Chapman Instruments, Inc.

Shu W Wang

Thomas C Bristow

John E Stephan

A system for non-contact measurement of thickness of a test object. A laser beam is split into two identical directly opposed input beams. A calibration object of known thickness causes beams to be reflected from sides of the test object. Each reflected beam passes through sensing means including a pinhole aperture and a photodiode sensor. Maximum sensor output defines first and second focal points a known distance apart. The calibration object is removed, and the test object is inserted into the path of the input beams, creating focus position intensity curves for the reflected beams. By determining the deviation, at maximum photodiode output, of the positions of the test object reflecting surfaces from the positions of the calibration object surfaces, the test object thickness can be readily and accurately determined.

Method and apparatus for measuring wafer thickness

A system for non-contact measurement of thickness of an object. A laser beam is split into two identical input beams that are directly opposed. A calibration object of known thickness causes beams to be reflected from sides of the test object. Each reflected beam passes through auto-focus means including a quad sensor coupled to focusing means on the input beam, causing each input beam to be focused on the calibration object, thereby defining first and second focal points a known distance apart. The focus is locked and focus error data are generated for each beam. The calibration object is removed, and the test object is inserted into the path of the focused input beams, creating focus error signals for the reflected beams. By determining the deviation of the positions of the test object reflecting surfaces from the positions of the calibration object surfaces, the test object thickness can be readily and accurately determined.

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Rochester, NY, United States of America

Shu W Wang