The present disclosure relates to an embedded flash memory cell having a common source oxide layer with a substantially flat top surface, disposed between a common source region and a common erase gate, and a method of formation. In some embodiments, the embedded flash memory cell has a semiconductor substrate with a common source region separated from a first drain region by a first channel region and separated from a second drain region by a second channel region. A high-quality common source oxide layer is formed by an in-situ steam generation (ISSG) process at a location overlying the common source region. First and second floating gate are disposed over the first and second channel regions on opposing sides of a common erase gate having a substantially flat bottom surface abutting a substantially flat top surface of the common source oxide layer.