JPH11213935A - Sample cross-section observing method in fib-sem device and fib-sem device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a sample cross-section observing method in a FIB(focused ion beam)-SEM(inline-type scanning electron microscope) device and the FIB- SEM device, enabling a sample worked by a FIB to be observed with sufficient contrast with good resolution, and without taking it out of the device, by a scanning electron microscope. SOLUTION: An ion beam is generated from an ion gun 3 in a FIB column 1, and a sample 7 is worked by applying the ion beam to the sample. After an opening is formed by the work, a stage 18 is 180 deg. rotated, and further, the stage 18 is inclined greatly. By the rotation and inclination of the stage 18, a cross-section part D of the opening 20 of the sample 7 can be caused to face the FIB column 1. In this state, the amount of current of the ion beam applied to the sample 7 is reduced. As a result, a cross-section surface layer can be worked longitudinally on the order of nm at the cross-section part to be worked of the sample. After such surface treatment is conducted, a SEM image of the worked cross-section part of the sample is observed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for observing a sample cross section in a FIB-SEM apparatus and 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. Related to the device.

[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.

[0007]

However, the above-mentioned F
In the IB-SEM apparatus, when a cross-sectional image is observed with an electron beam, the cross-section immediately after cutting is too flat, so that a sufficient contrast cannot be obtained with a secondary electron image, and the resolution is degraded. doing. In addition, in observation using an electron beam, depending on the sample, the cut-out cross section is contaminated due to contamination or the like by observation using a scanning electron microscope, and the resolution is similarly reduced.

For this reason, as a general technique for observing the image of the flat cross section with a scanning electron microscope at a high resolution as described above, a sample is subjected to chemical treatment (wet etching or the like) by fracturing or FIB processing the sample. It is known that a step is created between various materials to improve the efficiency of secondary electron emission from the edge, thereby improving the contrast of a scanning electron microscope image after the chemical treatment.

However, in order to perform these processes, it is necessary to take out the sample once out of the apparatus after the FIB processing, and when this is done, when the sample is put in the apparatus again, the processing place is changed. It takes a lot of trouble to find out, and it is obvious that many steps and time are spent. Further, when the target sample is a large one such as an 8-inch wafer, it is necessary to cut the sample into small chips.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to observe an FIB-processed sample with a scanning electron microscope with sufficient contrast and high resolution without taking the sample out of the apparatus. Possible FIB-SE
Sample cross-section observation method and FIB-SEM in M apparatus
The realization of the device.

[0011]

An FI based on the first invention is provided.
The method for observing a sample cross section in a B-SEM apparatus has a function of irradiating a sample with a focused ion beam and an SEM function of irradiating an electron beam on a sample cross section processed by the focused ion beam and observing a scanning electron microscope image. In a FIB-SEM apparatus provided with, a sample is etched and processed by irradiating the sample with an ion beam having a relatively large current amount, and after processing, the sample is rotated and tilted so that the processed cross section faces the ion beam; It is characterized in that a processed cross section is irradiated with an ion beam having a relatively small current amount, and then the sample is rotated and tilted to observe a scanning electron microscope image of the processed cross section.

In the first invention, the sample is etched and processed by irradiating the sample with an ion beam having a relatively large current amount, and after processing, the sample is rotated and tilted so that the processed cross section faces the ion beam. The section is irradiated with an ion beam having a relatively small current amount, and then the sample is rotated and tilted to observe a scanning electron microscope image of the processed section.

According to a second aspect, in the first aspect, the ion beam is scanned on the processed cross section of the sample after the etching processing, and a SIM image is observed based on a signal obtained based on the scanning.

According to a third aspect of the present invention, in the first aspect, when irradiating an ion beam having a relatively small current amount to the processed cross section, the ion beam is scanned in a predetermined area, and the scanning is performed from top to bottom of the predetermined area. Scanning was performed bidirectionally from bottom to top.

In a fourth aspect based on the first aspect, the sample is etched and processed by irradiating the sample with an ion beam having a relatively large current amount, and after the processing, the sample is rotated by 180 ° to obtain a relatively large angle. The processing section was inclined so as to face the ion beam.

A FIB-SEM apparatus according to a fifth aspect of the present invention has a function of irradiating a sample with a focused ion beam and irradiating an electron beam on a cross section of the sample processed by the focused ion beam to observe a scanning electron microscope image. SE that can do
In a FIB-SEM apparatus having an M function, a means for switching the current amount of the focused ion beam between a relatively large current amount and a relatively small current amount, a unit for rotating and tilting the sample, A function of irradiating the sample with an ion beam, etching the sample, processing the sample, rotating and tilting the sample after processing so that the processed cross section faces the ion beam, and irradiating the processed cross section with an ion beam with a relatively small current amount. It is characterized by having.

In the fifth invention, the sample is etched and processed by irradiating the sample with an ion beam having a relatively large current amount, and after processing, the sample is rotated and tilted so that the processed cross section faces the ion beam. The section is irradiated with an ion beam having a relatively small current amount, and then the sample is rotated and tilted to observe a scanning electron microscope image of the processed section.

According to a sixth aspect, in the fifth aspect, a function is provided in which the irradiation area of the ion beam and the electron beam does not change even when the sample is rotated or tilted.

[0019]

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 each lens. 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.

An electron gun 9 and a focusing lens 1 for focusing an electron beam generated from the electron gun 9 are provided in the SEM column 2.
0, an objective lens 11, and a deflector 12 for two-dimensionally scanning the electron beam. The focusing lens 10 and the objective lens 11 for the electron beam are mainly electromagnetic lenses.

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.

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 by controlling the intensity of each lens. 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 scanning the sample with the electron beam two-dimensionally or linearly, a scanning signal is supplied from the SEM control unit 13 to the deflector 12. Note that the SEM control unit 13 and the FIB control unit 8
It is controlled by the 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 the 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.

As described above, in such a conventional normal operation, since the cross section D is flat, a secondary electron image with sufficient contrast and high resolution cannot be obtained. In the present invention, after the opening 20 is formed by ion beam processing as shown in FIG.
The stage controller 19 controls the stage 18, rotates the stage 18 by 180 °, and further tilts the stage 18 by a large angle (for example, 60 °).

FIG. 3 shows this state. By rotating and tilting the stage, the cross section D of the opening 20 of the sample 7 is
It can face B column 1. That is, it is possible to irradiate the ion beam from a direction almost perpendicular to the processing cross section D. In this state, the FIB
The column 1 is controlled, and the focusing lens 4 and the objective lens 5 are controlled to reduce the amount of current of the ion beam irradiating the sample 7. This current amount is, for example, about several pA.

In this state, the ion beam IB is two-dimensionally scanned in a short time (for example, a television scanning speed) at the cross section D of the sample by the deflector 6. As a result, in the cross section D of the sample, the processing of the cross section surface layer in the vertical direction can be performed in units of nm. In this case, when the same charge is applied to the various semiconductor materials in the cross section when the same charge is applied to the materials, the etching speed is different due to the difference in the bonding force of the crystals, and thus a step due to the difference in the material is formed.

That is, the processed sample is taken out of the apparatus, and the same processing as when the surface layer of the sample cross section is chemically treated is performed.
It can be performed in an arbitrary place in a short time without taking out the sample from the apparatus and without using a chemical agent or the like. In this case, if a gas having selectivity is introduced while irradiating the sample with an ion beam having a weak current amount, a cross section equivalent to that obtained by further chemical treatment can be obtained.

As the control in the depth direction of the observation section of the sample in such a process, the following three methods can be appropriately executed. The first method is a method in which the amount of ion beam current applied to the sample surface is kept constant, and the scanning speed of the ion beam is set to a slower scanning speed than the television scanning speed, thereby performing processing control in a fine depth direction. is there.

In the television scanning mode, the sample surface is cleaned by etching of several nm. In the slow mode, the sample surface is machined for several tens to several hundreds of nm, and the cross section is peeled off vertically while observing the image, so that defects etc. that may be buried deep in the sample can be reliably found. Can be.

In the second method, the ion beam current applied to the sample section is selected from several pA to several tens pA,
This is a method for controlling the processing depth. In the third method, the depth of the surface to be etched is determined by scanning the ion beam in a bidirectional manner from top to bottom and bottom to top, instead of the normal one direction from top to bottom. Is a method of controlling so as to be constant from top to bottom.

After performing such a secondary sample surface treatment with the ion beam, the processing section D is made to face the scanning electron microscope column 2. This operation is performed by rotating and tilting the sample stage 18. By this operation, the sample 7 has, for example, a positional relationship as shown in FIG. 1, and the processed section D is two-dimensionally scanned by the electron beam EB from the SEM column 2.

The image of the cross section of the sample observed based on the secondary electrons obtained by the scanning of the electron beam becomes a scanning electron microscope image in which the contrast is greatly enhanced compared to immediately after the FIB processing. By such an operation, it is possible to finish the surface at an arbitrary place, in an arbitrary range, and at an arbitrary depth on the sample, and not only to improve the resolution of the sample cross section, but also to increase the depth to several nm from the cross section. It is also possible to dig out foreign matter that might be buried (in the case of failure analysis).

After processing the sample by the FIB, when performing processing control in the fine depth direction of the processing section D, an ion beam having an extremely weak current amount is scanned on the processing section D and generated at that time. It is effective to detect the secondary electrons thus obtained by a secondary electron detector, obtain a SIM image of the processing section D, and designate a region for performing fine processing control in the depth direction from the SIM image.

When the above-described process is added to the FIB-SEM apparatus as a “soft etching function”, a specific operation sequence is as follows. After the FIB processing, an SEM image is observed, and if necessary, a “soft etching function” button is pressed. The rotation and tilt of the stage are performed, and the processing section D where the SEM image has been observed faces the FIB column 1, and the mode is switched to the FIB observation mode. When a weak ion beam is scanned and the SIM image is observed to set the area and the start of soft etching is instructed from the host computer, the FIB scans the screen from top to bottom and from bottom to top at the speed of slow or television scanning. And scan alternately. Again, the button for returning to the SEM observation mode is pressed, the stage is rotated and tilted, and the SEM image is observed after the cross-section processing in the SEM observation mode.

When the processing section D faces the FIB column 1 after processing the sample with the FIB to form an opening, a computer is used so that the processing place D does not escape from the observation field of view due to the rotation and inclination of the sample. It is necessary to have a eucentric function to control the stage. With this function, the observation function of the SIM and the observation function of the SEM can be switched without displacement.

Further, by mechanically aligning and electrically controlling the FIB column and the SEM column and controlling the height of the sample surface, the ion beam and the electron beam can irradiate the same observation point of the sample.

Although the embodiment of the present invention has been described in detail, the present invention is not limited to this embodiment. For example, in the present invention, secondary electrons are detected when an electron beam or ion beam is scanned on a sample, but reflected electrons or reflected ions are detected, and an image is displayed based on the detection signal. You may do it. In addition, when a processed cross section of a sample is subjected to surface treatment by scanning with an ion beam having a small current amount, if a gas having selectivity is introduced into the portion, a cross-sectional image equivalent to a more chemically processed one can be obtained. .

[0044]

As described above, in the first invention,
The sample is etched and processed by irradiating the sample with an ion beam with a relatively large current amount, and after processing, the sample is rotated and tilted so that the processed cross section faces the ion beam, and ions with a relatively small current amount are applied to the processed cross section. The sample was irradiated and then the sample was rotated and tilted to observe the scanning electron microscope image of the processed cross section, so that the processed cross section could be selectively etched and an image with sufficient contrast and good resolution could be obtained. Obtainable.

According to the second aspect, in the first aspect, the ion beam is scanned on the processed cross section of the sample after the etching processing, and the SIM image is observed based on a signal obtained based on the scanning. In addition, it is possible to perform the selective etching of the processed cross section while observing an image.

According to a third aspect, in the first aspect, when irradiating the ion beam with a relatively small current amount to the processed cross section, the ion beam is scanned in a predetermined area, and the scanning is performed from top to bottom of the predetermined area. Since the scanning is performed bidirectionally from the bottom to the top, the etching depth above and below the scanning region can be kept constant.

According to a fourth aspect of the present invention, in the first aspect, the sample is etched and processed by irradiating the sample with an ion beam having a relatively large amount of current. Since the processing section is inclined so as to face the ion beam, it is possible to perform fine etching using a small ion beam on a cross section etched by an ion beam having a large current amount.

According to the fifth aspect of the present invention, the sample is etched and processed by irradiating the sample with an ion beam having a relatively large current amount. After the processing, the sample is rotated and tilted so that the processed cross section faces the ion beam. Since the cross section is irradiated with an ion beam having a relatively small current amount, and then the sample is rotated and tilted, it becomes possible to observe a scanning electron microscope image of the processed cross section. Therefore, the same effect as that of the first invention is achieved. You.

According to the sixth aspect, in the fifth aspect, a function is provided in which the irradiation area of the ion beam and the electron beam does not change even by rotation and inclination of the sample, so that it is not necessary to perform complicated sample positioning. .

[Brief description of the drawings]

FIG. 1 is a diagram showing 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 a relationship between a sample, a FIB column, and a SEM column after the sample is rotated and tilted.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 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 Secondary electron detector 16 Amplifier 17 Cathode ray Tube 18 Stage 19 Stage control unit

Claims (6)

[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 a SEM apparatus, the sample is etched and processed by irradiating the sample with an ion beam having a relatively large current amount, and after processing, the sample is rotated and tilted so that the processed cross section faces the ion beam, and the processed cross section is relatively small. A sample section observation method in a FIB-SEM apparatus in which a current amount of an ion beam is irradiated, and then the sample is rotated and tilted to observe a scanning electron microscope image of a processed section. 2. The sample in the FIB-SEM apparatus according to claim 1, wherein an ion beam is scanned on a cross section of the sample after the etching process, and a SIM image is observed based on a signal obtained based on the scanning. Section observation method. 3. When irradiating an ion beam with a relatively small current amount to a processing section, the ion beam is scanned in a predetermined area, and the scanning is performed bidirectionally from top to bottom and from bottom to top in the predetermined area. A method for observing a sample cross section in a FIB-SEM apparatus according to claim 1. 4. A sample is etched and processed by irradiating the sample with an ion beam having a relatively large current amount, and after processing, the sample is rotated by 180 ° and tilted at a relatively large angle to face the processed cross section to the ion beam. 2. The method for observing a cross section of a sample in an FIB-SEM apparatus according to claim 1, wherein: 5. A 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, means for switching the current amount of the focused ion beam between a relatively large current amount and a relatively small current amount, rotating the sample,
Means for inclining and irradiating the sample with an ion beam having a relatively large current amount to etch and process the sample; after processing, the sample is rotated and tilted so that the processed section faces the ion beam; A FIB-SEM device having a function of irradiating an ion beam with a small current amount. 6. The FIB-SEM apparatus according to claim 5, wherein the irradiation area of the ion beam and the electron beam does not change even when the sample is rotated or tilted.