Split-gate thin film storage NVM cell with reduced load-up/trap-up effects
A semiconductor process and apparatus are disclosed for forming a split-gate thin film storage NVM device ( 10 ) by forming a select gate structure ( 3 ) on a first dielectric layer ( 2 ) over a substrate ( 1 ); forming a control gate structure ( 6 ) on a second dielectric layer ( 5 ) having embedded nanocrystals ( 15, 16 ) so that the control gate ( 6 ) is adjacent to the select gate structure ( 3 ) but separated therefrom by a gap ( 8 ); forming a floating doped region ( 4 ) in the substrate ( 1 ) below the gap ( 8 ) formed between the select gate structure and control gate structure; and forming source/drain regions ( 11, 12 ) in the substrate to define a channel region that includes the floating doped region ( 4 ).
1. A method for forming a semiconductor device comprising:
forming a first gate structure on a first dielectric layer over a substrate;
forming a second gate structure on a second dielectric layer over the substrate so that the second gate structure is adjacent to the first gate structure but separated from the first gate structure by a gap formed between the first gate structure and second gate structure, where the second dielectric layer comprises a plurality of nanocrystals;
forming a floating doped region in the substrate below the gap formed between the first gate structure and second gate structure; and
forming first and second source/drain regions in the substrate adjacent to the first gate structure and second gate structure, said first and second source/drain regions defining a channel region that includes the floating doped region.
2. The method of claim 1 , where forming a floating doped region comprises:
implanting ions having a first predetermined conductivity type around the first gate structure before the second gate structure is formed, thereby forming a first implant region in the substrate that is adjacent to the first gate structure;
forming a first spacer structure on a sidewall of the first gate structure to mask a first portion of the first implant region that is adjacent to the first gate structure; and
implanting ions having a second opposite conductivity type around the first spacer structure and into the first implant region before the second gate structure is formed, thereby forming the floating doped region from the first portion of the first implant region that has not been implanted with the ions having the second opposite conductivity type.
3. The method of claim 1 , where forming a floating doped region comprises:
using a vertical implant process to selectively implant ions having a first predetermined conductivity type around the first gate structure before the second gate structure is formed, thereby forming a first implant region in the substrate that is adjacent to the first gate structure;
using an angled implant process to selectively implant ions having a second opposite conductivity type around the first gate structure and into the first implant region before the second gate structure is formed, where the first gate structure masks a first portion of the first implant region that is adjacent to the first gate structure, thereby forming the floating doped region from the first portion of the first implant region that has not been implanted with the ions having the second opposite conductivity type.
4. The method of claim 1 , where forming a floating doped region comprises:
forming a solid source spacer structure on a sidewall of the first gate structure and in contact with the substrate area adjacent to the first gate structure before the second gate structure is formed, where the solid source spacer structure comprises dopants of a predetermined conductivity type;
annealing the solid source spacer structure to drive dopants from the solid source spacer structure into the substrate before the second gate structure is formed, thereby forming the floating doped region in the substrate adjacent to the first gate structure.
5. The method of claim 1 , where forming a floating doped region comprises:
removing a portion of a gap dielectric layer formed in the gap that separates the first gate structure and second gate structure, thereby forming a remnant dielectric layer in the gap while leaving the first gate structure and second gate structure substantially intact; and
implanting ions having a first predetermined conductivity type through the remnant dielectric layer in the gap, thereby forming the floating doped region in the substrate below the gap formed between the first gate structure and second gate structure.
6. The method of claim 1 , where forming a floating doped region comprises:
selectively removing a portion of the substrate below the gap that separates the first gate structure and second gate structure while leaving the first gate structure and second gate structure substantially intact, thereby forming an opening in the substrate below the gap; and
epitaxially growing a doped semiconductor region selectively in the opening while not growing on the select and second gate structures, thereby forming the floating doped region in the substrate below the gap formed between the first gate structure and second gate structure.
7. The method of claim 1 , where forming a second gate structure comprises:
forming a first spacer structure on a sidewall of the first gate structure before the second gate structure is formed, thereby defining a first portion of the substrate below the first spacer structure;
forming a second dielectric layer comprising a plurality of nanocrystals over the first spacer structure and substrate;
depositing a polysilicon layer over the second dielectric layer; and
anisotropically etching the polysilicon layer to form the second gate structure that is adjacent to the first gate structure but separated from the first gate structure by a gap formed between the first gate structure and second gate structure and containing the first spacer structure and a portion of the second dielectric layer.
8. The method of claim 7 , where forming a floating doped region comprises:
selectively removing the first spacer structure to form an opening between the first gate structure and second gate structure and over the first portion of the substrate while leaving the first gate structure and second gate structure substantially intact; and
implanting ions having a first predetermined conductivity type through the opening and into the first portion of the substrate, thereby forming the floating doped region in the substrate below the gap formed between the first gate structure and second gate structure.
9. The method of claim 8 , further comprising growing a dielectric layer to fill the opening at least in part by oxidizing nanocrystals in the second dielectric layer that are located in the gap formed between the first gate structure and second gate structure.
10. A method for forming a semiconductor non-volatile memory device, comprising:
forming a split-gate structure over a dielectric layer formed on a semiconductor substrate, where the split-gate structure comprises a select gate structure and an adjacent control gate structure that is separated from the select gate structure by a gap;
forming a floating doped region in the semiconductor substrate below the gap during formation of the split-gate structure; and
forming a source/drain region in the semiconductor substrate on first and second sides of the split-gate structure.
11. The method of claim 10 , where the floating doped region reduces electrical influence of gap nanocrystals formed in the gap or in the dielectric layer.
12. The method of claim 10 , where forming a split-gate structure comprises forming the control gate structure before forming the floating doped region and select gate structure.
13. The method of claim 10 , where forming a split-gate structure comprises forming the select gate structure before forming the floating doped region and the control gate structure.
14. The method of claim 10 , where forming a split-gate structure comprises forming the select gate structure and control gate structure before forming the floating doped region.
15. A method for forming a semiconductor non-volatile memory device, comprising:
forming a split-gate structure over a dielectric layer formed on a semiconductor substrate, where the split-gate structure comprises a select gate structure and an adjacent control gate structure that is separated from the select gate structure by a gap;
forming a floating doped region in the semiconductor substrate below the gap which reduces electrical influence in the semiconductor substrate of nanocrystals formed in the gap relative to nanocrystals formed in the dielectric layer under the control gate structure; and
forming a source/drain region in the semiconductor substrate on first and second sides of the split-gate structure.
16. The method of claim 15 , where forming a split-gate structure comprises forming the control gate structure before forming the floating doped region and select gate structure.
17. The method of claim 15 , where forming a split-gate structure comprises forming the select gate structure before forming the floating doped region and the control gate structure.
18. The method of claim 15 , where forming a split-gate structure comprises forming the select gate structure and control gate structure before forming the floating doped region.