Semiconductor structure with airgap
A field effect transistor (FET) with an underlying airgap and methods of manufacture are disclosed. The method includes forming an amorphous layer at a predetermined depth of a substrate. The method further includes forming an airgap in the substrate under the amorphous layer. The method further includes forming a completely isolated transistor in an active region of the substrate, above the amorphous layer and the airgap.
1. A method, comprising:
forming an amorphous layer under an active region of a substrate;
forming an airgap in the substrate under the amorphous layer; and
forming an isolated transistor in the active region, above the amorphous layer and the airgap.
2. The method of claim 1 , wherein the isolated transistor is surrounded by shallow trench isolation regions.
3. The method of claim 2 , wherein the transistor is formed as a completely isolated transistor.
4. The method of claim 1 , wherein amorphous layer is formed by an ion implantation process, prior to the formation of the transistor.
5. The method of claim 1 , wherein the formation of the amorphous layer comprises:
forming a resist on the substrate;
patterning the resist to form an opening over the active region; and
performing the ion implantation process through the opening, prior to the formation of the transistor and airgap.
6. The method of claim 5 , wherein the formation of the airgap comprises:
etching the substrate with NH 4 OH to form a trench and an undercut extending laterally below the active region; and
filling the trench with a material,
wherein the amorphous layer is an etch stop layer for the etching of the substrate.
7. The method of claim 6 , wherein the material is poly material deposited within the trench.
8. The method of claim 1 , further comprising forming another amorphous layer on a bottom surface of the airgap.
9. The method of claim 1 , further comprising forming a perimeter of amorphous material surrounding the active region of the transistor.
10. The method of claim 1 , wherein the ion implantation process comprises ion implanting species of Ge or Ar.
11. The method of claim 1 , further comprising oxidizing a bottom surface of a lateral undercut to form an amorphous layer on a bottom surface of the airgap opposing the amorphous material.