Floating body memory cell having gates favoring different conductivity type regions
View Patent ↗A method for fabricating floating body memory cells (FBCs), and the resultant FBCs where gates favoring different conductivity type regions are used is described. In one embodiment, a p type back gate with a thicker insulation is used with a thinner insulated n type front gate. Processing, which compensates for misalignment, which allows the different oxide and gate materials to be fabricated is described.
1. A memory device comprising:
a linear semiconductor fin disposed on a substrate, the linear semiconductor fin having a top surface and a longest direction;
a first gate structure disposed on one side of the linear semiconductor fin, the first gate structure having a top surface and a longest direction, the top surface of the first gate structure above the top surface of the linear semiconductor fin with respect to the substrate, and the longest direction of the first gate structure orthogonal to the longest direction of the semiconductor fin;
a second gate structure disposed on an opposite side of the linear semiconductor fin, the second gate structure having a top surface and a longest direction, the top surface of the second gate structure above the top surface of the linear semiconductor fin with respect to the substrate, and the longest direction of the second gate structure orthogonal to the longest direction of the semiconductor fin and parallel with the longest direction of the first gate structure; and
one of the first or second structures having a more favorable characteristic for retaining charge in the linear semiconductor fin than the other of the gate structures, wherein the first gate structure has a gate dielectric comprising a first dielectric layer and a second, different, dielectric layer, and the second gate structure has a gate dielectric comprising the second dielectric layer but not the first dielectric layer.
2. The memory device of claim 1 , wherein one of the first and second gate structures has a gate with a different work function than the gate in the other gate structure.
3. The memory device of claim 1 , wherein the linear semiconductor fin includes an n type source and drain region, the second gate structure has a thinner gate dielectric than the first gate structure, and the first gate structure has a gate with a work function favoring a p type device.
4. The memory device of claim 3 , wherein the linear semiconductor fin is formed from a bulk silicon substrate.
5. The memory device of claim 4 , wherein the linear semiconductor fin is doped with a p type dopant.
6. The memory device of claim 1 , wherein the first dielectric layer comprises silicon dioxide, and the second dielectric layer comprises a high-k material.
7. A memory including:
a plurality of first and second, parallel, spaced-apart linear semiconductor fins disposed on a substrate, the linear semiconductor fins each having a top surface and a longest direction, and having alternate first and second regions between the linear semiconductor fins defined by side surfaces on adjacent linear semiconductor fins facing each other;
first gate structures disposed on alternate first regions of the linear semiconductor fins, each first gate structure having a top surface and a longest direction, the top surface of each of the first gate structures above the top surfaces of each of the linear semiconductor fins with respect to the substrate, and the longest direction of each of the first gate structures orthogonal to the longest direction of each of the semiconductor fins;
second gate structures disposed on alternate second regions of the linear semiconductor fins, each second gate structure having a top surface and a longest direction, the top surfaces of each of the second gate structures above the top surfaces of each of the linear semiconductor fins with respect to the substrate, and the longest direction of each of the second gate structures orthogonal to the longest direction of each of the semiconductor fins and parallel with the longest direction of each of the first gate structures;
wherein the first gate structures have a gate dielectric comprising a first dielectric layer and a second, different, dielectric layer, and the second gate structures have a gate dielectric comprising the second dielectric layer but not the first dielectric layer.
8. The memory of claim 7 , wherein the linear semiconductor fins include n type source and drain regions, and the gate dielectric thickness of the first gate structures is thicker than the gate dielectric thickness of the second gate structures.
9. The memory of claim 8 , wherein the gate material of the first gate structures is formed from a metal having a work function in the range of approximately 4.6 to 5.2 eV.
10. The memory of claim 9 , wherein the linear semiconductor fins are integral with a bulk silicon substrate.
11. The memory of claim 7 , wherein the first dielectric layer comprises silicon dioxide, and the second dielectric layer comprises a high-k material.