# Patent

## Title
Semiconductor device and structure

## Abstract

A semiconductor device, including: a first semiconductor layer including first transistors, wherein the first transistors are interconnected by at least one metal layer including aluminum or copper; and a second mono-crystallized semiconductor layer including second transistors and overlaying the at least one metal layer, wherein the at least one metal layer is in-between the first semiconductor layer and the second mono-crystallized semiconductor layer, wherein the second mono-crystallized semiconductor layer is less than 100 nm in thickness, and wherein the second transistors include horizontally oriented transistors.

## Background
This application is a continuation of U.S. patent application Ser. No. 13/251,271, filed on Oct. 2, 2011, of which priority to is claimed. The contents of the foregoing applications are incorporated herein by reference.


BACKGROUND OF THE INVENTION
1. Field of the Invention
This application relates to the general field of Integrated Circuit (IC) devices and fabrication methods, and more particularly to multilayer or Three Dimensional Integrated Circuit (3D IC) devices and fabrication methods.
2. Discussion of Background Art
Logic chips such as microprocessors and Systems-on-Chips (SoCs) typically include a significant amount of on-die memory. This on-die memory can be in the form of Static Random Access Memory (SRAM), Dynamic Random Access Memory (DRAM), Flash Memory and/or another type of memory. In many chips today, as much as 50%-80% of the die area could be consumed by these memory types. Additionally, integrating memories such as DRAM with logic technologies may be difficult, and may add additional costs. Techniques to reduce area overhead of memories embedded on the chip, henceforth referred to as embedded memory, will be useful. Methods to improve performance of embedded memories, reduce power consumption, and reduce integration penalties with logic technologies will also be helpful.
3D stacking of semiconductor chips is one avenue to tackle issues with embedded memories. By arranging transistors in 3 dimensions instead of 2 dimensions (as was the case in the 1990s), embedded memories can be placed in a separate device layer from the logic transistors. This may allow unique optimization of logic and memory transistors and interconnects. However, there may be many barriers to practical implementation of 3D stacked chips. These include:

    
    
        Constructing transistors in ICs typically require high temperatures (higher than about 700° C.) while wiring levels are constructed at low temperatures (lower than about 400° C.). Copper or Aluminum wiring levels, in fact, can get damaged when exposed to temperatures higher than about 400° C. If transistors were arranged in 3 dimensions along with wires, it may have the challenge described below. For example, consider a 2 layer stack of transistors and wires, i.e. Bottom Transistor Layer, above it Bottom Wiring Layer, above it Top Transistor Layer and above it Top Wiring Layer. When the Top Transistor Layer is constructed using Temperatures higher than about 700° C., it can damage the Bottom Wiring Layer.
        Generally due to the above mentioned problem with forming transistor layers above wiring layers at temperatures lower than about 400° C., the semiconductor industry has largely explored alternative architectures for 3D stacking. In these alternative architectures, Bottom Transistor Layers, Bottom Wiring Layers and Contacts to the Top Layer may be constructed on one silicon wafer. Top Transistor Layers, Top Wiring Layers and Contacts to the Bottom Layer may be constructed on another silicon wafer. These two wafers may be bonded to each other and contacts may be aligned, bonded and connected to each other. Unfortunately, the size of Contacts to the other Layer may be large and the number of these Contacts may be small. In fact, prototypes of 3D stacked chips today utilize as few as about 10,000 conductive connections between two layers (‘vertical connectivity’), compared to billions of conductive connections within a layer (‘horizontal connectivity’). This low connectivity between layers may be because of two reasons: (i) Landing pad size may need to be relatively large due to alignment issues during wafer bonding. These could be due to many reasons, including bowing of wafers to be bonded to each other, thermal expansion differences between the two wafers, and lithographic or placement misalignment. This misalignment between two wafers may potentially limit the minimum contact landing pad area for electrical connection between two layers; (ii) The contact size may need to be relatively large. Forming contacts to another stacked wafer typically may involve having a Through-Silicon Via (TSV) on a chip. Etching deep holes in silicon with small lateral dimensions and filling them with dielectric and metal to form TSVs may not be easy. This may place a restriction on lateral dimensions of TSVs, which in turn may impact TSV density and contact density to another stacked layer. Therefore, connectivity between two the embedded memory and logic transistors may be limited.
    
    


U.S. Pat. No. 7,052,941 from Sang-Yun Lee (“S-Y Lee”) describes methods to construct embedded memories with vertical transistors above wiring layers at less than 400° C. In these single crystal Si transistors, current flow in the transistor's channel region is in the vertical direction. Unfortunately, however, almost all semiconductor devices in the market today (logic, DRAM, flash memory) utilize horizontal (or planar) transistors due to their many advantages, and it may be difficult to convince the industry to move to vertical transistor technology.
It is highly desirable to circumvent these issues and build 3D stacked embedded memories with a reasonable connection density to logic transistors.
SUMMARY
The invention may be directed to multilayer or Three Dimensional Integrated Circuit (3D IC) devices and fabrication methods.
In one aspect, a semiconductor device, including: a first semiconductor layer including first transistors, wherein the first transistors are interconnected by at least one metal layer including aluminum or copper; and a second mono-crystallized semiconductor layer including second transistors and overlaying the at least one metal layer, wherein the at least one metal layer is in-between the first semiconductor layer and the second mono-crystallized semiconductor layer, wherein the second mono-crystallized semiconductor layer is less than 100 nm in thickness, and wherein the second transistors include horizontally oriented transistors.
In another aspect, an integrated device, including: a first monocrystalline layer including first transistors; a first metal layer including copper or aluminum and providing connections to the first transistors; and a second layer including monocrystalline material and including at least one memory cell constructed above the first metal layer, wherein the at least one memory cell includes second transistors, wherein the second transistors include drain and source that are horizontally oriented with respect to the second layer; and at least one via through the second layer providing connection between at least one of the second transistors and at least one of the first transistors, wherein said at least one via has a radius of less than 100 nm.
In another aspect, an integrated device, including: a semiconductor substrate and at least one metal layer, wherein the metal layer includes copper or aluminum; and an overlying layer including monocrystalline material of less than 100 nm thickness including memory regions, wherein the memory regions include horizontally oriented transistors.
In another aspect, an integrated device, including: a semiconductor substrate including first transistors and at least one metal layer providing connection to the transistors, wherein the metal layer includes copper or aluminum; and an overlying layer including monocrystalline material overlying the metal layer including memory regions, wherein the memory regions include horizontally oriented transistors and at least one via through the overlying layer providing connection between the memory regions and at least one of the first transistors, and wherein the at least one via has a radius of less than 100 nm.
In another aspect, an integrated device comprising a first monocrystalline layer comprising logic circuit regions and a second monocrystalline layer comprising memory regions constructed above first monocrystalline layer, wherein the memory regions comprise second transistors, wherein said second transistors comprise drain and source that are horizontally oriented with respect to the second monocrystalline layer, and a multiplicity of vias through the second monocrystalline layer providing connections between the memory regions and the logic circuit regions, wherein at least one of the multiplicity of vias have a radius of less than 100 nm.
In another aspect, an integrated device comprising a first monocrystalline layer comprising logic circuit regions and a second monocrystalline layer of less than 150 nm thickness, comprising memory regions constructed above the first monocrystalline layer, wherein the memory regions comprise second transistors, wherein the memory regions comprise volatile memory, and wherein the logic circuit regions comprise memory management circuits to extend the proper functionality of the volatile memory.
In another aspect, an integrated device comprising at least one memory region and at least one logic region wherein the memory region is volatile memory, and wherein the volatile memory comprises a multiplicity of memory cells, wherein each of the memory cells comprises two ports, and wherein the logic region comprises refresh logic to refresh the memory cells using one of the ports.
In another aspect, an integrated device comprising at least one memory region and at least one logic region, comprising a semiconductor substrate and at least one metal layer, wherein the metal layer comprises copper or aluminum and an overlying monocrystalline layer of less than 100 nm thickness comprising memory regions, wherein the memory regions comprise horizontally oriented transistors.
Illustrated advantages of the embodiments may include one or more of the following. A 3DIC device with horizontal or horizontally oriented transistors and devices in mono-crystalline silicon can be built at low temperatures. The 3D IC construction of partially preformed layers of transistors provides a high density of layer to layer interconnect.
The 3D ICs offer many significant potential benefits, including a small footprint—more functionality fits into a small space. This extends Moore's Law and enables a new generation of tiny but powerful devices. The 3D ICs have improved speed—The average wire length becomes much shorter. Because propagation delay may be proportional to the square of the wire length, overall performance increases. The 3D ICs consume low power—Keeping a signal on-chip reduces its power consumption by ten to a hundred times. Shorter wires also reduce power consumption by producing less parasitic capacitance. Reducing the power budget leads to less heat generation, extended battery life, and lower cost of operation. The vertical dimension adds a higher order of connectivity and opens a world of new design possibilities. Partitioning a large chip to be multiple smaller dies with 3D stacking could potentially improve the yield and reduce the fabrication cost. Heterogeneous integration—Circuit layers can be built with different processes, or even on different types of wafers. This means that components can be optimized to a much greater degree than if built together on a single wafer. Components with incompatible manufacturing could be combined in a single device. The stacked structure may hinder attempts to reverse engineer the circuitry. Sensitive circuits may also be divided among the layers in such a way as to obscure the function of each layer. 3D integration may allow large numbers of vertical vias between the layers. This may allow construction of wide bandwidth buses between functional blocks in different layers. A typical example would be a processor and memory 3D stack, with the cache memory stacked on top of the processor. This arrangement may allow a bus much wider than the typical 128 or 256 bits between the cache and processor. Wide buses in turn alleviate the memory wall problem.



BRIEF DESCRIPTION OF THE DRAWINGS
Various embodiments of the invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:
FIG. 1 illustrates the embedded memory portion of a standard 2D integrated circuit (prior art);
FIG. 2 illustrates the 3D stacking of embedded memory using through-silicon via (TSV) technology (prior art);
FIG. 3 is an exemplary drawing illustration of the 3D stacking of monolithic 3D DRAM with logic with TSV technology;
FIG. 4A-G are exemplary drawing illustrations of a process for monolithic 3D stacking of logic with DRAM produced using multiple memory layers and shared lithography steps;
FIG. 5 is an exemplary drawing illustration of different configurations possible for monolithically stacked embedded memory and logic;
FIG. 6A-J are exemplary drawing illustrations of a process flow for constructing monolithic 3D capacitor-based DRAMs with lithography steps shared among multiple memory layers;
FIG. 7 illustrates a capacitor-based DRAM cell and capacitor-less floating-body RAM cell prior art);
FIG. 8A-B are exemplary drawing illustrations of potential challenges associated with high field effects in floating-body RAM;
FIG. 9 is an exemplary drawing illustration of how a floating-body RAM chip may be managed when some memory cells may have been damaged;
FIG. 10 is an exemplary drawing illustration of a methodology for implementing the bad block management scheme described with respect to FIG. 9;
FIG. 11 is an exemplary drawing illustration of wear leveling techniques and methodology utilized in floating body RAM;
FIG. 12A-B are exemplary drawing illustrations of incremental step pulse programming techniques and methodology utilized for floating-body RAM;
FIG. 13 is an exemplary drawing illustration of different write voltages utilized for different dice across a wafer;
FIG. 14 is an exemplary drawing illustration of different write voltages utilized for different parts of a chip (or die);
FIG. 15 is an exemplary drawing illustration of write voltages for floating-body RAM cells may be based on the distance of the memory cell from its write circuits;
FIG. 16A-C are exemplary drawing illustrations of configurations useful for controller functions;
FIG. 17A-B are exemplary drawing illustrations of controller functionality and architecture applied to applications;
FIG. 18 is an exemplary drawing illustration of a cache structure in a floating body RAM chip;
FIG. 19 is an exemplary drawing illustration of a dual-port refresh scheme for capacitor-based DRAM;
FIG. 20 is an exemplary drawing illustration of a double gate device used for monolithic 3D floating-body RAM;
FIG. 21A is an exemplary drawing illustration of a 2D chip with memory, peripheral circuits, and logic circuits;
FIG. 21B is an exemplary drawing illustration of peripheral circuits may be stacked monolithically above or below memory arrays;
FIG. 21C is an exemplary drawing illustration of peripheral circuits may be monolithically stacked above and below memory arrays;
FIG. 22 is an exemplary drawing illustration of a Bipolar Junction Transistor;
FIG. 23A-C are exemplary drawing illustrations of the behavior of the embedded BJT during the floating body operation, programming, and erase.
FIG. 24 is an exemplary drawing illustration of energy band alignments;
FIG. 25A-B is an exemplary drawing illustration of a double-gated floating body NMOSFET;
FIG. 26 is an exemplary drawing illustration of FinFET floating body structure;
FIG. 27 is an exemplary drawing illustration of back-to-back two-transistor floating body structure;
FIG. 28 is an exemplary drawing illustration of a side-to-side two-transistor floating body structure;
FIG. 29A is an exemplary drawing illustration of a reticle of a repeatable device structure;
FIG. 29B is an exemplary drawing illustration of the application of a dicing line mask to a continuous array;
FIG. 30A is an exemplary drawing illustration of a floating-body memory cell suitable for use in a continuous array memory;
FIG. 30B is an exemplary drawing illustration of a continuous array of the memory cells of FIG. 30A with an etching pattern defining an exemplary 4×4 array;
FIG. 31A is an exemplary drawing illustration of chamfering the custom function etching shape for stress relief;
FIG. 31B is an exemplary drawing illustration of potential depths of custom function etching a continuous array in 3DIC; and,
FIG. 31C is an exemplary drawing illustration of a method to passivate the edge of a custom function etch of a continuous array in 3DIC;
FIG. 32A-J are exemplary drawing illustrations of a process flow for constructing monolithic 3D capacitor-based DRAMs with lithography steps shared among multiple memory layers;
FIG. 33 is an exemplary drawing illustration of a floating body RAM that may not require high electric fields for write; and
FIG. 34A-L are exemplary drawing illustrations of a process flow for constructing monolithic 3D DRAMs with lithography steps shared among multiple memory layers that may not require high electric fields for write.



DETAILED DESCRIPTION
Embodiments of the invention are described herein with reference to the drawing figures. Persons of ordinary skill in the art will appreciate that the description and figures illustrate rather than limit the invention and that in general the figures are not drawn to scale for clarity of presentation. Such skilled persons will also realize that many more embodiments are possible by applying the inventive principles contained herein and that such embodiments fall within the scope of the invention which is not to be limited except by the appended claims.
Some drawing illustration figures may describe process flows for building devices. These process flows, which may be a sequence of steps for building a device, may have many structures, numerals and labels that may be common between two or more adjacent steps. In such cases, some labels, numerals and structures used for a certain step's figure may have been described in the previous steps' figures.
FIG. 1 illustrates an exemplary top view of a prior art 2D integrated circuit 106 which may have logic circuits 104 (such as, for example, arithmetic logic units, instruction fetch units, and instruction decode units) as well as memory circuits such as SRAM blocks 102. The SRAM blocks 102 may be concentrated in one area of the chip (shown) or there may be significant amounts of SRAM in multiple areas of the chip. Typically, in many 2D integrated circuits, embedded memory blocks such as SRAM may consume a bigger percentage of chip area with every successive technology generation. Furthermore, some chips may use DRAM as an embedded memory in addition to SRAM or in place of SRAM. Hence, substantially all or portions of SRAM blocks 102 may include DRAM memory.
FIG. 2 shows a prior art illustration of embedded memory that may be in a 3D stacked layer above or below a logic chip and may be electrically connected to the logic chip using through-silicon via (TSV) technology. With TSV technology, two chips or wafers or transistor layers may be constructed separately, and then may be attached to each other using bonding and electrical vertical connections between the two chips or wafers or transistor layers may be made with through-silicon vias (TSVs). This type of configuration may allow embedded memory to be built with its own optimized technology and the logic chip to be built with its own optimized technology, thereby potentially improving the system. The embedded memory could be a volatile memory such as DRAM and/or SRAM, or any other type of memory, such as non-volatile memory (NVM). The example illustrated in FIG. 2 may include transistor regions of a top chip 202, interconnect dielectric regions of a top chip 204, metal interconnect regions of a top chip 206, solder bumps of a top chip 208, interconnect dielectric regions of a bottom chip 214, metal interconnect regions of a bottom chip 216, through-silicon via 212, dielectric regions surrounding a through-silicon via 210, solder bumps of a bottom chip 218, transistor regions of a bottom chip 222, and packaging substrate 220. The top chip may be a DRAM chip and the bottom chip may be a logic chip. Alternatively, the top chip may be a logic chip and the bottom chip may be a DRAM chip. Alternatively, SRAM may be used instead of DRAM in these configurations. The embedded memory elements such as DRAM may be built with an optimized for DRAM technology and may have optimized transistors, interconnect layers and other components such as capacitors.
FIG. 3 illustrates an embodiment of the invention, wherein monolithic 3D DRAM constructed with lithography steps shared among multiple memory layers may be stacked above or below a logic chip. DRAM, as well as SRAM and floating body DRAM, may be considered volatile memory, whereby the memory state may be substantially lost when supply power is removed. Monolithic 3D DRAM constructed with lithography steps shared among multiple memory layers (henceforth called M3DDRAM-LSSAMML) could be constructed using techniques, for example, described in co-pending published patent application 2011/0121366 (FIGS. 98A-H to FIGS. 100A-L). One configuration for 3D stack M3DDRAM-LSSAMML and logic 310 may include logic chip 304, M3DDRAM-LSSAMML chip 306, solder bumps 308, and packaging substrate 302. M3DDRAM-LSSAMML chip 306 may be placed above logic chip 304, and logic chip 304 may be coupled to packaging substrate 302 via solder bumps 308. A portion of or substantially the entirety of the logic chip 304 and the M3DDRAM-LSSAMML chip 306 may be processed separately on different wafers and then stacked atop each other using, for example, through-silicon via (TSV) stacking technology. This stacking may be done at the wafer-level or at the die-level or with a combination. Logic chip 304 and the M3DDRAM-LSSAMML chip 306 may be constructed in a monocrystalline layer or layers respectively. Another configuration for 3D stack M3DDRAM-LSSAMML and logic 320 may include logic chip 316, M3DDRAM-LSSAMML chip 314, solder bumps 318 and packaging substrate 312. Logic chip 316 may be placed above M3DDRAM-LSSAMML chip 314, and M3DDRAM-LSSAMML chip 314 may be coupled to packaging substrate 312 via solder bumps 318. A portion of or substantially the entirety of the logic chip 316 and the M3DDRAM-LSSAMML chip 314 may be processed separately on different wafers and then stacked atop each other using, for example, through-silicon via (TSV) stacking technology. This stacking may be done at the wafer-level or at the die-level or with a combination. The transistors in the monocrystalline layer or layers may be horizontally oriented, i.e., current flowing in substantially the horizontal direction in transistor channels, substantially between drain and source, which may be parallel to the largest face of the substrate or wafer. The source and drain of the horizontally oriented transistors may be within the same monocrystalline layer. A transferred monocrystalline layer may have a thickness of less than about 150 nm.
FIG. 4A-G illustrates an embodiment of the invention, wherein logic circuits and logic regions, which may be constructed in a monocrystalline layer, may be monolithically stacked with monolithic 3D DRAM constructed with lithography steps shared among multiple memory layers (M3DDRAM-LSSAMML), the memory layers or memory regions may be constructed in a monocrystalline layer or layers. The process flow for the silicon chip may include the following steps that may be in sequence from Step (1) to Step (5). When the same reference numbers are used in different drawing figures (among FIG. 4A-G), they may be used to indicate analogous, similar or identical structures to enhance the understanding of the invention by clarifying the relationships between the structures and embodiments presented in the various diagrams—particularly in relating analogous, similar or identical functionality to different physical structures.
Step (1): This may be illustrated with FIG. 4A-C. FIG. 4A illustrates a three-dimensional view of an exemplary M3DDRAM-LSSAMML that may be constructed using techniques described in patent application 2011/0121366 (FIGS. 98A-H to FIGS. 100A-L). FIG. 4B illustrates a cross-sectional view along the II direction of FIG. 4A while FIG. 4C illustrates a cross-sectional view along the III direction of FIG. 4A. The legend of FIG. 4A-C may include gate dielectric 402, conductive contact 404, silicon dioxide 406 (nearly transparent for illustrative clarity), gate electrode 408, n+ doped silicon 410, silicon dioxide 412, and conductive bit lines 414. The conductive bit lines 414 may include metals, such as copper or aluminum, in their construction. The M3DDRAM-LSSAMML may be built on top of and coupled with vertical connections to peripheral circuits 400 as described in patent application 2011/0092030. The DRAM may operate using the floating body effect. Further details of this constructed M3DDRAM-LSSAMML are provided in patent application 2011/0121366 (FIGS. 98A-H to FIGS. 100A-L).

Step (2): This may be illustrated with FIG. 4D. Activated p Silicon layer 416 and activated n+ Silicon layer 418 may be transferred atop the structure shown in FIG. 4A using a layer transfer technique, such as, for example, ion-cut. P Silicon layer 416 and n+ Silicon layer 418 may be constructed from monocrystalline silicon. Further details of layer transfer techniques and procedures are provided in patent application 2011/0121366. A transferred monocrystalline layer, such as silicon layer 418, may have a thickness of less than about 150 nm.

Step (3): This may be illustrated with FIG. 4E. The p Silicon layer 416 and the n+ Silicon layer 418 that were shown in FIG. 4D may be lithographically defined and then etched to form monocrystalline semiconductor regions including p Silicon regions 420 and n+ Silicon regions 422. Silicon dioxide 424 (nearly transparent for illustrative clarity) may be deposited and then planarized for dielectric isolation amongst adjacent monocrystalline semiconductor regions.

Step (4): This may be illustrated with FIG. 4F. The p Silicon regions 420 and the n+ Silicon regions 422 of FIG. 4E may be lithographically defined and etched with a carefully tuned etch recipe, thus forming a recessed channel structure such as shown in FIG. 4F and may include n+ source and drain Silicon regions 426, p channel Silicon regions 428, and oxide regions 430 (nearly transparent for illustrative clarity). Clean processes may then be used to produce a smooth surface in the recessed channel.

Step (5): This may be illustrated with FIG. 4G. A low temperature (less than about 400° C.) gate dielectric and gate electrode, such as hafnium oxide and TiAlN respectively, may be deposited into the etched regions in FIG. 4F. A chemical mechanical polish process may be used to planarize the top of the gate stack. Then a lithography and etch process may be used to form the pattern shown in FIG. 4G, thus forming recessed channel transistors that may include gate dielectric regions 436, gate electrode regions 432, silicon dioxide regions 440 (nearly transparent for illustrative clarity), n+ Silicon source and drain regions 434, and p Silicon channel and body regions 438.

A recessed channel transistor for logic circuits and logic regions may be formed monolithically atop a M3DDRAM-LSSAMML using the procedure shown in Step (1) to Step (5). The processes described in Step (1) to Step (5) do not expose the M3DDRAM-LSSAMML, and its associated metal bit lines 414, to temperatures greater than about 400° C.

Persons of ordinary skill in the art will appreciate that the illustrations in FIGS. 4A through 4G are exemplary only and are not drawn to scale. Such skilled persons will further appreciate that many variations may be possible such as, for example, the recessed channels etched in FIG. 4F may instead be formed before p Silicon layer 416 and n+ Silicon layer 418 may be etched to form the dielectric isolation and p Silicon regions 420 and n+ Silicon regions 422. Moreover, various types of logic transistors can be stacked atop the M3DDRAM-LSSAMML without exposing the M3DDRAM-LSSAMML to temperatures greater than about 400° C., such as, for example, junction-less transistors, dopant segregated Schottky source-drain transistors, V-groove transistors, and replacement gate transistors. This is possible using procedures described in patent application 2011/0121366 (FIGS. 98A-H to FIGS. 100A-L). The memory regions may have horizontally oriented transistors and vertical connections between the memory and logic layers may have a radius of less than 100 nm. These vertical connections may be vias, such as, for example, thru layer vias (TLVs), through the monocrystalline silicon layers connecting the stacked layers, for example, logic circuit regions within one monocrystalline layer to memory regions within another monocrystalline layer. Additional (eg. third or fourth) monocrystalline layers that may have memory regions may be added to the stack. Decoders and other driver circuits of said memory may be part of the stacked logic circuit layer or logic circuit regions. The memory regions may have replacement gate transistors, recessed channel transistors (RCATs), side-gated transistors, junction-less transistors or dopant-segregated Schottky Source-Drain transistors, which may be constructed using techniques described in patent applications 20110121366 and Ser. No. 13/099,010, the contents of the foregoing applications are incorporated herein by reference. Many other modifications within the scope of the illustrated embodiments of the invention will suggest themselves to such skilled persons after reading this specification. Thus the invention is to be limited only by the appended claims.
FIG. 5 illustrates an embodiment of the invention wherein different configurations for stacking embedded memory with logic circuits and logic regions may be realized. One stack configuration 510 may include embedded memory solution 506 made in a monocrystalline layer monolithically stacked atop the logic circuits 504 made in a monocrystalline layer using monolithic 3D technologies and vertical connections described in patent applications 20110121366 and Ser. No. 13/099,010, the contents of the foregoing applications are incorporated herein by reference. Logic circuits 504 may include metal layer or layers which may include metals such as copper or aluminum. Stack configuration 510 may include input/output interconnect 508, such as, for example, solder bumps and a packaging substrate 502. Another stack configuration 520 may include the logic circuits 516 monolithically stacked atop the embedded memory solution 514 using monolithic 3D technologies described in patent applications 20110121366 and Ser. No. 13/099,010, the contents of the foregoing applications are incorporated herein by reference. Embedded memory solution 514 may include metal layer or layers which may include metals such as copper or aluminum. Stack configuration 520 may include an input/output interconnect 518, such as, for example, solder bumps and a packaging substrate 512. The embedded memory solutions 506 and 514 may be a volatile memory, for example, SRAM. In this case, the transistors in SRAM blocks associated with embedded memory solutions 506 and 514 may be optimized differently than the transistors in logic circuits 504 and 516, and may, for example, have different threshold voltages, channel lengths and/or other parameters. The embedded memory solutions 506 and 514, if constructed, for example, as SRAM, may have, for example, just one device layer with 6 or 8 transistor SRAM. Alternatively, the embedded memory solutions 506 and 514 may have two device layers with pMOS and nMOS transistors of the SRAM constructed in monolithically stacked device layers using techniques described patent applications 20110121366 and Ser. No. 13/099,010, the contents of the foregoing applications are incorporated herein by reference. The transistors in the monocrystalline layer or layers may be horizontally oriented, i.e., current flowing in substantially the horizontal direction in transistor channels, substantially between drain and source, which may be parallel to the largest face of the substrate or wafer. The source and drain of the horizontally oriented transistors may be within the same monocrystalline layer. A transferred monocrystalline layer, such as logic circuits 504, may have a thickness of less than about 150 nm.
Persons of ordinary skill in the art will appreciate that the illustrations in FIG. 5 are exemplary only and are not drawn to scale. Such skilled persons will further appreciate that many variations may be possible such as, for example, the embedded memory solutions 506 and 514, if constructed, for example, as SRAM, may be built with three monolithically stacked device layers for the SRAM with architectures similar to “The revolutionary and truly 3-dimensional 25F2 SRAM technology with the smallest S3 (stacked single-crystal Si) cell, 0.16 um2, and SSTFT (stacked single-crystal thin film transistor) for ultra high density SRAM”, Symposium on VLSI Technology, 2004 by Soon-Moon Jung, et al. but implemented with technologies described in patent applications 20110121366 and Ser. No. 13/099,010, the contents of the foregoing applications are incorporated herein by reference. Moreover, the embedded memory solutions 506 and 514 may be embedded DRAM constructed with stacked capacitors and transistors. Further, the embedded memory solutions 506 and 514 may be embedded DRAM constructed with trench capacitors and transistors. Moreover, the embedded memory solutions 506 and 514 may be capacitor-less floating-body RAM. Further, the embedded memory solutions 506 and 514 may be a resistive memory, such as RRAM, Phase Change Memory or MRAM. Furthermore, the embedded memory solutions 506 and 514 may be a thyristor RAM. Moreover, the embedded memory solutions 506 and 514 may be a flash memory. Furthermore, embedded memory solutions 506 and 514 may have a different number of metal layers and different sizes of metal layers compared to those in logic circuits 504 and 516. This is because memory circuits typically perform well with fewer numbers of metal layers (compared to logic circuits). Many other modifications within the scope of the illustrated embodiments of the invention described herein will suggest themselves to such skilled persons after reading this specification. Thus the invention is to be limited only by the appended claims. Many of the configurations described with FIG. 5 may represent an integrated device that may have a first monocrystalline layer that may have logic circuit layers and/or regions and a second monolithically stacked monocrystalline layer that may have memory regions. The memory regions may have horizontally oriented transistors and vertical connections between the memory and logic layers may have a radius of less than 100 nm. These vertical connections may be vias, such as, for example, thru layer vias (TLVs), through the monocrystalline silicon layers connecting the stacked layers, for example, logic circuit regions within one monocrystalline layer to memory regions within another monocrystalline layer. Additional (eg. third or fourth) monocrystalline layers that may have memory regions may be added to the stack. Decoders and other driver circuits of said memory may be part of the stacked logic circuit layer or logic circuit regions. The memory regions may have replacement gate transistors, recessed channel transistors (RCATs), side-gated transistors, junction-less transistors or dopant-segregated Schottky Source-Drain transistors, which may be constructed using techniques described in patent applications 20110121366 and Ser. No. 13/099,010, the contents of the foregoing applications are incorporated herein by reference.
FIG. 6A-J illustrates an embodiment of the invention, wherein a horizontally-oriented monolithic 3D DRAM array may be constructed and may have a capacitor in series with a transistor selector. No mask may utilized on a “per-memory-layer” basis for the monolithic 3D DRAM shown in FIGS. 6A-J, and substantially all other masks may be shared among different layers. The process flow may include the following steps which may be in sequence from Step (A) to Step (H). When the same reference numbers are used in different drawing figures (among FIGS. 5A-J), the reference numbers may be used to indicate analogous, similar or identical structures to enhance the understanding of the invention by clarifying the relationships between the structures and embodiments presented in the various diagrams—particularly in relating analogous, similar or identical functionality to different physical structures.
Step (A): Peripheral circuits 602, which may include high temperature wiring, made with metals such as, for example, tungsten, and which may include logic circuit regions, may be constructed. Oxide layer 604 may be deposited above peripheral circuits 602. FIG. 6A shows a drawing illustration after Step (A).

Step (B): FIG. 6B illustrates the structure after Step (B). N+ Silicon wafer 608 may have an oxide layer 610 grown or deposited above it. Hydrogen may be implanted into the n+ Silicon wafer 608 to a certain depth indicated by hydrogen plane 606. Alternatively, some other atomic species, such as Helium, may be (co-)implanted. Thus, top layer 612 may be formed. The bottom layer 614 may include the peripheral circuits 602 with oxide layer 604. The top layer 612 may be flipped and bonded to the bottom layer 614 using oxide-to-oxide bonding to form top and bottom stack 616.

Step (C): FIG. 6C illustrates the structure after Step (C). The top and bottom stack 616 may be cleaved at the hydrogen plane 606 using methods including, for example, a thermal anneal or a sideways mechanical force. A CMP process may be conducted. Thus n+ Silicon layer 618 may be formed. A layer of silicon oxide 620 may be deposited atop the n+ Silicon layer 618. At the end of this step, a single-crystal n+ Silicon layer 618 may exist atop the peripheral circuits 602, and this has been achieved using layer-transfer techniques.

Step (D): FIG. 6D illustrates the structure after Step (D). Using methods similar to Step (B) and (C), multiple n+ silicon layers 622 (now including n+ Silicon layer 618) may be formed with associated silicon oxide layers 624. Oxide layer 604 and oxide layer 610, which were previously oxide-oxide bonded, are now illustrated as oxide layer 611.

Step (E): FIG. 6E illustrates the structure after Step (E). Lithography and etch processes may then be utilized to make a structure as shown in the figure. The etch of multiple n+ silicon layers 622 and associated silicon oxide layers 624 may stop on oxide layer 611 (shown), or may extend into and etch a portion of oxide layer 611 (not shown). Thus exemplary patterned oxide regions 626 and patterned n+ silicon regions 628 may be formed.

Step (F): FIG. 6F illustrates the structure after Step (F). A gate dielectric, such as, for example, silicon dioxide or hafnium oxides, and gate electrode, such as, for example, doped amorphous silicon or TiAlN, may be deposited and a CMP may be done to planarize the gate stack layers. Lithography and etch may be utilized to define the gate regions, thus gate dielectric regions 632 and gate electrode regions 630 may be formed.

Step (G): FIG. 6G illustrates the structure after Step (G). A trench, for example two of which may be placed as shown in FIG. 6G, may be formed by lithography, etch and clean processes. A high dielectric constant material and then a metal electrode material may be deposited and polished with CMP. The metal electrode material may substantially fill the trenches. Thus high dielectric constant regions 638 and metal electrode regions 636 may be formed, which may substantially reside inside the exemplary two trenches. The high dielectric constant regions 638 may be include materials such as, for example, hafnium oxide, titanium oxide, niobium oxide, zirconium oxide and any number of other possible materials with dielectric constants greater than or equal to 4. The DRAM capacitors may be defined by having the high dielectric constant regions 638 in between the surfaces or edges of metal electrode regions 636 and the associated stacks of n+ silicon regions 628.

Step (H): FIG. 6H illustrates the structure after Step (H). A silicon oxide layer 627 may then be deposited and planarized. The silicon oxide layer is shown transparent in the figure for clarity. Bit Lines 640 may then be constructed. Contacts may then be made to Bit Lines, Word Lines and Source Lines of the memory array at its edges. Source Line contacts can be made into stair-like structures using techniques described in “Bit Cost Scalable Technology with Punch and Plug Process for Ultra High Density Flash Memory,” VLSI Technology, 2007 IEEE Symposium on, vol., no., pp. 14-15, 12-14 Jun. 2007 by Tanaka, H.; Kido, M.; Yahashi, K.; Oomura, M.; et al., following which contacts can be constructed to them. Formation of stair-like structures for Source Lines could be done in steps prior to Step (H) as well. Vertical connections may be made to peripheral circuits 602 (not shown).

FIG. 6I and FIG. 6J show cross-sectional views of the exemplary memory array along FIG. 6H planes II and III respectively. Multiple junction-less transistors in series with capacitors constructed of high dielectric constant materials such as high dielectric constant regions 638 can be observed in FIG. 6I.

A procedure for constructing a monolithic 3D DRAM has thus been described, with (1) horizontally-oriented transistors—i.e. current flowing in substantially the horizontal direction in transistor channels, (2) some of the memory cell control lines—e.g., source-lines SL, constructed of heavily doped silicon and embedded in the memory cell layer, (3) side gates simultaneously deposited over multiple memory layers for transistors, and (4) monocrystalline (or single-crystal) silicon layers obtained by layer transfer techniques such as ion-cut. The transistors in the monocrystalline layer or layers may be horizontally oriented, i.e., current flowing in substantially the horizontal direction in transistor channels, substantially between drain and source, which may be parallel to the largest face of the substrate or wafer. The source and drain of the horizontally oriented transistors may be within the same monocrystalline layer. A transferred monocrystalline layer, such as n+ Silicon layer 618, may have a thickness of less than about 150 nm.

Persons of ordinary skill in the art will appreciate that the illustrations in FIGS. 6A through 6J are exemplary only and are not drawn to scale. Such skilled persons will further appreciate that many variations may be possible such as, for example, layer transfer techniques other than the described hydrogen implant and ion-cut may be utilized. Moreover, while FIG. 6A-J described the procedure for forming a monolithic 3D DRAM with substantially all lithography steps shared among multiple memory layers, alternative procedures could be used. For example, procedures similar to those described in FIGS. 33A-K, FIGS. 34A-L and FIGS. 35A-F of patent application Ser. No. 13/099,010, the contents of the foregoing application is incorporated herein by reference, may be used to construct a monolithic 3D DRAM. The memory regions may have horizontally oriented transistors and vertical connections between the memory and logic/periphery layers may have a radius of less than 100 nm. These vertical connections may be vias, such as, for example, thru layer vias (TLVs), through the monocrystalline silicon layers connecting the stacked layers, for example, logic circuit regions within one monocrystalline layer to memory regions within another monocrystalline layer. Additional (eg. third or fourth) monocrystalline layers that may have memory regions may be added to the stack. Decoders and other driver circuits of said memory may be part of the stacked logic circuit layer or logic circuit regions. Many other modifications within the scope of the illustrated embodiments of the invention will suggest themselves to such skilled persons after reading this specification. Thus the invention is to be limited only by the appended claims.
FIG. 32A-J illustrates an embodiment of the invention, wherein a horizontally-oriented monolithic 3D DRAM array may be constructed and may have a capacitor in series with a transistor selector. No mask may utilized on a “per-memory-layer” basis for the monolithic 3D DRAM shown in FIGS. 32A-J, and substantially all other masks may be shared among different layers. The process flow may include the following steps which may be in sequence from Step (A) to Step (H). When the same reference numbers are used in different drawing figures (among FIGS. 32A-J), the reference numbers may be used to indicate analogous, similar or identical structures to enhance the understanding of the invention by clarifying the relationships between the structures and embodiments presented in the various diagrams—particularly in relating analogous, similar or identical functionality to different physical structures.
Step (A): Peripheral circuits 3202, which may include high temperature wiring, made with metals such as, for example, tungsten, and may include logic circuit regions, may be constructed. Oxide layer 3204 may be deposited above peripheral circuits 3202. FIG. 32A shows a drawing illustration after Step (A).

Step (B): FIG. 32B illustrates the structure after Step (B). N+ Silicon wafer 3208 may have an oxide layer 3210 grown or deposited above it. Hydrogen may be implanted into the n+ Silicon wafer 3208 to a certain depth indicated by hydrogen plane 3206. Alternatively, some other atomic species, such as Helium, may be (co-)implanted. Thus, top layer 3212 may be formed. The bottom layer 3214 may include the peripheral circuits 3202 with oxide layer 3204. The top layer 3212 may be flipped and bonded to the bottom layer 3214 using oxide-to-oxide bonding to form top and bottom stack 3216.

Step (C): FIG. 32C illustrates the structure after Step (C). The top and bottom stack 3216 may be cleaved at the hydrogen plane 3206 using methods including, for example, a thermal anneal or a sideways mechanical force. A CMP process may be conducted. Thus n+ Silicon layer 3218 may be formed. A layer of silicon oxide 3220 may be deposited atop the n+ Silicon layer 3218. At the end of this step, a single-crystal n+ Silicon layer 3218 may exist atop the peripheral circuits 3202, and this has been achieved using layer-transfer techniques.

Step (D): FIG. 32D illustrates the structure after Step (D). Using methods similar to Step (B) and (C), multiple n+ silicon layers 3222 (now including n+ Silicon layer 3218) may be formed with associated silicon oxide layers 3224. Oxide layer 3204 and oxide layer 3210, which were previously oxide-oxide bonded, are now illustrated as oxide layer 3211.

Step (E): FIG. 32E illustrates the structure after Step (E). Lithography and etch processes may then be utilized to make a structure as shown in the figure. The etch of multiple n+ silicon layers 3222 and associated silicon oxide layers 3224 may stop on oxide layer 3211 (shown), or may extend into and etch a portion of oxide layer 3211 (not shown). Thus exemplary patterned oxide regions 3226 and patterned n+ silicon regions 3228 may be formed.

Step (F): FIG. 32F illustrates the structure after Step (F). A gate dielectric, such as, for example, silicon dioxide or hafnium oxides, and gate electrode, such as, for example, doped amorphous silicon or TiAlN, may be deposited and a CMP may be done to planarize the gate stack layers. Lithography and etch may be utilized to define the gate regions, thus gate dielectric regions 3232 and gate electrode regions 3230 may be formed.

Step (G): FIG. 32G illustrates the structure after Step (G). A trench, for example two of which may be placed as shown in FIG. 32G, may be formed by lithography, etch and clean processes. A high dielectric constant material and then a metal electrode material may be deposited and polished with CMP. The metal electrode material may substantially fill the trenches. Thus high dielectric constant regions 3238 and metal electrode regions 3236 may be formed, which may substantially reside inside the exemplary two trenches. The high dielectric constant regions 3238 may be include materials such as, for example, hafnium oxide, titanium oxide, niobium oxide, zirconium oxide and any number of other possible materials with dielectric constants greater than or equal to 4. The DRAM capacitors may be defined by having the high dielectric constant regions 3238 in between the surfaces or edges of metal electrode regions 3236 and the associated stacks of n+ silicon regions 3228.

Step (H): FIG. 32H illustrates the structure after Step (H). A silicon oxide layer 3227 may then be deposited and planarized. The silicon oxide layer is shown partially transparent in the figure for clarity. Bit Lines 3240 may then be constructed. Word Lines 3242 may then be constructed. Contacts may then be made to Bit Lines, Word Lines and Source Lines of the memory array at its edges. Source Line contacts can be made into stair-like structures using techniques described in “Bit Cost Scalable Technology with Punch and Plug Process for Ultra High Density Flash Memory,” VLSI Technology, 2007 IEEE Symposium on, vol., no., pp. 14-15, 12-14 Jun. 2007 by Tanaka, H.; Kido, M.; Yahashi, K.; Oomura, M.; et al., following which contacts can be constructed to them. Formation of stair-like structures for Source Lines could be done in steps prior to Step (H) as well. Vertical connections may be made to peripheral circuits 602 (not shown).

FIG. 32I and FIG. 32J show cross-sectional views of the exemplary memory array along FIG. 32H planes II and III respectively. Multiple junction-less transistors in series with capacitors constructed of high dielectric constant materials such as high dielectric constant regions 3238 can be observed in FIG. 32I.

A procedure for constructing a monolithic 3D DRAM has thus been described, with (1) horizontally-oriented transistors—i.e. current flowing in substantially the horizontal direction in transistor channels, (2) some of the memory cell control lines—e.g., source-lines SL, constructed of heavily doped silicon and embedded in the memory cell layer, (3) side gates simultaneously deposited over multiple memory layers for transistors, and (4) monocrystalline (or single-crystal) silicon layers obtained by layer transfer techniques such as ion-cut. The transistors in the monocrystalline layer or layers may be horizontally oriented, i.e., current flowing in substantially the horizontal direction in transistor channels, substantially between drain and source, which may be parallel to the largest face of the substrate or wafer. The source and drain of the horizontally oriented transistors may be within the same monocrystalline layer. A transferred monocrystalline layer, such as n+ Silicon layer 3218, may have a thickness of less than about 150 nm.

Persons of ordinary skill in the art will appreciate that the illustrations in FIGS. 32A through 32J are exemplary only and are not drawn to scale. Such skilled persons will further appreciate that many variations may be possible such as, for example, layer transfer techniques other than the described hydrogen implant and ion-cut may be utilized. Moreover, while FIG. 32A-J described the procedure for forming a monolithic 3D DRAM with substantially all lithography steps shared among multiple memory layers, alternative procedures could be used. For example, procedures similar to those described in FIGS. 33A-K, FIGS. 34A-L and FIGS. 35A-F of patent application Ser. No. 13/099,010, the contents of the foregoing application is incorporated herein by reference, may be used to construct a monolithic 3D DRAM. The technique of making Word Lines perpendicular to the source-lines may be analogously used for flash memories, resistive memories and floating body DRAM with lithography steps shared among multiple memory layers. The memory regions may have horizontally oriented transistors and vertical connections between the memory and logic/periphery layers may have a radius of less than 100 nm. These vertical connections may be vias, such as, for example, thru layer vias (TLVs), through the monocrystalline silicon layers connecting the stacked layers, for example, logic circuit regions within one monocrystalline layer to memory regions within another monocrystalline layer. Many other modifications within the scope of the illustrated embodiments of the invention described herein will suggest themselves to such skilled persons after reading this specification. Thus the invention is to be limited only by the appended claims.
Circuit and System Techniques for Managing a Floating-Body RAM Array
Over the past few years, the semiconductor industry has been actively pursuing floating-body RAM technologies as a replacement for conventional capacitor-based DRAM or as a replacement for embedded DRAM/SRAM. In these technologies, charge may be stored in the body region of a transistor instead of having a separate capacitor. This could have several potential advantages, including lower cost due to the lack of a capacitor, easier manufacturing and potentially scalability. There are many device structures, process technologies and operation modes possible for capacitor-less floating-body RAM. Some of these are included in “Floating-body SOI Memory: The Scaling Tournament”, Book Chapter of Semiconductor-On-Insulator Materials for Nanoelectronics Applications, pp. 393-421, Springer Publishers, 2011 by M. Bawedin, S. Cristoloveanu, A. Hubert, K. H. Park and F. Martinez (“Bawedin”).
FIG. 7 shows a prior art illustration of capacitor-based DRAM and capacitor-less floating-body RAM. A capacitor-based DRAM cell 706 may be schematically illustrated and may include transistor 702 coupled in series with capacitor 704. The transistor 702 may serve as a switch for the capacitor 704, and may be ON while storing or reading charge in the capacitor 704, but may be OFF while not performing these operations. One illustrative example capacitor-less floating-body RAM cell 718 may include transistor source and drain regions 712, gate dielectric 710, gate electrode 708, buried oxide 716 and silicon region 714. Charge may be stored in the transistor body region 720. Various other structures and configurations of floating-body RAM may be possible, and are not illustrated in FIG. 7. In many configurations of floating-body RAM, a high (electric) field mechanism such as impact ionization, tunneling or some other phenomenon may be used while writing data to the memory cell. High-field mechanisms may be used while reading data from the memory cell. The capacitor-based DRAM cell 706 may often operate at much lower electric fields compared to the floating-body RAM cell 718.
FIG. 8A-8B illustrates some of the potential challenges associated with possible high field effects in floating-body RAM. The Y axis of the graph shown in FIG. 8A may indicate current flowing through the cell during the write operation, which may, for example, consist substantially of impact ionization current. While impact ionization may be illustrated as the high field effect in FIG. 8A, some other high field effect may alternatively be present. The X axis of the graph shown in FIG. 8B may indicate some voltage applied to the memory cell. While using high field effects to write to the cell, some challenges may arise. At low voltages 820, not enough impact ionization current may be generated while at high voltages 822, the current generated may be exponentially higher and may damage the cell. The device may therefore work only at a narrow range of voltages 824.
A challenge of having a device work across a narrow range of voltages is illustrated with FIG. 8B. In a memory array, for example, there may be millions or billions of memory cells, and each memory individual cell may have its own range of voltages between which it operates safely. Due to variations across a die or across a wafer, it may not be possible to find a single voltage that works well for substantially all members of a memory array. In the plot shown in FIG. 8B, four different memory cells may have their own range of “safe” operating voltages 802, 804, 806 and 808. Thus, it may not be possible to define a single voltage that can be used for writing substantially all cells in a memory array. While this example described the scenario with write operation, high field effects may make it potentially difficult to define and utilize a single voltage for reading substantially all cells in a memory array. This situation may be unique to floating-body RAM and may not be generally present in capacitor-based DRAM. Solutions to this potential problem may be required.
FIG. 9 illustrates an embodiment of the invention that describes how floating-body RAM chip 910 may be managed wherein some memory cells within floating-body RAM chip 910 may have been damaged due to mechanisms, such as, for example, high-field effects after multiple write or read cycles. For example, a cell rewritten a billion times may have been damaged more by high field effects than a cell rewritten a million times. As an illustrative example, floating-body RAM chip 910 may include nine floating-body RAM blocks, 901, 902, 903, 904, 905, 906, 907, 908 and 909. If it is detected, for example, that memory cells in floating-body RAM block 905 may have degraded due to high-field effects and that redundancy and error control coding schemes may be unable to correct the error, the data within floating-body RAM block 905 may be remapped in part or substantially in its entirety to floating-body RAM block 908. Floating-body RAM block 905 may not be used after this remapping event.
FIG. 10 illustrates an embodiment of the invention of an exemplary methodology for implementing the bad block management scheme described with respect to FIG. 9. For example, during a read operation, if the number of errors increases beyond a certain threshold, an algorithm may be activated. The first step of this algorithm may be to check or analyze the causation or some characteristic of the errors, for example, if the errors may be due to soft-errors or due to reliability issues because of high-field effects. Soft-errors may be transient errors and may not occur again and again in the field, while reliability issues due to high-field effects may occur again and again (in multiple conditions), and may occur in the same field or cell. Testing circuits may be present on the die, or on another die, which may be able to differentiate between soft errors and reliability issues in the field by utilizing the phenomenon or characteristic of the error in the previous sentence or by some other method. If the error may result from floating-body RAM reliability, the contents of the block may be mapped and transferred to another block as described with respect to FIG. 9 and this block may not be reused again. Alternatively, the bad block management scheme may use error control coding to correct the bad data and may provide the user data about the error and correction. The read operation may end.
FIG. 11 illustrates an embodiment of the invention wherein wear leveling techniques and methodology may be utilized in floating body RAM. As an illustrative example, floating-body RAM chip 1110 may include nine floating-body RAM blocks 1101, 1102, 1103, 1104, 1105, 1106, 1107, 1108 and 1109. While writing data to floating-body RAM chip 1110, the writes may be controlled and mapped by circuits that may be present on the die, or on another die, such that substantially all floating-body RAM blocks, such as 1101-1109, may be exposed to an approximately similar number of write cycles. The leveling metric may utilize the programming voltage, total programming time, or read and disturb stresses to accomplish wear leveling, and the wear leveling may be applied at the cell level, or at a super-block (groups of blocks) level. This wear leveling may avoid the potential problem wherein some blocks may be accessed more frequently than others. This potential problem typically limits the number of times the chip can be written. There are several algorithms used in flash memories and hard disk drives that perform wear leveling. These techniques could be applied to floating-body RAM due to the high field effects which may be involved. Using these wear leveling procedures, the number of times a floating body RAM chip can be rewritten (i.e. its endurance) may improve.
FIG. 12A-B illustrates an embodiment of the invention wherein incremental step pulse programming techniques and methodology may be utilized for floating-body RAM. The Y axis of the graph shown in FIG. 12A may indicate the voltage used for writing the floating-body RAM cell or array and the X axis of the graph shown in FIG. 12A may indicate time during the writing of a floating-body RAM cell or array. Instead of using a single pulse voltage for writing a floating-body RAM cell or array, multiple write voltage pulses, such as, initial write pulse 1202, second write pulse 1206 and third write pulse 1210, may be applied to a floating-body RAM cell or array. Write voltage pulses such as, initial write pulse 1202, second write pulse 1206 and third write pulse 1210, may have differing voltage levels and time durations (‘pulse width’), or they may be similar. A “verify” read may be conducted after every write voltage pulse to detect if the memory cell has been successfully written with the previous write voltage pulse. A “verify” read operation may include voltage pulses and current reads. For example, after initial write pulse 1202, a “verify” read operation 1204 may be conducted. If the “verify” read operation 1204 has determined that the floating-body RAM cell or array has not finished storing the data, a second write pulse 1206 may be given followed by a second “verify” read operation 1208. Second write pulse 1206 may be of a higher voltage and/or time duration (shown) than that of initial write pulse 1202. If the second “verify” read operation 1208 has determined that the floating-body RAM cell or array has not finished storing the data, a third write pulse 1210 may be given followed by a third “verify” read operation 1212. Third write pulse 1210 may be of a higher voltage and/or time duration (shown) than that of initial write pulse 1202 or second write pulse 1206. This could continue until a combination of write pulse and verify operations indicate that the bit storage is substantially complete. The potential advantage of incremental step pulse programming schemes may be similar to those described with respect to FIG. 7 and FIG. 8A-8B as they may tackle the cell variability and other issues, such as effective versus applied write voltages.
FIG. 12B illustrates an embodiment of the invention of an exemplary methodology for implementing a write operation using incremental step pulse programming scheme described with respect to FIG. 12A. Although FIG. 12B illustrates an incremental step pulse programming scheme where subsequent write pulses may have higher voltages, the flow may be general and may apply to cases, for example, wherein subsequent write pulses may have higher time durations. Starting a write operation, a write voltage pulse of voltage V1 may be applied to the floating-body RAM cell or array, following which a verify read operation may be conducted. If the verify read indicates that the bit of the floating-body RAM cell or array has been written satisfactorily, the write operation substantially completes. Otherwise, the write voltage pulse magnitude may be increased (+ΔV1 shown) and further write pulses and verify read pulses may be given to the memory cell. This process may repeat until the bit is written satisfactorily.
Persons of ordinary skill in the art will appreciate that the illustrations in FIGS. 12A through 12B are exemplary only and are not drawn to scale. Such skilled persons will further appreciate that many variations may be possible such as, for example, pulses may utilize delivered current rather than measured or effective voltage, or some combination thereof. Moreover, multiple write pulses before a read verify operation may be done. Further, write pulses may have more complex shapes in voltage and time, such as, for example, ramped voltages, soaks or holds, or differing pulse widths. Furthermore, the write pulse may be of positive or negative voltage magnitude and there may be a mixture of unipolar or bipolar pulses within each pulse train. The write pulse or pulses may be between read verify operations. Further, ΔV1 may be of polarity to decrease the write program pulse voltage V1 magnitude. Moreover, an additional ‘safety’ write pulse may be utilized after the last successful read operation. Further, the verify read operation may utilize a read voltage pulse that may be of differing voltage and time shape than the write pulse, and may have a different polarity than the write pulse. Furthermore, the write pulse may be utilized for verify read purposes. Many other modifications within the scope of the illustrated embodiments of the invention described herein will suggest themselves to such skilled persons after reading this specification. Thus the invention is to be limited only by the appended claims.
FIG. 13 illustrates an embodiment of the invention wherein optimized and possibly different write voltages may be utilized for different dice across a wafer. As an illustrative example, wafer 1300 may include dice 1302, 1304, 1306, 1308, 1310, 1312, 1314, 1316, 1318, 1320, 1322 and 1324. Due to variations in process and device parameters across wafer 1300, which may be induced by, for example, manufacturing issues, each die, for example die 1302, on wafer 1300 may suitably operate at its own optimized write voltage. The optimized write voltage for die 1302 may be different than the optimized write voltage for die 1304, and so forth. During, for example, the test phase of wafer 1300 or individual dice, such as, for example, die 1302, tests may be conducted to determine the optimal write voltage for each die. This optimal write voltage may be stored on the floating body RAM die, such as die 1302, by using some type of non-volatile memory, such as, for example, metal or oxide fuse-able links, or intentional damage programming of floating-body RAM bits, or may be stored off-die, for example, on a different die within wafer 1300. Using an optimal write voltage for each die on a wafer may allow higher-speed, lower-power and more reliable floating-body RAM chips.
Persons of ordinary skill in the art will appreciate that the illustrations in FIG. 13 are exemplary only and are not drawn to scale. Such skilled persons will further appreciate that many variations may be possible such as, for example, while FIG. 13 discussed using optimal write voltages for each die on the wafer, each wafer in a wafer lot may have its own optimal write voltage that may be determined, for example, by tests conducted on circuits built on scribe lines of wafer 1300, a ‘dummy’ mini-array on wafer 1300, or a sample of floating-body RAM dice on wafer 1300. Moreover, interpolation or extrapolation of the test results from, such as, for example, scribe line built circuits or floating-body RAM dice, may be utilized to calculate and set the optimized programming voltage for untested dice. For example, optimized write voltages may be determined by testing and measurement of die 1302 and die 1322, and values of write voltages for die 1308 and die 1316 may be an interpolation calculation, such as, for example, to a linear scale. Many other modifications within the scope of the illustrated embodiments of the invention described herein will suggest themselves to such skilled persons after reading this specification. Thus the invention is to be limited only by the appended claims.
FIG. 14 illustrates an embodiment of the invention wherein optimized for different parts of a chip (or die) write voltages may be utilized. As an illustrative example, wafer 1400 may include chips 1402, 1404, 1406, 1408, 1410, 1412, 1414, 1416, 1418, 1420, 1422 and 1424. Each chip, such as, for example, chip 1412, may include a number of different parts or blocks, such as, for example, blocks 1426, 1428, 1430, 1432, 1434, 1436, 1438, 1440 and 1442. Each of these different parts or blocks may have its own optimized write voltage that may be determined by measurement of test circuits which may, for example, be built onto the memory die, within each block, or on another die. This optimal write voltage may be stored on the floating body RAM die, such as die 1402, by using some type of non-volatile memory, such as, for example, metal or oxide fuse-able links, or intentional damage programming of floating-body RAM bits, or may be stored off-die, for example, on a different die within wafer 1400, or may be stored within a block, such as block 1426.
FIG. 15 illustrates an embodiment of the invention wherein write voltages for floating-body RAM cells may be substantially or partly based on the distance of the memory cell from its write circuits. As an illustrative example, memory array portion 1500 may include bit-lines 1510, 1512, 1514 and 1516 and may include memory rows 1502, 1504, 1506 and 1508, and may include write driver circuits 1550. The memory row 1502 with memory cells may be farthest away from the write driver circuits 1550, and so, due to the large currents of floating-body RAM operation, may suffer a large IR drop along the wires. The memory row 1508 with memory cells may be closest to the write driver circuits 1550 and may have a low IR drop. Due to the IR drops, the voltage delivered to each memory cell of a row may not be the same, and may be significantly different. To tackle this issue, write voltages delivered to memory cells may be adjusted based on the distance from the write driver circuits. When the IR drop value may be known to be higher, which may be the scenario for memory cells farther away from the write driver circuits, higher write voltages may be used. When the IR drop may be lower, which may be the scenario for memory cells closer to the write driver circuits, lower write voltages may be used.
Write voltages may be tuned based on temperature at which a floating body RAM chip may be operating. This temperature based adjustment of write voltages may be useful since required write currents may be a function of the temperature at which a floating body RAM device may be operating. Furthermore, different portions of the chip or die may operate at different temperatures in, for example, an embedded memory application. Another embodiment of the invention may involve modulating the write voltage for different parts of a floating body RAM chip based on the temperatures at which the different parts of a floating body RAM chip operate. Refresh can be performed more frequently or less frequently for the floating body RAM by using its temperature history. This temperature history may be obtained by many methods, including, for example, by having reference cells and monitoring charge loss rates in these reference cells. These reference cells may be additional cells placed in memory arrays that may be written with known data. These reference cells may then be read periodically to monitor charge loss and thereby determine temperature history.
In FIG. 9 to FIG. 15, various techniques to improve floating-body RAM were described. Many of these techniques may involve addition of additional circuit functionality which may increase control of the memory arrays. This additional circuit functionality may be henceforth referred to as ‘controller circuits’ for the floating-body RAM array, or any other memory management type or memory regions described herein. FIG. 16A-C illustrates an embodiment of the invention where various configurations useful for controller functions are outlined. FIG. 16A illustrates a configuration wherein the controller circuits 1602 may be on the same chip 1606 as the memory arrays 1604. FIG. 16B illustrates a 3D configuration 1612 wherein the controller circuits may be present in a logic layer 1608 that may be stacked below the floating-body RAM layer 1610. As well, FIG. 16B illustrates an alternative 3D configuration 1614 wherein the controller circuits may be present in a logic layer 1618 that may be stacked above a floating-body RAM array 1616. 3D configuration 1612 and alternative 3D configuration 1614 may be constructed with 3D stacking techniques and methodologies, including, for example, monolithic or TSV. FIG. 16C illustrates yet another alternative configuration wherein the controller circuits may be present in a separate chip 1620 while the memory arrays may be present in floating-body chip 1622. The configurations described in FIG. 16A-C may include input-output interface circuits in the same chip or layer as the controller circuits. Alternatively, the input-output interface circuits may be present on the chip with floating-body memory arrays. The controller circuits in, for example, FIG. 16, may include memory management circuits that may extend the useable endurance of said memory, memory management circuits that may extend the proper functionality of said memory, memory management circuits that may control two independent memory blocks, memory management circuits that may modify the voltage of a write operation, and/or memory management circuits that may perform error correction and so on. Memory management circuits may include hardwired or soft coded algorithms.
FIG. 17A-B illustrates an embodiment of the invention wherein controller functionality and architecture may be applied to applications including, for example, embedded memory. As an illustrated in FIG. 17A, embedded memory application die 1798 may include floating-body RAM blocks 1704, 1706, 1708, 1710 and 1712 spread across embedded memory application die 1798 and logic circuits or logic regions 1702. In an embodiment of the invention, the floating-body RAM blocks 1704, 1706, 1708, 1710 and 1712 may be coupled to and controlled by a central controller 1714. As illustrated in FIG. 17B, embedded memory application die 1796 may include floating-body RAM blocks 1724, 1726, 1728, 1730 and 1732 and associated memory controller circuits 1734, 1736, 1738, 1740 and 1742 respectively, and logic circuits or logic regions 1744. In an embodiment of the invention, the floating-body RAM blocks 1724, 1726, 1728, 1730 and 1732 may be coupled to and controlled by associated memory controller circuits 1734, 1736, 1738, 1740 and 1742 respectively.
FIG. 18 illustrates an embodiment of the invention wherein cache structure 1802 may be utilized in floating body RAM chip 1806 which may have logic circuits or logic regions 1844. The cache structure 1802 may have shorter block sizes and may be optimized to be faster than the floating-body RAM blocks 1804. For example, cache structure 1802 may be optimized for faster speed by the use of faster transistors with lower threshold voltages and channel lengths. Furthermore, cache structure 1802 may be optimized for faster speed by using different voltages and operating conditions for cache structure 1802 than for the floating-body RAM blocks 1804.
Persons of ordinary skill in the art will appreciate that the illustrations in FIGS. 9 through 18 are exemplary only and are not drawn to scale. Such skilled persons will further appreciate that many variations may be possible such as, for example, many types of floating body RAM may be utilized and the invention may not be limited to any one particular configuration or type. For example, monolithic 3D floating-body RAM chips, 2D floating-body RAM chips, and floating-body RAM chips that might be 3D stacked with through-silicon via (TSV) technology may utilize the techniques illustrated with FIG. 9 to FIG. 18. Many other modifications within the scope of the illustrated embodiments of the invention described herein will suggest themselves to such skilled persons after reading this specification. Thus the invention is to be limited only by the appended claims.
FIG. 33 illustrates a floating-body RAM cell that may require lower voltages than previous cells and may operate without the use of high-field effects. In FIG. 33, 3302 may be a p-type substrate, 3304 may be an n-well region, 3306 may be a p+ region, 3308 may be a n+ region, 3310 may be a word-line, 3312 may be a gate dielectric, 3314 may be a p type region and 3316 may be a second n+ region. The device may be controlled with four terminals, represented by T1, T2, T3 and T4. Several bias schemes may be used with a device such as this one. Further details of this floating-body RAM cell and its bias schemes may be described in pending patent application 2011/0019482.
FIG. 34A-L illustrates an embodiment of the invention, wherein a horizontally-oriented monolithic 3D Floating-Body RAM array may be constructed that may not require high-field effects for write operations. One mask may utilized on a “per-memory-layer” basis for the monolithic 3D DRAM shown in FIGS. 34A-L, and all other masks may be shared between different layers. The process flow may include the following steps which may be in sequence from Step (A) to Step (K). When the same reference numbers are used in different drawing figures (among FIGS. 34A-K), the reference numbers may be used to indicate analogous, similar or identical structures to enhance the understanding of the invention by clarifying the relationships between the structures and embodiments presented in the various diagrams—particularly in relating analogous, similar or identical functionality to different physical structures.
Step (A): FIG. 34A illustrates the structure after Step (A). Using procedures similar to those described in FIG. 32A-C, a monocrystalline p Silicon layer 3408 may be layer transferred atop peripheral circuits 3402. Peripheral circuits 3402 may utilize high temperature wiring (interconnect metal layers), made with metals, such as, for example, tungsten, and may include logic circuit regions. Oxide-to-oxide bonding between oxide layers 3404 and 3406 may be utilized for this transfer, in combination with ion-cut processes.

Step (B): FIG. 34B illustrates the structure after Step (B). Using a lithography step, implant processes and other process steps, n+ silicon regions 3412 may be formed. Thus p-silicon regions 3410 may be formed.

Step (C): FIG. 34C illustrates the structure after Step (C). An oxide layer 3414 may be deposited atop the structure shown in FIG. 34B.

Step (D): FIG. 34D illustrates the structure after Step (D). Using methods similar to Steps (A), (B) and (C), multiple silicon layers having n+ silicon regions 3420 and p silicon regions 3418 may be formed with associated silicon oxide layers 3416. Oxide layer 3404 and oxide layer 3406, which were previously oxide-oxide bonded, are now illustrated as oxide layer 3416.

Step (E): FIG. 34E illustrates the structure after Step (E). Using lithography, multiple implant processes, and other steps such as resist strip, p+ silicon regions 3424 may be formed in multiple layers. 3422 may represent p silicon regions, 3420 may indicate n+ silicon regions and silicon oxide layers 3416. A Rapid Thermal Anneal (RTA) may be conducted to activate dopants in all layers. The multiple implant steps for forming p+ silicon regions 3424 may have different energies when doping each of the multiple silicon layers.

Step (F): FIG. 34F illustrates the structure after Step (F). Lithography and etch processes may then be utilized to make a structure as shown in the figure. The etch of multiple silicon layers and associated silicon oxide layers may stop on oxide layer 3486 (shown), or may extend into and etch a portion of oxide layer 3486 (not shown). Thus exemplary patterned oxide regions 3430 and patterned regions of n+ silicon 3428, p silicon 3426 and p+ silicon 3432 may be formed.

Step (G): FIG. 34G illustrates the structure after Step (G). A gate dielectric, such as, for example, silicon dioxide or hafnium oxides, and gate electrode, such as, for example, doped amorphous silicon or TiAlN, may be deposited and a CMP may be done to planarize the gate stack layers. Lithography and etch may be utilized to define the gate regions, thus gate dielectric regions 3434 and gate electrode regions 3436 may be formed.

Step (H): FIG. 34H illustrates the structure after Step (H). Silicon dioxide (not shown) may be deposited and then planarized. In FIG. 34H and subsequent steps in the process flow, the overlying silicon dioxide regions may not be shown for clarity.

Step (I): FIG. 34I illustrates the structure after Step (I). Openings may be created within the (transparent) silicon oxide regions utilizing lithography and etch steps and other processes such as resist and residue cleaning. A contact material which may include, such as, for example, metal silicide, may be formed in these openings following which a chemical mechanical polish step may be conducted to form conductive regions 3438.

Step (J): FIG. 34J illustrates the structure after Step (J). A trench, for example two of which may be placed as shown in FIG. 34J, may be formed by lithography, etch and clean processes. The trench etch may etch multiple silicon layers and associated silicon oxide layers and may stop on oxide layer 3486 or may extend into and etch a portion of oxide layer 3486. A conductive contact material, such as aluminum, copper, tungsten and associated barrier metals, such as Ti/TiN, may then be filled in the trenches, thus forming conductive contact regions 3440.

Step (K): FIG. 34K illustrates the structure after Step (K). Wiring 3442 may be formed. The terminals of memory cells may include conductive regions 3438, gate electrode regions 3436, p+ silicon regions 3432 and conductive contact regions 3440. Contacts may then be made to terminals of the memory array at its edges. Contacts to regions 3432 at the edges of the array can be made into stair-like structures using techniques described in “Bit Cost Scalable Technology with Punch and Plug Process for Ultra High Density Flash Memory,” VLSI Technology, 2007 IEEE Symposium on, vol., no., pp. 14-15, 12-14 Jun. 2007 by Tanaka, H.; Kido, M.; Yahashi, K.; Oomura, M.; et al., following which contacts can be constructed to them. Formation of stair-like structures for regions 3432 at the edges of the array could be done in steps prior to Step (K) as well.

FIG. 34L illustrates a single cell of the memory array. p+ regions 3494, p regions 3498, n+ silicon regions 3496, gate dielectric regions 3492, gate electrode regions 3490 and conductive contact regions 3488 may be parts of the memory cell. This cell may be operated using bias schemes described in pending patent application 2011/0019482. Alternatively, some other bias scheme may be used.

A procedure for constructing a monolithic 3D DRAM has thus been described, with (1) horizontally-oriented transistors—i.e. current flowing in substantially the horizontal direction in transistor channels, (2) some of the memory cell control lines may be constructed of heavily doped silicon and embedded in the memory cell layer, (3) side gates simultaneously deposited over multiple memory layers for transistors, (4) monocrystalline (or single-crystal) silicon layers obtained by layer transfer techniques such as ion-cut, and (5) high-field effects may not be required for write operations. The transistors in the monocrystalline layer or layers may be horizontally oriented, i.e., current flowing in substantially the horizontal direction in transistor channels, substantially between drain and source, which may be parallel to the largest face of the substrate or wafer. The source and drain of the horizontally oriented transistors may be within the same monocrystalline layer. A transferred monocrystalline layer, such as p Silicon layer 3408, may have a thickness of less than about 150 nm.

Persons of ordinary skill in the art will appreciate that the illustrations in FIGS. 34A through 34L are exemplary only and are not drawn to scale. Such skilled persons will further appreciate that many variations may be possible such as, for example, layer transfer techniques other than the described hydrogen implant and ion-cut may be utilized. Moreover, while FIG. 34A-L described the procedure for forming a monolithic 3D DRAM with one mask per memory layer and all other masks may be shared among multiple memory layers, alternative procedures could be used. For example, p+ regions 3432 may be formed by using an additional lithography step on a “per-layer” basis that may not be shared among all memory layers. Alternatively, both p+ regions 3432 and n+ regions 3428 may be formed with multiple energy implants and masks shared among all memory layers. Alternatively, procedures similar to those described in patent application Ser. No. 13/099,010, the contents of the foregoing application is incorporated herein by reference, may be used to construct the monolithic 3D DRAM. Alternatively, the directions of some or all of the wiring/terminals of the array may be perpendicular to the directions shown in FIG. 34A-K to enable easier biasing. The memory regions may have horizontally oriented transistors and vertical connections between the memory and logic/periphery layers may have a radius of less than 100 nm. These vertical connections may be vias, such as, for example, thru layer vias (TLVs), through the monocrystalline silicon layers connecting the stacked layers, for example, logic/periphery circuit regions within one monocrystalline layer to memory regions within another monocrystalline layer. Additional (eg. third or fourth) monocrystalline layers that may have memory regions may be added to the stack. Decoders and other driver circuits of said memory may be part of the stacked logic circuit layer or logic circuit regions. Many other modifications within the scope of the illustrated embodiments of the invention will suggest themselves to such skilled persons after reading this specification. Thus the invention is to be limited only by the appended claims.
Refresh Schemes for DRAMs and Floating Body RAM Arrays
Refresh may be a key constraint with conventional capacitor-based DRAM. Floating-body RAM arrays may require better refresh schemes than capacitor-based DRAM due to the lower amount of charge they may store. Furthermore, with an auto-refresh scheme, floating-body RAM may be used in place of SRAM for many applications, in addition to being used as an embedded DRAM or standalone DRAM replacement.
FIG. 19 illustrates an embodiment of the invention wherein a dual-port refresh scheme may be utilized for capacitor-based DRAM. A capacitor-based DRAM cell 1900 may include capacitor 1910, select transistor 1902, and select transistor 1904. Select transistor 1902 may be coupled to bit-line 1920 at node 1906 and may be coupled to capacitor 1910 at node 1912. Select transistor 1904 may be coupled to bit-line 1921 at node 1908 and may be coupled to capacitor 1910 at node 1912. Refresh of the capacitor-based DRAM cell 1900 may be performed using the bit-line 1921 connected to node 1908, for example, and leaving the bit-line 1920 connected to node 1906 available for read or write, i.e, normal operation. This may tackle the key challenge that some memory arrays may be inaccessible for read or write during refresh operations. Circuits required for refresh logic may be placed on a logic region located either on the same layer as the memory, or on a stacked layer in the 3DIC. The refresh logic may include an access monitoring circuit that may allow refresh to be conducted while avoiding interference with the memory operation. The memory or memory regions may, for example, be partitioned such that one portion of the memory may be refreshed while another portion may be accessed for normal operation. The memory or memory regions may include a multiplicity of memory cells such as, for example, capacitor-based DRAM cell 1900.
Persons of ordinary skill in the art will appreciate that the illustrations in FIG. 19 are exemplary only and are not drawn to scale. Such skilled persons will further appreciate that many variations may be possible such as, for example, a dual-port refresh scheme may be used for standalone capacitor based DRAM, embedded capacitor based DRAM that may be on the same chip or on a stacked chip, and monolithic 3D DRAM with capacitors. Moreover, refresh of the capacitor-based DRAM cell 1900 may be performed using the bit-line 1920 connected to node 1906 and leaving the bit-line 1921 connected to node 1908 available for read or write. Many other modifications within the scope of the illustrated embodiments of the invention described herein will suggest themselves to such skilled persons after reading this specification. Thus the invention is to be limited only by the appended claims.
Other refresh schemes may be used for monolithic 3D DRAMs and for monolithic 3D floating-body RAMs similar to those described in US patent application 2011/0121366 and in FIG. 6A-J of this patent application. For example, refresh schemes similar to those described in “The ideal SoC memory: 1T-SRAMTM,” Proceedings of the ASIC/SOC Conference, pp. 32-36, 2000 by Wingyu Leung, Fu-Chieh Hsu and Jones, M.-E may be used for any type of floating-body RAM. Alternatively, these types of refresh schemes may be used for monolithic 3D DRAMs and for monolithic 3D floating body RAMs similar to those described in US patent application 2011/0121366 and in FIG. 6A-J of this patent application. Refresh schemes similar to those described in “Autonomous refresh of floating body cells”, Proceedings of the Intl. Electron Devices Meeting, 2008 by Ohsawa, T.; Fukuda, R.; Higashi, T.; et al. may be used for monolithic 3D DRAMs and for monolithic 3D floating body RAMs similar to those described in US patent application 2011/0121366 and in FIG. 6A-J of this patent application.
FIG. 20 illustrates an embodiment of the invention in which a double gate device may be used for monolithic 3D floating-body RAM wherein one of the gates may utilize tunneling for write operations and the other gate may be biased to behave like a switch. As an illustrative example, nMOS double-gate DRAM cell 2000 may include n+ region 2002, n+ region 2010, oxide regions 2004 (partially shown for illustrative clarity), gate dielectric region 2008 and associated gate electrode region 2006, gate dielectric region 2016 and associated gate electrode region 2014, and p-type channel region 2012. nMOS double-gate DRAM cell 2000 may be formed utilizing the methods described in FIG. 6A-J of this patent application. For example, the gate stack including gate electrode region 2006 and gate dielectric region 2008 may be designed and electrically biased during write operations to allow tunneling into the p-type channel region 2012. The gate dielectric region 2008 thickness may be thinner than the mean free path for trapping, so that trapping phenomena may be reduced or eliminated.
Persons of ordinary skill in the art will appreciate that the illustrations in FIG. 20 are exemplary only and are not drawn to scale. Such skilled persons will further appreciate that many variations may be possible such as, for example, a pMOS transistor may be used in place of or in complement to nMOS double gate DRAM cell 2000. Moreover, nMOS double gate DRAM cell 2000 may be used such that one gate may be used for refresh operations while the other gate may be used for standard write and read operations. Furthermore, nMOS double-gate DRAM cell 2000 may be formed by method such as described in US patent application 20110121366. Many other modifications within the scope of the illustrated embodiments of the invention described herein will suggest themselves to such skilled persons after reading this specification. Thus the invention is to be limited only by the appended claims.
FIG. 21A illustrates a conventional chip with memory wherein peripheral circuits 2106 may substantially surround memory arrays 2104, and logic circuits or logic regions 2102 may be present on the die. Memory arrays 2104 may need to be organized to have long bit-lines and word-lines so that peripheral circuits 2106 may be small and the chip's array efficiency may be high. Due to the long bit-lines and word-lines, the energy and time needed for refresh operations may often be unacceptably high.
FIG. 21B illustrates an embodiment of the invention wherein peripheral circuits may be stacked monolithically above or below memory arrays using techniques described in patent application 2011/0121366, such as, for example, monolithic 3D stacking of memory and logic layers. Memory array stack 2122 may include memory array layer 2108 which may be monolithically stacked above peripheral circuit layer 2110. Memory array stack 2124 may include peripheral circuits 2112 which may be monolithically stacked above memory array layer 2114. Memory array stack 2122 and Memory array stack 2124 may have shorter bit-lines and word-lines than the configuration shown in FIG. 21A since reducing memory array size may not increase die size appreciably (since peripheral circuits may be located underneath the memory arrays). This may allow reduction in the time and energy needed for refresh.
FIG. 21C illustrates an embodiment of the invention wherein peripheral circuits may be monolithically stacked above and below memory array layer 2118 using techniques described in US patent application 2011/0121366, such as, for example, monolithic 3D stacking of memory and logic layers including vertical connections. 3D IC stack 2100 may include peripheral circuit layer 2120, peripheral circuit layer 2116, and memory array layer 2118. Memory array layer 2118 may be monolithically stacked on top of peripheral circuit layer 2116 and then peripheral circuit layer 2120 may then be monolithically stacked on top of memory array layer 2118. This configuration may have shorter bit-lines and word-lines than the configuration shown in FIG. 21A and may allow shorter bit-lines and word-lines than the configuration shown in FIG. 21B. 3D IC stack 2100 may allow reduction in the time and energy needed for refresh. A transferred monocrystalline layer, such as, for example, memory array layer 2118 and peripheral circuit layer 2120, may have a thickness of less than about 150 nm.
Persons of ordinary skill in the art will appreciate that the illustrations in FIGS. 21A through 21C are exemplary only and are not drawn to scale. Such skilled persons will further appreciate that many variations may be possible such as, for example, 3D IC stack may include, for example, two memory layers as well as two logic layers. Many other modifications within the scope of the illustrated embodiments of the invention described herein will suggest themselves to such skilled persons after reading this specification. Thus the invention is to be limited only by the appended claims.
FIG. 22 illustrates the cross-section of a floating body with embedded n layer NMOSFET 2200 with n+ source region 2204, n+ drain region 2206, p-well body 2208, gate metal and gate dielectric stack 2202, n layer 2210, and p substrate 2212. The n+ source region 2204, n+ drain region 2206, and p-well body 2208 may be of typical NMOSFET doping. As an embodiment of the invention, n layer 2210 may be formed by dopant ion implantation and dopant activation or by layer transfer below the p-well body 2208 of the floating body NMOSFET. Thus an NPN Bipolar Junction Transistor (BJT), referred hereafter as the embedded BJT, may be formed using the n+ source region 22014 as the emitter, the p-well body 2208 (floating) as the base, and the underlying n layer 2210 as the collector.
FIGS. 23A-C illustrate the behavior of the embedded BJT during the floating body operation, programming, and erase. The horizontal direction may indicate position within the transistor and the vertical direction may indicate the energy level of the electrons and holes and energy bands. “Emitter” in FIG. 23A-C may represent n+ source region 2204, “Base (FB)” in FIG. 23A-C may represent p-well body 2208 (floating), and “Collector” in FIG. 23A-C may represent n layer region 2210.
FIG. 23A illustrates the electronic band diagram of the embedded BJT when there may be only a small concentration of holes in the p-well body 2208. The conduction band 2302, valence band 2304, electrons 2306, and holes in p-well body 2308 are shown under this condition where there may be low hole concentration in the p-well body 2308, and the embedded BJT may remain turned off, with no current flowing through the BJT, regardless of collector bias.
FIG. 23B illustrates the electronic band diagram of the embedded BJT when there may be a significant concentration of holes in the p base region that may be enough to turn on the p-n diode formed by the p-well body 2308 and the emitter n+ source region 2304. The conduction band 2322, valence band 2324, electrons 2326, and holes 2328 are shown under this condition where there may be significant concentration of holes in the p-well body 2308, and the embedded BJT may turn on. The p-base region potential may allow electrons to flow from the emitter to the base, and the holes to flow from the base to the emitter. The electrons that arrive at the base and do not recombine may continue on to the collector and may then be swept towards the collector terminal by the collector reverse bias.
FIG. 23C illustrates the BJT band diagram with the impact ionization process 2346 which may create electron-hole pairs in the collector region given high enough collector bias to generate a field of at least approximately 1E6 V/cm in the said region. The BJT band diagram includes conduction band 2342, valence band 2344. The newly generated electrons flow in the direction of the collector terminal 2348, together with the original electrons, while the newly generated holes flow in the opposite direction towards the base/floating body 2350. This flow of holes into the base/floating body region acts to refresh the floating body such that they add to the hole population in the base/floating body 2350. Henceforth, this refresh scheme may be referred to as the “embedded BJT floating body refresh scheme”.
In order to give favorable conditions for impact ionization to occur in the collector region, it may be desired to keep the BJT gain β=IC/IB as high as possible. Thus, the p-base/p-well body 2208 among the two n regions n+ source region 2204 and n+ drain region 2206 may be designed to be about 50 nm or thinner, and the p base/p-well body 2208 and collector n layer 2210 may be highly doped with a value greater than approximately 1E18/cm3 for providing a high electric field favorable to the impact ionization process.
Moreover, a heterostructure bipolar transistor (HBT) may be utilized in the floating body structure by using silicon for the emitter region material, such as n+ source region 2204 in FIG. 22, and SiGe for the base and collector regions, such as p-well body 2208 and the underlying n layer 2210 respectively, as shown in FIG. 22, thus giving a higher beta than a regular BJT.
FIG. 24 illustrates the energy band alignments of Silicon 2402 with bandgap of 1.1 eV, Si conduction band 2410, Si valence band 2412, and Germanium 2404 with bandgap of 0.7 eV, Ge conduction band 2420, Ge valence band 2422. The offset between the Si conduction band 2410 and the Ge conduction band 2420 may be −0.14 eV, and the offset between the Si Si valence band 2412 and the Ge valence band 2422 may be −0.26 eV. Persons of ordinary skill in the art will recognize that SiGe will have band offsets in its conduction and valence bands in linear proportion to the molar ratio of its Silicon and Germanium components. Thus, the HBT will have most of its band alignment offset in the valence band, thereby providing favorable conditions in terms of a valence band potential well for collecting and retaining holes.
Double-Gated Floating Body:
FIG. 25A illustrates the cross-section of a floating body NMOSFET 2500 with top gate metal and dielectric stack 2502 and bottom gate metal and dielectric stack 2514, source/emitter n+ region 2504, n+ drain region 2506, p floating body 2508, n collector region 2510, and second n collector region 2512.
As an embodiment of the invention, n collector region 2510 and second n collector region 2512 may be formed by dopant ion implantation and dopant activation, using the same mask (self-aligned) as for the source region 2504 and drain region 2506, but with higher implant energies.
The embedded BJT structure formed by source/emitter n+ region 2504, p floating body 2508, n collector region 2510 can be used for the embedded BJT floating body refreshing scheme as discussed above. The bottom gate metal and dielectric stack 2514 may be biased with a negative voltage to increase hole retention. The second n collector region 2512 may be utilized to further optimize hole generation, by acting together with n+ drain region 2506 and p floating body 2508 as another BJT substructure utilizing the embedded BJT floating body refresh scheme above. The bottom gate metal and dielectric stack 2514 can be used with the bottom MOSFET structure, including n collector region 2510, p floating body 2508, second n collector region 2512, and bottom gate and dielectric stack 2514, for hole generation.
FIG. 25B illustrates the top view of an embodiment of the invention, the device 2550 including gate metal and dielectric stack 2552 formed on a side of the p floating body 2558, and second gate metal and dielectric stack 2564 formed on the opposite side of the p floating body 2558, source/emitter n+ region 2554, n+ drain region 2556, n collector region 2560, and second n collector region 2562.
The source/emitter n+ region 2554, n+ drain region 2556, n collector region 2560, and second n collector region 2562 may be formed via dopant ion implantation and dopant activation with the geometry defined using a lithographic mask.
The embedded BJT structure formed by source/emitter n+ region 2554, p floating body 2558, n collector region 2560 may be used for the embedded BJT floating body refresh scheme as discussed above. The second gate metal and dielectric stack 2564 may be biased with a negative voltage to increase hole retention. The second n collector region 2562 may be utilized to further optimize hole generation, by acting together with n+ drain region 2556 and p floating body 2558 as another BJT substructure utilizing the embedded BJT floating body refresh scheme above. The second gate metal and dielectric stack 2564 may be used with the second MOSFET substructure, which may include n collector region 2560, p floating body 2558, second n collector region 2562, and second gate and dielectric stack 2564, for hole generation.
FinFET Floating Body:
FIG. 26 illustrates the cross-section of a FinFET floating body structure 2600 with surrounding gate dielectrics 2602 on three sides of the channel (only the top gate stack is shown), n+ source region 2604, n+ drain region 2606, p floating body 2608, and n collector region 2614 on the bottom side of the floating body 2608 insulated from the source and drain regions by oxide regions 2610 and 2612. A spacer patterning technology using a sacrificial layer and a chemical vapor deposition spacer layer developed by Y-K Choi et al (IEEE TED vol. 49 no. 3 2002) may be used to pattern the Silicon fin for the FinFET. As an embodiment of the invention, n collector region 2614 may be formed by dopant ion implantation and dopant activation, and oxide regions 2610 and 2612 may be formed by ion implantation of oxygen which, upon thermal anneal, may react with silicon to form the oxide.
The embedded BJT structure formed by n+ source region 2604 as emitter, p floating body 2608 as base, n collector region 2614 may be used for the embedded BJT floating body refresh scheme as discussed above.
Back-to-Back Transistor Structure:
FIG. 27 illustrates a back-to-back two-transistor configuration 2700 where n+ drain region 2706, n+ source/emitter region 2708, p floating body region 2712 and gate metal and dielectric stack 2702 may form a NMOSFET transistor used for the reading and programming p floating body region 2712 N+ source/emitter region 2708 as emitter, p floating body region 2712 as base, and n+ collector region 2710 may form a BJT transistor which may be used for the embedded BJT floating body refreshing scheme described above. The dummy gate and dielectric stack 2704 may remain unbiased, and the source/emitter region 2708 may be tied to ground during device operation. Using a conventional CMOS planar 2D flow, n+ drain region 2706, n+ source/emitter region 2708, and n+ collector region 2710 may be formed by a self-aligned to gate dopant ion implantation and thermal anneal, and the gate dielectrics of gate metal and dielectric stack 2702 and dummy gate metal and dielectric stack 2704 may be formed by oxide growth and/or deposition.
Side-to-Side Transistor Structure:
FIG. 28 illustrates a side-to-side two-transistor configuration 2800 where n+ drain region 2806, n+ source/emitter region 2808, p floating body region 2812 and gate metal and dielectric stack 2802 may form a NMOSFET transistor used for the reading and programming of the p floating body region 2812. N+ source/emitter region 2808 as emitter, p floating body region 2812 as base, and n+ collector 2810 may form a BJT transistor which may be used for the embedded BJT floating body refreshing scheme described above. The dummy gate and dielectric stack 2804 may remain unbiased, and the source/emitter region 2808 may be tied to ground during device operation. Using a conventional CMOS planar 2D flow, n+ drain region 2806, n+ source/emitter region 2808, and n+ collector region 2810 may be formed by a self-aligned to gate dopant ion implantation and thermal anneal, and the gate dielectrics of gate metal and dielectric stack 2802 and dummy gate metal and dielectric stack 2804 may be formed by oxide growth and/or deposition.
Persons of ordinary skill in the art will appreciate that the illustrations in FIGS. 22 through 28 are exemplary only and are not drawn to scale. Such skilled persons will further appreciate that many variations may be possible such as, for example, a PNP embedded BJT may be constructed by constructing p type regions in the place of the n type regions shown, and n type regions in the place of the p regions shown. Additionally, n layer 2210 may be a formed region. Moreover, n+ source region 2204, n+ drain region 2206, and p-well body 2208 doping concentrations may be factors of about 10 and 100 different than above. Further, gate metal and dielectric stacks, such as gate metal and dielectric stack 2802, may be formed with Hi-k oxides, such as, for example, hafnium oxides, and gate metals, such as, for example, TiAlN. Many other modifications within the scope of the invention described herein will suggest themselves to such skilled persons after reading this specification. Thus the invention is to be limited only by the appended claims.
Continuous Array Approaches:
In general, logic devices may need varying amounts of logic, memory, and I/O, and memory devices, such as, for example, floating body DRAM, may need varying amounts of I/O, logic, and controller circuits. The continuous array (“CA”) of U.S. Pat. No. 7,105,871 allows flexible definition of the logic device size, yet for any size the ratio among the three components remained fixed, barring minor boundary effect variations. Further, there exist other types of specialized logic that may be difficult to implement effectively using standard logic such as DRAM, Flash memory, DSP blocks, processors, analog functions, or specialized I/O functions such as SerDes. The continuous array of prior art does not provide an effective solution for these specialized yet not common enough functions that would justify their regular insertion into CA wafer.
Some embodiments of the invention enable a different and more flexible approach. Additionally the prior art proposal for continuous array were primarily oriented toward Gate Array and Structured ASIC where the customization includes some custom masks. In contrast, the some embodiments of the invention propose an approach which could fit well with memory and logic including embodiments without any custom masks. Instead of adding a broad variety of such blocks into the CA which would make it generally area-inefficient, and instead of using a range of CA types with different block mixes which would require large number of expensive mask sets, some embodiments of the current allow using Through Silicon Via or monolithic 3DIC approaches to enable a new type of configurable system.
The technology of “Package of integrated circuits and vertical integration” has been described in U.S. Pat. No. 6,322,903 issued to Oleg Siniaguine and Sergey. Accordingly, an embodiment of the invention suggests the use of CA tiles, each made of one type, or of very few types, of elements. The target system may then be constructed using desired number of tiles of desired type stacked on top of each other and electrically connected with TSVs or monolithic 3D approaches, thus, a 3D Configurable System may result.
FIG. 29A illustrates an embodiment of the invention wherein a continuous array of, for example, floating-body RAM cells or logic cells, may fill a full reticle sized area 2903 with floating-body DRAM memory cells as described above or with the exemplary 8×12 array 8402 pattern of FIG. 84A of US patent application 2011/0121366 respectively. Reticle sized area 2903, such as shown by FIG. 29A, may then be repeated across the entire wafer to form a wafer-sized continuous array of device structures (not shown). One or more custom lithographic and etch steps may be utilized to define custom dice lines within the wafer-sized continuous array of device structures, which may also be called a generic wafer. Accordingly a specific custom device may be diced from the previously generic wafer. The custom dice lines may be created by etching away some of the structures such as transistors of the continuous array or floating body DRAM as illustrated in FIG. 29B. This custom function etching may have a shape of multiple thin strips 2904 created by a custom mask, such as a dicing line mask, to etch away a portion of the devices. Thus custom forming logic or memory function, blocks, arrays, or devices 2906 (for clarity, not all possible blocks are labeled). A portion of these logic functions, blocks, arrays, or devices 2906 may be interconnected horizontally with metallization and may be electrically connected with vertical connections to circuitry above and below using TSV or utilizing the monolithic 3D variation, including, for example, some of the embodiments in this document and US patent application 2011/0121366. The invention may allow the use of a generic continuous array and then a customization process may be applied to construct multiple device sizes out of the same mask set. Therefore, for example, a continuous array as illustrated in FIG. 29A may be customized to a specific device size by etching the multiple thin strips 2904 as illustrated in FIG. 29B. Accordingly, wafers may be processed using one generic mask set of more than ten masks and then multiple device offerings may be constructed by a few custom function masks which may define specific sizes out of the generic continues array structure. And, accordingly, the wafer may then be diced to different device sizes for each device offering.
The concept of customizing a Continuous Array can be applied to logic, memory, I/O and other structures. Memory arrays have non-repetitive elements such as bit and word decoders, or sense amplifiers, which may need to be tailored to each memory size. An embodiment of the invention is to tile substantially the entire wafer with a dense pattern of memory cells, and then customize it using selective etching as before (custom function etching), and providing the required non-repetitive structures through an adjacent logic layer below or above the memory layer.
FIG. 30A is a drawing illustration of an exemplary floating-body DRAM cell 3020, with its word line 3022, bit line 3024, and transistor 3026. Such a bit cell may be typically densely packed and highly optimized for a given process. While terminal 3098 is shown to be connected to a “ground” voltage in FIG. 30A, one familiar with the art will recognize that it may be given a specific non-zero voltage as well.
A dense floating-body DRAM array 3030 (an exemplary memory region) may be constructed of a plurality of floating-body DRAM cells 3020 as illustrated in FIG. 30B. For example, a four by four array 3032 may be defined through custom etching away the cells in channel 3034, leaving bit lines 3036 and word lines 3038 unconnected. These word lines 3038 may be then electrically connected to an adjacent logic layer below or above that may have a word decoder (not shown). Similarly, the bit lines 3036 may be driven by another decoder such as bit line decoder (not shown). Connections may be made to other circuits such as sense amplifiers. A feature of this approach may be that the customized logic, such as word decoders, bit line decoders, and sense amplifiers, may be provided from below or above in close vertical proximity to the area where it may be needed, thus assuring high performance customized memory blocks.
Persons of ordinary skill in the art will appreciate that the illustrations in FIGS. 29 through 30 are exemplary only and are not drawn to scale. Such skilled persons will further appreciate that many variations may be possible such as, for example, the CA concept may include pre-defined scribe-lines, such as described in a US patent application 2011/0121366 FIG. 84. Moreover, memory architectures in addition to floating-body RAM, such as, for example, RRAM, SRAM, and conductive bridge, may utilize the continuous array concept and 3D IC application. Moreover, dense floating-body DRAM array 3030 may be a substantially wafer-sized CA or may less than a wafer-sized CA. Many other modifications within the scope of the invention described herein will suggest themselves to such skilled persons after reading this specification. Thus the invention is to be limited only by the appended claims.
As illustrated in FIG. 31A, the custom dicing line mask referred to in the FIG. 29B discussion to create multiple thin strips 2904 for etching may be shaped to create chamfered block corners 3102 of custom blocks 3104 to relieve stress. Custom blocks 3104 may include functions, blocks, arrays, or devices of architectures such as logic, FPGA, I/O, or memory.
As illustrated in FIG. 31B, this custom function etching and chamfering may extend thru the BEOL metallization of one device layer of the 3DIC stack as shown in first structure 3150, or extend thru the entire 3DIC stack to the bottom substrate and shown in second structure 3170, or truncate at the isolation of any device layer in the 3D stack as shown in third structure 3160. The cross sectional view of an exemplary 3DIC stack may include second layer BEOL dielectric 3126, second layer interconnect metallization 3124, second layer transistor layer 3122, substrate layer BEOL dielectric 3116, substrate layer interconnect metallization 3114, substrate transistor layer 3112, and substrate 3110.
Passivation of the edge created by the custom function etching may be accomplished as follows. If the custom function etched edge is formed on a layer or strata that is not the topmost one, then it may be passivated or sealed by filling the etched out area with dielectric, such as a Spin-On-Glass (SOG) method, and CMPing flat to continue to the next 3DIC layer transfer or TSV bonding. As illustrated in FIG. 31C, the topmost layer custom function etched edge may be passivated with an overlapping layer or layers of material including, for example, oxide, nitride, or polyimide. Oxide may be deposited over custom function etched block edge 3180 and may be lithographically defined and etched to overlap the custom function etched block edge 3180 shown as oxide structure 3184. Silicon nitride may be deposited over wafer and oxide structure 3184, and may be lithographically defined and etched to overlap the custom function etched block edge 3180 and oxide structure 3184, shown as nitride structure 3186.
In such way a single expensive mask set can be used to build wafers for different memory sizes and finished through another mask set that may be used to build logic wafers that can be customized by a few metal layers.
Persons skilled in the art will recognize that it is now possible to assemble a true monolithic 3D stack of mono-crystalline silicon layers or strata with high performance devices using advanced lithography that repeatedly reuse same masks, with only few custom metal masks for each device layer. Such person will also appreciate that one can stack in the same way a mix of disparate layers, some carrying transistor array for general logic and other carrying larger scale blocks such as memories, analog elements, Field Programmable Gate Array (FPGA), and I/O. Moreover, such a person would also appreciate that the custom function formation by etching may be accomplished with masking and etching processes such as, for example, a hard-mask and Reactive Ion Etching (RIE), or wet chemical etching, or plasma etching. Furthermore, the passivation or sealing of the custom function etching edge may be stair stepped so to enable improved sidewall coverage of the overlapping layers of passivation material to seal the edge.
It will also be appreciated by persons of ordinary skill in the art that the invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the embodiments of the invention includes both combinations and sub-combinations of the various features described herein above as well as modifications and variations which would occur to such skilled persons upon reading the foregoing description. Thus the invention is to be limited only by the appended claims.

## Claims

1. A semiconductor device, comprising:
a first semiconductor layer comprising first transistors,
wherein said first transistors are interconnected by at least one metal layer comprising aluminum or copper; and

a second mono-crystallized semiconductor layer comprising second transistors and overlaying said at least one metal layer,
wherein said at least one metal layer is in-between said first semiconductor layer and said second mono-crystallized semiconductor layer,
wherein said second mono-crystallized semiconductor layer is less than 100 nm in thickness, and
wherein said second transistors comprise horizontally oriented transistors.

2. A semiconductor device according to claim 1, further comprising:
a plurality of connection paths between said second transistors and said first transistors,
wherein said plurality of connection paths comprise vias through said second mono-crystallized semiconductor layer, and
wherein at least one of said vias have a radius of less than 100 nm.

3. A semiconductor device according to claim 1, further comprising:
a plurality of connection paths between said second transistors and said first transistors, and said first semiconductor layer comprising first alignment marks,
wherein at least one of said connection paths has a contact to said second transistors, and
wherein said contact is aligned to one of said first alignment marks.

4. A mobile phone comprising a semiconductor device according to claim 1.

5. A semiconductor device according to claim 1 wherein at least one of said second transistors is one of:
(i) a replacement gate transistor;
(ii) a recessed channel transistor (RCAT);
(iii) a side-gated transistor;
(iv) a junction-less transistor;
(v) a Finfet transistor;
(vi) a double gate transistor; or
(vii) a dopant-segregated Schottky Source Drain Transistor.

6. An integrated device, comprising;
a first monocrystalline layer comprising first transistors;
a first metal layer comprising copper or aluminum and providing connections to said first transistors; and
a second layer comprising monocrystalline material and comprising at least one memory cell constructed above said first metal layer,
wherein said at least one memory cell comprises second transistors,
wherein said second transistors comprise drain and source that are horizontally oriented with respect to said second layer; and

at least one via through said second layer providing connection between at least one of said second transistors and at least one of said first transistors,
wherein said at least one via has a radius of less than 100 nm.

7. An integrated device according to claim 6, further comprising;
a third layer comprising monocrystalline material and comprising memory regions,
wherein said memory regions comprise third transistors, and
wherein at least one of said third transistors substantially overlays one of said second transistors.

8. An integrated device according to claim 6, wherein the decoder logic for selecting said at least one memory cell comprises said first transistors.

9. An integrated device according to claim 6, wherein said at least one memory cell is a DRAM cell utilizing capacitors.

10. An integrated device according to claim 6, wherein said at least one memory cell is a floating body DRAM cell.

11. An integrated device according to claim 6, wherein said at least one memory cell is an SRAM cell.

12. An integrated device according to claim 6, wherein said second layer is less than 100 nm in thickness.

13. A mobile phone comprising a semiconductor device according to claim 6.

14. A semiconductor device according to claim 6, wherein said at least one via is aligned to said first metal layer.

15. An integrated device, comprising:
a semiconductor substrate and at least one metal layer,
wherein said metal layer comprises copper or aluminum; and

an overlying layer comprising monocrystalline material of less than 100 nm thickness comprising memory regions,
wherein said memory regions comprise horizontally oriented transistors.

16. An integrated device according to claim 15 wherein
at least one of said horizontally oriented transistors is one of:
(i) a replacement gate transistor;
(ii) a recessed channel transistor (RCAT);
(iii) a side-gated transistor;
(iv) a junction-less transistor;
(v) a Finfet transistor;
(vi) a double gate transistor; or
(vii) a dopant-segregated Schottky Source Drain Transistor.

17. An integrated device according to claim 15, further comprising:
a memory management circuit to extend the proper functionality of said memory regions.

18. An integrated device according to claim 15, further comprising:
a multiplicity of vias through said overlying layer providing connections between said memory regions and said metal layer,
wherein at least one of said multiplicity of vias have a radius of less than 100 nm.

19. An integrated device according to claim 15, further comprising:
a third layer comprising monocrystalline material and comprising second memory regions,
wherein said second memory regions comprise third transistors, and
wherein at least one of said third transistors substantially overlays one of said horizontally oriented transistors.

20. A mobile phone comprising a semiconductor device according to claim 15.

21. An integrated device, comprising:
a semiconductor substrate comprising first transistors and at least one metal layer providing connection to said transistors,
wherein said metal layer comprises copper or aluminum; and

an overlying layer comprising monocrystalline material overlying said metal layer comprising memory regions,
wherein said memory regions comprise horizontally oriented transistors and at least one via through said overlying layer providing connection between said memory regions and at least one of said first transistors, and
wherein said at least one via has a radius of less than 100 nm.

22. An integrated device according to claim 21, further comprising:
a memory management circuit to extend the proper functionality of said memory regions.

23. An integrated device according to claim 21, wherein said monocrystalline material is less than 100 nm in thickness.

24. An integrated device according to claim 21, further comprising:
a third layer comprising monocrystalline material and comprising second memory regions,
wherein said second memory regions comprise third transistors, and
wherein at least one of said third transistors substantially overlays one of said horizontally oriented transistors.

25. A mobile phone comprising a semiconductor device according to claim 21.