Phase Change Memory Cell Resistive Liner

Abstract

A phase change memory (PCM) cell includes a first electrode, a heater electrically connected to the first electrode, a PCM material electrically connected to the heater, a second electrode electrically connected to the PCM material, and a resistive liner in direct contact with and electrically connected to a sidewall of the heater and the PCM material.

Description

[Technical Field]

[0001] The present invention relates to computer memory, and more particularly to a phase change material memory device having a resistive liner. [Background technology]

[0002] Phase change memory (PCM) can be utilized for both training and inference in analog computing for artificial intelligence. PCM structures can include phase change memristive devices with tunable conductivity and high overall device resistance with high retention to minimize energy consumption. This tuning can be a result of creating an amorphous phase within the PCM material. However, the resistance of PCM materials can change over time, which can adversely affect the integrity of stored data. Summary of the Invention

[0003] According to one embodiment of the present disclosure, a phase change memory (PCM) cell includes a first electrode, a heater electrically connected to the first electrode, a PCM material electrically connected to the heater, a second electrode electrically connected to the PCM material, and a resistive liner in direct contact with and electrically connected to a sidewall of the heater and the PCM material.

[0004] According to one embodiment of the present disclosure, a method of manufacturing a PCM cell includes forming a first electrode, forming a first electrically insulating layer on the first electrode, forming a resistive liner on the first electrically insulating layer, forming a heater extending from the first electrode and through the first electrically insulating layer and the resistive liner, forming a PCM material on the heater and the resistive liner, and forming a second electrode on the PCM material.

[0005] According to one embodiment of the present disclosure, a PCM cell includes a first electrode, a heater in direct contact and electrical connection with the first electrode, a PCM material in direct contact and electrical connection with the heater, a second electrode in direct contact and electrical connection with the PCM material, and a first resistive liner in direct contact and electrical connection with the heater and the PCM material.

[0006] According to one embodiment of the present disclosure, a PCM cell includes a first electrode, a heater electrically connected to the first electrode, a PCM material electrically connected to the heater, a second electrode electrically connected to the PCM material, and a resistive liner in direct contact with and electrically connected to a sidewall of the heater, the resistive liner having an L-shaped cross-section with a first leg extending along the sidewall of the heater and a second leg extending outward from the heater.

[0007] According to one embodiment of the present disclosure, a method of manufacturing a PCM cell includes forming a first electrode, forming a first electrically insulating layer on the first electrode, forming a heater extending from the first electrode and through the first electrically insulating layer, forming a resistive liner on the first electrically insulating layer and on a portion of the heater whereby the portion of the heater is not covered by the resistive liner, forming a PCM material on the heater and the resistive liner, and forming a second electrode on the PCM material.

[0008] Preferred embodiments of the present invention will now be described, by way of example only, and with reference to the following drawings, in which: [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view of a PCM cell including a resistive liner according to one embodiment of the present disclosure. [Figure 2A] 1A-1C are a series of cross-sectional views of a PCM cell and the flow of electricity therethrough in different states, according to one embodiment of the present disclosure. [Figure 2B]1A-1C are a series of cross-sectional views of a PCM cell and the flow of electricity therethrough in different states, according to one embodiment of the present disclosure. [Figure 2C] 1A-1C are a series of cross-sectional views of a PCM cell and the flow of electricity therethrough in different states, according to one embodiment of the present disclosure. [Figure 3A] 2B is a schematic representation of the electrical pathway of FIG. 2A according to one embodiment of the present disclosure. [Figure 3B] 2C is a schematic representation of the electrical pathway of FIG. 2B according to one embodiment of the present disclosure. [Figure 3C] 2D is a schematic representation of the electrical pathway of FIG. 2C according to one embodiment of the present disclosure. [Figure 4A] 1A-1C are a series of cross-sectional views of a method for fabricating a PCM cell according to one embodiment of the present disclosure. [Figure 4B] 1A-1C are a series of cross-sectional views of a method for fabricating a PCM cell according to one embodiment of the present disclosure. [Figure 4C] 1A-1C are a series of cross-sectional views of a method for fabricating a PCM cell according to one embodiment of the present disclosure. [Figure 4D] 1A-1C are a series of cross-sectional views of a method for fabricating a PCM cell according to one embodiment of the present disclosure. [Figure 4E] 1A-1C are a series of cross-sectional views of a method for fabricating a PCM cell according to one embodiment of the present disclosure. [Figure 4F] 1A-1C are a series of cross-sectional views of a method for fabricating a PCM cell according to one embodiment of the present disclosure. [Figure 4G] 1A-1C are a series of cross-sectional views of a method for fabricating a PCM cell according to one embodiment of the present disclosure. [Figure 5] FIG. 10 is a cross-sectional view of an alternative PCM cell having an alternative resistive liner according to one embodiment of the present disclosure. [Figure 6A] 1A-1C are a series of cross-sectional views of an alternative PCM cell in one of different states and the flow of electricity therethrough, according to an embodiment of the present disclosure. [Figure 6B]1A-1C are a series of cross-sectional views of an alternative PCM cell in one of different states and the flow of electricity therethrough, according to an embodiment of the present disclosure. [Figure 6C] 1A-1C are a series of cross-sectional views of an alternative PCM cell in one of different states and the flow of electricity therethrough, according to an embodiment of the present disclosure. [Figure 7A] 1A-1C are a series of cross-sectional views of a method for fabricating an alternative PCM cell according to one embodiment of the present disclosure. [Figure 7B] 1A-1C are a series of cross-sectional views of a method for fabricating an alternative PCM cell according to one embodiment of the present disclosure. [Figure 7C] 1A-1C are a series of cross-sectional views of a method for fabricating an alternative PCM cell according to one embodiment of the present disclosure. [Figure 7D] 1A-1C are a series of cross-sectional views of a method for fabricating an alternative PCM cell according to one embodiment of the present disclosure. [Figure 7E] 1A-1C are a series of cross-sectional views of a method for fabricating an alternative PCM cell according to one embodiment of the present disclosure. [Figure 7F] 1A-1C are a series of cross-sectional views of a method for fabricating an alternative PCM cell according to one embodiment of the present disclosure. [Figure 7G] 1A-1C are a series of cross-sectional views of a method for fabricating an alternative PCM cell according to one embodiment of the present disclosure. [Figure 7H] 1A-1C are a series of cross-sectional views of a method for fabricating an alternative PCM cell according to one embodiment of the present disclosure. [Figure 8] FIG. 10 is a cross-sectional view of another alternative PCM cell having another alternative resistive liner according to an embodiment of the present disclosure. [Figure 9] FIG. 10 is a cross-sectional view of another alternative PCM cell having another alternative resistive liner according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] Various embodiments of the present disclosure are described herein with reference to the associated drawings. Alternate embodiments may be devised without departing from the scope of the present disclosure. It is noted that various connections and relationships (e.g., over, below, adjacent, etc.) are described between elements in the following description and drawings. These connections and / or relationships may be direct or indirect unless otherwise specified, and the present disclosure is not intended to be limiting in this respect. Thus, a connection of entities may refer to a direct or indirect connection, and a relationship between entities may be a direct or indirect relationship. As an example of an indirect relationship, a reference in this description to forming layer "A" over layer "B" includes a situation in which one or more intermediate layers (e.g., layers "C" and "D") are between layer "A" and layer "B," as long as the associated properties and functions of layer "A" and layer "B" are not substantially altered by the intermediate layer(s).

[0011] The following definitions and abbreviations are used for understanding the claims and the specification. As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having," "contains," or "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, mixture, process, method, article, or device comprising a list of elements is not necessarily limited to only those elements, but may include other elements not expressly listed or inherent in such composition, mixture, process, method, article, or device. Furthermore, any numerical ranges contained herein include their limits unless expressly stated otherwise.

[0012] For purposes of the following description, the terms “upper,” “lower,” “right,” “left,” “vertical,” “horizontal,” “top,” “bottom,” and derivatives thereof, refer to the described structures and methods as oriented in the drawing figures. The terms “overlying,” “atop,” “on top,” “positioned on,” or “positioned atop” mean that a first element, such as a first structure, is above a second element, such as a second structure, and that an intervening element, such as an interfacial structure, may be present between the first and second elements. The term “direct contact” means that a first element, such as a first structure, and a second element, such as a second structure, are connected without an intermediate conductive, insulating, or semiconducting layer at the interface of the two elements. It should be noted that the term "selective to," such as "a first element selective to a second element," means that the first element can be etched and the second element can act as an etch stop.

[0013] For the sake of brevity, conventional techniques related to semiconductor device and integrated circuit (IC) fabrication may or may not be described in detail herein. Additionally, various tasks and process steps described herein may be incorporated into more comprehensive procedures or processes having additional steps or functions not described in detail herein. In particular, because the various steps in the fabrication of semiconductor devices and semiconductor-based ICs are well known, for the sake of brevity, many conventional steps will only be briefly described herein or will be omitted entirely without providing well-known process details.

[0014] Generally, the various processes used to form microchips that will be packaged into ICs fall into four general categories: film deposition, removal / etching, semiconductor doping, and patterning / lithography.

[0015] Deposition can be any process that grows, coats, or otherwise transfers material onto a wafer. Available techniques include physical vapor deposition (PVD), chemical vapor deposition (CVD), electrochemical deposition (ECD), molecular beam epitaxy (MBE), and more recently, atomic layer deposition (ALD), among others. Another deposition technique is plasma-enhanced chemical vapor deposition (PECVD), a process that uses energy in a plasma to induce reactions on the wafer surface that would normally require the high temperatures associated with conventional CVD. Energetic ion bombardment during PECVD deposition can also improve the electrical and mechanical properties of the film.

[0016] Removal / etching can be any process that removes material from a wafer. Examples include etch processes (wet or dry), chemical mechanical planarization (CMP), and the like. One example of a removal process is ion beam etching (IBE). Generally, IBE (or milling) refers to a dry plasma etch method that utilizes a remote broad-beam ion / plasma source to remove substrate material by physically inert gas means, chemically reactive gas means, or both. Like other dry plasma etch techniques, IBE offers benefits such as etch rate, anisotropy, selectivity, uniformity, aspect ratio, and minimal substrate damage. Another example of a dry removal process is reactive ion etching (RIE). Generally, RIE uses a chemically reactive plasma to remove material deposited on the wafer. With RIE, plasma is generated under low pressure (vacuum) by an electromagnetic field. High-energy ions from the RIE plasma attack and react with the wafer surface, removing material.

[0017] Semiconductor doping generally involves modifying electrical properties by diffusion or ion implantation, or both, for example, by doping the source and drain of a transistor. These doping processes are followed by furnace annealing or rapid thermal annealing (RTA). The annealing serves to activate the implanted dopants. Films, both conductors (e.g., polysilicon, aluminum, copper, etc.) and insulators (e.g., various forms of silicon dioxide, silicon nitride, etc.), are used to connect and isolate transistors and their components. Selective doping of various regions of a semiconductor substrate allows the substrate's conductivity to change with the application of voltage. By creating structures of these various components, millions of transistors can be constructed and wired together to form the complex circuitry of modern microelectronic devices.

[0018] Semiconductor lithography can be the formation of three-dimensional relief images or patterns on a semiconductor substrate for subsequent transfer of the pattern to a substrate. In semiconductor lithography, the patterns are formed with a light-sensitive polymer called photoresist. The lithography and etch pattern transfer steps are repeated multiple times to build the many wires that connect the millions of transistors in the complex structures and circuits that make up transistors. Each pattern printed on the wafer is aligned with the previous pattern, gradually building up conductors, insulators, and selectively doped regions to form the final device.

[0019] 1 is a cross-sectional view of a PCM cell 100 for use, for example, in an integrated circuit (not shown). In the illustrated embodiment, the PCM cell 100 includes a bottom electrode 102, a heater 104, an insulator 106, a resistive liner 108, a spacer 110, a PCM material 112, and a top electrode 114. The heater 104 is in direct contact with and electrically connected to the bottom electrode 102 at a bottom end, and the heater 104 extends upward from the bottom electrode 102 to an opposite top end. A bottom portion of the heater 104 is surrounded by an insulator 106, which is in direct contact with the sidewalls of the heater 104 and the top of the bottom electrode 102. The insulator 106 is also in direct contact with the underside of the resistive liner 108, which is in direct contact with and electrically connected to the heater 104. The heater 104 extends through the resistive liner 108 and the spacer 110, both of which surround and are in direct contact with the sidewalls of the heater 104. The bottom of the spacer 110 is in direct contact with the top of the resistive liner 108, and the top end of the heater 104 shares a boundary (i.e., is flush with) the top end of the spacer 110. The PCM material 112 extends over and is in direct contact with the spacer 110, the resistive liner 108, the insulator 106, and the heater 104. The PCM material 112 is thereby electrically connected to the top end of the heater 104 and to the outside of the resistive liner 108. The top side of the PCM material 112 is also in direct contact with and is electrically connected to the top electrode 114.

[0020] In the illustrated embodiment, the cross-section of the PCM cell 100 (entering the page in FIG. 1 ) may be square, but in other embodiments, the cross-section may be rectangular, oval, circular, or any other suitable shape. Furthermore, the widths of the PCM material 112 and the top electrode 114 are the same, while the width of the heater 104 is substantially reduced (e.g., 3-7 times smaller or about 5 times smaller). The PCM cell 100 may thereby be said to have a mushroom configuration, allowing current to flow from the bottom electrode 102 to the top electrode 114 through the heater 104, resistive liner 108, and PCM material 112. Furthermore, the PCM cell 100 may be electrically connected to a substrate 116 of the bottom electrode 102 and a via 118 of the top electrode 114. The substrate 116 may be, for example, an integrated circuit component such as a field-effect transistor, and the via 118 may be, for example, a metal interconnect.

[0021] In the illustrated embodiment, the bottom electrode 102 and the top electrode 114 are composed of a highly electrically conductive material, such as a metal or metal compound, e.g., titanium nitride (TiN) or tungsten (W). The heater 104 is composed of TiN or a highly resistive metal, e.g., titanium tungsten (TiW), tantalum nitride (TaN), or titanium aluminide (TiAl), and is an electrode with a relatively narrow cross-sectional area that targets the current passed through the PCM cell 100. This allows the heater 104 to generate heat through resistive heating during electrical pulses, which can be used to selectively change the temperature of the PCM material 112, e.g., above the crystallization and melting temperatures of the PCM material 112. Additionally, the heater 104 can be composed of multiple different electrically conductive materials, which can be arranged in multiple layers.

[0022] In the illustrated embodiment, the insulator 106 and spacers 110 are composed of a dielectric (electrically insulating) material, such as, for example, silicon nitride (SiN), silicon oxide (SiO), or silicon carbonitride (SiNC). In some embodiments, the insulator 106 is the same material as the spacers 110, while in other embodiments, the insulator 106 is a different material than the spacers 110. The resistive liner 108 is composed of a conductive material that typically has a higher resistivity than commonly used pure metal conductors, such as copper (Cu), aluminum (Al), titanium (Ti), gold (Au), or silver (Ag). Such materials can be, for example, aluminum nitride (AlN), boron nitride (BN), aluminum oxide (AlO), TaN, TiN, tungsten nitride (WN), cobalt tungsten (CoW), nickel tungsten (NiW), or yttrium oxide (YO). The resistance of the resistive liner 108 is substantially greater (e.g., 5 to 50 times greater, or about 20 times greater) than the resistance of the heater 104. Furthermore, the resistance of the resistive liner 108 is substantially greater (e.g., 10 to 40 times greater, or about 20 times greater) than the resistance of the low-resistivity polycrystalline state PCM material 112 and substantially less (e.g., 5 to 50 times less, or about 10 times less) than the resistance of the high-resistivity amorphous state PCM material 112. The resistivity of the resistive liner 108 can be, for example, 0.1 ohm-micrometer (Ωμm) to 1 kiloohm-micrometer (kΩμm).

[0023] In the illustrated embodiment, the PCM material 112 consists essentially of a phase change material such as germanium antimony telluride (GST), gallium antimony telluride (GaST), or silver iridium antimony telluride (AIST) material, although other materials may be used as desired. Examples of other PCM materials can include, but are not limited to, germanium telluride materials (GeTe), silicon antimony tellurium (Si-Sb-Te) alloys, gallium antimony tellurium (Ga-Sb-Te) alloys, germanium bismuth tellurium (Ge-Bi-Te) alloys, indium tellurium (In-Se) alloys, arsenic antimony tellurium (As-Sb-Te) alloys, silver indium antimony tellurium (Ag-In-Sb-Te) alloys, Ge-In-Sb-Te alloys, Ge-Sb alloys, Sb-Te alloys, Si-Sb alloys, Ge-Te alloys, and combinations thereof. The PCM material 112 can be undoped or doped (e.g., doped with one or more of oxygen (O), nitrogen (N), silicon (Si), or Ti). The terms "composed essentially" or "consist essentially" as used herein with respect to materials in different layers indicate that other materials, if present, do not substantially alter the basic properties of the listed materials. For example, a PCM material 112 consisting essentially of GST material does not include other materials that substantially alter the basic properties of the GST material.

[0024] In the illustrated embodiment, the PCM cell 100 can be operated as a memory cell by passing a current pulse from the bottom electrode 102 to the top electrode 114 to program the PCM cell 100. This can be done at various voltages and / or for various durations to read or write values ​​to the PCM cell 100. For example, to write, a high voltage (e.g., 1 volt (V) to 4 V) can be used for a short duration, which can allow the heater 104 to locally heat the PCM material 112 above its melting point. When the current flow stops, the PCM material 112 can rapidly cool, which forms an amorphous zone 120 in a process called "resetting." The zone 120 is a dome-shaped region of the PCM material 112 that has an amorphous configuration, while the remainder of the PCM material 112 is still in a polycrystalline configuration. Generally, this amorphous configuration has no defined structure. However, localized, loose crystalline nuclei (i.e., small crystallized regions of the phase change material 112) may exist within the zones 120. The creation of the zones 120 can increase the electrical resistance across the PCM cell 100 compared to a polycrystalline-only configuration (such as the PCM cell 100 of FIG. 2A). These resistance values ​​of the PCM cell 100 can be read without changing the state of the PCM material 112 (including the PCM material 112 of the zones 120) or the resistance value of the PCM cell 100, for example, by sending a low voltage (e.g., 0.2 V) current pulse from the bottom electrode 102 to the top electrode 114.

[0025] Additionally, the PCM material 112 can be rewritten back to a polycrystalline-only configuration by "setting" the PCM cell 100. One method of rewriting the PCM material 112 uses a high-voltage (e.g., 1 V-4 V) electrical pulse for a short duration (e.g., 10 nanoseconds (ns)) that can heat the PCM material 112 above its crystallization point, but not to its melting point. Because the crystallization temperature is lower than the melting temperature, when the current is stopped, the PCM material 112 can anneal and form crystals. Another method of rewriting the PCM material 112 uses an electrical pulse with a relatively long (e.g., 1 microsecond) trailing edge (as opposed to a square pulse with a relatively short trailing edge on the order of nanoseconds) that is strong enough to heat the PCM material 112 above its melting point, after which the PCM material 112 is slowly cooled, allowing crystals to form. Either of these processes reduces the electrical resistance across the PCM cell 100 compared to having an amorphous zone 120 (as in the PCM cell 100 of FIG. 1). This new resistance value can then be read using a low voltage (e.g., 0.2 V) current without changing the state of the PCM material 112 or the resistance value of the PCM cell 100.

[0026] In some embodiments, the melting temperature of the PCM material 112 is approximately 600°C. In some embodiments, the crystallization temperature of the PCM material 112 is approximately 180°C. Furthermore, the process of setting and resetting the PCM cell 100 can occur iteratively, and in some embodiments, different zones 120 with different resistances can be created within the PCM material 112 (e.g., by having different sized zones 120 and / or different amounts of crystallization nuclei within the zones 120, as shown in FIGS. 2B and 2C). This allows the PCM cell 100 to have a variety of distinct resistances that can be created by varying the reset parameters. Thus, if the PCM cell 100 is considered to represent digits of information, these digits can be non-binary (as opposed to traditional bits). However, in some embodiments, the PCM cell 100 can be used as a bit by having or not having uniform zones 120 within the PCM material 112. In such an embodiment, the PCM cell 100 can have a high resistance (also known as a low voltage output or a "0") or a low resistance (also known as a high voltage output or a "1").

[0027] The components and configuration of the PCM cell 100 allow for the inclusion of the resistive liner 108 while still allowing the heater 104 to directly contact the PCM material 112. This prevents the resistive liner 108 from affecting the programming of the PCM cell 100 (e.g., changing the set resistance), as would be the case if the resistive liner 108 were perfectly positioned between the heater 104 and the PCM material 112. Additionally, the spacer 110 reduces the contact area between the heater 104 and the PCM material 112 to only the size of the top of the heater 104. This reduces the amount of contact area between the heater 104 and the PCM material 112 so that the electricity flowing from the heater 104 is concentrated. This allows the electrical pulse to have a lower power because there is a small area of ​​the PCM material 112 that is melted or crystallized during resetting or setting, respectively. This is in contrast to a situation where the spacer 110 is not present so that the PCM material 112 contacts the top and sides of the heater 104, and the electrical pulse would require high power to affect the phase of the PCM material 112.

[0028] 2A-2C are a series of cross-sectional views of the PCM cell 100 in different states and the electrical flow therethrough. FIGS. 3A-3C are schematic representations of the electrical paths of FIGS. 2A-2C, respectively. More specifically, the PCM material 112 is exclusively polycrystalline in FIGS. 2A and 3A, the PCM material 112 has small amorphous zones 120 in FIGS. 2B and 3B, and the PCM material 112 has large amorphous zones 120 in FIGS. 2C and 3C. Accordingly, FIGS. 2A-2C and 3A-3C are discussed in conjunction with one another.

[0029] In the illustrated embodiment, the electrical resistance of the resistive liner 108 is between the electrical resistance of the PCM material 112 in the polycrystalline phase and the electrical resistance of the PCM material 112 in the amorphous phase (due to zone 120). For example, the resistance of the amorphous phase PCM material 112 may be 100 times greater than the resistance of the crystalline phase PCM material 112. In such embodiments, the resistance of the resistive liner 108 may be, for example, 10 to 40 times greater than the resistance of the crystalline phase PCM material 112. In some embodiments, the resistance of the resistive liner 108 may be, for example, about 20 times greater than the resistance of the crystalline phase PCM material 112. For example, if the crystalline resistance of the PCM material 112 may be between 10 kΩ and 100 kΩ, the amorphous resistance of the PCM material 112 may be between 1 megaohm (MΩ) and 10 MΩ, and the resistance of the resistive liner 108 may be between 200 kΩ and 2 MΩ.

[0030] As is well known in the art, electricity will flow through all available paths. When a set of parallel paths have similar resistance, electricity will flow in similar amounts through those paths. However, if the paths have significantly different resistances, electricity will flow more substantially through the low resistance path(s). In such a situation, the overall resistance of the set of parallel paths will be dominated by the resistance of the low resistance path(s).

[0031] In the embodiment shown in FIG. 2A , the PCM material 112 is only in the polycrystalline phase. Because the heater 104 is a conductive material and the insulator 106 is not, the electrical pulse will flow substantially along path 122 from the bottom electrode 102 through the heater 104. Because the crystalline PCM material 112 is a better conductor than the resistive liner 108, path 122 extends directly through the PCM material 112 to the top electrode 114. The reason path 122 is the dominant electrical path is illustrated in FIG. 3A , which shows the PCM cell 100 as a physical schematic on the left and an electrical schematic on the right. As discussed above, the electrical pulse travels from the bottom electrode BE to the top electrode TE, and the resistance of the crystallized PCM material C is lower than the resistance of the resistive liner L and the insulator I. Therefore, path 122 extends through the PCM material C.

[0032] In the embodiment shown in FIG. 2B , the PCM material 112 includes a small amorphous zone 120. Because the heater 104 is a conductive material and the insulator 106 is not, the electrical pulse will flow substantially along path 124 from the bottom electrode 102 through the heater 104. Because the crystalline PCM material 112 and resistive liner 108 are better conductors than the amorphous zone 120, path 124 avoids traveling through the bulk of the amorphous zone 120. Instead, path 124 bifurcates, with a portion of path 124 traveling through the resistive liner 108 and the crystalline portion of the PCM material 112 to the top electrode 114, and a portion of path 124 traveling through a short portion of the amorphous zone 120 and the crystalline portion of the PCM material 112 to the top electrode 114. The reason path 124 is the dominant electrical path is shown in FIG. 3B . 3B shows PCM cell 100 as a physical schematic on the left and an electrical schematic on the right. As discussed above, an electrical pulse travels from bottom electrode BE to top electrode TE. The resistance of crystallized PCM material C is lower than the resistance of resistive liner L, insulator I, and zone Z, which in turn is lower than the resistance of zone Z. Thus, path 124 extends primarily through resistive liner L and PCM material C.

[0033] In the embodiment shown in FIG. 2C, the PCM material 112 includes a large amorphous zone 120. Because the heater 104 is a conductive material and the insulator 106 is not, the electrical pulse will flow substantially along path 126 from the bottom electrode 102 through the heater 104. Because the crystalline PCM material 112 and resistive liner 108 are better conductors than the amorphous zone 120, path 126 avoids traveling through the bulk of the amorphous zone 120. Because the amorphous zone 120 is so large, path 126 extends through the resistive liner 108 and crystalline PCM material 112 to the top electrode 114, completely avoiding the amorphous zone 120. The reason path 126 is the dominant electrical path is illustrated in FIG. 3C, which shows the PCM cell 100 as a physical schematic on the left and an electrical schematic on the right. As discussed above, the electrical pulse travels from the bottom electrode BE to the top electrode TE. The resistance of the crystallized PCM material C is lower than the resistance of the resistive liner L, the insulator I, and the zone Z, which in turn is lower than the resistance of the zone Z. Thus, the path 126 extends primarily through the resistive liner L and the PCM material C.

[0034] A consequence of paths 122-126 being different from one another when PCM cell 100 is in different states is that the effect of resistance drift within PCM material 112 (e.g., in zone 120) is diluted by resistive liner 108 because the resistance of resistive liner 108 is constant, while the resistance of PCM material 112 can change over time (e.g., due to the size of amorphous zone 120 changing over time).

[0035] 4A-4G are a series of cross-sectional views of a method for fabricating a PCM cell 100. In FIG. 4A, a substrate 116 is provided and a bottom electrode 102 is formed on the substrate 116. Additionally, a dielectric 128 is formed on the substrate 116 to electrically insulate the bottom electrode 102 from other components, if necessary. The substrate 116 may be composed of any suitable semiconductor material. For example, the substrate 116 may be formed using any type of semiconductor substrate or wafer, including, but not limited to, silicon, silicon-germanium, Group IV semiconductor materials, Group III-V semiconductor materials, Group II-VI semiconductor materials, silicon-on-insulator (SOI), or other known semiconductor materials used in semiconductor chips. In some embodiments, the substrate 116 includes one or more semiconductor devices, such as transistors, isolation trenches, contacts, and the like. In some embodiments, the bottom electrode 102 resides on a semiconductor device or contact within the semiconductor substrate 116. In some embodiments, the bottom electrode connects to contacts (not shown) that extend through an intermediate dielectric (not shown) to underlying access circuitry or transistors (not shown) in the substrate 116. In Figure 4B, the insulator 106, the resistive liner 108, and the dielectric 130 are formed on the bottom electrode 102 and the dielectric 128. In Figure 4C, a via is formed through the dielectric 130, the resistive liner 108, and the insulator 106 (down to the bottom electrode 102). This via is then filled to form the heater 104. In Figure 4D, the dielectric 130 is removed to expose the resistive liner 108 and a portion of the sidewalls and top of the heater 104.

[0036] In FIG. 4E, spacers 110 are formed, for example, by depositing a layer of spacer material, masking the spacer material, and using RIE to remove excess spacer material. In some embodiments, insulator 106, spacer 110, dielectric 128, and dielectric 130 are composed of the same material; in other embodiments, some or all of them are different from one another. In FIG. 4F, portions of resistive liner 108 that are not underneath spacer 110 are removed to expose portions of insulator 106. In some embodiments, this occurs during the RIE process used in FIG. 4E to form spacers 110. In FIG. 4G, PCM material 112 and top electrode 114 are formed on heater 104, insulator 106, resistive liner 108, and spacer 110. This can be done, for example, using one or more masks and an RIE process.

[0037] The PCM cell 100 may thereby be fabricated such that the resistive liner 108 only underlies a portion of the PCM material 112 and does not require an additional mask (due to the presence of the spacers 110) to be formed to its final size. Furthermore, forming the spacers 110 allows the height of the heater 104 to be less critical than in some other embodiments. In some of these other embodiments, for example, the top of the heater 104 may be flush with the top of the resistive liner 108. In such embodiments, the sidewalls of the heater 104 are not in contact with the PCM material 112 despite the absence of the spacers 110. However, because the resistive liner 108 may be very thin (e.g., between 1 nanometer (nm) and 10 nm), planarizing the heater 104 to be flush with the resistive liner 108 may be difficult without removing portions of the resistive liner 108.

[0038] Figure 5 is a cross-sectional view of an alternative PCM cell 200. In the embodiment shown, PCM cell 200 is similar to PCM cell 100 (shown in Figure 1), except that a resistive liner 208 contacts the PCM material 112 along the outside and top, and the spacer 210 is correspondingly different. As such, the same reference numerals will be used for PCM cell 200, and corresponding components are the same as for PCM cell 100. However, reference numerals that are 100 higher are used for components of PCM cell 200 that differ from components in PCM cell 100.

[0039] In the embodiment shown, the resistive liner 208 has an L-shaped cross-section with a leg 232 extending outward from the heater 104 and a leg 234 extending along the sidewall of the heater 104. The upper side of the leg 234, which is flush with the spacer 210 and the top of the heater 104, is thereby in direct contact with and electrically connected to the PCM material 112, and the outer side of the leg 232 is in direct contact with and electrically connected to the PCM material 112.

[0040] 6A-6C are a series of cross-sectional views of the PCM cell 200 in different states and the flow of electricity therethrough. In the embodiment shown in FIG. 6A, the PCM material 112 is only in the polycrystalline phase. Because the heater 104 is a conductive material and the insulator 106 is not, the electrical pulse will flow substantially along path 222 from the bottom electrode 102 through the heater 104. Because the crystalline PCM material 112 is a better conductor than the resistive liner 208, path 222 extends directly through the PCM material 112 to the top electrode 114.

[0041] In the embodiment shown in FIG. 6B , the PCM material 112 includes a small amorphous zone 120. Because the heater 104 is a conductive material and the insulator 106 is not, the electrical pulse will flow substantially along a path 224 from the bottom electrode 102 through the heater 104. Because the crystalline PCM material 112 and resistive liner 208 are better conductors than the amorphous zone 120, the path 224 avoids traveling through the bulk of the amorphous zone 120. Instead, the path 224 forks, with a portion of the path 224 traveling through the leg 234 and the crystalline portion of the PCM material 112 to the top electrode 114, a portion of the path 224 traveling through the leg 232 and the crystalline portion of the PCM material 112 to the top electrode 114, and a portion of the path 224 traveling through a short portion of the zone 120 and the crystalline portion of the PCM material 112 to the top electrode 114.

[0042] In the embodiment shown in Figure 6C, the PCM material 112 includes a large amorphous zone 120. Because the heater 104 is a conductive material and the insulator 106 is not, the electrical pulse will flow substantially along a path 226 from the bottom electrode 102 through the heater 104. Because the crystalline PCM material 112 and resistive liner 208 are better conductors than the amorphous zone 120, path 226 avoids traveling through the bulk of the amorphous zone 120. Because the amorphous zone 120 is so large, path 226 extends through the legs 232 of the resistive liner 208 and the crystalline PCM material 112 to the top electrode 114, avoiding the amorphous zone 120.

[0043] A consequence of paths 222-226 being different from one another when PCM cell 200 is in different states is that the effect of resistance drift in PCM material 112 (e.g., in zone 120) is diluted by resistive liner 208 because the resistance of resistive liner 208 is constant, while the resistance of PCM material 112 can change over time (e.g., due to the size of zone 120 changing over time).

[0044] 7A-7H are a series of cross-sectional views of a method for fabricating a PCM cell 200. In FIG. 7A, a substrate 116 is provided and a bottom electrode 102 is formed on the substrate 116. Furthermore, a dielectric 128 is formed on the substrate 116 to electrically insulate the bottom electrode 102 from other components, if necessary. In FIG. 7B, an insulator 106 and a dielectric 130 are formed on the bottom electrode 102 and the dielectric 128. In some embodiments, the insulator 106 and the dielectric 130 are composed of the same material, while in other embodiments, they are composed of different materials. In such latter embodiments, only a single thick layer of the insulator 106 may be deposited (without a second deposition of the dielectric 130). In FIG. 7C, a via is formed through the dielectric 130 and the insulator 106 (down to the bottom electrode 102). This via is then filled to form the heater 104. 7D, the dielectric 130 is removed to expose the insulator 106 and a portion of the sidewalls and top of the heater 104. In embodiments where the insulator 106 is a thick layer that takes the place of the dielectric 130, a depth-controlled etch (e.g., a timed recess etch) can be performed to reduce the insulator 106 to its final thickness.

[0045] In FIG. 7E, resistive liner 208 is formed on the sidewalls and top of insulator 106 and heater 104. In FIG. 7F, spacers 210 are formed, for example, by depositing a layer of spacer material, masking the spacer material, and using RIE to remove excess spacer material. In some embodiments, insulator 106, spacer 210, dielectric 128, and dielectric 130 are composed of the same material; in other embodiments, some or all of them are different from one another. In FIG. 7G, portions of resistive liner 208 not under spacer 210 are removed to expose a portion of insulator 106 and the top of heater 104. Furthermore, the top of spacer 210 is planarized to be flush with the tops of heater 104 and resistive liner 208. In FIG. 7H, PCM material 112 and top electrode 114 are formed on heater 104, insulator 106, resistive liner 208, and spacer 210. This may be done, for example, using one or more masks and an RIE process.

[0046] The PCM cell 200 may thereby be fabricated such that the resistive liner 208 only underlies a portion of the PCM material 112 and does not require an additional mask (due to the presence of the spacers 210) to be formed to its final size. Additionally, forming the spacers 210 allows the height of the heater 104 to be less critical than in some other embodiments.

[0047] 8 is a cross-sectional view of PCM cell 300 having insulators 306-1 through 306-4 (collectively "insulators 306") and resistive liners 308-1 through 308-4 (collectively "resistive liners 308"). In the illustrated embodiment, PCM cell 300 is similar to PCM cell 100 (shown in FIG. 1), except that multiple resistive liners 308 and multiple insulators 306 are present, and spacer 310 is correspondingly different. As such, the same reference numerals will be used for PCM cell 300, and corresponding components are the same as in PCM cell 100. However, reference numerals that are 200 higher are used for components of PCM cell 300 that differ from components in PCM cell 100.

[0048] In the embodiment shown, each resistive liner 308 is in direct contact and electrically connected with the heater 104 and the PCM material 112, but each resistive liner 308 is not in direct contact with any other resistive liner 308. Instead, the resistive liners 308 are spaced from one another by insulators 306. Although there are four insulators 306 and four resistive liners 308 shown in Figure 8, in other embodiments there can be more or fewer insulators 306 and resistive liners 308.

[0049] The multiple insulators 306 and resistive liner 308 may be formed, for example, by adding multiple alternating layers during steps similar to those shown in Figure 4B. In some embodiments, the insulator 306 is composed of a material different from that of the spacers 310 such that the spacers 310 are not etched during the process of removing the insulator portions 306-2 through 306-4 and the resistive liner portions 308-1 through 308-4 to expose the insulator portion 306-1 during steps similar to those shown in Figure 4F.

[0050] Although the resistive liners 308 function the same as the single resistive liner portion 108 (shown in FIG. 1 ), having multiple resistive liners 308 allows for greater material selection for the resistive liners 308. For example, if a particular overall resistance is required, a higher resistance material can be used compared to an embodiment using only a single resistive liner 108, because multiple resistive liners 308 can act as parallel resistors and lower the overall resistance. Thus, if a particular material is desired to be used, the number of insulators 306 and resistive liners 308 can be set accordingly.

[0051] FIG. 9 is a cross-sectional view of a PCM cell 400 having insulators 406-1 through 406-4 (collectively "insulators 406") and a resistive liner 408. In the illustrated embodiment, PCM cell 400 is similar to PCM cell 200 (shown in FIG. 5), except that there are multiple legs 434-1 through 434-4 (collectively "legs 434") of resistive liner 408 spaced apart by multiple insulators 406-1 through 406-4 (collectively "insulators 406"), and the spacer 410 is correspondingly different. As such, the same reference numerals will be used for PCM cell 400, and corresponding components are the same as in PCM cell 200. However, reference numerals that are 200 higher will be used for components of PCM cell 400 that differ from components in PCM cell 200.

[0052] In the embodiment shown, the resistive liner 408 has a finned cross-section with legs 432 that extend along the sidewalls of the heater 104 and legs 434 that extend outward from the heater 104. The upper sides of the legs 432, which are flush with the spacer 410 and the top of the heater 104, are thereby in direct contact with and electrically connected to the PCM material 112, and the outer sides of the legs 434 are in direct contact with and electrically connected to the PCM material 112. While there are four insulators 406 and four legs 434 shown in Figure 9, in other embodiments there may be more or fewer insulators 406 and legs 434.

[0053] The multiple insulators 406 and resistive liner 408 can be formed, for example, by adding multiple alternating layers (per FIG. 4B) after steps similar to those shown in FIG. 7E. In some embodiments, the insulator 406 is composed of a material different from that of the spacer 410 such that the spacer 410 is not etched during the process of removing the insulator portions 406-2 through 406-4 and the resistive liner 408 to expose the insulator portion 406-1 during steps similar to those shown in FIG. 7G.

[0054] Although resistive liner 408 functions the same as resistive liner 208 (shown in FIG. 5 ), having multiple legs 434 allows for greater material selection for resistive liner 408. For example, if a particular overall resistance is desired, a higher resistance material can be used compared to an embodiment using only two legs 232 and 234 (with resistive liner 208), because multiple legs 434 can act as parallel resistors and lower the overall resistance of resistive liner 408. Thus, if a particular material is desired to be used, the number of insulators 406 and legs 434 can be set accordingly.

[0055] Further discussion of some exemplary embodiments The following is a non-exclusive description of some exemplary embodiments of the present disclosure.

[0056] A PCM cell according to an exemplary embodiment of the present disclosure includes, among other things, a first electrode, a heater electrically connected to the first electrode, a PCM material electrically connected to the heater, a second electrode electrically connected to the PCM material, and a resistive liner in direct contact with and electrically connected to a sidewall of the heater and the PCM material.

[0057] The PCM cell of the preceding paragraph may optionally include any one or more of the following features, configurations, or further components or combinations thereof, additionally and / or alternatively.

[0058] A further embodiment of the above PCM cell, wherein the PCM material is in direct contact with the end of the heater.

[0059] A further embodiment of any of the above PCM cells, further comprising an electrically insulating spacer in direct contact with a sidewall of the heater and a portion of the resistive liner, such that the resistive liner is only in direct contact with the PCM material at the outer ends of opposing resistive liners of the heater.

[0060] Further embodiments of any of the above PCM cells, further comprising an electrically insulating layer between and in direct contact with the first electrode and the resistive liner.

[0061] A further embodiment of any of the above PCM cells, wherein the width of the PCM material is 3 to 7 times the width of the heater.

[0062] A method of manufacturing a PCM cell according to an exemplary embodiment of the present disclosure includes, among other things, forming a first electrode, forming a first electrically insulating layer on the first electrode, forming a resistive liner on the first electrically insulating layer, forming a heater extending from the first electrode and through the first electrically insulating layer and the resistive liner, forming a PCM material on the heater and the resistive liner, and forming a second electrode on the PCM material.

[0063] The method of the preceding paragraphs may optionally include any one or more of the following features, configurations, or further components or combinations thereof, additionally or alternatively or both.

[0064] A further embodiment of the above method, further comprising forming a second electrically insulating layer on the resistive liner, wherein the heater extends through the second electrically insulating layer.

[0065] Further embodiments of any of the preceding methods, further comprising removing the second electrically insulating layer after forming the heater.

[0066] Further embodiments of any of the above methods, further comprising removing a portion of the resistive liner to expose a portion of the first electrically insulating layer.

[0067] A further embodiment of any of the preceding methods, further comprising forming a dielectric spacer on the resistive liner around the heater prior to removing the portion of the resistive liner.

[0068] A PCM cell according to an exemplary embodiment of the present disclosure includes, among other things, a first electrode, a heater in direct contact and electrically connected with the first electrode, a PCM material in direct contact and electrically connected with the heater, a second electrode in direct contact and electrically connected with the PCM material, and a first resistive liner in direct contact and electrically connected with the heater and the PCM material.

[0069] The PCM cell of the preceding paragraph may optionally include any one or more of the following features, configurations, or further components or combinations thereof, additionally and / or alternatively.

[0070] A further embodiment of the PCM cell above, further comprising a dielectric spacer surrounding the heater and on a portion of the first resistive liner such that the heater is only in direct contact with the PCM material at ends of the heater opposite the first electrode, and the first resistive liner is only in direct contact with the PCM material at outer ends of the first resistive liner opposite the heater.

[0071] Further embodiments of any of the above PCM cells, further comprising an electrically insulating layer between and in direct contact with the first electrode and the first resistive liner.

[0072] A further embodiment of any of the above PCM cells, further comprising a second resistive liner in direct contact with and electrically connected to the heater and the PCM material, the second resistive liner being spaced apart from the first resistive liner.

[0073] A further embodiment of any of the above PCM cells, further comprising an electrically insulating layer between the first resistive liner and the second resistive liner.

[0074] A PCM cell according to an exemplary embodiment of the present disclosure includes, among other things, a first electrode, a heater electrically connected to the first electrode, a PCM material electrically connected to the heater, a second electrode electrically connected to the PCM material, and a resistive liner in direct contact with and electrically connected to a sidewall of the heater, the resistive liner having an L-shaped cross-section with a first leg extending along the sidewall of the heater and a second leg extending outward from the heater.

[0075] The PCM cell of the preceding paragraph may optionally include any one or more of the following features, configurations, or further components or combinations thereof, additionally and / or alternatively.

[0076] A further embodiment of the above PCM cell, further comprising a dielectric spacer positioned over a portion of the resistive liner such that the resistive liner is only in direct contact with the PCM material at the first end of the first leg and the second end of the second leg.

[0077] Further embodiments of any of the above PCM cells, further comprising an electrically insulating layer between and in direct contact with the first electrode and the resistive liner.

[0078] A further embodiment of any of the above PCM cells, wherein the resistive liner further comprises a third leg extending outwardly from the heater and spaced apart from the second leg.

[0079] A further embodiment of any of the above PCM cells, further comprising an electrical insulating layer between the second leg and the third leg.

[0080] A method of manufacturing a PCM cell according to an exemplary embodiment of the present disclosure includes, among other things, forming a first electrode, forming a first electrically insulating layer on the first electrode, forming a heater extending from the first electrode and through the first electrically insulating layer, forming a resistive liner on the first electrically insulating layer and on a portion of the heater whereby the portion of the heater is not covered by the resistive liner, forming a PCM material on the heater and the resistive liner, and forming a second electrode on the PCM material.

[0081] The method of the preceding paragraphs may optionally include any one or more of the following features, configurations, or further components or combinations thereof, additionally or alternatively or both.

[0082] A further embodiment of the above method, wherein forming the resistive liner comprises forming a resistive liner over the heater and removing a portion of the resistive liner to expose a portion of the heater.

[0083] Further embodiments of any of the above methods, further comprising removing a portion of the resistive liner to expose a portion of the first electrically insulating layer.

[0084] A further embodiment of any of the preceding methods, further comprising forming a dielectric spacer on the resistive liner around the heater prior to removing the portion of the resistive liner.

[0085] A further embodiment of any of the above methods, further comprising forming a second electrically insulating layer on the first electrically insulating layer prior to forming the heater.

[0086] The description of various embodiments of the present invention has been presented for purposes of illustration, but is not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope of the described embodiments. The terms used herein have been selected to best explain the principles of the embodiments, practical applications, or technical improvements over technology found in the market, or to enable those skilled in the art to understand the embodiments disclosed herein.

Claims

1. A phase change memory (PCM) cell, comprising: a first electrode; a heater electrically connected to the first electrode; a PCM material electrically connected to the heater; a second electrode electrically connected to the PCM material; a resistive liner in direct contact with and electrically connected to the heater sidewall and the PCM material; Equipped with the PCM material is in direct contact with an end of the heater; a phase change memory (PCM) cell further comprising an electrically insulating spacer in direct contact with the sidewall of the heater and a portion of the resistive liner, such that the resistive liner is in direct contact with the PCM material only at an outer end of the resistive liner opposite the heater.

2. The PCM cell of claim 1 further comprising an electrically insulating layer between and in direct contact with said first electrode and said resistive liner.

3. The PCM cell of claim 2 , wherein the width of the PCM material is 3 to 7 times the width of the heater.

4. 1. A method of manufacturing a phase change memory (PCM) cell, comprising: forming a first electrode; forming a first electrically insulating layer on the first electrode; forming a resistive liner on the first electrically insulating layer; forming a heater extending from the first electrode through the first electrically insulating layer and the resistive liner; forming a PCM material on the heater and the resistive liner; forming a second electrode on the PCM material; and forming a second electrically insulating layer over the resistive liner; Including, The method wherein the heater extends through the second electrically insulating layer.

5. The method of claim 4 further comprising removing the second electrically insulating layer after forming the heater.

6. The method of claim 5 further comprising removing a portion of the resistive liner to expose a portion of the first electrically insulating layer.

7. The method of claim 6 , further comprising forming a dielectric spacer on the resistive liner around the heater prior to removing the portion of the resistive liner.

8. A phase change memory (PCM) cell, comprising: a first electrode; a heater in direct contact with and electrically connected to the first electrode; a PCM material in direct contact with and electrically connected to said heater; a second electrode in direct contact with and electrically connected to the PCM material; a first resistive liner in direct contact with and electrically connected to the heater and the PCM material; a dielectric spacer surrounding the heater and over a portion of the first resistive liner such that the heater is in direct contact with the PCM material only at an end of the heater opposite the first electrode, and the first resistive liner is in direct contact with the PCM material only at an outer end of the first resistive liner opposite the heater; A phase change memory (PCM) cell comprising:

9. 10. The PCM cell of claim 8, further comprising an electrically insulating layer between and in direct contact with said first electrode and said first resistive liner.

10. 10. The PCM cell of claim 8, further comprising a second resistive liner in direct contact and electrical connection with the heater and the PCM material, the second resistive liner being spaced apart from the first resistive liner.

11. The PCM cell of claim 10 further comprising an electrically insulating layer between the first resistive liner and the second resistive liner.

12. A phase change memory (PCM) cell, comprising: a first electrode; a heater electrically connected to the first electrode; a PCM material electrically connected to the heater; a second electrode electrically connected to the PCM material; a resistive liner in direct contact with and electrically connected to a sidewall of the heater; the resistive liner has an L-shaped cross-section with a first leg extending along the sidewall of the heater and a second leg extending outward from the heater; a dielectric spacer positioned over a portion of the resistive liner such that the resistive liner is in direct contact with the PCM material only at a first end of the first leg and a second end of the second leg.

13. A phase change memory (PCM) cell, comprising: a first electrode; a heater electrically connected to the first electrode; a PCM material electrically connected to the heater; a second electrode electrically connected to the PCM material; a resistive liner in direct contact with and electrically connected to a sidewall of the heater; the resistive liner has an L-shaped cross-section with a first leg extending along the sidewall of the heater and a second leg extending outward from the heater; A phase change memory (PCM) cell further comprising an electrically insulating layer between the first electrode and the resistive liner and in direct contact with the first electrode and the resistive liner.

14. A phase change memory (PCM) cell, comprising: a first electrode; a heater electrically connected to the first electrode; a PCM material electrically connected to the heater; a second electrode electrically connected to the PCM material; a resistive liner in direct contact with and electrically connected to a sidewall of the heater; the resistive liner has an L-shaped cross-section with a first leg extending along the sidewall of the heater and a second leg extending outward from the heater; The resistive liner further comprises a third leg extending outward from the heater and spaced apart from the second leg.

15. The PCM cell of claim 14 further comprising an electrical insulating layer between the second leg and the third leg.

16. 1. A method of manufacturing a phase change memory (PCM) cell, comprising: forming a first electrode; forming a first electrically insulating layer on the first electrode; forming a heater extending from the first electrode through the first electrically insulating layer; forming a resistive liner on the first electrically insulating layer and on a portion of the heater, whereby the portion of the heater is not covered by the resistive liner; forming a PCM material on the heater and the resistive liner; and forming a second electrode on the PCM material; A method comprising:

17. forming the resistive liner forming the resistive liner over the heater; and The method of claim 16, comprising removing a portion of the resistive liner to expose a portion of the heater.

18. 17. The method of claim 16, further comprising removing a portion of the resistive liner to expose a portion of the first electrically insulating layer.

19. 20. The method of claim 18, further comprising forming a dielectric spacer on the resistive liner around the heater prior to removing the portion of the resistive liner.

20. 17. The method of claim 16, further comprising forming a second electrically insulating layer on the first electrically insulating layer prior to forming the heater.

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