Non-volatile memory with flat cell structures and air gap isolation
High-density semiconductor memory is provided with enhancements to gate-coupling and electrical isolation between discrete devices in non-volatile memory. The intermediate dielectric between control gates and charge storage regions is varied in the row direction, with different dielectric constants for the varied materials to provide adequate inter-gate coupling while protecting from fringing fields and parasitic capacitances. Electrical isolation is further provided, at least in part, by air gaps that are formed in the column (bit line) direction and/or air gaps that are formed in the row (word line) direction.
1. A non-volatile memory, comprising:
a first column of non-volatile storage elements including a first set of charge storage regions arranged in a column direction and separated from a surface of a substrate by a tunnel dielectric and a first set of intermediate dielectric regions overlying the first set of charge storage regions;
a second column of non-volatile storage elements adjacent to the first column of non-volatile storage elements in a row direction, the second column including a second set of charge storage regions separated from the surface of the substrate by a tunnel dielectric and a second set of intermediate dielectric regions overlying the second set of charge storage regions;
an isolation region in the substrate between an active area underlying the first column of non-volatile storage elements and an active area underlying the second column of non-volatile storage elements;
a bit line air gap formed in the isolation region; and
a set of dielectric caps formed over the bit line air gap between the first column of non-volatile storage elements and the second column of non-volatile storage elements, at least a portion of each cap extending continuously in the row direction over the bit line air gap between and at a level adjacent to corresponding intermediate dielectric regions of the first column and the second column, the set of dielectric caps having a lower dielectric constant than a dielectric constant of the intermediate dielectric regions.
2. A non-volatile memory according to claim 1 , further comprising:
a set of bridges formed below the set of dielectric caps, each bridge extending in the row direction between an adjacent charge storage region in the first set and the second set.
3. A non-volatile memory according to claim 2 , wherein:
the first set of charge storage regions and the second set of charge storage regions each include a plurality of charge storage layers; and
each bridge extends vertically along less than all of the plurality of charge storage layers for corresponding charge storage regions of the first column and the second column that are adjacent in the row direction.
4. A non-volatile memory according to claim 3 , wherein each bridge includes a lower surface defining a portion of an upper endpoint for the bit line air gap.
5. A non-volatile memory according to claim 1 , wherein:
each dielectric cap includes an upper surface having a recess formed therein.
6. A non-volatile memory according to claim 5 , further comprising:
a control gate layer divided into control gate strips that extend continuously in the row direction across the first column and the second column;
wherein each control gate strip includes a protrusion that extends into the recess of each dielectric cap.
7. A non-volatile memory according to claim 6 , wherein:
the control gate layer is a second control gate layer;
the first column includes a first set of control gate regions that are formed from a first control gate layer;
the second column includes a second set of control gate regions that are formed from the first control gate layer; and
an upper surface of the set of dielectric caps is below a level of an upper surface of the control gate regions of the first set and the control gate regions of the second set.
8. A non-volatile memory according to claim 7 , wherein:
each control gate strip extends vertically below a level of an upper surface of the first set of control gate regions and an upper surface of the second set of control gate regions.
9. A non-volatile memory array according to claim 1 , wherein the bit line air gap has an upper endpoint defined at least in part by a lower surface of each dielectric cap.
10. A non-volatile memory array according to claim 9 , wherein:
the first column of non-volatile storage elements extends in a column direction a first length over the first active area;
the second column of non-volatile storage elements extends in the column direction the first length over the first active area;
the isolation region is elongated in the substrate the first length in the column direction; and
the bit line air gap extends the first length in the column direction.
11. A non-volatile memory array according to claim 10 , further comprising:
a first row of non-volatile storage elements extending in a row direction across the substrate surface, the row direction being perpendicular to the column direction, the first row including a first non-volatile storage element of the first column, a first non-volatile storage element of the second column and a first control gate strip extending in the row direction and being shared by the first non-volatile storage elements of the first and second columns;
a second row of non-volatile storage elements extending in the row direction across the substrate surface, the second row including a second non-volatile storage element of the first column, a second non-volatile storage element of the second column and a second control gate strip extending in the row direction and being shared by the second non-volatile storage elements of the first and second columns; and
a word line air gap elongated in the row direction and extending in the column direction at least a portion of a distance between the first row and the second row.
12. A non-volatile memory array according to claim 1 , wherein:
the first column of non-volatile storage elements includes a first plurality of NAND strings; and
the second column of non-volatile storage elements includes a second plurality of NAND strings.
13. A non-volatile memory, comprising:
a first column of non-volatile storage elements overlying a first active area of a substrate having a surface, each non-volatile storage element of the first column including an intermediate dielectric region;
a second column of non-volatile storage elements overlying a second active area of the substrate and adjacent to the first column of non-volatile storage elements in a row direction, each non-volatile storage element of the second column including an intermediate dielectric region;
a bit line air gap formed in the substrate between the first active area and the second active area; and
a set of dielectric caps formed over the bit line air gap between the first column of non-volatile storage elements and the second column of non-volatile storage elements, each dielectric cap extending between corresponding intermediate dielectric regions of the first column and the second column that are adjacent in the row direction, the set of dielectric caps having a lower dielectric constant than a dielectric constant of the intermediate dielectric regions, at least a portion of each dielectric cap extending continuously in the row direction over the bit line air gap at a level adjacent to the corresponding intermediate dielectric regions above the substrate surface.
14. The non-volatile memory of claim 13 , wherein:
each non-volatile storage element of the first column includes a control gate region separated from a charge storage region by the intermediate dielectric region;
each non-volatile storage element of the second column includes a control gate region separated from a charge storage region by the intermediate dielectric region; and
the non-volatile memory further comprises a plurality of control gate strips overlying a row of non-volatile storage elements, each row of non-volatile storage elements including corresponding non-volatile storage elements of the first column and the second column that are adjacent in the row direction.
15. The non-volatile memory of claim 14 , further comprising:
a set of bridges formed below the set of dielectric caps, each bridge extending in the row direction between an adjacent charge storage region in the first set and the second set.
16. The non-volatile memory of claim 15 , wherein:
the first set of charge storage regions and the second set of charge storage regions each include a plurality of charge storage layers; and
each bridge extends vertically along less than all of the plurality of charge storage layers for corresponding charge storage regions of the first column and the second column that are adjacent in the row direction.
17. A non-volatile memory, comprising:
a first column of non-volatile storage elements overlying a first active area of a substrate, each non-volatile storage element of the first column including a control gate region separated from a charge storage region by an intermediate dielectric region;
a second column of non-volatile storage elements overlying a second active area of the substrate and adjacent to the first column of non-volatile storage elements in a row direction, each non-volatile storage element of the second column including a control gate region separated from a charge storage region by an intermediate dielectric region;
a bit line air gap formed in the substrate between the first active area and the second active area;
a set of dielectric caps formed over the bit line air gap between the first column of non-volatile storage elements and the second column of non-volatile storage elements, each dielectric cap having an upper surface over the bit line air gap that is below a level of an upper surface of the control gate regions of the first column and the second column and above a level of a lower surface of the intermediate dielectric regions of the first column and the second column; and
a plurality of control gate lines extending in the row direction over the first column and the second column of non-volatile storage elements, each control gate line is coupled to corresponding control gate regions of the first column and the second column that are adjacent in the row direction.
18. The non-volatile memory of claim 17 , wherein:
each dielectric cap extends between corresponding intermediate dielectric regions of the first column and the second column that are adjacent in the row direction, the set of dielectric caps having a lower dielectric constant than a dielectric constant of the intermediate dielectric regions.
19. The non-volatile memory of claim 18 , wherein:
each dielectric cap includes an upper surface having a recess formed therein; and
each control gate line includes a protrusion that extends into the recess of each dielectric cap.
20. The non-volatile memory of claim 19 , further comprising:
a set of bridges formed below the set of dielectric caps, each bridge extending in the row direction between an adjacent charge storage region in the first set and the second set;
wherein the first set of charge storage regions and the second set of charge storage regions each include a plurality of charge storage layers; and
wherein each bridge extends vertically along less than all of the plurality of charge storage layers for corresponding charge storage regions of the first column and the second column that are adjacent in the row direction.