Method for forming hole pattern

Abstract

A photosensitive material film is formed by applying, on an etch target film deposited on a semiconductor substrate, a photosensitive material containing a hardly alkaline-soluble base polymer including a polymer in which a principal chain has cycloolefin and a saturated or non-saturated polycyclic alkyl group is bonded to the principal chain, and an acid generator including an onium salt compound. The photosensitive material film is irradiated with ArF excimer laser through a photomask so as to form a hole-patterned photosensitive material film. A hole pattern is formed in said etch target film by subjecting the etch target film to plasma etching using plasma at a plasma density of 1×1010/cm3 or more with the hole-patterned photosensitive material film used as an etching mask.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a method for forming a hole pattern. More particularly, it relates to a method for forming a fine hole pattern of an etch target film formed on a semiconductor substrate through dry etching of the etch target film by using an etching mask of a hole-patterned photosensitive material film with ArF excimer laser used as exposing light.

[0002] As a conventional example, a method for forming a hole pattern disclosed in Japanese Laid-Open Patent Publication No. 2000-66384 will now be described with reference to FIGS. 5A through 5C. FIG. 5B is a cross-sectional view taken along line VB-VB of FIG. 5A.

[0003] In this conventional method, a chemically amplified resist material having the following constituents is used:

[0004] Base polymer: a polymer in which an adamantyl group is bonded as a protecting group to an acrylic copolymer

[0005] Acid generator: onium salt

[0006] Solvent: propylene glycol monomethyl ether acetate

[0007] First, as shown in FIGS. 5A and 5B, the chemically amplified resist material having the aforementioned constituents are applied on an etch target film 2 formed on a semiconductor substrate 1, and the resultant is annealed at 90 for 90 seconds, thereby forming a photosensitive material film 3 with a thickness of 700 nm.

[0008] Next, the photosensitive material film 3 is irradiated with KrF excimer laser through a photomask having a transmission portion with a diameter of, for example, 300 nm, and then, annealing is carried out as PEB (post-exposure baking) at 110 for 90 seconds. Thereafter, the photosensitive material film 3 is developed. Thus, the photosensitive material film 3 is formed into a hole pattern having a hole 3a with a diameter of, for example, 300 nm.

[0009] Then, as shown in FIG. 5C, the etch target film 2 is subjected to plasma etching by using the hole-patterned photosensitive material film 3 as an etching mask. Thus, a hole 2a for a contact hole or a via hole is formed in the etch target film 2.

[0010] Recently, there are increasing demands for a higher degree of integration and further refinement of semiconductor integrated circuit devices. Accordingly, the shape of the hole 2a formed in the etch target film 2 is required to be more vertical (so as to attain an angle of the side wall of 75 through 90 degrees) and the aspect ratio (the depth of the hole/the diameter of the hole) is required to be increased. For example, when the aspect ratio of the hole 2a is approximately 1 through 2, a substantially vertical shape (with the angle of the side wall of 75 through 90 degrees) is required and the hole 3a is required to be formed to attain a high aspect ratio of approximately 2 or more.

[0011] Furthermore, as shown in FIGS. 6A and 6B, there arises a problem that the hole 2a formed in the etch target film 2 has not only a star-like plane shape but also a diameter (hole size) much larger than the desired value (300 nm).

[0012] According to Japanese Laid-Open Patent Publication No. 2000-66384, in order to form the hole 2a with a high aspect ratio in the etch target film 2, plasma with a plasma density of 1×1010/cm3 or more, which is higher than a conventionally employed density, is used in the plasma etching so as to form the hole 2a of the etch target film 2 in a circular plane shape. Furthermore, the acid generator including an onium salt compound is used so as to prevent the hole size from becoming much larger than the desired value.

[0013] In the lithography process for forming the hole-patterned photosensitive material film, KrF excimer laser (of a wavelength of 248 nm) is conventionally used as the exposing light. Recently, however, in order to cope with the higher degree of integration and further refinement of semiconductor integrated circuits, ArF excimer laser (of a wavelength of 193 nm) is proposed to be used as the exposing light. When the ArF excimer laser is used, the hole size can be reduced to approximately 200 nm.

[0014] However, when the photosensitive material film formed from the aforementioned chemically amplified resist material is irradiated with the ArF excimer laser for forming the hole pattern, although the onium salt compound is used as the acid generator, the hole of the etch target film is formed in a star-like plane shape and the hole size is much larger than the desired value (200 nm).

[0015] FIG. 7 shows the relationship between the plasma density and the plane shape and the hole size of a hole formed through the lithography process using ArF excimer laser as the exposing light. The relationship of FIG. 7 is obtained in the case where an etch target film of BPSG (boro-phospho silicate glass) with a thickness of 1200 nm formed on a silicon substrate is subjected to plasma etching by using a hole-patterned photosensitive material film with a thickness of 700 nm, and the hole size is set to 200 nm.

[0016] In this case, in a low plasma density region corresponding to an RIE region where the plasma density is lower than 1×1010/cm3, the hole formed in the etch target film has a circular plane shape and the hole size is 200 nm, which is substantially equal to that of the hole-patterned photosensitive material film. In contrast, in a high plasma density region where the plasma density is 1×1010/cm3 or more, the hole formed in the etch target film has a star-like plane shape and the hole size is enlarged.

[0017] Accordingly, it is understood that although the acid generator including the onium salt compound is used, when the plasma density is 1×1010/cm3 or more, the plane shape of the hole formed in the etch target film is changed from a circular shape to a star-like shape and the hole size is abruptly enlarged.

[0018] When the hole has a star-like plane shape or the hole size is much larger than a desired value, a metal film filled in the hole is connected to an interconnect that should not be electrically connected to the metal film. As a result, there arises a problem that an abnormal leakage current flows or that the device characteristic is degraded.

[0019] FIGS. 8A and 8B show the relationship between the reduction of the hole size and the problem of the star-like plane shape of the hole or the enlargement of the hole size. FIG. 8A shows a hole with a hole size of 0.20 {grave over (l)}m and FIG. 8B shows a hole with a hole size of 0.30 {grave over (l)}m. In either case, the hole size is enlarged by approximately 0.5 {grave over (l)}m.

[0020] In the hole of FIG. 8B, the enlargement rate of the hole size is 1.17 (0.35/0.30), and in the hole of FIG. 8A, the enlargement rate of the hole size is 1.25 (0.25/0.20). In other words, even when the hole size is enlarged by the same dimension, the enlargement rate is increased as the hole size is reduced, which largely affects the plane shape of the hole to change it to a star-like shape.

SUMMARY OF THE INVENTION

[0021] In consideration of the aforementioned conventional problems, an object of the invention is, in forming a fine hole pattern with a high aspect ratio by irradiating a photosensitive material film made from a chemically amplified resist material with ArF excimer laser, forming a hole in a circular plane shape in an etch target film and preventing the hole from having a diameter much larger than a desired value (200 nm).

[0022] In order to achieve the object, the present inventors have variously examined the cause of the star-like plane shape of a hole formed in an etch target film, resulting in finding the following: In the case where an acrylic copolymer is used as a base polymer, although the base polymer is good for attaining high sensitivity and high resolution, when a hole pattern of the etch target film is formed by plasma etching at a plasma density of 1×1010/cm3 or more, the wall of the hole is easily scraped.

[0023] This is because the photosensitive material film is exposed to the high density plasma, so that a straight-chain bond is broken in the acrylic copolymer, which makes the etching resistance of the photosensitive material film uneven. The etching resistance of the photosensitive material film at issue corresponds to the specialty of a pattern of the hole pattern, and means, in an actual device, that the remaining rate of the photosensitive material film is very high in a hole pattern as compared with that in a line pattern. Therefore, in the case where the etch target film is subjected to the plasma etching, stress can be easily collected in a hole pattern than in a line pattern, and hence, the shape of a hole pattern is more easily changed.

[0024] The etching resistance at issue corresponds to the change to the star-like shape caused because of the distribution in the etch rate of the photosensitive material film. It does not correspond to improvement of etch selectivity between the photosensitive material film and the etch target film (namely, prevention of the photosensitive material film from being etched while etching the etch target film) as described in, for example, paragraph [0070] of Japanese Laid-Open Patent Publication No. 10-254140.

[0025] In the case where polyhydroxystyrene, which is widely used as a base polymer of a chemically amplified resist material in using KrF excimer laser as the exposing light, is used in the exposure of ArF excimer laser, a pattern is difficult to form because the light transmittance is low.

[0026] The present invention was devised on the basis of the aforementioned findings, and specifically, the first method for forming a hole pattern of this invention comprises the steps of forming a photosensitive material film by applying, on an etch target film deposited on a semiconductor substrate, a photosensitive material containing a hardly alkaline-soluble base polymer including a polymer in which a principal chain has cycloolefin and a saturated or non-saturated polycyclic alkyl group is bonded to the principal chain, and an acid generator including an onium salt compound; forming a hole-patterned photosensitive material film by irradiating the photosensitive material film with ArF excimer laser through a photomask; and forming a hole pattern in the etch target film by subjecting the etch target film to plasma etching using plasma at a plasma density of 1×1010/cm3 or more with the hole-patterned photosensitive material film used as an etching mask.

[0027] The second method for forming a hole pattern of this invention comprises the steps of forming a photosensitive material film by applying, on an etch target film deposited on a semiconductor substrate, a photosensitive material containing a hardly alkaline-soluble base polymer including a polymer in which a principal chain is composed of cyclo with three or more folds ring, and an acid generator including an onium salt; forming a hole-patterned photosensitive material film by irradiating the photosensitive material film with ArF excimer laser through a photomask; and forming a hole pattern in the etch target film by subjecting the etch target film to plasma etching using plasma at a plasma density of 1×1010/cm3 or more with the hole-patterned photosensitive material film used as an etching mask.

[0028] According to the first or second method for forming a hole pattern of this invention, since the base polymer has high stability against heat and plasma, the wall of the hole formed in the photosensitive material film is difficult to scrape even when plasma etching is carried out by using plasma at a high density of 1×1010/cm3 or more. Accordingly, a hole having a high aspect ratio and a good plane shape with a hole size not largely enlarged as compared with a desired value can be formed in the etch target film. Also, since the acid generator includes an onium salt compound, the resistance of the photosensitive material film against the plasma etching can be further improved.

[0029] As a result, a metal film filled in the hole of the etch target film is not connected to an interconnect that should not be electrically connected to the metal film, and hence, the problem of an abnormal leakage current or degradation of the device characteristic can be prevented.

[0030] In the first method for forming a hole pattern, the polymer preferably includes a norbornene derivative.

[0031] Alternatively, in the first method for forming a hole pattern, the polymer preferably includes norbornene and a norbornene derivative.

[0032] In the first method for forming a hole pattern, the polycyclic alkyl group is preferably an adamantyl group, a tricyclodecyl group or a tetracyclododecyl group.

[0033] In the second method for forming a hole pattern, the polymer preferably includes a tricyclodecene derivative, a tetracyclododecene derivative, a pentacyclopentadecene derivative or a hexacycloheptadecene derivative.

[0034] In the second method for forming a hole pattern, a saturated or non-saturated polycyclic alkyl group is preferably bonded to the principal chain of the polymer.

[0035] In the first or second method for forming a hole pattern, the plasma etching is preferably carried out by using a first voltage for generating plasma and a second voltage for inducing ions of the plasma toward the semiconductor substrate.

[0036] Thus, the plasma etching can be definitely carried out by using plasma at a high density of 1×1010/cm3 or more.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIGS. 1A, 1B and 1C are diagrams for showing procedures in a method for forming a hole pattern according to Embodiment 1 or 2 of the invention, and specifically, FIG. 1A is a plane view, FIG. 1B is a cross-sectional view taken along line IB-IB of FIG. 1A and FIG. 1C is a cross-sectional view;

[0038] FIGS. 2A and 2B are diagrams for showing another procedure in the method for forming a hole pattern of Embodiment 1 or 2, and specifically, FIG. 2A is a plane view and FIG. 2B is a cross-sectional view taken along line IIB-IIB of FIG. 2A;

[0039] FIGS. 3A, 3B and 3C are diagrams for showing procedures in a method for forming a hole pattern according to Embodiment 3 of the invention, and specifically, FIG. 3A is a plane view, FIG. 3B is a cross-sectional view taken along line IIIB-IIIB of FIG. 3A and FIG. 3C is a cross-sectional view;

[0040] FIGS. 4A, 4B and 4C are diagrams for showing other procedures in the method for forming a hole pattern of Embodiment 3, and specifically, FIG. 4A is a cross-sectional view, FIG. 4B is a plane view and FIG. 4C is a cross-sectional view taken along line IVC-IVC of FIG. 4B;

[0041] FIGS. 5A, 5B and 5C are diagrams for showing procedures in a conventional method for forming a hole pattern, and specifically, FIG. 5A is a plane view, FIG. 5B is a cross-sectional view taken along line VB-VB of FIG. 5A and FIG. 5C is a cross-sectional view;

[0042] FIGS. 6A and 6B are diagrams for explaining problems of the conventional method for forming a hole pattern, and specifically, FIG. 6A is a plane view and FIG. 6B is a cross-sectional view taken along line VIB-VIB of FIG. 6A;

[0043] FIG. 7 is a characteristic diagram for showing the relationship between plasma density and the plane shape and hole size of a hole formed through a lithography process using ArF excimer laser as exposing light; and

[0044] FIGS. 8A and 8B are diagrams for explaining the relationship between reduction of a hole size and a problem of a star-like plane shape of a hole or enlargement of a hole size.

DETAILED DESCRIPTION OF THE INVENTION

[0045] EMBODIMENT 1

[0046] A method for forming a hole pattern according to Embodiment 1 of the invention will now be described with reference to FIGS. 1A through 1C, 2A and 2B.

[0047] In Embodiment 1, a chemically amplified resist material having the following constituents is used:

[0048] Base polymer: a hardly alkaline-soluble polymer in which an adamantyl group is bonded as a protecting group to a copolymer of a norbornene derivative and maleic anhydride

[0049] Acid generator: triphenylsulfonium triflate, that is, an onium salt compound

[0050] Solvent: a mixed solvent of propylene glycol monomethyl ether acetate and ethyl lactate

[0051] First, as shown in FIGS. 1A and 1B, the chemically amplified resist material having the aforementioned constituents is applied on an etch target film 11 deposited on a semiconductor substrate 10, and then, annealing is carried out at 90 for 90 seconds, thereby forming a photosensitive material film 12 with a thickness of 700 nm. Subsequently, the photosensitive material film 12 is irradiated with ArF excimer laser through a photomask having a transmission portion with a diameter of, for example, 200 nm, and then, annealing is carried out as PEB at 110 for 90 seconds.

[0052] Next, an irradiated portion (exposed portion) of the photosensitive material 12 is dissolved in a developer of a 2.38% TMAH aqueous solution. Thus, the photosensitive material film 12 is formed into a hole pattern made from an unirradiated portion (unexposed portion) of the photosensitive material film and having a hole 12a with a hole size of 200 nm.

[0053] The chemically amplified resist material has transmittance of 55% or more against the ArF excimer laser, and hence, the hole 12a with a hole size of 200 nm can be formed.

[0054] When the photosensitive material film is patterned by using KrF excimer laser as the exposing light instead of the ArF excimer laser with the other conditions of the method of Embodiment 1 unchanged, a hole with a hole size of 200 nm cannot be formed.

[0055] However, since the aforementioned chemically amplified resist material is used in Embodiment 1, the hole-patterned photosensitive material film 12 having a hole size of 200 nm can be formed through the pattern exposure using the ArF excimer laser as the exposing light.

[0056] Next, as shown in FIG. 1C, the etch target film 11 is subjected to plasma etching with the hole-patterned photosensitive material film 12 used as an etching mask under the following conditions:

[0057] Plasma etching system: induction coupling plasma (ICP) system

[0058] Etching gas: a C2F6 gas

[0059] Degree of vacuum in chamber: 665 through 1330 kPa

[0060] Bias power: 1000 W

[0061] Source power: 2100 W

[0062] The plasma density is thus set to 1×1010/cm3 through 1×1012/cm3. In this manner, a hole 11a is formed in the etch target film 11.

[0063] When the hole 11a is formed in the etch target film 11 under the above-described conditions, the hole 11a with a circular plane shape and a hole size of approximately 205 nm can be formed without largely enlarging the hole size as compared with the desired value as shown in FIGS. 2A and 2B.

[0064] Furthermore, according to Embodiment 1, when the hole 11a has an aspect ratio of approximately 1 through 2, it is formed in a substantially vertical shape (with an angle of the side wall of 75 through 90 degrees). Moreover, when the hole 11a has a high aspect ratio of 2 through 8, it is formed in a shape with the side wall tapered toward the bottom, namely, with the cross-sectional dimension reduced toward the bottom.

[0065] Although an adamantyl group is used as the protecting group in this embodiment, a non-substituted polycyclic alkyl group such as a tricyclodecyl group and a tetracyclododecyl group may be used instead. Alternatively, a substituted polycyclic alkyl group in which a hydroxyl group or an alkoxy group is substituted for such a group may be used instead.

[0066] Although the copolymer of a norbornene derivative and maleic anhydride is used as the base polymer in this embodiment, a norbornene derivative, a copolymer of norbornene and a norbornene derivative or a copolymer of norbornene, a norbornene derivative and maleic anhydride may be used instead.

[0067] EMBODIMENT 2

[0068] A method for forming a hole pattern according to Embodiment 2 of the invention will now be described with reference to FIGS. 1A through 1C, 2A and 2B.

[0069] In Embodiment 2, a chemically amplified resist material having the following constituents is used:

[0070] Base polymer: a hardly alkaline-soluble polymer in which an adamantyl group is bonded as a protecting group to a copolymer of a tricyclodecene derivative and maleic anhydride

[0071] Acid generator: triphenylsulfonium triflate, that is, an onium salt compound

[0072] Solvent: a mixed solvent of propylene glycol monomethyl ether acetate and ethyl lactate

[0073] First, as shown in FIGS. 1A and 1B, the chemically amplified resist material having the aforementioned constituents is applied on an etch target film 11 deposited on a semiconductor substrate 10, and then, annealing is carried out at 90 for 90 seconds, thereby forming a photosensitive material film 12 with a thickness of 700 nm. Subsequently, the photosensitive material film 12 is irradiated with ArF excimer laser through a photomask having a transmission portion with a diameter of, for example, 200 nm, and then, annealing is carried out as the PEB at 110 for 90 seconds.

[0074] Next, an irradiated portion (exposed portion) of the photosensitive material 12 is dissolved in a developer of a 2.38% TMAH aqueous solution. Thus, the photosensitive material film 12 is formed into a hole pattern made from an unirradiated portion (unexposed portion) of the photosensitive material film and having a hole 12a with a hole size of 200 nm.

[0075] The chemically amplified resist material has transmittance of 55% or more against the ArF excimer laser, and hence, the hole 12a with a hole size of 200 nm can be formed.

[0076] When the photosensitive material film is patterned by using KrF excimer laser as the exposing light instead of the ArF excimer laser with the other conditions of the method of Embodiment 2 unchanged, a hole with a hole size of 200 nm cannot be formed.

[0077] However, since the aforementioned chemically amplified resist material is used in Embodiment 2, the hole-patterned photosensitive material film 12 having a hole size of 200 nm can be formed through the pattern exposure using the ArF excimer laser as the exposing light.

[0078] Next, as shown in FIG. 1C, the etch target film 11 is subjected to plasma etching with the hole-patterned photosensitive material film 12 used as an etching mask under the following conditions:

[0079] Plasma etching system: induction coupling plasma (ICP) system

[0080] Etching gas: a C2F6 gas

[0081] Degree of vacuum in chamber: 665 through 1330 kPa

[0082] Bias power: 1000 W

[0083] Source power: 2100 W

[0084] The plasma density is thus set to 1×1010/cm3 through 1×1012/cm3. In this manner, a hole 11a is formed in the etch target film 11.

[0085] When the hole 11a is formed in the etch target film 11 under the above-described conditions, the hole 11a with a circular plane shape and a hole size of approximately 203.5 nm can be formed as shown in FIGS. 2A and 2B, and thus the enlargement of the hole size is suppressed as compared with that in Embodiment 1.

[0086] This is because a tricyclodecene derivative is included in the base polymer, namely, the base polymer has a triple cyclo-ring differently from the norbornene derivative used in Embodiment 1, and hence, the etching resistance is improved. Accordingly, the enlargement of the hole size can be further suppressed in Embodiment 2 than in Embodiment 1.

[0087] Furthermore, according to Embodiment 2, when the hole 11a has an aspect ratio of approximately 1 through 2, it is formed in a substantially vertical shape (with an angle of the side wall of 75 through 90 degrees). Moreover, when the hole 11a has a high aspect ratio of 2 through 8, it is formed in a shape with the side wall tapered toward the bottom, namely, with the cross-sectional dimension reduced toward the bottom.

[0088] Although a tricyclodecene derivative, that is, a polymer having a triple cyclo-ring, is used in this embodiment, a tetracyclododecene derivative having a four-fold cyclo-ring, a pentacyclopentadecene derivative having a five-fold cyclo-ring or a hexacyclopentadecene derivative having a six-fold cyclo-ring may be used instead. When a polymer having a cyclo-ring of four or more folds is thus used, the resistance against etching in high density plasma can be further improved. Therefore, the enlargement of the hole size can be further suppressed so as to form a hole in a better shape.

[0089] Although an adamantyl group is used as the protecting group in this embodiment, a non-substituted polycyclic alkyl group such as a tricyclodecyl group and a tetracyclododecyl group may be used instead. Alternatively, a substituted polycyclic alkyl group in which a hydroxyl group or an alkoxy group is substituted for such a group may be used instead.

[0090] Thus, the resistance against etching in high density plasma can be further improved, and hence, the enlargement of the hole size can be further suppressed so as to form a hole in a better shape.

[0091] Furthermore, since the polymer composed of cyclo with three or more folds ring is used as the base polymer in this embodiment, when an acetal group, a tert-butoxycarbonyloxy group or the like is used as the protecting group instead of a polycyclic alkyl group, the enlargement of the hole size can be suppressed so as to form a hole in a good shape.

[0092] Although the copolymer of a tricyclodecene derivative and maleic anhydride is used as the base polymer in this embodiment, a tetracyclododecene derivative, a copolymer of tetracyclododecene and a tetracyclododecene derivative, a copolymer of tetracyclododecene, a tetracyclododecene derivative and maleic anhydride, a copolymer of norbornene and a tetracyclododecene derivative or a copolymer of norbornene, a tetracyclododecene derivative and maleic anhydride may be used instead.

[0093] Although an onium salt compound is singly used as the acid generator in Embodiment 1 or 2, a mixture of an onium salt compound with another acid generator such as a sulfonimide compound, a halogen-containing compound, a sulfone compound and a sulfonic ester compound may be used instead.

[0094] An acid generator of a sulfonimide compound, a halogen-containing compound, a sulfone compound or a sulfonic ester compound is preferred because it is more stable against annealing at 160 or more and plasma than a diazomethane compound.

[0095] Furthermore, an onium salt compound has a stronger property for inhibiting dissolution of a base polymer including a polyhydroxystyrene derivative than the other acid generators. Therefore, when the acid generator includes an onium salt compound, the solubility of the unexposed portion of the photosensitive material film 12 in the developer can be reduced. Accordingly, the acid generator including an onium salt compound alone is good because the etching rate of the photosensitive material film 12 in the plasma etching can be lowered.

[0096] Any onium salt compound may be used as far as it can generate an acid through irradiation with ArF excimer laser. Examples of the onium salt compound are a sulfonium salt compound such as triphenylsulfonium methane, an iodonium salt compound such as diphenyliodonium trifluoromethane sulfonate, a pyridinium salt compound, a phosonium salt compound, an oxonium salt compound and an ammonium salt compound.

[0097] Among the onium salt compounds, a sulfonium salt compound and an iodonium salt compound are particularly preferred, and preferable examples of the sulfonium salt compound and the iodonium salt compound are triphenylsulfonium triflate, triphenylsulfonium propionate, triphenylsulfonium hexaflate and diphenyliodonium triflate.

[0098] Now, the weight average molecular weight of the base polymer and the mixing rate of the acid generator in the chemically amplified resist material used in Embodiment 1 or 2 will be described.

[0099] The weight average molecular weight of the base polymer is preferably 3000 through 30000 measured based on the gel permeation chromatography. When the weight average molecular weight is smaller than 3000, the coating property of the photosensitive material film is degraded, and when the weight average molecular weight exceeds 30000, the solubility in the developer is degraded so as to degrade the fine processing property. In contrast, when the weight average molecular weight is 3000 through 30000, the shape of the hole is not affected.

[0100] The mixing rate of the acid generator is preferably 0.1 through 20 parts by weight based on 100 parts by weight of the polymer component of the base polymer. When the mixing rate of the acid generator is smaller than 0.1 part by weight, the amount of the generated acid is too small to form a pattern, and when the mixing rate of the acid generator exceeds 20 parts by weight, the whole acid generator cannot be dissolved in the solvent. In contrast, when the mixing rate of the acid generator is 0.1 through 20 parts by weight, the shape of the hole is not affected.

[0101] EMBODIMENT 3

[0102] A method for forming a hole pattern according to Embodiment 3 of the invention will now be described with reference to FIGS. 3A through 3C and 4A through 4C. FIG. 3B is a cross-sectional view taken along line IIIB-IIIB of FIG. 3A, and FIG. 4C is a cross-sectional view taken along line IVC-IVC of FIG. 4B.

[0103] A chemically amplified resist material used in Embodiment 3 is the same as that of Embodiment 1 or 2.

[0104] First, as shown in FIGS. 3A and 3B, an anti-reflection film 22 is deposited on an etch target film 21 of, for example, a BPSG film with a thickness of 1200 nm deposited on a semiconductor substrate 20, and the chemically amplified resist material is applied on the anti-reflection film 22. Thereafter, annealing is carried out at 90 for 90 seconds, thereby forming a photosensitive material film 23 with a thickness of 700 nm. The anti-reflection film 22 is formed in order to suppress the standing wave effect of the photosensitive material film 23 and to improve the dimensional evenness.

[0105] Next, the photosensitive material film 23 is irradiated with ArF excimer laser through a photomask having a transmission portion with a diameter of, for example, 200 nm, and annealing is then carried at 110 for 90 seconds as the PEB. Subsequently, an irradiated portion (exposed portion) of the photosensitive material film 23 is dissolved in a developer of a 2.38% TMAH aqueous solution. Thus, the photosensitive material film 23 is formed into a hole pattern made from an unirradiated portion (unexposed portion) of the photosensitive material film and having a hole 23a with a hole size of 200 nm.

[0106] Then, as shown in FIG. 3C, the anti-reflection film 22 is etched by using the hole-patterned photosensitive material film 23 as an etching mask, thereby forming a hole 22a in the anti-reflection film 22.

[0107] Next, as shown in FIG. 4A, the etch target film 21 is subjected to plasma etching under the same conditions as in Embodiment 1 or 2 by using the hole-patterned photosensitive material film 23 as an etching mask. Thus, a hole 21a is formed in the etch target film 21.

[0108] When the hole 21a is thus formed in the etch target film 21, the hole 21a can be formed in a circular plane shape with a hole size not largely enlarged as compared with the desired value as shown in FIGS. 4B and 4C.

Claims

1. A method for forming a hole pattern comprising the steps of:

forming a photosensitive material film by applying, on an etch target film deposited on a semiconductor substrate, a photosensitive material containing a hardly alkaline-soluble base polymer including a polymer in which a principal chain has cycloolefin and a saturated or non-saturated polycyclic alkyl group is bonded to the principal chain, and an acid generator including an onium salt compound;

forming a hole-patterned photosensitive material film by irradiating said photosensitive material film with ArF excimer laser through a photomask; and

forming a hole pattern in said etch target film by subjecting said etch target film to plasma etching using plasma at a plasma density of 1×1010/cm3 or more with said hole-patterned photosensitive material film used as an etching mask.

2. The method for forming a hole pattern of claim 1,

wherein said polymer includes a norbornene derivative.

3. The method for forming a hole pattern of claim 1,

wherein said polymer includes norbornene and a norbornene derivative.

4. The method for forming a hole pattern of claim 1,

wherein said polycyclic alkyl group is an adamantyl group, a tricyclodecyl group or a tetracyclododecyl group.

5. The method for forming a hole pattern of claim 1,

wherein said plasma etching is carried out by using a first voltage for generating plasma and a second voltage for inducing ions of the plasma toward said semiconductor substrate.

6. A method for forming a hole pattern comprising the steps of:

forming a photosensitive material film by applying, on an etch target film deposited on a semiconductor substrate, a photosensitive material containing a hardly alkaline-soluble base polymer including a polymer in which a principal chain is composed of cyclo with three or more folds ring, and an acid generator including an onium salt;

forming a hole-patterned photosensitive material film by irradiating said photosensitive material film with ArF excimer laser through a photomask; and

forming a hole pattern in said etch target film by subjecting said etch target film to plasma etching using plasma at a plasma density of 1×1010/cm3 or more with said hole-patterned photosensitive material film used as an etching mask.

7. The method for forming a hole pattern of claim 6,

wherein said polymer includes a tricyclodecene derivative, a tetracyclododecene derivative, a pentacyclopentadecene derivative or a hexacycloheptadecene derivative.

8. The method for forming a hole pattern of claim 6,

wherein a saturated or non-saturated polycyclic alkyl group is bonded to the principal chain of said polymer.

9. The method for forming a hole pattern of claim 6,

wherein said plasma etching is carried out by using a first voltage for generating plasma and a second voltage for inducing ions of the plasma toward said semiconductor substrate.