According to an illustrative example, a method of forming a semiconductor structure comprises providing a semiconductor substrate comprising a first feature and a second feature. A material layer is formed over the first feature and the second feature. A mask is formed over the first feature. At least one etch process adapted to form a sidewall spacer structure adjacent the second feature from a portion of the material layer is performed. The mask protects a portion of the material layer over the first feature from being affected by the at least one etch process. An ion implantation process is performed. The mask remains over the first feature during the ion implantation process.