Renesas: fin-shaped MONOS Flash memory cells for MCUs in 16/14nm process nodes and beyond
Renesas Electronics announced its successful development of the world’s first split-gate metal-oxide nitride oxide silicon (SG-MONOS) flash memory cells employing transistors with fin-shape for use in microcontrollers with on-chip flash memory having a circuit linewidth of 16 to 14 nm or finer. SG-MONOS technology is reliable for use in automotive applications and Renesas currently mass produces 40nm MCUs using this technology, and 28nm MCUs are under development. The successful development shows promising scalability of the SG-MONOS technology to 16/14nm process nodes and beyond.
Employing a fin structure for embedded flash memory can become a big challenge depending on the structure of the flash memory. Two types of embedded flash memories have been proposed and implemented: the floating-gate and charge trap. Compared with floating-gate memory, the charge trap flash memory which Renesas has been utilizing in recent years has superior charge retention characteristics and a proven track record in automotive MCUs requiring a high level of reliability. Also, since the memory functional material is formed on the surface of the silicon substrate, they are comparatively easy to be extended into a three-dimensional fin structure. In contrast, floating-gate flash memory cells have a complex structure, and therefore it is difficult to integrate it into a fin structure.
Another advantage of SG-MONOS over the floating-gate structure is that the memory cell structure is maintained after replacing the dummy polysilicon gate electrode with the metal gate electrode, which is the process used to manufacture advanced logic CMOS devices with high dielectric gate insulators and metal gate electrodes.