High capacity DRAM trench capacitor and methods of fabricating same

• US 5,065,273 A
• Filed: 12/04/1990
• Issued: 11/12/1991
• Est. Priority Date: 12/04/1990
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Rajeevakumar, Thekkemadathil V.
• Primary Examiner(s): GRIFFIN, DONALD
• Application Number:
  US07/622,257
• Time in Patent Office: 343 Days
• Field of Search: 361/311, 361/312, 361/313, 437/52, 357/23.6, 357/51
• US Class Current: 361/313
• CPC Class Codes: H10B 12/37 the capacitor being at least partially in a trench in the substrate

Abstract

A trench capacitor and a method of forming same within an integrated circuit. The capacitor includes a first plate electrode having a surface area comprised of an inner surface area of the trench and an outer surface area of an upstanding pillar structure that is formed within the trench and which extends upwardly from a bottom surface thereof. The pillar structure is physically and electrically contiguous with the semiconductor substrate and has the same type of electrical conductivity. The capacitor further includes a second plate electrode comprised of a region of electrically conductive material that substantially fills a volume of the trench. The capacitor further includes a thin layer of dielectric material interposed between the first plate electrode and the second plate electrode. The second plate electrode is conductively coupled to a planar access device through a conductive, self-aligned surface strap.

Claims

1. A trench capacitor formed within an integrated circuit, comprising:

a substrate having a depression within a surface thereof; and

capacitor means formed within the depression, the capacitor means including a first plate electrode means having a surface area comprised of an inner surface area of the depression and an outer surface area of a pillar structure extending upwardly from a bottom surface of the depression, the pillar structure being physically and electrically contiguous with the substrate, the capacitor means further including a second plate electrode means comprised of a region of electrically conductive material that substantially fills a volume of the depression not occupied by the pillar structure, the capacitor means further comprising a thin layer of dielectric material interposed between the first plate electrode means and the second plate electrode means.

2. A trench capacitor as set forth in claim 1 wherein the substrate is comprised of monocrystalline silicon having a first type of electrical conductivity and wherein the pillar structure is comprised of polycrystalline silicon also having the first type of electrical conductivity.

3. A trench capacitor as set forth in claim 2 wherein the first type of electrical conductivity is p-type and wherein the monocrystalline silicon and the polycrystalline silicon each have an impurity doping concentration of greater than approximately 10¹⁹ atoms/cm³.

4. A trench capacitor as set forth in claim 2 wherein the substrate includes a surface region surrounding the depression, the surface region having a second type of electrical conductivity and a depth that is approximately equal to or less than a distance of a top of the pedestal structure from the surface of the substrate.

5. A trench capacitor as set forth in claim 1 and further comprising an electrically conductive strap disposed over the surface of the substrate for electrically coupling the second plate electrode to a terminal of a planar access device.

6. A trench capacitor as set forth in claim 5 wherein the strap is self-aligned to the terminal.

7. A trench capacitor as set forth in claim 5 and further comprising a layer comprised of an electrical insulator that overlies the conductive strap for electrically insulating the conductive strap from any overlying electrically conductive regions.

8. A trench capacitor as set forth in claim 5 and further comprising a wordline conductor that is vertically disposed above the conductive strap, the wordline conductor being electrically insulated from the conductive strap.

9. A trench capacitor as set forth in claim 1 wherein the depression has a substantially square or rectangular top surface area and a depth of approximately six microns.

10. A trench capacitor as set forth in claim 1 wherein a top surface area of the depression has dimensions of approximately one micron by approximately 1.2 microns and a depth within a range of approximately 4.5 microns to approximately six microns.

11. A trench capacitor as set forth in claim 1 wherein a bottom surface of the pillar structure is disposed upon the bottom surface of the depression.

12. A trench capacitor as set forth in claim 1 wherein a bottom surface of the pillar structure is embedded within the substrate and extends by a given depth below the bottom surface of the depression.

13. A trench capacitor as set forth in claim 12 wherein the given depth is within a range of approximately 0.1 to approximately 0.25 microns.

14. A trench capacitor as set forth in claim 1 wherein the dielectric material has a thickness of approximately 60 Angstroms to approximately 100 Angstroms.

15. A trench capacitor as set forth in claim 1 wherein the surface of the substrate has a region of Shallow Trench Isolation formed therein for electrically insulating the trench capacitor from an adjacent trench capacitor.

16. A trench capacitor as set forth in claim 1 wherein the depression includes an electrically insulating collar disposed around a top portion thereof.

17. A method of fabricating a trench capacitor within an integrated circuit, comprising the steps of:

providing a substrate having a major surface, the substrate being comprised of a semiconductor material having a first type of electrical conductivity;

removing a portion of the substrate to form a trench that extends from the major surface down into the substrate to a predetermined depth;

forming an upstanding pedestal structure within the trench, the pedestal structure being formed to extend upwardly from a bottom surface of the trench to a height that is less than the predetermined depth, the pedestal structure being comprised of a semiconductor material having the first type of electrical conductivity;

covering exposed inner surfaces of the trench and exposed outer surfaces of the pedestal structure with a layer comprised of an electrical insulator; and

filling a remaining volume of the trench with an electrically conductive material, whereby the inner surfaces of the trench and the outer surfaces of the pedestal structure form a first plate of a capacitor means, the layer of electrical insulator forms a capacitor means dielectric, and surfaces of the electrically conductive material that are in contact with the layer of electrical insulator form a second plate of the capacitor means.

18. A method as set forth in claim 17 and further comprising the steps of:

fabricating a planar access device upon the surface of the substrate; and

electrically coupling a terminal of the planar access device to the electrically conductive material.

19. A method as set forth in claim 18 wherein the step of electrically coupling includes a step of depositing a silicide strap such that the silicide strap is self-aligned to the terminal and such that the silicide strap also overlies and is conductively coupled to a portion of the electrically conductive material that fills the trench.

21. A method as set forth in claim 17 and further including a step of fabricating a plurality of wordlines, wherein a first plurality of wordlines are fabricated upon the major surface of the substrate by a two-step process that includes a first step of forming a wordline to a first thickness and a second step of increasing the first thickness by a second thickness to a third thickness.

22. A method as set forth in claim 21 wherein a second plurality of wordlines are fabricated such that each is vertically disposed above the major surface of the substrate and enclosed within an electrical insulator.

23. A method as set forth in claim 22 wherein the second plurality of wordlines are fabricated contemporaneously with the second step of increasing the first thickness by the second thickness.

20. A method as set forth 19 and further including a step of fabricating a wordline conductor such that is vertically disposed over the silicide strap.

24. A memory cell, comprising;

a trench capacitor formed within an opening into a semiconductor substrate, the trench capacitor including first plate electrode means and second plate electrode means having a dielectric material interposed therebetween; and

an access device having a first terminal coupled to the second plate electrode means, wherein

the first plate electrode means has a surface area that includes an inner surface area of the opening and an outer surface area of a structure that extends into the opening from a bottom surface of the opening, the structure being electrically coupled to the semiconductor substrate, and wherein the second plate electrode means is comprised of an electrically conductive material that overlies the dielectric material.

25. A memory cell as set forth in claim 24 wherein the structure is comprised of polycrystalline silicon.

26. A memory cell as set forth in claim 24 wherein the first terminal of the access device is coupled to the second plate electrode means with an electrically conductive strap disposed over the surface of the substrate.

27. A memory cell as set forth in claim 24 and further comprising a wordline conductor coupled to a second terminal of the access device and a bitline conductor coupled to a third terminal of the access device.