# Patent

## Title
Memory utilizing oxide-conductor nanolaminates

## Abstract

Structures, systems and methods for floating gate transistors utilizing oxide-conductor nanolaminates are provided. One floating gate transistor embodiment includes a first source/drain region, a second source/drain region, and a channel region therebetween. A floating gate is separated from the channel region by a first gate oxide. The floating gate includes oxide-conductor nanolaminate layers to trap charge in potential wells formed by different electron affinities of the oxide-conductor nanolaminate layers.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is related to the following co-pending, commonly assigned U.S. patent applications: “Memory Utilizing Oxide Nanolaminates,” Ser. No. 10/190,717, and “Memory Utilizing Oxide-Nitride Nanolaminates,” Ser. No. 10/190,689, each of which disclosure is herein incorporated by reference.
FIELD OF THE INVENTION
The present invention relates generally to semiconductor integrated circuits and, more particularly, to memory utilizing oxide-conductor nanolaminates.
BACKGROUND OF THE INVENTION
Many electronic products need various amounts of memory to store information, e.g. data. One common type of high speed, low cost memory includes dynamic random access memory (DRAM) comprised of individual DRAM cells arranged in arrays. DRAM cells include an access transistor, e.g. a metal oxide semiconducting field effect transistor (MOSFET), coupled to a capacitor cell.
Another type of high speed, low cost memory includes floating gate memory cells. A conventional horizontal floating gate transistor structure includes a source region and a drain region separated by a channel region in a horizontal substrate. A floating gate is separated by a thin tunnel gate oxide. The structure is programmed by storing a charge on the floating gate. A control gate is separated from the floating gate by an intergate dielectric. A charge stored on the floating gate effects the conductivity of the cell when a read voltage potential is applied to the control gate. The state of cell can thus be determined by sensing a change in the device conductivity between the programmed and un-programmed states.
With successive generations of DRAM chips, an emphasis continues to be placed on increasing array density and maximizing chip real estate while minimizing the cost of manufacture. It is further desirable to increase array density with little or no modification of the DRAM optimized process flow.
Multilayer insulators have been previously employed in memory devices. The devices in the above references employed oxide-tungsten oxide-oxide layers. Other previously described structures described have employed charge-trapping layers implanted into graded layer insulator structures.
More recently oxide-nitride-oxide structures have been described for high density nonvolatile memories. All of these are variations on the original MNOS memory structure discribed by Fairchild Semiconductor in 1969 which was conceptually generalized to include trapping insulators in general for constructing memory arrays.
Studies of charge trapping in MNOS structures have also been conducted by White and others.
Some commercial and military applications utilized non-volatile MNOS memories.
However, these structures did not gain widespread acceptance and use due to their variability in characteristics and unpredictable charge trapping phenomena. They all depended upon the trapping of charge at interface states between the oxide and other insulator layers or poorly characterized charge trapping centers in the insulator layers themselves. Since the layers were deposited by CVD, they are thick, have poorly controlled thickness and large surface state charge-trapping center densities between the layers.
Flash memories based on electron trapping are well known and commonly used electronic components. Recently NAND flash memory cells have become common in applications requiring high storage density while NOR flash memory cells are used in applications requiring high access and read speeds. NAND flash memories have a higher density because 16 or more devices are placed in series, this increases density at the expense of speed.
Thus, there is an ongoing need for improved DRAM technology compatible floating gate transistor cells. It is desirable that such floating gate transistor cells be fabricated on a DRAM chip with little or no modification of the DRAM process flow. It is further desirable that such floating gate transistor cells provide increased density and high access and read speeds.
REFERENCES


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SUMMARY OF THE INVENTION
The above mentioned problems for creating DRAM technology compatible floating gate transistor cells as well as other problems are addressed by the present invention and will be understood by reading and studying the following specification. This disclosure describes a flash memory device, programmable logic array device or memory address and decode correction device with an oxide-conductor nanolaminate floating gate rather than a conventional polysilicon floating gate.
In particular, an embodiment of the present invention includes a floating gate transistor utilizing oxide-conductor nanolaminates. The floating gate transistor includes a first source/drain region, a second source/drain region, and a channel region therebetween. A floating gate is separated from the channel region by a first gate oxide. The floating gate includes oxide-conductor nanolaminate layers to trap charge in potential wells formed by different electron affinities of the oxide-conductor nanolaminate layers.
These and other embodiments, aspects, advantages, and features of the present invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art by reference to the following description of the invention and referenced drawings or by practice of the invention. The aspects, advantages, and features of the invention are realized and attained by means of the instrumentalities, procedures, and combinations particularly pointed out in the appended claims.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a block diagram of a metal oxide semiconductor field effect floating gate transistor (MOSFET) in a substrate according to the teachings of the prior art.
FIG. 1B illustrates the MOSFET of FIG. 1A operated in the forward direction showing some degree of device degradation due to electrons being trapped in the gate oxide near the drain region over gradual use.
FIG. 1C is a graph showing the square root of the current signal (Ids) taken at the drain region of the conventional MOSFET versus the voltage potential (VGS) established between the gate and the source region.
FIG. 2A is a diagram of an embodiment for a programmed floating gate transistor, having oxide-conductor nanolaminate layers, which can be used as a floating gate transistor cell according to the teachings of the present invention.
FIG. 2B is a diagram suitable for explaining a method embodiment by which a floating gate transistor, having oxide-conductor nanolaminate layers, can be programmed to achieve the embodiments of the present invention.
FIG. 2C is a graph plotting the current signal (Ids) detected at the drain region versus a voltage potential, or drain voltage, (VDS) set up between the drain region and the source region (Ids vs. VDS).
FIG. 3 illustrates a portion of an embodiment of a memory array according to the teachings of the present invention.
FIG. 4 illustrates an embodiment for an electrical equivalent circuit for the portion of the memory array shown in FIG. 3.
FIG. 5 illustrates an energy band diagram for an embodiment of a gate stack according to the teachings of the present invention.
FIG. 6 is a graph which plots electron affinity versus the energy bandgap for various insulators.
FIGS. 7A–7B illustrates an embodiment for the operation of a floating gate transistor cell having oxide-conductor nanolaminate layers according to the teachings of the present invention.
FIG. 8 illustrates the operation of a conventional DRAM cell.
FIG. 9 illustrates an embodiment of a memory device according to the teachings of the present invention.
FIG. 10 is a schematic diagram illustrating a conventional NOR-NOR programmable logic array.
FIG. 11 is a schematic diagram illustrating generally an architecture of one embodiment of a programmable logic array (PLA) with logic cells, having oxide-conductor nanolaminate layers according to the teachings of the present invention.
FIG. 12 is a block diagram of an electrical system, or processor-based system, utilizing oxide-conductor nanolaminates constructed in accordance with the present invention.



DETAILED DESCRIPTION
In the following detailed description of the invention, reference is made to the accompanying drawings which form a part hereof, and in which is shown, by way of illustration, specific embodiments in which the invention may be practiced. In the drawings, like numerals describe substantially similar components throughout the several views. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the present invention.
The terms wafer and substrate used in the following description include any structure having an exposed surface with which to form the integrated circuit (IC) structure of the invention. The term substrate is understood to include semiconductor wafers. The term substrate is also used to refer to semiconductor structures during processing, and may include other layers that have been fabricated thereupon. Both wafer and substrate include doped and undoped semiconductors, epitaxial semiconductor layers supported by a base semiconductor or insulator, as well as other semiconductor structures well known to one skilled in the art. The term conductor is understood to include semiconductors, and the term insulator is defined to include any material that is less electrically conductive than the materials referred to as conductors. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.
FIG. 1A is useful in illustrating the conventional operation of a MOSFET such as can be used in a DRAM array. FIG. 1A illustrates the normal hot electron injection and degradation of devices operated in the forward direction. As is explained below, since the electrons are trapped near the drain they are not very effective in changing the device characteristics.
FIG. 1A is a block diagram of a metal oxide semiconductor field effect floating gate transistor (MOSFET) 101 in a substrate 100. The MOSFET 101 includes a source region 102, a drain region 104, a channel region 106 in the substrate 100 between the source region 102 and the drain region 104. A gate 108 is separated from the channel region 108 by a gate oxide 110. A sourceline 112 is coupled to the source region 102. A bitline 114 is coupled to the drain region 104. A wordline 116 is coupled to the gate 108.
In conventional operation, a drain to source voltage potential (Vds) is set up between the drain region 104 and the source region 102. A voltage potential is then applied to the gate 108 via a wordline 116. Once the voltage potential applied to the gate 108 surpasses the characteristic voltage threshold (Vt) of the MOSFET a channel 106 forms in the substrate 100 between the drain region 104 and the source region 102. Formation of the channel 106 permits conduction between the drain region 104 and the source region 102, and a current signal (Ids) can be detected at the drain region 104.
In operation of the conventional MOSFET of FIG. 1A, some degree of device degradation does gradually occur for MOSFETs operated in the forward direction by electrons 117 becoming trapped in the gate oxide 110 near the drain region 104. This effect is illustrated in FIG. 1B. However, since the electrons 117 are trapped near the drain region 104 they are not very effective in changing the MOSFET characteristics.
FIG. 1C illustrates this point. FIG. 1C is a graph showing the square root of the current signal (Ids) taken at the drain region versus the voltage potential (VGS) established between the gate 108 and the source region 102. The change in the slope of the plot of √{square root over (Ids)} versus VGS represents the change in the charge carrier mobility in the channel 106.
In FIG. 1C, ΔVT represents the minimal change in the MOSFET's threshold voltage resulting from electrons gradually being trapped in the gate oxide 110 near the drain region 104, under normal operation, due to device degradation. This results in a fixed trapped charge in the gate oxide 110 near the drain region 104. Slope 103 represents the charge carrier mobility in the channel 106 for FIG. 1A having no electrons trapped in the gate oxide 110. Slope 105 represents the charge mobility in the channel 106 for the conventional MOSFET of FIG. 1B having electrons 117 trapped in the gate oxide 110 near the drain region 104. As shown by a comparison of slope 103 and slope 105 in FIG. 1C, the electrons 117 trapped in the gate oxide 110 near the drain region 104 of the conventional MOSFET do not significantly change the charge mobility in the channel 106.
There are two components to the effects of stress and hot electron injection. One component includes a threshold voltage shift due to the trapped electrons and a second component includes mobility degradation due to additional scattering of carrier electrons caused by this trapped charge and additional surface states. When a conventional MOSFET degrades, or is “stressed,” over operation in the forward direction, electrons do gradually get injected and become trapped in the gate oxide near the drain. In this portion of the conventional MOSFET there is virtually no channel underneath the gate oxide. Thus the trapped charge modulates the threshold voltage and charge mobility only slightly.
One of the inventors, along with others, has previously described programmable memory devices and functions based on the reverse stressing of MOSFET's in a conventional CMOS process and technology in order to form programmable address decode and correction in U.S. Pat. No. 6,521,950 entitled “MOSFET Technology for Programmable Address Decode and Correction.” That disclosure, however, did not describe write once read only memory solutions, but rather address decode and correction issues. One of the inventors also describes write once read only memory cells employing charge trapping in gate insulators for conventional MOSFETs and write once read only memory employing floating gates. The same are described in co-pending, commonly assigned U.S. patent applications, entitled “Write Once Read Only Memory Employing Charge Trapping in Insulators,” Ser. No. 10/177,077, and “Write Once Read Only Memory Employing Floating Gates,” Ser. No. 10/177,083. The present application, however, describes floating gate transistor cells having oxide-conductor nanolaminate layers and their use in integrated circuit device structures.
According to the teachings of the present invention, normal flash memory cells can be programmed by operation in the reverse direction and utilizing avalanche hot electron injection to trap electrons on the floating gate of the floating gate transistor. When the programmed floating gate transistor is subsequently operated in the forward direction the electrons trapped on the floating gate cause the channel to have a different threshold voltage. The novel programmed floating gate transistors of the present invention conduct significantly less current than conventional flash cells which have not been programmed. These electrons will remain trapped on the floating gate unless negative control gate voltages are applied. The electrons will not be removed from the floating gate when positive or zero control gate voltages are applied. Erasure can be accomplished by applying negative control gate voltages and/or increasing the temperature with negative control gate bias applied to cause the trapped electrons on the floating gate to be re-emitted back into the silicon channel of the MOSFET.
FIG. 2A is a diagram of an embodiment for a programmed floating gate transistor cell 201 having oxide-conductor nanolaminate layers according to the teachings of the present invention. As shown in FIG. 2A the floating gate transistor cell 201 includes a floating gate transistor in a substrate 200 which has a first source/drain region 202, a second source/drain region 204, and a channel region 206 between the first and second source/drain regions, 202 and 204. In one embodiment, the first source/drain region 202 includes a source region 202 for the floating gate transistor cell 201 and the second source/drain region 204 includes a drain region 204 for the floating gate transistor cell 201. FIG. 2A further illustrates the floating gate transistor cell 201 having oxide-conductor nanolaminate layers 208 serving as a floating gate 208 and separated from the channel region 206 by a first gate oxide 210. An sourceline or array plate 212 is coupled to the first source/drain region 202 and a transmission line 214 is coupled to the second source/drain region 204. In one embodiment, the transmission line 214 includes a bit line 214. Further as shown in FIG. 2A, a control gate 216 is separated from the oxide-conductor nanolaminate layers 208, or floating gate 208, by a second gate oxide 218.
As stated above, floating gate transistor cell 201 illustrates an embodiment of a programmed floating gate transistor. This programmed floating gate transistor has a charge 217 trapped in potential wells in the oxide-conductor nanolaminate layers 208, or floating gate 208, formed by the different electron affinities between materials in the structures 208, 210 and 218. In one embodiment, the charge 217 trapped on the floating gate 208 includes a trapped electron charge 217.
FIG. 2B is a diagram suitable for explaining the method by which the oxide-conductor nanolaminate layers 208, or floating gate 208, of the floating gate transistor cell 201 of the present invention can be programmed to achieve the embodiments of the present invention. As shown in FIG. 2B the method includes programming the floating gate transistor. Programming the floating gate transistor includes applying a first voltage potential V1 to a drain region 204 of the floating gate transistor and a second voltage potential V2 to the source region 202.
In one embodiment, applying a first voltage potential V1 to the drain region 204 of the floating gate transistor includes grounding the drain region 204 of the floating gate transistor as shown in FIG. 2B. In this embodiment, applying a second voltage potential V2 to the source region 202 includes biasing the array plate 212 to a voltage higher than VDD, as shown in FIG. 2B. A gate potential VGS is applied to the control gate 216 of the floating gate transistor. In one embodiment, the gate potential VGS includes a voltage potential which is less than the second voltage potential V2, but which is sufficient to establish conduction in the channel 206 of the floating gate transistor between the drain region 204 and the source region 202. As shown in FIG. 2B, applying the first, second and gate potentials (V1, V2, and VGS respectively) to the floating gate transistor creates a hot electron injection into the oxide-conductor nanolaminate layers 208, or floating gate 208, of the floating gate transistor. In other words, applying the first, second and gate potentials (V1, V2, and VGS respectively) provides enough energy to the charge carriers, e.g. electrons, being conducted across the channel 206 that, once the charge carriers are near the source region 202, a number of the charge carriers get excited into the oxide-conductor nanolaminate layers 208. Here the charge carriers become trapped in potential wells in the oxide-conductor nanolaminate layers 208 formed by the different electron affinities between materials in the structures 208, 210 and 218.
In an alternative embodiment, applying a first voltage potential V1 to the drain region 204 of the floating gate transistor includes biasing the drain region 204 of the floating gate transistor to a voltage higher than VDD. In this embodiment, applying a second voltage potential V2 to the source region 202 includes grounding the sourceline or array plate 212. A gate potential VGS is applied to the control gate 216 of the floating gate transistor. In one embodiment, the gate potential VGS includes a voltage potential which is less than the first voltage potential V1, but which is sufficient to establish conduction in the channel 206 of the floating gate transistor between the drain region 204 and the source region 202. Applying the first, second and gate potentials (V1, V2, and VGS respectively) to the floating gate transistor creates a hot electron injection into the oxide-conductor nanolaminate layers 208 of the floating gate transistor. In other words, applying the first, second and gate potentials (V1, V2, and VGS respectively) provides enough energy to the charge carriers, e.g. electrons, being conducted across the channel 206 that, once the charge carriers are near the drain region 204, a number of the charge carriers get excited into the oxide-conductor nanolaminate layers 208, or floating gate 208. Here the charge carriers become trapped in potential wells in the oxide-conductor nanolaminate layers 208 formed by the different electron affinities between materials in the structures 208, 210 and 218, as shown in FIG. 2A.
In one embodiment of the present invention, the method is continued by subsequently operating the floating gate transistor in the forward direction in its programmed state during a read operation. Accordingly, the read operation includes grounding the source region 202 and precharging the drain region a fractional voltage of VDD. If the device is addressed by a wordline coupled to the gate, then its conductivity will be determined by the presence or absence of stored charge in the oxide-conductor nanolaminate layers 208, or floating gate 208. That is, a gate potential can be applied to the gate 216 by a wordline 220 in an effort to form a conduction channel between the source and the drain regions as done with addressing and reading conventional DRAM cells.
However, now in its programmed state, the conduction channel 206 of the floating gate transistor will have a higher voltage threshold and will not conduct.
FIG. 2C is a graph plotting a current signal (IDS) detected at the second source/drain region 204 versus a voltage potential, or drain voltage, (VDS) set up between the second source/drain region 204 and the first source/drain region 202 (IDS vs. VDS). In one embodiment, VDS represents the voltage potential set up between the drain region 204 and the source region 202. In FIG. 2C, the curve plotted as 205 represents the conduction behavior of a conventional floating gate transistor where the transistor is not programmed (is normal or not stressed) according to the teachings of the present invention. The curve 207 represents the conduction behavior of the programmed floating gate transistor (stressed), described above in connection with FIG. 2A, according to the teachings of the present invention. As shown in FIG. 2C, for a particular drain voltage, VDS, the current signal (IDS2) detected at the second source/drain region 204 for the programmed floating gate transistor (curve 207) is significantly lower than the current signal (IDS1) detected at the second source/drain region 204 for the conventional floating gate transistor cell (curve 205) which is not programmed according to the teachings of the present invention. Again, this is attributed to the fact that the channel 206 in the programmed floating gate transistor of the present invention has a different voltage threshold.
Some of these effects have recently been described for use in a different device structure, called an NROM, for flash memories. This latter work in Israel and Germany is based on employing charge trapping in a silicon nitride layer in a non-conventional flash memory device structure. Charge trapping in silicon nitride gate insulators was the basic mechanism used in MNOS memory devices, charge trapping in aluminum oxide gates was the mechanism used in MIOS memory devices, and one of the present inventors, along with another, has previously disclosed charge trapping at isolated point defects in gate insulators. However, none of the above described references addressed forming transistor cells utilizing charge trapping in potential wells in oxide insulator nanolaminate layers formed by the different electron affinities of the insulators.
FIG. 3 illustrates an embodiment for a portion of a memory array 300 according to the teachings of the present invention. The memory in FIG. 3, is shown illustrating a number of vertical pillars, or floating gate transistor cells, 301-1, 301-2, . . . , 301-N, formed according to the teachings of the present invention. As one of ordinary skill in the art will appreciate upon reading this disclosure, the number of vertical pillar are formed in rows and columns extending outwardly from a substrate 303. As shown in FIG. 3, the number of vertical pillars, 301-1, 301-2, . . . , 301-N, are separated by a number of trenches 340. According to the teachings of the present invention, the number of vertical pillars, 301-1, 301-2, . . . , 301-N, serve as floating gate transistors including a first source/drain region, e.g. 302-1 and 302-2 respectively. The first source/drain region, 302-1 and 302-2, is coupled to a sourceline 304. As shown in FIG. 3, the sourceline 304 is formed in a bottom of the trenches 340 between rows of the vertical pillars, 301-1, 301-2, . . . , 301-N. According to the teachings of the present invention, the sourceline 304 is formed from a doped region implanted in the bottom of the trenches 340. A second source/drain region, e.g. 306-1 and 306-2 respectively, is coupled to a bitline (not shown). A channel region 305 is located between the first and the second source/drain regions.
As shown in FIG. 3, oxide-conductor nanolaminate layers or floating gate, shown generally as 309, are separated from the channel region 305 by a first oxide layer 307 in the trenches 340 along rows of the vertical pillars, 301-1, 301-2, . . . , 301-N. In the embodiment shown in FIG. 3, a wordline 313 is formed across the number of pillars and in the trenches 340 between the oxide-conductor nanolaminate layers 309. The wordline 313 is separated from the pillars and the oxide-conductor nanolaminate layers 309, or floating gate 309, by a second oxide layer 317. Here the wordline 313 serves as a control gate 313 for each pillar.
FIG. 4 illustrates an electrical equivalent circuit 400 for the portion of the memory array shown in FIG. 3. As shown in FIG. 4, a number of vertical floating gate transistor cells, 401-1, 401-2, . . . , 401-N, are provided. Each vertical floating gate transistor cell, 401-1, 401-2, . . . , 401-N, includes a first source/drain region, e.g. 402-1 and 402-2, a second source/drain region, e.g. 406-1 and 406-2, a channel region 405 between the first and the second source/drain regions, and oxide-conductor nanolaminate layers serving as a floating gate, shown generally as 409, separated from the channel region by a first oxide layer.
FIG. 4 further illustrates a number of bit lines, e.g. 411-1 and 411-2. According to the teachings of the present invention as shown in the embodiment of FIG. 4, a single bit line, e.g. 411-1 is coupled to the second source/drain regions, e.g. 406-1 and 406-2, for a pair of floating gate transistor cells 401-1 and 401-2 since, as shown in FIG. 3, each pillar contains two floating gate transistor cells. As shown in FIG. 4, the number of bit lines, 411-1 and 411-2, are coupled to the second source/drain regions, e.g. 406-1 and 406-2, along rows of the memory array. A number of word lines, such as wordline 413 in FIG. 4, are coupled to a control gate 412 of each floating gate transistor cell along columns of the memory array. According to the teachings of the present invention, a number of sourcelines, 415-1, 415-2, . . . , 415-N, are formed in a bottom of the trenches between rows of the vertical pillars, described in connection with FIG. 3, such that first source/drain regions, e.g. 402-2 and 402-3, in column adjacent floating gate transistor cells, e.g. 401-2 and 401-3, separated by a trench, share a common sourceline, e.g. 415-1. And additionally, the number of sourcelines, 415-1, 415-2, . . . , 415-N, are shared by column adjacent floating gate transistor cells, e.g. 401-2 and 401-3, separated by a trench, along rows of the memory array 400. In this manner, by way of example and not by way of limitation referring to column adjacent floating gate transistor cells, e.g. 401-2 and 401-3, separated by a trench, when one column adjacent floating gate transistor cell, e.g. 401-2, is being read its complement column adjacent floating gate transistor cell, e.g. 401-3, can operate as a reference cell.
FIG. 5 illustrates an energy band diagram for an embodiment of a gate stack according to the teachings of the present invention. As shown in FIG. 5, the embodiment consists of insulator stacks, 501-1, oxide-conductor nanolaminate 501-2 and insulator stacks 501-3, e.g. SiO2/oxide-conductor nanolaminate layers/SiO2. The structure shown in FIG. 5 illustrates the present invention's use in various embodiments of metallic conductors, doped oxide conductors, and metals as a nanolaminate between two layers of silicon oxide.
Tantalum nitride, titanium nitride, and tungsten nitride are mid-gap work function metallic conductors described for use in CMOS devices. Tantalum nitride, titanium nitride, and tungsten nitride are employed in the present invention as oxide-conductor nanolaminate layers, formed by atomic layer deposition (ALD). These metallic conductors have large electron affinities around 4.7 eV which is larger than the 4.1 ev electron affinity of silicon oxide.
In some embodiments according to the teachings of the present invention, atomic layer deposition, ALD, of a number of other conductors is used to form the nanolaminate structures. As described in more detail below, the oxide-conductor nanolaminate layers used in the present invention include:

    (i) Metallic Conductors, TaN, TiN, WN, NbN, MoN
    (ii) Doped Oxide Conductors, ZnOS
    (iii) Metals, including tungsten, W, and Nickel, Ni


As mentioned above, Titanium nitride, tantalum nitride and tungsten nitride are mid-gap work function metallic conductors, with no or zero band gaps and large electron affinities as shown in FIG. 6, commonly described for use in CMOS devices.
Method of Formation
This disclosure describes the use of oxide-conductor nanolaminate layers as floating gates to trap charge in potential wells formed by the different electron affinities of the insulator layers. These layers formed by ALD are of atomic dimensions, or nanolaminates, with precisely controlled interfaces and layer thickness. Operation of the device specifically depends on and utilizes the electron affinity of the oxide-conductor nanolaminate layers being higher than that of silicon oxide. This creates a potential energy well in the multi-layer nanolaminate gate insulator structure.
Atomic Layer Deposition of Metallic Conductors
TaN: Plasma-enhanced atomic layer deposition (PEALD) of tantalum nitride (Ta—N) thin films at a deposition temperature of 260° C. using hydrogen radicals as a reducing agent for Tertbutylimidotris(diethylamido)tantalum has been described. The PEALD yielded superior Ta—N films with an electric resistivity of 400 μΩcm and no aging effect under exposure to air. The film density is higher than that of Ta—N films formed by typical ALD, in which NH3 is used instead of hydrogen radicals. In addition, the as-deposited films are not amorphous, but rather polycrystalline structure of cubit TaN. The density and crystallinity of the films increased with the pulse time of hydrogen plasma. The films are Ta-rich in composition and contain around 15 atomic % of carbon impurity. In the PEALD of Ta—N films, hydrogen radicals are used a reducing agent instead of NH3, which is used as a reactant gas in typical Ta—N ALD. Films are deposited on SiO2 (100 nm)/Si wafers at a deposition temperature of 260° C. and a deposition pressure of 133 Pa in a cold-walled reactor using (Net2)3 Ta=Nbut [tertbutylimidotris(diethylamido)tantalum, TBTDET] as a precursor of Ta. The liquid precursor is contained in a bubbler heated at 70° C. and carried by 35 sccm argon. One deposition cycle consist of an exposure to a metallorganic precursor of TBTDET, a purge period with Ar, and an exposure to hydrogen plasma, followed by another purge period with Ar. The Ar purge period of 15 seconds instead between each reactant gas pulse isolates the reactant gases from each other. To ignite and maintain the hydrogen plasma synchronized with the deposition cycle, a rectangular shaped electrical power is applied between the upper and lower electrode. The showerhead for uniform distribution of the reactant gases in the reactor, capacitively coupled with an rf (13.56 MHz) plasma source operated at a power of 100 W, is used, as the upper electrode. The lower electrode, on which a wafer resides, is grounded. Film thickness and morphology are analyzed by field emission scanning electron microscopy.
TiN: Atomic layer deposition (ALD) of amorphous TiN films on SiO2 between 170° C. and 210° C. has been achieved by the alternate supply of reactant sources, Ti[N(C2H5CH3)2]4 [tetrakis(ethylmethylamino)titanium:TEMAT] and NH3. These reactant sources are injected into the reactor in the following order: TEMAT vapor pulse, Ar gas pulse, NH3 gas pulse and Ar gas pulse. Film thickness per cycle saturated at around 1.6 monolayers per cycle with sufficient pulse times of reactant sources at 200° C. The results suggest that film thickness per cycle could exceed 1 ML/cycle in ALD, and are explained by the rechemisorption mechanism of the reactant sources. An ideal linear relationship between number of cycles and film thickness has been confirmed.
TiN and TaN: Deposition of thin and conformal copper films of has been examined using atomic layer deposition, ALD, of TiN and TaN as possible seed layer for subsequent electro-deposition. The copper films are deposited on glass as well as Ta, TIN, and TaN films on Si wafers. Typical resistivities of these films range from 4.25 μΩcm for 20 nm thick copper films to 1.78 μΩcm for 120 nm thick films. The adhesion of the copper films deposited on TiN and TaN at 300° C. is excellent. These films are highly conformal over high aspect ratio trenches.
TiN, TaNx, NbN, and MoNx: Atomic layer deposition of Tin, TaNx, NbN, and MoNx thin films from the corresponding metal chlorides and 1,1-dimethyl-hydrazine (DMHy) have been studied. Generally, the same films deposited at 400° C. exhibit better characteristics compared to the films deposited at the same temperature using NH3 as the nitrogen source. In addition, films can be deposited at lower temperatures down to 200° C. Even though the carbon content in the films is quite high, in the range of 10 atom %, the results encourage further studies. The effect of carbon on the barrier properties and the use of other possibly less carbon-contaminating hydrazine derivatives can be considered.
WN: Tungsten nitride films have been deposited with atomic layer control using sequential surface reactions. The tungsten nitride film growth is accomplished by separating the binary reaction 2WF6+NH3−>W2N+3HF+9/2 F2 into two half-reactions. Successive application of the WF6 and NH3 half-reactions in an ABAB . . . sequence produce tungsten nitride deposition at substrate temperatures between 600 and 800 K. Transmission Fourier transform infrared (FTIR) spectroscopy has been used to monitor the coverage Of WFx* and NHy* surface species on high surface area particles during the WF6 and NH3 half-reactions. The FTIR spectroscope results demonstrate the WF6 and NH3 half-reactions are complete and self-limiting at temperatures >600 K. In situ spectroscopic ellipsometry has been used to monitor the film growth on Si(100) substrate vs. temperature and reactant exposure. A tungsten nitride deposition rate of 2.55 Å/AB cycle is measured at 600–800 K for WF6 and NH3 reactant exposure>3000 L and 10,000 L, respectively. X-ray photoelectron spectroscopy depth-profiling experiments have been used to determine that the films had a W2N stoichiometry with low C and O impurity concentrations. X-ray diffraction investigations reveal that the tungsten nitride films are microcrystalline. Atomic force microscopy measurements of the deposited films illustrate remarkably flat surface indicating smooth film growth. These smooth tungsten nitride films deposited with atomic layer have been be used as diffusion control for Cu on contact and via holes.
Atomic Layer Deposition of Doped Oxide Conductors
ZnO: ZnO can be deposited by ALD. The aim of previous experiments is to improve the performance of Cd-free ZnO/Cu(JnGa)Se2 solar cells using a high-resistivity ZnO buffer layer. Buffer layers are deposited by atomic layer deposition (ALD) using diethylzinc (DEZn) and H2O as reactant gases. The structural and electrical properties of the ZnO films on glass substrates have been characterized. A high resistivity of more than 103 Ωcm and a transmittance of above 80% in the visible range were obtained. Suticai Chaitsak et al. focused on determining the optimum deposition parameters for the ALD-ZnO buffer layer. Results indicate that the thickness and resistivity of the ALD-ZnO buffer layer, as well as the heat treatment prior to the deposition of the buffer layer, affect the device characteristics. The best efficiency obtained with an ALD-ZnO buffer layer of solar cells without an antireflective coating is 12.1%. The reversible light soaking effect is observed in these devices. ZoO itself however is highly resistive, doping ZnO as described below is required to make it conductive and useful here.
ZnOS: The chemical vapor atomic layer deposition technique is used to deposit thin films of ZnO1−xSx on glass and silicon substrates. Film composition is varied from x=0 to x=0.95, and measurements of bandgap and resistivity yielded surprising minima at x ̃0.6. Results of Rutherford backscattering, X-ray, and luminescence measurements are also presented. Both one- and two phase films are visible in scanning electron microcopy, and an amorphous phases is also apparent. A continuously variable mixed film is not observed due to the large lattice mismatch between ZnO and ZnS. Films of ZnO1−xSx are deposited using dimethyzinc, 1% hydrogen sulfide in nitrogen, and the trace oxygen and/or water present (up to 2 ppm) in ultrahigh-purity (UHP) nitrogen. The dimethyzinc is contained in a stainless steel cylinder equipped with a dip tube. To lower the dimethylzinc vapor pressure, the cylinder is held at 273 K using an ice water bath. Prepurified nitrogin served as a carrier gas for the dimethylzinc. Gas pressure are given in the table below:













Nitrogen flush pressure
 50 psig


Dimethylzinc cylinder pressure
 50 psig


Hydrogen sulfide cylinder pressure
 30, 50, or 70 psig


Dimethylzinc reaction time
  2 s


Hydrogen sulfide reaction time
  5 s


Nitrogen purge times
 11 s at a standard flow rate of



1 L/mm


Delay to allow nitrogen back-
0 8 s


pressure to drop









The electrical resistivity, mobility, and carrier concentration results from Hall measurements on some samples are given in the following table:














X in
Resistivity,
Donor concentration,
Mobility,


ZnO1−xSx
Ω cm
cm−3
cm2/V s


















0
0.0048
4.8 × 1019
13.2


0.25
0.101
1.7 × 1018
36.1


0.56
0.042
1.66 × 1019 
32.2


0.66
1.28
2.0 × 1017
24


0.82
8.27
2.4 × 1016
28


0.92
67.9
2.61 × 1015 
94









Atomic Layer Deposition of Metal Films

W: The atomic layer deposition (ALD) of tungsten (W) films has been demonstrated using alternate exposure of tungsten hexafluoride (WF6) and disilane (Si2H6). The present investigation explored the kinetics of the WF6 and Si2H6 surface reactions during W ALD at 303–623 K using Auger electron spectroscopy technique. The reaction of WF6 with the Si2H6-saturated W surface proceeded to completion at 373–573 Kelvin (K). The WF6 reaction displayed a reactive sticking coefficient of S=0.4 and required an exposure of 30 L (1 L=1*10−6 Torr s) to achieve saturation at 573 K. The WF6 exposures necessary to reach saturation increased with decreasing temperature. At surface temperatures <373 K, the WF6 reaction did not consume all the silicon (Si) surface species remaining from the previous Si2H6 exposure. The reaction of Si2H6 with the WF6-saturated W surface displayed three kinetic regimes. In the first region at slow Si2H6 exposures < or=50 L, the Si2H6 reaction is independent of temperature and had a reactive striking coefficient of S ̃5*10−2. In the second kinetic region at intermediate Si2H6 exposure of 50–300 L, the Si2H6 reaction showed an apparent saturation behavior with Si thickness at saturation at increased at substrate temperature. At high Si2H6 exposures of 300-1*105/L, additional Si is deposited with an approximately logarithmic dependence on Si2H6 exposure. The Si2H6 reaction in this third kinetic region had an activation energy E=2.6 kcal/mol and the Si thickness deposited by a 1.6*105 L Si2H6 exposure increased with temperature from 3.0 Å at 303 K to 6.6 Å at 623 K. These kinetic results should help to explain W ALD growth rates observed at different exposures and substrate temperatures.
Ni: A thin film of elementary nickel is formed by atomic layer deposition (ALD). The deposition cycle consisted of two consecutive chemical reaction steps: an oxidizing step and a reducing step. An atomic layer of nickel oxide is made by sequentially supplying bis(cyclopentadienyl)-nickel as a nickel precursor and water as an oxidation agent; the preformed atomic layer of nickel oxide is then reduced to elementary nickel metal by exposure to hydrogen radical at a deposition temperature of 165° C. Auger electron spectroscopy analysis detected negligible oxygen content in the grown films, indicating that the hydrogen radical had completely reduced the nickel oxide to metallic film films. In addition, carbon impurities in the film dropped from 16 atomic % to less than 5 atomic % during the reaction. The proposed two-stage ALD method for elementary metal is successful in forming continuous and conformal nickel films. The nickel films formed an effective glue layer between chemical vapor deposited copper and diffusion barrier layer of TiN. The addition of a 1 μm thick copper film to a 15 nm thick nickel glue layer over a TiN barrier film is excellent, with no failures occurring during adhesive tape peel tests.
Memory Devices
This disclosure describes a flash memory device, programmable logic array device or memory address and decode correction device with a conductor nanolaminate floating gate rather than a conventional polysilicon floating gate. In some embodiments acccording to the teachings of the present invention, the gate insulator structure shown in FIG. 5 is employed in a wide variety of different flash memory type devices. That is, in embodiments of the present invention, the gate structure embodiment of FIG. 5, having silicon oxide-conductor-silicon oxide-nanolaminates, is used in place of the gate structure provided in the following commonly assigned patents: U.S. Pat. Nos. 5,936,274; 6,143,636; 5,973,356; 6,238,976; 5,991,225; 6,153,468; and 6,124,729.
In embodiments of the present invention, the gate structure embodiment of FIG. 5, having silicon oxide-conductor silicon oxide-nanolaminates, is used in place of the gate structure provided in the following commonly assigned pending applications: Forbes, L., “Write Once Read Only Memory Employing Charge Trapping in Gate Insulators,” application Ser. No. 10/177,077; Forbes, L., “Write Once Read Only Memory Employing Floating Gates application Ser. No. 10/177,083; Forbes, L., “Write Once Read Only Memory With Large Work Function Floating Gates,” application Ser. No. 10/177,213; Forbes, L., “Nanocrystal Write Once Read Only Memory For Archival Storage,” application Ser. No. 10/177,214; Forbes, L., “Ferroelectric Write Once Read Only Memory For Archival Storage,” application Ser. No. 10/177,082; Forbes, L., Vertical NROM Having a Storage Density of 1 Bit Per 1F2 application Ser. No. 10/177,208; Forbes, L., “Multistate NROM Having a Storage Density Much Greater Than 1 Bit Per 1F2,” application Ser. No. 10/177,211; Forbes, L., “NOR Flash Memory Cell With high Storage Density,” application Ser. No. 10/177,483.
According to the teachings of the present invention, embodiments of the novel floating gate transistor herein, which are substituted for the gate structures described in the references above, are programmed by grounding a source line and applying a gate voltage and a voltage to the drain to cause channel hot electron injection. To read the memory state, the drain and ground or source have the normal connections and the conductivity of the floating gate transistor determined using low voltages so as not to disturb the memory state. The devices can be erased by applying a large negative voltage to the gate.
In embodiments of the present invention, the gate structure embodiment of FIG. 5, having silicon oxide-conductor-silicon oxide-nanolaminates, is used in place of the gate structure provided in the following commonly assigned patents: U.S. Pat. Nos. 5,936,274, 6,143,636, 5,973,356 and 6,238,976 (vertical flash memory devices with high density); U.S. Pat. Nos. 5,991,225 and 6,153,468 (programmable memory address and decode circuits); and U.S. Pat. No. 6,124,729 (programmable logic arrays).
Further, in embodiments of the present invention, the gate structure embodiment of FIG. 5, having silicon oxide-metal oxide-silicon oxide-conductor nanolaminates, is used in place of the gate structure provided in the following: Eitan, B. et al., “NROM: A novel localized Trapping, 2-Bit Nonvolatile Memory Cell,” IEEE Electron Device Lett., 21(11), 543–545 (November 2000); Eitan, B. et al., “Characterization of Channel Hot Electron Injection by the Subthreshold Slope of NROM device, IEEE Electron Device Lett., 22(11), 556–558 (November 2001); Maayan, E. et al., “A 512 Mb NROM Flash Data Storage Memory with 8 MB/s Data Rate,” Dig. IEEE Int. Solid-State Circuits Conf., 100–101 (2002). In these embodiments, the gate structure embodiment of FIG. 5, having silicon oxide-metal oxide-silicon oxide-conductor nanolaminates used in place of the gate structures in those references, can be programmed in the reverse direction and read in the forward direction to obtain more sensitivity in the device characteristics to the stored charge.
All of the above references are incorporated herein in full. The gate structure embodiment of FIG. 5, having silicon oxide-conductor-silicon oxide-nanolaminates, are herein used in place of the gate structure provided in those references to support the various embodiments of the present invention. That is, the present invention incorporates the multitude of device structures described in those references to create a multitude of new embodiments which utilize electron trapping in potential wells formed by the floating gate oxide-conductor nanolaminate structure shown in FIG. 5, rather than employing other floating gates, as recited in many of the above references. In an embodiment, a floating gate transistor array includes a number of floating gate transistor cells extending from a substrate, where the number of floating gate transistor cells operate as equivalent to a floating gate transistor having a size equal to or less than 2.0 lithographic feature squared (2F2). In an embodiment, an electronic system includes a number of floating gate transistors, where each floating gate transistor operates as equivalent to a floating transistor having a size equal to or less than 2.0 lithographic feature squared (2F2).
Sample Operation
FIGS. 7A–B and 8 are embodiments useful in illustrating the use of charge storage in the oxide-conductor nanolaminate layers to modulate the conductivity of the floating gate transistor cell according to the teachings of the present invention. That is, FIGS. 7A–7B illustrates the operation of an embodiment for a novel floating gate transistor cell 701 formed according to the teachings of the present invention. And, FIG. 8 illustrates the operation of a conventional DRAM cell 701. As shown in FIG. 7A, the embodiment consists of a gate insulator stack having insulator layers, 710, 708 and 718, e.g. SiO2/oxide-conductor nanolaminate layers/SiO2. In the embodiment of FIG. 7A, the gate insulator stack having insulator layers, 710, 708 and 718, has a thickness 711 thicker than in a conventional DRAM cell, e.g. 801 and is equal to or greater than 10 nm or 100 Å (10−6 cm). In the embodiment shown in FIG. 7A a floating gate transistor cell has dimensions 713 of 0.1 μm (10−5 cm) by 0.1 μm. The capacitance, Ci, of the structure depends on the dielectric constant, ∈i, and the thickness of the insulating layers, t. In an embodiment, the dielectric constant is 0.3×1031 12 F/cm and the thickness of the insulating layer is 10−6 cm such that Ci=∈i/t, Farads/cm2 or 3×10−7 F/cm2. In one embodiment, a charge of 1012 electrons/cm2 is programmed into the oxide-conductor nanolaminate layers of the floating gate transistor cell. Here the charge carriers become trapped in potential wells in the oxide-conductor nanolaminate layers 708 formed by the different electron affinities of the insulators 710, 708 and 718, as shown in FIG. 7A. This produces a stored charge ΔQ=1012 electrons/cm2×1.6×10−19 Coulombs. In this embodiment, the resulting change in the threshold voltage (ΔVt) of the floating gate transistor cell will be approximately 0.5 Volts (ΔVt=ΔQ/Ci or 1.6×10−7/3×10−7=1⁄2 Volt). For ΔQ=1012 electrons/cm3 in an area of 10−10 cm2, this embodiment of the present invention involves trapping a charge of approximately 100 electrons in the oxide-conductor nanolaminate layers 708 of the floating gate transistor cell. In this embodiment, an original VT is approximately 1⁄2 Volt and the VT with charge trapping is approximately 1 Volt.
FIG. 7B aids to further illustrate the conduction behavior of the novel floating gate transistor cell of the present invention. As one of ordinary skill in the art will understand upon reading this disclosure, if the floating gate transistor cell is being driven with a control gate voltage of 1.0 Volt (V) and the nominal threshold voltage without the floating gate charged is 1⁄2 V, then if the oxide-conductor nanolaminate layers are charged the floating gate transistor cell of the present invention will be off and not conduct. That is, by trapping a charge of approximately 100 electrons in the oxide-conductor nanolaminate layers of the floating gate transistor cell, having dimensions of 0.1 μm (10−5 cm) by 0.1 μm, will raise the threshold voltage of the floating gate transistor cell to 1.0 Volt and a 1.0 Volt control gate potential will not be sufficient to turn the device on, e.g. Vt=1.0 V, I=0.
Conversely, if the nominal threshold voltage without the oxide-conductor nanolaminate layers charged is 1⁄2 V, then I=μCox×(W/L)×((Vgs−Vt)2/2), or 12.5 μA, with μCox=μC1=100 μA/V2 and W/L=1. That is, the floating gate transistor cell of the present invention, having the dimensions describe above will produce a current I=100 μA/V2×(1⁄4)×(1⁄2)=12.5 μA. Thus, in the present invention an un-written, or un-programmed floating gate transistor cell can conduct a current of the order 12.5 μA, whereas if the oxide-conductor nanolaminate layers are charged then the floating gate transistor cell will not conduct. As one of ordinary skill in the art will understand upon reading this disclosure, the sense amplifiers used in DRAM arrays, and as describe above, can easily detect such differences in current on the bit lines.
By way of comparison, in a conventional DRAM cell 850 with 30 femtoFarad (fF) storage capacitor 851 charged to 50 femto Coulombs (fC), if these are read over 5 nS then the average current on a bit line 852 is only 10 μA (I=50 fC/5 ns=10 μA). Thus, storing a 50 fC charge on the storage capacitor equates to storing 300,000 electrons (Q=50 fC/(1.6×10−19)=30×104=300,000 electrons).
According to the teachings of the present invention, the floating gate transistor cells, having the gate structure with oxide-conductor nanolaminate layers, in the array are utilized not just as passive on or off switches as transfer devices in DRAM arrays but rather as active devices providing gain. In the present invention, to program the floating gate transistor cell “off,” requires only a stored charge in the oxide-conductor nanolaminate layers of about 100 electrons if the area is 0.1 μm by 0.1 μm. And, if the floating gate transistor cell is un-programmed, e.g. no stored charge trapped in the oxide-conductor nanolaminate layers, and if the floating gate transistor cell is addressed over 10 nS a current of 12.5 μA is provided. The integrated drain current then has a charge of 125 fC or 800,000 electrons. This is in comparison to the charge on a DRAM capacitor of 50 fC which is only about 300,000 electrons. Hence, the use of floating gate transistor cells, having the gate structure with oxide-conductor nanolaminate layers, in the array as active devices with gain, rather than just switches, provides an amplification of the stored charge, in the oxide-conductor nanolaminate layers, from 100 to 800,000 electrons over a read address period of 10 nS.
Sample Device Applications
In FIG. 9 a memory device is illustrated according to the teachings of the present invention. The memory device 940 contains a memory array 942, row and column decoders 944, 948 and a sense amplifier circuit 946. The memory array 942 consists of a plurality of floating gate transistor cells 900, having oxide-conductor nanolaminate layers in the gate stack, whose word lines 980 and bit lines 960 are commonly arranged into rows and columns, respectively. The bit lines 960 of the memory array 942 are connected to the sense amplifier circuit 946, while its word lines 980 are connected to the row decoder 944. Address and control signals are input on address/control lines 961 into the memory device 940 and connected to the column decoder 948, sense amplifier circuit 946 and row decoder 944 and are used to gain read and write access, among other things, to the memory array 942.
The column decoder 948 is connected to the sense amplifier circuit 946 via control and column select signals on column select lines 962. The sense amplifier circuit 946 receives input data destined for the memory array 942 and outputs data read from the memory array 942 over input/output (I/O) data lines 963. Data is read from the cells of the memory array 942 by activating a word line 980 (via the row decoder 944), which couples all of the memory cells corresponding to that word line to respective bit lines 960, which define the columns of the array. One or more bit lines 960 are also activated. When a particular word line 980 and bit lines 960 are activated, the sense amplifier circuit 946 connected to a bit line column detects and amplifies the conduction sensed through a given floating gate transistor cell and transferred to its bit line 960 by measuring the potential difference between the activated bit line 960 and a reference line which may be an inactive bit line. Again, in the read operation the source region of a given cell is couple to a grounded sourceline or array plate (not shown). The operation of Memory device sense amplifiers is described, for example, in U.S. Pat. Nos. 5,627,785; 5,280,205; and 5,042,011, all assigned to Micron Technology Inc., and incorporated by reference herein.
FIG. 10 shows a conventional NOR-NOR logic array 1000 which is programmable at the gate mask level by either fabricating a thin oxide gate transistor, e.g. logic cells 1001-1, 1001-2, . . . , 1001-N and 1003-1, 1003-2, . . . , 1003-N, at the intersection of lines in the array or not fabricating a thin oxide gate transistor, e.g. missing thin oxide transistors, 1002-1, 1002-2, . . . , 1002-N, at such an intersection. As one of ordinary skill in the art will understand upon reading this disclosure, the same technique is conventionally used to form other types of logic arrays not shown. As shown in FIG. 10, a number of depletion mode NMOS transistors, 1016 and 1018 respectively, are used as load devices.
The conventional logic array shown in FIG. 10 includes a first logic plane 1010 which receives a number of input signals at input lines 1012. In this example, no inverters are provided for generating complements of the input signals. However, first logic plane 1010 can include inverters to produce the complementary signals when needed in a specific application.
First logic plane 1010 includes a number of thin oxide gate transistors, e.g. transistors 1001-1, 1001-2, . . . , 1001-N. The thin oxide gate transistors, 1001-1, 1001-2, . . . , 1001-N, are located at the intersection of input lines 1012, and interconnect lines 1014. In the conventional PLA of FIG. 10, this selective fabrication of thin oxide gate transistor, e.g. transistors 1001-1, 1001-2, . . . , 1001-N, is referred to as programming since the logical function implemented by the programmable logic array is entered into the array by the selective arrangement of the thin oxide gate transistors, or logic cells, 1001-1, 1001-2, . . . , 1001-N, at the intersections of input lines 1012, and interconnect lines 1014 in the array.
In this embodiment, each of the interconnect lines 1014 acts as a NOR gate for the input lines 1012 that are connected to the interconnect lines 1014 through the thin oxide gate transistors, 1001-1, 1001-2, . . . , 1001-N, of the array. For example, interconnection line 1014A acts as a NOR gate for the signals on input lines 1012A and 1012B. That is, interconnect line 1014A is maintained at a high potential unless one or more of the thin oxide gate transistors, 1001-1, 1001-2, . . . , 1001-N, that are coupled to interconnect line 1014A are turned on by a high logic level signal on one of the input lines 1012. When a control gate address is activated, through input lines 1012, each thin oxide gate transistor, e.g. transistors 1001-1, 1001-2, . . . , 1001-N, conducts which performs the NOR positive logic circuit function, an inversion of the OR circuit function results from inversion of data onto the interconnect lines 1014 through the thin oxide gate transistors, 1001-1, 1001-2, . . . , 1001-N, of the array.
As shown in FIG. 10, a second logic plane 1024 is provided which includes a number of thin oxide gate transistor, e.g. transistors 1003-1, 1003-2, . . . , 1003-N. The thin oxide gate transistors, 1003-1, 1003-2, . . . , 1003-N, are located at the intersection of interconnect lines 1014, and output lines 1020. Here again, the logical function of the second logic plane 1024 is implemented by the selective arrangement of the thin oxide gate transistors, 1003-1, 1003-2, . . . , 1003-N, at the intersections of interconnect lines 1014, and output lines 1020 in the second logic plane 1024. The second logic plane 1024 is also configured such that the output lines 1020 comprise a logical NOR function of the signals from the interconnection lines 1014 that are coupled to particular output lines 1020 through the thin oxide gate transistors, 1003-1, 1003-2, . . . , 1003-N, of the second logic plane 1024. Thus, in FIG. 10, the incoming signals on each line are used to drive the gates of transistors in the NOR logic array as the same is known by one of ordinary skill in the art and will be understood by reading this disclosure.
FIG. 11 illustrates an embodiment of a novel in-service programmable logic array (PLA) formed with logic cells having a floating gate structure with oxide-conductor nanolaminate layers, according to the teachings of the present invention. In FIG. 11, PLA 1100 implements an illustrative logical function using a two level logic approach. Specifically, PLA 1100 includes first and second logic planes 1110 and 1122. In this example, the logic function is implemented using NOR-NOR logic. As shown in FIG. 11, first and second logic planes 1110 and 1122 each include an array of, logic cells, having a gate structure with oxide-conductor nanolaminate layers, which serve as driver floating gate transistors, 1101-1, 1101-2, . . . , 1101-N, and 1102-1, 1102-2, . . . , 1102-N respectively, formed according to the teachings of the present invention. The driver floating gate transistors, 1101-1, 1101-2, . . . , 1101-N, and 1102-1, 1102-2, . . . , 1102-N, have their first source/drain regions coupled to source lines or a conductive source plane. These driver floating gate transistors, 1101-1, 1101-2, . . . , 1101-N, and 1102-1, 1102-2, . . . , 1102-N are configured to implement the logical function of FPLA 1100. The driver floating gate transistors, 1101-1, 1101-2, . . . , 1101-N, and 1102-1, 1102-2, . . . , 1102-N are shown as n-channel floating gate transistors. However, the invention is not so limited. Also, as shown in FIG. 11, a number of p-channel metal oxide semiconductor (PMOS) floating gate transistors are provided as load device floating gate transistors, 1116 and 1124 respectively, having their source regions coupled to a voltage potential (VDD). These load device floating gate transistors, 1116 and 1124 respectively, operate in complement to the driver floating gate transistors, 1101-1, 1101-2, . . . , 1101-N, and 1102-1, 1102-2, . . . , 1102-N to form load inverters.
It is noted that the configuration of FIG. 11 is provided by way of example and not by way of limitation. Specifically, the teachings of the present application are not limited to programmable logic arrays in the NOR-NOR approach. Further, the teachings of the present application are not limited to the specific logical function shown in FIG. 11. Other logical functions can be implemented in a programmable logic array, with the driver floating gate transistors, having a gate structure with oxide-conductor nanolaminate layers, 1101-1, 1101-2, . . . , 1101-N, and 1102-1, 1102-2, . . . , 1102-N and load device floating gate transistors, 1116 and 1124 respectively, of the present invention, using any one of the various two level logic approaches.
First logic plane 1110 receives a number of input signals at input lines 1112. In this example, no inverters are provided for generating complements of the input signals. However, first logic plane 1110 can include inverters to produce the complementary signals when needed in a specific application.
First logic plane 1110 includes a number of driver floating gate transistors, having a gate structure with oxide-conductor nanolaminate layers, 1101-1, 1101-2, . . . , 1101-N, that form an array. The driver floating gate transistors, 1101-1, 1101-2, . . . , 1101-N, are located at the intersection of input lines 1112, and interconnect lines 1114. Not all of the driver floating gate transistors, 1101-1, 1101-2, . . . , 1101-N, are operatively conductive in the first logic plane. Rather, the driver floating gate transistors, 1101-1, 1101-2, . . . , 1101-N, are selectively programmed, as has been described herein, to respond to the input lines 1112 and change the potential of the interconnect lines 1114 so as to implement a desired logic function. This selective interconnection is referred to as programming since the logical function implemented by the programmable logic array is entered into the array by the driver floating gate transistors, 1101-1, 1101-2, . . . , 1101-N, that are used at the intersections of input lines 1112, and interconnect lines 1114 in the array.
In this embodiment, each of the interconnect lines 1114 acts as a NOR gate for the input lines 1112 that are connected to the interconnect lines 1114 through the driver floating gate transistors, 1101-1, 1101-2, . . . , 1101-N, of the array 1100. For example, interconnection line 1114A acts as a NOR gate for the signals on input lines 1112A, 1112B and 1112C. Programmability of the driver floating gate transistors, 1101-1, 1101-2, . . . , 1101-N is achieved by trapping charge carriers in potential wells in the oxide-conductor nanolaminate layers of the gate stack, as described herein. When the oxide-conductor nanolaminate layers are charged, that driver floating gate transistor, 1101-1, 1101-2, . . . , 1101-N will remain in an off state until it is reprogrammed. Applying and removing a charge to the oxide-conductor nanolaminate layers, is performed by tunneling charge into the oxide-conductor nanolaminate layers of the driver floating gate transistors, 1101-1, 1101-2, . . . , 1101-N. A driver floating gate transistors, 1101-1, 1101-2, . . . , 1101-N programmed in an off state remains in that state until the charge is removed from the oxide-conductor nanolaminate layers.
Driver floating gate transistors, 1101-1, 1101-2, . . . , 1101-N not having their corresponding gate structure with oxide-conductor nanolaminate layers charged operate in either an on state or an off state, wherein input signals received by the input lines 1112A, 1112B and 1112C determine the applicable state. If any of the input lines 1112A, 1112B and 1112C are turned on by input signals received by the input lines 1112A, 1112B and 1112C, then a ground is provided to load device floating gate transistors 1116. The load device floating gate transistors 1116 are attached to the interconnect lines 1114. The load device floating gate transistors 1116 provide a low voltage level when any one of the driver floating gate transistors, 1101-1, 1101-2, . . . , 1101-N connected to the corresponding interconnect line 1114 is activated. This performs the NOR logic circuit function, an inversion of the OR circuit function results from inversion of data onto the interconnect lines 1114 through the driver floating gate transistors, 1101-1, 1101-2, . . . , 1101-N of the array 1100. When the driver floating gate transistors, 1101-1, 1101-2, . . . , 1101-N are in an off state, an open is provided to the drain of the load device floating gate transistors 1116. The VDD voltage level is applied to corresponding input lines, e.g. the interconnect lines 1114 for second logic plane 1122 when a load device floating gate transistors 1116 is turned on by a clock signal received at the gate of the load device floating gate transistors 1116. Each of the driver floating gate transistors, 1101-1, 1101-2, . . . , 1101-N described herein are formed according to the teachings of the present, having a gate structure with oxide-conductor nanolaminate layers.
In a similar manner, second logic plane 1122 comprises a second array of driver floating gate transistors, 1102-1, 1102-2, . . . , 1102-N that are selectively programmed to provide the second level of the two level logic needed to implement a specific logical function. In this embodiment, the array of driver floating gate transistors, 1102-1, 1102-2, . . . , 1102-N is also configured such that the output lines 1120 comprise a logical NOR function of the signals from the interconnection lines 1114 that are coupled to particular output lines 1120 through the driver floating gate transistors, 1102-1, 1102-2, . . . , 1102-N of the second logic plane 1122.
Programmability of the driver floating gate transistors, 1102-1, 1102-2, . . . , 1102-N is achieved by trapping charge carriers in potential wells in the oxide-conductor nanolaminate layers of the gate stack, as described herein. When the oxide-conductor nanolaminate layers are charged, that driver floating gate transistor, 1102-1, 1102-2, . . . , 1102-N will remain in an off state until it is reprogrammed. Applying and removing a charge to the oxide-conductor nanolaminate layers are performed by tunneling charge into the oxide-conductor nanolaminate layers of the driver floating gate transistors, 1101-1, 1101-2, . . . , 1101-N. A driver floating gate transistor, e.g. 1102-1, 1102-2, . . . , 1102-N, programmed in an off state remains in that state until the charge is removed from the oxide-conductor nanolaminate layers.
Driver floating gate transistors, 1102-1, 1102-2, . . . , 1102-N not having their corresponding gate structure with oxide-conductor nanolaminate layers charged operate in either an on state or an off state, wherein signals received by the interconnect lines 1114 determine the applicable state. If any of the interconnect lines 1114 are turned on, then a ground is provided to load device floating gate transistors 1124 by applying a ground potential to the source line or conductive source plane coupled to the floating gate transistors first source/drain region as described herein. The load device floating gate transistors 1124 are attached to the output lines 1120. The load device floating gate transistors 1124 provide a low voltage level when any one of the driver floating gate transistors, 1102-1, 1102-2, . . . , 1102-N connected to the corresponding output line is activated. This performs the NOR logic circuit function, an inversion of the OR circuit function results from inversion of data onto the output lines 1120 through the driver floating gate transistors, 1102-1, 1102-2, . . . , 1102-N of the array 1100. When the driver floating gate transistors, 1102-1, 1102-2, . . . , 1102-N are in an off state, an open is provided to the drain of the load device floating gate transistors 1124. The VDD voltage level is applied to corresponding output lines 1120 for second logic plane 1122 when a load device floating gate transistor 1124 is turned on by a clock signal received at the gate of the load device floating gate transistors 1124. In this manner a NOR-NOR electrically programmable logic array is most easily implemented utilizing the normal PLA array structure. Each of the driver floating gate transistors, 1102-1, 1102-2, . . . , 1102-N described herein are formed according to the teachings of the present, having a gate structure with oxide-conductor nanolaminate layers.
Thus FIG. 11 shows an embodiment for the application of the novel floating gate transistor cells, having a gate structure with oxide-conductor nanolaminate layers, in a logic array. If a driver floating gate transistors, 1101-1, 1101-2, . . . , 1101-N, and 1102-1, 1102-2, . . . , 1102-N, is programmed with a negative charge trapped in potential wells, formed with the oxide-conductor nanolaminate layers, it is effectively removed from the array. In this manner the array logic functions can be programmed even when the circuit is in the final circuit or in the field and being used in a system.
The absence or presence of charge trapped in potential wells, formed by the oxide-conductor nanolaminate layers, is read by addressing the input lines 1112 or control gate lines and y-column/sourcelines to form a coincidence in address at a particular logic cell. The control gate line would for instance be driven positive at some voltage of 1.0 Volts and the y-column/sourceline grounded, if the oxide-conductor nanolaminate layers are not charged with electrons then the floating gate transistor would turn on tending to hold the interconnect line on that particular row down indicating the presence of a stored “one” in the cell. If this particular floating gate transistor cell has charge trapped in potential wells, formed by the oxide-conductor nanolaminate layers, the floating gate transistor will not turn on and the presence of a stored “zero” is indicated in the cell. In this manner, data stored on a particular floating gate transistor cell can be read.
Programming can be achieved by hot electron injection. In this case, the interconnect lines, coupled to the second source/drain region for the floating gate transistor cells in the first logic plane, are driven with a higher drain voltage like 2 Volts for 0.1 micron technology and the control gate line is addressed by some nominal voltage in the range of twice this value. Erasure is accomplished by driving the control gate line with a large positive voltage and the sourceline and/or backgate or substrate/well address line of the floating gate transistor with a negative bias so the total voltage difference is in the order of 3 Volts causing electrons to tunnel out of the oxide-conductor nanolaminate layers of the driver floating gate transistors. Writing can be performed, as also described above, by normal channel hot electron injection
One of ordinary skill in the art will appreciate upon reading this disclosure that a number of different configurations for the spatial relationship, or orientation of the input lines 1112, interconnect lines 1114, and output lines 1120 are possible.
FIG. 12 is a block diagram of an electrical system, or processor-based system, 1200 utilizing floating gate transistor cells with a gate structure having oxide-conductor nanolaminate layers. By way of example and not by way of limitation, memory 1212 is constructed in accordance with the present invention to have floating gate transistor cells with a gate structure having oxide-conductor nanolaminate layers. The same applies to floating gate transistors in the CPU, etc., the invention is not so limited. The processor-based system 1200 may be a computer system, a process control system or any other system employing a processor and associated memory. The system 1200 includes a central processing unit (CPU) 1202, e.g., a microprocessor, that communicates with the NOR flash memory 1212 and an I/O device 1208 over a bus 1220. It must be noted that the bus 1220 may be a series of buses and bridges commonly used in a processor-based system, but for convenience purposes only, the bus 1220 has been illustrated as a single bus. A second I/O device 1210 is illustrated, but is not necessary to practice the invention. The processor-based system 1200 can also includes read-only memory (ROM) 1214 and may include peripheral devices such as a floppy disk drive 1204 and a compact disk (CD) ROM drive 1206 that also communicates with the CPU 1202 over the bus 1220 as is well known in the art.
It will be appreciated by those skilled in the art that additional circuitry and control signals can be provided, and that the memory device 1200 has been simplified to help focus on the invention. In one embodiment, at least one of the floating gate transistor cells, having a gate structure with oxide-conductor nanolaminate layers in memory 1212 includes a programmed floating gate transistor cell according to the teachings of the present invention.
It will be understood that the embodiment shown in FIG. 12 illustrates an embodiment for electronic system circuitry in which the novel floating gate transistor cells of the present invention are used. The illustration of system 1200, as shown in FIG. 12, is intended to provide a general understanding of one application for the structure and circuitry of the present invention, and is not intended to serve as a complete description of all the elements and features of an electronic system using the novel floating gate transistor cell structures. Further, the invention is equally applicable to any size and type of memory device 1200 using the novel floating gate transistor cells of the present invention and is not intended to be limited to that described above. As one of ordinary skill in the art will understand, such an electronic system can be fabricated in single-package processing units, or even on a single semiconductor chip, in order to reduce the communication time between the processor and the memory device.
Applications containing the novel floating gate transistor cell of the present invention as described in this disclosure include electronic systems for use in memory modules, device drivers, power modules, communication modems, processor modules, and application-specific modules, and may include multilayer, multichip modules. Such circuitry can further be a subcomponent of a variety of electronic systems, such as a clock, a television, a cell phone, a personal computer, an automobile, an industrial control system, an aircraft, and others.
CONCLUSION
This disclosure describes the use of oxide-conductor nanolaminate layers as floating gates to trap charge in potential wells formed by the different electron affinities of the oxide-conductor nanolaminate layers. That is, this disclosure describes a flash memory device, programmable logic array device or memory address and decode correction device with a conductor nanolaminate floating gate rather than a conventional polysilicon floating gate.
It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

## Claims

1. A floating gate transistor, comprising:
a first source/drain region;
a second source/drain region;
a channel region between the first and the second source/drain regions;
a floating gate separated from the channel region by a first oxide layer, wherein the floating gate region includes oxide-conductor nanolaminate layers, wherein the nanolaminate layers include a layer of a metal conductor formed using an atomic layer deposition process;
a control gate separated from the floating gate by a second oxide layer; and
circuitry coupled to the floating gate transistor to program the floating gate in a reverse direction, and to read the floating gate in a forward direction.

2. The floating gate transistor of claim 1, wherein the oxide-conductor nanolaminate layers include Tantalum Nitride (TaN).

3. The floating gate transistor of claim 1, wherein the oxide-conductor nanolaminate layers include Titanium Nitride (TiN).

4. The floating gate transistor of claim 1, wherein the oxide-conductor nanolaminate layers include Tungsten Nitride (WN).

5. The floating gate transistor of claim 1, wherein the oxide-conductor nanolaminate layers include Niobium Nitride (NbN).

6. The floating gate transistor of claim 1, wherein the oxide-conductor nanolaminate layers include Molybdenum Nitride (MoN).

7. The floating gate transistor of claim 1, wherein the oxide-conductor nanolaminate layers include Zinc-Oxide-Silicon (ZnOS).

8. The floating gate transistor of claim 1, wherein the metal conductor includes Tungsten (W).

9. The floating gate transistor of claim 1, wherein the oxide-conductor nanolaminate layers include Nickel (Ni).

10. A floating gate transistor array, comprising:
a number of floating gate transistor cells formed on a substrate, wherein each floating gate transistor cell includes a source region, a drain region, a channel region between the source and the drain regions, and a floating gate separated from the channel region by a first gate oxide, and a control gate separated from the floating gate by a second gate oxide, and wherein the floating gate region includes oxide-conductor nanolaminate layers, wherein the nanolaminate layers include a layer of a metal conductor formed using an atomic layer deposition process;
a number of bit lines coupled to the drain region of each floating gate transistor cell along rows of the floating gate transistor array;
a number of word lines coupled to the control gate of each floating gate transistor cell along columns of the memory array;
a number of sourcelines, wherein the source region of each floating gate transistor cell is coupled to the number of sourcelines along rows of the floating gate transistor cells; and
circuitry coupled to at least one transistor cell to program the transistor cell in a reverse direction, and to read the transistor cell in a forward direction.

11. The floating gate transistor array of claim 10, wherein the oxide-conductor nanolaminate layers include Tantalum Nitride (TaN).

12. The floating gate transistor of claim 10, wherein the oxide-conductor nanolaminate layers include Titanium Nitride (TiN).

13. The floating gate transistor array of claim 10, wherein the oxide-conductor nanolaminate layers include Tungsten Nitride (WN).

14. The floating gate transistor array of claim 10, wherein the oxide-conductor nanolaminate layers include Niobium Nitride (NbN).

15. The floating gate transistor array of claim 10, wherein the oxide-conductor nanolaminate layers include Molybdenum Nitride (MoN).

16. The floating gate transistor array of claim 10, wherein the oxide-conductor nanolaminate layers include Zinc-Oxide-Silicon (ZnOS).

17. The floating gate transistor array of claim 10, wherein the metal conductor includes Tungsten (W).

18. The floating gate transistor array of claim 10, wherein the oxide-conductor nanolaminate layers include Nickel (Ni).

19. A floating gate transistor array, comprising:
a number of floating gate transistor cells formed on a substrate, wherein each floating gate transistor cell includes a source region, a drain region, a channel region between the source and the drain regions, and a floating gate separated from the channel region by a first gate oxide, and a control gate separated from the floating gate by a second gate oxide, and wherein the floating gate region includes oxide-conductor nanolaminate layers with charge trapping in potential wells formed by different electron affinities of the oxide-conductor nanolaminate layers;
a number of bit lines coupled to the drain region of each floating gate transistor cell along rows of the floating gate transistor array;
a number of word lines coupled to the control gate of each floating gate transistor cell along columns of the memory array;
a number of sourcelines, wherein the source region of each floating gate transistor cell is coupled to the number of sourcelines along rows of the floating gate transistor cells; and
wherein at least one of floating gate transistor cells is a programmed floating gate transistor having one of a number of charge levels trapped in the floating gate, wherein the one of a number of charge levels trapped in the floating gate includes a charge of approximately 100 electrons.

20. The floating gate transistor array of claim 19, the number of floating gate transistor cells is configured as active devices with gain to provide amplification of stored charge from 100 to 800,000 electrons over a read address period of 10 nS.

21. The floating gate transistor array of claim 19, wherein the number of floating gate transistor cells extending from a substrate operate as equivalent to a floating gate transistor having a size equal to or less than 2.0 lithographic feature squared (2F2).

22. A programmable logic array, comprising:
a plurality of input lines for receiving an input signal;
a plurality of output lines; and
one or more arrays having a first logic plane and a second logic plane connected between the input lines and the output lines, wherein the first logic plane and the second logic plane comprise a plurality of logic cells arranged in rows and columns for providing a sum-of-products term on the output lines responsive to a received input signal, wherein each logic cell includes a floating gate transistor cell including:
a first source/drain region;
a second source/drain region;
a channel region between the first and the second source/drain regions;
a floating gate separated from the channel region by a first gate oxide, wherein the floating gate region includes oxide-conductor nanolaminate layers, wherein the nanolaminate layers include a layer of a metal conductor formed using an atomic layer deposition process;
a control gate separated from the floating gate by a second gate oxide; and
circuitry coupled to the floating gate transistor cell to program the floating gate in a reverse direction, and to read the floating gate in a forward direction.

23. The programmable logic array of claim 22, wherein the oxide-conductor nanolaminate layers include Tantalum Nitride (TaN).

24. The programmable logic array of claim 22, wherein the oxide-conductor nanolaminate layers include Titanium Nitride (TiN).

25. The programmable logic array of claim 22, wherein the oxide-conductor nanolaminate layers include Tungsten Nitride (WN).

26. The programmable logic array of claim 22, wherein the oxide-conductor nanolaminate layers include Niobium Nitride (NbN).

27. The programmable logic array of claim 22, wherein the oxide-conductor nanolaminate layers include Molybdenum Nitride (MoN).

28. The programmable logic array of claim 22, wherein the oxide-conductor nanolaminate layers include Zinc-Oxide-Silicon (ZnOS).

29. The programmable logic array of claim 22, wherein the metal conductor includes Tungsten (W).

30. The programmable logic array of claim 22, wherein the oxide-conductor nanolaminate layers include Nickel (Ni).