Patent ID: 11961919
Assignee: TAIWAN SEMICONDUCTOR MANUFACTURING COMPANY LTD.
Field: Semiconductors (Electrical engineering)
Classification: CPC H  B | IPC H

Claim 0:
1. A method of forming a semiconductor device, the method comprising:
forming a fin protruding above a substrate, wherein a top portion of the fin comprises a layer stack, the layer stack comprising alternating layers of a first semiconductor material and a second semiconductor material;
forming a dummy gate structure over the fin;
forming source/drain regions in the fin on opposing sides of the dummy gate structure;
removing the dummy gate structure to expose the first semiconductor material and the second semiconductor material under the dummy gate structure;
selectively removing the exposed first semiconductor material by performing a first etching process, wherein after the first etching process, the second semiconductor material remains to form nanostructures; and
after the first etching process, increasing distances between adjacent nanostructures by performing a second etching process different from the first etching process, wherein the first etching process is performed using a first etchant selective to the first semiconductor material, and the second etching process is performed using a second etchant selective to the second semiconductor material, wherein the first etchant comprises F2 and HF, and the second etchant comprises NF3 and NH3, wherein after the first etching process and before the second etching process, a middle portion of each of the nanostructures has a first shape in a first cross-section along a direction perpendicular to a longitudinal axis of the fin, wherein after the second etching process, the middle portion of each of the nanostructures has a second shape in the first cross-section, wherein the first shape is a rectangular shape, and the second shape is an obround shape.