Illumination sources used for optical metrology systems typically have demanding operational requirements and tight tolerances to provide accurate metrology data. In some applications, it may be desirable to provide illumination with continuous tenability of the center wavelength and bandwidth. For example, in a scatterometry overlay metrology system, the sensitivity of an overlay measurement may vary significantly for different wavelengths of illumination based on small variations in the overlay targets. Accordingly, precise control of the center wavelength of the illumination beam over a continuous range of wavelengths may provide accurate measurements for a wide range of conditions. Further, it may be desirable to provide illumination at a high brightness to facilitate tight focusing and high focused intensities. Accordingly, independent control of the bandwidth of the illumination beam may provide control over the brightness of an illumination beam.
However, typical tunable light sources may suffer from low brightness for one or more illumination wavelengths, a low steepness between transmitted and filtered illumination wavelengths, an inability to independently modify a central wavelength and a bandwidth of illumination, intensity noise, spectral instabilities, or the like. Therefore, it would be desirable to provide a system and method for curing defects such as those of the identified above.
USPTO Backgrounds
USPTO Backgrounds