Method and apparatus for eliminating word line bending by source side implantation
View Patent ↗A method and apparatus for coupling to a source line is disclosed. A semiconductor structure having an array of memory cells arranged in rows and columns is described. The array of memory cells includes a source region that is implanted with n-type dopants isolated between an adjoining pair of the non-intersecting STI regions and isolated from a drain region during the implantation. A source contact is located along a row of drain contacts that are coupled to drain regions of a row of memory cells and the source contact is coupled to the source region for providing electrical coupling with a plurality of source lines. The isolating of the implanted source region from the drain region during the implanting enables coupling of the source contact to the source lines while maintaining the n-type dopants between the STI regions and avoiding lateral diffusion to a bit-line.
1. A method of forming a source line contact in a non-volatile memory comprising:
masking a column in a matrix of memory cells, said column perpendicular to said source line and aligned with a plurality of source contact regions and said masking allowing for an implant of n-type dopants only in a region on a source side of said memory cells;
forming a plurality of source implants in said regions on the source side of said memory cells, said memory cells arranged in a matrix of rows and columns, said matrix including at least one row of drain contacts for accessing drain regions in associated rows of memory cells in said matrix of memory cells;
coupling said plurality of source implants to a plurality of source lines that are perpendicular to said column of source implants, for providing electrical coupling of said plurality of said source lines to said plurality of source implants; and
further coupling a plurality of source contacts to said plurality of source implants, each of said plurality of source contacts located in-line with an associated row of drain contacts.
2. The method as recited in claim 1 , further comprising:
forming a plurality of word lines in said array of memory cells perpendicular to said column of source implants, wherein each of said plurality of word lines comprises a straight word line.
3. The method as recited in claim 1 , further comprising:
annealing said columns of n-doped source implants thermally to partially drive diffusion of said n-type dopants under said word lines in said matrix of memory cells.
4. The method as recited in claim 3 , further comprising:
implanting said n-type dopants after formation of a plurality of STI columns, said plurality of STI columns isolating columns of memory cells and said masking isolating said source side regions in said matrix of memory cells.
5. The method as recited in claim 3 , wherein implanting said n-type dopants is performed after said forming said plurality of word lines.
6. The method as recited in claim 1 , wherein at least one memory cell of said matrix of memory cells comprises a flash memory cell.
7. The method as recited in claim 1 , further comprising:
arranging said matrix of memory cells in a NOR type configuration.
8. The method as recited in claim 1 , wherein each of said plurality of source lines comprises a common source line.
9. A method of forming a source line contact in an array of memory cells comprising:
forming a plurality of shallow trench isolation (STI) regions in non-intersecting columns in a silicon substrate, said plurality of STI regions isolating a plurality of columns of silicon in said silicon substrate;
masking said columns of silicon to isolate a plurality of regions under a source side of said memory cells from a plurality of regions in said columns of silicon under a drain side of said memory cells;
implanting n-type dopants in said plurality of regions under said source side of said memory cells to form a plurality of source region implants;
forming a plurality of common source lines across said array of memory cells, said plurality of common source lines perpendicular to said columns of silicon as the location of said source region implants;
coupling said plurality of common source lines to said source region implants in said array of memory cells; and
forming a source contact along a row of drain contacts associated with a row of memory cells perpendicular to said silicon column containing said source region implants, said source contact coupled to at least one of said source region implants.
10. The method as recited in claim 9 , further comprising:
forming a plurality of tunnel oxide layers on a semiconductor substrate between respective source and drain regions;
forming a plurality of floating gates formed on said plurality of tunnel oxide layers;
forming a plurality of interpoly dielectric layers on said plurality of floating gate layers; and
forming a plurality of control gates on said plurality of interpoly dielectric layers.
11. The method as recited in claim 10 , further comprising:
annealing said structure thermally to drive said n-type dopants partially under adjacent gate layers of said memory cells, said annealing preceding said forming said plurality of a common source lines.
12. The method as recited in claim 9 , further comprising:
forming a plurality of word lines that are non-intersecting across said array of memory cells, said plurality of word lines coupled to a plurality of control gates in said array of memory cells, said plurality of word lines exhibiting straightness with a column that aligns with said source regions and adjacent to said source contact.