# Patent

## Title
Double self-aligned phase change memory device structure

## Abstract

A double self-aligned phase change memory device structure, comprising spaced-apart facing phase change memory film members symmetrically arranged with respect to one another, each of the phase change memory film members at an upper portion thereof being in contact with a separate conductive element, and each of the phase change memory film members being in a range of from 5 nm to 25 nm in thickness. Also described are various methods of making such phase change memory device structure.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a U.S. national phase under the provisions of 35 U.S.C. §371 of International Patent Application No. PCT/US13/67145 filed Oct. 28, 2013, which in turn claims the benefit of priority under 35 USC 119 of U.S. Provisional Patent Application No. 61/720,283 filed Oct. 30, 2012 in the name of Jun-Fei Zheng for DOUBLE SELF-ALIGNED PHASE CHANGE MEMORY DEVICE STRUCTURE. The disclosures of such International Patent Application No. PCT/US 13/67,145 and U.S. Provisional Patent Application No. 61/720,283 are hereby incorporated herein by reference, in their respective entireties, for all purposes.


FIELD
The present disclosure relates to double self-aligned phase change memory device structures and methods of making the same.
DESCRIPTION OF THE RELATED ART
Phase change memory (PCM) is a type of non-volatile computer memory that utilizes differences in the electrical resistivity of the crystalline and amorphous phase states of memory materials. Devices that incorporate PCM typically comprise substrates on which a particular memory material (e.g., a chalcogenide) is deposited.
The memory material is characteristically deposited within structures (such as holes, trenches, or the like) in or on the surfaces of the substrate. Patterned electrodes are also deposited on the substrate to allow for the conduction of current. The conduction of current is effected through the deposited memory material, with the level of current being dependent on the resistivity and heating efficiency of such memory material and its alloy properties on phase change.
Memory materials used in the manufacture of PCM devices include germanium antimony telluride (GST) and germanium-telluride (GeTe). The GST materials can function in principle very effectively as phase change material for a volume, v, having characteristic dimensions as small as 5 nm. The trend is to make PCM devices based on GST with characteristic dimensions in the regime of 30 to 10 nm or less in future generations of devices.
To confine the heat for phase change, PCM material-containing structures may be fabricated with surrounding or otherwise associated dielectric material, and the structure may embody aspect ratios or dimensional characteristics that facilitate heating efficiency. The deposition of the phase change memory material can be carried out by vapor deposition processes, e.g., chemical vapor deposition (CVD) or atomic layer deposition (ALD), to produce films of useful character for phase change memory applications inside a cavity, e.g., a hole or trench in a substrate.
In addition to the deposition of phase change memory materials into existing substrate surface structures such as cavities, e.g., holes or trenches, phase change memory device structures can also be fabricated as confined cell equivalent structures by initially forming the phase change memory material, and then surrounding the phase change memory material with dielectric material. The phase change memory material in such applications may be in a very small cell structure having correspondingly small top and bottom contact areas, e.g., areas on the order of 5-10 nm×50-100 nm (thickness of contact metal x width of contact metal) permitted by current lithography capability, with the phase change memory material extended at a height of 30 nm or more. In such cell structures, the phase change memory material is surrounded by thermally and electrically insulating materials.
SUMMARY
The present disclosure relates to double self-aligned phase change memory device structures and methods of making the same.
In one aspect, the disclosure relates to a double self-aligned phase change memory device structure, comprising spaced-apart facing phase change memory film members symmetrically arranged with respect to one another, each of the phase change memory film members at an upper portion thereof being in contact with a separate conductive element, and each of the phase change memory film members being in a range of from 5 nm to 25 nm in thickness.
In another aspect, the disclosure relates to a method of forming a memory device structure of the disclosure, comprising the process flow illustrated in FIGS. 1-4 herein.
In a further aspect, the disclosure relates to a method of forming a memory device structure of the disclosure, comprising the process flow illustrated in FIGS. 10-23 herein.
Other aspects, features and embodiments of the disclosure will be more fully apparent from the ensuing description and appended claims.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1-4 show a process flow for fabricating a phase change memory device sidewall line cell structure.
FIG. 5 is a front elevation view of a phase change memory device cell structure, as fabricated by a process flow sequence as shown in FIGS. 1-4.
FIG. 6 is a perspective view of the phase change memory device cell structure.
FIGS. 7-9 show perspective schematic views of different cell structures and their respective contact areas.
FIGS. 10-23 illustrate a schematic process flow for forming a double self-aligned phase change memory device structure.
FIG. 24 is a schematic cross-sectional elevation view of a double self-aligned phase change memory device structure.
FIG. 25 is an enlarged portion of the phase change memory device structure of FIG. 24, showing the details of the phase change film member and associated TiN layer.
FIG. 26 is a schematic cross-sectional elevation view of a double self-aligned phase change memory device structure of a general type shown in FIG. 24, but wherein the transitional segment of the multi-segmented phase change memory film element has been removed by etch processing.



DETAILED DESCRIPTION
The present disclosure relates to double self-aligned phase change memory device structures and methods of making the same.
In one aspect, the disclosure relates to a double self-aligned phase change memory device structure, comprising spaced-apart facing phase change memory film members symmetrically arranged with respect to one another, each of the phase change memory film members at an upper portion thereof being in contact with a separate conductive element, and each of the phase change memory film members being in a range of from 5 nm to 25 nm in thickness.
Such memory device structure may be fabricated with a protecting layer disposed on facing surfaces of said phase change memory film members. The protecting layer may extend downwardly from an upper end of each phase change memory film member over the facing surface thereof to a lower portion of the phase change memory film member. In various embodiments, the structure may be fabricated, with a dielectric material between the protecting layers of the phase change memory film members.
In the memory device structure, each of the phase change memory film members may be of any suitable thickness, e.g., a thickness in a range of from 8 to 20 nm, a thickness in a range of from 10 to 15 nm, a thickness in a range of from 5 to 15 nm, or any other suitable thickness effective for performance of the memory device structure in a phase change memory implementation.
In various embodiments, each phase change memory film member may have a height appropriate to the phase change memory implementation of the structure, e.g., in a range of from 20 to 80 nm, in a range of from 30 to 75 nm, or any other suitable range of height values.
The phase change memory material itself may comprise any suitable material, e.g., a chalcogenide, such as a germanium-antimony-tellurium alloy, or a germanium telluride alloy.
In some embodiments of the memory device structure of the disclosure, the phase change memory material film members may be arranged in a confined cell arrangement comprising a cross-spacer structure wherein the phase change memory material film members are positioned transversely to and reposed on titanium nitride members. In such cross-spacer structure, the contact area of each phase change memory film member and the titanium nitride member on which it is reposed may be in a range of for example from 50 to 150 nm2, a range of from 80 to 120 nm2, or any other suitable contact area range.
The memory device structure of the disclosure may include arrangements in which each phase change memory material film member comprises an upper planar segment, an intermediate angular transition segment, and a lower planar segment, arranged so that the upper planar segment and lower planar segment of each phase change memory material film member are generally parallel to one another and to respective upper planar and lower planar segments of the other phase change memory material film member facing it, wherein transverse spacing distance between upper planar segments of the respective phase change memory material film members is greater than transverse spacing distance between lower planar segments of the respective phase change memory film members. In such structural arrangements, the intermediate angular transition segment may be of a generally planar character, or may be in a curvate or other non-planar conformation.
In other embodiments of the every device structure of the present disclosure, each phase change memory material film member may comprise an upper planar segment and a lower planar segment, elevationally spaced apart from one another, and arranged so that the upper planar segment and lower planar segment of each phase change memory material film member are generally parallel to one another and to respective upper planar and lower planar segments of the other phase change memory material film member facing it, wherein transverse spacing distance between upper planar segments of the respective phase change memory material film members is greater than transverse spacing distance between lower planar segments of the respective phase change memory film members.
The present disclosure further contemplates various methods of forming memory device structures of the disclosure, as hereinafter more fully described, and including the process flow illustrated in FIGS. 1-4 herein, as well as the process flow illustrated in FIGS. 10-23 herein.
The features, aspects, and advantages of the double self-aligned phase change memory device structures of the present disclosure, and methods of making the same, are more fully illustrated with respect to the ensuing description of FIGS. 1-26.
FIGS. 1-4 show a process flow for fabricating a phase change memory device sidewall line cell structure.
FIG. 1 illustrates a trench in a substrate on which a phase change material, e.g., an alloy such as germanium-antimony-tellurium (GST) or germanium telluride (GeTe) is conformally deposited by a vapor deposition process, e.g., MOCVD process, to form a phase change memory material film on wall surface of the trench. Such conformal deposition yields a central open core region in the interior volume of the trench that is bounded by the phase change memory material film on wall surface of the trench.
FIG. 2 shows the structure of FIG. 1 in which a conformal protecting layer of suitable material is deposited over the phase change memory material film. Next, a vertical anisotropic spacer etch is carried out, yielding the structure shown in FIG. 3. Thereafter, the gap in the central open core of the structure is filled with suitable material, e.g., dielectric material, followed by chemical mechanical planarization, and formation of the top electrode members, yielding the structure as shown in FIG. 4, in which the vertically extending phase change memory film members have a thickness of 10 nm.
FIG. 5 is a front elevation view of a phase change memory device cell structure, as fabricated by a process flow sequence as shown in FIGS. 1-4. The vertically extending phase change memory film member has a thickness of 10 nm, and the height of the phase change memory film may be in a range of from 30 to 75 nm, as illustrated.
FIG. 6 is a perspective view of the phase change memory device cell structure, showing two GST members in a cross-spacer structure on respective TiN members.
FIGS. 7-9 show perspective schematic views of different cell structures and their respective contact areas.
FIG. 7 shows a self-aligned wall storage arrangement including a GST member having a transverse dimension of about 45 nm and a height of 30 nm or more, reposed on a TiN member having a corresponding transverse dimension of about 45 nm and a thickness of 10 nm. The contact area of the GST member with the TiN member in such arrangement is 450 nm2, and the arrangement exhibits a reset current of approximately 0.2 mA.
FIG. 8 shows a dashboard cell structure in which the GST member has a height of 30 nm and a thickness of approximately 7.5 nm. Each of the GST member and the TiN member has a width dimension on the order of 25 nm. The contact area of the GST member with the TiN member in such arrangement is approximately 200 nm2, and the arrangement exhibits a reset current of approximately 0.08 mA.
FIG. 9 shows a cross-spacer structure in which the GST member has a height of 30 nm, and is positioned transversely to the TiN member. The contact area of the GST member with the TiN member in such arrangement is approximately 100 nm2.
FIGS. 10-23 illustrate a schematic process flow for forming a double self-aligned phase change memory device structure.
FIG. 10 is a perspective view of a trench structure in a SiO2 substrate. As shown in FIG. 11, a TiN film is deposited on the trench structure, e.g., at a thickness on the order of 10 nm. FIG. 12 shows a protective insulating material being deposited over the TiN film. An anisotropic etch with over-etching is next carried out, to form the structure shown in FIG. 13. Conformal deposition of GST is thereafter carried out, to form the structure shown in FIG. 14. A protective insulating layer then is deposited on the GST, to form the structure shown in FIG. 15.
An anisotropic etch of the GST next is conducted to yield the structure shown in FIG. 16, following which SiO2 is filled in the trench, as illustrated in FIG. 17. Next, chemical mechanical planarization (CMP) is carried out to remove excess SiO2, yielding the structure as shown in FIG. 18. A top metal layer then is deposited, to form the structure shown in FIG. 19. A resist then is applied to the metal layer to define the self-alignment structure, as shown in FIG. 20, and the resist is developed to form the structure shown in FIG. 21. Next, metal is selectively removed to isolate the top electrode members as illustrated in FIG. 22.
FIG. 23 shows the resulting structure of a double isolated PCM arrangement. The GST region 1 is identified in FIG. 23 as an upper portion of the GST film, and is the active region of the device. The GST region 2 is identified in FIG. 23 as a lower portion of the GST film, and is an inactive portion of the device, since electrical field at such lower portion is zero.
FIG. 24 is a schematic cross-sectional elevation view of a double self-aligned phase change memory device structure 100 of the present disclosure, according to one embodiment thereof. The device structure 100 comprises silicon dioxide (SiO2) 102 bounding the double self-aligned phase change memory film members 104, 106, which may be formed of GST, GT, or other phase change material.
Each of the phase change memory film members 104, 106 comprises a bottom upwardly extending segment 116 that is coupled to a top upwardly extending segment 112 by an angled transitional segment 114 therebetween. The transitional segment 114 may have any suitable angle in relation to the top and bottom segments 112, 116 of the phase change memory film members, e.g., 45°. Layers 108, 110, 122 and 124 comprise titanium nitride (TiN), and layers 118 and 120 are layers of protective material for the TiN in the double self-aligned phase change memory device structure.
In the FIG. 24 structure, the upper phase change memory segment 112 in region “A” is active. The lower phase change memory segment 116 and transition segment 114 in region “B” are inactive, although the transition segment 114 effects some heat loss (heat dissipation) in the operation of the device structure.
FIG. 25 is an enlarged portion of the phase change memory device structure 100 of FIG. 24, showing the details of the phase change film member and associated TiN layer. In the FIG. 25 drawing, the components of the structure are numbered correspondingly with respect to the reference numerals in FIG. 24.
In the FIG. 24 phase change memory device structure, the phase change memory material in transition segment 114 may be selectively removed, e.g., by over-etching during the anisotropic etching step (FIG. 16) for removal of the transition segment. By such modification, the upper segment 112 of phase change memory material is not electrically or thermally associated with the lower segment 116, and, as discussed, only the upper segment of phase change memory material constitutes the active phase change memory material in the structure.
Such a modified phase change memory device structure is shown in FIG. 26, which is a schematic illustration of the double self-aligned phase change memory device structure corresponding to that shown in FIG. 24, but wherein the transition segment has been selectively removed so that the upper segment 112 of phase change memory material is physically isolated from the lower segment 116 of such material.
While the disclosure has been set out herein in reference to specific aspects, features and illustrative embodiments, it will be appreciated that the utility of the disclosure is not thus limited, but rather extends to and encompasses numerous other variations, modifications and alternative embodiments, as will suggest themselves to those of ordinary skill in the field of the present disclosure, based on the description herein. Correspondingly, the invention as hereinafter claimed is intended to be broadly construed and interpreted, as including all such variations, modifications and alternative embodiments, within its spirit and scope.

## Claims

1. A double self-aligned phase change memory device structure, comprising spaced-apart facing phase change memory film members symmetrically arranged with respect to one another, each of the phase change memory film members at an upper portion thereof being in contact with a separate conductive element, and each of the phase change memory film members being in a range of from 5 nm to 25 nm in thickness.

2. The memory device structure of claim 1, wherein a protecting layer is disposed on facing surfaces of said phase change memory film members.

3. The memory device structure of claim 2, wherein the protecting layer extends downwardly from an upper end of each phase change memory film member over the facing surface thereof to a lower portion of the phase change memory film member.

4. The memory device structure of claim 3, further comprising a dielectric material between the phase change memory film members.

5. The memory device structure of claim 1, wherein each of the phase change memory film members has a thickness in a range of from 8 nm to 20 nm.

6. The memory device structure of claim 1, wherein each of the phase change memory film members has a thickness in a range of from 10 to 15 nm.

7. The memory device structure of claim 1, wherein each of the phase change memory film members has a thickness in a range of from 5 to 15 nm.

8. The memory device structure of claim 1, wherein each phase change memory film member has a height in a range of from 20 to 80 nm.

9. The memory device structure of claim 1, wherein each phase change memory film member has a height in a range of from 30 to 75 nm.

10. The memory device structure of claim 1, wherein each of the phase change memory film members comprises a chalcogenide.

11. The memory device structure of claim 1, wherein each of the phase change memory film members comprises a germanium-antimony-telluride alloy.

12. The memory device structure of claim 1, wherein each of the phase change memory film members comprises a germanium telluride alloy.

13. The memory device structure of claim 1, wherein the phase change memory film members are arranged in a confined cell arrangement comprising a cross-spacer structure wherein the phase change memory film members are reposed on titanium nitride members.

14. The memory device structure of claim 13, wherein a contact area of each phase change memory film member and the titanium nitride member on which it is reposed is in a range of from 50 to 150 nm2.

15. The memory device structure of claim 13, wherein a contact area of each phase change memory film member and the titanium nitride member on which it is reposed is in a range of from 80 to 120 nm2.

16. A double self-aligned phase change memory device structure, comprising spaced-apart facing phase change memory film members symmetrically arranged with respect to one another, each of the phase change memory film members at an upper portion thereof being in contact with a separate conductive element, and each of the phase change memory film members being in a range of from 5 nm to 25 nm in thickness, wherein each phase change memory film member comprises an upper planar segment, an intermediate angular transition segment, and a lower planar segment, arranged so that the upper planar segment and lower planar segment of each phase change memory film member are generally parallel to one another and to respective upper planar and lower planar segments of the other phase change memory film member facing it, wherein spacing distance between upper planar segments of the respective phase change memory film members is greater than spacing distance between lower planar segments of the respective phase change memory film members.

17. The memory device structure of claim 16, wherein the intermediate angular transition segment is generally planar.

18. A double self-aligned phase change memory device structure, comprising spaced-apart facing phase change memory film members symmetrically arranged with respect to one another, each of the phase change memory film members at an upper portion thereof being in contact with a separate conductive element, and each of the phase change memory film members being in a range of from 5 nm to 25 nm in thickness, wherein each phase change memory film member comprises an upper planar segment and a lower planar segment, elevationally spaced apart from one another, and arranged so that the upper planar segment and lower planar segment of each phase change memory material film member are generally parallel to one another and to respective upper planar and lower planar segments of the other phase change memory material film member facing it, wherein spacing distance between upper planar segments of the respective phase change memory material film members is greater than spacing distance between lower planar segments of the respective phase change memory film members.

19. A method of forming a double self-aligned memory device structure of claim 1, comprising:
depositing a phase change material to form spaced-apart facing phase change memory film members symmetrically arranged with respect to one another, wherein each of the phase change memory film members is in a range of from 5 nm to 25 nm in thickness; and
forming conductive elements so that each of the phase change memory film members at an upper portion thereof is in contact with a separate conductive element.

20. The method of claim 19, wherein the spaced-apart facing phase change memory film members are formed so that they are physically isolated from one another in the memory device structure.