JPS60146439A - Potential measuring device - Google Patents

Abstract

PURPOSE:To measure potential by energy analysis of secondary electrons without lengthening the focal distance of a magnetic field lens by placing a detector of the secondary electrons above the magnetic lens. CONSTITUTION:The secondary electrons emitted from a sample 1 are absorbed by the first grid 2 while being subjected to an inverse electric field at the second grid 3 and only the secondary electrons having the big initial speed pass through the second grid 3. The third grid 14, which is attached above a magnetic field lens 7 while having equipotential to the first grid 2 is located down to right over the second grid plate 3 while absorbing the secondary electrons having passed through the second grid 3 and guiding them upward. The secondary electrons are further absorbed by the high electric fields of the scintillators 5a and 5b through the fourth conically made grid 13 for radiating while giving impact thereon. Thereby, the focal distance L of the magnetic field lens 7 can be shortened while reducing the electron beam diameter.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a scanning electron microscope, and particularly to a scanning electron microscope that uses an electron beam as a probe to perform both functional inspection and high-resolution morphological inspection of LSI. It is something.

[Background of the invention]

It is known that if a device for analyzing the energy of secondary electrons is added to a scanning electron microscope, it is possible to determine the potential of the area irradiated with the electron beam by 811 degrees (see Japanese Patent Publication No. 47-51024). FIG. 1 shows a secondary electron analyzer and its surroundings of a scanning electron microscope incorporating a secondary electron analyzer. A first grid plate 2 is placed above the sample 1, and a potential of several hundred pols 1- is applied to it. Further above, a second grid plate 3 is arranged, which includes, for example, -
5V is applied. An electron beam 15 emitted from an electron gun (not shown) is focused by a magnetic field lens 7 composed of a magnetic path 8 and an excitation coil 9, and reaches a minimum diameter on the sample 1. This electron beam 15 is connected to the main scanning coil 12 and the lower scanning coil 11.
It is now possible to scan the sample 1 or irradiate an arbitrary point.

The reason why there are two stages, upper and lower, is to ensure that the scanned electron beam always passes through the center point of the lens action of the magnetic field lens 7.

Secondary electrons 16 emitted from the sample 1 by electron beam irradiation are attracted by the electric field created by the first grid plate 2. However,
Since -5V is applied to the second grid plate 3, the secondary electrons 16 are subjected to a reverse electric field.

As a result, secondary electrons that can pass through the second grid plate 3 are limited to those with an initial velocity (velocity that they had when leaving the sample I) of 5 eV or more. The secondary electrons that have passed through the second grid plate 3 are attracted by the suction cylindrical grid 4 (to which a voltage of several hundred volts is applied), and are further attracted to the scintillator 5 to which +10 kV is applied, and are struck by 9#. emit light. This light is guided to a secondary electron amplifier tube 17 by a light guide 6. In this way, only secondary electrons with energy of λ゛6 are detected. When the potential of sample 1 changes, sample 11
J\1 Since the initial velocity of the emitted secondary electrons changes, the second
A change occurs in the amount of secondary electrons passing through the grid plate 3.

When the sample 1 becomes a positive potential, the amount of detected secondary electrons decreases, and when the sample 1 becomes a negative potential, it increases. In this way, it becomes possible to know the change in the potential of the sample as the difference in the detected amount of secondary 1u particles. - of the target sample to be measured using an electron beam
The L sample is a micro LSI. Therefore, it is desirable that the diameter of the electron beam on the sample 1 be 0.1 μm or less.

However, in the conventional structure shown here, the focal length of the magnetic field lens 7 is (not accurate, but in most cases approximately), which is the focal length of the first grid plate 2, the second grid plate 3, Since the suction cylinder grating 144 and the like must be placed between the sample 1 and the magnetic field lens 7, the length becomes about 5 cm. For this reason, there is a drawback that the lens aberration of the magnetic field lens 7 becomes large and the diameter of the electron beam becomes large. In particular, low speed (~
If an electron beam (ntv) is used, the increase will be even more remarkable.

[Purpose of the invention]

The present invention has been made with this point in mind, and an object of the present invention is to provide a novel potential measuring device that can measure potential by energy analysis of secondary electrons without increasing the focal length of a magnetic field lens. It is something to do.

[Summary of the invention]

The long focal length when an energy analyzer is attached is mainly caused by the size of the secondary electron detector section (absorption grid 4 in FIG. 1). Therefore, the present invention has a structure in which the secondary electron detector is placed above the magnetic field lens, and the focus of the magnetic field is shortened by 1) 11.

[Embodiments of the invention]

FIG. 2 is an embodiment of the present invention. The secondary electrons emitted from sample 1/1 are attracted by the first grid (plate) 2, and are subjected to a reverse electric field by the second grid (plate) S, so that only the secondary electrons with high initial velocity are attracted to the second grid (plate). Pass through Grid 3. Everything up to this point is the same as before. In this embodiment, the magnetic field L/grid 4, which is placed above the lens and has the same potential as the first grid 2, is placed directly above the second grid plate 3. 2. The secondary electrons that have passed through the grid 3 are attracted and guided upward. At this time, the secondary electrons create a complicated trajectory in the magnetic field of the magnetic lens, but in terms of bk 8M L) the secondary electrons diverge above the magnetic lens 7 where the magnetic field disappears.
It becomes 6a and 16b. These secondary electrons are further attracted by a fourth grid 13 formed into a conical shape.

The attracted secondary electrons are attracted by the high electric fields of scintillators 5a and 5b provided on both sides of the fourth grid 13, and impact this to emit light. With this structure, it is possible to shorten the focal length I- of the magnetic field lens 7 to 1 to 1.5 valences. Note that 68° 6b in Figure 1 is a light guide.

The focal length of a conventional 4+5 magnetic field lens is 5(2)l.
However, in the present invention, this was changed to 1 to 1,5 Cr+l
It is possible to shorten it to . As a result of this shortening, the spherical aberration of the magnetic field lens is reduced to 1/40th, and the chromatic aberration is reduced to approximately 1/3. This effect is reflected in the electron beam diameter. For example, when a field emission type electron gun is combined with a conventional structure, the electron beam diameter of 500 people at an accelerating voltage of 1 kV is different from that of the structure of the present invention. As a result, the electron beam diameter was reduced to 200
People can improve.

〔Effect of the invention〕

As explained above, by configuring the JL according to the present invention so that the secondary electron detector is placed above the magnetic field lens, it is possible to shorten the focal length of the magnetic field lens, and it is suitable for practical use. The effect is great.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating a conventional 4J structure incorporating a secondary electron energy analyzer, and FIG. 2 is a diagram illustrating an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Sample, 2... First grid, 3... Second grid, 5a, 5b... Scintillator, 6a, 6b...
...L-guide, 7...Magnetic field lens, 13...
4th grid. Bud 1 Calm! 20

Claims (1)

[Claims] A magnetic field lens narrows the primary electron beam and irradiates it onto the sample, and a magnetic field lens located between the magnetic field lens and the sample allows only high-speed secondary electrons emitted from the sample by the primary electron beam irradiation to pass through. and a secondary electron analyzer located above the magnetic field lens. A potential measuring device comprising a secondary electron detector for detecting secondary electrons.