| CPC H01L 21/823475 (2013.01) [H01L 21/02274 (2013.01); H01L 21/31053 (2013.01); H01L 21/764 (2013.01); H01L 21/823431 (2013.01); H01L 23/528 (2013.01); H01L 27/0886 (2013.01); H01L 29/41791 (2013.01)] | 20 Claims |

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1. A semiconductor structure having a frontside and a backside, comprising:
an isolation structure at the backside;
one or more transistors at the frontside, the one or more transistors having source/drain epitaxial features;
two metal plugs through the isolation structure and contacting two of the source/drain epitaxial features from the backside; and
a dielectric liner filling a space between the two metal plugs, wherein the dielectric liner partially or fully surrounds an air gap between the two metal plugs.
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