JP3457875B2 - Method for observing sample cross section in FIB-SEM apparatus and FIB-SEM apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sample cross-section observing method and FIB-SEM in a FIB-SEM apparatus in which a sample is irradiated with a focused ion beam to be processed and the processed cross section is observed by a scanning electron microscope function. Regarding the device.

[0002]

2. Description of the Related Art Focused ion beam (FIB-Focused Io)
The n beam) device is a device that focuses an ion beam from an ion source into thin beams, irradiates a processed sample, and processes the sample by etching or the like. Among the application fields of this FIB device, the etching technique by FIB has become quite popular.

The FIB apparatus using this technique is widely used not only for micromachining, but also for defect analysis of semiconductor devices and preparation of transmission electron microscope samples. In particular, it is becoming an indispensable device for three-dimensional analysis of semiconductor devices, which has received the most attention. In addition, at present, dual beam (Dual Beam-), which is a conventional in-line scanning electron microscope (SEM) device with FIB function, is added.
DB) devices are gradually becoming popular.

The DB device is a composite device capable of performing a process of performing etching processing as a conventional FIB device and then transferring and observing a sample to an SEM device in order to correspond to a semiconductor failure analysis device.

This is similar to a normal FIB single-function machine, in which the upper surface of the sample is irradiated with an ion beam to perform an etching process at an arbitrary position, and after the completion of the process, the etching process is immediately performed without moving the sample. It has an advantage that the cross section can be observed by an SEM image. As a result, it is expected that the failure analysis will be extremely powerful, the process time will be shortened, the yield management and speed associated with it will be reduced, the floor area will be reduced due to the combined equipment, and the price will be reduced. Is expected to progress.

The configuration of the FIB-SEM apparatus described above is roughly divided into an FIB control section, an SEM control section, and a control section of a stage on which a sample is placed, and each is controlled by a host computer. In this device, usually, the sample is etched by applying an ion beam from above 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 makes 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 perpendicularly to the sample surface.

[0007]

However, the above-mentioned F
In the IB-SEM apparatus, when the cross-sectional image is observed by an electron beam, the cross section immediately after being cut out is too flat, and therefore, a sufficient contrast cannot be obtained with the secondary electron image, and the resolution is deteriorated. is doing. Further, in the observation with the electron beam, depending on the sample, the cut out section is contaminated due to contamination adhered by the scanning electron microscope observation, and similarly the resolution is lowered.

Therefore, as a general method for observing the image of the above flat cross section with high resolution in a scanning electron microscope, the sample is broken or the FIB processed sample is chemically treated (wet etching or the like). It is known that a step is formed between various materials by applying the above method to improve the secondary electron emission efficiency from the edge, thereby improving the contrast of the scanning electron microscope image after the chemical treatment.

However, in order to perform these treatments, it is necessary to take the sample out of the apparatus once after the FIB processing, and this causes the processing place to be changed when the sample is put in the apparatus again. It is very time consuming to find, 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.

The present invention has been made in view of the above points, and an object of the present invention is to perform observation with a scanning electron microscope with sufficient contrast and high resolution without taking out a FIB-processed sample from the outside of the apparatus. FIB-SE that can
Method for observing sample cross section in M apparatus and FIB-SEM
To realize the device.

[0011]

FI based on the first invention
The sample cross-section observation method in the B-SEM apparatus is performed by using an ion beam of a first current amount obtained from the same ion source and a first ion beam .
It has a function of irradiating the sample with an ion beam having a second current amount smaller than the flow rate, and an SEM function of irradiating the sample cross section processed by the focused ion beam with the electron beam to observe a scanning electron microscope image. FIB-SE equipped
In the M apparatus, the sample is irradiated with an ion beam of a first current amount to be etched and processed, and after the process, the sample is rotated and tilted so that the processed cross section faces the ion beam, and the second cross section is formed on the processed cross section. Irradiate with an ion beam of current and process
It is characterized in that a step is formed on the cross section due to a difference in material, 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 irradiated with the ion beam having the first current amount to etch and process the sample, and after processing, the sample is rotated and tilted so that the processed cross section faces the ion beam. Irradiating the cross section with an ion beam of a second current amount to create a step difference in the processed cross section due to the difference in material ,
Then, the sample is rotated and tilted to observe a scanning electron microscope image of the processed cross section.

In a second aspect of the invention, in the first aspect of the invention, an ion beam is scanned on the processed cross section of the sample after the etching process, and a SIM image is observed by a signal obtained based on this scanning.

According to a third aspect of the present invention, in the first aspect, when the processed cross section is irradiated with the ion beam having the second current amount, the ion beam is scanned in a predetermined area, and this scanning is performed from above to below the predetermined area. The scanning is bidirectional from bottom to top.

A fourth invention is the same as the first invention .
The first current of the ion beam is irradiated to a sample processing a sample by etching, machining after sample is rotated 180 °, further
The processed cross section was made to face the ion beam by tilting.

The FIB-SEM apparatus according to the 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
In the FIB-SEM apparatus having the M function, the current amount of the focused ion beam is changed to the first current amount and the first current amount.
Means for switching to a smaller second current amount, means for rotating and tilting the sample, and means for irradiating the sample with an ion beam of the first current amount to etch and process the sample, and rotating and tilting the sample after processing. The processed cross section is made to face the ion beam, and the processed cross section is irradiated with the ion beam of the second current amount.
Te is characterized by having a function that causes a level difference due to the difference in material processing section.

In the fifth invention, the sample is irradiated with the ion beam having the first current amount to etch and process the sample, and after processing, the sample is rotated and tilted so that the processed cross section faces the ion beam. The cross section is irradiated with an ion beam having a second current amount, and then the sample is rotated and tilted to observe a scanning electron microscope image of the processed cross section.

According to a sixth aspect of the invention, in the fifth aspect of the invention, the irradiation area of the ion beam and the electron beam does not change even if the sample is rotated and tilted.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows the F according to the present invention.
IB-SEM apparatus is shown, 1 is a column of FIB,
2 is a column of SEM. In FIB column 1,
An ion gun 3, a focusing lens 4 for focusing the ion beam generated and accelerated by the ion gun 3, an objective lens 5, and a deflector 6 for two-dimensionally scanning the ion beam are provided. An electrostatic lens is mainly used as the focusing lens 4 for the ion beam and the objective lens 5.

The ion beam generated from the ion gun 3 is
The focusing lens 4 and the objective lens 5 finely focus on the sample 7, and the irradiation position of the ion beam with which the sample 7 is irradiated can be scanned by the deflector 6. These focusing lens 4, objective lens 5, and deflector 6
Are controlled by the FIB controller 8.

For example, when changing the current amount of the ion beam with which the sample 7 is irradiated, 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 focusing is changed to control the amount of the ion beam passing through a diaphragm (not shown) provided in the optical path of the ion beam. When the sample is two-dimensionally or linearly scanned with the ion beam, the FIB controller 8 supplies a scanning signal to the deflector 6.

In the SEM column 2, an electron gun 9 and a focusing lens 1 for focusing the electron beam generated by the electron gun 9 are focused.
0, an objective lens 11, and a deflector 12 for two-dimensionally scanning an electron beam. An electromagnetic lens is mainly used as the focusing lens 10 and the objective lens 11 for the electron beam.

The electron beam generated from the electron gun 9 is finely 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. Is configured. The focusing lens 10, the objective lens 11, and the deflector 12 are controlled by the SEM controller 13.

For example, when changing the current amount of the electron beam with which the sample 7 is irradiated, the focusing lens 10 and the objective lens 11 are controlled by the SEM controller 13 and the intensity of each lens is controlled to control the electron beam. Change the degree of focusing,
It controls the amount of the electron beam passing through a diaphragm (not shown) provided in the optical path of the electron beam. Further, when the electron beam is two-dimensionally or linearly scanned on the sample, a scanning signal is supplied from the SEM controller 13 to the deflector 12. The SEM controller 13 and the FIB controller 8 are
It is controlled by the host computer 14.

Secondary electrons generated from the sample by irradiating the sample 7 with the electron beam or the ion beam are detected by the secondary electron detector 15. After 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 the stage 18. The stage 18 is configured to be capable of two-dimensional horizontal movement, rotation, and tilt by a stage controller 19. The stage controller 19 includes a host computer 14
Controlled by. The operation of such a configuration will be described below.

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

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

In the usual FIB-SEM apparatus, after forming the opening 20 for the sample 7, S for the section D.
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 in the cathode ray tube 17.

By the way, as described above, it is impossible to obtain a secondary electron image having a sufficient contrast and a high resolution because the section D is flat in such a conventional operation. In the present invention, after forming the opening 20 by processing the ion beam as shown in FIG.
The stage control unit 19 controls the stage 18, rotates the stage 18 by 180 °, and further tilts the stage 18 largely (for example, 60 °).

This state is shown in FIG. By rotating and inclining the stage, the cross-sectional portion D of the opening 20 of the sample 7 is FI.
It is possible to face the B column 1. That is, it is possible to irradiate the processed cross-section portion D with the ion beam from a direction close to vertical. In this state, the FIB control unit 8
The column 1 is controlled and the focusing lens 4 and the objective lens 5 are controlled to reduce the current amount of the ion beam with which the sample 7 is irradiated. This current amount is, for example, about several pA.

In this state, the ion beam IB is two-dimensionally scanned for a short time (eg, television scanning speed) by the deflector 6 on the cross section D of the sample. As a result, in the cross-section portion D of the sample, the cross-section surface layer can be processed in the vertical direction in units of nm. In this case, the various semiconductor materials in the cross-section, given the same charge by the material, due to differences in binding strength of the crystal, since the rate at which edge switch ring are different, so that it is stepped due to the difference in materials.

That is, the processed sample is taken out from the apparatus, and the same treatment as that of chemically treating the surface layer of the sample cross section is performed.
It can be performed at any place in a short time without taking out the sample from the device and without using chemicals or the like. In this case, if a selective gas is introduced while irradiating the sample with an ion beam having a weak current amount, it is possible to obtain a cross section equivalent to a more chemically processed one.

As the control in the depth direction of the observation cross 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 selected as a television scanning speed and a slow slow speed to perform fine processing control in the depth direction. is there.

In the television scanning mode, the sample surface is cleaned by etching a few nm. In slow mode, the surface of the sample is processed to tens to hundreds of nanometers, and while observing the image, the cross section is peeled off vertically to ensure that defects, etc. that might be buried deep in the sample are found. You can

The second method is to select the ion beam current amount applied to the sample cross section from several pA to several tens pA,
This is a method of controlling the processing depth. The third method is to scan the depth of the surface to be etched by performing bidirectional scanning from top to bottom and bottom to top, rather than the usual one direction from top to bottom. Is a method of controlling so that is constant from top to bottom.

After performing the secondary sample surface treatment with such an ion beam, the processed 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 is brought into a positional relationship as shown in FIG. 1, for example, 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 remarkably enhanced as compared with immediately after the FIB processing. By such an operation, it is possible to finish the surface in an arbitrary area, in an arbitrary range, and to an arbitrary depth, and not only to improve the resolution of the sample cross section but also to a depth of several nm from the cross section. It is possible to dig out foreign matter (in the case of failure analysis) that may be buried.

When the sample is processed by the FIB and then the processing control in the fine depth direction of the processed cross section D is performed, an ion beam having an extremely weak current amount is scanned in the processed cross section D and generated at that time. It is effective to detect the secondary electrons with a secondary electron detector, obtain a SIM image of the processed cross section D, and specify a region for fine processing control in the depth direction from the SIM image.

When the above process is added to the FIB-SEM device as the "soft etching function", the specific operation sequence is as follows. Observe the SEM image after FIB processing, and press the "soft etching function" button if necessary. The stage is rotated and tilted, the processed cross section D where the SEM image is observed faces the FIB column 1, and the mode is switched to the FIB observation mode. When we scan the weak ion beam, observe the SIM image, set the area, and instruct the host computer to start soft etching, the FIB scans the screen from top to bottom and from bottom to top at the slow or television scanning speed. And scan alternately. The button for returning to the SEM observation mode is pressed again, the stage is rotated and tilted to enter the SEM observation mode, and the SEM image after the cross-section processing is observed.

When the processed cross section D is made to face the FIB column 1 after the sample is processed by the FIB to form the opening, a computer is used to prevent the processed place D from escaping from the observation visual field by the rotation and inclination of the sample. It is necessary to have a eucentric function to control the stage. With this function, the SIM and SEM observation functions can be switched without displacement.

Further, the ion beam and the electron beam can irradiate the same observation point of the sample by the mechanical alignment of the FIB column and the SEM column and the electrical control and the control of the sample surface height.

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

[0044]

As described above, according to the first invention,
A first current of the ion beam is irradiated to a sample processing a sample by etching, a processed cross section and a post-process sample is tilted and rotated to face the ion beam, a first electrodeposition machining section
Irradiating with an ion beam with a second current amount smaller than the flow rate
Then, a step due to the difference in material is generated in the processed section, and then the sample is rotated and tilted to observe the scanning electron microscope image of the processed section, so that the processed section can be selectively etched. An image with sufficient contrast and high resolution can be obtained.

In the second invention, in the first invention, the ion beam is scanned on the processed cross-section after the etching processing of the sample, and the SIM image is observed by the signal obtained based on this scanning. It is possible to perform the selective etching of the processed cross section while observing the image.

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

[0047] In the fourth invention, in the first invention, the
The first current of the ion beam is irradiated to a sample processing a sample by etching, machining after sample is rotated 180 °, further
Since the processed cross section is made to incline to face the ion beam, the cross section etched by the ion beam having the first current amount can be finely etched by using the ion beam having the second current amount. .

In the fifth invention, the sample is etched by irradiating the sample with the ion beam having the first current amount, and after the sample is processed, the sample is rotated and tilted so that the processed cross section faces the ion beam. Irradiating the cross section with an ion beam of a second current amount to create a step difference in the processed cross section due to the difference in material ,
After that, the sample can be rotated and tilted to observe the scanning electron microscope image of the processed cross section, so that the same effect as that of the first invention can be achieved.

According to the sixth aspect of the invention, in the fifth aspect of the invention, the irradiation area of the ion beam and the electron beam is not changed even by the rotation and tilt of the sample, so that it is not necessary to perform troublesome alignment of the sample. .

[Brief description of drawings]

FIG. 1 shows 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 the relationship between a sample after rotation and tilting of the sample and the FIB column and SEM column.

[Explanation of symbols]

1 FIB column 2 SEM column 3 ion gun 4,10 Focusing lens 5,11 Objective lens 6,12 deflector 7 samples 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 stages 19 Stage control unit

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-5-267409 (JP, A) JP-A-9-180667 (JP, A) JP-A-4-76437 (JP, A) JP-A-4- 116843 (JP, A) JP 9-22110 (JP, A) JP 9-259810 (JP, A) JP 4-12446 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01J 37/317 G01N 1/28 G01N 1/32 H01J 37/28 H01L 21/66

Claims (6)

(57) [Claims] And 1. A function of irradiating the same with the ion beam of the first current of the ion beam and the first current amount is smaller than the second amount of current from the ion source to the sample, processed by a focused ion beam In a FIB-SEM apparatus having an SEM function capable of irradiating an electron beam on the cross section of a sample thus formed and observing a scanning electron microscope image, the sample is irradiated with an ion beam of a first current amount to etch the sample. After processing, the processed sample is rotated and tilted so that the processed cross section faces the ion beam, and the processed cross section is irradiated with the ion beam of the second current amount, and the processed cross section is made of different materials.
The FI was designed so that a step was generated by the test, and then the sample was rotated and tilted to observe a scanning electron microscope image of the processed cross section.
Method for observing sample cross section in B-SEM apparatus. 2. The sample in the FIB-SEM apparatus according to claim 1, wherein the processed cross-section after etching the sample is scanned with an ion beam, and a SIM image is observed by a signal obtained based on the scanning. Section observation method. 3. When irradiating a processed cross section with an ion beam of a second current amount, the ion beam is scanned in a predetermined region, and this scanning is performed bidirectionally from top to bottom and bottom to top of the predetermined region. The method for observing a sample cross section in the FIB-SEM apparatus according to claim 1, wherein 4. A sample is irradiated with an ion beam of a first current amount to etch and process the sample.
The FIB-SEM according to claim 1, wherein the processed cross section is made to face the ion beam by being rotated by 0 ° and further tilted.
Method for observing cross section of sample in apparatus. 5. A FIB- having a function of irradiating a sample with a focused ion beam and an SEM function of irradiating a sample cross section processed by the focused ion beam with an electron beam to observe a scanning electron microscope image. In the SEM device, the current amount of the focused ion beam is set to the first current amount and the first current amount.
A means for switching to a second current amount smaller than the flow rate , a means for rotating and tilting the sample, an ion beam having a first current amount applied to the sample to etch and process the sample, and the processed sample is rotated. The processed cross section is made to face the ion beam by inclining, and the processed cross section is irradiated with the ion beam of the second current amount.
To, FIB-SEM apparatus having a function that causes a level difference due to the difference in material processing section. 6. The FIB-SEM apparatus according to claim 5, which has a function of keeping the irradiation area of the ion beam and the electron beam unchanged even when the sample is rotated and tilted.