Method for manufacturing porous structure and method for forming pattern Number:7,090,784 from the United States Patent and Trademark Office (PTO) owispatent

Title: Method for manufacturing porous structure and method for forming pattern

Abstract: A pattern forming material contains a block copolymer or graft copolymer and forms a structure having micro polymer phases, in which, with respect to at least two polymer chains among polymer chains constituting the block copolymer or graft copolymer, the ratio between N/(Nc-No) values of monomer units constituting respective polymer chains is 1.4 or more, where N represents total number of atoms in the monomer unit, Nc represents the number of carbon atoms in the monomer unit, No represents the number of oxygen atoms in the monomer unit.

Patent Number: 7,090,784 Issued on 08/15/2006 to Asakawa,   et al.

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Inventors:	Asakawa; Koji (Kawasaki, JP), Hiraoka; Toshiro (Yokohama, JP), Akasaka; Yoshihiro (Kawasaki, JP), Hotta; Yasuyuki (Funabashi, JP)
Assignee:	Kabushiki Kaisha Toshiba (Kawasaki, JP)
Appl. No.:	10/347,956
Filed:	January 22, 2003

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Related U.S. Patent Documents

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	Application Number	Filing Date	Patent Number	Issue Date
	09588721	Jun., 2000	6565763

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Foreign Application Priority Data

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Jun 07, 1999 [JP]			11-159479
Sep 16, 1999 [JP]			11-262326
Jun 06, 2000 [JP]			2000-169263

Current U.S. Class:	216/41 ; 216/49; 216/56; 521/61
Current International Class:	C08J 9/26 (20060101)
Field of Search:	216/22,24,40,41,49,56,61,67 521/61

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References Cited [Referenced By]

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Foreign Patent Documents

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Other References

Zehner, R.W. et al Selective Decoration of a Phase-Separated Diblock Copolymer with Thiol-Pasivated Gold Nanocrystals: Langmuir, Jan. 20, 1998, 14 (2) 241-244. cited by other . Hahm, J. et al Cylinder Alignment in Annular Structures of Microphase-Separated Polystyrene-b-Poly(metyhl methacrylate): Langmuir, Apr. 14, 2000, 16, 4766-4769. cited by other . Buck, E. et al "Surface-Induced Microphase Separation in Spin-Cast Ultrathin Diblock copolymer Films on Silicon Substrate before and after Annealing" Macromolecules, Mar. 2, 2001, 34, 2172-2178. cited by other . Joachim P. Spatz, et al., "Micellar Inorganic-Polymer Hybrid Systems-A tool for Nanolithography," Adv. Mater., 1999, 11, No. 2, pp. 149-153. cit- ed by other . Joachim P. Spatz: et al., "Ultrathin Diblock Copolymer/Titanium Laminates--A Tool for Nanolithography," Adv. Mater., 1998, 10, No. 11, pp. 849-852. cited by other . Christopher Harrison, et al., "Lithography with a mask of block copolymer microstructures," J. Vac. Sci. Technol., B 16(2), Mar./Apr. 1998, pp. 544-551. cited by other . P. Mansky, et al., "Nanolithographic templates from diblock copolymer thin films," Appl. Phys. Lett. 68 (18), Apr. 29, 1996, pp. 2586-2588. cited by other . P. Mansky, et al., "Nanometer Scale Periodic Modulation of a 2-D Electron System with Block Copolymers," Bull. Am. Phy. Soc., vol. 36, No. 3, 1991, p. 1051. cited by other . T.L. Morkved, et al., "Local Control of Microdomain Orientation in Diblock Copolymer Thin Films with Electric Fields," Science, vol. 273, Aug. 16, 1996, pp. 931-933. cited by other . Miri Park, et al., "Block Copolymer Lithography: Periodic Arrays of--10.sup.11 Holes in 1 Square Centimeter," Science, vol. 276, May 30, 1997, pp. 1401-1404. cited by other . Dominic Walsh, et al., "Morphosynthesis of Calcium Carbonate (Vaterite) Microsponges," Adv. Mater., 1999, 11, No. 4, pp. 324-329. cited by other . Markus Templin, et al., "Organically Modified Aluminosilicate Mesostructures from Block Copolymer Phases," Science, vol. 278, Dec. 5, 1997, pp. 1795-1798. cited by other . Jeff W. Labadie, et al., "Nanopore Foams of High Temperature Polymers," IEEE Transactions of Components, Hybrids, and Manufacturing Technology, vol. 15, No. 6, Dec. 1992, pp. 925-930. cited by other.

Primary Examiner: Alanko; Anita
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt, P.C.

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Parent Case Text

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This application is a Divisional application of U.S. application Ser. No. 09/588,721, now U.S. Pat. No. 6,565,763.

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Claims

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What is claimed is:

1. A method for forming a pattern comprising: on a substrate, forming a film comprised of a pattern forming material, wherein the pattern forming material comprises a block copolymer or graft copolymer comprising: a polymer chain comprising a repeating unit represented by the following formula: ##STR00020## wherein R.sup.1 and R.sup.2 independently represent a substituted or unsubstituted alkyl group, aryl group aralkyl group or alkoxyl group having 1 to 20 carbon atoms; and a thermally decomposable polymer chain; forming a microphase-separated structure in the film, said microphase-separated structure comprising a thermally decomposable polymer phase and a remaining polymer phase; removing the thermally decomposable polymer phase from the microphase-separated structure by heating said film to a thermal decomposition temperature or more, to form a pattern of the microphase-separated structure; and transferring the pattern of the microphase-separated structure to the substrate by etching the substrate using the remaining polymer phase in the film as a mask.

2. The method according to claim 1, wherein the thermally decomposable polymer is selected from the group consisting of a polyethylene oxide and a polypropylene oxide.

3. The method according to claim 1, wherein thermally decomposable polymer chain is selected from the group consisting of a polyethylene oxide chain, a polypropylene oxide chain, a polyacrylic acid chain, and a polymethacrylic acid derivative chain.

4. The method of claim 1, wherein the block copolymer or the graft copolymer comprises a polymer chain selected from the group consisting of a polyacrylonitrile chain, a polyacrylonitrile derivative chain, a polyaniline derivative chain, a polyparaphenylene derivative chain, and a polymer chain having a perylene skeleton in side chains or a main chain.

5. A method for manufacturing a porous structure, comprising: forming a molded product comprised of a pattern forming material, wherein the pattern forming material comprises a block copolymer or a graft copolymer comprising: a polymer chain comprising a repeating unit represented by the following formula: ##STR00021## wherein R.sup.1 and R.sup.2 independently represent a substituted or unsubstituted alkyl group, aryl group aralkyl group or alkoxyl group having 1 to 20 carbon atoms; and a thermally decomposable polymer chain; forming a microphase-separated structure in the molded product, said microphase-separated structure comprising a thermally decomposable polymer phase and a remaining polymer phase; and forming a porous structure having the remaining polymer phase by removing the thermally decomposable polymer phase by heating said molded product to a thermal decomposition temperature or more.

6. The method according to claim 5, wherein the molded product of the pattern forming material is a film formed on a substrate, and the microphase-separated structure is a sea-island structure or cylindrical structure, and wherein the pores of the porous structure are filled with the inorganic material, followed by removing the porous structure to form a pattern of the inorganic material in a form of dots or filaments.

7. The method according to claim 5, wherein thermally decomposable polymer chain is selected from the group consisting of a polyethylene oxide chain, a polypropylene oxide chain, a polyacrylic acid chain, and a polymethacrylic acid derivative chain.

8. The method according to claim 5, further comprising filling one or more pores of the porous structure with an inorganic material.

9. The method according to claim 5, further comprising using said porous structure as at least part of one or more electrodes in an electrochemical cell comprising at least a pair of electrodes and an electrolyte layer interposed between the electrodes.

10. The method according to claim 9, wherein the porous structure has a three-dimensional network structure comprising microdomains, and said porous structure comprises a continuous pore having correlation distances at both 2 {square root over (3)} times and 4 times a radius of gyration of cross section of the microdomains.

11. The method according to claim 9, wherein the porous structure is a porous carbon structure.

12. The method according to claim 11, wherein the porous carbon structure has cylindrical pores having an average size from 0.1 to 100 nm which are arranged in a honeycomb manner.

13. The method according to claim 5, wherein the porous structure has a three-dimensional network structure comprising microdomains, and said porous structure comprises a continuous pore having correlation distances at both 2 {square root over (3)} times and 4 times a radius of gyration of cross section of the microdomains.

14. The method according to claim 5, wherein the porous structure is a porous carbon structure.

15. The method according to claim 5, wherein the porous carbon structure has cylindrical pores having an average size from 0.1 to 100 nm which are arranged in a honeycomb manner.

16. The method of claim 5, wherein the block copolymer or the graft copolymer comprises a polymer chain selected from the group consisting of a polyacrylonitrile chain, a polyacrylonitrile derivative chain, a polyaniline derivative chain, a polyparaphenylene derivative chain, and a polymer chain having a perylene skeleton in side chains or a main chain.

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Description

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BACKGROUND OF THE INVENTION

The present invention relates to a material that is capable of forming a pattern of the order of nanometers in a self-organized manner on a substrate, the pattern being utilized as a mask for forming a nanopattern excellent in regularity. The present invention also relates to a material that is capable of forming a bulk structure of the order of nanometers in a self-organized manner, the structure being utilized as it is as a nanostructure of high regularity, or utilized as a template for forming another nanostructure of high regularity. The material of the present invention is applied for manufacturing a magnetic recording medium for hard disks having a recording density of 10 Gbit/inch.sup.2 or more, an electrochemical cell, a solar cell, a photovoltaic device, a light emitting device, a display, a light modulating device, an organic FET device, a capacitor, a high-precision filter, etc.

Needs for a fine pattern or structure are increasingly desired, as improvement in performance of electronic parts. In the electronic parts such as LSI and liquid crystal display, for example, micro-fabrication techniques are required. Many devices such as an electric cell and a capacitor are required small volume and large surface area. In future, a high-density three-dimensional packaging will be needed. Lithography is employed in these processes, and thus the manufacturing cost becomes higher as more micro-fabrications are needed.

On the other hand, there is a technical field where precision as high as in the case of the lithography is not needed, although a patterning of the order of nanometers is required. However, a simple patterning method has not known hitherto, there is no other choice to form a fine pattern by lithography using an electronic beam or deep ultraviolet ray in such a technical field. As mentioned above, in the lithography technique, operations are complicated and enormous investment is required as the processing dimension becomes smaller.

Under these circumstances, as a simple pattern forming method alternative to the lithography technique, a method utilizing a structure having micro polymer phases formed in a self-developed manner from a block copolymer.

For example, P. Mansky et al. have reported, in Appl. Phys. Lett., Vol. 68, No. 18, p. 2586 2588, a method in that a sea-island type microphase-separated film made of a block copolymer of polystyrene and polyisoprene is formed on a substrate, the polyisoprene is decomposed by ozonation and removed to form a porous film, and the substrate is etched using the porous film as a mask, thereby forming a pattern, to which the structure having micro polymer phases is transferred, on the substrate. In addition, M. Park et al. have reported, in Science, Vol. 276, 1401 1406, a method in that a sea-island type microphase-separated film made of a block copolymer of polystyrene and polyisoprene is formed on a substrate, the polyisoprene phase is doped with osmium oxide by a vapor phase reaction to improve etch resistance, and a pattern is formed using the polyisoprene phase selectively doped with osmium oxide as a mask.

Such a method using the microphase separation of the block copolymer is simple and inexpensive as compared with the lithography technique. However, the ozonation is complicated as well as needs relatively long reaction time, so that it is difficult to improve throughput. Also, since the osmium oxide has high level of toxicity, it is scarcely used in general purpose from the viewpoint of safety.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a pattern forming material and a method for forming a pattern, which show high process throughput and capable of forming very easily a planar pattern or three-dimensional structure of the order of nanometers having considerable regularity.

A still another object of the present invention is to provide a method for manufacturing easily a magnetic recording medium, a field emission display, a field emission cathode, a separator and electrode for an electrochemical cell, a catalytic electrode for a fuel cell, a filter, etc., by making use of the aforementioned material.

A pattern forming material according to the present invention comprises a block copolymer or graft copolymer having two polymer chains whose ratio between N/(Nc-No) values of respective monomer units is 1.4 or more, where N represents total number of atoms in the monomer unit, Nc represents the number of carbon atoms in the monomer unit, No represents the number of oxygen atoms in the monomer unit.

The block copolymer or graft copolymer satisfies the conditions is typically that having a polymer chain containing aromatic rings and an acrylic polymer chain.

A pattern forming material of the present invention contains a block copolymer or graft copolymer having a polysilane chain and a carbon-based organic polymer chain.

A method for forming a pattern of the present invention comprises steps of: forming a molded product made of an above-mentioned pattern forming material; forming a structure having micro polymer phases in the molded product; and dry-etching the molded product to remove selectively a polymer phase from the structure having micro polymer phases, thereby forming a porous structure.

A method for forming a pattern of the present invention comprises steps of: forming a film made of an above-mentioned pattern forming material on a substrate; forming a structure having micro polymer phases in the film; selectively removing a polymer phase from the structure having micro polymer phases formed in the film by dry-etching; and etching the substrate using remaining another polymer phase as a mask, thereby transferring the structure having micro polymer phases to the substrate.

A method for forming a pattern of the present invention comprises steps of: forming a pattern transfer film on a substrate; forming a film made of a pattern forming material comprising a block copolymer or graft copolymer having two polymer chains whose ratio between dry etch rates is 1.3 or more on the pattern transfer film; forming a structure having micro polymer phases in the film; selectively removing a polymer phase from the structure having micro polymer phases formed in the film by dry-etching; etching the pattern transfer film using remaining another polymer phase as a mask, thereby transferring the structure having micro polymer phases to the pattern transfer film; and etching the substrate using the pattern transfer film as a mask to which the structure having micro polymer phases is transferred, thereby transferring the structure having micro polymer phases to the substrate.

Another pattern forming material of the present invention contains a block copolymer or graft copolymer having a polymer chain whose main chain is cut by irradiation with an energy beam and an indecomposable polymer chain against irradiation with an energy beam.

An electron beam is typically used as the energy beam. The polymer chain whose main chain is cut by irradiation with the energy beam is typically an acrylic chain substituted by a methyl group or halogen at .alpha.-position or a polysilane chain.

A method for forming a pattern of the present invention comprises steps of: forming a molded product made of an above-mentioned pattern forming material; forming a structure having micro polymer phases in the molded product; irradiating the molded product with an energy beam, thereby cutting a main chain of a polymer phase in the structure having micro polymer phases; and selectively removing the polymer chain whose main chain is cut by development or etching, thereby forming a porous structure consisting of remaining another polymer phase.

A method for forming a pattern of the present invention comprises steps of: forming a film made of an above-mentioned pattern forming material on a substrate; forming a structure having micro polymer phases in the film; irradiating the film with an energy beam, thereby cutting the main chain of a polymer phase in the structure having micro polymer phases; selectively removing the polymer chain whose main chain is cut from the structure having micro polymer phases by etching; and etching the substrate using remaining another polymer phase as a mask, thereby transferring the structure having micro polymer phases to the substrate.

A method for forming a pattern of the present invention comprises steps of: forming a pattern transfer film on a substrate; forming a film made of an above-mentioned pattern forming material on the pattern transfer film; forming a structure having micro polymer phases in the film; irradiating the film with an energy beam, thereby cutting the main chain of a polymer phase in the structure having micro polymer phases; selectively removing the polymer chain whose main chain is cut from the structure having micro polymer phases by etching; etching the pattern transfer film using remaining another polymer phase as a mask, thereby transferring the pattern of the structure having micro polymer phases to the pattern transfer film; and etching the substrate using the pattern transfer film to which the pattern of the structure having micro polymer phases is transferred as a mask, thereby transferring the structure having micro polymer phases to the substrate.

A still another pattern forming material of the present invention comprises a block copolymer or graft copolymer comprising: a polymer chain comprising a repeating unit represented by the following formula:

##STR00001## where R.sup.1 and R.sup.2 independently represent a substituted or unsubstituted alkyl group, aryl group aralkyl group or alkoxyl group having 1 to 20 carbon atoms, and a thermally decomposable polymer chain.

The thermally decomposable polymer chain is typically a polyethylene oxide chain and a polypropylene oxide chain.

A method for forming a pattern of the present invention comprises steps of: forming a film made of a pattern forming material comprising a block copolymer or graft copolymer having at least one thermally decomposable polymer chain on a substrate; forming a structure having micro polymer phases in the film; removing the thermally decomposable polymer phase from the structure having micro polymer phases by heating to a thermal decomposition temperature or more; etching the substrate using remaining another polymer phase as a mask, thereby transferring the pattern of the structure having micro polymer phases to the substrate.

A method for forming a pattern of the present invention comprises steps of: forming a pattern transfer film on a substrate; forming a film made of a pattern forming material comprising a block copolymer or graft copolymer having at least one thermally decomposable polymer chain on the pattern transfer film; forming a structure having micro polymer phases in the film; removing the thermally decomposable polymer phase from the structure having micro polymer phases by heating to a thermal decomposition temperature or more; etching the pattern transfer film using remaining another polymer phase as a mask, thereby transferring the pattern of the structure having micro polymer phases to the pattern transfer film; etching the substrate using the pattern transfer film as a mask, to which the pattern of the structure having micro polymer phases is transferred, thereby transferring the pattern of the structure having micro polymer phases to the substrate.

A method for forming a pattern of the present invention comprises steps of: forming a molded product made of a pattern forming material comprising a block copolymer or graft copolymer having at least one thermally decomposable polymer chain; forming a structure having micro polymer phases in the molded product; removing the thermally decomposable polymer phase by heating to a thermal decomposition temperature or more, thereby forming a porous structure consisting of remaining another polymer phase; and filling pores of the porous structure with an inorganic material.

An electrochemical cell of the present invention comprises a pair of electrodes and a separator interposed between the electrodes and impregnated with an electrolyte, wherein the separator is constituted by a porous structure formed by selectively removing a polymer phase from a block copolymer or graft copolymer having a structure having micro polymer phases.

An electrochemical cell of the present invention comprises a pair of electrodes and an electrolyte layer interposed between the electrodes, wherein at least a part of the electrodes is constituted by a porous structure formed by selectively removing a polymer phase from a block copolymer or graft copolymer having a structure having micro polymer phases. The porous structure typically made of carbon.

A hollow fiber filter of the present invention is made of a porous structure formed by selectively removing a polymer phase from a block copolymer or graft copolymer having a structure having micro polymer phases.

A method for manufacturing a porous carbon structure of the present invention comprises steps of: mixing a precursor of thermosetting resin, a surfactant, water and oil, thereby preparing a microemulsion in which colloidal particles containing the precursor of thermosetting resin are dispersed; curing the precursor of thermosetting resin unevenly distributed in the colloidal particles; removing the surfactant, water and oil from the colloidal particles, thereby providing porous structures of cured thermosetting resin; firing to carbonize the porous structures.

A still another method for forming a pattern of the present invention comprises steps of: applying a blend of a polymer including a metal particle and a block copolymer or graft copolymer to a substrate to form a film; forming a structure having micro polymer phases in the film and segregating the metal particles covered with the polymer in a central portion of a polymer phase or at an interface between the polymer phases in the block copolymer or the graft copolymer; selectively or entirely removing the polymer phases by etching in which the metal particles are segregated, thereby leaving the metal particles.

The method is suitably applicable to magnetic recording medium by depositing a magnetic material on the remaining metal particles. Also, the method is suitable applicable to manufacture of a field emission by depositing a conductor or semiconductor on the remained metal particles to form emitters.

A method for manufacturing a capacitor of the present invention comprises steps of: forming a film made of a blend of a polymer including a metal particle and a block copolymer or graft copolymer; allowing the film to form a lamella structure having micro polymer phases and segregating the metal particles covered with the polymer in a central portion of each polymer phase in the lamella structure; and aggregating the metal particles to form a metal layer in the central portion of each polymer phase in the lamella structure.

A method for manufacturing a catalytic layer of a fuel cell of the present invention comprises steps of: forming a film made of a blend of a block copolymer or graft copolymer including a metal particle and a block copolymer or graft copolymer; forming a structure having micro polymer phases in the film and segregating the metal particles covered with the polymer at an interface between the polymer phases forming the structure having micro polymer phases; and selectively removing a polymer phase in the structure having micro polymer phases, thereby leaving the metal particles on a surface of remaining another polymer phase.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIGS. 1A and 1B are atomic force micrographs (AFM) showing examples of structures having micro polymer phases of the block copolymers according to the present invention;

FIGS. 2A to 2D are diagrammatic views showing examples of structures having micro polymer phases of the block copolymers according to the present invention;

FIG. 3 is a graph showing the relationship between N/(Nc-No) value and dry etch rate of various polymers;

FIGS. 4A to 4C are cross-sectional views showing a method of manufacturing the magnetic recording medium of the present invention;

FIG. 5 is a cross-sectional view of an electrochemical cell according to the present invention;

FIG. 6 is a cross-sectional view of another electrochemical cell according to the present invention;

FIG. 7 is a cross-sectional view of a direct methanol fuel cell according to the present invention;

FIGS. 8A to 8C are schematic views showing a method of manufacturing the capacitor according to the present invention;

FIG. 9 is a cross-sectional view of a field emission display according to the present invention;

FIG. 10 is a cross-sectional view of another field emission display according to the present invention;

FIG. 11 is an SEM micrograph of a carbon structure manufactured in the present invention;

FIG. 12 is an SEM micrograph of a carbon structure manufactured in the present invention; and

FIG. 13 is a perspective view showing a catalytic layer of a fuel cell according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described in more detail.

The principle of the present invention is that a film or a bulk-molded product of a block copolymer or graft copolymer is formed, which copolymer is allowed microphase-separation, and then a polymer phase is selectively removed, thereby forming a porous film or porous structure having a pattern of the order of nanometers. The resultant porous film can be used for a mask for etching an underlayer to transfer the pattern. Also, the porous structure can be used as it is for various applications as well as can be used for a template for forming another porous structure. In the present invention, a difference in dry etch rates, decomposition properties against an energy beam or thermal decomposition properties between two polymer phases is used in order to remove selectively a polymer phase from a structure having micro polymer phases. Since it is not necessary to use a lithography technique, high throughput and reduced cost can be obtained.

First, the block copolymer and graft copolymer will be described. The block copolymer means a linear copolymer in which homopolymer chains are bonded together in a form of blocks. A typical example of the block copolymer is an A-B type block copolymer in which an A polymer chain having a repeating unit A and a B polymer chain having a repeating unit B are connected each other and having a structure of: -(AA--AA)-(BB--BB)-. It is possible to employ a block copolymer in which three of more kinds of polymer chains are bonded together. In the case of a triblock copolymer, any of A-B-A type, B-A-B type and A-B-C type can be employed. A star type block copolymer in which one or more kinds of polymer chains extend radialy from a central portion can be employed. A block copolymer of (A-B)n type or (A-B-A)n type having four or more blocks can be employed. The graft copolymer has a structure comprising a polymer main chain and another pendent polymer chains as side chains. In the graft copolymer, plural kinds of polymers may be pendant as side chains. Also, a combination of a block copolymer and a graft copolymer comprising a block copolymer, such as A-B type, A-B-A type and B-A-B type, and pendent polymer chains C can be employed.

The block copolymer is preferable compared to the graft copolymer because a polymer having a narrow molecular weight distribution can be easily obtained and its composition ratio is also easily controlled. Note that, in the following description, the block copolymer will be mainly described, though the description concerning the block copolymer is applicable as it is to the graft copolymer.

The block copolymer and graft copolymer can be synthesized by various polymerization methods. The most preferable method is a living polymerization method. In the living anion polymerization or living cation polymerization methods, the polymerization of a monomer is initiated with a polymerization initiator capable of generating an anion or an cation, and then another monomer is successively added thereto, thus a block copolymer can be synthesized. A monomer having a double bond such as vinyl compound or butadiene, a cyclic ether monomer such as ethylene oxide, or a cyclic oligosiloxane monomer can be used as a monomer. It is also possible to use a living radical polymerization method. According to the living polymerization method, the molecular weight and copolymer ratio can be precisely controlled, thus making it possible to synthesize a block copolymer having a narrow molecular weight distribution. In the case where the living polymerization is employed, it is preferable to dry sufficiently a solvent with a desiccant such as metal sodium and to prevent oxygen from mixing thereto using a method of freeze drying or bubbling of an inert gas. The polymerization reaction is preferably carried out under flow of an inert gas and under a pressurized condition of preferably two atm or more. The pressurized condition is preferred because contamination of water and oxygen from outside the reaction vessel can be prevented effectively as well as reaction process can be performed in relatively low cost.

A block copolymer and graft copolymer can also be synthesized by a reaction between macromers such as telechelic polymers or by polymerizing a different type of monomer from a macromer terminal as a polymerization initiation point. By making use of a reactive processing method, a block copolymer and graft copolymer can also be synthesized in situ by advancing the above reaction in the process of forming a structure having micro polymer phases. For example, an A polymer, in which reactive terminal groups or side chain groups are introduced, and a B monomer are mixed, and then the monomer is polymerized by a method such as heating, light irradiation and addition of a catalyst in the process of forming a structure having micro polymer phases, thus a block or graft copolymer comprising a polymer A and polymer B can be synthesized. In addition, a block or graft copolymer can be synthesized in situ even by a method in which two or more kinds of telechelic polymers each having a complementary bonding group at the ends or side chains are blended.

It is preferable for a chemical bond linking the polymer chains with each other to be a covalent bond from a viewpoint of bond strength, and particularly preferable to be a carbon-carbon bond or a carbon-silicon bond.

Since special equipment and skill are required in the synthesis methods of a block copolymer or a graft copolymer as compared with the general radical polymerization, these methods have been mainly adopted in a research laboratory level, and therefore, the industrial applications thereof have been very limited in view of cost. However, in the technical fields such as an electronic industry where highly value-added products are manufactured, a sufficient cost effectiveness can be obtained even if a block copolymer or a graft copolymer is employed.

The block copolymer and graft copolymer, unlike a random copolymer, can form a structure, i.e., a structure having micro polymer phases, in which an A phase consisting of aggregated A polymer chains are spatially separated from a B phase consisting of aggregated B polymer chains. In a phase separation given by a general polymer, i.e., a macrophase separation, since two polymer chains can be completely separated to each other, thus ultimately two phases are completely separated. Also, the scale of fluctuation generation is 1 .mu.m or so, the size of a unit cell is 1 .mu.m or more. On the contrary, the size of a unit cell in the microphase separation given by a block copolymer of graft copolymer is not made larger than the size of a molecular chain, which is in the order of several nanometers or several tens nanometers. In addition, the structure having micro polymer phases exhibits morphology in which fine unit cells are very regularly arrayed.

Various types of morphology of the structure having micro polymer phases will be described. FIGS. 1A and 1B are microphotographs with an atomic force microscope (AMF) of a polystyrene (PS)-polymethacrylate (PMMA) block copolymer, which show plan views of structures having micro polymer phases. FIG. 1A is referred to as a dot structure or a sea-island structure, whereas FIG. 1B is referred to as a worm-like structure. FIGS. 2A to 2D show schematic views of the structures having micro polymer phases viewed stereoscopically. FIG. 2A is referred to as a sea-island structure in which another phases are spherically distributed in one phase. FIG. 2B is referred to as a cylindrical structure in which another phases in a rod-like form are regularly distributed in one phase. FIG. 2C is referred to as a bicontinuous structure. FIG. 2D is referred to as a lamella structure in which A phases and B phases are alternately and regularly laminated.

The structure having micro polymer phases of a block copolymer or graft copolymer can be formed in the following manner. For example, a block copolymer or graft copolymer is dissolved in a suitable solvent to prepare a coating solution, which is applied to a substrate to form a film. The film is annealed at a temperature above a glass transition temperature of the polymers, thus a favorable phase-separated structure can be formed. It is also possible to use a method that a copolymer is melted and annealed at a temperature in the range between above the glass transition temperature and below the phase transition temperature to allow the copolymer to form a structure having micro polymer phases, and the structure having micro polymer phases is fixed at room temperature. A structure having micro polymer phases can also be formed by slowly casting a solution of a copolymer. A structure having micro polymer phases can also be formed by a method that a copolymer is melted and molded into a desired shape by a hot press molding, an injection molding and a transfer molding, etc., followed by annealing.

According to the Flory-Huggings theory, it is required for the phase separation between an A polymer and B polymer that the free energy .DELTA.G of mixing must be positive. If the A polymer and B polymer are hard to be blended and the repulsive force between two polymers is intense, a phase separation easily occurs. In addition, the microphase separation easily occurs as a degree of polymerization of the block copolymer becomes large, and therefore, there is a lower limit in the molecular weight. However, polymers of respective phases forming the phase-separated structure are not necessarily incompatible with each other. As long as the precursor polymers of these polymers are incompatible with each other, the structure having micro polymer phases can be formed. After a phase-separated structure is formed by use of the precursor polymers, the precursor polymers can be reacted by heating, light irradiation or addition of a catalyst to be converted into desired polymers. When the reaction conditions are suitably selected at that time, the phase-separated structure formed by the precursor polymers is not destroyed.

The phase separation is most liable to occur when the composition ratio of an A polymer and B polymer is 50:50. This means that a structure having micro polymer phases that is formed most easily is a lamella structure. On the contrary, there may be a case where, even by raising the content of one polymer, it is difficult to form a sea-island structure containing small islands consisting of the other polymer. Therefore, the molecular weight of the block copolymer may be an important factor in order to obtain a desired structure having micro polymer phases.

However, it is very difficult to polymerize a block copolymer with precisely controlling the molecular weight. Therefore, it may be possible to adjust the composition ratio by measuring the molecular weight of the synthesized block copolymer and blending a homopolymer so as to give a desired composition ratio. The addition amount of the homopolymer is set to 100 parts by weight or less, preferably 50 parts by weight or less, and more preferably 10 parts by weight or less to 100 parts by weight of the block copolymer. If the addition amount of the homopolymer is excessive, there is a possibility to disrupt the structure having micro polymer phases.

In addition, if the difference between the solubilities of the two polymer constituting the block copolymer is too large, there may be occur a phase separation between the A-B block copolymer and the A homopolymer. In order to avoid the particular phase separation as much as possible, it is preferable to lower the molecular weight of the A homopolymer. This is because the A homopolymer having a low molecular weight increases the negative value of the enthoropy term in the Flory-Huggins equation, making it easy for the A-B block copolymer and the A homopolymer to be blended together. In addition, the fact that the molecular weight of the A homopolymer is lower than molecular weight of the A block in the block copolymer leads to thermodynamic stability. Taking the thermodynamic stability into consideration, it is preferable that the molecular weight of the A homopolymer is lower than two thirds of the molecular weight of the A block constituting the block copolymer. On the other hand, if the molecular weight of the A homopolymer is lowered to less than 1,000, it may possibly be blended to the B block in the block copolymer, which is not preferable. In addition, taking the glass transition temperature into consideration, the molecular weight of the A homopolymer is more preferably 3,000 or more.

When a thin film consisting of the pattern forming material of the present invention is formed, it is preferable to apply a homogeneous solution. When the homogeneous solution is used, it is possible to prevent hysteresis during film formation from being remained. If the coating solution is inhomogeneous as the case where micelles having a relatively large particle size are produced in the solution, it is made difficult to form a regular pattern due to mixing of an irregular phase-separated structure or it takes a long time to form a regular pattern, which is not preferable.

The solvent for dissolving the block copolymer should desirably be a good solvent to two kinds of polymers constituting the block copolymer. The repulsive force between polymer chains is proportional to a square of the difference in solubility parameter between two kinds of polymer chains. Consequently, when the good solvent to the two polymers is employed, it makes the difference in solubility parameter between two kinds of polymer chains smaller and makes free energy of the system smaller, which leads to an advantageous condition for a phase separation.

When a thin film of a block copolymer is intended to form, it is preferable to employ a solvent having a high boiling point of 150.degree. C. or more so as to make it possible to prepare a homogeneous solution. When a bulk-molded product of a block copolymer is intended to form, it is preferable to employ a solvent having a low boiling point such as THF, toluene and methylene chloride.

Examples of pattern forming materials used in the present invention will be described hereinafter. First, a pattern forming material consisting of a block copolymer or graft copolymer comprising two or more polymer chains whose difference in dry etch rates is large will be described. The pattern forming material of the present invention comprises a block copolymer or graft copolymer comprising at least two polymer chains whose ratio between N/(Nc-No) values of respective monomer units is 1.4 or more, where N represents total number of atoms in the monomer unit, Nc represents the number of carbon atoms in the monomer unit, No represents the number of oxygen atoms in the monomer unit, and a block copolymer and a graft copolymer comprising a polysilane chain and a carbon-based organic polymer chain. The condition that the ratio between N/(Nc-No) values is 1.4 or more with respect to two polymer chains means the fact that the etching selectivity of each polymer chain constituting the structure having micro polymer phases is large. Namely, when the pattern forming material that meets the above condition is allowed to form a structure having micro polymer phases and then is subjected to dry etching, a polymer phase is selectively etched and the other polymer phase is left remained.

The parameter of N/(Nc-No) will be described in detail below. In this parameter, N is a total number of atoms per segment (which corresponds to monomer unit) of a polymer; Nc is the number of carbon atom; and No is the number of oxygen atom. The parameter is an index indicating the dry etch resistance of a polymer, in that the etch rate by dry etching is made higher (or the dry etch resistance is lowered) as the value of the parameter becomes larger. In other words, there is a following relationship between the etch rate V.sub.etch and the aforementioned parameter.

V.sub.etch.varies.N/(Nc-No)

This tendency is scarcely dependent on the types of etching gas such as Ar, O.sub.2, CF.sub.4, H.sub.2, etc. (J. Electrochem. Soc., 130, 143(1983)). As for the etching gas, in addition to Ar, O.sub.2, CF.sub.4 and H.sub.2 that are described in the above publication, it is also possible to employ C.sub.2F.sub.6, CHF.sub.3, CH.sub.2F.sub.2, CF.sub.3Br, N.sub.2, NF.sub.3, Cl.sub.2, CCl.sub.4, HBr, SF.sub.6, etc. Note that, the parameter has nothing to do with the etching of an inorganic material such as silicon, glass and metal.

The specific value of the parameter can be calculated by referring to the following chemical formula. Since the monomer unit of polystyrene (PS) is C.sub.8H.sub.8, the parameter is expressed as 16/(8-0)=2. Since the monomer unit of polyisoprene (PI) is C.sub.5H.sub.8, the parameter is expressed as 13/(5-0)=2.6. Since the monomer unit of polymethacrylate (PMMA) is C.sub.5O.sub.2H.sub.8, the parameter is expressed as 15/(5-2)=5. Therefore, in the block copolymer of PS-PMMA, it is expected that the etch resistance of PS is higher, and only PMMA is likely etched. For example, it has been confirmed that, when the block copolymer is subjected to a reactive ion etching (RIE) with flowing CF.sub.4 in a flow rate of 30 sccm and setting the pressure to 0.01 Torr under the conditions of 150 W in progressive wave and 30 W in reflective wave, PMMA is etched at an etch rate that is 4.+-.0.3 times faster than PS.

##STR00002##

FIG. 3 shows a relationship between the N/(Nc-No) value of each polymer and the etch rate thereof. The abbreviations employed in FIG. 3 respectively represent the following polymers. SEL-N=(trade name, Somer Kogyo Co., Ltd.), PMMA=polymethyl methacrylate, COP=glycidyl methacrylate-methyl acrylate copolymer, CP-3=methacrylate-t-butyl methacrylate copolymer, PB=polybenzyl methacrylate, FBM=polyhexafluorobutyl methacrylate, FPM=polyfluoropropyl methacrylate, PMIPK=polymethyl isopropenyl ketone, PS=polystyrene, CMS=chloromethlated styrene, P.alpha.MS=poly(.alpha.-methylstyrene), PVN=polyvinylnaphthalene, PVB=polyvinylbiphenyl, and CPB=cyclized polybutadiene. As shown in the figure, it is found that the relationship of V.sub.etch.varies.N/(Nc-No) is effected.

In a polymer including an aromatic ring and having many double bonds, the value of the above parameter becomes smaller in general because the ratio of carbon is relatively increased. As seen from the afore-mentioned parameter, the larger the number of carbon atom in the polymer (the smaller the value of the parameter), the higher the dry etch resistance, and the larger the number of oxygen atom in the polymer (the larger the value of the parameter), the lower the dry etch resistance. This can be described qualitatively as follows. Namely, carbon is less reactive to radicals, and hence is chemically stable. Therefore, a polymer containing a large number of carbon atoms is hardly reactive to various kinds of radicals, which leads to improve etch resistance. Whereas oxygen is highly reactive to radicals, so that a polymer having a large number of oxygen atoms is etched at a high etch rate, and thus has low etch resistance. Additionally, when oxygen is included in a polymer, oxygen radicals may be easily generated. Therefore, when a fluorine-based etching gas such as CF.sub.4 is employed, F radicals are multiplied due the effect of oxygen radicals and the radicals taking part in the etching are increased, leading to increase the etch rate. An acrylic polymer has high oxygen content and a small number of double bonds, which brings about increase in the value of the above parameter, so that it can be easily etched.

Therefore, typical block copolymers having a large difference in dry etch-rates comprise an aromatic ring-containing polymer chain and an acrylic polymer chain. An example of the aromatic ring-containing polymer chain includes a polymer chain synthesized by polymerizing at least one monomer selected from the group consisting of vinyl naphthalene, styrene and derivatives thereof. An example of the acrylic polymer chain includes a polymer chain synthesized by polymerizing at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, crotonic acid and derivatives thereof.

As mentioned above, when the ratio of the N/(Nc-No) parameter between the A polymer chain and the B polymer chain constituting the pattern forming material is 1.4 or more, it is possible to obtain a clear pattern etching. When this ratio is 1.5 or more, preferably 2 or more, it is possible to ensure a large difference in etch rates between two kinds of polymer chain, thereby making it possible to enhance the stability in the processing. It is preferable in the actual dry etching that the etching selectivity between two kinds of polymer chains be 1,3 or more, more preferably 2 or more, still more preferably 3 or more. When the ratio of the N/(Nc-No) parameter between the A polymer chain and the B polymer chain constituting the pattern forming material is 1.4 or more, it is possible to obtain a satisfactory pattern by means of etching without employing a polymer chain to which a metal element is doped or a metal element is introduced. Since patterning can be performed without employing a metal element, the material is very useful for manufacturing various electronic devices in which metal impurities bring about problems.

In order to enhance the etching selectivity in the case where O.sub.2 gas is employed as an etching gas, it is especially preferable to use a silicon-containing polymer chain as a polymer chain having higher etch resistance and a halogen-containing polymer chain as a polymer chain having lower etch resistance. As the silicon-containing polymer chain, a silicon-containing aromatic polymer chain such as poly(p-trimethylsilyl styrene) is preferred. AS the halogen-containing polymer chain, a halogen-containing acrylic polymer chain such as poly(chloroethyl methacrylate) is preferred.

Another pattern forming material consisting of a block copolymer or graft copolymer comprising two or more kinds of polymer chains having large difference in etch rates will be described. A pattern forming material of the present invention comprises a block copolymer or graft copolymer comprising a polysilane chain and a carbon-based organic polymer chain.

The block copolymer having a polysilane chain can be synthesized by copolymerization between a polystyrene-based macromer and dichlorosilane as disclosed by S. Demoustier-Champagne et al (Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 31, 2009 2014(1993)), or by living polymerization between polysilane using masked disilene and methacrylates as disclosed by Sakurai et al (Japan Chemical Society, 76th Spring Meeting, Preprint I, Lecture No. 4B513). Since polysilane is a silicon-based polymer, which can be dry-etched easier than a general carbon-based polymer.

The polysilane chain employed in the pattern forming material of the present invention comprises any one of the repeating units represented by the following chemical formulas at least partly.

##STR00003##

where R.sup.1, R.sup.2, R.sup.3 and R.sup.4 respectively represent a substituted or unsubstituted alkyl, aryl or aralkyl group having 1 to 20 carbon atoms.

The polysilane may be a homopolymer or a random copolymer, or may be a block copolymer having a structure in which two kinds of polysilane are linked together via an oxygen atom, a nitrogen atom, an aliphatic group or an aromatic group. Examples of the polysilane include poly(methylphenylsilane), poly(diphenylsilane), poly(methylchloromethylphenylsilane), poly(dihexylsilane), poly(propylmethylsilane), poly(dibutylsilane), and a random and block copolymer thereof.

Next, a pattern forming material utilizing difference in decomposition properties by an energy beam between two or more polymer chains constituting a block copolymer or graft copolymer will be described. The pattern forming material of the present invention comprises a block copolymer or graft copolymer comprising a polymer chain whose main chain is cut by irradiation with an energy beam and an indecomposable polymer chain against irradiation with an energy beam. The polymer chain whose main chain has been cut by irradiation with the energy beam can be removed by means of wet etching such as rinsing with a solvent or by evaporation by heat treatment. Thus, a fine pattern or a structure retaining a structure having micro polymer phases can be formed without a dry etching process. There are some cases depending on the types of electronic materials where a dry etching process is not applicable or a wet etching process is more preferable in view of manufacturing cost even if a dry etching process is applicable. Therefore, it is very advantageous not to use a dry etching process.

Since a block copolymer has two or more kinds of polymers linked through a chemical bond, the block copolymer is generally hard to be developed even if one polymer chain represents high solubility to a developer. However, when a block copolymer of polystyrene (PS) and polymethyl methacrylate (PMMA), for example, is irradiated with an electron beam, the main chain of PMMA is cut, so that only the PMMA phase can be dissolved in the developer. The developer is not particularly restricted as long as it can selectively dissolve out to remove the decomposed polymer chain, and therefore it may be a water-based solvent or an organic solvent. In the case of PMMA, methyl isobutyl ketone (MIBK), ethyl lactate, acetone, etc., can be employed. In order to adjust the solubility of the polymer, other solvent such as isopropyl alcohol (IPA) may be added to the developer as well as a surfactant may be added. Ultrasonic cleaning may be performed during development. Since the polymer chain after decomposition is lowered in molecular weight and can be evaporated by heat treatment, it can be easily removed.

At least one polymer constituting a block copolymer or graft copolymer is cut in the main chain by irradiation with an energy beam such as an electron beam, an X-ray, a .gamma.-ray and a heavy particle beam. An electron beam, an X-ray and a .gamma.-ray are preferred since they can penetrate deep into the molded product of the polymer and advantageous in view of reducing processing cost because of relatively low cost in irradiation equipment. In particular, the electron beam and X-ray are more preferable, and further the electron beam is most preferable because it brings about high efficiency for decomposition of the polymer chain by its irradiation. As an electron beam source, various types of electron beam accelerators such as Cockcroft-Walton type, Van de Graaff type, resonance transformer type, insulated-core transformer type, or linear type, dynamitron type and radio frequency type can be employed.

The polymer chains decomposed by an energy beam include those having a methyl group at .alpha.-position such as polypropylene, polyisobutylene, poly(.alpha.-methylstyrene), polymethacrylic acid, polymethyl methacrylate, polymethacrylamide and polymethyl isopropenyl ketone. Also, a polymer chain whose .alpha.-position is substituted by a halogen atom exhibits higher decomposition property in main chain. Further, methacrylate polymers whose ester group is substituted by a fluorinated carbon or halogenated carbon such as polytrifluoromethyl methacrylate, polytrifluoromethyl-.alpha.-acrylate, polytrifluoroethyl methacrylate, polytrifluoroethyl-.alpha.-acrylate and polytrichloroethyl-.alpha.-acrylate are more preferable because they exhibit high sensitivity to the energy beam. In the case where the energy beam is an X-ray, it is preferable that the polymer contains a metal element because it brings about improvement in decomposition efficiency.

The main chain of another at least one polymer chain constituting the block copolymer is indecomposable against irradiation with an energy beam. A polymer capable of cross-linking by irradiation with the energy beam is more preferred. As the polymer chain indecomposable against irradiation with the energy beam, those having a hydrogen atom at the .alpha.-position of