Displacement measuring apparatus, electron beam inspection apparatus, and displacement measuring method

An electron beam inspection apparatus comprising:

• an illumination optical system configured to irradiate, with a beam, from an oblique direction a surface of a target object with a figure pattern formed thereon;
• a sensor configured to receive a reflected light from the surface of the target object irradiated with the beam;
• an optical system configured to diverge the reflected light in a Fourier plane with respect to the surface of the target object;
• a camera configured to image a diverged beam in the Fourier plane;
• a gravity center shift amount calculation circuitry configured to calculate a gravity center shift amount of the reflected light in a light receiving surface of the sensor, based on a light quantity distribution of the beam imaged by the camera;
• a measurement circuitry configured to measure a heightwise displacement of the surface of the target object by an optical lever method, using information on a corrected gravity center position which is obtained by correcting a gravity center position of the reflected light received by the sensor by using the gravity center shift amount;
• a secondary electron image acquisition mechanism configured to acquire a secondary electron image of the figure pattern by scanning the surface of the target object with an electron beam while adjusting a focus position of the electron beam based on a measured value of heightwise displacement of the surface of the target object, and by detecting a secondary electron including a reflected electron emitted from the target object due to the scanning with the electron beam;
• and
• a comparison circuitry configured to compare, using a reference image, the secondary electron image with the reference image.

A displacement measuring method comprising:

• receiving, by a sensor, a reflected light from a surface of a target object, due to that the surface of the target object is irradiated from an oblique direction with a beam;
• imaging, by a camera, a diverged beam in a Fourier plane with respect to the surface of the target object;
• calculating a gravity center shift amount of the reflected light in a light receiving surface of the sensor, based on a light quantity distribution of the beam imaged by the camera;
• and
• measuring a heightwise displacement of the surface of the target object by an optical lever method, using information on a corrected gravity center position which is obtained by correcting a gravity center position of the reflected light received by the sensor by using the gravity center shift amount, and outputting a measured result.