The device 100 post the operation 20 is shown in FIGS. 5, 6A, and 6B collectively. FIG. 6A is a cross-sectional view of the trimmed S/D regions 110a along the A-A′ line of FIG. 5. FIG. 6B is a cross-sectional view of the fin 110 along the B-B′ line of FIG. 5. Referring to FIG. 6A, the fin 110 in the S/D regions 110a is trimmed to have a new width Wfin2 that is smaller than Wfin. In some embodiments, as discussed above, the converted exterior layer 124 has a wider thickness around the center height of the fin 110 than around top and bottom of the fin 110. After the removing of the converted exterior layer 124, the sidewalls of the fin 110 curve in towards the center, as illustrated in the FIG. 6A. For clarity, the Wfin2 is measured at half height of the fin 110 (Hfin2/2). Similarly, the surface 123 of the exposed portion of the fin 110 in the channel region 110b may also curve in under the dummy gate stacked 120.
