Pattern forming method, actinic ray-sensitive or radiation-sensitive resin composition, actinic ray-sensitive or radiation-sensitive film, manufacturing method of electronic device, and electronic device

A pattern forming method comprising:

• (i) a process of forming a film using an actinic ray-sensitive or radiation-sensitive resin composition containing a Resin (P) including a Repeating Unit (a1) having a group capable of being decomposed by acid and generating a carboxyl group, and a Compound (B) capable of generating acid through irradiation of actinic rays or radiation;
• (ii) a process of exposing the film using actinic rays or radiation;
• and
• (iii) a process of developing the exposed film using a developer including an organic solvent containing a hetero atom and carbon atoms having 7 or more carbon atoms to form a negative tone pattern,
• wherein a value X obtained by substituting a number of each atom included in the Repeating Unit (a1) after being decomposed by acid and generating a carboxyl group in the following general formula is 0<X≦5,
• X=(total number of atoms configuring repeating unit after being decomposed by acid)/[(number of carbon atoms)−(number of atoms that are neither carbon atoms nor hydrogen atoms)].