A composition for forming a thermosetting silicon-containing film, a silicon-containing film formed from the composition, a substrate containing the silicon-containing film, and a pattern formation method are provided to improve the etching selectivity between organic materials. A composition for forming a thermosetting silicon-containing film comprises a silicon-containing compound which is obtained by the hydrolysis condensation of a hydrolyzable silicon compound using an acid as a catalyst; at least one compound represented by L_aH_bX or M_aH_bA; a monovalent or divalent C1-C30 organic acid; a mono or more valent alcohol having a cyclic ether substituent; and an organic solvent, wherein L is Li, Na, K, Rb or Cs; X is OH or a monovalent or divalent C1-C30 organic group; a is an integer of 1 or more; b is an integer of 0 or more; M is a sulfonium group, an iodonium group or an ammonium group; and A is X or a non-nucleophilic counterion.
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