Patent Application
20110233513
The present invention relates to a semiconductor structure and a method of fabricating the same. More particularly, the present invention relates to a semiconductor structure including at least one layer of an interfacial dielectric material located on an upper surface of a carbon-based material. The at least one layer of interfacial dielectric material that is in contact with the upper surface of the carbon-based material has at least the same short-range crystallographic bonding structure as the crystallographic bonding structure of the carbon-based material. The present invention also provides a method of forming such a semiconductor structure as well as electronic devices built upon the semiconductor structure.
Several trends presently exist in the semiconductor and electronics industry including, for example, devices are being fabricated that are smaller, faster and require less power than the previous generations of devices. One reason for these trends is that personal devices such as, for example, cellular phones and personal computing devices, are being fabricated that are smaller and more portable. In addition to being smaller and more portable, personal devices also require increased memory, more computational power and speed. In view of these ongoing trends, there is an increased demand in the industry for smaller and faster transistors used to provide the core functionality of the integrated circuits used in these devices.
Accordingly, in the semiconductor industry there is a continuing trend toward fabricating integrated circuits (ICs) with higher densities. To achieve higher densities, there has been, and continues to be, efforts toward down scaling the dimensions of the devices on semiconductor wafers generally produced from bulk silicon. These trends are pushing the current technology to its limits. In order to accomplish these trends, high densities, smaller feature sizes, smaller separations between features, and more precise feature shapes are required in integrated circuits (ICs).
Significant resources go into down scaling the dimensions of devices and increasing packing densities. For example, significant time may be required to design such down scaled transistors. Moreover, the equipment necessary to produce such devices may be expensive and/or processes related to producing such devices may have to be tightly controlled and/or be operated under specific conditions. Accordingly, there are significant costs associated with exercising quality control over semiconductor fabrication.
In view of the above, the semiconductor industry is pursuing graphene to achieve some of the aforementioned goals. Graphene, which is essentially a flat sheet of carbon atoms, is a promising material for radio frequency (RF) transistors and other electronic transistors. Typical RF transistors are made from silicon or more expensive semiconductors such as, for example, indium phosphide (InP). In graphene, and for the same voltage, electrons travel around 10 times faster than in InP, or 100 times faster than in silicon. Graphene transistors will also consume less power and could turn out to be cheaper than those made from silicon or InP.
Graphene electronic devices operating at 26 gigaHertz have been fabricated and the ultimate graphene device operating performance is expected to be in the tetraHertz range. However, building such graphene devices is generally difficult to achieve. One reason for this difficulty is that the bonding between graphene and other materials, e.g., dielectric materials and/or conductive materials, is difficult due to the graphene changing electronic structure and properties when a bonding interface is created.
In one aspect of the present disclosure, a semiconductor structure is provided that includes at least one layer of an interfacial dielectric material located on an upper surface of a carbon-based material. The at least one layer of interfacial dielectric material has at least the same short-range crystallographic bonding structure as that of the carbon-based material and, as such, the at least one layer of interfacial dielectric material, that is in contact, does not change the electronic structure of the carbon-based material. The term “short-range order” as used throughout the present application denotes that the interfacial dielectric material can be composed of a mixture of partially amorphous and hexagonal bonding phases. In one embodiment, the interfacial dielectric has the same crystallographic bonding structure as that of the carbon-based material. In a further embodiment, the interfacial dielectric and the carbon-based material both have a hexagonal crystallographic bonding structure.
Moreover, the at least one layer of interfacial dielectric material is bonded to the carbon-based material via van der Waals forces. By ‘van der Waals’ forces it meant the process by which molecules are attracted to each other, via electrostatic forces. These intermolecular attractions are weaker than both ionic and covalent bonding. Bonding through the van der Waals forces occurs through dipole interactions. Dipolar molecules are the types of molecules involved in this type of bonding. In dipolar molecules, the electronegativity difference between the covalently bonded atoms exceeds or equals 0.4 but is less than or equal to 2.0. This difference in electronegativity causes the electrons of the molecule to become unequally distributed. The atoms within the molecule that have the higher electronegativity attract the electrons from those with less electronegativity. The atoms with the higher electronegativity acquire a slightly negative charge, denoted by δ−. The atoms with less electronegativity acquire a slightly positive charge, denoted by δ+. These regions of the molecules are magnetically attracted to the oppositely charged regions of other dipolar molecules. In this way, the dipolar molecules are bonded to one another, and it is this bonding that constitutes van der Waals bonding.
The presence of the at least one layer of interfacial dielectric material having at least the same short-range crystallographic bonding structure as that of the carbon-based material improves the interfacial bonding between the carbon-based material and any overlying material layer, including a dielectric material, a conductive material or a combination of a dielectric material and a conductive material. The improved interfacial bonding, in turn, facilitates formation of devices including a carbon-based material as an active element of the device.
In one embodiment of the invention, the carbon-based material is graphene and the interfacial dielectric material is hexagonal boron nitride. Applicants observe that graphene and boron nitride both have a hexagonal crystallographic bonding structure, and that low temperature amorphous boron nitride and/or carbon boron nitride have some of the same short-range hexagonal crystallographic bonding like graphene, and, as such can be employed herein. Moreover, graphene has a similar bonding length (C—C bond length of 1.42 Å) to pure hexagonal boron nitride (B—N bond length of 1.43 Å).
In another aspect of the present disclosure, an electronic device such as, for example, a transistor, including the aforementioned semiconductor structure is provided. In particular, the present invention provides, in one embodiment, an electronic device that includes a carbon-based material, wherein a portion of the carbon-based material defines a device channel. The electronic device further includes at least one layer of an interfacial dielectric material located on an upper surface of the device channel, wherein the at least one layer of interfacial dielectric material has at least the same short-range crystallographic bonding structure as that of the carbon-based material. In one embodiment, the at least one layer of interfacial dielectric material has the same crystallographic bonding structure as that of the carbon-based material. The electronic device still further includes at least one layer of a dielectric material located on an uppermost surface of the at least one layer of interfacial dielectric material, and at least one layer of a conductive material located on an uppermost surface of the at least one layer of dielectric material. The electronic device even further includes at least two regions making electrical contact to portions of the carbon-based material that are adjacent to the device channel.
In still another aspect of the present disclosure, a method of providing the above mentioned semiconductor structure is provided. The method of the present disclosure includes forming at least one layer of an interfacial dielectric material on an upper surface of a carbon-based material, wherein the at least one layer of interfacial dielectric material has at least the same short-range crystallographic bonding structure as that of the carbon-based material. In one embodiment, the at least one layer of interfacial dielectric material has the same crystallographic bonding structure as that of the carbon-based material. The aforementioned method can be integrated into any existing FET process flow.
In the following description, numerous specific details are set forth, such as particular structures, components, materials, dimensions, processing steps and techniques, in order to provide an understanding of some aspects of the present invention. However, it will be appreciated by one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known structures or processing steps have not been described in detail in order to avoid obscuring the invention.
It will be understood that when an element as a layer, region or substrate is referred to as being “on” or “over” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or “directly over” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.
Embodiments of the present invention will now be described in greater detail by referring to the following discussion and drawings that accompany the present application. The drawings of the present application, which are referred to herein below in greater detail, are provided for illustrative purposes and, as such, they are not drawn to scale.
Reference is first made to
The term ‘semiconductor material’ denotes any material that has semiconductor properties. Examples of semiconductor materials that can be located beneath the carbon-based material 12 include, but are not limited to Si, SiGe, SiGeC, SiC, Ge alloys, GaAs, InAs, InP, BN and other III/V or II/VI compound semiconductors. In addition to these listed types of semiconductor materials, the semiconductor material that can be present beneath the carbon-based material 12 can also be a layered semiconductor such as, for example, Si/SiGe, Si/SiC, silicon-on-insulators (SOIs) or silicon germanium-on-insulators (SGOIs), BN and other III/V or II/VI compound semiconductors. In some embodiments of the invention, the semiconductor material beneath the carbon-based material 12 is a Si-containing semiconductor material, i.e., a semiconductor material that includes silicon. The semiconductor material that can be employed beneath the carbon-based material 12 can be single crystalline, polycrystalline, multicrystalline, and/or hydrogenated-amorphous. The semiconductor materials that can be employed beneath the carbon-based material 12 can be undoped, doped or contain doped and undoped regions therein.
The dielectric material that can be located beneath the carbon-based material 12 includes any material having insulator properties. Examples of dielectric materials that can be located beneath the carbon-based material 12 include, but are not limited to glass, SiO2, SiN, plastic, or diamond-like carbon, BN, CxBN or a mixture of amorphous/hexagonal bonding boron nitride and carbon boron nitride.
The conductive material that can be located beneath the carbon-based material 12 includes any material having electrical conductive properties. Examples of such conductive materials include, but are not limited to a metal, or a transparent conductor including, for example, a metal oxide or other conductive forms of carbon.
In one embodiment of the invention, the carbon-based material 12 shown in
The graphene that can be used as the carbon-based material 12 can be formed utilizing techniques that are well known in the art. For example, the graphene that can be employed as the carbon-based material 12 can be formed by mechanical exfoliation of graphite, epitaxial growth on silicon carbide, epitaxial growth on metal substrates, hydrazine reduction in which a graphene oxide paper is placed in a solution of pure hydrazine which reduces the graphene oxide paper into single-layered graphene, and sodium reduction of ethanol, i.e., by the reduction of ethanol by sodium metal, followed by pyrolysis of the ethoxide product and washing to remove sodium salts. Another method of forming graphene can be from carbon nanotubes.
In another embodiment of the present invention, the carbon-based material 12 includes at least one carbon nanotube, which can be single walled or multiwalled. The carbon nanotubes employed in the present invention typically have a folded hexagonal crystallographic bonding structure. Although a single carbon nanotube can be used in the present invention, an array of carbon nanotubes is typically used. When carbon nanotubes are employed in the present invention as carbon-based material 12, the carbon nanotubes can be formed utilizing techniques that are well known to those skilled in the art for forming the same. Examples of suitable techniques that can be used in forming carbon nanotubes include, but are not limited to arc discharge, laser ablation, chemical vapor deposition, and plasma enhanced chemical vapor deposition. Other possible carbon-based materials that can be employed include graphite with a short-range hexagonal and amorphous crystallographic bonding structure and various forms of carbon materials with a slightly distorted hexagonal crystallographic bonding structure, such as, for example, Lonsdaleite or densely packed hexagonal bonding phase fullerene.
Notwithstanding the type of carbon-based material 12 employed in the present invention, the carbon-based material 12 can be orientated parallel to an underlying substrate, or perpendicular to an underlying substrate. A parallel oriented carbon-based material 12 is shown in the drawings of the present application by way of one possible orientation for the carbon-based material 12.
The thickness of the carbon-based material 12 can vary depending on the type of carbon-based material 12 employed as well as the technique that was employed in forming the same. Typically, and in one embodiment of the invention, the carbon-based material 12 has a thickness from 0.2 nm to 10 nm, with a thickness from 0.34 nm to 3.4 nm being more typical. Other thicknesses besides those mentioned can also be employed in the present invention.
Referring now to
The at least one layer of the interfacial dielectric material 16 is a thin layer, whose thickness is typically from 0.2 nm to 10 nm, with a thickness from 0.3 nm to 3 nm being more typical. The at least one layer of the interfacial dielectric material 16 that is formed on the bare upper surface 14 of the carbon-based material 12 has a short-range crystallographic bonding structure, typically hexagonal, that is similar to the crystallographic bonding structure of the carbon-based material 12. Moreover, the at least one layer of the interfacial dielectric material 16 is bonded to the bare upper surface 14 of the carbon-based material 12 by van der Waals forces. By ‘van der Waals’ forces it meant the process by which molecules are attracted to each other, via electrostatic forces. No other type of bonding, such as ionic or covalent, is present at the interface between the carbon-based material 12 and the at least one layer of the interfacial dielectric material 16.
The type of the at least one layer of the interfacial dielectric material 16 that is employed in the present invention is dependent on the crystallographic bonding structure of the underlying carbon-based material 12. For example, when the underlying carbon-based material 12 has a hexagonal bonding crystallographic bonding structure, then the interfacial dielectric material 16 employed in the present invention also has a short-range hexagonal crystallographic bonding structure. Examples of interfacial dielectric materials that have a short-range hexagonal bonding crystallographic bonding structure and thus can be employed in one embodiment of the invention include, but are not limited to hexagonal boron nitride or a mixture of amorphous and hexagonal bonding boron nitride and carbon boron nitride.
Other interfacial dielectric materials that can be used include, but are not limited to SiC, SiBN, SiCBN that have an amorphous phase, with some hexagonal bonding phase mixed therein. These materials have similar crystallographic hexagonal bonding like hexagonal boron nitride.
The above combination of various carbon-based materials and the suitable short-range hexagonal crystallographic bonding can be used in combination to produce working electronic devices.
The at least one layer of the interfacial dielectric material 16 can be formed utilizing conventional deposition processes that are well known to those skilled in the art. For example, the at least one layer of the interfacial dielectric material 16 can be formed by atomic layer deposition (ALD), plasma enhanced atomic layer deposition (PE-ALD), chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), evaporation, molecular beam epitaxy, photo chemical vapor deposition (including laser/UV photo assisted CVD), and spin-on dielectric processes.
In the various processes mentioned above, suitable precursors can be used in forming the at least one layer of the interfacial dielectric material 16. The precursors that can be used may include a single precursor in which at least one of the atoms of the interfacial dielectric material is present, or multiple precursors can be employed in forming the at least one layer of the interfacial dielectric material 16.
In one embodiment of the invention, and when the at least one layer of the interfacial dielectric material 16 is hexagonal boron nitride, ALD or PE-ALD is typically employed in forming the interfacial dielectric material. In this particular embodiment of the invention, the hexagonal boron nitride can be formed from at least one precursor that includes boron and optionally nitrogen. In another embodiment of the invention and when hexagonal boron nitride is employed as the at least one layer of the interfacial dielectric material 16, the hexagonal boron nitride is formed from a first precursor that includes boron and a second precursor that includes nitrogen. In embodiments of the invention in which hexagonal boron nitride is formed, the precursor(s) includes borazine, vinyl borazine, trivinylborazine, trimethyl borazine, trimethyl trivinyl borazine, tris(dimethylamino) borane, B2H6, B10H14 and a boron hydride cluster. In some embodiments, nitrogen or a nitrogen-containing material can be added as a second precursor to form the hexagonal boron nitride material.
It is observed that the presence of the at least one layer of the interfacial dielectric material 16 provides an enhanced bonding interface to the underlying carbon-based material 12 which is not present when the at least one layer of the interfacial dielectric material 16 is not formed on the carbon-based material 12. The enhanced bonding interface that is achieved when the at least one layer of the interfacial dielectric material 16 is present on the carbon-based material 12 increases the bond strength of other material layers to the carbon-based material 12, which is not obtainable when the at least one layer of the interfacial dielectric material 16 is not present on the carbon-based material 12. In some embodiments of the invention, a greater than 100% increase in bonding strength between the carbon-based dielectric material 12 that includes the at least one layer of the interfacial dielectric material 16 and an overlying material layer, i.e., dielectric material and/or conductive material) can be obtained as compared to the same structure that does not include the at least one layer of the interfacial dielectric material 16. In fact, without the presence of the at least one layer of the interfacial dielectric material, most dielectrics and/or metals will not be able to adhere or bond with graphene.
Referring now to
Examples of dielectric materials that can be employed as the at least one other material layer 18 include any insulating material such as for example, an oxide, a nitride, an oxynitride or a multilayered stack thereof. In one embodiment of the invention, the dielectric material that can be employed as the at least one other material layer 18 includes a semiconductor oxide, a semiconductor nitride or a semiconductor oxynitride. In another embodiment of the invention, the dielectric material that can be employed as the at least one other material layer 18 includes a dielectric metal oxide or mixed metal oxide having a dielectric constant that is greater than the dielectric constant of silicon oxide, e.g., 3.9. Typically, the dielectric material that can be employed as the at least one other material layer 18 has a dielectric constant greater than 4.0, with a dielectric constant of greater than 8.0 being more typical. Such dielectric materials are referred to herein as a high k dielectric. Exemplary high k dielectrics include, but are not limited to HfO2, ZrO2, La2O3, Al2O3, TiO2, SrTiO3, LaAlO3, Y2O3, HfOxNy, ZrOxNy, La2OxNy, Al2OxNy, TiOxNy, SrTiOxNy, LaAlOxNy, Y2OxNy, SiON, SiNx, a silicate thereof, and an alloy thereof. Multilayered stacks of these high k materials can also be employed as the at least one other material layer 18. Each value of x is independently from 0.5 to 3 and each value of y is independently from 0 to 2.
The thickness of the dielectric material that can be employed as the at least one other material layer 18 may vary depending on the technique used to form the same. Typically, the dielectric material that can be employed as the at least one other material layer 18 has a thickness from 1 nm to 10 nm, with a thickness from 2 nm to 5 nm being more typical. When a high k dielectric is employed as the dielectric material, the high k dielectric can have an effective oxide thickness on the order of, or less than, 1 nm.
The dielectric material that can be employed as the at least one other material layer 18 can be formed by methods well known in the art. In one embodiment of the invention, the dielectric material that can be employed as the at least one other material layer 18 can be formed by a deposition process such as, for example, chemical vapor deposition (CVD), thermal or plasma enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD), molecular beam deposition (MBD), pulsed laser deposition (PLD), liquid source misted chemical deposition (LSMCD), and atomic layer deposition (ALD). Alternatively, the dielectric material employed as layer 18 can be formed by a thermal process such as, for example, thermal oxidation and/or thermal nitridation.
In the embodiments in which the at least one other material layer 18 includes a conductive material, the conductive material can include any conductive material including, but not limited to polycrystalline silicon, polycrystalline silicon germanium, an elemental metal, (e.g., tungsten, titanium, tantalum, aluminum, nickel, ruthenium, palladium and platinum), an alloy of at least one elemental metal, an elemental metal nitride (e.g., tungsten nitride, aluminum nitride, and titanium nitride), an elemental metal silicide (e.g., tungsten silicide, nickel silicide, and titanium silicide) and multilayered combinations thereof. In one embodiment, the conductive material that can be employed as layer 18 can be comprised of an nFET metal gate. In another embodiment, the conductive material that can be employed as layer 18 can be comprised of a pFET metal gate. In a further embodiment, the conductive material that can be employed as layer 18 can be comprised of polycrystalline silicon. The polysilicon conductive material can be used alone, or in conjunction with another conductive material such as, for example, a metal conductive material and/or a metal silicide material.
The conductive material that is employed as layer 18 can be formed utilizing a conventional deposition process including, for example, chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), evaporation, physical vapor deposition (PVD), sputtering, chemical solution deposition, atomic layer deposition (ALD) and other like deposition processes. When Si-containing materials are used as the conductive material, the Si-containing materials can be doped within an appropriate impurity by utilizing either an in-situ doping deposition process or by utilizing deposition, followed by a step such as ion implantation or gas phase doping in which the appropriate impurity is introduced into the Si-containing material. When a metal silicide is formed, a conventional silicidation process is employed.
The as-deposited conductive material typically has a thickness from 1 nm to 100 mm, with a thickness from 3 nm to 30 nm being even more typical.
Referring now to
In particular,
The electronic device 30 shown in
Referring now to
The electronic device 50 shown in
While the present invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in forms and details may be made without departing from the spirit and scope of the present invention. It is therefore intended that the present invention not be limited to the exact forms and details described and illustrated, but fall within the scope of the appended claims.
