3  US 9,383,646 B2  4  is disclosed wherein C2x represents a fullerene with x at least  10, y is 1-6, n is 0-1, alkyl is a branched or unbranched,  substituted or unsubstituted divalent alkyl chain of 1-16 car- bans with or without one or more heteroatoms substituted  into the chain, aryl is a substituted or unsubstituted divalent  phenyl group, heteroaromatic group, or fused aromatic or  fused heteroaromatic group, and R is H or an acid labile 15  group.  An  example of a disclosed methanofullerene com› prises the general formula:  In a second embodiment, the methanofullerene of the  above embodiment includes divalent alkyl groups comprising  a substituted or unsubstituted methylene, ethylene or 1,3- propylene group, and the divalent aryl group comprises a  substituted or unsubstituted phenylene group.  In a third embodiment, the methanofullerene of all the  above embodiments includes R as either H or an acid labile  alkoxycarbonyl group.  In a fourth embodiment, the methanofullerene of the above  embodiments includes divalent alkyl group wherein the het› eroatoms are one or more of oxygen, nitrogen, sulfur, or  oxides of sulfur and/or the alkyl chains may be substituted  with fluorine atoms.  In a fifth embodiment, a negative-tone photoresist compo› sition is disclosed comprising at least one of any of the metha› nofullerenes of the above embodiments, at least one photo  acid generator, at least one crosslinker, and at least one sol- vent, wherein the crosslinker crosslinks at least with the  methanofullerene when processed.  In a sixth embodiment, the negative-tone photoresist com› position of the above embodiments is disclosed wherein the at  least one photoacid generator comprises an onium salt com› pound, a sulfone imide compound, a halogen-containing  compound, a sulfone compound, a sulfonate ester compound,  a quinone-diazide compound, or a diazomethane compound.  In a seventh embodiment, the negative-tone photoresist  composition of any of the above embodiments is disclosed  wherein the at least one crosslinker comprises an acid sensi› tive monomer or polymer.  In an eighth embodiment, the negative-tone photoresist  composition of any of the above embodiments is disclosed  wherein at least one methanofullerene comprising the general  formula is also included:  wherein xis at least 10, y is 1-6, a is 1-10 and R is Hor an acid  labile group and the ----CH$_{2}$----CH$_{2}$ - group may be substi› tuted with fluorine atoms.  An  example of a disclosed metha› nofullerene comprises the general formula:  In other embodiments, the above methanofullerenes con- tain only partially blocked hydroxy groups. In these cases the  R groups of the above structures are different and one of the  R groups in the molecule is an H while the other R group in the  molecule is an acid labile group, as described above. To  obtain these molecules, the acid labile group is only partially  hydrolyzed. The amount ofH groups in these hybrid metha› nofullerenes ranges between about 1 % and about 90%.  In a further embodiment, a process for using any of the  above mentioned negative-tone compositions is disclosed  including the steps of obtaining a substrate, applying any one  of the photoresist compositions of the above embodiments to  a desired wet thickness, optionally heating the coated sub› strate to remove a majority of the solvent to obtain a desired  thickness, imagewise exposing the coating to actinic radia- tion, removing the unexposed areas of the coating, and  optionally heating the remaining coating.  In still a further embodiment, the process of the above  embodiment is disclosed including a further step of either  heating the imagewise exposed coating prior to removing the  unexposed areas of the coating or exposing the coating to  infrared exposure.  In still a further embodiment, the process of the above  embodiment is disclosed wherein the unexposed areas are  removed by treating with an organic solvent composition.  In still a further embodiment, the process of the above  embodiment is disclosed wherein the actinic radiation is  ultraviolet, extreme ultraviolet, beyond extreme ultraviolet,  charged particle beam or electron beam.  In all the above embodiments, the fullerene may be substi- tuted with more than one type of methanofullerene.  In still further embodiments, disclosed and claimed herein  are negative working photosensitive compositions which  contain crosslinkable materials which are protected by acid  labile protecting groups.  In still a further embodiment are compositions and method  for two-step photoresist processes using negative working  photosensitive compositions that contain crosslinkable mate› rials which are protected by acid labile protecting groups.  Such crosslinkable materials include monomers, oligomers  and polymers, wherein acid generated from the acid generator  removes the acid-labile group from the polymer, oligomer or  monomer in a first step, followed by crosslinking the  COO-alkyl-aryl-(CH2)n-O-Rl  COO-alkyl-aryl-(CH2)n-O-R  y  COO-alkyl-aryl-(CH2)n-O-Rl  COO-alkyl-aryl-(CH2)n-O-R  y  COO-alkyl-aryl-(CH2)n-O-Rl  COO-alkyl-aryl-(CH2)n-O-R  y  COO-alkyl-aryl-(CH2)n-O-Rl  COO-alkyl-aryl-(CH2)n-O-R  y 