Barrier region underlying source/drain regions for dual-bit memory devices
View Patent ↗One embodiment of the present invention relates to a memory cell. The memory cell comprises a substrate and a stacked gate structure disposed on the substrate, wherein the stacked gate structure comprises a charge trapping dielectric layer that is adapted to store at least one bit of data. The memory cell further includes a source and drain in the substrate, wherein the source and drain are disposed at opposite sides of the stacked gate structure. A barrier region is disposed substantially beneath the source or the drain and comprises an inert species. Other embodiments are also disclosed.
1. A memory cell, comprising:
a substrate having a thickness;
a stacked gate structure disposed on the substrate, the stacked gate structure comprising a charge trapping dielectric layer that is adapted to store at least one bit of data;
a source in the substrate, the source disposed at a side of the stacked gate structure;
a drain in the substrate, the drain disposed at the other side of the stacked gate structure; and
a barrier region disposed substantially beneath the source or the drain and comprising at least one of helium, neon, argon, krypton, or xenon,
wherein the barrier region is characterized by a retrograde doping profile that varies across a vertical thickness of the substrate.
2. The memory cell of claim 1 , wherein the barrier region is associated with the source so as to deter electrical carriers from propagating through the substrate between the memory cell and an adjacent memory cell.
3. The memory cell of claim 2 , wherein the memory cell is a flash memory cell that is adapted to store at least two bits of data.
4. The memory cell of claim 2 , wherein the barrier region comprises a sidewall that is aligned with the stacked gate structure.
5. The memory cell of claim 1 , wherein the barrier region comprises a sidewall that extends under the plurality of stacked gate structures.
6. The memory cell of claim 1 , wherein the at least one of helium, neon, argon, krypton, or xenon are implanted at a doping concentration of about 1E14 to about 1E15 cm −3 .
7. The memory cell of claim 1 , wherein the at least one of helium, neon, argon, krypton, or xenon are implanted at energies between about 60 keV and about 130 keV.
8. The memory cell of claim 1 , wherein the retrograde doping profile has a non-zero value in the source and peaking at a position in the barrier region that is below the source.
9. A nonvolatile memory, comprising:
a substrate having a thickness;
a column of memory cells of the nonvolatile memory disposed on the substrate, the column of memory cells comprising a plurality of stacked gate structures disposed on the substrate, each stacked gate structure comprising a change trapping dielectric layer that is adapted to store at least a bit of data;
a source disposed in the substrate at a side of the row of memory cells;
a drain disposed in the substrate at the other side of the row of memory cells and defining a channel region between the source and drain; and
a barrier region, wherein the barrier region comprises at least one of helium, neon, argon, krypton, or xenon, and wherein the barrier region is characterized by a retrograde doping profile that varies across a vertical thickness of the substrate.
10. The nonvolatile memory of claim 9 , wherein the barrier region is associated with the drain so as to deter electrical carriers from propagating through the substrate between the memory cell and an adjacent memory cell.
11. The nonvolatile memory of claim 10 , wherein the barrier region comprises a side that is aligned with the plurality of stacked gate structures.
12. The nonvolatile memory of claim 9 , further comprising:
a poly layer disposed over one of the stacked gate structures, wherein the poly layer is selectively biased to facilitate the storage of the at least one bit of data.
13. The nonvolatile memory of claim 9 , wherein the at least one of helium, neon, argon, krypton, or xenon are implanted at a doping concentration of about 1E14 to about 1E15 cm −3 .
14. The nonvolatile memory of claim 9 , wherein the at least one of helium, neon, argon, krypton, or xenon are implanted at energies between about 60 keV and about 130 keV.