Patent DE-102006007320-A1 (DE)
Title: Transmission electron microscope to analyze fine structure of materials in science and industry, has inputting device to input distance or spatial size between two points, and calculating device to calculate defocus amount of objective lens
Inventor: KASAI HIROTO
IPC: H01J37/26
Filed: 2006-02-16
Abstract: A transmission electron microscope comprises an inputting device for inputting a distance or spatial size between any two points desired to be observed by an operator, and a calculating device for calculating a defocus amount of an objective lens in which contrast of an image is high and phase contrast transfer function reducing a false image effect. A transmission electron microscope comprises: (1) an electron source (1); (2) an electron extractor electrode; (3) an acceleration tube for accelerating an extracted electron; (4) an illumination lens (2) for adjusting an electron beam emerged from the acceleration tube; (5) a sample holder for applying the electron beam from the illumination lens on a sample; (6) a deflection coil for deflecting the electron before being incident on the sample; (7) an objective lens (5) on which the electron beam transmitted through and scattered from the sample is incident; (8) an accelerating voltage source for controlling an accelerating voltage of the acceleration tube; (9) an objective lens power source for controlling an objective lens current of the objective lens; (10) a deflection coil power source for controlling a deflection coil current of the deflection coil; and (11) an inputting device for inputting a distance or spatial size d between any two points of the sample desired to be observed. A defocus amount (delta fc) of the objective lens based on equation [delta fc(d)=1/2(Cs.lambda 2>/d2>+d2>/lambda )], where delta fc is defocus amount of objective lens giving high contrast to input value, Cs is a spherical aberration coefficient of objective lens, lambda is a wavelength of electron beam, and d is a distance or spatial size between two selected points] is calculated. A focal length variation of an objective lens A of the objective lens expressed by an equation [delta =Cc square root of (delta V/V)2>+(delta I/I)2>+(delta E/V)2>, where delta is a focal length variation of objective lens, Cc is a chromatic aberration coefficient of objective lens, delta V/V is an accelerating voltage stability, delta I/I is an objective lens current stability, delta E/V is a spread of energy in an electron beam to accelerating voltage (V)] or a divergence angle beta of an incident electron beam to the sample (3) is a parameter (9). Phase contrast transfer functions (6) (PCTF) in the range in which the influence on an electron microscope image given by a phase inversion component can be neglected is determined. One of the determined functions PCTF in which the phase inversion component is relatively small is selected. The state of the one selected function PCTF is realized by the electron microscope by using the focal length variation of an objective lens delta as a parameter and modulating the accelerating voltage, and a modulated value delta V added to the accelerating voltage source is determined by calculation of an equation [delta V=V{square root of (-4.In(k.PCTF(dinv).dinv4>)/pi 2>.Cc2>.lambda 2>)-(2delta I/I)2>-(delta E/V)2>}, where delta V is a modulating signal added to an accelerating voltage, V is accelerating voltage, k is proportionality constant based on k=0.1-0.2, PCTF(dinv) is an intensity of a phase inversion component giving a maximum phase inversion component, Cc is a chromatic aberration coefficient of objective lens, lambda wavelength of electron beam, delta I/I is objective lens current stability, and delta E/V is a spread of energy in an electron beam to an accelerating voltage]. The modulated value delta V is superimposed on the accelerating voltage of the accelerating voltage source.