A fabrication method of a semiconductor device is described. Generally, the method includes forming a customizable oxide-nitride-oxide (ONO) stack over a substrate in an in-situ atomic layer deposition (ALD) tool or chamber. Radical oxidation or oxide deposition process steps are performed to form tunnel dielectric layer overlying the substrate. Silicon nitride deposition process steps are also performed to form a multi-layer charge trapping (CT) layer in which at least some of the process parameters of silicon nitride deposition process steps are adjusted when forming the first and second CT sub-layers of the multi-layer CT layer. Subsequently, radical oxidation or oxide deposition process steps are performed in the ALD tool to form a blocking dielectric layer overlying the multi-layer CT layer.