Method for forming an air gap around a through-silicon via

1. A method comprising:

forming a first cavity in a substrate;

filling the first cavity with a sacrificial material;

lining the first cavity with an oxide material prior to filling the first cavity with the sacrificial material;

forming a second cavity in the substrate, through the sacrificial material and the oxide material, by removing a portion of the sacrificial material, a portion of the oxide material, and a portion of the substrate below the sacrificial material;

filling the second cavity with a conductive material;

removing a remaining portion of the sacrificial material to form an air gap between the conductive material and the substrate; and

forming a cap over the air gap.

2. The method according to claim 1 , further comprising:

forming a photoresist over the substrate and the sacrificial material;

patterning the photoresist; and

removing the photoresist over the portion of the sacrificial material, prior to forming the second cavity.

3. The method according to claim 2 , further comprising:

forming a protective oxide layer over the sacrificial material prior to forming the photoresist.

4. The method according to claim 3 , further comprising:

removing the protective oxide layer prior to removing the remaining portion of the sacrificial material.

5. The method according to claim 1 , further comprising:

lining the second cavity with an oxide material prior to filling the second cavity with the conductive material,

wherein the air gap is formed between the substrate and the oxide material.

6. The method according to claim 5 , further comprising:

lining the second cavity with a liner material after lining the second cavity with the oxide material and prior to filling the cavity with the conductive material.

7. The method according to 1 , wherein the second cavity is formed deeper than the first cavity and the second cavity is narrower than the first cavity, further comprising removing a bottom portion of the substrate to expose the conductive material.

8. A method comprising:

forming at least one first cavity in a substrate;

conformally depositing an oxide material over the substrate and lining the first cavity;

filling the oxide-lined first cavity with a polymer material;

forming an oxide protection layer over the polymer material and the substrate;

forming a second cavity through the oxide protection layer, the polymer material, the oxide material, and a portion of the substrate, the second cavity having a diameter smaller than a diameter of the first cavity;

conformally depositing an isolation material followed by a conductive liner material over the substrate and lining the second cavity;

filling the lined cavity with a conductive material;

polishing the conductive material, the liner material, the oxide protection layer, and the oxide material down to an upper surface of the substrate;

removing a remaining portion of the polymer material to form an air gap between the isolation material and the oxide material; and

forming a cap over the air gap.