Jan. 10, 2019  28  US 2019/0010119 Al  trimethylpropyl group, a l-adamantyl-1-methylethyl group,  a l-methyl-1-(2-norbornyl)ethyl group, a l-methyl-1-(tetra› hydrofuran-2-yl)ethyl group, a l-methyl-1-(7-oxanorbor› nan-2-yl)ethyl group, a 1-methylcyclopentyl group, a 1-eth› ylcyclopentyl  group,  a  1-propylcyclopentyl  group,  a  1-cyclopentylcyclopentyl group, a 1-cyclohexylcyclopentyl  group, a 1-(2-tetrahydrofuril)cyclopentyl group, a 1-(7-ox› anorbornan-2-yl)cyclopentyl group, a 1-methylcyclohexyl  group, a 1-ethylcyclohexyl group, a 1-cyclopentylcyclo› hexyl group, a 1-cyclohexylcyclohexyl group, a 2-methyl- 2-norbornyl group, a 2-ethyl-2-norbornyl group, a 8-methyl- 8-tricyclo[5.2.l .02•6]decyl group, a 8-ethyl-8-tricyclo[5.2.1.  0 2 • 6 ]decyl group, a 3-methyl-3-tetracyclo[ 4.4.0.1 2 • $^{5 }$.1 7 • 10 ]  dodecyl  group,  a  3-ethyl-3-tetracyclo[ 4.4.0.1 2 • $^{5 }$.1 7 • 10 ]  dodecyl group, a 2-methyl-2-adamantyl group, a 2-ethyl-2- adamantyl group, a l-methyl-3-oxo-l-cyclohexyl group, a  l-methyl-1-(tetrahydrofuran-2-yl)ethyl group, a 5-hydroxy- 2-methyl-2-adamantyl group, and 5-hydroxy-2-ethyl-2-ada› mantyl group.  [0116]  In addition, an acetal group shown by the following  general formula (B2-1) is often used as the acid-labile group.  This acetal group is a useful choice as an acid-labile group  that stably provides a pattern whose interface with a sub› strate is relatively rectangular,  wherein  RA  has the same meaning as defined above; each  R 12  independently represents a halogen atom, a linear,  branched, or cyclic acyloxy group having 2 to 8 carbon  atoms optionally substituted with a halogen atom, a linear,  branched, or cyclic alkyl group having 1 to  6  carbon atoms  optionally substituted with a halogen atom, or a linear,  branched, or cyclic alkoxy group having 1 to  6  carbon atoms  optionally substituted with a halogen atom; A 2  represents a  single bond or a linear, branched, or cyclic alkylene group  having 1 to 10 carbon atoms optionally having an ether bond  between a carbon-carbon bond thereof; "s" is 0 or 1; "t" is  an integer of0 to 2; "c" is an integer satisfying 0scs5+2t-e;  "d" is 0 or 1; "e" is an integer of 1 to 3; Xis an acid-liable  group when "e" is 1, and is a hydrogen atom or an acid-liable  group when "e" is 2 or more with the proviso that at least one  of X is an acid-liable group.  [0113]  In the repeating unit B2, one or more of the  phenolic hydroxyl group bonded to an aromatic ring is  protected by an acid-liable group, or the carboxyl group  bonded to an aromatic ring is protected by an acid-liable  group. The acid-liable group like this is not particularly  limited, and any group can be adopted so long as it is  decomposed by an acid to form an acidic group that have  been used for many known chemically amplified resist  components.  [0114]  In the general formula (B2), it is preferable to select  a tertiary alkyl group as the acid-liable group ofX. When X  is a tertiary alkyl group, it is possible to provide a pattern  with small LER even when a resist film is formed so as to  have a film thickness of 10 to 100 nm and a fine pattern is  formed so as to have a line width of 45 nm or less. These  tertiary alkyl groups each have 4 to 18 carbon atoms so as  to obtain a monomer for the polymerization by distillation.  Illustrative examples of the alkyl substituent on the tertiary  carbon of the tertiary alkyl group include a linear, branched,  or cyclic alkyl substituent having 1 to 15 carbon atoms  optionally having an oxygen-containing functional group(s)  such as an ether group and a carbonyl group, in which the  alkyl substituents on the tertiary carbon may be bonded with  each other to form a ring.  [0115]  Illustrative examples of the alkyl substituent on the  tertiary carbon of the tertiary alkyl group include a methyl  group, an ethyl group, a propyl group, an adamantyl group,  a norbornyl group, a tetrahydrofuran-2-yl group, 7-oxanor› bornan-2-yl group, a cyclopentyl group, 2-tetrahydrofuril  group, a tricyclo[5.2.l.0 2 • 6 ]decyl group, a tetracyclo[4.4.0.  1 2 • $^{5}$.1 7 • $^{10}$]dodecyl group, and 3-oxo-1-cyclohexyl group.  The tertiary alkyl group that has these substituents is not  particularly limited,  and illustrative examples thereof  include a tert-butyl group, a tert-pentyl group, a l-ethyl-1- methylpropyl group, a 1,1-diethylpropyl group, a 1,1,2- [0118]  In the general formula (B2-1 ), Y preferably repre› sents a polycyclic alkyl group having 7 to 30 carbon atoms.  These Y enables the inventive resist composition to have  higher resolution. When Y represents a polycyclic alkyl  group, it is preferable to form a bond between the acetal  oxygen and the secondary carbon constituting the polycyclic  structure. When the bond is on a secondary carbon of the  ring structure, the polymer compound is more stable and the  resist composition has better storage stability compared to  the case in which the bond is on a tertiary carbon, thereby  preventing the resolution from degradation. This instance is  preferable compared to the case in which Y is bonded on a  primary carbon that mediate the linear alkyl having one or  [0117]  In this formula, R 16  is appropriately selected in  accordance with design of the group decomposable by an  acid. For example, a hydrogen atom is selected in design  including decomposition by a strong acid while securing  relatively high stability, and a linear alkyl group is selected  in design using relatively high reactivity for higher sensi› tivity to pH. In case of designing larger change of solubility  by decomposition with the terminal being substituted with a  relatively large alkyl group, R 16  preferably contains a sec› ondary carbon having a bond with an acetal carbon, although  it depends on the combination of an acid generator and a  basic compound that are blended to the resist composition of  the present invention. Illustrative examples of R  16  in which  acetal carbon is bonded to a secondary carbon include an  isopropyl group, a sec-butyl group, a cyclopentyl group, and  a cyclohexyl group.  wherein R 16  represents a hydrogen atom, or a linear,  branched, or cyclic alkyl group having 1 to 10 carbon atoms;  and Y represents a linear, branched, or cyclic alkyl group  having 1 to 30 carbon atoms.  (B2)  Rl6  -0~0-Y  (B2-1) 