Image generation apparatus

1. An image generation apparatus for generating an image of a specimen by scanning the specimen with a charged-particle beam and detecting secondary electrons emitted from the specimen, said apparatus comprising:

an XY stage on which the specimen can be placed;

an electron-optics column having an electron gun, a deflector, a condenser lens, and an objective lens;

a secondary-electron detector configured to detect the secondary electrons;

a displacement detector configured to detect a displacement of the XY stage;

a stage-position measuring device configured to specify a position of the XY stage based on an output signal of the displacement detector;

an accelerometer configured to detect vibration of the electron-optics column;

an acceleration-signal processing device configured to process an output signal of the accelerometer;

an imaging device configured to convert an output signal of the secondary-electron detector into an image;

a deflection-controlling device configured to control operation of the deflector; and

a control computer for controlling operations of the deflection-controlling device and the acceleration-signal processing device,

wherein the deflection-controlling device configured to add up a first vibration signal, outputted from the acceleration-signal processing device, and a second vibration signal, outputted from the stage-position measuring device, to produce a deflection correcting signal, and cause the deflector to correct deflection of the charged-particle beam based on the deflection correcting signal.

2. The image generation apparatus according to claim 1 , wherein:

the acceleration-signal processing device has a band-pass filter configured to filter the output signal of the accelerometer; and

the band-pass filter has a passband which is preset based on a frequency of the vibration of the electron-optics column.

3. The image generation apparatus according to claim 2 , wherein the control computer is configured to:

obtain, from the imaging device, a first image of the specimen which has been generated without correcting the deflection of the charged-particle beam;

produce a first frequency spectrum by performing a frequency analysis on the first image;

obtain, from the imaging device, a second image of the specimen which has been generated while correcting the deflection of the charged-particle beam based only on the second vibration signal;

produce a second frequency spectrum by performing a frequency analysis on the second image;

subtract the second frequency spectrum from the first frequency spectrum to calculate a difference at each of frequencies;

determine a frequency band in which the difference is larger than a threshold value; and

set the frequency band to the passband of the band-pass filter.

4. The image generation apparatus according to claim 1 , wherein the displacement detector comprises a laser interferometer having a reference mirror disposed adjacent to the objective lens and a measurement mirror secured to the XY stage.

5. The image generation apparatus according to claim 4 , further comprising:

a low-pass filter disposed between the stage-position measuring device and the deflection-controlling device, the low-pass filter being configured to allow passage of only frequencies lower than a natural frequency of a member to which the reference mirror is secured.

6. The image generation apparatus according to claim 1 , wherein the XY stage includes an electrostatic chuck configured to hold the specimen.

7. An image generation method for generating an image of a specimen by scanning the specimen with a charged-particle beam and detecting secondary electrons emitted from the specimen, said method comprising:

generating a first image of the specimen on an XY stage without correcting deflection of the charged-particle beam;

producing a first frequency spectrum by performing a frequency analysis on the first image;

generating a second image of the specimen on the XY stage while correcting the deflection of the charged-particle beam in a direction to remove vibration of the XY stage;

producing a second frequency spectrum by performing a frequency analysis on the second image;

subtracting the second frequency spectrum from the first frequency spectrum to calculate a difference at each of frequencies;

determining a frequency band in which the difference is larger than a threshold value;

setting the frequency band to a passband of a band-pass filter;

producing a first vibration signal representing vibration of an electron-optics column which has an electron gun, a deflector, a condenser lens, and an objective lens;

passing the first vibration signal through the band-pass filter;

producing a second vibration signal representing vibration of the XY stage;

adding the first vibration signal, which has passed through the band-pass filter, to the second vibration signal to produce a deflection correcting signal; and

generating an image of the specimen by scanning the specimen on the XY stage with the charged-particle beam and detecting secondary electrons emitted from the specimen while the deflector is correcting the deflection of the charged-particle beam based on the deflection correcting signal.