Method for manufacturing diffraction grating and method for manufacturing replica grating

A method for manufacturing a diffraction grating, the method comprising:

• a step (a) of preparing a wafer having, on a front surface thereof, a pattern having a shape in which concave portions and convex portions are alternately arranged;
• a step (b) of, after the step (a), forming a metal film on the front surface of the wafer and forming, on a part of a front surface of the metal film, a first transfer area to which the shape of the pattern is transferred;
• a step (c) of, after the step (b), removing the metal film from the wafer;
• a step (d) of, after the step (c), bonding a back surface of the metal film to a first glass substrate via a bonding agent;
• a step (e) of, before step (d) or any other preceding steps, preparing a third restraint jig having a circular shape in plan view and having a third opening that is circular in plan view in a central portion thereof;
• and
• a step (f) of preparing a first fixing plate having a fourth opening that is circular in plan view in a central portion thereof, a second glass substrate that is circular in plan view, and a load applying member for applying a load to the first glass substrate, wherein
• the step (d) is performed in a vacuum atmosphere,
• the back surface of the metal film and a bonding surface of the first glass substrate that are bonded via the bonding agent are flat surfaces,
• the step (d) is performed in a state where the third restraint jig is installed on the back surface of the metal film around the first transfer area such that the first transfer area is located inside the third opening in plan view,
• the second glass substrate is provided inside the fourth opening,
• the metal film around the first transfer area is fixed between the third restraint jig and the first fixing plate, and
• the step (d) is performed by pressing the first glass substrate toward the back surface of the metal film by the load applying member from a state where the metal film is installed on the second glass substrate such that the front surface of the metal film faces the second glass substrate, the bonding agent is provided on the back surface of the metal film, and the first glass substrate is provided at a position physically separated from the back surface of the metal film.