51  US 6,939,662 B2  52  These acetal groups are advantageous in that they exhibit  a great acid-decomposability that increases the range of  selection of the acid-producing compounds to be used in  combination therewith, making it possible to enhance the  sensitivity of the composition and inhibit the change of  properties of the composition with time between exposure  and heating. Particularly preferred is an acetal group con- taining as 1-alkoxy component of acetal group an alkoxy  Examples of the acid-decomposable group include  -O-C(R 19 )(R 20 )(R 21 ), -O-C(R 19 )(R 20 )(OR$_{22}$ ),  -O-COO-C(R 19 )(R 20 )(R 21 ), -O-C(R 01 )(R$_{02}$)COO- C(R 19)(R20)(R21), -COO-C(R 19 )(R 20 )(R 21 ), and 65  -COO-C(R 19 )(R 20 )(OR 22 ). R 01  and R$_{02 }$ each indepen› dently represent a hydrogen atom or an alkyl, cycloalkyl,  The resin (A3) has a group which is capable of decom› posing to become alkali-soluble by the action of an acid  (acid-decomposable group). In this arrangement, when acted  on by an acid, the resin (A3) decomposes to increase in its  solubility in an alkaline developer. The acid-decomposable  group may be possessed by the repeating unit having a group  represented by the formula (Z), maybe Di’, D$_{1 }$ or D$_{2 }$ in the  repeating units represented by the formulae (Illa), (Illb) and  (IVb) or may be possessed by other repeating units.  Specific preferred examples of the acid-decomposable  group include tertiary alkyl ether or ester groups such as  t-butyl group, 5-amyl group, l-alkyl-1-cyclohexyl group,  2-alkyl-2-adamanthyl group, 2-adamanthyl-2-propyl group  and 2-( 4-methylcyclohexyl)-2-propyl group, acetal or acetal  ester groups such as l-alkoxy-1-ethoxy group and tetrahy- dropyranyl group, t-alkylcarbonate groups, and  t-alkylcarbonylmethoxy groups. Particularly preferred  among these acid-decomposable groups are acetal groups  such as l-alkoxy-1-ethoxy group and tetrahydropyranyl  group.  Examples of the substituents on these groups include  those having an active hydrogen such as amino group, amide  group, ureide group, urethane group, hydroxyl group and  carboxyl group, halogen atoms (e.g., fluorine atom, chlorine  atom, bromine atom, iodine atom), alkoxy groups (e.g.,  methoxy group, ethoxy group, propoxy group, butoxy  group), thioether groups, acyl groups (e.g., acetyl group,  propanoyl group, butoxy group), acyloxy groups ( e.g.,  acetoxy group, propanoyl group, benzoyl group), alkoxy› carbonyl groups (e.g., methoxycarbonyl group, ethoxycar› bonyl group, propoxycarbonyl group), cyano groups, and  nitro groups.  An example of the ring formed by the connection of two  of  R$_{19 }$ to  R$_{22 }$ is a 3-membered to 8-membered ring. Specific  examples of such a ring include cyclopropane ring, cyclo- pentane ring, cyclohexane ring, furane ring, pyrane ring,  dioxonol ring, and 1,3-dioxolane ring.  Preferred examples of the aralkyl groups include C$_{7}$-C$_{12 }$ aralkyl groups. Examples of the aralkyl group include ben› zyl group, phenethyl group, and naphthylmethyl group.  Preferred examples of the aryl groups include  C$_{6}$-C$_{10 }$aryl  groups. Examples of the aryl group include phenyl group,  tolyl group, dimethylphenyl group, 2,4,6-trimethylphenyl  group, naphthyl group, anthryl group, and 9,10- dimethoxyanthryl group.  Preferred examples of the alkenyl groups include C$_{2}$-C$_{8 }$ alkenyl groups. Examples of the alkenyl group include vinyl  group, allyl group, butenyl group, and cyclohexenyl group.  The cycloalkyl group may be monocyclic or polycyclic.  Preferred examples of the monocyclic cycloalkyl group  include C$_{3}$-C$_{8 }$ cycloalkyl groups. Examples of the  cycloalkyl group include cyclopropyl group, cyclopentyl  group, cyclohexyl group, cyclobutyl group, and cyclooctyl  group, Preferred examples of the polycyclic cycloalkyl  group include C$_{6}$-C 20  cycloalkyl groups. Examples of the  cycloalkyl group include adamanthyl group, norbornyl  group, isoboronyl group, camphanyl group, dicyclopentyl  group, a-pinene group, tricyclodecanyl group, tetracy- clododecyl group, and androstanyl group.  The aforementioned alkyl group is preferably a  CcC$_{8 }$ alkyl group. Examples of such an alkyl group include methyl  group, ethyl group, propyl group, n-butyl group, sec-butyl  group, hexyl group, 2-ethylhexyl group, and octyl group.  alkenyl, aralkyl or aryl group which may have substituents.  R$_{19 }$ to  R$_{22 }$ may be the same or different and each represent  an alkyl, cycloalkyl, alkenyl, aralkyl or aryl group, which  may have a substituent. Two of  R$_{19}$ ,  R$_{20 }$ and  R$_{21 }$ or two of  R$_{19}$ ,  R$_{20 }$ and  R$_{22 }$ may be bonded to each other to form a ring.  -continued  oyo~ 0  H  I  °’’¢ 