Abstract:
Phase change memories may exhibit improved properties and lower cost in some cases by forming the phase change material layers in a planar configuration. A heater may be provided below the phase change material layers to appropriately heat the material to induce the phase changes. The heater may be coupled to an appropriate conductor.

Description:
BACKGROUND  
         [0001]    This invention relates generally to electronic memories and particularly to electronic memories that use phase change material.  
           [0002]    Phase change materials may exhibit at least two different states. The states may be called the amorphous and crystalline states. Transitions between these states may be selectively initiated. The states may be distinguished because the amorphous state generally exhibits higher resistivity than the crystalline state. The amorphous state involves a more disordered atomic structure. Generally any phase change material may be utilized. In some embodiments, however, thin-film chalcogenide alloy materials may be particularly suitable.  
           [0003]    The phase change may be induced reversibly. Therefore, the memory may change from the amorphous to the crystalline state and may revert back to the amorphous state thereafter, or vice versa, in response to temperature changes. In effect, each memory cell may be thought of as a programmable resistor, which reversibly changes between higher and lower resistance states. The phase change may be induced by resistive heating.  
           [0004]    Existing phase change memories may exhibit various disadvantages. Thus, there is a need for better ways to form phase change memories. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is an enlarged, partial cross-sectional view of one embodiment of the present invention;  
         [0006]    [0006]FIG. 2 is an enlarged, partial cross-sectional view of the embodiment shown in FIG. 1 in the course of fabrication;  
         [0007]    [0007]FIG. 3 is an enlarged, partial cross-sectional view corresponding to FIG. 2 at a subsequent stage;  
         [0008]    [0008]FIG. 4 is an enlarged cross-sectional view at a subsequent stage;  
         [0009]    [0009]FIG. 5 is an enlarged, partial cross-sectional view of another embodiment of the present invention at an early stage of manufacture;  
         [0010]    [0010]FIG. 6 is an enlarged, partial cross-sectional view at a subsequent stage of manufacture in accordance with one embodiment of the present invention;  
         [0011]    [0011]FIG. 7 is an enlarged, partial cross-sectional view at a subsequent stage of manufacture in accordance with one embodiment of the present invention;  
         [0012]    [0012]FIG. 8 is an enlarged, partial cross-sectional view of the embodiment shown in FIG. 7 at a subsequent stage of fabrication in accordance with one embodiment of the present invention;  
         [0013]    [0013]FIG. 9 is an enlarged, partial cross-sectional view of still another embodiment of the present invention;  
         [0014]    [0014]FIG. 10 is an enlarged, partial cross-sectional view of an early stage of manufacturing of the embodiment shown in FIG. 9 in accordance with one embodiment of the present invention;  
         [0015]    [0015]FIG. 11 is an enlarged, partial cross-sectional view of the embodiment shown in FIG. 10 in accordance with one embodiment of the present invention at a subsequent stage of manufacture;  
         [0016]    [0016]FIG. 12 is an enlarged, partial cross-sectional view at a subsequent stage of manufacture in accordance with still another embodiment of the present invention;  
         [0017]    [0017]FIG. 13 is an enlarged, partial cross-sectional view of still another stage of manufacture in accordance with one embodiment of the present invention;  
         [0018]    [0018]FIG. 14 is an enlarged, partial cross-sectional view of still a later stage of manufacture in accordance with one embodiment of the present invention;  
         [0019]    [0019]FIG. 15 is an enlarged, partial cross-sectional view of still a later stage of manufacture in accordance with one embodiment of the present invention;  
         [0020]    [0020]FIG. 16 is an enlarged, partial cross-sectional view at an early stage of manufacture in accordance with another technique for forming a structure shown in FIG. 9 in accordance with one embodiment of the present invention;  
         [0021]    [0021]FIG. 17 is an enlarged, partial cross-sectional view of the embodiment shown in FIG. 16 at a subsequent stage of manufacture in accordance with one embodiment of the present invention;  
         [0022]    [0022]FIG. 18 is an enlarged, partial cross-sectional view of still another embodiment of the present invention;  
         [0023]    [0023]FIG. 19 is an enlarged, partial cross-sectional view of the embodiment shown in FIG. 18 at an early stage of manufacture;  
         [0024]    [0024]FIG. 20 is an enlarged, partial cross-sectional view at a subsequent stage of manufacture in accordance with one embodiment of the present invention;  
         [0025]    [0025]FIG. 21 is an enlarged, partial cross-sectional view of the embodiment shown in FIG. 20 at a subsequent stage of manufacture in accordance with one embodiment of the present invention;  
         [0026]    [0026]FIG. 22 is an enlarged, partial cross-sectional view at a subsequent stage in accordance with one embodiment of the present invention;  
         [0027]    [0027]FIG. 23 is an enlarged, partial cross-sectional view at a subsequent stage in accordance with one embodiment of the present invention;  
         [0028]    [0028]FIG. 24 is an enlarged, partial cross-sectional view at a subsequent stage in accordance with one embodiment of the present invention;  
         [0029]    [0029]FIG. 25 is an enlarged, partial cross-sectional view of still another embodiment of the present invention; and  
         [0030]    [0030]FIG. 26 is a schematic depiction of a system in one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0031]    Referring to FIG. 1, the phase change memory  10  may include a upper electrode  12  on top of a phase change material layer. In one embodiment of the present invention, the layer  14  includes a chalcogenide material. Examples of phase change memory material include, but are not limited to, chalcogenide element(s) compositions of the class of tellurium-germanium-antimony (TexGeySbz) material or GeSbTe alloys, although the scope of the present invention is not limited to just these. Alternatively, another phase change material may be used whose electrical properties (e.g., resistance, capacitance, etc.) may be changed through the application of energy such as, for example, light, heat, or electrical current. The layer  14  is substantially planar in one embodiment of the present invention.  
         [0032]    A heater  18  may be formed essentially beneath the layer  14 . The heater  18  may be formed of titanium silicon nitride, tantalum nitride, or other resistive heating materials. The heater  18  may include a resistive material that generates resistive heating.  
         [0033]    A conductor  20  extends through an electrical insulator  16  to contact the heater  18  and to provide current for the heater  18 . Any electrically insulating material may be used. The insulator  16  may be located over a semiconductor substrate  11  such that the layer  14  is parallel to the substrate  11  and perpendicular to the conductor  20 .  
         [0034]    In some embodiments, the planar nature of the phase change material stack may improve step coverage, improve interface cleanness, add options for better thermal insulation, and generate more reproducible device performance.  
         [0035]    Referring to FIG. 2, in accordance with one process for forming the structure shown in FIG. 1, initially, a glue layer  24  may be deposited on top of an insulator  16  over a substrate  11 . The glue layer  24  may improve the adhesion of the layer  14  to the insulator  16 . An example of a glue layer is a polysilicon layer. A resist  22  may be formed over the layer  24 .  
         [0036]    In accordance with one embodiment of the present invention, an electron beam patterning technique may be utilized to form the pattern  26  in the resist  22 . The use of the electron beam patterning may result in smaller critical dimensions being transferred to the resist  22 . The pattern  26  and the resist  22  may be utilized to form an aperture  28  which extends through the resist  22  and ultimately acts as an etching mask for etching through the glue layer  24  and the insulator  16  as shown in FIG. 3.  
         [0037]    In other embodiments, other techniques to form openings may be used including phase shift masking, chromeless phase shift masking, or conventional lithography with a spacer.  
         [0038]    Referring to FIG. 4, the lower portion of the aperture  28  may be filled with a conductive material  30 , such as tungsten, aluminum, or copper, as a few examples. The conductive material  30  may then be dipped or etched (wet or dry) back to reduce the height of the conductive material  30 . Thereupon, another conductive material  32  may be deposited. This conductive material  32  may, for example, be any of the heater materials described previously including titanium silicon nitride or the material  32  may be titanium aluminum nitride, or tantalum nitride. Thereafter, a chemical mechanical polishing (CMP) step may be utilized to planarize the upper surface of the structure.  
         [0039]    Turning next to FIG. 5, another technique for forming the structure shown in FIG. 1 begins by forming an appropriately sized pore  36  in an insulator  16  over a suitable substrate (not shown). In this example, conventional lithography may be utilized. An appropriate pattern may be formed through the glue layer  24  and the insulator  16  to etch an appropriate pore  36 . The pore  36  may then be coated with a sidewall spacer material  34  which may be any suitable material including oxide and nitride. The sidewall spacer material  34  reduces the size of the opening  36  and compensates for the limitations of the lithography.  
         [0040]    The pore  36  may then be filled with a conductive material  38 , such as tungsten, as shown in FIG. 6. The conductive material  38  may then be dipped or etched (wet or dry) back to create the depression  40  as shown in FIG. 7. The dipped or etched back depression  40  may then be filled with a second conductive material  42  such as titanium silicon nitride, as indicated in FIG. 8. The heater  18  (FIG. 1) may comprise the material  42  over a conductor  20  (FIG. 1) comprising the material  38 .  
         [0041]    Referring to FIG. 9, in accordance with still another embodiment of the present invention, a phase change memory  10   a  may include an upper electrode  12  over a phase change material layer  14  that, again, is in a planar configuration. A heater  46  is arranged under the phase change material layer  14 . The heater  46  may be defined in an insulator  44 . The heater  46  is coupled to a conductor  48  defined in an insulator  16 .  
         [0042]    Referring to FIG. 10, in accordance with one embodiment for forming the structure shown in FIG. 9, initially the conductive material  48  is defined within a pore within an insulator  16  using conventional techniques. The insulator  16  may then be covered with an adhesion promotion layer or glue layer  52  and an insulator  50 .  
         [0043]    The insulator  50  may then be patterned to form the opening  54 , as shown in FIG. 11, using any appropriate lithography technology. While an embodiment is provided in which conventional lithography is utilized, the opening  54  may also be formed using electron beam lithography or phase shift masking, as two additional examples. With electron beam lithography or phase shift masking, a sidewall spacer may be unnecessary in some situations.  
         [0044]    Referring to FIG. 12, in accordance with an embodiment in which conventional lithography is utilized, the opening  54  may be coated with a sidewall spacer material  56 . The sidewall spacer  58  may be formed, as shown in FIG. 13, using an anisotropic etching technique.  
         [0045]    Using the sidewall spacer  58  as a mask, the glue layer  52  may be etched through to the conductive material  48  as shown in FIG. 14. Then, as shown in FIG. 15, the heater material  46  may be deposited in the remaining opening  60 .  
         [0046]    Turning next to FIG. 16, in accordance with another technique for forming the memory  10   a , a pair of layers  62  and  64  may have an aperture  60  transferred to those layers. In one embodiment, the aperture  60  is transferred using an electron beam lithography technique. The aperture  60  communicates with a conductive material layer  48  formed within an insulator  16 . Thereafter, a heater material  62  may be formed in the aperture  60 , as shown in FIG. 17, to electrically couple to the conductive material  48 . A suitable phase change material layer may be built up over the heater  62  and an upper electrode may be added as described previously.  
         [0047]    Moving next to FIG. 18, a phase change memory  10   b  may include an upper electrode  12  over a phase change material layer  14 . A ring shaped heater  78  may be positioned underneath the layer  14 . The heater  78  may be in communication with a cup-shaped conductive material  70  defined within an insulator  16 .  
         [0048]    In accordance with one embodiment for forming a structure shown in FIG. 18, initially, insulating sidewall spacers  66  may be formed, as described previously, within an aperture  68  in an insulator  16  over a suitable semiconductor substrate as shown in FIG. 19.  
         [0049]    Moving to FIG. 20, the opening  68 , shown in FIG. 19, may be covered with a conductive material  70 . The conductive material  70  may be in turned filled with a fill material  72 , such as insulator, as shown in FIG. 21.  
         [0050]    The structure shown in FIG. 21 may be planarized to achieve the structure shown in FIG. 22. Next, the conductive material  70  may be dipped or etched back to produce the ring-shaped dip  76  as shown in FIG. 23. The dip  76  may then be filled with a heater material  78 , as shown in FIG. 24, to produce the ring-shaped heater  66  coupled to the cup-shaped conductive material  70 .  
         [0051]    Turning to FIG. 25, the phase change memory  10   c  may include an upper electrode  12  over a phase change material layer  14 . A heater  18  may be positioned under the layer  14  within a glue layer  79  and a thermal insulating layer  80 . The layer  80  may overlie an insulator  82  which has a pore defining a conductive material  20  as described previously.  
         [0052]    The thermal insulative layer  80  provides better thermal insulation than other insulating materials, such as oxide. The layer  80  may be used in any of the embodiments described previously. The layer  80  may have four or more times lower thermal conductivity than oxide in one embodiment. For example, the layer  80  may be xerogel or organic polymers.  
         [0053]    A xerogel is a gel which has the liquid removed from its pores. A xerogel results from a super critical drying process. Thus, a xerogel is a gel dried at temperatures close to room temperature and under atmospheric pressure. The xerogel is the result of gentle drying to avoid cracking associated with the very low permeability of the solid network. The xerogel may have ten or more times lower thermal conductivity than oxide.  
         [0054]    In some embodiments, the structures described herein may reduce the processing steps and critical mask layers required for conventional process flows. These flows may enable the use of optimum materials in the right place for optimal thermal efficiency in some embodiments. Thus, some embodiments of the present invention may exhibit one or more of the following properties: lower costs through fewer masking processes, and better performance through less wasted heat in thermal coupling.  
         [0055]    A processor-based system  84 , shown in FIG. 26, may include a processor  86  that may, for example, be a digital signal processor or a general purpose processor. The processor  86  may be coupled by a bus  88  to a wireless interface  90 , in a wireless embodiment, and the phase change memory  10  which may be, for example, any of the embodiments described above. However, the present invention is not in any way limited to wireless applications.  
         [0056]    While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.