Patent Application
20080063982
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the preferred embodiments and are not necessarily drawn to scale.
The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.
In immersion lithography, deep ultraviolet (DUV) light or energy, e.g., at about 193 nm, is used to expose a layer of photoresist, which is a polymer film that reacts when exposed to light or energy disposed on a workpiece. A fluid is disposed between a projection lens system and the workpiece. Immersion lithography is one of the main contenders for printing very small electronic circuit features on silicon wafers. Similar to a concept that has been used in optical microscopy, immersion fluids are beginning to be used in optical lithography between the last lens element of a lithographic imaging system and the resist layer in order to enabling imaging of smaller feature sizes onto the wafer.
Immersion lithography for imaging structures down to about 45 nm half pitch resolution currently uses clean water as an immersion fluid. The refractive index of water at a 193 nm wavelength used in immersion lithography is nfluid=1.44. For achieving resolution in high numerical immersion lithography tools having features below 40 nm half pitch, higher refractive index fluids will be needed. Generally, immersion fluids are required to have a high refractive index, e.g., of about 1.2 to 1.8, and are required to be transparent in the deep ultraviolet (DUV) spectral range. Immersion fluids should also be photostable and chemically inert towards photoresists and optics of the projection lens system, and should be liquid to permit rapid scanning.
Various fluids are being researched for use in immersion lithography. It is particularly important to use a fluid in immersion lithography that will not damage the photoresist on a wafer and that will not damage the optics of the projection lens system of a lithography system, for example. The industry has tended to focus on water-based high index fluids having refractive indexes that are modified by introducing additional substances, although other options are also explored. For example, perfluoropolyether oils have been considered, but are not expected to yield high refractive indices.
Dielectric nanoparticles suspended in a liquid phase, or so-called nanocomposite fluids, have been considered, with a focus on the synthesis of alumina suspensions, as described by Chumanov, G., et al., in “Nanocomposite Liquids for 193 nm Immersion Lithography,” 2004, 14 pp., Sematech, Austin, Tex., which is hereby incorporated herein by reference. Alumina suspensions were synthesized through the hydrolysis and condensation of aluminium alkoxides in a two phase system. The size of the alumina particles ranged from 5 to 100 nm, and the refractive index of such suspension was expected to be around n=1.6. However, it is difficult to achieve a low variation in refractive index with very well controlled size distributions of nanoparticles, particularly, a very narrow size distribution around a small nanoparticle size, for example.
The addition of ionic surfactants has been considered, e.g., anionic and cationic surfactants that form aggregates (micelles) in aqueous solutions above a certain critical micelle concentration, as described by Zimmerman, P. A., et al., in “Amplification of the Index of Refraction of Aqueous Immersion Fluids by Ionic Surfactants,” Sematech Resist Advisory Group Meeting, 08-08-2004, 17 pp., Austin, Tex., which is hereby incorporated herein by reference. The introduction of zeolite nanoparticles to fluids has also been proposed, as described by Gejo, J. L., et al., in “Amplification of the Index of Refraction of Aqueous Immersion Fluids: Nanoparticle Dispersions,” Sematech Resist Advisory Group Meeting, September 2005, 21 pp., Sematech, Austin, Tex., which is hereby incorporated herein by reference. However, zeolite nanoparticles are problematic because of their wide particle size range (5 to 1,000 nm), which causes an excessive amount of Mie scattering.
The addition of salts to fluids increases the refractive index but produces radicals under DUV irradiation that chemically attack optics and resist. Altering the refractive index of a fluid by adding a salt to the fluid is described by Gejo, J. L., et al., in “Amplification of the Index of Refraction of Aqueous Immersion Fluids: Nanoparticle Dispersions,” Sematech Resist Advisory Group Meeting, September 2005, 21 pp., Sematech, Austin, Tex., which is incorporated herein by reference.
Willson, G., et al., in “University of Texas at Austin Immersion Lithography Progress Report,” Sematech Resist Advisory Group Meeting, 08-08-2004, 22 pp., Austin, Tex., which is hereby incorporated herein by reference, also disclose some salts considered as candidates for increasing the refractive index of water. Table 1 shows some combinations of salts disclosed on p. 10 by Willson et al., that could be used to increase the refractive index of water, with anion (the first row) and cation (the first column) combinations of salts illustrated.
However, most of these salts, indicated by the checkmarks, chemically formed in aqueous solutions, comprise very aggressive fluids.
Thus, although the introduction of salts appears to have the most promise in increasing the index of refraction of a liquid, an adequate method of introducing salts to a liquid for immersion lithography that does not impact the optics lifetime or degrade or attack the resist on a semiconductor wafer has yet to be found.
Embodiments of the present invention provide novel methods of adding salts and other substances to a fluid to alter the properties of the fluid, such as the refractive index or index of refraction. Fullerene cages are used to contain the property-altering substance, preventing the salt or other substance from causing damage to materials the fluid comes into contact with.
A fullerene is a chemical having a dome or cage-like structure of atoms. Fullerenes are typically substantially spherical, for example. Carbon may be formed in the shape of a fullerene, e.g., C60. Fullerenes comprise a plurality of atoms, usually of the same type, bonded together in a structure of a cage and having a hollow interior. The cage structures typically comprise many faces shaped as hexagons and pentagons, similar to the shape of geodesic domes, for example. Materials other than carbon may also be formed into fullerenes and may have different numbers of atoms in each fullerene, for example.
Embodiments of the present invention achieve technical advantages by using fullerenes to contain atoms or molecules within the cage-like structure of a fullerene, changing the properties of a fluid, yet the cage-like structure of the fullerenes prevents the atoms or molecules from deleteriously affecting objects or substances the fluid comes into contact with.
A support 218 for the device 222 is adapted to support the device 222 during the lithography process. The wafer support 218 may comprise a wafer stage or exposure chuck, for example. A lithography mask 214 is disposed between an illuminator 212 and the projection lens system 216. The illuminator 212 is adapted to expose the semiconductor device 222 to light or energy through the mask 214 and projection lens system 216 to transfer the pattern of the mask 214 to the layer of photoresist 226 disposed over the workpiece 224 of the semiconductor device 222. The semiconductor device 222 and the mask 214 may both be moved from one side to the other during a scanning process to expose the layer of photoresist 226, for example.
The fluid 220 preferably comprises a liquid such as de-ionized water. The fluid 220 may also comprise other liquids, such as water, highly purified water, distilled water, or distilled de-ionized water. The fluid 220 preferably includes a plurality of first atoms, wherein sets of the first atoms comprise the shape of at least one fullerene. At least one second atom is disposed in an interior of at least some of the fullerenes of first atoms. The fluid 220 may also include a surfactant, to be described further herein. In some embodiments, the fluid 220 may include a solvent, also to be described further herein.
The fluid 220 is introduced between the last element or lens 228 of the projection lens system 216 and the semiconductor device 222 during the exposure process, e.g., by an immersion head (not shown) clamped to the end of the lens system 216 or to another part of the immersion exposure tool 210. The immersion head is also referred to in the art as a shower head, for example.
The wafer support 218 and the wafer 222 are moved during the patterning of the individual die or regions of die on the wafer 222, e.g., from one side to another, and thus the immersion exposure tool 210 is also referred to in the art as an immersion lithography scanner. The projection lens system 216 is typically quite large and therefore usually remains stationary, for example. The wafer support 218 typically has recessed areas formed therein so that the wafer 222 is recessed when placed on the wafer support 218, for example, not shown.
The fluid 220 is typically provided by a nozzle or by input and output ports within the immersion head (not shown), for example. During an exposure process, the fluid 220 generally continuously flows, to provide temperature stability for the immersion head and other components of the immersion exposure tool 210. In some immersion exposure tools 210, when the lens system 216 is not being used to expose the wafer 222, a closing disk may be used to close the end of the immersion head. The immersion exposure tool 210 may include a fluid handler adapted to provide the fluid 220 which may be coupled to the immersion head by a hose or other fluid-delivering means, for example.
The wafer 222 typically includes a workpiece with a layer of radiation sensitive material 226 such as a photoresist disposed thereon. The pattern from the mask or reticle 214 is imaged onto the photoresist 226 using a beam of radiation or light (e.g., energy) emitted from the lens system 216. The beam is emitted from an energy source 212, such as a light source or an illuminator, and the beam is passed through the lens system 216 to the photoresist 226 of the wafer 222. After exposure of the photoresist, the patterned photoresist is later used as a mask while portions of a material layer of the semiconductor workpiece 224 disposed over the workpiece 224 or potions of the workpiece 224 are etched away or are otherwise altered.
The fluid 220 makes contact with a portion of the top surface of the wafer 222 and the bottom surface of the last element 228 of the projection lens system 216. The immersion head (not shown) includes ports that may comprise an annular ring of ports for supplying the fluid 220 between the wafer 222 and the immersion head. The ports may comprise input and output ports for injecting and removing the fluid 220, for example. In some embodiments, a fluid pad between the projection lens system 216 and the wafer 222 is moved from field to field as the wafer 222 is moved, i.e., the entire wafer 222 is not covered with water: only the portion under the last lens element 228 of the projection lens system 216 is covered in the fluid 222 during an exposure process.
In accordance with a preferred embodiment of the present invention, a novel fluid 220 for use in immersion lithography systems and other applications is disclosed herein. Embodiments of the present invention also include methods of creating the fluid 220, and immersion lithography systems 210 and tools that utilize the fluid 220. Embodiments of the present invention also include methods of fabricating semiconductor devices 222 using an immersion lithography system 210 implementing the fluid 220.
The fullerene 230 comprises a plurality of hexagon faces 234 and pentagon faces 236, for example. Some of the first atoms 232 comprise hexagon faces 234 and others comprise pentagon faces 236, as shown, for example. In the example shown, a C60 is shown, that includes 20 hexagon faces 234 and 12 pentagon faces 236, with each pentagon face 236 being surrounded by hexagon faces 236, for example. The C60 fullerene 230 may be about 7 Angstroms in diameter, for example. Alternatively, the fullerene 230 may comprise other materials and may comprise other sizes, for example.
The second atom 246 preferably comprises a different type of atom than the first atoms 232, for example. The second atom 246 preferably comprises a salt, an oxide, an insulator, a conductor, a semiconductor, a metal, an acid, a polymer, a chloride, a fluoride, or combinations thereof, as examples, although other materials may also be used. The second atom 246 may comprise one or more atoms, and may comprise one or more molecules, for example. The second atoms 246 preferably comprise LiCl, LiBr, Li-Acetate, CdCl2, KCl, KBr, K-Acetate, KS2O3, HgCl2, LaCl3, NaCl, NaBr, Na-Acetate, NaS2O3, NaSCN, MgCl2, MnCl2, SiCl4, TiNO3, RbNO3, RbBr, Rb-Acetate, SmCl3, KI, TbCl3, LuCl3, PbCl2, TlF, Ba(SCN)2, NbCl5, CeCl3, NdCl3, EuCl3, Gd(NO3)3, HOCl3, TaCl5, GdCl3, TlI, RbCl3, RhCl3, CsCl, CsBr, Cs-Acetate, NH4C1, NH4Br, NH4-Acetate, NH4—S2O3, NH4—SCN, NH4—SO4, NH4—S2O4, NH4—H2PO4, TMA-Cl, TMA-BR, TMA-Acetate, PrCl3, Al2O3, HFO2, Sio2, BaF2, CaF2, LaF2, AlPO, S, O C, F3, H, Na, Al, Si, Ca, Sr, Si3N4, SiC, or combinations thereof, as examples, although other materials may also be used.
Preferably, the second atoms 246 are adapted to alter a property of the fluid being manufactured, e.g., fluid 220 shown in
The second atom 246 may be formed in the interior 238 of the fullerenes 230 by introducing gases of the second atom 246 to the fullerenes 230 of the first atoms 232, for example. The fullerenes 230 may be formed in the presence of the gas of the second atom 246, forming the second atoms 246 in the fullerenes 230, for example.
In some embodiments of the present invention, before the fullerenes 260 containing the second atom 246 in the interior 238 thereof are disposed in a liquid, preferably, the fullerenes 260 are combined with a surfactant 262. The surfactant 262 prevents the fullerene 260 cages from grouping together, for example.
The surfactant 262 preferably comprises an anion or a cation. For example, the surfactant 262 may comprise an anionic surfactant, such as sodium dodecyl sulfate, sodium decyl sulfate, or sodium tetradecyl sulfate. The surfactant 262 may comprise a cationic surfactant, such as cetyl trimethyl ammonium chloride or cetyl trimethyl ammonium bromide. The surfactant 262 may alternatively comprise other materials, for example.
In some embodiments, the liquid 266 may comprise a solvent, for example. The solvent preferably comprises a solvent in the aromatic family, in one embodiment. The solvent may comprise toluene, xylene, hexane, tetahydrofuran (THF), acetonitrile (ACN), or octanol, as examples. The liquid may also include a cosolvent-water systems where appropriate for the type of solvent, or mixtures of a solvent and water, such as methanol-water, ethanol-water, tetrahydrofuran-water, acetonitrile-water, or octanol-water, as examples. The liquid may alternatively comprise other solvents.
Advantageously, the at least one second atom 246 alters a property of the liquid 220, such as by increasing the index of refraction of the liquid 220, and the fullerene cage 230 comprising the first atoms 232 prevents the at least one second atom 246 from deleteriously affecting a material exposed to the fluid 220, e.g., under intensive DUV light exposure, such as the layer of photoresist 226 formed on the workpiece 224 and/or the projection lens system 216 optics (see
In some embodiments, for example, the second atoms 246 are adapted to provide matching of the index of refraction nfluid of the fluid 220 with the index of refraction of the projection lens system 216, e.g., the index of refraction nglass of the last element 228 of the projection lens system 216, and also with the index of refraction nresist of the layer of photoresist 226, as shown in
Embodiments of the present invention include semiconductor devices 222 manufactured using the novel fluids 220 described herein in an immersion lithography system 210, and methods of fabricating semiconductor devices 222. For example, referring again to
To pattern a material layer of the workpiece 224 or the workpiece 224, energy such as light is directed from the last lens element 228 through the fluid 220 and towards the layer of radiation sensitive material 226 disposed on the workpiece 224, e.g., in the region of the workpiece 224 disposed immediately beneath the last lens element 228. The energy has preferably been passed through the lithography mask 214 comprising the desired pattern for the material layer or layers to be patterned on the workpiece 224, for example. The layer of radiation sensitive material 226 is then developed, and the layer of radiation sensitive material 226 is used as a mask while the material layer or layers of the workpiece 224 to be patterned are etched away, for example.
Preferably, a workpiece 222 is affected with the projection lens system 210 with the novel fluid 220 disposed between the projection lens system 216 and the layer of photoresist 226 of the semiconductor device 222. For example, affecting the workpiece using the lithography mask comprises patterning the layer of photosensitive material 226 using the lithography mask 214 and the projection lens system 216. Affecting the workpiece 224 may comprise altering the material layer of the workpiece 224 through the patterned layer of photosensitive material 226. For example, altering the material layer of the workpiece 224 may comprise etching the material layer, implanting the material layer with a substance, or depositing another material layer over the material layer.
In one embodiment, a method of lithography for semiconductor devices 222 includes providing an immersion exposure tool 210 having a wafer support 218, a projection lens system 216, an immersion head (e.g., proximate the last element 228 of the lens system 216, not shown) adapted to dispose a fluid 220 between the projection lens system 216 and the wafer support 218, and an energy source 212 proximate the projection lens system 216. A workpiece 224 is provided having a radiation sensitive material 226 disposed thereon. The workpiece 224 is positioned on the wafer support 218, and a novel fluid 220 described herein is disposed between the workpiece 224 and the projection lens system 216. The fluid 220 includes a liquid 266 (see
Advantages of preferred embodiments of the present invention include providing novel fluids 220 for immersion lithography systems 210 and other applications. The fluids 220 prevent damage to a semiconductor workpiece 222, to portions of the immersion lithography system, and other materials that come into contact with the fluid 220, yet allow for the refractive index of the fluid or other properties of the fluid 220 to be adjusted or tuned.
The novel fluids 220 and methods of forming thereof are useful in other applications where certain properties of a fluid 220 are required, yet changing the fluid 220 by adding a substance cannot be achieved because the fluid 220 would be created that would be damaging or that would cause an undesired effect. Fullerenes 230 may be implanted or embedded with the property-altering substance 246a and/or 246b, and the fullerene structures 230 prevent the property-altering substance, e.g., the second atoms 246a and/or third atoms 246b, from deleteriously affecting materials that the fluid 220 comes into contact with.
Advantageously, the fullerenes 230 may comprise C60, which are sufficiently small so that Mie scattering does not present a problem. One second atom 246a or third atom 246b may be disposed inside the fullerenes 230, or alternatively, larger fullerenes 230 may be used so that two or more atoms 246a and/or 246b, or alternatively, small molecules, may be disposed inside the fullerenes, 230, for example.
Furthermore, advantageously, the chemistry of the second atom 246 is separated using physics, by caging the second atom 246 within the fullerenes 230. Therefore, a desired physical property of the fluid 220 is achieved while avoiding deleterious chemical effects from the presence of the second atom 246.
Although embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For example, it will be readily understood by those skilled in the art that many of the features, functions, processes, and materials described herein may be varied while remaining within the scope of the present invention. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
