US Patent 10461154 Bottom isolation for nanosheet transistors on bulk substrate

A method of forming nanosheets that includes providing a stack of semiconductor material layers on a supporting bulk substrate. A first undercut region filled with a first dielectric material is formed extending from the opening into the bulk semiconductor substrate underlying the semiconductor material layers of the at least two stacks of semiconductor material layers. A second undercut region into the bulk semiconductor substrate filled with a second dielectric material from a side of the at least two stacks of semiconductor material layers that is opposite a side of the at least two stacks of semiconductor material layer at which the first undercut region is positioned. The first and second dielectric material merged that provide a full isolation region.