Semiconductor device with isolation structure

A semiconductor structure, comprising:

• a substrate with a memory device area and a logic device area;
• fin structures with first fin portions disposed on the memory device area of the substrate and second fin portions disposed on the logic device area of the substrate;
• a first pair of gate structures disposed on the first fin portions in the memory device area;
• a second pair of gate structures disposed on the second fin portions in the logic device area, wherein the second pair of gate structures is electrically isolated from the first pair of gate structures;
• a first isolation structure interposed between the first pair of gate structures, wherein the first isolation structure comprises a first pair of nitride liners, a first oxide liner interposed between the first pair of nitride liners, and a first oxide fill layer;
• and
• a second isolation structure interposed between the second pair of gate structures, wherein the second isolation structure comprises a second pair of nitride liners, a second oxide liner interposed between the second pair of nitride liners, and a second oxide fill layer, and wherein the second oxide liner is thicker than the first oxide liner.

A method, comprising:

• forming first and second gate structures on first and second fin structures disposed on a substrate;
• forming first and second isolation trenches across the first and second gate structures, respectively,
• wherein the first isolation trench divides the first gate structure into a first pair of gate structures electrically isolated from each other and the second isolation structure divides the second gate structure into a second pair of gate structures electrically isolated from each other, and
• wherein the forming the first and second isolation trenches comprises forming the first isolation trench to extend a first distance into the substrate and forming the second isolation trench to extend a second distance into the substrate, wherein the second distance is substantially equal to the first distance;
• and
• forming first and second isolation structures within the first and second isolation trenches, respectively, wherein the forming the first and second isolation structures comprises forming the first isolation structure with a first dielectric constant and forming the second isolation structure with a second dielectric constant higher than the first dielectric constant.