Flash memory device with three-dimensional half flash structure and methods for forming the same
A flash memory device and method of making the same are disclosed. The flash memory device is located on a substrate and includes a floating gate electrode, a tunnel dielectric layer located between the substrate and the floating gate electrode, a smaller length control gate electrode and a control gate dielectric layer located between the floating gate electrode and the smaller length control gate electrode. The length of a major axis of the smaller length control gate electrode is less than a length of a major axis of the floating gate electrode.
1. A flash memory cell located on a substrate comprising:
a source region and a drain region in the substrate;
a channel region in the substrate, extending in a first direction from the source region to the drain region;
a tunnel dielectric layer on the channel region;
a floating gate electrode on the tunnel dielectric layer;
a control gate dielectric layer on the floating gate electrode;
a smaller length control gate electrode on the control gate dielectric layer, wherein a length of the smaller length control gate electrode in the first direction is less than a length of the floating gate electrode in the first direction; and
a fourth electrical contact contacting the control gate dielectric layer over the channel region and including an outermost sidewall located opposite the smaller length control gate electrode and over the floating gate electrode.
2. The flash memory cell of claim 1 , further comprising:
a first electrical contact electrically connected to one of the source region or the drain region in the substrate;
a second electrical contact electrically connected to the other of the source or drain region; and
a third electrical contact electrically connected to the smaller length control gate electrode.
3. The flash memory cell of claim 2 , further comprising a fifth electrical contact electrically connected to the control gate dielectric layer.
4. The flash memory cell of claim 2 , wherein the source region comprises an active extension region and a deep active region and the drain region comprises an active extension region and a deep active region.
5. The flash memory cell of claim 4 , wherein the active extension regions have a dopant concentration of 2×10 20 to 2×10 21 .
6. The flash memory cell of claim 3 , wherein the memory device is configured such that the memory device is programmed and erased by applying a voltage to the fourth electrical contact and read by applying a voltage to the fifth electrical contact.
7. The flash memory cell of claim 1 , further comprising:
a first sidewall spacer located over sidewalls of the tunnel dielectric layer, the floating gate electrode and the control gate dielectric layer;
a second sidewall spacer located over sidewalls of the smaller length control gate electrode; and
a third sidewall spacer located over sidewalls of the tunnel dielectric layer, the floating gate electrode, the control gate dielectric layer and the smaller length control gate electrode.
8. The flash memory cell of claim 1 , wherein the control gate dielectric layer comprises a first oxide layer, a second oxide layer and a nitride layer located between the first oxide layer and the second oxide layer.
9. The flash memory cell of claim 8 , wherein a thickness of the second oxide layer is 5-10% greater than a thickness of the first oxide layer.
10. An array of flash memory cells comprising:
a two-dimensional array of flash memory cells, each of the flash memory cells comprising:
a tunnel dielectric layer on a semiconductor substrate having a first conductivity type;
a pair of active regions formed in the semiconductor substrate on opposing sides of the tunnel dielectric layer, and having a second conductivity type;
a channel region in the semiconductor substrate, extending in a first direction between the pair of active regions;
a floating gate electrode on the tunnel dielectric layer;
a control gate dielectric layer on the floating gate electrode;
a smaller length control gate electrode on the control gate dielectric layer, wherein a length of the smaller length control gate electrode in the first direction is less than a length of the floating gate electrode in the first direction; and
an electrical contact contacting the control gate dielectric layer over the channel region and including an outermost sidewall located opposite the smaller length control gate electrode and over the floating gate electrode.
11. The array of flash memory cells of claim 10 , wherein the flash memory cells have a first pitch in the first direction and a second pitch less than the first pitch in a second direction perpendicular to the first direction.
12. The array of flash memory cells of claim 11 , further comprising:
shallow trench isolation regions located between the flash memory cells in the first direction.
13. A memory cell, comprising:
a source region and a drain region in a substrate;
a channel region in the substrate, extending in a first direction from the source region to the drain region;
a floating gate electrode on the channel region;
a control gate dielectric layer on the floating gate electrode and having a first length in the first direction;
a control gate on the control gate dielectric layer and having a second length in the first direction less than the first length; and
a first contact contacting the control gate dielectric layer over the channel region and including an outermost sidewall located opposite the control gate and over the floating gate electrode.
14. The memory cell of claim 13 , further comprising:
a second contact contacting the control gate dielectric layer.
15. The memory cell of claim 14 , wherein the first contact is for programming and erasing the memory cell, and the second contact is for reading the memory cell.
16. The memory cell of claim 14 , further comprising:
a third contact electrically connected to the control gate.
17. The memory cell of claim 13 , wherein the control gate comprises:
a first sidewall substantially aligned with a first sidewall of the control gate dielectric layer and a first sidewall of the floating gate electrode; and
a second sidewall opposite the first sidewall of the control gate, and located on the control gate dielectric layer.
18. The memory cell of claim 17 , further comprising:
a first sidewall spacer on the first sidewall of the control gate, the first sidewall of the control gate dielectric layer and the first sidewall of the floating gate electrode; and
a second sidewall spacer on the second sidewall of the control gate, and located on the control gate dielectric layer.
19. The memory cell of claim 18 , wherein the first contact contacts the control gate dielectric layer adjacent to the second sidewall spacer.
20. The memory cell of claim 13 , wherein the control gate dielectric layer comprises:
a first oxide layer having a first thickness on the floating gate electrode;
a nitride layer on the first oxide layer; and
a second oxide layer having a second thickness greater than the first thickness on the nitride layer, wherein the first contact contacts a surface of the second oxide layer.