Detection of defects using transient contrast

An electron beam apparatus for detecting defects in circuitry formed on a semiconductor substrate, the apparatus comprising:

• an electron source for generating a primary electron beam;
• a lens system configured to focus the primary electron beam onto a surface of a target substrate;
• a beam deflector configured to controllably deflect the primary electron beam;
• a detector configured to detect scattered electrons emitted from the target substrate;
• and
• control electronics configured to perform a first scan by scanning the primary electron beam in a first scan direction relative to the target substrate such that a first voltage-contrast image is detected, perform a second scan by scanning the primary electron beam in a second scan direction relative to the target substrate such that a second voltage-contrast image is detected, wherein the second scan direction is non-parallel to the first scan direction;
• and
• a data processor configured to compare the first and second voltage-contrast images to detect electrically-active defects.

An apparatus for detecting defects in circuitry formed on a semiconductor wafer, the method comprising:

• means for performing a first scan of said circuitry by scanning a primary electron beam in a first scan direction relative to said circuitry;
• means for detecting secondary electrons emitted during the first scan so as to form a first voltage-contrast image;
• means for performing a second scan of said circuitry by scanning the primary electron beam in a second scan direction relative to said circuitry, wherein the second scan direction is non-parallel to the first scan direction;
• means for detecting secondary electrons emitted during the second scan so as to form a second voltage-contrast image;
• and
• means for comparing the first and second voltage-contrast images to detect electrically-active defects.