Method to increase charge retention of non-volatile memory manufactured in a single-gate logic process
View Patent ↗A non-volatile memory cell with increased charge retention is fabricated on the same substrate as logic devices using a single-gate conventional logic process. A silicide-blocking dielectric structure is formed over a floating gate of the NVM cell, thereby preventing silicide formation over the floating gate, while allowing silicide formation over the logic devices. Silicide spiking and bridging are prevented in the NVM cell, as silicide-blocking dielectric structure prevents silicide metal from coming in contact with the floating gate or adjacent sidewall spacers. The silicide-blocking dielectric layer may expose portions of the active regions of the NVM cell, away from the floating gate and adjacent sidewall spacers, thereby enabling silicide formation on these portions. Alternately, the silicide-blocking dielectric layer may cover the active regions of the NVM cell during silicide formation. In this case, silicide-blocking dielectric layer may be thinned or removed after silicide formation.
1. A method of fabricating a non-volatile memory cell comprising:
forming a plurality of active regions in a semiconductor substrate;
forming a floating gate electrode over first portions of the active regions, the floating gate electrode connecting various elements of the non-volatile memory cell;
forming a patterned silicide-blocking layer over the floating gate electrode, whereby the patterned silicide-blocking layer fully covers and prevents silicide formation on the portions of the floating gate electrode located over the active regions;
forming the silicide, wherein the patterned silicide-blocking layer prevents silicide formation on the portions of the floating gate electrode located over the active semiconductor regions; then
forming a pre-metal dielectric over the silicide and the patterned silicide-blocking layer;
forming a first mask over the pre-metal dielectric, wherein the first mask includes openings where contacts are to be formed through the patterned silicide-blocking layer;
performing a partial etch of the pre-metal dielectric through the openings in the first mask;
forming a second mask over the pre-metal dielectric, wherein the second mask includes openings where all contacts are to be formed; and then
performing a contact etch through the openings of the second mask, wherein the contact etch extends through the patterned silicide-blocking layer.
2. The method of claim 1 , wherein the step of forming the patterned silicide-blocking layer comprises exposing second portions of the active regions, the method further comprising forming the silicide on the exposed second portions of the active regions.
3. The method of claim 2 , wherein the step of forming the patterned silicide-blocking layer results in the patterned silicide-blocking layer extending over active semiconductor regions of adjacent non-volatile memory cells.
4. The method of claim 1 , further comprising using the patterned silicide-blocking layer to prevent silicide formation on at least one of the active regions.
5. The method of claim 1 , further comprising:
doping a first region of the floating gate electrode with p-type impurities; and
doping a second region of the floating gate electrode with n-type impurities, wherein a p-n interface is formed in the floating gate electrode.
6. The method of claim 5 , further comprising:
forming an active region isolation region in the semiconductor substrate; and
forming the p-n interface over the active isolation region.
7. The method of claim 6 , wherein the step of forming the patterned silicide-blocking layer comprises exposing the p-n interface of the floating gate electrode, the method further comprising forming the silicide on the exposed p-n interface of the floating gate electrode.
8. The method of claim 1 , further comprising:
forming a dielectric sidewall spacer adjacent to the floating gate electrode; and
forming the patterned silicide-blocking layer such that the patterned silicide-blocking layer covers the dielectric sidewall spacer.
9. The method of claim 1 , further comprising forming silicide regions on at least one of the active regions, the silicide regions being located entirely within, and separated from, edges of the at least one of the active regions.
10. The method of claim 1 , wherein the step of forming the second mask comprises depositing a hard-mask film.
11. The method of claim 1 , further comprising:
forming the first mask by forming a first set of openings through a photoresist layer; and
forming the second mask by subsequently forming a second set of openings through the photoresist layer.
12. The method of claim 1 , further comprising:
forming the first mask by forming a first set of openings through a first photoresist layer; and
forming the second mask by forming a second set of openings through a second photoresist layer.
13. The method of claim 1 , wherein the contact etch exposes the silicide and the plurality of active regions.
14. The method of claim 1 , further comprising removing the first mask prior to forming the second mask.
15. The method of claim 1 , further comprising fabricating the non-volatile memory cell using a single-gate process.
16. A method of fabricating a non-volatile memory system comprising:
fabricating a non-volatile memory cell;
forming a patterned silicide-blocking layer over the non-volatile memory cell;
forming silicide, wherein the patterned silicide-blocking layer prevents silicide formation on the non-volatile memory cell; then
forming a pre-metal dielectric over the patterned silicide-blocking layer;
forming a first mask over the pre-metal dielectric, wherein the first mask includes openings where contacts are to be formed through the patterned silicide-blocking layer;
performing a partial etch of the pre-metal dielectric through the openings in the first mask;
forming a second mask over the pre-metal dielectric, wherein the second mask includes openings where all contacts are to be formed; and then
performing a contact etch through the openings of the second mask, wherein the contact etch extends through the patterned silicide-blocking layer.
17. The method of claim 16 , wherein the non-volatile memory cell is fabricated by:
forming a plurality of active regions in a semiconductor substrate, wherein at least two of these active regions are separated by a field dielectric region; and
forming a floating gate electrode over portions of the plurality of active regions.
18. The method of claim 17 , wherein the contact etch exposes the silicide and the plurality of active regions.
19. The method of claim 17 , further comprising:
forming a dielectric sidewall spacer adjacent to the floating gate electrode; and
forming the patterned silicide-blocking layer such that the patterned silicide-blocking layer covers the dielectric sidewall spacer.
20. The method of claim 16 , further comprising:
forming the first mask by forming a first set of openings through a photoresist layer; and
forming the second mask by subsequently forming a second set of openings through the photoresist layer.
21. The method of claim 16 , further comprising removing the first mask prior to forming the second mask.
22. The method of claim 16 , further comprising fabricating the non-volatile memory cell using a single-gate process.
23. A method of fabricating a non-volatile memory system comprising:
fabricating a non-volatile memory cell;
forming a patterned silicide-blocking layer over the non-volatile memory cell;
forming silicide, wherein the patterned silicide-blocking layer prevents silicide formation on the non-volatile memory cell; then
forming a pre-metal dielectric over the patterned silicide-blocking layer;
forming a first mask over the pre-metal dielectric, wherein the first mask includes a first set of openings;
performing a partial etch of the pre-metal dielectric through the first set of openings in the first mask;
forming a second mask over the pre-metal dielectric, wherein the second mask includes a second set of openings, wherein a subset of the second set of openings are in the same locations as the first set of openings; and then
performing a contact etch through the second set of openings, wherein the contact etch extends through the patterned silicide-blocking layer.
24. The method of claim 23 , wherein the non-volatile memory cell is fabricated by:
forming a plurality of active regions in a semiconductor substrate, wherein at least two of these active regions are separated by a field dielectric region; and
forming a floating gate electrode over portions of the plurality of active regions.
25. The method of claim 24 , wherein the contact etch exposes the silicide and the plurality of active regions.
26. The method of claim 24 , further comprising:
forming a dielectric sidewall spacer adjacent to the floating gate electrode; and
forming the patterned silicide-blocking layer such that the patterned silicide-blocking layer covers the dielectric sidewall spacer.
27. The method of claim 23 , further comprising:
forming the first mask by forming the first set of openings through a photoresist layer; and
forming the second mask by subsequently forming another set of openings through the photoresist layer.
28. The method of claim 23 , further comprising removing the first mask prior to forming the second mask.
29. The method of claim 23 , further comprising fabricating the non-volatile memory cell using a single-gate process.