Patent Application
20230099724
Embodiments of the disclosure are in the field of advanced integrated circuit structure fabrication and, in particular, to memory devices having ferroelectric capacitors coupled between intersecting bitlines and wordlines.
For the past several decades, the scaling of features in integrated circuits has been a driving force behind an ever-growing semiconductor industry. Scaling to smaller and smaller features enables increased densities of functional units on the limited real estate of semiconductor chips. For example, shrinking transistor size allows for the incorporation of an increased number of memory or logic devices on a chip, lending to the fabrication of products with increased capacity. The drive for ever-more capacity, however, is not without issue. The necessity to optimize the performance of each device becomes increasingly significant.
For example, conventional memory devices face a variety of challenges, particularly with respect to increased capacitor density. Embodiments of the present disclosure address these and other issues.
In some embodiments, memory devices including ferroelectric capacitors coupled between intersecting bitlines and wordlines are described. In the following description, numerous specific details are set forth, such as specific integration and material regimes, in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to one skilled in the art that embodiments of the present disclosure may be practiced without these specific details. In other instances, well-known features, such as integrated circuit design layouts, are not described in detail in order to not unnecessarily obscure embodiments of the present disclosure. Furthermore, it is to be appreciated that the various embodiments shown in the Figures are illustrative representations and are not necessarily drawn to scale.
The following detailed description is merely illustrative in nature and is not intended to limit the embodiments of the subject matter or the application and uses of such embodiments. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Any implementation described herein as exemplary is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following
This specification includes references to “one embodiment” or “an embodiment.” The appearances of the phrases “in one embodiment” or “in an embodiment” do not necessarily refer to the same embodiment. Particular features, structures, or characteristics may be combined in any suitable manner consistent with this disclosure.
Terminology. The following paragraphs provide definitions or context for terms found in this disclosure (including the appended claims):
“Comprising.” This term is open-ended. As used in the appended claims, this term does not foreclose additional structure or operations.
“Configured To.” Various units or components may be described or claimed as “configured to” perform a task or tasks. In such contexts, “configured to” is used to connote structure by indicating that the units or components include structure that performs those task or tasks during operation. As such, the unit or component can be said to be configured to perform the task even when the specified unit or component is not currently operational (e.g., is not on or active). Reciting that a unit or circuit or component is “configured to” perform one or more tasks is expressly intended not to invoke 35 U.S.C. § 112, sixth paragraph, for that unit or component.
“First,” “Second,” etc. As used herein, these terms are used as labels for nouns that they precede, and do not imply any type of ordering (e.g., spatial, temporal, logical, etc.).
“Coupled”—The following description refers to elements or nodes or features being “coupled” together. As used herein, unless expressly stated otherwise, “coupled” means that one element or node or feature is directly or indirectly joined to (or directly or indirectly communicates with) another element or node or feature, and not necessarily mechanically.
In addition, certain terminology may also be used in the following description for the purpose of reference only, and thus are not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “side”, “outboard”, and “inboard” describe the orientation or location or both of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import.
“Inhibit”—As used herein, inhibit is used to describe a reducing or minimizing effect. When a component or feature is described as inhibiting an action, motion, or condition it may completely prevent the result or outcome or future state completely. Additionally, “inhibit” can also refer to a reduction or lessening of the outcome, performance, or effect which might otherwise occur. Accordingly, when a component, element, or feature is referred to as inhibiting a result or state, it need not completely prevent or eliminate the result or state.
Embodiments described herein may be directed to front-end-of-line (FEOL) semiconductor processing and structures. FEOL is the first portion of integrated circuit (IC) fabrication where the individual devices (e.g., transistors, capacitors, resistors, etc.) are patterned in the semiconductor substrate or layer. FEOL generally covers everything up to (but not including) the deposition of metal interconnect layers. Following the last FEOL operation, the result is typically a wafer with isolated transistors (e.g., without any wires).
Embodiments described herein may be directed to back-end-of-line (BEOL) semiconductor processing and structures. BEOL is the second portion of IC fabrication where the individual devices (e.g., transistors, capacitors, resistors, etc.) get interconnected with wiring on the wafer, e.g., the metallization layer or layers. BEOL includes contacts, insulating layers (dielectrics), metal levels, and bonding sites for chip-to-package connections. In the BEOL part of the fabrication stage contacts (pads), interconnect wires, vias and dielectric structures are formed. For modern IC processes, more than 10 metal layers may be added in the BEOL.
Embodiments described below may be applicable to FEOL processing and structures, BEOL processing and structures, or both FEOL and BEOL processing and structures. In particular, although an exemplary processing scheme may be illustrated using a FEOL processing scenario, such approaches may also be applicable to BEOL processing. Likewise, although an exemplary processing scheme may be illustrated using a BEOL processing scenario, such approaches may also be applicable to FEOL processing.
One or more embodiments may be implemented to realize a 3D ferroelectric RAM (FRAM, FeRAM, or F-RAM) to potentially increase monolithic integration of backend logic plus memory in SoCs of future technology nodes. To provide context, a FRAM is a random-access memory similar in construction to dyanmic random-access memory (DRAM) but uses a ferroelectric layer instead of a dielectric layer to achieve non-volatility. Conventionally, both FRAM and DRAM are one transistor (1T)/one capacitor (1C) cell arrays, where each cell comprises an access transistor in the front end coupled to a single capacitor. The capacitor may be coupled to a bitline (COB) higher in the stack in the semiconductor back end.
As introduced above, conventional memory devices face a variety of challenges particularly with respect to increased capacitor density. For example, current FeRAM devices typically require a Si-based selection device, and current FeRAM devices are of relatively low density and not stackable in the 1T-1C configuration.
The current approach in conventional FeRAM devices is to use a DRAM-like capacitor with atomic layer deposition (ALD) ferroelectrics and, design the architecture of the memory array with a few bits per cell. However, not all ferroelectrics are ALD capable, and the “few bits per cell” fabricated in a trench has an intrinsic variability depending on their depth. In particular, the use of trench capacitors limits the thickness of the dielectric to ˜CD/3 and cannot be used with low Ec ferroelectrics such as perovskites. Additionally, the process complexity is relatively high for making trench capacitors requiring via patterning. Embodiments of the present disclosure address these and other issues by providing a capacitor fabricated at the cross-section between metal lines (e.g., bitlines and wordlines) of the memory device.
Memory device 100 further includes a capacitor 140 coupled between bitline 110 and wordline 130. As shown in
Using ferroelectrics with a high Pr (e.g., bewteen about 80 uC/cm{circumflex over ( )}2 and 200 uC/cm{circumflex over ( )}2) allow embodiments of the present disclosure to provide an adequate sensing margin within a reduced device size relative to conventional devices. For example, given a Pr=100 uC/cm{circumflex over ( )}2, then 2 Pr=2 pC/um2. Given sensing is 2 fC then the ferroelectric Area=0.001 um2. For two decks bit cell area is only 0.0005 um2, and for 4 decks the bitcell area is just 0.00025 um2.
Embodiments of the present disclosure provide a number of advantages over conventional solutions, including with respect to performance, density, and fabrication efficiency. For example, referring again to
Embodiments of the present disclosure may also provide significant improvements to fabrication efficiency and production cost of the memory device. For example, while not shown in
In some embodiments, as illustrated in
However, number of bitlines in the tile does not necessarily equal to the number of wordlines: the tile can be a rectangular shaped rather than a square. In some embodiments, for example, the plurality of capacitors for a given bitline includes at least four capacitors. In some embodiments, a thin-film-based select transistor or a thin-film-based selector diode (not shown) may be coupled to each bitline.
The capacitor 140 may be formed from any suitable ferroelectric material or combination of materials. In some embodiments, for example, the ferroelectric material comprises a nitride ferroelectric material which can be aluminum scandium nitride (e.g., AlSc1N or AlScN). Additionally or alternatively, the ferroelectric material may comprise an oxide which can be a perovskite material or HfO2-based material.
Embodiments of the present disclosure may operate in conjunction with a 2-deck memory array structure as illustrated in
In the 2-deck array of
Implementations of embodiments of the invention may be formed or carried out on a substrate, such as a semiconductor substrate. In one implementation, the semiconductor substrate may be a crystalline substrate formed using a bulk silicon or a silicon-on-insulator substructure. In other implementations, the semiconductor substrate may be formed using alternate materials, which may or may not be combined with silicon, that include but are not limited to germanium, indium antimonide, lead telluride, indium arsenide, indium phosphide, gallium arsenide, indium gallium arsenide, gallium antimonide, or other combinations of group III-V or group IV materials. Although a few examples of materials from which the substrate may be formed are described here, any material that may serve as a foundation upon which a semiconductor device may be built falls within the spirit and scope of the present invention.
A plurality of transistors, such as metal-oxide-semiconductor field-effect transistors (MOSFET or simply MOS transistors), may be fabricated on the substrate. In various implementations of the invention, the MOS transistors may be planar transistors, nonplanar transistors, or a combination of both. Nonplanar transistors include FinFET transistors such as double-gate transistors and tri-gate transistors, and wrap-around or all-around gate transistors such as nanoribbon and nanowire transistors. Although the implementations described herein may illustrate only planar transistors, it should be noted that the invention may also be carried out using nonplanar transistors.
Each MOS transistor includes a gate stack formed of at least two layers, a gate dielectric layer and a gate electrode layer. The gate dielectric layer may include one layer or a stack of layers. The one or more layers may include silicon oxide, silicon dioxide (SiO2) and/or a high-k dielectric material. The high-k dielectric material may include elements such as hafnium, silicon, oxygen, titanium, tantalum, lanthanum, aluminum, zirconium, barium, strontium, yttrium, lead, scandium, niobium, and zinc. Examples of high-k materials that may be used in the gate dielectric layer include, but are not limited to, hafnium oxide, hafnium silicon oxide, lanthanum oxide, lanthanum aluminum oxide, zirconium oxide, zirconium silicon oxide, tantalum oxide, titanium oxide, barium strontium titanium oxide, barium titanium oxide, strontium titanium oxide, yttrium oxide, aluminum oxide, lead scandium tantalum oxide, and lead zinc niobate. In some embodiments, an annealing process may be carried out on the gate dielectric layer to improve its quality when a high-k material is used.
The gate electrode layer is formed on the gate dielectric layer and may consist of at least one P-type workfunction metal or N-type workfunction metal, depending on whether the transistor is to be a PMOS or an NMOS transistor. In some implementations, the gate electrode layer may consist of a stack of two or more metal layers, where one or more metal layers are workfunction metal layers and at least one metal layer is a fill metal layer.
For a PMOS transistor, metals that may be used for the gate electrode include, but are not limited to, ruthenium, palladium, platinum, cobalt, nickel, and conductive metal oxides, e.g., ruthenium oxide. A P-type metal layer will enable the formation of a PMOS gate electrode with a workfunction that is between about 4.9 eV and about 5.2 eV. For an NMOS transistor, metals that may be used for the gate electrode include, but are not limited to, hafnium, zirconium, titanium, tantalum, aluminum, alloys of these metals, and carbides of these metals such as hafnium carbide, zirconium carbide, titanium carbide, tantalum carbide, and aluminum carbide. An N-type metal layer will enable the formation of an NMOS gate electrode with a workfunction that is between about 3.9 eV and about 4.2 eV.
In some implementations, the gate electrode may consist of a “U”-shaped structure that includes a bottom portion substantially parallel to the surface of the substrate and two sidewall portions that are substantially perpendicular to the top surface of the substrate. In another implementation, at least one of the metal layers that form the gate electrode may simply be a planar layer that is substantially parallel to the top surface of the substrate and does not include sidewall portions substantially perpendicular to the top surface of the substrate. In further implementations of the invention, the gate electrode may consist of a combination of U-shaped structures and planar, non-U-shaped structures. For example, the gate electrode may consist of one or more U-shaped metal layers formed atop one or more planar, non-U-shaped layers.
In some implementations of the invention, a pair of sidewall spacers may be formed on opposing sides of the gate stack that bracket the gate stack. The sidewall spacers may be formed from a material such as silicon nitride, silicon oxide, silicon carbide, silicon nitride doped with carbon, and silicon oxynitride. Processes for forming sidewall spacers are well known in the art and generally include deposition and etching process steps. In an alternate implementation, a plurality of spacer pairs may be used, for instance, two pairs, three pairs, or four pairs of sidewall spacers may be formed on opposing sides of the gate stack.
As is well known in the art, source and drain regions are formed within the substrate adjacent to the gate stack of each MOS transistor. The source and drain regions are generally formed using either an implantation/diffusion process or an etching/deposition process. In the former process, dopants such as boron, aluminum, antimony, phosphorous, or arsenic may be ion-implanted into the substrate to form the source and drain regions. An annealing process that activates the dopants and causes them to diffuse further into the substrate typically follows the ion implantation process. In the latter process, the substrate may first be etched to form recesses at the locations of the source and drain regions. An epitaxial deposition process may then be carried out to fill the recesses with material that is used to fabricate the source and drain regions. In some implementations, the source and drain regions may be fabricated using a silicon alloy such as silicon germanium or silicon carbide. In some implementations the epitaxially deposited silicon alloy may be doped in situ with dopants such as boron, arsenic, or phosphorous. In further embodiments, the source and drain regions may be formed using one or more alternate semiconductor materials such as germanium or a group III-V material or alloy. And in further embodiments, one or more layers of metal and/or metal alloys may be used to form the source and drain regions.
One or more interlayer dielectrics (ILD) are deposited over the MOS transistors. The ILD layers may be formed using dielectric materials known for their applicability in integrated circuit structures, such as low-k dielectric materials. Examples of dielectric materials that may be used include, but are not limited to, silicon dioxide (SiO2), carbon doped oxide (CDO), silicon nitride, organic polymers such as perfluorocyclobutane or polytetrafluoroethylene, fluorosilicate glass (FSG), and organosilicates such as silsesquioxane, siloxane, or organosilicate glass. The ILD layers may include pores or air gaps to further reduce their dielectric constant.
Depending on its applications, computing device 200 may include other components that may or may not be physically and electrically coupled to the board 202. These other components include, but are not limited to, volatile memory (e.g., DRAM), non-volatile memory (e.g., ROM), flash memory, a graphics processor, a digital signal processor, a crypto processor, a chipset, an antenna, a display, a touchscreen display, a touchscreen controller, a battery, an audio codec, a video codec, a power amplifier, a global positioning system (GPS) device, a compass, an accelerometer, a gyroscope, a speaker, a camera, and a mass storage device (such as hard disk drive, compact disk (CD), digital versatile disk (DVD), and so forth).
The communication chip 206 enables wireless communications for the transfer of data to and from the computing device 200. The term “wireless” and its derivatives may be used to describe circuits, devices, systems, methods, techniques, communications channels, etc., that may communicate data through the use of modulated electromagnetic radiation through a non-solid medium. The term does not imply that the associated devices do not contain any wires, although in some embodiments they might not. The communication chip 206 may implement any of a number of wireless standards or protocols, including but not limited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE 802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE, GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well as any other wireless protocols that are designated as 3G, 4G, 5G, and beyond. The computing device 200 may include a plurality of communication chips 206. For instance, a first communication chip 206 may be dedicated to shorter range wireless communications such as Wi-Fi and Bluetooth and a second communication chip 206 may be dedicated to longer range wireless communications such as GPS, EDGE, GPRS, CDMA, WiMAX, LTE, Ev-DO, and others.
The processor 204 of the computing device 200 includes an integrated circuit die packaged within the processor 204. In some implementations of the invention, the integrated circuit die of the processor includes one or more devices, such as MOS-FET transistors built in accordance with implementations of the invention. The term “processor” may refer to any device or portion of a device that processes electronic data from registers and/or memory to transform that electronic data into other electronic data that may be stored in registers and/or memory.
The communication chip 206 also includes an integrated circuit die packaged within the communication chip 206. In accordance with another implementation of the invention, the integrated circuit die of the communication chip includes one or more devices, such as MOS-FET transistors built in accordance with implementations of the invention.
In further implementations, another component housed within the computing device 200 may contain an integrated circuit die that includes one or more devices, such as MOS-FET transistors built in accordance with implementations of the invention.
In various implementations, the computing device 200 may be a laptop, a netbook, a notebook, an ultrabook, a smartphone, a tablet, a personal digital assistant (PDA), an ultra-mobile PC, a mobile phone, a desktop computer, a server, a printer, a scanner, a monitor, a set-top box, an entertainment control unit, a digital camera, a portable music player, or a digital video recorder. In further implementations, the computing device 200 may be any other electronic device that processes data.
The interposer 300 may be formed of an epoxy resin, a fiberglass-reinforced epoxy resin, a ceramic material, or a polymer material such as polyimide. In further implementations, the interposer 300 may be formed of alternate rigid or flexible materials that may include the same materials described above for use in a semiconductor substrate, such as silicon, germanium, and other group III-V and group IV materials.
The interposer 300 may include metal interconnects 308 and vias 310, including but not limited to through-silicon vias (TSVs) 312. The interposer 300 may further include embedded devices 314, including both passive and active devices. Such devices include, but are not limited to, capacitors, decoupling capacitors, resistors, inductors, fuses, diodes, transformers, sensors, and electrostatic discharge (ESD) devices. More complex devices such as radio-frequency (RF) devices, power amplifiers, power management devices, antennas, arrays, sensors, and MEMS devices may also be formed on the interposer 300. In accordance with embodiments of the invention, apparatuses or processes disclosed herein may be used in the fabrication of interposer 300.
Although specific embodiments have been described above, these embodiments are not intended to limit the scope of the present disclosure, even where only a single embodiment is described with respect to a particular feature. Examples of features provided in the disclosure are intended to be illustrative rather than restrictive unless stated otherwise. The above description is intended to cover such alternatives, modifications, and equivalents as would be apparent to a person skilled in the art having the benefit of the present disclosure.
The scope of the present disclosure includes any feature or combination of features disclosed herein (either explicitly or implicitly), or any generalization thereof, whether or not it mitigates any or all of the problems addressed herein. Accordingly, new claims may be formulated during prosecution of the present application (or an application claiming priority thereto) to any such combination of features. In particular, with reference to the appended claims, features from dependent claims may be combined with those of the independent claims and features from respective independent claims may be combined in any appropriate manner and not merely in the specific combinations enumerated in the appended claims.
The following examples pertain to further embodiments. The various features of the different embodiments may be variously combined with some features included and others excluded to suit a variety of different applications.
Example embodiment 1 includes a memory device, comprising: a bitline; a wordline perpendicular to the bitline; and a capacitor coupled between the bitline and the wordline, wherein the capacitor comprises a ferroelectric material with a remnant polarization of about 80 uC/cm{circumflex over ( )}2 or greater.
Example embodiment 2 includes the memory device of example embodiment 1 or some other example herein, wherein the remnant polarization of the ferroelectric material is between about 80 uC/cm{circumflex over ( )}2 and 200 uC/cm{circumflex over ( )}2.
Example embodiment 3 includes the memory device of example embodiment 1 or some other example herein, further comprising a plurality of wordlines and a plurality of capacitors comprising the ferroelectric material, each respective capacitor from the plurality of capacitors coupled between the bitline and a respective wordline from the plurality of wordlines.
Example embodiment 4 includes the memory device of example embodiment 3 or some other example herein, wherein the plurality of capacitors includes at least four capacitors.
Example embodiment 5 includes the memory device of example embodiment 1 or some other example herein, further comprising a thin-film-based select transistor coupled to the bitline or a thin-film-based select diode coupled to the bitline.
Example embodiment 6 includes the memory device of example embodiment 1 or some other example herein, wherein the ferroelectric material includes a nitride comprising aluminum scandium nitride (AlScN).
Example embodiment 7 includes the memory device of example embodiment 1 or some other example herein, wherein the ferroelectric material comprises a perovskite material.
Example embodiment 8 includes the memory device of example embodiment 1 or some other example herein, wherein the capacitor comprises a plurality of layers.
Example embodiment 9 includes the memory device of example embodiment 1 or some other example herein, wherein the bitline is a first bitline, the memory device further comprising a second bitline parallel to the first bitline and perpendicular to the wordline.
Example embodiment 10 includes the memory device of example embodiment 9 or some other example herein, wherein the capacitor is a first capacitor, the memory device further comprising a second capacitor comprising the ferroelectric material and coupled to the second bitline and the wordline.
Example embodiment 11 includes a memory device, comprising: a bitline; a plurality of wordlines perpendicular to the bitline; and a plurality of capacitors comprising a ferroelectric material, each respective capacitor from the plurality of capacitors coupled between the bitline and a respective wordline from the plurality of wordlines.
Example embodiment 12 includes the memory device of example embodiment 11 or some other example herein, wherein the ferroelectric material has a remnant polarization of about 80 uC/cm{circumflex over ( )}2 or greater.
Example embodiment 13 includes the memory device of example embodiment 12 or some other example herein wherein the remnant polarization of the ferroelectric material is between about 80 uC/cm{circumflex over ( )}2 and 200 uC/cm{circumflex over ( )}2.
Example embodiment 14 includes the memory device of example embodiment 11 or some other example herein, wherein the plurality of capacitors includes at least four capacitors.
Example embodiment 15 includes the memory device of example embodiment 11 or some other example herein, further comprising a select transistor coupled to the bitline.
Example embodiment 16 includes the memory device of any of example embodiments 11-15 or some other example herein, wherein the ferroelectric material comprises aluminum scandium nitride (AlScN).
Example embodiment 17 includes the memory device of example embodiment 11 or some other example herein, wherein the ferroelectric material comprises a perovskite material.
Example embodiment 18 includes the memory device of example embodiment 11 or some other example herein, wherein the capacitor comprises a plurality of layers.
Example embodiment 19 includes the memory device of any of example embodiments 11-18 or some other example herein, wherein the bitline is a first bitline, the memory device further comprising a second bitline parallel to the first bitline and perpendicular to the plurality of wordlines.
Example embodiment 20 includes the memory device of example embodiment 19 or some other example herein, further comprising a second plurality of capacitors comprising the ferroelectric material, wherein each respective capacitor from the second plurality of capacitors is coupled between the second bitline and a respective wordline from the plurality of wordlines.
Example embodiment 21 includes a computing device, comprising: a board; and a component coupled to the board, the component including a memory device, comprising: a bitline; a wordline perpendicular to the bitline; and a capacitor coupled between the bitline and the wordline, wherein the capacitor comprises a ferroelectric material with a remnant polarization of 80 uC/cm{circumflex over ( )}2 or greater.
Example embodiment 22 includes the computing device of example embodiment 21 or some other example herein, further comprising: a processor coupled to the board, a communication chip coupled to the board, or a camera coupled to the board.
Example embodiment 23 includes the computing device of any of example embodiments 21 or 22 or some other example herein, wherein the component is a packaged integrated circuit die.
Example embodiment 24 includes a computing device, comprising: a board; and a component coupled to the board, the component including a memory device, comprising: a bitline; a plurality of wordlines perpendicular to the bitline; and a plurality of capacitors comprising a ferroelectric material, each respective capacitor from the plurality of capacitors coupled between the bitline and a respective wordline from the plurality of wordlines.
Example embodiment 25 includes the computing device of example embodiment 24 or some other example herein, further comprising: a processor coupled to the board, a communication chip coupled to the board, or a camera coupled to the board.
