Silicon-containing polymer, film-forming composition, method for forming silicon-containing polymer coating, method for forming silica-based coating, and production method for silicon-containing polymer

A method for forming a silica-based coating, the method comprising:

• forming a coated film by applying a film-forming composition onto a substrate;
• the film-forming composition comprising a silicon-containing polymer (A) and a solvent (S),
• the silicon-containing polymer comprising at least one of poly- or oligo-siloxane chain and poly-or oligo-silane chain in a molecular chain, wherein one or more groups represented by a following formula (1) are bound onto a silicon atom in the silicon-containing polymer;
• —R1—S—R2—SiR3nR4(3-n) (1)
• wherein, in the formula (1), R1 and R2 are each independently a hydrocarbon group having 1 or more and 10 or less carbon atoms, R3 is a hydroxy group or a group to form a silanol group by hydrolysis, R4 is an optionally substituted hydrocarbon group having 1 or more and 10 or less carbon atoms, and n is an integer of 1 or more and 3 or less;
• drying the coated film to form a silicon-containing polymer coating;
• and then
• baking the silicon-containing polymer coating or baking the coated film.