3D metrology expedites dev't of 3D NAND Flash, FinFETs

Applied Materials Inc. (AM) has revealed that it has come up with a solution to the most serious problems facing 3D flash chip stacks and 3D FinFETs in a paper presented at the International Society for Optics and Photonics (SPIE) in San Jose, California.

3D NAND flash memory and 3D FinFET transistors have been enabled by critical-dimension scanning electron microscopy (CD-SEM). By applying techniques only recently proven effective in the research lab, AM's VeritySEM 5i could not only allow semiconductor makers to speed development of 3D FinFETs but also to finally enable 3D flash memory cubes to be brought to the mass market.

"The industry is transitioning from 2D to 3D," said Ofer Adan, global product and technology manager for PDC. "So we have the logic guys transitioning to 3D transistors, FinFETS, and the memory guys are transitioning from 2D NAND flash to 3D NAND flash where you stack your NAND device vertically."

Both 3D FinFETs and 3D NAND flash cubes are derived from 2D semiconductors, but until now there were no tools to make the CD-SEM measurements to get high-yields during mass production. (Source: Applied Materials)

The big problem that manufacturers have with FinFETs is turning them all off at precisely the same voltage, the only way you take advantage of the low leakage and subsequent cool running afforded by 3D FinFET transistors. To control leakage power, you need to control all the different aspects of the 3D gate, the fin height and width, the gate height (sticking out of oxide) and the slope of the gate sides. Unfortunately, none of these parameters can be accurately measured with traditional 2D semiconductor metrology equipment.

Standard 2D metrology technique (right) do not allow the necessary measurements to be made to determine if the desired parameters are being met (left). (Source: Applied Materials)

The problem with 3D NAND devices is even worse, since the measurements to be made are inside the 3D cube, resulting in only Samsung claiming to be manufacturing devices, and those are not commercially available, but are only being supplied to select cloud customers with no data publicly available on architecture of yields.

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