Patent ID: 12245530

While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

DETAILED DESCRIPTION

Aspects of the present disclosure relate to phase change memory and, more specifically, to gradually changing the conductance of the phase change memory through a concentric ring-shaped heater. While the present disclosure is not necessarily limited to such applications, various aspects of the disclosure may be appreciated through a discussion of various examples using this context.

A phase change memory (PCM) may include a bottom electrode and a top electrode with a phase change material between the two. As discussed above, conventional phase change memories (PCMs) and their corresponding phase change materials have two states—amorphous and crystalline. The amorphous state may be referred to as a RESET state and the crystalline state may be referred to as a SET state. To switch the phase change material between the two states, the PCM may also include a heater (sometimes called the bottom electrode contact) that sends current pulses through the heater (from the electrode) and into the phase change material. When the phase change material is in a crystalline state, the heater may convert the material into an amorphous state by sending short high current pulses to rapidly heat the phase change material and then quenching or cooling it. When the phase change material is in an amorphous state, the heater may convert the material into a crystalline state by sending a longer, but lower current, pulse(s) to heat the phase change material to a crystallization temperature for a prolonged period of time (without cooling the material) to allow for the material to become crystalline.

When the phase change material (of the phase change memory) is in an amorphous state (or a RESET state), the phase change material may have a high resistivity and a low conductivity (i.e., high electrical resistivity and low electrical conductivity), and current may not travel quickly through the phase change material. Alternatively, when the phase change material is in a crystalline state (or a SET state), the phase change material may have a low resistivity and a high conductivity (i.e., low electrical resistivity and high electrical conductivity), and current may travel quickly through the phase change material. The data may be stored in the phase change memory (PCM) using the contrast between the resistances of the two states (or phases). Further, each state may correspond to a binary value, with an amorphous state corresponding to a 0 and a crystalline state corresponding to a 1. PCM has many benefits, such as increased speeds (compared to other types of memory), non-volatile capabilities, less power requirements, etc., however, conventional PCMs may have abrupt changes between the phases, particularly at the amorphous state (i.e., an abrupt change to the RESET state).

Resistance, as referred to herein, may be an electrical resistance, and may refer to the objection or opposition of current flow through an object. Resistivity, as referred to herein, may be an electrical resistivity, and may refer to the resistance (i.e., electrical resistance) per unit area of an object and/or material. Resistivity may, for example, be calculated using the magnitude of the electric field and the magnitude of the current density (i.e., the magnitude of the electric field divided by the magnitude of the current density). Resistance may be calculated, for example, by multiplying the resistivity by the length of the object and/or material and dividing by the cross-sectional area of the object and/or material. When resistivity remains constant, the resistance of an object can be changed by changing the length, width, etc. of the object. For example, a titanium nitride (TiN) material may have different amounts of resistance depending on the length, width, etc. of the TiN object, however the resistivity of TiN may remain the same.

Similarly, conductance, as referred to herein, may be an electrical conductance, and may refer to the ease of current flow through an object (i.e., how easily current flows through an object). Conductivity, as referred to herein, may be an electrical conductivity, and may refer to the conductance (i.e., electrical conductance) per unit area of an object and/or material. When conductivity remains constant, the conductance of an object can be changed by changing the length, width, etc. of the object. Resistivity and conductivity are intrinsic properties, whereas resistance and conductance are extrinsic properties.

In PCMs, when current travels through the heater, heat is generated (for instance, through the Joule heating effect) and the heat can change the phase of the phase change material from a crystalline to an amorphous phase (or vice versa, depending on the amount of heat and whether there is a quench). Therefore, the greater the electrical conductance or the lesser the electrical resistance (referred to herein as conductance and resistance, respectively), the greater the flow of current traveling through the heater and the greater the amount of heat generated from the flowing current.

PCM has many possible applications, such as analog computing, cognitive computing, neuromorphic applications, etc. However, in various applications, it may be desired to have a PCM with multiple states, instead of just an amorphous state and a crystalline state. For instance, it may be desired to have a PCM with phase-change materials that are in a partially amorphous state and a partially crystalline state. Having multiple states may allow for a more gradual transition between the different conductance (for example, between the high conductance of the crystalline state and the low conductance of the amorphous state), which may be beneficial for many PCM applications. For instance, conventional PCMs may abruptly change between crystalline and amorphous states, however the gradual transition between the states and their corresponding conductance values may accelerate multiply and accumulate operations as well as achieve a symmetrical (and gradual) long-term depression and long-term potentiation (which may be very beneficial for PCM applications such as cognitive computing, neuromorphic applications, etc.). In conventional PCMs, it may be difficult to progressively and gradually increase and decrease the conductance of the PCM as at least the RESET phase (i.e., changing to the amorphous state) is typically very abrupt.

The present disclosure provides a ring-shaped heater, a system, and a method for gradually changing the conductance of the phase change memory through a concentric ring-shaped heater. The concentric ring-shaped heater may have multiple concentric layers of heating material (i.e., heating layers), and each heating layer may be separated by an insulator layer. With these different layers as well as the concentric shape the layers are in, the multiple heating layers (in the single heater) may act similar to multiple PCMs in parallel. This allows for each individual heating layer to have different levels of conductance and/or resistance, which then transfers different amounts of heat to different areas of the phase change material (of the PCM).

For example, a heating layer with a high conductance may rapidly heat the phase change material in the area near the specific heating layer (as greater amounts of current flow are travelling through the specific heating layer, therefore generating more heat), which may change the phase change material in this area from a crystalline solid to an amorphous solid (as crystalline solids may be converted to amorphous solids by rapidly heating them and then quenching or cooling them). This way, when one portion of the phase change material (of the PCM) is RESET to an amorphous state with high resistance, other portions of the phase change material may still be in a crystalline state due to the amount of heat and conductance from heating layers near those portions of the phase change material. Amorphous solids may be converted to crystalline solids by keeping the material (for example, the phase change material) at a crystallization temperature for a prolonged period of time, or at least enough time for the material to become crystallized, without cooling the material. Therefore, in another example, if a phase change material is in an amorphous state, portions of the material could be converted to a crystalline state if the specific heating layer(s) in that area maintained a crystallization temperature for a prolonged period of time without cooling. Through the concentric ring-shaped heater, there may be more phases (such as intermediate phases with both crystalline and amorphous areas) and the transitions between phases of the phase change material is more gradual, while the physics of the phase change material (such as the melting point, boiling point, etc.) are not fundamentally changed.

Referring now toFIG.1A, an example phase change memory100with a concentric ring-shaped heater is depicted, according to some embodiments.FIG.1Apresents a cross-sectional view of the phase change memory100. Phase change memory100includes a substrate170, a bottom electrode160, a heater130, a phase change material120, and a top electrode110. The substrate170may be a semiconductor substrate, in some instances. In some instances, the substrate170may include other devices such as transistors, isolation structures, contacts, etc. The phase change memory100includes two electrodes—a bottom electrode160and a top electrode110—with a phase change material120between the two. The electrodes110and160may send electrons and currents back and forth, ultimately sending the currents into the phase change material120, which may alter its state (i.e., to an amorphous state and/or crystalline state). In some embodiments, the bottom electrode160is smaller than the top electrode110so that more current/heat enters the phase change material120from the bottom electrode160and changes the phase of the phase change material120at the area closest to the bottom electrode160. In some embodiments, the bottom electrode160and/or the top electrode110are made of a metal material such as copper, tungsten, titanium nitride (TiN), etc.

The phase change material120is a material that is able to change from a crystalline phase to an amorphous phase and vice versa. Example phase change materials120include germanium-antimony-tellurium (or Ge2Sb2Te5, referred to herein as GST), GeTe/Sb2Te3, or any other alternative materials.

The heater130(sometimes called a bottom electrode contact) is located between the bottom electrode160and the phase change material120. Because the heater130makes contact with both the bottom electrode160and the phase change material120, the heater130is able to channel the current from the bottom electrode160and expose the phase change material120to the current from the bottom electrode160at the contact point between the heater130and the phase change material120(i.e., concentrate the current at the contact point). In some embodiments, the bottom electrode160and the heater130may be referred to together as a heating electrode.

Put in different terms, the bottom portion of heater130is proximately connected to the top portion of bottom electrode160. The top portion of heater130is proximately connected to the bottom portion of the phase change material120. Lastly, the top portion of the phase change material120is proximately connected to the top electrode110.

As used herein, the term “proximately connected” describes a connection between two components in relation the remainder of one of those components. For example, heater130can be described as proximately connected to the bottom end of phase change material120as compared to the top end of the phase change material120because heater130is connected more directly to the bottom end of phase change material120than the top end. Thus, even though heater130may have an electrical connection to both the top and bottom ends of phase change material120, heater130is more directly connected to the bottom portion of phase change material120that the top portion of phase change material120. By this reasoning, therefore, heater130is proximately connected to the bottom portion of phase change material120, as illustrated.

FIG.1Bdepicts a second view of heater130, according to some embodiments. As discussed herein, in conventional PCMs, the phase change material may abruptly change from SET to RESET (i.e., crystalline to amorphous) or vice versa, without any gradual change between phases. However, in some instances, it is desirable to have a gradual change between the phases, as the gradual change may introduce more phases (which may introduce multibit storage), accelerate operations such as multiply and accumulate, etc. Heater130enables a gradual change between phases of the phase change material120, through the concentric ring-shape and the multiple layers of the heater130. For instance, heater130includes heating layers150a,150b, and150c(referred to collectively as heating layers150) that transmit heat (i.e., current) from the bottom electrode160to the phase change material120. Each heating layer150is separated by an insulator spacer (or layer)140a,140b, and/or140c(referred to collectively as insulator spacers140). The insulator spacers140are made of insulator material with a high resistance (for example, higher than the conductive heating layers), therefore preventing and/or reducing current from the bottom electrode160to the phase change material120through the insulator spacers140. In some embodiments, the insulator spacers140are made of a solid material. In some embodiments, the insulator spacers140are made of silicon nitride (SiN), silicon dioxide (SiO2), or any other insulator material. The heating layers150may be made of titanium nitride (TiN), tantalum nitride (TaN), titanium, copper, tungsten, or any other conductor material.

In some embodiments, different insulator spacers140may comprise different materials. For example, insulator spacer140amay be a SiN spacer, insulator spacer140bmay be a SiO2spacer, and insulator spacer140cmay again be a SiN spacer. Similarly, in some embodiments, different heating layers150may comprise different materials. For example, heating layer150amay comprise TiN, heating layer150bmay comprise TaN, and heating layer150cmay comprise titanium. The different materials may have different conductivities and resistivities, which may result in various heating layers150having different conductivities. For example, titanium has a lower conductivity than TiN and TaN, TiN has a higher conductivity than titanium but a lower conductivity than TaN, and TaN has a higher conductivity than both TiN and titanium. Having heating layers150with different materials of different conductivities may allow more or less current/heat from the bottom electrode160to reach the phase change material, depending on the material(s)—and the corresponding resistivities and/or conductivities—of the heating layer150. This may result in different portions of the phase change material120(for example, corresponding to the heating layer150they are nearest to) having different levels of resistance and/or resistivity and, in some instances, different phases.

In some embodiments, the heating layers150may have different compositions. For instance, even if each heating layer150is made up of TiN, various heating layers150may include different amounts of titanium and nitrogen, therefore changing the compositions of the components within the heating layers150. For example, heating layers150with higher compositions of titanium may have higher conductivity (and lower resistivity) compared to heating layers150with higher compositions of nitrogen.

In some embodiments, the heating layers150may have various thicknesses and/or lengths. Changing the thicknesses and/or lengths of the heating layers150may change the conductance of the various heating layers150. For example, heating layers150with a greater thickness may transfer more current/heat than thinner heating layers150. Similarly, in another example, heating layers150with shorter lengths between the bottom electrode160and the phase change material120may transfer current/heat more quickly than longer heating layers150, which may expose the phase change material120to more heat/current in areas with heating layers150with shorter lengths. This is discussed further herein in relation toFIG.17.

Further, as depicted inFIG.1B, each heating layer150and insulator spacer140may be in a concentric ring shape. This concentric ring shape includes an insulator core (i.e., insulator spacer140a) and alternating layers of heating layers150and insulator spacers140. The concentric ring-shape, the plurality of heating layers150, and the insulator spacers140between each heating layer150allow each heating layer150to execute in parallel, and act similar to multiple resistors running in parallel. This may allow each heating layer150(or at least multiple heating layers150) to execute with different resistance (or conductance) levels, which then results in different areas of the phase change material120being exposed to the current (and the corresponding heat generated from the current) from the heater at different amounts, times, etc. which allows the phase change material120to more gradually change between phases. Although heater130has three heating layers150and three insulator spacers140, the heater130may have any number of heating layers150and insulator spacers140(as long as there is an insulator spacer140separating each heating layer150).

In some embodiments, as depicted inFIG.1A, top electrode110, phase change material120, heater130, and bottom electrode160are surrounded by (for example, encapsulated in) a dielectric125. The dielectric125may act as an electric insulator to prevent the current and heat from the electrodes110and160and the heater130to transfer to any other materials in a computer system (as the phase change memory100may be one component within a computer system).

Referring toFIG.2, a first intermediary step200of depositing a dielectric layer is depicted, according to some embodiments. In some instances,FIGS.2-9depict the steps to form a phase change memory with a concentric ring-shaped heater (depicted inFIG.10, for instance). In some embodiments,FIGS.2-9depict the steps to form phase change memory100(FIG.1).FIGS.2-9may depict a cross-sectional view of forming the phase change memory with the concentric ring-shaped heater. The components of the phase change memory depicted inFIGS.2-9may not be to scale, and instead may be enlarged to better illustrate the phase change memory and its formation.

To form a PCM with a concentric ring-shaped heater, the PCM may start with a substrate270. The substrate270may be a semiconductor substrate, in some instances, and may include other devices (e.g., transistors, isolation structures, contacts, etc.). A bottom electrode260may be formed on top of the substrate270, for example using a complementary metal-oxide semiconductor (CMOS) back end of the line (BEOL) damascene process. The bottom electrode260is surrounded by dielectric265aand265b(referred to collectively as dielectric265), for instance to protect the bottom electrode260and preventing any other components of the computer system (i.e., outside of the PCM) from being exposed to the current/heat from the bottom electrode260. As an example, the bottom electrode260may be tungsten and may be surrounded by a low-k dielectric.

To start forming the heater portion of the PCM, a second dielectric225may be deposited on top of the bottom electrode260and the existing dielectric265. In some embodiments, dielectric225and dielectric265may be made up of silicon nitride (SiN), silicon dioxide (SiO2), or any other dielectric material. In some embodiments, dielectric265and dielectric225may be different materials. In some embodiments, dielectric265and dielectric225may be the same material. In some instances, when dielectric265and dielectric225are the same material, the bottom electrode260may not initially be surrounded by dielectric265, and instead dielectric265may be deposited at the same time as dielectric225.

Referring toFIG.3, a second intermediary step300of creating a via opening is depicted, according to some embodiments. Once the dielectric225is deposited on top of the bottom electrode260(and in some instances, the dielectric265), the dielectric225may be patterned to form a via opening210. This may separate the dielectric225into dielectric225aand225b(referred to collectively as dielectric225). For instance, the dielectric225may be etched to create the via opening210directly above the bottom electrode260.

Referring toFIG.4, a third intermediary step400of depositing conductive heating and insulator spacer layers is depicted, according to some embodiments. Once the dielectric225has been patterned and the via opening210(FIG.3) has been created, the layers of conductive heating and insulator spacers can be deposited. First, a conductive heating layer230may be deposited so that the conductive heating layer230has contact with the bottom electrode260. Then an insulator spacer235may be deposited on top of the conductive heating layer230. This process may repeat, alternating between conductive heating layers and insulator spacers.FIG.4depicts two conductive heating layers230and240, and two insulator spacers235and245, but any number of conductive heating layers and insulator spacers may be used. For example, there may be five conductive heating layers and five insulator spacers.

In some embodiments, each layer (i.e., the conductive heating layers230and240and the insulator spacers235and245) may be deposited through a cyclic deposition. A cyclic deposition deposits the material in a circle and/or closed curve, such that each layer is its own closed curve. Deposition techniques such as atomic layer deposition (ALD), chemical vapor deposition (CVD), and/or laser induced chemical vapor disposition (LCVD) may be used to deposit the conductive heating layers230and240and the insulator spacers235and245. In some embodiments, each layer may be deposited individually. By using cyclic deposition techniques to deposit each layer, each layer may form a concentric ring-shape.

In some embodiments, one or more of the conductive heating layers may be different thicknesses, different materials, etc. This way, each conductive heating layer230and240may have a different conductance and resistance, which may help vary the quickness and/or amount of the phase change material that changes stages (i.e., between crystalline and amorphous). This is further discussed herein.

Referring toFIG.5, a fourth intermediary step500of depositing a sacrificial layer of insulator material is depicted, according to some embodiments. When the layers (230,235,240, and245) are deposited (depicted inFIG.4), an opening should remain in the middle of the concentric ring-shape of the layers so that there is room to deposit the sacrificial layer280. Sacrificial layer280may be deposited using the same cyclic deposition methods used inFIG.4. In some embodiments, a sacrificial layer280is essentially a placeholder layer that is used to help create and/or hold a spot for future materials. The sacrificial layer280may be selectively removed, or entirely removed, as other materials are put in its place. In this instance, the sacrificial layer280is used to help create an opening to expose each of the heating layers230and240to the bottom electrode260and to act as a placeholder for future conductor materials. These steps will be further discussed herein. The thickness of the sacrificial layer280may be used to determine the size of the opening (discussed further herein, and depicted inFIG.6). Therefore, the thickness of the sacrificial layer280may be predetermined (e.g., by the system and/or a user) in order to have a proper sized opening. In some embodiments, the sacrificial layer280is an insulator material such as SiN or SiO2. In some embodiments, the sacrificial layer280is an insulator material different than the insulator spacer245, so that when sacrificial layer280is removed in future steps (discussed further herein), the removal process does not also remove insulator spacer245.

Referring toFIG.6, a fifth intermediary step600of patterning an opening290through the layers is depicted, according to some embodiments. As discussed above, the thickness of the sacrificial layer280may define the size of the opening290. As depicted inFIG.5, there is a small opening in the middle of the sacrificial layer280. The layers230,235,240,245, and the sacrificial layer280may be patterned in order to extend the opening290created by the sacrificial layer280. For example, the layers may be etched through, starting with the sacrificial layer, then the insulator spacer245, the conductive heating layer240, and then the insulator spacer235, so that an opening is created all the way down to conductive heating layer230.

Additionally, the top side portions of the layers245,240,235, and sacrificial layer280may be etched such that the conductive heating layer230is the only layer with a portion extending over the dielectric225aand225b. This may result in two sides of each layer—235aand235bof insulator spacer235,240aand240bof conductive heating layer240,245aand245bof insulator spacer245, and280aand280bof sacrificial layer280—separated by the opening290.

In some embodiments, the etching of the portions of the layers245,240,235, and sacrificial layer280may be executed using reactive-ion etching (RIE). In some embodiments, a cyclic RIE (for example, a SiN RIE followed by a cyclic TiN/SiO2RIE when the conductive heating layer240comprises TiN, the insulator spacers235and245comprise SiO2, and the sacrificial layer280comprises SiN) may be executed, cyclically removing the portion of each layer one by one. In some embodiments, the opening290may be patterned prior to the RIE (or another form of etching). In some embodiments, the RIE may occur prior to patterning the opening290. In some embodiments, patterning the opening and conducting the RIE may occur concurrently.

Referring toFIG.7, a sixth intermediary step700of removing the sacrificial layer280is depicted, according to some embodiments. A portion of the sacrificial layer280may have already been removed using an etching method such as RIE (discussed above). However, two portions of the sacrificial layer280aand280bremained, separated by the opening290, as depicted byFIG.6.FIG.7depicts the partially formed phase change memory after the removal of the sacrificial layers280aand280b. In some embodiments, the remaining portions of the sacrificial layer280aand280bmay be removed using RIE, buffered oxide etching, or other forms of etching. In some embodiments, the sacrificial layer280may be made of a different material than the insulator spacer245. For example, the sacrificial layer280may comprise silicon nitride (SiN) and the insulator spacer245may comprise silicon oxide (SiO2). In these instances, the sacrificial layer280may be removed using wet etching methods to selectively remove the sacrificial layer280without removing the insulator spacer245. For example, hydrogen fluoride or phosphoric acid may be used to selectively wet etch the silicon nitride sacrificial layer280without removing the silicon oxide insulator spacer245. Once the sacrificial layer280is removed, there may be an opening290extending to the conductive heating layer230and a larger opening292in the areas that the sacrificial layer280previously sat.

Referring toFIG.8, a seventh intermediary step800of depositing a conformal coating250of a conductor material is depicted, according to some embodiments. The conformal coating250may fill the opening, or via,290and may partially fill the larger opening, or via,292. In some embodiments, the conformal coating250is a conductor material (for example, TiN). In some embodiments, the conformal coating250is a same conductor material as one or more of the conductive heating layers230and240. By filling the opening290, the conformal coating250may expose each of the conductive heating layers230and240to the bottom electrode260. This allows for any currents transmitted from the bottom electrode260to transmit through the conductive heating layers230and240and the conformal coating250. The conformal coating250may conform to the contours and openings of the existing portions of the phase change memory, which may allow the conformal coating250to fill the opening290. The conformal coating250may be deposited using similar methods as the previous layer depositions (discussed inFIGS.4and5) such as atomic layer deposition (ALD), chemical vapor deposition (CVD), and/or laser induced chemical vapor disposition (LCVD).

Referring toFIG.9, an eighth intermediary step900of removing some portions of the layers and depositing an insulator core is depicted, according to some embodiments. Intermediary step900may include etching the top side portions of the conformal coating250as well as any remaining portions of the layers230,235,240, and245that remain above the dielectric225. The etching may be executed using the same or similar methods as discussed above in relation toFIG.6. The etching may result in conformal coating250acting as another conductive heating layer, therefore conformal coating250may also be referred to as conductive heating layer250. Further, by etching any excess layers230,235,240,245, and250, the heating component (comprising conductive heating layers230,240, and250as well as insulator spacers235, and245) may be in a concentric ring-shape.

In addition to etching any excess layers230,235,240,245, and250, the remaining opening, or via, may be filled with an insulator material. This results in an insulator core255at a center of the concentric ring-shaped heater (comprising conductive heating layers230,240, and250as well as insulator spacers235, and245and the insulator core255). In some embodiments, the insulator core255is composed of the same material as the dielectric225. The insulator core255may prevent too much current from being transmitted to the phase change material, which helps make the change between phases more gradual.

In some embodiments, once the opening is filled with the insulator core255, the surfaces of the phase change memory may be polished (for example, using chemical mechanical polishing (CMP)), this may smooth any exposed surfaces, particularly the top surfaces of the dielectric225, conductive heating layers230,240, and250, insulator spacers235and245, and insulator core255, as these surfaces have been etched at different times and sometimes even repeatedly etched. Polishing the surfaces may smooth out any slight imperfections due to the etching.

Referring toFIG.10, a fully formed phase change memory1000with a concentric ring-shaped heater is depicted, according to some embodiments. Once the concentric ring-shaped heater (comprising conductive heating layers230,240, and250as well as insulator spacers235, and245and the insulator core255) is formed, the heater may be topped with a phase change material (here, GST220) and a top electrode210. In this exemplary instance, the phase change material is GST220, however GST220may be replaced with other comparable phase change materials.

In phase change memory1000, each of the conductive heating layers230,240, and250are exposed to the bottom electrode260through the conductive stud275(which is the filled opening that was previously opening290). Through conductive stud275, each conductive heating layer230,240, and250may transmit current into GST220(which is the phase change material). The portions of GST220that are exposed to the current may change phases, in some instances. This is further discussed inFIG.11.

Insulator spacers235and245as well as insulator core255may prevent GST220from being exposed to too much current, which could result in an abrupt change between phases. For example, if exposed to too much current, GST220may abruptly change from a crystalline phase to an amorphous phase, which may not be beneficial for certain phase change memory applications. Phase change memory1000may allow for a gradual change of phases for GST220.

Although phase change memory1000depicts only dielectric265and dielectric225, the top electrode210and the GST220may also be surrounded by dielectric, similar to phase change memory100(FIG.1). Additionally, phase change memory1000is a cross-sectional view of the phase change memory. In a top down view of phase change memory1000, the heater (comprising conductive heating layers230,240, and250as well as insulator spacers235, and245and the insulator core255) has a concentric ring-shape similar or the same as heater130(FIG.1).

Referring toFIG.11, a phase change memory1100with a phase change material with both crystalline and amorphous phases is depicted, according to some embodiments. As discussed herein, a concentric ring-shaped heater (for instance, comprising conductive heating layers230,240, and250as well as insulator spacers235, and245and the insulator core255) enables a more gradual transition of phases for GST220. In addition, the concentric ring-shaped heater may enable more phases of GST220, such as intermediate phases with both crystalline phases and amorphous phases. Phase change memory1100and GST220depicts an exemplary intermediate phase.

As discussed herein, the conductive heating layers230,240, and250may be different materials, thicknesses, etc., which may affect the conductance and resistance of each conductive heating layer230,240, and250. This means that the current from the bottom electrode260may not be exposed to the GST220at the same amounts and/or the same speeds based on how the current is transmitted through each conductive heating layer. For example, conductive heating layer230may be made up of a material that has more resistivity than conductive heating layers240and250. Therefore, in this example, conductive heating layer230may resist some of the current from bottom electrode260and may not transmit as much current to GST220as conductive heating layers240and250. Therefore, as depicted inFIG.11, the GST220may be crystalline and not amorphous in the areas near conductive heating layer230because heating layer230may not transmit enough current to change the phase of GST220to amorphous.

However, in this example, the materials of conductive heating layers240and250may be more conductive and less resistive than conductive heating layer230, and more current may have been transmitted from the bottom electrode260to the GST220through these layers, resulting in amorphous areas1112,1102,1104, and1114in the areas of the GST220near conductive heating layers240and250. Further, amorphous areas1102and1104are larger than amorphous areas1112and1114. In this example, this may be because conductive heating layer250is made of a material even more conductive than conductive heating layer240. Therefore, although the same amount of current may have been transmitted from bottom electrode260, conductive heating layer230may have blocked the most amount of current from reaching GST220(due to the resistivity of the material of layer230), conductive heating layer240may have blocked some of the current from reaching GST220(due to the greater conductivity than layer230but lesser conductivity than layer250), and conductive heating layer250may have transmitted the most current through to GST220(due to the greater conductivity than the other layers). Amorphous areas1102and1104may have been exposed to the most current/heat from layer250, therefore they may be larger than amorphous areas1112and1114.

In another example, conductive heating layers240and250may comprise the same materials, however conductive heating layer250may have a greater width (i.e., may be more thick) than conductive heating layer240. In this example, amorphous areas1102and1104may have formed more quickly than amorphous layers1112and1114, because areas1102and1104of GST220may have been exposed to a larger area of current through conductive heating layer250(so areas1102and1104may have been more rapidly heated and then quenched through conductive heating layer250) compared to conductive heating layer240. As conductive heating layer240is made of the same material (and has the same conductance and resistance) as conductive heating layer250, areas1112and1114of GST220do become amorphous, however it make take a longer period of time than the time to form amorphous areas1102and1104, due to the lower area of contact between conductive heating layer240and GST220. Therefore, amorphous areas1102and1104are larger than amorphous areas1112and1114.

Referring toFIG.12, an array1200of phase change memory cells is depicted, according to some embodiments. In some instances (for example, in neuromorphic computing), a system may include multiple phase change memory cells1210a-i(referred to collectively as phase change memory cells1210). Each phase change memory cell1210may correspond to phase change memory100(FIG.1), phase change memory1000(FIG.10), and/or phase change memory1100(FIG.11). Phase change memory cells1210could also correspond to phase change memory1400(FIG.14) and/or phase change memory1500(FIG.15), in some instances). Phase change memory array1200may have inputs1-mand outputs1-nwith an array of phase change memory cells1210in between.

Referring toFIG.13, an intermediate step1300of a second exemplary phase change memory1400(FIG.4) with a concentric ring-shaped heater is depicted, according to some embodiments. Phase change memory1000(FIG.10) and1100(FIG.11) may be an exemplary phase change memory with a concentric ring-shaped heater, however there may be alternative structures of a phase change memory with a concentric ring-shaped heater. Phase change memory1400(FIG.4) is one alternative structure to a phase change memory with a concentric ring-shaped heater. Intermediate step1300is an intermediate phase of forming phase change memory1400. In intermediate step1300, there is a substrate1370, bottom electrode1360, dielectric1365aand1365b(referred to collectively as dielectric1365, as well as dielectric1325aand1325b(referred to collectively as dielectric1325. These may correspond to substrate270, bottom electrode260, dielectric265, and dielectric225, respectively (fromFIGS.2-11).

However, unlike intermediate step400(FIG.4) where each layer is distributed on top of each other without adjusting the previous layer, intermediate step1300may deposit conductive heating layer1330and then insulator spacer1335similar (or the same as) intermediate step400, but then may selectively remove portions of the insulator spacer1335before distributing any additional layers. For instance, as depicted, the bottom and top side portions of insulator spacer1335have been selectively removed so that only the side portions1335aand1335bremain. Without any selective removal, insulator spacer1335may have looked the same or similar to insulator spacer235(FIGS.2-11). In some instances, the portions of insulator spacer1335are selectively removed through a RIE. In some instances, the portions of insulator spacer1335may be selectively removed using etching techniques such as buffered oxide etching, hydrogen fluoride etching, phosphoric acid etching, or any other method of etching.

Once only portions1335aand1335bremain on insulator spacer1335, conductive heating layer1340may be distributed (for example, the same way conductive heating layer1330was distributed). By selectively removing insulator spacer1335, conductive heating layer1340is in direct contact with conductive heating layer1330, and is therefore able to receive current from bottom electrode1360through conductive heating layer1330. This may eliminate the need for a sacrificial layer280(as depicted inFIG.5), patterning an opening through the layers (as depicted inFIG.6), and depositing a conformal coating to form stud250(as depicted inFIG.8andFIG.10) to connect the conductive heating layers to the bottom electrode.

Once each conductive heating layer1330and1340are deposited, an insulator layer1350is deposited on top of the heating layer1340and fills the opening in the center. Insulator layer1350acts as the insulator core (and may be referred to as insulator core1350).

Although only two conductive heating layers1330and1340and only one insulator spacer1335are depicted, there may be any number of conductive heating layers. Each conductive heating layer may be separated by an insulator spacer, and each insulator spacer may be selectively removed (similar/the same as insulator spacer1335) so that each conductive heating layer has direct contact to the conductive heating layer below it.

Referring toFIG.14, the second exemplary phase change memory1400with a concentric ring-shaped heater is depicted, according to some embodiments. In some embodiments, phase change memory1400is the fully formed phase change memory that was in the process of being formed at intermediate phase1300(depicted inFIG.13). Before phase change memory is fully formed (as depicted in phase change memory1400), the portions of conductive heating layers1330and1340as well as insulator core1350that sit on top of dielectric1325may be removed (similar to intermediary step900(FIG.9) and/or intermediary step600(FIG.6)). Further, in some instances, the materials may be polished (for example, using CMP) prior to depositing GST1320and the top electrode1310. In phase change memory1400, the heater is still a concentric ring-shaped heater, however, unlike phase change memory1000(FIG.10) and/or1100(FIG.11), each conductive heating layer1330and1340has direct contact with each other on the bottom portion of the heater, therefore the current from the bottom electrode1360is able to reach each conductive heating layer (e.g.,1340) through the first conductive heating layer1330.

Referring toFIG.15, a third exemplary phase change memory1500with a concentric ring-shaped heater is depicted, according to some embodiments. Phase change memory1500may be similar to phase change memory1400and may be formed in a similar manner. For example, substrate1570, bottom electrode1560, dielectric1565, dielectric1525, conductive heating layer1530, insulator spacer1535, and conductive heating layer1540may correspond to substrate1370, bottom electrode1360, dielectric1365, dielectric1325, conductive heating layer1330, insulator spacer1335, and conductive heating layer1340(FIG.13andFIG.14) respectively. Further, insulator core1555may correspond to insulator core1350(FIGS.13and14). Phase change memory1500includes an additional conductive heating layer1550and an additional insulator spacer1545, however these layers may be deposited and selectively removed in the same, or similar, methods as conductive heating layers1330and1340and insulator spacer1335(FIG.13).

However, unlike in phase change memory1400(FIG.14), in phase change memory1500conductive heating layer1530may be patterned and/or etched to shorten its length. In some embodiments, conductive heating layer1530may be etched before depositing insulator spacer1535. In some embodiments, conductive heating layer1530may be etched after all the other layers have been deposited and etched or patterned, but before polishing. Although only conductive heating layer1530has been shortened, any of the conductive heating layers may be shortened. When a conductive heating layer has been shortened, the length of the insulator spacers (such as insulator spacer1535) may also be adjusted in order to maintain a cohesive shape of the concentric ring-shaped heater.

Additionally, as discussed herein, the conductive heating layers may be different widths. In phase change memory1500, conductive heating layer1530has a larger width and conductive heating layers1540and1550have a smaller (i.e., thinner) width. Because conductive heating layer1530has a greater width, more of PCM1520may be exposed to current in those areas, so PCM1520may change phases more quickly in the areas near conductive heating layer1530. Further, conductive heating layer1530is shorter in length than the other conductive heating layers, therefore the PCM1520may be exposed to current even more quickly (and may change phases even more quickly) because conductive heating layer1530has a higher conductance than conductive heating layers1540and1550.

Referring toFIG.16, a flowchart of an exemplary method1600for forming a phase change memory with a concentric ring-shaped heater is depicted, according to some embodiments. In some embodiments, method1600may be an overall method for forming a phase change memory (such as phase change memory100(FIG.1), phase change memory1000(FIG.10), phase change memory1100(FIG.11), phase change memory1400(FIG.14), and/or phase change memory1500(FIG.15).

Method1600includes operation1610to form a bottom electrode on top of a semiconductor substrate. In some instances, the bottom electrode is formed on top of the semiconductor substrate using a CMOS BEOL damascene process. In some embodiments, this operation may correspond to intermediate step200(FIG.2).

Method1600includes operation1615to deposit a dielectric layer on top of the bottom electrode. This may correspond to intermediate step300(FIG.3). In some embodiments, as depicted inFIG.2andFIG.3, a preexisting dielectric may surround either side of the bottom electrode, and the dielectric layer may be deposited on top of the preexisting dielectric and the bottom electrode. In some embodiments, depositing the dielectric layer may include depositing the dielectric surrounding the bottom electrode (e.g., dielectric265(FIG.2)).

Method1600includes operation1620to pattern the dielectric layer to create a via opening. The dielectric may initially be deposited in a large layer (for example, as depicted inFIG.2) and the dielectric may need to be patterned to create an opening for the concentric layers to be deposited within. In some embodiments, operation1620corresponds to intermediate step300(FIG.3).

Method1600includes operation1625to cyclically deposit a plurality of conductive heating layers and operation1630to deposit a plurality of insulator spacers. In some embodiments, (for example, when operation1625corresponds to intermediate step400(FIG.4)) operations1625and1630may be executed concurrently with alternating layers of conductive heating layers and insulator spacers being deposited. In some embodiments (for example, when forming phase change memory1400(FIG.14) and/or phase change memory1500(FIG.15)), a first conductive heating layer may be cyclically deposited and then a first insulator spacer may be cyclically deposited, and then the first insulator spacer may be selectively removed so that that the second conductive heating layer, when it is deposited, has direct contact with the first conductive heating layer. These steps may be repeated for each conductive heating layer and each insulator spacers so that each conductive heating layer has contact with the previous heating layer and is able to receive current transmitted from the bottom electrode. In some embodiments, after a conductive heating layer is deposited, it may be patterned and/or etched to shorten the length.

In some embodiments, when a phase change memory such as phase change memory1000(FIG.10) and/or phase change memory1100(FIG.11) is formed, method1600may further include depositing a sacrificial layer of insulator material leaving a small opening in the center, extending the opening by patterning through the conductive heating layers and the insulator spacers (resulting in an opening that extends to the first conductive heating layer), etching the side portions of the layers so that the first conductive heating layer is the only layer with a portion extending over the dielectric, removing the remainder of the sacrificial layer, and/or depositing a conformal coating to fill the patterned opening (creating a stud) and partially coat the exposed layers. This may correspond to intermediate steps300-800(FIGS.3-8) discussed herein. These steps may be skipped when each insulator layer is selectively removed (discussed above).

In some embodiments, method1600may include depositing an insulator core (not depicted inFIG.16). When the phase change memory is formed as depicted inFIGS.2-10, depositing an insulator core may correspond to intermediate step900(FIG.9). In these instances, operation1635may occur prior to depositing the insulator core so that any portions of the layers (i.e., conductive heating layers and insulator spacers) that extend above the dielectric layer may be removed and then the insulator core may be deposited at the center of the concentric rings/layers.

In some embodiments, when a phase change memory is formed as depicted inFIGS.13and14, and/or15, an insulator layer may be deposited (as discussed herein) on top of a top concentric heating layer, and this insulator layer may act as the insulator core and the final insulator spacer. In these instances, operation1635may occur after the insulator layer/core is deposited (as depicted inFIGS.13and14) so that the top side portions of the insulator layer are removed with the other layers.

Method1600includes operation1635to remove portions of the plurality of conductive heating layers from the dielectric layer. To form the final concentric ring-shape of the heater, excess portions of the layers may be removed. In some instances, such as when the insulator layers have previously been selectively removed, only portions of the conductive heating layers may be removed. In some instances, both excess portions of conductive heating layers and excess portions of insulator spacers may be removed in this operation. In some embodiments, removing portions of the conductive heating layers and/or the insulator spacers may include etching any portions of the layers that are above the dielectric. In some instances, operation1635corresponds to intermediary step900(FIG.9).

Method1600includes operation1640to deposit a phase change memory material and operation1645to deposit a top electrode. The phase change material (or phase change memory material) may be deposited or formed using similar, or the same, methods as forming the bottom electrode and the semiconductor substrate. In some instances, the phase change memory material and/or the top electrode may be patterned to remove any excess portions.

Method1600is only one possible method of forming a phase change memory with a concentric ring-shaped heater.

The present invention may be a system, a method, etc. at any possible technical detail level of integration. The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to some embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the blocks may occur out of the order noted in the Figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions.

The descriptions of the various embodiments of the present disclosure have been presented for purposes of illustration but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.