Method for acquiring settling time

A method for acquiring a settling time comprising:

• forming, using a deflector that deflects a charged particle beam based on a deflection signal from a DAC (digital/analog converter) amplifier, a reference pattern in a manner such that both ends of a width dimension of the reference pattern are written by two beam shots which are different from each other, by setting a settling time of the DAC amplifier to be a first time and deflecting the charged particle beam onto a target object by the deflector so that a deflection movement amount of the charged particle beam is smaller than an evaluation deflection movement amount for evaluating the settling time of the DAC amplifier;
• forming, while variably setting the settling time of the DAC amplifier to be a plurality of second times which are different from each other, an evaluation pattern in a manner such that both ends of a width dimension of the evaluation pattern being a same design width dimension as that of the reference pattern are written by two beam shots which are successively shot, by deflecting the charged particle beam onto the target object by the deflector, for each of the plurality of second times set variably, such that a deflection movement amount of a second beam shot of the two beam shots which are successively shot is equivalent to the evaluation deflection movement amount for evaluating the settling time of the DAC amplifier;
• measuring the width dimension of the reference pattern;
• measuring the width dimension of the evaluation pattern for the each of the plurality of second times set variably;
• calculating a difference between the width dimension of the evaluation pattern concerned and the width dimension of the reference pattern, for the each of the plurality of second times set variably;
• and
• acquiring a settling time of the DAC amplifier necessary for performing deflection by the deflection movement amount, using the difference for the each of the plurality of second times.