JP2000251750A - Focused ion beam device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focused ion beam device capable of machining a sample with high precision. SOLUTION: In order to prevent an emission current Ie from fluctuating while using a liquid metal ion source 110, an applying voltage Vsup of a suppressor electrode 114 is controlled corresponding to the current value Ie of an ampere meter 312. When the voltage Vsup is changed, an optical axis of an electrostatic lens 200 formed parasitically between the suppressor electrode 114 and an extraction electrode is changed, to shift an irradiation position of an ion beam. Therefore, in order to prevent the position shift, the position of the suppressor electrode 114 is shifted in the horizontal direction, to correct the optical axis of the lens 200.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focused ion beam apparatus using a liquid metal ion source.

[0002]

2. Description of the Related Art A focused ion beam apparatus is a FIB (Focus).
It is also called an “ed ion beam” device, and is a device that focuses metal ions by an ion optical system and irradiates the sample with a sample. Focused ion beam devices are, for example, scanning ion microscopes
(Scanning Ion Microscope; SIM) In addition to being used for observation, deposition and etching of a thin film can be performed without using a mask.

A liquid metal ion source is usually used as an ion source of a focused ion beam device. The liquid metal ion source is also called an LMIS (Liquid Metal Ion Source), and is a device that extracts ions from a molten metal and generates an ion beam. In a liquid metal ion source, a liquid metal is attached to the surface of a needle-like emitter electrode, and a concentrated electric field is generated at the tip of the emitter electrode to extract metal ions. To generate a concentrated electric field,
Extractor and Suppressor
Is used.

In the focused ion beam apparatus, when a voltage is applied to the extraction electrode and the suppression electrode, an electrostatic lens is parasitically formed between the extraction electrode and the suppression electrode. Then, the characteristics of the electrostatic lens change with the change in the voltage applied to the extraction electrode and the suppression electrode.
If the optical axis or the focal length of the electrostatic lens changes, the irradiation position or the focus of the ion beam shifts, and it becomes impossible to perform high-precision three-dimensional processing on the sample. For this reason, the conventional focused ion beam apparatus has been used with the voltage of the extraction electrode and the suppression electrode kept at a constant voltage in order to prevent the characteristics of the electrostatic lens from changing.

[0005]

The conventional focused ion beam apparatus has a drawback that the emission current (that is, the amount of ions emitted from the emitter electrode) fluctuates as the operating time becomes longer. Such a change in the emission current is caused by an increase in impurities, oxide films and the like attached to the emitter electrode, a change in the thickness of the liquid metal film formed on the tip of the emitter electrode, and the like.

When the emission current fluctuates, the current of the ions actually supplied to the sample (hereinafter referred to as "sample current") fluctuates, so that the deposition rate and the etching rate of the thin film change. High-precision three-dimensional processing cannot be performed. Here, in order to prevent the fluctuation of the emission current, the strength of the concentrated electric field generated at the tip of the emitter electrode may be adjusted by changing the voltage of the extraction electrode or the suppression electrode. However, as described above, when the voltage of the extraction electrode or the suppression electrode is changed, the characteristics of the electrostatic lens parasitically formed between the extraction electrode and the suppression electrode change. Accuracy deteriorates.

[0007] The present invention has been made in view of such problems of the related art, and has as its object to provide a focused ion beam apparatus capable of processing a sample with high accuracy.

[0008]

(1) According to the present invention, a metal ion is extracted from a liquid metal attached to the tip of an emitter electrode by a concentrated electric field generated at the tip of the emitter electrode using an extraction electrode and a suppression electrode. The present invention relates to a focused ion beam apparatus for irradiating a sample with a metal ion using an ion optical system.

Voltage control means for fixing the voltage of the extraction electrode and controlling the voltage of the suppression electrode so that the current of the emitter electrode becomes constant, and a parasitic capacitance between the suppression electrode and the extraction electrode. In order to correct a change in the optical axis of the lens, a position adjusting means is provided for adjusting the position of the suppression electrode according to a voltage change of the suppression electrode. According to this device, the current of the emitter electrode can be made constant by controlling the voltage of the suppression electrode, and the optical axis change of the parasitic electrostatic lens accompanying the voltage change of the suppression electrode can be adjusted. Can be corrected. Therefore, the sample can be processed with high accuracy. (2) The focused ion beam device according to the present invention adjusts the voltage of the deflection electrode in the optical system according to the voltage change of the suppression electrode in order to correct the change of the ion beam irradiation position based on the change of the characteristic of the electrostatic lens. It is desirable to further include a deflection voltage correcting means for correcting.

Thus, the influence of the change of the optical axis of the electrostatic lens can be corrected, and the processing accuracy of the sample can be further improved. (3) Here, all or any of an aligner, a stig meter, and a deflector can be used as the deflection electrode. This makes it possible to improve the processing accuracy at low cost by using existing ion optical components. (4) In the focused ion beam device according to the present invention, in order to correct a change in the focal length of the electrostatic lens, an objective lens voltage correction for correcting the voltage of the objective lens in the optical system according to the voltage change of the suppression electrode. Desirably, means are further provided.

Thus, the influence of the change in the focal length of the electrostatic lens can be suppressed, and the processing accuracy of the sample can be further improved. (5) The focused ion beam device according to the present invention further includes condenser lens voltage correction means for correcting the voltage of the condenser lens in the optical system based on the current value detected by the stop means in the optical system. Is desirable.

By controlling not only the current of the emitter electrode but also the current detected by the aperture means in the optical system, the amount of ions actually supplied to the sample can be controlled with high precision. Therefore, the processing accuracy of the sample can be further improved.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the size, shape, and arrangement of each component are only schematically shown to an extent that the present invention can be understood, and numerical conditions described below are merely examples. .

1 to 3 are views showing the configuration of a focused ion beam apparatus 100 according to this embodiment. FIG. 1 is a schematic perspective view showing a main part mechanism of the focused ion beam apparatus 100, and FIG. FIG. 3 is an enlarged conceptual diagram illustrating a cross-sectional structure of the liquid metal ion source 110, and FIG. 3 is a block diagram illustrating an electrical configuration of the focused ion beam device 100. Liquid metal ion source 1
10, the needle 111 is provided in the coiled reservoir 1
11a and a needle-like emitter electrode 111b.
The reservoir 111a is used to hold a liquid metal, that is, an ionic material (not shown) in a molten state. When the liquid metal held in the reservoir 111a flows out,
A liquid metal film is formed on the surface of the emitter electrode 111b. Then, by generating a concentrated electric field at the tip of the emitter electrode 111b, metal ions are extracted from the liquid metal film at the tip. The needle 111 can be formed of, for example, tungsten. Gallium can be used as the ionic material, for example.

The filament 112 is connected to a current source 311a.
The needle 111 is heated by the electric current supplied from the needle 111 (indicated by reference numeral 311 in FIG. 3). Thereby, the ionic material such as gallium can be maintained in a molten state. Also, depending on the temperature of the filament 112, the emitter electrode 1
The thickness of the liquid metal film formed on the surface of 11b can be controlled. The magnitude of the emission current Ie also depends on this film thickness. The emission current Ie is measured by the ammeter 3
12 measured.

The base 113 includes a filament 112,
The holding electrode 114 described later is held. This base 113
Is formed of an insulating material such as glass. A low positive or negative suppression voltage Vsup is applied to the suppression electrode 114 by a voltage source 311b (indicated by reference numeral 311 in FIG. 3). In this embodiment, the intensity of the concentrated electric field generated at the tip of the emitter electrode 111b is adjusted by controlling the suppression voltage Vsup. Then, by such adjustment, the emission current Ie is controlled to a constant value. Further, the suppression electrode 114 is configured so that the driving mechanism 313 can adjust the position in the horizontal direction.

A voltage source 311c is connected to the extraction electrode 115.
(Indicated by reference numeral 311 in FIG. 3), for example, an extraction voltage Vext of several tens of kilovolts is applied. With this extraction voltage Vext, a very high concentrated electric field can be generated at the tip of the emitter electrode 111b. Then, metal ions are extracted from the liquid metal by the concentrated electric field.

The cathode 116 is connected to a voltage source 311d (FIG. 3).
In this case, it is connected to the negative terminal (indicated by reference numeral 311) and grounded. Thus, the potential difference between the cathode 116 and the emitter electrode 111b, that is, the acceleration voltage becomes Vacc. By the electric field generated by the accelerating voltage Vacc, metal ions extracted from the tip of the emitter electrode 111b are accelerated, and an ion beam 150 is formed.

Condenser lens 1 of ion optical system 120
21 forms a parallel beam by refracting the ion beam 150 by generating an electric field. The voltage of the condenser lens 121 is applied by a voltage source 321. Further, as described later, in this embodiment, the movable diaphragm 124 is controlled by controlling the refractive index of the condenser lens 121.
By adjusting the ion beam 150 flowing into the
Adjust the sample current.

The beam blanker 122 is used for the ion beam 1
When it is not desired to irradiate the sample 160 with 50, an electric field is generated to refract the ion beam 150. The voltage at beam blanker 122 is applied by voltage source 322.
The aligner 123 generates an electric field to generate the ion beam 1.
Adjust 50 axes. The voltage of the aligner 123 is applied by a voltage source 323.

The movable diaphragm 124 has a plurality of through holes having different diameters, and the diameter of the ion beam 150 is adjusted by using one of these through holes. The through holes used are
The position is selected by moving the position of the movable aperture 124 by the drive mechanism 324a. The current of ions flowing into the movable throttle 124 without passing through the through hole is measured by an ammeter 324b.
Is measured by

The stigmator 125 adjusts the beam shape so that the irradiation surface of the ion beam 150 becomes circular by generating an electric field. Stigmeter 125
Is applied by a voltage source 325. The objective lens 126 adjusts the focal length according to the strength of the electric field, and focuses the ion beam 150 on the surface of the sample 160. The voltage of the objective lens 126 is applied by a voltage source 326.

The deflector 127 scans the irradiation position of the ion beam 150 by an electric field. Deflector 12
The voltage of 7 is applied by a voltage source 327. Also,
The secondary electron detector 130 detects secondary electrons generated when the surface of the sample 160 is irradiated with the ion beam 150, and transmits the secondary electrons to the monitor 330. The gas gun 140 sprays the deposition gas and the etching gas supplied from the gas supply mechanism 340 on the surface of the sample 160.

The control unit 300 includes current sources 312 and 324b
, And the secondary electron detection result from the monitor 330. Then, based on these input values, the power supplies 311, 321-323, 324a, 325-327
And controls the mechanisms 312, 324 a, and 340. next,
The operation of the focused ion beam device 100 will be described.

First, the control unit 300 includes a driving mechanism 313,
324a to control the suppression electrode 114 and the movable diaphragm 1
24 is moved to a predetermined position. Next, the control unit 300
Controls each current source and voltage source to set the supply current and applied voltage to initial values. Thus, the emission of the ion beam 150 by the liquid metal ion source 110 is started.

Here, when the voltages Vsup and Vext are applied to the suppression electrode 114 and the extraction electrode 115, an electrostatic lens 200 is parasitically formed in the space between the suppression electrode 114 and the extraction electrode 115 (FIG. 2). reference). afterwards,
In the same manner as the conventional focused ion beam apparatus, the sample 160
, Microscopic observation, thin film deposition, thin film etching, and the like. When depositing or etching the sample 160, the gas supply mechanism 340 is controlled to start supplying gas to the sample 160.

When the use time of the liquid metal ion source 110 is extended, the emission current Ie fluctuates. Generally, when the usage time reaches a certain time, the emission current Ie starts to increase. As described above, the value of the emission current Ie is measured by the ammeter 312,
Sent to control unit 300. The control section 300 maintains the current Ie at the set value by adjusting the suppression voltage Vsup while the extraction electrode Vext is fixed.

In general, when the suppression voltage Vsup changes, the lens characteristics of the parasitic electrostatic lens 200 change accordingly. In this embodiment, the position of the suppression electrode 114 can be adjusted to suppress a change in the optical axis of the electrostatic lens 200 due to a change in the suppression voltage Vsup. This position adjustment is performed by the drive mechanism 313. Control unit 300
Controls the drive mechanism 313 such that the position adjustment is performed according to the amount of change in the suppression voltage Vsup. Suppression electrode 114
Is mainly performed in a direction perpendicular to the ion beam 150.

The control unit 300 performs one-point drift correction using the detection result of the secondary electrons. As described above, secondary electrons are detected by the secondary electron detector 130 and monitored by the monitor 330, and the detection result is sent to the control unit 300. The controller 300 corrects the deviation of the irradiation direction of the ion beam due to the change in the characteristic of the parasitic electrostatic lens 200 using the result of the detection of the secondary electrons. This drift correction can be performed, for example, by superimposing a correction voltage on voltages applied to the aligner 123 and the stigmator 125. Further, by superimposing the correction voltage on the applied voltage of the stig meter 125 and the deflector 127, or by superimposing the correction voltage on all of the applied voltages of the ion optical members 123, 125, and 127,
Drift correction can be performed.

Further, the control unit 300 controls the objective lens 12
The focal length of No. 6 is corrected. That is, the control unit 300
A change in the focus of the ion beam due to a change in the characteristics of the parasitic electrostatic lens 200 is corrected by superimposing a correction voltage on the voltage applied to the objective lens 126. In addition, the control unit 30
For 0, it is desirable to correct the voltage applied to the condenser lens 121 using the current value input from the ammeter 324b. That is, the control unit 300 corrects the voltage applied to the condenser lens 121 so that the current value of the ions flowing into the movable diaphragm 124 without passing through the through-hole does not change before and after the position adjustment of the suppression electrode 114. . By performing this correction, more accurate sample current control can be performed.

As described above, according to the focused ion beam apparatus 100 of this embodiment, the suppression voltage Vsu
Since the emission current Ie can be kept constant by controlling p, the sample current can be stabilized, and therefore, the accuracy of the deposition rate and the etching rate for the sample 160 can be improved.

Further, according to this embodiment, the position correction of the suppression electrode 114, the drift correction for the ion beam 150, and the focal length correction of the objective lens 126 are performed, so that the processing position accuracy accompanying the characteristic change of the parasitic lens 200 is achieved. Can be prevented from deteriorating. Aligner 1
By performing drift correction by using the 23, the stig meter 125, and the deflector 127, the correction can be performed inexpensively by using the ion optical member used in the conventional apparatus as it is.

Further, according to this embodiment, the sample current can be further stabilized by correcting the voltage applied to the condenser lens 121 using the current value of the ions flowing into the movable diaphragm 124. In addition, the accuracy of the deposition rate and the etching rate can be further improved.

[0034]

As described above in detail, according to the present invention, it is possible to provide a focused ion beam apparatus capable of processing a sample with high accuracy.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a configuration of a main part of a focused ion beam device according to an embodiment.

FIG. 2 is a conceptual diagram showing an enlarged cross-sectional structure of the liquid metal ion source shown in FIG.

FIG. 3 is a block diagram for explaining an electrical configuration of the focused ion beam device according to the embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 Focused ion beam device 110 Liquid metal ion source 120 Ion optical system 121 Condenser lens 122 Beam blanker 123 Aligner 124 Movable stop 125 Stigmeter 126 Objective lens 127 Objective lens 128 Deflector 130 Secondary electron detector 140 Gas gun 150 Ion beam 160 Sample

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Claims (5)

[Claims] 1. A concentrated electric field generated at the tip of an emitter electrode using an extraction electrode and a suppression electrode extracts metal ions from a liquid metal attached to the tip of the emitter electrode, and the metal ions are extracted using an ion optical system. A focused ion beam device that irradiates the sample with a voltage, wherein the voltage of the extraction electrode is fixed, and the voltage of the suppression electrode is controlled so that the current of the emitter electrode is constant. Position adjusting means for adjusting the position of the suppression electrode in accordance with a change in the voltage of the suppression electrode, in order to correct a change in the optical axis of the electrostatic lens parasitic to the extraction electrode. Focused ion beam device. 2. A deflection voltage correction for correcting a voltage of a deflection electrode in the optical system according to a voltage change of the suppression electrode in order to correct a change in an ion beam irradiation position based on a change in characteristics of the electrostatic lens. 2. The focused ion beam apparatus according to claim 1, further comprising: means. 3. The focused ion beam apparatus according to claim 2, wherein the deflection electrode includes at least one of an aligner, a stig meter, and a deflector. 4. An objective lens voltage correcting means for correcting a voltage of an objective lens in the optical system according to a voltage change of the suppression electrode in order to correct a change in a focal length of the electrostatic lens. The focused ion beam device according to claim 1, wherein: 5. A condenser lens voltage correcting means for correcting a voltage of a condenser lens in the optical system based on a current value detected by a diaphragm means in the optical system. Item 5. The focused ion beam device according to any one of Items 1 to 4.