US 9,086,623 B2  7  8  The present invention makes it feasible to provide a resist  composition that excels in resolution and etching resistance  performance and ensures reduction of development residue  defects and to provide a method of forming a pattern with the  use of the resist composition.  The present invention will be described below.  With respect to the expression of a group ( atomic group)  used in this specification, the expression even when there is  no mention of "substituted and unsubstituted" encompasses  groups not only having no substituent but also having sub› stituents. For example, the expression "alkyl groups" encom› passes not only alkyls having no substituent (unsubstituted  alkyls) but also alkyls having substituents (substituted  alkyls).  In the present invention, the terms "actinic rays" and  "radiation" mean, for example, a mercury lamp bright line  spectrum, far ultraviolet rays represented by an excimer laser,  extreme ultraviolet rays (EUV light), X-rays, electron beams  (EB) and the like. In the present invention, the term "light"  means actinic rays or radiation.  The expression "exposure" used herein, unless otherwise  noted, means not only light irradiation using a mercury lamp,  far ultraviolet, X-rays, EUV light, etc. but also lithography  using particle beams, such as an electron beam and an ion  beam.  The method of forming a pattern according to the present  invention comprises the operations of forming an actinic-ray› or radiation-sensitive resin composition into a film, the  actinic-ray- or radiation-sensitive resin composition compris› ing an acid-decomposable resin that contains a group that  when acted on by an acid, is decomposed to thereby produce  a polar group and contains an aromatic group and comprising  a nonionic acid generator; exposing the film to light; and  developing the exposed film with a developer comprising an  organic solvent to thereby form a negative pattern.  It  has been found by the inventors that the method of  forming a pattern according to the present invention in which  use is made of the above actinic-ray- or radiation-sensitive  resin composition makes it feasible to form a pattern excel› ling in resolution and etching resistance performance while  ensuring reduction of development residue defects in espe› cially the negative pattern formation through exposure by  means of a KrF light, electron beams or an EUV light and  development with a developer comprising an organic solvent.  First, the actinic-ray- or radiation-sensitive resin composi› tion for use in the pattern forming method of the present  invention (hereinafter also referred to as "the actinic-ray- or  radiation-sensitive resin composition of the present inven› tion" or "the composition of the present invention") will be  described in detail below.  In this connection, the actinic-ray- or radiation-sensitive  film of the present invention is a film formed from the actinic› ray- or radiation-sensitive resin composition of the present  invention. For example, it is a film formed by applying the  actinic-ray- or radiation-sensitive resin composition onto a  substrate.  <Actinic-Ray- or Radiation-Sensitive Resin Composi- tion>  The actinic-ray- or radiation-sensitive resin composition of  the present invention finds application in negative develop› ment ( development in which upon exposure, exposed areas  come to have a decreased solubility in a developer to thereby  remain as a pattern while unexposed areas are removed).  Namely, the actinic-ray- or radiation-sensitive resin compo- In the general formulae, each ofR$_{36 }$to R$_{39 }$independently  represents an alkyl group, a cycloalkyl group, an aryl group,  As the group cleaved by the action of an acid, there can be  mentioned, for example, -C(R$_{36}$)(R$_{37}$)(R$_{38}$), ----C(R$_{36}$)(R$_{37}$)  (OR$_{39}$), ----C(R $_{01}$)(R$_{02}$)(OR$_{39}$ ) or the like.  It  is preferred for the acid-decomposable group to be a  group whose hydrogen atom is replaced by a group cleaved  by the action of an acid.  The alcoholic hydroxyl group refers to a hydroxyl group  bonded to a hydrocarbon group, which is other than the  hydroxyl group (phenolic hydroxyl group) directly bonded to  an aromatic ring. Any aliphatic alcohol substituted at its a-po› sition with an electron withdrawing group, such as a fluorine  atom, as an acid group (for example, a fluorinated alcohol  group (a hexafluoroisopropanol group, etc.)) is not included  in the category of the alcoholic hydroxyl group.  It  is preferred  for the alcoholic hydroxyl group to be a hydroxyl whose pKa  value is in the range of 12 to 20.  The polar group is not particularly limited as long as it is  rendered poorly soluble or insoluble in a developer compris› ing an organic solvent. As preferred polar groups, there can be  mentioned an acid group (group dissociated in a 2.38 mass%  aqueous tetramethylammonium hydroxide solution conven› tionally used as a resist developer), such as a carboxyl group  or a sulfonic acid group, an alcoholic hydroxyl group and the  like.  It  is preferred for the acid-decomposable group to have a  structure in which a polar group is protected by a group that  when acted on by an acid, is decomposed and cleaved.  The resin (A) comprises a repeating unit containing an  acid-decomposable group.  [Repeating Unit Containing an Acid-Decomposable  Group]  Incidentally, the resin (A) is a resin that when acted on by  an acid, increases its polarity to thereby increase its solubility  in an alkali developer.  The resin (A) for use in the actinic-ray- or radiation-sensi› tive resin composition of the present invention is a resin  (hereinafter also referred to as "an acid-decomposable resin")  comprising a repeating unit containing a group (hereinafter  also referred to as "an acid-decomposable group") that when  acted on by an acid, is decomposed to thereby produce a polar  group. The resin (A) is a resin that when acted on by an acid,  increases its polarity to thereby decrease its solubility in a  developer comprising an organic solvent. The resin (A) fur› ther contains an aromatic group. This aromatic group may be  contained in the repeating unit containing the acid-decom› posable group, or in a repeating unit other than this repeating  unit. Hereinafter, both of these repeating units are each  referred to as "a repeating unit containing an aromatic group."  [1] Resin (A) that when acted on by an acid, decreases its  solubility in an organic solvent  The actinic-ray- or radiation-sensitive resin composition of  the present invention is typically a resist composition. From  the viewpoint that especially high effects can be attained, it is  preferred for the same to be a negative resist composition  (namely, resist composition for organic solvent develop› ment). Moreover, the composition of the present invention is  typically a chemically amplified resist composition.  sition of the present invention can be an actinic-ray- or radia› tion-sensitive resin composition for organic solvent develop› ment that is used in the development with a developer  comprising an organic solvent. Herein, the expression "for  organic solvent development" means usage in at least the  operation of developing with a developer comprising an  organic solvent.  DETAILED DESCRIPTION OF THE INVENTION 