Local trap-rich isolation
A trap-rich polysilicon layer is interposed between the active (SOI) layer and the underlying handle portion of a semiconductor substrate to prevent or minimize parasitic surface conduction effects within the active layer and promote device linearity. In various embodiments, the trap-rich layer extends vertically through a portion of an isolation layer and laterally therefrom between the isolation layer and the handle portion of the substrate to underlie a portion of the device active area.
1. A method of manufacturing a semiconductor device, comprising:
forming an isolation trench through a first semiconductor layer of a semiconductor substrate and partially through an isolation layer underlying the first semiconductor layer;
forming spacers on sidewalls of the isolation trench;
forming a lateral cavity within the isolation layer extending from the isolation trench between a portion of the isolation layer and a second semiconductor layer underlying the isolation layer;
forming a polysilicon layer within the isolation trench and the lateral cavity;
forming a gate oxide layer over the first semiconductor layer and overlying the polysilicon layer within the lateral cavity;
forming a polysilicon gate over the gate oxide layer;
forming a dielectric layer over the polysilicon gate;
etching a contact via through the dielectric layer; and
forming a contact within the contact via in electrical communication with the polysilicon gate, wherein a portion of the first semiconductor layer overlying the polysilicon layer within the lateral cavity comprises an active layer of a switch field effect transistor.
2. The method of claim 1 , wherein forming the isolation trench comprises etching through at least 50% of a thickness of the isolation layer.
3. The method of claim 1 , wherein the isolation trench is formed peripheral to a portion of the first semiconductor layer.
4. The method of claim 1 , wherein the lateral cavity underlies a portion of the first semiconductor layer.
5. The method of claim 1 , wherein forming the lateral cavity comprises selectively etching the isolation layer with respect to the spacers, the first semiconductor layer, and the second semiconductor layer.
6. The method of claim 1 , wherein the polysilicon layer fills the isolation trench and the lateral cavity.
7. The method of claim 1 , wherein the polysilicon layer is formed directly over the second semiconductor layer.
8. The method of claim 1 , wherein the polysilicon layer is formed peripheral to and below a portion of the first semiconductor layer.
9. The method of claim 1 , further comprising implanting a dopant into the first semiconductor layer to form an active region.
10. The method of claim 1 , further comprising etching the polysilicon layer below a top surface of the isolation layer within the isolation trench.
11. The method of claim 10 , further comprising forming a second dielectric layer on the polysilicon layer within the isolation trench.