High-κ capped blocking dielectric bandgap engineered SONOS and MONOS
A blocking dielectric engineered, charge trapping memory cell includes a charge trapping element that is separated from a gate by a blocking dielectric including a buffer layer in contact with the charge trapping element, such as silicon dioxide which can be made with high-quality, and a second capping layer in contact with said one of the gate and the channel. The capping layer has a dielectric constant that is higher than that of the first layer, and preferably includes a high-κ material. The second layer also has a conduction band offset that is relatively high. A bandgap engineered tunneling layer between the channel and the charge trapping element is provided which, in combination with the multilayer blocking dielectric described herein, provides for high-speed erase operations by hole tunneling. In an alternative, a single layer tunneling layer is used.
1. A method for manufacturing a charge trapping memory comprising:
defining a semiconductor body including a channel region on a semiconductor body, the channel region having a channel surface, and source and drain terminals adjacent the channel;
defining a gate;
forming a dielectric stack between the channel surface and the gate, including forming a tunneling dielectric layer on one of the channel surface and the gate; forming a charge trapping dielectric layer on the tunneling dielectric layer; and forming a blocking dielectric layer on the charge trapping dielectric layer, wherein forming the blocking dielectric layer includes forming a first layer of material having a dielectric constant κ 1 in contact with the charge trapping dielectric layer and forming a second layer of material having a dielectric constant κ 2 in contact with the other of the channel surface and the gate, where κ 2 is greater than κ 1 , and the second layer has thickness less than κ 2 /κ 1 times that of the first layer.
2. The method of claim 1 , wherein the dielectric stack has an effective oxide thickness EOT of less than 160 Angstroms, the tunneling dielectric layer has an effective oxide thickness EOT between about 40 and 55 Angstroms and the blocking dielectric layer has an effective oxide thickness EOT of less than 95 Angstroms.
3. The method of claim 1 , wherein the tunneling dielectric layer comprises a combination of materials having negligible charge trapping efficiency, and arranged to establish a relatively low valence band energy level near the channel surface, and an increase in valence band energy level at a first offset from the channel surface and an decrease in valence band energy at a second offset more than 2 nm from the channel surface.
4. The method of claim 1 , wherein the dielectric constant of the second layer is greater than 7.
5. The method of claim 1 , wherein the gate comprises a metal, a metal compound, n+ doped polysilicon or p+ doped polysilicon.
6. The method of claim 1 , wherein the tunneling dielectric layer comprises a first silicon oxide layer adjacent the channel and having a thickness of 18 Å or less, a silicon nitride layer on the first silicon oxide layer having a thickness of 30 Å or less, and a silicon oxide layer on the silicon nitride layer having a thickness of 35 Å or less.
7. The method of claim 1 , wherein the tunneling dielectric layer comprises a single layer of silicon dioxide or silicon oxynitride having a thickness from about 3 to 5 nm.
8. A method of forming a memory device, comprising:
providing a substrate;
forming a first dielectric layer over the substrate;
forming a charge storage layer over the first dielectric layer;
forming a second dielectric layer over the charge storage layer;
forming a third dielectric layer over the second dielectric layer, wherein the third layer has a thickness and a dielectric constant both of which are greater than those of the second dielectric layer; and
forming a metal gate over the third dielectric layer.
9. The method of claim 8 , wherein in combination the first dielectric layer, the charge storage layer, the second dielectric layer and the third dielectric layer have an effective oxide thickness EOT of less than 31 nanometers.
10. The method of claim 8 , wherein the first dielectric layer comprises a combination of materials having negligible charge trapping efficiency, and arranged to establish a relatively low valence band energy level near the channel surface, and an increase in valence band energy level at a first offset from the channel surface and an decrease in valence band energy at a second offset more than 2 nm from the channel surface.
11. The method of claim 8 , wherein the dielectric constant of the third dielectric layer is greater than 7.
12. The method of claim 8 , wherein the first dielectric layer comprises a first silicon oxide layer adjacent the channel and having a thickness of 18 Å or less, a silicon nitride layer on the first silicon oxide layer having a thickness of 30 Å or less, and a silicon oxide layer on the silicon nitride layer having a thickness of 35 Å or less.
13. The method of claim 8 , wherein the first dielectric layer comprises a single layer of silicon dioxide or silicon oxynitride having a thickness from about 3 to 5 nm.