The stereoscopic observation method is a technique that gives a stereoscopic view of an image by combining plural sheets of images of different field-of-view angles in regard to the same field of view, and attains a measurement of the stereoscopic image. The stereoscopic observation method uses a shift of parallax of a corresponding point to attain the stereoscopic shape; however, since it is unable to recognize the shift of parallax satisfactorily in an out-of-focus domain, it is unable to attain the stereoscopic shape, which is a constraint of this method. The method attains the stereoscopic view by observing plural sheets of images measured with the tilt angle of a sample (or beam) varied, separately with right and left eyes by using various techniques.
Patent Document 1:
JP-A No. 75263/2002
Patent Document 2:
JP-A No. 184336/2002
Non-Patent Document 1:
J. Vac. Sci. Technol. B, Vol. 18, No. 6, November/December 2000, Mitsugu Sato and Fumio Mizuno, “Depth of field at high magnifications of scanning electron microscopes.”
Non-Patent Document 2:
Scan Tech 2000, Preliminary Report, Tsuyosi Kohaku, Mitsugu Sato and Jun Takane, “Automatic adjustment function of optical axis, and automatic expansion function of focal depth,” pp. 2–5 (2002).
Non-Patent Document 3:
Scan Tech 2000, Preliminary Report, Norio Baba (Kogakuin University), “Three-dimensional automatic measurement by the stereoscopic observation method.”
The constraint of the conventional stereoscopic observation method will be described with FIG. 15, FIG. 16A, and FIG. 16B. FIG. 15 is an explanatory chart viewed from the sectional direction of a sample, which typically illustrates the formation of an image in viewing the scanning electron microscope image stereoscopically. Hereunder, the scanning electron microscope will be abbreviated to the SEM. FIGS. 16A and 16B illustrate images by the SEM when the image is viewed stereoscopically under the condition of FIG. 15, in which FIG. 16A illustrates an image by the SEM when the sample or the incident electron is tilted by +θ degree, and FIG. 16B illustrates an image by the SEM when the sample or the incident electron is tilted by −θ degree.
When irradiating an incident electron 151 to a sample 153 from the +θ tilted direction, the method attains an image 161 on the monitor as illustrated in FIG. 16A. Here on the image 161, the domain corresponding to a domain 155 being in focus, illustrated in FIG. 15, is a domain 163. When irradiating an incident electron 152 to the sample 153 from the −θ tilted direction, the method attains an image 162 on the monitor as illustrated in FIG. 16B. Here on the image 162, the domain corresponding to a domain 154 being in focus, illustrated in FIG. 15, is the domain 163. To synthesize these two sheets of images 161, 162 and make a three-dimensional display of them will make it possible to give a stereoscopic view of the in-focus domain 163 only, and impossible to give a stereoscopic view of the out-of focus domain except the domain 163. Thus, the domain to give a stereoscopic view depends on the depth of focus of the SEM.
The depth of focus of the SEM is given by the following expression (1) (the non-patent document 1).fdmin=2√{square root over (Vacc)}Rmin2  (1)Where, fdmin represents the depth of focus, Vacc the accelerating voltage, and Rmin the resolution.
As clearly seen from this expression, the depth of focus of the SEM becomes shallower as the resolution becomes higher. When the depth of focus is shallow, the in-focus domain is narrow. Accordingly, a trial for a stereoscopic view will attain only a part of the stereoscopic shape. The stereoscopic observation method using a recent high-resolution SEM has a narrow domain to give a stereoscopic view; that is, it is unable to attain correct height information only in a part of domain inside an image, which is a problem to be solved. Thus, there has been an earnest demand for the three-dimensional image observation method capable of attaining the stereoscopic shape and height difference distribution of an image to cover the whole domain.