Patent Abstract:
Methods for fabricating sublithographic, nanoscale polymeric microstructures utilizing self-assembling block copolymers, and films and devices formed from these methods are provided.

Full Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 12/106,562, filed Apr. 21, 2008, now U.S. Pat. No. 8,114,300. 
    
    
     TECHNICAL FIELD 
     Embodiments of the invention relate to methods of fabricating 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. Making electrical contacts to conductive lines has become a significant challenge as the dimensions of semiconductor features shrink to sizes that are not easily accessible by conventional lithography. Optical lithographic processing methods have difficulty fabricating structures and features at the sub-30 nanometer level. The use of self-assembling diblock copolymers presents another route to patterning at nanoscale 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. 
     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 5-50 nm. 
     In some applications, the self-assembled films are further processed to selectively remove one of the blocks, leaving the other polymer block as an etch mask on the substrate. However, in some applications, the polymer block that is removed does not extend completely through the film and requires an additional etch of material to expose the underlying substrate, resulting in a reduction in the aspect ratio of the mask openings and the subsequently etched line or other opening in the substrate. 
     It would be useful to provide methods of fabricating films of ordered nanostructures that can be readily used to in semiconductor manufacturing. 
    
    
     
       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  illustrates an elevational, cross-sectional view of the substrate showing a block copolymer material within trenches in a substrate. 
         FIG. 2  illustrates a cross-sectional view of the substrate of  FIG. 1  at a subsequent stage showing a self-assembled block copolymer film composed of parallel cylinders within the trenches.  FIG. 2A  is a top plan view of a portion of the substrate of  FIG. 2  taken along line  2 A- 2 A. 
         FIG. 3  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.  FIGS. 3A and 3B  are elevational, cross-sectional views of the substrate depicted in  FIG. 3  taken along lines  3 A- 3 A and  3 B- 3 B, respectively. 
         FIG. 4  illustrates a top plan view of the substrate of  FIG. 3  at a subsequent stage showing the formation of trenches in a material layer formed on a substrate.  FIGS. 4A and 4B  illustrate elevational, cross-sectional views of a portion of the substrate depicted in  FIG. 4  taken, respectively, along lines  4 A- 4 A and  4 B- 4 B. 
         FIGS. 5 and 8  are top plan views of the substrate of  FIG. 4  at subsequent stages in the fabrication of a self-assembled block copolymer film according to an embodiment of the disclosure.  FIGS. 5A and 8A  illustrate elevational, cross-sectional views of a portion of the substrate depicted in  FIGS. 5 and 8  taken along lines  5 A- 5 A to  8 A- 8 A, respectively.  FIGS. 5B and 8B  are cross-sectional views of the substrate depicted in  FIGS. 5 and 8  taken along lines  5 B- 5 B to  8 B- 8 B, respectively.  FIG. 8C  is a top plan view of the substrate depicted in  FIG. 8A  taken along lines  8 C- 8 C. 
         FIGS. 9 and 10  are top plan views of the substrate of  FIG. 8  at subsequent stages, illustrating an embodiment of the removal of one of the polymer blocks to form a mask to etch the substrate.  FIGS. 9A and 10A  illustrate elevational, cross-sectional views of a portion of the substrate depicted in  FIGS. 9 and 10  taken along lines  9 A- 9 A and  10 A- 10 A, respectively.  FIGS. 9B and 10B  are cross-sectional views of the substrate depicted in  FIGS. 9 and 10  taken along lines  9 B- 9 B to  10 B- 10 B, respectively. 
         FIG. 11  is a top plan view of the substrate of  FIG. 10  at a subsequent stage, illustrating filling of the etched openings in the substrate.  FIGS. 11A and 11B  illustrate elevational, cross-sectional views of a portion of the substrate depicted in  FIG. 11  taken along lines  11 A- 11 A and  11 B- 11 B, 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. 
     “L o ” as used herein is the inherent periodicity or pitch value (bulk period or repeat unit) of structures that self-assemble upon annealing from a self-assembling (SA) block copolymer. “L B ” as used herein is the periodicity or pitch value of a blend of a block copolymer with one or more of its constituent homopolymers. “L” is used herein to indicate the center-to-center cylinder pitch or spacing of cylinders of the block copolymer or blend, and is equivalent to “L o ” for a pure block copolymer and “L B ” for a copolymer blend. 
       FIGS. 1 and 2  illustrate the fabrication of a self-assembled film from a cylindrical-phase block copolymer (e.g., PS-b-P2VP) to form cylinders that are oriented parallel to the substrate surface. As shown in  FIG. 1 , a substrate  10  (with active areas  12 ) is provided with an overlying material layer  14  that has been etched to form trenches  16  separated by spacers  18 . The trenches include sidewalls  20 , ends  22  and a floor  24  that are preferential wetting to the minority block of the block copolymer material, e.g., oxide, etc. The width (w t ) of the trenches  16  is about 1.5*L and the depth (D t ) is about L. The thickness (t) of the block copolymer material  26  is about 1.5*L. 
     As depicted in  FIGS. 2 and 2A , annealing produces a self-assembled film  28  composed of parallel cylinders  30  (diameter (d)˜0.5*L) of the minority block (e.g., P2VP) embedded within (or surrounded by) a matrix  32  of the majority block (e.g., PS) of the block copolymer material. A brush layer  30   a  (thickness 0.5*L) forms on the preferential wetting surfaces (e.g., oxide, etc.) of the trenches and over the surface of the material layer  14  as a bilayer composed of the minority block wetting the trench surfaces. For example, a layer of P2VP domains will wet oxide interfaces, with attached PS domains directed away from the oxide material. 
     The resulting film  28  with parallel cylinders  30  can be used, for example, for patterning lines, but is not useful for fabricating an etch mask for patterning vias. In addition, a thickness of the block copolymer material  26  at about 1.5*L is required at the time of annealing to produce the parallel cylinders as continuous lines. 
     In embodiments of the invention, a polymer material (e.g., film, layer) is prepared by guided self-assembly of block copolymers, with both polymer domains at the air interface. Block copolymer materials spontaneously assemble into periodic structures by microphase separation of the constituent polymer blocks after annealing, forming ordered domains at nanometer-scale dimensions. In embodiments of the invention, a cylindrical-phase block copolymer layer with ordered structures is formed as a base layer or film within a trench and used as a template to induce ordering of a subsequently deposited cylindrical-phase block copolymer resulting in a stacked double- or multi-layer structure having perpendicular-oriented cylinders in a polymer matrix. Following self-assembly, the pattern of perpendicular-oriented cylinders that is formed can then be used, for example, as an etch mask for patterning nanosized features (e.g., vias) into the underlying substrate through selective removal of one block of the self-assembled block copolymer. 
     A method for fabricating a self-assembled block copolymer material that defines an array of nanometer-scale, perpendicular-oriented cylinders according to an embodiment of the invention is illustrated in  FIGS. 3-8 . 
     The described embodiment involves a thermal anneal of a cylindrical-phase block copolymer in combination with a graphoepitaxy technique that utilizes a lithographically defined trench as a guide with a floor, sidewalls and ends that are preferential wetting to one polymer block and function as constraints to induce self-assembly of the block copolymer of the base layer into an ordered one-dimensional (1-D) array of perpendicular-oriented cylindrical domains (“perpendicular cylinders”) within a polymer matrix, and the cylindrical-phase block copolymer of the overlying layer into cylinders in a polymer matrix oriented perpendicular and registered to the underlying perpendicular cylinders. In some embodiments, multiple lines of the underlying perpendicular cylinders can be formed in each trench with the overlying perpendicular-oriented cylinders. 
     The term “perpendicular cylinders” used herein is understood to refer to the structure of the minority block of the base layer within the trenches, which shape can range from a half-sphere to an elongated cylinder with a rounded end, and is embedded within (surrounded by) a matrix of the majority block with a face wetting the air interface. The conditions provided in embodiments of the invention induce an orientational transition relative to the trench floor/substrate from parallel-oriented cylinders (“surface-parallel” cylinders) to perpendicular-oriented cylinders (“surface-normal” cylinders). 
     As depicted in  FIGS. 3-3B , a substrate  10 ′ is provided. As further illustrated, conductive lines  12 ′ (or other active area, e.g., semiconducting regions) are situated within the substrate  10 ′. 
     A material layer  14 ′ (or one or more material layers) is formed over the substrate  10 ′ and etched to form trenches  16 ′ that are oriented perpendicular to an array of conductive lines  12 ′, as shown in  FIGS. 4-4B . Portions of the material layer  14 ′ form a spacer  18 ′ outside and between the trenches. The trenches  16 ′ are structured with opposing sidewalls  20 ′, opposing ends  22 ′, a floor  24 ′, a width (w t ), a length (l t ) and a depth (D t ). 
     In any of the described embodiments, a single trench or multiple trenches can be formed in the material layer  14 ′, and can span the entire width of an array of lines (or other active area). In embodiments of the invention, the substrate  10 ′ is provided with an array of conductive lines  12 ′ (or other active areas) at a pitch of L. The trench or trenches are formed over the active areas  12 ′ (e.g., lines) such that when the block copolymer material is annealed, each cylinder will be situated above a single active area  12 ′ (e.g., conductive line). In some embodiments, multiple trenches are formed with the ends  22 ′ of each adjacent trench  16 ′ aligned or slightly offset from each other at less than 5% of L such that cylinders in adjacent trenches are aligned and situated above the same line  12 ′. 
     Single or multiple trenches  16 ′ (as shown) can be formed using a lithographic tool having an exposure system capable of patterning at the scale of L (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. 
     A method called “pitch doubling” or “pitch multiplication” can also be used for extending the capabilities of photolithographic techniques beyond their minimum pitch, as described, for example, in U.S. Pat. No. 5,328,810 (Lowrey et al.), U.S. Pat. No. 7,115,525 (Abatchev, et al.), US 2006/0281266 (Wells) and US 2007/0023805 (Wells). Briefly, a pattern of lines is photolithographically foamed in a photoresist material overlying a layer of an expendable material, which in turn overlies a substrate, the expendable material layer is etched to form placeholders or mandrels, the photoresist is stripped, spacers are formed on the sides of the mandrels, and the mandrels are then removed leaving behind the spacers as a mask for patterning the substrate. Thus, where the initial photolithography formed a pattern defining one feature and one space, the same width now defines two features and two spaces, with the spaces defined by the spacers. As a result, the smallest feature size possible with a photolithographic technique is effectively decreased down to about 30 nm or less. 
     Factors in forming a 1-D array of perpendicular cylinders within the trenches include the width (w t ) of the trench, the formulation of the block copolymer or blend to achieve the desired pitch (L), and the total volume or thickness (t 2 ) of the block copolymer material within the trench at the end of the anneal at less than 2*L. 
     The width (w t ) of the trench can be varied according to the desired number of rows and pattern of perpendicular cylinders. In the illustrated embodiment, the trenches  16 ′ are constructed with a width (w t ) of about 1.5*L (or 1.5× the pitch value) of the block copolymer to form a single row of perpendicular cylinders. A cast block copolymer material (or blend) of about L and having a total thickness of less than 2*L at the end of anneal will self-assemble within the trenches  16 ′ into perpendicular cylinders in a single row or line that is aligned with the sidewalls down the center of each trench  16 ′ with a center-to-center pitch distance (p) between adjacent perpendicular cylinders at or about the pitch distance or L value of the block copolymer material. For example, in using a cylindrical-phase block copolymer with an about 35 nm pitch value or L, the width (w t ) of the trenches  16 ′ can be about 1.5*35 nm or about 55 nm to form a single row of perpendicular cylinders (each at about 20 nm diameter). 
     There is a shift from two rows to one row of the perpendicular cylinders as the width (w t ) of the trench is decreased and/or the periodicity (L value) of the block copolymer is increased, for example, by forming a ternary blend by the addition of both constituent homopolymers. The boundary conditions of the trench sidewalls  20 ′ in both the x- and y-axis impose a structure wherein each trench contains “n” number of features (e.g., n lines of perpendicular cylinders). 
     For example, in embodiments of the invention in which a trench has a width greater than 1.5*L, for example, a width of about 2*L to about 2.5*L, a cylindrical-phase block copolymer with a pitch of L and having a total thickness of less than 2*L at the end of anneal will self-assemble to form perpendicular cylinders in a hexagonal array or a zigzag pattern with adjacent cylinders offset by about 0.5*L for the length (b) of the trench, rather than a single line row of perpendicular cylinders each separated by about L (center-to-center distance) and aligned with the sidewalls down the center of the trench. For example, a cylindrical-phase block copolymer material having a L value of about 35 nm within a trench having a width of about 2-2.5*L or about 70-87.5 nm will self-assemble to form a hexagonal array of perpendicular cylinders (about 20 nm diameter) with a center-to-center pitch distance between adjacent cylinders of about 0.5*L value. 
     The depth (D t ) of the trenches  16 ′ is effective to direct lateral ordering of the block copolymer material during the anneal. In embodiments of the invention, the depth (D t ) of the trenches  16 ′ is at or less than the final thickness (t 2 ) of the block copolymer material (D t ≦t 2 ), which minimizes the formation of a meniscus and variability in the thickness of the block copolymer material across the trench width. In some embodiments, the trench depth is about 50-90% less, or about one-half to about two-thirds (about ½-⅔, or about 50%-67%) less than the final thickness (t 2 ) of the block copolymer material within the trench. 
     The length (l t ) of the trenches  16 ′ is according to the desired number of perpendicular cylinders in a row, and is generally at or about n*L or an integer multiple of L, and typically within a range of about n*10 to about n*100 nm (with n being the number of features or structures, e.g., perpendicular cylinders). 
     The width of the mesas or spacers  18 ′ between adjacent trenches can vary and is generally about L to about n*L. In some embodiments, the trench dimension is about 20-100 nm wide (w t ) and about 100-25,000 μm in length (l t ) with a depth (D t ) of about 10-100 nm. 
     The trench sidewalls  20 ′, ends  22 ′ and floor  24 ′ are preferential wetting by a minority block of the block copolymer to induce registration of cylinders (of the minority block) in a perpendicular orientation to the trench floor as the polymer blocks self-assemble to form the base layer  28 ′. The substrate  10 ′ and material layer  14 ′ can be formed from the same or a highly similar material that is inherently preferential wetting to the minority (preferred) polymer block (e.g., PMMA of a PS-b-PMMA material) or, in other embodiments, a preferential wetting material can be applied onto the surfaces of the trenches  16 ′. 
     To provide preferential wetting surfaces, for example, in the use of a PS-b-PMMA or PS-b-PVP block copolymer, the substrate  10 ′ and the material layer  14 ′ can be composed of an inherently preferential wetting material such as a clean silicon surface (with native oxide), oxide (e.g., silicon oxide, SiO x ), silicon nitride, silicon oxycarbide, indium tin oxide (ITO), silicon oxynitride, and resist materials such as methacrylate-based resists and polydimethyl glutarimide resists, among other materials, which exhibit preferential wetting toward the preferred block (e.g., the minority block) (e.g., PMMA, PVP, etc.). Upon annealing and self-assembly of the block copolymer material, the preferred (minority) block (e.g., the PMMA block, PVP block, etc.) will form a thin interface layer along the preferential wetting surfaces  20 ′,  22 ′,  24 ′ of the trenches. 
     In other embodiments utilizing PS-b-PMMA, a preferential wetting material such as a polymethylmethacrylate (PMMA) polymer modified with an —OH containing moiety (e.g., hydroxyethyl methacrylate) can be applied onto the surfaces of the trenches. An OH-modified PMMA can be applied, for example, by spin coating and then heating (e.g., to about 170° C.) to allow the terminal —OH groups to end-graft to oxide surfaces (e.g., sidewalls  20 ′, ends  22 ′, floor  24 ′). Non-grafted material can be removed 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. 
     Referring now to  FIGS. 5-5B , a self-assembling, cylindrical-phase block copolymer material  26 ′ having an inherent pitch at or about L o  (or a ternary blend of block copolymer and homopolymers blended to have a pitch at or about L B ) is deposited into the trenches  16 ′ to form a base layer  28 ′. 
     Nonlimiting examples of diblock copolymers include, for example, poly(styrene)-b-poly(methylmethacrylate) (PS-b-PMMA) or other PS-b-poly(acrylate) or PS-b-poly(methacrylate), poly(styrene)-b-poly(vinylpyridine) (PS-b-PVP), poly(styrene)-b-poly(lactide) (PS-b-PLA), and poly(styrene)-b-poly(tert-butyl acrylate) (PS-b-PtBA), poly(styrene)-b-poly(ethylene-co-butylene (PS-b-(PS-co-PB)), poly(styrene)-b-poly(ethylene oxide) (PS-b-PEO), polybutadiene-b-poly(vinylpyridine) (PB-b-PVP), poly(ethylene-alt-propylene)-b-poly(vinylpyridine) (PEP-b-PVP), and poly(styrene)-b-poly(dimethylsiloxane) (PS-b-PDMS), among others, with PS-b-PMMA used in the illustrated embodiment. Other types of block copolymers (i.e., triblock or multiblock copolymers) can be used. Examples of triblock copolymers include ABC copolymers such as poly(styrene-b-methyl methacrylate-b-ethylene oxide) (PS-b-PMMA-b-PEO), and ABA copolymers such as PS-PMMA-PS, PMMA-PS-PMMA, and PS-b-PI-b-PS, among others. 
     In some embodiments of the invention, the block copolymer or blend is constructed such that the minor domain can be selectively removed. 
     The L value of the block copolymer can be modified, for example, by adjusting the molecular weight of the block copolymer. The block copolymer material can also be formulated as a binary or ternary blend comprising a block copolymer and one or more homopolymers (HPs) of the same type of polymers as the polymer blocks in the block copolymer, to produce a blend that will swell the size of the polymer domains and increase the L value. The concentration of homopolymers in a blend can range from 0 to about 60 wt-%. Generally, when added to a polymer material, both homopolymers are added to the blend in about the same ratio or amount. An example of a ternary diblock copolymer/homopolymer blend is a PS-b-PVP/PS/PVP blend, for example, 60 wt-% of 32.5 K/12 K PS-b-PVP, 20 wt-% of 10K PS, and 20 wt-% of 10K PVP. Another example of a ternary diblock copolymer/homopolymer blend is a PS-b-PMMA/PS/PMMA blend, for example, 60 wt-% of 46K/21K PS-b-PMMA, 20 wt-% of 20K polystyrene and 20 wt-% of 20K poly(methyl methacrylate). Yet another example is a blend of 60:20:20 (wt-%) of PS-b-PEO/PS/PEO, or a blend of about 85-90 wt-% PS-b-PEO and up to 10-15 wt-% PEO homopolymer. 
     The film morphology, including the domain sizes and periods (L) of the microphase-separated domains, can be controlled by chain length of a block copolymer (molecular weight, MW) and volume fraction of the AB blocks of a diblock copolymer to produce cylindrical morphologies (among others). For example, in embodiments of the invention, for volume fractions at ratios of the two blocks generally between about 60:40 and 80:20, the diblock copolymer will microphase separate and self-assemble into periodic perpendicular cylinder domains of polymer B within a matrix of polymer A. An example of a cylinder-forming PS-b-PVP copolymer material (L o ˜28 nm) to form about 14 nm diameter perpendicular cylinder PVP domains in a matrix of PS is composed of about 70 wt-% PS and 30 wt-% PVP with a total molecular weight (M n ) of 44.5 kg/mol. An example of a cylinder-forming PS-b-PMMA copolymer material (L o =35 nm) to form about 20 nm diameter perpendicular cylinder PMMA domains in a matrix of PS is composed of about 70 wt-% PS and 30 wt-% PMMA with a total molecular weight (M n ) of 67 kg/mol. As another example, a PS-b-PLA copolymer material (L=49 nm) can be composed of about 71 wt-% PS and 29 wt-% PLA with a total molecular weight (M n ) of about 60.5 kg/mol to form about 27 nm diameter perpendicular cylinder PLA domains in a matrix of PS. 
     The block copolymer material can be deposited by spin casting (spin-coating) from a dilute solution (e.g., about 0.25-2 wt % solution) of the block copolymer in an organic solvent such as dichloroethane (CH 2 Cl 2 ) or toluene, for example. Capillary forces pull excess block copolymer material  26 ′ (e.g., greater than a monolayer) into the trenches  16 ′. As shown in  FIG. 5A , a thin layer or film  26   a ′ of the block copolymer material can be deposited onto the material layer  14 ′ outside the trenches, e.g., on the mesas/spacers  18 ′. Upon annealing, the thin film  26   a ′ (in excess of a monolayer) will flow off the mesas/spacers  18 ′ into the trenches leaving a structureless brush layer on the material layer  14 ′ from a top-down perspective. 
     Referring now to  FIGS. 6-6B , the block copolymer material  26 ′ is then annealed to form the self-assembled base layer  28 ′. 
     Upon annealing, the cylindrical-phase block copolymer material (e.g., PS-b-PMMA) will self-assemble in response to the constraints provided by the width (w t ) of the trench  16 ′ and the character of the cylindrical-phase block copolymer composition  26 ′ (e.g., PS-b-PMMA having an inherent pitch at or about L) combined with trench surfaces  20 ′,  22 ′,  24 ′ that are preferential wetting by the minority or preferred block of the block copolymer (e.g., the PMMA block), and a total thickness (t 2 ) of the BCP material  26 ′ within the trench of less than 2*L at the end of anneal. Enthalpic forces drive the wetting of a preferential-wetting surface by the preferred block (e.g., the minority block). In some embodiments in which the width (w) of the trench is greater than 1.5*L, an ordered hexagonal array of perpendicular cylinders can be formed in each trench. 
     The resulting base layer  28 ′ is composed of a monolayer of perpendicular cylinder domains  34 ′ of the preferred (minority) block (e.g., PMMA) within a matrix  36 ′ of the majority polymer block (e.g., PS) oriented perpendicular to the trench floor  24 ′ and registered and aligned parallel to the trench sidewalls  20 ′ in a row down the middle of each trench for the length of the trench and spaced apart at a center-to-center pitch distance of about L. A face  38 ′ of the perpendicular cylinders wets the air interface (surface exposed) and the opposing ends  40 ′ are embedded in (surrounded by) the polymer matrix  36 ′. The diameter (d) of the perpendicular cylinders  34 ′ will generally be about one-half of the center-to-center distance (pitch distance, p) between the perpendicular cylinders. Upon annealing, a layer of the minority (preferred) block segregates to and wets the sidewalls  20 ′, ends  22 ′ and floor  24 ′ of the trenches to form a thin brush wetting layer  34   a ′ with a thickness of generally about 0.5*L. The brush layer  34   a ′ is a bilayer of the minority block domains (e.g., PMMA) wetting trench (e.g., oxide) interfaces with attached majority block domains (e.g., PS) directed away from the trench surfaces and in contact with the majority block domains (e.g., PS) of the matrix  36 ′ at the surface of the perpendicular cylinder domains  34 ′. 
     The resulting morphology of the annealed polymer material base layer  28 ′, i.e., the perpendicular orientation of the perpendicular cylinders  34 ′, can be examined, for example, using atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM). 
     In some embodiments, the self-assembled base layer  28 ′ is defined by an array of perpendicular cylinders  34 ′ in a polymer matrix  36 ′ and a brush layer  34   a ′ (at about 0.5*L thick), each cylinder  34 ′ having a rounded end  40 ′ and a diameter at or about 0.5*L, with the number (n) of perpendicular cylinders in the row according to the length of the trench, and the center-to-center distance (pitch distance, p) between perpendicular cylinders at or about L. 
     The block copolymer material  26 ′ is cast into the trenches  16 ′ to an initial thickness (t 1 ) such that upon completion of inflow of polymer material off the mesas/spacers  18 ′ into the trenches and at the end of the anneal, the total volume or thickness (t 2 ) of the block copolymer material  26 ′ will induce and result in the formation of perpendicular cylinders  34 ′ in the trench. 
     In embodiments of the invention, the block copolymer material  26 ′ within the trenches at the end of the anneal has an insufficient volume of polymer material to fully form surface parallel cylinders ( 30 ) that would typically result under the same or similar conditions (e.g., of trench width (w t ), trench depth (D t ), block copolymer material at about L, preferentially wetting trench surfaces). The total volume or thickness (t 2 ) of the block copolymer (BCP) material  26 ′ after the anneal is effective to induce a transition from a surface parallel to a surface normal (or perpendicular) orientation of cylindrical domains relative to the trench floor/substrate surface. The thickness of the block copolymer material  26 ′ can be measured, for example, by ellipsometry techniques. 
     For example, to form the surface parallel cylinder morphology  30  as illustrated in  FIGS. 1 and 2 , in the application of a block copolymer (such as PS-b-P2VP) in which the minority block (e.g., P2VP) is strongly preferentially wetting to the trench surfaces (e.g., oxide) and the majority block is preferential wetting to the air interface (e.g., PS, which has a lower surface tension, preferentially wets a clean dry air atmosphere), a typical thickness (t) of the block copolymer material  26  at the end of the anneal to form a monolayer of parallel cylinders (and a brush layer  30   a ) is t=b+L (where b is the thickness of the brush layer  30   a  at about 0.5*L), or t=0.5*L+L=1.5*L. 
     According to embodiments of the invention, the thickness (t 2 ) of a block copolymer material  26 ′ such as PS-b-P2VP at the end of the anneal should be sufficiently less than the thickness t=b+L (e.g., t&lt;1.5*L) to result in a switch in the orientation of the cylinders from surface parallel ( FIG. 2 , cylinders  30 ) to perpendicular (or surface normal) ( FIG. 6A , cylinders  34 ′) while retaining the brush layer  34   a ′ in contact with the trench surfaces  20 ′,  22 ′,  24 ′. In addition, the face  38 ′ of the perpendicular cylinders  34 ′ wets the air interface and the opposing ends  40 ′ are rounded. In some embodiments, the total volume or thickness (t 2 ) of a PS-b-P2VP block copolymer material  26 ′ (or similar polymer material) after inflow from the mesas/spacers  18 ′ and at the end of anneal is about 5-30% less (or about 10-20% less) than the 1.5*L value of the block copolymer material, or t 2 ˜70-95%*(1.5*L). For example, for a PS-b-P2VP block copolymer material where L=35 nm, the PS-b-P2VP block copolymer material  26 ′ can be cast into the trenches  16 ′ and the polymer material  26   a ′ caused to flow into the trenches wherein the total volume or thickness (t 2 ) of the block copolymer material  26 ′ at the end of anneal is [(about 0.70 to about 0.95)*(1.5*35 nm)], or about 36.75-49.9 nm thick. 
     In embodiments utilizing a block copolymer (such as PS-b-PMMA) in which the minority block (e.g., PMMA) is preferentially wetting to trench surfaces (e.g., oxide) and both the minority block and the majority block (e.g., PS) wet the air interface equally well, the typical thickness (t 2 ) of the block copolymer material  26  to form a monolayer of parallel cylinders (over a brush layer  30   a ) ( FIGS. 1 and 2 ) is generally t 2 ˜L. According to embodiments of the invention, a film  26 ′ of a block copolymer material such as PS-b-PMMA within the trenches  16 ′ at the end of anneal should be at less than the L value or t 2 &lt;L to result in a reorientation of the cylinders from parallel to perpendicular with a brush layer  34   a ′ in contact with the trench surfaces  20 ′,  22 ′,  24 ′. In this application, the cylinders  34 ′ have a shorter length and appear as half-spheres due to the rounded opposing ends  40 ′. In some embodiments, the total volume or thickness (t 2 ) of a PS-b-PMMA block copolymer material  26 ′ (or similar material) after inflow from the mesas/spacers  18 ′ and at the end of anneal is about 5-30% less (or about 10-20% less) than the L value of the block copolymer material, or t 2 ˜70-95%*(1*L). For example, for a PS-b-PMMA block copolymer material where L=35 nm, the PS-b-PMMA block copolymer material  26 ′ can be cast into the trenches  16 ′ and the polymer material  26   a ′ caused to flow into the trenches wherein the total volume or thickness (t 2 ) of the block copolymer material  26 ′ after the anneal is [(about 0.70 to about 0.95)*(35 nm)], or about 24.5-33.25 nm thick, resulting in surface normal (perpendicular) cylinders  34 ′ within the trenches  16 ′. 
     In embodiments utilizing a block copolymer material (such as PS-b-PDMS) in which the minority block (e.g., PDMS) preferentially wets both the trench surfaces and air interface, the typical thickness (t 2 ) of the block copolymer material  26  to form a monolayer of parallel cylinders (over a brush layer  30   a ) ( FIGS. 1 and 2 ) is generally t 2 =2*L. According to embodiments of the invention, a film  26 ′ of a block copolymer material such as PS-b-PDMS within trenches  16 ′ at the end of anneal should have a thickness (t 2 ) of less than about 2*L (or at t 2 &lt;2*L) to result in a reorientation to perpendicular cylinders  34 ′ ( FIG. 6A ) in which the cylinders are perpendicular to the trench floor  24 ′ with rounded ends  40 ′. In some embodiments, the total volume or thickness (t 2 ) of PS-b-PDMS block copolymer material  26 ′ (or similar material) after anneal is about 5-30% less (or about 10-20% less) than 2*L value of the block copolymer material, or t 2 ˜70-95%*(2*L). For example, for a PS-b-PDMS block copolymer material where L=35 nm, the PS-b-PDMS block copolymer material  26 ′ can be cast into the trenches  16 ′ and the polymer material  26   a ′ caused to flow into the trenches wherein the total volume or thickness (t 2 ) of the block copolymer material  26 ′ after the anneal is [(about 0.70 to about 0.95)*(2*35 nm)], or about 49-66.5 nm thick. 
     The polymer material  26 ′ can be annealed to form the polymer base layer  28 ′, 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 in response to the preferential wetting of the trench surfaces  20 ′,  22 ′,  24 ′. For example, a PS-b-PMMA copolymer film can be annealed at a temperature of about 150-275° C. in a vacuum oven for about 1-24 hours to achieve the self-assembled morphology. 
     The block copolymer material  26 ′ can be globally heated or, in other embodiments, a zone or localized thermal anneal can be applied to portions or sections of the block copolymer material  26 ′. For example, the substrate can be moved across a temperature gradient  42 ′ ( FIG. 6A ), for example, a hot-to-cold temperature gradient, positioned above (as shown) or underneath the substrate (or the thermal source can be moved relative to the substrate, e.g., arrow→) such that the block copolymer material self-assembles upon cooling after passing through the heat source. Only those portions of the block copolymer material that are heated above the glass transition temperature of the component polymer blocks will self-assemble, and areas of the material that were not sufficiently heated remain disordered and unassembled. “Pulling” the heated zone across the substrate can result in faster processing and better ordered structures relative to a global thermal anneal. 
     After the block copolymer material is annealed and ordered, the base layer (film)  28 ′ can then be treated to crosslink one of the polymer domains to fix and enhance the strength of the polymer domain, for example, the polymer matrix  36 ′ (e.g., the PS segments to make the PS matrix insoluble). The polymer block can be structured to inherently crosslink (e.g., upon UV exposure) or formulated to contain a crosslinking agent. 
     Generally, the block copolymer material  26   a ′ outside the trenches will not be thick enough to result in self-assembly. Optionally, the unstructured thin film  26   a ′ of the block copolymer material outside the trenches (e.g., on mesas/spacers  18 ′) can be removed, as illustrated in  FIGS. 6A and 6B , for example, by an etch technique or a planarization process. For example, the trench regions can be selectively exposed through a reticle (not shown) to crosslink only the annealed and self-assembled polymer material  28 ′ within the trenches  16 ′, and a wash can then be applied with an appropriate solvent (e.g., toluene) to remove the non-crosslinked portions of the block copolymer material  26   a ′ (e.g., on the spacers  18 ′), leaving the registered self-assembled base layer  28 ′ within the trench and exposing the surface ( 18 ′) of the material layer  14 ′ above/outside the trenches. In another embodiment, the polymer material  26 ′ can be crosslinked globally, a photoresist material can be applied to pattern and expose the areas of the polymer material  26   a ′ outside the trench regions, and the exposed portions of the polymer material  26   a ′ can be removed, for example by an oxygen (O 2 ) plasma treatment. 
     The annealed and self-assembled base film  28 ′ is then used as a template for inducing the ordering of an overlying cylindrical-phase block copolymer material such that the cylindrical domains of the annealed second film will orient perpendicular and registered to the underlying pattern of perpendicular cylinders in the base film. 
     As depicted in  FIGS. 7-7B , a cylindrical-phase block copolymer (BCP) material  44 ′ having an inherent pitch at or about the L value of the block copolymer material  26 ′ of the base layer  28 ′ (or a ternary blend of block copolymer and homopolymers blended to have a pitch at or about the L value) is deposited (e.g., by spin casting) onto the annealed (and crosslinked) base layer  28 ′ within the trenches  16 ′. The block copolymer material  44 ′ can be deposited to a thickness (t 3 ) at or about its L value. The minority domain of the BCP material  44 ′ is either identical to or preferentially wets the perpendicular cylinder (minority) domains  34 ′ of the underlying base layer  28 ′. 
     The block copolymer material  44 ′ is then annealed to form a self-assembled material layer  46 ′ over the base layer  28 ′, as depicted in  FIGS. 8A-8C . The polymer material  44 ′ can be annealed, for example, by thermal annealing. 
     During the anneal, the chemical pattern of the perpendicular cylinder (minor) domains  34 ′ of the base layer  28 ′ templates and imposes an induced ordering effect on the self-assembling cylindrical-phase block copolymer material  44 ′ to form a layer  46 ′ of perpendicular-oriented cylinders  48 ′ of the minority (preferred) block (e.g., PMMA) within a polymer matrix  50 ′ of the majority block (e.g., PS), with the cylinders registered to the underlying pattern of perpendicular cylinders  34 ′ of the base layer  28 ′. The diameter of the perpendicular cylinders  48 ′ is at or about 0.5*L. 
     In addition, parallel cylinders  30 ′ embedded in the matrix  50   a ′ and a brush layer  30   a ′ will form over the preferential wetting material layer  14 ′, as shown in  FIGS. 8A-8B . 
     Intrinsic periods of the two block copolymer materials  26 ′,  44 ′ can be matched, for example, through a ternary blend of either or both of the copolymer materials with one or more homopolymers to adjust the polymer periods (L 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. In embodiments of the method, the same cylindrical-phase block copolymer material is used for both block copolymer materials  26 ′,  44 ′. 
     The annealed and self-assembled polymer layer  46 ′ can then be treated to cross-link one of the polymer segments (e.g., the PS matrix  50 ′), as previously described. 
     After annealing and ordering of the cylindrical-phase BCP material  44 ′ to form polymer material layer  46 ′, one of the block components can be selectively removed to produce a porous film that can be used, for example, as a lithographic template or mask to pattern the underlying substrate  10 ′ in a semiconductor processing to define a regular pattern of nanometer sized openings (i.e., about 10-100 nm). 
     As illustrated in  FIGS. 9-9B , in some embodiments, the cylindrical domains  48 ′ and the underlying perpendicular cylinders  34 ′ of the base layer  28 ′ are selectively removed to form a porous film of regular cylindrical-shaped voids or openings  54 ′ within a polymer matrix  36 ′,  50 ′ that are registered to the trench sidewalls  20 ′. For example, selective removal of PMMA domains  34 ′,  48 ′ from a cross-linked PS matrix  36 ′,  50 ′ can be performed, for example, by application of an oxygen (O 2 ) plasma, or by a chemical dissolution process such as acetic acid sonication by first irradiating the sample (ultraviolet (UV) radiation, 1 J/cm^2 254 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. 
     As shown, a portion of the PS matrix  36 ′ situated underneath the openings  54 ′ and over the trench floor  24 ′ remains after the removal of the PMMA domains  34 ′,  48 ′. The underlying PS matrix  36 ′ can be removed, for example, by a reactive ion etch (RIE) using an oxygen plasma, for example, to expose the underlying substrate  10 ′ at the trench floor  24 ′, as illustrated in  FIGS. 10-10B . A resulting polymer film  52 ′ is composed of cylindrical openings  54 ′ within the polymer matrix  36 ′,  50 ′ (e.g., of PS). The RIE etch may thin the polymer matrix  50 ′, as shown, although not to a significant extent. 
     An embodiment of the application of the polymer film  52 ′ is as an etch mask to form openings in the substrate  10 ′. For example, as illustrated in  FIGS. 10-10B , the polymer film  52 ′ can then be used as a mask to etch (arrows ↓) a series of cylindrical openings or contact holes  56 ′ (shown in phantom) to the conductive lines  12 ′ or other active area (e.g., semiconducting region, etc.) in the underlying substrate  10 ′ (or an underlayer), for example, using a selective RIE plasma etch process. 
     Further processing can then be performed as desired. For example, as depicted in  FIGS. 11-11B , the residual polymer material  52 ′ (e.g.,  50 ′,  34   a ′,  36 ′) can be removed and the substrate openings  56 ′ can be filled with a material  58 ′ such as a metal or metal alloy such as Cu, Al, W, Si, and Ti 3 N 4 , among others, to form arrays of cylindrical contacts to the conductive lines  12 ′. The cylindrical openings  56 ′ in the substrate can also be filled with a metal-insulator-metal stack to form capacitors with an insulating material such as SiO 2 , Al 2 O 3 , HfO 2 , ZrO 2 , SrTiO 3 , and the like. 
     Methods of the disclosure provide a means of generating self-assembled diblock copolymer films composed of perpendicular-oriented cylinders in a polymer matrix. The methods provide ordered and registered elements on a nanometer scale that can be prepared more inexpensively than by electron beam lithography, EUV photolithography or conventional photolithography. The feature sizes produced and accessible by this invention cannot be easily prepared by conventional photolithography. Since the domain sizes and periods (L) involved in this method are determined by the chain length of a block copolymer (MW), resolution can exceed other techniques such as conventional photolithography. Processing costs using the technique are significantly less than extreme ultraviolet (EUV) photolithography, which has comparable resolution. The described methods and systems can be readily employed and incorporated into existing semiconductor manufacturing process flows and provide a low cost, high-throughput technique for fabricating small structures. 
     Embodiments of the invention eliminate the need for preparing trench floors that wet both blocks of a block copolymer to form perpendicular-oriented cylinders from block copolymer materials. While forming a neutral wetting trench floor can be accomplished, for example, by forming a neutral wetting material (e.g., random copolymer material) on the trench floor, it requires either processes that are not conventional to semiconductor manufacturing and/or extra processing steps. The present methods do not require unconventional processes for manufacturing the required structures. 
     In addition, embodiments of the disclosure providing chemical pattern templating of the upper layer provide fast processing of BCP materials relative to other methods of registering block copolymers such as processes that utilize graphoepitaxy with selective/neutral wetting trench or groove surfaces alone. The present methods provide formation of nanostructures in a manner that is more readily manufacturable. 
     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.

Technology Classification (CPC): 6