Method and apparatus for automatic adjustment of electron optics system and astigmatism correction in electron optics device

An electron optics system automatic adjustment method for automatically adjusting an electron optics system of an electron optics device, comprising the steps of:

• carrying out a focal point adjustment by changing a refractive index of an objective lens of the electron optics device;
• storing a prescribed number of images sequentially obtained by the electron optics device at focal points adjusted by the focal point adjustment;
• calculating a moving amount of a sample image in said prescribed number of images stored by the storing step;
• judging whether an adjustment of the electron optics system of the electron optics device is necessary or not according to the moving amount of the sample image calculated by the calculating step;
• and
• adjusting the electron optics system of the electron optics device according to the moving amount of the sample image when the judging step judges that the adjustment of the electron optics system of the electron optics device is necessary.

An article of manufacture, comprising:

• a computer usable medium having computer readable program code means embodied therein for causing a computer to function as an electron optics system automatic adjustment apparatus for automatically adjusting an electron optics system of an electron optics device, the computer readable program code means including:
• first computer readable program code means for causing said computer to control the electron optics device to carry out a focal point adjustment by changing a refractive index of an objective lens of the electron optics device;
• second computer readable program code means for causing said computer to store a prescribed number of images sequentially obtained by the electron optics device at focal points adjusted by an operation of the first computer readable program code means;
• third computer readable program code means for causing said computer to calculate a moving amount of a sample image in said prescribed number of images stored by an operation of the second computer readable program code means;
• fourth computer readable program code means for causing said computer to judge whether an adjustment of the electron optics system of the electron optics device is necessary or not according to the moving amount of the sample image calculated by the third computer readable program code means;
• and
• fifth computer readable program code means for causing said computer to control the electron optics device to adjust the electron optics system of the electron optics device according to the moving amount of the sample image when the fourth computer readable program code means judges that the adjustment of the electron optics system of the electron optics device is necessary.

An astigmatism correction apparatus for correcting an astigmatism in an electron optics device by adjusting a stigmater of a charged particle beam optical system in the electron optics device, comprising:

• a secondary particle signal extraction unit for extracting secondary particle signals resulting from a two-dimensional scan of a charged particle beam over a sample by the electron optics device;
• a Fourier transform unit for calculating a power spectrum by applying a two-dimensional Fourier transform to the secondary particle signals extracted by the secondary particle signal extraction unit;
• a binarization unit for binarizing the power spectrum calculated by the Fourier transform unit to obtain a binarized image;
• an axis extraction unit for obtaining a principal axis and an axis perpendicular to the principal axis of the binarized image obtained by the binarization unit;
• an astigmatism information calculation unit for determining an intensity and a direction of the astigmatism by obtaining a distance between two points at which a sample image region in the binarized image intersects with the principal axis and a distance between two points at which the sample image region in the binarized image intersect with the axis perpendicular to the principal axis;
• and
• an adjustment unit for adjusting the stigmater of the charged particle beam optical system according to the intensity and the direction of the astigmatism determined by the astigmatism information calculation unit.

An astigmatism correction method for correcting an astigmatism in an electron optics device by adjusting a stigmater of a charged particle beam optical system in the electron optics device, comprising the steps of:

• extracting secondary particle signals resulting from a two-dimensional scan of a charged particle beam over a sample by the electron optics device;
• calculating a power spectrum by applying a two-dimensional Fourier transform to the secondary particle signals extracted by the extracting step;
• binarizing the power spectrum calculated by the calculating step to obtain a binarized image;
• obtaining a principal axis and an axis perpendicular to the principal axis of the binarized image obtained by the binarizing step;
• determining an intensity and a direction of the astigmatism by obtaining a distance between two points at which a sample image region in the binarized image intersects with the principal axis and a distance between two points at which the sample image region in the binarized image intersect with the axis perpendicular to the principal axis;
• and
• adjusting the stigmater of the charged particle beam optical system according to the intensity and the direction of the astigmatism determined by the determining step.

An article of manufacture, comprising:

• a computer usable medium having computer readable program code means embodied therein for causing a computer to function as an astigmatism correction apparatus for correcting an astigmatism in an electron optics device by adjusting a stigmater of a charged particle beam optical system in the electron optics device, the computer readable program code means including:
• first computer readable program code means for causing said computer to extract secondary particle signals resulting from a two-dimensional scan of a charged particle beam over a sample by the electron optics device;
• second computer readable program code means for causing said computer to calculate a power spectrum by applying a two-dimensional Fourier transform to the secondary particle signals extracted by the first computer readable program code means;
• third computer readable program code means for causing said computer to binarize the power spectrum calculated by the second computer readable program code means to obtain a binarized image;
• fourth computer readable program code means for causing said computer to obtain a principal axis and an axis perpendicular to the principal axis of the binarized image obtained by the third computer readable program code means;
• fifth computer readable program code means for causing said computer to determine an intensity and a direction of the astigmatism by obtaining a distance between two points at which a sample image region in the binarized image intersects with the principal axis and a distance between two points at which the sample image region in the binarized image intersect with the axis perpendicular to the principal axis;
• and
• sixth computer readable program code means for causing said computer to control the electron optics device to adjust the stigmater of the charged particle beam optical system according to the intensity and the direction of the astigmatism determined by the fifth computer readable program code means.

An article of manufacture, comprising:

• a computer usable medium having computer readable program code means embodied therein for causing a computer to function as an astigmatism correction apparatus for correcting an astigmatism in an electron optics device by adjusting a stigmater of a charged particle beam optical system in the electron optics device, the computer readable program code means including:
• first computer readable program code means for causing said computer to control the electron optics device to adjust a focal point of a lens system of the charged particle beam optical system according to a secondary particle signal image produced by extracting secondary particle signals resulting from a two-dimensional scan of a charged particle beam over a sample;
• and
• second computer readable program code means for causing said computer to control the electron optics device to correct the astigmatism by adjusting the stigmater so as to make the astigmatism of the charged particle beam small according to the secondary particle signal image for which the focal point is adjusted by an operation of the first computer readable program code means.