The patent's assignee for patent number 8618217 is
News editors obtained the following quote from the background information supplied by the inventors: "The present invention relates to a topcoat composition for use in the process of producing a semiconductor such as IC, in the production of a circuit board for liquid crystal, thermal head and the like, and in the lithography process of other photofabrication; an alkali developer-soluble topcoat film using the composition; and a pattern forming method using the topcoat film. More specifically, the present invention relates to a topcoat composition suitable for exposure by an immersion-type projection exposure apparatus using a light source that emits far ultraviolet light at a wavelength of 300 nm or less; an alkali developer-soluble topcoat film using the composition; and a pattern forming method using the topcoat film.
"Along with the finer fabrication of a semiconductor device, there is becoming shorter the wavelength of the exposure light source and higher the numerical aperture (high NA) of the projection lens, and an exposure machine with NA of 0.84 using an ArF excimer laser having a wavelength of 193 nm as a light source has been so far developed. As commonly well known, these features can be expressed by the following formulae: (Resolving power)=k.sub.1(.lamda./NA) (Depth of focus)=.+-.k.sub.2.lamda./NA.sup.2 wherein .lamda. is the wavelength of the exposure light source, NA is the numerical aperture of the projection lens, and k.sub.1 and k.sub.2 are coefficients related to the process.
"In order to realize still shorter wavelength and higher resolving power, studies are being made on an exposure machine where an F.sub.2 excimer laser having a wavelength of 157 nm is used as the light source. However, the lens material used for the exposure apparatus so as to realize shorter wavelength and the material used for the resist are very limited and therefore, it is extremely difficult to stabilize the production cost or quality of the apparatus and materials. This may lead to a failure in outfitting the exposure apparatus and the resist each assured of sufficiently high performance and stability within a required time period.
"Conventionally, a so-called immersion method of filling a high refractive-index liquid (hereinafter sometimes referred to as an 'immersion liquid') between the projection lens and the sample has been known as a technique of increasing the resolving power in an optical microscope.
"As for the 'effect of immersion', assuming that .lamda..sub.0 denotes the wavelength of exposure light in air, n denotes the refractive index of the immersion liquid to air and .theta. denotes the convergence half-angle of beam and that NA.sub.0=sin .theta., the above-described resolving power and depth of focus when immersed can be expressed by the following formulae: (Resolving power)=k.sub.1(.lamda..sub.0/n)/NA.sub.0 (Depth of focus)=.+-.k.sub.2(.lamda..sub.0/n)/NA.sub.0.sup.2
"That is, the effect of immersion is equal to use of an exposure wavelength of 1/n. In other words, in the case of a projection optical system with the same NA, the depth of focus can be made n times larger by the immersion.
"This is effective for all pattern profiles and can be combined with super-resolution techniques which are being studied at present, such as phase-shift method and modified illumination method.
"Examples of the apparatus where this effect is applied to the transfer of a fine image pattern of a semiconductor device are described in JP-A-57-153433 and JP-A-7-220990 (the term 'JP-A' as used herein means an 'unexamined published Japanese patent application').
"JP-A-10-303114 indicates that the control of refractive index of the immersion liquid is important because a change in the refractive index of the immersion liquid brings about deterioration of the projected image due to wave front aberration of the exposure machine, and discloses an immersion liquid with a refractive index of which the temperature coefficient is controlled to a certain range, or, as a suitable immersion liquid, water where the surface tension is decreased or an additive of increasing the surface activity is added. However, the additive is not disclosed or the resist suitable for immersion exposure techniques is not discussed.
"Recent progress of the immersion exposure technique is reported, for example, in SPIE Proc., 4688, 11 (2002) and J. Vac. Sci. Tecnol. B, 17 (1999). In the case of using an ArF excimer laser as the light source, in view of safety on handling as well as transmittance and refractive index at 193 nm, pure water (refractive index at 193 nm: 1.44) is considered most promising as the immersion liquid.
"In the case of using an F.sub.2 excimer laser as the light source, a fluorine-containing solution is being studied in view of balance between transmittance and refractive index at 157 nm, but those satisfied from the aspect of environmental safety or refractive index have been not yet found out. The immersion exposure technique is expected to be most soon mounted on an ArF exposing machine in view of the degree of immersion effect and the maturity of resist.
"Since the advent of a resist for a KrF excimer laser (248 nm), an image forming method called chemical amplification is used as the image forming method for a resist so as to compensate the reduction in the sensitivity due to light absorption. To describe this by taking as an example the image forming method using positive chemical amplification, an acid generator in the exposed area decomposes upon exposure to generate an acid, the acid generated is used as a reaction catalyst in the post-exposure baking (PEB) to convert the alkali-insoluble group into an alkali-soluble group, and the exposed area is removed by alkali development.
"In the immersion exposure, the resist film is exposed through a photomask in the state of an immersion liquid being filled between the resist film and the optical lens, and the pattern of the photomask is thereby transferred to the resist film. At this times there is a case where an image is not formed due to permeation of the immersion liquid into the inside of the resist film (Nikkei Micro-Device, April, 2004). Also, it is feared that due to elution of an organic substance or the like from the resist film into the immersion liquid, impurities are mixed in the immersion liquid and contaminate the lens or exposure apparatus to hinder the exposure.
"In order to avoid such a problem, a method of providing a topcoat film between the resist film and the lens to prevent the resist from coming into direct contact with water is known (see, for example, Nikkei Micro-Device, April, 2004).
"It is not clarified yet what a material is suitable for the topcoat, but studies by the present inventors reveal that depending on the material of the topcoat, bad coating uniformity on the resist film or generation of particles after aging or storage may occur. In this respect, improvement is necessary. Also, there is room for improvement on the sensitivity of the underlying resist film."
As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventor's summary information for this patent: "An object of the present invention is to provide a topcoat composition capable of forming a topcoat film that can be separated in the developing step in the fine pattern-forming process by immersion exposure and is assured of a large receding contact angle for the immersion liquid (e.g. water) and excellent followability of the immersion liquid, an alkali developer-soluble topcoat film using the composition, and a pattern forming method using the topcoat film.
"The present invention includes the following constructions, and the above-described object of the present invention can be attained by these constructions.
"(1) A topcoat composition to be applied on a resist film to form a topcoat film, comprising:
"(A) an alkali-soluble resin;
"(B) a compound containing at least one of an Si atom and an F atom, and increasing a contact angle on a surface of the topcoat film; and
"(C) a solvent.
"(2) The topcoat composition as described in (1) above,
"wherein when the topcoat film is formed by adding the compound (B) in an amount of 1 part by mass based on 100 parts by mass of the total solid amount of the topcoat film but not including the solid amount of the compound (B), the compound (B) increases a receding contact angle of the topcoat film by 5.0% or more when compared with a receding contact angle of the topcoat film formed by the same topcoat composition except for not containing the compound (B).
"(3) The topcoat composition as described in (1) or (2) above,
"wherein a content of a polar group(s) in the compound (B) (number of a polar group(s)/molecular weight) is 80% or less of that in the resin (A).
"(4) The topcoat composition as described in any of (1) to (3) above,
"wherein the compound (B) is insoluble in an alkali developer.
"(5) The topcoat composition as described in any of (1) to (4) above,
"wherein the resin (A) has a polar group represented by formula (1):
"wherein R.sub.1 and R.sub.2 is the same or different and each independently represents a hydrogen atom or an alkyl group, and R.sub.1 and R.sub.2 may combine with each other to form a ring.
"(6) The topcoat composition as described in any of (1) to (5) above,
"wherein the solvent (C) contains an alcohol solvent.
"(7) The topcoat composition as described in any of (1) to (4) and (6) above,
"wherein the resin (A) has a polar group represented by formula (2):
"wherein R.sub.3 represents an alkyl group or a cycloalkyl group.
"(8) The topcoat composition as described in any of (1) to (7) above,
"wherein an addition amount of the compound (B) is 10 mass % or less based on an entire amount of solid contents of the topcoat composition.
"(9) The topcoat composition as described in any of (1) to (8) above,
"wherein the compound (B) is a solid at an ordinary temperature.
"(10) The topcoat composition as described in any of (1) to (9) above,
"wherein the topcoat film is soluble in an alkali developer.
"(11) An alkali developer-soluble topcoat film, comprising:
"(B) a compound containing at least one of an Si atom and an F atom, and increasing a contact angle on a surface of the topcoat film, the compound (B) covering partially or entirely a surface of the topcoat film,
"wherein the topcoat film has a receding contact angle for water of 70.degree. or more.
"(12) The alkali developer-soluble topcoat film as described in (11) above, which has a coverage of the compound (B) on the surface of the topcoat film of 30% or more.
"(13) A pattern forming method, comprising:
"applying the topcoat composition described in any of (1) to (10) above on a resist film to form a topcoat film; and
"exposing and developing the resist film.
"(14) The pattern forming method as described in (13) above,
"wherein the resist film is exposed in water as an immersion liquid."
For additional information on this patent, see:
Keywords for this news article include: Electronics, Semiconductor,
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