Fluorine Effects Originating From the CVD-W Process on Charge-Trap Flash Memory Cells

The fluorine (F) effect originating from the chemical vapor deposited (CVD) tungsten (W) process on charge-trap flash memory devices was systematically investigated, and the CVD-W memory was compared with physical vapor deposited (PVD) W memory. The residual F in the CVD-W diffused into Al2O3 and Si3N4 layers, generating shallow charge-trapping sites in each layer. These generated charge-trapping sites were considered to be responsible for the fast-erase and poor-retention characteristics at room temperature in the CVD-W compared to the related characteristics in the PVD-W memory. The generation of charge-trapping sites caused by the residual F in each layer was also supported by the trap density calculation in the Si3N4 and constant current stress test for the Al2O3 layer.