Onto Innovation Inc.
Optical metrology device for measuring samples having thin or thick films

Abstract:

An optical metrology device includes an aperture that can be adjusted based on the thickness of the film on a sample. The aperture is adjusted to have a first aperture configuration or a second aperture configuration, where the second aperture configuration allows more light to pass. The aperture may be adjusted to use the second aperture configuration, e.g., if the thickness of the film produces a lateral shift from each internal reflection in the film at least 80% of the measurement spot size or the film thickness is greater than a predesignated amount, or if the light measured with the first aperture configuration and second aperture configuration differs by more than a predetermined threshold. The aperture may be in the source arm of the optical system, e.g., between the light source and the sample, or the receiver arm of the optical system, e.g., between the sample and the detector.