The present invention relates to a scanning tunnel microscope and more particularly to a scanning tunnel microscope which is designed in such a way that a position of a desired portion on a specimen to be observed with the scanning tunnel microscope is previously positioned by utilizing a scanning electron microscope so that an observation can be then made with respect to the positioned portion.
With respect to a prior art apparatus which is constructed by combining a scanning tunnel microscope (hereinafter, referred to as simply "an STM", when applicable) with a scanning electron microscope (hereinafter, referred to as simply "a SEM", when applicable), the description is shown in an article "Review of Scientific Instruments 60", April, 1989, pp. 789 to 791. In the apparatus described in this article, a specimen is mounted on a specimen holder in such a way that its surface makes an angle of 45.degree. with an electron beam of the SEM. The specimen is then moved towards a probe of the STM by a coarse movement mechanism referred to as an inchworm utilizing a piezoactuator, which serves to linearly move a specimen in a direction perpendicular to the electron beam, so as to approach to a position at a predetermined distance from the probe which allows the tunnel effect to be generated. The probe of the STM is attached to a fine movement mechanism referred to as a piezotripod, so that it is moved along the surface of the specimen, thus performing a scanning operation. The above-mentioned elements constituting the STM are fitted to a stage of the SEM within a specimen chamber of the SEM.
In the prior art apparatus described above, there is provided therein only the coarse movement mechanism which serves lineally to make the specimen approach to the probe to be located in an area allowing generation of the tunnel effect, and also a SEM stage for searching for the probe by utilizing the SEM is not clear in construction.
JP-A-63-116349 (the term JP-A used herein means that the patent application was laid open to public inspection but has not been examined) and JP-A-63-298951 disclose that a position on a specimen to be observed with a STM is previously positioned by utilizing a SEM and that a specimen is adapted to be moved in a two dimensional manner along its surface with its surface being inclined at 45.degree. with an electron beam.
Moreover, JP-A-64-79603 discloses a microscope which is designed in such a way that a specimen is observed at a low magnification with a SEM and the same specimen is observed at a high magnification with a STM.
The prior art described above discloses that a position to be observed with an STM with a higher magnification is determined using a SEM, and then an observation is made with the STM. However, when the apparatus is actually operated, even if the position of the specimen is set in such a way that an observation position determined by the SEM goes to a predetermined position within a visual field of an electron microscope image by the SEM, it is not necessarily easy to make the probe of the STM scan accurately over the observation position determined by the SEM since the position of the probe of the STM is not precisely defined with respect to an image by the SEM.
In other words, only when the relationship among the specimen, the probe and the electron beam is accurately determined, the position positioned by the SEM can be observed accurately at a high magnification with the STM.