Abstract: Pattern formation methods comprise: (a) forming an underlayer on a substrate, wherein the underlayer has a thickness of 5 microns or more; (b) forming a photoresist layer on the underlayer, wherein the photoresist layer is formed from a photoresist composition comprising a silicon-containing polymer, a photoacid generator, and a solvent, wherein the silicon-containing polymer comprises as polymerized units a monomer of formula (I): wherein: R1 is independently chosen from H, F, OH, C1-C6 alkyl, C1-C6 haloalkyl, C1-C6 hydroxy-haloalkyl, C1-C6 alkoxy, or C1-C6 haloalkoxy; R2 is independently chosen from H or F; R3 is independently chosen from H, F, CH3, CF3, CHF2, or CH2F; comprises an acid cleavable group; and m is an integer from 0 to 2; (c) patternwise exposing the photoresist layer to activating radiation; (d) developing the exposed photoresist layer to form a photoresist pattern; and (f) transferring the pattern of the photoresist pattern into the underlayer using the photoresist pattern as an etch mas