Memory cells

Some embodiments include memory cells having programmable material between a pair of electrodes. The programmable material includes a material selected from the group consisting of a metal silicate with a ratio of metal to silicon within a range of from about 2 to about 6, and metal aluminate with a ratio of metal to aluminum within a range of from about 2 to about 6. Some embodiments include methods of forming memory cells. First electrode material is formed. Programmable material is formed over the first electrode material, with the programmable material including metal silicate and/or metal aluminate. Second electrode material is formed over the programmable material, and then an anneal is conducted at a temperature within a range of from about 300° C. to about 500° C. for a time of from about 1 minute to about 1 hour.

TECHNICAL FIELD

Memory cells and methods of forming memory cells.

BACKGROUND

Memory is one type of integrated circuitry, and is used in computer systems for storing data. Integrated memory is usually fabricated in one or more arrays of individual memory cells. The memory cells are configured to retain or store memory in at least two different selectable states. In a binary system, the states are considered as either a “0” or a “1”. In other systems, at least some individual memory cells may be configured to store more than two levels or states of information.

There is a continuing effort to produce smaller and denser integrated circuits. The smallest and simplest memory cell will likely be comprised of two electrically conductive electrodes having a programmable material received between them. The programmable material has two or more selectable and electrically differentiable memory states, which enables storing of information by an individual memory cell. The reading of the cell comprises determination of which of the memory states the programmable material is in, and the writing of information to the cell comprises placing the programmable material in a predetermined memory state. Memory devices that utilize changes in resistivity across programmable material to transition from one memory state to another are sometimes referred to as Resistive Random Access Memory (RRAM) cells.

There is a continuing goal to improve performance characteristics of memory cells, and a continuing goal to improve yield of memory cells from fabrication processes. It would therefore be desirable to develop new memory cells, and to develop new methods of forming memory cells.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Some embodiments include memory cells containing programmable material which includes metal silicate and/or metal aluminate; and some embodiments include methods of making such memory cells. Example embodiments are described with reference toFIGS. 1-11.

Referring toFIG. 1, an example embodiment memory cell10is illustrated. Such memory cell includes a first electrode12, a second electrode14, and a programmable material16between the first and second electrodes.

The first and second electrodes may comprise any suitable compositions or combinations of compositions. In some embodiments, the first electrode12will comprise, consist essentially of, or consist of a metal selected from the group consisting of hafnium, lanthanum, ruthenium, titanium, zirconium and mixtures thereof. In such embodiments, the first electrode may be referred to as a reactive electrode, in that the metals of such electrode may be suitable for reacting with the programmable material during formation and/or operation of the memory cell.

In some embodiments, the second electrode14may consist of a composition which is non-reactive relative to the composition of the programmable material; and may, for example, comprise, consist essentially of, or consist of one or more of hafnium nitride, lanthanum nitride, ruthenium nitride, titanium nitride and zirconium nitride.

In some example embodiments, the first electrode12will comprise, consist essentially of, or consist of a metal selected from the group consisting of hafnium, lanthanum, ruthenium, titanium, zirconium and mixtures thereof; and the second electrode14will comprise, consist essentially of or consist of a metal nitride comprising the metal of the first electrode. For instance, in some embodiments the first electrode12may comprise titanium while the second electrode14comprises titanium nitride.

The programmable material16may comprise, consist essentially, or consist of one or both of metal silicate and metal aluminate. The metal silicate may be selected from the group consisting of hafnium silicate, lanthanum silicate, ruthenium silicate, titanium silicate, zirconium silicate, and mixtures thereof; and the metal aluminate may be selected from the group consisting of hafnium aluminate, lanthanum aluminate, ruthenium aluminate, titanium aluminate, zirconium aluminate and mixtures thereof.

In some embodiments, the programmable material comprises a region which includes a composition selected from the group consisting of a metal silicate with a ratio of metal to silicon within a range of from about 2 to about 6, and a metal aluminate with a ratio of metal to aluminum with a range of from about 2 to about 6. Utilization of such compositions within programmable materials of RRAM cells is found to improve yield of functional cells during a fabrication process relative to processes forming analogous cells lacking such compositions of metal silicate and/or metal aluminate, and to improve durability of the RRAM cells relative to cells lacking such compositions of metal silicate and/or metal aluminate. Thus, inclusion of one or both of metal silicate with a ratio of metal to silicon within a range of from about 2 to about 6, and metal aluminate with a ratio of metal to aluminum within a range of from about 2 to about 6 in RRAM cells may improve yield and performance of the cells relative to conventional RRAM cells. In some embodiments, the utilization of metal silicate having a ratio of metal to silicon within the range of from about 2 to about 6 and/or metal aluminate having a ratio of metal to aluminum within the range of from about 2 to about 6 is found to improve low current operation of memory cells and reset characteristics of memory cells.

In some embodiments, the programmable material16may be a single homogeneous composition extending from directly against the first electrode to directly against the second electrode. In some embodiments, the programmable material16may comprise a concentration gradient of metal within one or both of metal aluminate and metal silicate. For instance, the programmable material may comprise a first composition adjacent the first electrode12, and a second composition adjacent the second electrode14. The first composition may comprise the metal silicate with a ratio of metal to silicon within a range of from about 2 to about 6, and/or the metal aluminate with a ratio of metal to aluminum within a range of from about 2 to about 6; and the second composition may comprise metal silicate having a ratio of metal to silicon of at least about 8 and/or metal aluminate having a ratio of metal to aluminum of at least about 8. In such embodiments, the first composition may be directly against a reactive electrode, the second composition may be directly against a non-reactive electrode, and the programmable material may have a concentration gradient of metal which extends from the first composition to the second composition such that the concentration of metal increases across the programmable material along a direction from the reactive electrode to the non-reactive electrode.

In a specific example embodiment, the reactive electrode may consist essentially of titanium, the nonreactive electrode may comprise titanium nitride, and the programmable material may consist essentially of hafnium silicate. A region of the programmable material directly against the reactive electrode may have a ratio of hafnium to silicon within a range of from about 3 to about 6, a region of the programmable material directly against the nonreactive electrode may have a ratio of hafnium to silicon of at least about 8, and the programmable material may comprise a concentration gradient of hafnium which increases along a direction from the reactive electrode to the nonreactive electrode. The region adjacent the nonreactive electrode has a higher dielectric constant than the region adjacent the reactive electrode (i.e., may be considered to have a higher ratio of hafnium oxide relative to silicate), which may improve yield and/or device performance in some embodiments. The concentration gradient may be any suitable gradient, including, for example, a linear gradient or a stepped gradient.

Although the reactive electrode and the nonreactive electrode are described to be the electrodes below and above the programmable material16, respectively, in the embodiment ofFIG. 1; in other embodiments the relative positions of the reactive and nonreactive electrodes may be reversed so that the reactive electrode is above programmable material16and the nonreactive electrode is below such programmable material. Similarly, any of the other embodiments described herein may be constructed with an illustrated arrangement of electrodes, or with an opposite arrangement in which the electrodes (and possibly one or more regions between the electrodes) are reversed relative to the illustrated arrangement.

FIG. 2diagrammatically illustrates a plurality of operational states (a so-called “UNBIASED” state, “RESET” state, and “SET” state) utilizing band gap diagrams. The example embodiment comprises a first electrode12consisting of titanium, a second electrode14consisting of titanium nitride, and programmable material16consisting of hafnium silicate with the ratio of hafnium to silicon being about 3:1.

The “RESET” and “SET” states have different resistivities relative to one another, and correspond to different memory states of the memory cell10. Operation of memory cell10comprises programming the memory cell to place it in either the “RESET” state or the “SET” state, and later reading the memory cell to determine which of the two states it is in. In some embodiments, operation of the memory cell may comprise a mechanism in which the reactive electrode is utilized to form a thin layer of hafnium oxide, lanthanum oxide, ruthenium oxide, titanium oxide and/or zirconium oxide in a region of the programmable material directly adjacent such reactive electrode through reaction of metal from the reactive electrode (specifically, hafnium, lanthanum, ruthenium, titanium and/or zirconium) with oxygen of the programmable material. Such thin layer may be modulated during operation of the memory cell to operably switch the memory cell between a low resistance state and a high resistance state. For instance, conductivity through the programmable material may be operably altered as follows. The resistance may be decreased by pulling more oxygen into the thin layer to increase an amount of oxygen vacancies within a metal silicate matrix and/or metal aluminate matrix, and the resistance may be increased by pulling more oxygen from the thin layer into the metal silicate matrix and/or metal aluminate matrix to decrease the amount of oxygen vacancies within such matrices. The possible mechanism of operation of a memory cell through modulation of oxygen vacancies is provided to assist the reader in understanding the embodiments described herein, and is not to limit any of such embodiments except to the extent, if any, that the mechanism is explicitly recited in the claims which follow.

In some embodiments, the thin oxide layer may be provided as part of the programmable material, and accordingly the reactive electrode may be replaced with any suitable conductive material.FIG. 3shows an example embodiment memory cell10ahaving a programmable material16acomprising an oxide20over a composition18. In some embodiments, the oxide20may comprise, consist essentially of, or consist of hafnium oxide, lanthanum oxide, ruthenium oxide, titanium oxide and/or zirconium oxide; and the composition18and may include a region having one or both of metal silicate with a ratio of metal to silicon within a range of from about 2 to about 6, and metal aluminate with a ratio of metal to aluminum within a range of from about 2 to about 6. In some embodiments, the oxide20may have a thickness of from about 10 Å to about 50 Å. In such embodiments, the composition18and may have a thickness of at least about 50 Å, and in some embodiments may have a thickness of at least about 100 Å.

The memory cell10aofFIG. 3comprises the first and second electrodes12and14. In some embodiments, the composition18may be homogeneous between the electrode12and the oxide20. In other embodiments, the composition may comprise a metal concentration gradient analogous to the various gradients described above with reference toFIG. 1. In yet other embodiments, the material18may comprise two or more discrete compositions analogous to embodiments described below with reference toFIGS. 4-7.

Referring toFIG. 4, a memory cell10bis shown to comprise a programmable material16bhaving two regions22and24, with the regions being of different compositions relative to one another.

In some embodiments, one of the regions22and24comprises a composition having metal silicate with a ratio of metal to silicon within a range of from about 2 to about 6 and/or having metal aluminate with a ratio of metal to aluminum within a range of from about 2 to about 6. In such embodiments, the other of the regions22and24may comprise a composition having metal silicate with a ratio of metal to silicon of greater than 6 (and in some embodiments at least about 8) and/or having metal aluminate with a ratio of metal to aluminum of greater than 6 (and in some embodiments at least about 8).

The electrodes12and14may comprise any suitable materials, and in some embodiments may be a reactive electrode and a nonreactive electrode of the types described above with reference toFIG. 1. For instance, in some embodiments electrode12may be a reactive electrode consisting of one or more of hafnium, lanthanum, ruthenium, titanium and zirconium. The region22directly adjacent such reactive electrode may comprise a first composition selected from the group consisting of metal silicate with a ratio of metal to silicon within a range of from about 2 to about 6, and metal aluminate with a ratio of metal to aluminum within a range of from about 2 to about 6. For instance, in some embodiments the region22may comprise, consist essentially of, or consist of hafnium silicate with a ratio of hafnium to silicon of about 3. The region24may comprise a second composition selected from the group consisting of a metal silicate with a ratio of metal to silicon of at least about 6, and a metal aluminate with a ratio of metal to aluminum of at least about 6. For instance, in some embodiments the region24may comprise, consist essentially of, or consist of hafnium silicate with a ratio of hafnium to silicon of about 8. The electrode14directly against the second region24may be a nonreactive electrode, and in some embodiments may comprise, consist essentially of, or consist of a metal nitride.

FIG. 5diagrammatically illustrates a plurality of operational states (a so-called “UNBIASED” state, “RESET” state, and “SET” state) of theFIG. 4memory cell utilizing band gap diagrams. The example embodiment comprises a first electrode12consisting of titanium, a second electrode14consisting of titanium nitride, and programmable material16bcomprising a first region22consisting of hafnium silicate with the ratio of hafnium to silicon of about 3:1; and comprising a second region24consisting of hafnium silicate with the ratio of hafnium to silicon of about 8:1.

In some embodiments, the region22may be considered to be a “switching region” where changes occur that lead to the different resistivity between the “RESET” state and the “SET” state. The memory cell ofFIG. 5may be considered to be different than that ofFIG. 2in that the memory cell ofFIG. 5comprises a higher dielectric constant region24between the switching region and the nonreactive electrode14, whereas the memory cell ofFIG. 2has the switching region directly against such nonreactive electrode. The inclusion of the higher dielectric constant region24in the embodiment ofFIG. 5may enable a higher field in a memory state of the memory cell (for instance, the “SET” state) as compared to the memory cell ofFIG. 2for a same applied voltage, due to a field distribution between the regions22and24. Utilization of two regions in the embodiment ofFIG. 5is found to improve performance and yield of memory cells relative to the embodiment ofFIG. 2.

Although the embodiment ofFIGS. 4 and 5comprises two regions of programmable material between the first and second electrodes12and14, in other embodiments there may be more than two regions of the programmable material between the first and second electrodes. For instance,FIG. 6shows an example embodiment memory cell10chaving programmable material16cwith three regions30-32between the electrodes12and14, andFIG. 7shows an example embodiment memory cell10dhaving programmable material16dwith four regions40-43between electrodes12and14.

In some embodiments, the regions30-32ofFIG. 6may be referred to as first, second and third regions, respectively. Each of the regions may comprise one or both of metal silicate and metal aluminate. In some embodiments, the first and third regions30and32may comprise compositions selected from the group consisting of metal silicate with a ratio of metal to silicon within a range of from about 2 to about 6, and metal aluminate with a ratio of metal to aluminum within a range of from about 2 to about 6; and the second region31may comprise a composition selected from the group consisting of a metal silicate with a ratio of metal to silicon of at least about 6, and a metal aluminate with a ratio of metal to aluminum of at least about 6. The compositions of the first and third regions may be identical to one another in some embodiments, and may be different from one another in other embodiments. The metal within regions30-32may comprise one or more of hafnium, lanthanum, ruthenium, titanium and zirconium, in some embodiments. In an example embodiment, the first and third regions30and32may both consist of hafnium silicate with a ratio of hafnium to silicon of about 3; and the second region31may consist of hafnium silicate with a ratio of hafnium to silicon of about 8.

In some embodiments, the regions40-43ofFIG. 7may be referred to as first, second, third and fourth regions, respectively. Each of the regions may comprise one or both of metal silicate and metal aluminate. In some embodiments, the first and third regions40and42may comprise compositions selected from the group consisting of metal silicate with a ratio of metal to silicon within a range of from about 2 to about 6, and metal aluminate with a ratio of metal to aluminum within a range of from about 2 to about 6; and the second and fourth regions41and43may comprise a composition selected from the group consisting of a metal silicate with a ratio of metal to silicon of at least about 6, and a metal aluminate with a ratio of metal to aluminum of at least about 6. The compositions of the first and third regions may be identical to one another in some embodiments, and may be different from one another in other embodiments. Similarly, the compositions of the second and fourth regions may be identical to one another in some embodiments, and may be different from one another in other embodiments. The metal within regions40-43may comprise one or more of hafnium, lanthanum, ruthenium, titanium and zirconium, in some embodiments. In an example embodiment, the first and third regions40and42may both consist of hafnium silicate with a ratio of hafnium to silicon of about 3; and the second and fourth regions41and43may both consist of hafnium silicate with a ratio of hafnium to silicon of about 8.

The programmable materials16b-dofFIGS. 4,6and7may have any suitable thicknesses, and in some embodiments may have thicknesses of at least about 100 Å. In such embodiments, the various regions of the programmable materials may have any suitable thicknesses. For instance, the regions22and24ofFIG. 4may each have the same thickness as one another in some embodiments, or may have different thicknesses from one another in other embodiments. Analogously, the regions30-32ofFIG. 6may have the same thicknesses as one another, or at least one of the regions may have a different thickness than at least one other region; and the regions40-43ofFIG. 7may have the same thicknesses as one another, or at least one of the regions may have a different thickness than at least one other region.

The memory cells ofFIGS. 1-7may be formed with any suitable processing. An example embodiment method for forming the memory cell10ofFIG. 1is described with reference toFIGS. 8-11. Analogous processing may be utilized for forming other example embodiment memory cells, such as the memory cells ofFIGS. 3-7.

Referring toFIG. 8, a semiconductor construction50is shown to comprise conductive material52over a base54. The base may comprise, consist essentially of, or consist of monocrystalline silicon, and may be referred to as a semiconductor substrate, or as a portion of a semiconductor substrate. The terms “semiconductive substrate,” “semiconductor construction” and “semiconductor substrate” mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above. In some embodiments, the base may correspond to a semiconductor substrate containing one or more materials associated with integrated circuit fabrication. In such embodiments, such materials may correspond to one or more of refractory metal materials, barrier materials, diffusion materials, insulator materials, etc.

The conductive material52is ultimately patterned into the first electrode12ofFIG. 1, and may comprise any of the compositions discussed above regarding such first electrode. The conductive material52may be formed utilizing any suitable processing, including, for example, one or more of atomic layer deposition (ALD), chemical vapor deposition (CVD), and physical vapor deposition (PVD).

Referring toFIG. 9, programmable material56is formed over and directly against the conductive material52. The programmable material56may comprise any of the compositions discussed above regarding programmable material16ofFIG. 1. The programmable material may be formed utilizing any suitable processing, including, for example, one or more of ALD, CVD and PVD.

Referring toFIG. 10, a conductive material58is formed over the programmable material56. The material58is ultimately patterned into the second electrode14ofFIG. 1, and may comprise any of the compositions discussed above regarding such second electrode. The conductive material58may be formed utilizing any suitable processing, including, for example, one or more of ALD, CVD and PVD. In some embodiments, materials52and58may be referred to as first and second electrode materials, respectively. The materials52,56and58are patterned into a memory cell60analogous to the memory cell10ofFIG. 1. The materials52,56and58may be patterned into the memory cell configuration utilizing any suitable processing. The illustrated memory cell may be representative of a plurality of memory cells which are formed as part of an integrated memory array.

Referring toFIG. 11, the memory cell60is annealed at a temperature within a range of from about 300° C. to about 500° C. for a time of from about 1 minute to about 1 hour, (for instance, the anneal may be conducted under conditions which maintain the materials52,56and58at a temperature of about 400° C. for a time of about 30 minutes). The anneal is represented by arrows62inFIG. 11.

The anneal ofFIG. 11is conducted after formation of electrode material58. Although the anneal is shown conducted after patterning the materials52,56and58into memory cell60, in other embodiments the anneal may be conducted prior to patterning of one or more of materials52,56and58into a memory cell configuration. In some embodiments, the anneal ofFIG. 11is found to improve yield and/or performance of memory cells as compared to analogous memory cells formed with processing lacking such anneal. The performance improvement may include improvement in durability (i.e. lifetime) of memory cells in some embodiments.

The construction50may be kept under an inert atmosphere (for instance, N2) during the anneal.

The anneal ofFIG. 11may be utilized for treating any of the memory cell constructions described herein. For instance, such anneal may be utilized for treating a construction of the type shown inFIG. 3in which programmable material comprises a dielectric material20formed over a region18comprising one or both of metal silicate and metal aluminate. In such embodiments, the dielectric material may be formed utilizing any suitable processing, including, for example, one or both of ALD and CVD. As another example, such anneal may be utilized for treating constructions of the types shown inFIGS. 4,6and7in which the forming of the programmable material comprises forming multiple different compositions containing metal aluminate and/or metal silicate.

The memory cells discussed above may be incorporated into electronic systems. Such electronic systems may be used in, for example, memory modules, device drivers, power modules, communication modems, processor modules, and application-specific modules, and may include multilayer, multichip modules. The electronic systems may be any of a broad range of systems, such as, for example, clocks, televisions, cell phones, personal computers, automobiles, industrial control systems, aircraft, etc.

The cross-sectional views of the accompanying illustrations only show features within the planes of the cross-sections, and do not show materials behind the planes of the cross-sections in order to simplify the drawings.

When a structure is referred to above as being “on” or “against” another structure, it can be directly on the other structure or intervening structures may also be present. In contrast, when a structure is referred to as being “directly on” or “directly against” another structure, there are no intervening structures present. When a structure is referred to as being “connected” or “coupled” to another structure, it can be directly connected or coupled to the other structure, or intervening structures may be present. In contrast, when a structure is referred to as being “directly connected” or “directly coupled” to another structure, there are no intervening structures present.

Some embodiments include a memory cell having a first electrode, a second electrode, and programmable material between the first and second electrodes. The programmable material comprises a region containing a material selected from the group consisting of a metal silicate with a ratio of metal to silicon within a range of from about 2 to about 6, and a metal aluminate with a ratio of metal to aluminum within a range of from about 2 to about 6.

Some embodiments include a memory cell having a first electrode, a second electrode and programmable material between the first and second electrodes. The programmable material has a first region comprising a material selected from the group consisting of a metal silicate with a ratio of metal to silicon within a range of from about 2 to about 6, and a metal aluminate with a ratio of metal to aluminum within a range of from about 2 to about 6. The programmable material has a second region comprising a material selected from the group consisting of a metal silicate with a ratio of metal to silicon of greater than 6, and a metal aluminate with a ratio of metal to aluminum of greater than 6.

Some embodiments include a memory cell having a first electrode, a second electrode and programmable material between the first and second electrodes. The first electrode consists of metal selected from the group consisting of hafnium, lanthanum, ruthenium, titanium, zirconium, and mixtures thereof. The programmable material has a first region directly against the first electrode and comprising a first composition selected from the group consisting of a metal silicate with a ratio of metal to silicon within a range of from about 2 to about 6, and a metal aluminate with a ratio of metal to aluminum within a range of from about 2 to about 6. The programmable material has a second region directly against the second electrode and comprising a second composition selected from the group consisting of a metal silicate with a ratio of metal to silicon of at least about 6, and a metal aluminate with a ratio of metal to aluminum of at least about 6.

Some embodiments include a method of forming a memory cell. First electrode material is formed over a base, and programmable material is formed over the first electrode material. The programmable material includes a region comprising a composition selected from the group consisting of a metal silicate with a ratio of metal to silicon within a range of from about 2 to about 6, and a metal aluminate with a ratio of metal to aluminum within a range of from about 2 to about 6. Second electrode material is formed over the programmable material. After the second electrode material is formed, the memory cell is annealed at a temperature within a range of from about 300° C. to about 500° C. for a time of from about 1 minute to about 1 hour.