Flash new laws [NAND flash memory circuits]

Abstract

The rapid growth in NAND flash capacity has made it possible to store hundreds of thousands of images from high-end digital still cameras. But the most recent increases in claimed capacity are coming at the expense of increased die size. The Samsung 64 Gb NAND flash memory was built using a technique called self-aligned double-patterning in an attempt to overcome problems with defining on-chip features as small as 30 nm across using light with a wavelength more than six times longer than that. Double patterning works by using two complementary masks exposed one at a time to ease the demands on lithography. In effect, two patterns spaced at 60 nm are overlapped to produce the 30 nm features. Double-patterning slows down the lithography process and restricts what can be printed, making it unpopular among logic users. But it may be viable for bulk memory production as those designs are far more regular.