JPH0580100B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus such as an X-ray microanalyzer that analyzes a minute portion of a sample by irradiating the sample with an electron beam or an ion beam. This invention relates to a method for setting the cross-sectional diameter of a charged particle beam.

Since the above-mentioned analyzer provides an average analysis result of the area irradiated with the charged particle beam, it is important to appropriately set the diameter of the charged particle beam probe depending on the purpose of analysis. Conventionally, the following method was used to set the probe diameter.
X-ray microanalyzers and the like are equipped with optical microscopes for visually observing the sample surface and positioning the sample, so a sample that emits fluorescence is set at the sample position and irradiated with a charged particle beam to fluoresce. While observing the light emitting spot with an optical microscope, the excitation current of the objective lens is adjusted so that the spot diameter becomes the desired diameter, and then the fluorescent sample and the sample to be analyzed are exchanged. Such a method is very complicated, time consuming, and extremely inefficient.

The present invention aims to provide a method in which the probe diameter is automatically adjusted by specifying a desired probe diameter. The present invention will be explained below with reference to the drawings.

In FIG. 1, 1 is the main surface of the objective lens. Reference numeral 2 indicates a point at which the charged particle beam is converged by the upper lens, and an image of this point is formed in the sample space by the objective lens. 3 is an analysis sample. The distance from the convergence point 2 to the objective lens main surface 1 is a, and the distance from the objective lens main surface 1 is
The distance from to the surface of the sample 3 is lo, and the distance from the objective lens main surface 1 to the image 4 of the convergence point 2 by the same lens is b. Also, if the effective aperture diameter on the main surface 1 of the objective lens is 2R, and the diameter of the irradiation area on the surface of the sample 3, that is, the probe diameter is 2r, then the proportional relationship is r/R=b-lo/b, so b=R・lo /R-r…
...(1) In equation (1), R and lo are constants determined by the device, and r is the desired probe radius, which is determined by the person conducting the analysis. Therefore, using equation (1), we can find out how much b should be. If the focal length of the objective lens that gives this b is f, then 1/f=1/a+1/b, so by substituting equation (1) for b from f=ab/a+b, we get f=a(Rlo)/( R-r)/a+(Rlo)/(
R−r)≡P(r), and the focal length f is a function P(r) of only the probe radius r. It is known that, for example, in the case of an electromagnetic lens, there is a relationship between the focal length f and the ampere turns Ni of the excitation coil as shown in FIG. Here, fmin is the minimum focal length determined by the shape of the lens pole piece, and Nimax is a value of 13.5√, where V is the electron beam acceleration voltage. Since there is a monotonic functional relationship between the focal length and the ampere-turns of the excitation coil within a certain range of ampere-turns, determining the focal length determines the required ampere-turns, and therefore the excitation current i is determined as one. That is, the excitation current i is i/√V=Q(f)=Q(P(r))≡R(r) From the above equation, if the particle acceleration voltage and probe diameter are determined by i=√R(r), the objective The excitation current of the lens is determined. To actually determine the excitation current i according to the above formula, it is possible to create an appropriate approximation formula for the function R(r) and determine it by calculation, but by changing V It is also possible to draw a curve of the relationship with and determine it on the diagram.

FIG. 3 shows an embodiment of the present invention in which the excitation current i of the objective lens is automatically set to a predetermined value when the probe diameter is specified using the above formula. 5
is a function generator, and when the position of the slider of the potentiometer 6 is set according to the scale of the probe diameter, a voltage signal proportional to the probe diameter is input to the function generator. 7 is an accelerating voltage detector. The function generator 5 outputs logR(r) for the input probe diameter.
A logarithmic converter 8 logarithmically converts the output of the accelerating voltage detector 7. In the configurations 7 and 8, a variable resistor that obtains log√ in conjunction with the setting of the acceleration voltage may be used. The output of the function generator 5 and the output of the logarithmic converter 8 are added in an adder circuit 9, and the output of the adder circuit 9 is antilogarithmically converted in an antilogarithmic converter 10 and input to an objective lens excitation current control circuit 11. Although this embodiment is based on an analog system, it is also possible to use a digital system, and a computer can also be used. Furthermore, although the explanation so far has concerned the case where the convergence point of the charged particle beam by the objective lens is located below the sample, it goes without saying that the exact same concept can be applied even when the point is located above the sample.

According to the present invention, by specifying the probe diameter of the charged particle beam, the focal length of the objective lens (in the case of an electromagnetic lens, the excitation current) can be directly determined, and the measurement sample and fluorescent sample can be exchanged one by one. This eliminates the above-mentioned labor and improves the efficiency of analysis operations, and also makes it easier to automate analysis (for example, decide on various probe diameters and use a program to select various probe diameters and perform analysis). It has the advantage of being able to

[Brief explanation of the drawing]

Figure 1 is a diagram explaining the principle of the method of the present invention, Figure 2 is a diagram explaining the principle of the method of the present invention.
The figure is a graph showing the relationship between the focal length of the electromagnetic lens and the ampere turns of the coil, and FIG. 3 is a block diagram of an example of an apparatus for carrying out the method of the present invention. DESCRIPTION OF SYMBOLS 1... Main surface of objective lens, 2... Convergence point of charged particle beam by upper lens, 3... Sample, 4...
...An image of two points by an objective lens.

Claims (1)

[Claims] 1 When the probe diameter is arbitrarily set by shifting the objective lens focus with respect to the sample position, a signal corresponding to the objective lens focal length is generated from the specified probe diameter using the functional relationship between the objective lens focal length and the probe diameter. A method for setting a probe diameter for a charged particle beam, the method comprising: controlling an objective lens excitation current by a signal outputted by means for controlling the probe diameter of a charged particle beam.