JPH03272554A - Scanning electron microscope for section observation and section observing method using it - Google Patents

Abstract

PURPOSE:To cut out a section of a semiconductor wafer in its specified place precisely and quickly and observe it by performing electron beam scan over the section which was cut out by scanning with an ion beam, and detecting reflex electrons reflected by the semiconductor wafer. CONSTITUTION:The section of a semiconductor wafer 27 cut out by the ion beam scan of an ion beam scanning means 220 is scanned with an electron beam 30 using an electron beam scanning means 100, and an electron detecting means 21 detects reflex electrons which are reflected by the semiconductor wafer 27 due to the electron beam scan. Accordingly the section observing is made by a scan region observing means 26 through utilization of the reflex electrons simultaneously with cutting-out of the section to be observed. This enables observing the section of semiconductor wafer in its specified place upon cutting out precisely and quickly.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a scanning electron microscope for cross-sectional observation and a cross-sectional observation method using the same, and particularly to a scanning electron microscope for cross-sectional observation that observes the cross-sectional state of a semiconductor wafer. This article relates to an electron microscope and a cross-sectional observation method using the same.

[Prior Art] Conventionally, a scanning electron microscope (hereinafter referred to as SEM) has been known as a device for performing surface observation and cross-sectional observation in failure analysis and process evaluation of semiconductor integrated circuits. This SE
M (Scanning Electron Mic
In the cross-sectional observation method using L)
The method used was to cut the Ueno\ so that the desired cross section of the Ueno\ could be observed.

FIG. 7 is a perspective view of a semiconductor wafer required when using the conventional SEM cross-sectional observation method. 7th
A cross-sectional observation method using a conventional SEM will be described with reference to the drawings. A plurality of chips are formed on the semiconductor wafer 27. First, a cross-sectional observation test chip 28 to be subjected to cross-sectional observation is selected. Thereafter, the semiconductor wafer 27 is cut so that the observed cross section 129 of the test chip 28 for cross-sectional observation appears. After the observed cross section 129 of the cross-sectional observation test chip 28 was exposed in this manner, the observed cross section 129 was observed in cross section using an SEM. In this way, conventionally, the semiconductor wafer 27 has been manually cut in order to expose the observation cross section 129 of the test chip 28 for cross-section observation.

[Problems to be Solved by the Invention] As described above, in the method of observing a cross section of a semiconductor wafer using a conventional SEM, when observing a cross section, the observation cross section 129 of the test chip 28 for cross section observation is exposed. Therefore, the semiconductor wafer 27 has been cut manually. In this method of cutting the semiconductor Ueno X27, a portion corresponding to the observed cross section 129 to be observed is manually cut, so it is very difficult to accurately expose the cross section at a specific location. Furthermore, this method has the disadvantage that it takes a long time to prepare the sample and observe the cross section. Furthermore, since the semiconductor wafer is cut to perform cross-sectional observation, the wafer cannot be subjected to any subsequent wafer processing.

As a result, a problem arises in that a wafer for cross-sectional observation must be prepared for each wafer process. In other words, in the conventional cross-sectional observation method using an SEM, the wafer is manually cut, so it is not possible to accurately expose the cross-section at a specific location, and it takes a long time to observe the cross-section. In addition, a wafer for cross-sectional observation was required for each wafer process.

Therefore, in order to improve the conventional cross-sectional observation method using SEM, an FIB (Focused
-Ion-Beam) A cross-sectional observation method using a cross-sectional observation electron microscope with an integrated lens barrel has been proposed. These are, for example, J, AppH, Phys, 62 (
6) 15 September 1987
It is disclosed in F2163 to P2168. As a cross-sectional observation method using this proposed cross-sectional observation electron microscope, first, an electron beam and an ion beam are aligned using reference marks. After observing the processing location using an electron beam, processing is performed using an ion beam. If such a cross-sectional observation electron microscope is used, there is an advantage that there is no need to manually break the semiconductor wafer in order to perform cross-sectional observation.

However, in this proposed cross-sectional observation electron microscope, S
Since EM observation is performed using secondary electrons generated from the semiconductor wafer, SEM observation cannot be performed simultaneously with FIB processing. In other words, when scanning a semiconductor wafer with FIB and SEM, secondary electrons are generated from the semiconductor wafer, so even if you simultaneously observe the cross section of the semiconductor wafer with SEM when cutting out the cross section of the semiconductor wafer with FIB, the SEM It is not possible to detect only secondary electrons caused by scanning. Therefore, in this proposed cross-sectional observation electron microscope, when cutting out the observed cross-section, the FIB
It is necessary to repeat the process of cutting out a predetermined amount using SEM and then observing the cross section using SEM, which poses a problem in that it is difficult to shorten the time required to cut out the observed cross section.

Furthermore, at the same time as cutting out the observed cross section by FIB, SE
Since observation using M is not possible, there is a problem in that it is difficult to obtain an observed cross section of a specific location more accurately.

This invention was made to solve the above-mentioned problems, and provides a scanning electron microscope for cross-sectional observation that can more accurately cut out and observe a cross-section of a specific part of a semiconductor wafer in a short time, and the same. The purpose of this study is to provide a cross-sectional observation method using

[Means for Solving the Problem] The invention according to the first claim includes an ion beam scanning means for scanning a semiconductor wafer with an ion beam to cut out a cross section, and a cross section of the semiconductor wafer cut out by the ion beam scanning means. an electron beam scanning means for scanning an electron beam, and a means for detecting secondary electrons generated from the semiconductor wafer by the scanning of the ion beam and the electron beam, and backscattered electrons reflected from the semiconductor wafer by the scanning of the electron beam. It includes an electron detector □ and scanning area observing means for observing the cross-sectional state of the area scanned by the electron beam scanning means based on the detection result of the electron detecting means.

The invention according to claim 2 includes a step of moving a sample stage on which a semiconductor wafer is installed to the vicinity of an area where cross-sectional observation is to be performed, and after moving the sample stage, scanning an ion beam in the vicinity of the area where cross-sectional observation is to be performed to conduct semiconductor wafers. A step of generating secondary electrons from the wafer, detecting the generated secondary electrons, and setting a position for cross-sectional observation; and a step of scanning the ion beam at the set position for cross-sectional observation and cutting out the cross-section. Then, when cutting out the cross section, an electron beam is scanned over the cross section,
a step of detecting backscattered electrons reflected from the semiconductor wafer to observe the process of cutting out the cross section, and scanning the cross section cut out in the step of cutting out the cross section with an electron beam to generate secondary electrons from the semiconductor wafer; and detecting the second electron to observe the cross-sectional state of the cross-section scanned by the electron beam.

[Operation] In the invention according to the first claim, an electron beam is scanned by the electron beam scanning means on a cross section of the semiconductor wafer cut out by ion beam scanning by the ion beam scanning means, and the electron beam is reflected from the semiconductor wafer by the electron beam scanning. Since the reflected electrons are detected by the electron detection means, cross-sectional observation is performed using the reflected electrons while simultaneously cutting out the cross section to be observed.

In the invention according to the second claim, after the sample stage on which the semiconductor wafer is installed is moved to the vicinity of the area where cross-section observation is to be performed, an ion beam is scanned to the position where cross-section observation is to be performed to cut out the cross-section; An electron beam is scanned over the cross section, and reflected electrons reflected from the semiconductor wafer are detected by the scanning of the electron beam to observe the cutting process of the cross section, so that the cross section to be observed is processed and the cross section is observed at the same time.

Embodiment of the Invention FIG. 1 is a schematic diagram of a scanning electron microscope for cross-sectional observation showing an embodiment of the invention. Referring to FIG. 1, the scanning electron microscope for cross-sectional observation includes an SEM lens barrel portion 100 and an F
It includes an IB lens barrel section 200 and a sample chamber section 300.

The SEM lens barrel portion 100 includes an electron gun 1 for generating an electron beam and an electron beam 30 generated from the electron gun 1.
A SEM lunes 2 for focusing, a SEM blanking coil 3 for turning on and off the electron beam focused by the SEM lunes 2, and a SEM blanking coil 3 for scanning the electron beam 3o that has passed through the SEM blanking fill 3. and an SEM second SEM deflection coil 5 for refocusing the electron beam 30 that has passed through the SEM deflection coil 5.
lens 4. Electron gun 1. SEM second lens 2 and SEM second lens 4. SEM blanking coil 3. S
Each of the EM deflection coils 5 includes an electron gun driving power source 6.
SEM lens power supply 7, SEM blanking power supply 8. S.E.
An M deflection power source 9 is connected.

The FIB lens barrel portion 200 includes a liquid metal ion source 10 for generating an ion beam and an FI for focusing an ion beam 31 generated from the liquid metal ion source 10.
FI for turning on and off the ion beam 31 focused by the B-th lunse 11 and the FIB-th lunse 11
B blanking electrode 12 and FIB blanking electrode 12
F for refocusing the ion beam 31 that has passed through
It includes a second IB lens 13 and an FIB deflection electrode 14 for deflecting the ion beam 31 focused by the second FIB lens 13. Liquid metal ion source 10. The FIB lens 11, the FIB second lens 1B, the FIB blanking electrode 12° and the FIB deflection electrode 14 are connected to an ion source driving power source 15. FIB lens power supply 16. FIB
Blanking power supply 17. A FIB deflection power supply 18 is connected.

The sample chamber section 300 includes a sample stand 19 for setting a semiconductor wafer 27, a sample stand drive device 20 for moving one sample stand, and detects backscattered electrons reflected by the semiconductor wafer 27 of the electron beam 30. and a secondary electron detection means 23 for detecting secondary electrons generated from the semiconductor wafer 27 by scanning of the electron beam 30 and the ion beam 31. A backscattered electron detector control power supply 22 and a secondary electron detector control power supply 24 are connected to the backscattered electron detector 21 and the secondary electron detector 23, respectively. Furthermore, the backscattered electron detector 2
1 and the secondary electron detector 23, a detection signal amplifier 25 is provided.
is connected to the detection signal amplifier 25, and the observation CRT 2
6 is connected.

The observation CRT 26 is equipped with an SEM deflection power supply 9 and an FIB
A deflection power source 18 is connected. Further, the SEM lens barrel portion 100 is attached at an incident angle of about 60 degrees to one sample stage so that the cross section of the sample can be observed. FIB
The lens barrel portion 200 is attached substantially perpendicularly to the sample stage 19.

Note that the acceleration voltage of the SEM lens barrel portion 100 is set to be higher than IKV. Further, the backscattered electron detector 21 and the secondary electron detector 23 are controlled by a backscattered electron detector control power source 22 and a secondary electron detector control power source 24. That is, the signals detected by the backscattered electron detector 21 and the secondary electron detector 23 are amplified by the detection signal amplifier 25, and are output to the observation CRT 26 in synchronization with the scanning synchronization signal 35.
will be displayed on the screen. Note that a bias voltage is applied to the backscattered electron detector 21 in order to prevent secondary electrons generated during scanning of the electron beam 30 and the ion beam 31 from being detected.

FIG. 2 is a plan view of a semiconductor wafer used in the cross-sectional observation method using the scanning electron microscope for cross-sectional observation shown in FIG. A plurality of chips are formed on the semiconductor wafer 27, and among them, a test chip 28 for cross-sectional observation is selected in advance.

3 to 5 are schematic diagrams for explaining a cross-sectional observation process in which cross-sectional observation is performed using the cross-sectional observation scanning electron microscope shown in FIG. 1. A cross-sectional observation method will be explained with reference to FIGS. 1 to 5. First, with reference to FIG. 3, a process of setting an ion beam scanning area for cutting out a cross section by scanning the ion beam 31 will be described. The sample stage 19 (see FIG. 1) is automatically or manually moved by the sample stage driving device 20 (see FIG. 1) to the vicinity 50 of the cutting area where cross-sectional observation is to be performed.

The ion beam 31 is scanned in the vicinity of the cutting region 50 to detect the secondary electrons 34 generated from the semiconductor wafer 27, and the image thereof is displayed on the observation CRT 26. This observation C
Based on the display of the RT 26, the position of the ion beam scanning area 29 for cutting out is specified using a human-powered device such as a keyboard or a mouse. In this case, the detector is 2
Only the secondary electron detector 23 is activated.

Next, with reference to FIG. 4, a process of cutting out a cross section to be observed using the sputter etching function by scanning the ion beam 31 will be described. First, the ion beam scan area 29 is scanned with an ion beam to start cutting out a cross section. At the same time, a backscattered electron detector 21 detects backscattered electrons 32 in a cross section cut out by scanning the electron beam 30 .

A detection signal from the backscattered electron detector 21 is amplified by a detection signal amplifier and displayed on a CRT 26 for observation. Thereby, the cutting process by the ion beam 31 can be monitored. In this case, only the backscattered electron detector 21 is operated, and the secondary electron detector 23 is not operated. In this way,
The cutting process is monitored in real time and the ion beam scan is immediately stopped when the required cross section is obtained. As a result, a cross section of an ultrafine region at a specific location can be obtained more accurately than in conventional proposed improvements. Moreover, compared to the conventional proposed improvement example, the observed cross section can be cut out in a shorter time, and the cross-sectional observation process can be speeded up.

Next, with reference to FIG. 5, a process for observing a cross section cut out by scanning the ion beam 31 will be described. Only the electron beam 30 is scanned over the cross section cut out by the scanning of the ion beam 31. Secondary electrons 33 generated from the semiconductor wafer 27 by the scanning of the electron beam 30 are detected by the secondary electron detector 23 . A detection signal from the secondary electron detector 23 is amplified by a detection signal amplifier 25 and displayed on a CRT 26 for observation. This secondary electron observation allows highly accurate cross-sectional observation. In this manner, in this embodiment, an arbitrary cross section can be cut out with extremely high precision and observed immediately, so that the cross section of a minute area can be efficiently observed. It can also be applied to cross-sectional observation of minute foreign matter mixed in during a certain process, and is therefore effective in controlling the cleanliness of wafer processes.

Further, as the backscattered electron detector 21 and the secondary electron detector 23, a scintillator, a photomultiplier tube, etc. are used. In this embodiment, a backscattered electron detector 21 and a secondary electron detector 23 are used.
are provided independently, but the same one may be used.

FIG. 6 is a schematic diagram of a scanning electron microscope for cross-sectional observation in which a common electron detector is used as a backscattered electron detector and a secondary electron detector according to another embodiment of the present invention. ! 6
Referring to the figure, the secondary electron detector 23 is also used as a backscattered electron detector. That is, the backscattered electron detector 21,
When a common secondary electron detector 23 is used, this effect can be obtained by switching the bias voltage using the switch 40. Specifically, secondary electrons usually have an energy of several tens to hundreds of eV, whereas reflected electrons have an energy close to that of the incident electron beam 30, for example, 1
If 0KeVSEM, ~10KeV, IKeVSE
If M, it is ~IKeV. Therefore, by setting the bias voltage of the detector to a reverse bias of a little less than IKeV, only reflected electrons can be detected.

Thereby, only the image of reflected electrons by the electron beam 30 can be monitored. In this embodiment, the secondary electron detector 23 detects secondary electrons 33 generated by the electron beam 30 and secondary electrons 3 generated by the ion beam 31.
4. However, if the relative symmetry becomes a problem depending on the irradiation position of the brightness of the secondary electron image, multiple secondary electron detectors can be installed at appropriate positions for optimization. Good too. Furthermore, in this example, the same ion beam was used for cutting out the cross section and for setting the scanning area, but the present invention is not limited to this. If irradiation damage is a problem, try to minimize the ion beam irradiation amount by reducing the ion beam current or importing the secondary electron image into the image memory, etc. Good too. Furthermore, in this example, physical sputtering of sample constituent atoms by direct etching with an ion beam was used; however, the present invention is not limited to this; a reactive gas is introduced through a nozzle, and an assisted etching function is achieved through a chemical reaction. You may also use this together to cut out the cross section. In addition, in this embodiment, one test chip 2 for cross-sectional observation is placed in the wafer 27.
8, the process was evaluated by monitoring the entire process, but the present invention is not limited to this, and may be used for failure analysis of semiconductor devices.

As described above, in the scanning electron microscope for cross-sectional observation shown in FIG.
0 integrally and by newly installing a backscattered electron detector 21 in addition to the secondary electron detector 23,
When cutting out the observation cross section with the ion beam 31,
By scanning the electron beam 30 and detecting the reflected electrons, cross-sectional observation can be performed in real time. Therefore, it is possible to more accurately cut out and observe a cross section of a specific location of an arbitrary chip within a wafer in a short time.

In the cross-sectional observation method using the scanning electron microscope for cross-sectional observation shown in FIG. Backscattered electron detector 2
1, the process of cutting out the observation section by the ion beam 31 can be observed in real time.

Therefore, ion beam scanning can be stopped immediately when a necessary cross section is obtained, and the observed cross section can be processed more accurately.

[Effects of the Invention] According to the invention described in the first claim, the ion beam scanning means scans the ion beam at the position where the cross section of the semiconductor wafer is to be observed to cut out the cross section, and the cut cross section is scanned by the electron beam scanning means. By scanning the electron beam and detecting the backscattered electrons reflected from the semiconductor wafer using an electron detection means, the cross section to be observed is cut out and at the same time the cross-sectional observation is performed using the backscattered electrons, so it is possible to detect a specific location on the semiconductor wafer. cross section can be cut out and observed more accurately and in a shorter time.

According to the invention set forth in claim 2, after the sample stage on which the semiconductor wafer is installed is moved to the vicinity of the area where the cross section is to be observed, the ion beam is scanned at the position where the cross section is to be observed to cut out the cross section; By scanning an electron beam across the cross section of the semiconductor wafer and detecting the reflected electrons reflected from the semiconductor wafer to detect the process of cutting out the cross section, the cross section can be observed while simultaneously processing the cross section to be observed. It is possible to accurately cut out and observe the cross section in a short time.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a scanning electron microscope for cross-sectional observation showing an embodiment of the present invention, and FIG. 2 is a diagram of a semiconductor wafer used in the cross-sectional observation method using the scanning electron microscope for cross-sectional observation shown in FIG. FIGS. 3 to 5 are observation process diagrams for explaining the cross-sectional observation method using the scanning electron microscope for cross-sectional observation shown in FIG. 1, and FIG. 6 is a diagram showing another embodiment of the present invention. A schematic diagram of a scanning electron microscope for cross-sectional observation when a common electron detector is used as a backscattered electron detector and a secondary electron detector according to an example, and FIG. FIG. 2 is a perspective view of a semiconductor wafer. In the figure, 1 is an electron gun, 5 is an SEM deflection coil, and 10
14 is a liquid metal ion source, 14 is a FIB deflection electrode, 21 is a backscattered electron detector, 23 is a secondary electron detector, 25 is a detection signal amplifier, 26 is an observation CRT 127 is a sample (semiconductor wafer), 30 is an electron beam, 31 is an ion beam, and 40 is a changeover switch. In addition, in the figures, the same reference numerals indicate the same or corresponding parts. Also 1 figure 300--wipe collar! @ 8 minutes 50 Akira 2 figures 2 days'! -, Figure 3 and Figure 6

Claims (2)

[Claims] (1) A scanning electron microscope for cross-sectional observation that irradiates a cross-section of a semiconductor wafer with an electron beam to observe the cross-sectional state of the semiconductor wafer, the scanning electron microscope comprising: an ion beam that scans the semiconductor wafer with an ion beam to cut out the cross-section; a beam scanning means; an electron beam scanning means for scanning the electron beam on a cross section of the semiconductor wafer cut out by the ion beam scanning means; an electron beam generated from the semiconductor wafer by scanning the ion beam and the electron beam; electron detection means for detecting secondary electrons and reflected electrons reflected from the semiconductor wafer by scanning of the electron beam; and an area scanned by the electron beam scanning means based on the detection result of the electron detection means. A scanning electron microscope for cross-sectional observation, including a scanning area observation means for observing a cross-sectional state. (2) A cross-sectional observation method using a scanning electron microscope for cross-sectional observation in which the cross-sectional state of the semiconductor wafer is observed by irradiating the cross-section of the semiconductor wafer with an electron beam, the sample stage on which the semiconductor wafer is installed. a step of moving the sample stage to the vicinity of the area where cross-sectional observation is to be performed; and after moving the sample stage, scanning an ion beam to the vicinity where the cross-sectional observation is to be performed to generate secondary electrons from the semiconductor wafer; a step of detecting electrons and setting a position for performing the cross-sectional observation; a step of scanning an ion beam at the set position for performing the cross-sectional observation to cut out a cross-section; scanning the beam and detecting backscattered electrons reflected from the semiconductor wafer to observe the process of cutting out the cross section; and scanning the electron beam over the cross section cut out in the step of cutting out the cross section to remove the semiconductor wafer. A cross-sectional observation method using a scanning electron microscope for cross-sectional observation, comprising the steps of: generating secondary electrons from a cross-section, detecting the secondary electrons, and observing a cross-sectional state of a cross-section scanned by the electron beam.