Analysis of Fluorine Effects on Charge-Trap Flash Memory of W/TiN/Al2O3/Si3N4/SiO2/Poly-Si Gate Stack

Abstract

A charge-trap flash (CTF) memory stack of chemical vapor deposition (CVD) tungsten (W) was systematically compared with a physical vapor deposited (PVD) W memory stack. The residual F in the CVD W was diffused into Al2O3, Si3N4, SiO2, and the interface at SiO2/poly-Si after the subsequent annealing process at 900 °C for 1 s. The diffused F increased the SiO2 thickness and altered the charge-trap density in the Al2O3, Si3N4, SiO2, and SiO2/poly-Si interface, and this eventually affected memory performance and reliability. The memory window and program/erase retention properties degraded while the charge-transport and endurance characteristics improved with the CVD W memory as compared to the PVD W memory.