US Patent 10396177 Prevention of extension narrowing in nanosheet field effect transistors

Methods of forming the same include forming a stack of layers of alternating materials, including first layers of sacrificial material and second layers of channel material. The first layers are recessed relative to the second layers with an etch that etches the second layers at a slower rate than the first layers to taper ends of the second layers. First spacers are formed in recesses formed by recessing the first layers. Second spacers are formed in recesses formed by recessing the first layers. The first spacers are etched to expose sidewalls of the second spacer. Source/drain extensions are formed in contact with exposed ends of the second layers.