Trench dram cell with vertical device and buried word lines

• US 5,977,579 A
• Filed: 12/03/1998
• Issued: 11/02/1999
• Est. Priority Date: 12/03/1998
• Status: Expired due to Term

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Micron Technology, Inc.
• Inventors: Noble, Wendell P.
• Primary Examiner(s): WOJCIECHOWICZ, EDWARD JOSEPH
• Application Number:
  US09/204,072
• Time in Patent Office: 334 Days
• Field of Search: 257/296, 257/301, 257/302, 257/304, 257/311, 257/618
• US Class Current: 257/302
• CPC Class Codes: H10B 12/0383 wherein the transistor is vertical
• CPC Class Codes: H10B 12/0385 Making a connection between the transistor and the capacitor, e.g. buried strap

Abstract

A DRAM array having trench capacitor cells of potentially 4F² surface area (F being the photolithographic minimum feature width), and a process for fabricating such an arrays. The array has a cross-point cell layout in which a memory cell is located at the intersection of each bit line and each word line. Each cell in the array has a vertical device such as a transistor, with the source, drain, and channel regions of the transistor being formed from epitaxially grown single crystal silicon. The vertical transistor is formed above the trench capacitor.

Claims

1. An integrated circuit memory cell comprising:

a substrate;

a trench capacitor formed in said substrate and having a conductive area and a first insulating layer between the conductive area and said substrate;

a vertically stacked transistor having first, second and third stacked conductivity regions formed over said substrate, the second region being of a first conductivity type, and the first and third regions being of a second conductivity type, wherein the second region resides between said first and third regions, said vertically stacked transistor having a first vertical side and a second vertical side, wherein one of the vertical sides of the first stacked conductivity region is in contact with the conductive area of said trench capacitor;

a second insulating layer between the first stacked conductivity region and said substrate;

a third insulating layer positioned on one of the vertical sides of the second stacked conductivity region;

a word line over said third insulating layer and positioned to form a gate of said transistor; and

a bit line in contact with said third stacked conductivity region.

2. The memory cell of claim 1, wherein the cell is a dynamic random access memory cell.

3. The memory cell of claim 1, further comprising a body line positioned on the other vertical side of the second stacked conductivity region from the third insulating layer.

4. The memory cell of claim 3, wherein the body line is a doped polysilicon line.

5. The memory cell of claim 4, wherein the body line is doped to a first conductivity type.

6. The memory cell of claim 1, wherein the first, second, and third conductive regions are doped silicon regions.

7. The memory cell of claim 1, wherein the first conductivity type is p-type, and the second conductivity type is n-type.

8. The memory cell of claim 1, wherein the first conductivity type is n-type, and the second conductivity type is p-type.

9. The memory cell of claim 1, wherein the first insulating layer is a layer of oxide.

10. The memory cell of claim 1, wherein the first insulating layer is a layer of ON.

11. The memory cell of claim 1, wherein the first insulating layer is a layer of ONO.

12. The memory cell of claim 1, wherein said trench capacitor is formed in a trench on one of the vertical sides of said vertically stacked transistor.

13. The memory cell of claim 12, wherein the conductive area of said trench capacitor comprises a lower portion that extends across the entire width of the trench, and an upper portion that connects the lower portion to said vertically stacked transistor.

14. The memory cell of claim 12, wherein the trench is on the same vertical side of said vertically stacked transistor as the body line.

15. The memory cell of claim 12, wherein the trench is on a different vertical side of said vertically stacked transistor as the body line.

16. The memory cell of claim 1, wherein the word line is a doped polysilicon line.

17. The memory cell of claim 16, wherein the word line is doped to a second conductivity type.

18. The memory cell of claim 1, wherein the bit line is a doped polysilicon line.

19. The memory cell of claim 18, wherein the bit line is doped to a second conductivity type.

20. The memory cell of claim 1, wherein the memory cell has an area of approximately 4F² or less, where F is the minimum lithographic feature size.

21. A DRAM cell comprising:

a vertical transistor having a first doped silicon region formed on a substrate, a second doped silicon region formed on the first doped silicon region, and a third doped silicon region formed on the second doped silicon region;

a trench capacitor located below said vertical transistor in the substrate and having a doped polysilicon electrode, wherein the electrode is in contact with the first doped silicon region;

an insulating layer located between said vertical transistor and the substrate;

a conductive line gating the second doped silicon region; and

a bit line in contact with the third doped silicon region.

22. The DRAM cell of claim 21, wherein the substrate is doped to a first conductivity type, and the polysilicon electrode is doped to a second conductivity type.

23. The DRAM cell of claim 22, wherein the first and third doped silicon regions are doped to a second conductivity type, and the second doped silicon region is doped to a first conductivity type.

24. The DRAM cell of claim 21, wherein the first doped silicon region is the drain of said vertical transistor, the second doped silicon region is the body of said vertical transistor, and the third doped silicon region is the source of said vertical transistor.

25. The DRAM cell of claim 21, wherein said insulating layer is a layer of silicon dioxide.

26. The DRAM cell of claim 21, further comprising a body line in contact with the second doped silicon region.

27. The DRAM cell of claim 26, wherein the word line is doped to a second conductivity type, and the body line is doped to a first conductivity type.

28. The DRAM cell of claim 21, wherein the bit line is a doped polysilicon line of a second conductivity type.

29. The DRAM cell of claim 21, wherein the cell has an area of approximately 4F² or less, where F is the minimum lithographic feature size.

30. A DRAM cell comprising:

a vertical transistor having a first doped silicon region formed on a substrate, a second doped silicon region formed on the first doped silicon region, and a third doped silicon region formed on the second doped silicon region, wherein the second doped silicon region is of a first conductivity type, and the first and third doped silicon regions are of a second conductivity type, wherein the vertical transistor has a first and a second vertical sides;

a trench capacitor located in a trench in the substrate on the first vertical side of said vertical transistor and having a doped polysilicon electrode of a second conductivity type, wherein the electrode is in contact with the first doped silicon region, and having a dielectric layer between the electrode and the substrate;

a first insulating layer located between said vertical transistor and the substrate;

a body line of a first conductivity type in contact with the second doped silicon region on the first vertical side of said vertical transistor;

a conductive line of a second conductivity type gating the second doped silicon region on the second vertical side of said vertical transistor, wherein a second insulating layer lies between the conductive line and the second doped silicon region; and

a bit line of a second conductivity type in contact with the third doped silicon region.

31. A semiconductor memory array comprising:

a substrate;

a plurality of memory cells arranged into an array of rows and columns, wherein each memory cell comprises a trench capacitor located in the substrate and a vertical transistor having first, second and third regions located above the trench capacitor, wherein the first region of the vertical transistor adjoins the trench capacitor, each memory cell having an area of 4F² where F is the minimum lithographic feature size;

a plurality of bit lines, wherein each bit line is in contact with the third region of each vertical transistor in a respective column; and

a plurality of buried word lines, wherein each word line adjoins the second region of each vertical transistor in a respective row, and is separated from the second region by an insulating layer.

32. The memory array of claim 31, wherein the substrate is a silicon substrate.

33. The memory array of claim 32, wherein the substrate is doped to a first conductivity type.

34. The memory array of claim 33, wherein the trench capacitor of each memory cell is located in a trench on one side of the vertical transistor.

35. The memory array of claim 34, wherein the trench capacitor further comprises a doped polysilicon electrode of a second conductivity type having a lower portion that extends across the entire width of the trench, and an upper portion that connects the lower portion to the vertical transistor.

36. The memory array of claim 35, wherein the trench capacitor further comprises a dielectric layer located between the lower portion of the electrode and the walls and bottom of the trench.

37. The memory array of claim 36, wherein the dielectric layer is a layer of material selected from the group consisting of oxide, ON, ONO and other suitable dielectric material.

38. The memory array of claim 31, wherein the trench capacitor has an area of approximately 1F², where F is the minimum lithographic feature size.

39. The memory array of claim 31, wherein the vertical transistor has an area of approximately 1F², where F is the minimum lithographic feature size.

40. The memory array of claim 31, wherein the first, second and third regions of the vertical transistor are doped silicon regions, wherein the first and the third regions are doped to a second conductivity type, and the second region is doped to a first conductivity type.

41. The memory array of claim 40, wherein the plurality of bit lines are doped polysilicon lines of a second conductivity type, and the plurality of buried word lines are doped polysilicon lines of a second conductivity type.

42. The memory array of claim 31, further comprising a plurality of buried body lines, wherein each body line is in contact with the second region of each vertical transistor in a respective column.