JPH09251846A - Scanning type charged particle beam device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deterioration of an image contrast resulted from electric charge by setting a minimum potential on a secondary electron passage higher than a potential of a sample table. SOLUTION: A secondary electron passage is covered with a cylindrical electrode 12, to which a positive voltage of about several tens volt is applied. When a potential of the applied positive voltage is higher than a sample surface potential, a potential barrier on the secondary electron passage disappears. Consequently, even when the surface of a sample 6 is electrically charged at a positive potential, all secondary electrons can reach a secondary electron detector 10. Therefore, variations in potential of a minimum potential portion of the secondary electron passage enable a voltage contrast to be observed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an observation device using an electron beam or an ion beam, such as a scanning electron microscope or a focused ion beam device.

[0002]

2. Description of the Related Art A scanning electron microscope used for observing semiconductor devices is taken as an example.

FIG. 1 shows the principle and structure of a scanning electron microscope. The electron beam 2 emitted from the electron gun 1 is narrowed down by the converging lens 3 and the objective lens 4, and the sample stage 5
Focus on the surface of the sample 6 mounted on. At the same time, the trajectory of the electron beam 2 is deflected by the deflector 7 and two-dimensionally scans the sample surface. Secondary electrons 8 are emitted from the sample portion irradiated with the electron beam 2. Secondary electron 8
Traverses the objective lens and passes through the mesh electrode 9
Be attracted to. A high voltage of about 10 kv is applied to the mesh electrode 9. The secondary electrons passing through the mesh electrode 9 are detected by the secondary electron detector 10,
Converted to electrical signals. This secondary electron signal is used for brightness-modulating the display 11 after undergoing signal processing such as amplification. The display 11 has an electron beam 2
Scanning is performed in synchronization with the scanning on the sample surface, and a secondary electron image is formed on the display screen.

In the secondary electron path from the sample surface to the secondary electron detector 10 through the objective lens, the magnetic poles and magnetic paths of the sample table 5 and the objective lens 4 are grounded. It has a barrier (the lowest potential part).

[0005]

When observing an insulator sample, the sample surface is charged by being irradiated with an electron beam. The negative charge on the sample surface causes image defects such as halation. Generally 1k for application to semiconductor devices
Using a low energy electron beam of about eV, observation is performed with the surface of the sample being positively charged.

However, a positive charge, that is, a positive sample surface potential causes a decrease in secondary electron detection signal, that is, a decrease in image contrast.

The case where the sample surface is not charged is shown in FIG.
Shown in

The sample surface potential is at the ground potential of 0, like the sample table 5. Therefore, the secondary electrons 8 emitted from the sample surface have energy higher than 0 potential. Therefore, all the secondary electrons are the potential barriers of the secondary electron passages;
The secondary electron detector 10 can be reached by surpassing the zero potential. No reduction in image contrast occurs.

FIG. 2C shows the case where the sample surface is charged and is at a positive potential.

A part of the secondary electrons 8 emitted from the surface of the sample, a low energy part indicated by diagonal lines in the secondary electron energy distribution, has energy lower than the potential barrier (0 potential). These low-energy secondary electrons cannot overcome the potential barrier of the secondary electron passage. Since low energy secondary electrons cannot reach the secondary electron detector 10, the image contrast is reduced.

At the initial stage of electron beam irradiation and until the charge on the surface of the sample is saturated, the secondary electron image changes in the direction in which the image contrast decreases.

The kinetic energy distribution of secondary electrons has a peak at several eV, and the positive potential of the sample surface is 10 e.
If it goes up to about V, image formation becomes difficult.

An object of the present invention is to provide a means for eliminating the reduction in image contrast due to charging.

[0014]

The minimum potential of the secondary electron passage is set higher than the potential of the sample stage by, for example, about several tens of volts.

The secondary electrons have enough energy to overcome the potential barrier of the secondary electron passage. Therefore, the image contrast does not decrease.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The potential barrier of the secondary electron passage is formed by the objective lens portion. The secondary electron passage in this portion is covered with the cylindrical electrode 12, as shown in FIG. Cylinder electrode 12
A positive voltage of about several tens of V is applied to. If the applied positive voltage is higher than the sample surface potential, the potential barrier of the secondary electron passage is eliminated. If the potential barrier is eliminated, all the secondary electrons can reach the secondary electron detector even if the sample surface is charged and has a positive potential.

By making the potential of the lowest potential portion of the secondary electron passage variable, the voltage contrast can be observed.

As a charged particle beam scanning method on the sample surface,
Although the method of deflecting the electron beam is shown, it is also possible to scan while moving the sample table. Further, scanning may be performed by combining electron beam deflection and sample stage movement.

Although the case where the sample table is grounded is shown, the sample table, that is, the sample may be held at a certain potential.

Although the electron beam is used as the charged particle beam, an ion beam may be used.

[0021]

According to the present invention, the emitted secondary electrons all have energy large enough to overcome the potential barrier of the secondary electron passage, and the image contrast is not deteriorated.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of the principle and configuration of a scanning electron microscope.

FIG. 2 is an explanatory diagram of a relationship between a sample surface potential, a secondary electron passage potential distribution, and a secondary electron energy distribution.

FIG. 3 is an explanatory view showing one embodiment of the present invention.

[Explanation of symbols]

2 ... Electron beam, 4 ... Objective lens, 5 ... Sample stage, 6 ... Sample, 9 ... Mesh electrode, 10 ... Secondary electron detector, 12 ...
Cylindrical electrode.

Claims (5)

[Claims] 1. A sample stage on which a sample for observation is placed, and a charged particle beam generation system for generating a charged particle beam,
A convergent lens system for narrowing down the charged particle beam on the sample surface, a charged particle beam deflection system for scanning the charged particle beam on the sample surface, and a mutual interaction between the charged particle beam and the sample. As a result of the action, in a scanning charged particle beam device having a secondary charged particle detection system for detecting secondary charged particles emitted from the sample surface after passing through at least a part of the convergent lens system, The potential of the secondary charged particle passage from the sample surface to the secondary charged particle detector is lower than the potential of the sample table in the case of secondary particles having a positive charge,
A scanning charged particle beam device characterized in that in the case of secondary particles having a negative charge, the potential is made higher than the potential of the sample stage. 2. The scanning charged particle beam device according to claim 1, wherein the potential of the lowest potential portion of the secondary negatively charged particle passage or the potential of the highest potential portion of the secondary positively charged particle passage is variable. 3. The scanning charged particle beam device according to claim 1, wherein the charged particle beam is an electron beam. 4. The scanning charged particle beam device according to claim 3, wherein the secondary charged particles are secondary electrons. 5. The scanning charged particle beam device according to claim 1, wherein the charged particle beam is an ion beam.