Method to form a polysilicon nanocrystal thin film storage bitcell within a high k metal gate platform technology using a gate last process to form transistor gates
View Patent ↗A process integration is disclosed for fabricating non-volatile memory (NVM) cells ( 105 - 109, 113 - 115 ) on a first flash cell substrate area ( 111 ) which are encapsulated in one or more planar dielectric layers ( 116 ) prior to forming an elevated substrate ( 117 ) on a second CMOS transistor area ( 112 ) on which high-k metal gate electrodes ( 119 - 120, 122 - 126, 132, 134 ) are formed 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 nonvolatile memory cell gate structures over one or more first substrate areas of a wafer, each nonvolatile memory cell gate structure comprising one or more polysilicon layers;
forming a first dielectric layer over the wafer to protect at least the one or more polysilicon layers in each nonvolatile memory cell gate structure;
epitaxially growing an elevated substrate in one or more openings formed in the first dielectric layer over one or more second substrate areas of the wafer;
forming a plurality of sacrificial transistor gate structures over the elevated substrate while protecting the one or more polysilicon layers in each nonvolatile memory cell gate structure with the first dielectric layer;
forming a second dielectric layer on the first dielectric layer, where the second dielectric layer has a substantially flat upper surface which exposes an upper surface of the plurality of sacrificial transistor gate structures;
selectively removing at least part of the plurality of sacrificial transistor gate structures to form a plurality of gate electrode openings in the second dielectric layer without removing the plurality of non-volatile memory cell gate structures;
forming a plurality of high-k metal gate electrodes in the plurality of gate electrode openings which are elevated above the plurality of nonvolatile memory cell gate structures.
2. The semiconductor fabrication process of claim 1 , where forming the plurality of nonvolatile memory cell gate structures comprises forming a plurality of split-gate bitcells, each comprising a polysilicon control gate formed on a nanocrystal layer that at least partially overlaps a polysilicon select gate.
3. The semiconductor fabrication process of claim 1 , where forming the plurality of nonvolatile memory cell gate structures comprises forming a plurality of split-gate bitcells, each comprising a spacer control gate and a nanocrystal layer formed adjacent to a sidewall of a polysilicon select gate.
4. The semiconductor fabrication process of claim 1 , where forming the plurality of nonvolatile memory cell gate structures comprises forming a plurality of split-gate bitcells, each comprising a polished and recessed control gate formed adjacent to a charge storage layer comprising a plurality of discrete storage elements, where the charge storage layer separates the polished and recessed control gate from an adjacent polysilicon select gate.
5. The semiconductor fabrication process of claim 1 , where forming the plurality of nonvolatile memory cell gate structures comprises forming a plurality of split-gate bitcells, each comprising an in-laid control gate formed adjacent to a nanocrystal layer which separates the in-laid control gate from an adjacent polysilicon select gate.
6. The semiconductor fabrication process of claim 1 , where forming the first dielectric layer comprises:
depositing a conformal oxide layer over the wafer to cover the plurality of non-volatile memory cell gate structures, and
planarizing the conformal oxide layer with a chemical mechanical polish process to form a substantially flat upper surface to protect at least the one or more polysilicon layers in each nonvolatile memory cell gate structure.
7. The semiconductor fabrication process of claim 1 , where epitaxially growing the elevated substrate comprises:
patterning one or more openings in the first dielectric layer to expose one or more second substrate areas of the wafer while leaving other portions of the first dielectric layer over the plurality of nonvolatile memory cell gate structures;
selectively growing an epitaxial semiconductor layer in the one or more openings in the first dielectric layer, and
polishing the epitaxial semiconductor layer to form the elevated substrate having an elevated substrate surface which is at least as high as a top surface of the plurality of nonvolatile memory cell gate structures.
8. The semiconductor fabrication process of claim 1 , where forming the plurality of high-k metal gate electrodes comprises:
forming a metal layer in the plurality of gate electrode openings; and
polishing the metal layer down to be substantially coplanar with the second dielectric layer to define the plurality of high-k metal gate electrodes which are elevated above the plurality of nonvolatile memory cell gate structures.
9. The semiconductor fabrication process of claim 1 , where selectively removing at least part of the plurality of sacrificial transistor gate structures comprises:
applying one or more poly etch processes to remove one or more polysilicon layers from the plurality of sacrificial transistor gate structures without removing the one or more polysilicon layers from the plurality of non-volatile memory cell gate structures.
10. The semiconductor fabrication process of claim 1 , where forming the plurality of sacrificial transistor gate structures comprises:
forming one or more high-k dielectric layers over the elevated substrate using a dielectric material which has a dielectric constant value of 7.0 or greater while protecting the one or more polysilicon layers in each nonvolatile memory cell gate structure;
depositing one or more polysilicon gate electrode layers over the one or more high-k dielectric layers while protecting the one or more polysilicon layers in each nonvolatile memory cell gate structure; and
patterning and etching the one or more polysilicon gate electrode layers and one or more high-k dielectric layers formed over the elevated substrate to form the plurality of sacrificial transistor gate structures.
11. The semiconductor fabrication process of claim 10 , where selectively removing at least part of the plurality of sacrificial transistor gate structures comprises applying one or more poly etch processes to remove the one or more polysilicon gate electrode layers to expose an underlying high-k gate dielectric layer in the plurality of gate electrode openings in the second dielectric layer.
12. The semiconductor fabrication process of claim 11 , 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 second dielectric layer.