Method of forming a semiconductor structure comprising insulating layers with different thicknesses

e ce cThe method of forming a semiconductor structure in a substrate comprises, forming a first trench with a first width Wand a second trench with a second width W, wherein the first width Wis larger than the second width W, depositing a protection material, lining the first trench, covering the substrate surface and filling the second trench and removing partially the protection material, wherein a lower portion of the second trench remains filled with the protection material.