Abstract: Disclosed are a method of forming a pattern structure including a silicon nitride. According to the embodiment of the present disclosure, the method of forming a pattern structure includes a step of providing, into a substrate processing apparatus, a substrate having one surface on which a pattern structure including a recess region in which an opening periphery portion and a bottom portion are made of a first silicon nitride is formed, a deposition step of depositing a second silicon nitride on the first silicon nitride, an etching step of etching the second silicon nitride, and a step of performing steps in one cycle n times until the first silicon nitride constituting the bottom portion is removed.