# Patent

## Title
Crosslinkable graft polymer non-preferentially wetted by polystyrene and polyethylene oxide

## Abstract

Methods for fabricating a random graft PS-r-PEO copolymer and its use as a neutral wetting layer in the fabrication of sublithographic, nanoscale arrays of elements including openings and linear microchannels utilizing self-assembling block copolymers, and films and devices formed from these methods are provided. In some embodiments, the films can be used as a template or mask to etch openings in an underlying material layer.

## Background
TECHNICAL FIELD
Embodiments of the invention relate to methods of fabricating nanoscale arrays of micro-vias, microchannels and microstructures by use of thin films of self-assembling block copolymers, and devices resulting from those methods, including methods and materials for producing neutral wetting surfaces for use in such methods.
BACKGROUND OF THE INVENTION
As the development of nanoscale mechanical, electrical, chemical and biological devices and systems increases, new processes and materials are needed to fabricate nanoscale devices and components. Conventional optical lithographic processing methods are not able to accommodate fabrication of structures and features much below the 100 nm level. The use of self assembling diblock copolymers presents another route to patterning at nanometer dimensions. Diblock copolymer films spontaneously assemble into periodic structures by microphase separation of the constituent polymer blocks after annealing, for example by thermal annealing above the glass transition temperature of the polymer or by solvent annealing, forming ordered domains at nanometer-scale dimensions. Following self assembly, one block of the copolymer can be selectively removed and the remaining patterned film used as an etch mask for patterning nanosized features into the underlying substrate. Since the domain sizes and periods (Lo) involved in this method are determined by the chain length of a block copolymer (MW), resolution can exceed other techniques such as conventional photolithography, while the cost of the technique is far less than electron beam lithography or EUV photolithography, which have comparable resolution.
The film morphology, including the size and shape of the microphase-separated domains, can be controlled by the molecular weight and volume fraction of the AB blocks of a diblock copolymer to produce lamellar, cylindrical, or spherical morphologies, among others. Another important factor in the film morphology is the affinity between the diblock copolymer and the underlying surface.
Preferential wetting interfaces tend to direct the morphology of the self-assembled film. Most surfaces have some degree of preferential wetting causing the copolymer material to assemble into lines that are parallel to the surface. However, in some applications, it is desirable to produce structures that are perpendicular to a surface, requiring a neutral wetting surface (equal affinity for both blocks (AB) of the block copolymer to allow both blocks of the copolymer material to wet the surface, and using entropic forces to drive both blocks to wet the neutral wetting surface. However, neutral wetting surfaces are relatively uncommon and often require that the surface of the material layer to be modified to provide a neutral wetting interface.
Neutral wetting surfaces on silicon oxide (SiOx) or silicon nitride (SiN) have been provided by applying a neutral wetting polymer, which is fabricated by adjusting the amount of one monomer to the other, and is wetting to both blocks of a self-assembling (SA) block copolymer. For example, in the use of a diblock copolymer composed of PS-b-PMMA, a PS-r-PMMA random copolymer (60% PS) (which exhibits non-preferential or neutral wetting toward both PS and PMMA blocks and includes a cross-linkable element) has been cast as a film onto SiOx and cross-linked using UV radiation or thermal processing to form a neutral-wetting mat that loses solubility and adheres to the surface but is not chemically-bound or grafted to the surface.
Additional issues arise in the use of cylindrical-phase PS-b-PMMA block copolymers to form self-assembled films whereby, under a typical anneal (at about 180-190° C.), both PS and PMMA blocks wet the air-interface to produce lines of air-exposed half-cylinders that do not completely extend to the underlying substrate. Upon removal of the half-cylinder polymer block (e.g., PMMA) to form an etch mask or template, the underlying polymer matrix (e.g., of PS) must then be etched to expose the underlying substrate to be etched.
A prospective alternate material for forming a self-assembling polymer film is poly(styrene-b-ethylene oxide) (PS-b-PEO) diblock copolymers, which have been shown to be less defect tolerant (i.e., form larger crystalline grains) than PS-b-PMMA with better ordering. Cylinder-forming PS-b-PEO diblock copolymer materials have been used to produce perpendicular oriented and highly ordered, hexagonally close-pitched cylinders that orient perpendicular to surfaces via solvent annealing of the copolymer layer. Solvent annealing caused initial domain segregation at the film-air interface with both polymer blocks wetting the air interface, which was driven downward toward the underlying substrate as the solvent evaporated and the film dried.
However, because the substrate interface is somewhat preferential wetting, a layer of the minority polymer block is formed over the substrate, which prevents the polymer domains from completely extending from the film-air interface to the substrate itself. In addition, the use of solvent annealing to form either perpendicular cylinders or parallel lamella produces the same structure universally over the substrate, which is undesirable in many applications.
It would be useful to provide a method and system for forming self-assembling polymer films such as PS-b-PEO that overcome existing problems.



BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention are described below with reference to the following accompanying drawings, which are for illustrative purposes only. Throughout the following views, the reference numerals will be used in the drawings, and the same reference numerals will be used throughout the several views and in the description to indicate same or like parts.
FIG. 1 is a diagram illustrating the reaction for preparing a random copolymer according to an embodiment of the present disclosure.
FIG. 2 illustrates a diagrammatic top plan view of a portion of a substrate at a preliminary processing stage according to an embodiment of the present disclosure, showing the substrate with trenches. FIG. 2A is an elevational, cross-sectional view of the substrate depicted in FIG. 2 taken along lines 2A-2A. FIG. 2B is an elevational, cross-sectional view of the substrate depicted in FIG. 2 in another embodiment, taken along lines 2B-2B.
FIGS. 3-5 illustrate diagrammatic top plan views of the substrate of FIG. 2 at various stages of the fabrication of a self-assembled block copolymer film according to an embodiment of the present disclosure. FIGS. 3A-5A illustrate elevational, cross-sectional views of embodiments of a portion of the substrate depicted in FIGS. 3-5 taken, respectively, along lines 3A-3A to lines 5A-5A. FIG. 5B is a view of a portion of FIG. 5A in a subsequent processing step.
FIG. 6 illustrates a diagrammatic top plan view of a portion of a substrate at a processing stage according to another embodiment of the present disclosure in the fabrication of a self-assembled block copolymer film utilizing a cylindrical-phase block copolymer. FIG. 6A is an elevational, cross-sectional view of the substrate depicted in FIG. 6 taken along lines 6A-6A.
FIGS. 7 and 8 illustrate top plan views of the substrate of FIG. 6 at a subsequent processing stage according to embodiments of the disclosure. FIGS. 7A and 8A illustrate elevational, cross-sectional views of the substrate depicted in FIGS. 7 and 8 taken, respectively, along lines 7A-7A and 8A-8A. FIGS. 7B and 8B are views of FIGS. 7A and 8A, respectively, in a subsequent processing stage.
FIG. 9 illustrates a diagrammatic top plan view of a portion of a substrate at a processing stage according to another embodiment of the present disclosure in the fabrication of a self-assembled block copolymer film utilizing a cylindrical-phase block copolymer. FIG. 9A is an elevational, cross-sectional view of the substrate depicted in FIG. 9 taken along lines 9A-9A.
FIGS. 10 and 11 illustrate top plan views of the substrate of FIG. 6 at a subsequent processing stage according to embodiments of the disclosure. FIGS. 10A and 11A illustrate elevational, cross-sectional views of the substrate depicted in FIGS. 10 and 11 taken, respectively, along lines 10A-10A and 11A-11A. FIGS. 10B and 11B are views of FIGS. 10A and 11A, respectively, in a subsequent processing stage.
FIG. 12 illustrates a diagrammatic top plan view of a portion of a substrate at a preliminary processing stage according to another embodiment of the disclosure, showing patterning of the neutral wetting layer. FIG. 12A is an elevational, cross-sectional view of the substrate depicted in FIG. 12 taken along lines 12A-12A.
FIGS. 13-18 illustrate diagrammatic top plan views of the substrate of FIG. 12 at subsequent processing stages. FIGS. 13A-18A illustrate elevational, cross-sectional views of embodiments of a portion of the substrate depicted in FIGS. 13-18 taken, respectively, along lines 13A-13A to lines 18A-18A. FIGS. 15B, 17B, and 18B are elevational, cross-sectional views of the substrate of FIGS. 15, 17 and 18 taken along lines 15B-15B, 17B-17B and 18B-18B, respectively.
FIGS. 19A-19B are cross-sectional views of the substrate depicted in FIGS. 18A-18B, at a subsequent processing step according to an embodiment of the invention. FIG. 20 is a top plan view of the substrate of FIGS. 19A-19B in a subsequent processing step. FIGS. 20A-20B are cross-sectional views of the substrate illustrated in FIG. 20, taken along lines 20A-20A and 20B-20B, respectively.
FIG. 21 is a top plan view of the substrate of FIG. 18 at subsequent processing stage according to another embodiment of the invention. FIGS. 21A-21B are cross-sectional views of the substrate shown in FIG. 21, taken along lines 21A-21A and 21B-21B, respectively. FIG. 22 is a top plan view of the substrate of FIG. 21 in a subsequent processing step. FIGS. 22A-22B are cross-sectional views of the substrate illustrated in FIG. 22, taken along lines 22A-22A and 22B-22B, respectively.



DETAILED DESCRIPTION OF THE INVENTION
The following description with reference to the drawings provides illustrative examples of devices and methods according to embodiments of the invention. Such description is for illustrative purposes only and not for purposes of limiting the same.
In the context of the current application, the term “semiconductor substrate” or “semiconductive substrate” or “semiconductive wafer fragment” or “wafer fragment” or “wafer” will be understood to mean any construction comprising semiconductor material, including but not limited to bulk semiconductive materials such as a semiconductor wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure including, but not limited to, the semiconductive substrates, wafer fragments or wafers described above.
“Lo” is the inherent pitch (bulk period or repeat unit) of structures that self assemble upon annealing from a self-assembling (SA) block copolymer or a blend of a block copolymer with one or more of its constituent homopolymers.
Steps in a method for synthesizing a crosslinkable graft polymer that is neutrally wetting to polystyrene (PS) and poly(ethylene oxide) (PEO) according to an embodiment of the invention are illustrated in FIG. 1. The resulting random copolymer can be used, for example, to form a cross-linked, insoluble polymer mat that is neutral wetting to a polystyrene/poly(ethylene oxide) block copolymer (PS-b-PEO) for fabricating polymer films composed of ordered domains of the self-assembled polymer blocks.
The random graft copolymer of the invention can be prepared by first polymerizing para-chloromethylstyrene and styrene monomers together to form a random copolymer. In some embodiments, p-chloromethylstyrene comprises the majority (y>50%) of the monomers by weight. In other embodiments, no polystyrene is employed and only p-chloromethylstyrene monomer is used (y=100%), wherein the resultant polymer is a p-chloromethylstyrene homopolymer.
The random copolymer of the invention can be produced, for example, by a free-radical polymerization reaction. Free-radical polymerization is well-known in the art and generally has three stages: initiation, propagation, and termination. Initiation is the formation of an active center (free radical) and generally requires the use of a free-radical initiator. A common type of free-radical initiator is a molecule such as a peroxide (e.g., benzoyl peroxide) or 2,2′-azo-bis-isobutyrylnitrile (AIBN), which decomposes into two or more separate free radicals. The free radical reacts with the vinyl group of a monomer to form a new molecule with the active center on the β-carbon of the former vinyl group. The active center of the new molecule can then react with a series of other monomer molecules in the propagation stage to form a growing polymer chain. The polymerization terminates when two active centers react with each other to form a polymer inactivated to further monomer addition.
Other reactions can, and usually do, occur during the propagation stage. Chief among these reactions are branching, which occurs when the free radical reacts with the middle of a polymer chain to form a side chain, and scission, which occurs when a polymer chain breaks into two or more separate chains. As a result of the random nature of the termination reactions, as well as the branching and scission reactions, the polymer chains formed by a free radical reaction can vary widely in length and weight. This variation of polymer chains is characterized by a broad molecular weight distribution (MWD), also known as polydispersity, which is defined as the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), or Mw/Mn. Frequently, free-radical polymerization produces polymers with an MWD of 3 or more.
In some embodiments, the random copolymer of the invention can also be produced by a controlled/“living” polymerization. In contrast to free-radical polymerization, living polymers tend to have a low polydispersity (MWD). Living polymers are produced by a reversible polymerization reaction that has no termination step. Instead, the polymer and the monomer reach an equilibrium between monomer addition and monomer deletion reactions. Living polymerization processes include, for example, reversible addition fragmentation chain transfer (RAFT) polymerization processes, nitroxide mediated polymerization (NMP) processes, and atom transfer radical polymerization (ATRP) processes.
A RAFT process is a degenerative chain transfer process based on free-radical polymerization. RAFT agents frequently contain thiocarbonyl-thio groups, The polymeric radicals and other radicals react with the C═S bond leading to the formation of transient, stabilized radical intermediates. An NMP process, also known as stable-free radical mediated polymerization (SFRP), is another free radical polymerization using a 2,2,6,6-tetramethylpiperidinyloxy (TEMPO) derivative as the initiator, as further described below. An ATRP process is based on the use of radical polymerization to convert monomers to polymers using an initiator (e.g., an alkyl halide), a catalyst (e.g., a transition metal such as iron or copper complexed by one or more ligands) and a deactivator.
FIG. 1 illustrates an embodiment of a method for producing the random copolymer using a “living” polymer reaction. As depicted, initially a reaction mixture can be formed by combining the monomers para-chloromethylstyrene and styrene (when present) with a polymerization initiator. In some embodiments, the initiator is 1-[TEMPO]ethyl benzene, which will reversibly form TEMPO and an ethyl benzene radical upon heating. The ethyl benzene radical will react with the monomers to sequentially insert the monomers. The polymer chain (I) is reversibly terminated with a TEMPO group at its reactive end when in its non-reactive state. Although not shown, the TEMPO-terminated copolymer (I) is in equilibrium with free TEMPO and non-TEMPO-terminated copolymer.
The copolymer (I) can be prepared using a solution polymerization process or bulk polymerization conditions. In a solution polymerization, the monomers and initiator can be dissolved in a suitable solvent such as toluene. Examples of other potential solvents include, without limitation, xylene, acetylene, propylene glycol, methyl ether, methyl acetate and the like. In a bulk polymerization, the monomers themselves are the reaction solvent, and the reaction can be carried out at atmospheric pressure and moderate temperatures, e.g., about 70° C. Higher or lower pressures and temperatures can be used; such reaction conditions are considered within the scope of this invention.
The copolymer (I) itself precipitates out of the solution by adding the reaction solution to a “poor” solvent such as methanol, allowing easy recovery of the polymer (I). If desired, the recovered copolymer (I) can be washed and dried. The copolymer (I) can then be re-dissolved prior to the grafting reaction.
The resulting copolymer (I) can be reacted with one or more oligomers or polymers of poly(ethylene oxide) (PEO) as shown in FIG. 1, where R is a hydrogen or alkyl group. In some embodiments, the PEO is prepared such that only one end of the poly(ethylene oxide) is nucleophilic. An example of a suitable reagent is monomethoxy poly(ethylene glycol) (MPEG) made reactive by deprotonation of the lone hydroxyl group.
In FIG. 1, the subscripts m and y refer to the number fraction of reactants styrene and p-chloromethylstyrene, respectively, based on the total number of all such reactants that are incorporated into the polymer, i.e., where m+y=100%. The subscript z is the number fraction of the total number of mers that are grafted with PEO. The amount Z of PEO oligomers or polymer chains used in the grafting reaction is selected such that the resulting material can be cast to provide a surface that is neutral, or non-preferential, wetting to both polystyrene (PS) and to PEO, e.g., both PS and PEO have identical interfacial energies on a film of the polymer material. The hydroxyl group of the ethylene oxide oligomer/polymer reacts to displace the chlorine atom from the chloromethyl group of the polymer with units derived from p-chloromethylstyrene to form a graft polymer (II). In particular, the amount of PEO oligomers/polymers chains is selected to be less than the number of chlorine atoms available on the chloromethyl moieties. As such, some chlorine atoms will remain on the graft polymer (II) for reactions to attach the cross-linking functional groups.
The grafting reaction is conveniently carried out in solution. Organic solvents, such as toluene, are appropriate solvents for this grafting reaction. The grafting reaction can be carried out at atmospheric pressure and moderate temperatures, e.g. about 70° C. Higher or lower pressures and temperatures can be used and such reaction conditions are considered within the scope of this invention.
The graft copolymer (II) is then reacted to attach azide cross-linking groups to the polymer chain to form an azide-functionalized polymer (III). For example, the grafted copolymer can be reacted with sodium azide (NaN3), as shown in FIG. 1, which reacts to displace the remaining chlorine atom from the chloromethyl group of the polymer with units derived from p-chloromethylstyrene. Suitable azide having the characteristic formula R(N3)x can be used in place of the sodium azide, where x>zero (0) and R is a metal atom other than sodium, a hydrogen atom or an ammonium radical. A stoichiometric excess of the azide group (e.g., sodium azide) can be used to completely displace all the chlorine atoms still present on the polymer chains and maximize the number of cross-linking moieties. Reaction conditions for attaching the azide groups can be similar to the previous reaction conditions for polymerization and/or for grafting.
The resulting azide-functionalized graft copolymer (III) can be purified, if desired, by a conventional method. One such method is to precipitate the polymer (III) from solution, e.g., by adding to a “poor” solvent such as methanol, wash the precipitate, and dry the precipitate under low temperatures (e.g., less than or equal to about 100° C.).
The azidomethyl groups serve as crosslinking moieties, which can be activated either thermally (by heating) or photolytically (by exposure to ultraviolet (UV) light) to initiate crosslinking reactions of the azido functional groups and form crosslinked films of poly(styrene-g-ethylene oxide-r-para-azidomethylstyrene) (PS-g-PEO-g-p-azidomethylstyrene, or PS-r-PEO). The random polymers are designed to interact with both blocks of a self-assembling PEO-b-PS diblock copolymer. The molecular weight (MW) of the random polymers is generally at about 30,000-50,000. An example of a random copolymer can comprise about 20-80% PEO, about 80-20% PS (including grafted segments) and about 1-5% of azidomethylstyrene. Thin films of the resulting polymers can be cast onto a substrate and fixed in place by thermally or photolytically crosslinking the polymers to form a mat that is neutral wetting to PS and PEO and insoluble due to the crosslinking. The ability to photolytically crosslink the random polymer allows for patterning of the polymer layer and registration of a PS-b-PEO film that is cast and annealed onto the substrate bearing the patterned mat.
Films of PS-b-PEO can be coated on a substrate bearing a layer (mat) composed of the crosslinked, neutral wetting random PS-r-PEO polymer of the invention and, upon annealing, the PS-b-PEO film will self-assemble into morphologies that are oriented in response to the neutral wetting properties of the crosslinked random polymer mat. For example, annealing a cylinder-phase PS-b-PEO film will orient the cylinders perpendicular to the substrate bearing the crosslinked polymer mat.
Processing conditions of embodiments of the invention use a graphoepitaxy technique utilizing the sidewalls of trenches as constraints to induce orientation and registration of a film of a self-assembling diblock copolymer to form an ordered array pattern registered to the trench sidewalls. In some embodiments, selective removal of one of the polymer domains can be performed to produce a template that can be used as a mask to etch features in an underlying substrate.
Steps in a method for using the random graft PS-r-PEO copolymer of the invention for fabricating a thin film from a self assembling (SA) PS-b-PEO block copolymer that defines nanometer-scale linear array patterns according to embodiments of the invention are illustrated in FIGS. 2-5.
In the described embodiment, a lamellar-phase PS-b-PEO block copolymer film is deposited onto a layer of the described random graft copolymer which provides a surface that is neutral wetting to both PS and PEO (exhibits non-preferential wetting toward PS and PEO). Upon annealing, the block copolymer film self-assembles to form a registered and lamellar array of alternating polymer-rich blocks (PS and PEO) that extend the length of the trench and are oriented perpendicular to the trench floor and parallel to the sidewalls.
To produce a lamellar polymer film within the trenches using a lamellar-phase PS-b-PEO block copolymer, the surface of the sidewalls and edges of the trenches are preferential wetting by one block of the copolymer and the trench floors are neutral wetting (equal affinity for both blocks of the copolymer) to allow both blocks of the copolymer material to wet the floor of the trench. Entropic forces drive the wetting of a neutral wetting surface by both blocks, resulting in the formation of a layer of perpendicular lamellae across the width of each trench.
In an embodiment shown in FIGS. 2-2A, a layer 12 of the PS-r-PEO random copolymer of the invention has been formed on a substrate 10 prior to forming the overlying material layer 14. The substrate 10 can be composed, for example, of silicon, silicon oxide, silicon nitride, silicon oxynitride, silicon oxycarbide, among other materials.
A solution of the azidomethylstyrene-functionalized random copolymer (PS-r-PEO) in a solvent such as toluene, xylene, chloroform, and benzene, among others, in which both monomers are soluble (e.g., about 1% w/v solution) can be applied as a layer 12 onto the substrate 10 to a thickness of about 1-100 nm, for example, by spin-coating. The random copolymer is cast to a minimum thickness such that the block PS-PEO cast above the random copolymer layer will entangle without contacting the underlying substrate. The PS-r-PEO random copolymer can then be UV crosslinked (e.g., 1-5 MW/cm^2 exposure for about 15 seconds to about 30 minutes) or thermally crosslinked (e.g., at about 170° C. for about 4 hours), whereupon the copolymer forms a crosslinked mat on the surface of the substrate 10.
A material layer 14 can then be formed over the crosslinked PS-r-PEO random copolymer layer 12 and etched to form trenches 16 to expose the layer 12 as a neutral wetting surface on the floor or bottom surface 18 of the trench. The trenches 16 are structured with opposing sidewalls 22, opposing ends 24, a width (wt), a length (lt) and a depth (Dt). Adjacent trenches are separated by a spacer (or crest) 20. The trenches can be formed using a lithographic tool having an exposure system capable of patterning at the scale of Lo (10-100 nm). Such exposure systems include, for example, extreme ultraviolet (EUV) lithography, proximity X-rays and electron beam (e-beam) lithography, as known and used in the art. Conventional photolithography can attain (at smallest) about 58 nm features.
Referring now to FIG. 2B, in another embodiment, the material layer 14′ can be formed on the substrate 10′ and etched to form the trenches 16′, and the neutral wetting random copolymer 12′ can then applied to the trench floors 18′. For example, the random copolymer can be cast or spin coated as a blanket film over the material layer 14′ and into the trenches, and then photo-exposed through a mask or reticle (not shown) to selectively crosslink the random copolymer only within the trenches to form the neutral wetting layer 12′. Non-crosslinked random copolymer material outside the trenches (e.g., on the spacers 20′) can be subsequently removed.
A self-assembling (SA) lamellar-phase diblock copolymer material is then deposited into the trenches and processed such that the copolymer material will self-assemble to form a lamellar film composed of perpendicular-oriented, alternating polymer-rich blocks across the width of the trench. In the illustrated example, the diblock copolymer is a poly(styrene-block-ethylene oxide) (PS-b-PEO) block copolymer.
The trench sidewalls, edges and floors influence the self-assembly of the polymer blocks and the structuring of the array of nanostructures within the trenches. The trench sidewalls 22 and ends 24 are structured to be preferential wetting by one block of the block copolymer to induce registration of lamellae as the polymer blocks self-assemble. The material layer 14 defining the trench surfaces can be a material that is inherently preferential wetting to one of the blocks, or in other embodiments, a layer of a preferential wetting material can be applied onto the surfaces of the trenches. For example, in the use of a PS-b-PEO block copolymer, in some embodiments, the material layer 14 can be composed of silicon (with native oxide), oxide (e.g., silicon oxide, SiOx) or other inorganic films, for example, which exhibits preferential wetting toward the PEO block to result in the assembly of a thin (e.g., 1⁄4 pitch) interface layer of PEO and alternating PEO and PS lamellae (e.g., 1⁄2 pitch) within each trench in the use of a lamellar-phase block copolymer material.
The boundary conditions of the trench sidewalls in both the x- and y-axis impose a structure wherein each trench contains “n” number of lamellae. Factors in forming a single array or layer of nanostructures within the trenches include the width and depth of the trench, the formulation of the block copolymer to achieve the desired pitch (Lo), and the thickness (t) of the copolymer film.
The trenches 16 are constructed with a width (wt) such that a block copolymer (or blend) will self assemble upon annealing into a single layer of n lamellae spanning the width (wt) of the trench, with the center-to-center distance of adjacent lamellae being at or about Lo. In using a lamellar-phase block copolymer, the width (wt) of the trenches is a multiple of the inherent pitch value (Lo) of the polymer being equal to or about nLo (“n*Lo”), typically ranging from about n*10 to about n*100 nm (with n being the number of features or structures). The application and annealing of a lamellar-phase block copolymer material having an inherent pitch value of Lo in a trench having a width (wt) at or about Lo will result in the formation of a single layer of n lamellae spanning the width and registered to the sidewalls for the length of the trench. In some embodiments, the trench dimension is about 50-500 nm wide (wt) and about 1,000-10,000 μm in length (lt), with a depth (Dt) of about 50-500 nm.
Referring now to FIGS. 3-3A, a layer 26 of a self-assembling lamellar-phase PS-b-PEO diblock copolymer material having an inherent pitch at or about Lo (or a ternary blend of block copolymer and homopolymers blended to have a pitch at or about Lo) is deposited, typically by spin casting (spin-coating) onto the floor 18 of the trenches 16. The PS-b-PEO block copolymer material can be deposited, for example, by spin casting a dilute solution (e.g., about 0.25-2 wt % solution) of the PS-b-PEO copolymer in an organic solvent such as dichloroethane (CH2Cl2), toluene or chloroform, for example.
The thickness (t1) of the PS-b-PEO diblock copolymer layer 26 and at or about the Lo value of the PS-b-PLO copolymer material such that the film layer will self assemble upon annealing to form a single layer of lamellae across the width (wt) of the trench. In some embodiments, the trench depth (Dt) is greater than the film thickness (t1). A typical thickness (t1) of a lamellar-phase PS-b-PEO block copolymer film 26 is about ±20% of the Lo value of the copolymer (e.g., about 10-100 nm) to form alternating polymer-rich lamellar blocks having a width of about 0.5 Lo (e.g., 5-50 nm) within each trench. In the use of a solvent anneal, the film can be much thicker than Lo, e.g., up to about +1000% of the Lo value. The thickness of the film 26 can be measured, for example, by ellipsometry techniques. As shown, a thin film 26 of the block copolymer material can be deposited onto the spacers 20 of the material layer 14; this film will form a monolayer of lamellae in a parallel orientation with no apparent structure from a top-down (etching) perspective.
The volume fractions of the two blocks (AB) of the PS-b-PEO diblock copolymer are generally at a ratio between about 50:50 and 60:40. An example of a lamellae-forming symmetric diblock copolymer is PS-b-PEO with a weight ratio of about 50:50 (PS:PEO) and total molecular weight (Mn) of about 19 kg/mol. Although PS-b-PEO diblock copolymers are used in the illustrative embodiments of this disclosure, triblock or multiblock copolymers can also be used.
The PS-b-PEO block copolymer material can also be formulated as a binary or ternary blend comprising a PS-b-PEO block copolymer and one or more homopolymers (i.e., polystyrene (PS) and polyethylene oxide (PEO) to produce blends that swell the size of the polymer domains and increase the Lo value of the polymer. The volume fraction of the homopolymers can range from 0 to about 40%. An example of a ternary diblock copolymer blend is a PS-b-PEO/PS/PEO blend. The Lo value of the polymer can also be modified by adjusting the molecular weight of the block copolymer, e.g., for lamellae, Lo ̃(MW)2/3.
Referring now to FIGS. 4-4A, the PS-b-PEO block copolymer film 26 is then annealed to cause the polymer blocks to phase separate and self assemble according to the preferential and neutral wetting of the trench surfaces 18, 22, 24 to form a self-assembled polymer film 28.
In some embodiments, the film 26 can be solvent annealed. In a solvent anneal, the film is swollen by exposure to a vapor of a “good” solvent for both blocks and then removal of the vapor. Vapors of a solvent such as benzene, chloroform or a chloroform/octane mixture, for example, can be exposed to the film 26 to slowly swell both blocks (PS, PEO) of the film. The solvent and solvent vapors are then allowed to slowly evaporate to dry the film, resulting in self-assembled lamellar domains oriented perpendicular to the substrate 10. The presence of the neutral wetting PS-r-PEO random block copolymer film 12 over the surface of the substrate 10 on the floors 18 of the trenches allows the self-assembling polymer domains to extend completely from the film-air interface to the substrate surface (trench floors 18).
The PS-PEO copolymer film can also be thermally annealed at the annealing temperature (e.g., about 150-250° C.) in an atmosphere that is saturated (but not supersaturated) with a solvent in which both blocks are soluble. The solvent-saturated vapor maintains a neutral air interface in conjunction with the surface interface with the neutral wetting random copolymer layer 12. The existence of both neutral wetting air and surface interfaces induces the formation of perpendicular features throughout the film by thermal annealing over regions coated with the neutral-wetting random copolymer of the invention.
The constraints provided by the width (wt) of the trenches and the character of the copolymer composition combined with preferential or neutral wetting surfaces within the trenches result, upon annealing, in a single layer of n lamellae across the width (wt) of the trench. The number “n” or pitches of lamellar blocks within a trench is according to the width (wt) of the trench and the molecular weight (MW) of the PS-r-PEO block copolymer. As shown in FIG. 4A, lamellar-phase block copolymer material will, upon annealing, self assemble into a film 28 composed of perpendicular-oriented, alternating polymer-rich blocks 30, 32 spanning the width (wt) of the trench 16 at an average pitch value at or about Lo. For example, depositing and annealing an about 50:50 PS:PEO block copolymer film (e.g., Mn=19 kg/mol; Lo=19 nm) in an about 250 nm wide trench will subdivide the trench into about 12 lamellar pitches. The resulting morphology of the annealed film 28 (i.e., perpendicular orientation of lamellae) can be examined, for example, using atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM).
Optionally, the annealed and ordered film 28 can then be treated to crosslink the polymer segments to fix and enhance the strength of the self-assembled polymer blocks 30, 32 within the trench 16 (e.g., to crosslink the PS segments). The polymers can be structured to inherently crosslink (e.g., upon exposure to ultraviolet (UV) radiation, including deep ultraviolet (DUV) radiation), or one or both of the polymer blocks of the copolymer material can be formulated to contain a crosslinking agent. Optionally, the material 26 outside the trench (e.g., on spacer 20) can then be removed as shown. If the material layer 12 is a hard mask (e.g., not etched) relative to etching of substrate to at a later step, the removal of material 26 outside the trench is not necessary.
For example, in one embodiment, the trench regions can be selectively exposed through a reticle (not shown) to crosslink only the self-assembled film 28 within the trench 16, and a wash can then be applied with an appropriate solvent (e.g., toluene) to remove the non-crosslinked portions of the film 28 (e.g., material 26 on the spacer 20) leaving the registered self-assembled film within the trench and exposing the surface of material layer 14 above/outside the trench (e.g., the spacer 20). In another embodiment, the annealed film 28 can be crosslinked globally, a photoresist layer can be applied to pattern and expose the areas of the film outside the trench regions (e.g., over the spacers 20), and the exposed portions of the film can be removed, for example by an oxygen (O2) plasma treatment. In other embodiments, the spacers 20 are narrow in width, for example, a width (ws) of one of the copolymer domains (e.g., about Lo) such that the material 26 on the spacers is minimal and no removal is required.
Referring now to FIGS. 5-5A, one of the block components can be selectively removed to produce a thin film 34 that can be used, for example, as a lithographic template or mask to pattern the underlying substrate 10 in a semiconductor processing to define regular patterns in the nanometer size range (i.e., about 10-100 nm).
For example, selective removal of PEO domains 30 will result in openings (slits) 36 separated by vertically oriented walls composed of PS domains 32, and the neutral wetting PS-r-PEO random copolymer layer 12 exposed on the trench floor 18. Removal of the water-soluble PEO phase domains can be performed, for example, by exposure of the film to aqueous hydroiodic acid or exposure to water alone, which will draw PEO to the surface without cleaving the bonds to the PS domains. In embodiments in which the PS-b-PEO block copolymer includes an acid-cleavable linker (e.g., trityl alcohol linker) positioned between the polymer blocks, exposure of the film to an aqueous acid (e.g., trifluoroacetic acid) or to an acid vapor can be performed to cleave the polymer into PEO and PS fragments (S. Yurt et al., “Scission of Diblock Copolymers into Their Constituent Blocks,” Mcacromolecules 2006, 39, 1670-1672). Rinsing with water can then be performed to remove the cleaved PEO domains. In other embodiments, exposure to water to draw the PEO domains to the surface followed by a brief oxygen (O2) plasma etch can also be performed to remove the PEO domains on the surface of the film to form voids and reveal underlying PS domains.
In embodiments in which the PS phase domains 32 are removed, the openings (slits) are separated by walls composed of the PEO domains 30.
In some embodiments, the resulting film 34 has a corrugated surface that defines a linear pattern of fine, nanometer-scale, parallel slits (openings) 36 about 5-50 nm wide and several microns in length (e.g., about 10-4000 μm), the individual slits separated by walls (e.g., of block 32) about 5-50 nm wide, providing an aspect ratio ranging from about 1:2 to about 1:20. For example, removal of the PEO domains affords a PS mask of sublithographic dimensions, for example, a pitch of about 35 nm (17.5 nm PS domain). A smaller pitch can be dialed in by using lower molecular weight diblock copolymers.
The films can be used, for example, as a lithographic template or etch mask to pattern (arrows ↓↓) the underlying substrate 10, for example, by a non-selective RIE etching process, to delineate a series of channels or grooves 38, shown in phantom in FIG. 5A, extending to an active area or element 40 in the substrate or an underlayer. In some embodiments, the channels 38 can then be filled with a material 42 as illustrated in FIG. 5B, for example, a conductive material (e.g., metal) to form nanowire channel arrays for transistor channels, semiconductor capacitors, and other structures, or a dielectric material to separate active areas (e.g., substrate 10). Further processing can then be performed as desired.
The films provide linear arrays having long range ordering and registration for a wide field of coverage for templating a substrate. The films are useful as etch masks for producing close pitched nanoscale channel and grooves that are several microns in length, for producing features such as floating gates for NAND flash with nanoscale dimensions. By comparison, photolithography techniques are unable to produce channels much below 60 nm wide without high expense. Resolution can exceed other techniques such as conventional photolithography, while fabrication costs utilizing methods of the disclosure are far less than electron beam (E-beam) or EUV photolithographies which have comparable resolution.
A method according to another embodiment of the invention for forming thin films of a cylindrical-phase, self-assembling PS-b-PEO block copolymer that define an array of perpendicularly-oriented cylinders in a polymer matrix is illustrated with reference to FIGS. 6-8. The described embodiment utilizes topographical features, the sidewalls and ends of trenches, as constraints to induce orientation and registration of cylindrical copolymer domains to achieve an array of hexagonal-packed and perpendicularly-oriented cylinders within a polymer matrix registered to the trench sidewalls.
As described with reference to FIGS. 2-2A, a trench 16′′ can be etched in a material layer 14′′ to expose a neutral wetting surface 12′′ (composed of the PS-r-PEO random copolymer of the invention on an underlying substrate 10′′. The width (wt) of the trench 16′′ is at or about Lo*cos(π/6) or Lo*0.866, which defines the number of rows of cylinders, and the trench length (lt) is at or about mLo, which defines the number of cylinders per row. The ends 24′′ of the trenches are angled to the sidewalls 22 as shown in FIG. 6, for example, at an about 60° angle, and in some embodiments can be slightly rounded.
The trenches are also structured such that the trench floor 18′′ is neutral wetting to both blocks of the PS-b-PEO block copolymer material, and the sidewalls 22′′ and ends 24′′ are preferential wetting by the minority block of the copolymer. Entropic forces drive the wetting of a neutral-wetting surface by both blocks, resulting in a perpendicular orientation of the self-assembled cylinders. As previously described, a neutral wetting layer 12′′ can be provided, for example, by applying the PS-r-PEO random copolymer of the invention onto the surface of the substrate 10′′ (e.g., spin-coating) and crosslinking the copolymer layer before forming the material layer 14′′ and the trenches 16′′ to expose the neutral wetting layer 12′′ forming the trench floors 18′′.
As previously described, sidewalls 22′′ and ends 24′′ that are preferential wetting toward the PEO block of a PS-b-PEO diblock copolymer can be provided by a material layer 14′′ composed, for example, of oxide. Upon annealing, the PEO block of the PS-b-PEO copolymer layer will segregate to the sidewalls and ends of the trench to form a wetting layer (30a′′ in FIGS. 6-6A).
With reference to FIGS. 3-3A, a layer 26′′ of a cylindrical-phase PS-b-PEO diblock copolymer material having an inherent pitch at or about Lo (or blend with homopolymers) is deposited onto the neutral wetting PS-r-PEO random copolymer layer 12′′ on the floor 18′′ of the trench 16′′ to a thickness (t1) of less than or about equal to the Lo value of the copolymer material to up to about 1.5×Lo (or larger if annealed by solvent annealing) such that the copolymer film layer will self assemble upon annealing to form a hexagonal array of perpendicular cylindrical domains having a diameter of about 0.5 Lo (e.g., about 20 nm) in the middle of a polymer matrix within each trench (e.g., with the adjacent cylindrical domains having a center-to-center distance of at or about Lo (e.g., about 35-40 nm).
The PS-b-PEO block copolymer film 26′′ is then annealed, resulting in a self-assembled lamellar film 28′′ as shown in FIGS. 6-6A. The character of the cylindrical-phase block copolymer composition 26′′ combined with a neutral wetting trench floor 18′′ and preferential wetting sidewalls 22′′ and ends 24′′, and constraints provided by the width (wt) of trench 16′′ results, upon annealing, in a hexagonal array of perpendicularly-oriented cylindrical domains 30′′ of the minor polymer block (i.e., like domains) (e.g., PEO) within a matrix 32′′ of the major polymer block (e.g., PS). A thin layer 30a′′ of the minor polymer block (e.g., PEO) wets the sidewalls 18′′. The hexagonal array contains n single rows of cylinders according to the width (wt) of the trench with the cylinders 30′′ in each row being offset from the cylinders in the adjacent rows. Each row contains a number of cylinders, generally m cylinders, which number can vary according to the length (lt) of the trench and the shape of the trench end (e.g., rounded, angled, etc.) with some rows having greater or less than m cylinders. The cylinders 38a′′ are generally spaced apart at a pitch distance (p1) at or about Lo between each cylinder in the same row and an adjacent row (center-to-center distance), and at a pitch distance (p2) at or about Lo*cos(π/6) or 0.866 Lo being the distance between two parallel lines where one line bisects the cylinders in a given row and the other line bisects the cylinders in an adjacent row.
Optionally, the annealed film 28′′ can then treated to crosslink the polymer segments (e.g., to crosslink the PS matrix 32′′). As previously described, the polymers can be structured to inherently crosslink, or one or both of the polymer blocks of the copolymer material can be formulated to contain a crosslinking agent. The polymer material remaining on the spacers 20′′ can then be optionally removed as previously described.
One of the block components can then be selectively removed from the self-assembled 28′′ film. In one embodiment shown in FIGS. 7-7A, the cylindrical domains 30′′ can be removed to produce a film 34a′′ composed of the matrix 32′′ with a hexagonal array of cylindrical openings 36′′. In another embodiment shown in FIGS. 8-8B, the matrix 32′′ can be removed to produce a film 34b′′ composed of a hexagonal array of cylinders 30′′ on the substrate 10′′. The resulting films 34a′′, 34b′′ can be used, for example, as a lithographic template or mask to pattern the underlying substrate 10′′ in a semiconductor processing to define regular patterns in the nanometer size range (i.e., about 5-50 nm).
For example, referring to FIGS. 7-7A, selective removal of the minor block cylinders 30′′ (e.g., PEO) will result in a film 34a′′ composed of a hexagonal array of openings 36′′ within the matrix 32′′ of the major block (e.g., PS), the openings having a diameter of about 5-50 nm and an aspect ratio generally at least about 1:2 and ranging from about 1:2 to about 1:20. The film 34a′′ can be used as an etch mask to pattern (arrows ↓↓) the underlying substrate 10′′ to form an array of openings 38′′ (shown in phantom in FIG. 7A) to an active area or element 40′′ in the substrate 10′′. Further processing can then be performed as desired, for example, the removal of the residual matrix 32′′ (e.g., PS) and filling of the openings 38′′ in substrate 10′′ as shown in FIG. 7B, with a material 42′′ such as a metal or conductive alloy such as Cu, Al, W, Si, and Ti3N4, among others, to form contacts, for example, to an underlying active area or conductive line 40′′, or with a metal-insulator-metal stack to form capacitors with an insulating material such as SiO2, Al2O3, HfO2, ZrO2, SrTiO3, among other dielectrics.
In another embodiment illustrated in FIGS. 8-8A, the selective removal of the major block matrix 32′′ (e.g., PEO) will provide a film 34b′′ composed of a hexagonal array of the minor block cylinders 30′′ (e.g., PS) on the substrate 10′′. Such an embodiment would require a majority PEO block copolymer and sidewalls composed of a material that is selectively PS-wetting (e.g., a gold sidewall or PS-grafted to the sidewall material). The film 34b′′ composed of cylinders 30′′ can be used as an etch mask (arrows ↓↓) to etch a patterned opening 38′′ in the underlying substrate 10′′ (shown in phantom in FIG. 8A) with the substrate 10′′ etched to form cylinders masked by the cylindrical elements 30′′ of the film 34b′′. Further processing can then be conducted, for example, the removal of the residual polymer mask 34b′′ (i.e., cylinders 30′′) and the deposition of a material 42′′ distinct from substrate 10′′ into the opening 36′′ to provide a differential surface, as illustrated in FIG. 8B. For example, an opening 36′′ in a silicon substrate 10′′ can be filled with a dielectric material such as SiO2, with the cylinders of the residual substrate 10′′ (e.g., of silicon) providing contacts to an underlying active area or metal lines 40′′.
In an embodiment of a method to produce a one-dimensional (1-D) array of perpendicularly-oriented cylinders as illustrated in FIGS. 9-11, the foregoing process for forming a hexagonal array of cylinders with a cylindrical-phase PS-b-PEO block copolymer can be modified by utilizing the trench sidewalls and ends as constraints to induce orientation and registration of cylindrical copolymer domains in a single row parallel to the trench sidewalls.
Referring to FIGS. 2-2A, in embodiments to provide a single row of cylinders within a polymer matrix, a trench 16′′′ is structured to have a width (wt) that is at or about 1.5-1.75* the Lo value of the block copolymer material. The material layer 14′′′ (e.g., oxide) exposed on the sidewalls 22′′′ and ends 24′′′ is preferential wetting by the minority block (e.g., the PEO block) of the PS-b-PEO diblock copolymer, and the substrate 10′′′ (e.g., silicon) bear a layer 12′′′ of the PS-r-PEO random copolymer of the invention, which is exposed at the trench floors 18′′′ and neutral wetting to both blocks of the PS-b-PEO copolymer material.
A cylindrical-phase PS-b-PEO diblock copolymer material 26′′′ (or blend with homopolymers) having an inherent pitch at or about Lo can be deposited onto the PS-r-PEO layer 12′′′ on the trench floor 18′′′ to a thickness (t1) of less than or about equal to the Lo value of the copolymer material to up to about 1.5×Lo (as shown in FIGS. 3-3A). The block copolymer film 26′′′ is then annealed, whereupon the copolymer film layer will self assemble to form a film 28′′′, as illustrated in FIGS. 9-9A. The constraints provided by the width (wt) of trench 16′′′ and the character of the block copolymer composition 26′′′ combined with a neutral wetting trench floor 18′′′ and preferential wetting sidewalls 22′′′ and ends 24′′′ results in a one-dimensional (1-D) array or single row of perpendicularly-oriented cylindrical domains 30′′′ of the minority polymer block (e.g., PEO) within a matrix 32′′′ of the major polymer block (e.g., PS), with the minority block segregating to the sidewalls 18′′′ of the trench to form a wetting layer 30a′′′. In some embodiments, the cylinders have a diameter at or about 0.5 Lo (e.g., about 20 nm), the number n of cylinders in the row is according to the length of the trench, and the center-to-center distance (pitch distance) (p) between each like domain (cylinder) is at or about Lo (e.g., about 40 nm). Optionally, the annealed cylindrical-phase film 28′′′ can be treated to crosslink the polymer segments (e.g., the PS matrix 32′′′).
Selective removal of one of the block components can then be performed to produce, for example, a film that can be used as a mask to etch the underlying substrate 10′′′. For example, referring to FIGS. 10-10A, selective removal of the minor block cylinders 30′′′ (e.g., PEO) will result in a film 34a′′′ composed of a 1-D array of cylindrical openings 36′′′ within the matrix 32′′′ of the major block (e.g., PS), the openings having a diameter of about 5-50 nm and an aspect ratio of about 1:2 to about 1:20. The film 34a′′′ can be used as an etch mask to pattern (arrows ↓↓) the underlying substrate 10′′′ to form an array of openings 38′′′ (shown in phantom in FIG. 10A) extending to an active area or element 40′′′. The residual film 34a′′′ can then be removed and the openings 38′′′ in the substrate 10′′′ can be filled as shown in FIG. 10B with a material 42′′′, for example, a metal or conductive alloy to provide a 1-D array of contacts to an underlying active area or line contact 40′′′, for example, or with metal-insulator-metal stack to form capacitors.
In another embodiment depicted in FIGS. 11-11B, the selective removal of the major block matrix component 32′′′ (e.g., PEO) will provide a film 34b′′′ composed of a 1-D array of the minor block cylinders 30′′′ (e.g., PS). The film 34b′′′ can be used as a mask or template in an etch process (arrows ↓↓) to form a patterned opening 38′′′ (shown in phantom in FIG. 11A) in the underlying substrate 10′′′, with the masked substrate 10′′′ etched to form cylinders. The residual polymer mask 34b′′′ (cylinders 30′′′) can then be removed and a material 42b′′′ such as a dielectric material (e.g., oxide) that is distinct from the substrate 10′′′ (e.g., silicon) can be deposited to fill the opening 36′′ to provide a differential surface to the substrate 10′′ cylinders, which can provide contacts to an underlying active area or metal line 40′′′, for example.
In another embodiment of the invention, graphoepitaxy (topographic features, e.g., sidewalls, ends, etc.) is used to influence the formation of arrays in one dimension, and the trench floors provide a wetting pattern that can be used to chemically control formation of the arrays in a second dimension. A layer 12′′′′ of the PS-r-PEO random copolymer layer of the invention is formed on a substrate 10′′′′, and crosslinked in select regions or sections 12a′′′′, for example, by photo-exposure (arrows ↓↓) through a reticle or a mask 44′′′′ as shown in FIGS. 12-12A, or through a patterned resist layer 46′′′′ as depicted in FIGS. 13-13A (which is subsequently removed). The non-crosslinked regions 12b′′′′ of the PS-r-PEO random copolymer layer 12′′′′ can be removed, for example, by wet processing using an appropriate solvent to expose the underlying substrate 10′′′′, resulting in a pattern of discrete regions or sections of the crosslinked random copolymer layer 12a′′′′ (neutral wetting) and sections of the exposed substrate 10′′′′ (preferential wetting) on the trench floor 18′′′′, as shown in FIGS. 14-14A.
As depicted in FIGS. 15-15B, a material layer 14′′′′ can then be formed and trenches 16′′′′ etched to expose the crosslinked sections 12a′′′′ of the PS-r-PEO random copolymer layer and sections of the exposed substrate 10′′′′ on the trench floors 18′′′′ as a series of stripes oriented perpendicular to the trench sidewalls 22′′′′. The trench floors 18′′′′ are thus defined by alternating preferential wetting sections (substrate 10′′′′) and neutral wetting sections (a mat of the crosslinked PS-r-PEO random copolymer 12a′′′′). In some embodiments, each of the sections can have a width (wr1) at or about Lo, and in other embodiments, the neutral wetting (PS-r-PEO) sections 12a′′′′ can have a width (wr2) at or about nLo and the preferential wetting (substrate) sections 10′′′′ a width at or about Lo. The trench sidewalls 22′′′′ and edges 24′′′′ (e.g., of oxide) are preferential wetting to the minority block (e.g., PEO) of the PS-b-PEO diblock copolymer.
Referring now to FIGS. 16-16A, a cylindrical-phase PS-b-PEO block copolymer film 26′′′′ (e.g., having a pitch Lo) is cast or spin coated into the trenches 16′′′′ to a film thickness (t) of about Lo, and then thermally annealed as previously described. The differing wetting patterns on the trench floor 18′′′′ imposes ordering on the PS-b-PEO block copolymer film 26′′′′ as it is annealed, resulting in a 1-D array of alternating perpendicular-oriented cylinders 30b′′′′ and parallel-oriented cylinders 30c′′′′ for the length (nLo) of each trench 16′′′′, as shown in FIGS. 17-17B. In some embodiments, the film structure is composed of a series of n perpendicular cylinders 30b′′′′ for the width (w1) of each neutral wetting PS-r-PEO polymer section 12a′′′′ on either side of a region of a single parallel-oriented half-cylinder 30c′′′′ for the width (w2) of each preferential wetting section (exposed substrate 10′′′′).
Optionally, the annealed film 28′′′′ can then be treated to crosslink the polymer segments (e.g., the PS matrix 32′′′′) as previously described. Material outside the trenches can be optionally removed, for example, from the spacers 20′′′′.
Selective removal of one of the polymer domains (i.e., cylinders or matrix) can then be performed to produce a template for use in patterning the substrate 10′′′′. For example, as shown in FIGS. 18-18B, selective removal of the cylindrical domains 30b′′′′, 30c′′′′ (e.g., of PEO) will produce an array of openings 36a′′′′, 36b′′′′ within a polymer matrix 32′′′′ (e.g., of PS), which will vary according to the orientation of the cylindrical domains within the trenches. Only openings 36a′′′′ will extend to the trench floor 18′′′′, with majority block matrix component 32′′′′ (e.g., PS) remaining underneath the half-cylinder openings 36b′′′′. 
As shown in FIGS. 19A-19B, the resulting film 34′′′′ can be then used in patterning (arrows ↓↓) substrate 10′′′′ to form a configuration of cylindrical openings 38′′′′ (shown in phantom) extending to an active area or element 40′′′′. The film 34′′′′ can then be removed and the openings 38′′′′ can be filled with a material 42′′′′ (e.g., metal, conductive alloy) as shown in FIGS. 20-20B to provide a series of perpendicular contacts 42′′′′ to underlying active areas or elements (e.g., line contact) 40′′′′, with additional processing as desired.
In yet another embodiment illustrated in FIGS. 21-21B, selective removal of the major block matrix component 32′′′′ (e.g., PEO) will provide a film 34′′′′ composed of an array of the minor block cylinders 30b′′′′ (e.g., PS) on the substrate 10′′′′, which can be used to etch (arrows ↓↓) openings 38′′′′ in substrate 10′′′′ (shown in phantom), with the masked portions of the substrate 10′′′′ etched in the form of cylinders. The residual mask 34′′′′ (cylinders 30′′′′) can be removed and, as shown in FIGS. 22-22B, a material 42′′′′ distinct from the substrate 10′′′′ (e.g., silicon) such as a dielectric material (e.g., oxide) can be deposited to fill the opening 36′′′′ as a differential material than the substrate 10′′′′ cylinders, which can provide, for example, contacts to an underlying active area or metal line 40′′′′.
Embodiments of the invention provide ordered and registered elements on a nanometer scale that can be prepared more inexpensively than by electron beam lithography or EUV photolithography. The feature sizes produced and accessible by this invention cannot be prepared by conventional photolithography.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement which is calculated to achieve the same purpose may be substituted for the specific embodiments shown. This application is intended to cover any adaptations or variations that operate according to the principles of the invention as described. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof. The disclosures of patents, references and publications cited in the application are incorporated by reference herein.

## Claims

1. A process for preparing a random graft copolymer, comprising:
reacting a reaction mixture comprising p-chloromethylstyrene monomers to form a p-chloromethylstyrene homopolymer comprising chloromethyl moieties and repeating units derived from p-chloromethylstyrene;
reacting the p-chloromethylstyrene homopolymer with one or more oligomers or polymers of poly(ethylene oxide) to form a graft copolymer comprising chloromethyl moieties, wherein the poly(ethylene oxide) has only one nucleophilic end; and,
reacting the graft copolymer with an azide compound to displace chlorine atoms of the chloromethyl moieties to form azidomethyl moieties on the graft copolymer, wherein the azide compound selected from the consisting of sodium azide or R(N3)x, where R is a metal atom other than sodium, a hydrogen atom or an ammonium radical, and x is greater than zero.

2. The process of claim 1, wherein the p-chloromethylstyrene homopolymer is reacted with an amount of the oligomers or polymers of poly(ethylene oxide) which is stoichiometrically less than the amount of chloromethyl moieties on the p-chloromethylstyrene homopolymer.

3. The process of claim 2, wherein the graft copolymer is reacted with an amount of the azide compound which is stoichiometrically greater than the amount of chloromethyl moieties remaining on the p-chloromethystyrene homopolymer after reaction with the poly(ethylene oxide).

4. The process of claim 1, wherein the p-chloromethylstyrene homopolymer is a living polymer.

5. The process of claim 1, wherein the reaction mixture further comprises an initiator.

6. The process of claim 5, wherein the initiator is selected from the group consisting of an alkoxyamine, a thiocarbonyl-thiol compound, an alkyl halide, benzoyl peroxide, and 2,2′-azo-bis-isobutyrylnitrile.

7. The process of claim 1, wherein one or more of the reactions is conducted in a solvent.

8. A process for preparing a random graft copolymer, comprising:
reacting a reaction mixture comprising p-chloromethylstyrene and styrene to form polymer chains that comprise chloromethyl moieties and repeating units derived from p-chloromethylstyrene and styrene, wherein the reaction mixture comprises p-chloromethylstyrene in a molecular amount greater than a molecular amount of the styrene;
reacting the polymer chains with one or more oligomers or polymers of poly(ethylene oxide) to form a graft copolymer comprising chloromethyl moieties, wherein the poly(ethylene oxide) has only one nucleophilic end; and,
reacting the graft copolymer with an azide compound to displace chlorine atoms of the chloromethyl moieties to form azidomethyl moieties on the graft copolymer.

9. The process of claim 8, wherein the reaction mixture is a bulk reaction mixture without an additional solvent.

10. A method of forming a random graft copolymer layer that is neutral wetting to both polystyrene and polyethylene oxide, comprising:
applying a solution comprising an azido-functionalized random graft copolymer to a substrate to form the random graft copolymer layer, and
crosslinking the random graft copolymer layer;

wherein the random graft copolymer is formed by:
reacting a reaction mixture comprising p-chloromethylstyrene monomers to form a p-chloromethylstyrene homopolymer comprising chloromethyl moieties and repeating units derived from p-chloromethylstyrene;
reacting the p-chloromethylstyrene homopolymer with one or more oligomers or polymers of poly(ethylene oxide) to form a graft copolymer comprising chloromethyl moieties, wherein the poly(ethylene oxide) has only one nucleophilic end; and,
reacting the graft copolymer with an azide compound to displace chlorine atoms of the chloromethyl moieties to form azidomethyl moieties on the graft copolymer, wherein the azide compound selected from the group consisting of sodium azide or R(N3)x, where R is a metal atom other than sodium, a hydrogen atom or an ammonium radical, and x is greater than zero.

11. The method of claim 10, wherein the reaction mixture comprises styrene and the polymer chains further comprise repeating units derived from styrene.

12. The method of claim 10, wherein the crosslinking is conducted by exposure to ultraviolet light or heat.

13. The method of claim 10, wherein the random graft copolymer layer is on a floor of a trench having sidewalls that are preferentially wetting to one block of a block copolymer, and the process further comprises:
forming a film comprising a self-assembling block copolymer on the random graft copolymer layer to a thickness of about the Lo value of the block copolymer; and
annealing the film to form a layer comprising self-assembled polymer domains registered to the sidewalls of the trench and oriented perpendicular to the trench floor.

14. The method of claim 13, further comprising crosslinking polymer domains of the annealed film layer.

15. The method of claim 13, wherein annealing the film comprises solvent annealing.

16. The method of claim 13, wherein annealing the film comprises thermal annealing with a partial pressure of saturated solvent vapor.

17. The method of claim 13, wherein the block copolymer comprises a poly(styrene-b-ethylene oxide) block copolymer.

18. The method of claim 13, wherein the block copolymer is a lamellar-phase block copolymer composition.

19. The method of claim 13, wherein the block copolymer is a cylindrical-phase block copolymer composition.

20. The method of claim 10, further comprising,
after forming the random graft copolymer layer, masking one or more portions of the said copolymer layer;
crosslinking exposed portions of said copolymer layer; and
selectively removing non-crosslinked portions of said copolymer layer to expose portions of the substrate.

21. The method of claim 20, wherein the random graft copolymer layer is on a floor of a trench having sidewalls that are preferentially wetting to a minor block of a block copolymer, and the process further comprises:
forming a film comprising a cylindrical-phase block copolymer on the random graft copolymer layer to a thickness of about the Lo value of the block copolymer; and
annealing the film to form a layer comprising self-assembled cylindrical polymer domains, wherein perpendicular-oriented cylindrical domains are situated on the crosslinked random graft copolymer layer and parallel-oriented half cylindrical domains are situated on the portions of the exposed substrate.

22. The method of claim 20, further comprising, after crosslinking the random graft copolymer layer, masking one or more portions of the copolymer layer and removing exposed portions of the copolymer layer to expose the substrate.

23. The method of claim 22, wherein removing the exposed portions of the copolymer layer comprises an oxygen etch.

24. The process of claim 8, wherein the polymer chains are reacted with an amount of the oligomers or polymers of poly(ethylene oxide) which is stoichiometrically less than the amount of chloromethyl moieties on the polymer chains.

25. The process of claim 8, wherein the azide compound selected from the group consisting of sodium azide or R(N3)x, where R is a metal atom other than sodium, a hydrogen atom or an ammonium radical, and x is greater than zero.

26. The process of claim 8, wherein the reaction mixture further comprises an initiator.

27. The process of claim 8, wherein one or more of the reactions is conducted in a solvent.

28. A method of forming a random graft copolymer layer that is neutral wetting to both polystyrene and polyethylene oxide, comprising:
applying a solution comprising an azido-functionalized random graft copolymer to a substrate to form the random graft copolymer layer; and
crosslinking the random graft copolymer layer;
wherein the random graft copolymer is formed by:
reacting a reaction mixture comprising p-chloromethylstyrene and styrene to form polymer chains that comprise chloromethyl moieties and repeating units derived from p-chloromethylstyrene and styrene, wherein the reaction mixture comprises p-chloromethylstyrene in a molecular amount greater than a molecular amount of the styrene;
reacting the polymer chains with one or more oligomers or polymers of poly(ethylene oxide) to form a graft copolymer comprising chloromethyl moieties, wherein the poly(ethylene oxide) has only one nucleophilic end; and,
reacting the graft copolymer with an azide compound to displace chlorine atoms of the chloromethyl moieties to form azidomethyl moieties on the graft copolymer.

29. The method of claim 28, wherein the random graft copolymer layer is on a floor of a trench having sidewalls that are preferentially wetting to one block of a block copolymer, and the process further comprises:
forming a film comprising a self-assembling block copolymer on the random graft copolymer layer to a thickness of about the Lo value of the block copolymer; and
annealing the film to form a layer comprising self-assembled polymer domains registered to the sidewalls of the trench and oriented perpendicular to the trench floor.

30. The method of claim 29, wherein the block copolymer is a lamellar-phase block copolymer composition.

31. The method of claim 29, wherein the block copolymer is a cylindrical-phase block copolymer composition.

32. The method of claim 28, further comprising,
after forming the random graft copolymer layer, masking one or more portions of said copolymer layer;
crosslinking exposed portions of said copolymer layer; and
selectively removing non-crosslinked portions of said copolymer layer to expose portions of the substrate.

33. The method of claim 32, wherein the random graft copolymer layer is on a floor of a trench having sidewalls that are preferentially wetting to a minor block of a block copolymer, and the process further comprises:
forming a film comprising a cylindrical-phase block copolymer on the random graft copolymer layer to a thickness of about the Lo value of the block copolymer; and
annealing the film to form a layer comprising self-assembled cylindrical polymer domains, wherein perpendicular-oriented cylindrical domains are situated on the crosslinked random graft copolymer layer and parallel-oriented half cylindrical domains are situated on the portions of the exposed substrate.

34. The method of claim 32, further comprising, after crosslinking the random graft copolymer layer, masking one or more portions of the copolymer layer and removing exposed portions of the copolymer layer to expose the substrate.