JPH11213936A - Fib-sem device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a FIB-SEM device enabling worked depth of FIB(focused ion beam) working to be monitored on a real-time basis by means of a SEM (inline-type scanning electron microscope) image. SOLUTION: An ion beam from a FIB column and an electron beam from a SEM column are applied at the same time on a sample, and the sample is worked by the ion beam, and if an image of the sample is monitored at the same time by means of the electron beam, a negative voltage is applied from a power supply 34 to a mesh electrode 31 by a switch 33. As a result, only elastically scattering electrons and non-elastically scattering electrons of high energy based on the irradiation of electrons to the sample are detected by a detector 15. By introducing a detection signal from the detector 15 into a cathode-ray tube, an image obtained by a scanning electron microscope function can be displayed on the cathode-ray tube, and an image of a cross-section of the sample can be monitored by a SEM even in the midst of working of the sample by a FIB.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a FIB-SEM apparatus for processing a sample by irradiating it with a focused ion beam and observing the processed cross section with a scanning electron microscope function.

[0002]

2. Description of the Related Art FIB-Focused Io
The n Beam) device is a device that focuses an ion beam from an ion source finely, irradiates the processed sample with light, and processes the sample by etching or the like. Among the application fields of the FIB apparatus, the etching technique using the FIB has become quite popular.

[0003] FIB apparatuses using this technique are widely used not only for micromachining, but also for failure analysis of semiconductor devices and preparation of transmission electron microscope samples. In particular, it is becoming an indispensable device for three-dimensional analysis of a semiconductor device that has received the most attention. At present, a dual beam (Dual Beam-) which adds a FIB function to a conventional in-line scanning electron microscope (SEM) device is now available.
DB) devices are also gradually spreading.

[0004] The DB apparatus is a composite apparatus which can perform a process of etching a conventional FIB apparatus, transferring a sample to an SEM apparatus, and observing the sample, in order to correspond to a semiconductor failure analysis apparatus.

[0005] In the same manner as in a normal FIB single function machine, an ion beam is irradiated on the upper surface of a sample to etch an arbitrary place, and after the processing is completed, the etching process is immediately performed without moving the sample. This has the advantage that the cross section can be observed with an SEM image. As a result, tremendous power for failure analysis and shortening of the process time, yield management and speed associated therewith, floor area reduction and price reduction due to complex equipment are expected, etc. Is expected to advance.

The configuration of the above-mentioned FIB-SEM apparatus is roughly divided into a FIB control section, an SEM control section, and a control section for a stage on which a sample is placed, and each of them is controlled by a host computer. In this device, usually, the sample is etched by applying an ion beam from above the sample in the vertical direction,
An electron beam is applied to the cross section of the hole at an angle of 30 ° from the sample surface, and the structure of the cross section is observed. The sample processed by the ion beam creates a cross section perpendicular to the sample surface,
The cross section depends on the current amount of the ion beam and the probe diameter, but is cut out almost perpendicular to the sample surface.

In this FIB-SEM apparatus, as described above, immediately after processing by the FIB, the SEM is performed without moving the sample.
Not only the merit of observing, but also FIB
It has the feature that the progress of processing by FIB and the state of the depth of a processing hole, which were impossible with a single machine, can be monitored from the side by SEM.

The outline of the processing depth monitoring function that is provided as standard in the current apparatus is as follows. First, after setting a processing area, a processing size, and a scanning speed on the processing parameter screen, SIM or SEM is selected as a processing depth monitor. For example, SEM is selected as a processing depth monitor and processing is started.

After the processing area is scanned once by FIB (one frame), the mode is switched to the SEM image observation mode. The processing area is scanned an arbitrary number of times at the television scanning speed by the SEM, and the images are integrated and stored in the memory.

After the SEM image capture is completed, the processing scan of the sample is started again by the FIB. Thereafter, the processing is performed to an arbitrary depth (arbitrary time) while repeating processing by the FIB and taking in the SEM image. Here, the captured S
Observe the EM image, and when the processing progresses to a sufficient depth, the FIB
Stop processing by.

When the SIM is selected as the machining depth monitor, the SIM is not taken in but the SIM is taken.
(Scanning ion microscope) Capture an image. If the processing depth monitor is turned off, the processing is continuously performed.

[0012]

However, the above-mentioned F
The IB-SEM apparatus has a problem in that, when monitoring the processing depth based on the SEM image, the entire processing time becomes longer because the SEM image needs to be captured, and the processing speed becomes relatively slow.

That is, the cause of such a problem is the FI
When the sample is irradiated with an electron beam during the B-processing scan and the SEM image is captured, the intensity of the processed region becomes too high due to the increase in the secondary electron signal due to both beams, making observation difficult. One beam cannot be scanned, and irradiation of the FIB to the sample is stopped during monitoring of the SEM image.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a FIB capable of monitoring a processing depth of FIB processing in real time by using an SEM image.
-To realize a SEM device.

[0015]

An FI based on the first invention is provided.
The B-SEM apparatus has a FIB function of irradiating a sample with a focused ion beam and an SEM function of irradiating an electron beam on a cross section of the sample processed by the focused ion beam and observing a scanning electron microscope image. In the SEM device, a detector is provided for selectively detecting inelastic scattered electrons and elastic scattered electrons having relatively high energy among signals generated from the sample by simultaneous irradiation of the focused ion beam and the electron beam. It is characterized in that a scanning electron microscope image is displayed based on a signal from the detector.

In the first invention, a detector for selectively detecting inelastic scattered electrons and elastic scattered electrons having relatively high energies among signals generated from a sample by simultaneous irradiation of a focused ion beam and an electron beam. And a scanning electron microscope image is displayed based on the signal from the detector.

According to a second aspect, in the first aspect, the detector has a double mesh electrode, and a positive voltage is applied to an electrode of the mesh electrode close to the sample, and a positive voltage is applied to the other electrode. Alternatively, a negative voltage can be selectively applied, and when detecting inelastic scattered electrons and elastic scattered electrons having relatively high energy, a negative voltage is applied to the other electrode.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a diagram of F according to the present invention.
1 shows an IB-SEM apparatus, where 1 is a FIB column,
2 is an SEM column. In FIB column 1,
An ion gun 3, a focusing lens 4 for focusing an accelerated ion beam generated from the ion gun 3, an objective lens 5, and a deflector 6 for two-dimensionally scanning the ion beam are provided. The focusing lens 4 and the objective lens 5 for the ion beam are mainly electrostatic lenses.

The ion beam generated from the ion gun 3 is
The focusing lens 4 and the objective lens 5 narrowly focus on the sample 7, and the irradiation position of the ion beam irradiated on the sample 7 can be scanned by the deflector 6. These focusing lens 4, objective lens 5, deflector 6
Is controlled by the FIB control unit 8.

For example, when the current amount of the ion beam irradiated on the sample 7 is changed, the focusing lens 4 and the objective lens 5 are controlled by the FIB control unit 8, and the intensity of each lens is controlled to control the intensity of the ion beam. The degree of convergence is changed to control the amount of the ion beam passing through a stop (not shown) provided in the optical path of the ion beam. When the ion beam is two-dimensionally or linearly scanned on the sample, a scanning signal is supplied from the FIB control unit 8 to the deflector 6.

The SEM column 2 has an electron gun 9 and a focusing lens 1 for focusing an electron beam generated from the electron gun 9.
0, an objective lens 11, and a deflector 12 for two-dimensionally scanning the electron beam.

The electron beam generated from the electron gun 9 is narrowly focused on the sample 7 by the focusing lens 10 and the objective lens 11, and the irradiation position of the electron beam irradiated on the sample 7 can be scanned by the deflector 12. It is configured as follows. The focusing lens 10, the objective lens 11, and the deflector 12 are controlled by the SEM control unit 13. In addition,
Electromagnetic lenses are mainly used for the focusing lens 10 and the objective lens 11 for the electron beam.

For example, when the current amount of the electron beam irradiated on the sample 7 is changed, the focusing lens 10 and the objective lens 11 are controlled by the SEM control unit 13, and the intensity of each lens is controlled to control the intensity of the electron beam. Changing the degree of convergence,
The amount of the electron beam passing through a stop (not shown) provided in the optical path of the electron beam is controlled. When the electron beam is two-dimensionally or linearly scanned on the sample, a scanning signal is supplied from the SEM control unit 13 to the deflector 6. The SEM controller 13 and the FIB controller 8 are controlled by a host computer 14.

Secondary electrons generated from the sample by irradiating the sample 7 with an electron beam or an ion beam are detected by a secondary electron detector 15. The signal detected by the detector 15 is amplified by the amplifier 16,
It is supplied to the cathode ray tube 17 via the host computer 14.

The sample 7 is placed on a stage 18. The stage 18 is configured to be capable of two-dimensional movement, rotation, and tilt in the horizontal direction by a stage control unit 19. The stage control unit 19 controls the host computer 14
Is controlled by The operation of such a configuration will now be described.

First, the sample 7 is processed by the FIB. This sample was processed by the ion gun 3 in the FIB column 1.
An ion beam is generated from the laser beam, and the ion beam is narrowly focused on the sample 7 by the focusing lens 4 and the objective lens 5, and the ion beam is linearly scanned by the deflector 6. At this time, the sample stage 18 is moved in a direction perpendicular to the direction of the linear scanning of the ion beam.

FIG. 2 shows this state. The sample 7 is slowly moved in the direction opposite to the arrow S, while the ion beam IB is scanned in a line in a direction perpendicular to the plane of the drawing. At this time, the current amount of the ion beam IB is, for example, about 1000 pA in order to maintain a large processing rate. As a result, a rectangular opening 20 is formed in the sample 7. The depth of the opening 20 depends on the current amount of the ion beam,
It depends on the scanning speed of the ion beam and the moving speed of the sample.

In an ordinary FIB-SEM apparatus, after the opening 20 for the sample 7 is formed, the S
The electron beam EB is emitted from the EM column 2 and the electron beam is two-dimensionally scanned at the cross section D. Secondary electrons generated from the cross section D based on this scanning are detected by the secondary electron detector 15. Since this detection signal is supplied to the cathode ray tube 17, a scanning electron microscope image of the cross section D is obtained on the cathode ray tube 17.

When a sample is irradiated with an ion beam, signal particles generated from the sample include neutral particles, positive ions,
These are negative ions and secondary electrons. The energies of these signal particles are 0 to 100 as shown in FIG.
eV and secondary electrons not shown in FIG. 3 are about 0 to several eV.

On the other hand, when the sample is irradiated with an electron beam, signals generated from the sample include secondary electrons, elastic scattered electrons (reflected electrons), and inelastic scattered electrons. As shown in FIG. 4, the energies of these signals are as follows: the secondary electron energy is the same as that in the case of ion irradiation; 0 to several eV, inelastic scattered electrons are several eV to less than the primary electron beam energy, and elastic scattered electrons are primary Equal to the electron beam energy.

FIG. 5 shows an example of a secondary electron detector commonly used. The detector includes a scintillator 21 that emits light by irradiation with electrons, a light guide 22 that transmits light from the scintillator 21, and a photomultiplier tube 23 that converts light from the light guide 22 into electrons and amplifies them. Is provided with a mesh-shaped collection electrode 24 on the front surface. A high positive voltage is applied to the scintillator 21 from a power supply 25 and
, A positive voltage is applied from the power supply 26.

In such a detector, the collecting electrode 24
Is applied with a positive voltage of several tens of volts, and the electrodes 24 efficiently collect secondary electrons. The secondary electrons collected by the electrode 24 are accelerated toward the scintillator 21 and collide with the scintillator, causing the scintillator 21 to emit light. The light from the scintillator 21 enters the photomultiplier tube 23 via the light guide 22, and the electrons are multiplied according to the intensity of the light.

Now, in the detector shown in FIG. 5, when the ion beam and the electron beam are simultaneously irradiated on the sample,
Secondary electrons generated by the ion beam and secondary electrons generated by the electron beam are similarly detected.
Therefore, as the detector 15 in the apparatus shown in FIG. 1 based on the present invention, the detector having the configuration shown in FIG. 6 is used.

In FIG. 6, the same components as those of the conventional detector of FIG. 5 are denoted by the same reference numerals. In the detector 15 of FIG. 6, double mesh electrodes 30 and 31 are arranged on the front surface of the scintillator 21. A positive voltage is applied to the mesh electrode 30 on the sample side, and a positive or negative voltage can be switched and applied to the mesh electrode 31 on the scintillator 21 side.

That is, the power source 32 is connected to the mesh electrode 30.
And a positive voltage of several tens V is applied. The mesh electrode 31 is connected to a power supply 32 for generating a positive voltage or a power supply 34 for generating a negative voltage (−several tens of volts) via a switch 33.

For example, when the mesh electrodes 30 and 31 are connected to the power supply 32 by the switch 33 and a positive voltage is applied to both the electrodes 30 and 31, secondary electrons generated from the sample can be obtained.
Negative ions, inelastic scattered electrons, and elastic scattered electrons pass through the mesh electrodes 30 and 31 and collide with the scintillator 21 to be detected.

On the other hand, when the switch 33 is switched and the mesh electrode 31 is connected to the power source 34, positive ions generated from the sample are eliminated by the mesh electrode 30 on the sample side. Further, secondary electrons and negative ions from the sample can pass through the mesh electrode 30 but are excluded by the mesh electrode 31 on the scintillator 21 side.

However, elastic scattered electrons and inelastic scattered electrons having high energy can pass through the mesh electrode 31 having a negative potential. As a result, the particles that can pass through both the mesh electrodes 30 and 31 and reach the scintillator 21 of the detector 15 are only elastic scattered electrons and inelastic scattered electrons having high energy.

By using the detector having such a configuration, for example, when the irradiation of the ion beam from the FIB column 1 is stopped and the sample is irradiated with the electron beam from the SEM column 2 to obtain a sample image, The switch 33 connects the mesh electrodes 30 and 31 to the power supply 32 by the switch 33 so that secondary electrons mainly from the sample can enter the scintillator 21.

On the other hand, the sample is irradiated with the ion beam from the FIB column 1 and the electron beam from the SEM column 2 at the same time to process the sample with the ion beam and simultaneously monitor the sample image with the electron beam. Is
The switch 33 applies a negative voltage from the power supply 34 to the mesh electrode 31. As a result, the detector 15 detects only elastic scattered electrons and inelastic scattered electrons having high energy based on the irradiation of the sample with the electron beam.

When the detection signal from the detector 15 is led to the cathode ray tube 17, an image obtained by the scanning electron microscope function can be displayed on the cathode ray tube 17, and the sample is processed by the FIB. Even in the middle, the image of the sample cross section can be monitored by the SEM.

[0042]

As described above, in the first invention,
A detector that selectively detects inelastic scattered electrons and elastic scattered electrons having relatively high energy among signals generated from the sample by simultaneous irradiation of the focused ion beam and the electron beam is provided, and a signal from the detector is provided. , The scanning electron microscope image is displayed on the basis of the SEM, so that the image of the sample cross section can be monitored by the SEM even while the sample is being processed by the FIB.

According to a second aspect, in the first aspect, the detector has a double mesh electrode, and a positive voltage is applied to an electrode of the mesh electrode closer to the sample, and a positive voltage is applied to the other electrode. Alternatively, a negative voltage is selectively applied, and when detecting inelastic scattered electrons and elastic scattered electrons having relatively high energy, a negative voltage is applied to the other electrode. The image of the cross section of the sample can be monitored by the SEM even during the processing.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of a FIB-SEM device according to the present invention.

FIG. 2 is a view showing a processed cross section of a sample.

FIG. 3 is a diagram showing an energy distribution of positive ions and negative ions.

FIG. 4 is a diagram showing an energy distribution of secondary electrons, inelastic scattered electrons, and elastic scattered electrons.

FIG. 5 is a diagram showing a configuration of a conventional detector.

FIG. 6 is a diagram showing an example of a configuration of a detector according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 FIB column 2 SEM column 3 Ion gun 4,10 Focusing lens 5,11 Objective lens 6,12 Deflector 7 Sample 8 FIB control unit 9 Electron gun 13 SEM control unit 14 Host computer 15 Detector 16 Amplifier 17 Cathode ray tube 18 Stage 19 Stage control unit

Claims (2)

[Claims] 1. An FIB having a function of irradiating a sample with a focused ion beam and a SEM function of irradiating an electron beam on a cross section of the sample processed by the focused ion beam and observing a scanning electron microscope image. In the SEM device, a detector is provided for selectively detecting inelastic scattered electrons and elastic scattered electrons having relatively high energy among signals generated from the sample by simultaneous irradiation of the focused ion beam and the electron beam. FIB-SEM device that displays a scanning electron microscope image based on a signal from a vessel. 2. The detector has a double mesh electrode, and a positive voltage can be selectively applied to an electrode of the mesh electrode close to the sample, and a positive or negative voltage can be selectively applied to the other electrode. 2. The FIB-S according to claim 1, wherein a negative voltage is applied to the other electrode when detecting inelastic scattered electrons and elastic scattered electrons having relatively high energy.
EM equipment.