Forming placeholder for backside contact

A method of forming a semiconductor structure comprising:

• forming a recess for a source/drain (S/D) region of a transistor on a substrate;
• forming a liner covering sidewalls of the recess;
• creating an opening below the recess in the substrate;
• forming a placeholder by filling the opening with a first material;
• forming the S/D region in the recess above the first placeholder;
• removing the placeholder from a backside of the substrate to expose a bottom surface of the S/D region;
• and
• forming a backside contact contacting the bottom surface of the S/D region.

A semiconductor structure comprising:

• a transistor having a first and a second source/drain (S/D) region;
• a backside contact in contact with a bottom surface of the first S/D region;
• and
• a placeholder underneath the second S/D region,
• wherein the placeholder is embedded in a backside interlevel-dielectric (BILD) layer and includes a first portion and a second portion of a first and a second material, the first and the second material are different from each other and different from a material of the BILD layer.