Analysis of fluorine effects on TANOS (TiN-$Al_2O_3$-$Si_3N_4$-$SiO_2$-polysilicon) memory devices for 3D NAND Flash

Abstract

The importance of 3-dimensional (3D) integration technology increases for higher memory density in NAND Flash memory field. Chemical vapor deposition (CVD) method is essential to realize 3D NAND Flash memory. Tungsten (W) is widely used for gate electrode material because of its low resistivity, superior gap filling ability, and presence of proper precursor which is stable at room temperature. Fluorine atoms which are originated from tungsten hexafluoride (WF6) precursor diffuse through grain boundary of TiN, and then incorporate into memory cell after post metal annealing process. Although it is known that the fluorine is highly reactive due to its electro-negativity, the effect of fluorine on charge trap flash memory devices is not systemically studied. In this paper, we propose the effect of fluorine on charge trap flash (CTF) memory devices by analyzing the memory performance and reliability. Finally, the effect of fluorine on each thin film of CTF memory was systemically analyzed and the mechanism of degradation of CTF memory was confirmed.