Split gate nanocrystal memory integration
View Patent ↗A process integration is disclosed for fabricating non-volatile memory (NVM) cells having spacer control gates ( 108 ) along with a high-k-metal-poly select gate ( 121, 123, 127 ) and one or more additional in-laid high-k metal CMOS transistor gates ( 121, 124, 128 ) using a gate-last HKMG CMOS process flow without interfering with the operation or reliability of the NVM cells.
1. A semiconductor fabrication process comprising:
forming a plurality of sacrificial gate structures over a wafer, comprising a sacrificial select gate structure formed over a non-volatile memory cell area of the wafer and one or more sacrificial gate structures formed over the wafer outside of the non-volatile memory cell area;
forming a charge storage layer on a first sidewall of the sacrificial select gate structure to extend over an adjacent control channel region;
depositing a polysilicon layer on the charge storage layer to cover at least top and side surfaces of the sacrificial select gate structure and the adjacent control channel region;
forming a patterned etch mask on the polysilicon layer to protect a first portion of the polysilicon layer extending from the first sidewall of the sacrificial select gate structure to the adjacent control channel region;
etching the polysilicon layer with the patterned etch mask in place to remove the polysilicon layer except for the first portion of the polysilicon layer;
removing the patterned etch mask;
anisotropically etching the first portion of the polysilicon layer to form a spacer control gate adjacent to the charge storage layer formed on the first sidewall of the sacrificial select gate structure, where the spacer control gate has an upper surface which is recessed below an upper surface of the sacrificial select gate structure;
forming a planarized dielectric layer over the wafer which protects at least the spacer control gate and which exposes at least an upper surface of the plurality of sacrificial gate structures;
selectively removing at least part of the plurality of sacrificial gate structures to form a plurality of gate electrode openings in the planarized dielectric layer without removing the spacer control gate, where the plurality of gate electrode openings comprises a select gate electrode opening where the sacrificial select gate structure was formed; and
forming a plurality of high-k metal gate electrodes in the gate electrode openings while protecting the spacer control gate with the planarized dielectric layer, thereby forming a split-gate structure over the non-volatile memory cell area comprising the spacer control gate adjacent to the charge storage layer and a high-k metal select gate electrode formed in the select gate electrode opening.
2. The semiconductor fabrication process of claim 1 , where forming the plurality of sacrificial gate structures comprises:
forming one or more gate dielectric layers on the wafer;
forming a polysilicon layer on the one or more gate dielectric layers to cover the wafer; and
selectively etching the polysilicon layer and one or more gate dielectric layers to form a plurality of patterned sacrificial gate structures on the wafer.
3. The semiconductor fabrication process of claim 1 , where forming the plurality of sacrificial gate structures comprises:
forming one or more high-k dielectric layers over the wafer using a dielectric material which has a dielectric constant value of 7.0 or greater;
depositing one or more barrier metal layers over the one or more high-k dielectric layers;
depositing one or more polysilicon layers over the one or more barrier metal layers; and
patterning and etching the one or more polysilicon layers, barrier metal layers, and high-k dielectric layers to form the plurality of sacrificial gate structures.
4. The semiconductor fabrication process of claim 1 , further comprising selectively etching a recess into the substrate and adjacent to the first sidewall of the sacrificial select gate structure prior to forming the charge storage layer, thereby forming a recessed surface which is below a top surface of the wafer.
5. The semiconductor fabrication process of claim 1 , where forming the planarized dielectric layer comprises:
depositing an oxide layer over the wafer to cover the plurality of sacrificial gate structures; and
planarizing the oxide layer with a chemical mechanical polish process to form a substantially flat upper surface to protect at least the spacer control gate and to expose at least the upper surface of the plurality of sacrificial gate structures.
6. The semiconductor fabrication process of claim 1 , where forming the plurality of high-k metal gate electrodes comprises:
forming one or more metal-based layers in the plurality of gate electrode openings; and
polishing the one or more metal-based layers down to be substantially coplanar with the planarized dielectric layer to define the plurality of high-k metal gate electrodes, each having an upper surface which is elevated above the upper surface of the spacer control gate.
7. The semiconductor fabrication process of claim 1 , where forming the plurality of high-k metal gate electrodes comprises:
depositing a first metal interface layer in the plurality of gate electrode openings to cover an underlying high-k dielectric layer;
depositing one or more metal gate electrode layers in the plurality of gate electrode openings to cover the first metal interface layer; and
applying one or more polish and/or etch steps to form a plurality of planarized high-k metal-gate electrodes that are substantially coplanar with the planarized dielectric layer.
8. A method for forming a semiconductor device comprising:
providing a wafer comprising a first region and a second region for non-volatile memory cells;
forming a plurality of sacrificial transistor gate electrodes over the first and second regions, comprising a sacrificial select gate electrode over the second region;
forming a charge storage layer comprising a plurality of discrete storage elements on a first sidewall of the sacrificial select gate electrode to extend over an adjacent control channel region;
depositing a polysilicon layer to cover the charge storage layer formed on the first sidewall of the sacrificial select gate electrode to extend over the adjacent control channel region;
forming a patterned etch mask on the polysilicon layer to protect a first portion of the polysilicon layer extending from the first sidewall of the sacrificial select gate layer to the adjacent control channel region while leaving exposed a second portion of the polysilicon layer extending from a second, opposite sidewall of the sacrificial select gate layer;
etching the polysilicon layer with the patterned etch mask in place to remove the second portion of the polysilicon layer and leave the first portion of the polysilicon layer in place;
removing the patterned etch mask; then
anisotropically etching the first portion of the polysilicon layer to form a spacer control gate adjacent to the charge storage layer to cover the adjacent control channel, where the spacer control gate electrode has an upper surface that is below an upper surface of the sacrificial select gate electrode;
forming one or more source/drain regions in the second region of the wafer that are adjacent to the sacrificial select gate electrode and the spacer control gate electrode; and
forming a plurality of metal gates by replacing the sacrificial select gate electrode with a metal select gate electrode in the second region while replacing the plurality of sacrificial transistor gate electrodes with a corresponding plurality of metal gate electrodes in the first region using a replacement gate process, thereby forming a non-volatile memory cell in the second region comprising the metal select gate electrode, charge storage layer, and spacer control gate.
9. The method of claim 8 , where forming the plurality of sacrificial transistor gate electrodes comprises:
forming a first high-k gate dielectric layer on the wafer in the first and second regions;
forming a first polysilicon layer over the first high-k gate dielectric layer in the first and second regions; and
patterning the first polysilicon layer and first high-k gate dielectric layer to define the plurality of sacrificial transistor gate electrodes.
10. The method of claim 8 , where forming the plurality of sacrificial transistor gate electrodes comprises:
forming one or more high-k dielectric layers over the wafer using a dielectric material which has a dielectric constant value of 7.0 or greater;
depositing one or more barrier metal layers on the one or more high-k dielectric layers;
depositing one or more polysilicon layers over the one or more barrier metal layers; and
patterning and etching the one or more polysilicon layers, barrier metal layers, and high-k dielectric layers to form the plurality of sacrificial transistor gate electrodes.
11. The method of claim 8 , further comprising selectively recessing the wafer adjacent to the sacrificial select gate electrode to form a recessed surface which is below a top surface of the wafer.
12. The method of claim 8 , where forming the plurality of metal gates comprises:
forming a planarized dielectric layer which exposes an upper surface of the plurality of sacrificial transistor gate electrodes while protecting the spacer control gate electrode;
selectively removing at least part of the plurality of sacrificial transistor gate electrodes to form gate electrode openings in the planarized dielectric layer; and
forming a high-k metal gate electrode in each gate electrode opening.
13. The method of claim 12 , where forming the plurality of metal gates comprises:
forming one or more metal-based layers in the gate electrode openings formed in the planarized dielectric layer; and
polishing the one or more metal-based layers down to be substantially coplanar with the planarized dielectric layer to define a plurality of high-k metal gate electrodes, each having an upper surface which is elevated above the upper surface of the spacer control gate electrode.
14. The method of claim 12 , where forming a planarized dielectric layer comprises:
depositing an oxide layer over the wafer to cover the plurality of sacrificial transistor gate electrodes, and
planarizing the oxide layer with a chemical mechanical polish process to form a substantially flat upper surface to protect at least the spacer control gate electrode and to expose at least the upper surface of the plurality of sacrificial transistor gate electrodes.