Reducing the impact of charged particle beams in critical dimension analysis

A method for measuring a feature on a wafer, the method comprising:

• aligning an electron beam to the start of a first scan interval that includes a first edge of the feature;
• illuminating the wafer with the electron beam when the scan position of the electron beam is at the start of the first scan interval;
• scanning the wafer over the length of the first scan interval;
• preventing the electron beam from illuminating the wafer when the scan position of the electron beam reaches the end of the first scan interval;
• aligning the electron beam to the start of a second scan interval that includes a second edge of the feature;
• illuminating the wafer with the electron beam when the scan position of the electron beam is at the start of the second scan interval;
• scanning the wafer over the length of the second scan interval;
• and
• preventing the electron beam from illuminating the wafer when the scan position of the electron beam reaches the end of the second scan interval.

A method for measuring a feature on a wafer, the feature including at least two edges, the method comprising:

• scanning the wafer with an electron beam in a first scan interval that includes at least a portion of a first edge of the feature;
• preventing the electron beam from illuminating the wafer while moving the scan position of the electron beam across a portion of the wafer to a second scan interval that includes at least a portion of a second edge of the feature;
• scanning the wafer with the electron beam in the second scan interval;
• and
• determining a distance between the first and second edges of the feature, based on a signal representative of emissions from the feature and/or wafer caused by the interaction of the electron beam and the feature and/or wafer.