JP3544483B2 - Ion beam equipment - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ion beam device provided with a gas ion source.
[0002]
[Prior art]
An ion gun which ionizes a gas by an electron impact method and then accelerates generated ions to form an ion beam is widely used for ion etching in surface analysis.
[0003]
The main purposes of ion etching in surface analysis are 1) cleaning to remove dirt attached to the sample surface, and 2) analysis of element composition distribution in the depth direction. To gradually strip off the constituent elements from the surface. Analysis using the latter method is called depth profiling.
[0004]
In order to ionize gas by the electron impact method, a gas ion gun having a structure shown in FIG. 1 is used. This ion gun operates as follows.
[0005]
The filament 1 is energized and heated to emit thermoelectrons from the filament 1. The electrons are accelerated by a constant electric field (about 100 to 200 V) and introduced into the grid 2 which is an ionization chamber. The electrons moving in the grid collide with gas molecules floating in the grid with a certain probability and ionize them. The ions generated in this manner are accelerated by the ion extraction electrode 3 and pass through holes provided in the extraction electrode 3 to form an ion beam. The filament heating current is controlled so that the amount of electrons flowing into the grid (this is usually called an emission current amount) is constant. This is called a constant emission current method. In some cases, a magnet 4 may be provided to superimpose a magnetic field to increase the efficiency of ionization.
[0006]
Now, the filament breaks when the ion gun is operated for a long time, and must be replaced with a new one. The most predominant cause of this disconnection is that the electric field around the filament draws ions in the direction of the filament, causing the filament to be ion-sputtered. This electric field is always controlled to a constant value in order to perform constant emission current control.
[0007]
The next most dominant cause of breakage is evaporation of the filament itself, as the filament is heated to a high temperature in a vacuum. For these reasons, the wire diameter of the filament is gradually reduced due to ion sputtering and evaporation of itself due to long-term use, resulting in a final disconnection.
[0008]
The degree to which the filament is ion-sputtered depends on the amount of emission current and the pressure of the gas introduced into the ionization chamber. For both parameters, the larger the value, the greater the amount of sputtered filament Consumption becomes severe.
[0009]
Also, if these values are the same, the lower the ion acceleration voltage, the more the filament is consumed. This is because the higher the ion acceleration voltage, the larger the amount of ions extracted from the ionization chamber by the ion extraction electrode, and conversely, the smaller the amount of ions flying to the filament side. Therefore, the filament is most consumed when the gas is introduced into the ionization chamber, the emission current is flowing, and the ion acceleration voltage is not applied.
[0010]
Also, the amount of evaporation of the filament itself increases as the filament temperature increases. In other words, the intensity increases as the amount of emission current increases.
[0011]
[Problems to be solved by the invention]
Incidentally, in such an ion gun, an emission current is controlled so that a predetermined amount flows while the gas is introduced into the ionization chamber, and an ion acceleration voltage is applied between the grid and the extraction electrode when ion etching is required. At this time, if the purpose is to clean the sample surface for a short time, introduce the gas into the ionization chamber only for the required period, and stop the gas introduction into the ionization chamber immediately after the cleaning is completed. Although ion sputtering can be suppressed, the gas is often kept introduced for a certain period of time in consideration of the fact that ion etching may have to be performed several times.
[0012]
Further, when performing depth profiling, it is general that the gas is always introduced into the ionization chamber during the analysis. This is because, in depth profiling, ion etching and elemental composition analysis are considered as one cycle, and this cycle is performed tens to hundreds of times. Therefore, gas introduction to the ionization chamber is performed “on / off” at each cycle. ), It is necessary to wait for each cycle until the gas pressure in the ionization chamber becomes stable, that is, until the conditions for obtaining a constant amount of ion current are satisfied. This is because the time becomes longer.
[0013]
Therefore, in actual use, the time during which the filament is most consumed, that is, the total time during which the ion acceleration voltage is not applied, is the time during which ion etching must be actually performed, that is, the ion acceleration voltage is reduced. In many cases, a situation in which the applied time is longer than the total time occurs, which results in a very short life of the filament.
[0014]
On the other hand, from the moment when the filament is disconnected, the ionization chamber becomes inoperable. Therefore, occurrence of disconnection during analysis, particularly during depth profiling, must be avoided as much as possible, and it is desired that the life of the filament be as long as possible.
[0015]
The present invention has been made in view of the above points, and an object of the present invention is to provide an ion beam apparatus capable of minimizing filament consumption.
[0016]
[Means for Solving the Problems]
The invention according to claim 1 is provided with an ion beam apparatus configured to irradiate the gas with electrons generated by the filament to ionize the gas, apply an accelerating voltage to the ion extraction means, and extract the ions from the ion gun. A surface analyzer, wherein the filament is heated and controlled such that an emission current amount when the acceleration voltage is not applied is smaller than an emission current amount when the acceleration voltage is applied. It is.
A second aspect of the present invention is the surface analyzer according to the first aspect, wherein the heating of the filament is controlled so that the emission current amount does not become zero.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0018]
FIG. 2 is a diagram showing an example of the ion beam device of the present invention.
[0019]
In FIG. 2, reference numeral 5 denotes a vacuum container of the gas ion gun. Argon gas stored in a gas storage chamber 6 is introduced into the vacuum container 5 via a gas flow control valve 7. The gas pressure in the vacuum vessel 5 is measured by a pressure measuring device (not shown), and a gas flow controller (not shown) connected to this pressure measuring device The gas flow control valve 7 is controlled so as to maintain the pressure.
[0020]
In the vacuum vessel 5, a filament 8 for generating electrons, an ionization chamber 9, and an extraction electrode 10 for extracting cations generated in the ionization chamber 9 are arranged.
[0021]
The filament 8 is connected to an emission current controller 11 and to the ionization chamber 9 via an emission power supply 12. Further, the ionization chamber 9 is connected to an extraction electrode 10 maintained at a ground potential via an ion acceleration power supply 13. The emission power supply 12 is connected to an emission power control unit 14, and the ion acceleration power supply 13 is connected to an ion acceleration power control unit 15.
[0022]
An ion beam optical system 16 is disposed downstream of such an ion gun, and the ion beam optical system 16 includes a converging lens, an objective lens, a deflector, and the like. Reference numeral 17 denotes a sample chamber in which a sample 18 is placed. Reference numeral 19 denotes an analyzer such as an Auger electron spectrometer attached to the sample chamber 17.
[0023]
Reference numeral 20 denotes a host computer, and the host computer 20 is connected to the CPU 21 via a bus. The bus is connected to the emission current control unit 11, the emission power control unit 14, the ion acceleration power control unit 15, the analyzer 19, and the memory unit 22 including a ROM and a RAM. The above-described depth profiling analysis program and the like are written in the ROM of the memory unit 22.
[0024]
The apparatus configuration of FIG. 2 has been described above. Next, the operation of this apparatus will be described.
[0025]
As described above, the gas pressure in the vacuum vessel 5 is maintained at a predetermined pressure. In this state, when the operator gives an instruction for depth profiling to the host computer 20, the host computer 20 notifies the CPU 21 that the instruction has been given. Upon receiving this instruction, the CPU 21 sends a control signal to each component based on the depth profiling program written in the ROM of the memory unit 22.
[0026]
The depth profiling program is programmed so that sample analysis and ion etching are performed alternately. The CPU 21 first instructs the analyzer 19 to start analysis. Then, the analyzer 19 starts sample analysis.
[0027]
Further, the CPU 21 sends a signal for turning off the ion acceleration voltage to the ion acceleration power supply control unit 15 so that the sample is not irradiated with the ion beam during the sample analysis. Upon receiving this signal, the ion acceleration power supply control unit 15 controls the ion acceleration power supply 13 so that the ion acceleration voltage becomes 0 V.
[0028]
Further, the CPU 21 sends a control signal for setting the emission current amount to, for example, 0.5 mA to the emission current amount control unit 11 and sets the potential of the filament 8 to a negative potential of several hundred volts with respect to the ionization chamber 9. Is transmitted to the emission power control unit 14.
[0029]
Upon receiving this control signal, the emission current controller 11 heats the filament 8, and the filament 8 generates thermoelectrons. Further, since the emission power supply control unit 14 controls the emission power supply 12 so that the potential of the filament 8 becomes as described above, the thermoelectrons generated in the filament 8 are accelerated toward the ionization chamber 9 and enter the ionization chamber. I do. When the emission current flows between the filament 8 and the ionization chamber 9 in this way, the emission current amount control unit 11 controls the heating amount of the filament 8 so that the emission current amount becomes 0.5 mA.
[0030]
By the way, as will be described later, the emission current amount during ion etching of the sample is usually set to about 20 to 30 mA, and the value of 0.5 mA is a considerably lower value. When the material of the filament is, for example, tungsten, the temperature of the filament is about 2,700 degrees when the emission current is 20 to 30 mA. Thus, when the emission current is 0.5 mA, the filament temperature becomes about 2,500 degrees. , 200 degrees lower. For this reason, the evaporation amount of the filament is considerably reduced as compared with the conventional method, that is, the method in which the same emission current flows during the sample analysis as during the ion etching.
[0031]
Further, when the amount of emission current is reduced in this manner, the ionization rate of the gas in the ionization chamber 9 decreases, and ions are not generated much. For this reason, the amount of the generated cations irradiating the filament is considerably smaller than that of the above-described conventional method. That is, the amount of ion sputtering of the filament is considerably smaller than in the conventional method.
[0032]
When the sample analysis by the analyzer 19 is completed, the CPU 21 sends a control signal to the emission current controller 11 to set the emission current to, for example, 30 mA for ion etching of the sample. The emission current amount control unit 11 receiving this control signal controls the heating amount of the filament 8 so that the emission current amount becomes 30 mA. Due to this increase in the amount of emission current, ionization of the gas in the ionization chamber 9 becomes intense, and many ions are generated.
[0033]
Further, the CPU 21 sends a control signal (a signal for turning on the ion acceleration voltage) for setting the potential of the ionization chamber 9 to a positive potential of several kV with respect to the extraction electrode 10 to the ion acceleration power supply control unit 15. Upon receiving this signal, the ion acceleration power supply control unit 15 controls the ion acceleration power supply 13 so that the potential of the ionization chamber 9 becomes such that the cations generated in the ionization chamber 9 are directed toward the extraction electrode 10. Accelerated.
[0034]
The ions that have passed through the extraction electrode 10 are converged and deflected by the ion beam optical system 16 and irradiate the sample 18. The sample 18 is etched by this irradiation.
[0035]
When such ion etching is performed for a predetermined time, the CPU 21 sends a signal of turning off the ion acceleration voltage to the ion acceleration power supply control unit 15. Upon receiving this signal, the ion acceleration power supply control unit 15 controls the ion acceleration power supply 13 so that the ion acceleration voltage becomes 0 V. By this control, the release of the generated cations from the extraction electrode 10 stops, and the ion etching of the sample 18 ends.
[0036]
Further, the CPU 21 sends a control signal for setting the emission current amount to the above-mentioned 0.5 mA to the emission current amount control unit 11, so that after the ion etching of the sample is completed, the emission current amount becomes 0.5 mA, and the filament temperature becomes lower. It is about 200 degrees lower than before. Even after the ion etching of the sample is completed, the potential of the filament 8 is kept at a negative potential of several hundred volts with respect to the ionization chamber 9.
[0037]
Next, the CPU 21 instructs the analyzer 19 to start analysis. Upon receiving the instruction, the analyzer 19 performs a sample analysis. When the sample analysis is completed, the above-described ion etching and the sample analysis are repeatedly performed a predetermined number of times.
[0038]
As described above, in the apparatus of FIG. 2, the emission current is set to an extremely low value while the ion accelerating voltage is not applied in order to extend the life of the filament. The feature of the present invention is that it is not completely reduced to zero, for the following reason.
[0039]
When the amount of emission current is completely reduced to zero, the filament temperature rapidly decreases to near normal temperature. When the filament is heated again, the filament rapidly expands and contracts due to rapid cooling and heating. By repeating this cycle many times, there is a very high possibility that the filament will be disconnected due to a cause other than consumption by ion sputtering and evaporation of the filament itself, for example, generation of a crack from a specific crystal grain boundary.
[0040]
In the above example, the emission current amount was set to 0.5 mA when the ion acceleration voltage was off, and was set to 30 mA when the ion acceleration voltage was on. However, in the apparatus shown in FIG. Can be set. For example, when the emission current amount can be set between 0.1 and 30 mA in increments of 0.1 mA, when the ion acceleration voltage is not applied, about 0.1 to 1 mA is applied. The value may be set to about 20 to 30 mA when the ion acceleration voltage is applied.
[0041]
Although the apparatus of FIG. 2 has been described above, FIG. 3 shows an example in which a circuit for controlling the amount of emission current and on / off of ion etching is configured by an analog circuit.
[0042]
In FIG. 3, the filament 23 is connected to the emission current control unit 24. The emission current amount control unit 24 includes a reference resistor R ₁ for determining the emission current amount I ₁ when no ion acceleration voltage is applied, and an emission current amount I ₂ (I ₂ > I ₁ ) when the ion acceleration voltage is applied. a reference resistor R ₂ that determines the, the selector switch a is connected to switch any of those of the reference resistor on the other hand with, and a feedback control circuit 25. The feedback control circuit 25 is connected to the changeover switch A, the feedback control circuit 25, as the emission current flowing between the filament 23 and the ionization chamber 26 becomes the I ₁ or I _2, the heating filament 23 It controls the current.
[0043]
Further, the filament 23 is connected to the ionization chamber 26 via an emission power supply 27. Further, the ionization chamber 26 is connected to an ion acceleration voltage generation circuit 28, and the ion acceleration voltage generation circuit 28 is connected to a changeover switch B. The changeover switch B is switched and connected to one of the ion acceleration voltage value setting reference resistor _R0 and the ground electrode E.
[0044]
In such a configuration, at the time of sample analysis, the changeover switch B is connected to the ground electrode E side, and by this connection, the ion acceleration voltage generation circuit 28 applies the acceleration voltage between the ionization chamber 26 and the extraction electrode (not shown). Do not apply.
[0045]
Further, the changeover switch A is configured to be switched in conjunction with the switching of the changeover switch B, the selector switch A is connected to a reference resistor R ₁ side as shown by a dotted line in FIG. With this connection, the feedback control circuit 25 heats the filament 23 so that the emission current amount becomes, for example, 0.5 mA.
[0046]
On the other hand, at the time of ion etching of the sample, the changeover switch B is connected to the reference resistor _R0 side. With this connection, the ion acceleration voltage generation circuit 28 causes the ion acceleration voltage to be applied between the ionization chamber 26 and the extraction electrode (not shown). Apply.
[0047]
Further, the switching of the changeover switch B, the selector switch A is connected to a reference resistor R ₂ side as shown by a solid line in FIG. By this connection, the feedback control circuit 25 heats the filament 23 so that the emission current amount becomes, for example, 30 mA.
[0048]
Even with such an analog circuit, the emission current amount is set to an extremely low value while the ion acceleration voltage is not applied, and the life of the filament can be extended.
[0049]
By the way, in the above-described example, since the emission current amount control section performs the feedback control, it is necessary to apply the electron acceleration voltage between the filament and the ionization chamber even when the ion acceleration voltage is off. That is, when the electron acceleration voltage is turned off, the emission current stops flowing, and the emission current amount control unit heats the filament more than necessary.
[0050]
However, if the emission current is prevented from flowing when the ion acceleration voltage is turned off, ionization of the gas is not performed, and ion sputtering of the filament due to cations can be suppressed.
[0051]
Therefore, a filament heating control unit is provided separately from the emission current amount control unit, and when the ion acceleration voltage is turned off, the application of the electron acceleration voltage is stopped, and the filament heating amount is controlled by the filament heating control unit to control the ion acceleration voltage. What is necessary is just to make it less than at the time of ON. When the electron acceleration voltage is off, the control of the emission current amount control unit is interrupted.
[Brief description of the drawings]
FIG. 1 is a view for explaining a gas ion gun.
FIG. 2 is a diagram showing an example of the ion beam device of the present invention.
FIG. 3 is a diagram showing an example of the ion beam device of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Filament, 2 ... Grid, 3 ... Ion extraction electrode, 4 ... Magnet, 5 ... Vacuum container, 6 ... Gas storage chamber, 7 ... Gas flow control valve, 8 ... Filament, 9 ... Ionization chamber, 10 ... Extraction electrode 11: emission current amount control unit, 12: emission power supply, 13: ion acceleration power supply, 14: emission power supply control unit, 15: ion acceleration power supply control unit, 16: ion beam optical system, 17: sample chamber, 18: sample, 19 ... analyzer, 20 ... host computer, 21 ... CPU, 22 ... memory section, 23 ... filament, 24 ... emission current control section, 25 ... feedback control circuit, 26 ... ionization chamber, 27 ... emission power supply, 28 ... ion accelerating voltage generating circuit, A, B ... changeover _{switch, R 1, R 2, R} 0 ... reference resistance, E ... ground electrode

Claims (2)

A surface analyzer equipped with an ion beam device configured to irradiate the gas with electrons generated by a filament to ionize the gas, apply an accelerating voltage to the ion extraction means, and extract ions from the ion gun, A surface analyzer in which the filament is heated and controlled such that an emission current amount when the acceleration voltage is not applied is smaller than an emission current amount when the acceleration voltage is applied . 2. The surface analyzer according to claim 1, wherein the heating of the filament is controlled so that the emission current does not become zero.

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