Patent ID: 7692128

Claim:
A method for setting a reference point of focus control of an optical apparatus which comprises a two-dimensional imaging device having a plurality of light receiving elements aligned in two-dimensional array for capturing a transmittance image of a sample and optically inspecting the sample or optically measuring a physical quantity of the sample using the transmittance sample image captured by said two-dimensional imaging device, a stage for supporting the sample, an illumination light source for projecting illumination light toward the sample from a rear side of the sample, an objective lens for receiving transmittance light transmitted through the sample, a two-dimensional imaging device for receiving light emitted from the objective lens to form a two-dimensional image of the sample, an auto-focus mechanism for controlling the position of the objective lens along its optical axis during inspection or measurement of the sample, and a reference pattern which has Becke effect; the method comprising the steps of: positioning the reference pattern within the field of the objective lens, projecting the illumination light emitted from the illumination light source toward the reference pattern from a rear side of the reference pattern, capturing an image of the reference pattern by use of the two-dimensional imaging device to form a two-dimensional image of the reference pattern, sequentially moving the objective lens along its optical axis to detect the position of the objective lens along its optical axis when Becke line disappears from the image of the reference pattern captured by the two-dimensional imaging device, and setting a control target point of the auto-focus mechanism with respect to a position of the objective lens at which the Becke line disappears from the image of the reference pattern.