Patent Application
20070228523
1. Technical Field
The invention relates to nano-scale devices and the fabrication of nano-scale devices. In particular, the invention relates to reducing a size, spacing and/or pitch dimension of features in a nano-scale device or structure.
2. Description of Related Art
A consistent trend in semiconductor technology since its inception is toward smaller and smaller device dimensions and higher and higher device densities. As a result, an area of semiconductor technology that recently has seen explosive growth and generated considerable interest is nanotechnology. Nanotechnology is concerned with the fabrication and application of so-called nano-scale structures, structures having dimensions that are often 50 to 100 times smaller than conventional semiconductor structures. Nano-imprinting lithography is a technique used to fabricate nano-scale structures.
Nano-imprinting lithography uses a mold to imprint nano-scale structures on a substrate using a top-down scaling technique. A mold typically contains a plurality of protruding and/or recessed regions or ‘features’ having some nano-scale dimensions. Typically, the features of the mold are imprinted on a substrate coated with a viscous polymer precursor. Thus, the features on the mold are complementary to the desired device features (e.g., nanowires). The dimensions achieved for the features on the mold, such as nanowire width and pitch, ultimately affect the dimensions achieved for the desired device features. A mold can be fabricated using electron beam (e-beam) lithography or x-ray lithography to define a pattern and a dry etching process, typically reactive ion etching (RIE), to create features from the pattern in the mold in the nano-scale and/or micro-scale range(s). Various lithography steps are repeated in a serial manner in an attempt to achieve smaller dimensions. The current e-beam or x-ray lithographies are limited in yielding molds with a nanowire width less than about 15 nm and a nanowire pitch less than about 30 nm. In addition, the e-beam and x-ray lithographic processes are very slow processes rendering such serial repetition of steps undesirable for achieving smaller dimensions. Moreover, significant improvements in the conventional e-beam and x-ray lithographic steps are necessary to achieve a feature pitch dimension less than about 30 nm and/or a feature width or a feature spacing of less than about 15 nm. Such improvements are not cost effective since an inherent limitation in these lithographic processes restricts achieving features sizes smaller than about 15 nm. It has been reported that feature sizes of approximately 10 nm are achievable with these conventional processes. However, usually there is a trade-off between the line-width and the line-spacing (i.e., pitch) and feature quality. Thus, these dimensions are estimates of the limits on the feature size and spacing achievable conventionally.
Accordingly, it would be desirable to fabricate nano-scale devices or structures with greater nano-scale feature density at potentially lower cost than conventionally fabricated with e-beam or x-ray lithography and RIE. Such fabricated nano-scale devices would solve a long-standing need in the developing area of a “top-down” fabrication approach in nanotechnology.
In some embodiments of the present invention, a method of reducing feature dimensions of a nano-scale device is provided. The method of reducing comprises consuming a surface of a device substrate. The device has a pattern of spaced apart first nanowires on the substrate surface. The consumption reduces a dimension of the first nanowires. The method of reducing further comprises forming a second nanowire in a trench between adjacent ones of the first nariowires. As a result of forming, the device comprises a set of features that includes the first nanowires with the reduced dimension and the second nanowire spaced from the adjacent first nanowires by sub-trenches.
In other embodiments of the present invention, a method of fabricating a nano-scale device with reduced feature dimensions is provided. The method of fabricating comprises forming a plurality of spaced apart first nanowire features on a substrate. The first features are spaced apart from one another by first gaps. The method of fabricating further comprises consuming the surface of the substrate, such that the consumed surface reduces a dimension of the first features. The method of fabricating further comprises forming a second nanowire feature in a first gap between adjacent first features. As such, the device has a set of features that comprises the reduced-dimension first features and the second feature separated from the first features by second gaps that are narrower than the first gaps.
In other embodiments of the present invention, a nano-scale device with reduced feature dimensions is provided. The nano-scale device comprises first nanowires formed on a substrate. The first nanowires are spaced apart on the substrate. The nano-scale device further comprises a second nanowire added on the substrate in a gap between adjacent ones of the first nanowires. The second nanowire and the first nanowires have a similar material characteristic. The added second nanowire effectively decreases a core width of the first nanowires.
Certain embodiments of the present invention have other features in addition to and in lieu of the features described hereinabove. These and other features of some embodiments of the invention are detailed below with reference to the following drawings.
The various features of embodiments of the present invention may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, where like reference numerals designate like structural elements, and in which:
Embodiments of the present invention are directed to fabrication of nano-scale devices or structures and nano-scale devices thus fabricated. In some embodiments, the device fabrication and the device thus fabricated are used in imprint lithography. In some embodiments, the device fabrication and the device thus fabricated are used in one or more of photonic, electronic, sensing, nanofluidic and catalysis applications, for example. In each embodiment, the fabrication and the fabricated device includes consumption of a substrate surface to form a sacrificial sheath or shell on the substrate that is later removed. When the sheath is removed, a core dimension of the substrate is reduced that translates to a reduced dimension of a feature defined on the substrate surface. As such, smaller and/or closer spaced nano-scale features can be achieved on the substrate than features achieved without the consumption. In particular, one or more of size, spacing and/or pitch of the features are reduced and a number of the features is increased as a result of the various embodiments of the present invention. Moreover, a number of the features is increased as a result of various embodiments of the present invention.
While described below with respect to imprint lithography applications, it is intended that the various embodiments of the present invention include device fabrication for devices used in other applications than imprint lithography, such as for the above-mentioned exemplary photonic, electronic, sensing, nanofluidic and catalysis device applications. Therefore, the scope of the embodiments described herein is not intended to be limited to imprinting molds and imprint lithography applications. For example, references to ‘mold substrate’ and ‘surface’ of an imprinting mold extend equally to a device substrate, a substrate or wafer, and a surface of a substrate or wafer.
In some embodiments of the present invention, a method of reducing feature dimensions of a nano-scale structure or device is provided. The method of reducing feature dimensions is described below with respect to an imprinting mold as the nano-scale device by way of example and not limitation herein. According to the method of the present invention, an amount of a surface of the imprinting mold is consumed. The mold has imprintable nanowire features formed on the surface. The consumed mold surface results in the formation of ‘core-shell’ or ‘core-sheath’ structured features until the sheath is removed. The sheath is made up of a sacrificial material used to consume the surface. The remaining core of the mold underneath the sheath includes the imprintable nanowires. Since the sheath requires consumption of the mold surface, a core dimension of the imprintable nanowires on the surface gets reduced.
In some embodiments, the method is applied to a preexisting imprinting mold that has one or both of nano-scale and micro-scale imprintable features already defined therein. In other embodiments, such imprintable features are fabricated on a substrate using known techniques including, but not limited to one or more of e-beam and/or x-ray lithography and dry etching, such as reactive ion etching (RIE) and/or anisotropic wet chemical etching. Then, the method of reducing is applied to the fabricated features according to the present invention. As such, in some embodiments of the present invention, a method of fabricating a nano-imprinting mold with reduced feature dimensions is provided.
Hereinafter, a ‘preexisting’ mold refers to an imprinting mold having a pattern of one or both of nano-scale and micro-scale imprintable features defined therein using conventional or known techniques for forming features on a mold or a substrate or wafer, such as one or more of e-beam lithography, x-ray lithography and anisotropic etching (e.g., RIE), or using techniques that become available to the skilled artisan for such feature formation. The preexisting imprinting mold also may be considered an off-the-shelf (OTS) imprinting mold. Moreover, an ‘imprintable feature’ includes a feature of the mold pattern that ultimately defines an imprinted structure after an imprinting process (i.e., using imprint lithography). As such, a nano-scale feature of the mold pattern is also referred to herein as a nanowire feature or a pair of nanowires or adjacent nanowires spaced apart or separated by a trench or gap, for example, and may include within its scope a corresponding feature that is micro-scale unless otherwise indicated.
For the purposes of the embodiments of the present invention, a ‘feature dimension’ of a feature on an imprinting mold includes one or more of a height dimension, a width dimension, a spacing dimension between adjacent features and a pitch dimension that is (are) reduced. For example, assume that a typical ‘nano-scale’ pitch dimension of adjacent features is as small as about 30 nm, for example and without limitation herein, using the conventional patterning and fabrication techniques mentioned above. In this example, a nanowire feature may be about 15 nm wide and spaced from an adjacent nanowire feature by about 15 nm or some other combination that sums to the pitch dimension of approximate 30 nm (i.e., the pitch equals the feature width plus the space between the adjacent features). According to the embodiments of the present invention, the preexisting pitch dimension is decreased or reduced about in half, for example, to at least about 15 nm, as is further described below. Moreover, various embodiments of the present invention further reduce the reduced pitch dimension incrementally, such as in half, etc., depending on how many times the methods of the present invention are repeated.
In some embodiments, the mold material is silicon (Si) and consuming 110 a surface comprises growing a thermal oxide on the surface of the silicon mold. The thermal oxide encroaches into the silicon mold material to consume some of the silicon as silicon dioxide (SiO2) to form a SiO2 shell on the silicon core. Germanium (Ge) is another example of a semiconductor mold material that may be used according to various embodiments.
In other embodiments, the mold material is a metal. In these embodiments, consuming 110 a surface of the mold to form a shell on the metal core comprises growing and/or depositing a consumption material on the surface of the metal mold such that an amount of the surface is consumed. The consumption material encroaches into the metal mold surface to consume the metal as a respective shell of the metal. For example, a silicon layer is deposited on a titanium mold and annealed to thus consume 110 some of the titanium to grow and form a titanium silicide (TiSi2) shell for the purposes of these embodiments. In another example, TiSi2 can be deposited on the titanium mold using CVD, for example. The chemical vapor deposited TiSi2 consumes 110 some of the underlying titanium of the mold to grow and form a TiSi2 shell or sheath also for the purposes of these embodiments. Regardless of the embodiment, the consumption layer or sacrificial shell effectively reduces a dimension of the mold core, as further described herein. Herein, ‘grown and/or deposited’ and ‘growing and/or depositing’, and their counterparts, such as ‘growing’ or ‘depositing’, may be referred to herein generally as ‘formed’ and ‘forming’, respectively, for simplicity purposes and without limitation.
As mentioned above, the preexisting mold has a feature defined therein in the typical nano-scale feature size range defined above as achievable with e-beam and/or x-ray lithography and RIE, for example. For simplicity of discussion only, the preexisting mold will be described as having a pair of adjacent nanowire features separated by a trench formed on or in (i.e., of) a mold core or mold substrate of the mold, for example. These features of the preexisting mold may be referred to herein as ‘mold core’ features, which will be better understood with reference to ‘added’ features described below. It should be understood that the preexisting mold may have more than a pair of nanowires, including a plurality of spaced apart nanowires, wherein a nanowire is separated from adjacent nanowires by a trench, space or a gap, and still be within the scope of the various embodiments of the present invention. Moreover, in some embodiments, a preexisting imprinting mold may be considered a mold having both first nanowires, formed previously, and added second nanowires between adjacent first nanowires that were added by the method of the present invention. In these embodiments, both the first nanowires and the second nanowires will have a feature dimension reduced by repeating the method of the present invention.
The method 100 of reducing further comprises forming 120 another or an additional nanowire feature in the trench between the nanowire pair, such that the mold comprises a set of features that includes the nanowire pair and the additional nanowire spaced from the nanowire pair by sub-trenches.
Hereinafter, the method 100 of reducing feature dimensions will be described with reference to the silicon mold embodiment for simplicity of discussion only and not by way of limitation. It should be understood that the steps of the method 100 according to this embodiment are similarly applicable to other mold material embodiments, wherein terms used below related to ‘oxidation’, ‘oxidizing’ and ‘oxide’ are essentially interchangeable with corresponding terms related to other consumption means and materials, such as the silicide, nitride, carbide and sulfide shells, for example, as will be evident to those skilled in the art. All such consumption materials and methods and effectively interchangeable terms are within the scope of the various embodiments of the present invention.
Referring to
In some embodiments, the surface of the mold core 202 is thermally oxidized 112 using known techniques. For example, a mold 200 made from a silicon wafer is thermally oxidized 112 by growing or forming a silicon dioxide layer 212 on (and in) the surface of the silicon mold 200 using heat and, in some embodiments, the introduction of oxygen in a controlled atmosphere. The embedded silicon dioxide reduces the size of the silicon core 202 of the mold 200.
Consuming 110 further comprises depositing 114 an oxide layer 214 (or a second material layer 214) on the thermal oxide layer 212 to a thickness Ox2. In some embodiments, the oxide layer 214 is deposited 114 on the thermal oxide layer 212 using plasma enhanced chemical vapor deposition (PECVD), for example, of silicon dioxide at about 400° C.
Referring to
The oxide layers 212, 214 are selectively removed 122 from the trench bottom 222 using known techniques including, but not limited to, reactive ion etching (RIE), which provides directional or anisotropic selective etching of the oxides and not the mold core 202. For example, when the mold 200 is a silicon wafer and the oxide layers 212, 214 are silicon dioxide layers, RIE will directionally etch the silicon dioxide in a horizontal plane along the trench bottom 222 much more than it will etch the silicon dioxide in a vertical plane of the trench. Other dry or wet etching techniques known in the art to provide selective anisotropic etching of the oxide layers may be used instead of or in addition to RIE, according to the method 100.
Forming 120 further comprises adding 124 a material 224 to the etched trench bottom 222 that also fills the trench, which will ultimately become an added nanowire 224. Referring to
The added material 224 is selected from materials that integrate with the mold core material during adding 124 to provide similar material and/or mechanical characteristics to the mold core material and includes using a material the same as the mold core 202. Such added material 224 is distinguished from a conventional method of adding a metal to a semiconductor mold core to form metal nanowires alternating with semiconductor nanowires, since the metal nanowires and semiconductor nanowires have different material and/or mechanical characteristics.
For example, when the mold core material is silicon, the added material 224 may be epitaxial-grown silicon with well-defined crystallographic boundaries according to some embodiments of the present invention. In this example, the epitaxial or single crystalline silicon may be grown in a chemical vapor deposition reactor to at least fill the trench. Alternatively, an amorphous silicon material 224 may be deposited or added 124 to the trench using PECVD, e-beam evaporation or sputtering, for example. In another example, when the mold core material is a metal, such as titanium, the added nanowire material 224 may be a metal material with similar characteristics to the metal core, such as using added titanium to a titanium mold core. Ti can be deposited by one or more of evaporation, sputtering, and CVD.
In still another example, when the metal core is titanium, the added material 224 may be deposited TiSi2, for example. The added TiSi2 224 is deposited such that it does not necessarily consume the surface on which it is deposited relative to the exemplary TiSi2 sacrificial sheath that is grown and/or deposited to consume 110 the Ti surface, as described above. Moreover, contact between the added TiSi2 224 and the Ti surface is restricted to the exposed Ti core in the etched trench. Regardless of the material of the core and of the added nanowire, a flexibility exists according to the embodiments of the method 100 such that the sacrificial sheath or consumption layer is grown on the surface using the mold core material in its formation, while the added material 224 is deposited on the etched surface to form the added nanowire that is integral with the mold core.
With respect to the above example using TiSi2 as the added material 224, the nano-scale structure that results from the method 100 is a nano-scale device (or nano-device) instead of a nano-imprinting mold. This nano-device has nano-scale features including both Ti core nanowires and TiSi2 nanowires. This nano-device is useful for sensing, for example, in which selectivity is desired. For example, a species being sensed by this nano-sensor may have different binding characteristics to the different nanowire materials.
In some embodiments of adding 124, the material 224 is added 124 to completely fill the trench and cover exposed surfaces of the oxide layer 214 on the mold 200, as illustrated by way of example in
Referring again to
According to the various embodiments of the method 100, forming 120 an additional nanowire using the removal processes described above ensures essentially vertical sidewalls and planar surfaces of the resultant nano-scale features, which are desirable for the nano-imprinting mold 200′ or other nano-scale device 200′. For example, removing 122, 126 the oxide layers use directional etching to ensure the essentially vertical nanowire sidewalls and essentially planar sub-trench bottoms. Moreover, those embodiments that also use a planarization technique ensure essentially planar horizontal nanowire end or apex surfaces.
The method 100 of reducing feature dimensions further reduces the width N1w of each preexisting nanowire of the mold core 202 by two times the thickness OX1d of the embedded portion of the thermal oxide layer 212 to a reduced width N1rw (i.e., N1w=N1w−2Ox1d) of the mold core 202′. The added nanowire has a width N2w equal to a width Tw of the preexisting trench of mold core 202 before consumption 110 that is reduced by the thickness Ox2 of the second oxide layer 214 and a thickness (Ox1−Ox1d) of a non-embedded portion of the thermal oxide layer 212 times two (i.e., N2w=Tw−2(Ox2+(Ox1−Ox1d)) of the nano-imprinting mold 200′. The method 100 of reducing feature dimensions further reduces a pitch P of the preexisting nanowires, defined as the width N1w of a preexisting nanowire and the width Tw of the preexisting trench between adjacent preexisting nanowires, to a reduced pitch Pr equal to the reduced nanowire width N1w plus the sub-trench width Sw (i.e., Pr=N1w+Sw) of the nano-imprinting mold 200′.
In effect, the method 100 of reducing feature dimensions decreases one or more of a core width, a core height and a core depth at least of a first imprintable feature (i.e., one or both of a nanowire and a trench). For example, a core width N1w dimension of each preexisting nanowire is reduced in proportion to a depth OX1d that the thermal oxide encroaches into the mold core 202. Further, repeating the method 100 on the nano-imprinting mold 200′ will further add additional nanowires and decrease the width dimension of each existing nanowire (i.e., the reduced core width N1rw of the preexisting nanowires and the width N2w of the added nanowire), proportionally as described above. As a result, the collective nanowires have one or both of a closer spacing, in part due to the additional nanowires between adjacent nanowires, and a smaller pitch, in part due to the reduced nanowire width from the consumption 110 (i.e., one or both of N1rw and N2rw). The closer spacing and smaller pitch is relative to the preexisting imprinting mold 200 before the method 100 is used to reduce feature dimensions, and further relative to before the method 100 is repeated on the nano-imprinting mold 200′.
As an example, a preexisting silicon imprinting mold has initial nanowires formed in the mold core with an initial nanowire core width N1w about 40 nm, an initial nanowire height N1h about 100 nm, and an initial nanowire spacing (trench width) Tw about 80 nm. The initial pitch P is 120 nm. A thermal oxide layer 212 with a thickness Ox1 of about 10.9 nm reduces the silicon nanowire core width N1w to N1rw equal to about 30 nm and the trench width Trw to about 68.2 nm. In this example, it is assumed that about 46% of the thermal oxide thickness Ox1 will embed into the mold core during thermal oxidation. As such, the embedded thickness Ox1d equals about 5 nm so that the reduced nanowire core width N1rw equals N1w−2 OX1d or (˜40−2(˜5))=about 30 nm, and the trench width Tw is reduced by Tw−2(Ox1−OX1d) or (˜80−2(˜10.9−˜5))=about 68.2 nm.
However, assume for this example that one desires a 30 nm trench width Trw, then another oxide layer 214 is deposited (e.g., PECVD oxide) over the thermal oxide layer 212 that has a thickness Ox2 about 19.1 nm. The oxidized trench bottom is then exposed down to the mold core using RIE, for example, of the oxide layers to expose about a 30 nm wide mold core surface of the trench bottom in the oxidized trench. In other words, the exposed mold core width in the trench bottom equals Tw−2((Ox1−OX1d)+Ox2) or ˜80−2((˜10.9−˜5)+˜19.1)=about 30 nm. A silicon nanowire material is added to exposed mold core surface of the trench bottom to a thickness of about 130 nm, such as by epitaxial silicon deposition in a CVD reactor, for example. A horizontal surface of the mold is polished using CMP, for example, to a depth of about 50 nm followed by removing the remaining oxide materials, such as with wet chemical etching, for example.
In this example, a mold pattern with reduced feature dimensions according to various embodiments of the present invention results. The mold pattern includes nanowires with a width N1rw, N2w of about 30 nm, a height N1rh, N2h of about 80 nm (i.e., ˜130 nm−˜50 nm), a spacing or sub-trench width Sw of about 30 nm (i.e., Ox1+Ox2=˜10.9+˜19.1), and a resultant pitch Pr of about 60 nm (i.e., N1rw+Sw or N2w+Sw) or about one half of the initial pitch P of about 120 nm. Then the method 100 can be repeated on the resultant mold until a desired or target nanowire width and pitch are achieved. In other words, each time the method 100 is sequentially performed on a previous resultant mold, the number of nanowires increases. Further, the nanowire width and pitch dimensions will be reduced in a current resultant mold to approximately half of those dimensions of the previous resultant mold.
In some embodiments of the method 100, the method 100 further comprises providing the preexisting imprinting mold before consumption 110 and formation 120. The preexisting imprinting mold may be provided using an off-the-shelf imprinting mold in some embodiments. Alternatively, the imprinting mold may be fabricated using techniques mentioned above including, but not limited to, e-beam lithography, x-ray lithography and an anisotropic etching, such as a dry etching technique including, but not limited to, RIE or plasma etching in some embodiments to form features in a mold substrate. In these alternative embodiments, the method 100 of reducing feature dimensions is a method of fabricating a nano-scale device or structure with reduced feature dimensions according to the present invention. The method of fabricating is described herein with respect to fabricating a nano-imprinting mold by way of example and is intended to include within its scope the fabrication of other nano-scale devices, as mentioned above.
The method of fabricating comprises forming imprintable features separated by trenches on a mold substrate.
Referring to
The nano-imprinting mold 300 further comprises a second nanowire 324 added to the mold substrate 302 in at least one of the trenches 306 between adjacent first nanowires 304. The second nanowire 324 is added such that it is spaced from each of the adjacent first nanowires 304 by sub-trenches 326 which are narrower than the trenches 306. The second nanowire 324 differs from the first nanowires 304 in that the second nanowire 324 is not shaped or formed in and of the mold core 302a. Instead, the second nanowire 324 is made of a material added to or deposited on the mold substrate 302 (i.e., the surface of the trench bottom). The second nanowire 324 is added onto the mold substrate 302 by a material deposition process using techniques that are known in the art, including but not limited to, CVD, plasma enhanced CVD (or PECVD), molecular beam epitaxy (MBE), metal-organic CVD (MOCVD), sputtering and evaporation. For example, the material of the second nanowire 324 may be added silicon, such as epitaxial-grown silicon, when the mold substrate 302 is a silicon wafer having a silicon mold core 302a.
The second nanowire 324 added in the trench 306 between adjacent first nanowires 304 effectively decreases a feature dimension, such as a spacing Tw between the first nanowires 304 to a spacing between adjacent nanowires 304, 324 of the nano-imprinting apparatus 300 equal to the width Sw of the sub-trench 326. The decrease in the spacing Tw dimension is proportional to a width of the second nanowire 324 in the trench 306.
In some embodiments of the nano-imprinting mold 300, a core width dimension N1w of the first nanowires 304 is also decreased by and when the second nanowire 324 is added in the trench 306. In such embodiments, the added second nanowire 324 further effectively decreases a pitch P of the first nanowires 304 to a pitch Pr of the collective adjacent nanowires 304, 324 of the nano-imprinting mold 300. In some embodiments, the decrease in the core width of the first nanowires 304 and the decrease in the pitch are a result of the consumption of the mold core and etching of the consumed mold core to form the second nanowire 324, such as the consumption 110 and the removal 122, 126 described above for the method 100 of reducing feature dimensions.
In some embodiments, the nano-imprinting mold 300 comprises the first nanowires 304, as described above, and means for reducing a dimension of the first nanowires. In these embodiments, the means for reducing a dimension is the second nanowire 324 that effectively decreased one or more of a width dimension of the first nanowires 304, a spacing dimension between adjacent nanowires 304, 324 and a pitch dimension between adjacent nanowires 304, 324.
In some embodiments not illustrated, the nano-imprinting mold 300 may further comprise an additional nanowire in a sub-trench 326 between a first nanowire 304 and a second nanowire 324 illustrated in
An example of nano-structure fabrication by imprint lithography using the nano-imprinting mold 300 of the present invention is described with reference to
As illustrated in
In some embodiments, the nano-scale device 200′, 300 illustrated in
Thus, there have been described various embodiments of a nano-imprinting mold with reduced feature dimensions, a method of reducing feature dimensions on an imprinting mold, and a method of fabricating a nano-imprinting mold with reduced feature dimensions. More generally, there have been described various embodiments of a nano-scale device with closely spaced features and a method of fabrication thereof that includes reducing a feature dimension of the device. It should be understood that the above-described embodiments are merely illustrative of some of the many specific embodiments that represent the principles of the present invention. Clearly, those skilled in the art can readily devise numerous other arrangements without departing from the scope of the present invention as defined by the following claims.
The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Contract No. MDA972-01-3-0005 awarded by the Defense Advanced Research Projects Agency.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10943559 | Sep 2004 | US |
| Child | 11710314 | Feb 2007 | US |
