Hitachi, Ltd.

Hiroshi Makihara

Shunji Maeda

Minoru Yoshida

Yukihiro Shibata

Yoshitada Oshida

Kenji Oka

Yasuhiko Nakayama

Nobuhiko Aoki

An automatic focus detection method comprises the steps of: irradiating onto a single spot of a sample a plurality of beams of illuminating light transmitted and condensed through an objective lens in a symmetrically diagonal manner with respect to an optical axis of the objective lens; branching reflected light from the same spot of the illuminated sample after transmission through the objective lens, in directions of illumination symmetrical with respect to the optical axis so as to obtain a plurality of optical images; and causing a photoelectric conversion device to receive the branched optical images for conversion to an electric signal representing light intensity distribution of the images, whereby a defocus of the sample is detected based on a discrepancy between the optical axis and the center of the light intensity distribution.

Automatic focus detection method, automatic focus detection apparatus,

A plate thickness measuring method and apparatus, is provided wherein a fine pattern is projected on the front and rear surfaces of an object to be measured via object lenses oppositely provided on the front and rear surfaces of the object to be measured in its thickness. The image of the projected pattern on the object to be measured is formed via said object lenses, and the contrast of the formed pattern image is detected. Then the object lenses are moved slightly to achieve the maximum of the contrast, or to perform an automatic focusing control. The thickness of the object to be measured can then be estimated from the difference of the positions of the object lenses at which the maximum contrast, or the focused condition, are obtained.

Plate thickness measuring method and apparatus

Growing community of inventors

Yokohama, Japan

Hiroshi Makihara