Method and structures for improving substrate loss and linearity in SOI substrates

1. A method, comprising:

(a) forming gate structures in an active region and dummy gate structures in an inactive region and on a top surface of a silicon layer separated from a supporting substrate by a buried oxide layer;

(b) removing said dummy gate structures and said buried oxide layer from said inactive regions to form a trench extending through said silicon layer and said buried oxide layer to said substrate;

(c) ion implanting an electrically inert species into said substrate in said inactive regions and not into gate structures, said silicon layer, said buried oxide layer and said substrate in said active regions; and

(d) depositing a dielectric material over said active and inactive regions to form a dielectric layer, said dielectric material filling said trench.

2. The method of claim 1 , wherein after (d), a top surface of said dielectric layer over said active regions is coplanar with a top surface of said dielectric layer over said inactive region.

3. The method of claim 1 , further including:

before (a) forming dielectric trench isolation in said active region and dummy dielectric trench isolation in said inactive region, said dielectric trench isolation extending from said top surface of said silicon layer to said buried oxide layer; and

(b) includes removing said dummy dielectric trench isolation from said inactive regions.

4. The method of claim 1 , wherein said electrically inert species is selected from the group consisting argon, neon, krypton and xenon.

5. The method of claim 1 , wherein said ion implanting damages the crystal structure of said substrate and creates traps to convert mobile charge to fixed charge.