Embodiments described herein generally relate to conformal oxidation processes for flash memory devices. In conventional oxidation processes for gate structures, growth rates have become too fast, ultimately creating non-conformal films. To create a preferred growth rate for SiO2 on SiNx films, embodiments in this disclosure use a thermal combustion of a ternary mixture of H2+O2+N2O to gain SiO2 out of Si containing compounds. Using this mixture provides a lower growth in comparison with using only H2 and O2, resulting in a lower sticking coefficient. The lower sticking coefficient allows an optimal amount of atoms to reach the bottom of the gate, improving the conformality in 3D NAND SiO2 oxidation layers, specifically for ONO replacement tunneling gate formation.