The present invention provides a patterning process, which comprises step of forming a BPSG film on the under layer film by using a composition for forming a coating type BPSG film including a base polymer and an organic compound with a content of 25 parts by mass or more of the organic compound with respect to 100 parts by mass of the base polymer, the base polymer having a silicon containing unit, a boron containing unit and a phosphorus containing unit with a total content of the boron containing unit and the phosphorus containing unit being 10 mol % or more, the organic compound having two or more hydroxyl groups or carboxyl groups per one molecule. There can be provided a patterning process in which a fine mask pattern can be formed on the substrate to be processed by the multilayer resist method, and the residue of the resist under layer film on the mask pattern can be removed cleanly enough to process the substrate to be processed without causing damage to the substrate to be processed and the under layer film.