Charged particle beam writing apparatus, drift amount calculation method, and charged particle beam writing method

A drift amount calculation method comprising:

• emitting a charged particle beam to be irradiated onto a substrate to be written;
• deflecting the charged particle beam to a desired irradiation position on the substrate;
• generating shot data from writing data, the shot data including a shot position and beam on/off time for each shot;
• detecting electrons reflected or emitted from the substrate toward the deflector;
• and
• calculating a first drift amount of the irradiation position of the charged particle beam on the substrate based on a current amount obtained from the detected electrons and a time elapsed from detecting the current to performing correction.

A charged particle beam writing method, comprising:

• emitting a charged particle beam to be irradiated onto a substrate to be written;
• deflecting the charged particle beam to a desired irradiation position on the substrate;
• generating shot data from writing data, the shot data including a shot position and beam on/off time for each shot;
• detecting electrons reflected or emitted from the substrate toward the deflector;
• calculating a first drift amount of the irradiation position of the charged particle beam on the substrate based on a current amount obtained from the detected electrons and a time elapsed from detecting the current to performing correction;
• calculating a correction amount for a positional deviation of irradiation based on the first drift amount;
• and
• correcting the irradiation position based on the shot data and the correction amount.