Structure for confining the switching current in phase memory (PCM) cells

• US 20060226409A1
• Filed: 04/06/2005
• Published: 10/12/2006
• Est. Priority Date: 04/06/2005
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Rossnagel, Stephen M., Lam, Chung Hon, Schrott, Alejandro G., Burr, Geoffrey W.
• Granted Patent: US 7,488,967 B2
• Time in Patent Office: Days
• US Class Current: 257/2
• CPC Class Codes: H10N 70/066 by filling of openings, e.g. damascene method
• CPC Class Codes: H10N 70/231 based on solid-state phase change, e.g. between amorphous and crystalline phases, Ovshinsky effect
• CPC Class Codes: H10N 70/826 adapted for essentially vertical current flow, e.g. sandwich or pillar type devices
• CPC Class Codes: H10N 70/828 Current flow limiting means within the switching material region, e.g. constrictions
• CPC Class Codes: H10N 70/8828 Tellurides, e.g. GeSbTe

Abstract

Disclosed are a phase change memory cell and a method of forming the memory cell. The memory cell comprises a main body of phase change material connected directly to a bottom contact and via a narrow channel of phase change material to a top contact. The channel is tapered from the top contact towards the main body. A minimum width of the channel has a less than minimum lithographic dimension and is narrower than a width of the main body. Therefore, the channel provides a confined region for the switching current path and restricts phase changing to within the channel. In addition an embodiment of the memory cell isolates the main body of phase change material by providing a space between the phase change material and the cell walls. The space allows the phase change material to expand and contract and also limits heat dissipation.

Claims

1. A phase change memory cell comprising:

an insulator;

a phase change material within said insulator and comprising a main body and a narrow portion,

wherein a width measurement of said narrow portion is narrow relative to a width measurement of said main body such that resistance switching of said phase change material in response to an applied electric current is confined to said narrow portion of said phase change material.

2. The phase change memory cell of claim 1, wherein said narrow channel increases a density of said applied current passing through said phase change material and thereby restricts said resistance switching to within said narrow portion of said phase change material.

3. The phase change memory cell of claim 1, further comprising sidewall spacers within said insulator;

wherein said sidewall spacers are configured to delimit a narrow channel for said narrow portion of said phase change material that is tapered towards said main body of said phase change material.

4. The phase change memory cell of claim 1, further comprising:

a first contact electrically connected to said main body of said phase change material; and

a second contact electrically connected to said narrow portion of said phase change material,

wherein said first contact and said second contact are adapted to pass said applied electric current through said phase change material in order to trigger resistance switching of said phase change material.

5. The phase change memory cell of claim 1, wherein said width measurement of said narrow portion of said phase change material is less than a current state-of-the-art minimum lithographic dimension.

6. The phase change memory cell of claim 1, wherein said phase change material comprises a binary alloy comprising two of germanium, antimony and tellurium

7. The phase change memory cell of claim 1, wherein said phase change material comprises a ternary alloy comprising germanium, antimony and tellurium.

8. A phase change memory cell comprising:

an insulator;

a cavity in a lower portion of said insulator, wherein said cavity comprises sidewalls;

a channel in an upper portion of said insulator;

wherein said channel opens into said cavity;

a phase change material comprising a main body of said phase change material within said cavity and a narrow portion of said phase change material within said channel; and

a space that isolates said phase change material within said cavity from said sidewalls of said cavity, thereby, allowing said phase change material to expand and contract and limiting heat dissipation from said non-switching portion.

9. The phase change memory cell of claim 8, wherein a width measurement of said narrow portion of said phase change material in said channel is narrow relative to a width measurement of said main body of phase change material such that resistance switching of said phase change material in response to an applied electric current is confined to said narrow portion of said phase change material within said channel.

10. The phase change memory cell of claim 9, wherein said width measurement of said narrow portion of said phase change material is less than a current state-of-the-art minimum lithographic dimension.

11. The phase change memory cell of claim 8, wherein said channel is tapered towards said main body of said phase change material.

12. The phase change memory cell of claim 8, further comprising:

a first contact electrically connected to said main body of said phase change material; and

a second contact electrically connected to said narrow portion of said phase change material,

wherein said first contact and said second contact are adapted to pass an applied electric current through said phase change material in order to trigger resistance switching of said phase change material.

13. The phase change memory cell of claim 12, wherein said channel increases a density of said applied current passing through said phase change material and thereby restricts said resistance switching to within said narrow portion of said phase change material in said channel.

14. The phase change memory cell of claim 8, wherein said phase change material comprises a binary alloy comprising two of germanium, antimony and tellurium.

15. The phase change memory cell of claim 8, wherein said phase change material comprises a ternary alloy comprising germanium, antimony and tellurium.

17. The method of claim 15, wherein said process of etching said first recess comprises lithographically patterning a photo-resist layer such that said first recess has a width measurement with a current state-of-the-art minimum lithographic dimension, and

wherein said etching of said second recess forms said second recess to be smaller than said current state-of-the-art minimum lithographic dimension.

18. The method of claim 15, wherein said process of forming said sidewall spacers comprises depositing a spacer material layer comprising one of a silicon oxide, silicon nitride and aluminum oxide to form an approximately conformal layer of said spacer material layer over said insulator and over said nitride layer in said first recess.

19. The method of claim 15, further comprising:

forming a first contact electrically connected to said main body of said phase change material;

forming a second contact electrically connected to said narrow portion of said phase change material; and

wherein said first contact and said second contact are adapted to pass an applied electric current through said phase change material in order to trigger resistance switching of said phase change material.

20. The method of claim 19, wherein said channel increases a density of said applied current passing through said phase change material and thereby restricts said resistance switching to within said narrow portion of said phase change material in said channel.

16. A method of forming a phase change memory cell comprising:

etching a first recess through an insulator to a nitride layer;

forming a sidewall spacer in said first recess;

etching a second recess, smaller than said first recess, through said nitride layer thereby forming a tapered channel to a phase change material layer; and

depositing an additional amount of said phase change material into said channel such that a narrow portion of said phase change material is formed with a main body of said phase change material.

21. A method of forming a phase change memory cell comprising:

etching a first recess through an insulator to a phase change material layer;

forming an oxide over said insulator and on said phase change material layer in said first recess;

forming sidewall spacers on said oxide in said first recess;

etching a second recess, smaller than said first recess, through said oxide thereby forming a tapered channel to said phase change material layer; and

depositing an additional amount of said phase change material into said channel such that a narrow portion of said phase change material is formed with a main body of said phase change material.

22. The method of claim 21, wherein said process of etching said first recess comprises lithographically patterning a photo-resist layer such that said first recess has a width measurement with a current state-of-the-art minimum lithographic dimension, and

wherein said etching of said second recess forms said second recess to be smaller than said current state-of-the-art minimum lithographic dimension.

23. The method of claim 21, wherein said process of forming said oxide comprises depositing a low thermal conductivity oxide layer to form an approximately conformal oxide layer over said insulator and over said first phase change material layer in said first recess, and

wherein said process of depositing said sidewall spacers comprises depositing a spacer material layer comprises one of silicon nitride and aluminum oxide to form an approximately conformal layer over said nitride layer.

24. The method of claim 21, further comprising:

forming a first contact electrically connected to said main body of said phase change material; and

forming a second contact electrically connected to said narrow portion of said phase change material,

wherein said first contact and said second contact are adapted to pass an applied electric current through said phase change material in order to trigger resistance switching of said phase change material.

25. The method of claim 23, wherein said channel increases a density of said applied current passing through said phase change material and thereby restricts said resistance switching to within said narrow portion of said phase change material in said channel.

26. A method of forming a phase change memory cell comprising:

etching a first recess through a hydrofluoric acid etch-resistant layer to an oxide layer;

depositing a nitride layer into said first recess;

etching a second recess, smaller than said first recess, through said nitride layer to a liner layer;

isotropically etching said oxide layer from within said second recess to form a cavity between said hydrofluoric acid etch-resistant layer and said liner layer,

wherein a remaining portion of said first recess and said second recess forms a tapered channel to said cavity; and

depositing a phase change material into said cavity and said channel.

27. The method of claim 26, wherein said process of depositing said phase change material comprises sputtering said phase change material such that a main body of said phase change material extends from said liner layer to said channel, such that a narrow portion of said phase change material fills said channel, and such that a measurement of said main body of phase change material is greater than a width measurement of said channel.

28. The method of claim 27, wherein said process of sputtering said phase change material further comprises sputtering said phase change material into said cavity such that said main body of phase change material extends pyramid-like to said channel and a space remains in said cavity and isolates said main body of said phase change material from said insulator layer.

29. The method of claim 26, wherein said process of etching said first recess comprises lithographically patterning a photo-resist layer such that said first recess has a width measurement with a current state-of-the-art minimum lithographic dimension, and

wherein said etching of aid second recess forms said second recess to be smaller than said current state-of-the-art minimum lithographic dimension.

30. The method of claim 27, further comprising:

forming a first contact electrically connected to said main body of said phase change material; and

forming a second contact electrically connected to said narrow portion of said phase change material,

wherein said first contact and said second contact are adapted to pass an applied electric current through said phase change material in order to trigger resistance switching of said phase change material.

31. The method of claim 30, wherein said channel increases a density of said applied current passing through said phase change material and thereby restricts said resistance switching to within said narrow portion of said phase change material in said channel.