Boron Surface Passivation of Phase Change Memory Material

Techniques for improving switching properties of phase change memory devices by boron surface passivation of the phase change memory material are provided. In one aspect, a phase change memory device includes: one or more phase change memory cells, each having a phase change material between a bottom electrode and a top electrode; and a boron-containing and nitrogen-containing bilayer on sidewalls of the phase change material to protect the phase change material from exposure to oxygen. An ovonic threshold switch can be implemented between the bottom electrode and the top electrode, in series with the phase change material. A method of fabricating the present phase change memory devices is also provided.

FIELD OF THE INVENTION

The present invention relates to phase change memory devices, and more particularly, to techniques for improving switching properties of phase change memory devices by boron surface passivation of the phase change memory material.

BACKGROUND OF THE INVENTION

A resistive processing unit or RPU stores information based on the resistance of the RPU. For instance, during programming, a SET operation is used to program the RPU to a low-resistance state representing a data value such as a logic ‘1’ or a logic ‘0’. A subsequent RESET operation is then used to return the RPU to its previous high-resistance state.

A phase change material is a type of material that can be switched from one phase to another. Based on the properties of the different phases, phase change materials are ideal for use as the switching material in RPU-based phase change memory devices. Specifically, phase change materials provide a relatively high resistance when in an amorphous phase, and a relatively low resistance when in a crystalline phase.

During processing, however, exposure of the phase change material to air leads to oxidation. Oxidation of the phase change material can undesirably change its crystallization temperature and composition, both of which can impact the switching behavior of the phase change material.

Accordingly, techniques for protecting the phase change material in phase change memory devices from exposure to oxygen would be desirable.

SUMMARY OF THE INVENTION

The present invention provides techniques for improving switching properties of phase change memory devices by boron surface passivation of the phase change memory material. In one aspect of the invention, a phase change memory device is provided. The phase change memory device includes: one or more phase change memory cells, each having a phase change material between a bottom electrode and a top electrode; and a boron-containing and nitrogen-containing bilayer on sidewalls of the phase change material to protect the phase change material from exposure to oxygen.

In another aspect of the invention, another phase change memory device is provided. The phase change memory device includes: one or more phase change memory cells, each having a phase change material between a bottom electrode and a top electrode; a boron-containing and nitrogen-containing bilayer on sidewalls of the phase change material to protect the phase change material from exposure to oxygen; and an ovonic threshold switch, between the bottom electrode and the top electrode, that is in series with the phase change material.

In yet another aspect of the invention, a method of fabricating a phase change memory device is provided. The method includes: forming a stack of device materials on a substrate, the stack of device materials having a phase change material; patterning the stack of device materials into one or more phase change memory cells; and contacting the phase change memory cells with boron-containing and nitrogen-containing plasmas under conditions sufficient to form a boron-containing and nitrogen-containing bilayer on sidewalls of the phase change material to protect the phase change material from exposure to oxygen.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As provided above, the oxidation of exposed phase change memory materials can undesirably lead to changes in its crystallization temperature and composition, both of which impact the switching behavior of the phase change material. Advantageously, the present techniques employ a surface treatment using boron passivation to protect the sidewalls of the phase change memory material from exposure to oxygen. As will be described in detail below, the present boron surface passivation vastly improves the switching properties of the phase change memory material.

Referring to methodology100shown inFIG.1, the present techniques for fabricating a phase change memory device in accordance with the present techniques involve first forming a phase change memory device stack on a substrate (see step102). The phase change memory device stack includes a phase change material sandwiched between a bottom electrode and a top electrode, with other intervening materials as described in detail below.

According to an exemplary embodiment, the substrate is a bulk semiconductor wafer, such as a bulk silicon (Si), bulk germanium (Ge), bulk silicon germanium (SiGe) and/or bulk III-V semiconductor wafer. Alternatively, the substrate can be a semiconductor-on-insulator (SOI) wafer. A SOI wafer includes a SOI layer separated from an underlying substrate by a buried insulator. When the buried insulator is an oxide it is also referred to herein as a buried oxide or BOX. The SOI layer can include any suitable semiconductor material(s), such as Si, Ge, SiGe and/or a III-V semiconductor. Further, the substrate may already have pre-built structures such as transistors, diodes, capacitors, resistors, interconnects, wiring, etc.

A wide variety of materials can be employed as the phase change material in accordance with the present techniques. In the sense that it can exist in amorphous and crystalline form, almost any material is a phase change material, such as metals, semiconductors or insulators. However, only a small group of materials has the properties that makes them technologically useful phase change materials, with a high on/off resistance ratio, fast switching times and good data retention. Many technologically relevant phase change materials are chalcogenides, i.e., they contain one or more chalcogenide elements. Chalcogenide elements are those elements in Group 16 of the periodic table, e.g., sulfur (S), selenium (Se) and/or tellurium (Te). Thus, according to one exemplary embodiment, the present phase change material is a chalcogenide alloy that includes the chalcogenide element Te, in addition to other elements such as antimony (Sb) and/or germanium (Ge), forming the alloys Sb2Te3, GeTe, and/or Ge2Sb2Te5(GST225or simply GST). However, other technologically relevant materials for use as the present phase change material that are not chalcogenides include, but are not limited to, III-V semiconductor materials (such as gallium antimonide (GaSb)) and/or Ge—Sb based alloys. Furthermore, additional elements such as silver (Ag), indium (In), nitrogen (N), silicon (Si) and/or bismuth (Bi) can be added to any of the above phase change materials to optimize their properties.

As highlighted above, the present phase change material can be switched between two states, a poly-crystalline (or single-crystal) state and an amorphous state. In the poly-crystalline state, each grain of the present phase change material is a perfect crystal and the phase change material is conductive (almost metallic). It is notable, however, that each of the grains is randomly oriented with respect to the other grains resulting in an overall poly-crystalline material. In the amorphous state, there is no order in the material and the phase change material is highly resistive. These two states make phase change materials particularly well-suited for storing data.

In step104, a lithography and etching process is employed to pattern the phase change memory device stack into at least one individual phase change memory cell. Doing so exposes sidewalls of the phase change material to oxidation. Without further treatment, this oxidation can lead to alterations of the phase change material (such as its crystallization temperature and composition) which can undesirably impact the switching behavior of the phase change material as described above.

However, in order to protect the phase change material from the effects of this oxygen exposure, in step106the phase change memory cell(s) is/are next contacted with boron-containing and nitrogen-containing plasmas under conditions (duration, flow rate, etc.) sufficient to form a thin, protective BxNy/BzOmbilayer (where, e.g., 1≤x≤5, 1≤y≤5, 1≤z≤5, and 1≤m≤5) on, and encapsulating, the sidewalls of the phase change material. This BxNy/BzOmbilayer protects the sidewalls of the phase change material from air exposure, thereby improving the switching properties of the phase change material. Namely, the boron is an oxygen getter. Thus, exposure of the phase change memory cell(s) to the boron-containing and nitrogen-containing plasmas initially forms a BzOmlayer on the sidewalls of the phase change material which reduces the phase change material sidewall oxide. A layer of BxNythen forms on top of the BzOmlayer to passivate the surface and protect the sidewalls of the phase change material from air exposure. The combination of the BzOmlayer and the BxNylayer deposited on the sidewalls of the phase change material in step106is what is referred to herein as a ‘bilayer’.

Preferably, only a thin layer of BxNy/BzOmis deposited on the sidewalls of the phase change material. For instance, in one exemplary embodiment, the BzOmlayer has a thickness of from about 2 nanometers (nm) to about 25 nm and ranges therebetween, and similarly the BxNylayer has a thickness of from about 2 nm to about 25 nm and ranges therebetween. In that case, the total thickness of the BxNy/BzOmbilayer is from about 4 nm to about 50 nm and ranges therebetween.

In general, a plasma is a gas in which a significant percentage of the atoms or molecules are ionized. Processes such as plasma-enhanced chemical vapor deposition (PECVD) deposit materials from a gas state to a solid state on a given substrate. According to an exemplary embodiment, the boron-containing plasma contains diborane (B2H6) gas and the nitrogen-containing plasma contains a combination of nitrogen (N2) gas and hydrogen (H2) gas, N2/H2(e.g., N2900 standard cubic centimeters per minute (sccm) and H2100 sccm), and a process such as PECVD is used to deposit the protective BxNy/BzOmbilayer on the sidewalls of the phase change material from these gaseous precursors.

In that regard, according to an exemplary embodiment, step106for forming the protective BxNy/BzOmbilayer on the sidewalls of the phase change material is carried out in a PECVD processing chamber whereby a number of (sub) steps is performed to introduce a sequence of boron-containing and/or nitrogen-containing gaseous precursors into the PECVD processing chamber as shown, for example, in methodology200ofFIG.2. These gaseous precursors are used to generate the boron-containing and nitrogen-containing plasmas within the PECVD processing chamber.

For instance, the phase change memory cell(s) is/are placed in the PECVD processing chamber and, in step202, a combination of boron-containing and (first) nitrogen-/hydrogen-containing gaseous precursors, e.g., B2H6+N2/H2, is introduced to the PECVD processing chamber (at a flow rate of B2H6from about 500 sccm to about 550 sccm and ranges therebetween, N2from about 900 sccm to about 950 sccm and ranges therebetween, and H2from about 100 sccm to about 150 sccm and ranges therebetween) for a duration of from about 2 seconds to about 4 seconds and ranges therebetween. These gaseous precursors are used to generate boron-containing and nitrogen-containing plasmas in the PECVD chamber that are contacted with the phase change memory cell(s) during formation of the BxNy/BzOmbilayer (where, e.g., 1≤x≤5, 1≤y≤5, 1≤z≤5, and 1≤m≤5) on the sidewalls of the phase change material.

In step204, a (second) nitrogen-/hydrogen-containing gaseous precursor, e.g., N2/H2, is then introduced to the PECVD processing chamber (at a flow rate of N2from about 900 sccm to about 950 sccm and ranges therebetween, and H2from about 100 sccm to about 150 sccm and ranges therebetween) for a duration of from about 5 seconds to about 7 seconds and ranges therebetween. This gaseous precursor is used to generate a nitrogen-containing plasma in the PECVD chamber that is contacted with the phase change memory cell(s) during formation of the BxNy/BzOmbilayer (where, e.g., 1≤x≤5, 1≤y≤5, 1≤z≤5, and 1≤m≤5) on the sidewalls of the phase change material. Following step204, the PECVD processing chamber is purged of the gaseous precursors.

In step206, a (third) nitrogen-/hydrogen-containing gaseous precursor, e.g., N2/H2, is introduced to the PECVD processing chamber (at a flow rate of N2from about 900 sccm to about 950 sccm and ranges therebetween, and H2from about 100 sccm to about 150 sccm and ranges therebetween) for a duration of from about 5 seconds to about 7 seconds and ranges therebetween. This gaseous precursor is used to generate a nitrogen-containing plasma in the PECVD chamber that is contacted with the phase change memory cell(s) during formation of the BxNy/BzOmbilayer (where, e.g., 1≤x≤5, 1≤y≤5, 1≤z≤5, and 1≤m≤5) on the sidewalls of the phase change material.

As shown inFIG.2, steps202-206are repeated n times to build up the BxNy/BzOmbilayer on the sidewalls of the phase change material. As provided above, the thickness of the BxNy/BzOmbilayer can be from about 4 nm to about 50 nm and ranges therebetween. According to an exemplary embodiment, this BxNy/BzOmbilayer thickness is achieved by performing 10 cycles of steps202-206, i.e., n=10.

An exemplary implementation of methodology100ofFIG.1and methodology200ofFIG.2to fabricate a phase change memory device in accordance with the present techniques is now described by way of reference toFIGS.3-5. For instance, as described in conjunction with the description of step102ofFIG.1above, the process begins with the formation of a (phase change memory) device stack on a substrate. See, for example,FIG.3.

Namely, as shown inFIG.3, a phase change memory device stack304has been formed on a substrate302. As provided above, substrate302can be a bulk semiconductor wafer, such as a bulk Si, bulk Ge, bulk SiGe and/or bulk III-V semiconductor wafer, or an SOI wafer with an SOI layer formed form a semiconductor material(s) such as Si, Ge, SiGe and/or a III-V semiconductor. Further, substrate302may already have pre-built structures such as transistors, diodes, capacitors, resistors, interconnects, wiring, etc.

According to an exemplary embodiment, phase change memory device stack304includes a bottom electrode306disposed on the substrate302, a (first) buffer layer308disposed on the bottom electrode306, an ovonic threshold switch (OTS)310disposed on the buffer layer308, a (second) buffer layer312disposed on the OTS310, a phase change material314disposed on the buffer layer312, a (third) buffer layer316disposed on the phase change material314, and a top electrode318disposed on the buffer layer316.

It is notable that the configuration of phase change memory device stack304shown inFIG.3is merely an example that is being provided to illustrate the present techniques for forming the protective BxNy/BzOmbilayer on the sidewalls of the phase change material314. Thus, it is to be understood that the techniques described herein are more generally applicable to any phase change memory having a phase change material with exposed sidewalls, and should not be construed as being limited to any particular phase change memory configuration(s).

Suitable materials for the bottom electrode306include, but are not limited to, metals such as titanium (Ti), tantalum (Ta), cobalt (Co), ruthenium (Ru), tungsten (W) and/or aluminum (Al), metal nitrides such as titanium nitride (TiN), tantalum nitride (TaN), tungsten nitride (WN) and/or aluminum nitride (AlN) and/or a doped semiconductor, which can be deposited onto the substrate302using a process such as chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), sputtering, evaporation, electrochemical plating, etc. According to an exemplary embodiment, the bottom electrode306has a thickness of from about 10 nm to about 50 nm and ranges therebetween.

Buffer layer308provides an etch stop for subsequent patterning of the phase change memory device stack304and serves to prevent intermixing of the phase change memory device stack304materials. Suitable buffer layer308materials include, but are not limited to, carbon (C), silicon carbide (SiC), silicon (Si), tantalum (Ta), tantalum nitride (TaN), tantalum carbide (TaC), tungsten (W), tungsten nitride (WN), tungsten carbide (WC), titanium (Ti), titanium nitride (TiN) and/or titanium carbide (TiC), which can be deposited using a process such as CVD, ALD or PVD. According to an exemplary embodiment, buffer layer308has a thickness of from about 10 nm to about 30 nm and ranges therebetween. Further, while shown as a single layer, buffer layer308can optionally be composed of multiple layers, each one containing at least one of the above-provided materials.

As will be described in detail below, the present phase change memory devices can include an array of phase change memory cells arranged in a cross-point configuration between a plurality of first/second metal lines positioned below/above the phase change memory cells. With such a cross-point array, one of the phase change memory cells will be present at each intersection of the first and second metal lines. In that regard, OTS310aids in the selection of an individual one of the phase change memory cells in the array. Namely, OTS310is placed in series with the phase change material314and acts as a switch that, with an applied current, switches from a highly resistive state to a conductive state. When the current is removed, OTS310returns to its highly resistive state.

Suitable materials for the OTS310include, but are not limited to, arsenic selenium germanium silicon (AsSeGeSi), arsenic selenium germanium silicon carbide (AsSeGeSiC), arsenic selenium germanium silicon nitride (AsSeGeSiN), arsenic selenium germanium silicon tellurium (AsSeGeSiTe), arsenic selenium germanium silicon tellurium sulfide (AsSeGeSiTeS), arsenic tellurium germanium silicon (AsTeGeSi) and/or arsenic tellurium germanium silicon nitride (AsTeGeSiN), which can be deposited using a process such as CVD, ALD or PVD. According to an exemplary embodiment, OTS310has a thickness of less than or equal to about 50 nm, e.g., from about 10 nm to about 45 nm and ranges therebetween.

Like buffer layer308, buffer layer312provides an etch stop and serves to prevent intermixing of the phase change memory device stack304materials. Suitable buffer layer312materials include, but are not limited to, C, SiC, Si, Ta, TaN, TaC, W, WN, WC, Ti, TiN and/or TiC, which can be deposited using a process such as CVD, ALD or PVD. According to an exemplary embodiment, buffer layer312has a thickness of from about 10 nm to about 30 nm and ranges therebetween. Further, while shown as a single layer, buffer layer312can optionally be composed of multiple layers, each one containing at least one of the above-provided materials.

As provided above, a wide variety of materials can be employed as phase change material314in accordance with the present techniques. For instance, according to an exemplary embodiment, phase change material314is a chalcogenide alloy that includes the chalcogenide element Te, in addition to other elements such as Sb and/or Ge, e.g., Sb2Te3, GeTe, and/or Ge2Sb2Te5. Alternatively, embodiments are also contemplated herein where phase change material314is a non-chalcogenides material such as, but not limited to, GaSb and/or Ge—Sb based alloys. Furthermore, additional elements such as Ag, In, N, Si and/or Bi can be added to any of the above phase change materials to optimize their properties.

In one exemplary embodiment, the phase change material314is deposited using a process such as PVD or CVD. Of course, the specific targets (PVD) or precursors (CVD) for the deposition process depend on the particular phase change material being formed. For example, when physical vapor deposition (PVD) is used to deposit Ge2Sb2Te5the most common source is a Ge2Sb2Te5target. Alternatively, separate elemental Ge, Sb and Te targets can also be used by adjusting the flux from each target to obtain the desired composition. In another exemplary embodiment, molecular beam epitaxy is used to deposit Ge2Sb2Te5. When molecular beam epitaxy is used, the sources may be individual Knudsen effusion cells. Namely, each cell contains one of the alloy elements (Ge, Sb or Te), and the flux of each element is controlled by the effusion cell temperature. In one exemplary implementation, the deposition of phase change material314is performed at a high substrate temperature, for example, at a substrate temperature of from about 150 degrees Celsius (° C.) to about 300° C. and ranges therebetween. For instance, with Ge2Sb2Te5the preferred substrate temperature range is from about 175° C. to about 200° C. and ranges therebetween to produce the crystalline form of Ge2Sb2Te5. By contrast, a room temperature deposition would generally yield an amorphous material when Ge2Sb2Te5is deposited. However, some phase change materials such as Sb2Te3would be crystalline even at deposition temperatures below 100° C. According to an exemplary embodiment, the phase change material314has a thickness of from about 5 nm to about 50 nm and ranges therebetween.

Like buffer layers308and312above, buffer layer316provides an etch stop and serves to prevent intermixing of the phase change memory device stack304materials. Suitable buffer layer316materials include, but are not limited to, C, SiC, Si, Ta, TaN, TaC, W, WN, WC, Ti, TiN and/or TiC, which can be deposited using a process such as CVD, ALD or PVD. According to an exemplary embodiment, buffer layer316has a thickness of from about 10 nm to about 30 nm and ranges therebetween. Further, while shown as a single layer, buffer layer316can optionally be composed of multiple layers, each one containing at least one of the above-provided materials.

Suitable materials for the top electrode318include, but are not limited to, metals such as Ti, Ta, Co, Ru, W and/or Al, metal nitrides such as TiN, TaN, WN and/or AlN, and/or a doped semiconductor, which can be deposited using a process such as CVD, ALD, PVD, sputtering, evaporation, electrochemical plating, etc. According to an exemplary embodiment, the top electrode318has a thickness of from about 5 nm to about 20 nm and ranges therebetween.

Standard lithography and etching techniques are then used to pattern the phase change memory device stack304into at least one individual phase change memory cell404. SeeFIG.4. With standard lithography and etching techniques, a lithographic stack (not shown), e.g., photoresist/anti-reflective coating/organic planarizing layer, is used to pattern a hardmask402with the footprint and location of the phase change memory cell(s)404to be patterned in the phase change memory device stack304. Suitable hardmask402materials include, but are not limited to, silicon nitride (SiN), silicon dioxide (SiO2), titanium nitride (TiN) and/or silicon oxynitride (SiON). An etch is then performed to transfer the pattern from hardmask402to the underlying phase change memory device stack304. Alternatively, hardmask402can be formed by other suitable techniques, including but not limited to, sidewall image transfer (SIT), self-aligned double patterning (SADP), self-aligned quadruple patterning (SAQP), and other self-aligned multiple patterning (SAMP). A directional (i.e., anisotropic) etching process such as reactive ion etching can be employed for the stack etch.

As shown inFIG.4, the phase change memory device stack304is patterned down to the bottom electrode306. Thus, each phase change memory cell404formed includes the bottom electrode306, a patterned portion of the buffer layer308(given reference numeral308′), a patterned portion of the OTS310(given reference numeral310′), a patterned portion of the buffer layer312(given reference numeral312′), a patterned portion of the phase change material314(given reference numeral314′), a patterned portion of the buffer layer316(give reference numeral316′), and a patterned portion of the top electrode318(given reference numeral318′). It is notable that the patterning of phase change memory device stack304can involve a series of reactive ion etching steps for which buffer layers308,312and/or316can serve as etch stops, as highlighted above.

Patterning of the phase change memory device stack304leaves the sidewalls of the phase change material314′ exposed to oxygen. As described in detail above, oxidation of the phase change material can undesirably lead to changes in its crystallization temperature and composition, both of which impact the switching behavior of the phase change material. Thus, as shown inFIG.5, the techniques described in conjunction with the description of methodology100ofFIG.1and methodology200ofFIG.2are employed to form a boron-containing and nitrogen-containing bilayer502on the sidewalls of the phase change material314′ that advantageously serves to encapsulate and protect the phase change material from exposure to oxygen. By this process the boron-containing and nitrogen-containing bilayer502can also form on the sidewalls of the OTS310′, as shown inFIG.5.

Referring to magnified view504, according to an exemplary embodiment, the boron-containing and nitrogen-containing bilayer502includes a BzOmlayer506(where, e.g., 1≤z≤5 and 1≤m≤5) disposed on the sidewalls of the phase change material314′, and a BxNylayer508(where, e.g., 1≤x≤5 and 1≤y≤5) disposed on the BzOmlayer506. The boron-containing and nitrogen-containing bilayer502is thin. For example, in one embodiment, the BzOm506layer has a thickness of from about 2 nm to about 25 nm and ranges therebetween, and the BxNylayer508has a thickness of from about 2 nm to about 25 nm and ranges therebetween. In that case, the total thickness of the BxNy/BzOm, bilayer is from about 4 nm to about 50 nm and ranges therebetween.

Namely, as provided above, boron-containing and nitrogen-containing bilayer502can be formed, in accordance with the present techniques, by contacting the phase change memory cell(s)404with boron-containing and nitrogen-containing plasmas under conditions (e.g., duration, flow rate, etc.) sufficient to form the boron-containing and nitrogen-containing bilayer502(e.g., BxNy/BzOm) on the sidewalls of the phase change material314′. Namely, boron is an oxygen getter. Thus, exposure of the phase change memory cell(s)404to the boron-containing and nitrogen-containing plasmas initially form a BzOmlayer on the sidewalls of the phase change material which reduces the phase change material sidewall oxide. A layer of BxNythen forms on top of the BzOmlayer to passivate the surface and protect the sidewalls of the phase change material from air exposure.

For instance, as described above, deposition of the boron-containing and nitrogen-containing bilayer502(e.g., BxNy/BzOm) can be carried out in a PECVD processing chamber with a sequence of boron-containing and/or nitrogen-containing gaseous precursors to generate the respective plasmas within the PECVD processing chamber. One such exemplary sequence is detailed in methodology200ofFIG.2, above. With that sequence, a 3-step process is performed using B2H6+N2/H2, N2/H2(and purge), and N2/H2plasmas, which is then repeated for multiple cycles.

Specifically, using the sequence of methodology200as a non-limiting, illustrative example, the (patterned) phase change memory cell(s)404are placed into a PECVD processing chamber. The boron-containing and nitrogen-containing bilayer502(e.g., BxNy/BzOm) is then formed on the sidewalls of the phase change material314′ by introducing a combination of boron-containing and (first) nitrogen-/hydrogen-containing gaseous precursors, e.g., B2H6+N2/H2, to the PECVD processing chamber for a duration of from about 2 seconds to about 4 seconds and ranges therebetween. According to an exemplary embodiment, a flow rate of the B2H6gaseous precursor is from about 500 seem to about 550 seem and ranges therebetween, a flow rate of the N2gaseous precursor is from about 900 seem to about 950 seem and ranges therebetween, and a flow rate of the H2gaseous precursor is from about 100 seem to about 150 seem and ranges therebetween. These gaseous precursors generate boron-containing and nitrogen-containing plasmas in the PECVD chamber that are contacted with the phase change memory cell(s)404.

Next, a (second) nitrogen-/hydrogen-containing gaseous precursor, e.g., N2/H2, is then introduced to the PECVD processing chamber for a duration of from about 5 seconds to about 7 seconds and ranges therebetween, after which the PECVD processing chamber is purged of the gaseous precursors. According to an exemplary embodiment, a flow rate of the N2gaseous precursor is from about 900 seem to about 950 seem and ranges therebetween, and a flow rate of the H2gaseous precursor is from about 100 seem to about 150 seem and ranges therebetween. This gaseous precursor is used to generate a nitrogen-containing plasma in the PECVD chamber that is contacted with the phase change memory cell(s)404.

Following the purging of the PECVD processing chamber, another (third) nitrogen-/hydrogen-containing gaseous precursor, e.g., N2/H2, is introduced to the PECVD processing chamber for a duration of from about 5 seconds to about 7 seconds and ranges therebetween. According to an exemplary embodiment, a flow rate of the N2gaseous precursor is from about 900 seem to about 950 seem and ranges therebetween, and a flow rate of the H2gaseous precursor is from about 100 seem to about 150 seem and ranges therebetween. This gaseous precursor is used to generate a nitrogen-containing plasma in the PECVD chamber that is contacted with the phase change memory cell(s)404. These 3 steps are then preferably repeated (e.g., 10 times) to build up the BxNy/BzOmbilayer on the sidewalls of the phase change material314′. Without being bound by any theory in particular, it is thought that by depositing BxNylayer by layer, the first few BxNywill form a rich oxygen containing film (i.e., BzOm) due to the trapping of oxygen by boron. Once this oxygen-rich layer is created, the remainder of the film will grow as BxNy, thereby forming the present BxNy/BzOmbilayer.

As will be described in detail below, forming the present boron-containing and nitrogen-containing bilayer502on the sidewalls of the phase change material314′ vastly improves its switching properties, as compared to untreated samples. For instance, improved switching properties include switching speeds that are significantly greater than the untreated samples.

FromFIG.5it can be seen that the present phase change memory cell404structure includes the phase change material314′ between the bottom electrode306and the top electrode318′. The sidewalls of the phase change material314′ are protected by the boron-containing and nitrogen-containing bilayer502. Also present between the bottom electrode306and the top electrode318′ is the OTS310′ in series with the phase change material314′. The buffer layers308′,312′ and316′ are present below the OTS310′, between the OTS310′ and the phase change material314′, and above the phase change material314′, respectively.

As highlighted above, one configuration of the present phase change memory device contemplated herein is as a cross-point array of the phase change memory cells404. See, for example,FIG.6. As shown inFIG.6, an exemplary cross-point array600includes a plurality of first metal lines602oriented orthogonal to a plurality of second metal lines604. Phase change memory cells404are located between the first metal lines602and the second metal lines604. To look at it another way, the first metal lines602are present below phase change memory cells404and the second metal lines604are present above phase change memory cells404. Further, the array of phase change memory cells404is arranged such that one of the phase change memory cells404is present at the intersection of each given first metal line602and second metal lines604. Thus, each of the phase change memory cells404can be individually accessed via the respective first and second metal lines602and604. While not explicitly shown in FIG.6, it is to be understood that each of the phase change memory cells404shown therein is configured as described above, and includes a protective boron-containing and nitrogen-containing bilayer502on the sidewalls of the phase change material314′, an OTS310′ in series with the phase change material314′, buffer layers308′,312′ and316′ below the OTS310′, between the OTS310′ and the phase change material314′, and above the phase change material314′, respectively, etc.

The present techniques are now further described by way of reference to the following non-limiting examples. For instance, plot700A inFIG.7Aprovides secondary ion mass spectroscopy (SIMS) data that show elemental (germanium (Ge), antimony (Sb), tellurium (Te), boron (B), nitrogen (N) and oxygen (O)) depth profiling of a sample phase change memory material (GST) before treatment (labeled “Reference”), as compared to plot700B inFIG.7Bwhich provides SIMS data that show elemental (germanium (Ge), antimony (Sb), tellurium (Te), boron (B), nitrogen (N) and oxygen (O)) depth profiling of the sample phase change memory material (GST) after the present boron-containing and nitrogen-containing plasma treatment to form the boron-containing and nitrogen-containing bilayer on the sidewalls of the sample phase change memory material (labeled “BN treated”). Plots700A and700B are log scale graphs.

Notably, by comparingFIG.7A(before treatment) andFIG.7B(after treatment), it can be seen that the oxygen profile differs for the untreated versus treated samples. Namely, in the Reference (untreated) plot700A the oxygen profile goes up closer to the surface—likely from oxidation of the phase change memory material, whereas in the BN treated plot700B, the oxygen profile drops at the near surface (or sidewall) region, forming a barrier for oxygen.

FIG.8is a plot800illustrating enhancements in switching speed that are achieved using the present BxNy/BzOmprotective bilayer on the sidewalls of the phase change memory device material. Specifically, plot800compares the switching speed (based on crystallization fraction and pulse width) of a reference phase change memory cell with an untreated Ge2Sb2Te5(GST) phase change material—no protective bilayer (labeled “Reference”) and another phase change memory cell having a 5 nm BxNy/BzOmprotective bilayer on the sidewalls of the GST phase change material (labeled “5 nm BN on GST”). As shown in plot800, the sample having the BxNy/BzOmprotective bilayer exhibited a significantly faster switching speed than the untreated reference sample.