The present invention is a polyvalent ammonium salt compound having two or more ammonium ions per molecule, the polyvalent ammonium salt compound being represented by the following general formula (A-1). This can provide: a composition for forming a silicon-containing resist underlayer film with which it is possible to form a silicon-containing resist underlayer film that has an appropriate etching rate and can improve LWR and CDU in an ultra-fine pattern in a multilayer resist method; a polyvalent ammonium salt compound to be contained in the composition; and a patterning process using the composition.

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