# Patent

## Title
Registered structure formation via the application of directed thermal energy to diblock copolymer films

## Abstract

Methods for fabricating sub-lithographic, nanoscale linear microchannel arrays over surfaces without defined features utilizing self-assembling block copolymers, and films and devices formed from these methods are provided. Embodiments of the methods use a multi-layer induced ordering approach to align lamellar films to an underlying base film within trenches, and localized heating to anneal the lamellar-phase block copolymer film overlying the trenches and outwardly over the remaining surface.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation of U.S. patent application Ser. No. 11/714,336, filed Mar. 6, 2007, now U.S. Pat. No. 8,083,953, the entire contents of which is hereby incorporated by reference herein.


TECHNICAL FIELD
Embodiments of the invention relate to methods of fabricating nanoscale linear arrays of microstructures and microchannels by use of thin films of self-assembling block copolymers, and devices resulting from those 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 a 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. For example, for volume fractions at ratios greater than about 80:20 of the two blocks (AB) of a diblock polymer, a block copolymer film will microphase separate and self-assemble into a periodic spherical domains with spheres of polymer B surrounded by a matrix of polymer A. For ratios of the two blocks between about 60:40 and 80:20, the diblock copolymer assembles into a periodic hexagonal close-packed or honeycomb array of cylinders of polymer B within a matrix of polymer A. For ratios between about 50:50 and 60:40, lamellar domains or alternating stripes of the blocks are formed. Domain size typically ranges from 5 nm to 50 nm.
Diblock copolymer thin films of cylindrical and lamellar phases may both form striped phases relative to an interface. For cylindrical phase films, a striped pattern results from parallel cylinder orientation, while for lamellar phase films, a striped pattern results from perpendicular domain orientation. From a top down view, perpendicular-oriented lamellae and parallel-oriented cylinders appear similar, e.g., as parallel lines.
Graphoepitaxy techniques using defined topography such as trench edges have been used in an attempt to orient and order copolymer domains and control registration and alignment of the self-assembled blocks to form a desired pattern. By comparison, thin films prepared on a flat substrate and annealed do not have any preferential orientation of domains and will assemble into a disordered fingerprint-like structure despite extensive annealing. Although registered and ordered arrays of cylinders have been produced within trenches, the fabrication of an ordered array of repeat structures outside of the confines of the trenches and over large areas has not been realized in a manufacturable process.
It would be useful to provide a method of fabricating films of linear arrays of ordered nanostructures that overcome these 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, 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. 1A 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. FIGS. 1B and 1C are elevational, cross-sectional views of embodiments of the substrate depicted in FIG. 1A taken along lines 1B/1C-1B/1C. FIG. 1D is an elevational, cross-sectional view of a substrate used in another embodiment of the invention.
FIGS. 2A-6A illustrate diagrammatic top plan views of the substrate of FIG. 1A at various stages of the fabrication of a self-assembled block copolymer film according to an embodiment of the present disclosure. FIGS. 2B to 6B and 2C to 6C illustrate elevational, cross-sectional views of embodiments of a portion of the substrate depicted in FIGS. 2A-6A taken, respectively, along lines 2B/2C-2B/2C to lines 6B/6C-6B/6C.
FIGS. 7A and 7B illustrate elevational, cross-sectional views of the substrate depicted in FIG. 5B, showing annealing of a portion of the film at various stages according to an embodiment of the disclosure by use of a laser source illuminated through a mask or reticle.
FIG. 8A illustrates a diagrammatic top plan view of the substrate of FIG. 1A, showing an incorporation of thermally conductive lines in the substrate for localized heating of the film layer according to an embodiment of the disclosure. FIG. 8B illustrates an elevational, cross-sectional view of the substrate depicted in FIG. 8A taken along line 8B-8B.
FIG. 9 illustrates an elevational, cross-sectional view of the substrate of FIG. 1A, showing an incorporation of an absorptive material layer for localized heating of the film layer according to another embodiment of the disclosure.
FIG. 10A illustrates a diagrammatic top plan view of the substrate of FIG. 1A, showing an incorporation of a reflective material layer on the exposed surfaces outside of the trenches for localized heating of the film layer according to another embodiment of the disclosure. FIG. 10B is an elevational, cross-sectional view of the substrate depicted in FIG. 10A taken along line 10B-10B.
FIGS. 11A and 11B illustrate embodiments of heating the substrate of FIG. 5B by zoned annealing techniques.
FIG. 12A illustrates a diagrammatic top plan view of a portion of the substrate of FIG. 6A at a subsequent stage. FIGS. 12B and 12D illustrate elevational, cross-sectional views of the substrate depicted in FIG. 12A taken along lines 12B/12D-12B/12D. FIG. 12C illustrates an intermediate structure showing the removal of half-cylindrical domains in a step prior to FIG. 12D.



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 terms “semiconductor substrate,” or “semiconductive substrate,” “semiconductive wafer fragment,” “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.
Processing conditions of embodiments of the invention use a graphoepitaxy technique utilizing sidewalls of trenches as constraints to induce orientation and registration of a first film of a self-assembling diblock copolymer to form an ordered linear array pattern registered to the sidewalls of the trenches. The first polymer film is then used as a template or base layer for inducing ordering of a subsequently deposited lamellar-phase block copolymer film such that, upon annealing, lamellar domains within the trenches orient perpendicularly and are registered to underlying structures, resulting in a stacked double- or multi-layer structure having a striped pattern.
Steps in a method for fabricating thin films from self-assembling (SA) block copolymers that define nanometer-scale linear array patterns according to embodiments of the invention are illustrated in FIGS. 1A-12D.
The method first forms a multi-layer pattern within trenches by forming a polymer base film or template with ordered structures within the trenches for inducing the ordering of an overlying lamellar phase block copolymer film such that the lamellar domains are oriented perpendicularly and registered to the underlying assembled domains of the base film.
The base layer within the trenches can be formed from a lamellar-phase block copolymer film, which upon annealing, forms a registered lamellar array of alternating polymer-rich blocks that extend the length and are oriented parallel to the sidewalls and perpendicular to the floor of the trenches. In other embodiments, the base layer is formed from a cylindrical-phase block copolymer material, which upon annealing, forms lines of half-cylinders in a polymer matrix extending the length and oriented parallel to the sidewalls and floor of the trenches. The assembled base film is then used as a template for inducing the ordering of an overlying lamellar-phase block copolymer film such that the lamellar domains of the annealed film are oriented perpendicularly and registered to the underlying pattern of the base film within the trenches.
To produce a base polymer film within the trenches using a lamellar-phase 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. 1A and 1B, a substrate 10 is provided bearing a neutral wetting surface. The substrate 10 can comprise, for example, silicon (with native oxide), oxide (e.g., silicon oxide, SiOx), or an inorganic film. In the illustrated embodiment, a neutral wetting layer 12 is formed on the substrate 10 prior to forming an overlying material layer 14 (e.g., oxide). Etching through the material layer 14 to form trenches 16 exposes an underlying neutral wetting layer 12 as a floor or bottom surface 18 of the trenches 16. The trenches 16 are separated by a spacer or crest 20 having a width (ws) and are structured with opposing sidewalls 22, opposing ends or edges 24, a width (wt), a length (lt) and a depth (Dt).
A neutral wetting surface can be provided, for example, by applying a neutral wetting polymer to form the layer 12 on the surface of the substrate 10. In the use of a self-assembling (SA) diblock copolymer composed of PS-b-PMMA, a random PS:PMMA copolymer brush layer (PS-r-PMMA)), which exhibits non-preferential or neutral wetting toward PS and PMMA can be applied by spin-coating onto the surface of substrate 10. The brush can be affixed by grafting (on an oxide substrate) or by cross-linking (any surface) using UV radiation or thermal processing. For example, a random copolymer solution composed of PS and PMMA with hydroxyl end group(s) (e.g., about 58% PS) can be applied to the surface of the substrate 10 as a layer about 5 nm to 10 nm thick and end-grafted by heating at about 160° C. for about 48 hours.
In another embodiment, a surface that is neutral wetting to PS-b-PMMA can be prepared by spin-coating a blanket layer of a photo- or thermally cross-linkable random copolymer such as a benzocyclobutene- or azidomethylstyrene-functionalized random copolymer of styrene and methyl methacrylate (e.g., poly(styrene-r-benzocyclobutene-r-methyl methacrylate (PS-r-PMMA-r-BCB))) onto the surface of the substrate 10 prior to forming the material layer 14. For example, such a random copolymer can comprise about 42% PMMA, about (58−x) % PS and x % (e.g., about 2% to 3%) of either polybenzocyclobutene or poly(para-azidomethylstyrene)). An azidomethylstyrene-functionalized random copolymer can be UV cross-linked (e.g., 1-5 mW/cm2 exposure for about 15 seconds to about 30 minutes) or thermally cross-linked (e.g., at about 170° C.). A benzocyclobutene-functionalized random copolymer can be thermally cross-linked (e.g., at about 200° C. for about 4 hours or at about 250° C. for about 10 minutes).
Another neutral wetting surface for PS-b-PMMA can be provided by hydrogen-terminated silicon, which can be prepared by a conventional process, for example, by a fluoride ion etch of a silicon substrate 10 (with native oxide present, about 12 Åto 15 Å) for example, by immersion in aqueous solution of hydrogen fluoride (HF) and buffered HF or ammonium fluoride (NH4F), by HF vapor treatment, by exposure to hot H2 vapor, or by a hydrogen plasma treatment (e.g., atomic hydrogen).
Referring now to FIG. 1C, 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 material 12 then applied to the floors 18 of the trenches 16. For example, floors 18 of the trenches 16 that are neutral wetting to PS-b-PMMA can be prepared by spin-coating PS-r-PMMA-r-BCB onto the surface of the substrate 10 within the trenches 16 and thermally cross-linking the polymer (e.g., at 190° C., for 4 hours) to form a crosslinked polymer mat as neutral wetting layer 12. Capillary forces pull the random copolymer to the bottom of deep trenches. Non-cross-linked polymer material can be subsequently removed.
The sidewalls 22 of the trenhes 16 are preferential wetting by one block of the copolymer to induce formation of lamellae as the blocks self-assemble. The material layer 14 defining the surfaces of trenches 16 can be an inherently preferential wetting material, or in other embodiments, a layer of a preferential wetting material can be applied onto the surfaces of the trenches 16.
For example, in the use of poly(styrene-block-methyl methacrylate) (PS-b-PMMA), an oxide (e.g., silicon oxide, SiOx) or a clean silicon surface (with native silicon oxide) exhibits preferential wetting toward the PMMA block to result in the assembly of a thin (e.g., 1⁄4 pitch) interface layer of PMMA and alternating PMMA and PS lamellae (e.g. 1⁄2 pitch) within each trench in the use of a lamellar-phase block copolymer material. Other preferential wetting surfaces to PMMA can be provided, for example, by silicon nitride, silicon oxycarbide, polymethylmethacrylate (PMMA) polymer grafted to a sidewall material such as silicon oxide, and resist materials such as methacrylate-based resists. For example, a PMMA that is modified with a moiety containing one or more hydroxyl (—OH) groups (e.g., hydroxyethylmethacrylate) can be applied by spin coating and then heated (e.g., to about 170° C.) to allow the OH groups to end-graft to the oxide sidewalls 22 and ends 24 of the trenches 16. Non-grafted material can be removed from the neutral wetting layer 12 by rinsing with an appropriate solvent (e.g., toluene). See, for example, Mansky et al., Science, 1997, 275, 1458-1460, and In et al., Langmuir, 2006, 22, 7855-7860, the disclosures of which are incorporated by reference herein.
Referring now to FIG. 1D, in other embodiments using a cylindrical-phase block copolymer to form a base polymer film within the trenches, the surfaces of the floor 18′, sidewalls 22′ and the ends 24′ of the trenches 16′ are preferential wetting by the minority block of the copolymer to induce formation of parallel lines of half-cylinders wetting an air interface (surface exposed) down the middle of each trench 16′ aligned parallel to the sidewalls 22′ and floor 18′ of the trenches 16′. For example, substrate 10′ can be composed of an inherently preferential wetting material such as a clean silicon surface (with native silicon oxide) and material layer 14′ can be composed of oxide (e.g., SiOx). Both materials exhibit preferential wetting toward the PMMA block to result in an assembly of a thin interface layer of PMMA on the sidewalls 22′ of the trenches 16′ as well as PMMA cylinders in the center of a PS matrix within each trench 16′. Other preferential wetting surfaces to PMMA can be provided, for example, by silicon nitride, silicon oxycarbide, and PMMA polymer grafted to a sidewall material such as silicon oxide, and resist materials such as methacrylate-based resists. See, for example, C. T. Black and O. Bezencenet, “Nanometer-Scale Pattern Registration and Alignment by Directed Diblock Copolymer Self-Assembly,” IEEE Transactions on Nanotechnology, 2004, 3(3), 412-415; C. T. Black, “Self-Aligned Self-Assembly of Multi-Nanowire Silicon Field Effect Transistors,” Applied Physics Letters, 2005, 87, 163116; R. Ruiz, R. L. Sandstrom and C. T. Black, “Induced Orientational Order in Symmetric Diblock Copolymer Thin-Films,” Advanced Materials, 2007, 19(4), 587-591, the disclosures each of which are hereby incorporated by reference herein.
The sidewalls, edges and floors of the trenches influence the structuring of the array of nanostructures within the trenches. The boundary conditions of the sidewalls of the trenches in both the x- and y-axis impose a structure wherein each trench contains n number of features (i.e., cylinders or 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” structures spanning the width (wt) of the trench 16, with each structure (i.e., cylinders or lamellae) being separated by a value of Lo (from center-to-center). The width (wt) of the trenches 16 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). In embodiments of the invention, the depth (Dt) of the trenches 16 is greater than or at about Lo in using a lamellar-phase block copolymer for the base layer (FIGS. 1B and 1C), and less than Lo in using a cylindrical-phase block copolymer (e.g., trench 16′ as depicted in FIG. 1D). The application and annealing of a 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” structures spanning the width and registered to the sidewalls for the length of the trench. In some embodiments, the trench dimension is about 50 nm to 500 nm wide (wt) and about 1,000 μm to 10,000 μm in length (lt), with a depth (Dt) of about 50 nm to 500 nm in using a lamellar-forming block copolymer, and about 50 nm to 2000 nm wide (wt) with a depth (Dt) of about 15 nm to 25 nm in using a cylinder-forming block copolymer. The width (ws) of the spacer or crest 20 between adjacent trenches is at or about an integral multiple of Lo such that as the film situated on the crest 20 is annealed, the expanding registered fronts will be matched and aligned where they converge. The spacer width (ws) can vary from about the width (wt) of the trench 16 to up to about 10× to 20× the trench width.
The trenches 16, 16′ can be formed using a lithographic tool having an exposure system capable of patterning at the scale of Lo (10 nm to 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 FIGS. 2A-2C, a self-assembling (SA) block copolymer material 26, 26′ 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 then deposited, typically by spin casting (spin-coating), onto the floor 18, 18′ of the trenches 16, 16′. The block copolymer material 26, 26′ can be deposited onto a patterned surface by spin casting from a dilute solution (e.g., about 0.2 5wt% to 2 wt % solution) of the copolymer in an organic solvent such as dichloroethane (CH2Cl2) or toluene, for example.
As illustrated in FIG. 2B, in embodiments using a lamellar-phase block copolymer for the base layer, with a trench depth (Dt) of greater than or at about Lo, a layer of the first block copolymer material 26 is deposited into the trenches 16 to a thickness (t1) less than the trench depth (Dt), for example, at about one-half of the trench depth, and at or about the Lo value of the block copolymer material 26 such that a copolymer film layer will self-assemble upon annealing to form a single layer of lamellae across the width (wt) of the trench 16.
As shown in FIG. 2C, in embodiments using a cylindrical-phase block copolymer for the base layer, with a trench depth (Dt) less than Lo, a layer of the first block copolymer material 26′ is deposited into the trenches 16′ to a thickness (t1) greater than the trench depth (Dt), but less than Lo such that the copolymer film layer will self-assemble upon annealing to form a single layer of parallel lines of half-cylinders across the width (wt) of the trench.
A typical thickness (t1) of a lamellar-phase block copolymer film 26 is about ±20% of the Lo value of the polymer (e.g., about 10 nm to 100 nm) to form, for example, alternating polymer-rich lamellar blocks having a width of about Lo (e.g., 25 nm to 35 nm). The thickness (t1) of a cylindrical-phase block copolymer film 26 is less than Lo to form parallel-oriented half-cylinders of one block having a diameter of about Lo in a matrix of another block within each trench 16. The thickness of the copolymer film layer can be measured, for example, by ellipsometry techniques.
Although diblock copolymers are used in the illustrative embodiments, other types of block copolymers (i.e., triblock or multiblock copolymers) can be used. Examples of diblock copolymers include poly(styrene-block-methyl methacrylate) (PS-b-PMMA), polyethyleneoxide-polyisoprene, polyethyleneoxide-polybutadiene, polyethyleneoxide-polystyrene, polyethyleneoxide-polymethylmethacrylate, polystyrene-polyvinylpyridine, polystyrene-polyisoprene (PS-b-PI), polystyrene-polybutadiene, polybutadiene-polyvinylpyridine, and polyisoprene-polymethylmethacrylate, among others. Examples of triblock copolymers include poly(styrene-block methyl methacrylate-block-ethylene oxide). One of the polymer blocks of the block copolymer should be selectively and readily removable in order to fabricate an etch mask or template from the annealed film.
In embodiments in which the base or template layer is formed from a lamellar-forming diblock copolymer, the volume fractions of the two blocks (AB) are generally at a ratio between about 50:50 and 60:40. An example of a lamellae-forming symmetric diblock copolymer is PS-b-PMMA with a weight ratio of about 50:50 (PS:PMMA) and total molecular weight (Mn) of about 51 kg/mol.
In other embodiments in which the base layer is formed using a cylindrical-phase diblock copolymer, the volume fractions of the two blocks (AB) are generally at a ratio between about 60:40 and 80:20. An example of a cylindrical phase diblock copolymer material is PS-b-PMMA (Lo=35 nm) composed of about 70% PS and 30% PMMA (weight ratio of 70:30) with a total molecular weight (Mn) of 67 kg/mol to form about 20 nm diameter half-cylinder PMMA domains in a matrix of PS. To achieve an annealed base film in which the half-cylinders or lamellae are surface exposed, the Chi value of the polymer blocks (e.g., PS and PMMA) at common annealing temperatures is generally small such that an air interface is equally or non-selectively wetting to both blocks.
The block copolymer material can also be formulated as a binary or ternary blend comprising an SA block copolymer and one or more homopolymers of the same type of polymers as the polymer blocks in the block copolymer, 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-PMMA/PS/PMMA blend, for example, 46K/21K PS-b-PMMA containing 40% 20K polystyrene and 20K poly(methylmethacrylate). 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.
Optionally, ellipticity (“bulging”) can be induced in the structures by creating a slight mismatch between the trench and the spacer widths and the inherent pitch (Lo) of the block copolymer or ternary blend, as described, for example, by Cheng et al., “Self-assembled One-Dimensional Nanostructure Arrays,” Nano Lett., 2006, 6(9), 2099-2103, the disclosure of which is incorporated by reference herein, which then reduces the stresses that result from such mismatches.
Referring now to FIGS. 3A-3C, the first block copolymer film 26 is then annealed, for example, by thermal annealing to above the glass transition temperature of the component blocks of the copolymer material to cause the polymer blocks to separate and self-assemble according to the preferential and neutral wetting of the trench surfaces 16, 18, 22, to form a self-assembled block copolymer structure 28. For example, a PS-b-PMMA copolymer film can be annealed at a temperature of about 180° C. to 195° C. in a vacuum oven (not shown) for about 1 to 24 hours to achieve the self-assembled morphology. The film can also be solvent annealed, for example, by slowly swelling both blocks of the film with a solvent, then slowly evaporating the solvent.
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 results, upon annealing, in a single layer of n elements across the width (wt) of the trench. The number “n” or pitches of elements (e.g., lamellar blocks or half-cylinders) within a trench is according to the width (wt) of the trench and the molecular weight (MW) of the block copolymer.
For example, as shown in FIG. 3B, a lamellar-phase block copolymer material used to form the base layer 28 will, upon annealing, self-assemble into 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:PMMA block copolymer film (Mn=51 kg/mol; Lo=32 nm) in an about 250 nm wide trench will subdivide the trench into about eight (8) lamellar structures.
In another embodiment, as illustrated in FIG. 3C, annealing of a cylindrical-phase copolymer material to form the base layer 28′ will result in parallel-oriented half-cylinders 30′ within a polymer matrix 32′ spanning the width (Wt) of the trench 16′, with each half-cylinder 30′ being separated by an average value of at or about Lo, and an interface layer 30a′ along the sidewalls 22′ and the floor 18′. For example, depositing and annealing a 70:30 PS:PMMA block copolymer film (Mn=67 kg/mol; Lo=35 nm) in an about 250 nm wide trench will subdivide the trench into about seven (7) half-cylinder structures.
The resulting morphologies of the annealed base film 28, 28′ (i.e., perpendicular orientation of lamellae or parallel orientation of half-cylinders 30′) can be examined, for example, using atomic force microscopy (AFM), transmission electron microscopy (TEM), or scanning electron microscopy (SEM).
The annealed and ordered base film 28, 28′ is then treated to cross-link the polymer segments to fix and enhance the strength of the self-assembled polymer blocks 30, 32 and 30′, 32′ within the trenches 16, 16′ (e.g., to cross-link the PS segments). The polymers can be structured to inherently cross-link (e.g., upon UV exposure), or one or both of the polymer blocks of the copolymer material can be formulated to contain a cross-linking agent.
For example, in one embodiment, the trench regions can selectively be exposed through a reticle to cross-link only the self-assembled film 28, 28′ within the trenches 16, 16′. A wash can then be applied with an appropriate solvent such as toluene, to remove the non-cross-linked portions of the film 28, 28′(e.g., on the spacer or crest 20, 20′) leaving the registered self-assembled base film within the trenches 16, 16′ and exposing the surface of material layer 14, 14′ above/outside the trenches 16, 16′ (e.g., the crest 20, 20′). As shown in FIGS. 3B and 3C, a neutral wetting layer 34, 34′ can then be formed on the exposed surface of the material layer 14, 14′ (e.g., oxide), for example, by applying and grafting or cross-linking a random copolymer brush layer (e.g., PS-r-PMMA) on the surface.
In another embodiment, the entire annealed film 28, 28′ can be cross-linked globally. A photoresist layer can be applied to pattern and expose the areas of the film outside the trench regions (e.g., over the crests 20, 20′), and the exposed portions of the film 28, 28′ can be removed, for example, by an oxygen (O2) plasma treatment. The photoresist can then be removed (e.g., stripped). A neutral wetting film can then be formed on the exposed portions of the material layer 14, 14′ above the regions of the trench 16, 16′ (e.g., the crests 20, 20′). In other embodiments, a film of a photo-cross-linkable, neutral wetting random copolymer can be globally applied (e.g., cast) and photoexposed through a reticle to selectively cross-link the neutral wetting film only over the portions of the material layer 14, 14′ above the trenches 16, 16′ (e.g., the crests 20, 20′). Non-grafted or non-cross-linked portions of the neutral wetting film (e.g., within the trenches 16, 16′) can then be removed, for example, by a solvent rinse (e.g., toluene). See, for example, Hawker et al., “Improving the Manufacturability and Structural Control of Block Copolymer Lithography,” Abstracts of Papers, 232nd ACS National Meeting, San Francisco, Calif., Sep. 10-14, 2006, the disclosure of which is incorporated by reference herein.
Referring now to FIGS. 4A-4C, a layer of a lamellar-phase block copolymer material 36 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 then deposited (e.g., by spin casting) onto the annealed and cross-linked base film 28 within the trenches 16 and onto the neutral wetting layer 34 overlying the material layer 14 (e.g., crest 20) outside the trenches 16. The copolymer material 25 can be spin cast, for example, from a dilute solution of the copolymer in an organic solvent (e.g., about 0.25 wt % to 2 wt % solution).
The lamellar-phase block copolymer layer 36 is cast over the neutral wetting layer 34, 34′ (e.g., over crest 20) and the base film 28 within the trenches 16 to a thickness (t2) at or about the Lo value of the block copolymer material 36 such that, upon annealing, the copolymer film layer 36 will self-assemble to form a single layer of perpendicular-oriented lamellar domains each having a width (W2) of about Lo.
As shown in FIGS. 5A-5C, annealing of the lamellar-phase block copolymer layer 36 is then conducted to cause the polymer blocks to separate and self-assemble into a film 38, 38′ composed of perpendicular-oriented lamellar-phase domains 40, 42 and 40′, 42′ in a striped pattern, for example, at about 180° C. to 195° C. for a PS-b-PMMA copolymer film. An annealing process is performed to achieve ordering of the lamellar blocks across plateaus or crests 20, 20′ between the trenches 16, 16′ and other areas of the substrate 10, 10′ that are without constraints or defined features or boundaries (e.g., sidewalls 22, 22′ and/or edges 24, 24′ of trenches 16, 16′) to which self-assembling copolymer blocks can align.
Current methods for annealing a block copolymer film to cause microphase separation of the polymer blocks involve placing the film-coated substrate into a vacuum oven and heating the entire film globally and simultaneously at a single set temperature and time period. However, while global heating may produce a film that is ordered and registered within the trenches, on areas of the substrate beyond the confines of the trenches that lack constraints or topographic features to which the copolymer film can self-align or that will drive the self-assembling blocks in a set direction, the block copolymer film will self-assemble into randomly ordered structures in a meandering fingerprint-type configuration. See, for example, R. Ruiz, R. L. Sandstrom and C. T. Black, “Induced Orientational Order in Symmetric Diblock Copolymer Thin-Films,” Advanced Materials, 2007, 19(4), 587-591. That layout and the lack of ordering of repeat structures make the film unusable for most templating applications.
Rather than performing a global heating of the film, embodiments of the invention utilize techniques for performing an anneal of the copolymer film by a localized application of thermal energy to portions of the polymer film that have registry to them.
With reference to FIGS. 4A-4C, initially, a limited area of the lamellar-forming film 36, 36′ over and above the trenches 16, 16′, region “A” shown as dashed line “A” in FIG. 4A, is selectively heated to cause self-assembly of the polymer domains and produce ordered lamellar domains that are registered to the underlying base film 28, 28′ within the trenches 16, 16′. During the anneal, the base film 28, 28′ imposes an induced ordering effect on the overlying self-assembling lamellar film 36, 36′ to reproduce the underlying pattern of the base film 28, 28′. Intrinsic periods of the two block copolymer materials 26, 36 and 26′, 36′ can be matched, for example, through a ternary blend of either or both of the copolymer materials 26, 36 and 26′, 36′ with one or more homopolymers to adjust the polymer periods (Lo values). See, for example, R. Ruiz, R. L. Sandstrom and C. T. Black, “Induced Orientational Order in Symmetric Diblock Copolymer Thin-Films,” Advanced Materials, 2007, 19(4), 587-591, the disclosure of which is incorporated by reference herein.
As illustrated in FIGS. 5A-5C, this initial anneal results in the formation of a single layer 38, 38′ of assembled and ordered, perpendicular-oriented lamellar domains 40, 42 and 40′, 42′ that are registered to the underlying assembled domains of the base film 28, 28′ within the trenches 16, 16′, i.e., the lamellar domains 30, 32 and 30′, 32′ (FIG. 5B) or the half-cylinders 30′ and matrix domains 32′ (FIG. 5C) of the base film 28, 28′ within the trenches 16, 16′. The annealed copolymer layer 38, 38′ comprises alternating stripes of the two components of the lamellar-phase block copolymer. Only those portions of the copolymer film 36, 36′ that are heated above the glass transition temperature of the component polymer blocks will self-assemble, and areas of the copolymer film 36, 36′ situated outside of region “A” that were not sufficiently heated remain as the initially deposited disordered and unassembled block copolymer film 36, 36′. A temperature gradient can be provided across the substrate 10, 10′, with the temperature above the glass transition temperature in regions where annealing of the film occurs to produce registered and ordered structures, and below the glass transition temperature in areas outside of those regions.
Following the annealing and ordering of the copolymer film 38 within region “A”, the zone of thermal heating (“thermal corona”) is expanded laterally, using the initially formed self-assembled lamellar structure 38 over the trenches 16 to induce an ordering effect on the adjacently situated unannealed portion of the polymer film 36 beyond the edges 24 of the trenches 16 (region “B1”). In some embodiments, the localized heating of the lamellar-forming film 36 is performed to limit heating to about three through four to six through eight pitches or repeat units, Lo, of the copolymer film 30 at a time, e.g., to dashed line of region “B1” in FIGS. 5A-5C. The newly annealed portion of the film (i.e., region “B1”) will then self-assemble into perpendicular-oriented lamellar domains in an ordered repeat pattern that matches and is registered to the previously formed adjacent array within region “A”, as shown in FIGS. 6A-6C. Once the ordering of lamellae within the annealed zone has been completed, the zone of heating can be further expanded laterally (region “B2”) to anneal additional portions of the second block copolymer film adjacent to the previously annealed and ordered portion of the film (i.e., region “B1”) to extend the range of ordered structures over the substrate 10 until the desired pattern repeat structure is obtained.
In one embodiment, depicted in FIGS. 7A and 7B, annealing of the lamellar-phase block copolymer layer 36 is accomplished by focused and localized thermal heating of a targeted area (e.g., region “A”) by directing a laser source 44 of short-UV wavelength onto the film. The laser source 44 (with adequate power) can be illuminated through a mask (or reticle) 46 or masking elements associated with a laser beam apparatus that shades all areas except for the trenches or inner portions of the trenches. Where the rate of microphase domain segregation is on the order of heat transfer through the film 36, the sections of the film situated above the ordered cylindrical film within the trenches will self-assemble first and in registry with the pattern of the underlying base film 28. The continued addition of thermal energy radiating laterally from the initially assembled, registered portion of the film 36 (within region “A”) can be applied to result in regular, registered self-assembly across the breadth of the lamellar-phase film 36 (regions “B1” as in FIG. 5A). The beam of laser source 44 can also be expanded (e.g., defocused) to widen the area of coverage of the film 36, or step-scanned or sweep-scanned across the substrate 10 (arrow in FIG. 7B), with the scanning rate set appropriately. The laser source is applied at appropriate parameters (e.g., wavelength, pulse length, intensity) to anneal the targeted area of the film 36. The anneal can be provided using a pulsed laser source.
In another embodiment, illustrated in FIGS. 8A and 8B, a series of thin conductive lines 48 of a thermally conductive material (e.g., metal) can be formed in or on the substrate 10 prior to forming the material layer 14. As shown, the conductive lines 48 are provided to extend beneath the trenches 16, and optionally to extend under the material layer 14 beyond the trenches 16. Heat can be generated through the conductive lines 48 to initially anneal the film (see FIGS. 7A and 7B) above the trenches 16, and then to radiate laterally to anneal areas of the film adjacent to the self-assembled film 38 (see FIGS. 7A and 7B) above the trenches 16.
In yet another embodiment, selective localized heating of the lamellar-phase film 36 can be provided by selectively applying an absorptive material layer 50 to substrate 10 prior to depositing the neutral wetting layer 12 and the material layer 14, as shown in the embodiment depicted in FIG. 9, or a reflective material layer 50′ to the surface of the material layer 14′ outside of the trenches (e.g., the crests 20′) as depicted in FIGS. 10A and 10B. Upon application of a radiative heat source (e.g., infrared (IR) heat source or quartz lamp) (arrows ↓), there will be a difference in absorption and/or reflectivity between the area having the reflective or absorptive material layer 50, 50′ thereon and those areas that do not, such that localized areas of the film 36 will be heated to above the glass transition temperature while surrounding material will be below that temperature. As lamellae form, the power of the light source can then be slowly increased to expand the area having a temperature above the glass transition temperature, allowing the ordered formation of lamellae along the advancing hot zone. Examples of suitable materials for the absorptive material layer 50 (FIG. 9) include absorptive materials such as silicon carbide and organic infrared (IR) or near-infrared (NIR) absorbers such as Lumogen fluorescent dyes (e.g., Lumogen IR 765 and Lumogen IR 788) (BASF), among others. In other embodiments, the neutral wetting layer 12 can be modified or tailored with absorptive functionality. Examples of suitable materials for layer 50′ (FIGS. 10A and 10B) include reflective metals such as aluminum (Al), tungsten (W), chromium (Cr), copper (Cu), ruthenium (Ru), nickel (Ni), among others.
In some embodiments, such as shown in FIG. 9, the backside of the substrate 10 (e.g., wafer) can be heated (arrows ↑) to produce differences in emissivity between the bottom (floor) 18 of trench 16 and the surrounding areas to yield a desired temperature gradient. A coating 50 of a low emissivity material (e.g., a metal such as aluminum, tungsten, etc.) can be applied to the floors 18 of trench 16 which will radiate less heat and maintain a higher temperature than the surrounding area.
In another embodiment, the film 36 can be annealed in a moving temperature gradient (zone annealed). For example, as illustrated in FIG. 11A, the film 36 can be moved across a hot-cold temperature gradient 52a positioned above the film 36 or beneath the substrate 10 (as shown) at a translational set speed (e.g., about 0.05 μm to 10 μm/second) using a motorized translation stage 54 whereupon ordering of nanostructures occurs at the backside as the film 36 re-cools after passing under or over the heat source. In another embodiment shown in FIG. 11B, a heat source can be positioned above the film 36 (e.g., heat source 52b) and/or or beneath the substrate 10 (e.g., heat source 52b′) and moved across the film 36 using a motorized mechanism.
Referring now to FIGS. 12A-12C, after annealing and the lamellar-phase block copolymer material 36 is ordered to form film 38, one of the block components can be selectively removed to produce a thin film 56 that can be used, for example, as a lithographic template or mask to pattern the underlying substrate 10 (and material layer 14 on the crests 20) in a semiconductor processing to define regular patterns in the nanometer size range (i.e., about 10 nm to 100 nm). Within the trenches 16, selective removal of both a lamellar domain (e.g., 40) and the underlying polymer domain of the base film (e.g., 30) is performed.
For example, as illustrated in FIG. 12B, selective removal of the PMMA domains 30, 40 will result in openings (slits) 58 separated by vertically oriented PS lamellar domains 32/42 with the trench floor 18 (e.g., neutral wetting layer 12 or substrate 10) exposed where the PMMA was removed. Removal of the PMMA phase domains 30, 40 can be performed, for example, by application of an oxygen (O2) plasma, or by a chemical dissolution process such as acetic acid sonication by first irradiating the sample (ultraviolet (UV) radiation, 1 J/cm2 254 nm light), then ultrasonicating the film in glacial acetic acid, ultrasonicating in deionized water, and rinsing the film in deionized water to remove the degraded PMMA.
Referring to FIG. 12C, in the use of a cylindrical-phase base film (28′ in FIG. 6C), the PS matrix 32′ situated underneath the half-cylinders 30′ and over the floors 18′ of trench 16′ remains after the removal of the PMMA domains, and is removed, for example, by plasma O2 etch, prior to a patterning process to expose the underlying substrate 10′ as illustrated in FIG. 12D.
In another embodiment, the selective removal of PS phase domains 32, 42 will result in openings (slits) 58 separated by PMMA lamellar domains 30, 40.
In some embodiments, the resulting films have a corrugated surface that defines a linear pattern of fine, nanometer-scale, parallel slits (openings) 58 about 5 nm to 50 nm wide and several microns in length (e.g., about 10 μm to 4000 μm), the individual slits 58 separated by a polymer matrix 42 about 5 nm to 50 nm wide. For example, removal of the PMMA domains affords a PS mask of sub-lithographic dimensions, for example, a pitch of about 35 nm (e.g., a 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 (and layer 14), for example, by a non-selective RIE etching process, to delineate a series of channels or grooves 60, shown in phantom in FIG. 12B. In some embodiments, the channels can then be filled with a conductive material (e.g., metal) to form nanowire channel arrays for transistor channels, semiconductor capacitors, and other structures, or with a dielectric material to separate active areas. 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 channels 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.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement that 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 method for forming a polymer material, comprising:
annealing a first block copolymer material within a trench in a substrate to form a base material comprising an ordered array of polymer domains;
forming a second block copolymer material over the base material within the trench and over a substrate surface adjacent the trench; and
selectively annealing a portion of the second block copolymer material overlying the base material relative to another portion of the second block copolymer material overlying the substrate surface adjacent the trench to form another ordered array of polymer domains comprising polymer domains registered to corresponding polymer domains of the base material.

2. The method of claim 1, further comprising annealing the another portion of the second block copolymer material to form an additional ordered array of polymer domains over the substrate surface adjacent the trench.

3. The method of claim 1, wherein selectively annealing a portion of the second block copolymer material overlying the base material relative to another portion of the second block copolymer material overlying the substrate surface adjacent the trench comprises directing a laser source of short-UV wavelength onto the portion of the second block copolymer material.

4. The method of claim 1, wherein selectively annealing a portion of the second block copolymer material overlying the base material relative to another portion of the second block copolymer material overlying the substrate surface adjacent the trench comprises conducting heat through conductive elements within the substrate and extending a length of the trench.

5. The method of claim 1, further comprising conducting heat through conductive elements within the substrate and lateral to the trench to selectively anneal the another portion of the second block copolymer material.

6. The method of claim 1, wherein selectively annealing a portion of the second block copolymer material overlying the base material relative to another portion of the second block copolymer material overlying the substrate surface adjacent the trench comprises globally applying a heat source to heat an absorptive material or a reflective material only located over a floor of the trench.

7. The method of claim 1, wherein at least one of annealing the first block copolymer material and selectively annealing a portion of the second block copolymer material overlying the base material comprises applying heat to a backside of the substrate.

8. A method for forming a polymer material, comprising:
annealing a first block copolymer material within a trench in a substrate to form a base material comprising an ordered array of polymer domains;
forming a second block copolymer material on the base material; and
annealing only a portion of the second block copolymer material to form another ordered array of polymer domains comprising polymer domains registered to corresponding polymer domains of the base material.

9. A method for forming a polymer material, comprising:
forming a first block copolymer material on surfaces of a trench in a substrate and on a substrate surface adjacent the trench;
annealing the first block copolymer material to form a base material comprising an ordered array of polymer domains within the trench;
selectively cross-linking the base material within the trench;
removing a non-cross-linked portion of the first block copolymer material on the substrate surface adjacent the trench;
forming a second block copolymer material on the base material within the trench and on the substrate surface adjacent the trench; and
annealing the second block copolymer material only on the base material within the trench to form another ordered array of polymer domains comprising polymer domains registered to corresponding polymer domains of the base material.

10. A method for forming a polymer material, comprising:
forming a first block copolymer material on surfaces of a trench in a substrate and on a substrate surface adjacent the trench;
annealing the first block copolymer material to form an annealed first block copolymer material on the substrate surface adjacent the trench and a base material comprising an ordered array of polymer domains within the trench;
globally cross-linking the annealed first block copolymer material and the base material;
masking the base material;
removing the annealed first block copolymer material to expose the substrate surface adjacent the tele-trench;
forming a second block copolymer material over the base material and on the exposed substrate surface adjacent the trench; and
annealing the second block copolymer material only overlying the base material to form another ordered array of polymer domains comprising polymer domains registered to corresponding polymer domains of the base material.

11. The method of claim 10, wherein removing the annealed first block copolymer material comprises subjecting the annealed first block copolymer material to an oxygen plasma treatment.

12. A method of forming a polymer material, comprising:
forming a first block copolymer material in a trench;
annealing the first block copolymer material to form a base material comprising self-assembled polymer domains;
forming a second block copolymer material over at least the base material; and
selectively annealing the second block copolymer material overlying the base material to form additional self-assembled polymer domains comprising polymer domains registered to corresponding polymer domains of the base material.

13. The method of claim 12, wherein forming a first block copolymer material in a trench comprises forming the first block copolymer comprising a lamellar-phase block copolymer in the trench.

14. The method of claim 13, wherein annealing the first block copolymer material to form a base material comprising self-assembled polymer domains comprises forming alternating lamellar domains oriented parallel to sidewalls of the trench and oriented perpendicular to a floor of the trench.

15. The method of claim 12, wherein forming a first block copolymer material in a trench comprises forming the first block copolymer comprising a cylindrical-phase block copolymer in the trench.

16. The method of claim 15, wherein annealing the first block copolymer material to form a base material comprising self-assembled polymer domains comprises forming lines of half-cylinder polymer domains in a polymer matrix, the lines of half-cylinder polymer domains extending parallel to sidewalls and a floor of the trench.

17. The method of claim 12, wherein selectively annealing the second block copolymer material overlying the base material to form additional self-assembled polymer domains comprising polymer domains registered to corresponding polymer domains of the base material comprises forming the additional self-assembled polymer domains to comprise lamellar polymer domains registered to corresponding lamellar polymer domains of the base material.