Forming insulator fin structure in isolation region to support gate structures

A method for forming a semiconductor device comprising:

• forming a plurality of composite fin structures across a semiconductor substrate including active regions and isolation regions, wherein the composite fin structures include semiconductor fin portions over the active regions and dielectric fin portions over the isolation regions, said forming the plurality of composite fin structures comprising forming a plurality of semiconductor fin structures across the semiconductor substrate including the active regions and the isolation regions, forming a hardmask dielectric on the semiconductor substrate contacting the semiconductor fin structure sidewalls, wherein an upper surface of the semiconductor fin structures is exposed, removing portions of the semiconductor fin structures present on the isolation regions of the substrate to form fin trenches having sidewalls defined by the hard mask, wherein portions of the semiconductor fin structures present on the active regions of the substrate remain to provide the semiconductor fin portion, and forming the dielectric fin portions in the fin trenches adjacent to the semiconductor fin portions present on the active regions of the substrate;
• forming gate structures on a channel region of the semiconductor fin portions present on the active regions of the substrate and the dielectric fin portions on the isolation regions;
• and
• forming epitaxial source and drain regions on source and drain portions of the semiconductor fin portions present on the active region, wherein the dielectric fin portions support the gate structure over the isolation regions.