JP2000182557A - Charged particle beam device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently guide the secondary charged particles to a secondary charged particle detecting unit provided between a sample and an objective lens by applying the voltage having the same polarity with the secondary charged particles generated by the irradiation of the charged corpsular beam to the sample to an electrode under the sample and the objective lens or an electrode forming the objective lens. SOLUTION: A voltage at -20 V is applied to a stage 18 to be loaded with a solid sample, and a voltage at -50 V is applied to a sample side lens electrode of an objective lens 4 using an Einzel lens for electrostatic lens. An electrode 17 for drawing the secondary electron is provided immediately under the objective lens 4, and a voltage at +50 V is applied to the electrode 17, and a coil 19 for generating the magnetic field vertical to the beam incident direction of the drawing electrode 17 is provided, and the current to be flowed to the coil 19 is adjusted in response to the voltage to be applied to the drawing electrode 17, and the secondary electron drawn by the drawing electrode 17 is guided in a micro channel plate MCP direction. With this structure, return of the secondary electron to the sample is prevented even if the sample is charged, and the secondary electron is drawn to the drawing electrode 17, and bent by the magnetic field, and the secondary electron is detected without lowering the detection efficiency even in the case of a low-detecting-voltage type MCP.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charged particle beam apparatus capable of detecting secondary charged particles generated by charged particle beam irradiation with high efficiency, and more particularly to an ion beam irradiation apparatus such as an ion beam irradiation apparatus. The present invention relates to an apparatus that requires a secondary charged particle detector between a sample and an objective lens.

[0002]

2. Description of the Related Art In recent years, electron beams and ion beams have been actively applied in a variety of industries. Especially recently,
Focused ion beam (FI) using a liquid metal ion source
B) Since the device can obtain a high current and a fine beam,
Semiconductor device wiring repair equipment, failure analysis equipment, TEM /
It is widely used as a processing machine such as an SEM sample preparation device.

[0003] Further, there has been developed an apparatus utilizing a feature that lithography, ion implantation, etching, and the like in a semiconductor manufacturing process can be performed without using a mask (maskless). Furthermore, when FIB is applied to the so-called secondary ion mass spectrometry, which irradiates the sample surface with an ion beam and analyzes secondary ions ejected by sputtering, component analysis in the submicron region of the sample surface becomes possible. Become. As described above, FIB technology is applied in a wide variety of fields, and the market is expected to further expand in the future. As the charged particle detector of these devices, the detector of the FIB device is
Since it is necessary to switch the electron and ion particles appropriately for detection, an MCP (micro channel plate) is generally used as a detector. On the other hand, detectors for electron beam applied devices are mainly detectors that combine a scintillator and a photomultiplier, but the amplification factor, dark current, and response speed are the same as those of a photomultiplier, but they are compact and generate electrical signals without passing through the photomultiplier. MCPs are also widely used because they can be taken out directly from a vacuum.

The MCP has a thin plate-like structure in which a large number of microtube-shaped electron multipliers are assembled, and is used so that secondary charged particles generated by a primary beam are attracted by an MCP pre-stage voltage. The secondary charged particles accelerated by the pull-in voltage collide with a microtube-shaped electron multiplier and generate many electrons. The electrons are further amplified in an avalanche manner while being accelerated by a voltage called an interstage voltage, and an electrode for receiving the amplified electrons is provided at the end of the MCP and detected as a current. This is the principle of operation of the MCP.

[0005]

SUMMARY OF THE INVENTION The present invention solves the following problems in order to improve the detection efficiency of secondary charged particles.

[0006] In an ion beam irradiation apparatus, which is one of charged particle beam apparatuses, a secondary charged particle detector is generally arranged below an objective lens (on the sample side). This is for the following reason.

In general, an electrostatic electron lens is used for an ion beam irradiation apparatus. This is because a magnetic field type electron lens having a low refractive power is not suitable for ions having a larger mass than electrons.

This electrostatic electron lens is formed by laminating a plurality of electrodes in the direction of the optical axis of a charged particle beam, and a certain potential is applied to a certain electrode. This strong potential attracts or repels the secondary charged particles trying to pass through the lens, and acts to prevent the passage of the secondary charged particles in the electrostatic electron lens. Therefore, it is practically difficult to dispose the secondary charged particle detector on the objective lens (on the charged particle source side). Under such circumstances, in the ion beam irradiation apparatus, the detector is arranged between the objective lens and the sample, but has the following problems.

In the electrostatic electron lens, since a voltage is applied to the electrodes constituting the lens, depending on the applied voltage,
There is a problem that the secondary charged particles are wound up on the objective lens.

If the distance between the sample and the objective lens is increased in order to eliminate such adverse effects, the focal length of the objective lens increases, and the lens aberration (particularly, chromatic aberration) and the lens magnification increase. For this reason, there is a problem that the minimum beam diameter increases and the resolution of the device deteriorates.

On the other hand, a scintillator detector, which is one of the detectors for detecting secondary charged particles, can increase the detection efficiency by applying a secondary electron attraction voltage of up to about 10 kV. However, when cross-section observation is performed, secondary charged particles do not come out of the depth of the cross-section to the region where the pull-in voltage of the detector acts (the upper surface of the sample). This is not a problem limited to the scintillator detector, and the same applies to a detector employing the MCP.

Further, in the case of the MCP detector, unlike the scintillator, there are optimum conditions for the voltage of the secondary charged particles and the amplification factor of the detector, so that the voltage cannot be increased carelessly. Therefore, there is a problem that a sufficient pull-in voltage cannot be applied.

[0013] It is an object of the present invention to provide a charged particle beam apparatus which can eliminate the above-mentioned factors which lower the detection efficiency in an apparatus for detecting secondary charged particles under an objective lens.

[0014]

According to the present invention, in order to achieve the above object, a charged particle source and an objective lens for focusing a charged particle beam emitted from the charged particle source and irradiating the sample with a focused particle beam are provided. In a charged particle beam device equipped with a secondary charged particle detector that detects secondary charged particles generated due to irradiation of the charged particle beam on the sample, the sample, the secondary charged particle detector A first voltage applying means for applying a voltage having the same polarity as the polarity of the secondary charged particles to be detected; and an electrode disposed below the objective lens or an electrode constituting the objective lens, A second voltage applying unit that applies a voltage having the same polarity as the polarity of the particles; the secondary charged particle detector includes a suction mechanism that suctions the secondary charged particles; Characterized by being arranged in It is to provide a charged particle beam device.

According to such a configuration, the secondary charged particles generated from the sample can be efficiently guided to the secondary charged particle detector. According to the above configuration, an electrode disposed below the objective lens, or an electrode configuring the objective lens,
A voltage having the same polarity as the charged particles generated in the sample is applied to each of the samples.

By creating such a state,
The secondary charged particles generated in the sample are not drawn into the aperture of the objective lens.
The secondary charged particles are not attracted to the sample. That is, a series of passages are formed from the secondary charged particle generation source to the secondary charged particle detector, thereby improving the detection efficiency of the secondary charged particle detector.

In order to achieve the above object, the present invention provides a charged particle beam having a charged particle source and an objective lens for focusing charged particles emitted from the charged particle source and irradiating the charged sample with a sample. In the apparatus, an accelerating electrode for accelerating secondary charged particles generated due to irradiation of the sample with a charged particle beam, and the secondary charged particles accelerated by the accelerating electrode, the objective lens and the sample A charged particle beam device comprising a magnetic field deflector that deflects a secondary charged particle detector disposed therebetween.

According to such a configuration, the secondary charged particles can be accelerated by the potential difference between the sample and the accelerating electrode, and the accelerated secondary charged particles are deflected by the magnetic field deflector, It is possible to introduce secondary charged particles into the secondary charged particle detector while maintaining a high acceleration voltage. In particular, in the case of the MCP detector, the secondary charged particles can be introduced into the secondary charged particle detector in a highly accelerated state without breaking the optimum conditions of the pull-in voltage.

The magnetic field generated by the magnetic field deflector can also eliminate the adverse effect that secondary charged particles generated in the sample are drawn in the direction of the objective lens opening.

In particular, the surface of an insulator sample is polarized under the influence of the accelerating electrode and has a positive or negative charge. This works to efficiently guide the secondary electrons in the deep section to the sample surface, and the secondary charged particles that have come out of the surface are strongly affected by the intake electrode and go to the secondary charged particle detector. Therefore, it can be introduced into the secondary charged particle detector in a state where it has been once accelerated to a desired acceleration voltage.

A voltage having the same polarity as that of the secondary charged particles detected by the secondary charged particle detector is applied to the sample,
By applying a voltage having the same polarity as the polarity of the secondary charged particles to an electrode disposed below the objective lens or an electrode constituting the objective lens, and employing the acceleration electrode and the magnetic field deflector, the secondary Needless to say, the efficiency of detecting charged particles is further improved.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In general, the energy distribution of secondary electrons generated by irradiation of an electron or ion beam is not completely coincident as shown in FIG.
It has a peak at V and extends to about 50 eV. Further, this distribution does not depend on the energy of the electrons irradiating the individual sample or the type of the individual sample. The emission direction of the generated secondary electrons changes in intensity according to the COS rule (FIG. 2) with respect to the angle starting from the direction perpendicular to the surface, and the above energy is superimposed on this.

Therefore, in order to obtain good secondary electron detection efficiency, a pull-in voltage to the detector of about several eV is required near the secondary electron generation point. However, when there is a portion of the GND potential between the detector and the secondary electron generation point, the pull-in voltage of the detector is obstructed by the GND potential, and a large drop-in voltage to the detector near the secondary electron generation point. And it is difficult to generate.

Therefore, the detection efficiency of the apparatus changes strongly depending on the mounting position of the detector and the structure around the secondary electron generation point. Furthermore, even if the structure is not disturbed by the GND potential, if the detector is released from the secondary electron generation point, the detection efficiency depends on the boundary condition but becomes worse in inverse proportion to the square of the distance. .

The case of a focused ion beam apparatus will be described with reference to FIG.

The ion beam 2 extracted from the Ga liquid metal ion source 1 is accelerated to 30 kV, passes through a beam limiting aperture 3, is focused by an objective lens 4, and irradiates a sample 5. The ion beam is controlled by a deflection control 6 so as to scan the sample in a plane, and is scanned by a deflector 7. At this time, the secondary electrons 8 generated from the sample 5 are detected by the detector 9 and amplified,
The detection signal of the detector 9 is luminance-modulated in synchronization with the deflection signal of the deflection control 6 and displayed on the CRT 10.

Since an ion beam has a large sputtering effect unlike an electron beam, it can be used for fine processing. for that reason,
The ion beam device is used as a processing machine.

In the case where the processed sample is an individual insulator, it is necessary to suppress the charging of the sample during the processing in order to accurately process the insulator. For this reason, the processing position is positively irradiated with a low-acceleration electron beam to suppress charging of the sample. In this case, in the electron image, the irradiation electron and the secondary electron signal are mixed, so the processing location is confirmed and the processing result is observed in the secondary ion image.

Further, if a fluorescent plate is used as the detector, the fluorescent plate is contaminated with ions or destroyed by sputtering, so that the luminous efficiency of the fluorescent plate deteriorates. Therefore, the fluorescent plate cannot be used as a light emitter of the detector. For this reason, an MCP that can selectively detect ions and electrons by switching the pull-in voltage is used.

On the other hand, secondary electrons can be detected without any problem using a detector or a fluorescent plate or using an MCP.

FIG. 4 shows an embodiment of a conventional detector using an MCP.

An MCP 11 was used for the secondary electron 8 detection surface, and a fluorescent plate 12 was provided at the subsequent stage. The secondary electrons 8 are MCP1
The light is drawn by the voltage applied to the light-incident surface 1 and collides with the MCP 11, and passes while repeating the collision. The electrons 13 that have passed through the MCP 11 in an increased number are accelerated by the scintillator voltage and irradiate the fluorescent screen 12. The electrons 13 are converted into light by collision with the scintillator, and the light is extracted outside the vacuum by the light guide 14.

The light is detected by the photomultiplier 15 and further amplified and returned to an electric signal. In the configuration of the detector of this embodiment, a sufficiently bright signal can be taken out in one stage of the MCP even if the beam current is 1 pA.

In this configuration, in order to optimize the amplification factor of the MCP, the front voltage of the MCP needs to be <1 kV. However, at this voltage, particles with a low secondary electron pull-in voltage and high energy, and particles whose direction jumps in the opposite direction to the detector cannot be detected. That is, the voltage applied to the MCP has an optimum value for secondary electron detection due to the trade-off relationship between the amplification factor of the MCP and the detection efficiency, and the detection efficiency is limited in this sense.

Further, there is an MCP having an annual type in which a hole is formed in the center of the MCP, and the MCP can be attached directly below the objective lens without disturbing the ion beam. In this case, high detection efficiency can be obtained even at a low pull-in voltage close to the beam incident point. However, in recent years, the beam has been miniaturized, and the lens working distance has been shortened as much as possible to narrow the beam using a lens having a short focal length. In this case, one of the problems is that it has become difficult to mount the MCP directly below the objective lens.

A detector in which the MCP is excluded from the present detector is as follows:
Although a relatively clear image can be obtained even when a cross section of a sample such as a semiconductor sample that is partially charged is observed, it is necessary to apply a voltage of 6 to 9 kV to the fluorescent plate.

In particular, since the semiconductor sample has a layered structure of an insulator and a metal wiring, charges are likely to accumulate in the insulating layer when observing a cross section, and are charged negatively by electron irradiation and positively charged by ion irradiation. For this reason, a portion having a different potential is generated between the metal layer and the insulating layer in the cross section, the 0 potential portion is bright, the + charged portion and the -charged portion are darkened, a potential contrast occurs, and the brightness of the image is increased.

Further, secondary electrons from a deep portion of the cross section are easily trapped in a portion charged to +. Under such circumstances, secondary electrons do not emerge on the sample surface, and the detection efficiency is extremely reduced.

The present invention has solved these problems. An embodiment of the present invention will be described with reference to FIG.

A mechanism 16 for spontaneously emitting secondary electrons to the surface of the sample was provided in order to actively take out the secondary electrons generated in the deep part of the individual to the surface of the sample. For this, a stage 18 on which an individual sample was placed and a mechanism for setting the stage and the individual sample to the same potential were provided. The objective lens 4 was provided with a mechanism capable of applying a voltage to the lens electrode 41 on the sample side using an Einzel lens as an electrostatic lens.

A voltage of −20 V was applied to the stage 18 and a voltage of −50 V was applied to the lens electrode 41. An electrode 17 for drawing secondary electrons is provided directly below the objective lens.
7 was applied with +50 V. Further, a coil 19 for generating a magnetic field perpendicular to the direction of incidence of the beam was provided.

The current flowing through the coil 19 was adjusted in accordance with the voltage applied to the pull-in electrode 17 so that the secondary electrons just drawn in by the pull-in electrode 17 were guided toward the MCP detector.

As a result, even when the sample is positively charged, the secondary electrons are drawn into the lead-in electrode and bent by the magnetic field without returning to the sample, so that the MCP having a low detection voltage is used. Could be detected without lowering the detection efficiency.

Further, even in the case of a negatively charged sample, secondary electrons are usually attracted to the GND potential near the secondary electron generation point, making detection difficult. , There is a pull-in electrode near the secondary electron generation point,
In addition, since there is no GND potential near the secondary electron generation point, the secondary electrons are reliably guided to the lead-in electrode and are bent by the magnetic field, so that the detection efficiency is reduced even if an MCP having a low detection voltage is used. Could be detected.

The combination of these mechanisms is selective, and the selection can increase the detection efficiency with a simpler mechanism.

Also, as shown in FIG. 6, the secondary electrons whose energy has been adjusted by the pull-in electrode 17 can be guided to the detector 9 by drawing a specific orbit in the magnetic field B section 20.

In addition, as shown in FIG. 7, it is possible to draw a specific trajectory toward the detector 9 using the electric field E unit 21.

The ease with which a charged particle bends due to a magnetic field is inversely proportional to 積 of the product of the energy and the mass of the charged particle. Thus, for example, in the case of Ga ions of 30 kV, the magnetic field for forming a bend having the same radius of curvature is about 19,600 times that of 10 eV electrons for Ga ions. Therefore, even if a magnetic field is generated to bend secondary electrons just below the objective lens, there is no effect on the primary beam.

Also, the ease with which the charged particles bend due to the electric field is proportional to the energy of the charged particles. Therefore, in the case of a secondary beam of about 50 eV and a primary beam of 30 kV, Ga ions are used at a voltage that can control the secondary electrons. Is approximately 3000 times smaller than the secondary electrons, and is hardly affected by the primary beam.

That is, when the primary beam is a Ga ion beam of 30 kV, the detection efficiency can be increased without being affected by a voltage or a magnetic field that is sufficient to control the secondary electrons. The following effects can be obtained by utilizing these principle effects.

In addition to the detector, a negative voltage (-Vs) is applied to the sample, and an electrode is provided on the surface facing the sample, similarly to the negative voltage (-Vobj).
) Is applied. This electrode may be a part of an objective lens. However, 0 <Vs <Vobj.

In this case, the secondary electrons generated by the irradiation of the primary beam do not return to the sample unless the sample is charged.
Also, there is no absorption by the objective lens. In other words, in this situation, there is no potential gradient near the secondary electron generating portion where secondary electrons flow.

For this reason, secondary electrons flow on the GND side, but if there is a detector, the secondary electrons change their traveling direction under the action of the pull-in voltage of the detector and are detected by the detector. This method has a simple configuration and can reduce the distance between the objective and the sample. Even if the detector is placed between the objective lens and the sample, the detection can be performed without lowering the detection efficiency. Furthermore, an electrode for taking in secondary electrons is attached immediately below the objective lens, and a voltage is applied. The energy of secondary electrons is adjusted by this electrode, and a magnetic field perpendicular to the primary beam is applied to bend the traveling direction of the secondary electrons. The traveling direction at this time is set so as to proceed to a region where the pull-in voltage of the detector acts strongly.
For this purpose, the magnetic field strength is adjusted according to the take-in voltage in order to optimize the bending trajectory of the secondary electrons.

In this case, the surface of the insulator sample is polarized and positively affected by the voltage applied. Due to this effect, the secondary electrons in the deep section are guided to the sample surface, and are strongly influenced by the capture electrode, and travel from the sample to the upper capture electrode without going to the detector. In this process, the electrons are accelerated to the take-in voltage.
Thereafter, a magnetic field is applied so as to bend and extract to the extent of the action of the detector when entering the area where the magnetic field reaches.

By using the MCP, it is possible to avoid the problem of reduced charged particle detection efficiency, which has been a problem.

To summarize the above, charged particles (signals) under conditions where the drawing voltage does not reach the bottom of the cross-section (deep hole) even if the MCP detector is used and the distance between the sample and the MCP is large However, sufficient detection efficiency can be obtained. Further, even with a detector other than the MCP, the detection efficiency can be increased by the same means.

[0057]

According to the present invention, it is possible to detect secondary charged particles with high efficiency, particularly in a charged particle beam apparatus in which a secondary charged particle detector is arranged between a sample and an objective lens. Become.

[Brief description of the drawings]

FIG. 1 shows secondary electron energy distribution.

FIG. 2 is a COS rule of emitted electrons.

FIG. 3 is a focused ion beam apparatus.

FIG. 4 is an embodiment of a conventional detector.

FIG. 5 shows an embodiment of the present invention.

FIG. 6 shows another embodiment.

FIG. 7 shows another embodiment.

[Description of Signs] 1 ... Ion source, 2 ... Ion beam, 3 ... Beam limiting aperture, 4 ... Objective lens, 5 ... Sample, 6 ... Deflection control, 7
... deflector, 8 ... secondary electron, 9 ... detector, 10 ... CRT,
11: MCP, 12: Fluorescent plate, 13: Electron, 14: Light guide, 15: Photomaru, 16: Mechanism of spontaneous emission of secondary electrons to the surface, 17: Drop-in electrode, 18: Stage,
19: coil, 20: magnetic field B part, 21: electric field E part.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G032 AA00 AB20 AF08 5C033 NN01 NP01 5C034 AA02 AA09 5F004 BA11 CB05 DB00

Claims (9)

[Claims] 1. A charged particle source, an objective lens for converging a charged particle beam emitted from the charged particle source and irradiating the sample with a charged particle beam, and an objective lens generated by the irradiation of the sample with the charged particle beam In a charged particle beam device provided with a secondary charged particle detector for detecting secondary charged particles, a voltage having the same polarity as the polarity of the secondary charged particles detected by the secondary charged particle detector is applied to the sample. And a second voltage applying means for applying a voltage having the same polarity as the polarity of the secondary charged particles to an electrode disposed below the objective lens or an electrode constituting the objective lens. Means, wherein the secondary charged particle detector has a suction mechanism for sucking the secondary charged particles, and is disposed between the sample and the objective lens. 2. A charged particle beam apparatus according to claim 1, wherein said objective lens is an electrostatic electron lens. 3. A charged particle beam apparatus according to claim 2, wherein said charged particle beam is an ion beam. 4. An accelerating electrode for accelerating secondary charged particles according to claim 2, wherein an electrode arranged under the objective lens or an electrode constituting the objective lens and the sample are arranged. And a magnetic field deflector for deflecting the accelerated secondary charged particles to the secondary charged particle detector. 5. The charged particle beam apparatus according to claim 4, wherein said secondary charged particle detector includes a channel plate. 6. A charged particle beam apparatus according to claim 1, wherein a voltage applied by said second voltage applying means is higher than a voltage applied by said first voltage applying means. . 7. A charged particle beam apparatus comprising: a charged particle source; and an objective lens for focusing charged particles emitted from the charged particle source and irradiating the charged particle beam to a sample. An accelerating electrode for accelerating secondary charged particles generated due to the accelerating electrode, the secondary charged particles accelerated by the accelerating electrode, a secondary charged particle detector disposed between the objective lens and the sample A charged particle beam device comprising a magnetic field deflector for deflecting. 8. A charged particle beam apparatus according to claim 7, wherein said secondary charged particle detector includes a channel plate. 9. A charged particle beam apparatus according to claim 7, wherein said objective lens is an electrostatic electron lens.