JPH03113354A - Antistatic method and antistatic device used for the method - Google Patents

Abstract

PURPOSE:To prevent the surface of a sample from being charged electrostatically by an easy and secure method by holding the sample in an electron atmosphere. CONSTITUTION:The antistatic device 6 consists of a plate-shaped target 9 which is arranged nearby a sample table 4, a holding table 10 where the target 9 is fixed, and an electron gun 11 which the target 9 is irradiated with an electron beam. When the target 9 is irradiated with an electron beam emitted by the electron gun 11 while an X-ray Photoelectron Spectro-scopy(XPS) analyzing device is in operation, secondary electrons 20 are generated by the target 9 and the periphery of the sample 6 is held in an electron atmosphere. Then those electrons are attracted to the surface of the sample which is charged electrostatically (positively) as shown by an arrow A. Namely, the sample 5 is neutralized electrically with electrons having negative charges and the quantity of electrostatic charging becomes zero, so the sample is prevented from being charged electrostatically.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an antistatic method and an antistatic device used in the method, and more specifically, to a method for preventing static electricity on a sample that is positively charged during physical analysis. The present invention relates to an antistatic method for preventing electrostatic charging, and an antistatic device directly used in the antistatic method.

1 When analyzing samples such as unutilized semiconductors and insulators by physical means, XPS (X-rayPhoto,
Auger Electron 5p analysis method, AES (Auger Electron 5p
ec-troscopy1 analysis method, SIMS (
Secondary ion Mass Spectr
This is generally carried out using an analysis method such as the ometry1 analysis method.

In these analytical methods, energetic particles such as X-rays, electron beams, and ion beams are used as primary radiation sources, and these normal sources are irradiated onto the sample to detect the secondary radiation emitted from the surface of the sample. Secondary particles (photoelectrons, Auger electrons, secondary ions, etc.)
Various analyzes are performed by detecting the energy, mass, etc. of

By the way, when the sample is an insulator or a semiconductor with high electrical resistance, for example in the XPS analysis method, the surface of the sample is "positively" charged by irradiation with X-rays. Therefore, since the negatively charged photoelectrons are attracted to the sample side, the measured kinetic energy value of the photoelectrons is lower than the kinetic energy value of the photoelectrons of the actual sample (sample in an uncharged state). , it is not possible to investigate the true physical properties of the sample itself.

Therefore, in the past, as shown in FIG. 7, the charges on the sample 52 are electrically neutralized by irradiating the sample 52 with a low voltage electron beam 53 on the surface of which the energy reference film 51 is formed. This prevents static electricity. That is, by irradiating the sample surface with an electron beam 53 accelerated to several volts to several hundred volts with a current value that is predicted to eliminate the charge, the amount of charge is brought to "zero" and charge is prevented. Ta. Here, as the energy reference film 51, a vapor-deposited film made of gold, silver, etc., hydrocarbon stain, or the like has been used.

In addition, in SIMS analysis, etc., physical analysis is performed by irradiating the sample with an ion beam, so if the sample is an insulator or a semiconductor with high electrical resistance, the surface of the sample is Positively charged. Therefore, in this case as well, charging was prevented by irradiating the sample with an electron beam, as described above.

However, the conventional antistatic methods described above have the following problems. That is, (1) since the electrical properties of the sample differ from sample to sample, the amount of charge on the sample also differs from sample to sample. therefore.

The irradiation conditions of an electron gun that emits an electron beam must be set for each sample to be analyzed, which makes handling of the apparatus complicated.

(2) When the energy reference film 51 is not formed, the irradiation voltage and irradiation current are increased.

The kinetic energy of the detected photoelectrons, etc. increases, and the sample surface eventually becomes negatively charged.

Therefore, in the conventional method, it is necessary to form the energy reference film 51 in order to prevent the insulator sample from being charged. That is, a preliminary process of forming the energy reference film 51 is required, and physical characteristics such as the kinetic energy cannot be easily investigated.

■When analyzing polymer materials or oxide materials, the surfaces of these samples may be decomposed by electron beam irradiation.

■The electron beam is irradiated onto the sample surface under certain irradiation conditions. Therefore, in cases where the sample surface is non-uniformly charged, such as a powdered insulator sample, it is impossible to completely reduce the amount of charge on the sample surface to "zero," and sufficient antistatic methods are necessary. In some cases, it may not be possible to do so.

In view of the above problems, it is an object of the present invention to provide an antistatic method that can prevent the surface of a sample from being charged using a simple and reliable method, and an antistatic device that is most suitable for use with the antistatic method. .

In order to achieve the above object, the antistatic method according to the present invention was invented to prevent secondary particles emitted from the sample surface by irradiating energetic particles onto the sample surface. This antistatic method prevents the sample from being charged in an analytical method for detecting electrostatic charges, and is characterized by holding the sample in an electronic atmosphere.

Furthermore, the antistatic device used in the above antistatic method includes a target for generating secondary electrons, and an electron gun that irradiates the target with electrons, and the target is located near the sample stage on which the sample is placed. It is characterized by being located in

Moreover, instead of the target, a thermionic generation source is arranged near the sample stage on which the sample is placed.

Furthermore, the present invention is characterized in that the target or the thermionic generation source is equipped with a power source for applying a bias voltage.

According to the antistatic method described above, since the sample is held in an electron atmosphere, negatively charged electrons are attracted to the positively charged sample surface, causing the sample surface to become electrically neutral. The amount of charge becomes "zero". In addition, the electrons are attracted to the sample surface depending on the strength of the electric field formed by the charge on the sample surface, so even if the sample is non-uniformly charged, the sample is electrically neutralized and further electrons are absorbed into the sample surface. Even if there are excess electrons in the atmosphere, the electrons only pass over the surface of the sample, and the sample is not negatively charged.

Further, according to the antistatic device, the target is irradiated with the electron beam (-electrons) emitted from the electron gun, and secondary electrons are generated from the target, so that the area around the sample easily becomes an electron atmosphere.

Further, even if a thermoelectron generation source such as a W (tungsten) filament is used instead of the target, an electron atmosphere can easily be created around the sample as described above.

Furthermore, by equipping the target or the thermionic source with a power source for applying a bias voltage, it becomes possible to apply a negative bias to the target or the thermionic source, thereby increasing the electron energy in the electron atmosphere. It becomes possible to increase the

Therefore, it is possible to electrically neutralize even a sample with a large amount of charge, and the amount of charge on the sample becomes "zero."
becomes.

Husband Yo Hereinafter, embodiments of the present invention will be explained in detail based on the drawings.

FIG. 2 is a conceptual diagram schematically showing an xPS analyzer equipped with an antistatic device according to the present invention.

A spectrometer body 2 is connected to the upper part of the device body 1, and an electron lens 3 extends from the center of the spectrometer body 2 toward the device body 1. A sample stage 4 is arranged below. A sample 5 is placed on the top of the sample stand 4, and the sample 5 is placed on the right side of the sample stand 4 in the figure.
An antistatic device 6 is provided to prevent charging of the sample stage 4.
An X-ray generator 8 is disposed at the upper left in the figure.

Further, a suction pump 7 is provided below the apparatus main body 1 to reduce the pressure inside the apparatus main body 1.

The antistatic device 6 includes a plate-shaped target 9 (in the figure, it is mounted obliquely with respect to a vertical plane) disposed near the sample stage 4, a holding stage 10 to which the target 9 is fixed, and a Electron gun 11 that irradiates the target 9 with an electron beam
It is composed of.

Although the target 9 is made of Au in this example,
It may be formed of a conductive material, and may be formed of other metal materials.

In the xPS analyzer configured in this way, when X-rays are emitted from the X-ray generator 8 under reduced pressure and irradiated onto the surface of the sample 5, photoelectrons are emitted from the surface of the sample 5, and the electron lens detected by the spectrometer main body 2 via 3,
The kinetic energy (binding energy) of photoelectrons is measured.

In other words, if the sample 5 is made of an insulator other than a conductor or a semiconductor with high electrical resistance, if the sample is irradiated with X-rays and photoelectrons (negative charges) are generated, the sample 5 will not be grounded. , a positive charge having the same amount of charge as the photoelectron charge is generated on the sample surface and charged. therefore,
The photoelectrons are attracted to the sample 5 side, and their kinetic energy is measured to be lower than the kinetic energy in an uncharged state, making it impossible to measure the true kinetic energy, and comparing the non-monochromatic energy line widths. It is known that when X-rays with a wide range of targets are used, the amount of charge is in the range of several volts to several tens of volts. Therefore, in this example, a strong electric field with an energy of several eV to several tens of square meters is created around the sample 5 to attract these electrons to the sample 5 side, thereby electrically neutralizing the sample surface. By setting the amount of charge to "zero," the sample 5 is prevented from being charged.

That is, while the XPS analyzer is in operation, the electron gun 1
When an electron beam is emitted from the sample 1 and irradiated onto the target 9, secondary electrons 20 are generated from the target 9, and the periphery of the sample 5 is maintained in an electron atmosphere as shown in FIG. And these electrons, as shown by arrow A,
It is attracted to the surface of the sample 5, which is positively charged. In other words, the sample 5 is electrically neutralized by the negatively charged electrons, and the amount of charge becomes "zero," making it possible to prevent the sample 5 from being charged. As described above, according to the antistatic method of the present invention, it is possible to effectively prevent electrostatic charges without forming the energy reference film 51 (see FIG. 7) made of a vapor-deposited film of gold or the like as in the conventional method. can.

Table 1 shows the correlation between the current value of the electron beam (-order electrons) emitted from the electron gun 11 and the antistatic effect. In this example, sample 5 is AI2□0. A thin film of Au was deposited on the single crystal surface of Al2. A on Os
Antistatic effect 2 was evaluated by measuring the A u 4 f 7/2 binding energy of u. The K(a) line of Al1, which is not monochromatic as an X-ray (hν=148
6.6 eV), the diameter of the electron beam emitted from the electron gun 11 was set to approximately 1 mmφ, and the acceleration voltage was set to 1 mm.
It was set to 00V. .

In this example, the Au vapor deposited film was formed to evaluate the antistatic effect, and in actual XPS analysis, such a vapor deposited film was not formed to prevent charging. Needless to say, it is possible.

(Hereinafter, blank spaces) Table 1 Binding energy is unique to a substance, and the binding energy of A u 4 f 7/2 of a sample in an uncharged case is 83.7 eV. Moreover, the following relationship exists between the axial alignment energy and the kinetic energy of photoelectrons.

(X-ray energy kinetic energy) bond energy Therefore, when the sample is positively charged, its bond energy is measured to be larger than the bond energy of the sample in the uncharged state (83.7 eV). becomes.

As is clear from Table 1, in the initial state (state where the electron beam is not irradiated), sample 5 is "positive".
However, when the electron beam is irradiated to the target 9 to generate secondary electrons, the current value of the electron beam becomes 5.
The amount of charge gradually decreases until it reaches 0 μA.
Even if the electron beam current value is increased to 50 μA or more, the binding energy does not become less than 83.7 eV. In other words, when the electron beam current value is increased to 50 μA or more, the surface of the sample 5 becomes “negative”. The amount of charge becomes "zero" without being charged. In other words, only the amount of secondary electrons 20 corresponding to the positive charge on the surface of the sample 5 is attracted to the sample 5 side and becomes electrically neutral. If there are excess electrons, these electrons simply pass through the surface of the sample 5.

Furthermore, as shown in FIG. 3, even when positive charges are unevenly charged on the sample 12, the secondary electrons 20 are attracted depending on the amount of charge on the sample 12, and the sample 12 becomes electrically It is neutralized and the amount of charge becomes "zero." That is, even when positive charges are unevenly distributed on the surface of the sample 12,
The secondary electrons 20 are attracted according to the strength of the electric field formed on the surface of the sample 12, reach a predetermined location on the surface of the sample 12, and are electrically neutralized to prevent charging.

Table 2 shows sample 1 whose surface is nonuniformly charged with positive charges.
2, the binding energy was measured.

That is, as the sample 12, as shown in FIG.
AJ2203 powder 14...(
The bonding energy of Ag2p and the Au
The binding energy of 4f7/2 was measured.

In addition, as in the above example, K(α) of AI2 is used as the X-ray.
(hν=1486.6eV), an electron gun with an electron beam diameter of approximately 1 mmφ, and an acceleration voltage of 10
Measurements were made with the setting set to 0v.

Table 2 As is clear from Table 2, since the Au plate 13 is a conductor, charges are accumulated on its surface.

The binding energy also shows a constant value (83.7 eV), but since it is an insulator /1. O, powder 14..., l12p
The binding energy of changes depending on the current value of the electron beam. That is, uncharged Aβgoz powder 1
The binding energy of Ag2p in 4... is 119.4 eV, but when the current value of the electron beam is low (10 μ8 or less), the AgzOa powder 14 on the Au plate 13 is positively charged. Therefore, by irradiating the target 9 with an electron beam having a large binding energy and a current value of 20 μA or more, the amount of charge can be reduced to “zero”. Even if the current value of the electron beam is further increased, for the same reason as mentioned above, the electrons only pass through the surface of the sample 12, and the sample 12 is not negatively charged.

FIG. 5 is a conceptual diagram of an antistatic device showing another embodiment, in which the target 9 is equipped with a power source 15 for applying bias. In recent xPS analysis, in order to improve the resolution of measured values, monochromatic X-rays with narrow energy lines are often used. However, when monochromatic X-rays are used in this way, the amount of charge on the sample (insulator) is large, and an electron atmosphere with a large energy of about 100 eV is required. If only the beam is irradiated, the energy amount of the secondary electrons 20 may be insufficient.

Therefore, in this embodiment, a bias applying power source 15 is provided and a negative bias is applied to the target 9, so that the sample 5 is held in an electron atmosphere having high energy. Table 3 shows the relationship between the bias voltage and the binding energy of Au4f7/2 when a bias voltage is applied to the target 9.

Note that A2 K(α) rays were used as monochromatic X-rays, and the electron beam acceleration voltage was set to 300 V and the electron beam current was set to 50 μA.

(The following is a blank space) Table 3 When using a non-monochromatic X-ray source, the amount of charge on the sample 5 is small, so even if a negative bias is not applied to the target 9, an electron beam with a current value of 50 μA can be used. Although it is possible to prevent charging using the secondary electrons 20 generated (see Table 1), when the amount of charging is large, the applied bias voltage becomes important for preventing charging, and as is clear from Table 3, By applying a negative bias of about -90V, it is possible to prevent charging. FIG. 6 shows an antistatic device showing yet another embodiment,
A thermionic generation source 16 is arranged near the sample stage 4 on which the sample 17 is placed.

Specifically, the thermionic generation source 16 is made of W (tungsten).
The filament 18 is composed of a filament 18 and a heating power source 19 that heats the filament 18. Then, a voltage is applied to the heating power source 19 and the filament 18
is heated, thermoelectrons 21 are emitted from the filament 18, and the sample 17 is held in an electron atmosphere. In addition, in FIG. 6, a bias applying power source 15 is provided in consideration of the case where the sample 17 has a large amount of charge, but when the amount of charge is small, a negative bias is applied to the thermionic source 16. This is not necessary, and the bias application power supply 15 can be omitted.

It goes without saying that the present invention is not limited to the above-mentioned embodiments and can be modified without departing from the scope of the invention. It is widely applicable and is not limited to XPS analysis methods. That is, for example, SIMS analysis method, I5S (Ion Scattering 5pec
troscopy1 analysis method, UPS (Ultravio
let Ph, otoelectron 5pectr
Of course, it is also applicable to other analysis methods such as oscopy) analysis method.

As detailed above, in the present invention, since the sample is held in an electron atmosphere, electrons corresponding to the amount of charge on the sample surface are attracted to the sample surface side, and the sample becomes electrically charged. The amount of charge becomes "zero" and charging can be prevented.

Further, even if there are excessive electrons in the electron atmosphere, these electrons only pass through the sample surface, and the sample is not negatively charged. That is, there is no need to provide an energy reference film as in the conventional case, and charging can be easily and effectively prevented.

Furthermore, as described above, since electrons are attracted according to the amount of charge on the sample, even if charges are unevenly accumulated on the sample surface, charging can be easily prevented.

Furthermore, since charging can be prevented without directly irradiating the sample with an electron beam, there is no possibility of decomposition of the sample, and the method can be applied to a wide range of samples such as polymeric materials and oxide materials.

Furthermore, the antistatic device according to the present invention includes a target for generating secondary electrons and an electron gun that irradiates the target with electrons, and the target is arranged near the sample stage on which the sample is placed. Therefore, it is possible to easily create an electronic atmosphere around the sample. Further, by disposing the thermionic emission source near the sample stage on which the sample is placed, it is possible to easily create an electron atmosphere around the sample. With such a simple device, the sample can be easily held in an electronic atmosphere, and charging can be prevented.

Furthermore, by equipping the target or thermionic source with a power source for applying a bias voltage, it becomes possible to apply a negative bias to the target or thermionic source.

Therefore, it is possible to more effectively prevent electrification even for a sample with a large amount of electrification.

[Brief explanation of drawings]

Figure 1 is a conceptual diagram for explaining an embodiment of the antistatic method according to the present invention, and Figure 2 is an xP equipped with an antistatic device.
A cross-sectional view schematically showing the S analyzer, FIG. 3 is a conceptual diagram of the main part for explaining another embodiment of the antistatic method according to the present invention, and FIG. 4 is provided for another embodiment. A cross-sectional view of the sample, FIG. 5 is a conceptual diagram of the main parts schematically showing another embodiment of the antistatic device, and FIG. 6 is a conceptual diagram of the main parts schematically showing still another embodiment of the antistatic device. 7 are conceptual diagrams for explaining the conventional antistatic method. 4... Sample stage, 5... Sample, 9... Target,
DESCRIPTION OF SYMBOLS 11... Electron gun, 12... Sample, 15... Power supply for bias application, 16... Thermionic generation source, 17... Sample. Figure 2 Figure 3 Figure 4 Sword J Figure 5 Figure 6

Claims (5)

[Claims] (1) An antistatic method for preventing the sample from being charged in an analysis method in which the sample surface is irradiated with energetic particles and secondary particles emitted from the sample surface are detected, the method comprising: An antistatic method characterized by holding in an atmosphere. (2) An antistatic device used in the antistatic method according to claim 1, comprising a target for generating secondary electrons and an electron gun for irradiating the target with electrons, the target being An antistatic device characterized in that it is disposed near a sample stage on which a sample is placed. (3) An antistatic device used in the antistatic method according to claim 1, characterized in that the thermionic generation source is disposed near the sample stage on which the sample is placed. Device. (4) The antistatic device according to claim 2, wherein the target is equipped with a power source for applying a bias voltage. (5) The antistatic device according to claim 3, wherein the bias voltage application power source is provided in the thermionic generation source.