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

Claim 12:
13. A method of forming a semiconductor device, the method comprising:
forming a fin over a substrate, the fin comprising a semiconductor strip protruding above the substrate and a layer stack over the semiconductor strip, 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 over the fin on opposing sides of the dummy gate structure;
forming an inter-layer dielectric (ILD) layer over the fin around the dummy gate structure;
after forming the ILD layer, removing the dummy gate structure to expose the first semiconductor material and the second semiconductor material disposed under the dummy gate structure;
removing the exposed first semiconductor material using a first etching process, wherein after the first etching process, the remaining second semiconductor material form channel regions of the semiconductor device; and
after the first etching process, reshaping the channel regions using a second etching process different from the first etching process, wherein reshaping the channel regions comprises reducing thicknesses of middle portions of the channel regions and changing sidewall profiles of the middle portions of the channel regions, wherein a cross-section of the middle portion of each of the channel regions along a direction perpendicular to a longitudinal axis of the fin has a first shape before reshaping the channel regions, and has a second shape after reshaping the channel regions, wherein the first shape is a rectangular shape, and the second shape is a discorectangle shape, wherein the first etching process is performed using a first gas mixture comprising a first etching gas and a first carrier gas, wherein the first etching gas comprising F2 and HF, wherein the second etching process is performed using a second gas mixture comprising a second etching gas and a second carrier gas, wherein the second etching gas comprises F2 and NH3, wherein in the second gas mixture, a volume mixing ratio between F2 and NH3 is between about 1:4 and about 1:40, and a volume percentage of the second etching gas in the second gas mixture is between about 1:1 and about 1:10.