Phase change switch with self-aligned heater and RF terminals

A method of forming a phase change switching device includes providing a substrate, forming first and second RF terminals on the substrate, forming a strip of phase change material on the substrate that is connected between the first and second RF terminals, forming a heating element adjacent to the strip of phase change material such that the heating element is configured to control a conductive state of the strip of phase change material. The first and second RF terminals and the heating element are formed by a lithography process that self-aligns the heating element with the first and second RF terminals.

BACKGROUND

Modern electronics applications require switching devices capable of accommodating very high frequency signals. For example, fifth generation wireless applications (5G) will operate in frequency bands of 24.25 GHz (gigahertz) or greater. Maintaining the correct ON/OFF ratio/isolation versus insertion loss/RON(on-resistance) and COFF(off-capacitance) is difficult or impossible to achieve in current semiconductor switching technologies, such as CMOS technology. Phase change switches represent one promising alternative technology that can meet the requirements for high frequency applications. A phase change switch utilizes a phase change material to control a conductive connection between two terminals. The switching operation is performed by transitioning the phase change material between states, e.g., through the application of heat to the phase change material. While promising, phase change switches are in the early stages of development and some design challenges are yet to be resolved. For example, this device concept is sensitive to variation in device parameters such as RON(on-resistance) COFF(off-capacitance), power consumption, linearity, etc., due to minor variations in the physical features of the device associated with manufacturing process variation. Accordingly, there is a need improve upon the manufacturing techniques used to form phase change switches.

SUMMARY

A method of forming a phase change switching device is disclosed. According to an embodiment, the method comprises providing a substrate, forming first and second RF terminals on the substrate, forming a strip of phase change material on the substrate that is connected between the first and second RF terminals, forming a heating element adjacent to the strip of phase change material such that the heating element is configured to control a conductive state of the strip of phase change material, wherein the first and second RF terminals and the heating element are formed by a lithography process that self-aligns the heating element with the first and second RF terminals.

Separately or in combination, the method further comprises forming a region of electrically insulating material on the substrate, and forming a first trench and a second trench in the region of electrically insulating material by the lithography process, wherein the first and second RF terminals are formed in the first and second trenches, respectively.

Separately or in combination, the method further comprises forming a third trench in the region of electrically insulating material by the lithography process, and wherein the heating element is formed in the third trench.

Separately or in combination, the first, second and third trenches are each formed simultaneously by a single masked etching step.

Separately or in combination, the first and second RF terminals are formed in the first and second trenches, respectively, before forming the third trench, and wherein forming the third trench comprises using the first and second RF terminals as an etch mask.

Separately or in combination, the heating element has a different metal composition as the first and second RF terminals.

Separately or in combination, the heating element is disposed below the strip of phase change material.

Separately or in combination, the heating element is disposed above the strip of phase change material.

According to another embodiment, the method comprises forming a region of electrically insulating material on the substrate, depositing a first metal layer on the region of electrically insulating material, structuring the first metal layer to form first, second and third laterally isolated sections of the first metal layer; and configuring the first, second and third laterally isolated sections of the first metal layer such that the first and second laterally isolated sections are first and second RF terminals of the phase change switching device, respectively, and such that the third laterally isolated section is a heating element of the phase change switching device.

Separately or in combination, structuring the first metal layer comprises forming first, second and third trenches in the region of electrically insulating material, depositing the first metal layer on the region of electrically insulating material to fill the first, second and third trenches; and planarizing an upper surface of the first metal layer so as to form the first, second and third laterally isolated sections of the first metal layer, wherein the first, second and third trenches are formed by a lithography process that self-aligns the third trench with the first and second trenches.

Separately or in combination, forming first, second and third trenches comprises performing a masked etching process that forms the first, second and third trenches simultaneously.

Separately or in combination, the method further comprises providing an etch stop layer within the region of electrically insulating material, and wherein the masked etching process is performed by etching the region of electrically insulating material until each of the first, second and third trenches reach the etch stop layer.

Separately or in combination, the first metal layer comprises any one or more of: tungsten, tantalum, titanium, and platinum.

Separately or in combination, the method further comprises forming a strip of phase change material on the substrate, wherein the heating element is formed adjacent to the strip of phase change material such that the heating element is configured to control a conductive state of the strip of phase change material.

According to another embodiment, the method comprises providing a substrate, forming a region of electrically insulating material on the substrate, depositing a first metal layer on the of electrically insulating material, structuring the first metal layer to form first and second laterally isolated sections of the first metal layer, forming a central trench in the region of electrically insulating material in between the first and second laterally isolated sections of the first metal layer, forming a second metal region in central first trench, configuring the first and second isolated sections of the first metal layer to be first and second RF terminals of the phase change switching device, respectively, and configuring the second metal region to be a heating element of the phase change switching device that is configured to control a conductive connection between the first and second RF terminals, wherein the central trench is formed by a lithography process that self-aligns the central trench with the first and second laterally isolated sections of the first metal layer.

Separately or in combination, the lithography process comprises forming a hardmask layer over the first and second laterally isolated sections of the first metal layer, forming an opening in the hardmask layer that exposes inner ends of the first and second laterally isolated sections of the first metal layer; and etching the region of electrically insulating material through the opening to form the first trench.

Separately or in combination, the method further comprises depositing a dielectric layer after forming the central trench so as to cover the inner ends of the first and second laterally isolated sections with the dielectric layer, depositing a second metal layer in the central trench over the dielectric layer; and planarizing an upper surface of the second metal layer so as to remove sections of the second metal layer that are outside of the central trench, and wherein the second metal region is formed by the second metal layer.

Separately or in combination, structuring the first metal layer to form first and second laterally isolated sections of the first metal layer comprises forming first and second trenches in the region of electrically insulating material, depositing the first metal layer to fill the first and second trenches, and planarizing an upper surface of the first metal layer so as to form the first laterally isolated section of the first metal layer in the first trench, and form the second laterally isolated section of the first metal layer in the second trench.

Separately or in combination, the heating element has a different metal composition as the first and second RF terminals.

Separately or in combination, the method further comprises forming a strip of phase change material on the substrate, wherein the heating element is formed adjacent to the strip of phase change material such that the heating element is configured to control a conductive state of the strip of phase change material.

DETAILED DESCRIPTION

Embodiments of a PCM (phase change material) switching device and corresponding methods of forming the phase change switching device are described herein. The PCM switching device comprises a strip of phase change material connected between first and second RF terminals, and a heating element disposed adjacent to the strip of phase change material. The heating element is configured to control a conductive connection between the first and second RF terminals by heating the strip of phase change material. Advantageously, the heating element is self-aligned to the first and second RF terminals. As a result, the device has less variation in performance parameters attributable to process variation, e.g., capacitance between the heating element and the RF terminals, thermal resistance between the heating element and the surrounding regions of the PCM switching device. Moreover, the self-aligned techniques for forming the heating element and the RF terminals advantageously eliminate costly lithography steps.

Referring toFIG.1, a PCM switching device100is depicted, according to an embodiment. The PCM switching device100includes a substrate102. Generally speaking, the substrate102may include any material that is compatible with semiconductor processing techniques, e.g., deposition, etching, etc. For example, the substrate102may include semiconductor materials such as silicon (Si), carbon, silicon carbide (SiC), silicon germanium (SiGe), etc. In another example, the substrate102includes non-semiconductor material, e.g., sapphire, glass, diamond, etc. In one particular embodiment, the substrate102is a commercially available bulk semiconductor wafer, e.g., a silicon wafer. In another example, the substrate102is a so-called SOI (Silicon on Insulator) substrate102, which includes a buried layer of insulating material. The substrate102includes a main surface, which may be a substantially planar surface.

The PCM switching device100includes a region of electrically insulating material104that is formed on the main surface of the substrate102. Generally speaking, the region of electrically insulating material104can comprise any electrically insulating material that can be formed through typical semiconductor processing techniques such as CVD (chemical vapor deposition). Examples of these electrically insulating materials include semiconductor oxides and nitrides, e.g., silicon nitride (SiN), silicon dioxide (SiO2), silicon oxynitride (SiOXNY), etc. In another embodiment, the region of electrically insulating material104comprises aluminum nitride (AIN). The region of electrically insulating material104may be thermally insulating or thermally conductive. The region of electrically insulating material104may include multiple layers of the same or different material.

The PCM switching device100further includes first and second RF terminals106,108. The first and second RF terminals106,108may be formed from an electrically conductive metal, e.g., copper, aluminum, alloys thereof, etc. As shown, the PCM switching device100may further comprise an upper level metallization110that is electrically connected to the first and second RF terminals106,108by vertical through-via structures112. The upper level metallization110can be a structured metallization e.g., copper, aluminum, alloys thereof, etc., and the vertical through-via structures112comprise a conductive metal such as tungsten, copper, nickel, aluminum, etc. The upper level metallization110may be connected to or form externally accessible terminals of the PCM switching device100.

The PCM switching device100further includes a strip of phase change material114. The strip of phase change material114may have an elongated geometry that extends lengthwise parallel to the main surface of the substrate102. The strip of phase change material114is formed from a material that can be transitioned between two different phases that each have different electrical conductivity. For example, strip of phase change material114may comprise a material that changes from an amorphous state to a crystalline state based upon the application of heat to the phase change material, wherein the phase change material is electrically insulating (i.e., blocks a conductive connection) in the amorphous state and is electrically conductive (i.e., provides a low-resistance current path) in the crystalline state. Generally speaking, phase change materials having this property include chalcogenides and chalcogenide alloys. Specifically, these phase change materials include germanium-antimony-tellurium (GST), germanium-tellurium, and germanium-antimony.

The strip of phase change material114is connected between the first and second RF terminals106,108. That is, the strip of phase change material114is in low-ohmic contact with both the first and second RF terminals106,108, either through direct physical contact or by one or more conductive intermediaries that provide a low-resistance electrical connection. In one example, a conductive material such as TiN, W, TiPtAu is provided between the first and second RF terminals106,108and the phase change material to improve the electrical connection between the two. When the strip of phase change material114is in a conductive state, current flows between the first and second RF terminals106,108in a current flow direction of the strip of phase change material114.

The PCM switching device100further includes at least one heating element116. The heating element116is arranged adjacent to the strip of phase change material114. In the depicted embodiment, the strip of phase change material114is disposed above each of the first and second RF terminals106,108and the heating element116. The heating element116is arranged and configured to apply heat to the strip of phase change material114. For example, the heating element116may comprise a conductive or semi-conductive material that converts electrical energy into heat through ohmic heating. The heating element116may be connected between electrically conductive heating terminals, which are not shown in the cross-sectional view ofFIG.1. For example, the heating element116may extend transversely to the current flow direction of the phase change material114and contact heating terminals that are in locations that are spaced apart from the cross-sectional plane ofFIG.1. The heating terminals are electrically conductive structures that can be biased to force a current through the heating element. The heating element116is separated from the strip of phase change material114by an insulating liner118. The insulating liner118electrically isolates the heating element116from the strip of phase change material114while simultaneously permitting substantial heat transfer between the two. To this end, the insulating liner118may be a relatively thin (e.g., less than 1 μm thick and more typically less than 100 nm thick) layer of dielectric material, e.g., silicon dioxide (SiO2), silicon nitride (SiN), etc.

The working principle of the PCM switching device100is as follows. The heating element116is configured to control a conductive connection between the first and second RF terminals106,108by applying heat to the strip of phase change material114. In an OFF state of the PCM switching device100, the phase change material of the strip of phase change material114is in an amorphous state or partially amorphous. As a result, the strip of phase change material114blocks a voltage applied to the first and second RF terminals106,108. In an ON state of the PCM switching device100, the phase change material of the strip of phase change material114is in a crystalline state. As a result, the strip of phase change material114provides a low-resistance electrical connection between the first and second RF terminals106,108. The PCM switching device100performs a switching operation by using the heating element116to heat the strip of phase change material114. The phase change material may be transitioned to the amorphous state by applying a short pulses (e.g., pulses in the range of 50-1,000 nanoseconds) of high intensity heat which causes the phase change material to reach a melting temperature, e.g., in the range of 600° C. to 750° C., followed by a rapid cooling of the material. This is referred to as a “reset pulse.” The phase change material may be transitioned to the crystalline state by applying longer duration pulses (e.g., pulses in the range of 0.5-10 microseconds) of lower intensity heat, which causes the phase change material to reach a temperature at which the material quickly crystallizes and is highly conductive, e.g., in the range of 250° C. to 350° C. This is referred to as a “set pulse.”

According to an embodiment, the first and second RF terminals106,108and the heating element116are formed by a lithography process that self-aligns the heating element116with the first and second RF terminals106,108. This means that one photomask and one lithography step form the first and second RF terminals106,108and the heating element116, either by directly forming these features or by forming features such as structured mask layers, trenches, etc. which in turn determine the geometry of the first and second RF terminals106,108and the heating element116. A lithography step utilizes a photomask has a pre-defined pattern that selectively blocks light to replicate the pre-defined pattern in a photosensitive material e.g., a photoresist layer, that is formed on a semiconductor substrate102. This pattern is used to create the first and second RF terminals106,108and the heating element116through a sequence of processing steps, e.g., etching, deposition, polishing, etc. In some of the processes described herein, the heating element116and the first and second RF terminals106,108are formed simultaneously with one etching step. In other processes described herein, the first and second RF terminals106,108are formed by an initial etching step, and the heating element116is subsequently formed by a second etching step that uses the first and second RF terminals106,108as an etch mask. In either case, the first and second RF terminals106,108and the heating element116are self-aligned because each feature owes its geometry to one lithography step.

The advantages of forming the first and second RF terminals106,108and the heating element116according to a self-aligned technique include the following. The location of the heating element116relative to the first and second RF terminals106,108may be well-controlled. For example, the heating element116may be centered between the first and second RF terminals106,108to a great degree of precision. Separately or in combination, the spacing between the heating element116and the first and second RF terminals106,108may be well-controlled to a great degree of precision. By contrast, in a device wherein the first and second RF terminals106,108and the heating element116are not self-aligned (i.e., having a geometry defined by two different lithography steps), the location of the heating element116relative to the first and second RF terminals106,108and/or the spacing between the heating element116and the first and second RF terminals106,108is not as well-controlled, due to the possibility of mask misalignment. Even minor misalignment can have significant impact in device performance by altering the capacitive coupling between the heating element116and the first and second RF terminals106,108and/or by altering the thermal resistance of the heating element116to the ambient environment. The self-aligned technique described herein substantially mitigates this issue by removing a potential source of unreliability in the manufacturing process. Moreover, the self-aligned technique advantageously eliminates costly lithography steps.

Referring toFIG.2, selected process steps for forming the PCM switching device100ofFIG.1are shown.

As shown inFIG.2A, a substrate102is provided and a region of electrically insulating material104is formed on the main surface of the substrate102. The region of electrically insulating material104can be formed by a deposition technique such as CVD (chemical vapor deposition) wherein one or more layers of electrically insulating material, e.g., silicon nitride (SiN), silicon dioxide (SiO2), silicon oxynitride (SiOXNY), etc., are formed on the substrate102. A first trench120, a second trench122, and a third trench124are formed in the region of electrically insulating material104. The first, second and third trenches120,122,124may be formed by a lithography process that self-aligns the third trench124with the first and second trenches120,122. For example, a layer of photoresist material (not shown) may be provided on the region of electrically insulating material104and lithographically patterned using a photomask (not shown) to form openings in the layer of photoresist material. The patterned photomask can be used directly as an etch mask to form the first, second and third trenches120,122,124. Alternatively, the patterned photomask can be used to form corresponding openings in a hardmask layer (not shown), which in turn is used to etch the first, second and third trenches120,122,124. In either case, an etching process, e.g., chemical etch, reactive ion etching, plasma etching, etc., can be performed to etch the region of electrically insulating material104. As a result, the first, second and third trenches120,122,124are formed to be self-aligned with one another.

According to an embodiment, an etch stop layer126is provided within the region of electrically insulating material104. The etch stop layer126is less selective to the etchant that is used to form the first, second and third trenches120,122,124than the superjacent region of the electrically insulating material104. For example, the etch stop layer126may include a nitride and/or a metal whereas the superjacent material includes an oxide. In this case, the masked etching process is performed by etching the region of electrically insulating material104until each of the first, second and third trenches120,122,124reach the etch stop layer126. In this way, the depth of the first, second and third trenches120,122,124and hence the thickness of the functional elements of the PCM switching device100is well-controlled.

As shown inFIG.2B, a first metal layer128is deposited on the region of electrically insulating material104. The first metal layer128is conformably deposited so as to completely fill the first, second and third trenches120,122,124. That is, a thickness of the first metal layer128is at least equal to the depth of the first, second and third trenches120,122,124. Generally speaking, the first metal layer128can comprise any metal or metal alloy with sufficient material properties to perform the function of the heating element116as described above. Examples of these metals include tungsten, tantalum, titanium, platinum, and any alloy or combination thereof.

As shown inFIG.2C, an upper surface of the first metal layer128is planarized. The planarization step can be performed using any technique that successively removes material from the upper surface of the first metal layer128, e.g., polishing such as CMP (chemical-mechanical polishing). The planarization step removes all portions of the first metal layer128outside of the first, second and third trenches120,122,124. As a result, first, second, and third sections130,132,134of the first metal layer128remain within the trenches. The first, second, and third sections130,132,134are laterally isolated from one another, meaning that there is no conductive path between each section.

Subsequent processing may be performed after the step illustrated inFIG.2Cto complete the PCM switching device100. The strip of phase change material114and the insulating liner118may be formed by blanket deposition and subsequent masked etching step, for example. A further layer or layers of the electrically insulating material may be formed on top of the functional elements of the PCM switching device100by a deposition technique such as CVD (chemical vapor deposition), for example. The upper level metallization110and the through via112may be formed by etching and deposition techniques, for example. In the completed device, the first and second laterally isolated sections130,132of the first metal layer128correspond to the first and second RF terminals106,108of the PCM switching device100, respectively, and the third laterally isolated section134of the first metal layer128corresponds to the heating element116of the PCM switching device100.

Instead of the process illustrated with respect toFIGS.2A-2C, alternate metal structuring techniques may be used to create the first, second, and third laterally isolated sections130,132,134of the first metal layer128. For example, the first metal layer128may be deposited on a planar surface of electrically insulating material and subsequently structured using direct metal etching techniques, such as wet or dry etching techniques. In another example, the first, second, and third laterally isolated sections130,132,134of the first metal layer128may be formed by a lift-off technique. According to this technique, a structured layer of lift-off material is provided on a planar surface of the electrically insulating material. The first metal layer128is conformally deposited on the structured layer so as to fill the openings of the structured layer of lift-off material. The lift-off material is removed, e.g., by chemical dissolution such that the only portions of the first metal layer128disposed within openings remain. In each case, only one photomask is used to structure the first metal layer128and the first, second, and third laterally isolated sections130,132,134are self-aligned.

Referring toFIG.3, a PCM switching device100is depicted, according to an embodiment. The PCM switching device100may be substantially identical to the PCM switching device100described with reference toFIG.1, except that the strip of phase change material114is disposed below each of the first and second RF terminals106,108and the heating element116.

Referring toFIG.4, selected process steps for forming the PCM switching device100ofFIG.3are shown.

As shown inFIG.4A, a substrate102is provided and a region of electrically insulating material104is formed on the main surface of the substrate102. Subsequently, the strip of phase change material114and the insulating liner118are formed. This may be done by depositing a blanket layer of phase change material on the region of electrically insulating material104and subsequently structuring this blanket layer in a similar manner as previously described. The insulating liner118may be formed as a blanket layer and structured at the same time as the phase change material. Alternatively, the insulating liner118may be formed by a separate sequence of deposition and etching.

As shown inFIG.4B, electrically insulating material is further deposited to grow the region of electrically insulating material104. As a result, the strip of phase change material114and the insulating liner118are embedded within the region of electrically insulating material104. A planarization step, e.g., polishing such as CMP (chemical-mechanical polishing) may be performed after the deposition of the electrically insulating material so as to planarize the upper surface of the electrically insulating material104, thereby preparing this surface for the masked etching step described below.

As shown inFIG.4C, first, second and third trenches120,122,124are formed in region of the electrically insulating material. The first, second and third trenches120,122,124may be formed by a self-aligned masked etching technique, e.g., in the same manner as described with reference toFIG.2B. The third trench124is formed to expose the insulating liner118and the first and second trenches120,122is formed to expose the outer ends of the strip of phase change material114.

As shown inFIG.4D, first, second, and third sections130,132,134of the first metal layer128are formed within the first, second and third trenches120,122,124, respectively. This may be done by depositing a first metal layer128and subsequently planarizing the first metal layer128in a similar manner as described with reference toFIGS.2B-2C. As a result, the functional elements of the PCM switching device100are formed. Subsequent processing may be performed after the step illustrated inFIG.4Dto complete the PCM switching device100in a similar manner as previously described.

Referring toFIG.5, a PCM switching device100is depicted, according to an embodiment. The PCM switching device100differs from the previously described embodiments in the following way. In the previously described embodiments, each of the first and second RF terminals106,108and the heating element116are formed by the first metal layer128, and hence have the same metal composition. By contrast, in the PCM switching device100ofFIG.5, the heating element116has a different metal composition as the first and second RF terminals106,108. For example, the first and second RF terminals106,108may be formed from a first metal or metal alloy with preferable electrically conductive characteristics, e.g., copper, aluminum, alloys thereof. The heating element116may be formed from a second metal or metal alloy that is different from the first metal or metal alloy and has preferable heating characteristics, e.g., tantalum, tungsten, nickel, etc. and alloys thereof. In this way, there is no tradeoff between the preferable characteristics for the heating element116and the preferable characteristics for the first and second RF terminals106,108. Additionally, the PCM switching device100comprises a dielectric layer136that separates the first and second RF terminals106,108and the heating element116. The thickness of the dielectric layer136can be well-controlled according to the deposition technique described below such that advantageous control over the lateral positioning of the heating element116is maintained.

Referring toFIG.6, selected process steps for forming the PCM switching device100ofFIG.5are shown.

As shown inFIG.6A, a substrate102is provided and a region of electrically insulating material104is formed on the main surface of the substrate102. First and second laterally isolated sections130,132of a first metal layer128are formed in the region of electrically insulating material104, e.g., using the same technique described with reference toFIGS.2A-2C. The first metal layer128used to form the first and second laterally isolated sections130,132may comprise a first metal or metal alloy with preferable conductive characteristics, e.g., copper, aluminum, alloys thereof.

As shown inFIG.6B, a hardmask layer138is formed over the first and second laterally isolated sections of the first metal layer128. The thickness and material composition of the hardmask layer138are such that the hardmask layer138prevents the first and second laterally isolated sections130,132from being etched during the subsequent etching process to be described below. The hardmask layer138is structured, e.g., using a lithographic patterning technique, to form an opening that exposes inner ends of first and second laterally isolated sections130,132. Subsequently, an etching process (e.g., wet chemical etch, reactive ion etching, plasma etching, etc.) is performed to remove the electrically insulating material through the opening in the hardmask layer138. During this etching step, the first and second laterally isolated sections130,132, which correspond to the first and second RF terminals106,108of the PCM switching device100, are used as an etch mask to form a central trench140(shown inFIG.6C) in between the first and second laterally isolated sections130,132. The central trench140is thus self-aligned to the first and second laterally isolated sections130,132of the first metal layer128, as the geometry of the central trench140is directly defined by the first and second RF terminals106,108, and the geometry of each structures is attributable to a single photomask.

As shown inFIG.6C, a dielectric layer136is deposited within the central trench140such that the dielectric layer136covers the inner ends of the first and second laterally isolated sections130,132. The dielectric layer136may be a relatively thin (e.g., less than 1 μm thick and more typically less than 100 nm thick) layer of dielectric material, e.g., silicon dioxide (SiO2), silicon nitride (SiN), etc.

As shown inFIG.6D, a second metal layer142is deposited in the central trench140over the dielectric layer136. The second metal layer142may be conformally deposited with sufficient thickness to completely fill the central trench140. The second metal layer142may comprise a second metal or metal alloy with preferable heating characteristics, e.g., tantalum, tungsten, nickel, etc. and alloys thereof.

As shown inFIG.6E, an upper surface of the second metal layer142is planarized so as to remove sections of the second metal layer142that are outside of the central trench140. The planarization step can be performed using any technique that successively removes material from the upper surface of the second metal layer142, e.g., polishing such as CMP (chemical-mechanical polishing). As a result, a second metal region164is formed in the central trench140, wherein the second metal region164has a different material composition as the first and second laterally isolated sections130,132.

After performing the above-described steps, the second metal region164can be configured as the heating element116of the PCM switching device100described with reference toFIG.6, and the first and second laterally isolated sections130,132of the first metal layer128can be configured as the first and second RF terminals106,108of the PCM switching device100according to previously describe techniques. For example, the insulating liner118and the strip of phase change material114may be formed on top of the second metal region164by masked etching techniques. As illustrated inFIG.5, a via166may be formed that extends through the dielectric layer136so as to complete the electrical connection between the strip of phase change material114and the first and second RF terminals106,108.

Referring toFIG.7, a PCM switching device100is depicted, according to an embodiment. The PCM switching device100may be substantially identical to the PCM switching device100described with reference toFIG.5, except that the strip of phase change material114is disposed below each of the first and second RF terminals106,108and the heating element116. In this case, the dielectric layer136provides the electrical isolation between the strip of phase change material114and the heating element116in a similar manner as the previously described insulating liner118.

Referring toFIG.8, selected process steps for forming the PCM switching device100ofFIG.7are shown.

As shown inFIG.8A, a substrate102is provided and a region of electrically insulating material104is formed on the main surface of the substrate102. A strip of phase change material114is formed to be embedded within the region of electrically insulating material104, e.g., in a similar manner as previously described with reference toFIG.4B. A planarization step, e.g., polishing such as CMP (chemical-mechanical polishing) may be performed after the deposition of the electrically insulating material so as to form a planar upper surface in the region of electrically insulating material104, thereby preparing this surface for the masked etching step described below.

As shownFIG.8B, first and second laterally isolated sections130,132of a first metal layer128are formed in the region of electrically insulating material104. The first and second laterally isolated sections130,132may be formed by forming first and second trenches120,122in the region of electrically insulating material104, depositing the first metal layer128to fill the first and second trenches120,122, and planarizing an upper surface of the first metal layer128, e.g., in a similar manner as previously described with reference toFIG.6A.

As shown inFIG.8C, a hardmask layer138is formed over the first and second laterally isolated sections130,132of the first metal layer128, an opening is formed in the hardmask layer138that exposes inner ends of the first and second laterally isolated sections130,132of the first metal layer128, and the region of electrically insulating material104is etched through the opening to form the central trench140, e.g., in a similar manner as previously described with reference toFIG.6B.

As shown inFIG.8D, a dielectric layer136is deposited within the central trench140such that the dielectric layer136covers the inner ends of the first and second laterally isolated sections130,132, e.g., in a similar manner as previously described with reference toFIG.6C.

As shown inFIG.8E, a second metal region164is formed in the central trench140over the dielectric layer136, e.g., in a similar manner as previously described with reference toFIGS.6D-6E.

The methods and structures disclosed herein with reference to specific figures are equally applicable to all other embodiments to the extent consistent with these other embodiments. For instance, particular techniques, materials, steps and so-forth describing a method of forming a device represented by one figure may be applied to any other method represented by other figures, to the extent consistent with these other methods. Likewise, particular device features, structures or arrangements disclosed in connection with a device represented by one figure may be incorporated into a device represented any other figures, to the extent consistent with these other devices.

The term “electrically connected,” “directly electrically connected” and the like as used herein describes a permanent low-impedance connection between electrically connected elements, for example a direct contact between the relevant elements or a low-impedance connection via a metal and/or a highly doped semiconductor.