel. This has to be controlled at an angle of taper of precisely 89.8 degrees, Esfarjani said.

"The NAND market will be with us and growing for years to come. 2D NAND continues with the planar floating gate cell and 3-D NAND will carry us beyond the 10nm limit," concluded Esfarjani.

During questions at the end of his talk Esfarjani was asked if he could share information about the materials that IMFT is using to create the dielectric and gates within the vertical channel. He confirmed that IMFT is working on new materials but said that some information is too good to share.

- Peter Clarke
??EE Times

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