JPS62133655A - Probe diameter measuring device for charged corpuscular beam - Google Patents

Abstract

PURPOSE:To make it possible to measure a minute probe diameter, so far not possible to measure, by measuring plurally the probe diameter at the points extended from the smallest probe. CONSTITUTION:By placing a probe diameter measuring device variable in the optical axis (height) direction, and the probe diameter at a specific sampling position is computed from plural measurements. First, a sample board 14 is moved to the position where the tip of a knife edge 16 is at the electron beam radiating position, through a controller 25 and a sample board control unit 23. Then, the electron beams 11 are scanned to intersect the knife edge 16, the transmitting beam current is synchronized to a deflecting signal fed by a Faraday cup 18 to a deflector 15, and the value is detected. The detected signal is input to the Y of an XY recorder 24 through a signal multiplier 21 and a differential unit 22, while the deflecting signal is input to the X. The lateral axis of the recorder output indicates the scanning position and the vertical axis shows the differential signal intensity. The distance between two intersecting points of a straight line 1/e of the differential signal intensity and a differential signal wave is measured as the probe diameter d to be found.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a charged particle beam probe diameter measuring device, and more particularly to a device that accurately measures minute probe diameters.

[Background of the invention]

The conventional probe diameter 81 is determined by scanning an electron beam across a knife section provided at the same height as the sample surface, as described in Japanese Patent Publication No. 58-4314, and measuring the reflection from the knife. The probe diameter was determined from the rate of change in secondary electrons, absorption current, and transmission current. However, there is a limit to measurement due to dirt, electrostatic charge, etc. on the knife, and the lower limit was about 0.1 μm.

[Purpose of the invention]

An object of the present invention is to provide an apparatus for measuring the diameter of a microprobe of a charged particle beam.

[Summary of the invention]

The feature of the present invention is to measure the probe diameter at multiple positions shifted from the sample surface in the optical axis direction or the probe diameter for multiple focus current values using a known method such as the Knifezi method. The method is to extrapolate the probe diameter of the beam. According to this method.

It is possible to obtain minute probe diameters that cannot be measured using conventional probe diameter measurement methods.

The present invention will be explained in detail with reference to FIG. Figure 1 shows the trajectory of the beam when spherical aberration and chromatic aberration are considered. In the figure, the Z direction is the optical axis direction of the beam 11. At this time, the probe diameter increases as Z changes in the optical axis direction from the position Z where the probe diameter is minimum. This increase can be approximated by a straight line or a curve. Therefore, to find the probe diameter at Z=Zo, the position of the Zo area Z -ffl, Z -1! l"l l...
・+Z −1 or Z > Zo position Zl of the o area,
Approximate curves (straight lines) are obtained by measuring the probe diameters of Zi..., Zn by known means such as the Knifezi method. Let the value of Z = Zo of these curves be the probe diameter. Alternatively, the prologue diameter is obtained from the intersection of the two curves (straight lines).

Also, the change in the focus current Δ■ is the Z of the focus position.
If the change in direction can be considered to be equal to the change in direction ΔZ, the same effect as changing Z can be produced by changing the focus current, and the probe diameter at the time of focusing can be determined by the same method as described above.

[Embodiments of the invention]

An embodiment of the present invention will be described below.

FIG. 2 is a schematic configuration diagram in which the probe diameter f1M determining device of the present invention is applied to a scanning electron microscope using an electron beam as a charged particle beam. In the figure, in the lens barrel section 10, an electron beam generated from an electron gun is focused by a lens system, and a minute electron beam 11. is formed. The electron beam 1sll scans the test sample 13 one-dimensionally or two-dimensionally by a deflection signal supplied to the deflector 15 via the controller 25 and the deflection amplifier 19.

A method and apparatus for measuring an electron beam spot diameter according to the present invention will be described below.

In FIG. 2, the Z-axis is taken downward from the optical axis, and the position of the surface of the test sample 13 is taken as the origin of the Z-axis (Z=O). The probe diameter of the electron beam focused on this sample surface was determined as follows. A vertical fine movement bag [1
Equipped with a knife 1.6 that is movable in the Z direction at 7,
A Faraday cup] 8 is provided below the knife.

To measure the probe diameter using this knife,
First, the sample stage 1 is
4 is moved so that the tip of the knife 16 is at the electron beam irradiation position. Next, the electron beam 11 is scanned across the knife 16, and the transmitted beam current is detected by the Faraday cup 18 in synchronization with the deflection signal supplied to the deflector 15.

This detection signal is input to the Y of the XY recorder 24 via the signal amplifier 21 and the differentiator 22. A deflection signal is input to X. The recorder output will be as shown in Figure 3. In FIG. 3, the horizontal axis corresponds to the scanning position, and the vertical axis corresponds to the differential signal intensity. The distance between the two intersections of the 1/e straight line of the differential signal intensity and the differential signal waveform was determined as the probe diameter d.

The height Z of the knife is controlled by the vertical fine movement device 17, and the height Z is adjusted from Z = 20.0 μm below the sample surface (Z>O) to 100.0 μm.
The probe diameter was measured by the Knifezi method at 20 μm intervals. Note that the position of Z=0 was determined mechanically.

The results are shown in the graph of FIG. The horizontal axis is Z and the vertical axis is the probe diameter d. An optimal straight line was found from these measured values using the least squares method, d=4.8Xi 0-87. +
3×10'''' [m], and the beam diameter do at the sample surface (z=o) was found to be do=0.03 μm.

In addition, in the case of chromatic aberration) spherical West aberration, the position where the beam is focused by moving the knife up and down is Z = Zo, and z>
Measure the probe diameter in each region of Zo and Z < Zo, find the optimal straight line in each region, and find the intersection point Z = Zo
It is also possible to find the probe diameter from ``.Also, if spherical aberration cannot be ignored, the optimal straight line is determined in the Z > Zo region, and the optimal curve d=at (-Z)'' is determined in the Z:Zo region.
It is also possible to find +bx and find the probe diameter d from their intersection.

Furthermore, in the region where the change in focus current Δ■ and the change in focus position ΔZ satisfy ΔZ sword Δ■, instead of changing the position of the knife, the focus current ■ is changed,
The probe diameter can be determined by the same method as above.

As described above, according to this embodiment, the minimum probe diameter is calculated by moving the knife or changing the focus current value and determining the probe diameters at multiple out-of-focus points by 41. Therefore, it is possible to obtain minute probe diameters that could not be obtained using conventional probe diameter measurement methods.

〔Effect of the invention〕

According to the present invention, the minimum probe diameter is calculated by measuring multiple probe diameters at points that are wider than the smallest probe, so it is possible to obtain minute probe diameters that could not be measured using conventional probe diameter measurement methods. It has the effect of allowing you to

['tt explanation of the drawings] Fig. 1 is a beam trajectory diagram when spherical aberration and chromatic aberration are taken into account, Fig. 2 is a schematic configuration diagram to which the probe shed Δ1q determining device according to the present invention is applied, and Fig. 3 is a diagram of the trajectory of the beam when spherical aberration and chromatic aberration are taken into account. FIG. 4 is a graph of an example of measurement showing the relationship between the height and the diameter of the bead 11.

1...Objective lens principal plane, 2...Spherical aberration,;3.
・Chromatic aberration, 10...Electron lens barrel section, 11...Electron beam, 12...Sample chamber, 13...Sample, 14...Sample stage, ]5...Deflector, 16...・Naifetsuji, 1
7... Vertical fine movement device, 18... Faraday cup,
19... Deflection amplifier, 20... Vertical fine movement device controller, 21... Signal amplifier.

22... Differentiator, 23... Sample controller, 24...
xy th l concave Z (, & 俄) 2nd

Claims (1)

[Scope of Claims] 1. A focusing means for focusing a charged particle beam onto a thin probe on a predetermined sample, a deflection means for scanning the charged particle beam on the sample surface, and a probe for measuring the diameter of the probe. A charged particle beam apparatus having a probe diameter measuring device is characterized in that the probe diameter measuring device is movable in the optical axis (height) direction and the probe diameter at a predetermined sample position is calculated from a plurality of measured values. Wire probe diameter measuring device. 2. A charged particle beam probe diameter measuring device that determines the minimum probe diameter by fixing the probe diameter measuring device and measuring the probe diameter for a plurality of focus current values.