JPH02132741A - Electron beam device - Google Patents

Abstract

PURPOSE:To obtain a scan electron microscope image having high resolution and picture quality by controlling the excitation of an electron lens based on the signal showing the voltage applied to a first anode and the signal displaying the voltage applied to a second anode. CONSTITUTION:The means is provided which generates the signal showing the excitation quantity of an electron lens, needed to minimize a sample irradiation electron beam diameter based on the signal displaying the voltage applied to a first anode 2 and the signal showing the voltage applied to a second anode 3, and required to maximize a sample irradiation electron beam current value in the condition of the minimized diameter, and the excitation of the electron lens is controlled based on a signal generated. That is, a table is memorized in a memory 12, the table shows the excitation current value in a focusing lens 10, needed to minimize the sample irradiation electron beam diameter to the various set values of acceleration voltage Va, and required to maximize the sample irradiation electron beam current value in the condition of the minimized diameter. Consequently a scan electron microscope image having high resolution and picture quality can be obtained by even an unskilled operator.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electron beam device, and more particularly to an electron beam device equipped with a field emission type electron gun.

[Prior Art] Conventionally, in a scanning electron microscope equipped with a thermionic emission type electron gun, due to the optical characteristics of the thermionic emission type electron gun, the diameter of the electron beam irradiated on the sample decreases as the sample irradiation current decreases. It has been known. Therefore, in a scanning electron microscope equipped with a thermionic emission electron gun, in order to obtain a high-resolution scanning electron microscope image, the electron microscope operator must perform an operation to reduce the sample irradiation current to a desired sample irradiation current value. is being carried out.

[Problems to be Solved by the Invention] Recently, scanning electron microscopes equipped with field emission electron guns have been frequently used to obtain high-resolution, high-quality secondary electron images. However, in a scanning electron microscope equipped with a field emission electron gun, there is a practical region where the sample irradiation electron beam diameter does not decrease even if the sample irradiation current is reduced. It is not possible to obtain a high-resolution, high-quality scanning electron microscope image simply by reducing the sample irradiation current, as if operating a scanning electron microscope equipped with the scanner.

In consideration of the above-mentioned problems, the present invention provides an electron beam device that allows even an unskilled operator to easily irradiate a sample with an electron beam of the maximum sample irradiation electron beam current value while minimizing the sample irradiation electron beam diameter. It is intended to.

[Means for Solving the Problems] The present invention includes a cathode, a first anode for forming an extraction electric field between the cathode, and a cathode for accelerating an electron beam emitted from the cathode and passing through the first anode. In an electron beam apparatus comprising a second anode, and an electron lens for focusing the electron beam that has passed through the second anode and irradiating it onto a sample, a signal representing a voltage applied to the first anode; Based on a signal representing the voltage applied to the second anode, determine the amount of excitation of the electron lens necessary to minimize the diameter of the electron beam irradiating the sample and to maximize the current value of the electron beam irradiating the sample in the state of the minimum diameter. The electronic lens is characterized in that it includes means for generating a representative signal, and means for controlling excitation of the electron lens based on the generated signal.

[Operation: To minimize the sample irradiation electron beam diameter and maximize the sample irradiation electron beam current value based on the signal representing the voltage applied to the first anode and the signal representing the voltage applied to the second anode. By providing a means for generating a signal representing the required excitation amount of the electron lens, and by controlling the excitation of the electron lens based on the signal generated by the means, scanning electron beams with high resolution and high image quality can be obtained. Obtain a microscopic image.

[Example] Hereinafter, an example of the present invention will be described based on the drawings. 1st
The figure is an apparatus configuration diagram for explaining one embodiment of the present invention, Figure 2 is a diagram showing the relationship between sample irradiation current and sample irradiation current diameter in a scanning electron microscope using a field emission electron gun, and Figure 3
The figure shows the relationship between the minimum sample irradiation electron beam diameter and acceleration voltage.
FIG. 4 is a diagram for explaining a table stored in the memory for controlling the amount of excitation of the electron lens based on the acceleration voltage and the extraction voltage.

In Figure 1, 1 is a needle cathode, 2 is a first anode, and 3 is a second anode.
1 is an anode, 4 is an extraction power source, 5 is an acceleration power source, 9 is a sample, 10 is a focusing lens, 11 is an objective lens, 12 is a memory, and 13 is an electron lens control section.

The lens control unit 13 is configured to control the excitation current value of the focusing lens 10 based on the data from the memory 12, and to realize the instructed sample irradiation current.

First, the operator of the electron microscope applies a voltage Ve to the power source 4 between the cathode 1 and the first anode 2, and a voltage Ve from the power source 5 between the cathode 1 and the second anode.
An accelerating voltage Va is applied between the anodes 3. Here, the voltage value is set by a Va/Ve ratio based on a combination of several types of Va values and Ve values, and the set voltage value is stabilized and controlled to be maintained at a constant value. There is.

When the extraction voltage Ve and acceleration voltage Va are set,
An electron beam is emitted from the cathode 1 by the extraction voltage Ve. The electron beam emitted from the cathode 1 and passing through the first anode 2 is accelerated toward the second anode 3, passes through the electron beam passage hole of the two anodes 3, and enters the focusing lens 10. Then, the electron beam is focused by the focusing lens 10 and introduced into the objective lens 11, and is focused and irradiated onto the sample 9 by the objective lens.

Now, when the extraction voltage Ve is set to a constant value, for example, 5KV, the relationship between the sample irradiation current 1p and the sample irradiation electron beam diameter R is measured using the acceleration voltage Va as a parameter, and the relationship as shown in FIG. 2 is obtained. It became clear that there is. In Figure 2, the vertical axis is the sample irradiation electron beam diameter;
The horizontal axis represents the sample irradiation electron beam current, and the curve a is Va
- For IKV, curve b is Va - For 5KV, curve C
The case of V a - 40 KV is shown. As is clear from the figure, there is a point at which the diameter of the electron beam irradiating the sample no longer decreases even if the sample irradiation electron beam current is reduced. The starting point P a - PC of the region at each acceleration voltage is the point where the irradiation current is maximum when the beam diameter is the smallest. The conditions expressed by these points correspond to the optimum sample irradiation conditions for obtaining a high-resolution secondary electron image with a good signal-to-noise ratio.

Note that by determining these points P for various acceleration voltages, a curve as shown by a dotted line in the figure is drawn. When this curve is expressed with the acceleration voltage on the horizontal axis and the sample irradiation electron beam current on the vertical axis, it becomes as shown in FIG. 3.

In the memory 12, not only when the extraction voltage Ve is 5 KV, but also when Ve is variously changed, the sample irradiation electron beam diameter is set to the minimum for various set values of the accelerating voltage Va,
A table representing the excitation current value D of the focusing lens 10 necessary to maximize the current value of the electron beam irradiating the sample in the state of the minimum diameter is stored. Each of these data is obtained as follows. That is, while operating the field emission electron gun with the extraction voltage Vex and the acceleration voltage Vaj, the sample irradiation current! One piece of data is obtained by measuring the sample irradiation current diameter R while changing p, and measuring and recording the excitation current Dlj of the focusing lens 10 at the starting point where the sample irradiation electron beam diameter stops changing. And acceleration voltage vaj
from Va1 to Va2 + va3 + ..., Van
A set of data (data at constant voltage VeL) can be obtained by performing the above measurements while changing the voltage and determining the excitation current D11-Din of the focusing lens 10 in each case. Similar work is done to change the extraction voltage Ve1 from Vel to Ve2.
,Ve3,...,Ve. All data can be obtained by varying up to l1. An example of the contents of the memory 12 in which the data obtained in this way is stored as a table is shown in FIG. Therefore, the electron lens control unit 13 refers to the data in the memory 12 based on the output signals (signals representing voltage) of the extraction power source 4 and the acceleration power source 5, and minimizes the sample irradiation electron beam diameter and the sample irradiation electron beam current. A signal representing the amount of excitation of the focusing lens 10 necessary to maximize the value is read into the control section 13. Then, the electron lens control unit 13 controls the excitation amount of the focusing lens 10 based on the read data, and applies the electron beam to the sample under the conditions that the sample irradiation electron beam diameter is the minimum and the sample irradiation electron beam current value is the maximum. I am trying to irradiate it to

In the above-described configuration, it is assumed that the operator of the electron microscope sets, for example, Ve-Ve2 and Va-Va3, and the electron gun enters the operating state. The control unit 13 is connected to the power source 4
and (Ve2) in the table stored in the memory as shown in FIG.
, Va3) and specify the address corresponding to the data D2.
Read out 3.

Then, the control unit 13 controls the excitation current value of the focusing lens 11 based on the read data to minimize the sample irradiation electron beam diameter, and maximizes the sample irradiation electron beam current value in the state of the minimum diameter. Set the conditions to Therefore, the sample is irradiated with the electron beam under the conditions that the sample irradiation electron beam diameter is the minimum and the sample irradiation electron beam current value is the maximum. In addition, when the acceleration voltage of the electron gun is changed to Val, (Ve2,
The address corresponding to Va1) is specified and the data D21
is read out and the excitation current of the focusing lens 10 is changed based on the data, so that the sample is always irradiated with the electron beam under the conditions that the sample irradiation electron beam diameter is the minimum and the sample irradiation electron beam current value is the maximum. . Therefore, a high-resolution secondary electron image can always be obtained.

[Effect of the invention] As is clear from the above explanation, according to the present invention, the first
Minimize the sample irradiation electron beam diameter based on a signal representing the voltage applied to the anode and a signal representing the voltage applied to the second anode, and maximize the sample irradiation electron beam current value in the state of the minimum diameter. By providing a means for generating a signal representing the necessary excitation amount of the electron lens and a means for controlling the excitation of the electron lens based on the generated signal, even an unskilled operator can easily control the sample irradiation electrons. It is possible to provide an electron beam device that can easily irradiate a sample with an electron beam of the maximum sample irradiation electron beam current value while minimizing the wire diameter. Therefore,
When this apparatus is applied to a scanning electron microscope, even an unskilled operator can obtain a high-resolution, high-quality scanning electron microscope image.

[Brief explanation of drawings]

FIG. 1 is an apparatus configuration diagram for explaining an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between sample irradiation current and sample irradiation current diameter in a scanning electron microscope using a field emission electron gun.
Fig. 3 is a diagram showing the relationship between the minimum sample irradiation electron beam diameter and accelerating voltage, and Fig. 4 is a diagram explaining a table used when controlling the excitation amount of the electron lens based on the accelerating voltage and extraction voltage. It is. 1: Needle cathode 2: First anode 3: Second anode 4: Extraction power source 5: Acceleration power source 9: Sample 10: Focusing lens 11: Objective lens] 2: Memory
13:Electronic lens control unit
. -(kV) Figure 1

Claims (1)

[Claims] a cathode and a first electrode for forming an extraction electric field between the cathode and the cathode;
An anode, a second anode for accelerating the electron beam emitted from the cathode and passing through the first anode, and an electron lens for focusing the electron beam passing through the second anode and irradiating it onto the sample. In the electron beam apparatus, the sample irradiation electron beam diameter is minimized based on a signal representing the voltage applied to the first anode and a signal representing the voltage applied to the second anode, and the sample is irradiated in the state of the minimum diameter. Means for generating a signal representing the amount of excitation of the electron lens necessary to maximize the electron beam current value, and means for controlling excitation of the electron lens based on the generated signal. An electron beam device featuring: