Non-volatile memory device with improved immunity to erase saturation and method for manufacturing same
A non-volatile memory device having a control gate on top of the second dielectric (interpoly or blocking dielectric), at least a bottom layer of the control gate in contact with the second dielectric being constructed in a material having a predefined high work-function and showing a tendency to reduce its work-function when in contact with a group of certain high-k materials after full device fabrication. At least a top layer of the second dielectric, separating the bottom layer of the control gate from the rest of the second dielectric, is constructed in a predetermined high-k material, chosen outside the group for avoiding a reduction in the work-function of the material of the bottom layer of the control gate. In the manufacturing method, the top layer is created in the second dielectric before applying the control gate.
1. A method for manufacturing a non-volatile memory device, comprising the steps of:
providing a substrate comprising a channel between two doped regions;
applying a first dielectric on top of the channel, the first dielectric being a tunnel dielectric;
applying a charge storage medium on top of the tunnel dielectric;
applying a second dielectric on top of the charge storage medium; and
applying a control gate on top of the second dielectric, wherein at least a bottom layer of the control gate in contact with the second dielectric comprises a material having a predefined high work-function and showing a tendency to reduce its work-function when in contact with a group of high-k materials after full device fabrication;
wherein before applying the control gate, at least a top layer is constructed in the second dielectric for separating the control gate from the rest of the second dielectric, the top layer comprising a predetermined material, chosen outside the group for avoiding a reduction in the work-function of the material of the control gate,
wherein at least an upper part of the second dielectric comprises a high-k material of the group,
and wherein the top layer is constructed by nitridation of the high-k material.
2. The method according to claim 1 , wherein the second dielectric is substantially completely constructed in the high-k material which is substantially completely nitrided.
3. The method according to claim 1 , wherein the nitridation comprises a decoupled plasma nitridation.
4. The method according to claim 1 , wherein the nitridation comprises an ammonia anneal step.
5. The method according to claim 1 , wherein the material of at least the bottom layer of the control gate is chosen such that its work-function is above the work-function of the material of the channel.
6. The method according to claim 5 , wherein the material of at least the bottom layer of the control gate is a material with metallic characteristics.
7. The method according to claim 6 , wherein the control gate comprises:
a metal inserted polysilicon structure (MIPS) comprising a thin metallic screening layer in direct contact with the top layer of the second dielectric; and
a thick polysilicon layer on top of the MIPS.
8. The method according to claim 5 , wherein the control gate is substantially completely constructed in a p-type semiconductor material.