The metallization scheme based on 3 metal layers was introduced in 3Xnm NAND Flash Single Level Cell (SLC) to reduce the chip size. However, the reliability issue related to hydrogen was caused by the additional PETEOS film deposition, which acts as the source of radical hydrogen. The passivated hydrogen at the Si/SiO2 interface can create the traps as a result of incomplete bonding through the electrical stresses. The outgoing levels of hydrogen before and after the added PETEOS deposition were measured using thermal desorption spectroscopy (TDS). By PETEOS alloy, although a number of characteristic improvements were obtained, the reliability capability was not reached to that of the previous 2 Metal structure. From the various annealing processes, it was found that hydrogen outgassing had been hindered by SiN layer on Cu metal layer. Therefore, via contact areas between Cu2 and Al were increased using dummy mask, thereby enhancing hydrogen outgassing. As the result, the similar reliability performance was obtained when it was compared to that of the metal 2 scheme. This paper presents the detailed analysis about the reliability degradation and introduces a solution in terms of hydrogen outgassing.