A method used during semiconductor device fabrication comprises forming at least two types of transistors. A first transistor type may comprise a CMOS transistor comprising gate oxide and having a wide active area and/or a long channel, and the second transistor type may comprise a NAND comprising tunnel oxide and having a narrow active area and/or short gate length. The transistors are exposed to a nitridation ambient which, due to their differences in sizing, results in nitridizing the tunnel oxide in its entirely but only partially nitridizing the gate oxide. Various process embodiments and completed structures are disclosed.