| CPC H01L 21/823431 (2013.01) [H01L 21/823418 (2013.01); H01L 27/0886 (2013.01); H01L 27/0924 (2013.01)] | 20 Claims |

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1. A device comprising:
a semiconductor substrate;
isolation regions in the semiconductor substrate;
a protruding semiconductor fin higher than top surfaces of the isolation regions;
a gate stack on the protruding semiconductor fin;
a gate spacer on a sidewall of the gate stack, wherein the gate spacer contacts the sidewall of the gate stack to form a vertical interface;
a semiconductor region connecting to an end of the protruding semiconductor fin;
a contact etch stop layer over the semiconductor region;
an inter-layer dielectric over the contact etch stop layer; and
a dummy fin comprising:
a first portion directly underlying the gate stack and the gate spacer, wherein a sidewall of the first portion contacts a portion of the contact etch stop layer, and wherein the sidewall of the first portion of the dummy fin is in a vertical plane that is parallel to the vertical interface; and
a second portion overlapped by the contact etch stop layer.
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