JPH0472600A - X-ray radiating position confirmation device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention provides an X-ray irradiation position suitable for a fine area X-ray analyzer that irradiates a fine X-ray beam and detects diffraction X-rays, fluorescent X-rays, electrons, etc. emitted from the beam. Concerning confirmation device. [Prior art] In the past, it was considered difficult to focus an X-ray beam to about micrometers, but in recent years, it has been possible to focus the X-ray beam from an X-ray generator through a glass tube. Approximately 5μm fine X&! Beam is now available. Using this beam, a device has been developed that can analyze diffraction
Physics, Volume 27. Number 11, 19
88. Elle 2203-Elle 2206 pages (Japa
nese Journal of Applie
d Physics, νol. 27 No, 11. 1988. pp, L2203-L
2206) Ko. Like this x&! As beams become smaller, confirmation of the X-ray irradiation position on the sample becomes a major technical issue. With conventional equipment, which has a beam diameter of several millimeters, a plate coated with phosphor is placed at the sample position, and the size and irradiation position of the X-ray beam can be visually confirmed from the light emitted from the plate. However, since the phosphor coating particles have a size of several hundred micrometers or more, such a simple method cannot be applied when the X-ray beam diameter is reduced to about micrometers. For this reason, in the conventional device reported above, as shown in FIG. The focal point and the X-ray irradiation position on the sample are made to coincide with each other, and in actual various analyses, the laser light scattered on the sample surface is magnified with an optical microscope 27, and its image is photographed with a television camera 24. A method has been adopted in which the laser beam irradiation position is specified as the X-ray irradiation position. .

[Problem to be solved by the invention] However, in the above method, the minimum size of the laser beam that can be focused on the sample is about 10 μm, which is larger than the X-ray beam diameter, so it is difficult to accurately identify the X-ray irradiation position. The problem was that it was difficult to Furthermore, it takes several hours to align the irradiation positions of the X-ray and the laser beam, and there is also the problem that if the optical axes of the two beams are misaligned for some reason, it cannot be detected. Furthermore, this method uses an aspheric combination mirror (io mutually perpendicular cylindrical mirror).
ular cylindrical m1rror)
and Walter 8 mirror (hyperboloid and paraboloid mirror)
It had the disadvantage that it was difficult to apply to minute X-ray beam forming methods other than the aforementioned glass tubes, such as d paraboloid m1rror (X-ray microscopy, Cambridge at the University Press 1960, pp. 105-114).
-ray Microscopy, Cambrid
ge at the Llniversity pre
ss, 1960, pp. 105-114)]. The present invention does not involve the indirect method using the above-mentioned laser beam, but rather directly observes the X-ray irradiation part, thereby identifying the irradiation position of a minute X-ray beam of several μm or smaller with high precision, and An object of the present invention is to provide an X-ray irradiation position confirmation device that can be applied to various fine X-ray beam forming methods. [Means for Solving the Problems] As shown in FIG. 1, the present invention provides that when an electron beam 3 is irradiated to cover a region 2 irradiated with a fine X-ray beam 1, the X-rays and the electron beam are The basic principle is that the emission efficiency of the secondary electrons 4 from the irradiated area is different from the emission efficiency from the area 5 irradiated with the electron beam alone. This is because photoelectrons are emitted when X-rays are irradiated, and charges generated within the sample 6 accumulate (charge up) on the sample surface and interface, changing the local potential of the sample, and emitting secondary electrons due to electron beam irradiation. This is because it affects efficiency. For example, even if a silicon single crystal substrate has a natural oxide film of several nanometers on the surface, charges generated within the substrate by X-ray irradiation accumulate at the interface between the substrate and the oxide film, causing a change in the surface potential of several eV. Furthermore, the influence of this X-ray irradiation on the secondary electron image depends on the energy of the incident X-ray and the structure and material of the sample.
When a silicon highly integrated circuit was irradiated with xi ranging from several 100 eV to about 50 keV, a change in secondary electron emission efficiency due to electron beam irradiation was observed at any X-ray energy. In order to apply this phenomenon to confirmation of minute X-ray irradiation position, the first step is to
As shown in the figure, an area that includes the X-ray irradiation area and is sufficiently wider than the area is irradiated with the electron beam. For this purpose, there are a method of increasing the diameter of the electron beam itself and a method of irradiating the electron beam, and a method of scanning a fine electron beam to widen the irradiation area. On the other hand, secondary electrons are detected using a cathode ray tube (cathode ray tube), which corresponds to the number of emitted electrons from each position on the sample.
The image is enlarged and displayed as a two-dimensional image on a display device such as a ray tube. In this image, the planar structure of the sample (for example, the element shape of a highly integrated circuit) can be observed, and the number of secondary electrons in the X-ray irradiated area is higher than in other areas, so the irradiated XI You can check the beam diameter and irradiation position. The image processing method for confirming the X-ray irradiation position described above includes the following two types of beam irradiation methods. The first is 2 obtained when both X-ray and electron beams are irradiated.
This is a method of confirming the X-ray irradiation position from the difference between the secondary electron two-dimensional distribution image and the image obtained when the electron beam is irradiated alone. The second method is to confirm the X-ray irradiation position by superimposing a secondary electron (photoelectron) image obtained during irradiation with an X-ray beam alone on a secondary electron image obtained during irradiation with an electron beam alone. In the first method, if the difference between the two-dimensional images is not large, after obtaining the difference image, artificially increase the contrast of the two-dimensional image with the background of the minute difference, By again superimposing the two-dimensional image upon irradiation with an electron beam alone, it is possible to easily confirm the X-ray irradiation position. Also, the second
In this method, the contrast of the image obtained when irradiating X-rays alone with the background is artificially increased, and the image is superimposed on the secondary electron distribution image when irradiating only electron beams. [Function] The present invention is a method of observing the effect of X-rays on the photoelectrons emitted from a sample by X-ray irradiation or the secondary electron emission efficiency during electron beam irradiation, so the X-ray irradiation area can be directly confirmed. Therefore, the optical axis misalignment of both beams can be detected while observing the X-ray irradiation position, and the misalignment can be corrected. No problems arise. In addition, since the alignment of the X-ray and electron beam irradiation areas can be done while observing the secondary electron image, it can be completed in a few minutes, eliminating the long time required to align the optical axes of the laser beam and the X-ray beam. do not need. Furthermore, in the present invention, each beam of X-rays and electron beams is irradiated from an independent system as shown in Figure 1, so there are no restrictions on the fine X-ray formation method that can be applied, unlike the conventional method using laser light. . In the present invention, when outputting the distribution of secondary electron emission within a sample to a display device such as a cathode ray tube, the two-dimensional image of the secondary electron distribution is electrically magnified. The above-mentioned scanning electron beam irradiation method can magnify up to tens of thousands of times, and also has Q, 1. The surface resolution of a two-dimensional image can be increased to about pm, and the X-ray irradiation position can be specified with high accuracy even when the X-ray beam diameter is 1 μm or less. [Example] Tip 1! L.1 An embodiment of the present invention will be described using FIG. 2. Using an X-ray focusing system 7 made of a glass tube similar to that used in the conventional example described above, a minute X-ray beam 1 with a diameter of about 1 μm was formed, making it possible to irradiate any position on the sample. On the other hand, electrons [3] were emitted from a field emission type electron gun 9 and were focused by an electromagnetic lens system 10 to form a fine beam. Note that the beam can be scanned in the X-Y directions using the coil 11 provided in the above lens system. Next, the 2 emitted when the sample is irradiated with X-rays or electron beams.
The next electron is detected by a detector 1 consisting of a scintillator and an electron multiplier.
Detected in 2. Then, an output signal proportional to the number of secondary electrons was transmitted to a cathode ray tube 13, which is a display device. At this time, an electron beam is scanned within the cathode ray tube for two-dimensional display.
Scanning was performed in synchronization with the primary electron beam 3 irradiated onto the sample, so that the electron beam irradiation position on the sample corresponded to the two-dimensional image on the display device. In this example, the resolution of the secondary electron two-dimensional image was designed to be approximately 70 nm. Next, a 4 megabit dynamic memory was used as the test sample 6 of this example. Secondary electron image with cathode ray tube" - 50
The memory peripheral circuit section, which has a relatively rough pattern, was irradiated with X-rays under magnification of 00 times to perform WR inspection. As a result, the brightness of the display surface of the cathode ray tube is slightly brighter in the X-ray irradiated area than in other areas5, and the area is slightly wider than the 0°8 μm wide pattern formed on the integrated circuit. The X-ray beam is 1.0~1.5μ from
It was confirmed that the diameter was m. In the above embodiment, the electron beam single irradiation area 5 of the X-ray irradiation unit 2
Because there is little difference in brightness on the cathode ray tube and it is difficult to distinguish it from high secondary electron emission regions in protruding structures on the sample, it took experience to identify the xi irradiation position. Therefore, in this embodiment, as shown in FIG. 4, the image 14 obtained when both the X-ray and electron beams are irradiated is
The digital converter 15 converts it into a digital signal and stores it in the image storage device 16. Next, the difference between the secondary electron image 17 obtained when the electron beam is irradiated alone and the above-mentioned stored image is taken, and the image 18 of this difference is obtained. The brightness is artificially increased, the contrast with the background is emphasized, digital-to-analog conversion is performed, and the above secondary electron image 1 is regenerated.
7, and the X-ray irradiation position was confirmed from the composite image 19. This image processing made it easier to determine the X-ray irradiation position. In particular, the change in secondary electron emission efficiency due to X-ray irradiation is small, and X-rays can be easily applied to samples with complex structures such as the memory parts of highly integrated circuits, which have many high secondary electron emitting parts due to severe unevenness. You can now check the irradiation position. 1.5.3 In this example, the same fine X-ray and electron beam irradiation system as in Example 1 was used. However, in this example, a method of scanning an electron beam and a method of irradiating with a stationary electron beam whose diameter has been expanded to about 10 μm can be selected and applied. As shown in FIG. 5, the secondary electrons 4 emitted from the sample 6 are magnified into a two-dimensional image by an electromagnetic lens system 21 and projected onto a two-dimensional detector 20 called a channel plate or an image plate. The secondary electrons 4 that have entered the detector 20 are converted into light with a brightness proportional to the number of secondary electrons 4 provided on the surface of the detector by a fluorescent screen 22, and guided to a television camera 24 by an optical waveguide 23 and imaged. The above image is electrically enlarged and displayed on the cathode ray tube 13. In identifying the X-ray irradiation part, as in Example 2,
A method that utilizes the difference between the image obtained when irradiating X-rays and electron beams simultaneously and the image obtained when irradiating electron beams alone, and an image that emphasizes the contrast with the background of the photoelectron image obtained when irradiating X-rays alone. A method is adopted in which the X-ray irradiation area is identified from the high brightness area on the cathode ray tube by superimposing it on the image obtained during irradiation. Next, in examining the performance of the X-ray irradiation position confirmation device, the same highly integrated circuit element as in Example 1 was used as a sample. It was possible to identify the X-ray irradiation position using any of the above electron beam irradiation methods and image comparison methods. However, the method of Example 1 was superior in image resolution. Note that in this example, high position identification accuracy was obtained when a scanning electron beam was used and the same image processing method as in Example 2 was adopted. At this time, the xliA beam diameter obtained from the high brightness area on the image is 2~2
．． It was found that the diameter was 5 μm, which was approximately twice the diameter of the actual irradiated X-ray beam. [Effects of the Invention] The present invention is a method for directly observing the X-ray irradiated area on a sample, and can solve various problems that occurred with the conventional indirect method using reflected laser light. That is, it has the following effects. (1)X4! The optical axis of the electron beam can be adjusted in a short time. (2) Since the deviation between both optical axes can be detected at all times, there is no error in identifying the X-ray irradiation position. (3) The irradiation position of a minute X-ray beam of several μm or smaller can be specified with high accuracy. (4) It can also be applied to fine X-ray formation methods other than glass thin tube X-ray focusing mechanisms. Furthermore, the irradiation
It has the advantage of being able to measure the line beam diameter.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the relationship between the irradiation areas of X-rays and electron beams on a sample, showing the principle of the present invention. FIG. The figure is an explanatory diagram of a conventional X-ray irradiation position confirmation system using a laser beam, Figure 4 is a configuration diagram of an image processing system used in an embodiment of the present invention, and Figure 5 is another embodiment of the present invention. It is a block diagram which shows the arrangement|positioning of the beam irradiation system and detection system of the X-ray irradiation position confirmation apparatus which becomes an example. Explanation of symbols 1: X-ray beam, 2: X-ray irradiation area, 3: Electron beam, 42nd order electron, 5: Electron beam irradiation area, 6: Sample, 7
. . . X-ray focusing system, 8 . ...display device (
Cathode ray tube), 14...2 during X-ray and electron beam irradiation
Next electron image, 15... Analog/digital converter 16 ・
Image storage, processing device, ]-7. Secondary electron image when irradiated with electron beam alone, 18. Difference between secondary electron images of 14 and 17, 19.
・Composition of 17 and 18 (1< 20-2-dimensional secondary electron detector, 21. Electromagnetic lens for detection. 22. Fluorescent plate for electron-light conversion, 23. Optical waveguide. 24. Television camera, 25. Laser light. 26. Laser beam condensing lens, 27... Optical microscope 28 Laser%+
Round 43 Figure/3 2nd part ■4 Figure

Claims (1)

[Claims] 1. A means for irradiating a sample with an X-ray beam, a means for irradiating a primary electron beam so as to cover the irradiation area of the X-ray beam, and a primary electron beam emitted from the sample surface. A secondary electron detector for detecting secondary electrons, and identifying the X-ray irradiation position by detecting the difference between the two beam irradiation part and the primary electron beam single irradiation part among the secondary electrons. An X-ray irradiation position confirmation device characterized by comprising means for 2. The X-ray irradiation position confirmation device according to claim 1, further comprising means for scanning the primary electron beam so as to cover the irradiation area of the X-ray beam. 3. The above-mentioned secondary electron detector is a two-dimensional detector, and an electromagnetic lens is installed between the sample and the detector.
The X-ray irradiation position confirmation device according to claim 1 or 2, wherein the dimensional shape is enlarged and projected onto the detector. 4. A means for outputting the scanning of the primary irradiation electron beam and the intensity of the secondary electrons emitted from each scanning position on a two-dimensional surface of a display device or a storage device while corresponding to the irradiation position on the sample. The X-ray irradiation position confirmation device according to claim 2, characterized in that: 5. Means for determining the difference between the secondary electron images obtained when irradiating both the X-ray and primary electron beam and when irradiating the primary electron beam alone, and the contrast between the secondary electron intensity difference image and the background. Claims 1 to 4 further include means for artificially increasing the X-ray irradiation area, and means for making it easier to observe the X-ray irradiated area by superimposing it on the secondary electron image before taking the difference again. The X-ray irradiation position confirmation device described. 6. A means for irradiating the above-mentioned X-ray or primary electron beam alone, and each secondary electron 2 obtained during the above-mentioned beam irradiation.
5. The X-ray irradiation position confirmation device according to claim 1, further comprising means for superimposing dimensional images on the same display device to enable observation of the X-ray irradiation part.