TaN and $hbox{Al}_{2}hbox{O}_{3}$ Sidewall Gate-Etch Damage Influence on Program, Erase, and Retention of Sub-50-nm TANOS nand Flash Memory Cells

摘要

The sidewall gate-etch damage influence on the electrical behavior of 48-nm $hbox{TaN}/hbox{Al}_{2}hbox{O}_{3}/hbox{SiN}/hbox{SiO}_{2}/hbox{Si}$ (TANOS) nand charge-trapping memory cells is investigated in detail. This etch damage occurs at the sidewall of the high work-function TaN metal gate and high- $k$ $hbox{Al}_{2}hbox{O}_{3}$ blocking-oxide layers and adversely affects the electrical performance and the mechanical stability of small-ground-rule TANOS cells. Both issues could be solved for 48-nm TANOS cells by the introduction of a new integration scheme, which includes a removable encapsulation liner. This SiN liner protects the TaN sidewall from the etch damage during the aggressive $hbox{Al}_{2}hbox{O}_{3}$ high- $k$ etch process. The optimum of the 48-nm electrical cell performance was found for a 4-nm encapsulation liner thickness. In contrast to 48-nm TANOS cells, the encapsulation liner thickness does not affect the electrical performance of large 5-$mu hbox{m}$-long-and-wide memory cells. The memory cell performance dependence on the TANOS liner thickness and memory cell size is explained by a damaged $hbox{Al}_{2} hbox{O}_{3}$ region approximately 3–4 nm thick at the block oxide side wall. As a result, the reported etch damage exhibits a new scaling issue for TANOS memory cells around the 20-nm technology node when the total encapsulation liner thickness approaches half of the memory cell length.