METHOD FOR MANUFACTURING SEMICONDUCTOR DEVICES

Abstract

Method for manufacturing a semiconductor device, comprising the method: Forming a stack of nanotubes (211), wherein individual nanotubes (101) are aligned with adjacent nanotubes (101); Deposition of a load-bearing layer (401) over the stack of nanotubes (211); Removing the supporting layer (401), wherein the removal of the supporting layer (401) further removes at least one layer of nanotubes (101) from the stack of nanotubes (211); Deposition of a gate electrode (703) over a remaining section of the stack of nanotubes (211); and after removing the supporting layer (401), removing a spacer material (129) around at least one nanotube (101) within the remaining section of the stack of nanotubes (211).

Description

BACKGROUND

[0001] Semiconductor devices are used in a wide variety of electronic applications, such as personal computers, mobile phones, digital cameras, and other electronic equipment. Semiconductor devices are typically fabricated by the sequential deposition of insulating or dielectric layers, conductive layers, and semiconductor layers of material over a semiconductor substrate, and by structuring the various material layers using lithography to create circuit components and elements.

[0002] The semiconductor industry continuously improves the integration density of various electronic components (e.g., transistors, diodes, resistors, capacitors, etc.) by constantly reducing the minimum element size, thus enabling more components to be integrated into a given area. As element size continues to shrink in the semiconductor manufacturing process, further challenges arise that need to be addressed.

[0003] Prior art relating to the subject matter of the invention can be found, for example, in US 2020 / 0 075 875 A1 and US 2018 / 0 366 666 A1.

[0004] The invention is defined by the main claim and the dependent claims. Further embodiments of the invention are described by the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Aspects of this disclosure are best understood with reference to the following detailed description in conjunction with the accompanying drawings. It should be noted that, in accordance with industry practice, various features are not shown to scale. In fact, the dimensions of the various features may have been arbitrarily enlarged or reduced for the sake of clarity. Fig. Figures 1A to 1B illustrate the filtering of a carbon nanotube solution according to some embodiments. Fig. Figures 2A to 2B illustrate the placement of a stack of nanotubes on a substrate according to some embodiments. Fig. Figures 3A to 3B illustrate a first thinning of the stack of nanotubes according to some embodiments. Fig. Figures 4A to 4B illustrate the deposition of a load-bearing layer according to some embodiments. Fig. Figures 5A to 5B illustrate a second thinning of the stack of nanotubes according to some embodiments. Fig. Figures 6A to 6B illustrate the removal of spacers around the nanotubes according to some embodiments. Fig. Figures 7A to 7D illustrate the formation of a transistor according to some embodiments. DETAILED DESCRIPTION

[0006] The following disclosure provides many different embodiments or examples of the implementation of various features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. For example, the formation of a first element or a second element in the following description may include embodiments in which the first and second elements are formed in direct contact, and it may also include embodiments in which further elements can be formed between the first and second elements, so that the first and second elements do not have to be in direct contact. Furthermore, this disclosure may repeat reference numbers and / or letters of the various examples. This repetition is for the sake of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and / or configurations described.

[0007] Furthermore, spatially relative terms such as "below," "underneath," "lower," "above," "upper," and the like may be used herein for a simpler description of the relationship of one element or feature to one or more other elements or features, as illustrated in the figures. These spatially relative terms are intended to encompass various orientations of the device in use or operation, in addition to the orientation shown in the figures. The device may be oriented differently (rotated by 90 degrees or in another orientation), and the spatially relative terms used herein may be interpreted accordingly.

[0008] Embodiments are now described with respect to certain configurations that utilize a vacuum and filtering system to deposit and align a stack of carbon nanotubes. Once the stack of carbon nanotubes is formed, a controlled reduction process can be used to fabricate one or more layers of carbon nanotubes, which are then used to form semiconductor devices. However, the embodiments presented herein are intended to be illustrative, as the concepts can be applied in a wide variety of configurations, such as various front-end-of-line (FEOL) and back-end-of-line (BEOL) processes.

[0009] Now, with reference to Fig. 1A to 1B illustrate a system 100 to carbon nanotubes 101 (in Fig. 1A not shown, but below with reference to Fig. (Figure 1B illustrated and described) to deposit and align. In one embodiment, the system 100 comprises a vacuum chamber 103 connected to a filter 105 by a connecting tube 107. In another embodiment, the vacuum chamber 103 may be a chamber with a first inlet 109 and a first outlet 111. In another embodiment, the vacuum chamber 103 may be sized and shaped to enhance its ability to help carbon nanotubes 101 deposit and align within the system 100. In some embodiments, the vacuum chamber 103 may be shaped like an Erlenmeyer flask, although any suitable shape, such as a cylindrical shape, a hollow rectangular tube, an octagonal shape, or the like, may also be used. Furthermore, the vacuum chamber 103 may be enclosed by a housing 113 made of a material inert to the various process materials.Thus, while the housing 113 can be any suitable material capable of withstanding the chemicals and pressures involved in the filtration process, in one embodiment the housing 113 can be glass, steel, stainless steel, nickel, aluminum, alloys thereof, combinations thereof, and the like. However, any suitable material can be used for the housing 113 of the vacuum chamber 103.

[0010] A vacuum pump 115 can be connected to the first outlet 111. In one embodiment, the vacuum pump 115 is used to help generate the desired vacuum within the vacuum chamber 103, the pressure differential of which can then be used to help filter the carbon nanotubes 101 from a solution and deposit the carbon nanotubes 101 onto the filter 105 by reducing and controlling the pressure within the vacuum chamber 103. Any suitable method for reducing the pressure in the vacuum chamber 103 can be used.

[0011] The connecting pipe 107 extends through a seal and into the first inlet 109 of the vacuum chamber 103, connecting the vacuum chamber 103 to the filter 105. In one embodiment, the connecting pipe 107 serves to connect the vacuum chamber 103 to the filter 105, allowing the application of the pressure differential between the vacuum chamber 103 and one side of the filter 105. In one embodiment, the connecting pipe 107 can be any suitable material capable of withstanding the pressures and chemicals involved, and in some embodiments, it can be a material such as glass, steel, stainless steel, nickel, aluminum, alloys thereof, combinations thereof, and the like. However, any suitable material can be used.

[0012] Now illustrated with reference to filter 105 Fig. 1A an external view of filter 105 and the location of filter 105 within system 100, while Fig. Figure 1B illustrates an internal view of filter 105. As shown in Fig. Figure 1B illustrates that in some embodiments the filter 105 comprises a filter membrane 117 (in Fig. 1A not shown, but in Fig. (1B) is shown, which is used to filter the carbon nanotubes 101 from a carbon nanotube solution 123 when the carbon nanotube solution 123 is drawn through the filter membrane 117 from the vacuum chamber 103 by the pressure difference. In one embodiment, the filter membrane 117 can be a material such as polycarbonate, polytetrafluoroethylene, or polyvinylidene fluoride, with a pore diameter smaller than that of the carbon nanotubes 101 (in order to filter the carbon nanotubes 101), such as between approximately 0.01 µm and approximately 10 µm. However, any suitable material and pore diameter can be used.

[0013] Furthermore, while the pore size described above is sufficient to easily remove the carbon nanotubes 101 from the carbon nanotube solution 123, the use of a simple filter alone may not be sufficient to align the carbon nanotubes 101 during the filtration process. Therefore, in some embodiments, the filter membrane 117 is used to also generate an electrostatic field (in Fig. 1B (represented by the circled negative signs, which are labeled 119), which can be used to align the carbon nanotubes 101 when the carbon nanotubes 101 enter the electrostatic field 119 during the filtration process. In some embodiments, the electrostatic field 119 can be passively generated, while in other embodiments, the electrostatic field 119 can be actively generated during the filtration process.

[0014] Firstly, with regard to embodiments in which the electrostatic field 119 is passively generated, the filter membrane 117 can be used to generate the electrostatic field 119 by coating the filter membrane 117 with a coating material (for the sake of clarity, not shown separately in Fig. Figure 1B illustrates the process, passively generating the desired electrostatic field 119. In one embodiment, the coating material may comprise a hydrophilic material such as poly(vinylpyrrolidone) (PVP), hexamethyldisilazane (HMDS), aluminum oxide (Al2O3), combinations thereof, or the like. However, any suitable material may be used.

[0015] In embodiments where poly(vinylpyrrolidone) is used as the coating material, the poly(vinylpyrrolidone) passively generates the desired electrostatic field 119. In such embodiments, the electrostatic field 119 can have a voltage between approximately 0 V and approximately 10 V at a distance between approximately 0 nm and approximately 10 nm. However, any suitable electrostatic field 119 can be generated using passive generation, and all such methods of generating the electrostatic field can be used.

[0016] In another embodiment, the electrostatic field 119 can be actively generated either before or during the filtration process by capturing negative charges. In such an embodiment, instead of permanently coating the filter membrane 117 with a single material, the filter membrane 117 is actively charged with a surfactant before the filtration process. For example, in some embodiments, the surfactant can be a negatively charged material such as sodium dodecyl sulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), sodium deoxycholate (DOC), combinations thereof, or the like. However, any suitable surfactant can be used.

[0017] In one embodiment, the surfactant can be introduced with the filter membrane 117 before the introduction of the carbon nanotube solution 123. In another embodiment, the surfactant can be introduced with the filter membrane 117 by flowing the surfactant over and / or through the filter membrane 117, such that at least a portion of the negative charge is captured by the surfactant on the filter membrane 117 and remains at least partially in place during a subsequent filtration process.

[0018] In another embodiment, the surfactant can be included as a component of the carbon nanotube solution 123. In such an embodiment, the surfactant can be contained within the carbon nanotube solution 123, instead of flowing over the filter membrane 117 before the carbon nanotube solution 123 is introduced. In other embodiments, the surfactant can flow over the filter membrane 117 before the filtration process and is also reintroduced within the carbon nanotube solution 123. Any suitable combination of processes for introducing the surfactant with the filter membrane 117 can be used, and all such processes are intended to be fully encompassed within the scope of these embodiments.

[0019] In embodiments where the electrostatic field 119 is generated using a surfactant in an active generation process, the surfactant actively generates the desired electrostatic field 119 in each filtration process. In such embodiments, the electrostatic field 119 can have a voltage between approximately 0 V and approximately 10 V at a distance between approximately 0 nm and approximately 10 nm. However, any suitable electrostatic field 119 can be generated using active generation, and all such methods of generating the electrostatic field can be used.

[0020] Once again with a view to Fig. 1A illustrated Fig. 1A also includes a solution container 121, which is connected to a side of the filter 105 that faces the vacuum chamber 103. In one embodiment, the solution container 121 can be used to hold a carbon nanotube solution 123 (see Fig. 1B) to store and / or supply to the filter 105. In one embodiment, the solution container 121 can be a container made of a material that can withstand the pressure and chemicals involved in the filtration process, and in some embodiments can be a material such as glass, steel, stainless steel, nickel, aluminum, alloys thereof, combinations thereof, and the like. However, any suitable material can be used.

[0021] In another embodiment, the solution container 121 can serve as an inlet for the carbon nanotube solution 123 to enter the filter 105, while the carbon nanotube solution 123 can be stored and / or even generated separately from the filter 105. For example, in some embodiments, the carbon nanotube solution 123 can be mixed with and / or stored before being introduced into the filter 105, and the solution container 121, instead of being a standalone system that is attached to and removed from the system 100, is a supply system that provides a continuous supply of the carbon nanotube solution 123 during the filtration process.

[0022] The carbon nanotube solution 123 comprises the carbon nanotubes 101 dispersed in a solvent 125. In one embodiment, the carbon nanotubes 101 can be single-walled carbon nanotubes formed using any suitable process, such as a carbon arc discharge process (with subsequent purification), a laser vaporization process, catalyzed chemical vapor deposition, ball milling and subsequent annealing, diffusion flame synthesis, electrolysis, heat treatment of a polymer, low-temperature solid pyrolysis, combinations thereof, or the like. However, any suitable process for producing the carbon nanotubes 101 can be used, and all such processes are fully provided for to be included within the scope of the embodiments.

[0023] Optionally, in some embodiments, the carbon nanotubes 101 can be surrounded by spacers 129, which can serve a dual purpose: as a cleaning agent for the carbon nanotubes 101 and as a means of distributing the carbon nanotubes 101 within the carbon nanotube solution 123. Furthermore, by controlling the thickness of the spacers 129 around each of the carbon nanotubes 101, the spacing of the carbon nanotubes 101 after they are aligned with each other can also be controlled.

[0024] In one embodiment, the spacers 129 can be a material that can be placed and removed from the carbon nanotubes as desired, while also not adversely interfering with the manufacturing processes between placement and removal. For example, in certain embodiments, the spacer 129 can be a material such as a surfactant (e.g., sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, sodium deoxycholate, etc.), a polymer (e.g., poly-[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(6,6'-{2,2'-bipyridine}), isoindigo-based poly-(9,9-dioctylfluorene), poly-[9-(1-octylonoyl)-9H-carbazole-2,7-diyl, etc.), a dielectric (e.g., HfO2 / SiO2 / Al2O, etc.), or other nanotubes (e.g., a boron nitride nanotube, a MoS2 nanotube, etc.). However, any suitable material or combination of materials can be used to surround and coat the carbon nanotubes 101 during the filtration process.

[0025] The spacers 129 can be placed around the carbon nanotubes 101 using any suitable process. For example, processes such as chemical vapor deposition, atomic layer deposition, surfactant wrapping, polymer wrapping, combinations thereof, or the like can be used to place the spacers 129 around the individual carbon nanotubes 101. Furthermore, in embodiments where the spacers 129 are used to control the distance between adjacent carbon nanotubes 101 when the carbon nanotubes 101 have deposited adjacent to each other, the spacers 129 can have a thickness of between approximately 0 nm and approximately 10 nm. However, any suitable placement method and any suitable thickness can be used.

[0026] In one embodiment, the carbon nanotube solution 123 is formed by placing the carbon nanotubes 101 (with or without spacers 129) in a solvent 125. In one embodiment, the solvent 125 can be used to contain the carbon nanotubes 101 during transport and also to provide a suitable medium for the carbon nanotubes 101 to settle in the desired sequence orientation during the filtration process (described below). In some embodiments, the solvent 125 can be a solvent such as water (H₂O), toluene, trichloroethane, tetrahydrofuran, or chloroform. However, any suitable material can be used for the solvent 125.

[0027] In one embodiment, the carbon nanotubes 101 can have a concentration within a solvent 125 that is high enough to allow efficient settling of the carbon nanotubes 101, but not so high that the sheer number of carbon nanotubes 101 interferes with the settling process. Thus, the carbon nanotubes 101 can have a concentration within the carbon nanotube solution 123 between approximately 0.001 mg / ml and approximately 1 mg / ml. However, any suitable concentration can be used.

[0028] While the carbon nanotube solution 123 is comprehensively described as the solvent 125 and the carbon nanotubes 101, this description is intended to be illustrative. In particular, the carbon nanotube solution 123 can include any other suitable or desirable additives, such as the surfactant used for actively generating the desired electrostatic field 119. All such additives are fully included in the scope of the embodiments.

[0029] To initiate the filtration process, the carbon nanotube solution 123 is placed inside the solution vessel 121, and the solution vessel 121 is connected to the filter 105, allowing the carbon nanotube solution 123 to flow to the filter membrane 117. Furthermore, a vacuum is created in the vacuum chamber 103 using the vacuum pump 115 as a driving force to draw the carbon nanotube solution 123 through the filter membrane 117. In one embodiment, the vacuum pump 115, which is connected to the first outlet 111, can be used to reduce the pressure in the vacuum chamber 103 to between approximately 0.13 Pa and approximately 101325 Pa. However, any suitable pressure can be used.

[0030] When a vacuum is present in the vacuum chamber 103, a pressure differential is created between a first side of the filter membrane 117, which faces the vacuum chamber 103, and a second side of the filter membrane 117, which faces the carbon nanotube solution 123. With this pressure differential applied, the carbon nanotube solution 123 is drawn through the filter membrane 117 and filters the carbon nanotubes 101 out of the solvent 125 as the solvent 125 flows through the filter membrane 117, while the filter membrane 117 captures the carbon nanotubes 101 that are too large to pass through it.

[0031] Furthermore, when the electrostatic field 119 is present at the filter membrane 117 (either passively or actively generated), a combination of an electrostatic field 119 and van der Waals attractive forces work to align the carbon nanotubes 101 when the carbon nanotubes 101 are deposited on the filter membrane 117, so that the carbon nanotubes 101 are deposited parallel to each other and aligned with each other. In particular, in an embodiment in which the carbon nanotubes 101 have a negative charge (e.g. from the negatively charged surfactants that are wound around the carbon nanotubes 101 as spacers 129) and the electrostatic field 119 also has a negative charge, the electrostatic field 119 causes the carbon nanotubes 101 to align themselves parallel to each other when the carbon nanotubes 101 are filtered through the filter membrane 117.

[0032] As the filtration process continues, the carbon nanotubes 101 are deposited within the carbon nanotube solution 123 as a first layer 131, with the carbon nanotubes 101 aligned side by side within the first layer 131. Furthermore, as a first layer 131 of carbon nanotubes 101 is deposited, a second layer 201, a third layer 203, a fourth layer 205, a fifth layer 207, and a sixth layer 209 of carbon nanotubes 101 are deposited to form a stack 211 of carbon nanotubes 101 (in Fig. 1B not illustrated, but further below regarding Fig. 2A described and illustrated). Any suitable number of layers of the carbon nanotubes 101 can be deposited during the filtration process.

[0033] Fig. Figures 2A to 2B illustrate that when the stack of 211 carbon nanotubes 101 is deposited on the filter membrane 117, the stack of 211 carbon nanotubes 101 can be transferred to a first dielectric layer 215 located above a first substrate 217, wherein Fig. 2A a cross-sectional view of the top view from Fig. Figure 2B shows through line A to A'. In one embodiment, the first substrate 217 can be a support material, such as a silicon material (e.g., a silicon wafer), a germanium material, a silicon-germanium material, a gallium arsenide material, but other substrates, such as semiconductor-on-insulator (SOI), strained SOI, silicon-germanium-on-insulator, glass substrate, combinations thereof, or the like, are also possible. However, any suitable material can be used for the first substrate 217.

[0034] The first dielectric layer 215 is located above the first substrate 217 and is used to insulate devices subsequently formed on the first substrate 217. In one embodiment, the first dielectric layer 215 is a dielectric such as silicon dioxide, aluminum oxide, combinations thereof, or the like, deposited on the first substrate 217 using a deposition process such as chemical vapor deposition, sputtering, atomic layer deposition, combinations thereof, or the like. However, any suitable material and deposition process can be used.

[0035] Furthermore, it illustrates Fig. 2A The first dielectric layer 215 is shown to be directly on and in physical contact with the first substrate 217; however, this is for illustrative purposes only. Instead, other dielectrics and other substrate materials (e.g., silicon, germanium, gallium arsenide, combinations thereof, or the like) may also be present between the first dielectric layer 215 and the first substrate 217. All such combinations of layers may be used, and all are fully provided for and included in the scope of the embodiments.

[0036] When the first dielectric layer 215 is positioned over the first substrate 217, the stack 211 of carbon nanotubes 101 is transferred from the filter membrane 117 to the first dielectric layer 215. In one embodiment, the transfer can be accomplished by initially removing the filter membrane 117 from the system 100 and then applying a transfer layer (not shown separately) to the stack 211 of carbon nanotubes 101. In another embodiment, the transfer layer can be a material that can be used to hold and protect the stack 211 of carbon nanotubes 101 and also to allow easy removal of the transfer layer once the stack 211 of carbon nanotubes 101 has been transferred. For example, the transfer layer can be polycarbonate (PC), polymethyl methacrylate (PMMA), although any other suitable material, such as methylacrylic resin or novolac resin, or the like, can be used instead.

[0037] In one embodiment where the transfer layer is PMMA, the transfer layer can be placed on the stack 211 of the carbon nanotubes 101, for example, using a spin coating process, although any other suitable deposition process can also be used. After application, the PMMA can be cured and solidified. This solidified PMMA protects the stack 211 of the carbon nanotubes 191 and also allows the transfer layer to move and control the stack 211 of the carbon nanotubes 191.

[0038] Once the transfer layer has been applied over the stack 211 of carbon nanotubes 101, the transfer layer can be used to position the stack 211 of carbon nanotubes 101 over the first substrate 217 and in contact with the first dielectric layer 215. The placement of the stack 211 of carbon nanotubes 101 can be achieved by controlling the transfer layer (with the stack 211 of carbon nanotubes 101 attached) and using the transfer layer to position the stack 211 of carbon nanotubes 101.

[0039] Furthermore, in certain embodiments, the stack 211 of carbon nanotubes 101 can have a greater orientation along one face of the stack 211 than along another face of the stack 211. In such embodiments, the stack 211 of carbon nanotubes 101 can be positioned such that the face with the greater orientation points towards or is in physical contact with the first substrate 217. However, any suitable placement can be used.

[0040] When the stack 211 of carbon nanotubes 101 is placed on the first dielectric layer 215, the transfer layer can be removed. In one embodiment, the transfer layer can be removed using a stripping or etching process to remove the transfer layer material from the stack 211 of carbon nanotubes 101. Thus, while the materials used to remove the transfer layer may depend at least partially on the material chosen for the transfer layer, in one embodiment where the transfer layer is PMMA, the transfer layer can be removed by applying acetone to the PMMA, which dissolves the PMMA.

[0041] However, as an ordinary person skilled in the art will recognize, the use of PMMA for the transfer layer, and the use of the transfer layer in general, is not intended to restrict the embodiments. Instead, any suitable method for transferring the stack 211 of carbon nanotubes 101 and integrating the stack 211 of carbon nanotubes 101 into a manufacturing process flow can be used. Any other suitable method for transferring the stack 211 of carbon nanotubes 101 is fully included within the scope of the embodiments.

[0042] When the stack of carbon nanotubes 101 (211) is transferred, it can consist of between approximately 30 and 60 layers. Thus, the stack of carbon nanotubes 101 can have a thickness between approximately 50 nm and approximately 100 nm. However, any suitable number of carbon nanotubes 101 and any suitable thickness can be used.

[0043] Furthermore, by using the solution-based filtration method as described above, a high-density and extremely pure layer of carbon nanotubes 101 can be obtained. For example, the carbon nanotubes can have a purity exceeding approximately 99.99%. Additionally, each layer of carbon nanotubes 101 can have a density of approximately 500 carbon nanotubes per micron. However, any suitable purity and density can be used.

[0044] Fig. Figures 3A to 3B illustrate that when the stack 211 of carbon nanotubes 101 was transferred to the first dielectric layer 215, the thickness of the stack 211 of carbon nanotubes 101 can be reduced, wherein Fig. 3A a cross-sectional view of the top view of Fig. 3B illustrated by line A to A'. In one embodiment, the reduction can be achieved using a destructive thinning process (shown in Fig. 3A by the arrows labeled 301). For example, in some embodiments, the destructive thinning process 301 can be carried out using a process such as reactive ion dry etching, sonic treatment thinning, dissolution thinning, chemical intercalation thinning, mechanical grinding, chemical-mechanical polishing, chemical polishing, combinations thereof, or the like. However, any suitable thinning process may be used.

[0045] In one embodiment, the stack 211 of carbon nanotubes 101 can be thinned such that only a desired number of carbon nanotubes (e.g., the first layer 131 of carbon nanotubes 101 and the second layer 201 of carbon nanotubes 101) remain within a reduced stack 303 of carbon nanotubes 101. In one embodiment, the reduced stack 303 of carbon nanotubes 101 can have between approximately 3 and approximately 6 layers of carbon nanotubes 101. Thus, the reduced stack 303 of carbon nanotubes 101 can have a thickness between approximately 5 nm and approximately 10 nm. However, any suitable number of carbon nanotubes 101 and any suitable thickness can be used.

[0046] However, the destructive thinning processes 301 as described above are not perfect. While many of the carbon nanotubes 101 that are to be removed are indeed removed, the use of the destructive thinning processes 301 also damages at least some of the carbon nanotubes 101 that were present in the layers that were to be removed, without necessarily removing them (e.g., the third layer 203 of the carbon nanotubes 101, the fourth layer 205 of the carbon nanotubes 101, the fifth layer 207 of the carbon nanotubes 101, and the sixth layer 209 of the carbon nanotubes 101), thereby forming damaged carbon nanotubes 305.

[0047] Fig. Figures 4A to 4B illustrate that when the stack 211 of carbon nanotubes 101 is reduced to the reduced stack 303 of carbon nanotubes 101, a supporting layer 401 is deposited over the reduced stack 303 of carbon nanotubes 101, wherein Fig. 4A a cross-sectional view of the top view of Fig. 4B illustrated by line A to A'. In one embodiment, the supporting layer 401 acts as an adhesive layer for a subsequent non-destructive thinning process (in Fig. 4A to 4B not illustrated, but further below with reference to Fig. (5A to 5B explained and illustrated). Thus, in some embodiments, the material of the supporting layer 401 can be a metal such as nickel, molybdenum, tungsten, platinum, bismuth, combinations thereof, or the like. In such an embodiment, the material of the supporting layer 401 can be deposited using a vapor deposition process, a sputtering process, an atomic layer deposition process, combinations thereof, or the like. Any suitable deposition process can be used.

[0048] In other embodiments, the supporting layer 401 can be an organic material such as polymethyl methacrylate (PMMA), polyvinyl acetate (PVA), polyvinylpyrrolidone (PVP), polypropylene carbonate (PPC), other polycyclic aromatic hydrocarbons (PAHs), phenyltrimethoxysilane (PTMS), polydimethylsiloxane (PDMS), rosin, combinations thereof, or the like. In embodiments such as this, the material of the supporting layer 401 can be deposited using a deposition process such as spin coating or the like. However, any suitable material and deposition process can be used.

[0049] Fig. Figures 5A to 5B illustrate that when the supporting layer 401 has been deposited, further carbon nanotubes 101 (e.g., the second layer 201 of carbon nanotubes) are removed from the reduced stack 303 of carbon nanotubes 101 to form an operative layer 503, wherein Fig. 5A a cross-sectional view of the top view of Fig. 5B is illustrated by line A to A'. In one embodiment, and to avoid damage to underlying layers, the further carbon nanotubes 101 are formed using a non-destructive thinning process (in Fig. 5A is shown by the arrows labeled 501).

[0050] In some embodiments, the non-destructive thinning process 501 can be carried out by removing the supporting layer 401 using a process such as mechanical exfoliation. In one particular embodiment using mechanical exfoliation, an adhesive material such as adhesive tape can be applied to the supporting layer 401. After application and adhesion to the supporting layer 401, force can be applied to the adhesive material to remove the supporting layer 401.

[0051] In addition to simply removing the supporting layer 401 alone, removing the supporting layer 401 also removes the damaged carbon nanotubes 305 covered by the supporting layer 401, as well as one or more layers of the carbon nanotubes 101 (e.g., the second layer 201 of the carbon nanotubes 101 in Fig. 5A). Thus, the non-destructive thinning process 501 can be used to remove the damaged carbon nanotubes 305 so that the damaged carbon nanotubes 305 cannot interfere with subsequent processes. Furthermore, the non-destructive thinning process 501 can also be used to further thin the reduced stack 303 of carbon nanotubes 101 without generating any more damaged carbon nanotubes 101.

[0052] Furthermore, while the mechanical exfoliation process described above is one such process that can be used to remove the supporting layer 401 and reduce the thickness of the reduced stack 303, this description is intended to be illustrative. Instead, any suitable non-destructive thinning process can be used, such as the use of a sacrificial metal layer for thinning by carbon diffusion during annealing, the removal of the spacer 129 introduced into the structured carbon nanotube film (e.g., the stack 211) by either chemical processes or vacuum annealing, or thinning of the reduced stack 303 by sonic treatment or mechanical release. Any such non-destructive thinning process can be used, and all such processes are fully intended to be included within the scope of the embodiments.

[0053] Once the operational layer 503 has been formed from carbon nanotubes 101, it can consist of a single layer of carbon nanotubes 101. Thus, the operational layer 503 can have a thickness between approximately 1 nm and approximately 1.5 nm. However, any suitable number of carbon nanotubes 101 and any suitable thickness can be used.

[0054] In the embodiment described in Fig. As illustrated in Figures 3A to 5B, the destructive thinning process 301 can be performed to reduce the stack 211 of carbon nanotubes 101, leaving only two layers of carbon nanotubes 101, while the non-destructive thinning process 501 removes only a single layer of carbon nanotubes 101, leaving a single layer of carbon nanotubes 101. However, this is for illustrative purposes only. Instead, any suitable combination or repetition of steps can be used to obtain the operative layer 503 of carbon nanotubes 101.

[0055] For example, in some embodiments, the destructive thinning process 301 can be omitted entirely or performed instead to remove only a minimal number of layers of the carbon nanotubes 101 (e.g., to remove one or two layers of the carbon nanotubes 101). In such an embodiment, most or the intended thinning to obtain the operative layer 503 of the carbon nanotubes 101 is performed using a non-destructive thinning process 501. Furthermore, if such a non-destructive thinning process 501 is insufficient to thin the stack 211 of the carbon nanotubes 101, the non-destructive thinning process 501 can be repeated one or more times to remove successive layers of the carbon nanotubes 101 until the desired number of layers of carbon nanotubes 101 is reached.Any suitable number of iterations in any order may be used, and all such combinations shall fall entirely within the scope of the embodiments.

[0056] Fig. Figures 6A to 6B illustrate that when the operative layer 503 of the carbon nanotubes 101 has been formed, the spacers 129 can optionally be removed from around the carbon nanotubes 101, wherein Fig. 6A a cross-sectional view of the top view of Fig. Figure 6B is illustrated by lines A to A'. In an embodiment in which the spacers 129 are a surfactant or a polymer, the spacers 129 can be removed using a tempering process, wherein the temperature of the spacer material 129 is increased until either the material evaporates (if possible) or otherwise undergoes thermal decomposition, after which the material can be easily removed.

[0057] In another embodiment, where the material of the spacers 129 is a dielectric, the spacers 129 can be removed using an etching process. In a particular embodiment, the spacers 129 can be removed using a wet etching process with an etchant that is selective for the material of the spacers 129. However, any suitable etching or other removal process can be used.

[0058] By using the spacer 129 during alignment and then removing the spacer 129, the spacing of the remaining carbon nanotubes 101 can be precisely controlled by adjusting the thickness of the spacer 129. Thus, in some embodiments, the carbon nanotubes 101 can have a spacing between approximately 0 nm and approximately 100 nm. However, any suitable spacing can be used.

[0059] Fig. Figures 7A to 7B illustrate an isometric view (in Fig. 7A) and a top view (in Fig. 7B), in which the operative layer 503 of the carbon nanotubes 101 is used to form a planar transistor 700. Further illustrated Fig. 7C a first cross-sectional view of the planar transistor 700 through line CC' and Fig. Figure 7D illustrates a second cross-sectional view of the planar transistor 700 through line D-D'. In particular, once the operative layer 503 of the carbon nanotubes 101 has been formed, source / drain contacts 707, gate spacers 705, a gate dielectric 701, and a gate electrode 703 can be formed. However, any suitable combination of structures can be used.

[0060] In one embodiment, source / drain contacts 707 can be formed on opposite sides of a channel region located within the carbon nanotubes 101 and in contact with the sidewalls of source / drain regions also located within the carbon nanotubes 101 on opposite sides of the channel region. According to some embodiments, the formation of the source / drain contacts 707 includes the formation and structuring of an etching mask such as a photoresist (in Fig. (Figures 7A to 7D not shown separately), so that the regions where the source / drain contacts 707 are to be formed are exposed, while other regions are covered by the etch mask. A conductive layer, such as a metal layer (e.g., tungsten, cobalt, combinations thereof, or the like), is then deposited as a cover layer. A removal process is then performed, lifting off the etch mask and also removing the portions of the conductive layer on the etch mask. Thus, source / drain contacts 707 remain as shown in the Fig. 7A to 7D shown.

[0061] Once the source / drain contacts 707 have been formed, the gate spacers 705 can be formed to separate the source / drain contacts 707 from the gate electrode 703. In one embodiment, the gate spacers 705 can be formed by conformal deposition of an insulating material and subsequent anisotropic etching of the insulating material. The insulating material of the gate spacers 705 can be silicon oxide, silicon nitride, silicon oxynitride, silicon carbonitride, a combination thereof, or the like. However, any suitable material and deposition process can be used.

[0062] Once the material for the gate spacer 705 has been formed, the gate dielectric 701 can be formed. In one embodiment, the gate dielectric 701 comprises one or more dielectric layers, such as one or more layers of silicon oxide, silicon nitride, metal oxide, metal silicate, or the like. For example, in some embodiments, the gate dielectric 701 comprises a dielectric with a high k-value, such as a metal oxide or silicate of hafnium, aluminum, zirconium, lanthanum, manganese, barium, titanium, lead, and combinations thereof. The gate dielectric 701 may comprise a dielectric layer with a k-value above approximately 7.0. The formation methods for the gate dielectric 701 may include forming a gate dielectric layer (in Fig. (7A to 7D not illustrated separately) by a deposition process such as molecular beam deposition (MBD), ALD, PECVD, and the like. However, any suitable materials and manufacturing processes may be used to deposit the material for gate dielectric 701.

[0063] Once the material for the gate dielectric 701 has been deposited, the material for the gate electrode 703 is deposited. The material for the gate electrode 703 can be deposited by initially forming a gate electrode layer (in Fig.(Figures 7A to 7D not shown separately). In one embodiment, the gate electrode layer comprises a conductive material and may be selected from the group consisting of polycrystalline silicon (poly-Si), polycrystalline silicon germanium (poly-SiGe), metallic nitrides, metallic silicides, metallic oxides, and metals. Examples of metallic nitrides include tungsten nitride, molybdenum nitride, titanium nitride, and tantalum nitride, or combinations thereof. Examples of metallic silicides include tungsten silicide, titanium silicide, cobalt silicide, nickel silicide, platinum silicide, erbium silicide, or combinations thereof. Examples of metallic oxides include ruthenium oxide, indium tin oxide, or combinations thereof. Examples of metals include tantalum, tungsten, titanium, aluminum, copper, molybdenum, nickel, platinum, etc.

[0064] In one embodiment, the gate electrode layer can be deposited by chemical vapor deposition (CVD), sputtering, or other techniques known and used in the prior art for depositing conductive materials. The thickness of the gate electrode layer can range from approximately 20 nm to approximately 4,000 nm. The top surface of the gate electrode layer typically has a non-planar surface and can be planarized prior to structuring or etching the gate electrode layer. Dopants can, but need not, be implanted into the gate electrode layer at this location. Dopants can be introduced, for example, by molecular doping techniques involving charge transfer.

[0065] Once the gate electrode layer has been formed, the gate electrode layer, the gate dielectric layer, and the gate spacers 705 can be planarized. In one embodiment, the material of the gate electrode layer and the material of the gate dielectric layer are planarized to form the gate electrode 703 and the gate dielectric 701, for example, using a chemical-mechanical polishing process. However, any suitable planarization method can be used.

[0066] After planarization, the source / drain contacts 707 can be exposed from any remaining overlying material (e.g., the material of the gate spacer 705) if desired. In some embodiments, the source / drain contacts 707 can be exposed, for example, using a photolithographic masking and etching process, whereby a photoresist is deposited and structured to lie over and protect portions of the gate spacer 705, the gate dielectric 701, and the gate electrode 703, while other portions are exposed. After protection, an etching process, such as a reactive ion etching process, can be used to expose portions of the source / drain contacts 707. However, any suitable process can be used to expose the source / drain contacts 707 for further processing, such as the formation of an overlying metallization layer.

[0067] By utilizing the non-destructive thinning process 501 to perform the final thinning steps and obtain the operational layer 503, all damaged carbon nanotubes 101 can be removed from the structure and are therefore not present to potentially interfere with subsequent fabrication processes. Furthermore, such a process allows for a greater degree of control over the thinning process, enabling a very precise determination of how many layers of carbon nanotubes 101 can be used. All these advantages help to increase the yield and make the process more efficient by avoiding defects that might otherwise occur, resulting in devices with improved performance for achieving targets beyond the 2 nm node.

[0068] In one embodiment of a method for fabricating a semiconductor device, the method comprises: forming a stack of nanotubes, wherein individual nanotubes are aligned with adjacent nanotubes; depositing a support layer over the stack of nanotubes; removing the support layer, wherein the removal of the support layer further removes at least one layer of nanotubes from the stack of nanotubes; and depositing a gate electrode over a remaining portion of the stack of nanotubes. In one embodiment, the method further comprises, after the removal of the support layer, removing a spacer material around at least one nanotube within the remaining portion of the stack of nanotubes. In one embodiment, forming the stack of nanotubes comprises filtering the individual nanotubes through a filter membrane.In one embodiment, the filter membrane has a first electrostatic field during the filtering of the individual nanotubes. In another embodiment, the individual nanotubes are surrounded by a spacer material during the filtering process, the spacer material having a second electrostatic field. In one embodiment, the stack of nanotubes has a nanotube density of approximately 500 nanotubes per micrometer. In another embodiment, the spacer material comprises a surfactant.

[0069] In another embodiment, a method for fabricating a semiconductor device comprises: filtering a carbon nanotube solution through a filter membrane, the filter membrane having an electrostatic field, wherein during filtering a first layer of carbon nanotubes, a second layer of carbon nanotubes, and a third layer of carbon nanotubes are deposited on the filter membrane; transferring the first layer of carbon nanotubes, the second layer of carbon nanotubes, and the third layer of carbon nanotubes onto a dielectric layer over a substrate; removing the third layer of carbon nanotubes by a destructive removal process; removing the second layer of carbon nanotubes by a non-destructive removal process; and forming a gate electrode over the first layer of carbon nanotubes after removing the second layer of carbon nanotubes.In one embodiment, the destructive removal process comprises a reactive ion etching process. In another embodiment, the non-destructive removal process comprises a mechanical exfoliation process. In another embodiment, the mechanical exfoliation process further comprises the deposition of a support layer over the second layer of carbon nanotubes, wherein the mechanical exfoliation process removes both the support layer and the second layer of carbon nanotubes. In another embodiment, the mechanical exfoliation process further removes carbon nanotubes that are damaged during the destructive removal process. In another embodiment, the method further comprises the removal of a spacer material from carbon nanotubes within the first layer of carbon nanotubes. In another embodiment, the first layer of carbon nanotubes has a density of approximately 500 nanotubes per micrometer.

[0070] In yet another embodiment, a method for fabricating a semiconductor device comprises: taking up a solution, wherein the solution comprises carbon nanotubes; aligning the carbon nanotubes into a stack of aligned carbon nanotubes using a first electrostatic field; placing the stack of aligned carbon nanotubes on a dielectric; first thinning the stack of aligned carbon nanotubes by a first process; second thinning the stack of aligned carbon nanotubes by a second process that differs from the first process; and depositing a source / drain contact in electrical connection with the stack of aligned carbon nanotubes after the second thinning of the stack of aligned carbon nanotubes.In one embodiment, after the second thinning of the stack of aligned carbon nanotubes, the stack thickness is less than 2 nm. In one embodiment, the first process is an etching process. In another embodiment, the second process is an exfoliation process. In one embodiment, the first electrostatic field is generated by a material located on a filter membrane. In another embodiment, the carbon nanotubes are surrounded by a spacer material during alignment, the spacer material generating a second electrostatic field.

Claims

[1] Method for manufacturing a semiconductor device comprising the method: Forming a stack of nanotubes (211), wherein individual nanotubes (101) are aligned with adjacent nanotubes (101); Deposition of a load-bearing layer (401) over the stack of nanotubes (211); Removing the supporting layer (401), wherein the removal of the supporting layer (401) further removes at least one layer of nanotubes (101) from the stack of nanotubes (211); Deposition of a gate electrode (703) over a remaining section of the stack of nanotubes (211); and after removing the supporting layer (401), removing a spacer material (129) around at least one nanotube (101) within the remaining section of the stack of nanotubes (211). [2] Method of claim 1, wherein forming the stack of nanotubes (211) comprises filtering the individual nanotubes (101) through a filter membrane. [3] Method of claim 2, wherein the filter membrane has a first electrostatic field during the filtering of the individual nanotubes (101). [4] Method of claim 3, wherein the individual nanotubes (101) are surrounded by a spacer material (129) when filtering the individual nanotubes (101), wherein the spacer material (129) has a second electrostatic field. [5] Method of claim 4, wherein the stack of nanotubes (211) has a nanotube density of approximately 500 nanotubes per micrometer. [6] Method of claim 4 or 5, wherein the spacer material (129) comprises a surfactant. [7] Method for manufacturing a semiconductor device comprising the method: Filtering a carbon nanotube solution (123) through a filter membrane, wherein the filter membrane has an electrostatic field, wherein during the filtering a first layer of carbon nanotubes (101), a second layer of carbon nanotubes (101) and a third layer of carbon nanotubes (101) are deposited on the filter membrane; Transfer of the first layer of carbon nanotubes (101), the second layer of carbon nanotubes (101) and the third layer of carbon nanotubes (101) onto a dielectric layer (215) via a substrate (217); Removal of the third layer of carbon nanotubes (101) using a destructive removal process (301); Removal of the second layer of carbon nanotubes (101) using a non-destructive removal process (501); and Forming a gate electrode (703) over the first layer of carbon nanotubes (101) after removing the second layer of carbon nanotubes (101). [8] Method of claim 7, wherein the destructive removal process (301) comprises a reactive ion etching process. [9] Method of claim 8, wherein the non-destructive removal process (501) comprises a mechanical exfoliation process. [10] The method of claim 9, wherein the mechanical exfoliation process further comprises the deposition of a supporting layer (401) over the second layer of carbon nanotubes (101), wherein the mechanical exfoliation process removes the supporting layer (401) and the second layer of carbon nanotubes (101) equally. [11] Method of claim 10, wherein the mechanical exfoliation process further comprises carbon nanotubes (101) which are damaged during the destructive removal process. [12] Method of any one of claims 7 to 11, further comprising the removal of a spacer material (129) from carbon nanotubes (101) within the first layer of carbon nanotubes (101). [13] The method of claim 12, wherein the first layer of carbon nanotubes (101) has a density of approximately 500 nanotubes per micrometer. [14] Method for manufacturing a semiconductor device comprising the method: Taking up a solution (123) wherein the solution contains carbon nanotubes (101); Aligning the carbon nanotubes (101) using a first electrostatic field into a stack (211) of aligned carbon nanotubes (101); Placing the stack (211) of aligned carbon nanotubes (101) on a dielectric (215); First thinning of the stack (211) of aligned carbon nanotubes (101) using a first process (301); Second thinning of the stack (211) of aligned carbon nanotubes (101) using a second process (501) that differs from the first process (301); and Deposition of a source / drain contact (707) in electrical connection with the stack (211) of aligned carbon nanotubes (101) after the second thinning of the stack (211) of aligned carbon nanotubes (101). [15] Method of claim 14, wherein after the second thinning of the stack (211) of aligned carbon nanotubes (101) the thickness of the stack (211) of aligned carbon nanotubes (101) is less than 2 nm. [16] Method of claim 14 or 15, wherein the first process (301) is an etching process. [17] Method of claim 16, wherein the second process (501) is an exfoliation process. [18] Method of any one of claims 14 to 17, wherein the first electrostatic field is generated by a material located on a filter membrane. [19] Method of claim 18, wherein the carbon nanotubes (101) are surrounded by a spacer material (129) when aligning the carbon nanotubes (101), the spacer material (129) generating a second electrostatic field.

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