Radiant energy – Inspection of solids or liquids by charged particles – Electron microscope type
Reexamination Certificate
2000-02-14
2003-04-15
Lee, John R. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Electron microscope type
C250S306000, C250S307000
Reexamination Certificate
active
06548811
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is related to transmission electron microscopes and methods of inspection using them, and in particular, to methods of inspection of semiconductor substrates.
A method of detecting crystal defects in specimen using conventional transmission electron microscopes has been disclosed, for example, in Transmission Electron Microscopy, Plenum Publishing Corporation (1996), p.379~p.445. In this method, the sample is tilted so that the electron beam satisfies the diffraction conditions for the crystal defect of the specimen, and a specific diffraction electron beam is made to pass through using objective lens aperture while all other electron beams are cut off, thereby detecting the crystal defect by increasing the contrast of the crystal defect.
In the above method of detecting crystal defects in specimen using conventional transmission electron microscopes, the transmission electron microscope image is observed while setting the specimen inclination in various directions, and the presence or absence of crystal defects is judged from the contrast of the image.
However, in the range in which the specimen stage can be adjusted mechanically, it is difficult to make the shift in the image when the specimen is inclined to smaller than about 1 &mgr;m. As a result, in order to inspect the presence or absence of crystal defects at the same location, it was necessary to move the specimen stage manually so as to observe the same field of view whenever the specimen inclination is changed, and hence a long time was necessary until the crystal defect could be detected. Therefore, inspecting for the rate of occurrence of crystal defects over a wide field of view was almost impossible because of the extremely long time required for such an inspection. On the other hand, although it is possible to inspect for the rate of occurrence of crystal defects over a wide field of view by limiting the direction of electron beam incidence to only one direction, since the detection of crystal defects is strongly dependent upon the direction of incidence of the electron beam, as has been described above, it is possible that the crystal defects are not detected even if they are present, and hence it is not possible to inspect for the accurate rate of occurrence of crystal defects. In addition, after inspecting for the rate of occurrence of crystal defects over a wide field of view, if it is necessary to observe in detail a specific defect location part, it is necessary to move the specimen stage thereby bringing the position of that defect to within the field of view for analysis.
However, all stage movements are done manually, and since the operator has to calculate the address positions of the defect locations, it becomes necessary to start moving the stage from the origin of counting the position each time while counting the address, it takes a considerably long time to move to the location where each defect was detected, and also, there is the problem that the stage cannot be moved to the correct location of the defect because of manual errors in counting the address.
For example, consider that there are 256×256 memory cells in one memory mat, these are subjected to the presence or absence of defects with the direction of electron beam irradiation being limited to one direction. It takes 30 seconds to inspect the memory cells in units of 16 cells and to verify the presence or absence of defects in each image, which is the total time including time required to move the stage manually, to adjust the focus, and to judge the presence or absence of defects by manual observation. Under these conditions, in order to complete the inspection, it takes a very long time of 1.4 days (=(256×256)/(16×0.5)=2048 minutes). Because of this, this inspection method is not practical since even the defect detection rate is low and a very long time is required for inspection.
A method of inspection using a conventional electron microscope apparatus has been disclosed, for example, in Japanese Unexamined Patent Publication No. Hei 10-74813. In this method, the sample is irradiated with an electron beam, and the image is obtained from the intensity of the secondary electrons generated from the surface of the specimen, and the judgment of defects is made from the contrast of the image. Further, as has been disclosed in Japanese Unexamined Patent Publication No. Hei 5-215694, as a method other than electron microscopes, the specimen is irradiated with X-rays, a transmission image of the specimen pattern is obtained and the judgment of defects is made from that pattern.
In the above inspection methods using an electron microscope apparatus, since the sample is irradiated with an electron beam and the image is obtained from the intensity of the secondary electrons generated from the surface of the specimen, although it is possible to judge the shape defects on the surface of the specimen, it is not at all possible to evaluate the crystal defects in the specimen. In addition, when the pattern of the specimen is observed by irradiating the specimen with X-rays, only the shape of the specimen can be observed, and the crystal defects in the specimen cannot be evaluated.
SUMMARY OF THE INVENTION
In the conventional method of inspecting crystal defects in the specimen using a transmission electron microscope apparatus, since the crystal surface satisfying the black conditions appears as a contrast in the transmission electron microscope image, it is not possible to judge that there are no defects by merely observing from one direction. Therefore, it is necessary to set the specimen inclination at various angles and to judge the presence or absence of crystal defects from the image contrast, it takes a very long time to judge the presence or absence of crystal defects in one section to be inspected, and an extremely long time is required to inspect for the crystal defect occurrence rate in a wide field of view. In addition, in a wide field of view, the defect detection rate decreases if the inspection for determining the crystal defect occurrence rate is done by limiting the direction of electron beam incidence to only one direction. In addition, after inspecting, during observation and analysis in detail of a specific defect location part, it is necessary for the operator to move manually the specimen stage to the address location of the part with the defect, and hence a long time is required to move the stage to the defect detection part, and also there is the possibility of not being able to move to the defect detection part because of human errors in counting the address. Further, in the method in which the image is obtained from the secondary electrons emitted from the specimen surface and the Good or No Good judgment is made from the contrast of that image, although it is possible to judge the shape defects on the surface of the specimen, it is not at all possible to evaluate the crystal defects in the specimen. In addition, even in the method of observing the pattern of the specimen when it is irradiated with X-rays, it is only possible to observe the shape of the specimen. The purpose of the present invention is to provide a transmission electron microscope apparatus and a method of inspection using such an apparatus, in which it is possible to detect automatically the crystal defects and shape abnormalities in the specimen over a wide area of the specimen at both a high speed and a high probability rate, and also possible, during detailed analysis after inspection, to set automatically the parts where crystal defects or shape abnormalities were detected to the analysis position.
In particular, the present invention is intended to provide a method and apparatus for identifying crystal defects in the base material caused by preparation using a base material having a crystalline structure.
For example, if we consider that there are 256×256 memory cells in one memory mat, and it takes 0.5 seconds to judge the presence or absence of defects by inspectin
Kakibayashi Hiroshi
Nakamura Kuniyasu
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Lee John R.
Quash Anthony
LandOfFree
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