Detection of focal point of objective lens by means of a two-split sensor
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United States of America Patent
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Aug 29, 2000
Grant Date -
N/A
app pub date -
Apr 20, 1999
filing date -
Apr 22, 1998
priority date (Note) -
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status (Latency Note)
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Abstract
A focal point detecting apparatus for an objective lens is disclosed for inspecting whether or not the focal point of the objective lens used in an electron microscope, an optical inspecting apparatus, a laser processing apparatus, etc. is positioned on a surface of a target object. The focal point detecting apparatus comprises for entering an optical beam for detecting a focal point from a position deviant from an optical axis of an objective lens to a surface of a target object to be inspected through at least the objective lens; and two two-split sensors on which the optical beam reflected from the surface of the target object so as to pass again through the objective lens is converged by at least a condenser lens. The two two-split sensors are arranged at the same optical inclination in front of and behind the position on which the reflected optical beam is converged by the condenser lens when the focal point of the objective lens is positioned on the surface of the target object.
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