Spot-size control in reflection-based and scatterometry-based X-ray metrology systems

An X-ray system includes, first and second X-ray channels (XCs), a spot sizer and a processor. The first XC is configured to: (i) direct a first X-ray beam for producing a spot on a surface of a sample, and (ii) produce a first signal responsively to a first X-ray radiation received from the surface. The spot sizer is positioned at a distance from the surface and is shaped and positioned to set the spot size by passing to the surface a portion of the first X-ray beam. The second XC is configured to: (i) direct a second X-ray beam to the surface, and (ii) produce a second signal responsively to a second X-ray radiation received from the surface, and the processor is configured to: (i) perform an analysis of the sample based on the first signal, and (ii) estimate the size of the spot based on the second signal.