WO2022104591A1

WO2022104591A1 - Vertical 3d pcm memory cell and program read scheme

Info

Publication number: WO2022104591A1
Application number: PCT/CN2020/129760
Authority: WO
Inventors: Jun Liu
Original assignee: Yangtze Advanced Memory Industrial Innovation Center Co., Ltd
Priority date: 2020-11-18
Filing date: 2020-11-18
Publication date: 2022-05-27
Also published as: CN112567525B; CN112567525A

Abstract

A three-dimensional memory architecture with a new vertical 3D phase change material (PCM) Memory Cell and Program/Read Scheme is disclosed. The scheme provides a lower cost and other benefits. In the proposed integration scheme for vertical 3D x-point memory, word lines are all formed together with replacement metal, and local bit lines are all formed vertically perpendicular to word lines, with global bit lines connecting local bit lines in different pages. PCM cells are formed in the recess of word lines while ovonic threshold switch (OTS) thin film is deposited as continuous film because of insulator property. The vertical 3D X-point provides more flexible scaling and cost reduction path compared to conventional stacked 3D x-point architecture. Multiple embodiments of cell array architectures are also presented.

Description

[Title established by the ISA under Rule 37.2] VERTICAL 3D PCM MEMORY CELL AND PROGRAM READ SCHEME

TECHNICAL FIELD

The present disclosure generally relates to three-dimensional electronic memories, and more particularly, to forming an improved memory architecture having several advantages over current self-aligned double patterning (SADP) semiconductors.

BACKGROUND

Planar memory cells are scaled to smaller sizes by improving process technology, circuit design, programming algorithm, and fabrication process. However, as feature sizes of the memory cells approach a lower limit, planar process and fabrication techniques become challenging and costly. As such, memory density for planar memory cells approaches an upper limit. A three-dimensional (3D) memory architecture can address the density limitation in planar memory cells.

Phase-change memory (PCM) is a non-volatile solid-state memory technology that exploits reversible, thermally-assisted switching of phase-change materials like chalcogenide compounds such as GST (Germanium-Antimony-Tellurium) , between states with different electrical resistance. The fundamental storage unit (the “cell” ) can be programmed into a number of different states, or levels, which exhibit different resistance characteristics. Programmable cell-states can be used to represent different data values, permitting storage of information.

PCM cells are programmed or erased by thermal self heating to induce an amorphous or crystalline state to denote 1 and 0. Programming current is directly proportional to the size and cross-sectional area of the PCM cell. In single-level PCM devices, each cell can be set to one of two states, a “SET” state and a “RESET” state, permitting storage of one bit per cell. In the RESET state, which corresponds to a wholly amorphous state of the phase-change material, the electrical resistance of the cell is very high. By heating to a temperature above its crystallization point and then cooling, the phase-change material can be transformed into a low-resistance, fully-crystalline state. This low-resistance state provides the SET state of the cell. If the cell is then heated to a high temperature, above the melting point of the phase-change material, the material reverts to the fully-amorphous RESET state on rapid cooling.

In addition, large programming current requirements also lend to large program voltage requirements. Reading and writing of data in PCM cells is achieved by applying appropriate voltages to the phase-change material via a pair of electrodes associated with each cell. In a write operation, the resulting programming signal causes Joule heating of the phase- change material to an appropriate temperature to induce the desired cell-state on cooling. Reading of PCM cells is performed using cell resistance as a metric for cell-state. An applied read voltage causes current to flow through the cell.

This current is dependent on resistance of the cell. Measurement of the cell current therefore provides an indication of the programmed cell state. A sufficiently low read voltage is used for this resistance metric to ensure that application of the read voltage does not disturb the programmed cell state. Cell state detection can then be performed by comparing the resistance metric with predefined reference levels. Programming current (I) is typically in the order of 100-200μA. The voltage drop may be significant if the write line (WL) and bit line (BL) in the cell encounters large resistance.

In commercial 3D X-point memory, bit lines and word lines are formed of tungsten (W) that is relatively high in resistivity. The memory chip is composed of many small memory arrays (tile) and risk large voltage drops of word lines and bit lines during program operation. Voltage drops due to word line and bit line resistances will cause memory cells to experience different program currents that may lead to over programming or under programming along the word line and bit line. In addition, tungsten resistivity rapidly increases with smaller critical dimensions or CD due to electron scattering at surfaces and grain boundaries.

In commercial 3D x-point memory, WL and BL are formed of 20nm/20nm L/Spattern. Memory cells are formed at the cross point of perpendicular WL and BLs. Two stacks of WL/BL/Memory cells are stacked in order to improve bit density. Typically, in current commercial 3D x-point memory, a bottom cell is formed first by patterning both BL and WL to define a bottom pillar memory cell. The formation of the pillar memory cell is then followed by top cell stack deposition and BL/WL patterning to define a top pillar memory cell. Each stack is formed with two Self-aligned Double Patterning (SADP) patterning steps. SADP is a form of double patterning. It is sometimes referred to as pitch division, spacer or sidewall-assisted double patterning. Further scaling of the semiconductor will add more stacks on top to lower cost. However, the cost benefit will diminish because of the high cost associated with additional SADP patterning for each stack.

Thus there is a need in the art for a memory cell stack that will minimize the cost associated with additional SADP patterning for each stack and still increase memory size. There is also a need in the art for a new cell architecture that is low cost and provides additional benefits in place of additional SADP patterning for each memory stack.

SUMMARY

The following summary is included in order to provide a basic understanding of aspects and features of the disclosure. This summary is not an extensive overview and as such it is not intended to particularly identify key or critical elements or to delineate the scope of the disclosure. Its sole purpose is to present concepts in a summarized format.

In one aspect, a new A New Vertical 3D PCM Memory Stack is disclosed. Multiple metal WLs are stacked on top of each other and separated by dielectric layers. Each stack is composed of perpendicular horizontal word lines and vertical bit lines. The Memory cell is self-aligned to the word line and bit line.

In one aspect, a new 3D X-Point Memory cell is disclosed. The memory cell is formed as a horizontal cell between a perpendicular of a word line and a bit line. Depending on the implementation, the memory cell is formed in a recess.

In another aspect, a method for forming a new 3D X-Point Memory Stack. The method includes depositing multiple nitride layer/polycrystalline silicon (Ni/Poly Si or Poly) layer stacks, forming circular holes through the stacks, recessing the polycrystalline silicon (poly) to form a phase change material (PCM) memory in the recess, depositing an ovonic threshold switch (OTS) and metal material to form vertical bit lines, forming a parallel line cutting oxide/nitride (ox/nit) stack perpendicular to previously formed line segments, and removing the poly and back fill with metal to form word lines.

A Vertical 3-D PCM architecture is also disclosed. The architecture has each finger composed of eight or six channel holes and/or six to eight holes. The finger is separated by a gate line slit. Each vertical local bit line is connected to a different global bit line in the finger.

In another aspect, a three-dimensional memory architecture with a new vertical 3D phase change material (PCM) Memory Cell and Program/Read Scheme is disclosed. The scheme provides a lower cost and other benefits. In the proposed integration scheme for vertical 3D x-point memory, word lines are all formed together with replacement metal, and local bit lines are all formed vertically perpendicular to word lines, with global bit lines connecting local bit lines in different pages. PCM cells are formed in the recess of word lines while ovonic threshold switch (OTS) thin film is deposited as continuous film because of insulator property. The vertical 3D X-point provides more flexible scaling and cost reduction path compared to conventional stacked 3D x-point architecture. Multiple embodiments of cell array architectures are also presented. Additional benefits of the new architecture include, but are not limited to, replacement of WLs not requiring additional Self-aligned Double Patterning (SADP) that can increase cost of production. Another benefit is shared WLs and BLs between adjacent memory cells, and lower WL and BL resistance due to shared WL and BLs. In addition, there are no misalignment issues between different stacks. The new architecture is highly extendable to more stacks without requiring increasing lithography steps. The new technology may be extended to other resistive memory technologies. These and other benefits are possible through the disclosed new technology.

In accordance with an aspect, a three-dimensional memory cell structure includes at least one memory cell stack, the memory cell stack having a selector, a phase change memory cell, and a first electrode and a second electrode. The phase change memory cell is disposed between the first and the second electrode. Each memory cell stack has a word line and a bit line perpendicular to each other and coupled to the memory cell stack. The memory cell stack is self-aligned with respect to the word line and the bit line. The word line and the bit line are formed with a self-aligned metal for improved programming and increased array size. Depending on the implementation, the metal is tungsten or other metal.

In accordance with an aspect, a method of forming a three-dimensional memory comprises further comprises forming multiple nitride/poly stack, forming holes in the stack for subsequent cell and bit line definitions and recessing the poly then filling the recess with a PCM material followed by dry or wet etch back. Depending on the embodiment, the filling of the recess includes using only a PCM material, using a Carbon and PCM material, or using a Carbon and PCM material and a carbon material. The filling of the recess may be done in an ordered sequence wherein the sequence of materials previously listed is the sequence of the filling of the recess. In addition the recess may form a pocket cell for the filling of the above materials. The method further includes depositing an OTS material as selector, depositing tungsten (W) or other metal followed by Chemical mechanical polishing or planarization (CMP) to form local bit lines, forming cuts in the stack and remove polycrystalline silica with wet etch, and gap filling with WL metal to form a WL. Depending on the implementation, the gap fill is applied to the cell stack with an atomic layer deposition oxide, a spin on dielectric or a flowable chemical vapor deposition oxide. CMP with an oxide and/or nitride compound may or may not be applied to the cell stack depending on the implementation.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects, features and advantages of the present disclosure will be further appreciated when considered with reference to the following description of exemplary embodiments and accompanying drawings, wherein like reference numerals represent like elements. In describing the exemplary embodiments of the present disclosure illustrated in the drawings, specific terminology may be used for the sake of clarity.

However, the aspects of the present disclosure are not intended to be limited to the specific terms used.

Figs. 1A and 1B are isometric views of a prior three-dimensional cross point memory.

Figs. 2A, 2B-1, 2B-2 and 2C are views of a section of a three-dimensional cross point memory showing formation of multiple nitride/polycrystalline stacks, forming holes in the stacks, and Fig. 2C is a diagram showing abbreviations for layers in the cell stack.

Figs. 3A and 3B are plan views of the three-dimensional cross point memory in accordance with the embodiment of Figs. 2A-2C with filling the recess with phase change material (PCM) , and depositing an ovonic threshold switch (OTS) material as a selector, respectively.

Figs. 4A and 4B are plan views of the three-dimensional cross point memory in accordance with the embodiment of Figs. 3A and 3B showing depositing metal followed by chemical mechanical planarization or polishing (CMP) to form local bit lines and forming cuts in the stack and removing the polycrystalline silica (poly Si) , respectively.

Fig. 5 is a plan view of the three-dimensional cross point memory in accordance with the embodiment of Figs. 4A and 4B showing formation of Write lines (WL) .

Fig. 6A is a plan view of the three-dimensional cross point memory in accordance with the embodiment of Fig. 5 and showing each global bit line (GBL) connected to an individual local bit line (LBL) in each page and multiple LBLs in multiple pages, and Fig. 6B is a schematic showing an array architecture of Fig. 6A.

Fig. 7A is a plan view of the three-dimensional cross point memory in accordance with the embodiment of Figs. 6A-6B and showing global bit lines (GBL) and local bit lines (LBL) and Word Lines (WL) of a selected cell having a voltage bias, and Fig. 7B is a schematic showing the cell biasing architecture of Fig. 7A.

Fig. 8A is a plan view of the three-dimensional cross point memory in accordance with another embodiment and showing each global bit line (GBL) connected to an individual local bit line (LBL) in each page and multiple LBLs in multiple pages, and Fig. 8B is a schematic showing an array architecture of Fig. 8A.

Fig. 9A is a plan view of the three-dimensional cross point memory in accordance with another embodiment and showing each global bit line (GBL) connected to an individual local bit line (LBL) in each page and multiple LBLs in multiple pages, and Fig. 9B is a schematic showing an array architecture of Fig. 9A.

Figs. 10A, 10B and 10C are views for another embodiment of a section of a three-dimensional cross point memory showing formation of multiple nitride/polycrystalline stacks, forming holes in the stacks, and Fig. 2C still used as a diagram showing abbreviations for layers in the cell stack.

Figs. 11A and 11B are plan views of the three-dimensional cross point memory in accordance with the embodiment of Figs. 10A-10C with recessing the polycrystalline silica (poly) and then filling the recess with phase change material (PCM) , and depositing an ovonic threshold switch (OTS) material as a selector, respectively.

Fig. 12 is a plan view of the three-dimensional cross point memory in accordance with the embodiment of Figs. 11A and 11B showing depositing metal followed by chemical mechanical planarization or polishing (CMP) to form local bit lines and forming cuts in the stack and removing the polycrystalline silica (poly Si) , respectively, and showing formation of Write lines (WL) .

Figs. 13A, 13B and 13C are views for another embodiment of a section of a three-dimensional cross point memory showing formation of multiple nitride/polycrystalline stacks, forming holes in the stacks, and Fig. 2C still used as a diagram showing abbreviations for layers in the cell stack.

Fig. 14A and 14B are plan views of the three-dimensional cross point memory in accordance with the embodiment of Figs. 13A-13C showing recessing the poly crystalline silica (poly) and then filling the recess with phase change material (PCM) , and depositing an ovonic threshold switch (OTS) material as a selector, respectively.

Fig. 15 is a plan view of the three-dimensional cross point memory in accordance with the embodiment of Figs. 14A and 14B showing depositing metal followed by chemical mechanical planarization or polishing (CMP) to form local bit lines and forming cuts in the stack and removing the polycrystalline silica (poly Si) , respectively, and showing formation of Write lines (WL) .

DETAILED DESCRIPTION

Although specific configurations and arrangements are discussed, it should be understood that this is done for illustrative purposes only. A person skilled in the pertinent art will recognize that other configurations and arrangements can be used without departing from the spirit and scope of the present disclosure. It will be apparent to a person skilled in the pertinent art that the present disclosure can also be employed in a variety of other applications.

It is noted that references in the specification to “one embodiment, ” “an embodiment, ” “an example embodiment, ” “some embodiments, ” and the like, merely indicate that the embodiment described may include a particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Further, when a particular feature, structure or characteristic is described in connection with an embodiment, it would be within the knowledge of a person skilled in the pertinent art to affect such feature, structure or characteristic in connection with other embodiments whether or not explicitly described.

In general, terminology may be understood at least in part from usage in context. For example, the term “one or more” as used herein, depending at least in part upon context, may be used to describe any feature, structure, or characteristic in a singular sense or may be used to describe combinations of features, structures or characteristics in a plural sense. Similarly, terms, such as “a, ” “an, ” or “the, ” again, may be understood to convey a singular usage or to convey a plural usage, depending at least in part upon context.

It should be readily understood that the meaning of “on, ” “above, ” and “over” in the present disclosure should be interpreted in the broadest manner such that “on” not only means “directly on” something but also includes the meaning of “on” something with an intermediate feature or a layer there between, and that “above” or “over” not only means the meaning of “above” or “over” something but can also include the meaning it is “above” or “over” something with no intermediate feature or layer there between (i.e., directly on something) .

Further, spatially relative terms, such as “beneath, ” “below, ” “lower, ” “above, ” “upper, ” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element (s) or feature (s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

The term “substrate” as used herein may refer to any workpiece on which formation or treatment of material layers is desired. Non-limiting examples include silicon, germanium, silica, sapphire, zinc oxide, silicon carbide, aluminum nitride, gallium nitride, Spinel, silicon on oxide, silicon carbide on oxide, glass, gallium nitride, indium nitride, aluminum nitride, glasses, polycrystalline silica, combinations or alloys thereof, and other solid materials. The substrate itself can be patterned. Materials added on top of the substrate can be patterned or can remain unpattern. Furthermore, the substrate can include a wide array of semiconductor materials, including but not limited to silicon, germanium, gallium arsenide, indium phosphide, and the like. Alternatively, the substrate can be made from an electrically non-conductive material, such as a glass, a plastic, or a sapphire wafer.

As used herein, the term “layer” refers to a material portion including a region with a thickness. A layer can extend over the entirety of an underlying or overlying structure, or may have an extent less than the extent of an underlying or overlying structure. Further, a layer can be a region of a homogeneous or inhomogeneous continuous structure that has a thickness less than the thickness of the continuous structure. For example, a layer can be located between any pair of horizontal planes between, or at, a top surface and a bottom surface of the continuous structure. A layer can extend horizontally, vertically, and/or along a tapered surface. A substrate can be a layer, can include one or more layers therein, and/or can have one or more layer thereupon, thereabove, and/or therebelow. A layer can include multiple layers. For example, an interconnect layer can include one or more conductor and contact layers (in which contacts, interconnect lines, and/or vias are formed) and one or more dielectric layers.

The term “horizontal” as used herein will be understood to be defined as a plane parallel to the plane or surface of the substrate, regardless of the orientation of the substrate. The term “vertical” will refer to a direction perpendicular to the horizontal as previously defined. Terms such as “above” , “below” , “bottom” , “top” , “side” (e.g. sidewall) , “higher” , “lower” , “upper” , “over” , and “under” , are defined with respect to the horizontal plane. The term “on” means there is direct contact between the elements. The term “above” will allow for intervening elements.

As used herein, a material (e.g. a dielectric material or an electrode material) will be considered to be “crystalline” if it exhibits greater than or equal to 30%crystallinity as measured by a technique such as x-ray diffraction (XRD) . Amorphous material is considered non-crystalline.

As used herein, the terms “first, ” “second, ” and other ordinals will be understood to provide differentiation only, rather than imposing any specific spatial or temporal order.

As used herein, the term “oxide” (of an element) will be understood to include additional components besides the element and oxygen, including but not limited to a dopant or alloy. As used herein, the term “nitride” (of an element) will be understood to include additional components besides the element and nitrogen, including but not limited to a dopant or alloy.

As used herein, the term “Damascene” will be understood to mean a Damascene Process. In this process, the underlying silicon oxide insulating layer is patterned with open trenches or channels where the conductor should be located. A thick coating of copper that significantly overfills the trenches is deposited on the insulator, and chemical-mechanical planarization (CMP) is used to remove the copper (known as overburden) that extends above the top of the insulating layer. Copper sunken within the trenches or channels of the insulating layer is not removed and becomes the patterned conductor. Damascene processes generally form and fill a single feature with copper per Damascene stage. Dual-Damascene processes generally form and fill two features with copper at once.

Furthermore, as used herein the term “Self-aligned double Patterning (SADP) ” is a form of double patterning. It is sometimes referred to as pitch division, spacer or sidewall-assisted double patterning. The SADP process uses one lithography step and additional deposition and etch steps to define a spacer-like feature. Generally, in the SADP process, the first step is to form mandrels on a substrate. Then, the pattern is covered with a deposition layer. The deposition layer is then etched, which, in turn, forms spacers. Finally, the top portion undergoes a chemical mechanical polishing or planarization (CMP) step.

The present technology is applied to a new vertical 3D X-Point PCM Memory and program/read scheme to, among other things, lower production costs. The new propose three-dimensional memory architecture provides a lower cost and other benefits. In the proposed integration scheme for vertical 3D x-point memory, word lines are formed together with replacement metal, and local bit lines are all formed vertically perpendicular to word lines, with global bit lines connecting local bit lines in different pages. PCM cells are formed in the recess of word lines while ovonic threshold switch (OTS) thin film is deposited as continuous film because of insulator property. Vertical 3D X-point provides, among other things, more flexible scaling and cost reduction path compared to conventional stacked 3D x-point architecture. Multiple embodiments of cell array architectures are also presented herrein. Additional benefits of the new architecture include, but are not limited to, replacement of WLs not requiring additional Self-aligned Double Patterning (SADP) that can increase cost of production, shared WLs and BLs between adjacent memory cells, and lower WL and BL resistance due to shared WL and BLs. In addition, there are no misalignment issues between different stacks. The new architecture is highly extendable to more stacks without requiring increasing lithography steps. The new technology may be extended to other resistive memory technologies. In addition the new technology disclosed herein may be utilized in other resistive memory technologies.

Adverting to the Figures, shown is a generalized prior example of a three-dimensional (3D) memory in FIG. 1A. In particular, Fig. 1A is an isometric view of a section of three-dimensional crosspoint memory. The memory includes a first layer of memory cells 5 and a second layer of memory cells 10. Between the first layer of memory cells 5 and second layer of memory cells is a number of word lines 15 extending in the X direction. Above the first layer of memory cells 5 is a number of first bit lines 20 extending along the Y direction, and below the second layer of memory cells is a number of second bit lines 25 extending along the Y direction. Further, as can be seen from the figure, the sequential structure of bit lines -memory cells -word lines -memory cells may be repeated along the Z direction to realize a stacked configuration. In any event, an individual memory cell may be accessed by selectively activating the word line and bit line corresponding to the cell.

In FIG. 1B, shown is a single section 100 of the cell structure in FIG. 1A. Shown is a top cell bit line 110 connected to a top cell stack 150. Stack 150 is composed of several layers that will be described herein in the improvement of this standard stack 150. Perpendicular to the top cell bit line 110 is top cell write line 130 and bottom cell write line 140. Connected to bottom cell write line 140 is a bottom cell stack 160. Parallel to top cell bit line 110 is bottom cell bit line 120. Bottom cell bit line 120 is coupled to the bottom cell stack 160. Like cell stack 150, cell stack 160 is also made of several layers. FIGS. 1A and 1B illustrate the general structure of a 3D X-Point Memory cell that terminology is used herein to describe the improvement. The FIG. 1A depicts the section as viewed along the Z (depth) direction. The section includes a number of word lines, e.g. word lines 130, 140, extending in the X (horizontal) direction, a number of top cell bit lines, e.g.,

bit lines

110, 120, extending along the Y (vertical) direction and corresponding to a top cell array of memory cells 150, and a number of bottom cell bit lines extending along the vertical direction and corresponding to a bottom cell array of memory cells 160. Reference will be made to X and Y directions utilizing the directional model shown in FIGS. 1A-1B. FIGS. 1A-1B illustrates the general structure of a 3D X-Point Memory cell, and that terminology is used herein to describe the improvement. The word lines, top cell bit lines, and bottom cell bit lines may or may not, depending on the embodiment, be typically formed according to a 20 nm /20 nm Line /Space (L/S) pattern, and formed on a silicon substrate. Moreover, the memory may employ complementary metal-oxide semiconductor (CMOS) technology.

As stated above, issue of reusing SADP patterning for each stack is addressed by the present enclosure. Adverting to FIG. 2A is a plane view of a structure in the x-direction showing forming a multiple layer nitride/polycrystalline silica (poly or poly Si) stack 200. Stack 200 comprises alternating layers having a plurality of nitride layer 204 and a plurality of polycrystalline silica layer 211. Depending on the embodiment the layers may alternate with the nitride layer a top position and/or bottom position as shown in FIG. 2A. A substrate 201 is used in the forming of the multiple nitride/polycrystalline silica stack 200. FIG. 2B-1 is a top down view of the stack 200 in FIG. 2A. Illustrated is the forming of a plurality of holes 202 or channel holes 202that penetrate the stack for subsequent memory cell and bit line definitions. The hole 202 penetrates all the layers of stack 200 to the substrate 201. Depending on the implementation, the holes 202 may or may not penetrate partially trough stack 202 and/or penetrate stack 200 at various depths. For the illustration shown herein, the holes 202 are of uniform depth and penetrate completely through stack 200 to the substrate 201. However, this embodiment is not meant to limit the scope of the invention to any such embodiment.

A cross-sectional view of FIG. 2B-1 is taken along line A-A and viewed in the x-direction similar to FIG. 2A. This cross-sectional view is shown in FIG. 2B-2. Shown in FIG. 2B-2 are finger 1, finger 2, and finger 3. A plurality of fingers may be utilized in the present disclosure as well as the number of holes. Depending on the embodiment the number of holes may be 6 to 8 or 6 or 8 holes. Fingers 1-3 are formed by the holes in the stack 200. FIG. 2C illustrates a layer key. The layer key illustrates various layers that may or may not be added to stack 200. Again, layer 204 is a nitride layer. Examples of such materials include, but are not limited to, metal nitrides such as TiN, TiAlN, TaN, BN, metal oxide nitrides such as TiON, metal silicides such as PtSi, semiconductors such as silicon or germanium (with and without doping) , reduced metal oxides such as TiOx (x<2 indicates reduction) , metals such as W, Ni, Co, or carbon based materials.

Layer 211 is a polycrystalline silica or poly crystalline silicon (poly or poly-Si) material. Depending on the embodiment layer 211 may include any film thickness and may typically be 2-5μm. Layer 208 is an ovonic threshold switch (OTS) material. Typically the OTS material is a glass based switch that after being brought from the highly resistive state to the conducting state returns to the highly resistive state when the current falls below a holding current value. Again, any OTS material may be utilized with the preset disclosure.

Layer 206 is a phase change material (PCM) memory cell layer. Again, PCM is a non-volatile solid-state memory technology that exploits reversible, thermally-assisted switching of phase-change materials like chalcogenide compounds such as GST (Germanium-Antimony-Tellurium) , between states with different electrical resistance. The fundamental storage unit (the “cell” ) can be programmed into a number of different states, or levels, which exhibit different resistance characteristics. Programmable cell-states can be used to represent different data values, permitting storage of information.

Layer 205 is an electrode layer. The electrodes can be formed of any convenient electrically-conductive material, typically a metallic material (e.g. a pure metal or a metal compound, alloy or other mixture) or a doped semiconductor material such as silicon. Moreover, while the features described are particularly advantageous for multi-level cells, these features can also be applied to advantage in single-level cells in some embodiments.

Layer 210 is a tungsten layer. Tungsten may be used as the metal for defining write and bit lines depending on the embodiment. Again any metal based material may utilize the principles of the present disclosure. Again, as previously stated the use of the terms first, second and third is to provide differentiation only, rather than imposing any specific spatial or temporal order. For example, the carbon electrode may be interchangeable and the reference to the terms first, second and third are merely used as a reference to describe adjacent elements. The layers are abbreviated as: Nitride/Poly Si/OTS/PCM/carbon electrode/W (tungsten) as shown in FIG. 2C. Reference numeral 201 refers to the substrate or an oxide layer depending on the implementation.

FIG. 3A shows

exemplary cell fingers

1, 2, and 3. Each finger is made of several layers as previously described. The

fingers

1, 2, and 3 are similar in function and composition. For the description of materials disclosed herein, similar reference numerals to common elements in various figures denote similar material and functions of the elements shown and described. Also illustrated is the recessing of the poly Si layers. The recessing of these poly Si layers 211 may be achieved by various methods known by those skilled in the art. Depending on the implementation all the layers 211 may be recessed or a selected amount of layers 211 may be recessed. The recess is defined by removal of material from polycrystalline silica (poly Si) layer 211, or the recess defined by a partially removed polycrystalline silica layer. The recessing is followed by filling the recess formed with a PCM material 206 as shown in FIG. 3A. The filling of the PCM material 211 may or may not be followed by dry or wet etch back. Wet etching may be used to remove the poly Si material 211 for filling with the PCM material 206. Depending on the implementation, ammonium hydroxide or hydrogen peroxide may be utilized in the etching process.

Shown in FIG. 3B is depositing an OTS material 208 over

fingers

1, 2, 3. These depositing forms an encapsulation layer of OTS layer 208 over the fingers and covers a top of the substrate 201. The OTS or ovonic threshold switch 208 in each finger stack is used as a selector.

FIG. 4A illustrates a depositing of a metal or in this embodiment tungsten (W) 210 into holes 202 in FIG. 3B. Depending on the embodiment, the fill of the metal material into holes 202 may be level or not level with the top layer of the stack, and in this example top layer 204. The fill or deposit of W or other material is followed by a chemical mechanical polishing or planarization (CMP) process to form local bit lines. Oxide/nitride chemical mechanical planarization (CMP) treatment may produce an oxide layer if so desired. FIG. 4B illustrates forming cuts in the stack 200 and removing poly Si with wet etching to form gaps 209 in the fingers. Typically deposition may be accomplished by Chemical vapor deposition (CVD) . In this process a vacuum deposition method is used to produce high quality, high-performance, solid materials. In typical CVD, the wafer (substrate) is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. Other methods may also be utilized depending on the implementation.

FIG. 5 illustrates filling the gaps 209 in FIG. 4B with Word Line (WL) metal 210 or material to form Word Lines. The WL material may be material used by those skilled in the art. If gap fill is desired to be used, gap fill may be obtained through atomic layer deposition oxide, Spin on Dielectric (SOD) or flowable chemical vapor deposition (CVD) oxide. Examples of gap fill materials, include, but are not limited to, gallium arsenide (GaAs) , indium gallium arsenide (InGaAs) , gallium nitride (GaN) , aluminum nitride (AlN) , cadmium sulfide (CdS) , cadmium selenide (CdSe) , cadmium tellurite (CdTe) , zinc sulfide (ZnS) , lead sulfide (PbS) and lead selenide (PbSe) and Cobalt based compounds and any combination thereof.

FIGS. 6A and 6B illustrate global bit lines (GBL) connected to an individual local bit line (LBL) in each page or section of the stack, and multiple LBLs in multiple pages as the stack is increased. FIG. 6A shows

global bit lines

1 and 2 labeled 610 and 620 respectively. GBL1 or 610 and GBL2 or 620 are in communication with vertical local bit lines LBLa labeled 630 and LBLb labeled 640, respectively as shown in FIG. 6A. Word lines are formed horizontally to the vertical local bit lines as shown in WL1 labeled 660 and WL 2 labeled 670 respectively. Depending on the embodiment, the word lines are in communication with the local bit lines. As shown in FIG. 6B, an array architecture is shown. The dark dots represent the vertical bit lines in Fig. 6A. Shown in array 650 are

global bit lines

610, 620, 653, and 654 for

GBL

1, 2, 3, and 4 respectively. In this example two sections or pages are shown page 655 for page 1 and page 656 for page 2. However, it is within the scope of the disclosure to have many pages as the stack is built. The given structure is given only to describe the principles of the present methods and systems of this disclosure. Each GBL is connected to an individual LBL in each page as shown in FIG. 6B. Shown is LBLa (630) and LBLi (668) in communication with GBL 1 (610) . LBLc (662) and LBLg (667) is in communication with GBL2 (620) . LBLb (640) and LBLf (664) is in communication with GBL4 (654) . LBLd (663) and LBLh (665) is in communication with GBL3 (653) .

FIGS. 7A and 7B illustrate cell biasing for the figures in FIGS 6A-6B where similar reference numerals represent similar structures. Shown is the GBL 610 and LBL 630 of a selected cell 700 belonging to a cell 710 that is biased at +Vhh and a Word Line (WL) 670 biased at -Vll. All other GBL/LBL and WLs are biased at 0 as shown for

reference numerals GBL

620, 653 and 654 for example.

Selected cell

700 and 710 is biased at Vhh+Vll, for example. An unselected cell such as 720 is biased at either Vhh or Vll or 0.

FIGS. 8A and 8B is a second embodiment of an array architecture of FIGS. 6A and 6B for stack 200. Illustrated is each GBL is connected to an individual LBL in each page, and multiple LBLs in multiple pages. This array architecture embodiment may require self-aligned quadruple patterning (SAQP) . SAQP like SADP is multiple patterning (or multi-patterning) class of technologies for manufacturing integrated circuits (ICs) , developed for photolithography to enhance the feature density. It is expected to be necessary for a 10 nm and 7 nm node semiconductor processes and beyond. The premise is that a single lithographic exposure may not be enough to provide sufficient resolution. Hence additional exposures would be needed, or else positioning patterns using etched feature sidewalls (using spacers) would be necessary. Shown in FIG. 8A shows

global bit lines

1 and 2 labeled 810 and 820 respectively. GBL1 or 810 and GBL2 or 820 are in communication with vertical local bit lines LBLa labeled 830 and LBLb labeled 840, respectively as shown in FIG. 8A. Word lines are formed horizontally to the vertical local bit lines as shown in WL1 labeled 860 and WL 2 labeled 870 respectively. Depending on the embodiment, the word lines are in communication with the local bit lines. As shown in FIG. 8B, an array architecture is shown. The dark dots represent the vertical bit lines in Fig. 8A. Shown in array 850 are

global bit lines

810, 820, 853, 854, 856 and 857 for

BL

1, 2, 3, 4, 5, and 6, respectively. In this example two pages are shown, for example, page 855 for page 1 and page 856 for page 2. However, it is within the scope of the disclosure to have many pages as the stack is built. The given structure is given only to describe the principles of the present methods and systems of this disclosure. Each GBL is connected to an individual LBL in each page as shown in FIG. 8B. Shown is LBLa (830) in communication with GBL 1 (810) . LBLc (862) is in communication with GBL2 (820) . LBLe (865) is in communication with GBL 3 (853) . LBLb (840) is in communication with GBL4 (854) . LBLd (863) is in communication with GBL5 (856) . And LBLf (864) is in communication with GBL 6 (857) .

FIGS. 9A-9B illustrate a third embodiment to FIGS. 6A-6B. Illustrated is each GBL is connected to an individual LBL in each page, and multiple LBLs in multiple pages. This array architecture embodiment may require self-aligned quadruple patterning (SAQP) as in the second embodiment shown in FIGS 8A-8B. Shown in FIG. 8A shows

global bit lines

1 and 2 labeled 910 and 920 respectively. GBL1 or 910 and GBL2 or 920 are in communication with vertical local bit lines LBLa labeled 930 and LBLb labeled 940, respectively as shown in FIG. 9A. Word lines are formed horizontally to the vertical local bit lines as shown in WL1 labeled 960 and WL 2 labeled 970 respectively. Depending on the embodiment, the word lines are in communication with the local bit lines. As shown in FIG. 9B, an array architecture is shown. The dark dots represent the vertical bit lines in Fig. 9A. Shown in array 950 are

global bit lines

910, 920, 953, 954, 956, 957, 958, and 959 for

BL

1, 2, 3, 4, 5, 6, 7, and 8 respectively. In this example one page is shown, for example, page 955 for page 1. However, it is within the scope of the disclosure to have many pages as the stack is built. The given structure is given only to describe the principles of the present methods and systems of this disclosure. Each GBL is connected to an individual LBL in each page as shown in FIG. 9B. Shown is LBLa (930) in communication with GBL 1 (910) . LBLc (962) is in communication with GBL2 (920) . LBLe (965) is in communication with GBL 3 (953) . LBLf (964) is in communication with GBL 7 (958) . LBLg (969) is in communication with GBL4 (954) . LBLd (963) is in communication with GBL6 (957) . LBLf (964) is in communication with GBL 7 (958) . And LBLh (967) is in communication with GBL 8 (959) .

FIGS. 10A-C, FIGS. 11-11B, FIG. 12, are illustrations of a fourth embodiment of the present disclosure. Shown is another alternate description of the core ideas, concepts methods structure material composition and/or process steps to achieve the goals of the disclosure. FIGS. 10A, 10B, and 10C have similar structures and reference numerals as FIGS. 2A, 2B-2 and 2B-1, respectively with similar descriptions previously described. FIGS. 10A, 10B and 10C illustrates forming a multiple nitride/poly stack 200 and forming holes or channel holes 202 in the stack for subsequent cell and bit line definitions.

FIGS. 11-11B have similar reference numerals and structures as FIGS 3A-3B previously described. FIG. 11A however, illustrates differently than FIG. 3A in that FIG. 11A shows recessing the poly and filling the recess with carbon layer 205 and PCM material 206 to form a pocket cell defined by both

material layers

205 and 206. The recess is formed with dry or wet etch back. FIG 11B illustrates depositing an OTS material 208 as a selector.

FIG. 12 illustrates depositing tungsten or other metal followed by CMP to form local bit lines. Similar reference numerals and structures shown in FIGs 4A-4C and FIG. 5 illustrate common structures and description. Form cuts in the stack 200 are made and poly Si is removed typically by wet etching techniques. The gap formed by the wet etching is filled with Word Line metal to form word lines, for example 660 and 670 in FIG. 12. Again the differences between the embodiments in the previous FIGS 4A-4C FIG 5 and FIG 6A is the addition of filling the recess with carbon layer 205 and PCM material 206 to form a pocket cell, instead of using only the PCM material 206.

FIGS. 13A, 13B, 13C, FIGS. 14A-14B, and FIG. 15, are illustrations of a fifth embodiment of the present disclosure. Shown is another alternate description of the core ideas, concepts methods structure material composition and/or process steps to achieve the goals of the disclosure. FIGS. 13A, 13B, and 13C have similar structures and reference numerals as FIGS. 2A, 2B-2 and 2B-1, respectively with similar descriptions previously described. FIGS. 13A, 13B and 13C illustrates forming a multiple nitride/poly stack 200 and forming holes or channel holes 202 in the stack for subsequent cell and bit line definitions.

FIGS. 14-14B have similar reference numerals and structures as FIGS 3A-3B previously described. FIG. 11A however, illustrates differently than FIG. 3A, and previous FIG. 11A in that FIG. 14A shows recessing the poly and filling the recess with carbon layer 205 and PCM material 206 and again carbon layer 205 to form a pocket cell defined by both

material layers

205 and 206. The recess is formed with dry or wet etch back. FIG 14B illustrates depositing an OTS material 208 as a selector.

FIG. 15 illustrates depositing tungsten or other metal followed by CMP to form local bit lines. Similar reference numerals and structures shown in FIGs 4A-4C and FIG. 5 illustrate common structures and description. Form cuts in the stack 200 are made and poly Si is removed typically by wet etching techniques. The gap formed by the wet etching is filled with Word Line metal to form word lines, for example 660 and 670 in FIG. 15. Again the differences between the embodiments in the previous FIGS 4A-4C FIG 5 and FIG 6A and FIGs 11A-B and 12 are the addition of filling the recess with carbon layer 205 and PCM material 206 and then again a second carbon layer 205 to form a pocket cell, instead of using only the PCM material 206 as shown in FIG. 5, or the PCM material 206 and one layer of carbon 205 as shown as an illustrative example in FIG. 12.

Most of the foregoing alternative examples are not mutually exclusive, but may be implemented in various combinations to achieve unique advantages. As these and other variations and combinations of the features discussed above may be utilized without departing from the subject matter defined by the claims, the foregoing description of the embodiments should be taken by way of illustration rather than by way of limitation of the subject matter defined by the claims. As an example, the preceding operations do not have to be performed in the precise order described above. Rather, various steps can be handled in a different order, such as reversed, or simultaneously. Steps can also be omitted unless otherwise stated. In addition, the provision of the examples described herein, as well as clauses phrased as "such as, " "including" and the like, should not be interpreted as limiting the subject matter of the claims to the specific examples; rather, the examples are intended to illustrate only one of many possible embodiments. Further, the same reference numbers in different drawings may identify the same or similar elements.

Although the present disclosure herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present disclosure. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present disclosure as defined by the appended claims.

Claims

A vertical three-dimensional phase change material memory cell structure, comprising:

at least one memory cell stack, the memory cell stack having a selector, a phase change material (PCM) memory cell, and a first electrode and a second electrode; the PCM memory cell disposed between the first and the second electrode;

each memory cell stack having a horizontal word line and a vertical bit line perpendicular to each other and coupled to the memory cell stack, and wherein the memory cell stack is self-aligned with respect to the word line and the bit line; and

wherein, the memory cell is self-aligned to the word line and the bit line and formed with a metal for improved programming and increased array size.
The vertical three-dimensional phase change material memory cell structure according to claim 1, wherein,

the memory cell is formed as a horizontal cell between the perpendicular word line and bit line,

the stack including alternating layers having a plurality of nitride layers and a plurality of polycrystalline silica layer (poly Si) , and

the PCM memory cell in each stack is formed in a recess between the nitride layers, and the recess defined by a partially removed polycrystalline silica layer therebetween.
The vertical three-dimensional phase change material memory cell structure according to claim 1, wherein the word line and/or the bit line is formed with a damascene process.
The vertical three-dimensional phase change material memory cell structure according to claim 1, wherein the metal is a tungsten (W) material.
The vertical three-dimensional phase change material memory cell structure according to claim 1, further comprising additional memory cells in a region above or below a two-dimensional region defined by the word line.
The vertical three-dimensional phase change material memory cell structure according to claim 1, wherein a subarray or a tile size is increased to improve array efficiency.
A vertical three-dimensional X-Point phase change material (PCM) memory architecture, comprising:

a plurality of nitride/polycrystalline silica memory stacks wherein each stack defines a plurality of channel holes in a vertical direction for a plurality of memory cells and a plurality of bitlines;

the stacks forming a plurality of fingers having the channel holes therebetween;

each pair of fingers define a gate line slit and each finger is separated by the gate line slit;

wherein the plurality of bit lines contains a vertical local bit line connected to a different global bit line in the finger; and

wherein, the vertical local bit line and the global bit line are formed from a metal material to electrically access each memory cell.
The vertical three-dimensional X-Point PCM memory architecture according to claim 7, wherein the local bit line is vertical and a word line is horizontal and coupled thereto.
The vertical three-dimensional X-Point PCM memory architecture according to claim 7, wherein the number of channel holes for each finger is six or eight channel holes.
A method of forming a three-dimensional memory stack comprising:

forming a stack having a plurality of layers of nitride and polycrystalline silica;

forming a plurality of holes in the stack for subsequent cell and bit line definitions;

recessing the polycrystalline silica to form a recess and filling the recess with a phase change material (PCM) followed by a dry or a wet etch back;

depositing on the stack an ovonic threshold switch (OTS) material as a selector;

depositing tungsten (W) or another metal on the stack followed by a chemical mechanical polishing or planarization (CMP) to form a plurality of local vertical bit lines;

forming cuts in the stack and removing polycrystalline silica with the wet etch; and

gap filling with a Word Line metal to form a plurality of Word Lines.
The method according to claim 10, wherein the plurality of holes is six to eight holes.
The method according to claim 10, wherein the recessing of the polycrystalline silica further comprises forming a pocket cell and filling the recess with and ordered sequence of a Carbon and the phase change memory.
The method according to claim 10, wherein the recessing of the polycrystalline silica further comprises forming a pocket cell and filling the recess with an ordered sequence of a Carbon, the phase change material and a carbon material.
The method according to claim 10, wherein the plurality of holes further defines a plurality of fingers and each finger is separated by a gate line slit.
The method according to claim 14, wherein the vertical local bit line is connected to a different global bit line in the finger.