Preparing patterned neutral layers and structures prepared using the same

Embodiments provided herein provide methods for preparing patterned neutral layers using photolithography, and structures prepared using the same. A method of preparing a structure may include disposing a film over a surface of a substrate, and removing plurality of elongated trenches from the film so as to define a plurality of spaced lines. A neutral layer may be disposed over the outer surface of each line, and may include a neutral group attached to the outer surface of that line via a covalent bond or a hydrogen bond. The surface of the substrate between the lines may be substantially free of the neutral layer.

BACKGROUND

This application generally relates to preparing patterned layers using photolithography, and structures prepared using the same.

The electronics industry has spent a significant amount of time and effort to reduce the lateral dimensions of patterned materials in electronic devices. For example, photolithography is a widely known technique in which light is used to pattern a photoresist, that then is used to pattern another material, such as to define lines, trenches, holes, or more complex patterns. In photolithography, the lateral dimensions of the pattern defined in the photoresist may be the same as the lateral dimensions of the other material. The electronics industry continues to research techniques for reducing the size of lateral features within photolithographically defined patterns.

It would be desirable to define patterns having smaller lateral dimensions than are presently achievable using photolithography. Such patterns may be referred to as “sub-lithographic.” One exemplary method for achieving sub-lithographic patterns in materials utilizes directed self-assembly (DSA) of block copolymers, which also may be referred to as guided self-assembly or templated self-assembly. DSA has the potential to extend scaling for lines, trenches, and holes.

DETAILED DESCRIPTION

Embodiments provided herein provide methods for preparing patterned neutral layers using photolithography, and structures prepared using the same. As used herein, a “neutral layer” also may be referred to as an “orientation control layer,” and can have a composition that is selected to provide a surface tension that is approximately the same as a surface tension of a first block of a block copolymer that may be disposed thereon, e.g., has a “neutral” surface tension relative to that block. Accordingly, the block copolymer may minimize its free energy by preferentially orienting the blocks such that the first block is disposed over, and in contact with, the neutral layer.

Embodiments provided herein provide methods for preparing patterned neutral layers in which the neutral layers may be selectively disposed over the outer surfaces of lines that are defined over the surface of a substrate, in such a manner that the surface of the substrate between the lines may be substantially free of the neutral layer. For example, a film may be disposed over the surface of the substrate. A plurality of elongated trenches may be removed from the film so as to define a plurality of spaced lines disposed over the surface of the substrate. Each line has an outer surface, upon which a neutral layer then is disposed. The neutral layer may include a neutral group attached to the outer surface of the line via a covalent bond or a hydrogen bond. The surface of the substrate can be substantially free of the neutral layer. In some embodiments, the lines are defined using a photoresist, such as a negative photoresist or a positive photoresist, e.g., by irradiating elongated portions of the photoresist through a bright mask and then dissolving non-irradiated portions of the photoresist. The irradiated portions define the lines, and the dissolved non-irradiated portions define the trenches. The neutral layer may be disposed over the outer surface of each line by applying to that line a precursor that includes the neutral group and a reactive group covalently bound to the neutral group, and reacting the reactive group of the applied precursor with the outer surface of the line so as to form the covalent bond or the hydrogen bond. In comparison, the other approaches such as illustrated inFIGS. 1A-1Bmay dispose the neutral layer over the surface of the substrate using a greater number and complexity of processing steps that also may reduce the quality and reproducibility of the pattern of the neutral layer, e.g., by patterning the neutral layer using lift-off of patterned photoresist.

FIG. 1Aillustrates an exemplary scheme100for patterning lines within a block copolymer using DSA. Step101of scheme100includes patterning a positive photoresist on a bottom anti-reflective coating (BARC) disposed on a substrate. More specifically, portions of the photoresist are irradiated with light and subsequently removed using a developer so as to form trenches, thus defining the lines illustrated at step101ofFIG. 1A. The patterned photoresist then is hardened at step102. At step103, a neutral layer is deposited over the patterned photoresist and the BARC, and at step104the patterned photoresist then is removed (“lift off”) so as to leave behind a patterned neutral layer. A block copolymer (BCP) is coated over the patterned neutral layer at step105, and then annealed at step106which causes one block of the BCP to become pinned to the neutral layer. The copolymer blocks of the BCP are selected such that, when one block becomes pinned to the neutral layer, the blocks self-assemble into lines having a pitch that is a multiple of the pitch of the pattern within the neutral layer.

FIG. 1Billustrates an alternative scheme110for patterning lines within a block copolymer using DSA. Step111of scheme100includes disposing a cross-linked polystyrene (PS) guide material as a substrate, and then patterning a positive photoresist on the PS material. More specifically, portions of the photoresist are irradiated with light and subsequently removed using a developer so as to form trenches, thus defining the lines illustrated at step112ofFIG. 1A. The patterned photoresist then is trim etched at step113to form narrower lines. At step114, the narrowed lines of photoresist are used as a mask to pattern the PS material, and subsequently stripped. At step115, the patterned PS material is coated, a neutral brush is grafted thereto, and the assembly is baked and subsequently rinsed at step116so as to leave behind a patterned neutral layer. A BCP then is coated over the patterned neutral layer at step117, and then annealed at step118which causes one block of the BCP to become pinned to the neutral layer and causes the blocks to self-assemble into lines having a pitch that is a multiple of the pitch of the pattern within the neutral layer. For further details about schemes such as illustrated inFIGS. 1A-1B, see Somervell et al., Proc. of SPIE Vol. 8325, 83250G-1 to 83250G-14, the entire contents of which are incorporated by reference herein.

First, exemplary structures that may be formed using the present methods will be described. Then, exemplary methods that may be used to form such structures will be described in greater detail. Lastly, some exemplary structures that were formed using the present methods will be described.

FIGS. 2A and 2Brespectively illustrate cross-sectional and plan views of structures that include patterned neutral layers, in accordance with some embodiments. As perhaps best seen inFIG. 2A, structure20includes substrate200having a surface201that includes optional non-reactive layer210, a plurality of spaced lines220disposed over surface210of the substrate, and a neutral layer230disposed over the outer surface of each line. Surface201of substrate200can be substantially free of the neutral layer, such that the neutral layer230can be located substantially only upon the outer surfaces of lines200. In one example, neutral layer230includes a neutral group attached to the outer surface of that line via a covalent bond or a hydrogen bond, as described in greater detail below.

Substrate200may include any suitable material or combination of materials known in the art. For example, substrate200may include one or more of a semiconductor material, a conductive material, or an insulative material. Non-limiting examples of suitable semiconductor materials suitable for use in substrate200include silicon (Si), germanium (Ge), gallium phosphide (GaP), gallium nitride (GaN), gallium arsenide (GaAs), indium phosphide (InP), and silicon carbide (SiC). In one illustrative embodiment, substrate200includes an Si wafer. Nonlimiting examples of suitable conductive materials suitable for use in substrate200include metals such as copper, aluminum, platinum, gold, or silver. Nonlimiting examples of suitable insulative materials suitable for use in substrate200include sapphire, glasses such as silicon oxide (SiOx), polymers such as polystyrene, aerogels, and silicon nitride (SiN).

Substrate200may, for example, include a wafer, e.g., a single-crystal wafer, or may include a film disposed over a solid support such as glass or sapphire. The substrate may be monocrystalline, and optionally may have a particular crystalline orientation. For example, Si substrates are available in various crystallographic orientations, such as [100] or [111], either of which may be suitable. Alternatively, the substrate may include a polycrystalline or amorphous material.

Substrate200may also have structures defined therein, such as conductive lines, insulator layers, doped semiconductor regions, and the like. For example, in the embodiment illustrated inFIGS. 2A-2B, the upper surface201of substrate200includes optional non-reactive layer210. By “non-reactive” it is meant that layer210is selected so as to inhibit the formation of covalent bonds or hydrogen bonds with the reactive group of the precursor used to form neutral layer230, and thus to inhibit the formation of neutral layer230upon the upper surface201of substrate200. For example, layer210may include a layer of material that is deposited onto substrate200so as to define the upper surface201of substrate200. As one example, layer210may include a bottom anti-reflective coating (BARC) such as known in the art. Alternatively, the upper surface201of substrate200may be physically or chemically modified so as to form layer210that inhibits reactions between the material of which substrate200is formed and the reactive group of the precursor used to form neutral layer. Such arrangements may be described as a non-reactive layer disposed over a bulk material. In one illustrative example, a floating additive with carbon backbone structure, e.g., a fluoro-containing polymer, may be applied to substrate200or to layer210disposed thereon. The floating additive can “float” to the upper surface of substrate200or layer210and can inhibit formation of the neutral layer at that surface. In another illustrative example, if substrate200includes silicon, layer210may not include silicon. However, it should be noted that non-reactive layer210is purely optional. Indeed, numerous materials suitable for use in substrate200need not be further treated or have any non-reactive layer disposed upon so as to be non-reactive with the reactive group of the precursor used to form neutral layer230.

As perhaps best seen inFIG. 2A, a plurality of spaced lines220are disposed over the upper surface201of substrate200. Lines220can be spaced relative to one another so as to have a suitable pitch, for example, a pitch of between about 10 and about 1000 nm, e.g., a pitch of between about 10 nm and about 100 nm, e.g., a pitch of between about 20 and about 500 nm, e.g., a pitch of between about 50 and about 250 nm, e.g., a pitch of between about 75 nm and about 150 nm. In some embodiments, lines220can have a width between about 10 nm and about 200 nm, e.g., a width of between about 20 nm and about 100 nm, e.g., a width of between about 20 nm and about 80 nm, e.g., a width of between about 30 nm and about 70 nm. In one illustrative example, the width of lines220is approximately equal to the minimum feature size achievable by the photolithographic node being used to form lines220, e.g., as described below with reference toFIG. 4A. Lines220further may have any suitable thickness, e.g., may have a thickness of about 10 nm to about 1000 nm, e.g., about 20 nm to about 500 nm, e.g., about 50 nm to about 250 nm. Additionally, note that although lines220are illustrated inFIG. 2Aas having a generally rectangular cross-section, lines220may have any suitably shaped cross-section. For example, lines220may have curved cross-sections, square cross-sections, triangular cross-sections, or saw-tooth cross sections, and the like. For example, in the illustrative Examples provided further below with reference toFIGS. 6A-6D and 7A-7D, lines220may have a curved cross-section.

Spaced lines220may include any suitable material or combination of materials known in the art. In some embodiments, spaced lines220include a photoresist. For example, as described in greater detail below with reference toFIG. 4A, spaced lines220may be defined by disposing a photoresist over the surface201of substrate200, and then removing a plurality of elongated trenches from the photoresist. In one illustrative embodiment, the photoresist is a negative photoresist. In another illustrative embodiment, the photoresist is a positive photoresist. The width and pitch of the trenches removed from the photoresist defines the width and pitch of lines220. Without wishing to be bound by any theory, it is believed that the increased strength resulting from cross-linking lines220of a photoresist prior to removing trenches from other, non-cross-linked portions of the photoresist may improve the quality and durability of lines220, such that lines220suitably may be subjected to further processing such as the deposition of neutral layer230thereon without significant degradation. For some nonlimiting examples of suitable photoresists and methods of patterning the same, see U.S. Patent Publication No. 2013/0005150 to Ogihara et al., the entire contents of which are incorporated by reference herein.

It should be noted that although use of a photoresist may be included in some circumstances, any suitable material or combination of materials may be used to define lines220. For example, spaced lines220may include one or more of a semiconductor material, a conductive material, or an insulative material. Non-limiting examples of suitable semiconductor materials suitable for use in substrate200include silicon (Si), germanium (Ge), gallium phosphide (GaP), gallium nitride (GaN), gallium arsenide (GaAs), indium phosphide (InP), and silicon carbide (SiC). Nonlimiting examples of suitable conductive materials suitable for use in spaced lines220include metals such as copper, aluminum, platinum, gold, or silver. Nonlimiting examples of suitable insulative materials suitable for use in spaced lines220include sapphire, glasses such as silicon oxide (SiOx), polymers such as polystyrene, aerogels, and silicon nitride (SiN).

As shown inFIGS. 2A-2B, a neutral layer230is disposed over the outer surface of each line220. In some embodiments, the neutral layer is substantially continuous over the entire outer surface of each line220. As described in greater detail below with reference toFIGS. 4A-4C, neutral layer230for each line can include a neutral group that is attached to the outer surface of that line via a covalent bond or a hydrogen bond. Exemplary covalent bonds suitably that may be used include ester bonds, amide bonds, and sulfonamide bonds. Additionally, the covalent bond between the neutral group and the outer surface of line220may include a cross-linker, wherein the neutral group is covalently bonded to the cross-linker, and the cross-linker is covalently bonded to the outer surface of line220. Exemplary hydrogen bonds suitably that may be used include halide bonds, methyl trihalide bonds, and amine bonds.

Neutral layer230may include any suitable composition known in the art, or yet to be developed, that that is selected to provide a surface tension that is approximately the same as a surface tension of a first block of a block copolymer that may be disposed thereon, e.g., has a “neutral” surface tension relative to that block. Accordingly, the block copolymer may minimize its free energy by preferentially orienting the blocks such that the first block is disposed over, and in contact with, the neutral layer. Particular neutral layers, sometimes referred to as “orientation control layers,” for use in preferentially orienting a particular block of a particular block copolymer, are known. It is believed that any such neutral layers or orientation control layers suitably may be adapted for use with certain embodiments provided herein.

In one nonlimiting example, U.S. Patent Publication No. 2009/0179001 to Cheng et al., the entire contents of which are incorporated by reference herein, discloses the use of epoxy-containing cycloaliphatic acrylic polymers as orientation control layers for block copolymer thin films, e.g., poly(styrene-b-methyl methacrylate) (PS-b-PMMA) diblock copolymers, as well as poly(styrene-b-vinyl pyridine), poly(styrene-b-butadiene), poly(styrene-b-isoprene), poly(styrene-b-alkenyl aromatics), poly(isoprene-b-ethylene oxide), poly(styrene-b-(ethylene-propylene)), poly(ethylene oxide-b-caprolactone), poly(butadiene-b-ethylene oxide), poly(styrene-b-t-butyl(meth)acrylate), poly(methyl methacrylate-b-t-butyl methacrylate), poly(ethylene oxide-b-propylene oxide), poly(styrene-b-tetrahydrofuran), poly(styrene-b-isoprene-b-ethylene oxide), or a combination comprising at least one of the foregoing block copolymers. Or, in another nonlimiting example, Jung et al., “Fabrication of Diverse Metallic Nanowire Arrays Based on Block Copolymer Self-Assembly,” Nano Lett. 10(9): 3722-3726 (2010), the entire contents of which are incorporated by reference herein, discloses the use of a polydimethylsiloxane (PDMS) brush layer as an orientation control layer for a poly(styrene-b-dimethylsiloxane) (PS-PDMS) diblock copolymer thin film.

Additionally, it should be appreciated that lines220may have any suitable shape and geometry in the lateral dimension, and need not necessarily be elongated or parallel to one another as is illustrated inFIGS. 2A-2B. For example, lines220suitably may be curved in the lateral dimension, or may include discrete islands, e.g., round or polygonal islands, such as square islands, or may include a layer having apertures defined therein, e.g., round or polygonal apertures, such as square apertures.

FIGS. 3A and 3Brespectively illustrate cross-sectional and plan views of structure30that includes patterned neutral layers having self-assembled block copolymers disposed thereon, in accordance with some embodiments. As perhaps best seen inFIG. 3A, structure30includes substrate200having a surface201that includes optional non-reactive layer210, a plurality of spaced lines220disposed over surface201of the substrate, a neutral layer230disposed over the outer surface of each line, and a block copolymer310disposed over the neutral layer230over the outer surface of each line220as well as over surface201of the substrate. Substrate201, optional layer210, lines220, and neutral layer230may be substantially as described above with reference toFIGS. 2A-2B. One or more blocks of block copolymer310may be disposed over surface201of substrate200, while one or more blocks of block copolymer310may be disposed over neutral layer230. In some embodiments, neutral layer230pins at least one block of the block copolymer. For example, in the embodiment illustrated inFIGS. 3A-3B, block copolymer310includes an “A-B” type di-block copolymer, in which the “A” block is pinned to neutral layer230, and the block “B” is disposed between the “A” blocks. Note that the spatial frequency (inverse of pitch) of the “A” blocks within copolymer310can be an integer multiple of the spatial frequency of lines220. For example, in the exemplary embodiment illustrated inFIGS. 3A-3B, the spatial frequency of the “A” blocks is approximately twice the spatial frequency of lines220. Accordingly, because lines220are defined lithographically, the pattern of block copolymer310may be considered to be sublithographic. Note that any suitable type of block copolymer may be used, including diblock copolymers, triblock copolymers, and so on. Block copolymers, and suitable neutral groups for causing preferential orientation of one or more blocks of such block copolymers, are known in the art.

Exemplary methods for preparing structures including patterned neutral layers now will be described with reference toFIGS. 4A-4C, and exemplary intermediate structures that may be formed using such methods also will be described with reference toFIGS. 5A-5F.

FIG. 4Aillustrates steps in a method400for preparing structures that include patterned neutral layers optionally having self-assembled block copolymers disposed thereon, in accordance with some embodiments. Method400includes disposing a film over the surface of a substrate (step410). For example, as illustrated inFIG. 5A, film220′ may be disposed over surface201of substrate200. As noted above with reference toFIGS. 2A-2B, substrate200optionally may include non-reactive film210disposed over a bulk material. Film220′ may include any suitable material, such as a photoresist, e.g., negative photoresist or positive photoresist.

Method400illustrated inFIG. 4Acontinues with removing a plurality of elongated trenches from the film so as to define a plurality of spaced lines disposed over the surface of the substrate, each line having an outer surface (step420). For example,FIG. 5Billustrates an embodiment in which film220′ includes a photoresist. The trenches may be removed by irradiating elongated portions220″ of film220′, e.g., through bright mask500, and then dissolving non-irradiated portions of the film using photolithographic techniques well known in the art. The irradiated portions may define the lines, and the dissolved non-irradiated portions may define the trenches, e.g., lines220separated from one another by trenches510illustrated inFIG. 5C.

Method400illustrated inFIG. 4Acontinues with disposing a neutral layer over the outer surface of each line (step430). The neutral layer can include a neutral group that is attached to the outer surface of the line via a covalent bond or a hydrogen bond, and the surface of the substrate is substantially free of the neutral layer, e.g., as described above with reference toFIGS. 2A-2B. Disposing the neutral layer over the line may, for example, include applying to the line a precursor that includes the neutral group and a reactive group covalently bound to the neutral group. The reactive group of the applied precursor may react with the outer surface of the line so as to form a covalent bond.

FIG. 4Billustrates steps in a method for covalently bonding a neutral layer to a line over the surface of a substrate, e.g., for executing step430ofFIG. 4A, in accordance with some embodiments.FIG. 4Bincludes applying a fluid that includes the precursor to the line (step431). For example, as illustrated inFIG. 5D, a fluid230′ that includes the precursor may be applied to at least the plurality of lines220, and optionally also to the surface201of substrate200. Suitable methods for applying fluids to substrates (and features thereon) are known in the art, and include, for example, spin-coating, spraying, dipping, and the like. As noted above, the precursor can include a reactive group and a neutral group covalently bound to one another.

Continuing with method430illustrated inFIG. 4B, the direct covalent bond or hydrogen bond may be formed between the reactive group of the precursor and the outer surface of the line (step432). For example, in embodiments in which lines220include a photoresist, the outer surface of the lines may include carboxyl (COOH) groups, and the reactive group of the precursor may include a group that reacts with the carboxyl group of the line so as to form a covalent bond, such as a hydroxyl group (—OH) that forms an ester bond, an amine group (—R1R2N, in which R1and R2independently may be hydrogen or a carbon-containing group) that forms an amide bond, or a sulfonamide group (—NH2SO2) that forms a sulfonamide bond. Or, for example, the precursor may include a group that reacts with the carboxyl group of the line so as to form a hydrogen bond, such as a halide group (—X, where X is F−or Cl−) that forms a halide bond, a methyl trihalide group (—CX3, where X is F or CO that forms a trimethyl halide bond, or an amine group (R1R2N, in which R1and R2independently may be hydrogen or a carbon-containing group) that forms an amine bond. In one illustrative embodiment, the fluid is heated so as to facilitate formation of the covalent bond or the hydrogen bond.

FIG. 5Eschematically illustrates an exemplary manner in which a precursor may react with the outer surface of a line220in the inset portion ofFIG. 5Ddenoted “5E.” Each precursor molecule510may include neutral group520and reactive group530covalently bound to one another (bond indicated by short straight line). The outer surface of line220may include reactive sites540. The reactive group530of precursor molecule510may react with reactive site540, so as to form covalent bonds or hydrogen bonds (collectively indicated by dotted line) such as described above or known in the art, and disposing neutral groups520adjacent to the surface of line220. In some embodiments, a sufficient amount of precursor molecules510are provided and react with reactive sites540such that neutral groups520substantially cover the entire outer surface of each line220and thus form a substantially continuous neutral layer over the entire outer surface of each line220. In some embodiments, optional non-reactive layer210(or, absent non-reactive layer210, the upper surface of substrate200) lacks reactive sites540, such that the reactive group530of precursor molecule510substantially does not react with layer210or the surface of substrate200, and accordingly the surface of substrate200can remain substantially free of the neutral layer.

Note that although heating the applied fluid, such as in step432ofFIG. 4B, may facilitate or reduce the time for forming a covalent bond or a hydrogen bond between each reactive group530and reactive site540, that such heating may not necessarily be required, and should be considered optional. Additionally, as illustrated inFIG. 4B, after the reaction between the precursor and the outer surface of line220, any unreacted precursor optionally may be removed (step433).

FIG. 4Cillustrates steps in an alternative method for covalently bonding a neutral layer to a line over the surface of a substrate, e.g., for executing an alternative430′ to step430ofFIG. 4A, in accordance with some embodiments.FIG. 4Cincludes applying a fluid that includes the precursor and a cross-linker to the line (step431′). For example, in a manner analogous to that illustrated inFIG. 5D, a fluid that includes the precursor and the cross-linker may be applied to at least the plurality of lines220, and optionally also to the surface201of substrate200. Suitable methods for applying fluids to substrates (and features thereon) are known in the art, and include, for example, spin-coating, spraying, dipping, and the like. As noted above, the precursor can include a reactive group and a neutral group covalently bound to one another.

Continuing with alternative method430′ illustrated inFIG. 4C, the reactive group of the precursor may be covalently bonded to the cross-linker, and the cross-linker covalently bonded to the outer surface of the line (step432′).FIG. 5Fschematically illustrates the manner in which a precursor and cross-linker may react with one another and in which the cross-linker may react with the outer surface of a line220in a region analogous to that illustrated in the inset portion ofFIG. 5Ddenoted “5E.” Each precursor molecule510′ may include neutral group520′ and reactive group530′ covalently bound by one another (bond indicated by short straight line). The outer surface of line220may include reactive sites540′. The reactive group530′ of precursor molecule510may react cross-linker550, which in turn may react with reactive site540′, so as to form covalent bonds such as described above or known in the art, and disposing neutral groups520′ adjacent to the surface of line220. In some embodiments, a sufficient amount of precursor molecules510′ and cross-linker550are provided and react with reactive sites540′ such that neutral groups520′ substantially cover the entire outer surface of each line220′ and thus form a substantially continuous neutral layer over the entire outer surface of each line220. In some embodiments, optional non-reactive layer210(or, absent non-reactive layer210, the upper surface of substrate200) lacks reactive sites540′, such that cross-linker550substantially does not react with layer210or the surface of substrate200, and accordingly the surface of substrate200can remain substantially free of the neutral layer and the cross-linker.

Note that the applied fluid optionally may be heated so as to facilitate or reduce the time for forming covalent bonds between each reactive group530′ and cross-linker550and between reactive site540′ and cross-linker550. Additionally, as illustrated inFIG. 4C, after the reaction between the precursor and the outer surface of line220, any unreacted precursor and cross-linker optionally may be removed (step433′).

FIGS. 6A-6D and 7A-7Dare micrograph images of samples prepared using the methods ofFIGS. 4A-4C, in accordance with some embodiments.FIG. 6Aillustrates photomicrographs of three samples that include lines of commercially available AIM8335 photoresist with crosslinker formed using deposition and photolithographic patterning, baking, and etching over a BARC disposed over a silicon substrate, in accordance with steps410and420illustrated inFIG. 4A. InFIG. 6A, the lines had a pitch (P) of 100 nm, and the average width of the lines in the three samples respectively were measured to be 34.9 nm, 37.0 nm, and 45.0 nm.FIG. 7Aillustrates photomicrographs of three samples that were prepared analogously as forFIG. 6A, but for which the lines had a pitch (P) of 126 nm, and the average width of the lines in the three samples respectively were measured to be 33.0 nm, 36.3 nm, and 45.9 nm.

FIG. 6Billustrates photomicrographs of the three samples illustrated inFIG. 6Aafter depositing a neutral layer thereon in accordance with step430ofFIG. 4Aand steps431′ and432′ ofFIG. 4C. Specifically, the neutral layer was a random copolymer of PS-PMMA having a hydroxyl (—OH) endgroup that was covalently bound to carboxyl groups of the photoresist using a cross-linker, followed by a wash with tetramethyl ammonium hydroxide (TMAH). InFIG. 6B, the average width of the lines in the three samples respectively were measured to be 48.9 nm, 53.9 nm, and 57.3 nm.FIG. 7Billustrates photomicrographs of the three samples illustrated in FIG.7A after depositing a neutral layer thereon in a manner analogous to that described above with reference toFIG. 6B. InFIG. 7B, the average width of the lines in the three samples respectively were measured to be 57.6 nm, 56.7 nm, and 57.4 nm. Accordingly, it may be understood that application of the neutral layer increased the average width of the lines for the P=100 nm samples by about 14 nm, 16.9 nm, and 12.3 nm, respectively, and for the P=126 nm samples by about 24.6 nm, 20.4 nm, and 11.5 nm, respectively.

FIG. 6Cillustrates a photomicrograph of a cross-section of the sample ofFIG. 6Bhaving an average line width of 48.9 nm, in which it may be seen that a critical dimension (CD) of about 39 nm was measured, and in which the neutral layer-coated lines have a curved cross-section.FIG. 6Dillustrates a photomicrograph of a cross-section of the sample ofFIG. 6Bhaving an average line width of 57.3 nm, in which it may be seen that a critical dimension (CD) of about 53 nm was measured, and in which the neutral layer-coated lines have a curved cross-section.FIG. 7Cillustrates a photomicrograph of a cross-section of the sample ofFIG. 7Bhaving an average line width of 57.6, in which it may be seen that a critical dimension (CD) of about 53 nm was measured, and in which the neutral layer-coated lines have a curved cross-section.FIG. 7Dillustrates a photomicrograph of a cross-section of the sample ofFIG. 7Bhaving an average line width of 57.4 nm, in which it may be seen that a critical dimension (CD) of about 65 nm was measured, and in which the neutral layer-coated lines have a curved cross-section.

Accordingly, it may be appreciated that the present structures and methods provide patterned neutral layers that are highly reproducible, made with relative ease, and that suitably may be used in subsequent processing, e.g., to preferentially orient a block within a block copolymer.

Accordingly, in one embodiment, a method of preparing a structure includes disposing a film over a surface of a substrate. A plurality of elongated trenches may be removed from the film so as to define a plurality of spaced lines disposed over the surface of the substrate. Each line has an outer surface. A neutral layer may be disposed over the outer surface of each line. The neutral layer may include a neutral group attached to the outer surface of that line via a covalent bond or a hydrogen bond. The surface of the substrate between the lines may be substantially free of the neutral layer.

In another embodiment, a structure includes a substrate having a surface, and a plurality of spaced lines disposed over the surface of the substrate, each line having an outer surface. The structure further includes a neutral layer disposed over the outer surface of each line. The neutral layer includes comprising a neutral group attached to the outer surface of that line via a covalent bond or a hydrogen bond. The surface of the substrate between the lines may be substantially free of the neutral layer.

In yet another embodiment, a structure includes a substrate having a surface, and a plurality of spaced lines disposed over the surface of the substrate, each line having an outer surface. The plurality of spaced lines are defined by removing a plurality of elongated trenches from a photoresist. The structure further includes a neutral layer disposed over the outer surface of each line. The neutral layer includes a neutral group attached to the outer surface of that line via a covalent bond or a hydrogen bond. The surface of the substrate between the lines may be substantially free of the neutral layer.