Aberration effects in an optical measuring microscope.

The effects of aberrations on the accuracy and repeatability of critical dimension measurements made with an optical microscope are examined theoretically and practically. Aberrations in microscope objectives are studied to determine their effects on the image profiles of narrow ($#x2248;2-microAm) line objects, such as the geometries on integrated circuits. A diffraction theory model is developed and used to investigate the effects of the primary aberrations. Microscope objectives from different manufacturers are examined, and agreement between the theoretical and practical image intensity profiles is demonstrated. It is concluded that the aberrations in many commercially available objective lenses introduce significant errors into semiconductor geometry measurements.