A semiconductor structure includes a plurality of semiconductor fins on an upper surface of a semiconductor substrate. The semiconductor fins spaced apart from one another by a respective trench to define a fin pitch. A multi-layer electrical isolation region is contained in each trench. The multi-layer electrical isolation region includes an oxide layer and a protective layer. The oxide layer includes a first material on an upper surface of the semiconductor substrate. The protective layer includes a second material on an upper surface of the oxide layer. The second material is different than the first material. The first material has a first etch resistance and the second material has a second etch resistance that is greater than the first etch resistance.